Preparation method of superfine iron phosphate

Abstract

The invention discloses a preparation method of superfine iron phosphate, and belongs to the technical field of preparation of lithium ion positive electrode materials. The preparation method of the superfine iron phosphate comprises the following steps: carrying out reduction and deoxidation treatment on oxide scale to obtain reduced iron; mixing the reduced iron with phosphoric acid, performing dissolution reaction, and filtering to obtain filtrate; mixing the filtrate, hydrogen peroxide and a surfactant, performing precipitation reaction, and collecting a solid-phase component to obtain an iron phosphate crude product; and calcining the iron phosphate crude product to obtain the superfine iron phosphate. The surfactant polypropylene methyl carboxymethyl ester is added in the iron phosphate precipitation process, compared with a traditional iron phosphate preparation technology, the superfine iron phosphate of a porous structure can be directly prepared through treatment, and the technological process is simple. According to the preparation process, the granularity of the iron phosphate product can be reduced, the morphology of the iron phosphate can be changed, the production qualification rate of the product is improved, and the method has a very good application value.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion positive electrode material preparation, and in particular to a method for preparing ultrafine iron phosphate. Background Art

[0002] Lithium iron phosphate, as a lithium-ion battery positive electrode material processed from iron phosphate, has been widely used in many fields such as electric vehicles, energy storage systems, and portable electronic devices due to its high safety performance, long cycle life, and low cost. As a precursor for the preparation of lithium iron phosphate, the quality of iron phosphate is crucial. In particular, the purity of battery-grade iron phosphate is usually required to reach more than 99.5%, the impurity content needs to be strictly controlled, and the particle size needs to be evenly distributed, usually at the nanometer or submicron level. These characteristics play a key role in improving the electrochemical performance of the battery. Therefore, iron phosphate and its processed product lithium iron phosphate play a vital role in the development of lithium-ion battery technology. The methods for preparing iron phosphate in industry mainly include:

[0003] 1. Chemical precipitation method: dissolve the iron source and phosphorus source in a stoichiometric ratio, adjust the pH value and temperature to generate iron phosphate precipitate, filter, wash and dry to obtain battery-grade iron phosphate; the precipitation method has the characteristics of simple process, low cost and suitability for large-scale production, but there are problems such as insufficient product purity and uneven particle size distribution.

[0004] 2. Hydrothermal method: Dissolve the iron source and phosphorus source in water, place them in a high-pressure reactor for hydrothermal reaction, and obtain battery-grade iron phosphate after filtering, washing and drying. The hydrothermal method has high requirements for equipment and is difficult to mass produce.

[0005] 3. Solution-gel method: dissolve the iron source and phosphorus source in a solvent, add a chelating agent to form a sol, and obtain battery-grade iron phosphate through gelation, drying and calcination; the sol-gel method has a complex process and high cost.

[0006] 4. Template method: Use a hard template or a soft template to control the morphology and structure of iron phosphate, and after removing the template, a porous or hollow battery-grade iron phosphate is obtained; the template method is complex and costly.

[0007] These traditional processes for preparing iron phosphate generally have problems such as high iron source prices and long process flows. In addition, the particle size of the obtained iron phosphate is generally large, with an average particle size generally above 10 μm, which is not suitable for preparing nano- or submicron-sized iron phosphate with a porous particle structure. Summary of the invention

[0008] The object of the present invention is to provide a method for preparing ultrafine iron phosphate to solve the above-mentioned problems in the background technology. The present invention adds a surfactant polypropylene methyl carboxymethyl ester during the precipitation of iron phosphate. Compared with the traditional iron phosphate preparation process, the process can directly prepare ultrafine iron phosphate with a porous structure, and the process is simple. According to the process of the present invention, the particle size of the product iron phosphate can be reduced and the morphology of the iron phosphate can be changed, the qualified rate of product production can be improved, and it has good application value.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] One of the technical solutions of the present invention is to provide a method for preparing ultrafine iron phosphate, comprising the following steps:

[0011] The iron oxide scale is subjected to reduction and deoxidation treatment to obtain reduced iron;

[0012] The reduced iron is mixed with phosphoric acid, dissolved and reacted, and filtered to obtain a filtrate;

[0013] The filtrate, hydrogen peroxide and surfactant are mixed, a precipitation reaction is performed, and a solid phase component is collected to obtain a crude iron phosphate product;

[0014] The crude iron phosphate is calcined to obtain the ultrafine iron phosphate.

[0015] Preferably, the particle size of the reduced iron is 20-100 mesh.

[0016] Preferably, the reducing agent of the reduction deoxidation treatment is coal, and the reduction degree of the iron oxide scale is 0-100wt% and is not 0.

[0017] More preferably, the reduction degree of the iron oxide scale is 0-30wt%.

[0018] Preferably, the molar ratio of the iron element in the reduced iron to the phosphorus element in the phosphoric acid is 1:1-5; and the concentration of the phosphoric acid is 10-40wt%.

[0019] Preferably, the dissolution reaction is carried out at a temperature of 50-90°C and for 60 minutes.

[0020] Preferably, the dissolution reaction is carried out at a stirring speed of 350 r / min.

[0021] Preferably, the surfactant is polypropylene methyl carboxymethyl ester.

[0022] Preferably, the amount of hydrogen peroxide added is 100-140 mol% of the theoretical amount.

[0023] Preferably, the precipitation reaction temperature is 60-100°C, and the time is 0-2h and not 0.

[0024] More preferably, the reaction time of the precipitation reaction is counted from the end of the addition of hydrogen peroxide, and the hydrogen peroxide is added intermittently in equal amounts, specifically once every 30 minutes for a total of 3 times.

[0025] Preferably, the precipitation reaction is carried out at a stirring speed of 350 r / min.

[0026] Preferably, after collecting the solid phase components, a water washing step is further included; the amount of washing water used in the water washing is 5-10 times the quality of the crude iron phosphate.

[0027] Preferably, the calcination treatment is carried out at a temperature of 600-800°C and for a time of 4-24 hours.

[0028] The second technical solution of the present invention is to provide an ultrafine iron phosphate obtained according to the above preparation method.

[0029] The beneficial technical effects of the present invention are as follows:

[0030] The present invention provides a method for preparing ultrafine ferric phosphate. Compared with the traditional method for preparing ferric phosphate from ferrous sulfate, the production process of the present invention does not produce waste brine, the product performance is more excellent, and the process is simple, the investment is small, and the production cost is low. Compared with the process for preparing ferric phosphate from secondary reduction of iron powder, the present invention does not require high reduction degree, the iron source is cheap, and the cost is low.

[0031] The present invention adds surfactant polypropylene methyl carboxymethyl ester during the precipitation process of iron phosphate. Compared with the traditional iron phosphate preparation process, the treatment can directly prepare ultrafine iron phosphate with a porous structure, and the process is simple.

[0032] The preparation process according to the present invention can reduce the particle size of the iron phosphate product and change the morphology of the iron phosphate, thereby improving the production qualification rate of the product and having good application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0034] Figure 1 This is a scanning electron microscope image of the battery-grade iron phosphate prepared in Example 1;

[0035] Figure 2 This is the XRD diffraction pattern of the battery-grade iron phosphate prepared in Example 1;

[0036] Figure 3 This is a particle size distribution diagram of the battery-grade iron phosphate prepared in Example 1-4;

[0037] Figure 4 This is a comparison chart of the particle sizes of the battery-grade iron phosphates prepared in Example 1 and Example 5. DETAILED DESCRIPTION

[0038] Now, various exemplary embodiments of the present invention are described in detail, and this detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics and embodiments of the present invention. It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention.

[0039] In addition, for the numerical range in the present invention, it is understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value in any stated value or stated range, and each smaller range between any other stated value or intermediate value in the range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0040] Unless otherwise specified, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. It should be noted that the parts not described in detail in the present invention are conventional operating means in the art and are not the focus of the present invention.

[0041] The words “include,” “including,” “have,” “contain,” etc. used in the present invention are open-ended terms, meaning including but not limited to.

[0042] All raw materials used in the following examples and comparative examples of the present invention are commercially available products.

[0043] Example 1

[0044] A method for preparing ultrafine iron phosphate, the steps are as follows:

[0045] Step 1: 30 g of oxidized iron sheet briquettes and anthracite are mixed and subjected to reduction and deoxidation treatment (temperature is 1200° C., time is 30 min) to obtain reduced iron (the reduction degree of the oxidized iron sheet is 90.12%);

[0046] Step 2: Mix the reduced iron and phosphoric acid (the phosphoric acid concentration is 20wt%, and the iron-phosphorus ratio is 1:3), dissolve and react at 70°C and a stirring speed of 350r / min for 1h, and filter to obtain a filtrate;

[0047] Step 3, mixing the filtrate, hydrogen peroxide and a surfactant (the amount of hydrogen peroxide added is 110 mol% of the theoretical amount, and the hydrogen peroxide is added intermittently in equal amounts, once every 30 minutes for a total of 3 times, and 1 g of polypropylene methyl carboxymethyl ester is added as a surfactant during the reaction), and the precipitation reaction is carried out at 100° C. and a stirring speed of 350 r / min for 1 hour, and the solid phase component is collected and washed with deionized water to obtain a crude iron phosphate;

[0048] Step 4: calcine the crude iron phosphate at 600° C. for 4 hours to obtain battery-grade iron phosphate that meets the requirements.

[0049] Figure 1 This is a scanning electron microscope image of the battery-grade iron phosphate prepared in Example 1.

[0050] from Figure 1 It can be seen that the battery-grade iron phosphate material prepared in Example 1 has a porous structure, and the particle size is submicron and nanometer, and is evenly distributed.

[0051] Figure 2 This is the XRD diffraction pattern of the battery-grade iron phosphate prepared in Example 1.

[0052] Example 2

[0053] A method for preparing ultrafine iron phosphate, the steps are as follows:

[0054] Step 1: 30 g of oxidized iron sheet briquettes and anthracite are mixed and subjected to reduction and deoxidation treatment (temperature is 900° C., time is 30 min) to obtain reduced iron (the reduction degree of the oxidized iron sheet is 27.66%);

[0055] Step 2: Mix the reduced iron and phosphoric acid (the phosphoric acid concentration is 20wt%, and the iron-phosphorus ratio is 1:3), dissolve and react at 70°C and a stirring speed of 350r / min for 1h, and filter to obtain a filtrate;

[0056] Step 3, mixing the filtrate, hydrogen peroxide and a surfactant (the amount of hydrogen peroxide added is 110 mol% of the theoretical amount, and the hydrogen peroxide is added intermittently in equal amounts, once every 30 minutes for a total of 3 times, and 1 g of polypropylene methyl carboxymethyl ester is added as a surfactant during the reaction), and the precipitation reaction is carried out at 100° C. and a stirring speed of 350 r / min for 1 hour, and the solid phase component is collected and washed with deionized water to obtain a crude iron phosphate;

[0057] Step 4: calcine the crude iron phosphate at 600° C. for 4 hours to obtain battery-grade iron phosphate that meets the requirements.

[0058] Example 3

[0059] A method for preparing ultrafine iron phosphate, the steps are as follows:

[0060] Step 1: 30 g of oxidized iron sheet briquettes and anthracite are mixed and subjected to reduction and deoxidation treatment (temperature is 1000° C., time is 30 min) to obtain reduced iron (the reduction degree of the oxidized iron sheet is 48.23%);

[0061] Step 2: Mix the reduced iron and phosphoric acid (the phosphoric acid concentration is 20wt%, and the iron-phosphorus ratio is 1:3), dissolve and react at 70°C and a stirring speed of 350r / min for 1h, and filter to obtain a filtrate;

[0062] Step 3, mixing the filtrate, hydrogen peroxide and a surfactant (the amount of hydrogen peroxide added is 110 mol% of the theoretical amount, and the hydrogen peroxide is added intermittently in equal amounts, once every 30 minutes for a total of 3 times, and 1 g of polypropylene methyl carboxymethyl ester is added as a surfactant during the reaction), and the precipitation reaction is carried out at 100° C. and a stirring speed of 350 r / min for 1 hour, and the solid phase component is collected and washed with deionized water to obtain a crude iron phosphate;

[0063] Step 4: calcine the crude iron phosphate at 600° C. for 4 hours to obtain battery-grade iron phosphate that meets the requirements.

[0064] Example 4

[0065] A method for preparing ultrafine iron phosphate, the steps are as follows:

[0066] Step 1: 30 g of oxidized iron sheet briquettes and anthracite are mixed and subjected to reduction and deoxidation treatment (temperature is 1100° C., time is 30 min) to obtain reduced iron (the reduction degree of the oxidized iron sheet is 73.41%);

[0067] Step 2: Mix the reduced iron and phosphoric acid (the phosphoric acid concentration is 20wt%, and the iron-phosphorus ratio is 1:3), dissolve and react at 70°C and a stirring speed of 350r / min for 1h, and filter to obtain a filtrate;

[0068] Step 3, mixing the filtrate, hydrogen peroxide and a surfactant (the amount of hydrogen peroxide added is 110 mol% of the theoretical amount, and the hydrogen peroxide is added intermittently in equal amounts, once every 30 minutes for a total of 3 times, and 1 g of polypropylene methyl carboxymethyl ester is added as a surfactant during the reaction), and the precipitation reaction is carried out at 100° C. and a stirring speed of 350 r / min for 1 hour, and the solid phase component is collected and washed with deionized water to obtain a crude iron phosphate;

[0069] Step 4: calcine the crude iron phosphate at 600° C. for 4 hours to obtain battery-grade iron phosphate that meets the requirements.

[0070] Figure 3 This is the particle size distribution diagram of the battery-grade iron phosphate prepared in Examples 1-4.

[0071] Figure 3900°C refers to the product of Example 2, 1000°C refers to the product of Example 3, 1100°C refers to the product of Example 4, and 1200°C refers to the product of Example 1.

[0072] Example 5 (without adding polypropylene methyl carboxymethyl ester)

[0073] A method for preparing ultrafine iron phosphate, the steps are as follows:

[0074] Step 1: 30 g of oxidized iron sheet briquettes and anthracite are mixed and subjected to reduction and deoxidation treatment (temperature is 1200° C., time is 30 min) to obtain reduced iron (the reduction degree of the oxidized iron sheet is 90.12%);

[0075] Step 2: Mix the reduced iron and phosphoric acid (the phosphoric acid concentration is 20wt%, and the iron-phosphorus ratio is 1:3), dissolve and react at 70°C and a stirring speed of 350r / min for 1h, and filter to obtain a filtrate;

[0076] Step 3, the filtrate and hydrogen peroxide were mixed (the amount of hydrogen peroxide added was 110 mol% of the theoretical amount, and the hydrogen peroxide was added intermittently in equal amounts, once every 30 minutes for a total of 3 times), and the precipitation reaction was carried out at 100° C. and a stirring speed of 350 r / min for 1 hour, and the solid phase components were collected and washed with deionized water to obtain a crude iron phosphate;

[0077] Step 4: calcine the crude iron phosphate at 600° C. for 4 hours to obtain battery-grade iron phosphate that meets the requirements.

[0078] Figure 4 This is a comparison chart of the particle sizes of the battery-grade iron phosphates prepared in Example 1 and Example 5.

[0079] Depend on Figure 4 It can be seen that the particle size of the iron phosphate prepared in Example 1 with the addition of the surfactant polypropylene methyl carboxymethyl ester is significantly smaller than that of the iron phosphate in Example 5, and the particle size distribution is more concentrated.

[0080] Comparative Example 1

[0081] The same as Example 1, except that the dissolution temperature in step 2 is modified to 50°C, 60°C, 80°C, 90°C, and 100°C respectively.

[0082] Comparative Example 2

[0083] The same as Example 1, except that the concentration of phosphoric acid in step 2 is modified to 10wt%, 30wt% and 40wt% respectively.

[0084] Comparative Example 3

[0085] The same as Example 1, except that the iron-to-phosphorus ratio of the iron element in the reduced iron and the phosphorus element in the phosphoric acid in step 2 is modified to 1 / 1, 1 / 2, 1 / 4, and 1 / 5, respectively.

[0086] Effect verification

[0087] 1. The battery-grade iron phosphate materials prepared in Examples 1-4 were subjected to physical and chemical analysis. The test indicators and data results are shown in Table 1.

[0088] Table 1 Test data

[0089]

[0090] The results in Table 1 show that the Fe content, P content, Fe / P and other elements of the iron phosphate prepared in Examples 1-4 of the present invention all meet the requirements of the corresponding standards, and the particle size distribution is uniform.

[0091] 2. Comparison of the dissolution rates of the above low-grade iron powder under different reaction conditions, the results are shown in Table 2.

[0092] Table 2 Comparative Examples 1-3 Dissolution Rate

[0093]

[0094]

[0095] It can be seen from Table 2 that the dissolution rate of low-grade iron powder is affected by reaction temperature, iron-phosphorus ratio and phosphoric acid concentration.

[0096] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing ultrafine ferric phosphate, characterized in that: The following steps are involved: The iron oxide scale is subjected to reduction and deoxidation treatment to obtain reduced iron; The reduced iron is mixed with phosphoric acid, dissolved and reacted, and filtered to obtain a filtrate; The filtrate, hydrogen peroxide and surfactant are mixed, a precipitation reaction is performed, and a solid phase component is collected to obtain a crude iron phosphate product; The crude iron phosphate is calcined to obtain the ultrafine iron phosphate.

2. The preparation method according to claim 1, characterized in that: The reducing agent of the reduction deoxidation treatment is coal, and the reduction degree of the iron oxide scale is 0-100wt% and is not 0.

3. The preparation method according to claim 1, characterized in that: The molar ratio of the iron element in the reduced iron to the phosphorus element in the phosphoric acid is 1:1-5; and the concentration of the phosphoric acid is 10-40wt%.

4. The preparation method according to claim 1, characterized in that: The temperature of the dissolution reaction is 50-90° C. and the time is 60 minutes.

5. The preparation method according to claim 1, characterized in that: The surfactant is polypropylene methyl carboxymethyl ester.

6. The preparation method according to claim 1, characterized in that: The amount of hydrogen peroxide added is 100-140 mol% of the theoretical amount.

7. The preparation method according to claim 1, characterized in that: The precipitation reaction temperature is 60-100°C, and the time is 0-2h and is not 0.

8. The preparation method according to claim 1, characterized in that: The calcination treatment is carried out at a temperature of 600-800°C and for a time of 4-24 hours.

9. Ultrafine iron phosphate obtained according to the preparation method according to any one of claims 1 to 8.

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