Doped ferromanganese phosphate precursor material and preparation method thereof

Abstract

The invention provides a doped ferromanganese phosphate precursor and a preparation method thereof. The specific preparation method comprises the following steps: mixing titanium dioxide byproduct ferrous sulfate, manganese salt and magnesium salt with water to obtain a solution A; adding dilute phosphoric acid into the solution A to obtain a solution B; adding ammonia water into the solution B to adjust the pH to obtain mixed slurry C; adding hydrogen peroxide into the mixed slurry C for heating reaction, and after the reaction is finished, performing suction filtration and drying to obtain powder; and calcining the powder at high temperature to obtain the magnesium-doped ferromanganese phosphate precursor. The titanium dioxide byproduct ferrous sulfate is used as an iron source, and magnesium impurities in the ferrous sulfate are used for magnesium doping, so that the further impurity removal cost is reduced; magnesium in-situ doping is carried out through a liquid phase method, magnesium and other elements are combined more tightly, the prepared magnesium-doped ferromanganese phosphate is uniform in morphology and easier to realize atomic-scale mixing, and lithium ferromanganese phosphate prepared by taking the magnesium-doped ferromanganese phosphate as a precursor also shows excellent electrochemical performance and lower specific surface area.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery cathode materials, specifically relating to a doped manganese iron phosphate precursor material and its preparation method. Background Technology

[0002] Compared to lithium iron phosphate (LFP), lithium manganese iron phosphate (LFP) not only boasts superior safety and long cycle life, but also exhibits a high redox potential of 4.1V and higher energy density. Therefore, it is considered an upgraded alternative to LFP, making it one of the most promising lithium-ion battery cathode materials. Currently, most industrially produced LFP is still synthesized using high-temperature solid-state methods. In solid-state ion doping, metal salts or oxides are typically added and milled / calcined with other raw materials. However, achieving atomic-level mixing in solid-state processes is difficult, leading to problems such as uneven solid solution and poor batch-to-batch stability.

[0003] The main methods for preparing titanium dioxide are the sulfuric acid process and the chloride process. The main byproduct of the sulfuric acid process is ferrous sulfate. By removing impurities from this byproduct, ferrous sulfate can be used as a raw material for lithium-ion battery cathode materials, improving both economic value and environmental benefits. However, ferrous sulfate, a byproduct of titanium dioxide production, typically contains metallic impurities such as titanium, magnesium, manganese, and aluminum, resulting in low purity. Removing these impurities would lead to higher costs.

[0004] CN202411545284.2 discloses a method for preparing battery-grade ferromanganese phosphate using ferrous chloride, a byproduct of titanium dioxide production. This method utilizes manganese from crude ferrous chloride by removing impurities and enriching iron and manganese elements. CN202311743108.5 discloses a method for preparing titanium-doped ferromanganese phosphate precursors based on ferrous sulfate, a byproduct of titanium slag production. This method recovers iron from the ferrous sulfate and uses it to prepare the ferromanganese phosphate precursor, while retaining titanium from the titanium slag for doping modification of the cathode material. CN202310841061.X discloses a method for preparing lithium iron manganese phosphate cathode material based on ferrous sulfate, a byproduct of titanium dioxide production. By adjusting the pH range, the ferrous sulfate can remove impurities such as titanium, magnesium, and aluminum during the hot dissolution process while retaining manganese impurities.

[0005] While the aforementioned patents propose using titanium dioxide byproducts to prepare ferromanganese phosphate precursors, and subsequently lithium manganese iron phosphate, they do not effectively utilize the magnesium element present. Existing technologies, although proposing the mixing of iron and magnesium sources for doping to synthesize lithium manganese iron phosphate cathode materials, all use pure iron or magnesium sources and do not disclose how to utilize the magnesium element in titanium dioxide byproducts. Therefore, this invention provides a ferromanganese phosphate precursor doped with magnesium from titanium dioxide byproducts and its preparation method. Summary of the Invention

[0006] To address the above problems, this invention provides a method for preparing a doped manganese iron phosphate precursor, comprising the following steps: S1. Add the by-products of titanium dioxide, namely ferrous sulfate, manganese salt, and magnesium salt, to water and stir until homogeneous to obtain solution A; S2. Add dilute phosphoric acid aqueous solution to solution A to obtain solution B; S3. Add ammonia water dropwise to solution B to adjust the pH, and obtain mixed slurry C; S4. Add hydrogen peroxide to the mixed slurry C and heat it to react. After the reaction is complete, filter and dry to obtain powder. S5. The powder obtained in S4 is calcined at high temperature to obtain magnesium-doped manganese iron phosphate precursor.

[0007] The manganese salt in S1 is at least one of manganese sulfate, manganese acetate, manganese nitrate, or manganese dichloride; the magnesium salt is at least one of magnesium acetate, magnesium pyruvate, magnesium chloride, magnesium sulfate, or magnesium propionate.

[0008] The mass concentration of the dilute phosphoric acid aqueous solution described in S2 is 30%~70%.

[0009] The pH of S3 is 4-7, preferably 4.5; the mass concentration of the ammonia water is 20-23%.

[0010] The hydrogen peroxide concentration in S4 is 25-30%, the reaction temperature is 70-80℃, and the reaction time is 2-5h; the drying conditions are: heat preservation at 70-90℃ for 10-24h.

[0011] The by-products of titanium dioxide, namely ferrous sulfate, manganese salt, phosphoric acid, and hydrogen peroxide, are calculated as iron, manganese, phosphorus, and hydrogen peroxide, respectively. The molar ratio of the by-products of titanium dioxide, namely ferrous sulfate, manganese salt, phosphoric acid, and hydrogen peroxide, is (0.2-0.5):(0.5-0.8):(1.0-1.05):(0.5-1).

[0012] The high-temperature calcination conditions described in S5 are: 300~500℃ for 3~7 hours.

[0013] The titanium dioxide by-product ferrous sulfate in S1 contains 1000~4000ppm of magnesium, <2ppm of manganese, and <200ppm of metals other than magnesium and iron; the magnesium-doped manganese ferric phosphate precursor in S5 contains 2000-10000ppm of magnesium.

[0014] The present invention also provides a doped manganese iron phosphate precursor, which is prepared by the above preparation method.

[0015] The present invention also provides a doped lithium manganese iron phosphate, wherein the raw materials for preparation include the doped lithium manganese iron phosphate precursor, carbon source and lithium source as described in claim 9.

[0016] The beneficial effects of this invention are as follows: (1) The raw materials selected in this invention are low cost, and the magnesium impurities in the titanium dioxide byproduct ferrous sulfate are fully utilized for in-situ doping of magnesium atoms, which reduces the cost increase caused by further impurity removal of ferrous sulfate.

[0017] (2) The present invention uses a one-step liquid phase method for preparation, which is simple and can synthesize manganese iron phosphate in large quantities, which is beneficial for subsequent industrial production.

[0018] (3) The magnesium-doped manganese iron phosphate precursor synthesized by the liquid phase method of the present invention has a uniform morphology, making it easier to achieve atomic-level mixing and more uniform solid solution of manganese iron; moreover, the present invention achieves in-situ doping of magnesium by liquid phase method, and the atomic bonding of in-situ doping is more compact, exhibiting better electrochemical performance and lower specific surface area compared with non-in-situ magnesium doping. Attached Figure Description

[0019] Figure 1 This is a comparison diagram of the XRD pattern of the manganese iron phosphate prepared in Example 1 with that of the standard card.

[0020] Figure 2 This is a SEM image of the manganese iron phosphate prepared in Example 1. Detailed Implementation

[0021] The embodiments of the present invention will be described in detail below with reference to the examples. The following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention.

[0022] The ferrous sulfate content in the titanium dioxide by-product ferrous sulfate used in the following examples and comparative examples is 185~190 g / kg, and the content of metal impurities is shown in Table 1.

[0023] Example 1 Preparation of magnesium-doped ferromanganese phosphate precursor: 874g of ferrous sulfate (impurity content shown in Table 1), a byproduct of titanium dioxide production, 318g of manganese sulfate, and 2.42g of magnesium acetate tetrahydrate were added to 2500mL of deionized water and stirred until homogeneous to form solution A. Subsequently, 321g of 85% phosphoric acid was added to 260mL of deionized water to form a dilute phosphoric acid aqueous solution. Then, all the dilute phosphoric acid aqueous solution was added to mixed solution A to react and form solution B. Ammonia solution with a mass concentration of 22.45% was added dropwise to adjust the pH of the mixed solution to 4.5 to form mixed slurry C. Then, 302g of hydrogen peroxide with a mass concentration of 25% was added to mixed slurry C and reacted in a water bath at 75℃ for 3h. After filtration, the filter residue was kept at 80℃ in an oven for 12h. The dried powder was transferred to a muffle furnace and kept at 450℃ for 6h to finally obtain the magnesium-doped ferromanganese phosphate precursor material.

[0024] Figure 1The image shows a comparison of the XRD pattern of the manganese iron phosphate sample prepared in this embodiment with the MnPO4 standard card (PDF#51-1548). The image shows high and sharp peaks, and no impurity peaks were observed, indicating that the doping of magnesium atoms does not change the crystal structure of the material. Figure 2 SEM images show that the prepared manganese iron phosphate sample is a spindle-shaped sphere with a diameter of about 2 μm and a relatively uniform size distribution.

[0025] Preparation of magnesium-doped lithium manganese iron phosphate: 145.72g of manganese iron phosphate precursor, 41.28g of lithium carbonate and 3.18g of glucose were added to 500mL of deionized water and stirred evenly to obtain a mixed slurry. The slurry was then milled to control the particle size of the output particle size to D50≤300μm. The slurry was then transferred to a spray dryer for drying and then fluidized bed sintering under nitrogen atmosphere protection for 8h at 650℃ to finally obtain magnesium-doped lithium manganese iron phosphate.

[0026] Example 2 Preparation of magnesium-doped manganese ferric phosphate precursor: Unlike Example 1, the content of ferrous sulfate impurity byproduct of titanium dioxide is different, and the amount of magnesium acetate tetrahydrate added is 3.03g. The rest is the same as in Example 1, and magnesium-doped manganese ferric phosphate precursor material is obtained.

[0027] Preparation of magnesium-doped lithium manganese iron phosphate: 145.72g of manganese iron phosphate precursor, 41.28g of lithium carbonate and 3.18g of glucose were added to 500mL of deionized water and stirred evenly to obtain a mixed slurry. The slurry was then milled to control the particle size of the output particle size to D50≤300μm. The slurry was then transferred to a spray dryer for drying and then fluidized bed sintering under nitrogen atmosphere protection for 8h at 650℃ to finally obtain magnesium-doped lithium manganese iron phosphate.

[0028] Example 3 Preparation of magnesium-doped manganese ferric phosphate precursor: Unlike Example 1, the content of ferrous sulfate impurity byproduct of titanium dioxide is different, and the amount of magnesium acetate tetrahydrate added is 3.58g. The rest is the same as in Example 1, and magnesium-doped manganese ferric phosphate precursor material is obtained.

[0029] Preparation of magnesium-doped lithium manganese iron phosphate: 145.72g of manganese iron phosphate precursor, 41.28g of lithium carbonate and 3.18g of glucose were added to 500mL of deionized water and stirred evenly to obtain a mixed slurry. The slurry was then milled to control the particle size of the output particle size to D50≤300μm. The slurry was then transferred to a spray dryer for drying and then fluidized bed sintering under nitrogen atmosphere protection for 8h at 650℃ to finally obtain magnesium-doped lithium manganese iron phosphate.

[0030] Example 4 Preparation of magnesium-doped manganese ferric phosphate precursor: Unlike Example 1, the content of ferrous sulfate impurity byproduct of titanium dioxide was different, and the amount of magnesium acetate tetrahydrate added was 3.26g. The rest was the same as in Example 1, and magnesium-doped manganese ferric phosphate precursor material was obtained.

[0031] Preparation of magnesium-doped lithium manganese iron phosphate: 145.72g of manganese iron phosphate precursor, 41.28g of lithium carbonate and 3.18g of glucose were added to 500mL of deionized water and stirred evenly to obtain a mixed slurry. The slurry was then milled to control the particle size of the output particle size to D50≤300μm. The slurry was then transferred to a spray dryer for drying and then fluidized bed sintering under nitrogen atmosphere protection for 8h at 650℃ to finally obtain magnesium-doped lithium manganese iron phosphate.

[0032] In the magnesium-doped manganese iron phosphate precursor materials prepared in Examples 1-4 above, the magnesium content was 8750±10ppm.

[0033] Example 5 Preparation of magnesium-doped manganese iron phosphate precursor: Unlike Example 1, magnesium acetate tetrahydrate was replaced with magnesium pyruvate, and the mass of magnesium pyruvate added was 2.24 g. The rest was the same as in Example 1, and magnesium-doped manganese iron phosphate precursor material was obtained.

[0034] Preparation of magnesium-doped lithium manganese iron phosphate: 145.72g of manganese iron phosphate precursor, 41.28g of lithium carbonate and 3.18g of glucose were added to 500mL of deionized water and stirred evenly to obtain a mixed slurry. The slurry was then milled to control the particle size of the output particle size to D50≤300μm. The slurry was then transferred to a spray dryer for drying and then fluidized bed sintering under nitrogen atmosphere protection for 8h at 650℃ to finally obtain magnesium-doped lithium manganese iron phosphate.

[0035] Example 6 Preparation of magnesium-doped manganese iron phosphate precursor: Unlike Example 1, magnesium acetate tetrahydrate was replaced with magnesium propionate, and the mass of magnesium propionate added was 2.00 g. The rest was the same as in Example 1, and magnesium-doped manganese iron phosphate precursor material was obtained.

[0036] Preparation of magnesium-doped lithium manganese iron phosphate: 145.72g of manganese iron phosphate precursor, 41.28g of lithium carbonate and 3.18g of glucose were added to 500mL of deionized water and stirred evenly to obtain a mixed slurry. The slurry was then milled to control the particle size of the output particle size to D50≤300μm. The slurry was then transferred to a spray dryer for drying and then fluidized bed sintering under nitrogen atmosphere protection for 8h at 650℃ to finally obtain magnesium-doped lithium manganese iron phosphate.

[0037] Comparative Example 1 Preparation of magnesium-doped ferromanganese phosphate precursor: Unlike Example 1, the ferrous sulfate by-product of titanium dioxide was replaced with high-purity ferrous sulfate, and the mass of magnesium acetate tetrahydrate added was 4.30 g. The rest was the same as in Example 1, and the magnesium-doped ferromanganese phosphate precursor material was obtained, in which the magnesium content was 8756 ppm.

[0038] Preparation of magnesium-doped lithium manganese iron phosphate: 145.72g of manganese iron phosphate precursor, 41.28g of lithium carbonate and 3.18g of glucose were added to 500mL of deionized water and stirred evenly to obtain a mixed slurry. The slurry was then milled to control the particle size of the output particle size to D50≤300μm. The slurry was then transferred to a spray dryer for drying and then fluidized bed sintering under nitrogen atmosphere protection for 8h at 650℃ to finally obtain magnesium-doped lithium manganese iron phosphate.

[0039] Comparative Example 2 163.64g of iron phosphate, 141.86g of manganese tetroxide, 41.28g of lithium carbonate, 340.32g of phosphoric acid, 4.19g of magnesium acetate tetrahydrate, and 3.18g of glucose were sequentially added to 500mL of deionized water and stirred until homogeneous to obtain a mixed slurry. The slurry was then milled to control the particle size at D50≤300μm. It was then transferred to a spray dryer for drying and then fluidized bed sintering under a nitrogen atmosphere for 8 hours to obtain magnesium-doped manganese iron phosphate.

[0040] Comparative Example 3 Preparation of magnesium-doped manganese ferrophosphate precursor: 874g of ferrous sulfate (a byproduct of titanium dioxide) and 318g of manganese sulfate were added to 2500mL of deionized water and stirred until homogeneous to form solution A. Then, 321g of 85% phosphoric acid was added to 260mL of deionized water to form a dilute phosphoric acid aqueous solution (47wt%). Subsequently, all the dilute phosphoric acid aqueous solution was added to mixed solution A to react and form solution B. Ammonia water with a mass concentration of 22.45% was added dropwise to adjust the pH of the mixed solution to 4.5 to form mixed slurry C. Then, 302g of hydrogen peroxide with a mass concentration of 25% was added to mixed slurry C and reacted in a water bath at 75℃ for 3h. After filtration, the filter residue was kept at 80℃ for 12h. The dried powder was transferred to a muffle furnace and kept at 450℃ for 6h to finally obtain the magnesium-doped manganese ferrophosphate precursor material.

[0041] Preparation of magnesium-doped lithium manganese iron phosphate: 145.72g of manganese iron phosphate precursor, 2.42g of magnesium acetate tetrahydrate, 41.28g of lithium carbonate and 3.18g of glucose were added to 500mL of deionized water and stirred evenly to obtain a mixed slurry. The slurry was then milled to control the particle size at D50≤300μm. The slurry was then transferred to a spray dryer for drying and then fluidized bed sintering under nitrogen atmosphere for 8h at 650℃ to obtain magnesium-doped lithium manganese iron phosphate.

[0042] Table 1. Content of ferrous sulfate impurities from titanium dioxide by-products used in the examples and comparative examples.

[0043] Analysis and testing: The magnesium-doped lithium manganese iron phosphate, PVDF, and carbon nanotubes prepared in the above examples and comparative examples were mixed uniformly at a mass ratio of 92:4:4, and NMP was added to form a slurry. This slurry was then coated onto electrode sheets using a coating machine. The electrode sheets were placed in a vacuum drying oven and dried at 80°C for 12 hours. A positive electrode sheet with a diameter of 12 mm was then formed by punching holes. Using 1 mol / L lithium hexafluorophosphate as the electrolyte, a polyethylene membrane as the separator, and a lithium metal sheet as the reference electrode, the materials were assembled into CR2032 coin cells in an argon-filled glove box. Electrochemical performance was tested at 25°C. The coin cells were tested using a Land-CT2001A battery testing system, with a test voltage range of 2.5~4.5V. The electrical performance and specific surface area test results are shown in Table 2.

[0044] Table 2. Electrical performance and specific surface area test results of lithium manganese iron phosphate.

[0045] Results Analysis: Table 2 shows that each embodiment exhibits superior electrochemical performance compared to the comparative example, with a significant reduction in material specific surface area. This indicates a synergistic effect between the magnesium impurities in the titanium dioxide byproduct ferrous sulfate and the added magnesium source during the doping process. Furthermore, in-situ doping strengthens the bond between magnesium and other elements, resulting in superior performance in lithium iron phosphate (LFP). Comparing Examples 1, 5, and 6 reveals variations in the synergistic effect between the magnesium impurities in the byproduct and different added magnesium sources. Magnesium pyruvate exhibits the best synergistic effect, achieving a 0.1C discharge capacity of 155.6 mAh / g in LFP preparation, demonstrating excellent rate performance. Additionally, comparing Examples 1-4 shows that higher magnesium impurity content in the titanium dioxide byproduct ferrous sulfate leads to better performance in the downstream LFP. Comparing Examples 1 and Comparative Example 3 shows that adding the magnesium source during the preparation of ferromanganese phosphate produces a better synergistic effect, and in-situ doping strengthens the bond between magnesium and other elements, resulting in superior performance.

Claims

1. A method for preparing a doped manganese iron phosphate precursor, characterized in that, Includes the following steps: S1. Add the by-products of titanium dioxide, namely ferrous sulfate, manganese salt, and magnesium salt, to water and stir until homogeneous to obtain solution A; S2. Add dilute phosphoric acid aqueous solution to solution A to obtain solution B; S3. Add ammonia water dropwise to solution B to adjust the pH, and obtain mixed slurry C; S4. Add hydrogen peroxide to the mixed slurry C and heat it to react. After the reaction is complete, filter and dry to obtain powder. S5. The powder obtained in S4 is calcined at high temperature to obtain magnesium-doped manganese iron phosphate precursor.

2. The method for preparing a doped manganese iron phosphate precursor according to claim 1, characterized in that, The manganese salt in S1 is at least one of manganese sulfate, manganese acetate, manganese nitrate, or manganese dichloride; the magnesium salt is at least one of magnesium acetate, magnesium pyruvate, magnesium chloride, magnesium sulfate, or magnesium propionate.

3. The method for preparing a doped manganese iron phosphate precursor according to claim 1, characterized in that, The mass concentration of the dilute phosphoric acid aqueous solution described in S2 is 30%~70%.

4. The method for preparing a doped manganese iron phosphate precursor according to claim 1, characterized in that, The pH of S3 is 4-7, preferably 4.5; the mass concentration of the ammonia water is 20-23%.

5. The method for preparing a doped manganese iron phosphate precursor according to claim 1, characterized in that, The hydrogen peroxide concentration in S4 is 25-30%, the reaction temperature is 70-80℃, and the reaction time is 2-5h; the drying conditions are: heat preservation at 70-90℃ for 10-24h.

6. The method for preparing a doped manganese iron phosphate precursor according to claim 1, characterized in that, The by-products of titanium dioxide, namely ferrous sulfate, manganese salt, phosphoric acid, and hydrogen peroxide, are calculated as iron, manganese, phosphorus, and hydrogen peroxide, respectively. The molar ratio of the by-products of titanium dioxide, namely ferrous sulfate, manganese salt, phosphoric acid, and hydrogen peroxide, is (0.2-0.5):(0.5-0.8):(1.0-1.05):(0.5-1).

7. The method for preparing a doped manganese iron phosphate precursor according to claim 1, characterized in that, The high-temperature calcination conditions described in S5 are: 300~500℃ for 3~7 hours.

8. The method for preparing a doped manganese iron phosphate precursor according to claim 1, characterized in that, The magnesium content in the titanium dioxide by-product ferrous sulfate in S1 is 1000~4000ppm; the magnesium content in the magnesium-doped manganese ferric phosphate precursor in S5 is 2000-10000ppm.

9. A doped manganese iron phosphate precursor, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 8.

10. A doped lithium manganese iron phosphate, characterized in that, The raw materials include the doped manganese iron phosphate precursor as described in claim 9, a carbon source, and a lithium source.

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