METHOD FOR RECYCLING THE ELECTROLYTE SOLUTION OF A LITHIUM-ION BATTERY

Abstract

A method for recycling a lithium-ion battery electrolyte solution, comprising the following steps: Step 1) Discharging and freezing a waste lithium-ion battery; disassembling the thus frozen waste lithium-ion battery to obtain a battery core containing an electrolytic solution; Step 2) Immersing the battery core obtained in step 1) in a lithium hydroxide solution containing a catalyst for a reaction of 0.3 h to 3 h; Step 3) Taking out the battery core after the reaction in step 2) and washing the battery core with a lithium hydroxide solution to obtain a washing solution; mixing the washing solution and the lithium hydroxide solution after the reaction in step 2) to obtain a mixed solution; Step 4) Filtering the mixed solution obtained in step 3) to obtain a filtrate and a filter residue; Step 5) Mixing the filter residue obtained in step 4) and a hydrofluoric acid solution, heating and evaporating the resulting mixture to dryness and calcining the dried material at a temperature of 550 °C to 750 °C for 0.4 to 2.5 h to obtain an anhydrous lithium salt; Step 6) Mixing the anhydrous lithium salt obtained in step 5) and an organic solvent, introducing PF5 gas to allow a reaction, wherein the reaction is carried out under a pressure of 0.2 MPa to 0.8 MPa for 0.5 h to 3 h, and performing filtration to obtain an organic liquid; and Step 7) Freezing and filtering the organic liquid obtained in step 6) to obtain crystals of lithium hexafluorophosphate; wherein in step 2) the catalyst comprises at least one of quaternary ammonium salt and methyldiethanolamine.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery recycling, in particular to a method for recycling a lithium-ion battery electrolyte solution. BACKGROUND

[0002] Currently, LiCoO2, LiNiO2, LiMn O 24LiFePO4 and a ternary material are used as the cathode material for a lithium-ion battery. The cathode material, the conductive acetylene black agent, and the organic binder are coated on aluminum foil to form the cathode, and a carbon foil material and an amorphous carbon material are coated on copper foil to form the negative electrode. The electrolyte salts in the electrolyte solution are generally lithium salts such as LiPF6, LiCF3SO3, and LiBF4. Commonly used solvents include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC).

[0003] The production of lithium-ion batteries in China is experiencing strong growth, and the number of lithium-ion batteries scrapped at the end of their service life is increasing year by year. Scrapped lithium-ion batteries contain not only cobalt, which has high recycling value, but also metals such as iron, aluminum, and copper, as well as organic electrolyte solutions, which have potential economic value and high pollution potential. Recycling and disposal of used lithium-ion batteries can not only eliminate the source of pollution but also realize the recycling and reuse of resources.

[0004] Lithium-ion battery recycling technology can be divided into fire, wet, and biological processes. In fire and wet treatment, the recycling of the electrolyte solution is generally not considered, which poses major safety risks to production and also causes relatively serious environmental pollution. During fire treatment, the organic solvent in the electrolyte solution evaporates or burns to decompose into water vapor and CO2, while LiPF6 rapidly decomposes into PF5 gas when heated in the air, eventually forming fluorine-containing flue gases and soot, which are discharged to the outside. During wet treatment of waste batteries, such as the decomposition of the lithium electrolyte salt LiPF6, HF and PF5 form highly soluble fluorides, which pollute the water with fluorine.The transformation and migration of fluorine-containing exhaust gases and wastewater into the environment directly or indirectly endangers human health. In addition, a biological method, namely microbial leaching, can also be used to treat lithium battery waste. Microorganisms can be used to convert useful components of the system into soluble compounds and selectively extract them to obtain metal-containing solutions, thereby achieving the separation of target components from contaminant components and ultimately recycling useful metals. The metabolic process of microorganisms is mainly used for the selective leaching of cobalt, lithium, and other metal elements, but it is not possible to effectively recycle and dispose of the electrolytic solution at the same time.

[0005] CN109585963A discloses a method for recovering and treating electrolyte solutions from spent lithium-ion batteries, comprising the following steps: freezing the spent lithium-ion battery in liquid nitrogen; removing the frozen battery and crushing the battery using a cryogenic mill to obtain a crushed mixture; completely immersing the crushed mixture in a container filled with a saturated lithium carbonate solution for a specified period of time while maintaining a specified ratio; successively filtering the reaction product with a coarse sieve and a fine sieve to obtain an oversize product and a filtrate; and finally separating an organic solvent and a lithium carbonate solution from the filtrate in an oil-water separator by the action of gravity.the organic solvent is removed via the upper liquid outlet of the separator, while the lithium carbonate solution is removed via the lower liquid outlet;

[0006] JP2014189452A describes a process for producing lithium fluoride powder, comprising the following steps: preparing an aqueous solution containing at least one lithium compound selected from the group consisting of lithium carbonate, lithium hydroxide, lithium nitrate, lithium chloride, and lithium sulfate, wherein the pH of the solution is adjusted to 4 or less; reacting hydrogen fluoride with the lithium compound in the aqueous solution to obtain a precipitate containing lithium fluoride; filtering the precipitate; and drying the filtered precipitate at 150-500°C under a nitrogen atmosphere, wherein the pH of the adhering water is 4 or less.

[0007] Currently, research on recycling waste lithium-ion batteries mainly focuses on high-quality electrode materials containing non-ferrous metals such as cobalt, lithium, nickel, and copper. However, the electrolyte solution is volatile and difficult to recycle, so little research and practice has been done on the recycling of the electrolyte solution. However, the volatilization of the electrolyte solution produces an unpleasant and irritating odor, and the hydrolysis of the lithium salt in the electrolyte solution produces toxic arsenide, phosphide, and fluoride, which are very harmful to the human body and the environment. This has become an unavoidable problem. On the one hand, the electrolyte solution accounts for about 12% of the total cost of the battery.Due to insufficient production capacity for electrolyte solutions and the monopoly of foreign companies on the production technology for high-purity lithium salts, recycling the electrolyte solution for reuse has high economic value. However, since the electrolyte solution itself is toxic to the environment and the human body, the electrolyte solution must be effectively treated from the perspective of safety and environmental protection. SUMMARY

[0008] The following is a summary of the technical solutions described in detail in the present disclosure. This summary is not intended to limit the scope of the claims.

[0009] In order to overcome the problem that the lithium-ion battery electrolyte solution cannot be recycled in an environmentally friendly and efficient manner in the prior art, the present application aims to provide a method for recycling the lithium-ion battery electrolyte solution.

[0010] In order to achieve the above-mentioned object, the present application provides a method for recycling an electrolytic solution of a lithium-ion battery according to independent claim 1.

[0011] In the method for recycling the electrolyte solution of the lithium-ion battery, the components of the electrolyte solution in step 1) preferably contain at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate and methyl ethyl carbonate.

[0012] The disassembled battery core is placed in a lithium hydroxide solution containing a catalyst. On the one hand, the solvent of the electrolyte solution (e.g., dimethyl carbonate) is decomposed into alcohols and carbon dioxide under the action of the catalyst, and the carbon dioxide reacts with lithium hydroxide to produce lithium carbonate precipitates. On the other hand, the dissolved lithium hexafluorophosphate in the electrolyte solution reacts with lithium hydroxide, the equation being as follows: LiPF6+14LiOH=6LiOH·LiF↓+Li3PO4↓+4H2O

[0013] By reacting the precipitate with hydrofluoric acid, the hydroxide and carbonate groups in the precipitate are removed, and the following reactions occur: LiOH+HF=LiF+H2O Li2CO3+2HF=2LiF+H2O+CO2 LiF+HF=LiHF2

[0014] By further calcination, LiHF2 is decomposed into lithium fluoride and hydrogen fluoride, yielding the anhydrous lithium salt containing only lithium fluoride and lithium phosphate; and then the anhydrous lithium salt is reacted with phosphorus pentafluoride in an organic solvent to obtain regenerated lithium phosphate, the process being as follows, using acetonitrile as an example: LiF+PF5+4CH3CN → Li(CH3CN)4PF6 → LiPF6

[0015] Preferably, in the method for recycling the lithium-ion battery electrolyte solution in step 1), the freezing is carried out at a temperature of not more than -50°C; more preferably, the freezing is carried out at a temperature of ≤-55°C; and even more preferably, the freezing is carried out at a temperature of ≤-60°C.

[0016] Preferably, in the process for recycling the lithium-ion battery electrolyte solution in step 2), the quaternary ammonium salt is a chloride or bromide salt, the total number of carbon atoms on the hydrocarbon group is ≤12; in some preferred examples of the present application, the catalyst is at least one of [(CH3)3NCH2CH2Cl]Cl or [(CH3CH2)3NCH2CH2OH]Cl.

[0017] Preferably, in the method for recycling the lithium-ion battery electrolyte solution in step 2), the concentration of the catalyst is 5 g / L to 60 g / L; more preferably, the concentration of the catalyst is 8 g / L to 55 g / L; and even more preferably, the concentration of the catalyst is 10 g / L to 50 g / L.

[0018] Preferably, in the process for recycling the lithium-ion battery electrolyte solution in step 2), the concentration of lithium hydroxide is 0.1 mol / l to 4 mol / l.

[0019] In the method for recycling the lithium-ion battery electrolyte solution, the reaction in step 2) takes 0.4 h to 2.5 h, and more preferably 0.5 h to 2 h.

[0020] In the method for recycling the lithium-ion battery electrolyte solution, in step 2), an amount of the lithium hydroxide solution sufficient to cover the battery core is preferably used.

[0021] Preferably, in the method for recycling the lithium-ion battery electrolyte solution in step 3), the concentration of the lithium hydroxide solution is 0.1 mol / l to 4 mol / l.

[0022] Preferably, in the method for recycling the lithium-ion battery electrolyte solution in step 5), hydrogen fluoride is recycled by heating and evaporating to dryness; and further preferably, the hydrogen fluoride is recycled by heating to a temperature of 50°C to 70°C.

[0023] Preferably, in the process for recycling the lithium-ion battery electrolyte solution in step 5), the calcination is carried out at a temperature of 600 °C to 700 °C.

[0024] Preferably, in the method for recycling the lithium-ion battery electrolyte solution in step 5), the calcination is carried out for 0.5 h to 2 h.

[0025] Preferably, in the process for recycling the lithium-ion battery electrolyte solution in step 6), the organic solvent comprises at least one of the following: acetonitrile, diethyl ether, pyrrole, and pyridine; more preferably, the organic solvent comprises one of the following: acetonitrile, diethyl ether, and pyrrole; even more preferably, the organic solvent is one of the following: acetonitrile and diethyl ether.

[0026] Preferably, in the method for recycling the lithium-ion battery electrolyte solution in step 6), the liquid-solid ratio of the organic solvent to the anhydrous lithium salt is 30 to 60 ml: 1 g; more preferably, the liquid-solid ratio of the organic solvent to the anhydrous lithium salt is 35 to 55 ml: 1 g; even more preferably, the liquid-solid ratio of the organic solvent to the anhydrous lithium salt is 40 to 50 ml: 1 g.

[0027] Preferably, in the process for recycling the lithium-ion battery electrolyte solution in step 6), the reaction is carried out under a pressure of 0.25 MPa to 0.75 MPa; even more preferably, the reaction is carried out under a pressure of 0.3 MPa to 0.7 MPa.

[0028] Preferably, in the method for recycling the lithium-ion battery electrolyte solution in step 6), the reaction is carried out for 0.8 h to 2.5 h; more preferably, the reaction is carried out for 1 h to 2 h.

[0029] Preferably, in the method for recycling the lithium-ion battery electrolyte solution in step 6), the filtration is carried out at a temperature of 40°C to 80°C; more preferably, the filtration is carried out at a temperature of 45°C to 75°C; even more preferably, the filtration is carried out at a temperature of 50°C to 70°C.

[0030] Preferably, in the method for recycling the lithium-ion battery electrolyte solution in step 7), the freezing is carried out at a temperature of -40°C to -10°C; more preferably, the freezing is carried out at a temperature of -35°C to -15°C; and even more preferably, the freezing is carried out at a temperature of -30°C to -20°C.

[0031] Preferably, the method for recycling the lithium-ion battery electrolyte solution in step 7) further comprises a step of drying a filter cake obtained by filtering, and the drying is carried out under a nitrogen atmosphere; more preferably, the drying is carried out at a temperature of 0°C to 8°C, and the drying is carried out for 10 h to 26 h; even more preferably, the drying is carried out at a temperature of 0°C to 5°C, and the drying is carried out for 12 h to 24 h.

[0032] The beneficial effects of this application are the following: 1. According to this application, the waste lithium-ion battery is frozen and then disassembled to prevent the electrolyte solution from evaporating and decomposing and polluting the environment. The lithium hexafluorophosphate produced according to the method of this application has high purity and meets the standard requirement of "HG / T 4066-2015 Lithium Hexafluorophosphate Electrolyte Solution." 2. Because the electrolytic solution of the waste battery has been used for a long time, there are many impurities inside, making it difficult to reuse the electrolytic solution. Especially because side reactions of various esters occur in the solvent, which makes the solvent basically impossible to reuse. In this application, the electrolytic solution generates alcohols and carbon dioxide through catalytic decomposition, which are easily soluble in water. This avoids aggregation and fire hazards caused by the insolubility of the electrolytic solution and water. In addition, under the action of lithium hydroxide, the reaction is further promoted. Both fluorine and lithium in the lithium hexafluorophosphate electrolytic solution have high economic value.Lithium hydroxide is used to precipitate lithium hexafluorophosphate, and then a series of reactions are carried out to obtain regenerated lithium hexafluorophosphate. The entire process consumes only lithium hydroxide, and recycling costs are low. 3. Taking advantage of the fact that lithium phosphate is insoluble in organic solvents, lithium hexafluorophosphate is produced by reacting lithium fluoride with phosphorus pentafluoride, and then lithium phosphate is separated to obtain pure lithium hexafluorophosphate.

[0033] After reading and understanding the drawings and the detailed description, further aspects can be understood. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings serve to further understand the present technical solution and are part of the description. Together with the examples of the present disclosure, they serve to explain the present technical solution and do not represent a limitation of the present technical solution. Fig. is a schematic representation of a method for recycling a lithium-ion battery electrolyte solution according to an example. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0035] The content of the present application is described in more detail below using specific examples. Unless otherwise stated, the raw materials or devices used in the examples can be obtained from conventional commercial channels or obtained by prior art methods. Unless otherwise stated, the inspection or testing methods are those customary in the prior art. Example 1

[0036] With reference to the schematic representation in Fig. In the present example, the process for recycling a lithium-ion battery electrolyte solution comprises the following steps: 1) after the used lithium-ion battery was discharged, it was frozen with liquid nitrogen to below -60 °C; 2) the frozen lithium-ion battery was disassembled and a battery core with an electrolyte solution was removed; 3) the battery core was immersed in a lithium hydroxide solution with a catalyst for 2 hours, the battery core was completely covered by the liquid, the concentration of the lithium hydroxide solution was 0.1 mol / L, the catalyst was methyldiethanolamine with a concentration of 10 g / L; 4) The battery core obtained after the reaction in step 3) was taken out and washed with a lithium hydroxide solution having a concentration of 0.1 mol / L to obtain a washing solution; the washing solution was mixed with the lithium hydroxide solution obtained after the reaction in step 3) to obtain a mixed solution; 5) the mixed solution was filtered to obtain filtrate and filter residue; 6) the filter residue was added to a sufficient amount of hydrofluoric acid solution, the mixture was heated and then evaporated to dryness to recycle excess hydrogen fluoride, and then calcined at 600 °C for 2 hours to obtain anhydrous lithium salt; 7) According to a liquid-solid ratio of 40 ml:1 g, the anhydrous lithium salt was added to anhydrous acetonitrile, and the mixture was reacted for 2 h in a closed environment, where PF5 gas was slowly introduced so that the reaction system pressure was 0.3 MPa. After the reaction, the mixture was heated to 50 °C and filtered to obtain an organic liquid. 8) the organic liquid was frozen to -30 °C to separate the crystals and filtered to obtain a filter cake; and 9) The filter cake was dried for 24 hours at 0 °C under nitrogen atmosphere to obtain lithium hexafluorophosphate.

[0037] The prepared lithium hexafluorophosphate complies with the requirements of the standard “HG / T 4066-2015 Duplication deleted Lithium Hexafluorophosphate Electrolyte Solution.” Example 2

[0038] With reference to the schematic representation in Fig. In the present example, the process for recycling a lithium-ion battery electrolyte solution comprises the following steps: 1) after the used lithium-ion battery was discharged, it was frozen with liquid nitrogen to below -60 °C; 2) the frozen lithium-ion battery was disassembled and a battery core with an electrolyte solution was removed; 3) the battery core was immersed in a lithium hydroxide solution containing a catalyst for 1 hour, the battery core was completely covered by the liquid, the concentration of the lithium hydroxide solution was 2 mol / L, the catalyst was [(CH3)3NCH2CH2Cl]Cl with a concentration of 30 g / L; 4) The battery core obtained after the reaction in step 3) was taken out and washed with a lithium hydroxide solution having a concentration of 2 mol / L to obtain a washing solution; the washing solution was mixed with the lithium hydroxide solution obtained after the reaction in step 3) to obtain a mixed solution; 5) the mixed solution was filtered to obtain filtrate and filter residue; 6) the filter residue was added to a sufficient amount of hydrofluoric acid solution, the mixture was heated and evaporated to dryness to recycle excess hydrogen fluoride, and then calcined at 650 °C for 1 hour to obtain anhydrous lithium salt; 7) According to a liquid-solid ratio of 45 ml:1 g, the anhydrous lithium salt was added to anhydrous acetonitrile, and the mixture was reacted for 1.5 h in a closed environment, where PF5 gas was slowly introduced so that the reaction system pressure was 0.5 MPa. After the reaction, the mixture was heated to 60 °C and filtered to obtain an organic liquid. 8) the organic liquid was frozen to -25 °C to separate the crystals and filtered to obtain a filter cake; and 9) The filter cake was dried for 18 hours at 3 °C under nitrogen atmosphere to obtain lithium hexafluorophosphate.

[0039] The prepared lithium hexafluorophosphate complies with the requirements of the standard "HG / T 4066-2015 Lithium Hexafluorophosphate Electrolyte Solution. Example 3

[0040] With reference to the schematic representation in Fig. In the present example, the process for recycling a lithium-ion battery electrolyte solution comprises the following steps: 1) after the used lithium-ion battery was discharged, it was frozen with liquid nitrogen to below -60 °C; 2) the frozen lithium-ion battery was disassembled and a battery core with an electrolyte solution was removed; 3) the battery core was immersed in a lithium hydroxide solution containing a catalyst for 0.5 hours, the battery core was completely covered by the liquid, the concentration of the lithium hydroxide solution was 4 mol / L, the catalyst was [(CH3CH2)3NCH2CH2OH]Cl with a concentration of 50 g / L; 4) The battery core obtained after the reaction in step 3) was taken out and washed with a lithium hydroxide solution having a concentration of 4 mol / L to obtain a washing solution; the washing solution was mixed with the lithium hydroxide solution obtained after the reaction in step 3) to obtain a mixed solution; 5) the mixed solution was filtered to obtain filtrate and filter residue; 6) the filter residue was added to a sufficient amount of hydrofluoric acid solution, the mixture was heated and evaporated to dryness to recycle excess hydrogen fluoride, and then calcined at 700 °C for 0.5 hours to obtain anhydrous lithium salt; 7) According to a liquid-solid ratio of 50 mL:1 g, the anhydrous lithium salt was added to anhydrous diethyl ether, and the mixture was reacted for 1 h in a closed environment, slowly introducing PF5 gas to maintain a pressure of 0.7 MPa. After the reaction, the mixture was heated to 70 °C and filtered to obtain an organic liquid. 8) the organic liquid was frozen to -20 °C to separate the crystals and filtered to obtain a filter cake; and 9) The filter cake was dried for 24 hours at 5 °C under nitrogen atmosphere to obtain lithium hexafluorophosphate.

[0041] The prepared lithium hexafluorophosphate complies with the requirements of the standard "HG / T 4066-2015 Lithium Hexafluorophosphate Electrolyte Solution".

Claims

[1] A method for recycling a lithium-ion battery electrolyte solution, comprising the following steps: Step 1) Discharging and freezing a waste lithium-ion battery; disassembling the thus frozen waste lithium-ion battery to obtain a battery core containing an electrolytic solution; Step 2) Immersing the battery core obtained in step 1) in a lithium hydroxide solution containing a catalyst for a reaction of 0.3 h to 3 h; Step 3) Taking out the battery core after the reaction in step 2) and washing the battery core with a lithium hydroxide solution to obtain a washing solution; mixing the washing solution and the lithium hydroxide solution after the reaction in step 2) to obtain a mixed solution; Step 4) Filtering the mixed solution obtained in step 3) to obtain a filtrate and a filter residue; Step 5) Mixing the filter residue obtained in step 4) and a hydrofluoric acid solution, heating and evaporating the resulting mixture to dryness and calcining the dried material at a temperature of 550 °C to 750 °C for 0.4 to 2.5 h to obtain an anhydrous lithium salt; Step 6) Mixing the anhydrous lithium salt obtained in step 5) and an organic solvent, introducing PF5 gas to allow a reaction, wherein the reaction is carried out under a pressure of 0.2 MPa to 0.8 MPa for 0.5 h to 3 h, and performing filtration to obtain an organic liquid; and Step 7) Freezing and filtering the organic liquid obtained in step 6) to obtain crystals of lithium hexafluorophosphate; wherein in step 2) the catalyst comprises at least one of quaternary ammonium salt and methyldiethanolamine. [2] A method for recycling the lithium-ion battery electrolyte solution according to claim 1, wherein in step 1), the components of the electrolyte solution comprise at least one of the following: Ethylene carbonate, propylene carbonate, dimethyl carbonate and methyl ethyl carbonate. [3] A method for recycling the lithium-ion battery electrolyte solution according to claim 1, wherein in step 6), the organic solvent comprises at least one of acetonitrile, diethyl ether, pyrrole, and pyridine. [4] A method for recycling the lithium-ion battery electrolyte solution according to claim 1, wherein in step 6), the liquid-solid ratio of the organic solvent to the anhydrous lithium salt is 30-60 ml: 1 g. [5] A method for recycling the lithium-ion battery electrolyte solution according to claim 1, wherein in step 6), the filtration is carried out at a temperature of 40°C to 80°C. [6] A method for recycling the lithium-ion battery electrolyte solution according to claim 1, wherein in step 7), the freezing is carried out at a temperature of -40 °C to -10 °C.

Images