Porous iron phosphate, preparation method therefor and use thereof

Abstract

The present disclosure relates to the technical field of battery materials, and in particular to porous iron phosphate, a preparation method therefor and a use thereof. The preparation method comprises the following steps: (1) mixing an iron source, a phosphorus source and an oxidizing solution, adding a pH regulator, and synthesizing a crude iron phosphate hydrate; (2) mixing the crude iron phosphate hydrate prepared in the step (1) with an aging solution for aging, performing solid-liquid separation, and then washing to obtain a solid; and (3) sintering the solid obtained in the step (2) to obtain the porous iron phosphate. The preparation method can effectively remove impurity elements, the prepared porous iron phosphate has high compaction density, and the endurance capability of batteries can be effectively improved.

Description

A kind of porous iron phosphate and its preparation method and application Technical Field

[0001] The present disclosure belongs to the technical field of battery materials, and in particular relates to a porous iron phosphate and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are one of the most common rechargeable batteries and are widely used in electric vehicles, portable electronic devices, energy storage systems, and other fields. The properties of the cathode material in lithium-ion batteries have a crucial impact on the battery's performance and stability. Lithium iron phosphate, a common cathode material for lithium-ion batteries, is highly favored due to its relatively long cycle life and good thermal stability.

[0003] However, during the synthesis of iron phosphate, due to the different sources of raw materials, some undesirable impurities such as nickel (Ni), cobalt (Co), manganese (Mn), and sulfur (S) are often introduced. These impurities may reduce the performance of the positive electrode material and limit the overall performance of the battery. This results in a low compaction density of the LiFePO4 material, which in turn leads to a relatively low energy density, limiting the battery's endurance, especially for applications with high energy density requirements such as electric vehicles.

[0004] Summary of the Invention

[0005] The present disclosure aims to address at least one of the technical problems in the related art. To this end, the present disclosure proposes a porous iron phosphate, a preparation method, and applications thereof. The preparation method can effectively remove impurity elements, and the prepared porous iron phosphate has a high compaction density, which can effectively improve the battery life.

[0006] The above technical objectives of the present disclosure are achieved through the following technical solutions:

[0007] A method for preparing porous ferric phosphate comprises the following steps: (1) mixing an iron source, a phosphorus source and an oxidant solution, and adding a pH regulator to synthesize crude ferric phosphate hydrate; (2) mixing the crude ferric phosphate hydrate prepared in step (1) with an aging liquid for aging, and washing after solid-liquid separation to obtain a solid; and (3) sintering the solid obtained in step (2) to obtain the porous ferric phosphate.

[0008] In one embodiment, in step (1), both the iron source and the phosphorus source contain impurities, and the impurities include at least one of Ni, Co, Mn, Cl and S.

[0009] In one embodiment, in step (1), the iron source is at least one of ferrous sulfate, ferrous chloride and ferrous nitrate.

[0010] In one embodiment, in step (1), the phosphorus source is phosphoric acid.

[0011] In one embodiment, in step (1), the oxidant solution is hydrogen peroxide.

[0012] In one embodiment, in step (1), the pH adjuster is aqueous ammonia.

[0013] In one embodiment, in step (1), after adjustment by the pH adjuster, the pH of the reaction system is 1.5-2.5.

[0014] In one embodiment, in step (1), after adjustment by the pH adjuster, the pH of the reaction system is 1.8-2.0.

[0015] In one embodiment, in step (1), the crude ferric phosphate hydrate is crude ferric phosphate dihydrate.

[0016] In one embodiment, in step (1), the crude ferric phosphate dihydrate is synthesized by one of the following processes: an ammonia method, a sodium method, and an iron powder method.

[0017] In one embodiment, in step (1), the particle size of the crude ferric phosphate dihydrate is 1-20 μm.

[0018] In one embodiment, in step (1), the particle size of the crude ferric phosphate dihydrate is 2-15 μm.

[0019] In one embodiment, in step (2), the aging liquid is obtained by mixing compound A, compound B and water, the compound A is at least one of phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid and sodium fluoride, and the compound B is at least one of ferrous sulfate and ferrous chloride.

[0020] In one embodiment, the concentration of the anion in the compound A in the aging solution is 0.1-2 mol / L, and the concentration of the cation in the compound B in the aging solution is 0.03-1 mol / L.

[0021] In one embodiment, the concentration of the anion in the compound A in the aging solution is 0.1-1 mol / L, and the concentration of the cation in the compound B in the aging solution is 0.05-0.5 mol / L.

[0022] In one embodiment, in step (2), the aging temperature is 60-150° C., and the aging time is 5-35 hours.

[0023] In one embodiment, in step (2), the aging temperature is 80-100° C., and the aging time is 10-30 h.

[0024] In one embodiment, in step (2), the solid-liquid ratio of the crude ferric phosphate hydrate and the aging liquid is 5-40 g:100 mL.

[0025] In one embodiment, in step (2), the solid-liquid ratio of the crude ferric phosphate hydrate and the aging liquid is 10-30 g:100 mL.

[0026] In one embodiment, in step (3), the sintering temperature is 400-1200° C., and the sintering time is 1-8 hours.

[0027] In one embodiment, in step (3), the sintering temperature is 500-1000° C., and the sintering time is 1-5 hours.

[0028] Since impurities are easily encapsulated during the synthesis of crude ferric phosphate dihydrate, the aging process is postponed to prevent the ions in the aging solution from being encapsulated inside the ferric phosphate dihydrate particles. Since the crystal form of the ferric phosphate dihydrate has grown relatively complete when aging begins, the impurities will no longer be encapsulated. Therefore, the impurity ions in the product can be replaced by the ions in the aging solution during the aging process.

[0029] Principle of impurity ion introduction: ①Cation radius Fe 3+ (64pm)<Mn 2+ (66pm)<Co 2+ (74ppm)≈Ni 2+ (74pm)<Fe 2+ (76pm), since Fe in ferric phosphate is trivalent, Ni 2+ 、Mn 2+ Relative to Co 2+ It is more difficult to enter the iron phosphate lattice. At the same time, since the pH of the iron phosphate synthesis process is generally controlled at around 1.5-2.0, which does not reach the pH of cationic precipitation, the impurities in the product are mainly brought in by encapsulation, and the total amount of cationic impurities introduced is limited; ② Anion group SO4 2- (230pm)<PO4 3- (238pm), SO4 2- It is relatively easier to enter the iron phosphate lattice, and the ratio of anionic impurities introduced is relatively high.

[0030] Take Ni 2+ 、SO4 2- Introduction process example, Ni 2+ 、SO4 2- Theoretical reactions that may occur during the introduction process:

[0031] Ni 2+ +SO4 2- →NiSO4 (slightly soluble in acid), 3Ni 2+ +2PO43- →Ni3(PO4)2(soluble in acid)Ni 2+ +HPO4 2- →NiHPO4;Ni 2+ +SO4 2- →NiSO4 (slightly soluble in acid), Fe 3+ +SO4 2- →Fe2(SO4)3(soluble in acid).

[0032] Take Ni 2+ 、SO4 2- An example of isomorphous substitution process after introduction, Ni 2+ with Fe 2+ The ionic radius is close, and the Ni introduced into the product 2+ Fe 2+ Possibility of substitution, SO4 2- With PO4 3- The ionic radius is close, and the SO4 introduced into the product 2- Existence is PO4 3- Substitution possibility, stability PO4 3- >SO4 2- . With Fe 2+ PO4 3- Taking the introduction of cationic and anionic groups into the aging liquid as an example, the principle of the substitution process is as follows:

[0033] NiSO4+Fe 2+ →FeSO4+Ni 2+ ,Ni3(PO4)2+Fe 2+ →Fe3(PO4)2+Ni 2+ ,NiHPO4+Fe 2+ →FeHPO4+Ni 2+ ;NiSO4+2PO4 3- →Ni3(PO4)2+SO4 2- ,Ni3(PO4)2+Fe 2+ →Fe3(PO4)2+Ni 2+ ,Fe2(SO4)3+2PO4 3- →2FePO4+3SO4 2- FeSO4 and Fe3(PO4)2 cannot exist stably in strong acid solutions, and the Fe3(PO4)2 generated during the aging process will dissolve.

[0034] The role of the aging process is to free some of the impurity ions from the crystal lattice. Small particles of iron phosphate are more soluble than large particles. The dissolution and precipitation processes occur simultaneously. Although the growth units in the solution have not changed, the reaction always tends to proceed in the direction of low energy. After a period of aging, the precipitate will rearrange according to the inherent lattice direction, which is conducive to the integrity of the crystal shape and the progress of isomorphous substitution.

[0035] A porous iron phosphate is prepared by the above-mentioned preparation method.

[0036] In one embodiment, the specific surface area of ​​the porous iron phosphate is 35-40m 2 / g.

[0037] In one embodiment, the specific surface area of ​​the porous iron phosphate is 36.01-38.15m 2 / g.

[0038] In one embodiment, the content of Ni in the porous ferric phosphate is ≤150 ppm, the content of Mn is ≤100 ppm, and the content of S is ≤350 ppm.

[0039] In one embodiment, the content of Ni in the porous ferric phosphate is ≤115 ppm, the content of Mn is ≤98 ppm, and the content of S is ≤341 ppm.

[0040] A positive electrode material includes the porous iron phosphate as described above.

[0041] A battery comprises the positive electrode material as described above.

[0042] The beneficial effects of the present disclosure are:

[0043] (1) In the preparation method of the porous iron phosphate disclosed in the present invention, impurity elements such as nickel, cobalt, manganese, and sulfur in the iron phosphate are successfully removed through the aging process, thereby improving the purity of the prepared porous iron phosphate;

[0044] (2) In the preparation method of the porous ferric phosphate disclosed herein, since more than 50% of impurities can be removed through the aging process, the source of impurity-containing raw materials in the synthesis process of the porous ferric phosphate is greatly increased, the acceptable range of impurities is increased, and the production cost is reduced;

[0045] (3) The porous iron phosphate prepared by the preparation method disclosed in the present invention has a large specific surface area, which helps to improve battery performance;

[0046] (4) The preparation method disclosed herein removes impurity elements in the raw materials and increases the specific surface area of ​​the product, so that the charge and discharge capacity and compaction performance of the positive electrode material prepared using the porous iron phosphate disclosed herein are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG1 is a cross-sectional SEM image of crude ferric phosphate dihydrate obtained in the preparation process of Example 1 of the present disclosure after aging for 5 hours;

[0048] FIG2 is a cross-sectional SEM image of the crude ferric phosphate dihydrate obtained in the preparation process of Example 1 of the present disclosure after aging for 10 hours;

[0049] FIG3 is a cross-sectional SEM image of the crude ferric phosphate dihydrate obtained in the preparation process of Example 1 of the present disclosure after aging for 20 hours;

[0050] FIG4 is a cross-sectional SEM image of the crude ferric phosphate dihydrate obtained in the preparation process of Example 2 of the present disclosure after aging for 10 hours;

[0051] FIG5 is a cross-sectional SEM image of the crude ferric phosphate dihydrate obtained in the preparation process of Comparative Example 1 of the present disclosure after aging for 20 hours;

[0052] FIG6 is a cross-sectional SEM image of the crude ferric phosphate dihydrate obtained in the preparation process of Comparative Example 2 of the present disclosure after aging for 20 hours. DETAILED DESCRIPTION

[0053] The present disclosure is further described below with reference to specific embodiments.

[0054] Example 1:

[0055] A method for preparing porous iron phosphate comprises the following specific steps:

[0056] (1) Synthesis: Ferrous sulfate, phosphoric acid, and hydrogen peroxide containing Ni impurities were mixed, and the pH was adjusted to 1.8 with ammonia water to synthesize crude ferric phosphate dihydrate. The filter cake was filtered and washed to obtain a filter cake. The filter cake was dried and tested, and the Ni and S contents in the filter cake were measured to be 413 ppm and 1105 ppm, respectively.

[0057] (2) Liquid preparation: 139g of ferrous sulfate, 230g of phosphoric acid and water were mixed to prepare 10L of aging liquid, wherein the Fe 2+ PO4 3- The molar concentrations are 0.05 mol / L and 0.2 mol / L respectively;

[0058] (3) Aging: 2000 g of crude ferric phosphate dihydrate synthesized in step (1) was placed in 10 L of aging solution at 90° C. for 20 h, followed by solid-liquid separation, washing and drying at 100° C.;

[0059] (4) Sintering: After drying, the powder is sintered at 600°C for 3 hours to dehydrate and desulfurize to obtain porous iron phosphate.

[0060] Figures 1, 2 and 3 are cross-sectional SEM images of the crude ferric phosphate dihydrate aged for 5 h, 10 h and 20 h in Example 1, respectively. From the cross-sectional morphology, it can be seen that with the extension of the aging time, the internal pores and microcracks increase. The increase in pores proves that dissolution and substitution have occurred, and is more conducive to the desulfurization of the material during the sintering process.

[0061] Example 2:

[0062] A method for preparing porous iron phosphate comprises the following specific steps:

[0063] (1) Synthesis: After mixing ferrous sulfate containing Ni impurities, phosphoric acid, and hydrogen peroxide, the pH was adjusted to 1.8 with ammonia water to synthesize crude ferric phosphate dihydrate. The filter cake was filtered and washed to obtain a filter cake. The filter cake was dried and tested. The Ni and S contents in the filter cake were measured to be 441 ppm and 1048 ppm, respectively.

[0064] (2) Liquid preparation: 695g of ferrous sulfate, 1152g of phosphoric acid and water were mixed to prepare 10L of aging liquid, wherein the Fe 2+ PO4 3- The molar concentrations are 0.25 mol / L and 1 mol / L respectively;

[0065] (3) Aging: 2000 g of crude ferric phosphate dihydrate synthesized in step (1) was placed in 10 L of aging solution at 90° C. for 10 h, followed by solid-liquid separation, washing and drying at 100° C.;

[0066] (4) Sintering: After drying, the powder is sintered at 600°C for 3 h to dehydrate and desulfurize to obtain porous iron phosphate.

[0067] Figure 4 is a cross-sectional SEM image of the crude ferric phosphate dihydrate after aging for 10 days in Example 2. From the cross-sectional morphology, it can be seen that under high concentrations of phosphoric acid and ferrous iron, the pores and microcracks inside the particles increase sharply after aging, and there are more fine particles around the particles, which proves that the effect of aging substitution is more obvious.

[0068] Example 3:

[0069] A method for preparing porous iron phosphate comprises the following specific steps:

[0070] (1) Synthesis: Ferrous sulfate containing Mn impurities, phosphoric acid, and hydrogen peroxide were mixed, and the pH was adjusted to 2.0 with sodium hydroxide solution to synthesize crude ferric phosphate dihydrate. The filter cake was filtered and washed to obtain a filter cake. After drying, the Mn and S contents were tested to be 348 ppm and 1103 ppm, respectively.

[0071] (2) Liquid preparation: 139g of ferrous sulfate, 1152g of phosphoric acid and water were mixed to prepare 10L of aging liquid, wherein the Fe2+ PO4 3- The molar concentrations were 0.05 mol / L and 1 mol / L respectively;

[0072] (3) Aging: 3000 g of crude ferric phosphate dihydrate synthesized in step (1) was placed in 10 L of aging solution at 90° C. for 10 h, followed by solid-liquid separation, washing and drying at 100° C.;

[0073] (4) Sintering: After drying, the powder is sintered at 600°C for 3 hours to dehydrate and desulfurize to obtain porous iron phosphate.

[0074] Example 4:

[0075] A method for preparing porous iron phosphate comprises the following specific steps:

[0076] (1) Synthesis: Ferrous sulfate containing Mn impurities, phosphoric acid, and hydrogen peroxide were mixed, and the pH was adjusted to 2.0 with sodium hydroxide solution to synthesize crude ferric phosphate dihydrate. The filter cake was filtered and washed to obtain a filter cake. After drying, the Mn and S contents were tested to be 391 ppm and 995 ppm, respectively.

[0077] (2) Liquid preparation: 279g of ferrous sulfate, 1152g of phosphoric acid and water were mixed to prepare 10L of aging liquid, wherein the Fe 2+ PO4 3- The molar concentration is 0.05mol / L and 1mol / L;

[0078] (3) Aging: 3000 g of crude ferric phosphate dihydrate synthesized in step (1) was placed in 10 L of aging solution at 90° C. for 20 h, followed by solid-liquid separation, washing and drying at 100° C.;

[0079] (4) Sintering: After drying, the powder is sintered at 600°C for 3 hours to dehydrate and desulfurize to obtain porous iron phosphate.

[0080] Comparative Example 1:

[0081] This comparative example provides a method for preparing ferric phosphate. The main difference between the preparation method and Example 1 is that the Fe 2+ The concentrations are different:

[0082] (1) Synthesis: Ferrous sulfate, phosphoric acid, and hydrogen peroxide containing Ni impurities were mixed, and the pH was adjusted to 1.8 with ammonia water to synthesize crude ferric phosphate dihydrate. The filter cake was filtered and washed to obtain a filter cake. The filter cake was dried and tested, and the Ni and S contents in the filter cake were measured to be 422 ppm and 1171 ppm, respectively.

[0083] (2) Liquid preparation: 28g of ferrous sulfate, 230g of phosphoric acid and water were mixed to prepare 10L of aging liquid, wherein the Fe in the aging liquid was2+ PO4 3- The molar concentrations are 0.01mol / L and 0.2mol / L respectively;

[0084] (3) Aging: 2000 g of crude ferric phosphate dihydrate synthesized in step (1) was placed in 10 L of aging solution at 90° C. for 20 h, followed by solid-liquid separation, washing and drying at 100° C.;

[0085] (4) Sintering: After drying, the powder is sintered at 600°C for 3 hours to dehydrate and desulfurize to obtain iron phosphate.

[0086] Figure 5 is a cross-sectional SEM image of the crude ferric phosphate dihydrate obtained in the preparation process of Comparative Example 1 after aging for 20 hours. It can be seen from the internal microcracks and pore structure that they are significantly reduced compared with Example 1. A layer containing a pore structure is formed on the outer layer of the spherical structure, and there are fewer pores inside the particles. This preliminarily proves that isomorphous substitution has not been completed inside, mainly due to the poor aging effect.

[0087] Comparative Example 2:

[0088] This comparative example provides a method for preparing ferric phosphate. The main difference between the preparation method and Example 1 is that pure water is used for purification:

[0089] (1) Synthesis: After mixing ferrous sulfate, phosphoric acid, and hydrogen peroxide containing Ni impurities, the pH was adjusted to 1.8 with ammonia water to synthesize crude ferric phosphate dihydrate. The filter cake was filtered and washed to obtain a filter cake. The filter cake was dried and tested. The Ni and S contents in the filter cake were measured to be 435 ppm and 1058 ppm, respectively.

[0090] (2) Liquid preparation: Take 10L of pure water as the aging liquid, where Fe 2+ PO4 3- The molar concentration is 0 mol / L;

[0091] (3) Aging: 2000 g of crude ferric phosphate dihydrate synthesized in step (1) was placed in 10 L of aging solution at 90° C. for 20 h, followed by solid-liquid separation, washing and drying at 100° C.;

[0092] (4) Sintering: After drying, the powder is sintered at 600°C for 3 hours to dehydrate and desulfurize to obtain iron phosphate.

[0093] Figure 6 is a cross-sectional SEM image of the crude ferric phosphate dihydrate obtained in the preparation process of Comparative Example 2 after aging for 20 hours. It can be seen from the internal microcracks and pore structure that the reduction is more obvious compared with Comparative Example 1, and the pore structure in the outer layer of the spherical structure is thinner. Compared with Comparative Example 2, there is less isomorphous substitution inside the particles and the aging effect is worse.

[0094] Comparative Example 3:

[0095] This comparative example provides a method for preparing ferric phosphate. The main difference between the preparation method and Example 1 is the aging temperature:

[0096] (1) Synthesis: After mixing ferrous sulfate, phosphoric acid, and hydrogen peroxide containing Ni impurities, the pH was adjusted to 1.8 with ammonia water to synthesize crude ferric phosphate dihydrate. The filter cake was filtered and washed to obtain a filter cake. The filter cake was dried and tested. The Ni and S contents in the filter cake were measured to be 405 ppm and 1058 ppm, respectively.

[0097] (2) Liquid preparation: 139g of ferrous sulfate, 230g of phosphoric acid and water were mixed to prepare 10L of aging liquid, wherein the Fe 2+ PO4 3- The molar concentrations are 0.05 mol / L and 0.2 mol / L respectively;

[0098] (3) Aging: 2000 g of crude ferric phosphate dihydrate synthesized in step (1) was placed in 10 L of aging solution at 50° C. for 20 h, followed by solid-liquid separation, washing and drying at 100° C.;

[0099] (4) Sintering: After drying, the powder is sintered at 600°C for 3 hours to dehydrate and desulfurize to obtain iron phosphate.

[0100] Comparative Example 4:

[0101] This comparative example provides a method for preparing ferric phosphate. The main difference between the preparation method and Example 1 is that the Fe 2+ PO4 3- The concentrations are different:

[0102] (1) Synthesis: After mixing ferrous sulfate, phosphoric acid, and hydrogen peroxide containing Ni impurities, the pH was adjusted to 1.8 with ammonia water to synthesize crude ferric phosphate dihydrate. The filter cake was filtered and washed to obtain a filter cake. The filter cake was dried and tested. The Ni and S contents in the filter cake were measured to be 401 ppm and 1093 ppm, respectively.

[0103] (2) Liquid preparation: 1529g of ferrous sulfate, 1268g of phosphoric acid and water were mixed to prepare 10L of aging liquid, wherein the Fe 2+ PO4 3- The molar concentrations were 0.55 mol / L and 1.1 mol / L respectively;

[0104] (3) Aging: 2000 g of crude ferric phosphate dihydrate synthesized in step (1) was placed in 10 L of aging solution at 90° C. for 20 h, followed by solid-liquid separation, washing and drying at 100° C.;

[0105] (4) Sintering: After drying, the powder is sintered at 600°C for 3 hours to dehydrate and desulfurize to obtain iron phosphate.

[0106] Since the concentration of anions and cations in the aging liquid is relatively high and the replacement effect is more obvious, the particles may become too loose and severely broken during aging, making filtration more difficult. Industrialization is prone to drawbacks and is therefore not easy to adopt.

[0107] Test example:

[0108] 1. The physical and chemical indicators of the porous iron phosphate prepared in Examples 1-4 and the iron phosphate prepared in Comparative Examples 1-4 were tested respectively. The specific element data were obtained by ICP-AES testing. The test results are shown in Table 1.

[0109] Table 1: Physical and chemical index test results

[0110] As shown in Table 1, in the preparation methods of Examples 1-4, the Ni, Mn, and S contents are significantly lower than those of the materials before aging by adding aging liquid, wherein the Ni content is ≤115ppm, the Mn content is ≤98ppm, and the S content is ≤341ppm, which proves that the aging has achieved good results, and the specific surface area of ​​the prepared porous iron phosphate is 36.01-38.15m 2 / g; Ni and S in Comparative Examples 1, 2, and 3 are higher than those in Example 1, and BET is low, which proves that the reduction of the ion concentration in the aging liquid and the reduction of the aging temperature will significantly reduce the aging effect, among which the ion concentration in the aging liquid has a greater impact on the aging effect; the ion concentration in the aging liquid in Comparative Example 4 is too high. Although the Ni removal effect is more effective, due to the large number of pore structures during the aging process, the material is too loose, and the particle breakage phenomenon occurs, resulting in a small particle size and difficulty in filtration, and therefore it is not easy to adopt.

[0111] 2. Electrochemical Testing: Positive electrode materials were synthesized using the iron phosphate prepared in Examples 1-4 and Comparative Examples 1-4 as raw materials. After fabricating batteries from these cathode materials, the electrochemical performance of the batteries was tested. Specific data were obtained using equipment such as an electrochemical workstation. Initial discharge capacity and initial efficiency were tested at room temperature (25°C), a charge-discharge voltage of 2.0-3.65V, and an initial charge-discharge rate of 0.1C. Cyclic performance over 200 cycles and powder compaction performance were tested at room temperature (25°C), a charge-discharge voltage of 2.0-3.65V, and a charge-discharge rate of 1C. The test results are shown in Table 2.

[0112] Table 2. Battery electrochemical performance test results

[0113] As shown in Table 2, the compacted density of the lithium iron phosphate products prepared in Examples 1-3 is 2.49 g / cm 3And above, the first discharge specific capacity of the prepared battery can reach 158.30mAh / g and above, the first charge and discharge efficiency can reach 98.38% and above, and the capacity retention rate after 200 cycles of 1C can reach 96.38% and above. The electrochemical performance is significantly better than that of comparative examples 1-3, indicating that the porous iron phosphate obtained through the over-aging process has improved the powder characteristics and can improve the compaction density and discharge specific capacity of the synthesized lithium iron phosphate.

Claims

1. A method for preparing porous iron phosphate, Features: The following steps are involved: (1) After mixing the iron source, phosphorus source and oxidant solution, a pH adjuster is added to synthesize crude iron phosphate hydrate (2) mixing the crude iron phosphate hydrate prepared in step (1) with an aging liquid for aging, separating the solid from the liquid and then washing to obtain a solid; (3) Sintering the solid obtained in step (2) to obtain the porous iron phosphate.

2. A method for preparing porous iron phosphate according to claim 1, Features: In step (1), both the iron source and the phosphorus source contain impurities, and the impurities include at least one of Ni, Co, Mn, Cl and S.

3. The method for preparing porous iron phosphate according to claim 1, Features: In step (1), the iron source is at least one of ferrous sulfate, ferrous chloride and ferrous nitrate.

4. The method for preparing porous iron phosphate according to claim 1, Features: In step (1), the phosphorus source is phosphoric acid.

5. The method for preparing porous iron phosphate according to claim 1, Features: In step (1), the oxidant solution is hydrogen peroxide.

6. The method for preparing porous iron phosphate according to claim 1, Features: In step (1), the pH adjusting agent is aqueous ammonia.

7. A method for preparing porous iron phosphate according to claim 6, Features: In step (1), after adjustment by the pH adjusting agent, the pH of the reaction system is 1.5-2.

5.

8. The method for preparing porous iron phosphate according to claim 1, Features: In step (1), the crude ferric phosphate hydrate is crude ferric phosphate dihydrate.

9. A method for preparing porous iron phosphate according to claim 8, Features: In step (1), the particle size of the crude ferric phosphate dihydrate is 1-20 μm.

10. The method for preparing porous iron phosphate according to claim 1, Features: In step (2), the aging liquid is obtained by mixing compound A, compound B and water, wherein compound A is at least one of phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid and sodium fluoride, and compound B is at least one of ferrous sulfate and ferrous chloride.

11. A method for preparing porous iron phosphate according to claim 10, Features: The concentration of the anions in the compound A in the aging solution is 0.1-2 mol / L, and the concentration of the cations in the compound B in the aging solution is 0.03-1 mol / L.

12. The method for preparing porous iron phosphate according to claim 1, Features: In step (2), the aging temperature is 60-150° C., and the aging time is 5-35 hours.

13. The method for preparing porous iron phosphate according to claim 1, Features: In step (2), the solid-liquid ratio of the crude ferric phosphate hydrate and the aging liquid is 5-40 g:100 mL.

14. The method for preparing porous iron phosphate according to claim 1, Features: In step (3), the sintering temperature is 400-1200° C., and the sintering time is 1-8 hours.

15. A porous iron phosphate, Features: The invention is prepared by the preparation method according to any one of claims 1 to 14.

16. The porous iron phosphate according to claim 15, Features: The specific surface area of ​​the porous iron phosphate is 35-40m 2 / g.

17. The porous iron phosphate according to claim 15, Features: The content of Ni in the porous iron phosphate is ≤150ppm, the content of Mn is ≤100ppm, and the content of S is ≤350ppm.

18. A positive electrode material, Features: The porous iron phosphate comprises the porous iron phosphate according to any one of claims 15 to 17.

19. A battery, Features: Comprising the positive electrode material as claimed in claim 18.

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