System for recycling electrolyte of lithium ion battery

Abstract

The utility model belongs to the field of chemical engineering, and discloses a system for recycling lithium ion battery electrolyte, which comprises a heating device, a primary condensing device, a separating device, a pyrolysis device, a pre-condensing device, a primary condensing device, a secondary condensing device and a tertiary condensing device which are connected in sequence, the system is used for recycling PF5 in lithium salt pyrolysis gas and PF5 generated in the solvent heating volatilization process, and the PF5 recycling rate can be increased; the system is provided with a multi-stage condensation structure, main impurities are recycled in a set temperature section, and the purity of recycled PF5 is high.

Description

Technical Field

[0001] The utility model relates to the field of chemical industry, in particular to a system for recycling lithium ion battery electrolyte. Background Art

[0002] Waste lithium-ion batteries are mainly composed of shell, positive electrode, negative electrode, diaphragm and electrolyte. The current mainstream recycling process is to crush the waste lithium-ion batteries under a protective atmosphere for multi-level physical sorting, and sort out the shell, diaphragm, positive and negative electrode powder, copper and aluminum particles (powder) for recycling.

[0003] For the recovery of electrolyte components, the conventional process is to use vacuum distillation combined with condensation to recover organic solvents. Lithium hexafluorophosphate is decomposed into PF5 gas by heating, and the PF5 gas is passed into a LiF solution to synthesize the electrolyte. In fact, when recovering organic solvents, side reactions often occur in the electrolyte from use to scrapping and recycling, crushing and drying. In addition to PF5, the pyrolysis gas still contains high-boiling organic solvent gas, moisture, HF, POF3 and other impurity gases. If the pyrolysis gas is directly reacted with LiF to prepare the electrolyte, it will affect the purity and performance of the electrolyte. In addition, a large amount of inert gas is consumed in the process of recycling and processing of waste lithium-ion batteries, which further increases the cost.

[0004] One of the main purposes of thermal cracking recovery of lithium-ion batteries is to recover LiF and PF5. The inventors further discovered that impurity gases such as POF3 are generated while PF5 is generated; at the same time, lithium hexafluorophosphate is a substance with very low thermal stability and may still crack at the volatilization temperature.

[0005] Problems existing in the prior art include but are not limited to the following two:

[0006] 1. The impurity content in the cracking gas is complex, and it is difficult to obtain high-purity hexafluorophosphate by simple absorption;

[0007] 2. In the existing lithium-ion battery electrolyte recycling, under the premise of ensuring high purity, the recovery efficiency of PF5 is not high.

[0008] Therefore, the technical problem solved in this case is: how to improve the recovery purity of PF5 and fully recycle PF5 during the process of recovering electrolyte by cracking method. Utility Model Content

[0009] The main purpose of the utility model is to provide a system for recovering lithium-ion battery electrolyte, which recovers PF5 in lithium salt cracking gas and PF5 generated during solvent heating and volatilization, and can improve the recovery rate of PF5; the system is equipped with a multi-stage condensation structure, recovers major impurities in a set temperature section, and the recovered PF5 has a higher purity.

[0010] In order to achieve the above purpose, the utility model provides the following technical solutions:

[0011] A system for recycling lithium-ion battery electrolyte, comprising:

[0012] Heating device: used to heat the disassembled lithium-ion battery to a temperature at which the solvent evaporates, thereby obtaining a first gas and a solid material;

[0013] Primary condensing device: used for condensing the first gas to obtain condensate and uncondensed gas;

[0014] Separation device: used for separating the uncondensed gas obtained from the primary condensation device to obtain a second gas and sending the second gas to the secondary condensation device through a pipeline, wherein the second gas contains phosphorus pentafluoride;

[0015] Pyrolysis device: used to heat the solid material to the temperature of lithium salt cracking to obtain the third gas and solid slag;

[0016] Pre-condensing device: used for condensing the third gas, removing the organic solvent from the third gas, and obtaining the fourth gas;

[0017] A primary condensing device: used for condensing the fourth gas, removing hydrogen fluoride and water from the fourth gas, and obtaining a fifth gas;

[0018] Secondary condensation device: used for condensing the second gas and the fifth gas, removing POF3 from the second gas and the fifth gas, and obtaining the sixth gas;

[0019] The third-stage condensation device is used to condense the sixth gas so as to condense the phosphorus pentafluoride in the sixth gas to obtain liquid phosphorus pentafluoride.

[0020] The beneficial effects of the technical solution of the utility model are:

[0021] In this system, PF5 can be purified and recovered by treating the cracking gas through multi-stage condensation. The purity of the recovered PF5 can be improved through three-stage condensation. At the same time, the PF5 produced by the decomposition of a small amount of lithium salt when the solvent evaporates can be recovered, thereby achieving the purpose of fully recovering PF5.

[0022] Specifically, when the heating device heats and volatilizes the solvent, the lithium salt decomposes to produce PF5, and the solvent is recovered by the primary condensing device. The uncondensed gas is processed by the separation device to obtain the second gas containing PF5, which not only realizes the recovery of the solvent, but also realizes the preliminary separation of PF5 in this process.

[0023] The pyrolysis device mainly heats and cracks the lithium salt in the battery to obtain cracked gas, removes organic solvents through the pre-condensation device, removes impurities such as HF and water through the first-stage condensation device, and obtains the fifth gas containing PF5, POF3 and nitrogen. The second gas and the fifth gas are condensed through the second-stage condensation device to remove POF3, and then PF5 is condensed through the third-stage condensation device to obtain PF5 with high purity. The second gas is introduced into the second-stage condensation device to achieve effective separation of organic solvents, HF, water and other impurities, which is conducive to the subsequent recovery and treatment of organic solvents, HF, water and other impurities; at the same time, since the second gas has a low temperature, it can be mixed with the fifth gas to condense the fifth gas. Combined with the condensation operation of the second-stage condensation device, the condensation of POF3 can be achieved faster without significantly increasing the load of the second-stage condensation device.

[0024] Based on this, the utility model achieves sufficient and high-purity recovery of PF5 through the above optimization. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a pipeline flow chart of Example 1 of the utility model. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the utility model to clearly and completely describe the technical solution of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0027] Example 1

[0028] refer to Figure 1 , a system for recycling lithium-ion battery electrolyte, comprising:

[0029] Heating device 1: used to heat the disassembled lithium-ion battery to a temperature at which the solvent evaporates, thereby obtaining a first gas and a solid material;

[0030] Primary condensing device 7: used for condensing the first gas to obtain condensate and uncondensed gas;

[0031] A separation device 8 is used to separate a second gas containing fluorine compounds from the uncondensed gas obtained from the primary condensation device 7; the separation device 8 delivers the second gas to the secondary condensation device 5 through a pipeline;

[0032] Pyrolysis device 2: used to heat the solid material to the temperature of lithium salt cracking to obtain the third gas and solid slag;

[0033] Pre-condensing device 3: used for condensing the third gas, removing the organic solvent from the third gas, and obtaining the fourth gas;

[0034] The primary condensing device 4 is used for condensing the fourth gas, removing hydrogen fluoride and water from the fourth gas, and obtaining the fifth gas;

[0035] Secondary condensation device 5: used for condensing the second gas and the fifth gas, removing POF3 from the second gas and the fifth gas, and obtaining the sixth gas;

[0036] The third-stage condensation device 6 is used to condense the sixth gas, so as to condense the phosphorus pentafluoride in the sixth gas to obtain liquid phosphorus pentafluoride.

[0037] Through the above system, the primary condensation device 7 recovers the low-boiling organic solvent;

[0038] The pre-condensing device 3 is used to recover the high boiling solvent in the cracked gas, i.e. the third gas;

[0039] The low-boiling organic solvent refers to a solvent with a boiling point below 150°C, and the remaining solvents are high-boiling solvents;

[0040] The primary condensation device 4 is used to separate water and HF from the fourth gas;

[0041] The secondary condensation device 5 is used to separate and remove POF3 from the second gas and the fifth gas;

[0042] The tertiary condensation device 6 is used to recover PF5.

[0043] A more complete process flow of this embodiment is as follows:

[0044] Step 1: crush 1 ton of cylindrical waste lithium iron phosphate batteries under nitrogen protection;

[0045] In lithium iron phosphate batteries, the main organic solvents of the electrolyte are ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), with a mass ratio of 3:1:6.

[0046] The lithium salt is lithium hexafluorophosphate, accounting for 13% of the weight of the electrolyte;

[0047] 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;

[0048] Step 2: The crushed material is sent to a low-temperature furnace (heating device 1), evaporated at 120° C. for 2 hours under a nitrogen atmosphere, the evaporated organic solvent is extracted, the pressure in the furnace is maintained at a slightly negative pressure, and the organic solvent is condensed and recovered by a water-cooled tubular condenser (primary condensing device 7), and the solvent, i.e., the first gas, is fully evaporated in the low-temperature furnace to obtain a solid material; the first gas contains a volatile low-boiling solvent and a small amount of phosphorus pentafluoride and other gases generated by the decomposition of lithium salts, and the solid material is a high-boiling solvent, a diaphragm, a battery shell, a positive electrode, a negative electrode, and a lithium salt;

[0049] The primary condensing device 7 uses cooling water at 0-5°C as a refrigerant to condense the first gas, and discharges uncondensed gas, which contains a small amount of uncondensed low-boiling solvent and phosphorus pentafluoride and other gases that cannot be completely condensed at the refrigerant temperature; the uncondensed gas is introduced into a cold trap (separation device 8) using supercooled salt water at -20°C as a refrigerant to obtain a second gas, which is relatively pure PF5, POF3 and nitrogen;

[0050] Step 3: The dried solid material is then sent to a pyrolysis furnace (i.e., pyrolysis device 2) and kept at 200°C for 1.5 hours under a nitrogen atmosphere, so that lithium hexafluorophosphate decomposes PF5 and mixes with impurity gases to obtain a third gas and solid slag; the third gas contains organic solvents, nitrogen, moisture, PF5, HF, and POF3; the solid slag is recovered and processed through other systems.

[0051] Step 4: Send the third gas to the pre-condensation device 3 to remove the high-boiling organic solvent in the third gas; the pre-condensation device 3 is a water-cooled tubular condenser, and cooling water at 0-5°C is introduced into the pre-condensation device. The uncondensed gas discharged from the pre-condensation device is the fourth gas. The fourth gas removes most of the organic solvent on the basis of the third gas;

[0052] Step 5: The fourth gas is sent to a tubular condenser (primary condensing device 4), the refrigerant of the primary condensing device 4 is frozen brine, the temperature of the frozen brine is -5°C to 0°C, 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;

[0053] Generally speaking, the refrigerant temperature in the tubular condenser should be significantly lower than the boiling point of the object to be condensed, and can even be close to the freezing point of the object. 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.

[0054] Step 6: Mix the fifth gas and the second gas, and send them into a tubular condenser (secondary condensation device 5) for condensation to remove POF3 in the gas, thereby obtaining a sixth gas; the refrigerant used in the secondary condensation device 5 is liquid nitrogen, and the condensation temperature is -60°C;

[0055] Step 7: Send the sixth gas to the tubular condenser (three-stage condensing device 6) for condensation, and collect liquid PF5. The refrigerant used in the three-stage condensing device 6 is liquid nitrogen, and the condensation temperature is -140°C.

[0056] Preferably, the heating device 1 is connected to a nitrogen pipe 9, which is used to provide a protective gas - nitrogen to the low-temperature furnace; a vacuum pump 10 is connected between the heating device 1 and the primary condensing device 7, and the vacuum pump 10 is used to maintain a slightly negative pressure state 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.

[0057] The uncondensed gas discharged from the primary condensation device 7 is directly sent to the post-treatment device for harmless treatment and then discharged without being treated by a cold trap. The recovery rate of PF5 is 85.1%, and 2.5% of PF5 is not effectively recovered. Through the above process, the recovery rate of the recovered low-boiling organic solvent reaches 81.6%, and the recovery rate of PF5 reaches 87.6%, with a purity of 99.88%.

[0058] From the above results, it can be found that a small amount of lithium salt will decompose during the process of solvent heating and volatilization;

[0059] This embodiment uses a primary condensation device to recover the solvent, and the uncondensed gas is processed by a separation device to obtain a second gas containing PF5, which not only realizes the recovery of the solvent but also realizes the preliminary separation of PF5 in this process;

[0060] In this embodiment, by introducing the second gas into the secondary condensation device 5 and mixing it with the fifth gas containing nitrogen, PF5, and POF3, it is possible to achieve effective separation of impurities such as organic solvents, HF and water, which is beneficial to the subsequent recovery and treatment of impurities such as organic solvents, HF and water, while reducing the load of the secondary condensation device 5, improving the separation efficiency of POF3, and facilitating the recovery of PF5.

[0061] Specifically, if the second gas is introduced into the pre-condensation device, it will cause the organic solvent, HF, water and other impurities to condense together to form an emulsion, which is not conducive to the subsequent recovery and treatment of the organic solvent, HF, water and other impurities. If the second gas is introduced into the primary condensation device, it will lead to a large amount of gas in the primary condensation, increasing the burden of condensation separation. The second gas is introduced into the secondary condensation device to achieve effective separation of organic solvents, HF, water and other impurities, which is conducive to the subsequent recovery and treatment of organic solvents, HF, water and other impurities. At the same time, since the temperature of the second gas is relatively low, after it is mixed with the fifth gas, the fifth gas can be condensed. Combined with the condensation operation of the secondary condensation device, the condensation of POF3 can be achieved faster without significantly increasing the load of the secondary condensation device.

[0062] In practical applications, the nickel-cobalt-manganese-oxide lithium ternary battery can be processed by referring to the above process.

[0063] The objects processed by the system of the present invention include not only cylindrical lithium-ion batteries, but also lithium-ion batteries in other forms such as square aluminum shells can be recycled.

[0064] Although the embodiments of the present invention 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 spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A system for recovering lithium-ion battery electrolyte, characterized in that: include: Heating device: used to heat the disassembled lithium-ion battery to a temperature at which the solvent evaporates, thereby obtaining a first gas and a solid material; Primary condensing device: used for condensing the first gas to obtain condensate and uncondensed gas; Separation device: used for separating the uncondensed gas obtained from the primary condensation device to obtain a second gas and sending the second gas to the secondary condensation device through a pipeline, wherein the second gas contains phosphorus pentafluoride; Pyrolysis device: used to heat the solid material to the temperature of lithium salt cracking to obtain the third gas and solid slag; Pre-condensing device: used for condensing the third gas, removing the organic solvent from the third gas, and obtaining the fourth gas; A primary condensing device: used for condensing the fourth gas, removing hydrogen fluoride and water from the fourth gas, and obtaining a fifth gas; Secondary condensation device: used for condensing the second gas and the fifth gas, removing POF3 from the second gas and the fifth gas, and obtaining the sixth gas; The third-stage condensation device is used to condense the sixth gas so as to condense the phosphorus pentafluoride in the sixth gas to obtain liquid phosphorus pentafluoride.

2. The system according to claim 1, characterized in that The pre-condensing device, the primary condensing device, the secondary condensing device, the tertiary condensing device and the primary condensing device are tubular condensers.

3. The system according to claim 1, characterized in that The separation device is a cold trap.

4. The system according to any one of claims 1 to 3, characterized in that: The heating device is connected with a nitrogen pipe.

5. The system according to claim 1, characterized in that A vacuum pump is connected between the heating device and the primary condensing device, the inlet of the vacuum pump is connected to the heating device, and the outlet of the vacuum pump is connected to the inlet of the primary condensing device.

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