A type of spherical iron phosphate, its preparation method and application

Abstract

This invention discloses a spherical iron phosphate, its preparation method, and its applications, belonging to the field of iron phosphate preparation technology. The preparation method provided by this invention includes the following steps: mixing ferric sulfate and phosphoric acid in water and then carrying out a hydrothermal reaction; controlling the molar ratio of iron to phosphorus to be greater than 1; after the reaction, adding ammonium dihydrogen phosphate, ensuring that the total molar amount of ammonium dihydrogen phosphate and phosphoric acid is not less than the molar amount of iron, and then carrying out a hydrothermal reaction; after the reaction, sequentially washing, filtering, spray drying, and sintering to obtain the spherical iron phosphate. The spherical iron phosphate obtained using the preparation method of this invention has the characteristics of high tap density, narrow particle size distribution, high specific surface area, high crystallinity, and no severe agglomeration. Lithium iron phosphate materials prepared using this iron phosphate as a precursor can achieve high compaction, low sintering temperature, low powder resistivity, and high specific capacity.

Description

Technical Field

[0001] This invention relates to the field of ferric phosphate preparation technology, and in particular to a spherical ferric phosphate, its preparation method, and its application. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Lithium iron phosphate (LiFePO4) with an olivine structure is one of the cathode materials used in power lithium-ion batteries. Due to its advantages such as high safety, long cycle life, environmental friendliness, and low cost, LiFePO4 has become one of the most promising cathode materials in the lithium-ion battery industry. LiFePO4 prepared using iron phosphate as the iron source precursor, combined with lithium source compounds and additives, exhibits high electrochemical activity and tap density. Iron phosphate, as a precursor to LiFePO4, has advantages such as non-toxicity, low cost, and structural stability. Its physicochemical properties, to a certain extent, determine the overall performance of the final LiFePO4 product; therefore, it is necessary to prepare an iron phosphate material with good performance.

[0004] Currently, the commonly used processes for synthesizing iron phosphate are mainly divided into two types: one is the sodium co-precipitation process using ferrous sulfate, phosphoric acid, and liquid alkali as raw materials, and the other is the ammonium co-precipitation process using ferrous sulfate and ammonium dihydrogen phosphate as raw materials. Both processes produce iron phosphate with problems such as low tap density, low reactivity as a precursor, poor crystallinity, severe agglomeration, and excessively wide particle size distribution. Patent CN115231539A proposes a wet process for preparing iron phosphate, using ferric chloride and ammonium dihydrogen phosphate as raw materials. This improves upon the traditional wet process's need for pH adjustment and reaction rate control, but it still does not address the key characteristics of iron phosphate that affect lithium iron phosphate synthesis.

[0005] Therefore, how to provide a method for preparing ferric phosphate to reduce its agglomeration, increase its specific surface area to make it more reactive, and improve its crystallinity to improve the overall electrical properties of the finished ferric phosphate is an urgent problem to be solved. Summary of the Invention

[0006] In view of this, the present invention provides a spherical iron phosphate, its preparation method and application. The iron phosphate obtained by the preparation method of the present invention has a spherical morphology, high tap density, narrow particle size distribution, high specific surface area, high crystallinity and no serious agglomeration. The lithium iron phosphate material prepared by using this iron phosphate as a precursor can achieve the effects of high compaction, low sintering temperature, low powder resistivity and high specific capacity.

[0007] In a first aspect, the present invention provides a method for preparing spherical iron phosphate, comprising the following steps:

[0008] S1. Mix ferric sulfate and phosphoric acid in water and carry out a hydrothermal reaction; control the molar ratio of iron to phosphorus to be greater than 1;

[0009] S2. After the reaction in step S1 is completed, add ammonium dihydrogen phosphate to ensure that the total molar amount of ammonium dihydrogen phosphate and phosphoric acid is not less than the molar amount of iron, and then carry out a hydrothermal reaction.

[0010] After the reactions in steps S3 and S2 are completed, the mixture is washed, filtered, spray-dried, and sintered in sequence to obtain spherical iron phosphate.

[0011] Preferably, in step S1, the molar ratio of iron to phosphorus is 1:(0.52-0.6); and the molar ratio of ammonium dihydrogen phosphate in step S2 to phosphoric acid in step S1 is 1:(0.8-1.1).

[0012] Preferably, the ferric sulfate mentioned in step S1 is obtained by oxidizing ferrous sulfate with an oxidizing agent.

[0013] Furthermore, the oxidant is selected from one or more of hydrogen peroxide, ozone, oxygen, sodium peroxide, potassium persulfate, or ammonium persulfate.

[0014] Furthermore, the ferrous sulfate is obtained by removing impurities from ferrous sulfate, a byproduct of titanium dioxide production, using a purification agent; the purification agent is selected from one or more of Na2S, (NH4)2S, or BaS.

[0015] Preferably, the hydrothermal reaction temperature in steps S1 and S2 is 140–200°C, and the reaction time is 1–5 h.

[0016] Preferably, the hydrothermal reaction in step S1 also contains a surfactant, and the amount of the surfactant added is 0.03 to 0.06 wt%.

[0017] Furthermore, the surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dioctyl succinate sulfonate, sodium dodecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate, or sodium stearate.

[0018] Preferably, the feed rate of the spray dryer is 3-8 L / h, the inlet temperature is 220-250℃, and the outlet temperature is 110-120℃.

[0019] Preferably, the sintering step S3 specifically involves heating to 450–550°C at a heating rate of 3–8°C / min and holding at that temperature for 2–6 hours.

[0020] Secondly, the present invention provides spherical iron phosphate prepared by the above preparation method.

[0021] Thirdly, the present invention provides an application of the aforementioned spherical iron phosphate, wherein the spherical iron phosphate is used to prepare lithium iron phosphate cathode materials.

[0022] Compared with the prior art, the present invention has achieved the following beneficial effects:

[0023] (1) This invention uses a two-stage hydrothermal reaction (high-pressure liquid phase method) to prepare iron phosphate dihydrate material. The hydrothermal reaction itself can make the raw materials more uniformly dispersed during the precipitation process and the precipitation reaction temperature is higher, which improves the purity and precipitation efficiency of the product iron phosphate. In addition, this invention adds two different phosphorus sources (phosphoric acid and ammonium dihydrogen phosphate) to the two stages of hydrothermal reaction respectively, so that the subsequent precipitation can be wrapped and precipitated on the existing iron phosphate crystals. On the basis of further improving the compactness of the crystallized product, more mesoporous voids can be retained, which is macroscopically manifested as an increase in specific surface area, which is beneficial to improving the reactivity of the final product anhydrous iron phosphate.

[0024] (2) The present invention uses spray drying + sintering to remove the water of crystallization in ferric phosphate dihydrate. Spray drying can further shrink the large voids inside the precipitate to increase the tap density. At the same time, the morphology of the spherical aggregated ferric phosphate obtained is conducive to the increase of tap density. It can also shorten the time required for subsequent sintering to remove the water of crystallization, and make the anhydrous ferric phosphate after sintering more crystalline.

[0025] (3) The iron phosphate material prepared by the present invention has the characteristics of high tap density, narrow particle size distribution, high specific surface area, high crystallinity and no serious agglomeration. The lithium iron phosphate material prepared by using this iron phosphate as a precursor can achieve the effects of high tap density, low sintering temperature, low powder resistance and high specific capacity. Attached Figure Description

[0026] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation thereof. Obviously, those skilled in the art can obtain other drawings based on these drawings without any inventive effort.

[0027] Figure 1 This is a scanning electron microscope image of the spherical anhydrous iron phosphate material prepared in Example 1 of the present invention, with a magnification of 2k.

[0028] Figure 2 This is a scanning electron microscope image of the spherical anhydrous iron phosphate material prepared in Example 1 of the present invention, with a magnification of 100k.

[0029] Figure 3This is a particle size distribution diagram of the spherical anhydrous iron phosphate material prepared in Example 1 of the present invention. Detailed Implementation

[0030] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0031] In a first aspect, the present invention provides a method for preparing spherical iron phosphate, comprising the following steps:

[0032] S1. Mix ferric sulfate and phosphoric acid in water and carry out a hydrothermal reaction; control the molar ratio of iron to phosphorus to be greater than 1;

[0033] S2. After the reaction in step S1 is completed, add ammonium dihydrogen phosphate to ensure that the total molar amount of ammonium dihydrogen phosphate and phosphoric acid is not less than the molar amount of iron, and then carry out a hydrothermal reaction.

[0034] After the reactions in steps S3 and S2 are completed, the mixture is washed, filtered, spray-dried, and sintered in sequence to obtain spherical iron phosphate.

[0035] This invention employs a two-stage hydrothermal reaction (high-pressure liquid phase method) to prepare ferric phosphate dihydrate. The hydrothermal reaction allows for more uniform dispersion of the raw materials during precipitation, and a higher reaction temperature, thus improving the purity and precipitation efficiency of the ferric phosphate product. Simultaneously, this invention adds two different phosphorus sources in the two stages of the hydrothermal reaction to adjust the concentration of the reactants, ensuring that the growth rate of the precipitate crystals is slightly higher than the nucleation rate, thereby increasing the compactness of the crystallized product. Phosphoric acid is added first to maintain the pH of the precipitation system at around 2-3, at which lower pH conditions facilitate the formation of spherical ferric phosphate precipitates. The subsequent addition of ammonium dihydrogen phosphate for the second stage reaction increases the pH of the system to a certain extent, accelerating the precipitation rate. This allows subsequent precipitates to encapsulate the existing spherical ferric phosphate crystals, further improving the compactness of the crystallized product while retaining more mesoporous voids, resulting in a larger specific surface area and thus enhancing the reactivity of the final product, anhydrous ferric phosphate. Because the synthesis of lithium iron phosphate follows the shrinking core reaction kinetic model, molten lithium salt forms a lithium iron phosphate product layer on the surface of iron phosphate. As the reaction proceeds, the reaction interface between the iron phosphate (core phase) and lithium iron phosphate (shell phase) phases moves inward, and the core phase gradually shrinks until it is completely converted into lithium iron phosphate. Therefore, the existence of mesoporous pores can promote the penetration and diffusion of reactants, increase the rate of shrinking reaction, and thus increase the reaction activity.

[0036] Ferric phosphate dihydrate can be prepared after two stages of hydrothermal reaction. This invention uses spray drying and sintering to remove the water of crystallization in ferric phosphate dihydrate. Spray drying can further shrink the large voids inside the precipitate to increase the tap density. At the same time, the morphology of the resulting spherical aggregated ferric phosphate, i.e., quasi-spherical ferric phosphate, is conducive to increasing the tap density. It can also shorten the time required for subsequent sintering to remove the water of crystallization, resulting in higher crystallinity of the anhydrous ferric phosphate after sintering.

[0037] In step S1 of this invention, the molar ratio of iron to phosphorus is preferably 1:(0.52-0.6), and the molar ratio of ammonium dihydrogen phosphate in step S2 to phosphoric acid in step S1 is preferably 1:(0.8-1.1), most preferably 1:1. This invention divides the phosphorus source into two parts, adding them in two stages to react with ferric sulfate to generate ferric phosphate dihydrate.

[0038] In this invention, the ferric sulfate mentioned in step S1 is obtained by oxidizing ferrous sulfate with an oxidizing agent, wherein the oxidizing agent is selected from one or more of hydrogen peroxide, ozone, oxygen, sodium peroxide, potassium persulfate, or ammonium persulfate. This invention does not impose special limitations on the mixing method of ferric sulfate and phosphoric acid in water; any mixing method commonly used in the art is acceptable. Preferably, this invention involves adding phosphoric acid to the ferric sulfate aqueous solution and stirring to mix. This invention does not impose special limitations on the concentration of the ferric sulfate aqueous solution; any concentration of ferric sulfate aqueous solution commonly used in hydrothermal reactions in the art is acceptable. Preferably, this invention uses Fe... 3+ The concentration is 0.5–1 mol / L.

[0039] In this invention, the ferrous sulfate is obtained by removing impurities from ferrous sulfate, a byproduct of titanium dioxide production, using a purification agent. The purification agent is selected from one or more of Na₂S, (NH₄)₂S, or BaS, and can remove copper ion impurities and other metal ion impurities that can form sulfides. Using ferrous sulfate, a byproduct of titanium dioxide production, as the raw material for ferrous sulfate can significantly reduce the preparation cost. This invention does not impose special limitations on the purification process; any purification process for ferrous sulfate, a byproduct of titanium dioxide production, commonly used by those skilled in the art can be employed.

[0040] In this invention, the hydrothermal reaction temperature in steps S1 and S2 is 140–200°C, more preferably 140–160°C; the reaction time is 1–5 h, more preferably 1–2 h.

[0041] In this invention, the hydrothermal reaction in step S1 also contains a surfactant, the amount of which is 0.03–0.06 wt%, meaning that the mass fraction of sodium dodecylbenzenesulfonate relative to the total mass of sodium dodecylbenzenesulfonate, phosphoric acid, ferric sulfate, and water is 0.03–0.06 wt%. The presence of the surfactant can regulate the morphology of ferric phosphate, promoting the formation of flower-like spherical ferric phosphate precipitates. In this invention, the surfactant is preferably an anionic surfactant, specifically selected from one or more of sodium dodecylbenzenesulfonate, sodium dioctyl succinate sulfonate, sodium dodecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate, or sodium stearate.

[0042] This invention does not impose special limitations on the washing and filtering steps in step S3; commonly used washing and filtering steps in the art can be used. After filtration, the filter cake is retained, and then water is added to form a slurry for use in the subsequent spray drying process.

[0043] In this invention, the feed rate of the spray dryer is 3–8 L / h, the inlet temperature is 220–250°C, and the outlet temperature is 110–120°C. This invention does not impose any special limitations on the specific steps and equipment used in the spray drying process.

[0044] In this invention, the sintering step S3 specifically involves heating to 450-550°C at a heating rate of 3-8°C / min and holding for sintering for 2-6 hours.

[0045] This invention also provides spherical iron phosphate prepared by the above method, wherein the resulting spherical iron phosphate D50 particles have a particle size between 8 and 9 μm and a specific surface area of ​​17.5 m². 2 Above / g, tap density is 0.8g / cm³ 3 above.

[0046] This invention also provides an application of the aforementioned spherical iron phosphate, wherein the spherical iron phosphate is used to prepare lithium iron phosphate cathode materials. This invention does not impose any particular limitation on the method for preparing lithium iron phosphate using iron phosphate; commonly used methods in the art can be employed.

[0047] The technical solution of the present invention will be further described below with reference to specific embodiments. The term "room temperature" as used below refers to 25±3℃.

[0048] In the following examples, the preparation process of the ferrous sulfate solution is as follows: Deionized water is added to ferrous sulfate (a byproduct of titanium dioxide production) to prepare a crude ferrous sulfate solution. Sufficient Na₂S is then added, and the solution is stirred at 30 r / min for 25 min at room temperature using a magnetic stirrer. After stirring, the solution is allowed to stand for 30 min, and impurities are removed by filtration to obtain a pure ferrous sulfate solution. The Fe content in the solution is then determined using a potentiometric titrator. 2+The content was measured, and hydrogen peroxide was continuously added to the solution until it was completely oxidized to Fe. 3+ Finally, a 0.8 mol / L ferric sulfate solution was obtained.

[0049] Example 1

[0050] This embodiment provides a method for preparing spherical iron phosphate.

[0051] (1) Add an appropriate amount of phosphoric acid to the ferric sulfate solution, control the molar ratio of Fe to P to be 1:0.55, and add 0.04wt% sodium dodecylbenzenesulfonate (relative to the total mass of sodium dodecylbenzenesulfonate, phosphoric acid, ferric sulfate and water). Stir evenly on a magnetic stirrer at a speed of 20r / min, and then transfer it to a high-pressure reactor for hydrothermal reaction at 150℃ for 1.5h to obtain mixture A;

[0052] (2) After the reaction in step (1) is completed, add ammonium dihydrogen phosphate in the same amount as phosphoric acid to mixture A, continue the hydrothermal reaction for 1 hour to obtain mixture B, let it stand at room temperature for 25 minutes, wash and filter mixture B with deionized water four times, and retain the filter cake.

[0053] (3) The filter cake obtained in step (2) is mixed with deionized water to form a slurry, and the slurry is pumped into a spray drying furnace with a feed rate of 5L / h, an inlet temperature of 240℃, and an outlet temperature of 115℃. Then, the light yellow powder obtained from spray drying is collected by cyclone, sieved, and transferred to a high-temperature kiln. Compressed air is introduced, and the mixture is sintered at 500℃ for 1.5h. The heating rate of the high-temperature kiln is 5℃ / min to obtain a spherical anhydrous iron phosphate material.

[0054] Figure 1 and Figure 2 These are scanning electron microscope images of the spherical anhydrous iron phosphate material prepared in this embodiment. Figure 3 The figure shows the particle size distribution of the spherical anhydrous iron phosphate material prepared in this embodiment. As can be seen from the figure, the morphology of the obtained iron phosphate material is spherical aggregate, without excessive agglomeration and with a narrow particle size distribution.

[0055] Example 2

[0056] The difference between this embodiment and embodiment 1 is that in step (1), the molar ratio of Fe to P is controlled to be 1:0.6.

[0057] Example 3

[0058] The difference between this embodiment and embodiment 1 is that in step (1), the molar ratio of Fe to P is controlled to be 1:0.52.

[0059] Example 4

[0060] The difference between this embodiment and embodiment 1 is that sodium dioctyl succinate sulfonate is used instead of sodium dodecylbenzene sulfonate in step (2).

[0061] Comparative Example 1

[0062] This comparative example uses a sodium co-precipitation process to prepare ferric phosphate. The specific steps are as follows:

[0063] Add an appropriate amount of phosphoric acid to the ferric sulfate solution, controlling the molar ratio of Fe to P to be 1:1.3. Stir the solution evenly on a magnetic stirrer at a speed of 20 r / min to convert it into a ferric phosphate solution with a pH of 1.8-2. Add liquid alkali (30 wt% sodium hydroxide solution) to precipitate the ferric phosphate. After aging at 85℃, the ferric phosphate precipitate is obtained. After standing and separating into layers, it is filtered while hot. The filter residue is the product ferric phosphate. After drying in an oven at 100℃, it is ground to obtain a white to yellowish powdery ferric phosphate dihydrate product. The ferric phosphate dihydrate is placed in a quartz boat and calcined at 500℃ for 3 hours in an air atmosphere to obtain anhydrous ferric phosphate material.

[0064] Comparative Example 2

[0065] The difference between this comparative example and Example 1 is that this comparative example only underwent one high-temperature liquid-phase reaction, and the phosphorus source was only phosphoric acid. The specific steps are as follows:

[0066] (1) Add an appropriate amount of phosphoric acid to the ferric sulfate solution, control the molar ratio of Fe to P to be 1:1.1, and add 0.04 wt% sodium dodecylbenzenesulfonate (relative to the total mass of sodium dodecylbenzenesulfonate, phosphoric acid, ferric sulfate and water). Stir evenly on a magnetic stirrer at a speed of 20 r / min, and then transfer it to a high-pressure reactor for hydrothermal reaction at 150℃ for 2.5 h to obtain mixture A. Wash and filter mixture A with deionized water four times, and retain the filter cake.

[0067] (3) The filter cake obtained in step (2) is mixed with deionized water to form a slurry, and the slurry is pumped into a spray drying furnace with a feed rate of 5L / h, an inlet temperature of 240℃, and an outlet temperature of 115℃. Then, the light yellow powder obtained from spray drying is collected by cyclone, sieved, and transferred to a high-temperature kiln. Compressed air is introduced, and the mixture is sintered at 500℃ for 1.5h. The heating rate of the high-temperature kiln is 5℃ / min to obtain anhydrous iron phosphate material.

[0068] Comparative Example 3

[0069] The difference between this comparative example and Example 1 is that this comparative example does not include the spray drying step. Step (3) of this comparative example is as follows:

[0070] (3) After drying the filter cake obtained in step (2) in an oven at 100°C, grind it to obtain a white-yellow powdered iron phosphate dihydrate product. Then, transfer the dried iron phosphate dihydrate powder into a high-temperature kiln, introduce compressed air, and sinter at 500°C for 1.5 hours. The heating rate of the high-temperature kiln is 5°C / min to obtain anhydrous iron phosphate material.

[0071] Comparative Example 4

[0072] The difference between this comparative example and Example 1 is that ammonium dihydrogen phosphate and phosphoric acid were added simultaneously. The specific steps are as follows:

[0073] (1) Add appropriate amounts of phosphoric acid and ammonium dihydrogen phosphate to the ferric sulfate solution, controlling the molar ratio of Fe to P to be 1:1.1 and the molar ratio of phosphoric acid to ammonium dihydrogen phosphate to be 1:1; at the same time, add 0.04wt% sodium dodecylbenzenesulfonate (relative to the total mass of sodium dodecylbenzenesulfonate, phosphoric acid, ferric sulfate and water), stir evenly on a magnetic stirrer at a speed of 20r / min, and then transfer it to a high-pressure reactor for hydrothermal reaction at 150℃ for 1.5h to obtain mixture A; after standing at room temperature for 25min, wash and filter mixture A four times with deionized water, and retain the filter cake;

[0074] (2) The filter cake obtained in step (1) is mixed with deionized water to form a slurry, and the slurry is pumped into a spray drying furnace with a feed rate of 5L / h, an inlet temperature of 240℃, and an outlet temperature of 115℃. Then, the light yellow powder obtained from spray drying is collected by cyclone, sieved, and transferred to a high-temperature kiln. Compressed air is introduced, and the mixture is sintered at 500℃ for 1.5h. The heating rate of the high-temperature kiln is 5℃ / min to obtain anhydrous iron phosphate material.

[0075] Test case

[0076] 1. Preparation of lithium iron phosphate cathode material:

[0077] The iron phosphate prepared in Examples 1-4 or Comparative Examples 1-4 was mixed with lithium carbonate, glucose, and PEG4000 to form a slurry, which was then ground uniformly to obtain a precursor slurry. The molar ratio of iron phosphate to lithium carbonate was 1.05:0.5, glucose accounted for 9 wt% of the total powder, and PEG4000 accounted for 2 wt% of the total powder. After spray drying and air jet milling, the mixture was transferred to a roller kiln and sintered at 500°C for 5 h under a nitrogen atmosphere, followed by sintering at 640°C for 14 h. After demagnetization and sieving, lithium iron phosphate cathode material (LFP) was obtained.

[0078] The properties of the iron phosphate and lithium iron phosphate materials prepared in Examples 1-4 and Comparative Examples 1-4 were measured, and the test results are shown in Table 1.

[0079] Table 1. Performance test results of iron phosphate and lithium iron phosphate in the examples and comparative examples.

[0080]

[0081] As shown in Table 1, compared with Comparative Example 1, the spherical iron phosphate prepared in the Examples has a higher specific surface area, resulting in higher reactivity in the subsequent synthesis of lithium iron phosphate. This leads to more uniform diffusion of the lithium source in the iron phosphate crystal phase. Without sacrificing specific surface area, the Examples also exhibit higher tap density, resulting in better compaction performance of the synthesized lithium iron phosphate compared to that synthesized in Comparative Example 1. Furthermore, the lithium iron phosphate powder obtained from the Examples has lower resistivity, further demonstrating the high reactivity of the precursor. + The diffusion is more uniform, resulting in higher purity of the lithium iron phosphate phase, thus reducing the powder resistance. In addition, the iron phosphate in the example undergoes a hot spray and sintering process, which makes its crystallinity higher and further reduces the powder resistance of the prepared lithium iron phosphate.

[0082] Compared to Comparative Examples 2 and 4, the lithium iron phosphate in this example, due to the use of a two-stage high-pressure liquid phase method and two phosphorus sources with different functions, has a larger specific surface area and higher tap density, resulting in higher compaction and lower powder resistivity of the subsequently produced lithium iron phosphate. Compared to Comparative Example 3, the lithium iron phosphate in this example has a higher tap density and higher crystallinity, thus producing lithium iron phosphate powder with lower resistivity.

[0083] 2. Button Battery Preparation: Conductive carbon black was added to an N-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF), followed by lithium iron phosphate cathode material (lithium iron phosphate, PVDF, and conductive carbon black in a mass ratio of 90:5:5) prepared using iron phosphate as a precursor in the examples or comparative examples. The mixture was stirred until homogeneous, and the slurry was evenly coated onto aluminum foil using a coating machine to form an electrode sheet. The coated electrode sheet was placed in a vacuum drying oven at 120°C and vacuum dried for 6 hours. The electrode sheet was then removed and rolled on a roller press for later use. Button batteries were assembled in a glove box under an argon atmosphere. The electrolyte was a mixture of ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) containing 1M LiPF6 (EC, DEC, and DMC in a volume ratio of 1:1:1). A lithium metal sheet was used as the counter electrode. Capacity testing was conducted on an Arbin BT2000 battery tester in the United States, with a charge / discharge voltage range of 2 to 3.75V and charge / discharge rates of 0.1C, 0.5C, and 1C, respectively. The results are shown in Table 2.

[0084] Table 2. Electrical performance of button batteries assembled from lithium iron phosphate prepared by the examples and comparative examples.

[0085]

[0086] Note: The 3.1V & 1C capacity ratio refers to the coin cell capacity utilized when discharged at a 1C rate to 3.1V.

[0087] The lithium iron phosphate prepared in the example has higher reactivity and crystallinity, resulting in higher specific capacity at various discharge rates. Its overall electrical performance is superior to that of the lithium iron phosphate prepared in the comparative example.

[0088] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing spherical iron phosphate, characterized in that, Includes the following steps: S1. Mix ferric sulfate and phosphoric acid in water and carry out a hydrothermal reaction; control the molar ratio of iron to phosphorus to be 1:(0.52~0.6); S2. After the reaction in step S1 is completed, add ammonium dihydrogen phosphate so that the total molar amount of ammonium dihydrogen phosphate and phosphoric acid is not less than the molar amount of iron. The molar ratio of ammonium dihydrogen phosphate to phosphoric acid is 1:(0.8~1.1). Then carry out the hydrothermal reaction. After the S3 and S2 reactions are completed, the mixture is washed, filtered, spray-dried, and sintered in sequence to obtain spherical iron phosphate. The hydrothermal reaction temperature in steps S1 and S2 is 140~200℃, and the reaction time is 1~5h; the feed rate of the spray drying is 3~8L / h, the inlet temperature is 220~250℃, and the outlet temperature is 110~120℃; the sintering step in step S3 is specifically as follows: the temperature is raised to 450~550℃ at a heating rate of 3~8℃ / min, and sintered at that temperature for 2~6h.

2. The preparation method according to claim 1, characterized in that, The ferric sulfate mentioned in step S1 is obtained by oxidizing ferrous sulfate with an oxidizing agent; the oxidizing agent is selected from one or more of hydrogen peroxide, ozone, oxygen, sodium peroxide, potassium persulfate or ammonium persulfate.

3. The preparation method according to claim 2, characterized in that, The ferrous sulfate is obtained by removing impurities from ferrous sulfate, a byproduct of titanium dioxide production, using a purification agent; the purification agent is selected from one or more of Na2S, (NH4)2S, or BaS.

4. The preparation method according to claim 1, characterized in that, The hydrothermal reaction in step S1 also contains a surfactant, and the amount of the surfactant added is 0.03~0.06wt%.

5. The preparation method according to claim 4, characterized in that, The surfactant is selected from one or more of sodium dodecylbenzenesulfonate, sodium dioctyl succinate sulfonate, sodium dodecyl sulfate, sodium hexadecyl sulfate, sodium octadecyl sulfate, or sodium stearate.

6. The spherical iron phosphate prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the near-spherical iron phosphate as described in claim 6, characterized in that, The aforementioned spherical iron phosphate was used to prepare lithium iron phosphate cathode materials.

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