WO2024021255A1 - 一种包覆型普鲁士白及其制备方法和应用 - Google Patents

一种包覆型普鲁士白及其制备方法和应用 Download PDF

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WO2024021255A1
WO2024021255A1 PCT/CN2022/119466 CN2022119466W WO2024021255A1 WO 2024021255 A1 WO2024021255 A1 WO 2024021255A1 CN 2022119466 W CN2022119466 W CN 2022119466W WO 2024021255 A1 WO2024021255 A1 WO 2024021255A1
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prussian white
coated
solution
potassium
white
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PCT/CN2022/119466
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French (fr)
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李永光
李长东
徐学留
刘更好
阮丁山
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广东邦普循环科技有限公司
湖南邦普循环科技有限公司
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Priority to GB2311864.9A priority Critical patent/GB2627835A/en
Publication of WO2024021255A1 publication Critical patent/WO2024021255A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
    • C01C3/00—Cyanogen; Compounds thereof
    • C01C3/08—Simple or complex cyanides of metals
    • C01C3/12—Simple or complex iron cyanides
    • 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
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—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
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/01—Particle morphology depicted by an image
    • C01P2004/03—Particle morphology depicted by an image obtained by SEM
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/80—Particles consisting of a mixture of two or more inorganic phases
    • C01P2004/82—Particles consisting of a mixture of two or more inorganic phases two phases having the same anion, e.g. both oxidic phases
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2006/00—Physical properties of inorganic compounds
    • C01P2006/40—Electric properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention belongs to the technical field of new energy storage batteries, and specifically relates to a coated Prussian white and its preparation method and application.
  • sodium-ion cathode materials have lower manufacturing costs.
  • sodium cathode materials sodium is a common element, which significantly reduces the manufacturing cost of the material and is becoming more and more popular in the energy storage industry.
  • Prussian white polymer has strong water absorption and has a great impact on the cycle performance and rate performance of the battery core. Therefore, it is of great significance to reduce the water content and water absorption of the material.
  • Coating is a common material modification method, and there are currently many methods of coating Prussian White.
  • the conventional coating reaction generally first prepares the material to be coated through liquid phase synthesis, filtration, washing, drying and other processes, and then puts the material to be coated back into the reaction kettle. After adding water to slurry, the coating is added to the kettle. The coating reaction is carried out with the coating agent, and the second filtration, washing, and drying processes are carried out to obtain the coated and modified product. The entire process is cumbersome, has repeated steps, takes too long, and has a high loss rate.
  • the present invention aims to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention proposes a coated Prussian white and its preparation method and application.
  • the coated Prussian white provided by the invention can reduce the water absorption of Prussian white and improve the performance of sodium ion batteries; its preparation process is simple and can greatly shorten the preparation time.
  • a first aspect of the present invention provides a coated Prussian white.
  • the chemical formula of the coated Prussian white is K x Na 2-x AFe(CN) 6
  • x 0.06-0.3.
  • the coated Prussian white is produced by washing Prussian white with a potassium salt solution under the action of centrifugal force, so that at least part of the sodium ions on the surface are replaced by potassium ions.
  • a second aspect of the present invention provides a method for preparing coated Prussian white.
  • a method for preparing coated Prussian white includes the following steps:
  • the Prussian white is washed with a potassium salt solution so that at least part of the sodium ions on its surface are replaced by potassium ions; then it is washed and dried to obtain a coated Prussian white; the rotation frequency that generates the centrifugal force is 10 -60Hz.
  • the rotation frequency for generating the centrifugal force is 15-50 Hz; further preferably, the rotation frequency for generating the centrifugal force is 20-40 Hz.
  • the test found that when using potassium salt solution to wash Prussian white, the control of centrifugal force is one of the important factors affecting the coating effect.
  • the frequency of rotation is too low during washing, the centrifugal force on the potassium salt solution is insufficient and it is difficult to infiltrate the Prussian White; when the frequency of rotation is too high during washing, that is, the number of revolutions is too high, the centrifugal effect is too strong and the potassium salt solution is easily thrown away quickly. away from the equipment and the contact time with Prussian White is too short to achieve a good coating effect.
  • the equipment for generating the centrifugal force is not limited, and a centrifuge is commonly used in this process.
  • the centrifuge can not only complete the process of washing Prussian white, but also perform the subsequent washing process, reducing the number of material transfers and simplifying the preparation process.
  • the potassium salt in the potassium salt solution is at least one of potassium sulfate, potassium nitrate, potassium chloride or potassium citrate.
  • the concentration of the potassium salt solution is 0.3-3 mol/L; further, the concentration of the potassium salt solution is 0.5-2 mol/L.
  • the amount of the potassium salt solution is 20%-100% of the amount of the Prussian white. Such as 20%, 25%, 30%, 35%, 40%, 50%, 60%, 70%, 80%, 90%.
  • the washing time is 2-15 minutes; more preferably, the washing time is 5-10 minutes.
  • Prussian white is washed with potassium salt solution, and the control of washing time can effectively prevent the deterioration of the coating layer.
  • the potassium salt solution is added to Prussian white, it will almost completely react within a few minutes.
  • the washing process includes the reaction and aging process
  • a good coating effect can be achieved. If the washing time is too long, the potassium ions originally in the coating layer on the surface of the material will migrate and diffuse into the material under aqueous solution conditions, causing the coating layer to deteriorate and more holes to appear on the surface of the material. After using it to prepare a battery, The contact area between the material and the electrolyte increases and the stability decreases.
  • the drying temperature is 150-180°C.
  • the Prussian white can be a product purchased directly or a product prepared by a conventional method.
  • the Prussian white is prepared by the following method:
  • the concentration of the sodium ferrocyanide solution is 0.3-0.6 mol/L.
  • the metal salt in the metal salt solution is one or more of nickel, cobalt, manganese, ferrous sulfate, nitrate, acetate, and chloride salt.
  • the concentration of the metal salt solution is 0.5-2mol/L.
  • the reaction pH is controlled to be 6.5-9.5.
  • the complexing agent is at least one of citric acid, maleic acid, lycic acid, ethylenediaminetetraacetic acid, sodium citrate, and ammonia.
  • the concentration of the complexing agent solution is 0.5-5 mol/L.
  • a method for preparing coated Prussian white includes the following steps:
  • the third aspect of the present invention provides an application of coated Prussian white.
  • a positive electrode sheet includes the above-mentioned coated Prussian white.
  • a fourth aspect of the invention provides a sodium ion battery.
  • a sodium ion battery includes the above-mentioned positive electrode sheet.
  • the battery cathode material is a sodium ion battery cathode material.
  • the technical solution provided by the present invention uses a potassium salt solution to wash Prussian white under the action of centrifugal force.
  • the potassium salt solution flows through Prussian white, since the KSP of potassium-based Prussian white is lower, the potassium ions in the solution can partially replace the Prussian white surface.
  • Sodium ions (the actual utilization rate of potassium salt is 10%-30%, and eventually potassium replaced 3%-30% of the sodium in Prussian white), forming a coating layer on the surface of the material, and the structure of the core of the material is Na 2 AFe ( CN) 6 , the coating layer structure is K 2 AFe(CN) 6 , and A is one or more of nickel, cobalt, manganese and ferrous iron.
  • uncoated Prussian white When uncoated Prussian white is taken out after drying, it easily absorbs moisture in the air, causing the product to have a high moisture content; the coated Prussian white formed after washing has fewer water molecule channels due to surface lattice distortion, and the material When dried and taken out, the water absorption will be greatly reduced, and the moisture content of the resulting product will be significantly reduced.
  • the coating layer due to the existence of the coating layer, it can effectively improve the structural stability of the material during the charge and discharge process, reduce side reactions with the electrolyte, improve interface stability and cycle performance, and the rate performance of the material is also greatly improved. , the specific capacity at high rates is almost twice that of the uncoated material.
  • the present invention uses a potassium salt solution to wash Prussian white under the action of centrifugal force.
  • the Prussian white is well coated, forming a coating layer with a core of Na 2 AFe(CN) 6 It is K 2 AFe(CN) 6 coated Prussian white.
  • This coating method distorts the material lattice and reduces the spacing and channels, which can effectively reduce the water absorption of Prussian white and help improve the stability of battery materials; at the same time, it can also greatly improve the performance of sodium-ion batteries prepared using it.
  • the rate performance especially the specific capacity of the battery at high rate (5C), is almost twice that of the uncoated material battery.
  • the preparation method provided by the present invention can also effectively avoid the migration and diffusion of potassium ions in the coating layer into the interior of Prussian White, causing more holes to appear on the surface of the material, reducing the risk of coating layer degradation and improving the stability of the material.
  • the present invention uses potassium salt solution to wash Prussian white under the action of centrifugal force.
  • the coating process can be completed in a centrifuge, that is, in the normal washing step, a step of washing with potassium salt solution can be inserted. There is no need to It is completed in the reaction kettle, which reduces the number of material transfers, simplifies the preparation process, shortens the preparation time, greatly saves manpower and material resources, and reduces production costs.
  • Figure 1 is a process flow chart for preparing coated Prussian white in Example 1;
  • Figure 2 is an SEM image of the coated Prussian white prepared in Example 1;
  • Figure 3 is an SEM image of the Prussian white prepared in Comparative Example 1;
  • Figure 4 is an SEM image of the coated Prussian white prepared in Comparative Example 2.
  • the raw materials, reagents or devices used in the following examples can be obtained from conventional commercial sources, or can be obtained by existing known methods.
  • a coated Prussian white with the chemical formula K 0.2 Na 1.8 MnFe(CN) 6 including an inner core layer and a cladding layer.
  • the inner core has a chemical formula of Na 2 MnFe(CN) 6 and the cladding layer has a chemical formula of K 2 MnFe (CN) 6 .
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.5, and then ages the reacted slurry for 18 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • Coating Prussian White Keep the centrifuge rotating at 20Hz, and then pass 0.5mol/L potassium sulfate solution into the centrifuge to wash the filter cake.
  • the amount of potassium sulfate used is 50 moles of Prussian white in the centrifuge. %, calculate the flow rate of the potassium sulfate solution so that the time for washing the Prussian white filter cake is 8 minutes.
  • Potassium ions partially replace the sodium ions on the surface of the Prussian white to form a coating layer. After testing, the coating utilization rate of potassium sulfate is about 20%, and potassium replaces about 10% of the sodium amount.
  • a coated Prussian white with the chemical formula K 0.1 Na 1.9 MnFe(CN) 6 including an inner core layer and a cladding layer.
  • the inner core has a chemical formula of Na 2 MnFe(CN) 6 and the cladding layer has a chemical formula of K 2 MnFe (CN) 6 .
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.2, and then ages the reacted slurry for 12 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • Coating Prussian white Keep the centrifuge rotating at 20Hz, and then pass 0.5mol/L potassium sulfate solution into the centrifuge to wash the filter cake.
  • the amount of potassium sulfate used is 25 moles of Prussian white in the centrifuge. %, calculate the flow rate of the potassium sulfate solution so that the time for washing the Prussian white filter cake is 6 minutes.
  • Potassium ions partially replace the sodium ions on the surface of the Prussian white to form a coating layer. After testing, the coating utilization rate of potassium sulfate is about 20%, and potassium replaces about 5% of the sodium amount.
  • the inner core has a chemical formula of Na 2 Fe[Fe(CN) 6 ] and a cladding layer.
  • the chemical formula of is K 2 Fe[Fe(CN) 6 ].
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.1, and then ages the reacted slurry for 12 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • Coating Prussian white Keep the centrifuge rotating at 30Hz, and then pass 2mol/L potassium chloride salt solution into the centrifuge to wash the filter cake.
  • the amount of potassium chloride used is the molar amount of Prussian white in the centrifuge. 60%, calculate the flow rate of the potassium chloride solution so that the time for washing the Prussian white filter cake is 5 minutes, and the potassium ions partially replace the sodium ions on the surface of the Prussian white to form a coating layer. After testing, the coating utilization rate of potassium chloride is about 13%, and potassium replaces about 4% of the sodium amount.
  • a coated Prussian white its chemical formula is K 0.08 Na 1.92 CoFe(CN) 6 , including an inner core layer and a cladding layer.
  • the chemical formula of the inner core is Na 2 CoFe(CN) 6 and the chemical formula of the cladding layer is K 2 CoFe (CN) 6 .
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.0, and then ages the reacted material for 18 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • Coating Prussian white Keep the centrifuge rotating at 30Hz, and then pass 2mol/L potassium chloride salt solution into the centrifuge to wash the filter cake.
  • the amount of potassium chloride used is the molar amount of Prussian white in the centrifuge. 60%, calculate the flow rate of the potassium sulfate solution so that the time for washing the Prussian white filter cake is 5 minutes. Potassium ions partially replace the sodium ions on the surface of the Prussian white to form a coating layer. After testing, the coating utilization rate of potassium sulfate is about 13%, and potassium replaces about 4% of the sodium amount.
  • a coated Prussian white with the chemical formula K 0.1 Na 1.9 MnFe(CN) 6 including an inner core layer and a cladding layer.
  • the inner core has a chemical formula of Na 2 MnFe(CN) 6 and the cladding layer has a chemical formula of K 2 MnFe (CN) 6 .
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 7.8, and then ages the reacted slurry for 12 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • Coating Prussian white Keep the centrifuge rotating at 20Hz, and then pass 1 mol/L potassium nitrate salt solution into the centrifuge to wash the filter cake.
  • the amount of potassium nitrate used is 50% of the molar amount of Prussian white in the centrifuge. , calculate the flow rate of the potassium sulfate solution so that the time for washing the Prussian white filter cake is 10 minutes.
  • Potassium ions partially replace the sodium ions on the surface of the Prussian white to form a coating layer. After testing, the coating utilization rate of potassium nitrate is about 20%, and potassium replaces about 5% of the sodium amount.
  • a coated Prussian white its chemical formula is K 0.16 Na 1.84 MnFe(CN) 6 , including an inner core layer and a cladding layer.
  • the chemical formula of the inner core is Na 2 MnFe(CN) 6 and the chemical formula of the cladding layer is K 2 MnFe (CN) 6 .
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.5, and then ages the reacted slurry for 18 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • Coating Prussian white Keep the centrifuge rotating at 40Hz, and then pass 0.5mol/L potassium sulfate solution into the centrifuge to wash the filter cake.
  • the amount of potassium sulfate used is 50 moles of Prussian white in the centrifuge. %, calculate the flow rate of the potassium sulfate solution so that the time for washing the Prussian white filter cake is 5 minutes.
  • Potassium ions partially replace the sodium ions on the surface of the Prussian white to form a coating layer. After testing, the coating utilization rate of potassium sulfate is about 20%, and potassium replaces about 8% of the sodium amount.
  • a coated Prussian white with the chemical formula K 0.12 Na 1.88 MnFe(CN) 6 including an inner core layer and a cladding layer.
  • the inner core has a chemical formula of Na 2 MnFe(CN) 6 and the cladding layer has a chemical formula of K 2 MnFe (CN) 6 .
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.5, and then ages the reacted slurry for 18 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • Coating Prussian white Keep the centrifuge rotating at 10Hz, and then pass 0.5mol/L potassium sulfate salt solution into the centrifuge to wash the filter cake.
  • the amount of potassium sulfate used is 50 of the molar amount of Prussian white in the centrifuge. %, calculate the flow rate of the potassium sulfate solution so that the time for washing the Prussian white filter cake is 8 minutes.
  • Potassium ions partially replace the sodium ions on the surface of the Prussian white to form a coating layer. After testing, the coating utilization rate of potassium sulfate is about 20%, and potassium replaces about 6% of the sodium amount.
  • a coated Prussian white with the chemical formula K 0.12 Na 1.88 MnFe(CN) 6 including an inner core layer and a cladding layer.
  • the inner core has a chemical formula of Na 2 MnFe(CN) 6 and the cladding layer has a chemical formula of K 2 MnFe (CN) 6 .
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.5, and then ages the reacted slurry for 18 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • a coated Prussian white with the chemical formula K 0.14 Na 1.86 MnFe(CN) 6 including an inner core layer and a cladding layer.
  • the inner core has a chemical formula of Na 2 MnFe(CN) 6 and the cladding layer has a chemical formula of K 2 MnFe (CN) 6 .
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.5, and then ages the reacted slurry for 18 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • a coated Prussian white its chemical formula is K 0.24 Na 1.76 MnFe(CN) 6 , including an inner core layer and a cladding layer.
  • the chemical formula of the inner core is Na 2 MnFe(CN) 6 and the chemical formula of the cladding layer is K 2 MnFe (CN) 6 .
  • a method for preparing coated Prussian white including the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.5, and then ages the reacted slurry for 18 hours. Pass the Prussian white slurry in the aging tank to the centrifuge for filtration, remove the mother liquor in the slurry, and leave the filter cake in the centrifuge.
  • Comparative Example 1 does not use potassium salt solution to wash the filter cake in step (2).
  • the remaining preparation steps are the same as Example 1 to prepare an uncoated Prussian white product with the chemical formula of Na 2 MnFe(CN) 6 .
  • Comparative Example 2 uses the traditional method of coating in a reactor to prepare coated Prussian white. Specifically, it includes the following steps:
  • the solution undergoes a precipitation reaction in the reaction kettle, controls the flow rate of sodium ferrocyanide, keeps the reaction pH at 8.2, and then ages the reacted slurry for 12 hours.
  • the Prussian white slurry in the aging tank is led to a centrifuge for filtration, and the mother liquor in the slurry is removed to obtain a Prussian white filter cake.
  • Figure 2 is an SEM image of the coated Prussian white prepared in Example 1.
  • the coating process was performed in a centrifuge, and a small amount of coating can be seen on the surface of the material.
  • Figure 3 is an SEM image of the uncoated Prussian white prepared in Comparative Example 1. The material is not coated and has a smooth surface with no attachments.
  • Figure 4 is an SEM image of the coated Prussian White prepared in Comparative Example 2.
  • the coating process was carried out in the kettle, and the aging time was 30 minutes. A large number of holes appeared on the surface of the material, and the morphology was seriously deteriorated. This was caused by potassium ions etching into the interior of the material. Similarly, there was also a small amount of attachments formed on the surface of the material after dissolution and recrystallization. .
  • Comparative Example 2 Compared with Comparative Example 1, a large number of holes appeared on the surface of the coated Prussian white obtained by the conventional method, the moisture content increased instead of decreasing, and the discharge specific capacity at 0.1C and 5C was significantly reduced, and the product performance was seriously deteriorated.
  • the coated Prussian white prepared in Examples 2-6 has similar effects to Example 1, and its moisture content is reduced, and the 5C discharge specific capacity is significantly improved compared to Comparative Example 1.
  • the 5C discharge specific capacity of the coated Prussian White prepared in Examples 7-10 has also been significantly improved; compared with Examples 1-6, the 0.1C discharge specific capacity is equivalent, but the water content is the same as that of 5C The discharge specific capacity is slightly worse than that of Example 1-6.
  • the coated Prussian white prepared by washing under the action of centrifugal force provided by the present invention can reduce the water absorption and moisture content of Prussian white, and significantly improve the charge-discharge ratio of the sodium-ion battery prepared using it at high rates. Capacity; the rotation frequency and washing time that generate centrifugal force will also affect the stability of sodium batteries, especially the discharge specific capacity at high rates (5C).

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Abstract

一种包覆型普鲁士白及其制备方法和应用，该包覆型普鲁士白的化学式为K xNa 2 - xAFe(CN) 6，由化学式为Na 2AFe(CN) 6的内核和化学式为K 2AFe(CN) 6的包覆层组成，其中，x＝0.06-0.6，A为Ni 2+、Co 2+、Mn 2+或Fe 2+中的至少一种。该制备方法包括于离心力作用下，采用钾盐溶液洗涤普鲁士白，使其表面的至少一部分钠离子被钾离子所取代而制得。包覆型普鲁士白能够降低普鲁士白的吸水性，也能够大幅度提升利用其制备的钠离子电池的倍率性能。

Description

一种包覆型普鲁士白及其制备方法和应用 技术领域
本发明属于新型储能电池技术领域，具体涉及一种包覆型普鲁士白及其制备方法和应用。
背景技术
随着碳酸锂价格的提高，极大地压缩了锂离子电池的利润。较于锂离子正极材料，钠离子正极材料的制造成本更低。在钠正极材料中，钠是一种常见元素，这使得材料的制造成本显著降低，在储能行业越来越受到青睐。作为钠离子正极材料的一种，普鲁士白由具有较强的吸水性，对电芯的循环性能和倍率性能有极大影响，所以降低材料的含水量和吸水性具有重要意义。
包覆是一种常见的材料改性方法，目前也有较多对普鲁士白进行包覆的方法。其中，常规包覆反应，一般是先经过液相合成、过滤、洗涤、干燥等工序制备出待包覆物料，然后将待包覆物料投回反应釜，加水浆化后，往釜内加入包覆剂进行包覆反应，再进行第二遍过滤、洗涤、干燥工序，才能得到包覆改性的产品。整个工序流程繁琐、步骤重复、用时过长、损失率高。有的包覆方法为了减少工序、提高收率，会将液相合成反应制备出的含有待包覆物的浆料留在反应釜中，保持一定的温度和搅拌，再添加包覆剂进行反应，只需经过一遍过滤、洗涤、干燥工序，就能得到所需的包覆改性材料。但是这种方法也有较多弊端，如合成反应制备出的浆料中含有大量盐杂质，会对包覆反应产生干扰，从而影响产品性能等。若采用该方法对普鲁士白进行包覆，必然会影响普鲁士白的纯度，从而影响钠离子电池的性能。
因此，亟需提供一种包覆型普鲁士白，其制备工序简单，能够大大缩短制备时间，且制备的普鲁士白材料，能够提高钠离子电池的性能。
发明内容
本发明旨在至少解决上述现有技术中存在的技术问题之一。为此，本发明提出一种包覆型普鲁士白及其制备方法和应用。本发明提供的包覆型普鲁士白能够降低普鲁士白的吸水性，提高钠离子电池的性能；且其制备工序简单，能够大大缩短制备时间。
本发明第一方面提供了一种包覆型普鲁士白。
具体地，一种包覆型普鲁士白，所述包覆型普鲁士白的化学式为K xNa 2-xAFe(CN) 6，所述包覆型普鲁士白由化学式为Na 2AFe(CN) 6的内核和化学式为K 2AFe(CN) 6的包覆层组成，其中，x＝0.06-0.6，A为Ni 2+、Co 2+、Mn 2+、Fe 2+中的至少一种。
优选地，在所述化学式中，x＝0.06-0.3。
优选地，所述包覆型普鲁士白由普鲁士白于离心力作用下，经钾盐溶液洗涤，使其表面的至少一部分钠离子被钾离子所取代而制得。
本发明第二方面提供了一种包覆型普鲁士白的制备方法。
具体地，一种包覆型普鲁士白的制备方法，包括以下步骤：
于离心力作用下，采用钾盐溶液洗涤普鲁士白，使其表面的至少一部分钠离子被钾离子所取代；然后经水洗、干燥，制得包覆型普鲁士白；产生所述离心力的转动频率为10-60Hz。
优选地，产生所述离心力的转动频率为15-50Hz；进一步优选地，产生所述离心力的转动频率为20-40Hz。试验发现采用钾盐溶液洗涤普鲁士白时，对离心力的控制是影响包覆效果的重要因素之一。洗涤时当转动的频率过低，钾盐溶液受到的离心力不足，很难浸润普鲁士白；洗涤时转动的频率过高，即转数过高，则离心效果太强，钾盐溶液容易被快速甩离设备，与普鲁士白的接触时间太短，不能起到良好的包覆效果。
可以理解的是，产生所述离心力的设备不受限制，在该工艺中常用的为离心机。采用离心机不仅可以完成洗涤普鲁士白的工艺，还能进行后续的水洗工序，减少物料的转移次数，简化制备工序。
优选地，所述钾盐溶液中的钾盐为硫酸钾、硝酸钾、氯化钾或柠檬酸钾中的至少一种。
优选地，所述钾盐溶液的浓度为0.3-3mol/L；进一步钾盐溶液的浓度为0.5-2mol/L。
优选地，所述钾盐溶液的物质的量为所述普鲁士白的物质的量的20％-100％。如20％、25％、30％、35％、40％、50％、60％、70％、80％、90％。
优选地，所述洗涤的时间为2-15分钟；更优选地，所述洗涤的时间为5-10分钟。采用钾盐溶液洗涤普鲁士白，对洗涤时间的控制能够有效防止包覆层劣化。将钾盐溶液加入普鲁士白中后，数分钟内几乎就能完全反应，反应后经短暂的陈化(即洗涤过程中包括反应和陈化过程)，即能达到良好的包覆效果。若洗涤时间过长，则原本处在材料表面包覆层的钾离子就会在水溶液条件下向材料内部迁移扩散，使包覆层劣化、材料表面出现较多孔洞，利用其制备成电池后，材料与电解液的接触面积增大，稳定性降低。
优选地，所述干燥的温度为150-180℃。
可以理解的是，所述普鲁士白可以为直接购买的产品，也可以是经常规方法制备的产品。
优选地，所述普鲁士白通过以下方法制备得到：
于保护气体气氛下，将亚铁氰化盐溶液、金属盐溶液和络合剂溶液混合，于40-95℃下反应，然后将反应所得的浆料陈化6-48h，离心分离去分离液，得到所述普鲁士白。
优选地，所述亚铁氰化钠溶液的浓度为0.3-0.6mol/L。
优选地，所述金属盐溶液中的金属盐为镍、钴、锰、亚铁的硫酸盐、硝酸盐、醋酸盐、 氯化盐中的一种或多种。
优选地，所述金属盐溶液的浓度为0.5-2mol/L。
优选地，在进行所述反应时，控制反应pH为6.5-9.5。
优选地，所述络合剂为柠檬酸、马来酸、枸杞酸、乙二胺四乙酸、柠檬酸钠、氨水中的至少一种。
优选地，所述络合剂溶液的浓度为0.5-5mol/L。
更为具体地，一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)配制亚铁氰化盐溶液、金属盐溶液和络合剂溶液，向反应釜中通入保护气体以防氧化，将温度升高到40-95℃，将所述亚铁氰化钠溶液、金属盐溶液、络合剂溶液加入反应釜中，反应，控制亚铁氰化盐溶液的加入量，保持反应时pH值为6.5-9.5，然后将反应后的浆料陈化6-48h，再离心分离去分离液，得到所述普鲁士白；
(2)将所述普鲁士白置于离心机中，控制离心机的转动频率为10-60Hz，采用钾盐溶液洗涤普鲁士白，使钾离子部分取代普鲁士白表面的钠离子，形成包覆层，然后经水洗去杂质，再于150-180℃下干燥，制得所述包覆型普鲁士白。
本发明第三方面提供了一种包覆型普鲁士白的应用。
具体地，上述包覆型普鲁士白在制备电池正极材料中的应用。
一种正极片，包括上述包覆型普鲁士白。
本发明第四方面提供了一种钠离子电池。
具体地，一种钠离子电池，包括上述正极片。
优选地，所述电池正极材料为钠离子电池正极材料。
本发明提供的技术方案，于离心力作用下采用钾盐溶液洗涤普鲁士白，钾盐溶液流过普鲁士白时，由于钾系普鲁士白的KSP更低，溶液中的钾离子可以部分取代普鲁士白表面的钠离子(钾盐的实际利用率为10％-30％，最终钾取代了普鲁士白中钠数量的3％-30％)，在材料表面形成包覆层，材料内核的结构为Na 2AFe(CN) 6，包覆层结构为K 2AFe(CN) 6，A为镍、钴、锰、亚铁的一种或多种。另外，材料表面还会有少量附着物，是物料溶解后再结晶形成的，其结构与包覆层一致。经洗涤形成的包覆型普鲁士白，一方面，由于K离子半径比Na离子半径稍大，K在取代Na时，材料晶格发生畸变，间距和通道变小。未经包覆的普鲁士白在干燥后取出时，容易吸收空气中的水分，造成产品含水量偏高；经洗涤形成的包覆型普鲁士白，由于表面晶格畸变造成水分子通道减小，材料在干燥取出时，吸水性会大幅度降低，所得产品的含水量明显下降。另一方面，由于包覆层的存在，能够有效提高材料在充放电过程中的结构稳定性，并减少与电解液的副反应，提高界面稳定性和循环性能，材料的倍率性能也大 幅度提升，高倍率下的比容量几乎是未包覆材料的2倍。
相对于现有技术，本发明的有益效果如下：
(1)本发明于离心力作用下采用钾盐溶液洗涤普鲁士白，通过控制产生离心力的转动频率、洗涤时间，使普鲁士白得到良好包覆，形成内核为Na 2AFe(CN) 6、包覆层为K 2AFe(CN) 6的包覆型普鲁士白。该包覆方式使材料晶格发生畸变，间距和通道变小，能够有效降低普鲁士白的吸水性，有利于提高电池材料的稳定性；同时，也能够大幅度提升利用其制备的钠离子电池的倍率性能，尤其使电池在高倍率下(5C)的比容量几乎是未包覆材料电池的2倍。
(2)本发明提供的制备方法还能有效避免包覆层中钾离子向普鲁士白内部迁移扩散，使材料表面出现较多孔洞，降低包覆层劣化风险，提高材料的稳定性。
(3)本发明于离心力作用下采用钾盐溶液洗涤普鲁士白，该包覆过程能够在离心机中完成，即在正常的洗涤步骤中，插入一步钾盐溶液洗涤的工序即可，不需要在反应釜中完成，减少了物料的转移次数，简化了制备工序，缩短了制备时间，大幅度节省了人力、物力，降低了生产成本。
附图说明
图1为实施例1制备包覆型普鲁士白的工艺流程图；
图2为实施例1制备的包覆型普鲁士白的SEM图；
图3为对比例1制备的普鲁士白的SEM图；
图4为对比例2制备的包覆型普鲁士白的SEM图。
具体实施方式
为了让本领域技术人员更加清楚明白本发明所述技术方案，现列举以下实施例进行说明。需要指出的是，以下实施例对本发明要求的保护范围不构成限制作用。
以下实施例中所用的原料、试剂或装置如无特殊说明，均可从常规商业途径得到，或者可以通过现有已知方法得到。
实施例1
一种包覆型普鲁士白，其化学式为K 0.2Na 1.8MnFe(CN) 6，包括内核层和包覆层，内核的化学式为Na 2MnFe(CN) 6，包覆层的化学式为K 2MnFe(CN) 6。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.5mol/L的亚铁氰化钠溶液、1.6mol/L的硫酸锰溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到65℃，将亚铁氰化钠溶液、硫酸锰溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸锰溶液流量的1.2倍。溶液在反应 釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.5，再将反应后的浆料陈化18h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在20Hz旋转，再将0.5mol/L的硫酸钾盐溶液通入离心机中洗涤滤饼，硫酸钾的使用量为离心机中普鲁士白摩尔量的50％，计算出硫酸钾溶液的流量，使洗涤普鲁士白滤饼的时间为8分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，硫酸钾的包覆利用率约为20％，钾取代了钠数量的约10％。
(3)洗涤干燥：将离心机中经钾盐溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.4倍。再将滤饼在180℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.2Na 1.8MnFe(CN) 6。
以上制备方法的工艺流程图如图1所示。
实施例2
一种包覆型普鲁士白，其化学式为K 0.1Na 1.9MnFe(CN) 6，包括内核层和包覆层，内核的化学式为Na 2MnFe(CN) 6，包覆层的化学式为K 2MnFe(CN) 6。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.4mol/L的亚铁氰化钠溶液、2mol/L的硫酸锰溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到75℃，将亚铁氰化钠溶液、硫酸锰溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸锰溶液流量的2倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.2，再将反应后的浆料陈化12h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在20Hz旋转，再将0.5mol/L的硫酸钾盐溶液通入离心机中洗涤滤饼，硫酸钾的使用量为离心机中普鲁士白摩尔量的25％，计算出硫酸钾溶液的流量，使洗涤普鲁士白滤饼的时间为6分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，硫酸钾的包覆利用率约为20％，钾取代了钠数量的约5％。
(3)洗涤干燥：将离心机中经硫酸钾溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.4倍。再将滤饼在180℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.1Na 1.9MnFe(CN) 6。
实施例3
一种包覆型普鲁士白，其化学式为K 0.08Na 1.92Fe[Fe(CN) 6]，包括内核层和包覆层，内核的化学式为Na 2Fe[Fe(CN) 6]，包覆层的化学式为K 2Fe[Fe(CN) 6]。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.5mol/L的亚铁氰化钠溶液、1.5mol/L的硫酸亚铁溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到75℃，将亚铁氰化钠溶液、硫酸亚铁溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸亚铁溶液流量的1.5倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.1，再将反应后的浆料陈化12h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在30Hz旋转，再将2mol/L的氯化钾盐溶液通入离心机中洗涤滤饼，氯化钾的使用量为离心机中普鲁士白摩尔量的60％，计算出氯化钾溶液的流量，使洗涤普鲁士白滤饼的时间为5分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，氯化钾的包覆利用率约为13％，钾取代了钠数量的约4％。
(3)洗涤干燥：将离心机中经氯化钾溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.5倍。再将滤饼在180℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.08Na 1.92Fe[Fe(CN) 6]。
实施例4
一种包覆型普鲁士白，其化学式为K 0.08Na 1.92CoFe(CN) 6，包括内核层和包覆层，内核的化学式为Na 2CoFe(CN) 6，包覆层的化学式为K 2CoFe(CN) 6。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.4mol/L的亚铁氰化钠溶液、2mol/L的硫酸钴溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到85℃，将亚铁氰化钠溶液、硫酸钴溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸钴溶液流量的2倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.0，再将反应后的物料陈化18h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在30Hz旋转，再将2mol/L的氯化钾盐溶液通入离心机中洗涤滤饼，氯化钾的使用量为离心机中普鲁士白摩尔量的60％，计算出硫酸钾溶液的流量，使洗涤普鲁士白滤饼的时间为5分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，硫酸钾的包覆利用率约为13％，钾取代了钠数量的约4％。
(3)洗涤干燥：将离心机中经氯化钾溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.5倍。再将滤饼在180℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.08Na 1.92CoFe(CN) 6。
实施例5
一种包覆型普鲁士白，其化学式为K 0.1Na 1.9MnFe(CN) 6，包括内核层和包覆层，内核的化学式为Na 2MnFe(CN) 6，包覆层的化学式为K 2MnFe(CN) 6。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.4mol/L的亚铁氰化钠溶液、2mol/L的硫酸锰溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到75℃，将亚铁氰化钠溶液、硫酸锰溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸锰溶液流量的1.5倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为7.8，再将反应后的浆料陈化12h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在20Hz旋转，再将1mol/L的硝酸钾盐溶液通入离心机中洗涤滤饼，硝酸钾的使用量为离心机中普鲁士白摩尔量的50％，计算出硫酸钾溶液的流量，使洗涤普鲁士白滤饼的时间为10分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，硝酸钾的包覆利用率约为20％，钾取代了钠数量的约5％。
(3)洗涤干燥：将离心机中经硝酸钾溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.4倍。再将滤饼在170℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.1Na 1.9MnFe(CN) 6。
实施例6
一种包覆型普鲁士白，其化学式为K 0.16Na 1.84MnFe(CN) 6，包括内核层和包覆层，内核的化学式为Na 2MnFe(CN) 6，包覆层的化学式为K 2MnFe(CN) 6。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.5mol/L的亚铁氰化钠溶液、1.6mol/L的硫酸锰溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到65℃，将亚铁氰化钠溶液、硫酸锰溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸锰溶液流量的1.2倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.5，再将反应后的浆料陈化18h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在40Hz旋转，再将0.5mol/L的硫酸钾盐溶液通入离心机中洗涤滤饼，硫酸钾的使用量为离心机中普鲁士白摩尔量的50％，计算出硫酸钾溶液的流量，使洗涤普鲁士白滤饼的时间为5分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，硫酸钾的包覆利用率约为20％，钾取代了钠数量的约8％。
(3)洗涤干燥：将离心机中经钾盐溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.4倍。再将滤饼在180℃下干燥，得到包覆型普鲁 士白产品，化学式为K 0.16Na 1.84MnFe(CN) 6。
实施例7
一种包覆型普鲁士白，其化学式为K 0.12Na 1.88MnFe(CN) 6，包括内核层和包覆层，内核的化学式为Na 2MnFe(CN) 6，包覆层的化学式为K 2MnFe(CN) 6。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.5mol/L的亚铁氰化钠溶液、1.6mol/L的硫酸锰溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到65℃，将亚铁氰化钠溶液、硫酸锰溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸锰溶液流量的1.2倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.5，再将反应后的浆料陈化18h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在10Hz旋转，再将0.5mol/L的硫酸钾盐溶液通入离心机中洗涤滤饼，硫酸钾的使用量为离心机中普鲁士白摩尔量的50％，计算出硫酸钾溶液的流量，使洗涤普鲁士白滤饼的时间为8分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，硫酸钾的包覆利用率约为20％，钾取代了钠数量的约6％。
(3)洗涤干燥：将离心机中经钾盐溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.4倍。再将滤饼在180℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.12Na 1.88MnFe(CN) 6。
实施例8
一种包覆型普鲁士白，其化学式为K 0.12Na 1.88MnFe(CN) 6，包括内核层和包覆层，内核的化学式为Na 2MnFe(CN) 6，包覆层的化学式为K 2MnFe(CN) 6。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.5mol/L的亚铁氰化钠溶液、1.6mol/L的硫酸锰溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到65℃，将亚铁氰化钠溶液、硫酸锰溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸锰溶液流量的1.2倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.5，再将反应后的浆料陈化18h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在60Hz旋转，再将0.5mol/L的硫酸钾盐溶液通入离心机中洗涤滤饼，硫酸钾的使用量为离心机中普鲁士白摩尔量的50％，计算出硫酸钾溶液的流量，使洗涤普鲁士白滤饼的时间为8分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，硫酸钾的包覆利用率约为20％，钾取代了钠数量的约6％。
(3)洗涤干燥：将离心机中经钾盐溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.4倍。再将滤饼在180℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.12Na 1.88MnFe(CN) 6。
实施例9
一种包覆型普鲁士白，其化学式为K 0.14Na 1.86MnFe(CN) 6，包括内核层和包覆层，内核的化学式为Na 2MnFe(CN) 6，包覆层的化学式为K 2MnFe(CN) 6。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.5mol/L的亚铁氰化钠溶液、1.6mol/L的硫酸锰溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到65℃，将亚铁氰化钠溶液、硫酸锰溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸锰溶液流量的1.2倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.5，再将反应后的浆料陈化18h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在20Hz旋转，再将0.5mol/L的硫酸钾盐溶液通入离心机中洗涤滤饼，硫酸钾的使用量为离心机中普鲁士白摩尔量的50％，计算出硫酸钾溶液的流量，使洗涤普鲁士白滤饼的时间为3分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，硫酸钾的包覆利用率约为20％，钾取代了钠数量的约7％。
(3)洗涤干燥：将离心机中经钾盐溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.4倍。再将滤饼在180℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.14Na 1.86MnFe(CN) 6。
实施例10
一种包覆型普鲁士白，其化学式为K 0.24Na 1.76MnFe(CN) 6，包括内核层和包覆层，内核的化学式为Na 2MnFe(CN) 6，包覆层的化学式为K 2MnFe(CN) 6。
一种包覆型普鲁士白的制备方法，包括以下步骤：
(1)合成普鲁士白：配制0.5mol/L的亚铁氰化钠溶液、1.6mol/L的硫酸锰溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到65℃，将亚铁氰化钠溶液、硫酸锰溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸锰溶液流量的1.2倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.5，再将反应后的浆料陈化18h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，将滤饼留在离心机中。
(2)包覆普鲁士白：保持离心机在20Hz旋转，再将0.5mol/L的硫酸钾盐溶液通入离心机中洗涤滤饼，硫酸钾的使用量为离心机中普鲁士白摩尔量的50％，计算出硫酸钾溶液的流 量，使洗涤普鲁士白滤饼的时间为15分钟，钾离子部分取代普鲁士白表面的钠离子，形成包覆层。经测试，硫酸钾的包覆利用率约为20％，钾取代了钠数量的约12％。
(3)洗涤干燥：将离心机中经钾盐溶液洗涤包覆后的滤饼继续用纯水进行洗涤，除去滤饼中的杂质，洗水体积为陈化浆料体积的0.4倍。再将滤饼在180℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.24Na 1.76MnFe(CN) 6。
对比例1
对比例1是在步骤(2)中不使用钾盐溶液洗涤滤饼，其余制备步骤与实施例1相同，制备未包覆的普鲁士白产品，化学式为Na 2MnFe(CN) 6。
对比例2
对比例2是采用传统在反应釜中进行包覆的方法制备包覆型普鲁士白，具体，包括以下步骤：
(1)合成普鲁士白：配制0.4mol/L的亚铁氰化钠溶液、2mol/L的硫酸锰溶液和2mol/L的柠檬酸钠溶液。往反应釜中加入适量纯水，到达搅拌桨位置，开启搅拌，然后向反应釜中通入氮气以防氧化，再将温度升高到75℃，将亚铁氰化钠溶液、硫酸锰溶液、柠檬酸钠溶液用计量泵同时泵入反应釜中，柠檬酸钠溶液的流量为硫酸锰溶液流量的2倍。溶液在反应釜中发生沉淀反应，控制亚铁氰化钠的流量，保持反应pH为8.2，再将反应后的浆料陈化12h。将陈化槽中的普鲁士白浆料通往离心机进行过滤，脱去浆料中的母液，得普鲁士白滤饼。
(2)包覆普鲁士白：将普鲁士白滤饼投入反应釜中，加水浆化，开启搅拌，往釜内加入0.5mol/L的硫酸钾溶液，硫酸钾的使用量为反应釜中普鲁士白摩尔量的10％。在反应釜中进行包覆，硫酸钾几乎完全反应。陈化30min后，将反应釜中的浆料立即通往离心机中过滤、洗涤，得到滤饼，再将滤饼在180℃下干燥，得到包覆型普鲁士白产品，化学式为K 0.2Na 1.8MnFe(CN) 6。
产品效果测试
对实施例1-10以及对比例1-2制备的普鲁士白产品进行测试。
具体测试方法和测试结果如下：
(1)采用扫描电子显微镜分析实施例1、对比例2制备包覆型普鲁士白，以及对比例1制备的未包覆的普鲁士白产品。
图2为实施例1制备的包覆型普鲁士白的SEM图，在离心机中进行包覆工序，材料表面可以看到少量包覆物。图3为对比例1制备的未包覆的普鲁士白的SEM图，材料未进行包覆，表面光滑，无附着物；图4为对比例2制备的包覆型普鲁士白的SEM图，在反应釜中进行包覆工序，陈化时间为30min，材料表面出现大量孔洞，形貌严重劣化，这是由钾离子向材料 内部蚀刻造成的，同样，材料表面也有溶解后再结晶形成的少量附着物。
(2)采用干法粒度仪测试实施例1-10以及对比例1-2制备的普鲁士白产品的粒径。
(3)采用自动水分测定仪在150℃干燥1h测试实施例1-10以及对比例1-2制备的普鲁士白产品的水分含量(wt％)。
(4)利用实施例1-10以及对比例1-2制备的普鲁士白产品做成正极片，以金属钠做负极，NaPF 6的碳酸乙烯酯(EC)/碳酸二乙酯(DEC)溶液做电解液，在手套箱中装配成扣式半电池。然后在2.0-4.0V的电压范围内，分别在0.1C和5C倍率下测试电池的充放电比容量。
测试结果如表1所示。
表1测试结果
Figure PCTCN2022119466-appb-000001
由表1可知，实施例1与对比例1相比，材料的形貌变化不大，但包覆后材料(实施例1制备的包覆型普鲁士白)的水分大幅度降低，0.1C放电比容量几乎不变，但5C放电比容量得到显著提高。对比例2与对比例1相比，采用常规方法得到的包覆型普鲁士白的表面出现大量孔洞，水分不降反增，且0.1C和5C放电比容量都大幅度降低，产品性能严重劣化。实施例2-6制备的包覆型普鲁士白与实施例1的效果类似，其水分含量均有降低，5C放电比容量相较于对比例1都得到了显著提升。实施例7-10制备的包覆型普鲁士白相较于对比例1，其5C放电比容量也得到了显著提升；与实施例1-6相比，0.1C放电比容量相当，但水含量 与5C放电比容量略差于实施例1-6。由此可见，本发明提供的在离心力作用下通过洗涤方式制备的包覆型普鲁士白能够降低普鲁士白的吸水性和水分含量，显著提高利用其制备的钠离子电池在高倍率下的充放电比容量；而对产生离心力的转动频率以及洗涤时间也会影响钠电池的稳定性，尤其是高倍率(5C)下的放电比容量。

Claims (10)

  1. 一种包覆型普鲁士白，其特征在于，所述包覆型普鲁士白的化学式为K xNa 2-xAFe(CN) 6，所述包覆型普鲁士白由化学式为Na 2AFe(CN) 6的内核和化学式为K 2AFe(CN) 6的包覆层组成，其中，x＝0.06-0.6，A为Ni 2+、Co 2+、Mn 2+、Fe 2+中的至少一种。
  2. 根据权利要求1所述的包覆型普鲁士白，其特征在于，在所述化学式中，x＝0.06-0.3。
  3. 权利要求1或2所述的包覆型普鲁士白的制备方法，其特征在于，包括以下步骤：
    于离心力作用下，采用钾盐溶液洗涤普鲁士白，使其表面的至少一部分钠离子被钾离子所取代；然后经水洗、干燥，制得包覆型普鲁士白；产生所述离心力的转动频率为10-60Hz。
  4. 根据权利要求3所述的制备方法，其特征在于，产生所述离心力的转动频率为15-50Hz；优选地，产生所述离心力的转动频率为20-40Hz。
  5. 根据权利要求3所述的制备方法，其特征在于，所述钾盐溶液中的钾盐为硫酸钾、硝酸钾、氯化钾、柠檬酸钾中的至少一种。
  6. 根据权利要求3所述的制备方法，其特征在于，所述钾盐溶液的浓度为0.3-3mol/L。
  7. 根据权利要求3、5-6任一项所述的制备方法，其特征在于，所述钾盐溶液的物质的量为所述普鲁士白的物质的量的20％-100％。
  8. 根据权利要求3所述的制备方法，其特征在于，所述洗涤的时间为2-15分钟；优选地，所述洗涤的时间为5-10分钟。
  9. 一种正极片，其特征在于，包括权利要求1或2所述的包覆型普鲁士白。
  10. 一种钠离子电池，其特征在于，包括权利要求9所述的正极片。
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