Method for regenerating positive electrode active material, regenerated positive electrode active material manufactured thereby, and secondary battery comprising same

Abstract

The present invention relates to a method for regenerating a regenerated positive electrode active material, a regenerated positive electrode active material manufactured thereby, and a secondary battery including same and, more specifically, to a method for regenerating a positive electrode active material, a regenerated positive electrode active material manufactured thereby, and a secondary battery including same, the method comprising the steps of: recovering the cathode active material by thermally treating a spent positive electrode that has a cathode active material layer formed on a current collector, to thermally decompose the binder and conductive material in the positive electrode active material layer; performing primary milling on the recovered positive electrode active material; adding a lithium precursor to the primarily annealed positive electrode active material, followed by annealing at 400 to 1000°C; and performing secondary milling on the annealed positive electrode active material. According to the present invention, by performing primary milling without a washing process on the positive electrode active material recovered after thermal treatment of the spent positive electrode, adding a lithium precursor to the primarily milled positive electrode active material, annealing, and then performing secondary milling, damage to the particle surface of the positive electrode active material is prevented, uniformity of the particle size of the regenerated positive electrode active material is achieved, and particle growth is suppressed. This results in a method for regenerating a positive electrode active material with excellent battery performance.

Description

Method for regenerating a cathode active material, a regenerated cathode active material manufactured thereby, and a secondary battery comprising the same

[0001] 〔Cross-citation with the applicant(s)〕

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0103933, dated August 9, 2023, the entire contents of which are incorporated herein by reference.

[0003] The present invention relates to a method for regenerating a regenerated positive electrode active material, a regenerated positive electrode active material manufactured thereby, and a secondary battery including the same, and more particularly, to a method for regenerating a positive electrode active material, which is recovered after heat-treating a waste positive electrode and then milling the recovered positive electrode active material without a washing process, adding a lithium precursor to the first-milled positive electrode active material and annealing it, and then milling the annealed positive electrode active material a second time, thereby preventing surface damage to the positive electrode active material, uniformizing the particle size of the regenerated positive electrode active material, and minimizing particle size increase, thereby providing excellent battery characteristics, and furthermore, is environmentally friendly because no acid is used in the process for recovering and regenerating the positive electrode active material, and thus, process costs are reduced because neutralization and wastewater treatment are not required, and since the positive electrode active material is regenerated as is without decomposition, no metal elements are discarded, and since no organic solvent is used, there is no generation of toxic gases or risk of explosion, and the economic feasibility and productivity are greatly improved, and to a regenerated positive electrode active material manufactured thereby, and a secondary battery including the same.

[0004] A lithium secondary battery is largely composed of a cathode in which a positive active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative active material layer is coated on a metal foil such as copper, a separator that prevents the positive and negative electrodes from mixing, and an electrolyte that allows lithium ions to move between the positive and negative electrodes.

[0005] The positive electrode active material layer mainly uses lithium oxide as an active material, and the negative electrode active material layer mainly uses carbon material as an active material. The lithium oxide generally contains rare metals such as cobalt, nickel, or manganese, and thus, much research is being conducted to recover and recycle rare metals from the positive electrode of a lithium secondary battery that is discarded after use or the positive electrode scrap generated in the lithium secondary battery manufacturing process (hereinafter referred to as “spent positive electrode”).

[0006] Conventional techniques for recovering rare metals from spent anodes mostly involve dissolving the spent anodes in hydrochloric acid, sulfuric acid, or nitric acid, and then extracting cobalt, manganese, nickel, etc. with an organic solvent to use them again as raw materials for synthesizing anode active materials.

[0007] However, the method of extracting rare metals using acids has the problem of environmental pollution, requires a neutralization process and a wastewater treatment process, which significantly increases the process cost, and has the disadvantage of not being able to recover lithium, the main metal of the positive electrode active material.

[0008] To overcome these shortcomings, a method of directly regenerating the positive electrode active material from the spent positive electrode without decomposing it (direct recycled method) has been recently studied, and four types of this method have been introduced, including calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

[0009] However, although the above-mentioned firing method is a simple process, it has the disadvantages of generating foreign substances on the surface of the regenerated positive electrode active material that reduce the output performance of the battery, generating waste gas, and consuming a lot of energy.

[0010] In addition, the above solvent dissolution method can obtain a regenerated positive electrode active material with a relatively clean surface, but has the disadvantage of poor stability due to the solvent such as N-methyl-2-pyrrolidone (NMP) used to dissolve the binder being a toxic gas and having a risk of explosion, and requiring an expensive solvent recovery process.

[0011] In addition, the above aluminum foil melting method has good process stability, low process cost, and easy binder removal, but has the disadvantages of generating foreign substances that are difficult to remove on the surface of the regenerated positive electrode active material, and generating hydrogen gas during the process of removing the aluminum foil, which poses a risk of explosion.

[0012] Lastly, although the above crushing and screening method has the advantage of being the simplest process, it has the disadvantages of being difficult to completely separate the current collector and the positive electrode active material, the particle size distribution of the positive electrode active material changes during the crushing process, and the binder remains, which deteriorates the battery characteristics of the regenerated positive electrode active material.

[0013] Therefore, there is an urgent need to develop a method for safely regenerating cathode active materials with improved output performance without discarding metal elements from the waste cathode, in an environmentally friendly manner, with fewer processes and costs.

[0014] In order to solve the problems of the prior art as described above, the present invention provides a method for regenerating a positive electrode active material having excellent battery characteristics, which comprises the steps of: first milling a positive electrode active material recovered after heat-treating a waste positive electrode without a washing process; adding a lithium precursor to the first-milled positive electrode active material; annealing; and second-milling, thereby preventing surface damage to the positive electrode active material; uniformizing the particle size of the regenerated positive electrode active material; and minimizing particle size increase. In addition, the method is environmentally friendly because no acid is used in the recovery and regeneration process of the positive electrode active material; thus, neutralization and wastewater treatment are not required, thereby reducing process costs; and since the positive electrode active material is regenerated as it is without decomposition, no metal elements are discarded; since no organic solvent is used, there is no generation of toxic gases or risk of explosion; and the method for regenerating a positive electrode active material having excellent battery characteristics is provided.

[0015] In addition, the present invention aims to provide a secondary battery including a positive electrode active material having excellent battery characteristics.

[0016] The above and other objects of the present invention can all be achieved by the present invention described below.

[0017] In order to achieve the above object, I) the present invention provides a method for regenerating a positive electrode active material, characterized by comprising the steps of: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector to thermally decompose a binder and a conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer; first milling the recovered positive electrode active material; adding a lithium precursor to the first-milled positive electrode active material and annealing it at 400 to 1000°C; and second milling the annealed positive electrode active material.

[0018] II) In the above I), the positive electrode active material layer is preferably at least one selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, a nickel-cobalt-manganese (NCM)-based positive electrode active material, a nickel-cobalt-aluminum (NCA)-based positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and may contain 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li.

[0019] III) In the above I) or II), the heat treatment can preferably be performed at 300 to 650°C in an air or oxygen atmosphere.

[0020] IV) In the above I) to III), the first and second milling can preferably be performed using a centrifugal mill or a jet mill, respectively.

[0021] V) In the above I) to IV), the first and second milling can preferably be performed at 6000 to 20000 rpm, respectively.

[0022] VI) In the above I) to IV), the positive electrode active material obtained after the second milling may preferably have an increase rate of average particle diameter of 14% or less compared to the positive electrode active material in the waste positive electrode, and a standard deviation of the average particle diameter may be 3.0 or less.

[0023] VII) In the above I) to V), the lithium precursor may preferably include at least one of LiOH, Li2CO3, LiNO3, and Li2O.

[0024] VIII) In the above I) to VII), the lithium precursor may preferably be added in an amount capable of providing lithium corresponding to 1 to 40 mol% when the total lithium in the raw material positive electrode active material is 100 mol%.

[0025] IX) In the above I) to VIII), the annealing can preferably be performed at 400 to 1000°C.

[0026] X) In the above I) to IX), the method for regenerating the positive electrode active material may preferably include a step of washing the secondarily milled positive electrode active material; a step of surface-coating the secondarily milled positive electrode active material; or a step of surface-coating the secondarily milled positive electrode active material after washing it.

[0027] XI) In the above I) to X), the weight ratio of the annealed positive electrode active material and the washing solution in the washing step may preferably be 1:0.5 to 1:10.

[0028] XII) In the above I) to XI), the surface coating may be preferably performed by coating at least one of a metal, an organic metal, and a carbon component on the surface in a solid or liquid manner and then heat-treating at 100 to 1200°C.

[0029] In addition, XIII) The present invention provides a regenerated cathode active material, characterized in that it is at least one selected from the group consisting of a lithium nickel oxide (LNO) cathode active material, a nickel-cobalt-manganese (NCM) cathode active material, a nickel-cobalt-aluminum (NCA) cathode active material, and a nickel-cobalt-manganese-aluminum (NCMA) cathode active material, and contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li, and the standard deviation of the average particle diameter of the regenerated cathode active material is 3.0 or less.

[0030] XIV) In the above XIII), the positive electrode active material may preferably have a surface coated with a coating agent containing metal or carbon.

[0031] XV) In the above XIII) or XIV), the metal may preferably be boron (B), tungsten (W) or a mixture thereof.

[0032] In addition, XVI) The present invention provides a regenerated positive electrode active material characterized by being manufactured by a positive electrode active material regeneration method according to I) to XII).

[0033] In addition, XVII) The present invention provides a secondary battery characterized by including a regenerative positive electrode active material according to any one of XIII) to XVI).

[0034] According to the present invention, after heat-treating a waste positive electrode, the recovered positive electrode active material is first milled without a washing process, a lithium precursor is added to the first-milled positive electrode active material, annealed, and then second-milled, thereby preventing surface damage to the positive electrode active material and reducing the process cost, and the particle size of the regenerated positive electrode active material is uniform and the increase in particle size is minimized, so that the particle distribution is similar to that of the positive electrode active material in the waste positive electrode, thereby improving battery characteristics, and is environmentally friendly because it does not use acid, and thus the process cost is reduced because neutralization and wastewater treatment are not required, and the positive electrode active material is regenerated as it is without decomposition, so that no metal elements are discarded, and the current collector is not dissolved, so that it can be recovered, and there is no risk of toxic gases or explosion because no organic solvent is used, and there is an effect of providing a method for regenerating a positive electrode active material suitable for mass production using an easy-to-manage process such as heat treatment or sedimentation, a positive electrode active material regenerated thereby and having excellent battery characteristics, and a secondary battery including the same.

[0035] The following drawings attached to this specification illustrate embodiments of the present invention and, together with the detailed description given below, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be construed as being limited to the matters described in these drawings.

[0036] Figure 1 is a drawing showing anode scrap that is discarded after cutting an electrode plate from a cathode sheet.

[0037] Figure 2 is a graph showing the particle distribution of the regenerated positive electrode active material or the newly produced positive electrode active material obtained in Example 1, Reference Example, and Comparative Examples 1 to 3.

[0038] Figure 3 is a graph showing the particle distribution of the regenerated positive electrode active material or the newly produced positive electrode active material obtained in Examples 1 and 2, Reference Example, Comparative Examples 1 and 4.

[0039] Figure 4 is a flowchart for a regeneration process of a positive electrode active material according to the present invention.

[0040]

[0041] The present inventors, while studying a method for improving the battery characteristics of a recycled positive electrode active material in a method for directly regenerating the positive electrode active material from a waste positive electrode without decomposing the positive electrode active material (direct recycled method), discovered that when the positive electrode active material recovered after heat treatment is first milled without washing, a lithium precursor is added to the first-milled positive electrode active material, annealed, and then second-milled, surface damage of the regenerated positive electrode active material is prevented, the particle size is uniformized, and the increase in particle size is reduced, so that the particle distribution becomes similar to that of the positive electrode active material in a virgin positive electrode, thereby improving the battery characteristics of the regenerated positive electrode active material, and based on this, they devoted themselves to further research and completed the present invention.

[0042]

[0043] Hereinafter, a method for regenerating a positive electrode active material of the present invention, a positive electrode active material regenerated therefrom, and a secondary battery including the same are described in detail.

[0044] However, the terms or words used in this specification and claims cannot be interpreted as limited to their usual or dictionary meanings, and should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own application in the best way. Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are only one embodiment of the present invention and do not represent all of the technical idea of ​​the present invention, and it should be understood that there may be various equivalents and modified examples that can replace them, and that they can be arranged, replaced, combined, separated, or designed in various other configurations.

[0045] All technical and scientific terms used in this document, unless otherwise defined, have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains.

[0046]

[0047] Method for regenerating positive electrode active material

[0048] The method for regenerating a positive electrode active material of the present invention comprises the steps of: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector to thermally decompose a binder and a conductive material within the positive electrode active material layer, thereby recovering the positive electrode active material within the positive electrode active material layer; milling the recovered positive electrode active material for the first time; adding a lithium precursor to the positive electrode active material subjected to the first milling and annealing at 400 to 1000°C; And a step of secondary milling of the annealed positive electrode active material; In this case, surface damage of the regenerated positive electrode active material is prevented, process costs are reduced, and the particle size of the regenerated positive electrode active material is uniform and the increase in particle size is minimized, thereby providing a positive electrode active material with excellent battery characteristics, and in addition, since no acid is used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly, and since neutralization and wastewater treatment are not required, process costs are reduced, and since the positive electrode active material is regenerated as it is without decomposition, no metal elements are discarded, and since the current collector is not dissolved, its recovery is possible, and since no organic solvent is used, there is no risk of toxic gas generation or explosion, and since a process that is easy to manage, such as heat treatment or sedimentation, it has the advantage of being suitable for mass production.

[0049] Below, the method for regenerating the positive electrode active material is explained in detail step by step.

[0050]

[0051] (a) A step of recovering positive electrode active material from a waste positive electrode.

[0052] According to the present invention, the step of recovering a positive electrode active material from a waste positive electrode (a) may preferably be a step of recovering a positive electrode active material in a positive electrode active material layer by heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector to thermally decompose a binder and a conductive material in the positive electrode active material layer, and in this case, the process is simple and has the effect of cleanly removing the binder, conductive material, and current collector.

[0053] The above-mentioned waste positive electrode may preferably be a positive electrode separated from a lithium secondary battery discarded after use, a defective positive electrode sheet or positive electrode scrap generated in a lithium secondary battery manufacturing process, and more preferably, a positive electrode scrap remaining after punching out a positive electrode plate from a positive electrode sheet.

[0054]

[0055] The positive electrode active material layer of the above step (a) may preferably include a positive electrode active material, a binder, and a conductive material.

[0056]

[0057] The above-mentioned positive electrode active material layer may be at least one selected from the group consisting of, for example, a lithium nickel oxide (LNO)-based positive electrode active material, a nickel-cobalt-manganese (NCM)-based positive electrode active material, a nickel-cobalt-aluminum (NCA)-based positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and in this case, excellent reversible capacity and thermal stability are achieved.

[0058] The above-described positive electrode active material may be at least one 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 compound such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide such as LiNiO2; nickel manganese-based lithium composite metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co), and more preferably, nickel manganese-based lithium composite metal oxide, NCM-based lithium composite transition metal oxide, or a mixture thereof, in which case, excellent reversible capacity and thermal stability are achieved.

[0059] As another specific example, the positive electrode active material is represented by the following chemical formula 1

[0060] [Chemical Formula 1]

[0061] Li a Ni x Mn y Co z M w O 2+δ

[0062] (In the above chemical formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti and Mg, and 1 <a≤0.1, 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=1이다.)로 표시되는 화합물일 수 있다.

[0063]

[0064] The above-mentioned positive electrode active material contains, for example, 60 mol% or more of Ni, preferably 80 mol% or more of Ni, and more preferably 81 mol% or more of Ni based on 100 mol% of the total metals excluding Li, and within this range, it has excellent effects in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0065] In this description, the Ni content is not particularly limited when measured using a measurement method such as IC (Ion Chromatography) commonly used in the technical field to which the present invention belongs, and specific examples thereof include an IC-ICP (Inductively Coupled Plasma) analysis device, an IC-ICP-MS analysis device, or an IC-ICP-AEC analysis device.

[0066]

[0067] The above conductive material may be, for example, a carbon-based conductive material, and preferably, carbon black, CNT, or a mixture thereof.

[0068] 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.

[0069]

[0070] The above heat treatment can be performed, for example, in an air or oxygen atmosphere, in which case the binder and conductive material are thermally decomposed into CO2 and H2O and removed, thereby separating the positive electrode active material from the current collector, and the separated positive electrode active material has the advantage of being easily sorted in powder form.

[0071] 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 to 99%, and within this range, there is an advantage in that the stability of Ni in the active material is increased while being removed without leaving any binder or conductive material residue.

[0072] The purity % of the above oxygen may be volume % or mol %.

[0073] The purity of the oxygen of this invention is not particularly limited when measured by a measurement method commonly used in the technical field to which the present invention belongs.

[0074]

[0075] The above heat treatment can be performed at, for example, 300 to 650°C, preferably 400 to 630°C, more preferably 500 to 600°C, even more preferably 530 to 600°C, and even more preferably 530 to 580°C, and within this range, the current collector does not melt, and only the binder, etc. is removed, so that the positive electrode active material is easily separated from the current collector.

[0076] The heat treatment time may be preferably 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, even more preferably 30 minutes to 2 hours, and even more preferably 30 minutes to 1 hour, and within this range, the current collector does not melt, and only the binder, etc. is removed, so that the positive electrode active material is easily separated from the current collector.

[0077] In this description, the heat treatment time refers to the time spent at the corresponding heat treatment temperature, and the time spent reaching the corresponding heat treatment temperature is not counted.

[0078] The above heat treatment may be performed at a temperature increase rate of, for example, 1 to 20°C / min, preferably 2 to 15°C / min, more preferably 3 to 10°C / min, and even more preferably 3 to 7°C / min, and within this range, it can be performed without causing a strain on the heat treatment equipment, and has the advantage of not causing thermal shock to the anode scrap.

[0079]

[0080] The following drawing 1 shows the anode scrap that is discarded after cutting the anode plate from the anode sheet.

[0081] Referring to Fig. 1, a positive electrode sheet (30) is manufactured by coating a positive electrode active material layer (20) including a positive electrode active material, a conductive material, a binder, etc. on a long sheet-shaped positive electrode current collector, aluminum foil (10), and then the positive electrode sheet (30) is punched to a certain size to produce a positive electrode plate (40), and the remaining portion is then used to produce positive electrode scrap (50). The punching is one means of cutting the positive electrode sheet.

[0082] In addition, the above-mentioned positive electrode active material layer (20) is formed by coating a slurry containing a mixture of positive electrode active material, conductive material, binder, and solvent on aluminum foil (10). Since the slurry is very sensitive to the environment such as temperature, it is not easy to set the coating conditions, and thus waste positive electrode sheets are generated until conditions for manufacturing a positive electrode sheet (30) of the desired quality are found through a certain test.

[0083] For reference, in the examples below, anode scrap was used as the anode.

[0084]

[0085] (b) Step of first milling the recovered positive electrode active material

[0086] The method for regenerating a positive electrode active material of the present invention includes (b) a step of first milling the recovered positive electrode active material, in which case the particle size of the positive electrode active material becomes uniform, thereby providing a positive electrode active material having excellent battery characteristics, and since the washing process of the recovered positive electrode active material is omitted, damage to the surface of the positive electrode active material is prevented, and there is an advantage in that economic efficiency and productivity are greatly improved.

[0087]

[0088] The above first milling can be performed using, for example, a centrifugal mill or a jet mill, and is preferably a centrifugal mill. In this case, there is an advantage in that the recovered positive electrode active material is uniformly pulverized, thereby making the particles uniform.

[0089] The above first milling can be performed at, for example, 6000 to 20000 rpm, preferably 8000 to 18000 rpm, more preferably 9000 to 16000 rpm, even more preferably 11000 to 14000 rpm, and even more preferably 11000 to 13000 rpm, and within this range, there are advantages of excellent grinding efficiency, non-breakage of the positive electrode active material particles, and excellent productivity. When the milling speed is less than 6000 rpm, there is no milling effect, and when it exceeds 20000 rpm, breakage of the positive electrode active material particles occurs.

[0090] The above first milling can be performed for, for example, 5 to 150 seconds, preferably 10 to 120 seconds, more preferably 10 to 100 seconds, even more preferably 15 to 80 seconds, even more preferably 15 to 60 seconds, and particularly preferably 15 to 40 seconds, and within this range, there are advantages of excellent grinding efficiency, non-breakage of the particles of the positive electrode active material, and excellent productivity.

[0091] The average particle diameter of the positive electrode active material after the first milling may be, for example, 7.0 to 9.0 ㎛, preferably 7.3 to 8.5 ㎛, and more preferably 7.5 to 8.5 ㎛, and within this range, there is an effect of improving battery characteristics.

[0092]

[0093] In this description, the particle distribution and average particle diameter can be measured using a measurement method commonly used in the relevant technical field, and for example, the laser diffraction method can be used. Specifically, after the particles of the positive electrode active material are dispersed in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device such as Microtrac MT 3000, and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W, and the average particle diameter (D50) based on 50% of the particle diameter distribution in the measuring device can be calculated, and the standard deviation can be obtained by calculating it with respect to the average particle diameter (D50).

[0094]

[0095] The centrifugal mill may have, for example, a filter size of 0.08 to 10.0 mm, preferably 0.08 to 7 mm, more preferably 0.08 to 5 mm, even more preferably 0.08 to 3 mm, even more preferably 0.08 to 2 mm, and particularly preferably 0.08 to 1.0 mm, and within this range, there is an advantage in that the size of the positive electrode active material particles is uniform.

[0096] In this description, the filter size of the centrifugal mill is not particularly limited as long as it is a filter size commonly used in the technical field to which the present invention belongs. For example, the filter of the centrifugal mill is in the shape of a circular band, and the band is densely perforated with small holes like a sieve, and the filter size refers to the size of the holes.

[0097]

[0098] (c) A step of adding a lithium precursor to the first milled positive electrode active material and annealing at 400 to 1000°C.

[0099] The method for regenerating a positive electrode active material of the present invention includes (c) a step of adding a lithium precursor to a first milled positive electrode active material and annealing at 400 to 1000°C, in which case there is an effect of improving the battery characteristics of the regenerated positive electrode active material by improving crystallinity, such as increasing crystallinity or restoring crystal structure.

[0100]

[0101] The above (c) annealing step may preferably be a step of adding a lithium precursor to the recovered positive electrode active material and annealing in oxygen (O2) or air at 400 to 1000°C, more preferably 600 to 900°C, and in this case, there is an effect of improving the battery characteristics of the regenerated positive electrode active material by improving the crystallinity, such as increasing the crystallinity of the positive electrode active material or restoring the crystal structure.

[0102]

[0103] The lithium precursor may preferably be at least one selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0104]

[0105] The lithium precursor may preferably be added in an amount equal to at least the amount of lithium reduced from the amount of lithium in the positive electrode active material of step (a) based on the amount of lithium in the recovered positive electrode active material, and as a specific example, when the positive electrode active material of step (a) is a positive electrode active material represented by the chemical formula 1, the lithium precursor may be added in an amount such that the molar ratio of lithium is 0.0001 to 0.2, preferably 0.001 to 0.02, more preferably 0.005 to 0.017, even more preferably 0.007 to 0.015, and even more preferably 0.009 to 0.013, based on the molar ratio of lithium in the positive electrode active material, and within this range, the lithium insufficient in the regenerated positive electrode active material is supplemented, thereby improving the crystallinity, such as increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0106] In this paper, the molar ratio of lithium to other metals in the positive electrode active material was measured using an ICP analyzer. While this can be measured using a standard ICP analyzer commonly used in laboratories, there is no variation depending on the measuring device or method.

[0107]

[0108] As another example, the lithium precursor may be added in an amount capable of providing lithium corresponding to 1 to 40 mol%, preferably 1 to 30 mol%, more preferably 3 to 20 mol%, even more preferably 7 to 17 mol%, and even more preferably 7 to 11 wt%, when the total lithium contained in the raw material positive electrode active material is 100 mol%.

[0109] In this article, raw material is the opposite of 'recycled' and means something that was first created.

[0110]

[0111] The above annealing is performed, for example, under conditions of 400 to 1000°C in an air or oxygen atmosphere, preferably 400 to 900°C, more preferably 400 to 800°C, even more preferably 450 to 750°C, and even more preferably 450 to 710°C, and within this range, the crystal structure is recovered, so that the output performance of the battery is excellent.

[0112] In addition, the annealing temperature can be controlled within a limited range depending on the melting point of the lithium precursor. For example, in the case of LiCO3, the melting point is 723°C, so annealing can be performed at preferably 700 to 900°C, more preferably 710 to 780°C, and in the case of LiOH, the melting point is 462°C, so annealing can be performed at preferably 400 to 600°C, more preferably 450 to 480°C, and within this range, the crystal structure is recovered, so that the output performance of the battery is excellent.

[0113] The above annealing temperature may preferably be a temperature exceeding the melting point of the lithium precursor, but if it exceeds 1000°C, thermal decomposition of the positive electrode active material may occur, resulting in a decrease in battery performance, so it may preferably be 1000°C or lower.

[0114] The above annealing time is, for example, 1 hour or more or 15 hours or less, preferably 1 to 15 hours, more preferably 2 to 10 hours, even more preferably 3 to 8 hours, even more preferably 4 to 6 hours, and as a specific example, around 5 hours is preferable, and within this range, crystal structure recovery is sufficiently achieved and there is an economic advantage.

[0115] The above annealing temperature can be reached at a heating rate of preferably 1 to 10°C / min, more preferably 1 to 7°C / min, and even more preferably 2 to 4°C / min, and in this case, the crystallinity of the regenerated positive electrode active material is further increased, thereby having the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0116] The above annealing step includes, for example, a cooling process, and the cooling process may be, for example, natural cooling in a furnace, in which case the crystallinity of the regenerated positive electrode active material is further increased, thereby having the effect of improving the battery characteristics of the regenerated positive electrode active material.

[0117] In this description, annealing may follow the definition used in the technical field to which the present invention belongs, and as a specific example, it may be defined as a heat treatment operation to cure deformation or lattice defects and increase crystallinity by heating a positive electrode active material having a deformed structure or lattice defects at a temperature above the recrystallization temperature, at which atoms of the main component can sufficiently diffuse and move, for an appropriate period of time.

[0118]

[0119] (d) Secondary milling step of the annealed positive electrode active material

[0120] The method for regenerating a positive electrode active material of the present invention includes a step of secondary milling of an annealed positive electrode active material, in which case the particle size of the positive electrode active material increased during the annealing step is reduced, thereby providing a regenerated positive electrode active material having a particle size similar to that of the positive electrode active material in a waste positive electrode, and has the advantage of improving battery characteristics.

[0121] The above secondary milling can be performed using, for example, a centrifugal mill or a jet mill, and is preferably performed using a centrifugal mill. In this case, the particle size of the positive electrode active material increased during the annealing step is reduced, so that the particle size is similar to that of the positive electrode active material in the waste positive electrode, and there is an advantage in that the battery characteristics are improved.

[0122] The above secondary milling can be performed at, for example, 6000 to 20000 rpm, preferably 8000 to 20000 rpm, more preferably 10000 to 19000 rpm, even more preferably 12000 to 19000 rpm, still more preferably 14000 to 19000 rpm, and particularly preferably 16000 to 19000 rpm, and within this range, the grinding efficiency is excellent, the particle size of the positive electrode active material becomes similar to the particle size of the positive electrode active material in the waste positive electrode, and there is an advantage of excellent productivity.

[0123] The above secondary milling can be performed for, for example, 5 to 150 seconds, preferably 10 to 120 seconds, more preferably 10 to 100 seconds, even more preferably 10 to 80 seconds, and even more preferably 15 to 60 seconds, and within this range, there are advantages of excellent grinding efficiency, non-breakage of the particles of the positive electrode active material, and excellent productivity.

[0124] The average particle diameter of the positive electrode active material after the secondary milling may be, for example, 7.0 to 11.0 ㎛, preferably 7.5 to 10 ㎛, more preferably 7.5 to 9.0 ㎛, and even more preferably 8.0 to 9.0 ㎛, and within this range, there is an effect of improving battery characteristics.

[0125] The regenerated positive electrode active material obtained after the secondary milling may have, for example, a standard deviation of the average particle diameter of 3.0 or less, preferably 2.7 or less, more preferably 2.5 or less, and even more preferably 0.1 to 2.5, and within this range, the particle distribution is similar to that of the positive electrode active material in the waste positive electrode, thereby having the advantage of improving battery characteristics.

[0126]

[0127] The positive electrode active material obtained after the secondary milling may have an increase rate of the average particle diameter of, for example, 14% or less, preferably 12% or less, more preferably 10% or less, even more preferably 8% or less, and even more preferably 0.1 to 8% compared to the positive electrode active material in the raw material. Within this range, the positive electrode active material in the raw material has an average particle diameter and particle distribution similar to that of the positive electrode active material, thereby having the advantage of improving battery characteristics. The increase rate of the average particle diameter can be calculated by the following mathematical formula 1.

[0128] [Mathematical Formula 1]

[0129] Increase rate of average particle diameter (%) = [(ba) / a]*100

[0130] (In the above mathematical expression 1, a is the average particle diameter of the raw material positive electrode active material, and b is the average particle diameter of the regenerated positive electrode active material measured after the second milling.)

[0131]

[0132] (e) Step of washing the secondary milled positive electrode active material

[0133] The method for regenerating a cathode active material of the present invention comprises (c) a step of washing the secondary milled cathode active material, in which case the lithium precursor is removed with a small amount of washing solution, thereby preventing degradation of battery performance and gas generation due to the subsequent reaction between the residual lithium precursor and the electrolyte, and eliminating the need for wastewater treatment. In particular, there is an advantage in that the lithium precursor, which is more likely to remain due to the high content of nickel in the high-nickel cathode active material, is removed with a small amount of washing solution.

[0134] In this description, a high nickel positive electrode active material refers to a positive electrode active material containing nickel at 60 mol% or more based on 100 mol% of the total metals other than Li.

[0135]

[0136] The above washing may preferably include a step of mixing the second-milled positive electrode active material with the washing solution, followed by a step of filtering, and a step of drying the positive electrode active material in the solid content obtained after the filtering. In this case, there is an effect of effectively removing excess lithium that is likely to remain in the positive electrode active material.

[0137]

[0138] The above washing step may be, for example, a weight ratio of the secondary milled positive electrode active material to the washing solution of 1:0.5 to 1:10, preferably 1:0.5 to 1:7, more preferably 1:0.5 to 1:5, even more preferably 1:0.5 to 1:3, still more preferably 1:0.5 to 1:2, and particularly preferably 1:0.5 to 1.5, in which case there is an advantage that lithium precursors such as LiOH and Li2CO3, which are likely to remain, are effectively removed. In particular, there is an advantage that lithium precursors such as LiOH and Li2CO3, which are more likely to remain due to the excessive addition of lithium, are effectively removed to suppress the cation mixing phenomenon that is likely to occur in high-nickel positive electrode active materials. This cation mixing phenomenon is a phenomenon that occurs because the particle sizes of nickel and lithium are similar.

[0139] In particular, when the annealed active material and the cleaning solution are mixed in a weight ratio of 1:0.5 to 1:2, preferably 1:0.5 to 1.5, there is an effect of further improving the initial discharge capacity (DCH) and efficiency of the regenerated positive electrode active material.

[0140] The above-mentioned cleaning solution may preferably be water, more preferably distilled water or deionized water, and in this case, there is an effect of effectively removing lithium precursors such as LiOH, Li2CO3, etc., which are more likely to remain due to excessively added lithium, in order to suppress the cation mixing phenomenon that is likely to occur in the high-nickel positive electrode active material.

[0141]

[0142] The above washing step may include, for example, a step of mixing a secondary milled positive electrode active material with a washing solution and then filtering it, and a step of drying the positive electrode active material in a solid content obtained after the filtering. In this case, there is an effect of effectively removing excess lithium that is likely to remain in the positive electrode active material.

[0143] The above filtration may preferably be a pressure-reducing filtration using a filter.

[0144] The drying may be preferably performed 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.

[0145] The above drying can preferably be carried out in vacuum drying.

[0146] In the present invention, vacuum drying is not particularly limited as long as it is a conventional vacuum drying in the technical field to which the present invention belongs, and may include drying in a partial vacuum state or a low pressure state, for example.

[0147]

[0148] (f) Step of surface coating the washed positive electrode active material

[0149] The method for regenerating a positive electrode active material of the present invention includes a step of (f) surface coating a washed positive electrode active material, in which case the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0150]

[0151] As another example, the method for regenerating a positive electrode active material of the present invention includes a step of (f') surface-coating a second-milled positive electrode active material, in which case the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0152]

[0153] The surface coating is preferably performed by coating a coating agent containing at least one of a metal, an organic metal, and a carbon component on the surface in a solid or liquid manner and then heat-treating at 100 to 1200°C. In this case, the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0154]

[0155] The coating agent containing the above metal is preferably a coating agent containing at least one selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V and Y, more preferably a coating agent containing at least one selected from the group consisting of B, W, Al, Ti and Mg, and 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 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.

[0156] The coating agent containing the above metal may be, for example, an oxide, acid, etc. containing the metal as an element in the molecule.

[0157] The coating agent containing the above-mentioned organic metal is not particularly limited as long as it is a coating agent containing an organic metal compound commonly used in the technical field to which the present invention belongs and containing the above-mentioned metal, and a specific example thereof may be a metal alkoxide, etc.

[0158] The coating agent containing the above carbon component is not particularly limited as long as it is a coating agent containing a carbon component commonly used in the technical field to which the present invention belongs, and a specific example thereof may be a sugar such as sucrose.

[0159]

[0160] The coating agent may be included in an amount of 0.001 to 0.3 mol%, for example, based on the components coated on the surface of the actual positive electrode active material excluding the solvent, relative to 100 mol% of the metal in the positive electrode active material before the coating treatment, 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%, and within this range, there is an effect of improving structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0161]

[0162] The heat treatment time is preferably 1 to 16 hours, more preferably 3 to 7 hours, and within this range, the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0163]

[0164] The coating method is not particularly limited if it is a coating method commonly used in the technical field to which the present invention pertains, and examples thereof include a liquid method in which a liquid coating agent is prepared and mixed with a 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 a coating agent is precipitated onto the surface of a positive electrode active material in an aqueous solution state, a method utilizing a reaction between a gaseous coating agent and a positive electrode active material, or a sputtering method.

[0165]

[0166] The above metal, organic metal, and carbon component may be, for example, spherical, plate-shaped, square, or needle-shaped, and such shapes can be controlled by changing process conditions, etc. during the manufacturing process, and the definition of each shape is not particularly limited as long as it follows the definition commonly recognized in the technical field to which the present invention belongs.

[0167] The coating agent preferably has an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m2 / g, more preferably has an average diameter of 10 to 100 nm and a specific surface area of ​​20 to 100 m2 / g, and is uniformly attached to the surface of the positive electrode active material within this range, thereby imparting structural stability to the positive electrode active material, thereby improving problems of deterioration of life characteristics and electrochemical performance due to lattice deformation or collapse of the crystal structure of the positive electrode active material.

[0168] In the present invention, the average diameter can be measured by a measuring method commonly used in the technical field to which the present invention belongs, and for example, can be measured using a laser diffraction method. Specifically, after dispersing the particles of the positive electrode active material in a dispersion medium, the particles are introduced into a commercially available laser diffraction particle size measuring device such as Microtrac MT 3000, and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W, and the average particle diameter (D50) based on 50% of the particle diameter distribution in the measuring device can be calculated.

[0169] In this description, the specific surface area can be measured by a measurement method commonly used in the technical field to which the present invention belongs, for example, by the BET (Brunauer-Emmett-Teller) method, and specifically, can be calculated from the nitrogen gas adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan.

[0170]

[0171] Regenerated cathode active material

[0172] The regenerated positive electrode active material of the present invention is characterized by being manufactured by the regenerated positive electrode active material method described above, and in this case, it has excellent electrochemical performance, capacity characteristics, and resistance characteristics.

[0173]

[0174] In addition, the regenerated cathode active material of the present invention is at least one selected from the group consisting of a lithium nickel oxide (LNO)-based cathode active material, a nickel-cobalt-manganese (NCM)-based cathode active material, a nickel-cobalt-aluminum (NCA)-based cathode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based cathode active material, and contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li, and is characterized in that the standard deviation of the average particle diameter of the regenerated cathode active material is 3.0 or less, and in this case, there is an excellent effect in battery characteristics.

[0175] The above-mentioned regenerated positive electrode active material may preferably have a standard deviation of an average particle diameter of 2.7 or less, more preferably 2.5 or less, and within this range, the particle size distribution of the positive electrode active material in the waste positive electrode is similar to that of the positive electrode active material, and there is an advantage of improved battery characteristics.

[0176] The above-mentioned regenerated positive electrode active material may have an increase rate of the average particle diameter of 14% or less, preferably 12% or less, more preferably 10% or less, even more preferably 8% or less, and even more preferably 0.1 to 8% compared to the average particle diameter of the positive electrode active material in the spent positive electrode, and within this range, the particle diameter distribution of the positive electrode active material in the spent positive electrode is similar to that of the positive electrode active material in the spent positive electrode, and has the advantage of improving battery characteristics.

[0177]

[0178] The above-described regenerative positive electrode active material may preferably include at least one 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 compound such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide such as LiNiO2; nickel manganese-based lithium composite metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). In this case, the electrochemical performance, resistance characteristics, and capacity characteristics are excellent.

[0179] The above regenerative positive electrode active material is a specific example of the following chemical formula 1

[0180] [Chemical Formula 1]

[0181] Li a Ni x Mn y Co z M w O 2+δ

[0182] (In the above chemical formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti and Mg, and 1 <a≤1.1, 0<x<0.95, 0<y<0.8, 0<z<1.0, 0≤w≤0.1, -0.02≤δ≤0.02, x+y+z+w=1이다.)로 표시되는 화합물을 포함할 수 있고, 이 경우 전기화학적 성능, 저항 특성 및 용량 특성 등이 우수한 효과가 있다.

[0183]

[0184] The above-mentioned regenerative positive electrode active material preferably contains 80 mol% or more of Ni based on 100 mol% of the total metals other than Li, and more preferably contains 81 mol% or more, and within this range, it has excellent effects in terms of initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0185]

[0186] The above-mentioned regenerative positive electrode active material may have a surface coated with, for example, metal or carbon, and is preferably coated with metal. In this case, the structural stability of the positive electrode active material is improved without chemical and physical changes in the positive electrode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. In addition, the physicochemical properties are also improved due to the effect of reducing the amount of residual lithium and reducing pH by substituting a different element on the surface of the positive electrode active material.

[0187]

[0188] The metal is preferably at least one selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V and Y, more preferably at least one selected from the group consisting of B, W, Al, Ti and Mg, even more preferably boron (B), tungsten (W) or a mixture thereof, even more preferably tungsten (W) and boron (B), and a specific example is tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0189]

[0190] The coating agent may be included, for example, in an amount of 0.001 to 0.3 mol% relative to 100 mol% of the metal in the positive electrode active material before coating treatment, 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%, and within this range, it has the effect of improving structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0191] The surface coating is preferably performed by coating a coating agent containing at least one of a metal, an organic metal, and a carbon component on the surface in a solid or liquid manner and then heat-treating at 100 to 1200°C, more preferably 200 to 1000°C, and even more preferably 250 to 800°C. In this case, the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0192]

[0193] The following Figure 4 is a flowchart for a regeneration process of a positive electrode active material according to one embodiment of the present invention.

[0194] Referring to Figure 4, first, anode scrap is prepared using a waste cathode (Step S10). For example, a slurry prepared by mixing NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride with NMP (N-methyl pyrrolidone) is coated on aluminum foil and dried in a vacuum oven at approximately 120°C to produce a cathode sheet. After stamping out cathode plates of a certain size, the remaining cathode scrap can be prepared.

[0195] The above-mentioned positive electrode scrap has a positive electrode active material layer on aluminum foil, and the positive electrode active material layer has a structure in which a binder binds the positive electrode active material and the conductive material after the solvent evaporates. Therefore, when the binder is removed, the positive electrode active material is separated from the aluminum foil.

[0196]

[0197] Next, the prepared positive electrode scrap is shredded into an appropriate size (step S20). Here, shredding includes cutting or shredding the positive electrode scrap into a size that is easy to handle. As a specific example, the shredded positive electrode scrap may have a size of 1 cm x 1 cm. The shredding may be performed using various dry crushing equipment, such as a hand mill, pin mill, disc mill, cutting mill, or hammer mill, or a high-speed cutter to increase productivity.

[0198] The above crushing can be preferably performed or not, and the size of the pieces, etc. can be determined by considering the characteristics required by the equipment used in the handling of the positive electrode scrap and the subsequent process. For example, if equipment capable of continuous processing is used, the positive electrode scrap must be crushed into smaller pieces because the fluidity must be good.

[0199]

[0200] Next, the shredded 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 and conductive material.

[0201] The above heat treatment is preferably performed at 300 to 650°C in air, in which case the binder and conductive agent are thermally decomposed into CO2 and H2O and removed. Since the binder is removed, the positive electrode active material is separated from the positive electrode active material layer.

[0202] It's crucial that the above heat treatment be performed in air. If heat treatment is performed in a reducing or inert gas atmosphere, the binder and conductive agent will carbonize rather than decompose. Carbonization leaves carbon components on the surface of the positive electrode active material, degrading the performance of the reusable positive electrode active material. However, if heat treatment is performed in air, the carbon components in the binder and conductive agent react with oxygen and disappear into gases such as CO and CO2, thus removing both the binder and conductive agent.

[0203] The above heat treatment is preferably performed at 300 to 650°C, and as a specific example, at 550°C. At temperatures below 300°C, it is difficult to remove the binder, making it impossible to separate the current collector. At temperatures above 650°C, the current collector melts, making it impossible to separate the current collector.

[0204] The above heat treatment is preferably performed at a temperature increase rate of 1 to 20°C / min, more preferably at a temperature increase rate of 3 to 10°C / min, and a specific example is 5°C / min. Within this range, the heat treatment can be performed without causing a strain on the heat treatment equipment, and has the advantage of not causing thermal shock to the anode scrap.

[0205] The above heat treatment can be performed for a period of time sufficient to allow the binder to be sufficiently thermally decomposed, for example, preferably 30 minutes or more, more preferably 30 minutes to 5 hours, and a specific example is about 30 minutes. Within this period, the binder is sufficiently thermally decomposed and also has the effect of excellent thermal decomposition efficiency.

[0206] The above heat treatment is performed using various types of furnaces, for example, a box-type furnace, and considering productivity, a rotary kiln capable of continuous treatment.

[0207] After the above heat treatment, it can be cooled slowly or rapidly in the air.

[0208]

[0209] Next, the recovered positive electrode active material is subjected to primary milling (step S40).

[0210] It is important that the above first milling step directly mills the recovered positive electrode active material without a washing process. In this case, the surface of the positive electrode active material is not damaged, the particles of the positive electrode active material are made uniform, and the process cost is reduced by not performing a washing process.

[0211] The above first milling can be performed using, for example, a centrifugal mill or a jet mill, and specifically, a centrifugal mill can be used. In this case, the particles of the recovered positive electrode active material are uniform, which has the advantage of improving battery characteristics.

[0212] The above first milling can be performed, for example, at 6000 to 20000 rpm, specifically 12000 rpm, and within this range, there are advantages of excellent grinding efficiency, non-breakage of positive electrode active material particles, and high productivity.

[0213] The above first milling can be performed for, for example, 5 to 150 seconds, specifically 30 seconds, and within this range, there are advantages of excellent grinding efficiency, non-breakage of the particles of the positive electrode active material, and excellent productivity.

[0214] The average particle diameter of the positive electrode active material after the first milling may be, for example, 7.0 to 9.0 ㎛, preferably 7.5 to 8.5 ㎛, and more preferably 8.0 to 8.5 ㎛, and within this range, there is an effect of improving battery characteristics.

[0215]

[0216] Next, a lithium precursor is added to the first milled positive electrode active material and annealed (step S50).

[0217] Since lithium loss occurs in the positive electrode active material during the preceding step S30, the above-mentioned annealing step compensates for such lithium loss in step S50. In addition, since a deformation structure (e.g., Co3O4 in the case of LCO active material) may appear on the surface of the positive electrode active material during the preceding step, the crystal structure of the positive electrode active material is restored through annealing in step S45 to improve the battery characteristics of the regenerated positive electrode active material or restore it to the level of a newly formed positive electrode active material. Here, 'newly formed' is a concept opposite to 'regenerated', and means something that is created for the first time, and is the same as the 'raw material' used in the detailed description and examples of the invention.

[0218] LiOH is used as a specific example of the above lithium precursor.

[0219] It is preferable that the lithium precursor be added in an amount at least equal to the molar ratio of lithium lost compared to the molar ratio of lithium and other metals in the newly formed 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 will increase resistance, and therefore, an appropriate amount of lithium precursor must be added.

[0220] In one embodiment, when the molar ratio of lithium (Li) to another metal (M) in the new cathode active material is 1, the lithium precursor may be added in an amount such that the molar ratio of lithium is 0.001 to 0.4, preferably in an amount such that the molar ratio of lithium is 0.01 to 0.4, and more preferably in an amount such that the molar ratio of lithium is 0.09 to 0.2. As a specific example, when the lithium precursor is added in an amount equivalent to the loss ratio of the lithium content in the new cathode active material based on the ICP analysis results, the capacity improvement effect is shown to be equivalent to that of the new cathode active material. Here, the ICP analysis results have an error value of approximately ±0.02.

[0221]

[0222] In one embodiment, the lithium precursor may be added in an amount capable of providing lithium corresponding to 1 to 40 mol% when the total lithium contained in the recovered positive electrode active material is 100 mol%, more preferably 1 to 15 mol%, and even more preferably 7 to 11 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.

[0223]

[0224] The above annealing is performed in an air or oxygen atmosphere at, for example, a temperature of 400 to 1000°C, preferably 400 to 900°C, more preferably 400 to 800°C, and even more preferably 450 to 710°C, and this temperature should be adjusted within a limited range depending on the type of lithium precursor.

[0225] The above annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, at a temperature exceeding 1000°C, thermal decomposition of the positive electrode active material occurs, resulting in a decrease in performance, so it should not exceed 1000°C. Accordingly, when Li2CO3 is used as the lithium precursor, the annealing temperature is suitably 700 to 900°C, more suitably 710 to 780°C, and even more preferably 750 to 780°C. In addition, when LiOH is used as the lithium precursor, the annealing temperature is suitably 400 to 600°C, more preferably 450 to 480°C, and even more preferably 470 to 480°C.

[0226] The above annealing time is preferably 1 hour or longer, preferably 15 hours or shorter, and more preferably 4 to 6 hours. A longer annealing time allows sufficient crystal structure recovery, but even long-term annealing does not significantly affect performance. The annealing equipment used in this process may be identical or similar to that used in the heat treatment step S30.

[0227]

[0228] Next, the annealed positive electrode active material is subjected to secondary milling (step S60).

[0229] The above secondary milling step S60 reduces the particle size of the positive electrode active material increased during the above annealing step S50 to be similar to the particle size of the positive electrode active material in the waste positive electrode, thereby improving battery characteristics.

[0230] The above secondary milling can be performed using, for example, a centrifugal mill or a jet mill, and as a specific example, a centrifugal mill can be used, and in this case, there is an advantage in that the particle size of the positive electrode active material is reduced without damaging the particles.

[0231] The above secondary milling can be performed at, for example, 6,000 to 20,000 rpm, specifically 18,000 rpm, and within this range, there are advantages of excellent milling efficiency, reduction in the particle size of the positive electrode active material, and excellent productivity.

[0232] The above secondary milling can be performed for, for example, 5 to 150 seconds, specifically 30 seconds, and within this range, there are advantages of excellent grinding efficiency, non-breakage of the particles of the positive electrode active material, and excellent productivity.

[0233] The average particle diameter of the positive electrode active material after the secondary milling may be, for example, 7.0 to 11.0 ㎛, preferably 7.5 to 10 ㎛, more preferably 7.5 to 9.0 ㎛, and even more preferably 8.0 to 9.0 ㎛, and within this range, there is an effect of improving battery characteristics.

[0234]

[0235] Next, as an optional step, the second-milled positive electrode active material is washed (step S70).

[0236] In the above annealing step S40, since the lithium precursor that did not participate in the reaction exists on the surface of the positive electrode active material in the form of LiOH and Li2CO3, a residual lithium removal process is required to remove this. In particular, high-content Ni-based positive electrode active materials require an excessive amount of Li due to the cation mixing phenomenon, which makes it easy for lithium impurities such as lithium carbonate (Li2CO3) to remain on the surface. These impurities can later react with the electrolyte to lower the performance of the battery and generate gases, so they must be thoroughly removed.

[0237] The above washing can preferably be performed using distilled water, which has the advantage of being safe and inexpensive while not dissolving transition metals present in the positive electrode active material.

[0238]

[0239] The above washing is preferably performed by mixing the annealed positive electrode active material and the washing solution in a weight ratio of 1:0.5 to 1:10, specifically 1:1, filtering the mixture, and then drying the obtained solid positive electrode active material.

[0240] The mixing of the annealed positive electrode active material and the cleaning solution is preferably performed by stirring, and the stirring is not particularly limited, but may be mechanical stirring, magnetic stirring, or ultrasonic stirring.

[0241] The above mechanical stirring includes, for example, an impeller, and is preferably performed under conditions of 250 to 350 RPM and 3 to 10 minutes.

[0242] The above filtration is preferably vacuum filtration using a filter, and the above drying is vacuum drying at 120 to 140°C.

[0243]

[0244] Next, as an optional step, surface coating can be performed on the washed positive electrode active material (step S80).

[0245] The above surface coating is, for example, a method of coating a coating agent containing a metal, organic metal, or carbon component on a surface in a solid or liquid manner and then heat-treating it. If the heat-treatment temperature is too low, a surface protective layer by the desired heterogeneous metal is not formed, and if the heat-treatment temperature is too high, the performance of the battery deteriorates due to thermal decomposition of the positive electrode active material.

[0246] Specifically, when a metal oxide or acid such as B, W, or BW is coated on a washed cathode active material and then heat-treated, a surface protective layer such as a lithium borooxide layer is formed on the surface of the cathode active material.

[0247] The solid or liquid method of the above surface coating may be, for example, mixing, milling, spray drying or grinding.

[0248]

[0249] If the molar ratio of lithium to other metals in the positive electrode active material is 1:1 in the annealing step S50, the lithium in the positive electrode active material and the coating agent react in the surface coating step S60, so that the molar ratio of lithium to other metals in the positive electrode active material becomes less than 1:1, and such a regenerated positive electrode active material cannot fully exhibit 100% of the battery capacity. However, if the lithium precursor is added in excess in the annealing step S50 so that the molar ratio is 0.0001 to 0.1 more than that of the other metals in the positive electrode active material, a surface protective layer is formed in the surface coating step S60, so that the molar ratio of lithium to other metals in the positive electrode active material naturally becomes 1:1, and thus the battery capacity decrease does not occur.

[0250]

[0251] secondary battery

[0252] The secondary battery of the present invention includes a regenerated positive electrode active material manufactured by the method for regenerating the positive electrode active material, and in this case, the particle distribution of the regenerated positive electrode active material is similar to that of the positive electrode active material in the spent positive electrode, thereby significantly improving battery characteristics. In addition, the process for recovering and regenerating the positive electrode active material does not use acid or organic solvent, so it is environmentally friendly, and in particular, the initial washing process is omitted, thereby providing excellent economic efficiency and productivity.

[0253] In addition, the secondary battery of the present invention includes the positive electrode active material, and in this case, the average particle diameter and standard deviation of the regenerated positive electrode active material are similar to those of the positive electrode active material in the spent positive electrode, so that the battery characteristics are greatly improved, and in addition, since no acid or organic solvent is used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly, and in particular, since the initial washing process is omitted, it has excellent economic efficiency and productivity.

[0254]

[0255] The secondary battery of the present invention may include all of the contents of the positive electrode active material and the regeneration method thereof described above. Therefore, redundant description thereof is omitted herein.

[0256]

[0257] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0258]

[0259] [Example]

[0260] Example 1

[0261] After the positive electrode plate was pressed, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide containing 87 mol% nickel based on 100 mol% of the remaining metals excluding Li) was crushed and heat-treated in air at 590°C for 30 minutes to remove the binder and conductive agent, and the current collector and positive electrode active material were separated and the positive electrode active material was recovered. Here, the temperature increase rate until the heat treatment temperature was reached was 5°C / min, and air was supplied at 10 L / min.

[0262] The recovered positive electrode active material was first milled using a centrifugal mill (Retsch ZM200) at 12,000 rpm for 30 seconds. After the first milling, the average particle diameter (D50) of the positive electrode active material was 7.9 μm.

[0263] LiOH, a lithium precursor, was added to the first milled positive electrode active material in an amount that can provide 15 mol% of lithium when the total lithium in the raw positive electrode active material is 100 mol%, and annealed in air at a sintering temperature of 750°C for 5 hours. Here, air was supplied at a rate of 3 L / min.

[0264] The above annealed positive electrode active material was milled a second time using a centrifugal mill at 18,000 rpm for 30 seconds. After the second milling, the average particle diameter (D50) of the positive electrode active material was 8.99 μm.

[0265]

[0266] Example 2

[0267] The same procedure as in Example 1 was followed, except that the first milling was performed at 12,000 rpm for 30 seconds and the second milling was performed at 12,000 rpm for 30 seconds.

[0268]

[0269] Comparative Example 1

[0270] The same procedure as Example 1 was followed, except that the first milling and second milling were not performed.

[0271]

[0272] Comparative Example 2

[0273] The same procedure as Example 1 was followed, except that secondary milling was not performed.

[0274]

[0275] Comparative Example 3

[0276] The same procedure as Example 1 was followed, except that the first milling was not performed.

[0277]

[0278] Comparative Example 4

[0279] After the positive electrode plate was pressed, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide, nickel content 87 mol% based on 100 mol% of the remaining metals excluding Li) was crushed and heat-treated in air at 590°C for 30 minutes to remove the binder and conductive agent, and the current collector and positive electrode active material were separated and recovered. Here, the temperature increase rate until the heat treatment temperature was reached was 5°C / min, and air was supplied at 10 L / min.

[0280] The recovered positive electrode active material was washed by immersing it in distilled water and stirring it simultaneously. At this time, the recovered positive electrode active material: distilled water was stirred at a weight ratio of 1:10 at 500 rpm for 10 minutes, and then only the active material was extracted by vacuum filtration using a filter.

[0281] The above-mentioned washed cathode active material was dried overnight at 100°C, and then LiOH, a lithium precursor, was added in an amount capable of providing 15 mol% of lithium when the total lithium in the raw cathode active material is 100 mol%, and annealed in air at a sintering temperature of 750°C for 5 hours. Here, air was supplied at 3 L / min.

[0282]

[0283] Reference example

[0284] Fresh NCM-based lithium composite transition metal oxide (nickel content of 87 mol% based on 100 mol% of the remaining metals excluding Li) rather than a regenerative cathode active material was used.

[0285]

[0286] [Test Example I: Particle Distribution of Regenerated and New Positive Electrode Active Materials]

[0287] The regenerated positive electrode active materials or new positive electrode active materials obtained in Examples 1 and 2, Comparative Examples 1 to 4, and Reference Examples were measured using a laser diffraction method. Specifically, after the particles of the regenerated positive electrode active material were dispersed in a dispersion medium, they were introduced into a commercially available laser diffraction particle size measuring device such as Microtrac MT 3000, and ultrasonic waves of about 28 kHz were irradiated at an output of 60 W to measure the particle distribution, and the average particle diameter and its standard deviation based on 50% of the particle diameter distribution, and the increase rate of the particle diameter were calculated. The increase rate of the particle diameter was calculated based on the Reference Example.

[0288] The average particle diameter and standard deviation thereof, and particle size increase rate of the regenerated positive electrode active material or the newly produced positive electrode active material obtained in Examples 1 and 2, Comparative Examples 1 to 4, and Reference Examples are shown in Table 1 below.

[0289] In addition, the particle distribution map measured with the regenerated positive electrode active material or the new positive electrode active material obtained in Example 1, Reference Example, and Comparative Examples 1 to 3 is shown in FIG. 2 below, and the particle distribution map measured with the regenerated positive electrode active material or the new positive electrode active material obtained in Examples 1, 2, Reference Example, and Comparative Examples 1 and 4 is shown in FIG. 3 below.

[0290]

[0291] Classification Average particle diameter (㎛)Standard deviation of average particle diameterParticle diameter increase rate (%)Example 18.992.477.41Example 29.442.5712.78Comparative example 114.026.2967.50Comparative example 211.884.6041.94Comparative example 39.703.5715.89Comparative example 410.413.6924.37Reference example 8.372.16-

[0292] As can be seen in Table 1 above, Examples 1 and 2 according to the present invention have a reduced average particle diameter and its standard deviation, and a particle diameter increase rate compared to Comparative Examples 1 to 4, and are similar to the reference example (new positive electrode active material), so it can be expected that the battery characteristics are further improved.

[0293]

[0294] As shown in Figure 2 below, Example 1 according to the present invention exhibited a particle distribution similar to that of the reference example (new positive electrode active material), and thus it could be expected that the battery characteristics would be further improved.

[0295] In addition, as shown in Figure 3 below, Examples 1 and 2 according to the present invention exhibited a particle distribution similar to that of the reference example (new positive electrode active material), so it could be expected that the battery characteristics would be further improved.

[0296]

[0297] [Explanation of symbols]

[0298] 10: Whole house

[0299] 20: Active material layer

[0300] 30: Bipolar sheet

[0301] 40: Bipolar plate

[0302] 50: Bipolar scrap

Claims

1. A step of heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector to thermally decompose a binder and a conductive material within the positive electrode active material layer, thereby recovering the positive electrode active material within the positive electrode active material layer; A step of first milling the recovered positive electrode active material; A step of adding a lithium precursor to the first milled positive electrode active material and annealing at 400 to 1000°C; and characterized by including a step of secondary milling of the annealed positive electrode active material; Method for regenerating positive electrode active material.

2. In paragraph 1, The above cathode active material layer is at least one selected from the group consisting of a lithium nickel oxide (LNO) cathode active material, a nickel-cobalt-manganese (NCM) cathode active material, a nickel-cobalt-aluminum (NCA) cathode active material, and a nickel-cobalt-manganese-aluminum (NCMA) cathode active material, and is characterized in that it contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li. Method for regenerating positive electrode active material.

3. In paragraph 1, The above heat treatment is characterized in that it is performed at 300 to 650°C in an air or oxygen atmosphere. Method for regenerating positive electrode active material.

4. In paragraph 1, The above first and second milling are characterized in that they are performed using a centrifugal mill or a jet mill, respectively. Method for regenerating positive electrode active material.

5. In paragraph 1, The above first and second milling are characterized in that they are each performed at 6000 to 20000 rpm. Method for reusing positive electrode active material.

6. In paragraph 1, The positive electrode active material obtained after the above second milling is characterized in that the increase rate of the average particle diameter is 14% or less compared to the positive electrode active material in the raw material, and the standard deviation of the average particle diameter is 3.0 or less. Method for regenerating positive electrode active material.

7. In paragraph 1, The lithium precursor is characterized in that it comprises at least one of LiOH, Li2CO3, LiNO3 and Li2O. Method for regenerating positive electrode active material.

8. In paragraph 1, The lithium precursor is characterized in that it is added in an amount capable of providing lithium corresponding to 1 to 40 mol% when the total lithium in the raw material cathode active material is 100 mol%. Method for regenerating positive electrode active material.

9. In paragraph 1, The above annealing is characterized in that it is performed in air at 400 to 1000°C. Method for regenerating positive electrode active material.

10. In paragraph 1, The method for regenerating the positive electrode active material is characterized by including a step of washing the second-milled positive electrode active material; a step of surface-coating the second-milled positive electrode active material; or a step of surface-coating the second-milled positive electrode active material after washing it. Method for regenerating positive electrode active material.

11. In paragraph 10, The weight ratio of the annealed positive electrode active material and the cleaning solution in the above washing step is characterized in that it is 1:0.5 to 1:

10. Method for regenerating positive electrode active material.

12. In paragraph 10, The above surface coating is characterized by coating at least one of a metal, an organic metal, and a carbon component on the surface in a solid or liquid manner and then heat-treating at 100 to 1200°C. Method for regenerating positive electrode active material.

13. At least one selected from the group consisting of lithium nickel oxide (LNO)-based cathode active materials, nickel, cobalt, manganese (NCM)-based cathode active materials, nickel, cobalt, aluminum (NCA)-based cathode active materials, and nickel, cobalt, manganese, aluminum (NCMA)-based cathode active materials, and containing 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li, and characterized in that the standard deviation of the average particle diameter of the regenerated cathode active material is 3.0 or less. Regenerated cathode active material.

14. In paragraph 1, The above positive electrode active material is characterized in that the surface is coated with a coating agent containing metal or carbon. Regenerated cathode active material.

15. In paragraph 14, The above metal is characterized by being boron (B), tungsten (W) or a mixture thereof. Regenerated cathode active material.

16. Characterized in that it comprises a positive electrode active material according to any one of claims 13 to 15. Secondary battery.

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