NANOBLADE FERROPHATE AND ITS MANUFACTURING PROCESS

Abstract

Method for producing a nanosheet iron phosphate, comprising the following steps: (1) Dissolving a phosphorus source and an iron source in an acidic solution to obtain a phosphoric iron solution; (2) Heating 50% of the total quantity of the phosphate iron solution to boiling, adding a precipitating agent and diluting the reaction to obtain a primary iron phosphate slurry; and (3) Dropwise addition of the remaining phosphorus iron solution to the primary iron phosphate suspension and heating of the resulting mixture to react and obtain iron phosphate; wherein the dilution of the reaction in step (2) comprises dilution with water and aging, wherein a volume ratio of added water to the portion of the phosphoric iron solution is 2 - 20 : 1; and wherein in step (3) prior to the addition of the remaining phosphoric iron solution to the primary iron phosphate suspension the process further comprises the addition of the precipitating agent to the remaining phosphoric iron solution.

Description

TECHNICAL FIELD

[0001] The present invention relates to the technical field of battery materials, in particular to a nanosheet iron phosphate and its production method. BACKGROUND

[0002] Iron phosphate is used as a valuable chemical product in ceramics, pigments, additives, catalysts, food, and other industries. In recent years, iron phosphate has been used to produce lithium iron phosphate cathode materials for lithium-ion batteries due to its unique chemical structure.

[0003] Currently, one of the methods for synthesizing lithium iron phosphate is the iron phosphate process, in which iron phosphate is mainly used as a precursor, wet-ground, and mixed with a lithium source and a carbon source, and the lithium iron phosphate cathode material is prepared through a carbothermal reduction process. Iron phosphate can simultaneously provide an iron and phosphorus source, and only a lithium salt and a carbon source need to be added during batch processing. Therefore, the overall performance of the prepared lithium iron phosphate cathode material is largely determined by the chemical composition, structure, physicochemical properties, and reactivity of the iron phosphate precursor.Furthermore, the manufacturing cost of lithium iron phosphate cathode materials is largely determined by the iron phosphate precursor. Since high-purity iron phosphate has low conductivity, it diffuses slowly during the charging and discharging process of lithium batteries, which impairs the performance of lithium iron phosphate batteries. Therefore, it is necessary to modify the lithium iron phosphate. Research has shown that nanocrystallization of iron phosphate can improve the electrochemical performance of the materials. Currently, the hydrothermal method is the main method for producing nanomaterials.This is a chemical reaction that uses water as a solvent in a closed container under high pressure, high temperature, and other conditions. Therefore, the method places higher demands on equipment and poses safety concerns. Therefore, it is urgently necessary to develop a method for producing iron phosphate at the nanoscale that is cost-effective, simple, and safe.

[0004] CN 1 02 009 968 A discloses a production process for nanoflaky FePO4·2H2O. The production process comprises the following steps: preparing an iron salt solution and phosphoric acid, wherein the molar dosage ratio of the iron salt to H3PO4 is as follows: Fe:P = 1:1 - 1:5; dissolving a surfactant used as an additive in the iron salt solution or the phosphoric acid, wherein the concentration of the surfactant is not less than 3 g / L; dropwise adding the phosphoric acid to the iron salt solution or dropwise adding the iron salt solution to the phosphoric acid and stirring; then isolating for 6-24 hours at 70-90 °C; and filtering the obtained precipitates, and then washing and drying the precipitates. The process provided by the invention can be used to produce a monoclinic or orthorhombic nanoflaky FePO4·2H2O crystal.

[0005] CN 1 10 294 466 A discloses a production process for iron phosphate nanosheets. The production process comprises the steps of slowly adding iron oxide black to phosphoric acid at a concentration of 1.5–3.0 mol / L, stirring and heating for reaction, and, after the reaction, obtaining iron phosphate nanosheets through suction filtration, washing, drying, dehydration, and other steps. The iron phosphate produced by this process has a nanosheet-like morphology, a nanosheet thickness of 70–80 nanometers, and a large specific surface area. By optimizing the reaction conditions, no pH adjustment or addition of oxidants is required during the reaction process; interference with anionic and cationic impurities is effectively avoided, and the iron phosphate obtained by this process is free of impurity phases and highly pure.In addition, less water is used to wash the iron phosphate precipitate, the cost of iron phosphate synthesis is reduced, and environmental pollution is reduced.

[0006] CN 1 04 817 059 A discloses a process for producing a battery-grade iron phosphate from a reaction between iron powder and phosphoric acid. The process comprises the following steps: mixing iron powder with dilute phosphoric acid to generate Fe(H2PO4)2 by reaction, then adding an oxidizing agent to generate an iron phosphate precipitate by oxidation; obtaining a high-purity battery-grade iron phosphate, i.e., iron phosphate dihydrate. The iron phosphate dihydrate is a nanometer-sized, scale-like crystal of the metastrengite (phosphosiderite) crystal form. The process for producing the battery-grade iron phosphate from the reaction between the iron powder and phosphoric acid is technically simple and practical in application, without introducing other impurity ions.The filter fluid and cleaning solution can be reused, eliminating waste and wastewater, and keeping costs low. Therefore, the process for producing battery-grade iron phosphate from the reaction between iron powder and phosphoric acid is an environmentally friendly, green technology.

[0007] CN 1 12 645 299 A discloses a production process and the use of iron phosphate, comprising the following steps: mixing a phosphorus source and an iron source, adding them to an acid solution, filtering, collecting a filtrate to obtain an acidic iron-phosphorus solution, and heating and stirring the acidic iron-phosphorus solution to obtain a slurry containing iron phosphate; filtering the slurry to obtain an iron phosphate solid and a precipitate mother liquor; and washing, filtering, and drying the iron phosphate solid to obtain iron phosphate. SUMMARY

[0008] The present invention aims to solve at least one of the above-mentioned technical problems existing in the prior art. Therefore, the present invention provides a nanosheet iron phosphate and its production method. This method can regulate the morphology of the iron phosphate and increase the specific surface area and compaction density of the iron phosphate.

[0009] In order to achieve the above-mentioned objects, the following technical solutions are used in the present invention.

[0010] The present invention provides a process for producing a nanosheet iron phosphate comprising the following steps: (1) Dissolving a phosphorus source and an iron source in an acidic solution to obtain a phosphorus iron solution; (2) heating 50% of a total amount of the phosphorus iron solution to boiling, adding a precipitating agent, and diluting the reaction to obtain a primary iron phosphate slurry; and (3) Adding the remaining phosphorus iron solution dropwise to the primary iron phosphate slurry and heating the resulting mixture to react to obtain iron phosphate; wherein diluting the reaction in step (2) comprises diluting with water and aging, wherein the volume ratio of added water to the portion of phosphorus iron solution is 2-20:1; wherein step (3) further comprises adding the precipitant to the remaining phosphorus iron solution prior to adding the remaining phosphorus iron solution to the primary iron phosphate slurry. The precipitant is added after boiling, then water is added to dilute the reaction, and nucleation is stimulated by drastic changes in reaction conditions (such as temperature, free acid) during the addition of water.

[0011] Preferably, step (3) further comprises filtering, washing and drying the iron phosphate.

[0012] In step (1), the iron source is preferably at least one substance selected from the group consisting of elemental iron, iron salt, magnetite and hematite.

[0013] More preferably, when the iron source is elemental iron and / or iron(II) salt, an oxidizing agent is also preferably added to the phosphorus iron solution.

[0014] The preferred oxidizing agent is hydrogen peroxide.

[0015] Elemental iron is preferred as iron powder.

[0016] More preferably, the iron salt is at least one selected from the group consisting of iron phosphate, iron sulfate, iron nitrate, and iron chloride.In step (1), the phosphorus source is preferably at least one selected from the group consisting of: phosphoric acid, hydrogen phosphate, hydroxyethylene diphosphonate, and aminotrimethylene phosphonate.

[0017] In step (1), the acidic solution is preferably at least one selected from the group consisting of sulfuric acid, hydrochloric acid, and nitric acid.

[0018] Preferably, the acidic solution in step (1) has a concentration of 1 mol / l to 18 mol / l.

[0019] More preferably, the acidic solution in step (1) has a concentration of 2 mol / l to 10 mol / l.

[0020] Preferably, the phosphorus iron solution in step (1) has an iron element concentration of 20 g / l to 75 g / l, more preferably 30 g / l to 65 g / l.

[0021] Preferably, the phosphorus iron solution in step (1) has a phosphorus element concentration of 11 g / l to 42 g / l, preferably 17 g / l to 36 g / l.

[0022] In step (1), the phosphorus iron solution preferably has an iron-phosphorus ratio (molar ratio) of 1: 0.95 - 1.05.

[0023] Preferably, in step (2), water is added for dilution during the dilution of the reaction, wherein the volume ratio of added water to the portion of the phosphorus iron solution is 3 - 10 : 1.

[0024] The amount of water added to dilute the reaction is very important for this reaction. If the amount of water added is too small, too much free acid is produced during dilution, and the iron and phosphorus concentrations are too high, which is not conducive to the formation of crystal nuclei. If too much water is added, the iron and phosphorus concentrations in the phosphorus iron solution are too low to form crystal nuclei.

[0025] In step (2), the precipitant is preferably at least one selected from the group consisting of titanium chloride, titanium sulfate, titanium dioxide, aluminum chloride, aluminum sulfate and iron phosphate.

[0026] In step (2), the amount of precipitant added is preferably 0.1% to 50% of the total amount of iron and phosphorus in the portion of the phosphorus iron solution, and more preferably 1% to 20%. Adding the precipitant before dilution can not only promote a precipitation reaction but also regulate the growth of the product and control its morphology.

[0027] Preferably, the dilution of the reaction in step (2) comprises dilution with water and aging. The dilution of the reaction is divided into two steps. The first step is the continuous addition of water, and the water addition time is 5 min to 120 min; the second step is aging, and the aging lasts 5 min to 240 min, more preferably 10 min to 180 min.

[0028] The crystal nucleus is formed during the dilution of the reaction, and the crystal nucleus gradually accumulates and grows after aging, making it more stable.

[0029] Preferably, in step (3), the amount of precipitant added is 0.05% to 25% of the total amount of iron and phosphorus in the remaining phosphorus iron solution, and more preferably 0.2% to 10%.

[0030] More preferably, in step (3), the residual phosphorus iron solution is dropped into the primary iron phosphate slurry for 10 to 120 minutes.

[0031] Preferably, in step (3), the temperature for heating the resulting mixture for reaction is 30°C to 95°C, and the reaction time is 30 minutes to 360 minutes; more preferably, the temperature is 40°C to 95°C. Temperature has a greater influence on the iron phosphate. The higher the temperature, the more non-activated molecules become activated molecules. The more activated molecules, the more effective collisions and the faster the reaction rate. However, if the temperature is too high, the evaporation capacity of the solution increases, thereby increasing the acidity in the system, which is not conducive to the growth of iron phosphate.

[0032] A nano-iron phosphate is produced using the process described above. The nanosheet iron phosphate has a particle size D50 of 200 nm to 300 nm and a specific surface area of ​​40 m 2 / g up to 43 m 2 / g and a compaction density of 2.4 g / cm 3up to 2.8 g / cm 3 . Compared with the prior art, the present invention has the following advantages.

[0033] 1. In the present disclosure, the phosphorus source and the iron source are used as starting materials. The primary iron phosphate is prepared by diluting the precipitation reaction. Then, the precipitant is added for the two-stage precipitation to regulate the growth of the iron phosphate, thereby controlling the morphology of the iron phosphate. The added precipitant can not only regulate the morphology but also act as a dopant, increasing the specific surface area and compaction density of the iron phosphate. The preparation process eliminates high temperature, high pressure, and other harsh conditions and is safe and simple. No other impurities are introduced during the reaction, which is environmentally friendly and cost-effective.

[0034] 2. The nanosheet iron phosphate produced by the process of the present invention has a D50 of 200 nm to 300 nm, a specific surface area of ​​40 m 2 / g up to 43 m 2 / g and a compaction density of 2.4 g / cm 3 up to 2.8 g / cm 3 . BRIEF DESCRIPTION OF THE CHARACTERS

[0035] The present invention is explained in more detail with reference to the accompanying drawings and embodiments. Fig. 1 shows a scanning electron micrograph (SEM) of an iron phosphate product according to Embodiment 1 of the present invention. Fig. 2 shows an X-ray diffraction pattern (XRD) of the iron phosphate product according to Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS Embodiment 1

[0036] A method for producing a nanosheet iron phosphate described in this embodiment comprises the following steps: (1) Sodium phosphate and iron nitrate were dissolved in 2 mol / L sulfuric acid solution to obtain a phosphorus iron solution with an iron concentration of 45 g / L and a phosphorus concentration of 25 g / L. The phosphorus iron solution was divided into Part A and Part B for use (the volume ratio of Part A and Part B was 1:1); (2) The phosphorus iron solution A was heated to boiling, and after adding titanium sulfate in an amount of 5% of the total amount of phosphorus and iron in the phosphorus iron solution A, the reaction was diluted by adding water, with water being added for 30 minutes. After adding water and then resting for 120 minutes for aging, a primary iron phosphate slurry was obtained; (3) 2% titanium sulfate was added to the iron phosphorus solution B, then added to the primary iron phosphate slurry for 60 minutes, and the resulting mixture was heated to react at 80 °C for 120 minutes with stirring to obtain iron phosphate; and (4) The obtained iron phosphate was filtered, washed and dried to obtain an iron phosphate product.

[0037] Fig. Figure 1 shows an SEM image of the iron phosphate product from Embodiment 1 of the present invention. Fig. 1 it was evident that the iron phosphate particles prepared in Example 1 were uniformly distributed and had a sheet-like structure with a particle size of ~250 nm without agglomeration.

[0038] Fig. Figure 2 shows an XRD pattern of the iron phosphate product from Embodiment 1 of the present invention. Fig.2, it can be seen that the XRD pattern of the prepared iron phosphate had a one-to-one match with the characteristic peaks of the spectrum of the standard card (72-0471), and its diffraction peaks were sharp, the characteristic peaks were obvious, and there were no unnecessary impurity peaks, indicating that iron phosphate with high crystallinity was obtained. Example 2

[0039] A method for producing a nanosheet iron phosphate described in this embodiment comprises the following steps: (1) Sodium hydrogen phosphate and ferrous sulfate were dissolved in 3 mol / L sulfuric acid solution to obtain a phosphorus iron solution with an iron concentration of 53 g / L and a phosphorus concentration of 29 g / L. The phosphorus iron solution was divided into Part A and Part B for use (the volume ratio of Part A and Part B was 1:1). (2) The phosphorus iron solution A was heated to boiling, and after adding aluminum sulfate in an amount of 6% of the total amount of phosphorus and iron, 6 times the volume of the phosphorus iron solution of water was continuously added for 50 minutes. After adding water and then resting for 150 minutes for aging, a primary iron phosphate slurry was obtained; (3) 2% aluminum sulfate was added to the phosphoric iron solution B, then continuously added to the primary iron phosphate slurry for 40 minutes, and then the resulting mixture was heated to react with stirring for 90 minutes to obtain iron phosphate; and (4) The obtained iron phosphate was filtered, washed and dried to obtain an iron phosphate product. Example 3

[0040] A method for producing a nanosheet iron phosphate described in this embodiment comprises the following steps: (1) Potassium phosphate and ferric chloride were dissolved in 2 mol / L sulfuric acid solution to obtain a phosphorus iron solution with an iron concentration of 49 g / L and a phosphorus concentration of 26 g / L. The phosphorus iron solution was divided into Part A and Part B for use (the volume ratio of Part A and Part B was 1:1); (2) The phosphorus iron solution A was heated to boiling, and after adding titanium chloride in an amount of 3% of the total amount of phosphorus and iron, five times the volume of water was continuously added over 40 minutes. After adding water and then resting for 120 minutes for aging, a primary iron phosphate slurry was obtained; (3) 3% titanium chloride was added to the iron phosphorus solution B, then continuously added to the primary iron phosphate slurry for 50 minutes, and then the resulting mixture was heated to 85 °C for 100 minutes with stirring to obtain iron phosphate; and (4) The obtained iron phosphate was filtered, washed and dried to obtain an iron phosphate product. Comparison example 1

[0041] A process for producing a nanosheet iron phosphate according to this comparative example comprised the following steps: (1) Sodium phosphate and ferrous sulfate were dissolved in 2 mol / L sulfuric acid to obtain an acidic iron solution and an acidic phosphorus solution, which were formulated into an acidic phosphorus iron solution with an iron to phosphorus ratio of 1:1.03; (2) Oxygen was introduced into the acidic phosphorus iron solution to oxidize for 2 hours until Fe 2+in the solution to Fe 3+ was oxidized, then aqueous ammonia was added to adjust to pH 3, and the mixture was reacted at 90 °C for 3 hours, and then iron phosphate was obtained by liquid-solid separation; and (3) the obtained iron phosphate was washed, filtered and dried to obtain an iron phosphate product. Comparison example 2

[0042] A process for producing a nanosheet iron phosphate according to this comparative example comprised the following steps: (1) Preparation of an iron feedstock liquid: According to the molar ratios of Fe2(SO4)3: (H2SO4+H3PO4) = 1: 0.2 and H2SO4: H3PO4 = 9:1, ferrous sulfate solution, sulfuric acid solution and phosphoric acid solution were mixed to obtain an iron sulfate feedstock liquid, wherein the iron sulfate feedstock liquid had a pH of 1.03 and the mass concentration of the iron element in the iron sulfate feedstock liquid was 84 g / L; (2) Preparation of the phosphate feedstock: Ammonium phosphate was dissolved in water to obtain a phosphate feedstock. The mass concentration of the phosphorus element in the phosphate feedstock was 45 g / L. (3) Synthesis reaction procedure: The phosphate starting liquid obtained in step (2) was gradually added to the ferrous sulfate starting liquid obtained in step (1) with stirring in a ratio such that the molar ratio of iron in the ferrous sulfate starting liquid to phosphorus in the phosphate solution was 1:1, and a mixed solution was obtained. The mixed solution was then heated to 90 °C and reacted for 3 hours to obtain an iron phosphate slurry. (4) the obtained iron phosphate was washed, filtered and dried to obtain an iron phosphate product. Comparison example 3

[0043] A process for producing a nanosheet iron phosphate according to this comparative example comprised the following steps: (1) An aqueous solution containing 0.05 mol / L iron nitrate and 0.05 mol / L phosphoric acid was prepared to obtain a starting material A; (2) 0.1 mol / L aqueous ammonium phosphate solution was prepared to obtain a starting material B, and 1 L of the starting material A and 1 L of the starting material B were rapidly mixed using a membrane dispersion micromixer to obtain a slurry C; and (3) The slurry C was subjected to hydrothermal treatment at a treatment temperature of 100 °C under atmospheric pressure for 0.2 hours, then a precipitate was filtered off from the slurry C, and then the precipitate was washed and dried to obtain an iron phosphate product. Comparison example 4

[0044] Compared with the embodiment 1, no precipitant was added in step (2) in this comparative example. Comparison example 5

[0045] Compared to Example 1, in this Comparative Example no water was added to dilute the reaction in step (2). Table 1 Comparison of the specific test data between the iron phosphate produced according to the working examples 1-3 and the iron phosphate produced in the comparative examples Particle size D50 (nm) Compaction density (g / cm 3 ) Specific surface area (m 2 / G) Example 1 249 2.57 41.32 Example 2 260 2.41 40.20 Example 3 255 2.47 40.63 Comparison example 1 3200 2.19 22.96 Comparison example 2 5300 1.96 17.63 Comparison example 3 3700 2.11 20.42 Comparison example 4 2980 1.97 24.3 Comparison example 5 2200 2.15 30.65

[0046] From the data in Table 1, it can be seen that the iron phosphate products produced in the embodiments of the present invention are nanoscale iron phosphates, while the iron phosphate products produced in the comparative examples are microscale iron phosphates. Table 1 shows that the produced nanoscale iron phosphate can significantly improve the specific surface area and compaction density of iron phosphate.

Claims

[1] A process for producing a nanosheet iron phosphate, comprising the following steps: (1) Dissolving a phosphorus source and an iron source in an acidic solution to obtain a phosphorus iron solution; (2) heating 50% of the total amount of the phosphorus iron solution to boiling, adding a precipitating agent and diluting the reaction to obtain a primary iron phosphate slurry; and (3) Adding the remaining phosphorus iron solution dropwise into the primary iron phosphate slurry and heating the resulting mixture for reaction to obtain iron phosphate; wherein diluting the reaction in step (2) comprises diluting with water and aging, wherein a volume ratio of added water to the portion of the phosphorus iron solution is 2-20:1; and wherein in step (3) prior to adding the residual phosphorus iron solution to the primary iron phosphate slurry, the method further comprises adding the precipitant to the residual phosphorus iron solution. [2] The method of claim 1, wherein step (3) further comprises filtering, washing and drying the iron phosphate. [3] The method according to claim 1, wherein in step (1), the iron source is at least one selected from a group consisting of elemental iron, iron salt, magnetite, and hematite; and wherein, in the case where the iron source is elemental iron and / or a ferrous salt, an oxidizing agent is added in addition to the phosphoric iron solution. [4] The process according to claim 1, wherein in step (1) the phosphorus source is at least one selected from a group consisting of phosphoric acid, hydrogen phosphate, hydroxyethylene diphosphonate and aminotrimethylene phosphonate. [5] The method according to claim 1, wherein in step (1) the acidic solution is at least one selected from a group consisting of sulfuric acid, hydrochloric acid and nitric acid. [6] The process according to claim 1, wherein in step (2) the precipitating agent is at least one selected from a group consisting of titanium chloride, titanium sulfate, titanium dioxide, aluminum chloride, aluminum sulfate, and iron phosphate. [7] Nanosheet iron phosphate produced by the process according to any one of claims 1 to 6, wherein the nanosheet iron phosphate has a sheet diameter D50 of 200 nm to 300 nm, a specific surface area of 40 m 2 / g up to 43 m 2 / g and a compaction density of 2.4 g / cm 3 up to 2.8 g / cm 3 has.

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