Method for recovering lithium from waste lithium iron phosphate batteries using deep eutectic solvent

Abstract

The present invention provides a method for recycling lithium in waste lithium iron phosphate batteries by using a low eutectic solvent. The waste lithium iron phosphate batteries are completely discharged to obtain a battery positive electrode sheet, and the battery positive electrode sheet is heated under nitrogen to obtain lithium iron phosphate powder; a carboxylic acid compound containing both hydroxyl and carboxyl groups is used as a hydrogen bond donor, and an amino acid is used as a hydrogen bond acceptor, and mixed in deionized water to obtain a low eutectic solvent; the lithium iron phosphate powder is placed in the low eutectic solvent to leach lithium, and a lithium ion solution is obtained after solid-liquid separation, thereby completing the recovery of lithium in waste lithium iron phosphate batteries. The present invention utilizes the hydrogen bond network and strong electrostatic effect of carboxylic acid compounds containing hydroxyl and carboxyl groups and amino acids, and the two synergistically improve the acidity of the leaching environment, forming a low eutectic solvent with good fluidity, high lithium leaching rate, and short reaction time. The present invention realizes a green and non-toxic leaching process and maximizes the recovery value of waste lithium iron phosphate batteries, and has industrial application value.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium iron phosphate battery recycling, and in particular to a method for recycling lithium in waste lithium iron phosphate batteries using a low eutectic solvent. Background Art

[0002] In recent years, the production of lithium-ion batteries has experienced explosive growth, and the market share of lithium iron phosphate has been on the rise. The main reasons are: low cost, high cost performance, long cycle life of lithium iron phosphate batteries; and higher safety compared to ternary materials. With the rapid increase in the number of lithium iron phosphate batteries, the number of scrapped and retired batteries has also increased sharply, making it more important to recycle and reuse waste lithium iron phosphate batteries. Harmless treatment and resource recycling of waste lithium iron phosphate batteries can effectively reduce the environmental pressure caused by a large amount of waste, bring considerable economic benefits, and are also of great significance to the development of lithium-ion batteries.

[0003] At present, the main processes for recycling lithium iron phosphate positive electrode materials are dry recycling and wet recycling. The dry process has high energy costs, is accompanied by a large amount of harmful flue gas emissions, and is prone to cause serious environmental pollution; while the wet process has low costs, high metal recovery rates, and flexible treatment methods, and is currently the mainstream recycling process route. However, the current wet recovery process leaching agents mostly use inorganic strong acids (hydrochloric acid, sulfuric acid, nitric acid, etc.), for example: a method for extracting lithium from waste lithium iron phosphate powder with announcement number CN112626357B, and a method for recovering lithium from lithium iron phosphate with publication number CN108899601A, both disclose a recovery method for extracting lithium from waste lithium iron phosphate with sulfuric acid; however, this method has the problem of involving corrosive reagents in the reaction process, which poses an environmental threat, and only recovers the metal in the form of compounds, and does not achieve the effect of efficient resource utilization of recycling-regeneration.

[0004] In response to the above problems, the invention patent (publication number CN111041216 B) discloses a method for extracting and recovering the positive electrode metal materials of waste ternary lithium batteries by using propylene glycol low eutectic solvent. The method uses propylene glycol and different types of hydrogen bond acceptors to mix at room temperature and then, under heating conditions, ultrasonically prepare a low eutectic solvent. The positive electrode material foil is added to the low eutectic solvent, and the electrode material is recovered by heating and extraction. Although this method successfully recovers the positive electrode metal materials, the low eutectic solvent used can only improve the leaching rate under high temperature and extended time, which is not conducive to industrial application. In addition, this method is a method for recovering positive electrode metal materials from ternary lithium batteries. The materials, properties and applications of lithium iron phosphate batteries and ternary lithium batteries are different. Therefore, how to efficiently and greenly recycle lithium iron phosphate positive electrode materials is still an urgent problem to be solved.

[0005] In view of this, it is necessary to design an improved method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to provide a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. By preparing a low eutectic solvent with good fluidity and high lithium leaching efficiency for waste lithium iron phosphate batteries, the lithium in the battery can be efficiently recovered in a shorter time and at a lower temperature, so as to achieve a green and non-toxic leaching process and maximize the recovery value of waste lithium iron phosphate batteries, which has industrial application value.

[0007] To achieve the above-mentioned object of the invention, the present invention provides a method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent, comprising the following steps:

[0008] S1. placing a waste lithium iron phosphate battery in a discharge solution, disassembling it after it is completely discharged to obtain a positive electrode sheet of the battery; heating the positive electrode sheet of the battery to 500-700° C. under a nitrogen atmosphere to obtain lithium iron phosphate powder;

[0009] S2, mixing a hydrogen bond donor and a hydrogen bond acceptor in deionized water, and stirring in a constant temperature heated magnetic stirrer until a clear solution is obtained, wherein the clear solution is a low eutectic solvent; the hydrogen bond donor is a carboxylic acid compound containing both hydroxyl and carboxyl groups; and the hydrogen bond acceptor is an amino acid;

[0010] S3, placing the lithium iron phosphate powder of step S1 in the low eutectic solvent of step S2, stirring and leaching in a constant temperature heating magnetic stirrer, the leaching temperature is 10-90° C., and the leaching time is 1-4 h;

[0011] S4, separating and treating the liquid treated in step S3 to obtain a lithium ion solution, thereby completing the recovery of lithium in the waste lithium iron phosphate battery.

[0012] As a further improvement of the present invention, in step S2, the hydrogen bond donor is one of citric acid, malic acid, and lactic acid; the hydrogen bond acceptor is one of glycine, alanine, and proline.

[0013] As a further improvement of the present invention, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:(0.5-1.2), and the molar ratio is preferably 1:1.

[0014] As a further improvement of the present invention, in step S2, in step S2, the molar ratio of the hydrogen bond donor, the hydrogen bond acceptor, and the deionized water is 1:(0.5-1.2):1.

[0015] As a further improvement of the present invention, in step S3, the mass ratio of the lithium iron phosphate powder to the low eutectic solvent is 1:(15~25).

[0016] As a further improvement of the present invention, in step S3, the leaching temperature during stirring in the constant temperature heating magnetic stirrer is preferably 60-90°C, and the time is 2-2.5h.

[0017] As a further improvement of the present invention, in step S2, the hydrogen bond donor is citric acid, and the hydrogen bond acceptor is glycine; the stirring temperature is 40-60° C., and the stirring time is 2-2.5 h.

[0018] As a further improvement of the present invention, in step S2, the stirring speed of the constant temperature heating magnetic stirrer is 800~1200 r / min; in step S3, the stirring speed of the constant temperature heating magnetic stirrer is 600~900 r / min.

[0019] As a further improvement of the present invention, in step S1, the discharge solution is a saturated sodium chloride solution.

[0020] As a further improvement of the present invention, in step S4, the separation treatment includes one of membrane filtration, centrifugation, and suction filtration.

[0021] The beneficial effects of the present invention are:

[0022] 1. The present invention provides a method for recovering lithium from waste lithium iron phosphate batteries by using a low eutectic solvent. The waste lithium iron phosphate batteries are completely discharged and disassembled to obtain a positive electrode sheet of the battery. The positive electrode sheet of the battery is heated under nitrogen to obtain lithium iron phosphate powder. A hydrogen bond donor and a hydrogen bond acceptor are mixed in deionized water and stirred at a constant temperature until a clear low eutectic solvent is obtained, wherein the hydrogen bond donor is a carboxylic acid compound containing both hydroxyl and carboxyl groups, and the hydrogen bond acceptor is an amino acid. Finally, the lithium iron phosphate powder is placed in a low eutectic solvent, stirred and leached at a constant temperature, and the solution is separated to obtain a lithium ion solution, thereby completing the recovery of lithium from waste lithium iron phosphate batteries. The present invention prepares a low eutectic solvent with good fluidity and high efficiency in leaching lithium from waste lithium iron phosphate batteries, and efficiently recovers lithium from the battery in a short time and at a low temperature, thereby realizing a green and non-toxic leaching process and maximizing the recovery value of waste lithium iron phosphate batteries, and has industrial application value.

[0023] 2. The present invention uses a carboxylic acid compound containing both hydroxyl and carboxyl groups as a hydrogen bond donor and an amino acid as a hydrogen bond acceptor to prepare a low eutectic solvent; the two not only have a hydrogen bond effect to form a hydrogen bond network, but also the amino group of the amino acid and the hydroxyl and carboxyl groups of the carboxylic acid compound have a strong electrostatic effect during the formation of the low eutectic solvent. Under the hydrogen bond network and strong electrostatic effect, the degree of melting point reduction is promoted, which is also beneficial to the stability of the solvent, forming a low eutectic solvent with a high lithium leaching rate. In addition, the present invention adopts two different organic acids as hydrogen bond donors and acceptors respectively, which synergistically improve the acidity of the leaching environment. The acidic condition is more conducive to the recovery of lithium in waste lithium iron phosphate batteries, overcoming the disadvantages of the traditional method of introducing highly corrosive inorganic acids to recover lithium iron phosphate, causing serious environmental pollution and only being able to recover it in the form of compound metals; and both acids are easily soluble in water and can be mixed with deionized water, so that the low eutectic solvent has good fluidity, the kinetic energy of the lithium iron phosphate powder molecules is increased, the mobility is improved, and the lithium iron phosphate powder is fully contacted and reacted, which saves reaction time and is more conducive to improving the leaching rate and leaching efficiency of lithium in the recovery of lithium iron phosphate.

[0024] 3. The low eutectic solvent of the present invention adopts two different organic acids as hydrogen bond donors and acceptors respectively, overcoming the technical prejudice in the prior art that organic acids can only be used as hydrogen bond donors for low eutectic solvents. By selecting two acids with hydrogen bonds and strong electrostatic effects, the leaching rate of lithium in lithium iron phosphate is improved, and the leaching time is shortened. It has a good leaching effect on lithium in waste lithium iron phosphate batteries at a leaching temperature of 10-90°C, and the leaching rate has reached more than 90% at 60°C, which is of great significance for the recovery of lithium in waste lithium iron phosphate.

[0025] 4. The low eutectic solvent has easy-to-obtain raw materials, low preparation cost, is not volatile, and has weak corrosiveness. It is safer during operation and has high leaching efficiency, which effectively improves the purity of the recovered metallic lithium. It is easy to operate when used to recover lithium from waste lithium iron phosphate batteries, which makes up for the current complex process. At the same time, it is environmentally friendly, easy to store, and has good market prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a schematic flow chart of a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent.

[0027] Figure 2 The figure shows the variation trend of lithium leaching rate with leaching temperature in Examples 1 to 4 and Examples 8 to 12. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] It should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only structures and / or processing steps closely related to the scheme of the present invention are shown in the drawings, while other details that are not closely related to the present invention are omitted.

[0030] In addition, it should be noted that the terms "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0031] See also Figure 1 As shown, a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent comprises the following steps:

[0032] S1. placing the waste lithium iron phosphate battery in a discharge solution, disassembling it after it is completely discharged to obtain a positive electrode sheet of the battery; heating the positive electrode sheet of the battery to 500-700° C. in a nitrogen atmosphere to obtain lithium iron phosphate powder;

[0033] S2, mixing a hydrogen bond donor and a hydrogen bond acceptor in deionized water, and stirring in a constant temperature heated magnetic stirrer until a clear solution is obtained, wherein the clear solution is a low eutectic solvent; the hydrogen bond donor is a carboxylic acid compound containing both hydroxyl and carboxyl groups; the hydrogen bond acceptor is an amino acid;

[0034] S3, placing the lithium iron phosphate powder of step S1 in the low eutectic solvent of step S2, stirring and leaching in a constant temperature heating magnetic stirrer, the leaching temperature is 10-90°C, and the leaching time is 1-4 hours; wherein the mass ratio of the lithium iron phosphate powder to the low eutectic solvent is 1:(15-25);

[0035] S4, separating and treating the liquid treated in step S3 to obtain a lithium ion solution, thereby completing the recovery of lithium in the waste lithium iron phosphate battery.

[0036] In particular, in step S2, the hydrogen bond donor is one of citric acid, malic acid, and lactic acid; the hydrogen bond acceptor is one of glycine, alanine, and proline. A carboxylic acid compound containing both hydroxyl and carboxyl groups is used as a hydrogen bond donor, and an amino acid is used as a hydrogen bond acceptor to prepare a low eutectic solvent; the two not only have a hydrogen bond effect to form a hydrogen bond network, but also the amino group of the amino acid and the hydroxyl and carboxyl groups of the carboxylic acid compound have a strong electrostatic effect during the formation of the low eutectic solvent. Under the hydrogen bond network and strong electrostatic effect, the melting point is reduced, and the stability of the solvent is also promoted, forming a low eutectic solvent with a high lithium leaching rate.

[0037] In addition, the present invention adopts two different organic acids as hydrogen bond donors and acceptors respectively, which synergistically improve the acidity of the leaching environment. The acidic condition is more conducive to the recovery of lithium in waste lithium iron phosphate batteries, and overcomes the disadvantages of the traditional method of introducing highly corrosive inorganic acids to recover lithium iron phosphate, which seriously pollutes the environment and can only be recovered in the form of compound metals; and both acids are easily soluble in water and can be mixed with deionized water, so that the low eutectic solvent has good fluidity, increases the kinetic energy of the lithium iron phosphate powder molecules during processing, improves the mobility, fully contacts and reacts with the lithium iron phosphate powder, saves reaction time, and is more conducive to improving the leaching rate and leaching efficiency of recovering lithium in lithium iron phosphate, so that it has a good leaching effect within the leaching temperature of 10-90°C.

[0038] Specifically, the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1: (0.5-1.2), and the molar ratio is preferably 1: 1. By regulating the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor, the hydrogen bond effect and strong electrostatic effect between the two can be maximized on the basis of cost saving; and a better lithium leaching rate can be achieved during application.

[0039] In step S2, in step S2, the molar ratio of hydrogen bond donor, hydrogen bond acceptor and deionized water is 1: (0.5-1.2): 1. Mixing the water-soluble hydrogen bond donor and hydrogen bond acceptor in deionized water and other organic solvents can improve the fluidity of the low eutectic solvent, facilitate the stretching and contact between molecules, and improve the hydrogen bond and electrostatic force between the hydrogen bond donor and the hydrogen bond acceptor.

[0040] Preferably, the hydrogen bond donor is citric acid and the hydrogen bond acceptor is glycine; there is a stronger electrostatic interaction between citric acid and glycine, forming a low eutectic solvent with a higher lithium leaching rate.

[0041] Preferably, in step S3, the leaching temperature during stirring is 60-90°C, and the leaching time is 2-2.5 h. Under the preferred conditions, when recycling lithium from waste lithium iron phosphate batteries, the leaching rate reaches more than 90% at 60°C, and the time used is short and the leaching efficiency is high.

[0042] Specifically, in step S2, the temperature of the constant temperature heating magnetic stirrer during stirring is 40~60°C, the time is 2~2.5h, and the stirring speed of the constant temperature heating magnetic stirrer is 800~1200 r / min; in step S3, the stirring speed of the constant temperature heating magnetic stirrer is 600~900 r / min.

[0043] In some specific embodiments, in step S1, the discharge solution is a saturated sodium chloride solution.

[0044] In some specific embodiments, in step S4, the separation treatment includes one of membrane filtration, centrifugation, and suction filtration. The separation treatment preferably uses membrane filtration, which can reduce the impurity content in the filtrate and improve the recovery purity of lithium.

[0045] The low eutectic solvent of the present invention adopts two different organic acids as hydrogen bond donors and acceptors respectively, overcoming the technical prejudice that organic acids can only serve as hydrogen bond donors, and by selecting two acids with hydrogen bonds and strong electrostatic effects, the leaching rate of lithium in lithium iron phosphate is improved, and the leaching time is shortened, which is of great significance for the recovery of lithium in waste lithium iron phosphate; and the raw materials of the low eutectic solvent are easy to obtain, the preparation cost is low, it is not easy to volatilize, and the corrosiveness is weak, the safety is higher during the operation process, and the leaching efficiency is high, which effectively improves the purity of the recovered metallic lithium; when used for recovering lithium in waste lithium iron phosphate batteries, the operation is simple, which makes up for the current complex process status, and at the same time, it is environmentally friendly and easy to store, and has a good market prospect.

[0046] Example 1

[0047] This embodiment provides a method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent, comprising the following steps:

[0048] S1. Place the waste lithium iron phosphate battery in a saturated sodium chloride solution, completely discharge it, and then disassemble it to obtain a positive electrode sheet of the battery; place the positive electrode sheet of the battery in a vacuum atmosphere tubular electric furnace, and heat it to 600° C. under a nitrogen atmosphere to separate the lithium iron phosphate powder from the aluminum foil to obtain the lithium iron phosphate powder;

[0049] S2, mixing citric acid and glycine in deionized water, wherein the molar ratio of citric acid, glycine and deionized water is 1:1:1, and stirring in a constant temperature heating magnetic stirrer at 80°C and 1000 r / min for 1 h until a clear solution is obtained, wherein the clear solution is the deep eutectic solvent;

[0050] S3, placing 1g of lithium iron phosphate powder in step S1 into a beaker containing the low eutectic solvent in step S2, with a mass ratio of 1:20, placing the beaker in a constant temperature heated magnetic stirrer for stirring and leaching, the leaching temperature is 60°C, the leaching time is 2 h, the rotation speed is 800r / min, and the lithium in the positive electrode material is leached;

[0051] S4. After the leaching is completed, the beaker is taken out from the agitator, and the liquid and solid of the reaction product are separated by a filter membrane to obtain a lithium ion solution, thereby completing the recovery of lithium in the waste lithium iron phosphate battery.

[0052] Embodiment 2-4

[0053] Embodiments 2 to 4 provide a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Embodiment 1, the difference is that in step S3, the leaching temperatures are 20°C, 40°C, and 80°C, respectively. The rest is roughly the same as Embodiment 1 and will not be repeated here.

[0054] Embodiment 5-6

[0055] Examples 5 to 6 provide a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S3, the leaching time is 1 h and 4 h, respectively, and the rest is roughly the same as Example 1, which will not be repeated here.

[0056] Example 7

[0057] This embodiment provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S3, the leaching temperature is 80°C and the time is 4 h. The rest is roughly the same as Example 1 and will not be repeated here.

[0058] In order to eliminate the interference of unnecessary factors, the waste lithium iron phosphate batteries used in Examples 1 to 7 are the same, and the positive electrode of the battery contains 4.47% Li, 26.59% Fe, 16.45% P, and 52.49% other. The lithium ion solutions obtained in Examples 1 to 7 were tested by atomic absorption spectroscopy for Li + The content of Li in 1g of lithium iron phosphate positive electrode powder was analyzed. + The content was analyzed and the lithium leaching rate was calculated. The results are shown in the following table.

[0059] Table 1 Test results of Examples 1 to 7

[0060]

[0061] It can be seen from Table 1 that when the leaching temperature is in the range of 10-90°C, the lithium leaching rate continues to increase, and at 60°C the leaching rate has reached 91.02%. When the leaching temperature continues to increase, the lithium leaching rate increases, but not significantly. Therefore, from the perspective of saving resources, the leaching temperature is limited to 10-90°C; the influence of leaching time is similar to that of temperature. In Example 1, 2 h already has a higher lithium leaching rate, so the leaching time is limited to 1-4 h.

[0062] Embodiments 8 to 12

[0063] Examples 8 to 12 provide a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S3, the leaching temperatures are 10°C, 30°C, 50°C, 70°C, and 90°C, respectively. The rest is roughly the same as Example 1 and will not be repeated here.

[0064] See also Figure 2 As shown, using the calculation results of Examples 1 to 4 and Examples 8 to 12, the variation trend of lithium leaching rate with leaching time is obtained. Figure 2 It can be seen that at 10°C, the lithium leaching rate is 67.8%. Between 10°C and 60°C, as the leaching temperature increases, the leaching rate increases rapidly, reaching more than 90% at 60°C; as the temperature continues to rise, the leaching rate also increases. This shows that the present invention has successfully prepared a low eutectic solvent that can realize lithium recovery in waste lithium iron phosphate batteries at a relatively low temperature.

[0065] Comparative Example 1

[0066] Comparative Example 1 provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S2, citric acid is not added as a hydrogen bond donor, and the rest is roughly the same as Example 1, which will not be repeated here.

[0067] Comparative Example 2

[0068] Comparative Example 2 provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S2, glycine is not added as a hydrogen bond donor, and the rest is roughly the same as Example 1, which will not be repeated here.

[0069] Comparative Example 3

[0070] Comparative Example 3 provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S2, choline chloride is used as a hydrogen bond acceptor, and the rest is roughly the same as Example 1, which will not be repeated here.

[0071] Comparative Example 4

[0072] Comparative Example 4 provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S2, propylene glycol is used as a hydrogen bond donor, and the rest is roughly the same as Example 1, which will not be repeated here.

[0073] Comparative Example 5

[0074] Comparative Example 5 provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S2, oxalic acid is used as a hydrogen bond donor, and the rest is roughly the same as Example 1, which will not be repeated here.

[0075] Comparative Example 6

[0076] Comparative Example 6 provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that step S2 is not performed, and in step S3, hydrochloric acid is used instead of the low eutectic solvent. The rest is roughly the same as Example 1 and will not be repeated here.

[0077] In order to eliminate the interference of unnecessary factors, the waste lithium iron phosphate batteries used in Comparative Examples 1 to 6 are the same, and the positive electrode of the battery contains 4.47% Li, 26.59% Fe, 16.45% P, and 52.49% other. The lithium ion solutions obtained in Comparative Examples 1 to 6 were tested by atomic absorption spectroscopy for Li + The content of Li in 1g of lithium iron phosphate positive electrode powder was analyzed. + The content was analyzed and the lithium leaching rate was calculated. The results are shown in the following table.

[0078] Table 2 Test results of comparative examples 1 to 6

[0079]

[0080] As can be seen from Table 2, in Comparative Examples 1 to 2, when there is only a citric acid hydrogen bond donor or a glycine hydrogen bond acceptor, the strong electrostatic effect of the two cannot be exerted, and only the hydrogen bond effect of one of the materials is used to leach lithium, resulting in a significant decrease in its leaching rate. From the data of Comparative Examples 3 to 5, it can be seen that it is difficult to exert the synergistic effect of the two substances in Example 1 by replacing the hydrogen bond acceptor or hydrogen bond donor with other types of substances. In Comparative Example 6, hydrochloric acid is used to recover lithium from lithium iron phosphate. Although the leaching rate is high, hydrochloric acid has strong corrosiveness and poor environmental protection, and the waste liquid generated requires special treatment, which increases the recovery cost.

[0081] Embodiment 13

[0082] This embodiment provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S2, malic acid is used as a hydrogen bond donor. The rest is roughly the same as Example 1 and will not be repeated here. Test results Li in solution + The content is 0.03862g, and the highest leaching rate reaches 86.4%.

[0083] Embodiment 14

[0084] This embodiment provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S2, lactic acid is used as a hydrogen bond donor and alanine is used as a hydrogen bond acceptor. The rest is roughly the same as Example 1 and will not be repeated here. Test results Li in solution + The content is 0.04023g, and the highest leaching rate reaches 90.0%.

[0085] Embodiment 15

[0086] This embodiment provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent. Compared with Example 1, the difference is that in step S2, proline is used as a hydrogen bond acceptor, and the rest is roughly the same as Example 1, which will not be repeated here. Test results Li in solution + The content is 0.020234g, and the highest leaching rate reaches 63.33%.

[0087] In summary, the present invention provides a method for recovering lithium from waste lithium iron phosphate batteries using a low eutectic solvent, wherein the waste lithium iron phosphate battery is completely discharged and disassembled to obtain a battery positive electrode sheet, and the battery positive electrode sheet is heated under nitrogen to obtain lithium iron phosphate powder; a hydrogen bond donor and a hydrogen bond acceptor are mixed in deionized water, and stirred at a constant temperature until a clear low eutectic solvent is obtained; finally, the lithium iron phosphate powder is placed in a low eutectic solvent, stirred and leached at a constant temperature, and the solution is separated to obtain a lithium ion solution, thereby completing the recovery of lithium from waste lithium iron phosphate batteries. The present invention uses a carboxylic acid compound containing both hydroxyl and carboxyl groups as a hydrogen bond donor, and an amino acid as a hydrogen bond acceptor to prepare a low eutectic solvent; the two not only have a hydrogen bond effect to form a hydrogen bond network, but also the amino group of the amino acid and the hydroxyl and carboxyl groups of the carboxylic acid compound have a strong electrostatic effect during the formation of the low eutectic solvent, and under the hydrogen bond network and strong electrostatic effect, a large degree of melting point reduction is promoted, and the stability of the solvent is also promoted, forming a low eutectic solvent with a high lithium leaching rate. In addition, the present invention adopts two different organic acids as hydrogen bond donors and acceptors respectively, which synergistically improves the acidity of the leaching environment. The acidic conditions are more conducive to the recovery of lithium in waste lithium iron phosphate batteries, overcoming the disadvantages of the traditional need to introduce highly corrosive inorganic acids to recover lithium iron phosphate, which seriously pollutes the environment and can only be recovered in the form of compound metals; and both acids are easily soluble in water, and can be mixed with deionized water, so that the fluidity of the low eutectic solvent is good, the kinetic energy of the lithium iron phosphate powder molecules is increased, the mobility is improved, and the lithium iron phosphate powder is fully contacted and reacted, which saves reaction time and is more conducive to improving the leaching rate and leaching efficiency of lithium in the recovery of lithium iron phosphate. The present invention prepares a low eutectic solvent with good fluidity and high efficiency for leaching lithium from waste lithium iron phosphate batteries, and efficiently recovers lithium in the battery in a short time and at a lower temperature, thereby realizing a green and non-toxic leaching process and maximizing the recovery value of waste lithium iron phosphate batteries, and has industrial application value.

[0088] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent, characterized in that: The following steps are involved: S1, placing the waste lithium iron phosphate battery in a discharge solution, disassembling it after it is completely discharged to obtain a positive electrode sheet of the battery; heating the positive electrode sheet of the battery to 500-700° C. under a nitrogen atmosphere to obtain lithium iron phosphate powder; S2. Mix the hydrogen bond donor and the hydrogen bond acceptor in deionized water, and stir in a constant temperature heated magnetic stirrer until a clear solution is obtained, wherein the clear solution is a low eutectic solvent; specifically, the hydrogen bond donor is one of citric acid, malic acid, and lactic acid; the hydrogen bond acceptor is one of glycine, alanine, and proline; and the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:(0.5-1.2); S3, placing the lithium iron phosphate powder of step S1 in the low eutectic solvent of step S2, stirring and leaching in a constant temperature heating magnetic stirrer, the leaching temperature is 10-90° C., and the leaching time is 1-4 hours; S4, separating and treating the liquid treated in step S3 to obtain a lithium ion solution, thereby completing the recovery of lithium in the waste lithium iron phosphate battery.

2. The method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent according to claim 1, characterized in that: The molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:

1.

3. The method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent according to claim 1, characterized in that: In step S2, the molar ratio of the hydrogen bond donor, the hydrogen bond acceptor and the deionized water is 1:(0.5-1.2):

1.

4. The method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent according to claim 1, characterized in that: In step S3, the mass ratio of the lithium iron phosphate powder to the low eutectic solvent is 1:(15-25).

5. The method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent according to claim 1, characterized in that: In step S2, the leaching temperature is 60-90°C, and the leaching time is 2-2.5 hours.

6. The method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent according to claim 1, characterized in that: In step S2, the hydrogen bond donor is citric acid, and the hydrogen bond acceptor is glycine; the stirring temperature is 40 to 60° C., and the stirring time is 2 to 2.5 hours.

7. The method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent according to claim 1, characterized in that: In step S2, the stirring speed of the constant temperature heating magnetic stirrer is 800-1200 r / min; in step S3, the stirring speed of the constant temperature heating magnetic stirrer is 600-900 r / min.

8. The method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent according to claim 1, characterized in that: In step S1, the discharge solution is a saturated sodium chloride solution.

9. The method for recovering lithium from waste lithium iron phosphate batteries using a deep eutectic solvent according to claim 1, characterized in that: In step S4, the separation treatment includes one of membrane filtration, centrifugation, and suction filtration.

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