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

Abstract

The present invention relates to a method for regenerating positive electrode active material and a regenerated positive electrode active material produced therefrom, and more particularly to a method for regenerating positive electrode active material and a regenerated positive electrode active material produced therefrom, characterized by comprising: (a) a step of heat-treating a waste positive electrode composition containing positive electrode active material, conductive material, binder, and solvent to remove the solvent; (b) a step of pulverizing the waste positive electrode composition from which the solvent has been removed; (c) a step of heat-treating the pulverized waste positive electrode composition at 300 to 650°C to remove the binder and conductive material and recover the positive electrode active material; (d) a step of adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (e) a step of washing the annealed positive electrode active material with a cleaning solution. According to the present invention, a waste positive electrode composition containing positive electrode active material, conductive material, binder, and solvent is subjected to low-temperature heat treatment to remove the solvent, powdered, and then heat-treated. This process cleanly removes the binder and conductive material, restoring the structure to that of fresh positive electrode active material. The method provides a regenerated positive electrode active material with excellent thermal stability, reduced lithium residue, and superior initial capacity and life characteristics for secondary batteries. The present invention also provides a regenerated positive electrode active material produced therefrom.

Description

[Technical Field]

[0001] [Cross-reference with related applications] This application is an application claiming priority rights based on Korean Patent Application No. 10-2024-0018703 dated February 7, 2024, and Korean Patent Application No. 10-2025-0014491, refiled thereunder on February 5, 2025, and all contents disclosed in the documents of said Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to a method for regenerating positive electrode active material and the regenerated positive electrode active material produced therefrom. More specifically, the present invention relates to a method for regenerating positive electrode active material in which a waste positive electrode composition containing positive electrode active material, conductive material, binder, and solvent is subjected to low-temperature heat treatment to remove the solvent, powdered, and then heat-treated, thereby completely removing the binder and conductive material, restoring the structure to that of fresh positive electrode active material, resulting in excellent thermal stability, reduced residual lithium, excellent initial capacity and life characteristics of secondary batteries, environmental friendliness as no acid is used in the recovery and regeneration process, reduced process costs as neutralization and wastewater treatment are not required, no metal elements are discarded as the positive electrode active material is regenerated without decomposition, no toxic gas generation or explosion risk is present as no organic solvents are used, and economic efficiency and productivity are greatly improved. [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 is manufactured by applying a positive electrode composition containing a positive electrode active material, a binder, a conductive material, and a solvent to a metal foil such as aluminum, drying it, and then press-molding it.

[0005] The positive electrode active material mainly uses lithium-based oxides, which generally contain rare metals such as cobalt, nickel, or manganese.

[0006] The positive electrode composition, comprising the positive electrode active material, binder, conductive material, and solvent, is not easily mixed. Therefore, the process involves repeatedly adding and stirring these components in a specific order to adjust the concentration of solids, composition ratio, or viscosity of the slurry, and adding a predetermined dispersant as needed. Although the positive electrode composition is produced in large quantities, if the produced composition is defective and does not possess the desired physical properties, it is not possible to adjust the properties by adding specific components, and therefore the entire quantity is discarded.

[0007] Furthermore, the manufactured cathode composition is moved to a pipeline and subjected to a coating process where it is applied to metal foil via a slit die and dried. However, if the pipeline becomes clogged due to excessive fine powder in the cathode composition or uneven dispersion, the entire manufactured cathode composition is discarded.

[0008] Furthermore, if any of the manufactured positive electrode composition remains after being applied to the metal foil, it will gel over time, causing solid components to precipitate and reducing its dispersion, and should therefore be discarded.

[0009] Thus, the waste generated from the manufacturing and coating processes of cathode compositions, as well as environmental pollution due to the toxicity of solvents, poses a problem.

[0010] Therefore, there is a need to develop methods for safely and environmentally friendly recycling of waste cathode compositions, using fewer processes and at lower costs, to produce cathode active materials with improved output performance that do not contain discarded metal elements. [Overview of the project] [Problems that the invention aims to solve]

[0011] To solve the problems of the conventional technology described above, the present invention aims to provide a method for regenerating positive electrode active materials in which a waste positive electrode composition containing positive electrode active material, conductive material, binder, and solvent is subjected to low-temperature heat treatment to remove the solvent, powdered, and then heat-treated, thereby completely removing the binder and conductive material, restoring the structure to that of fresh positive electrode active material, resulting in excellent thermal stability, reduced residual lithium, excellent initial capacity and life characteristics of secondary batteries, environmentally friendly as no acid is used in the recovery and regeneration process, reduced process costs as neutralization and wastewater treatment are not required, no metal elements are discarded as the positive electrode active material is regenerated without decomposition, and there is no risk of generating toxic gases or explosions as organic solvents are not used, thus greatly improving economic efficiency and productivity.

[0012] Furthermore, the present invention aims to provide a positive electrode active material that exhibits excellent thermal stability and a reduced amount of residual lithium.

[0013] 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]

[0014] To achieve the above objectives, I) the present invention provides a method for regenerating a positive electrode active material, comprising: (a) heat-treating a waste positive electrode composition containing a positive electrode active material, a conductive material, a binder, and a solvent to remove the solvent; (b) pulverizing the waste positive electrode composition from which the solvent has been removed; (c) heat-treating the pulverized waste positive electrode composition at 300 to 650°C to remove the binder and conductive material and recover the positive electrode active material; (d) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (e) washing the annealed positive electrode active material with a cleaning solution.

[0015] II) In I) above, the waste cathode composition may be in the form of a slurry.

[0016] III) In the above I) or II), the heat treatment in step (a) may be carried out at 80 to 120 °C.

[0017] IV) In the above I) to III), the heat treatment in step (a) may be carried out for 30 minutes to 4 hours.

[0018] V) In the above I) to IV), the pulverization in step (b) may be by dry grinding.

[0019] VI) In the above I) to V), the dry grinding may be carried out using a hand mill, a pin mill, a disk mill, a cutting mill, or a hammer mill.

[0020] VII) In the above I) to VI), the pulverization step (b) may further include a sieving step after pulverization.

[0021] VIII) In the above I) to VII), the powder obtained through step (b) may have an average particle size of 45 μm or less.

[0022] IX) In the above I) to VIII), the positive electrode active material may be one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active materials, nickel-cobalt-manganese (NCM)-based positive electrode active materials, nickel-cobalt-aluminum (NCA)-based positive electrode active materials, nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active materials, and lithium iron phosphate (LFP)-based positive electrode active materials.

[0023] X) In the above I) to IX), the solvent may be one or more selected from the group consisting of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, and water.

[0024] XI) In I) to X) above, the lithium precursor may contain one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0025] XII) In steps I) to XI) above, the lithium precursor in step (d) 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.

[0026] XIII) In I) to XII) above, the cleaning solution may be water or an aqueous solution of a basic lithium compound.

[0027] XIV) In I) to XIII) above, the method for regenerating the positive electrode active material may further include (f) the step of surface coating the cleaned positive electrode active material.

[0028] Furthermore, XV) The present invention is 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, nickel-cobalt-manganese-aluminum (NCMA)-based cathode active materials, and lithium iron phosphate (LFP)-based cathode active materials, wherein the c-axis length of the crystal structure measured by XRD (X-ray diffraction) is 14.200~14.210 Å and the cell volume is 101.65~101.75 Å. 3 The present invention provides a positive electrode active material characterized by having a crystal size of 82 to 90 nm and a thermal decomposition temperature of 700°C or higher, as measured by TGA (Thermogravimetric analysis).

[0029] XVI) In I) to XV) above, the surface of the positive electrode active material may be coated with a coating agent containing metal or carbon. [Effects of the Invention]

[0030] According to the present invention, by removing the solvent from waste positive electrode composition that does not meet the specifications generated during the manufacturing process of the positive electrode, waste positive electrode composition that clogs the pipeline during the process of coating the positive electrode composition onto metal foil, or the remaining amount of waste positive electrode composition after coating onto a current collector by low-temperature heat treatment, pulverizing it, and then heat-treating it, the binder and conductive material in the waste positive electrode composition are cleanly removed by smooth contact with air or oxygen, thereby restoring it to the structure of a fresh positive electrode active material. This provides a positive electrode active material with excellent thermal stability, reduced lithium residue, and excellent capacity and life characteristics for secondary batteries.

[0031] Furthermore, since no acid is used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly. Because neutralization and wastewater treatment are not required, process costs are reduced. Since the positive electrode active material is regenerated without decomposition, no metal elements are discarded. Because organic solvents are not used, there is no risk of generating toxic gases or explosions. This method offers significant improvements in economic efficiency and productivity, providing a method for regenerating positive electrode active material.

[0032] 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. [Brief explanation of the drawing]

[0033] [Figure 1] This graph shows the initial capacity of each of the recycled cathode active materials produced in Example 1 and Comparative Example 1, evaluated using a coin half cell. [Figure 2] This graph shows the lifetime characteristics of the recycled or newly produced cathode active materials manufactured in Example 1 and the Reference Example, evaluated using a coin half cell. [Figure 3] This graph shows the results of TGA (Thermogravimetric analysis) analysis of the regenerated cathode active materials produced in Example 1 and Comparative Example 1. [Figure 4] This is a flowchart illustrating one embodiment of the present invention, for the regeneration process of a waste cathode composition. [Modes for carrying out the invention]

[0034] The inventors have confirmed that by removing the solvent from waste positive electrode composition that does not meet specifications generated during the manufacturing process of the positive electrode, or the remaining amount of waste positive electrode composition after coating it on the positive electrode current collector, by low-temperature heat treatment, pulverizing it, and then heat-treating it, the binder and conductive material are cleanly removed by smooth contact with air or oxygen. The regenerated positive electrode active material is restored to the structure of fresh positive electrode active material, exhibits excellent thermal stability, reduces the amount of residual lithium, and further improves the initial capacity and life characteristics of the secondary battery. Based on this, they continued their research and completed the present invention.

[0035] The following describes in detail, step by step, the method for regenerating the positive electrode active material described herein.

[0036] However, the terms and words used in this specification and in the claims are not to be interpreted in their ordinary or dictionary sense, but rather in a sense and concept consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention. Therefore, it should be understood that the embodiments and configurations shown in the drawings described herein are merely examples of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can substitute for them and that can be arranged, substituted, combined, separated or designed in various other configurations.

[0037] 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.

[0038] Method for regenerating positive electrode 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 composition containing positive electrode active material, conductive material, binder, and solvent to remove the solvent; (b) pulverizing the waste positive electrode composition from which the solvent has been removed; (c) heat-treating the pulverized waste positive electrode composition at 300 to 650°C to remove the binder and conductive material and recover the positive electrode active material; (d) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (e) washing the annealed positive electrode active material with a cleaning solution. In this case, the recovered regenerated positive electrode active material is restored to the structure of fresh positive electrode active material, resulting in excellent thermal stability, reduced residual lithium, excellent initial capacity and life characteristics of secondary batteries, environmental friendliness, reduced process costs, no discarded metal elements, no risk of toxic gas generation or explosion, and significant improvements in economy and productivity.

[0039] The following is a detailed explanation of the regeneration method for the positive electrode active material, broken down into stages.

[0040] (a) A step of heat-treating the waste cathode composition to remove the solvent. In the present invention, the method for regenerating positive electrode active material includes (a) a step of heat-treating a waste positive electrode composition containing positive electrode active material, conductive material, binder, and solvent to remove the solvent, which has the advantage that the subsequent step of powdering the positive electrode composition is easy.

[0041] The waste positive electrode composition may take the form of a slurry, for example, and may be a defective slurry in which the composition of the positive electrode composition does not meet the standard, a defective slurry generated due to clogging of pipelines or the like during the coating process, or residual slurry remaining after being applied to the current collector.

[0042] The heat treatment may, for example, be carried out in an air or oxygen atmosphere, which has the advantage of easily removing the solvent, thereby facilitating the subsequent powdering of the cathode composition.

[0043] The oxygen atmosphere may, for example, have a purity of 59% or higher, preferably 70% or higher, more preferably 80% or higher, even more preferably 90% or higher, and even more preferably 90-99%. Within this range, the solvent can be easily removed, which has the advantage of facilitating the subsequent powdering of the cathode composition.

[0044] The purity percentage of the oxygen may be in volume percentage or mol%.

[0045] 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.

[0046] The heat treatment temperature may be, for example, 80 to 120°C, preferably 85 to 115°C, and more preferably 90 to 110°C. Within this range, the solvent is completely removed, which has the advantage of facilitating the subsequent powdering of the cathode composition.

[0047] The heat treatment time may be, for example, 30 minutes to 4 hours, preferably 1 hour to 3.5 hours, more preferably 1.5 hours to 3 hours, and even more preferably 1.5 hours to 2.5 hours. Within this range, the solvent is completely removed, which has the advantage of facilitating the subsequent powdering of the cathode composition.

[0048] The positive electrode active material is preferably a lithium cobalt oxide such as LiCoO2 (hereinafter referred to as "LCO"); a lithium manganese oxide such as LiMnO2 or LiMn2O4; a lithium iron phosphate compound such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA; lithium nickel cobalt aluminum oxide); a lithium nickel oxide such as LiNiO2; a nickel manganese-based lithium composite metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and an NCM-based lithium composite transition metal oxide in which a part of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). It may be one or more selected from the group consisting of, more preferably, a nickel manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof. In this case, there is an effect of excellent reversible capacity and thermal stability.

[0049] As still another specific example, the positive electrode active material has the following Chemical Formula 1 (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the Chemical Formula 1, M includes one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented by.

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

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

[0052] The solvent is for mixing the positive electrode active material, binder, and / or conductive material, and may be a solvent commonly used in the art to which the present invention belongs.

[0053] The solvent may, for example, be one or more selected from the group consisting of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, and water.

[0054] The aforementioned waste cathode composition may, as an example, further contain a dispersant.

[0055] The dispersant may, as an example, be one or more selected from the group consisting of cellulosic compounds, polyalkylene oxides, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl ether, polyvinyl sulfonic acid, polyvinyl chloride (PVC), polyvinylidene fluoride, chitosans, starch, amylose, polyacrylamide, poly-N-isopropylacrylamide, poly-N,N-dimethylacrylamide, polyethyleneimine, polyoxyethylene, poly(2-methoxyethoxyethylene), poly(acrylamide-co-diallyldimethylammonium chloride), acrylonitrile-butadiene-styrene (ABS) copolymer, acrylate-styrene-acrylonitrile (ASA) copolymer, a mixture of acrylate-styrene-acrylonitrile (ASA) copolymer and propylene carbonate, styrene-acrylonitrile (SAN) copolymer, and methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) copolymer.

[0056] (b) Step of pulverizing the waste cathode composition from which the solvent has been removed. The method for regenerating positive electrode active material of the present invention includes (b) the step of pulverizing the waste positive electrode composition from which the solvent has been removed. In this case, the subsequent heat treatment step completely removes the binder and conductive material in the positive electrode composition without leaving any residue, thereby restoring the structure to that of a fresh positive electrode active material, which has the effect of having excellent thermal stability and a reduced amount of residual lithium.

[0057] The pulverization in step (b) above literally means turning the material into a powder or making it into a powder. For example, this may be done by dry grinding, which has the advantage of being uniformly ground.

[0058] In this description, the dry conditions are not particularly limited as long as they are dry conditions as generally defined in the art to which the present invention pertains. For example, they may be conditions in which no solvent is added and / or dry conditions and / or conditions under which a dry grinding apparatus is used.

[0059] The dry grinding described above is not particularly limited as long as it is a dry grinding method commonly used in the art to which the present invention belongs, and preferably a hand mill, pin mill, disc mill, cutting mill, or hammer mill can be used. In this case, there is an advantage that the cathode composition from which the solvent has been removed is uniformly ground, and the powdered cathode composition can be immediately introduced into the heat treatment step.

[0060] The (b) pulverization step may preferably further include a step of sieving after pulverizing the waste cathode composition, more preferably a sieve with a mesh size of 230 to 500, even more preferably a sieve with a mesh size of 270 to 450, even more preferably a sieve with a mesh size of 325 to 450, and particularly preferably a sieve with a mesh size of 325. In this case, the particle size of the cathode composition becomes uniform and larger particles are removed, which has the advantage of improving the degree of dispersion when manufacturing the recycled cathode active material as a slurry.

[0061] The powdered waste cathode composition obtained through step (b) above may have an average particle size of, for example, 45 μm or less, preferably 40 μm or less, more preferably 35 μm or less, and even more preferably 10 to 35 μm. Within this range, the uniform particle size of the powdered waste cathode composition has the advantage of allowing the binder and conductive material to be cleanly removed in the subsequent heat treatment step.

[0062] In this description, the average particle size 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 to measure the average particle size (D) of the particle size distribution in the measuring device based on 50% of the particle size distribution. 50 It is possible to calculate ).

[0063] (c) Step of recovering the cathode active material from the powdered waste cathode composition. The method for regenerating positive electrode active material of the present invention includes the step of (c) heat-treating the powdered waste positive electrode composition at 300 to 650°C to remove the binder and conductive material and recover the positive electrode active material, preferably including the step of (c) heat-treating the powdered waste positive electrode composition at 300 to 650°C in an air or oxygen atmosphere to remove the binder and conductive material and recover the positive electrode active material. In this case, the powdered waste positive electrode composition is able to come into smooth contact with air or oxygen, so that the binder and conductive material are thermally decomposed into CO2 and H2O and completely removed, restoring the structure to that of fresh positive electrode active material, which has the advantages of excellent thermal stability and reduced residual lithium.

[0064] The heat treatment temperature may preferably be 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 580°C. Within this range, the binder and conductive material are completely removed, restoring the structure to that of a fresh positive electrode active material, which has the advantages of excellent thermal stability and reduced residual lithium.

[0065] 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 binder and conductive material are completely removed, restoring the structure to that of a fresh positive electrode active material, which has the advantages of excellent thermal stability and reduced lithium residue.

[0066] In this description, the heat treatment time refers to the time spent processing at the heat treatment temperature, and the time it takes to reach that heat treatment temperature is not included in the calculation.

[0067] The aforementioned heat treatment has the advantage that the temperature rise rate is, for example, 1 to 20°C / min, preferably 3 to 10°C / min, and more preferably 3 to 7°C / min, and within this range, the burden on the heat treatment apparatus is suppressed and thermal shock and other problems are not generated in the powdered positive electrode composition.

[0068] The waste cathode composition may, for example, include a dispersant, and the dispersant is not particularly limited as long as it is a dispersant that is removed by thermal decomposition at the heat treatment temperature.

[0069] (d) Adding a lithium precursor to the recovered positive electrode active material and performing annealing. The present invention provides a method for regenerating positive electrode active material, which includes the step of (d) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C. This method provides a positive electrode active material with excellent initial discharge capacity, output performance, capacitance characteristics, and resistance characteristics. It also eliminates the washing step of the recovered active material, significantly improving economy and productivity, and minimizing damage to the positive electrode active material.

[0070] The (d) annealing step may preferably be a step in which the recovered positive electrode active material is annealed in oxygen (O2) or air at 400 to 1000°C without washing, in which case there is an effect of improving the battery characteristics of the regenerated positive electrode active material by improving its crystallinity, such as by increasing the crystallinity of the positive electrode active material or restoring its crystal structure.

[0071] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0072] Preferably, 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 (d) is the positive electrode active material represented by chemical formula 1, the amount of lithium 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 0.17, particularly more preferably 0.007 to 0.015, and most preferably 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.

[0073] As another example, the lithium precursor may be added in an amount equivalent to 1 to 25 mol%, more preferably 1 to 20 mol%, and even more preferably 3 to 17 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.

[0074] As yet another example, when the raw material positive electrode active material is a lithium iron phosphate compound, the lithium precursor may be added in an amount corresponding to 0 to 25 mol%, more preferably in an amount corresponding to 0.1 to 20 mol%, and even more preferably in an amount corresponding to 1 to 17 mol%, such that no residual precursor that can increase the resistance remains in the regenerated positive electrode active material is found to be very useful for improving battery characteristics, and since the crystal structure can be restored with a smaller amount of lithium precursor than conventional methods, there is an economic advantage.

[0075] 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 400-720°C, even more preferably at 450-700°C, and even more preferably at 550-670°C. Within this range, the crystal structure is restored, which has the effect of improving the output performance of the battery.

[0076] 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.

[0077] The annealing temperature can preferably be reached at a heating rate of 1 to 10°C / min, more preferably at 1 to 5°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.

[0078] 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.

[0079] 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.

[0080] The positive electrode active material obtained after step (d) above may have a surface LiOH content of, for example, 0.90% by weight or less, preferably 0.85% by weight or less, more preferably 0.001 to 0.85% by weight, and even more preferably 0.01 to 0.85% by weight, and within this range, a positive electrode active material with excellent initial capacity and lifetime characteristics is provided.

[0081] The positive electrode active material obtained after step (d) may have a surface Li2CO3 content of 0.7% by weight or less, preferably 0.6% by weight or less, more preferably 0.001 to 0.6% by weight, and even more preferably 0.01 to 0.6% by weight, and within this range, a positive electrode active material with excellent initial capacity and lifetime characteristics is provided.

[0082] The positive electrode active material obtained after step (d) above may have a total amount of LiOH and Li2CO3 remaining on the surface of 1.6% by weight or less, preferably 1.4% by weight or less, more preferably 0.001 to 1.4% by weight, and even more preferably 0.01 to 1.4% by weight, and within this range, a positive electrode active material with excellent initial capacity and lifetime characteristics is provided.

[0083] In this description, the content of LiOH and Li2CO3 remaining on the surface of the positive electrode active material can be measured by a measurement method commonly used in the art to which this invention belongs. For example, 5 g of positive electrode active material is dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and then filtered to remove the positive electrode active material. The resulting filtrate is then titrated with a 0.1 M HCl solution, and the change in pH value is measured to obtain a pH titration curve. Using the obtained pH titration curve, the amount of residual LiOH and Li2CO3 in the positive electrode active material can be calculated.

[0084] The positive electrode active material obtained after step (d) above may have a residual fluorine (F) content of, for example, 4000 to 9000 mg / kg, preferably 5000 to 8000 mg / kg, and more preferably 6000 to 7000 mg / kg. Within this range, the conductive material and binder are sufficiently thermally decomposed and cleanly removed, which has the advantage of providing excellent initial capacity and life characteristics for the positive electrode active material.

[0085] In this description, the residual fluorine (F) content can be measured by a measurement method commonly used in the art to which the present invention pertains, and specifically, it can be measured using an ICP (inductively coupled plasma) analyzer.

[0086] (e) A step of washing the annealed positive electrode active material with a cleaning solution. The present invention provides a method for regenerating a positive electrode active material, which includes (e) a step of washing the annealed positive electrode active material with a cleaning solution. This method has the advantage of improving battery characteristics by removing lithium compounds that remain on the surface of the positive electrode active material after the addition of the lithium precursor and are unable to participate in the reaction.

[0087] The cleaning process may preferably include the steps of mixing the annealed positive electrode active material with a cleaning solution, filtering the mixture, and drying the solid positive electrode active material obtained after filtering. In this case, the excess lithium that tends to remain in the positive electrode active material is effectively removed.

[0088] The drying may be carried out preferably at 100 to 500°C, more preferably at 120 to 400°C, even more preferably at 120 to 300°C, and even more preferably at 120 to 200°C, which has the advantage of effectively removing residual Li.

[0089] The drying method may preferably be vacuum drying.

[0090] In this description, vacuum drying is not particularly limited as long as it is a vacuum drying method commonly used in the art to which the present invention pertains.

[0091] The cleaning process may preferably include the steps of mixing the annealed positive electrode active material with a cleaning solution in a weight ratio of 1:3 to 1:20, more preferably 1:5 to 1:15, and even more preferably 1:7 to 1:12, followed by filtration, and drying the solid positive electrode active material obtained after filtration. In this case, lithium precursors such as LiOH and Li2CO3 are effectively removed.

[0092] The cleaning solution may, for example, be water or an aqueous solution of a basic lithium compound, preferably water. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain on the surface of the positive electrode active material, can be cleanly removed with a small amount of cleaning solution, eliminating the need for wastewater treatment and significantly improving the output performance of the battery.

[0093] The water is more 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 positive electrode active material, can be easily removed with a small amount of cleaning solution. This eliminates the need for wastewater treatment and significantly improves the output performance of the battery.

[0094] The basic lithium compound aqueous solution may preferably contain more than 0% by weight and 15% by weight or less of the lithium compound, more preferably more than 0% by weight and 10% by weight or less, or 0.1 to 10% by weight of the lithium compound. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain on the surface of the positive electrode active material, can be cleanly removed with a small amount of cleaning solution, eliminating the need for wastewater treatment and significantly improving the output performance of the battery.

[0095] The mixing of the annealed positive electrode active material and the cleaning solution is preferably carried out by stirring, and the stirring is not particularly limited, but may be mechanical stirring or ultrasonic stirring.

[0096] The stirring may be carried out for preferably 30 minutes or less, more preferably 20 minutes or less, even more preferably 15 minutes or less, and even more preferably 5 to 10 minutes, and within this range, there is the advantage that residual lithium is effectively removed.

[0097] The stirring can be performed, for example, at 200 to 1000 rpm, preferably 300 to 800 rpm, and more preferably 400 to 700 rpm, and within this range, there is the advantage that residual lithium is effectively removed.

[0098] The aforementioned filtration can be carried out, for example, by vacuum filtration using a filter, or by using a filter press.

[0099] (f) A step of surface coating the cleaned positive electrode active material to obtain a reusable positive electrode active material. The method for regenerating positive electrode active material of the present invention preferably includes the step of (f) 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 properties of the positive electrode active material itself.

[0100] The aforementioned surface coating is preferably applied to the surface using a coating agent containing one or more of metals, organometallics, and carbon components in a solid-phase or liquid-phase manner, followed by heat treatment at 100 to 1200°C, more preferably 200 to 1000°C, and even more preferably 250 to 800°C. In this case, the structural stability and electrochemical performance are improved while maintaining the properties of the positive electrode active material itself.

[0101] 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). A specific example is a coating agent containing tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0102] The coating agent containing the metal may, for example, be an oxide or acid that contains the metal as an element in its molecule.

[0103] 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.

[0104] 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.

[0105] The coating agent, for example, may be contained in an amount of 0.001 to 0.3 mol%, preferably 0.01 to 0.3 mol%, more preferably 0.01 to 0.15 mol%, still more preferably 0.01 to 0.1 mol%, and even more preferably 0.01 to 0.05 mol% based on 100 mol% of the metal in the cathode active material before the coating treatment, with respect to the components actually coated on the surface of the cathode active material excluding the solvent. Within this range, there is an effect of improving the structural stability and electrochemical performance while maintaining the properties of the cathode active material itself as they are.

[0106] The heat treatment time is preferably 1 to 16 hours, more preferably 3 to 7 hours. Within this range, there is an effect of improving the structural stability and electrochemical performance while maintaining the properties of the cathode active material itself as they are.

[0107] The coating method is not particularly limited as long as it is a coating method commonly used in the technical field to which the present invention pertains. For example, a liquid phase method in which a liquid coating agent is produced and mixed with the cathode active material, a mechanochemical method using 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 cathode active material in an aqueous solution state, a method utilizing the reaction between a gaseous coating agent and the cathode active material, or a sputtering method may be used.

[0108] The metal, organometallic, and carbon components may, for example, be spherical, plate-shaped, angular, or needle-shaped. Such shapes can be adjusted by changing process conditions and the like during the manufacturing process, and the definitions for each shape are not particularly limited as long as they follow the definitions generally recognized in the technical field to which the present invention pertains.

[0109] The coating agent preferably has an average diameter of 1 to 1000 nm and a specific surface area of 10 to 100 m 2 / g, and more preferably has an average diameter of 10 to 100 nm and a specific surface area of 20 to 100 m 2The concentration may be as low as / g, and within this range, it can uniformly adhere to the surface of the positive electrode active material, thereby imparting structural stability to the 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.

[0110] 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 ).

[0111] 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.

[0112] The regenerated positive electrode active material obtained in step (f) above may have a crystal structure with a axis length of 2.871 to 2.888 Å, preferably 2.872 to 2.878 Å, and more preferably 2.874 to 2.876 Å, measured by XRD, and within this range, there is an effect of improving the battery characteristics.

[0113] The regenerated positive electrode active material obtained in step (f) above may have a c-axis length of the crystal structure measured by XRD of 14.200 to 14.210 Å, preferably 14.202 to 14.208 Å, and more preferably 14.204 to 14.208 Å, and within this range, there is an effect of improving the battery characteristics.

[0114] The regenerated cathode active material obtained in step (f) above has a cell volume measured by XRD of, for example, 101.65 to 101.75 Å. 3 Preferably 101.67~101.72 Å 3 More preferably 101.68~101.71 Å 3 This is acceptable, and within this range, there is an effect of improving battery characteristics.

[0115] The regenerated cathode active material obtained in step (f) above may have a crystal size of 82 to 90 nm, preferably 84 to 88 nm, as measured by XRD, and within this range, there is an effect of improving the battery characteristics.

[0116] In this description, the lengths of the a-axis and c-axis of the crystal structure, the cell volume, and the crystal size measured by XRD can be measured by measurement methods commonly used in the art to which the present invention belongs. For example, the lengths of the a-axis and c-axis of the crystal structure and the cell volume can be measured by calculating the data obtained by X-ray diffraction analysis using CuKα rays as a source for the positive electrode active material using the Rietveld refinement method (XRD). The crystal size can be estimated using peak broadening of the X-ray diffraction data obtained by XRD analysis, and the crystal size can be obtained by quantitatively calculating it using Scherrer's equation.

[0117] The regenerated positive electrode active material obtained in step (f) above may have a thermal decomposition temperature measured by TGA (Thermogravimetric analysis) of, for example, 700°C or higher, preferably 720°C or higher, and more preferably 730-800°C. Within this range, it has the effect of having excellent thermal stability and improved battery characteristics.

[0118] Regenerated cathode active material The regenerated cathode active material of the present invention is characterized by being manufactured by the method for regenerating a cathode active material as described above. In such a case, it has the effect of improving the output performance of the battery and being excellent in electrochemical performance, resistance characteristics, and capacity characteristics.

[0119] Further, the regenerated cathode active material of the present invention is one or more selected from the group consisting of lithium nickel oxide (LNO)-based cathode active materials, nickel-cobalt-manganese (NCM)-based cathode active materials, nickel-cobalt-aluminum (NCA)-based cathode active materials, nickel-cobalt-manganese-aluminum (NCMA)-based cathode active materials, and lithium iron phosphate (LFP)-based cathode active materials. The length of the c-axis of the crystal structure measured by XRD (X-Ray Diffraction) is 14.200 to 14.210 Å, the cell volume is 101.65 to 101.75 Å 3 , and the crystallite size is 82 to 90 nm, and the thermal decomposition temperature measured by TGA (Thermogravimetric analysis) is 700 °C or higher. In such a case, it has the effect of being excellent in thermal stability, reducing the residual amount of lithium, and being excellent in the initial capacity and life characteristics of the secondary battery.

[0120] As yet another specific example, the regenerated cathode active material has the following Chemical Formula 1 (Chemical Formula 1) Li a Ni x Mn y Co z M w O 2+δ (In the above Chemical Formula 1, M contains one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.) It may be a compound represented by this, and in this case, it has the effect of being excellent in thermal stability, reducing the residual amount of lithium, and being excellent in the initial capacity and life characteristics of the secondary battery.

[0121] The regenerated positive electrode active material may have a crystal structure with a-axis length of 2.871 to 2.888 Å, preferably 2.872 to 2.878 Å, and more preferably 2.874 to 2.876 Å, measured by XRD, and within this range, there is an effect of improving battery characteristics.

[0122] The regenerated positive electrode active material may have a c-axis length of the crystal structure measured by XRD of, for example, 14.200 to 14.210 Å, preferably 14.202 to 14.208 Å, and more preferably 14.204 to 14.208 Å, and within this range, there is an effect of improving battery characteristics.

[0123] The aforementioned regenerated cathode active material has a cell volume of 101.65 to 101.75 Å, as measured by XRD, for example. 3 Preferably 101.67~101.72 Å 3 More preferably 101.68~101.71 Å 3 This is acceptable, and within this range, there is an effect of improving battery characteristics.

[0124] The regenerated positive electrode active material may have a crystal size of 82-90 nm, preferably 84-88 nm, as measured by XRD, and within this range, there is an effect of improving battery characteristics.

[0125] The aforementioned regenerated positive electrode active material may have a thermal decomposition temperature measured by TGA (Thermogravimetric Analysis) of, for example, 700°C or higher, preferably 720°C or higher, and more preferably 730-800°C. Within this range, it exhibits excellent thermal stability and improves battery characteristics.

[0126] The regenerated 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 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 physicochemical properties as well.

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

[0128] 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 positive electrode active material itself.

[0129] The aforementioned surface coating is preferably applied to the surface using a coating agent containing one or more of metals, organometallics, and carbon components in a solid-phase or liquid-phase manner, followed by heat treatment at 100 to 1200°C, more preferably 200 to 1000°C, and even more preferably 250 to 800°C. In this case, the structural stability and electrochemical performance are improved while maintaining the properties of the positive electrode active material itself.

[0130] Figure 4 below is a flowchart illustrating one embodiment of the present invention, showing the regeneration process for the positive electrode active material.

[0131] Referring to Figure 4, first, the waste cathode composition is prepared (step S10).

[0132] The waste cathode composition is a defective cathode composition slurry that does not meet the standards in terms of solid content concentration, composition ratio, or viscosity, generated during the manufacturing process of the cathode composition; a cathode composition slurry in which problems such as filter clogging occurred during the process of coating the metal foil; or a cathode composition slurry remaining after coating the metal foil.

[0133] The waste positive electrode composition may contain a positive electrode active material, a conductive material, and a binder, and may be in the form of a slurry.

[0134] The aforementioned waste cathode composition may further contain a dispersant.

[0135] Next, the waste cathode composition is heat-treated to remove the solvent (step S20).

[0136] Here, the heat treatment is performed to facilitate the subsequent powdering process by drying and removing the solvent in the waste cathode composition.

[0137] The heat treatment can be carried out in an air or oxygen atmosphere. Specifically, it can be carried out in an air atmosphere, which has the advantage of facilitating the subsequent powdering process by removing the solvent.

[0138] The heat treatment temperature may be, for example, 80 to 120°C, or more specifically, 100°C. Within this range, all solvent is removed, which has the advantage of facilitating the subsequent powdering process.

[0139] The aforementioned heat treatment time may be, for example, 30 minutes to 4 hours, or more specifically, 2 hours. Within this range, the solvent is completely dried and removed, which has the advantage of facilitating the subsequent powdering process.

[0140] The heat treatment described above is carried out using various types of furnaces, for example, a box-type furnace, and preferably a rotary kiln capable of continuous processing is used, taking productivity into consideration.

[0141] Next, the waste cathode composition from which the solvent has been removed is powdered (step S30).

[0142] Here, pulverization is performed to facilitate contact between the waste cathode composition and air or oxygen in the subsequent heat treatment step.

[0143] The aforementioned pulverization is performed by dry grinding, and can be done using a hand mill, pin mill, disc mill, cutting mill, or hammer mill. For example, a pin mill can be used.

[0144] The powdered waste cathode composition can be sieved, preferably using a sieve with a mesh size of 230 to 500, and more specifically, using a sieve with a mesh size of 325. As described above, sieving makes the particle size of the cathode composition uniform and removes larger particles, which has the advantage of improving the degree of dispersion when manufacturing the recycled cathode active material as a slurry.

[0145] The powdered waste cathode composition has an average particle size of preferably 45 μm or less, and may be 10 to 35 μm in specific examples. In this case, there is the advantage that the binder and conductive material are cleanly removed in the subsequent heat treatment process.

[0146] Next, the powdered waste cathode composition is heat-treated (step S40).

[0147] Here, the heat treatment is performed to thermally decompose the binder and conductive material in the powdered waste cathode composition.

[0148] The powdered waste cathode composition is heat-treated at 300-650°C to remove the binder and conductive material, and the cathode active material is recovered.

[0149] The heat treatment in step S40 is carried out in an air or oxygen atmosphere, specifically in air.

[0150] Through the heat treatment in air described above, the binder and conductive material in the positive electrode active material layer are thermally decomposed into CO2 and H2O and removed. Since the conductive material and binder are removed, the positive electrode active material is obtained from the positive electrode composition.

[0151] It is important that the aforementioned heat treatment be carried out in air or in the presence of oxygen. However, if the heat treatment is performed in a reducing gas or inactive gas atmosphere, the binder and conductive material will carbonize instead of being thermally decomposed. When carbonization occurs, carbon components remain on the surface of the positive electrode active material, reducing the performance of the reused positive electrode active material. However, when the heat treatment is performed in air, the carbon components in the binder and conductive material react with oxygen and disappear as gases such as CO and CO2, so the binder and conductive material are completely removed.

[0152] 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, and above 650°C, cation mixing occurs due to a change in the structure of the positive electrode active material.

[0153] In this description, cation mixing refers to the process where, during heat treatment at high temperatures, lithium, with its high vapor pressure, evaporates more easily than other elements, leaving an empty layer of lithium ions, and Ni... 2+ This refers to an irreversible reaction in which a substance is substituted.

[0154] The heat treatment preferably has a temperature rise rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, the burden on the heat treatment apparatus is suppressed, and there is an advantage in that thermal shock and other problems are not caused to the positive electrode composition.

[0155] The aforementioned heat treatment can be carried out for a period of time sufficient to allow the binder and conductive material to be sufficiently thermally decomposed, preferably for 30 minutes or more, more preferably for 30 minutes to 5 hours, and specifically for around 30 minutes. Within this range, the binder and conductive material are sufficiently thermally decomposed, and the thermal decomposition efficiency is excellent.

[0156] 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.

[0157] After the heat treatment, the device can be slowly or rapidly cooled in the atmosphere.

[0158] Next, lithium precursor is added to the recovered positive electrode active material and annealing is performed (step S50).

[0159] Since lithium is lost from the positive electrode active material during the preceding steps S30 and S40, step S50 replenishes the amount of lithium lost. In addition, since deformation structures (for example, Co3O4 in the case of LCO active material) may form on the surface of the positive electrode active material during the preceding steps, step S50 improves the battery characteristics of the regenerated positive electrode active material by restoring the crystal structure of the positive electrode active material through annealing, thereby restoring it to the level of a newly manufactured positive electrode active material. Here, "newly manufactured" is the opposite concept of "regenerated," meaning it is manufactured for the first time, and is the same word as "raw material" used in the examples. Furthermore, the life characteristics and resistance characteristics of the regenerated positive electrode active material are improved by including calcium or calcium compounds in the positive electrode active material.

[0160] The lithium precursor includes one or more of LiOH, Li2CO3, LiNO3, and Li2O, and in one embodiment, LiOH is used.

[0161] 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 lost lithium will leave unreacted lithium precursor in the regenerated positive electrode active material, which increases resistance; therefore, it is necessary to add an appropriate amount of lithium precursor.

[0162] In one embodiment, based on the case where the molar ratio of lithium in the newly generated positive electrode active material is 1 in relation to other metals (M), an amount of lithium precursor can be added such that the lithium molar ratio is 0.001 to 0.4. Preferably, an amount of lithium precursor can be added such that the lithium molar ratio is 0.01 to 0.4, and more preferably, an amount of lithium precursor can be added such that the lithium molar ratio is 0.09 to 0.2. As a specific example, by adding lithium precursor in proportion to the ratio lost relative to the lithium content in the newly generated positive electrode active material, based on the results of ICP analysis, a capacity improvement effect equivalent to that of the newly generated positive electrode active material can be obtained. Here, the results of ICP analysis have an error value of approximately ±0.02.

[0163] In one embodiment, the lithium precursor may be added in an amount corresponding to 1 to 25 mol%, more preferably 1 to 20 mol%, and even more preferably 3 to 17 mol%, when the total lithium contained in the positive electrode active material of the raw materials is considered to be 100 mol%, and within this range, no residual precursor that can increase the resistance of the regenerated positive electrode active material remains, which is very useful for improving battery characteristics.

[0164] The annealing process is carried out, for example, in air under conditions of 400 to 1000°C, preferably under conditions of 600 to 900°C, and this temperature needs to be modified within a limited range depending on the type of lithium precursor.

[0165] The annealing temperature is preferably a temperature that exceeds the melting point of the lithium precursor. However, temperatures exceeding 1000°C should not exceed 1000°C, as this will cause thermal decomposition of the positive electrode active material and a decrease in performance. For example, when Li2CO3 is used as the lithium precursor, the annealing temperature is preferably 700 to 900°C, more preferably 710 to 780°C, and even more preferably 750 to 780°C. When LiOH is used as the lithium precursor, the annealing temperature is preferably 400 to 600°C, more preferably 450 to 480°C, and even more preferably 470 to 480°C.

[0166] The annealing time is, for example, often 1 hour or more, preferably 15 hours or less, and more preferably 4 to 6 hours. 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 apparatus can be the same as or similar to that used in the heat treatment step S40.

[0167] The annealing temperature can preferably be reached at a heating rate of 1 to 10°C / min, and specifically at a heating rate of 2 to 4°C / min. In this case, the crystallinity of the regenerated cathode active material is further increased, which has the effect of improving the battery characteristics of the regenerated cathode active material.

[0168] Step S50, annealing, includes, for example, a cooling step, which may, specifically, 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.

[0169] Next, as a cleaning step, the annealed positive electrode active material is washed with a cleaning solution (step S60).

[0170] The cleaning in step S60 requires a residual lithium removal step because lithium precursors that did not participate in the reaction in the annealing step S50 are present on the surface of the positive electrode active material in the form of LiOH and Li2CO3. These impurities in the form of LiOH and Li2CO3 can later react with the electrolyte, degrading the battery's performance and generating gas, so they must be thoroughly removed.

[0171] Preferably, the cleaning is performed by mixing the annealed positive electrode active material with the cleaning solution in a weight ratio of 1:3 to 1:20. Specifically, the annealed positive electrode active material is mixed with the cleaning solution in a weight ratio of 1:10. In this case, residual lithium is removed with a small amount of cleaning solution, which has the advantage of obtaining a positive electrode active material with excellent initial discharge capacity and life characteristics.

[0172] The cleaning solution may, for example, be water or an aqueous solution of a basic lithium compound, preferably water. In this case, the cleaning solution effectively removes lithium precursors such as LiOH and Li2CO3 that tend to remain on the surface of the positive electrode active material, thereby significantly improving the output performance of the battery.

[0173] 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.

[0174] The mixing of the annealed positive electrode active material and the cleaning solution is preferably carried out by stirring, and the stirring is not particularly limited, but may be mechanical stirring or ultrasonic stirring.

[0175] The mechanical stirring is preferably carried out at 100 to 1000 rpm for 5 to 30 minutes, and more preferably at 250 to 350 rpm for 5 to 10 minutes.

[0176] The filtration is preferably reduced-pressure filtration using a filter, and the drying is preferably vacuum drying at 50 to 140°C.

[0177] Next, a surface coating can be applied to the cleaned positive electrode active material (step S70).

[0178] The aforementioned surface coating involves, for example, applying a coating agent containing a metal, organometallic, or carbon component to the surface in a solid-phase or liquid-phase manner, 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 performance of the battery will deteriorate due to the thermal decomposition of the positive electrode active material.

[0179] 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.

[0180] 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.

[0181] secondary battery The secondary battery of the present invention includes a regenerated positive electrode active material produced by the method for regenerating the positive electrode active material. In this case, the battery exhibits excellent thermal stability, significantly improved output performance (rate performance), and superior electrochemical performance, resistance characteristics, and capacitance characteristics.

[0182] The secondary battery of the present invention may include all of the above-described positive electrode active material and regeneration method. Therefore, redundant descriptions thereof are omitted here.

[0183] 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.

[0184] [Examples] Example 1 An attempt was made to manufacture a positive electrode composition slurry with a composition ratio of positive electrode active material:conductive material:binder of 97.5:1.5:1. However, the manufactured positive electrode composition slurry had a composition ratio of 98.5:1:0.5, which was not correct, so the prepared positive electrode composition was discarded.

[0185] At this time, the waste cathode composition contained an NCMA-based lithium composite transition metal oxide (with a molar ratio of Ni:Co:Mn:Al of 88:7:4:1) as the cathode active material, polyvinylidene fluoride (PVDF) as the binder, Super-C as the conductive material, and N-methyl-2-pyrrolidone as the solvent (cathode active material:conductive material:binder = 98.5:1:0.5). The waste cathode composition was heat-treated in air at 100°C for 2 hours to dry and remove the solvent.

[0186] The waste cathode composition from which the solvent had been removed was dry-milled using a pin mill, and then sieved using a sieve with a mesh size of 325 to obtain waste cathode composition powder with an average particle size of 35 μm or less.

[0187] The aforementioned waste cathode composition powder was heat-treated in air at 550°C for 30 minutes to remove the binder and conductive material, and the cathode active material was recovered. The temperature rise rate to reach the heat treatment temperature was 5°C / min, and air was supplied at 3 L / min.

[0188] The recovered positive electrode active material was immediately treated with LiOH as a lithium precursor without a washing step, and annealed in air at 650°C for 5 hours. At this time, the lithium precursor was added in an amount equivalent to 15 mol% when the total amount of lithium in the positive electrode active material used as raw material for the positive electrode composition was set to 100 mol%.

[0189] The annealed positive electrode active material and distilled water were mixed in a 1:10 weight ratio, stirred for 5 minutes under 300 rpm, and then filtered under reduced pressure to obtain the solids. The solids were vacuum-dried at 100-130°C for 12 hours to obtain the washed positive electrode active material. Air was supplied at a rate of 3 L / min.

[0190] 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. The temperature rise rate until the heat treatment temperature was reached was 2°C / min, and air was supplied at 3 L / min.

[0191] In this document, 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.

[0192] Comparative Example 1 In this example, the procedure was carried out in the same manner as in Example 1, except that the waste cathode composition from which the solvent had been removed was immediately heat-treated in air at 550°C for 30 minutes, without going through the step of dry grinding and sieving to produce a powder.

[0193] Reference example Instead of reused active material, we used fresh NCMA-based lithium composite transition metal oxide (with a molar ratio of Ni:Co:Mn:Al of 88:7:4:1).

[0194] [Test Example I: Residual Lithium Content] The residual lithium content of the positive electrode active material annealed in Example 1 and Comparative Example 1 was measured as follows, and the results are shown in Table 1 below.

[0195] *Residual lithium content: 5 g of annealed positive electrode active material was dispersed in 100 ml of distilled water and mixed at 300 rpm for 5 minutes. The positive electrode active material was then filtered, and the resulting filtrate was titrated with a 0.1 M HCl solution while measuring the change in pH to obtain a pH titration curve. Using the obtained pH titration curve, the residual amounts of LiOH and Li2CO3 in the positive electrode active material were calculated.

[0196] [Table 1]

[0197] As can be seen from Table 1 above, in Example 1, where the cathode composition from which the solvent was removed according to the present invention was powdered and then heat-treated, the residual lithium content was significantly reduced compared to Comparative Example 1, where the heat treatment was performed without the powdering step.

[0198] [Test Example II: Residual Fluorine (F) Content] The fluorine (F) content remaining in the positive electrode active material annealed in Example 1 and Comparative Example 1 was measured using an ICP analyzer, and the results are shown in Table 2 below. While this can be measured using a general ICP analyzer commonly used in laboratories, there is no deviation due to the measuring device or method.

[0199] [Table 2]

[0200] As can be seen from Table 2 above, Example 1, in which the positive electrode composition from which the solvent according to the present invention was removed was powdered and then heat-treated, had a higher residual fluorine content than Comparative Example 1. From this, it can be seen that in Example 1, the conductive material and binder were sufficiently thermally decomposed and cleanly removed compared to Comparative Example 1. When the conductive material and binder in the positive electrode composition are thermally decomposed, they exist on the surface of the positive electrode active material in the form of LiF. In Example 1, which was heat-treated after powdering, the positive electrode composition came into smooth contact with air, so the conductive material and binder were thermally decomposed without residue, resulting in a high residual fluorine content. In Comparative Example 1, since the powdering step was not performed, the positive electrode composition did not come into smooth contact with air, and therefore the thermal decomposition of the conductive material and binder was not sufficiently carried out, resulting in a low residual fluorine content.

[0201] [Test Example III: XRD Analysis] The regenerated cathode active materials or newly produced cathode active materials prepared in Example 1 and the Reference Example were subjected to XRD analysis, and the lengths of the a-axis and c-axis of the crystal structure, the cell volume, and the crystal size were measured and are shown in Table 3 below.

[0202] [Table 3]

[0203] As shown in Table 3 above, it can be confirmed that Example 1 has a similar level of a-axis length, c-axis length, cell volume, and crystal size to the reference example. From this, it can be seen that the structure of the regenerated cathode active material in Example 1 was restored to the level of or higher than that of the raw material cathode active material.

[0204] [Test Example IV: Evaluation of Coin Half Cells] The electrochemical performance of the regenerated or newly produced cathode active materials manufactured in Example 1, Comparative Example 1, and Reference Example was measured through evaluation of a coin half cell (hereinafter referred to as "CHC") as described below, and the results are shown in Figures 1 and 2 below.

[0205] *CHC production: 96% by weight of recycled cathode active material, 2% by weight of carbon black as a conductive material, and 2% by weight of PVdF as a binder were weighed and mixed with N-methyl-2-pyrrolidone (NMP) to produce a slurry. After producing a cathode by coating aluminum foil with this slurry, CHC was produced, and its electrochemical performance (charging capacity CH, discharge capacity DCH, and efficiency Eff (%)) was evaluated under conditions containing ethylene carbonate (EC):dimethylmethyl carbonate (DMC) = 3:7 (by weight ratio) as the electrolyte and other additives.

[0206] *Evaluation of initial CHC capacity (CH and DCH): Each cell underwent a single charge-discharge cycle at 25°C under the following conditions. The results are shown in Figure 1 below.

[0207] Charging (CH): 0.2C, CC (Constant Current) / CV (Constant Voltage), 4.25V, 0.05C cutoff Discharge (DCH): 0.2C, CC, 2.5V cutoff

[0208] *Evaluation of CHC high-temperature lifetime 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 1, which is shown in Figure 2 below.

[0209] Charging: 0.33C, CC / CV, 4.5V, 0.05C cutoff Discharge: 0.33C, CC, 3.0V, 0.05C cutoff

[0210] [Formula 1] Capacity retention rate (%) = (Discharge capacity after N cycles / Discharge capacity after 1 cycle) × 100

[0211] Figure 1 below shows the results of CHC evaluation performed on the regenerated cathode active materials produced in Example 1 and Comparative Example 1, respectively, and is a graph showing the initial charge / discharge capacity.

[0212] As shown in Figure 1 below, the regenerated cathode active material according to the present invention (Example 1) exhibited superior initial charge / discharge capacity compared to Comparative Example 1.

[0213] Furthermore, Figure 2 below shows the results of CHC evaluation performed on the regenerated or newly generated cathode active materials produced in Example 1 and the Reference Example, respectively, and is a graph showing the change in capacity retention rate with respect to the number of cycles (Cycle No.). Referring to this, it was confirmed that the regenerated cathode active material according to the present invention (Example 1) had a capacity retention rate at high temperatures that was similar to or better than that of the newly generated cathode active material (Reference Example) up to 20 cycles, and after 20 cycles, it was confirmed that the capacity retention rate of Example 1 decreased slightly compared to the Reference Example.

[0214] [Test Example V: Analysis of Heat Treatment Temperature by TGA] The weight change rate due to heat treatment temperature was analyzed for the regenerated cathode active materials produced from Example 1 and Comparative Example 1 using TGA, and the results are shown in Figure 3 below. At this time, the temperature conditions were set to start at 50°C and end at 900°C, with a heating rate of 5°C / min.

[0215] Referring to Figure 3 below, thermal decomposition of Example 1 began at 740°C or higher, while thermal decomposition of Comparative Example 1 began at 600°C. From this, it can be seen that Example 1 has superior thermal stability compared to Comparative Example 1.

Claims

1. (a) A step of heat-treating a waste positive electrode composition containing positive electrode active material, conductive material, binder and solvent to remove the solvent, (b) A step of pulverizing the waste cathode composition from which the solvent has been removed, (c) A step of heat-treating the powdered waste cathode composition at 300 to 650°C to remove the binder and conductive material and recover the cathode active material, (d) Adding a lithium precursor to the recovered cathode active material and annealing it at 400 to 1000°C, (e) A method for regenerating a positive electrode active material, comprising the step of washing the annealed positive electrode active material with a cleaning solution.

2. The method for regenerating a positive electrode active material according to claim 1, wherein the waste positive electrode composition in step (a) is in the form of a slurry.

3. The method for regenerating a positive electrode active material according to claim 1, wherein the heat treatment in step (a) is performed at 80 to 120°C.

4. The method for regenerating a positive electrode active material according to claim 1, wherein the heat treatment in step (a) is performed for 30 minutes to 4 hours.

5. The method for regenerating a positive electrode active material according to claim 1, wherein the pulverization step in (b) is performed by dry grinding.

6. The method for regenerating a positive electrode active material according to claim 5, wherein the dry grinding is performed using a hand mill, pin mill, disc mill, cutting mill, or hammer mill.

7. The method for regenerating a positive electrode active material according to claim 1, wherein the pulverization step in (b) further comprises a sieving step after pulverization.

8. The method for regenerating a positive electrode active material according to claim 1, wherein the average particle size of the powder obtained in step (b) is 45 μm or less.

9. The method for regenerating a positive electrode active material according to claim 1, 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, nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and lithium iron phosphate (LFP)-based positive electrode active material.

10. The method for regenerating a positive electrode active material according to claim 1, wherein the solvent is one or more selected from the group consisting of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, and water.

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

12. The method for regenerating a positive electrode active material according to claim 1, wherein the lithium precursor in step (d) 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.

13. The method for regenerating a positive electrode active material according to claim 1, wherein the cleaning solution is water or an aqueous solution of a basic lithium compound.

14. The method for regenerating the positive electrode active material according to claim 1, further comprising the step of surface coating the cleaned positive electrode active material.

15. 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, nickel-cobalt-manganese-aluminum (NCMA)-based cathode active materials, and lithium iron phosphate (LFP)-based cathode active materials. The c-axis length of the crystal structure, as measured by XRD (X-ray diffraction), was 14.200–14.210 Å, and the cell volume was 101.65–101.75 Å. ３ , and the crystal size is 82-90 nm. A positive electrode active material characterized by having a thermal decomposition temperature of 700°C or higher, as measured by TGA (thermogravimetric analysis).

16. The positive electrode active material according to claim 15, wherein the surface of the positive electrode active material is coated with a coating agent containing metal or carbon.

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