Method for recovering lithium battery electrolyte by combining supercritical extraction distillation and molecular distillation

Abstract

The present invention provides a method for recovering lithium battery electrolyte by combining supercritical extraction distillation and molecular distillation, and relates to the technical field of lithium battery electrolyte recovery. The method of the present invention comprises the following steps: passing the lithium battery electrolyte into an extraction distillation tower, and passing supercritical carbon dioxide or supercritical carbon dioxide mixed with an entrainer into the bottom of the extraction distillation tower, performing continuous countercurrent extraction, discharging the gas phase after extraction distillation from the top of the extraction distillation tower, and discharging the liquid phase from the bottom of the extraction distillation tower; collecting the liquid phase discharged from the extraction distillation tower, cooling to precipitate the solid, separating the solid, and obtaining lithium salt; collecting the gas phase discharged from the extraction distillation tower, reducing the pressure to allow carbon dioxide to escape, and obtaining an organic solvent; vacuum distilling to separate the low boiling point organic solvent in the organic solvent, and molecular distilling to separate the chain carbonate and the cyclic carbonate. The present invention can efficiently separate the lithium salt and the organic solvent, and separate the chain carbonate and the cyclic carbonate, and the separation product has high yield and high purity.

Description

Technical Field

[0001] The invention relates to the technical field of lithium battery electrolyte recovery, and in particular to a method for recovering lithium battery electrolyte by combining supercritical extraction rectification and molecular distillation. Background Art

[0002] With the popularization of new energy vehicles in my country, the demand for lithium batteries has increased year by year. Recycling and treating waste lithium batteries and reducing environmental damage have become issues that must be addressed in the sustainable development of lithium batteries. Lithium battery electrolyte is a carrier for ion transmission between the positive and negative electrodes in lithium batteries and is an important component of lithium batteries. Lithium battery electrolyte mainly includes lithium salts and organic solvents, among which lithium salts mainly include lithium tetrafluoroborate (LiBF 4 ), lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), etc., organic solvents mainly include cyclic carbonates and chain carbonates, etc. In the prior art, extraction or distillation methods are usually used to separate and recycle the electrolyte, but there are still problems such as low recovery efficiency and low purity of the recovered product. Summary of the invention

[0003] Based on this, it is necessary to provide a method for recovering lithium battery electrolyte by combining supercritical extraction distillation and molecular distillation to address the above problems. This method can efficiently separate lithium salts and organic solvents, and separate chain carbonates and cyclic carbonates in organic solvents. The separated products have high yield and high purity, which helps to reduce pollution to the environment.

[0004] The method of recovering lithium battery electrolyte by combining supercritical carbon dioxide and molecular distillation of the present invention comprises the following steps:

[0005] Extraction distillation: The lithium battery electrolyte is passed into an extraction distillation tower, and supercritical carbon dioxide or supercritical carbon dioxide mixed with an entrainer is passed into the bottom of the extraction distillation tower for continuous countercurrent extraction. The gas phase after extraction distillation is discharged from the top of the extraction distillation tower, and the liquid phase is discharged from the bottom of the extraction distillation tower;

[0006] Lithium salt recovery: collect the liquid phase discharged from the extraction distillation tower, cool it down to precipitate the solid, separate the solid, and obtain lithium salt;

[0007] Extraction agent separation: collect the gas phase discharged from the extraction distillation tower, reduce the pressure to allow carbon dioxide to escape, and obtain the organic solvent;

[0008] Organic solvent separation: vacuum distillation is used to separate low-boiling point organic solvents from organic solvents, wherein the low-boiling point organic solvents are organic solvents having a boiling point lower than that of chain carbonates, chain carbonates from organic solvents are separated by molecular distillation, and cyclic carbonates are separated by molecular distillation, and low-boiling point organic solvents, chain carbonates, cyclic carbonates and electrolyte waste residues are recovered separately.

[0009] The above method uses supercritical extraction distillation to separate the organic solvent and lithium salt in the lithium battery electrolyte, and then uses vacuum distillation and molecular distillation to separate the low-boiling point organic solvent (such as entrainer, etc.), chain carbonate and cyclic carbonate in the organic solvent. It can realize continuous distillation separation of lithium battery electrolyte, with a large processing capacity, high yield and high purity of the separated and recovered products, which helps to reduce pollution to the environment.

[0010] Moreover, the distillation temperature of molecular distillation is much lower than the boiling point, and the high vacuum environment can prevent carbonate oxidation and darkening, and can continuously and stably separate multiple components.

[0011] It can be understood that the low boiling point organic solvent mentioned above refers to an organic solvent having a boiling point lower than that of the linear carbonate in the system at the same pressure, such as an entrainer.

[0012] In one embodiment, the entrainer is selected from one or more of anhydrous methanol, anhydrous ethanol or ethyl butyl ketone. Under normal pressure, the boiling point of anhydrous methanol is 64.7°C, the boiling point of anhydrous ethanol is 78.4°C, and the boiling point of ethyl butyl ketone is 75.6°C.

[0013] Ethyl butyl ketone has low viscosity, low boiling point, is easy to separate and has medium polarity. At the same time, the present invention is in a dry carbon dioxide atmosphere, avoiding the decomposition of conductive salts (electrolytes) in the air or when encountering water and water vapor to produce toxic gases (such as HF, PF5, etc.).

[0014] In one of the embodiments, in the extractive distillation step, the extractive distillation tower is filled with glass beads with a diameter of 2.5 to 10 mm, the tower height is 3 to 15 m, the tower inner diameter is 200 to 500 mm, and ultrasonic treatment is performed simultaneously with the extractive distillation, the ultrasonic frequency is 25 to 100 KHz, and the power is 50 to 200 W.

[0015] Glass beads do not react chemically with the electrolyte, dirt is easy to clean, the filler has a large porosity and a large specific surface area, and can effectively transmit ultrasonic waves, which is conducive to sufficient quality change.

[0016] Ultrasonic treatment helps to disperse the materials during the soaking process, accelerates the interphase mass transfer rate, and improves the extraction efficiency.

[0017] In one of the embodiments, in the extractive distillation step, the pressure in the extractive distillation tower is 25-35 MPa and the temperature is 40-50°C.

[0018] In one embodiment, during the lithium salt recovery step, the temperature is 35-45°C.

[0019] In one embodiment, in the extractant separation step, the pressure is 6-8 MPa and the temperature is 50-55°C.

[0020] In one embodiment, in the organic solvent separation step, the vacuum degree of vacuum distillation is <2000Pa and the temperature is 35-40°C; the vacuum degree when separating linear carbonates is ≤50Pa and the temperature is 45-50°C; the vacuum degree when separating cyclic carbonates is ≤1Pa and the temperature is 90-95°C.

[0021] In one embodiment, the method for recovering lithium battery electrolyte is carried out in a lithium battery electrolyte separation and recovery system, wherein the lithium battery electrolyte separation and recovery system comprises an extractive distillation tower, a separation kettle, a thin film evaporator, a first molecular distiller and a second molecular distiller which are fluidically connected in sequence;

[0022] The extractive distillation tower comprises a tower body and a jacket, wherein a light component outlet is provided at the top of the tower body, a heavy component outlet is provided at the bottom of the tower body, and a cavity is provided between the light component outlet and the heavy component outlet; a supercritical fluid nozzle is provided at the lower end of the tower body, a material nozzle is provided above the supercritical fluid nozzle, the supercritical fluid nozzle and the material nozzle are arranged oppositely, the supercritical fluid nozzle is connected to a supercritical fluid pipeline, and the material nozzle is connected to a material pipeline; the cavity between the supercritical fluid nozzle and the material nozzle is filled with fillers, and there are gaps between the fillers for the supercritical fluid and the material to exchange substances; the jacket is arranged around the outer wall of the tower body, and the jacket is used to heat the tower body;

[0023] The heavy component outlet of the extractive distillation tower is connected to a collecting kettle;

[0024] The extractive distillation step is carried out in an extractive distillation tower, the lithium salt recovery step is carried out in a collecting kettle, the extractant separation step is carried out in the separation kettle, the vacuum distillation in the organic solvent separation step is carried out in the thin film evaporator, the separation of chain carbonate is carried out in the first molecular distillation instrument, and the separation of cyclic carbonate is carried out in the second molecular distillation instrument.

[0025] Among them, in the extraction distillation tower, a supercritical fluid (i.e., supercritical carbon dioxide) can be introduced into the tower body through a supercritical fluid nozzle, and the material to be separated and recovered (lithium battery electrolyte) can be introduced into the tower body through a material nozzle. The supercritical fluid rises, the material falls, and the filler disperses the above components evenly, so that the supercritical fluid and the material are fully in contact for quality exchange. The material includes components such as organic solvents and salts, and the solubility in the supercritical fluid is different. The organic solvent is dissolved in the supercritical fluid and rises and is taken out of the tower body. Heavy components such as salts are concentrated and discharged and collected from the heavy component outlet below the tower body. Through the above structure, extraction and distillation are integrated to achieve continuous countercurrent distillation. The organic solvent and salt in the material can be efficiently separated, and the processing continuity is high, the processing volume is large, the separated product purity is high, and the pollutants are few.

[0026] The above-mentioned lithium battery electrolyte separation and recovery system first uses a supercritical fluid extraction distillation tower to separate the organic solvent and salts of the electrolyte, and then uses a separation kettle to separate the organic solvent and the supercritical fluid; the supercritical fluid is sometimes mixed with an entrainer to increase the solubility of the separated component in the gas phase, and the electrolyte contains a variety of organic solvents, so there are many types of organic solvents in the separation kettle. This system uses a thin film evaporator to separate the low-boiling point organic solvent (such as entrainer, etc.) in the organic solvent mixture, and then uses a molecular distillation instrument to separate the organic solvents in the electrolyte. The above-mentioned system can not only realize the separation of organic solvents and salts in the electrolyte, but also separate the organic solvents according to the difference in boiling points, further improve the separation effect, and is conducive to the recycling of different types of organic solvents.

[0027] In one of the embodiments, an ultrasonic generator is provided on the tower body for generating ultrasonic waves to vibrate the filler.

[0028] In one embodiment, the tower body is formed by splicing a number of unit towers up and down, and the unit towers are fluidically connected to each other; a tower plate is provided at the connection between two adjacent unit towers, and the tower plate separates the cavities of the two unit towers; the height of the unit tower body is 1 to 5m; and the material nozzle is arranged at the upper end of the unit tower.

[0029] Preferably, except for the uppermost unit tower, each unit tower has a material nozzle at its upper end, and multiple material nozzles can simultaneously feed materials, or one of them can be selected to inject materials. Different numbers of unit towers can be selected for extractive distillation according to processing requirements.

[0030] The use of multiple unit towers can further improve the extraction and distillation efficiency, the quality exchange effect, and the purity of the separated products.

[0031] Preferably, the number of unit towers is 3.

[0032] In one of the embodiments, the material pipeline and part of the supercritical fluid pipeline are laid around the jacket, and the heat source in the jacket is used to preheat the material in the material pipeline and the supercritical fluid in the supercritical fluid pipeline.

[0033] Materials and supercritical fluids need to be preheated before entering the tower body. Laying the material pipeline and the supercritical fluid pipeline in the jacket can use the heat medium in the jacket for preheating, thereby improving the utilization rate of heat.

[0034] In one embodiment, the supercritical fluid nozzle is connected to a confluence pipe, the confluence pipe is respectively connected to a supercritical fluid pipe and an entrainer pipe, and the supercritical fluid pipe and the entrainer pipe are arranged in parallel. The above structure can be used to mix the entrainer into the supercritical fluid, and the entrainer can increase the solubility of the component to be separated in the gas component and improve the extraction efficiency.

[0035] In one embodiment, the separation kettle comprises a kettle body and a water jacket heating layer arranged on the outer wall of the kettle body, the water jacket heating layer is used to heat the organic solvent mixture in the kettle body, and the water jacket heating layer is provided with a water inlet and a drain outlet.

[0036] In one embodiment, the collecting kettle is connected to the material pipeline. The concentrated electrolyte in the collecting kettle can enter the supercritical fluid extraction and distillation tower through the material pipeline to continue extraction and distillation, thereby further improving the separation effect.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The method for recovering lithium battery electrolyte of the present invention uses supercritical extraction distillation to separate organic solvents and lithium salts in lithium battery electrolyte, and then uses vacuum distillation and molecular distillation to separate low-boiling point organic solvents, chain carbonates and cyclic carbonates in the organic solvent, which can realize continuous distillation separation of lithium battery electrolyte, has a large processing capacity, and has a high yield and purity of separated and recovered products, which helps to reduce pollution to the environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the structure of the supercritical fluid extraction distillation tower in the embodiment.

[0040] Figure 2 Schematic diagram of the structure of the unit tower in the embodiment.

[0041] Figure 3 Schematic diagram of the structure of the lithium battery electrolyte separation and recovery system in the embodiment.

[0042] Among them, 1. supercritical fluid extraction distillation tower, 11. tower body, 111. light component outlet, 112. heavy component outlet, 113. unit tower, 114. tower plate, 115. sealing ring, 12. cavity, 13. supercritical fluid nozzle, 131. supercritical fluid pipeline, 132. entrainer pipeline, 14. material nozzle, 141. material pipeline, 15. filler, 16. jacket, 17. ultrasonic generator; 2. collecting kettle, 3. separation kettle, 31. kettle body, 32. water jacket heating layer, 4. thin film evaporator, 5. first molecular distillation instrument, 6. second molecular distillation instrument. DETAILED DESCRIPTION

[0043] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0044] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0046] Example 1

[0047] A supercritical fluid extraction distillation tower 1, comprising a tower body 11 and a jacket 16, such as Figure 1-2 As shown, the tower body 11 is composed of three unit towers 113 spliced ​​up and down. The bottom of the unit tower 113 is provided with an internal thread, and the top is provided with an external thread matching the internal thread. Two adjacent unit towers 113 are threadedly connected. In order to improve the sealing of the connection, a sealing ring 115 is provided at the connection. The outer wall of the tower body 11 is provided with a jacket 16, and the jacket 16 can heat the tower body 11. The tower body 11 in this embodiment has a height of 3m, and each unit tower 113 has a height of 1m and an inner diameter of 200mm.

[0048] The tower body 11 is cylindrical, with a light component outlet 111 at the top and a heavy component outlet 112 at the bottom. There is a cavity 12 between the light component outlet 111 and the heavy component outlet 112, and the cavity 12 provides space for the material and the extractant to contact. The lower end of the lowest unit tower 113 is provided with an upward supercritical fluid nozzle 13, the supercritical fluid nozzle 13 is connected to the confluence pipeline, and the confluence pipeline is respectively connected to the supercritical fluid pipeline 131 and the entrainer pipeline 132. The supercritical fluid pipeline 131 and the entrainer pipeline 132 are arranged in parallel, the supercritical fluid pipeline 131 is used to transport supercritical fluid (such as supercritical carbon dioxide), and the entrainer pipeline 132 is used to transport entrainer (such as methanol, ethanol or ethyl butyl ketone). The supercritical fluid and the entrainer can be mixed in the confluence pipeline and passed into the cavity 12. By controlling the valve, the supercritical fluid or the supercritical fluid mixed with the entrainer can be passed into the cavity 12.

[0049] Except for the topmost unit tower 113, the upper ends of the other unit towers 113 are provided with downward material nozzles 14, which are connected to the material pipeline 141, and can pass the material to be separated (such as lithium battery electrolyte) into the cavity 12. The bottom of each unit tower 113 is provided with a tower plate 114, which can separate adjacent unit towers 113, and the tower plate 114 can also receive fillers 15. The tower plate 114 is provided with a plurality of through holes, which can allow the liquid phase (i.e., the material) to stay on the tower plate 114 and flow down, and the gas phase (i.e., the supercritical fluid) can pass through the through holes and rise. The cavity 12 in each unit tower 113 is filled with fillers 15. The fillers 15 in this embodiment are glass beads with a diameter of 2.5 to 10 mm. The glass beads do not react chemically with the electrolyte, and the dirt is easy to clean. The filler 15 has a large porosity and a large specific surface area, which is conducive to sufficient quality change. By adjusting the pipes and valves connected to each unit tower 113, it can be adjusted to a single-unit tower 113 mode or a mode in which multiple unit towers 113 are connected in series.

[0050] To further improve the extraction and distillation effect, an ultrasonic generator 17 is provided at the bottom of the lowest unit tower 113 to generate ultrasonic waves to vibrate the filler 15. Preferably, the ultrasonic treatment frequency is 50-100 KHz. Ultrasonic treatment helps to disperse the materials during the soaking process, accelerates the interphase mass transfer rate, and improves the extraction efficiency.

[0051] Usually, the material and the supercritical fluid need to be preheated. To improve the heat utilization rate, part of the material pipeline 141 and the supercritical fluid pipeline 131 are laid around the jacket 16 and preheated using the heat medium in the jacket 16.

[0052] Example 2

[0053] An electrolyte separation and recovery system, such as Figure 3As shown, it includes a supercritical fluid extraction distillation tower 1, a collecting kettle 2, a separation kettle 3, a thin film evaporator 4, a first molecular distillation apparatus 5 and a second molecular distillation apparatus 6 which are fluidically connected in sequence. The supercritical fluid extraction distillation tower 1 is the supercritical fluid extraction distillation tower 1 in Example 1.

[0054] The heavy component outlet 112 of the supercritical fluid extraction distillation tower 1 is connected to the collecting kettle 2, and the collecting kettle 2 is used to collect the concentrated electrolyte after extraction distillation. In order to further improve the separation and purification effect, the collecting kettle 2 is connected to the material pump on the material pipeline 141, and the concentrated electrolyte in the collecting kettle 2 can be pumped into the material pipeline 141, and passed into the tower body 11 through the material nozzle 14 to continue the extraction distillation. The separation kettle 3 is used to collect organic solvents. The separation kettle 3 includes a kettle body 31 and a water jacket heating layer 32 arranged on the outer wall of the kettle body 31. The water jacket heating layer 32 is used to heat the organic solvent in the kettle body 31. The water jacket heating layer 32 is provided with a water injection port and a drain port, which are used to inject hot water and discharge hot water respectively. The thin film evaporator 4 is used to distill out low-boiling organic solvents. The first molecular distiller 5 is used to separate chain carbonates, and the second molecular distiller 6 is used to separate cyclic carbonates.

[0055] Example 3

[0056] A method for recovering lithium battery electrolyte by combining supercritical extraction distillation and molecular distillation is carried out using the electrolyte separation and recovery system of Example 2.

[0057] Clean the used lithium-ion batteries and discharge them completely. Put the batteries and the prepared material tanks into a glove box protected by high-purity nitrogen, open the batteries, carefully take out the electrolyte and put it into the material tank. The main components of the electrolyte of used lithium batteries are lithium salts and organic solvents, and also contain a certain amount of impurities. Lithium salts include lithium tetrafluoroborate, lithium hexafluorophosphate and lithium perchlorate, and organic solvents include cyclic carbonates and chain carbonates. Cyclic carbonates mainly include ethylene carbonate and propylene carbonate, and chain carbonates include dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and ethyl propyl carbonate.

[0058] The specific processing flow is as follows:

[0059] 1) Three unit towers 113 are activated, which are named as the first unit tower, the second unit tower and the third unit tower from bottom to top. Supercritical carbon dioxide is introduced into the bottom of the first unit tower, and materials (i.e., lithium battery electrolyte) are introduced into the upper ends of the first unit tower and the second unit tower. The tower is 3 meters high and the inner diameter is 200mm. The extraction pressure in the supercritical fluid extraction distillation tower 1 is controlled to be 35MPa, the extraction temperature is 45°C, and the cycle time is 1h. At the same time, ultrasound is turned on, the ultrasonic frequency is 25KHz, and the power is 50W. The total flow rate of the material in the tower is 1kg / h, and the supercritical carbon dioxide circulation volume is 2kg / h.

[0060] 2) Through the extractive distillation of the supercritical fluid extractive distillation tower 1, the concentrated electrolyte flows into the collecting kettle 2 through the heavy component outlet 112, and the temperature in the collecting kettle 2 is controlled to be 40° C. to precipitate lithium salt.

[0061] 3) The organic solvent in the electrolyte is dissolved in the extractant and enters the separation kettle 3 along with the extractant. After detection by ICP OES (Inductively Coupled Plasma Emission Spectrometer), the recovered organic solvent extract does not contain lithium. The pressure in the separation kettle 3 is controlled to 6MPa and the temperature is 50°C. The carbon dioxide escapes to a storage tank at 4°C and liquefies. The carbon dioxide can be recycled.

[0062] 4) The organic solvent in the separation kettle 3 is introduced into the thin film evaporator 4, the vacuum degree in the thin film evaporator 4 is controlled to be 1000 Pa, the temperature is controlled to be 35° C., and 2 wt % of low boiling point organic matter is distilled out.

[0063] 5) The remaining components of step 4) are passed into the first molecular distillation apparatus 5, the vacuum degree is controlled to be 50Pa, the temperature is 50°C, and the chain carbonate mixture is distilled out (the yield is more than 95%). In the first molecular distillation apparatus 5, the chain carbonate mixture is a light component, and the cyclic carbonate containing impurities is a heavy component. Under normal pressure, the boiling point of dimethyl carbonate is 90.1°C, the boiling point of diethyl carbonate is 110°C, the boiling point of ethyl methyl carbonate is 109.2°C, and the boiling point of ethyl propyl carbonate is 90.0°C.

[0064] 6) The cyclic carbonate containing impurities is passed into the second molecular distillation apparatus 6, the vacuum is controlled to be 1Pa, the temperature is 95°C, and the cyclic carbonate mixture is distilled out (the yield is more than 95%). In the second molecular distillation apparatus 6, the cyclic carbonate mixture is a light component, and the electrolyte waste residue is a heavy component. Under normal pressure, the boiling point of ethylene carbonate is 243.0°C, and the boiling point of propylene carbonate is 240.0°C.

[0065] It can be seen that the distillation temperature of molecular distillation is much lower than the boiling point of carbonate at normal pressure, which can effectively avoid the oxidation of carbonate and prevent the color of carbonate from darkening.

[0066] In this embodiment, no entrainer was introduced, and the total recovery rate of the organic solvent was about 75%.

[0067] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0068] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for recovering lithium battery electrolyte by combining supercritical extraction distillation and molecular distillation, It is characterized in that The following steps are involved: Extraction distillation: The lithium battery electrolyte is passed into the extraction distillation tower, and supercritical carbon dioxide is introduced into the bottom of the extraction distillation tower for continuous countercurrent extraction. The gas phase after extraction distillation is discharged from the top of the extraction distillation tower, and the liquid phase is discharged from the bottom of the extraction distillation tower. The extraction distillation tower is filled with glass beads with a diameter of 2.5~10mm, the tower height is 3~15m, and the inner diameter of the tower is 200~500mm. Ultrasonic treatment is carried out while extracting and distilling. The frequency of ultrasound is 25~100KHz and the power is 50~200W. The pressure in the extraction distillation tower is 35MPa and the temperature is 45℃. Lithium salt recovery: collect the liquid phase discharged from the extraction distillation tower, cool it to 35-45°C to precipitate solids, separate the solids, and obtain lithium salts; Extraction agent separation: collect the gas phase discharged from the extraction distillation tower, reduce the pressure to allow carbon dioxide to escape, and obtain the organic solvent; Organic solvent separation: vacuum distillation is used to separate low-boiling point organic solvents from organic solvents, wherein the low-boiling point organic solvents are organic solvents having a boiling point lower than that of chain carbonates, chain carbonates from organic solvents are separated by molecular distillation, and then cyclic carbonates are separated by molecular distillation, and low-boiling point organic solvents, chain carbonates, cyclic carbonates and electrolyte waste residues are recovered respectively; the vacuum degree of vacuum distillation is 1000Pa and the temperature is 35°C; the vacuum degree of separation of chain carbonates is 50Pa and the temperature is 50°C; the vacuum degree of separation of cyclic carbonates is 1Pa and the temperature is 95°C; The lithium battery electrolyte is recovered in a lithium battery electrolyte separation and recovery system, wherein the lithium battery electrolyte separation and recovery system comprises an extraction distillation tower, a separation kettle, a thin film evaporator, a first molecular distillation instrument and a second molecular distillation instrument which are fluidically connected in sequence; The extractive distillation tower comprises a tower body and a jacket, wherein a light component outlet is provided at the top of the tower body, and a heavy component outlet is provided at the bottom of the tower body, and the tower body is formed by splicing a plurality of unit towers up and down, and the plurality of unit towers are fluidically connected to each other; a cavity is provided between the light component outlet and the heavy component outlet; a supercritical fluid nozzle is provided at the lower end of the tower body, and the material nozzle is provided at the upper end of the unit tower, and the supercritical fluid nozzle and the material nozzle are arranged oppositely, the supercritical fluid nozzle is connected to a supercritical fluid pipeline, and the material nozzle is connected to a material pipeline; the cavity between the supercritical fluid nozzle and the material nozzle is filled with fillers, and there are gaps between the fillers for material exchange between the supercritical fluid and the material; the jacket is arranged around the outer wall of the tower body, and the jacket is used to heat the tower body; The heavy component outlet of the extractive distillation tower is connected to a collecting kettle; The extractive distillation step is carried out in an extractive distillation tower, the lithium salt recovery step is carried out in a collecting kettle, the extractant separation step is carried out in the separation kettle, the vacuum distillation in the organic solvent separation step is carried out in the thin film evaporator, the separation of chain carbonate is carried out in the first molecular distillation instrument, and the separation of cyclic carbonate is carried out in the second molecular distillation instrument.

2. The method according to claim 1, It is characterized in that In the extractant separation step, the pressure is 6 MPa and the temperature is 50°C.

3. The method according to claim 1, It is characterized in that The tower body is provided with an ultrasonic generator for generating ultrasonic waves to vibrate the filler.

4. The method according to claim 1, It is characterized in that A tower plate is provided at the connection of two adjacent unit towers, and the tower plate separates the cavities of the two unit towers; the height of the unit tower body is 1m.

5. The method according to any one of claims 3 or 4, It is characterized in that The material pipeline and part of the supercritical fluid pipeline are laid around the jacket, and the heat source in the jacket is used to preheat the material in the material pipeline and the supercritical fluid in the supercritical fluid pipeline.

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