Method for regenerating positive electrode active material, regenerated positive electrode active material produced therefrom, and secondary battery including the same

Abstract

The present invention relates to a method for regenerating a cathode active material, a regenerated cathode active material manufactured using the method, and a secondary battery including the same. More specifically, the present invention relates to a method for regenerating a cathode active material, the method including the steps of: heat-treating a waste cathode having a cathode active material layer formed on a current collector to recover the cathode active material in the cathode active material layer by thermally decomposing the binder and conductive material in the cathode active material layer; primary-milling the recovered cathode active material; adding a lithium precursor to the primarily-milled cathode active material and annealing it at 400 to 1000°C; and secondary-milling the annealed cathode active material; a regenerated cathode active material manufactured using the method, and a secondary battery including the same. According to the present invention, the cathode active material recovered after heat treatment of waste cathodes is subjected to primary milling without a washing step, and a lithium precursor is added to the primary milled cathode active material, followed by annealing and secondary milling. This prevents damage to the surface of the cathode active material particles, uniforms the particle size of the recycled cathode active material, and reduces the increase in particle size, thereby providing a method for recycling cathode active material with excellent battery characteristics.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0103933, filed on August 9, 2023, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for regenerating a cathode active material, a regenerated cathode active material manufactured using the same, and a secondary battery including the same. More specifically, the present invention relates to a method for regenerating a cathode active material, which involves heat-treating a used cathode and then recovering the recovered cathode active material without a washing process, primarily milling the recovered cathode active material without a washing process, adding a lithium precursor to the primarily milled cathode active material, annealing the resulting material, and then secondary milling the annealed cathode active material. This prevents surface damage to the cathode active material, uniforms the particle size of the regenerated cathode active material, and minimizes particle size increase, resulting in excellent battery properties. Furthermore, the cathode active material recovery and regeneration process does not use an acid, which is environmentally friendly and eliminates the need for neutralization and wastewater treatment, thereby reducing process costs. The cathode active material is regenerated directly without decomposition, so there are no metal elements to be discarded. Furthermore, no organic solvents are used, so there is no risk of toxic gas generation or explosion. These results demonstrate significant improvements in economy and productivity. [Background technology]

[0003] Lithium secondary batteries are broadly composed of a positive electrode in which a positive electrode active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative electrode active material layer is coated on a metal foil such as copper, a separator that prevents the positive electrode and negative electrode from mixing, and an electrolyte that allows lithium ions to move between the positive electrode and negative electrode.

[0004] The positive electrode active material layer mainly uses a lithium-based oxide as an active material, and the negative electrode active material layer mainly uses a carbon material as an active material. However, the lithium-based oxide generally contains rare metals such as cobalt, nickel, or manganese. Therefore, much research has been conducted into recovering and reusing rare metals from the positive electrodes of lithium secondary batteries that are discarded after use or from positive electrode scraps generated in the manufacturing process of lithium secondary batteries (hereinafter referred to as "waste positive electrodes").

[0005] Conventional techniques for recovering rare metals from used positive electrodes mostly involve dissolving the used positive electrodes in hydrochloric acid, sulfuric acid, or nitric acid, then extracting cobalt, manganese, nickel, etc. with an organic solvent and using them again as raw materials for synthesizing positive electrode active materials.

[0006] However, the method of extracting rare metals using acid has the disadvantage of causing environmental pollution, requiring a neutralization process and a wastewater treatment process, which significantly increases the process cost, and making it impossible to recover lithium, the main metal in the positive electrode active material.

[0007] To overcome these drawbacks, direct recycling methods have recently been studied to directly recycle cathode active materials from waste cathodes without decomposing them. These methods can be broadly divided into four types: calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

[0008] However, although the calcination method is simple, it has drawbacks in that foreign matter that reduces the output performance of the battery is generated on the surface of the regenerated positive electrode active material, waste gas is generated, and energy consumption is high.

[0009] In addition, although the solvent dissolution method can produce recycled cathode active materials with a relatively clean surface, it has the disadvantage of being unstable because the solvent used to dissolve the binder, such as N-methyl-2-pyrrolidone (NMP), is a toxic gas and has the risk of explosion, and requires an expensive solvent recovery process.

[0010] In addition, the aluminum foil dissolution method has good process stability, low process costs, and easy binder removal, but has drawbacks in that it generates foreign matter that is difficult to remove on the surface of the recycled cathode active material, and hydrogen gas is generated during the aluminum foil removal process, which may pose an explosion risk.

[0011] Finally, the crushing and screening method has the advantage of being the simplest process, but has the disadvantages that it is difficult to completely separate the current collector from the cathode active material, the particle size distribution of the cathode active material changes during the crushing process, and the binder remains, which can deteriorate the battery characteristics of the recycled cathode active material.

[0012] Therefore, there is an urgent need to develop a method for safely and environmentally friendly regeneration of a positive electrode active material from waste positive electrodes, which does not contain any discarded metal elements and has improved output performance, with fewer steps and less cost. Summary of the Invention [Problem to be solved by the invention]

[0013] To address the above-mentioned problems of the prior art, the present invention provides a method for regenerating a cathode active material by heat-treating a used cathode and then subjecting the recovered cathode active material to primary milling without a washing process. The method then adds a lithium precursor to the primary-milled cathode active material, annealing it, and then subjecting it to secondary milling. This prevents surface damage to the cathode active material, uniforms the particle size of the regenerated cathode active material, and minimizes particle size increase. This method also provides a regenerated cathode active material with excellent battery characteristics. Furthermore, the cathode active material recovery and regeneration process does not use an acid, which is environmentally friendly and eliminates the need for neutralization and wastewater treatment, thereby reducing process costs. The cathode active material is regenerated directly without decomposition, so there are no metal elements to be discarded. Furthermore, no organic solvents are used, so there is no risk of toxic gas generation or explosion. This method significantly improves economy and productivity. The present invention also provides a regenerated cathode active material regenerated using the method, which has excellent battery characteristics.

[0014] Another object of the present invention is to provide a secondary battery containing a positive electrode active material with excellent battery characteristics.

[0015] The above and other objects of the present invention can all be achieved by the present invention described below. [Means for solving the problem]

[0016] In order to achieve the above object, I) the present invention provides a method for regenerating a positive electrode active material, comprising the steps of: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector, and recovering the positive electrode active material in the positive electrode active material layer by thermally decomposing the binder and conductive material in the positive electrode active material layer; primary milling the recovered positive electrode active material; adding a lithium precursor to the primarily milled positive electrode active material and annealing it at 400 to 1000°C; and secondary milling the annealed positive electrode active material.

[0017] II) In I), the positive electrode active material layer is preferably at least one 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 may contain 60 mol % or more of Ni based on 100 mol % of the total of the remaining metals excluding Li.

[0018] III) In the above I) or II), the heat treatment may be preferably carried out at 300 to 650° C. in an air or oxygen atmosphere.

[0019] IV) In the above I) to III), the primary and secondary milling may be preferably carried out using a centrifugal mill or a jet mill, respectively.

[0020] V) In the above I) to IV), the primary and secondary milling may be preferably carried out at 6,000 to 20,000 rpm, respectively.

[0021] VI) In the above I) to V), the cathode active material obtained after the secondary milling may preferably have an average particle size increase rate of 14% or less relative to the cathode active material in the raw material, and a standard deviation of the average particle size of 3.0 or less.

[0022] VII) In the above I) to VI), the lithium precursor may preferably include any one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0023] VIII) In the above I) to VII), the lithium precursor may be added in an amount that can provide lithium equivalent to 1 to 40 mol % when the total amount of lithium in the raw material positive electrode active material is taken as 100 mol %.

[0024] IX) In the above I) to VIII), the annealing may be preferably carried out at a temperature of 400 to 1000°C.

[0025] X) In the above I) to IX), the method for regenerating the positive electrode active material may preferably include a step of washing the secondary-milled positive electrode active material, a step of surface-coating the secondary-milled positive electrode active material, or a step of washing and then surface-coating the secondary-milled positive electrode active material.

[0026] XI) In the above I) to X), in the washing step, the weight ratio of the secondary milled positive electrode active material to the washing solution may be preferably 1:0.5 to 1:10.

[0027] XII) In the above I) to XI), the surface coating may be preferably performed by coating the surface with one or more of a metal, an organic metal, and a carbon component by a solid phase or liquid phase method, followed by heat treatment at 100 to 1200°C.

[0028] Furthermore, XIII) the present invention provides a recycled positive electrode active material, which is at least one 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 is characterized in that it contains 60 mol % or more of Ni, based on 100 mol % of the total of the remaining metals excluding Li, and the standard deviation of the average particle size of the recycled positive electrode active material is 3.0 or less.

[0029] XIV) In the above XIII), the surface of the regenerated positive electrode active material may preferably be coated with a coating agent containing metal or carbon.

[0030] XV) In the above XIII) or XIV), the metal may preferably be boron (B), tungsten (W), or a mixture thereof.

[0031] Furthermore, XVI) the present invention provides a regenerated positive electrode active material, which is produced by the method for regenerating a positive electrode active material according to any one of I) to XII) above.

[0032] Furthermore, XVII) the present invention provides a secondary battery comprising a regenerated positive electrode active material according to any one of XIII) to XVI). [Effects of the Invention]

[0033] According to the present invention, the cathode active material recovered after heat treatment of waste cathodes is subjected to primary milling without a washing process. A lithium precursor is added to the primary milled cathode active material, annealed, and then secondary milled. This prevents surface damage to the cathode active material, reducing processing costs. The recycled cathode active material has a uniform particle size, minimizing particle size increase and a particle distribution similar to that of the cathode active material in the waste cathodes, resulting in improved battery performance. The method is environmentally friendly because it does not use acid, eliminating the need for neutralization or wastewater treatment, thereby reducing processing costs. The cathode active material is recycled directly without decomposition, eliminating the need for discarded metal elements. The current collector is not dissolved, allowing it to be recovered. The method does not use organic solvents, eliminating the risk of toxic gas generation or explosion. The method uses processes that are easy to manage, such as heat treatment and sedimentation, thereby providing a method for regenerating cathode active material suitable for mass production. It also provides a cathode active material recycled from the method and having excellent battery performance, and a secondary battery including the same.

[0034] The drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further understand the technical concept of the present invention. Therefore, the present invention should not be interpreted as being limited to the details shown in these drawings. [Brief explanation of the drawings]

[0035] [Figure 1] FIG. 10 is a diagram showing positive electrode scraps that are discarded after cutting electrode plates from a positive electrode sheet. [Figure 2]1 is a graph showing the particle distribution of the recycled positive electrode active materials or new positive electrode active materials obtained in Example 1, Reference Example, and Comparative Examples 1 to 3. [Figure 3] 1 is a graph showing the particle distribution of recycled positive electrode active materials or new positive electrode active materials obtained in Examples 1 and 2, Reference Example, and Comparative Examples 1 and 4. [Figure 4] 2 is a flowchart of a process for regenerating a positive electrode active material according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] The inventors were researching a method for directly recycling used cathodes without decomposing them to produce cathode active material, thereby improving the battery characteristics of the recycled cathode active material. They found that if the cathode active material recovered after heat treatment was subjected to primary milling without cleaning, and then a lithium precursor was added to the primary milled cathode active material, annealed, and then subjected to secondary milling, surface damage to the recycled cathode active material was prevented, particle size was uniformed, particle size increase was reduced, and the particle distribution became similar to that of the cathode active material in virgin cathodes, thereby improving the battery characteristics of the recycled cathode active material. Based on this, they continued their research and completed the present invention.

[0037] Hereinafter, the method for regenerating a positive electrode active material according to the present invention, the positive electrode active material regenerated therefrom, and a secondary battery including the same will be described in detail.

[0038] However, the terms and words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, but should be construed as meanings and concepts that correspond to the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of terms in order to best describe his or her invention. Therefore, it should be understood that the embodiments described in this specification and the configurations shown in the drawings are merely one embodiment of the present invention and do not represent the entire technical idea of ​​the present invention, and therefore various equivalents and modifications that can be substituted for them may exist, and they may be arranged, substituted, combined, separated, or designed in various other configurations.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0040] Method for regenerating positive electrode active material The method for regenerating a positive electrode active material of the present invention is characterized by including the steps of: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector, and recovering the positive electrode active material in the positive electrode active material layer by thermally decomposing the binder and conductive material in the positive electrode active material layer; primary milling the recovered positive electrode active material; adding a lithium precursor to the primary milled positive electrode active material and annealing it at 400 to 1000°C; and secondary milling the annealed positive electrode active material. In this case, surface damage to the regenerated positive electrode active material is prevented, process costs are reduced, and the regeneration is easy. The particle size of the cathode active material is uniform and the increase in particle size is minimized, providing a cathode active material with excellent battery characteristics. Furthermore, since the recovery and regeneration process of the cathode active material does not use acid, it is environmentally friendly and does not require neutralization or wastewater treatment, reducing process costs. Since the cathode active material is regenerated as is without decomposition, there are no metal elements to be discarded. Since the current collector is not dissolved, it can be recovered. Since no organic solvent is used, there is no risk of toxic gas generation or explosion. Furthermore, since processes such as heat treatment and sedimentation are easily managed, it is suitable for mass production.

[0041] Hereinafter, the method for regenerating the positive electrode active material will be described in detail step by step.

[0042] (a) A step of recovering a positive electrode active material from a waste positive electrode The step (a) of recovering a positive electrode active material from a used positive electrode according to the present invention may preferably be a step of recovering the positive electrode active material from the used positive electrode by heat-treating a used positive electrode having a positive electrode active material layer formed on a current collector and thermally decomposing the binder and conductive material in the positive electrode active material layer. In this case, the process is simple and has the effect of completely removing the binder, conductive material, and current collector.

[0043] The discarded positive electrodes may preferably be positive electrodes separated from used and discarded lithium secondary batteries, defective positive electrode sheets or positive electrode scraps generated during the manufacturing process of lithium secondary batteries, or more preferably positive electrode scraps remaining after punching out positive electrode plates from positive electrode sheets.

[0044] The positive electrode active material layer in step (a) may preferably include a positive electrode active material, a binder, and a conductive material.

[0045] The positive electrode active material layer may be, for example, at least one 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, which has the effect of providing excellent reversible capacity and thermal stability.

[0046] The positive electrode active material is preferably at least one 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 oxide (NCA); lithium nickel oxides such as LiNiO2; nickel manganese-based lithium composite metal oxides in which part of nickel (Ni) in the lithium nickel oxide is replaced by manganese (Mn); and NCM-based lithium composite transition metal oxides in which part of nickel (Ni) in the lithium nickel oxide is replaced by manganese (Mn) and cobalt (Co). More preferably, it is a nickel manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof. In this case, there is an effect of excellent reversible capacity and thermal stability.

[0047] As still another specific example, the positive electrode active material has the following Chemical Formula 1 (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the Chemical Formula 1, M contains at least one selected from the group consisting of B, W, Al, Ti, and Mg, and 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.) It may be a compound represented by

[0048] As an example, the positive electrode active material contains Ni in an amount of 60 mol% or more, preferably 80 mol% or more, more preferably 81 mol% or more, based on 100 mol% of the total of the metals excluding Li. Within this range, there is an effect of excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0049] In the present application, the Ni content may be measured by a measurement method using IC (Ion Chromatography) or the like, which is commonly used in the technical field to which the present invention pertains, without particular limitation. For example, the Ni content may be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS (Mass Spectrometer), or an IC-ICP-AES (Atomic Emission Spectrometer).

[0050] The conductive material may be, for example, a carbon-based conductive material, and preferably may be carbon black, CNT (carbon nanotube), or a mixture thereof.

[0051] The binder may be, for example, a polymer binder, preferably polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR), or a mixture thereof, and more preferably polyvinylidene fluoride.

[0052] The heat treatment may be performed, for example, in an air or oxygen atmosphere. In this case, the binder and the conductive material are thermally decomposed into CO and HO and removed, thereby separating the positive electrode active material from the current collector. The separated positive electrode active material has an advantage that it can be easily sorted in a powder form.

[0053] The purity of the oxygen may be, for example, 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, there are advantages in that the binder and conductive material are removed without remaining and the stability of Ni in the active material is increased.

[0054] The oxygen purity % may be volume % or mol %.

[0055] The purity of oxygen in the present application is not particularly limited, as long as it is measured by a measurement method commonly used in the technical field to which the present invention pertains.

[0056] The heat treatment can be carried out, for example, at 300 to 650°C, preferably 400 to 630°C, more preferably 500 to 600°C, even more preferably 530 to 600°C, and even more preferably 530 to 580°C. Within this range, the current collector does not dissolve and only the binder and the like are removed, which has the advantage that the positive electrode active material can be easily separated from the current collector.

[0057] The heat treatment time may be 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, the current collector is not dissolved and only the binder and the like are removed, which has the advantage that the positive electrode active material can be easily separated from the current collector.

[0058] In the present application, the heat treatment time refers to the time required for treatment at the heat treatment temperature, and does not include the time required to reach the heat treatment temperature.

[0059] The heat treatment may be performed at a temperature increase rate of, for example, 1 to 20°C / min, preferably 2 to 15°C / min, more preferably 3 to 10°C / min, and even more preferably 3 to 7°C / min. Within this range, the heat treatment can be performed without placing strain on the heat treatment equipment, and there are advantages in that no thermal shock or the like is caused to the cathode scrap.

[0060] FIG. 1 shows the cathode scrap that is discarded after cutting the cathode plates from the cathode sheet.

[0061] 1, a long sheet-shaped positive electrode current collector, aluminum foil 10, is coated with a positive electrode active material layer 20 containing a positive electrode active material, a conductive material, a binder, etc. to produce a positive electrode sheet 30, which is then punched to a predetermined size to produce a positive electrode plate 40, with the remaining portion being generated as positive electrode scrap 50. Punching is one method of cutting the positive electrode sheet.

[0062] In addition, the positive electrode active material layer 20 is formed by coating a slurry containing a positive electrode active material, a conductive material, a binder, a solvent, etc., on the aluminum foil 10. Since the slurry is very sensitive to environmental factors such as temperature, it is very difficult to determine the coating conditions. Therefore, waste positive electrode sheets are generated until the conditions for manufacturing a positive electrode sheet 30 of desired quality are found through predetermined tests.

[0063] For reference, in the following examples, scrap positive electrodes were used as waste positive electrodes.

[0064] b) A step of performing primary milling on the recovered positive electrode active material The method for regenerating a positive electrode active material of the present invention includes (b) a step of primarily milling the recovered positive electrode active material. In this case, the particle size of the positive electrode active material becomes uniform, thereby providing a positive electrode active material with excellent battery characteristics. In addition, since the step of washing the recovered positive electrode active material is omitted, surface damage to the positive electrode active material is prevented, and economic efficiency and productivity are significantly improved.

[0065] The primary milling may be performed using, for example, a centrifugal mill or a jet mill, preferably a centrifugal mill. In this case, the recovered positive electrode active material is uniformly milled, which has the advantage of uniformly dispersing the particles.

[0066] The primary milling can be carried out at, for example, 6,000 to 20,000 rpm, preferably 8,000 to 18,000 rpm, more preferably 9,000 to 16,000 rpm, even more preferably 11,000 to 14,000 rpm, and even more preferably 11,000 to 13,000 rpm. Within this range, there are advantages such as excellent milling efficiency, no cracking of the positive electrode active material particles, and excellent productivity. If the milling speed is less than 6,000 rpm, the milling effect is ineffective, and if it exceeds 20,000 rpm, cracking of the positive electrode active material particles occurs.

[0067] The primary milling can be carried out for, for example, 5 to 150 seconds, preferably 10 to 120 seconds, more preferably 10 to 100 seconds, even more preferably 15 to 80 seconds, even more preferably 15 to 60 seconds, and particularly preferably 15 to 40 seconds. Within this range, there are advantages such as excellent milling efficiency, no cracking of the positive electrode active material particles, and excellent productivity.

[0068] After the primary milling, the average particle size of the positive electrode active material may be, for example, 7.0 to 9.0 μm, preferably 7.3 to 8.5 μm, and more preferably 7.5 to 8.5 μm, and within this range, there is an effect of improving battery characteristics.

[0069] In the present application, the particle distribution and average particle size may be measured by a measurement method commonly used in the technical field to which the present invention pertains, for example, by a laser diffraction method. Specifically, particles of a positive electrode active material may be dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer such as a Microtrac MT 3000. Ultrasonic waves of about 28 kHz and an output of 60 W may be irradiated to the dispersion, and the average particle size (D50) based on 50% of the particle size distribution measured by the analyzer may be calculated. The standard deviation may be calculated based on the average particle size (D50).

[0070] The centrifugal mill may have a filter size of, for example, 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, still more preferably 0.08 to 2 mm, and particularly preferably 0.08 to 1.0 mm. Within this range, there is an advantage that the size of the positive electrode active material particles is uniform.

[0071] In the present application, the filter size of the centrifugal mill is not particularly limited as long as it is a filter size commonly used in the technical field to which the present invention pertains. As an example, the filter of the centrifugal mill has a circular band-like shape, and the band has small holes densely packed like a sieve, and the filter size refers to the size of the holes.

[0072] (c) Adding a lithium precursor to the primary milled positive electrode active material and annealing at 400 to 1000°C The method for regenerating a positive electrode active material of the present invention includes (c) adding a lithium precursor to the primarily milled positive electrode active material and annealing the material at 400 to 1000°C. In this case, the crystallinity is improved by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0073] The annealing step (c) may preferably be a step of adding a lithium precursor to the recovered positive electrode active material and annealing in oxygen (O2) or air at 400 to 1000°C, more preferably 600 to 900°C. In this case, the crystallinity of the positive electrode active material is improved, for example, by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the recycled positive electrode active material.

[0074] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O.

[0075] The lithium precursor is preferably added in an amount that is at least the amount of lithium that is reduced from the amount of lithium in the positive electrode active material in step (a), based on the amount of lithium in the recovered positive electrode active material. As a specific example, when the positive electrode active material in step (a) is a positive electrode active material represented by Chemical Formula 1, the lithium precursor is added in an amount that results in a lithium molar ratio of 0.0001 to 0.2 relative to the lithium molar ratio in this positive electrode active material, preferably an amount that results in a lithium molar ratio of 0.001 to 0.02, more preferably an amount that results in a lithium molar ratio of 0.005 to 0.017, even more preferably an amount that results in a lithium molar ratio of 0.007 to 0.015, and even more preferably an amount that results in a lithium molar ratio of 0.009 to 0.013. Within this range, the lithium that is insufficient in the regenerated positive electrode active material is replenished, and the crystallinity is improved, such as by increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0076] In this application, the molar ratio of lithium to other metals in the positive electrode active material was measured using an ICP analyzer. This can be measured using a common ICP analyzer commonly used in laboratories, and there is no deviation due to the measurement device or method.

[0077] As another example, the lithium precursor may be added in an amount that provides 1 to 40 mol% of lithium when the total amount of lithium contained in the raw positive electrode active material is 100 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% of lithium. Within this range, no residual precursor that could increase resistance remains in the regenerated positive electrode active material, which is very useful for improving battery characteristics, and is economically advantageous because the crystal structure can be restored with a smaller amount of lithium precursor than conventional methods.

[0078] In this application, raw material is the opposite of "recycled" and means produced for the first time.

[0079] As an example, the annealing can be carried out in an air or oxygen atmosphere at a temperature of 400 to 1000°C, preferably 400 to 900°C, more preferably 400 to 800°C, even more preferably 450 to 750°C, and even more preferably 450 to 710°C. Within this range, the crystal structure is restored, which has the effect of improving the battery's output performance.

[0080] The annealing temperature can be adjusted within a limited range depending on the melting point of the lithium precursor. For example, since the melting point of LiCO3 is 723°C, annealing can be preferably performed at 700 to 900°C, more preferably 710 to 780°C. Since the melting point of LiOH is 462°C, annealing can be preferably performed at 400 to 600°C, more preferably 450 to 480°C. Within this range, the crystal structure is restored, resulting in excellent battery output performance.

[0081] The annealing temperature may preferably be a temperature exceeding the melting point of the lithium precursor. However, if the annealing temperature exceeds 1000°C, thermal decomposition of the positive electrode active material may occur, resulting in a decrease in battery performance. Therefore, it is preferable that the annealing temperature be 1000°C or less.

[0082] The annealing time is, for example, 1 hour or more or 15 hours or less, preferably 1 to 15 hours, more preferably 2 to 10 hours, even more preferably 3 to 8 hours, and even more preferably 4 to 6 hours. As a specific example, it is preferably around 5 hours. Within this range, the crystal structure is sufficiently restored and there is an economic advantage.

[0083] The annealing temperature can be reached preferably at a temperature rise rate of 1 to 10°C / min, more preferably at a temperature rise rate of 1 to 7°C / min, and even more preferably at a temperature rise rate of 2 to 4°C / min. In this case, the crystallinity of the regenerated positive electrode active material is further increased, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0084] The annealing step may, for example, include a cooling process, and the cooling process may be, for example, natural cooling in a furnace. In this case, the crystallinity of the recycled positive electrode active material may be further increased, thereby improving the battery characteristics of the recycled positive electrode active material.

[0085] In the present application, annealing may follow the definition used in the technical field to which the present invention belongs. For example, annealing may be defined as a heat treatment operation in which a positive electrode active material having a deformed structure or lattice defects is heated for an appropriate time at a temperature at or above the recrystallization temperature at which atoms of the main component therein can sufficiently diffuse and move, thereby healing the deformation or lattice defects and increasing crystallinity.

[0086] (d) Secondary milling of the annealed positive electrode active material The method for regenerating a cathode active material of the present invention includes a step of secondary milling the annealed cathode active material. In this case, the particle size of the cathode active material, which had increased during the annealing step, is reduced to provide a regenerated cathode active material having a particle size similar to that of the cathode active material in the waste cathode, thereby advantageously improving battery characteristics.

[0087] The secondary milling may be performed using, for example, a centrifugal mill or a jet mill, preferably a centrifugal mill. In this case, the particle size of the cathode active material, which has increased through the annealing step, is reduced to a size similar to that of the cathode active material in the waste cathode, thereby improving battery characteristics.

[0088] The secondary milling can be carried out, for example, at 6,000 to 20,000 rpm, preferably 8,000 to 20,000 rpm, more preferably 10,000 to 19,000 rpm, even more preferably 12,000 to 19,000 rpm, still more preferably 14,000 to 19,000 rpm, and particularly preferably 16,000 to 19,000 rpm. Within this range, there are advantages such as excellent milling efficiency, the particle size of the positive electrode active material becoming similar to the particle size of the positive electrode active material in the waste positive electrodes, and excellent productivity.

[0089] The secondary milling can be carried out for, for example, 5 to 150 seconds, preferably 10 to 120 seconds, more preferably 10 to 100 seconds, even more preferably 10 to 80 seconds, and even more preferably 15 to 60 seconds. Within this range, there are advantages such as excellent milling efficiency, no cracking of the positive electrode active material particles, and excellent productivity.

[0090] After the secondary milling, the average particle size of the positive electrode active material may be, for example, 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, there is an effect of improving battery characteristics.

[0091] The recycled positive electrode active material obtained after the secondary milling may have, for example, a standard deviation of the average particle size of 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 is similar to that of the positive electrode active material in the waste positive electrode, which has the advantage of improving the battery characteristics.

[0092] The cathode active material obtained after the secondary milling may have an average particle size increase rate of 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% relative to the cathode active material in the raw material. Within this range, the average particle size and particle distribution are similar to those of the cathode active material in the raw material, which has the advantage of improving battery characteristics. The average particle size increase rate can be calculated using Equation 1 below.

[0093] [Formula 1] Increase rate of average particle size (%) = [(ba) / a] × 100 (In the above formula 1, a is the average particle size of the raw positive electrode active material, and b is the average particle size of the recycled positive electrode active material measured after the secondary milling.)

[0094] (e) Step of washing the secondary milled positive electrode active material The method for regenerating a cathode active material of the present invention includes (c) a step of washing the cathode active material after secondary milling. In this case, the lithium precursor is removed with a small amount of washing solution, which has the advantage of preventing the subsequent deterioration of battery performance and gas generation due to the reaction between the remaining lithium precursor and the electrolyte and eliminating the need for wastewater treatment. In particular, the lithium precursor, which is more likely to remain in a high-nickel cathode active material due to its high Ni content, can be removed with a small amount of washing solution.

[0095] In the present application, a high-nickel positive electrode active material refers to a positive electrode active material that contains 60 mol % or more of nickel, based on 100 mol % of the total of the remaining metals excluding Li.

[0096] The washing step may preferably include the steps of mixing the second-milled cathode active material with a washing solution, followed by filtering the mixture, and drying the solid cathode active material obtained after the filtration. In this case, excess lithium that tends to remain in the cathode active material can be effectively removed.

[0097] For example, the washing step may be performed at a weight ratio of secondary milled cathode active material to washing solution of 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, and particularly preferably 1:0.5 to 1.5. This method has the advantage of effectively removing lithium precursors such as LiOH and Li2CO3 that tend to remain. In particular, excess lithium is added to suppress cation mixing, which tends to occur in high-nickel cathode active materials, thereby effectively removing lithium precursors such as LiOH and Li2CO3 that tend to remain. This cation mixing occurs due to the similar particle sizes of nickel and lithium.

[0098] In particular, when the secondary milled 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 regenerated positive electrode active material are further improved.

[0099] The cleaning solution may be preferably water, more preferably distilled water or deionized water. In this case, lithium precursors such as LiOH, LiCO, etc., which tend to remain due to excessive lithium addition to suppress cation mixing that tends to occur in high-nickel positive electrode active materials, can be effectively removed.

[0100] For example, the washing step may include a step of mixing the second-milled cathode active material with a washing solution, followed by filtering, and a step of drying the solid cathode active material obtained after the filtration. In this case, an excess amount of lithium that tends to remain in the cathode active material may be effectively removed.

[0101] The filtration may preferably be vacuum filtration using a filter.

[0102] The drying can be carried out at a temperature of preferably 100 to 500°C, more preferably 120 to 400°C, even more preferably 120 to 300°C, and even more preferably 120 to 200°C.

[0103] The drying may preferably be carried out by vacuum drying.

[0104] In the present invention, the vacuum drying is not particularly limited as long as it is a common vacuum drying in the technical field to which the present invention pertains, and may include, for example, drying in a partial vacuum state or a low pressure state.

[0105] (f) Surface-coating the washed positive electrode active material The method for regenerating a positive electrode active material of the present invention includes a step (f) of surface-coating the washed positive electrode active material, which has the effect of improving the structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0106] As another example, the method for regenerating a positive electrode active material of the present invention includes a step (f') of surface-coating the secondary-milled positive electrode active material, which has the effect of improving the structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0107] The surface coating is preferably performed by coating the surface with a coating agent containing at least one of a metal, an organic metal, and a carbon component in a solid or liquid phase manner, followed by heat treatment at 100 to 1200°C. In this case, the structural stability and electrochemical performance of the positive electrode active material can be improved while maintaining the properties of the positive electrode active material itself.

[0108] The metal-containing coating agent is preferably 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 a coating agent containing one or more selected from the group consisting of B, W, Al, Ti, and Mg, even more preferably a coating agent containing boron (B), tungsten (W), or a mixture thereof, and even more preferably a coating agent containing tungsten (W) and boron (B). A specific example is a coating agent containing tungsten boride (WB), in which case resistance characteristics and life characteristics are improved.

[0109] The coating agent containing the metal may be, for example, an oxide or acid containing the metal as an element in its molecule.

[0110] The coating agent containing the organometallic is not particularly limited as long as it is a coating agent that is commonly used in the technical field to which the present invention pertains and contains an organometallic compound containing the metal, and a specific example thereof may be a metal alkoxide.

[0111] The carbon-containing coating agent is not particularly limited as long as it is a carbon-containing coating agent commonly used in the technical field to which the present invention pertains, and a specific example thereof may be a sugar such as sucrose.

[0112] For example, the coating agent may be contained in an amount of 0.001 to 0.3 mol %, preferably 0.01 to 0.3 mol %, more preferably 0.01 to 0.15 mol %, even more preferably 0.01 to 0.1 mol %, and even more preferably 0.01 to 0.05 mol %, based on the components actually coated on the surface of the positive electrode active material excluding the solvent, relative to 100 mol % of the metal in the positive electrode active material before the coating treatment. Within this range, the structural stability and electrochemical performance are improved while the properties of the positive electrode active material itself are maintained.

[0113] The heat treatment time is preferably 1 to 16 hours, more preferably 3 to 7 hours. Within this range, the properties of the positive electrode active material itself are maintained as they are, while the structural stability and electrochemical performance are improved.

[0114] The coating method is not particularly limited as long as it is a coating method commonly used in the technical field to which the present invention pertains, and examples thereof include a liquid phase method in which a liquid coating agent is prepared and mixed with a positive electrode active material, a mechanochemical method using high mechanical energy such as ball milling, a fluidized bed coating method, a spray drying method, a precipitation method in which a coating agent in an aqueous solution state is precipitated on the surface of a positive electrode active material, a method utilizing a reaction between a gaseous coating agent and a positive electrode active material, and a sputtering method.

[0115] The metal, organometallic, and carbon components may be, for example, spherical, plate-like, angular, or needle-like, and such shapes can be adjusted by changing process conditions during the manufacturing process. The definition of each shape is not particularly limited as long as it follows the definition generally accepted in the technical field to which the present invention belongs.

[0116] The coating agent preferably has an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m 2 / g, and more preferably, the average diameter is 10 to 100 nm and the specific surface area is 20 to 100 m2 / g, and within this range, the particles are uniformly attached to the surface of the positive electrode active material, imparting structural stability to the positive electrode active material, thereby improving the problems of deterioration in life characteristics and electrochemical performance due to lattice deformation and collapse of the crystal structure of the positive electrode active material.

[0117] In the present application, the average diameter can be measured by a measurement method commonly used in the technical field to which the present invention pertains, for example, by using a laser diffraction method. Specifically, particles of a positive electrode active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer such as a Microtrac MT 3000. Ultrasonic waves of about 28 kHz and an output of 60 W are irradiated to the dispersion, and the average particle size (D50) based on 50% of the particle size distribution measured by the analyzer can be calculated.

[0118] In the present application, the specific surface area can be measured by a measurement method commonly used in the technical field to which the present invention pertains, for example, by the BET (Brunauer-Emmett-Teller) method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77 K) using a BELSORP-mino II from BEL Japan.

[0119] Regenerated cathode active material The regenerated positive electrode active material of the present invention is characterized by being produced by the above-described method for regenerating a positive electrode active material, and in this case, has the effect of being excellent in electrochemical performance, capacity characteristics, and resistance characteristics.

[0120] In addition, the recycled cathode active material of the present invention is at least one selected from the group consisting of lithium nickel oxide (LNO)-based cathode active materials, nickel cobalt manganese (NCM)-based cathode active materials, nickel cobalt aluminum (NCA)-based cathode active materials, and nickel cobalt manganese aluminum (NCMA)-based cathode active materials, and is characterized in that it contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li, and the standard deviation of the average particle size of the recycled cathode active material is 3.0 or less, which has the effect of providing excellent battery characteristics.

[0121] The recycled positive electrode active material may have a standard deviation of the average particle size of preferably 2.7 or less, more preferably 2.5 or less. Within this range, the particle size distribution is similar to that of the positive electrode active material in the waste positive electrode, which has the advantage of improving the battery characteristics.

[0122] The recycled positive electrode active material may have an average particle size increase rate of 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% relative to the average particle size of the positive electrode active material in the waste positive electrodes. Within this range, the particle size distribution is similar to that of the positive electrode active material in the waste positive electrodes, which has the advantage of improving battery characteristics.

[0123] 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 oxide (NCA; lithium nickel cobalt aluminum oxide); lithium nickel oxides such as LiNiO2; nickel manganese-based lithium composite metal oxides in which part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxides in which part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). In this case, there is an effect of excellent electrochemical performance, resistance characteristics, capacity characteristics, etc.

[0124] Specific examples of the recycled positive electrode active material include the following Chemical Formula 1 (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the 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). It can include compounds represented by this, and in this case, there is an effect of excellent electrochemical performance, resistance characteristics, capacity characteristics, etc.

[0125] The recycled positive electrode active material preferably contains 80 mol% or more of Ni, more preferably 81 mol% or more, based on 100 mol% of the total of the metals excluding Li. Within this range, there is an effect of excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0126] For example, the recycled cathode active material may have a surface coated with metal or carbon, preferably metal. In this case, the structural stability of the cathode active material is improved without any chemical or physical changes to the cathode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. Furthermore, the surface of the cathode active material is substituted with a different element, thereby reducing the amount of residual lithium and the pH, thereby improving physicochemical properties.

[0127] The metal is preferably at least one 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 at least one selected from the group consisting of B, W, Al, Ti, and Mg, even more preferably boron (B), tungsten (W), or a mixture thereof, and even more preferably tungsten (W) and boron (B). A specific example is tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0128] For example, the coating agent may be contained in an amount of 0.001 to 0.3 mol %, preferably 0.01 to 0.3 mol %, more preferably 0.01 to 0.15 mol %, even more preferably 0.01 to 0.1 mol %, and still more preferably 0.01 to 0.05 mol %, relative to 100 mol % of the metal in the positive electrode active material before the coating treatment. Within this range, the properties of the positive electrode active material itself are maintained as they are, while the structural stability and electrochemical performance are improved.

[0129] The surface coating is preferably performed by coating the surface with a coating agent containing at least one of a metal, an organic metal, and a carbon component in a solid or liquid phase manner, followed by heat treatment at 100 to 1200°C, more preferably 200 to 1000°C, and even more preferably 250 to 800°C. In this case, the structural stability and electrochemical performance are improved while the properties of the positive electrode active material itself are maintained.

[0130] FIG. 4 is a flowchart showing a process for regenerating a positive electrode active material according to one embodiment of the present invention.

[0131] Referring to Figure 4, first, cathode scraps are prepared as waste cathodes (step S10). For example, a slurry is prepared by mixing NCM-based lithium transition metal composite oxide, carbon black, and polyvinylidene fluoride with NMP (N-methyl pyrrolidone), and the mixture is coated on aluminum foil and dried in a vacuum oven at approximately 120°C to prepare a cathode sheet. After punching out cathode plates of a certain size, the remaining cathode scraps can be prepared.

[0132] The cathode scrap has a cathode active material layer on an aluminum foil, and after the solvent evaporates, the cathode active material layer has a structure in which the cathode active material and the conductive material are bound by the binder. Therefore, when the binder is removed, the cathode active material is separated from the aluminum foil.

[0133] Next, the prepared cathode scrap is crushed to an appropriate size (step S20). Here, crushing includes cutting or shredding the cathode scrap to a size that is easy to handle. As a specific example, the crushed cathode scrap may be 1 cm x 1 cm in size. For example, the crushing may be performed using various dry crushing devices such as a hand mill, pin mill, disc mill, cutting mill, or hammer mill, or a high-speed cutter may be used to increase productivity.

[0134] The decision as to whether or not to crush the cathode scrap and the size of the pieces can be made taking into consideration the handling of the cathode scrap and the properties required for the equipment used in the subsequent steps. For example, when using equipment capable of continuous processing, the cathode scrap must have good fluidity, so it is necessary to crush it into even smaller pieces.

[0135] Next, the crushed positive electrode scrap is heat-treated to recover the positive electrode active material (step S30). Here, the heat treatment is carried out to thermally decompose the binder and the conductive material.

[0136] The heat treatment is preferably carried out in air at 300 to 650°C, in which case the binder and conductive material are thermally decomposed into CO2 and H2O and removed. As the binder is removed, the positive electrode active material is separated from the positive electrode active material layer.

[0137] It is important that the heat treatment be performed in air. However, if the heat treatment is performed in a reducing or inert gas atmosphere, the binder and conductive material will carbonize without being thermally decomposed. Carbonization leaves carbon components on the surface of the cathode active material, reducing the performance of the reused cathode active material. However, if the heat treatment is performed in air, the carbon components in the binder and conductive material react with oxygen and disappear as gases such as CO and CO2, removing both the binder and conductive material.

[0138] The heat treatment is preferably carried out at 300 to 650°C, specifically at 550°C. If the temperature is lower than 300°C, it is difficult to remove the binder, making it impossible to separate the current collectors. If the temperature exceeds 650°C, the current collectors melt, making it impossible to separate them.

[0139] The heat treatment is preferably carried out at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, specifically 5°C / min. Within this range, there are advantages in that the load on the heat treatment equipment is reduced and no thermal shock occurs to the cathode scrap.

[0140] The heat treatment may be carried out for a period of time sufficient to thermally decompose the binder, preferably for 30 minutes or more, more preferably for 30 minutes to 5 hours, and specifically for about 30 minutes. Within this range, the binder is sufficiently thermally decomposed and the thermal decomposition efficiency is excellent.

[0141] The heat treatment may be carried out using various types of furnaces, for example, a box-type furnace, or, in consideration of productivity, a rotary kiln capable of continuous treatment.

[0142] After the heat treatment, the material can be cooled slowly or rapidly in the air.

[0143] Next, the recovered positive electrode active material is subjected to primary milling (step S40).

[0144] In the primary milling step, it is important to immediately mill the recovered cathode active material without a washing process. In this case, the surface of the cathode active material is not damaged, the particles of the cathode active material are uniform, and the washing process is not performed, which has the effect of reducing process costs.

[0145] The primary milling may be performed using, for example, a centrifugal mill or a jet mill. Specifically, a centrifugal mill may be used. In this case, the particles of the recovered positive electrode active material are uniform, which is advantageous in that the battery characteristics are improved.

[0146] The primary milling can be carried out at, for example, 6000 to 20000 rpm, specifically 12000 rpm. Within this range, there are advantages such as excellent milling efficiency, no cracking of the positive electrode active material particles, and excellent productivity.

[0147] The primary milling can be performed for, for example, 5 to 150 seconds, specifically 30 seconds. Within this range, there are advantages such as excellent milling efficiency, no cracking of the positive electrode active material particles, and excellent productivity.

[0148] After the primary milling, the average particle size of the positive electrode active material may be, for example, 7.0 to 9.0 μm, preferably 7.5 to 8.5 μm, and more preferably 8.0 to 8.5 μm, and within this range, there is an effect of improving battery characteristics.

[0149] Next, a lithium precursor is added to the primarily milled positive electrode active material, and annealing is performed (step S50).

[0150] The annealing step replenishes the lithium lost in the positive electrode active material during step S30. Furthermore, since a deformed structure (e.g., Co3O4 in the case of an LCO active material) may develop on the surface of the positive electrode active material during the previous steps, step S50 restores the crystalline structure of the positive electrode active material through annealing, thereby improving the battery performance of the regenerated positive electrode active material or restoring it to the level of a virgin positive electrode active material. Here, "virgin" is the opposite concept of "regenerated," meaning something that has been produced for the first time, and is the same term as "raw material" used in the detailed description and examples of the invention.

[0151] As the lithium precursor, LiOH is specifically used.

[0152] The lithium precursor is preferably added in an amount at least equal to the molar ratio of the lost lithium relative to the molar ratio of lithium to other metals in the newly generated positive electrode active material used in the positive electrode active material layer. If an amount of lithium precursor that is excessively greater than the amount of lost lithium is added, unreacted lithium precursor will remain in the regenerated positive electrode active material, which increases resistance, so it is necessary to add an appropriate amount of lithium precursor.

[0153] In one embodiment, the lithium precursor can be added in an amount that results in a lithium molar ratio of 0.001 to 0.4, preferably 0.01 to 0.4, and more preferably 0.09 to 0.2, based on the case where the molar ratio of lithium (Li) to other metal (M) in the new positive electrode active material is 1. Specifically, adding the lithium precursor in an amount that corresponds to the ratio of lithium lost in the new positive electrode active material based on the results of ICP analysis can improve capacity to a level equivalent to that of the new positive electrode active material. The ICP analysis results have an error of approximately ±0.02.

[0154] In one embodiment, the lithium precursor may be added in an amount that provides lithium equivalent to 1 to 40 mol %, more preferably 1 to 15 mol %, and even more preferably 7 to 11 mol %, when the total amount of lithium contained in the recovered positive electrode active material is 100 mol %. Within this range, no residual precursor that may increase resistance remains in the recycled positive electrode active material, which is very useful for improving battery characteristics.

[0155] The annealing is carried out, for example, in an air or oxygen atmosphere at a temperature of 400 to 1000°C, preferably 400 to 900°C, more preferably 400 to 800°C, and even more preferably 450 to 710°C. This temperature needs to be adjusted within a limited range depending on the type of lithium precursor.

[0156] The annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, temperatures exceeding 1000°C cause thermal decomposition of the positive electrode active material, resulting in a decrease in performance, so the temperature should not exceed 1000°C. For example, when Li2CO3 is used as the lithium precursor, the annealing temperature is preferably 700 to 900°C, more preferably 710 to 780°C, and even more preferably 750 to 780°C. Furthermore, when LiOH is used as the lithium precursor, the annealing temperature is preferably 400 to 600°C, more preferably 450 to 480°C, and even more preferably 470 to 480°C.

[0157] The annealing time is, for example, 1 hour or more, preferably 15 hours or less, and more preferably 4 to 6 hours. If the annealing time is long, the crystal structure may be sufficiently restored, but even if annealing is performed for a long time, there is no significant change in performance. Note that the annealing equipment can be the same as or similar to that used in the heat treatment step S30.

[0158] Next, the annealed positive electrode active material is subjected to secondary milling (step S60).

[0159] The secondary milling step S60 reduces the particle size of the cathode active material, which has increased during the annealing step S50, to the same particle size as that of the cathode active material in the waste cathode, thereby improving battery characteristics.

[0160] The secondary milling may be performed using, for example, a centrifugal mill or a jet mill, and specifically, a centrifugal mill may be used. In this case, there is an advantage that the particle size of the positive electrode active material is reduced without damaging the particles.

[0161] The secondary milling may be performed at a speed of, for example, 6,000 to 20,000 rpm, specifically, 18,000 rpm. Within this range, there are advantages in that milling efficiency is excellent, the particle size of the positive electrode active material is reduced, and productivity is excellent.

[0162] The secondary milling may be performed for, for example, 5 to 150 seconds, specifically 30 seconds. Within this range, there are advantages in that the milling efficiency is excellent, the particles of the positive electrode active material are not broken, and productivity is excellent.

[0163] After the secondary milling, the average particle size of the positive electrode active material may be, for example, 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, there is an effect of improving battery characteristics.

[0164] Next, as an optional step, the positive electrode active material that has been subjected to the second milling is washed (step S70).

[0165] Lithium precursors that did not participate in the reaction in the annealing step S50 remain on the surface of the positive electrode active material in the form of LiOH and Li2CO3, so a residual lithium removal process is required. In particular, high-content Ni-based positive electrode active materials require an excess amount of Li due to the cation mixing phenomenon, which makes it easy for lithium impurities such as lithium carbonate (Li2CO3) to remain on the surface. These impurities must be thoroughly removed because they may later react with the electrolyte, reducing battery performance and generating gas.

[0166] The washing can be preferably carried out using distilled water, which is safe and inexpensive and has the advantage that the transition metals present in the positive electrode active material are not eluted.

[0167] The washing is preferably carried out by mixing the secondary milled cathode active material and the washing solution in a weight ratio of 1:0.5 to 1:10, specifically 1:1, filtering the mixture, and then drying the obtained solid cathode active material.

[0168] The mixing of the secondarily milled positive electrode active material and the cleaning solution is preferably performed by stirring, and the stirring may be, but is not limited to, mechanical stirring, magnetic stirring, or ultrasonic stirring.

[0169] The mechanical stirring includes, for example, an impeller, and is preferably carried out at 250 to 350 rpm for 3 to 10 minutes.

[0170] The filtration is preferably reduced pressure filtration using a filter, and the drying is vacuum drying at 120 to 140°C.

[0171] Next, as an optional step, the washed positive electrode active material can be surface coated (step S80).

[0172] For example, the surface coating is performed by coating the surface with a coating agent containing a metal, an organic metal, or a carbon component in a solid or liquid phase manner, followed by heat treatment. If the heat treatment temperature is too low, the desired surface protection layer made of a different metal will not be formed, and if the heat treatment temperature is too high, the battery performance will be reduced due to thermal decomposition of the positive electrode active material.

[0173] Specifically, when a metal oxide or acid such as B, W, or BW is coated on a washed cathode active material and then heat-treated, a surface protection layer such as a lithium boron oxide layer is formed on the surface of the cathode active material.

[0174] The solid or liquid phase method of the surface coating may be, for example, mixing, milling, spray drying, or grinding.

[0175] If the annealing step S50 is performed to achieve a 1:1 molar ratio of lithium to other metals in the cathode active material, the lithium in the cathode active material will react with the coating agent in the surface coating step S80, resulting in a lithium:other metals in the cathode active material molar ratio of less than 1:1, and this regenerated cathode active material will not be able to fully utilize its battery capacity. However, if the lithium precursor is added in excess in the annealing step S50, so that it is present in an amount of 0.0001 to 0.1 molar ratio greater than the other metals in the cathode active material, a surface protective layer will be formed in the surface coating step S80, naturally achieving a 1:1 molar ratio of lithium to other metals in the cathode active material, and no capacity loss will occur.

[0176] secondary battery The secondary battery of the present invention includes a recycled cathode active material produced by the method for recycling a cathode active material. In this case, the particle distribution of the recycled cathode active material is similar to that of the cathode active material in the waste cathode, which has the effect of significantly improving battery characteristics. Furthermore, since no acid or organic solvent is used in the recovery and recycling process of the cathode active material, it is environmentally friendly. In particular, since the initial water washing process is omitted, it has the effect of being economical and productive.

[0177] In addition, the secondary battery of the present invention includes the above-described cathode active material. In this case, the average particle size and standard deviation of the recycled cathode active material are similar to those of the cathode active material in the waste cathode, which has the effect of significantly improving battery characteristics. Furthermore, since no acid or organic solvent is used in the recovery and regeneration process of the cathode active material, it is environmentally friendly. In particular, since the initial water washing process is omitted, it has the effect of being excellent in economy and productivity.

[0178] The secondary battery of the present invention may include all of the above-described positive electrode active materials and regeneration methods thereof, and therefore, redundant description thereof will be omitted here.

[0179] Preferred examples are presented below to aid in understanding the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. Naturally, such changes and modifications also fall within the scope of the appended claims.

[0180] [Example] Example 1 The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil, cathode active material: NCM-based lithium composite transition metal oxide, containing 87 mol% nickel, based on 100 mol% of the total of the remaining metals excluding Li) was crushed and heat-treated in air at 590°C for 30 minutes to remove the binder and conductive material. The current collector and cathode active material were separated and then recovered. The temperature was increased at a rate of 5°C / min to reach the heat treatment temperature, and air was supplied at 10 L / min.

[0181] The recovered positive electrode active material was subjected to primary milling using a centrifugal mill (ZM200 manufactured by Retsch) at 12,000 rpm for 30 seconds. After primary milling, the average particle size (D50) of the positive electrode active material was 7.9 μm.

[0182] The lithium precursor LiOH was added to the primary milled cathode active material in an amount that would provide 15 mol% of lithium, assuming that the total lithium in the raw cathode active material was 100 mol%, and the mixture was annealed in air at a firing temperature of 750°C for 5 hours, with air supplied at a rate of 3 L / min.

[0183] The annealed positive electrode active material was subjected to secondary milling using a centrifugal mill at 18,000 rpm for 30 seconds. After secondary milling, the average particle size (D50) of the positive electrode active material was 8.99 μm.

[0184] Example 2 The same procedures as in Example 1 were carried out, except that the primary milling was carried out at 12,000 rpm for 30 seconds and the secondary milling was carried out at 12,000 rpm for 30 seconds.

[0185] Comparative Example 1 The same procedure as in Example 1 was carried out, except that the primary milling and secondary milling were not carried out.

[0186] Comparative Example 2 The same procedure as in Example 1 was carried out except that the secondary milling was not carried out.

[0187] Comparative Example 3 The same procedure as in Example 1 was carried out except that the primary milling was not carried out.

[0188] Comparative Example 4 The cathode scrap discarded after punching out the cathode plates (current collector: aluminum foil; cathode active material: NCM-based lithium transition metal oxide, nickel content 87 mol%, based on 100 mol% of the total of the remaining metals excluding Li) was crushed and heat-treated in air at 590°C for 30 minutes to remove the binder and conductive material. The current collector and cathode active material were separated and then recovered. The temperature was increased at a rate of 5°C / min to reach the heat treatment temperature, and air was supplied at 10 L / min.

[0189] The recovered positive electrode active material was washed by immersing it in distilled water and stirring it at the same time. At this time, the weight ratio of the recovered positive electrode active material to distilled water was 1:10, and the mixture was stirred at 500 rpm for 10 minutes, and then the active material alone was extracted by vacuum filtration using a filter.

[0190] The washed cathode active material was dried overnight at 100°C, and then a lithium precursor, LiOH, was added in an amount that provided 15 mol% of lithium, assuming a total of 100 mol% of lithium in the raw cathode active material, and annealed in air at a firing temperature of 750°C for 5 hours. Here, air was supplied at a rate of 3 L / min.

[0191] Reference Example Instead of a recycled positive electrode active material, a fresh NCM-based lithium transition metal composite oxide (nickel content 87 mol % based on the total of 100 mol % of the remaining metals excluding Li) was used.

[0192] [Test Example I: Particle distribution of regenerated and new positive electrode active material] The recycled positive electrode active materials and virgin positive electrode active materials obtained in Examples 1 and 2, Comparative Examples 1 to 4, and the Reference Example were measured using a laser diffraction method. Specifically, particles of the recycled positive electrode active material were dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size analyzer such as a Microtrac MT 3000. Ultrasound of approximately 28 kHz was irradiated at an output of 60 W to measure the particle distribution, and the average particle size and its standard deviation based on 50% of the particle size distribution, as well as the particle size increase rate, were calculated. The particle size increase rate was calculated based on the Reference Example.

[0193] The average particle size, its standard deviation, and particle size increase rate of the recycled or new positive electrode active materials obtained in Examples 1 and 2, Comparative Examples 1 to 4, and Reference Example are shown in Table 1 below.

[0194] FIG. 2 shows the particle distribution measured for the recycled positive electrode active materials or new positive electrode active materials obtained in Example 1, Reference Example, and Comparative Examples 1 to 3, and FIG. 3 shows the particle distribution measured for the recycled positive electrode active materials or new positive electrode active materials obtained in Examples 1 and 2, Reference Example, and Comparative Examples 1 and 4.

[0195] [Table 1]

[0196] As can be seen from Table 1 above, in Examples 1 and 2 according to the present invention, the average particle size, its standard deviation, and the rate of increase in particle size were reduced compared to Comparative Examples 1 to 4, and were similar to the Reference Example (new positive electrode active material), so it was expected that the battery characteristics would be further improved.

[0197] As shown in FIG. 2, Example 1 according to the present invention exhibits a particle distribution similar to that of the Reference Example (new positive electrode active material), and therefore it was expected that the battery characteristics would be further improved.

[0198] Furthermore, as shown in FIG. 3, Examples 1 and 2 according to the present invention exhibited particle distributions similar to that of the Reference Example (new positive electrode active material), and therefore it was expected that the battery characteristics would be further improved. [Explanation of symbols]

[0199] 10 Current collector 20 Active material layer 30 Positive electrode sheet 40 positive electrode plate 50 cathode scrap

Claims

1. a step of recovering the positive electrode active material from the positive electrode active material layer by thermally treating the waste positive electrode having the positive electrode active material layer formed on the current collector and thermally decomposing the binder and the conductive material in the positive electrode active material layer; a step of subjecting the recovered positive electrode active material to primary milling; adding a lithium precursor to the primarily milled positive electrode active material and annealing at 400 to 1000°C; and performing a secondary milling on the annealed positive electrode active material.

2. 2. The method of claim 1, wherein the positive electrode active material layer is at least one 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 contains 60 mol % or more of Ni based on 100 mol % of the total of the remaining metals excluding Li.

3. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the heat treatment is carried out at 300 to 650° C. in an air or oxygen atmosphere.

4. The method of claim 1 , wherein the primary milling and the secondary milling are performed using a centrifugal mill or a jet mill, respectively.

5. 2. The method of claim 1, wherein the primary milling and the secondary milling are each performed at a speed of 6,000 to 20,000 rpm.

6. 2. The method for regenerating a positive electrode active material according to claim 1, wherein the positive electrode active material obtained after the second milling has an average particle size increase rate of 14% or less relative to the positive electrode active material in the raw material, and a standard deviation of the average particle size is 3.0 or less.

7. The lithium precursor is LiOH, Li ２ CO ３ , LiNO ３ and Li ２ 2. The method for regenerating a positive electrode active material according to claim 1, wherein the positive electrode active material contains one or more of:

8. The lithium precursor is added in an amount that can provide lithium equivalent to 1 to 40 mol % when the total lithium in the raw material positive electrode active material is 100 mol %. The method for regenerating a positive electrode active material according to claim 1.

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

10. 2. The method of claim 1, wherein the method comprises: washing the secondary-milled cathode active material; surface-coating the secondary-milled cathode active material; or washing and then surface-coating the secondary-milled cathode active material.

11. 11. The method of claim 10, wherein in the washing step, the weight ratio of the secondary milled cathode active material to the washing solution is 1:0.5 to 1:

10.

12. 11. The method of claim 10, wherein the surface coating is performed by coating the surface with at least one of a metal, an organic metal, and a carbon component in a solid or liquid phase manner, followed by heat treatment at 100 to 1200°C.

13. A regenerated positive electrode active material, which is at least one 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, Contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li, The recycled positive electrode active material is characterized in that the standard deviation of the average particle size of the recycled positive electrode active material is 3.0 or less.

14. The recycled positive electrode active material according to claim 13, wherein the surface of the recycled positive electrode active material is coated with a coating agent containing metal or carbon.

15. The regenerated cathode 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 any one of claims 13 to 15.

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