A method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder

Abstract

This invention belongs to the field of lithium battery recycling and reuse technology, and discloses a method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder, including the following steps: (1) fully contacting lithium iron phosphate battery powder with phosphoric acid in an aqueous solution, stirring at a constant temperature to dissolve lithium iron phosphate, and separating the solid and liquid to obtain a lithium-containing filtrate; (2) adding hydrogen peroxide solution to the lithium-containing filtrate, oxidizing ferrous ions to ferric ions, then adding lithium hydroxide to adjust the pH value, filtering to remove precipitates, and obtaining a filtrate containing lithium dihydrogen phosphate; (3) evaporating and concentrating the filtrate containing lithium dihydrogen phosphate, then slowly cooling and crystallizing, and filtering to obtain crude lithium dihydrogen phosphate; (4) dissolving the crude lithium dihydrogen phosphate, adding phosphoric acid to adjust the pH value of the aqueous solution, evaporating and concentrating to crystallize, filtering to obtain wet lithium dihydrogen phosphate, and finally drying to obtain battery-grade lithium dihydrogen phosphate product. The method of this invention has a short process flow, low production cost, high product yield, is easy to industrialize, and has good economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery recycling and reuse technology, specifically relating to a method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder. Background Technology

[0002] With the development of new energy technologies, new energy vehicles and energy storage equipment are rapidly emerging, leading to a surge in demand for lithium-ion batteries. Lithium iron phosphate (LiFePO4) batteries are widely used due to their low cost, high energy density, and excellent safety performance. However, due to their large-scale use, it is estimated that by 2025, the world will have 1.36 million tons of waste LiFePO4 batteries. If these waste batteries are not effectively disposed of, they will not only result in the loss of significant metal resources but also pollute the environment. Therefore, developing efficient and economical recycling processes for waste LiFePO4 batteries is a global priority.

[0003] Currently, lithium dihydrogen phosphate (LDP) is used as the lithium source for preparing lithium iron phosphate. This avoids the environmental pollution caused by the large amounts of ammonia produced by ammonium dihydrogen phosphate (MDP), while simultaneously providing both lithium and phosphorus sources, exhibiting good process stability and uniformity. However, the traditional preparation process for battery-grade LDP mainly involves neutralization of phosphoric acid and lithium hydroxide, followed by evaporation and crystallization. This process is lengthy and complex, making it difficult to control the quality and yield of the obtained LDP. CN101638225B discloses a method for preparing battery-grade lithium dihydrogen phosphate using lithium carbonate and phosphoric acid as raw materials. CN102351160B discloses a method for preparing battery-grade lithium dihydrogen phosphate using high-purity lithium carbonate precipitation mother liquor. CN103553016B discloses a method for preparing lithium dihydrogen phosphate using lithium hydroxide, ammonium dihydrogen phosphate and polyphosphoric acid as raw materials, and using it as an intermediate product of lithium iron phosphate cathode material. Of the three methods disclosed, the first can be classified as a traditional process route. The second method uses sodium salt in the preparation process to increase the sodium impurity content in the product. The third method is an improvement on the traditional process route, but ammonia gas is generated in the process. In addition, in the prior art, waste lithium iron phosphate battery powder obtained from waste lithium iron phosphate batteries is used as raw material to obtain lithium carbonate and / or iron phosphate through various processes, such as CN113321194B and CN114988382B; while CN116462169A discloses a method for preparing battery-grade lithium dihydrogen phosphate by full element recycling of waste lithium iron phosphate, which has too many process steps, a complicated preparation process, high requirements for operators, and difficulty in controlling the production process. Summary of the Invention

[0004] In view of the technical problems existing in the prior art, the purpose of this invention is to provide a method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder. This method has a high efficiency, short process, low cost, and is environmentally friendly.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder includes the following steps:

[0007] Step (1): Add waste lithium iron phosphate battery powder (60 mesh) to deionized water at a solid-liquid mass ratio of 1:(1-5), and stir thoroughly; then add the powder at a molar ratio of Li... + Add phosphoric acid solution to H3PO4 = 1:(1~6), stir at 25~60℃ for 2~6h, filter, and obtain lithium-containing filtrate and filter residue containing carbon and other insoluble impurities;

[0008] Step (2), according to the molar ratio Fe 2+ The ratio of H2O2 is 1 to 2:1. Add 30 wt% hydrogen peroxide to the lithium-containing filtrate obtained in step (1) to completely oxidize the ferrous ions to ferric ions. Then add lithium hydroxide solution to adjust the pH value to 2 to 3. Aged at 70 to 100°C, filtered to remove impurities such as iron phosphate and aluminum phosphate, to obtain lithium dihydrogen phosphate filtrate.

[0009] Step (3): Heat the lithium dihydrogen phosphate filtrate obtained in step (2) to 120-135°C, evaporate and concentrate until crystals precipitate, then slowly cool to 40°C and cool to crystallize to obtain crude lithium dihydrogen phosphate.

[0010] Step (4): Dissolve crude lithium dihydrogen phosphate in water, add phosphoric acid to adjust the pH to 2-3, filter, heat the filtrate to 120-130℃, evaporate and concentrate until crystals precipitate, then slowly cool to 35-40℃, filter to obtain wet lithium dihydrogen phosphate; after drying, obtain battery-grade lithium dihydrogen phosphate product.

[0011] Preferably, in step (1), the solid-liquid mass ratio of waste lithium iron phosphate battery powder to deionized water is 1:(2-4), more preferably 1:3; Li + The ratio of H3PO4 to phosphoric acid is 1:(2-5), more preferably 1:3; the concentration of the phosphoric acid solution is 85% (mass percentage); the stirring temperature is 25°C and the stirring time is 4 hours.

[0012] Preferably, the aging temperature in step (2) is 90-100℃, and more preferably 100℃.

[0013] Preferably, in step (3), the lithium dihydrogen phosphate filtrate is heated to 125-135°C, preferably 135°C.

[0014] Preferably, the cooling temperature in step (4) is 40°C; the drying temperature is 105-120°C, preferably 105°C.

[0015] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows:

[0016] (1) This invention utilizes waste lithium iron phosphate battery powder to prepare battery-grade lithium dihydrogen phosphate, which is used to produce lithium iron phosphate products with stable quality, thus realizing the resource utilization of waste lithium iron phosphate.

[0017] (2) Compared with the prior art, the present invention directly prepares battery-grade lithium dihydrogen phosphate through acid leaching-iron removal-concentration crystallization. The process route is simple and efficient, avoiding quality and yield losses caused by complex preparation processes. After steps 1 and 2, the lithium dihydrogen phosphate filtrate obtained has an extremely high lithium dihydrogen phosphate content and a very low impurity content. Iron and other metal elements in the waste battery powder are basically removed in the form of precipitation after treatment with hydrogen peroxide solution and lithium hydroxide solution.

[0018] (3) This invention utilizes the solubility of lithium dihydrogen phosphate and the difference in concentration and solubility with other metal salts to prepare lithium dihydrogen phosphate by evaporation and crystallization. In the process, no raw materials containing other metal elements (such as sodium and potassium) or non-metal elements (such as sulfur, chlorine, and nitrogen) are used, which can prevent the introduction of impurities and facilitate the preparation of high-purity lithium dihydrogen phosphate.

[0019] (4) In this invention, the amount of deionized water added and the solid-liquid ratio of the reaction have a significant impact on the reaction and the reaction products. When the liquid-solid ratio is small, the solid products will coat part of the reactants, preventing them from contacting the liquid phase, resulting in an incomplete reaction and a decrease in the lithium leaching rate. When the liquid-solid ratio increases to a certain value, the reaction proceeds fully, and the lithium leaching rate gradually stabilizes. If the solid-liquid ratio is further increased, the amount of wastewater will increase, increasing economic costs. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the present invention. Detailed Implementation

[0021] The present invention will now be described in detail through specific embodiments.

[0022] In each embodiment, the waste lithium iron phosphate battery powder raw material comes from Tianjin Batray Technology Co., Ltd., and the content of each metal element is shown in Table 1.

[0023] Table 1. Content (mass%) of various metal elements in waste lithium iron phosphate battery powder raw materials (60 mesh)

[0024] Li Fe Cu Al Na Ca Ni Co Mn 2.693 23.472 2.076 1.379 0.365 0.075 0.130 0.065 0.391

[0025] Example 1

[0026] A method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder includes the following steps:

[0027] (1) Weigh 300g of lithium iron phosphate battery powder (60 mesh), add it to 900g of deionized water, stir thoroughly, then add 402.7g of 85wt% phosphoric acid, stir at 25℃ for 4h, filter, and obtain lithium-containing filtrate and filter residue (containing carbon powder).

[0028] (2) Add 127g of 30wt% hydrogen peroxide solution to the lithium-containing filtrate, then adjust the pH to 2 with 1mol / L lithium hydroxide solution, age at 90℃, filter to remove impurities such as iron phosphate and aluminum phosphate, and obtain lithium dihydrogen phosphate filtrate.

[0029] (3) Heat the filtrate containing lithium dihydrogen phosphate to 120°C, evaporate and concentrate until crystals precipitate, then slowly cool to 40°C and cool to crystallize to obtain crude lithium dihydrogen phosphate.

[0030] (4) Dissolve crude lithium dihydrogen phosphate in water, add 85 wt% phosphoric acid to adjust the pH to 2, filter, heat the filtrate to 120°C, evaporate and concentrate until crystals precipitate, slowly cool to 40°C, and filter to obtain wet lithium dihydrogen phosphate (this process removes impurities such as copper, sodium, calcium, nickel, cobalt, and manganese); dry at 105°C to obtain battery-grade lithium dihydrogen phosphate. The composition analysis of battery-grade lithium dihydrogen phosphate is shown in Table 2. The product quality meets YS / T 967-2014, and the lithium leaching rate is 98%, with a total recovery rate of 95%.

[0031] Example 2

[0032] A method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder includes the following steps:

[0033] (1) Weigh 300g of lithium iron phosphate battery powder (60 mesh), add it to 900g of deionized water, stir thoroughly, then add 671.2g of 85wt% phosphoric acid, stir at 25℃ for 4h, filter, and obtain lithium-containing filtrate and filter residue (containing carbon powder).

[0034] (2) Add 127g of 30wt% hydrogen peroxide solution to the lithium-containing filtrate, then adjust the pH to 2 with 1mol / L lithium hydroxide solution, age at 90℃, filter to remove impurities such as iron phosphate and aluminum phosphate, and obtain lithium dihydrogen phosphate filtrate.

[0035] (3) Heat the filtrate containing lithium dihydrogen phosphate to 135°C, evaporate and concentrate until crystals precipitate, then slowly cool to 40°C and cool to crystallize to obtain crude lithium dihydrogen phosphate.

[0036] (4) Dissolve crude lithium dihydrogen phosphate in water, add 85 wt% phosphoric acid to adjust the pH to 2, filter, heat the filtrate to 120°C, evaporate and concentrate until crystals precipitate, slowly cool to 40°C, and filter to obtain wet lithium dihydrogen phosphate (this process removes impurities such as copper, sodium, calcium, nickel, cobalt, and manganese); dry at 105°C to obtain battery-grade lithium dihydrogen phosphate. The composition analysis of battery-grade lithium dihydrogen phosphate is shown in Table 2. The product quality meets YS / T 967-2014, and the lithium leaching rate is 97%, with a lithium recovery rate of 96%.

[0037] Example 3

[0038] A method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder includes the following steps:

[0039] (1) Weigh 300g of lithium iron phosphate battery powder (60 mesh), add it to 900g of deionized water, stir thoroughly, then add 402.7g of 85wt% phosphoric acid, stir at 60℃ for 4h, filter, and obtain lithium-containing filtrate and filter residue (carbon powder).

[0040] (2) Add 127g of 30wt% hydrogen peroxide solution to the lithium-containing filtrate, then adjust the pH to 2 with 1mol / L lithium hydroxide solution, age at 90℃, filter to remove impurities such as iron phosphate and aluminum phosphate, and obtain lithium dihydrogen phosphate filtrate.

[0041] (3) Heat the filtrate containing lithium dihydrogen phosphate to 130°C, evaporate and concentrate until crystals precipitate, then slowly cool to 40°C and cool to crystallize to obtain crude lithium dihydrogen phosphate.

[0042] (4) Dissolve crude lithium dihydrogen phosphate in water, add 85 wt% phosphoric acid to adjust the pH to 2, filter, heat the filtrate to 120°C, evaporate and concentrate until crystals precipitate, slowly cool to 40°C, filter to obtain wet lithium dihydrogen phosphate (this process removes impurities such as copper, sodium, calcium, nickel, cobalt, and manganese), and dry at 105°C to obtain battery-grade lithium dihydrogen phosphate product. The composition analysis of the battery-grade lithium dihydrogen phosphate product is shown in Table 2. The product quality meets YS / T 967-2014, and the lithium leaching rate is 97%, and the lithium recovery rate can reach 96%.

[0043] Comparative Example 1

[0044] A method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder includes the following steps:

[0045] (1) Weigh 300g of lithium iron phosphate battery powder (60 mesh), add it to 600g of deionized water, stir thoroughly, then add 402.7g of 85wt% phosphoric acid, stir at 60℃ for 4h, filter, and obtain lithium-containing filtrate and filter residue (containing carbon powder).

[0046] (2) Add 127g of 30wt% hydrogen peroxide solution to the lithium-containing filtrate, then adjust the pH to 2 with 1mol / L lithium hydroxide solution, age at 90℃, filter to remove impurities such as iron phosphate and aluminum phosphate, and obtain lithium dihydrogen phosphate filtrate.

[0047] (3) Heat the filtrate containing lithium dihydrogen phosphate to 130°C, evaporate and concentrate until crystals precipitate, then slowly cool to 40°C and cool to crystallize to obtain crude lithium dihydrogen phosphate.

[0048] (4) Dissolve crude lithium dihydrogen phosphate in water, add 85 wt% phosphoric acid to adjust the pH to 2, filter, heat the filtrate to 120°C, evaporate and concentrate until crystals precipitate, slowly cool to 40°C, filter to obtain wet lithium dihydrogen phosphate; dry at 105°C to obtain battery-grade lithium dihydrogen phosphate product. The composition analysis of battery-grade lithium dihydrogen phosphate is shown in Table 2. The product quality meets YS / T967-2014, the lithium leaching rate is only 75%, and the total yield is 62%.

[0049] Comparative Example 2

[0050] A method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder includes the following steps:

[0051] (1) Weigh 300g of lithium iron phosphate battery powder (60 mesh), add it to 900g of deionized water, stir thoroughly, then add 402.7g of 85wt% phosphoric acid, stir at 25℃ for 4h, filter, and obtain lithium-containing filtrate and filter residue (containing carbon powder).

[0052] (2) Add 127g of 30wt% hydrogen peroxide solution to the lithium-containing filtrate, then adjust the pH to 2 with 1mol / L lithium hydroxide solution, age at 90℃, filter to remove impurities such as iron phosphate and aluminum phosphate, and obtain lithium dihydrogen phosphate filtrate.

[0053] (3) Heat the filtrate containing lithium dihydrogen phosphate to 120°C, evaporate and concentrate until crystals precipitate, then slowly cool to 40°C and cool to crystallize to obtain crude lithium dihydrogen phosphate.

[0054] (4) Dissolve crude lithium dihydrogen phosphate in water, add 85 wt% phosphoric acid to adjust the pH to 2, filter, heat the filtrate to 80°C, evaporate and concentrate until crystals precipitate, slowly cool to 40°C, filter to obtain wet lithium dihydrogen phosphate; dry at 105°C to obtain battery-grade lithium dihydrogen phosphate product. The composition analysis of battery-grade lithium dihydrogen phosphate is shown in Table 2. The product quality does not meet YS / T967-2014, the lithium leaching rate is 97%, and the total recovery rate is 95%.

[0055] Comparative Example 3

[0056] A method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder includes the following steps:

[0057] (1) Weigh 300g of lithium iron phosphate battery powder (60 mesh), add it to 900g of deionized water, stir thoroughly, then add 402.7g of 85wt% phosphoric acid, stir at 25℃ for 4h, filter, and obtain lithium-containing filtrate and filter residue (containing carbon powder).

[0058] (2) Add 127g of 30wt% hydrogen peroxide solution to the lithium-containing filtrate, then adjust the pH to 2 with 1mol / L lithium hydroxide solution, age at 90℃, filter to remove impurities such as iron phosphate and aluminum phosphate, and obtain lithium dihydrogen phosphate filtrate.

[0059] (3) Heat the filtrate containing lithium dihydrogen phosphate to 120°C, evaporate and concentrate until crystals precipitate, then slowly cool to 40°C and cool to crystallize to obtain crude lithium dihydrogen phosphate.

[0060] (4) Dissolve crude lithium dihydrogen phosphate in water, add 85 wt% phosphoric acid to adjust the pH to 2, filter, heat the filtrate to 120°C, evaporate and concentrate until crystals precipitate, slowly cool to 50°C, filter to obtain wet lithium dihydrogen phosphate; dry at 105°C to obtain battery-grade lithium dihydrogen phosphate product. The composition analysis of battery-grade lithium dihydrogen phosphate is shown in Table 2. The product quality basically meets YS / T 967-2014, the lithium leaching rate is 69%, and the total recovery rate is 54%.

[0061] The battery-grade lithium dihydrogen phosphate samples prepared in Examples 1-3 and Comparative Examples 1-3 were analyzed and compared with national standards. The results are shown in Table 2.

[0062] Table 2. Analysis and national standards of battery-grade lithium dihydrogen phosphate samples prepared in Examples 1-3 and Comparative Examples 1-3.

[0063]

[0064] Note: A certain amount of the battery-grade lithium dihydrogen phosphate products obtained in Examples 1-3 and Comparative Examples 1-3 were weighed as samples. Each sample was dried for a sufficient period of time before the contents in the table were measured.

[0065] As can be seen from Table 2, the preparation method of battery-grade lithium dihydrogen phosphate of the present invention is simple, with mild reaction conditions and low production cost. The battery-grade lithium dihydrogen phosphate obtained in Examples 1-3 has high content and low impurity content, meeting the raw material index requirements for lithium-ion battery cathode materials.

[0066] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications that do not depart from the spirit and principle of the present invention should be considered equivalent substitutions and are included within the protection scope of the present invention.

Claims

1. A method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder, characterized in that, Includes the following steps: Step (1): Add the waste lithium iron phosphate battery powder obtained by sieving through a 60-mesh sieve to deionized water at a solid-liquid mass ratio of 1:1-5, and stir thoroughly; then add the powder at a molar ratio of Li... + H3PO4 was added to a phosphoric acid solution at a ratio of 1:(1-6), stirred at 25-60°C for 2-6 hours, and then filtered to obtain a lithium-containing filtrate and a filter residue containing carbon; wherein the concentration of the phosphoric acid solution was 85 wt%. Step (2), according to the molar ratio Fe 2+ The ratio of H2O2 is 1 to 2:

1. 30 wt% hydrogen peroxide is added to the lithium-containing filtrate obtained in step (1) to completely oxidize the ferrous ions to ferric ions. Then, lithium hydroxide solution is added to adjust the pH value to 2 to 3. The filtrate is aged at 70 to 100 °C and filtered to remove impurities, thereby obtaining a lithium dihydrogen phosphate filtrate. The impurities include iron phosphate and aluminum phosphate. Step (3): Heat the lithium dihydrogen phosphate filtrate obtained in step (2) to 120-135 °C, evaporate and concentrate until crystals precipitate, then slowly cool to 40 °C and cool to crystallize to obtain crude lithium dihydrogen phosphate. Step (4): Dissolve crude lithium dihydrogen phosphate in water, add phosphoric acid with a concentration of 85wt% to adjust the pH value to 2-3, filter, heat the filtrate to 120℃, evaporate and concentrate until crystals precipitate, slowly cool to 40℃, filter to obtain wet lithium dihydrogen phosphate; after drying, obtain battery-grade lithium dihydrogen phosphate product.

2. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (1), the solid-liquid mass ratio of waste lithium iron phosphate battery powder and deionized water is 1:(2-4).

3. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (1), Li + H3PO4 is 1:(2-5).

4. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (1), after adding the phosphoric acid solution, the stirring temperature is 25℃ and the stirring time is 4h.

5. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (2), the aging temperature is 90-100℃.

6. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (3), the lithium dihydrogen phosphate filtrate is heated to 125-135℃.

7. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 1, characterized in that: In step (4), the drying temperature is 105~120 ℃.

8. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 2, characterized in that: In step (1), the solid-liquid mass ratio of waste lithium iron phosphate battery powder and deionized water is 1:

3.

9. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 3, characterized in that: In step (1), Li + The ratio of H3PO4 to H3PO4 is 1:

3.

10. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 5, characterized in that: In step (2), the aging temperature is 100℃.

11. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 6, characterized in that: In step (3), the lithium dihydrogen phosphate filtrate is heated to 135°C.

12. The method for preparing lithium dihydrogen phosphate from waste lithium iron phosphate battery powder according to claim 7, characterized in that: In step (4), the drying temperature is 105℃.

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