Method for recycling positive electrode active material, recycled positive electrode active material manufactured thereby, and secondary battery comprising same

Abstract

The present invention relates to a method for recycling a positive electrode active material, a recycled positive electrode active material manufactured thereby, and a secondary battery comprising same and, more specifically, to a method for recycling a positive electrode active material, a recycled positive electrode active material manufactured thereby, and a secondary battery comprising same, the method comprising the steps of: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300°C to 650°C and thermally decomposing a binder and a conductive material in the positive electrode active material layer so as to recover a positive electrode active material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material and annealing same at 400°C to 1000°C under an oxygen atmosphere; and washing the annealed positive electrode active material. According to the present invention, the positive electrode active material results in significantly reduced waste water and reduced residual lithium on the surface of the positive electrode active material and has excellent resistance characteristics and lifespan characteristics. Also, the method for recycling a positive electrode active material is eco-friendly because no acid is used in recovery and recycling processes, and thus does not require neutralization and waste water treatment, thereby reducing processing costs, the method directly recycles the positive electrode active material without decomposition such that no metal elements are discarded, the method does not use an organic solvent such that there is no risk of toxic gas generation or explosion, and in particular, the method omits a washing step such that economic feasibility and productivity are greatly improved.

Description

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

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

[0002] This application claims the benefit of priority from Korean Patent Application No. 10-2023-0094928, filed July 20, 2023, and Korean Patent Application No. 10-2024-0087611, filed July 3, 2024, which is hereby incorporated by reference in its entirety.

[0003] The present invention relates to a method for regenerating a positive electrode active material, a regenerated positive electrode active material manufactured therefrom, and a secondary battery including the same, and more particularly, to a method for reusing a positive electrode active material, wherein a waste positive electrode is sintered at a predetermined temperature, a lithium precursor is directly added thereto without a washing process, and then the lithium precursor is annealed under an oxygen atmosphere, thereby removing the residual lithium of the positive electrode active material with a small amount of washing solution, thereby significantly reducing waste water while reducing the residual lithium on the surface of the positive electrode active material and producing a positive electrode active material having excellent resistance characteristics and lifespan characteristics, and a method for reusing 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 waste water treatment are not required, and does not decompose the positive electrode active material and is thus regenerated as is, so there is no waste of metal elements, and since no organic solvent is used, there is no generation of toxic gases or risk of explosion, and in particular, a washing process is omitted, thereby greatly improving economic efficiency and productivity.

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

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

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

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

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

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

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

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

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

[0013] Therefore, there is an urgent need to develop a method for safely regenerating cathode active materials with improved output performance without discarding metal elements from waste cathodes, using a small process and at a low cost, in an environmentally friendly manner.

[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 in which a lithium precursor is added directly without a washing process after calcining a waste cathode at a predetermined temperature, and the residual lithium of the cathode active material is removed with a small amount of washing solution, thereby significantly reducing waste water while reducing residual lithium on the surface of the cathode active material and providing a cathode active material with excellent resistance characteristics and lifespan characteristics, and further, no acid is used in the recovery and regeneration process of the cathode active material, which is environmentally friendly, and thus neutralization and waste water treatment are not required, and thus process costs are reduced, and no metal elements are discarded because the cathode active material is regenerated as it is without decomposition, and no organic solvent is used, so there is no generation of toxic gases or risk of explosion, and in particular, the washing process is omitted, thereby greatly improving economic efficiency and productivity.

[0015] In addition, the present invention aims to provide a secondary battery having excellent initial discharge capacity, rate performance, and capacity characteristics.

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

[0017] In order to achieve the above object, I) the present invention provides a method for regenerating a positive electrode active material, characterized by comprising the steps of: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose a binder and a conductive agent in the positive electrode active material layer, thereby recovering the positive electrode material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C in an oxygen atmosphere; and washing the annealed positive electrode active material.

[0018] II) In the above I), the positive electrode active material layer may preferably contain Ni in an amount of 60 mol% or more based on 100 mol% of the total metals excluding Li.

[0019] III) In the above I) or II), the positive electrode active material recovered after the thermal decomposition can preferably be provided to the annealing without washing.

[0020] IV) In the above I) to III), the recovered positive electrode active material of the annealing step may preferably contain crystalline LiF.

[0021] V) In the above I) to IV), the annealing step can preferably supply oxygen at 1 to 20 L / min.

[0022] VI) In the above I) to V), the oxygen may preferably have a purity of 59% or more.

[0023] VII) In the above I) to VI), the oxygen atmosphere may preferably not contain carbon dioxide (CO2).

[0024] VIII) In the above I) to VII), the lithium precursor may preferably include at least one of LiOH, Li2CO3, LiNO3, and Li2O.

[0025] IX) In the above I) to VIII), the lithium precursor may preferably be added in an amount corresponding to 1 mol% to 40 mol% when the total lithium contained in the recovered positive electrode active material is 100 mol%.

[0026] X) In the above I) to IX), the washing may preferably be performed at a weight ratio of 1:0.5 to 1:4 between the annealed positive electrode active material and the washing solution.

[0027] XI) In the above I) to X), the washed positive electrode active material may preferably have a residual Li2CO3 amount of 0.17 wt% or less.

[0028] XII) In the above I) to XI), the method for regenerating the positive electrode active material may preferably include a step of surface-coating the washed positive electrode active material to obtain a regenerable positive electrode active material.

[0029] XIII) In the above I) to XII), the surface coating may be preferably performed by coating at least one of a metal, an organic metal, and a carbon component on the surface in a solid or liquid manner and then heat-treating at 100 to 1200°C.

[0030] In addition, XIV) The present invention provides a regenerated positive electrode active material characterized by being manufactured by a method for regenerating a positive electrode active material according to I) to XIII).

[0031] In addition, XV) The present invention provides a regenerated cathode active material, characterized in that it is at least one selected from the group consisting of a lithium nickel oxide (LNO) cathode active material, a nickel-cobalt-manganese (NCM) cathode active material, a nickel-cobalt-aluminum (NCA) cathode active material, and a nickel-cobalt-manganese-aluminum (NCMA) cathode active material, contains crystalline LiF, and has a Li2CO3 residual amount of 0.17 wt% or less.

[0032] XVI) In the above XV), the regenerative positive electrode active material may preferably contain Ni in an amount of 60 mol% or more based on 100 mol% of the total remaining metals excluding Li.

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

[0034] In addition, XVIII) The present invention provides a secondary battery characterized by including the regenerative positive electrode active material of XIV) to XVII).

[0035] According to the present invention, by directly adding a lithium precursor without a washing process after calcining a waste positive electrode at a predetermined temperature and annealing under an oxygen atmosphere, and then cleanly removing the residual Li of the positive electrode active material with a small amount of washing liquid, waste water is greatly reduced while residual lithium on the surface of the positive electrode active material is reduced, and a positive electrode active material having excellent resistance characteristics and life characteristics is provided, and further, 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 waste water treatment are not required, process costs are reduced, and since the positive electrode active material is regenerated as it is without decomposition, no metal elements are discarded, and since no organic solvent is used, there is no generation of toxic gases or risk of explosion, and in particular, since the process after calcining the waste positive electrode is omitted, the economy and productivity are greatly improved.

[0036] 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.

[0037] Figure 1 is a drawing showing anode scrap that is discarded after cutting an electrode plate from a cathode sheet.

[0038] Figure 2 is an SEM photograph of the regenerated positive electrode active material manufactured in Example 1 and Comparative Example 1.

[0039] Figure 3 is a graph showing the change in capacity retention rate (%) and resistance increase rate (%) according to the number of cycles as a result of performing charge / discharge cycles on coin cells (Coin Half Cells, CHC) to which the regenerated positive electrode active materials manufactured in Examples 1 and 2 and Comparative Examples 1 to 3 were applied.

[0040] Figure 4 is a flowchart for a regeneration process of a positive electrode active material according to the present invention.

[0041] The present inventors, while studying a method for improving the electrochemical performance, resistance characteristics, and capacity characteristics of a recycled positive electrode active material in a method for directly regenerating the positive electrode active material from a waste positive electrode without decomposing the positive electrode active material (direct recycled method), discovered that when a waste positive electrode is sintered at a predetermined temperature, a lithium precursor is added directly without a washing process, and then annealed in an oxygen atmosphere and the residual lithium is washed away from the surface of the positive electrode active material, the residual lithium on the surface of the positive electrode active material is reduced and the residual lithium is cleanly removed with a small amount of washing solution, thereby significantly reducing waste water while improving the battery characteristics of the regenerated positive electrode active material, and based on this, they devoted themselves to further research and completed the present invention.

[0042]

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

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

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

[0046]

[0047] Method for regenerating positive electrode active material

[0048] The method for regenerating a positive electrode active material of the present invention comprises the steps of: heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose a binder and a conductive material in the positive electrode active material layer, thereby recovering the positive electrode active material in the positive electrode active material layer; adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C in an oxygen atmosphere; and washing the annealed positive electrode active material. In this case, waste water is greatly reduced, residual lithium on the surface of the positive electrode active material is reduced, and a positive electrode active material having excellent resistance characteristics and lifespan characteristics is provided. In addition, since no acid is used in the recovery and regeneration process, it is environmentally friendly, and since neutralization and waste water treatment are not required, process costs are reduced. Since the positive electrode active material is regenerated as it is without being decomposed, no metal elements are discarded. Since no organic solvent is used, there is no generation of toxic gases or risk of explosion. In particular, since the washing process is omitted, there are advantages of greatly improving economy and productivity.

[0049]

[0050] Below, the method for regenerating the positive electrode active material is explained in detail step by step.

[0051]

[0052] (a) A step of recovering positive electrode active material from a waste positive electrode

[0053] According to the present invention, the step of recovering a positive electrode active material from a waste positive electrode (a) may preferably be a step of recovering a positive electrode active material in a positive electrode active material layer by heat-treating a waste positive electrode having a positive electrode active material layer formed on a current collector at 300 to 650°C to thermally decompose a binder and a conductive material in the positive electrode active material layer, and in this case, the process is simple and has the effect of cleanly removing the binder, conductive material, and current collector.

[0054] The above-mentioned waste cathode may preferably be a cathode separated from a lithium secondary battery discarded after use, a defective cathode sheet or cathode scrap generated in a lithium secondary battery manufacturing process, and more preferably, a cathode scrap remaining after punching out a cathode plate from a cathode sheet.

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

[0056] 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.

[0057] As another specific example, the positive electrode active material is represented by the following chemical formula 1

[0058] [Chemical Formula 1]

[0059] Li a Ni x Mn y Co z M w O 2+δ

[0060] (In the above chemical formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti and Mg, and 1 <a≤1.1, 0<x<0.95, 0<y<0.8, 0<z<1.0, 0≤w≤0.1, -0.02≤δ≤0.02, x+y+z+w=1이다.)로 표시되는 화합물일 수 있다.

[0061]

[0062] The above-mentioned positive electrode active material contains, for example, 60 mol% or more of Ni, preferably 80 mol% or more, and more preferably 81 mol% or more, based on 100 mol% of the total metals excluding Li, and within this range, it has excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0063] 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.

[0064]

[0065] The above conductive material may be, for example, a carbon-based conductive material, and preferably, carbon black, carbon nanotubes (CNTs), or a mixture thereof.

[0066] 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.

[0067]

[0068] The above heat treatment can be performed, for example, in an air or oxygen atmosphere, and preferably can be performed in an oxygen atmosphere. In this case, the binder and the conductive material are thermally decomposed into CO2 and H2O and removed, thereby separating the positive electrode active material from the current collector, and the separated positive electrode active material has the advantage of being easily sorted in powder form.

[0069]

[0070] The oxygen may have a purity of, for example, 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90 to 99%, and within this range, there is an advantage in that the stability of Ni in the active material is increased while being removed without leaving any binder or conductive material residue.

[0071] The purity % of the above oxygen may be volume % or mol %.

[0072] The purity of the oxygen of this invention is not particularly limited when measured by a measurement method commonly used in the technical field to which the present invention belongs.

[0073] The above oxygen atmosphere may not contain, for example, carbon dioxide (CO2), in which case the positive electrode active material is easily separated from the current collector, and the separated positive electrode active material has the advantage of being easily sorted into powder form.

[0074] The above oxygen atmosphere may include, for example, argon as a component other than oxygen, in which case the positive electrode active material is easily separated from the current collector, and the separated positive electrode active material has the advantage of being easily sorted into powder form.

[0075] The oxygen can be supplied at, 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, the positive electrode active material can be easily separated from the current collector, and the separated positive electrode active material has the advantage of being easily sorted into a powder form.

[0076]

[0077] The above heat treatment temperature may be preferably 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 600°C, and within this range, the current collector does not melt, and only the binder, etc. is removed, so that the positive electrode active material is easily separated from the current collector.

[0078] 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.

[0079] 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.

[0080]

[0081] 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.

[0082]

[0083] The following drawing 1 shows the anode scrap that is discarded after cutting the anode plate from the anode sheet.

[0084] Referring to Fig. 1, a positive electrode sheet (30) is manufactured by coating a positive electrode active material layer (20) including a positive electrode active material, a conductive material, a binder, etc. on a long sheet-shaped positive electrode current collector, aluminum foil (10), and then the positive electrode sheet (30) is punched to a certain size to produce a positive electrode plate (40), and the remaining portion is then used to produce positive electrode scrap (50). The punching is one means of cutting the positive electrode sheet.

[0085] In addition, the above-mentioned positive electrode active material layer (20) is formed by coating a slurry containing a mixture of positive electrode active material, conductive material, binder, and solvent on aluminum foil (10). Since the slurry is very sensitive to the environment such as temperature, it is not easy to set the coating conditions, and thus waste positive electrode sheets are generated until conditions for manufacturing a positive electrode sheet (30) of the desired quality are found through a certain test.

[0086] For reference, in the examples below, anode scrap was used as the anode.

[0087]

[0088] The positive electrode active material recovered after the above pyrolysis can preferably be provided for annealing directly without washing, in which case the washing process is omitted, which greatly improves economy and productivity, and has the advantage of improving battery performance by including crystalline LiF.

[0089]

[0090] (b) A step of adding a lithium precursor to the recovered positive electrode active material and annealing it.

[0091] The method for reusing a positive electrode active material of the present invention includes (b) a step of adding a lithium precursor to the recovered positive electrode active material and annealing under an oxygen atmosphere. In this case, by annealing under an oxygen atmosphere, residual lithium on the surface of the positive electrode active material is reduced, and crystallinity is improved, such as by increasing crystallinity or restoring crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material. In addition, the washing process of the recovered positive electrode active material is omitted, so that economic efficiency and productivity are greatly improved.

[0092]

[0093] The recovered positive electrode active material may preferably contain crystalline LiF, and in this case, there is an advantage of providing a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics. Therefore, it is preferable to directly add a lithium precursor to the recovered positive electrode active material and anneale it without washing to improve battery characteristics.

[0094]

[0095] The above annealing step can supply oxygen at, for example, 1 to 20 L / min, preferably 3 to 15 L / min, more preferably 3 to 10 L / min, and even more preferably 3 to 7 L / min, and within this range, there is an advantage in that residual lithium on the surface of the positive electrode active material is reduced and crystallinity is improved, such as increased crystallinity or recovery of crystal structure.

[0096]

[0097] 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, the residual lithium on the surface of the positive electrode active material is reduced and the crystallinity is improved by increasing crystallinity or restoring the crystal structure.

[0098]

[0099] The above oxygen atmosphere may not contain, for example, carbon dioxide (CO2), in which case there is an advantage in that contact with carbon dioxide is suppressed, thereby maximizing the effect of reducing residual lithium on the surface of the positive electrode active material.

[0100] The above oxygen atmosphere may include, for example, argon as a component other than oxygen, in which case there is an advantage of improved crystallinity, such as increased crystallinity or recovery of crystal structure of the positive electrode active material.

[0101]

[0102] The lithium precursor may preferably be at least one selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0103]

[0104] The lithium precursor may preferably be added in an amount equal to at least the amount of lithium reduced from the molar ratio of lithium in the positive electrode active material of step (a) based on the amount of lithium in the recovered positive electrode active material, and more preferably, may be added in an amount such that the molar ratio of lithium is 0.0001 to 0.2 based on the molar ratio of lithium in the positive electrode active material of step (a), and within this range, the lithium insufficient in the regenerated positive electrode active material is supplemented, thereby improving the crystallinity, such as increasing the crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0105] The lithium precursor may be added in an amount corresponding to 1 to 40 mol%, preferably 1 to 25 mol%, more preferably 1 to 17 mol%, even more preferably 3 to 17 mol%, and particularly preferably 7 to 15 mol%, when the total amount of lithium contained in the recovered positive electrode active material is 100 mol%, and is very useful for improving battery characteristics.

[0106]

[0107] 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 Li2CO3, the melting point is 723°C, so it can be annealed at preferably 700 to 900°C, more preferably 700 to 800°C, and even more preferably 710 to 780°C. In the case of LiOH, the melting point is 462°C, so it can be annealed at preferably 400 to 720°C, more preferably 420 to 700°C, even more preferably 450 to 700°C, even more preferably 450 to 600°C, and even more preferably 450 to 480°C. Within this range, the crystal structure is recovered, so that the output performance of the battery is excellent.

[0108] 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.

[0109]

[0110] The above annealing time may be, for example, 1 hour or more, preferably 1 to 15 hours, more preferably 4 to 13 hours, and even more preferably 6 to 12 hours, and within this range, the crystal structure is restored, resulting in excellent output performance of the battery.

[0111]

[0112] The annealed positive electrode active material may have, for example, a Li2CO3 residual amount of 1.34 wt% or less, preferably 1.10 wt% or less, more preferably 0.95 wt% or less, and even more preferably 0.1 to 0.95 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0113] The above annealed positive electrode active material may have, for example, a LiOH residual amount of 1.0 wt% or less, preferably 0.1 to 1.0 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0114] The annealed positive electrode active material may have, for example, a total of Li2CO3 residue and LiOH residue of 2.22 wt% or less, preferably 2.0 wt% or less, more preferably 1.90 wt% or less, and even more preferably 0.1 to 1.90 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0115] In this invention, the amount of LiOH and Li2CO3 remaining on the surface of the positive electrode active material can be measured using a pH titrator MATi 06 (Metrohm). Specifically, 5 g of the positive electrode active material is dispersed in 100 ml of distilled water, mixed at 500 rpm for 5 minutes, filtered to remove the active material, and the resulting solution is titrated with a 0.1 M HCl solution, while measuring the change in pH value to obtain a pH titration curve. The amount of LiOH remaining and the amount of Li2CO3 remaining in the positive electrode active material are calculated using the pH titration curve obtained above.

[0116]

[0117] (c) Step of washing the annealed positive electrode active material

[0118] The method for regenerating a cathode active material of the present invention includes (c) a step of washing the annealed cathode active material, in which case, a lithium precursor that is likely to remain in the cathode active material is removed with a small amount of washing solution, thereby preventing a decrease in battery performance and gas generation due to a reaction between the residual lithium precursor and the electrolyte, and has the advantage of significantly reducing wastewater.

[0119]

[0120] 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 excess lithium that is likely to remain in the positive electrode active material.

[0121] The above drying may be preferably performed at 100 to 500°C, more preferably at 120 to 400°C, even more preferably at 120 to 300°C, and even more preferably at 120 to 200°C, and has the advantage that residual Li is effectively removed within this range.

[0122] The above drying can preferably be carried out under vacuum.

[0123] In this description, vacuum drying is not particularly limited as long as it is vacuum drying commonly performed in the technical field to which the present invention belongs.

[0124]

[0125] The above washing may be, for example, a weight ratio of the annealed positive electrode active material to the washing solution of 1:0.5 to 1:4, preferably 1:0.5 to 1:3, more preferably 1:0.5 to 1:2, and even more preferably 1:0.5 to 1:1.5, and within this range, the washing solution is greatly reduced, so that wastewater treatment is unnecessary, and lithium precursors such as LiOH and Li2CO3, which are likely to remain in the positive electrode active material, are effectively removed. Conventionally, the positive electrode active material recovered after heat treatment of the waste positive electrode is washed with water and then annealed. In this case, in order to remove the residual lithium in the washing step, a washing solution of 30 times or more the weight of the positive electrode active material is required, but in the present invention, the recovered positive electrode active material is immediately annealed and then washed without washing, so that the residual lithium is easily removed with a small amount of washing solution, and the wastewater is greatly reduced, while the residual lithium removal efficiency is superior compared to the conventional one.

[0126]

[0127] The above-mentioned cleaning solution may preferably be water or an aqueous alkaline lithium compound solution, and more preferably water. In this case, lithium precursors such as LiOH, Li2CO3, etc., which are likely to remain on the surface of the positive electrode active material, are cleanly removed with a small amount of the cleaning solution, thereby significantly reducing waste water while significantly improving the output performance of the battery.

[0128] The water is preferably distilled water or deionized water, and in this case, lithium precursors such as LiOH and Li2CO3, which tend to remain on the surface of the positive electrode active material, are cleanly removed with a small amount of washing liquid, thereby greatly reducing waste water and significantly improving the output performance of the battery.

[0129] 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 cleanly removed with a small amount of washing solution, thereby significantly reducing wastewater and significantly improving the output performance of the battery.

[0130]

[0131] The mixing of the annealed positive electrode active material and the cleaning solution is preferably performed by stirring, and the stirring is not particularly limited, but may be, for example, impeller stirring, magnetic stirring, or ultrasonic stirring.

[0132] 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 is effectively removed.

[0133]

[0134] The above-mentioned washed positive electrode active material may have, for example, a Li2CO3 residual amount of 0.17 wt% or less, preferably 0.15 wt% or less, more preferably 0.13 wt% or less, and even more preferably 0.05 to 0.13 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0135] The above-mentioned washed positive electrode active material may have a LiOH residual amount of, for example, 0.42 wt% or less, preferably 0.39 wt% or less, more preferably 0.05 to 0.39 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0136] The above-mentioned washed positive electrode active material may have a total amount of Li2CO3 residue and LiOH residue of, for example, 0.054 wt% or less, preferably 0.052 wt% or less, more preferably 0.05 to 0.052 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0137]

[0138] (d) A step of obtaining a reusable positive electrode active material by surface-coating the washed positive electrode active material.

[0139] The method for regenerating a positive electrode active material of the present invention includes the step of (d) surface-coating a washed positive electrode active material to obtain a reusable positive electrode active material, and in this case, there is an effect of improving structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0140] The surface coating is preferably performed by coating a coating agent containing at least one of a metal, an organic metal, and a carbon component on the surface in a solid or liquid manner and then heat-treating at 100 to 1200°C, more preferably 200 to 1000°C, and even more preferably 250 to 800°C. In this case, the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0141]

[0142] The coating agent including the above metal is preferably 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, and even more preferably a coating agent including boron (B), tungsten (W) or a mixture thereof, and even more preferably a coating agent containing tungsten (W) and boron (B), and a specific example thereof is a coating agent including tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0143] The coating agent containing the above metal may be, for example, an oxide, acid, etc. containing the above metal as an element in the molecule.

[0144] 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.

[0145] 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.

[0146]

[0147] 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.

[0148]

[0149] The above heat treatment temperature may be preferably 100 to 1000°C, more preferably 200 to 1000°C, and even more preferably 200 to 500°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.

[0150] The heat treatment time is preferably 1 to 16 hours, more preferably 3 to 7 hours, and within this range, the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0151]

[0152] 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.

[0153]

[0154] 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.

[0155] 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.

[0156] 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.

[0157] 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 under liquid nitrogen temperature (77K) using BELSORP-mino II of BEL Japan.

[0158]

[0159] The positive electrode active material according to the method for regenerating the positive electrode active material of the present invention may have, for example, a Li2CO3 residual amount of 0.17 wt% or less, preferably 0.15 wt% or less, more preferably 0.13 wt% or less, and even more preferably 0.05 to 0.13 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0160]

[0161] The positive electrode active material according to the regeneration method of the above positive electrode active material is, for example, LiOH. The residual amount may be preferably 0.42 wt% or less, preferably 0.39 wt% or less, and more preferably 0.05 to 0.39 wt%, and within this range, the positive electrode active material has excellent resistance characteristics and life characteristics.

[0162]

[0163] The positive electrode active material according to the above method for regenerating the positive electrode active material may have a total amount of residual Li2CO3 and residual LiOH of, for example, 0.054 wt% or less, preferably 0.052 wt% or less, more preferably 0.05 to 0.052 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0164]

[0165] Regenerated cathode active material

[0166] The regenerated positive electrode active material of the present invention is characterized by being manufactured by a method for regenerating the positive electrode active material, and in this case, waste water is greatly reduced while residual lithium on the surface of the positive electrode active material is reduced, and there is an advantage of excellent resistance characteristics and life characteristics.

[0167]

[0168] In addition, the regenerative positive electrode active material of the present invention is at least one selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, a nickel-cobalt-manganese (NCM)-based positive electrode active material, a nickel-cobalt-aluminum (NCA)-based positive electrode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and is characterized in that it contains crystalline LiF and has a Li2CO3 residual amount of 0.17 wt% or less, and in this case, there is an advantage in that residual lithium on the surface of the positive electrode active material is reduced and resistance characteristics and life characteristics are excellent.

[0169] The above-mentioned regenerative positive electrode active material contains, for example, 60 mol% or more of Ni, preferably 80 mol% or more, and more preferably 81 mol% or more, based on 100 mol% of the total metals excluding Li, and within this range, it has excellent effects in terms of initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0170]

[0171] The above-described regenerative positive electrode active material may preferably include at least one selected from the group consisting of lithium cobalt oxide such as LiCoO2 (hereinafter referred to as 'LCO'); lithium manganese oxide such as LiMnO2 or LiMn2O4; lithium iron phosphate compound such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxide such as LiNiO2; nickel manganese-based lithium composite metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn); and NCM-based lithium composite transition metal oxide in which some of nickel (Ni) in the lithium nickel oxide is replaced with manganese (Mn) and cobalt (Co). In this case, the electrochemical performance, resistance characteristics, and capacity characteristics are excellent.

[0172] The above regenerative positive electrode active material is a specific example of the following chemical formula 1

[0173] [Chemical Formula 1]

[0174] Li a Ni x Mn y Co z M w O 2+δ

[0175] (In the above chemical formula 1, M includes at least one selected from the group consisting of B, W, Al, Ti and Mg, and 1 <a≤1.1, 0<x<0.95, 0<y<0.8, 0<z<1.0, 0≤w≤0.1, -0.02≤δ≤0.02, x+y+z+w=1이다.)로 표시되는 화합물을 포함할 수 있고, 이 경우 전기화학적 성능, 저항 특성 및 용량 특성 등이 우수한 효과가 있다.

[0176]

[0177] The above-mentioned regenerative positive electrode active material preferably contains 80 mol% or more of Ni, more preferably 81 mol% or more, and even more preferably 81 to 95 mol%, and within this range, there is an excellent effect in charge capacity, resistance characteristics, and capacity characteristics.

[0178]

[0179] The above-described LiF crystal can be defined as having a peak in the XRD spectrum based on 2theta at 38 to 40°, preferably at 38.5 to 39°, in which case it has excellent effects in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0180] The above-described LiF may be included in an amount of, for example, 0.1 to 1 wt% based on the total weight of the positive electrode active material, preferably 0.3 to 1 wt%, and more preferably 0.3 wt% or more and less than 1 wt%, and within this range, it has excellent effects in initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0181] In this description, the content of LiF in a crystalline phase 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) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AEC analyzer. Here, the presence or absence of a crystalline phase of LiF can be confirmed by an XRD spectrum, and the content of LiF can be measured using a measurement method such as IC.

[0182]

[0183] The above-described LiF may be included in the surface of the regenerated positive electrode active material at, for example, 0.1 to 10 wt%, preferably 0.1 to 8 wt%, and more preferably 0.1 to 7 wt%, based on the XPS surface analysis spectrum, and within this range, it has excellent effects on initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0184] In the present invention, the crystalline LiF content on the surface of the regenerative positive electrode active material can be measured using XPS ((X-ray photoelectron spectroscopy) surface analysis spectrum (K-alpha, Nexsa (Thermo Fisher Scientific)), and the XPS surface analysis spectrum can quantify the composition ratio or elements of the constituent elements by using the area or height of photoelectrons emitted from the surface of the sample.

[0185]

[0186] The above-mentioned regenerated positive electrode active material may have a residual Li2CO3 content of, for example, 0.17 wt% or less, preferably 0.15 wt% or less, more preferably 0.13 wt% or less, and even more preferably 0.05 to 0.13 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0187] The above regenerative positive electrode active material is LiOH The residual amount may be, for example, 0.42 wt% or less, preferably 0.39 wt% or less, more preferably 0.05 to 0.39 wt%, and within this range, the positive electrode active material has excellent resistance characteristics and life characteristics.

[0188] The sum of the Li2CO3 residual amount and the LiOH residual amount of the above-mentioned regenerated positive electrode active material may be, for example, 0.054 wt% or less, preferably 0.052 wt% or less, more preferably 0.05 to 0.052 wt%, and within this range, the positive electrode active material has the advantage of excellent resistance characteristics and life characteristics.

[0189]

[0190] 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.

[0191]

[0192] 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.

[0193]

[0194] 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 positive electrode active material before coating treatment, preferably 0.01 to 0.3 mol%, more preferably 0.01 to 0.15 mol%, even more preferably 0.01 to 0.1 mol%, and even more preferably 0.01 to 0.05 mol%, and within this range, it has the effect of improving structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0195]

[0196] The surface coating is preferably performed by coating a coating agent containing at least one of a metal, an organic metal, and a carbon component on the surface in a solid or liquid manner and then heat-treating at 100 to 1200°C, more preferably 200 to 1000°C, and even more preferably 250 to 800°C. In this case, the properties of the positive electrode active material itself are maintained while improving structural stability and electrochemical performance.

[0197] The above positive electrode active material may preferably be a regenerated positive electrode active material, in which case there is an advantage of excellent economic efficiency and productivity.

[0198]

[0199] The following Figure 4 is a flowchart for a regeneration process of a positive electrode active material according to one embodiment of the present invention.

[0200] Referring to Figure 4, first, anode scrap is prepared using a waste cathode (Step S10). For example, a slurry prepared by mixing NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride with NMP (N-methyl pyrrolidone) is coated on aluminum foil and dried in a vacuum oven at approximately 120°C to produce a cathode sheet. From this, a cathode plate of a certain size is stamped out, and the remaining cathode scrap can be prepared.

[0201] 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.

[0202]

[0203] Next, the prepared positive electrode scrap is shredded into an appropriate size (step S20). Here, shredding includes cutting or shredding the positive electrode scrap into a size that is easy to handle. As a specific example, the shredded positive electrode scrap may have a size of 1 cm x 1 cm. The shredding may be performed using various dry crushing equipment, such as a hand mill, pin mill, disc mill, cutting mill, or hammer mill, or a high-speed cutter to increase productivity.

[0204] 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.

[0205]

[0206] Next, the positive electrode scrap is heat-treated to recover the positive electrode active material (step S30). Here, the heat treatment is performed to thermally decompose the binder within the active material layer.

[0207] Through the above heat treatment, the binder and conductive material within the active material layer are thermally decomposed into CO2 and H2O and removed. Since the binder is removed, the positive electrode active material is separated from the current collector, and the separated positive electrode active material can be easily separated into powder form. Therefore, step S30 alone can separate the 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.

[0208] It is important to perform the above heat treatment in an air or oxygen atmosphere, preferably an oxygen atmosphere. If the heat treatment is performed in a reducing gas or inert gas atmosphere, the binder and conductive agent will be carbonized without thermal decomposition. If carbonized, the carbon component will remain on the surface of the positive electrode active material, which will deteriorate the performance of the reusable positive electrode active material. However, if the heat treatment is performed in an air or oxygen atmosphere, specifically in an oxygen atmosphere, the carbon component in the binder and conductive agent will react with oxygen and disappear into gases such as CO and CO2, so that both the binder and conductive agent are removed. More specifically, the heat treatment can be performed under oxygen with a purity of 95% and argon with a purity of 5%, where carbon dioxide is removed.

[0209] The above heat treatment is preferably performed at 300 to 650°C, and as a specific example, at 590°C. At temperatures below 300°C, it is difficult to remove the binder, making it impossible to separate the current collector. At temperatures above 650°C, the current collector melts, making it impossible to separate the current collector.

[0210] 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 17°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.

[0211] 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.

[0212] 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.

[0213] After the above heat treatment, it can be cooled slowly or rapidly in the air.

[0214]

[0215] Next, a lithium precursor is added to the recovered positive electrode active material and annealed under an oxygen atmosphere (step S40).

[0216] It is important that the annealing step of the above step S40 directly adds a lithium precursor to the recovered positive electrode active material and anneals it without a washing process. In this case, the crystalline LiF formed on the surface of the positive electrode active material in the preceding heat treatment step S30 is included as is in the regenerated positive electrode active material, which has the advantage of improving the battery characteristics when applied to a secondary battery.

[0217] In addition, the annealing step is preferably carried out under oxygen, and is carried out under oxygen having a purity of 59% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and still more preferably 90 to 99%, and specifically, is carried out under oxygen 95% and argon 5% with carbon dioxide removed, in which case there is an advantage of reducing residual lithium on the surface of the positive electrode active material and improving battery characteristics.

[0218] In the above step S40, oxygen can be supplied at, for example, 1 to 20 L / min, and as a specific example, 3 to 8 L / min, and within this range, there is an advantage in that residual lithium on the surface of the positive electrode active material is reduced and crystallinity is improved, such as increased crystallinity or recovery of crystal structure.

[0219] In addition, since lithium loss occurs in the positive electrode active material during the preceding step S30, such lithium loss is supplemented in step S40. In addition, since a deformation structure (e.g., Co3O4 in the case of LCO active material) may appear on the surface of the positive electrode active material during the preceding step, in step S40, the crystal structure of the positive electrode active material is restored through annealing under oxygen, 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 'regeneration', and means something that is created for the first time, and is the same as the 'raw material' used in the examples.

[0220] LiOH is used as a specific example of the above lithium precursor.

[0221] It is preferable that the lithium precursor be added in an amount at least equal to the molar ratio of lithium lost compared to the molar ratio of lithium and other metals in the newly formed positive electrode active material used in the positive electrode active material layer. Adding an excessive amount of lithium precursor compared to the amount of lithium lost will leave unreacted lithium precursor in the regenerated positive electrode active material, which will increase resistance, and therefore, an appropriate amount of lithium precursor must be added.

[0222] In one embodiment, when the molar ratio of lithium in the new positive electrode active material is 1 with respect to the other metal (M), the lithium precursor may be added in an amount such that the molar ratio of lithium is 0.001 to 0.4, preferably in an amount such that the molar ratio of lithium is 0.01 to 0.4, and more preferably in an amount such that the molar ratio of lithium is 0.09 to 0.2. As a specific example, when the lithium precursor is added in an amount equivalent to the loss ratio of lithium content in the new positive electrode active material based on the ICP analysis results, the capacity improvement effect is shown to be equivalent to that of the new positive electrode active material. Here, the ICP analysis results have an error value of approximately ±0.02.

[0223] In one embodiment, the lithium precursor may be added in an amount corresponding to 1 to 40 mol%, more preferably 1 to 25 mol%, even more preferably 1 to 17 mol%, even more preferably 3 to 17 mol%, and particularly preferably 7 to 15 mol%, when the total lithium contained in the recovered positive electrode active material is 100 mol%, and is very useful for improving battery characteristics.

[0224] The above annealing is performed in an oxygen (O2) atmosphere at, for example, a temperature of 400 to 1000°C, preferably at a temperature of 600 to 900°C, and this temperature should be adjusted within a limited range depending on the type of lithium precursor.

[0225] The above annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, at a temperature exceeding 1000°C, thermal decomposition of the positive electrode active material occurs, resulting in a deterioration in performance, so it should not exceed 1000°C. Accordingly, when Li2CO3 is used as the lithium precursor, the annealing temperature is suitably 700 to 900°C, more preferably 700 to 800°C, even 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 is suitably 400 to 720°C, more preferably 420 to 700°C, and most preferably 450 to 700°C.

[0226]

[0227] The above annealing time is preferably set to 1 hour or more, for example, and preferably 1 to 15 hours, more preferably 4 to 13 hours, and even more preferably 6 to 12 hours, and a specific example is 10 hours. A long annealing time allows sufficient recovery of the crystal structure, but even long-term annealing does not significantly affect performance. In this case, the annealing equipment may be the same or similar equipment as that used in the heat treatment step S30.

[0228]

[0229] Next, the annealed positive electrode active material is washed (step S50).

[0230] Since the lithium precursor that did not participate in the reaction in the annealing step S40 exists on the surface of the positive electrode active material in the form of LiOH and Li2CO3, a residual lithium removal process is required to remove this. The impurities in the form of LiOH and Li2CO3 must be thoroughly removed as they can later react with the electrolyte, deteriorate the performance of the battery, and generate gases.

[0231] The above washing may be performed at a weight ratio of 1:0.5 to 1:4 between the annealed positive electrode active material and the washing solution, and specifically, may be at a weight ratio of 1:1. In this case, residual lithium is removed with a small amount of washing solution, so that waste water is greatly reduced, and there is an advantage in that a positive electrode active material with excellent resistance characteristics and life characteristics can be obtained.

[0232]

[0233] The washing may preferably be performed using distilled water or an aqueous solution of a basic lithium compound containing more than 0 wt% and less than 10 wt% of a basic lithium compound, more preferably distilled water, in which case there is an advantage of being safe and inexpensive while not dissolving transition metals present in the positive electrode active material.

[0234]

[0235] 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.

[0236] The mixing of the annealed positive electrode active material and the cleaning solution is preferably performed by stirring, and the stirring is not particularly limited, but may be mechanical stirring or ultrasonic stirring.

[0237] The above mechanical stirring is preferably performed under conditions of 100 to 1000 RPM and 5 to 30 minutes, more preferably 250 to 350 RPM and 5 to 10 minutes.

[0238] The above filtration is preferably vacuum filtration using a filter, and the above drying is vacuum drying at 50 to 140°C.

[0239]

[0240] Next, as an optional step, surface coating can be performed on the washed positive electrode active material (step S60).

[0241] The above 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 manner and then heat-treating it. If the heat-treatment temperature is too low, a surface protective layer by the desired heterogeneous metal is not formed, and if the heat-treatment temperature is too high, the performance of the battery deteriorates due to thermal decomposition of the positive electrode active material.

[0242] Specifically, when a metal oxide or acid such as B, W, or BW is coated on a washed cathode active material and then heat-treated, a surface protective layer such as a lithium borooxide layer is formed on the surface of the cathode active material.

[0243] The solid or liquid method of the above surface coating may be, for example, mixing, milling, spray drying or grinding.

[0244]

[0245] If the molar ratio of lithium to other metals in the positive electrode active material is 1:1 in the annealing step S40, the lithium in the positive electrode active material and the coating agent react in the surface coating step S60, so that the molar ratio of lithium to other metals in the positive electrode active material becomes 'less than 1:1', and such a regenerated positive electrode active material cannot fully exhibit 100% of the battery capacity. However, if the lithium precursor is added in excess in the annealing step S40 so that it contains 0.0001 to 0.1 molar ratio more than 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 reduction does not occur.

[0246]

[0247] secondary battery

[0248] The secondary battery of the present invention includes the above-described regenerated positive electrode active material, and in this case, the lithium remaining in the positive electrode active material is significantly reduced, so that the resistance characteristics and life characteristics are excellent. In addition, the residual lithium is cleanly removed with a small amount of washing liquid, so that waste water is greatly reduced, and since no acid or organic solvent is used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly, and in particular, since the initial washing process is omitted, it has excellent economic efficiency and productivity.

[0249]

[0250] The secondary battery of the present invention may include all of the contents of the positive electrode active material and the regeneration method thereof described above. Therefore, redundant description thereof is omitted herein.

[0251]

[0252] 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.

[0253]

[0254] [Example]

[0255] Example 1

[0256] After the positive electrode plate was pressed, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide (nickel content 88 mol%)) was crushed and heat-treated at 590°C for 30 minutes in an oxygen atmosphere to remove the binder and conductive material, and the current collector and positive electrode active material were separated, and then the positive electrode active material was recovered. Here, the temperature increase rate until the heat treatment temperature was reached was 5°C / min, and the oxygen atmosphere contained 95% oxygen and 5% argon (hereinafter referred to as “reactive gas”) and did not contain carbon dioxide. In addition, the reactive gas was supplied at 10 L / min.

[0257] LiOH, a lithium precursor, was added directly to the recovered positive electrode active material without washing, and annealed at 700°C for 10 hours under a reactive gas. In addition, the reactive gas was supplied at a rate of 3 L / min. At this time, the lithium precursor was added in an amount corresponding to 15 mol% when the total lithium contained in the recovered positive electrode active material is 100 mol%.

[0258] The above annealed positive electrode active material and distilled water were mixed in a 1:1 weight ratio, stirred at 500 rpm for 5 minutes, and then filtered under reduced pressure to obtain a solid. The solid was vacuum-dried at 100 to 130°C for 12 hours to obtain a washed positive electrode active material.

[0259] The above-mentioned washed cathode active material was mixed with boric acid (H3BO3) in a solid state and heated at 300°C for 5 hours to produce a final regenerated cathode active material coated with boron. Here, boric acid was added in an amount corresponding to 700 ppm of boron lost in the previous process, the temperature increase rate until reaching the heat treatment temperature was 2°C / min, and air was supplied at 3 L / min.

[0260] In this paper, the molar ratio of lithium to other metals in the positive electrode active material was measured using an ICP analyzer. While this can be measured using a standard ICP analyzer commonly used in laboratories, there is no variation depending on the measuring device or method.

[0261] Additionally, ppm in this document is based on weight unless otherwise defined.

[0262]

[0263] Example 2

[0264] A regenerated positive electrode active material was manufactured in the same manner as in Example 1, except that the reactive gas was supplied at 8 L / min in the annealing step of Example 1.

[0265]

[0266] Comparative Example 1

[0267] A regenerated positive electrode active material was manufactured in the same manner as in Example 1, except that the annealing step of Example 1 was performed in air.

[0268]

[0269] Comparative Example 2

[0270] A regenerated positive electrode active material was manufactured in the same manner as in Example 1, except that the annealing step of Example 1 was performed in air and air was supplied at 8 L / min.

[0271]

[0272] Comparative Example 3

[0273] The same procedure as in Example 1 was followed, except that the recovered positive electrode active material was washed with a basic lithium compound aqueous solution after heat-treating the positive electrode scrap in Example 1, and then annealed by adding LiOH, a lithium precursor. Here, the basic lithium compound aqueous solution contained 15 wt% of LiOH, and the weight ratio of the recovered positive electrode active material to the basic lithium compound aqueous solution was 1:1 for washing.

[0274]

[0275] [Test Example I: Residual lithium content after annealing]

[0276] The residual lithium content of the positive electrode active materials obtained after annealing in Examples 1 and 2 and Comparative Examples 1 and 2 was measured as follows, and the results are shown in Table 1 below.

[0277] * Residual lithium content: Measured using a pH titrator MATi 06 (Metrohm). Specifically, 5 g of the positive electrode active material was dispersed in 100 ml of distilled water, mixed at 500 rpm for 5 minutes, filtered to remove the active material, and titrated with a 0.1 M HCl solution to measure the change in pH value to obtain a pH titration curve. The obtained pH titration curve was used to calculate the residual LiOH and Li2CO3 amounts in the positive electrode active material.

[0278]

[0279] Classification LiOH (wt%) Li2CO3 (wt%) Total (wt%) Example 10.9890.8611.851 Example 20.9560.9251.882 Comparative Example 10.8201.7582.579 Comparative Example 20.8141.9632.777

[0280] As can be confirmed in Table 1 above, in Examples 1 and 2 according to the present invention, the amount of residual Li2CO3, the amount of residual LiOH, and the total amount thereof were reduced compared to Comparative Examples 1 and 2, and in particular, the amount of residual LiOH was greatly reduced.

[0281] [Test Example II: Residual Lithium Content of Regenerated Positive Electrode Active Material]

[0282] The residual lithium content of the regenerated positive electrode active material obtained after washing in Examples 1 and 2 and Comparative Examples 1 and 2 was measured as described above, and the results are shown in Table 2 below.

[0283]

[0284] Classification LiOH (wt%) Li2CO3 (wt%) Total (wt%) Example 10.41 10.119 0.530 Example 20.379 0.136 0.515 Comparative Example 10.37 20.22 10.593 Comparative Example 20.30 20.248 0.550

[0285] As can be confirmed in Table 2 above, in Examples 1 and 2 according to the present invention, the residual Li2CO3 amount, residual LiOH amount, and the total amount thereof were reduced compared to Comparative Examples 1 and 2, and in particular, the residual Li2CO3 amount was greatly reduced, so it could be expected that the battery characteristics were further improved.

[0286] [Experimental Example III: SEM Analysis]

[0287] The regenerated positive electrode active materials obtained in Example 1 and Comparative Example 1 were photographed using a SEM device, and are shown in Figure 2 below. The SEM images were taken using a standard SEM device commonly used in laboratories. Specifically, the images were taken using HITACHI's s-4200. However, there was no deviation depending on the measuring device or method.

[0288]

[0289] As can be seen in the following Figure 2, the regenerated positive electrode active material manufactured in Example 1 had no impurities on the surface and maintained a relatively spherical particle shape compared to the regenerated positive electrode active material manufactured in Comparative Example 1, and it was confirmed that the regenerated positive electrode active material manufactured in Comparative Example 1 had impurities remaining on the surface and the particles were broken and clumped together.

[0290]

[0291] [Experimental Example IV: CHC Cell Evaluation]

[0292] The capacity retention rate and resistance increase rate of the CHC (Coin Half Cell) manufactured using the regenerated positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were measured through the CHC evaluation as follows, and the results are shown in Fig. 3 and Table 3 below.

[0293] * CHC manufacturing: 96.5 wt% of the recycled positive electrode active material, 1.5 wt% of the conductive material carbon black, and 2 wt% of the binder PVdF were weighed and mixed with NMP to prepare a positive electrode active material slurry. The prepared positive electrode active material slurry was applied to a 20 μm thick aluminum foil, dried at 130°C for 1 hour, and then rolled to produce a positive electrode. Lithium metal was used as the negative electrode.

[0294] After bonding the manufactured positive and negative electrodes with a separator, an electrolyte containing ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7 by weight ratio and other additives was injected to manufacture CHC. After aging the manufactured CHC at 25 ℃ for 10 hours, it was charged to 4.25 V with a 0.05 C cut off at a constant current of 0.1 C in CC-CV mode, and then activated by discharging to 2.5 V with a constant current of 0.1 C, and then cycle evaluation was performed.

[0295] * Measurement of capacity retention at high temperature (45 ℃): Each of the CHCs manufactured with the regenerated positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 was formed at a 0.1 C rate, and then charged at a constant current of 0.33 C at 45 ℃ to 4.25 V with a 0.05 C cut off. Thereafter, discharge was performed to 2.5 V at a constant current of 0.33 C. The charge and discharge behavior was considered as one cycle, and this cycle was repeated 25 times. The discharge capacity after one cycle to the discharge capacity after 25 cycles were measured using a PNE-05-0.1 charger / discharger (Manufacturer: PNE Solution Co., Ltd., 5 V, 0.1 A), and the discharge capacity after one cycle was set as the initial capacity. Afterwards, the 25th discharge capacity and the initial capacity (100%) were compared to calculate the capacity retention rate using the following mathematical formula 1, and the results are shown in Figure 3 and Table 3 below.

[0296] [Mathematical Formula 1]

[0297] Capacity retention rate (%) = (discharge capacity after high temperature cycling / initial discharge capacity)*100

[0298] * Measurement of resistance increase rate at high temperature (45 ℃): Each of the CHCs manufactured with the regenerated positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 3 was formed at a 0.1 C rate, and then charged at a constant current of 0.33 C at 45 ℃ to 4.25 V with a 0.05 C cut off. Thereafter, discharge was performed to 2.5 V at a constant current of 0.33 C. The charge and discharge behavior was considered as one cycle, and the degree of resistance increase was measured while repeating this cycle 25 times, and the resistance increase rate was calculated using the following mathematical equation 2, and the results are shown in FIG. 3 and Table 3 below.

[0299] [Equation 2]

[0300] Resistance increase rate (%) = {(DCIR2-DCIR1) / DCIR1} *100

[0301] (In the above mathematical expression 2, DCIR1 represents the measured resistance (Ohm) at 1 cycle, and DCIR2 represents the measured resistance (Ohm) at 25 cycles.)

[0302]

[0303] Capacity retention rate (%; 25 cycles) Resistance increase rate (%; 25 cycles) Example 193.75 3.3 Example 293.25 9.4 Comparative example 187.6 95.2 Comparative example 286.9 97.6 Comparative example 391.07 5.8

[0304] As shown in Table 3 above, the regenerative positive electrode active materials according to the present invention (Examples 1 and 2) had a higher capacity retention rate than Comparative Examples 1 to 3, and the resistance increase rate was significantly lower, in the range of 53 to 60%, confirming that the battery characteristics were greatly improved.

[0305] In addition, as shown in the following Figure 3, it was confirmed that the regenerative positive electrode active material according to the present invention (Examples 1 and 2) had a high capacity retention rate and a significantly low resistance increase rate even when the number of cycles increased compared to Comparative Examples 1 to 3, thereby improving battery characteristics.

Claims

1. A step of recovering the positive active material within the positive active material layer by heat-treating a waste positive electrode, on which a positive active material layer is formed on a current collector, at 300 to 650 ℃ to thermally decompose the binder and conductive material within the positive active material layer; A step of adding a lithium precursor to the recovered positive electrode active material and annealing at 400 to 1000 °C under an oxygen atmosphere; and Characterized by including a step of washing the annealed positive electrode active material. Method for regenerating positive electrode active material.

2. In Paragraph 1, The above positive active material layer is characterized by containing 60 mol% or more of Ni based on 100 mol% of the total remaining metals excluding Li. Method for regenerating positive electrode active material.

3. In Paragraph 1, Characterized by providing the anode active material recovered after the above pyrolysis to the above annealing without washing. Method for regenerating positive electrode active material.

4. In Paragraph 1, The recovered positive active material from the annealing step is characterized by containing crystalline LiF. Method for regenerating positive electrode active material.

5. In Paragraph 1, The annealing step described above is characterized by supplying oxygen at a rate of 1 to 20 L / min. Method for regenerating positive electrode active material.

6. In Paragraph 1, The above oxygen is characterized by having a purity of 59% or higher. Method for regenerating positive electrode active material.

7. In Paragraph 1, The above oxygen atmosphere is characterized by not containing carbon dioxide (CO2). Method for regenerating positive electrode active material.

8. In Paragraph 1, The above lithium precursor is characterized by comprising one or more of LiOH, Li2CO3, LiNO3, and Li2O. Method for regenerating positive electrode active material.

9. In Paragraph 1, The lithium precursor is characterized by being added in an amount corresponding to 1 mol% to 40 mol% when the lithium contained in the recovered cathode active material is considered to be a total of 100 mol%. Method for regenerating positive electrode active material.

10. In Paragraph 1, The above washing is characterized by a weight ratio of annealed positive electrode active material to washing solution of 1:0.5 to 1:

4. Method for regenerating positive electrode active material.

11. In Paragraph 1, The above-described washed positive electrode active material is characterized by having a residual Li2CO3 content of 0.17 weight% or less. Method for regenerating positive electrode active material.

12. In Paragraph 1, The above method for regenerating the positive active material is characterized by including the step of surface coating the washed positive active material to obtain a regenerable positive active material. Method for regenerating positive electrode active material.

13. In Paragraph 1, The above surface coating is characterized by coating one or more of metals, organometallics, and carbon components onto the surface in a solid or liquid manner, and then heat-treating at 100 to 1200 ℃. Method for regenerating positive electrode active material.

14. Characterized by being manufactured by the method of regenerating the positive active material according to claims 1 to 13 Regenerative positive electrode active material.

15. One or more selected from the group consisting of lithium nickel oxide (LNO)-based cathode active materials, nickel-cobalt-manganese (NCM)-based cathode active materials, nickel-cobalt-aluminum (NCA)-based cathode active materials, and nickel-cobalt-manganese-aluminum (NCMA)-based cathode active materials, and Contains crystalline LiF, Characterized by a residual Li2CO3 content of 0.17 weight% or less Regenerative positive electrode active material.

16. In Paragraph 15, The above-described regenerated cathode active material is characterized by containing 60 mol% or more of Ni based on 100 mol% of the total remaining metals excluding Li. Regenerative positive electrode active material.

17. In Paragraph 15, The above-mentioned regenerated cathode active material is characterized by having its surface coated with a coating agent containing metal or carbon. Regenerative positive electrode active material.

18. Characterized by including a regenerated cathode active material according to any one of claims 14 to 17 Secondary battery.

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