Method for recycling electrolyte of waste lithium battery

Abstract

The application provides a method for recycling electrolyte of waste lithium battery, which comprises the following steps: disassembling the fully discharged waste lithium battery into positive and negative electrode powder or positive and negative electrode sheet, collecting light components by using negative pressure air induction during the disassembling process, immersing the residual electrolyte in the positive and negative electrode powder or positive and negative electrode sheet into solvent I to obtain leaching liquor, performing primary rectification on the leaching liquor to obtain material II and recyclable solvent I, adding water into the material II under heating condition to decompose solutes in the material II to generate gas phase and material III, passing the gas phase into a salt solution to generate fluoride product, performing secondary rectification on the material III to obtain solvent II, and finally recycling the electrolyte. The application reduces the corrosion of hydrofluoric acid generated by the decomposition of lithium hexafluorophosphate on equipment in the subsequent lithium battery recycling process, improves the utilization rate of fluorine resources, effectively avoids the generation of harmful substances, reduces environmental pollution, and has important significance for battery material recycling and the whole battery recycling industry.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium battery recycling, in particular to a method for recycling and utilizing electrolyte of waste lithium battery. BACKGROUND

[0002] New energy vehicles are one of China's strategic emerging industries, and high-performance lithium battery technology is the key to realizing the national new energy vehicle strategy and the double carbon target. Power batteries account for 1 / 3 of the vehicle cost and 1 / 4 of the weight, with a service life of 5-8 years. Power batteries are about to enter a retirement wave. According to forecasts, the retired power battery volume will be about 780,000 tons in 2025, and the recycling market size will exceed 40 billion yuan. If not properly handled, it will cause significant damage to energy reserves, environmental protection, and human health.

[0003] Currently, waste lithium battery recycling is mostly focused on high-value positive materials, and there is little research on electrolyte recovery. The most commonly used lithium salt in commercial lithium-ion batteries is LiPF6, which accounts for ~15% of the total mass of the electrolyte. Organic solvents account for more than 80%, mainly including cyclic carbonates (PC, EC), chain carbonates (DEC, DMC, EMC), etc. Additives have the characteristics of strong specificity, small dosage, and multiple types. Lithium hexafluorophosphate is easily decomposed into PF5, HF, POF3, and other toxic products when exposed to air, which can cause serious harm to the human body and the environment. Dimethyl carbonate and diethyl carbonate are hazardous chemicals that need to be properly collected and disposed of. Fluorine is a national non-renewable strategic resource, and its resource cost is increasing. The mass fraction of fluorine in lithium hexafluorophosphate is 75.04%, which is much higher than that of ore. From the perspectives of resources and environmental protection, electrolyte recovery and treatment are urgent.

[0004] Currently, the main recovery of electrolyte in retired batteries is lithium elements, and solvents and fluorine are treated harmlessly. Patent CN111704151A separates the fluorine and phosphorus of lithium hexafluorophosphate in waste electrolyte, recycles lithium and fluorine in the form of lithium fluoride, and adds a phosphorus removal agent for phosphorus harmlessness treatment to achieve the harmless utilization of waste electrolyte. Patent CN 105229843B uses carbonate solvents to extract the electrolyte of waste batteries, adds water or inorganic acid under reduced pressure to recover volatile gases, and reacts fluorine in volatile gases with calcium to generate calcium fluoride, and recovers organic components. Patent CN 104105803B adjusts the pH of the lithium-containing solution and then adds carbon dioxide or water-soluble carbonate to precipitate lithium carbonate, and recovers fluorine and phosphorus in the form of fluoride and phosphate, respectively. Patent CN109193062A uses an organic solvent to leach and crush battery materials, adds a potassium ion compound or a metal ion compound solution to the leaching solution for reaction, and separates to obtain potassium hexafluorophosphate or other hexafluorophosphates.

[0005] The mass fraction of fluorine in lithium hexafluorophosphate is as high as 75.04%, and the decomposition in air is slow. If the decomposition is not complete, residues will be left in the positive and negative electrode materials, increasing the corrosion of the equipment in subsequent positive and negative electrode material processing. Fluorine-proof equipment needs to be considered, which will greatly increase the equipment investment. Although the organic solvent is not expensive, some of them are dangerous chemicals, and the amount used is large. If lithium hexafluorophosphate is completely decomposed and then treated and the solvent is recycled, the economic value of battery recycling will be greatly improved. SUMMARY

[0006] In view of the problems in the prior art, the present application provides a method for recycling electrolyte of retired lithium ion batteries, which aims to completely decompose lithium hexafluorophosphate in the electrolyte and recycle it in the form of fluoride, and recycle the solvent after purification, thereby realizing harmless treatment of the electrolyte. The present application is a research on the pretreatment of waste battery recycling, which can reduce the requirements of subsequent processing on equipment and has important significance for the entire battery recycling industry.

[0007] To solve the above technical problems, the present application adopts the following technical scheme:

[0008] A method for recycling electrolyte of waste lithium batteries, wherein the waste lithium batteries are fully discharged and then disassembled into positive and negative electrode powders or positive and negative electrode sheets. During the disassembly process, light components are collected by using negative pressure induced air. The residual electrolyte in the positive and negative electrode powders or positive and negative electrode sheets is leached with a solvent I to obtain a leaching solution. The leaching solution is subjected to primary rectification to obtain the solvent I and a material II. The solvent I can be recycled. Under heating conditions, a certain amount of water is added to the material II, so that the solute in the electrolyte is decomposed to generate a gas phase and a material III. The gas phase is introduced into a salt solution containing lithium / calcium / aluminum / magnesium ions to generate fluoride products such as lithium fluoride, calcium fluoride, aluminum fluoride and magnesium fluoride. The material III is subjected to secondary rectification to obtain a solvent II, thereby realizing harmless and high-value utilization of the electrolyte. The specific steps are as follows:

[0009] (1) Battery disassembly process: the waste lithium batteries are fully discharged and then disassembled into positive and negative electrode powders or positive and negative electrode sheets. During the disassembly process, light components with low boiling point and easy volatilization in the electrolyte are collected by using negative pressure induced air;

[0010] (2) Leaching process: the positive and negative electrode powders or positive and negative electrode sheets obtained in step (1) are added into a solvent I to leach the solvent and lithium salt remaining in the powders or electrode sheets. Filtration separation is performed to obtain a leaching solution and a material I. The material I is directly used for subsequent positive and negative electrode material recycling;

[0011] (3) Primary rectification process: the leaching solution obtained in step (2) is subjected to primary rectification under reduced pressure to separate pure solvent I and a material II. The solvent I is recycled;

[0012] (4) lithium salt decomposition process: nitrogen is introduced into the material II obtained in step (3), water is added under heating conditions to react, so that the solute of the material II is decomposed, to obtain a gas phase and a material III;

[0013] (5) absorption reaction process: the gas phase obtained in step (4) is introduced into a salt solution to perform an absorption reaction, so as to absorb hydrogen fluoride therein, and at the same time, fluoride is generated by reaction;

[0014] (6) secondary rectification process: the material III obtained in step (4) is subjected to secondary rectification, so that the heavy components in the electrolyte are further rectified and purified to obtain the solvent II, and the remaining samples are concentrated for treatment.

[0015] Further, the fully discharged waste lithium battery in step (1) is discharged in a salt solution or on a discharging device, and the voltage of the fully discharged waste lithium battery is less than 1.2V. The waste lithium battery disassembling process in step (1) is carried out in two ways, one is to obtain positive and negative electrode powders after the battery is crushed and sorted by a crushing and sorting device, and the other is to obtain positive and negative electrode sheets after the battery is flexibly disassembled and the electrode sheets are separated.

[0016] Further, the light component in step (1) refers to an electrolyte solvent with a boiling point less than 130℃, including dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate.

[0017] Further, the solvent I in step (2) refers to a solvent with a boiling point less than 100℃, which is miscible with the carbonate solvent in the electrolyte and can dissolve lithium hexafluorophosphate, including dimethyl carbonate, acetone, ethanol, propanol, isopropanol, ethylene glycol dimethyl ether, butanone, etc. The amount of solvent I is 1-5 times the weight of the positive and negative electrode powders or the positive and negative electrode sheets.

[0018] Further, in the primary rectification process in step (3), the operating temperature of the primary vacuum rectification is 50-80℃, and the vacuum degree is 0.05-0.1MPa.

[0019] Further, in the lithium salt decomposition process of step (4), the reaction is heated, and water is added to accelerate the decomposition of the solute in the electrolyte to generate a gas phase containing hydrogen fluoride. The solute refers to lithium salt containing lithium hexafluorophosphate; the gas phase contains hydrogen fluoride generated by the decomposition of the solute; the amount of water added is in a molar ratio of (1.0-1.2):1 to lithium hexafluorophosphate, the reaction temperature is 60-130℃, and the reaction time is 2-48h.

[0020] Further, in the absorption reaction process of step (5), the cation contained in the salt solution is one of lithium, calcium, aluminum or magnesium; the concentration of the cation in the salt solution is 0.1-3 mol / L. The fluoride is one of lithium fluoride, calcium fluoride, aluminum fluoride, magnesium fluoride; specifically, the gas phase containing hydrogen fluoride generated by the decomposition of the solute is introduced into the salt solution containing excess lithium / calcium / aluminum / magnesium ions to perform an absorption reaction, to generate fluoride precipitates such as lithium fluoride, calcium fluoride, aluminum fluoride or magnesium fluoride, wherein the lithium ions in the salt solution come from one or more of lithium hydroxide, lithium nitrate, lithium acetate, lithium carbonate, lithium lactate, lithium chloride, the calcium ions in the salt solution come from one or more of calcium hydroxide, calcium chloride, calcium oxide, the aluminum ions in the salt solution come from one or more of aluminum sulfate, aluminum nitrate, alum, and the magnesium ions in the salt solution come from one or more of magnesium chloride, magnesium sulfate, magnesium acetate.

[0021] Further, in the secondary rectification process of step (6), the operating temperature of the secondary reduced-pressure distillation is 120-200 DEG C, and the vacuum degree is 1 kPa-0.08 MPa.

[0022] Further, in step (6), the heavy component is an electrolyte solvent with a boiling point greater than 200 DEG C, including propylene carbonate and ethylene carbonate.

[0023] Further, the purity of the recovered fluoride is greater than or equal to 98%, which can be reused as a resource; the purity of the recovered solvent I and solvent II is both greater than or equal to 99%, wherein the solvent I can be recycled, and the solvent II can be used to reconfigure the electrolyte, or can be used as a solvent or additive.

[0024] The present application fully discharges the waste lithium battery, disassembles it into positive and negative electrode powder or positive and negative electrode sheet, collects the light components in the electrolyte during the disassembly process, and only leaves the solute and heavy components in the electrolyte part of the positive and negative electrode powder or positive and negative electrode sheet. The solute is leached with a solvent to obtain a leaching solution, the leaching solution is subjected to reduced-pressure distillation to obtain a pure solvent, the pure solvent can be recycled, the heavy component can be completely decomposed into hydrogen fluoride after reacting for a certain period of time in the presence of water, the hydrogen fluoride reacts with excess electrolyte solution to generate fluoride salt precipitates, the heavy component is subjected to distillation to obtain a pure solvent, and finally the electrolyte is recycled and utilized.

[0025] The present application has the beneficial effects that: the present application harmless treatment and utilization of the electrolyte in the waste lithium battery, especially the lithium hexafluorophosphate remaining in the positive and negative electrode powder or positive and negative electrode sheet, compared with the prior art, the process is simple and has high feasibility, and the utilization rate of fluorine element is high. The present application can greatly reduce the corrosion of hydrogen fluoride to equipment in the subsequent positive and negative electrode powder or positive and negative electrode sheet treatment process, greatly reduces the pollution and damage of the comprehensive recycling of waste lithium batteries to the environment, and has important significance for the whole battery recycling process. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the present application, the following will briefly introduce the present application using the accompanying drawings. Obviously, the drawings described below are only some embodiments of the present application, and all other drawings obtained by those skilled in the art without creative effort based on these drawings also belong to the protection scope of the present application.

[0027] Figure 1 The process flow chart of the method for recycling and utilizing waste lithium battery electrolyte.

[0028] Figure 2 The SEM image of lithium fluoride generated in the absorption reaction process. DETAILED DESCRIPTION

[0029] The technical solutions of the present application will be described clearly and completely below by combining the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort also belong to the protection scope of the present application.

[0030] Embodiment 1

[0031] The method for recycling and utilizing waste lithium battery electrolyte in this embodiment is as follows:

[0032] The retired soft-packaged battery is placed on the battery charging and discharging equipment to discharge, so that the voltage is reduced to 1.0 V. The soft-packaged battery is cut, the core and shell are separated, and the pole piece is separated by using a flexible disassembling equipment to obtain the positive and negative pole pieces. In the disassembling process, the easily volatile components in the electrolyte are collected by using the negative pressure induced air. The disassembled positive and negative pole pieces are immersed with dimethyl carbonate to obtain the immersion liquid. The amount of dimethyl carbonate is 2 times the weight of the positive and negative pole pieces. The immersion liquid is subjected to one-time rectification under the condition of 60℃ and 0.08 MPa to obtain dimethyl carbonate with a purity of 99.4%, which can be recycled. Nitrogen gas is introduced into the rectification bottom and water is added, and the molar ratio of water to lithium hexafluorophosphate is 1.0:1. The nitrogen gas and the generated hydrogen fluoride are introduced into a 2 mol / L calcium chloride solution to generate calcium fluoride with a purity of 98.5% after washing. The lithium salt decomposition substrate is subjected to two-time vacuum rectification under the condition of 200℃ and 70 KPa to obtain propylene carbonate with a purity of 99.5%.

[0033] Embodiment 2

[0034] The method for recycling and utilizing waste lithium battery electrolyte in this embodiment is as follows:

[0035] The retired soft package battery is discharged in sodium chloride solution, so that the discharge voltage is less than 1.2V, and the soft package battery is cut, core-shell separated, and pole piece separated by using a flexible disassembly device to obtain positive and negative pole pieces. In the disassembly process, the volatile components in the electrolyte are collected by using a negative pressure air guide method. The disassembled positive and negative pole pieces are immersed in acetone to obtain an immersion liquid. The amount of acetone is 1 times the weight of the positive and negative pole pieces. The immersion liquid is subjected to one-time rectification under the condition of 50℃ and 0.07MPa to obtain acetone with a purity of 99.8%, which can be recycled. Nitrogen is introduced into the rectification bottom, heated to 70℃, and water is added for reaction for 32h. The molar ratio of the amount of water added to lithium hexafluorophosphate is 1.1:1. Nitrogen and generated hydrogen fluoride are introduced into a 3mol / L calcium chloride solution to generate calcium fluoride with a purity of 98.9% after washing. The lithium salt decomposition bottom is subjected to two-time vacuum rectification under the condition of 170℃ and 60KPa to obtain ethylene carbonate with a purity of 99.4%.

[0036] Example 3

[0037] The method for recycling the electrolyte of the waste lithium battery in this example is as follows:

[0038] The retired 18650 battery is discharged on a battery charging and discharging device, so that the voltage is reduced to 1.0V. After disassembly and crushing, positive and negative pole powders are obtained. In the disassembly process, the volatile components in the electrolyte are collected by using a negative pressure air guide method. The disassembled positive and negative pole pieces are immersed in isopropyl alcohol to obtain an immersion liquid. The amount of isopropyl alcohol is 3 times the weight of the positive and negative pole powders. The immersion liquid is subjected to one-time rectification under the condition of 80℃ and 0.05MPa to obtain isopropyl alcohol with a purity of 99.5%, which can be recycled. Nitrogen is introduced into the rectification bottom, heated to 80℃, and water is added for reaction for 20h. The molar ratio of the amount of water added to lithium hexafluorophosphate is 1.2:1. Nitrogen and generated hydrogen fluoride are introduced into a 0.5mol / L lithium hydroxide solution to generate lithium fluoride with a purity of 99.7% after washing. The lithium salt decomposition bottom is subjected to two-time vacuum rectification under the condition of 120℃ and 1KPa to obtain ethylene carbonate with a purity of 99.2%.

[0039] Example 4

[0040] The method for recycling the electrolyte of the waste lithium battery in this example is as follows:

[0041] The retired aluminum shell battery is discharged in the ammonium chloride solution, so that the discharge voltage is less than 1.2V, the positive and negative electrode powders are obtained after disassembling, crushing and sorting equipment, the volatile components in the electrolyte are collected by using the negative pressure induced air during the disassembling process, the disassembled positive and negative electrode sheets are immersed in ethanol to obtain the immersion liquid, the amount of ethanol is 5 times the weight of the positive and negative electrode powders, the immersion liquid is subjected to one-time rectification under the condition of 50℃ and 0.1MPa to obtain ethanol, the purity of the ethanol is 99.4%, the ethanol can be recycled, nitrogen is introduced into the rectification bottom, heated to 100℃ and water is added for reaction for 10h, the molar ratio of the amount of water to lithium hexafluorophosphate is 1.05:1, the nitrogen and generated hydrogen fluoride are introduced into the 1.5mol / L lithium chloride solution to generate lithium fluoride, the purity of the lithium fluoride after washing is 99.3%, and the lithium salt decomposition bottom is subjected to two-time vacuum rectification under the condition of 130℃ and 50KPa to obtain propylene carbonate, the purity of the propylene carbonate is 99.6%.

[0042] Example 5

[0043] The method for recycling the waste lithium battery electrolyte in the embodiment is as follows:

[0044] The retired square shell battery is discharged on the charge-discharge instrument, so that the voltage is reduced to 1.0V, the square shell battery is cut, the core and shell are separated, the electrode sheets are separated and the like by using the flexible disassembling equipment, the volatile components in the electrolyte are collected by using the negative pressure induced air during the disassembling process, the disassembled positive and negative electrode sheets are immersed in butanone to obtain the immersion liquid, the amount of butanone is 4 times the weight of the positive and negative electrode sheets, the immersion liquid is subjected to one-time rectification under the condition of 60℃ and 0.07MPa to obtain butanone, the purity of the butanone is 99.4%, the butanone can be recycled, nitrogen is introduced into the rectification bottom, heated to 130℃ and water is added for reaction for 2h, the molar ratio of the amount of water to lithium hexafluorophosphate is 1.12:1, the nitrogen and generated hydrogen fluoride are introduced into the 0.8mol / L aluminum sulfate solution to generate aluminum fluoride, the purity of the aluminum fluoride after washing is 98.5%, and the lithium salt decomposition bottom is subjected to two-time vacuum rectification under the condition of 150℃ and 40KPa to obtain ethylene carbonate, the purity of the ethylene carbonate is 99.3%.

[0045] Verification effect

[0046] Table 1 is the process condition of recycling the waste lithium battery electrolyte in the embodiment.

[0047]

[0048] The above only describes the embodiments of the present application and does not limit the present application, any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for recycling electrolyte from waste lithium batteries, characterized in that... Includes the following steps: (1) Battery dismantling process: After the waste lithium battery is fully discharged, it is dismantled into positive and negative electrode powder or positive and negative electrode sheet. During the dismantling process, the low boiling point and easily volatile light components in the electrolyte are collected by negative pressure ventilation. (2) Leaching process: Add the positive and negative electrode powder or positive and negative electrode sheet obtained in step (1) to solvent I to leach the solvent and lithium salt remaining in the powder or electrode sheet, filter and separate to obtain leachate and material I, and material I is directly used for subsequent positive and negative electrode material recycling. (3) First distillation process: The leachate obtained in step (2) is subjected to a first vacuum distillation to separate pure solvent I and material II. Solvent I is recycled. (4) Lithium salt decomposition process: Nitrogen gas is introduced into material II obtained in step (3), and water is added under heating conditions to react, so that the solute in material II decomposes to obtain gas phase and material III; (5) Absorption reaction process: The gas phase obtained in step (4) is passed into the salt solution to carry out the absorption reaction, so as to absorb the hydrogen fluoride therein, and at the same time, fluoride is generated by the reaction. (6) Secondary distillation process: The material III obtained in step (4) is subjected to secondary distillation to further distill and purify the heavy components in the electrolyte to obtain solvent II, and the remaining sample is processed centrally.

2. The method for recycling electrolyte from waste lithium batteries according to claim 1, characterized in that: The process of fully discharging the waste lithium battery described in step (1) is carried out in a salt solution or on a discharge device. The voltage of the waste battery after full discharge is less than 1.2V. The dismantling process of the waste lithium battery described in step (1) is carried out in two ways: one is to obtain positive and negative electrode powder after the battery is crushed and sorted by a crushing and sorting device, and the other is to obtain positive and negative electrode sheets after the battery is flexibly dismantled and the electrode sheets are separated.

3. The method for recycling electrolyte from waste lithium batteries according to claim 1, characterized in that: The light components mentioned in step (1) refer to electrolyte solvents with a boiling point of less than 130°C, including dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

4. The method for recycling electrolyte from waste lithium batteries according to claim 1, characterized in that: Solvent I mentioned in step (2) refers to a solvent with a boiling point of less than 100°C, which is miscible with carbonate solvents in the electrolyte and can dissolve lithium hexafluorophosphate, including dimethyl carbonate, acetone, ethanol, isopropanol or butanone. The amount of solvent I used is 1-5 times the weight of the positive and negative electrode powder or positive and negative electrode sheet.

5. The method for recycling electrolyte from waste lithium batteries according to claim 1, characterized in that: In the single distillation process described in step (3), the operating temperature of the single vacuum distillation is 50-80℃ and the vacuum degree is 0.05-0.1MPa.

6. The method for recycling electrolyte from waste lithium batteries according to claim 1, characterized in that: In the lithium salt decomposition process of step (4), the reaction is heated and water is added at the same time to accelerate the decomposition of the solute in the electrolyte to generate a gas phase containing hydrogen fluoride. The molar ratio of water added to lithium hexafluorophosphate is (1.0-1.2):1, the reaction temperature is 60-130℃, and the reaction time is 2-48h.

7. The method for recycling electrolyte from waste lithium batteries according to claim 1, characterized in that: In the absorption reaction process of step (5), the cation contained in the salt solution is one of lithium, calcium, aluminum or magnesium; the concentration of the cation in the salt solution is 0.1-3 mol / L, and the fluoride is one of lithium fluoride, calcium fluoride, aluminum fluoride or magnesium fluoride.

8. The method for recycling electrolyte from waste lithium batteries according to claim 1, characterized in that: In the secondary distillation process of step (6), the operating temperature of the secondary vacuum distillation is 120-200℃ and the vacuum degree is 1kPa-0.08MPa.

9. The method for recycling electrolyte from waste lithium batteries according to claim 1, characterized in that: The recombinant components described in step (6) are electrolyte solvents with a boiling point greater than 200°C, including propylene carbonate and ethylene carbonate.

10. The method for recycling electrolyte from waste lithium batteries according to any one of claims 1-9, characterized in that: The purity of the recovered fluoride is ≥98%, and the purity of both the recovered solvent I and solvent II is ≥99%.

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