A reusable eutectic solvent for waste lithium iron phosphate cathode materials and its recycling method

Abstract

This invention discloses a reusable eutectic solvent for waste lithium iron phosphate cathode materials and a recycling method, relating to the field of lithium iron phosphate leaching technology. The invention is prepared by mixing hydrogen bond acceptors and hydrogen bond donors. The hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is a mixture of citric acid and ascorbic acid. The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 0.5~2:1, and the molar ratio of the citric acid to the ascorbic acid is also 0.5~2:1. By setting a eutectic solvent with mixed hydrogen bond donors, efficient leaching of lithium iron phosphate can be achieved at low temperatures, while simultaneously improving product purity and enabling recycling. The entire process generates no wastewater or waste gas.

Description

Technical Field

[0001] This invention relates to the field of lithium iron phosphate extraction technology, specifically, to a reusable eutectic solvent for waste lithium iron phosphate cathode materials and a recycling method. Background Technology

[0002] With increasing environmental awareness and the depletion of traditional energy sources, new energy vehicles are becoming the main development direction of the future automotive industry. Among them, lithium iron phosphate (LFP) batteries are gaining increasing market popularity due to their excellent thermal stability, cycle performance, environmental friendliness, and cost-effectiveness. However, lithium batteries typically have a lifespan of 8-10 years, and the growing demand for LFP batteries leads to a rapid increase in used batteries. If not properly disposed of, this will cause serious environmental pollution and waste of secondary resources. Recycling used LFP batteries not only benefits environmental protection but also promotes resource recycling, increases corporate economic benefits, and fosters the healthy development of the industry.

[0003] Currently, the main recycling processes for spent lithium iron phosphate batteries include hydrometallurgy and pyrometallurgy. Pyrometallurgy suffers from low recovery rates, high energy consumption, and waste gas generation. Hydrometallurgy, on the other hand, offers high recovery rates and produces high-purity products, making it the dominant recycling process in the market. This study addresses the problems of high acid and alkali consumption, large amounts of wastewater, and high costs associated with hydrometallurgical processes by providing a novel method for recovering valuable metals from lithium iron phosphate batteries using a low-eutectic flux. Summary of the Invention

[0004] The purpose of this invention is to provide a reusable eutectic solvent for waste lithium iron phosphate cathode materials and a recycling method. By setting a eutectic solvent with mixed hydrogen bond donors, it is possible to achieve efficient leaching of lithium iron phosphate at low temperatures, improve product purity, and recycle the product. The entire process generates no wastewater or waste gas.

[0005] To achieve the above objectives, the present invention employs the following technical means:

[0006] A eutectic solvent for recyclable waste lithium iron phosphate cathode material is prepared by mixing hydrogen bond acceptors and hydrogen bond donors. The hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is a mixture of citric acid and ascorbic acid. The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 0.5~2:1, and the molar ratio of the citric acid to the ascorbic acid is 0.5~2:1.

[0007] Preferably, the hydrogen bond acceptor and the hydrogen bond donor are mixed at an environment of 60°C to 80°C.

[0008] Furthermore, after the hydrogen bond acceptor and the hydrogen bond donor are mixed, the water mass concentration is controlled to be 30%~40%.

[0009] A method for recycling reusable waste lithium iron phosphate cathode material, wherein the aforementioned reusable waste lithium iron phosphate cathode material eutectic solvent is used to recycle the lithium iron phosphate cathode material;

[0010] Lithium iron phosphate powder was mixed with a eutectic solvent and subjected to a first heating and stirring reaction. Oxalic acid was then added, and the ferrous oxalate precipitate was collected by filtration to obtain the first filtrate.

[0011] The first filtrate is passed through ozone, heated and stirred, and then filtered to collect the ferric hydroxide precipitate to obtain the second filtrate.

[0012] The second filtrate was evaporated and concentrated, and lithium dihydrogen phosphate was collected by filtration to obtain the third filtrate.

[0013] After adding hydrogen bond donors to the third filtrate, the third filtrate can be reused as a eutectic solvent.

[0014] Furthermore, the temperature of the first heating and stirring is 70℃~90℃, and the stirring time is 120min~240min.

[0015] Furthermore, the solid content concentration of the lithium iron phosphate powder after mixing with the eutectic solvent is 20 g / L.

[0016] Furthermore, the molar concentration of the oxalic acid is 2 mol / L.

[0017] Furthermore, after adding hydrogen bond donors to the third filtrate, it is stirred at 80°C for 60 minutes and then reused.

[0018] This process utilizes choline chloride, citric acid, and ascorbic acid to prepare a eutectic solvent. The release of H+ provides a weakly acidic environment and a reducing agent. Through acidic protonation, carboxyl and hydroxyl groups form hydrogen bonds with the Fe-O octahedra and PO tetrahedra of lithium iron phosphate, and coordinate with Li+ and Fe2+, thus disrupting the lithium iron phosphate crystal structure and increasing the leaching rate. Oxalic acid is added to selectively precipitate Fe2+ in the solution, yielding ferrous oxalate, a key raw material for preparing high-density lithium iron phosphate. After filtration, ozone is introduced to oxidize the remaining ferrous ions and oxalic acid in the solution, raising the pH. Fiber hydroxide precipitate is then removed by filtration. Lithium hydroxide or phosphoric acid is added to adjust the Li / P ratio, and the solution is evaporated and concentrated to prepare lithium dihydrogen phosphate, another key raw material for high-density lithium iron phosphate. After filtering the lithium dihydrogen phosphate, a small amount of lost citric acid and ascorbic acid is added to the solution, allowing the eutectic solvent to be reused.

[0019] Choline chloride has strong hydrogen bonding and electrostatic interactions with citric acid and ascorbic acid, forming a hydrogen bond network. By adjusting the ratio, polarity and solubility can be increased, viscosity can be reduced, and a stable solvent network can be formed.

[0020] Choline chloride provides the system with a wide liquid temperature range (-20℃ to 200℃), which facilitates the recycling of the eutectic solvent after the evaporation and crystallization of lithium dihydrogen phosphate. Chloride ions can coordinate with lithium ions, reducing the surface activation energy of lithium iron phosphate, enhancing ionic strength, and promoting mass transfer efficiency.

[0021] Ascorbic acid has strong reducing properties, while citric acid has strong acidity. Their combination provides an acidic environment, reducing ferric iron (Fe³⁺) and lowering the activation energy for Fe³⁺ reduction and Li⁺ migration, thus disrupting the lithium iron phosphate crystal structure and promoting leaching. Furthermore, citric acid can complex with trace amounts of ferric iron in the solution, increasing the purity of ferrous oxalate.

[0022] The choline chloride / citric acid / ascorbic acid system can achieve efficient leaching of lithium iron phosphate at low temperatures, while improving product purity and allowing for recycling. The entire process generates no wastewater or waste gas and has promising application prospects. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] Therefore, the following detailed description of embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other.

[0026] A eutectic solvent for recyclable waste lithium iron phosphate cathode material is prepared by mixing hydrogen bond acceptors and hydrogen bond donors. The hydrogen bond acceptor is choline chloride, and the hydrogen bond donor is a mixture of citric acid and ascorbic acid. The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 0.5~2:1, and the molar ratio of the citric acid to the ascorbic acid is 0.5~2:1.

[0027] Preferably, the hydrogen bond acceptor and the hydrogen bond donor are mixed at an environment of 60°C to 80°C.

[0028] Furthermore, after the hydrogen bond acceptor and the hydrogen bond donor are mixed, the water mass concentration is controlled to be 30%~40%.

[0029] A method for recycling reusable waste lithium iron phosphate cathode material, wherein the aforementioned reusable waste lithium iron phosphate cathode material eutectic solvent is used to recycle the lithium iron phosphate cathode material;

[0030] Lithium iron phosphate powder was mixed with a eutectic solvent and subjected to a first heating and stirring reaction. Oxalic acid was then added, and the ferrous oxalate precipitate was collected by filtration to obtain the first filtrate.

[0031] The first filtrate is passed through ozone, heated and stirred, and then filtered to collect the ferric hydroxide precipitate to obtain the second filtrate.

[0032] The second filtrate was evaporated and concentrated, and lithium dihydrogen phosphate was collected by filtration to obtain the third filtrate.

[0033] After adding hydrogen bond donors to the third filtrate, the third filtrate can be reused as a eutectic solvent.

[0034] Furthermore, the temperature of the first heating and stirring is 70℃~90℃, and the stirring time is 120min~240min.

[0035] Furthermore, the solid content concentration of the lithium iron phosphate powder after mixing with the eutectic solvent is 20 g / L.

[0036] Furthermore, the molar concentration of the oxalic acid is 2 mol / L.

[0037] Furthermore, after adding hydrogen bond donors to the third filtrate, it is stirred at 80°C for 60 minutes and then reused.

[0038] The following examples illustrate this point.

[0039] Example 1

[0040] Choline chloride, citric acid, ascorbic acid and water were mixed and heated and stirred to obtain a eutectic solvent, wherein the ratio of hydrogen bond acceptor to hydrogen bond donor was 1:1, the ratio of citric acid to ascorbic acid was 1:1, the water mass concentration was 30%, the heating and stirring temperature was 60℃, and the time was 90min.

[0041] The obtained eutectic solvent was mixed with lithium iron phosphate powder at a solid-liquid ratio of 20 g / L, and then heated and stirred for leaching at a temperature of 70°C for 120 min.

[0042] Add oxalic acid solution with a molar concentration of 2 mol / L, and filter to obtain ferrous oxalate precipitate;

[0043] Ozone is introduced, the mixture is heated and stirred, and the resulting ferric hydroxide precipitate is filtered out.

[0044] Evaporation and concentration, followed by filtration, yielded lithium dihydrogen phosphate.

[0045] The filtered solution was replenished with citric acid and ascorbic acid, and stirred at 80°C for 60 min to regenerate the eutectic solvent.

[0046] Example 2

[0047] Choline chloride, citric acid, ascorbic acid and water were mixed and heated and stirred to obtain a eutectic solvent, wherein the ratio of hydrogen bond acceptor to hydrogen bond donor was 1:1, the ratio of citric acid to ascorbic acid was 2:1, the water mass concentration was 35%, the heating and stirring temperature was 70℃, and the time was 120min.

[0048] The obtained eutectic solvent was mixed with lithium iron phosphate powder at a solid-liquid ratio of 20 g / L, and then heated and stirred for leaching at a temperature of 80°C for 180 min.

[0049] Add oxalic acid solution with a molar concentration of 2 mol / L, and filter to obtain ferrous oxalate precipitate;

[0050] Ozone is introduced, the mixture is heated and stirred, and the resulting ferric hydroxide precipitate is filtered out.

[0051] Evaporation and concentration, followed by filtration, yielded lithium dihydrogen phosphate.

[0052] The filtered solution was replenished with citric acid and ascorbic acid, and stirred at 80°C for 60 min to regenerate the eutectic solvent.

[0053] Example 3

[0054] Choline chloride, citric acid, ascorbic acid and water were mixed and heated and stirred to obtain a eutectic solvent, wherein the ratio of hydrogen bond acceptor to hydrogen bond donor was 1:1, the ratio of citric acid to ascorbic acid was 1:2, the water mass concentration was 40%, the heating and stirring temperature was 80℃, and the time was 150min.

[0055] The obtained eutectic solvent was mixed with lithium iron phosphate powder at a solid-liquid ratio of 20 g / L, and then heated and stirred for leaching at a temperature of 90 °C for 240 min.

[0056] Add oxalic acid solution with a molar concentration of 2 mol / L, and filter to obtain ferrous oxalate precipitate;

[0057] Ozone is introduced, the mixture is heated and stirred, and the resulting ferric hydroxide precipitate is filtered out.

[0058] Evaporation and concentration, followed by filtration, yielded lithium dihydrogen phosphate.

[0059] The filtered solution was replenished with citric acid and ascorbic acid, and stirred at 80°C for 60 min to regenerate the eutectic solvent.

[0060] Example 4

[0061] Choline chloride, citric acid, ascorbic acid and water were mixed and heated and stirred to obtain a eutectic solvent, wherein the ratio of hydrogen bond acceptor to hydrogen bond donor was 2:1, the ratio of citric acid to ascorbic acid was 1:1, the water mass concentration was 30%, the heating and stirring temperature was 60℃, and the time was 90min.

[0062] The obtained eutectic solvent was mixed with lithium iron phosphate powder at a solid-liquid ratio of 20 g / L, and then heated and stirred for leaching at a temperature of 70°C for 120 min.

[0063] Add oxalic acid solution with a molar concentration of 2 mol / L, and filter to obtain ferrous oxalate precipitate;

[0064] Ozone is introduced, the mixture is heated and stirred, and the resulting ferric hydroxide precipitate is filtered out.

[0065] Evaporation and concentration, followed by filtration, yielded lithium dihydrogen phosphate.

[0066] The filtered solution was replenished with citric acid and ascorbic acid, and stirred at 80°C for 60 min to regenerate the eutectic solvent.

[0067] Example 5

[0068] Choline chloride, citric acid, ascorbic acid and water were mixed and heated and stirred to obtain a eutectic solvent, wherein the ratio of hydrogen bond acceptor to hydrogen bond donor was 2:1, the ratio of citric acid to ascorbic acid was 2:1, the water mass concentration was 35%, the heating and stirring temperature was 70℃, and the time was 120min.

[0069] The obtained eutectic solvent was mixed with lithium iron phosphate powder at a solid-liquid ratio of 20 g / L, and then heated and stirred for leaching at a temperature of 80°C for 180 min.

[0070] Add oxalic acid solution with a molar concentration of 2 mol / L, and filter to obtain ferrous oxalate precipitate;

[0071] Ozone is introduced, the mixture is heated and stirred, and the resulting ferric hydroxide precipitate is filtered out.

[0072] Evaporation and concentration, followed by filtration, yielded lithium dihydrogen phosphate.

[0073] The filtered solution was replenished with citric acid and ascorbic acid, and stirred at 80°C for 60 min to regenerate the eutectic solvent.

[0074] Example 6

[0075] Choline chloride, citric acid, ascorbic acid and water were mixed and heated and stirred to obtain a eutectic solvent, wherein the ratio of hydrogen bond acceptor to hydrogen bond donor was 2:1, the ratio of citric acid to ascorbic acid was 1:2, the water mass concentration was 40%, the heating and stirring temperature was 80℃, and the time was 150 min.

[0076] The obtained eutectic solvent was mixed with lithium iron phosphate powder at a solid-liquid ratio of 20 g / L, and then heated and stirred for leaching at a temperature of 90 °C for 240 min.

[0077] Add oxalic acid solution with a molar concentration of 2 mol / L, and filter to obtain ferrous oxalate precipitate;

[0078] Ozone is introduced, the mixture is heated and stirred, and the resulting ferric hydroxide precipitate is filtered out.

[0079] Evaporation and concentration, followed by filtration, yielded lithium dihydrogen phosphate.

[0080] The filtered solution was replenished with citric acid and ascorbic acid, and stirred at 80°C for 60 min to regenerate the eutectic solvent.

[0081] Example 7

[0082] Choline chloride, citric acid, ascorbic acid and water were mixed and heated and stirred to obtain a eutectic solvent, wherein the ratio of hydrogen bond acceptor to hydrogen bond donor was 1:2, the ratio of citric acid to ascorbic acid was 1:1, the water mass concentration was 30%, the heating and stirring temperature was 60℃, and the time was 90min.

[0083] The obtained eutectic solvent was mixed with lithium iron phosphate powder at a solid-liquid ratio of 20 g / L, and then heated and stirred for leaching at a temperature of 70°C for 120 min.

[0084] Add oxalic acid solution with a molar concentration of 2 mol / L, and filter to obtain ferrous oxalate precipitate;

[0085] Ozone is introduced, the mixture is heated and stirred, and the resulting ferric hydroxide precipitate is filtered out.

[0086] Evaporation and concentration, followed by filtration, yielded lithium dihydrogen phosphate.

[0087] The filtered solution was replenished with citric acid and ascorbic acid, and stirred at 80°C for 60 min to regenerate the eutectic solvent.

[0088] Example 8

[0089] Choline chloride, citric acid, ascorbic acid and water were mixed and heated and stirred to obtain a eutectic solvent, wherein the ratio of hydrogen bond acceptor to hydrogen bond donor was 1:2, the ratio of citric acid to ascorbic acid was 2:1, the water mass concentration was 35%, the heating and stirring temperature was 70℃, and the time was 120min.

[0090] The obtained eutectic solvent was mixed with lithium iron phosphate powder at a solid-liquid ratio of 20 g / L, and then heated and stirred for leaching at a temperature of 80°C for 180 min.

[0091] Add oxalic acid solution with a molar concentration of 2 mol / L, and filter to obtain ferrous oxalate precipitate;

[0092] Ozone is introduced, the mixture is heated and stirred, and the resulting ferric hydroxide precipitate is filtered out.

[0093] Evaporation and concentration, followed by filtration, yielded lithium dihydrogen phosphate.

[0094] The filtered solution was replenished with citric acid and ascorbic acid, and stirred at 80°C for 60 min to regenerate the eutectic solvent.

[0095] Example 9

[0096] Choline chloride, citric acid, ascorbic acid and water were mixed and heated and stirred to obtain a eutectic solvent, wherein the ratio of hydrogen bond acceptor to hydrogen bond donor was 1:2, the ratio of citric acid to ascorbic acid was 1:2, the water mass concentration was 40%, the heating and stirring temperature was 80℃, and the time was 150min.

[0097] The obtained eutectic solvent was mixed with lithium iron phosphate powder at a solid-liquid ratio of 20 g / L, and then heated and stirred for leaching at a temperature of 90 °C for 240 min.

[0098] Add oxalic acid solution with a molar concentration of 2 mol / L, and filter to obtain ferrous oxalate precipitate;

[0099] Ozone is introduced, the mixture is heated and stirred, and the resulting ferric hydroxide precipitate is filtered out.

[0100] Evaporation and concentration, followed by filtration, yielded lithium dihydrogen phosphate.

[0101] The filtered solution was replenished with citric acid and ascorbic acid, and stirred at 80°C for 60 min to regenerate the eutectic solvent.

[0102] Comparative Example 1

[0103] The preparation method is basically the same as that in Example 1, except that only citric acid is used as a hydrogen bond donor and ascorbic acid is not used, resulting in a decrease in leaching rate and a decrease in the purity of ferrous oxalate in the product.

[0104] Comparative Example 2

[0105] The preparation method is basically the same as that in Example 1, except that only ascorbic acid is used as a hydrogen bond donor and citric acid is not used, resulting in a decrease in leaching rate and a decrease in the purity of ferrous oxalate in the product.

[0106] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recycling a waste lithium iron phosphate cathode material, characterized in that, The application discloses a method for recycling waste lithium iron phosphate cathode material, and belongs to the field of waste lithium ion battery recycling. The method comprises the following steps: The lithium iron phosphate powder is mixed with the deep eutectic solvent, and after the first heating and stirring reaction is completed, oxalic acid is added, the ferrous oxalate precipitate is collected by filtration, and the first filtrate is obtained; The first filtrate is passed into ozone, and the second heating and stirring is performed, the iron hydroxide precipitate is collected by filtration, and the second filtrate is obtained; The second filtrate is concentrated by evaporation, and the lithium dihydrogen phosphate is collected by filtration, and the third filtrate is obtained; After the hydrogen bond donor is supplemented in the third filtrate, the third filtrate can be reused as the deep eutectic solvent.

2. The method according to claim 1, wherein, The hydrogen bond acceptor and the hydrogen bond donor are mixed at 60-80 DEG C.

3. The method according to claim 1 or 2, characterized in that, After the hydrogen bond acceptor and the hydrogen bond donor are mixed, the water mass concentration is controlled to be 30-40%.

4. The method according to claim 1, wherein, The temperature of the first heating and stirring is 70-90 DEG C, and the stirring time is 120-240 min.

5. The method according to claim 1, wherein the method is characterized in that, After the lithium iron phosphate powder is mixed with the deep eutectic solvent, the solid content concentration is 20 g / L.

6. The method according to claim 1, wherein the method is characterized by, The molar concentration of the oxalic acid is 2 mol / L.

7. The method according to claim 1, wherein the method is characterized in that, After the hydrogen bond donor is supplemented in the third filtrate, the third filtrate is reused after being stirred at 80 DEG C for 60 min.