Method for recovering positive electrode active material

Abstract

The present invention relates to a method for recovering a positive electrode active material. A method for recovering a positive electrode active material according to the present invention comprises: a first step in which a positive electrode including a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material and a binder is immersed in an organic solvent capable of dissolving the binder, thereby separating the positive electrode mixture layer and the positive electrode current collector; a second step for removing the positive electrode current collector to obtain a first processing solution containing the positive electrode active material, the binder, and the organic solvent; a third step for removing at least a portion of the organic solvent contained in the first processing solution; a fourth step for adding water to the first processing solution to precipitate the binder, and separating the precipitated binder to obtain a second processing solution containing the positive electrode active material, the water, and the organic solvent; a fifth step for separating the positive electrode active material from the second processing solution to obtain a third processing solution containing the water and the organic solvent; and a sixth step for removing the water from the third processing solution and recovering the organic solvent.

Description

Method for recovering positive electrode active material

[0001] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0074043, filed June 5, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for recovering a cathode active material from a cathode of a waste battery or cathode scrap generated during a cathode 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 forming a positive electrode composite layer containing a positive electrode active material, a binder, etc. on a positive electrode current collector. At this time, 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 supply and demand worldwide due to the limited number of countries producing it. Therefore, recovering the positive electrode active material from waste positive electrodes or positive electrode scrap generated during the positive electrode manufacturing process and recycling it as a raw material can not only secure price competitiveness but also generate additional revenue. Recently, research has been conducted on methods for recovering and recycling positive electrode active materials from waste batteries or positive electrode scrap generated during the battery production process.

[0005] Conventionally, a method has been applied in which the positive electrode or positive electrode scrap of a waste battery is crushed into powder, then a pretreatment process is performed to powder the positive electrode composite layer by classifying it, then the binder is removed through heat treatment, and then the valuable metal is extracted by putting it in an acid solution.

[0006] However, in the case of the mechanical pulverization method, there is a risk of fire and dust explosion when lithium metal contained in micrometer-sized fine powder comes into contact with moisture, and since the positive electrode collector is also pulverized during pulverization, a large amount of substances contained in the positive electrode collector (e.g., aluminum) are contained as impurities in the final recovered powder, so a separate purification process must be performed to remove impurities in the recovered powder. However, there is a problem in that valuable metals are lost during the purification process, which lowers the recovery rate of valuable metals.

[0007] In addition, according to the conventional method, since toxic hydrogen fluoride gas is generated during the heat treatment process for removing the binder, there is a problem in that an additional gas treatment facility must be installed to treat the hydrogen fluoride gas, which increases the process cost.

[0008] Therefore, there is a need to develop a method that can reduce process costs and effectively recover positive electrode active materials.

[0009] The present invention is intended to solve the above problems, and to provide a method for recovering positive electrode active materials at a relatively low cost, which is environmentally friendly because it does not generate toxic gases, has excellent work safety, and can be used.

[0010] In one aspect, the present invention provides a method for recovering a positive electrode active material, comprising: a first step of immersing a positive electrode including a positive electrode current collector and a positive electrode composite layer including a positive electrode active material and a binder in an organic solvent capable of dissolving the binder to separate the positive electrode composite layer and the positive electrode current collector; a second step of removing the positive electrode current collector and obtaining a first treatment solution including the positive electrode active material, the binder and the organic solvent; a third step of removing at least a portion of the organic solvent included in the first treatment solution; a fourth step of adding water to the first treatment solution to precipitate a binder and separating the precipitated binder to obtain a second treatment solution including the positive electrode active material, the water and the organic solvent; a fifth step of separating the positive electrode active material from the second treatment solution to obtain a third treatment solution including the water and the organic solvent; and a sixth step of removing water from the third treatment solution and recovering the organic solvent.

[0011] At this time, the organic solvent may be, for example, N-methyl pyrrolidone, and the first step may be performed while applying heat and / or vibration.

[0012] In the first step, the immersion may be performed for 10 to 200 minutes, preferably 20 to 180 minutes, and more preferably 40 to 180 minutes.

[0013] Meanwhile, in the second step, the binder may be adsorbed onto the positive electrode active material to form a precipitate, and in this case, the third step may be performed by removing the supernatant of the first treatment solution.

[0014] Alternatively, the third step may be performed by filtering the first treatment solution to selectively remove only the organic solvent.

[0015] It is preferable that the third step is performed so that the solid content in the first treatment solution after removing the organic solvent becomes 10 wt% to 95 wt%.

[0016] Meanwhile, in the fourth step, it is preferable that the water be added in an amount of 5% to 95% by volume based on the total volume of the first treatment solution.

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

[0018] If necessary, a step of washing and drying the positive electrode active material separated from the second treatment solution may be additionally included after the above step 5.

[0019] The sixth step above can be performed by fractional distillation of the third treatment solution. The organic solvent obtained in the sixth step above can be reused in the first step above.

[0020] The method for recovering a positive electrode active material according to the present invention separates the positive electrode current collector and the positive electrode composite layer by dissolving the binder by immersing the positive electrode in an organic solvent capable of dissolving the binder without using a pulverization process, so that dust generation or explosion can be suppressed, thereby ensuring excellent work safety.

[0021] In addition, the method for recovering a cathode active material 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.

[0022] In addition, the method for recovering a positive electrode active material according to the present invention can reduce the amount of water used in binder precipitation by performing a process of removing at least a portion of the organic solvent from the first treatment solution after removing the positive electrode current collector, thereby increasing the reactivity between water and binder, and can reduce the amount of energy consumed in distilling water and the organic solvent during fractional distillation of the third treatment solution.

[0023] In addition, the cathode active material according to the present invention has low process costs because it does not require expensive equipment such as crushing equipment or gas treatment equipment.

[0024] Figure 1 is a photograph showing the state of the positive electrode collector when the positive electrode collector is taken out after a certain period of time has passed after the positive electrode is immersed in an N-methyl pyrrolidone solvent without ultrasonic treatment.

[0025] Figure 2 is a photograph showing the state of the positive electrode collector after the positive electrode was immersed in an N-methyl pyrrolidone solvent, ultrasonic waves were irradiated for 20 minutes, and the positive electrode collector was taken out after a certain period of time.

[0026] Hereinafter, the present invention will be described in more detail.

[0027] The method for recovering a positive electrode active material according to the present invention comprises: (1) a first step of immersing a positive electrode including a positive electrode current collector and a positive electrode composite layer including a positive electrode active material and a binder in an organic solvent capable of dissolving the binder to separate the positive electrode composite layer and the positive electrode current collector; (2) a second step of removing the positive electrode current collector and obtaining a first treatment solution including the positive electrode active material, a binder and the organic solvent; (3) a third step of removing at least a portion of the organic solvent included in the first treatment solution; (4) a fourth step of adding water to the first treatment solution to precipitate a binder and separating the precipitated binder to obtain a second treatment solution including the positive electrode active material, the water and the organic solvent; (5) a fifth step of separating the positive electrode active material from the second treatment solution to obtain a third treatment solution including the water and the organic solvent; and (6) a sixth step of removing water from the third treatment solution and recovering the organic solvent.

[0028]

[0029] (1) Step 1: Positive collector separation step

[0030] First, the anode is immersed in an organic solvent capable of dissolving the binder.

[0031] At this time, the positive electrode may be a positive electrode separated from a waste battery or a positive electrode scrap generated during the positive electrode manufacturing process.

[0032] The positive electrode includes a positive electrode current collector and a positive electrode composite layer formed on one or both sides of the positive electrode current collector. At this time, the positive electrode current collector may be a positive electrode collector generally used in the relevant technical field, and may be, for example, an aluminum alloy foil, a stainless steel foil, a nickel alloy foil, or an aluminum foil or a stainless steel foil surface-treated with carbon, nickel, titanium, silver, etc., and may preferably be an aluminum alloy foil. The positive electrode composite layer may include a positive electrode active material and a binder, and may further include a conductive material or a dispersant, if necessary. The positive electrode active material may be a positive electrode active material generally used in the relevant technical field, and may include, for example, a lithium nickel-based composite transition metal oxide such as lithium iron phosphate; a lithium cobalt-based oxide; a lithium manganese-based oxide; a lithium nickel-cobalt-manganese oxide, a lithium nickel-cobalt-aluminum oxide, or a combination thereof, and may preferably include a lithium nickel-based composite transition metal oxide.

[0033] 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.

[0034]

[0035] Meanwhile, the organic solvent is a solvent capable of dissolving a binder included in the positive electrode composite layer, and may be, for example, N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropyl alcohol, etc., and preferably N-methyl pyrrolidone.

[0036] When the positive electrode is immersed in an organic solvent as described above, the binder is dissolved by the organic solvent, causing the adhesive force between the positive electrode current collector and the positive electrode active material particles to disappear, resulting in the separation of the positive electrode current collector and the positive electrode active material.

[0037] The above immersion can be performed for a period of time sufficient to allow the binder to sufficiently dissolve, for example, 40 to 200 minutes, preferably 40 to 180 minutes.

[0038]

[0039] Meanwhile, after the above immersion, a step of applying heat and / or vibration may be additionally performed, if necessary. Applying heat to the organic solvent accelerates the dissolution of the binder in the organic solvent, and applying vibration accelerates the separation of the positive electrode composite layer from the positive electrode current collector, thereby shortening the process time.

[0040] Specifically, the step of applying heat may be performed by a method of heating the organic solvent to 25°C to 80°C, preferably 50°C to 70°C, and more preferably 50°C to 60°C, and the step of applying vibration may be performed by a method of generating mechanical vibration by irradiating the organic solvent with ultrasonic waves or applying bubbling.

[0041]

[0042] Figure 1 shows photographs showing the state of a positive electrode current collector after the positive electrode was immersed in an N-methyl pyrrolidone solvent without ultrasonic treatment and then removed after a certain period of time. In addition, Figure 2 shows photographs showing the state of a positive electrode current collector after the positive electrode was immersed in an N-methyl pyrrolidone solvent, then ultrasonicated for 20 minutes and then removed after a certain period of time.

[0043] Referring to Figures 1 and 2, when immersed for 40 minutes without ultrasonic treatment, the positive electrode composite layer (black powder) was hardly separated from the positive electrode current collector, whereas when ultrasonic treatment was performed, a significant amount of the positive electrode composite layer (black powder) was separated even after immersion for 40 minutes. This shows that the separation of the positive electrode composite layer is accelerated by ultrasonic treatment.

[0044]

[0045] When the positive electrode current collector and the positive electrode composite layer are separated in the above manner, work safety is excellent because no dust generation or explosion occurs.

[0046]

[0047] (2) Step 2: Positive collector removal step

[0048] When the positive electrode composite layer is sufficiently separated from the positive electrode current collector through the above first step, the positive electrode current collector is removed, and a first treatment solution containing the positive electrode active material, binder, and the organic solvent is obtained.

[0049] In the first treatment solution, which is the solution after the positive electrode collector has been removed, the positive electrode active material and binder may be present in a suspended state in an organic solvent, or aggregates of the positive electrode active material and binder may be present in a precipitated state at the bottom of the first treatment solution.

[0050] In the first step, if the binder is completely dissolved in the organic solvent, the positive electrode active material and the binder may exist in a suspended state in the organic solvent, and if the binder is not completely separated from the positive electrode active material but is adsorbed on the surface of the positive electrode active material particles, the positive electrode active material particles may be entangled with each other by the binder to form aggregates, which may exist in the form of sediments deposited at the bottom of the first treatment solution.

[0051]

[0052] (3) Step 3: Organic solvent removal step

[0053] Next, at least a portion of the organic solvent is removed from the first treatment solution. When at least a portion of the organic solvent is removed from the first treatment solution, the content of the organic solvent is reduced, which increases the reactivity between water and the binder in the fourth step described below, thereby reducing the amount of water used for binder precipitation. Furthermore, this reduces the content of water and organic solvent in the third treatment solution in the sixth step described below, thereby reducing the amount of energy consumed in distilling water and the organic solvent during fractional distillation.

[0054] The removal of the organic solvent can be performed, for example, by a method of removing the supernatant of the first treatment solution or a method of selectively removing the organic solvent through filtering.

[0055] When the positive electrode active material and binder exist in the form of a precipitate in the first treatment solution, the organic solvent can be removed by a simple method of removing the supernatant.

[0056] Meanwhile, when the positive electrode active material and binder are suspended in the first treatment solution, only the organic solvent, excluding the positive electrode active material and binder, which are solid components, can be selectively removed through a filter.

[0057] The third step is preferably performed so that the solid content in the first treatment solution after the organic solvent is removed is 10 to 95 wt%, preferably 40 to 95 wt%, more preferably 60 to 95 wt%, and even more preferably 80 to 95 wt%. When the amount of organic solvent removed satisfies the above range, the amount of water required for binder precipitation in the fourth step described below can be effectively reduced. If the amount of organic solvent removed is too large, a problem may occur in which binder separation does not occur smoothly even if water is added in the subsequent process.

[0058]

[0059] (4) Step 4: Binder separation step

[0060] Next, water is added to the first treatment solution from which at least a portion of the organic solvent has been removed. Binders such as PVDF and PVDF-co-HFP dissolved in the organic solvent react with water to crystallize and precipitate in a solid state.

[0061] At this time, the water is preferably added in an amount of 5 to 95 vol%, preferably 10 to 90 vol%, more preferably 40 to 90 vol%, and even more preferably 60 to 90 vol%, based on the total volume of the first treatment solution. When the amount of water added satisfies the above range, the binder precipitation in the first treatment solution occurs smoothly. If the amount of water added is too little, the content of unprecipitated binder increases, making it difficult to reuse the organic solvent, and if the amount of water added is too much, a lot of energy may be consumed to purify the organic solvent in the sixth step described below.

[0062]

[0063] When the binder is precipitated through the above process, the precipitated binder is separated. At this time, the separation of the binder can be performed, for example, by removing the binder floating on the solution surface.

[0064] After removing the precipitated binder as described above, the remaining solution contains positive electrode active material, water, and an organic solvent. For convenience, the residual solution containing positive electrode active material, water, and an organic solvent will be referred to as a second treatment solution.

[0065]

[0066] Meanwhile, the binder separation step may be performed more than once, for example, 1 to 10 times, preferably 1 to 5 times.

[0067]

[0068] (5) Step 5: Positive electrode active material recovery step

[0069] Next, the positive electrode active material is separated from the second treatment solution, and a third treatment solution containing water and an organic solvent is obtained.

[0070] At this time, the separation of the positive electrode active material can be performed using 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 second treatment solution through gravity separation, or selectively discharging only the liquid phases of water and organic solvent from the second treatment solution through filtering can be used, but are not limited thereto.

[0071]

[0072] Meanwhile, if necessary, after the fifth 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 second treatment solution.

[0073] 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.

[0074] The above drying is intended to remove organic solvents and water remaining in the positive electrode active material, and may be performed, for example, 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, degree of stirring, partial pressure, etc. of the drying system.

[0075] 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.

[0076]

[0077] (6) Step 6: Organic solvent separation step

[0078] Next, water is removed from the third treatment solution obtained in the fifth step, and the organic solvent is recovered. This step can be performed, for example, by fractional distillation of the third 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 first step of separating the positive electrode composite layer and the positive electrode current collector by immersing the positive electrode including the positive electrode current collector and the positive electrode composite layer including the positive electrode active material and the binder in an organic solvent capable of dissolving the binder; A second step of removing the positive electrode current collector and obtaining a first treatment solution containing the positive electrode active material, binder, and the organic solvent; A third step of removing at least a portion of the organic solvent contained in the first treatment solution; A fourth step of adding water to the first treatment solution from which at least a portion of the organic solvent has been removed to precipitate a binder, and separating the precipitated binder to obtain a second treatment solution containing the positive electrode active material, the water, and the organic solvent; A fifth step of obtaining a third treatment solution containing the water and the organic solvent by separating the positive electrode active material from the second treatment solution; and A method for recovering a positive electrode active material, comprising a sixth step of removing water from the third treatment solution and recovering an organic solvent.

2. In paragraph 1, A method for recovering a positive electrode active material in which the organic solvent is N-methyl pyrrolidone.

3. In paragraph 1, A method for recovering a positive electrode active material, wherein the first step is performed by applying at least one of heat and vibration.

4. In paragraph 1, A method for recovering a positive electrode active material, wherein the binder is adsorbed on the positive electrode active material to form a precipitate in the second step.

5. In paragraph 4, A method for recovering a positive electrode active material, wherein the third step is performed by removing the supernatant of the first treatment solution.

6. In paragraph 1, The third step is a method for recovering a positive electrode active material, wherein the first treatment solution is filtered to selectively remove only the organic solvent.

7. In paragraph 1, A method for recovering a positive electrode active material, wherein the third step is performed so that the solid content in the first treatment solution becomes 10 wt% to 95 wt% after removing the organic solvent.

8. In paragraph 1, A method for recovering a cathode active material, wherein in the fourth step, the water is added in an amount of 5% to 95% by volume based on the total volume of the first treatment solution.

9. In paragraph 1, A method for recovering a positive electrode active material, wherein in the fifth step, separating the positive electrode active material from the second treatment solution is performed by precipitating the positive electrode active material in the second treatment solution and then separating it by gravity.

10. In paragraph 1, A method for recovering a positive electrode active material, wherein in the fifth step, separating the positive electrode active material from the second treatment solution is performed by filtering the second treatment solution.

11. In paragraph 1, A method for recovering a positive electrode active material, further comprising a step of washing and drying the positive electrode active material separated from the second treatment solution after the above step 5.

12. In paragraph 1, The above 6th step is a method for recovering a positive electrode active material, which is performed by fractional distillation of a third treatment solution.

13. In paragraph 1, A method for recovering a positive electrode active material, wherein the organic solvent obtained in the above 6th step is reused in the above 1st step.

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