Method for synchronously realizing selective extraction of lithium and direct regeneration of iron phosphate

Abstract

The present application relates to waste lithium ion battery material recycling and regeneration technical field, especially to a kind of method for simultaneously realizing lithium selective extraction and direct regeneration of iron phosphate.The method includes the following steps: providing the positive pole powder of waste iron lithium phosphate battery;Hydrogen bond donor and hydrogen bond acceptor are mixed, heated and stirred to obtain eutectic solvent, hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid, citric acid, hydrogen bond acceptor is ethylene glycol;The eutectic solvent is diluted with water, then the positive pole powder and oxidizing agent are added, heated and stirred, filtered to obtain lithium-containing leaching solution and leaching residue;Lithium-containing leaching solution is treated by concentration and impurity removal, then saturated sodium carbonate solution is added to carry out lithium precipitation reaction to obtain lithium carbonate;The leaching residue is calcined to obtain iron phosphate.The present application uses specific eutectic solvent to treat the positive pole powder of waste iron lithium phosphate battery, and lithium selective extraction and direct regeneration of iron phosphate can be simultaneously realized under mild conditions.

Description

Technical Field

[0001] This invention relates to the field of waste lithium-ion battery material recycling and regeneration technology, and in particular to a method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate. Background Technology

[0002] With the rapid development of the new energy vehicle industry, the large-scale recycling of spent lithium-ion batteries has become a global focus. Lithium iron phosphate (LFP) batteries dominate the market due to their high safety and long cycle life, but the efficient recovery of lithium from their cathode materials and the resource utilization of the iron phosphate framework still face technological bottlenecks. In traditional recycling processes, hydrometallurgical methods often use strong acids (such as sulfuric acid and hydrochloric acid) to leach metal ions. This presents problems such as acid mist volatilization and equipment corrosion, and requires the addition of reducing agents (such as hydrogen peroxide and sodium sulfite) to destroy the olivine structure of lithium iron phosphate, resulting in complex processes and high wastewater treatment costs. While pyrometallurgical methods can achieve large-scale processing, high-temperature calcination easily causes phase transformation deactivation of iron phosphate, making it difficult to directly reuse as a precursor, thus limiting economic viability.

[0003] In recent years, eutectic solvents (DES) have been explored for use in battery recycling due to their low toxicity and high designability. However, while existing DES technologies can selectively extract lithium, they disrupt the ferric phosphate framework, and the reactions require high temperatures (>80°C) or prolonged stirring, resulting in high energy consumption. Furthermore, traditional processes for separating lithium from iron and phosphorus often rely on multi-stage extraction or precipitation, which is cumbersome and leads to high metal loss rates. Therefore, there is a need to develop a green, efficient, and novel recycling technology that can simultaneously achieve selective lithium extraction and direct regeneration of ferric phosphate. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate, aiming to solve the problem that existing methods cannot simultaneously achieve selective lithium extraction and direct regeneration of iron phosphate.

[0005] The technical solution of the present invention is as follows:

[0006] This invention provides a method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate, comprising:

[0007] Step S1: Provide cathode powder from waste lithium iron phosphate batteries;

[0008] Step S2: Mix the hydrogen bond donor and the hydrogen bond acceptor, heat and stir to obtain a eutectic solvent. The hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid, and citric acid. The hydrogen bond acceptor is ethylene glycol.

[0009] Step S3: Dilute the eutectic solvent obtained in step S2 with water to obtain diluted eutectic solvent, then add the positive electrode powder and oxidant from step S1, heat and stir, filter to obtain lithium-containing leachate and leachate residue.

[0010] Step S4: The lithium-containing leachate obtained in step S3 is concentrated and impurity removed, and then a saturated sodium carbonate solution is added to carry out a lithium precipitation reaction to obtain lithium carbonate.

[0011] Step S5: The leaching residue obtained in step S3 is calcined to obtain ferric phosphate.

[0012] Optionally, in step S2, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:0.5~1.2.

[0013] Optionally, in step S2, the heating temperature for mixing and stirring is 25℃~80℃, and the heating time is 30min~60min.

[0014] Optionally, in step S3, the mass fraction of the diluted eutectic solvent is 1wt% to 20wt%; the mass ratio of the cathode powder to the diluted eutectic solvent is 1:5 to 20; the oxidant is 10wt% to 30wt% hydrogen peroxide, and the amount of hydrogen peroxide added is 5vol% to 15vol%.

[0015] Optionally, in step S3, the heating temperature for heating and stirring is 60℃~90℃, and the heating time is 60min~120min.

[0016] Optionally, in step S4, the concentration process specifically includes: concentrating the lithium-containing leachate obtained in step S3 to a concentration of 18 g / L to 30 g / L;

[0017] The impurity removal process specifically includes: adjusting the pH value to 10-12 using a 5wt%~10wt% sodium hydroxide solution for impurity removal.

[0018] Optionally, in step S4, the mass fraction of the saturated sodium carbonate solution is 25wt%~30wt%, and the amount of saturated sodium carbonate solution added satisfies the molar ratio of carbonate ions to lithium ions in the lithium-containing leachate being 0.6~0.75:1;

[0019] The lithium precipitation reaction is carried out at a temperature of 90℃~95℃ for 1h~3h.

[0020] Optionally, in step S5, the calcination temperature is 600℃~800℃, the calcination time is 3h~6h, and the calcination atmosphere is air.

[0021] Optionally, step S5 is followed by step S6: mixing the lithium carbonate obtained in step S4 and the iron phosphate obtained in step S5 with a carbon source, ball milling, and calcining to obtain lithium iron phosphate.

[0022] Optionally, in step S6, the molar ratio of lithium carbonate to iron phosphate is 0.5~0.6:1.

[0023] Optionally, the carbon source is glucose, and the amount of glucose added is 10wt% to 15wt% of the mass of the iron phosphate.

[0024] Optionally, in step S6, the calcination temperature is 350℃~800℃, the calcination time is 8h~12h, and the calcination atmosphere is argon.

[0025] Beneficial effects: (1) The method provided by this invention can simultaneously achieve selective lithium extraction and direct regeneration of iron phosphate, thereby obtaining battery-grade lithium carbonate and battery-grade lithium iron phosphate, forming a closed-loop recycling path of "leaching-regeneration". In addition, the method of this invention has the advantages of being green and environmentally friendly, low cost, efficient separation of lithium and iron, and high added value of products, and has a good application prospect. (2) This invention uses a specific low eutectic solvent to treat the cathode powder of waste lithium iron phosphate batteries. Under mild conditions, selective lithium extraction can be achieved, while maintaining the integrity of the iron phosphate skeleton. The leaching residue can be directly reused as an iron phosphate precursor. That is, high-value iron phosphate can be obtained simultaneously during the selective lithium extraction process, eliminating the iron reduction-re-oxidation step in the traditional process and simplifying the recycling process. (3) This invention uses a specific low eutectic solvent as the leaching medium. The solvent has good biodegradability, is green and environmentally friendly, avoids the harmful gas emissions of the traditional strong acid system, and does not require a high-pressure environment in the reaction. It has low energy consumption, is compatible with existing hydrometallurgical equipment, and can be rapidly promoted to the industrial level without modifying the production line. Attached Figure Description

[0026] Figure 1 The present invention provides a flowchart of a method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate.

[0027] Figure 2 The XRD pattern of ferric phosphate obtained in step (5) of Examples 1-3 is shown. Detailed Implementation

[0028] This invention provides a method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0029] like Figure 1 As shown, this embodiment of the invention provides a method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate, comprising:

[0030] Step S1: Provide cathode powder from waste lithium iron phosphate batteries;

[0031] Step S2: Mix the hydrogen bond donor and the hydrogen bond acceptor, heat and stir to obtain a eutectic solvent. The hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid, and citric acid. The hydrogen bond acceptor is ethylene glycol.

[0032] Step S3: Dilute the eutectic solvent obtained in step S2 with water to obtain diluted eutectic solvent, then add the positive electrode powder and oxidant from step S1, heat and stir, filter to obtain lithium-containing leachate and leachate residue.

[0033] Step S4: The lithium-containing leachate obtained in step S3 is concentrated and impurity removed, and then a saturated sodium carbonate solution is added to carry out a lithium precipitation reaction to obtain lithium carbonate.

[0034] Step S5: The leaching residue obtained in step S3 is calcined to obtain ferric phosphate.

[0035] This invention employs a specific eutectic solvent as the leaching medium to treat the cathode powder of spent lithium iron phosphate batteries. The resulting lithium-containing leachate is concentrated, impurity-removed, and then subjected to a lithium precipitation reaction in a saturated sodium carbonate solution to obtain battery-grade lithium carbonate. Simultaneously, the leaching residue retains the intact iron phosphate framework and can be directly reused as an iron phosphate precursor. Calcination yields high-value-added iron phosphate. Thus, selective extraction of lithium and direct regeneration of iron phosphate from spent lithium iron phosphate battery cathode materials are achieved under mild conditions. The method provided by this invention offers advantages such as simplified process, environmental friendliness, low cost, efficient lithium-iron separation, and high-value-added products, demonstrating promising application prospects.

[0036] In some implementations, step S1 specifically includes:

[0037] S11. After the waste lithium iron phosphate battery is fully discharged, it is disassembled, dried and cooled to obtain the positive electrode sheet.

[0038] S12. The positive electrode sheet is immersed in pure water at 25℃~60℃ for peeling to obtain positive electrode material and aluminum foil; the positive electrode material is dried, crushed and sieved to obtain positive electrode powder.

[0039] In some embodiments, in step S2, the hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid, and citric acid, and the hydrogen bond acceptor is ethylene glycol. The eutectic solvent obtained by mixing the hydrogen bond donor and acceptor avoids the iron-containing acidic waste liquid or hazardous HF gas generated by traditional acid leaching, and has the advantages of high biodegradability and environmental friendliness. The phosphate or carboxylic acid groups of polydentate ligands such as phytic acid and citric acid can preferentially bond with Li through the lone pair electrons of the oxygen atom. + Stable coordination is formed, while iron (Fe) 3+ / Fe 2+ Due to its larger ionic radius and different electronic configuration, lithium is more likely to form FePO4 precipitate at a specific pH, thus achieving selective leaching of lithium. The Li in the leachate... + Lithium carbonate can be obtained through a precipitation reaction involving evaporation and concentration. Furthermore, by adjusting the ratio of hydrogen bond donors such as formic acid / phytic acid, the pH of the solvent system can be precisely controlled (1.5~3.5). Within this range, the Li-O bonds in LiFePO4 break, while the Fe-PO4 lattice remains stable, preventing excessive dissolution of iron. Additionally, hydrogen bond donors in the eutectic solvent (such as citric acid and formic acid) can suppress impurity ions (Al). 3+ Cu 2+ Co-precipitation simplifies subsequent purification steps.

[0040] In some embodiments, in step S2, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:0.5 to 1.2, for example, it can be 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.1, 1:1.2, etc., preferably 1:0.8 to 1.0. Eutectic solvents obtained within this molar ratio range have low viscosity, good stability, and can be recycled multiple times.

[0041] In some embodiments, in step S2, the heating temperature for mixing and heating is 25°C to 80°C (e.g., 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, etc.), and the heating time is 30 min to 60 min (e.g., 30 min, 40 min, 50 min, 60 min, etc.).

[0042] In some embodiments, in step S3, the mass fraction of the diluted eutectic solvent is 1wt% to 20wt% (e.g., 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 15wt%, 20wt%). Diluting the eutectic solvent obtained in step S2 with water can control its viscosity and save costs.

[0043] In some embodiments, in step S3, the mass ratio of the positive electrode powder to the diluted eutectic solvent is 1:5 to 20 (e.g., 1:5, 1:10, 1:15, 1:20, etc.). Within this mass ratio range, the lithium-ion leaching rate can reach 99%, while the iron leaching rate is less than 1%, achieving selective leaching of lithium ions.

[0044] In some embodiments, in step S3, the oxidant is 10wt%~30wt% hydrogen peroxide (e.g., 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, etc.), and the amount of hydrogen peroxide added is 5vol%~15vol% (e.g., 5vol%, 6vol%, 7vol%, 8vol%, 9vol%, 10vol%, 11vol%, 12vol%, 13vol%, 14vol%, 15vol%). The role of the hydrogen peroxide oxidant is to regulate the pH value, oxidize the divalent iron in lithium iron phosphate to trivalent iron, and combine with phosphate to form iron phosphate precipitate.

[0045] In some embodiments, in step S3, the heating temperature for heating and stirring is 60℃~90℃ (e.g., 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, etc.), and the heating time is 60min~120min (e.g., 60min, 70min, 80min, 90min, 100min, 110min, 120min, etc.). Under these heating and stirring conditions, the leaching effect of valuable metals is better.

[0046] In some implementations, step S3 specifically includes:

[0047] The eutectic solvent obtained in step S2 is diluted with water to a mass fraction of 1wt%~20wt%, and then the cathode powder from step S1 and 10wt%~30wt% hydrogen peroxide are added. The mass ratio of cathode powder to diluted eutectic solvent is 1:5~20, and the amount of hydrogen peroxide added is 5vol%~15vol%. The mixture is heated and stirred at 60℃~90℃ for 60min~120min. After filtration, lithium-containing leachate and leachate residue are obtained.

[0048] In some embodiments, step S4, the concentration process specifically includes: concentrating the lithium-containing leachate obtained in step S3 to a concentration of 18 g / L to 30 g / L; the impurity removal process specifically includes: adjusting the pH value to 10 to 12 using 5 wt% to 10 wt% sodium hydroxide for impurity removal. The purpose of the concentration process is to allow lithium ions to undergo a lithium precipitation reaction, as a low lithium ion concentration in the leachate will prevent the lithium ion from reacting with the saturated sodium carbonate solution. The purpose of the impurity removal process is to remove trace amounts of impurity ions such as aluminum and copper ions that may be present in the leachate, ensuring the acquisition of high-purity lithium carbonate.

[0049] In some embodiments, in step S4, the mass fraction of the saturated sodium carbonate solution is 25wt%~30wt% (e.g., 25wt%, 26wt%, 27wt%, 28wt%, 29wt%, 30wt%, etc.). The saturated sodium carbonate solution can undergo a lithium precipitation reaction with lithium ions in the lithium-containing leachate to obtain battery-grade lithium carbonate.

[0050] In some embodiments, in step S4, the amount of saturated sodium carbonate solution added satisfies the molar ratio of carbonate ions to lithium ions in the lithium-containing leachate being 0.6~0.75:1.

[0051] In some embodiments, in step S4, the reaction temperature of the lithium precipitation reaction is 90℃~95℃ (90℃, 91℃, 92℃, 93℃, 94℃, 95℃, etc.), and the reaction time is 1h~3h (e.g., 1h, 2h, 3h, etc.). Under these lithium precipitation reaction conditions, lithium carbonate with high recovery rate can be obtained.

[0052] In some implementations, step S4 specifically includes:

[0053] The lithium-containing leachate obtained in step S3 is concentrated to a concentration of 18 g / L to 30 g / L. Then, the pH value is adjusted to 10 to 12 using a 5 wt% to 10 wt% sodium hydroxide solution to remove impurities. Next, a 25 wt% to 30 wt% saturated sodium carbonate solution is added to carry out a lithium precipitation reaction at a temperature of 90℃ to 95℃ for 1 h to 3 h to obtain lithium carbonate.

[0054] In some embodiments, step S5 specifically includes: calcining the leaching residue obtained in step S3 at 600℃~800℃ for 3h~6h to obtain ferric phosphate.

[0055] In this embodiment, the purpose of calcination is to burn off the residual carbon in the leaching residue to obtain pure iron phosphate.

[0056] In some embodiments, in step S5, the calcination temperature is 600℃~800℃ (e.g., 600℃, 650℃, 700℃, 750℃, 800℃, etc.), the calcination time is 3h~6h (e.g., 3h, 4h, 5h, 6h, etc.), and the calcination atmosphere is air.

[0057] In some embodiments, step S5 is followed by step S6: mixing the lithium carbonate obtained in step S4 and the iron phosphate obtained in step S5 with a carbon source, ball milling, and calcining to obtain lithium iron phosphate.

[0058] In some embodiments, step S6 specifically includes: mixing and ball-milling the lithium carbonate obtained in step S4 and the iron phosphate obtained in step S5 with a carbon source, and calcining at 350°C to 800°C for 8 to 12 hours to obtain lithium iron phosphate.

[0059] In this embodiment, ball milling makes the materials more uniformly mixed, and calcination allows lithium carbonate, iron phosphate, and carbon source to be mixed at high temperature to obtain lithium iron phosphate.

[0060] In some embodiments, in step S6, the molar ratio of lithium carbonate to iron phosphate is 0.5~0.6:1.

[0061] In some embodiments, in step S6, the carbon source is glucose, and the amount of glucose added is 10wt% to 15wt% of the mass of the iron phosphate.

[0062] In some embodiments, in step S6, the calcination temperature is 350℃~800℃ (e.g., 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, etc.), the calcination time is 8h~12h (e.g., 8h, 9h, 10h, 11h, 12h, etc.), and the calcination atmosphere is argon.

[0063] The present invention will be further described below through specific embodiments.

[0064] Example 1

[0065] This embodiment provides a method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate, including the following steps:

[0066] (1) After the waste lithium iron phosphate battery is fully discharged, it is disassembled, dried and cooled to obtain a positive electrode sheet; the positive electrode sheet is soaked in pure water at 60°C for 2 minutes to peel off, and positive electrode material and aluminum foil are obtained; the positive electrode material is dried at 80°C, crushed by a crusher after drying, and then screened with a 200-mesh sieve to obtain 200-mesh positive electrode powder.

[0067] (2) Mix formic acid and ethylene glycol in a molar ratio of 1:1 and heat and stir at 60°C for 30 min to obtain a eutectic solvent.

[0068] (3) Dilute the eutectic solvent obtained in step (2) with water to a mass fraction of 3wt%, add the 200 mesh positive electrode powder in step (1) to the diluted eutectic solvent, wherein the mass ratio of the positive electrode powder to the diluted eutectic solvent is 1:10, then add 6 vol% of hydrogen peroxide with a mass fraction of 30wt% for oxidation, heat and stir at 60℃ for 120 min, and filter to obtain lithium-containing leachate and leachate residue.

[0069] (4) The lithium-containing leachate obtained in step (3) is concentrated to a concentration of 20 g / L, and then the pH value is adjusted to 12 using 10 wt% sodium hydroxide solution to remove impurities. Then, 25 wt% saturated sodium carbonate solution is added to carry out the lithium precipitation reaction. The amount of saturated sodium carbonate solution added satisfies the molar ratio of carbonate ions to lithium ions in the lithium-containing leachate of 0.6:1. The lithium precipitation reaction temperature is 90℃ and the lithium precipitation reaction time is 2 h to obtain lithium carbonate.

[0070] (5) The leaching residue obtained in step (3) is calcined in air at 700°C for 4 hours to obtain ferric phosphate.

[0071] (6) The lithium carbonate obtained in step (4) and the iron phosphate obtained in step (5) are mixed and ball-milled with glucose. The molar ratio of lithium carbonate to iron phosphate is 0.52:1, and the amount of glucose added is 15 wt% of the mass of the iron phosphate. The mixture is calcined at 450°C for 4 hours under an argon atmosphere and then calcined at 800°C for 10 hours to obtain lithium iron phosphate.

[0072] Element content test:

[0073] 1. The metal content in the positive electrode powder obtained in step (1) above was tested by inductively coupled plasma (ICP), and the results are shown in Table 1.

[0074] Table 1

[0075]

[0076] 2. ICP testing was performed on the metal content of the lithium-containing leachate obtained in step (3) above, and the leaching rates of lithium and iron were calculated respectively. The calculation method for the leaching rate is as follows: Where i represents an element, m i The content of element "i" in waste lithium iron phosphate powder, C i and V i The values ​​represent the concentration and volume of element "i" in the leachate, respectively. The results are shown in Table 2.

[0077] Table 2

[0078]

[0079] 3. The metal content of the iron phosphate obtained in step (5) above was tested by ICP, and the results are shown in Table 3.

[0080] Table 3

[0081]

[0082] According to the results in Tables 1-3, the leaching rate of Li in the lithium-containing leachate obtained in step (3) of Example 1 reached 99.33%, while the leaching rate of Fe was only 0.03%. This shows that the eutectic solvent of the present invention can selectively leach lithium. The Fe content in the iron phosphate obtained in step (5) reached 36.353 wt%, the P content reached 20.932 wt%, and the iron-to-phosphorus ratio (Fe:P) was 0.96, which meets the standard for battery-grade iron phosphate. This indicates that the method of the present invention can simultaneously achieve selective extraction of lithium and direct regeneration of iron phosphate, thereby obtaining battery-grade lithium carbonate and battery-grade lithium iron phosphate, realizing the green regeneration of cathode materials in waste lithium iron phosphate batteries.

[0083] Example 2

[0084] This embodiment provides a method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate, including the following steps:

[0085] (1) After the waste lithium iron phosphate battery is fully discharged, it is disassembled, dried and cooled to obtain a positive electrode sheet; the positive electrode sheet is soaked in pure water at 60°C for 2 minutes to peel off, and positive electrode material and aluminum foil are obtained; the positive electrode material is dried at 80°C, crushed by a crusher after drying, and then screened with a 200-mesh sieve to obtain 200-mesh positive electrode powder.

[0086] (2) Mix acetic acid and ethylene glycol in a molar ratio of 1:1 and heat and stir at 60°C for 30 min to obtain a eutectic solvent.

[0087] (3) Dilute the eutectic solvent obtained in step (2) with water to a mass fraction of 6wt%, add the 200 mesh positive electrode powder in step (1) to the diluted eutectic solvent, wherein the mass ratio of the positive electrode powder to the diluted eutectic solvent is 1:15, then add 8 vol% of hydrogen peroxide with a mass fraction of 30wt% for oxidation, heat and stir at 60℃ for 120 min, and filter to obtain lithium-containing leachate and leachate residue.

[0088] (4) The lithium-containing leachate obtained in step (3) is concentrated to a concentration of 20 g / L, and then the pH value is adjusted to 12 using 10 wt% sodium hydroxide solution to remove impurities. Then, 25 wt% saturated sodium carbonate solution is added to carry out the lithium precipitation reaction. The amount of saturated sodium carbonate solution added satisfies the molar ratio of carbonate ions to lithium ions in the lithium-containing leachate of 0.6:1. The lithium precipitation reaction temperature is 90℃ and the lithium precipitation reaction time is 3 h to obtain lithium carbonate.

[0089] (5) The leaching residue obtained in step (3) is calcined in air at 700°C for 4 hours to obtain ferric phosphate.

[0090] (6) The lithium carbonate obtained in step (4) and the iron phosphate obtained in step (5) are mixed and ball-milled with glucose. The molar ratio of lithium carbonate to iron phosphate is 0.52:1, and the amount of glucose added is 15 wt% of the mass of the iron phosphate. The mixture is calcined at 450°C for 4 hours under an argon atmosphere and then calcined at 800°C for 10 hours to obtain lithium iron phosphate.

[0091] Element content test:

[0092] 1. The metal content in the positive electrode powder obtained in step (1) above was tested by inductively coupled plasma (ICP), and the results are shown in Table 4.

[0093] Table 4

[0094]

[0095] 2. ICP testing was performed on the metal content in the lithium-containing leachate obtained in step (3) above, and the leaching rates of lithium and iron were calculated separately. The leaching rate was calculated using the same method as in Example 1. The results are shown in Table 5.

[0096] Table 5

[0097]

[0098] 3. The metal content of the iron phosphate obtained in step (5) above was tested by ICP, and the results are shown in Table 6.

[0099] Table 6

[0100]

[0101] According to the results in Tables 4-6, the Li leaching rate in the lithium-containing leachate obtained in step (3) of Example 2 reached 99.10%, while the Fe leaching rate was only 0.06%. This shows that the eutectic solvent of the present invention can selectively leach lithium. The Fe content in the iron phosphate obtained in step (5) reached 36.612 wt%, the P content reached 20.881 wt%, and the iron-to-phosphorus ratio (Fe:P) was 0.97, which meets the standard for battery-grade iron phosphate. This indicates that the method of the present invention can simultaneously achieve selective extraction of lithium and direct regeneration of iron phosphate, thereby obtaining battery-grade lithium carbonate and battery-grade lithium iron phosphate, realizing the green regeneration of cathode materials in waste lithium iron phosphate batteries.

[0102] Example 3

[0103] This embodiment provides a method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate, including the following steps:

[0104] (1) After the waste lithium iron phosphate battery is fully discharged, it is disassembled, dried and cooled to obtain a positive electrode sheet; the positive electrode sheet is soaked in pure water at 60°C for 2 minutes to peel off, and positive electrode material and aluminum foil are obtained; the positive electrode material is dried at 80°C, crushed by a crusher after drying, and then screened with a 200-mesh sieve to obtain 200-mesh positive electrode powder.

[0105] (2) Mix propionic acid and ethylene glycol in a molar ratio of 2:1 and heat and stir at 60°C for 30 min to obtain a eutectic solvent.

[0106] (3) Dilute the eutectic solvent obtained in step (2) with water to a mass fraction of 15wt%, add the 200 mesh positive electrode powder in step (1) to the diluted eutectic solvent, wherein the mass ratio of the positive electrode powder to the diluted eutectic solvent is 1:15, then add 10 vol% of hydrogen peroxide with a mass fraction of 30wt% for oxidation, heat and stir at 60℃ for 120 min, and filter to obtain lithium-containing leachate and leachate residue.

[0107] (4) The lithium-containing leachate obtained in step (3) is concentrated to a concentration of 20 g / L, and then the pH value is adjusted to 12 using 10 wt% sodium hydroxide solution to remove impurities. Then, 25 wt% saturated sodium carbonate solution is added to carry out the lithium precipitation reaction. The amount of saturated sodium carbonate solution added satisfies the molar ratio of carbonate ions to lithium ions in the lithium-containing leachate of 0.6:1. The lithium precipitation reaction temperature is 90℃ and the lithium precipitation reaction time is 3 h to obtain lithium carbonate.

[0108] (5) The leaching residue obtained in step (3) is calcined in air at 700°C for 4 hours to obtain ferric phosphate.

[0109] (6) The lithium carbonate obtained in step (4) and the iron phosphate obtained in step (5) are mixed and ball-milled with glucose. The molar ratio of lithium carbonate to iron phosphate is 0.52:1, and the amount of glucose added is 15 wt% of the mass of the iron phosphate. The mixture is calcined at 450°C for 4 hours under an argon atmosphere and then calcined at 800°C for 10 hours to obtain lithium iron phosphate.

[0110] Element content test:

[0111] 1. The metal content in the positive electrode powder obtained in step (1) above was tested by inductively coupled plasma (ICP), and the results are shown in Table 7.

[0112] Table 7

[0113]

[0114] 2. ICP testing was performed on the metal content in the lithium-containing leachate obtained in step (3) above, and the leaching rates of lithium and iron were calculated separately. The leaching rate was calculated using the same method as in Example 1. The results are shown in Table 8.

[0115] Table 8

[0116]

[0117] 3. The metal content of the iron phosphate obtained in step (5) above was tested by ICP, and the results are shown in Table 9.

[0118] Table 9

[0119]

[0120] According to the results in Tables 7-9, the leaching rate of Li in the lithium-containing leachate obtained in step (3) of Example 3 reached 98.5%, while the leaching rate of Fe was only 0.05%. This shows that the eutectic solvent of the present invention can selectively leach lithium. The Fe content in the iron phosphate obtained in step (5) reached 36.714 wt%, the P content reached 20.615 wt%, and the iron-to-phosphorus ratio (Fe:P) was 0.98, which meets the standard for battery-grade iron phosphate. This indicates that the method of the present invention can simultaneously achieve selective extraction of lithium and direct regeneration of iron phosphate, thereby obtaining battery-grade lithium carbonate and battery-grade lithium iron phosphate, realizing the green regeneration of cathode materials in waste lithium iron phosphate batteries.

[0121] In addition, X-ray diffraction (XRD) tests were performed on the iron phosphate obtained in step (5) of Examples 1-3. Figure 2The image shows the XRD pattern of ferric phosphate obtained in step (5) of Examples 1-3. According to the image, the XRD characteristic peaks of ferric phosphate prepared in Examples 1-3 correspond one-to-one with the standard card peaks of ferric phosphate. No other impurity peaks appear, indicating that the prepared ferric phosphate has high crystallinity and stable quality, which meets the expected crystal structure requirements for ferric phosphate preparation.

[0122] Comparative Example 1

[0123] This comparative example provides a leaching method for waste lithium iron phosphate battery cathode powder, comprising the following steps:

[0124] (1) The positive electrode powder used is the 200-mesh positive electrode powder obtained in step (1) of Example 1.

[0125] (2) Mix oxalic acid and choline chloride in a molar ratio of 2:1 and heat and stir at 80°C for 30 min to obtain a eutectic solvent.

[0126] (3) Add the 200-mesh positive electrode powder from step (1) to the eutectic solvent, wherein the mass ratio of the positive electrode powder to the eutectic solvent is 1:10. Heat and stir at 80°C for 120 min, and filter to obtain lithium-containing leachate and leachate residue.

[0127] Element content test:

[0128] ICP testing was performed on the metal content in the lithium-containing leachate obtained in step (3) above, and the leaching rates of lithium and iron were calculated separately. The leaching rate was calculated using the same method as in Example 1. The results are shown in Table 10.

[0129] Table 10

[0130]

[0131] According to the results in Table 10, the leaching rate of Li in the lithium-containing leachate obtained in step (3) of Comparative Example 1 reached 95.83%, and the leaching rate of Fe was as high as 88.56%. It can be seen that iron and lithium were leached at the same time, and lithium could not be leached selectively. The leaching residue obtained could not be directly calcined to obtain iron phosphate. It was impossible to simultaneously achieve selective extraction of lithium and direct regeneration of iron phosphate.

[0132] Comparative Example 2

[0133] This comparative example provides a leaching method for waste lithium iron phosphate battery cathode powder, comprising the following steps:

[0134] (1) The positive electrode powder used is the 200-mesh positive electrode powder obtained in step (1) of Example 1.

[0135] (2) Mix lactic acid and ethylene glycol in a molar ratio of 1:1 and heat and stir at 80°C for 30 min to obtain a eutectic solvent.

[0136] (3) Add the 200-mesh positive electrode powder from step (1) to the eutectic solvent, wherein the mass ratio of the positive electrode powder to the eutectic solvent is 1:10. Heat and stir at 80°C for 120 min, and filter to obtain lithium-containing leachate and leachate residue.

[0137] Element content test:

[0138] ICP testing was performed on the metal content in the lithium-containing leachate obtained in step (3) above, and the leaching rates of lithium and iron were calculated separately. The leaching rate was calculated using the same method as in Example 1. The results are shown in Table 11.

[0139] Table 11

[0140]

[0141] According to the results in Table 11, the leaching rate of Li in the lithium-containing leachate obtained in step (3) of Comparative Example 2 reached 97.64%, and the leaching rate of Fe was as high as 92.15%. It can be seen that iron and lithium were leached efficiently at the same time, but lithium could not be leached selectively. The leaching residue obtained could not be directly calcined to obtain iron phosphate. It was impossible to achieve selective extraction of lithium and direct regeneration of iron phosphate at the same time.

[0142] In summary, by using a specific eutectic solvent as the leaching medium, this invention enables the selective extraction of lithium and direct regeneration of iron phosphate from waste lithium iron phosphate battery cathode materials under mild conditions. Furthermore, it allows the preparation of battery-grade lithium iron phosphate cathode materials, thus achieving green regeneration of cathode materials from waste lithium iron phosphate batteries.

[0143] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate, characterized in that, include: Step S1: Provide cathode powder from waste lithium iron phosphate batteries; Step S2: Mix the hydrogen bond donor and the hydrogen bond acceptor, heat and stir to obtain a eutectic solvent. The hydrogen bond donor is one or more of formic acid, acetic acid, propionic acid, pyruvic acid, phytic acid, and citric acid. The hydrogen bond acceptor is ethylene glycol. Step S3: Dilute the eutectic solvent obtained in step S2 with water to obtain diluted eutectic solvent, then add the positive electrode powder and oxidant from step S1, heat and stir, filter to obtain lithium-containing leachate and leachate residue. Step S4: The lithium-containing leachate obtained in step S3 is concentrated and impurity removed, and then a saturated sodium carbonate solution is added to carry out a lithium precipitation reaction to obtain lithium carbonate. Step S5: The leaching residue obtained in step S3 is calcined to obtain ferric phosphate; In step S2, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:0.5~1.2; In step S3, the pH value of the diluted eutectic solvent is 1.5~3.

5.

2. The method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, In step S2, the heating temperature for mixing and stirring is 25℃~80℃, and the heating time is 30min~60min.

3. The method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, In step S3, the mass fraction of the diluted eutectic solvent is 1wt% to 20wt%; the mass ratio of the positive electrode powder to the diluted eutectic solvent is 1:5 to 20; the oxidant is 10wt% to 30wt% hydrogen peroxide, and the amount of hydrogen peroxide added is 5vol% to 15vol%.

4. The method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, In step S3, the heating temperature for heating and stirring is 60℃~90℃, and the heating time is 60min~120min.

5. The method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, In step S4, the concentration process specifically includes: concentrating the lithium-containing leachate obtained in step S3 to a concentration of 18 g / L to 30 g / L; The impurity removal process specifically includes: adjusting the pH value to 10-12 using a 5wt%~10wt% sodium hydroxide solution for impurity removal.

6. The method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, In step S4, the mass fraction of the saturated sodium carbonate solution is 25wt%~30wt%, and the amount of saturated sodium carbonate solution added satisfies the molar ratio of carbonate ions to lithium ions in the lithium-containing leachate being 0.6~0.75:

1. The lithium precipitation reaction is carried out at a temperature of 90℃~95℃ for 1h~3h.

7. The method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, In step S5, the calcination temperature is 600℃~800℃, the calcination time is 3h~6h, and the calcination atmosphere is air.

8. The method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate according to claim 1, characterized in that, The step S5 is followed by the step of mixing lithium carbonate obtained in step S4 and iron phosphate obtained in step S5 with a carbon source, ball milling, and calcining to obtain lithium iron phosphate.

9. The method for simultaneously achieving selective lithium extraction and direct regeneration of iron phosphate according to claim 8, characterized in that, The molar ratio of lithium carbonate to iron phosphate is 0.5~0.6:1; The carbon source is glucose, and the amount of glucose added is 10wt%~15wt% of the mass of the ferric phosphate. The calcination temperature is 350℃~800℃, the calcination time is 8h~12h, and the calcination atmosphere is argon.

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