A comprehensive recycling and regeneration method for waste electrolyte of lithium ion battery

Abstract

The present invention provides a comprehensive recycling and regeneration method for waste electrolyte of lithium ion batteries, comprising the following steps: step 1: after dehydrating and decolorizing the collected electrolyte, the mixed alcohol solvent is subjected to multi-stage ultra-vacuum decompression azeotropic distillation, the gas at the top of the tower is condensed and liquefied, and the alcohol solvent and the carbonate solvent are separated by a membrane separation method, wherein the alcohol solvent is recycled again; step 2: the bottom liquid of the tower is deacidified and dehydrated, low-temperature crystallized, filtered, and impurities are washed away with a solvent, and then low-temperature dried to obtain lithium hexafluorophosphate solid; step 3: the lithium hexafluorophosphate solid and the carbonate solvent are mixed, the components are analyzed, and other components are appropriately added to prepare a new electrolyte. The present invention can continuously process the electrolyte, avoid the decomposition of the electrolyte after contacting water and air, the lithium hexafluorophosphate recovery rate is high, and impurities are effectively removed, the electrolyte regeneration is realized, and new economic value is generated while reducing environmental pollution.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery recycling and regeneration, and in particular to a comprehensive recycling and regeneration method for waste electrolyte of lithium ion batteries. Background Art

[0002] Lithium-ion batteries have become the focus of the new energy battery field due to their advantages such as high operating voltage, high energy density, low pollution and long working life. They are widely used in various fields such as electric vehicles, energy storage systems, 3C products, medical equipment, military equipment, etc., bringing convenience to people's production and life. At present, China's annual lithium-ion battery production is several hundred GWh, and the electrolyte production is in the hundreds of thousands of tons. With the large-scale use of lithium-ion batteries, the recycling and treatment of waste lithium-ion batteries has gradually become prominent. As the world's largest producer and seller of new energy vehicles, my country will have about 60,000 tons of batteries to be scrapped in 2020 alone. Lithium-ion batteries contain a large amount of metals and organic matter, and improper treatment will cause serious environmental pollution problems. At present, the recycling work of many companies is mainly aimed at precious metals in electrode materials, while lithium-ion battery electrolytes are only harmlessly treated to meet environmental protection requirements, and there is a lack of green and efficient technical means for recycling. In fact, the recycling of lithium-ion battery electrolytes is very necessary. On the one hand, the electrolyte of lithium-ion batteries is easy to volatilize in the air, easily produce HF gas, and have an unpleasant irritating odor. The lithium salt in it is easy to hydrolyze to produce toxic arsenide, phosphide and fluoride, which are extremely harmful to the human body and the environment. Proper recycling and treatment of lithium-ion batteries has a high environmental value. On the other hand, the electrolyte accounts for about 12% of the total cost of the battery. If it can be recycled and regenerated through appropriate methods, it can generate considerable economic value.

[0003] Lithium-ion battery electrolytes are mainly composed of three parts: (1) high-purity organic solvents, including ethers, esters and carbonates, such as ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), etc.; (2) electrolyte lithium salts, such as lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4) and lithium hexafluorophosphate (LiPF6); (3) necessary additives, such as vinylene carbonate (VC), methyl phenylcarbamate (MPC), dimethyl sulfoxide (DMSO), etc. When recycling the electrolyte, it is generally difficult to separate and purify the various components separately due to the complex composition of the electrolyte and the similar melting and boiling points of some components. Currently, most existing technologies are to extract metallic lithium from the electrolyte, but these methods often leave a large amount of residual mixed organic solution, which is difficult to use in industrial applications. Generally, it can only be treated as hazardous waste, which increases the cost of treatment and causes waste of resources.

[0004] At present, some patents have been used to recover lithium hexafluorophosphate by vacuum distillation of electrolyte. For example, patent application (CN201110427431.2) discloses a method for recycling waste lithium-ion battery electrolyte, which separates organic solvents and solid lithium hexafluorophosphate materials contained in the electrolyte by high vacuum vacuum distillation, and then crystallizes and purifies the obtained crude lithium hexafluorophosphate to obtain pure lithium hexafluorophosphate. In fact, it is difficult to make most organic solvents reach boiling point by only one vacuum vacuum distillation. A large amount of organic solvents still remain after distillation, and it is difficult to evaporate all solvents and leave solid lithium hexafluorophosphate. For example, patent application (CN201810012129.2) discloses a process for recycling waste lithium-ion battery electrolyte, which is to obtain concentrated filtrate by vacuum distillation of pure electrolyte filtrate, and make new electrolyte after analysis and supplementation of effective components. This method not only leaves lithium hexafluorophosphate in the concentrated filtrate, but also leaves various impurities in the waste electrolyte, such as PF6-, LiF, HF, etc., in the concentrated solution. After the electrolyte is re-formed, the performance of the electrolyte will be greatly affected, making the practicality of this method reduced. The patent application (CN201910746383.X) discloses a harmless recovery and treatment method for electrolytes in waste lithium-ion batteries. After the battery is cut, it is soaked in a colored lime milk solution. After full reaction and stratification, it is divided into an organic phase, an aqueous solution phase, an organic phase with a density greater than water, and a solid residue phase. However, the organic phase recovered by this method needs to be handed over to the electrolyte manufacturer for further processing. Since the recovered organic phase contains different electrolyte additives and decomposition products, and different manufacturers have different requirements for the composition of organic solvents, the practicality of this method is greatly limited. At the same time, the solid residue obtained is a mixture of CaF2 and Ca3(PO4)2, which is difficult to further separate and utilize. Therefore, it is particularly important to comprehensively recycle the effective components of lithium-ion battery electrolytes and try to remove various impurities in waste electrolytes that affect their performance. Summary of the invention

[0005] In order to overcome the problems of poor recovery effect, large amount of waste generated, inability to effectively remove electrolyte impurities and insufficient recovery of effective components in existing electrolyte recovery and utilization methods, the present invention provides a comprehensive recovery and regeneration method for waste electrolyte of lithium ion batteries, which aims to extract organic solvents and lithium hexafluorophosphate from waste electrolyte to the greatest extent, effectively remove impurities, generate less waste, and comprehensively recycle waste electrolyte. The waste electrolyte treated by the present invention is based on the collected liquid waste electrolyte, and the sources include lithium ion battery recovery plants, lithium ion battery production plants, and electrolytes obtained by disassembling lithium ion batteries through other devices. The present invention can process waste electrolytes of various sources, different models and different qualities, and realize recovery and regeneration by recovering the common effective components therein.

[0006] The specific plan is as follows:

[0007] A comprehensive recycling and regeneration method for waste electrolyte of lithium ion batteries, characterized in that it comprises the following steps:

[0008] Step 1: After the collected electrolyte is dehydrated and decolorized, it is mixed with an alcohol solvent and subjected to multi-stage ultra-vacuum reduced pressure azeotropic distillation, the gas at the top of the tower is condensed and liquefied, and the alcohol solvent and the carbonate solvent are separated by a membrane separation method, wherein the alcohol solvent is recycled;

[0009] Step 2: The bottom liquid is deacidified and dehydrated, low-temperature crystallized, filtered, and impurities are washed away with a solvent, and then low-temperature dried to obtain lithium hexafluorophosphate solid;

[0010] Step 3: Mix lithium hexafluorophosphate solid and carbonate solvent, analyze the components, and add other ingredients as appropriate to prepare a new electrolyte.

[0011] A comprehensive recycling and regeneration method for waste electrolyte of lithium-ion batteries, characterized in that the specific steps are as follows:

[0012] Step (1): the collected electrolyte is decolorized and dehydrated by passing through activated carbon and molecular sieves to obtain a colorless or light yellow transparent and clear electrolyte;

[0013] Step (2): the electrolyte is mixed with an alcohol solvent and then passed into a multi-stage scraper film evaporator for ultra-vacuum reduced pressure azeotropic distillation. The obtained bottom liquid is mixed with the alcohol solvent and then passed into the next stage scraper film evaporator. After multi-stage treatment, the bottom liquid is discharged. The top gas in this process is passed into a condensing device for liquefaction and then discharged;

[0014] Step (3): separating the condensate of the gas at the top of the tower by a membrane to separate the alcohol solvent from the carbonate mixed solvent contained in the electrolyte, such as ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), etc., wherein the alcohol solvent is recycled, and the carbonate mixed solvent is subjected to an anion exchange resin to remove HF, and then subjected to activated carbon dehydration treatment to extract the mixed solvent;

[0015] Step (4): removing HF from the bottom liquid of the tower after multi-stage distillation by anion exchange resin, then dehydrating it by molecular sieve and activated carbon, crystallizing it at low temperature, and obtaining crystals after vacuum filtration. The crystals are repeatedly washed with a solvent, and dried at low temperature under an inert atmosphere to obtain clean lithium hexafluorophosphate crystals;

[0016] Step (5): Mix and dissolve the carbonate mixed solvent obtained in step 3 and the lithium hexafluorophosphate finally obtained in step 4 in a certain proportion, detect the proportion of each component in the mixed solution, add a certain amount of solvent and electrolyte additives, and compound into a new electrolyte.

[0017] As a further improvement of the present invention, in step (1), the material-liquid ratio of the molecular sieve and activated carbon to the treated electrolyte is 1:0.5 to 1:2, and the process is kept isolated from air, and the treated electrolyte is continuously passed into the device of step (2).

[0018] As a further improvement of the present invention, the distillation temperature in step (2) is 40 to 80°C, the vacuum degree is 0 to 10 kPa, and the condensation temperature is -40 to 0°C.

[0019] As a further improvement of the present invention, the alcohol solvent in step (2) includes one or more alcohols such as methanol, ethanol, propanol, etc., and the volume ratio of the alcohol solvent to the electrolyte is 0.2:1 to 1:1.

[0020] As a further improvement of the present invention, in the step (2), the electrolyte is passed through a multi-stage scraped film evaporator for treatment at 3 to 6 stages.

[0021] As a further improvement of the present invention, the membrane in step (3) is a nanofiltration membrane that selectively permeates alcohol solvents.

[0022] As a further improvement of the present invention, the temperature of the low-temperature crystallization in step (4) is -40 to -10°C, and the crystallization time is 8 to 20 hours.

[0023] As a further improvement of the present invention, the solvent for washing the crystals in step (4) is a pure solvent with extremely low solubility in lithium hexafluorophosphate, the drying process temperature is 20-40° C., and the inert gas used is high-purity nitrogen, helium, etc.

[0024] As a further improvement of the present invention, the detection method of HF is to take a certain mass of the mixed solution in the glove box and add it to a GC injection bottle or other transparent vials with rubber stopper caps, add bromothymol blue as an indicator, insert a syringe filled with sodium methoxide and other standard solutions into the rubber stopper of the vial for dropwise titration, weigh the mass of the consumed standard solution after the titration is completed, calculate the mass ratio of free acid in the solution as the HF content, and ensure that the mass ratio of HF is less than 50 ppm.

[0025] As a further improvement of the present invention, the mixed solution obtained in step (5) must ensure that the HF content in the solution is below 50 ppm and the water content is below 20 ppm before compounding.

[0026] The beneficial effects of the present invention are:

[0027] 1. The principle of ultra-vacuum reduced pressure distillation and azeotropic distillation is used to reduce the boiling point of the organic solvent in the electrolyte as much as possible, and the organic solvent is extracted and separated to the greatest extent at a temperature that ensures that lithium hexafluorophosphate will not decompose;

[0028] 2. The scraper film evaporator is used for distillation, which has high evaporation intensity, high operating flexibility and short heating time;

[0029] 3. By using a multi-stage circulation method to supplement the azeotropic solvent for distillation multiple times, the addition ratio of the azeotropic solvent and the concentration of the bottom liquid can be flexibly controlled to achieve a balance between extraction efficiency and operating costs;

[0030] 4. The alcohol solvents used for azeotropic distillation can be continuously recycled through membrane separation, which reduces the cost of electrolyte recycling, reduces the generation of waste liquid, and makes the whole process more environmentally friendly;

[0031] 5. The treatment process of waste electrolyte is connected front and back, which can be continuously fed and produced, which not only improves the production efficiency, but also ensures that the whole process is isolated from air and water, avoids the decomposition of lithium hexafluorophosphate, and improves the recovery rate of waste electrolyte;

[0032] 6. By extracting lithium hexafluorophosphate and organic solvent separately, impurities can be left in the filtrate after the tower bottom liquid is cooled and crystallized, ensuring the purity and stability of the composite electrolyte components. Electrolyte additives can be added according to different application requirements, thereby improving the practicality of the composite electrolyte;

[0033] 7. The present invention can process waste electrolyte in an environmentally friendly manner, realize the comprehensive recycling of effective components of waste electrolyte, save resources, protect the environment, and generate good economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0036] Example 1

[0037] As shown in the figure, a comprehensive recycling and regeneration method for waste electrolyte of lithium-ion batteries, the specific steps are as follows:

[0038] Step (1): 1000 ml of the spent electrolyte was passed through an adsorption tower filled with 500 g of granular activated carbon for adsorption for 8 h, and then passed through an adsorption tower filled with 500 g of granular 13X molecular sieve for adsorption for 8 h, at which time the electrolyte changed from light yellow to nearly transparent light yellow;

[0039] Step (2): the electrolyte is mixed with 1 volume of an alcohol solvent, the alcohol solvent being composed of a 40% methanol solution and a 60% ethanol solution, and is introduced into a scraped film evaporator at a rate of 20 ml / min, the scraper rotation speed is set to 5 r / s, water is introduced into the shell side of the evaporator as a heat exchange medium, the evaporation temperature is set to 70°C, and the evaporator is connected to a vacuum pump to make the system vacuum degree 5 kPa;

[0040] Step (3): the bottom liquid obtained after evaporation in the scraper film evaporator in step (2) is mixed with an alcohol solvent again and continuously passed into the next-stage scraper film evaporator for distillation, and the mixed alcohol solvent, evaporation temperature and vacuum degree are kept consistent with those in step (2);

[0041] Step (4): repeating step (3) in three-stage, four-stage and five-stage scraped film evaporators, and finally draining the bottom liquid in the five-stage scraped film evaporator; wherein the top of the five-stage scraped film evaporator is connected to the shell side of the cooler, and the refrigerant in the tube side of the cooler is cooled to a temperature of -20°C, and then draining the gas condensate at the top of the tower;

[0042] Step (5): the gas condensate at the top of the tower is filtered through a nanofiltration membrane, the number of membrane elements in each membrane shell is 4, the operating pressure is 2.1 MPa, the alcohol solvent is separated from the carbonate mixed solvent contained in the top condensate, including EC, DMC, EMC, DEC, PC, etc., the alcohol solvent is passed through steps (2), (3), and (4) for recycling, and the carbonate mixed solvent is discharged;

[0043] Step (6): After the carbonate mixed solvent is passed through an anion exchange resin column to remove HF, it is then passed through the two adsorption towers in step (1) to remove trace amounts of water, and 700 ml of solvent is collected;

[0044] Step (7): The bottom liquid derived from step (4) is passed through the same anion exchange resin and adsorption tower as step (6) to obtain 150 ml of solution, and the solution is transferred to a crystallization kettle for low-temperature crystallization for 20 hours at a crystallization temperature of -40°C. The crystals are vacuum filtered to obtain crystals, and then the crystals are rinsed three times with n-hexane. After drying under nitrogen atmosphere, 98 g of clean lithium hexafluorophosphate crystals are obtained. The electrolyte density is 1.28 g / cm3, and the mass ratio of lithium hexafluorophosphate in the electrolyte is 12%. The recovery rate of lithium hexafluorophosphate is 63.8%;

[0045] Step (8): Mix and dissolve the solvent obtained in step (5) and the lithium hexafluorophosphate solid obtained in step (7), take 1 ml of the mixed solution in a glove box, dilute it 100 times, take 1 ml of the diluted solution and put it into a GC injection bottle, add a drop of bromothymol blue solution, and use a syringe filled with sodium methoxide solution to titrate drop by drop until it changes color, then calculate the HF content to be 40 ppm, take a drop of the mixed solution with a micro syringe and drip it into a Karl Fischer moisture detector, take the average of three measurements, and measure the water content to be 13 ppm;

[0046] Step (9): Conduct component analysis, add organic solvent and lithium hexafluorophosphate solid, add appropriate amount of electrolyte additives, and prepare electrolyte products.

[0047] Example 2

[0048] Step (1): In a glove box with a nitrogen atmosphere, pour 300 ml of the spent electrolyte into a beaker containing 300 g of granular activated carbon and soak for 5 h. Then filter and pour into a beaker containing 300 g of granular 13X molecular sieve and soak for 8 h. Filter and pour out. The electrolyte changes from yellow to light yellow.

[0049] Step (2): the electrolyte was mixed with 150 ml of anhydrous methanol solvent, and passed into a scraper thin film evaporator at a rate of 10 ml / min. The scraper rotation speed was set to 2 r / s. Water was passed into the shell of the evaporator as a heat exchange medium. The evaporation temperature was set to 40°C. The evaporator was connected to a vacuum pump to make the system vacuum degree 10 kPa.

[0050] Step (3): the bottom liquid obtained after evaporation in the scraper film evaporator in step (2) is mixed with 150 ml of anhydrous methanol again and passed into the next-stage scraper film evaporator for distillation, and the mixed alcohol solvent, evaporation temperature and vacuum degree are consistent with those in step (2);

[0051] Step (4): repeating step (3) in the third-stage scraped film evaporator, and then draining the bottom liquid; wherein the tops of the three-stage scraped film evaporators are all connected to the shell side of the cooler, and the refrigerant in the tube side of the cooler is cooled to a temperature of -10°C, and then draining the gas condensate from the top of the tower;

[0052] Step (5): the gas condensate at the top of the tower is filtered through a nanofiltration membrane, the number of membrane elements in each membrane shell is 4, the operating pressure is 2.1 MPa, the alcohol solvent is separated from the carbonate mixed solvent contained in the top condensate, including EC, DMC, EMC, DEC, PC, etc., the alcohol solvent is passed through steps (2), (3), and (4) for recycling, and the carbonate mixed solvent is discharged;

[0053] Step (6): After the carbonate mixed solvent is passed through an anion exchange resin column to remove HF, it is then passed into the beaker containing the regenerated molecular sieve in step (1) to remove trace amounts of water, and 210 ml of solvent is collected;

[0054] Step (7): The bottom liquid of step (4) is passed through the same anion exchange resin and adsorption tower as step (6) to obtain 78 ml of solution, and the solution is transferred to a crystallization kettle for low-temperature crystallization for 8 hours at a crystallization temperature of -10°C. The crystals are vacuum filtered to obtain crystals, and then the crystals are rinsed three times with toluene. After drying under nitrogen atmosphere, 21 g of clean lithium hexafluorophosphate crystals are obtained. The electrolyte density is 1.19 g / cm3, and the mass ratio of lithium hexafluorophosphate in the electrolyte is 12%. The recovery rate of lithium hexafluorophosphate is 49.0%;

[0055] Step (8): Mix and dissolve the solvent obtained in step (5) and the lithium hexafluorophosphate solid obtained in step (7), take 1 ml of the mixed solution in a glove box, dilute it 100 times, take 1 ml of the diluted solution and put it into a GC injection bottle, add a drop of bromothymol blue solution, and use a syringe filled with sodium methoxide solution to titrate drop by drop until it changes color, then calculate the HF content to be 30 ppm, take a drop of the mixed solution with a micro syringe and drip it into a Karl Fischer moisture detector, take the average of three measurements, and measure the water content to be 18 ppm;

[0056] Step (9): Conduct component analysis, add organic solvent and lithium hexafluorophosphate solid, add appropriate amount of electrolyte additives, and prepare electrolyte products.

[0057] Example 3

[0058] Step (1): 10 L of spent electrolyte was passed through an adsorption tower filled with 10 kg of granular activated carbon for adsorption for 5 h, and then passed through an adsorption tower filled with 500 g of granular 13X molecular sieve for adsorption for 12 h, at which time the electrolyte changed from light yellow to a colorless, transparent and clear liquid;

[0059] Step (2): the electrolyte in step (1) and 2 times the volume of an alcohol solvent are introduced into a mixing barrel with a stirring blade, wherein the alcohol solvent is composed of a 30% methanol solution, a 40% ethanol solution and a 10% propanol solution. The electrolyte mixed with the alcohol solvent is introduced into a scraped film evaporator at a rate of 10 ml / min from the mixing barrel, the scraper rotation speed is set to 5 r / s, water is introduced into the shell side of the evaporator as a heat exchange medium, the evaporation temperature is set to 80°C, and the evaporator is connected to a vacuum pump to make the system vacuum degree 2 kPa;

[0060] Step (3): the bottom liquid obtained after evaporation in the scraper film evaporator in step (2) is not mixed with the alcohol solvent and is directly passed into the next-stage scraper film evaporator for distillation, and the evaporation temperature and vacuum degree are consistent with those in step (2);

[0061] Step (4): repeating step (3) in three-stage, four-stage, five-stage and six-stage scraped film evaporators, and finally draining the bottom liquid in the six-stage scraped film evaporator; wherein the top of the six-stage scraped film evaporator is connected to the shell side of the cooler, and the refrigerant in the tube side of the cooler is cooled to a temperature of -40°C, and then draining the gas condensate at the top of the tower;

[0062] Step (5): the gas condensate at the top of the tower is filtered through a nanofiltration membrane, the number of membrane elements in each membrane shell is 4, the operating pressure is 2.1 MPa, the alcohol solvent is separated from the carbonate mixed solvent contained in the top condensate, including EC, DMC, EMC, DEC, PC, etc., the alcohol solvent is passed through steps (2), (3), and (4) for recycling, and the carbonate mixed solvent is discharged;

[0063] Step (6): After the carbonate mixed solvent is passed through a two-stage anion exchange resin column to remove HF, it is then passed through the two adsorption towers regenerated in step (1) to remove trace amounts of water, and 8.5 L of solvent is collected;

[0064] Step (7): The bottom liquid derived from step (4) is passed through the same anion exchange resin and adsorption tower as step (6) to obtain 1.17 L of solution, and the solution is transferred to a crystallization kettle for low-temperature crystallization for 24 hours at a crystallization temperature of -40°C. The crystals are vacuum filtered to obtain crystals, and then the crystals are rinsed three times with n-hexane. After drying at 20°C for 12 hours under nitrogen atmosphere, 1.09 kg of clean lithium hexafluorophosphate crystals are obtained. The electrolyte density is 1.21 g / cm3, and the mass ratio of lithium hexafluorophosphate in the electrolyte is 12%. The recovery rate of lithium hexafluorophosphate is 75.1%;

[0065] Step (8): Mix and dissolve the solvent obtained in step (5) and the lithium hexafluorophosphate solid obtained in step (7), take 1 ml of the mixed solution in a glove box, dilute it 50 times, take 2 ml of the diluted solution and put it into a glass bottle with a rubber stopper, add three drops of bromothymol blue solution, and use a syringe filled with sodium methoxide solution to titrate drop by drop until it changes color, then calculate the HF content to be 48 ppm, take a drop of the mixed solution with a micro syringe and drip it into a Karl Fischer moisture detector, take the average of three measurements, and measure the water content to be 10 ppm;

[0066] Step (9): Conduct component analysis, add organic solvent and lithium hexafluorophosphate solid, add appropriate amount of electrolyte additives, and prepare electrolyte products.

[0067] Through multiple tests and verifications, the recovery efficiency of lithium hexafluorophosphate by the method of the present invention is about 48-75%, and the recovery efficiency is related to factors such as the ratio of mixed alcohol solvents, alcohol solvent components, evaporator stages and evaporation temperature. When the evaporation stage is high, the recovery efficiency of lithium hexafluorophosphate is high, and the HF content contained in the corresponding composite electrolyte is higher. The lithium hexafluorophosphate and carbonate solvents recovered within the parameter range required by the present invention meet the technical requirements specified in the industry standard HG / T 4067-2015 for lithium hexafluorophosphate electrolyte after composite.

[0068] The technical means disclosed in the scheme of the present invention are not limited to the technical means disclosed in the above-mentioned implementation mode, but also include technical schemes composed of any combination of the above-mentioned technical features. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also regarded as the protection scope of the present invention.

Claims

1. A comprehensive recovery and regeneration method for waste electrolyte of lithium ion batteries, characterized in that: The following steps are involved: Step 1: After the collected electrolyte is dehydrated and decolorized, it is mixed with an alcohol solvent and subjected to multi-stage ultra-vacuum reduced pressure azeotropic distillation, the gas at the top of the tower is condensed and liquefied, and the alcohol solvent and the carbonate solvent are separated by a membrane separation method, wherein the alcohol solvent is recycled; Step 2: The bottom liquid is deacidified and dehydrated, low-temperature crystallized, filtered, and impurities are washed away with a solvent, and then low-temperature dried to obtain lithium hexafluorophosphate solid; Step 3: Mix lithium hexafluorophosphate solid and carbonate solvent, analyze the components, and add other ingredients appropriately to prepare a new electrolyte; The specific steps are as follows: Step (1): the collected electrolyte is decolorized and dehydrated by passing through activated carbon and molecular sieves to obtain a colorless or light yellow transparent and clear electrolyte; Step (2): the electrolyte is mixed with an alcohol solvent and then passed into a multi-stage scraper film evaporator for ultra-vacuum reduced pressure azeotropic distillation. The obtained bottom liquid is mixed with the alcohol solvent and then passed into the next stage scraper film evaporator. After multi-stage treatment, the bottom liquid is discharged. The top gas in this process is passed into a condensing device for liquefaction and then discharged; Step (3): separating the condensate of the gas at the top of the tower by a membrane to separate the alcohol solvent from the carbonate mixed solvent contained in the electrolyte, wherein the alcohol solvent is recycled, and the carbonate mixed solvent is subjected to an anion exchange resin to remove HF, and then subjected to an activated carbon dehydration treatment to extract the mixed solvent; Step (4): removing HF from the bottom liquid of the tower after multi-stage distillation by anion exchange resin, then dehydrating it by molecular sieve and activated carbon, crystallizing it at low temperature, and obtaining crystals after vacuum filtration. The crystals are repeatedly washed with a solvent, and dried at low temperature under an inert atmosphere to obtain clean lithium hexafluorophosphate crystals; Step (5): mixing and dissolving the carbonate mixed solvent obtained in step 3 and the lithium hexafluorophosphate finally obtained in step 4 in a certain proportion, detecting the proportion of each component in the mixed solution, adding a certain amount of solvent and electrolyte additive, and compounding a new electrolyte; In the step (1), the material-liquid ratio of the molecular sieve and the activated carbon to the treated electrolyte is 1:0.5 to 1:

2. During this process, the air is kept isolated, and the treated electrolyte is continuously introduced into the device of step (2). The distillation temperature in the step (2) is 40 to 80°C, the vacuum degree is 2 to 10 kPa, and the condensation temperature is -40 to 0°C. The alcohol solvent in the step (2) includes one or more of methanol, ethanol, and propanol, and the volume ratio of the alcohol solvent to the electrolyte is 0.2:1 to 1:

1.

2. The comprehensive recycling and regeneration method for waste electrolyte of lithium ion batteries according to claim 1, characterized in that: In the step (2), the electrolyte is passed through a multi-stage scraper thin film evaporator for treatment in 3 to 6 stages.

3. The comprehensive recycling and regeneration method for waste electrolyte of lithium ion batteries according to claim 1, characterized in that: The membrane in step (3) is a nanofiltration membrane that selectively permeates alcohol solvents.

4. The comprehensive recycling and regeneration method for waste electrolyte of lithium ion batteries according to claim 1, characterized in that: The temperature of the low-temperature crystallization in step (4) is -40 to -10°C, and the crystallization time is 8 to 20 hours.

5. The comprehensive recycling and regeneration method for waste electrolyte of lithium ion batteries according to claim 1, characterized in that: The solvent used to wash the crystals in step (4) is a pure solvent with extremely low solubility in lithium hexafluorophosphate, and the drying process temperature is 20 to 40°C.

6. The comprehensive recycling and regeneration method for waste electrolyte of lithium ion batteries according to claim 1, characterized in that: The mixed solution obtained in step (5) must ensure that the HF content in the solution is below 50 ppm and the water content is below 20 ppm before compounding.

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