CN113044823B - Iron phosphate material and preparation method and application thereof - Google Patents

Iron phosphate material and preparation method and application thereof Download PDF

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CN113044823B
CN113044823B CN202110205677.9A CN202110205677A CN113044823B CN 113044823 B CN113044823 B CN 113044823B CN 202110205677 A CN202110205677 A CN 202110205677A CN 113044823 B CN113044823 B CN 113044823B
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iron phosphate
raw material
iron
salt raw
slurry
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CN113044823A (en
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林奕
彭超
颜志雄
万文治
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Hunan Yacheng New Energy Co ltd
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Hunan Yacheng New Material Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/37—Phosphates of heavy metals
    • C01B25/375—Phosphates of heavy metals of iron
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • 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
    • C01P2004/60—Particles characterised by their size
    • C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/62—Submicrometer sized, i.e. from 0.1-1 micrometer
    • 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

Abstract

The invention discloses an iron phosphate material and a preparation method and application thereof, wherein the iron phosphate material is composed of a large-particle iron phosphate material and a small-particle iron phosphate material; the preparation method comprises the following steps: mixing a phosphorus salt raw material solution, an iron salt raw material solution and a phosphoric acid solution, and heating for reaction to prepare iron phosphate seed crystals; continuously adding an iron salt raw material liquid and a phosphorus salt raw material liquid for crystallization reaction, so that iron phosphate seed crystals continuously grow up to prepare iron phosphate slurry I; mixing the iron phosphate slurry I and the ferric salt raw material liquid, and adding the phosphorus salt raw material liquid for reaction to obtain an iron phosphate slurry II; and carrying out filter pressing, washing and drying on the iron phosphate slurry II to obtain the iron phosphate material. The method has simple process and can be used for industrial production, and the method can control the particle size of the large-particle iron phosphate and the ratio between the large particles and the small particles. The compaction density of the lithium iron phosphate synthesized by taking the ferric phosphate obtained by the method as a precursor exceeds 2.4g/cm3。

Description

Iron phosphate material and preparation method and application thereof
Technical Field
The invention relates to the technical field of lithium batteries, in particular to an iron phosphate material and a preparation method and application thereof.
Background
The lithium battery prepared from the olivine-structured lithium iron phosphate has the advantages of large discharge capacity, long cycle life, high safety, environmental friendliness and the like, and is widely applied to the fields of new energy automobiles, communication base stations, energy storage equipment and the like. However, the battery system using lithium iron phosphate as the anode material has low energy density, which limits the application of lithium iron phosphate in power batteries. Research and practice show that the energy density of the lithium iron phosphate battery can be effectively improved by improving the capacity and the voltage platform or the compaction density of the lithium iron phosphate battery. At present, the capacity and the voltage platform of lithium iron phosphate are close to theoretical values, and the lifting space is smaller. The most effective way to increase the energy density of lithium iron phosphate is to increase the compacted density of lithium iron phosphate.
In the related technology, a method of multiple compaction, multiple sintering or size grain composition is mostly adopted to improve the compaction density of the lithium iron phosphate anode material.
The first method and the multi-stage sintering method: filling spherical small-particle lithium iron phosphate into gaps of large-particle lithium iron phosphate, and preparing a high-compaction-density lithium iron phosphate positive electrode material by adopting a three-stage sintering (low-temperature sintering, medium-temperature sintering and high-temperature sintering) method; although the prepared lithium iron phosphate cathode material has higher compacted density and excellent electrochemical performance. However, the multi-stage sintering method is complicated in process, and energy consumption and cost caused by multiple sintering are high.
The second method comprises a large-size particle grading method: in the grinding stage, large-particle lithium iron phosphate slurry and small-particle lithium iron phosphate are respectively prepared by controlling the grinding time, then are mixed according to a certain proportion, and are dried and thermally treated to prepare high-compaction-density lithium iron phosphate; according to the method, the lithium iron phosphate slurry with different particle sizes is prepared by controlling the grinding time, and the batch stability of the product is poor. In the related technology, a ferrous sulfate solution is used for preparing an iron hydroxide filter cake, and then phosphate, a dispersing agent and dilute acid are added to prepare small-particle iron phosphate slurry with the particle size of 0.2-0.4 mu m; meanwhile, reacting a ferric iron source with calcium phosphate to prepare large-particle iron phosphate slurry with the particle size of 3-16 mu m; and then mixing, washing, atomizing and dehydrating the small-particle iron phosphate slurry and the large-particle iron phosphate slurry according to a certain proportion to prepare the high-purity high-compaction anhydrous iron phosphate. When the method is applied in a large scale, two production lines of large-particle iron phosphate slurry and small-particle iron phosphate slurry need to be established at the same time, and the production efficiency is low. And the ferric hydroxide, which is an intermediate product of the small-particle ferric phosphate slurry prepared by the method, belongs to a metastable colloid, has strong adsorption capacity on impurity ions, and is extremely difficult to filter and precipitate, so that the process consumes too long time. In addition, the invention utilizes the reaction of the ferric iron source and the calcium phosphate powder to prepare the large-particle iron phosphate slurry, the reaction condition is harsh, the complete reaction of the calcium phosphate powder is difficult to ensure, and the calcium phosphate is easily entrapped in the prepared iron phosphate particles.
In view of this, it is necessary to develop an iron phosphate material for lithium iron phosphate with high tap density and a preparation method thereof.
Disclosure of Invention
The first technical problem to be solved by the invention is as follows: an iron phosphate material having a dense interior and a high tap density.
The second technical problem to be solved by the invention is as follows: the preparation method of the iron phosphate material has low cost and simple operation.
The third technical problem to be solved by the invention is as follows: the application of the iron phosphate material is provided.
In order to solve the first technical problem, the technical scheme provided by the invention is as follows: an iron phosphate material comprising a large particle iron phosphate material and a small particle iron phosphate material;
wherein the particle size of the large-particle iron phosphate material is 2-10 mu m;
the particle size of the small-particle ferric phosphate material is 0.05-1 mu m;
the internal structure of the ferric phosphate material is compact.
According to some embodiments of the invention, the dense structure is a non-porous or a less porous structure.
According to some embodiments of the invention, the mass ratio of the large-particle iron phosphate material to the small-particle iron phosphate material is 1:3 to 9.
According to some embodiments of the invention, the mass fraction of the large-particle iron phosphate material is 10% to 25%.
According to some embodiments of the invention, the mass fraction of the small particle iron phosphate material is between 75% and 95%.
The iron phosphate material according to the embodiment of the invention has at least the following beneficial effects: according to the invention, the large-particle iron phosphate material and the small-particle iron phosphate material are matched, and the small-particle iron phosphate is filled into the gap of the large-particle iron phosphate, so that the tap density of the iron phosphate is obviously improved, and the iron phosphate can be used for preparing the lithium iron phosphate with high tap density.
To solve the second technical problem, the present invention provides the following technical solutions: the preparation method of the iron phosphate material comprises the following steps:
s1, preparing iron phosphate slurry I:
preparing materials: preparing a phosphorus salt raw material solution and an iron salt raw material solution, dividing the phosphorus salt raw material solution into a phosphorus salt raw material solution A, a phosphorus salt raw material solution B and a phosphorus salt raw material solution C, and dividing the iron salt raw material solution into an iron salt raw material solution A, an iron salt raw material solution B and an iron salt raw material solution C;
seed crystal reaction: taking a phosphoric acid solution as a base solution, simultaneously adding a phosphorus salt raw material solution A and an iron salt raw material solution A, heating and reacting to convert the mixture into white slurry I, stopping stirring, standing for solid-liquid layering, and then pumping out supernatant to obtain a solid-phase material;
and (3) crystallization reaction: under the condition of stirring, adding a phosphorus salt raw material solution B and an iron salt raw material solution B into a solid-phase material for multiple times, converting into a white slurry II after heating reaction, stopping stirring, standing again, and after solid and liquid are layered, pumping away supernatant;
repeating the crystallization reaction step until the D50 particle size of the white slurry II reaches 2-10 mu m, thus obtaining the iron phosphate slurry I;
s2, preparing iron phosphate slurry II: mixing iron phosphate slurry I and iron salt raw material liquid C, adding the phosphorus salt raw material liquid C, heating for reaction, and converting into white slurry III to obtain iron phosphate slurry II;
s3, drying: performing solid-liquid separation on the iron phosphate slurry II, collecting a solid phase part, washing and drying to obtain the iron phosphate material;
wherein the ratio of the amount of the iron atoms in the iron phosphate slurry I to the amount of the iron atoms in the iron salt raw material liquid in step S2 is 1: 3-9.
The proportion of the ferric phosphate slurry I and the ferric salt raw material liquid added in the step S2 is controlled, so that the respective proportion of the large and small particles in the ferric phosphate large and small particle compound structure is controlled.
According to some embodiments of the invention, the phosphorus salt feedstock comprises at least one of monohydrogen phosphate and dihydrogen phosphate; preferably, the monohydrogen phosphate comprises at least one of ammonium monohydrogen phosphate, sodium monohydrogen phosphate, and potassium monohydrogen phosphate; preferably, the dihydrogen phosphate salt includes at least one of ammonium dihydrogen phosphate, sodium dihydrogen phosphate, and potassium dihydrogen phosphate.
According to some embodiments of the invention, the ferric salt feed solution comprises at least one of ferric and ferrous salts; preferably, the iron salt comprises at least one of ferric chloride, ferric nitrate, and ferric sulfate; preferably, the ferrous salt includes at least one of ferrous chloride, ferrous nitrate, and ferrous sulfate.
According to some embodiments of the present invention, when the ferric salt raw material solution comprises ferrous salt, the ferric salt raw material solution is subjected to oxidation treatment before the reaction is performed until the ferrous ion is not contained in the ferric salt raw material solution any more.
According to some embodiments of the invention, the oxidizing agent selected for the oxidation treatment is hydrogen peroxide.
According to some embodiments of the invention, the ratio of the amount of hydrogen peroxide to ferrous ion species is 1 to 2: 1.
According to some embodiments of the invention, the concentration of the species of phosphorus atoms in the phosphorus salt feed solution is between 0.5mol/L and 1.5 mol/L.
According to some embodiments of the invention, the iron source solution contains iron atoms in an amount of 0.5 to 1.5 mol/L.
According to some embodiments of the present invention, the ratio of the amount of phosphorus atoms to iron atoms in the white slurry i in the seed reaction step is 0.8 to 1.5: 1.
According to some embodiments of the present invention, the ratio of the phosphorus atoms in the phosphoric acid solution to the amount of phosphorus atoms in the phosphorus salt raw material solution added for the crystallization reaction is 1:3 to 1: 7.
According to some embodiments of the present invention, the ratio of the amount of the phosphorus atoms in the phosphorus salt raw material solution to the amount of the iron atoms in the iron salt raw material solution added in the crystallization reaction step is 1.1 to 1.7: 1.
According to some embodiments of the present invention, the heating temperature of the crystallization reaction in the step S1 is 80 ℃ to 100 ℃.
According to some embodiments of the present invention, the reaction time in the crystallization reaction in the step S1 is 1 to 3 hours.
According to some embodiments of the present invention, the heating temperature of the seed crystal reaction in the step S1 is 80 ℃ to 100 ℃.
According to some embodiments of the present invention, the reaction time in the seed reaction in step S1 is 1 to 3 hours.
In step S1, an iron source material liquid and a phosphorus salt material liquid are continuously added with the iron phosphate slurry generated by the crystallization reaction as a seed crystal, and the materials are transported from the surface of the seed crystal under stirring and react and precipitate on the surface of the seed crystal to promote the seed crystal to grow continuously. The control of the granularity of the large-particle iron phosphate particles can be realized by controlling the times of seed crystal reaction (namely the cycle times of sedimentation, supernatant extraction, feeding, reaction and sedimentation).
According to some embodiments of the invention, the stirring rate of the reaction in step S1 is 100rpm to 400 rpm.
According to some embodiments of the present invention, the adding speed of the phosphate raw material solution in step S1 is controlled to be 30mL/min to 60mL/min, and the adding speed of the iron salt raw material solution is controlled to be 30mL/min to 60 mL/min.
According to some embodiments of the invention, the heating temperature in the step S2 is 80 ℃ to 100 ℃.
According to some embodiments of the invention, the reaction time in step S2 is 1h to 3 h.
According to some embodiments of the invention, the stirring rate of the reaction in step S2 is 200rpm to 600 rpm.
According to some embodiments of the present invention, the phosphate feedstock solution in step S2 is fed by direct pouring.
In step S2, the phosphorus salt raw material liquid is added to the mixture of the iron phosphate slurry I and the iron salt raw material liquid by direct pouring, so that the saturation of the reaction is greatly improved, the collision between phosphate ions and iron ions is increased, the crystal nucleation rate is significantly increased, and new iron phosphate crystal seeds are newly generated in the system, thereby obtaining an iron phosphate slurry in which large-particle iron phosphate and small-particle iron phosphate coexist. The proportion of large-particle iron phosphate and small-particle iron phosphate is regulated and controlled by controlling the proportion of the iron phosphate slurry I and the ferric salt raw material liquid.
According to some embodiments of the present invention, the ratio of the amount of iron atoms in the iron salt raw material solution to the amount of phosphorus atoms in the phosphate raw material solution added in step S2 is 1:1 to 1: 1.5.
The preparation method of the iron phosphate material according to the embodiment of the invention has at least the following beneficial effects: the preparation method has simple process and strong operability; the iron phosphate slurry with a large and small particle compound structure can be obtained through two main processes.
In order to solve the third technical problem, the technical scheme provided by the invention is as follows: the iron phosphate material is applied to preparation of a lithium iron phosphate material.
According to some embodiments of the invention, the lithium iron phosphate material is used for the preparation of a lithium ion battery cathode material.
According to some embodiments of the present invention, the method for preparing the lithium iron phosphate material is a high temperature solid phase method.
The application of the iron phosphate material according to the embodiment of the invention has at least the following beneficial effects: the lithium iron phosphate material prepared from the iron phosphate material is selected, and the maximum available compaction density of the obtained lithium iron phosphate pole piece is 2.35g/cm3～2.60g/cm3In the meantime.
Drawings
Figure 1 is an SEM image of an iron phosphate material prepared according to a first embodiment of the present invention;
FIG. 2 is an SEM image of an iron phosphate material prepared according to example two of the present invention;
FIG. 3 is an SEM image of an iron phosphate material prepared according to comparative example one of the present invention;
FIG. 4 is an SEM image of an iron phosphate material prepared according to comparative example II of the present invention;
FIG. 5 is an SEM image of an iron phosphate material prepared according to comparative example III of the present invention;
figure 6 is a cross-sectional SEM image of an iron phosphate material prepared according to a first embodiment of the present invention.
Detailed Description
The concept and technical effects of the present invention will be clearly and completely described below in conjunction with the embodiments to fully understand the objects, features and effects of the present invention. It is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and those skilled in the art can obtain other embodiments without inventive effort based on the embodiments of the present invention, and all embodiments are within the protection scope of the present invention.
The first embodiment of the invention is as follows: a preparation method of an iron phosphate material comprises the following steps:
s1, preparing iron phosphate slurry I:
preparing materials: preparing 1.2mol/L ammonium monohydrogen phosphate solution and 0.5mol/L ferric sulfate solution.
Seed crystal reaction: adding water into 49g of 80% phosphoric acid solution to dilute the solution to 1L of the solution as a base solution, and adding the base solution into a reaction kettle; 2L of ammonium monohydrogen phosphate solution (1.2mol/L) and 2L of iron sulfate solution (0.5mol/L) were added to the reaction vessel in a cocurrent feed at a stirring rate of 240 rpm; after the addition is finished, heating to 88 ℃, and continuously reacting for 3 hours at the temperature to obtain white slurry; wherein, the feeding speeds of the ammonium monohydrogen phosphate solution and the ferric sulfate solution are both 30 mL/min.
And (3) crystallization reaction: stopping stirring, and pumping 2L of supernatant when the white slurry is settled and layered for 30 min; stirring was started to 200rpm, and 2.7L of ammonium monohydrogen phosphate solution (1.2mol/L) and 2.3L of iron sulfate solution (0.5mol/L) were added to the reaction kettle in a concurrent addition manner over 90 min; and after the charging is finished, keeping the temperature for 1h to obtain white slurry, and repeating the crystallization reaction step until the particle size of the iron phosphate slurry D50 reaches 8 mu m to obtain the iron phosphate slurry I.
S2, preparing iron phosphate slurry II: mixing 1L of ferric sulfate solution (0.5mol/L) with the ferric phosphate slurry I, and controlling the molar ratio of iron atoms in the ferric phosphate slurry I to iron ions in the ferric sulfate solution to be 1: 4. Under the condition of controlling the stirring speed to be 300rpm, 1.2L of ammonium monohydrogen phosphate solution (1.2mol/L) is directly added into the reaction kettle, then the temperature is raised to 88 ℃, and the reaction is continued for 2h, so that iron phosphate slurry II is obtained.
S3, preparing an iron phosphate material: and (4) carrying out filter pressing, washing and drying on the iron phosphate slurry II to obtain the iron phosphate material.
The scanning electron microscope image of the iron phosphate material prepared in the first embodiment of the present invention is shown in fig. 1, and it is known from fig. 1 that the iron phosphate material prepared in the first embodiment of the present invention obviously has two iron phosphate particles with different sizes, wherein the diameter of the large-particle iron phosphate material is 6 μm to 9 μm, and the diameter of the small-particle iron phosphate is 0.2 μm to 1 μm.
The second embodiment of the invention is as follows: a preparation method of an iron phosphate material comprises the following steps:
s1, preparing iron phosphate slurry I:
preparing materials: preparing 1.1mol/L ammonium monohydrogen phosphate solution and 0.5mol/L ferric sulfate solution.
Seed crystal reaction: adding water into 73.5g of phosphoric acid solution with the mass concentration of 80% to dilute the solution to 1L of the solution to be used as a base solution, and adding the base solution into a reaction kettle; 2L of ammonium monohydrogen phosphate solution (1.1mol/L) and 2L of ferric sulfate solution (0.5mol/L) were added to the reaction kettle in a cocurrent addition at a stirring rate of 200 rpm; after the addition is finished, heating to 88 ℃, and continuously reacting for 3 hours at the temperature to obtain white slurry; wherein, the feeding speeds of the ammonium monohydrogen phosphate solution and the ferric sulfate solution are both 40 mL/min.
And (3) crystallization reaction: stopping stirring, and pumping 2L of supernatant when the white slurry is settled and layered for 30 min; starting stirring to 200rpm, adding 2.95L of ammonium monohydrogen phosphate solution (1.1mol/L) and 2.05L of ferric sulfate solution (0.5mol/L) into the reaction kettle in a cocurrent flow feeding mode within 100min, keeping the temperature for 1h after feeding is finished to obtain white slurry, and repeating the crystallization reaction step until the granularity of the ferric phosphate slurry D50 reaches 4.5 mu m to obtain the ferric phosphate slurry I.
S2, preparing iron phosphate slurry II: mixing 1L of ferric sulfate solution (0.5mol/L) with the ferric phosphate slurry I, and controlling the molar ratio of iron atoms in the ferric phosphate slurry I to iron ions in the ferric sulfate solution to be 1: 3. Under the condition of controlling the stirring speed to be 300rpm, 1.5L of ammonium monohydrogen phosphate solution (1.1mol/L) is directly added into a reaction kettle, the temperature is raised to 88 ℃ after the addition is finished, and the reaction is continued for 2h, so that iron phosphate slurry II is obtained.
S3, preparing an iron phosphate material: and (4) carrying out filter pressing, washing and drying on the iron phosphate slurry II to obtain the iron phosphate material.
The scanning electron micrograph of the iron phosphate material prepared in the second example of the present invention is shown in fig. 2, and it can be seen from fig. 2 that the iron phosphate prepared in the second example also has two different sizes of iron phosphate particles, wherein the large particle iron phosphate has a diameter of 2 μm to 5 μm, and the small particle iron phosphate has a diameter of 0.2 μm to 1 μm.
The third embodiment of the invention is as follows: a preparation method of an iron phosphate material comprises the following steps:
s1, preparing iron phosphate slurry I:
preparing materials: ammonium monohydrogen phosphate solution with the concentration of 0.65mol/L and ferric nitrate solution with the concentration of 0.5mol/L are prepared.
Seed crystal reaction: adding water into 20g of 80% phosphoric acid solution to dilute the solution to 1L of the solution as a base solution, and adding the base solution into a reaction kettle; 2L of ammonium monohydrogen phosphate solution (0.65mol/L) and 2L of ferric sulfate solution (0.5mol/L) were added to the reaction kettle in a concurrent addition at a stirring rate of 200 rpm; after the addition is finished, heating to 88 ℃, and continuously reacting for 3 hours at the temperature to obtain white slurry; wherein, the feeding speeds of the ammonium monohydrogen phosphate solution and the ferric sulfate solution are both 30 mL/min.
And (3) crystallization reaction: stopping stirring, and pumping 2L of supernatant when the white slurry is settled and layered for 30 min; stirring was turned on to 200rpm, and 2.5L of ammonium monohydrogen phosphate solution (0.65mol/L) and 2.5L of iron nitrate solution (0.5mol/L) were added to the reaction kettle in a concurrent addition over 60 min; and after the charging is finished, keeping the temperature for 1h to obtain white slurry, and then repeating the crystallization reaction step until the particle size of the iron phosphate slurry D50 reaches 3 mu m to obtain the iron phosphate slurry I.
S2, preparing iron phosphate slurry II: 1L of ferric nitrate solution (0.5mol/L) and the ferric phosphate slurry I are mixed, and the molar ratio of iron atoms in the ferric phosphate slurry I to iron ions in the ferrous sulfate solution is controlled to be 1: 7. Under the condition of controlling the stirring speed to be 300rpm, 1.2L of ammonium monohydrogen phosphate solution (0.65mol/L) is directly added into the reaction kettle, the temperature is raised to 88 ℃ after the feeding is finished, and the reaction is continued for 2h, so that iron phosphate slurry II is obtained.
S3, preparing an iron phosphate material: and (4) carrying out filter pressing, washing and drying on the iron phosphate slurry II to obtain the iron phosphate material.
The first comparative example of the present invention is: a preparation method of an iron phosphate material comprises the following steps:
s1, preparing iron phosphate slurry: 2L of ferrous sulfate solution with the iron element substance quantity concentration of 1mol/L is taken as a base solution, 2L of ammonium monohydrogen phosphate solution with the phosphorus element substance quantity concentration of 1.3mol/L is pumped into a reaction kettle under the condition of continuous stirring (240rpm), and the feeding speed of the ammonium monohydrogen phosphate solution is controlled to be 40mL/min, wherein the ammonium monohydrogen phosphate solution contains 1.2mol of hydrogen peroxide. After the charging is finished, the temperature is raised to 88 ℃, and the reaction is continued for 3 hours, thus obtaining the iron phosphate slurry.
S2, dehydrating the iron phosphate slurry: and (3) carrying out filter pressing, washing and drying on the iron phosphate slurry to obtain the iron phosphate material.
The scanning electron microscope image of the iron phosphate material prepared in the first comparative example of the invention is shown in fig. 3, and it is known from fig. 3 that the iron phosphate particles prepared in the first comparative example have a single size, the diameter of a single iron phosphate particle is 0.2 μm to 0.5 μm, and the iron phosphate material prepared in the first comparative example does not have a composite morphology with mixed large and small particles.
The second comparative example of the present invention is: a preparation method of an iron phosphate material comprises the following steps: this comparative example uses a procedure similar to that of example one, differing from example one in that: in the preparation step of the iron phosphate slurry ii, the molar ratio of iron atoms in the iron phosphate slurry i to iron atoms in the iron salt raw material liquid was controlled to be 3: 1.
The SEM results of the iron phosphate material according to comparative example two of the present invention are shown in fig. 4, and it can be seen from fig. 4 that the iron phosphate obtained according to comparative example two also has a composite morphology in which large and small particles are mixed, but the number of large particles is significantly greater than that of small particles. This indicates that when the ratio of iron atoms in the iron phosphate slurry I to iron atoms in the iron salt raw material liquid added in step S2 is too large, the ratio of large particles in the prepared iron phosphate is large.
The third comparative example of the present invention is: a preparation method of an iron phosphate material comprises the following steps: this comparative example uses a procedure similar to that of example one, differing from example one in that: in the preparation step of the iron phosphate slurry ii, the molar ratio of iron atoms in the iron phosphate slurry i to iron atoms in the iron salt raw material liquid was controlled to 1: 15.
The iron phosphate materials prepared in the first to third embodiments and the first to third comparative examples are also used for preparing lithium iron phosphate materials, and the method comprises the following steps:
s01: mixing the iron phosphate material prepared by the method, lithium carbonate and glucose, and performing sanding treatment on the mixture, wherein the mass ratio of the iron phosphate material to the lithium carbonate to the glucose is 8:2: 1.
And S02, drying the slurry obtained by sanding at 90 ℃, and then carrying out heat treatment for 8h at 800 ℃ in a nitrogen atmosphere to obtain the lithium iron phosphate material.
The SEM results of the iron phosphate material according to comparative example No. three of the present invention are shown in fig. 5, and it can be seen from fig. 5 that only a small amount of large particles, mostly small particles, are present in the iron phosphate material according to comparative example No. three. This indicates that when the ratio of iron atoms in the iron phosphate slurry I to iron atoms in the iron salt raw material liquid added in step S2 is too small, the ratio of small particles in the obtained iron phosphate is large.
By combining the preparation methods and the micro-morphologies of the first embodiment and the second to third comparative examples, the method provided by the invention realizes the regulation and control of the proportion of the large and small particles in the final iron phosphate material by controlling the quantitative proportion of the iron atoms in the iron phosphate slurry I and the iron atoms in the iron salt raw material liquid, and prepares the iron phosphate materials with different particle size gradations.
By combining the preparation methods and the microscopic morphologies of the first to third embodiments of the present invention, the method provided by the present invention controls the growth of the iron phosphate material by multiple sedimentation during the preparation step of the iron phosphate slurry i, thereby effectively controlling the particle size of the iron phosphate.
The compacted densities of the lithium iron phosphate positive electrode materials prepared from the iron phosphate materials corresponding to the first to third embodiments of the present invention and the first to third comparative examples are shown in table 1.
TABLE 1 compacted densities of lithium iron phosphate materials prepared from iron phosphate materials corresponding to examples one-third of the present invention and comparative examples one-third
Example one Example two EXAMPLE III Comparative example 1 Comparative example No. two Comparative example No. three
Density of compaction 2.53g/cm3 2.48g/cm3 2.50g/cm3 2.23g/cm3 2.19g/cm3 2.28g/cm3
The compacted densities of the lithium iron phosphate anode materials prepared from the iron phosphate materials of the embodiment of the invention are respectively 2.53g/cm3、2.48g/cm3And 2.50g/cm3. The compacted density of the lithium iron phosphate cathode material prepared based on the ferric phosphate of the comparative example is only 2.23g/cm3This is because the iron phosphate prepared by the method provided by the embodiment of the inventionThe lithium iron phosphate anode material has a composite shape with mixed large and small particles, and when the lithium iron phosphate prepared from the iron phosphate with the shape is accumulated, the small particles can be filled in gaps among large particles, so that the compaction density of the lithium iron phosphate anode material is greatly improved. Meanwhile, the interior of the prepared iron phosphate material is of a non-porous or less-porous compact structure (as shown in fig. 6), and the compact density of the lithium iron phosphate cathode material can be further improved by the internally-compact iron phosphate material.
The iron phosphate materials prepared based on the comparative examples two to three also have iron phosphate particles with two different sizes, but the compaction density of the lithium iron phosphate positive electrode material prepared based on the comparative examples two to three iron phosphate is only 2.19g/cm3And 2.28g/cm3. In the case of comparative example II, the iron phosphate produced had an excessive number of large particles and an insufficient number of small particles, resulting in inefficient filling of the voids between the large particles and a lower compacted density. Furthermore, the compacted density of comparative example two was even lower than comparative example one, since when the particle size was too large, the voids between the particles increased. For the third comparative example, the prepared iron phosphate has too few large particles and too many small particles, and the unreasonable gradation cannot significantly improve the compaction density of the lithium iron phosphate cathode material.
In addition, electrochemical performance data (chargeability) of the lithium iron phosphate positive electrode materials prepared from the iron phosphate materials corresponding to the first to third examples of the present invention and the first to third comparative examples are shown in table 2.
Table 2. electrochemical performance data of lithium iron phosphate materials prepared from iron phosphate materials corresponding to examples one to three of the present invention and comparative examples one to three
Figure BDA0002950437890000101
As shown in table 2, the first to third examples all exhibited higher discharge capacities, and there was no significant difference from the first comparative example, which indicates that the lithium iron phosphate material prepared by using the iron phosphate material prepared by the present invention as a precursor can still ensure excellent electrochemical performance under the condition of obtaining a high compaction density. In conclusion, the preparation method disclosed by the invention is simple in process and strong in operability; the iron phosphate slurry with a large and small particle compound structure can be obtained through two main processes, and the prepared iron phosphate material has the characteristic of compact structure inside. In the related art, when preparing the iron phosphate slurry or the lithium iron phosphate slurry with a large-particle complex structure, a large-particle iron phosphate (or lithium iron phosphate) slurry and a small-particle iron phosphate (or lithium iron phosphate) slurry are respectively prepared, and then the large-particle slurry and the small-particle slurry are mixed according to a certain proportion. The method has complex process, two different production lines are required to be established to respectively prepare large-particle size and small-particle size during the amplification production, and meanwhile, the uniform mixing of the large-particle size and the small-particle size is difficult to realize during the material mixing, and the stability of the product batch is poor. In addition, the iron phosphate material with the large and small particle compound structure prepared in the related technology has more internal pores and does not have the structural characteristic of internal compactness.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the gist of the present invention. Furthermore, the embodiments of the present invention and the features of the embodiments may be combined with each other without conflict.

Claims (9)

1. A preparation method of an iron phosphate material is characterized by comprising the following steps: the method comprises the following steps:
s1, preparing iron phosphate slurry I:
preparing materials: preparing a phosphorus salt raw material solution and an iron salt raw material solution, dividing the phosphorus salt raw material solution into a phosphorus salt raw material solution A, a phosphorus salt raw material solution B and a phosphorus salt raw material solution C, and dividing the iron salt raw material solution into an iron salt raw material solution A, an iron salt raw material solution B and an iron salt raw material solution C;
seed crystal reaction: taking a phosphoric acid solution as a base solution, simultaneously adding a phosphorus salt raw material solution A and an iron salt raw material solution A, heating and reacting to convert the mixture into white slurry I, stopping stirring, standing for solid-liquid layering, and then pumping out a supernatant; obtaining a solid-phase material;
and (3) crystallization reaction: under the condition of stirring, adding a phosphorus salt raw material solution B and an iron salt raw material solution B into the solid-phase material for multiple times, converting into a white slurry II after heating reaction, stopping stirring, standing again, and after solid and liquid are layered, pumping away supernatant; repeating the crystallization reaction step until the D50 particle size of the white slurry II reaches 2-10 mu m, thus obtaining the iron phosphate slurry I;
s2, preparing iron phosphate slurry II: mixing the iron phosphate slurry I and the ferric salt raw material liquid C, adding the phosphorus salt raw material liquid C, heating for reaction, and converting into a white slurry III to obtain an iron phosphate slurry II;
s3, drying: performing solid-liquid separation on the iron phosphate slurry II, collecting a solid phase part, washing and drying to obtain the iron phosphate material;
wherein the ratio of the amount of the iron atoms in the iron phosphate slurry I to the amount of the iron atoms in the iron salt raw material liquid in step S2 is 1: 3-9.
2. The method of claim 1, wherein: the mass concentration of phosphorus atoms in the phosphorus salt raw material liquid is 0.5-1.5 mol/L; the mass concentration of iron atoms in the ferric salt raw material liquid is 0.5-1.5 mol/L.
3. The method of claim 1, wherein: in the crystallization reaction step, the mass ratio of phosphorus atoms to iron atoms in the white slurry I is 0.8-1.5: 1.
4. The method of claim 3, wherein: the ratio of the phosphorus atoms in the phosphoric acid solution to the amount of phosphorus atoms in the phosphorus salt raw material solution added for the crystallization reaction is 1:3 to 1: 7: 1.
5. the method of claim 3, wherein: the ratio of the amount of phosphorus atoms to iron atoms in the phosphorus salt raw material solution and the iron salt raw material solution added in the crystallization reaction step is 1.1-1.7: 1.
6. The method of claim 3, wherein: the heating temperature of the seed crystal reaction in the step S1 is 80-100 ℃; the seed crystal reaction time in the step S1 is 1-3 h.
7. The method of claim 3, wherein: the heating temperature of the crystallization reaction in the step S1 is 80-100 ℃; the crystallization reaction time in the step S1 is 1-3 h.
8. The method of claim 3, wherein: the ratio of the amount of the iron atoms in the iron salt raw material solution to the amount of the phosphorus atoms in the phosphate raw material solution added in step S2 is 1:1 to 1: 1.5.
9. The method of claim 3, wherein: the heating temperature in the step S2 is 80-100 ℃; the reaction time in the step S2 is 1-3 h.
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