Method for regenerating positive electrode active material and regenerated positive electrode active material manufactured therefrom

Abstract

The present invention relates to a method for producing a positive electrode active material and a positive electrode active material produced thereby, and more particularly, to a method for producing a positive electrode active material and a positive electrode active material produced thereby, characterized by comprising: (a) heat-treating a waste positive electrode on which a positive electrode active material layer has been formed on a current collector, and thermally decomposing the binder and conductive material in the active material layer to separate the current collector from the positive electrode active material layer and recover the positive electrode active material in the active material layer; (b) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C for 8 to 12 hours; and (c) washing the annealed positive electrode active material with a cleaning solution.

Description

[Technical Field]

[0001] The present invention relates to a method for regenerating positive electrode active material and the regenerated positive electrode active material produced thereby. More specifically, the present invention relates to a method for regenerating positive electrode active material in which, after heat-treating a waste positive electrode, a lithium precursor is immediately added to the recovered positive electrode active material containing single particles without a pre-cleaning step, and the material is annealed at a predetermined temperature for a predetermined time. This reduces the residual lithium on the surface of the positive electrode active material, and restores the crystal structure and grain size of the positive electrode active material to the level of newly produced positive electrode active material. This results in a positive electrode active material with excellent efficiency, lifespan, and resistance characteristics when applied to lithium secondary batteries. Furthermore, the recovery and regeneration process does not use acid, making it environmentally friendly. Neutralization and wastewater treatment are not required, thus reducing process costs. Since the positive electrode active material is regenerated without decomposition, no metal elements are discarded. Since organic solvents are not used, there is no risk of generating toxic gases or explosions. The pre-cleaning step is omitted, and single-particle positive electrode active material is directly regenerated from the waste positive electrode, greatly improving economic efficiency and productivity. [Background technology]

[0002] [Cross-reference with related applications] This application is an application claiming priority based on Korean Patent Application No. 10-2024-0029793 dated 29 February 2024 and Korean Patent Application No. 10-2025-0004744, refiled thereunder on 13 January 2025, and all content disclosed in the documents of said Korean Patent Application is incorporated herein by reference.

[0003] Lithium-ion batteries are broadly classified into a positive electrode, which has a positive electrode active material layer coated with metal foil such as aluminum; a negative electrode, which has a negative electrode active material layer coated with metal foil such as copper; a separation membrane to prevent the positive and negative electrodes from mixing; and an electrolyte that allows lithium ions to move between the positive and negative electrodes.

[0004] The positive electrode active material layer mainly uses lithium-based oxides as the active material, and the negative electrode active material layer mainly uses carbon materials as the active material. Examples of lithium-based oxides include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.), and lithium iron phosphate compounds (LiFePO4). Among these, lithium cobalt oxide has the advantage of a high operating voltage and excellent capacity characteristics, but the high price and unstable supply of cobalt, its raw material, make it difficult to commercially apply to high-capacity batteries. Lithium nickel oxide, on the other hand, has poor structural stability, making it difficult to achieve sufficient lifespan characteristics. Lithium manganese oxide, while having excellent stability, suffers from poor capacity characteristics. Therefore, to compensate for the shortcomings of lithium transition metal oxides, lithium composite transition metal oxides containing two or more transition metals have been developed. Among these, lithium nickel cobalt manganese oxide, containing Ni, Co, and Mn, is widely used in electric vehicle batteries.

[0005] However, lithium nickel cobalt manganese oxide has a problem in that particle cracking easily occurs during the rolling process when manufacturing the positive electrode, and cracks occur inside the particles during the charge-discharge process, increasing the contact area with the electrolyte, which increases the generation of gas due to side reactions with the electrolyte and the degeneration of the active material, thereby reducing the lifespan characteristics.

[0006] To improve this, lithium nickel cobalt manganese oxide, consisting of high-strength single particles, is used as the positive electrode. However, when discarded after use, its high strength makes recovery difficult, and even if recovered, problems such as a decrease in crystallinity lead to a decline in battery performance.

[0007] On the other hand, since the positive electrode contains rare metals such as cobalt, nickel, or manganese, much research is being conducted on recovering and reusing these rare metals from the positive electrodes of lithium secondary batteries that are discarded after use, or from positive electrode scrap generated during the manufacturing process of lithium secondary batteries (hereinafter referred to as "waste positive electrodes").

[0008] Conventional techniques for recovering rare metals such as cobalt, nickel, or manganese from waste cathodes mostly involve dissolving the waste cathode in hydrochloric acid, sulfuric acid, or nitric acid, then extracting the cobalt, manganese, nickel, etc., with an organic solvent, and using them again as raw materials for the synthesis of cathode active materials.

[0009] However, acid-based extraction methods for rare metals have environmental pollution problems, as they require neutralization and wastewater treatment processes, significantly increasing process costs, and they have the drawback of not being able to recover lithium, the main metal in the cathode active material.

[0010] To overcome these drawbacks, recent research has focused on methods for directly recycling positive electrode active materials from waste positive electrodes without decomposing them (direct recycling methods). Four main types of such methods have been introduced: calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

[0011] However, although the aforementioned firing method is simple in its process, it has the disadvantages of generating foreign matter on the surface of the recycled positive electrode active material that reduces the output performance of the battery, generating waste gas, and consuming a large amount of energy.

[0012] Furthermore, while the aforementioned solvent dissolution method can produce a regenerated cathode active material with a relatively clean surface, it has the disadvantage of poor stability and the need for an expensive solvent recovery process because the solvent used to dissolve the binder, such as N-methyl-2-pyrrolidone (NMP), is a toxic gas and poses an explosion risk.

[0013] Furthermore, while the aluminum foil melting method has good process stability, low process costs, and easy binder removal, it has the disadvantages of generating foreign matter that is difficult to remove on the surface of the recycled cathode active material, and of generating hydrogen gas during the aluminum foil removal process, which poses a risk of explosion.

[0014] Finally, although the crushing and screening method has the advantage of being the simplest process, it is difficult to completely separate the current collector and the positive electrode active material. There are disadvantages that the particle size distribution of the positive electrode active material changes during the crushing process, the binder remains, and the battery characteristics of the recycled positive electrode active material deteriorate.

[0015] Therefore, there is an urgent need to develop a method for recycling single-particle positive electrode active materials from waste positive electrodes containing single-particle positive electrode active materials in an environmentally friendly and safe manner with few processes and costs, without reducing the output performance and without discarded metal elements.

Summary of the Invention

Problems to be Solved by the Invention

[0016] In order to solve the problems of the prior art as described above, the present invention directly adds a lithium precursor to the positive electrode active material containing single particles recovered after heat-treating a waste positive electrode, without a pre-washing step, and anneals at a predetermined temperature for a predetermined time, thereby reducing the residual lithium on the surface of the positive electrode active material and restoring the crystal structure and crystal grain size of the positive electrode active material to the level of a new positive electrode active material, providing a positive electrode active material with excellent efficiency, life characteristics, and resistance characteristics when applied to a lithium secondary battery. Also, since an acid is not used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly, and since neutralization and wastewater treatment are not required, the process cost is reduced. Since the positive electrode active material is regenerated as it is without being decomposed, there are no discarded metal elements, and since an organic solvent is not used, there is no risk of generating toxic gases or explosion. The pre-washing step is omitted, and single-particle positive electrode active materials are directly regenerated from waste positive electrodes, aiming to provide a method for regenerating positive electrode active materials with greatly improved economic efficiency and productivity.

[0017] Also, the present invention aims to provide a secondary battery with excellent initial discharge capacity and capacity characteristics.

[0018] The above object and other objects of the present invention can all be achieved by the present invention described below. [Means for solving the problem]

[0019] To achieve the above objective, I) The present invention provides a method for regenerating positive electrode active material, comprising: (a) heat-treating a waste positive electrode in which a positive electrode active material layer containing single-particle positive electrode active material is formed on a current collector, thereby thermally decomposing the binder and conductive material in the positive electrode active material layer, separating the current collector from the positive electrode active material layer, and recovering the positive electrode active material containing single particles in the positive electrode active material layer; (b) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C for 8 to 12 hours; and (c) washing the annealed positive electrode active material with a cleaning solution; or ( The present invention provides a method for regenerating single-particle mid-nickel positive electrode active material, comprising the steps of: (a) heat-treating a waste positive electrode on which a positive electrode active material layer containing single-particle mid-nickel positive electrode active material is formed on a current collector, thereby thermally decomposing the binder and conductive material in the positive electrode active material layer, separating the current collector from the positive electrode active material layer, and recovering the single-particle mid-nickel positive electrode active material in the positive electrode active material layer; (b) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C for 8 to 12 hours; and (c) washing the annealed positive electrode active material with a cleaning solution.

[0020] In this description, "mid-nickel cathode active material" can mean a cathode active material containing 40 mol% or more nickel, specifically 40-70 mol%, relative to 100 mol% of the total metals excluding lithium, i.e., 100 mol% of the total transition metals.

[0021] II) In I) above, the positive electrode active material comprises one or more selected from the group consisting of nickel-cobalt-manganese (NCM) positive electrode active material, nickel-cobalt-aluminum (NCA) positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA) positive electrode active material, and may contain Ni in an amount of 40 mol% or more, based on a total of 100 mol% of the remaining metals excluding Li.

[0022] III) In step I) or II) above, the heat treatment in step (a) can be carried out at 300 to 650°C.

[0023] IV) In steps I) to III) above, the positive electrode active material recovered in step (a) can be provided to the annealing without washing.

[0024] V) In steps I) to IV) above, in step (b), the lithium precursor may be added in an amount that is at least less than the molar ratio of lithium in the positive electrode active material in step (a), based on the amount of lithium in the recovered positive electrode active material.

[0025] VI) In I) to V) above, the lithium precursor may contain one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0026] VII) In I) to VI) above, the cleaning in step (c) may include the steps of mixing the annealed positive electrode active material with the cleaning solution, filtering the mixture, and drying the solid portion of the positive electrode active material obtained after filtering.

[0027] VIII) In I) to VII) above, the cleaning solution may be water or an aqueous solution of a basic lithium compound.

[0028] IX) In I) to VIII) above, the method for regenerating the positive electrode active material may include the step of surface coating the cleaned positive electrode active material to obtain a reusable positive electrode active material.

[0029] X) In I) to IX) above, the surface coating can be applied to the surface by coating one or more of metals, organometallics, and carbon components in a solid-phase or liquid-phase manner, and then heat-treated at 100 to 1200°C.

[0030] XI) In I) to X) above, the positive electrode active material regenerated by the positive electrode active material regeneration method has a D5 value of 1.95 μm or more on the particle size distribution diagram (PSD), or D 95 The value may be 7.11 μm or greater.

[0031] Furthermore, XII) The present invention relates to a cathode active material comprising one or more 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, comprising single particles and / or having a lattice constant of the a-axis of 2.8763 to 2.8783 Å, a lattice constant of the c-axis of 14.200 to 14.250 Å, and a crystal grain size of 148 nm or more, and / or having a D5 value of 1.95 μm or more on a particle size distribution diagram (PSD), or D 95 The present invention provides a positive electrode active material characterized by having a value of 7.11 μm or greater.

[0032] XIII) In XII) above, the positive electrode active material is, on the particle size distribution diagram (PSD), D 50 The value can range from 3.45 to 3.91 μm.

[0033] XIV) In the above XII) or XIII), the positive electrode active material may contain a total of 1.09% by weight or less of LiOH and Li2CO3.

[0034] XV) In the above XII) to XIV), the positive electrode active material may contain Ni in an amount of more than 70 mol%, based on a total of 100 mol% of the remaining metals excluding Li.

[0035] XVI) In the above XII) to XV), the surface of the positive electrode active material may be coated with a coating agent containing metal or carbon.

[0036] XVII) In XII) to XVI), the positive electrode active material may be a regenerated positive electrode active material.

[0037] Furthermore, the present invention provides a secondary battery characterized by containing a positive electrode active material as described in any one of the above items XV) XII) to XVII). [Effects of the Invention]

[0038] According to the present invention, by immediately adding a lithium precursor to a positive electrode active material containing single particles recovered after heat treatment of a waste positive electrode, without a prior washing step, and annealing it at a predetermined temperature for a predetermined time, the residual lithium on the surface of the positive electrode active material is reduced, and the crystal structure and grain size of the positive electrode active material are restored to the level of newly generated positive electrode active material, thereby providing a positive electrode active material with excellent efficiency, lifetime characteristics, and resistance characteristics.

[0039] Furthermore, this method offers several advantages, including the ability to easily and directly regenerate single-particle positive electrode active material from waste positive electrodes without degrading battery performance, environmental friendliness as it does not use acid in the recovery and regeneration process, reduced process costs as neutralization and wastewater treatment are not required, no metal elements are discarded as the positive electrode active material is regenerated without decomposition, and the absence of organic solvents eliminates the risk of toxic gas generation and explosions. In particular, the pre-cleaning process is omitted, and single-particle positive electrode active material is directly regenerated from waste positive electrodes, resulting in significantly improved economy and productivity. [Brief explanation of the drawing]

[0040] The following drawings accompanying this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further illustrate the technical concept of the present invention. Therefore, the present invention should not be construed as being limited to the matters depicted in these drawings. [Figure 1] This figure shows positive electrode scrap that is discarded after the electrode plates are cut from the positive electrode sheet. [Figure 2] This is an SEM image of the cathode active material regenerated in Example 1. [Figure 3] This is an SEM image of the cathode active material regenerated in Example 2. [Figure 4]This is an SEM image of the cathode active material regenerated in Comparative Example 1. [Figure 5] This is an SEM image of the cathode active material regenerated in Comparative Example 2. [Figure 6] This is an SEM image of the cathode active material regenerated in Comparative Example 3. [Figure 7] This is an SEM image of the cathode active material regenerated in Comparative Example 4. [Figure 8] This is an SEM image of a newly generated cathode active material as a reference example. [Figure 9] This is a flowchart of the regeneration process for the positive electrode active material according to the present invention. [Best Mode for Carrying Out the Invention]

[0041] The inventors of this invention were researching a direct recycled method for directly regenerating single-particle positive electrode active material from waste positive electrodes without decomposition, thereby regenerating it as positive electrode active material with superior output performance (rate performance, etc.). They discovered that when single-particle positive electrode active material recovered by heat treatment of waste positive electrodes is immediately combined with a lithium precursor without a pre-washing step and annealed at a predetermined temperature for a predetermined time, the residual lithium on the surface of the regenerated single-particle positive electrode active material decreases, and the crystal structure and grain size of the regenerated single-particle positive electrode active material recover to the level of newly generated positive electrode active material. This improved the efficiency, life characteristics, and resistance characteristics of the manufactured lithium secondary battery. Based on this, they continued their research and completed the present invention.

[0042] The following describes in detail the regenerated positive electrode active material, its regeneration method, and a secondary battery containing the same.

[0043] However, terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention. Therefore, it should be understood that the embodiments and configurations shown in the drawings described herein are merely embodiments of the present invention and do not represent the entirety of the technical idea of ​​the present invention, and that there may be various equivalents and modifications that can substitute for them, and that they may be arranged, substituted, combined, separated or designed in various other configurations.

[0044] All technical and scientific terms used herein have the same meaning as those commonly understood by those with ordinary skill in the art to which this invention pertains, unless otherwise defined.

[0045] Method for regenerating single-particle cathode active material The present invention provides a method for regenerating positive electrode active material, comprising the steps of: (a) heat-treating a waste positive electrode in which a positive electrode active material layer containing single-particle positive electrode active material is formed on a current collector, thereby thermally decomposing the binder and conductive material in the active material layer to separate the current collector from the positive electrode active material layer and recover the positive electrode active material containing single particles in the positive electrode active material layer; (b) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C for 8 to 12 hours; and (c) washing the annealed positive electrode active material with a cleaning solution. In this case, the residual lithium on the surface of the positive electrode active material is reduced, and the crystal structure and grain size of the positive electrode active material are restored to the level of newly generated positive electrode active material, thereby providing a regenerated single-particle positive electrode active material with excellent efficiency, life characteristics, and resistance characteristics for the manufactured lithium secondary battery. Furthermore, since no acid is used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly, and because neutralization and wastewater treatment are not required, process costs are reduced. Since the positive electrode active material is regenerated without decomposition, no metal elements are discarded, and since organic solvents are not used, there is no risk of generating toxic gases or explosions. In particular, since single-particle positive electrode active material can be easily and directly regenerated from waste positive electrodes without any decrease in battery performance, it has the advantage of greatly improving economic efficiency and productivity.

[0046] Furthermore, the method for regenerating positive electrode active material of the present invention is characterized by comprising the steps of: (a) heat-treating a waste positive electrode in which a positive electrode active material layer containing single-particle mid-nickel positive electrode active material is formed on a current collector, and thermally decomposing the binder and conductive material in the positive electrode active material layer to separate the current collector from the positive electrode active material layer and recover the single-particle mid-nickel positive electrode active material in the active material layer; (b) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C for 8 to 12 hours; and (c) washing the annealed positive electrode active material with a cleaning solution. In this case, the residual lithium on the surface of the positive electrode active material is reduced, and the crystal structure and crystal grain size of the positive electrode active material are restored to the level of newly generated positive electrode active material, thereby providing a regenerated single-particle mid-nickel positive electrode active material with excellent efficiency, life characteristics, and resistance characteristics for the manufactured lithium secondary battery. Furthermore, since no acid is used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly, and because neutralization and wastewater treatment are not required, process costs are reduced. Since the positive electrode active material is regenerated without decomposition, no metal elements are discarded, and since organic solvents are not used, there is no risk of generating toxic gases or explosions. In particular, since single-particle positive electrode active material can be easily and directly regenerated from waste positive electrodes without any decrease in battery performance, it has the advantage of greatly improving economic efficiency and productivity.

[0047] The following is a detailed explanation of the regeneration method for the positive electrode active material, broken down into stages.

[0048] (a) Step of recovering single-particle cathode active material from the spent cathode. The (a) step of recovering single-particle positive electrode active material from a waste positive electrode according to the present invention preferably includes the step of heat-treating the waste positive electrode, on which a positive electrode active material layer containing single-particle positive electrode active material is formed on a current collector, to thermally decompose the binder and conductive material in the active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material containing single particles in the positive electrode active material layer. When positive electrode active material is recovered under such conditions, the process is simple and has the effect of cleanly removing the binder, conductive material and current collector.

[0049] As another example, the step of (a) recovering positive electrode active material from a waste positive electrode according to the present invention may preferably include the step of heat-treating a waste positive electrode in which a positive electrode active material layer containing single-particle mid-nickel positive electrode active material is formed on a current collector, thereby thermally decomposing the binder and conductive material in the active material layer, separating the current collector from the positive electrode active material layer, and recovering the single-particle mid-nickel positive electrode active material in the active material layer. When mid-nickel positive electrode active material is recovered under such conditions, the process is simple and has the effect of cleanly removing the binder, conductive material, and current collector.

[0050] The waste positive electrode may preferably be a positive electrode separated from a lithium secondary battery that has been discarded after use, a defective positive electrode sheet or positive electrode scrap generated in the manufacturing process of a lithium secondary battery, and more preferably positive electrode scrap remaining after punching out a positive electrode plate from a positive electrode sheet.

[0051] The positive electrode active material layer in step (a) above may preferably include a positive electrode active material, a binder, and a conductive material.

[0052] The positive electrode active material may preferably be one or more selected from the group consisting of lithium cobalt oxide such as LiCoO2 (hereinafter referred to as "LCO"), lithium manganese oxide such as LiMnO2 or LiMn2O4, lithium iron phosphate compounds such as LiFePO4, lithium nickel cobalt aluminum oxide (NCA), lithium nickel oxide such as LiNiO2, nickel-manganese lithium composite metal oxides in which a portion of the nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn), and NCM-based lithium composite transition metal oxides in which a portion of the nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). More preferably, it is a nickel-manganese lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof, in which case there is an effect of excellent reversible capacity and thermal stability.

[0053] As another specific example, the positive electrode active material may be a compound represented by the following Chemical Formula 1, and in this case, there is an effect of excellent reversible capacity and thermal stability.

[0054] (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the Chemical Formula 1, M contains 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.)

[0055] As an example, the positive electrode active material can contain Ni at 40 mol% or more, 40 to 95 mol%, more preferably 40 to 70 mol% (at this time, the positive electrode active material can be referred to as a mid nickel positive electrode active material) based on a total of 100 mol% of the remaining metals excluding Li. Within this range, there is an effect that the initial discharge capacity, output performance, capacity characteristics, and resistance characteristics of the applied lithium secondary battery are excellent.

[0056] In this description, when the nickel content is measured by a measurement method using IC (Ion Chromatography) or the like commonly used in the technical field to which the present invention belongs, it is not particularly limited. As a specific example, it can be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AEC analyzer.

[0057] The positive electrode active material recovered in step (a) above may preferably be single particles, and more preferably may not contain secondary particles. In this case, since the particles do not break during the electrode manufacturing process, there is no degradation of battery performance due to fine powder, and the regenerated positive electrode active material has excellent lifespan characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging.

[0058] The aforementioned single particle may be any single particle commonly used in the art to which the present invention belongs, insofar as it conforms to the definition of the present invention. For example, it may be a particle consisting of 30 or fewer nodules, preferably a particle consisting of 1 to 20 nodules, more preferably a particle consisting of 1 to 10 nodules, even more preferably a particle consisting of 1 to 5 nodules, and most preferably a particle consisting of 1 nodule. In this case, since the particles do not break during the electrode manufacturing process, there is no degradation of battery performance due to fine powder, and the regenerated positive electrode active material has excellent lifespan characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging.

[0059] In this description, a nodule refers to a particle unit body that constitutes a single particle, and can mean either a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which grain boundaries are not visible when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope (SEM) or electron backscatter diffraction pattern analyzer (EBSD).

[0060] In this description, the number of nodules refers to the average number of nodules in the positive electrode active material particles. This can be determined by cutting the positive electrode containing the positive electrode active material using ion milling, obtaining a cross-sectional image of the thickness direction of the cut positive electrode using a scanning electron microscope (SEM), selecting at least 30 particles each for the positive electrode active material particles with the largest particle size and the positive electrode active material particles with the smallest particle size within the cross-sectional image, and then measuring the number of nodules in the cross-section of each positive electrode active material particle through SEM image analysis, and then taking the arithmetic mean of these values.

[0061] The aforementioned single particle has an average particle size (D 50 The thickness may preferably be 2 to 10 μm, more preferably 2 to 8 μm, and even more preferably 3 to 6 μm.

[0062] In this description, the average particle size (D 50 The average particle size (D) can be defined as the particle size that corresponds to 50% of the cumulative volume in the Particle Size Distribution (PSD). 50 ) can be measured, for example, using the laser diffraction method. Specifically, the average particle size (D) of the positive electrode active material can be measured. 50 The measurement method involves dispersing the positive electrode active material particles in a dispersion medium, then introducing them into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiating them with ultrasound at approximately 28 kHz with an output of 60 W, and then measuring the average particle size (D) corresponding to 50% of the cumulative volume in the measuring device. 50 It is possible to calculate ).

[0063] The conductive material may, for example, be a carbon-based conductive material, and preferably, carbon black, CNTs, or a mixture thereof.

[0064] 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.

[0065] In step (a) above, the heat treatment can be carried out at, for example, 300 to 650°C, preferably 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 580°C. Within this range, the current collector does not melt, and only the binder and the like are removed, which has the advantage of easily separating the positive electrode active material from the current collector.

[0066] The aforementioned heat treatment has a temperature rise rate of, for example, 1 to 20°C / min, preferably 3 to 10°C / min, and more preferably 3 to 7°C / min. Within this range, it can be carried out without putting undue strain on the heat treatment equipment and has the advantage of not causing thermal shock to the positive electrode scrap.

[0067] The aforementioned heat treatment can be carried out, for example, in an air or oxygen atmosphere, preferably in air. In this case, the carbon components in the binder and conductive material react with oxygen and disappear as gases such as CO and CO2, which has the advantage of completely removing the binder and conductive material.

[0068] The oxygen may have a purity of, for example, 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90-99%. Within this range, the binder and conductive material are removed without residue, which has the advantage of increasing the stability of Ni in the regenerated positive electrode active material.

[0069] The purity percentage of the oxygen may be in volume percentage or mol%.

[0070] The purity of oxygen described herein is not particularly limited when measured by a measurement method commonly used in the art to which the present invention pertains.

[0071] The air or oxygen can be supplied at a rate of, for example, 1 to 20 L / min, preferably 1 to 15 L / min, more preferably 2 to 10 L / min, and even more preferably 3 to 7 L / min. Within this range, the positive electrode active material can be easily separated from the current collector, and the separated positive electrode active material can be easily sorted into powder form.

[0072] The heat treatment time may preferably be 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 does not melt, and only the binder and the like are removed, which has the advantage of easily separating the positive electrode active material from the current collector.

[0073] In this description, the heat treatment time refers to the time spent processing at the heat treatment temperature, and the time it takes to reach that heat treatment temperature is not included in the calculation.

[0074] The positive electrode active material recovered in step (a) above can preferably be immediately provided to the annealing step without prior cleaning. In this case, the cleaning step is omitted, lithium loss is prevented, the crystal structure of the positive electrode active material can be easily changed in subsequent steps, improving the battery's charging capacity, resistance characteristics, and capacitance characteristics. Furthermore, no wastewater is generated, and the process is simplified, resulting in significant improvements in economy and productivity.

[0075] In this description, pre-washing can refer to washing performed before introducing the lithium precursor, and post-washing can refer to washing performed after introducing the lithium precursor and annealing.

[0076] Referring to Figure 1, a positive electrode sheet 30 is manufactured by coating a long sheet-shaped aluminum foil 10, which is a positive electrode current collector, with a positive electrode active material layer 20 containing positive electrode active material, conductive material, binder, etc. Then, this is punched out to a certain size to produce a positive electrode plate 40, and positive electrode scrap 50 is generated from the remaining portion. The punching is one means of cutting the positive electrode sheet.

[0077] Furthermore, the positive electrode active material layer 20 is formed by coating the aluminum foil 10 with a slurry containing a mixture of positive electrode active material, conductive material, binder, and solvent. Because the slurry is highly sensitive to environmental factors such as temperature, it is difficult to determine the coating conditions. As a result, waste positive electrode sheets such as positive electrode scrap 50 are generated before the conditions for producing a positive electrode sheet 30 of the desired quality are found through predetermined tests.

[0078] For reference, in the embodiment described below, positive electrode scrap 50 was used as the waste positive electrode.

[0079] (b) Adding a lithium precursor to the recovered cathode active material and annealing it. The present invention provides a method for regenerating positive electrode active material, which includes (b) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C for 8 to 12 hours. In this case, the crystal grain size of the regenerated positive electrode active material increases, and the crystal structure is restored to the level of the newly generated positive electrode active material, thereby providing a positive electrode active material with excellent efficiency, lifetime characteristics, and resistance characteristics. Furthermore, the pre-cleaning step for the recovered positive electrode active material is omitted, which has the advantage of greatly improving economy and productivity.

[0080] The annealing time is preferably 8 to 12 hours, more preferably 9 to 12 hours, more preferably 9 to 11 hours, and more preferably around 10 hours. Within this range, the crystal structure of the single-particle positive electrode active material is sufficiently restored, the size of the crystal grains increases, and the crystal structure recovers to the level of newly formed positive electrode active material, resulting in excellent battery efficiency, life characteristics, and resistance characteristics. If the annealing time is exceeded, the amount of residual LiOH increases, and the performance of the battery deteriorates.

[0081] The annealing step (b) can preferably be performed by adding a lithium precursor to the recovered positive electrode active material and annealing in an air or oxygen (O2) atmosphere, preferably in air. In this case, improving the crystallinity, such as increasing the crystallinity of the positive electrode active material or restoring the crystal structure, has the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0082] The annealing temperature may preferably be 500 to 900°C, more preferably 600 to 880°C, and even more preferably 700 to 800°C. In this case, improving the crystallinity, such as increasing the crystallinity of the positive electrode active material or restoring its crystal structure, has the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0083] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0084] In step (b), the lithium precursor can be added in an amount that is at least a decrease from the molar ratio of lithium in the positive electrode active material in step (a), based on the amount of lithium in the recovered positive electrode active material. Specifically, when the recovered positive electrode active material in step (a) is the positive electrode active material represented by chemical formula 1, the amount added is such that the molar ratio of lithium in this positive electrode active material is 0.0001 to 0.2, preferably 0.001 to 0.1, more preferably 0.001 to 0.07, and even more preferably The amount of lithium added can be such that the molar ratio is 0.001 to 0.03, more preferably 0.001 to 0.02, particularly preferably 0.005 to 0.017, and even more preferably 0.007 to 0.015. As a most preferred example, the amount of lithium added can be such that the molar ratio is 0.009 to 0.013. Within this range, the deficient lithium in the regenerated cathode active material is replenished, and the battery characteristics of the regenerated cathode active material are improved by improving crystallinity, such as by increasing crystallinity or restoring the crystal structure.

[0085] As yet another example, the lithium precursor may be added in an amount equivalent to 1 to 40 mol%, preferably 1 to 30 mol%, and more preferably 7 to 20 mol%, when the total amount of lithium contained in the raw material positive electrode active material is considered to be 100 mol%, and within this range, no residual precursor that can increase the resistance remains in the regenerated positive electrode active material, which is very useful for improving battery characteristics, and it has an economic advantage because the crystal structure can be restored with a smaller amount of lithium precursor than conventional methods.

[0086] The annealing temperature can be adjusted within a limited range depending on the melting point of the lithium precursor. For example, in the case of LiCO3, since the melting point is 723°C, annealing can preferably be performed at 700-900°C, more preferably at 710-780°C. In the case of LiOH, since the melting point is 462°C, annealing can preferably be performed at 400-600°C, more preferably at 450-480°C. Within this range, the crystal structure is restored, resulting in excellent battery efficiency, lifespan characteristics, and resistance characteristics.

[0087] The annealing temperature may preferably be higher than the melting point of the lithium precursor; however, if it exceeds 1000°C, thermal decomposition of the positive electrode active material may occur, potentially leading to a decrease in battery performance; therefore, a temperature of 1000°C or lower is preferable.

[0088] The annealing temperature can preferably be reached at a heating rate of 1 to 10°C / min, more preferably at 1 to 7°C / min, and even more preferably at 2 to 4°C / min. In this case, the crystallinity of the regenerated positive electrode active material is further increased, which has the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0089] The annealing step, for example, includes a cooling step, which may, in specific cases, be natural cooling in a furnace. In this case, the crystallinity of the regenerated cathode active material is further increased, thereby improving the battery characteristics of the regenerated cathode active material.

[0090] In this description, annealing can be defined according to the definition used in the art to which this invention belongs. Specifically, it can be defined as a heat treatment operation that heals deformation or lattice defects and increases crystallinity of a positive electrode active material that has a deformed structure or lattice defects by heating it for an appropriate time at a temperature above the recrystallization temperature, in which the atoms of the main component can sufficiently diffuse and move.

[0091] (c) Step of cleaning the annealed positive electrode active material (post-cleaning) The method for regenerating a positive electrode active material of the present invention includes (c) a step of washing the annealed positive electrode active material with a cleaning solution, which has the advantage of preventing a decrease in battery performance and the generation of gas due to subsequent reactions between the residual lithium precursor and the electrolyte, by removing lithium precursors that tend to remain on the surface of the positive electrode active material with the cleaning solution.

[0092] The cleaning process may preferably include the steps of mixing the annealed positive electrode active material with a cleaning solution, filtering the mixture, and drying the solid positive electrode active material obtained after filtering. In this case, the excess lithium that tends to remain in the positive electrode active material is effectively removed.

[0093] The cleaning process may preferably include the steps of mixing the annealed positive electrode active material with a cleaning solution, filtering the mixture, and drying the solid positive electrode active material obtained after filtering. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain on the surface of the positive electrode active material, are effectively removed with a small amount of cleaning solution, thereby reducing wastewater.

[0094] The annealed active material and the cleaning solution may be mixed, for example, in a weight ratio of 1:0.5 to 1:5.5, preferably 1:0.5 to 1:4.5, more preferably 1:0.5 to 1:3.5, and even more preferably 1:0.5 to 1:2.5. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain on the surface of the positive electrode active material, are effectively removed with a small amount of cleaning solution, thereby reducing wastewater.

[0095] The cleaning solution may preferably be water or an aqueous solution of a basic lithium compound, and more preferably water can be used as the cleaning solution. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain due to the excess lithium added to suppress the cation mixing phenomenon that is likely to occur in regenerated positive electrode active materials, particularly regenerated mid-nickel positive electrode active materials, can be effectively removed with a small amount of cleaning solution. This eliminates the need for wastewater treatment and significantly improves the output performance of the battery.

[0096] The water is preferably distilled water or deionized water. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain on the surface of the regenerated positive electrode active material, are effectively removed with a small amount of cleaning solution, thereby reducing wastewater and significantly improving the output performance of the battery.

[0097] The basic lithium compound aqueous solution may preferably contain more than 0% by weight and up to 15% by weight of the lithium compound, and more preferably more than 0% by weight and up to 10% by weight of the lithium compound. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain on the surface of the positive electrode active material, can be effectively removed with a small amount of cleaning solution, thereby reducing wastewater and significantly improving the output performance of the battery.

[0098] The mixing of the annealed positive electrode active material and the cleaning solution is preferably carried out by stirring, and while the stirring is not particularly limited, mechanical stirring or ultrasonic stirring may be used.

[0099] The stirring may be carried out for preferably 30 minutes or less, more preferably 20 minutes or less, even more preferably 15 minutes or less, and even more preferably 5 to 10 minutes, within this range in which residual lithium is effectively removed.

[0100] (d) A step of surface coating the cleaned positive electrode active material to obtain a reusable positive electrode active material. The method for regenerating positive electrode active material of the present invention includes the step of selectively (d) surface coating the cleaned positive electrode active material to obtain a reusable positive electrode active material, in which case the structural stability and electrochemical performance are improved while maintaining the excellent properties of the positive electrode active material itself.

[0101] Preferably, the surface coating involves coating the surface with a coating agent containing one or more of metals, organometallics, and carbon components using a solid-phase or liquid-phase method, followed by heat treatment at 100 to 1200°C. In this case, the structural stability and electrochemical performance are improved while maintaining the excellent properties of the positive electrode active material itself.

[0102] The aforementioned metal-containing coating agent may preferably contain 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 may contain one or more selected from the group consisting of B, W, Al, Ti, and Mg; even more preferably, it may contain boron (B), tungsten (W), or a mixture thereof; and even more preferably, it may contain tungsten (W) and boron (B). A specific example is a coating agent containing tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0103] The boron-containing coating agent is preferably H3BO3, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, C 13 H 19 It may be one or more selected from the group consisting of BO3, C3H9B3O6, and (C3H7O)3B, and more preferably H3BO3, in which case there is an effect of improving the resistance characteristics and life characteristics of the lithium secondary battery to which it is applied.

[0104] The coating agent containing the aforementioned metal may, for example, be an oxide or acid that contains the aforementioned metal as an element in its molecule.

[0105] The aforementioned organometallic coating agent is not particularly limited as long as it is a coating agent commonly used in the art to which the present invention belongs and contains an organometallic compound containing the aforementioned metal, and specific examples include metal alkoxides.

[0106] The coating agent containing the carbon component is not particularly limited as long as it is a coating agent containing a carbon component commonly used in the art to which the present invention belongs, and a specific example may be a sugar such as sucrose.

[0107] As an example, the coating agent may be present in an amount of 0.001 to 0.3 mol%, preferably 0.01 to 0.3 mol%, more 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 component that is actually coated on the surface of the positive electrode active material excluding the solvent, relative to 1 mol% of the metal in the positive electrode active material before coating treatment. Within this range, the coating agent has the effect of improving structural stability and electrochemical performance while maintaining the excellent properties of the positive electrode active material itself.

[0108] The heat treatment temperature is preferably 100 to 1000°C, more preferably 200 to 1000°C, and even more preferably 200 to 500°C. Within this range, there is no deterioration in performance due to thermal decomposition of the regenerated positive electrode active material, and the structural stability and electrochemical performance are improved.

[0109] The heat treatment time can preferably be 1 to 16 hours, more preferably 3 to 7 hours. Within this range, it is possible to improve structural stability and electrochemical performance while maintaining the excellent properties of the positive electrode active material itself.

[0110] The coating method is not particularly limited as long as it is a coating method commonly used in the art to which the present invention belongs. For example, it may be a liquid-phase method in which a liquid coating agent is manufactured and mixed with the positive electrode active material, a mechanochemical method using the high mechanical energy of ball milling, a fluidized bed coating method, a spray drying method, a precipitation method in which the coating agent is precipitated on the surface of the positive electrode active material in an aqueous solution, a method that utilizes the reaction between the gas-phase coating agent and the positive electrode active material, or a sputtering method.

[0111] The aforementioned metal, organometallic, and carbon components may, for example, be spherical, plate-shaped, angular, or needle-shaped, and such shapes can be adjusted by changing process conditions during the manufacturing process. The definitions of each shape are not particularly limited, as long as they conform to definitions generally accepted in the art to which this invention belongs.

[0112] The coating agent preferably has an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m². 2 It may also be / g, and more preferably the average diameter is 10 to 100 nm and the specific surface area is 20 to 100 m 2 The concentration may be as low as / g, and within this range, it can uniformly adhere to the surface of the regenerated positive electrode active material, thereby imparting structural stability to the regenerated positive electrode active material and improving problems such as the deterioration of lifetime characteristics and electrochemical performance due to lattice deformation and collapse of the crystal structure of the positive electrode active material.

[0113] In this description, the average diameter can be measured by a measurement method commonly used in the art to which the present invention pertains. For example, it can be measured using the laser diffraction method. Specifically, particles of the positive electrode active material are dispersed in a dispersion medium, then introduced into a commercially available laser diffraction particle size analyzer such as Microtrac MT 3000, and ultrasonic waves of approximately 28 kHz are irradiated at an output of 60 W. The average particle size (D) at the 50% reference of the particle size distribution in the measuring device is then measured. 50 It is possible to calculate ).

[0114] In this description, the specific surface area can be measured by a measurement method commonly used in the art to which the present invention pertains. For example, it can be measured by the BET (Brunauer-Emmett-Teller) method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan.

[0115] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method may have a D5 value on the particle size distribution diagram (PSD) of, for example, 1.95 μm or more, preferably 1.96 μm or more, more preferably 1.96 to 2.20 μm, and even more preferably 1.98 to 2.1 μm, and within this range, it has the effect of being excellent in efficiency, lifetime characteristics and resistance characteristics.

[0116] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method is, on the particle size distribution diagram (PSD), D 50 The value may be, for example, 3.45 to 3.91 μm, preferably 3.50 to 3.90 μm, and more preferably 3.70 to 3.90 μm, and within this range, there is an effect of excellent efficiency, lifetime characteristics, and resistance characteristics.

[0117] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method is, on the particle size distribution diagram (PSD), D 95 The value may be, for example, 7.11 μm or more, preferably 7.15 μm or more, more preferably 7.15 to 7.60 μm, and even more preferably 7.15 to 7.55 μm, and within this range, there is an effect of excellent efficiency, lifetime characteristics, and resistance characteristics.

[0118] In this description, the particle size distribution diagram can be obtained by measuring the particle size of the positive electrode active material using a laser diffraction particle size analyzer. Specifically, using the laser diffraction method, particles of the positive electrode active material are dispersed in a dispersion medium, then introduced into a laser diffraction particle size analyzer (Microtrac MT 3000), and after irradiating with ultrasound at approximately 28 kHz with an output of 60 W, the particle size distribution is measured at 5% (D5) and 50% (D5) of the volume accumulated in the analyzer. 50 ), and 95% (D 95 The particle size corresponding to ) was measured. Here, the particle size corresponding to 50% of the cumulative volume was defined as the average particle size (D 50 )

[0119] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method may preferably contain LiOH in an amount of 0.17% by weight or less, more preferably 0.11% by weight or less, even more preferably 0.09% by weight or less, and even more preferably 0.01 to 0.09% by weight. Within this range, there is an effect of excellent initial discharge capacity, output performance (rate performance), and capacity characteristics.

[0120] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method may preferably contain Li2CO3 in an amount of 0.96% by weight or less, more preferably 0.1 to 0.96% by weight. Within this range, there is an effect of excellent initial discharge capacity and capacity characteristics.

[0121] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method may preferably contain a total of 1.09% by weight or less of Li2CO3 and LiOH, more preferably 1.00% by weight or less, even more preferably 0.98% by weight or less, and even more preferably 0.01 to 0.98% by weight. Within this range, there is an effect of excellent initial discharge capacity and capacity characteristics.

[0122] In this description, the residual Li content can be measured using a pH titrator T5 (Mettler Toledo). Specifically, 5 g of positive electrode active material is dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and then filtered to remove the active material. The resulting solution (filtrate) is titrated with a 0.1 M HCl solution, and the change in pH value is measured to obtain a pH titration curve. Using the obtained pH titration curve, the residual amounts of LiOH and Li2CO3 in the positive electrode active material are calculated.

[0123] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method may have a lattice constant of the a-axis measured by XRD analysis of, for example, 2.8763 to 2.8783 Å, preferably 2.8767 to 2.8782 Å, more preferably 2.8770 to 2.8781 Å, and even more preferably 2.8776 to 2.8781 Å, and within this range, it has the effect of recovering to a lattice structure similar to that of the raw material positive electrode active material.

[0124] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method may have a c-axis lattice constant measured by XRD analysis of, for example, 14.200 to 14.250 Å, preferably 14.203 to 14.250 Å, more preferably 14.205 to 14.249 Å, and even more preferably 14.235 to 14.249 Å, and within this range, it has the effect of recovering to a lattice structure similar to that of the raw material positive electrode active material.

[0125] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method may, for example, have a crystallite size (crystallite size) measured by XRD analysis of 148 nm or more, preferably 149 nm or more, more preferably 149 to 168 nm, even more preferably 149 to 157 nm, and even more preferably 149 to 152 nm. In this case, by annealing at a predetermined temperature for a predetermined time, the crystallite size increases, and the crystal structure of the positive electrode active material is restored to the level of the newly regenerated positive electrode active material, which has the advantage of being excellent in efficiency, lifetime characteristics, and resistance characteristics.

[0126] In this description, the lattice parameter and crystallite size of the positive electrode active material can be measured by XRD analysis. Specifically, the lattice parameter can be calculated by indexing the data measured through XRD (X-Ray Diffraction) analysis using Cu Kα X-rays with the Rietveld refinement method, and the crystallite size can be calculated using Scherrer's equation from the XRD measurement data.

[0127] In this description, a crystal line refers to a single-crystal particle unit having a regular arrangement of atoms.

[0128] Furthermore, the present invention can provide a regenerated positive electrode active material characterized by being manufactured by the method for regenerating the positive electrode active material, and when the regenerated positive electrode active material of the present invention is applied, it has the effect of being excellent in the initial discharge capacity, output performance, capacity characteristics and resistance characteristics of the battery.

[0129] Single-particle positive electrode active material The positive electrode active material of the present invention is one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and contains single particles, and / or has a lattice constant of the a-axis of 2.8763 to 2.8783 Å, a lattice constant of the c-axis of 14.200 to 14.250 Å, and a crystal grain size of 148 nm or more, and / or has a D5 value of 1.95 μm or more on the particle size distribution diagram (PSD), or D 95 A characteristic feature is that the value is 7.11 μm or greater. In this case, the residual lithium on the surface of the positive electrode active material decreases, and the crystal structure of the positive electrode active material recovers to the level of newly formed positive electrode active material. When applied to lithium secondary batteries, this has the effect of providing excellent battery efficiency, life characteristics, and resistance characteristics.

[0130] 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 compounds such as LiFePO4, lithium nickel cobalt aluminum oxide (NCA), lithium nickel oxide such as LiNiO2, nickel-manganese lithium composite metal oxides in which a portion of the nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn), and NCM lithium composite transition metal oxides in which a portion of the 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, and capacitance characteristics.

[0131] The positive electrode active material may, as a specific example, be a compound represented by the following chemical formula 1, in which case it has the effect of having excellent electrochemical performance, resistance characteristics, and capacitance characteristics.

[0132] (chemical formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the above 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、x+y+z+w=1である。)

[0133] The positive electrode active material may have a D5 value on the particle size distribution diagram (PSD) of, for example, 1.95 μm or more, preferably 1.96 μm or more, more preferably 1.96 to 2.20 μm, and even more preferably 1.98 to 2.10 μm, and within this range, it has the effect of having excellent efficiency, lifetime characteristics, and resistance characteristics.

[0134] The positive electrode active material is, on the particle size distribution diagram (PSD), D 50 The value may be, for example, 3.45 to 3.91 μm, preferably 3.50 to 3.90 μm or more, and more preferably 3.70 to 3.90 μm, and within this range, there is an effect of excellent efficiency, lifetime characteristics, and resistance characteristics.

[0135] The positive electrode active material is, on the particle size distribution diagram (PSD), D 95 The value may be, for example, 7.11 μm or more, preferably 7.15 μm or more, more preferably 7.15 to 7.60 μm, even more preferably 7.15 to 7.55 μm, and even more preferably 7.15 to 7.30 μm, and within this range, there is an effect of excellent efficiency, lifetime characteristics, and resistance characteristics.

[0136] The positive electrode active material preferably contains a total of 1.09% by weight or less of Li2CO3 and LiOH, more preferably 1.00% by weight or less, even more preferably 0.98% by weight or less, and even more preferably 0.01 to 0.98% by weight, and within this range, there is an effect of excellent initial discharge capacity and capacity characteristics.

[0137] The positive electrode active material preferably contains 0.96% by weight or less of Li2CO3, more preferably 0.1 to 0.96% by weight, and within this range, it has the effect of having excellent initial discharge capacity and capacity characteristics.

[0138] The positive electrode active material preferably contains LiOH in an amount of 0.17% by weight or less, more preferably 0.11% by weight or less, even more preferably 0.09% by weight or less, and even more preferably 0.01 to 0.09% by weight, and within this range, there is an effect of excellent initial discharge capacity, output performance (rate performance), and capacity characteristics.

[0139] The positive electrode active material may have a lattice constant of the a-axis measured by XRD analysis of, for example, 2.8763 to 2.8783 Å, preferably 2.8767 to 2.8782 Å, more preferably 2.8770 to 2.8781 Å, and even more preferably 2.8776 to 2.8781 Å. Within this range, it has the effect of restoring a lattice structure similar to that of the raw material positive electrode active material.

[0140] The positive electrode active material may have a c-axis lattice constant measured by XRD analysis of, for example, 14.200 to 14.250 Å, preferably 14.203 to 14.250 Å, more preferably 14.205 to 14.249 Å, and even more preferably 14.235 to 14.249 Å. Within this range, it has the effect of restoring to a lattice structure similar to that of the raw material positive electrode active material.

[0141] The aforementioned positive electrode active material may have a crystal grain size measured by XRD analysis of, for example, 148 nm or more, preferably 149 nm or more, more preferably 149 to 168 nm, even more preferably 149 to 157 nm, and even more preferably 149 to 152 nm. Within this range, the crystal grain size is similar to that of the newly generated positive electrode active material, and it has the advantage of being excellent in efficiency, lifetime characteristics, and resistance characteristics, as well as improved capacity.

[0142] The positive electrode active material preferably contains more than 70 mol% Ni, more preferably 71 to 95 mol%, and even more preferably 80 to 95 mol%, based on a total of 100 mol% of the remaining metals excluding Li. Within this range, there is an advantage in having excellent battery characteristics.

[0143] The positive electrode active material may preferably contain single particles and more preferably not contain secondary particles. In this case, the particles do not break during the electrode manufacturing process, so there is no degradation of battery performance due to fine powder, and the positive electrode active material has excellent lifespan characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging.

[0144] The positive electrode active material may, for example, have its surface coated with a metal or carbon, preferably a metal. In this case, the structural stability of the positive electrode active material is improved without any chemical or physical changes to the positive electrode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. Furthermore, the substitution of a different element on the surface of the positive electrode active material reduces the amount of residual lithium and lowers the pH, thereby improving the physicochemical properties of the battery.

[0145] The coating preferably comprises one or more elements 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 comprising one or more elements selected from the group consisting of B, W, Al, Ti, and Mg, even more preferably being boron (B), tungsten (W), or a mixture thereof, and even more preferably being 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.

[0146] The coating agent may, for example, be present 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%, within this range, while maintaining the excellent properties of the positive electrode active material itself, it has the effect of improving structural stability and electrochemical performance.

[0147] Preferably, the surface coating can be applied to the surface by coating with a coating agent containing one or more of metals, organometallics, and carbon components in a solid-phase or liquid-phase manner, followed by heat treatment at 100 to 1200°C. In this case, the structural stability and electrochemical performance are improved while maintaining the excellent properties of the positive electrode active material itself.

[0148] The positive electrode active material may, for example, be a regenerated positive electrode active material, which has the advantage of being economical and highly productive.

[0149] Figure 9 is a flowchart illustrating one embodiment of the present invention, showing the regeneration process for a single-particle cathode active material.

[0150] Referring to Figure 9, first, positive electrode scrap is prepared as waste positive electrode (step S10).

[0151] For example, a slurry prepared by mixing single-particle NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride with NMP (N-methyl pyrrolidone) is coated onto aluminum foil and dried in a vacuum oven at approximately 120°C to produce a cathode sheet. After punching out cathode plates of a certain size, the remaining cathode scrap can be prepared.

[0152] The aforementioned positive electrode scrap has a positive electrode active material layer on an aluminum foil, and after the solvent evaporates, the positive electrode active material layer has a structure in which a binder binds the positive electrode active material and the conductive material. Therefore, when the binder is removed, the positive electrode active material is separated from the aluminum foil.

[0153] NCM-based lithium composite transition metal oxides can specifically be cathode active materials containing single-particle mid-nickel.

[0154] Next, the prepared positive electrode scrap is crushed into appropriate sizes (step S20).

[0155] Here, crushing includes cutting or shredding the positive electrode scrap into a size that is easy to handle. Specifically, the crushed positive electrode scrap may be 1 cm x 1 cm in size. The crushing may be carried out using various dry grinding equipment such as a hand mill, pin mill, disc mill, cutting mill, or hammer mill, and a high-speed cutting machine may be used to increase productivity.

[0156] Preferably, the crushing process can be decided by considering the handling of the positive electrode scrap and the characteristics required by the equipment used in subsequent processes, such as whether or not to crush the scrap and the size of the small pieces. However, if equipment capable of continuous processing is used, good fluidity is required, so the positive electrode scrap must be crushed into even smaller pieces.

[0157] Next, the positive electrode scrap is heat-treated to recover the positive electrode active material (step S30).

[0158] Here, the heat treatment is performed to thermally decompose the binder in the active material layer. As described above, through the heat treatment, the binder and conductive material in the active material layer are thermally decomposed into CO2 and H2O and removed. Since the binder is removed, the positive electrode active material is separated from the current collector, and the separated positive electrode active material can be easily sorted into powder form. Therefore, even with just step S30, the active material layer can be separated from the current collector, and the positive electrode active material in the active material layer can be recovered in powder form.

[0159] The recovered positive electrode active material may contain single particles, and specifically, it may not contain secondary particles. In this case, since the particles do not break during the electrode manufacturing process, there is no degradation in battery performance due to fine powder, and the positive electrode active material has excellent lifespan characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging.

[0160] The aforementioned heat treatment can be carried out in air or an oxygen atmosphere, specifically in air. When heat treatment is performed in a reducing gas or inactive gas atmosphere, the binder and conductive material carbonize instead of being thermally decomposed. When carbonization occurs, carbon components remain on the surface of the positive electrode active material, reducing the performance of the reused positive electrode active material. However, when heat treatment is carried out in air or an oxygen atmosphere, the carbon components in the binder and conductive material react with oxygen and disappear as gases such as CO and CO2, thus completely removing the binder and conductive material.

[0161] The heat treatment is preferably carried out at 300 to 650°C, and specifically at 550°C. Below 300°C, it is difficult to remove the binder, making it impossible to separate the current collector, and above 650°C, the current collector melts, making it impossible to separate the current collector.

[0162] The heat treatment preferably has a temperature rise rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, the burden on the heat treatment equipment is suppressed, and there is an advantage in not causing thermal shock to the positive electrode scrap.

[0163] The aforementioned heat treatment can be carried out for a period of time sufficient to adequately decompose the binder, preferably 30 minutes or more, more preferably 30 minutes to 5 hours, and specifically around 30 minutes. Within this range, the binder is adequately decomposed, and the decomposition efficiency is excellent.

[0164] The aforementioned heat treatment can be carried out using various types of furnaces, for example, a box-type furnace, or, considering productivity, a rotary kiln capable of continuous processing.

[0165] After the heat treatment, the device can be slowly or rapidly cooled in the atmosphere.

[0166] Next, a lithium precursor is added to the recovered positive electrode active material and annealed (step S40).

[0167] In the annealing step, it is important to immediately add a lithium precursor to the recovered positive electrode active material without a water washing step and perform annealing. In this case, the preceding washing step is omitted, lithium loss is prevented, the crystal structure of the positive electrode active material changes easily in the subsequent steps, improving the battery's charging capacity, resistance characteristics, and capacity characteristics. Furthermore, no wastewater is generated, the process is simplified, and economic efficiency and productivity are greatly improved, resulting in improved battery performance.

[0168] Furthermore, since lithium is lost from the positive electrode active material during the preceding step S30, step S40 replenishes this lost lithium. In addition, since deformation structures (for example, Co3O4 in the case of LCO active material) may form on the surface of the single-particle positive electrode active material during the preceding steps, step S40 improves the battery characteristics of the regenerated single-particle positive electrode active material by restoring the crystal structure of the single-particle positive electrode active material through annealing, thereby restoring it to the level of a newly produced positive electrode active material. Here, "newly produced" is the opposite concept of "regenerated," meaning it is manufactured for the first time, and is the same word as "raw material" used in the examples.

[0169] As a specific example of the lithium precursor, Li2CO3 is used.

[0170] The lithium precursor is preferably added in an amount equal to at least the molar ratio of the lost lithium, compared 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. Adding an excessive amount of lithium precursor compared to the amount of lithium lost will leave unreacted lithium precursor in the regenerated positive electrode active material, which increases resistance; therefore, it is necessary to add an appropriate amount of lithium precursor. For example, if the molar ratio of lithium to other metals in the newly generated positive electrode active material is 1, an amount of lithium precursor can be added such that the lithium molar ratio is 0.001 to 0.4, and preferably, an amount of lithium precursor can be added such that the lithium molar ratio is 0.01 to 0.2.

[0171] As a specific example, adding a lithium precursor at a molar ratio of 0.09 to 0.1 (based on lithium metal), which is the ratio of the lithium lost relative to the lithium content in the newly generated cathode active material based on the results of ICP analysis, can improve the capacity to a level equivalent to that of the newly generated cathode active material. Here, the results of ICP analysis have an error value of approximately ±0.02.

[0172] The aforementioned annealing time is, for example, 8 to 12 hours, and specifically 10 hours. This increases the size of the crystal grains of the single-particle positive electrode active material, allowing for sufficient recovery of the crystal structure and restoring it to the level of newly formed positive electrode active material. This improves the efficiency, lifespan, and resistance characteristics of the manufactured lithium secondary battery. Furthermore, the pre-washing step for the recovered positive electrode active material is omitted, preventing lithium loss. This allows the crystal structure of the positive electrode active material to change easily in subsequent steps, improving the battery's charging capacity, resistance characteristics, and capacity characteristics. Additionally, no wastewater is generated, and the process is simplified, resulting in significant improvements in economy and productivity.

[0173] In this case, the annealing equipment can be the same as or similar to that used in the heat treatment step S30.

[0174] The aforementioned annealing is carried out, for example, in oxygen (O2) or air under conditions of 400 to 1000°C, and more specifically, in air under conditions of 750°C.

[0175] The annealing temperature is preferably a temperature that exceeds the melting point of the lithium precursor. However, temperatures exceeding 1000°C should not exceed 1000°C, as this will cause thermal decomposition of the positive electrode active material and a decrease in performance. For example, when Li2CO3 is used as the lithium precursor, an annealing temperature of 700 to 900°C is appropriate, more preferably 710 to 780°C, and most preferably 750 to 780°C. When LiOH is used as the lithium precursor, an annealing temperature of 400 to 600°C may be appropriate, more preferably 450 to 480°C, and most preferably 470 to 480°C.

[0176] Next, the annealed positive electrode active material is cleaned (step S50).

[0177] In the cleaning step S50, lithium precursors that were unable to participate in the reaction in the annealing step S40 and are present on the surface of the positive electrode active material in the form of LiOH and Li2CO3 are removed. Lithium impurities such as lithium carbonate (Li2CO3) that remain on the surface of the regenerated positive electrode active material need to be removed because they may later react with the electrolyte, degrade the performance of the battery, and generate gas.

[0178] In the cleaning step S50, preferably, the positive electrode active material and the cleaning solution from the annealing step S40 are mixed in a weight ratio of 1:0.5 to 1:5.5, specifically 1:1, filtered, and then the obtained solid positive electrode active material is dried. In this case, residual lithium is removed with a small amount of cleaning solution, which has the advantage of reducing wastewater.

[0179] The cleaning solution can preferably be distilled water or an aqueous solution of a basic lithium compound containing more than 0% to 10% by weight of a basic lithium compound, and more preferably distilled water can be used as the cleaning solution. In this case, it is safe and inexpensive, and has the advantage that transition metals present in the regenerated positive electrode active material are not leached out.

[0180] Preferably, the cleaning process involves mixing the annealed positive electrode active material with a cleaning solution, filtering it, and then drying the resulting solid portion of the positive electrode active material.

[0181] The mixing of the annealed positive electrode active material and the cleaning solution is preferably carried out by stirring, and while the stirring is not particularly limited, mechanical stirring or ultrasonic stirring may be used.

[0182] The mechanical stirring can preferably be carried out at 250 to 350 rpm for 3 to 10 minutes.

[0183] The filtration is preferably reduced-pressure filtration using a filter, and the drying may be vacuum drying at 120-140°C.

[0184] Next, as a selective step, the cleaned positive electrode active material can be surface coated (step S60).

[0185] Surface coating, for example, involves applying a coating agent containing metal, organometallic, or carbon components to the surface using a solid-phase or liquid-phase method, followed by heat treatment. However, if the heat treatment temperature is too low, the desired surface protective layer of dissimilar metals will not form, and if the heat treatment temperature is too high, the thermal decomposition of the positive electrode active material will degrade the battery's performance.

[0186] Specifically, a metal oxide such as B, W, or BW, or an acid, is coated onto the cleaned positive electrode active material, and then heat-treated to form a surface protective layer, such as a lithium boron oxide layer, on the surface of the positive electrode active material.

[0187] The solid-phase or liquid-phase method for the surface coating may, for example, be a method such as mixing, milling, spray drying, or grinding.

[0188] If the annealing step S40 is performed to make the molar ratio of lithium to other metals in the positive electrode active material 1:1, then in the surface coating step S60, the lithium in the regenerated positive electrode active material reacts with the coating agent, causing the molar ratio of lithium to other metals in the positive electrode active material to fall below 1:1. As a result, such a regenerated positive electrode active material will not be able to fully utilize its 100% battery capacity. However, if the lithium precursor is added in excess in the annealing step S40 to be 0.0001 to 0.1 more molars relative to the other metals in the regenerated positive electrode active material, then in the surface coating step S60, a surface protective layer is formed, naturally making the molar ratio of lithium to other metals in the positive electrode active material 1:1, and preventing a decrease in battery capacity.

[0189] secondary battery The secondary battery of the present invention includes the regenerated single-particle positive electrode active material. In this case, the lithium component remaining on the surface of the positive electrode active material is greatly reduced, resulting in excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics. Furthermore, since no acid or organic solvent is used in the recovery and regeneration process of the single-particle positive electrode active material, it is environmentally friendly, and in particular, the omission of the initial water washing process results in excellent economic efficiency and productivity.

[0190] The secondary battery of the present invention may include all of the above-described details regarding the regenerated single-particle positive electrode active material and its regeneration method. Therefore, redundant descriptions thereof are omitted here.

[0191] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the present invention, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such changes and modifications fall within the scope of the appended claims.

[0192] [Examples] Example 1 The positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide (containing 61 mol% Ni, based on a total of 100 mol% of the remaining metals excluding Li; single particle)) discarded after punching out the positive electrode plate was crushed, and then heat-treated in air at 550°C for 30 minutes to remove the binder and conductive material, separate the current collector and positive electrode active material, and then recover the positive electrode active material. Here, the rate of temperature rise to reach the heat treatment temperature was 5°C / min, and air was supplied at 3 L / min.

[0193] The recovered cathode active material was confirmed to be a single particle through SEM imaging.

[0194] Without washing, lithium precursor Li2CO3 was immediately added to the recovered positive electrode active material, and the mixture was annealed under air at 750°C for 10 hours. Air was supplied at a rate of 3 L / min. At this time, the amount of lithium precursor added was such that it provided 10 mol% of lithium, assuming that the total amount of lithium contained in the positive electrode active material in the raw materials was 100 mol%.

[0195] The annealed positive electrode active material and distilled water were mixed in a 1:1 weight ratio, stirred for 5 minutes under conditions of 300 rpm, and then filtered under reduced pressure to obtain the solids. The solids were vacuum-dried at 130°C for 12 hours to obtain the washed positive electrode active material.

[0196] The cleaned positive electrode active material was coated with boric acid and then heated at 300°C for 5 hours to produce the final regenerated positive electrode active material. Here, the boric acid was added at a concentration of 1000 ppm based on the total weight of the positive electrode active material, the temperature rise rate until the heat treatment temperature was reached was 2°C / min, and air was supplied at 3 L / min.

[0197] Here, the molar ratio of lithium to other metals in the positive electrode active material was measured using an ICP analyzer. While this can be done using a standard ICP analyzer commonly used in laboratories, there is no deviation due to the specific measuring device or method.

[0198] In this document, ppm refers to weight unless otherwise defined.

[0199] Example 2 In the above-described Example 1, the recycled cathode active material was produced in the same manner as in Example 1, except that the NCM-based lithium composite transition metal oxide (single particle containing 61 mol% Ni based on a total of 100 mol% of the remaining metals excluding Li) in the cathode scrap discarded after punching out the cathode plate was replaced with an NCM-based lithium composite transition metal oxide (containing 81 mol% or more Ni based on a total of 100 mol% of the remaining metals excluding Li). Furthermore, the recovered cathode active material was confirmed to be single particles through SEM imaging.

[0200] Comparative Example 1 The regenerated cathode active material was produced in the same manner as in Example 1, except that the annealing step was performed at 750°C for 5 hours.

[0201] Comparative Example 2 The regenerated cathode active material was produced in the same manner as in Example 1, except that the annealing step was performed at 750°C for 15 hours.

[0202] Comparative Example 3 In the above-described Example 1, the recycled cathode active material was produced in the same manner as in Example 1, except that the NCM-based lithium composite transition metal oxide (single particle containing 61 mol% Ni based on a total of 100 mol% of the remaining metals excluding Li) in the cathode scrap discarded after punching out the cathode plate was replaced with NCM-based lithium composite transition metal oxide (secondary particle containing 61 mol% Ni based on a total of 100 mol% of the remaining metals excluding Li). Furthermore, the recovered cathode active material was confirmed to be secondary particles through SEM imaging.

[0203] Comparative Example 4 In the above-described Example 1, the recycled positive electrode active material was produced in the same manner as in Example 1, except that the NCM-based lithium composite transition metal oxide (single particle containing 61 mol% Ni based on a total of 100 mol% of the remaining metals excluding Li) in the positive electrode scrap discarded after punching out the positive electrode plate was replaced with NCM-based lithium composite transition metal oxide (secondary particle containing 81 mol% Ni based on a total of 100 mol% of the remaining metals excluding Li). The recovered positive electrode active material was confirmed to be secondary particles through SEM imaging.

[0204] Reference example Instead of reused active material, a fresh NCM-based lithium composite transition metal oxide (containing 61 mol% Ni, based on a total of 100 mol% of the remaining metals excluding Li, with an average particle size of 3.99 μm) was prepared. The fresh cathode active material was confirmed to be a single particle through SEM imaging.

[0205] [Test Example I: Particle Size Analysis and Residual Lithium Content] The residual lithium content of the regenerated or newly generated cathode active materials manufactured or prepared in Examples 1 and 2, Comparative Examples 1 to 4, and the Reference Example was measured as follows, and the results are shown in Table 1 below.

[0206] *Particle size analysis: Using the laser diffraction method, particles of the positive electrode active material are dispersed in a dispersion medium, then introduced into a laser diffraction particle size analyzer (Microtrac MT 3000), and after irradiating with ultrasound at approximately 28 kHz with an output of 60 W, the particle size is measured at 5% (D5) and 50% (D5) of the volume accumulated in the analyzer. 50 ) and 95% (D 95 The particle size corresponding to ) was measured, along with the minimum particle size (Dmix) and the maximum particle size (Dmax). Here, the particle size corresponding to 50% of the cumulative volume was defined as the average particle size (D 50 )

[0207] *The residual lithium content was measured using a pH titrator T5 (Mettler Toledo). Specifically, 5 g of positive electrode active material was dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, filtered to remove the active material, and the resulting filtrate was titrated with a 0.1 M HCl solution while measuring the change in pH to obtain a pH titration curve. Using the obtained pH titration curve, the residual amounts of LiOH and Li2CO3 in the positive electrode active material were calculated.

[0208] [Table 1]

[0209] As shown in Table 1 above, the single-particle regenerated cathode active materials of Examples 1 and 2 according to the present invention have D5 and D5 compared to the single-particle regenerated cathode active materials of Comparative Examples 1 and 2. 50 and D 95 The size was somewhat larger and at a similar level to the newly generated cathode active material in the reference example, and in particular, it was confirmed that Example 1 was even more similar to the reference example. Also, the single-particle regenerated cathode active material of Example 2 was similar to the reference example and D 50 and D 95 There are some differences, but these are due to differences in nickel content.

[0210] Furthermore, Comparative Examples 3 and 4 are secondary particles, and compared to the single-particle regenerated cathode active material of Examples 1 and 2, D5 and D50 and D 95 The values ​​were very large, and from this, it could be predicted that Examples 1 and 2, compared to Comparative Examples 3 and 4, had less fine powder and therefore fewer side reactions, resulting in superior lifetime characteristics.

[0211] Furthermore, as shown in Table 1 above, it was confirmed that the regenerated positive electrode active materials of Examples 1 and 2 according to the present invention had a residual amount of LiOH similar to or less than that of the reference example, which is a newly generated positive electrode active material. From this, it could be predicted that the degradation of battery performance due to residual LiOH in the regenerated positive electrode active material of the present invention would be similar to or even less than that of the newly generated positive electrode active material.

[0212] On the other hand, in Comparative Example 2, the amount of residual LiOH increased significantly due to excessive annealing.

[0213] [Example Test II: SEM Analysis] The regenerated or newly created cathode active materials manufactured or prepared in Examples 1 and 2, Comparative Examples 1 to 4, and the Reference Example were imaged using a scanning electron microscope (SEM) and are shown in Figures 2 to 8, respectively. The SEM images were taken using a general-purpose SEM commonly used in laboratories. Specifically, a Hitachi S-4200 was used. However, there was no deviation due to the measurement equipment or method.

[0214] As can be seen from Figures 2 and 3 below, the regenerated cathode active material produced in Examples 1 and 2 was a single particle, broken into small particles and dispersed, and was found to be similar to the reference example of the newly generated cathode active material in Figure 8.

[0215] Furthermore, as can be seen from Figures 4 and 5 below, the regenerated positive electrode active materials produced in Comparative Examples 1 and 2 were single particles, did not break into smaller particles, and were found to be aggregated.

[0216] On the other hand, as can be seen from Figures 6 and 7 below, the regenerated cathode active materials produced in Comparative Examples 3 and 4 were secondary particles and were less prone to cracking and dispersion than the regenerated cathode active material produced in Example 1, and were found to be somewhat aggregated.

[0217] [Test Example III: Evaluation of CHC Cells] The electrochemical performance of the regenerated or newly generated cathode active materials manufactured or prepared in Examples 1 and 2, Comparative Examples 1 to 3, and the Reference Example was measured through evaluation using a CHC cell as described below, and the results are shown in Table 2 below.

[0218] *Evaluation of CHC cells: 97.5 wt% recycled cathode active material, 1.15 wt% carbon black (a conductive material), and 1.35 wt% PVdF (a binder) were weighed and mixed with NMP to produce a slurry. This slurry was coated onto aluminum foil to produce a cathode, and then Coin Half Cells (CHCs) were manufactured. The electrochemical performance (charging capacity, discharging capacity, and efficiency) was evaluated under conditions of 3-4.25V cut, initial formation of 0.1C / 0.1C charge / discharge, and an electrolyte with a weight ratio of ethylene carbonate (EC):dimethyl carbonate (DMC):ethyl methyl carbonate (EMC) = 3:4:3, along with other additives.

[0219] [Table 2]

[0220] As shown in Table 2 above, the single-particle regenerated cathode active materials of Examples 1 and 2 according to the present invention exhibited even better initial charge capacity (CH) and initial discharge capacity (DCH) compared to the regenerated cathode active materials of Comparative Examples 1 to 3, reaching the level of the newly generated cathode active material in the reference example. In particular, it was confirmed that the initial discharge capacity, which is the most important characteristic in secondary batteries, was even better.

[0221] [Example Test IV: XRD Analysis] The regenerated or newly created cathode active materials manufactured or prepared in Examples 1 and 2, Comparative Examples 1 to 4, and the Reference Example were measured by XRD analysis to determine the a-axis lattice constant, c-axis lattice constant, and crystal grain size, respectively, and are shown in Table 3 below.

[0222] *Lattice parameter and crystallite size: These were measured by XRD analysis, specifically through X-ray diffraction (XRD) analysis using Cu Kα X-rays. The lattice parameter was calculated by indexing the XRD measurement data using the Rietveld refinement method, and the crystallite size was calculated using the Scherrer equation based on the XRD measurement data.

[0223] [Table 3]

[0224] As shown in Table 3 above, the single-particle regenerated cathode active material according to the present invention (Examples 1 and 2) was found to be even more similar to the newly generated cathode active material of the reference example in terms of the lattice constant of the a-axis, lattice constant of the c-axis, and crystal grain size of the regenerated cathode active material of Comparative Examples 1 to 4, and it was predicted that the battery characteristics would be further improved. [Explanation of Symbols]

[0225] 10 Current collector 20 Active material layer 30 Positive electrode sheets 40 Positive plate 50 Positive electrode scrap

Claims

1. (a) A step of heat-treating a waste positive electrode in which a positive electrode active material layer containing single-particle positive electrode active material is formed on a current collector, thereby thermally decomposing the binder and conductive material in the positive electrode active material layer, separating the current collector from the positive electrode active material layer, and recovering the positive electrode active material containing single particles in the positive electrode active material layer, (b) Adding a lithium precursor to the recovered cathode active material and annealing it at 400 to 1000°C for 8 to 12 hours, (c) A method for regenerating a positive electrode active material, characterized by comprising the step of washing the annealed positive electrode active material with a cleaning solution.

2. (a) A step of heat-treating a waste positive electrode in which a positive electrode active material layer containing single-particle mid-nickel positive electrode active material is formed on a current collector, thereby thermally decomposing the binder and conductive material in the positive electrode active material layer, separating the current collector from the positive electrode active material layer, and recovering the single-particle mid-nickel positive electrode active material in the positive electrode active material layer, (b) Adding a lithium precursor to the recovered cathode active material and annealing it at 400 to 1000°C for 8 to 12 hours, (c) A method for regenerating single-particle mid-nickel cathode active material, characterized by comprising the step of washing the annealed cathode active material with a cleaning solution.

3. The method for regenerating a positive electrode active material according to claim 1 or 2, wherein the positive electrode active material comprises one or more selected from the group consisting of nickel-cobalt-manganese (NCM) positive electrode active material, nickel-cobalt-aluminum (NCA) positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA) positive electrode active material, and contains Ni in an amount of 40 mol% or more, based on 100 mol% of the total of the remaining metals excluding Li.

4. The method for regenerating a positive electrode active material according to claim 1 or 2, characterized in that the heat treatment in step (a) above is performed at 300 to 650°C.

5. A method for regenerating a positive electrode active material according to claim 1 or 2, characterized in that the positive electrode active material recovered in step (a) above is provided to annealing without washing.

6. The method for regenerating a positive electrode active material according to claim 1 or 2, characterized in that, in step (b), the lithium precursor is added in an amount that is at least a decrease from the molar ratio of lithium in the positive electrode active material in step (a), based on the amount of lithium in the recovered positive electrode active material.

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

8. The method for regenerating a positive electrode active material according to claim 1 or 2, characterized in that the cleaning in step (c) comprises the steps of mixing the annealed positive electrode active material with a cleaning solution, filtering the mixture, and drying the solid portion of the positive electrode active material obtained after filtering.

9. The method for regenerating a positive electrode active material according to claim 1 or 2, characterized in that the cleaning solution is water or an aqueous solution of a basic lithium compound.

10. The method for regenerating the positive electrode active material according to claim 1 or 2, characterized in that it includes the step of surface coating the cleaned positive electrode active material to obtain a reusable positive electrode active material.

11. The method for regenerating a positive electrode active material according to claim 10, characterized in that the surface coating is applied to the surface by coating one or more of metals, organometallics, and carbon components in a solid-phase or liquid-phase manner, followed by heat treatment at 100 to 1200°C.

12. The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method is, on the particle size distribution diagram (PSD), D ５ If the value is 1.95 μm or larger, or D ９５ A method for regenerating a positive electrode active material according to claim 1, characterized in that the value is 7.11 μm or more.

13. A positive electrode active material comprising one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, Including single particles and / or The lattice constant of the a-axis measured by XRD analysis is 2.8763–2.8783 Å, the lattice constant of the c-axis is 14.200–14.250 Å, and the grain size is 148 nm or larger, and / or On the particle size distribution diagram (PSD), D ５ If the value is 1.95 μm or larger, or D ９５ A positive electrode active material characterized by having a value of 7.11 μm or more.

14. The positive electrode active material has a D ５０ value of 3.45 to 3.91 μm on the particle size distribution diagram (PSD), and is the positive electrode active material according to claim 13, characterized in that.

15. The positive electrode active material is LiOH and Li ２ CO ３ The positive electrode active material according to claim 13 or 14, characterized in that it contains a total of 1.09% by weight or less.

16. The positive electrode active material according to claim 13, characterized in that the positive electrode active material contains more than 70 mol% of Ni, based on 100 mol% of the total of the remaining metals excluding Li.

17. The positive electrode active material according to claim 13, characterized in that the surface of the positive electrode active material is coated with a coating agent containing metal or carbon.

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