Iron phosphate as well as preparation method and application thereof

Abstract

The invention provides iron phosphate as well as a preparation method and application thereof, and relates to the technical field of lithium ion batteries. Specifically, the method comprises the following steps: removing aluminum ions and titanium ions in a byproduct rutile mother solution of titanium dioxide prepared by a sulfuric acid method, and purifying to obtain an iron source solution with a specific total iron concentration; preparing a phosphorus source solution, mixing the phosphorus source solution with the iron source solution, carrying out a reaction at 50-65 DEG C, and carrying out filter pressing and washing to obtain a primary washing filter cake; pulping the primary washing filter cake, adding hydrogen peroxide, adjusting the pH after reaction, heating, aging and storing, and then carrying out filter pressing, washing and calcining to obtain the anhydrous iron phosphate. The iron phosphate material with low specific surface area and high compaction density is prepared from the by-product low-acid rutile mother liquor produced from titanium dioxide, can be used for preparing a lithium iron phosphate material with high compaction density, can be applied to the field of lithium ion batteries, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular, to a ferric phosphate and a preparation method and application thereof. Background Art

[0002] In the structure of a lithium-ion battery, the cathode material is the most core component of the lithium battery, and its quality directly determines the performance of new energy vehicles. In recent years, the cathode materials of lithium-ion batteries have been developing towards high energy density, long cycle life, low cost, and environmental protection. However, the battery system composed of lithium iron phosphate has a low tap density, which limits its application in power batteries. The tap density has a great influence on the battery performance and is an important parameter in the production of lithium-ion batteries; in order to improve the energy density, it is generally necessary to increase the tap density as much as possible. The current process focuses on using physical and mechanical methods to mix solid lithium iron phosphate during the preparation process, but the general compaction effect is not obvious, which will lead to uneven mixing, ineffective filling of small particles, and unstable performance.

[0003] Ferric phosphate is one of the important raw materials for preparing lithium iron phosphate. In conventional preparation methods, solid-phase processes such as carbothermal reduction method and high-temperature solid-phase method can be used, or liquid-phase processes such as hydrothermal method and self-heating evaporation method can be used to prepare lithium iron phosphate cathode materials from ferric phosphate. In the above processes, performance indicators such as the specific surface area, particle size, morphology, and structure of ferric phosphate play a crucial role in the electrochemical performance of the synthesized lithium iron phosphate material, and the properties such as the size and tap density of the lithium iron phosphate material largely depend on the relevant properties of ferric phosphate.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a preparation method of ferric phosphate to solve the technical problem of low tap density of lithium iron phosphate cathode materials from the raw material side of ferric phosphate, and to realize the resource utilization and high-value reuse of the by-product low-acid rutile mother liquor in the titanium white preparation process.

[0006] The second object of the present invention is to provide a ferric phosphate with the effects of low specific surface area and high tap density.

[0007] The third object of the present invention is to provide a lithium iron phosphate with good tap density performance.

[0008] The fourth object of the present invention is to provide a lithium-ion battery with good energy density, low internal resistance, improved rate performance, and cycle stability.

[0009] The fifth object of the present invention is to provide an electrical equipment.

[0010] To achieve the above object of the present invention, the following technical solutions are specifically adopted:

[0011] A method for preparing iron phosphate, comprising the following steps:

[0012] (1) Removing aluminum ions and titanium ions from the by-product rutile mother liquor in the preparation of titanium dioxide by the sulfuric acid method, purifying and obtaining an iron source solution with a total iron concentration of 80 g / L to 100 g / L;

[0013] (2) Preparing a phosphorus source solution with a pH of 7 to 8; mixing the phosphorus source solution with the iron source solution, and reacting at 50 °C to 65 °C; after the reaction is completed, obtaining a first-washed filter cake through pressure filtration and washing;

[0014] (3) Pulping the first-washed filter cake at 50 °C to 65 °C, adding hydrogen peroxide, adjusting the pH to 1.6 to 2.0 after the reaction; heating to 80 °C to 95 °C for heat preservation treatment, and then obtaining anhydrous iron phosphate through pressure filtration, washing and calcination.

[0015] An iron phosphate is prepared by using the method for preparing iron phosphate described above.

[0016] A lithium iron phosphate is prepared by using the iron phosphate described above.

[0017] A lithium ion battery is prepared by using the iron phosphate or the lithium iron phosphate described above.

[0018] An electrical equipment includes the lithium ion battery described above.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] (1) In the present invention, a high-iron-salt-concentration iron source material is prepared by purifying the by-product rutile mother liquor in the preparation of titanium dioxide by the sulfuric acid method; by using the high-concentration iron source material, the number of molecules per unit volume is increased, the intermolecular distance is reduced, thereby significantly increasing the probability of mutual collision between reactant molecules, that is, the chance of reaction increases, realizing the acceleration of the formation rate of iron phosphate crystal nuclei, rapid nucleation, the subsequent growth being dominant, the growth of primary particles, and obtaining an iron phosphate product with a smaller specific surface area.

[0021] (2) In order to improve the compactness when primary particles of iron phosphate form secondary particles and expand the particle size distribution range of secondary iron phosphate particles, the present invention adjusts the feeding rate of the phosphorus source into the iron source and the stirring rate twice. By adding slowly in the early stage and using the already formed iron phosphate as the attachment point for continuous growth, and accelerating the dropping rate in the later stage to make the particles more compact, the overall particle size is significantly increased. At the same time, the stirring rate is fast in the front and slow in the back. A faster stirring rate is conducive to the full reaction of the materials, and a slower stirring rate is conducive to the growth of secondary aggregates and is more conducive to water washing, and a higher tap density of iron phosphate and its derived high tap density lithium iron phosphate materials are prepared. Detailed Embodiments

[0022] The technical solutions of the present invention will be clearly and completely described below in conjunction with the detailed embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention. Those not specified in the embodiments are carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0023] The first aspect of the present invention is to provide a method for preparing iron phosphate.

[0024] (1) Remove aluminum ions and titanium ions from the by-product rutile mother liquor of titanium dioxide prepared by the sulfuric acid method, purify and obtain an iron source solution with a total iron concentration of 80 g / L to 100 g / L.

[0025] In the present invention, the rutile mother liquor is obtained as a by-product in the process of producing titanium dioxide by the sulfuric acid method; the production process of sulfuric acid method titanium dioxide mainly includes steps such as acid digestion, hydrolysis, calcination, and post-treatment; and the rutile mother liquor may not be directly produced as a product of a certain step, but is obtained together as a by-product or waste in some steps.

[0026] As a preferred embodiment, in the present invention, the rutile mother liquor includes: ferrous 100 g / L to 110 g / L, aluminum 0.2 g / L to 0.4 g / L, and titanium 0.2 g / L to 0.6 g / L.

[0027] As a preferred embodiment, in the present invention, the iron source solution includes: ferrous 80 g / L to 90 g / L, aluminum 0 to 0.01 g / L, and titanium 0 to 0.01 g / L.

[0028] As a preferred embodiment, the method for removing aluminum ions and titanium ions includes the following steps: adding an alkali to the rutile mother liquor to adjust the pH of the rutile mother liquor to 4.3 - 5.0. The alkali used includes but is not limited to sodium hydroxide or potassium hydroxide. After adjusting the pH, solid-liquid separation is carried out to remove the solid-phase precipitates of aluminum and silicon.

[0029] As a preferred embodiment, the purification includes the following steps: adjusting the pH of the reaction solution to 1.85 - 2.0 with an acid.

[0030] It should be noted that after the purification, evaporation and concentration or addition of deionized water are carried out to obtain the iron source solution with the corresponding total iron concentration; the suitable total iron concentration is helpful for the subsequent reaction with the phosphorus source and obtaining a phosphoric acid iron material with a suitable morphology and structure.

[0031] (2) Prepare a phosphorus source solution with a pH of 7 - 8; mix the phosphorus source solution with the iron source solution and carry out the reaction at 50°C - 65°C; after the reaction ends, a first-wash filter cake is obtained through pressure filtration and washing.

[0032] As a preferred embodiment, the preparation method of the phosphorus source solution includes the following steps: reacting phosphoric acid with an alkali solution to obtain the phosphorus source solution; in some more preferred embodiments, the alkali solution includes but is not limited to sodium hydroxide solution, potassium hydroxide solution, ammonia water, etc.

[0033] As a more preferred embodiment, the phosphorus content in the phosphorus source solution is 3 wt.% - 6 wt.%; it can be understood that by limiting the phosphorus content, the water content in the phosphorus source solution can be restricted to a certain extent to avoid using a too diluted or thick phosphorus solution, which may affect the subsequent synthesis reaction of phosphoric acid iron.

[0034] As a preferred embodiment, the phosphorus source solution is added dropwise to the iron source solution and the reaction is carried out at 50°C - 65°C; the addition includes the following steps:

[0035] S1. Add 1 / 4 - 1 / 2 volume of the phosphorus source solution to the iron source solution within 1 hour, and at the same time stir the reaction solution at a rate of 300 rpm - 450 rpm;

[0036] S2. Add the remaining volume of the phosphorus source solution to the reaction solution within 1 hour - 2 hours, and at the same time stir the reaction solution at a rate of 100 rpm - 250 rpm.

[0037] As a preferred embodiment, based on the iron atoms in the iron source solution and the phosphorus atoms in the phosphorus source solution, the molar ratio of the iron source solution to the phosphorus source solution is (1 to 1.3):1, including but not limited to any one of 1:1, 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1 or any ratio range formed by any two of them.

[0038] (3) Pulp the first-washed filter cake at 50°C to 65°C, add hydrogen peroxide, and adjust the pH to 1.6 to 2.0 after the reaction; raise the temperature to 80°C to 95°C for heat preservation treatment, and then obtain anhydrous iron phosphate through pressure filtration, washing, and calcination.

[0039] As a preferred embodiment, the concentration of the pulp obtained by pulping is 5 wt.% to 15 wt.%.

[0040] As a preferred embodiment, the hydrogen peroxide is added in the form of hydrogen peroxide solution, and the concentration of the hydrogen peroxide solution is 20 wt.% to 40 wt.%.

[0041] As a preferred embodiment, based on the iron atoms in the first-washed filter cake, the molar ratio of the hydrogen peroxide to the first-washed filter cake is 0.5 to 0.8, including but not limited to any one of 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8 or any ratio range formed by any two of them.

[0042] As a preferred embodiment, when adjusting the pH to 1.6 to 2.0, phosphoric acid is used as the acidic adjustment agent.

[0043] As a preferred embodiment, the temperature for raising the temperature includes but not limited to any one of 80, 82, 84, 85, 86, 88, 90, 92, 94, 95 (°C) or any ratio range formed by any two of them.

[0044] As a preferred embodiment, the heat preservation treatment time includes: after the reaction solution turns white, heat preservation for 1 h to 3 h.

[0045] As a preferred embodiment, the calcination temperature is 550°C to 600°C, and the calcination time is 2 h to 4 h.

[0046] The second aspect of the present invention lies in providing an iron phosphate prepared by using the preparation method of the iron phosphate described in the first aspect.

[0047] As a preferred embodiment, the specific surface area of the iron phosphate is 6 m 2 / g to 8 m 2 / g.

[0048] The third aspect of the present invention is to provide a lithium iron phosphate, which is prepared from the lithium iron phosphate as described in the second aspect.

[0049] As a preferred embodiment, the tap density of the lithium iron phosphate is 2.55 g / cm 3 ~2.63 g / cm 3 .

[0050] It can be understood that the present invention does not impose any restrictions on the preparation method of the lithium iron phosphate; those skilled in the art can prepare it from the lithium iron phosphate as a raw material in a conventional or unconventional manner. Conventional methods include, but are not limited to, solid-phase processes such as carbothermal reduction method and high-temperature solid-phase method, or liquid-phase processes such as hydrothermal method and self-heating evaporation method. At the same time, it can be prepared by grading based on other exogenous lithium iron phosphates.

[0051] The fourth aspect of the present invention is to provide a lithium-ion battery, which is prepared from the lithium iron phosphate as described in the second aspect or the lithium iron phosphate as described in the third aspect.

[0052] It can be understood that the lithium-ion battery should include positive and negative electrodes, electrolyte, separator, and other necessary or unnecessary functional components or packaging components, etc. Those skilled in the art can make any selection and combination thereof; when the lithium-ion battery contains the lithium iron phosphate or lithium iron phosphate described in the present invention, a lithium-ion battery positive electrode should be prepared first based on the lithium iron phosphate or lithium iron phosphate. The positive electrode can be a lithium iron phosphate positive electrode or a composite positive electrode containing lithium iron phosphate; that is, regardless of whether other positive electrode active materials are also used in the lithium-ion battery, it can be regarded as an embodiment of the present invention.

[0053] The fifth aspect of the present invention is to provide an electrical device, including the lithium-ion battery as described in the fourth aspect.

[0054] The electrical device can be any device or apparatus that relies on electric energy to work or operate, including but not limited to new energy vehicles, building electrical equipment, industrial electrical appliances, household and agricultural electrical appliances, etc.; when including the lithium-ion battery, any electrical device equipped with the lithium-ion battery can belong to an embodiment of the present invention.

[0055] Example 1

[0056] (1) Take 0.5 L of the by-product low-acid rutile mother liquor of titanium dioxide. First, adjust the pH to 4.8 with sodium hydroxide solution, filter out trivalent aluminum ions and tetravalent titanium ions, then adjust the pH to 1.90 for purification with sulfuric acid solution, and then add water to adjust to obtain solution A with a total iron concentration of 85 g / L. The element contents of the initial raw material low-acid rutile mother liquor and the purified solution A in this example are shown in Table 1 below.

[0057] Table 1

[0058] Total iron (g / L) Al (ppm) Ti (ppm) Low-acid rutile mother liquor 107.40 405.34 317.28 Solution A 71.60 1.69 Not detected

[0059] (2) Prepare a phosphate solution with phosphoric acid and sodium hydroxide to have a pH of 8 and a phosphorus content of 3 wt% for later use.

[0060] (3) Take 0.5 L of solution A and use the phosphate solution according to a molar ratio of iron to phosphorus of 1:1; drop the phosphate solution into solution A, with a total duration of 2 h, and conduct a heating reaction at 60 °C, which is divided into the following steps:

[0061] S1: 1 / 3 of the volume of the phosphate solution is dropped into solution A at a rate of 4.37 mL / min within the first 1 h, with rapid stirring at a speed of 350 rpm;

[0062] S2: The remaining 2 / 3 of the volume of the phosphate solution is dropped into solution A at a rate of 8.73 mL / min within the next 1 h, with slow stirring at a speed of 150 rpm;

[0063] After the reaction in S2, a reaction slurry is obtained. After pressure filtration and washing three times, a first-washed filter cake is obtained.

[0064] (4) Take the first-washed filter cake and prepare a 15 wt.% slurry at 60 °C. Add hydrogen peroxide with a concentration of 20% to the slurry, where the molar ratio of hydrogen peroxide to iron atoms is 0.5:1; after the pH of the slurry stabilizes, add phosphoric acid to adjust the pH = 2.0; then raise the temperature to 90 °C, keep the slurry at this temperature for 2 h after it turns white, and obtain a filter cake of dihydrate iron phosphate after pressure filtration and washing. Further calcine the filter cake to obtain anhydrous iron phosphate.

[0065] Example 2

[0066] It is basically the same as Example 1, with the only difference being that in step (3), the phosphate solution is used according to a molar ratio of iron to phosphorus of 1.3:1.

[0067] Example 3

[0068] It is basically the same as Example 1, with the only difference being that in step (3), the heating reaction is carried out at 50 °C, which is divided into the following steps:

[0069] S1: 1 / 4 of the volume of the phosphate solution is dropped into solution A at a rate of 4.37 mL / min within the first 40 min, with rapid stirring at a speed of 350 rpm;

[0070] S2: The remaining 3 / 4 of the volume of the phosphate solution is dropped into solution A at a rate of 8.73 mL / min within the next 80 min, with slow stirring at a speed of 150 rpm.

[0071] Example 4

[0072] It is basically the same as Example 1, except that in step (3):

[0073] S1: 1 / 3 of the volume of the phosphate salt is dropped into solution A at a rate of 4.37 mL / min within the first 50 min, with rapid stirring at a speed of 450 rpm;

[0074] S2: The remaining 2 / 3 of the volume of the phosphate salt is dropped into solution A at a rate of 8.73 mL / min within the subsequent 70 min, with slow stirring at a speed of 250 rpm.

[0075] Example 5

[0076] It is basically the same as Example 1, except that in step (4), a washed filter cake is prepared into a 10 wt.% slurry at 60 °C, and hydrogen peroxide with a concentration of 40% is added to the slurry, where the molar ratio of hydrogen peroxide to iron atoms is 0.75:1.

[0077] Comparative Example 1

[0078] It is basically the same as Example 1, except that step (3) is entirely replaced with:

[0079] Take 0.5 L of solution A and use a phosphate salt solution with an iron-to-phosphorus molar ratio of 1:1; the phosphate salt solution is uniformly dropped into solution A within 2 h, and a heating reaction is carried out under stirring at 60 °C and 350 rpm; after the reaction, a reaction slurry is obtained, and after pressure filtration and washing three times, a washed filter cake is obtained.

[0080] Comparative Example 2

[0081] It is basically the same as Example 1, except that in step (1), water is added to adjust to obtain solution A with a total iron concentration of 50 g / L.

[0082] Table 2

[0083]

[0084] As can be seen from Table 2, compared with the comparative examples, the iron phosphate prepared in the examples of the present invention has a lower ratio and a higher compaction; the iron phosphate prepared by the preparation process of the present invention is prepared into lithium iron phosphate according to the conventional method of the prior art, and the measured compaction density of the prepared lithium iron phosphate can reach 2.51 g / cm 3 ; Therefore, the iron phosphate prepared in the examples of the present invention can be used to prepare lithium iron phosphate with a higher compaction density, and thus a lithium-ion battery with high capacity, high energy density, good stability and good cycling performance can be obtained, which has good application prospects.

[0085] Although the present invention has been illustrated and described with reference to specific embodiments, it should be understood that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it; those of ordinary skill in the art should understand that without departing from the spirit and scope of the present invention, the technical solutions described in the foregoing embodiments may be modified, or some or all of the technical features may be equivalently replaced; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention; therefore, this means that all such replacements and modifications that fall within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing ferric phosphate, characterized in that: The steps include: (1) removing aluminum ions and titanium ions from rutile mother liquor, a byproduct of preparing titanium dioxide by a sulfuric acid process, and purifying and obtaining an iron source solution with a total iron concentration of 80 g / L to 100 g / L; (2) preparing a phosphorus source solution with a pH of 7 to 8; mixing the phosphorus source solution with the iron source solution, and reacting at 50° C. to 65° C.; after the reaction is completed, filtering and washing to obtain a washed filter cake; (3) beating the washed filter cake at 50° C. to 65° C., adding hydrogen peroxide, and adjusting the pH to 1.6 to 2.0 after the reaction; heating to 80° C. to 95° C. for heat preservation, and then obtaining anhydrous iron phosphate by filter pressing, washing and calcining.

2. The method for preparing ferric phosphate according to claim 1, characterized in that: The rutile mother liquor comprises: 100 g / L to 110 g / L of ferrous iron, 0.2 g / L to 0.4 g / L of aluminum and 0.2 g / L to 0.6 g / L of titanium; And / or, the iron source solution includes: 80 g / L to 90 g / L of ferrous iron, 0 to 0.01 g / L of aluminum and 0 to 0.01 g / L of titanium.

3. The method for preparing ferric phosphate according to claim 1, characterized in that: In step (1), the removal comprises: adding alkaline solution to the rutile mother liquor until the pH value is 4.3 to 5.0, and performing solid-liquid separation to remove aluminum ions and titanium ions in the rutile mother liquor; The purification includes: adjusting the pH of the reaction solution to 1.85-2.0 by acid.

4. The method for preparing ferric phosphate according to claim 1, characterized in that: In step (2), the preparation of the phosphorus source solution includes: reacting phosphoric acid with an alkali solution to obtain the phosphorus source solution; Preferably, the phosphorus content in the phosphorus source solution is 3 wt.% to 6 wt.%.

5. The method for preparing ferric phosphate according to claim 1, characterized in that: In step (2), the reaction comprises: S1, adding 1 / 4 to 1 / 2 volume of the phosphorus source solution to the iron source solution within 1 hour, while stirring the reaction solution at a rate of 300 rpm to 450 rpm; S2. Add the remaining volume of the phosphorus source solution dropwise into the reaction solution within 1 to 2 hours, and stir the reaction solution at a rate of 100 to 250 rpm.

6. The method for preparing ferric phosphate according to claim 1, characterized in that: In step (2), the molar ratio of the iron source solution to the phosphorus source solution is (1-1.3):1, calculated based on the iron atoms in the iron source solution and the phosphorus atoms in the phosphorus source solution; And / or, in step (3), the molar ratio of the hydrogen peroxide to the first washed filter cake is 0.5 to 0.8 based on the iron atoms in the first washed filter cake.

7. A kind of iron phosphate, characterized in that: Prepared by the method for preparing iron phosphate according to any one of claims 1 to 6; Preferably, the specific surface area of ​​the iron phosphate particles is 6 m 2 / g~8m 2 / g.

8. A lithium iron phosphate, characterized in that: Prepared by the iron phosphate as claimed in claim 7; Preferably, the compaction density of the lithium iron phosphate is 2.55 g / cm 3 ~2.63g / cm 3 .

9. A lithium ion battery, characterized in that: It is prepared using the iron phosphate as described in claim 7 or the lithium iron phosphate as described in claim 8.

10. An electrical device, characterized in that: Comprising the lithium ion battery as claimed in claim 9.

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