Method and system for recovering electrolyte from lithium-ion battery

Abstract

The present application belongs to the field of new energy. Disclosed is a method for recovering an electrolyte from a lithium-ion battery. The method comprises the following steps: step 1, crushing a lithium-ion battery, heating same, and collecting a first gas and a solid; step 2, collecting tail gas obtained from primary condensation, so as to obtain a second gas; step 3, cracking the solid obtained in step 1, so as to obtain a third gas; step 4, removing an organic solvent, water and HF in the third gas by means of condensation, so as to obtain a fifth gas; step 5, mixing the fifth gas and the second gas, and subjecting the resulting gas mixture to secondary condensation to remove gases other than PF5, so as to obtain a sixth gas; and step 6, subjecting the sixth gas to third-stage condensation, and collecting liquid PF5. The method can effectively recover PF5, which has a relatively high purity. Further provided in the present application is a system for implementing the method.

Description

A lithium-ion battery electrolyte recovery method and system

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 5, 2023, with application number 202311654080.8, and invention name “A method and system for recovering lithium-ion battery electrolyte”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of new energy, and specifically to a method and system for recycling lithium-ion battery electrolyte. Background Art

[0003] Lithium-ion batteries primarily consist of a casing, positive electrode, negative electrode, separator, and electrolyte. Currently, the mainstream recycling process for used lithium-ion batteries involves crushing them under a protective atmosphere and performing multi-stage physical sorting to separate and recycle the casing, separator, positive and negative electrode powders, and copper and aluminum particles (powder).

[0004] For the recovery of electrolyte components, the conventional process is to use vacuum distillation combined with condensation to recover organic solvents, while lithium hexafluorophosphate is decomposed into PF5 gas by heating, and then the PF5 gas is passed into a solution containing LiF to synthesize the electrolyte. However, when recycling the electrolyte, lithium hexafluorophosphate often undergoes side reactions during the use of the electrolyte until the battery is scrapped, and the inert atmosphere is not strictly controlled during the recovery, crushing and drying processes. This can easily lead to the pyrolysis gas containing high-boiling point organic solvent gases, moisture, HF, POF3 and other impurity gases in addition to PF5. If the pyrolysis gas is directly reacted with LiF to produce lithium hexafluorophosphate, it will affect the purity and performance of the product. In addition, a large amount of inert gas is consumed in the process of recycling and processing waste lithium-ion batteries, further increasing the processing cost.

[0005] One of the main purposes of thermal cracking recovery of lithium-ion batteries is to recover LiF and PF5. Further research has found that impurity gases such as POF3 are also generated during the production of PF5. At the same time, lithium hexafluorophosphate has very low thermal stability and can still crack at volatile temperatures. Therefore, a major problem with existing technologies is that the recovered liquid product is impure and the recovery of PF5 is insufficient.

[0006] Therefore, the technical problem to be solved by this application is: how to improve the recovery rate and recovery purity of PF5 when recovering the electrolyte by the cracking method. Summary of the Invention

[0007] The main purpose of the present application is to provide a method for recovering lithium-ion battery electrolyte, which recovers lithium salt cracking gas generated in the solvent volatilization stage and lithium salt cracking gas generated in the cracking stage. At the same time, combined with the multi-stage condensation process, the main impurities are separated in the set temperature section, and the lithium salt cracking gas generated in the solvent volatilization stage that has been pre-separated is injected into the multi-stage condensation stage, which can effectively recover PF5 with high purity.

[0008] At the same time, the present application also provides a system for implementing the method.

[0009] To achieve the above objectives, this application provides the following technical solutions:

[0010] A method for recovering lithium-ion battery electrolyte comprises the following steps:

[0011] Step 1: After crushing the lithium-ion battery, heating under inert gas protection to volatilize at least part of the solvent in the electrolyte, collecting a first gas and a solid, and performing primary condensation on the first gas to remove at least part of the solvent in the first gas, wherein the heating temperature is 100-150° C.;

[0012] Step 2: collecting the tail gas after primary condensation, separating the fluorine-containing substances produced by the decomposition of the lithium salt from the tail gas to obtain a second gas containing PF5;

[0013] Step 3: cracking the solid obtained in step 1 under inert gas protection and at the cracking temperature of the lithium salt, collecting the tail gas generated by the cracking to obtain a third gas, wherein the third gas contains an organic solvent, nitrogen, water, PF5, HF, and POF3;

[0014] The cracking temperature is higher than the heating temperature;

[0015] Step 4: removing the organic solvent, water, and HF from the third gas by condensation to obtain the fifth gas;

[0016] Preferably, the step 4 specifically includes:

[0017] Step 41: pre-condensing the third gas to remove the organic solvent in the third gas to obtain a fourth gas;

[0018] Step 42: performing primary condensation on the fourth gas to remove water and HF from the fourth gas to obtain a fifth gas.

[0019] Step 5: The fifth gas and the second gas are mixed and subjected to secondary condensation to remove other gases except PF5 to obtain a sixth gas;

[0020] Step 6: The sixth gas is subjected to three-stage condensation to collect liquid PF5.

[0021] Preferably, the above-mentioned method for recovering lithium-ion battery electrolyte comprises the following steps:

[0022] Step 1: After crushing the lithium-ion battery, heat it to 100-150° C. under inert gas protection to volatilize at least part of the solvent in the electrolyte, collect the first gas and solid, and perform primary condensation. The primary condensation temperature is -20-20° C., preferably -10-10° C., and more preferably 0-5° C.;

[0023] In this step, the electrolyte of the crushed lithium-ion battery evaporates at the volatilization temperature. Generally, people would think that a relatively pure solvent is obtained; however, at this temperature, a small amount of lithium hexafluorophosphate will decompose to produce PF5; therefore, the effective recycling of the second gas produced in step 2 is one of the important guarantees for achieving efficient recovery of PF5.

[0024] The present application does not impose any specific restrictions on the pressure during the heating process of step 1, as long as it can meet the purpose of this application. Taking the organic solvents commonly used in the field as examples: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl propionate and propyl acetate; the boiling points of each solvent are: ethylene carbonate 240°C; propylene carbonate 242°C; dimethyl carbonate 90°C; diethyl carbonate 126-128°C; ethyl methyl carbonate 107°C; ethyl acetate 77°C; propyl propionate 136°C; propyl acetate 102°C; referring to the above examples, under normal pressure, if the heating temperature is 100°C, at least part of the solvent includes ethyl acetate and dimethyl carbonate; if the heating temperature is 110°C, at least part of the solvent includes ethyl acetate, dimethyl carbonate, propyl acetate and ethyl methyl carbonate; if the heating temperature is 150°C, at least part of the solvent includes ethyl acetate, dimethyl carbonate, propyl acetate, ethyl methyl carbonate, diethyl carbonate and propyl propionate.

[0025] Generally speaking, the solvent volatilization temperature can be selected to be 100-150°C; if it is selected to be 100°C, it is recommended to maintain the system at a slightly negative pressure to further reduce the solvent boiling point.

[0026] In the above process, solvents with a boiling point above 150°C generally will not be evaporated in large quantities and will proceed to step 3.

[0027] Step 2: collecting the tail gas after primary condensation, and separating the fluorine-containing substances produced by the decomposition of the lithium salt from the tail gas to obtain a second gas;

[0028] In this step, the second gas is subjected to subsequent secondary condensation. This step 2, combined with steps 5 and 6, can solve the problems of low purity and recovery rate in traditional solutions.

[0029] This step fully considers the problem of lithium salt decomposition at the volatilization temperature. By continuing to condense, PF5 and other fluorine-containing compounds are separated and sent to the subsequent process for further purification.

[0030] Step 3: The solid obtained in step 1 is cracked under an inert gas protection and at the cracking temperature of the lithium salt, and the tail gas generated by the cracking is collected to obtain a third gas, wherein the third gas contains an organic solvent, nitrogen, water, PF5, HF, and POF3; and the volatilization temperature is lower than the cracking temperature;

[0031] The cracking temperature in this step is generally 150-500°C; preferably 200-300°C; more preferably 200-250°C;

[0032] In some embodiments of the present application, the cracking temperature is 150°C, 170°C, 200°C, 250°C, 300°C, 350°C, 400°C, 450°C or 500°C;

[0033] The composition of cracking tail gas is relatively complex, generally including but not limited to: nitrogen (the main component), water, HF, PF5, POF3, and high-boiling solvents. Possible high-boiling solvents include but are not limited to: ethylene carbonate (EC), propylene carbonate (PC), and dimethyl sulfoxide (DMSO). High-boiling solvents generally come from: high-boiling point organic solvents that do not evaporate in the low-temperature volatilization stage, very small amounts of oligomers of solvents with unsaturated bonds, and cracking products of binders in separators and cathode materials. Therefore, the next step is to condense these high-boiling solvents.

[0034] Step 41: pre-condensing the third gas to remove the organic solvent in the third gas to obtain a fourth gas; the pre-condensation temperature is -20 to 20°C; preferably -10 to 10°C; more preferably 0 to 5°C;

[0035] The main purpose of this step is to remove high boiling solvents.

[0036] In some embodiments of the present application, the optional pre-condensation temperature is -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C or 20°C;

[0037] Step 42: performing primary condensation on the fourth gas to remove water and HF in the fourth gas to obtain a fifth gas; the temperature of the primary condensation is -39 to 19° C., preferably -20 to 0° C., and more preferably -10 to 0° C.;

[0038] In some embodiments of the present application, the optional primary condensation temperature is -39°C, -35°C, -30°C, -25°C, -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C or 19°C;

[0039] This step mainly produces a hydrofluoric acid solution, so the equipment used in this step should be more effectively designed for corrosion resistance to increase the service life of the equipment;

[0040] Step 5: The fifth gas and the second gas are mixed and subjected to secondary condensation to obtain a sixth gas; the temperature of the secondary condensation is -84 to -40°C; preferably -70 to -50°C; more preferably -70 to -60°C;

[0041] In some embodiments of the present application, the optional secondary condensation temperature is -84°C, -80°C, -70°C, -60°C, -50°C, -45°C or -40°C;

[0042] The purpose of this step is mainly to condense materials with boiling points below 0°C, such as POF3;

[0043] The boiling point of POF3 is -39.8°C and the boiling point of PF5 is -84.6°C; therefore, to separate POF3 and PF5, it is only necessary to control the condensation temperature to be lower than the boiling point of PF5.

[0044] In order to separate the two more effectively, it is better to set the lower limit of the condensation temperature to -70°C.

[0045] Step 6: condense the sixth gas in three stages to collect liquid PF5; the temperature of the three-stage condensation is -196 to -85°C; preferably -130 to -100°C; more preferably -120 to -110°C;

[0046] In some embodiments of the present application, the optional temperature of the third-stage condensation is -196°C, -180°C, -170°C, -160°C, -150°C, -140°C, -130°C, -120°C, -110°C, -100°C, -90°C or -85°C;

[0047] The purpose of this step is mainly to collect liquid PF5 with higher purity.

[0048] In the above-mentioned lithium-ion battery electrolyte recovery method, the step 2 removes the organic solvent by condensation or by adsorption and desorption of an adsorbent.

[0049] In practice, the above two methods each have their own advantages. If condensation is used to remove the organic solvent, the operation is simple and the steps are few, but the amount of nitrogen is large. When it is combined with step 5, the condensation temperature requirement of step 5 is higher. If adsorption and desorption are used, the amount of nitrogen used is small. A small amount of nitrogen can be used to first analyze the fluorine-containing compounds, thereby reducing the gas processing volume in step 5 and thus reducing the energy consumption of step 5.

[0050] In the above-mentioned lithium-ion battery electrolyte recovery method, the method for separating the fluorine-containing substances produced by the decomposition of lithium salts from the tail gas in step 2 is specifically: using a cold trap to perform a condensation operation and controlling the condensation temperature to -30 to -10°C to separate the organic solvent and the fluorine-containing substances.

[0051] In the above-mentioned lithium-ion battery electrolyte recovery method, the step 2 is: adsorbing the tail gas after primary condensation by activated carbon, and then desorbing the adsorbed activated carbon using nitrogen; the temperature of the nitrogen used for desorption is 40-120°C.

[0052] At the same time, the present application also discloses a system for implementing any of the above methods, comprising a heating device for volatilizing at least part of the solvent in the electrolyte, a pyrolysis device for pyrolyzing the lithium salt in the solid generated by heating of the heating device, a pre-condensing device for condensing the third gas, a primary condensing device for condensing the fourth gas, a secondary condensing device for condensing the fifth gas, and a tertiary condensing device for condensing the sixth gas, which are connected in sequence; the heating device is connected to a primary condensing device for condensing the first gas and a separation device for separating fluorine-containing compounds from the tail gas of the primary condensing device; the separation device sends the second gas to the secondary condensing device through a pipeline.

[0053] In the above system, the pre-condensing device, the primary condensing device, the secondary condensing device, the tertiary condensing device, and the primary condensing device are tubular condensers.

[0054] In the above system, the separation device is a cold trap, and the cold source of the cold trap is liquid nitrogen or refrigerated brine with a temperature of -30 to -10°C.

[0055] In the above system, the separation device includes at least two parallel adsorption tanks using activated carbon as an adsorption carrier; the adsorption tanks are provided with nitrogen pipes for inputting hot nitrogen for desorption of the activated carbon.

[0056] One of the above technical solutions of this application has at least one of the following advantages or beneficial effects:

[0057] In this method, the cracking gas is treated by multi-stage condensation to recover PF5, and the PF5 produced in step 1 is treated to further achieve full recovery of PF5;

[0058] In this method, the tail gas after solvent condensation is separated into fluorine-containing gas and then combined into the secondary condensation, which can effectively simplify the process and improve the efficiency.

[0059] In this method, the PF5 recovered is of high purity through ultra-low temperature three-stage condensation.

[0060] In production experiments, it was found that the best option is to let the second gas flow into the secondary condensation. The second gas is almost a fluorine-containing compound with an ultra-low boiling point and a low temperature. If the second gas is flowed into the pre-condensation device, it will cause impurities such as organic solvents, HF and water to condense together to form an emulsion, which is not conducive to the subsequent recovery and treatment of impurities such as organic solvents, HF and water; if the second gas is flowed into the primary condensation device, the amount of condensed gas will increase in the primary condensation, increasing the burden of condensation separation; the second gas will be collected in the secondary condensation to achieve the goal of optimal energy consumption.

[0061] Based on this, this application achieves sufficient and high-purity recovery of PF5 through the above optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0063] FIG1 is a pipeline flow chart of the first part of this application;

[0064] FIG2 is a pipeline flow chart of the second part of this application;

[0065] In Figures 1 and 2, the labels are: 1. Heating device; 2. Pyrolysis device; 3. Pre-condensing device; 4. Primary condensing device; 5. Secondary condensing device; 6. Tertiary condensing device; 7. Primary condensing device; 8. Cold trap; 9. First nitrogen pipe; 10. Vacuum pump; 11. Activated carbon canister; 12. Desorption gas pipeline; 13. Inlet; 14. First outlet; 15. Second outlet; 16. Third outlet. DETAILED DESCRIPTION

[0066] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments of the present application, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of this application.

[0067] Part 1

[0068] Before describing the process in detail, the production system for this section will be described. Referring to Figure 1 , the system specifically comprises the following devices: a heating device 1, a pyrolysis device 2 for pyrolyzing the lithium salt in the solid produced by the heating device, a pre-condensation device 3 for condensing the third gas, a primary condensation device 4 for condensing the fourth gas, a secondary condensation device 5 for condensing the fifth gas, and a tertiary condensation device 6 for condensing the sixth gas, all connected in sequence. The heating device is connected to a primary condensation device 7 for condensing the first gas and a separation device for separating fluorine-containing compounds from the tail gas of the primary condensation device. The separation device delivers the second gas to the secondary condensation device via a pipeline. The heating device 1 is connected to a first nitrogen pipe 9 for providing nitrogen as a protective gas to the low-temperature furnace. A vacuum pump 10 is connected between the heating device 1 and the primary condensation device 7 to maintain a slightly negative pressure within the low-temperature furnace. The inlet of the vacuum pump 10 is connected to the heating device 1, and the outlet of the vacuum pump 10 is connected to the inlet of the primary condensation device 7.

[0069] The heating device 1 used in the embodiment is a low-temperature furnace, which is connected to a first nitrogen pipe 9 for introducing nitrogen into the low-temperature furnace as a protective gas. The vacuum pump 10 draws nitrogen, volatile organic solvents, etc. into the primary condensing device 7. The low-temperature furnace is maintained at a slightly negative pressure by the vacuum pump 10. The pyrolysis device 2 is a pyrolysis furnace, and the pre-condensing device 3, the primary condensing device 4, the secondary condensing device 5, and the tertiary condensing device 6 are all tubular condensers; the separation device is a cold trap 8.

[0070] Example 1

[0071] A method for recovering lithium-ion battery electrolyte, comprising the following steps:

[0072] Step 1: Crushing 1 ton of cylindrical waste lithium iron phosphate batteries under nitrogen protection;

[0073] In lithium iron phosphate batteries, the main organic solvent composition of the electrolyte is: ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), with a mass ratio of 3:1:6;

[0074] The lithium salt is lithium hexafluorophosphate, which accounts for 13% of the weight of the electrolyte;

[0075] The active material of the positive electrode is lithium iron phosphate, and the current collector is carbon-coated aluminum foil; the mass ratio of lithium iron phosphate, conductive agent SuperP, adhesive PVDF and carbon nanotubes (CNT) on the current collector is 95.8:1:2.5:0.7;

[0076] Step 2: The crushed material is sent to a low-temperature furnace and evaporated at 100°C for 2 hours under a nitrogen atmosphere. The evaporated organic solvent (first gas) is extracted by a vacuum pump, and the pressure in the furnace is maintained at a slightly negative pressure by the vacuum pump. The material is condensed and recovered by a water-cooled tubular condenser (primary condensing device). The solvent is fully evaporated in the low-temperature furnace to obtain a solid material (containing a high-boiling solvent); the primary condensing device discharges uncondensed gas, and the uncondensed gas is introduced into a cold trap with -20°C supercooled brine as a refrigerant to obtain a second gas, which contains relatively pure PF5, POF3 and nitrogen; 5°C cooling water is introduced into the primary condensing device;

[0077] Step 3: The solid material is then fed into a pyrolysis furnace and kept at 180°C for 1.5 hours under a nitrogen atmosphere. The lithium hexafluorophosphate decomposes to produce PF5 and impurity gases to obtain a third gas; the third gas contains an organic solvent, nitrogen, water, PF5, HF, and POF3;

[0078] Step 41: Send the third gas into a pre-condensing device to remove the high-boiling organic solvent in the third gas; the pre-condensing device is a water-cooled tubular condenser (pre-condensing device), and 5°C cooling water is passed into the pre-condensing device. The uncondensed gas discharged from the pre-condensing device is the fourth gas.

[0079] Step 42: The fourth gas is fed into a tubular condenser (a primary condensing device). The refrigerant of the primary condensing device is chilled brine at a temperature of -5°C to 0°C. The HF and water are fully condensed to obtain a fifth gas. The fifth gas contains only nitrogen, PF5, POF3, and trace amounts of unidentified impurities.

[0080] In this application, the refrigerant temperature in the tubular condenser should be significantly lower than the boiling point of the object to be condensed. The reason is that the amount of nitrogen in the fourth gas is relatively large and the gas flow rate is relatively fast. If the condensation temperature is too high, the object to be condensed will not be fully condensed.

[0081] Step 5: The fifth gas and the second gas are mixed and sent to a tubular condenser (a secondary condensing device) for condensation to obtain a sixth gas; the refrigerant used in the secondary condensing device is liquid nitrogen, and the condensation temperature is -50 to -40°C;

[0082] Step 6: Send the sixth gas into a tubular condenser (three-stage condensing device) for condensation to collect liquid PF5. The refrigerant used in the three-stage condensing device is liquid nitrogen, and the condensation temperature is -120 to -110°C.

[0083] Example 2

[0084] A method for recovering lithium-ion battery electrolyte, comprising the following steps:

[0085] Step 1: crushing 1 ton of cylindrical waste lithium iron phosphate batteries (model parameters are the same as those in Example 1) under nitrogen protection;

[0086] Step 2: The crushed material is sent to a low-temperature furnace and evaporated at 120°C for 2 hours under a nitrogen atmosphere. The evaporated organic solvent (first gas) is extracted by a vacuum pump, and the pressure in the furnace is maintained at a slightly negative pressure by the vacuum pump. The gas is condensed and recovered by a water-cooled tubular condenser (primary condensing device). The solvent is fully evaporated in the low-temperature furnace to obtain a solid material; the primary condensing device discharges uncondensed gas, and the uncondensed gas is introduced into a cold trap with -15°C supercooled brine as a refrigerant to obtain a second gas, which contains relatively pure PF5, POF3 and nitrogen; 5°C cooling water is introduced into the primary condensing device;

[0087] Step 3: The solid material is then fed into a pyrolysis furnace and kept at 200°C for 1.5 hours under a nitrogen atmosphere. The lithium hexafluorophosphate decomposes to produce PF5 and impurity gases to obtain a third gas; the third gas contains an organic solvent, nitrogen, water, PF5, HF, and POF3;

[0088] Step 41: Send the third gas into a pre-condensing device to remove the high-boiling organic solvent in the third gas; the pre-condensing device is a water-cooled tubular condenser (pre-condensing device), and 5°C cooling water is passed into the pre-condensing device. The uncondensed gas discharged from the pre-condensing device is the fourth gas.

[0089] Step 42: The fourth gas is fed into a tubular condenser (a primary condensing device). The refrigerant of the primary condensing device is chilled brine at a temperature of -5°C to 0°C. The HF and water are fully condensed to obtain a fifth gas. The fifth gas contains only nitrogen, PF5, POF3, and trace amounts of unidentified impurities.

[0090] Step 5: The fifth gas and the second gas are mixed and sent to a tubular condenser (a secondary condensing device) for condensation to obtain a sixth gas; the refrigerant used in the secondary condensing device is liquid nitrogen, and the condensation temperature is -60 to -50°C;

[0091] Step 6: The sixth gas is sent to a tubular condenser (three-stage condensing device) for condensation to collect liquid PF5. The refrigerant used in the three-stage condensing device is liquid nitrogen, and the condensation temperature is -130 to -120°C.

[0092] Example 3

[0093] A method for recovering lithium-ion battery electrolyte, comprising the following steps:

[0094] Step 1: crushing 1 ton of cylindrical waste lithium iron phosphate batteries (model parameters are the same as those in Example 1) under nitrogen protection;

[0095] Step 2: The crushed material is sent to a low-temperature furnace and evaporated at 140°C for 2 hours under a nitrogen atmosphere. The evaporated organic solvent (first gas) is extracted by a vacuum pump, and the pressure in the furnace is maintained at a slightly negative pressure by the vacuum pump. The material is condensed and recovered by a water-cooled tubular condenser (primary condensing device). The solvent is fully evaporated in the low-temperature furnace to obtain a solid material; the primary condensing device discharges uncondensed gas, and the uncondensed gas is introduced into a cold trap with -30°C supercooled brine as a refrigerant to obtain a second gas, which is relatively pure PF5, POF3 and nitrogen; 5°C cooling water is introduced into the primary condensing device;

[0096] Step 3: The dried solid material is then fed into a pyrolysis furnace and kept at 250°C for 1.5 hours in a nitrogen atmosphere to decompose lithium hexafluorophosphate to produce PF5 and impurity gases, thereby obtaining a third gas containing an organic solvent, nitrogen, water, PF5, HF, and POF3.

[0097] Step 41: Send the third gas into a pre-condensing device to remove the high-boiling organic solvent in the third gas; the pre-condensing device is a water-cooled tubular condenser (pre-condensing device), and 5°C cooling water is passed into the pre-condensing device. The uncondensed gas discharged from the pre-condensing device is the fourth gas.

[0098] Step 42: The fourth gas is fed into a tubular condenser (a primary condensing device). The refrigerant of the primary condensing device is chilled brine at a temperature of -5°C to 0°C. The HF and water are fully condensed to obtain a fifth gas. The fifth gas contains only nitrogen, PF5, POF3, and trace amounts of unidentified impurities.

[0099] Step 5: The fifth gas and the second gas are mixed and sent to a tubular condenser (a secondary condensing device) for condensation to obtain a sixth gas; the refrigerant used in the secondary condensing device is liquid nitrogen, and the condensation temperature is -70 to -60°C;

[0100] Step 6: Send the sixth gas into a tubular condenser (three-stage condensing device) for condensation to collect liquid PF5. The refrigerant used in the three-stage condensing device is liquid nitrogen, and the condensation temperature is -140 to -130°C.

[0101] Example 4

[0102] A method for recovering lithium-ion battery electrolyte, comprising the following steps:

[0103] Step 1: Crushing 1 ton of waste square aluminum shell ternary batteries under nitrogen protection;

[0104] The positive electrode material of the ternary battery is: nickel-cobalt-manganese ternary material, whose chemical formula is LiNi 0.5 Mn 0.3 Co 0.2 O2;

[0105] The main organic solvent composition of the electrolyte is: ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate, with a mass ratio of 25:5:15:55;

[0106] The lithium salt is lithium hexafluorophosphate, with a content of 12.5 wt%;

[0107] The active material of the positive electrode is a ternary material (chemical formula is LiNi 0.5 Mn 0.3 Co 0.2 O2), the current collector is carbon-coated aluminum foil; the mass ratio of the ternary material, conductive agent SuperP, and adhesive PVDF on the current collector is 96.8:2:1.2

[0108] Step 2: The crushed material is sent to a low-temperature furnace and evaporated at 120°C for 2 hours under a nitrogen atmosphere. The evaporated organic solvent (first gas) is extracted by a vacuum pump, and the pressure in the furnace is maintained at a slightly negative pressure by the vacuum pump. The material is condensed and recovered by a water-cooled tubular condenser (primary condensing device). The solvent is fully evaporated in the low-temperature furnace to obtain a solid material (containing a high-boiling solvent); the primary condensing device discharges uncondensed gas, and the uncondensed gas is introduced into a cold trap with -20°C supercooled brine as a refrigerant to obtain a second gas, which contains relatively pure PF5, POF3 and nitrogen; 5°C cooling water is introduced into the primary condensing device;

[0109] Step 3: The solid material is then fed into a pyrolysis furnace and kept at 220°C for 1.5 hours under a nitrogen atmosphere. The lithium hexafluorophosphate decomposes to produce PF5 and impurity gases to obtain a third gas; the third gas contains an organic solvent, nitrogen, water, PF5, HF, and POF3;

[0110] Step 41: Send the third gas into a pre-condensing device to remove the high-boiling organic solvent in the third gas; the pre-condensing device is a water-cooled tubular condenser (pre-condensing device), and 5°C cooling water is passed into the pre-condensing device. The uncondensed gas discharged from the pre-condensing device is the fourth gas.

[0111] Step 42: The fourth gas is fed into a tubular condenser (a primary condensing device). The refrigerant of the primary condensing device is chilled brine at a temperature of -5°C to 0°C. The HF and water are fully condensed to obtain a fifth gas. The fifth gas contains only nitrogen, PF5, POF3, and trace amounts of unidentified impurities.

[0112] Step 5: The fifth gas and the second gas are mixed and sent to a tubular condenser (a secondary condensing device) for condensation to obtain a sixth gas; the refrigerant used in the secondary condensing device is liquid nitrogen, and the condensation temperature is -50 to -40°C;

[0113] Step 6: Send the sixth gas into a tubular condenser (three-stage condensing device) for condensation to collect liquid PF5. The refrigerant used in the three-stage condensing device is liquid nitrogen, and the condensation temperature is -120 to -110°C.

[0114] Example 5

[0115] A method for recovering lithium-ion battery electrolyte, comprising the following steps:

[0116] Step 1: Crushing 1 ton of waste square aluminum shell ternary batteries under nitrogen protection;

[0117] The positive electrode material of the ternary battery is: nickel-cobalt-manganese ternary material, whose chemical formula is LiNi 0.5 Mn 0.3 Co 0.2 O2;

[0118] The main organic solvent composition of the electrolyte is: ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate, with a ratio of 30:35:35;

[0119] The lithium salt is lithium hexafluorophosphate, with a content of 12.5 wt%;

[0120] The active material of the positive electrode is a ternary material (chemical formula is LiNi 0.5 Mn 0.3 Co 0.2 O2), the current collector is carbon-coated aluminum foil; the mass ratio of the ternary material, conductive agent SuperP, and adhesive PVDF on the current collector is 96.8:2:1.2;

[0121] Step 2: The crushed material is sent to a low-temperature furnace and evaporated at 140°C for 2 hours under a nitrogen atmosphere. The evaporated organic solvent (first gas) is extracted by a vacuum pump, and the pressure in the furnace is maintained at a slightly negative pressure by the vacuum pump. The material is condensed and recovered by a water-cooled tubular condenser (primary condensing device). The solvent is fully evaporated in the low-temperature furnace to obtain a solid material (containing a high-boiling solvent); the primary condensing device discharges uncondensed gas, and the uncondensed gas is introduced into a cold trap with -20°C supercooled brine as a refrigerant to obtain a second gas, which contains relatively pure PF5, POF3 and nitrogen; 5°C cooling water is introduced into the primary condensing device;

[0122] Step 3: The solid material is then fed into a pyrolysis furnace and kept at 240°C for 2 hours under a nitrogen atmosphere. The lithium hexafluorophosphate decomposes to produce PF5 and impurity gases to obtain a third gas; the third gas contains an organic solvent, nitrogen, water, PF5, HF, and POF3;

[0123] Step 41: Send the third gas into a pre-condensing device to remove the high-boiling organic solvent in the third gas; the pre-condensing device is a water-cooled tubular condenser (pre-condensing device), and 5°C cooling water is passed into the pre-condensing device. The uncondensed gas discharged from the pre-condensing device is the fourth gas.

[0124] Step 42: The fourth gas is fed into a tubular condenser (a primary condensing device). The refrigerant of the primary condensing device is chilled brine at a temperature of -5°C to 0°C. The HF and water are fully condensed to obtain a fifth gas. The fifth gas contains only nitrogen, PF5, POF3, and trace amounts of unidentified impurities.

[0125] Step 5: The fifth gas and the second gas are mixed and sent to a tubular condenser (a secondary condensing device) for condensation to obtain a sixth gas; the refrigerant used in the secondary condensing device is liquid nitrogen, and the condensation temperature is -70 to -60°C;

[0126] Step 6: Send the sixth gas into a tubular condenser (three-stage condensing device) for condensation to collect liquid PF5. The refrigerant used in the three-stage condensing device is liquid nitrogen, and the condensation temperature is -120 to -110°C.

[0127] Comparative Example 1

[0128] The method is generally the same as Example 1, except that the uncondensed gas discharged from the primary condensation device in step 2 is directly sent to an external tail gas treatment device for harmless treatment.

[0129] Comparative Example 2

[0130] The method is generally the same as Example 4, except that the uncondensed gas discharged from the primary condensation device in step 2 is directly sent to the external tail gas treatment equipment for harmless treatment.

[0131] Example 6

[0132] The same as Example 3, except for the following points:

[0133] The temperature of the low temperature furnace in step 2 is 150°C;

[0134] In step 2, the primary condensing device discharges uncondensed gas, which is then introduced into a cold trap using -10°C supercooled brine as a refrigerant to obtain a second gas; cooling water at 20°C is introduced into the primary condensing device;

[0135] The temperature of the frozen brine in step 42 is -39°C;

[0136] In step 5, the temperature of the secondary condensation is -84 to -75°C;

[0137] In step 6, the tertiary condensation temperature is -196°C to -180°C.

[0138] Example 7

[0139] The same as Example 3, except for the following points:

[0140] In step 2, the primary condensing device discharges uncondensed gas, which is then introduced into a cold trap using -20°C supercooled brine as a refrigerant to obtain a second gas; cooling water at -10°C is introduced into the primary condensing device;

[0141] In step 5, the temperature of the secondary condensation is -50 to -40°C;

[0142] In step 6, the tertiary condensation temperature is -95 to -85°C.

[0143] Part 2

[0144] Before describing the process in detail, let's first introduce the production system for this part. Referring to Figure 2, it specifically includes the following devices: a heating device 1, a pyrolysis device 2 for pyrolyzing the lithium salt in the solid produced by heating the heating device 1, a pre-condensing device 3 for condensing the third gas, a primary condensing device 4 for condensing the fourth gas, a secondary condensing device 5 for condensing the fifth gas, and a tertiary condensing device 6 for condensing the sixth gas, all connected in sequence. The heating device is connected to a primary condensing device 7 for condensing the first gas and a separation device for separating fluorine-containing compounds from the tail gas of the primary condensing device 7. The separation device delivers the second gas to the secondary condensing device via a pipeline. The heating device 1 is connected to a first nitrogen pipe 9 for providing nitrogen as a protective gas to the low-temperature furnace. A vacuum pump 10 is connected between the heating device 1 and the primary condensing device 7. The vacuum pump 10 is used to maintain a slightly negative pressure in the low-temperature furnace. The inlet of the vacuum pump 10 is connected to the heating device 1, and the outlet of the vacuum pump 10 is connected to the inlet of the primary condensing device 7.

[0145] The heating device 1 used in the embodiment is a low-temperature furnace, which is connected to a first nitrogen pipe 9 for introducing nitrogen into the low-temperature furnace as a protective gas; in addition, it also includes a vacuum pump 10, which draws nitrogen, volatile organic solvents, etc. into the primary condensing device 7. The low-temperature furnace maintains a slightly negative pressure in the furnace through the vacuum pump 10. The pyrolysis device 2 is a pyrolysis furnace, and the pre-condensing device 3, the first condensing device 4, the second condensing device 5, and the third condensing device 6 are all tubular condensers; the separation device is two sets of parallel activated carbon canisters 11, which are filled with activated carbon, and each activated carbon canister 11 has three outlets, namely a first outlet 14, a second outlet 15, and a third outlet 16. The inlet 13, the first outlet 14, the second outlet 15, and the third outlet 16 of each activated carbon canister 11 are provided with a valve; each Each activated carbon canister 11 is provided with a desorption gas pipeline 12 for introducing hot nitrogen, and a valve is also provided on the desorption gas pipeline; when one activated carbon canister 11 is in an adsorption state, the other activated carbon canister 11 is in a desorption state; in the adsorption state, the inlet 13 and the first outlet 14 are opened, and the remaining channels are closed, and the first outlet 14 discharges nitrogen to an external exhaust gas treatment device for harmless treatment; in the desorption state, the inlet 13, the first outlet 14, and the third outlet 16 are closed, and the desorption gas pipeline 12 and the second outlet 15 are opened; the second outlet 15 is connected to a secondary condensing device; after the first stage of desorption is completed, the nitrogen temperature of the desorption gas pipeline is increased, and the second stage of desorption is carried out. At this time, the second outlet 15 is closed, and the third outlet 16 is opened, and the desorbed gas is discharged to an external exhaust gas treatment device for harmless treatment.

[0146] Example 8

[0147] The lithium-ion battery electrolyte recovery method adopts the system shown in Figure 2, which specifically includes the following steps:

[0148] Step 1: crushing 1 ton of cylindrical waste lithium iron phosphate batteries (model parameters are the same as those in Example 1) under nitrogen protection;

[0149] Step 2: The crushed material is sent to a low-temperature furnace and evaporated at 120°C for 2 hours under a nitrogen atmosphere. The evaporated organic solvent (first gas) is extracted by a vacuum pump, and the pressure in the furnace is maintained at a slightly negative pressure by a vacuum pump. The material is condensed and recovered by a water-cooled tubular condenser (primary condensing device). The solvent is fully evaporated in the low-temperature furnace to obtain a solid material; the primary condensing device discharges uncondensed gas, and the uncondensed gas is introduced into a separation device to obtain a second gas, which contains relatively pure PF5, POF3 and nitrogen; 5°C cooling water is introduced into the primary condensing device;

[0150] When the activated carbon tank of the separation device is in the adsorption state, it will adsorb organic solvents, fluorine-containing gases, and water; the temperature of the uncondensed gas is not high, and the adsorption capacity of the activated carbon is the strongest at this time;

[0151] When the activated carbon canister is in the desorption state, it is divided into the first stage of desorption and the second stage of desorption. The nitrogen temperature of the first stage of desorption is 40-45°C; the temperature needs to be strictly controlled to prevent the organic solvent from being desorbed. In this temperature range, most of the PF5 and POF3 can be released; the ventilation time is about 0.5-1h, and then enters the second stage of desorption. At this time, the nitrogen temperature is increased to about 110°C. At this time, the activated carbon releases all the adsorbed gases, which are mainly organic solvents. These gases are harmlessly treated. The amount of nitrogen used in the entire desorption process is 3 to 5 times the volume of the activated carbon, which is much lower than the volume of nitrogen introduced during the heating process in step 1;

[0152] Step 3: The dried solid material is then fed into a pyrolysis furnace and kept at 200°C for 1.5 hours under a nitrogen atmosphere. The lithium hexafluorophosphate decomposes to produce PF5 and impurity gases to obtain a third gas; the third gas contains an organic solvent, nitrogen, water, PF5, HF, and POF3;

[0153] Step 41: Send the third gas into a pre-condensing device to remove the high-boiling organic solvent in the third gas; the pre-condensing device is a water-cooled tubular condenser (pre-condensing device), and 5°C cooling water is passed into the pre-condensing device. The uncondensed gas discharged from the pre-condensing device is the fourth gas.

[0154] Step 42: The fourth gas is fed into a tubular condenser (a primary condensing device). The refrigerant of the primary condensing device is chilled brine at a temperature of -5°C to 0°C. The HF and water are fully condensed to obtain a fifth gas. The fifth gas contains only nitrogen, PF5, POF3, and trace amounts of unidentified impurities.

[0155] Step 5: The fifth gas and the second gas are mixed and sent to a tubular condenser (a secondary condensing device) for condensation to obtain a sixth gas; the refrigerant used in the secondary condensing device is liquid nitrogen, and the condensation temperature is -70 to -60°C;

[0156] Step 6: Send the sixth gas into a tubular condenser (three-stage condensing device) for condensation to collect liquid PF5. The refrigerant used in the three-stage condensing device is liquid nitrogen, and the condensation temperature is -140 to -130°C.

[0157] Part III Data Statistics and Analysis

[0158] The amount of PF5 obtained after the three-stage condensation of the embodiment and the comparative example and the amount of solvent recovered by the condensation device in step 2 were counted. The results are shown in Table 1 below.

[0159] Table 1 Recovery results

[0160] Result analysis:

[0161] 1. It can be seen from Examples 1-3 that PF5 with high purity and recovery rate can be obtained by the method of the present application; within an appropriate range, increasing the low-temperature volatilization temperature and the pyrolysis temperature can improve the recovery rate of organic solvents and PF5 to a certain extent, but since the organic solvent is consumed during the process from use to scrapping of the battery, its recovery rate is generally lower than the theoretical content, and PF5 is easily reacted with organic solvents and the like during the recovery process, further reducing its recovery rate.

[0162] In addition, through a comprehensive comparison of Examples 1-3 and Examples 6-7, it can be seen that for the recovery of low-boiling organic solvents, the primary condensation temperature should be lowered as much as possible within the set temperature range to avoid low primary condensation efficiency, which will cause excessive organic solvent gas to enter the separation device, increase the difficulty and cost of separation, and may cause the organic gas to enter the secondary condensation for condensation, resulting in gas loss; secondly, lowering the primary condensation temperature and the secondary condensation temperature within the set temperature range can improve the condensation and impurity removal effect, and avoid impurity gas from entering the tertiary condensation for condensation to reduce the purity of PF5; finally, lowering the tertiary condensation temperature can improve the condensation effect of PF5 gas and increase the recovery rate of PF5.

[0163] 2. As shown in Example 1 and Comparative Example 1, for both spent lithium iron phosphate batteries and ternary batteries, re-separation of the recovered tail gas from light organic solvents can increase the PF5 yield by approximately 3%. Therefore, the treatment of tail gas from light organic solvents is a very important task. The higher recovery rate of low-boiling organic solvents in Comparative Example 1 than in Example 1 may be due to slight differences between battery batches, and the solvent recovery error is within the normal range of results.

[0164] At the same time, it should be noted that in the above-mentioned embodiments and comparative examples, when calculating the recovery rate, the theoretical content of the electrolyte in 1 ton of cylindrical waste lithium iron phosphate batteries is estimated to be about 150 kg, and the low-boiling organic solvent (boiling point less than 150 ° C) in the main organic solvent component accounts for about 70% of the total weight of the solvent, equivalent to 60.9% of the total weight of the electrolyte, and LiPF6 accounts for about 13% of the total weight of the electrolyte. The theoretical yield of 100% recovery of PF5 after cracking is 16.2 kg;

[0165] It is estimated that the electrolyte content in 1 ton of waste square aluminum shell ternary batteries is about 120 kg, and the low-boiling organic solvent (boiling point less than 150°C) accounts for about 70% of the main organic solvent components, equivalent to 61.2% of the total weight of the electrolyte; LiPF6 accounts for about 12.5% ​​of the total weight of the electrolyte, so the theoretical yield when PF5 is 100% recovered after cracking is 12.4 kg. The above results are calculated based on the estimated theoretical yield.

[0166] Since it cannot be guaranteed that every used battery is exactly the same, but their basic contents are similar, the data in Table 1 above is only used as a basis for inferring data trends and is not an error-free result for the specific recovery rate.

[0167] 3. It can be seen from Example 8 that the purpose of the present application can also be achieved by using activated carbon for adsorption and desorption; in the process of using activated carbon for adsorption and desorption, the desorption temperature is too high, causing the light solvent to enter the secondary condensation, forming a solid film on the inner wall of the secondary condensation pipe, affecting heat conduction, and ultimately slightly reducing the purity of PF5 in the tertiary condensation; the desorption temperature is too low, resulting in the inability to effectively desorb the fluorine-containing gas, resulting in a decrease in the yield of PF5.

[0168] The use of activated carbon for desorption in this application takes advantage of the high vapor pressure of PF5 and the low vapor pressure of organic solvents. The desorption temperature ranges of the two are quite different, thus achieving efficient desorption of PF5.

[0169] By comparing Example 8 with Example 1, it can be seen that although the method and equipment of Example 8 are more complex, under the same parameters, the purity of its PF5 is higher. The reason is that compared with the nitrogen gas used as the second gas in Example 1, the nitrogen used for desorption is less, resulting in a smaller total amount of secondary condensed gas, which has a better condensation effect on POF3. Therefore, it is necessary to select the appropriate process according to the working conditions.

[0170] Although the embodiments of the present application have been shown and described, those skilled in the art will appreciate that various changes, modifications, substitutions, and variations may be made to the embodiments without departing from the principles and intent of the present application, and that the scope of the present application is defined by the claims and their equivalents.

Claims

1. A method for recovering electrolyte of a lithium-ion battery, characterized in that: The steps include: Step 1: After the lithium-ion battery is crushed, it is heated under the protection of an inert gas to volatilize at least part of the solvent in the electrolyte, a first gas and a solid are collected, and the first gas is subjected to primary condensation to remove at least part of the solvent in the first gas, wherein the heating temperature is 100 to 150° C.; Step 2: collecting the tail gas after primary condensation, separating the fluorine-containing substances produced by the decomposition of the lithium salt from the tail gas to obtain a second gas, wherein the second gas contains PF5; Step 3: cracking the solid obtained in step 1 under the protection of inert gas and at the cracking temperature of lithium salt, collecting the tail gas generated by the cracking to obtain a third gas, wherein the third gas contains an organic solvent, nitrogen, water, PF5, HF, and POF3; The cracking temperature is higher than the heating temperature; Step 4: removing the organic solvent, water and HF in the third gas by condensation to obtain a fifth gas; Step 5: Mix the fifth gas and the second gas and perform secondary condensation to remove other gases except PF5 to obtain a sixth gas; Step 6: The sixth gas is subjected to three-stage condensation to collect liquid PF5.

2. The lithium ion battery electrolyte recovery method according to claim 1, characterized in that: The step 4 specifically includes: Step 41: pre-condensing the third gas to remove the organic solvent in the third gas to obtain a fourth gas; Step 42: performing primary condensation on the fourth gas to remove water and HF in the fourth gas to obtain a fifth gas.

3. The lithium ion battery electrolyte recovery method according to claim 1, characterized in that: In step 2, the method for separating the fluorine-containing substance produced by the decomposition of lithium salt from the tail gas is specifically: removing the organic solvent in the tail gas by condensation or removing the organic solvent in the tail gas by adsorption and desorption of an adsorbent to obtain the fluorine-containing substance.

4. The lithium ion battery electrolyte recovery method according to claim 3, characterized in that: The method for separating the fluorine-containing substances produced by the decomposition of lithium salt from the tail gas in step 2 is specifically: using a cold trap to perform a condensation operation and controlling the condensation temperature to -30 to -10°C to separate the organic solvent and the fluorine-containing substances.

5. The lithium ion battery electrolyte recovery method according to claim 3, characterized in that: The method for separating the fluorine-containing substances produced by the decomposition of lithium salt from the tail gas in step 2 is specifically: the tail gas after primary condensation is adsorbed by activated carbon, and then the activated carbon after adsorption is desorbed by nitrogen; the temperature of the nitrogen used for desorption is 40-120°C.

6. The lithium ion battery electrolyte recovery method according to claim 1, characterized in that: The condensation temperature of the primary condensation is -20 to 20°C; And / or, the condensation temperature of the secondary condensation is -84 to -40°C; And / or, the condensation temperature of the third-stage condensation is -196 to -85°C.

7. The method for recovering electrolyte of a lithium ion battery according to claim 6, characterized in that: The condensation temperature of the primary condensation is -10 to 10°C; And / or, the condensation temperature of the secondary condensation is -70 to -50°C; And / or, the condensation temperature of the third-stage condensation is -130 to -100°C.

8. The method for recovering electrolyte of a lithium ion battery according to claim 2, characterized in that: The condensation temperature of the pre-condensation is -20 to 20°C; And / or, the condensation temperature of the first-stage condensation is -39 to 19°C.

9. The lithium ion battery electrolyte recovery method according to claim 8, characterized in that: The pre-condensation temperature is -10 to 10°C; And / or, the temperature of the primary condensation is -20 to 0°C.

10. A system for implementing the method according to any one of claims 1 to 9, characterized in that: The invention comprises a heating device for volatilizing at least part of the solvent in the electrolyte, a pyrolysis device for pyrolyzing the lithium salt in the solid produced by heating the heating device, a pre-condensing device for condensing the third gas, a primary condensing device for condensing the fourth gas, a secondary condensing device for condensing the fifth gas, and a tertiary condensing device for condensing the sixth gas, which are connected in sequence; the heating device is connected with a primary condensing device for condensing the first gas and a separation device for separating fluorine-containing compounds from the tail gas of the primary condensing device; The separation device delivers the second gas to the secondary condensation device through a pipeline.

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