Cation-doped iron phosphate as well as preparation method and application thereof

Abstract

The invention relates to cation-doped iron phosphate as well as a preparation method and application thereof, the preparation method comprises the following steps: firstly, mixing phosphoric acid containing iron and magnesium with an extraction system for extraction and aluminum removal to obtain aluminum-removed phosphoric acid; mixing the aluminum-removed phosphoric acid obtained in the step (1), an iron source and an oxidizing agent to obtain iron phosphate dihydrate; and finally, calcining the iron phosphate dihydrate obtained in the step (2) to obtain Mg < 2 + > doped iron phosphate. The Mg < 2 + >-doped iron phosphate is prepared by doping magnesium ions into crystal lattices of iron phosphate to generate defects by utilizing iron ions and magnesium ions in the iron-containing magnesium phosphate, the yield is preferably up to 89.89% or above, the utilization rate of Mg in the raw materials is up to 88.16% or above, the utilization rate of Fe is preferably up to 98.70% or above, and the Mg < 2 + >-doped iron phosphate has the advantages of high electrochemical performance, simple preparation process and low cost. And a low-cost high-quality raw material is provided for the lithium iron phosphate material.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to a cation-doped iron phosphate and a preparation method and application thereof. Background Art

[0002] Iron phosphate is an important metal phosphate and is widely used as an important precursor for preparing lithium iron phosphate, a cathode material for lithium-ion batteries. At present, iron phosphate, as a source of trivalent iron, is gradually replacing other precursors and becoming the core precursor for producing lithium iron phosphate cathode materials with high stacking density, discharge rate and capacity due to its low price and high chemical stability. It is also widely used in the fields of catalysts, steel, coatings and sewage treatment. For example, iron phosphate can be used as a snail killer in organic agriculture because it is non-toxic to organisms. Iron phosphate can also be applied to metal surfaces to protect against oxidation. Iron phosphate can also be coated on the surface of ternary materials to prevent side reactions when electrolytes and ternary materials come into contact, thereby improving electrochemical performance.

[0003] At present, lithium iron phosphate materials, as the mainstream of the power and energy storage market, have changed from insufficient production capacity of high-quality materials to insufficient supply of iron phosphate, the raw material of lithium iron phosphate. People are focusing on expanding the production capacity of iron phosphate and seeking cheaper raw materials. There are now a large number of studies on the preparation of iron phosphate using wet phosphoric acid. For example, CN116946996A discloses a method for preparing iron phosphate, which uses a by-product ferrous purified liquid as an iron source, a wet phosphoric acid purified liquid as a phosphorus source, and a mixed oxidant oxidation reaction to obtain an oxidizing liquid, and the oxidizing liquid is precipitated, aged, washed and dried to obtain an iron phosphate product. This method has low extraction and impurity removal efficiency, and the electrochemical performance of the obtained iron phosphate is poor, and the process flow is long and the device structure is complex, resulting in high cost.

[0004] CN118405676A discloses a production process for preparing battery-grade iron phosphate from wet-process phosphoric acid and related acids. The process obtains battery-grade iron phosphate through extraction, concentration defluorination, chemical defluorination, preparation of NH4H2PO4 solution, reaction, oxidation, pH adjustment, separation and precipitation, washing and drying. The process involves multiple extraction and phase separation processes, the operation process is quite complicated, and the cost of raw materials is relatively high.

[0005] The prior art method of preparing ferric phosphate using wet phosphoric acid has the problem of failing to fully utilize the impurity Fe in the wet phosphoric acid. 3+ and Mg 2+ , low iron phosphate yield and relatively poor electrochemical performance. Therefore, how to efficiently use wet phosphoric acid to prepare iron phosphate products with high electrochemical performance has become an urgent problem to be solved in the field of lithium battery materials. Summary of the invention

[0006] In order to solve the above technical problems, the present invention makes full use of the iron ions and magnesium ions in the iron-magnesium phosphate, realizes cation doping, effectively regulates the lattice structure of the iron phosphate product, forms lattice defects to affect the electronic structure of the iron phosphate, changes its electron transmission path and mobility, thereby improving the electrochemical properties of the iron phosphate, and provides high-quality raw materials for the preparation of high-performance lithium iron phosphate materials. It also solves the problem of resource waste of iron ions and magnesium ions in wet-process phosphoric acid, realizes the high-value utilization of wet-process phosphoric acid, and reduces the raw material cost of lithium iron phosphate materials.

[0007] To achieve this object, the present invention adopts the following technical solutions:

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

[0009] (1) mixing the iron-magnesium-containing phosphoric acid and the extraction system to extract and remove aluminum to obtain aluminum-removed phosphoric acid;

[0010] (2) mixing the aluminum-removing phosphate, the iron source and the oxidant described in step (1) to obtain ferric phosphate dihydrate;

[0011] (3) calcining the iron phosphate dihydrate described in step (2) to obtain Mg 2+ Doped iron phosphate.

[0012] The iron-magnesium-containing phosphoric acid in step (1) of the present invention is derived from wet-process phosphoric acid, which is phosphoric acid obtained by decomposing phosphate rock powder with an inorganic acid such as sulfuric acid, nitric acid or hydrochloric acid, and then separating and purifying it. It is worth noting that in the production process of wet-process phosphoric acid, all the iron ions and magnesium ions in the phosphate rock will enter the phosphoric acid solution and exist in the form of ions.

[0013] The present invention makes full use of iron-containing magnesium phosphoric acid to prepare Mg 2+ Doped iron phosphate, magnesium ions are doped into the lattice of iron phosphate, thereby obtaining a cation-doped iron phosphate product with high electrochemical performance, wherein the unit cell volume of magnesium ion-doped iron phosphate is reduced, shortening the Li + The charge and discharge transmission path is improved, thereby improving electron mobility; in addition, the iron ions in the iron-magnesium phosphate can also participate in the preparation process of iron phosphate. Compared with the traditional wet phosphoric acid preparation of iron phosphate, the step of extracting and removing iron ions and magnesium ions is omitted, the amount of iron source added is reduced, and the high-value utilization of wet phosphoric acid is achieved. 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 phosphate 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-magnesium phosphate in step (1) is 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) comprises an extractant or a combination of an extractant and a diluent, preferably a combination of the extractant and a diluent.

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

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

[0019] Preferably, the volume ratio of the iron-magnesium-containing 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.

[0020] The present invention further preferably has a volume ratio of the iron-containing magnesium phosphoric acid to the extraction system of 1: (1-5), which is conducive to the sufficient removal of aluminum ions; if the volume ratio of the iron-containing magnesium phosphoric acid to the extraction system is too small, the extraction cost will increase and the aluminum ion extraction distribution ratio will decrease; if the volume ratio of the iron-containing magnesium phosphoric acid to the extraction system is too large, the aluminum ion extraction rate will be low and the aluminum ion removal cannot be achieved.

[0021] Preferably, the temperature for extracting and removing aluminum in step (1) is 20-90°C, for example, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or 90°C, etc., preferably 55-90°C.

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

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

[0024] Preferably, the pre-treatment comprises filtration.

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

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

[0027] Preferably, the iron salt comprises iron sulfate.

[0028] Preferably, the iron powder comprises any one of industrial iron powder, reduced iron powder or pig iron powder, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of industrial iron powder and reduced iron powder, a combination of reduced iron powder and pig iron powder, or a combination 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 dealuminized 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 prefers that the molar ratio of phosphorus in the dealuminized phosphoric acid to iron in the iron source is (1-2): (1-3), which is conducive to the preparation of an iron phosphate product with an iron-phosphorus ratio in the range of 0.96-1.02; if the molar ratio of phosphorus in the dealuminized phosphoric acid to iron in the iron source is low, the product composition will change, and the iron-phosphorus ratio in the obtained product will be high; if the molar ratio of phosphorus in the dealuminized phosphoric acid to iron in the iron source is high, phosphoric acid molecules that are difficult to elute will be attached to the product, 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 50-100°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C, etc., preferably 80-100°C.

[0033] Preferably, the first reaction time is 2 to 9 hours, for example, it can be 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 of aqueous ammonia, KOH solution or NaOH solution, or a combination of at least two of them, wherein typical but non-limiting combinations include a combination of aqueous ammonia and KOH solution, a combination of KOH solution and NaOH solution, or a combination of aqueous ammonia and NaOH solution, etc.

[0036] Preferably, the first pH is adjusted to a pH value of 2.5 to 3.5, for example, 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 15-100 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., preferably 40-70 r / min.

[0039] The present invention further preferably has the stirring speed of 40 to 70 r / min, which is beneficial to the formation of iron phosphate products and the control of particle size morphology; if the stirring speed is too low, it will cause the local concentration to be too high or too low, thereby affecting the reaction; if the stirring speed is too high, it will hinder the agglomeration of crystal particles, thereby increasing the difficulty of forming particles with larger particle size.

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

[0041] Preferably, the mass ratio of the ferrous dihydrogen phosphate solution to the oxidant is 1:(0.01-0.10), 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 60-100°C, for example, 60°C, 70°C, 80°C, 90°C or 100°C.

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

[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, 1, 1.5, 2, 1.5, 3, 3.5, 4, 4.5 or 5.

[0046] Preferably, after the second reaction, a suspension of ferric phosphate dihydrate is first obtained; and the suspension of ferric phosphate dihydrate is then 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 450-550°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, 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 in the figure, the preparation method comprises the following steps:

[0050] (1) According to the volume ratio of 1: (1 to 5), Fe 3+ Content>0.2wt%, Mg 2+ The iron-magnesium-containing phosphoric acid with a content of more than 0.8 wt% is mixed with an extraction system, and the aluminum is extracted and removed at 20 to 90° C. for 5 to 60 minutes to obtain aluminum-removed phosphoric acid;

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

[0052] (2) The aluminum-free phosphate and the iron source are first mixed at 50-100° C.

[0053] Under stirring conditions of 15 to 100 r / min, a first reaction is performed for 2 to 9 hours, and during the first reaction, a first pH value is adjusted to 2.5 to 3.5 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 to 0.10), and a second reaction is performed at 60 to 100° C. for 1 to 2 hours, and during the second reaction, a second pH value is adjusted to 1 to 5 to obtain ferric phosphate dihydrate;

[0054] The molar ratio of phosphorus in the dealuminized phosphate to iron in the iron source is (1-2):(1-3); the iron source includes any one of iron salt, iron powder or iron-containing waste or a combination of at least two thereof;

[0055] (3) calcining the iron phosphate dihydrate in step (2) at 450-550° C. for 1-3 h to obtain Mg 2+ Doped iron phosphate.

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

[0057] In the cation-doped iron phosphate of the present invention, cations are doped into the lattice of iron phosphate and occupy part of the Fe sites in the original lattice, thereby generating defects inside the lattice to change the transmission path of electrons and improve electron mobility, thereby obtaining conductive properties with excellent conductive properties.

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

[0059] The present invention further preferably has a particle size of 20 to 60 nm for the cation-doped iron phosphate, which is smaller than the particle size of conventional iron phosphate products and can provide a higher specific surface area, thereby increasing the contact area with the electrolyte, thereby helping to improve the subsequent lithium ion transmission rate at the solid-liquid interface in the lithium iron phosphate battery material, thereby increasing the capacity of the battery; 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 the lithium iron phosphate material; in addition, small particle size materials usually have better structural stability, can alleviate the volume effect generated during the charge and discharge process, and improve the cycle stability of the battery.

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

[0061] In a third aspect, 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 of the present invention can be used as a raw material for preparing lithium iron phosphate battery materials, and the prepared lithium iron phosphate material has cation defects, exhibits excellent electrochemical properties, and reduces the raw material cost of production.

[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 the present invention makes full use of iron ions and magnesium ions in iron-magnesium phosphate, and magnesium ions are doped into the lattice of iron phosphate to generate cationic defects to improve its electrochemical performance, and further regulates the extraction and aluminum removal process parameters and the raw material ratio of aluminum-removing phosphate, iron source and oxidant, reaction temperature, pH value and other parameters, thereby further improving the utilization rate of Mg and Fe in the raw materials, 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, thereby reducing the amount of iron source required for preparing iron phosphate, and Mg is reduced. 2+ The yield of the doped iron phosphate product is 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+ , with cation defects, an iron-phosphorus ratio in the range of 0.9650 to 0.9907, a particle size of 20 to 60 nm, and excellent electrochemical properties.

[0066] (3) The application of the cation-doped iron phosphate provided by the present invention can be used as a raw material for preparing lithium iron phosphate battery materials, providing a low-cost high-quality raw material for the preparation of lithium iron phosphate materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 The present invention provides a process flow chart of the method for preparing cation-doped iron phosphate. DETAILED DESCRIPTION

[0068] For the convenience of understanding the present invention, the present invention lists the following embodiments. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0069] 1. Implementation

[0070] Example 1

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

[0072] (1) filtering the iron-containing magnesium phosphoric acid to remove solid impurities; then mixing the iron-containing magnesium phosphoric acid with the extraction system in a volume ratio of 1:2. 3+ The content is 0.29wt%, Mg 2+ The iron-magnesium-containing phosphoric acid with a content of 0.80 wt% is mixed with an extraction system consisting of 30 mL of tributyl phosphate and 60 mL of isobutyl alcohol, and the extraction is performed at 55° C. for 15 minutes to remove aluminum, thereby obtaining aluminum-free phosphoric acid;

[0073] (2) The dealuminized phosphoric acid of step (1) is first mixed with ferric sulfate, wherein the molar ratio of phosphorus in the dealuminized phosphoric acid to iron in the ferric sulfate is 1.02:1, and a first reaction is carried out at 90° C. and 60 r / min stirring conditions for 4.5 hours, and during the first reaction, a first pH value is adjusted to a pH value of 2.6, and a ferrous dihydrogen phosphate solution is obtained after filtering; then, the ferrous dihydrogen phosphate solution is secondly mixed with hydrogen peroxide at a mass ratio of 1:0.06, and a second reaction is carried out at 95° C. for 1.8 hours, and during the second reaction, a second pH value is adjusted to a pH value of 2, and then ferrous phosphate dihydrate is obtained after filtering, washing and drying;

[0074] (3) calcining the iron phosphate dihydrate described in step (2) at 500° C. for 2.5 h to obtain Mg 2+ Doped iron phosphate.

[0075] Example 2

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

[0077] (1) filtering the iron-containing magnesium phosphoric acid to remove solid impurities; then mixing the iron-containing magnesium phosphoric acid with the extraction system in a volume ratio of 1:5. 3+ The content is 0.78wt%, Mg 2+ The iron-magnesium-containing phosphoric acid with a content of 1.36 wt % is mixed with an extraction system consisting of 40 mL of tributyl phosphate and 60 mL of isobutyl alcohol, and the extraction is performed at 55° C. for 50 min to remove aluminum, thereby obtaining aluminum-free phosphoric acid;

[0078] (2) The dealuminized phosphoric acid of step (1) is first mixed with industrial iron powder, wherein the molar ratio of phosphorus in the dealuminized phosphoric acid to iron in ferric sulfate is 1:1.05, and a first reaction is carried out at 50° C. and 40 r / min stirring conditions for 9 hours, and during the first reaction, the first pH is adjusted to a pH value of 3.5, and a ferrous dihydrogen phosphate solution is obtained after filtration; and then the ferrous dihydrogen phosphate solution is secondly mixed with hydrogen peroxide at a mass ratio of 1:0.01, and a second reaction is carried out at 60° C. for 1.5 hours, and during the second reaction, the second pH is adjusted to a pH value of 5, and then ferrous phosphate dihydrate is obtained after filtration, washing and drying;

[0079] (3) calcining the iron phosphate dihydrate in step (2) at 550° C. for 1 h to obtain Mg 2+ Doped iron phosphate.

[0080] Example 3

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

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

[0083] (2) The dealuminized phosphoric acid of step (1) is first mixed with industrial iron powder, wherein the molar ratio of phosphorus in the dealuminized phosphoric acid to iron in ferric sulfate is 1.5:1, and a first reaction is carried out at 100° C. and 70 r / min stirring conditions for 2 h, and during the first reaction, the first pH is adjusted to a pH value of 2.5, and a ferrous dihydrogen phosphate solution is obtained after filtering; and then the ferrous dihydrogen phosphate solution is secondly mixed with hydrogen peroxide at a mass ratio of 1:0.10, and a second reaction is carried out at 70° C. for 1 h, and during the second reaction, the second pH is adjusted to a pH value of 1.5, and then ferrous phosphate dihydrate is obtained after filtering, washing and drying;

[0084] (3) calcining the iron phosphate dihydrate described in step (2) at 450° C. for 3 h to obtain Mg 2+ Doped iron phosphate.

[0085] Example 4

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

[0087] Example 5

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

[0089] Example 6

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

[0091] Due to the low stirring speed in the preparation method described in this embodiment, the prepared Mg 2+ Mg in doped iron phosphate 2+ Uneven doping leads to a decrease in the quality of iron phosphate products and their electrochemical properties.

[0092] Example 7

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

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

[0095] 2. Comparison

[0096] Comparative Example 1

[0097] This comparative example provides a method for preparing ferric phosphate. The preparation method is the same as Example 1 except that the step of extracting and removing iron ions and magnesium ions is not omitted. After filtering and removing solid impurities in step (1) of Example 1, an ammonium bifluoride extractant is used to extract iron ions and magnesium ions before extracting and removing aluminum.

[0098] Since the iron ions and magnesium ions in the iron-containing magnesium phosphate are removed in this embodiment, the obtained iron phosphate product is almost free of magnesium ions, and the utilization rate of Mg and Fe in the iron-containing magnesium phosphate is almost 0; thus, no defects are observed, that is, the prepared iron phosphate product is a conventional iron phosphate product not doped with magnesium ions, and its electrochemical performance is far inferior to that of the Mg phosphate obtained in Example 1. 2+ Doped iron phosphate products.

[0099] Comparative Example 2

[0100] This comparative example provides a method for preparing iron phosphate, wherein the iron phosphate prepared in comparative example 1 is mixed with magnesium sulfate, and then calcined at a high temperature (500° C.) to allow the magnesium element to enter the lattice of the iron phosphate to obtain Mg 2+ Doped iron phosphate.

[0101] Since Mg in this comparative example 2+ The doping method is solid phase reaction method, which has the problem of uneven doping, that is, incomplete reaction. The utilization rate of Mg in magnesium sulfate is only 50.94. Compared with Example 1, the electrochemical property of the product obtained in this comparative example is lower, and Mg 2+ The yield of the doped iron phosphate product dropped to 60.52%.

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

[0103] Table 1

[0104]

[0105] Note: “ / ” in the table means there is no relevant data.

[0106] From Table 1, we can see that:

[0107] (1) It can be seen from Examples 1 to 3 that the present invention fully utilizes the iron ions and magnesium ions in the iron-containing magnesium phosphate to dope the magnesium ions into the iron phosphate lattice, thereby generating cation defects and obtaining a cation-doped iron phosphate product; the utilization rate of Mg in the iron-containing magnesium phosphate is as high as 88.16% or more, the utilization rate of Fe in the iron-containing magnesium phosphate is as high as 98.70% or more, and the utilization rate of Mg in the iron-containing magnesium phosphate is as high as 98.70% or more. 2+ The yield of doped iron phosphate is as high as 89.89%. 2+ The iron-phosphorus ratio of the doped iron phosphate product meets the requirements and has excellent electrochemical properties.

[0108] (2) It can be seen from Examples 1 and 4 to 5 that, compared with Example 1, the molar ratio of phosphorus in the dealuminized phosphate to iron in the iron source in Example 4 is relatively small, resulting in Mg 2+ The yield of the doped iron phosphate product decreased to 80.25%; due to the large molar ratio of phosphorus in the dealuminized phosphate to iron in the iron source described in Example 5, Mg 2+ The yield of the doped iron phosphate product decreased to 76.30%; thus, the present invention further preferably has a molar ratio of phosphorus in the dealuminized phosphoric acid to iron in the iron source of (1-2): (1-3), which further improves the obtained Mg 2+ Yield of doped iron phosphate product.

[0109] (3) It can be seen from Examples 1 and 6-7 that compared with Example 1, due to the lower stirring speed in Example 6, Mg 2+ The doping is uneven, the utilization rate of Mg in iron-magnesium phosphate is reduced to 89.93%, the utilization rate of Fe is reduced to 90.41%, and the utilization rate of Mg is reduced to 90.41%. 2+ The yield of the doped iron phosphate product decreased to 82.72%, and the iron-phosphorus ratio decreased to 0.9003; in Example 7, the stirring speed was high, and the utilization rate of Mg in the iron-magnesium phosphoric acid was only 89.27%, the utilization rate of Fe decreased to 88.03%, and the utilization rate of Mg 2+ The yield of the doped iron phosphate product dropped to 80.53%, and the iron-phosphorus ratio dropped to 0.8960, which did not improve the doping effect; it can be seen that the present invention further preferably sets the stirring speed to 40-70 r / min, so that the magnesium ions are fully doped in the lattice of the iron phosphate, thereby further improving the electrochemical performance of the product, and further improving the Mg 2+ Yield of doped iron phosphate product.

[0110] (4) It can be seen from Example 1 and Comparative Examples 1 and 2 that, compared with Example 1, since the iron ions and magnesium ions in the iron-containing magnesium phosphate are not fully utilized in Comparative Example 1, there is almost no magnesium ion doping in the product, which leads to no defects, affecting electron migration, and will lead to poor conductivity of subsequent battery materials; in Comparative Example 2, the method of mixed doping of iron phosphate and magnesium sulfate is adopted, and the utilization rate of Mg in magnesium sulfate is only 50.94. The electrochemical properties of the product obtained in this comparative example are low, and Mg 2+ The yield of the doped iron phosphate product is only 60.52%; therefore, the present invention directly uses the Mg prepared from iron-containing magnesium phosphoric acid. 2+ The doped iron phosphate product has a high yield and provides high-quality raw materials for the preparation of lithium iron phosphate materials.

[0111] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing cation-doped iron phosphate, characterized in that: The preparation method comprises the following steps: (1) mixing the iron-magnesium-containing phosphoric acid and the extraction system to extract and remove aluminum to obtain aluminum-removed phosphoric acid; (2) mixing the aluminum-removing phosphate, the iron source and the oxidant described in step (1) to obtain ferric phosphate dihydrate; (3) calcining the iron phosphate dihydrate described in step (2) to obtain Mg 2+ Doped iron phosphate.

2. The preparation method according to claim 1, characterized in that: The Fe in the iron-containing magnesium phosphate in step (1) 3+ Content>0.2wt%; Preferably, the Mg in the iron-magnesium phosphate in step (1) is 2+ Content ≥ 0.8wt%.

3. The preparation method according to claim 1 or 2, characterized in that: The extraction system in step (1) comprises an extractant or a combination of an extractant and a diluent, preferably a combination of the extractant and a diluent; Preferably, the extractant comprises any one or a combination of at least two of di(2-ethylhexyl)phosphate, tributyl phosphate, secondary carbon primary amine, di(alkylphenyl)phosphoric acid or di(3,5-dimethylphenyl)phosphoric acid; Preferably, the diluent includes any one of isobutyl alcohol, aviation kerosene or No. 260 solvent oil, or a combination of at least two of them.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The volume ratio of the iron-magnesium-containing phosphoric acid to the extraction system in step (1) is 1:(1-5); Preferably, the temperature of the extraction and aluminum removal in step (1) is 20 to 90° C., preferably 55 to 90° C.; Preferably, the extraction and aluminum removal time in step (1) is 5 to 60 minutes.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The mixing in step (2) comprises: first mixing the aluminum-removing phosphoric acid in step (1) with an iron source to obtain a ferrous dihydrogen phosphate solution through a first reaction; and second mixing the ferrous dihydrogen phosphate solution with an oxidant to obtain ferric phosphate dihydrate through a second reaction; Preferably, the iron source comprises any one of iron salt, iron powder or iron-containing waste or a combination of at least two thereof; Preferably, the molar ratio of phosphorus in the dealuminized phosphoric acid to iron in the iron source is (1-2):(1-3); Preferably, the temperature of the first reaction is 50-100°C, preferably 80-100°C; Preferably, the first reaction time is 2 to 9 hours; Preferably, the first reaction process also includes a first pH adjustment; Preferably, the solution used for the first pH adjustment includes any one of ammonia water, KOH solution or NaOH solution, or a combination of at least two thereof; Preferably, the first pH is adjusted to a pH value of 2.5 to 3.5; Preferably, the first reaction is accompanied by stirring; Preferably, the stirring speed is 15 to 100 r / min, preferably 40 to 70 r / min; Preferably, the oxidant comprises any one of hydrogen peroxide, oxygen or ozone, or a combination of at least two thereof; Preferably, the mass ratio of the ferrous dihydrogen phosphate solution to the oxidant is 1:(0.01-0.10); Preferably, the temperature of the second reaction is 60-100°C; Preferably, the second reaction time is 1 to 2 hours; Preferably, the second reaction process further includes a second pH adjustment; Preferably, the second pH is adjusted to a pH value of 1-5.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The calcination temperature in step (3) is 450-550° C. Preferably, the calcination time in step (3) is 1 to 3 hours.

7. The preparation method according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: (1) According to the volume ratio of 1: (1 to 5), Fe 3+ Content>0.2wt%, Mg 2+ The iron-magnesium-containing phosphoric acid with a content of more than 0.8 wt% is mixed with an extraction system, and the aluminum is extracted and removed at 20 to 90° C. for 5 to 60 minutes to obtain aluminum-removed phosphoric acid; The extraction system comprises an extractant or a combination of an extractant and a diluent; the extractant comprises any one of di(2-ethylhexyl)phosphate, tributyl phosphate, secondary carbon primary amine, di(alkylphenyl)phosphoric acid or di(3,5-dimethylphenyl)phosphoric acid or a combination of at least two thereof; the diluent comprises any one of isobutyl alcohol, aviation kerosene or No. 260 solvent oil or a combination of at least two thereof; (2) performing a first mixing of the aluminum-free phosphoric acid in step (1) and an iron source, and performing a first reaction for 2 to 9 hours at 50 to 100° C. and 15 to 100 r / min stirring conditions, and adjusting the pH value to 2.5 to 3.5 during the first reaction, to obtain a ferrous dihydrogen phosphate solution; and then performing a second mixing of the ferrous dihydrogen phosphate solution and an oxidant in a mass ratio of 1:(0.01 to 0.10), and performing a second reaction for 1 to 2 hours at 60 to 100° C., and adjusting the pH value to 1 to 5 during the second reaction, to obtain ferric phosphate dihydrate; The molar ratio of phosphorus in the dealuminized phosphate to iron in the iron source is (1-2):(1-3); the iron source includes any one of iron salt, iron powder or iron-containing waste or a combination of at least two thereof; (3) calcining the iron phosphate dihydrate in step (2) at 450-550° C. for 1-3 h to obtain Mg 2+ Doped iron phosphate.

8. 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 7.

9. The cation-doped iron phosphate according to claim 8, characterized in that: The particle size of the cation-doped iron phosphate is 20 to 60 nm; Preferably, the magnesium content in the iron phosphate is 0.2-2.2 wt %.

10. Use of the cation-doped iron phosphate as claimed in claim 8 or 9, 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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