Method for recycling positive electrode active material, recycled positive electrode active material prepared by method, and secondary battery including same

Abstract

The invention discloses a method for recycling a positive electrode active material, a recycled positive electrode active material prepared by the method, and a secondary battery including the recycled positive electrode active material. More specifically, the present invention relates to a method for recycling a positive electrode active material, a recycled positive electrode active material prepared by the method, and a secondary battery including the recycled positive electrode active material, the method comprising: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 DEG C to 650 DEG C; thermally decomposing the binder and the conductive material in the positive electrode active material layer to recover the positive electrode active material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material and annealing at 400 DEG C to 1000 DEG C in an oxygen atmosphere; and washing the annealed positive electrode active material. According to the recycling method of the positive electrode active material, waste water can be greatly reduced, residual lithium on the surface of the positive electrode active material can be reduced, and the positive electrode active material shows excellent resistance and service life characteristics. In addition, since no acid is used in the recovery and regeneration processes, the method is environmentally friendly; as neutralization and wastewater treatment are not needed, the process cost can be reduced; as the positive electrode active material in the method is not decomposed and is directly regenerated, waste metal elements are not generated; no organic solvent is used in the method, so that the danger of generating toxic gas or exploding does not exist; especially, since the method omits a washing process, economic feasibility and productivity are significantly improved.

Description

Technical Field

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS)

[0002] This application claims priority from Korean Patent Application No. 10-2023-0094928 filed on July 20, 2023, and Korean Patent Application No. 10-2024-0087611 filed on July 3, 2024, both filed in the Korean Intellectual Property Office, the disclosures of each of which are incorporated herein by reference.

[0003] The present invention relates to a method for recycling positive electrode active materials, a recycled positive electrode active material prepared using the method, and a secondary battery including the recycled positive electrode active material. More specifically, the method relates to a method for recycling positive electrode active materials, comprising: immediately adding a lithium precursor after calcining a spent positive electrode at a predetermined temperature without performing a washing process, annealing the waste positive electrode under an oxygen atmosphere, and then removing residual lithium from the positive electrode active material with a small amount of washing liquid, thereby significantly reducing wastewater and residual lithium on the surface of the positive electrode active material, resulting in the positive electrode active material exhibiting excellent resistance and lifespan characteristics. Furthermore, since no acid is used in the recycling and regeneration process, the method is environmentally friendly; since neutralization and wastewater treatment are not required, process costs can be reduced; since the positive electrode active material is directly regenerated without decomposition, no waste metal elements are generated; since no organic solvent is used, there is no risk of generating toxic gases or explosions; and, in particular, since the washing process is omitted, economic feasibility and productivity are significantly improved. Background Art

[0004] Generally speaking, a lithium secondary battery is composed of: a positive electrode formed by coating a positive electrode active material layer on a metal foil such as aluminum; a negative electrode formed by coating a negative electrode active material layer on a metal foil such as copper; a separator for preventing the positive electrode and the negative electrode from mixing; and an electrolyte that enables lithium ions to move between the positive electrode and the negative electrode.

[0005] In the positive electrode active material layer, lithium-based oxides are mainly used as active materials. In the negative electrode active material layer, carbon materials are mainly used as active materials. Generally, lithium-based oxides contain rare metals such as cobalt, nickel, and manganese. Therefore, people are actively researching the recovery and regeneration of rare metals from the positive electrodes of discarded lithium secondary batteries after use or the positive electrode waste generated during the manufacture of lithium secondary batteries (hereinafter referred to as "waste positive electrodes").

[0006] According to the relevant technology for recovering rare metals from waste positive electrodes, the waste positive electrodes are dissolved with hydrochloric acid, sulfuric acid or nitric acid, and rare metals such as cobalt, manganese, and nickel are extracted with organic solvents. The extracted metals are then used as raw materials for synthesizing positive electrode active materials.

[0007] However, acid extraction of rare metals requires neutralization and wastewater treatment due to environmental pollution, significantly increasing process costs. Furthermore, lithium, the primary metal in the positive electrode active material, cannot be recovered through these methods.

[0008] To address these shortcomings, researchers are studying methods for directly recycling the cathode active materials from spent cathodes without decomposing them (direct recycling methods). These methods primarily include calcination, solvent dissolution, aluminum (Al) foil dissolution, and pulverization and screening.

[0009] The calcination method is simple, but has disadvantages such as the formation of foreign matter on the surface of the recycled positive electrode active material, which reduces the battery's rate performance. In addition to the above disadvantages, it also produces waste gas and consumes too much energy.

[0010] Furthermore, the solvent dissolution method can produce recycled cathode active materials with relatively clean surfaces. However, since the solvents used to dissolve the binder (such as N-methyl-2-pyrrolidone (NMP)) are toxic gases and pose an explosion hazard, this method has poor stability and requires expensive solvent recovery processes.

[0011] In addition, the aluminum foil dissolution method has good process stability, low process cost, and easy binder removal. However, foreign matter that is difficult to remove forms on the surface of the regenerated positive electrode active material, and hydrogen is generated during the removal of the aluminum foil, which poses an explosion risk.

[0012] Finally, the crushing and screening method can be performed using the simplest process of the above methods. However, it is difficult to completely separate the current collector from the positive electrode active material, the particle size distribution of the positive electrode active material will change during the crushing process, and the battery characteristics of the recycled positive electrode active material will deteriorate due to residual binder.

[0013] Therefore, there is an urgent need to develop a method to regenerate cathode active materials with improved battery performance safely and at low cost through a simple process in an environmentally friendly manner without losing the metal elements in the spent cathode. Summary of the Invention

[0014]

Technical Issues

[0015] Therefore, the present invention is made precisely to address the above-mentioned problems. One of the purposes of the present invention is to provide a method for recycling positive electrode active materials. The method comprises: calcining a waste positive electrode at a predetermined temperature, not immediately adding a lithium precursor and not performing a washing step, and annealing the waste positive electrode in an oxygen atmosphere, and then removing the residual lithium in the positive electrode active material with a small amount of washing liquid. This significantly reduces wastewater and the amount of lithium remaining on the surface of the positive electrode active material, allowing the positive electrode active material to exhibit excellent resistance and life characteristics. In addition, since no acid is used in the recycling and regeneration process of the positive electrode active material, the method is environmentally friendly; since neutralization and wastewater treatment are not required, process costs can be reduced; since the positive electrode active material is directly regenerated without decomposition, no waste metal elements are generated; since no organic solvent is used, there is no risk of generating toxic gases or explosions; and in particular, since the washing step is omitted, economic feasibility and productivity are significantly improved.

[0016] Another object of the present invention is to provide a secondary battery having excellent initial discharge capacity, rate capability, and capacity characteristics.

[0017] The above and other objects can be achieved by the present disclosure described below.

[0018]

Technical solution

[0019] According to one aspect of the present invention, the above and other purposes can be achieved by providing 1) a method for recycling positive electrode active materials, the method comprising: heat treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300°C to 650°C to thermally decompose the binder and the conductive material in the positive electrode active material layer, thereby recovering the positive electrode material in the positive electrode material layer; adding a lithium precursor to the recovered positive electrode active material and annealing it at 400°C to 1000°C under an oxygen atmosphere; and washing the annealed positive electrode active material.

[0020] II) In I), the positive electrode active material layer may preferably contain 60 mol% or more of Ni based on 100 mol% of the total amount of other metals except Li.

[0021] III) In I) or II), the positive electrode active material recovered after thermal decomposition may be annealed preferably without washing.

[0022] IV) In I) to III), during the annealing process, the recovered positive electrode active material may preferably contain crystalline LiF.

[0023] V) In I) to IV), during the annealing process, oxygen gas may be preferably supplied at 1 L / min to 20 L / min.

[0024] VI) In I) to V), the purity of oxygen may preferably be 59% or higher.

[0025] VII) In I) to VI), the oxygen atmosphere may preferably contain no carbon dioxide (CO2).

[0026] VIII) In I) to VII), the lithium precursor may preferably comprise one or more of LiOH, Li2CO3, LiNO3 and Li2O.

[0027] IX) In I) to VIII), when the total amount of lithium contained in the recovered positive electrode active material is 100 mol %, the amount of the lithium precursor added may preferably be 1 mol % to 40 mol %.

[0028] X) In I) to IX), during the washing process, the weight ratio of the annealed positive electrode active material to the washing liquid may preferably be 1:0.5 to 1:4.

[0029] XI) In I) to X), the amount of Li2CO3 remaining in the positive electrode active material after washing may preferably be 0.17 wt% or less.

[0030] XII) In I) to XI), the method for recycling the positive electrode active material may preferably include surface coating the washed positive electrode active material to obtain a reusable positive electrode active material.

[0031] XIII) In the surface coating described in I) to XII), one or more of the metal, organometallic and carbon components may preferably be coated on the surface in a solid phase or liquid phase and then heat treated at 100°C to 1200°C.

[0032] According to another aspect of the present invention, there is provided XIV) a recycled positive electrode active material produced by the method for recycling the positive electrode active material according to I) to XIII).

[0033] According to another aspect of the present invention, there is provided XV) a recycled positive electrode active material, wherein the recycled positive electrode active material is one or more selected from the group consisting of: lithium nickel oxide (LNO)-based positive electrode active material, nickel·cobalt·manganese (NCM)-based positive electrode active material, nickel·cobalt·aluminum (NCA)-based positive electrode active material, nickel·cobalt·manganese·aluminum (NCMA)-based positive electrode active material, and contains crystalline LiF, and the amount of Li2CO3 remaining in the recycled positive electrode active material is 0.17 wt% or less.

[0034] XVI) In XV), the recycled positive electrode active material may preferably contain 60 mol% or more of Ni based on 100 mol% of the total amount of other metals except Li.

[0035] XVII) In XV) or XVI), the reused positive electrode active material may preferably be surface-coated with a coating agent containing metal or carbon.

[0036] According to still another aspect of the present invention, there is provided XVIII) a secondary battery comprising the recycled positive electrode active material of XIV) to XVII).

[0037] Beneficial effects

[0038] According to the present invention, a method for recycling positive electrode active materials is provided. The method comprises calcining a spent positive electrode at a predetermined temperature, immediately adding a lithium precursor without washing, annealing the spent positive electrode in an oxygen atmosphere, and then cleanly removing the residual lithium in the positive electrode active material with a small amount of washing liquid. This method significantly reduces wastewater and the amount of lithium remaining on the surface of the positive electrode active material, resulting in the positive electrode active material exhibiting excellent resistance and lifespan characteristics. Furthermore, since no acid is used in the recycling and regeneration of the positive electrode active material, the method is environmentally friendly; since neutralization and wastewater treatment are not required, process costs can be reduced; since the positive electrode active material is directly regenerated without decomposition, no waste metal elements are generated; and since no organic solvent is used, there is no risk of toxic gas generation or explosion. In particular, since the post-calcination process of the spent positive electrode is omitted, economic efficiency and productivity are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The following drawings attached to this specification illustrate embodiments of the present invention, and the technical concept of the present invention can be further understood in conjunction with the specific embodiments described below. Therefore, the present invention is not limited to these drawings.

[0040] Figure 1 A diagram showing positive electrode scrap discarded after electrode plates are cut from a positive electrode sheet.

[0041] Figure 2 SEM images of the recycled positive electrode active materials produced in Example 1 and Comparative Example 1 are shown.

[0042] Figure 3 The capacity retention (%) and resistance increase (%) after charge / discharge cycles on coin half cells (CHCs) using the recycled positive active materials manufactured in Examples 1 and 2 and Comparative Examples 1 to 3 are shown as a function of the number of cycles.

[0043] Figure 4 A flow chart showing a regeneration process of the positive electrode active material of the present invention. DETAILED DESCRIPTION

[0044] The present inventors, focusing on methods for directly reusing positive electrode active materials from spent positive electrodes without decomposing them, have studied methods for improving the electrochemical, resistance, and capacity characteristics of the recycled positive electrode active materials. Their research has confirmed that by adding a lithium precursor immediately after calcining the spent positive electrode at a predetermined temperature without performing a washing step, annealing the spent positive electrode in an oxygen atmosphere, and then washing to remove residual lithium from the surface of the positive electrode active material, the amount of residual lithium on the surface of the positive electrode active material can be reduced, and the residual lithium can be cleanly removed with a small amount of washing liquid, thereby significantly reducing wastewater and improving the battery characteristics of the recycled positive electrode active material. Based on these results, the present inventors conducted further research and ultimately completed the present invention.

[0045] Hereinafter, the method for recycling a cathode active material of the present invention, the recycled cathode active material prepared using the method, and a secondary battery including the recycled cathode active material will be described in detail.

[0046] The terms and words used in this specification and the appended claims should not be interpreted as being limited to their ordinary meanings or dictionary meanings, but should be interpreted as having meanings and concepts that match the technical spirit of the present invention so as to describe the present invention in the best possible way. In addition, since the configurations shown in the embodiments and drawings of this specification are merely embodiments of the present invention and do not represent the entire technical spirit of the present invention, it should be understood that there are many equivalents and variations that can replace the above-mentioned configurations, and the present invention can be arranged, replaced, combined, separated or designed in various other configurations.

[0047] Unless defined otherwise, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0048] Method for recycling positive electrode active materials

[0049] The present invention's method for recycling positive electrode active materials includes the following steps: heat-treating a spent positive electrode having a positive electrode active material layer formed on a current collector at 300°C to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material and annealing it at 400°C to 1000°C under an oxygen atmosphere; and washing the annealed positive electrode active material. This method significantly reduces wastewater production, reduces residual lithium on the surface of the positive electrode active material, and exhibits excellent resistance and lifespan characteristics. Furthermore, since no acid is used in the recycling process of the positive electrode active material, the method is environmentally friendly. Neutralization and wastewater treatment are not required, reducing process costs. Since the positive electrode active material is directly regenerated without decomposition, no waste metal elements are generated. Since no organic solvent is used, there is no risk of toxic gas generation or explosion. In particular, since the washing step is omitted, economic feasibility and productivity are significantly improved.

[0050] The following will explain in detail the recycling method of the positive electrode active material step by step.

[0051] (a) Step of recovering positive electrode active material from spent positive electrode

[0052] According to the present invention, step (a) of recovering the positive electrode active material from the waste positive electrode can preferably be a step of heat-treating the waste positive electrode having a positive electrode active material layer formed on a current collector at 300°C to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer. In this case, the process can be simplified, and the binder, conductive material, and current collector can be cleanly removed.

[0053] The waste positive electrode can preferably be a positive electrode separated from a discarded lithium secondary battery after use, or a defective positive electrode sheet or positive electrode waste generated in the process of manufacturing a lithium secondary battery, more preferably a positive electrode waste remaining after punching a positive electrode sheet to obtain a positive electrode plate.

[0054] The positive electrode active material layer of step (a) preferably includes a positive electrode active material, a binder, and a conductive material.

[0055] The positive electrode active material may preferably include one or more selected from the group consisting of: lithium cobalt oxides, such as LiCoO2 (hereinafter referred to as "LCO"); lithium manganese oxides, such as LiMnO2 or LiMn2O4; lithium iron phosphate compounds, such as LiFePO4; lithium nickel cobalt aluminum oxides (NCA); lithium nickel oxides, such as LiNiO2; nickel-manganese-based lithium composite metal oxides obtained by substituting part of nickel (Ni) in lithium nickel oxide with manganese (Mn); and NCM-based lithium composite transition metal oxides obtained by substituting part of nickel (Ni) in lithium nickel oxide with manganese (Mn) and cobalt (Co). More preferably, the positive electrode active material may be a nickel-manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof. In this case, the reversible capacity and thermal stability may be more excellent.

[0056] As another specific example, the positive electrode active material may include a compound represented by the following Chemical Formula 1:

[0057] [Chemical Formula 1]

[0058] Li a Ni x Mn y Co z M w O 2+δ

[0059] In Chemical Formula 1, M includes one or more selected from the group consisting of: B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.

[0060] For example, based on 100 mol% of the total amount of other metals except Li, the content of Ni in the positive electrode active material may be 60 mol% or more, preferably 80 mol% or more. Within this range, the initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics may be excellent.

[0061] In the present disclosure, the Ni content can be measured by ion chromatography (IC) commonly used in the technical field to which the present invention pertains. As a specific example, an inductively coupled plasma (IC-ICP) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AEC analyzer can be used.

[0062] For example, the conductive material may be a carbon-based conductive material, preferably carbon black, carbon nanotubes (CNT), or a mixture thereof.

[0063] For example, the binder may be a polymer binder, preferably polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR) or a mixture thereof, more preferably polyvinylidene fluoride.

[0064] The heat treatment can be performed in an air atmosphere or an oxygen atmosphere, preferably in an oxygen atmosphere. In this case, since the binder and the conductive material are thermally decomposed into CO2 and H2O, the positive electrode active material can be separated from the current collector, and the separated positive electrode active material can be easily selected in the form of a powder.

[0065] The purity of oxygen can be, for example, 59% or more, preferably 70% or more, more preferably 80% or more, more preferably 90% or more, and even more preferably 90% to 99%. Within this range, the binder and conductive material can be completely removed, which can improve the stability of Ni in the active material.

[0066] The purity (%) of oxygen can be expressed in volume % or mole %.

[0067] The purity of oxygen in the present invention can be measured using a commonly used measurement method in the technical field to which the present invention belongs, without any particular limitation.

[0068] The oxygen atmosphere may not contain, for example, carbon dioxide (CO 2 ). In this case, the positive electrode active material can be easily separated from the current collector, and the separated positive electrode active material can be easily selected in a powder form.

[0069] In addition to oxygen, the oxygen atmosphere may also contain, for example, argon. In this case, the positive electrode active material can be easily separated from the current collector, and the separated positive electrode active material can be easily selected in the form of powder.

[0070] The oxygen supply rate may be, for example, 1 L / min to 20 L / min, preferably 3 L / min to 17 L / min, more preferably 5 L / min to 15 L / min, and more preferably 7 L / min to 13 L / min. Within this range, the positive electrode active material can be easily separated from the current collector, and the separated positive electrode active material can be easily selected in powder form.

[0071] The heat treatment temperature may be preferably 400 to 600° C., more preferably 500 to 600° C., and further preferably 530 to 600° C. Within this range, the positive active material can be easily separated from the current collector because the current collector is not melted but only the binder is removed.

[0072] The heat treatment time is preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, further preferably 30 minutes to 2 hours, and further preferably 30 minutes to 1 hour. Within this range, the positive electrode active material can be easily separated from the current collector because the current collector does not melt but only removes the binder.

[0073] In the present invention, the heat treatment time refers to the time for heat treatment at the corresponding heat treatment temperature, and does not include the time required to reach the corresponding heat treatment temperature.

[0074] The heat treatment can be performed at a heating rate of, for example, 1°C / min to 20°C / min, preferably 3°C / min to 10°C / min, and more preferably 3°C / min to 7°C / min. Within this range, the heat treatment can be performed without burdening the heat treatment equipment, and thermal shock to the positive electrode waste can be prevented.

[0075] Down Figure 1 Shown is the positive electrode scrap discarded after cutting the positive electrode sheet to obtain the positive electrode plates.

[0076] See also Figure 1 A positive electrode active material layer 20 containing a positive electrode active material, a conductive material, and a binder is coated on an aluminum foil 10, which serves as a long sheet of positive electrode current collector, to produce a positive electrode sheet 30. The positive electrode sheet 30 is then punched out to a predetermined size to produce a positive electrode plate 40. The remaining portion after punching is positive electrode scrap 50. Punching is a method of cutting the positive electrode sheet.

[0077] Furthermore, the positive electrode active material layer 20 is formed by coating the aluminum foil 10 with a slurry containing a mixture of the positive electrode active material, a conductive material, a binder, and a solvent. Because the slurry is highly sensitive to environmental factors such as temperature, determining the coating conditions is difficult. Consequently, until the conditions for producing positive electrode sheets 30 of the desired quality are determined through predetermined tests, waste positive electrode sheets are generated.

[0078] For reference, in the following examples, cathode scrap was used as the spent cathode.

[0079] Preferably, the positive electrode active material that has been thermally decomposed and then recovered can be directly annealed without washing. In this case, since the washing process is omitted, economic feasibility and productivity are significantly improved, and since crystalline LiF is contained, battery performance can be improved.

[0080] (b) Adding a lithium precursor to the recovered positive electrode active material and performing annealing

[0081] The method for recycling positive electrode active materials of the present invention includes the step of (b) adding a lithium precursor to the recovered positive electrode active material and annealing the recovered positive electrode active material under an oxygen atmosphere. Annealing the recovered positive electrode active material under an oxygen atmosphere can reduce residual lithium on the surface of the positive electrode active material. This can improve the battery characteristics of the recovered positive electrode active material due to improved crystallinity, such as increased crystallinity or restored crystal structure. Furthermore, since the recovered positive electrode active material does not undergo a washing process, economic feasibility and productivity can be significantly improved.

[0082] The recovered positive electrode active material may preferably contain crystalline LiF. In this case, since a positive electrode active material having excellent initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics can be provided, from the perspective of improving battery characteristics, it is preferred to directly add a lithium precursor to the recovered positive electrode active material without washing and then perform annealing.

[0083] In the annealing step, oxygen gas may be supplied at, for example, 1 L / min to 20 L / min, preferably 3 L / min to 15 L / min, more preferably 3 L / min to 10 L / min, and even more preferably 3 L / min to 7 L / min. Within this range, the amount of lithium remaining on the surface of the positive electrode active material can be reduced, and improvements in crystallinity such as increased crystallinity or restoration of the crystal structure can be achieved.

[0084] The purity of oxygen can be, for example, 59% or more, preferably 70% or more, more preferably 80% or more, more preferably 90% or more, and even more preferably 90% to 99%. Within this range, the amount of lithium remaining on the surface of the positive electrode active material can be reduced, and excellent crystallinity improvement such as increased crystallinity or restoration of the crystal structure can be achieved.

[0085] The oxygen atmosphere may not contain, for example, carbon dioxide (CO 2 ). In this case, contact with carbon dioxide can be suppressed, thereby reducing the amount of lithium remaining on the surface of the positive electrode active material.

[0086] The oxygen atmosphere may contain, for example, argon as a component other than oxygen. In this case, it is possible to achieve improved crystallinity of the positive electrode active material, such as increased crystallinity or restoration of the crystal structure.

[0087] The lithium precursor may preferably include one or more selected from LiOH, Li2CO3, LiNO3, and Li2O.

[0088] Based on the amount of lithium in the recovered positive active material, the amount of lithium precursor added may preferably correspond to the amount of lithium reduced based on the molar ratio of lithium in the positive active material in step (a). More preferably, based on the molar ratio of lithium in the positive active material in step (a), the amount of lithium precursor added corresponds to a lithium molar ratio of 0.0001 to 0.2. Within this range, by supplementing lithium in the recovered positive active material, the crystallinity can be increased, or the crystal structure can be restored, thereby improving crystallinity. Therefore, the battery characteristics of the recovered positive active material can be improved.

[0089] When the total amount of lithium contained in the recovered positive electrode active material is 100 mol%, the amount of lithium precursor added is preferably 1 mol% to 40 mol%, more preferably 1 mol% to 25 mol%, further preferably 1 mol% to 17 mol%, even more preferably 3 mol% to 17 mol%, and particularly preferably 7 mol% to 15 mol%. Within this range, the battery characteristics can be improved because there is no residual precursor that increases the resistance of the recovered positive electrode active material.

[0090] The annealing temperature can be adjusted within a limited range depending on the melting point of the lithium precursor. For example, Li2CO3 can be annealed at a melting point of 723°C, preferably 700°C to 900°C, more preferably 700°C to 800°C, and even more preferably 710°C to 780°C. LiOH can be annealed at a melting point of 462°C, preferably 400°C to 720°C, more preferably 420°C to 700°C, even more preferably 450°C to 700°C, even more preferably 450°C to 600°C, and particularly preferably 450°C to 480°C. Within this range, the crystal structure can be restored, resulting in excellent rate performance of the battery.

[0091] The annealing temperature may preferably be a temperature exceeding the melting point of the lithium precursor. However, when the annealing temperature exceeds 1000°C, thermal decomposition of the positive electrode active material may occur, resulting in a decrease in battery performance. Therefore, the annealing temperature is preferably 1000°C or less.

[0092] The annealing time may be, for example, 1 hour or longer, preferably 1 to 15 hours, more preferably 4 to 13 hours, and even more preferably 6 to 12 hours. Within this range, the crystal structure can be restored, thus providing excellent rate performance of the battery.

[0093] The amount of residual Li2CO3 in the positive electrode active material after annealing may be, for example, 1.34 wt% or less, preferably 1.10 wt% or less, more preferably 0.95 wt% or less, and more preferably 0.1 wt% to 0.95 wt%. Within this range, the positive electrode active material exhibits excellent resistance and lifespan characteristics.

[0094] The amount of LiOH remaining in the positive electrode active material after annealing may be, for example, 1.0 wt % or less, preferably 0.1 wt % to 1.0 wt %. Within this range, the positive electrode active material has excellent resistance and life characteristics.

[0095] In the positive electrode active material after annealing, the total amount of residual Li2CO3 and residual LiOH can be, for example, 2.22 wt% or less, preferably 2.0 wt% or less, more preferably 1.90 wt% or less, and more preferably 0.1 wt% to 1.90 wt%. Within this range, the positive electrode active material has excellent resistance and life characteristics.

[0096] In the present disclosure, a pH titrator (T5, Mettler Toledo) can be used to measure the amount of LiOH and Li2CO3 remaining on the surface of the positive electrode active material. Specifically, 5g of the positive electrode active material is dispersed in 100ml of distilled water, mixed at a speed of 500rpm for 5 minutes, and then filtered to filter out the active material and obtain a filtrate. The filtrate is titrated with 0.1M HCl solution to measure the change in pH value. A pH titration curve is obtained based on the measurement results. The amount of LiOH and Li2CO3 remaining in the positive electrode active material is calculated using the pH titration curve.

[0097] (c) Washing the annealed positive electrode active material

[0098] The method for recycling positive electrode active materials of the present invention includes step (c): washing the annealed positive electrode active material with a washing solution. In this case, a small amount of washing solution can be used to remove residual lithium precursor from the positive electrode active material. Consequently, in subsequent processes, battery performance degradation and gas generation caused by the reaction of residual lithium precursor with the electrolyte can be prevented, and wastewater production can be significantly reduced.

[0099] The washing step may preferably include filtering the annealed positive electrode active material after mixing it with a washing liquid, and drying the solid positive electrode active material obtained after filtering. In this case, excess lithium remaining in the positive electrode active material can be effectively removed.

[0100] The drying temperature may be preferably 100° C. to 500° C., more preferably 120° C. to 400° C., further preferably 120° C. to 300° C., and even more preferably 120° C. to 200° C. Within this range, residual Li can be effectively removed.

[0101] Drying can preferably be performed by vacuum drying.

[0102] In the present disclosure, the present invention may use a vacuum drying method commonly used in the technical field to which the present invention belongs without particular limitation.

[0103] During washing, the weight ratio of the annealed positive electrode active material to the washing liquid can be, for example, 1:0.5 to 1:4, preferably 1:0.5 to 1:3, more preferably 1:0.5 to 1:2, and even more preferably 1:0.5 to 1:1.5. Within this range, the amount of washing liquid can be greatly reduced, eliminating the need for wastewater treatment, and lithium precursors that may remain in the positive electrode active material, such as LiOH and Li2CO3, can be effectively removed. Typically, the positive electrode active material recovered after heat treatment of the spent positive electrode is washed and then annealed. In this case, in order to remove the residual lithium in the washing step, a washing liquid of at least 30 times the weight of the positive electrode active material is required. However, in the present invention, the recovered positive electrode active material is directly annealed without washing and then washed, so the residual lithium can be easily removed with only a small amount of washing liquid. As a result, wastewater can be significantly reduced, and the removal efficiency of residual lithium is better than that of the existing situation.

[0104] The washing liquid can preferably be water or an aqueous alkaline lithium compound solution, preferably water. In this case, the lithium precursor (such as LiOH, Li2CO3) remaining on the surface of the positive electrode active material can be completely removed with a small amount of washing liquid. This can greatly reduce wastewater and significantly improve the rate performance of the battery.

[0105] The water is preferably distilled water or deionized water. In this case, the lithium precursors (such as LiOH and Li2CO3) remaining on the surface of the positive electrode active material can be completely removed with a small amount of detergent. This can greatly reduce wastewater and significantly improve the rate performance of the battery.

[0106] The alkaline lithium compound aqueous solution preferably includes greater than 0% by weight and less than 15% by weight of the lithium compound, more preferably greater than 0% by weight and less than 10% by weight of the lithium compound. In this case, the lithium precursor (such as LiOH, Li2CO3) remaining on the surface of the positive electrode active material can be completely removed with a small amount of washing liquid. This can greatly reduce wastewater and significantly improve the rate performance of the battery.

[0107] The mixing of the annealed positive electrode active material and the washing liquid is preferably performed by stirring. The stirring is not particularly limited, and for example, it can be impeller stirring, magnetic stirring, or ultrasonic stirring.

[0108] The stirring time is preferably within 30 minutes, more preferably within 20 minutes, more preferably within 15 minutes, and more preferably within 5 to 10 minutes. Within this range, residual lithium can be effectively removed.

[0109] In the washed positive electrode active material, the amount of residual Li2CO3 can be, for example, 0.17 wt% or less, preferably 0.15 wt% or less, more preferably 0.13 wt% or less, and more preferably 0.05 wt% to 0.13 wt%. Within this range, the positive electrode active material has excellent resistance and life characteristics.

[0110] The amount of residual LiOH in the washed positive electrode active material may be, for example, 0.42 wt % or less, preferably 0.39 wt % or less, and more preferably 0.05 wt % to 0.39 wt %. Within this range, the positive electrode active material exhibits excellent resistance and lifespan characteristics.

[0111] In the washed positive electrode active material, the total amount of residual Li2CO3 and residual LiOH can be, for example, 0.054 wt% or less, preferably 0.052 wt% or less, and more preferably 0.05 wt% to 0.052 wt%. Within this range, the positive electrode active material has excellent resistance and life characteristics.

[0112] (d) Obtaining a reusable positive electrode active material by coating the surface of the washed positive electrode active material

[0113] The method for recycling a positive electrode active material of the present invention optionally includes step (d): coating the surface of the washed positive electrode active material to obtain a reusable positive electrode active material. In this case, the structural stability and electrochemical performance of the positive electrode active material can be improved while maintaining the inherent properties of the positive electrode active material.

[0114] When coating the surface, preferably, the surface may be coated with a coating agent containing one or more of a metal, an organic metal, and a carbon component in a solid phase or a liquid phase, and then heat treated at 100° C. to 1200° C., more preferably 200° C. to 1000° C., and still more preferably 250° C. to 800° C. In this case, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0115] The metal-containing coating agent may preferably be a coating agent containing one or more selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V, and Y. More preferably, it is a coating agent containing one or more selected from the group consisting of B, W, Al, Ti, and Mg. Further preferably, it is a coating agent containing boron (B), tungsten (W), or a mixture thereof. Further preferably, it is a coating agent containing tungsten (W) and boron (B). A specific example thereof is a coating agent containing tungsten boride (WB). In this case, the resistance characteristics and life characteristics can be improved.

[0116] For example, the coating agent containing a metal may be an oxide or an acid or the like containing a metal as an element in its molecule.

[0117] As the coating agent containing an organic metal, a coating agent containing an organic metal compound containing a metal commonly used in the field to which the present invention pertains can be used without particular limitation. As a specific example, a metal alkoxide can be used.

[0118] As the coating agent containing a carbon component, any carbon-containing coating agent commonly used in the art to which the present invention pertains can be used without particular limitation. Specific examples thereof include sugars such as sucrose.

[0119] For example, based on the components coated on the surface of the positive electrode active material excluding the solvent, the content of the coating agent can be 0.001 mol % to 0.3 mol %, preferably 0.01 mol % to 0.3 mol %, more preferably 0.01 mol % to 0.15 mol %, further preferably 0.01 mol % to 0.1 mol %, and further preferably 0.01 mol % to 0.05 mol %. Within this range, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0120] The heat treatment temperature may be preferably 100 to 1,000° C., more preferably 200 to 1,000° C., and further preferably 200 to 500° C. Within this range, performance degradation due to thermal decomposition of the positive electrode active material may be prevented, and structural stability and electrochemical performance may be improved.

[0121] The heat treatment time is preferably 1 to 16 hours, more preferably 3 to 7 hours. Within this range, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0122] The coating method of the present invention can be any coating method commonly used in the field to which the present invention belongs, without particular limitation. For example, a liquid method of mixing a positive electrode active material with a liquid coating agent, a mechanochemical method utilizing the high mechanical energy of ball milling, a fluidized bed coating method, a spray drying method, a precipitation method of precipitating a coating agent onto the surface of a positive electrode active material in an aqueous solution, a method utilizing a reaction between a vapor phase coating agent and a positive electrode active material, or a sputtering method can be employed.

[0123] For example, the metal, organometallic, and carbon components may have a spherical, plate-like, square, or needle-like shape. Such shapes can be controlled, for example, by varying the process conditions during the preparation process. The shapes are not particularly limited, as long as they conform to generally accepted definitions in the art to which the present invention pertains.

[0124] The coating agent preferably has an average diameter of 1 nm to 1000 nm and a diameter of 10 nm.2 / g to 100m 2 / g specific surface area, more preferably having an average diameter of 10nm to 100nm and 20m 2 / g to 100m 2 The specific surface area of ​​the positive electrode material should be within a certain range. Within this range, the coating agent can be uniformly adhered to the surface of the positive electrode active material, thereby improving the structural stability of the positive electrode active material. Therefore, it is possible to prevent the shortening of the life of the positive electrode active material and the degradation of electrochemical performance due to lattice deformation or crystal structure collapse.

[0125] In the present disclosure, the average diameter can be measured using a measurement method commonly used in the field of the present invention. For example, the average diameter can be measured by laser diffraction. Specifically, the positive electrode active material particles are dispersed in a dispersion medium, and the dispersed particles are placed in a commercially available laser diffraction particle size measurement device such as the Microtrac MT 3000. The particles are irradiated with ultrasonic waves having an output power of 60W and a frequency of approximately 28kHz. The average particle diameter (D50) is then calculated based on the 50% percentile of the particle size distribution in the measurement device.

[0126] In the present disclosure, the specific surface area can be measured by a measurement method commonly used in the field to which the present invention belongs. For example, the specific surface area can be measured by the Brunauer-Emmett-Teller (BET) method. Specifically, the specific surface area can be calculated based on the amount of nitrogen adsorbed at liquid nitrogen temperature (77K) using the BELSORP-mino II produced by BEL Corporation of Japan.

[0127] In the positive electrode active material prepared by the method for recycling a positive electrode active material according to the present invention, the amount of residual Li2CO3 can be, for example, 0.17 wt% or less, preferably 0.15 wt% or less, more preferably 0.13 wt% or less, and further preferably 0.05 wt% to 0.13 wt%. Within this range, the positive electrode active material exhibits excellent resistance and lifespan characteristics.

[0128] In the positive electrode active material prepared according to the method for recycling a positive electrode active material, the amount of residual LiOH is preferably 0.42 wt% or less, preferably 0.39 wt% or less, and more preferably 0.05 wt% to 0.39 wt%. Within this range, the positive electrode active material exhibits excellent resistance and lifespan characteristics.

[0129] In the positive electrode active material prepared according to the method for recycling a positive electrode active material, the total amount of residual Li2CO3 and residual LiOH can be, for example, 0.054 wt% or less, preferably 0.052 wt% or less, and more preferably 0.05 wt% to 0.052 wt%. Within this range, the positive electrode active material has excellent resistance and life characteristics.

[0130] Reusing positive electrode active materials

[0131] The recycled positive electrode active material of the present invention is manufactured according to the above-mentioned recycling method of the positive electrode active material. In this case, wastewater is greatly reduced, the residual lithium on the surface of the positive electrode active material is reduced, and the resistance and life characteristics are excellent.

[0132] In addition, the recycled positive electrode active material of the present invention is one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active materials, nickel cobalt manganese (NCM)-based positive electrode active materials, nickel cobalt aluminum (NCA)-based positive electrode active materials, and nickel cobalt manganese aluminum (NCMA)-based positive electrode active materials, containing crystalline LiF, and the amount of Li2CO3 remaining in the recycled positive electrode active material is 0.17% by weight or less. In this case, the residual lithium on the surface of the positive electrode active material is reduced, and the resistance and life characteristics are excellent.

[0133] The recycled positive electrode active material contains, for example, 60 mol% or more, preferably 80 mol% or more, and more preferably 81 mol% or more of Ni, based on 100 mol% of the total amount of other metals excluding Li. Within this range, the initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics are all excellent.

[0134] The recycled positive electrode active material preferably includes one or more selected from the group consisting of: lithium cobalt oxide, such as LiCoO2 (hereinafter referred to as "LCO"); lithium manganese oxide, such as LiMnO2 or LiMn2O4; lithium iron phosphate compounds, such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide, such as LiNiO2; nickel-manganese-based lithium composite metal oxide obtained by replacing part of the nickel (Ni) in lithium nickel oxide with manganese (Mn); and NCM-based lithium composite transition metal oxide obtained by replacing part of the nickel (Ni) in lithium nickel oxide with manganese (Mn) and cobalt (Co). In this case, the electrochemical performance, resistance characteristics, capacity characteristics, etc. are all excellent.

[0135] As a specific example, the recycled positive active material may include a compound represented by the following Chemical Formula 1:

[0136] [Chemical Formula 1]

[0137] Li a Ni x Mn y Co z M w O 2+δ

[0138] In Chemical Formula 1, M includes one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1. In this case, the electrochemical performance, resistance characteristics, and capacity characteristics can all be excellent.

[0139] The recycled positive electrode active material may preferably contain 80 mol% or more, more preferably 81 mol% or more, and still more preferably 81 mol% to 95 mol% of Ni. Within this range, the charge capacity, resistance characteristics, and capacity characteristics can all be excellent.

[0140] Crystalline LiF can be defined as having a peak at 2θ of 38° to 40°, preferably 38.5° to 39° in the XRD spectrum. In this case, the initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics are all excellent.

[0141] Based on the total weight of the positive electrode active material, the content of crystalline LiF can be, for example, 0.1 wt% to 1 wt%, preferably 0.3 wt% to 1 wt%, and more preferably more than 0.3 wt% and less than 1 wt%. Within this range, the initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics are all excellent.

[0142] In the present disclosure, the content of crystalline LiF can be measured by ion chromatography (IC) commonly used in the technical field to which the present invention pertains. Specifically, an ion chromatography (IC)-inductively coupled plasma (ICP) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AEC analyzer can be used to measure the content of LiF crystals. Here, the crystal phase of LiF can be confirmed by XRD spectrum, and the content of LiF can be determined by the method of IC.

[0143] For example, based on the XPS surface analysis spectrum, the content of crystalline LiF on the surface of the recycled positive electrode active material can be 0.1 wt% to 10 wt%, preferably 0.1 wt% to 8 wt%, and more preferably 0.1 wt% to 7 wt%. Within this range, the initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics can be excellent.

[0144] In the present disclosure, the content of crystalline LiF on the surface of the recycled positive electrode active material can be measured using an X-ray photoelectron spectroscopy (XPS) surface analysis spectrum (K-alpha, Nexsa, Thermo Fisher Scientific). Based on the XPS surface analysis spectrum, the constituent elements or the composition ratio of elements can be quantified using the area or height of the photoelectrons emitted from the sample surface.

[0145] In the recycled positive electrode active material, the amount of residual Li2CO3 can be, for example, 0.17 wt% or less, preferably 0.15 wt% or less, more preferably 0.13 wt% or less, and more preferably 0.05 wt% to 0.13 wt%. Within this range, the positive electrode active material has excellent resistance and life characteristics.

[0146] The amount of residual LiOH in the recycled positive electrode active material may be, for example, 0.42 wt% or less, preferably 0.39 wt% or less, and more preferably 0.05 wt% to 0.39 wt%. Within this range, the positive electrode active material exhibits excellent resistance and lifespan characteristics.

[0147] In the recycled positive electrode active material, the sum of the residual Li2CO3 and the residual LiOH can be, for example, 0.054 wt% or less, preferably 0.052 wt% or less, and more preferably 0.05 wt% to 0.052 wt%. Within this range, the positive electrode active material exhibits excellent resistance and lifespan characteristics.

[0148] The positive electrode active material may be surface-coated with, for example, metal or carbon, preferably metal. This improves the structural stability of the positive electrode active material without chemical or physical changes to the material, and improves electrochemical properties such as rate capability, lifespan, and capacity. Furthermore, by substituting a foreign element on the surface of the positive electrode active material, the amount of residual lithium can be reduced and the pH value lowered, thereby improving physical and chemical properties.

[0149] The metal preferably includes one or more selected from the group consisting of boron, tungsten, aluminum, titanium, magnesium, nickel, cobalt, manganese, silicon, zirconium, vanadium, vanadium, and vanadium. More preferably, it includes one or more selected from the group consisting of boron, tungsten, aluminum, titanium, and magnesium. Furthermore, it preferably includes boron (B), tungsten (W), or a mixture thereof. Furthermore, it preferably includes tungsten (W) and boron (B). A specific example includes tungsten boride (WB). In this case, resistance characteristics and life characteristics can be improved.

[0150] For example, based on 1 mol% of metal in the positive electrode active material before coating, the content of the coating agent can be 0.001 mol% to 0.3 mol%, preferably 0.01 mol% to 0.3 mol%, more preferably 0.01 mol% to 0.15 mol%, more preferably 0.01 mol% to 0.1 mol%, and further preferably 0.01 mol% to 0.05 mol%. Within this range, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0151] The surface coating may be preferably performed by coating the surface with a coating agent containing one or more of a metal, an organic metal, and a carbon component in a solid or liquid form, and heat-treating the surface at 100° C. to 1200° C., more preferably 200° C. to 1000° C., and still more preferably 250° C. to 800° C. In this case, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0152] The positive electrode active material is preferably a recycled positive electrode active material, in which case economic feasibility and productivity are excellent.

[0153] Down Figure 4 FIG. 1 is a flow chart for explaining a positive electrode active material recycling process according to an embodiment of the present invention.

[0154] refer to Figure 4 First, positive electrode waste is prepared as waste positive electrode (step S10). For example, a slurry prepared by adding N-methylpyrrolidone (NMP) to an NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride and mixing them is coated on aluminum foil and then dried in a vacuum oven set at approximately 120°C to obtain a positive electrode sheet. The positive electrode sheet is then punched into a positive electrode plate of a certain size. During this process, positive electrode waste is generated.

[0155] Positive electrode waste consists of aluminum foil and a positive electrode active material layer formed on the aluminum foil. After the solvent evaporates, the positive electrode active material layer has a structure consisting of positive electrode active material and conductive material bonded together by a binder. By removing the binder, the positive electrode active material is separated from the aluminum foil.

[0156] Next, the prepared positive electrode waste is crushed into pieces of appropriate size (step S20). Here, crushing includes cutting or chopping the positive electrode waste into a size that is easy to handle. Specifically, the size of the crushed positive electrode waste can be 1 cm × 1 cm. For example, dry crushing equipment (such as a hand grinder, pin mill, disc mill, cutting mill, and hammer mill) can be used for crushing. In order to improve production efficiency, a high-speed cutter can be used.

[0157] Preferably, whether to crush the positive electrode waste and the size of the fragments can be determined based on the characteristics of the equipment used in the processing and subsequent processes. For example, when using equipment that can process continuously, it is necessary to crush the positive electrode waste into smaller fragments because the fragments need to have good fluidity.

[0158] Next, the positive electrode waste is heat-treated to recover the positive electrode active material (step S30). Here, the heat treatment is performed to thermally decompose the binder in the active material layer.

[0159] Through the heat treatment, the binder and conductive material in the active material layer are thermally decomposed into CO2 and H2O, which are then removed. Since the binder has been removed, the positive electrode active material is separated from the current collector, and the separated positive electrode active material can be easily sorted into powder form. Therefore, in step S30 alone, the active material layer can be separated from the current collector, and the positive electrode active material in the active material layer can also be recovered as a powder.

[0160] It is important that the heat treatment be carried out in an air atmosphere or an oxygen atmosphere, preferably in an oxygen atmosphere. When the heat treatment is carried out in a reducing gas or inert gas atmosphere, the binder and the conductive material are carbonized rather than thermally decomposed. When the binder and the conductive material are carbonized, the carbon component remains on the surface of the positive electrode active material, resulting in a decrease in the performance of the recycled positive electrode active material. In contrast, when the heat treatment is carried out in an air atmosphere or an oxygen atmosphere, especially in an oxygen atmosphere, both the binder and the conductive material are removed because the carbon component in the binder and the conductive material reacts with oxygen, is converted into gases such as CO and CO2 and disappears. More specifically, the heat treatment can be carried out in the presence of oxygen with a purity of 95% and argon with a concentration of 5%.

[0161] The heat treatment is preferably performed at 300° C. to 650° C., specifically 590° C. Below 300° C., the binder is difficult to remove, so the current collector may not separate. The current collector melts above 650° C., so the current collector may not separate.

[0162] The heat treatment is preferably performed at a heating rate of 1°C / min to 20°C / min, more preferably 3°C / min to 17°C / min, specifically 5°C / min. Within this range, the heat treatment can be performed without burdening the heat treatment equipment and can prevent thermal shock to the cathode waste.

[0163] The heat treatment can be performed until the binder is completely thermally decomposed, preferably for 30 minutes or more, more preferably for 30 minutes to 5 hours, specifically for about 30 minutes. Within this range, the binder can be completely thermally decomposed and the thermal decomposition efficiency can be excellent.

[0164] For example, various types of furnaces can be used for heat treatment. For example, a box furnace can be used. Considering productivity, a rotary kiln capable of continuous processing can be used.

[0165] After heat treatment, slow cooling or rapid cooling can be carried out in air.

[0166] Next, a lithium precursor is added to the recovered positive electrode active material, and annealing is performed under an oxygen atmosphere (step S40 ).

[0167] In the annealing step (step S40), it is important to immediately add the lithium precursor to the recovered positive electrode active material and perform annealing without performing a washing process. In this case, since the recycled positive electrode active material contains crystalline LiF formed on the surface of the positive electrode active material in the previous heat treatment step (step S30), the battery characteristics can be improved when the recycled positive electrode active material is used in a secondary battery.

[0168] In addition, annealing is preferably performed in an oxygen atmosphere, specifically in the presence of oxygen having a purity of 59% or more, preferably 70% or more, more preferably 80% or more, more preferably 90% or more, and even more preferably 90% to 99%, specifically in the presence of 95% oxygen and 5% argon with carbon dioxide removed. In this case, the residual lithium on the surface of the positive electrode active material can be reduced, thereby improving battery characteristics.

[0169] In step S40, oxygen gas may be supplied at a rate of, for example, 1 L / min to 20 L / min, specifically 3 L / min to 8 L / min. Within this range, the amount of lithium remaining on the surface of the positive electrode active material may be reduced, and crystallinity may be improved, such as increased crystallinity or restoration of the crystal structure.

[0170] In addition, in the previous step S30, lithium loss occurs in the positive electrode active material. In step S40, the amount of lithium loss is replenished. In addition, in the previous step, a deformed structure may be formed on the surface of the positive electrode active material (for example, Co3O4 in the case of LCO active material). In step S40, the crystal structure of the positive electrode active material can be restored by annealing in the presence of oxygen, thereby improving the battery characteristics of the recycled positive electrode active material, or restoring the battery characteristics of the recycled positive electrode active material to the level of battery characteristics of the newly made positive electrode active material. The "newly made" here is a concept opposite to "reuse", and the newly made material refers to the material manufactured for the first time. The newly made material is the same word as the "raw material" in the embodiment.

[0171] LiOH is used as a specific example of the lithium precursor.

[0172] Based on the molar ratio of lithium to other metals in the fresh positive electrode active material contained in the positive electrode active material layer, it is preferred to add a lithium precursor in an amount that minimizes the molar ratio of lithium loss. If the amount of lithium precursor added is excessive relative to the amount of lithium loss, unreacted lithium precursor may remain in the recycled positive electrode active material, increasing resistance. Therefore, it is necessary to add an appropriate amount of lithium precursor.

[0173] As an embodiment, based on the case where the molar ratio of lithium to other metals (M) in the fresh positive active material is 1, the amount of lithium precursor added can satisfy the molar ratio of lithium of 0.001 to 0.4, preferably the molar ratio of lithium of 0.01 to 0.4, and more preferably the molar ratio of lithium of 0.09 to 0.2. As a specific example, when the lithium precursor is added at a loss rate relative to the lithium content in the fresh positive active material, based on the ICP analysis results, the capacity can be increased to a level comparable to that of the fresh positive active material. Here, the error value of the ICP analysis result is approximately ±0.02.

[0174] As one embodiment, when the total amount of lithium contained in the recycled positive electrode active material is 100 mol%, the amount of the lithium precursor added may be 1 mol% to 40 mol%, more preferably 1 mol% to 25 mol%, more preferably 1 mol% to 17 mol%, even more preferably 3 mol% to 17 mol%, and particularly preferably 7 mol% to 15 mol%. Within this range, the battery characteristics can be improved due to the absence of residual precursors that increase the resistance of the recycled positive electrode active material.

[0175] Annealing can be performed, for example, in an oxygen (O 2 ) atmosphere at 400° C. to 1000° C., preferably 600° C. to 900° C. In this case, the temperature should be determined within a limited range depending on the type of the lithium precursor.

[0176] The annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, since the positive electrode active material undergoes thermal decomposition at temperatures exceeding 1000°C, resulting in performance degradation, the annealing temperature should not exceed 1000°C. When Li2CO3 is used as the lithium precursor, the annealing temperature is preferably 700°C to 900°C, more preferably 700°C to 800°C, further preferably 710°C to 780°C, and most preferably 750°C to 780°C. In addition, when LiOH is used as the lithium precursor, the annealing temperature is preferably 400°C to 720°C, more preferably 420°C to 700°C, and most preferably 450°C to 700°C.

[0177] For example, the annealing time is preferably more than 1 hour, preferably less than 1 hour and less than 15 hours, more preferably 4 to 13 hours, more preferably 6 to 12 hours, and specifically 10 hours. When the annealing time is long, the crystal structure can be fully restored, but even if annealing for a long time, the performance will not be significantly affected. In this case, the annealing equipment can use the same or similar equipment as the step S30 in which the heat treatment is performed.

[0178] Next, the annealed positive electrode active material is washed (step S50 ).

[0179] Since the lithium precursor that failed to react in the annealing step S40 exists on the surface of the positive electrode active material in the form of LiOH and Li2CO3, a residual lithium removal process is required to remove LiOH and Li2CO3. Impurities in the form of LiOH and Li2CO3 can react with the electrolyte, reducing battery performance and generating gas, so these impurities should be thoroughly removed.

[0180] During washing, the weight ratio of the annealed positive electrode active material to the washing liquid can be 1:0.5 to 1:4, specifically 1:1. In this case, only a small amount of washing liquid is needed to remove residual lithium, thereby greatly reducing wastewater, and the positive electrode active material has excellent resistance and life characteristics.

[0181] In washing, distilled water or an aqueous alkaline lithium compound solution containing greater than 0% by weight and less than 10% by weight of an alkaline lithium compound is preferably used, and distilled water is more preferably used. In this case, safety can be ensured, costs can be reduced, and dissolution of transition metals contained in the positive electrode active material can be prevented.

[0182] Washing is preferably performed by mixing the annealed positive electrode active material with a washing liquid and drying the resulting solid positive electrode active material.

[0183] The mixing of the annealed positive electrode active material and the washing solution is preferably performed by stirring. The stirring method is not particularly limited and can be mechanical stirring or ultrasonic stirring.

[0184] Mechanical stirring is preferably performed at a speed of 100 to 1000 RPM for 5 to 30 minutes, more preferably at a speed of 250 to 350 RPM for 5 to 10 minutes.

[0185] The filtration is preferably performed by vacuum filtration using a filter, and the drying is preferably performed by vacuum drying at 50°C to 140°C.

[0186] Next, as an optional step, the surface of the washed positive electrode active material may be coated (step S60 ).

[0187] For example, in surface coating, the surface is coated with a coating agent containing a solid or liquid metal, organic metal, or carbon, and then heat-treated. If the heat treatment temperature is too low, the dissimilar metal may not form the desired surface protective layer. If the heat treatment temperature is too high, battery performance may decline due to thermal decomposition of the positive electrode active material.

[0188] Specifically, when the washed positive electrode active material is coated with a metal oxide such as B, W, and BW or an acid and then heat-treated, a surface protective layer such as a lithium boron oxide layer is formed on the surface of the positive electrode active material.

[0189] Surface coating can be performed using solid phase or liquid phase methods, examples being mixing, grinding, spray drying or milling.

[0190] When the molar ratio of lithium to other metals in the positive electrode active material is 1:1 in the annealing step S40, the lithium in the positive electrode active material reacts with the coating agent in the surface coating step S60, and the molar ratio of lithium to other metals in the positive electrode active material is less than 1:1. In this case, the capacity of the battery containing the recycled positive electrode active material may not be fully (up to 100%) realized. However, in the annealing step S40, when an excess amount of lithium precursor is added so that the molar ratio of lithium to other metals in the positive electrode active material exceeds 0.0001 to 0.1, a surface protective layer is formed in the surface coating step S60, so that the molar ratio of lithium to other metals in the positive electrode active material becomes 1:1, thereby preventing the battery capacity from decreasing.

[0191] secondary batteries

[0192] The secondary battery of the present invention includes recycled positive electrode active materials. This significantly reduces residual lithium in the positive electrode active material, resulting in excellent resistance and lifespan characteristics. Furthermore, since residual lithium can be removed with a small amount of washing liquid, wastewater production is significantly reduced. Furthermore, since the recovery and regeneration of the positive electrode active material does not require the use of acids and organic solvents, the secondary battery is highly environmentally friendly. In particular, since the initial washing step is omitted, economic feasibility and productivity are excellent.

[0193] The description of the secondary battery of the present invention can cover all the above descriptions about the positive electrode active material and the method for recycling the positive electrode active material, so they will not be repeated in this specification.

[0194] The present invention will be described in more detail below with reference to the following preferred embodiments. However, these embodiments are only for illustrative purposes and should not be considered as limiting the scope and spirit of the present invention. In addition, it will be appreciated by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention, and such changes and modifications are also within the scope of the appended claims.

[0195] Example

[0196] Example 1

[0197] After punching the positive electrode plate, the discarded positive electrode waste (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide (nickel content: 88 mol%)) was crushed and heat-treated at 590°C for 30 minutes in an oxygen atmosphere to remove the binder and conductive material, and to separate the current collector from the positive electrode active material. Next, the positive electrode active material was recovered. Here, the heating rate before reaching the heat treatment temperature was 5°C / min, and the oxygen atmosphere (hereinafter referred to as "reaction gas") contained 95% oxygen and 5% argon, but did not contain carbon dioxide. The reaction gas was supplied at 10 L / min.

[0198] The recovered cathode active material was added directly to the lithium precursor LiOH without washing and annealed at 700°C for 10 hours under a reaction gas supply rate of 3 L / min. The amount of lithium precursor added was 15 mol% based on a total lithium content of 100 mol% in the recovered cathode active material.

[0199] The annealed positive electrode active material was mixed with distilled water at a weight ratio of 1:1, stirred at 500 rpm for 5 minutes, and then vacuum filtered to obtain a solid. The solid was vacuum dried at 100°C to 130°C for 12 hours to obtain a washed positive electrode active material.

[0200] The washed positive electrode active material was mixed with boric acid (H3BO3) in a solid state and heated at 300°C for 5 hours to obtain the final recycled positive electrode active material coated with boron. Here, the amount of boric acid added was equivalent to the 700 ppm of boron lost in the previous process. The material was heated at a heating rate of 2°C / min until it reached the heat treatment temperature, and the air supply rate was 3 L / min.

[0201] In the present disclosure, an IC analyzer is used to measure the molar ratio of lithium to other metals in the positive electrode active material. In this case, a general ICP analyzer widely used in laboratories can be used, but the measurement equipment or method does not cause deviation.

[0202] In this specification, ppm is based on weight unless otherwise specified.

[0203] Example 2

[0204] A recycled positive electrode active material was manufactured in the same manner as in Example 1, except that the reaction gas was applied at a rate of 8 L / min in the annealing step of Example 1.

[0205] Comparative Example 1

[0206] A recycled positive electrode active material was manufactured in the same manner as in Example 1, except that the annealing in Example 1 was performed under an air atmosphere.

[0207] Comparative Example 2

[0208] A recycled positive electrode active material was manufactured in the same manner as in Example 1, except that the annealing in Example 1 was performed under an air atmosphere and the air was supplied at 8 L / min.

[0209] Comparative Example 3

[0210] Recycled positive electrode active material was produced in the same manner as in Example 1, except that the positive electrode active material recovered from the heat treatment of the positive electrode waste in Example 1 was washed with an alkaline lithium compound aqueous solution and then annealed with the addition of LiOH, a lithium precursor. The alkaline lithium compound aqueous solution contained 15% by weight of LiOH, and the weight ratio of the recovered positive electrode active material to the alkaline lithium compound aqueous solution used for washing was 1:1.

[0211] [Test Example 1: Residual Lithium Content after Annealing]

[0212] The residual lithium content in the positive electrode active material obtained after annealing in each of Examples 1 and 2 and Comparative Examples 1 and 2 was measured, and the results are shown in Table 1 below.

[0213] *Residual lithium content: The residual lithium content was measured using a pH titrator (MATi 06, Metrohm). Specifically, 5 g of the positive electrode active material was dispersed in 100 ml of distilled water, mixed at a speed of 500 rpm for 5 minutes, and then filtered to filter out the active material and obtain a filtrate. The filtrate was titrated with 0.1 M HCl solution to measure the change in pH. A pH titration curve was obtained based on the measurement results. The amount of LiOH and Li2CO3 remaining in the positive electrode active material was calculated using the pH titration curve.

[0214]

Table 1

[0215] Classification LiOH (wt%) <![CDATA[Li2CO3 (wt%)]]> Total amount (weight %) Example 1 0.989 0.861 1.851 Example 2 0.956 0.925 1.882 Comparative Example 1 0.820 1.758 2.579 Comparative Example 2 0.814 1.963 2.777

[0216] As shown in Table 1, it can be confirmed that, in the case of Examples 1 and 2 of the present invention, the amount of residual Li2CO3, the amount of residual LiOH, and their total amount are all reduced compared to Comparative Examples 1 and 2, and the amount of residual LiOH is greatly reduced.

[0217] [Test Example II: Residual Lithium Content in Recycled Positive Electrode Active Materials]

[0218] The recycled positive electrode active materials obtained in each of Examples 1 and 2 and Comparative Examples 1 and 2 were washed and then the residual lithium content thereof was measured. The results are shown in Table 2 below.

[0219]

Table 2

[0220] Classification LiOH (wt%) <![CDATA[Li2CO3 (wt%)]]> Total amount (weight %) Example 1 0.411 0.119 0.530 Example 2 0.379 0.136 0.515 Comparative Example 1 0.372 0.221 0.593 Comparative Example 2 0.302 0.248 0.550

[0221] As shown in Table 2, it can be seen that compared with Comparative Examples 1 and 2, in the case of Examples 1 and 2 of the present invention, the amount of residual Li2CO3, the amount of residual LiOH and their total amount are all reduced, especially the amount of residual Li2CO3 is greatly reduced, thereby further improving the battery characteristics.

[0222] [Test Example III: SEM Analysis]

[0223] The recycled positive electrode active materials obtained in Example 1 and Comparative Example 1 were photographed using a SEM device as follows Figure 2 The SEM images were taken using a commonly used SEM instrument in our laboratory. Specifically, they were taken using a HITACHI S-4200. However, there is no deviation due to the measurement equipment or method.

[0224] as follows Figure 2 As shown, it can be confirmed that, compared with the recycled positive electrode active material prepared in Comparative Example 1, in the case of the recycled positive electrode active material prepared in Example 1, there are no impurities on the surface and the particle shape is relatively spherical, while in the case of the recycled positive electrode active material prepared in Comparative Example 1, impurities remain on the surface and the particles are broken and aggregated together.

[0225] [Test Example IV: CHC Battery Cell Evaluation]

[0226] The capacity retention and resistance increase of the coin half cells (CHCs) made of the recycled positive active material obtained in each of Examples 1 and 2 and Comparative Examples 1 to 3 were measured by the following CHC evaluation. The results are as follows Figure 3 and shown in Table 3.

[0227] *CHC cell production: 96.5 wt% of recycled positive electrode active material, 1.5 wt% of carbon black as a conductive material, and 2 wt% of PVdF as a binder were weighed and mixed with NMP to prepare a positive electrode active material slurry. This slurry was coated onto 20 μm thick aluminum foil, dried at 130°C for 1 hour, and then roll-pressed to form the positive electrode. Lithium metal was used as the negative electrode.

[0228] After bonding the prepared positive and negative electrodes to the separator, an electrolyte containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a weight ratio of 3:7, along with other additives, was injected to produce CHC. The prepared CHC was aged at 25°C for 10 hours and then charged to 4.25V in CC-CV mode at a constant current of 0.1C and a cutoff of 0.05C. It was then activated by discharging at a constant current of 0.1C to 2.5V. Cycling evaluation was then performed.

[0229] *Measurement of capacity retention at high temperature (45°C): The recycled positive active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were respectively made into CHC and formed at a rate of 0.1C, and then charged to 4.25V at a constant current of 0.33C under the conditions of 45°C and 0.05C cutoff value. Next, it was discharged to 2.5V at a constant current of 0.33C. The charging and discharging behavior was regarded as one cycle, and the cycle was repeated 25 times. The discharge capacity after 1 cycle and the discharge capacity after 25 cycles were measured using a PNE-05-0.1 charger and discharger (manufacturer: PNE Solution Co., Ltd., 5V, 0.1A). The discharge capacity after 1 cycle was set to the initial capacity. Then, the 25th discharge capacity was compared with the initial capacity (100%), and the capacity retention was calculated by the following equation 1, and the results are shown below. Figure 3 and Table 3.

[0230] [Equation 1]

[0231] Capacity retention (%) = (discharge capacity after high temperature cycle / initial discharge capacity) × 100

[0232] *Measurement of resistance increase rate at high temperature (45°C): The recycled positive active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were respectively made into CHC, formed at a rate of 0.1C, and then charged to 4.25V at a constant current of 0.33C under the conditions of 45°C and 0.05C cutoff value. Next, it was discharged to 2.5V at a constant current of 0.33C. The charging and discharging behavior was regarded as one cycle. After repeating this cycle 25 times, the resistance increase rate was measured. The resistance increase rate was calculated according to the following equation 2, and the results are shown below Figure 3 and Table 3.

[0233] [Equation 2]

[0234] Resistance increase rate (%) = {(DCIR2-DCIR1) / DCIR1} × 100

[0235] In Equation 2, DCIR1 represents the resistance (ohms) measured at 1 cycle, and DCIR2 represents the resistance (ohms) measured at 25 cycles.

[0236]

Table 3

[0237] Classification Capacity retention (%; 25 cycles) Resistance increase rate (%; 25 cycles) Example 1 93.7 53.3 Example 2 93.2 59.4 Comparative Example 1 87.6 95.2 Comparative Example 2 86.9 97.6 Comparative Example 3 91.0 75.8

[0238] As shown in Table 3, it can be confirmed that the recycled positive electrode active materials of the present invention (Examples 1 and 2) exhibit high capacity retention and significantly lower resistance increase (53% to 60%) compared with Comparative Examples 1 to 3, thereby exhibiting greatly improved battery characteristics.

[0239] In addition, if Figure 3 As shown, it can be confirmed that the recycled positive electrode active materials of the present invention (Examples 1 and 2) show a higher capacity retention rate and a significantly lower resistance increase rate compared with Comparative Examples 1 to 3 even if the number of cycles increases, thereby showing greatly improved battery characteristics.

Claims

1. A method for recycling a positive electrode active material, the method comprising: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300° C. to 650° C. to thermally decompose a binder and a conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material and annealing the recovered positive electrode active material at 400° C. to 1000° C. under an oxygen atmosphere; and The annealed positive electrode active material is washed.

2. The method according to claim 1, wherein The positive electrode active material layer includes 60 mol % or more of Ni based on 100 mol % of the total amount of other metals except Li.

3. The method according to claim 1, wherein The positive electrode active material recovered after thermal decomposition was annealed without washing.

4. The method according to claim 1, wherein During the annealing process, the recovered positive active material contains crystalline LiF.

5. The method according to claim 1, wherein During the annealing process, oxygen gas was supplied at 1 L / min to 20 L / min.

6. The method of claim 1, wherein: The purity of oxygen is above 59%.

7. The method of claim 1, wherein: The oxygen atmosphere does not contain carbon dioxide (CO2).

8. The method of claim 1, wherein: The lithium precursor includes one or more of LiOH, Li2CO3, LiNO3 and Li2O.

9. The method of claim 1, wherein: When the total amount of lithium contained in the recovered positive electrode active material is 100 mol %, the amount of the lithium precursor added is 1 mol % to 40 mol %.

10. The method of claim 1, wherein: During the washing process, the weight ratio of the annealed positive electrode active material to the washing liquid is 1:0.5 to 1:

4.

11. The method of claim 1, wherein: The amount of Li2CO3 remaining in the positive electrode active material after washing was 0.17 wt% or less.

12. The method of claim 1, wherein: The method for recycling a positive electrode active material includes surface coating the washed positive electrode active material to obtain a reusable positive electrode active material.

13. The method of claim 1, wherein: During the surface coating process, one or more of metal, organometallic and carbon components are coated on the surface in a solid or liquid phase, and then heat-treated at 100°C to 1200°C. 14 . A recycled positive electrode active material produced by the method for recycling a positive electrode active material according to claim 1 .

15. A recycled positive electrode active material, wherein: The recycled positive electrode active material is one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active materials, nickel·cobalt·manganese (NCM)-based positive electrode active materials, nickel·cobalt·aluminum (NCA)-based positive electrode active materials, and nickel·cobalt·manganese·aluminum (NCMA)-based positive electrode active materials, and contains crystalline LiF, and The amount of Li2CO3 remaining in the recycled positive electrode active material was 0.17 wt% or less.

16. The recycled positive electrode active material according to claim 15, wherein The recycled positive electrode active material includes 60 mol % or more of Ni based on 100 mol % of the total amount of other metals except Li.

17. The recycled positive electrode active material according to claim 15, wherein The surface of the recycled positive active material is coated with a coating agent containing metal or carbon. 18 . A secondary battery comprising the recycled positive electrode active material according to claim 14 .

Images