Cation-doped iron phosphate and preparation method and application thereof

Abstract

The application relates to a cation-doped iron phosphate and a preparation method and application thereof, the preparation method comprising the following steps: firstly, mixing iron-containing magnesium phosphate and an extraction system to carry out extraction aluminum removal to obtain aluminum-removed phosphoric acid; secondly, mixing the aluminum-removed phosphoric acid in step (1), an iron source and an oxidizing agent to obtain iron phosphate dihydrate; and finally, calcining the iron phosphate dihydrate in step (2) to obtain Mg 2+ Doped iron phosphate; by utilizing iron ions and magnesium ions in iron-containing magnesium phosphate, magnesium ions are doped into the crystal lattice of iron phosphate to produce defects, and Mg 2+ The doped iron phosphate has a yield of preferably more than 89.89%, the utilization rate of Mg in the raw material is more than 88.16%, the utilization rate of Fe is preferably more than 98.70%, the doped iron phosphate has high electrochemical performance, the preparation process is simple, and the doped iron phosphate provides low-cost high-quality raw materials for lithium iron phosphate materials.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and in particular to a cation-doped iron phosphate, its preparation method, and its application. Background Technology

[0002] Iron phosphate (FePO4) is an important metal phosphate widely used as a key precursor in the preparation of lithium iron phosphate (LFP) cathode materials for lithium-ion batteries. Currently, as a source of trivalent iron, FePO4 is gradually replacing other precursors due to its low cost and high chemical stability, becoming the core precursor for producing LFP cathode materials with high packing density, discharge rate, and capacity. It is also widely used in catalysts, steel, coatings, and wastewater treatment. For example, FePO4 is non-toxic to organisms and can be used as a molluscicide in organic agriculture. It can also be applied to metal surfaces for oxidation protection, and coating ternary materials with FePO4 prevents side reactions from the electrolyte and improves electrochemical performance.

[0003] Currently, lithium iron phosphate (LFP) materials are the mainstream in the power and energy storage markets. The shortage has shifted from a lack of high-quality material production capacity to a shortage of iron phosphate, the raw material for LFP. Efforts are focused on expanding LFP production capacity and seeking cheaper raw materials. Extensive research has been conducted on preparing LFP using wet-process phosphoric acid. For example, CN116946996A discloses a method for preparing LFP, which uses a purified ferrous byproduct as the iron source and a purified wet-process phosphoric acid solution as the phosphorus source. After oxidation with a mixed oxidant, an oxidized solution is obtained. This solution is then precipitated, aged, washed, and dried to obtain the LFP product. However, this method has low extraction and impurity removal efficiency, resulting in poor electrochemical performance of the prepared LFP. Furthermore, the process is lengthy and the equipment is complex, leading to high costs.

[0004] CN118405676A discloses a production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids. This process involves extraction, concentration and defluorination, chemical defluorination, preparation of NH4H2PO4 solution, reaction, oxidation, pH adjustment and separation of precipitate, washing and drying to obtain battery-grade iron phosphate. It involves multiple extraction and phase separation processes, the operation process is quite complex, and the raw material cost is high.

[0005] Existing methods for preparing iron phosphate using wet-process phosphoric acid fail to fully utilize the impurities Fe in the wet-process phosphoric acid. 3+ and Mg 2+ Due to its low yield and relatively poor electrochemical performance, the preparation of high-electrochemical-performance iron phosphate products using wet-process phosphoric acid has become an urgent problem to be solved in the field of lithium battery materials. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention fully utilizes iron and magnesium ions in iron-magnesium phosphoric acid to achieve cation doping, effectively controlling the crystal structure of iron phosphate products, forming lattice defects to affect the electronic structure of iron phosphate, changing its electron transport path and mobility, thereby improving the electrochemical performance of iron phosphate. This provides high-quality raw materials for the preparation of high-performance lithium iron phosphate materials, and solves the problem of resource waste of iron and magnesium ions in wet-process phosphoric acid, realizing the high-value utilization of wet-process phosphoric acid and reducing the raw material cost of lithium iron phosphate materials.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing cation-doped iron phosphate, the method comprising the following steps:

[0009] (1) Iron-containing magnesium phosphoric acid and the extraction system are mixed and extracted to remove aluminum, resulting in aluminum-free phosphoric acid;

[0010] (2) Mix the aluminum-free phosphoric acid, iron source and oxidant described in step (1) to obtain iron phosphate dihydrate;

[0011] (3) Calcining the ferric phosphate dihydrate obtained in step (2) yields Mg 2+ Doped iron phosphate.

[0012] The iron-magnesium phosphoric acid mentioned in step (1) of this invention is derived from wet-process phosphoric acid, which is obtained by decomposing phosphate rock powder with inorganic acids such as sulfuric acid, nitric acid, or hydrochloric acid, followed by separation and purification. It is worth noting that during the wet-process phosphoric acid production process, all the iron and magnesium ions in the phosphate rock will enter the phosphoric acid solution and exist in ionic form.

[0013] This invention fully utilizes iron-containing magnesium phosphate to prepare Mg 2+ Doped iron phosphate involves incorporating magnesium ions into the crystal lattice of iron phosphate, resulting in a cation-doped iron phosphate product with high electrochemical performance. The magnesium ion-doped iron phosphate has a smaller unit cell volume, shortening the Li-Li content in lithium iron phosphate materials. + The charging and discharging transport path is improved, thereby increasing electron mobility. In addition, the iron ions in iron-magnesium phosphoric acid can also participate in the preparation process of iron phosphate. Compared with the traditional wet process for preparing iron phosphate, the step of extracting and removing iron and magnesium ions is omitted, the amount of iron source added is reduced, the high-value utilization of wet process phosphoric acid is realized, the preparation process of high-conductivity iron phosphate is simplified, and the raw material production cost of lithium iron phosphate materials is reduced.

[0014] Preferably, the Fe in the iron-containing magnesium phosphoric acid in step (1) 3+The content is >0.2wt%, for example, it can be 0.25wt%, 0.28wt%, 0.30wt%, 0.35wt%, 0.40wt%, 0.45wt%, 0.50wt%, 0.55wt%, 0.60wt%, 0.65wt%, 0.70wt%, 0.75wt%, or 0.80wt%, etc.

[0015] Preferably, the Mg in the iron-containing magnesium phosphoric acid in step (1) 2+ The content is ≥0.8wt%, for example, it can be 0.8wt%, 0.82wt%, 0.85wt%, 0.90wt%, 0.95wt%, 1.0wt%, 1.05wt%, 1.10wt%, 1.15wt%, 1.20wt%, 1.25wt%, 1.30wt%, 1.35wt%, 1.40wt%, 1.45wt%, or 1.50wt%, etc.

[0016] Preferably, the extraction system in step (1) includes an extractant or a combination of an extractant and a diluent, and more preferably, the combination of the extractant and the diluent.

[0017] Preferably, the extractant comprises any one or a combination of at least two of di(2-ethylhexyl) phosphate, tributyl phosphate, secondary carbon amine, di(alkylphenyl) phosphate, or di(3,5-dimethylphenyl) phosphate, wherein typical but non-limiting combinations include combinations of di(2-ethylhexyl) phosphate and tributyl phosphate, combinations of tributyl phosphate and secondary carbon amine, or combinations of di(2-ethylhexyl) phosphate and secondary carbon amine, etc.

[0018] Preferably, the diluent includes any one or a combination of at least two of isobutanol, aviation kerosene, or No. 260 solvent oil, such as a combination of isobutanol and aviation kerosene, or a combination of isobutanol and No. 260 solvent oil.

[0019] Preferably, the volume ratio of iron-magnesium phosphoric acid to the extraction system in step (1) is 1:(1-5), for example, it can be 1:1, 1:2, 1:3, 1:4 or 1:5, etc.

[0020] The present invention further preferably uses a volume ratio of iron-magnesium phosphate to the extraction system of 1:(1-5), which is beneficial to the full removal of aluminum ions. If the volume ratio of iron-magnesium phosphate to the extraction system is too small, it will lead to an increase in extraction cost and a decrease in the aluminum ion extraction distribution ratio. If the volume ratio of iron-magnesium phosphate to the extraction system is too large, it will lead to a low aluminum ion extraction rate and failure to remove aluminum ions.

[0021] Preferably, the temperature for aluminum removal during step (1) is 20 to 90°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or 90°C, and preferably 55 to 90°C.

[0022] Preferably, the extraction time for aluminum removal in step (1) is 5 to 60 minutes, for example, it can be 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes, 45 minutes, 50 minutes, 55 minutes or 60 minutes.

[0023] Preferably, before mixing in step (1), the iron-containing magnesium phosphoric acid is pretreated to remove solid impurities.

[0024] Preferably, the pretreatment includes filtering.

[0025] Preferably, the mixing in step (2) includes: the aluminum-free phosphoric acid and the iron source in step (1) are first mixed and reacted to obtain a ferrous dihydrogen phosphate solution; then the ferrous dihydrogen phosphate solution is mixed with an oxidant in a second reaction to obtain ferric phosphate dihydrate.

[0026] Preferably, the iron source includes any one or a combination of at least two of iron salts, iron powder, or iron-containing waste, wherein typical but non-limiting combinations include combinations of iron salts and iron powder, combinations of iron powder and iron-containing waste, or combinations of iron salts and iron-containing waste, etc.

[0027] Preferably, the iron salt includes ferric sulfate.

[0028] Preferably, the iron powder includes any one or a combination of at least two of industrial iron powder, reduced iron powder, or pig iron powder, wherein typical but non-limiting combinations include combinations of industrial iron powder and reduced iron powder, combinations of reduced iron powder and pig iron powder, or combinations of industrial iron powder and pig iron powder, etc.

[0029] Preferably, the iron-containing waste includes iron filings and / or iron slag.

[0030] Preferably, the molar ratio of phosphorus in the aluminum phosphate to iron in the iron source is (1-2):(1-3), for example, it can be 1:1, 1:2, 1:3, 2:1 or 2:3, etc.

[0031] The present invention further preferably uses a molar ratio of phosphorus in the aluminum-removed phosphate to iron in the iron source of (1-2):(1-3), which is beneficial for preparing iron phosphate products with an iron-phosphorus ratio in the range of 0.96-1.02. If the molar ratio of phosphorus in the aluminum-removed phosphate to iron in the iron source of is too low, the composition of the product will change, and the iron-phosphorus ratio in the obtained product will be too high. If the molar ratio of phosphorus in the aluminum-removed phosphate to iron in the iron source of is too high, the product will have phosphate molecules that are difficult to wash off, and the iron-phosphorus ratio will not meet the requirements of HG / T4701-2021 "Iron Phosphate for Batteries".

[0032] Preferably, the temperature of the first reaction is 50 to 100°C, for example, it can be 50°C, 60°C, 70°C, 80°C, 90°C or 100°C, and is more preferably 80 to 100°C.

[0033] Preferably, the reaction time is 2 to 9 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours or 9 hours.

[0034] Preferably, the first reaction process also includes a first pH adjustment.

[0035] Preferably, the solution used for the first pH adjustment includes any one or a combination of at least two of ammonia, KOH solution or NaOH solution, wherein typical but non-limiting combinations include a combination of ammonia and KOH solution, a combination of KOH solution and NaOH solution, or a combination of ammonia and NaOH solution, etc.

[0036] Preferably, the first pH is adjusted to a pH value of 2.5 to 3.5, for example, it can be 2.5, 2.8, 3.0, 3.2 or 3.5.

[0037] Preferably, the first reaction is accompanied by stirring.

[0038] Preferably, the stirring speed is 15 to 100 r / min, for example, it can be 15 r / min, 25 r / min, 35 r / min, 45 r / min, 55 r / min, 65 r / min, 75 r / min, 85 r / min or 100 r / min, etc., and preferably 40 to 70 r / min.

[0039] The present invention further preferably uses a stirring speed of 40-70 r / min, which is beneficial to the formation of ferric phosphate products and the control of particle size and morphology. If the stirring speed is too low, it will lead to excessively high or low local concentrations, thereby affecting the reaction. If the stirring speed is too high, it will hinder the agglomeration of crystalline particles, thereby increasing the difficulty of forming larger particles.

[0040] Preferably, the oxidant includes any one or a combination of at least two of hydrogen peroxide, oxygen, or ozone, wherein typical but non-limiting combinations include combinations of hydrogen peroxide and oxygen, combinations of hydrogen peroxide and ozone, or combinations of oxygen and ozone, etc.

[0041] Preferably, the mass ratio of the ferrous dihydrogen phosphate solution to the oxidant is 1:(0.01 to 0.10), for example, it can be 1:0.01, 1:0.02, 1:0.05, 1:0.08 or 1:0.10, etc.

[0042] Preferably, the temperature of the second reaction is 60 to 100°C, for example, 60°C, 70°C, 80°C, 90°C or 100°C.

[0043] Preferably, the second reaction time is 1 to 2 hours, for example, 1 hour, 1.2 hours, 1.4 hours, 1.6 hours, 1.8 hours, or 2 hours.

[0044] Preferably, the second reaction process also includes a second pH adjustment.

[0045] Preferably, the second pH is adjusted to a pH value of 1 to 5, for example, it can be 1, 1.5, 2, 1.5, 3, 3.5, 4, 4.5 or 5, etc.

[0046] Preferably, after the second reaction, a ferric phosphate dihydrate suspension is first obtained; then, the ferric phosphate dihydrate suspension is subjected to solid-liquid separation, washing and drying in sequence to obtain the ferric phosphate dihydrate.

[0047] Preferably, the calcination temperature in step (3) is 450 to 550°C, for example, 450°C, 480°C, 500°C, 520°C or 550°C.

[0048] Preferably, the calcination time in step (3) is 1 to 3 hours, for example, it can be 1 hour, 1.5 hours, 2 hours, 2.5 hours or 3 hours.

[0049] As a further preferred technical solution of the present invention, refer to Figure 1 The process flow shown includes the following steps in the preparation method:

[0050] (1) Fe is mixed in a volume ratio of 1:(1~5). 3+ Content > 0.2wt%, Mg 2+ Iron-containing magnesium phosphate with a content >0.8wt% was mixed with the extraction system and extracted at 20-90℃ for 5-60 min to remove aluminum, thus obtaining aluminum-removed phosphate;

[0051] The extraction system includes an extractant or a combination of an extractant and a diluent; the extractant includes any one or a combination of at least two of di(2-ethylhexyl) phosphate, tributyl phosphate, secondary carbon amine, di(alkylphenyl) phosphate, or di(3,5-dimethylphenyl) phosphate; the diluent includes any one or a combination of at least two of isobutanol, aviation kerosene, or No. 260 solvent oil.

[0052] (2) The aluminum-removed phosphoric acid described in step (1) is first mixed with an iron source at 50–100°C.

[0053] Under stirring conditions of 15–100 r / min, the first reaction is carried out for 2–9 h, and the pH is adjusted to 2.5–3.5 during the first reaction to obtain a ferrous dihydrogen phosphate solution; then, the ferrous dihydrogen phosphate solution is mixed with an oxidant in a mass ratio of 1:(0.01–0.10), and the mixture is carried out for 1–2 h at 60–100 °C, and the pH is adjusted to 1–5 during the second reaction to obtain ferric phosphate dihydrate.

[0054] The molar ratio of phosphorus in the aluminum-free phosphoric acid to iron in the iron source is (1-2):(1-3); the iron source includes any one or a combination of at least two of iron salts, iron powder, or iron-containing waste.

[0055] (3) Calcining the ferric phosphate dihydrate obtained in step (2) at 450–550°C for 1–3 hours yields Mg 2+ Doped iron phosphate.

[0056] In a second aspect, the present invention provides a cation-doped iron phosphate, which is prepared by the preparation method described in the first aspect.

[0057] The cation-doped iron phosphate of this invention involves cations being doped into the lattice of iron phosphate, occupying some of the original Fe sites in the lattice, thereby creating defects inside the lattice, changing the electron transport path, improving electron mobility, and thus obtaining electrical conductivity with excellent conductivity.

[0058] Preferably, the particle size of the cation-doped iron phosphate is 20-60 nm, for example, it can be 20 nm, 30 nm, 40 nm, 50 nm or 60 nm.

[0059] The present invention further preferably uses cation-doped iron phosphate with a particle size of 20-60 nm, which is smaller than that of conventional iron phosphate products. This provides a higher specific surface area, thereby increasing the contact area with the electrolyte and helping to improve the transport rate of lithium ions at the solid-liquid interface in subsequent lithium iron phosphate battery materials, thus increasing the battery capacity. At the same time, the smaller particle size reduces the diffusion distance of lithium ions in the solid phase, thereby accelerating the charge and discharge speed of lithium iron phosphate materials. In addition, small-particle-size materials generally have better structural stability, which can alleviate the volume effect generated during charge and discharge and improve the cycle stability of the battery.

[0060] Preferably, the magnesium content in the cation-doped iron phosphate is 0.2 to 2.2 wt%, for example, it can be 0.2 wt%, 0.4 wt%, 0.6 wt%, 0.8 wt%, 1.0 wt%, 1.5 wt%, 1.8 wt%, 2.0 wt%, or 2.2 wt%.

[0061] Thirdly, the present invention provides an application of the cation-doped iron phosphate described in the second aspect, wherein the cation-doped iron phosphate is used as a raw material for preparing lithium iron phosphate battery materials.

[0062] The cation-doped iron phosphate described in this invention can be used as a raw material for preparing lithium iron phosphate battery materials. The resulting lithium iron phosphate materials have cation defects, exhibiting excellent electrochemical performance, and the raw material cost of production is reduced.

[0063] Compared with the prior art, the present invention has at least the following beneficial effects:

[0064] (1) The method for preparing cation-doped iron phosphate provided by this invention fully utilizes iron and magnesium ions in iron-magnesium phosphoric acid. Magnesium ions are doped into the crystal lattice of iron phosphate, generating cation defects to improve its electrochemical performance. Furthermore, by controlling the extraction and aluminum removal process parameters, as well as the raw material ratios of aluminum-removing phosphoric acid, iron source, and oxidant, reaction temperature, and pH, the utilization rate of Mg and Fe in the raw materials is further improved. The utilization rate of Mg is preferably as high as 88.16% or more, and the utilization rate of Fe is preferably as high as 98.7% or more, reducing the amount of iron source required for the preparation of iron phosphate. 2+ The yield of doped iron phosphate products was preferably as high as 89.89% or more, achieving low-cost preparation of Mg with high electrochemical performance. 2+ Doped iron phosphate products.

[0065] (2) The cation-doped iron phosphate provided by the present invention is doped with Mg 2+ It has cation defects, an iron-to-phosphorus ratio in the range of 0.9650 to 0.9907, a particle size of 20 to 60 nm, and excellent electrochemical performance.

[0066] (3) Application of the cation-doped iron phosphate provided by the present invention: The cation-doped iron phosphate can be used as a raw material for preparing lithium iron phosphate battery materials, providing a low-cost and high-quality raw material for the preparation of lithium iron phosphate materials. Attached Figure Description

[0067] Figure 1 This is a process flow diagram of the preparation method of cation-doped iron phosphate provided by the present invention. Detailed Implementation

[0068] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0069] I. Implementation Examples

[0070] Example 1

[0071] This embodiment provides a method for preparing cation-doped iron phosphate, the method comprising the following steps:

[0072] (1) Filter the iron-containing magnesium phosphate to remove solid impurities; then, according to the volume ratio of iron-containing magnesium phosphate to the extraction system of 1:2, add Fe 3+ The content is 0.29 wt%, Mg 2+ An extraction system consisting of 0.80 wt% iron-containing magnesium phosphoric acid, 30 mL of tributyl phosphate, and 60 mL of isobutanol was mixed and extracted at 55 °C for 15 min to remove aluminum, thus obtaining aluminum-removed phosphoric acid.

[0073] (2) The aluminum-free phosphoric acid and ferric sulfate obtained in step (1) are first mixed, wherein the molar ratio of phosphorus in the aluminum-free phosphoric acid to iron in the ferric sulfate is 1.02:1. The mixture is stirred at 90°C and 60 r / min for 4.5 h, and the pH is adjusted to 2.6 during the first reaction. After filtration, a ferrous dihydrogen phosphate solution is obtained. Then, the ferrous dihydrogen phosphate solution is mixed with hydrogen peroxide at a mass ratio of 1:0.06. The mixture is stirred at 95°C for 1.8 h, and the pH is adjusted to 2 during the second reaction. After filtration, washing and drying, ferric phosphate dihydrate is obtained.

[0074] (3) Calcining the ferric phosphate dihydrate obtained in step (2) at 500°C for 2.5 h yields Mg 2+ Doped iron phosphate.

[0075] Example 2

[0076] This embodiment provides a method for preparing cation-doped iron phosphate, the method comprising the following steps:

[0077] (1) Filter the iron-containing magnesium phosphoric acid to remove solid impurities; then, according to the volume ratio of iron-containing magnesium phosphoric acid to the extraction system of 1:5, add Fe 3+ The content is 0.78 wt%, Mg 2+ An extraction system consisting of 1.36 wt% iron-containing magnesium phosphoric acid, 40 mL of tributyl phosphate, and 60 mL of isobutanol was mixed and extracted at 55 °C for 50 min to remove aluminum, thus obtaining aluminum-free phosphoric acid.

[0078] (2) The aluminum-removing phosphoric acid obtained in step (1) is first mixed with industrial iron powder. The molar ratio of phosphorus in the aluminum-removing phosphoric acid to iron in ferric sulfate is 1:1.05. The mixture is stirred at 50°C and 40 r / min for 9 hours. During the first reaction, the pH is adjusted to 3.5. After filtration, ferrous dihydrogen phosphate solution is obtained. Then, the ferrous dihydrogen phosphate solution is mixed with hydrogen peroxide at a mass ratio of 1:0.01. The mixture is stirred at 60°C for 1.5 hours. During the second reaction, the pH is adjusted to 5. After filtration, washing and drying, ferric phosphate dihydrate is obtained.

[0079] (3) Calcining the ferric phosphate dihydrate obtained in step (2) at 550°C for 1 hour yields Mg 2+ Doped iron phosphate.

[0080] Example 3

[0081] This embodiment provides a method for preparing cation-doped iron phosphate, the method comprising the following steps:

[0082] (1) Filter the iron-containing magnesium phosphoric acid to remove solid impurities; then, according to the volume ratio of iron-containing magnesium phosphoric acid to the extraction system of 1:1, add Fe 3+ The content is 0.52 wt%, Mg 2+ An extraction system consisting of 1.17 wt% iron-containing magnesium phosphoric acid, 40 mL of secondary carbon primary amine, and 20 mL of aviation kerosene (No. 3 jet fuel) was mixed and extracted at 90 °C for 60 min to remove aluminum, yielding aluminum-removed phosphoric acid.

[0083] (2) The aluminum-removing phosphoric acid obtained in step (1) is first mixed with industrial iron powder, wherein the molar ratio of phosphorus in the aluminum-removing phosphoric acid to iron in ferric sulfate is 1.5:1. The mixture is stirred at 100°C and 70 r / min for 2 hours, and the pH is adjusted to 2.5 during the first reaction. After filtration, ferrous dihydrogen phosphate solution is obtained. Then, the ferrous dihydrogen phosphate solution is mixed with hydrogen peroxide at a mass ratio of 1:0.10. The mixture is stirred at 70°C for 1 hour, and the pH is adjusted to 1.5 during the second reaction. After filtration, washing and drying, ferric phosphate dihydrate is obtained.

[0084] (3) Calcining the ferric phosphate dihydrate obtained in step (2) at 450°C for 3 hours yields Mg. 2+ Doped iron phosphate.

[0085] Example 4

[0086] This embodiment provides a method for preparing cation-doped iron phosphate. Except for step (2), in which the molar ratio of phosphorus in aluminum phosphate to iron in the iron source is 1:3.5, the preparation method is the same as in Example 1.

[0087] Example 5

[0088] This embodiment provides a method for preparing cation-doped iron phosphate. Except for step (2), in which the molar ratio of phosphorus in aluminum phosphate to iron in the iron source is 2:0.8, the preparation method is the same as in Example 1.

[0089] Example 6

[0090] This embodiment provides a method for preparing cation-doped iron phosphate. Except for the stirring speed of 15 r / min, the preparation method is the same as that in Example 1.

[0091] Because the stirring speed in the preparation method described in this embodiment is relatively low, the obtained Mg 2+ Mg in doped iron phosphate 2+ Uneven doping leads to a decline in the quality and electrochemical performance of iron phosphate products.

[0092] Example 7

[0093] This embodiment provides a method for preparing cation-doped iron phosphate. Except for the stirring speed of 100 r / min, the preparation method is the same as that in Example 1.

[0094] Because the stirring speed is high in the preparation method described in this embodiment, the obtained Mg 2+ The doped iron phosphate crystals cannot grow.

[0095] II. Comparative Example

[0096] Comparative Example 1

[0097] This comparative example provides a method for preparing iron phosphate. Except for the step of extraction to remove iron and magnesium ions, the method is the same as in Example 1 except that after filtering to remove solid impurities in step (1) of Example 1, iron and magnesium ions are extracted with ammonium bifluoride extractant before aluminum removal.

[0098] Because iron and magnesium ions were removed from the iron-magnesium phosphate in this embodiment, the resulting iron phosphate product was almost free of magnesium ions, and the utilization rate of Mg and Fe in the iron-magnesium phosphate was almost zero. Therefore, no defects were observed, meaning the prepared product was a conventional iron phosphate product without magnesium ions, and its electrochemical performance was far inferior to that of the Mg-containing product obtained in Example 1. 2+ Doped iron phosphate products.

[0099] Comparative Example 2

[0100] This comparative example provides a method for preparing ferric phosphate. The ferric phosphate obtained in Comparative Example 1 is mixed with magnesium sulfate, and then calcined at a high temperature (500°C) to allow magnesium to enter the ferric phosphate crystal lattice, yielding Mg. 2+ Doped iron phosphate.

[0101] Because of Mg in this comparative example 2+ The doping method was a solid-state reaction, which suffers from uneven doping and incomplete reaction. The utilization rate of Mg in magnesium sulfate was only 50.94%. Compared with Example 1, the electrochemical properties of the product obtained in this comparative example are lower, and Mg... 2+ The yield of the doped iron phosphate product decreased to 60.52%. III. Tests and Results

[0102] The Mg prepared by the methods provided in the above embodiments and comparative examples 2+ The yield of doped iron phosphate, its Mg content, and the iron-to-phosphorus ratio were tested, and the results are shown in Table 1.

[0103] Table 1

[0104]

[0105] Note: " / " in the table indicates that there is no relevant data.

[0106] As shown in Table 1:

[0107] (1) As can be seen from Examples 1 to 3, the present invention fully utilizes the iron and magnesium ions in iron-magnesium phosphoric acid, doping magnesium ions into the iron phosphate lattice to generate cation defects, thereby obtaining a cation-doped iron phosphate product; the utilization rate of Mg in iron-magnesium phosphoric acid is as high as 88.16% or more, the utilization rate of Fe in iron-magnesium phosphoric acid is as high as 98.70% or more, and the utilization rate of Mg is as high as 98.70% or more. 2+ The yield of doped iron phosphate was as high as 89.89% or more, and the Mg produced was... 2+ The iron-to-phosphorus ratio in the doped iron phosphate product meets the requirements, and it exhibits excellent electrochemical performance.

[0108] (2) As can be seen from Examples 1 and 4-5, compared with Example 1, the molar ratio of phosphorus in the aluminum phosphate to iron in the iron source in Example 4 is smaller, resulting in Mg 2+ The yield of the doped iron phosphate product decreased to 80.25%; this was due to the excessively high molar ratio of phosphorus in the aluminum phosphate to iron in the iron source described in Example 5, resulting in Mg... 2+ The yield of the doped iron phosphate product decreased to 76.30%; therefore, it can be seen that the present invention further optimizes the molar ratio of phosphorus in the aluminophosphate to iron in the iron source to be (1-2):(1-3), which further improves the yield of Mg. 2+ Yield of doped iron phosphate products.

[0109] (3) As can be seen from Examples 1 and 6-7, compared with Example 1, the stirring speed in Example 6 was lower, resulting in Mg 2+ Uneven doping resulted in a decrease in the utilization rate of Mg in iron-magnesium phosphoric acid to 89.93% and the utilization rate of Fe to 90.41%. 2+ The yield of the doped iron phosphate product decreased to 82.72%, and the iron-to-phosphorus ratio decreased to 0.9003. In Example 7, the stirring speed was relatively high, and the utilization rate of Mg in the iron-magnesium phosphate was only 89.27%, while the utilization rate of Fe decreased to 88.03%. 2+ The yield of the doped iron phosphate product decreased to 80.53%, and the iron-to-phosphorus ratio decreased to 0.8960, without improving the doping effect. Therefore, this invention further optimizes the stirring speed to 40–70 r / min, further ensuring sufficient magnesium ion doping into the iron phosphate lattice, thereby further improving the electrochemical performance of the product and further enhancing the Mg content. 2+ Yield of doped iron phosphate products.

[0110] (4) As can be seen from Example 1 and Comparative Examples 1 and 2, compared with Example 1, Comparative Example 1 did not fully utilize the iron and magnesium ions in iron-containing magnesium phosphate, resulting in almost no magnesium ion doping in the product, thus leading to the absence of defects and affecting electron migration, which will result in poor conductivity of the subsequent battery material; Comparative Example 2 used a mixed doping method of iron phosphate and magnesium sulfate, and the utilization rate of Mg in magnesium sulfate was only 50.94%. The electrochemical properties of the product obtained in this comparative example were low, and Mg... 2+ The yield of doped iron phosphate products was only 60.52%; therefore, this invention directly utilizes iron-containing magnesium phosphate to prepare Mg 2+ The high yield of doped iron phosphate products provides high-quality raw materials for the preparation of lithium iron phosphate materials.

[0111] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing cation-doped iron phosphate, characterized in that, The preparation method includes the following steps: (1) Iron-containing magnesium phosphoric acid and the extraction system are mixed and extracted to remove aluminum, resulting in aluminum-free phosphoric acid; (2) Mix the aluminum-removed phosphoric acid, iron source and oxidant described in step (1) to obtain ferric phosphate dihydrate; (3) Calcining the ferric phosphate dihydrate obtained in step (2) yields Mg. 2+ Doped iron phosphate; The volume ratio of iron-containing magnesium phosphate to the extraction system in step (1) is 1:(1~5); In step (2), the molar ratio of phosphorus in the aluminum phosphate to iron in the iron source is (1~2):(1~3); The extraction system described in step (1) includes a combination of an extractant and a diluent; The extractant includes any one or a combination of at least two of di(2-ethylhexyl) phosphate, tributyl phosphate, secondary carbon amine, di(alkylphenyl) phosphate, or di(3,5-dimethylphenyl) phosphate; The diluent includes any one or a combination of at least two of isobutanol, aviation kerosene, or No. 260 solvent oil.

2. The preparation method according to claim 1, characterized in that, Step (1) The Fe in the iron-containing magnesium phosphoric acid 3+ Content > 0.2 wt%.

3. The preparation method according to claim 1, characterized in that, Step (1) The Mg in the iron-magnesium phosphoric acid 2+ Content ≥0.8 wt%.

4. The preparation method according to claim 1, characterized in that, The extraction temperature for aluminum removal in step (1) is 20~90℃.

5. The preparation method according to claim 4, characterized in that, The extraction temperature for aluminum removal in step (1) is 55~90℃.

6. The preparation method according to claim 1, characterized in that, The extraction time for aluminum removal in step (1) is 5~60 min.

7. The preparation method according to claim 1, characterized in that, The mixing in step (2) includes: the aluminum-free phosphoric acid and the iron source in step (1) are first mixed and reacted to obtain a ferrous dihydrogen phosphate solution; then the ferrous dihydrogen phosphate solution is mixed with an oxidant in a second reaction to obtain ferric phosphate dihydrate.

8. The preparation method according to claim 1, characterized in that, The iron source includes any one or a combination of at least two of iron salts, iron powder, or iron-containing waste.

9. The preparation method according to claim 7, characterized in that, The temperature of the first reaction is 50~100℃.

10. The preparation method according to claim 9, characterized in that, The temperature of the first reaction is 80~100℃.

11. The preparation method according to claim 7, characterized in that, The first reaction takes 2 to 9 hours.

12. The preparation method according to claim 7, characterized in that, The first reaction process also includes a first pH adjustment.

13. The preparation method according to claim 12, characterized in that, The solution used for the first pH adjustment includes any one or a combination of at least two of ammonia, KOH solution, or NaOH solution.

14. The preparation method according to claim 12, characterized in that, The first pH is adjusted to a pH value of 2.5~3.

5.

15. The preparation method according to claim 7, characterized in that, The first reaction was also accompanied by stirring.

16. The preparation method according to claim 15, characterized in that, The stirring speed is 15~100 r / min.

17. The preparation method according to claim 16, characterized in that, The stirring speed is 40~70 r / min.

18. The preparation method according to claim 1, characterized in that, The oxidant includes any one or a combination of at least two of hydrogen peroxide, oxygen, or ozone.

19. The preparation method according to claim 7, characterized in that, The mass ratio of the ferrous dihydrogen phosphate solution to the oxidant is 1:(0.01~0.10).

20. The preparation method according to claim 7, characterized in that, The temperature of the second reaction is 60~100℃.

21. The preparation method according to claim 7, characterized in that, The second reaction takes 1 to 2 hours.

22. The preparation method according to claim 7, characterized in that, The second reaction also includes a second pH adjustment.

23. The preparation method according to claim 22, characterized in that, The second pH is adjusted to a pH value of 1-5.

24. The preparation method according to claim 1, characterized in that, The calcination temperature in step (3) is 450~550℃.

25. The preparation method according to claim 1, characterized in that, The calcination time in step (3) is 1 to 3 hours.

26. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Fe is mixed in a volume ratio of 1:(1~5). 3+ Content > 0.2 wt%, Mg 2+ Iron-containing magnesium phosphate with a content >0.8 wt% was mixed with the extraction system and extracted at 20~90℃ for 5~60 min to remove aluminum, thus obtaining aluminum-removed phosphate; The extraction system comprises a combination of an extractant and a diluent; the extractant comprises any one or a combination of at least two of di(2-ethylhexyl) phosphate, tributyl phosphate, secondary carbon amine, di(alkylphenyl) phosphate, or di(3,5-dimethylphenyl) phosphate; the diluent comprises any one or a combination of at least two of isobutanol, aviation kerosene, or No. 260 solvent oil. (2) The aluminum-free phosphoric acid obtained in step (1) is first mixed with an iron source, and stirred at 50~100℃ and 15~100r / min for 2~9h for a first reaction, and the pH is adjusted to 2.5~3.5 during the first reaction to obtain a ferrous dihydrogen phosphate solution; then, the ferrous dihydrogen phosphate solution is second mixed with an oxidant at a mass ratio of 1:(0.01~0.10), and stirred at 60~100℃ for 1~2h for a second reaction, and the pH is adjusted to 1~5 during the second reaction to obtain ferric phosphate dihydrate; The molar ratio of phosphorus in the aluminum-free phosphoric acid to iron in the iron source is (1~2):(1~3); the iron source includes any one or a combination of at least two of iron salts, iron powder, or iron-containing waste. (3) Calcining the ferric phosphate dihydrate obtained in step (2) at 450~550℃ for 1~3h to obtain Mg 2+ Doped iron phosphate.

27. A cation-doped iron phosphate, characterized in that, The cation-doped iron phosphate is prepared by the preparation method according to any one of claims 1 to 26.

28. The cation-doped iron phosphate according to claim 27, characterized in that, The particle size of the cation-doped iron phosphate is 20~60 nm.

29. The cation-doped iron phosphate according to claim 27, characterized in that, The magnesium content in the ferric phosphate is 0.2~2.2 wt%.

30. An application of the cation-doped iron phosphate as described in any one of claims 27-29, characterized in that, The cation-doped iron phosphate is used as a raw material for preparing lithium iron phosphate battery materials.

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