Direct recycling method of positive electrode active material and positive electrode active material regenerated thereby

Abstract

An embodiment of the present invention is for stably restoring a layered structure when regenerating a positive electrode active material that has degraded due to lithium and nickel deficiency, and provides a direct recycling method of a positive electrode active material and the positive electrode active material regenerated thereby. The direct recycling method comprises the steps of: preparing a positive electrode including a waste positive electrode active material recovered from a waste lithium-ion battery; electrochemically plating nickel on the surface of the positive electrode through cyclic voltammetry; recovering a nickel-plated positive electrode active material from the nickel-plated positive electrode; and obtaining a regenerated positive electrode active material by heat-treating the nickel-plated positive electrode active material.

Description

Direct recycling method of cathode active material and cathode active material recycled thereby

[0001] The present invention relates to a method for regenerating a positive electrode active material, and more specifically, to a method for directly recycling a positive electrode active material and a positive electrode active material regenerated thereby.

[0002] Lithium-ion batteries are widely used in various industrial fields, including electric vehicles, energy storage systems, and portable electronic devices; consequently, the volume of used lithium-ion batteries being discarded is also continuously increasing. In particular, since the cathode active materials of lithium-ion batteries contain expensive transition metals such as nickel, cobalt, and manganese, the development of recycling technologies for spent lithium-ion batteries has emerged as a critical task from the perspective of resource recovery and environmental protection.

[0003] Conventional lithium-ion battery recycling technology has primarily been based on methods of individually separating and recovering the metal elements constituting the cathode active material. For example, a widely used process involves extracting transition metals such as nickel, cobalt, and manganese from waste cathode active material and then synthesizing them into precursor forms to manufacture new cathode active materials. While this method may be advantageous for recovering metal resources, it has limitations, including a complex process, high energy consumption, and the loss of the crystal structural value of the existing cathode active material.

[0004] In contrast, direct recycling technology, which restores the performance of spent cathode active materials while maintaining their chemical composition and crystal structure as much as possible, is attracting attention as a more efficient and sustainable alternative. Direct recycling technology offers advantages in terms of process simplification and energy savings by utilizing the spent NCM itself as the regeneration target, rather than breaking down the cathode active material into its elemental level. In particular, given that NCM-based cathode active materials are widely used in commercial batteries, the potential for their direct recycling holds significant industrial importance.

[0005] However, NCM cathode active materials undergo structural degradation during repeated charging and discharging and long-term use, and it is frequently reported that they fail to fully recover their initial performance even after the direct recycling process. For example, as the layered structure on the cathode surface collapses and a phase transition to a rock-salt or spinel phase occurs, lithium ion diffusion is inhibited, and an increase in resistance at the cathode-electrolyte interface may be induced.

[0006] Conventional research has primarily attributed the main cause of such degradation to lithium loss, or lithium deficiency. Accordingly, regeneration processes have generally applied a method of replenishing the lithium content by supplying an additional lithium source and performing high-temperature heat treatment. However, problems have been raised that it is difficult to completely restore the crystal structure of the degraded cathode active material with simple lithium replenishment alone, and that excessive lithium addition can lead to the formation of residual lithium compounds on the surface or a decrease in electrochemical performance.

[0007] Therefore, research on direct recycling technology capable of effectively restoring structural stability and electrochemical performance by comprehensively considering degradation causes, including not only lithium but also transition metals, while maintaining the spent NCM cathode active material itself, is recognized as an essential task.

[0008] [Prior Art Literature]

[0009] (Patent Document 0001) Republic of Korea Registered Patent Publication No. 10-2889630

[0010] The technical problem to be solved by the present invention is to provide a direct recycling method for a positive electrode active material that can effectively restore the structural and chemical properties of the positive electrode active material by directly recycling the degraded positive electrode active material, plating it with nickel, and then heat-treating it, and to provide the positive electrode active material regenerated thereby.

[0011] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below.

[0012] To achieve the above technical objective, one embodiment of the present invention provides a method for the direct recycling of a positive electrode active material, comprising the steps of: preparing a positive electrode containing a waste positive electrode active material recovered from a waste lithium secondary battery; electrochemically plating nickel onto the surface of the positive electrode through a cyclic voltammetry method; recovering a nickel-plated positive electrode active material from the nickel-plated positive electrode; and heat-treating the nickel-plated positive electrode active material to obtain a regenerated positive electrode active material.

[0013] The above positive electrode active material may be characterized by comprising one or more selected from the group consisting of lithium nickel oxide (LNO)-based, nickel-cobalt-manganese (NCM)-based, nickel-cobalt-aluminum (NCA)-based, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active materials.

[0014] In the step of electrochemically plating nickel on the surface of the anode, the cyclic voltammetry may be characterized by being performed with a lower potential set to 2.0 V to 3.0 V so that metallic nickel is plated on the surface of the anode.

[0015] In the step of electrochemically plating nickel on the surface of the anode, the cyclic voltammetry may be characterized by being performed with a lower potential set to 2.4 V to 2.6 V so that metallic nickel is plated on the surface of the anode.

[0016] In the step of electrochemically plating nickel on the surface of the anode, the cyclic voltammetry may be characterized by being set and performed 3 to 7 times.

[0017] The method may further include a step of mixing the nickel-plated positive electrode active material and a lithium source between the step of recovering the nickel-plated positive electrode active material and the step of obtaining the regenerated positive electrode active material.

[0018] In the step of mixing the nickel-plated positive electrode active material and the lithium source, the molar ratio of lithium in the lithium source to the transition metal in the positive electrode active material may be greater than 1.0 and less than 1.3.

[0019] In the step of obtaining the regenerated positive electrode active material, the heat treatment may be characterized as being performed in a range of 800 ℃ to 950 ℃.

[0020] In the step of obtaining the regenerated positive electrode active material, the regenerated positive electrode active material having a layered crystal structure can be obtained by heat-treating the nickel-plated positive electrode active material.

[0021] To achieve the above technical objective, another embodiment of the present invention provides a positive electrode active material regenerated by the direct recycling method of the positive electrode active material described above.

[0022] To achieve the above technical objective, another embodiment of the present invention provides a positive electrode for a lithium secondary battery comprising the positive electrode active material described above.

[0023] The present invention can preserve the chemical composition and crystal structural characteristics of existing cathode active materials by directly recycling degraded waste cathode active materials.

[0024] In addition, the present invention can mitigate structural degradation associated with the uneven distribution or defects of nickel within the anode active material that may occur during repeated charging and discharging processes by plating the waste anode containing the degraded waste anode active material with nickel.

[0025] In addition, the present invention can improve the uniformity of nickel plating by setting the lower limit potential of the gentle voltammetry to a potential below which nickel reduction is initiated in the step of electrochemically plating metallic nickel on the surface of a waste anode.

[0026] In addition, the direct recycling method of the positive electrode active material of the present invention can suppress the formation of a rock-salt phase or a spinel phase of the positive electrode active material and can stably restore a layered structure.

[0027] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims.

[0028] FIG. 1 is a schematic diagram showing a two-electrode system as one embodiment of the step of electrochemically plating nickel in the direct recycling method of the positive electrode active material of the present invention.

[0029] Figure 2 is a graph showing the results of the analysis of the structural characteristics of the positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0030] Figure 3 is an SEM image of the positive electrode active material after nickel plating and heat treatment according to the direct recycling method of the positive electrode active material of the present invention.

[0031] Figures 4a to 4d are graphs showing the nickel content distribution (FIB-TEM line mapping) of the positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0032] Figure 4e is a graph showing the results of Raman spectrum analysis of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0033] Figure 4f is a graph showing the XRD pattern analysis results of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0034] Figure 4g is a graph showing the results of the analysis of the lattice constant and c / a ratio of the positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0035] Figure 5a is a graph showing the cycle life characteristics of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0036] FIG. 5b is a graph showing the capacity characteristics according to the change in current density of the positive active material regenerated by the direct recycling method of the positive active material of the present invention.

[0037] FIG. 5c is a graph showing the first cycle cyclic voltammetry (CV) curve of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0038] FIG. 5d is a graph showing the results of the electrochemical impedance (EIS) analysis of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0039] The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is therefore not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0040] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0041] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0042] Embodiments of the present invention will be described in detail below with reference to the attached drawings.

[0043]

[0044] Referring to FIG. 1, a method for direct recycling of a positive electrode active material according to one embodiment of the present invention will be described.

[0045] FIG. 1 is a schematic diagram showing a two-electrode system as one embodiment of the step of electrochemically plating nickel in the direct recycling method of the positive electrode active material of the present invention.

[0046] Referring to FIG. 1, a direct recycling method for a positive electrode active material according to one embodiment of the present invention may include the steps of: preparing a positive electrode containing a waste positive electrode active material recovered from a waste lithium secondary battery (S100); electrochemically plating nickel onto the surface of the positive electrode through a cyclic voltammetry method (S200); recovering a nickel-plated positive electrode active material from the nickel-plated positive electrode (S300); and heat-treating the nickel-plated positive electrode active material to obtain a regenerated positive electrode active material (S400).

[0047] The above-mentioned positive electrode active material may include one or more selected from the group consisting of lithium nickel oxide (LNO)-based, nickel-cobalt-manganese (NCM)-based, nickel-cobalt-aluminum (NCA)-based, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active materials, but the material of the above-mentioned positive electrode active material is not limited to the above examples.

[0048] For example, the positive electrode active material according to the present invention may be an NCM-based positive electrode active material.

[0049] First, a cathode containing waste cathode active material recovered from a waste lithium secondary battery can be prepared (S100).

[0050] In the step (S110) of recovering waste cathode active material from the waste cathode of the above-mentioned waste lithium secondary battery, the waste lithium secondary battery may be a lithium secondary battery that has been disposed of after use, a defective lithium secondary battery generated during the lithium secondary battery manufacturing process, etc.

[0051] Secondly, nickel can be electrochemically plated on the surface of the anode through cyclic voltammetry (S200).

[0052] In the process of recycling cathode active materials for lithium-ion batteries, a key challenge is to identify the cause of degradation that occurs during use and to eliminate or compensate for it.

[0053] Conventional technology recognized lithium deficiency as the primary cause of degradation in cathode active materials and focused on methods involving heat treatment after replenishing the lithium source; however, this approach had the problem that it was difficult to sufficiently recover from structural degradation occurring during repeated charging and discharging processes.

[0054] Accordingly, the inventors recognized that the degradation of the positive electrode active material is not caused solely by lithium defects, but that nickel defects occurring during repeated charging and discharging processes are also one of the important degradation factors.

[0055] Accordingly, based on this understanding, the present invention can compensate for nickel defects in the degraded positive electrode active material by including a step of electrochemically plating nickel in a process of directly recycling the positive electrode active material, and thereby more stably restore the layered structure of the regenerated positive electrode active material.

[0056] In one embodiment of the present invention, the step (S200) of electrochemically plating nickel on the surface of the anode may be configured with a two-electrode system including a working electrode and a counter electrode to plate via cyclic voltammetry, but the electrode system is not limited to the above example.

[0057] The above working electrode may be an anode containing the above waste anode active material, and the above counter electrode may include platinum (Pt), but the material of the above counter electrode is not limited to the above examples.

[0058] The step (S200) of electrochemically plating nickel on the surface of the anode can be performed through cyclic voltammetry.

[0059] The upper limit potential of the above cyclic voltammetry can be set to 0.0 V to 2.0 V, but the upper limit potential is not limited to the above range.

[0060] For example, the upper potential limit of the cyclic voltammetry according to the present invention may be 1.0 V.

[0061] The lower limit potential of the above-mentioned cyclic voltammetry can be set to a potential lower than or equal to the potential at which the reduction of nickel ions begins, preferably set to 2.0 V to 3.0 V, and more preferably set to 2.4 V to 2.6 V, but the lower limit potential is not limited to the above range.

[0062] When the lower limit potential of the above-mentioned cyclic voltammetry is set to 2.4 V to 2.6 V, the reduction reaction of nickel is sufficiently induced while preventing excessive nickel plating, thereby allowing nickel to be uniformly plated on the surface of the anode.

[0063] The number of cycles of the above-mentioned cyclic voltammetry may be set to 3 to 7 times, but the number of cycles is not limited to the above range.

[0064] For example, the number of cycles according to the present invention may be 5 times.

[0065] In the step (S200) of electrochemically plating nickel on the surface of the anode, nickel is uniformly plated on the surface of the anode at a potential below which nickel reduction begins, thereby compensating for nickel defects caused by degradation and stably restoring the layered crystal structure of the regenerated anode active material.

[0066] Third, a nickel-plated anode active material can be recovered from the nickel-plated anode (S300).

[0067] The step (S300) of recovering the nickel-plated anode active material from the nickel-plated anode may further include heat treatment.

[0068] The heat treatment for recovering the nickel-plated anode active material may be performed for 1 to 5 hours at a temperature range of 500 ℃ to 700 ℃, but the conditions of the heat treatment are not limited to the above examples.

[0069] For example, the heat treatment for recovering the nickel-plated anode active material according to the present invention can be performed at a temperature of 600°C for 2 hours.

[0070] The step (S300) of recovering the nickel-plated anode active material can recover the nickel-plated anode active material by removing the conductive material and binder remaining on the nickel-plated anode through the heat treatment.

[0071] Between the step of recovering the nickel-plated positive active material (S300) and the step of obtaining the regenerated positive active material (S400), the method may further include the step of mixing the nickel-plated positive active material and the lithium source (S350).

[0072] The above lithium source may include sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides, or oxyhydroxides containing lithium, and preferably, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7, or mixtures thereof may be used, but the types of the above lithium source are not limited to the above examples.

[0073] For example, the lithium source according to the present invention may be LiOH·H2O.

[0074] In the step (S350) of mixing the nickel-plated positive electrode active material and the lithium source, the lithium source may be added in excess of the theoretical amount, and the molar ratio of lithium in the lithium source to the transition metal in the positive electrode active material may be greater than 1.0 and less than 1.3, but the molar ratio of lithium to the transition metal is not limited to the above example.

[0075] For example, the molar ratio of the lithium to the transition metal may be 1.1.

[0076] When the molar ratio of the lithium to the transition metal is greater than 1.0 and less than 1.3, sufficient lithium is provided to compensate for the lithium loss occurring in the step (S400) of obtaining a regenerated positive active material by heat-treating the nickel-plated positive active material described later, thereby suppressing the lithium deficiency in the positive active material and stably restoring the layered structure of the regenerated positive active material together with the nickel deficiency compensated by the step (S200) of electrochemically plating nickel on the surface of the positive.

[0077] Finally, the nickel-plated positive active material can be heat-treated to obtain a regenerated positive active material (S400).

[0078] In the step (S400) of obtaining a regenerated positive active material by heat-treating the nickel-plated positive active material, the heat treatment may be performed for 3 to 12 hours at a temperature range of 800 ℃ to 950 ℃, but the heat treatment conditions for obtaining the regenerated positive active material are not limited to the above examples.

[0079] For example, the heat treatment to obtain the regenerated positive electrode active material according to the present invention can be performed at 850°C for 6 hours.

[0080] In the step (S400) of obtaining a regenerated positive active material by heat treating the nickel-plated positive active material, the nickel introduced on the surface of the positive active material diffuses into the interior of the particle, thereby compensating for nickel defects that occurred during repeated charging and discharging processes, and the nickel acts as a catalyst that promotes the reformation of transition metal-oxygen bonds during the heat treatment process, so that the layered structure that collapsed due to degradation can be stably reformed.

[0081]

[0082] A positive electrode for a lithium secondary battery according to another embodiment of the present invention will be described.

[0083] A positive electrode for a lithium secondary battery according to one embodiment of the present invention may include the positive electrode active material described above.

[0084] In one embodiment, the positive electrode for a lithium secondary battery of the present invention may be manufactured by including the step (S10) of mixing the positive electrode active material described above with a conductive material and a binder to form a slurry; and the step (S20) of applying and drying the slurry on a current collector to form a positive electrode.

[0085] A detailed description of the components of the above-described cathode for the lithium secondary battery that overlap with the cathode active material described above will be omitted. However, even if a description of such components is omitted, it is not intended that such components are not included in any embodiment.

[0086] In the step (S10) of mixing the above positive active material with a conductive material and a binder to form a slurry, the conductive material may include graphite, carbon black, carbon nanotubes, graphene, etc., but the type of conductive material is not limited to the above examples.

[0087] For example, the conductive material according to the present invention may be carbon black (Super P).

[0088] In the step (S10) of mixing the above positive active material with a conductive material and a binder to form a slurry, the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), polyacrylic acid (PAA), polyimide (PI), etc., but the type of binder is not limited to the above examples.

[0089] For example, the binder according to the present invention may be polyvinylidene fluoride (PVDF).

[0090] The step (S10) of mixing the above positive active material with a conductive material and a binder to form a slurry may further include mixing a solvent.

[0091] The above solvent may include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), acetone, tetrahydrofuran (THF), ethyl acetate, isopropanol, ethanol, water, etc., but the types of the above solvent are not limited to the above examples.

[0092] For example, the solvent according to the present invention may be N-methyl-2-pyrrolidone (NMP).

[0093] In the step (S130) of forming an anode by applying and drying the slurry on a current collector, the current collector may include aluminum (Al), copper (Cu), nickel (Ni), titanium (Ti), etc., but the type of current collector is not limited to the above examples.

[0094] For example, the current collector according to the present invention may be aluminum (Al).

[0095] The anode of the present invention can have improved electrochemical performance compared to an anode active material regenerated by a conventional anode active material regeneration method by manufacturing using the anode active material described above.

[0096]

[0097] The present invention will be explained in more detail below through examples and experimental examples. However, the present invention is not limited to the following manufacturing examples and experimental examples.

[0098] In the following description, degraded waste cathode active material that has not undergone a recycling process will be referred to as “SNCM”.

[0099] In addition, the regenerated cathode active material, which undergoes a recycling process but is subjected to heat treatment after lithium replenishment, will be described as “RNCM.”

[0100] In addition, the positive active material regenerated by the direct recycling method of the positive active material of the present invention is named “NPxNCM,” wherein x is distinguished and explained by simply stating the lower limit potential in the cyclic voltammetry as a number. As an example, the regenerated positive active material, which is the positive active material regenerated by the direct recycling method of the positive active material of the present invention and has nickel plating performed with a lower limit potential of 2.4 V, may be named “NP24NCM.”

[0101]

[0102] <Example> Preparation of a cathode active material (NPxNCM) regenerated by the direct recycling method of the cathode active material of the present invention

[0103] A powdered NCM-based spent cathode active material recovered from spent lithium secondary batteries was prepared. The spent cathode active material powder was mixed with carbon black (Super P) and polyvinylidene fluoride (PVDF) to prepare a slurry. At this time, the slurry was uniformly mixed using N-methyl-2-pyrrolidone (NMP) as a solvent, then coated onto a current collector and dried to form a cathode.

[0104] In order to uniformly proceed with nickel plating on both sides of the anode, a two-electrode system including Pt electrodes on both sides of the anode was configured, and nickel plating was performed using cyclic voltammetry (CV) in an electrolyte solution containing nickel ions. At this time, the nickel plating was performed with an upper potential limit of 1 V, a lower potential limit of 2.4 V to 2.7 V, and a voltage scan rate of 0.1 mV / s, for a total of 5 cycles.

[0105] At this time, the above electrolyte solution was prepared by dissolving 300 g / L NiSO4·6H2O, 45 g / L NiCl2·6H2O, and 45 g / L H3BO3 in deionized water and stirring at a temperature of 35 ℃ to ensure sufficient mixing.

[0106] After nickel plating was completed on the surface of the anode, the nickel-plated anode was heated in an air atmosphere at a heating rate of 10 ℃ / min and calcined at 600 ℃ for 2 hours to remove carbon black and PVDF, and the nickel-plated anode active material was recovered in powder form.

[0107] LiOH·H2O was added to the nickel-plated positive active material at a molar ratio of approximately 10% excess relative to the transition metal in the positive active material, and then heat-treated at 850°C for 6 hours. The positive active material powder obtained from the heat treatment was washed twice with deionized water to remove residual lithium compounds, and then dried in a vacuum oven at 100°C for 24 hours to obtain a regenerated positive active material.

[0108]

[0109] <Comparative Example 1> SNCM Preparation

[0110] Powdered NCM-based spent cathode active material recovered from spent lithium-ion batteries was prepared.

[0111]

[0112] <Comparative Example 2> RNCM Manufacturing

[0113] LiOH·H2O was added to powdered NCM-based spent cathode active material recovered from spent lithium secondary batteries at a molar ratio of approximately 10% excess relative to the transition metal in the cathode active material, and then heat-treated at 850°C for 6 hours. The cathode active material powder obtained from the heat treatment was washed twice with deionized water to remove residual lithium compounds, and then dried in a vacuum oven at 100°C for 24 hours to obtain a regenerated cathode active material.

[0114]

[0115] <Experimental Example 1> Analysis of the structural characteristics of the cathode active material regenerated by the direct recycling method of the cathode active material of the present invention

[0116] FIG. 2 is a graph showing the results of the analysis of structural characteristics of a cathode active material regenerated by the direct recycling method of the cathode active material of the present invention. FIG. 2a is the HRTEM image and FFT pattern of SNCM, FIG. 2b is the HRTEM image and FFT pattern of RNCM, FIG. 2c is the HRTEM image and FFT pattern of NP25NCM, and FIG. 2d is a graph showing the results of comparing XRD patterns of SNCM, RNCM, and NP25NCM.

[0117] Referring to Fig. 2a, it was confirmed that in the case of SNCM, a rock-salt phase was predominantly formed on the surface, and in the FFT pattern, the diffraction signal corresponding to the (003) plane was hardly observed, while the signal corresponding to the (200) plane was observed.

[0118] Additionally, referring to Fig. 2b, in the case of RNCM, a structure in which a layered structure and a rock-salt phase coexist was observed, and in the FFT pattern, diffraction signals corresponding to the (003) plane and (101) plane appeared partially, but it was confirmed that diffraction signals corresponding to the (200) plane attributable to the rock-salt phase were also observed.

[0119] In addition, referring to FIG. 2c, in the case of the NP25NCM of the present invention, a layered structure was predominantly formed, and a diffraction signal corresponding to the (003) plane was clearly observed in the FFT pattern, and it was confirmed that the interlayer spacing was about 0.48 nm.

[0120] In addition, referring to FIG. 2d, it was confirmed that the diffraction peaks attributable to the layered structure (003), (10), (104) of the SNCM were significantly weakened, some of the diffraction peaks were recovered in the RNCM, and the diffraction peaks were clearly observed in the NP25NCM of the present invention.

[0121] Through this, it was confirmed that the cathode active material regenerated by the direct recycling method of the cathode active material of the present invention can mitigate structural deterioration caused by the uneven distribution or defect of nickel and stably restore the layered structure by replenishing lithium and heat treatment as well as plating nickel.

[0122]

[0123] <Experimental Example 2> Analysis of Nickel Plating Behavior and Microstructure Characteristics of Anode Active Material Regenerated by the Direct Recycling Method of the Anode Active Material of the Present Invention

[0124] FIG. 3 is an SEM image of a positive electrode active material after nickel plating and heat treatment according to the direct recycling method of the positive electrode active material of the present invention. FIG. 3a to 3d are SEM images of NP24NCM, NP25NCM, NP26NCM, and NP27NCM after nickel plating, respectively, and FIG. 3e to 3h are SEM images of NP24NCM, NP25NCM, NP26NCM, and NP27NCM after heat treatment, respectively.

[0125] Referring to Figures 3a to 3d, it was confirmed that the positive active material maintained its original secondary particle shape immediately after the electrochemical nickel plating process, and at NP24NCM, nickel was partially plated on the surface of particles approximately 200 nm in size. As the size of the nickel crystal grains plated on the surface of the positive active material increased towards NP25NCM and NP26NCM, and at NP27NCM, it was confirmed that the surface of the positive active material was completely covered with a nickel layer.

[0126] In addition, referring to Figures 3e to 3h, morphological changes were observed in which the secondary particles of the cathode active material were separated and converted into primary particles after undergoing the heat treatment process. It was confirmed that this was the result of lattice deformation induced by grain boundary regions due to oxygen release during the electrochemical nickel plating process. On the other hand, in the case of NP27NCM, it was confirmed that the secondary particle structure was maintained as oxygen release was suppressed during heat treatment by the thick nickel layer formed on the surface of the cathode active material acting as a physical barrier.

[0127] Through this, it was confirmed that as the lower limit potential of the cyclic voltammetry in the nickel plating step of the present invention gradually decreases, the nickel plating reaction proceeds relatively predominantly, thereby increasing the thickness of the nickel layer plated on the surface of the anode active material, and it was confirmed that the pattern of morphological change after heat treatment varies depending on the lower limit potential.

[0128]

[0129] <Experimental Example 3> Analysis of Nickel Distribution and Structural Characteristics of Positive Active Material Regenerated by the Direct Recycling Method of the Positive Active Material of the Present Invention

[0130] FIGS. 4a to 4d are graphs showing the nickel content distribution (FIB-TEM line mapping) of the cathode active material regenerated by the direct recycling method of the cathode active material of the present invention. (a) to (d) show cases where the lower limit potential in the cyclic voltammetry was set to 2.4, 2.5, 2.6, and 2.7 V, respectively.

[0131] Figure 4e is a graph showing the results of Raman spectrum analysis of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0132] Figure 4f is a graph showing the XRD pattern analysis results of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0133] FIG. 4g is a graph showing the results of the analysis of the lattice constants and c / a ratio of the cathode active material regenerated by the direct recycling method of the cathode active material of the present invention. (g-1) and (g-2) represent the a-axis and c-axis lattice constants of the layered structure of the cathode active material derived through Rietveld refinement, and (g-3) represents the ratio.

[0134] Referring to Figures 4a to 4d, it was observed that as the lower potential limit decreases, the nickel distribution diffuses further into the interior of the particle, and it was confirmed that a nickel distribution throughout the entire particle was observed in NP27NCM. Through this, it was confirmed that the pattern of nickel penetration into the interior of the particle can vary depending on the lower potential limit condition of the cyclic voltammetry in the nickel plating step of the present invention, and that nickel can penetrate relatively uniformly when the lower potential limit is set in the range of -2.4 V to -2.7 V.

[0135] In addition, referring to FIGS. 4e to 4g, it was confirmed that in the NP25NCM of the present invention, the A1g peak shifted to a relatively high wavenumber region, whereas in the SNCM and RNCM, it was located in a low wavenumber region. It was also confirmed that the intensity ratio of the (003) diffraction peak and the (104) diffraction peak in the XRD pattern was highest in the NP25NCM of the present invention, and that the Rwp value, which indicates the accuracy of Rietveld refining, was lowest in the NP25NCM of the present invention. Through this, it was confirmed that the bond between the transition metal and oxygen is restored by the nickel plating and heat treatment steps of the present invention, thereby forming a more aligned layered structure.

[0136]

[0137] <Experimental Example 4> Evaluation of the electrochemical performance of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention

[0138] Figure 5a is a graph showing the cycle life characteristics of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0139] FIG. 5b is a graph showing the capacity characteristics according to the change in current density of the positive active material regenerated by the direct recycling method of the positive active material of the present invention.

[0140] FIG. 5c is a graph showing the first cycle cyclic voltammetry (CV) curve of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0141] FIG. 5d is a graph showing the results of the electrochemical impedance (EIS) analysis of a positive electrode active material regenerated by the direct recycling method of the positive electrode active material of the present invention.

[0142] Referring to FIG. 5, the cathode active material regenerated according to the direct recycling method of the cathode active material of the present invention maintained relatively stable discharge capacity during the cycle and discharge characteristics under high-rate conditions compared to RNCM, and in the cyclic voltammetry curve, a tendency for side reactions in the high-voltage region to be suppressed was observed, and electrochemical impedance analysis confirmed that the charge transfer resistance and lithium ion diffusion behavior differed depending on the nickel plating conditions.

[0143] Through this, it was confirmed that the direct recycling method of the cathode active material of the present invention, by including a step of nickel plating, can improve the recovery of the layered crystal structure of the regenerated cathode active material, and accordingly, cycle stability and electrochemical performance can also be improved.

[0144]

[0145] Thus, it was confirmed that the direct recycling method of the cathode active material of the present invention can stably restore the layered structure by mitigating structural degradation related to the uneven distribution or defects of nickel within the waste cathode active material through nickel plating of the waste cathode containing the degraded waste cathode active material.

[0146]

[0147] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0148] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention.

Claims

1. A step of preparing a cathode containing waste cathode active material recovered from a spent lithium secondary battery; A step of electrochemically plating nickel onto the surface of the anode using cyclic voltammetry; A step of recovering a nickel-plated anode active material from the nickel-plated anode; and A method for direct recycling of a positive electrode active material, characterized by including the step of heat-treating the nickel-plated positive electrode active material to obtain a regenerated positive electrode active material.

2. In Paragraph 1, A method for direct recycling of a positive electrode active material, characterized in that the positive electrode active material comprises one or more selected from the group consisting of lithium nickel oxide (LNO)-based, nickel-cobalt-manganese (NCM)-based, nickel-cobalt-aluminum (NCA)-based, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active materials.

3. In Paragraph 1, In the step of electrochemically plating nickel onto the surface of the anode, A direct recycling method for an anode active material, characterized in that the above-described cyclic voltammetry is performed with a lower potential set to 2.0 V to 3.0 V so that metallic nickel is plated on the surface of the anode.

4. In Paragraph 1, In the step of electrochemically plating nickel onto the surface of the anode, A direct recycling method for an anode active material, characterized in that the above-described cyclic voltammetry is performed with a lower potential set to 2.4 V to 2.6 V so that metallic nickel is plated on the surface of the anode.

5. In Paragraph 1, In the step of electrochemically plating nickel onto the surface of the anode, A direct recycling method for a positive electrode active material, characterized in that the above-described cyclic voltammetry is set and performed 3 to 7 times.

6. In Paragraph 1, A step of recovering the nickel-plated anode active material; and Step of obtaining the above-mentioned regenerated positive active material; between A direct recycling method for a positive electrode active material, characterized by further including the step of mixing the nickel-plated positive electrode active material and a lithium source.

7. In Paragraph 6, In the step of mixing the nickel-plated positive electrode active material and the lithium source, A direct recycling method for a positive electrode active material, characterized in that the molar ratio of lithium in the lithium source to the transition metal in the positive electrode active material is greater than 1.0 and less than 1.

3.

8. In Paragraph 1, In the step of obtaining the above-mentioned regenerated positive electrode active material, A direct recycling method for a positive electrode active material, characterized in that the above heat treatment is performed in the range of 800 ℃ to 950 ℃.

9. In Paragraph 1, In the step of obtaining the above-mentioned regenerated positive electrode active material, A direct recycling method for a positive electrode active material characterized by obtaining a regenerated positive electrode active material having a layered crystal structure by heat treating the nickel-plated positive electrode active material.

10. Anode active material regenerated by the direct recycling method of the anode active material of paragraph 1.

11. A cathode for a lithium secondary battery comprising the cathode active material of claim 10.

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