Method for preparing lithium manganese iron phosphate from iron hydroxyphosphate and ferromanganese phosphate and application thereof

Abstract

The application provides a method for preparing lithium manganese iron phosphate from iron hydroxyphosphate and ferromanganous phosphate, wherein ferrous sulfate is purified to form a ferrous sulfate solution, hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution and ammonia water are sequentially added into the solution to react to form a mixed slurry, the mixed slurry is heated to a certain temperature and kept for a certain time, and then washed with water and filtered under pressure to form iron hydroxyphosphate precursors with different iron-phosphorus ratios; the iron hydroxyphosphate precursors are dried by flash evaporation and sintered at high temperature and then crushed to obtain iron hydroxyphosphate precursors with different iron-phosphorus ratios and different specific surface areas; the iron hydroxyphosphate precursors are crushed and mixed to obtain iron hydroxyphosphate products; the iron hydroxyphosphate products with high iron-phosphorus ratios and the iron hydroxyphosphate products with low iron-phosphorus ratios are mixed according to a certain proportion, and then mixed with lithium phosphate, ferromanganous phosphate, a carbon source and an additive according to a certain proportion and a process flow to obtain lithium manganese iron phosphate products.

Description

Technical Field

[0001] This invention relates to the technical field of lithium-ion battery cathode material preparation methods, and particularly to a method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, and its application. Background Technology

[0002] Lithium-ion batteries are one of the most common chemical power sources, with advantages such as high specific energy, high specific power, long cycle life, and no memory effect. They are ideal power sources for electric vehicles, digital products, and various power tools.

[0003] Lithium manganese iron phosphate (LMP) is a cathode active material used in lithium-ion batteries. Like lithium iron phosphate (LFP), LMP belongs to the phosphate-based cathode active materials and boasts advantages such as good cycle performance, excellent safety, and environmental friendliness. Common synthesis methods for LMP include high-temperature solid-state synthesis, hydrothermal synthesis, and sol-gel synthesis. However, producing high-quality LMP requires stricter control over the types of raw materials, precursor composition, key element ratios, preparation methods, and process parameters.

[0004] The basic approach to preparing lithium manganese iron phosphate (LFP) involves directly mixing lithium, manganese, iron, phosphorus, and carbon sources, along with compounds containing dopant elements, followed by grinding, drying, and sintering processes to obtain a doped LFP-carbon composite material. However, a problem with this method is that it is difficult to obtain a homogeneous mixture when mixing multiple raw materials simultaneously. Summary of the Invention

[0005] In view of the above, the present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, the present invention proposes a method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, and its application. This method uses ferrous sulfate as a material, adding hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate, and ammonia to synthesize ferric hydroxyphosphate, and uses lithium phosphate and ferrous manganese phosphate as the main raw materials to prepare lithium manganese iron phosphate with high compaction density and high capacity. Furthermore, this method has high production efficiency and low production cost, making it suitable for large-scale industrial production.

[0006] Therefore, in a first aspect, embodiments of the present invention provide a method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, the method comprising: adding ferrous sulfate, a byproduct of titanium dioxide, to a phosphorus source and a precipitant for purification, and obtaining a ferrous sulfate solution after pressure filtration; adding an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution; sequentially adding hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia to the ferrous sulfate solution, reacting for a period of time to form a mixed slurry, heating and holding the mixed slurry at a certain temperature for a period of time, and then repeatedly washing and pressure filtration to form ferric hydroxyphosphate precursors with different iron-phosphorus ratios; flash drying the ferric hydroxyphosphate precursors in a flash evaporator and sintering at high temperature for a certain time to obtain ferric hydroxyphosphate precursor products with different iron-phosphorus ratios and different specific surface areas; and then... The sintered material is pulverized using a mechanical mill and mixed with a ribbon mixer to obtain hydroxyferric phosphate products with different iron-phosphorus ratios and specific surface areas. Ferrous manganese phosphate and phosphoric acid are first ball-milled in a certain ratio, and then lithium phosphate is added. Wet grinding yields a nano-sized slurry. A certain amount of high-iron-phosphorus-ratio, high-specific-surface-area hydroxyferric phosphate, low-iron-phosphorus-ratio, low-specific-surface-area hydroxyferric phosphate, lithium phosphate, carbon source, and additives are added to the slurry and milled to obtain a nano-sized mixture. This mixture is then spray-dried to obtain a spray-dried material. The spray-dried material is sintered in a box furnace to obtain a sintered material. The sintered material is then pulverized using an air jet mill to obtain a pulverized material. The pulverized material is further processed through sieving, batching, and packaging to obtain the finished lithium manganese iron phosphate product.

[0007] Preferably, in step S1, the mass ratio of ferrous sulfate:phosphorus source:precipitant is 1:[0.001-0.005]:[0.005-0.007], the purification reaction temperature is 40℃, the reaction pH is 2.2-2.5, and the reaction time is 1h. The phosphorus source is one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, and sodium phosphate, and the precipitant is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia water. In step S2, the amount of phosphoric acid added is in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15. In step S3, when the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio: Fe / P = 1.475-1.490, high iron-phosphorus ratio hydroxyferric phosphate can be formed; when the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio: Fe / P = 1.460-1.475, low iron-phosphorus ratio hydroxyferric phosphate can be generated.

[0008] Preferably, in step S3, the water washing can be performed multiple times. The first water wash mainly removes impurities such as magnesium, manganese, and sulfur. In the final water wash, a 1:1 diluted ammonia solution is added to adjust the pH value to 6.5-7.0 to remove SO4. 2-Ions; the hydrogen peroxide concentration is 30%-60%, and the mixed slurry is heated to 60-80℃ and kept at that temperature for 3 hours.

[0009] Preferably, step S3 includes: adding excess hydrogen peroxide to the ferrous sulfate solution and continuing oxidation for a certain period of time; adding phosphoric acid solution to the oxidized ferrous sulfate solution, then dissolving ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃, and adding it to the oxidized ferrous sulfate solution; adding ammonia water to the ferrous sulfate solution to adjust the pH value of the solution to 3.00±0.02, reacting for a period of time to form a mixed slurry, heating and keeping the mixed slurry at a certain temperature for a period of time, and then washing and filtering it multiple times with water to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0010] Preferably, in step S4, the inlet air temperature of the flash evaporator is controlled at 220±20℃, the outlet air temperature at 110±5℃, the sintering atmosphere is air, the sintering temperature is 535-560℃, and the sintering time is 4-5h; in step S5, the particle size is controlled at D10≥1.0μm, D50: 6-15μm, D90≤60μm, the mixing frequency of the mixer is controlled at 35±2Hz, and the mixing time is 1-2h; the high-iron-phosphorus hydroxyferric phosphate has a high specific surface area, and its iron-phosphorus molar ratio satisfies: Fe / P=1.460-1.480, and its specific surface area satisfies: BET=15-20m². 2 / g; the low iron-to-phosphorus ratio hydroxyferric phosphate has a low specific surface area, and its iron-to-phosphorus molar ratio satisfies: Fe / P=1.440-1.460, and its specific surface area satisfies: BET=5-10m². 2 / g.

[0011] Preferably, step S6 includes: mixing iron source, manganese source, and phosphoric acid, then adding antioxidant and phosphorus source, controlling the pH value of the solution between 3.0 and 4.0 to obtain a mixed solution; adding a 16-20% ammonia solution A to a reaction vessel, and simultaneously adding the mixed solution and an 8-10% ammonia solution B under an inert gas atmosphere, controlling the pH value between 7.5 and 8.0, the reaction temperature at 25-40℃, aging for 1 hour after the addition is complete, and co-precipitating to prepare a manganese ferrous phosphate precursor; ball milling manganese ferrous phosphate and phosphoric acid in a certain ratio, then adding lithium phosphate, and wet grinding to obtain a nano-sized sand mill slurry.

[0012] Preferably, in step S61, the molar ratio of the added manganese source to the iron source is between 8:2 and 2:8, and the molar ratio of the sum of the added manganese source and the iron source to the phosphorus source is [1.41-1.43]:1. The amount of antioxidant added is 1% of the mass fraction of the iron source. The iron source is one or more of ferrous sulfate, hydrated ferrous sulfate, ferrous nitrate, and ferrous chloride. The manganese source is one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate. The phosphorus source is one or more of phosphoric acid, sodium phosphate, potassium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. The antioxidant is ascorbic acid. In step S62, the inert gas is one or more of nitrogen, argon, and helium, and the feeding time is 0.5-6 hours. In step S64, the Fe:Mn molar ratio in the ferrous manganese phosphate is between 2:8 and 8:2, and the amount of phosphoric acid added is between 0.5% and 5% of the mass fraction of ferrous manganese phosphate. In the sand milling slurry, according to the molar ratio Li:Fe:Mn:P = [1.03-1.04]:[0.2-0.8]:[0.2-0.8]:[1.03-1.04], the sand milling particle size in the sand milling slurry is controlled to be between 0.60 and 0.80 μm.

[0013] Preferably, in step S7, the molar ratio of the high-iron-phosphorus ratio hydroxyferric phosphate to the low-iron-phosphorus ratio hydroxyferric phosphate is between 2:8 and 8:2. In the mixture, according to the molar ratio, Li:Fe:Mn:P = [1.03-1.04]:[0.2-0.8]:[0.2-0.8]:[1.03-1.04]. The amount of carbon source added is based on the carbon content in the final product being between 1.2% and 1.6%. The additives are selected from one or more of titanium dioxide, ammonium metavanadate, and niobium pentoxide, and the doping amount is controlled between 300-3000 ppm. The abrasive particle size in the mixture is controlled between 0.30-0.50 μm. The mixture is then spray-dried. In step S8, the inlet air temperature is 200-220℃, the outlet air temperature is 80-110℃, and the blowing frequency is 80Hz. The spray particle size of the spray material is controlled between D50=20-40μm. In step S8, the sintering atmosphere is nitrogen, the sintering temperature is 750-780℃, the heating rate is 3℃ / min, the sintering time is 8-12h, and after natural cooling, the sintered material is obtained. During the pulverization process, the gas pressure is controlled between 0.2-0.4Mpa, the grading frequency is 80-200Hz, and the particle size of the pulverized material meets the following requirements: D10>0.35μm, D50=0.7-2.0μm, D90<10μm, D100<30μm.

[0014] Secondly, embodiments of the present invention provide a lithium-ion battery cathode material obtained by processing lithium iron phosphate obtained by using the method for preparing lithium manganese iron phosphate with hydroxy iron phosphate and ferrous manganese phosphate provided in the first aspect above.

[0015] Thirdly, embodiments of the present invention provide a lithium-ion battery, including the lithium-ion battery cathode material described in the second aspect above.

[0016] The method for preparing lithium manganese iron phosphate from ferrous hydroxyphosphate and ferrous manganese phosphate provided in this invention utilizes ferrous sulfate, a byproduct of titanium dioxide, to generate ferric sulfate. After adding other materials and reacting, ferrous hydroxyphosphate with different iron-to-phosphorus ratios is generated. Then, through different sintering processes, ferrous hydroxyphosphate products with high iron-to-phosphorus ratio and high specific surface area and low iron-to-phosphorus ratio and low specific surface area are obtained. First, ferrous manganese phosphate and phosphoric acid are ball-milled to acidify the ferrous manganese phosphate to a certain extent. Then, lithium phosphate is added and milled to a suitable particle size to obtain a milled slurry. Next, ferrous hydroxyphosphate with high iron-to-phosphorus ratio and high specific surface area, ferrous hydroxyphosphate with low iron-to-phosphorus ratio and low specific surface area, lithium phosphate, and additives are added to the milled slurry and mixed in a certain proportion to form a mixture. The mixture is then subjected to milling, spray drying, sintering, sieving, batching, and packaging processes to obtain the finished lithium manganese iron phosphate. This method uses a mixture of high and low iron-to-phosphorus ratio hydroxyferric phosphate, and introduces lithium phosphate and ferrous manganese phosphate. Hydroxyferric phosphate, as the iron source, provides large-particle lithium manganese iron phosphate, which is beneficial for improving the material's compaction density, conductivity, and capacity. Ferrous manganese phosphate, as both an iron and manganese source, helps improve the material's discharge voltage. First, ball milling ferrous manganese phosphate with phosphoric acid lowers the slurry's pH, dissolving and releasing some iron and manganese ions, facilitating the preparation of lithium manganese iron phosphate with particles <10nm. Subsequent sand milling of the slurry with high iron-to-phosphorus ratio and high specific surface area hydroxyferric phosphate and low iron-to-phosphorus ratio and low specific surface area hydroxyferric phosphate and lithium phosphate ensures that the sand milling time of the ferrous manganese phosphate precursor is much longer than that of the hydroxyferric phosphate, guaranteeing that the ferrous manganese phosphate particles are smaller than those of the hydroxyferric phosphate. This results in a better particle size distribution for the subsequently formed lithium manganese iron phosphate, further improving the material's compaction performance while maintaining electrochemical performance. Attached Figure Description

[0017] Figure 1 This is a flowchart of a method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate according to an embodiment of the present invention.

[0018] Figure 2 A flowchart of step S3 for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, provided in an embodiment of the present invention;

[0019] Figure 3 A flowchart of step S6 for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, provided in an embodiment of the present invention;

[0020] Figure 4 This is the SEM image of the high iron-to-phosphorus ratio and high specific surface area ferric hydroxyphosphate prepared in Example 1 of the present invention;

[0021] Figure 5 The image shows the SEM spectrum of the lithium iron phosphate cathode material prepared in Example 1 of this invention.

[0022] Figure 6 The XRD pattern of the high iron-to-phosphorus ratio and high specific surface area hydroxyferric phosphate prepared in Example 1 of this invention;

[0023] Figure 7 The image shows the XRD pattern of the lithium manganese iron phosphate cathode material prepared in Example 1 of this invention.

[0024] Figure 8 The charge-discharge curve (0.1C) of a coin cell assembled with the lithium manganese iron phosphate cathode material prepared in Example 1 of this invention.

[0025] Figure 9 The charge-discharge curve (0.2C) of a coin cell assembled with the lithium manganese iron phosphate cathode material prepared in Example 1 of this invention.

[0026] Figure 10 The charge-discharge curve (1C) of a coin cell assembled with the lithium manganese iron phosphate cathode material prepared in Example 1 of this invention. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided in this invention; however, those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0029] This invention provides a method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, which can be used to prepare lithium manganese iron phosphate with high compaction density and high capacity. Figure 1 As shown, this method includes:

[0030] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a phosphorus source and a precipitant for purification. After pressure filtration and purification, a ferrous sulfate solution is obtained.

[0031] The reaction was carried out in the following mass ratio: ferrous sulfate: phosphorus source: precipitant = 1: [0.001-0.005]: [0.005-0.007]. The purification reaction temperature was 40℃, the reaction pH was 2.2-2.5, and the reaction time was 1h.

[0032] In this embodiment, the phosphorus source can be one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, sodium phosphate, etc., and the precipitant can be one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia water, etc.

[0033] Step S2: Add an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution;

[0034] The amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15.

[0035] Step S3: Hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution and ammonia are added to ferrous sulfate solution in sequence and reacted for a period of time to form a mixed slurry. After heating and keeping the mixed slurry at a certain temperature for a period of time, it is washed with water and filtered repeatedly to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0036] In this embodiment, hydrogen peroxide is first added to fully oxidize ferrous ions into ferric ions, and then phosphoric acid and ammonium dihydrogen phosphate are added to adjust the solution ions to a suitable iron-phosphorus molar ratio. On the one hand, this can make the generated ferric hydroxyphosphate precursor more stable; on the other hand, it can make the generated ferric hydroxyphosphate precursor particles larger and easier to filter and wash.

[0037] Specifically, when the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio of Fe / P=1.475-1.490, high iron-phosphorus ratio hydroxyferric phosphate can be formed; when the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio of Fe / P=1.460-1.475, low iron-phosphorus ratio hydroxyferric phosphate can be generated.

[0038] In this embodiment, the hydrogen peroxide concentration is between 30% and 60%, and the mixed slurry is heated to 60-80°C and held at that temperature for 3 hours. The washing process can be repeated multiple times. The first wash primarily removes impurities such as magnesium, manganese, and sulfur. The final wash involves adding 1:1 diluted ammonia to adjust the pH to 6.5-7.0 to remove SO4. 2-Ions. Specifically, the water washing can be performed three times. The first and second water washes mainly remove impurities such as manganese, magnesium, and sulfur. In the third water wash, a 1:1 diluted ammonia solution is added to adjust the pH to 6.5-7.0 to remove SO4. 2- ion.

[0039] Specifically, in the first embodiment of the present invention, as Figure 2 As shown, step S3 includes:

[0040] Step S31: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time;

[0041] Step S32: Add the phosphoric acid solution to the oxidized ferrous sulfate solution, then dissolve the ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃, and add it to the oxidized ferrous sulfate solution.

[0042] Step S33: Add ammonia to the ferrous sulfate solution to adjust the pH of the solution to 3.00±0.02. After reacting for a period of time, a mixed slurry is formed. The mixed slurry is heated and kept at a certain temperature for a period of time, and then washed and filtered repeatedly with water to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0043] The heating temperature of the mixed slurry is 60-80℃, and the holding time is 3h.

[0044] Step S4: Flash dry the hydroxyferric phosphate precursor in a flash evaporator and sinter it at high temperature for a certain time to obtain hydroxyferric phosphate precursor products with different iron-phosphorus ratios and different specific surface areas.

[0045] The flash drying of the ferric hydroxyphosphate precursor is to remove free water. The inlet air temperature of the flash evaporator is controlled at 220±20℃, and the outlet air temperature is controlled at 110±5℃. The sintering atmosphere is air, the sintering temperature can be 535-560℃, and the sintering time can be 4-5 hours.

[0046] Step S5: The sintered material is crushed by a mechanical mill and mixed by a ribbon mixer to obtain hydroxy ferric phosphate products with different iron-phosphorus ratios and different specific surface areas.

[0047] During the pulverization process, the particle size is controlled as follows: D10 ≥ 1.0 μm, D50 6-15 μm, and D90 ≤ 60 μm. The mixing frequency of the mixer is controlled at 35 ± 2 Hz, and the mixing time can be 1-2 hours.

[0048] In this embodiment of the invention, the high-iron-phosphorus ferric phosphate has a high specific surface area, and its iron-phosphorus molar ratio satisfies: Fe / P = 1.460-1.480, and its specific surface area satisfies: BET = 15-20 m². 2 / g; The low iron-to-phosphorus ratio hydroxyferric phosphate precursor has a low specific surface area, and its iron-to-phosphorus molar ratio satisfies: Fe / P=1.440-1.460, and its specific surface area satisfies: BET=5-10m². 2 / g.

[0049] Step S6: First, ball mill ferrous manganese phosphate and phosphoric acid in a certain ratio, then add lithium phosphate and wet grind to obtain nano-sized sand slurry;

[0050] Specifically, such as Figure 3 As shown, step S6 includes:

[0051] Step S61: After mixing the iron source, manganese source, and phosphoric acid, add the antioxidant and phosphorus source, and control the pH of the solution between 3.0 and 4.0 to obtain a mixed solution;

[0052] The molar ratio of the added manganese source to the iron source is between 8:2 and 2:8, the molar ratio of the sum of the added manganese source and the iron source to the phosphorus source is [1.41-1.43]:1, and the amount of antioxidant added is 1% of the mass fraction of the iron source.

[0053] In this embodiment of the invention, the iron source can be one or more of ferrous sulfate, hydrated ferrous sulfate, ferrous nitrate, and ferrous chloride; the manganese source can be one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate; the phosphorus source can be one or more of phosphoric acid, sodium phosphate, potassium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate; and the antioxidant can be ascorbic acid.

[0054] Step S62: Add a 16-20% ammonia solution A to the reactor. Under an inert gas atmosphere, simultaneously add the mixed solution and an 8-10% ammonia solution B. Control the pH value between 7.5 and 8.0, and the reaction temperature at 25-40℃. After the addition is complete, age for 1 hour to co-precipitate and prepare the manganese ferrous phosphate precursor.

[0055] The inert gas can be one or more of nitrogen, argon, and helium, and the feeding time is 0.5-6 hours.

[0056] Step S63: The ferrous manganese phosphate precursor is filtered, washed with water, flash dried, sintered at high temperature, and then crushed and mixed to obtain the finished ferrous manganese phosphate product.

[0057] Step S64: First, ball mill ferrous manganese phosphate and phosphoric acid in a certain ratio, then add lithium phosphate and wet grind to obtain nano-sized sand slurry.

[0058] The Fe:Mn molar ratio in the ferrous manganese phosphate is between 2:8 and 8:2, and the amount of phosphoric acid added is 0.5%-5% of the mass fraction of the ferrous manganese phosphate. In the sand milling slurry, the sand milling particle size in the slurry is controlled to be between 0.60-0.80 μm according to the molar ratio Li:Fe:Mn:P=[1.03-1.04]:[0.2-0.8]:[0.2-0.8]:[1.03-1.04].

[0059] Step S7: Add a certain amount of high iron-phosphorus ratio and high specific surface area hydroxyferric phosphate, low iron-phosphorus ratio and low specific surface area hydroxyferric phosphate, lithium phosphate, carbon source and additives to the above sand milling material and obtain nano-sized mixture. After spray drying, obtain spray material.

[0060] In this embodiment of the invention, the molar ratio of high-iron-phosphorus-ratio hydroxyferric phosphate to low-iron-phosphorus-ratio hydroxyferric phosphate is between 2:8 and 8:2, preferably 3:7. The Fe:Mn molar ratio in ferrous manganese phosphate is between 2:8 and 8:2, preferably between 3:7 and 7:3. Furthermore, in the mixture, the molar ratio is Li:Fe:Mn:P = [1.03-1.04]:[0.2-0.8]:[0.2-0.8]:[1.03-1.04]. The amount of carbon source added is based on a carbon content of 1.2%-1.6% in the final product.

[0061] The carbon source can be one or more of sucrose, glucose, citric acid, starch, and polyethylene glycol. The additive can be one or more of titanium dioxide, ammonium metavanadate, and niobium pentoxide, with the doping amount controlled between 300-3000 ppm. The particle size of the abrasive in the mixture is controlled between 0.30-0.50 μm. In spray drying, the inlet air temperature can be 200-220℃, the outlet air temperature can be 80-110℃, the blowing frequency can be 80 Hz, and the final spray particle size in the sprayed material is controlled between D50 = 20-40 μm.

[0062] Step S8: The above sprayed material is placed in a box furnace for sintering to obtain sintered material, and the sintered material is pulverized by an air jet mill to obtain pulverized material;

[0063] During the sintering process, the sintering atmosphere is nitrogen, the sintering temperature is 750-780℃, the heating rate is 3℃ / min, and the sintering time is 8-12h. After natural cooling, the sintered material is obtained. During the pulverization process, the gas pressure is controlled between 0.2-0.4Mpa, the grading frequency is 80-200Hz, and the particle size of the final pulverized material meets the following requirements: D10>0.35μm, D50=0.7-2.0μm, D90<10μm, D100<30μm.

[0064] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished product of lithium manganese iron phosphate can be obtained.

[0065] The method for preparing lithium manganese iron phosphate from ferrous manganese phosphate provided in this invention involves purifying ferrous sulfate, a byproduct of titanium dioxide production, to obtain a ferrous sulfate solution. Hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia are then added sequentially to the ferrous sulfate solution, and the mixture is reacted for a period of time to form a mixed slurry. After multiple water washing and pressure filtration, ferrous phosphate precursors with different iron-to-phosphorus ratios are generated. These precursors are then subjected to different sintering processes to obtain ferrous phosphate products with high iron-to-phosphorus ratio and high specific surface area, and low iron-to-phosphorus ratio and low specific surface area. The ferrous phosphate prepared by this method involves first adding hydrogen peroxide to fully oxidize ferrous ions to ferric ions, then adding phosphoric acid and ammonium dihydrogen phosphate to adjust the solution ions to a suitable iron-to-phosphorus molar ratio. This process makes the generated ferrous phosphate precursor more stable. Furthermore, heating the mixed slurry to 60-80°C and holding it at that temperature for 3 hours results in larger ferrous phosphate precursor particles that are easier to filter and wash. During the water washing and purification stage, impurities are not easily trapped inside the crystals. After multiple water washes, the main impurities removed are magnesium, manganese, sulfur, and SO4. 2- The product contains few ions and other impurities, resulting in low impurity content and high purity. Furthermore, the iron-to-phosphorus ratio and specific surface area of ​​the hydroxyferric phosphate produced by this method are adjustable, allowing for the generation of hydroxyferric phosphates with different iron-to-phosphorus ratios as needed. Specifically, high iron-to-phosphorus ratio hydroxyferric phosphate particles are smaller, which can improve the material's discharge capacity; low iron-to-phosphorus ratio hydroxyferric phosphate particles are larger, which can improve the material's compaction density.

[0066] Furthermore, the manganese ferric phosphate prepared by this method can provide both a phosphorus source and utilize NH4+ by adding ammonium phosphate to the mixed solution. 4+ The coordination of Mn with ammonia water enables Mn to... 2+ Fe 2+ In the phosphate system, the precipitation rate is on the same order of magnitude, which meets the requirements of co-precipitation from the perspective of chemical reaction. The final obtained manganese ferrous phosphate has a dense secondary spherical particle structure, and the contents of Mn, Fe and P are uniform and the ratio is stable.

[0067] In subsequent steps, this method involves mixing high-iron-phosphorus ratio hydroxyferric phosphate and low-iron-phosphorus ratio hydroxyferric phosphate, then mixing them with lithium phosphate and manganese ferrous phosphate in a certain proportion, adding additives to form a mixture, and then subjecting the mixture to processes such as sand milling, spray drying, sintering, sieving, batching, and packaging to obtain the finished lithium manganese iron phosphate product.

[0068] This method uses a mixture of high and low iron-to-phosphorus ratio hydroxyferric phosphate and introduces lithium phosphate and ferrous manganese phosphate. Hydroxyferric phosphate serves as the iron source, providing a raw material for synthesizing large-particle lithium manganese iron phosphate, which improves the material's compaction density, conductivity, and capacity. Ferrous manganese phosphate serves as both an iron and manganese source, contributing to higher discharge voltage. First, ball milling ferrous manganese phosphate with phosphoric acid lowers the slurry's pH, dissolving and releasing some iron and manganese ions, facilitating the preparation of <10nm particles of lithium manganese iron phosphate. Subsequent sand milling of the slurry with high iron-to-phosphorus ratio and high specific surface area hydroxyferric phosphate and low iron-to-phosphorus ratio hydroxyferric phosphate and lithium phosphate ensures that the sand milling time for the ferrous manganese phosphate precursor is significantly longer than that for the hydroxyferric phosphate, guaranteeing smaller ferrous manganese phosphate particles and resulting in better particle size distribution in the subsequently formed lithium manganese iron phosphate. This further enhances the material's compaction performance while maintaining electrochemical properties.

[0069] The following detailed description, in conjunction with some specific embodiments, further illustrates the specific process and effects of the method for preparing lithium manganese iron phosphate using ferric hydroxyphosphate and ferrous manganese phosphate according to the present invention, but does not limit the scope of protection of the present invention.

[0070] Example 1

[0071] This embodiment provides a method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, including the following steps:

[0072] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a solution containing 4‰ phosphoric acid and 5‰ sodium hydroxide for purification. After pressure filtration, a ferrous sulfate solution is obtained.

[0073] Step S2: Add phosphoric acid to the ferrous sulfate solution according to the molar ratio n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution;

[0074] Step S3: Add excess 40% hydrogen peroxide to the ferrous sulfate solution, then add phosphoric acid solution and 30% ammonium dihydrogen phosphate solution to the ferrous sulfate solution so that the iron-phosphorus feeding ratio in the mixed slurry successively meets the iron-phosphorus molar ratio: Fe / P=1.490 and Fe / P=1.460. Then add ammonia water to the ferrous sulfate solution to form a mixed slurry. Heat the mixed slurry to 60℃, keep it at that temperature for 3 hours, and then wash and filter it multiple times with water to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0075] Step S4: The hydroxyferric phosphate precursor is flash-dried in a flash evaporator, with the flash evaporator inlet air temperature controlled at 200°C, and sintered in air atmosphere at 535°C and 560°C for 5 hours.

[0076] Step S5: The sintered material is crushed by mechanical mill, and the particle size is controlled as follows: D10≥1.0μm, D50:6-15μm, D90≤60μm. The material is then mixed by ribbon mixer at 35Hz for 1 hour to obtain hydroxy ferric phosphate with high iron-phosphorus ratio and high specific surface area and hydroxy ferric phosphate with low iron-phosphorus ratio and low specific surface area.

[0077] The SEM image of the high ferric phosphorus ratio and high specific surface area ferric phosphate prepared according to Example 1 is shown below. Figure 4 As shown.

[0078] The XRD pattern of the high ferric phosphorus ratio and high specific surface area ferric phosphate prepared according to Example 1 is shown below. Figure 6 As shown.

[0079] Step S6: Add 85% phosphoric acid to the ferromanganese phosphate precursor at a mass ratio of 1:200, ball mill for 60 min, and then add lithium phosphate for wet grinding to obtain a nano-sized sand mill slurry. The Fe:Mn molar ratio in the ferromanganese phosphate is 3:7. The sand mill slurry is prepared according to the molar ratio of Li:Fe:Mn:P = 1.03:0.3:0.7:1.03. The sand mill particle size D50 is controlled to be 0.60-0.62 μm.

[0080] Step S7: The above-mentioned sand-milled slurry is mixed with hydroxyferric phosphate (high iron-phosphorus ratio and high specific surface area), hydroxyferric phosphate (low iron-phosphorus ratio and low specific surface area), and lithium phosphate in a molar ratio of Li:Fe:Mn:P = 1.03:0.4:0.6:1.03. A carbon source mixture consisting of sucrose and polyethylene glycol, which makes the carbon content of the finished product 1.35%, and titanium dioxide with a doping amount of 2200ppm are added. The mixture is then sand-milled, and the sand-milled particle size is controlled at 0.50μm to obtain a nano-sized mixture. The mixture is then spray-dried, and the inlet air temperature is controlled at 220℃, the outlet air temperature at 100℃, and the blower frequency at 80Hz to obtain a spray material with a spray particle size D50 = 20-40μm.

[0081] Step S8: The above sprayed material is placed in a box furnace and sintered under a nitrogen atmosphere at a heating rate of 3℃ / min, a sintering temperature of 765℃, and a sintering time of 10h. After natural cooling, the sintered material is obtained. The sintered material is then pulverized by an air jet mill, with the air pressure controlled at 0.3Mpa and the grading frequency at 130Hz, to obtain pulverized material with particle sizes of D10>0.35μm, D50=0.8-1.8μm, D90<10μm, and D100<30μm.

[0082] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished product of lithium manganese iron phosphate can be obtained.

[0083] The SEM spectrum of the lithium iron phosphate cathode material prepared according to Example 1 is shown below. Figure 5 As shown.

[0084] The XRD pattern of the lithium iron phosphate cathode material prepared according to Example 1 is shown below. Figure 7 As shown.

[0085] Example 2

[0086] This embodiment provides a method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, including the following steps:

[0087] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a solution of phosphoric acid with a mass fraction of 3‰ and sodium hydroxide with a mass fraction of 5‰ for purification. After purification by pressure filtration, a ferrous sulfate solution is obtained.

[0088] Step S2: Add phosphoric acid to the ferrous sulfate solution according to the molar ratio n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution;

[0089] Step S3: Add excess 50% hydrogen peroxide to the ferrous sulfate solution, add phosphoric acid solution and 30% ammonium dihydrogen phosphate solution to the ferrous sulfate solution so that the iron-phosphorus feeding ratio in the mixed slurry successively meets the iron-phosphorus molar ratio: Fe / P=1.490 and Fe / P=1.460. Then add ammonia water to the ferrous sulfate solution to form a mixed slurry. Heat the mixed slurry to 60℃, keep it at that temperature for 3 hours, and then wash and filter it multiple times with water to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0090] Step S4: The hydroxyferric phosphate precursor is flash-dried in a flash evaporator, with the flash evaporator inlet air temperature controlled at 200°C, and sintered in air atmosphere at 545°C and 560°C for 4 hours.

[0091] Step S5: The sintered material is crushed by mechanical mill, and the particle size is controlled as follows: D10≥1.0μm, D50:6-15μm, D90≤60μm. The material is then mixed by ribbon mixer at 35Hz for 1 hour to obtain hydroxy ferric phosphate with high iron-phosphorus ratio and high specific surface area and hydroxy ferric phosphate with low iron-phosphorus ratio and low specific surface area.

[0092] Step S6: Add 85% phosphoric acid to the ferromanganese phosphate precursor at a mass ratio of 1:150, ball mill for 60 min, and then add lithium phosphate for wet grinding to obtain a nano-sized sand mill slurry. The Fe:Mn molar ratio in the ferromanganese phosphate is 4:6. The sand mill slurry is formulated according to the molar ratio of Li:Fe:Mn:P = 1.03:0.4:0.6:1.03. The sand mill particle size D50 is controlled to be 0.64-0.66 μm.

[0093] Step S7: The above-mentioned sand-milled slurry is mixed with hydroxyferric phosphate (high iron-phosphorus ratio and high specific surface area), hydroxyferric phosphate (low iron-phosphorus ratio and low specific surface area), and lithium phosphate in a molar ratio of Li:Fe:Mn:P = 1.03:0.5:0.5:1.03. A carbon source mixture consisting of sucrose and polyethylene glycol, which makes the carbon content of the finished product 1.45%, and ammonium metavanadate with a doping amount of 3000ppm are added. The mixture is then sand-milled, and the sand-milled particle size is controlled at 0.35μm to obtain a nano-sized mixture. The mixture is then spray-dried, and the inlet air temperature is controlled at 220℃, the outlet air temperature at 110℃, and the blower frequency at 80Hz to obtain a spray material with a spray particle size D50 = 20-40μm.

[0094] Step S8: The above sprayed material is placed in a box furnace and sintered under a nitrogen atmosphere. The heating rate is 3℃ / min, the sintering temperature is 770℃, and the sintering time is 8h. After natural cooling, the sintered material is obtained. The sintered material is then pulverized by an air jet mill, with the air pressure controlled at 0.3Mpa and the classification frequency at 130Hz, to obtain pulverized material with particle sizes of D10>0.35μm, D50=0.8-1.8μm, D90<10μm, and D100<30μm.

[0095] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished product of lithium manganese iron phosphate can be obtained.

[0096] Example 3

[0097] This embodiment provides a method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, including the following steps:

[0098] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a solution containing 2‰ phosphoric acid and 4‰ sodium hydroxide for purification. After pressure filtration, a ferrous sulfate solution is obtained.

[0099] Step S2: Add phosphoric acid to the ferrous sulfate solution according to the molar ratio n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution;

[0100] Step S3: Add excess 40% hydrogen peroxide to the ferrous sulfate solution, add phosphoric acid solution and 30% ammonium dihydrogen phosphate solution to the ferrous sulfate solution to make the iron-phosphorus feeding ratio in the mixed slurry meet the iron-phosphorus molar ratio: Fe / P=1.485 and Fe / P=1.465. Then add ammonia water to the ferrous sulfate solution to form a mixed slurry. Heat the mixed slurry to 60℃, keep it at that temperature for 3 hours, and then wash and filter it multiple times with water to form hydroxyferric phosphate precursors with different iron-phosphorus ratios.

[0101] Step S4: The hydroxyferric phosphate precursor is flash-dried in a flash evaporator, with the flash evaporator inlet air temperature controlled at 200°C, and sintered in air atmosphere at 540°C and 555°C for 4 hours.

[0102] Step S5: The sintered material is crushed by mechanical mill, and the particle size is controlled as follows: D10≥1.0μm, D50:6-15μm, D90≤60μm. The material is then mixed with a ribbon mixer at 35Hz for 1 hour to obtain hydroxy ferric phosphate with high iron-phosphorus ratio and high specific surface area and hydroxy ferric phosphate with low iron-phosphorus ratio and low specific surface area.

[0103] Step S6: Add 85% phosphoric acid to the ferromanganese phosphate precursor at a mass ratio of 1:180, ball mill for 60 min, and then add lithium phosphate for wet grinding to obtain a nano-sized sand mill slurry. The Fe:Mn molar ratio in the ferromanganese phosphate is 5:5. The sand mill slurry is formulated according to the molar ratio of Li:Fe:Mn:P = 1.03:0.5:0.5:1.03. The sand mill particle size D50 is controlled to be 0.66-0.68 μm.

[0104] Step S7: The above-mentioned sand-milled slurry is mixed with hydroxyferric phosphate (high iron-phosphorus ratio and high specific surface area), hydroxyferric phosphate (low iron-phosphorus ratio and low specific surface area), and lithium phosphate in a molar ratio of Li:Fe:Mn:P = 1.03:0.6:0.4:1.03. A carbon source mixture consisting of sucrose and polyethylene glycol, which makes the carbon content of the finished product 1.50%, and titanium dioxide with a doping amount of 3000ppm are added. The mixture is then sand-milled, and the sand-milled particle size is controlled at 0.40μm to obtain a nano-sized mixture. The mixture is then spray-dried, and the inlet air temperature is controlled at 210℃, the outlet air temperature at 100℃, and the blower frequency at 80Hz to obtain a spray material with a spray particle size D50 = 20-40μm.

[0105] Step S8: The above sprayed material is placed in a box furnace and sintered under a nitrogen atmosphere at a heating rate of 3℃ / min, a sintering temperature of 765℃, and a sintering time of 10h. After natural cooling, the sintered material is obtained. The sintered material is then pulverized by an air jet mill, with the air pressure controlled at 0.35Mpa and the grading frequency at 140Hz, to obtain pulverized material with particle sizes of D10>0.35μm, D50=0.8-1.8μm, D90<10μm, and D100<30μm.

[0106] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished product of lithium manganese iron phosphate can be obtained.

[0107] Comparative Example 1

[0108] This embodiment provides a method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, including the following steps:

[0109] Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a solution containing 6‰ phosphoric acid and 4‰ sodium hydroxide for purification. After purification by pressure filtration, a ferrous sulfate solution is obtained.

[0110] Step S2: Add phosphoric acid to the ferrous sulfate solution according to the molar ratio n(Fe):n(phosphoric acid) = 1:0.15 to lower the pH value of the ferrous sulfate solution;

[0111] Step S3: Add excess 10% hydrogen peroxide to the ferrous sulfate solution, add phosphoric acid solution and 30% ammonium dihydrogen phosphate solution to the ferrous sulfate solution to make the iron-phosphorus feeding ratio meet the iron-phosphorus molar ratio: Fe / P=1.44, then add ammonia water to the ferrous sulfate solution to form a mixed slurry, heat the mixed slurry to 40°C, keep it at the temperature for 2 hours, and then wash and filter it multiple times with water to form the hydroxyferric phosphate precursor;

[0112] Step S4: The hydroxyferric phosphate precursor is flash-dried in a flash evaporator, with the flash evaporator inlet air temperature controlled at 200°C, and sintered in air atmosphere at 525°C for 2 hours.

[0113] Step S5: The sintered material is crushed by mechanical mill, and the particle size is controlled as D10≥1.0μm, D50:6-15μm, D90≤60μm. The material is then mixed with a ribbon mixer at 35Hz for 1 hour to obtain hydroxyferric phosphate product with a single iron-phosphorus ratio and a single specific surface area.

[0114] Step S6: Add 85% phosphoric acid to the ferrous manganese phosphate precursor at a mass ratio of 1:200, ball mill for 60 min, and then add lithium phosphate for wet grinding to obtain a nano-sized sand mill slurry. The Fe:Mn molar ratio in the ferrous manganese phosphate is 2:8. The sand mill slurry is formulated according to the molar ratio of Li:Fe:Mn:P = 1.03:0.2:0.8:1.03. The sand mill particle size D50 is controlled to be 0.80-0.90 μm.

[0115] Step S7: The above-mentioned sand-milled slurry is mixed with hydroxyferric phosphate (high iron-phosphorus ratio and high specific surface area), hydroxyferric phosphate (low iron-phosphorus ratio and low specific surface area), and lithium phosphate in a molar ratio of Li:Fe:Mn:P = 1.03:0.3:0.7:1.03. A carbon source mixture consisting of sucrose and polyethylene glycol, which makes the carbon content of the finished product 1.10%, and titanium dioxide with a doping amount of 2200ppm are added. The mixture is then sand-milled, and the sand-milled particle size is controlled at 0.75μm to obtain a nano-sized mixture. The mixture is then spray-dried, and the inlet air temperature is controlled at 220℃, the outlet air temperature at 100℃, and the blower frequency at 80Hz to obtain a spray material with a spray particle size D50 = 20-40μm.

[0116] Step S8: The above sprayed material is placed in a box furnace and sintered under a nitrogen atmosphere at a heating rate of 3℃ / min, a sintering temperature of 765℃, and a sintering time of 10h. After natural cooling, the sintered material is obtained. The sintered material is then pulverized by an air jet mill, with the air pressure controlled at 0.35Mpa and the grading frequency at 140Hz, to obtain pulverized material with particle sizes of D10>0.35μm, D50=0.8-1.8μm, D90<10μm, and D100<30μm.

[0117] Step S9: After further processing the above-mentioned pulverized material through screening, batching, and packaging, the finished product of lithium manganese iron phosphate can be obtained.

[0118] To verify the quality of the lithium iron phosphate cathode material prepared by the method for preparing lithium iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate provided in the embodiments of the present invention, the lithium iron phosphate cathode material prepared in Examples 1-3 and Comparative Example 1 was dispersed in N-methylpyrrolidone with conductive agent carbon black and binder polyvinylidene fluoride at a mass ratio of 90:5:5. After ball milling and uniform dispersion, it was coated on aluminum foil and vacuum dried to obtain the cathode sheet. The electrolyte was 1 mol / L LiPF6, with a solvent volume ratio of EC:DMC:EMC = 1:1:1. The separator was Celgard polypropylene membrane, and the lithium metal sheet was used as the negative electrode. They were assembled into a coin cell. The test voltage range was 2.5V-4.5V. The battery was charged to 4.5V using a constant current and constant voltage charging method and discharged to 2.5V using a constant current discharging method. The charge and discharge currents were 0.1C for two cycles, 0.2C for two cycles, and 1C for two cycles. The test results are shown in Table 1. The charge-discharge curve (0.1C) of the coin cell assembled with the lithium manganese iron phosphate cathode material prepared in Example 1 of the present invention is as follows: Figure 8 As shown, the charge-discharge curve (0.2C) of the coin cell assembled with the lithium manganese iron phosphate cathode material prepared in Example 1 of the present invention is as follows. Figure 9 As shown, the charge-discharge curve (1C) of the coin cell assembled with the lithium manganese iron phosphate cathode material prepared in Example 1 of the present invention is as follows. Figure 10 As shown.

[0119] Table 1. Test items and test results for Examples 1-3 and Comparative Example 1

[0120]

[0121] Based on the above examples and comparative examples, and the test results obtained from the tests, the coin cells prepared with lithium manganese iron phosphate cathode material in Examples 1-3 showed significant improvements in the specific capacity of the first charge-discharge at 0.1C, the specific capacity of the first discharge at 0.2C, and the specific capacity of the discharge at 1C compared with Comparative Example 1.

[0122] In summary, the method for preparing lithium manganese iron phosphate from ferrous hydroxyphosphate and ferrous manganese phosphate provided in this invention utilizes ferrous sulfate, a byproduct of titanium dioxide, to generate ferric sulfate. After adding other materials and reacting, ferrous hydroxyphosphate with different iron-to-phosphorus ratios is generated. Then, through different sintering processes, ferrous hydroxyphosphate products with high iron-to-phosphorus ratio and high specific surface area, and those with low iron-to-phosphorus ratio and low specific surface area, are obtained. First, ferrous manganese phosphate and phosphoric acid are ball-milled to acidify the ferrous manganese phosphate to a certain extent. Then, lithium phosphate is added and milled to a suitable particle size to obtain a milled slurry. Next, ferrous hydroxyphosphate with high iron-to-phosphorus ratio and high specific surface area, and ferrous hydroxyphosphate with low iron-to-phosphorus ratio and low specific surface area, along with lithium phosphate and additives, are added to the milled slurry and mixed in a certain proportion to form a mixture. The mixture is then subjected to milling, spray drying, sintering, sieving, batching, and packaging processes to obtain the finished lithium manganese iron phosphate product. This method uses a mixture of high and low iron-to-phosphorus ratio hydroxyferric phosphate and introduces lithium phosphate and ferrous manganese phosphate. Hydroxyferric phosphate serves as the iron source, providing for the synthesis of large-particle lithium manganese iron phosphate, which is beneficial for improving the material's compaction density, conductivity, and capacity. Ferrous manganese phosphate serves as both the iron and manganese source, synthesizing small-particle lithium manganese iron phosphate, which is beneficial for improving the material's discharge voltage and discharge capacity. First, ferrous manganese phosphate is ball-milled with phosphoric acid to lower the pH of the slurry, dissolving and releasing some iron and manganese ions, facilitating the preparation of lithium manganese iron phosphate with particles <10nm. Subsequently, the addition of high iron-to-phosphorus ratio, high specific surface area hydroxyferric phosphate, and low iron-to-phosphorus ratio, low specific surface area hydroxyferric phosphate and lithium phosphate to the sand-milled slurry ensures that the sand-milling time of the ferrous manganese phosphate precursor is much longer than that of the hydroxyferric phosphate, guaranteeing that the ferrous manganese phosphate particles are smaller than those of the hydroxyferric phosphate. This results in a better particle size distribution in the subsequently formed lithium manganese iron phosphate, further improving the material's compaction performance while maintaining electrochemical performance.

[0123] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0124] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate, characterized in that, The method includes: Step S1: Add ferrous sulfate, a byproduct of titanium dioxide, to a phosphorus source and a precipitant for purification. After pressure filtration and purification, a ferrous sulfate solution is obtained. Step S2: Add an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution; Step S3: Hydrogen peroxide, phosphoric acid, ammonium dihydrogen phosphate solution, and ammonia are added sequentially to the ferrous sulfate solution, and the mixture is reacted for a period of time to form a mixed slurry. The mixed slurry is heated and kept at a certain temperature for a period of time, and then washed and filtered repeatedly with water to form a hydroxyferric phosphate precursor. Specifically, the iron-phosphorus feeding ratio in the mixed slurry is controlled to meet the iron-phosphorus molar ratio of Fe / P = 1.475-1.490 to form a high iron-phosphorus ratio hydroxyferric phosphate precursor; the iron-phosphorus feeding ratio in the mixed slurry is controlled to meet the iron-phosphorus molar ratio of Fe / P = 1.460-1.465 to form a low iron-phosphorus ratio hydroxyferric phosphate precursor. Step S4: The high-iron-phosphorus-ratio hydroxyferric phosphate precursor and the low-iron-phosphorus-ratio hydroxyferric phosphate precursor are flash-dried in a flash evaporator and sintered at high temperature for a certain time to obtain the high-iron-phosphorus-ratio hydroxyferric phosphate precursor product and the low-iron-phosphorus-ratio hydroxyferric phosphate precursor product, respectively. The sintering temperature is 535-560℃. Step S5: The high iron-to-phosphorus ratio hydroxy ferric phosphate precursor product and the low iron-to-phosphorus ratio hydroxy ferric phosphate precursor product obtained in step S4 are pulverized by mechanical mill and mixed by ribbon mixer to obtain the high iron-to-phosphorus ratio hydroxy ferric phosphate product and the low iron-to-phosphorus ratio hydroxy ferric phosphate product. Step S6: First, ball mill ferrous manganese phosphate and phosphoric acid in a certain ratio, then add lithium phosphate and wet grind to obtain nano-sized sand slurry; Step S7: Add a certain amount of high iron-phosphorus ratio hydroxy ferric phosphate, low iron-phosphorus ratio hydroxy ferric phosphate, lithium phosphate, carbon source and additives to the above sand milling material and sand mill to obtain a nano-sized mixture. After spray drying, a spray material is obtained. The molar ratio of the high iron-phosphorus ratio hydroxy ferric phosphate to the low iron-phosphorus ratio hydroxy ferric phosphate is between 2:8 and 8:

2. Step S8: The above sprayed material is placed in a box furnace for sintering to obtain sintered material, and the sintered material is pulverized by an air jet mill to obtain pulverized material; Step S9: After further sieving, batching and packaging of the above-mentioned pulverized material, the finished product of lithium manganese iron phosphate can be obtained.

2. The method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate according to claim 1, characterized in that, In step S1, the mass ratio of ferrous sulfate:phosphorus source:precipitant is 1:[0.001-0.005]:[0.005-0.007]. The purification reaction temperature is 40℃, the reaction pH is 2.2-2.5, and the reaction time is 1h. The phosphorus source is one or more of phosphoric acid, monoammonium phosphate, diammonium phosphate, and sodium phosphate. The precipitant is one or more of sodium hydroxide, potassium hydroxide, lithium hydroxide, and ammonia water. In step S2, the amount of phosphoric acid added is in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.

15.

3. The method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate according to claim 1, characterized in that, In step S3, the water washing is performed multiple times. The first water wash mainly removes impurities such as magnesium, manganese, and sulfur. In the final water wash, a 1:1 diluted ammonia solution is added to adjust the pH to 6.5-7.0 to remove SO4. 2- Ions; the hydrogen peroxide concentration is 30%-60%, and the mixed slurry is heated to 60-80℃ and kept at that temperature for 3 hours.

4. The method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate according to claim 1, characterized in that, Step S3 includes: Step S31: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time; Step S32: Add the phosphoric acid solution to the oxidized ferrous sulfate solution, then dissolve the ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃, and add it to the oxidized ferrous sulfate solution. Step S33: Add ammonia to the ferrous sulfate solution to adjust the pH of the solution to 3.00±0.

02. After reacting for a period of time, a mixed slurry is formed. The mixed slurry is heated and kept at a certain temperature for a period of time, and then washed and filtered repeatedly with water to form a high iron-to-phosphorus ratio hydroxyferric phosphate precursor and a low iron-to-phosphorus ratio hydroxyferric phosphate precursor.

5. The method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate according to claim 1, characterized in that, In step S4, the inlet air temperature of the flash evaporator is controlled at 220±20℃, the outlet air temperature at 110±5℃, the sintering atmosphere is air, and the sintering time is 4-5 hours. In step S5, the particle size is controlled at D10≥1.0μm, D50: 6-15μm, D90≤60μm, the mixing frequency of the mixer is controlled at 35±2Hz, and the mixing time is 1-2 hours. The high-iron phosphorus hydroxyferric phosphate has a high specific surface area, which satisfies the following: BET=15-20m². 2 / g; The low-iron-phosphorus ferric phosphate has a low specific surface area, which satisfies: BET=5-10m². 2 / g.

6. The method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate according to claim 1, characterized in that, Step S6 includes: Step S61: After mixing the iron source, manganese source, and phosphoric acid, add the antioxidant and phosphorus source, and control the pH of the solution between 3.0 and 4.0 to obtain a mixed solution; Step S62: Add a 16-20% ammonia solution A to the reactor. Under an inert gas atmosphere, simultaneously add the mixed solution and an 8-10% ammonia solution B. Control the pH value between 7.5 and 8.0, and the reaction temperature at 25-40℃. After the addition is complete, age for 1 hour to co-precipitate and prepare the manganese ferrous phosphate precursor. Step S63: The ferrous manganese phosphate precursor is filtered, washed with water, flash dried, sintered at high temperature, and then crushed and mixed to obtain the finished ferrous manganese phosphate product. Step S64: First, ball mill ferrous manganese phosphate and phosphoric acid in a certain ratio, and then add lithium phosphate and wet grind to obtain nano-sized sand slurry.

7. The method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate according to claim 6, characterized in that, In step S61, the molar ratio of the added manganese source to the iron source is between 8:2 and 2:8, and the molar ratio of the sum of the added manganese and iron sources to the phosphorus source is [1.41-1.43]:

1. The amount of antioxidant added is 1% of the mass fraction of the iron source. The iron source is one or more of ferrous sulfate, hydrated ferrous sulfate, ferrous nitrate, and ferrous chloride. The manganese source is one or more of manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate. The phosphorus source is one or more of phosphoric acid, sodium phosphate, potassium phosphate, ammonium dihydrogen phosphate, and diammonium hydrogen phosphate. The antioxidant is ascorbic acid. In step S62, the inert gas is one or more of nitrogen, argon, and helium, and the feeding time is 0.5-6 hours. In step S64, the Fe:Mn molar ratio in the ferrous manganese phosphate is between 2:8 and 8:2, and the amount of phosphoric acid added is between 0.5% and 5% of the mass fraction of ferrous manganese phosphate. In the sand milling slurry, according to the molar ratio Li:Fe:Mn:P = [1.03-1.04]:[0.2-0.8]:[0.2-0.8]:[1.03-1.04], the sand milling particle size in the sand milling slurry is controlled to be between 0.60 and 0.80 μm.

8. The method for preparing lithium manganese iron phosphate from ferric hydroxyphosphate and ferrous manganese phosphate according to claim 1, characterized in that, In step S7, the mixture is prepared according to the molar ratio of Li:Fe:Mn:P = [1.03-1.04]:[0.2-0.8]:[0.2-0.8]:[1.03-1.04]. The amount of carbon source added is based on the carbon content in the final product being between 1.2% and 1.6%. The additives are selected from one or more of titanium dioxide, ammonium metavanadate, and niobium pentoxide, with the doping amount controlled between 300-3000 ppm. The abrasive particle size in the mixture is controlled between 0.30-0.50 μm. During spray drying, the inlet air temperature is 200-220℃, and the outlet air temperature is... The temperature is 80-110℃, the blowing frequency is 80Hz, and the spray particle size in the spray material is controlled between D50=20-40μm; in step S8, the sintering atmosphere is nitrogen, the sintering temperature is 750-780℃, the heating rate is 3℃ / min, the sintering time is 8-12h, and after natural cooling, the sintered material can be obtained. During the crushing process, the gas pressure is controlled between 0.2-0.4Mpa, the grading frequency is 80-200Hz, and the particle size of the crushed material meets the following requirements: D10>0.35μm, D50=0.7-2.0μm, D90<10μm, D100<30μm.

9. A lithium-ion battery cathode material, characterized in that, The lithium-ion battery cathode material uses lithium manganese iron phosphate prepared by the method for preparing lithium manganese iron phosphate from hydroxy iron phosphate and ferrous manganese phosphate as described in any one of claims 1-8.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium-ion battery cathode material as described in claim 9.

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