A method for preparing lithium iron phosphate, a cathode material for new energy lithium batteries, using high-speed iron fly ash.

Abstract

The application relates to a method for preparing a new energy lithium battery positive electrode material lithium iron phosphate by using high-iron fly ash, and relates to a preparation method of the lithium iron phosphate. The application aims at solving the problems of high cost, difficult resource utilization and great environmental protection pressure of the existing high-iron fly ash. The method comprises the following steps: S1, preparing a ferrous sulfate solution; S2, adding H3PO4 solution into the ferrous sulfate solution, then adding ascorbic acid into the ferrous sulfate solution to obtain a mixed solution, and finally adding LiOH solution into the mixed solution to perform hydrothermal reaction. The application is used for preparing a new energy lithium battery positive electrode material lithium iron phosphate by using high-iron fly ash.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing lithium iron phosphate. BACKGROUND

[0002] High-iron fly ash is a complex and toxic solid residual byproduct generated in the process of coal chemical production. Compared with normal industrial byproducts, high-iron fly ash is more difficult to handle due to its toxic ingredients. Its toxicity mainly comes from containing various organic and inorganic compounds, which are derived from different grades of coal derivatives. Due to these toxic ingredients, high-iron fly ash is difficult to be directly recycled and utilized, and the treatment cost is expensive. A large amount of fly ash not only increases the risk of pollution to groundwater and air, but also has a negative impact on soil, air and ecological system.

[0003] In the soil, fly ash causes groundwater to be exposed to its water storage, changes the pH value and permeability of sediments, hinders the natural drainage system, and makes the groundwater unclear and unsuitable for drinking. While on the surface, untreated fly ash is exposed, which reduces air quality, causes ecological imbalance and increases natural disasters. Therefore, high treatment cost, difficult resource utilization and environmental pressure are the problems to be solved in fly ash management. SUMMARY

[0004] The present application aims to solve the problems of high-iron fly ash, such as high treatment cost, difficult resource utilization and high environmental pressure, and further provides a method for preparing lithium iron phosphate, a new energy lithium battery positive material, by using high-iron fly ash.

[0005] A method for preparing lithium iron phosphate, a new energy lithium battery positive material, by using high-iron fly ash, which is carried out according to the following steps:

[0006] I. ①Mix high-iron fly ash with sulfuric acid, heat at a temperature of 140℃-180℃ for 4h-6h, then filter and wash to obtain a filtrate;

[0007] ②Add sodium hydroxide solution to the filtrate to adjust the pH, react at room temperature for 3h-5h, and then a reddish-brown precipitate appears after the reaction is complete, then filter to obtain a filter residue;

[0008] ③Add ultrapure water to the filter residue, then add sulfuric acid and iron powder, react at a temperature of 60℃-80℃ for 10min-20min, and finally filter out the excess iron powder to obtain a ferrous sulfate solution;

[0009] II. ①Add ascorbic acid to the ferrous sulfate solution, then add H3PO4 solution at a dropwise addition rate of 5min / mL-6min / mL to obtain a mixed solution;

[0010] ②Dissolve LiOH H2O in deionized water to obtain a LiOH solution;

[0011] ③Under the condition that the dropping speed is 1 min / mL-1.5 min / mL, the LiOH solution is dropped into the mixed solution, and then placed in a high-pressure reaction kettle, under the condition that the hydrothermal temperature is 160°C-200°C, hydrothermal for 10h-12h, and then filtered to obtain a hydrothermal product, and finally washed and dried to obtain lithium iron phosphate.

[0012] The beneficial effects of the present application are:

[0013] In view of the problems caused by high-iron fly ash, the present application proposes an innovative technology to convert high-iron fly ash into lithium iron phosphate battery material. Through the purification and reforming process of the iron source precursor, the challenges of high cost, difficulty in resource utilization, and high environmental pressure in fly ash treatment can be effectively solved. By using this technology, a new energy lithium iron phosphate battery positive material is successfully prepared. As one of the most ideal positive materials for lithium ion batteries, it has high capacity, high safety performance, long service life, and high commercial value, realizing the solid waste resource utilization and high value utilization of high-iron fly ash. This not only provides an innovative way to solve environmental problems, but also makes a positive breakthrough in solid waste resource management, as follows:

[0014] 1. High value utilization of solid waste resources: By using high-iron fly ash, the efficient utilization of coal mine industrial solid waste resources is realized, and waste is converted into new energy lithium battery positive material with practical application value.

[0015] 2. Cost reduction: The method for preparing lithium iron phosphate battery positive material is relatively economical, which is expected to reduce the manufacturing cost of new energy lithium battery and improve its commercial competitiveness.

[0016] 3. Environmentally friendly: Through the reuse of waste resources, it is expected to reduce the demand for raw mineral resources and reduce the impact on the environment, realizing the environmentally friendly and high value utilization of solid waste resources.

[0017] 4. Innovation in new energy battery field: Using high-iron fly ash to prepare lithium battery positive material is an innovative attempt to traditional new energy battery materials, which expands the research field of new energy battery materials.

[0018] 5. Optimization of technical path: The purification and reforming process of the iron source precursor of high-iron fly ash is adopted, and through the optimization of the technical path, the problems of high cost and difficulty in resource utilization of high-iron fly ash are solved.

[0019] 6. Sustainable development direction: Converting coal mine industrial waste into new energy battery material conforms to the concept of sustainable development, and provides an innovative scheme with potential application value for the energy field.

[0020] Drawings

[0021] Figure 1 Technical route of ferrous sulfate solution prepared in step one of the present application;

[0022] Figure 2 XRD spectrum of lithium iron phosphate prepared in example one;

[0023] Figure 3 FT-IR spectrum of lithium iron phosphate prepared in example one;

[0024] Figure 4 SEM spectrum of lithium iron phosphate prepared in example one, (a) is a scale of 5 μm, (b) is a scale of 20 μm;

[0025] Figure 5 Thermogravimetric (TG) curve of lithium iron phosphate prepared in example one;

[0026] Figure 6 XRD spectrum of lithium iron phosphate prepared in a comparative experiment;

[0027] Figure 7 FT-IR spectrum of lithium iron phosphate prepared in a comparative experiment;

[0028] Figure 8 SEM spectrum of lithium iron phosphate prepared in a comparative experiment, (a) is a scale of 5 μm, (b) is a scale of 20 μm;

[0029] Figure 9 Thermogravimetric (TG) curve of lithium iron phosphate prepared in a comparative experiment. DETAILED DESCRIPTION

[0030] DETAILED DESCRIPTION Figure 1 Specific description: the present embodiment is a method for preparing a new energy lithium battery positive material lithium iron phosphate by using high-iron fly ash, which is carried out according to the following steps:

[0031] I. ①mixing high-iron fly ash with sulfuric acid, heating at a temperature of 140 ℃ to 180 ℃ for 4 h to 6 h, then filtering and washing to obtain a filtrate;

[0032] ②adding sodium hydroxide solution dropwise to the filtrate to adjust pH, reacting at room temperature for 3 h to 5 h, then filtering after the appearance of red-brown precipitate, to obtain a filter residue;

[0033] ③adding ultrapure water to the filter residue, then adding sulfuric acid and iron powder, reacting at a temperature of 60 ℃ to 80 ℃ for 10 min to 20 min, and finally filtering out the excess iron powder to obtain a ferrous sulfate solution;

[0034] II. ① Add ascorbic acid to the ferrous sulfate solution, then add H3PO4 solution at a drop rate of 5 min / mL to 6 min / mL to obtain a mixed solution;

[0035] ②Dissolve LiOH H2O in deionized water to obtain a LiOH solution;

[0036] ③Under the condition that the drop rate of the LiOH solution is 1 min / mL to 1.5 min / mL, the LiOH solution is added to the mixed solution, and then placed in a high-pressure reaction kettle, under the condition that the hydrothermal temperature is 160°C to 200°C, hydrothermal for 10h to 12h, and then filtered to obtain a hydrothermal product, which is finally washed and dried to obtain lithium iron phosphate.

[0037] The first step of the specific embodiment is to heat at a temperature of 140°C to 160°C for 4h to 6h, which effectively dissolves and activates the useful components in the high-iron fly ash through chemical reactions.

[0038] The first step of the specific embodiment is to heat at a temperature of 140°C to 160°C for 4h to 6h, which effectively dissolves and activates the useful components in the high-iron fly ash through chemical reactions.

[0039] Step one ② aims to neutralize the acidic conditions and make the product easier to handle.

[0040] The beneficial effects of the present embodiment are:

[0041] In view of the problems caused by high-iron fly ash, the present specific embodiment proposes an innovative technology to convert high-iron fly ash into lithium iron phosphate battery material. Through the purification and reforming process of the iron source precursor, the challenges of high cost, difficulty in resource utilization, and high environmental pressure of fly ash treatment can be effectively solved. Using this technology, a new energy lithium iron phosphate battery positive material is successfully prepared. This material is one of the most ideal positive materials for lithium ion batteries, with high capacity, high safety performance, long service life, and high commercial value, realizing the solid waste resource utilization and high value utilization of high-iron fly ash. This not only provides an innovative way to solve environmental problems, but also makes a positive breakthrough in solid waste resource management, as follows:

[0042] 1. High value utilization of solid waste resources: By using high-iron fly ash, the efficient utilization of coal mine industrial solid waste resources is realized, and waste is converted into new energy lithium battery positive material with practical application value.

[0043] 2. Cost reduction: The method of preparing lithium iron phosphate battery positive material is relatively economical, which is expected to reduce the manufacturing cost of new energy lithium battery and improve its commercial competitiveness.

[0044] 3. Environmentally friendly: By reusing waste resources, it is expected to reduce the demand for original mineral resources, reduce the impact on the environment, and realize the environmentally friendly and high-value utilization of solid waste resources.

[0045] 4. Innovation in the field of new energy batteries: Using high-speed rail fly ash in the preparation of lithium battery cathode materials is an innovative attempt to expand the research field of new energy battery materials.

[0046] 5. Technology path optimization: The process of purifying and reforming the iron source precursor of high-speed iron fly ash was adopted. By optimizing the technology path, the problems of high treatment cost and difficulty in resource utilization of high-speed iron fly ash were solved.

[0047] 6. Sustainable Development Direction: Converting coal mine industrial waste into new energy battery materials aligns with the concept of sustainable development and provides an innovative solution with potential application value in the energy sector.

[0048] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the mass percentage of iron in the high-speed iron fly ash mentioned in step one is 24% to 25%. Everything else is the same as in Specific Implementation Method One.

[0049] Specific Implementation Method Three: This implementation method differs from Specific Implementation Method One or Two in that: the concentration of sulfuric acid in step one ① is 3 mol / L to 3.68 mol / L; the concentration of sodium hydroxide solution in step one ② is 1.5 mol / L to 2.5 mol / L; and the concentration of sulfuric acid in step one ③ is 2 mol / L to 2.5 mol / L. Everything else is the same as in Specific Implementation Method One or Two.

[0050] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the mass ratio of high-speed iron fly ash to sulfuric acid in step one ① is 1g:(4-6)mL. Everything else is the same as in Specific Implementation Methods One to Three.

[0051] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: in step one, sodium hydroxide solution is added dropwise to the filtrate to adjust the pH to 12.5–13. Everything else is the same as in Specific Implementation Methods One to Four.

[0052] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five in that: the mass ratio of the filter residue to the volume of ultrapure water in step 1.③ is 1g:(30-32)mL; the mass ratio of the filter residue to the volume of sulfuric acid in step 1.③ is 1g:(2.5-6.5)mL; and the mass ratio of the filter residue to iron powder in step 1.③ is 1:(0.5-0.6). Everything else is the same as in Specific Implementation Methods One to Five.

[0053] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that the concentration of the H3PO4 solution mentioned in step two① is 14 mol / L to 15 mol / L. Everything else is the same as in Specific Implementation Methods One to Six.

[0054] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: the volume ratio of the ferrous sulfate solution to the mass ratio of ascorbic acid in step two① is 1 mL:(0.0041~0.0045) g; the volume ratio of the ferrous sulfate solution to the H3PO4 solution in step two① is 1:(0.020~0.022). Everything else is the same as in Specific Implementation Methods One to Seven.

[0055] Specific Implementation Method Nine: This implementation method differs from Specific Implementation Methods One to Eight in that the concentration of the LiOH solution mentioned in step two ② is 1.5 mol / L to 2.5 mol / L. Everything else is the same as in Specific Implementation Methods One to Eight.

[0056] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in that the volume ratio of the mixed solution to the LiOH solution in step two ③ is 1:(0.5-0.6). Everything else is the same as in Specific Implementation Methods One to Nine.

[0057] The beneficial effects of the present invention are verified using the following embodiments:

[0058] Example 1:

[0059] A method for preparing lithium iron phosphate, a cathode material for new energy lithium batteries, using high-speed iron fly ash, is carried out according to the following steps:

[0060] 1. Mix 5g of high-speed iron fly ash with 25mL of sulfuric acid with a concentration of 3.68mol / L, heat in an ultraviolet drying oven at 150℃ for 4h, then filter by vacuum pump and wash with deionized water to obtain filtrate.

[0061] ② Add 2 mol / L sodium hydroxide solution to the filtrate to adjust the pH to 12.5. React at room temperature for 4 hours. After the reaction is complete, a reddish-brown precipitate appears. Then filter the precipitate by vacuum pumping with circulating water to obtain the filter residue.

[0062] ③ Add 45 mL of ultrapure water to 1.47 g of filter residue, then add 4.5 mL of 2.3 mol / L sulfuric acid and 0.76 g of iron powder. React at 75 °C for 10 min. Finally, filter out the excess iron powder to obtain ferrous sulfate solution.

[0063] 2. ① Add 0.2g of ascorbic acid to 45mL of ferrous sulfate solution, and then add 0.92mL of 14.7mol / L H3PO4 solution at a dropping rate of 5min / mL to obtain a mixed solution;

[0064] ② Dissolve LiOH·H2O in deionized water to obtain a LiOH solution; the concentration of the LiOH solution is 1.8 mol / L;

[0065] ③ Under the condition of a dropping rate of 1.25 min / mL, LiOH solution was added dropwise to the mixed solution, and then placed in a high-pressure reactor. Under the condition of hydrothermal temperature of 180℃, the mixture was hydrothermally heated for 12 h. The hydrothermal product was obtained by filtration, and then washed multiple times with deionized water and anhydrous ethanol. The mixture was then dried in a vacuum drying oven at 65℃ for 12 h, and then ground to obtain lithium iron phosphate. The volume ratio of the mixed solution to the LiOH solution was 1:0.556.

[0066] The high-speed iron fly ash mentioned in step one is a solid waste produced by Guizhou Qianxi Chemical. Due to regional differences in Guizhou, the high-speed iron fly ash uses coal with a high iron content, including 24.26% FeO3, 24.88% SiO2, 17.85% Al2O3, 8.63% CaO, 3.73% ZrO2, 3.68% TiO2, 2.34% K2O, and 14.63% other components.

[0067] To ensure the effectiveness of the lithium iron phosphate preparation method, the same preparation method was used to ensure consistent experimental conditions, and different iron sources were employed in the experiments. Pure-phase ferrous sulfate heptahydrate was used as a different iron source, and the same preparation method was used as a control experiment. By analyzing and comparing the materials prepared using the two different iron sources, the influence of different iron sources on the performance of lithium iron phosphate was understood. Through chemical and structural analysis methods, the differences in crystal structure, grain size distribution, lattice arrangement, and surface morphology of lithium iron phosphate materials prepared using the two different iron sources were determined.

[0068] Comparative Experiment: This comparative experiment differs from Example 1 in that the ferrous sulfate solution was obtained by dissolving 4.1702 g of FeSO4·7H2O in 45 mL of deionized water. Everything else is the same as in Example 1.

[0069] Figure 2 The image shows the XRD pattern of lithium iron phosphate prepared in Example 1. It can be observed that the diffraction peaks of LiFePO4 are very sharp, and no other impurity peaks appear. This indicates that the impurity content in the purified ferrous sulfate solution is low, resulting in high crystallinity of the prepared LiFePO4 crystals. Figure 6The XRD patterns of lithium iron phosphate prepared for comparison experiments are shown in the figures. It can be seen from the figures that lithium iron phosphate prepared using pure-phase FeSO4·7H2O as the iron source exhibits high crystallinity, with clear and sharp diffraction peaks and no other impurity peaks, indicating a very complete crystal structure. Compared with lithium iron phosphate prepared using ferrous sulfate solution as the iron source in Example 1, the diffraction peaks of the two are basically consistent, further verifying the reproducibility and stability of the preparation process. Furthermore, by comparing the characteristic peaks of the samples prepared in the comparison examples and comparative experiments with the LiFePO4 standard card (JCPDS83-2092), it can be observed that they are basically consistent, further proving that both samples are lithium iron phosphate with a complete crystal structure.

[0070] Figure 3 The image shows the FT-IR spectrum of lithium iron phosphate prepared in Example 1; in the FT-IR spectrum, it was observed that at 950 cm⁻¹... -1 A weak band appears at 1100cm. -1 The area exhibits a sharp banded structure, which can be attributed to the symmetrical PO4 groups in LiFePO4. 3- The stretching vibrations of ions. This spectroscopic feature not only provides important clues for the identification of compounds, but also reflects the symmetry of their molecular structure and vibrational modes. Figure 7 To compare the FT-IR spectra of lithium iron phosphate prepared in the experiment; it can be seen from the figure that in the range of 950–1100 cm⁻¹ -1 The characteristic peaks within this range are essentially consistent with those of the lithium iron phosphate prepared in Example 1, both exhibiting the same tensile vibrations. This indicates the similarity of the chemical groups or bonds contained in the two lithium iron phosphate samples. Within this wavenumber range, the common phosphate group (PO4) is present. 3- Characteristic vibrations of lithium iron phosphate typically occur. FT-IR analysis confirmed that lithium iron phosphate prepared with a pure-phase iron source has similar structural features at the molecular level to the sample prepared with ferrous sulfate solution as the iron source in Example 1.

[0071] Figure 4 The images show the SEM spectra of lithium iron phosphate prepared in Example 1. (a) shows a scale bar of 5 μm, and (b) shows a scale bar of 20 μm. The microscopic images reveal the details of the surface and particle morphology of LiFePO4, which exhibits a tetrahedral or hexahedral crystal structure with a cross-sectional diameter in the range of 500–800 nm. Figure 8 For comparison, the SEM spectra of lithium iron phosphate prepared in the experiment are shown. (I) is at a scale bar of 5 μm, and (II) is at a scale bar of 20 μm. Regardless of whether the scale bar is 5 μm or 20 μm, Example 1 and the comparative experiment exhibit similar crystal structures and morphological characteristics at the microscopic level. This indicates that the different iron sources used in the preparation process all resulted in LiFePO4 particles with consistent crystal structures.

[0072] Figure 5 Thermogravimetric (TG) curve of lithium iron phosphate prepared in Example 1; Figure 9 The thermogravimetric (TG) curves of lithium iron phosphate prepared for comparison experiments are shown. Within the temperature range of room temperature to 250°C, both samples exhibited some weight loss, with the mass gradually decreasing as the temperature increased. Specifically, the sample prepared with ferrous sulfate solution in Example 1 had a residual mass of 96.29% after 800°C; while the sample prepared using pure-phase FeSO4·7H2O in the comparative experiment had a residual mass of 96.11% after 800°C. This indicates that the sample prepared using ferrous sulfate solution from high-iron fly ash has a slight advantage in terms of thermal stability.

Claims

1. A method for preparing a new energy lithium battery cathode material lithium iron phosphate from high-iron fly ash, characterized by It is carried out according to the following steps: I. ①mixing high-iron fly ash with sulfuric acid, heating at a temperature of 140-180℃ for 4-6h, then filtering and washing to obtain filtrate; The concentration of the sulfuric acid is 3-3.68mol / L; the mass of the high-iron fly ash to the volume of the sulfuric acid is 1g:(4-6)mL; ②adding sodium hydroxide solution into the filtrate to adjust pH to 12.5-13, reacting at room temperature for 3-5h, then filtering after the appearance of red-brown precipitate, to obtain filter residue; ③adding ultrapure water into the filter residue, then adding sulfuric acid and iron powder, reacting at a temperature of 60-80℃ for 10-20min, finally filtering out the excess iron powder to obtain ferrous sulfate solution; The concentration of the sulfuric acid is 2-2.5mol / L; the mass of the filter residue to the volume of the ultrapure water is 1g:(30-32)mL; the mass of the filter residue to the volume of the sulfuric acid is 1g:(2.5-6.5)mL; the mass ratio of the filter residue to the iron powder is 1:(0.5-0.6); II. ①adding ascorbic acid into the ferrous sulfate solution, then adding H3PO4 solution at a dropping speed of 5-6min / mL to obtain mixed solution; The concentration of the H3PO4 solution is 14-15mol / L; the volume of the ferrous sulfate solution to the mass of the ascorbic acid is 1mL:(0.0041-0.0045)g; the volume ratio of the ferrous sulfate solution to the H3PO4 solution is 1:(0.020-0.022); ②dissolving LiOH·H2O in deionized water to obtain LiOH solution; The concentration of the LiOH solution is 1.5-2.5mol / L; ③adding the LiOH solution into the mixed solution at a dropping speed of 1-1.5min / mL, then placing in a high-pressure reactor, hydrothermally treating at a temperature of 160-200℃ for 10-12h, filtering to obtain hydrothermal product, finally washing and drying to obtain lithium iron phosphate; The volume ratio of the mixed solution to the LiOH solution is 1:(0.5-0.6); The lithium iron phosphate is in tetrahedral or hexahedral crystal structure, with a section diameter of 500-800nm.

2. The method for preparing a positive material lithium iron phosphate for new energy lithium batteries from high-iron fly ash according to claim 1, characterized in that The mass percentage of iron in the high-iron fly ash in step I is 24-25%.

3. The method for preparing a positive material lithium iron phosphate for new energy lithium batteries from high-iron fly ash according to claim 1, characterized in that The concentration of the sodium hydroxide solution in step I ② is 1.5-2.5mol / L.

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