Process for the preparation of a granulometrically graded iron phosphate

Abstract

The embodiment of the specification discloses a preparation method of particle size graded iron phosphate. The method comprises the following steps: obtaining iron phosphate slurry A and iron phosphate slurry B; heating the iron phosphate slurry A until the color turns white, adding the iron phosphate slurry B into the iron phosphate slurry A to obtain a mixed slurry; heating the mixed slurry until the color turns white or off-white again, and keeping the temperature for a certain time to obtain a solid precipitate; and washing and calcining the solid precipitate to obtain particle size graded iron phosphate. The particle size graded iron phosphate has a three-section particle size distribution in a ladder shape, so that the particle size graded iron phosphate prepared by the segmented feeding form is composed of solid large particles and dispersed small agglomerates, artificial particle size grading is realized at the precursor end of lithium iron phosphate, and the compaction density of the prepared lithium iron phosphate is effectively improved.

Description

TECHNICAL FIELD

[0001] The present specification relates to the technical field of lithium ion battery materials, and in particular to a preparation method of particle size graded iron phosphate. BACKGROUND

[0002] As a precursor for synthesizing lithium iron phosphate, various performance indicators of iron phosphate have an important influence on the charge and discharge performance of the prepared lithium iron phosphate. With the vigorous development of the lithium iron phosphate market, the demand for lithium iron phosphate is rapidly increasing, and the gradually mature market has put forward higher requirements for the tap density of iron phosphate.

[0003] In order to improve the tap density, many processes currently add additives such as graphene to lithium iron phosphate to improve the tap density, but the cost is high. Tests have shown that the tap density of lithium iron phosphate cathode material is not only related to the size and density of the precursor particles, but also related to the particle size grading of the precursor particles. Generally, the tap density with good particle normal distribution.

[0004] Therefore, there is a need for a low-cost preparation scheme for particle size graded iron phosphate. SUMMARY

[0005] The present specification provides a preparation method of particle size graded iron phosphate to solve the technical problem of the need for a low-cost preparation scheme for particle size graded iron phosphate.

[0006] To solve the above technical problems, one or more embodiments of the present specification are implemented as follows:

[0007] In a first aspect, the present specification provides a preparation method of particle size graded iron phosphate, comprising: obtaining iron phosphate slurry A and iron phosphate slurry B; heating the iron phosphate slurry A to a white color, adding the iron phosphate slurry B to the iron phosphate slurry A to obtain a mixed slurry; heating the mixed slurry to white or powder white again, and then keeping the temperature for a certain period of time to obtain a solid precipitate; and washing and calcining the solid precipitate to obtain particle size graded iron phosphate, wherein the particle size graded iron phosphate has a three-section particle size distribution in a ladder shape.

[0008] In a second aspect, the present specification also provides a particle size graded iron phosphate, which has a three-section particle size distribution in a ladder shape, and the three-section particle size distribution in a ladder shape specifically includes: three peak values of volume density in the particle size distribution appear in sequence, the first peak value is 0.1-1 μm, the second peak value is 1-10 μm, and the third peak value is 10-100 μm.

[0009] The above at least one technical solution adopted by one or more embodiments of the present specification can achieve the following beneficial effects: by obtaining iron phosphate slurry A and iron phosphate slurry B; heating the iron phosphate slurry A to white color, adding the iron phosphate slurry B into the iron phosphate slurry A to obtain a mixed slurry; heating the mixed slurry to white or off-white again, and keeping the temperature for a certain period of time to obtain a solid precipitate; after washing and calcining the solid precipitate, a particle size graded iron phosphate is obtained, wherein the particle size graded iron phosphate has a three-section particle size distribution in a ladder shape, thereby preparing the particle size graded iron phosphate by the form of segmented feeding, and the particle size graded iron phosphate is obtained by the combination of solid large particles and dispersed small agglomerates, and the particle size grading is artificially realized at the precursor end of lithium iron phosphate, and the compaction density of the prepared lithium iron phosphate is effectively improved. BRIEF DESCRIPTION OF DRAWINGS

[0010] In order to more clearly illustrate the technical solutions in the embodiments of the present specification or the prior art, the drawings needed in the embodiment or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present specification, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0011] Figure 1 A flowchart of a preparation method of a particle size graded iron phosphate provided by an embodiment of the present specification is shown in the figure.

[0012] Figure 2 A flowchart of a preparation method of a particle size graded iron phosphate provided by an embodiment of the present specification is shown in the figure.

[0013] Figure 3 An electron microscope diagram of the prepared particle size graded iron phosphate provided by an embodiment of the present specification is shown in the figure.

[0014] Figure 4 A three-section particle size distribution diagram of the particle size graded iron phosphate provided by an embodiment of the present specification is shown in the figure. DETAILED DESCRIPTION

[0015] The embodiment of the present specification provides a preparation scheme of a particle size graded iron phosphate.

[0016] In order to enable those skilled in the art to better understand the technical solutions in the present specification, the technical solutions in the embodiments of the present specification will be described clearly and completely below with reference to the drawings in the embodiments of the present specification. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments of the present specification, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.

[0017] In a first aspect, as Figure 1 shown, Figure 1 A flowchart of a preparation method of a particle size graded iron phosphate provided by an embodiment of the present application is shown.

[0018] Figure 1 The flowchart in the above embodiment can include the following steps:

[0019] S102: Obtain iron phosphate slurry A and iron phosphate slurry B.

[0020] The iron phosphate slurry A and the iron phosphate slurry B can be configured based on the same amorphous filter cake slurry (amorphous refers to the fact that the iron phosphate in the iron phosphate slurry has not yet crystallized, which is characterized in that it cannot produce diffraction effects on X-rays).

[0021] The difference between the iron phosphate slurry A and the iron phosphate slurry B is that ammonium bisulfate, sulfuric acid and phosphoric acid need to be added to the initial solution of the amorphous filter cake slurry during the configuration process. Finally, the iron phosphate slurry A with a pH of 1.5, a conductivity of 50,000 us / cm and an iron ion concentration of 0.5-1 mol / L is configured, for example, by adding ammonium bisulfate, sulfuric acid and phosphoric acid to the initial solution in a mass ratio of 67.7:50:57 to obtain the iron phosphate slurry A; at the same time, ammonium bisulfate and sulfuric acid are added to the other initial solution in a mass ratio of 67.7:50 to configure the iron phosphate slurry B with a pH of 1.2, a conductivity of 30,000 us / cm and an iron ion concentration of 1-1.8 mol / L.

[0022] The ratio of the total molar amount of phosphoric acid and Fe elements in the configured iron phosphate slurry A is between 1:0.2 and 1:0.5, the ratio of the total molar amount of ammonium salt and Fe elements in the configured iron phosphate slurry A is between 1:0.05 and 1:0.5, and the molar mass ratio of the iron phosphate in the iron phosphate slurry A and the iron phosphate slurry B is between 1:1.5 and 1:3.5.

[0023] At this time, the obtained iron phosphate slurry A and B are both yellow.

[0024] S104, heat the iron phosphate slurry A until the color turns white, and add the iron phosphate slurry B to the iron phosphate slurry A to obtain a mixed slurry.

[0025] During the heating process, the iron phosphate slurry A may or may not turn white. When the temperature is heated to a certain degree (for example, 88 to 100°C), the color of the iron phosphate slurry A turns white.

[0026] At this time, the iron phosphate slurry B at room temperature can be added to the iron phosphate slurry A to obtain a mixed slurry, and the mixed slurry turns yellow again.

[0027] S106, the mixed slurry is heated to white or off-white again, and then kept at a temperature for a certain time to obtain a solid precipitate. The temperature is 88-100°C, and the time is 1.5-2 hours. The obtained solid precipitate is iron phosphate hydrate (usually iron phosphate dihydrate).

[0028] S108, the solid precipitate is washed and calcined to obtain iron phosphate with a particle size distribution. As shown in the following table, the iron phosphate has a three-stage particle size distribution with a ladder shape. Figure 2 Figure 2 The present specification provides a flowchart for preparing iron phosphate.

[0029] The finished iron phosphate prepared by conventional feeding is composed of iron phosphate agglomerate particles with substantially the same size. Such a precursor will form certain gaps between particles of lithium iron phosphate when prepared into lithium iron phosphate, and thus the lithium iron phosphate is not dense and has low compaction.

[0030] Corresponding to the first aspect, in a second aspect, the present specification also provides an iron phosphate with a particle size distribution. The iron phosphate has a three-stage particle size distribution with a ladder shape, and the three-stage particle size distribution specifically includes three peaks of volume density in the particle size distribution, the first peak is 0.1-1 μm, the second peak is 1-10 μm, and the third peak is 10-100 μm.

[0031] Preferably, the first peak is 0.14-0.16 μm, the second peak is 1.1-1.2 μm, and the third peak is 20-30 μm. The iron phosphate with this particle size distribution can better fill the gaps between larger iron phosphate agglomerates, and the prepared lithium iron phosphate has better compaction density. The iron phosphate with a three-stage particle size distribution with a ladder shape can be prepared in the manner corresponding to the first aspect.

[0032] The present application is segmented by feeding, and the iron phosphate is realized as a combination of solid large particles and dispersed small agglomerates (i.e., particle size distribution). In many cases, the larger the crystal grows, the longer the time, the better the density (the density will be larger), and thus the use of such a precursor to prepare lithium iron phosphate has high density of solid large particles of iron phosphate, and the dispersed small agglomerates fill the gaps between the solid large particles, making them more dense and more compact.

[0033] As shown in the following table, the iron phosphate has a three-stage particle size distribution with a ladder shape. Figure 3 Figure 3 ​​The scanning electron microscope (SEM) image of the prepared iron phosphate provided by the embodiment of the present application is shown in the following figure. The results of the scanning electron microscope show that the prepared iron phosphate is a combination of solid large particles and dispersed small agglomerates, and the pre-arranged particle size grading is achieved at the precursor end. Specifically, the prepared iron phosphate has a three-stage particle size grading distribution in a ladder shape.

[0034] As shown in the following figure, Figure 4 Figure 4 The three-stage particle size distribution of the iron phosphate provided by the embodiment of the present application is shown in the following figure. The three-stage particle size distribution in a ladder shape specifically includes: the first peak value is in the interval of 0.1 to 1 μm, the second peak value is in the interval of 1 to 10 μm, and the third peak value is in the interval of 10 to 100 μm.

[0035] Preferably, the first peak value is 0.14-0.16 μm, the second peak value is 1.1-1.2 μm, and the third peak value is 20 to 30 μm. The three-stage ladder distribution of the particle size, and the respective peak values differ by about one order of magnitude, can make the smaller small particles fill the gap between the large particles of the previous peak value.

[0036] For example, that is, the particles around the peak value of 1.1 to 1.2 μm can better fill the gap between the 20 to 30 μm particles, and the particles around the peak value of 0.14-0.16 μm can better fill the gap between the 1.1 to 1.2 μm particles, thereby achieving the three-stage particle size grading of the iron phosphate precursor, and the gap between the prepared lithium iron phosphate particles is smaller, that is, the gap filling on the order of 0.14-0.16 μm can be better, and the compaction density is higher.

[0037] Compared with the conventional iron phosphate, the specific capacity and the specific discharge capacity of the lithium iron phosphate prepared by the iron phosphate of the present application are comparable, but the compaction density is higher. As shown in Table 1, Table 1 is a comparison of basic data of the iron phosphate of the present application and the conventional iron phosphate.

[0038] Table 1

[0039]

[0040] ​The phosphoric iron slurry A and the phosphoric iron slurry B are obtained; the phosphoric iron slurry A is heated until the color turns white, the phosphoric iron slurry B is added into the phosphoric iron slurry A to obtain a mixed slurry; the mixed slurry is heated until it turns white or off-white again, and then is kept at the temperature for a certain time to obtain a solid precipitate; the solid precipitate is washed and calcined to obtain the phosphoric iron with particle size grading, wherein the phosphoric iron with particle size grading has a three-section particle size distribution in a ladder shape, so that the phosphoric iron with the combination of solid large particles and dispersed small agglomerates is prepared by the form of segmented feeding, the artificial particle size grading is realized at the precursor end of the lithium iron phosphate, and the compaction density of the prepared lithium iron phosphate is effectively improved.

[0041] The above describes certain embodiments of the present specification. Other embodiments are within the scope of the appended claims. In some cases, the actions or steps recited in the claims can be performed in a different order than the order in which they are recited and still achieve desirable results. In addition, the processes depicted in the figures do not necessarily require the particular order shown, or sequential order, to achieve the desired results. In certain implementations, multitasking and parallel processing can be advantageous or necessary.

[0042] The above only describes one or more embodiments of the present specification and does not limit the present specification. One or more embodiments of the present specification can have various modifications and changes for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of one or more embodiments of the present specification shall be included in the scope of claims of the present specification.

Claims

1. A method for preparing ferric phosphate with particle size distribution, comprising: Ferric phosphate slurry A and ferric phosphate slurry B are obtained, wherein the molar mass ratio of ferric phosphate in ferric phosphate slurry A and ferric phosphate slurry B is between 1:1 and 1.5:3.

5. Heat the ferric phosphate slurry A until it turns white, then add the ferric phosphate slurry B to the ferric phosphate slurry A to obtain a mixed slurry; When the mixed slurry is heated until it turns white or off-white again, it is kept at a certain temperature for a certain period of time to obtain a solid precipitate, wherein the temperature is 88 to 100°C. After washing and calcining the solid precipitate, ferric phosphate with particle size distribution is obtained, wherein the ferric phosphate with particle size distribution has a stepped three-stage particle size distribution. The ferric phosphate slurry A is prepared in the following manner: Amorphous ferric phosphate filter cake was obtained and slurried to obtain an initial solution. Ammonium bisulfate, sulfuric acid and phosphoric acid were added to the initial solution in a mass ratio of 67.7:50:57 to prepare ferric phosphate slurry A with pH 1.5, conductivity of 50,000 μS / cm and iron ion concentration of 0.5-1 mol / L. Accordingly, the ferric phosphate slurry B is prepared in the following manner: Amorphous ferric phosphate filter cake was obtained and slurried to obtain another initial solution. Ammonium bisulfate and sulfuric acid were added to the other initial solution at a mass ratio of 67.7:50 to prepare ferric phosphate slurry B with pH 1.2, conductivity of 30,000 μS / cm and iron ion concentration of 1-1.8 mol / L.

2. The method as described in claim 1, wherein, The ratio of total molar amounts of phosphoric acid and Fe in the iron phosphate slurry A is between 1:0.2 and 1:0.

5.

3. The method as described in claim 1, wherein, The total molar ratio of ammonium salt and Fe element in the iron phosphate slurry A is 1: Between 0.05 and 1:0.

5.

4. The method of claim 1, wherein, The calcination is carried out at 550-680°C for 2-5 hours, and the washing includes washing until the conductivity is below 5000 μS / cm.

5. The method of claim 1, wherein, The insulation temperature is 88 to 100°C, and the duration is 1.5 to 2 hours.

6. A particle size-graded ferric phosphate, prepared by any one of claims 1 to 5, wherein the ferric phosphate has a stepped three-segment particle size distribution, the stepped three-segment particle size distribution specifically comprising: The particle size distribution contains three peaks with sequentially increasing bulk density: the first peak is from 0.1 to 1 μm, the second peak is from 1 to 10 μm, and the third peak is from 10 to 100 μm.

7. The iron phosphate as described in claim 6, wherein the first peak value is 0.14-0.16 μm, the second peak value is 1.1-1.2 μm, and the third peak value is 20 to 30 μm.

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