Method for reuse of positive electrode active material, reused positive electrode active material prepared thereby, and secondary battery including the same

Abstract

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. More specifically, the method of the present invention comprises the steps of: thermally treating a waste positive electrode in which a positive electrode active material layer is formed on a current collector to thermally decompose a binder and a conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material; carrying out primary grinding on the recycled positive electrode active material; adding a lithium precursor to the primary-ground positive electrode active material, and annealing at 400 DEG C to 1000 DEG C; and performing secondary grinding on the annealed positive electrode active material. According to the present invention, a positive electrode active material recovered without a washing process is subjected to primary grinding after heat treatment of a waste positive electrode, a lithium precursor is added to the positive electrode active material subjected to the primary grinding, annealing is performed, and then the annealed positive electrode active material is subjected to secondary grinding. According to the present invention, damage to the surface of the positive electrode active material can be prevented, the particle size of the recycled positive electrode active material can be uniform, and an increase in the particle size can be minimized, thereby providing a method for recycling the positive electrode active material having excellent battery characteristics.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from Korean Patent Application No. 10-2023-0103933 filed on August 9, 2023, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. Technical Field

[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, according to the present invention, after heat treatment of spent positive electrodes, the positive electrode active material recovered without a washing process is subjected to a primary grinding process, a lithium precursor is added to the primary grinding process, the process is annealed, and the annealed positive electrode active material is then subjected to a secondary grinding process. This prevents surface damage to the positive electrode active material, ensures a uniform particle size of the recycled positive electrode active material, and minimizes particle size increase, thereby improving battery characteristics. Furthermore, the method is environmentally friendly because it does not use acid in the recovery and recycling of the positive electrode active material. Therefore, since neutralization and wastewater treatment are not required, process costs can be reduced. Furthermore, since the positive electrode active material is reused without decomposition, no metal elements are discarded. Furthermore, since no organic solvent is used, there is no risk of toxic gas generation or explosion. Furthermore, economic efficiency and productivity can be significantly improved. Background Art

[0004] Generally speaking, a lithium secondary battery is composed of the following: 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 studying the recovery and reuse 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 this method.

[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] While solvent dissolution can yield recycled cathode active materials with cleaner surfaces, this method suffers from poor stability and requires expensive solvent recovery processes because the solvents used to dissolve the binder, such as N-methyl-2-pyrrolidone (NMP), are toxic and explosive.

[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] 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 the residual binder.

[0013] Therefore, there is an urgent need to develop a method to safely reuse cathode active materials with improved output performance 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 has been developed in light of the above-mentioned problems, and an object of the present invention is to provide a method for recycling positive electrode active materials and a recycled positive electrode active material produced by the method having excellent battery characteristics. According to the present invention, by subjecting the recovered positive electrode active material without a washing process to a primary milling after heat treatment of the spent positive electrode, adding a lithium precursor to the primary milled positive electrode active material, annealing the material, and then secondary milling the annealed positive electrode active material, damage to the surface of the positive electrode active material can be prevented, the particle size of the recycled positive electrode active material can be uniform, and particle size increase can be minimized, thereby providing a recycled positive electrode active material having excellent battery characteristics. Furthermore, the method is environmentally friendly because it does not use acid in the recovery and reuse of the positive electrode active material. Therefore, since neutralization and wastewater treatment are not required, process costs can be reduced. Furthermore, since the positive electrode active material is reused without decomposition, no metal elements are discarded. Furthermore, since no organic solvent is used, there is no risk of toxic gas generation or explosion. Furthermore, economic efficiency and productivity can be significantly improved.

[0016] Another object of the present invention is to provide a secondary battery including a positive electrode active material having excellent battery characteristics.

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

[0018] [Technical solution]

[0019] I) According to one aspect of the present invention, a method for recycling positive electrode active materials is provided, the method comprising: heat treating a waste positive electrode having a positive electrode active material layer formed on a current collector 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; performing a primary grinding of the recovered positive electrode active material; adding a lithium precursor to the primary ground positive electrode active material and annealing the material at 400°C to 1000°C; and performing a secondary grinding of the annealed positive electrode active material.

[0020] II) According to I), the positive electrode active material layer may preferably include one or more selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, a nickel·cobalt·manganese (NCM)-based positive electrode active material, a nickel·cobalt·aluminum (NCA)-based positive electrode active material, and a nickel·cobalt·manganese·aluminum (NCMA)-based positive electrode active material, and the Ni content may be 60 mol% or more based on a total of 100 mol% of other metals other than Li.

[0021] III) According to I) or II), the heat treatment may be preferably performed at 300° C. to 650° C. in air or oxygen atmosphere.

[0022] IV) According to I) to III), the primary grinding and the secondary grinding may preferably be performed using a centrifugal mill or a jet mill.

[0023] V) According to I) to IV), the primary grinding and the secondary grinding may be preferably performed at 6000 rpm to 20000 rpm.

[0024] VI) According to I) to IV), the positive electrode active material obtained after the secondary grinding may preferably have an average particle size increase rate of 14% or less and an average particle size standard deviation of 3.0 or less, compared with the positive electrode active material in the waste positive electrode.

[0025] VII) According to I) to V), the lithium precursor may preferably include one or more selected from LiOH, Li2CO3, LiNO3 and Li2O.

[0026] VIII) According to I) to VII), the lithium precursor may be added in an amount that can provide lithium in an amount corresponding to 1 mol % to 40 mol % based on 100 mol % in total of lithium in the positive electrode active material used as a raw material.

[0027] IX) According to I) to VIII), annealing may be preferably performed at 400°C to 1000°C.

[0028] X) According to I) to IX), the method for recycling the positive electrode active material may preferably include: washing the secondary ground positive electrode active material; coating the surface of the secondary ground positive electrode active material; or washing the secondary ground positive electrode active material and then coating its surface.

[0029] XI) According to I) to X), in the washing step, the weight ratio of the annealed positive electrode active material to the washing liquid may preferably be 1:0.5 to 1:10.

[0030] XII) According to I) to XI), the surface coating may preferably be carried out by coating the surface with one or more of metal, organometallic and carbon components in solid or liquid form and heating the surface at 100°C to 1200°C.

[0031] XIII) According to another aspect of the present invention, there is provided a recycled positive electrode active material comprising one or more selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, a nickel·cobalt·manganese (NCM)-based positive electrode active material, a nickel·cobalt·aluminum (NCA)-based positive electrode active material, and a nickel·cobalt·manganese·aluminum (NCMA)-based positive electrode active material; wherein the Ni content is 60 mol% or more based on a total of 100 mol% of other metals other than Li; and the average particle size standard deviation is 3.0 or less.

[0032] XIV) According to XIII), the surface of the positive electrode active material may preferably be coated with a coating agent containing metal or carbon.

[0033] XV) According to XIII) or XIV), the metal may preferably be boron (B), tungsten (W) or a mixture thereof.

[0034] XVI) According to another aspect of the present invention, there is provided a recycled positive electrode active material prepared by the method described in I) to XII).

[0035] XVII) According to yet another aspect of the present invention, there is provided a secondary battery comprising the recycled positive electrode active material described in any one of XIII) to XVI).

[0036] [Beneficial effects]

[0037] The present invention provides a method for recycling positive electrode active materials, a recycled positive electrode active material prepared using the method and having excellent battery characteristics, and a secondary battery containing the recycled positive electrode active material. According to the present invention, by subjecting the recovered positive electrode active material, which has not been washed, to a primary milling after heat treatment of the spent positive electrode, adding a lithium precursor to the primary milled positive electrode active material, annealing the material, and then secondary milling the annealed positive electrode active material, damage to the surface of the positive electrode active material can be prevented, process costs can be reduced, the particle size of the recycled positive electrode active material can be uniform, particle size increase can be minimized, and the particle size distribution in the spent positive electrode can be similar to that of the positive electrode active material, thereby improving electrode characteristics. Furthermore, the method is environmentally friendly because it does not use acid. Therefore, since neutralization and wastewater treatment are not required, process costs can be reduced. Furthermore, since the positive electrode active material is reused without decomposition, no metal elements are wasted. Furthermore, since the current collector is not melted, the current collector can be recycled. Furthermore, since no organic solvent is used, there is no risk of toxic gas generation or explosion. Additionally, the method is suitable for mass production by using easy-to-manage methods such as heat treatment or precipitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The following drawings attached to this specification illustrate embodiments of the present invention and are presented to further understand the technical concept of the present invention in conjunction with the detailed description described below. Therefore, the present invention is not limited to these drawings.

[0039] Figure 1 This figure shows the positive electrode scraps discarded after the electrode plates are cut from the positive electrode sheet.

[0040] Figure 2: is a graph showing the particle distribution of the recycled positive electrode active material or the fresh positive electrode active material obtained in Example 1, Reference Example, and Comparative Examples 1 to 3.

[0041] Figure 3 Graphs showing particle distributions of the recycled positive electrode active materials or fresh positive electrode active materials obtained in Examples 1 and 2, Reference Example, and Comparative Examples 1 and 4.

[0042] Figure 4 is a flowchart for explaining the method for recycling the positive electrode active material of the present invention. DETAILED DESCRIPTION

[0043] The present inventors have studied a method for improving the battery characteristics of recycled positive electrode active materials by using a method of directly recycling the positive electrode active material from the waste positive electrode without decomposing the positive electrode active material (direct recycling method). During the above-mentioned research, the present inventors confirmed that if the positive electrode active material recovered without washing is ground once after heat treatment, a lithium precursor is added to the positive electrode active material subjected to the first grinding, annealing is performed, and then the annealed positive electrode active material is subjected to a second grinding, it is possible to prevent damage to the surface of the positive electrode active material, make the particle size uniform, reduce the increase in particle size, and the particle size distribution becomes similar to the particle size distribution of the positive electrode active material in the original positive electrode, thereby improving the electrode characteristics of the recycled positive electrode active material. Based on these results, the present inventors conducted further research to complete the present invention.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] Method for recycling positive electrode active materials

[0048] 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 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; subjecting the recovered positive electrode active material to primary grinding; adding a lithium precursor to the primary ground positive electrode active material and annealing it at 400°C to 1000°C; and subjecting the annealed positive electrode active material to secondary grinding. This method prevents surface damage to the positive electrode active material, reduces process costs, and ensures that the particle size of the recycled positive electrode active material is uniform, minimizing particle size increase, thereby providing a positive electrode active material with excellent battery characteristics. Furthermore, the method is environmentally friendly because it does not use acid in the recovery and reuse of the positive electrode active material. Therefore, neutralization and wastewater treatment are not required, reducing process costs. Furthermore, since the positive electrode active material is reused without decomposition, no waste metal elements are generated. Furthermore, since the current collector is not melted, the current collector can be recycled. In addition, since no organic solvent is used, there is no risk of generating toxic gases or explosion. In addition, the method is suitable for mass production by using easy-to-manage methods such as heat treatment or precipitation.

[0049] Hereinafter, each step of the method for recycling the positive electrode active material will be described in detail.

[0050] (a) Recovery of positive electrode active materials from spent positive electrodes

[0051] The step (a) of recovering the positive electrode active material from the waste positive electrode of the present invention may preferably be the step of heat-treating the waste positive electrode having a positive electrode active material layer formed on a current collector 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, a simple process can be implemented, and the binder, conductive material, and current collector can be completely removed.

[0052] 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.

[0053] The positive electrode active material layer of step (a) preferably includes a positive electrode active material, a binder, and a conductive material.

[0054] For example, the positive electrode active material layer may include 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. In this case, the reversible capacity and thermal stability may be excellent.

[0055] The positive electrode active material may preferably include 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 compound, such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide, such as LiNiO2; nickel-manganese-based lithium composite metal oxide obtained by substituting part of nickel (Ni) in lithium nickel oxide with manganese (Mn); and NCM-based lithium composite transition metal oxide 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 nickel-manganese-based lithium composite metal oxide, 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 a total of 100 mol% 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, and more preferably 81 mol% or more. Within this range, the initial discharge capacity, output performance, capacity characteristics, and resistance characteristics may be excellent.

[0061] In the present invention, the Ni content can be measured using ion chromatography (IC) commonly used in the technical field to which the present invention belongs. 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, CNTs 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] For example, the heat treatment can be performed in an air atmosphere or an oxygen atmosphere. In this case, the binder and the conductive material are thermally decomposed into CO2 and H2O and removed, thereby separating the positive electrode active material from the current collector, and the separated positive electrode active material is easily separated in the form of powder.

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

[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] For example, the heat treatment may be performed at 300° C. to 650° C., preferably 400° C. to 630° C., more preferably 500° C. to 600° C., even more preferably 530° C. to 600° C., even more preferably 530° C. to 580° C. Within this range, the positive electrode active material can be easily separated from the current collector because the current collector is not melted but only the binder is removed.

[0069] The heat treatment time is preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, even more preferably 30 minutes to 2 hours, and even more preferably 30 minutes to 1 hour. Within this range, since the current collector does not melt and only the binder is removed, the positive electrode active material can be easily separated from the current collector.

[0070] 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.

[0071] The heat treatment may be performed at a heating rate of 1°C / min to 20°C / min, preferably 2°C / min to 15°C / min, more preferably 3°C / min to 10°C / min, and even 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 scrap can be prevented.

[0072] Down Figure 1 This figure shows positive electrode scraps discarded after positive electrode plates are cut from positive electrode sheets.

[0073] 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.

[0074] 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.

[0075] For reference, in the following examples, cathode scrap was used as the spent cathode.

[0076] (b) Grinding the recovered positive electrode active material

[0077] The method for recycling the positive electrode active material of the present invention includes a step (b) of grinding the recovered positive electrode active material once. In this case, the particle size of the positive electrode active material can be uniform, thereby providing a positive electrode active material with excellent battery characteristics. In addition, since the washing process for the recovered positive electrode active material is omitted, damage to the surface of the positive electrode active material can be prevented, and the economic efficiency and productivity can be significantly improved.

[0078] For example, the primary milling can be performed using a centrifugal mill or a jet mill, preferably a centrifugal mill. In this case, the recovered positive electrode active material is uniformly pulverized, thereby obtaining uniform particles.

[0079] For example, a single grinding can be carried out at 6000 to 20000 rpm, preferably 8000 to 18000 rpm, more preferably 9000 to 16000 rpm, even more preferably 11000 to 14000 rpm, even more preferably 11000 to 13000 rpm. Within this range, the crushing efficiency can be excellent, the particle breakage of the positive electrode active material can be prevented, and the productivity can be improved. When the grinding speed is less than 6000 rpm, the grinding effect may not be significant. When the grinding speed exceeds 20000 rpm, the particle breakage of the positive electrode active material may occur.

[0080] For example, a grinding cycle can be performed for 5 to 150 seconds, preferably 10 to 120 seconds, more preferably 10 to 100 seconds, still more preferably 15 to 80 seconds, still more preferably 15 to 60 seconds, and still more preferably 15 to 40 seconds. Within this range, the crushing efficiency can be excellent, the particle breakage of the positive electrode active material can be prevented, and productivity can be improved.

[0081] For example, after a single grinding, the average particle size of the positive electrode active material may be 7.0 to 9.0 μm, preferably 7.3 to 8.5 μm, and more preferably 7.5 to 8.5 μm. Within this range, battery characteristics may be improved.

[0082] In the present disclosure, the particle distribution and the average particle size can be measured by a measurement method commonly used in the field to which the present invention belongs. For example, the particle distribution and the average particle size can be measured by a laser diffraction method. Specifically, the positive electrode active material particles are dispersed in a dispersion medium, the dispersed particles are placed in a commercially available laser diffraction particle size measuring device (such as Microtrac MT3000), and the particles are irradiated with ultrasonic waves of about 28 kHz with an output of 60 W. Then, the average particle size (D50) is calculated based on 50% of the particle size distribution in the measuring device, and the standard deviation of the average particle size (D50) can be calculated.

[0083] For example, the filter size of the centrifugal mill can be 0.08 to 10.0 mm, preferably 0.08 to 7 mm, more preferably 0.08 to 5 mm, even more preferably 0.08 to 3 mm, even more preferably 0.08 to 2 mm, even more preferably 0.08 to 1.0 mm. Within this range, the size of the positive electrode active material particles can be uniform.

[0084] In the present disclosure, the filter size of a centrifugal mill is not particularly limited if the filter size is commonly used in the art to which the present invention pertains. For example, the filter of a centrifugal mill has a circular bar shape. The bar has small pores that are tightly packed like a sieve, and the filter size refers to the size of the pores.

[0085] (c) Adding lithium precursor to the once-milled positive electrode active material and annealing at 400 to 1000°C

[0086] The method for recycling a positive electrode active material of the present invention includes the step (c) of adding a lithium precursor to the once-milled positive electrode active material and annealing at 400 to 1000° C. In this case, by improving crystallinity by increasing crystallinity or restoring the crystal structure, the battery characteristics of the recycled positive electrode active material can be improved.

[0087] The step (c) of performing annealing may preferably be a step of adding a lithium precursor to the recovered positive electrode active material and performing annealing under oxygen (O2) or air at 400°C to 1000°C, more preferably 600°C to 900°C. In this case, the crystallinity, such as the increase in the crystallinity of the positive electrode active material and the restoration of the crystal structure, can be improved, and the battery characteristics of the recycled positive electrode active material can be improved.

[0088] The lithium precursor may preferably include one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0089] The amount of lithium precursor added preferably corresponds to the amount of lithium in the recovered positive active material relative to the amount of lithium in the positive active material of step (a). As a specific example, when the positive active material of step (a) is a positive active material represented by Chemical Formula 1, the amount of lithium precursor added may correspond to a lithium molar ratio of 0.0001 to 0.2, preferably 0.001 to 0.2, more preferably 0.005 to 0.017, even more preferably 0.007 to 0.015, even more preferably 0.009 to 0.013. Within this range, by supplementing lithium in the reused positive active material, the crystallinity can be increased, or the crystal structure can be restored, thereby improving the crystallinity. Therefore, the battery characteristics of the reused positive active material can be improved.

[0090] In the present disclosure, the molar ratio of lithium to other metals in the positive electrode active material is measured using an ICP analyzer. In this case, a general-purpose ICP analyzer commonly used in laboratories can be used without deviation depending on the measuring device or method.

[0091] As another example, the amount of lithium precursor added can provide 1 to 40 mol%, preferably 1 to 30 mol%, more preferably 3 to 20 mol%, even more preferably 7 to 17 mol%, and even more preferably 7 to 11 mol%, based on a total of 100 mol% of lithium contained in the positive electrode active material as a raw material. Within this range, the battery characteristics can be improved because there is no residual precursor that causes an increase in the resistance of the recycled positive electrode active material. In addition, since the crystal structure can be restored with a small amount of lithium precursor, an economic advantage can be achieved compared to the past.

[0092] In this disclosure, raw material, as opposed to "reused," means something that is manufactured for the first time.

[0093] For example, annealing can be performed under air or oxygen atmosphere at 400° C. to 1000° C., preferably 400° C. to 900° C., more preferably 400° C. to 800° C., still more preferably 450° C. to 750° C., and still more preferably 450° C. to 710° C. Within this range, the crystal structure can be restored, and thus the rate performance of the battery can be excellent.

[0094] The annealing temperature can be adjusted within a limited range according to the melting point of the lithium precursor. For example, in the case of LiCO3 as a lithium precursor, its melting point is 723 ° C, so annealing can be preferably performed at 700 ° C to 900 ° C, more preferably 710 ° C to 780 ° C. In the case of LiOH as a lithium precursor, its melting point is 462 ° C, so annealing can be preferably performed at 400 to 600 ° C, more preferably 450 to 480 ° C. Within this range, the crystal structure can be restored, so the rate performance of the battery can be excellent.

[0095] The annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, when the annealing temperature exceeds 1,000°C, thermal decomposition of the positive electrode active material may occur, resulting in degradation of battery performance. Therefore, the annealing temperature is preferably 1,000°C or less.

[0096] For example, the annealing time may be preferably 1 to 15 hours, more preferably 2 to 10 hours, still more preferably 3 to 8 hours, still more preferably 4 to 6 hours, and as a specific example, about 5 hours. Within this range, the crystal structure can be fully recovered and economic efficiency can be improved.

[0097] The annealing temperature may be reached preferably at a heating rate of 1° C. / min to 10° C. / min, more preferably 1° C. / min to 7° C. / min, and even more preferably 2° C. / min to 4° C. / min. In this case, the crystallinity of the recycled positive electrode active material may be further increased, and thus the battery characteristics of the recycled positive electrode active material may be improved.

[0098] For example, the annealing step may include a cooling process. As a specific example, the cooling process may be natural cooling in a furnace. In this case, the crystallinity of the recycled positive electrode active material can be further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0099] In the present disclosure, annealing may follow the definition used in the technical field to which the present invention belongs. As a specific example, annealing may be defined as a heat treatment operation that repairs deformation or lattice defects and improves crystallinity by heating a positive electrode active material having a deformed structure or lattice defects at a temperature that allows sufficient diffusion and movement of atoms of the main components in the positive electrode active material (i.e., a temperature above the recrystallization temperature) for an appropriate period of time.

[0100] (d) Secondary grinding of the annealed positive electrode active material

[0101] The method for recycling positive electrode active materials of the present invention includes a step of secondary grinding of the annealed positive electrode active material. In this case, by reducing the particle size of the positive electrode active material that has increased due to the annealing step, a recycled positive electrode active material having a particle size similar to that of the positive electrode active material in the spent positive electrode can be provided, thereby improving battery characteristics.

[0102] For example, the secondary milling can be performed using a centrifugal mill or a jet mill, preferably a centrifugal mill. In this case, by reducing the particle size of the positive electrode active material increased by the annealing step, a recycled positive electrode active material having a particle size similar to that of the positive electrode active material in the spent positive electrode can be provided, and battery characteristics can be improved.

[0103] For example, the secondary grinding may be performed at 6000 to 20000 rpm, preferably 8000 to 20000 rpm, more preferably 10000 to 19000 rpm, still more preferably 12000 to 19000 rpm, still more preferably 14000 to 19000 rpm, and still more preferably 16000 to 19000 rpm. Within this range, the crushing efficiency can be excellent, a recycled positive electrode active material having a particle size similar to that of the positive electrode active material in the waste positive electrode can be provided, and productivity can be improved.

[0104] For example, the secondary grinding can be performed for 5 seconds to 150 seconds, preferably 10 seconds to 120 seconds, more preferably 10 seconds to 100 seconds, still more preferably 10 seconds to 80 seconds, and still more preferably 15 seconds to 60 seconds. Within this range, the crushing efficiency can be excellent, the particle breakage of the positive electrode active material can be prevented, and the productivity can be improved.

[0105] After secondary grinding, for example, the average particle size of the positive electrode active material may be 7.0 to 11.0 μm, preferably 7.5 to 10 μm, more preferably 7.5 to 9.0 μm, and even more preferably 8.0 to 9.0 μm. Within this range, battery characteristics may be improved.

[0106] After secondary grinding, for example, the average particle size standard deviation of the recycled positive electrode active material can be 3.0 or less, preferably 2.7 or less, more preferably 2.5 or less, and even more preferably 0.1 to 2.5. Within this range, the particle distribution of the recycled positive electrode active material can be similar to that of the positive electrode active material in the spent positive electrode, thereby improving battery characteristics.

[0107] After secondary grinding, for example, the average particle size growth rate of the obtained positive electrode active material can be 14% or less, preferably 12% or less, more preferably 10% or less, even more preferably 8% or less, and even more preferably 0.1% to 8% compared to the positive electrode active material in the positive electrode as a raw material. Within this range, the average particle size and particle distribution of the obtained positive electrode active material can be similar to those of the raw material positive electrode active material, thereby improving battery characteristics. The average particle size growth rate can be calculated by the following equation 1.

[0108] [Equation 1]

[0109] Average particle size growth rate (%) = [(ba) / a] × 100

[0110] In Equation 1, a represents the average particle size of the positive electrode active material as a raw material, and b represents the average particle size of the recycled positive electrode active material measured after secondary grinding.

[0111] (e) Washing the positive electrode active material after secondary grinding

[0112] The method for recycling the positive electrode active material of the present invention includes a step (e) of washing the positive electrode active material after secondary grinding. In this case, since the lithium precursor is removed with a small amount of washing liquid, the battery performance degradation and gas generation caused by the reaction between the residual lithium precursor and the electrolyte solution in the subsequent steps can be prevented, and wastewater treatment can be omitted. In particular, the lithium precursor that is more likely to remain due to the high Ni content in the high-nickel positive electrode active material can be removed with a small amount of washing liquid.

[0113] In the present disclosure, the high-nickel positive electrode active material refers to a positive electrode active material having a nickel content of 60 mol % or more based on 100 mol % in total of other metals excluding Li.

[0114] Washing may preferably include the steps of mixing the secondary ground positive electrode active material with a washing liquid and then filtering, and drying the solid positive electrode active material obtained after filtration. In this case, excess lithium remaining in the positive electrode active material can be effectively removed.

[0115] For example, in the washing step, the weight ratio of the positive electrode active material after secondary grinding to the washing liquid may be 1:0.5 to 1:10, preferably 1:0.5 to 1:7, more preferably 1:0.5 to 1.5, even more preferably 1:0.5 to 1:3, even more preferably 1:0.5 to 1:2, even more preferably 1:0.5 to 1.5. In this case, lithium precursors that are easily residual, such as LiOH and Li2CO3, can be effectively removed. In particular, lithium precursors such as LiOH and Li2CO3 that are more likely to remain due to the addition of excess lithium to suppress the cation mixing phenomenon that may occur in the high-nickel positive electrode active material can be effectively removed. The cation mixing phenomenon is a phenomenon that occurs due to the similar ion sizes of nickel and lithium.

[0116] In particular, when the annealed active material and the washing solution are mixed in a weight ratio of 1:0.5 to 1:2, preferably 1:0.5 to 1.5, the initial discharge capacity (DCH) and efficiency of the recycled positive active material can be further improved.

[0117] The washing liquid may be preferably water, more preferably distilled water or deionized water. In this case, lithium precursors such as LiOH and Li2CO3 that are more likely to remain due to the addition of excess lithium to suppress the cation mixing phenomenon that may occur in the high nickel positive active material can be effectively removed.

[0118] For example, washing may preferably include the steps of mixing the secondary ground positive electrode active material with a washing liquid and then filtering it, 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.

[0119] The filtration may preferably be pressure filtration using a filter.

[0120] Drying can be performed at preferably 100°C to 500°C, more preferably 120°C to 400°C, still more preferably 120°C to 300°C, still more preferably 120°C to 200°C.

[0121] The drying may preferably be vacuum drying.

[0122] The vacuum drying method commonly used in the technical field of the present invention can be used in the present invention without particular limitation. For example, vacuum drying can include drying under partial vacuum or low pressure.

[0123] (f) Coating the surface of the washed positive electrode active material

[0124] The method for recycling the positive electrode active material of the present invention includes the step (f) of coating the surface of the washed positive electrode active material. In this case, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0125] As another example, the method for recycling the positive electrode active material of the present invention includes a step (f') of coating the surface of the secondary ground positive electrode active material. In this case, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0126] When coating the surface, preferably, the surface can be coated 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 then heat-treated at 100° C. to 1200° C. In this case, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0127] The coating agent containing a metal 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. Still more preferably, it is a coating agent containing boron (B), tungsten (W), or a mixture thereof. Still more preferably, it is a coating agent containing tungsten (W) and boron (B). A specific example is a coating agent containing tungsten boride (WB). In this case, the resistance characteristics and life characteristics can be improved.

[0128] For example, the coating agent containing a metal may be an oxide or an acid containing a metal as an element in its molecule.

[0129] 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.

[0130] 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.

[0131] 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 %, even more preferably 0.01 mol % to 0.1 mol %, and even more preferably 0.01 mol % to 0.05 mol %. Within this range, structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0132] The heat treatment time may be 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.

[0133] 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.

[0134] For example, the metal, organometallic, and carbon components may have a spherical, plate-like, square, or needle-like shape. The shape can be controlled, for example, by varying the process conditions during the preparation process. The shapes are not particularly limited, as long as the shapes conform to generally accepted definitions in the art to which the present invention pertains.

[0135] 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.

[0136] In the present invention, 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 60 W and a frequency of approximately 28 kHz. The average particle diameter (D50) is then calculated based on the 50% percentile of the particle size distribution in the measurement device.

[0137] In the present invention, 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 a BELSORP-mino II manufactured by BEL Japan Co.

[0138] Recycling of positive electrode active materials

[0139] The recycled positive electrode active material of the present invention is prepared by the recycling method of the positive electrode active material. In this case, electrochemical performance, capacity characteristics and resistance characteristics can be excellent.

[0140] In addition, the recycled positive active material of the present invention may include one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive active materials, nickel cobalt manganese (NCM)-based positive active materials, nickel cobalt aluminum (NCA)-based positive active materials, and nickel cobalt manganese aluminum (NCMA)-based positive active materials; based on a total of 100 mol% of other metals other than Li, the Ni content may be 60 mol% or more; and the positive active material has an average particle size standard deviation of 3.0 or less. In this case, the battery characteristics may be excellent.

[0141] The average particle size standard deviation of the recycled positive electrode active material may be preferably 2.7 or less, more preferably 2.5 or less. Within this range, the diameter distribution of the recycled positive electrode active material can be similar to that of the spent positive electrode active material, and battery characteristics can be improved.

[0142] Compared to the average particle size of the positive electrode active material of the spent positive electrode, the average particle size increase rate of the recycled positive electrode active material can be 14% or less, preferably 12% or less, more preferably 10% or less, even more preferably 8% or less, and even more preferably 0.1% to 8%. Within this range, the diameter distribution of the recycled positive electrode active material can be similar to that of the spent positive electrode active material, and battery characteristics can be improved.

[0143] The recycled positive electrode active material preferably includes 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). In this case, the electrochemical performance, resistance characteristics, and capacity characteristics can be excellent.

[0144] As a specific example, the recycled positive electrode active material may be a compound represented by the following Chemical Formula 1.

[0145] [Chemical Formula 1]

[0146] Li a Ni x Mn y Co z M w O 2+δ

[0147] 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 be excellent.

[0148] Based on a total of 100 mol% of other metals except Li, the content of Ni in the recycled positive electrode active material is preferably 80 mol% or more, more preferably 81 mol% or more. Within this range, the initial discharge capacity, output performance, capacity characteristics, and resistance characteristics can be excellent.

[0149] For example, the surface of the recycled positive electrode active material may be coated with a metal or carbon, preferably a metal. In this case, the structural stability of the positive electrode active material can be improved without chemical or physical changes in the positive electrode active material, thereby improving the output performance, life characteristics, and electrochemical characteristics (such as capacity). In addition, substitution with foreign elements occurs on the surface of the positive electrode active material, and as a result, the amount of residual lithium and pH can be reduced, thereby improving the physicochemical properties.

[0150] The metal preferably includes 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 includes one or more selected from the group consisting of B, W, Al, Ti, and Mg. Furthermore, it further preferably includes boron (B), tungsten (W), or a mixture thereof. Furthermore, it further 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.

[0151] For example, based on 100 mol % of metal in the positive electrode active material before coating, the content of the coating agent may 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 even more preferably 0.01 mol % to 0.05 mol %. Within this range, structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0152] 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., 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.

[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] See also 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 about 120°C to obtain a positive electrode sheet. The positive electrode sheet is then punched into a positive electrode plate of a certain size. In this process, positive electrode waste is generated.

[0155] Positive electrode waste includes a positive electrode active material layer formed on aluminum foil. After the solvent evaporates, the positive electrode active material layer has a structure in which the positive electrode active material and the conductive material are bonded together by a binder. Therefore, when the binder is removed, the positive electrode active material separates 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. As a specific example, the size of the crushed positive electrode waste can be 1 cm × 1 cm. For example, dry crushing equipment (such as a hand grinder, a pin mill, a disc mill, a cutting mill, and a hammer mill) can be used for crushing. In order to improve productivity, 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 pulverized positive electrode scrap is heat-treated to recover the positive electrode active material (step S30). Here, the heat treatment is performed to thermally decompose the binder and the conductive material.

[0159] For example, the heat treatment can be performed at 300°C to 650°C in an air atmosphere. Here, the binder and the conductive material are thermally decomposed into CO2 and H2O and removed. Since the binder is removed, the positive electrode active material can be separated from the positive electrode active material layer.

[0160] It is important that the heat treatment be performed in an air atmosphere. When heat treatment is performed in a reducing or inert gas atmosphere, the binder and conductive material are carbonized rather than thermally decomposed. When the binder and conductive material are carbonized, the carbon components remain on the surface of the positive electrode active material, resulting in deterioration in the performance of the recycled positive electrode active material. In contrast, when heat treatment is performed in air, both the binder and conductive material are removed because the carbon components in the binder and conductive material react with oxygen, are converted into gases such as CO and CO2, and disappear.

[0161] The heat treatment is preferably performed at 300°C to 650°C, and as a specific example, at 550°C. When the heat treatment is performed at a temperature below 300°C, it is difficult to separate the current collector because the binder is not removed. When the heat treatment is performed at a temperature exceeding 650°C, the current collector melts, making it impossible to separate the current collector.

[0162] The heat treatment is performed at a heating rate of preferably 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, the heat treatment can be performed without burdening the heat treatment equipment, and thermal shock to the positive electrode scrap can be prevented.

[0163] The heat treatment may be performed until the adhesive is completely thermally decomposed. For example, the heat treatment may be performed for preferably 30 minutes or more, more preferably 30 minutes to 5 hours, with 30 minutes being a specific example. Within this range, the adhesive 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 treatment can be used.

[0165] After the heat treatment, slow cooling or rapid cooling in air may be performed.

[0166] Next, the recovered positive electrode active material is subjected to a primary grinding (step S40 ).

[0167] In the primary grinding process, it is important to directly grind the recovered positive electrode active material without the washing process. In this case, damage to the surface of the positive electrode active material can be prevented, the particles of the positive electrode active material can be uniform, and the process cost can be reduced by not performing the washing process.

[0168] For example, the primary milling can be performed using a centrifugal mill or a jet mill, preferably a centrifugal mill. In this case, the particles of the recovered positive electrode active material can be homogenized, thereby improving battery characteristics.

[0169] For example, the primary grinding may be performed at 6000 to 20000 rpm, particularly 12000 rpm. Within this range, the crushing efficiency may be excellent, the breakage of the positive electrode active material particles may be prevented, and the productivity may be improved.

[0170] For example, the grinding may be performed for 5 to 150 seconds, particularly 30 seconds. Within this range, the crushing efficiency may be excellent, the particles of the positive electrode active material may be prevented from being broken, and the productivity may be improved.

[0171] For example, after a single grinding, the average particle size of the positive electrode active material may be 7.0 to 9.0 μm, preferably 7.5 to 8.5 μm, and more preferably 8.0 to 8.5 μm. Within this range, battery characteristics may be improved.

[0172] Next, a lithium precursor is added to the once-milled positive electrode active material and annealing is performed (step S50 ).

[0173] In addition, in the previous step S30, lithium loss occurs in the positive electrode active material during the annealing step. In step S50, 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 S45, the crystal structure of the positive electrode active material can be restored by annealing, 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.

[0174] As a specific example, LiOH is used as the lithium precursor.

[0175] 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.

[0176] For example, when the molar ratio of lithium (Li) to other metals (M) in the fresh positive active material is 1, the amount of lithium precursor added can be such that the molar ratio of lithium is 0.001 to 0.4, preferably 0.01 to 0.4, and more preferably 0.09 to 0.2. As a specific example, when the amount of lithium precursor added corresponds to the loss ratio 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 equal to that of the fresh positive active material. Here, the ICP analysis results have an error value of about ±0.02.

[0177] For example, the amount of lithium precursor added can provide 1 to 40 mol%, preferably 1 to 15 mol%, and more preferably 7 to 11 mol%, of lithium based on 100 mol% of the total lithium contained in the recycled positive electrode active material. Within this range, battery characteristics can be improved because no residual precursor remains in the recycled positive electrode active material, which may increase resistance.

[0178] For example, annealing can be performed in air or oxygen atmosphere at 400 to 1000° C., preferably 400 to 900° C., more preferably 400 to 800° C., and still more preferably 450 to 710° C. In this case, the temperature should be determined within a limited range according to the type of lithium precursor.

[0179] The annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, since the positive electrode active material decomposes at a temperature exceeding 1000°C and performance deteriorates, 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 710°C to 780°C, and even more preferably 750°C to 780°C. In addition, when LiOH is used as the lithium precursor, the annealing temperature is preferably 400°C to 600°C, more preferably 450°C to 480°C, and even more preferably 470°C to 480°C.

[0180] For example, the annealing time is preferably 1 hour or longer, more preferably 15 hours or shorter, and even more preferably 4 to 6 hours. When the annealing time is longer, the crystal structure can be fully restored, and even long-term annealing will not significantly affect the performance. In this case, the same or similar equipment as that in step S30 for performing the heat treatment can be used as the annealing equipment.

[0181] Next, the annealed positive electrode active material is subjected to secondary grinding (step S60 ).

[0182] In the secondary grinding (step S60), the particle size of the positive electrode active material increased by the annealing step S50 is reduced, so that the particle size of the positive electrode active material becomes similar to that of the positive electrode active material in the waste positive electrode. Therefore, the battery characteristics can be improved.

[0183] For example, the secondary milling can be performed using a centrifugal mill or a jet mill, preferably a centrifugal mill. In this case, the particle size can be reduced without damaging the particles of the positive electrode active material.

[0184] For example, the secondary milling may be performed at 6000 to 20000 rpm, and as a specific example, at 18000 rpm. Within this range, the milling efficiency may be excellent, and the particle size of the positive electrode active material may be reduced, thereby improving productivity.

[0185] For example, the secondary grinding may be performed for 5 to 150 seconds, particularly 30 seconds. Within this range, the crushing efficiency may be excellent, the particles of the positive electrode active material may be prevented from being broken, and the productivity may be improved.

[0186] After secondary grinding, the average particle size of the positive electrode active material may be 7.0 to 11.0 μm, preferably 7.5 to 10 μm, more preferably 7.5 to 9.0 μm, and even more preferably 8.0 to 9.0 μm. Within this range, battery characteristics may be improved.

[0187] Next, as an optional step, the secondary ground positive electrode active material is washed (step S70 ).

[0188] Since the lithium precursor that fails to participate in the reaction 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. In particular, due to the cation mixing phenomenon, high nickel (Ni) positive electrode active materials require excess Li, which promotes the residue of lithium impurities such as lithium carbonate (Li2CO3) on the surface. In addition, these impurities may react with the electrolyte solution, thereby degrading battery performance and generating gas, so these impurities must be thoroughly removed.

[0189] Distilled water is preferably used for washing, in which case safety can be ensured, cost can be reduced, and dissolution of transition metals contained in the positive electrode active material can be prevented.

[0190] In the washing, the annealed positive electrode active material and the washing liquid are mixed at a weight ratio of 1:0.5 to 1:10 (1:1 as a specific example), filtered, and the obtained solid positive electrode active material is dried.

[0191] The mixing of the annealed positive electrode active material and the washing liquid is preferably performed by stirring. The stirring method is not particularly limited, but can be mechanical stirring, magnetic stirring or ultrasonic stirring.

[0192] The mechanical stirring includes an impeller, and may be preferably performed at 250 to 350 RPM for 3 to 10 minutes.

[0193] The filtration is preferably vacuum filtration using a filter, and the drying is preferably vacuum drying at 120°C to 140°C.

[0194] Next, as an optional step, the surface of the washed positive electrode active material may be coated (step S80 ).

[0195] 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.

[0196] 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.

[0197] Surface coating can be performed using solid phase or liquid phase methods, examples being mixing, grinding, spray drying or milling.

[0198] When the molar ratio of lithium to other metals in the positive electrode active material is 1:1 in the annealing step S50, 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 S50, 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.

[0199] secondary batteries

[0200] The secondary battery of the present invention includes a recycled positive electrode active material prepared using a method for recycling positive electrode active materials. In this case, because the particle distribution of the recycled positive electrode active material is similar to that of the positive electrode active material in the spent positive electrode, battery characteristics can be significantly improved. Furthermore, because acids and organic solvents are not used in the process of recovering and recycling the positive electrode active material, eco-friendliness is ensured. In particular, because the initial washing process is omitted, economical efficiency and productivity can be excellent.

[0201] Furthermore, the secondary battery of the present invention includes the aforementioned positive electrode active material. In this case, the average particle size and standard deviation of the recycled positive electrode active material are similar to those of the positive electrode active material in the spent positive electrode, significantly improving battery characteristics. Furthermore, since acids and organic solvents are not used during the recovery and reuse of the positive electrode active material, eco-friendliness is ensured. In particular, since the initial washing process is omitted, economic efficiency and productivity can be excellent.

[0202] The description of the secondary battery of the present invention may cover all the above descriptions on the positive electrode active material and the method for recycling the positive electrode active material, and thus repeated descriptions are omitted in this specification.

[0203] 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.

[0204] Example

[0205] Example 1

[0206] After punching the positive plates, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide, which contains 87 mol% nickel based on 100 mol% of all metals other than Li) was crushed and heat-treated in air at 590°C for 30 minutes to remove the binder and conductive material and separate the current collector and positive electrode active material. Through these processes, the positive electrode active material was recovered. At this time, the temperature was raised to the heat treatment temperature at a heating rate of 5°C / min, and air was supplied at a rate of 10 L / min.

[0207] The recovered positive electrode active material was subjected to primary milling at 12,000 rpm for 30 seconds using a centrifugal mill (ZM200, Retsch Co.) After the primary milling, the average particle size (D50) of the positive electrode active material was 7.9 μm.

[0208] LiOH as a lithium precursor was added to the once-milled positive electrode active material in an amount providing 15 mol% of lithium based on 100 mol% of lithium in the total amount of the positive electrode active material used as a raw material, and annealing was performed in air at a firing temperature of 750° C. for 5 hours. At this time, air was supplied at 3 L / min.

[0209] Secondary milling was performed on the annealed positive electrode active material at 18,000 rpm for 30 seconds. After the secondary milling, the average particle size (D50) of the positive electrode active material was 8.99 μm.

[0210] Example 2

[0211] The same procedure as in Example 1 was performed, except that the primary grinding was performed at 12,000 rpm for 30 seconds and the secondary grinding was performed at 12,000 rpm for 30 seconds.

[0212] Comparative Example 1

[0213] The same procedure as in Example 1 was performed except that the primary and secondary grinding were not performed.

[0214] Comparative Example 2

[0215] The same procedure as in Example 1 was performed except that the secondary grinding was not performed.

[0216] Comparative Example 3

[0217] The same procedure as in Example 1 was performed, except that the first grinding was not performed.

[0218] Comparative Example 4

[0219] After punching the positive plates, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide, which contains 87 mol% nickel based on 100 mol% of all metals other than Li) was crushed and heat-treated in air at 590°C for 30 minutes to remove the binder and conductive material and separate the current collector and positive electrode active material. Through these processes, the positive electrode active material was recovered. At this time, the temperature was raised to the heat treatment temperature at a heating rate of 5°C / min, and air was supplied at a rate of 10 L / min.

[0220] The recovered positive active material was washed by immersing the material in distilled water while stirring the material. At this time, the recovered positive active material was stirred with distilled water at a weight ratio of 1:10 at 500 rpm for 10 minutes, and then only the active material was extracted by vacuum filtration using a filter.

[0221] After the washed positive electrode active material was dried overnight at 100° C., LiOH as a lithium precursor was added in an amount that provided 15 mol% of lithium based on 100 mol% of lithium in the positive electrode active material used as a raw material, and annealing was performed in air at a firing temperature of 750° C. for 5 hours. At this time, air was supplied at 3 L / min.

[0222] Reference Example

[0223] Instead of reusing the positive electrode active material, a freshly prepared NCM-based lithium composite transition metal oxide (which contains 87 mol % of nickel based on 100 mol % of all metals except Li) was used.

[0224] [Experimental Example 1: Particle Distribution of Recycled and Freshly Prepared Positive Electrode Active Materials]

[0225] The particle distribution of the recycled positive active material or the fresh positive active material obtained in Examples 1 and 2, Comparative Examples 1 to 4 and the reference example was measured using a laser diffraction method. Specifically, the positive active material particles are dispersed in a dispersion medium, the dispersed particles are placed in a commercially available laser diffraction particle size measuring device (such as Microtrac MT3000), and the particles are irradiated with ultrasonic waves of about 28kHz with an output of 60W to measure the particle distribution. Then, the average particle size, its standard deviation and the particle size growth rate are calculated based on 50% of the measured particle size distribution. The particle size growth rate is calculated based on the reference example.

[0226] The average particle diameters, standard deviations and particle diameter growth rates of the recycled positive electrode active materials or fresh positive electrode active materials obtained in Examples 1 and 2, Comparative Examples 1 to 4 and Reference Example are shown in Table 1 below.

[0227] in addition, Figure 2The particle distribution of the recycled positive electrode active material or the fresh positive electrode active material obtained in Example 1, Reference Example, and Comparative Examples 1 to 3 is shown. Figure 3 Particle distributions of the recycled positive electrode active materials or fresh positive electrode active materials obtained in Examples 1 and 2, Reference Example, and Comparative Examples 1 and 4 are shown.

[0228] Table 1

[0229] Classification Average particle size (μm) Average particle size standard deviation Particle size growth rate (%) Example 1 8.99 2.47 7.41 Example 2 9.44 2.57 12.78 Comparative Example 1 14.02 6.29 67.50 Comparative Example 2 11.88 4.60 41.94 Comparative Example 3 9.70 3.57 15.89 Comparative Example 4 10.41 3.69 24.37 Reference Example 8.37 2.16 -

[0230] As shown in Table 1, in the case of Examples 1 and 2 of the present invention, the average particle size, its standard deviation, and the particle size growth rate were reduced compared to Comparative Examples 1 to 4, showing levels similar to those of the reference example (freshly prepared positive electrode active material). These results indicate that the battery characteristics were further improved.

[0231] like Figure 2 As shown, Example 1 of the present invention exhibits a particle distribution similar to that of the reference example (freshly prepared positive electrode active material), indicating that the battery characteristics are further improved.

[0232] In addition, if Figure 3 As shown, Examples 1 and 2 of the present invention exhibited similar particle distributions to that of the reference example (freshly prepared positive electrode active material), indicating improved battery characteristics.

[0233] [Explanation of Reference Numerals]

[0234] 10: Current collector

[0235] 20: Active material layer

[0236] 30: Positive electrode

[0237] 40: Positive plate

[0238] 50: Positive electrode waste

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 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; Grinding the recovered positive electrode active material once; adding a lithium precursor to the once-milled positive electrode active material and annealing the material at 400° C. to 1000° C.; and The annealed positive electrode active material is ground a second time.

2. The method according to claim 1, wherein The positive electrode active material layer includes one or more selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, a nickel·cobalt·manganese (NCM)-based positive electrode active material, a nickel·cobalt·aluminum (NCA)-based positive electrode active material, and a nickel·cobalt·manganese·aluminum (NCMA)-based positive electrode active material, and the Ni content is 60 mol% or more based on a total of 100 mol% of other metals other than Li.

3. The method according to claim 1, wherein The heat treatment is performed at 300° C. to 650° C. in air or an oxygen atmosphere.

4. The method according to claim 1, wherein The primary grinding and the secondary grinding are performed using a centrifugal mill or a jet mill.

5. The method according to claim 1, wherein The primary grinding and the secondary grinding are performed at 6000 rpm to 20000 rpm.

6. The method of claim 1, wherein: The positive electrode active material obtained after the secondary grinding has an average particle size increase rate of 14% or less and an average particle size standard deviation of 3.0 or less, compared to the positive electrode active material in the raw material.

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

8. The method of claim 1, wherein: The amount of the lithium precursor added can provide lithium in an amount corresponding to 1 to 40 mol % based on 100 mol % in total of lithium in the positive electrode active material used as a raw material.

9. The method of claim 1, wherein: The annealing is performed in air at 400° C. to 1000° C.

10. The method of claim 1, comprising: washing the secondary ground positive electrode active material; coating the surface of the secondary ground positive electrode active material; Alternatively, the secondary ground positive electrode active material is washed and then coated on the surface.

11. The method according to claim 10, wherein: In the washing step, the weight ratio of the annealed positive electrode active material to the washing solution is 1:0.5 to 1:

10.

12. The method of claim 10, wherein: Surface coating is performed by coating the surface with one or more of metal, organometallic and carbon components in solid or liquid form and heating the surface at 100°C to 1200°C.

13. A recycled positive electrode active material comprising one or more selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, a nickel·cobalt·manganese (NCM)-based positive electrode active material, a nickel·cobalt·aluminum (NCA)-based positive electrode active material, and a nickel·cobalt·manganese·aluminum (NCMA)-based positive electrode active material; The Ni content is 60 mol% or more based on 100 mol% of the total of other metals except Li; and The average particle size standard deviation is 3.0 or less.

14. The recycled positive electrode active material according to claim 1, wherein The surface of the positive electrode active material is coated with a coating agent containing metal or carbon.

15. The recycled positive electrode active material according to claim 14, wherein The metal is boron (B), tungsten (W) or a mixture thereof. 16 . A secondary battery comprising the recycled positive electrode active material according to claim 13 .

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