WO2022237642A1 - 磷酸铁锂正极材料及其制备方法和锂离子电池 - Google Patents

磷酸铁锂正极材料及其制备方法和锂离子电池 Download PDF

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WO2022237642A1
WO2022237642A1 PCT/CN2022/091178 CN2022091178W WO2022237642A1 WO 2022237642 A1 WO2022237642 A1 WO 2022237642A1 CN 2022091178 W CN2022091178 W CN 2022091178W WO 2022237642 A1 WO2022237642 A1 WO 2022237642A1
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lithium
iron phosphate
lithium iron
positive electrode
electrode material
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PCT/CN2022/091178
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English (en)
French (fr)
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徐云玲
徐茶清
陈俊越
曹文玉
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比亚迪股份有限公司
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Priority to CA3218477A priority Critical patent/CA3218477A1/en
Priority to EP22806608.0A priority patent/EP4340069A1/en
Priority to KR1020237042639A priority patent/KR20240006652A/ko
Priority to JP2023569872A priority patent/JP2024517022A/ja
Publication of WO2022237642A1 publication Critical patent/WO2022237642A1/zh
Priority to US18/505,077 priority patent/US20240079573A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M4/13—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
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/381—Alkaline or alkaline earth metals elements
    • H01M4/382—Lithium
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M10/05—Accumulators with non-aqueous electrolyte
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    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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    • H01M4/00—Electrodes
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of cathode materials, in particular to a lithium iron phosphate cathode material, a preparation method thereof, and a lithium ion battery.
  • Lithium iron phosphate cathode materials and ternary cathode materials are currently the two main cathode materials used in lithium-ion batteries. Based on their respective characteristics, there are obvious distinctions in application fields. Lithium iron phosphate cathode material has good safety and long cycle life, so it is widely used in the field of large passenger cars, while ternary cathode material has high energy density, and is widely used in the field of passenger vehicles.
  • the structure of lithium iron phosphate belongs to the orthorhombic olivine structure, and its volume change during charging and discharging is very small (6.8%), so it has excellent cycle performance, but its poor electron and ion
  • the conductivity also leads to its poor low temperature and rate performance, which makes it difficult to meet the requirements of power batteries for low temperature and rate.
  • Aiming at the poor low-temperature performance and rate performance of lithium iron phosphate cathode materials many improvements have been made and some progress has been made.
  • the low-temperature performance and rate performance of lithium iron phosphate cathode materials are not as good as those of ternary cathode materials. Compared with the material, there is still a certain gap.
  • the preparation method of lithium iron phosphate mainly includes solid-phase method and hydrothermal synthesis method (referred to as "wet method").
  • the solid-phase method is to mix lithium salt, phosphorus source, iron source and carbon source uniformly by mechanical mixing, and then
  • the lithium iron phosphate cathode material is obtained by spraying, sintering and air crushing processes. Due to the relatively mature technology and low cost, the prepared lithium iron phosphate has a high capacity and high compaction. It is currently adopted by most cathode manufacturers.
  • Lithium iron phosphate synthesized by solid phase method has the problems of low temperature and poor rate performance due to its large particle size.
  • the wet synthesis method has a greater advantage in low temperature and rate performance due to the smaller size of the obtained lithium iron phosphate.
  • the wet synthesis method has more heterogeneous phases in the lithium iron phosphate, and the synthesis process There are many influencing factors and poor consistency, so the capacity is low, and due to the presence of impurity phases, the content of magnetic substances is high, and the high temperature and cycle performance are poor.
  • the particle size of lithium iron phosphate prepared by wet synthesis is smaller, most of the primary particles are above 160nm, and the agglomeration is more serious.
  • the low temperature and rate performance are improved compared with the solid-phase method, they are still Difficult to meet the requirements of the power battery.
  • the purpose of this application is to provide a lithium iron phosphate cathode material and its preparation method and lithium ion Battery.
  • the first aspect of the present application provides a lithium iron phosphate positive electrode material
  • the expression of the lithium iron phosphate positive electrode material is LiFe 1-x M x PO 4 /C, where 0 ⁇ x ⁇ 0.05
  • M is at least one element selected from Mg, Al, Zr, Ti, Co, V, Mn, W, Sn, Nb and Mo;
  • the second aspect of the present application provides a method for preparing a lithium iron phosphate cathode material, the method comprising:
  • the lithium salt, phosphoric acid and iron salt are uniformly mixed under inert atmosphere conditions and then subjected to a hydrothermal reaction to obtain the first slurry;
  • the precursor is sintered, and the sintered product is subjected to air crushing treatment to obtain a lithium iron phosphate positive electrode material.
  • the third aspect of the present invention provides a lithium iron phosphate positive electrode material prepared by the above method.
  • the fourth aspect of the present invention provides a lithium ion battery, which includes the lithium iron phosphate cathode material as described above.
  • the present application has the following advantages:
  • the lithium iron phosphate positive electrode material of the present application has few impurity phases, small particle size of primary particles, good dispersibility, and narrow particle size distribution range. When used as a lithium battery positive electrode material, it is beneficial to improve the low temperature performance and rate of lithium ion batteries performance;
  • the content of the magnetic substance of the lithium iron phosphate positive electrode material of the present application is low, when used as the lithium ion battery positive electrode material, helps to reduce the self-discharge of the lithium ion battery, improves the high temperature storage performance and cycle performance of the lithium ion battery;
  • the bulk ion doping of the grain growth inhibitor improves the electronic conductance and ion conductance, It is conducive to the improvement of the rate performance, and by adding lithium supplements, the content of impurity phases and magnetic substances in the lithium iron phosphate cathode material is effectively reduced, which is conducive to improving the self-discharge performance, high-temperature storage performance and cycle performance.
  • Fig. 1 is the scanning electron microscope (SEM) picture of the lithium iron phosphate cathode material that the application embodiment 1 makes, and the magnification is 100k;
  • Fig. 2 is the scanning electron microscope (SEM) picture of the lithium iron phosphate cathode material that the application embodiment 2 makes, and the magnification is 100k;
  • Fig. 3 is the scanning electron microscope (SEM) picture of the lithium iron phosphate cathode material that the application embodiment 3 makes, and the magnification is 100k;
  • SEM 4 is a scanning electron microscope (SEM) image of the lithium iron phosphate cathode material prepared in Comparative Example 1 of the present application, with a magnification of 100k.
  • the first aspect of the present application provides a lithium iron phosphate positive electrode material, the expression of the lithium iron phosphate positive electrode material is LiFe 1-x M x PO 4 /C, where 0 ⁇ x ⁇ 0.05; M is selected from Mg, At least one element of Al, Zr, Ti, Co, V, Mn, W, Sn, Nb and Mo;
  • the lithium iron phosphate cathode material has small particle size, good dispersibility and narrow particle size distribution range. It should be noted that, in this application, the expression of the lithium iron phosphate positive electrode material is LiFe 1-x M x PO 4 /C. It can be understood that the structure of the lithium iron phosphate positive electrode material is C-coated LiFe 1-x M x PO 4 .
  • the content of carbon in the lithium iron phosphate positive electrode material is 1wt%-3.5wt%.
  • the total weight of the lithium iron positive electrode material, the content of carbon in the lithium iron phosphate positive electrode material is 1.4wt%-3.2wt%.
  • the lithium iron phosphate positive electrode material has few impurity phases, small particle size of primary particles, good dispersibility, and narrow particle size distribution range. When used as a lithium battery positive electrode material, it is beneficial to improve the low temperature performance and rate performance of the lithium ion battery.
  • the content of the magnetic substance in the lithium iron phosphate positive electrode material is 850 ppm by weight to 900 ppm by weight. In some other embodiments of the present application, the content of the magnetic substance in the lithium iron phosphate positive electrode material is 850 Weight ppm-885 weight ppm.
  • the lithium iron phosphate positive electrode material has a low content of magnetic substances, and when used as a lithium ion battery positive electrode material, it is beneficial to reduce the self-discharge of the lithium ion battery and improve the high temperature storage performance and cycle performance of the lithium ion battery.
  • the content of the magnetic substances involved in this application is obtained by testing with a JSII-G1 magnetic substance analyzer.
  • M is selected from at least one element among Mg, Al, Zr, Ti, Co, V, Mn, W, Sn, Nb and Mo, and in some embodiments of the present application, M is selected from Ti , at least one element of V and Nb.
  • the second aspect of the present application provides a method for preparing a lithium iron phosphate cathode material, the method comprising:
  • the lithium salt, phosphoric acid and iron salt are uniformly mixed under inert atmosphere conditions and then subjected to a hydrothermal reaction to obtain the first slurry;
  • the precursor is sintered, and the sintered product is subjected to air crushing treatment to obtain a lithium iron phosphate positive electrode material.
  • in-situ carbon coating and metal doping can improve the rate performance of lithium iron phosphate cathode materials to a certain extent, it is difficult to form effective in-situ coating and metal doping in the wet synthesis process.
  • Ion doping the main reasons are as follows: 1. If a carbon source is added during the wet synthesis process, because the reaction temperature is not high, it is difficult to carbonize in situ. In the subsequent washing process, because the carbon source is water-soluble, it will still be washed away 2. Metal ion doping can only diffuse into the interior of the material through the subsequent sintering process, and the reaction conditions in the hydrothermal synthesis stage are not enough to allow metal ions to enter the interior of the material.
  • the inventors of the present application have found that by using a dispersant and a grain growth inhibitor in combination with sand milling, the synergistic effect between the three ensures that the small-sized particles produced during the sand milling process are not agglomerated on the one hand and prevents the Its agglomerated growth in the subsequent sintering process avoids the formation of molten large particles.
  • the bulk ion doping of the grain growth inhibitor improves the electronic conductance and ion conductance, which is beneficial to the improvement of the rate performance.
  • the carbon source is added during the sanding process, because the carbon source is water-soluble, so the mixing and coating at the molecular level can be achieved.
  • the amounts of the lithium salt, phosphoric acid and iron salt meet: the molar ratio of lithium, phosphorus and iron is 2.8-3.2:1:1.
  • the amount of the organic carbon source is 8wt%-16wt%; the amount of the dispersant is 0.5wt%-5wt%; the grain The dosage of the growth inhibitor is 0.1wt%-6wt%. In some other embodiments of the present application, based on the dry basis of the second slurry, the dosage of the grain growth inhibitor is 0.3wt%-5wt%.
  • the amount of the lithium supplementing agent is 0.2wt%-5.5wt%.
  • the lithium supplement is used in an amount of 0.5wt%-5wt%.
  • based on the dry basis of the second slurry means to calculate based on the powder mass in the second slurry
  • “based on the dry basis of the third slurry” means to calculate The powder mass in the third slurry is used as the base number for calculation.
  • the powder quality in the second slurry is obtained by calculating the product of the quality of the second slurry and the solid content of the second slurry; the powder quality in the third slurry is calculated by the quality of the third slurry and The product of the solid content of the third slurry is calculated and obtained.
  • the solid content of the second slurry and the third slurry can be obtained by testing at 160° C. with a moisture tester.
  • the lithium salt is a soluble lithium salt, for example, the lithium salt can be selected from at least one of lithium chloride, lithium sulfate, lithium hydroxide and lithium nitrate.
  • the iron salt may be at least one selected from ferrous sulfate, ferrous chloride, ferrous nitrate and ferrous oxalate.
  • the organic carbon source in step (3), can be selected from sucrose, water-soluble phenolic resin, glucose, polyethylene glycol 6000 (ie PEG6000), hydroxymethyl cellulose, polyacrylamide ( (C 3 H 5 NO) n , weight average molecular weight of 5 million g/mol-12 million g/mol), starch and polyvinyl alcohol (weight average molecular weight of 200,000 g/mol-700,000 g/mol) at least one.
  • the dispersant is selected from sodium dodecyl sulfate, polyethylene glycol 200 (ie PEG200), polyethylene glycol 400 (ie PEG400), sodium lauryl sulfate, methyl At least one of amyl alcohol, sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate. Adding a dispersant during the sand grinding process can effectively inhibit the secondary agglomeration of small particles, which is beneficial to improve the low temperature and rate performance of the lithium iron phosphate cathode material.
  • the grain growth inhibitor is selected from magnesium chloride, magnesium nitrate, aluminum nitrate, zirconium nitrate, zirconium oxide, tetraethyl titanate, ethyl titanate, cobalt acetate, cobalt nitrate, di At least one of vanadium, ammonium metavanadate, manganese nitrate, manganese chloride, manganese sulfate, niobium pentachloride, tungsten disulfide, tin chloride, tin oxide, molybdenum sulfide and molybdenum oxide; In a manner, the concentration of the grain growth inhibitor is 0.3wt%-5wt%.
  • the grain growth inhibitor added in the process of sand grinding can play a role of "rolling crystal" in the subsequent sintering process, inhibiting the growth of particles, and at the same time providing metal ions entering the lithium iron phosphate lattice, improving the iron phosphate
  • the electronic and ionic conductivity of the lithium cathode material is conducive to improving the low temperature and rate performance of the lithium iron phosphate cathode material.
  • the lithium supplement agent is selected from at least one of lithium dihydrogen phosphate, lithium monohydrogen phosphate and lithium phosphate.
  • the impurity phase in the lithium iron phosphate positive electrode material can be reduced, and the content of its magnetic substance can be reduced.
  • the principle is: the phosphoric acid synthesized by hydrothermal process can be The interior of the lithium iron material is re-exposed. Under the action of the lithium supplement, the impurity iron phase inside the material can be re-converted into the lithium iron phosphate material through the subsequent sintering process, which effectively reduces the content of impurity phases and magnetic substances contained in the material. It is beneficial to improve the self-discharge performance, high-temperature storage performance and cycle performance of the lithium iron phosphate cathode material.
  • the solvent in step (1), is water; in some embodiments of the application, lithium salt, phosphoric acid and iron salt are mixed uniformly under inert atmosphere conditions, which can be used in the application
  • Inert gases include, but are not limited to, nitrogen or argon.
  • the conditions of the hydrothermal reaction are not particularly limited, and conventional process conditions in this field can be referred to.
  • the conditions of the hydrothermal reaction may include: a temperature of 130°C-200°C, The time is 2h-8h.
  • the first slurry is a lithium iron phosphate slurry containing a reaction mother liquor obtained after a hydrothermal reaction.
  • the pH of the first slurry is 5.5-7 .
  • the washing specifically includes: removing the reaction mother liquor in the first slurry, and then washing the centrifuged product with a dilute brine solution;
  • the dilute salt solution is selected from at least one of the aqueous solutions of lithium chloride, lithium nitrate, lithium dihydrogen phosphate, lithium monohydrogen phosphate and ammonium dihydrogen phosphate;
  • the concentration of the aqueous solution is 0.01wt%-2wt%.
  • the washing can be one wash or several step-by-step washes.
  • sand grinding in step (3), can reduce the primary particle size of the lithium iron phosphate positive electrode material, which is beneficial to improve its low temperature and rate performance.
  • the conditions of the sanding include: the line speed is 5m/s-15m/s, and the time is 0.5h-12h.
  • the control of the primary particle size of the lithium iron phosphate positive electrode material can be achieved by controlling the linear speed of the sand mill and the time of the sand mill; Agglomeration: By adding a grain growth inhibitor, the growth of particles and the adhesion and agglomeration of particles can be inhibited in the subsequent sintering process.
  • the inert atmosphere is a nitrogen atmosphere or a helium atmosphere.
  • step (4) the spray drying is to evaporate the water in the third slurry through flash evaporation, so as to obtain secondary spherical particles assembled from primary particles.
  • the conditions of the spray drying are not particularly limited, for example, the conditions of the spray drying may include: a solid content of 30-50wt%, a temperature of 90-105°C, and a time of 5-12h .
  • the sintering conditions are not particularly limited, and conventional process conditions in the art may be referred to.
  • the sintering conditions may include: a temperature of 650-760° C., and a time of 5-10 hours.
  • the sintering is performed under an inert atmosphere condition, and the inert gas that can be used in this application includes but not limited to nitrogen or argon.
  • the sintered product is secondary spherical particles assembled from primary particles; the air crushing is to break up the secondary spherical particles of the sintered product to obtain a dispersed lithium iron phosphate positive electrode Material primary granules.
  • the third aspect of the present application provides a lithium iron phosphate positive electrode material prepared by the above method.
  • the content of carbon in the lithium iron phosphate positive electrode material is 1wt%-3.5wt%. In some embodiments of the present application, based on the The total weight of the lithium iron phosphate positive electrode material, the content of carbon in the lithium iron phosphate positive electrode material is 1.4wt%-3.2wt%.
  • M is at least one element selected from Ti, V and Nb.
  • the fourth aspect of the present application provides a lithium ion battery, which includes the lithium iron phosphate cathode material as described above.
  • the lithium iron phosphate cathode material of the present application shows excellent low-temperature performance, rate performance, high-temperature performance and cycle performance in lithium-ion batteries.
  • the low-temperature capacity retention rate of the lithium iron phosphate cathode material at -20°C and 1C is 65%-80%. In some other embodiments of the application, the lithium iron phosphate cathode material is The low-temperature capacity retention rate at -20°C and 1C is 70%-80%. In other embodiments of the present application, the low-temperature capacity retention rate of the lithium iron phosphate cathode material at -20°C and 1C is 70%. -75%.
  • the discharge capacity retention rate of the lithium iron phosphate positive electrode material at 15C rate is 75%-86%.
  • the discharge capacity retention rate is 78%-86%.
  • the discharge capacity retention rate of the lithium iron phosphate positive electrode material at a rate of 15C is 81%-84%.
  • the high-temperature capacity remaining rate is 90%-99%. In some other embodiments of the present application, the lithium iron phosphate positive electrode material is After being stored at 60°C for 7 days, the high-temperature capacity remaining rate is 92%-99%. In other embodiments of the present application, after the lithium iron phosphate cathode material is stored at 60°C for 7 days, the high-temperature capacity remaining rate is 95%. -98.5%; In some embodiments of the present application, after the lithium iron phosphate positive electrode material is stored at 60°C for 7 days, the high temperature capacity recovery rate is 96.5%-102%.
  • the iron phosphate After the lithium cathode material is stored at 60°C for 7 days, the high-temperature capacity recovery rate is 99.5%-102%. In other embodiments of the present application, after the lithium iron phosphate cathode material is stored at 60°C for 7 days, the high-temperature capacity recovery The rate is 100%-101%.
  • the cycle capacity retention rate is above 95.5%. In some other embodiments of the present application, the lithium iron phosphate positive electrode material is After 500 cycles, the cycle capacity retention rate is above 96%. In other embodiments of the present application, the cycle capacity retention rate of the lithium iron phosphate cathode material is 96.8%-97.5% after 500 cycles at 1C rate.
  • the room temperature in this application refers to 25 ⁇ 2°C.
  • XPS spectrum It is obtained by testing an Escalab 250Xi X-ray photoelectron spectrometer equipped with Thermo Avantage V5.926 software purchased from Thermo Scientific, wherein the test conditions include: analysis area: a circle with a diameter of about 800 ⁇ m, information Depth: about 10nm; detection limit of atomic number percentage: 0.1%; test environment: temperature is 23.6°C, relative humidity is 50%, vacuum degree is 5.0 ⁇ 10 -8 Torr; voltage is 15kV, current is 23mA, power is 350W ; The X-ray scanning angle is 45.0 ⁇ ;
  • the electrochemical performance of the lithium iron phosphate cathode material was tested using a 2025-type button battery.
  • the preparation process of the 2025-type button battery is as follows:
  • Electrode preparation Fully mix lithium iron phosphate cathode material, acetylene black, and polyvinylidene fluoride (PVDF) with an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 100:1.5:2.5 to form a uniform cathode slurry
  • PVDF polyvinylidene fluoride
  • NMP N-methylpyrrolidone
  • the positive electrode slurry was coated on an aluminum foil and dried at 100° C. for 12 hours to make a positive electrode sheet with a diameter of 14 mm, wherein the loading capacity of the lithium iron phosphate positive electrode material was 5-10 mg/cm 2 .
  • Battery assembly In an argon-filled glove box with water content and oxygen content less than 5ppm, assemble the positive pole piece, separator, negative pole piece and electrolyte into a 2025-type button battery, and let it stand for 6 hours.
  • a metal lithium sheet with a diameter of 17 mm and a thickness of 1 mm was used as the negative electrode sheet; a polyethylene porous membrane (Celgard 2325) with a thickness of 25 ⁇ m was used as the separator; 1 mol/L LiPF 6 , ethylene carbonate (EC) and Equal volume mixture of diethyl carbonate (DEC).
  • the electrochemical performance test of the 2025-type button battery was carried out using the Shenzhen Newwell battery test system.
  • Low temperature capacity retention rate At room temperature, charge the battery at 0.1C to 3.8V at a constant current, then discharge at 0.1C to 2.5V at a constant current, charge the battery again at 0.1C to 3.8V at a constant current, and then After constant current discharge to 2.5V at 0.1C, charge to 3.8V at 0.5C to obtain the charging specific capacity of the battery at room temperature and 0.5C;
  • the discharge specific capacity of the battery at -20°C and 1C is obtained by current discharge to 2.0V; the ratio of the discharge specific capacity of the battery at -20°C and 1C to the charge specific capacity of the battery at room temperature and 0.5C is the low temperature of the battery capacity retention;
  • Discharge capacity retention rate charge to 3.8V at 0.2C rate, cut-off current is 0.02C, and then CC discharge to 2.5V at 15C rate, the ratio of discharge specific capacity at 15C rate to discharge specific capacity at 0.2C rate is is the discharge capacity retention rate at 15C rate;
  • High temperature capacity remaining rate and high temperature capacity recovery rate fully charge the battery at 0.1C, then store the battery in an oven at 60°C for 7 days, discharge it to 2.5V at 0.1C after taking it out, and then charge it to 2.5V at 0.1C 3.8V, then discharged to 2.5V; after high temperature storage, the ratio of the first discharge specific capacity of the battery discharged to 2.5V at 0.1C to the discharge specific capacity before storage is the high temperature capacity remaining rate; Charge to 3.8V, and then discharge to 2.5V The ratio of the discharge specific capacity to the discharge specific capacity before storage is the high temperature capacity recovery rate of the battery;
  • Cycle capacity retention at room temperature, after the battery is charged and discharged 500 times at a rate of 1C, the ratio of the specific capacity of the 500th discharge to the specific capacity of the first discharge is the cycle capacity retention.
  • LiFe 0.99 Nb 0.01 PO 4 /C is obtained as a lithium iron phosphate cathode material.
  • the precursor was placed in a nitrogen atmosphere, and sintered at 720°C for 8 hours. After the sintered product was subjected to air crushing, the lithium iron phosphate cathode material LiFe 0.975 V 0.025 PO 4 /C was obtained.
  • the precursor was placed in a nitrogen atmosphere, and sintered at 720°C for 8 hours. After the sintered product was subjected to air crushing, the lithium iron phosphate cathode material LiFe 0.99 Ti 0.01 PO 4 /C was obtained.
  • the lithium iron phosphate cathode material was prepared according to the method in Example 1, except that an equimolar amount of manganese chloride was used to replace the niobium pentachloride in step (3) to obtain the lithium iron phosphate cathode material LiFe 0 . 99 Mn 0.01 PO 4 /C.
  • the lithium iron phosphate positive electrode material was prepared according to the method of Example 1, except that, based on the dry basis of the second slurry, the amount of PEG200 (dispersant) was 0.4wt%, to obtain the lithium iron phosphate positive electrode material LiFe 0.99 Nb 0.01 PO 4 /C.
  • the lithium iron phosphate positive electrode material was prepared according to the method in Example 2, except that, based on the dry basis of the second slurry, the amount of vanadium pentoxide (grain growth inhibitor) was 0.25 wt%, to obtain a lithium iron phosphate positive electrode Material LiFe 0.996 V 0.004 PO 4 /C.
  • the lithium iron phosphate positive electrode material was prepared according to the method of Example 1, except that no dispersant and grain growth inhibitor were added in step (3), to obtain the lithium iron phosphate positive electrode material LiFePO 4 /C.
  • the lithium iron phosphate positive electrode material was prepared according to the method of Example 1, except that no dispersant and grain growth inhibitor were added in step (3), and no sand grinding was performed to obtain the lithium iron phosphate positive electrode material LiFePO 4 /C.
  • the lithium iron phosphate positive electrode material was prepared according to the method of Example 1, except that no sand grinding was performed in step (3), and the lithium iron phosphate positive electrode material LiFe 0..99 Nb 0.01 PO 4 /C was obtained.
  • the lithium iron phosphate positive electrode material was prepared according to the method of Example 1, except that no lithium replenishing agent was added in step (4) to obtain the lithium iron phosphate positive electrode material LiFe 0.99 Nb 0.01 PO 4 /C.
  • the present application has tested the scanning electron microscope images of the lithium iron phosphate cathode materials prepared in the above-mentioned examples and comparative examples, and exemplarily provides the SEM pictures of the lithium iron phosphate cathode materials prepared in Examples 1-3 and Comparative Example 1 , and the results are shown in Figures 1-4 respectively. It can be seen from Figures 1-4 that the primary particle size of the lithium iron phosphate material of the present application is small and the particle size distribution is uniform.
  • the present application tested the particle size distribution and the content of magnetic substances of the lithium iron phosphate cathode materials prepared in the above examples and comparative examples, and the specific test results are shown in Table 1.
  • Example 1 34 57 104 1.23 885 Example 2 twenty three 49 98 1.53 850 Example 3 42 65.2 110 1.04 865 Example 4 38 58 137 1.71 900 Example 5 35 61 152 1.92 890 Example 6 36 62 135 1.60 888 Comparative example 1 15 108 350 3.10 1165 Comparative example 2 35 98 400 3.72 2950 Comparative example 3 85 115 225 1.21 1205 Comparative example 4 34 56 105 1.27 2498
  • the method for preparing the lithium iron phosphate cathode material of the present application can obtain small particle size, good dispersibility, narrow particle size distribution and Lithium iron phosphate cathode material with low content of magnetic substances.
  • the present application tested the electrochemical properties of the lithium iron phosphate cathode materials prepared in the above examples and comparative examples, including: low-temperature capacity retention rate at -20°C and 1C, discharge capacity retention rate at 15C rate, storage at 60°C The high temperature capacity remaining rate and high temperature capacity recovery rate for 7 days, and the cycle capacity retention rate for 500 cycles at 1C rate, the specific test results are shown in Table 2.
  • the method for preparing lithium iron phosphate positive electrode material of the present application can obtain excellent rate performance, low temperature performance and high temperature performance by combining dispersants, grain growth inhibitors, lithium supplements and sand milling. Lithium iron phosphate cathode material.

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Abstract

公开了磷酸铁锂正极材料及其制备方法和锂离子电池。该磷酸铁锂正极材料的表达式为LiFe 1-xM xPO 4/C，式中，0＜x≤0.05；M选自Mg、Al、Zr、Ti、Co、V、Mn、W、Sn、Nb和Mo中的至少一种元素；其中，所述磷酸铁锂正极材料的粒径分布满足：(D90-D10)/D50＝1-2.17；所述磷酸铁锂正极材料中磁性物质的含量为850重量ppm-900重量ppm。

Description

磷酸铁锂正极材料及其制备方法和锂离子电池
优先权信息
本申请请求于2021年05月10日向中国国家知识产权局提交的、专利申请号为202110506894.1、申请名称为“磷酸铁锂正极材料及其制备方法和锂离子电池”的中国专利申请的优先权，并且其全部内容通过引用结合在本申请中。
技术领域
本申请涉及正极材料领域，具体涉及磷酸铁锂正极材料及其制备方法和锂离子电池。
背景技术
磷酸铁锂正极材料和三元正极材料(NCM和NCA)是目前锂离子电池主要采用的两种正极材料，基于其各自的特点，应用领域有较为明显的区分。磷酸铁锂正极材料具有较好的安全性和长循环使用寿命，因而被广泛应用于大型客车领域，而三元正极材料具有高能量密度，被广泛应用于乘用车领域。
磷酸铁锂的结构属于正交晶系的橄榄石结构，其在充放电过程中脱嵌锂的体积变化非常小(6.8％)，因而具备极其优异的循环性能，但其较差的电子和离子导电性也导致了其低温和倍率性能较差，难以满足动力电池对低温和倍率的要求。针对磷酸铁锂正极材料的低温性能和倍率性能较差的问题，目前已对此做了很多的改进并且取得了一定的进展，然而，磷酸铁锂正极材料的低温性能和倍率性能与三元正极材料相比仍然具有一定的差距。同时，由于生产过程中引入的铁类杂质导致磷酸铁锂正极材料中的磁性物质的含量较高，使得电池自放电严重甚至存在安全性的问题，这也是目前急需解决的一个关键难题。
磷酸铁锂的制备方法主要包括固相法和水热合成法(简称“湿法”)，固相法是通过将锂盐、磷源、铁源与碳源通过机械混合方式混合均匀，然后经喷雾、烧结和气碎工艺获得磷酸铁锂正极材料，该方法由于技术较为成熟，且成本较低，制备的磷酸铁锂容量较高，压实较高，目前被绝大多数正极厂家所采用，然而，固相法合成的磷酸铁锂因为颗粒尺寸大，存在低温和倍率性能较差的问题。相比于固相法，湿法合成方法由于获得的磷酸铁锂尺寸较小，低温和倍率性能上具有较大优势，然而，湿法合成技术制备的磷酸铁锂存在较多杂相，合成过程中影响因素较多，一致性较差，所以容量较低，且因存在杂相，磁性物质含量较高，高温和循环性能较差。与固相法相比，湿法合成制得的磷酸铁锂的颗粒尺寸虽然较小，但一次颗粒大多在160nm以上，且团聚较为严重，低温和倍率性能虽较固相法有所提高，但仍难以满足动力电池的要求。
公开内容
本申请的目的是为了克服现有技术存在的磷酸铁锂正极材料低温性能较差、倍率性能较差以及磁性物质含量较高的问题，提供一种磷酸铁锂正极材料及其制备方法和锂离子电池。
为了实现上述目的，本申请第一方面提供一种磷酸铁锂正极材料，所述磷酸铁锂正极材料的表达式为LiFe 1-xM xPO 4/C，式中，0＜x≤0.05；M选自Mg、Al、Zr、Ti、Co、V、Mn、W、Sn、Nb和Mo中的至少一种元素；
其中，所述磷酸铁锂正极材料的粒径分布满足：(D90-D10)/D50＝1-2.17；所述磷酸铁锂正极材料中磁性物质的含量为850重量ppm-900重量ppm。
本申请第二方面提供一种制备磷酸铁锂正极材料的方法，该方法包括：
(1)在溶剂的存在下，将锂盐、磷酸和铁盐在惰性气氛条件下混合均匀后进行水热反应，得到第一浆料；
(2)将所述第一浆料进行洗涤，得到第二浆料；
(3)向所述第二浆料中加入有机碳源、分散剂和晶粒生长抑制剂，在惰性气氛条件下进行砂磨，得到第三浆料；
(4)将所述第三浆料与补锂剂混合均匀，然后进行喷雾干燥，得到前驱体；
(5)将所述前驱体进行烧结，烧结产物经气碎处理后，得到磷酸铁锂正极材料。
本发明第三方面提供一种由如上所述的方法制备得到的磷酸铁锂正极材料。
本发明第四方面提供一种锂离子电池，其包括如上所述的磷酸铁锂正极材料。
通过上述技术方案，本申请具有如下优势：
(1)本申请的磷酸铁锂正极材料的杂相少，一次颗粒的粒度小，分散性好，粒度分布范围窄，作为锂电池正极材料使用时，有利于提高锂离子电池的低温性能和倍率性能；
(2)本申请的磷酸铁锂正极材料的磁性物质的含量低，作为锂离子电池正极材料使用时，有利于降低锂离子电池的自放电，提高锂离子电池的高温储存性能和循环性能；
(3)本申请的制备磷酸铁锂正极材料的方法，通过使用分散剂和晶粒生长抑制剂，并结合砂磨，三者之间协同作用，一方面保证了在砂磨过程中产生的小粒度颗粒不团聚，同时防止了其在后续烧结过程中的团聚性生长，避免了其形成熔融大颗粒，另一方面，晶粒生长抑制剂的体相离子掺杂改善了电子电导和离子电导，有利于实现倍率性能的提高，并且通过加入补锂剂，有效降低了磷酸铁锂正极材料中的杂相和磁性物质的含量，有利于改善磷酸铁锂正极材料的自放电性能、高温储存性能和循环性能。
本公开的附加方面和优点将在下面的描述中部分给出，部分将从下面的描述中变得明显，或通过本公开的实践了解到。
附图说明
此处所说明的附图用来提供对本申请的进一步理解，构成本申请的一部分，本申请的示意性实施例及其说明用于解释本申请，并不构成对本申请的不当限定。在附图中：
图1是本申请实施例1制得的磷酸铁锂正极材料的扫描电子显微镜(SEM)图，放大倍数为100k；
图2是本申请实施例2制得的磷酸铁锂正极材料的扫描电子显微镜(SEM)图，放大倍数为100k；
图3是本申请实施例3制得的磷酸铁锂正极材料的扫描电子显微镜(SEM)图，放大倍数为100k；
图4是本申请对比例1制得的磷酸铁锂正极材料的扫描电子显微镜(SEM)图，放大倍数为100k。
具体实施方式
在本文中所披露的范围的端点和任何值都不限于该精确的范围或值，这些范围或值应当理解为包含接近这些范围或值的值。对于数值范围来说，各个范围的端点值之间、各个范围的端点值和单独的点值之间，以及单独的点值之间可以彼此组合而得到一个或多个新的数值范围，这些数值范围应被视为在本文中具体公开。
本申请第一方面提供一种磷酸铁锂正极材料，所述磷酸铁锂正极材料的表达式为LiFe 1-xM xPO 4/C，式中，0＜x≤0.05；M选自Mg、Al、Zr、Ti、Co、V、Mn、W、Sn、Nb和Mo中的至少一种元素；
其中，所述磷酸铁锂正极材料的粒径分布满足：(D90-D10)/D50＝1-2.17；所述磷酸铁锂正极材料中磁性物质的含量为850重量ppm-900重量ppm。所述磷酸铁锂正极材料粒度小，分散性好，粒径分布范围窄。需要说明的是，本申请中，所述磷酸铁锂正极材料的表达式为LiFe 1-xM xPO 4/C可以理解为所述磷酸铁锂正极材料的结构为C包覆LiFe 1-xM xPO 4。
本申请一些实施方式中，基于所述磷酸铁锂正极材料的总重量，所述磷酸铁锂正极材料中碳的含量为1wt％-3.5wt％，本申请再一些实施方式中，基于所述磷酸铁锂正极材料的总重量，所述磷酸铁锂正极材料中碳的含量为1.4wt％-3.2wt％。
本申请一些实施方式中，所述磷酸铁锂正极材料的粒径分布满足：(D90-D10)/D50＝1-2.17，本申请再一些实施方式中，所述磷酸铁锂正极材料的粒径分布满足：(D90-D10)/D50＝1-1.55。所述磷酸铁锂正极材料的杂相少，一次颗粒的粒度小，分散性好，粒度分布范围窄，作为锂电池正极材料使用时，有利于提高锂离子电池的低温性能和倍率性能。
本申请一些实施方式中，所述磷酸铁锂正极材料中磁性物质的含量为850重量ppm -900重量ppm，本申请再一些实施方式中，所述磷酸铁锂正极材料中磁性物质的含量为850重量ppm-885重量ppm。所述磷酸铁锂正极材料的磁性物质的含量低，作为锂离子电池正极材料使用时，有利于降低锂离子电池的自放电，提高锂离子电池的高温储存性能和循环性能。本申请所涉及的磁性物质的含量是采用JSII-G1磁性物分析仪进行测试获得。
本申请一些实施方式中，M选自Mg、Al、Zr、Ti、Co、V、Mn、W、Sn、Nb和Mo中的至少一种元素，本申请再一些实施方式中，M选自Ti、V和Nb中的至少一种元素。
本申请第二方面提供一种制备磷酸铁锂正极材料的方法，该方法包括：
(1)在溶剂的存在下，将锂盐、磷酸和铁盐在惰性气氛条件下混合均匀后进行水热反应，得到第一浆料；
(2)将所述第一浆料进行洗涤，得到第二浆料；
(3)向所述第二浆料中加入有机碳源、分散剂和晶粒生长抑制剂，在惰性气氛条件下进行砂磨，得到第三浆料；
(4)将所述第三浆料与补锂剂混合均匀，然后进行喷雾干燥，得到前驱体；
(5)将所述前驱体进行烧结，烧结产物经气碎处理后，得到磷酸铁锂正极材料。
尽管在现有技术中，通过原位的碳包覆和金属掺杂能够在一定程度上提高磷酸铁锂正极材料的倍率性能，但是在湿法合成过程中，难以形成有效的原位包覆和离子掺杂，原因主要有：1、湿法合成过程中如果加入碳源，因为反应温度不高，难以原位碳化，在后续洗涤过程中，由于碳源是水溶性的，还是会被洗涤掉；2、金属离子掺杂是通过后续烧结过程中才能扩散到材料的内部，而在水热合成阶段的反应条件，尚不足以使金属离子进入材料内部。此外，砂磨虽然能够进一步减小水热合成的材料的粒度，但是粒度的减小也会导致团聚的发生，使得材料在后续的烧结过程中团聚长大，形成熔融大颗粒，不利于倍率性能的提高。
本申请的发明人发现，通过使用分散剂和晶粒生长抑制剂，并结合砂磨，三者之间协同作用，一方面保证了在砂磨过程中产生的小粒度颗粒不团聚，同时防止了其在后续烧结过程中的团聚性生长，避免了其形成熔融大颗粒，另一方面，晶粒生长抑制剂的体相离子掺杂改善了电子电导和离子电导，有利于实现倍率性能的提高。此外，在砂磨的过程中加入碳源，因为碳源是水溶性的，因此可以实现分子水平混合包覆。
本申请一些实施方式中，所述锂盐、磷酸和铁盐的用量满足：锂、磷和铁的摩尔比为2.8-3.2：1：1。
本申请一些实施方式中，以所述第二浆料的干基计，所述有机碳源用量为8wt％-16wt％；所述分散剂的用量为0.5wt％-5wt％；所述晶粒生长抑制剂的用量为0.1wt％-6wt％；本申请再一些实施方式中，以所述第二浆料的干基计，所述晶粒生长抑制剂用量为0.3wt％-5 wt％。
本申请一些实施方式中，以所述第三浆料的干基计，所述补锂剂的用量为0.2wt％-5.5wt％，本申请再一些实施方式中，以所述第三浆料的干基计，所述补锂剂的用量为0.5wt％-5wt％。
本申请中，“以所述第二浆料的干基计”即以所述第二浆料中的粉体质量为基数进行计算，“以所述第三浆料的干基计”即以所述第三浆料中的粉体质量为基数进行计算。所述第二浆料中的粉体质量通过第二浆料的质量和第二浆料的固含量的乘积计算获得；所述第三浆料中的粉体质量通过第三浆料的质量和第三浆料的固含量的乘积计算获得。第二浆料和第三浆料的固含量可以通过水分测试仪在160℃条件下测试获得。
本申请一些实施方式中，步骤(1)中，所述锂盐为可溶性锂盐，例如所述锂盐可以选自氯化锂、硫酸锂、氢氧化锂和硝酸锂中的至少一种。
本申请一些实施方式中，步骤(1)中，所述铁盐可以选自硫酸亚铁、氯化亚铁、硝酸亚铁和草酸亚铁中的至少一种。
本申请一些实施方式中，步骤(3)中，所述有机碳源可以选自蔗糖、水溶性酚醛树脂、葡萄糖、聚乙二醇6000(即PEG6000)、羟甲基纤维素、聚丙烯酰胺((C 3H 5NO) n，重均分子量为500万g/mol-1200万g/mol)、淀粉和聚乙烯醇(重均分子量为20万g/mol-70万g/mol)中的至少一种。
本申请一些实施方式中，所述分散剂选自十二烷基磺酸钠、聚乙二醇200(即PEG200)、聚乙二醇400(即PEG400)、十二烷基硫酸钠、甲基戊醇、三聚磷酸钠、六偏磷酸钠和焦磷酸钠中的至少一种。在砂磨的过程中加入分散剂，能够有效抑制小颗粒的二次团聚，有利于改善磷酸铁锂正极材料的低温和倍率性能。
本申请一些实施方式中，所述晶粒生长抑制剂选自氯化镁、硝酸镁、硝酸铝、硝酸锆、氧化锆、钛酸四乙酯、钛酸乙酯、醋酸钴、硝酸钴、五氧化二钒、偏钒酸铵、硝酸锰、氯化锰、硫酸锰、五氯化铌、二硫化钨、氯化锡、氧化锡、硫化钼和氧化钼中的至少一种；在本申请再一些实施方式中，所述晶粒生长抑制剂的浓度为0.3wt％-5wt％。在砂磨的过程中加入的晶粒生长抑制剂，能够在后续烧结过程中起到“轧晶”作用，抑制颗粒的长大，同时提供进入磷酸铁锂晶格的金属离子，提高了磷酸铁锂正极材料的电子和离子电导率，有利于改善磷酸铁锂正极材料的低温和倍率性能。
本申请一些实施方式中，所述补锂剂选自磷酸二氢锂、磷酸一氢锂和磷酸锂中的至少一种。所述制备磷酸铁锂正极材料的方法中，通过加入补锂剂，能够减少磷酸铁锂正极材料中的杂相，降低其磁性物质的含量，原理为：砂磨过程能够将水热合成的磷酸铁锂材料内部重新暴露，在补锂剂的作用下，材料内部的铁杂相经后续烧结过程，能够重新转化为 磷酸铁锂材料，有效降低了材料中含有的杂相和磁性物质的含量，有利于改善磷酸铁锂正极材料的自放电性能、高温储存性能和循环性能。
本申请一些实施方式中，步骤(1)中，所述溶剂为水；本申请再一些实施方式中，在惰性气氛条件下将锂盐、磷酸和铁盐混合均匀，在本申请中可以使用的惰性气体包括但不限于氮气或氩气。
本申请一些实施方式中，对所述水热反应的条件也没有特别地限定，可以参照本领域常规的工艺条件，例如，所述水热反应的条件可以包括：温度为130℃-200℃，时间为2h-8h。
本申请一些实施方式中，所述第一浆料为水热反应后得到的含有反应母液的磷酸铁锂浆料，本申请再一些实施方式中，所述第一浆料的pH为5.5-7。
本申请一些实施方式中，步骤(2)中，所述洗涤具体为：去除所述第一浆料中的反应母液，然后使用稀盐水溶液对离心产物进行洗涤；
其中，所述稀盐水溶液选自氯化锂、硝酸锂、磷酸二氢锂、磷酸一氢锂和磷酸二氢铵的水溶液中的至少一种；本申请再一些实施方式中，所述稀盐水溶液的浓度为0.01wt％-2wt％。所述洗涤可以为一次洗涤也可以为多次分步洗涤。
本申请一些实施方式中，步骤(3)中，进行砂磨能够降低磷酸铁锂正极材料的一次颗粒粒径，有利于改善其低温和倍率性能，为了进一步提高磷酸铁锂正极材料的低温和倍率性能，本申请再一些实施方式中，所述砂磨的条件包括：线速度为5m/s-15m/s，时间为0.5h-12h。
本申请一些实施方式中，通过控制砂磨的线速度和砂磨的时间，能够实现磷酸铁锂正极材料一次颗粒尺寸的控制；通过加入分散剂，能够防止小尺寸颗粒的磷酸铁锂的二次团聚；通过加入晶粒生长抑制剂，能够在后续的烧结过程中抑制颗粒的长大以及黏连团聚。
本申请一些实施方式中，所述惰性气氛为氮气气氛或者氦气气氛。
本申请一些实施方式中，步骤(4)中，所述喷雾干燥为通过闪蒸作用使第三浆料中的水分蒸发，从而得到由一次颗粒组装而成的二次球颗粒。
本申请一些实施方式中，对所述喷雾干燥的条件没有特别地限定，例如，所述喷雾干燥的条件可以包括：固含量为30-50wt％，温度为90-105℃，时间为5-12h。
本申请一些实施方式中，对所述烧结的条件也没有特别地限定，可以参照本领域常规的工艺条件，例如所述烧结的条件可以包括：温度为650-760℃，时间为5-10h。本申请再一些实施方式中，所述烧结在惰性气氛条件下进行，在本申请中可以使用的惰性气体包括但不限于氮气或氩气。
本申请一些实施方式中，所述烧结产物为由一次颗粒组装而成的二次球颗粒；所述气 碎是为了将所述烧结产物二次球颗粒打散，以得到分散的磷酸铁锂正极材料一次颗粒。
本申请第三方面提供一种由如上所述的方法制备得到的磷酸铁锂正极材料。所述磷酸铁锂正极材料的表达式为LiFe 1-xM xPO 4/C，式中，0＜x≤0.05；M选自Mg、Al、Zr、Ti、Co、V、Mn、W、Sn、Nb和Mo中的至少一种元素；其中，所述磷酸铁锂正极材料的粒径分布满足：(D90-D10)/D50＝1-2.17；所述磷酸铁锂正极材料中磁性物质的含量为850重量ppm-900重量ppm。
本申请一些实施方式中，所述磷酸铁锂正极材料的粒径分布满足：(D90-D10)/D50＝1-1.55；所述磷酸铁锂正极材料中磁性物质的含量为850重量ppm-885重量ppm。
本申请一些实施方式中，基于所述磷酸铁锂正极材料的总重量，所述磷酸铁锂正极材料中碳的含量为1wt％-3.5wt％，本申请的在一些实施方式中，基于所述磷酸铁锂正极材料的总重量，所述磷酸铁锂正极材料中碳的含量为1.4wt％-3.2wt％。
本申请一些实施方式中，M选自Ti、V和Nb中的至少一种元素。
本申请第四方面提供一种锂离子电池，其包括如上所述的磷酸铁锂正极材料。本申请的磷酸铁锂正极材料在锂离子电池中显示出优异的低温性能、倍率性能、高温性能以及循环性能。
本申请一些实施方式中，所述磷酸铁锂正极材料在-20℃、1C条件下的低温容量保持率为65％-80％，本申请再一些实施方式中，所述磷酸铁锂正极材料在-20℃、1C条件下的低温容量保持率为70％-80％，本申请另一些实施方式中，所述磷酸铁锂正极材料在-20℃、1C条件下的低温容量保持率为70％-75％。
本申请一些实施方式中，所述磷酸铁锂正极材料在15C倍率下的放电容量保持率为75％-86％，本申请再一些实施方式中，所述磷酸铁锂正极材料在15C倍率下的放电容量保持率为78％-86％，本申请另一些实施方式中，所述磷酸铁锂正极材料在15C倍率下的放电容量保持率为81％-84％。
本申请一些实施方式中，所述磷酸铁锂正极材料在60℃条件下储存7天后，高温容量剩余率为90％-99％，本申请再一些实施方式中，所述磷酸铁锂正极材料在60℃条件下储存7天后，高温容量剩余率为92％-99％，本申请另一些实施方式中，所述磷酸铁锂正极材料在60℃条件下储存7天后，高温容量剩余率为95％-98.5％；本申请一些实施方式中，所述磷酸铁锂正极材料在60℃条件下储存7天后，高温容量恢复率为96.5％-102％，本申请再一些实施方式中，所述磷酸铁锂正极材料在60℃条件下储存7天后，高温容量恢复率为99.5％-102％，本申请另一些实施方式中，所述磷酸铁锂正极材料在60℃条件下储存7天后，高温容量恢复率为100％-101％。
本申请一些实施方式中，所述磷酸铁锂正极材料在1C倍率下循环500圈后，循环容 量保持率在95.5％以上，本申请再一些实施方式中，所述磷酸铁锂正极材料在1C倍率下循环500圈后，循环容量保持率为96％以上，本申请另一些实施方式中，所述磷酸铁锂正极材料在1C倍率下循环500圈后，循环容量保持率为96.8％-97.5％。
以下将通过实施例对本申请进行详细描述。
以下实施例和对比例中，若无特别说明的情况下，所用原料均为市售品。
在没有特别说明的情况下，本申请所述室温是指25±2℃。
以下实施例和对比例中，相关参数通过以下测试方法得到：
(1)SEM形貌测试：通过日本日立HITACHI公司的S-4800型号的扫描电子显微镜测试得到；
(2)粒径分布：采用Smileview软件，通过日本日立HITACHI公司的S-4800型号的扫描电子显微镜在放大倍数为100k的SEM图中进行统计，先量取所有颗粒的短边尺寸，将所得数据导入至mintab软件中统计分析，获得D10、D50和D90数值，再根据它们的数值，计算得到粒径分布值。
(3)磁性物质的含量：采用JSII-G1磁性物分析仪进行测试，测试条件为：取10g的样料放入测量筒内直接测量；
(4)XPS图谱：通过购自Thermo Scientific公司配备有Thermo Avantage V5.926软件的Escalab 250Xi型X射线光电子能谱仪测试得到，其中，测试条件包括：分析区域：直径约800μm的圆形，信息深度：约10nm；原子个数百分比检测下限：0.1％；测试环境：温度为23.6℃，相对湿度为50％，真空度为5.0×10 -8Torr；电压为15kV，电流为23mA，功率为350W；X射线扫描角度为45.0゜；
(5)电化学性能测试：
以下实施例和对比例中，磷酸铁锂正极材料的电化学性能采用2025型扣式电池进行测试。
2025型扣式电池的制备过程具体如下：
极片制备：将磷酸铁锂正极材料、乙炔黑和聚偏二氟乙烯(PVDF)按照100：1.5：2.5的质量比与适量的N-甲基吡咯烷酮(NMP)充分混合，形成均匀的正极浆料，将正极浆料涂覆在铝箔上于100℃干燥12h后，制成直径为14mm正极极片，其中，所述磷酸铁锂正极材料的负载量为5-10mg/cm 2。
电池组装：在水含量与氧含量均小于5ppm的充有氩气的气手套箱内，将正极极片、隔膜、负极极片以及电解液组装成2025型扣式电池后，静置6h。其中，负极极片使用直径为17mm、厚度为1mm的金属锂片；隔膜使用厚度为25μm的聚乙烯多孔膜(Celgard 2325)； 电解液使用1mol/L的LiPF 6、碳酸乙烯酯(EC)和碳酸二乙酯(DEC)的等量混合液。
电化学性能测试：
以下实施例和对比例中，采用深圳新威尔电池测试系统对2025型扣式电池进行电化学性能测试。
低温容量保持率：在室温下，将电池在0.1C下恒流充电到3.8V，然后在0.1C下恒流放电到2.5V，再次将电池在0.1C下恒流充电到3.8V，然后在0.1C下恒流放电到2.5V后，在0.5C下恒流充电到3.8V，得到电池在室温、0.5C的充电比容量；接着将电池放入-20℃的冷柜中，在1C下恒流放电到2.0V，得到电池在-20℃、1C的放电比容量；电池在-20℃、1C的放电比容量与电池在室温、0.5C的充电比容量的比值，即为该电池的低温容量保持率；
放电容量保持率：0.2C倍率下充电到3.8V，截止电流为0.02C，然后在15C倍率下CC放电到2.5V，15C倍率下的放电比容量与0.2C倍率下的放电比容量的比值即为15C倍率下的放电容量保持率；
高温容量剩余率和高温容量恢复率：将电池0.1C下充满电，然后将电池置于60℃的烘箱中储存7天，取出后在0.1C下放电到2.5V，接着在0.1C下充电到3.8V，接着放电到2.5V；经过高温储存后所述在0.1C下放电到2.5V的电池首次放电比容量与储存前的放电比容量的比值即为高温容量剩余率；所述在0.1C下充电到3.8V，接着放电到2.5V后的放电比容量与储存前的放电比容量的比值即为该电池的高温容量恢复率；
循环容量保持率：在室温下，将电池在1C倍率下进行500次充放电循环后，第500次的放电比容量与第1次的放电比容量的比值即为循环容量保持率。
实施例1
(1)在氮气气氛条件下，将氢氧化锂、磷酸和氯化亚铁按照化学计量比(锂元素、磷元素和铁元素的摩尔比为3:1:1)加入去离子水中搅拌均匀，得到第一混合物，然后将第一混合物转移至高压反应釜中，在160℃条件下反应5h，得到第一浆料；
(2)将第一浆料进行离心，分离去除其反应母液，得到离心产物，然后使用浓度为0.05wt％的氯化锂溶液对离心产物进行洗涤，重复一次后，得到第二浆料；
(3)在氮气气氛条件下，以第二浆料的干基计(即以第二浆料中的粉体质量为基数)，向第二浆料中加入11wt％的葡萄糖、2.5wt％的五氯化铌和2wt％的PEG200，在线速度为10m/s的条件下砂磨5h，得到第三浆料；
(4)以第三浆料的干基计(即以第三浆料中的粉体质量为基数)，将1.32wt％的磷酸二氢锂加入到第三浆料中混合均匀，得到第二混合物，将第二混合物进行喷雾干燥，得到前驱体；
(5)将前驱体置于氮气气氛中，在720℃下烧结8h，烧结产物经气碎处理后，得到磷酸铁锂正极材料LiFe 0.99Nb 0.01PO 4/C。
实施例2
(1)在氮气气氛条件下，将氢氧化锂、磷酸和硫酸亚铁按照化学计量比(锂元素、磷元素和铁元素的摩尔比为3:1:1)加入去离子水中搅拌均匀，得到第一混合物，然后将第一混合物转移至高压反应釜中，在160℃条件下反应5h，得到第一浆料；
(2)将第一浆料进行离心，分离去除其反应母液，得到离心产物，然后使用浓度为0.05wt％的磷酸二氢锂溶液对离心产物进行洗涤，重复一次后，得到第二浆料；
(3)在氮气气氛条件下，以第二浆料的干基计(即以第二浆料中的粉体质量为基数)，向第二浆料中加入11wt％的葡萄糖、1.5wt％的五氧化二钒和2wt％的PEG400，在线速度为10m/s的条件下砂磨5h，得到第三浆料；
(4)以第三浆料的干基计(即以第三浆料中的粉体质量为基数)，将2.26wt％的磷酸二氢锂加入到第三浆料中混合均匀，得到第二混合物，将第二混合物进行喷雾干燥，得到前驱体；
(5)将前驱体置于氮气气氛中，在720℃下烧结8h，烧结产物经气碎处理后，得到磷酸铁锂正极材料LiFe 0.975V 0.025PO 4/C。
实施例3
(1)在氮气气氛条件下，将氢氧化锂、磷酸和硫酸亚铁按照化学计量比(锂元素、磷元素和铁元素的摩尔比为3:1:1)加入去离子水中搅拌均匀，得到第一混合物，然后将第一混合物转移至高压反应釜中，在160℃条件下反应5h，得到第一浆料；
(2)将第一浆料进行离心，分离去除其反应母液，得到离心产物，然后使用浓度为0.05wt％的磷酸二氢锂溶液对离心产物进行洗涤，重复一次后，得到第二浆料；
(3)在氮气气氛条件下，以第二浆料的干基计(即以第二浆料中的粉体质量为基数)，向第二浆料中加入11wt％的葡萄糖、2.5wt％的钛酸四丁酯和2wt％的PEG200，在线速度为10m/s的条件下砂磨5h，得到第三浆料；
(4)以第三浆料的干基计(即以第三浆料中的粉体质量为基数)，将1.69wt％的磷酸二氢锂加入到第三浆料中混合均匀，得到第二混合物，将第二混合物进行喷雾干燥，得到前驱体；
(5)将前驱体置于氮气气氛中，在720℃下烧结8h，烧结产物经气碎处理后，得到磷酸铁锂正极材料LiFe 0.99Ti 0.01PO 4/C。
实施例4
按照实施例1的方法制备磷酸铁锂正极材料，不同的是，采用等摩尔量的氯化锰替换步骤(3)中的五氯化铌，得到磷酸铁锂正极材料LiFe 0. 99Mn 0.01PO 4/C。
实施例5
按照实施例1的方法制备磷酸铁锂正极材料，不同的是，以第二浆料的干基计，PEG200(分散剂)的用量为0.4wt％，得到磷酸铁锂正极材料LiFe 0.99Nb 0.01PO 4/C。
实施例6
按照实施例2的方法制备磷酸铁锂正极材料，不同的是，以第二浆料的干基计，五氧化二钒(晶粒生长抑制剂)的用量为0.25wt％，得到磷酸铁锂正极材料LiFe 0.996V 0.004PO 4/C。
对比例1
按照实施例1的方法制备磷酸铁锂正极材料，不同的是，步骤(3)中不添加分散剂和晶粒生长抑制剂，得到磷酸铁锂正极材料LiFePO 4/C。
对比例2
按照实施例1的方法制备磷酸铁锂正极材料，不同的是，步骤(3)中不添加分散剂和晶粒生长抑制剂，且未进行砂磨，得到磷酸铁锂正极材料LiFePO 4/C。
对比例3
按照实施例1的方法制备磷酸铁锂正极材料，不同的是，步骤(3)中未进行砂磨，得到磷酸铁锂正极材料LiFe 0..99Nb 0.01PO 4/C。
对比例4
按照实施例1的方法制备磷酸铁锂正极材料，不同的是，步骤(4)中不添加补锂剂，得到磷酸铁锂正极材料LiFe 0.99Nb 0.01PO 4/C。
测试例
(1)形貌测试
本申请测试了上述实施例和对比例制得的磷酸铁锂正极材料的扫描电子显微镜图像，并且示例性地提供了实施例1-3和对比例1制得的磷酸铁锂正极材料的SEM图片，结果分 别如图1-4所示，从图1-4中可以看出，本申请的磷酸铁锂材料的一次粒径小，粒度分布均匀。
(2)物性测试
本申请测试了上述实施例和对比例制得的磷酸铁锂正极材料的粒径分布和磁性物的含量，具体测试结果如表1所示。
表1
编号 D10 D50 D90 (D90-D10)/D50 磁性物质/重量ppm
实施例1 34 57 104 1.23 885
实施例2 23 49 98 1.53 850
实施例3 42 65.2 110 1.04 865
实施例4 38 58 137 1.71 900
实施例5 35 61 152 1.92 890
实施例6 36 62 135 1.60 888
对比例1 15 108 350 3.10 1165
对比例2 35 98 400 3.72 2950
对比例3 85 115 225 1.21 1205
对比例4 34 56 105 1.27 2498
通过表1的结果可以看出，本申请的制备磷酸铁锂正极材料的方法通过结合分散剂、晶粒生长抑制剂、补锂剂以及砂磨可获得粒度小、分散性好、粒度分布窄以及磁性物质含量低的磷酸铁锂正极材料。
(3)电化学性能测试
本申请测试了上述实施例和对比例制得的磷酸铁锂正极材料的电化学性能，包括：-20℃、1C下的低温容量保持率，15C倍率下的放电容量保持率，60℃下储存7天的高温容量剩余率和高温容量恢复率，以及1C倍率下循环500次的循环容量保持率，具体测试结果如表2所示。
表2
Figure PCTCN2022091178-appb-000001
Figure PCTCN2022091178-appb-000002
通过表2的结果可以看出，本申请的制备磷酸铁锂正极材料的方法通过结合分散剂、晶粒生长抑制剂、补锂剂以及砂磨可获得倍率性能、低温性能以及高温性能俱佳的磷酸铁锂正极材料。
上面结合附图对本申请的实施例进行了描述，但是本申请并不局限于上述的具体实施方式，上述的具体实施方式仅仅是示意性的，而不是限制性的，本领域的普通技术人员在本申请的启示下，在不脱离本申请宗旨和权利要求所保护的范围情况下，还可做出很多形式，均属于本申请的保护之内。

Claims (20)

  1. 一种磷酸铁锂正极材料，其中，所述磷酸铁锂正极材料的表达式为LiFe 1-xM xPO 4/C，式中，0＜x≤0.05；M选自Mg、Al、Zr、Ti、Co、V、Mn、W、Sn、Nb和Mo中的至少一种元素；
    其中，所述磷酸铁锂正极材料的粒径分布满足：(D90-D10)/D50＝1-2.17；所述磷酸铁锂正极材料中磁性物质的含量为850重量ppm-900重量ppm。
  2. 根据权利要求1所述的磷酸铁锂正极材料，其中，基于所述磷酸铁锂正极材料的总重量，所述磷酸铁锂正极材料中碳的含量为1wt％-3.5wt％。
  3. 根据权利要求1或2所述的磷酸铁锂正极材料，其中，基于所述磷酸铁锂正极材料的总重量，所述磷酸铁锂正极材料中碳的含量为1.4wt％-3.2wt％。
  4. 根据权利要求1-3中任一项所述的磷酸铁锂正极材料，其中，所述磷酸铁锂正极材料中磁性物质的含量为850重量ppm-885重量ppm。
  5. 根据权利要求1-4中任一项所述的磷酸铁锂正极材料，其中，M选自Ti、V和Nb中的至少一种元素。
  6. 根据权利要求1-5中任一项所述的磷酸铁锂正极材料，其中，所述磷酸铁锂正极材料的粒径分布满足：(D90-D10)/D50＝1-1.55。
  7. 一种制备磷酸铁锂正极材料的方法，其中，所述方法包括：
    (1)在溶剂的存在下，将锂盐、磷酸和铁盐在惰性气氛条件下混合后进行水热反应，得到第一浆料；
    (2)将所述第一浆料进行洗涤，得到第二浆料；
    (3)向所述第二浆料中加入有机碳源、分散剂和晶粒生长抑制剂，在惰性气氛条件下进行砂磨，得到第三浆料；
    (4)将所述第三浆料与补锂剂混合，然后进行喷雾干燥，得到前驱体；
    (5)将所述前驱体进行烧结，烧结产物经气碎处理后，得到磷酸铁锂正极材料。
  8. 根据权利要求7所述的方法，其中，所述锂盐、所述磷酸和所述铁盐的用量满足：锂元素、磷元素和铁元素的摩尔比为2.8-3.2：1：1；
    以所述第二浆料的干基计，所述有机碳源用量为8wt％-16wt％；
    以所述第二浆料的干基计，所述分散剂的用量为0.5wt％-5wt％；
    以所述第二浆料的干基计，所述晶粒生长抑制剂的用量为0.1wt％-6wt％；
    以所述第三浆料的干基计，所述补锂剂的用量为0.2wt％-5.5wt％。
  9. 根据权利要求7或8所述的方法，其中，以所述第二浆料的干基计，所述晶粒生长抑制剂的用量为0.3wt％-5wt％。
  10. 根据权利要求7-9中任一项所述的方法，其中，以所述第三浆料的干基计，所述补锂剂的用量为0.5wt％-5wt％。
  11. 根据权利要求7-10中任一项所述的方法，其中，所述锂盐选自氯化锂、硫酸锂、氢氧化锂和硝酸锂中的至少一种；
    所述铁盐选自硫酸亚铁、氯化亚铁、硝酸亚铁和草酸亚铁中的至少一种。
  12. 根据权利要求7-11中任一项所述的方法，其中，所述有机碳源选自蔗糖、水溶性酚醛树脂、葡萄糖、聚乙二醇6000、羟甲基纤维素、聚丙烯酰胺、淀粉和聚乙烯醇中的至少一种，其中，所述聚丙烯酰胺的重均分子量为500万g/mol-1200万g/mol，所述聚乙烯醇的重均分子量为20万g/mol-70万g/mol；
    所述分散剂选自十二烷基磺酸钠、聚乙二醇200、聚乙二醇400、十二烷基硫酸钠、甲基戊醇、三聚磷酸钠、六偏磷酸钠和焦磷酸钠中的至少一种；
    所述晶粒生长抑制剂选自氯化镁、硝酸镁、硝酸铝、硝酸锆、氧化锆、钛酸四乙酯、钛酸乙酯、醋酸钴、硝酸钴、五氧化二钒、偏钒酸铵、硝酸锰、氯化锰、硫酸锰、五氯化铌、二硫化钨、氯化锡、氧化锡、硫化钼和氧化钼中的至少一种。
  13. 根据权利要求7-12中任一项所述的方法，其中，所述补锂剂选自磷酸二氢锂、磷酸一氢锂和磷酸锂中的至少一种。
  14. 根据权利要求7-13中任一项所述的方法，其中，步骤(1)中，所述水热反应的条件包括：温度为130℃-200℃，时间为2h-8h。
  15. 根据权利要求7-14中任一项所述的方法，其中，步骤(2)中，所述洗涤包括：去除所述第一浆料中的反应母液，然后使用稀盐水溶液对去除反应母液后的产物进行洗涤；所述稀盐水溶液选自氯化锂、硝酸锂、磷酸二氢锂、磷酸一氢锂和磷酸二氢铵的水溶液中的至少一种。
  16. 根据权利要求7-15中任一项所述的方法，其中，所述稀盐水溶液的浓度为0.01wt％-2wt％。
  17. 根据权利要求7-16中任一项所述的方法，其中，，步骤(3)中，所述砂磨的条件包括：线速度为5m/s-15m/s，时间为0.5h-12h。
  18. 根据权利要求7-17中任一项所述的方法，其中，步骤(4)中，所述喷雾干燥的条件包括：固含量为30wt％-50wt％，温度为90℃-105℃，时间为5h-12h；
    所述烧结的条件包括：温度为650℃-760℃，时间为5h-10h。
  19. 一种由权利要求7-18中任意一项所述的方法制备得到的磷酸铁锂正极材料。
  20. 一种锂离子电池，其特征在于，包括如权利要求1-6和19中任意一项所述的磷酸铁锂正极材料。
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CN116845235B (zh) * 2023-08-29 2024-04-02 深圳海辰储能控制技术有限公司 正极材料、正极极片及电池
CN118641438A (zh) * 2024-08-13 2024-09-13 四川富临新能源科技有限公司 一种检测磷酸铁锂浆料中磷酸二氢锂粒度的半定量分析方法

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