CN110683526B

CN110683526B - Method for controlling sulfate radical content in battery-grade iron phosphate

Info

Publication number: CN110683526B
Application number: CN201810731556.6A
Authority: CN
Inventors: 司秀荣; 吕霄; 苏亚静; 靳辰辰; 岳世学
Original assignee: Hebei Anz New Energy Technology Co ltd; North China Institute of Aerospace Engineering
Current assignee: Hebei Anz New Energy Technology Co ltd; North China Institute of Aerospace Engineering
Priority date: 2018-07-05
Filing date: 2018-07-05
Publication date: 2023-03-14
Anticipated expiration: 2038-07-05
Also published as: CN110683526A

Abstract

The invention discloses a method for controlling the content of sulfate radicals in battery-grade iron phosphate, which comprises the following steps: 1) Dissolving ferrous salt in phosphoric acid to prepare acid liquor, adding an oxidant into the acid liquor to oxidize to obtain oxidation liquid, wherein the oxidation rate of ferrous ions in the oxidation liquid is controlled to be 75-85%; 2) Adding a surfactant into the oxidizing solution, injecting the oxidizing solution into a reaction kettle, and quickly heating the oxidizing solution in the reaction kettle to 50-60 ℃; 3) Uniformly spraying a pH regulator into the oxidizing liquid in the reaction kettle, controlling the pH value to be 2.0-3.0, and reacting for 4-8 hours to obtain an iron phosphate product; and 4) washing the iron phosphate product with water, performing ultrasonic treatment by using ultrasonic equipment, and performing filter pressing. The method has the advantages of simple operation, low cost, easy industrialization and good sulfate radical removing effect.

Description

Method for controlling sulfate radical content in battery-grade iron phosphate

Technical Field

The invention belongs to the field of new materials, and particularly relates to a method for controlling the content of sulfate radicals in battery-grade iron phosphate.

Background

With the rapid development of new energy industries and power batteries, positive electrode materials of lithium iron phosphate and upstream materials of iron phosphate are being actively developed. The ferric phosphate has better electrochemical performance when being used as a lithium iron phosphate anode material, so that the ferric phosphate becomes a main framework material for producing lithium iron phosphate. At present, the industrial preparation method of iron phosphate is basically divided into a solid phase method and a hydrothermal method. The solid phase method has low synthesis technology cost, but the iron phosphate prepared by the product obtained by the solid phase method has no expected effect on the electrochemical performance. The hydrothermal synthesis method is a mainstream method adopted by various current large factories, raw materials adopted by the hydrothermal method are different, so that the method is slightly different in process production, a ferrous solution is used for oxidation and then is subjected to heating reaction with a phosphorus source, and alkali is used as a pH regulator. Therefore, a method for efficiently removing sulfate from battery grade iron phosphate is needed.

Disclosure of Invention

The technical purpose of the invention is to provide a method for controlling the sulfate radical content in battery-grade iron phosphate, which has the advantages of simple operation, low cost, easy industrialization and good effect.

The invention provides a method for controlling the content of sulfate radicals in battery-grade iron phosphate, which comprises the following steps:

1) Firstly, dissolving phosphoric acid in pure water to prepare a phosphoric acid aqueous solution, dissolving a ferrous salt in the phosphoric acid aqueous solution, adding an oxidant into the phosphoric acid aqueous solution, and oxidizing to obtain an oxidizing solution, wherein the oxidation rate of ferrous ions in the oxidizing solution is controlled to be 75-85%, and preferably 80%;

2) Adding a surfactant into the oxidizing solution, injecting the oxidizing solution into a reaction kettle, and heating the oxidizing solution in the reaction kettle to 50-60 ℃;

3) Uniformly spraying a pH regulator into the oxidizing liquid in the reaction kettle, controlling the pH value range to be 2.0-3.0, preferably 2.5-2.7, and reacting for 4-8 hours to obtain an iron phosphate product; and

4) Cleaning the iron phosphate product by using pure water, carrying out ultrasonic treatment by using ultrasonic equipment, then carrying out filter pressing,

wherein, in the step 1), the oxidation rate of the ferrous ions is calculated by the following formula: w (Fe) ²⁺ )/(w(Fe ³⁺ )+w(Fe ²⁺ ) X 100% where w (Fe) ²⁺ ) Represents Fe in the oxidizing solution ²⁺ Mass concentration of (b), w (Fe) ³⁺ ) Represents Fe in the oxidizing solution ³⁺ The mass concentration of (2).

In one embodiment, in step 1), the phosphoric acid has a concentration of 85 to 87 wt%, and the mass ratio of the phosphoric acid to pure water is 1.

In one embodiment, in step 1), hydrogen peroxide is added in a molar ratio of ferrous salt to hydrogen peroxide of 1.

In one embodiment, in step 2), the surfactant is added in an amount of 0.5 wt% to 2 wt%, preferably 1 wt%, based on the total weight of the oxidizing solution, and the surfactant may be cetyltrimethylammonium bromide (CTAB), PEG-20000, or the like.

In one embodiment, in step 2), the volume of the oxidizing liquid injected into the reaction tank is not more than 1/2 of the volume of the reaction tank, preferably 1/3 of the volume of the reaction tank.

In one embodiment, in step 2), the temperature increase rate of the oxidizing solution in the reaction kettle is 0.2 ℃/min to 1.5 ℃/min, preferably 1 ℃/min.

In one embodiment, in step 3), the pH adjuster may be a sodium hydroxide solution or an aqueous ammonia solution, preferably an aqueous ammonia solution with a mass concentration of 6% to 8%, and the pH adjuster is added as follows: and immersing the outlet of the pipeline which is filled with the pH regulator into the oxidation liquid within 3-5cm below the liquid level, and uniformly spraying the pH regulator into the oxidation liquid in a spraying mode.

In one embodiment, in step 4), the iron phosphate product is washed with hot water at a temperature of 80 ℃ or more and 100 ℃ or less, preferably 85 ℃.

In one embodiment, in step 4), the iron phosphate product is sonicated with a sonication device having a power range of 3000-7200w, preferably 5000w, for a sonication time of 10-30 minutes, preferably 20 minutes.

In one embodiment, in step 4), an organic acid or an auxiliary additive having an anion adsorbing function may be added, wherein the organic acid is oxalic acid, citric acid, fruit acid, or the like, and the auxiliary additive having an anion adsorbing function is poly-m-phenylenediamine.

The method of the invention has the following beneficial effects:

1. in the oxidation process, the oxidation rate of ferrous ions in the ferrous salt solution is controlled, and the mode is favorable for improving the reaction rate, shortening the first nucleation time of the product and effectively reducing sulfate radicals entering the product by controlling the coexistence proportion of the ferrous ions and the ferric ions in the oxidation solution.

2. The surfactant can increase the dispersion effect of the oxidation liquid, so that the reaction product particles are uniformly dispersed and are not easy to be violently increased, thereby effectively inhibiting sulfate radicals from being violently wrapped in the product and directly reducing the sulfate radical content.

3. The temperature of the oxidizing solution is quickly raised to 60 ℃, and then the pH regulator is added, so that the situation that sulfate radicals are continuously wrapped in a product due to reaction during the temperature raising period can be effectively avoided, when the reaction temperature is lower than 50 ℃, the reaction is slow, the industrialization is not facilitated, when the reaction temperature is higher than 70 ℃, the reaction is too violent, the operation control is not facilitated, and in addition, the first nucleation in the reaction is violent, so that the sulfate radical content is increased.

4. The outflow port of the pipeline which is communicated with the pH regulator is immersed into the oxidation liquid and is uniformly sprayed in a spraying mode, so that the reaction can be effectively controlled, the nucleation of the product is uniform, the reaction is not caked, the sulfate radical content is indirectly reduced, and the uniformity of the product can be improved.

5. The product is cleaned by hot water and ultrasonic equipment, so that sulfate radicals can be effectively removed from the product, and the sulfate radical content in the product is directly reduced.

Drawings

FIG. 1 shows the reaction temperatures at 50 ℃, 60 ℃ and 70 ℃ and the sulfate content of the product with different oxidation rates for ferrous ions.

FIG. 2 shows the comparison of the sulfate content in the reaction product after washing with washing water of different water temperatures.

Figure 3 shows the sulfate content in the product after the addition of no surfactant (i.e., 0.0%) and the addition of the surfactants CTAB (0.5%, 0.8%,1.0%, and 2.0%, based on weight percent).

Figure 4 shows the comparison of the sulphate content in the product after washing the product with different ultrasound powers and ultrasound times by means of an ultrasound device.

Figure 5 is a graph comparing sulfate ion content of iron phosphate prepared according to the methods of the present application and commercially available iron phosphate products (a and B).

Detailed Description

The present invention will be described in detail with reference to the following embodiments.

In the following examples, the sulfate content of the product was determined using an infrared carbon sulfur instrument. The method for measuring iron and ferrous ions in the oxidizing solution is as follows:

and (3) measuring the content of Fe in the oxidizing solution:

1. the sieved sample was weighed to the nearest 0.0002g. Placed in a 250ml beaker, moistened with a small amount of water, 25ml of hydrochloric acid is added, the petri dish is covered and the solution is added in a fume hood at low temperature. Washing the surface dish with a small amount of water, cooling, filtering with slow filter paper, washing the filter residue with water for 5-7 times, transferring the filtrate to a 250ml volumetric flask, diluting to scale, and shaking up. This was test solution A, ready for use.

2. 15ml of test solution A are pipetted out and placed in a 250ml conical flask, 5ml of hydrochloric acid are added and the flask is heated to boiling. While the flask was shaken while hot, the stannous chloride solution was added dropwise until the solution changed from brown to light yellow (if the solution became colorless upon addition, hydrogen peroxide was added dropwise until the solution became light yellow). Adding 4-5 drops of sodium tungstate indicator solution, and adding titanium trichloride solution drop by drop while shaking until the solution is light blue. Immediately cooled with running water, 50ml of water were added and the solution was titrated with a potassium dichromate-labeled titration solution until the blue color just faded. Adding water to dilute to 100ml, adding 10ml of sulfuric acid-phosphoric acid mixed solution and 3-4 drops of sodium diphenylaminesulfonate indicator solution, and titrating with a potassium dichromate standard titration solution until stable mauve (30 s does not disappear) is obtained. Meanwhile, a blank test is carried out, and the blank test solution is not added with a sample, and other operations and added reagents are the same as the solution.

And 3. A calculation formula of the Fe content w:

in the formula:

v ₀ titration of blank solution to consumption of standard titration solution of potassium dichromate in mL

v ₁ Titration of the test solution to the volume of standard titration solution of potassium dichromate in mL

c-accurate value of concentration of standard titration solution of potassium dichromate, unit is mol/L

m-mass of sample in g

M-molar mass number of iron, in g/mol (M = 55.85)

Fe in oxidizing solution ²⁺ The content determination of (A):

1. weighing the oxidation solution, adding 10mL of sulfuric acid and 4mL of phosphoric acid in sequence, titrating with a potassium permanganate solution, and observing color change while shaking until the solution becomes stable pale pink (30 s fastness), and reading the volume titrated by the potassium permanganate.

2. The calculation formula is as follows:

in the formula:

c-potassium permanganate concentration in mol/L

v-volume of potassium permanganate standard titration solution consumed by titration test solution, and unit is mL

m-weighing the mass of the oxidizing solution in g

Example 1 reaction temperature and Fe ²⁺ Effect of Oxidation Rate on sulfate content of the product

103.35g phosphoric acid with 85% concentration is slowly added into 1261.35g pure water to prepare acid liquor. Weighing 250g of ferrous sulfate heptahydrate, uniformly stirring and dissolving in the acid liquor, dividing the solution into 6 parts, respectively adding 43.38g, 45.65g, 47.5g, 48.9g, 50.45g and 60.75g of hydrogen peroxide with the concentration of 25%, fully oxidizing to prepare 6 oxidation solutions, controlling the oxidation rate of iron ions in the 6 oxidation solutions to be 70%,75%,80%,85%,90% and 95%, respectively, injecting the oxidation solutions into a reaction kettle until the injection amount reaches one third of the volume of the reaction kettle, respectively raising the temperature of the oxidation solutions to 50 ℃, 60 ℃ and 70 ℃, uniformly spraying an ammonia water solution with the concentration of 6-8% into the oxidation solutions, controlling the pH to be 2.7, reacting for 4-8 hours, cleaning with pure water with the resistivity of less than 20M omega cm (25 ℃), and carrying out filter pressing. And (4) carrying out high-temperature dehydration treatment on the product to obtain a final product.

As shown in fig. 1, when the temperature of the oxidizing solution is heated to 50 ℃ and 60 ℃, the content of sulfate radicals in the product is basically consistent, but the reaction rate is slow due to low temperature, which affects the industrial production efficiency. In addition, when the oxidation rate of ferrous ions is 75-85%, the sulfate content in the product is low. And at an oxidation rate of 80%, the sulfate content in the product was as low as 0.0125% by weight.

Example 2 Effect of wash Water temperature on sulfate content in product

Firstly, 20.67g of phosphoric acid with the concentration of 85 percent is slowly added into 252.27g of pure water to prepare acid liquor. Weighing 50g of ferrous sulfate heptahydrate, uniformly stirring and dissolving in the acid liquor, adding 20.8g of hydrogen peroxide with the concentration of 25%, fully oxidizing to obtain an oxidizing solution, controlling the oxidation rate of ferrous ions to be 80%, injecting the oxidizing solution into a reaction kettle until the injection amount reaches one third of the volume of the reaction kettle, rapidly heating the oxidizing solution in the reaction kettle to 60 ℃, uniformly spraying a pH regulator into the oxidizing solution, controlling the pH to be 2.7, reacting for 4-8 hours, cleaning by adopting cleaning water with different temperatures, and performing filter pressing. And (4) carrying out high-temperature dehydration treatment on the product to obtain a final product.

As shown in FIG. 2, the product washed with 85 ℃ washing water had a low sulfate content.

Example 3 Effect of surfactant (CTAB) content on sulfate content in the product

Firstly, 20.67g of phosphoric acid with the concentration of 85 percent is slowly added into 252.27g of pure water to prepare acid liquor. Weighing 50g of ferrous sulfate heptahydrate, uniformly stirring and dissolving in the acid liquor, adding 20.8g of hydrogen peroxide with the concentration of 25%, fully oxidizing to obtain an oxidizing solution, controlling the oxidation rate of ferrous ions to be 80%, adding a surfactant CTAB into the oxidizing solution, controlling the adding proportion to be 0.5-2 wt%, injecting the solution into a reaction kettle until the injection amount reaches one third of the volume of the reaction kettle, quickly heating the oxidizing solution in the reaction kettle to 60 ℃, uniformly spraying a pH regulator into the oxidizing solution, controlling the pH to be 2.7, reacting for 4-8 hours, cleaning with 85 ℃ cleaning water, and performing filter pressing. And (4) carrying out high-temperature dehydration treatment on the product to obtain a final product.

As shown in fig. 3, compared with the case of not adding the surfactant, the product obtained after adding the surfactant has a significantly lower sulfate content, and the surfactant in different proportions can reduce the sulfate content in the product, and the 1% and 2% addition have substantially the same effect on the sulfate content in the product, and considering the cost and the ease of operation, the more the surfactant is added, the more the foam is in the cleaning process, and the addition proportion is preferably 1 wt%.

Example 4 Effect of ultrasound Power and ultrasound time on sulfate content in products

The oxidation rate of ferrous ions was controlled to 80% in the same manner as in example 3, at this time, surfactant CTAB was added to the oxidizing solution in a weight ratio of 1 wt%, the above solution was injected into the reaction vessel in an amount of one third of the volume of the reaction vessel, and the oxidizing solution in the reaction vessel was rapidly heated to 60 ℃, at this time, pH adjuster was uniformly sprayed into the oxidizing solution and pH was controlled to 2.7, and after 4 to 8 hours of reaction, washing was performed by using washing water at 85 ℃, and after treatment by an ultrasonic device, press-filtering was performed. And (4) carrying out high-temperature dehydration treatment on the product to obtain a final product.

As shown in fig. 4, the sulfate content in the product is further reduced after the reactants are subjected to ultrasonic treatment, and the preferred ultrasonic treatment conditions are as follows: the ultrasonic power is 5000w, and the ultrasonic treatment is carried out for 20 minutes.

In summary, iron phosphate was prepared under the following conditions: the oxidation rate is 80%, the reaction temperature is 60 ℃, the CTAB content is 1%, the cleaning water temperature is higher than 80 ℃, the ultrasonic power and time are 5000w and 20 minutes respectively, and the sulfate radical content in the product can be as low as 0.0083 weight percent.

In addition, as shown in fig. 5, among the iron phosphate products obtained by the prior art in which sulfate groups are removed by pure water cleaning, for example, a battery-grade iron phosphate product (commercially available product a) produced by the new energy science and technology development limited company of hubei Mo Run in 2017 and a battery-grade iron phosphate product (commercially available product B) produced by the crambe aesculus science and technology limited company in 2017 in 10, the sulfate content was about 0.023% to 0.029%, while the sulfate content in the iron phosphate obtained in example 4 of this application was less than 0.015%. The process of the present invention can therefore control the sulfate ion of the iron phosphate product to a very low level compared to the prior art.

The scope of the present invention is not limited to the above embodiments, and includes all the contents of the claims, and those skilled in the art can implement all the contents of the claims from the above embodiments.

Claims

1. A method of controlling sulfate content in battery grade iron phosphate, comprising the steps of:

1) Firstly, dissolving phosphoric acid in pure water to prepare a phosphoric acid aqueous solution, dissolving a ferrous salt in the phosphoric acid aqueous solution, adding an oxidant into the phosphoric acid aqueous solution, and oxidizing to obtain an oxidizing solution, wherein the oxidation rate of ferrous ions in the oxidizing solution is controlled to be 75-85%;

3) Uniformly spraying a pH regulator into the oxidizing liquid in the reaction kettle, controlling the pH value within the range of 2.0-3.0, and reacting for 4-8 hours to obtain an iron phosphate product;

wherein, in the step1) Wherein the oxidation rate of the divalent iron ions is calculated by the following formula: w (Fe) ²⁺ )/(w(Fe ³⁺ )+w(Fe ²⁺ ) 100% of w (Fe) ²⁺ ) Represents Fe in the oxidizing solution ²⁺ Mass concentration of (1), w (Fe) ³⁺ ) Represents Fe in the oxidizing solution ³⁺ Mass concentration of (2).

2. The method according to claim 1, wherein in step 1), the oxidation rate of divalent iron ions in the oxidizing solution is controlled to 80%.

3. The method according to claim 1, wherein, in step 3), the pH is controlled to be in the range of 2.5-2.7.

4. The method according to claim 1, wherein in the step 1), the phosphoric acid concentration is 85-87 wt%, the mass ratio of the phosphoric acid concentration to the added pure water is 1; the ferrous salt is ferrous sulfate heptahydrate in solid form, the molar ratio of phosphoric acid to the ferrous salt is 1:1, and the oxidizing agent is hydrogen peroxide.

5. The process according to claim 4, wherein in step 1), hydrogen peroxide is added in a molar ratio of ferrous salt to hydrogen peroxide of 1.

6. The method according to claim 1, wherein, in step 2), the surfactant is added in an amount of 0.5-2 wt% based on the total weight of the oxidizing solution, and the surfactant is cetyltrimethylammonium bromide or PEG-20000.

7. The method as claimed in claim 1, wherein, in the step 2), the surfactant is added in an amount of 1 wt% based on the total weight of the oxidizing solution.

8. The method according to claim 1, wherein, in the step 2), the volume of the oxidizing liquid injected into the reaction tank is not more than 1/2 of the volume of the reaction tank.

9. The method as claimed in claim 1, wherein, in the step 2), the volume of the oxidizing liquid injected into the reaction tank is 1/3 of the volume of the reaction tank.

10. The method according to claim 1, wherein, in step 3), the pH adjuster is an aqueous sodium hydroxide solution or an aqueous ammonia solution, and is added in the following manner: and immersing the outlet of the pipeline which is filled with the pH regulator into the oxidation liquid within 3-5cm below the liquid level, and uniformly spraying the pH regulator into the oxidation liquid in a spraying mode.

11. The method according to claim 1, wherein in the step 3), the pH regulator is an aqueous ammonia solution with a mass concentration of 6-8%.

12. The method according to claim 1, wherein in step 4), the iron phosphate product is washed with hot water at a temperature of 80 ℃ or more and 100 ℃ or less.

13. The method according to claim 1, wherein in step 4), the iron phosphate product is washed with hot water at a temperature of 85 ℃.

14. The method according to claim 1, wherein in step 4) the iron phosphate product is sonicated with an ultrasonic device having a power range of 3000-7200w for a sonication time of 10-30 minutes.

15. The method according to claim 1, wherein in step 4) the iron phosphate product is sonicated with an ultrasonic device at a power of 5000w for a sonication time of 20 minutes.

16. The method according to claim 1, wherein, in step 4), an organic acid or an auxiliary additive having an anion-adsorbing function is added.

17. The method according to claim 16, wherein the organic acid is one selected from oxalic acid, citric acid or fruit acid, and the auxiliary additive having an anion adsorbing function is poly-m-phenylenediamine.