Iron phosphate material, method for preparing the same, and lithium iron phosphate material

Abstract

The application discloses a kind of iron phosphate material and its preparation method and lithium iron phosphate material, belong to positive material field.The iron phosphate material provided by the present application includes porous outer layer;And the pore area ratio of micropore, mesopore and macropore of the iron phosphate material meets 10%-20%:55%-65%:20%-30%;The pore size of the iron phosphate material is mainly mesopore, and the position distribution of outer layer hole is uniform, so that the iron phosphate material has good tap density and specific surface area.The iron phosphate material with the above structure is prepared by two precipitation reactions;First, obtain the inner core particles with relatively few pores by the first precipitation reaction;Then, the inner core particles obtained by the first precipitation reaction are used as crystal seeds, and by controlling the addition amount of citric acid and the inlet rate of oxidizing gas, the outer layer with relatively more pores and low impurity elements is prepared.

Description

Technical Field

[0001] This invention relates to the field of cathode materials, specifically to an iron phosphate material, its preparation method, and a lithium iron phosphate material. Background Technology

[0002] In recent years, the new energy industry has developed rapidly. Among them, lithium-ion batteries have been widely used in power batteries and energy storage materials due to their advantages such as high specific energy, high power density, and long lifespan. At the same time, compared with traditional cathode materials such as lithium cobalt oxide and lithium manganese oxide, lithium iron phosphate materials have become one of the most ideal cathode materials for power batteries due to their advantages such as structural stability, high safety performance, good cycle performance, wide availability of raw materials, and low cost.

[0003] Currently, tap density, specific surface area, and impurity element content have a significant impact on the performance of lithium iron phosphate (LFP) materials. Specifically, increasing the tap density is an effective way to improve the energy density per unit volume of the battery. Specific surface area is also a factor affecting LFP performance; a smaller specific surface area results in a smaller contact area between particles and a longer ion diffusion path. Furthermore, impurities in iron phosphate also affect the performance of the prepared LFP materials. Among them, sulfur has a significant impact on the particle morphology, discharge capacity, and cycle performance of LFP and needs to be controlled within a low range. Iron phosphate is an important precursor for LFP materials, and LFP materials inherit the morphology, structure, and properties of iron phosphate. Therefore, iron phosphate materials have high specific surface area, high tap density, and low impurity content, which are beneficial for improving the energy density of LFP batteries.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The present invention aims to provide an iron phosphate material and its preparation method, as well as a lithium iron phosphate material, wherein the provided iron phosphate material simultaneously possesses high real density and specific surface area.

[0006] To achieve the above objectives, the first aspect of the present invention provides an iron phosphate material, the iron phosphate material comprising a porous outer layer; and the pore area ratio of the micropores, mesopores and macropores of the iron phosphate material satisfies 10%-20%:55%-65%:20%-30%.

[0007] In some embodiments, the iron phosphate material satisfies at least one of the following characteristics 1-3:

[0008] Feature 1: The specific pore volume of the iron phosphate material is 0.06-0.10 cm³. 3 / g;

[0009] Feature 2: The tap density of the iron phosphate material is 1.15-1.35 g / cm³. 3 ;

[0010] Feature 3: The specific surface area of ​​the iron phosphate material is 6.40-7.30 m². 2 / g.

[0011] The second aspect of this invention provides a method for preparing the iron phosphate material provided in the first aspect of this invention, comprising:

[0012] Primary precipitation reaction: Ferrous ions in the ferrous salt solution are partially oxidized to ferric ions, and a portion of phosphorus source is added to carry out a primary precipitation reaction to obtain a primary slurry;

[0013] Secondary precipitation reaction: Citric acid is added to the primary slurry, then oxygen or air is bubbled in and the remaining phosphorus source is added to carry out a secondary precipitation reaction. After solid-liquid separation, the mixture is washed and dried to obtain hydrated ferric phosphate.

[0014] Calcination: The hydrated ferric phosphate is calcined to obtain ferric phosphate material.

[0015] In some embodiments, the partial oxidation refers to oxidizing 5%-20% of the ferrous ions in the ferrous salt solution to ferric ions;

[0016] And / or, the sulfur content percentage of the hydrated iron phosphate material is 0.0125wt%-0.0150wt%.

[0017] In some embodiments, the amount of citric acid added is 1wt%-8wt% of the theoretical yield of ferric phosphate;

[0018] Preferably, the amount of citric acid added is 1wt%-4wt% of the theoretical yield of ferric phosphate.

[0019] In some embodiments, the partial oxidation includes adding hydrogen peroxide to the ferrous salt solution at a rate of 0.2-0.5 L / h;

[0020] And / or, the oxygen or air inlet flow rate is 10-30 L / h.

[0021] In some embodiments, the ferrous salt in the ferrous salt solution includes at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate;

[0022] And / or, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

[0023] In some embodiments, the iron concentration in the ferrous salt solution is 0.8-1.2 mol / L;

[0024] And / or, the molar ratio of phosphorus in the phosphorus source to iron in the ferrous salt solution is 1:1.0-1.1.

[0025] In some embodiments, the temperature of both the primary precipitation reaction and the secondary precipitation reaction is 90-98°C;

[0026] And / or, the primary precipitation reaction includes maintaining the temperature for 1-3 hours after stopping the feeding;

[0027] And / or, the secondary precipitation reaction includes aging at a constant temperature for 3-6 hours after stopping the feeding;

[0028] And / or, the calcination temperature is 600-750℃, and the calcination time is 2-6h.

[0029] The third aspect of the present invention provides a lithium iron phosphate material, which is prepared from the iron phosphate material provided in the first aspect of the present invention or the iron phosphate material obtained by the preparation method provided in the second aspect of the present invention.

[0030] The beneficial effects of this invention include:

[0031] The iron phosphate material provided by this invention has a porous outer layer with uniformly distributed pores; the interior of the iron phosphate material is relatively dense while the outer layer is relatively loose, and the pore size of the material is mainly mesopore, which gives the iron phosphate material both good tap density and specific surface area.

[0032] The preparation method provided by this invention prepares the iron phosphate material with the above structure through two precipitation reactions. In the first precipitation reaction, by controlling the oxidation rate of ferrous ions in the ferrous salt solution, core particles with relatively few pores are obtained, which is beneficial to improving the overall tap density and structural stability of the material. In the second precipitation reaction, the particles obtained in the first precipitation reaction are used as seed crystals, and by controlling the amount of citric acid added and the rate of introduction of oxidizing gas, an outer layer with relatively more pores and low impurity elements is obtained. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a SEM image of an iron phosphate slice provided in Embodiment 1 of the present invention;

[0035] Figure 2 This is a SEM image of an iron phosphate slice provided in Comparative Example 1 of the present invention;

[0036] Figure 3The XRD pattern of ferric phosphate dihydrate provided in Embodiment 1 of the present invention;

[0037] Figure 4 The image shows the XRD pattern of iron phosphate provided in Example 1 of this invention. Detailed Implementation

[0038] The following detailed description, with appropriate reference to the accompanying drawings, discloses an iron phosphate material, its preparation method, and a lithium iron phosphate material according to the present invention. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0039] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. Specifically, "()", ")", "[", and "]" represent intervals, where "()" or ")" represents an open interval, meaning the endpoints of the interval are not included; and "[" and "]" represent a closed interval, meaning the endpoints of the interval are included. A range defined in this way can include endpoints or not, and can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range.

[0040] Specifically, for example, if the ranges 60-120 and 80-110 are listed for a specific parameter, it is understood that the ranges 60-110 and 80-120 are also expected. Furthermore, if the minimum range values ​​are listed as 1 and 2, and if the maximum range values ​​are listed as 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range “ab” represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range “0-5” means that all real numbers between “0-5” have been listed herein, and “0-5” is merely a shortened representation of these numerical combinations. Additionally, when a parameter is stated as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. If (10, 20) is listed, it is understood as any value in the interval 10-20 excluding 10 and 20; (10, 20] is understood as any value in the interval 10-20 excluding 10 but including 20.

[0041] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0042] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0043] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0044] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0045] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0046] The first aspect of the present invention provides an iron phosphate material, the iron phosphate material comprising a porous outer layer; and the pore area ratio of the micropores, mesopores and macropores of the iron phosphate material satisfies 10%-20%:55%-65%:20%-30%.

[0047] The micropores have a diameter of 0.35-2 nm, the mesopores have a diameter of 2-50 nm, and the macropores have a diameter of 50-170 nm. The pore area refers to the total surface area of ​​the pores per unit mass of material, and the pore area of ​​the mesopores refers to the total surface area of ​​the mesopores per unit mass of material, which is obtained by static volumetric testing and BET multi-point method calculation. Unless otherwise specified, the iron phosphate material described in this invention is anhydrous iron phosphate.

[0048] This invention provides a bilayer structure for iron phosphate material, comprising a relatively dense core and a relatively loose outer layer. This compact inner and loose outer structure provides both a good specific surface area and a good tap density. Furthermore, the pores in the outer layer are primarily mesopores, and their positions are uniformly distributed, which is beneficial for improving the ion diffusion and charge transport efficiency of the cathode material prepared in this way.

[0049] It can be understood that lithium iron phosphate material consists of a core and a shell. The shell is porous, and the porosity of the shell is higher than that of the core. The core is the iron phosphate in the center, and the shell is the iron phosphate near the outer surface, i.e., the outer layer.

[0050] In some embodiments, the specific pore volume of the iron phosphate material is 0.06-0.10 cm³. 3 / g.

[0051] Specific pore volume refers to the volume of pores per unit mass of material, which is obtained by static volumetric testing and BET multi-point calculation. The specific pore volume of the iron phosphate material is the sum of the specific pore volumes of mesopores, micropores, and macropores.

[0052] The second aspect of the present invention provides a method for preparing iron phosphate material provided in the first aspect, comprising: a primary precipitation reaction: partially oxidizing ferrous ions in a ferrous salt solution to ferric ions, and adding a portion of a phosphorus source to carry out a primary precipitation reaction to obtain a primary slurry;

[0053] Secondary precipitation reaction: Citric acid is added to the primary slurry, then oxygen or air is bubbled in and the remaining phosphorus source is added to carry out a secondary precipitation reaction. After solid-liquid separation, the mixture is washed and dried to obtain hydrated ferric phosphate.

[0054] Calcination: The hydrated ferric phosphate is calcined to obtain ferric phosphate material.

[0055] The primary precipitation reaction involves maintaining a constant temperature after feeding. This temperature maintenance helps obtain structurally stable seed crystals, which in turn facilitates the secondary precipitation reaction on the seed crystal surface. The addition of citric acid in the secondary precipitation reaction balances the dissolution and recrystallization processes on the surface of hydrated ferric phosphate during growth, promoting uniform growth of the outer pore structure. The use of oxygen or air as an oxidant in the secondary precipitation reaction reduces the precipitation rate, promoting a uniform pore distribution on the outer layer of ferric phosphate and reducing the accumulation of impurities during growth, while also significantly lowering costs.

[0056] In the two-stage precipitation reaction, the seed crystals formed in the first precipitation reaction are further grown on the surface of the seed crystals by citric acid and oxidizing gas in the second precipitation reaction. The resulting iron phosphate particles are relatively dense inside and relatively loose on the outside, with uniform pore distribution in the outer layer. Therefore, the resulting lithium iron phosphate material has good overall dispersion and regular morphology, giving it both high specific surface area and high tap density.

[0057] In some embodiments, partial oxidation refers to oxidizing 5%-20% of the ferrous ions in the ferrous salt solution to ferric ions.

[0058] If the oxidation rate of ferrous ions in the ferrous salt solution is too low, the particles will become larger and the specific surface area will decrease during the subsequent induction process; if the oxidation rate of ferrous ions in the ferrous salt solution is too high, the core will become larger, which is not conducive to the uniform distribution of pores in the outer shell. By controlling the amount of ferrous ions oxidized during the primary precipitation reaction, the size of the central part of the iron phosphate material can be controlled; the secondary precipitation reaction forms an outer layer of iron phosphate material with higher porosity and more uniform pore distribution than the central part.

[0059] In some embodiments, the sulfur content percentage of hydrated ferric phosphate is 0.0125wt%-0.0150wt%.

[0060] In some embodiments, the percentage of Al in hydrated ferric phosphate is 0.004wt%-0.008wt%; the percentage of Ca in hydrated ferric phosphate is 0.0005wt%-0.0012wt%; and the percentage of Ti in hydrated ferric phosphate is 0.0005wt%-0.0015wt%.

[0061] It should be noted that impurity elements such as Al, S, Ca, and Ti come from external contamination in the raw materials or preparation process. These impurity elements have a significant impact on the capacity and cycle performance of lithium iron phosphate materials prepared from iron phosphate materials. In particular, the S element has a significant impact on the morphology, discharge capacity, and cycle performance of the subsequently prepared lithium iron phosphate materials. Therefore, obtaining iron phosphate materials with low impurity element content is of great significance.

[0062] In some embodiments, the amount of citric acid added is 1wt%-8wt% of the theoretical yield of ferric phosphate;

[0063] Preferably, the amount of citric acid added is 1wt%-4wt% of the theoretical yield of ferric phosphate.

[0064] The theoretical yield of ferric phosphate is the theoretical yield of ferric phosphate that can be produced from ferrous salt in ferrous salt solution. An appropriate amount of citric acid is beneficial for the secondary precipitation process, allowing dissolution and recrystallization on the seed crystal surface, forming uniform pores on the outer layer of ferric phosphate. However, excessive citric acid will affect precipitation efficiency and also lead to larger outer core pores. Simultaneously, too low a citric acid content will not significantly reduce impurities and will also result in uneven distribution of outer core pores.

[0065] In some implementations, a precipitation reaction includes holding the mixture at a constant temperature for 1-3 hours after stopping the feeding.

[0066] Insulation helps stabilize the seed crystals obtained from the primary precipitation reaction and facilitates the secondary precipitation reaction to obtain iron phosphate materials with high tap and high specific surface area.

[0067] In some embodiments, the secondary precipitation reaction includes stopping the feeding and aging at a constant temperature for 3-6 hours. After aging, the slurry is filtered, washed, and dried to obtain hydrated ferric phosphate. The washing is carried out until the conductivity of the wash water is less than 500 μS / cm. The drying temperature is 90-120℃.

[0068] In some embodiments, the primary and secondary precipitation reactions include stirring at a speed of 600-900 rpm.

[0069] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0070] The features and performance of the present invention will be further described in detail below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0071] Example 1

[0072] First precipitation reaction: A 1.0 mol / L ferrous sulfate solution is added to the reaction vessel. After heating to 90°C, a 30% (w / w) hydrogen peroxide and phosphoric acid solution are added concurrently to the reaction vessel to carry out the reaction, until Fe... 2+ The oxidation rate is 10% and the molar amount of added phosphoric acid is the same as that of Fe. 3+ (Fe) 2+ When the molar ratio of the oxidized material to the slurry is 1:1, stop feeding, keep warm for 2 hours, and obtain the slurry.

[0073] The concentration of the phosphoric acid solution was 1.0 mol / L; the flow rate of the hydrogen peroxide was 0.2 L / h.

[0074] Secondary precipitation reaction: Citric acid is added to the slurry obtained from the primary precipitation reaction and stirred until homogeneous. Oxygen is then introduced into the reactor at a flow rate of 15 L / h, while phosphoric acid solution is added simultaneously to carry out the precipitation reaction until the ferrous ions are completely oxidized and the total molar amount of added phosphoric acid is equal to the Fe content in the ferrous salt. 2+ When the molar ratio of the two materials is 1:1, the feeding is stopped, and the material is kept warm and aged for 6 hours. After solid-liquid separation, the slurry is washed until the conductivity of the wash water is 400 μS / cm, and then dried at 105℃ to obtain hydrated ferric phosphate.

[0075] The amount of citric acid added is 2 wt% of the theoretical yield of ferric phosphate (calculated as ferrous salt); the concentration of the phosphoric acid solution is 1.0 mol / L; in this example and the following examples, "total molar amount of phosphoric acid" refers to the total molar amount of phosphoric acid added in the primary precipitation reaction and the secondary precipitation reaction; the stirring speed of the reactor during the primary precipitation reaction and the secondary precipitation reaction is 700 rpm.

[0076] Calcination reaction: Hydrated ferric phosphate was calcined at 650℃ for 4 hours to obtain ferric phosphate material.

[0077] Example 2

[0078] Ferric phosphate material was prepared according to the method in Example 1, with all other conditions being the same, except that the material was kept at the temperature for 3 hours after the addition was stopped in the first precipitation reaction.

[0079] The amount of citric acid added is 4 wt% of the theoretical yield of ferric phosphate (calculated as ferrous salt).

[0080] Example 3

[0081] First precipitation reaction: A 1.2 mol / L ferrous sulfate solution was added to the reaction vessel. After heating to 95°C, a 30% (w / w) hydrogen peroxide and phosphoric acid solution were added concurrently to the reaction vessel to carry out the reaction until Fe... 2+ The oxidation rate is 20% and the molar amount of added phosphoric acid is the same as that of Fe. 3+ (Fe) 2+ When the molar ratio of the oxidized material to the slurry is 1:1, stop feeding, keep warm for 1 hour, and obtain the slurry.

[0082] The concentration of the phosphoric acid solution was 1.1 mol / L; the flow rate of the hydrogen peroxide was 0.2 L / h.

[0083] Secondary precipitation reaction: Citric acid is added to the slurry obtained from the primary precipitation reaction and stirred until homogeneous. Oxygen is then introduced into the reactor at a flow rate of 15 L / h, while phosphoric acid solution is added simultaneously to carry out the precipitation reaction until the ferrous ions are completely oxidized and the total molar amount of added phosphoric acid is equal to the Fe content in the ferrous salt. 2+ When the molar ratio is 1:1, stop feeding and continue to keep warm and age for 4 hours. After solid-liquid separation, the slurry is washed until the conductivity of the wash water is 400 μS / cm and then dried at 105℃ to obtain hydrated ferric phosphate.

[0084] The amount of citric acid added was 2 wt% of the theoretical yield of ferric phosphate (calculated as ferrous salt); the concentration of the phosphoric acid solution was 1.1 mol / L; and the stirring speed of the reactor during the primary and secondary precipitation reactions was 700 rpm.

[0085] Calcination reaction: Hydrated ferric phosphate was calcined at 650℃ for 4 hours to obtain ferric phosphate material.

[0086] Example 4

[0087] Ferric phosphate material was prepared according to the method in Example 1, with all other conditions being the same, except that the amount of citric acid added was 1 wt% of the theoretical yield of ferrous phosphate (calculated as ferrous salt).

[0088] The secondary precipitation reaction was carried out under heat for 4 hours.

[0089] Calcine hydrated ferric phosphate at 700℃ for 4 hours.

[0090] Example 5

[0091] First precipitation reaction: A 1.0 mol / L ferrous sulfate solution was added to the reaction vessel. After heating to 98°C, a 30% (w / w) hydrogen peroxide and phosphoric acid solution were added concurrently to the reaction vessel to carry out the reaction until Fe... 2+ The oxidation rate is 10% and the molar amount of added phosphoric acid is the same as that of Fe. 3+ (Fe) 2+ When the molar ratio of the oxidized material to the slurry is 1:1, stop feeding, keep warm for 1 hour, and obtain the slurry.

[0092] The concentration of the phosphoric acid solution was 0.9 mol / L; the flow rate of the hydrogen peroxide was 0.2 L / h.

[0093] Secondary precipitation reaction: Citric acid is added to the slurry obtained from the primary precipitation reaction and stirred until homogeneous. Oxygen is then introduced into the reactor at a flow rate of 15 L / h, while phosphoric acid solution is added simultaneously to carry out the precipitation reaction until the ferrous ions are completely oxidized and the total molar amount of added phosphoric acid is equal to the Fe content in the ferrous salt. 2+ When the molar ratio of the two materials is 1:1, the feeding is stopped, and the material is kept warm and aged for 3 hours. After solid-liquid separation, the resulting slurry is washed until the conductivity of the wash water is 400 μS / cm, and then dried at 105℃ to obtain hydrated ferric phosphate.

[0094] The amount of citric acid added was 3 wt% of the theoretical yield of ferric phosphate (calculated as ferrous salt); the concentration of the phosphoric acid solution was 0.9 mol / L; and the stirring speed of the reactor during the primary and secondary precipitation reactions was 700 rpm.

[0095] Calcination reaction: Hydrated ferric phosphate was calcined at 750℃ for 4 hours to obtain ferric phosphate material.

[0096] Example 6

[0097] First precipitation reaction: A 1.0 mol / L ferrous sulfate solution was added to the reaction vessel. After heating to 98°C, a 30% (w / w) hydrogen peroxide and phosphoric acid solution were added concurrently to the reaction vessel to carry out the reaction until Fe...2+ The oxidation rate is 10% and the molar amount of added phosphoric acid is the same as that of Fe. 3+ (Fe) 2+ When the molar ratio of the oxidized material to the slurry is 1:1, stop feeding, keep warm for 1 hour, and obtain the slurry.

[0098] The concentration of the phosphoric acid solution was 1.0 mol / L; the flow rate of the hydrogen peroxide was 0.2 L / h.

[0099] Secondary precipitation reaction: Citric acid is added to the slurry obtained from the primary precipitation reaction and stirred until homogeneous. Oxygen is then introduced into the reactor at a flow rate of 15 L / h, while phosphoric acid solution is added simultaneously to carry out the precipitation reaction until the ferrous ions are completely oxidized and the total molar amount of added phosphoric acid is equal to the Fe content in the ferrous salt. 2+ When the molar ratio is 1:1, stop feeding and continue to keep warm and age for 4 hours. After solid-liquid separation, the slurry is washed until the conductivity of the wash water is 400 μS / cm and then dried at 105℃ to obtain hydrated ferric phosphate.

[0100] The amount of citric acid added was 6 wt% of the theoretical yield of ferric phosphate (calculated as ferrous salt); the concentration of the phosphoric acid solution was 1.0 mol / L; and the stirring speed of the reactor during the primary and secondary precipitation reactions was 700 rpm.

[0101] Calcination reaction: Hydrated ferric phosphate was calcined at 650℃ for 4 hours to obtain ferric phosphate material.

[0102] Example 7

[0103] First precipitation reaction: A 0.8 mol / L ferrous sulfate solution was added to the reaction vessel. After heating to 90°C, a 30% (w / w) hydrogen peroxide and phosphoric acid solution were added concurrently to the reaction vessel to carry out the reaction until Fe... 2+ The oxidation rate is 5% and the molar amount of added phosphoric acid is the same as that of Fe. 3+ (Fe) 2+ When the molar ratio of the oxidized material to the slurry is 1:1.05, stop feeding, keep warm for 2 hours, and obtain the slurry.

[0104] The concentration of the phosphoric acid solution was 1.0 mol / L; the flow rate of the hydrogen peroxide was 0.35 L / h.

[0105] Secondary precipitation reaction: Citric acid is added to the slurry obtained from the primary precipitation reaction and stirred until homogeneous. Then, air is introduced into the reactor at a flow rate of 10 L / h, while phosphoric acid solution is added to carry out the precipitation reaction until the ferrous ions are completely oxidized and the total molar amount of added phosphoric acid is equal to the Fe in the ferrous salt. 2+When the molar ratio of the two materials is 1:1.05, the feeding is stopped, and the material is kept warm and aged for 6 hours. After solid-liquid separation, the resulting slurry is washed until the conductivity of the wash water is 400 μS / cm, and then dried at 105℃ to obtain hydrated ferric phosphate.

[0106] The amount of citric acid added was 2 wt% of the theoretical yield of ferric phosphate (calculated as ferrous salt); the concentration of the phosphoric acid solution was 1.0 mol / L; and the stirring speed of the reactor during the primary and secondary precipitation reactions was 700 rpm.

[0107] Calcination reaction: Hydrated ferric phosphate was calcined at 700℃ for 2 hours to obtain ferric phosphate material.

[0108] Example 8

[0109] First precipitation reaction: A 1.0 mol / L ferrous sulfate solution is added to the reaction vessel. After heating to 90°C, a 30% (w / w) hydrogen peroxide and phosphoric acid solution are added concurrently to the reaction vessel to carry out the reaction, until Fe... 2+ The oxidation rate is 10% and the molar amount of added phosphoric acid is the same as that of Fe. 3+ (Fe) 2+ When the molar ratio of the oxidized material to the slurry is 1:1.1, stop feeding, keep warm for 2 hours, and obtain the slurry.

[0110] The concentration of the phosphoric acid solution was 1.0 mol / L; the flow rate of the hydrogen peroxide was 0.5 L / h.

[0111] Secondary precipitation reaction: Citric acid is added to the slurry obtained from the primary precipitation reaction and stirred until homogeneous. Then, air is introduced into the reactor at a flow rate of 30 L / h, while phosphoric acid solution is added to carry out the precipitation reaction until the ferrous ions are completely oxidized and the total molar amount of added phosphoric acid is equal to the Fe in the ferrous salt. 2+ When the molar ratio of the two materials is 1:1.1, the feeding is stopped, and the material is kept warm and aged for 6 hours. After solid-liquid separation, the slurry is washed until the conductivity of the wash water is 400 μS / cm, and then dried at 105℃ to obtain hydrated ferric phosphate.

[0112] The amount of citric acid added was 2 wt% of the theoretical yield of ferric phosphate (calculated as ferrous salt); the concentration of the phosphoric acid solution was 1.0 mol / L; and the stirring speed of the reactor during the primary and secondary precipitation reactions was 700 rpm.

[0113] Calcination reaction: Hydrated ferric phosphate was calcined at 600℃ for 6 hours to obtain ferric phosphate material.

[0114] Comparative Example 1

[0115] Ferric phosphate material was prepared according to the method in Example 1, with all other conditions being the same, except that citric acid was not added during the secondary precipitation reaction.

[0116] No air is introduced; hydrogen peroxide is used as the oxidant, and phosphoric acid solution is added to carry out the precipitation reaction.

[0117] Comparative Example 2

[0118] First precipitation reaction: A 1.0 mol / L ferrous sulfate solution was added to the reaction vessel. After heating to 95°C, a 30% (w / w) hydrogen peroxide and phosphoric acid solution were added concurrently to the reaction vessel to carry out the reaction until Fe... 2+ The oxidation rate is 10% and the molar amount of added phosphoric acid is the same as that of Fe. 3+ (Fe) 2+ When the molar ratio of the oxidized material to the slurry is 1:1, stop feeding, keep warm for 2 hours, and obtain the slurry.

[0119] The concentration of the phosphoric acid solution was 1.0 mol / L; the flow rate of the hydrogen peroxide was 0.2 L / h.

[0120] Secondary precipitation reaction: Citric acid is added to the slurry obtained from the primary precipitation reaction and stirred until homogeneous. Simultaneously, hydrogen peroxide and phosphoric acid solution are added to continue the precipitation reaction until the ferrous ions are completely oxidized and the total molar amount of added phosphoric acid equals the amount of Fe in the ferrous salt. 2+ When the molar ratio of the two materials is 1:1, the feeding is stopped, and the material is kept warm and aged for 6 hours. After solid-liquid separation, the slurry is washed until the conductivity of the wash water is 400 μS / cm, and then dried at 105℃ to obtain hydrated ferric phosphate.

[0121] The amount of citric acid added was 0.5 wt% of the theoretical yield of ferric phosphate (calculated as ferrous salt); the concentration of the phosphoric acid solution was 1.0 mol / L; and the stirring speed of the reactor during the primary and secondary precipitation reactions was 700 rpm.

[0122] Calcination reaction: Hydrated ferric phosphate was calcined at 700℃ for 4 hours to obtain ferric phosphate material.

[0123] Comparative Example 3

[0124] First precipitation reaction: A 1.0 mol / L ferrous sulfate solution is added to the reaction vessel. After heating to 80°C, a 30% (w / w) hydrogen peroxide and phosphoric acid solution are added concurrently to the reaction vessel to carry out the reaction, until Fe... 2+ The oxidation rate is 10% and the molar amount of added phosphoric acid is the same as that of Fe. 3+ (Fe) 2+ When the molar ratio of the oxidized material to the slurry is 1:1, stop feeding, keep warm for 3 hours, and obtain the slurry.

[0125] The concentration of the phosphoric acid solution was 1.0 mol / L; the flow rate of the hydrogen peroxide was 0.2 L / h.

[0126] Secondary precipitation reaction: Continue adding the remaining hydrogen peroxide and phosphoric acid solution to carry out the precipitation reaction until the ferrous ions are completely oxidized and the total molar amount of added phosphoric acid is equal to the Fe in the ferrous salt. 2+ When the molar ratio of the two materials is 1:1, the feeding is stopped, and the material is kept warm and aged for 6 hours. After solid-liquid separation, the slurry is washed until the conductivity of the wash water is 400 μS / cm, and then dried at 105℃ to obtain hydrated ferric phosphate.

[0127] The concentration of the phosphoric acid solution was 1.0 mol / L; the stirring speed of the reactor during the primary and secondary precipitation processes was 700 rpm.

[0128] Calcination reaction: Hydrated ferric phosphate was calcined at 750℃ for 4 hours to obtain ferric phosphate material.

[0129] Comparative Example 4

[0130] Ferric phosphate material was prepared according to the method in Example 1, with all other conditions being the same, except that citric acid was not added in the secondary precipitation reaction.

[0131] Comparative Example 5

[0132] Ferric phosphate material was prepared according to the method of Example 1, with all other conditions being the same, except that the heat preservation reaction was not carried out in the first precipitation reaction.

[0133] Citric acid is not added during the secondary precipitation reaction.

[0134] Comparative Example 6

[0135] First precipitation reaction: After adding a 1.0 mol / L ferrous sulfate solution to the reaction vessel, citric acid is added. The temperature is raised to 90℃, and then a 30% (w / w) hydrogen peroxide and phosphoric acid solution are added concurrently to the reaction vessel to carry out the reaction, controlling the Fe... 2+ The oxidation rate is 10% and the molar amount of added phosphoric acid is the same as that of Fe. 3+ (Fe) 2+ When the molar ratio of the oxidized material to the slurry is 1:1, stop feeding, keep warm for 2 hours, and obtain the slurry.

[0136] The amount of citric acid added was 2 wt% of the theoretical yield of ferric phosphate (calculated as ferrous salt); the concentration of the phosphoric acid solution was 1.0 mol / L; and the flow rate of hydrogen peroxide was 0.2 L / h.

[0137] Secondary precipitation reaction: Oxygen is then introduced into the reactor at a flow rate of 15 L / h, while phosphoric acid solution is added to carry out the precipitation reaction until the ferrous ions are completely oxidized and the total molar amount of added phosphoric acid is equal to the Fe in the ferrous salt. 2+ When the molar ratio of the two materials is 1:1, the feeding is stopped, and the material is kept warm and aged for 6 hours. After solid-liquid separation, the slurry is washed until the conductivity of the wash water is 400 μS / cm, and then dried at 105℃ to obtain hydrated ferric phosphate.

[0138] The concentration of the phosphoric acid solution was 1.0 mol / L; the stirring speed of the reactor during the primary and secondary precipitation processes was 700 rpm.

[0139] Calcination reaction: Hydrated ferric phosphate was calcined at 650℃ for 4 hours to obtain ferric phosphate material.

[0140] Comparative Example 7

[0141] Ferric phosphate material was prepared according to the method in Example 1, with all other conditions being the same, except that the Fe content was controlled during the primary precipitation reaction. 2+ The oxidation rate is 3%;

[0142] The hydrated ferric phosphate was calcined at 700℃ for 4 hours to obtain the ferric phosphate material.

[0143] Comparative Example 8

[0144] Ferric phosphate material was prepared according to the method in Example 1, with all other conditions being the same, except that the Fe content was controlled during the primary precipitation reaction. 2+ The oxidation rate is 40%;

[0145] The hydrated ferric phosphate was calcined at 700℃ for 4 hours to obtain the ferric phosphate material.

[0146] Comparative Example 9

[0147] Ferric phosphate material was prepared according to the method in Example 1, with all other conditions being the same, except that hydrogen peroxide with a mass percentage concentration of 30% was used in the secondary precipitation reaction process, and oxygen oxidation was not used.

[0148] [Testing of relevant parameters for hydrated ferric phosphate and ferric phosphate materials]

[0149] 1. Morphological characteristics

[0150] The iron phosphate samples of each embodiment and comparative example were tested using a scanning electron microscope. Figure 1 The image shows an SEM image of a slice of the iron phosphate material prepared in Example 1. It can be seen that the iron phosphate particles are relatively compact inside, and the outer layer of the iron phosphate particles has pores with uniform size and even distribution. Figure 2The SEM image of the iron phosphate slices prepared in Comparative Example 1 shows that the pore sizes of the outer layer of the iron phosphate particles are not uniform, and the pore distribution is relatively poor.

[0151] 2. Phase detection

[0152] The hydrated ferric phosphate and ferric phosphate samples of Example 1 were tested using an X-ray diffractometer. Figure 3 The XRD pattern of the hydrated iron phosphate material prepared in Example 1 shows that the hydrated iron phosphate has a pure monoclinic crystal form with no other impurities generated. The corresponding standard card is PDF#33-0666. Figure 4 The image shows the XRD pattern of the iron phosphate material prepared in Example 1. It can be seen that when calcined at this temperature, the iron phosphate crystallization is complete and no impurity phase appears.

[0153] 3. Specific surface area test

[0154] The specific surface area of ​​the iron phosphate materials in each embodiment and comparative example was analyzed and calculated using a BSD-660S A6B6 specific surface area analyzer and the BET multi-point method. The test results for each embodiment and comparative example are shown in Table 2.

[0155] 4. Element content test

[0156] The elemental content of the iron phosphate materials in each embodiment and comparative example was tested by inductively coupled plasma atomic emission spectrometry (ICP-AES). The iron phosphate and hydrated iron phosphate materials were first digested, and then diluted according to the appropriate dilution factor for testing. Elemental content was determined using the HG / T4701-2021 standard titration method. The test results for each embodiment and comparative example are shown in Tables 1 and 2.

[0157] 5. Tap density test

[0158] According to GB / T 5162-2006, the lithium iron phosphate materials of each embodiment and comparative example were tested using a BT-302 tap density meter. The test results of each embodiment and comparative example are shown in Table 2.

[0159]

[0160]

[0161] As shown in Table 2, compared with Comparative Examples 1-9, Examples 1-8 show a higher proportion of micropore and mesopore pore areas and a lower proportion of macropore pore areas, with larger specific pore volumes. Consequently, the corresponding iron phosphate materials possess both a high specific surface area and good tap density. Combining Tables 1 and 2, it can be seen that the hydrated iron phosphate obtained in Example 1 has a low impurity element content, with sulfur (S) content of only 0.0129 wt%, and the resulting iron phosphate material has a large specific surface area of ​​7.26 m². 2 / g, with a high tap density of 1.3g / cm³. 3 As can be seen from Examples 2-8, the hydrated iron phosphate material prepared by the method provided by the present invention has low levels of impurity elements, with sulfur (S) content ranging from 0.0129 to 0.0143 wt%, and a specific surface area of ​​6.48 to 7.26 m². 2 / g, tap density is 1.19-1.30 g / cm³ 3 .

[0162] Compared to Example 1, Comparative Example 4 did not add citric acid during the secondary precipitation reaction, and the sulfur content in the prepared hydrated iron phosphate material was 0.0242 wt%. The specific surface area and tap density of the prepared iron phosphate material were both reduced to 7.14 m². 2 / g and 1.19 g / cm 3 Compared to Example 1, Comparative Example 9 did not use oxygen or air as an oxidant during the secondary precipitation reaction, resulting in a hydrated iron phosphate material with a sulfur content of 0.0175 wt%. The specific surface area and tap density of the resulting iron phosphate material were both reduced to 6.35 m² / s. 2 / g and 1.11g / cm 3 Compared to Example 1, Comparative Example 1 did not add citric acid or use oxygen or air as an oxidant during the secondary precipitation reaction. As a result, the hydrated iron phosphate material prepared had higher levels of impurities, with an S content of 0.0331 wt%. The specific surface area and tap density of the prepared iron phosphate material were both reduced, to 6.32 m² / s. 2 / g and 1.09 g / cm 3 It can be seen that using only oxygen or air as an oxidant during the secondary precipitation reaction will increase the content of impurity elements in the prepared hydrated ferric phosphate, and reduce the specific surface area and tap density of the prepared ferric phosphate material. Furthermore, if neither oxygen nor air is used as an oxidant nor citric acid is added during the secondary precipitation reaction, the content of impurity elements in the prepared hydrated ferric phosphate will increase further, resulting in poor pore size uniformity of the prepared ferric phosphate material, and further reducing the specific surface area and tap density of the ferric phosphate material.

[0163] Compared to Example 1, Comparative Example 6 added the same amount of citric acid as in Example 1 during a single precipitation process, resulting in a hydrated iron phosphate material with a higher impurity element content, including an S element content of 0.0195 wt%. The specific surface area and tap density of the resulting iron phosphate material were also reduced, to 7.05 m² / s. 2 / g and 1.18 g / cm 3 Because the addition of citric acid during the secondary precipitation reaction involves dissolution and recrystallization, it reduces the accumulation of impurity elements in hydrated ferric phosphate, resulting in a more regular morphology and uniform pore size distribution in the ferric phosphate material. Adding citric acid during the primary reaction process cannot achieve the same effect.

[0164] Compared to Example 1, in Comparative Examples 7 and 8, the oxidation rate of ferrous ions in the ferrous salt was either below or above the specified range during the first precipitation reaction, resulting in hydrated ferric phosphate with a higher impurity element content and ferric phosphate materials with lower specific surface area and tap density. This is because if the oxidation rate of ferrous ions is too low in the first precipitation reaction, fewer seed crystals are generated, leading to larger particle size in the second-stage reaction, making it easier for impurities to be encapsulated and reducing the specific surface area. Conversely, if the oxidation rate of ferrous ions is too high in the first reaction, the precipitation growth process in the second reaction is uneven, resulting in uneven pore distribution and a decrease in specific surface area. Furthermore, as can be seen from Comparative Example 2, the amount of citric acid was too low to effectively prevent impurity deposition.

[0165] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A ferric phosphate material, characterized in that, The iron phosphate material includes a porous outer layer; and the pore area ratio of the micropores, mesopores, and macropores in the iron phosphate material satisfies 10%-20%: 55%-65%: 20%-30%. The preparation method of the iron phosphate material includes: Primary precipitation reaction: The ferrous ions in the ferrous salt solution are partially oxidized to ferric ions, and a portion of phosphorus source is added to carry out a primary precipitation reaction to obtain a primary slurry; the partial oxidation refers to oxidizing 5%-20% of the ferrous ions in the ferrous salt solution to ferric ions; Secondary precipitation reaction: Citric acid is added to the primary slurry, then oxygen or air is bubbled in and the remaining phosphorus source is added to carry out a secondary precipitation reaction. After solid-liquid separation, the slurry is washed and dried to obtain hydrated ferric phosphate. The amount of citric acid added is 1wt%-8wt% of the theoretical yield of ferric phosphate. The flow rate of oxygen or air bubbling in is 10-30L / h. Calcination: The hydrated ferric phosphate is calcined to obtain ferric phosphate material.

2. The iron phosphate material according to claim 1, characterized in that, The iron phosphate material satisfies at least one of the following characteristics 1-3: Feature 1: The specific pore volume of the iron phosphate material is 0.06-0.10 cm³. 3 / g; Feature 2: The tap density of the iron phosphate material is 1.15-1.35 g / cm³. 3 ; Feature 3: The specific surface area of ​​the iron phosphate material is 6.40-7.30 m². 2 / g.

3. The method for preparing the iron phosphate material according to claim 1 or 2, characterized in that, The preparation method includes: Primary precipitation reaction: The ferrous ions in the ferrous salt solution are partially oxidized to ferric ions, and a portion of phosphorus source is added to carry out a primary precipitation reaction to obtain a primary slurry; the partial oxidation refers to oxidizing 5%-20% of the ferrous ions in the ferrous salt solution to ferric ions; Secondary precipitation reaction: Citric acid is added to the primary slurry, then oxygen or air is bubbled in and the remaining phosphorus source is added to carry out a secondary precipitation reaction. After solid-liquid separation, the slurry is washed and dried to obtain hydrated ferric phosphate. The amount of citric acid added is 1wt%-8wt% of the theoretical yield of ferric phosphate. The flow rate of oxygen or air bubbling in is 10-30L / h. Calcination: The hydrated ferric phosphate is calcined to obtain ferric phosphate material.

4. The preparation method according to claim 3, characterized in that, The sulfur content percentage of the hydrated ferric phosphate is 0.0125wt%-0.0150wt%.

5. The preparation method according to claim 3, characterized in that, The amount of citric acid added is 1wt%-4wt% of the theoretical yield of ferric phosphate.

6. The preparation method according to claim 3, characterized in that, The partial oxidation involves adding hydrogen peroxide to the ferrous salt solution at a rate of 0.2-0.5 L / h.

7. The preparation method according to claim 3, characterized in that, The ferrous salt in the ferrous salt solution includes at least one of ferrous sulfate, ferrous chloride and ferrous nitrate. And / or, the phosphorus source includes at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and ammonium phosphate.

8. The preparation method according to claim 3, characterized in that, The iron concentration in the ferrous salt solution is 0.8-1.2 mol / L; And / or, the molar ratio of phosphorus in the phosphorus source to iron in the ferrous salt solution is 1:1.0-1.

1.

9. The preparation method according to claim 3, characterized in that, The temperature for both the primary and secondary precipitation reactions is 90-98℃. And / or, the primary precipitation reaction includes maintaining the temperature for 1-3 hours after stopping the feeding; And / or, the secondary precipitation reaction includes aging at a constant temperature for 3-6 hours after stopping the feeding; And / or, the calcination temperature is 600-750℃, and the calcination time is 2-6h.

10. A lithium iron phosphate material, characterized in that, The lithium iron phosphate material is prepared from the iron phosphate material of claim 1 or 2, or from the iron phosphate material prepared by any one of the preparation methods of claims 3-8.

Images