PREPARATION METHOD OF HETEROSITE IRON PHOSPHATE AND APPLICATION THEREOF

Abstract

The invention belongs to the field of battery material recovery, and discloses a preparation method and application of heterosite phosphate. The method comprises the following steps: mixing lithium iron phosphate with a solvent, adding an acid solution, and adjusting the pH to obtain an acidic lithium iron phosphate liquid; adding a transition metal additive to the acidic lithium iron phosphate liquid, and performing leaching in an intensifying micro-environment, followed by filtrating to obtain heterosite iron phosphate and a lithium-rich solution. The leaching rate of lithium in the leaching solution reaches 90.5-99.9%, and both of the iron and phosphorus content in the leaching solution are less than 0.1 ppm; the recovered heterosite iron phosphate has a purity of 99.9%, and the recovery rate of the heterosite iron phosphate is 99.3%.

Claims

1. A preparation method of heterosite iron phosphate, comprising the following steps: (1) mixing lithium iron phosphate with a solvent to obtain a slurry, adjusting the slurry to an acidic pH to obtain an acidic lithium iron phosphate liquid; (2) adding a transition metal additive to the acidic lithium iron phosphate liquid to obtain a mixture, performing leaching in an intensifying micro-environment to the mixture, followed by filtration to obtain the heterosite iron phosphate and a lithium-rich solution; the leaching in the intensifying micro-environment is to leach iron phosphate out of the acidic lithium iron phosphate liquid with microbubbles or under controlled pressure; wherein the microbubbles are produced by introducing a gas into the acidic lithium iron phosphate liquid; the controlled pressure increases the oxygen oxidation potential by changing the partial pressure of oxygen in the leaching environment; the microbubbles, or oxygen microbubbles/dissolved oxygen produced by the controlled pressure generate hydroxyl radicals under surface catalysis of the transition metal additive, used for improving the oxidation capacity and oxidation reaction rate of ferrous iron in the lithium iron phosphate liquid.

2. The preparation method according to claim 1, wherein in step (1), adjusting the slurry to the acidic pH is carried out by adding a liquid acid into the slurry, wherein the liquid acid is at least one selected from the group consisting of sulfuric acid, nitric acid, and hydrochloric acid; and the liquid acid has a concentration of 0.5-5 mol/L.

3. (canceled)

4. The preparation method according to claim 1, wherein in step (1), the lithium iron phosphate is recovered from a waste lithium iron phosphate cathode material.

5. The preparation method according to claim 1, wherein the microbubbles are generated by introducing a gas into the acidic lithium iron phosphate liquid, wherein the gas is air or oxygen; the microbubbles generated by introducing the gas into the acidic lithium iron phosphate liquid have diameters of 10-50 m.

6. The preparation method according to claim 1, wherein the controlled pressure is 0.05-1 Mpa.

7. The preparation method according to claim 1, wherein in step (2), the transition metal additive is at least one selected from the group consisting of nickel oxide, cobalt tetroxide, manganese dioxide, lithium cobaltate, lithium nickelate, lithium manganate, and lithium-nickel-cobalt manganate.

8. The preparation method according to claim 1, wherein in step (2), the acidic lithium iron phosphate liquid and the transition metal additive are in a mass-volume ratio of 50-400 g/L.

9. The preparation method according to claim 1, wherein in step (2), the lithium-rich solution is subjected to a purification process comprising the following steps: adjusting the lithium-rich solution to an alkaline pH; removing impurities to obtain a purified solution; then adding sodium carbonate to the purified solution to react; filtering and drying a resulting precipitate to obtain lithium carbonate.

10. Battery cathode material prepared by the preparation method of claim 1.

11. Battery cathode material prepared by the preparation method of claim 2.

12. Battery cathode material prepared by the preparation method of claim 3.

13. Battery cathode material prepared by the preparation method of claim 4.

14. Battery cathode material prepared by the preparation method of claim 5.

15. Battery cathode material prepared by the preparation method of claim 6.

16. Battery cathode material prepared by the preparation method of claim 7.

17. Battery cathode material prepared by the preparation method of claim 8.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0032] FIG. 1 is a process flow diagram of Example 1 for recovering the heterosite iron phosphate;

[0033] FIG. 2 is a schematic diagram of the leaching route of lithium iron phosphate;

[0034] FIG. 3 is an XRD pattern of the recovered heterosite iron phosphate in Example 1.

DETAILED DESCRIPTION OF THE ILLUSTRATED EXAMPLES

[0035] In order to fully understand the present invention, the preferred experimental scheme of the present invention will be described below in conjunction with examples to further illustrate the characteristics and advantages of the present invention. Any change or alteration that does not deviate from the gist of the present invention can be understood by those skilled in the art. The scope of protection of the invention is determined by the scope of the claims.

[0036] Where specific conditions are not indicated in the examples of the present invention, it shall be carried out under the conventional conditions or the conditions recommended by the manufacturer. The raw materials, reagents, etc. used without indicating their manufacturers are all conventional products commercially available.

Example 1

[0037] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps: [0038] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 2 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0039] (2) Adding cobalt tetroxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen into the mixture to generate microbubbles with a diameter of 50 m to perform leaching at 25 C. for 240 min; after the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of the lithium in the leaching solution reached 99.5%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.1 ppm.

Example 2

[0040] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps: [0041] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 6 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0042] (2) Adding manganese dioxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen into the mixture to generate microbubbles with a diameter of 50 m to perform leaching at 25 C. for 240 min; after the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution reached 93.9%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.01 ppm.

Example 3

[0043] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps: [0044] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 400 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 2 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0045] (2) Adding lithium-nickel-cobalt manganate to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen into the mixture to generate microbubbles with a diameter of 50 m to perform leaching at 25 C. for 240 min; after the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution reached 96.7%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.1 ppm.

Example 4

[0046] A preparation method of the isomorphoside-type iron phosphate of this embodiment comprises the following steps: [0047] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 6 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0048] (2) Adding manganese dioxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen into the mixture to generate microbubbles with a diameter of 10 m to perform leaching at 25 C. for 240 min. After the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution reached 98.6%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.01 ppm.

Example 5

[0049] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps: [0050] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 6 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0051] (2) Adding manganese dioxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen into the mixture to generate microbubbles with a diameter of 10 m to perform leaching at 80 C. for 240 min. After the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution reached 99.5%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.01 ppm.

Example 6

[0052] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps: [0053] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 6 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0054] (2) Adding lithium manganate to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen into the mixture to generate microbubbles with a diameter of 10 m to perform a leaching at 25 C. for 240 min. After the leaching is completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution reached 90.5%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.01 ppm.

Example 7

[0055] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps: [0056] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 400 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 6 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0057] (2) Adding manganese dioxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen into the mixture to generate microbubbles with a diameter of 10 m and performing leaching under 0.05 Mpa oxygen pressure, the leaching was carried out at 80 C. for 240 min. After the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution reached 90.5%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.01 ppm.

Example 8

[0058] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps: [0059] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 50 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 6 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0060] (2) Adding lithium manganate to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen at a pressure of 1 Mpa to the mixture, to perform a leaching at 80 C. for 240 min. After the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution reached 99.9%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.01 ppm.

Example 9

[0061] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps: [0062] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 400 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 2 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0063] (2) Adding lithium nickelate to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen into the mixture to generate microbubbles with a diameter of 50 m, to perform a leaching at 25 C. for 240 min. After the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution reached 99.9%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.1 ppm.

Example 10

[0064] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps: [0065] (1) Mixing lithium iron phosphate and water in a mass-volume ratio of 400 g/L to obtain a slurry, and then adding 2 mol/L hydrochloric acid to the slurry to maintain the pH at 2 during the leaching process to obtain an acidic lithium iron phosphate liquid; [0066] (2) Adding nickel oxide to the acidic lithium iron phosphate liquid to obtain a mixture, and introducing oxygen into the mixture to generate microbubbles with a diameter of 50 m, to perform a leaching at 80 C. for 30 min. After the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution reached 91.5%, and the content of iron and the content of phosphorus in the leaching solution were less than 0.1 ppm.

Comparative Example

[0067] A preparation method of the heterosite iron phosphate of this embodiment comprises the following steps:

[0068] Mixing lithium iron phosphate and water in a mass-volume ratio of 400 g/L to obtain a slurry, and then adding an acid to the slurry to maintain the pH at 2 during the leaching process to obtain an acidic lithium iron phosphate liquid; introducing oxygen into the mixture under normal pressure to perform a leaching at 80 C. for 30 min. After the leaching was completed, filtrating the mixture to obtain a lithium-rich solution and heterosite iron phosphate. The leaching rate of lithium in the leaching solution was 58.13%, and the leaching rates of iron and phosphorus in the leaching solution were 10.67% and 9.75%, respectively.

[0069] Comparison of the Results

[0070] 1. Recovery Rate

TABLE-US-00001 TABLE 1 Recovery rate of Example 1 and Comparative Example Recovery rate of Recovery rate of Recovered item Example 1 (%) Comparative Example (%) Heterosite iron phosphate 99.12 89.21

[0071] 2. Purity

TABLE-US-00002 TABLE 2 Elements contents in the lithium-rich solution Example Example Example Example Example Comparative Elements 1 2 3 4 5 Example Li 5.0428 4.7968 4.9399 5.0369 5.0829 2.9695 Cu 0 0 0 0 0 0 Fe <0.0001 <0.00001 <0.0001 <0.00001 <0.00001 4.3017 Al 0.9842 0.9634 0.9945 0.9872 1.010 1.1002

TABLE-US-00003 TABLE 3 Purity of the recovered heterosite iron phosphate Content of Content of Comparative Elements Example 1/% Example/% FePO.sub.4 87 82 Li 0.15 1.35 Cu 0 0 Al 0.03 0.04 Na 0.013 0.013 Mg 0.002 0.002 Ca 0.001 0.001 Zn 0.004 0.004 F 0.50 0.49

[0072] Performance Testing:

[0073] The lithium iron phosphate prepared from the iron phosphate recovered in the above Examples 1-3 and the comparative example were used as a cathode, graphite was used as an anode. A battery was assembled with the cathode and anode, and its first discharge test was performed at a rate of 1C.

TABLE-US-00004 TABLE 4 Performance test results Comparative Example 1 Example 2 Example 3 Example (lithium iron (lithium iron (lithium iron (lithium iron phosphate phosphate phosphate phosphate prepared from prepared from prepared from prepared from the recovered the recovered the recovered the recovered Item iron phosphate) iron phosphate) iron phosphate) iron phosphate) First discharge 157.1 156.9 157.2 155.6 capacity mAh/g Capacity after 100 152.4 151.33 152.06 147.9 cycles mAh/g Capacity retention 97.01 96.45 96.73 95.05 rate

[0074] The results are shown in Table 4. At a rate of 0.1C, the first discharge capacity of the lithium iron phosphate cathode material recovered in the present invention is higher than that of the heterosite iron phosphate recovered in the traditional method, and the first discharge capacity of Example 1 is 157.1 mAh/g, while the specific capacity of the comparative example is only 155.6 mAh/g.

[0075] FIG. 1 shows the process flow chart of the recovery of the heterosite iron phosphate in Example 1. From FIG. 1, it can be concluded that by subjecting lithium iron phosphate to pulping, adjusting pH value, leaching with microenvironment intensifying, and solid-liquid separation, a heterosite iron phosphate can be obtained.

[0076] It is illustrated in FIG. 2 that there are three main methods for leaching lithium iron phosphate. Method (I) involves oxidative leaching the lithium iron phosphate under strong acidic conditions to obtain a solution containing Li.sup.+, Fe.sup.3+, and PO.sub.4.sup.3, and then adjusting the pH of the solution to obtain an iron phosphate precipitated by the binding of Fe.sup.3+ and PO.sub.4.sup.3; Method (II) comprises leaching lithium iron phosphate under moderate acidity to obtain a solution containing Li.sup.+, Fe.sup.2+, and PO.sub.4.sup.3, and then using a strong oxidant to oxidize Fe.sup.2+ in the leaching solution to Fe.sup.3+, and then Fe.sup.3+ binding with PO.sub.4.sup.3 to form iron phosphate precipitation to achieve a selective Leaching. Method (III) is a selective leaching of lithium iron phosphate through direct oxidation and delithiation of lithium iron phosphate using strong oxidizing agents under weak acid conditions and produce a heterosite iron phosphate. In this method, due to the low mass transfer and oxidation potential of oxygen, although the oxidation of Fe.sup.2+ can be achieved to a certain extent, the oxidation capacity is weak. Therefore, in the actual process, intensifiers such as hydrogen peroxide, sodium persulfate, sodium hypochlorite, and ozone are usually used as oxidants to achieve the oxidation of Fe.sup.2+. When oxygen/air is used as the oxidant to leaching lithium iron phosphate cathode material, Fe.sup.2+ oxidation cannot be effectively carried out, resulting in high Fe.sup.2+ content in the leaching solution and poor selective leaching of lithium. Therefore, it is necessary to improve the oxidation capacity of oxygen to achieve efficient and selective leaching of lithium.

[0077] It can be seen from the XRD spectrum (FIG. 3) that after the leaching of lithium iron phosphate, the leaching slag is mainly composed of heterosite FePO.sub.4 and C. During the leaching process, carbon powder does not participate in the reaction, and LiFePO.sub.4 participates in the reaction to generate FePO.sub.4 in a new phase. Li in the cathode material reacts to form soluble lithium salt, which enters the solution.

[0078] The preparation method and application of an heterosite iron phosphate provided by the present invention are described in detail above. Specific examples are used in this article to illustrate the principle and implementation of the present invention. The description of the above examples It is only used to help understand the method and core idea of the present invention, including the best mode, and also enables any person skilled in the art to practice the present invention, including manufacturing and using any device or system, and implementing any combined method. It should be pointed out that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention. The scope of patent protection of the present invention is defined by the claims, and may include other embodiments that those skilled in the art can think of. If these other embodiments have structural elements that are not different from the literal expression of the claims, or if they include equivalent structural elements that are not substantially different from the literal expression of the claims, these other embodiments should also be included in the scope of the claims.