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WO2023227035A1 - 一种正极材料及其制备方法 - Google Patents

一种正极材料及其制备方法 Download PDF

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Publication number
WO2023227035A1
WO2023227035A1 PCT/CN2023/096086 CN2023096086W WO2023227035A1 WO 2023227035 A1 WO2023227035 A1 WO 2023227035A1 CN 2023096086 W CN2023096086 W CN 2023096086W WO 2023227035 A1 WO2023227035 A1 WO 2023227035A1
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Prior art keywords
cathode material
temperature
positive electrode
sodium
solution
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PCT/CN2023/096086
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English (en)
French (fr)
Inventor
任海朋
江卫军
陈思贤
郑晓醒
郝雷明
杨红新
高飞
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蜂巢能源科技股份有限公司
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Priority to EP23811105.8A priority Critical patent/EP4439716A1/en
Publication of WO2023227035A1 publication Critical patent/WO2023227035A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M10/54—Reclaiming serviceable parts of waste accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the field of sodium-ion battery materials, and specifically to a cathode material and a preparation method thereof.
  • lithium-ion batteries play an extremely important role in energy storage and power batteries. Due to the low distribution of lithium resources in the earth's crust, the price of lithium salts has risen rapidly, resulting in the cost price of raw materials. Rapidly increasing, and sodium-ion batteries are the main energy storage tool in the later stages of the development of the new energy industry due to their abundant sodium resources and low manufacturing costs. Although current research on sodium-ion batteries has achieved some impressive results, there are still many issues that require further research, especially cathode materials for sodium-ion batteries.
  • cathode materials for sodium-ion batteries there are two main categories of cathode materials for sodium-ion batteries, one is the metal oxidation type, and the other is the polyanionic type.
  • the polyanionic type has a higher electrode potential, a solid structural framework, good thermal stability and rapid
  • the sodium ion deintercalation kinetics has attracted widespread attention.
  • sodium-iron-based polyanionic materials due to the rich reserve of raw material iron and low price, and the simple material preparation process, sodium-iron-based polyanionic materials have great advantages in the pursuit of large-scale production, cost-effective and environmentally friendly sodium-ion battery cathode materials. It is expected to become a new generation of battery materials, but its capacity and cycle stability need to be further improved.
  • the technical problem to be solved by this application is to overcome the shortcomings of low capacity and poor cycle stability in the prior art, thereby providing a cathode material and a preparation method thereof.
  • the present application provides a cathode material, which includes a polyanionic sodium iron salt and graphene coated on the polyanion sodium iron salt.
  • the cathode material has a hollow porous structure.
  • the positive electrode material has a hollow porous spherical structure.
  • the inner diameter of the positive electrode material is The inner diameter of the cathode material is 0.5-9 ⁇ m, and the wall thickness is 1-13 ⁇ m. More preferably, the inner diameter of the positive electrode material is 1-5 ⁇ m, and the wall thickness is 2-5 ⁇ m.
  • the pore diameter of the cathode material is 50-500nm, the porosity is 3-18%, and the specific surface area is 5-40m 2 /g.
  • the pore diameter of the cathode material is 100-300nm, and the porosity is 5 ⁇ 12%, and the specific surface area is 10 ⁇ 30m 2 /g.
  • the pore diameter a, porosity b, and specific surface area c of the positive electrode material satisfy the following relationship: 200 ⁇ a ⁇ c/b ⁇ 800.
  • the molecular formula of the polyanion sodium iron salt is: Na x F y M q B r (AOn) z (P 2 O 7 ) m , where M is selected from Ti, V, Mn, Fe, Co, Ni , at least one of Cu and Zn, A is selected from one of silicon, phosphorus, sulfur, carbon and boron, B is La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Td, Dy, Er , at least one of Tm, Yb, Lu, Sc and Y, where 2 ⁇ x ⁇ 4, 0.5 ⁇ y ⁇ 3, 0 ⁇ q ⁇ 2, 0 ⁇ r ⁇ 0.3, and y+q+r ⁇ 3,0 ⁇ z ⁇ 3, 0 ⁇ m ⁇ 3, 1 ⁇ n ⁇ 4, and z and m are not 0 at the same time, and the chemical formula satisfies charge conservation; preferably, M is Mn, B is La, and A is P.
  • the molecular formula of the polyanion sodium iron salt is: Na x Fe y Mn q La r (PO 4 ) z (P 2 O 7 ) m , 3 ⁇ x ⁇ 4, 1.5 ⁇ y ⁇ 2, 1 ⁇ q ⁇ 1.5, 0.2 ⁇ r ⁇ 0.3, and y+q+r ⁇ 3, 1 ⁇ z ⁇ 2, 1 ⁇ m ⁇ 2.
  • the mass of the graphene accounts for 1%-20% of the total mass of the cathode material.
  • This application also provides a preparation method of cathode material, including the following steps:
  • Step S1 Mix carbon balls and water to prepare a bottom liquid, add an anion source, an alkaline solution and a metal solution containing iron salt to the bottom liquid to perform a precipitation reaction, add sodium salt to prepare a precursor solution;
  • Step S2 Place graphene in a vacuum environment to prepare a graphene film, electrospray the graphene film using a precursor solution, and calcine to obtain a positive electrode material with a hollow porous structure.
  • the iron salt is a conventional iron salt in the art, such as ferrous sulfate, ferric ammonium sulfate, ferrous ammonium sulfate, ferrous oxalate, ferric ammonium oxalate, ferrous chloride, ferric citrate, ferric ammonium citrate, At least one of iron phosphate and iron nitrate.
  • the feed rate of the electrospray is 4-10mL/h
  • the spray voltage is 10-20kV
  • the nozzle diameter is 8-12 ⁇ m
  • the discharge temperature is 50-90°C
  • the calcination temperature The temperature is 300-800°C and the time is 5-30h.
  • the calcination is to heat up to 350-450°C at a heating rate of 0.5-2°C/min in a nitrogen atmosphere, maintain this temperature for calcination for 3-5 hours, and then heat up to 650-850°C at a heating rate of 0.5-2°C/min. °C, maintain this temperature for calcination for 5-20h, preferably, the calcination is to heat up to 380-420°C at a heating rate of 0.8-1.5°C/min in a nitrogen atmosphere, maintain this temperature for calcination for 3-5h, and then calcine at 0.8-1.5°C /min heating rate to 680-720°C, and maintain this temperature for calcination for 8-12h.
  • step S1 also satisfies at least one of the following (1)-(7):
  • the metal solution also includes M salt and/or B salt; preferably, M is selected from at least one of Ti, V, Mn, Fe, Co, Ni, Cu and Zn; B is La, Ce, Pr , at least one of Nd, Pm, Sm, Eu, Gd, Td, Dy, Er, Tm, Yb, Lu, Sc and Y; more preferably, M is Mn and B is La;
  • the anion source is selected from at least one of silicon source, phosphorus source, sulfur source, carbon source and boron source; preferably, the anion source is selected from ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triphosphate At least one of ammonium, phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium ammonium hydrogen phosphate, pyrophosphate, sodium pyrophosphate, hypophosphorous acid, ammonium bicarbonate, ammonium sulfate, ammonium borate and ammonium silicate;
  • the precipitation reaction process also includes the step of adding protonic acid to the bottom liquid;
  • the anion source is a phosphorus source;
  • the ratio of the molar amount of phosphate ions in the phosphorus source added to the bottom liquid, the molar amount of hydrogen ions in the protonic acid, and the total molar amount of metal elements added to the bottom liquid is 2-4:1-8: 1-3, more preferably 2-4:1-2:1-3;
  • ammonium dihydrogen phosphate and citric acid there is 1 molecule of phosphate in 1 molecule of ammonium dihydrogen phosphate, and 1 molecule of citric acid electrolyzes to produce 2 molecules of hydrogen ions.
  • the pH value of the reaction liquid is controlled to be 2 to 5, preferably 2.2 to 3.2; during the precipitation reaction, the stirring speed is controlled to be 500 to 1000 rpm, preferably 600 to 800 rpm; during the precipitation reaction, the temperature of the reaction liquid is controlled to be 70 ⁇ 110°C, preferably 80 ⁇ 100°C;
  • the particle size of the carbon balls is 0.5-8.0 ⁇ m, preferably 1-4 ⁇ m;
  • the concentration of the metal solution is 0.5 ⁇ 3mol/L, preferably 0.6 ⁇ 1.5mol/L; the concentration of the anion source is 0.5 ⁇ 3mol/L; the metal solution and anion source are added dropwise at a dropping speed of 60-400mL/h into the bottom liquid, the time for dropwise reaction is 5-60h, preferably 10-30h;
  • the alkaline solution is ammonia water.
  • the ammonia water concentration is 0.5-1.5 mol/L;
  • the concentration of the bottom liquid is 50-200g/L.
  • the protonic acid is at least one of citric acid, oxalic acid, lactic acid and boric acid;
  • the phosphorus source is ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, phosphoric acid, sodium dihydrogen phosphate, dihydrogen phosphate At least one of sodium, sodium ammonium hydrogen phosphate, pyrophosphoric acid, sodium pyrophosphate and hypophosphorous acid.
  • the concentration of the protonic acid solution is 0.5 ⁇ 3mol/L.
  • the positive electrode material includes a polyanionic sodium iron salt and graphene coated outside the polyanionic sodium iron salt, the positive electrode material is a hollow porous structure, and the hollow porous structure is in contact with the polyanionic sodium iron salt.
  • the combination of graphene coated on the outside of the iron salt makes the cathode material have significantly improved charge and discharge performance and cycle stability.
  • the cathode material with a hollow porous structure has many highly open three-dimensional pores, which is conducive to the insertion and extraction of large-sized sodium ions. At the same time, it increases the contact area with the electrolyte, greatly improving the conductivity and charging capacity.
  • the graphene coated with polyanion sodium iron salt can greatly increase the adhesion of the material on the current collector, and the positive electrode plate The flexibility and ductility improve structural stability and thereby improve cyclic stability.
  • the cathode material provided by this application has a hollow porous spherical structure.
  • the inner diameter of the cathode material is controlled to 1 to 5 ⁇ m and the wall thickness is At 2 to 5 ⁇ m, the structural stability of the cathode material can be further improved, thereby improving the material's cycle performance and rate performance.
  • the cathode material provided by this application has a hollow porous spherical structure.
  • the porosity is 3-18%, and the specific surface area is 5-40m 2 /g.
  • the structural stability and rate performance of the material can be further improved.
  • the preparation method of the cathode material provided in this application is to prepare a bottom liquid by mixing carbon balls and water, add an anion source, an alkaline solution and a metal solution containing iron salt to the bottom liquid to perform a precipitation reaction, and add sodium salt , prepare a precursor solution, place graphene in a vacuum environment to prepare a graphene film, use the precursor solution to electrospray the graphene film, and calcine to obtain the cathode material.
  • a precursor of the polyanionic sodium iron salt is prepared on the carbon spheres through a precipitation reaction, and electrospraying is used to coat the precursor of the polyanionic sodium iron salt on the graphene, wherein the polyanionic sodium
  • the iron salt precursor covers the outside of the carbon spheres, and graphene is in the outermost layer of the material.
  • the carbon spheres are removed by calcination to obtain a positive electrode material with a hollow porous structure.
  • the preparation method is simple and convenient.
  • the preparation method of the cathode material provided in this application is by controlling the calcination conditions, that is, the calcination is to be heated to 350-450°C at a heating rate of 0.5-2°C/min in a nitrogen atmosphere, maintained at this temperature for 3-5 hours, and then The temperature is raised to 650-850°C at a heating rate of 0.5-2°C/min, and the temperature is maintained for 5-20 hours.
  • the calcination is heated to 380-420°C at a heating rate of 0.8-1.5°C/min in a nitrogen atmosphere.
  • the ratio of the molar amount of phosphate ions in the added phosphorus source and the molar amount of hydrogen ions in the protonic acid to the total molar amount of metal elements added in the bottom solution is (2 -4):(1-2):(1-3), this ratio can ensure that excess phosphate can generate pyrophosphate at high temperature in the later stage, which can further improve the stability of the material structure and provide sodium ion intercalation and extraction. channels to increase the capacity of the material.
  • Figure 1 is an infrared spectrum of the cathode material obtained in Example 1;
  • Figure 2 is a TEM image of the cathode material obtained in Example 1;
  • Figure 3 is an SEM image of the cathode material obtained in Example 1;
  • Figure 4 is a cycle performance diagram of the cathode material obtained in Example 1 in Experimental Example 3 at 0.2C, 1C and 5C rates;
  • Figure 5 is an XRD pattern of the cathode material obtained in Example 1.
  • the cathode material includes a polyanionic sodium iron salt and graphene coated on the polyanion sodium iron salt.
  • the cathode material has a wave number of 721cm -1 to 956cm - Segment 1 is POP bonded, corresponding to the P 2 O 7 group, that is, the pyrophosphate group; while segments 400 to 700cm -1 and 975 to 1300cm -1 are OPO and PO bonded respectively, corresponding to the PO 4 group, That is the phosphate group.
  • the molecular formula of the polyanion sodium iron salt is Na 4 (Fe 0.6 Mn 0.392 La 0.08 ) 3 (PO 4 ) 2 P 2 O 7 .
  • TEM and SEM images confirm that the cathode material has a hollow porous spherical structure.
  • the inner diameter, wall thickness, pore size, porosity and specific surface area of the cathode material are shown in Table 2.
  • the preparation method of the cathode material includes the following steps:
  • This embodiment provides a cathode material and a preparation method thereof.
  • the preparation method of the cathode material includes the following steps:
  • This embodiment provides a cathode material and a preparation method thereof.
  • the preparation method of the cathode material includes the following steps:
  • This embodiment provides a cathode material and its preparation method, which is basically the same as Embodiment 1. The only difference is that in step (1), carbon balls with a particle size of 8 ⁇ m are used, and the dropping time of the three solutions is 60 hours. , 530.3g of positive electrode material was obtained.
  • This embodiment provides a cathode material and a preparation method thereof, which are basically the same as those in Embodiment 1.
  • the only difference lies in that carbon balls with a particle size of 0.5 ⁇ m are used in step (1), and the dropping times of the three solutions are all After 5h, 658.2g of cathode material was obtained.
  • This embodiment provides a cathode material and a preparation method thereof, which are basically the same as the embodiment, and the only difference lies in: Calcination in step (2) is to raise the temperature to 400°C at a heating rate of 1°C/min, maintain this temperature for 4 hours, and then raise the temperature to 700°C at a heating rate of 1°C/min, maintain this temperature for calcination for 20 hours, and use a nitrogen atmosphere of 1L/min. , 634.5g of positive electrode material was obtained.
  • This embodiment provides a cathode material and its preparation method, which is basically the same as the embodiment. The only difference is that step (2) is calcined to 400°C at a heating rate of 1°C/min, maintained at this temperature for 4 hours, and then calcined. The temperature was raised to 700°C at a heating rate of 1°C/min, maintained at this temperature and calcined for 5 hours, with a nitrogen atmosphere of 1L/min, and 647.3g of positive electrode material was obtained.
  • the cathode material includes a polyanionic sodium iron salt and graphene coated on the polyanionic sodium iron salt.
  • the molecular formula of the polyanionic sodium iron salt is Na 4 Fe 3 (PO 4 ). 2 P 2 O 7 . Its preparation method includes the following steps:
  • the positive electrode material includes a polyanionic sodium iron salt and graphene coated on the polyanionic sodium iron salt.
  • the molecular formula of the polyanionic sodium iron salt is Na 4 (Fe 0.6 Co 0.392 Y 0.08 ) 3 (SO 4 ) 2 P 2 O 7 . Its preparation method includes the following steps:
  • the dried material into a tube furnace and calcine it in a nitrogen atmosphere, raise the temperature to 200°C at a heating rate of 1°C/min, maintain this temperature for 4 hours, then raise the temperature to 500°C at a heating rate of 1°C/min, and maintain Calcined at this temperature for 10 hours, nitrogen atmosphere 1L/min; the calcined material was sieved with 400 mesh to obtain 596.8g of positive electrode material.
  • This embodiment provides a cathode material and a preparation method thereof, which are basically the same as Example 1. The only difference is that citric acid is not added in step (1), and 649.2 g of cathode material is obtained.
  • This embodiment provides a cathode material and its preparation method, which is basically the same as Example 1. The only difference is that in step (1), citric acid is added dropwise at a speed of 200 ml/min to prepare 640.3 g of cathode material.
  • This comparative example provides a cathode material, including the following steps:
  • the dropping time of the three solutions is all 20 hours.
  • This embodiment provides a cathode material, including the following steps:
  • This comparative example provides a cathode material, including the following steps:
  • the dropping time of the three solutions is all 20 hours.
  • reaction After completion, add sodium carbonate at a Na:(Fe+Mn+La) molar ratio of 4:3 and stir at 700 rpm for 1 hour to obtain a precursor solution.
  • the cathode material of Example 1 was subjected to ICP elemental analysis, and the results are shown in the table below.
  • the pore diameter a (nm), porosity b%, and specific surface area c (m 2 /g) of the cathode material in each embodiment of the present application satisfy the following relationship: 200 ⁇ a ⁇ c/b ⁇ 800, and have good electrical properties.
  • PVDF conductive carbon black and adhesive polyvinylidene fluoride
  • NMP N - Methylpyrrolidone
  • Specific capacity test conditions 0.1C (120mA/g), voltage range 1.5V-4.05V test; and 5C, voltage range 1.5V-4.05V test; 2C, voltage range 1.5V-4.05V test;
  • Cycle performance test conditions 0.2C, 1C and 5C, the voltage range is 1.5V-4.05V, the cathode material of Test Example 1 was tested at room temperature for 500 weeks, see Figure 4;
  • the cathode materials of each embodiment and comparative example were tested for 500 cycles at room temperature at 1C, with a voltage range of 1.5V-4.05V, see the table below.
  • the positive electrode materials obtained in Examples 1-11 of the present application include polyanionic sodium iron salt and graphene coated on the polyanionic sodium iron salt. As can be seen from Table 2, the positive electrode material has a hollow porous structure. Compared with the For ratios 1-3, these cathode materials have significantly improved discharge capacity, cycle stability and rate performance.
  • Example 1 Comparing Example 1 with Examples 8 and 9, by controlling the type of metal elements within the preferred range, especially controlling the molecular formula of the polyanion sodium iron salt to be: Na x Fe y Mn q La r (PO 4 ) z ( P 2 O 7 ) m , 3 ⁇ x ⁇ 4, 1.5 ⁇ y ⁇ 2, 1 ⁇ q ⁇ 1.5, 0.2 ⁇ r ⁇ 0.3, and y+q+r ⁇ 3, 1 ⁇ z ⁇ 2, 1 ⁇ m ⁇ 2. Further improve the capacity, cycle stability and rate performance of the cathode material.
  • the molecular formula of the polyanion sodium iron salt to be: Na x Fe y Mn q La r (PO 4 ) z ( P 2 O 7 ) m , 3 ⁇ x ⁇ 4, 1.5 ⁇ y ⁇ 2, 1 ⁇ q ⁇ 1.5, 0.2 ⁇ r ⁇ 0.3, and y+q+r ⁇ 3, 1 ⁇ z ⁇ 2, 1 ⁇ m ⁇ 2.
  • Example 1 Comparing Example 1 with Examples 4-5, by optimizing the particle size of the carbon balls and controlling the dripping time within the preferred range, the inner diameter and wall thickness of the cathode material are within the preferred range of the present application, so that the capacity of the cathode material, Cycling stability and rate performance are further improved.
  • Example 1 Comparing Example 1 with Examples 6-7, by controlling the conditions of the calcination reaction within the preferred range, the pore size, porosity and specific surface area of the cathode material are within the preferred range, so that the capacity, cycle stability and The magnification performance is further improved.
  • Embodiment 1 controls the molar amount of phosphate ions in the phosphorus source added to the bottom liquid, the molar amount of hydrogen ions in the protonic acid, and the molar amount of the metal element added to the bottom liquid.
  • the total molar ratio is within the preferred range, so that pyrophosphate and phosphate radicals coexist in the calcined cathode material, further improving the capacity, cycle stability and rate performance of the cathode material.
  • the cathode material of Example 1 was tested by an X-ray diffractometer. It has a monoclinic phase structure, the space group is Pn2 1 a, and has the following unit cell parameters, The unit cell expansion rate is 2.12%.
  • the XRD pattern of the cathode material includes the following diffraction peaks at the 2 ⁇ angle:
  • the three strongest peaks are at angles of 15.582°, 24.393° and 32.142°.
  • the peak-to-peak intensity ratio of the three strongest XRD diffraction peaks of the positive electrode material is 1.56:1:1.47.
  • the prepared material is a composite pyrophosphate positive electrode material with good crystallinity and stable crystal structure.

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Abstract

本申请涉及钠离子电池材料领域，具体涉及一种正极材料及其制备方法，该正极材料包括聚阴离子钠铁盐和包覆在聚阴离子钠铁盐外的石墨烯，所述正极材料为空心多孔结构，该空心多孔结构与聚阴离子钠铁盐外面包覆的石墨烯相结合，使得正极材料具有明显提升的充放电性能和循环稳定性。

Description

一种正极材料及其制备方法
相关申请的交叉引用
本申请要求在2022年5月27日提交中国专利局、申请号为202210594559.6、发明名称为“一种正极材料及其制备方法”的中国专利申请的优先权，其全部内容通过引用的方式并入本文中。
技术领域
本申请涉及钠离子电池材料领域，具体涉及一种正极材料及其制备方法。
背景技术
随着新能源产业的快速发展，锂离子电池在储能及其动力电池方面有着及其重要的作用，因锂资源在地壳中分布含量较低，锂盐价格快速的上升，导致原料的成本价格急剧的增加，而钠离子电池由于钠资源及其丰富，而且制造成本低，因此钠离子电池是新能源行业发展后期的主要储能工具。目前，钠离子电池的研究虽然取得了一些可观的成绩，但仍有很多问题需要进一步研究，特别是钠离子电池正极材料。
目前钠离子电池正极材料主要有两大类，一种是金属氧化型，另一种是聚阴离子型，因聚阴离子型具有较高的电极电势，坚固的结构框架，良好的热稳定性以及快速的钠离子脱嵌动力学而受到广泛关注。其中，由于原材料铁元素储备丰富价格低廉，材料制备工艺简单，使得钠铁基聚阴离型材料在追求大规模生产，经济有效和环境友好的钠离子电池正极材料的竞争中具有很大优势，有望成为新一代电池材料，然而其容量和循环稳定性有待进一步提升。
发明内容
因此，本申请要解决的技术问题在于克服现有技术中的容量低和循环稳定性差的缺陷，从而提供一种正极材料及其制备方法。
为此，本申请提供了一种正极材料，所述正极材料包括聚阴离子钠铁盐和包覆在聚阴离子钠铁盐外的石墨烯，所述正极材料为空心多孔结构。
进一步地，所述正极材料为空心多孔的球状结构，优选地，所述正极材料的内径为 0.5～9μm，壁厚为1～13μm，更优选地，所述正极材料的内径为1～5μm，壁厚为2～5μm。
进一步地，所述正极材料的孔径为50-500nm，孔隙率为3～18％，比表面积为5～40m2/g，优选地，所述正极材料的孔径为100-300nm，孔隙率为5～12％，比表面积为10～30m2/g。
进一步地，所述正极材料的孔径a、孔隙率b、比表面积c满足以下关系式：200＜a×c/b＜800。
进一步地，所述聚阴离子钠铁盐的分子式为：NaxFeyMqBr(AOn)z(P2O7)m，其中，M选自Ti、V、Mn、Fe、Co、Ni、Cu和Zn中的至少一种，A选自硅、磷、硫、碳和硼中的一种，B为La、Ce、Pr、Nd、Pm、Sm、Eu、Gd、Td、Dy、Er、Tm、Yb、Lu、Sc和Y中至少一种，其中2≤x≤4，0.5≤y≤3，0≤q≤2，0≤r≤0.3，且y+q+r≤3，0≤z≤3，0≤m≤3，1≤n≤4，且z与m不同时为0，且化学式满足电荷守恒；优选地，M为Mn，B为La，A为P。
进一步地，所述聚阴离子钠铁盐的分子式为：NaxFeyMnqLar(PO4)z(P2O7)m，3≤x≤4，1.5≤y≤2，1≤q≤1.5，0.2≤r≤0.3，且y+q+r≤3，1≤z≤2，1≤m≤2。
进一步地，所述石墨烯的质量占正极材料总质量的1％-20％。
本申请还提供了一种正极材料的制备方法，包括如下步骤：
S1步骤：将碳球与水混合制得底液，向底液中加入阴离子源，以及碱性溶液和含铁盐的金属溶液进行沉淀反应，加入钠盐，制得前驱体溶液；
S2步骤：将石墨烯置于真空环境中，制得石墨烯膜，采用前驱体溶液对所述石墨烯膜进行电喷雾，煅烧，得到空心多孔结构的正极材料。
其中，所述铁盐为本领域常规的铁盐，例如硫酸亚铁、硫酸铁铵、硫酸亚铁铵、草酸亚铁、草酸高铁铵、氯化亚铁、柠檬酸铁、柠檬酸铁铵、磷酸铁、硝酸铁中至少一种。
进一步地，S2步骤中，电喷雾的进料速度为4-10mL/h，喷雾电压为10-20kV，喷嘴直径为8-12μm，出料温度为50-90℃；和/或，煅烧的温度为300-800℃，时间为5-30h。
进一步地，煅烧为在氮气气氛下以0.5-2℃/min的升温速率升温至350-450℃，维持该温度煅烧3-5h，然后以0.5-2℃/min的升温速率升温至650-850℃，维持该温度煅烧5-20h，优选地，煅烧为在氮气气氛下以0.8-1.5℃/min的升温速率升温至380-420℃，维持该温度煅烧3-5h，然后以0.8-1.5℃/min的升温速率升温至680-720℃，维持该温度煅烧8-12h。
进一步地，S1步骤还满足如下(1)-(7)中的至少一项：
(1)金属溶液中还包括M盐和/或B盐；优选地，M选自Ti、V、Mn、Fe、Co、Ni、Cu和Zn中的至少一种；B为La、Ce、Pr、Nd、Pm、Sm、Eu、Gd、Td、Dy、Er、Tm、Yb、Lu、Sc和Y中至少一种；更优选地，M为Mn，B为La；
(2)所述阴离子源选自硅源、磷源、硫源、碳源和硼源中的至少一种；优选的，所述阴离子源选自磷酸二氢铵、磷酸氢二铵、磷酸三铵、磷酸、磷酸二氢钠、磷酸氢二钠、磷酸氢钠铵、焦磷酸、焦磷酸钠、次亚磷酸、碳酸氢铵、硫酸铵、硼酸铵和硅酸铵中的至少一种；
(3)沉淀反应过程中还包括向底液中加入质子酸的步骤；所述阴离子源为磷源；
优选地，底液中加入的磷源中的磷酸根离子的摩尔量、质子酸中氢离子的摩尔量与底液中加入的金属元素的总摩尔量之比为2-4：1-8：1-3，更优选为2-4：1-2：1-3；
以磷酸二氢铵和柠檬酸(质子酸)为例，1分子磷酸二氢铵中存在1分子的磷酸根，1分子柠檬酸电解产生2分子氢离子。
(4)沉淀反应过程中控制反应液的pH值为2～5，优选为2.2～3.2；沉淀反应中控制搅拌转速为500～1000rpm，优选为600～800rpm；沉淀反应中控制反应液温度为70～110℃，优选为80～100℃；
(5)所述碳球的粒径为0.5-8.0μm，优选为1-4μm；
(6)金属溶液的浓度为0.5～3mol/L，优选为0.6～1.5mol/L；阴离子源的浓度为0.5～3mol/L；金属溶液和阴离子源以60-400mL/h的滴加速度滴加至底液中，滴加反应的时间为5-60h，优选为10-30h；
(7)所述碱性溶液为氨水，优选地，氨水浓度为0.5～1.5mol/L；
(8)底液的浓度为50-200g/L。
其中，所述质子酸为柠檬酸、草酸、乳酸和硼酸中的至少一种；所述磷源为磷酸二氢铵、磷酸氢二铵、磷酸三铵、磷酸、磷酸二氢钠、磷酸氢二钠、磷酸氢钠铵、焦磷酸、焦磷酸钠和次亚磷酸中的至少一种。质子酸溶液的浓度为0.5～3mol/L。
本申请技术方案，具有如下优点：
1.本申请提供的正极材料，所述正极材料包括聚阴离子钠铁盐和包覆在聚阴离子钠铁盐外的石墨烯，所述正极材料为空心多孔结构，该空心多孔结构与聚阴离子钠铁盐外面包覆的石墨烯相结合，使得正极材料具有明显提升的充放电性能和循环稳定性。一方面，空心多孔结构的正极材料有着较多的高度开放的三维孔道，有利于大粒径的钠离子的嵌入和脱出，同时增大了与电解液的接触面积，极大提高导电性和充放电性能，有效 避免钠离子在快速嵌入和脱出过程中而破坏钠电正极材料的结构，而通过聚阴离子钠铁盐外面包覆的石墨烯可以极大增加材料在集流体上的粘结力，正极正极极片的柔韧性和延展性，提高结构稳定性，从而提高循环稳定性。
2.本申请提供的正极材料，所述正极材料为空心多孔的球状结构，通过控制正极材料的内径为0.5～9μm，壁厚为1～13μm，尤其是控制内径为1～5μm，壁厚为2～5μm时，能够进一步提高正极材料的结构稳定性，进而提高材料的循环性能以及倍率性能。
3.本申请提供的正极材料，所述正极材料为空心多孔的球状结构，通过控制所述正极材料的孔径为50-500nm，孔隙率为3～18％，比表面积为5～40m2/g，尤其是控制所述正极材料的孔径的孔径为100-300nm，孔隙率为5～12％，比表面积为10～30m2/g时，能够进一步提高材料的结构稳定性及其倍率性能。
4.本申请提供的正极材料的制备方法，通过将碳球与水混合制得底液，向底液中加入阴离子源，以及碱性溶液和含铁盐的金属溶液进行沉淀反应，加入钠盐，制得前驱体溶液，将石墨烯置于真空环境中，制得石墨烯膜，采用前驱体溶液对所述石墨烯膜进行电喷雾，煅烧，得到正极材料。以碳球溶液为底液，通过沉淀反应在碳球上制得聚阴离子钠铁盐的前驱体，采用电喷雾将石墨烯包覆的聚阴离子钠铁盐的前驱体上，其中该聚阴离子钠铁盐前驱体覆盖在碳球外侧，而石墨烯在该材料的最外层，通过煅烧将碳球去除而得到空心多孔结构的正极材料，制备方法简单方便。
5.本申请提供的正极材料的制备方法，通过控制煅烧条件，即煅烧为在氮气气氛下以0.5-2℃/min的升温速率升温至350-450℃，维持该温度煅烧3-5h，然后以0.5-2℃/min的升温速率升温至650-850℃，维持该温度煅烧5-20h，尤其是，煅烧为在氮气气氛下以0.8-1.5℃/min的升温速率升温至380-420℃，维持该温度煅烧3-5h，然后以0.8-1.5℃/min的升温速率升温至680-720℃，维持该温度煅烧8-12h；使得正极材料的孔径、孔隙率和比表面积在优选的范围内，使得正极材料的容量、循环稳定性和倍率性能进一步提升。
6.本申请提供的正极材料的制备方法，加入的磷源中的磷酸根离子的摩尔量、质子酸中氢离子的摩尔量与底液中加入的金属元素的总摩尔量之比为(2-4):(1-2):(1-3)，此比例可以保证有多余的磷酸根在后期高温下可以生成焦磷酸根，能够进一步提高材料结构的稳定性以及提供钠离子嵌入脱出的通道，提高材料的容量。
附图说明
为了更清楚地说明本申请具体实施方式或现有技术中的技术方案，下面将对具体实 施方式或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图是本申请的一些实施方式，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据这些附图获得其他的附图。
图1是实施例1得到的正极材料的红外光谱图；
图2是实施例1得到的正极材料的TEM图；
图3是实施例1得到的正极材料的SEM图；
图4是实验例3中实施例1得到的正极材料0.2C、1C和5C倍率下的循环性能图；
图5是实施例1得到的正极材料的XRD图谱。
具体实施方式
提供下述实施例是为了更好地进一步理解本申请，并不局限于所述最佳实施方式，不对本申请的内容和保护范围构成限制，任何人在本申请的启示下或是将本申请与其他现有技术的特征进行组合而得出的任何与本申请相同或相近似的产品，均落在本申请的保护范围之内。
实施例中未注明具体实验步骤或条件者，按照本领域内的文献所描述的常规实验步骤的操作或条件即可进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规试剂产品。碳球购自先锋纳米材料公司，型号为XF252、XFP12、XFP13、XFP14、XFP05，平均粒径依次为0.5微米、1微米、2微米、4微米和8微米。
实施例1
本实施例提供了一种正极材料，该正极材料包括聚阴离子钠铁盐和包覆在聚阴离子钠铁盐外的石墨烯，其中，参见图1，该正极材料在波数721cm-1～956cm-1段为P-O-P键结合，对应着P2O7基团，即焦磷酸根基团；而400～700cm-1以及975～1300cm-1段分别为O-P-O和P-O键结合，对应着PO4基团，即磷酸根基团。该聚阴离子钠铁盐的分子式为Na4(Fe0.6Mn0.392La0.08)3(PO4)2P2O7。
参见图2和3，TEM和SEM图证实该正极材料为空心多孔的球状结构，该正极材料的内径、壁厚、孔径、孔隙率和比表面积见表2所示。
该正极材料的制备方法包括如下步骤：
(1)将硫酸铁、硫酸锰和硫酸镧按照金属元素的摩尔比为0.6：0.392：0.08混合，加水，制成金属盐总质量浓度为1.2mol/L的金属溶液。以纯水为溶剂，分别配制1mol/L的磷酸二氢铵溶液、0.5mol/L的氨水溶液和1mol/L的柠檬酸水溶液。将 粒径为2μm的碳球作为晶种加入纯水中，400rpm搅拌10min，制得浓度为100g/L的底液。将金属溶液、磷酸二氢铵溶液和柠檬酸水溶液分别以200ml/min、300ml/min和60ml/min的滴加速度加入底液中，三种溶液的滴加时间均为20小时，反应过程中还加入氨水溶液控制反应体系的pH值为2.5，控制转速700rpm，温度90℃。滴加结束后反应完成，然后按照Na:(Fe+Mn+La)摩尔比为4:3加入碳酸钠，700rpm搅拌1h，得到前驱体溶液，烘干后加水制成固含量为500g/L的前驱体溶液。
(2)将48g石墨烯放入到真空器皿中，得到石墨烯膜，然后使用电喷雾的方法，将2L固含量为500g/L的前驱体溶液喷雾在石墨烯膜上，电喷雾速度为6ml/h，喷雾电压为15KV，喷雾的喷嘴直径为10μm，出料口温度为80℃，可保证混合物的缓慢干燥，得到干燥物。将干燥物放入管式炉中在氮气气氛中进行煅烧，以1℃/min的升温速率升温至400℃，维持该温度煅烧4h，然后以1℃/min的升温速率升温至700℃，维持该温度煅烧10h，氮气气氛1L/min；将煅烧后的物料进行400目过筛，制成正极材料646.3g。
实施例2
本实施例提供了一种正极材料及其制备方法，该正极材料的制备方法包括如下步骤：
(1)将硫酸铁、硫酸锰和硫酸镧按照金属元素的摩尔比为0.6：0.392：0.08混合，加水，制成金属盐总质量浓度为1.3mol/L的金属溶液。以纯水为溶剂，分别配制1.2mol/L的磷酸二氢钠溶液、1mol/L的氨水溶液和1.2mol/L的柠檬酸水溶液。将粒径为1μm的碳球作为晶种加入纯水中，400rpm搅拌10min，制得浓度为150g/L的底液。将金属溶液、磷酸二氢钠溶液和柠檬酸分别以100ml/min、250ml/min和50ml/min的滴加速度加入底液中，三种溶液的滴加时间均为15小时，反应过程中还加入氨水溶液控制反应体系的pH值为3.2，控制转速600rpm，温度100℃。滴加结束后反应完成，然后按照Na:(Fe+Mn+La)摩尔比为4:3加入碳酸钠，700rpm搅拌1h，得到前驱体溶液，烘干后加水制成固含量为500g/L的前驱体溶液。
(2)将6g石墨烯放入到真空器皿中，得到石墨烯膜，然后使用电喷雾的方法，将2L固含量为500g/L的前驱体溶液喷雾在石墨烯膜上，电喷雾速度为10ml/h，喷雾电压为20KV，喷雾的喷嘴直径为10μm，出料口温度为70℃，可保证混合物的缓慢干燥，得到干燥物。将干燥物放入管式炉中在氮气气氛中进行煅烧，以1.5℃/min的升温速率升温至380℃，维持该温度煅烧4h，然后以0.8℃/min的升温速率升温至720℃，维持该温度煅烧12h，氮气气氛1L/min；将煅烧后的物料进行400目过筛，制成正极材料 603.6g。
实施例3
本实施例提供了一种正极材料及其制备方法，该正极材料的制备方法包括如下步骤：
(1)将硫酸铁、硫酸锰和硫酸镧按照金属元素的摩尔比为0.6：0.392：0.08混合，加水，制成金属盐总质量浓度为0.9mol/L的金属溶液。以纯水为溶剂，分别配制0.8mol/L的磷酸二氢铵溶液、1.5mol/L的氨水溶液和1.5mol/L的柠檬酸水溶液。将粒径为4μm的碳球作为晶种加入纯水中，400rpm搅拌10min，制得浓度为100g/L的底液。将金属溶液、磷酸二氢铵溶液和柠檬酸分别以200ml/min、380ml/min和50ml/min的滴加速度加入底液中，三种溶液的滴加时间均为20小时，反应过程中还加入氨水溶液控制反应体系的pH值为2.5，控制转速800rpm，温度80℃。滴加结束后反应完成，然后按照Na:(Fe+Mn+La)摩尔比为4:3加入碳酸钠，700rpm搅拌1h，得到前驱体溶液，烘干后加水制成固含量为500g/L的前驱体溶液。
(2)将120g石墨烯放入到真空器皿中，得到石墨烯膜，然后使用电喷雾的方法，将2L固含量为500g/L的前驱体溶液喷雾在石墨烯膜上，电喷雾速度为4ml/h，喷雾电压为10KV，喷雾的喷嘴直径为10μm，出料口温度为80℃，可保证混合物的缓慢干燥，得到干燥物。将干燥物放入管式炉中在氮气气氛中进行煅烧，以0.8℃/min的升温速率升温至400℃，维持该温度煅烧4h，然后以1.5℃/min的升温速率升温至700℃，维持该温度煅烧8h，氮气气氛1L/min；将煅烧后的物料进行400目过筛，制成正极材料718.5g。
实施例4
本实施例提供了一种正极材料及其制备方法，基本与实施例1相同，区别仅在于，步骤(1)中采用粒径为8μm的碳球，且三种溶液的滴加时间均为60h，制得正极材料530.3g。
实施例5
本实施例提供了一种正极材料及其制备方法，基本与实施例1相同，区别仅在于，步骤(1)中采用粒径为0.5μm的碳球，且三种溶液的滴加时间均为5h，制得正极材料658.2g。
实施例6
本实施例提供了一种正极材料及其制备方法，基本与实施例相同，区别仅在于， 步骤(2)煅烧为以1℃/min的升温速率升温至400℃，维持该温度煅烧4h，然后以1℃/min的升温速率升温至700℃，维持该温度煅烧20h，氮气气氛1L/min，制得正极材料634.5g。
实施例7
本实施例提供了一种正极材料及其制备方法，基本与实施例相同，区别仅在于，步骤(2)煅烧为以1℃/min的升温速率升温至400℃，维持该温度煅烧4h，然后以1℃/min的升温速率升温至700℃，维持该温度煅烧5h，氮气气氛1L/min，制得正极材料647.3g。
实施例8
本实施例提供了一种正极材料，该正极材料包括聚阴离子钠铁盐和包覆在聚阴离子钠铁盐外的石墨烯，该聚阴离子钠铁盐的分子式为Na4Fe3(PO4)2P2O7。其制备方法包括如下步骤：
(1)将硫酸铁加水，制成硫酸铁浓度为1.2mol/L的金属溶液。以纯水为溶剂，分别配制1mol/L的磷酸二氢铵溶液、0.5mol/L的氨水溶液和1mol/L的柠檬酸水溶液。将粒径为2μm的碳球作为晶种加入纯水中，400rpm搅拌10min，制得浓度为100g/L的底液。将金属溶液、磷酸二氢铵溶液和柠檬酸水溶液分别以200ml/min、300ml/min和60ml/min的滴加速度加入底液中，同时还加入氨水溶液控制反应体系的pH值为2.5，控制转速700rpm，温度90℃，三种溶液的滴加时间20小时。反应完成后按照Na:(Fe)摩尔比为4:3加入碳酸钠，700rpm搅拌1h，得到前驱体溶液，烘干后加水制成固含量为500g/L的前驱体溶液。
(2)将78.64g石墨烯放入到真空器皿中，得到石墨烯膜，然后使用电喷雾的方法，将2L固含量为500g/L前驱体溶液喷雾在石墨烯膜上，电喷雾速度为6ml/h，喷雾电压为15KV，喷雾的喷嘴直径为10μm，出料口温度为80℃，可保证混合物的缓慢干燥，得到干燥物。将干燥物放入管式炉中在氮气气氛中进行煅烧，以1℃/min的升温速率升温至400℃，维持该温度煅烧4h，然后以1℃/min的升温速率升温至700℃，维持该温度煅烧10h，氮气气氛1L/min；将煅烧后的物料进行400目过筛，制成正极材料，制得正极材料1031.4g。
实施例9
本实施例提供了一种正极材料，该正极材料包括聚阴离子钠铁盐和包覆在聚阴离子钠铁盐外的石墨烯，该聚阴离子钠铁盐的分子式为Na4(Fe0.6Co0.392Y0.08)3(SO4)2P2O7。其制备方法包括如下步骤：
(1)将硫酸铁、硫酸钴和硫酸钇按照金属元素的摩尔比为0.6：0.392：0.08混 合，加水，制成金属盐总质量浓度为1.2mol/L的金属溶液。以纯水为溶剂，分别配制1mol/L的磷酸二氢铵溶液、0.5mol/L的氨水溶液、1mol/L的柠檬酸水溶液及1mol/L的硫酸铵溶液。将粒径为2μm的碳球作为晶种加入纯水中，400rpm搅拌10min，制得浓度为100g/L的底液。将金属溶液、磷酸二氢铵溶液、柠檬酸和硫酸铵溶液分别以200ml/min、300ml/min、60ml/min和60ml/min的滴加速度加入底液中，同时还加入氨水溶液控制反应体系的pH值为2.5，控制转速700rpm，温度90℃，三种溶液的滴加时间均为20小时，反应完毕。反应完成后按照Na:(Fe)摩尔比为4:3加入碳酸钠，700rpm搅拌1h，得到前驱体溶液，烘干后加水制成固含量为500g/L的前驱体溶液。
(2)将44.5g石墨烯放入到真空器皿中，得到石墨烯膜，然后使用电喷雾的方法，将2L固含量为500g/L前驱体溶液喷雾在石墨烯膜上，电喷雾速度为6ml/h，喷雾电压为15KV，喷雾的喷嘴直径为10μm，出料口温度为80℃，可保证混合物的缓慢干燥，得到干燥物。将干燥物放入管式炉中在氮气气氛中进行煅烧，以1℃/min的升温速率升温至200℃，维持该温度煅烧4h，然后以1℃/min的升温速率升温至500℃，维持该温度煅烧10h，氮气气氛1L/min；将煅烧后的物料进行400目过筛，制得正极材料596.8g。
实施例10
本实施例提供了一种正极材料及其制备方法，基本与实施例1相同，区别仅在于，步骤(1)不添加柠檬酸，制得正极材料649.2g。
实施例11
本实施例提供了一种正极材料及其制备方法，基本与实施例1相同，区别仅在于，步骤(1)柠檬酸以200ml/min的速度滴加，制得正极材料640.3g。
对比例1
本对比例提供了一种正极材料，包括如下步骤：
(1)将硫酸铁、硫酸锰和硫酸镧按照金属元素的摩尔比为0.6：0.392：0.08混合，加水，制成金属盐总质量浓度为1.2mol/L的金属溶液。以纯水为溶剂，分别配制1mol/L的磷酸二氢铵溶液、0.5mol/L的氨水溶液和1mol/L的柠檬酸水溶液。将金属溶液、磷酸二氢铵溶液和柠檬酸水溶液分别以200ml/min、300ml/min和60ml/min的滴加速度加入纯水中，三种溶液的滴加时间均为20小时，反应过程中还加入氨水溶液控制反应体系的pH值为2.5，控制转速700rpm，温度90℃。反应完成后按照Na:(Fe+Mn+La)摩尔比为4:3加入碳酸钠，700rpm搅拌1h，得到前驱体 溶液，烘干后加水制成固含量为500g/L的前驱体溶液。
(2)将48g石墨烯放入到真空器皿中，得到石墨烯膜，然后使用电喷雾的方法，将2L固含量为500g/L前驱体溶液喷雾在石墨烯膜上，电喷雾速度为6ml/h，喷雾电压为15KV，喷雾的喷嘴直径为10μm，出料口温度为80℃，可保证混合物的缓慢干燥，得到干燥物。将干燥物放入管式炉中在氮气气氛中进行煅烧，以1℃/min的升温速率升温至400℃，维持该温度煅烧4h，然后以1℃/min的升温速率升温至700℃，维持该温度煅烧10h，氮气气氛1L/min；将煅烧后的物料进行400目过筛，制成正极材料。
对比例2
本实施例提供了一种正极材料，包括如下步骤：
(1)将硫酸铁、硫酸锰和硫酸镧按照金属元素的摩尔比为0.6：0.392：0.08混合，加水，制成金属盐总质量浓度为1.2mol/L的金属溶液。以纯水为溶剂，分别配制1mol/L的磷酸二氢铵溶液、0.5mol/L的氨水溶液和1mol/L的柠檬酸水溶液。将粒径为2μm的碳球作为晶种加入纯水中，400rpm搅拌10min，制得浓度为100g/L的底液。将金属溶液、磷酸二氢铵溶液和柠檬酸水溶液分别以200ml/min、300ml/min和60ml/min的滴加速度加入底液中，三种溶液的滴加时间均为20小时，反应过程中还加入氨水溶液控制反应体系的pH值为2.5，控制转速700rpm，温度90℃。反应完成后按照Na:(Fe+Mn+La)摩尔比为4:3加入碳酸钠，700rpm搅拌1h，得到前驱体溶液，烘干后加水制成固含量为500g/L的前驱体溶液。
(2)将前驱体溶液喷雾干燥，放入管式炉中在氮气气氛中进行煅烧，以1℃/min的升温速率升温至400℃，维持该温度煅烧4h，然后以1℃/min的升温速率升温至700℃，维持该温度煅烧10h，氮气气氛1L/min；将煅烧后的物料进行400目过筛，制成正极材料。
对比例3
本对比例提供了一种正极材料，包括如下步骤：
(1)将硫酸铁、硫酸锰和硫酸镧按照金属元素的摩尔比为0.6：0.392：0.08混合，加水，制成金属盐总质量浓度为1.2mol/L的金属溶液。以纯水为溶剂，分别配制1mol/L的磷酸二氢铵溶液、0.5mol/L的氨水溶液和1mol/L的柠檬酸水溶液。将金属溶液、磷酸二氢铵溶液和柠檬酸水溶液分别以200ml/min、300ml/min和60ml/min的滴加速度加入纯水中，三种溶液的滴加时间均为20小时，反应过程中还加入氨水溶液控制反应体系的pH值为2.5，控制转速700rpm，温度90℃。反应 完成后按照Na:(Fe+Mn+La)摩尔比为4:3加入碳酸钠，700rpm搅拌1h，得到前驱体溶液，烘干后加水制成固含量为500g/L的前驱体溶液。
(2)将前驱体溶液喷雾干燥，放入管式炉中在氮气气氛中进行煅烧，以1℃/min的升温速率升温至400℃，维持该温度煅烧4h，然后以1℃/min的升温速率升温至700℃，维持该温度煅烧10h，氮气气氛1L/min；将煅烧后的物料进行400目过筛，制成正极材料。
实验例1样品的ICP测试结果
对实施例1的正极材料进行ICP元素分析，结果见下表所示。
表1各元素含量测试
表1和图1可知，实施例1制得的正极材料中聚阴离子钠铁盐的化学式为：Na4(Fe0.6Mn0.392La0.08)3(PO4)2P2O7。
实验例2正极材料理化性能与电性能
测试方法：使用透射电镜测试正极材料的内径和壁厚以及使用比表面积测试仪器测试正极材料的孔径、孔隙率以及表面积，结果见表2所示。
表2正极材料的理化性能

本申请各实施例的正极材料的孔径a(nm)、孔隙率b％、比表面积c(m2/g)满足以下关系式：200＜a×c/b＜800，具有良好的电性能。
采用各实施例和对比例制得的正极材料按照如下方法组装扣电池：将正极材料、导电炭黑和粘合剂聚偏氟乙烯(PVDF)按90:5:5的质量比混合，用N-甲基毗咯烷酮(NMP)做溶剂，调成浆料，浆料固含量为65％，均匀涂敷在铝箔上，干燥后，压实，压实面密度为2.2g/cm3，于120℃真空干燥12h，得到正极片。负极采用金属锂片，隔膜为聚丙烯多孔膜，电解液lmol/L的NaPF6/EC+DEC+DMC(EC:DEC:DMC＝1：1：1体积比)。
比容量测试条件：0.1C(120mA/g)下，电压范围1.5V-4.05V测试；以及5C下，电压范围1.5V-4.05V测试；2C下，电压范围1.5V-4.05V测试；
循环性能测试条件：0.2C，1C和5C，电压范围均是1.5V-4.05V，测试实施例1的正极材料常温测试500周，参见图4；
1C下，各实施例和对比例的正极材料常温测试500周，电压范围1.5V-4.05V，参见下表。
表3正极材料的性能参数

本申请实施例1-11得到的正极材料包括聚阴离子钠铁盐和包覆在聚阴离子钠铁盐外的石墨烯，且由表2可知，所述正极材料为空心多孔结构，相比于对比例1-3来说，这些正极材料正极材料具有明显提高的放电容量、循环稳定性和倍率性能。
实施例1与实施例8和9相比较，通过控制金属元素的种类在优选的范围内，尤其是控制聚阴离子钠铁盐的分子式为：NaxFeyMnqLar(PO4)z(P2O7)m，3≤x≤4，1.5≤y≤2，1≤q≤1.5，0.2≤r≤0.3，且y+q+r≤3，1≤z≤2，1≤m≤2，使得正极材料容量、循环稳定性和倍率性能进一步提升。
实施例1与实施例4-5相比较，通过优选碳球的粒径和控制滴加时间在优选范围内使得正极材料的内径和壁厚在本申请优选的范围内，使得正极材料的容量、循环稳定性和倍率性能进一步提升。
实施例1与实施例6-7相比较，通过控制煅烧反应的条件在优选的范围内使得正极材料的孔径、孔隙率和比表面积在优选的范围内，使得正极材料的容量、循环稳定性和倍率性能进一步提升。
实施例1与实施例10-11相比较，实施例1通过控制底液中加入的磷源中的磷酸根离子的摩尔量、质子酸中氢离子的摩尔量与底液中加入的金属元素的总摩尔量之比在优选范围之内，使得焦磷酸根和磷酸根并存于煅烧后的正极材料中，使得正极材料的容量、循环稳定性和倍率性能进一步提升。
实施例3样品的XRD图谱
通过X射线衍射仪对实施例1的正极材料进行测试，其为单斜相结构，空间群为Pn21a；具有如下晶胞参数，晶胞膨胀率为2.12％。所述正极材料的XRD图谱包括如下2θ角所示的衍射峰：
表4正极材料的结构参数

其中三个最强峰的为角度为15.582°、24.393°和32.142°。所述正极材料的XRD的三强衍射峰峰强比为1.56:1:1.47，所制备材料为复合焦磷酸盐正极材料，且结晶性较好，晶体结构稳定。
显然，上述实施例仅仅是为清楚地说明所作的举例，而并非对实施方式的限定。对于所属领域的普通技术人员来说，在上述说明的基础上还可以做出其它不同形式的变化或变动。这里无需也无法对所有的实施方式予以穷举。而由此所引伸出的显而易见的变化或变动仍处于本发明创造的保护范围之中。

Claims (11)

  1. 一种正极材料，其特征在于，所述正极材料包括聚阴离子钠铁盐和包覆在聚阴离子钠铁盐外的石墨烯，所述正极材料为空心多孔结构。
  2. 根据权利要求1所述的正极材料，其特征在于，所述正极材料为空心多孔的球状结构，优选地，所述正极材料的内径为0.5～9μm，壁厚为1～13μm，更优选地，所述正极材料的内径为1～5μm，壁厚为2～5μm。
  3. 根据权利要求1或2所述的正极材料，其特征在于，所述正极材料的孔径为50-500nm，孔隙率为3～18％，比表面积为5～40m2/g，优选地，所述正极材料的孔径为100-300nm，孔隙率为5～12％，比表面积为10～30m2/g。
  4. 根据权利要求1-3中任一所述的正极材料，其特征在于，所述正极材料的孔径a、孔隙率b、比表面积c满足以下关系式：200＜a×c/b＜800。
  5. 根据权利要求1-4中任一所述的正极材料，其特征在于，所述聚阴离子钠铁盐的分子式为：NaxFeyMqBr(AOn)z(P2O7)m，其中，M选自Ti、V、Mn、Fe、Co、Ni、Cu和Zn中的至少一种，A选自硅、磷、硫、碳和硼中的一种，B为La、Ce、Pr、Nd、Pm、Sm、Eu、Gd、Td、Dy、Er、Tm、Yb、Lu、Sc和Y中至少一种，其中2≤x≤4，0.5≤y≤3，0≤q≤2，0≤r≤0.3，且y+q+r≤3，0≤z≤3，0≤m≤3，1≤n≤4，且z与m不同时为0，且化学式满足电荷守恒；优选地，M为Mn，B为La，A为P。
  6. 根据权利要求1-5中任一所述的正极材料，其特征在于，所述聚阴离子钠铁盐的分子式为：NaxFeyMnqLar(PO4)z(P2O7)m，3≤x≤4，1.5≤y≤2，1≤q≤1.5，0.2≤r≤0.3，且y+q+r≤3，1≤z≤2，1≤m≤2。
  7. 根据权利要求1-6中任一所述的正极材料，其特征在于，所述石墨烯的质量占正极材料总质量的1％-20％。
  8. 一种权利要求1-7中任一所述的正极材料的制备方法，其特征在于，包括如下步骤：
    S1步骤：将碳球与水混合制得底液，向底液中加入阴离子源，以及碱性溶液和含铁盐的金属溶液进行沉淀反应，加入钠盐，制得前驱体溶液；
    S2步骤：将石墨烯置于真空环境中，制得石墨烯膜，采用前驱体溶液对所述石墨烯膜进行电喷雾，煅烧，得到空心多孔结构的正极材料。
  9. 根据权利要求8所述的正极材料的制备方法，其特征在于，S2步骤中，电喷雾的进料速度为4-10mL/h，喷雾电压为10-20kV，喷嘴直径为8-12μm，出料温度为50-90℃；和/或，煅烧的温度为300-800℃，时间为5-30h。
  10. 根据权利要求9所述的正极材料的制备方法，其特征在于，煅烧为在氮气气氛下以0.5-2℃/min的升温速率升温至350-450℃，维持该温度煅烧3-5h，然后以0.5-2℃/min的升温速率升温至650-850℃，维持该温度煅烧5-20h，优选地，煅烧为在氮气气氛下以0.8-1.5℃/min的升温速率升温至380-420℃，维持该温度煅烧3-5h，然后以0.8-1.5℃/min的升温速率升温至680-720℃，维持该温度煅烧8-12h。
  11. 根据权利要求8-10中任一所述的制备方法，其特征在于，S1步骤还满足如下(1)-(8)中的至少一项：
    (1)金属溶液中还包括M盐和/或B盐；优选地，M选自Ti、V、Mn、Fe、Co、Ni、Cu和Zn中的至少一种；B为La、Ce、Pr、Nd、Pm、Sm、Eu、Gd、Td、Dy、Er、Tm、Yb、Lu、Sc和Y中至少一种；更优选地，M为Mn，B为La；
    (2)所述阴离子源选自硅源、磷源、硫源、碳源和硼源中的至少一种；优选的，所述阴离子源选自磷酸二氢铵、磷酸氢二铵、磷酸三铵、磷酸、磷酸二氢钠、磷酸氢二钠、磷酸氢钠铵、焦磷酸、焦磷酸钠、次亚磷酸、碳酸氢铵、硫酸铵、硼酸铵和硅酸铵中的至少一种；
    (3)沉淀反应过程中还包括向底液中加入质子酸的步骤；所述阴离子源为磷源；
    优选地，底液中加入的磷源中的磷酸根离子的摩尔量、质子酸中氢离子的摩尔量与底液中加入的金属元素的总摩尔量之比为2-4：1-8：1-3，更优选为2-4：1-2：1-3；
    (4)沉淀反应过程中控制反应液的pH值为2～5，优选为2.2～3.2；沉淀反应中控制搅拌转速为500～1000rpm，优选为600～800rpm；沉淀反应中控制反应液温度为70～110℃，优选为80～100℃；
    (5)所述碳球的粒径为0.5-8.0μm，优选为1-4μm；
    (6)金属溶液的浓度为0.5～3mol/L，优选为0.6～1.5mol/L；阴离子源的浓度为0.5～3mol/L；金属溶液和阴离子源以60-400mL/h的滴加速度滴加至底液中，滴加反应的时间为5-60h，优选为10-30h；
    (7)所述碱性溶液为氨水，优选地，氨水浓度为0.5～1.5mol/L；
    (8)底液的浓度为50-200g/L。
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