Method for extracting lithium hexafluorophosphate from waste lithium batteries

Abstract

The application provides a method for extracting lithium hexafluorophosphate from waste lithium batteries, and belongs to the field of waste lithium battery recycling. Waste lithium battery fragments are soaked in a first organic solvent, and a filtrate containing lithium hexafluorophosphate is obtained after filtration. The filtrate is evaporated to prepare a lithium hexafluorophosphate crude product. The crude product is dissolved in a second organic solvent, and then a redox active substance is added. Next, an oxidizing agent is added, and after standing, an organic phase and an aqueous phase are obtained. The organic phase dissolves a hydrophobic salt. The organic phase is subjected to vacuum distillation to obtain the hydrophobic salt. The hydrophobic salt is dissolved in a third organic solvent, and a lithium-containing reducing agent is added. Through a redox reaction, an organic solution containing uncharged molecules and lithium hexafluorophosphate is obtained. The organic solution is subjected to vacuum distillation and purification to obtain lithium hexafluorophosphate solids. The preparation method is simple, mature, easy to implement, and has engineering application value.

Description

Technical Field

[0001] This invention belongs to the field of waste lithium battery recycling, and more specifically, relates to a method for extracting lithium hexafluorophosphate from waste lithium batteries. Background Technology

[0002] With the development of the lithium-ion battery industry, the recycling of spent lithium-ion batteries has received increasing attention. Currently, lithium-ion battery recycling technologies mainly focus on the recycling of positive and negative electrode materials, while there is still no mature solution for electrolyte recycling.

[0003] In fact, spent lithium-ion batteries still contain a large amount of electrolyte, especially lithium hexafluorophosphate, which has high industrial value. Each ton of spent lithium-ion batteries contains approximately 15 kilograms of lithium hexafluorophosphate. Under current battery recycling processes, most of the lithium hexafluorophosphate is pyrolyzed at high temperatures, turning into fluorine-containing waste gas, which is then absorbed by alkaline solutions. This process undoubtedly wastes lithium hexafluorophosphate and may cause environmental pollution.

[0004] The main reason why lithium hexafluorophosphate is difficult to recycle is that it is not heat-resistant, easily hydrolyzed, and has a strong binding force with impurities. Once exposed to humid air or at temperatures above 60°C, lithium hexafluorophosphate decomposes to produce harmful substances such as hydrogen fluoride, lithium fluoride, trifluorophosphoric acid, phosphorus pentafluoride, and monofluorophosphoric acid. Furthermore, impurities generated during battery cycling, such as carbonate ions, carbonate solvents, carboxylate ions, and fluoride ions, bind tightly to lithium ions in lithium hexafluorophosphate and are difficult to remove at room temperature.

[0005] To solve the above problems, it is necessary to develop a method for extracting lithium hexafluorophosphate from waste lithium batteries. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for extracting lithium hexafluorophosphate from waste lithium batteries, aiming to solve the waste problem caused by the difficulty or lack of recycling of lithium hexafluorophosphate from waste lithium batteries in the prior art.

[0007] To achieve the above objectives, the present invention provides a method for extracting lithium hexafluorophosphate from waste lithium batteries, comprising the following steps:

[0008] S1: Disassemble and crush the waste lithium batteries, add the first organic solvent to soak the battery fragments, and filter to obtain a filtrate containing lithium hexafluorophosphate.

[0009] S2: Evaporate the solvent from the filtrate in step S1 to obtain crude lithium hexafluorophosphate;

[0010] S3: Dissolve the crude lithium hexafluorophosphate obtained in step S2 in a second organic solvent, and then add a reduced redox active substance to obtain a mixed solution. The second organic solvent is not completely miscible with water. The redox active substance has two states: oxidized and reduced. Its reduced state is an uncharged molecule, and its oxidized state is a positively charged ion. The oxidized and reduced states can be reversibly interconverted.

[0011] S4: Add an oxidant to the mixed solution obtained in step S3 and allow it to stand for phase separation, so that the redox active substance is oxidized into positive ions. After standing, an organic phase and an aqueous phase are obtained. The hydrophobic salt formed by the positive ions and hexafluorophosphate will preferentially dissolve in the organic phase.

[0012] S5: The organic phase obtained in step S4 is subjected to vacuum distillation to remove the solvent and obtain a hydrophobic salt.

[0013] S6: Dissolve the hydrophobic salt obtained in step S5 in a third organic solvent, add a lithium-containing reducing agent, and obtain an organic solution containing the uncharged molecule and lithium hexafluorophosphate through a redox reaction.

[0014] S7: The organic solution obtained in step S6 is subjected to vacuum distillation to remove the third solvent, directly obtaining lithium hexafluorophosphate, or

[0015] The organic solution obtained in step S6 is subjected to vacuum distillation to remove the third solvent, and then a nonpolar organic solvent is added to wash away the uncharged molecules, yielding solid lithium hexafluorophosphate, or

[0016] The organic solution obtained in step S6 is subjected to vacuum distillation to remove the third solvent, and then recrystallized to obtain solid lithium hexafluorophosphate.

[0017] In the above-mentioned inventive concept, crude lithium hexafluorophosphate contains many impurities, most of which are hydrophilic. Hexafluorophosphate ions, however, are rare anions with weak interactions with water molecules. They can combine with oxidized redox active substances to form hydrophobic salts, which preferentially dissolve in the organic phase rather than the aqueous phase, thus separating them from the vast majority of impurities. Furthermore, experiments have shown that the hydrophobic salts formed by the combination of hexafluorophosphate ions and oxidized redox active substances do not hydrolyze even under acidic conditions, thus significantly improving the extraction efficiency of hexafluorophosphate ions.

[0018] For some reduced redox molecules, they evaporate along with the solvent during vacuum distillation. The organic solution obtained in step S6 is subjected to vacuum distillation to remove the third solvent, directly yielding lithium hexafluorophosphate. Reduced redox molecules with such properties include 2,2,6,6-tetramethylpiperidine-1-oxo radical and ferrocene. Besides washing, recrystallization can also purify solid lithium hexafluorophosphate. Recrystallization can be achieved by dissolving a mixture of lithium hexafluorophosphate obtained from vacuum distillation and the reduced redox active substance in a suitable polar organic solvent, increasing the temperature to improve the solubility of lithium hexafluorophosphate in the organic solvent, and then cooling to allow the lithium hexafluorophosphate to crystallize out; or, based on the difference in solubility of lithium hexafluorophosphate in organic solvents, dissolving the mixture of lithium hexafluorophosphate obtained from vacuum distillation and the reduced redox active substance in a suitable polar good organic solvent, adding a poor solvent for lithium hexafluorophosphate to the solution to allow the lithium hexafluorophosphate to crystallize out.

[0019] Furthermore, the first organic solvent in step S1 is a polar solvent, which is one or more of esters, ethers, and nitrile solvents, with a boiling point not higher than 200°C, and is selected from one or more of dimethyl carbonate, ethyl acetate, butyl acetate, ethylene glycol diethyl ether, tetrahydrofuran, and acetonitrile.

[0020] In step S4, the oxidant is a mixed aqueous solution of hydrogen peroxide and sulfuric acid, or a mixed aqueous solution of hydrogen peroxide and hydrofluoric acid. Whether it is a mixed aqueous solution of hydrogen peroxide and sulfuric acid or a mixed aqueous solution of hydrogen peroxide and hydrofluoric acid, it is diluted with water to obtain a low concentration aqueous solution.

[0021] Furthermore, the second organic solvent is not completely miscible with water, and the second organic solvent is selected from one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, butyl acetate, and ethylene glycol diethyl ether.

[0022] Furthermore, in step S3, the redox active substance is one or more of nitrogen oxides and their derivatives, metallocene complexes, viologen compounds, phenothiazine compounds, and thiaanthra compounds, selected from one or more of 2,2,6,6-tetramethylpiperidine-1-oxy radical, ferrocene, methyl viologen, 10-methylphenothiazine, and thiaanthra.

[0023] Furthermore, in step S5, after obtaining the hydrophobic salt, the hydrophobic salt is rinsed with water to improve its purity, specifically as follows: water is added to the hydrophobic salt, the mass ratio of hydrophobic salt to water is 1:80~1:100, the mixture is thoroughly mixed, filtered, the precipitate and filtrate are separated, the process is repeated 3~5 times, and the resulting precipitate is dried to improve its purity.

[0024] Furthermore, in step S6, the third polar solvent is one or more of esters, ethers, and nitrile solvents, with a boiling point not higher than 200°C, selected from one or more of dimethyl carbonate, ethyl acetate, butyl acetate, ethylene glycol diethyl ether, tetrahydrofuran, and acetonitrile, and the water content in the third polar solvent is not greater than 1%.

[0025] Furthermore, in step S6, the lithium-containing reducing agent is a reducing substance selected from one or more of lithium metal, lithium hydride, lithium-intercalated graphite, and lithium-intercalated lithium titanate.

[0026] Furthermore, in step S7, the nonpolar organic solvent has a dielectric constant of less than 3, and is capable of dissolving reduced redox active substances, selected from one or more of toluene, chlorobenzene, n-hexane, and petroleum ether.

[0027] Furthermore, step S7 is followed by step S8, which is: further purifying the lithium hexafluorophosphate solid, specifically as follows: dissolving the lithium hexafluorophosphate solid with anhydrous hydrofluoric acid, filtering under low temperature vacuum, and then drying under vacuum at room temperature to complete the purification of lithium hexafluorophosphate.

[0028] Furthermore, sodium carbonate aqueous solution is added to the aqueous phase obtained after phase separation in step S4, mixed thoroughly, filtered, and the precipitate and filtrate are separated. This process is repeated 3 to 5 times. The resulting precipitate is lithium carbonate, wherein the concentration of sodium carbonate aqueous solution is 2% to saturation by mass. The aqueous phase obtained after phase separation in step S4 contains lithium ions and other hydrophilic impurities.

[0029] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0030] This invention proposes a novel approach and method for extracting lithium hexafluorophosphate. Utilizing the principle of solvent extraction, lithium ions and hexafluorophosphate ions in the battery are separated in different liquid phases, purified into different compounds, and then regenerated as pure lithium hexafluorophosphate through a redox reaction. This method is simple in principle, uses common materials, and involves a straightforward process, making it valuable for practical engineering applications. Attached Figure Description

[0031] Figure 1 This is a flowchart of a method for extracting lithium hexafluorophosphate from waste lithium batteries provided by the present invention;

[0032] Figure 2 This is a flowchart of the method for extracting lithium hexafluorophosphate from waste lithium batteries provided in Embodiment 1 of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0034] Figure 1 This is a flowchart of a method for extracting lithium hexafluorophosphate from waste lithium batteries provided by the present invention. As shown in the figure, it shows the main core steps, including: S1: Disassembling and crushing the waste lithium batteries, soaking the battery fragments in a first organic solvent, filtering to obtain a filtrate containing lithium hexafluorophosphate; S2: Evaporating to remove the solvent from the filtrate in step S1 to obtain crude lithium hexafluorophosphate; S3: Dissolving the crude lithium hexafluorophosphate obtained in step S2 in a second organic solvent, and then adding a reduced redox active substance to obtain a mixed solution. The second organic solvent is not completely miscible with water. The redox active substance has two states: oxidized and reduced. The reduced state is an uncharged molecule, and the oxidized state is a positively charged ion. The oxidized and reduced states can be reversibly interconverted. S4: Add an oxidant to the mixed solution obtained in step S3 and allow it to stand for phase separation, so that the redox active substance is oxidized into positive ions. After standing, an organic phase and an aqueous phase are obtained. The hydrophobic salt composed of the positive ions and hexafluorophosphate ions will preferentially dissolve in the organic phase. S5: Perform vacuum distillation on the organic phase obtained in step S4 to remove the solvent and obtain the hydrophobic salt. S6: Dissolve the hydrophobic salt obtained in step S5 in a third organic solvent, add a lithium-containing reducing agent, and obtain an organic solution containing the uncharged molecules and lithium hexafluorophosphate through a redox reaction. S7: Perform vacuum distillation on the organic solution obtained in step S6 to remove the third solvent, and then add a nonpolar organic solvent to wash away the uncharged molecules and obtain solid lithium hexafluorophosphate.

[0035] To illustrate the method of the present invention in more detail, the following detailed description is provided in conjunction with specific embodiments.

[0036] Example 1

[0037] Figure 2 A flowchart of the method for extracting lithium hexafluorophosphate from waste lithium batteries according to Embodiment 1 of the present invention is provided. As shown in the figure, this embodiment includes the following steps:

[0038] S1: Disassemble and crush a 100Ah waste lithium iron phosphate soft pack battery, add 1000ml of acetonitrile to the obtained battery fragments, so that the fragments are completely immersed in acetonitrile, filter and collect the filtrate.

[0039] S2: Vacuum evaporate the acetonitrile in the filtrate to obtain 26g of crude lithium hexafluorophosphate, which is in the form of a viscous paste.

[0040] S3: Dissolve crude lithium hexafluorophosphate in 100ml of dimethyl carbonate, and then add 35g of reduced ferrocene.

[0041] S4: Add 65g of 10% hydrogen peroxide solution and 2ml of 2mol / L sulfuric acid aqueous solution to an organic solution containing crude lithium hexafluorophosphate and reduced ferrocene. Shake thoroughly to mix, obtaining oxidized ferrocene. Allow the mixture to stand and separate into an organic phase and an aqueous phase. The salt composed of oxidized ferrocene and hexafluorophosphate preferentially dissolves in the organic phase.

[0042] S5: The organic phase obtained above is subjected to vacuum distillation to remove dimethyl carbonate, yielding a salt composed of oxidized ferrocene and hexafluorophosphate, namely ferrocene hexafluorophosphate.

[0043] Wash the oxidized salt composed of ferrocene and hexafluorophosphate with water: Add water to ferrocene hexafluorophosphate at a mass ratio of 1:80, mix thoroughly, filter, separate the precipitate and filtrate, repeat 3 times, and the resulting precipitate is ferrocene hexafluorophosphate. Then dry the obtained ferrocene hexafluorophosphate to improve its purity. A total of 40g of ferrocene hexafluorophosphate was obtained.

[0044] S6: Dissolve the ferrocene hexafluorophosphate obtained above in 100 ml of tetrahydrofuran with a water content of less than 0.2 ppm, add 1 g of lithium metal, and obtain an organic solution containing reduced ferrocene and lithium hexafluorophosphate through a redox reaction.

[0045] S7: The organic solution containing ferrocene and lithium hexafluorophosphate obtained above was subjected to vacuum distillation to remove tetrahydrofuran and reduced ferrocene, yielding 17g of lithium hexafluorophosphate solid.

[0046] The recovery rate of hexafluorophosphate was 95%, and its purity was 95% as determined by inductively coupled plasma mass spectrometry and nuclear magnetic resonance.

[0047] Example 2

[0048] Steps S1 to S7 are the same as in Example 1, except for step S8: further purifying the lithium hexafluorophosphate solid obtained in Example 1, specifically as follows: dissolving the lithium hexafluorophosphate solid in anhydrous hydrofluoric acid, vacuum filtering at low temperature (below -20°C), and vacuum drying at room temperature to obtain 15g of lithium hexafluorophosphate with a purity of 99.9%.

[0049] Example 3

[0050] A 10% (w / w) sodium carbonate aqueous solution was added to the aqueous phase containing lithium ions and other hydrophilic impurities obtained after phase separation in Example 1. The mixture was thoroughly mixed, filtered, and the precipitate and filtrate were separated. This process was repeated three times, and the resulting precipitate was lithium carbonate. The obtained lithium carbonate was dried under a vacuum of -0.1 MPa at 50°C, and 11 g of lithium carbonate was obtained. The lithium ion recovery rate was 95%, and its purity was determined to be 99% by nuclear magnetic resonance.

[0051] Example 4

[0052] The lithium carbonate and hydrochloric acid from Example 3 were mixed to obtain a lithium chloride solution. The lithium chloride solution was evaporated at 110°C to obtain anhydrous lithium chloride. Further, the solution was heated to 200°C under reduced pressure and in a dry HCl gas stream to obtain high-purity anhydrous lithium chloride. A mixed molten salt of LiCl / KCl was electrolyzed at 600°C to obtain metallic lithium. The obtained metallic lithium can be used as a lithium-containing reducing agent to prepare lithium hexafluorophosphate.

[0053] Example 5

[0054] S1: Disassemble and crush a 100Ah waste ternary 523 square battery, add 1000ml of dimethyl carbonate to the obtained battery fragments, so that the fragments are completely immersed in dimethyl carbonate, filter and collect the filtrate.

[0055] S2: Evaporate the dimethyl carbonate in the filtrate to obtain 27g of crude lithium hexafluorophosphate, which is a viscous liquid.

[0056] S3: Dissolve crude lithium hexafluorophosphate in 100 ml of propylene carbonate, and then add 36 g of reduced 2,2,6,6-tetramethylpiperidine-1-oxy free radical;

[0057] S4: Add 65g of 12% hydrogen peroxide solution and 3ml of 1mol / L sulfuric acid aqueous solution to an organic solution containing crude lithium hexafluorophosphate and reduced 2,2,6,6-tetramethylpiperidine-1-oxo radicals. Shake thoroughly to mix and obtain oxidized 2,2,6,6-tetramethyl-1-oxopiperidine cations. Allow the mixture to stand and separate the phases to obtain an organic phase and an aqueous phase. The salt formed by the oxidized 2,2,6,6-tetramethyl-1-oxopiperidine cations and hexafluorophosphate ions preferentially dissolves in the organic phase.

[0058] S5: The organic phase obtained above is subjected to vacuum distillation to remove propylene carbonate, and a salt composed of oxidized 2,2,6,6-tetramethyl-1-oxopiperidinium cation and hexafluorophosphate is obtained, namely 2,2,6,6-tetramethyl-1-oxopiperidinium hexafluorophosphate.

[0059] The oxidized salt composed of the 2,2,6,6-tetramethyl-1-oxopiperidine cation and hexafluorophosphate was rinsed with water: Water was added to 2,2,6,6-tetramethyl-1-oxopiperidine hexafluorophosphate at a mass ratio of 1:85. The mixture was thoroughly mixed, filtered, and the precipitate and filtrate were separated. This process was repeated three times. The resulting precipitate was 2,2,6,6-tetramethyl-1-oxopiperidine hexafluorophosphate. The obtained 2,2,6,6-tetramethyl-1-oxopiperidine hexafluorophosphate was then dried to improve its purity, yielding a total of 40 g of 2,2,6,6-tetramethyl-1-oxopiperidine hexafluorophosphate.

[0060] S6: Dissolve the 2,2,6,6-tetramethyl-1-oxopiperidine hexafluorophosphate obtained above in 100 ml of acetonitrile with a water content of less than 0.02 ppm, add 100 g of lithium-intercalated graphite, and obtain an organic solution containing reduced 2,2,6,6-tetramethylpiperidine-1-oxo radicals and lithium hexafluorophosphate through a redox reaction.

[0061] S7: The organic solution containing 2,2,6,6-tetramethylpiperidine-1-oxy radical and lithium hexafluorophosphate obtained above was subjected to vacuum distillation to remove acetonitrile. The mixture of lithium hexafluorophosphate and 2,2,6,6-tetramethylpiperidine-1-oxy radical obtained by vacuum distillation was dissolved in 200 ml of tetraethylene glycol dimethyl ether. 50 ml of n-hexane was added to the solution to allow lithium hexafluorophosphate to crystallize out, yielding 20 g of solid lithium hexafluorophosphate.

[0062] The recovery rate of hexafluorophosphate was 95%, and its purity was 97% as determined by inductively coupled plasma mass spectrometry and nuclear magnetic resonance.

[0063] Example 6

[0064] S1: Disassemble and crush a 10Ah waste lithium iron phosphate soft-pack battery, add 150ml of ethyl acetate to the obtained battery fragments, so that the fragments are completely immersed in ethyl acetate, and filter and collect the filtrate.

[0065] S2: Vacuum evaporate the ethyl acetate in the filtrate to obtain 3g of crude lithium hexafluorophosphate, which is a viscous liquid.

[0066] S3: Dissolve crude lithium hexafluorophosphate in 20 ml of ethylene glycol diethyl ether, and then add 7 g of reduced methyl viologen.

[0067] S4: Add 15g of 7% hydrogen peroxide solution and 4ml of 1mol / L sulfuric acid aqueous solution to the organic solution containing crude lithium hexafluorophosphate and reduced methyl viologen. Shake thoroughly to obtain oxidized methyl viologen. Allow the mixture to stand and separate the phases to obtain an organic phase and an aqueous phase. The salt composed of oxidized methyl viologen and hexafluorophosphate ions preferentially dissolves in the organic phase.

[0068] S5: The organic phase obtained above is subjected to vacuum distillation to remove ethylene glycol diethyl ether, and a salt composed of oxidized methyl viologen and hexafluorophosphate is obtained, namely methyl viologen hexafluorophosphate.

[0069] The oxidized salt composed of methyl viologen and hexafluorophosphate was rinsed with water: Water was added to methyl viologen hexafluorophosphate at a mass ratio of 1:95. The mixture was thoroughly mixed, filtered, and the precipitate and filtrate were separated. This process was repeated 3 times. The resulting precipitate was methyl viologen hexafluorophosphate. The obtained methyl viologen hexafluorophosphate was then dried to improve its purity, yielding a total of 7g of methyl viologen hexafluorophosphate.

[0070] S6: Dissolve the methyl viologen hexafluorophosphate obtained above in 30 ml of butyl acetate with a water content of less than 0.02 ppm, add 1 g of lithium hydride, and obtain an organic solution containing reduced methyl viologen and lithium hexafluorophosphate through a redox reaction.

[0071] S7: The organic solution containing methyl viologen and lithium hexafluorophosphate obtained above was subjected to vacuum distillation to remove butyl acetate, and then petroleum ether was added to wash away the reduced methyl viologen, yielding 2.3g of lithium hexafluorophosphate solid.

[0072] The recovery rate of hexafluorophosphate was 92%, and its purity was 98% as determined by inductively coupled plasma mass spectrometry and nuclear magnetic resonance.

[0073] Example 7

[0074] S1: Disassemble and crush a 30Ah waste lithium iron phosphate soft-pack battery, add 300ml of butyl acetate to the obtained battery fragments, and immerse the fragments completely in butyl acetate.

[0075] S2: Vacuum evaporate the butyl acetate in the filtrate to obtain 8g of crude lithium hexafluorophosphate, which is a viscous liquid.

[0076] S3: Dissolve crude lithium hexafluorophosphate in 40 ml of ethyl acetate, and then add 16 g of reduced 10-methylphenthiazide.

[0077] S4: Add 120 g of 7% hydrogen peroxide solution and 2 ml of 2 mol / L sulfuric acid aqueous solution to an organic solution containing crude lithium hexafluorophosphate and reduced 10-methylphenthiazide. Shake thoroughly to obtain oxidized 10-methylphenthiazide. Allow the mixture to stand and separate the phases to obtain an organic phase and an aqueous phase. The salt composed of oxidized 10-methylphenthiazide and hexafluorophosphate is preferentially dissolved in the organic phase.

[0078] S5: The organic phase obtained above is subjected to vacuum distillation to remove ethyl acetate, yielding a salt composed of oxidized 10-methylphenothiazine and hexafluorophosphate, namely 10-methylphenothiazine hexafluorophosphate.

[0079] The oxidized salt composed of 10-methylphenothiazine and hexafluorophosphate was rinsed with water: Water was added to 10-methylphenothiazine hexafluorophosphate at a mass ratio of 1:100. The mixture was thoroughly mixed, filtered, and the precipitate and filtrate were separated. This process was repeated 4 times. The resulting precipitate was 10-methylphenothiazine hexafluorophosphate. The obtained 10-methylphenothiazine hexafluorophosphate was then dried to improve its purity, yielding a total of 17g of 10-methylphenothiazine hexafluorophosphate.

[0080] S6: Dissolve the 10-methylphenothiazine hexafluorophosphate obtained above in 50 ml of ethylene glycol diethyl ether with a water content of less than 0.05 ppm, add 1 g of lithium metal, and obtain an organic solution containing reduced 10-methylphenothiazine and lithium hexafluorophosphate through a redox reaction.

[0081] S7: The organic solution containing 10-methylphenothiazine and lithium hexafluorophosphate obtained above is subjected to vacuum distillation to remove ethylene glycol diethyl ether. The mixture of lithium hexafluorophosphate and 10-methylphenothiazine obtained by vacuum distillation is dissolved in 250 ml of diethylene glycol dimethyl ether, the temperature is raised to 45°C, and then cooled to -40°C to allow lithium hexafluorophosphate to crystallize and precipitate, yielding 7 g of lithium hexafluorophosphate solid.

[0082] The recovery rate of hexafluorophosphate was 95%, and its purity was 98.6% as determined by inductively coupled plasma mass spectrometry and nuclear magnetic resonance.

[0083] Example 8

[0084] S1: Disassemble and crush a 40Ah waste lithium iron phosphate soft-pack battery, add 450ml of a mixed solvent of ethylene glycol diethyl ether and tetrahydrofuran to the obtained battery fragments, and completely immerse the fragments in the mixed solvent. The volume ratio of ethylene glycol diethyl ether to tetrahydrofuran is 1:1.

[0085] S2: Vacuum evaporate the mixed solvent of ethylene glycol diethyl ether and tetrahydrofuran to obtain 13g of crude lithium hexafluorophosphate, which is in the form of a viscous paste.

[0086] S3: Dissolve crude lithium hexafluorophosphate in 60 ml of a mixed solvent of diethyl carbonate and butyl acetate, with a volume ratio of 1:1, and then add 28 g of reduced thiamethoxam.

[0087] S4: Add 72g of 6% hydrogen peroxide solution and 5ml of 1mol / L sulfuric acid aqueous solution to the organic solution containing crude lithium hexafluorophosphate and reduced thiamethoxam. Shake thoroughly to mix and obtain oxidized thiamethoxam. Allow the mixture to stand and separate the phases to obtain an organic phase and an aqueous phase. The salt composed of oxidized thiamethoxam and hexafluorophosphate is preferentially dissolved in the organic phase.

[0088] S5: The organic phase obtained above is subjected to vacuum distillation to remove the mixed solution of butyl acetate and diethyl carbonate, and a salt composed of oxidized thiaanthra and hexafluorophosphate is obtained, namely thiaanthra hexafluorophosphate.

[0089] The oxidized salt composed of thiaethene and hexafluorophosphate was rinsed with water: Water was added to thiaethene hexafluorophosphate at a mass ratio of 1:98, and the mixture was thoroughly mixed, filtered, and the precipitate and filtrate were separated. This process was repeated 4 times. The precipitate obtained was thiaethene hexafluorophosphate. The obtained thiaethene hexafluorophosphate was then dried to improve its purity, yielding a total of 27g of thiaethene hexafluorophosphate.

[0090] S6: Dissolve the thiamethoxam hexafluorophosphate obtained above in 50 ml of a mixed solvent of dimethyl carbonate and ethyl acetate with a water content of less than 0.05 ppm, wherein the volume ratio of dimethyl carbonate to ethyl acetate is 1:1. Add 220 g of lithium titanate in lithium-intercalated state, and obtain an organic solution containing reduced thiamethoxam and lithium hexafluorophosphate through a redox reaction.

[0091] S7: The organic solution containing thiaanthracene and lithium hexafluorophosphate obtained above was subjected to vacuum distillation to remove ethyl acetate, and then n-hexane was added to wash away the reduced thiaanthracene, yielding 10g of lithium hexafluorophosphate solid.

[0092] The recovery rate of hexafluorophosphate was 95.5%, and its purity was 97.5% as determined by inductively coupled plasma mass spectrometry and nuclear magnetic resonance.

[0093] In this invention, the redox-active substances can be recycled.

[0094] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for extracting lithium hexafluorophosphate from waste lithium batteries, characterized in that, It includes the following steps: S1: Disassemble and crush the waste lithium batteries, add the first organic solvent to soak the battery fragments, and filter to obtain a filtrate containing lithium hexafluorophosphate. S2: Evaporate the solvent from the filtrate in step S1 to obtain crude lithium hexafluorophosphate; S3: Dissolve the crude lithium hexafluorophosphate obtained in step S2 in a second organic solvent, and then add a reduced redox active substance to obtain a mixed solution. The second organic solvent is not completely miscible with water. The redox active substance has two states: oxidized and reduced. Its reduced state is an uncharged molecule, and its oxidized state is a positively charged ion. The oxidized and reduced states can be reversibly interconverted. S4: Add an oxidant to the mixed solution obtained in step S3 and allow it to stand for phase separation, so that the redox active substance is oxidized into positive ions. After standing, an organic phase and an aqueous phase are obtained. The hydrophobic salt formed by the positive ions and hexafluorophosphate will preferentially dissolve in the organic phase. S5: The organic phase obtained in step S4 is subjected to vacuum distillation to remove the solvent and obtain a hydrophobic salt. S6: Dissolve the hydrophobic salt obtained in step S5 in a third organic solvent, add a lithium-containing reducing agent, and obtain an organic solution containing the uncharged molecule and lithium hexafluorophosphate through a redox reaction. S7: The organic solution obtained in step S6 is subjected to vacuum distillation to remove the third solvent, directly obtaining lithium hexafluorophosphate, or The organic solution obtained in step S6 is subjected to vacuum distillation to remove the third solvent, and then a nonpolar organic solvent is added to wash away the uncharged molecules, yielding solid lithium hexafluorophosphate, or The organic solution obtained in step S6 is subjected to vacuum distillation to remove the third solvent, and then recrystallized to obtain solid lithium hexafluorophosphate.

2. The method as described in claim 1, characterized in that, The first organic solvent in step S1 is a polar solvent, which is one or more of esters, ethers, and nitrile solvents, with a boiling point not exceeding 200℃, and is selected from one or more of dimethyl carbonate, ethyl acetate, butyl acetate, ethylene glycol diethyl ether, tetrahydrofuran, and acetonitrile. In step S4, the oxidant is a mixed aqueous solution of hydrogen peroxide and sulfuric acid, or the oxidant is a mixed aqueous solution of hydrogen peroxide and hydrofluoric acid.

3. The method as described in claim 2, characterized in that, The second organic solvent is not completely miscible with water, and the second organic solvent is selected from one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl acetate, butyl acetate, and ethylene glycol diethyl ether.

4. The method as described in claim 3, characterized in that, In step S3, the redox active substance is one or more of nitrogen oxides and their derivatives, metallocene complexes, viologen compounds, phenothiazine compounds and thiaanthracene compounds, selected from one or more of 2,2,6,6-tetramethylpiperidine-1-oxy radical, ferrocene, methyl viologen, 10-methylphenothiazine and thiaanthracene.

5. The method as described in claim 4, characterized in that, In step S5, after obtaining the hydrophobic salt, the hydrophobic salt is rinsed with water to improve its purity. Specifically, water is added to the hydrophobic salt, with a mass ratio of hydrophobic salt to water of 1:80 to 1:

100. The mixture is thoroughly mixed, filtered, and the precipitate and filtrate are separated. The washing process is repeated 3 to 5 times. Finally, the obtained precipitate is dried to improve its purity.

6. The method as described in claim 5, characterized in that, In step S6, the third organic solvent is one or more of esters, ethers, and nitrile solvents, with a boiling point not higher than 200°C, selected from one or more of dimethyl carbonate, ethyl acetate, butyl acetate, ethylene glycol diethyl ether, tetrahydrofuran, and acetonitrile, and the water content in the third polar solvent is not greater than 1%.

7. The method as described in claim 6, characterized in that, In step S6, the lithium-containing reducing agent is a reducing substance selected from one or more of lithium metal, lithium hydride, lithium-intercalated graphite, and lithium-intercalated lithium titanate.

8. The method as described in claim 7, characterized in that, In step S7, the dielectric constant of the nonpolar organic solvent is less than 3, and it can dissolve reduced redox active substances. It is selected from one or more of toluene, chlorobenzene, n-hexane and petroleum ether.

9. The method as described in claim 8, characterized in that, Step S7 is followed by step S8, which involves further purifying the lithium hexafluorophosphate solid. Specifically, the lithium hexafluorophosphate solid is dissolved in anhydrous hydrofluoric acid solution, filtered under low temperature vacuum, and then dried under vacuum at room temperature to complete the purification of lithium hexafluorophosphate.

10. The method as described in claim 9, characterized in that, Add sodium carbonate aqueous solution to the aqueous phase obtained after phase separation in step S4, mix thoroughly, filter, separate the precipitate and filtrate, and repeat the above process 3 to 5 times. The precipitate obtained is lithium carbonate, wherein the concentration of sodium carbonate aqueous solution is 2% to saturation by mass fraction. The aqueous phase obtained after phase separation in step S4 contains lithium ions and other hydrophilic impurities.

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