Method for recovering active metal from lithium secondary battery

Abstract

A method for recovering an active metal of a lithium secondary battery is provided. The method for recovering an active metal of a lithium secondary battery comprises preparing a waste cathode active material slurry, adding an antisolvent to the waste cathode active material slurry to form a first slurry, adding a coagulant to the first slurry to form a second slurry, separating the second slurry into solids and mother liquor by solid-liquid separation, recovering a solvent from the mother liquor, and recovering an active metal from the solids. In the step of forming the first slurry, the antisolvent is added to the waste cathode active material slurry such that the content of the antisolvent exceeds 10 volume% based on 100 volume% of the first slurry.

Description

Technology Field

[0001] The present disclosure relates to a method for recovering active metal from a lithium secondary battery. Background Technology

[0003] Rechargeable batteries are batteries capable of repeated charging and discharging, and with the advancement of the information and communication and display industries, they have been widely applied in portable electronic communication devices such as camcorders, mobile phones, and laptop PCs. Examples of rechargeable batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-hydrogen batteries; among these, lithium-ion batteries have been actively developed and applied due to their high operating voltage and energy density per unit weight, as well as advantages in charging speed and weight reduction.

[0004] A lithium secondary battery may include an electrode assembly comprising a positive electrode, a negative electrode, and a separator, and an electrolyte impregnating the electrode assembly. The lithium secondary battery may further include an outer casing, for example, in the form of a pouch, that accommodates the electrode assembly and the electrolyte.

[0005] As high-cost, valuable metals are used in the above-mentioned cathode active materials, more than 20% of the manufacturing cost is spent on manufacturing the cathode materials. In addition, as environmental protection issues have recently come to the forefront, research on recycling methods for cathode active materials is being conducted.

[0006] In addition, solvents such as N-Methyl-2-pyrrolidone (NMP) are used for coating the anode active material layer or for slurrying to recover active metals from the anode active material. There is a need for a method to efficiently recover these solvents for reuse in the manufacture of lithium secondary batteries or for other purposes. For example, when recovering the solvents by evaporative concentration, excessive energy is consumed or frequent failures of the concentration equipment may occur due to particles. The problem to be solved

[0008] One objective of the present disclosure is to provide a method for recovering active metal with high purity, high yield, and high efficiency from a waste cathode active material slurry of a lithium secondary battery.

[0009] One objective of the present disclosure is to provide a method for recovering a solvent with high purity, high yield, and high efficiency from a spent cathode active material slurry of a lithium secondary battery. means of solving the problem

[0011] A method for recovering an active metal of a lithium secondary battery according to embodiments of the present disclosure comprises the steps of: preparing a spent cathode active material slurry; adding an anti-solvent to the spent cathode active material slurry to form a first slurry; adding a coagulant to the first slurry to form a second slurry; separating the second slurry into solids and a mother liquor; recovering a solvent from the mother liquor; and recovering an active metal from the solids. In the step of forming the first slurry, the anti-solvent is added to the spent cathode active material slurry such that the content of the anti-solvent exceeds 10 volume% based on 100 volume% of the first slurry.

[0012] In one embodiment, a flocculant may be further added to the first slurry after the addition of the flocculant, or the flocculant may be added together with the flocculant to form the second slurry.

[0013] In one embodiment, the antisolvent comprises water, and the solvent may comprise NMP (N-Methyl-2-pyrrolidone).

[0014] In one embodiment, the solid-liquid separation may include performing at least one of sedimentation, centrifugation, and filtration on the second slurry.

[0015] In one embodiment, the coagulant may include at least one of an aluminum-based coagulant, an iron-based coagulant, a silicon-based coagulant, and a magnesium-based coagulant.

[0016] In one embodiment, the flocculation aid may include at least one of a polymer-based flocculation aid and bentonite.

[0017] In one embodiment, the polymer-based coagulation aid may include at least one selected from the group consisting of cationic polymers, anionic polymers, nonionic polymers, and natural polymers.

[0018] In one embodiment, in the step of forming the first slurry, the antisolvent may be added to the waste cathode active material slurry such that the content of the antisolvent is 15 volume% or more based on 100 volume% of the first slurry.

[0019] In one embodiment, solid-liquid separation of the second slurry can be performed by sedimentation.

[0020] In one embodiment, the content of the solvent may be 80 volume% or more based on the total volume% of the mother liquor.

[0021] In one embodiment, the waste anode active material slurry may include a waste anode active material, a binder, and the solvent.

[0022] In one embodiment, the solid may include the binder.

[0023] In one embodiment, the antisolvent comprises water, and the binder may comprise poly(vinylidene fluoride).

[0024] In one embodiment, the active metal may include lithium, nickel, cobalt, and manganese.

[0025] In one embodiment, the coagulant may be added in an amount of 200 ppm to 1000 ppm based on the weight of the spent cathode active material slurry.

[0026] In one embodiment, the aggregation aid can be added in an amount of 5 ppm to 50 ppm based on the weight of the spent cathode active material slurry.

[0027] In one embodiment, the weight ratio of the added coagulant and the coagulant aid may be 4:1 to 200:1. Effects of the invention

[0029] The method for recovering active metal from a lithium secondary battery according to the embodiments of the present disclosure can efficiently separate the solvent and active metal from a waste cathode active material slurry by means of antisolvent treatment, coagulant treatment and / or coagulant aid treatment, etc. Accordingly, the solvent and active metal can be recovered with high purity and high efficiency.

[0030] The active metal recovery method described above can prevent excessive energy consumption and equipment failure caused by particles during solid-liquid separation using the evaporation concentration method. Accordingly, the method can have improved process reliability and stability, and the lifespan of the solid-liquid separation equipment can be extended.

[0031] Through the active metal recovery method described above, the mother liquor and solid can be separated, and the solvent and active metal can be recovered, respectively. The recovered solvent can be purified and recycled, and the active metal at a high concentration in the solid can be recovered by a method such as wet metal extraction and reused as an anode active material. Accordingly, useful resources such as solvents like NMP and valuable metals can be recycled. Brief explanation of the drawing

[0033] FIG. 1 is a schematic process flow diagram of a method for recovering active metal of a lithium secondary battery according to one embodiment of the present disclosure. Figure 2 is a diagram showing the appearance of Comparative Example 2 and Examples 1 and 2 after solid-liquid separation. Specific details for implementing the invention

[0034] With reference to the drawings below, exemplary embodiments of the present disclosure are described in detail so that those skilled in the art can easily practice the present invention. However, this is merely illustrative and the present invention is not limited to the exemplary embodiments described.

[0035] As used in this specification, the term "precursor" is used to collectively refer to a compound containing a specific metal to provide the specific metal included in the electrode active material.

[0036] A lithium secondary battery is a secondary battery capable of charging and discharging through an external power source, and may be a secondary battery in which charging and discharging are repeatedly performed by absorbing and releasing lithium ions. The lithium secondary battery may include a case, an electrode assembly housed inside the case, and an electrolyte.

[0037] The electrode assembly may include an anode, a cathode, and a separator interposed between the anode and the cathode. The electrode assembly may be formed by repeatedly stacking anodes and cathodes and placing a separator between each anode and cathode. However, it is not limited thereto, and, for example, it may be in the form of a wound unit cell stacked in the order of anode, separator, and cathode.

[0038] The positive electrode may include a positive current collector and a positive active material layer on the positive current collector. The negative electrode may include a negative current collector and a negative active material layer on the negative current collector. The positive current collector and the negative current collector may include metals commonly used in the industry and are not particularly limited. For example, aluminum foil may be used as the positive current collector and copper foil as the negative current collector.

[0039] The positive active material layer and the negative active material layer may each include an active material and a binder commonly used in the industry. In one embodiment, the positive active material layer or the negative active material layer may further include a conductive material.

[0040] In one embodiment, the positive active material included in the positive active material layer may include an oxide containing lithium and a transition metal.

[0041] For example, the above positive active material may include a compound represented by the following chemical formula 1.

[0042] [Chemical Formula 1]

[0043] Li x M1 a M2 b M3 c O y

[0044] In Chemical Formula 1, M1, M2, and M3 may be transition metals selected from Ni, Co, Mn, Na, Mg, Ca, Ti, V, Cr, Cu, Zn, Ge, Sr, Ag, Ba, Zr, Nb, Mo, Al, Ga, or B. In Chemical Formula 1, 0 <x≤1.1, 2≤y≤2.2, 0<a<1, 0<b<1, 0<c<1, 0<a+b+c≤1일 수 있다.

[0045] In one embodiment, the positive electrode active material may be an NCM-based lithium oxide comprising nickel, cobalt, and manganese.

[0046] The above conductive material may include carbon-based materials such as, for example, graphite, carbon black, graphene, carbon nanotubes, etc.

[0047] FIG. 1 is a schematic process flow diagram of a method for recovering active metal of a lithium secondary battery according to one embodiment of the present disclosure.

[0048] A method for recovering an active metal of a lithium secondary battery according to embodiments of the present disclosure may include preparing a waste positive electrode active material slurry (step S10), adding an anti-solvent to the waste positive electrode active material slurry to form a first slurry (step S20), adding a coagulant to the first slurry to form a second slurry (step S30), separating the second slurry into a solid and a mother liquor by solid-liquid separation (step S40), recovering a solvent from the mother liquor (step S50), and recovering an active metal from the solid (step S60).

[0049] According to the above method for recovering active metals from lithium secondary batteries, subsequent solid-liquid separation can be performed more efficiently by antisolvent treatment and chemical coagulation treatment using a coagulant for the spent cathode active material slurry.

[0050] Accordingly, active metals can be recovered from waste cathode active material slurry with high efficiency and high purity.

[0051] In addition, the active metal is recovered, and the remaining solvent can be recovered with high purity.

[0052] In one embodiment, the content of the solvent may be 50 volume% or more based on the total volume% of the mother liquor. For example, the content of the solvent in the mother liquor may be 60 volume% or more, 80 volume% or more, 85 volume% or more, 90 volume% or more, or 95 volume% or more.

[0053] For example, during the manufacturing of a lithium secondary battery, the solvent may volatilize and be discharged in a gaseous state during the step of coating a positive electrode active material slurry onto a positive electrode current collector and drying it, and a recovered solvent solution can be obtained by recovering the gaseous solvent into a liquid state. For example, the solvent content in the recovered solvent solution may be 50 volume% or more, for example, 80 volume% or more, based on 100 volume% of the recovered solvent solution. A process for purifying the solvent to a high purity from such a recovered solvent solution can be carried out.

[0054] As described above, the solvent content of the mother liquor and the solvent content of the solvent recovery liquid may be similar. Therefore, for example, a mother liquor in which the solvent content is 50% or more or 80% or more based on 100% of the mother liquor volume can be directly introduced into the solvent purification process of the solvent recovery liquid recovered from the gaseous solvent. Accordingly, it may not be necessary to design a separate solvent purification process and install equipment for the mother liquor. Thus, the efficiency of the entire solvent recovery process is improved, and the solvent recovery rate can be increased.

[0055] According to the above method for recovering active metal of a lithium secondary battery, a waste positive electrode active material slurry can be prepared (step S10).

[0056] The positive active material slurry or the waste positive active material slurry described below may be formed, for example, by dissolving and dispersing a positive active material, a binder, etc. in a solvent.

[0057] Waste lithium secondary batteries may refer to lithium secondary batteries that have reached the end of their lifespan or are defective. If active metals are recovered from waste lithium secondary batteries, they can be reused in the manufacture of lithium secondary batteries. According to the embodiments of the present disclosure, both active metals and solvents can be recovered from waste lithium secondary batteries.

[0058] Waste cathode active material slurry can be obtained from waste lithium secondary batteries.

[0059] The waste cathode can be recovered by separating the cathode from the above-mentioned spent lithium secondary battery. The waste cathode comprises a cathode current collector (e.g., aluminum (Al)) and a cathode active material layer, and the cathode active material layer may include a conductive material and a binder together with the cathode active material.

[0060] In the present disclosure, "waste cathode active material slurry" may refer to a raw material used in the active metal recovery method described below after the cathode current collector has been substantially removed from the waste cathode. In one embodiment, the waste cathode active material slurry may include cathode active material particles such as the NCM-based lithium oxide. In one embodiment, the waste cathode active material slurry may partially include components derived from the binder or the conductive material.

[0061] In one embodiment, the spent anode active material slurry may comprise a spent anode active material, a binder, and a solvent. The spent anode active material slurry may further comprise a conductive material. The spent anode active material may comprise an active metal.

[0062] For example, waste cathode active material slurry may be generated during the cathode manufacturing process of a lithium secondary battery. For example, waste cathode active material slurry may be generated when converting process steps or changing conditions of a lithium secondary battery. For example, waste cathode active material slurry may include active material slurry remaining after coating on the cathode current collector and waste liquid generated during the cleaning of cathode manufacturing equipment. The waste liquid may contain solvents such as NMP.

[0063] The above active metal can be recovered from waste cathode active material. For example, the active metal can be recovered from lithium composite oxides (e.g., NCM-based lithium oxide).

[0064] In one embodiment, the active metal may include lithium, nickel, cobalt, and manganese. Alternatively, the active metal may further include manganese, nickel, chromium, or aluminum.

[0065] As a solvent included in the waste anode active material slurry, a solvent that dissolves or swells the binder, thoroughly wets the surface of the anode active material, uniformly disperses the conductive material, and stabilizes the slurry by minimizing metal leaching or corrosion of the anode current collector can be selected.

[0066] The binder may include, for example, poly(vinylidene fluoride), PVDF, poly(vinylidene fluoride-co-hexafluoropropylene copolymer (PVDF-HFP), a combination of poly(acrylic acid), PAA, and lithium polyacrylate (LiPAA), polyacrylonitrile (PAN), and polymethylmethacrylate (PMMA).

[0067] In one embodiment, the solvent may vary depending on the binder used. For example, if the binder is PVDF or PVDF-HFP, the solvent may include NMP (N-methyl-2-pyrrolidone).

[0068] For example, if the binder is a combination of PAA and LiPAA, the solvent may include at least one of water, ethanol, and isopropanol.

[0069] According to one embodiment, in a process for manufacturing a positive electrode of a lithium secondary battery, a waste positive electrode active material slurry may be generated when a process step is changed or conditions are changed. Alternatively, a waste positive electrode obtained from a lithium secondary battery may be crushed and a solvent such as NMP may be added to generate a waste positive electrode active material slurry.

[0070] The waste cathode active material slurry may contain the solvent through the introduction in the manufacturing process of a lithium secondary battery or intentional addition in the recovery process.

[0071] For example, when manufacturing an anode, PVDF can be dissolved by dispersing it in NMP to create an anode active material slurry, which can then be coated onto an anode current collector and dried. Gases such as NMP generated during the drying process can be treated by washing with water. Through this treatment, a liquid NMP solution in which NMP and other gases are captured in water may be generated. For example, the NMP solution can be recovered as high-purity NMP through a separate purification process.

[0072] For example, NMP can be intentionally added in a recovery or recycling process to prepare a waste cathode active material slurry. For example, PVDF can be converted from an insoluble state to a dissolved state to facilitate the separation of the cathode active material from the cathode current collector in the waste cathode. To achieve this, NMP can be added to swell or dissolve the PVDF.

[0073] In the step of preparing the spent anode active material slurry (step S10), the spent anode active material slurry may be prepared as described above, or by removing solid materials such as the anode active material settled by natural sedimentation as described below, but is not limited thereto.

[0074] In one embodiment, after preparing a waste cathode active material slurry, the cathode active material can be allowed to settle naturally. The settled cathode active material can be recovered primarily. Since the particle size of the cathode active material particles and / or the density of the cathode active material is large, most of the cathode active material can settle naturally. The settled cathode active material can be recovered and fed into an active metal recovery process described later. This can improve the recovery rate of the active metal.

[0075] In one embodiment, the content of the solvent based on the total weight of the spent cathode active material slurry may be 90 weight% or more or 95 weight% or more. For example, the content of the solvent may be 99 weight% or more.

[0076] In one embodiment, a first slurry can be formed by adding an antisolvent to the waste cathode active material slurry (step S20).

[0077] As the above antisolvent, a solvent that prevents the binder from dissolving almost when mixed with the binder contained in the waste cathode active material slurry may be used. For example, if the binder is PVDF or PVDF-HFP, the antisolvent may include at least one of water, ethanol, isopropanol, acetone, methyl ethyl ketone, acetonitrile, toluene, and hexane.

[0078] For example, if the binder is a combination of PAA and LiPAA, the antisolvent may include at least one of acetone, acetonitrile, methyl ethyl ketone, and ethyl acetate.

[0079] For example, if the binder is PAN, the antisolvent may include at least one combination of water, ethanol, isopropanol, acetone, methyl ethyl ketone, ethyl acetate, toluene, and hexane.

[0080] In one embodiment, the antisolvent may include water, and the binder may include PVDF.

[0081] In one embodiment, in the step of forming the first slurry (step S20), the antisolvent may be added to the waste cathode active material slurry such that the content of the antisolvent exceeds 10 volume% based on 100 volume% of the first slurry. For example, the content of the antisolvent may be 15 volume% or more, 20 volume% or more, or 25 volume% or more.

[0082] If the antisolvent is added to the waste cathode active material slurry such that the content of the antisolvent is 10 volume% or less based on 100 volume% of the first slurry, the subsequent solid-liquid separation (e.g., step S40) may not be easily performed. For example, if the antisolvent is added at 10 volume% or less, the boundary between the mother liquor and the solid may not be visually confirmed during the solid-liquid separation step. Alternatively, a large amount of suspended solids (SS) may be generated.

[0083] For example, on a laboratory scale, 50 to 150 ml, for example 100 ml, of antisolvent can be added to 400 ml of spent cathode active material slurry. For example, in a large-scale process, 8 m 3 2 m of the waste cathode active material slurry 3 Water (20 volume%) can be added.

[0084] For example, if the antisolvent is added at 10 volume% based on 100 volume% of the first slurry, the boundary between the mother liquor (e.g., supernatant) and the solid (e.g., precipitate) may not be visible to the naked eye during solid-liquid separation (e.g., precipitation).

[0085] For example, when the antisolvent is added at 14 volume%, even if some suspended solids are generated during solid-liquid separation, the boundary between the mother liquor and the solids can be observed visually, and the recovery rate of the active metal and the recovery rate of the solvent can be improved.

[0086] In one embodiment, the antisolvent may be added such that the content of the first slurry is 25 volume% or less based on 100 volume%. By controlling the antisolvent content to the range, the energy consumption for the subsequent separation and purification of the NMP solvent and active metal can be reduced.

[0087] Consequently, the first slurry may include the waste anode active material slurry and the antisolvent.

[0088] In the above first slurry formation process, the binder may gradually aggregate due to the antisolvent. In one embodiment, the antisolvent may include water, and the solvent may include NMP. In this case, the solubility of binders such as PVDF and PVDF-HFP in NMP is lowered by water, so that the binder may aggregate.

[0089] Next, a coagulant can be added to the first slurry to form a second slurry (step S30).

[0090] The above-mentioned coagulant may refer to a substance that electrically neutralizes the surface of fine particles within the spent cathode active material slurry, causing the fine particles to become unstable and clump together. For example, a positively charged metal salt (Al) of the coagulant. 3+ , Fe 3+ The surface charge of negatively charged microparticles can be neutralized by the above.

[0091] Chemical coagulation of solids may be induced by the above coagulant.

[0092] In one embodiment, the coagulant may include at least one of an aluminum-based coagulant, an iron-based coagulant, a silicon-based coagulant, and a magnesium-based coagulant.

[0093] Non-limiting examples of aluminum-based coagulants include aluminum sulfate (Al2(SO4)3), alum, poly aluminum chloride (PAC), and aluminum chloride.

[0094] Non-limiting examples of iron-based coagulants include iron(II) sulfate (FeSO4), iron(III) sulfate (Fe2(SO4)3), polyferric sulfate (PFS), iron(III) chloride (FeCl3), and polyferric chloride (PFC).

[0095] The above silicon-based coagulant may be a coagulant having silicon (Si) or silicate as the main component.

[0096] Non-limiting examples of silicon-based coagulants include sodium silicate (Na2SiO3), polysilicic acid, activated silica obtained by acid treatment of sodium silicate, polysilicate aluminum sulfate (PSAS), and polysilicate ferric sulfate (PSFS).

[0097] Non-limiting examples of magnesium-based coagulants include magnesium sulfate (MgSO4), magnesium chloride (MgCl2), magnesium hydroxide (Mg(OH)2), and basic magnesium carbonate.

[0098] In one embodiment, the coagulant may be added in an amount of 200 ppm to 1000 ppm based on the weight of the spent cathode active material slurry. For example, the coagulant may be added in an amount of 200 ppm to 400 ppm, 500 ppm to 700 ppm, or 800 ppm to 1000 ppm.

[0099] In one embodiment, in the step of forming the second slurry (step S30), a coagulant may be added to the first slurry and first stirring may be performed. Accordingly, the coagulant may be uniformly dispersed. In one embodiment, coagulation may occur gradually during the first stirring step.

[0100] For example, the above first stirring can be performed in a rapid mixing tank. By performing the above first stirring as rapid stirring, the colloidal particles in the coagulant and the waste anode active material slurry come into uniform contact and fine flocs can be easily formed.

[0101] In one embodiment, a flocculant may be further added to the first slurry after the addition of the flocculant, or the flocculant may be added together with the flocculant to form the second slurry.

[0102] The above-mentioned coagulation aid may refer to a substance that helps to further coagulate aggregated small particles to form larger flocs. For example, the above-mentioned coagulation aid can form flocs large enough to allow for sedimentation, centrifugation, or filtration in a subsequent solid-liquid separation step.

[0103] In one embodiment, the flocculation aid may include at least one of a polymer-based flocculation aid and bentonite.

[0104] In one embodiment, the polymer-based coagulation aid may include at least one selected from the group consisting of cationic polymers, anionic polymers, nonionic polymers, and natural polymers.

[0105] For example, if the above coagulation aid is a polymer-based coagulation aid, the polymer-based coagulation aid can physically bridge the particles after the addition of the coagulant to form flocs.

[0106] For example, if the above-mentioned coagulant aid is bentonite, the bentonite can adsorb to the particles after the addition of the coagulant, electrically neutralize them, and generate van der Waals forces to form flocs. For example, when plate-like bentonite is introduced into the first slurry, it swells to induce interlayer cation exchange, which can cause electrical neutralization of the particles coagulated by the addition of the coagulant.

[0107] In one embodiment, the coagulation aid may be added in an amount of 5 ppm to 50 ppm based on the weight of the spent cathode active material slurry. For example, the coagulation aid may be added in an amount of 10 ppm to 20 ppm. Preferably, the coagulation aid may be added in an amount of 10 ppm to 15 ppm.

[0108] In one embodiment, the weight ratio of the added coagulant and the coagulant aid may be 4:1 to 200:1.

[0109] In one embodiment, the second slurry may be formed by adding the coagulant aid together with the coagulant.

[0110] In one embodiment, in the step of forming the second slurry (step S30), a coagulant aid may be added to the first slurry to which the coagulant has been added, and secondary stirring may be performed. Accordingly, the coagulant aid may be uniformly dispersed within the second slurry. In one embodiment, floc formation may occur gradually during the secondary stirring step.

[0111] In one embodiment, the stirring speed of the second stirring may be slower than the stirring speed of the first stirring. For example, the second stirring may be performed in a slow mixing tank. By performing the second stirring as slow stirring, time can be secured for the fine flocs formed through the rapid first stirring described above to aggregate with each other and grow stably into large flocs.

[0112] In one embodiment, the stirring time of the second stirring may be longer than the stirring time of the first stirring. Accordingly, sufficient floc formation by the coagulation aid can be achieved, and process efficiency can be ensured.

[0113] Next, the second slurry can be separated into solids and mother liquid by solid-liquid separation (step S40).

[0114] In one embodiment, the second slurry may be in a state where aggregates or flocs containing the anode active material are formed by the coagulant or the coagulant aid. Accordingly, by solid-liquid separation, the second slurry may be separated into a solid containing a large amount of the aggregates and / or flocs and a mother liquor containing almost none of them.

[0115] In one embodiment, the solid-liquid separation may include performing at least one of precipitation, centrifugation, and filtration on the second slurry.

[0116] In one embodiment, the solid resulting from the solid-liquid separation may include a binder. The solid may further include waste cathode active material. The solid may further include a conductive material.

[0117] For example, when the above second slurry is separated into solid and liquid by sedimentation, the insoluble binder and waste cathode active material may turn into sediment or become dense suspended particles, which may sink downward by gravity.

[0118] In one embodiment, the sedimentation treatment time may be about 30 minutes or more, or about 30 minutes to 120 minutes. Preferably, it may be about 30 minutes to 60 minutes.

[0119] For example, when the second slurry is separated into solid and liquid by centrifugation, layer separation into a high-density binder and waste anode active material and the mother liquor can be performed within a short time.

[0120] In one embodiment, the centrifugal separation speed may be about 1500 rpm to 5000 rpm. Preferably, it may be about 2500 rpm to 3500 rpm.

[0121] In one embodiment, the mother liquor may be a supernatant obtained by precipitation or centrifugation. The supernatant may be a liquid containing almost no insoluble binder and waste cathode active material and containing a large amount of the antisolvent (e.g., water) and the solvent (e.g., NMP).

[0122] For example, when the second slurry is separated into solid and liquid by filtration, the second slurry is passed through a porous material such as a filter or membrane to filter out the binder and the waste cathode active material, which have relatively large particle sizes, and a filtrate containing a large amount of the antisolvent and the solvent can be obtained.

[0123] In one embodiment, solid-liquid separation of the second slurry can be performed by sedimentation or centrifugation. In this case, the second slurry in which solid-liquid separation by sedimentation is performed may be a first slurry to which both the coagulant and the coagulant aid have been added.

[0124] In one embodiment, solid-liquid separation of the second slurry can be performed by filtration. In this case, the second slurry in which solid-liquid separation by filtration is performed may be the first slurry with only a coagulant added.

[0125] In one embodiment, the solid may include lithium, nickel, cobalt, and manganese. Alternatively, the solid may further include chromium or aluminum. Alternatively, the solid may further include a carbon-based component and a fluorine-based component. The carbon-based component may be derived from a conductive material, etc. The fluorine-based component may be derived from a binder.

[0126] Next, the solvent can be recovered from the mother liquor (step S50), and the active metal can be recovered from the solid (step S60).

[0127] Alternatively, the active metal may be recovered first (step S60), and the solvent may be recovered (step S50). Alternatively, the solvent recovery step (step S50) and the active metal recovery step (step S60) may be performed simultaneously.

[0128] In one embodiment, the solvent recovery step (step S50) may include purifying a solvent, such as NMP, from the mother liquor. For example, a pretreatment process such as filtration to remove impurities from the mother liquor may be performed. The impurities may be substances other than the solvent, such as solid materials like binder fine particles or metal powder.

[0129] In the solvent recovery step according to one embodiment, the purity of the solvent can be increased through multi-stage distillation after the pretreatment. For example, when the solvent is NMP, since the boiling point of NMP is high and the boiling point of water (e.g., water inflow from the antisolvent or as an impurity) is low, two or more vacuum distillation columns can be used to remove the water-centered stream from the overhead and recover high concentration NMP from the bottom.

[0130] For example, the relatively higher boiling point by-product remaining at the bottom can be retained, and NMP can be recovered and re-condensed using evaporative steam.

[0131] For example, the mother liquor obtained according to one embodiment may be introduced into the purification process together with the NMP recovery liquid obtained from the NMP gas recovery process described above. Moisture may be primarily removed from the mixed stream of the mother liquor and the NMP recovery liquid to purify it, for example, to a purity of 90% by weight or higher, and then high-purity NMP with a purity of 99.5% by weight or higher may be obtained through methods such as multi-stage distillation.

[0132] However, the solvent recovery method is not limited to the method or process described above.

[0133] An active metal recovery step (step S60) according to one embodiment may include recovering the active metal by a wet process or a dry process.

[0134] In one embodiment, the method for recovering active metal by a wet process may include treating the solid after solid-liquid separation with an acid solution. In this case, a lithium precursor can be recovered from the solid through the acid solution treatment. Accordingly, the recovery efficiency of the lithium precursor can be further improved.

[0135] In one embodiment, the acid solution treatment may be a leaching process using an acidic extractant. For example, the acid solution treatment may extract a lithium precursor by mixing the solid with an acidic extractant diluted with a diluent and then adjusting the equilibrium pH. The transition metal may be extracted by mixing the solid from which the lithium precursor has been extracted with sulfuric acid, which is a stripping agent.

[0136] For example, the acidic extractant may include at least one selected from the group consisting of di-2-ethylhexylphosphoric acid, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester, a mixture of di-2-ethylhexylphosphoric acid and tri-butyl phosphate, and a mixture of 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester and tri-butyl phosphate.

[0137] For example, the above diluent may include a dearomatic hydrocarbon.

[0138] For example, the equilibrium pH may be about 5.5 to 6.5. The extraction rate of lithium can be effectively increased within the equilibrium pH range.

[0139] In one embodiment, transition metal-containing particles can be treated with an acid solution to form precursors in the form of acid salts of each transition metal. For example, sulfuric acid can be used as the acid solution. In this case, NiSO4, MnSO4, and CoSO4 can be recovered as transition metal precursors, respectively.

[0140] In one embodiment, the method for recovering active metal by a dry process can be carried out by the following process.

[0141] For example, the solid material after the solid-liquid separation described above may be heat-treated before being fed into the fluidized bed reactor or fixed-bed reactor described later. By removing or reducing impurities such as the conductive material and binder contained in the solid material through the heat treatment, the positive electrode active material (e.g., lithium-transition metal oxide) can be fed into the fluidized bed reactor with high purity.

[0142] The heat treatment temperature can be performed, for example, at about 100 to 500°C, preferably about 350 to 450°C. Within this range, the impurities can be substantially removed while preventing the decomposition and damage of the lithium-transition metal oxide.

[0143] In one embodiment, the solid can be introduced into a fluidized bed reactor or a fixed bed reactor and reduced to form a preliminary precursor mixture.

[0144] A reaction gas for converting the pre-precursor mixture into the fluidized bed reactor or fixed bed reactor may be supplied. According to exemplary embodiments, the reaction gas comprises a reducing gas, for example, hydrogen (H2) may be supplied.

[0145] In one embodiment, the lithium-transition metal oxide in the solid is reduced by the hydrogen gas to produce, for example, a preliminary lithium precursor including lithium hydroxide (LiOH) and lithium oxide (e.g., Li2O), and a transition metal or transition metal oxide. For example, Ni, Co, NiO, CoO, and MnO may be produced along with the lithium oxide by a reduction reaction.

[0146] The above reduction reaction can be carried out at about 400 to 700°C, preferably 450 to 550°C. Within the above reaction temperature range, the reduction reaction can be promoted without causing re-aggregation or recombination of the pre-lithium precursor and the transition metal / transition metal oxide.

[0147] In one embodiment, a carrier gas may be supplied into the fluidized bed reactor or the fixed bed reactor together with the reaction gas. For example, the carrier gas may include an inert gas such as nitrogen (N2) or argon (Ar).

[0148] For example, by the active metal recovery method described above, a preliminary precursor mixture comprising preliminary lithium precursor particles and transition metal-containing particles (e.g., said transition metal or transition metal oxide) may be formed. The preliminary lithium precursor particles may include, for example, lithium hydroxide, lithium oxide, and / or lithium carbonate. The preliminary lithium precursor particles may be recovered as a lithium precursor.

[0149] In one embodiment, the preliminary lithium precursor particles may be subjected to a water washing treatment. Through this washing treatment, the preliminary lithium precursor particles in the form of lithium hydroxide (LiOH) can be substantially dissolved in water and separated from the transition metal precursor for recovery. A lithium precursor substantially composed of lithium hydroxide can be obtained by using a crystallization process or the like to obtain the lithium hydroxide dissolved in water.

[0150] In one embodiment, preliminary lithium precursor particles in the form of lithium oxide and lithium carbonate can be substantially removed through the washing treatment. In one embodiment, preliminary lithium precursor particles in the form of lithium oxide and lithium carbonate can be converted at least partially into lithium hydroxide through the washing treatment.

[0151] In one embodiment, the preliminary lithium precursor particles can be reacted with a carbon-containing gas, such as carbon monoxide (CO) or carbon dioxide (CO2), to obtain lithium carbonate (e.g., Li2CO3) as a lithium precursor. A crystallized lithium precursor can be obtained through the reaction with the carbon-containing gas. For example, lithium carbonate can be collected by injecting the carbon-containing gas together during the washing process.

[0152] The crystallization reaction temperature using the carbon-containing gas may be, for example, in the range of about 60 to 150°C. In this temperature range, high-reliability lithium carbonate can be produced without damage to the crystal structure.

[0153] Subsequently, transition metal-containing particles can be recovered and treated with an acid solution to form precursors in the form of acid salts of each transition metal.

[0154] As described above, after collecting the lithium precursor through a dry process, the transition metal precursors are selectively extracted using an acid solution, thereby improving the purity and selectivity of each metal precursor.

[0155] In the following, embodiments of the present disclosure are further described with reference to specific experimental examples. The embodiments and comparative examples included in the experimental examples are merely illustrative of the present disclosure and do not limit the appended claims.

[0157] Example 1

[0158] A waste cathode active material slurry generated during a process step change in the cathode manufacturing process of a lithium secondary battery was prepared.

[0159] The above waste cathode active material slurry was allowed to naturally settle for 30 minutes, and the solid material (cathode active material) that settled to the bottom was recovered in the first stage.

[0160] After the above solid material was recovered, 100 ml of water was added to 400 ml of the remaining waste cathode active material slurry to prepare a first slurry, then 250 ppm of PAC (Poly Aluminum Chloride) was added and stirred at 180 rpm for 5 minutes. Subsequently, 10 ppm of a polymer-based coagulant (commercial polymer-based coagulant such as Nalco’s N855) was added and slowly stirred at 50 rpm for 10 minutes to prepare a second slurry.

[0161] Afterwards, the above second slurry was allowed to settle for 30 minutes to recover both the precipitate and the supernatant.

[0162] The above supernatant was mixed with the NMP recovery liquid obtained from the NMP gas recovery process and fed into the NMP purification process (multi-stage distillation facility).

[0163] After drying the above precipitate, transition metal precursors in the form of lithium, nickel, cobalt, and manganese sulfates were recovered by hydrogen reduction and sulfuric acid treatment.

[0165] Examples 2 to 6 and Comparative Examples 1 to 3

[0166] Examples 2 to 6 and Comparative Examples 1 to 3 were carried out in the same manner as Example 1, except that the addition of antisolvent, coagulant, and coagulant aid, the content, and the method of solid-liquid separation were different as shown in Table 1 below.

[0167] In the case of Examples 2 to 4, solid-liquid separation was performed by centrifuging at a speed of 3500 rpm for 5 minutes.

[0169] Antisolvent coagulant Coagulant aid High-value separation method type Content (Volume %) type Content (ppm) type Content (ppm) Example 1 water 20 PAC 250 Polymer system 10 precipitation Example 2 water 15 PAC 250 Polymer system 10 centrifugation Example 3 water 20 PFS 500 Polymer system 40 centrifugation Example 4 water 15 PFS 500 Polymer system 40 centrifugation Example 5 water 20 PAC 250 - - percolation Example 6 water 20 PAC 250 - - precipitation Comparative Example 1 - - PAC 250 Polymer system 10 precipitation Comparative Example 2 water 10 PAC 250 Polymer system 10 precipitation Comparative Example 3 water 20 - - Polymer system 10 precipitation

[0171] Experimental Example 1: Evaluation of solid-liquid separation status and solid-liquid separation rate

[0172] In the solid-liquid separation step of the active metal recovery method according to the examples and comparative examples, whether the material was separated into solids and mother liquor was evaluated.

[0173] In addition, the speed at which the solids and mother liquor were separated during the solid-liquid separation stage was evaluated and shown in the solid-liquid separation speed in Table 2 below.

[0175] Whether to separate high-value assets High-value separation speed Example 1 O speed Example 2 O speed Example 3 O speed Example 4 O speed Example 5 O speed Example 6 O slowness Comparative Example 1 X - Comparative Example 2 X - Comparative Example 3 X -

[0176] Referring to Table 2, in Examples 1 to 6, a first slurry was formed by adding an antisolvent to a waste cathode active material slurry such that the content of the antisolvent exceeded 10 volume% based on 100 volume% of the first slurry, and a second slurry was formed by adding a coagulant to the first slurry. In this case, solid-liquid separation occurred after the second slurry was formed, but in Comparative Examples 1 to 3, which did not satisfy at least one of the process conditions, solid-liquid separation did not occur even after a sufficient amount of time had elapsed.

[0177] In the case of Example 5, where a second slurry was formed using only a coagulant without a coagulant aid, fine particles coagulated due to the neutralization of charges with only the coagulant, forming aggregates of an appropriate size, and the aggregates were sufficiently filtered out by the filter during solid-liquid separation by filtration. However, in the case of Example 6, where only the solid-liquid separation method was changed to sedimentation under the conditions of Example 5, the size of the particles coagulated by the coagulant was small and the density was low, so solid-liquid separation by sedimentation occurred relatively slowly.

[0178] As such, it was confirmed that when the solid-liquid separation method is filtration, a coagulant aid is not essential, and when the solid-liquid separation method is sedimentation, using both a coagulant and a coagulant aid can improve the floc formation rate or the solid-liquid separation rate.

[0180] Experimental Example 2: Measurement of active metal content in mother liquor

[0181] The active metal content in the mother liquor after solid-liquid separation according to the examples and comparative examples was measured by ICP-OES (Agilent 700s) and is shown in Table 3 below. In the case of Example 6, which adopted precipitation using the solid-liquid separation method described above, the speed of solid-liquid separation was slower compared to Example 5, so the evaluation of the active metal content in the mother liquor was not performed.

[0183] Active metal content (weight ppm) in mother liquor Example 1 20 ppm or less Example 2 50 ppm or less Example 3 20 ppm or less Example 4 50 ppm or less Example 5 20 ppm or less Comparative Example 1 390 ppm or higher Comparative Example 2 390 ppm or higher Comparative Example 3 390 ppm or higher

[0184] Referring to Table 3, the content of the active metal in the mother liquor according to Examples 1 to 5 was detected to be low, at 20 ppm or less or 50 ppm or less. On the other hand, the content of the active metal in the mother liquor according to Comparative Examples 1 to 3 was detected to be high, at 390 ppm or more. That is, it can be seen that NMP can be effectively recovered from the mother liquor and the active metal can be effectively recovered from the solid by the active metal recovery method according to Examples 1 to 5.

[0186] Experimental Example 3: Observation of solid-liquid separation

[0187] According to Examples 1 and 2 and Comparative Example 2, which have different amounts of water added, the boundary between the solid and the mother liquor after solid-liquid separation and the occurrence of suspended solids were observed.

[0188] Figure 2 is a diagram showing the appearance of Comparative Example 2 and Examples 1 and 2 after solid-liquid separation.

[0189] Referring to Fig. 2, in the case of Comparative Example 2, where the water content was 10 volume%, solid-liquid separation did not occur.

[0190] In the case of Example 1, with a water content of 20 volume%, and Example 2, with a water content of 15 volume%, the boundary between the solids and the mother liquor was clearly visible to the naked eye. However, in the case of Example 2, with a water addition amount of 15 volume%, a small amount more suspended solids occurred compared to Example 1, with a water content of 20 volume%.

[0191] In other words, it can be seen that solid-liquid separation occurs when the antisolvent content exceeds 10 volume%, and solid-liquid separation occurs more effectively when the antisolvent content is 15 volume% or more, thereby recovering active metals with high purity and increasing the recovery rate of NMP from the mother liquor.

[0193] Experimental Example 4: Analysis of elements contained in mother liquor and solids

[0194] In the above-described Example 1, the results of analyzing the elements contained in the mother liquor and solids using an inductively coupled plasma analyzer (ICP-OES Agilent 700s) are shown in Table 4 below.

[0196] Detected component elements Lippm Nippm Coppm Mnppm Feppm Alppm Cwt% Fwt% Waste cathode active material slurry 11.1 58.6 17.6 0.9 2 1.2 - 0.02 Mother's fluid 17.6 <0.5 1.0 <0.5 <0.5 13.8 - <0.02 solids 890 6015 1375 80 430 5 57.4 11.3

[0197] Referring to Table 4 above, it can be seen that PVDF was separated into solids with high purity, as the fluorine in the mother liquor is below the detection limit. Additionally, since lithium, nickel, cobalt, manganese, aluminum, and carbon components were mostly detected in the solids, it can be seen that the active metals and conductive materials were mostly separated into solids.

Claims

Claim 1 A step of preparing a spent cathode active material slurry; a step of adding an anti-solvent to the spent cathode active material slurry to form a first slurry; a step of adding a coagulant to the first slurry to form a second slurry; a step of separating the second slurry into solids and a mother liquor by solid-liquid separation; and a step of recovering a solvent from the mother liquor. A method for recovering an active metal of a lithium secondary battery, comprising the step of recovering an active metal from the solid, wherein in the step of forming the first slurry, the antisolvent is added to the waste cathode active material slurry such that the content of the antisolvent exceeds 10 volume% based on 100 volume% of the first slurry, and further adding a flocculant after adding the flocculant to the first slurry, or adding the flocculant together with the flocculant to form the second slurry, wherein the weight ratio of the added flocculant and the flocculant is 4:1 to 200:

1. Claim 2 delete Claim 3 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein the antisolvent comprises water and the solvent comprises NMP (N-Methyl-2-pyrrolidone). Claim 4 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein the solid-liquid separation comprises performing at least one of precipitation, centrifugation, and filtration with respect to the second slurry. Claim 5 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein the coagulant comprises at least one of an aluminum-based coagulant, an iron-based coagulant, a silicon-based coagulant, and a magnesium-based coagulant. Claim 6 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein the aggregation aid comprises at least one of a polymer-based aggregation aid and bentonite. Claim 7 A method for recovering active metal of a lithium secondary battery according to claim 6, wherein the polymer-based aggregation aid comprises at least one selected from the group consisting of cationic polymers, anionic polymers, nonionic polymers, and natural polymers. Claim 8 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein, in the step of forming the first slurry, the antisolvent is added to the waste cathode active material slurry such that the content of the antisolvent is 15 volume% or more based on 100 volume% of the first slurry. Claim 9 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein solid-liquid separation of the second slurry is performed by precipitation. Claim 10 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein the content of the solvent is 80 volume% or more based on the total volume% of the mother liquor. Claim 11 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein the waste anode active material slurry comprises a waste anode active material, a binder, and the solvent. Claim 12 A method for recovering active metal of a lithium secondary battery according to claim 11, wherein the solid comprises the binder. Claim 13 A method for recovering active metal of a lithium secondary battery according to claim 12, wherein the antisolvent comprises water and the binder comprises poly(vinylidene fluoride). Claim 14 A method for recovering an active metal of a lithium secondary battery according to claim 1, wherein the active metal comprises lithium, nickel, cobalt, and manganese. Claim 15 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein the coagulant is added at a concentration of 200 ppm to 1000 ppm based on the weight of the waste anode active material slurry. Claim 16 A method for recovering active metal of a lithium secondary battery according to claim 1, wherein the aggregation aid is added in an amount of 5 ppm to 50 ppm based on the weight of the waste anode active material slurry. Claim 17 delete

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