PREPARATION METHOD AND APPLICATION OF IRON PHOSPHATE

Abstract

Disclosed are a preparation method and application of iron phosphate. The preparation method comprises: subjecting iron phosphate waste to calcination, dissolving it in an acid solution, and filtering to obtain filtrate, namely a solution A containing iron phosphorus; stirring a mixed solution of the solution A and a first alkali solution, adjusting pH of the mixed solution to acidity for reaction, and after washing and filtering to obtain second filter residue, namely an amorphous yellow iron phosphate filter cake; subjecting the yellow iron phosphate filter cake to aging and heating, adding phosphoric acid and a second alkali solution for reaction, followed by washing and filtering to obtain third filter residue, namely a basic ammonium iron phosphate filter cake, then drying to obtain basic ammonium iron phosphate crystal powder; and subjecting the basic ammonium iron phosphate crystal powder to calcination for dehydration and cooling to obtain iron phosphate.

Claims

1. A preparation method of iron phosphate, wherein the preparation method comprises steps of: step (1): subjecting iron phosphate waste to calcination to obtain calcinated waste, dissolving the calcinated waste in an acid solution, and filtering a resulting solution to obtain filtrate, the filtrate being a solution A containing iron and phosphorus elements; step (2): stirring a mixed solution of the solution A obtained in step (1) and a first alkali solution, adjusting pH of the mixed solution to acidity for reaction, and after washing and filtering to obtain second filter residue, the second filter residue being an amorphous yellow iron phosphate filter cake; step (3): subjecting the yellow iron phosphate filter cake to aging, slurrying and heating, adding orthophosphoric acid and a second alkali solution thereto for reaction, followed by washing and filtering to obtain third filter residue, the third filter residue being a basic ammonium iron phosphate filter cake, then drying the basic ammonium iron phosphate filter cake to obtain basic ammonium iron phosphate crystal powder; and step (4): subjecting the basic ammonium iron phosphate crystal powder to calcination for dehydration and cooling to obtain the iron phosphate; wherein in step (3), the orthophosphoric acid has a mass concentration of 80% to 90%, and after the orthophosphoric acid is added, a molar ratio of total iron to total phosphorus in a system is 1:(1.1-1.4); a formula of the basic ammonium iron phosphate is NH.sub.4Fe.sub.2(OH)(PO.sub.4).sub.2.Math.2H.sub.2O, and the basic ammonium iron phosphate has D50 of 1.5 μm-10 μm, tap density of 0.70 g/cm.sup.3-1.30 g/cm.sup.3, and specific surface area of 40 m.sup.2/g-60 m.sup.2/g; and the iron phosphate has D50 of 1 μm-10 μm, tap density of 0.80 g/cm.sup.3-1.30 g/cm.sup.3, and specific surface area of 5 m.sup.2/g-10 m.sup.2/g.

2. The preparation method of claim 1, wherein in step (1), the calcination is carried out for 1 hour to 5 hours at a temperature in a range from 250° C. to 450° C.; and wherein in step (1), the dissolution is carried out for 3 hours to 10 hours at a temperature in a range from 25° C. to 60° C.

3. The preparation method of claim 1, wherein in step (1), the acid solution is one selected from a group consisting of sulfuric acid, hydrochloric acid, and orthophosphoric acid; in a case where the acid solution is sulfuric acid, the sulfuric acid has a concentration in a range from 1 mol/L to 3 mol/L; and a molar ratio of SO.sub.4.sup.2− of the sulfuric acid to Fe.sup.3+ of the iron phosphate waste is (1.3-1.8): 1.

4. The preparation method of claim 1, wherein in step (2), a dosage ratio of the solution A containing iron and phosphorus elements to the first alkali solution is (10-3): 1.

5. The preparation method of claim 1, wherein the first alkali solution in step (2) and the second alkali solution in step (3) are each independently at least one selected from a group consisting of solutions of ammonia, urea, ammonium chloride and ammonium bicarbonate; and the first alkali solution and the second alkali solution each independently have a concentration of 10 wt %-30 wt %.

6. The preparation method of claim 1, wherein in step (2), the reaction is carried out for 0.1 to 0.5 hour at a temperature in a range from 30° C. to 50° C.; and wherein in step (2), the adjusting pH of the mixed solution means that the pH of the mixed solution is adjusted to a range of 1.5-2.5.

7. A method for preparation of batteries, comprising using the iron phosphate of claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0047] FIG. 1 is an XRD pattern of basic ammonium iron phosphate prepared in Example 1 of the present disclosure;

[0048] FIG. 2 is an SEM image of basic ammonium iron phosphate prepared in Example 1 of the present disclosure;

[0049] FIG. 3 is an XRD pattern of iron phosphate prepared in Example 1 of the present disclosure; and

[0050] FIG. 4 is an SEM image of iron phosphate prepared in Example 1 of the present disclosure.

DETAILED DESCRIPTION

[0051] In order to provide thorough understanding of the present disclosure, the preferred embodiments will be described below in conjunction with examples to further illustrate the features and advantages of the present disclosure. Any variations or modifications that do not deviate from the concept of the present disclosure can be understood by those skilled in the art, and the scope of protection of the present disclosure is determined by the scope of the claims.

[0052] Where specific conditions are not indicated in the examples of the present disclosure, they are conventional conditions or the conditions recommended by manufacturers. The raw materials, reagents, etc. used without an indication of the manufacturer are all conventional products that can be purchased commercially.

Example 1

[0053] A preparation method of iron phosphate in this example comprises steps of: [0054] (1) Subjecting 50 kg iron phosphate dihydrate waste to calcination at 350° C. for 3 hours to remove crystal water so as to obtain about 40 kg calcinated material; adding the calcainted material into a kettle containing 270 L of a 1.5 mol/L sulfuric acid solution and stirring at a rotational speed of 200 rpm, heating up the kettle to 50° C. for about 5 hours to dissolve the calcainted material, standing prior to filtering out filter residue with a precision filter and transferring the resulting filtrate to a storage tank to obtain a solution containing Fe.sup.3+ and PO.sub.4.sup.3−, with an iron content of 43.28 g/L and a phosphorus content of 24.78 g/L, and a molar ratio of Fe:P of 1:1.03; [0055] (2) With 50 L deionized water as bottom liquid, injecting the solution containing Fe.sup.3+ and PO.sub.4.sup.3− and ammonia water into a reaction kettle from a bottom at a feed rate ratio of the solution containing Fe.sup.3+ and PO.sub.4.sup.3− to ammonia water of 6:1 in parallel, finely adjusting the feed rate of ammonia water according to a pH real-time feedback system to adjust pH=2 so as to precipitate amorphous iron phosphate, performing reaction at 30° C. for 0.5 hour prior to solid-liquid separation, testing contents of residual Fe and P in the supernatant as 10 mg/L and 153 mg/L respectively (which indicates that Fe ions have been almost completely precipitated), and washing the reaction solution with water to a conductivity of 3500 μs/cm to obtain a yellow amorphous iron phosphate filter cake; [0056] (3) Putting the amorphous iron phosphate filter cake into an aging kettle, thoroughly stirring the amorphous iron phosphate filter cake for 2 hours to obtain a slurry at a stirring speed of 300 rpm with a solid content of the slurry controlled to 100 g/L, heating up the aging kettle to 95° C., pumping in parallel 2 L orthophosphoric acid (85 wt. %) and 5 L ammonia water (15 wt. %) into the slurry in the aging kettle with a peristaltic pump, aging for 5 hours at a certain stirring speed with pH of 2, then subjecting the aged slurry to washing with water to a conductivity of 400 μs/cm and solid-liquid separation to obtain a basic ammonium iron phosphate (NH.sub.4Fe.sub.2(OH)(PO.sub.4).sub.2.Math.2H.sub.2O) filter cake, followed by drying the filter cake at 180° C. for about 15 hours to obtain basic ammonium iron phosphate crystal powder, and testing the ammonium iron phosphate crystal powder for basic performance; and [0057] (4) Heating up the dried basic ammonium iron phosphate crystal powder in a muffle furnace to 350° C. for 3 hours at a heating rate of 5° C./min, then to 550° C. for 6 hours at a heating rate of 10° C./min, followed by naturally cooling down to room temperature to obtain 3.85 kg qualified battery-grade iron phosphate FePO.sub.4 with a yield greater than 96%, and finally testing and analyzing the resulting product for phase and performance.

[0058] The physical and chemical performance indexes of basic ammonium iron phosphate and iron phosphate obtained in this example are shown in Table 1:

TABLE-US-00001 TABLE 1 Basic Fe P Fe/P D10 D50 D90 (D90 − ammonium (wt %) (wt %) (μm) (μm) (μm) D10)/D50 iron 29.49 17.02 0.961 0.99 3.51 9.30 2.37 phosphate BET TD Ni Co Mn Ca Mg (m.sup.2/g) (g/cc) (wt %) (wt %) (wt %) (wt %) (wt %) 44.0 0.73 0.0001 0.0001 0.057 0.0001 0.0001 Na Cu Zn S Al Ti Mo (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 0.0005 0.0010 0.0001 0.0211 0.0023 0.0085 0.0001 Iron Fe P Fe/P D10 D50 D90 (D90 − phosphate (wt %) (wt %) (μm) (μm) (μm) D10)/D50 36.34 20.82 0.968 0.88 3.77 13.19 3.27 BET TD Ni Co Mn Ca Mg (m.sup.2/g) (g/cc) (wt %) (wt %) (wt %) (wt %) (wt %) 10.1 1.00 0.0001 0.0001 0.0121 0.0001 0.0001 Na Cu Zn S Al Ti Mo (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 0.0008 0.0012 0.0001 0.089 0.0021 0.0050 0.0001

[0059] FIGS. 1 and 2 are respectively an XRD pattern and an SEM image of basic ammonium iron phosphate prepared in Example 1, FIGS. 3 and 4 are respectively an XRD pattern and an SEM image of iron phosphate prepared in Example 1; and Table 1 shows the physical and chemical indexes of basic ammonium iron phosphate and iron phosphate prepared in Example 1. It can be seen from FIG. 1 that the basic ammonium iron phosphate prepared in Example 1 has relatively high phase purity and good crystallinity, and no other impurity phases are found. It can be seen from FIG. 2 that primary particles of the basic ammonium iron phosphate have a relatively large length-diameter ratio, and secondary particles have a nest-like spherical structure with good particle dispersion. It can be seen from FIG. 3 that the iron phosphate prepared in Example 1 has very good crystallinity and no other impurity phases are found. It can be seen from FIG. 4 that secondary particles of the prepared iron phosphate still have nest-like spherical structure, and the change is small before and after annealing; annealing only causes the primary particles to melt, the particle size is slightly larger and the specific surface area is reduced, so that the particle dispersion is still relatively good. Table 1 shows that the basic ammonium iron phosphate and iron phosphate of Example 1 have contents of iron and phosphorus as well as various other elements that meet the Chinese national standards for anhydrous iron phosphate, and have small dispersion of particle size distribution, narrow particle size distribution; in addition, the particle size distribution after calcination is wider than that before calcination, both tap densities before and after calcination are relatively high, and specific surface area is moderate. Therefore, the basic ammonium iron phosphate and iron phosphate of Example 1 are suitable as precursor materials for preparing lithium iron phosphate batteries.

Example 2

[0060] A preparation method of iron phosphate in this example comprises steps of: [0061] (1) Subjecting 10 kg iron phosphate waste to calcination at 400° C. for 5 hours to remove crystal water so as to obtain about 8 kg calcinated material; adding the calcainted material into a kettle containing 34 L of a 2.4 mol/L sulfuric acid solution and stirring at a rotational speed of 200 rpm, heating up the kettle to 50° C. for about 5 hours to dissolve the calcainted material, standing prior to filtering out filter residue with a precision filter and transferring the resulting filtrate to a storage tank to obtain a solution containing Fe.sup.3+ and PO.sub.4.sup.3−, with an iron content of 83.20 g/L and a phosphorus content of 47.9 g/L, and a molar ratio of Fe:P of 1:1.04; [0062] (2) With 50 L deionized water as bottom liquid, injecting the solution containing Fe.sup.3+ and PO.sub.4.sup.3− and ammonia water into a reaction kettle from a bottom at a feed rate ratio of the solution containing Fe.sup.3+ and PO.sub.4.sup.3− to ammonia water of 3:1 in parallel, finely adjusting the feed rate of ammonia water according to a pH real-time feedback system to adjust pH=2.5 so as to precipitate amorphous iron phosphate, performing reaction at 50° C. for 0.5 hour prior to solid-liquid separation, testing contents of residual Fe and P in the supernatant as 19 mg/L and 230 mg/L respectively (which indicates that Fe ions have been almost completely precipitated), and washing the reaction solution with water to a conductivity of 4500 μs/cm to obtain a yellow amorphous iron phosphate filter cake; [0063] (3) Putting the amorphous iron phosphate filter cake into an aging kettle, thoroughly stirring the amorphous iron phosphate filter cake for 2 hours to obtain a slurry at a stirring speed of 300 rpm with a solid content of the slurry controlled to 200 g/L, heating up the aging kettle to 95° C., pumping in parallel 1.5 L orthophosphoric acid (85 wt. %) and 4 L ammonia water (25 wt. %) into the slurry in the aging kettle with a peristaltic pump, aging for 8 hours at a certain stirring speed with pH of 2.5, then subjecting the aged slurry to washing with water to a conductivity of 300 μs/cm and solid-liquid separation to obtain a basic ammonium iron phosphate (NH.sub.4Fe.sub.2(OH)(PO.sub.4).sub.2.Math.2H.sub.2O) filter cake, followed by drying the filter cake at 150° C. for about 20 hours to obtain basic ammonium iron phosphate crystal powder, and testing a certain amount of ammonium iron phosphate for basic performance; and [0064] (4) Heating up the dried basic ammonium iron phosphate crystal powder in a muffle furnace to 300° C. for 4 hours at a heating rate of 3° C./min, then to 500° C. for 7 hours at a heating rate of 5° C./min, followed by naturally cooling down to room temperature to obtain 7.8 kg qualified battery-grade iron phosphate FePO.sub.4 with a yield greater than 97%, and finally testing and analyzing the resulting product for phase and performance.

[0065] The physical and chemical performance indexes of basic ammonium iron phosphate and iron phosphate obtained in this example are shown in Table 2:

TABLE-US-00002 TABLE 2 Basic Fe P Fe/P D10 D50 D90 (D90 − ammonium (wt %) (wt %) (μm) (μm) (μm) D10)/D50 iron 29.12 16.58 0.974 1.53 6.72 11.65 1.80 phosphate BET TD Ni Co Mn Ca Mg (m.sup.2/g) (g/cc) (wt %) (wt %) (wt %) (wt %) (wt %) 40.5 0.92 0.0001 0.0012 0.0049 0.0005 0.0002 Na Cu Zn S Al Ti Mo (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 0.0004 0.0010 0.0001 0.0073 0.0001 0.0011 0.0002 Iron Fe P Fe/P D10 D50 D90 (D90 − phosphate (wt %) (wt %) (μm) (μm) (μm) D10)/D50 36.11 20.52 0.976 1.73 6.99 12.96 1.61 BET TD Ni Co Mn Ca Mg (m.sup.2/g) (g/cc) (wt %) (wt %) (wt %) (wt %) (wt %) 7.60 1.21 0.0001 0.0009 0.0048 0.0006 0.0001 Na Cu Zn S Al Ti Mo (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 0.0005 0.0001 0.0001 0.0011 0.0001 0.0013 0.0001

[0066] The basic ammonium iron phosphate prepared in Example 2 has relatively high phase purity and good particle dispersion, no other impurity phases are found. The iron phosphate after calcination has very good crystallinity, and no other impurity phases are found. The basic ammonium iron phosphate and iron phosphate have contents of iron and phosphorus as well as various other elements that meet the Chinese national standards for anhydrous iron phosphate. The iron phosphate has tap density of 1.21 g/cm.sup.3 and specific surface area of 7.60 m.sup.2/g, which is suitable as a precursor material for preparing lithium iron phosphate batteries.

Example 3

[0067] A preparation method of battery-grade iron phosphate in this example comprises steps of: [0068] (1) Subjecting 4 kg iron phosphate waste to calcination at 300° C. for 3 hours to remove crystal water so as to obtain about 4 kg calcinated material; adding the calcainted material into a kettle containing 27 L of a 1.5 mol/L sulfuric acid solution and stirring at a rotational speed of 200 rpm, heating up the kettle to 50° C. for about 5 hours to dissolve the calcainted material, standing prior to filtering out filter residue with a precision filter and transferring the resulting filtrate to a storage tank to obtain a solution containing Fe.sup.3+ and PO.sub.4.sup.3−, with an iron content of 63.42 g/L and a phosphorus content of 37.17 g/L, and a molar ratio of Fe:P of 1:1.05; [0069] (2) With 20 L deionized water as bottom liquid, injecting the solution containing Fe.sup.3+ and PO.sub.4.sup.3− and ammonia water into a reaction kettle from a bottom at a feed rate ratio of the solution containing Fe.sup.3+ and PO.sub.4.sup.3− to ammonia water of 8:1 in parallel, finely adjusting the feed rate of ammonia water according to a pH real-time feedback system to adjust pH=1.5 so as to precipitate amorphous iron phosphate, performing reaction at 50° C. for 0.5 hour prior to solid-liquid separation, testing contents of residual Fe and P in the supernatant as 20 mg/L and 310 mg/L respectively (which indicates that Fe ions have been almost completely precipitated), and washing the reaction solution with water to a conductivity of 2500 μs/cm to obtain a yellow amorphous iron phosphate filter cake; [0070] (3) Putting the amorphous iron phosphate filter cake into an aging kettle, thoroughly stirring the amorphous iron phosphate filter cake for 1 hour to obtain a slurry at a stirring speed of 300 rpm with a solid content of the slurry controlled to 50 g/L, heating up the aging kettle to 80° C., pumping in parallel 1.5 L orthophosphoric acid (85 wt. %) and 4 L ammonia water (25 wt. %) into the slurry in the aging kettle with a peristaltic pump, aging for 10 hours at a certain stirring speed with pH of 2.5, then subjecting the aged slurry to washing with water to a conductivity of 300 μs/cm and solid-liquid separation to obtain a basic ammonium iron phosphate (NH.sub.4Fe.sub.2(OH)(PO.sub.4).sub.2.Math.2H.sub.2O) filter cake, followed by drying the filter cake at 120° C. for about 24 hours to obtain basic ammonium iron phosphate crystal powder, and testing a certain amount of ammonium iron phosphate for basic performance; and [0071] (4) Heating up the dried basic ammonium iron phosphate crystal powder in a muffle furnace to 350° C. for 4 hours at a heating rate of 5° C./min, then to 600° C. for 5 hours at a heating rate of 10° C./min, followed by naturally cooling down to room temperature to obtain 3.8 kg qualified battery-grade iron phosphate FePO.sub.4 with a yield greater than 95%, and finally testing and analyzing the resulting product for phase and performance.

[0072] The physical and chemical performance indexes of basic ammonium iron phosphate and iron phosphate obtained in this example are shown in Table 3:

TABLE-US-00003 TABLE 3 Basic Fe P Fe/P D10 D50 D90 (D90 − ammonium (wt %) (wt %) (μm) (μm) (μm) D10)/D50 iron 29.05 16.74 0.962 0.69 3.57 8.56 2.20 phosphate BET TD Ni Co Mn Ca Mg (m.sup.2/g) (g/cc) (wt %) (wt %) (wt %) (wt %) (wt %) 5.50 0.71 0.0002 0.0015 0.0042 0.0012 0.0011 Na Cu Zn S Al Ti Mo (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 0.0001 0.0001 0.0021 0.0035 0.0005 0.0009 0.0002 Iron Fe P Fe/P D10 D50 D90 (D90 − phosphate (wt %) (wt %) (μm) (μm) (μm) D10)/D50 36.25 20.44 0.983 0.86 4.01 8.89 2.00 BET TD Ni Co Mn Ca Mg (m.sup.2/g) (g/cc) (wt %) (wt %) (wt %) (wt %) (wt %) 5.50 0.80 0.0001 0.0018 0.0049 0.0010 0.0009 Na Cu Zn S Al Ti Mo (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) 0.0001 0.0002 0.0024 0.0002 0.0009 0.0010 0.0002

[0073] The basic ammonium iron phosphate and the iron phosphate prepared in Example 3 have good crystallinity, and no other impurity phases are found. The contents of iron and phosphorus as well as various other elements meet the Chinese national standards for anhydrous iron phosphate. The iron phosphate has tap density of 0.80 g/cm.sup.3 and specific surface area of 5.50 m.sup.2/g, which is suitable as a precursor material for preparing lithium iron phosphate batteries.

[0074] The iron phosphate prepared in the aforementioned Examples 1 to 3 and the commercially available iron phosphate are prepared into lithium iron phosphate under the same conditions according to a conventional method. The prepared lithium iron phosphate is tested for compaction density and other electrical properties, and the test results are shown in Table 4 below.

TABLE-US-00004 TABLE 4 First Specific discharge capacity at Compaction capacity at 0.1 C after Cycle density 0.1 C 50 cycles efficiency (g/cc) (mAh/g) (mAh/g) (%) Example 1 2.395 157.8 153.2 97.08 Example 2 2.362 156.9 152.5 97.20 Example 3 2.381 158.3 153.9 97.22 Commercially 2.375 157.5 153.1 97.21 available

[0075] The compact density and electrical properties of lithium iron phosphate powder prepared from the iron phosphate synthesized in the examples of the present disclosure are close to that of lithium iron phosphate powder prepared from commercially available iron phosphate, which indicates that the iron phosphate synthesized in the present disclosure meets the standards of battery-grade iron phosphate for lithium iron phosphate. The preparation method and application of iron phosphate provided by the present disclosure have been described in detail above. Specific examples are used herein to illustrate the principles and implementation of the present disclosure. The above description of examples is only for the purpose of helping understand methods and core concepts of the present disclosure, including best modes, and also enables any person skilled in the art to practice the present disclosure, including manufacture and use of any device or system, and implementation of any combined methods. It should be noted that several improvements and modifications can be made by those skilled in the art to the present disclosure without departing from the principles of the present disclosure, which improvements and modifications also fall within the protection scope claimed by the claims. The protection scope of the present disclosure is defined by the claims and may include other embodiments that can be thought of by those skilled in the art. 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 within the scope of the claims.