Method for preparing nanospheric iron phosphate by using ferroferric oxide and application thereof

Abstract

The application discloses a method for preparing nanospheric iron phosphate by using ferroferric oxide, and comprises the following steps: S1, mixing an iron source with a morphology control agent, adding deionized water for mixing and dispersion stirring; S2, simultaneously adding concentrated phosphoric acid and an oxidizing agent drop by drop, reacting for 0.5-1 hours, then heating, and continuously reacting to obtain white precipitate; S3, centrifuging, filtering, washing, low-temperature drying and high-temperature sintering the white precipitate to obtain nanospheric iron phosphate. The prepared iron phosphate nanoparticles are uniform, present nanospheric, have high tap density, are easy to flow, and have good dispersibility. The formed iron phosphate particles are uniform, spherical, easy to filter and wash, beneficial to subsequent solid-liquid separation, have reduced material moisture content, have narrow particle size distribution range, uniform morphology and particle size, large tap density, and can obviously improve the electrochemical performance of lithium iron phosphate when used for synthesizing lithium iron phosphate materials, and the 0.2C discharge specific capacity is above 160mA·h / g.

Description

Technical Field

[0001] This invention relates to a method for preparing nanospheres of iron phosphate using iron oxide and its application, specifically relating to the field of batteries. Background Technology

[0002] With the development of new energy technology, the application scenarios of lithium batteries are becoming increasingly widespread, and the usage of iron phosphate, the raw material for lithium iron phosphate, has also increased significantly. The traditional method for synthesizing iron phosphate involves reacting divalent / trivalent iron salts with phosphoric acid, followed by pH adjustment with an alkali. However, this process introduces new ions, reducing the purity of the iron phosphate. Furthermore, using iron oxide to prepare iron phosphate can generate magnetic impurities, affecting the safety and reliability of the iron phosphate when used as a cathode material in lithium iron phosphate batteries, and shortening battery life. Additionally, iron phosphate prepared by traditional precipitation methods has a loose structure, inconsistent morphology, and low tap density, resulting in poor electrochemical performance of the prepared lithium iron phosphate. It is also difficult to wash during the preparation process, as the material is viscous, has a high water content, and requires a large amount of deionized water for washing, leading to resource waste and high costs.

[0003] Chinese invention patent CN201910764380.9 discloses a method for preparing nano-sheet iron phosphate, which involves slowly adding iron(III) oxide to phosphoric acid of a certain concentration and heating the mixture to obtain iron phosphate precipitate. This method uses air as an oxidant, and ferrous ions are not completely oxidized to ferric ions under acidic conditions. The resulting material contains a large amount of ferrous ions, the iron(III) oxide reaction is incomplete, the iron-phosphorus ratio is not fixed, and there are many residual magnetic impurities after the reaction. Chinese invention patent CN201510020050.0 discloses a method for preparing spherical nano-iron phosphate, which uses ammonia to adjust the pH to prepare nano-spherical iron phosphate with high tap density and uniform particle size distribution. However, the introduction of ammonia ions reduces the purity of the iron phosphate. Chinese invention patent CN201410744374.4 discloses a method for preparing nano-iron phosphate from lithium iron phosphate using ultrasound, using soluble ferrous salts as raw materials. The prepared nano-iron phosphate has high purity, but the preparation cost is high. Summary of the Invention

[0004] To improve the purity and optimize the sphericity of the prepared iron phosphate, making it more suitable for use in lithium iron phosphate batteries, the first aspect of this invention provides a method for preparing nano-spherical iron phosphate using iron(III) oxide, comprising the following steps:

[0005] S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring.

[0006] S2 is simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction is allowed to proceed for 0.5-1 h. Then the temperature is increased and the reaction continues, resulting in a white precipitate.

[0007] S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstensibly at high temperature to obtain nanospheres of iron phosphate.

[0008] In a preferred embodiment, the weight ratio of the iron source to the morphology control agent is 1:(0.01-0.15).

[0009] In a preferred embodiment, the weight ratio of the iron source to the morphology control agent is 1:(0.05-0.09).

[0010] In a preferred embodiment, the weight ratio of the iron source to the morphology control agent is 1:0.07.

[0011] In a preferred embodiment, the iron source is iron(III) oxide, which is crushed and passed through a 150-160 mesh sieve before use.

[0012] In a preferred embodiment, the morphology control agent is selected from one or a combination of several of sodium dodecylbenzenesulfonate, sodium hexadecylbenzenesulfonate, sodium dodecylbenzenesulfonate, and sodium dodecyl diphenyl ether disulfonate.

[0013] In a preferred embodiment, the morphology control agent is sodium dodecylbenzenesulfonate.

[0014] During the experiment, the applicant discovered that using iron(III) oxide (Fe3O4) as the iron source and sodium dodecylbenzenesulfonate as the morphology control agent resulted in uniform, spherical iron phosphate nanoparticles with high tap density, good flowability, and good dispersibility. The applicant speculates that this is likely because sodium dodecylbenzenesulfonate, with its low surface tension and high intermolecular resistance, increases the dispersibility of iron phosphate and prevents the early precipitation and aggregation of iron phosphate crystals, thus avoiding the formation of iron phosphate precipitates with inconsistent morphologies. In particular, when the mass ratio of iron(III) oxide to sodium dodecylbenzenesulfonate is 1:(0.05-0.09), sodium dodecylbenzenesulfonate can control the formation of spherical iron phosphate crystals, resulting in uniform iron phosphate particles with high tap density, good flowability, and good dispersibility.

[0015] In a preferred embodiment, in step S1, the amount of deionized water added is 5-8 times the mass of the iron source, the stirring speed is 300-460 r / min, and the stirring time is 0.5-1 h.

[0016] During the experiment, the applicant discovered that ferric phosphate precipitates prepared using traditional precipitation methods have loose structures, inconsistent morphologies, and are viscous, making them inconvenient to use. This application addresses this by controlling the amount of deionized water used, which allows ferric phosphate crystals to remain suspended in the system initially, preventing premature precipitation and the formation of particles of varying sizes. Furthermore, the applicant incorporates a stirring speed of 300-460 r / min and a stirring time of 0.5-1 h during the reaction process to control the suspension time of the ferric phosphate, resulting in uniformly sized and stable particles. Under stirred flow, nano-spherical ferric phosphate is formed. These spherical nano-ferric phosphate particles are less prone to aggregation and adhesion, exhibiting high dispersibility. This reduces the viscosity of the material during subsequent use, facilitating filtration and washing, lowering the moisture content, and improving the convenience of subsequent use.

[0017] In a preferred embodiment, the concentrated phosphoric acid has a mass fraction of 85%-90% and is in water as the solvent, while the oxidant has a mass fraction of 20-40% and is in water as the solvent.

[0018] In a preferred embodiment, the amount of concentrated phosphoric acid used is 2.5-3.6 times the mass of the iron source, and the amount of oxidant used is 0.45-0.55 times the mass of the iron source.

[0019] In a preferred embodiment, the oxidant is hydrogen peroxide.

[0020] During the experiment, the applicant discovered that traditional methods for preparing iron phosphate using ferric oxide (Fe3O4) lead to incomplete oxidation of the ferric oxide, resulting in a large amount of ferrous iron impurities. This results in low purity of the iron phosphate and an unstable iron-to-phosphorus ratio in the product. This application uses ferric oxide as the iron source, reducing the cost of directly using ferrous iron. Furthermore, the simultaneous addition of concentrated phosphoric acid and hydrogen peroxide enhances the oxidation activity of the system, ensuring complete dissolution of the ferric oxide, controlling the generation of magnetic impurities, and ensuring a complete reaction of the ferric oxide, thus avoiding the generation of ferrous iron impurities. The resulting iron phosphate has high purity and a stable iron-to-phosphorus ratio, exhibiting excellent electrochemical performance in the subsequent manufacture of lithium iron phosphate.

[0021] In a preferred embodiment, the addition time of concentrated phosphoric acid and oxidant in step S2 is 0.5-1 h, the heating temperature is 85-100 °C, and the reaction time after heating is 2-3 h.

[0022] During the experiment, the applicant discovered that adding concentrated phosphoric acid and hydrogen peroxide dropwise to the system over a 0.5-hour dropping time allowed for complete dissolution of ferric oxide (Fe3O4). The ferric ions then combined with phosphate ions to form ferric phosphate. However, excessively rapid dropping led to an overly fast oxidation rate, causing the ferric ions to react with hydroxide ions to form ferric hydroxide, thus reducing the purity of the ferric phosphate. Conversely, excessively slow dropping resulted in insufficient oxidation of ferric oxide, forming ferrous ions and further decreasing purity. The applicant further discovered that increasing the temperature and continuing the reaction shifted the reaction to the right, improving the conversion rate of ferric phosphate.

[0023] In a preferred embodiment, the low-temperature drying temperature in step S3 is 100-150℃, the drying time is 5-8h, the high-temperature sintering temperature is 700-850℃, and the sintering time is 6-9h.

[0024] In a preferred embodiment, the phosphoric acid wastewater after washing the materials in step S3 can be recycled after distillation and concentration.

[0025] A second aspect of the present invention provides an application of a method for preparing nanospheres of iron phosphate using iron tetroxide, wherein the prepared nanospheres of iron phosphate are used to synthesize lithium iron phosphate materials.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The method for preparing nanosphere iron phosphate using iron oxide described in this invention uses iron oxide as the iron source and sodium dodecylbenzenesulfonate as the morphology control agent. The mass ratio of iron oxide and sodium dodecylbenzenesulfonate is 1:(0.05-0.09). The prepared iron phosphate nanoparticles are uniform, exhibit nanospheres, have high tap density, are easy to flow, and have good dispersibility.

[0028] (2) The method for preparing nano-spherical iron phosphate using iron oxide described in this invention involves crushing iron oxide and passing it through a 150-mesh sieve, then adding 5-8 times the mass of deionized water to form uniform iron phosphate particles that are spherical, easy to filter and wash, and facilitates solid-liquid separation during subsequent use, thereby reducing the moisture content of the material.

[0029] (3) The method for preparing nanosphere iron phosphate using iron oxide described in this invention involves adding concentrated phosphoric acid with a mass fraction of 85% and hydrogen peroxide with a mass fraction of 30%. The resulting iron phosphate has high purity, few magnetic impurities (controlled to within 1 ppm), few ferrous impurities, sufficient iron oxide reaction, and a stable iron-to-phosphorus ratio.

[0030] (4) The method for preparing nanosphere iron phosphate using iron oxide described in this invention has a dropwise addition time of concentrated phosphoric acid and oxidant of 0.5 h and a reaction time of 1 h. The resulting iron phosphate has high purity and high conversion rate.

[0031] (5) The method for preparing nanosphere iron phosphate using iron oxide described in this invention produces iron phosphate with a narrow particle size distribution range, uniform morphology and particle size, and high tap density. When used to synthesize lithium iron phosphate materials, it can significantly improve the electrochemical performance of lithium iron phosphate, with a 0.2C discharge specific capacity of over 160 mA·h / g. Attached Figure Description

[0032] Figure 1 The charge-discharge curves of the battery assembled from the lithium iron phosphate material prepared in Example 1 are shown.

[0033] Figure 2 The charge-discharge curves of the battery assembled from the iron phosphate synthesized from lithium iron phosphate material prepared in Comparative Example 1 are shown. Detailed Implementation

[0034] Example 1

[0035] A method for preparing nanospheres of iron phosphate using iron oxide (Fe3O4) includes the following steps:

[0036] S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring.

[0037] S2 was simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction was allowed to proceed for 1 hour. Then the temperature was increased and the reaction was continued to produce a white precipitate.

[0038] S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstensibly at high temperature to obtain nanospheres of iron phosphate.

[0039] The iron source is iron(III) oxide (Fe3O4), which is crushed and passed through a 150-mesh sieve before use. The morphology control agent is sodium dodecylbenzenesulfonate. The composition is: 55.77g iron(III) oxide, 5.02g sodium dodecylbenzenesulfonate, and 278.85g deionized water.

[0040] In step S1, the stirring speed is 300 r / min and the stirring time is 0.5 h.

[0041] The concentrated phosphoric acid has a mass fraction of 85%, the oxidant is hydrogen peroxide with a mass fraction of 30%, and the solvent is water. The total amount of concentrated phosphoric acid is 139.43 g, and the amount of hydrogen peroxide is 26.77 g.

[0042] In step S2, the concentrated phosphoric acid and oxidant are added dropwise over a period of 0.5 hours, the temperature is raised to 85°C, and the reaction is carried out for 2 hours after the temperature is raised.

[0043] In step S3, the low-temperature drying temperature is 100℃ and the drying time is 7h; the high-temperature sintering temperature is 700℃ and the sintering time is 7h.

[0044] Example 2

[0045] A method for preparing nanospheres of iron phosphate using iron oxide (Fe3O4) includes the following steps:

[0046] S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring.

[0047] S2 was simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction was allowed to proceed for 1 hour. Then the temperature was increased and the reaction was continued to produce a white precipitate.

[0048] S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstensibly at high temperature to obtain nanospheres of iron phosphate.

[0049] The iron source is iron(III) oxide (Fe3O4), which is crushed and passed through a 150-mesh sieve before use. The morphology control agent is sodium dodecylbenzenesulfonate. The composition is: 55.77g iron(III) oxide, 3.9g sodium dodecylbenzenesulfonate, and 390.39g deionized water.

[0050] In step S1, the stirring speed is 360 r / min and the stirring time is 1 h.

[0051] The concentrated phosphoric acid has a mass fraction of 85%, the oxidant is hydrogen peroxide with a mass fraction of 30%, and the solvent is water. The total amount of concentrated phosphoric acid is 167.31 g, and the amount of hydrogen peroxide is 29.56 g.

[0052] In step S2, the concentrated phosphoric acid and oxidant are added dropwise over a period of 0.5 hours, the temperature is raised to 90°C, and the reaction is carried out for 2.5 hours after the temperature is raised.

[0053] In step S3, the low-temperature drying temperature is 110℃ and the drying time is 6 hours; the high-temperature sintering temperature is 720℃ and the sintering time is 7 hours.

[0054] Example 3

[0055] A method for preparing nanospheres of iron phosphate using iron oxide (Fe3O4) includes the following steps:

[0056] S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring.

[0057] S2 was simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction was allowed to proceed for 1 hour. Then the temperature was increased and the reaction was continued to produce a white precipitate.

[0058] S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstensibly at high temperature to obtain nanospheres of iron phosphate.

[0059] The iron source is iron(III) oxide (Fe3O4), which is crushed and passed through a 150-mesh sieve before use. The morphology control agent is sodium dodecylbenzenesulfonate. The composition is: 55.77g iron(III) oxide, 4.46g sodium dodecylbenzenesulfonate, and 446.16g deionized water.

[0060] In step S1, the stirring speed is 320 r / min and the stirring time is 0.75 h.

[0061] The concentrated phosphoric acid has a mass fraction of 85%, the oxidant is hydrogen peroxide with a mass fraction of 30%, and the solvent is water. The total amount of concentrated phosphoric acid is 195.20 g, and the amount of hydrogen peroxide is 25.10 g.

[0062] In step S2, the concentrated phosphoric acid and oxidant are added dropwise over a period of 0.5 hours, the temperature is raised to 92°C, and the reaction is carried out for 3 hours after the temperature is raised.

[0063] In step S3, the low-temperature drying temperature is 150℃ and the drying time is 5 hours; the high-temperature sintering temperature is 750℃ and the sintering time is 6 hours.

[0064] Example 4

[0065] A method for preparing nanospheres of iron phosphate using iron oxide (Fe3O4) includes the following steps:

[0066] S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring.

[0067] S2 was simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction was allowed to proceed for 1 hour. Then the temperature was increased and the reaction was continued to produce a white precipitate.

[0068] S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstensibly at high temperature to obtain nanospheres of iron phosphate.

[0069] The iron source is iron(III) oxide (Fe3O4), which is crushed and passed through a 150-mesh sieve before use. The morphology control agent is sodium dodecylbenzenesulfonate. The composition is: 55.77g iron(III) oxide, 2.79g sodium dodecylbenzenesulfonate, and 334.62g deionized water.

[0070] In step S1, the stirring speed is 420 r / min and the stirring time is 1 h.

[0071] The concentrated phosphoric acid has a mass fraction of 85%, the oxidant is hydrogen peroxide with a mass fraction of 30%, and the solvent is water. The total amount of concentrated phosphoric acid is 178.46 g, and the amount of hydrogen peroxide is 30.67 g.

[0072] In step S2, the concentrated phosphoric acid and oxidant are added dropwise over a period of 0.5 hours, the temperature is raised to 95°C, and the reaction is carried out for 3 hours after the temperature is raised.

[0073] In step S3, the low-temperature drying temperature is 120℃ and the drying time is 7h; the high-temperature sintering temperature is 800℃ and the sintering time is 9h.

[0074] Comparative Example 1

[0075] A method for preparing ferric phosphate, using the same steps as in Example 2 of patent CN201910764380.9.

[0076] A certain amount of 85% phosphoric acid and deionized water were measured and prepared into a 2.5 mol / L phosphoric acid solution in a four-necked flask. At room temperature, 9.3 g of iron(III) oxide was slowly added to the phosphoric acid solution. The molar ratio of iron(III) oxide to phosphoric acid was 1:8. The mixture was heated to 80 °C and reacted for 4 h with a stirring speed of 400 r / min.

[0077] After the reaction was completed, ferric phosphate dihydrate precipitate was obtained. After filtration and washing, the filter cake was dried in a 110℃ forced-air drying oven for 6 hours and then dehydrated in a 700℃ muffle furnace for 8 hours to obtain nano-sheet ferric phosphate.

[0078] Comparative Example 2

[0079] A method for preparing nanospheres of iron phosphate using iron oxide (Fe3O4) includes the following steps:

[0080] S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring.

[0081] S2 was simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction was allowed to proceed for 1 hour. Then the temperature was increased and the reaction was continued to produce a white precipitate.

[0082] S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstensibly at high temperature to obtain nanospheres of iron phosphate.

[0083] The iron source is iron(III) oxide (Fe3O4), which is crushed and passed through a 150-mesh sieve before use. The morphology control agent is sodium dodecylbenzenesulfonate. The composition is: 55.77g iron(III) oxide, 2.23g sodium dodecylbenzenesulfonate, and 334.62g deionized water.

[0084] In step S1, the stirring speed is 420 r / min and the stirring time is 1 h.

[0085] The concentrated phosphoric acid has a mass fraction of 85%, the oxidant is hydrogen peroxide with a mass fraction of 30%, and the solvent is water. The total amount of concentrated phosphoric acid is 178.46 g, and the amount of hydrogen peroxide is 30.67 g.

[0086] In step S2, the concentrated phosphoric acid and oxidant are added dropwise over a period of 0.5 hours, the temperature is raised to 95°C, and the reaction is carried out for 3 hours after the temperature is raised.

[0087] In step S3, the low-temperature drying temperature is 120℃ and the drying time is 7h; the high-temperature sintering temperature is 800℃ and the sintering time is 7h.

[0088] Comparative Example 3

[0089] A method for preparing nanospheres of iron phosphate using iron oxide (Fe3O4) includes the following steps:

[0090] S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring.

[0091] S2 was simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction was allowed to proceed for 1 hour. Then the temperature was increased and the reaction was continued to produce a white precipitate.

[0092] S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstensibly at high temperature to obtain nanospheres of iron phosphate.

[0093] The iron source is iron(III) oxide (Fe3O4), which is crushed and passed through a 150-mesh sieve before use. The morphology control agent is sodium dodecylbenzenesulfonate. The composition is: 55.77g iron(III) oxide, 3.90g sodium dodecylbenzenesulfonate, and 223.08g deionized water.

[0094] In step S1, the stirring speed is 420 r / min and the stirring time is 1.5 h.

[0095] The concentrated phosphoric acid has a mass fraction of 85%, the oxidant is hydrogen peroxide with a mass fraction of 30%, and the solvent is water. The total amount of concentrated phosphoric acid is 178.46 g, and the amount of hydrogen peroxide is 29.56 g.

[0096] In step S2, the concentrated phosphoric acid and oxidant are added dropwise over a period of 0.5 hours, the temperature is raised to 90°C, and the reaction is carried out for 2.5 hours after the temperature is raised.

[0097] In step S3, the low-temperature drying temperature is 110℃ and the drying time is 8 hours; the high-temperature sintering temperature is 720℃ and the sintering time is 9 hours.

[0098] Comparative Example 4

[0099] A method for preparing nanospheres of iron phosphate using iron oxide (Fe3O4) includes the following steps:

[0100] S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring.

[0101] S2 was simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction was allowed to proceed for 1 hour. Then the temperature was increased and the reaction was continued to produce a white precipitate.

[0102] S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstensibly at high temperature to obtain nanospheres of iron phosphate.

[0103] The iron source is magnetite (Fe3O4), which is crushed and passed through a 150-mesh sieve before use. The morphology control agent is sodium dodecylbenzenesulfonate. The composition is: 55.77g magnetite, 3.90g sodium dodecylbenzenesulfonate, and 390.39g deionized water.

[0104] In step S1, the stirring speed is 360 r / min and the stirring time is 1 h.

[0105] The concentrated phosphoric acid has a mass fraction of 85%, the oxidant is hydrogen peroxide with a mass fraction of 30%, and the solvent is water. The total amount of concentrated phosphoric acid is 211.93 g, and the amount of hydrogen peroxide is 22.31 g.

[0106] In step S2, the concentrated phosphoric acid and oxidant are added dropwise over a period of 0.5 hours, the temperature is raised to 90°C, and the reaction is carried out for 2.5 hours after the temperature is raised.

[0107] In step S3, the low-temperature drying temperature is 110℃ and the drying time is 7h; the high-temperature sintering temperature is 720℃ and the sintering time is 9h.

[0108] Comparative Example 5

[0109] A method for preparing nanospheres of iron phosphate using iron oxide (Fe3O4) includes the following steps:

[0110] S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring.

[0111] S2 was simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction was allowed to proceed for 1 hour. Then the temperature was increased and the reaction was continued to produce a white precipitate.

[0112] S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstensibly at high temperature to obtain nanospheres of iron phosphate.

[0113] The iron source is iron(III) oxide (Fe3O4), which is crushed and passed through a 150-mesh sieve before use. The morphology control agent is sodium dodecylbenzenesulfonate. The composition is: 55.77g iron(III) oxide, 3.9g sodium dodecylbenzenesulfonate, and 390.39g deionized water.

[0114] In step S1, the stirring speed is 360 r / min and the stirring time is 1 h.

[0115] The concentrated phosphoric acid has a mass fraction of 85%, the oxidant is hydrogen peroxide with a mass fraction of 30%, and the solvent is water. The total amount of concentrated phosphoric acid is 167.31 g, and the amount of hydrogen peroxide is 29.56 g.

[0116] In step S2, the concentrated phosphoric acid and oxidant are added dropwise over a period of 0.5 hours, the temperature is raised to 90°C, and the reaction is carried out for 1.5 hours after the temperature is raised.

[0117] In step S3, the low-temperature drying temperature is 110℃ and the drying time is 7h; the high-temperature sintering temperature is 720℃ and the sintering time is 9h.

[0118] Performance testing

[0119] 1. Conversion rate of iron(III) oxide: Conversion rate = (moles of iron(III) oxide prepared / moles of iron(III) oxide) ÷ 3 × 100%

[0120] 2. Content of magnetic impurities in ferric phosphate: After adsorbing magnetic substances in ferric phosphate with a magnetic rod, the magnetic substances were dissolved in aqua regia. The intensity of the characteristic spectral lines of the magnetic elements (iron, zinc, nickel, chromium) was measured using inductively coupled plasma atomic emission spectrometry (ICP-AES) to calculate the content of magnetic substances in the ferric phosphate prepared in the examples and comparative examples.

[0121] 3. Tap density: The tap density of the iron phosphate prepared in the examples and comparative examples was tested using a tap density meter.

[0122] 4. Discharge specific capacity: The lithium iron phosphate materials prepared by the examples and comparative examples were combined into batteries, and the discharge specific capacity at 0.2C was tested.

[0123] The test results are shown in Table 1.

[0124] Table 1

[0125]

Claims

1. A method for preparing nano-spherical iron phosphate using iron(III) oxide, characterized in that, Includes the following steps: S1 iron source and morphology control agent are mixed, and deionized water is added for dispersion and stirring. S2 is simultaneously added dropwise with concentrated phosphoric acid and oxidant, and the reaction is allowed to proceed for 0.5-1 h. Then the temperature is increased and the reaction continues, resulting in a white precipitate. S3 centrifuges and filters the white precipitate, washes it, dries it at low temperature, and sinterstens it at high temperature to obtain nano-spherical iron phosphate. The weight ratio of the iron source to the morphology control agent is 1:(0.05-0.09); The iron source is iron(II,III) oxide, and the amount of concentrated phosphoric acid used is 2.5-3.6 times the mass of the iron source. In step S2, the added concentrated phosphoric acid and oxidant are added over a period of 0.5-1 hour, the temperature is raised to 85-100°C, and the reaction time after heating is 2-3 hours.

2. The method for preparing nano-spherical iron phosphate using iron oxide according to claim 1, characterized in that, The ferric oxide is crushed and passed through a 150-160 mesh sieve before use.

3. The method for preparing nano-spherical iron phosphate using iron oxide according to claim 1, characterized in that, The morphology control agent is selected from one or a combination of several of sodium dodecylbenzenesulfonate, sodium hexadecylbenzenesulfonate, sodium dodecylbenzenesulfonate, and sodium dodecyl diphenyl ether disulfonate.

4. The method for preparing nano-spherical iron phosphate using iron oxide according to claim 1, characterized in that, In step S1, the amount of deionized water added is 5-8 times the mass of the iron source, the stirring speed is 300-460 r / min, and the stirring time is 0.5-1 h.

5. The method for preparing nano-spherical iron phosphate using iron oxide according to claim 1, characterized in that, The concentrated phosphoric acid has a mass fraction of 85%-90%, and the oxidant has a mass fraction of 20-40%.

6. The method for preparing nano-spherical iron phosphate using iron oxide according to claim 1, characterized in that, The amount of oxidant used is 0.45-0.55 times the mass of the iron source.

7. The method for preparing nano-spherical iron phosphate using iron oxide according to claim 1, characterized in that, In step S3, the low-temperature drying temperature is 100-150℃, and the high-temperature sintering temperature is 700-850℃.

8. An application of the method for preparing nano-spherical iron phosphate using iron oxide according to any one of claims 1-7, characterized in that, The prepared nanospheres of iron phosphate were used to synthesize lithium iron phosphate materials.

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