Direct hydrothermal synthesis of globular iron phosphate
The preparation of hydrangea-shaped iron phosphate by direct hydrothermal synthesis solves the problems of high energy consumption and morphology control in traditional synthesis methods, realizing low-cost and environmentally friendly iron phosphate synthesis, improving the electrical properties and stability of the material, and making it suitable for lithium-ion batteries and supercapacitors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- WANHUA CHEM GRP CO LTD
- Filing Date
- 2024-12-02
- Publication Date
- 2026-06-02
Smart Images
Figure CN122126812A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of materials technology, and specifically to a direct hydrothermal synthesis method for hydrangea-shaped iron phosphate. Technical Background
[0002] Iron phosphate (FePO4) plays a crucial role as a high-efficiency cathode material in lithium-ion batteries, supercapacitors, and other energy storage devices. It is valued for its high theoretical capacity, excellent cycle stability, and environmental friendliness. However, traditional methods for synthesizing iron phosphate, mainly involving high-temperature solid-state reactions and solution-phase precipitation, have several limitations that hinder further improvements in material performance and its widespread application.
[0003] Current technologies for synthesizing iron phosphate face numerous challenges: the high-temperature synthesis process leads to high energy consumption and costs, while the difficulty in precisely controlling the morphology and particle size of the material affects battery performance; furthermore, the use of harmful chemicals burdens the environment, contradicting the concept of sustainable development. These limitations hinder the widespread application and market competitiveness of iron phosphate materials. Summary of the Invention
[0004] The present invention aims to overcome the above-mentioned limitations by providing an innovative direct hydrothermal synthesis method, which offers a method for synthesizing iron phosphate with lower energy consumption, higher cost-effectiveness, less environmental impact, and excellent electrical properties.
[0005] To achieve the above objectives, the present invention provides the following technical solution:
[0006] A direct hydrothermal synthesis method for hydrangea-shaped iron phosphate includes the following steps:
[0007] 1. Mix phosphorus source, iron source, complexing reagent, and water evenly, and heat to react to obtain iron phosphate dihydrate;
[0008] 2. The iron phosphate dihydrate was washed, dried, and calcined to obtain hydrangea-shaped iron phosphate.
[0009] Furthermore, in step 1, the phosphorus source is phosphoric acid, the iron source is iron oxide red, and the complexing reagent is one or more of EDTA (ethylenediaminetetraacetic acid), NTA (nitroglycerin), citric acid, or tartaric acid.
[0010] Furthermore, the mixing in step 1 can be carried out at room temperature, and the mixing process is accompanied by stirring, such as stirring for 1-3 hours until uniformly dispersed. The resulting solution contains 10-30 wt% phosphorus source, 5-10 wt% iron source, and 0.2-1 wt% complexing reagent.
[0011] Further, in step 1, the obtained mixed solution is transferred to a hydrothermal reactor and sealed, and heated to 80–120°C, preferably 90–110°C; the reaction is maintained for 12–24 hours, preferably 12–16 hours, to obtain iron phosphate dihydrate.
[0012] Further, in step 2, the obtained iron phosphate dihydrate is washed, preferably with deionized water, until the conductivity is below 500 μS / cm, and then the iron phosphate dihydrate is dried at a temperature of 60–100°C for 8–15 hours.
[0013] Furthermore, the roasting temperature in step 2 is 550–700°C, preferably 600–650°C, and the time is 3–6 hours.
[0014] The hydrangea-shaped ferric phosphate prepared by the above method in this invention has a specific surface area greater than or equal to 10 m². 2 With an iron-to-phosphorus ratio of 0.95–0.98, the prepared lithium iron phosphate has a compacted density of 2.5 g / cm³. 3 above.
[0015] The beneficial effects of this invention are as follows:
[0016] 1. Compared with traditional liquid-phase synthesis reactions, the direct hydrothermal synthesis method has a simpler process, avoids the use of oxidants such as hydrogen peroxide, is lower in cost and safer, and is in line with the concept of sustainable development.
[0017] 2. By optimizing the hydrothermal synthesis method, the morphology and particle size of the material can be controlled more precisely, thereby improving the electrical performance of lithium iron phosphate.
[0018] 3. The hydrangea-shaped iron phosphate has better structural stability and higher specific surface area and compaction density, which helps to improve the capacity and cycle stability of the material during battery charging and discharging. Attached Figure Description
[0019] Figure 1 This is a SEM image of the hydrangea-shaped iron phosphate material of Embodiment 1 of the present invention;
[0020] Figure 2 This is a SEM image of lithium iron phosphate prepared from the hydrangea-shaped iron phosphate material of Example 1 of the present invention;
[0021] Figure 3 This is a SEM image of the hydrangea-shaped iron phosphate material of Embodiment 2 of the present invention;
[0022] Figure 4 This is a SEM image of the hydrangea-shaped iron phosphate material of Example 4 of the present invention;
[0023] Figure 5 This is a SEM image of the blocky iron phosphate material of Comparative Example 2 of the present invention;
[0024] Figure 6 This is a SEM image of the sheet-like iron phosphate material of Comparative Example 3 of the present invention. Detailed Implementation
[0025] The technical solution of the present invention will be further described below with reference to specific embodiments. However, these embodiments are not intended to limit the scope of protection of the present invention. Any minor changes to the preparation process conditions without departing from the concept of the present invention should fall within the scope of protection of the present invention.
[0026] Example 1
[0027] S1. Prepare 1000 ml of a 20 wt% phosphoric acid solution, then add 71.5 g of iron oxide red, 2.61 g of EDTA, and 1.72 g of citric acid to the solution. Stir the above ingredients together for 1 hour at a stirring speed of 300 r / min.
[0028] S2. Transfer the above slurry to a hydrothermal reactor, seal it, and place it in an oven at 100°C for 15 hours of constant temperature reaction.
[0029] S3. After reacting for 15 hours, the hydrothermal reactor was removed from the oven and cooled to room temperature to obtain a pink ferric phosphate dihydrate slurry.
[0030] S4. The ferric phosphate dihydrate slurry is filtered and washed until the conductivity is below 500 μS / cm to obtain ferric phosphate dihydrate filter cake.
[0031] S5. Dry the ferric phosphate dihydrate filter cake for 12 hours at a drying temperature of 90℃ to obtain ferric phosphate dihydrate powder.
[0032] S6. Dehydrate ferric phosphate dihydrate by calcination at 600℃ for 4 hours. After calcination, cool to room temperature to obtain the hydrangea-shaped ferric phosphate product.
[0033] Example 2
[0034] S1. Prepare 1000 ml of a 20 wt% phosphoric acid solution, then add 71.5 g of iron oxide red, 2.61 g of EDTA, and 1.72 g of citric acid to the solution. Stir the above ingredients together for 1 hour at a stirring speed of 300 r / min.
[0035] S2. Transfer the above slurry to a hydrothermal reactor, seal it, and place it in an oven at 120°C for 12 hours.
[0036] S3. After reacting for 12 hours, the hydrothermal reactor was removed from the oven and cooled to room temperature to obtain a pink ferric phosphate dihydrate slurry.
[0037] S4. The ferric phosphate dihydrate slurry is filtered and washed until the conductivity is below 500 μS / cm to obtain ferric phosphate dihydrate filter cake.
[0038] S5. Dry the ferric phosphate dihydrate filter cake for 12 hours at a drying temperature of 100℃ to obtain ferric phosphate dihydrate powder.
[0039] S6. Dehydrate ferric phosphate dihydrate by calcination at 600℃ for 4 hours. After calcination, cool to room temperature to obtain the hydrangea-shaped ferric phosphate product.
[0040] Example 3
[0041] S1. Prepare 1000 ml of 11 wt% phosphoric acid solution, then add 60.0 g of iron oxide red, 1.57 g of EDTA, and 1.03 g of citric acid to the solution. Stir the above ingredients together for 1 hour at a stirring speed of 300 r / min.
[0042] S2. Transfer the above slurry to a hydrothermal reactor, seal it, and place it in an oven at 100°C for 15 hours of constant temperature reaction.
[0043] S3. After reacting for 15 hours, the hydrothermal reactor was removed from the oven and cooled to room temperature to obtain a pink ferric phosphate dihydrate slurry.
[0044] S4. The ferric phosphate dihydrate slurry is filtered and washed until the conductivity is below 500 μS / cm to obtain ferric phosphate dihydrate filter cake.
[0045] S5. Dry the ferric phosphate dihydrate filter cake for 12 hours at a drying temperature of 90℃ to obtain ferric phosphate dihydrate powder.
[0046] S6. Dehydrate ferric phosphate dihydrate by calcination at 550℃ for 4 hours. After calcination, cool to room temperature to obtain the hydrangea-shaped ferric phosphate product.
[0047] Example 4
[0048] S1. Prepare 1000 ml of 20 wt% phosphoric acid solution, then add 71.5 g of iron oxide red and 3.41 g of NTA to the solution. Stir the above raw materials for 1 hour at a stirring speed of 300 r / min.
[0049] S2. Transfer the above slurry to a hydrothermal reactor, seal it, and place it in an oven at 100°C for 8 hours of constant temperature reaction.
[0050] S3. After reacting for 8 hours, the hydrothermal reactor was removed from the oven and cooled to room temperature to obtain a pink ferric phosphate dihydrate slurry.
[0051] S4. The ferric phosphate dihydrate slurry is filtered and washed until the conductivity is below 500 μS / cm to obtain ferric phosphate dihydrate filter cake.
[0052] S5. Dry the ferric phosphate dihydrate filter cake for 12 hours at a drying temperature of 90℃ to obtain ferric phosphate dihydrate powder.
[0053] S6. Dehydrate ferric phosphate dihydrate by calcination at 550℃ for 4 hours. After calcination, cool to room temperature to obtain the hydrangea-shaped ferric phosphate product.
[0054] Example 5
[0055] S1. Prepare 1000 ml of 30 wt% phosphoric acid solution, then add 130 g of iron oxide red and 13 g of EDTA to the solution. Stir the above raw materials for 1 hour at a stirring speed of 300 r / min.
[0056] S2. Transfer the above slurry to a hydrothermal reactor, seal it, and place it in an oven at 100°C for 15 hours of constant temperature reaction.
[0057] S3. After reacting for 15 hours, the hydrothermal reactor was removed from the oven and cooled to room temperature to obtain a pink ferric phosphate dihydrate slurry.
[0058] S4. The ferric phosphate dihydrate slurry is filtered and washed until the conductivity is below 500 μS / cm to obtain ferric phosphate dihydrate filter cake.
[0059] S5. Dry the ferric phosphate dihydrate filter cake for 12 hours at a drying temperature of 90℃ to obtain ferric phosphate dihydrate powder.
[0060] S6. Dehydrate ferric phosphate dihydrate by calcination at 550℃ for 4 hours. After calcination, cool to room temperature to obtain the hydrangea-shaped ferric phosphate product.
[0061] Comparative Example 1
[0062] S1. Prepare 1000 ml of a 20 wt% phosphoric acid solution, then add 71.5 g of iron oxide red to the solution. Stir the above ingredients together for 1 hour at a stirring speed of 300 r / min.
[0063] S2. Transfer the above slurry to a hydrothermal reactor, seal it, and place it in an oven at 100°C for 15 hours of constant temperature reaction.
[0064] S3. After reacting for 15 hours, the hydrothermal reactor was removed from the oven and cooled to room temperature to obtain a pink ferric phosphate dihydrate slurry.
[0065] S4. The ferric phosphate dihydrate slurry is filtered and washed until the conductivity is below 500 μS / cm to obtain ferric phosphate dihydrate filter cake.
[0066] S5. Dry the ferric phosphate dihydrate filter cake for 12 hours at a drying temperature of 90℃ to obtain ferric phosphate dihydrate powder.
[0067] S6. Dehydrate ferric phosphate dihydrate by calcination at 600℃ for 4 hours. After calcination, cool to room temperature to obtain the finished flaky ferric phosphate product.
[0068] Comparative Example 2
[0069] S1. Prepare 1000 ml of a 20 wt% phosphoric acid solution, then add 71.5 g of iron oxide red, 2.61 g of EDTA, and 1.72 g of citric acid to the solution. Stir the above ingredients together for 1 hour at a stirring speed of 300 r / min.
[0070] S2. Transfer the above slurry to a hydrothermal reactor, seal it, and place it in an oven at 140°C for 15 hours of constant temperature reaction.
[0071] S3. After reacting for 15 hours, the hydrothermal reactor was removed from the oven and cooled to room temperature to obtain a pink ferric phosphate dihydrate slurry.
[0072] S4. The ferric phosphate dihydrate slurry is filtered and washed until the conductivity is below 500 μS / cm to obtain ferric phosphate dihydrate filter cake.
[0073] S5. Dry the ferric phosphate dihydrate filter cake for 12 hours at a drying temperature of 90℃ to obtain ferric phosphate dihydrate powder.
[0074] S6. Dehydrate ferric phosphate dihydrate by calcination at 600℃ for 4 hours. After calcination, cool to room temperature to obtain the finished product of lumpy ferric phosphate.
[0075] Comparative Example 3
[0076] S1. Prepare 1000 ml of 20 wt% phosphoric acid solution, then add 50 g of iron powder to the solution and react at 70 ℃ to obtain ferrous dihydrogen phosphate solution.
[0077] S2. Add 2.61g EDTA and 1.72g citric acid to the ferrous dihydrogen phosphate solution. Stir the above raw materials for 0.5 hours at a stirring speed of 300r / min and heat to 80℃.
[0078] S3. Weigh 66.3g of 27.5wt% hydrogen peroxide solution and add hydrogen peroxide solution dropwise to the above solution, controlling the dropwise addition time to 1 hour.
[0079] S4. After the addition is complete, maintain the temperature for 2 hours to react, and the solution will be converted into ferric phosphate dihydrate slurry.
[0080] S5. The ferric phosphate dihydrate slurry is filtered and rinsed until the conductivity is below 500 μS / cm to obtain ferric phosphate dihydrate filter cake.
[0081] S6. Dry the ferric phosphate dihydrate filter cake for 12 hours at a drying temperature of 90℃ to obtain ferric phosphate dihydrate powder.
[0082] S7. Dehydrate ferric phosphate dihydrate by calcination at 600℃ for 4 hours. After calcination, cool to room temperature to obtain the finished flaky ferric phosphate product.
[0083] Comparative Example 4
[0084] S1. Take 400g of deionized water and add 250g of ferrous sulfate to the deionized water to prepare a ferrous sulfate solution.
[0085] S2. Add 2.61g EDTA and 1.72g citric acid to the ferrous sulfate solution. Stir the above raw materials for 0.5 hours at a stirring speed of 300r / min and heat to 60℃.
[0086] S3. Weigh 66.3g of 27.5wt% hydrogen peroxide solution and add hydrogen peroxide solution dropwise to the above solution, controlling the dropwise addition time to 1 hour.
[0087] S4. After the addition is complete, maintain the temperature for 2 hours to react, and the solution will be converted into ferric phosphate dihydrate slurry.
[0088] S5. The ferric phosphate dihydrate slurry is filtered and rinsed until the conductivity is below 500 μS / cm to obtain ferric phosphate dihydrate filter cake.
[0089] S6. Dry the ferric phosphate dihydrate filter cake for 12 hours at a drying temperature of 90℃ to obtain ferric phosphate dihydrate powder.
[0090] S7. Dehydrate ferric phosphate dihydrate by calcination at 600℃ for 4 hours. After calcination, cool to room temperature to obtain the finished flaky ferric phosphate product.
[0091] Preparation Example
[0092] 100g of the iron phosphate product prepared in Examples 1-5 and Comparative Examples 1-4, 25g of industrial-grade lithium carbonate, 11g of sucrose, and 1500g of deionized water were weighed out respectively. The raw materials were stirred into a slurry, and the slurry was milled in a nano-mill until the particle size was below 500nm to obtain a mixed slurry. The slurry was spray-dried using a spray dryer to obtain lithium iron phosphate precursor powder. The lithium iron phosphate precursor powder was heated to 780°C in a tube furnace at a heating rate of 2°C / min, held at that temperature for 10 hours, and then cooled to room temperature. The tube furnace was in a nitrogen atmosphere. After cooling, lithium iron phosphate powder was obtained.
[0093] The iron phosphate and lithium iron phosphate prepared in Examples 1-5 and Comparative Examples 1-4 were characterized. The electrical performance testing methods for lithium iron phosphate all conformed to the requirements of GB / T36276-2023, and the cycle capacity retention was tested at a 1C rate. The characterization results are shown in Table 1.
[0094] Table 1 Characterization results of iron phosphate and performance test results of lithium iron phosphate
[0095]
[0096] By comparing the 0.1C charge-discharge data and 500-cycle capacity retention of the examples and comparative examples in Table 1, it can be found that the first-cycle efficiency, compaction density and cycle capacity retention of lithium iron phosphate prepared by ferric phosphate with ferric phosphate are significantly better than those of lithium iron phosphate prepared by non-ferric phosphate.
[0097] Comparative observation Figure 1 , Figure 3 ferric phosphate and hydrangea Figure 5 The superior performance of bulk ferric phosphate is attributed to the richer surface structure and larger specific surface area of the hydrangea-shaped ferric phosphate. (Through...) Figure 2 The SEM images of lithium iron phosphate show that lithium iron phosphate prepared from hydrangea-shaped iron phosphate can be sintered to obtain spheres of varying sizes, which gives it both excellent electrical properties and high compaction density.
[0098] Comparing Examples 1 and 2 with Comparative Example 2, it can be seen that the temperature of the hydrothermal process is extremely important for the formation of the hydrangea-like structure, and the lithium iron phosphate prepared from the blocky iron phosphate formed at high temperature has a significantly lower compaction density. In summary, the method provided by this invention can synthesize a hydrangea-like iron phosphate, whose excellent surface structure and large specific surface area give it significant advantages in chemical energy storage. It can be used to prepare lithium iron phosphate with high compaction density and excellent cycle performance, and has great potential for industrial application.
Claims
1. A direct hydrothermal synthesis method for hydrangea-shaped ferric phosphate, characterized in that, Includes the following steps: S1. Mix phosphorus source, iron source, complexing reagent and water evenly to obtain a solution; S2. The above solution is subjected to a hydrothermal reaction to obtain ferric phosphate dihydrate; S3. The iron phosphate dihydrate is washed, dried and calcined to obtain hydrangea-shaped iron phosphate.
2. The method according to claim 1, characterized in that, The phosphorus source in step S1 is phosphoric acid, and the phosphorus source accounts for 10-30 wt% of the solution.
3. The method according to claim 1, characterized in that, The iron source mentioned in step S1 is iron oxide red, and the iron source accounts for 5-10 wt% of the solution.
4. The method according to claim 1, characterized in that, The complexing agent in step S1 is selected from one or more of EDTA, NTA, citric acid and tartaric acid; preferably, the proportion of the complexing agent in the solution is 0.2 to 1 wt%.
5. The method according to claim 1, characterized in that, The temperature of the hydrothermal reaction process in step S2 is 80–120°C, preferably 90–110°C.
6. The method according to claim 1, characterized in that, The hydrothermal synthesis process described in step S2 has a reaction time of 12 to 24 hours, preferably 12 to 16 hours.
7. The method according to claim 1, characterized in that, The roasting process in step S3 is carried out at a temperature of 550–700°C, preferably 600–650°C, for a roasting time of 3–6 hours.
8. A hydrangea-shaped iron phosphate, characterized in that, The specific surface area of the hydrangea-shaped iron phosphate is greater than or equal to 10m². 2 / g, with an iron-to-phosphorus ratio of 0.95–0.98.