Process for the preparation of battery grade iron phosphate

Abstract

The present application relates to a battery grade iron phosphate preparation method, comprising the following steps: (1) using iron-containing hydrochloric acid pickling waste liquid as raw material, which contains 5-8wt% of ferrous iron; adding phosphoric acid solution in the iron-containing hydrochloric acid pickling waste liquid, transferring to the reaction kettle after stirring uniformly, adding catalyst and oxidant under stirring state to carry out catalytic oxidation reaction, ending the reaction after the content of ferrous iron in the reaction system is less than 0.03wt%, and obtaining liquid material containing polymeric iron; (2) putting the liquid material into alcohol-water solvent, continuously stirring to make the polymeric iron in it self-hydrolyze, cooling to produce crystallization, and after filtration and drying, obtaining iron phosphate product, which meets the product index of battery grade iron phosphate. The method can avoid using high-risk hydrogen peroxide and has small secondary pollution risk, and the prepared iron phosphate meets the battery grade requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of compound synthesis, in particular to a preparation method of battery-grade iron phosphate. BACKGROUND

[0002] The materials used in lithium ion batteries mainly include positive electrode materials, negative electrode materials, electrolytes, separator membranes, etc., wherein the positive electrode material plays a decisive role in the performance of lithium ion batteries, and the cost of the positive electrode material accounts for about 40% of the cost of lithium ion batteries. The positive electrode materials used in lithium ion batteries mainly include lithium iron phosphate, lithium cobaltate, lithium manganate, etc., and the positive electrode material with the lowest cost and the best safety performance and high-temperature resistance is lithium iron phosphate (LiFePO4), which has many advantages such as high theoretical capacity, moderate voltage platform, safety and environmental protection.

[0003] Iron phosphate (FePO4) is a precursor material of lithium iron phosphate, and its preparation method is also a research hotspot. Compared with ordinary iron phosphate, the preparation of battery-grade iron phosphate needs to accurately control the content of water, iron and phosphorus elements in the material and the particle size of the particles, and these indicators have a great influence on the performance of battery-grade iron phosphate.

[0004] The preparation method of ordinary iron phosphate is co-precipitation method, which mainly uses ferrous sulfate by-product of titanium white as raw material, reacts with a large amount of hydrogen peroxide after purification and refining, and finally obtains under certain pH conditions. However, the pretreatment process is long, and the use of hydrogen peroxide in the middle is dangerous and has harsh storage conditions. Finally, a large amount of washing water is produced to obtain battery-grade iron phosphate, which has a high risk of secondary pollution. SUMMARY

[0005] In order to solve the technical problems of large amount of oxidizing agent and large amount of wastewater in the preparation of iron phosphate, the present application provides a preparation method of battery-grade iron phosphate. The method can avoid the use of high-risk hydrogen peroxide and has a small risk of secondary pollution, and the prepared iron phosphate meets the requirements of battery grade.

[0006] In order to achieve the above purposes, the present application realizes the following technical scheme:

[0007] The preparation method of battery-grade iron phosphate comprises the following steps:

[0008] (1) Using iron-containing hydrochloric acid pickling waste liquid as raw material, which contains 5-8wt% of divalent iron; adding phosphoric acid solution in the iron-containing hydrochloric acid pickling waste liquid, stirring uniformly, and then transferring to a reaction kettle; under normal temperature and stirring state, adding catalyst and oxidizing agent for catalytic oxidation reaction, so that the content of divalent iron in the reaction system is less than 0.03wt%, and then the reaction is stopped to obtain a liquid material containing polymeric iron; the catalytic oxidation reaction is exothermic, and the liquid material is in a warm state;

[0009] (2) the liquid material is added into alcohol-water solvent with or without cooling, the polymeric iron therein is self-hydrolyzed under continuous stirring, crystallization is generated by cooling below room temperature, and the product of iron phosphate is obtained after filtration and drying, which meets the product index of battery-grade iron phosphate.

[0010] Further, the hydrochloric acid in the hydrochloric acid pickling waste liquid accounts for 3-5% of the mass; and the mass concentration of the phosphoric acid solution is greater than 30%.

[0011] Further, the oxidizing agent is oxygen or ozone; and the catalyst is a mixed solution of sodium nitrite and nitric acid, wherein the mass fraction of sodium nitrite in the mixed solution is 5%, and the amount of sodium nitrite is 0.5-0.8% of the weight of the hydrochloric acid pickling waste liquid.

[0012] Further, the mass ratio of the hydrochloric acid pickling waste liquid to the phosphoric acid in the phosphoric acid solution is 1:(0.015-0.025).

[0013] Further, the mass fraction of iron in the polymeric iron is greater than 6%, the basicity is greater than 10%, and the mass fraction of divalent iron in the iron is less than 0.05%.

[0014] Further, the alcohol-water solvent is an ethanol-water solvent, and the mass fraction of ethanol therein is 40-60%.

[0015] Further, the amount of the hydrochloric acid pickling waste liquid and the alcohol-water solvent is 1g:10L.

[0016] Beneficial technical effects:

[0017] The present application prepares the polymeric iron by preparing the hydrochloric acid pickling waste liquid containing iron and the phosphoric acid in a certain proportion, and then using the catalytic oxidation method to prepare the polymeric iron, and then using the solubility effect of the polymeric iron in the ethanol-water solution to obtain the iron phosphate by self-decomposition under a certain stirring condition. Compared with the traditional method for preparing the iron phosphate, the present application has the following advantages: the prepared iron phosphate has uniform particles, the quality is controllable, a large amount of washing water is not needed, the present application can avoid using the hydrogen peroxide which has high risk and has small secondary pollution risk, and the prepared iron phosphate meets the battery-grade requirements. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 The infrared spectrum (FT-IR) of the polymeric iron in the liquid material of Example 1;

[0019] Figure 2 The SEM image of the product of iron phosphate in Example 1, wherein the scale length in the image is 1μm. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application and the drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. The description of the at least one exemplary embodiment below is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0021] Unless specifically stated otherwise, the numerical values set forth in the examples herein are not limited to the preferred ranges set forth. Any text, methods, procedures, and materials instrumentalists known to those of ordinary skill in the related art can not be discussed in detail, but should be considered part of the specification where appropriate. In all examples shown and discussed herein, any specific value should be interpreted as merely exemplary, and not as a limitation. Therefore, other examples of the exemplary embodiments can have different values.

[0022] The experimental methods in the following embodiments without specific conditions are generally determined according to national standards; if there is no corresponding national standard, the international standard or the standard requirement proposed by the relevant enterprise is followed. Unless otherwise specified, all parts are parts by weight, and all percentages are percentages by weight.

[0023] The iron-containing hydrochloric acid pickling waste liquid used in the following cases is generated from the waste liquid after treating the surface of carbon steel in a domestic steel enterprise, specifically a carbon steel surface hydrochloric acid pickling waste liquid, which contains Fe 2+ The content of Fe is 7.6wt%, the content of HCl is 3.45wt%, and the impurities in the waste liquid are required to be executed according to Table 1 in HG / T 6112-2022 standard.

[0024] The base degree is the equivalent percentage of hydroxyl and trivalent iron, which is measured according to the determination method in section 6.5 of HG / T4672-2022.

[0025] Example 1

[0026] The preparation method of the battery-grade iron phosphate includes the following steps:

[0027] (1) using iron-containing hydrochloric acid pickling waste liquid (Fe 2+The intermediate product is obtained by using 300 g of the iron-containing hydrochloric acid pickling waste liquid (Fe content 7.6 wt%, HCl content 3.45 wt%) as raw material, adding 20 g of phosphoric acid solution (phosphoric acid content 31 wt%) into the iron-containing hydrochloric acid pickling waste liquid, stirring uniformly, and then transferring into a pressure-resistant reaction kettle, adding 30 g of sodium nitrite solution (a mixed solution of sodium nitrite and nitric acid, and the mass ratio of sodium nitrite in the mixed solution is 5%) under stirring at room temperature, and then performing catalytic oxidation reaction by oxygen, and the reaction is ended when the divalent iron content in the reaction system is less than 0.03 wt% (the reaction time is 40 min), and the intermediate product is a liquid material containing polymeric iron.

[0028] The intermediate product is subjected to infrared spectrum FT-IR test, and the specific results are shown in Figure 1 It can be seen from Figure 1 that in the infrared spectrum of the pressed sheet of the polymeric iron sample, there are strong absorption peaks at 3390 cm -1 ,

[0029] 1630 cm -1 , and weak absorption peaks at 1100 cm -1 , 600 cm -1 , etc.; the characteristic absorption peaks of Fe-OH, H-OH three hydroxyl stretching vibration are at 3360-3390 cm -1 , the characteristic absorption peak of coordinated water H-OH bending vibration is at 1630 cm －1 , and the characteristic absorption peak of bending vibration is at 1000 cm －1 ; in addition, the characteristic absorption peak of overall bending vibration is at 600 cm －1 , and the characteristic absorption peak of P-O vibration is at 1400 cm －1 .

[0030] The chemical formula of the polymeric iron of the intermediate product is Fe4(OH) n Cl 6-n (PO4) 2-n / 3 , wherein 0

[0031] (2) Since the catalytic oxidation reaction is exothermic, the liquid material is put into 3000 L of ethanol aqueous solvent (ethanol and water are in equal mass ratio) while hot, and the polymeric iron in the liquid material is subjected to self-hydrolysis under continuous stirring, and crystallization is generated after cooling to room temperature. The phosphoric iron product is obtained after filtration and vacuum drying at 105°C for 2 h, and the phosphoric iron product meets the product index of battery-grade phosphoric iron, and the specific index is shown in Table 1.

[0032] The SEM image of the ferric phosphate product in this embodiment is as follows: Figure 2 As shown, by Figure 2 As can be seen, the solid product in this embodiment has uniform, spherical particles with a particle size of about 4.2 μm, which is not significantly different from the morphology of iron phosphate prepared by traditional methods.

[0033] Example 2

[0034] The preparation method of battery-grade iron phosphate includes the following steps:

[0035] (1) Pickling waste liquid containing iron hydrochloric acid (Fe 2+ Using 7.6 wt% iron and 3.45 wt% HCl as raw materials, 25 g of phosphoric acid solution (containing 36 wt% phosphoric acid) was added to 500 g of the iron-containing hydrochloric acid pickling waste liquid. After stirring evenly, the solution was transferred to a pressure-resistant reactor. 55 g of sodium nitrite solution (a mixed solution of sodium nitrite and nitric acid, wherein the mass percentage of sodium nitrite in the mixed solution is 5%) was added under stirring at room temperature. Oxygen was then introduced to carry out a catalytic oxidation reaction. The reaction was stopped when the content of ferrous iron in the reaction system was lower than 0.03 wt% (reaction time was 50 min), and an intermediate product was obtained. The intermediate product is a liquid material containing multi-component polymeric iron.

[0036] The chemical formula of the intermediate product, multi-component polymeric iron, is Fe4(OH). n Cl 6-n (PO4) 2-n / 3 , where 0 < n < 6 (the specific n of the intermediate product was not calculated), where the mass percentage of iron is 6.54%, the basicity (equivalent percentage of hydroxyl to ferric iron) is 13.5%, and the mass percentage of ferrous iron in the iron element is less than 0.05%.

[0037] (2) Since the catalytic oxidation reaction is exothermic, the liquid material is placed into the container while it is still hot.

[0038] In 5000L of ethanol-water solvent (ethanol and water in equal mass ratio), the multi-component polymeric iron is subjected to self-hydrolysis under continuous stirring. After cooling to room temperature, crystals are produced. After filtration and vacuum drying at 105℃ for 2 hours, the iron phosphate product is obtained. The iron phosphate product meets the product indicators of battery-grade iron phosphate, and the specific indicators are shown in Table 1.

[0039] Example 3

[0040] The preparation method of battery-grade iron phosphate includes the following steps:

[0041] (1) Pickling waste liquid containing iron hydrochloric acid (Fe 2+The iron-containing hydrochloric acid pickling waste liquid (Fe content 7.6wt%, HCl content 3.45wt%) is used as raw material; 50g of phosphoric acid solution (phosphoric acid content 38wt%) is added to 800g of the iron-containing hydrochloric acid pickling waste liquid, which is stirred uniformly and then transferred to a pressure-resistant reaction kettle; 90g of sodium nitrite solution (a mixed solution of sodium nitrite and nitric acid, in which the mass ratio of sodium nitrite in the mixed solution is 5%) is added under stirring at room temperature; then oxygen is introduced for catalytic oxidation reaction, and the reaction is terminated when the divalent iron content in the reaction system is less than 0.03wt% (the reaction time is 52min); and an intermediate product is obtained, which is a liquid material containing polymeric iron.

[0042] The chemical formula of the polymeric iron in the intermediate product is Fe4(OH) n Cl 6-n (PO4) 2-n / 3 , wherein 0

[0043] (2) The liquid material is put into

[0044] 8000L of ethanol aqueous solvent (ethanol and water in equal mass ratio) while hot due to the heat generated by the catalytic oxidation reaction, and the polymeric iron in the liquid material is allowed to self-hydrolyze under continuous stirring; the mixture is cooled to room temperature to produce crystallization; and the phosphoric iron product is obtained after filtration and vacuum drying at 105°C for 2h, which meets the product indicators of battery-grade phosphoric iron, and the specific indicators are shown in Table 1.

[0045] Comparative Example 1

[0046] Phosphoric iron prepared by a traditional method:

[0047] 150g of ferrous sulfate (FeSO4·7H2O) is added to 1000mL of water and stirred to dissolve; then 150mL of sodium sulfide solution (50g / L) is added, stirred for 30min (rotation speed 50r / min), and then allowed to stand and filter; and the filtrate is reserved for use;

[0048] 500g of the filtrate (Fe 2+ content 2.3wt%) is taken, 20mL of concentrated phosphoric acid (85wt%) is added, and then stirred for 20min to adjust the pH value to 2.0-2.5; 2g of dodecylbenzenesulfonic acid and 3g of urea are added, 40g of hydrogen peroxide solution (effective content 10%) is added dropwise, allowed to stand for 60min, filtered, washed with a large amount of water, and then vacuum dried at 105°C for 2h; and the comparative example 1 phosphoric iron product is obtained after grinding with a superfine grinder.

[0049] The products of the above examples and comparative example are detected, and the specific results are shown in Table 1.

[0050] Table 1 product testing data of examples and comparative examples

[0051]

[0052]

[0053] As shown in Table 1, the prepared iron phosphate by the method of the present application has the same properties as the iron phosphate prepared by the traditional method; the prepared iron phosphate by the method of the present application has uniform particles, controllable quality, and does not need a large amount of washing water, the method of the present application can avoid using high-risk hydrogen peroxide and has a small risk of secondary pollution, and the prepared iron phosphate meets the battery grade requirements.

[0054] The above description is only the preferred specific implementation of the present application, but the protection scope of the present application is not limited to this, any person skilled in the art can make equivalent replacement or change according to the technical solution and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A process for the preparation of battery grade iron phosphate, characterized in that, The method comprises the following steps: (1) taking the iron-containing hydrochloric acid pickling waste liquid as raw material, which contains 5-8wt% of ferrous iron; adding phosphoric acid solution into the iron-containing hydrochloric acid pickling waste liquid, stirring uniformly, and then transferring to a reaction kettle; adding a catalyst under stirring at room temperature, and then introducing oxygen for catalytic oxidation reaction until the content of ferrous iron in the reaction system is less than 0.03wt%, and then the reaction is ended to obtain a liquid material containing polymeric iron; The mass concentration of the phosphoric acid solution is greater than 30%; The catalyst is a mixed solution of sodium nitrite and nitric acid, wherein the mass fraction of sodium nitrite in the mixed solution is 5%, and the amount of sodium nitrite is 0.5-0.8% of the weight of the iron-containing hydrochloric acid pickling waste liquid; (2) putting the liquid material into an alcohol-water solvent while hot, the alcohol-water solvent is an ethanol-water solvent, the mass fraction of ethanol in the solvent is 50%, and the polymeric iron in the liquid material is self-hydrolyzed under continuous stirring, and then the crystallization is generated after cooling to below room temperature, and the phosphoric iron product is obtained after filtration and drying, which meets the product index of battery-grade phosphoric iron.

2. The method of claim 1, wherein the battery grade iron phosphate is prepared by the steps of: The iron-containing hydrochloric acid pickling waste liquid also contains hydrochloric acid, and the mass fraction of hydrochloric acid in the liquid is 3-5%. ​ 3. The method of claim 1, wherein the battery grade iron phosphate is prepared by the steps of: The mass ratio of the iron-containing hydrochloric acid pickling waste liquid to the phosphoric acid in the phosphoric acid solution is 1:(0.015-0.025). ​ 4. The method of claim 1, wherein the battery grade iron phosphate is prepared by the steps of: The mass fraction of iron in the polymeric iron is greater than 6%, the basicity is greater than 10%, and the mass fraction of ferrous iron in the iron is less than 0.05%. ​ 5. The method of claim 1, wherein the battery grade iron phosphate is prepared by the steps of: The amount of the iron-containing hydrochloric acid pickling waste liquid and the alcohol-water solvent is 1g:10L. ​

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