A porous iron phosphate, its preparation method and application

Abstract

This disclosure pertains to the field of battery materials technology, and specifically relates to a porous iron phosphate, its preparation method, and its application. The preparation method includes the following steps: (1) mixing an iron source, a phosphorus source, and an oxidant solution, and then adding a pH adjuster to synthesize crude iron phosphate hydrate; (2) mixing the crude iron phosphate hydrate obtained in step (1) with an aging solution for aging, separating the solid and liquid, and washing to obtain a solid; (3) sintering the solid obtained in step (2) to obtain the porous iron phosphate. This preparation method can effectively remove impurity elements, and the prepared porous iron phosphate has a high compaction density, which can effectively improve the battery's endurance.

Description

TECHNICAL FIELD

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

[0002] Lithium ion batteries are one of the most common rechargeable batteries at present, and have been widely applied in fields such as electric vehicles, portable electronic devices, energy storage systems, etc. In lithium ion batteries, the performance of the positive electrode material has a crucial influence on the performance and stability of the battery. Lithium iron phosphate, as a common positive electrode material of lithium ion batteries, is favored due to its relatively high cycle life and good thermal stability.

[0003] However, in the synthesis process of iron phosphate, due to the difference in the source of raw materials, some impurity elements that are not expected to be introduced, such as nickel (Ni), cobalt (Co), manganese (Mn) and sulfur (S), etc. are often entrained. These impurity elements can reduce the performance of the positive electrode material and limit the overall performance of the battery. The compaction density of the LiFePO4 material is relatively low, which in turn leads to a relatively low energy density, limiting the endurance of the battery, especially for high energy density demanding applications such as electric vehicles. SUMMARY

[0004] The present disclosure aims to at least solve one of the technical problems existing in the related art. To this end, the present disclosure proposes a porous iron phosphate and a preparation method and application thereof, which can effectively remove impurity elements, and the porous iron phosphate prepared thereby has a high compaction density, which can effectively improve the endurance of the battery.

[0005] The above technical purpose of the present disclosure is achieved by the following technical solution:

[0006] A preparation method of a porous iron phosphate, comprising the following steps: (1) mixing an iron source, a phosphorus source and an oxidizing agent solution, then adding a pH adjusting agent to synthesize a crude iron phosphate hydrate; (2) mixing the crude iron phosphate hydrate prepared in step (1) with an aging liquid for aging, and after solid-liquid separation, washing to obtain a solid material; (3) sintering the solid material obtained in step (2) to obtain the porous iron phosphate.

[0007] In an embodiment, in step (1), the iron source and the phosphorus source both contain impurities, and the impurities include at least one of Ni, Co, Mn, Cl and S.

[0008] In an embodiment, in step (1), the iron source is at least one of ferrous sulfate, ferrous chloride and ferrous nitrate.

[0009] In an embodiment, in step (1), the phosphorus source is phosphoric acid.

[0010] In one embodiment, in step (1), the oxidizing agent solution is hydrogen peroxide.

[0011] In one embodiment, in step (1), the pH adjusting agent is ammonia.

[0012] In one embodiment, in step (1), after adjusting by the pH adjusting agent, the pH of the reaction system is 1.5-2.5.

[0013] In one embodiment, in step (1), after adjusting by the pH adjusting agent, the pH of the reaction system is 1.8-2.0.

[0014] In one embodiment, in step (1), the crude iron phosphate hydrate is crude iron phosphate dihydrate.

[0015] In one embodiment, in step (1), the crude iron phosphate dihydrate is synthesized by one of the following processes: ammonia method, sodium method, and iron powder method.

[0016] In one embodiment, in step (1), the particle size of the crude iron phosphate dihydrate is 1-20 μm.

[0017] In one embodiment, in step (1), the particle size of the crude iron phosphate dihydrate is 2-15 μm.

[0018] In one embodiment, in step (2), the aging solution is obtained by mixing compound A and compound B with water, wherein 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.

[0019] In one embodiment, the concentration of anions in the compound A in the aging solution is 0.1-2 mol / L, and the concentration of cations in the compound B in the aging solution is 0.03-1 mol / L.

[0020] In one embodiment, the concentration of anions in the compound A in the aging solution is 0.1-1 mol / L, and the concentration of cations in the compound B in the aging solution is 0.05-0.5 mol / L.

[0021] In one embodiment, in step (2), the temperature of aging is 60-150 °C, and the time of aging is 5-35 h.

[0022] In one embodiment, in step (2), the temperature of aging is 80-100 °C, and the time of aging is 10-30 h.

[0023] In one embodiment, in step (2), the solid-liquid ratio of the crude iron phosphate hydrate to the aging solution is 5-40 g: 100 mL.

[0024] In one embodiment, in step (2), the solid-liquid ratio of the mixing of the crude iron phosphate hydrate and the aging solution is 10-30 g: 100 mL.

[0025] In one embodiment, in step (3), the sintering temperature is 400-1200°C, and the sintering time is 1-8 h.

[0026] In one embodiment, in step (3), the sintering temperature is 500-1000°C, and the sintering time is 1-5 h.

[0027] Since impurities are easily encapsulated during the synthesis of crude iron phosphate dihydrate, in order to avoid the ions in the aging solution being encapsulated into the interior of the iron phosphate dihydrate particles, the aging process is placed after the aging process. Since the crystal form of the iron phosphate dihydrate is already relatively complete when the aging begins, impurities will not be encapsulated again, and thus the impurity ions in the product can be replaced by the ions in the aging solution during the aging process.

[0028] Impurity ion introduction principle: ①Cation radius Fe 3+ (64pm)<Mn 2+ (66pm)<Co 2+ (74ppm)≈Ni 2+ (74pm)<Fe 2+ (76pm), since Fe in iron phosphate is trivalent, Ni 2+ , Mn 2+ are more difficult to enter the iron phosphate crystal lattice than Co 2+ , and since the pH during the synthesis of iron phosphate is generally controlled at about 1.5-2.0, the cation precipitation pH has not been reached, thus the impurities in the product are mainly encapsulated and the total amount of cation impurities introduced is limited; ②Anion group SO4 2- (230pm)<PO4 3- (238pm), SO4 2- is relatively easier to enter the iron phosphate crystal lattice, and the proportion of anion impurities introduced is relatively high.

[0029] Taking the Ni 2+ , SO4 2- introduction process as an example, the theoretical reaction that may occur during the Ni 2+ , SO4 2- introduction process is:

[0030] Ni 2+ + SO4 2- → NiSO4 (slightly soluble in acid), 3Ni 2+ + 2PO4 3- → Ni3(PO4)2 (soluble in acid)

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

[0032] (soluble in acid).

[0033] Example of isomorphous substitution process after introduction of Ni 2+ , SO4 2- , Ni 2+ has close ionic radius with Fe 2+ , there is possibility of substitution of introduced Ni 2+ by Fe 2+ in product, SO4 2- has close ionic radius with PO4 3- , there is possibility of substitution of introduced SO4 2- by PO4 3- in product, stability PO4 3- > SO4 2- . Example of cation and anion groups introduced in aging solution as Fe 2+ , PO4 3- , substitution process principle is as follows:

[0034] NiSO4+ Fe 2+ → FeSO4+ Ni 2+ , Ni3(PO4)2+ Fe 2+ → Fe3(PO4)2+ Ni 2+ , NiHPO4+ Fe 2+ →

[0035] 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, Fe3(PO4)2 cannot exist stably in strong acid solution, there is dissolution process of generated Fe3(PO4)2 in aging process.

[0036] The role of the aging process is to partially dissociate the impurity ions from the crystal lattice. Small particles of iron phosphate are more easily dissolved than large particles. The dissolution and precipitation processes occur simultaneously. Although the growth units in the solution do not change, the reaction always tends to proceed in the direction of low energy. After aging for a period of time, the precipitate will rearrange according to the inherent crystal lattice orientation, which is conducive to the formation of complete crystal shapes and the occurrence of isomorphous substitution.

[0037] A porous iron phosphate prepared by the preparation method described above.

[0038] In an embodiment, the specific surface area of the porous iron phosphate is 35-40 m 2 / g.

[0039] In an embodiment, the specific surface area of the porous iron phosphate is 36.01-38.15 m 2 / g.

[0040] In an embodiment, the content of Ni in the porous iron phosphate is ≤150 ppm, the content of Mn is ≤100 ppm, and the content of S is ≤350 ppm.

[0041] In an embodiment, the content of Ni in the porous iron phosphate is ≤115 ppm, the content of Mn is ≤98 ppm, and the content of S is ≤341 ppm.

[0042] A positive electrode material comprising the porous iron phosphate described above.

[0043] A battery comprising the positive electrode material described above.

[0044] The beneficial effects of the present disclosure are:

[0045] (1) In the preparation method of the porous iron phosphate of the present disclosure, the aging process successfully removes impurity elements such as nickel, cobalt, manganese, and sulfur in the iron phosphate, thereby improving the purity of the prepared porous iron phosphate;

[0046] (2) In the preparation method of the porous iron phosphate of the present disclosure, more than 50% of the impurities can be removed through the aging process. Therefore, the sources of raw materials containing impurities in the synthesis process of the porous iron phosphate are greatly increased, the acceptable range of impurities is increased, and the production cost is reduced;

[0047] (3) The porous iron phosphate prepared by the preparation method of the present disclosure has a large specific surface area, which helps to improve the performance of the battery;

[0048] (4) The preparation method of the present disclosure removes impurity elements in the raw materials and increases the specific surface area of the product. Therefore, the charge and discharge capacity and the compaction performance of the positive electrode material prepared using the porous iron phosphate of the present disclosure are significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0049] Figure 1 Cross-sectional SEM image of the crude ferrous phosphate dihydrate obtained in the preparation process of Example 1 after aging for 5h;

[0050] Figure 2 Cross-sectional SEM image of the crude ferrous phosphate dihydrate obtained in the preparation process of Example 1 after aging for 10h;

[0051] Figure 3 Cross-sectional SEM image of the crude ferrous phosphate dihydrate obtained in the preparation process of Example 1 after aging for 20h;

[0052] Figure 4 Cross-sectional SEM image of the crude ferrous phosphate dihydrate obtained in the preparation process of Example 2 after aging for 10h;

[0053] Figure 5 Cross-sectional SEM image of the crude ferrous phosphate dihydrate obtained in the preparation process of Comparative Example 1 after aging for 20h;

[0054] Figure 6 Cross-sectional SEM image of the crude ferrous phosphate dihydrate obtained in the preparation process of Comparative Example 2 after aging for 20h. DETAILED DESCRIPTION

[0055] The present disclosure will be further described below in conjunction with specific examples.

[0056] Example 1:

[0057] A preparation method of porous ferrous phosphate, comprising the following specific steps:

[0058] (1) Synthesis: after mixing ferrous sulfate containing Ni impurities, phosphoric acid and hydrogen peroxide, ammonia is used to adjust the pH to 1.8, to synthesize crude ferrous phosphate dihydrate, filter and wash to obtain filter cake, and after drying the filter cake, test the filter cake, and measure the content of Ni and S in the filter cake as 413ppm and 1105ppm respectively;

[0059] (2) Liquid preparation: 139g of ferrous sulfate, 230g of phosphoric acid and water are mixed to prepare a 10L aging liquid, wherein the molar concentrations of Fe 2+ and PO4 3- in the aging liquid are 0.05mol / L and 0.2mol / L respectively;

[0060] (3) Aging: 2000g of crude ferrous phosphate dihydrate synthesized in step (1) is put into 10L of aging liquid with a temperature of 90℃ for aging for 20h, solid-liquid separation, 100℃ washing and drying;

[0061] (4) Sintering: after drying, the powder is sintered at a high temperature of 600℃ for 3h, to obtain porous ferrous phosphate by dehydration and desulfurization.

[0062] Figure 1 、 Figure 2 and Figure 3 are cross-sectional SEM images of the crude dihydrate iron phosphate aged for 5h, 10h and 20h respectively in Example 1. From the cross-sectional morphology, it can be seen that the internal pores and micro-cracks increase with the extension of the aging time. The increase of pores proves that the dissolution and substitution phenomenon occurs, which is also beneficial to the desulfurization of the material during sintering.

[0063] Example 2:

[0064] A method for preparing porous iron phosphate, comprising the following specific steps:

[0065] (1) Synthesis: After mixing ferrous sulfate containing Ni impurities, phosphoric acid and hydrogen peroxide, the pH is adjusted to 1.8 by using ammonia water to synthesize crude dihydrate iron phosphate. The filter cake is obtained by filtering and washing. After drying the filter cake, the content of Ni and S in the filter cake is measured to be 441ppm and 1048ppm respectively;

[0066] (2) Liquid preparation: 695g of ferrous sulfate, 1152g of phosphoric acid and water are mixed to prepare a 10L aging liquid, wherein the molar concentrations of Fe 2+ and PO4 3- in the aging liquid are 0.25mol / L and 1mol / L respectively;

[0067] (3) Aging: 2000g of crude dihydrate iron phosphate synthesized in step (1) is put into 10L aging liquid with a temperature of 90℃ for 10h. Solid-liquid separation is carried out, and the filter cake is washed and dried at 100℃;

[0068] (4) Sintering: After drying, the powder is sintered at a high temperature of 600℃ for 3h to obtain porous iron phosphate by dehydration and desulfurization.

[0069] Figure 4 is a cross-sectional SEM image of the crude dihydrate iron phosphate aged for 10h in Example 2. From the cross-sectional morphology, it can be seen that under the condition of high concentration of phosphoric acid and ferrous ion, the internal pores and micro-cracks of the particles increase sharply after aging, and there are more fine particles around the particles, which proves that the effect of substitution during aging is more obvious.

[0070] Example 3:

[0071] A method for preparing porous iron phosphate, comprising the following specific steps:

[0072] (1) Synthesis: After mixing ferrous sulfate containing Mn impurities, phosphoric acid and hydrogen peroxide, the pH is adjusted to 2.0 by using sodium hydroxide solution to synthesize crude dihydrate iron phosphate. The filter cake is obtained by filtering and washing. After drying the filter cake, the content of Mn and S is measured to be 348ppm and 1103ppm respectively;

[0073] (2) Liquid preparation: 139 g of ferrous sulfate, 1152 g of phosphoric acid and water are mixed to prepare 10 L of aging liquid, wherein the molar concentrations of Fe 2+ , PO4 3- in the aging liquid are 0.05 mol / L and 1 mol / L, respectively;

[0074] (3) Aging: 3000 g of the crude dihydrate iron phosphate synthesized in step (1) is put into 10 L of the aging liquid with a temperature of 90℃ for aging for 10 h, solid-liquid separation, washing at 100℃ and drying;

[0075] (4) Sintering: after drying, the powder is sintered at a high temperature of 600℃ for 3 h to obtain porous iron phosphate by dehydration and desulfurization.

[0076] Example 4:

[0077] A method for preparing porous iron phosphate, comprising the following specific steps:

[0078] (1) Synthesis: ferrous sulfate containing Mn impurities, phosphoric acid and hydrogen peroxide are mixed, then sodium hydroxide solution is used to adjust the pH to 2.0 to synthesize crude dihydrate iron phosphate, and the filter cake is obtained by filtration and washing, and the contents of Mn and S in the filter cake after drying are 391 ppm and 995 ppm, respectively;

[0079] (2) Liquid preparation: 279 g of ferrous sulfate, 1152 g of phosphoric acid and water are mixed to prepare 10 L of aging liquid, wherein the molar concentrations of Fe 2+ , PO4 3- in the aging liquid are 0.05 mol / L and 1 mol / L, respectively;

[0080] (3) Aging: 3000 g of the crude dihydrate iron phosphate synthesized in step (1) is put into 10 L of the aging liquid with a temperature of 90℃ for aging for 20 h, solid-liquid separation, washing at 100℃ and drying;

[0081] (4) Sintering: after drying, the powder is sintered at a high temperature of 600℃ for 3 h to obtain porous iron phosphate by dehydration and desulfurization.

[0082] Comparative Example 1:

[0083] This comparative example provides a method for preparing iron phosphate, and the main difference between the preparation method and Example 1 is that the concentration of Fe 2+ in the aging liquid is different:

[0084] (1) Synthesis: ferrous sulfate containing Ni impurities, phosphoric acid and hydrogen peroxide are mixed, then ammonia is used to adjust the pH to 1.8 to synthesize crude dihydrate iron phosphate, and the filter cake is obtained by filtration and washing, and the contents of Ni and S in the filter cake after drying are 422 ppm and 1171 ppm, respectively;

[0085] (2) Solution preparation: Mix 28g of ferrous sulfate and 230g of phosphoric acid with water to prepare 10L of aging solution, wherein the aging solution contains Fe 2+ PO4 3- The molar concentrations were 0.01 mol / L and 0.2 mol / L, respectively;

[0086] (3) Aging: 2000g of crude ferric phosphate dihydrate synthesized in step (1) is added to 10L of aging liquid at 90℃ and aged for 20h. Solid-liquid separation is performed, followed by washing and drying at 100℃.

[0087] (4) Sintering: After drying, the powder is sintered at 600℃ for 3 hours to obtain iron phosphate by dehydration and desulfurization.

[0088] Figure 5 The image shows a cross-sectional SEM image of the crude iron phosphate dihydrate obtained during the preparation 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 to Example 1. A porous structure is formed on the outer layer of the spherical structure, and there are fewer pores inside the particles. This preliminarily proves that isomorphic substitution was not completed inside, mainly due to the poor aging effect.

[0089] Comparative Example 2:

[0090] This comparative example provides a method for preparing ferric phosphate. The main difference between this method and Example 1 is that it uses pure water for purification.

[0091] (1) Synthesis: Ferrous sulfate containing Ni impurities, phosphoric acid, and hydrogen peroxide were mixed and the pH was adjusted to 1.8 with ammonia water to synthesize crude ferric phosphate dihydrate. After filtration and washing, filter cake was obtained. After drying the filter cake, the contents of Ni and S in the filter cake were measured to be 435 ppm and 1058 ppm, respectively.

[0092] (2) Solution preparation: Take 10L of pure water as the aging solution, in which Fe 2+ PO4 3- The molar concentration is 0 mol / L;

[0093] (3) Aging: 2000g of crude ferric phosphate dihydrate synthesized in step (1) is added to 10L of aging liquid at 90℃ and aged for 20h. Solid-liquid separation is performed, followed by washing and drying at 100℃.

[0094] (4) Sintering: After drying, the powder is sintered at 600℃ for 3 hours to obtain iron phosphate by dehydration and desulfurization.

[0095] Figure 6The image shows a cross-sectional SEM image of the crude iron dihydrate obtained during the preparation 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 significant compared to Comparative Example 1. The pore structure on the outer layer of the spherical structure is thinner. Compared to Comparative Example 2, there is less isomorphic substitution phenomenon inside the particles, and the aging effect is worse.

[0096] Comparative Example 3:

[0097] This comparative example provides a method for preparing ferric phosphate. The main difference between this method and Example 1 lies in the aging temperature:

[0098] (1) Synthesis: Ferrous sulfate containing Ni impurities, phosphoric acid, and hydrogen peroxide were mixed and the pH was adjusted to 1.8 with ammonia water to synthesize crude ferric phosphate dihydrate. After filtration and washing, filter cake was obtained. After drying the filter cake, the contents of Ni and S in the filter cake were measured to be 405 ppm and 1058 ppm, respectively.

[0099] (2) Solution preparation: Mix 139g of ferrous sulfate and 230g of phosphoric acid with water to prepare 10L of aging solution, wherein the aging solution contains Fe 2+ PO4 3- The molar concentrations were 0.05 mol / L and 0.2 mol / L, respectively;

[0100] (3) Aging: 2000g of crude ferric phosphate dihydrate synthesized in step (1) is added to 10L of aging liquid at 50℃ and aged for 20h. Solid-liquid separation is performed, followed by washing and drying at 100℃.

[0101] (4) Sintering: After drying, the powder is sintered at 600℃ for 3 hours to obtain iron phosphate by dehydration and desulfurization.

[0102] Comparative Example 4:

[0103] This comparative example provides a method for preparing iron phosphate. The main difference between this method and Example 1 lies in the amount of Fe in the aging solution. 2+ PO4 3- Different concentrations:

[0104] (1) Synthesis: Ferrous sulfate containing Ni impurities, phosphoric acid, and hydrogen peroxide were mixed and the pH was adjusted to 1.8 with ammonia water to synthesize crude ferric phosphate dihydrate. After filtration and washing, filter cake was obtained. After drying the filter cake, the contents of Ni and S in the filter cake were measured to be 401 ppm and 1093 ppm, respectively.

[0105] (2) Solution preparation: Mix 1529g of ferrous sulfate and 1268g of phosphoric acid with water to prepare 10L of aging solution, wherein the Fe in the aging solution is... 2+ PO4 3- The molar concentrations were 0.55 mol / L and 1.1 mol / L, respectively;

[0106] (3) Aging: 2000g of crude ferric phosphate dihydrate synthesized in step (1) is added to 10L of aging liquid at 90℃ and aged for 20h. Solid-liquid separation is performed, followed by washing and drying at 100℃.

[0107] (4) Sintering: After drying, the powder is sintered at 600℃ for 3 hours to obtain iron phosphate by dehydration and desulfurization.

[0108] Because the concentration of anions and cations in the aging solution is high, the displacement effect is more obvious. During aging, the particles are easily too loose and severely broken, making filtration difficult. This can lead to drawbacks in industrial application and is therefore not easy to use.

[0109] Experimental example:

[0110] 1. The physicochemical properties 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 elemental data were obtained by ICP-AES equipment. The test results are shown in Table 1.

[0111] Table 1: Test Results of Physicochemical Indicators

[0112]

[0113]

[0114] As shown in Table 1, in the preparation methods of Examples 1-4, the addition of aging solution resulted in significantly lower levels of Ni, Mn, and S compared to the raw materials before aging. Specifically, the Ni content was ≤115 ppm, the Mn content ≤98 ppm, and the S content ≤341 ppm, demonstrating the effective aging process. Furthermore, the specific surface area of ​​the prepared porous iron phosphate was between 36.01 and 38.15 m². 2 / g; In Comparative Examples 1, 2, and 3, Ni and S were all higher than in Example 1, and BET was lower, proving that a decrease in ion concentration in the aging solution and a decrease in aging temperature would significantly reduce the aging effect. Among them, the ion concentration in the aging solution had a greater impact on the aging effect. In Comparative Example 4, the ion concentration in the aging solution was too high. Although the Ni removal effect was more effective, the material was too loose due to the large number of pores during the aging process, resulting in particle breakage and small particle size, making filtration difficult and therefore not suitable for use.

[0115] 2. Electrochemical Testing: Iron phosphate prepared in Examples 1-4 and Comparative Examples 1-4 were used as raw materials to synthesize cathode materials. After the cathode materials were fabricated into batteries, the electrochemical performance of the batteries was tested. Specific data were obtained using equipment such as an electrochemical workstation. The initial discharge capacity and initial efficiency were tested at room temperature (25°C) with a charge / discharge voltage of 2.0-3.65V and an initial charge / discharge rate of 0.1C. The cycle performance and powder compaction performance for 200 cycles were tested at room temperature (25°C) with a charge / discharge voltage of 2.0-3.65V and a charge / discharge rate of 1C. The test results are shown in Table 2.

[0116] Table 2. Battery electrochemical performance test results

[0117]

[0118]

[0119] As shown in Table 2, the compacted density of the lithium iron phosphate products prepared in Examples 1-3 is 2.49 g / cm³. 3 The prepared batteries exhibit an initial discharge specific capacity of 158.30 mAh / g or higher, an initial charge-discharge efficiency of 98.38% or higher, and a capacity retention rate of 96.38% or higher after 200 cycles at 1C. 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 improves the powder characteristics and can increase the compaction density and discharge specific capacity of the synthesized lithium iron phosphate.

Claims

1. A method for preparing porous iron phosphate, characterized by: The method comprises the following steps: (1) mixing an iron source, a phosphorus source and an oxidizing agent solution, adding a pH regulator to synthesize a crude iron phosphate hydrate; (2) mixing the crude iron phosphate hydrate prepared in step (1) with an aging liquid to age, washing after solid-liquid separation to obtain a solid; (3) sintering the solid obtained in step (2) to obtain the porous iron phosphate; 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, the compound B is at least one of ferrous sulfate and ferrous chloride, the concentration of anions in the compound A in the aging liquid is 0.1-2 mol / L, the concentration of cations in the compound B in the aging liquid is 0.03-1 mol / L, the aging temperature is 60-150℃, the aging time is 5-35 h, and the solid-liquid ratio of the mixing of the crude iron phosphate hydrate and the aging liquid is 5-40 g:100 mL.

2. The method of claim 1, wherein: In step (1), the iron source and the phosphorus source both contain impurities, and the impurities include at least one of Ni, Co, Mn, Cl and S.

3. The method of claim 1, wherein: In step (1), the iron source is at least one of ferrous sulfate, ferrous chloride and ferrous nitrate.

4. The method of claim 1, wherein: In step (1), the phosphorus source is phosphoric acid.

5. The method of claim 1, wherein: In step (1), the oxidizing agent solution is hydrogen peroxide.

6. The method of claim 1, wherein: In step (1), the pH regulator is ammonia water.

7. The method of claim 6, wherein: In step (1), after the adjustment by the pH regulator, the pH of the reaction system is 1.5-2.

5.

8. The method of claim 1, wherein: In step (1), the crude iron phosphate hydrate is crude iron phosphate dihydrate.

9. The method of claim 8, wherein: In step (1), the particle size of the crude iron phosphate dihydrate is 1-20 μm.

10. The method of claim 1, wherein: In step (3), the sintering temperature is 400-1200℃, and the sintering time is 1-8 h.

11. A porous iron phosphate characterized in that: Prepared by the preparation method in any one of claims 1-10.

12. The porous iron phosphate of claim 11, wherein: The specific surface area of the porous iron phosphate is 35-40 m 2 / g.

13. The porous iron phosphate of claim 11, wherein: The content of Ni in the porous iron phosphate is ≤150 ppm, the content of Mn is ≤100 ppm, and the content of S is ≤350 ppm.

14. A positive electrode material, characterized by: The porous iron phosphate in any one of claims 11-13.

15. A battery, characterized by: The positive electrode material in claim 14.

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