Preparation of Lithium Iron Phosphate Nanospheres

Abstract

This invention relates to the preparation of lithium iron phosphate nanospheres. First, an FePO4 precursor is prepared using an iron and phosphorus source. Then, cerium sulfate and europium sulfate are added to Li3PO4 in a 1:1 doping ratio to prepare modified Li3PO4. Furthermore, a cationic surfactant, octadecyl dimethyl benzyl ammonium chloride, is added during the reaction of the FePO4 precursor and the modified Li3PO4. This invention utilizes modified Li3PO4 and the addition of the cationic surfactant octadecyl dimethyl benzyl ammonium chloride to achieve a better spherical shape in lithium iron phosphate. The addition of the surfactant has a significant impact on the particle size and morphology of iron phosphate, reducing particle aggregation and controlling particle growth. Modification of Li3PO4 with cerium sulfate and europium sulfate alters the interatomic spacing and positions within the crystal, causing cell shrinkage and changing the internal structure of the crystal, thus affecting the external morphology of iron phosphate. Doping with metal ions effectively increases the tap density of the material, thereby improving the volumetric capacity and cycle performance of lithium iron phosphate.

Description

Technical Field

[0001] This invention relates to the preparation of nanospheres, specifically lithium iron phosphate nanospheres, and particularly to the preparation of lithium iron phosphate nanospheres. Background Technology

[0002] In recent years, due to its advantages such as being pollution-free, having high energy density, and exhibiting good cycle stability, lithium-ion batteries, as a rechargeable energy storage system, have been considered a potential alternative to fossil fuels, alleviating increasingly prominent environmental and energy problems. Electrode materials, as a crucial component of lithium-ion batteries, are extremely important to select, as good electrode materials hold great promise for improving battery performance. Therefore, to ensure the excellent performance of lithium-ion batteries, high-performance electrode materials should be chosen.

[0003] Since 1997, LiFePO4 (lithium iron phosphate), a cathode material with advantages such as high theoretical capacity, good safety, long cycle life, and low cost, has attracted much attention. The charge-discharge process shows that the product of complete delithiation after charging is the iron phosphate phase. Due to its low cost and high chemical stability, FePO4, as a source of trivalent iron, is considered an ideal material for synthesizing lithium iron phosphate. The structure, morphology, and particle size distribution of iron phosphate all affect the performance of lithium iron phosphate. By controlling the crystal size and morphology of the iron phosphate precursor, it is possible to achieve large-scale production of LiFePO4 with high tap density, high discharge rate, and high capacity, overcoming the limitation of LiFePO4's ionic conductivity to a certain extent, thus enabling various high-efficiency applications in later stages. Therefore, as an important precursor for lithium iron phosphate, a cathode material for lithium-ion batteries, preparing iron phosphate precursors with good morphology, particle size, and other properties is the first and most crucial step. Summary of the Invention

[0004] To address the above problems, this invention incorporates a surfactant during the preparation of the FePO4 precursor, causing the iron phosphate to form a near-spherical shape. Furthermore, cerium sulfate and europium sulfate are used to modify Li3PO4. The modified Li3PO4 reacts with FePO4 to generate lithium iron phosphate, which alters the internal structure of the crystal and significantly improves the charge-discharge performance and other properties of lithium iron phosphate. The preparation process of this invention is simple and convenient. The modified FePO4 precursor obtained by this invention, along with the use of modified Li3PO4, further enhances the charge-discharge performance of lithium iron phosphate. The specific preparation steps are as follows:

[0005] Preparation of S1 and FePO4 precursors: (NH4)2Fe(SO4)2·6H2O and NH4H2PO4 in a molar ratio of 1:1 were dissolved in 500 mL of deionized water. The NH4H2PO4 solution was slowly added to the (NH4)2Fe(SO4)2·6H2O solution using a peristaltic pump. The mixture was stirred at 10℃~20℃ to form a homogeneous colloidal solution. Then, 1 mL~5 mL of 30% H2O2 solution was added dropwise as an oxidant to the colloidal solution. The solution was stirred for another 1 h~2 h to form a pale yellow FePO4·3H2O precipitate.

[0006] S2. Collect the precipitate in S1 by centrifugation, wash it repeatedly with deionized water, and dry the final product in a drying oven at 60℃~80℃ for 10h~12h. Place the FePO4·3H2O precursor in a muffle furnace and calcine it at 675℃~825℃ to obtain the iron source.

[0007] S3. Add cerium sulfate and europium sulfate in a 1:1 doping ratio to Li3PO4, stir evenly, and then transfer the mixed solution into a reaction vessel. React for 1 to 2 hours to obtain modified Li3PO4. The synergistic effect between cerium ions and europium ions makes the nanospheres exhibit a better spherical morphology. This morphology increases the contact area between the particles and the electrolyte, thereby significantly improving the electrical properties of the material.

[0008] S4. Take the iron source obtained in S2 and the modified Li3PO4 obtained in S3 at a mass ratio of 1:1.5, dissolve them in deionized water, stir evenly, and then add the cationic surfactant octadecyl dimethyl benzyl ammonium chloride. The amount of octadecyl dimethyl benzyl chloride added is 2.5% to 3.5% of the mass of the iron source. Then put it into a reaction vessel for hydrothermal reaction at pH 1.45, reaction temperature of 100℃ to 120℃, and reaction time of 4h to 6h. Collect the solid powder in the reaction vessel, filter it, and vacuum dry it at 50℃ to 80℃ for 2h to 3h. The FePO4 precursor is modified with the cationic surfactant octadecyl dimethyl benzyl chloride. The use of the cationic surfactant octadecyl dimethyl benzyl chloride, which has the effect of dispersing particles, can achieve effective control of particle size and morphology.

[0009] S5. Place the dried solid powder from S4 into a tube furnace and calcine it at 525℃~625℃ for 10h~16h under argon protection. Then cool it to room temperature to obtain the LiFePO4 product.

[0010] Preferably, the solution used in step S1 is 0.02 mol of (NH4)2Fe(SO4)2·6H2O and NH4H2PO4.

[0011] Preferably, the product in step S2 is dried in an 80°C drying oven for 12 hours.

[0012] Preferably, in step S3, the mixed solution is transferred into a reaction vessel and reacted for 1.5 hours.

[0013] Preferably, the amount of octadecyl dimethyl benzyl ammonium chloride added in step S4 is 3.0% of the mass of the iron source.

[0014] Preferably, in step S5, the furnace is calcined in a tube furnace at 625°C for 16 hours.

[0015] Preferably, the (NH4)2Fe(SO4)2·6H2O and NH4H2PO4 described in this invention were purchased from Henan Hancheng Environmental Protection Technology Co., Ltd.

[0016] Preferably, the cerium sulfate and europium sulfate used in this invention were purchased from Hubei Baidu Chemical Co., Ltd.

[0017] Preferably, the octadecyl dimethyl benzyl ammonium chloride of the present invention was purchased from Hubei Chengfeng Chemical Co., Ltd.

[0018] The beneficial effects of this invention are as follows:

[0019] 1. This invention relates to lithium iron phosphate nanospheres, in which the FePO4 precursor is modified with the cationic surfactant octadecyl dimethyl benzyl ammonium chloride. The use of octadecyl dimethyl benzyl ammonium chloride, a cationic surfactant with particle-dispersing properties, allows for effective control of particle size and morphology. Therefore, adding a small amount of surfactant as a dispersant can prevent or reduce particle agglomeration during the synthesis of iron phosphate particles, thereby obtaining powders with better morphology and uniform particle size, thus improving the tap density.

[0020] 2. This invention utilizes modified Li3PO4. The reaction between modified Li3PO4 and FePO4 can significantly improve the charge-discharge performance and other properties of lithium iron phosphate. Cerium and europium ions are typically embedded in the iron phosphate lattice, causing corresponding changes in the interatomic spacing and positions within the crystal, leading to cell shrinkage and altering the internal structure of the crystal, thus affecting the external morphology of iron phosphate. Doping with metal ions can effectively increase the tap density of the material, thereby improving the volumetric capacity and cycle performance of lithium iron phosphate. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a 10μm magnified SEM image of lithium iron phosphate without added surfactant according to the present invention.

[0023] Figure 2 This is a 10μm magnified SEM image of lithium iron phosphate with the addition of the cationic surfactant octadecyl dimethyl benzyl ammonium chloride according to the present invention.

[0024] Figure 3 This describes the effect of adding different iron source masses of octadecyl dimethyl benzyl ammonium chloride on the specific surface area of ​​nanospheres in Example 2 and Comparative Examples 2-5 of this invention.

[0025] Figure 4 This is a 5μm magnification SEM image of cerium sulfate and europium sulfate added in a 1:1 doping ratio according to the present invention.

[0026] Figure 5 This is a 5μm magnification SEM image of the cerium sulfate added in this invention.

[0027] Figure 6 This is a SEM image of europium sulfate added according to the present invention, magnified at 5 μm. Detailed Implementation

[0028] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the content of this invention and are not intended to limit this invention.

[0029] Example 1

[0030] Preparation of S1 and FePO4 precursor: (NH4)2Fe(SO4)2·6H2O and NH4H2PO4 (Henan Hancheng Environmental Protection Technology Co., Ltd.) with a molar ratio of 1:1 were dissolved in 500 mL of deionized water respectively. The NH4H2PO4 solution was slowly added to the (NH4)2Fe(SO4)2·6H2O solution using a peristaltic pump. The solution was stirred at 10 °C to form a uniform colloidal solution. Then, 3 mL of 30% H2O2 solution was added dropwise to the colloidal solution as an oxidant. The solution was stirred for another 2 h to form a pale yellow FePO4·3H2O precipitate.

[0031] S2. Collect the precipitate in S1 by centrifugation, wash it repeatedly with deionized water, and dry the final product in an 80℃ drying oven for 12h. Place the FePO4·3H2O precursor in a muffle furnace and calcine it at 725℃.

[0032] S3. Add cerium sulfate and europium sulfate (Hubei Baidu Chemical Co., Ltd.) in a doping ratio of 1:1 to Li3PO4, stir evenly, transfer the mixed solution into a reaction vessel, and react for 2 hours to obtain modified Li3PO4.

[0033] S4. Take the iron source obtained from S2 and the modified Li3PO4 obtained from S3 at a mass ratio of 1:1.5 and dissolve them in deionized water. Stir well and then add the cationic surfactant octadecyl dimethyl benzyl ammonium chloride (Hubei Chengfeng Chemical Co., Ltd.). The amount of octadecyl dimethyl benzyl ammonium chloride added is 3.0% of the mass of the iron source. Then put it into a reaction vessel for hydrothermal reaction at pH 1.45, reaction temperature 120℃, and reaction time 6h. Collect the solid powder in the reaction vessel, filter it, and vacuum dry it at 80℃ for 3h.

[0034] S5. The dried solid powder from S4 is placed in a tube furnace and calcined at 625°C for 16 hours under argon protection. After cooling to room temperature, the LiFePO4 product is obtained.

[0035] Comparative Example 1 did not add a cationic surfactant in step S3, and all other steps were the same as in Example 1.

[0036] Figure 1 It is lithium iron phosphate without added surfactants. Its particle dispersibility is poor, and its morphology is flaky particles with uneven particle distribution. Figure 2 The lithium iron phosphate (LFP) with the addition of the cationic surfactant octadecyl dimethyl benzyl ammonium chloride exhibits a near-spherical morphology. The addition of the surfactant significantly affects the particle size and morphology of LFP, reducing particle agglomeration and controlling particle growth. Spherical LFP improves material flowability and electrode compaction density, thereby increasing the volumetric energy density of LFP. Spherical LFP also facilitates the formation of uniform carbon coating, contributing to improved conductivity of the cathode material. The contact between spherical LFP particles is point contact, thus requiring less adhesive for fixation. Therefore, it can be concluded that adding the cationic surfactant octadecyl dimethyl benzyl ammonium chloride results in LFP powder with better morphology and uniform particle size, thus improving tap density.

[0037] Example 2

[0038] Preparation of S1 and FePO4 precursors: (NH4)2Fe(SO4)2·6H2O and NH4H2PO4 (Henan Hancheng Environmental Protection Technology Co., Ltd.) with a molar ratio of 1:1 were dissolved in 500 mL of deionized water respectively. The NH4H2PO4 solution was slowly added to the (NH4)2Fe(SO4)2·6H2O solution using a peristaltic pump. The mixture was stirred at 10 °C to form a homogeneous colloidal solution. Then, 3 mL of 30% H2O2 solution was added dropwise to the colloidal solution as an oxidant. The solution was stirred for another 2 h to form a pale yellow FePO4·3H2O precipitate.

[0039] S2. Collect the precipitate in S1 by centrifugation, wash it repeatedly with deionized water, and dry the final product in an 80℃ drying oven for 12h. Place the FePO4·3H2O precursor in a muffle furnace and calcine it at 725℃.

[0040] S3. Add cerium sulfate and europium sulfate (Hubei Baidu Chemical Co., Ltd.) in a doping ratio of 1:1 to Li3PO4, stir evenly, transfer the mixed solution into a reaction vessel, and react for 2 hours to obtain modified Li3PO4.

[0041] S4. Take the iron source obtained from S2 and the modified Li3PO4 obtained from S3 at a mass ratio of 1:1.5 and dissolve them in deionized water. Stir well and then add the cationic surfactant octadecyl dimethyl benzyl ammonium chloride (Hubei Chengfeng Chemical Co., Ltd.). The amount of octadecyl dimethyl benzyl ammonium chloride added is 3.0% of the mass of the iron source. Then put it into a reaction vessel for hydrothermal reaction at pH 1.45, reaction temperature 120℃, and reaction time 6h. Collect the solid powder in the reaction vessel, filter it, and vacuum dry it at 80℃ for 3h.

[0042] S5. The dried solid powder from S4 is placed in a tube furnace and calcined at 625°C for 16 hours under argon protection. After cooling to room temperature, the LiFePO4 product is obtained.

[0043] Comparative Example 2 was identical to Example 2 except that 0.5% of the iron source mass of octadecyl dimethyl benzyl ammonium chloride was added in step S3.

[0044] Comparative Example 3 was identical to Example 2 except that 1.0% of the iron source mass of octadecyl dimethyl benzyl ammonium chloride was added in step S3.

[0045] Comparative Example 4 was identical to Example 2 except that 2.0% of the iron source mass of octadecyl dimethyl benzyl ammonium chloride was added in step S3.

[0046] Comparative Example 5 was identical to Example 2 except that 4.0% of the iron source mass of octadecyl dimethyl benzyl ammonium chloride was added in step S3.

[0047] Figure 3 This study investigates the effect of the amount of octadecyl dimethyl benzyl ammonium chloride additive on the relative surface area. The effect of the amount of octadecyl dimethyl benzyl ammonium chloride on the relative surface area initially increases and then decreases, reaching a maximum value of 84.35 m² when the amount is 3.0% of the iron source mass fraction. 2 / g. Using octadecyl dimethyl benzyl ammonium chloride, a cationic surfactant with particle-dispersing properties, allows for effective control of particle size and morphology. Adding 3.0% (by mass) of octadecyl dimethyl benzyl ammonium chloride to the iron source increases the contact area between the lithium iron phosphate material and the electrolyte, shortening the Li-24mm contact time. + The migration path within the primary particles of LiFePO4 is beneficial for increasing the specific capacity of LiFePO4.

[0048] Example 3

[0049] Preparation of S1 and FePO4 precursors: (NH4)2Fe(SO4)2·6H2O and NH4H2PO4 (Henan Hancheng Environmental Protection Technology Co., Ltd.) with a molar ratio of 1:1 were dissolved in 500 mL of deionized water respectively. The NH4H2PO4 solution was slowly added to the (NH4)2Fe(SO4)2·6H2O solution using a peristaltic pump. The mixture was stirred at 10 °C to form a homogeneous colloidal solution. Then, 3 mL of 30% H2O2 solution was added dropwise to the colloidal solution as an oxidant. The solution was stirred for another 2 h to form a pale yellow FePO4·3H2O precipitate.

[0050] S2. Collect the precipitate in S1 by centrifugation, wash it repeatedly with deionized water, and dry the final product in an 80℃ drying oven for 12h. Place the FePO4·3H2O precursor in a muffle furnace and calcine it at 725℃.

[0051] S3. Add cerium sulfate and europium sulfate (Hubei Baidu Chemical Co., Ltd.) in a doping ratio of 1:1 to Li3PO4, stir evenly, transfer the mixed solution into a reaction vessel, and react for 2 hours to obtain modified Li3PO4.

[0052] S4. Take the iron source obtained from S2 and the modified Li3PO4 obtained from S3 at a mass ratio of 1:1.5 and dissolve them in deionized water. Stir well and then add the cationic surfactant octadecyl dimethyl benzyl ammonium chloride (Hubei Chengfeng Chemical Co., Ltd.). The amount of octadecyl dimethyl benzyl ammonium chloride added is 3.0% of the mass of the iron source. Then put it into a reaction vessel for hydrothermal reaction at pH 1.45, reaction temperature 120℃, and reaction time 6h. Collect the solid powder in the reaction vessel, filter it, and vacuum dry it at 80℃ for 3h.

[0053] S5. The dried solid powder from S4 is placed in a tube furnace and calcined at 625°C for 16 hours under argon protection. After cooling to room temperature, the LiFePO4 product is obtained.

[0054] Comparative Example 6 is identical to Example 3 except that cerium sulfate is added in step S4.

[0055] Comparative Example 7 was identical to Example 3 except that europium sulfate was added in step S4.

[0056] Figure 4 The images show SEM images of lithium iron phosphate nanospheres with a doping ratio of 1:1 cerium sulfate and europium sulfate. Figure 4 Not only does it exhibit the best sphericity, but it also boasts the smoothest surface, with primary particles ranging from 100 to 200 nm. The small size of these primary lithium iron phosphate particles can be attributed to the relatively small primary particles of ferrous phosphate itself. During sintering, lithium iron phosphate crystals transform from ferrous phosphate crystals, thus the particle size of ferrous phosphate directly influences the particle size of lithium iron phosphate, accelerating the conduction of electrons and ions between particles. Figure 5 This is a SEM image of lithium iron phosphate nanospheres doped with cerium sulfate. As can be seen from the image, the surface of the nanospheres is not smooth. Figure 6 This is a SEM image of lithium iron phosphate nanospheres doped with europium sulfate. The surface area of ​​the nanospheres is compared to... Figure 5 Slightly smooth, but not as good as... Figure 4 The nanospheres are smooth. This is likely due to the synergistic effect between cerium and europium ions, which gives the lithium iron phosphate nanospheres a better spherical morphology. This morphology increases the contact area between the particles and the electrolyte, thereby significantly improving the electrical properties of the material.

Claims

1. A method for preparing lithium iron phosphate nanospheres, characterized in that: The specific steps are as follows: Preparation of S1 and FePO4 precursor: Dissolve (NH4)2Fe(SO4)2·6H2O and NH4H2PO4 in 500 mL of deionized water at a molar ratio of 1:

1. Slowly add the NH4H2PO4 solution to the (NH4)2Fe(SO4)2·6H2O solution using a peristaltic pump. Stir at 10℃~20℃ to form a homogeneous colloidal solution. Then, add 1 mL~5 mL of 30% H2O2 solution as an oxidant to the colloidal solution. Stir the solution for another 1 h~2 h to form a pale yellow FePO4·3H2O precipitate. S2. Collect the precipitate from S1 by centrifugation, wash repeatedly with deionized water, and dry the final product in a drying oven at 60℃~80℃ for 10h~12h. The precursor is placed in a muffle furnace and calcined at a temperature of 675℃~825℃ to obtain an iron source; S3. Add cerium sulfate and europium sulfate in a 1:1 doping ratio to Li3PO4, stir until homogeneous, transfer the mixed solution to a reaction vessel, and react for 1-2 hours to obtain modified Li3PO4; S4. Take the iron source obtained in S2 and the modified Li3PO4 obtained in S3 at a mass ratio of 1:1.5 and dissolve them in deionized water. Stir evenly and then add the cationic surfactant octadecyl dimethyl benzyl ammonium chloride. The amount of octadecyl dimethyl benzyl ammonium chloride added is 2.5%~3.5% of the mass of the iron source. Then put it into a reaction vessel for hydrothermal reaction. The pH is 1.45, the reaction temperature is 100℃~120℃, and the reaction time is 4h~6h. Collect the solid powder in the reaction vessel, filter it, and then vacuum dry it at 50℃~80℃ for 2h~3h. S5. Place the dried solid powder from S4 into a tube furnace and calcine it at 525℃~625℃ for 10h~16h under argon protection. Cool it to room temperature to obtain the LiFePO4 product.

2. The method for preparing lithium iron phosphate nanospheres according to claim 1, characterized in that: The step S1 uses 0.02 mol of (NH4)2Fe(SO4)2·6H2O and NH4H2PO4.

3. The method for preparing lithium iron phosphate nanospheres according to claim 1 or 2, characterized in that: In step S2, the product is dried in an 80°C drying oven for 12 hours.

4. The method for preparing lithium iron phosphate nanospheres according to claim 1 or 3, characterized in that: In step S3, the mixed solution is transferred into a reaction vessel and reacted for 1.5 hours.

5. A method for preparing lithium iron phosphate nanospheres according to claim 1 or 4, characterized in that: In step S4, the amount of octadecyl dimethyl benzyl ammonium chloride added is 3.0% of the iron source mass.

6. A method for preparing lithium iron phosphate nanospheres according to claim 1 or 5, characterized in that: In step S5, the sample is calcined in a tubular furnace at 625 °C for 16 hours.

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