Method for regenerating cathode active material, and regenerated cathode active material prepared thereby

Abstract

The present invention relates to a method for regenerating a cathode active material, and a regenerated cathode active material prepared thereby. The method comprises the steps of: a) heat-treating, at 300-650 °C, a waste cathode, which has a cathode active material layer formed on a current collector, so as to thermally decompose a binder and a conductive material in the cathode active material layer, thereby separating the current collector from the cathode active material layer and recovering a cathode active material in the cathode active material layer; b) heat-treating the recovered cathode active material again at 350-700 °C for 1-10 hours; c) adding a lithium precursor to the reheated cathode active material and annealing same at 500-1,000 °C; d) washing the annealed cathode active material with a washing solution; and e) surface-coating the washed cathode active material with a coating agent.

Description

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

[0001] The present invention relates to a method for regenerating a positive electrode active material and a regenerated positive electrode active material manufactured therefrom, and more particularly, to a positive electrode active material which is recovered by heat-treating a waste positive electrode, and which is then subjected to reheat treatment, etc. instead of shear washing, thereby cleanly removing impurities derived from conductive materials or binders remaining on the surface of the recovered positive electrode active material, thereby reducing the internal and external resistance of the positive electrode active material, thereby providing a positive electrode active material having excellent efficiency, lifespan characteristics, and resistance characteristics of a lithium secondary battery, and a method for regenerating a positive electrode active material which is environmentally friendly because no acid is used in the recovery and regeneration process, and thus reduces process costs because neutralization and wastewater treatment are not required, and does not decompose the positive electrode active material and is thus regenerated as is, so there are no discarded metal elements, and since no organic solvent is used, there is no generation of toxic gases or risk of explosion, and since a shear washing process is omitted, the economy and productivity are greatly improved.

[0002] 〔Cross-citation with the applicant(s)〕

[0003] This application claims the benefit of priority from Korean Patent Application No. 10-2024-0029794, filed February 29, 2024, and Korean Patent Application No. 10-2025-0004745, filed January 13, 2025, which is hereby incorporated by reference in its entirety.

[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 solvent dissolution, aluminum foil dissolution, crushing and screening, and calcination.

[0009] However, although the above solvent dissolution method can obtain a regenerated positive electrode active material with a relatively clean surface, it has the disadvantages 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.

[0010] 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.

[0011] The above crushing and screening method has the advantage of being the simplest process, but has the disadvantages of being difficult to completely separate the current collector and the positive electrode active material, changing the particle size distribution of the positive electrode active material during the crushing process, and deteriorating the battery characteristics of the regenerated positive electrode active material due to the remaining binder.

[0012] Finally, the sintering method, although simple in process, has the disadvantages of producing 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. However, compared to other methods, it has the advantages of not producing toxic gases, not having the risk of explosion, and providing excellent battery characteristics. However, in the sintering method, impurities formed on the surface of the regenerated positive electrode active material are mainly removed through washing, but there is a problem that the impurities are not completely removed and waste water is generated due to washing, which increases production costs and deteriorates battery characteristics.

[0013] Therefore, there is a need to develop a method for regenerating a positive electrode active material that does not decompose the positive electrode active material in the waste positive electrode, thereby improving battery characteristics by regenerating the positive electrode active material without discarding any metal elements and cleanly removing impurities remaining on the surface of the regenerated positive electrode active material.

[0014] In order to solve the problems of the prior art as described above, the present invention provides a method for regenerating a cathode active material by heat-treating a waste cathode to recover a cathode active material, and reheat-treating the recovered cathode active material instead of shear washing, thereby cleanly removing impurities derived from conductive materials or binders remaining on the surface of the recovered cathode active material, reducing wastewater generation, and reducing internal and external resistance of the regenerated cathode active material to provide a cathode active material with excellent efficiency, lifespan characteristics, and resistance characteristics, and further, since no acid is used in the recovery and regeneration process of the cathode active material, it is environmentally friendly, and since neutralization and wastewater treatment are not required, process costs are reduced, and since the cathode active material is regenerated as it 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 since the shear washing process is omitted, economic feasibility and productivity are greatly improved.

[0015] In addition, the present invention aims to provide a regenerative positive electrode active material with reduced internal and external resistance.

[0016] In addition, the present invention aims to provide a secondary battery in which the internal and external resistance of a regenerative positive electrode active material is reduced, thereby delaying degradation.

[0017] The above and other objects of the present invention can all be achieved by the present invention described below.

[0018] 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: (a) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose a binder and a conductive agent in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; (b) re-heat-treating the recovered positive electrode active material at 350 to 700°C for 1 to 10 hours; (c) adding a lithium precursor to the re-heat-treated positive electrode active material and annealing at 500 to 1000°C; (d) washing the annealed positive electrode active material; and (e) surface-coating the washed positive electrode active material with a coating agent.

[0019] II) In the above I), the reheat treatment temperature in the step (b) may be 450 to 650°C.

[0020] III) In the above I) or II), the positive electrode active material layer may include at least one selected from the group consisting of 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.

[0021] IV) In the above I) to III), the heat treatment of step (a) can be performed for 30 minutes to 10 hours.

[0022] V) In the above I) to IV), the heat treatment of step (a) or the reheat treatment of step (b) can be performed in an air or oxygen atmosphere.

[0023] VI) In the above I) to V), the positive electrode active material reheat-treated in the above step (b) can be provided to the annealing in the above step (c) without washing.

[0024] VII) In the above I) to VI), the lithium precursor in the step (c) may be at least one selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0025] VIII) In the above I) to VII), in the step (c), the lithium precursor can be added in an amount at least reduced from the molar ratio of lithium in the positive electrode active material in the step (a) based on the amount of lithium in the reheat-treated positive electrode active material.

[0026] IX) In the above I) to VIII), the washing in step (d) may have a weight ratio of the positive electrode active material and the washing solution of 1:0.5 to 1:4.

[0027] X) In the above I) to IX), the washing in step (d) may include a step of mixing the annealed positive electrode active material and the washing solution and then filtering them, and a step of drying the positive electrode active material in the solid content obtained after the filtering.

[0028] XI) In the above I) to X), the washing solution may be water or a basic lithium compound aqueous solution.

[0029] XII) In the above I) to XI), the surface coating of step (e) can be 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 700°C.

[0030] XIII) In the above I) to XII), the regenerated positive electrode active material obtained after the surface coating may have an average resistance measured by a scanning diffusion resistance microscope (SSRM) of 6.42 log(R / Ω) or less.

[0031] In addition, XIV) 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, wherein the cathode active material is manufactured by coating a slurry of 96.5 wt% of the cathode active material, 1.5 wt% of carbon black, and 2 wt% of polyvinylidene fluoride (PVdF) in NMP (N-Methyl-2-pyrrolidone) on aluminum foil using a scanning diffusion resistivity microscope (SSRM) to manufacture a cathode electrode, embedding it in an epoxy resin, and then ion milling the same to manufacture a cross-section, and the average resistance measured on the cross-section is 6.42 log (R / Ω) or less, and / or the a-axis measured by X-ray diffraction analysis The lattice constant is 2.8742 to 2.8750 Å, the c-axis lattice constant is 14.203 to 14.209 Å, and the cell volume is 101.62 to 101.68 Å. 3 A cathode active material characterized by:

[0032] XV) In the above XIV), the positive electrode active material may have a crystallite size of 86 to 89 nm as measured by X-ray diffraction analysis.

[0033] XVI) In the above XIV) or XV), the positive electrode active material may have a surface coated with a coating agent containing metal or carbon.

[0034] XVII) In the above XIV) to XVI), the positive electrode active material may be a regenerated positive electrode active material.

[0035] In addition, the present invention provides a secondary battery characterized in that it includes a positive electrode active material of any one of XVII) to XVII).

[0036] According to the present invention, a waste positive electrode including a current collector and a positive electrode active material layer coated thereon is heat-treated to recover the positive electrode active material, and after reheating the recovered positive electrode active material, a lithium precursor is added directly without a washing process and annealing is performed, thereby reducing the internal and external resistance of the regenerated positive electrode active material, thereby providing a method for regenerating a regenerated positive electrode active material having excellent efficiency, lifespan characteristics, and resistance characteristics. In addition, by reheat-treating the recovered positive electrode active material instead of washing, impurities derived from a conductive material or binder are more cleanly removed, and by washing the annealed positive electrode active material with a small amount of washing solution, waste water is greatly reduced.

[0037] In addition, it is environmentally friendly because it does not use acid in the recovery and regeneration process of the positive electrode active material, and process costs are reduced because neutralization and wastewater treatment are not required, and the positive electrode active material is regenerated as it is without decomposition, so there are no discarded metal elements, and there is no risk of toxic gas generation or explosion because no organic solvent is used, and in particular, it has the effect of providing a method for regenerating positive electrode active materials that greatly improves economic efficiency and productivity because the shear washing process is omitted.

[0038] 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.

[0039] Figure 1 is a drawing showing anode scrap that is discarded after cutting an electrode plate from a cathode sheet.

[0040] FIG. 2 is a log scale image obtained by processing and changing the resistance value data obtained using a scanning diffusion resistance microscope (SSRM) into a log scale for each of the regenerated or new positive electrode active materials manufactured or prepared in Example 1, Comparative Examples 1 and 2, and Reference Example 1.

[0041] Figure 3 is a flowchart of a regeneration process of a positive electrode active material according to the present invention.

[0042] Figure 4 shows the results of weight change rates according to heat treatment temperature of the positive electrode active materials of Reference Examples 2 and 3, analyzed by TGA (Thermogravimetric Analysis).

[0043] The present inventors, while studying a method for directly regenerating a positive electrode active material with excellent battery performance, etc., without decomposing the positive electrode active material from a waste positive electrode (direct recycled method), confirmed that when a waste positive electrode is heat-treated at a predetermined temperature and then the recovered positive electrode active material is reheat-treated under predetermined conditions instead of washing, residual impurities derived from a conductive agent or binder are effectively removed, and the internal and external resistance of the positive electrode active material is reduced, thereby improving the efficiency, life characteristics, and resistance characteristics of a lithium secondary battery. Based on this, they devoted themselves to further research and completed the present invention.

[0044]

[0045] Hereinafter, the regenerative positive electrode active material of the present invention, the regeneration method thereof, and the secondary battery including the same are described in detail.

[0046] 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.

[0047] 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.

[0048]

[0049] Method for regenerating positive electrode active material

[0050] The method for regenerating a positive electrode active material of the present invention is characterized by comprising the steps of: (a) heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose a binder and a conductive agent in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; (b) re-heat-treating the recovered positive electrode active material at 350 to 700°C for 1 to 10 hours; (c) adding a lithium precursor to the re-heat-treated positive electrode active material and annealing at 500 to 1000°C; (d) washing the annealed positive electrode active material with a washing solution; and (e) surface-coating the washed positive electrode active material with a coating agent. In this case, since the impurities derived from the conductive agent or binder remaining on the surface of the recovered positive electrode active material through reheat treatment are cleanly removed, the internal and external resistance of the positive electrode active material is reduced, thereby improving the life characteristics of the secondary battery and reducing the generation of wastewater, thereby reducing the process cost. 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, the process cost is reduced, and since the positive electrode active material is regenerated as it is without decomposition, there are no discarded metal elements, and since no organic solvent is used, there is no generation of toxic gases or risk of explosion, and since the pre-washing process is omitted, there are advantages of greatly improving economy and productivity.

[0051]

[0052] Below, the method for regenerating positive electrode active materials is explained in detail step by step.

[0053]

[0054] (a) A step of recovering positive electrode active material from a waste positive electrode.

[0055] According to the present invention, the step of recovering a positive electrode active material from a waste positive electrode (a) may preferably include a step of heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose a binder and a conductive material within the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material within the positive electrode active material layer. In the case of positive electrode active material recovered under such conditions, the process is simple and has the effect of cleanly removing the binder, conductive material, and current collector.

[0056]

[0057] 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.

[0058] 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.

[0059] 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.

[0060] As another specific example, the positive electrode active material may be a compound represented by the following chemical formula 1, in which case it has excellent effects of reversible capacity and thermal stability.

[0061] [Chemical Formula 1]

[0062] Li a Ni x Mn y Co z M w O 2+δ

[0063] (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.)

[0064]

[0065] The above-mentioned positive electrode active material may contain, for example, 40 mol% or more of Ni, preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and even more preferably 80 mol% or more, particularly preferably 81 mol% or more, and even more preferably 81 to 95 mol%, based on 100 mol% of the total metals other than Li, and the charging capacity, resistance characteristics, and capacity characteristics of the lithium secondary battery applied within this range are excellent.

[0066] 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.

[0067]

[0068] The above conductive material may be, for example, a carbon-based conductive material, and preferably, carbon black, CNT, or a mixture thereof.

[0069] 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.

[0070]

[0071] In the above step (a), the heat treatment may be, for example, 300 to 650°C, preferably 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 580°C. Within this range, the current collector does not melt, and only the conductive material and binder are removed, so that the positive electrode active material is easily separated from the current collector. If the temperature range is exceeded, the current collector melts, making it difficult to separate only the positive electrode active material.

[0072] The above heat treatment can be performed at a temperature increase rate of, for example, 1 to 20°C / min, preferably 3 to 10°C / min, and more preferably 3 to 7°C / min, and can be performed within this range without causing a strain on the heat treatment equipment, and has the advantage of not causing thermal shock to the anode scrap.

[0073]

[0074] The above heat treatment can be carried out, for example, in an air or oxygen atmosphere, and preferably carried out in air. In this case, the carbon component in the binder and conductive material reacts with oxygen and disappears into gases such as CO and CO2, so there is an advantage in that the binder and conductive material are removed.

[0075] 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 positive electrode active material is increased while the binder and conductive agent are removed.

[0076] The purity % of the above oxygen may be volume % or mol %.

[0077] The purity of the oxygen of this invention is not particularly limited when measured using a measurement method commonly used in the technical field to which the present invention belongs.

[0078]

[0079] The air or oxygen can be supplied at a rate of, for example, 1 to 20 L / min, preferably 1 to 15 L / min, more preferably 2 to 10 L / min, and even more preferably 3 to 7 L / min, and within this range, the positive electrode active material can be easily separated from the current collector, and the separated positive electrode active material can be easily sorted into a powder form.

[0080]

[0081] 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.

[0082] 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.

[0083]

[0084] After the above heat treatment, the positive electrode active material can be recovered after cooling to room temperature, for example, by slow cooling or rapid cooling in the air.

[0085] In this description, room temperature may be a point within the range of 20 ± 5 ℃.

[0086] The above-mentioned recovered positive electrode active material may preferably be in powder form, in which case there is an advantage of being uniformly heat-treated in the subsequent reheat treatment step.

[0087]

[0088] In addition, the recovered positive electrode active material can be preferably sieved and then put into a reheat treatment step. In this case, since the positive electrode active material powder has a uniform size, the heat treatment is performed evenly, so impurities are cleanly removed, and the internal and external resistance of the positive electrode active material is reduced, so there is an advantage in that the efficiency, life characteristics, and resistance characteristics of the secondary battery are improved.

[0089] The above-mentioned sieve can be sieved through a sieve of, for example, 270 to 400 mesh, preferably 300 to 350 mesh, and in this case, the size of the recovered positive electrode active material is uniform, so that there is an advantage in that it is heat-treated evenly in the subsequent reheat treatment step.

[0090] In this description, the constitution is not particularly limited to a constitution method or constitution means commonly used in the technical field to which the present invention belongs, and as a specific example, it can be carried out by using an ultrasonic classifier or a sieve.

[0091]

[0092] Referring to the following drawing 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.

[0093] In addition, the positive electrode active material layer (20) is formed by coating a slurry containing a mixture of a positive electrode active material, a conductive agent, a binder, and a solvent on aluminum foil (10). Since the slurry is very sensitive to the environment such as temperature, it is difficult to control the coating conditions. Therefore, waste positive electrode sheets such as positive electrode scrap (50) are generated until conditions for manufacturing a positive electrode sheet (30) of the desired quality are found through a predetermined test.

[0094] For reference, in the following examples, anode scrap (50) was used as the positive electrode.

[0095]

[0096] (b) Step of reheating the recovered positive electrode active material

[0097] The method for regenerating a positive electrode active material of the present invention includes (b) a step of reheating the recovered positive electrode active material at 350 to 700°C for 1 to 10 hours, in which case, impurities derived from a conductive agent or binder remaining on the surface of the recovered positive electrode active material are cleanly removed, thereby reducing the internal and external resistance of the positive electrode active material, resulting in excellent efficiency, life characteristics, and resistance characteristics, and omitting shear washing, thereby reducing wastewater generation and reducing costs.

[0098]

[0099] The reheat treatment temperature of the above step (b) may be, for example, 350 to 700°C, or 400 to 700°C, preferably 450 to 650°C, more preferably 500 to 650°C, and even more preferably 550 to 620°C. Within this range, impurities derived from the conductive agent or binder remaining on the surface of the recovered positive electrode active material are cleanly removed, and the internal and external resistances of the positive electrode active material are reduced, so that there are advantages of excellent efficiency, life characteristics, and resistance characteristics. When the reheat treatment temperature is less than 350°C, thermal decomposition of impurities derived from the conductive agent or binder is not sufficient, and thus the effect of reducing the internal and external resistance is not realized. When it exceeds 700°C, the positive electrode active material deteriorates and degenerates, causing the internal and external resistances to increase.

[0100]

[0101] The reheat treatment time in the above step (b) can be preferably performed for 2 to 8 hours, more preferably 3 to 7 hours, and even more preferably 4 to 6 hours, and there is an advantage in that impurities derived from the conductive material or binder remaining in the recovered positive electrode active material within this range are cleanly removed.

[0102] 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.

[0103]

[0104] The reheat treatment in step (b) above can be performed, for example, in an air or oxygen atmosphere, and preferably can be performed in air. In this case, there is an advantage in that impurities derived from the conductive material or binder remaining on the surface of the recovered positive electrode active material are completely removed.

[0105] The air or oxygen can be supplied at a rate of, for example, 1 to 20 L / min, preferably 3 to 17 L / min, more preferably 5 to 15 L / min, and even more preferably 7 to 13 L / min, and within this range, there is an advantage in that impurities derived from the conductive material or binder remaining on the surface of the recovered positive electrode active material are cleanly removed.

[0106]

[0107] The reheat treatment temperature of step (b) is preferably the same as or higher than the heat treatment temperature of step (a), and more preferably, it can be performed at a higher temperature, since the collector is removed by the heat treatment of step (a). In this case, there is an advantage in that impurities derived from the conductive material or binder remaining in the recovered positive electrode active material are more cleanly removed.

[0108]

[0109] The difference between the reheat treatment temperature of the step (b) and the heat treatment temperature of the step (a) may be, for example, 20 to 180°C, preferably 20 to 130°C, more preferably 20 to 80°C, even more preferably 20 to 50°C, and even more preferably 25 to 35°C, and within this range, there is an advantage in that impurities derived from the conductive agent or binder remaining on the surface of the recovered positive electrode active material are more cleanly removed.

[0110]

[0111] The reheat treatment in step (b) above can be performed, for example, using the same equipment as the heat treatment in step (a).

[0112]

[0113] The cathode active material reheat-treated in the above step (b) can preferably be provided for annealing directly without washing, in which case the shear washing process is omitted, thereby reducing wastewater generation and minimizing damage to the cathode active material, thereby significantly improving economic efficiency and productivity.

[0114]

[0115] (c) Step of adding a lithium precursor to the reheat-treated positive electrode active material and annealing

[0116] The method for regenerating a positive electrode active material of the present invention includes (c) a step of adding a lithium precursor to a reheat-treated positive electrode active material and annealing at 500 to 1000°C, in which case a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided, and the process of pre-washing the recovered active material is omitted, thereby greatly improving economic efficiency and productivity and minimizing damage to the positive electrode active material.

[0117]

[0118] The above (c) annealing step may preferably be performed by adding a lithium precursor to the reheat-treated positive electrode active material and annealing in oxygen (O2) or air. In this case, there is an effect of improving the crystallinity of the positive electrode active material, such as increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0119] The above annealing temperature may be preferably 500 to 1000°C, more preferably 600 to 900°C, even more preferably 650 to 850°C, and even more preferably 700 to 800°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.

[0120]

[0121] The lithium precursor may preferably be at least one selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0122]

[0123] In the step (c), the lithium precursor may be added at least in an amount reduced from the molar ratio of lithium in the positive electrode active material of the step (a) based on the amount of lithium in the reheat-treated positive electrode active material, and as a specific example, when the positive electrode active material of the 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, for example, 0.0001 to 0.2, preferably 0.001 to 0.2, more preferably 0.005 to 0.19, even more preferably 0.01 to 0.18, even more preferably 0.05 to 0.17, and most preferably 0.09 to 0.16, with respect to the molar ratio of lithium of 1 in the positive electrode active material, and the lithium precursor may be added in an amount such that the molar ratio of lithium is increased or the crystal structure is recovered. Within this range, the lithium insufficient in the regenerated positive electrode active material is supplemented, and the crystallinity is improved, such as by increasing the crystallinity or recovering the crystal structure. By improving the battery characteristics of the regenerative positive electrode active material, there is an advantage.

[0124] As another example, the lithium precursor may be added in an amount corresponding to 1 to 40 mol% when the total lithium contained in the raw material positive electrode active material is 100 mol%, preferably may be added in an amount corresponding to 1 to 30 mol%, more preferably 3 to 25 mol%, and even more preferably may be added in an amount corresponding to 7 to 20 mol%, and within this range, lithium that may increase resistance in the regenerated positive electrode active material does not remain, so the battery characteristics are greatly improved, and the crystal structure can be restored with a smaller amount of lithium precursor than before, so there is an economic advantage.

[0125]

[0126] The above 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 750°C, more preferably 400 to 720°C, even more preferably 450 to 720°C, and even more preferably 550 to 720°C. Within this range, the crystal structure is recovered, so that the output performance of the battery is excellent.

[0127] 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.

[0128] The above annealing time may be, for example, 1 to 15 hours, preferably 2 to 15 hours, more preferably 4 to 13 hours, even more preferably 6 to 12 hours, and even more preferably 8 to 11 hours, and within this range, sufficient crystal structure recovery is achieved and there is an economic advantage.

[0129] The above annealing temperature can be reached at a heating rate of preferably 1 to 10°C / min, more preferably 1 to 5°C / min, and even more preferably 2 to 4°C / min, 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.

[0130] 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.

[0131]

[0132] 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.

[0133]

[0134] (d) Step of washing the annealed positive electrode active material (surface modification step)

[0135] The method for regenerating a positive electrode active material of the present invention includes (d) a step of washing the annealed positive electrode active material with a washing solution, in which case, a lithium precursor that is likely to remain on the surface of the positive electrode active material is removed with a small amount of the washing solution, thereby preventing a decrease in battery performance and gas generation due to a subsequent reaction between the residual lithium compound and the electrolyte, and reducing waste water.

[0136] The above washing may preferably include a step of mixing the annealed positive electrode active material and 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 lithium compounds that are likely to remain in the positive electrode active material.

[0137] The weight ratio of the annealed positive electrode active material and the cleaning solution may be, for example, 1:0.5 to 1:4, preferably 1:0.5 to 1:3, and more preferably 1:1 to 1:2.5, and within this range, there is an advantage in that the lithium compound remaining on the surface of the positive electrode active material is effectively removed with a small amount of the cleaning solution, and waste water is reduced.

[0138]

[0139] The above-mentioned cleaning solution may preferably be water or an aqueous solution of a basic lithium compound, and more preferably may be water. In this case, lithium compounds such as LiOH, Li2CO3, etc., which are likely to remain in the positive electrode active material, are effectively removed with a small amount of the cleaning solution, and while reducing waste water, the output performance of the battery is significantly improved.

[0140] The water may preferably be distilled water or deionized water, in which case, lithium compounds such as LiOH, Li2CO3, etc., which are likely to remain on the surface of the positive electrode active material, are effectively removed with a small amount of washing liquid, and while reducing waste water, the output performance of the battery is significantly improved.

[0141] The above basic lithium compound aqueous solution may preferably contain more than 0 wt% and less than 15 wt% of a lithium compound, more preferably more than 0 wt% and less than 10 wt% of a lithium compound, and in this case, lithium precursors such as LiOH and Li2CO3, which are likely to remain on the surface of the positive electrode active material, are effectively removed with a small amount of washing solution, thereby significantly improving the output performance of the battery without requiring wastewater treatment.

[0142]

[0143] 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 mechanical stirring or ultrasonic stirring may be used.

[0144] The above stirring can be preferably performed for less than 30 minutes, more preferably less than 20 minutes, even more preferably less than 15 minutes, and even more preferably 5 to 10 minutes, and within this range, residual lithium compounds are effectively removed.

[0145]

[0146] The above filtration can be performed, for example, by using a filter, a pressure-reducing filtration, or a filter press, in which case there is an advantage in that the washing solution and the positive electrode active material can be easily separated.

[0147]

[0148] The drying may be, for example, vacuum drying, and may be preferably performed in a vacuum state at a temperature of 70 to 200°C, more preferably 100 to 150°C, and even more preferably 120 to 140°C until there is no more weight change, for example, for 1 to 24 hours, and within this range, there is an effect of efficiently removing moisture contained in the washed positive electrode active material.

[0149] 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, for example, drying in a partial vacuum state or a low pressure state.

[0150]

[0151] In this description, pre-washing refers to washing performed before introducing a lithium precursor, and post-washing refers to washing performed after introducing a lithium precursor and annealing.

[0152]

[0153] (e) Step of surface coating the washed positive electrode active material

[0154] The method for regenerating a positive electrode active material of the present invention includes (e) a step of surface-coating a washed positive electrode active material with a coating agent, in which case the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0155] 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 700°C. In this case, the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0156]

[0157] The coating agent including the above metal may be a coating agent including 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 including at least one selected from the group consisting of B, W, Al, Ti and Mg, even more preferably a coating agent including boron (B), tungsten (W) or a mixture thereof, even more preferably a coating agent containing tungsten (W) and boron (B), and a specific example may be a coating agent containing tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0158] The coating agent containing the above metal may be, for example, an oxide, acid, etc. containing the metal as an element in the molecule.

[0159] 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.

[0160] 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.

[0161]

[0162] 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 1 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.

[0163]

[0164] The above heat treatment temperature may be preferably 150 to 600°C, more preferably 200 to 500°C, more preferably 250 to 450°C, and even more preferably 300 to 400°C, and within this range, there is an effect of improving structural stability and electrochemical performance without causing performance degradation due to thermal decomposition of the positive electrode active material.

[0165] The heat treatment time is preferably 1 to 10 hours, more preferably 2 to 8 hours, even more preferably 3 to 7 hours, still more preferably 4 to 6 hours, and particularly preferably 4.5 to 5.5 hours, 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.

[0166]

[0167] The above 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 belongs, and may be, for example, 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.

[0168]

[0169] 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.

[0170] The above 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, the average diameter is 10 to 100 nm, and the specific surface area is 20 to 100 m 2 / g, and within this range, it can be uniformly attached to the surface of the positive electrode active material, thereby imparting structural stability to the positive electrode active material, thereby improving the problems of deterioration of life characteristics and electrochemical performance due to lattice deformation or collapse of crystal structure of the positive electrode active material.

[0171] 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.

[0172] 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.

[0173]

[0174] After the surface coating, the obtained regenerated positive electrode active material is coated on aluminum foil using a scanning diffusion resistivity microscope (SSRM) to prepare a positive electrode, and the average resistance measured on a cross-section produced by embedding the positive electrode in an epoxy resin and then ion milling the slurry containing 96.5 wt% of the positive electrode active material, 1.5 wt% of carbon black, and 2 wt% of polyvinylidene fluoride (PVdF) in NMP (N-Methyl-2-pyrrolidone) is, for example, 6.42 log (R / Ω) or less, preferably 6.35 log (R / Ω) or less, more preferably 6.30 log (R / Ω) or less, and even more preferably 0.1 to 6.30 log (R / Ω). In this case, impurities derived from a conductive agent or binder remaining on the surface of the recovered positive electrode active material after the heat treatment are more cleanly removed by reheating at a predetermined temperature for a predetermined time instead of shear washing, thereby reducing the average resistance. The shear cleaning process is omitted, improving economy and productivity, and improving the efficiency, life characteristics, and resistance characteristics of the secondary battery.

[0175] After the surface coating, the obtained regenerated positive electrode active material is coated on aluminum foil using a scanning diffusion resistivity microscope (SSRM) with a slurry of 96.5 wt% of the positive electrode active material, 1.5 wt% of carbon black, and 2 wt% of polyvinylidene fluoride (PVdF) mixed in NMP (N-Methyl-2-pyrrolidone) to manufacture a positive electrode, and then the resistance value data obtained from the cross-section manufactured by embedding it in an epoxy resin and then ion milling is processed and changed into a log scale, and the average resistance standard deviation measured from the log scale image may be, for example, 0.42 or less, preferably 0.33 or less, preferably 0.31 or less, and more preferably 0.1 to 0.31. In this case, impurities derived from conductive materials or binders remaining on the surface of the recovered positive electrode active material after the heat treatment are more cleanly removed by reheating at a predetermined temperature for a predetermined time instead of shear washing, thereby reducing the average resistance, and the shear The washing process is omitted, improving economy and productivity, and improving the efficiency, lifespan, and resistance characteristics of secondary batteries.

[0176]

[0177] In this paper, the NX-10 AFM system (Park Systems) using the SSRM module can be used as a scanning diffusion resistance microscope, and SmartScan (Park Systems) can be used as the operating software. As specific operating conditions, the contact mode can be set, the acquired image pixels can be set to 1024 x 1024, the scan rate can be set to 0.2 Hz or more and 0.25 Hz or less, the bias can be set to 2.0 V or less, and the set point can be set to 1.0 V or less. In addition, as the AFM probe, solid diamond AFM probes (IMEC) made of boron-doped polycrystalline diamond with a length of 465 ㎛, a width of 50 ㎛, and a thickness of 5 ㎛ can be used.

[0178]

[0179] As an example, the a-axis lattice constant of the regenerated positive electrode active material obtained after the surface coating may be 2.8742 to 2.8750 Å, preferably 2.8744 to 2.8748 Å, and more preferably 2.8745 to 2.8747 Å, as measured by X-ray diffraction analysis, and the secondary battery has excellent efficiency, life characteristics, and resistance characteristics within this range.

[0180] As an example, the c-axis lattice constant of the regenerated positive electrode active material obtained after the surface coating may be 14.203 to 14.209 Å, preferably 14.204 to 14.207 Å, and more preferably 14.205 to 14.207 Å, as measured by X-ray diffraction analysis, and the secondary battery has excellent efficiency, life characteristics, and resistance characteristics within this range.

[0181] As an example, the cell volume of the regenerated positive electrode active material obtained after the surface coating is 101.62 to 101.68 Å as measured by X-ray diffraction analysis. 3 , preferably 101.64 to 101.67 Å 3 , more preferably 101.65 to 101.66 Å 3 It can be, and within this range, the efficiency, life characteristics, and resistance characteristics of the secondary battery are excellent.

[0182] As an example, the crystallite size of the regenerated positive electrode active material obtained after the surface coating may be 86 to 89 nm, preferably 87 to 89 nm, and more preferably 87 to 88 nm, as measured by X-ray diffraction analysis, and within this range, the efficiency, life characteristics, and resistance characteristics of the secondary battery are excellent.

[0183]

[0184] In addition, the present invention can provide a regenerated positive electrode active material characterized by being manufactured by the above positive electrode active material regeneration method, and in this case, it has excellent effects in terms of initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0185]

[0186] positive electrode active material

[0187] The cathode active material of the present invention is characterized by being manufactured by the above-described method for regenerating the cathode active material, and in this case, the internal and external resistance of the cathode active material is reduced, so that the efficiency, life characteristics, and resistance characteristics of the secondary battery are excellent.

[0188]

[0189] In addition, the cathode active material of the present invention 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 the cathode active material is manufactured by coating a slurry of 96.5 wt% of the cathode active material, 1.5 wt% of carbon black, and 2 wt% of polyvinylidene fluoride (PVdF) in NMP (N-Methyl-2-pyrrolidone) on aluminum foil using a scanning diffusion resistivity microscope (SSRM) to manufacture a cathode electrode, embedding it in an epoxy resin, and then ion milling the cross-section manufactured, and the average resistance measured on the a-axis is 6.42 log (R / Ω) or less and / or X-ray diffraction analysis The lattice constant is 2.8742 to 2.8750 Å, the c-axis lattice constant is 14.203 to 14.209 Å, and the cell volume is 101.62 to 101.68 Å. 3 It is characterized by the fact that, in this case, the internal and external resistance of the positive electrode active material is reduced, resulting in excellent efficiency, life characteristics, and resistance characteristics of the secondary battery.

[0190]

[0191] As another specific example, the positive electrode active material may include a compound represented by the following chemical formula 1, in which case the efficiency, life characteristics, and resistance characteristics are excellent.

[0192] [Chemical Formula 1]

[0193] Li a Ni x Mn y Co z M w O 2+δ

[0194] (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.)

[0195]

[0196] The above-mentioned positive electrode active material may contain, for example, 40 mol% or more of Ni, preferably 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, still more preferably 80 mol% or more, particularly preferably 81 mol% or more, and still more preferably 81 to 95 mol%, based on 100 mol% of the total metals excluding Li, and within this range, there are excellent effects in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0197]

[0198] The above positive electrode active material is manufactured by coating a slurry of 96.5 wt% of the positive electrode active material, 1.5 wt% of carbon black, and 2 wt% of polyvinylidene fluoride (PVdF) in N-Methyl-2-pyrrolidone (NMP) on aluminum foil using a scanning diffusion resistivity microscope (SSRM), embedding the slurry in an epoxy resin, and then ion milling the slurry to manufacture the positive electrode, and the average resistance measured on the cross-section may be, for example, 6.42 log(R / Ω) or less, preferably 6.35 log(R / Ω) or less, more preferably 6.30 log(R / Ω) or less, and even more preferably 0.1 to 6.30 log(R / Ω). In this case, impurities derived from a conductive agent or binder remaining on the surface of the positive electrode active material recovered after the heat treatment are more cleanly removed by reheat treatment at a predetermined temperature for a predetermined time instead of shear washing, so that the average resistance is reduced, and the shear washing process is omitted. It improves economic efficiency and productivity, and has excellent effects on the efficiency, life characteristics, and resistance characteristics of secondary batteries.

[0199] The above positive electrode active material is manufactured by coating a slurry of 96.5 wt% of the positive electrode active material, 1.5 wt% of carbon black, and 2 wt% of polyvinylidene fluoride (PVdF) in N-Methyl-2-pyrrolidone (NMP) on aluminum foil using a scanning diffusion resistivity microscope (SSRM), embedding the positive electrode in an epoxy resin, and then processing and changing the resistance value data obtained from a cross-section manufactured by ion milling into a log scale, and the average resistance standard deviation measured from the log scale image obtained by processing and changing the data may be, for example, 0.42 or less, preferably 0.33 or less, preferably 0.31 or less, and more preferably 0.1 to 0.31. In this case, impurities derived from a conductive agent or binder remaining on the surface of the positive electrode active material recovered after the heat treatment are more cleanly removed by reheating at a predetermined temperature for a predetermined time instead of shear washing, thereby reducing the average resistance, and the shear washing process By omitting it, economic efficiency and productivity are improved, and the efficiency, life characteristics, and resistance characteristics of the secondary battery are excellent.

[0200]

[0201] The above-mentioned positive electrode active material may have an a-axis lattice constant measured by X-ray diffraction analysis of, for example, 2.8742 to 2.8750 Å, preferably 2.8744 to 2.8748 Å, and more preferably 2.8745 to 2.8747 Å, and within this range, the efficiency, life characteristics, and resistance characteristics of the secondary battery are excellent.

[0202] The above-mentioned positive electrode active material may have a c-axis lattice constant measured by X-ray diffraction analysis of, for example, 14.203 to 14.209 Å, preferably 14.204 to 14.207 Å, and more preferably 14.205 to 14.207 Å, and within this range, the efficiency, life characteristics, and resistance characteristics of the secondary battery are excellent.

[0203] The above positive electrode active material has a cell volume of, for example, 101.62 to 101.68 Å as measured by X-ray diffraction analysis. 3 , preferably 101.64 to 101.67 Å 3 , more preferably 101.65 to 101.66 Å 3 It can be, and within this range, the efficiency, life characteristics, and resistance characteristics of the secondary battery are excellent.

[0204] The above-mentioned positive electrode active material may have a crystallite size measured by X-ray diffraction analysis of, for example, 86 to 89 nm, preferably 87 to 89 nm, and more preferably 87 to 88 nm, and within this range, the secondary battery has excellent efficiency, life characteristics, and resistance characteristics.

[0205]

[0206] The above-mentioned 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.

[0207]

[0208] 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.

[0209]

[0210] The coating agent may be included, for example, in an amount of 0.001 to 0.3 mol% relative to 1 mol% of metal in the regenerated 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, there is an effect of improving structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0211]

[0212] The above surface coating can be 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.

[0213]

[0214] The above-mentioned positive electrode active material may be, for example, a regenerative positive electrode active material, in which case it has the advantages of excellent economic efficiency and productivity.

[0215]

[0216] The following Figure 3 is a flowchart for a regeneration process of a positive electrode active material according to one embodiment of the present invention.

[0217]

[0218] Referring to Fig. 3, first, a positive electrode scrap is prepared as a positive electrode (step S10).

[0219] For example, a slurry prepared by mixing NCMA-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 120°C to produce a cathode sheet. After stamping out cathode plates of a certain size, the remaining cathode scrap can be prepared.

[0220] 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.

[0221]

[0222] Next, the prepared positive electrode scrap is crushed into an appropriate size (step S20).

[0223] 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 be 1 cm x 1 cm in size. 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.

[0224] 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.

[0225]

[0226] Next, the positive electrode scrap is heat-treated to recover the positive electrode active material (step S30).

[0227] Here, heat treatment is performed to thermally decompose the binder inside the active material layer.

[0228] As described above, the binder and conductive agent within the positive electrode active material layer are thermally decomposed into CO2 and H2O and removed through heat treatment. Since the binder is removed, the positive electrode active material is separated from the current collector, and the separated positive electrode active material can be easily sorted into a powder form. Therefore, step S30 alone can separate the positive electrode active material layer from the current collector, and further, the positive electrode active material within the active material layer can be recovered in powder form.

[0229] The above heat treatment can be performed in air or an oxygen atmosphere, and as a specific example, it can be performed in air. If the heat treatment is performed in a reducing gas or inert gas atmosphere, the binder and conductive agent are carbonized without thermal decomposition. If carbonized, the carbon component remains on the surface of the positive electrode active material, which reduces the performance of the regenerated positive electrode active material. However, if the heat treatment is performed in air or an oxygen atmosphere, the carbon component in the binder and conductive agent reacts with oxygen and disappears as gases such as CO and CO2, thereby removing the binder and conductive agent.

[0230] The above heat treatment is preferably performed at 300 to 650°C, and as a specific example, can be performed at 570°C. Below 300°C, it is difficult to remove the binder, making it impossible to separate the current collector. Above 650°C, the current collector melts, making it impossible to separate the current collector.

[0231] 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.

[0232] 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.

[0233] 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.

[0234] After the above heat treatment, the positive electrode active material can be recovered after cooling to room temperature, or by slow cooling or rapid cooling in the air.

[0235] In this description, room temperature may be a point within the range of 20 ± 5 ℃.

[0236]

[0237] The recovered positive electrode active material can be collected into a uniform size, for example, through a sieve, and preferably, the sieve can be sieved using a sieve of 270 to 400 mesh, more preferably, a sieve of 300 to 350 mesh. In this case, there is an advantage in that the positive electrode active material is evenly heat-treated in the subsequent reheat treatment step, so that the binder and conductive material are cleanly removed.

[0238]

[0239] Next, the recovered positive electrode active material is reheat-treated (step S40).

[0240] Here, the re-heat treatment is performed to more cleanly remove the binder and conductive agent remaining in the positive electrode active material recovered after the heat treatment in step S30. By performing the heat treatment instead of the shear washing, impurities derived from the binder or conductive agent are more easily removed, and by omitting the shear washing, there is an advantage in that the generation of wastewater is reduced.

[0241]

[0242] The above reheat treatment is performed in air or an oxygen atmosphere, and any impurities derived from binders or conductive materials remaining in the recovered positive electrode active material are completely removed, thereby reducing the internal and external resistance of the positive electrode active material, resulting in excellent efficiency, life characteristics, and resistance characteristics.

[0243] The air or oxygen can be supplied at a rate of, for example, 1 to 20 L / min, and as a specific example, at a rate of 3 L / min. Within this range, it has the effect of cleanly removing impurities derived from the binder or conductive material without damaging the positive electrode active material.

[0244]

[0245] The above reheat treatment temperature can be performed at 350 to 700°C, specifically 400 to 600°C, and within this range, the binder and conductive material are completely removed without damaging the positive electrode active material.

[0246] The above reheat treatment may preferably be performed at a temperature increase rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and a specific example is 5°C / min. Within this range, the temperature increase rate can be implemented without causing a strain on the heat treatment equipment, and has the advantage of not causing thermal shock to the positive electrode active material.

[0247]

[0248] The above reheat treatment time can be performed for, for example, 1 to 10 hours, and specifically, for 3 to 7 hours or 5 hours, and within this range, there is an effect of removing all impurities derived from the binder or conductive material without damaging the positive electrode active material.

[0249]

[0250] The reheat treatment temperature of step S40 may be preferably performed at a temperature equal to or higher than the heat treatment temperature of step S30, and more preferably at a higher temperature, since the collector is removed by the heat treatment of step S30. In this case, there is an advantage in that impurities derived from the conductive material or binder remaining in the recovered positive electrode active material are more cleanly removed.

[0251] The difference between the reheat treatment temperature of step S40 and the heat treatment temperature of step S30 may be, for example, 20 to 180°C, and specifically, 25 to 35°C, and there is an advantage in that impurities derived from the conductive material or binder remaining in the recovered positive electrode active material within this range are more cleanly removed.

[0252] The above reheat treatment may use the same or similar equipment as in the heat treatment step S30.

[0253] After the above reheat treatment, the positive electrode active material can be obtained by slow cooling or rapid cooling in the air, and in one embodiment, by cooling to room temperature.

[0254]

[0255] Next, a lithium precursor is added to the reheat-treated positive electrode active material and annealed (step S50).

[0256] It is important that the above annealing step be performed by adding a lithium precursor directly to the reheat-treated cathode active material and annealing it without a washing process. In this case, the pre-washing process is omitted, which greatly improves economic efficiency and productivity, and has the advantage of improving battery performance.

[0257]

[0258] In addition, since lithium loss occurs in the positive electrode active material during the preceding steps S30 and S40, such lithium loss is supplemented 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 steps, in step S50, the crystal structure of the positive electrode active material is restored through annealing, thereby improving the battery characteristics of the regenerated positive electrode active material or restoring it to the level of a newly formed positive electrode active material. Here, 'newly formed' is a concept opposite to 'regenerated', meaning something that is created for the first time, and is the same as the 'raw material' used in the examples.

[0259] LiOH is used as a specific example of the above lithium precursor.

[0260] 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 new positive electrode active material used in the positive electrode active material layer. Addition of a lithium precursor in an amount too excessive compared to the amount of lithium lost leaves unreacted lithium precursor in the regenerated positive electrode active material, which acts to increase resistance, and therefore, an appropriate amount of lithium precursor needs to be added. For example, when the molar ratio of lithium and other metals in the new positive electrode active material is 1, the lithium precursor may be added in an amount such that lithium is in a molar ratio of 0.001 to 0.4, and preferably, the lithium precursor may be added in an amount such that lithium is in a molar ratio of 0.01 to 0.2.

[0261] As a specific example, adding a lithium precursor at a molar ratio of 0.09 to 0.1 (based on lithium metal), which corresponds to the loss ratio relative to the lithium content in the new cathode active material based on ICP analysis results, results in a capacity improvement effect comparable to that of the new cathode active material. Here, the ICP analysis results have an error value of approximately ±0.02.

[0262]

[0263] The above annealing is performed in oxygen (O2) or air under conditions of, for example, 500 to 1000°C, and as a specific example, in air under conditions of 700 to 800°C, and this temperature should be adjusted within a limited range depending on the type of lithium precursor.

[0264] The above annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, since a temperature exceeding 1000°C causes thermal decomposition of the positive electrode active material, resulting in a deterioration in performance, the temperature should not exceed 1000°C. Accordingly, when Li2CO3 is used as the lithium precursor, the annealing temperature may be suitably 700 to 900°C, more preferably 710 to 780°C, and most preferably 750 to 780°C. In addition, when LiOH is used as the lithium precursor, the annealing temperature may be suitably 400 to 750°C, more preferably 450 to 720°C, and most preferably 550 to 720°C.

[0265]

[0266] The above annealing time is preferably 1 hour or longer, preferably 15 hours or shorter, and a specific example is 10 hours. A longer annealing time allows sufficient crystal structure recovery, but even long-term annealing does not significantly impact performance. The annealing equipment used in this process may be identical or similar to that used in the heat treatment step S30.

[0267]

[0268] Next, the annealed positive electrode active material is washed (step S60).

[0269] In the above washing step S60, lithium precursors that did not participate in the reaction in the above annealing step S50 and exist on the surface of the positive electrode active material in the form of LiOH and Li2CO3 are removed. Lithium impurities, such as lithium carbonate (Li2CO3), remaining on the surface of the regenerated positive electrode active material must be removed, as they may later react with the electrolyte to degrade battery performance and generate gas.

[0270] The above washing step S60 preferably involves mixing the positive electrode active material and the washing solution from the above annealing step S50 in a weight ratio of 1:0.5 to 1:4, specifically, a weight ratio of 1:1 to 1:2, filtering the mixture, and then drying the obtained solid positive electrode active material.

[0271]

[0272] The above-mentioned cleaning solution may preferably be a basic lithium compound aqueous solution containing more than 0 wt% and less than 10 wt% of water or a basic lithium compound, and more preferably, distilled water may be used as the cleaning solution. In this case, there is an advantage in that it is safe and inexpensive and does not dissolve transition metals present in the positive electrode active material.

[0273] The above water may preferably be distilled water or deionized water.

[0274] The above-mentioned basic lithium compound aqueous solution contains, for example, more than 0 wt% and less than 15 wt% of the basic lithium compound. If the lithium compound is not included, lithium supplementation is difficult, and if it exceeds 15 wt%, an excessive amount of lithium compound remains on the surface of the positive electrode active material, which may adversely affect a future annealing process.

[0275]

[0276] The above washing is preferably performed by mixing the annealed positive electrode active material and the washing solution, filtering the mixture, and then drying the obtained solid positive electrode active material.

[0277] The mixing of the annealed positive electrode active material and the cleaning solution is preferably performed while stirring, and the stirring is not particularly limited, but mechanical stirring or ultrasonic stirring may be used.

[0278] The above mechanical stirring is preferably performed under conditions of 250 to 350 rpm and 3 to 10 minutes.

[0279]

[0280] The above filtration can be performed, for example, by using a filter under reduced pressure or a filter press.

[0281] The above drying is, as a specific example, vacuum drying at 120 to 140°C.

[0282]

[0283] Next, surface coating can be performed on the washed positive electrode active material (step S70).

[0284] Surface coating is, for example, a method of coating a surface with a coating agent containing a metal, organic metal, or carbon component in a solid or liquid form 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.

[0285] Specifically, when a metal oxide or acid such as B, W, or BW is coated on the washed positive electrode active material and then heat-treated, a surface protective layer such as a lithium boron oxide layer is formed on the surface of the positive electrode active material.

[0286] The solid or liquid method of the above surface coating may be, for example, mixing, milling, spray drying or grinding.

[0287]

[0288] 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 S70, 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.

[0289]

[0290] secondary battery

[0291] The secondary battery of the present invention includes the above-described regenerated positive electrode active material, and in this case, the internal and external resistance of the positive electrode active material is reduced, so that the efficiency, life characteristics, and resistance characteristics of the secondary battery are excellent. 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 shear washing process is omitted, it has excellent economic efficiency and productivity.

[0292]

[0293] The secondary battery of the present invention may include all of the contents of the above-described regenerative positive electrode active material and the regeneration method thereof. Therefore, redundant description thereof is omitted herein.

[0294]

[0295] 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.

[0296]

[0297] [Example]

[0298] Example 1

[0299] After the positive electrode plate was pressed, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCMA-based lithium composite transition metal oxide (mol % ratio of Ni:Co:Mn:Al: 88:7:4:1)) was crushed and heat-treated in air at 570°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 3 L / min.

[0300] The above recovered positive electrode active material was sieved through a 325 mesh sieve to have a uniform particle size.

[0301] The above-mentioned cathode active material was re-heat-treated in air at 600°C for 5 hours.

[0302] LiOH, a lithium precursor, was added directly to the above-mentioned reheat-treated cathode active material without shear washing, and annealed under air at 700°C for 10 hours. In addition, air was supplied at 3 L / min. At this time, the lithium precursor was added in an amount capable of providing 15 mol% of lithium when the total lithium contained in the cathode active material in the raw material is assumed to be 100 mol%.

[0303] The above annealed positive electrode active material and distilled water were mixed in a 1:1 weight ratio, stirred at 300 rpm for 5 minutes, and then subjected to a post-washing process of obtaining a solid by filtration under reduced pressure. The solid was vacuum-dried at 130°C for 12 hours to obtain a washed positive electrode active material.

[0304] The above-mentioned washed cathode active material was coated with boric acid and then heated at 300°C for 5 hours to produce a final regenerated cathode active material. Here, boric acid was added in an amount corresponding to 500 ppm of boron lost in the post-washing process, the temperature increase rate until reaching the heat treatment temperature was 2°C / min, and air was supplied at 3 L / min.

[0305] Here, the molar ratio of lithium and other metals in the positive electrode active material was measured using an IC analyzer, etc. At this time, the measurement can be made using a general IC analyzer widely used in laboratories, but there is no deviation depending on the measuring device or method.

[0306]

[0307] Comparative Example 1

[0308] After the positive electrode plate was pressed, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCMA-based lithium composite transition metal oxide (mol % ratio of Ni:Co:Mn:Al: 88:7:4:1)) was crushed and heat-treated in air at 570°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 3 L / min.

[0309] The recovered positive electrode active material was subjected to shear washing. Shear washing was performed twice. In the first step, the positive electrode active material and distilled water were mixed at a weight ratio of 1:30, stirred at 300 rpm for 10 minutes, and filtered under reduced pressure to obtain the positive electrode active material. The positive electrode active material and distilled water were then mixed at a weight ratio of 1:10 and washed again.

[0310] LiOH, a lithium precursor, was added to the above-mentioned washed cathode active material and annealed at 700°C in air for 10 hours. In addition, air was supplied at 3 L / min. At this time, the lithium precursor was added in an amount capable of providing 15 mol% of lithium when the total lithium contained in the cathode active material in the raw material is assumed to be 100 mol%.

[0311] The above-mentioned annealed positive electrode active material was subjected to post-washing. The post-washing was performed by mixing the positive electrode active material and distilled water in a 1:1 weight ratio, stirring at 300 rpm for 5 minutes, and then filtering under reduced pressure to obtain a solid. The solid was vacuum-dried at 130°C for 12 hours to obtain the washed positive electrode active material.

[0312] The above-mentioned washed cathode active material was coated with boric acid and then heated at 300°C for 5 hours to produce a final regenerated cathode active material. Here, boric acid was added in an amount corresponding to 1000 ppm of boron lost in the previous process, the temperature increase rate until the heat treatment temperature was reached was 2°C / min, and air was supplied at 3 L / min.

[0313]

[0314] Comparative Example 2

[0315] The same procedure as in Comparative Example 1 was followed, except that the cathode active material recovered after heat treatment in Comparative Example 1 was not subjected to pre-washing, but rather a lithium precursor was directly added and annealing was performed, and boron was added in an amount corresponding to 500 ppm to the post-washed cathode active material.

[0316]

[0317] Comparative Example 3

[0318] The same procedure as Example 1 was followed, except that the reheat treatment temperature was changed to 300°C.

[0319]

[0320] Reference Example 1

[0321] Fresh NCMA-based lithium composite transition metal oxide (mol% ratio of Ni:Co:Mn:Al of 88:7:4:1) rather than a regenerative cathode active material was used.

[0322]

[0323] [Test Example I: Resistance Analysis and XRD Analysis]

[0324] The resistance and XRD analysis of the regenerated or newly produced positive electrode active materials manufactured or prepared in Example 1, Comparative Examples 1 to 3 and Reference Example 1 were performed to measure the a-axis lattice constant, c-axis lattice constant, cell volume and crystal grain size as follows, and the results are shown in Table 1 and Figure 2 below.

[0325]

[0326] * Electrode preparation: 96.5 wt% of the regenerated or newly produced positive electrode active materials prepared or prepared in Example 1, Comparative Examples 1 to 3 and Reference Example 1, 1.5 wt% of carbon black as a conductive material and 2 wt% of PVdF (Polyvinylidene Fluoride) as a binder were weighed and mixed with NMP (N-Methyl-2-pyrrolidone) to prepare a slurry. The prepared slurry was coated on aluminum foil to prepare a positive electrode. The prepared electrode was embedded in an epoxy resin and then a cross-section was prepared by ion milling.

[0327]

[0328] * Resistance analysis: The manufactured electrode cross-section was examined using a scanning diffusion resistance microscope, an NX-10 AFM system (Park Systems) with an SSRM module, and SmartScan (Park Systems) as the operating software. The specific operating conditions were set to Contact Mode, the acquired image pixels were set to 1024 x 1024, the scan rate was set to 0.2 Hz or more and 0.25 Hz or less, the bias was set to 2.0 V or less, and the set point was set to 1.0 V or less. In addition, as the AFM probe, solid diamond AFM probes (IMEC) with a length of 465 ㎛, a width of 50 ㎛, a thickness of 5 ㎛, and a boron-doped polycrystalline diamond (B-doped polycrystalline diamond) were used. The resistance value data obtained above was processed and changed to a log scale to obtain a log scale image. At this time, the resistance value data at four different locations on the same electrode cross-section were measured, and the average value thereof was used as the average resistance, and the standard deviation of the average value was used to calculate the average resistance standard deviation.

[0329]

[0330] * XRD Analysis: Lattice parameters and crystallite sizes were measured by XRD analysis, specifically, by XRD (X-Ray Diffraction) analysis using Cu Kα X-rays. The lattice parameters were calculated by indexing the XRD measurement data through Rietveld refinement, and the crystallite sizes were calculated using the Scherrer equation from the XRD measurement data. In addition, the cell volume was calculated as the product of the a-axis lattice constant and the c-axis lattice constant.

[0331]

[0332]

[0333] -: Immeasurable

[0334]

[0335] As shown in Table 1 above, it was confirmed that the average resistance and its standard deviation of the regenerated positive electrode active material of Example 1 according to the present invention were much lower than those of the regenerated positive electrode active materials of Comparative Examples 1 and 2, and also lower than that of Reference Example 1, which is a new positive electrode active material. From this, it was expected that Example 1 according to the present invention had an average resistance and an average resistance standard deviation within an image lower than that of a new positive electrode active material, as impurities derived from a conductive agent or binder were more cleanly removed by reheating the positive electrode active material recovered after heat treatment at a predetermined temperature and for a predetermined time, thereby improving the efficiency, life characteristics, and resistance characteristics of the secondary battery.

[0336] In addition, as shown in Table 1 above, it was confirmed that the a-axis lattice constant, c-axis lattice constant, cell volume, and crystal grain size of the regenerated positive electrode active material of Example 1 according to the present invention increased compared to Reference Example 1, which is a new positive electrode active material, according to XRD analysis.

[0337] Meanwhile, in Comparative Example 3, the temperature of the reheat treatment was low, so the binder and conductive material remained on the surface of the positive electrode active material after the reheat treatment, making it impossible to conduct resistance analysis and XRD analysis.

[0338]

[0339] In addition, as shown in FIG. 2 below, the electrode manufactured from the regenerated positive electrode active material according to the present invention (Example 1) has low resistance characteristics due to fewer high-resistance small particles, and is at a similar level to the electrode manufactured from the new positive electrode active material (Reference Example 1), but in the electrodes manufactured from the regenerated positive electrode active materials of Comparative Examples 1 and 2, a large number of high-resistance small particles of positive electrode active material were observed compared to Example 1. Through this, it was confirmed that the average resistance of the regenerated positive electrode active material of Example 1 was low. In FIG. 2 below, the binder or epoxy resin is shown in orange, and the darker the color, the higher the resistance, and the positive electrode active material is shown in blue to light green, and the closer it is to light green, the greater the resistance increases. In addition, the conductive material is shown in light light green.

[0340]

[0341] [Additional Example I]

[0342] Additional Example 1

[0343] The same procedure as Example 1 was followed, except that the reheat treatment was performed at 400°C.

[0344]

[0345] Additional Comparative Example 1

[0346] The same procedure as Example 1 was followed, except that the reheat treatment was performed at 800°C.

[0347]

[0348] [Experimental Example II: Resistance Analysis]

[0349] The resistance of the regenerated positive electrode active material manufactured in Additional Example 1 and Additional Comparative Example 1 was analyzed using the same method as in the above Test Example I, and the results are shown in Table 2 below.

[0350]

[0351] Addition Example 1Additional Comparative Example 1Image Average Resistance log(R / Ω)Image Within log(R / Ω)Standard DeviationAverage Resistance log(R / Ω)Image Within log(R / Ω)Standard Deviation16.380.446.470.5526.430.426.550.4336.420.386.440.4946.30.396.50.42Average (STDV)6.38(±0.06)0.416.49(±0.05)0.47

[0352] As shown in Table 2 above, Additional Example 1, which was reheat-treated at 400°C according to the present invention, had a low average resistance at the level of Reference Example 1, which is a new positive electrode active material, thereby confirming excellent efficiency, lifespan characteristics, and resistance characteristics of the secondary battery. On the other hand, Additional Comparative Example 1, which was reheat-treated at 800°C, which is outside the scope of the present invention, was confirmed to have a significantly increased average resistance, resulting in a deterioration in the performance of the secondary battery.

[0353]

[0354] [Additional Example II]

[0355] Reference Example 2

[0356] After the positive electrode plate was punched, the surface of the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCMA-based lithium composite transition metal oxide (mol% ratio of Ni:Co:Mn:Al is 88:7:4:1)) was scratched to obtain positive electrode material powder.

[0357]

[0358] Reference Example 3

[0359] After the positive electrode plate was pressed, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCMA-based lithium composite transition metal oxide (mol % ratio of Ni:Co:Mn:Al: 88:7:4:1)) was crushed and heat-treated in air at 570°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 3 L / min.

[0360]

[0361] [Experimental Example III: TGA Analysis]

[0362] The weight change rate according to the heat treatment time of the cathode material powder obtained in the above Reference Example 2 and the cathode active material recovered after heat treatment in Reference Example 3 was analyzed using TGA, and the results are shown in Figure 4 below. The temperature conditions during the TGA analysis started at 50°C and ended at 900°C, and the temperature was increased at a heating rate of 5°C / min.

[0363]

[0364] As shown in the following Figure 4, Reference Example 2 shows a large weight change at a heat treatment temperature of 300 to 750°C. From this, it can be determined that the temperature range for removing the binder and conductive material from the waste cathode material powder can be set to 300 to 750°C. However, since the current collector melts when the temperature exceeds 650°C, it was confirmed that the heat treatment temperature is preferably 300 to 650°C.

[0365] In addition, Reference Example 3 shows that the weight change begins at 350°C or higher and that the weight change occurs rapidly at over 700°C. From this, it can be seen that the reheat treatment temperature for removing impurities derived from the binder and conductive material in the recovered positive electrode active material is preferably 350 to 700°C.

[0366] Additionally, in Reference Example 3, the rapid weight change above 750°C was expected to be due to the deterioration and degradation of the positive electrode active material, which would result in an increase in battery resistance.

[0367]

[0368] [Explanation of symbols]

[0369] 10: Whole house

[0370] 20: Active material layer

[0371] 30: Bipolar sheet

[0372] 40: Bipolar plate

[0373] 50: Bipolar scrap

Claims

1. (a) A step of heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose a binder and a conductive material in the positive electrode active material layer, thereby separating the current collector from the positive electrode active material layer and recovering the positive electrode active material in the positive electrode active material layer; (b) a step of re-heat-treating the recovered positive electrode active material at 350 to 700°C for 1 to 10 hours; (c) a step of adding a lithium precursor to the reheat-treated positive electrode active material and annealing at 500 to 1000°C; (d) a step of washing the annealed positive electrode active material with a washing solution; and (e) a step of coating the surface of the washed positive electrode active material with a coating agent; characterized in that it comprises; Method for regenerating positive electrode active material.

2. In paragraph 1, In the above step (b), the reheat treatment temperature is characterized by being 450 to 650 ℃. Method for regenerating positive electrode active material.

3. In paragraph 1, The above positive electrode active material layer is characterized in that it includes at least one selected from the group consisting of a nickel-cobalt-manganese (NCM) positive electrode active material, a nickel-cobalt-aluminum (NCA) positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA) positive electrode active material. Method for regenerating positive electrode active material.

4. In paragraph 1, The heat treatment of step (a) is characterized in that it is performed for 30 minutes to 10 hours. Method for regenerating positive electrode active material.

5. In paragraph 1, The heat treatment of step (a) or the reheat treatment of step (b) is characterized in that it is performed in an air or oxygen atmosphere. Method for regenerating positive electrode active material.

6. In paragraph 1, Characterized in that the positive electrode active material reheat-treated in the above step (b) is provided to the annealing in the above step (c) without washing. Method for regenerating positive electrode active material.

7. In paragraph 1, In the above step (c), the lithium precursor is characterized in that it is at least one selected from the group consisting of LiOH, Li2CO3, LiNO3 and Li2O. Method for regenerating positive electrode active material.

8. In paragraph 1, In the step (c), the lithium precursor is added in an amount at least as much as the molar ratio of lithium in the cathode active material of the step (a) is reduced based on the amount of lithium in the reheat-treated cathode active material. Method for regenerating positive electrode active material.

9. In paragraph 1, The washing in the above step (d) is characterized in that the weight ratio of the positive electrode active material and the washing solution is 1:0.5 to 1:

4. Method for regenerating positive electrode active material.

10. In paragraph 1, The washing of the above step (d) is characterized by including a step of mixing the annealed positive electrode active material and the washing solution, then filtering the mixture, and a step of drying the positive electrode active material in the solid content obtained after the filtering. Method for regenerating positive electrode active material.

11. In paragraph 1, The above cleaning solution is characterized in that it is water or a basic lithium compound aqueous solution. Method for regenerating positive electrode active material.

12. In paragraph 1, The surface coating of the above step (e) is characterized in that it is 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 700°C. Method for regenerating positive electrode active material.

13. In paragraph 1, The regenerated positive electrode active material obtained after the surface coating is characterized in that the average resistance measured by scanning diffusion resistance microscopy (SSRM) is 6.42 log(R / Ω) or less. Method for regenerating positive electrode active material.

14. 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, The above cathode active material is manufactured by coating a slurry of 96.5 wt% of the cathode active material, 1.5 wt% of carbon black, and 2 wt% of polyvinylidene fluoride (PVdF) in N-Methyl-2-pyrrolidone (NMP) on aluminum foil using a scanning diffusion resistivity microscope (SSRM), embedding the cathode electrode in an epoxy resin, and then ion milling to produce a cross-section, and the average resistance measured is 6.42 log (R / Ω) or less and / or the a-axis lattice constant is 2.8742 to 2.8750 Å, the c-axis lattice constant is 14.203 to 14.209 Å, and the cell volume is 101.62 to 101.68 Å as measured by X-ray diffraction analysis. 3 characterized by Positive active material.

15. In paragraph 14, The above positive electrode active material is characterized in that the crystallite size measured by X-ray diffraction analysis is 86 to 89 nm. Positive active material.

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

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