Positive electrode active material and method for regenerating the same

Abstract

The present invention relates to a positive electrode active material and a method for regenerating the same, and more specifically, to 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, comprising single particles, with an F content of 5,700 to 6,500 mg / kg, and / or a lattice constant of the a-axis of 2.8753 to 2.8772 Å, a lattice constant of the c-axis of 14.243 to 14.255 Å, and a cell volume of 101.968 to 102.168 Å, as measured by XRD analysis. 3 The present invention relates to a positive electrode active material characterized by having a crystal grain size greater than 130 nm and less than or equal to 136 nm, and a method for regenerating the same.

Description

[Technical Field]

[0001] [Cross-reference with related applications] This application is an application claiming priority based on Korean Patent Application No. 10-2024-0029795 dated February 29, 2024, and Korean Patent Application No. 10-2025-0004743, refiled thereunder on January 13, 2025, and all contents disclosed in said Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material and a method for regenerating the same. More specifically, the present invention involves adding a lithium precursor immediately to a positive electrode active material containing single particles recovered after heat treatment of a waste positive electrode, without a pre-washing step, followed by annealing and then surface coating. However, the positive electrode active material is milled before and / or after annealing to ensure that the surface of the positive electrode active material contains fluorine (F) in a predetermined amount, and that the crystal structure and grain size of the positive electrode active material, as analyzed by XRD, are within a predetermined range. This makes it possible to obtain a positive electrode active material with excellent charging capacity, resistance characteristics, and capacitance characteristics. Furthermore, since no acid is used in the recovery and regeneration process, it is environmentally friendly, and since neutralization and wastewater treatment are not required, process costs are reduced. Because the positive electrode active material is regenerated without decomposition, no metal elements are discarded, and because no organic solvents are used, there is no risk of generating toxic gases or explosions. The pre-washing step is omitted, resulting in a method for regenerating positive electrode active material that greatly improves economy and productivity. [Background technology]

[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 from waste cathodes mostly involve dissolving the waste cathode in hydrochloric acid, sulfuric acid, or nitric acid, then extracting cobalt, manganese, nickel, etc., with an organic solvent, and using these as raw materials again 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 drawbacks such as the particle size distribution of the positive electrode active material changing during the crushing process, the binder remaining, and the battery characteristics of the recycled positive electrode active material degrading.

[0015] Therefore, there is an urgent need to develop a method that can regenerate single-particle positive electrode active material from waste positive electrodes containing single-particle positive electrode active material without discarded metal elements, with excellent output performance, fewer processes and costs, and being environmentally friendly and safe.

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 the waste positive electrode without a pre-washing step, anneals it, and then performs surface coating. However, by milling the positive electrode active material before and / or after annealing, fluorine (F) is included in a predetermined content on the surface of the positive electrode active material, and the crystal structure and crystal grain size of the positive electrode active material analyzed by XRD are adjusted to be within a predetermined range. Therefore, the present invention relates to providing a positive electrode active material excellent in charge capacity, resistance characteristics, and capacity characteristics. In addition, since the present invention does not use an acid in the recovery and regeneration process, it is environmentally friendly, does not require neutralization and wastewater treatment, thus reducing the process cost, regenerating the positive electrode active material as it is without decomposition, having no discarded metal elements, not using an organic solvent, having no risk of generating toxic gases or explosion, and omitting the pre-washing step, greatly improving the economy and productivity. The present invention relates to a method for regenerating a positive electrode active material containing single particles.

[0017] In addition, an object of the present invention is to provide a secondary battery excellent in initial discharge capacity and capacity characteristics by using the method for regenerating the positive electrode active material.

[0018] The above-mentioned and other objectives of the present invention can all be achieved by the present invention as described below. [Means for solving the problem]

[0019] To achieve the above objectives, I) The present invention comprises one or more cathode active materials selected from the group consisting of lithium nickel oxide (LNO)-based cathode active materials, nickel-cobalt-manganese (NCM)-based cathode active materials, nickel-cobalt-aluminum (NCA)-based cathode active materials, and nickel-cobalt-manganese-aluminum (NCMA)-based cathode active materials, and includes single particles, has a fluorine (F) content of 5,700 to 6,500 mg / kg, and / or has a lattice constant of 2.8753 to 2.8772 Å on the a-axis, a lattice constant of 14.243 to 14.255 Å on the c-axis, and a cell volume of 101.968 to 102.168 Å, as measured by X-ray diffraction analysis (XRD). 3 The present invention provides a positive electrode active material characterized by having a crystal grain size greater than 130 nm and less than or equal to 136 nm.

[0020] II) In I) above, the positive electrode active material may contain nickel (Ni) in an amount of 40 mol% or more, based on a total of 100 mol% of the remaining metals excluding lithium (Li).

[0021] III) In I) or II) above, the positive electrode active material may have a surface coated with a coating agent containing metal or carbon.

[0022] IV) In I) to III) above, the positive electrode active material may be a regenerated positive electrode active material.

[0023] Furthermore, V) The present invention provides a method for regenerating positive electrode active material, comprising the steps of: (a) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material including 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; (c) washing the annealed positive electrode active material with a cleaning solution; and (d) surface coating the washed positive electrode active material, wherein step (b) includes a step of milling the recovered positive electrode active material before annealing; and / or step (c) includes a step of milling the annealed positive electrode active material before washing; The present invention provides a method for regenerating positive electrode active material, comprising the steps of (a) heat-treating a waste positive electrode having a mid-nickel positive electrode active material layer formed on a current collector at 300 to 650°C to recover positive electrode active material including single particles in the positive electrode active material layer by thermal decomposition of the binder and conductive 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; (c) washing the annealed positive electrode active material with a cleaning solution; and (d) surface coating the washed positive electrode active material, wherein step (b) includes a step of milling the recovered positive electrode active material before annealing; and / or step (c) includes a step of milling the annealed positive electrode active material before washing.

[0024] 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.

[0025] In this description, the step of milling before annealing means milling the cathode active material recovered after heat treatment of the waste cathode before adding the lithium precursor.

[0026] VI) In I) to V) above, the positive electrode active material is one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and may contain Ni in an amount of 40 mol% or more, based on 100 mol% of the total of the remaining metals excluding Li.

[0027] VII) In V) to VI) above, the milling can be carried out using a centrifugal mill, a jet mill, or a pin mill.

[0028] VIII) In V) to VII) above, the milling can be performed at 6,000 to 18,000 rpm.

[0029] IX) In the above V) to VIII), the lithium precursor may contain one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0030] X) In steps V) to IX) 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.

[0031] XI) In steps V) to X) above, in step (c), the cleaning may be performed with a weight ratio of 1:0.5 to 1:5.5 between the annealed or milled positive electrode active material and the cleaning solution.

[0032] XII) In V) to XI) above, the cleaning in step (c) may include the steps of mixing the annealed or milled positive electrode active material with a cleaning solution, filtering the mixture, and drying the solid positive electrode active material obtained after filtering.

[0033] XIII) In steps V) to XII) above, the surface coating in step (d) can be performed by coating the surface with one or more of the following in a solid-phase or liquid-phase manner: metal, organometallic, and carbon components, followed by heat treatment at 100 to 1200°C.

[0034] Furthermore, XIV) The present invention provides a secondary battery characterized by containing the positive electrode active material described in any one of the above items I) to IV). [Effects of the Invention]

[0035] 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 cleaning step, annealing it, and then performing a surface coating, and by milling the positive electrode active material before and / or after annealing, the surface of the positive electrode active material contains fluorine (F) in a predetermined amount, and the crystal structure and crystal grain size of the positive electrode active material analyzed by X-ray diffraction (XRD) are adjusted to be within a predetermined range, thereby providing a positive electrode active material with excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0036] 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 because it does not use acid in the recovery and regeneration process of the positive electrode active material; reduced process costs because neutralization and wastewater treatment are not required; no discarded metal elements because the positive electrode active material is regenerated without decomposition; no risk of toxic gas generation or explosion because organic solvents are not used; and significant improvements in economy and productivity due to the omission of the pre-cleaning process. [Brief explanation of the drawing]

[0037] 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 graph shows the volume retention rate of the regenerated or newly generated cathode active materials manufactured or prepared in Examples 1-3 and Comparative Examples 1-5. [Figure 3] This is a flowchart illustrating the regeneration process for a cathode active material containing single particles according to the present invention. [Modes for carrying out the invention]

[0038] The inventors of the present invention were researching a direct recycled method for directly regenerating cathode active material containing single particles from waste cathodes without decomposing it, resulting in cathode active material with superior output performance (rate performance, etc.). They discovered that by heat-treating waste cathodes to recover single-particle cathode active material, immediately adding a lithium precursor and annealing it without a water washing step, and by performing milling on the recovered cathode active material before and / or after annealing, the regenerated single-particle cathode active material contains fluorine in a predetermined amount, and by adjusting the crystal structure and grain size analyzed by XRD to be within a predetermined range, the charging capacity, resistance characteristics, and capacity characteristics of the manufactured lithium secondary battery are greatly improved. Based on this, they continued their research and completed the present invention.

[0039] The positive electrode active material and its regeneration method described herein will be explained in detail below.

[0040] The terms and words used herein 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 represent only one embodiment of the present invention and do not represent the entire technical idea of ​​the present invention; therefore, there may be various equivalents and modifications that can substitute for them, and they may be arranged, substituted, combined, separated, or designed in various other configurations.

[0041] 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.

[0042] 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, with a F content of 5,700 to 6,500 mg / kg, and / or a lattice constant of the a-axis of 2.8753 to 2.8772 Å, a lattice constant of the c-axis of 14.243 to 14.255 Å, and a cell volume of 101.968 to 102.168 Å, as measured by X-ray diffraction analysis (XRD). 3 The positive electrode active material of the present invention is characterized by having a crystal grain size greater than 130 nm and less than or equal to 136 nm. By satisfying these conditions, when applied to a lithium secondary battery, the positive electrode active material of the present invention has the effect of being excellent in terms of battery charging capacity, resistance characteristics, and capacity characteristics.

[0043] 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.

[0044] The positive electrode active material may, as a specific example, include 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.

[0045] (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。)

[0046] As an example, the positive electrode active material can contain 40 mol% or more, 40 to 95 mol%, more preferably 40 to 70 mol%, of Ni (in this case, the positive electrode active material can be called a mid-nickel (Mid Ni) positive electrode active material), based on a total of 100 mol% of the remaining metals excluding Li. Within this range, there is an effect of excellent initial discharge capacity, output performance, capacitance characteristics, and resistance characteristics.

[0047] In this description, the Ni content is not particularly limited when measured using methods commonly used in the art to which the present invention pertains, such as IC (Ion Chromatography). For example, it can be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AECS analyzer.

[0048] 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.

[0049] 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 positive electrode material has excellent lifespan characteristics in high-voltage environments, high thermal stability, and low gas generation during charging and discharging.

[0050] In this description, a nodule means a particle unit body that constitutes a single particle, which is a single crystal lacking a crystalline grain boundary, or when observed at a magnification of 5000 to 20000 times using a Scanning Electron Microscope (SEM) or an Electron Backscatter Diffraction (EBSD) analyzer, it can mean a polycrystal that appears to have no grain boundary on the surface.

[0051] In this description, the number of nodules means the average value of the number of nodules of the positive electrode active material particles. After cutting the positive electrode containing the positive electrode active material by the ion milling method and obtaining a cross-sectional image in the thickness direction of the cut positive electrode using a Scanning Electron Microscope (SEM), at least 30 or more particles are selected for each of the positive electrode active material particles with the largest particles and the smallest particles in the cross-sectional image. Then, through SEM image analysis, the number of nodules in the cross-section of each positive electrode active material particle is measured and obtained by arithmetic averaging.

[0052] The single particle has an average particle size (D 50 ) that may preferably be 2 to 10 μm, more preferably 2 to 8 μm, and even more preferably 3 to 6 μm.

[0053] In this description, the average particle size (D 50 ) can be defined as the particle size corresponding to 50% of the volume cumulative amount in a particle size distribution diagram (Particle Size Distribution, PSD). The average particle size (D 50 ) can be measured, for example, using the laser diffraction method. Specifically, the average particle size (D 50The 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 ).

[0054] The positive electrode active material may preferably contain fluorine (F) in an amount of 5,700 to 6,500 mg / kg, more preferably 5,800 to 6,300 mg / kg, and even more preferably 5,800 to 6,100 mg / kg. Within this range, the material exhibits excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0055] In this description, the fluorine (F) content is not particularly limited when measured using methods commonly used in the art to which the present invention pertains, such as IC (Ion Chromatography). Specific examples include measurement using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AEC analyzer.

[0056] The positive electrode active material may have an a-axis lattice constant measured by XRD analysis of, for example, 2.8753 to 2.8772 Å, preferably 2.8760 to 2.8770 Å, more preferably 2.8762 to 2.8768 Å, and even more preferably 2.8764 to 2.8768 Å. If it is within this range, the a-axis lattice constant is reduced compared to the raw material positive electrode active material, resulting in a different lattice structure. When applied to a lithium secondary battery, this has the effect of providing excellent charging capacity, resistance characteristics, and capacity characteristics of the battery.

[0057] The positive electrode active material may have a c-axis lattice constant measured by XRD analysis that is, for example, 14.243 to 14.255 Å, preferably 14.245 to 14.254 Å, more preferably 14.247 to 14.254 Å, and even more preferably 14.249 to 14.254 Å. Within this range, the lithium concentration in the lattice increases along the c-axis, which represents the z-axis direction of the layered structure, resulting in excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0058] For example, the aforementioned positive electrode active material has a cell volume of 101.968–102.168 Å as measured by XRD analysis. 3 Preferably 101.980~102.163 Å 3 , more preferably 102.000~102.158 Å 3 More preferably 102.100~102.153 Å 3 It is acceptable for the values ​​to be within this range, and doing so has the effect of providing excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0059] The positive electrode active material may, for example, have a crystallite size measured by XRD analysis that is greater than 130 nm and less than or equal to 136 nm, preferably 131 to 135 nm, and more preferably 131 to 134 nm. Within this range, the crystallite size is larger compared to secondary particles, resulting in improved ionic conductivity and thus superior capacitance characteristics.

[0060] In this description, the lattice parameter, cell volume, 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, the cell volume can be calculated by the product of the lattice parameter on the a-axis and the lattice parameter on the c-axis, and the crystallite size can be calculated using Scherrer's equation from the XRD measurement data.

[0061] In this description, a crystal line refers to a single-crystal particle unit having a regular arrangement of atoms.

[0062] The positive electrode active material may, for example, have its surface coated with metal or carbon, preferably with metal. In this case, the structural stability of the positive electrode active material is improved without any chemical or physical changes to the regenerated positive electrode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. Furthermore, the substitution of different elements 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.

[0063] The coating agent preferably comprises 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 comprises one or more selected from the group consisting of B, W, Al, Ti, and Mg; even more preferably comprises boron (B), tungsten (W), or a mixture thereof; and even more preferably comprises 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.

[0064] The boron-containing coating agent is preferably H3BO3, B2O3, C6H5B(OH)2, (C6H5O)3B, [CH3(CH2)3O]3B, C13H 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.

[0065] The coating agent may, for example, be present in an amount of 0.001 to 0.3 mol% relative to 1 mol% of metal in the positive electrode active material before coating, 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, the structural stability and electrochemical performance are improved while maintaining the properties of the single-particle positive electrode active material itself.

[0066] 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 properties of the positive electrode active material itself.

[0067] 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.

[0068] 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 having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material including 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; (c) washing the annealed positive electrode active material with a cleaning solution; and (d) surface coating the washed positive electrode active material, wherein step (b) includes a step of milling the recovered positive electrode active material before annealing; and / or step (c) includes a step of milling the annealed positive electrode active material before washing. In this case, by including fluorine (F) in a predetermined amount on the surface of the positive electrode active material, and by having the crystal structure and grain size of the positive electrode active material analyzed by XRD within a predetermined range, a regenerated single-particle positive electrode active material with excellent charging capacity, resistance characteristics, and capacity characteristics for the applied lithium secondary battery is provided. Furthermore, since no acid is used in the recovery and regeneration process, it is environmentally friendly, and since neutralization and wastewater treatment are not required, process costs are reduced. As 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, single-particle positive electrode active material can be easily and directly regenerated from waste positive electrodes without degrading battery performance, resulting in significant improvements in economy and productivity.

[0069] As another example, the method for regenerating positive electrode active material of the present invention includes the steps of: (a) heat-treating a waste positive electrode having a mid-nickel positive electrode active material layer formed on a current collector at 300 to 650°C to recover positive electrode active material including single particles in the positive electrode active material layer by thermal decomposition of the binder and conductive 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; (c) washing the annealed positive electrode active material with a cleaning solution; and (d) surface coating the washed positive electrode active material, wherein step (b) includes a step of milling the recovered positive electrode active material before annealing; and / or step (c) includes a step of milling the annealed positive electrode active material before washing. In this case, by including fluorine (F) in a predetermined amount on the surface of the positive electrode active material, and by having the crystal structure and grain size of the positive electrode active material analyzed by XRD within a predetermined range, a recycled single-particle mid-nickel positive electrode active material with excellent charging capacity, resistance characteristics, and capacity characteristics for the applied lithium secondary battery is provided. Furthermore, since no acid is used in the recovery and recycling process, it is environmentally friendly, and since neutralization and wastewater treatment are not required, process costs are reduced. As the positive electrode active material is recycled without decomposition, no metal elements are discarded, and since no organic solvents are used, there is no risk of generating toxic gases or explosions. In addition, single-particle positive electrode active material can be easily and directly recycled from waste positive electrodes without degrading battery performance, resulting in significant improvements in economy and productivity.

[0070] In this description, the step of milling before annealing means milling the cathode active material recovered after heat treatment of the waste cathode before adding the lithium precursor. However, it is not limited to this, and the milling step may be performed after adding the lithium precursor to the cathode active material recovered after heat treatment of the waste cathode.

[0071] The following is a detailed explanation of the regeneration method for the positive electrode active material, broken down into stages.

[0072] (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 a step of heat-treating the waste positive electrode, on which a positive electrode active material layer has been formed on a current collector, at 300 to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material, including single particles, from 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.

[0073] As another example, the present invention may include the step of (a) heat-treating a waste positive electrode, on which a single-particle mid-nickel positive electrode active material layer is formed on a current collector, at 300 to 650°C to thermally decompose the binder and conductive material in the positive electrode active material layer, thereby recovering the single-particle mid-nickel positive electrode active material in the positive electrode active material layer. When the 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.

[0074] 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.

[0075] The positive electrode active material layer in step (a) above may preferably include a positive electrode active material, a binder, and a conductive material.

[0076] 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.

[0077] As another specific example, the positive electrode active material may be a compound represented by the following chemical formula 1.

[0078] (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。)

[0079] As an example, the positive electrode active material can contain 40 mol% or more, 40 to 95 mol%, more preferably 40 to 70 mol%, of Ni (in this case, the positive electrode active material can be called a mid-nickel positive electrode active material), based on a total of 100 mol% of the remaining metals excluding Li. Within this range, the initial discharge capacity, output performance, capacity characteristics, and resistance characteristics of the lithium secondary battery to which it is applied are excellent.

[0080] 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.

[0081] 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.

[0082] 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 ).

[0083] The conductive material may, for example, be a carbon-based conductive material, and preferably, carbon black, CNTs, or a mixture thereof.

[0084] 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.

[0085] In step (a) above, the heat treatment temperature may be, 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.

[0086] The aforementioned heat treatment may have 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 implemented without putting undue strain on the heat treatment equipment and has the advantage of not causing thermal shock to the positive electrode scrap.

[0087] 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.

[0088] 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, there is an advantage that the stability of Ni in the regenerated positive electrode active material is increased because the binder and conductive material are removed without residue.

[0089] The purity percentage of the oxygen may be in volume percentage or mol%.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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 the heat treatment temperature is not included in the calculation.

[0094] The positive electrode active material recovered in step (a) above can preferably be immediately subjected to a milling or annealing process without prior cleaning. In this case, the omission of the prior cleaning process has the advantage of greatly improving economy and productivity.

[0095] In this description, pre-washing can refer to washing performed before adding the lithium precursor, and post-washing can refer to washing performed after adding the lithium precursor and annealing.

[0096] Referring to Figure 1 below, 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.

[0097] 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 are generated before the conditions for producing a positive electrode sheet 30 of the desired quality are found through predetermined tests.

[0098] For reference, in the embodiment described below, positive electrode scrap was used as the waste positive electrode.

[0099] (b) Adding a lithium precursor to the recovered positive electrode active material and performing annealing. The method for regenerating positive electrode active material of the present invention may include the step of (b) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C. In this case, the crystal structure of the regenerated positive electrode active material is restored, providing a positive electrode active material with excellent efficiency, lifespan characteristics, and resistance characteristics. Furthermore, the pre-washing step of the recovered positive electrode active material is omitted, which has the advantage of greatly improving economy and productivity.

[0100] The annealing step may preferably include a step of milling the recovered positive electrode active material before annealing, specifically a step of milling before adding the lithium precursor. In this case, the aggregated particles during the heat treatment are broken down, allowing the lithium precursor to be uniformly supplied to the single-particle positive electrode active material in the subsequent annealing step, and the heat treatment restores the crystal structure, resulting in excellent efficiency, lifetime characteristics, and resistance characteristics. Unlike the secondary-particle positive electrode active material, the single-particle positive electrode active material has fewer pores within the particles, and in addition, if the particles are aggregated, it is difficult for the lithium precursor to be uniformly supplied to the positive electrode active material and heat treated. Therefore, it is preferable to break down the aggregated particles through milling. On the other hand, the recovered secondary-particle positive electrode active material is in a different state from the single-particle positive electrode active material, so the milling effect according to the present invention does not apply, and it does not transform into single-particle positive electrode active material even after milling.

[0101] Furthermore, by immediately milling the recovered positive electrode active material without a prior cleaning process, lithium loss due to cleaning is eliminated, resulting in even better efficiency, lifespan characteristics, and resistance characteristics.

[0102] The milling process can be carried out using, for example, a centrifugal mill, a jet mill, or a pin mill. Preferably, the milling process can be carried out using a pin mill, which has the advantage that aggregated particles are uniformly broken down and the surface of the positive electrode active material is not damaged.

[0103] The milling may be performed, for example, at a speed of 6,000 to 18,000 rpm, preferably 8,000 to 16,000 rpm, more preferably 10,000 to 13,000 rpm, and even more preferably 11,000 to 13,000 rpm. Within this range, aggregation of single-particle positive electrode active material is eliminated, and uniform heat treatment in the subsequent annealing step substantially improves the recovery of the crystal structure of the regenerated positive electrode active material, resulting in excellent efficiency, lifetime characteristics, and resistance characteristics.

[0104] 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.

[0105] 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.

[0106] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0107] 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 0.0 The amount of lithium added can be such that the molar ratio of lithium is 0.01 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 of lithium is 0.009 to 0.013. Within this range, the deficient lithium in the regenerated positive electrode active material is replenished, and the battery characteristics of the regenerated positive electrode active material are improved by improving crystallinity, such as by increasing crystallinity or restoring the crystal structure.

[0108] As 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.

[0109] 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 400-750°C, more preferably at 500-720°C, and even more preferably at 600-720°C. Within this range, the crystal structure is restored, resulting in excellent battery efficiency, lifespan characteristics, and resistance characteristics.

[0110] 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.

[0111] The annealing time is, for example, 1 hour or more and 15 hours or less, preferably 1 to 15 hours, more preferably 2 to 10 hours, even more preferably 3 to 8 hours, and even more preferably 4 to 6 hours. Specifically, around 5 hours is preferred. Within this range, the crystal structure is sufficiently restored, resulting in larger crystal grain size compared to secondary particles and improved ionic conductivity, which in turn provides excellent capacity characteristics.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] (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 that lithium precursors that tend to remain on the surface of the positive electrode active material are removed by the cleaning solution, thereby preventing a decrease in battery performance and the generation of gas due to the subsequent reaction between the residual lithium precursors and the electrolyte.

[0116] The cleaning step may preferably include a step of milling the annealed positive electrode active material before cleaning, in which case aggregated particles are broken down and uniformly dispersed, and lithium precursors and / or fluorine are effectively removed with a small amount of cleaning solution, resulting in reduced wastewater and, when subsequently applied to a battery, improved charging capacity, resistance characteristics and capacitance characteristics.

[0117] The milling described above can be carried out using, for example, a centrifugal mill, a jet mill, or a pin mill. Preferably, milling can be performed using a pin mill, which has the advantage that aggregated particles are uniformly broken down and the surface of the positive electrode active material is not damaged.

[0118] The milling may be performed, for example, at a speed of 6,000 to 18,000 rpm, preferably 8,000 to 16,000 rpm, more preferably 10,000 to 13,000 rpm, and even more preferably 11,000 to 13,000 rpm. Within this range, aggregation of positive electrode active material particles is eliminated, a uniform dispersion is formed, and impurities are easily removed in the post-washing process, resulting in improved charging capacity, resistance characteristics, and capacitance characteristics.

[0119] The cleaning process may preferably include the steps of mixing the annealed or milled 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, excess lithium that tends to remain on the positive electrode active material is effectively removed. Furthermore, in this case, lithium precursors such as LiOH and Li2CO3, and / or fluorine that tend to remain on the surface of the positive electrode active material are effectively removed with a small amount of cleaning solution, resulting in a reduction in wastewater.

[0120] The annealed or milled positive electrode 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, and / or fluorine, which tend to remain on the surface of the positive electrode active material, are effectively removed with a small amount of cleaning solution, resulting in a reduction in wastewater.

[0121] The cleaning solution may preferably be water or an aqueous solution of a basic lithium compound, and more preferably water. 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.

[0122] 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.

[0123] 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, and / or fluorine, 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 and significantly improving the output performance of the battery.

[0124] The mixing of the annealed positive electrode active material and the cleaning solution is preferably carried out by stirring, and although the stirring is not particularly limited, mechanical stirring or ultrasonic stirring can be used.

[0125] The stirring may be carried out for preferably no more than 30 minutes, more preferably no more than 20 minutes, even more preferably no more than 15 minutes, and even more preferably 5 to 10 minutes, within this range, residual lithium is effectively removed.

[0126] (d) A step of surface coating the cleaned positive electrode active material to obtain a reusable positive electrode active material. The method for regenerating a positive electrode active material of the present invention includes the step of (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.

[0127] 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.

[0128] The aforementioned metal-containing coating agent is preferably a coating agent containing one or more selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V, and Y, more preferably a coating agent containing one or more selected from the group consisting of B, W, Al, Ti, and Mg, even more preferably a coating agent containing boron (B), tungsten (W), or a mixture thereof, and even more preferably a coating agent containing tungsten (W) and boron (B), and specifically a coating agent containing tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0129] 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 can be used as a boron-containing coating agent, in which case the resistance characteristics and life characteristics are improved.

[0130] 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.

[0131] 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.

[0132] 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.

[0133] 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, there is an effect of improving structural stability and electrochemical performance while maintaining the excellent properties of the positive electrode active material itself.

[0134] 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 decrease in performance due to thermal decomposition of the regenerated positive electrode active material, and the structural stability and electrochemical performance are improved.

[0135] The heat treatment time can preferably be 1 to 16 hours, more preferably 3 to 7 hours. Within this range, the structural stability and electrochemical performance are improved while maintaining the properties of the positive electrode active material itself.

[0136] 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.

[0137] 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.

[0138] 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 value may be as low as / g, and within this range, it adheres uniformly 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 deterioration of lifetime characteristics and electrochemical performance due to lattice deformation and collapse of the crystal structure of the positive electrode active material.

[0139] 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 ).

[0140] 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.

[0141] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method preferably contains fluorine (F) in an amount of 5,700 to 6,500 mg / kg, more preferably 5,800 to 6,300 mg / kg, and even more preferably 5,800 to 6,100 mg / kg. Within this range, the positive electrode active material exhibits excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0142] In this description, the fluorine (F) content can be measured using an IC analyzer, and while it can be measured using a general IC analyzer commonly used in laboratories, there is no deviation due to the measuring device or method.

[0143] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method may have an a-axis lattice constant measured by XRD analysis of, for example, 2.8753 to 2.8772 Å, preferably 2.8760 to 2.8770 Å, more preferably 2.8762 to 2.8768 Å, and even more preferably 2.8764 to 2.8768 Å. Within this range, the a-axis lattice constant is reduced compared to the raw material positive electrode active material, resulting in a different lattice structure and the effect of superior charging capacity, resistance characteristics, and capacitance characteristics.

[0144] 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, 14.243 to 14.255 Å, preferably 14.245 to 14.254 Å, more preferably 14.247 to 14.254 Å, and even more preferably 14.249 to 14.254 Å. Within this range, the lithium concentration in the lattice increases along the c-axis, which represents the z-axis direction of the layered structure, resulting in excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0145] The positive electrode active material regenerated by the aforementioned positive electrode active material regeneration method has, for example, a cell volume measured by XRD analysis of 101.968 to 102.168 Å. 3 Preferably 101.980~102.163 Å 3 , more preferably 102.000~102.158 Å 3 More preferably 102.100~102.153 Å 3 It is acceptable for the values ​​to be within this range, and doing so has the effect of providing excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0146] The positive electrode active material regenerated by the above-mentioned positive electrode active material regeneration method may, for example, have a crystallite size measured by XRD analysis that is greater than 130 nm to 136 nm, preferably 131 to 135 nm, and more preferably 131 to 134 nm. Within this range, the crystallite size is larger compared to secondary particles, resulting in improved ionic conductivity and thus superior capacitance characteristics.

[0147] 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, in which case it has the effect of being excellent in initial discharge capacity, output performance, capacitance characteristics and resistance characteristics.

[0148] Figure 3 below is a flowchart illustrating one embodiment of the present invention, showing the regeneration process for the positive electrode active material.

[0149] Referring to Figure 3, first, prepare positive electrode scrap as waste positive electrode (step S10).

[0150] For example, a slurry prepared by mixing single-particle mid-nickel 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 positive electrode sheet. After punching out positive electrode plates of a certain size, the remaining positive electrode scrap can be prepared.

[0151] 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.

[0152] Next, the prepared positive electrode scrap is crushed into appropriate sizes (step S20).

[0153] 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.

[0154] 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 necessary, so the positive electrode scrap must be crushed into even smaller pieces.

[0155] Next, the positive electrode scrap is heat-treated to recover the positive electrode active material (step S30). Here, the heat treatment is performed to thermally decompose the binder 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.

[0156] 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.

[0157] 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 decomposing. 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. In contrast, when heat treatment is performed 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, so the binder and conductive material are completely removed.

[0158] The heat treatment is preferably carried out at 300 to 650°C, and specifically at 550°C. However, 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.

[0159] The heat treatment can preferably be carried out at a temperature rise rate of 1 to 20°C / min, more preferably at 3 to 10°C / min, and specifically at 5°C / min. Within this range, the burden on the heat treatment equipment is suppressed, and there is an advantage in that thermal shock and other problems are not caused to the positive electrode scrap.

[0160] 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 for about 30 minutes. Within this range, the binder is adequately decomposed, and the decomposition efficiency is excellent.

[0161] 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.

[0162] After the heat treatment, the device can be slowly or rapidly cooled in the atmosphere.

[0163] Next, the recovered positive electrode active material is subjected to primary milling (step S40).

[0164] In the aforementioned primary milling step, it is important to mill the recovered positive electrode active material immediately without a prior cleaning step. In this case, the surface of the single-particle positive electrode active material is not damaged, the aggregated positive electrode active material is broken down to make the particles uniform, and since no cleaning step is performed, lithium loss due to cleaning does not occur, resulting in even better efficiency, life characteristics, and resistance characteristics.

[0165] The primary milling described above can be performed using, for example, a centrifugal mill, a jet mill, or a pin mill. Specifically, primary milling can be performed using a pin mill, which has the advantage of not damaging the surface of the positive electrode active material of the recovered single particles, resulting in uniform particle size and improved battery characteristics.

[0166] The aforementioned primary milling can be performed, for example, at 6,000 to 18,000 rpm, specifically at 12,000 ppm. Within this range, there is the advantage that the surface of the single-particle positive electrode active material is not damaged, the particles are homogenized, and the battery characteristics are improved.

[0167] Next, a lithium precursor is added to the primary milled cathode active material and annealed (step S50).

[0168] The annealing step is performed because lithium is lost from the positive electrode active material during the preceding step S30. Therefore, in step S50, the amount of lithium lost is replenished. In addition, because a deformed structure (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 step, in step S50, the crystal structure of the single-particle positive electrode active material is restored through annealing, improving the battery characteristics of the regenerated single-particle positive electrode active material or restoring it to the level of the newly produced positive electrode active material. Here, "newly produced" is the opposite concept of "regenerated," meaning that it is manufactured for the first time, and is the same word as "raw material" used in the detailed description of the invention and examples.

[0169] As an example of the lithium precursor, one or more of LiOH, Li2CO3, LiNO3, and Li2O may be used, and LiOH can be used as a specific example.

[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, so 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 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 700°C.

[0173] The annealing temperature is preferably a temperature that exceeds the melting point of the lithium precursor. However, temperatures exceeding 1000°C will cause thermal decomposition of the positive electrode active material, resulting in a decrease in performance, so the temperature should not exceed 1000°C. For example, when Li2CO3 is used as the lithium precursor, 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 750°C is appropriate, more preferably 500 to 720°C, and most preferably 600 to 720°C.

[0174] The annealing time is, for example, often set to 1 hour or more, preferably 15 hours or less, and more preferably 4 to 6 hours, taking into consideration the recovery of the crystal structure. A longer annealing time allows for sufficient recovery of the crystal structure, but there is no significant change in performance even with prolonged annealing. The annealing equipment can be the same as or similar to that used in the heat treatment step S30.

[0175] Next, the annealed positive electrode active material is subjected to secondary milling (step S60).

[0176] The secondary milling step S60 improves battery characteristics by reducing the particle size of the regenerated positive electrode active material by allowing the aggregated particles from the annealing step S50 to break down, making it similar in size to the particle size of the positive electrode active material in the waste positive electrode. Furthermore, it has the advantage that lithium precursors and / or fluorine can be effectively removed with a small amount of cleaning solution in the subsequent cleaning process, resulting in reduced wastewater.

[0177] The aforementioned secondary milling can be carried out using, for example, a centrifugal mill, a jet mill, or a pin mill. Specifically, the milling process can be performed using a pin mill, which has the advantage of not damaging the particles of the regenerated cathode active material and reducing the particle size.

[0178] The aforementioned secondary milling can be performed at speeds of 6,000 to 16,000 rpm, for example, and specifically at 12,000 rpm. Within this range, it offers advantages such as excellent milling efficiency, reduced particle size of the regenerated cathode active material, and superior productivity.

[0179] Next, the secondary milled positive electrode active material is washed (step S70).

[0180] In the cleaning step S70, lithium precursors present on the surface of the positive electrode active material in the form of LiOH and Li2CO3, which were unable to participate in the reaction in the annealing step S50, are removed. Lithium impurities such as lithium carbonate (Li2CO3) remaining on the surface of the regenerated positive electrode active material need to be removed because they can later react with the electrolyte, degrade the battery's performance, and generate gas.

[0181] In the washing step S70, preferably, the positive electrode active material and the washing solution from the annealing step S50 are mixed in a weight ratio of 1:0.5 to 1:5.5, specifically 1:1, filtered, and then the obtained solid portion of the positive electrode active material is dried. In this case, the particles that have aggregated through milling in the previous step are broken down, which has the advantage of allowing residual lithium to be cleanly removed with a small amount of washing solution and reducing wastewater.

[0182] 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.

[0183] The cleaning process preferably 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.

[0184] The mixing of the annealed positive electrode active material and the cleaning solution is preferably carried out by stirring, and although the stirring is not particularly limited, mechanical stirring or ultrasonic stirring may be used.

[0185] The mechanical stirring is preferably carried out at 250 to 350 rpm for 3 to 10 minutes.

[0186] The filtration is preferably reduced-pressure filtration using a filter, and the drying may be vacuum drying at 120-140°C.

[0187] Next, a surface coating is applied to the cleaned positive electrode active material (step S80).

[0188] 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. If the heat treatment temperature is too low, the desired surface protective layer of dissimilar metals will not be formed, and if the heat treatment temperature is too high, the thermal decomposition of the positive electrode active material will degrade the battery's performance.

[0189] 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.

[0190] 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.

[0191] If the annealing step S50 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 S80, 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 during the annealing step S50 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 S80, 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.

[0192] secondary battery The secondary battery of the present invention includes the recycled single-particle positive electrode active material. In this case, by significantly reducing the amount of lithium remaining on the surface of the positive electrode active material, it exhibits excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics. Furthermore, since no acid or organic solvent is used in the recovery and recycling process of the positive electrode active material, it is environmentally friendly, and in particular, the pre-cleaning process is omitted, resulting in superior economic efficiency and productivity.

[0193] 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.

[0194] 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.

[0195] [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)) discarded after punching out the positive electrode plates 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 temperature rise rate to reach the heat treatment temperature was 5°C / min, and air was supplied at 3 L / min.

[0196] The recovered cathode active material was confirmed to be a single particle through SEM imaging.

[0197] The recovered positive electrode active material was immediately subjected to primary milling at 12,000 rpm using a pin mill without prior cleaning.

[0198] To the primary milled positive electrode active material, LiOH, a lithium precursor, was added in an amount that provided 10 mol% of lithium, assuming a total lithium content of 100 mol% in the positive electrode active material. The mixture was then annealed in air at a firing temperature of 700°C for 5 hours. Air was supplied at a rate of 3 L / min.

[0199] The annealed positive electrode active material was subjected to secondary milling at 12,000 rpm using a pin mill.

[0200] The secondary milled 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 solid content. The solid content was vacuum dried at 130°C for 12 hours to obtain the washed positive electrode active material.

[0201] 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 500 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.

[0202] 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.

[0203] In this document, ppm refers to weight unless otherwise defined.

[0204] Example 2 In Example 1, the regenerated cathode active material was produced in the same manner as in Example 1, except that primary milling was not performed.

[0205] Example 3 In Example 1, the regenerated cathode active material was produced in the same manner as in Example 1, except that secondary milling was not performed.

[0206] Comparative Example 1 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 61 mol% Ni based on a total of 100 mol% of the remaining metals excluding Li).

[0207] The positive electrode active material recovered after heat treatment was confirmed to be secondary particles through SEM imaging.

[0208] Comparative Example 2 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)) discarded after punching out the positive electrode plates 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 temperature rise rate to reach the heat treatment temperature was 5°C / min, and air was supplied at 3 L / min.

[0209] The recovered cathode active material was confirmed to be a single particle through SEM imaging.

[0210] The recovered positive electrode active material was washed by immersing it in distilled water and simultaneously stirring it. At this time, the recovered positive electrode active material and distilled water were mixed in a weight ratio of 1:10 and stirred at 500 rpm for 10 minutes, after which only the active material was extracted by vacuum filtration using a filter.

[0211] After drying the washed positive electrode active material overnight at 100°C, a lithium precursor, LiOH, was added in an amount that provided 10 mol% of lithium, assuming a total lithium content of 100 mol% in the raw material positive electrode active material. The mixture was then annealed in air at a firing temperature of 700°C for 5 hours. Air was supplied at a rate of 3 L / min.

[0212] 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.

[0213] 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 500 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.

[0214] Comparative Example 3 In this example, the regenerated cathode active material was produced in the same manner as in Example 1, except that boric acid was not added in the surface coating step of Example 1, and the final regenerated cathode active material was produced by heating at 300°C for 5 hours.

[0215] Comparative Example 4 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)) discarded after punching out the positive electrode plates 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 temperature rise rate to reach the heat treatment temperature was 5°C / min, and air was supplied at 3 L / min.

[0216] The recovered cathode active material was confirmed to be a single particle through SEM imaging.

[0217] The recovered positive electrode active material was immediately subjected to primary milling at 12,000 rpm using a pin mill without washing with water to produce regenerated positive electrode active material. Annealing, secondary milling, post-cleaning, and coating were not performed.

[0218] Comparative Example 5 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.

[0219] [Test Example I: Fluorine (F) Content] The fluorine content of the regenerated or newly generated cathode active materials manufactured or prepared in Examples 1-3 and Comparative Examples 1-5 was measured using an ICP analyzer, and the results are shown in Table 1 below. While this can be done using a general ICP analyzer commonly used in laboratories, there is no deviation due to the measuring device or method.

[0220] [Table 1]

[0221] As shown in Table 1 above, the fluorine content of the regenerated cathode active materials in Examples 1 to 3 according to the present invention was confirmed to be within the range of 5700 to 6500 ppm. On the other hand, the fluorine content of the regenerated cathode active material in Comparative Example 2 decreased after two washings, but a large amount of wastewater was generated, and lithium loss was also significant. The fluorine content of the regenerated cathode active material in Comparative Example 3 was at a similar level to that of Example 1, and through this, it was found that the surface coating does not affect the fluorine content.

[0222] Furthermore, the regenerated cathode active material of Comparative Example 4, which was manufactured by primary milling, showed a significantly increased fluorine content compared to Example 1.

[0223] Furthermore, Comparative Example 5, a newly generated cathode active material, had a low fluorine content, while Comparative Example 1, a regenerated cathode active material containing secondary particles, had a fluorine content at the same level as the example.

[0224] [Test Example II: Evaluation of CHC Cells (Coin Half Cells, CHCs)] The electrochemical performance of the regenerated or newly generated cathode active materials manufactured or prepared in Examples 1-3 and Comparative Examples 1-5 was measured through evaluation using a CHC cell as described below, and the results are shown in Table 2. *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 a cell (Coin Half Cell, CHC) was manufactured. The electrochemical performance (charge capacity CH, discharge capacity DCH, and charge / discharge efficiency Eff (%)) was evaluated under conditions of 3-4.45V cut, initial formation of 0.1C / 0.1C charge / discharge, electrolyte with a weight ratio of ethylene carbonate (EC):dimethyl carbonate (DMC):ethyl methyl carbonate (EMC) = 3:4:3, and other additives.

[0225] The charge and discharge efficiency was calculated using the following formula 1 and is shown in Table 2.

[0226] [Formula 1] Charge / discharge efficiency (%) = [Discharge capacity (mAh / g) / Charge capacity (mAh / g)] × 100

[0227] [Table 2]

[0228] As shown in Table 2 above, the regenerated cathode active materials of Examples 1 to 3 according to the present invention were found to have even better charging capacity (CH), discharging capacity (DCH), and / or charge / discharge efficiency (Eff) compared to the regenerated cathode active materials or newly generated cathode active materials of Comparative Examples 1 to 5. In particular, Comparative Example 2, in which washing was performed instead of milling, was found to have lower discharge efficiency and charge / discharge efficiency than Examples 1 to 3.

[0229] [Test Example III: XRD Analysis] The regenerated or newly created cathode active materials produced or prepared in Examples 1-3 and Comparative Examples 1-5 were measured by XRD analysis to determine the a-axis lattice constant, c-axis lattice constant, cell volume, and crystal grain size, respectively, and are shown in Table 3 below. *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 cell volume was calculated by the product of the lattice parameter on the a-axis and the lattice parameter on the c-axis. The crystallite size was calculated using Scherrer's equation based on the XRD measurement data.

[0230] [Table 3]

[0231] As shown in Table 3 above, the regenerated cathode active materials according to the present invention (Examples 1-3) were found to have different a-axis lattice constants, c-axis lattice constants, cell volumes, and grain sizes from the newly generated cathode active material (Comparative Example 5). Specifically, the a-axis lattice constant and cell volume were small, while the c-axis lattice constant and grain size were large. From this, it was found that the regenerated single-particle cathode active material according to the present invention has a different crystal structure and grain size from the newly generated cathode active material through milling before and / or after annealing. Furthermore, it was confirmed that the regenerated cathode active materials of Examples 1-3 also have different a-axis lattice constants, c-axis lattice constants, cell volumes, and grain sizes from the regenerated cathode active materials of Comparative Examples 1-4.

[0232] [Test Example IV: Evaluation of High-Temperature Life Characteristics] The capacity retention rate was measured as follows using CHC cells manufactured as described above from the regenerated or newly generated cathode active materials produced or prepared in Examples 1 to 3 and Comparative Examples 1 to 5, and the results are shown in Figure 2 below. *Evaluation of high-temperature life characteristics: At 45°C, each cell under the following conditions underwent 30 charge-discharge cycles, and the capacity retention rate for each cycle was calculated using the following formula 2, which is shown in Figure 2 below. Charge:0.33C, CC / CV, 4.5V, 0.05C cut-off Discharge:0.33C, CC, 3.0V, 0.05C cut-off

[0233] [Formula 2] Capacity retention rate (%) = (Discharge capacity after N cycles / Discharge capacity after 1 cycle) × 100

[0234] Figure 2 below shows the results of evaluating the lifetime characteristics of each of the following materials according to the present invention: regenerated single-particle cathode active material (Examples 1-3), regenerated secondary-particle cathode active material (Comparative Example 1), regenerated cathode active material washed without milling (Comparative Example 2), regenerated cathode active material heat-treated without adding boric acid in the surface coating step (Comparative Example 3), regenerated cathode active material performed up to the primary milling step (Comparative Example 4), and newly generated cathode active material (Comparative Example 5). The graph shows the capacity retention rate by cycle number.

[0235] Referring to this, it was confirmed that the regenerated cathode active material according to the present invention (Examples 1-3) has superior capacity retention compared to the regenerated cathode active materials of Comparative Examples 1-4, and is superior to the newly generated cathode active material (Comparative Example 5).

[0236] In particular, in Comparative Example 1, which contained secondary particle cathode active material, it was confirmed that the capacity retention rate decreased significantly despite milling being performed both before and after annealing. [Explanation of symbols]

[0237] 10 Current collector 20 Active material layer 30 Positive electrode sheets 40 Positive plate 50 Positive electrode scrap

Claims

1. 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, wherein the positive electrode active material is Contains single particles, The fluorine (F) content is 5,700 to 6,500 mg / kg, and / or X-ray diffraction (XRD) analysis revealed that the a-axis lattice constant was 2.8753–2.8772 Å, the c-axis lattice constant was 14.243–14.255 Å, and the cell volume was 101.968–102.168 Å. ３ A positive electrode active material characterized by having a crystal grain size greater than 130 nm and less than or equal to 136 nm.

2. The positive electrode active material according to claim 1, characterized in that the positive electrode active material contains nickel (Ni) in an amount of 40 mol% or more, based on a total of 100 mol% of the remaining metals excluding lithium (Li).

3. The positive electrode active material according to claim 1, characterized in that the surface of the positive electrode active material is coated with a coating agent containing metal or carbon.

4. The positive electrode active material according to any one of claims 1 to 3, characterized in that the positive electrode active material is a regenerated positive electrode active material.

5. (a) A step of recovering the positive electrode active material, including single particles, from the positive electrode active material layer by heat-treating the waste positive electrode, which has a positive electrode active material layer formed on a current collector, at 300 to 650°C, and thermally decomposing the binder and conductive 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, (c) A step of washing the annealed positive electrode active material with a cleaning solution, (d) a step of surface coating the cleaned positive electrode active material, In step (b) above, a step of milling the recovered positive electrode active material before annealing, and / or A method for regenerating a positive electrode active material, characterized in that step (c) above includes a step of milling the annealed positive electrode active material before washing.

6. (a) A step of recovering the positive electrode active material containing single particles in the mid-nickel positive electrode active material layer by heat-treating the waste positive electrode having a mid-nickel positive electrode active material layer formed on the current collector at 300 to 650°C, thereby thermally decomposing the binder and conductive material in the mid-nickel positive electrode active material layer, (b) Adding a lithium precursor to the recovered cathode active material and annealing it at 400 to 1000°C, (c) A step of washing the annealed positive electrode active material with a cleaning solution, (d) a step of surface coating the cleaned positive electrode active material, In step (b) above, a step of milling the recovered positive electrode active material before annealing, and / or A method for regenerating a positive electrode active material, characterized in that step (c) above includes a step of milling the annealed positive electrode active material before washing.

7. The method for regenerating a positive electrode active material according to claim 5 or 6, wherein the positive electrode active material is one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based 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.

8. The method for regenerating a positive electrode active material according to claim 5 or 6, characterized in that the milling is performed using a centrifugal mill, a jet mill, or a pin mill.

9. The method for regenerating a positive electrode active material according to claim 5 or 6, characterized in that the milling is performed at 6,000 to 18,000 rpm.

10. 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 5 or 6, characterized by containing one or more of the O compounds.

11. The method for regenerating a positive electrode active material according to claim 5 or 6, 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.

12. The method for regenerating a positive electrode active material according to claim 5 or 6, characterized in that, in step (c) above, the washing is performed such that the weight ratio of the annealed positive electrode active material or milled positive electrode active material to the washing solution is 1:0.5 to 1:5.

5.

13. The method for regenerating a positive electrode active material according to claim 5 or 6, characterized in that the cleaning in step (c) comprises the steps of mixing the annealed positive electrode active material or milled 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.

14. The method for regenerating a positive electrode active material according to claim 5 or 6, characterized in that the surface coating in step (d) involves coating the surface with 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.

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