Iron phosphate material, method for preparing the same, and use thereof

Abstract

The present disclosure provides a kind of iron phosphate material and its preparation method and application, belong to positive electrode material technical field;The preparation method of iron phosphate material provided in the present disclosure, by introducing acetone and C3-C5 alkyl diamine in the reaction process, and carry out three-stage reaction;Make the particle size of the prepared iron phosphate material be small, compaction density is high, specific surface area is large, purity is high.Simultaneously, the preparation method provided in the present disclosure is simple to operate, is conducive to actual production.

Description

Technical Field

[0001] This disclosure belongs to the field of cathode material technology, and particularly relates to an iron phosphate material, its preparation method and application. Background Technology

[0002] The most commonly used cathode materials in lithium batteries are lithium iron phosphate (LFP) and ternary materials. Among them, LFP has become a highly promising cathode material for lithium-ion batteries due to its advantages such as low cost, good high-temperature performance, large capacity, no memory effect, light weight, and environmental friendliness. Iron phosphate is an important precursor for the preparation of LFP, and its chemical composition, structure, physicochemical properties, and reactivity largely determine the overall performance of the resulting LFP cathode material. Currently, the main methods for preparing iron phosphate include hydrothermal methods, sol-gel methods, homogeneous precipitation methods, and microwave methods, each with its own advantages and disadvantages. Common problems with existing preparation methods include: numerous side reactions during the preparation process, high impurities in the obtained iron phosphate, low product purity, large primary particle size, small specific surface area, and low compaction density, all of which affect the performance of the subsequently prepared LFP cathode material. Summary of the Invention

[0003] The purpose of this disclosure is to overcome the shortcomings of the prior art and provide a ferric phosphate material with small particle size, high compaction density, large specific surface area, and high purity, as well as its preparation method and application.

[0004] To achieve the above objectives, in a first aspect of this disclosure, a method for preparing an iron phosphate material is provided, the method comprising the following steps:

[0005] Iron salts were dissolved in an aqueous acetone solution, and then C3-5 alkyldiamines were added to obtain an iron salt solution.

[0006] After adding phosphorus source solution to iron salt solution, the first reaction is carried out. After the first reaction is completed, the temperature is increased at the first rate to carry out the second reaction. After the second reaction is completed, the temperature is increased at the second rate to carry out the third reaction. After the third reaction is completed, the product is centrifuged, the precipitate is collected, washed, and dried to obtain the intermediate product.

[0007] The intermediate product was calcined to obtain ferric phosphate material.

[0008] The method for preparing iron phosphate material disclosed herein introduces acetone and C3-C5 alkyl diamine during the reaction process and carries out a three-stage reaction; this results in iron phosphate material with small particle size, high compaction density, large specific surface area, and high purity.

[0009] Specifically, the introduction of C3-C5 alkyldiamines, whose nitrogen atoms possess a lone pair of electrons and whose empty orbitals accept electrons, allows them to form a complex system. The C3-C5 alkyldiamine complexes some of the iron ions, regulating the formation rate of ferric phosphate. It also controls the growth direction of FePO4, thereby controlling the particle size, uniformity, and specific surface area of ​​the generated ferric phosphate. Adding acetone during the preparation process serves several purposes: first, as a solvent, acetone enhances the dispersibility of iron ions; second, the oxygen atoms in acetone also possess lone pairs of electrons, which can form complexes with iron ions, meaning the oxygen atoms in acetone participate in the coordination of iron ions along with the nitrogen atoms in the C3-C5 alkyldiamine, further regulating the formation rate of ferric phosphate and resulting in a concentrated particle size distribution, good consistency, and a large specific surface area; third, the volatility of acetone, combined with the subsequent three-stage programmed reactions, further regulates the reaction rate. The first reaction primarily utilizes acetone and C3-C5 alkyldiamine to complex some of the iron. The ions compete with each other, and the slow reaction generates nano-iron phosphate. The second and third reactions gradually increase the temperature at a certain rate to volatilize acetone. At this time, the concentration of C=O bonds in acetone complexed with iron ions decreases, releasing more iron ions. At the same time, the particles tend to aggregate, promoting the forward reaction between iron ions and phosphate ions. Finally, the acetone in the solution is completely volatilized. By controlling the temperature, the reaction is further promoted to complete the final reaction, resulting in high compaction density of the obtained iron phosphate. In addition, the slow iron phosphate formation process can also reduce impurity ions in the product and prevent surface-adsorbed impurities from remaining in the product due to excessively rapid precipitation, thereby improving the purity of the final iron phosphate material.

[0010] In one embodiment, the C3-5 alkyldiamine includes at least one of 1,2-propanediamine and 1,4-butanediamine.

[0011] In one embodiment, the C3-5 alkyldiamine is 1,2-propanediamine.

[0012] This study found that when the C3-5 alkyl diamine is further selected as 1,2-propanediamine, it can better complex with iron ions, thereby regulating the formation rate of iron phosphate and obtaining products with smaller particle size and larger specific surface area.

[0013] In one embodiment, the volume ratio of acetone, water and C3-5 alkyldiamine is acetone:water:C3-5 alkyldiamine = (0.5-1):1:(0.5-1).

[0014] This study found that when the volume ratio of acetone, water and C3-5 alkyldiamine in the acetone aqueous solution is further selected as (0.5-1):1:(0.5-1), acetone and C3-5 alkyldiamine have a better synergistic effect in reducing the formation rate of iron phosphate, thereby making the iron phosphate material smaller in particle size and more uniform in particle size distribution.

[0015] In one embodiment, rapid stirring is maintained during the addition of C3-5 alkyldiamine at a speed of 700-900 rpm.

[0016] In one embodiment, the C3-5 alkyldiamine is added dropwise at a rate of 0.5-1.5 mL / min. In another embodiment, the phosphorus source solution is added while stirring at a speed of 300-600 rpm.

[0017] In one embodiment, the phosphorus source solution is added by dripping at a rate of 4-6 mL / min.

[0018] In one embodiment, the mass-to-volume ratio of iron salt to aqueous acetone solution is 1 g:(3-5) mL.

[0019] This study found that a suitable mass-to-volume ratio of iron salt to acetone aqueous solution can result in a moderate concentration in the reaction system, thereby increasing the particle specific surface area and purity of the reaction product.

[0020] In one embodiment, the iron salt includes at least one of ferric sulfate and its hydrate, ferric chloride and its hydrate, and ferric nitrate and its hydrate.

[0021] In one embodiment, the phosphorus source includes at least one of phosphoric acid and phosphate.

[0022] In one embodiment, the molar ratio of iron in the iron salt to phosphorus in the phosphorus source is 1:1.

[0023] In one embodiment, the phosphorus source solution is an aqueous solution of a phosphorus source; the phosphorus source solution contains 10-30% by mass of the phosphorus source.

[0024] In one embodiment, the temperature of the first reaction is 20-30°C, and the reaction time is 0.5-1.5 h.

[0025] In one embodiment, the temperature of the second reaction is 70-80°C, and the reaction time is 0.5-1.5 h.

[0026] In one embodiment, the temperature of the third reaction is 100-110°C, and the time of the third reaction is 1.5-2.5 h.

[0027] In one embodiment, the first heating rate and the second heating rate are each independently 3-5°C / min.

[0028] In one embodiment, the time ratio of the first reaction time, the second reaction time, and the third reaction time is the first reaction time: the second reaction time: the third reaction time = 1:(1-2):(2-3).

[0029] This study reveals that the selection of reaction temperature and time in the three stages, as well as the selection of heating rates in the latter two stages, can not only help increase the specific surface area of ​​the product, but also improve its compaction density and purity. Specifically, the first stage, conducted at 20-30℃, mainly utilizes acetone and C3-5 alkyldiamine to complex some iron ions and form a competitive relationship, slowly generating nano-iron phosphate. Then, the temperature is increased at a certain rate. During the heating process, acetone slowly volatilizes, at which point the concentration of C=O bonds in acetone complexing with iron ions decreases, releasing more iron ions. Simultaneously, particles tend to aggregate, promoting the forward reaction between iron ions and phosphate ions, until the acetone in the solution is completely volatilized. Finally, the reaction is further promoted by slowly increasing the temperature to complete the final reaction.

[0030] In one embodiment, the washing is performed using anhydrous ethanol and deionized water.

[0031] In one embodiment, the calcination temperature is 500-650°C and the calcination time is 2-4 hours.

[0032] In one embodiment, the calcination is carried out in an inert gas environment; the inert gas includes at least one of nitrogen and rare gases.

[0033] In a second aspect, this disclosure provides an iron phosphate material prepared using the preparation method described in this disclosure.

[0034] The iron phosphate material prepared in this disclosure has a particle size between 321-394 nm and a specific surface area of ​​16.13 m². 2 / g or above, compacted density is 2.29g / cm³ 3 The sulfur peroxide content in the product is below 45 ppm.

[0035] In a third aspect of this disclosure, the application of the said iron phosphate material in the preparation of cathode materials is provided.

[0036] Compared with the prior art, the beneficial effects of this disclosure are as follows:

[0037] The method for preparing ferric phosphate material disclosed herein involves introducing acetone and C3-C5 alkyldiamine during the reaction process, and carrying out a three-stage reaction. This results in ferric phosphate material with small particle size, large specific surface area, high compaction density, and high purity. Furthermore, the preparation method provided herein is simple to operate and beneficial for practical production. Attached Figure Description

[0038] Figure 1 The image shows a SEM image of the iron phosphate material prepared in Example 1. Detailed Implementation

[0039] To better illustrate the purpose, technical solutions, and advantages of this disclosure, the following will provide further explanation of this disclosure in conjunction with specific embodiments.

[0040] Unless otherwise specified, the reagents, methods and equipment used in this disclosure are all conventional reagents, methods and equipment in the art.

[0041] Example 1

[0042] This disclosure provides an iron phosphate material, the preparation method of which includes the following steps:

[0043] (1) Mix 5 mL of acetone and 10 mL of deionized water evenly, then add 4.00 g of ferric sulfate and stir evenly. Then, at a stirring speed of 700 rpm, add 10 mL of 1,2-propanediamine dropwise at a rate of 1 mL / min (the volume ratio of acetone, deionized water and 1,2-propanediamine is 0.5:1:1). After the addition is complete, stir for 30 min to obtain an iron salt solution.

[0044] (2) At a stirring speed of 500 rpm, add phosphoric acid aqueous solution (the mass percentage of phosphoric acid in the phosphoric acid aqueous solution is 20%) dropwise to the iron salt solution at a speed of 5 mL / min, wherein the molar ratio of phosphorus in the phosphoric acid solution to iron in the iron salt solution is 1:1.

[0045] (3) After the addition is complete, the first reaction is carried out at 25°C for 1 hour. After the first reaction is completed, the temperature is increased to 70°C at a rate of 3°C / min for the second reaction for 1 hour. After the second reaction is completed, the temperature is increased to 100°C at a rate of 3°C / min for the third reaction for 2 hours. After the third reaction is completed, the temperature is cooled to room temperature and centrifuged to collect the precipitate. The precipitate is washed three times with anhydrous ethanol and deionized water. After washing, the precipitate is dried at 80°C to obtain the intermediate product.

[0046] (4) The intermediate product was placed under inert gas protection and calcined at 560°C for 3 hours. After calcination, it was cooled to obtain iron phosphate material.

[0047] Example 2

[0048] This disclosure provides an iron phosphate material, the only difference between the iron phosphate material and that in Example 1 is that in step (1), the volume ratio of acetone, deionized water and 1,2-propanediamine is 1:1:1.

[0049] Example 3

[0050] This disclosure provides an iron phosphate material, the only difference between the iron phosphate material and that in Example 1 is that in step (1), the volume ratio of acetone, deionized water and 1,2-propanediamine is 1:1:0.5.

[0051] Example 4

[0052] This disclosure provides an iron phosphate material, the only difference between the iron phosphate material and that in Example 1 is that in step (1), the volume ratio of acetone, deionized water and 1,2-propanediamine is 0.5:1:0.1.

[0053] Example 5

[0054] This disclosure provides an iron phosphate material, the only difference between the iron phosphate material and that in Example 1 is that in step (1), the volume ratio of acetone, deionized water and 1,2-propanediamine is 0.5:1:2.

[0055] Example 6

[0056] This disclosure provides an iron phosphate material, the only difference between the iron phosphate material and that of Example 1 is that in step (1), 1,4-butanediamine is used instead of 1,2-propanediamine.

[0057] Example 7

[0058] This embodiment provides an iron phosphate material, the only difference between the iron phosphate material and that in Embodiment 1 is in step (3), which is as follows:

[0059] After the addition was complete, the first reaction was carried out at 30°C for 1 hour. After the first reaction, the temperature was increased to 80°C at a rate of 5°C / min for 1 hour. After the second reaction, the temperature was increased to 110°C at a rate of 5°C / min for 2 hours. After the third reaction, the temperature was cooled to room temperature and centrifuged. The precipitate was collected, washed three times with anhydrous ethanol and deionized water, and dried at 80°C to obtain the intermediate product.

[0060] Example 8

[0061] This embodiment provides an iron phosphate material, the only difference between the iron phosphate material and that in Embodiment 1 is in step (3), which is as follows:

[0062] After the addition was complete, the first reaction was carried out at 35°C for 1 hour. After the first reaction, the temperature was increased to 90°C at a rate of 3°C / min for 1 hour. After the second reaction, the temperature was increased to 120°C at a rate of 3°C / min for 2 hours. After the third reaction, the temperature was cooled to room temperature and centrifuged. The precipitate was collected, washed three times with anhydrous ethanol and deionized water, and dried at 80°C to obtain the intermediate product.

[0063] Example 9

[0064] This embodiment provides an iron phosphate material, the only difference between the iron phosphate material and that in Embodiment 1 is in step (3), which is as follows:

[0065] After the addition was complete, the first reaction was carried out at 15°C for 1 hour. After the first reaction, the temperature was increased to 60°C at a rate of 3°C / min for the second reaction for 1 hour. After the second reaction, the temperature was increased to 90°C at a rate of 3°C / min for the third reaction for 2 hours. After the third reaction, the temperature was cooled to room temperature and centrifuged. The precipitate was collected, washed three times with anhydrous ethanol and deionized water, and dried at 80°C to obtain the intermediate product.

[0066] Example 10

[0067] This embodiment provides an iron phosphate material, the only difference between the iron phosphate material and that in Embodiment 1 is in step (3), which is as follows:

[0068] After the addition was complete, the first reaction was carried out at 25°C for 1 hour. After the first reaction, the temperature was increased to 70°C at a rate of 8°C / min for 1 hour. After the second reaction, the temperature was increased to 100°C at a rate of 8°C / min for 2 hours. After the third reaction, the temperature was cooled to room temperature and centrifuged. The precipitate was collected, washed three times with anhydrous ethanol and deionized water, and dried at 80°C to obtain the intermediate product.

[0069] Example 11

[0070] This embodiment provides an iron phosphate material, the only difference between the iron phosphate material and that in Embodiment 1 is in step (3), which is as follows:

[0071] After the addition was complete, the first reaction was carried out at 25°C for 1 hour. After the first reaction, the temperature was increased to 70°C at a rate of 1°C / min for the second reaction for 1 hour. After the second reaction, the temperature was increased to 100°C at a rate of 1°C / min for the third reaction for 2 hours. After the third reaction, the temperature was cooled to room temperature and centrifuged. The precipitate was collected, washed three times with anhydrous ethanol and deionized water, and dried at 80°C to obtain the intermediate product.

[0072] Example 12

[0073] This disclosure provides an iron phosphate material, the only difference between the iron phosphate material and Example 1 is that in step (3), the time of the first reaction: the time of the second reaction: the time of the third reaction = 1:2:3, and the total duration of the first reaction, the second reaction and the third reaction remains unchanged at 4h.

[0074] Example 13

[0075] This disclosure provides an iron phosphate material. The only difference between the iron phosphate material and Example 1 is that in step (3), the time of the first reaction: the time of the second reaction: the time of the third reaction = 0.5:1:2, and the total duration of the first reaction, the second reaction and the third reaction remains unchanged at 4h.

[0076] Example 14

[0077] This disclosure provides an iron phosphate material, the only difference between the iron phosphate material and Example 1 is that in step (3), the time of the first reaction: the time of the second reaction: the time of the third reaction = 1.5:1:2, and the total duration of the first reaction, the second reaction and the third reaction remains unchanged at 4h.

[0078] Comparative Example 1

[0079] This disclosure provides a comparative example of an iron phosphate material. The only difference between the iron phosphate material and Example 1 is that acetone is not added in step (1). The volume of acetone is made up with deionized water and 1,2-propanediamine, that is, the volume ratio of deionized water and 1,2-propanediamine is 1:1, and the total volume of the two is 25 mL.

[0080] Comparative Example 2

[0081] This disclosure provides a comparative example of an iron phosphate material. The only difference between the iron phosphate material and Example 1 is that 1,2-propanediamine is not added in step (1). The volume of 1,2-propanediamine is made up with an aqueous acetone solution, i.e., the total volume of the aqueous acetone solution is 25 mL, and the volume ratio of acetone to deionized water is 0.5:1.

[0082] Comparative Example 3

[0083] This disclosure provides a comparative example of an iron phosphate material, the only difference between the iron phosphate material and Example 1 being step (3). Step (3) of this comparative example is as follows:

[0084] After the addition was complete, the first reaction was carried out at 25°C for 1 hour. After the first reaction was completed, the temperature was increased to 100°C at a rate of 3°C / min for the second reaction for 3 hours. After the second reaction was completed, the mixture was cooled to room temperature and centrifuged. The precipitate was collected, washed three times with anhydrous ethanol and deionized water, and dried at 80°C to obtain the intermediate product.

[0085] Comparative Example 4

[0086] This disclosure provides a comparative example of an iron phosphate material, the only difference between the iron phosphate material and Example 1 being step (3). Step (3) of this comparative example is as follows:

[0087] After the addition was complete, the first reaction was carried out at 25°C for 1 hour. After the first reaction was completed, the temperature was increased to 70°C at a rate of 3°C / min for the second reaction for 3 hours. After the second reaction was completed, the mixture was cooled to room temperature and centrifuged. The precipitate was collected, washed three times with anhydrous ethanol and deionized water, and dried at 80°C to obtain the intermediate product.

[0088] Comparative Example 5

[0089] This disclosure provides a comparative example of an iron phosphate material, the only difference between the iron phosphate material and Example 1 being step (3). Step (3) of this comparative example is as follows:

[0090] After the addition was complete, the temperature was increased to 70°C at a rate of 3°C / min for the first reaction, which lasted for 2 hours. After the first reaction, the temperature was increased to 100°C at a rate of 3°C / min for the second reaction, which lasted for 2 hours. After the second reaction, the temperature was cooled to room temperature and centrifuged. The precipitate was collected, washed three times with anhydrous ethanol and deionized water, and then dried at 80°C to obtain the intermediate product.

[0091] Example of effect

[0092] This disclosure demonstrates the effectiveness of testing the particle size, specific surface area, compaction density, and sulfate content of the iron phosphate materials prepared in Examples 1-14 and Comparative Examples 1-5. Particle size was measured using a laser particle size analyzer; compaction density was measured using a compaction density meter; specific surface area was measured using the BET method; and sulfate content was measured using ICP-OES. The results are shown in Table 1. Additionally, the SEM image of the iron phosphate material prepared in Example 1 is shown below. Figure 1 As shown, from Figure 1 It can be seen from the results that the prepared ferric phosphate has no obvious agglomeration and good dispersibility;

[0093] Table 1

[0094]

[0095] As can be seen from Table 1, the phosphoric acid material prepared using the disclosed technical solution has a small particle size and a large specific surface area, as well as high compaction density and purity. Specifically, the compaction density of the obtained product is 2.29 g / cm³. 3 The particle size is between 321-394 nm, and the specific surface area is 16.13 m². 2 / g or more, and sulfur peroxide content below 45ppm;

[0096] As can be seen from Examples 1-5, the volume ratio of acetone, deionized water, and 1,2-propanediamine affects the performance of the product. When the volume ratio of acetone, deionized water, and 1,2-propanediamine is further optimized to (0.5-1):1:(1-2), the overall performance of the obtained product is better, with a compaction density of 2.35 g / cm³. 3 The specific surface area is above 21.63 m². 2 / g or more, and sulfur peroxide content below 18ppm;

[0097] As can be seen from Examples 1 and 7-11, the temperature and heating rate of the three reaction stages during the reaction process will affect the overall performance of the product; as can be seen from Examples 1 and 12-14, the reaction time ratio of the three reaction stages will also affect the overall performance of the product.

[0098] As can be seen from Example 1 and Comparative Examples 1-2, acetone and C3-5 alkyl diamine are both indispensable. Regardless of which one is not added, the compaction density of the resulting product decreases significantly, the sulfur peroxide content increases significantly, and the particle size distribution uniformity of the product also decreases significantly. Compared with Example 1, the compaction density in Comparative Examples 1-2 decreased by 11.11-12.76%, the sulfur peroxide content increased by 238.89-316.67%, and the specific surface area decreased by 35.38-38.88%.

[0099] As can be seen from Example 1 and Comparative Examples 3-5, all three reaction stages are indispensable. If any one of the reaction stages is missing, the performance of the product will be significantly reduced. Compared with Example 1, the compaction density in Comparative Examples 1-2 decreased by 6.58-8.23%, the sulfur peroxide content increased by 150.00-188.89%, and the specific surface area decreased by 31.06-32.40%.

Claims

1. A method for preparing an iron phosphate material, characterized in that, The preparation method includes the following steps: Iron salts were dissolved in an aqueous acetone solution, and then C3-5 alkyldiamines were added to obtain an iron salt solution. A first reaction was carried out after adding a phosphorus source solution to an iron salt solution. After the first reaction, the temperature was increased at a first rate to carry out a second reaction. After the second reaction, the temperature was increased at a second rate to carry out a third reaction. After the third reaction, the product was centrifuged, the precipitate was collected, washed, and dried to obtain the intermediate product. The temperature of the first reaction was 20-30℃. The intermediate product was calcined to obtain ferric phosphate material; The volume ratio of acetone, water and C3-5 alkyl diamine is acetone:water:C3-5 alkyl diamine = (0.5-1):1:(0.5-1).

2. The preparation method according to claim 1, characterized in that, The C3-5 alkyldiamine includes at least one of 1,2-propanediamine and 1,4-butanediamine.

3. The preparation method according to claim 1, characterized in that, The mass-to-volume ratio of the iron salt to the acetone aqueous solution is 1 g: (3-5) mL.

4. The preparation method according to claim 1, characterized in that, The iron salt includes at least one of ferric sulfate and its hydrate, ferric chloride and its hydrate, and ferric nitrate and its hydrate.

5. The preparation method according to claim 1, characterized in that, The phosphorus source includes at least one of phosphoric acid and phosphate.

6. The preparation method according to claim 1, characterized in that, The molar ratio of iron in the iron salt to phosphorus in the phosphorus source is 1:

1.

7. The preparation method according to claim 1, characterized in that, The reaction time for the first reaction is 0.5-1.5 hours.

8. The preparation method according to claim 1, characterized in that, The temperature of the second reaction is 70-80℃, and the reaction time is 0.5-1.5h.

9. The preparation method according to claim 1, characterized in that, The temperature of the third reaction is 100-110℃, and the reaction time is 1.5-2.5h.

10. The preparation method according to claim 1, characterized in that, The first heating rate and the second heating rate are each 3-5℃ / min independently.

11. The preparation method according to claim 1, characterized in that, The time ratio of the first reaction, the second reaction, and the third reaction is: first reaction time: second reaction time: third reaction time = 1:(1-2):(2-3).

12. The preparation method according to claim 1, characterized in that, The calcination temperature is 500-650℃, and the calcination time is 2-4h.

13. A type of iron phosphate material, characterized in that, The iron phosphate material is prepared by the preparation method described in any one of claims 1-12.

14. The application of the iron phosphate material as described in claim 13 in the preparation of cathode materials.

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