Preparation method of iron phosphate, lithium iron phosphate and lithium iron phosphate battery

Abstract

The invention provides a preparation method of iron phosphate, lithium iron phosphate and a lithium iron phosphate battery, and relates to the technical field of lithium iron phosphate batteries. Specifically, the method comprises the following steps: adding a polyferric agent into the iron phosphate production wastewater, adjusting the pH value, and carrying out solid-liquid separation to obtain a first liquid phase; preparing a solution containing an iron source, a phosphorus source and an oxidizing agent, adjusting the pH value and carrying out a precipitation reaction to obtain a second liquid phase; fully mixing the first liquid phase and the second liquid phase to obtain a first solid phase; dispersing the first solid phase to prepare slurry, and adjusting the pH through phosphoric acid to obtain a second solid phase; and carrying out aging reaction and calcining treatment on the second solid phase to obtain iron phosphate. Two iron phosphate precursors with different particle size distributions are prepared by controlling the particle sizes of the precursors at the reaction end to obtain the iron phosphate product with high compaction density, so that the lithium iron phosphate product with high energy density and high compaction density can be obtained, and the preparation method has a good application prospect in the field of lithium iron phosphate batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate batteries, and in particular, to a preparation method of iron phosphate, lithium iron phosphate and a lithium iron phosphate battery. Background Art

[0002] Lithium iron phosphate is widely used as a cathode material for lithium-ion batteries. It has advantages such as high specific capacity, good stability, long life, environmental friendliness, non-toxicity and low cost, and has good performance in industrial fields such as power and energy storage batteries, electric tools or small appliances. With the development of new energy vehicles and energy storage markets, lithium iron phosphate will see further growth in the future. With the rapid development of the lithium battery field, people have put forward higher requirements for the cruising range, charging speed and safety performance of electric vehicles, and correspondingly, there are also higher electrochemical performance requirements for lithium iron phosphate batteries.

[0003] If the electrochemical performance of a lithium iron phosphate battery is to be improved, a series of defects inherent in lithium iron phosphate itself need to be overcome, such as low tap density, poor low-temperature performance, low electronic conductivity and low lithium-ion diffusion coefficient. For the tap density, it is an important indicator of the energy density of the battery performance and determines the amount of electricity that can be stored in the battery under the same volume or weight; due to the low tap density and compaction density of lithium iron phosphate, the battery capacity of an equal-volume lithium iron phosphate battery is smaller than that of lithium cobaltate or ternary lithium-ion batteries, seriously affecting the energy density of the lithium battery. Existing technologies have tried to improve the tap density by means such as reducing the amount of coated carbon, increasing the sintering temperature, adjusting the molar ratio of main elements, and controlling the grinding particle size. However, it is difficult to achieve a balance among electrochemical performance, mechanical performance and safety performance with the above processes.

[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 iron phosphate, which is used to solve the problem of low tap density or compaction density of conventional iron phosphate when used as a precursor raw material for lithium iron phosphate.

[0006] The second object of the present invention is to provide a lithium iron phosphate.

[0007] The third object of the present invention is to provide a lithium iron phosphate battery.

[0008] In order to achieve the above objects of the present invention, the following technical solutions are specifically adopted:

[0009] A preparation method of iron phosphate includes the following steps:

[0010] (1) Adding polyiron reagent to the wastewater from iron phosphate production, adjusting the pH to 2.5 - 3.0, and performing solid-liquid separation after sufficient reaction to obtain a first liquid phase;

[0011] (2) preparing a solution containing an iron source, a phosphorus source and an oxidant, adjusting the pH to 1.8 to 2.5, performing a precipitation reaction and obtaining a second liquid phase;

[0012] (3) The first liquid phase and the second liquid phase are fully mixed at a mass ratio of 1: (5-20), and the solid-liquid separation is performed to obtain a first solid phase; the first solid phase is dispersed and prepared into a slurry, and the pH value is adjusted to 1.6-2.0 by phosphoric acid, and the second solid phase is obtained by solid-liquid separation after heating; and the second solid phase is calcined to obtain iron phosphate.

[0013] A lithium iron phosphate is prepared by using the iron phosphate prepared by the method for preparing iron phosphate.

[0014] A lithium iron phosphate battery comprises the lithium iron phosphate.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The present invention provides a method for preparing iron phosphate with high compaction density, wherein the particle size of the iron phosphate precursor is controlled at the reaction end to prepare two iron phosphate precursors with different particle size distributions, and a higher compaction density is obtained by combining the two particles; the present invention effectively improves the disadvantage of low compaction density when iron phosphate is used as a lithium iron phosphate positive electrode material, and can also meet the industrial demand for high energy density and high compaction density performance of lithium iron phosphate batteries. The present invention uses waste iron phosphate industrial wastewater as a resource reuse of a phosphorus source, realizes the high-value application of waste, and realizes the overall preparation method has the advantages of low cost, safety, environmental protection, and easy batch production. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A particle size classification diagram of Example 1 of the present invention is provided. DETAILED DESCRIPTION

[0019] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific 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 shall fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments whose manufacturers are not specified, they 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.

[0020] The first aspect of the present invention is to provide a method for preparing iron phosphate.

[0021] The method for preparing iron phosphate includes the following steps (1) to (3):

[0022] (1) Add polyferric agent to the iron phosphate production wastewater, adjust the pH to 2.5 - 3.0, and after sufficient reaction, perform solid-liquid separation to obtain the first liquid phase.

[0023] In the present invention, the wastewater generated by the conventional production process of iron phosphate is recycled and reused, and an amorphous iron phosphate is prepared in combination with the polyferric agent, showing good performance in terms of environmental protection and economic benefits.

[0024] As a preferred embodiment, the iron phosphate production wastewater includes: the wastewater produced in at least one production link such as the chemical reaction stage of the phosphorus source and the iron source, the pressure filtration stage, or the washing stage, after being adjusted with alkali to remove impurities, is separated and concentrated by a high-pressure reverse osmosis device to obtain HRO concentrated water; the iron phosphate production wastewater has characteristics such as high salinity, high concentration of metal ions, and multiple sulfate ions. In the current process, it is usually directly discharged or disposed of, and is used as a resource-based phosphorus source in this step.

[0025] As a preferred embodiment, the active ingredient of the polyferric agent includes polyferric sulfate.

[0026] As a preferred embodiment, in terms of the amount of substance, the usage ratio of phosphorus in the iron phosphate production wastewater to iron in the polyferric agent is 1:(1 - 2), including but not limited to any one of 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2 or any ratio interval composed of any two of them.

[0027] As a preferred embodiment, in this step, the pH is adjusted to any one or any numerical range composed of any two of 2.5, 2.6, 2.7, 2.8, 2.9, and 3.

[0028] As a preferred embodiment, the sufficient reaction can be carried out under auxiliary methods such as oscillation, stirring, shaker, centrifugation, and ultrasound to achieve sufficient mixing of the reaction components and accelerate the reaction process.

[0029] As a preferred embodiment, any of the solid-liquid separations involved in the present invention includes, but is not limited to, decantation, filtration, centrifugal separation, filter screen or membrane separation, etc.; in a more preferred embodiment, the solid-liquid separation is carried out by suction filtration in a low-yield production mode or a laboratory scenario, and the solid-liquid separation can be carried out through a filter screen in a batch large-scale production mode.

[0030] (2) Prepare a solution containing an iron source, a phosphorus source, and an oxidant, adjust the pH to 1.8 - 2.5, carry out a precipitation reaction, and obtain a second liquid phase.

[0031] In the present invention, a pure iron source and a phosphorus source that are not waste products are used for the reaction to obtain iron phosphate with an obvious particle size difference from step (1). The present invention controls the particle size of the iron phosphate precursor at the reaction end, prepares two iron phosphate precursors with different particle size distributions, and can obtain an iron phosphate product with a high compaction density after heat treatment in subsequent steps.

[0032] As a preferred embodiment, the iron source includes ferrous sulfate, the phosphorus source includes one or both of disodium hydrogen phosphate and sodium dihydrogen phosphate, and the oxidant includes hydrogen peroxide or oxygen, preferably hydrogen peroxide.

[0033] As a preferred embodiment, in terms of the amount of substance, the usage ratio of phosphorus in the phosphorus source to iron in the iron source is 1:(1 - 1.2).

[0034] As a preferred embodiment, in terms of the amount of substance, the usage ratio of the oxidant to iron in the iron source is (1.2 - 1.5):2.

[0035] As a preferred embodiment, in this step, the pH is adjusted to any one or any numerical range composed of any two of 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, and 2.5.

[0036] As a preferred embodiment, the temperature of the precipitation reaction is 50°C - 90°C, including but not limited to any one or any numerical range composed of any two of 50, 55, 60, 65, 70, 75, 80, 85, 90 (°C).

[0037] As a more preferred embodiment, the precipitation reaction is carried out under a stirring state of 100 rpm to 400 rpm, and the precipitation reaction time is 30 min to 90 min.

[0038] (3) The first liquid phase and the second liquid phase are fully mixed at a mass ratio of 1: (5-20), and the solid-liquid separation is performed to obtain a first solid phase; the first solid phase is dispersed and prepared into a slurry, and the pH value is adjusted to 1.6-2.0 by phosphoric acid, and the second solid phase is obtained by solid-liquid separation after heating; and the second solid phase is calcined to obtain iron phosphate.

[0039] As a preferred embodiment, the mass ratio of the first liquid phase to the second liquid phase includes but is not limited to any one of 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, and 1:20, or a ratio interval consisting of any two of the above.

[0040] As a preferred embodiment, after any of the solid-liquid separation in this step, the method further includes: washing; optionally, washing with water several times to avoid the adhesion of soluble impurities.

[0041] As a preferred embodiment, the concentration of the slurry is 8wt.% to 15wt.%.

[0042] As a preferred embodiment, the heating temperature is 80°C to 90°C, including but not limited to any one of 80, 82, 84, 85, 86, 88, 90 (°C) or a numerical range consisting of any two of them.

[0043] As a preferred embodiment, after adjusting the pH to 1.6-2.0 and heating, an aging reaction is carried out, and the time of the aging reaction is 1h-4h; after the aging reaction is completed, solid-liquid separation is carried out to obtain the second solid phase; it is worth noting that the operation sequence of adjusting the pH to 1.6-2.0 and heating in this step is not strictly limited, and can be carried out simultaneously or in any order.

[0044] As an optional implementation manner, the concentration of the slurry prepared with the first solid phase is 8% to 15%.

[0045] As a preferred embodiment, the calcination temperature is 500° C. to 700° C., and the calcination time is 2 h to 5 h.

[0046] As a preferred embodiment, a crushing treatment is further included after the calcination treatment; that is, those skilled in the art can obtain a product of iron phosphate with uniform particle size by any mechanical crushing or refining method.

[0047] The second aspect of the present invention is to provide a lithium iron phosphate.

[0048] The lithium iron phosphate is further prepared based on the iron phosphate obtained by the preparation method of iron phosphate as described in the first aspect. Based on what is described in the first aspect, the tap density of the lithium iron phosphate can reach 2.6 ± 0.3 g / cm 3 .

[0049] As a preferred embodiment, the preparation method of the lithium iron phosphate includes the following steps: after mixing and grinding the iron phosphate, a carbon source, and a lithium source, the lithium iron phosphate is obtained after spray drying, heat treatment, and crushing treatment.

[0050] As an alternative embodiment, the lithium source includes but is not limited to lithium carbonate, lithium hydroxide, lithium acetate, etc.; the carbon source includes but is not limited to glucose, sucrose, citric acid, polyethylene glycol, starch, or cellulose, etc. In some other alternative embodiments, the preparation raw materials further include an iron source, a phosphorus source, a dispersant, a dopant, etc., and those skilled in the art can make customized selections according to the performance requirements of the lithium iron phosphate.

[0051] The third aspect of the present invention is to provide a lithium iron phosphate battery.

[0052] The lithium iron phosphate battery includes the lithium iron phosphate as described in the second aspect. It can be understood that the lithium iron phosphate battery should include a positive electrode, a negative electrode, an electrolyte, a separator, and other necessary or non-necessary functional elements or packaging components, etc., and those skilled in the art can make any selection and combination thereof; when the lithium iron phosphate is included as a positive electrode active material in the positive electrode of the lithium iron phosphate battery, regardless of whether other active components are also used in the lithium iron phosphate battery, it can be regarded as an embodiment of the present invention. The positive electrode of the lithium iron phosphate battery should also include a current collector, a conductive agent, a binder, etc., and no restrictions are made on the selection of its components in the present invention.

[0053] The test table of the elemental composition of the HRO concentrated water and polyferric agents discharged during the production of iron phosphate used in each embodiment of the present invention is shown in Table 1 below.

[0054] Table 1

[0055] ICP (ppm) Concentrated water of HRO Polyferric agent Ca 2.91 231.29 Cd 0.00 0.96 Cr 0.00 20.19 K 29.80 39.51 Mg 0.68 2705.86 Mn 0.03 1129.22 Ni 0.04 20.27 Pb 0.00 3.84 Zn 0.00 35.93 Al 0.06 80.85 Co 0.00 0.00 Na 18822.01 1466.90 Cu 0.04 0.00 Ti 0.03 2277.80 Fe 1.39 110000.00 P 135.47 0.00

[0056] Example 1

[0057] (1) Add polyiron reagent to the concentrated HRO water discharged from the production of self-produced iron phosphate, control the iron-to-phosphorus ratio (molar ratio) to be 1.5, and control the pH of the mixed slurry to be 2.5; after the reaction, let it stand fully, and obtain the supernatant after stratification, and obtain the reaction slurry A containing amorphous iron phosphate in small particles in the lower layer.

[0058] (2) Prepare disodium hydrogen phosphate and ferrous sulfate according to an iron-to-phosphorus ratio (molar ratio) of 1. Weigh hydrogen peroxide (the molar ratio of ferrous ions to hydrogen peroxide is 2:1.5) and mix it with disodium hydrogen phosphate to obtain a solution; at a reaction temperature of 60 °C and a stirring speed of 300 rpm, add the iron salt to the solution, and control the pH of the mixed slurry to be 2.0 to obtain the reaction slurry B containing amorphous iron phosphate in large particles. As Figure 1 shown, the particle size classification diagrams of the reaction slurries A and B in this example are provided.

[0059] (3) After blending the reaction slurries A and B according to a mass ratio of 1:10, carry out suction filtration and water washing to obtain an amorphous iron phosphate filter cake with a particle size grading.

[0060] Slurry it to prepare a 10% aging slurry, place it in a constant temperature magnetic heating stirrer at 90 °C and stir, then add phosphoric acid to adjust the pH of the solution to 1.8, and after reacting for 1 h, carry out suction filtration and water washing to obtain a dihydrate iron phosphate filter cake.

[0061] After drying it, carry out high-temperature calcination at 550 °C for 2 h, and obtain an anhydrous iron phosphate product after crushing.

[0062] Example 2

[0063] It is basically the same as Example 1, the only difference is that:

[0064] In step (1), control the iron-to-phosphorus ratio to be 2, and in step (2), control the iron-to-phosphorus ratio to be 1.2.

[0065] Example 3

[0066] It is basically the same as Example 1, the only difference is that:

[0067] In step (1), control the pH of the mixed slurry to be 3, in step (2), control the pH of the mixed slurry to be 2.5, and in step (3), control the pH of the mixed slurry to be 2.

[0068] Example 4

[0069] It is basically the same as Example 1, the only difference is that:

[0070] In step (2), control the reaction temperature to be 80 °C and the stirring speed to be 100 rpm.

[0071] Example 5

[0072] Basically the same as Example 1, except that:

[0073] In step (2), reaction slurries A and B are blended at a mass ratio of 1:5.

[0074] Example 6

[0075] Basically the same as Example 1, except that:

[0076] In step (2), reaction slurries A and B are blended at a mass ratio of 1:20.

[0077] Comparative Example

[0078] (1) Disodium hydrogen phosphate and ferrous sulfate are configured according to an iron to phosphorus ratio (molar ratio) of 1. Weigh hydrogen peroxide (the molar ratio of ferrous ion to hydrogen peroxide is 2:1.5) and mix it with disodium hydrogen phosphate to obtain a solution. At a reaction temperature of 60 °C and a stirring speed of 300 rpm, add the iron salt to the solution and control the pH of the mixed slurry to 2.0 to obtain a reaction slurry containing amorphous iron phosphate.

[0079] (2) Place the slurry in a constant temperature magnetic heating stirrer at 90 °C and stir. Then add phosphoric acid to adjust the pH of the solution to 1.8. After reacting for 1 h, filter by suction and wash with water to obtain a dihydrate iron phosphate filter cake. After drying it, calcine it at 600 °C for 2 h and crush it to obtain an anhydrous iron phosphate product.

[0080] Test Example

[0081] The lithium iron phosphates prepared respectively from the iron phosphates obtained in the above examples and comparative examples are as follows: Mix the iron source, phosphorus source, lithium source, and carbon source according to the feeding ratio, where the molar ratio of the iron source, phosphorus source, and lithium source is 1:1:1.05. The addition amount of the carbon source is based on the phosphorus source and iron source converted to iron phosphate, and the addition amount of the carbon source is 10% of the mass of the iron phosphate; successively carry out sand grinding, spray drying, sintering, and pulverization to prepare lithium iron phosphate; among them, the spray inlet temperature is ~240 °C, the outlet temperature is ~90 °C, the sintering temperature is 720 °C, and the sintering duration is 8 h.

[0082] As shown in Table 2, the tap densities of the lithium iron phosphates corresponding to the above examples and comparative examples are provided.

[0083] Table 2

[0084]

[0085]

[0086] Although the present invention has been illustrated and described with reference to specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the same; 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) adding a polyferric agent to ferric phosphate production wastewater, adjusting the pH to 2.5-3.0, and performing solid-liquid separation after sufficient reaction to obtain a first liquid phase; (2) preparing a solution containing an iron source, a phosphorus source and an oxidant, adjusting the pH to 1.8 to 2.5, performing a precipitation reaction and obtaining a second liquid phase; (3) The first liquid phase and the second liquid phase are fully mixed at a mass ratio of 1: (5-20), and the solid-liquid separation is performed to obtain a first solid phase; the first solid phase is dispersed and prepared into a slurry, and the pH value is adjusted to 1.6-2.0 by phosphoric acid, and the second solid phase is obtained by solid-liquid separation after heating; and the second solid phase is calcined to obtain iron phosphate.

2. The method for preparing ferric phosphate according to claim 1, characterized in that: The molar ratio of phosphorus in the ferric phosphate production wastewater to iron in the polyferric agent is 1:(1-2).

3. The method for preparing ferric phosphate according to claim 1, characterized in that: The iron source includes ferrous sulfate, the phosphorus source includes one or both of disodium hydrogen phosphate and sodium dihydrogen phosphate, and the oxidant includes one or both of hydrogen peroxide or oxygen.

4. The method for preparing ferric phosphate according to claim 1, characterized in that: The molar ratio of phosphorus in the phosphorus source to iron in the iron source is 1:(1-1.2); And / or, the molar ratio of the oxidant to the iron in the iron source is (1.2-1.5):

2.

5. The method for preparing ferric phosphate according to claim 1, characterized in that: The temperature of the precipitation reaction is 50°C to 90°C; Preferably, the precipitation reaction is carried out under stirring, and the stirring speed is 100 rpm to 400 rpm.

6. The method for preparing ferric phosphate according to claim 1, characterized in that: The heating temperature is 80°C to 90°C.

7. The method for preparing ferric phosphate according to claim 1, characterized in that: The calcination temperature is 500° C. to 700° C., and the calcination time is 2 h to 5 h.

8. The method for preparing ferric phosphate according to claim 1, characterized in that: The particles in the first liquid phase have a D50 of less than 5 μm, and the particles in the second liquid phase have a D50 of more than 15 μm.

9. A lithium iron phosphate, characterized in that: Prepared by the iron phosphate prepared by the method for preparing iron phosphate according to any one of claims 1 to 7; The compaction density of the lithium iron phosphate is ≥2.55g / cm 3 .

10. A lithium iron phosphate battery, characterized in that: Comprising the lithium iron phosphate as described in claim 9.

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