Method for treating cleaning waste liquid

Abstract

The present invention relates to a method for treating cleaning waste liquid, comprising: a pretreatment step of removing a part of an organic solvent from cleaning waste liquid including a positive electrode active material, a binder, and an organic solvent; a first step of adding water to the cleaning waste liquid from which a part of the organic solvent has been removed to precipitate the binder; a second step of removing the precipitated binder to obtain a first treatment solution containing the positive electrode active material, the water, and the organic solvent; a third step of separating the positive electrode active material from the first treatment solution to obtain a second treatment solution containing the water and the organic solvent; and a fourth step of removing water from the second treatment solution and recovering the organic solvent.

Description

Method for treating cleaning wastewater

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0074044, filed June 5, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for treating cleaning waste liquid from a cathode material mixer generated during a battery manufacturing process.

[0003] Lithium secondary batteries typically consist of a positive electrode containing positive active material, a negative electrode containing negative active material, a separator, and an electrolyte. Charging and discharging occur through the intercalation and deintercalation of lithium ions. Lithium secondary batteries have the advantages of high energy density, high electromotive force, and high capacity, and are therefore widely used in various fields.

[0004] The positive electrode of a lithium secondary battery is manufactured by mixing a positive electrode active material, a binder, a conductive agent, and an organic solvent in a positive electrode material mixer to form a positive electrode slurry, coating the positive electrode slurry on a positive electrode current collector, and then drying and rolling. At this time, N-methylpyrrolidone is generally used as the organic solvent.

[0005] The cathode material mixer used in the manufacture of cathode slurry is cleaned with N-methyl pyrrolidone, a solvent for the cathode slurry, and the cleaning waste liquid discharged after cleaning the cathode material mixer contains cathode active material, binder, conductive material, and N-methyl pyrrolidone.

[0006] Meanwhile, the positive electrode active material includes lithium and transition metals such as nickel, cobalt, and manganese. Nickel and cobalt are relatively expensive metals, and cobalt, in particular, is known to be a metal with an unstable global supply due to the limited number of producing countries. In addition, N-methyl pyrrolidone, used in cleaning the positive electrode mixer, is also an expensive organic solvent.

[0007] Therefore, if the positive electrode active material and N-methyl pyrrolidone are recovered from the cleaning waste liquid generated after cleaning the positive electrode mixer and recycled as raw materials, not only can price competitiveness be secured, but additional profits can also be generated.

[0008] Previously, a method was proposed to recover N-methyl pyrrolidone by distilling the cathode mixer cleaning waste liquid in a distillation column. However, this method has the drawbacks of high distillation temperatures even under reduced pressure, and as the recovery progresses, the viscosity of the waste liquid remaining at the bottom of the distillation column increases, reducing distillation efficiency and causing contamination of the distillation column.

[0009] Therefore, there is a need to develop a new method that can effectively treat the cleaning wastewater of a cathode mixer.

[0010] The present invention is intended to solve the above problems, and to provide a method for treating the cleaning waste liquid of a cathode mixer at a relatively low cost and in an environmentally friendly manner because no toxic gases are generated.

[0011] In one aspect, the present invention provides a method for treating a cleaning wastewater, comprising: a pretreatment step of removing a portion of the organic solvent from a cleaning wastewater containing a positive electrode active material, a binder, and the organic solvent; a first step of adding water to the cleaning wastewater from which the portion of the organic solvent has been removed to precipitate the binder; a second step of removing the precipitated binder to obtain a first treatment solution containing the positive electrode active material, the water, and the organic solvent; a third step of separating the positive electrode active material from the first treatment solution to obtain a second treatment solution containing the water and the organic solvent; and a fourth step of removing water from the second treatment solution and recovering the organic solvent.

[0012] At this time, the cleaning waste liquid may be a waste liquid generated after cleaning the cathode material mixer, and the organic solvent may be, for example, N-methyl pyrrolidone.

[0013] The pretreatment step of partially removing the organic solvent can be performed by a method of precipitating the solid content in the washing waste liquid and then removing the supernatant, or by a method of selectively removing only the organic solvent by filtering the washing waste liquid.

[0014] The above pretreatment step is preferably performed so that the solid content in the washing waste liquid after removing the organic solvent is 40 wt% to 95 wt%, preferably 60 wt% to 95 wt%, and more preferably 80 wt% to 95 wt%.

[0015] Meanwhile, in the first step, it is preferable that the water be added in an amount of 0.5 to 50 times, preferably 0.5 to 10 times, and more preferably 0.5 to 2 times the total volume of the washing waste liquid.

[0016] Meanwhile, the second step can be performed by a method of removing binder precipitates floating on the upper surface of the washing waste liquid.

[0017] Next, in the third step, separating the positive electrode active material from the first treatment solution can be performed by a method of precipitating the positive electrode active material in the first treatment solution and then separating it by gravity, or a method of filtering the first treatment solution.

[0018] If necessary, a step of washing and drying the positive electrode active material separated from the first treatment solution may be additionally included after the third step.

[0019] The above fourth step can be performed by a method of fractionally distilling the second treatment solution.

[0020] The method for treating a cleaning waste liquid according to the present invention is environmentally friendly because it does not generate toxic hydrogen fluoride gas since the binder is separated through a crystallization precipitation process rather than a heat treatment.

[0021] In addition, when a pretreatment process for removing at least a portion of the organic solvent from the cleaning waste liquid is performed during the treatment of the cleaning waste liquid according to the present invention, the reactivity between water and binder is increased, so that the amount of water used for binder precipitation can be reduced, and the amount of energy consumed for distilling water and the organic solvent during the fractional distillation of the second treatment solution can be reduced.

[0022] Hereinafter, the present invention will be described in more detail.

[0023] The method for treating a cleaning waste liquid according to the present invention comprises: (1) a pretreatment step of removing at least a portion of the organic solvent from a cleaning waste liquid containing a positive electrode active material, a binder, and the organic solvent; (2) a first step of adding water to the cleaning waste liquid to precipitate a binder; (3) a second step of removing the precipitated binder to obtain a first treatment solution containing the positive electrode active material, the water, and the organic solvent; (4) a third step of separating the positive electrode active material from the first treatment solution to obtain a second treatment solution containing the water and the organic solvent; and (5) a fourth step of removing water from the second treatment solution and recovering the organic solvent.

[0024]

[0025] (1) Preprocessing stage

[0026] First, prepare the cleaning waste liquid.

[0027] At this time, the above-mentioned cleaning waste liquid may be the waste liquid generated after cleaning the positive electrode mixer. Positive electrode active material, binder, and / or conductive material, etc. remain inside the positive electrode mixer, and when cleaning the positive electrode mixer, an organic solvent that can dissolve the binder and discharge the residues inside the positive electrode mixer by slurrying them is used as the cleaning liquid. For example, N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, etc. can be used as the cleaning liquid for the positive electrode mixer, and N-methyl pyrrolidone can be preferably used.

[0028] The cleaning waste liquid generated after cleaning the cathode material mixer contains the cathode active material, binder, and organic solvent used as the cleaning liquid, and may optionally contain a conductive material.

[0029] Meanwhile, the positive electrode active material may be a positive electrode active material generally used in the relevant technical field, and may include, for example, lithium iron phosphate; lithium cobalt-based oxide; lithium manganese-based oxide; lithium nickel-based composite transition metal oxide such as lithium nickel-cobalt-manganese oxide, lithium nickel-cobalt-aluminum oxide, lithium nickel-cobalt-manganese-aluminum oxide, or a combination thereof, and preferably may include a lithium nickel-based composite transition metal oxide.

[0030] The above binder is for binding the positive electrode current collector and the positive electrode active material particles, and may be various binders commonly used in the art, for example, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polytetrafluoroethylene (PTFE), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated-EPDM, or a combination thereof, and preferably polyvinylidene fluoride.

[0031] Meanwhile, in the above-mentioned cleaning waste liquid, the positive electrode active material and binder may exist in a state of being suspended in an organic solvent, or aggregates of the positive electrode active material and binder may exist in a state of being precipitated at the bottom of the cleaning waste liquid.

[0032]

[0033] A pretreatment process is performed to remove at least a portion of the organic solvent from the prepared washing wastewater. Removing at least a portion of the organic solvent from the washing wastewater reduces the organic solvent content, thereby increasing the reactivity between water and binder, thereby reducing the amount of water used for binder precipitation. Furthermore, this reduces the water and organic solvent content in the second treatment solution in Step 4, which will be described later, thereby reducing the energy consumed in distilling the water and organic solvent during fractional distillation.

[0034] The removal of the organic solvent can be performed, for example, by a method of removing the supernatant of the washing waste liquid or a method of selectively removing the organic solvent through filtering.

[0035] When the positive electrode active material and binder exist in the form of a precipitate in the washing waste liquid, the organic solvent can be removed by a simple method of removing the supernatant.

[0036] Meanwhile, when the positive electrode active material and binder exist in a suspended state in the cleaning waste liquid, only the organic solvent excluding the positive electrode active material and binder, which are solid components, can be selectively removed through a filter.

[0037] The above pretreatment step is preferably performed so that the solid content in the washing waste liquid after the organic solvent is removed is 40 wt% to 95 wt%, preferably 60 wt% to 95 wt%, and more preferably 80 wt% to 95 wt%. When the amount of organic solvent removed satisfies the above range, the water content required for binder precipitation can be effectively reduced.

[0038] If the amount of organic solvent removed is too small, the amount of water required for binder precipitation increases, which increases energy consumption during organic solvent purification in the subsequent process. If the amount of organic solvent removed is too large, a problem may arise in which binder separation does not occur smoothly even if water is added in the subsequent process.

[0039]

[0040] (2) Step 1: Binder precipitation step

[0041] Next, water is added to the washing waste liquid from which some of the organic solvent has been removed to precipitate the binder.

[0042] When water is added to the washing waste liquid, binders such as PVDF and PVDF-co-HFP dissolved in the organic solvent react with water, crystallize, and precipitate out in a solid state.

[0043] At this time, it is preferable that the water be injected in an amount of 0.5 to 50 times, preferably 0.5 to 10 times, and more preferably 0.5 to 2 times the total volume of the washing waste liquid. When the amount of water injected satisfies the above range, the binder precipitation in the washing waste liquid occurs smoothly. If the amount of water injected is too little, the content of binder that is not precipitated but remains dissolved in the washing waste liquid increases, and if the amount of water injected is too much, a lot of energy may be consumed to purify the organic solvent in the fourth step described below.

[0044]

[0045] (3) Step 2: Binder separation step

[0046] When the binder dissolved in the washing waste liquid is precipitated through the above first step, the precipitated binder is separated.

[0047] As described above, when water is added to the washing waste liquid, the binder crystallizes and precipitates as the moisture is adsorbed at the ends of the binder. However, since a binder such as PVDF (bulk density: 0.288 g / cc) has a lower density than NMP (density: 1.03 g / cc) or water (density: 1 g / cc) contained in the washing waste liquid, the precipitated binder floats on the upper surface of the washing waste liquid. Specifically, when the binder is precipitated after adding water to the washing waste liquid, it exists as a white floating substance on the upper surface of the washing waste liquid.

[0048] Therefore, the binder can be separated from the washing waste liquid by removing the binder precipitate floating on the upper surface of the washing waste liquid.

[0049]

[0050] The above binder separation step may be performed one or more times, for example, one to ten times, preferably one to five times.

[0051]

[0052] After removing the precipitated binder as described above, the remaining solution contains the positive electrode active material, water, and an organic solvent. For convenience, the residual solution containing the positive electrode active material, water, and an organic solvent will be referred to as the first treatment solution.

[0053]

[0054] (4) Step 3: Positive electrode active material recovery step

[0055] Next, the positive electrode active material is separated from the first treatment solution, and a second treatment solution containing water and an organic solvent is obtained.

[0056] At this time, the separation of the positive electrode active material can be performed through various solid-liquid separation methods known in the art. For example, methods such as precipitating the positive electrode active material in a solid phase and then separating the positive electrode active material from the first treatment solution through gravity separation, or selectively discharging only the liquid phases of water and organic solvent from the first treatment solution through filtering can be used, but are not limited thereto.

[0057]

[0058] Meanwhile, if necessary, after the third step, a post-treatment process such as washing, drying, and removing impurities (purification) may be additionally performed on the positive electrode active material separated from the first treatment solution.

[0059] The above washing is intended to remove impurities on the surface of the positive electrode active material, and can be performed according to a washing method for the positive electrode active material generally known in the art, for example, by placing the positive electrode active material in water and stirring it.

[0060] The above drying is intended to remove organic solvents and water remaining in the positive electrode active material, and may be performed by drying the washed positive electrode active material at 80°C to 140°C, preferably 80°C to 120°C, but is not limited thereto. The drying temperature may vary depending on the airflow rate, degree of stirring, partial pressure, etc. of the drying system.

[0061] The positive electrode active material obtained through the above post-processing process can be recycled as a raw material for a battery or used to recover valuable metals through acid treatment, etc.

[0062]

[0063] (5) Step 4: Organic solvent separation step

[0064] Next, water is removed from the second treatment solution obtained in the third step, and the organic solvent is recovered. This step can be performed, for example, by fractional distillation of the second treatment solution. Since water and the organic solvent have different boiling points, fractional distillation can effectively separate the water and the organic solvent, and the purified organic solvent can be recovered by cooling the distilled organic solvent. The recovered organic solvent can be reused in the first step. Recycling the organic solvent in this way can reduce the consumption of the organic solvent, thereby reducing process costs.

Claims

1. A pretreatment step of removing a portion of the organic solvent from the cleaning waste liquid containing the positive electrode active material, binder, and the organic solvent; A first step of precipitating a binder by adding water to the washing waste liquid from which some of the organic solvent has been removed; A second step of separating the precipitated binder to obtain a first treatment solution containing the positive electrode active material, the water, and the organic solvent; A third step of obtaining a second treatment solution containing the water and the organic solvent by separating the positive electrode active material from the first treatment solution; and A method for treating a washing waste liquid, comprising a fourth step of removing water from the second treatment solution and recovering an organic solvent.

2. In paragraph 1, The above cleaning waste liquid is a method for treating cleaning waste liquid generated after cleaning a cathode material mixer.

3. In paragraph 1, A method for treating a washing waste liquid wherein the organic solvent is N-methyl pyrrolidone.

4. In paragraph 1, A method for treating a cleaning wastewater, wherein the above pretreatment step is performed so that the solid content in the cleaning solution becomes 40 wt% to 95 wt% after removing the organic solvent.

5. In paragraph 1, A method for treating a washing wastewater, wherein in the first step, the water is added in an amount of 0.5 to 50 times the total volume of the washing wastewater.

6. In paragraph 1, A method for treating a washing waste liquid, wherein the second step is performed by removing binder precipitates floating on the upper surface of the washing waste liquid.

7. In paragraph 1, A method for treating a washing wastewater, wherein in the third step, separating the positive electrode active material from the first treatment solution is performed by precipitating the positive electrode active material in the first treatment solution and then separating it by gravity.

8. In paragraph 1, A method for treating a cleaning wastewater, wherein in the third step, separating the positive electrode active material from the first treatment solution is performed by filtering the first treatment solution.

9. In paragraph 1, A method for treating a washing waste liquid, further comprising a step of washing and drying the positive electrode active material separated from the first treatment solution after the above step 3.

10. In paragraph 1, The above fourth step is a method for treating a washing wastewater, which is performed by fractionally distilling a second treatment solution.