CN115215313A

CN115215313A - High-compaction ferric phosphate material and preparation method thereof

Info

Publication number: CN115215313A
Application number: CN202210664327.3A
Authority: CN
Inventors: 侯愉婷; 童秋桃; 夏捷; 陈钊
Original assignee: Zhejiang Huayou Cobalt Co Ltd
Current assignee: Zhejiang Huayou Cobalt Co Ltd
Priority date: 2022-06-10
Filing date: 2022-06-10
Publication date: 2022-10-21
Anticipated expiration: 2042-06-10
Also published as: CN115215313B

Abstract

The application discloses a high compaction ferric phosphate material and a preparation method thereof, which comprises the following steps: preparing a first mixture system containing a phosphate source, a ferrous ion source and a first pH regulator, and carrying out a first reaction on the first mixture system to obtain a first slurry containing an amorphous ferrous phosphate octahydrate reaction precursor; adding a second pH regulator into the first slurry to obtain second slurry, wherein the second slurry is acidic; and adding an oxidizing substance into the second slurry to carry out a second reaction to obtain the ferric phosphate dihydrate material. The preparation method of the high-compaction ferric phosphate material can realize accurate regulation and control of supersaturation degree of iron ions and phosphate ions in a reaction system. The ferric phosphate dihydrate material which is densely piled, has larger primary particles and has the regular polyhedron micro-morphology is finally obtained by the preparation method. The preparation method has the advantages that each reaction condition is stable and controllable, and industrial application can be realized.

Description

High-compaction ferric phosphate material and preparation method thereof

Technical Field

The application belongs to the technical field of new energy material preparation, and particularly relates to a high-compaction ferric phosphate material and a preparation method thereof.

Background

The main methods for preparing high compacted iron phosphate products at present are: (1) By regulating and controlling the supersaturation degree of the solution, a large number of crystal nuclei are generated in an explosive nucleation mode, then the ferric phosphate precipitate is slowly separated out, and is gradually accumulated and grown by taking the crystal nuclei as the center, and finally, the compact accumulated ferric phosphate dihydrate particles are formed. After filtering and washing, the anhydrous iron phosphate is prepared through programmed drying and calcining. However, the control of the supersaturation degree of the solution in the initial nucleation stage in the method is difficult, and the situation that the supersaturation degree is too large or too small is easy to occur, so that the iron phosphate nucleation rate is too fast or too slow, and the number of primary particles is too large or too small. When the number of primary particles is too large, more bonding exists among the particles, and further, more pores exist, so that the preparation of high-compaction iron phosphate is not facilitated; when the primary particles are too small, the particles are easy to grow too large, the bonding among the particles is less, the pores are larger, and the preparation of high-compaction iron phosphate is not facilitated. (2) Generating different reaction precursors by regulating and controlling the rates of different reactions in a reaction system, and then carrying out phase transition on the reaction precursors to form compact-packed ferric phosphate dihydrate particles; filtering, washing, and carrying out programmed drying and calcining to prepare the anhydrous iron phosphate. However, the composition of the reaction precursor prepared in the wet synthesis stage in the method is generally difficult to strictly determine, and there is a great risk of product quality control, and in addition, an additional separation step needs to be introduced in the process partially related to the reaction precursor, so that the production efficiency is greatly reduced, and the practical value of the method is reduced. (3) Preparing iron phosphate dihydrate particles doped with carbon or titanium and other miscellaneous elements in a preposed manner by introducing a proper carbon source, a proper titanium source and the like into a coprecipitation system; filtering, washing, and carrying out programmed drying and calcining to prepare the doped anhydrous iron phosphate. However, the preparation method has high requirements on equipment and process control, is still in an exploration stage at present, and lacks of industrialization examples.

Disclosure of Invention

The application aims to overcome the defects of the prior art and provide a high-compaction ferric phosphate material and a preparation method thereof so as to solve the technical problems of difficult control of the supersaturation degree of a solution, high production cost and difficult industrialization in the preparation process of the conventional high-compaction ferric phosphate material.

In order to achieve the above object, in a first aspect of the present application, there is provided a method for preparing a high compacted iron phosphate material, comprising:

preparing a first mixture system containing a phosphate source, a ferrous ion source and a first pH regulator, and carrying out a first reaction on the first mixture system to obtain a first slurry containing an amorphous ferrous phosphate octahydrate reaction precursor;

adding a second pH regulator into the first slurry to obtain a second slurry, wherein the second slurry is acidic;

and adding an oxidizing substance into the second slurry to carry out a second reaction to obtain a dihydrate ferric phosphate material.

Furthermore, the pH value of the first mixture system is 2.8-12, and the oxidation-reduction potential is-0.8-0.24V.

Further, the first pH regulator is at least one of phosphoric acid, sulfuric acid, hydrochloric acid, ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonium bicarbonate, potassium bicarbonate, and sodium bicarbonate.

Further, the pH value of the second slurry is-0.5 to 1.5.

Further, the second pH regulator is at least one of sulfuric acid, hydrochloric acid and phosphoric acid.

Furthermore, a reducing substance is added into the first mixture system.

Further, the reducing substance is at least one of ascorbic acid, polyethylene glycol, acetone, and ethanol.

Further, the oxidizing substance is at least one of hydrogen peroxide, sodium hypochlorite and oxygen.

Further, the molar ratio of the iron element to the phosphorus element in the first mixture system is (3-3.1): 2; and/or

The temperature of the first reaction is 15-35 ℃, and the reaction time is 0.5-2 h; and/or

The temperature of the second reaction is 85-94 ℃, and the reaction time is 1-3 h.

In a second aspect of the present application, there is provided an iron phosphate material obtained by the method of the present application.

Compared with the prior art, the method has the following technical effects:

according to the preparation method of the high-compaction ferric phosphate material, on the basis of not additionally increasing related equipment, the amorphous ferrous phosphate octahydrate reaction precursor is generated in situ in the first mixture system by controlling the synthesis conditions, then the dissolution rate of the amorphous ferrous phosphate octahydrate reaction precursor is controlled by controlling the pH value of the second slurry, and the concentrations of phosphate radicals and ferrous ions in the reaction system are further regulated and controlled; and then, the supersaturation degree of iron ions and phosphate ions in the reaction system is accurately regulated and controlled by adding oxidizing substances. The ferric phosphate dihydrate material which is densely piled up, has large primary particles and has the regular polyhedral microstructure is finally obtained by the preparation method. The high-compaction iron phosphate material has the advantages of uniform particle size distribution and moderate particle size, and is suitable for preparing high-performance lithium iron phosphate materials.

Drawings

In order to more clearly illustrate the detailed description of the present application or the technical solutions in the prior art, the drawings used in the detailed description or the prior art description will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is an SEM image of a highly compacted iron phosphate material provided in example 1 of the present application;

FIG. 2 is an SEM image of a high compaction ferric phosphate material provided in example 7 of the present application;

FIG. 3 is an SEM image of a high compaction ferric phosphate material provided in example 8 of the present application;

FIG. 4 is an SEM image of a ferric phosphate material provided in comparative example 1 of the present application;

FIG. 5 shows Fe-P-H provided in the examples of the present application ₂ O is a potential-pH diagram.

Detailed Description

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of and not restrictive on the broad application.

In this application, the term "and/or" describes an association relationship of associated objects, which means that there may be three relationships, for example, a and/or B, which may mean: a alone, A and B together, and B alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.

In the present application, "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (a), b, and c", may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, and c may be single or plural, respectively.

It should be understood that, in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the execution sequence, some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used in the examples of this application and the appended claims, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

The weight of the related components mentioned in the specification of the embodiments of the present application may not only refer to the specific content of each component, but also refer to the proportional relationship of the weight of each component, and therefore, the proportional enlargement or reduction of the content of the related components according to the specification of the embodiments of the present application is within the scope disclosed in the specification of the embodiments of the present application. Specifically, the mass described in the specification of the examples of the present application may be a mass unit known in the chemical field such as μ g, mg, g, kg, etc.

The terms "first" and "second" are used for descriptive purposes only and are used for distinguishing purposes such as substances from one another and are not to be construed as indicating or implying relative importance or to implicitly indicate the number of technical features indicated. For example, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX, without departing from the scope of embodiments of the present application. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

In a first aspect, an embodiment of the present application provides a method for preparing a high-compaction ferric phosphate material, including the following steps:

(1) Preparing a first mixture system containing a phosphate source, a ferrous ion source and a first pH regulator, and carrying out a first reaction on the first mixture system to obtain a first slurry containing an amorphous ferrous phosphate octahydrate reaction precursor;

(2) Adding a second pH regulator into the first slurry to obtain a second slurry, wherein the second slurry is acidic;

(3) And adding an oxidizing substance into the second slurry to perform a second reaction to obtain the dihydrate ferric phosphate material.

Further, the ferric phosphate dihydrate material obtained in the step (3) is subjected to subsequent purification, drying and calcination to obtain the high-compaction ferric phosphate material. The high-compaction iron phosphate material can be used for further preparing a high-performance lithium iron phosphate material by adopting a conventional lithium iron phosphate preparation method.

According to the preparation method of the high-compaction ferric phosphate material, on the basis of not additionally increasing related equipment, the amorphous ferrous phosphate octahydrate reaction precursor is generated in situ in the first mixture system by controlling the synthesis conditions, then the dissolution rate of the amorphous ferrous phosphate octahydrate reaction precursor is controlled by controlling the pH value of the second slurry, and the concentrations of phosphate radicals and ferrous ions in the reaction system are further regulated and controlled; and then, the supersaturation degree of iron ions and phosphate ions in the reaction system is accurately regulated and controlled by adding oxidizing substances. The ferric phosphate dihydrate material which is densely stacked, has large primary particles and has the regular polyhedral microstructure is finally obtained by the preparation method of the embodiment of the application.

Further, the ferric phosphate dihydrate material of the embodiment of the application is subjected to subsequent drying and calcining treatment to obtain the highly compacted ferric phosphate material. The preparation method provided by the embodiment of the application has stable and controllable reaction conditions, and can realize industrial application.

In the step (1), the phosphate source may be a salt comprising at least one anion of phosphate, hydrogen phosphate, dihydrogen phosphate and at least one cation of quaternary ammonium ion, sodium ion or potassium ion, such as sodium phosphate, potassium phosphate, sodium hydrogen phosphate, ammonium dihydrogen phosphate, etc. The ferrous ion source may be at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate. According to the mol ratio of the phosphorus element to the iron element in the finally prepared iron phosphate, the mol ratio of the iron element to the phosphorus element in the first mixture system is controlled to be (3-3.1): 2.

the present examples prepare amorphous ferrous phosphate octahydrate reaction precursor by subjecting a first mixture system to a first reaction. In the process of preparing ferric phosphate dihydrate by the traditional coprecipitation method, if the supersaturation degree of the ferric phosphate dihydrate is too large, the nucleation and growth rate of the ferric phosphate dihydrate is too high, and too large or too small ferric phosphate dihydrate particles are generated, which is not beneficial to preparing high-compaction ferric phosphate, so that the free Fe in a reaction system needs to be reduced ²⁺ And PO ₄ ^3- Thereby reducing the supersaturation degree of the ferric phosphate dihydrate. And amorphous ferrous phosphate octahydrate (Fe) ₃ (PO) ₂ ·8H ₂ O) has very low solubility in the generation environment, so that the amorphous ferrous phosphate octahydrate is used as an intermediate, and free Fe in a reaction system can be reduced in situ ²⁺ And PO ₄ ^3- The concentration of (c). As shown in FIG. 5, it is reasonable to conclude the stable region of amorphous ferrous octaphosphate formation from the potential-pH diagram of the reaction system, i.e., the region A + B in FIG. 5, which is hatched, is the stable region of amorphous ferrous octaphosphate formation. Specifically, in the examples of the present application, the pH of the first mixture system can be controlled to 2.8 to 12 depending on the range of the region A + the region BThe oxidation-reduction potential is-0.8-0.24V.

The pH range of the system is controlled by adding a first pH adjusting agent to the first mixture system, and in this embodiment, the first pH adjusting agent may be at least one of phosphoric acid, sulfuric acid, hydrochloric acid, ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonium bicarbonate, potassium bicarbonate, and sodium bicarbonate, but is not limited thereto.

Further, it is also possible to determine whether or not it is necessary to add a reducing substance to the first mixture system to control the oxidation-reduction potential, depending on the pH value and the oxidation-reduction potential range of the first mixture system. When the pH and the oxidation-reduction potential of the first mixture system are in the region a in fig. 5, no additional reducing substance needs to be added to the first mixture system; when the pH and the oxidation-reduction potential of the first mixture system are in the region B in FIG. 5, the first mixture system requires addition of a reducing substance. In the embodiment of the present application, the reducing substance that may be added is at least one of ascorbic acid, polyethylene glycol, acetone, and ethanol, but is not limited thereto.

The first reaction for generating the amorphous ferrous phosphate octahydrate reaction precursor can be carried out at room temperature, in the embodiment of the application, the first reaction temperature is 15-35 ℃, the reaction temperature is a common indoor temperature, the reaction can naturally occur without additional heating, and the reaction energy consumption is reduced. During the first reaction, a bluish slurry was observed in the first mixture system, indicating the formation of amorphous ferrous phosphate octahydrate precursor. In the first reaction process, the stirring speed of the reaction system can be controlled to be 100-400 r/min, and the reaction time is 0.5-2 h.

In the step (2), an acidic second pH regulator is added into the first slurry for generating the amorphous ferrous phosphate octahydrate precursor, and the second slurry is controlled to be acidic, so that a part of the generated amorphous ferrous phosphate octahydrate precursor is rapidly dissolved under an acidic condition, and further Fe in the reaction system is increased ²⁺ And PO ₄ ^3- The concentration is favorable for generating more ferric phosphate dihydrate crystal nuclei in the initial stage of the reaction after the oxidizing substances are added in the subsequent step (3). With oxidationAddition of the active substance, generation of iron phosphate dihydrate crystal nucleus, and Fe in the reaction system ²⁺ And PO ₄ ^3- The concentration is reduced compared with the initial stage of the reaction, and with the slow dissolution of the amorphous ferrous phosphate octahydrate precursor and the slow change of the pH value of the reaction system, the Fe with smaller concentration can be maintained in the reaction system ²⁺ And PO ₄ ^3- Further inhibiting the excessive nucleation of the ferric phosphate dihydrate, controlling the slow growth of the ferric phosphate dihydrate, and finally forming the ferric phosphate dihydrate material which is densely stacked, has larger primary particles and has regular polyhedron morphology.

In the embodiment of the application, the pH value of the second slurry is controlled to be-0.5-1.5, so that the dihydrate ferric phosphate material with moderate primary particle size can be prepared, and the subsequent preparation of the high-compaction and high-performance lithium iron phosphate material is facilitated. In specific embodiments of the present application, the second pH adjusting agent may be at least one of sulfuric acid, hydrochloric acid, and phosphoric acid. The oxidizing substance can be at least one of hydrogen peroxide, sodium hypochlorite and oxygen.

After the addition of the oxidizing substance, the light blue slurry generated in the reaction system was observed to gradually turn yellow-white, indicating that the amorphous ferrous phosphate octahydrate precursor was gradually dissolved and Fe was present ²⁺ Is oxidized into Fe ³⁺ 。

In the examples of the present application, the temperature of the second reaction was controlled to 85 to 94 ℃ at which Fe in the reaction system was present ²⁺ Can be quickly oxidized and converted into Fe ³⁺ Finally, the dihydrate ferric phosphate material is generated. During the second reaction, it was observed that the slurry of the reaction system gradually changed from yellow to pale pink, indicating the formation of the iron phosphate dihydrate material. In the application, the time of the second reaction is controlled to be 1-3 h, and the crystal form of the product is completely transformed and the crystallinity is higher along with the prolonging of the reaction time until the product is completely transformed into the ferric phosphate dihydrate material.

In a second aspect of the present application, a ferric phosphate material obtained by the preparation method of the embodiment of the present application is provided. The high-compaction iron phosphate material provided by the embodiment of the application has the advantages of uniform particle size distribution and moderate particle size, and is suitable for preparing a high-performance lithium iron phosphate material.

The high compacted iron phosphate material and the preparation method thereof according to the embodiments of the present application are illustrated by the following specific examples.

Example 1

The embodiment 1 of the application provides a high-compaction ferric phosphate material and a preparation method thereof. The method comprises the following steps:

s1, preparing a 1.0mol/L ferrous chloride solution and a diammonium phosphate solution, and weighing the ferrous solution and the phosphate solution according to a molar ratio of Fe to P =3.

S2, weighing a reducing substance ascorbic acid, a pH regulator phosphoric acid and an oxidizing substance hydrogen peroxide (30% in molar excess compared with ferrous ions) for later use.

S3, dripping the reasonably prepared ferrous solution, phosphate solution, reducing substance ascorbic acid and pH regulator phosphoric acid into the reaction solution at a certain speed (41.7 mL/min, 8.3mL/min and 8.3mL/min in sequence), adjusting the pH of the solution to 2.8, adjusting the oxidation-reduction potential to 0.24V, stirring at a speed of 300r/min, and reacting for 1h to obtain light blue slurry containing the amorphous ferrous phosphate octahydrate reaction precursor.

And S4, adding phosphoric acid serving as a pH regulator into the slurry, regulating the pH of the slurry to 1.0, adding hydrogen peroxide into the slurry after 30min, and observing that the color of the slurry is changed from light blue to yellow white.

S5, heating the slurry by steam, controlling the temperature at 90 +/-2 ℃, changing the slurry from yellow to light pink after 50-60 min, and continuously reacting for 3h to obtain the ferric phosphate dihydrate material with a complete crystal structure.

And S6, pumping the ferric phosphate dihydrate into a filter press for pressure filtration and rinsing, and washing to the conductivity below 500 mu S/cm to obtain a clean filter cake.

And S7, feeding the filter cake into a drying rotary kiln according to a certain frequency, wherein the rotary kiln has the rotation frequency of 15Hz, the drying temperature is 110 ℃, the drying time is 8 hours, and the induced air frequency is 40Hz, so that the ferric phosphate dihydrate powder with a regular micro-morphology is obtained, and the SEM image of the ferric phosphate dihydrate powder is shown in figure 1.

And S8, feeding the dihydrate ferric phosphate powder into a calcination rotary kiln according to a certain frequency, wherein the rotary kiln rotation frequency is 12Hz, the calcination temperature is 300-300-550-550-550 ℃, the calcination is carried out for 6h, and the induced air frequency is 40Hz, so as to obtain the high-compaction anhydrous ferric phosphate powder with the orthogonal crystal form.

S9, performing jet milling and screening to remove iron, and obtaining a finished product of the high-compaction ferric phosphate material.

S10, weighing 151g of the finished ferric phosphate material, 37g of battery-grade lithium carbonate and 18g of sucrose, weighing 200mL of isopropanol, placing the isopropanol in a ball mill, and performing ball milling for 3 hours until the mixture is stopped to obtain mixed slurry.

S11, drying the mixed slurry, putting the dried mixed slurry into an alumina crucible, heating the mixed slurry to 700 ℃ in a tubular furnace at a speed of 200 ℃/h, keeping the temperature for 10h, stopping heating, and naturally cooling the mixed slurry in a dry furnace to room temperature. In the process, high-purity nitrogen is continuously introduced into the tubular furnace to obtain the lithium iron phosphate material.

Example 2

The embodiment 2 of the application provides a high-compaction ferric phosphate material and a preparation method thereof. The method comprises the following steps:

s1, preparing a 1.0mol/L ferrous sulfate solution and a diammonium phosphate solution, and weighing the ferrous sulfate solution and the phosphate solution according to a molar ratio of Fe: P =3.

S2, weighing reducing substance polyethylene glycol, pH regulator sulfuric acid and oxidizing substance hydrogen peroxide (30% excess compared with the molar weight of ferrous ions) for later use.

S3, dripping a reasonably prepared ferrous solution, a phosphate solution, a reducing substance polyethylene glycol and a pH regulator sulfuric acid into the reaction solution at a certain speed (41.7 mL/min, 8.3mL/min and 8.3mL/min in sequence), adjusting the pH of the solution to 3.0, adjusting the oxidation-reduction potential to-0.40V, stirring at a speed of 300r/min, and reacting for 1h to obtain light blue slurry containing the amorphous ferrous phosphate octahydrate reaction precursor.

S4, adding sulfuric acid serving as a pH regulator into the slurry, regulating the pH of the slurry to 0.5, adding hydrogen peroxide into the slurry after 30min, and observing that the color of the slurry is changed from light blue to yellow white.

And S6, pumping the ferric phosphate dihydrate into a filter press for pressure filtration and rinsing, and washing to the conductivity of below 500 mu S/cm to obtain a clean filter cake.

And S7, feeding the filter cake into a drying rotary kiln according to a certain frequency, wherein the rotary frequency of the rotary kiln is 15Hz, the drying temperature is 150 ℃, the drying time is 4 hours, and the induced air frequency is 40Hz, so that the ferric phosphate dihydrate powder with a regular micro-morphology is obtained.

S11, drying the mixed slurry, putting the dried mixed slurry into an alumina crucible, heating the mixed slurry to 700 ℃ in a tube furnace at the speed of 200 ℃/h, keeping the temperature for 10h, stopping heating, and naturally cooling the mixed slurry in a dry furnace to room temperature. In the process, high-purity nitrogen is continuously introduced into the tubular furnace to obtain the lithium iron phosphate material.

Example 3

The embodiment 3 of the application provides a high-compaction ferric phosphate material and a preparation method thereof. The method comprises the following steps:

S2, weighing a reducing substance acetone, a pH regulator ammonia water, hydrochloric acid and an oxidizing substance sodium hypochlorite (30% excess compared with the molar weight of ferrous ions) for later use.

And S3, dripping a ferrous solution, a phosphate solution, a reducing substance acetone and a pH regulator ammonia water which are reasonably prepared into a reaction solution at a certain speed (41.7 mL/min, 8.3mL/min and 8.3mL/min in sequence), regulating the pH of the solution to 6.0, regulating the oxidation-reduction potential to-0.00V, stirring at a speed of 300r/min, and reacting for 1h to obtain light blue slurry containing the amorphous ferrous phosphate octahydrate reaction precursor.

And S4, adding hydrochloric acid serving as a pH regulator into the slurry, regulating the pH of the slurry to 1.5, adding hydrogen peroxide into the slurry after 30min, and observing that the color of the slurry is changed from light blue to yellow white.

And S7, feeding the filter cake into a drying rotary kiln according to a certain frequency, wherein the rotary frequency of the rotary kiln is 15Hz, the drying temperature is 200 ℃, the drying time is 2 hours, and the induced air frequency is 40Hz, so that the ferric phosphate dihydrate powder with a regular micro-morphology is obtained.

And S8, further feeding the dihydrate ferric phosphate powder into a calcination rotary kiln according to a certain frequency, wherein the rotary kiln rotation frequency is 12Hz, the calcination temperature is 300-300-550-550 ℃, the calcination time is 8h, and the induced air frequency is 40Hz, so as to obtain the high-compaction anhydrous ferric phosphate powder with the orthogonal crystal form.

S9, performing air current crushing and screening for removing iron to obtain a high-compaction ferric phosphate material finished product.

Example 4

The embodiment 4 of the application provides a high-compaction ferric phosphate material and a preparation method thereof. The method comprises the following steps:

S2, weighing a reducing substance ascorbic acid, a pH regulator sodium hydroxide and phosphoric acid, and an oxidizing substance hydrogen peroxide (30% excess compared with the molar amount of ferrous ions) for later use.

S3, dripping the reasonably prepared ferrous solution, phosphate solution, reducing substance ascorbic acid and pH regulator sodium hydroxide into the reaction solution at a certain speed (41.7 mL/min, 8.3mL/min and 8.3mL/min in sequence), adjusting the pH of the solution to 7.0, adjusting the oxidation-reduction potential to-0.55V, stirring at a speed of 300r/min, and reacting for 1h to obtain light blue slurry containing the amorphous ferrous phosphate octahydrate reaction precursor.

And S4, adding phosphoric acid serving as a pH regulator into the slurry, regulating the pH of the slurry to 0.5, adding hydrogen peroxide into the slurry after 30min, and observing that the color of the slurry is changed from light blue to yellow white.

And S7, feeding the filter cake into a drying rotary kiln according to a certain frequency, wherein the rotary frequency of the rotary kiln is 15Hz, the drying temperature is 180 ℃, the drying time is 6 hours, and the induced air frequency is 40Hz, so that the ferric phosphate dihydrate powder with a regular micro-morphology is obtained.

And S8, further feeding the dihydrate ferric phosphate powder into a calcination rotary kiln according to a certain frequency, wherein the rotary kiln rotation frequency is 12Hz, the calcination temperature is 300-300-550-550-550 ℃, the calcination time is 8h, and the induced air frequency is 40Hz, so as to obtain the high-compaction anhydrous ferric phosphate powder with the orthogonal crystal form.

S10, weighing 151g of the finished ferric phosphate material, 37g of battery-grade lithium carbonate and 18g of sucrose, weighing 200mL of isopropanol, placing the isopropanol in a ball mill, and performing ball milling for 3 hours to obtain mixed slurry.

Example 5

Embodiment 5 of the present application provides a high compacted iron phosphate material and a preparation method thereof. The method comprises the following steps:

s1, preparing a 1.0mol/L ferrous chloride solution and a diammonium phosphate solution, and weighing the ferrous solution and the phosphate solution according to a molar ratio of Fe: P =3.

S2, weighing a reducing substance ascorbic acid, a pH regulator sodium carbonate and phosphoric acid, and an oxidizing substance hydrogen peroxide (30% excess compared with the molar amount of ferrous ions) for later use.

S3, dripping a reasonably prepared ferrous solution, a phosphate solution, a reducing substance ascorbic acid and a pH regulator sodium carbonate into the reaction solution at a certain speed (41.7 mL/min, 8.3mL/min and 8.3mL/min in sequence), adjusting the pH of the solution to 11, adjusting the oxidation-reduction potential to-0.55V, stirring at a speed of 300r/min, and reacting for 1h to obtain light blue slurry containing the amorphous ferrous phosphate octahydrate reaction precursor.

And S4, adding phosphoric acid serving as a pH regulator into the slurry, regulating the pH of the slurry to 1.5, adding hydrogen peroxide into the slurry after 30min, and observing that the color of the slurry is changed from light blue to yellow white.

And S7, feeding the filter cake into a drying rotary kiln according to a certain frequency, wherein the rotary frequency of the rotary kiln is 15Hz, the drying temperature is 200 ℃, the drying time is 3 hours, and the induced air frequency is 40Hz, so that the ferric phosphate dihydrate powder with a regular micro-morphology is obtained.

And S8, feeding the dihydrate ferric phosphate powder into a calcination rotary kiln according to a certain frequency, wherein the rotary kiln rotation frequency is 12Hz, the calcination temperature is 300-300-550-550-550 ℃, the calcination time is 5h, and the induced air frequency is 40Hz, so as to obtain the high-compaction anhydrous ferric phosphate powder with the orthogonal crystal form.

S10, weighing 151g of the finished ferric phosphate material, 37g of battery-grade lithium carbonate and 18g of sucrose, weighing 200mL of isopropanol, placing the isopropanol in a ball mill, and stopping ball milling for 3 hours to obtain mixed slurry.

Example 6

Embodiment 6 of the present application provides a high compacted iron phosphate material and a preparation method thereof. The method comprises the following steps:

s1, preparing a 1.0mol/L ferrous sulfate solution and a diammonium phosphate solution, and weighing the ferrous sulfate solution and the phosphate solution according to a molar ratio of Fe: P = 3.1.

S3, dripping a ferrous solution, a phosphate solution, a reducing substance ascorbic acid and a pH regulator sodium hydroxide which are reasonably prepared into a reaction solution at a certain speed (41.7 mL/min, 8.3mL/min and 8.3mL/min in sequence), adjusting the pH of the solution to 12, adjusting the redox potential to-0.80V, stirring at a speed of 300r/min, and reacting for 1h to obtain light blue slurry containing the amorphous ferrous phosphate octahydrate reaction precursor.

And S4, adding a pH regulator phosphoric acid into the slurry, regulating the pH of the slurry to 1.0, adding hydrogen peroxide into the slurry after 30min, and observing that the color of the slurry is changed from light blue to yellowish white.

And S7, feeding the filter cake into a drying rotary kiln according to a certain frequency, drying for 6 hours at the rotary kiln rotation frequency of 15Hz and the drying temperature of 180 ℃, and obtaining ferric phosphate dihydrate powder with a regular micro-morphology at the induced air frequency of 40 Hz.

Example 7

Embodiment 7 of the present application provides a high compacted iron phosphate material and a preparation method thereof. The method comprises the following steps:

And S3, dripping the reasonably prepared ferrous solution, phosphate solution, reducing substance ascorbic acid and pH regulator phosphoric acid into the reaction solution at a certain speed (41.7 mL/min, 8.3mL/min and 8.3mL/min in sequence), adjusting the pH of the solution to 3.0, adjusting the redox potential to-0.40V, stirring at a speed of 300r/min, and reacting for 1h to obtain light blue slurry containing the amorphous ferrous phosphate octahydrate reaction precursor.

And S4, adding phosphoric acid serving as a pH regulator into the slurry, regulating the pH of the slurry to 2.0, adding hydrogen peroxide into the slurry after 30min, and observing that the color of the slurry is changed from light blue to yellow white.

S8, feeding the dihydrate ferric phosphate powder into a calcination rotary kiln according to a certain frequency, wherein the rotary kiln rotation frequency is 12Hz, the calcination temperature is 300-300-550-550-550 ℃, the calcination time is 8h, and the induced air frequency is 40Hz, so that the high-compaction anhydrous ferric phosphate powder with the orthogonal crystal form is obtained, and the SEM picture of the powder is shown in figure 2.

Example 8

The application embodiment 8 provides a high-compaction ferric phosphate material and a preparation method thereof. The method comprises the following steps:

S2, weighing a reducing substance ascorbic acid, a pH regulator phosphoric acid and an oxidizing substance hydrogen peroxide (the molar excess of the hydrogen peroxide to ferrous ions is 30%) for later use.

S3, dropwise adding the reasonably prepared ferrous solution, phosphate solution, reducing substance ascorbic acid and pH regulator phosphoric acid into the reaction solution at certain rates of 41.7mL/min, 8.3mL/min and 8.3mL/min in sequence), adjusting the pH of the solution to 3.0, adjusting the redox potential to-0.40V, stirring at 300r/min, and reacting for 1h to obtain light blue slurry containing the amorphous ferrous phosphate octahydrate reaction precursor.

And S4, adding a pH regulator phosphoric acid into the slurry, regulating the pH of the slurry to 2.5, adding hydrogen peroxide into the slurry after 30min, and observing that the color of the slurry is changed from light blue to yellowish white.

And S7, feeding the filter cake into a drying rotary kiln according to a certain frequency, wherein the rotary kiln rotates at a frequency of 15Hz, the drying temperature is 180 ℃, the drying time is 6 hours, and the induced air frequency is 40Hz, so that the ferric phosphate dihydrate powder with a regular micro-morphology is obtained, and an SEM image of the ferric phosphate dihydrate powder is shown in FIG. 3.

Comparative example 1

Comparative example 1 of the present application provides an iron phosphate material and a method for preparing the same. The method comprises the following steps:

s1, preparing a 1.0mol/L ferrous chloride solution and a phosphate solution, and keeping the ferrous chloride solution and the phosphate solution at a molar ratio of Fe to P = 1.

S2, taking a mixed solution of ferrous salt and phosphate as a base solution, controlling the synthesis temperature to be 30 +/-5 ℃, stirring at a speed of 300r/min, pumping hydrogen peroxide (30% in molar excess compared with ferrous ions) into a reaction kettle, and feeding for 60min.

S3, heating the slurry by steam, controlling the temperature at 90 +/-2 ℃, converting the slurry from yellow to light pink after 50-60 min, and continuously reacting for 2h to obtain the ferric phosphate dihydrate material with a complete crystal structure.

And S4, pumping the ferric phosphate dihydrate into a filter press for pressure filtration and rinsing, and washing to the conductivity below 500 mu S/cm to obtain a clean filter cake.

And S5, feeding the filter cake into a drying rotary kiln according to a certain frequency, wherein the rotary kiln has the rotation frequency of 15Hz, the drying temperature of 120 ℃, the drying time of 6h and the induced air frequency of 40Hz, so as to obtain ferric phosphate dihydrate powder with a regular micro-morphology, and an SEM image of the ferric phosphate dihydrate powder is shown in FIG. 4.

S6, feeding the dihydrate ferric phosphate powder into a calcination rotary kiln according to a certain frequency, wherein the rotary kiln rotation frequency is 12Hz, the calcination temperature is 300-300-550-550-550 ℃, the calcination time is 6h, and the induced air frequency is 40Hz, so as to obtain the high-compaction anhydrous ferric phosphate powder with the orthogonal crystal form.

S7, performing air current crushing and screening for removing iron to obtain a high-compaction ferric phosphate material finished product.

S8, weighing 151g of the finished ferric phosphate material, 37g of battery-grade lithium carbonate and 18g of sucrose, weighing 200mL of isopropanol, placing the isopropanol in a ball mill, and stopping ball milling for 3 hours to obtain mixed slurry.

S9, drying the mixed slurry, putting the dried mixed slurry into an alumina crucible, heating the mixed slurry to 700 ℃ in a tubular furnace at the speed of 200 ℃/h, keeping the temperature for 10h, stopping heating, and naturally cooling the mixed slurry in a dry furnace to room temperature. In the process, high-purity nitrogen is continuously introduced into the tubular furnace to obtain the lithium iron phosphate material.

The iron phosphate powder and the lithium iron phosphate material prepared in example 1, example 3, example 5, example 7, example 8, and comparative example 1 were subjected to performance tests, and the test results are shown in table 1 below. In Table 1, span indicates the width of particle size distribution, D ₅₀ The average particle size is shown.

TABLE 1

As seen from Table 1 above, D iron phosphate was obtained in examples 1, 3 and 5 ₅₀ The ferric phosphate is prepared in the method of example 7 and example 8, and the ferric phosphate supersaturation degree in the system is adjusted by adjusting the ferrous phosphate dissolution rate, namely adjusting the pH value of the second slurry. The compacted density and electrical properties of the lithium iron phosphate prepared in examples 7 and 8 were inferior to those of the lithium iron phosphate prepared in examples 1, 3 and 5, indicating that the primary particle size of the iron phosphate prepared in examples 7 and 8 was too large. D iron phosphate prepared in examples 1, 3 and 5 ₅₀ The discharge capacity of the lithium iron phosphate prepared by the comparative example 1 is close to that of the iron phosphate prepared by the comparative example 1 (the iron phosphate prepared by the direct oxidation precipitation method in the comparative example 1), but the compaction density of the lithium iron phosphate prepared by the examples 1, 3 and 5 is obviously superior to that of the lithium iron phosphate prepared by the comparative example 1. In summary, it is shown that the primary particle sizes of the iron phosphates prepared in examples 1, 3, and 5 are moderate, which is advantageous for preparing high-compaction lithium iron phosphate materials.

Fig. 1 to 4 are Scanning Electron Microscope (SEM) images of the ferric phosphate dihydrate materials prepared in examples 1, 7, 8 and 1, respectively, from which it can be visually observed that the primary particles of the ferric phosphate dihydrate prepared in example 1 have a regular micro-morphology, and the size is between that of the ferric phosphate dihydrate materials prepared in examples 7, 8 and 1, and thus the anhydrous ferric phosphate prepared by the method for further preparing the lithium iron phosphate has a high compaction characteristic.

The above examples only express several embodiments of the present application, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present application. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the concept of the present application, which falls within the scope of protection of the present application. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. A preparation method of a high-compaction ferric phosphate material is characterized by comprising the following steps:

preparing a first mixture system containing a phosphate source, a ferrous ion source and a first pH regulator, wherein the first mixture system is subjected to a first reaction to obtain a first slurry containing an amorphous ferrous phosphate octahydrate reaction precursor;

and adding an oxidizing substance into the second slurry to perform a second reaction to obtain a dihydrate ferric phosphate material.

2. The method of claim 1, wherein the first mixture system has a pH of 2.8 to 12 and an oxidation-reduction potential of-0.8 to 0.24V.

3. The method for preparing a highly compacted iron phosphate material according to claim 1 or 2, wherein the first pH adjuster is at least one of phosphoric acid, sulfuric acid, hydrochloric acid, ammonia water, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonium hydrogen carbonate, potassium hydrogen carbonate, and sodium hydrogen carbonate.

4. The method of claim 1, wherein the second slurry has a pH of-0.5 to 1.5.

5. The method for preparing a highly compacted iron phosphate material according to claim 1 or 4, wherein the second pH adjusting agent is at least one of sulfuric acid, hydrochloric acid and phosphoric acid.

6. The method for producing a compacted iron phosphate material according to any one of claims 1, 2 and 4, wherein a reducing substance is further added to the first mixture system.

7. The method of claim 6, wherein the reducing substance is at least one of ascorbic acid, polyethylene glycol, acetone, and ethanol.

8. The method for preparing a high-compaction ferric phosphate material as claimed in any one of claims 1, 2 and 4, wherein the oxidizing substance is at least one of hydrogen peroxide, sodium hypochlorite and oxygen.

9. The method of claim 1, 2 or 4, wherein the molar ratio of iron to phosphorus in the first mixture system is (3-3.1): 2; and/or

10. An iron phosphate material, characterized in that it is obtained by a method for the preparation of a high compacted iron phosphate material according to any one of claims 1 to 9.