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

Abstract

The present invention relates to a method for regenerating a positive electrode active material, a regenerated positive electrode active material manufactured thereby, and a secondary battery comprising same and, more specifically, to a method for regenerating a positive electrode active material, a regenerated positive electrode active material manufactured thereby, and a secondary battery comprising same, wherein the method comprises the steps of: (a) pulverizing a waste positive electrode including a current collector and a positive electrode active material layer coated thereon with a pin mill under dry conditions to obtain the positive electrode active material layer as a powder; (b) heat-treating the positive electrode active material layer powder at 460-530℃ in the air to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing at 400-1000℃; and (d) washing the annealed positive electrode active material with a washing solution. The method for regenerating a positive electrode active material according to the present invention has the advantages that: the binder and the conductive material can be easily removed even at a lower heat treatment temperature than the prior art; damage to the positive electrode active material due to washing can be minimized; the loss of lithium in the positive electrode active material is reduced to restore the crystalline structure with a small amount of a lithium precursor, along with the recovery of a positive electrode active material superior in battery characteristics; no acids are used for the recovery and regeneration processes, which is eco-friendly and reduces process costs because of no requirement for the neuralization and waste water treatment in response thereto; no metal elements are discarded by regenerating the positive electrode active material as it is without decomposing the positive electrode active material; and there is no risk of toxic gas generation or explosion because no organic solvents are used.

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. 10-2023-0078759, filed June 20, 2023, and Korean Patent Application No. 10-2024-0005347, filed January 12, 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 produced therefrom, and a secondary battery including the same, and more particularly, to a method for regenerating a positive electrode active material, which comprises: pulverizing a spent positive electrode with a pin mill under dry conditions before heat-treating the positive electrode to obtain a positive electrode active material layer as a powder, heat-treating the powder at a lower temperature than in the past to recover the positive electrode active material, and directly adding a lithium precursor to the recovered positive electrode active material without washing and annealing the recovered positive electrode active material, thereby enabling easy removal of a binder and a conductive material even at a lower heat-treating temperature than in the past, minimizing damage to the positive electrode active material due to washing, reducing lithium loss in the positive electrode active material to restore the crystal structure with a small amount of lithium precursor, and providing a positive electrode active material having excellent capacity characteristics and lifespan characteristics; and a positive electrode active material recovery and regeneration process that is environmentally friendly because it does not use acid, and thus reduces process costs because neutralization and wastewater treatment are not required, and does not decompose the positive electrode active material and thus regenerates it 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 greatly improved 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 an easy process, at low cost, and 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, which comprises: grinding a waste cathode with a pin mill under dry conditions before firing, thereby obtaining a cathode active material layer as a powder; heat-treating this at a lower temperature than in the past to recover the cathode active material; directly adding a lithium precursor to the recovered cathode active material without washing and annealing it, thereby easily removing a binder and a conductive material even at a lower heat treatment temperature than in the past, minimizing damage to the cathode active material due to washing; reducing lithium loss in the cathode active material, thereby providing a cathode active material with excellent capacity characteristics and lifespan 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; since the cathode active material is regenerated as it is without decomposition, no metallic elements are discarded; since no organic solvent is used, there is no generation of toxic gases or risk of explosion; and the economy and productivity are greatly improved.

[0015] In addition, the present invention aims to provide a secondary battery having excellent initial charge / discharge capacity and life 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: (a) grinding a waste positive electrode including a current collector and a positive electrode active material layer coated thereon with a pin mill under dry conditions to obtain a positive electrode active material layer in the form of a powder; (b) heat-treating the obtained positive electrode active material layer powder in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (d) washing the annealed positive electrode active material with a washing solution.

[0018] II) In the above I), the grinding by the pin mill in the step (a) can be performed under conditions of 5000 to 10000 rpm.

[0019] III) In the above I) or II), step (a) may include a pretreatment step of shredding or cutting the positive electrode.

[0020] IV) In the above I) to III), the positive electrode active material recovered after heat treatment in step (b) can be provided to the annealing in step (c) without washing.

[0021] V) In the above I) to IV), the sum of surface residual LiOH and Li2CO3 of the positive electrode active material recovered after heat treatment can be controlled to 1.35 wt% or less in the step (b).

[0022] VI) In the above I) to V), the positive electrode active material is 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, and may contain at least 60 mol% of Ni based on 100 mol% of the total of the remaining metals excluding Li.

[0023] VII) In the above I) to VI), the heat treatment in step (b) can be performed for 1.5 to 6 hours.

[0024] VIII) In the above I) to VII), the lithium precursor may be added in an amount corresponding to 3 to 17 mol% when the total lithium in the raw material positive electrode active material used in the positive electrode active material layer is 100 mol%.

[0025] IX) In the above I) to VIII), the lithium precursor may include at least one of LiOH, Li2CO3, LiNO3, and Li2O.

[0026] X) In the above I) to IX), the annealing can be performed in oxygen or air at 400 to 1000°C.

[0027] XI) In the above I) to X), the washing liquid may be water.

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

[0029] XIII) In the above I) to XII), the surface coating 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 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, the present invention is XV) 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, wherein the positive electrode active material comprises at least 60 mol% of Ni based on 100 mol% of the total of the remaining metals excluding Li, the total of residual LiOH and Li2CO3 is 1.35 wt% or less, and the crystal structure measured by XRD has an a-axis length of 2.871 to 2.888 Å, a c-axis length of 14.200 to 14.210 Å, and a cell volume of 101.45 to 101.82 Å. 3 And a regenerative positive electrode active material characterized by a crystal size of 72 to 84 nm is provided.

[0032] XVI) In the above XV), the surface of the regenerative positive electrode active material may be coated with a coating agent containing metal or carbon.

[0033] In addition, XVII) The present invention provides a secondary battery characterized by including the regenerative positive electrode active material of XV) or XVI).

[0034] In addition, XVIII) The present invention provides a method for regenerating a positive electrode active material, characterized by comprising the steps of: (a) applying an impact force of 5.1 to 10.2 N (Newton) and a centrifugal force of 2600 to 10700 N (Newton) under dry conditions to a waste positive electrode including a current collector and a positive electrode active material layer coated thereon to obtain a positive electrode active material layer in the form of powder; (b) heat-treating the obtained positive electrode active material layer powder in air at 460 to 530°C to recover a positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (d) washing the annealed positive electrode active material with a washing solution.

[0035] According to the present invention, a waste positive electrode is pulverized with a pin mill under dry conditions before heat-treating to obtain a positive electrode active material layer as a powder, which is then heat-treated at a lower temperature than conventionally to recover the positive electrode active material, and a lithium precursor is directly added to the recovered positive electrode active material without washing and annealed, so that binders and conductive agents are easily removed even at a lower heat-treating temperature than conventionally, damage to the positive electrode active material due to washing is minimized, the shape of the small particles is maintained without being broken, the crystal size is reduced and the strain is reduced to minimize the occurrence of cracks in the active material, and lithium loss in the positive electrode active material is reduced to restore the crystal structure with a small amount of lithium precursor, thereby providing a positive electrode active material having excellent capacity characteristics and life characteristics.

[0036] In addition, according to the present invention, since no acid is used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly, and since neutralization and wastewater treatment are not required, process costs are reduced, and since the positive electrode active material is regenerated as is without decomposition, there are no discarded metal elements, and since no organic solvent is used, a positive electrode active material is provided that does not generate toxic gases or pose a risk of explosion.

[0037] 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.

[0038] Figure 1 is a drawing showing anode scrap that is discarded after cutting an electrode plate from a cathode sheet.

[0039] Figure 2 shows the results of weight change according to heat treatment time, as analyzed by TGA (Thermogravimetric Analysis) of the positive electrode active material layer powder obtained after pin milling.

[0040] Figure 3 shows the results of weight change according to heat treatment temperature, as analyzed by TGA (Thermogravimetric Analysis) of the positive electrode active material layer powder obtained after pin milling.

[0041] Figure 4 is an SEM cross-section of the regenerated positive electrode active material manufactured in Example 2-3.

[0042] Figure 5 is an SEM cross-section of the regenerated positive electrode active material manufactured in Comparative Example 2-1.

[0043] Figure 6 is an SEM cross-section of the regenerated positive electrode active material layer manufactured in Comparative Example 2-2.

[0044] Figure 7 is a graph showing the initial capacity according to charge and discharge as a result of coin cell evaluation for each of the regenerated positive electrode active materials manufactured in Examples 2-1 to 2-7 and Comparative Example 2-3.

[0045] Figure 8 is a graph showing the high-temperature life characteristics as a result of coin cell evaluation for each of the regenerated positive electrode active materials manufactured in Examples 2-1 to 2-7 and Comparative Example 2-1.

[0046] Figure 9 is a flowchart for a regeneration process of a positive electrode active material as one embodiment according to the present invention.

[0047] The present inventors have discovered that when a spent positive electrode is pulverized with a pin mill under dry conditions before heat-treating the waste positive electrode to obtain a positive electrode active material layer as a powder, heat-treating the powder to recover the positive electrode active material, and directly adding a lithium precursor to the recovered positive electrode active material without washing and annealing, binders and conductive agents are easily removed even at a lower heat-treating temperature than in the past, damage to the positive electrode active material due to washing is minimized, the particle shape is maintained without breaking, the crystal size is reduced and strain is reduced, cracks in the positive electrode active material are minimized, and the crystal structure can be recovered with a small amount of lithium precursor, which provides economic advantages and improves the battery characteristics of the regenerated positive electrode active material, and based on this, they have devoted themselves to further research and completed the present invention.

[0048]

[0049] Hereinafter, a method for regenerating a positive electrode active material of the present invention, a regenerated positive electrode active material manufactured thereby, and a secondary battery including the same are described in detail.

[0050] 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.

[0051] 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.

[0052]

[0053] Method for regenerating positive electrode active material

[0054] The method for regenerating a positive electrode active material of the present invention is characterized by comprising the steps of: (a) grinding a waste positive electrode including a current collector and a positive electrode active material layer coated thereon with a pin mill under dry conditions to obtain a positive electrode active material layer in the form of a powder; (b) heat-treating the obtained positive electrode active material layer powder in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (d) washing the annealed positive electrode active material with a washing solution. In this case, by performing heat treatment at a lower temperature than before, the amount of lithium residue generated during the thermal decomposition process of the binder and conductive material is reduced, the particle shape in the positive electrode active material is maintained, the crystal size is reduced, and the strain is reduced to minimize cracks, the amount of lithium precursor required for the crystal structure recovery process is reduced, and by annealing the recovered positive electrode active material directly without washing, there is the advantage of minimizing damage to the positive electrode active material, and improving battery characteristics.

[0055]

[0056] Below, the method for regenerating the positive electrode active material is explained in detail step by step.

[0057]

[0058] (a) A step of obtaining a positive electrode active material layer in powder form from a positive electrode

[0059] The method for regenerating a positive electrode active material of the present invention comprises the step of (a) grinding a waste positive electrode including a current collector and a positive electrode active material layer coated thereon with a pin mill under dry conditions to obtain a positive electrode active material layer in the form of a powder. In this case, the positive electrode active material layer and the current collector are easily separated, so that the positive electrode active material layer can be obtained in the form of a powder, and there is an advantage in that the binder and the conductive agent can be removed at a lower temperature than in the prior art in a subsequent heat treatment process. In this case, if a different type of grinder such as a blender, a mixer, or a disk mill is used in addition to the pin mill, the positive electrode active material layer and the current collector are not completely separated from the waste positive electrode, so that a portion of the current collector is mixed into the positive electrode active material layer, and a portion of the current collector exists in the regenerated positive electrode active material, thereby deteriorating the characteristics of the battery.

[0060]

[0061] The above pin mill is not particularly limited as long as it is a pin mill commonly used in the technical field to which the present invention pertains, but specifically, it may be composed of a rotating plate (Rotor) having pins (impact pillars) radially attached thereto and a fixed plate (Stator) configured to engage with the Rotor. The raw material is supplied to the center of the Rotor and the fixed plate (Stator) and is dispersed together with the air flow generated during rotation, and as the circumferential speed of the pins increases in turn, it is continuously subjected to a strong impact force to be crushed, and then passes through a screen again and is discharged. Such a pin mill can crush into a desired particle size by adjusting the shape and quantity of the pins, the size of the screen, etc. When the positive electrode scrap is crushed with a pin mill, the current collector pieces are finely chopped and the positive electrode active material layer is separated from the current collector pieces. The current collector pieces remain inside the screen, and the positive electrode active material layer that passes through the screen is discharged as a powder. The positive electrode active material layer powder is in the form of agglomeration of the positive electrode active material, a binder, and a conductive agent. In this way, the positive electrode active material layer and the current collector can be separated by grinding using a pin mill under dry conditions.

[0062]

[0063] The above-mentioned pulverization by the pin mill can be performed under conditions of, for example, 5000 to 10000 rpm, preferably 5000 to 8000 rpm, more preferably 5000 to 7000 rpm, and even more preferably 5500 to 6500 rpm, and within this range, the separation of the positive electrode active material layer and the current collector can be smoothly achieved, so that only the positive electrode active material layer powder can be separated. Specifically, below the above range, the positive electrode active material layer and the current collector are not separated, resulting in a decrease in productivity, and above the above range, there is a problem in that the current collector is mixed into the positive electrode active material layer powder.

[0064]

[0065] The above-mentioned pulverization by the pin mill can preferably be carried out in a dry room under a nitrogen atmosphere, and in this case, there is an advantage in that the heat generated during the pulverization process suppresses the conversion of lithium carbonate present in the positive electrode active material layer into lithium hydroxide, and the positive electrode active material layer is easily separated from the current collector.

[0066] In this description, a dry room means a room in which the temperature is 20 to 22°C and the wet bulb temperature is maintained at -60 to -50°C.

[0067]

[0068] The average particle diameter of the positive electrode active material layer obtained from the above powder may preferably be the same as or similar to the average particle diameter of the raw material positive electrode active material layer, and in this case, there is an advantage in that the battery characteristics of the regenerated positive electrode active material are excellent.

[0069]

[0070] Before crushing the above-mentioned positive electrode with a pin mill, a pretreatment step of, for example, shredding or cutting may be included, in which case there is an advantage in that the separation of the positive electrode active material layer and the current collector is easier.

[0071] The above shredding or cutting may be performed using, for example, dry crushing equipment, and specifically, may be one or more of a hand mill, a disc mill, a cutting mill, and a hammer mill, and a high-speed cutter may be used to increase productivity.

[0072]

[0073] In this description, the dry conditions are not particularly limited as long as they are dry conditions commonly defined in the technical field to which the present invention belongs, and may be, for example, a state in which no solvent is added and / or a dry state and / or a condition in which dry grinding equipment is used.

[0074]

[0075] 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.

[0076] 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.

[0077] The above-mentioned positive electrode active material is preferably 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, and may contain at least 60 mol% of Ni based on 100 mol% of the total of the remaining metals excluding Li, and in this case, excellent reversible capacity and thermal stability are achieved.

[0078]

[0079] 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 in electrochemical performance, resistance characteristics, and capacity characteristics.

[0080] [Chemical Formula 1]

[0081] Lia Ni x Mn y Co z M w O 2+δ

[0082] (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.)

[0083]

[0084] The above positive electrode active material may contain Ni in an amount of, for example, 60 mol% or more, preferably 80 mol% or more, more preferably 81 mol% or more, and even more preferably 81 to 95 mol%, based on 100 mol% of the total metals excluding Li, and within this range, there is an excellent effect in charge capacity, resistance characteristics, and capacity characteristics.

[0085]

[0086] 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-ICPMS analysis device, or an IC-ICP-AEC analysis device.

[0087]

[0088] The above conductive material may be, for example, a carbon-based conductive material, and preferably, carbon black, CNT, or a mixture thereof.

[0089] 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.

[0090]

[0091] (b) A step of heat-treating the obtained positive electrode active material layer powder.

[0092] The method for regenerating a positive electrode active material of the present invention includes (b) a step of heat-treating the obtained positive electrode active material layer powder in air at 460 to 530° C. to recover the positive electrode active material. In this case, the binder and the conductive agent can be removed at a lower temperature than before, thereby minimizing damage to the positive electrode active material, reducing the amount of lithium residue generated by thermal decomposition of the binder and the conductive agent, maintaining the shape of small particles in the positive electrode active material, making the crystal size small and reducing the strain to minimize cracks, and improving the battery characteristics of the regenerated positive electrode active material.

[0093]

[0094] The above heat treatment temperature may be preferably 480 to 530°C, more preferably 480 to 500°C, and within this range, damage to the positive electrode active material is minimized, the amount of lithium residue generated during the thermal decomposition process of the binder and conductive material is reduced, the particle shape is maintained without being broken, the crystal size is reduced, and the strain is reduced, thereby minimizing cracks in the positive electrode active material and improving battery characteristics.

[0095]

[0096] The above heat treatment time may be, for example, 1.5 to 6 hours, preferably 2 to 5.5 hours, more preferably 2 to 5 hours, even more preferably 2.5 to 5 hours, and even more preferably 3 to 5 hours, and within this range, thermal decomposition of the binder and the conductive material is actively performed, damage to the positive electrode active material is minimized, the amount of lithium residue generated during the decomposition process of the binder and the conductive material is reduced, the particle shape is maintained without being broken, the crystal size is reduced, and the strain is reduced, so that cracks in the positive electrode active material are minimized and battery characteristics are improved.

[0097] 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.

[0098]

[0099] The above heat treatment may be performed at a temperature increase rate of, for example, 1 to 20°C / min, preferably 1 to 10°C / min, more preferably 3 to 8°C / min, and even more preferably 4 to 6°C / min, and within this range, it can be performed without putting a strain on the heat treatment equipment, and has the advantage of not causing thermal shock, etc. to the positive electrode active material layer powder.

[0100] The above heat treatment equipment is not particularly limited, but may be a furnace of various shapes, for example, a box type furnace or a rotary kiln, if it is heat treatment equipment commonly used in the technical field to which the present invention belongs.

[0101] The above rotary kiln has the advantage of excellent productivity as it allows continuous processing.

[0102]

[0103] The sum of surface residual LiOH and Li2CO3 of the positive electrode active material recovered after heat treatment in the above step (b) may be, for example, 1.35 wt% or less, preferably 1.28 wt% or less, more preferably 1.10 wt% or less, and even more preferably 0.1 to 1.10 wt%, and within this range, a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0104] The step (b) above provides a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics within a range in which the Li2CO3 remaining on the surface of the positive electrode active material recovered after heat treatment is, for example, 0.40 wt% or less, preferably 0.32 wt% or less, more preferably 0.25 wt% or less, even more preferably 0.20 wt% or less, still more preferably 0.15 wt% or less, and particularly preferably 0.05 to 0.15 wt%.

[0105] The above step (b) provides a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics within a range where the LiOH remaining on the surface of the positive electrode active material recovered after heat treatment is, for example, 0.99 wt% or less, preferably 0.96 wt% or less, and more preferably 0.05 to 0.96 wt%.

[0106]

[0107] In this paper, the content of surface residual LiOH and Li2CO3 of the positive electrode active material can be measured using a pH titrator T5 (Mettler Toledo). Specifically, 5 g of the positive electrode active material is dispersed in 100 ml of distilled water, mixed at 300 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 obtained pH titration curve is used to calculate the residual LiOH and residual Li2CO3 in the positive electrode active material.

[0108]

[0109] The positive electrode active material recovered in the above step (b) can preferably be provided for annealing in the above step (c) without washing, and in this case, there is an effect of minimizing damage to the surface of the positive electrode active material and minimizing the phenomenon of the positive electrode active material consisting of secondary particles and the small particles being released to become primary particles.

[0110] In the present invention, 'primary particle' means a primary structure of a single particle, and 'secondary particle' may mean an aggregate or assembly formed by coagulation or assembly of primary particles by material or chemical bonding between primary particles, or in other words, a secondary structure.

[0111]

[0112] (c) A step of adding a lithium precursor to the recovered positive electrode active material and annealing it.

[0113] The method for regenerating a positive electrode active material of the present invention includes (c) a step of adding a lithium precursor to the recovered positive electrode active material and annealing at 400 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 washing process of the recovered active material is omitted, thereby greatly improving economic efficiency and productivity and minimizing damage to the positive electrode active material.

[0114]

[0115] The above (c) annealing step may preferably be a step of adding a lithium precursor to the recovered positive electrode active material without washing and annealing it at 400 to 1000°C 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.

[0116]

[0117] The lithium precursor may preferably be at least one selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0118]

[0119] 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 (b) based on the amount of lithium in the raw material positive electrode active material, and as a specific example, when the recovered positive electrode active material of step (b) is a positive electrode active material represented by the chemical formula 1, the lithium precursor may be added in an amount such that the molar ratio of lithium is 0.0001 to 0.2, preferably 0.001 to 0.02, more preferably 0.005 to 0.17, even more preferably 0.007 to 0.015, and even more preferably 0.009 to 0.013, based on the molar ratio of lithium in the positive electrode active material. 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.

[0120] The lithium precursor may be added in an amount corresponding to 3 to 17 mol%, preferably 5 to 15 mol%, and even more preferably 8 to 13 mol%, when the total lithium contained in the raw material positive electrode active material is 100 mol%, and within this range, no residual precursor that may increase the resistance of the regenerated positive electrode active material remains, which is very useful for improving battery characteristics, and the crystal structure can be restored with a smaller amount of lithium precursor than before, which has an economic advantage.

[0121]

[0122] 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 600°C, more preferably 450 to 480°C, and within this range, the crystal structure is recovered, so that the output performance of the battery is excellent.

[0123] 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.

[0124]

[0125] (d) A step of washing the annealed positive electrode active material with a washing solution.

[0126] 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 in 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 reaction between the residual lithium precursor and the electrolyte, and there is an advantage in that wastewater treatment is not required.

[0127]

[0128] 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.

[0129] 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.

[0130] The above drying may preferably be vacuum drying.

[0131] In this description, vacuum drying is not particularly limited to vacuum drying commonly performed in the technical field to which the present invention belongs.

[0132]

[0133] The above washing may preferably include a step of mixing an annealed positive electrode active material and a washing solution in a weight ratio of 1:1.5 to 1:5.5, followed by a step of filtering, and a step of drying the positive electrode active material of solid content obtained after the filtering. In this case, there is an effect of effectively removing lithium precursors such as LiOH and Li2CO3, which are more likely to remain due to excessively added lithium, in order to suppress the cation mixing phenomenon that is likely to occur in a high-nickel positive electrode active material. This cation mixing phenomenon is a phenomenon that occurs because the particle sizes of nickel and lithium are similar.

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

[0135]

[0136] The annealed active material and the cleaning solution may be mixed preferably in a weight ratio of 1:1.5 to 1:4, more preferably in a weight ratio of 1:1.5 to 1:3, and even more preferably in a weight ratio of 1:1.5 to 1:2.5. In this case, there is an effect of effectively removing lithium precursors such as LiOH and Li2CO3, which are more likely to remain due to the excessively added lithium, in order to suppress the cation mixing phenomenon that is likely to occur in the high-nickel positive electrode active material.

[0137] In particular, when the annealed active material and the cleaning solution are mixed in a weight ratio of 1:1.5 to 1:3, preferably 1:1.5 to 2.5, there is an effect of further improving the initial discharge capacity (DCH) and efficiency of the regenerated positive electrode active material.

[0138] In addition, the conventional technology of washing and then annealing the positive electrode active material recovered from the waste positive electrode after heat treatment requires a washing solution of at least 30 times the amount of the positive electrode active material to remove residual lithium in the washing step, but the present invention uses a small amount of washing solution by annealing and then washing the recovered positive electrode active material, thereby eliminating the need for wastewater treatment and providing an effect of superior efficiency in removing residual lithium compared to the conventional technology.

[0139] The above-mentioned cleaning solution may be, for example, water or an aqueous alkaline lithium compound solution, and preferably may be 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 improving the output performance of the battery without requiring wastewater treatment.

[0140] The water is more preferably distilled water or deionized water, 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 liquid, thereby significantly improving the output performance of the battery without requiring wastewater treatment.

[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 cleanly 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 may be mechanical stirring or ultrasonic stirring.

[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 is effectively removed.

[0145]

[0146] (e) A step of obtaining a reusable positive electrode active material by surface-coating the washed positive electrode active material.

[0147] The method for regenerating a positive electrode active material of the present invention includes the step of (e) 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.

[0148] 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.

[0149]

[0150] The coating agent containing the above metal is preferably a coating agent containing at least one selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V and Y, more preferably a coating agent containing at least one selected from the group consisting of B, W, Al, Ti and Mg, and even more preferably a coating agent containing boron (B), tungsten (W) or a mixture thereof, and even more preferably a coating agent containing tungsten (W) and boron (B), and a specific example is a coating agent containing tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0151] The coating agent containing the metal may be, for example, an oxide or acid containing the metal as an element within the molecule.

[0152] 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.

[0153] 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.

[0154]

[0155] 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.

[0156]

[0157] 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.

[0158]

[0159] 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.

[0160]

[0161] 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.

[0162]

[0163] 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.

[0164] 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.

[0165] 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.

[0166]

[0167] As another example, the method for regenerating a positive electrode active material of the present invention is characterized by including the steps of: (a) applying an impact force of 5.1 to 10.2 N (Newton) and a centrifugal force of 2600 to 10700 N (Newton) under dry conditions to a waste positive electrode including a current collector and a positive electrode active material layer coated thereon to obtain a positive electrode active material layer in the form of powder; (b) heat-treating the obtained positive electrode active material layer powder in air at 460 to 530°C to recover the positive electrode active material; (c) adding a lithium precursor to the recovered positive electrode active material and annealing it at 400 to 1000°C; and (d) washing the annealed positive electrode active material with a washing solution. In this case, by performing heat treatment at a lower temperature than before, the amount of lithium residue generated during the thermal decomposition process of the binder and conductive material is reduced, the particle shape in the positive electrode active material is maintained, the crystal size is reduced, and the strain is reduced to minimize cracks, the amount of lithium precursor required for the crystal structure recovery process is reduced, and by annealing the recovered positive electrode active material directly without washing, there is the advantage of minimizing damage to the positive electrode active material, and improving battery characteristics.

[0168]

[0169] In the above step (a), the impact force may preferably be 5.1 to 8.1 N (Newton), more preferably 5.1 to 7.1 N (Newton), and even more preferably 5.6 to 6.6 N (Newton), and within this range, the positive electrode active material layer and the current collector are smoothly separated, so that only the positive electrode active material layer powder can be separated. Specifically, below the above range, the positive electrode active material layer and the current collector are not separated, resulting in a decrease in productivity, and above the above range, there is a problem in that the current collector is mixed into the positive electrode active material layer powder.

[0170] In the above step (a), the centrifugal force may preferably be 2600 to 6900 N, more preferably 2600 to 5300 N, and even more preferably 3200 to 4500 N, and within this range, the positive electrode active material layer and the current collector can be smoothly separated, so that only the positive electrode active material layer powder can be separated. Specifically, below the above range, the positive electrode active material layer and the current collector are not separated, resulting in a decrease in productivity, and above the above range, there is a problem in that the current collector is mixed into the positive electrode active material layer powder.

[0171] Specifically, under the above dry conditions, the waste cathode in the crusher can be crushed with an impact force of 5.1 to 10.2 N (Newton) and discharged with a centrifugal force of 2600 to 10700 N (Newton).

[0172]

[0173] In this description, the method for measuring the impact force and centrifugal force is not particularly limited as long as it is a measurement method commonly used in the technical field to which the present invention belongs. For example, the mass (kg) of the waste anode, the rotational speed per minute (rpm) of the pin mill, and the radius (m) of the pin mill can be calculated using the following mathematical equations 1 and 3, with a grinding time of 1 second and a speed after the waste anode collides with the pin as 0.

[0174] [Mathematical Formula 1]

[0175] Centrifugal force (N) = m * v 2 / r

[0176] In the above mathematical expression 1, m is the mass (kg) of the positive electrode, v is the number of revolutions per minute (rpm) of the pin mill, converted to speed (m / s) using the following mathematical expression 2, and r is the radius (m) of the pin mill.

[0177] [Equation 2]

[0178] Speed ​​(m / s) = (2r * π * rpm) / 60

[0179] In the above mathematical expression 2, r is the radius (m) of the pin mill, π is the circumference ratio, and rpm is the rotational speed per minute (rpm) of the pin mill.

[0180] [Equation 3]

[0181] Impact force (N) = m * (v1-v2) / △t

[0182] In the above mathematical expression 3, m is the mass (kg) of the waste anode, v1 is the velocity (m / s) just before the waste anode collides with the pin, v2 is the velocity (m / s) after the waste anode collides with the pin, and △t is the collision time (sec.), i.e., the crushing time, which is the time taken from v1 to v2.

[0183] In the present invention, v2 is 0 and the collision time is 1 second.

[0184]

[0185] The above steps (b), (c), and (d) share all the technical features of steps (b), (c), and (d) of the method for regenerating a positive electrode active material described above. Therefore, the description of the overlapping portion will be omitted.

[0186]

[0187] Regenerated cathode active material

[0188] The regenerated positive electrode active material of the present invention is characterized by being manufactured by the above-described method for regenerating the positive electrode active material, and in this case, by performing heat treatment at a lower temperature than in the past, the amount of lithium residue generated during the thermal decomposition process of the binder and the conductive agent is reduced, the shape of small particles in the positive electrode active material is maintained, the crystal size is reduced, the strain is reduced, cracks are minimized, the amount of lithium precursor required for the crystal structure recovery process is reduced, and the recovered positive electrode active material is annealed directly without washing, thereby reducing damage to the positive electrode active material, and improving battery characteristics.

[0189]

[0190] In addition, the regenerative cathode active material of the present invention is at least one selected from the group consisting of a nickel-cobalt-manganese (NCM)-based cathode active material, a nickel-cobalt-aluminum (NCA)-based cathode active material, and a nickel-cobalt-manganese-aluminum (NCMA)-based cathode active material, and contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li, and the total of residual LiOH and Li2CO3 is 1.35 wt% or less, and the a-axis length of the crystal structure measured by XRD is 2.872 to 2.878 Å, the c-axis length is 14.200 to 14.210 Å, and the cell volume is 101.45 to 101.82 Å. 3 And it is characterized by a crystal size of 72 to 80 nm. In this case, by heat-treating at a lower temperature than before, damage to the positive electrode active material is minimized, the amount of lithium residue generated during the decomposition process of the binder and conductive material is reduced, the shape of the small particles is maintained without being broken, the crystal size is reduced, and the strain is reduced to minimize cracks in the positive electrode active material, and the recovered positive electrode active material is annealed without washing, thereby reducing damage to the positive electrode active material, and improving battery characteristics.

[0191]

[0192] As another specific example, the above regenerative positive electrode active material is represented by the following chemical formula 1

[0193] [Chemical Formula 1]

[0194] Li a Ni x Mn y Co z M w O 2+δ

[0195] (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 있고, 이 경우 전기화학적 성능, 저항 특성 및 용량 특성 등이 우수한 효과가 있다.

[0196]

[0197] 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% based on 100 mol% of the total metals other than Li, and within this range, there is an excellent effect in charge capacity, resistance characteristics, and capacity characteristics.

[0198]

[0199] The above-mentioned regenerated positive electrode active material may have a Li2CO3 residual amount of, for example, 0.40 wt% or less, preferably 0.32 wt% or less, more preferably 0.25 wt% or less, even more preferably 0.20 wt% or less, still more preferably 0.15 wt% or less, and particularly preferably 0.05 to 0.15 wt%, and within this range, a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0200] The above regenerative positive electrode active material is LiOH The residual amount may be, for example, 0.99 wt% or less, preferably 0.96 wt% or less, and more preferably 0.05 to 0.96 wt%, and within this range, a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0201] The above-mentioned regenerated positive electrode active material may have a total amount of Li2CO3 residue and LiOH residue of, for example, 1.35 wt% or less, preferably 1.28 wt% or less, more preferably 1.10 wt% or less, and even more preferably 0.1 to 1.10 wt%, and within this range, a positive electrode active material having excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics is provided.

[0202]

[0203] The a-axis length of the crystal structure of the above-mentioned regenerated positive electrode active material measured by XRD may be, for example, 2.871 to 2.888 Å, preferably 2.872 to 2.878 Å, more preferably 2.874 to 2.876 Å, and within this range, there is an effect of recovering a lattice structure similar to that of the raw positive electrode active material.

[0204] The c-axis length of the crystal structure of the above-mentioned regenerated positive electrode active material measured by XRD may be, for example, 14.200 to 14.210 Å, preferably 14.203 to 14.206 Å, and within this range, there is an effect of recovering a lattice structure similar to that of the raw positive electrode active material.

[0205] The above-mentioned regenerated cathode active material has a cell volume measured by XRD of, for example, 101.45 to 101.82 Å. 3 , preferably 101.55 to 101.67 Å 3 It can be, and within this range, there is an effect of recovery into a lattice structure similar to that of the raw material positive electrode active material.

[0206] The above-mentioned regenerated positive electrode active material may have a crystal size measured by XRD of, for example, 72 to 84 nm, preferably 72 to 82 nm, more preferably 72 to 80 nm, even more preferably 72 to 78 nm, and even more preferably 72 to 74 nm, and within this range, there is an effect of recovering a lattice structure similar to that of the raw positive electrode active material.

[0207]

[0208] The above-mentioned regenerative positive electrode active material may have a surface coated with, for example, metal or carbon, and is preferably coated with metal. In this case, the structural stability of the positive electrode active material is improved without chemical and physical changes in the positive electrode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. In addition, the physicochemical properties are also improved due to the effect of reducing the amount of residual lithium and reducing pH by substituting a different element on the surface of the positive electrode active material.

[0209]

[0210] 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.

[0211]

[0212] 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.

[0213]

[0214] 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.

[0215]

[0216] The following Figure 9 is a flowchart for a regeneration process of a positive electrode active material according to one embodiment of the present invention.

[0217] Referring to Figure 9, first, anode scrap is prepared using a waste cathode (step S10). For example, a slurry prepared by mixing NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride with NMP (N-methyl pyrrolidone) is coated on aluminum foil and dried in a vacuum oven at approximately 120°C to produce a cathode sheet. After stamping out cathode plates of a certain size, the remaining cathode scrap can be prepared.

[0218] The above 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.

[0219]

[0220] 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, a disc mill, a cutting mill, a hammer mill, or a high-speed cutter to increase productivity.

[0221] 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.

[0222]

[0223] Next, the crushed positive electrode scrap is crushed in a pin mill under dry conditions to obtain a positive electrode active material layer in powder form (step S30).

[0224] The above pin mill is composed of a rotating plate (Rotor) with pins (impact pillars) radially attached thereto and a fixed plate (Stator) that is arranged to engage with the rotating plate. The raw material is supplied to the center of the rotating plate (Rotor) and the fixed plate (Stator), and is dispersed along with the air flow generated during the rotation. As the circumferential speed of the pins increases, it is continuously subjected to strong impact force, and is pulverized. After passing through the screen again, the raw material is discharged. This pin mill can pulverize the raw material into a desired particle size by adjusting the shape and quantity of the pins and the size of the screen. When the positive electrode scrap is pulverized with the pin mill, the current collector pieces are finely chopped and the positive electrode active material layer is separated from the current collector pieces. The current collector pieces remain inside the screen, and the positive electrode active material layer that passes through the screen is discharged as a powder. The positive electrode active material layer powder is a form in which the positive electrode active material, binder, and conductive material are clumped together. In this way, the positive electrode active material layer and the current collector can be separated by pulverization using the pin mill under dry conditions.

[0225] The above-mentioned pulverization by the pin mill can be performed under conditions of, for example, 5000 to 10000 rpm, preferably 5000 to 8000 rpm, more preferably 5000 to 7000 rpm, and even more preferably 5500 to 6500 rpm, and as a specific example, is performed under conditions of 6000 rpm. Within this range, the separation of the positive electrode active material layer and the current collector is smooth, so that only the positive electrode active material layer powder can be separated. When the pulverization speed is less than 5000 rpm, the separation of the positive electrode active material layer and the current collector is not easy, and a long period of time is required for processing, and when the pulverization speed exceeds 10000 rpm, there is a problem that the current collector is mixed into the positive electrode active material layer powder.

[0226]

[0227] Next, the obtained positive electrode active material layer powder is heat-treated in air at 460 to 530°C to recover the positive electrode active material (step S40). Here, the heat treatment is performed to thermally decompose the binder and conductive material within the active material layer.

[0228] Through the above-described air heat treatment, the binder and conductive material within the active material layer are thermally decomposed into CO2 and H2O and removed. As the binder is removed, the positive electrode active material is separated from the positive electrode active material layer.

[0229] It's crucial that the above heat treatment be performed in air. If heat treatment is performed in a reducing or inert gas atmosphere, the binder and conductive agent will carbonize rather than undergo thermal decomposition. Carbonization leaves carbon components on the surface of the positive electrode active material, degrading the performance of the reusable positive electrode active material. However, if heat treatment is performed in air, the carbon components in the binder and conductive agent react with oxygen and disappear into gases such as CO and CO2, thus removing both the binder and conductive agent.

[0230] The above heat treatment is performed at a lower temperature than conventionally, 460 to 530°C, preferably 480 to 530°C, and more preferably 480 to 500°C, since the current collector has been separated in the previous process. Below 460°C, the thermal decomposition of the binder and the conductive agent is not smooth, and if it exceeds 530°C, the amount of lithium residue generated during the thermal decomposition of the binder and the conductive agent increases, the particle shape is broken, the crystal size increases, and the strain increases, which increases the occurrence of cracks in the positive electrode active material. In addition, there is an economic advantage of reducing costs by removing the binder and the conductive agent by performing the heat treatment at a lower temperature than conventionally.

[0231]

[0232] The heat treatment is preferably performed at a temperature increase rate of 1 to 20°C / min, more preferably 1 to 10°C / min, even more preferably 3 to 8°C / min, and even more preferably 4 to 6°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, etc., to the positive electrode active material layer powder.

[0233]

[0234] 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 1.5 to 6 hours, preferably 2 to 5.5 hours, more preferably 3 to 5 hours, and even more preferably 4 to 5 hours, and within this range, the binder is sufficiently thermally decomposed and also has an excellent thermal decomposition efficiency.

[0235] 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.

[0236] After the above heat treatment, it can be cooled slowly or rapidly in the air.

[0237]

[0238] Next, the recovered positive electrode active material is annealed by adding a lithium precursor (step S50).

[0239] It is important in the above annealing step to add a lithium precursor and anneal the recovered positive electrode active material directly 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 S40 is included as is in the regenerated positive electrode active material, which has the advantage of improving battery characteristics when applied to a secondary battery and minimizing damage to the positive electrode active material due to washing.

[0240]

[0241] In addition, since lithium loss occurs in the positive electrode active material during the preceding step 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 step, 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', and means something that is created for the first time, and is the same as the 'raw material' used in the examples.

[0242] The lithium precursor includes at least one of LiOH, Li2CO3, LiNO3, and Li2O, and LiOH is used as a specific example.

[0243] 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.

[0244] 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.

[0245]

[0246] In the preceding step S40, the amount of lithium lost is reduced by performing heat treatment at a lower temperature than before, so the lithium precursor is preferably added in an amount corresponding to 3 to 17 mol%, more preferably 5 to 15 mol%, and even more preferably 8 to 13 mol%, when the total lithium in the raw material positive active material used in the positive active material layer is 100 mol%.

[0247]

[0248] The above annealing is performed in air under conditions of, for example, 400 to 1000°C, preferably 600 to 900°C, and this temperature should be adjusted within a limited range depending on the type of lithium precursor.

[0249] The above annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, at a temperature exceeding 1000°C, thermal decomposition of the positive electrode active material occurs, resulting in a decrease in performance, so the temperature should not exceed 1000°C. Accordingly, when Li2CO3 is used as the lithium precursor, the annealing temperature is preferably 700 to 900°C, more preferably 710 to 780°C, and even more preferably 750 to 780°C. In addition, when LiOH is used as the lithium precursor, the annealing temperature is preferably 400 to 600°C, more preferably 450 to 480°C, and even more preferably 470 to 480°C.

[0250]

[0251] The above annealing time is preferably 1 hour or longer, preferably 15 hours or shorter, and more preferably 4 to 6 hours. A longer annealing time allows sufficient crystal structure recovery, but even long-term annealing does not significantly affect performance. The annealing equipment used in this process may be identical or similar to that used in the heat treatment step S40.

[0252]

[0253] Next, the annealed positive electrode active material is washed with a washing solution (step S60).

[0254] Since the lithium precursor that did not participate in the reaction in the above annealing step S50 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.

[0255] The above-mentioned washing solution can be mixed with the annealed positive electrode active material and the washing solution at a weight ratio of preferably 1:1.5 to 1:5.5, more preferably 1:1.5 to 1:4, even more preferably 1:1.5 to 1:3, and even more preferably 1:1.5 to 1:2.5. In this case, since residual lithium is removed with a small amount of the washing solution, there is an advantage in that a positive electrode active material having excellent initial discharge capacity, rate performance, and capacity characteristics can be obtained without the need for wastewater treatment.

[0256]

[0257] The above cleaning solution is preferably water, in which case it has the advantage of being safe, inexpensive, and not dissolving transition metals present in the positive electrode active material.

[0258]

[0259] 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.

[0260] 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.

[0261] 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.

[0262] The above filtration is preferably vacuum filtration using a filter, and the above drying is preferably vacuum drying at 50 to 140°C.

[0263]

[0264] Next, as an optional step, surface coating can be performed on the washed positive electrode active material (step S70).

[0265] 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.

[0266] 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.

[0267] The solid or liquid method of the above surface coating may be, for example, mixing, milling, spray drying or grinding.

[0268]

[0269] 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 S70, 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.

[0270]

[0271] secondary battery

[0272] The secondary battery of the present invention includes the above-described regenerated positive electrode active material, and in this case, by performing heat treatment at a lower temperature than in the past, the amount of lithium residue generated during the thermal decomposition process of the binder and the conductive material is reduced, the shape of small particles in the positive electrode active material is maintained, the crystal size is reduced, and the strain is reduced, thereby minimizing cracks and improving battery characteristics, and since residual lithium is cleanly removed with a small amount of washing solution, wastewater treatment is not required, and since acid and organic solvent are not used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly and has excellent economic efficiency and productivity.

[0273]

[0274] 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.

[0275]

[0276] 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.

[0277]

[0278] [Example]

[0279] Manufacturing Example 1

[0280] 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 (Ni:Co:Mn:Al molar ratio of 88:7:4:1)) was shredded and cut into 2 cm x 2 cm pieces, and then ground in a dry state with a pin mill to obtain a positive electrode active material layer as a powder. The grinding with the pin mill was performed under the condition of 6000 rpm. The average particle diameter (D50) of the positive electrode active material layer powder obtained after grinding was 8.9 μm, and the average particle diameter (D50) of the raw positive electrode active material was 8.4 μm.

[0281] The average particle diameter of the positive electrode active material layer powder was measured using the laser diffraction method. Specifically, the positive electrode active material particles were dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device such as Microtrac MT 3000, and ultrasonic waves of approximately 28 kHz were 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 was calculated.

[0282]

[0283] Manufacturing Example 2

[0284] 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 (Ni:Co:Mn:Al molar ratio of 88:7:4:1)) was shredded and cut, and then ground in a dry state with a blender (WARING COMMERCIAL BLENDER 8010S, model number HGBTWTS3) for 1 minute to obtain a positive electrode active material layer in powder form. The obtained positive electrode active material layer powder had an average particle diameter (D50) of 8.9 μm, and the average particle diameter (D50) of the raw positive electrode active material was 8.4 μm.

[0285]

[0286] [Experimental Example I: Heat Treatment Temperature Analysis Using TGA]

[0287] The weight change rate according to the heat treatment time of the positive electrode active material layer powder obtained from the above Manufacturing Example 1 was analyzed using TGA, and the results are shown in Figure 2 below. The temperature condition during the TGA analysis was started at 50°C, increased to 480°C at a heating rate of 5°C / min, maintained for 5 hours, and then increased again to 900°C at a heating rate of 5°C / min.

[0288]

[0289] As shown in Figure 2 below, the binder and conductive agent were thermally decomposed and the weight decreased up to 210 minutes of heat treatment time, and there was no change in the weight from 210 minutes to 510 minutes, but the weight increased slightly after 510 minutes. From this, it was found that the binder and conductive agent were no longer thermally decomposed even after the thermal decomposition time exceeded 510 minutes.

[0290]

[0291] [Experimental Example II: Analysis of Binder and Conductive Agent Thermal Decomposition Temperatures Using TGA]

[0292] The weight change rate according to the heat treatment temperature of the positive electrode active material layer powder obtained from the above Manufacturing Example 1 was analyzed using TGA, and the results are shown in Figure 3 below. At this time, the temperature conditions were started at 50°C and ended at 900°C, and the heating rate was 5°C / min.

[0293]

[0294] Referring to Figure 3 below, it was confirmed that the binder in the positive electrode active material layer powder began to undergo thermal decomposition at around 360°C, and the conductive agent began to undergo thermal decomposition at around 450°C. From this, it was confirmed that the positive electrode active material layer powder, in which the current collector was separated from the positive electrode scrap by pin mill grinding, can be heat-treated at a lower temperature than before to obtain a positive electrode active material from which the binder and conductive agent were sufficiently removed.

[0295] In addition, it was confirmed from the following Figure 3 that at a temperature below 460°C, where the binder is thermally decomposed and weight is reduced, the thermal decomposition of the binder is insufficient, making it difficult to remove the binder and conductive material from the positive electrode active material layer powder.

[0296]

[0297] Example 1-1

[0298] The positive electrode active material layer powder obtained in the above Manufacturing Example 1 was heat-treated in air at 480°C for 3 hours to recover the positive electrode active material. Here, the temperature increase rate until reaching the heat treatment temperature was 5°C / min.

[0299]

[0300] Example 1-2

[0301] The same procedure as Example 1-1 was followed, except that the positive electrode active material layer powder obtained in Manufacturing Example 1 was heat-treated in air at 500°C for 2 hours to recover the positive electrode active material.

[0302]

[0303] Example 1-3

[0304] The same procedure as Example 1-1 was followed, except that the positive electrode active material layer powder obtained in Manufacturing Example 1 was heat-treated in air at 520°C for 2 hours to recover the positive electrode active material.

[0305]

[0306] Example 1-4

[0307] The same procedure as Example 1-1 was followed, except that the positive electrode active material layer powder obtained in Manufacturing Example 1 was heat-treated in air at 480°C for 5 hours to recover the positive electrode active material.

[0308]

[0309] Comparative Example 1-1

[0310] After the positive electrode plate was cut, the discarded positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCMA-based lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio of 88:7:4:1)) was shredded and cut, and then heat-treated in air at 590°C for 2 hours to recover the positive electrode active material. The temperature increase rate until the heat treatment temperature was reached was 5°C / min.

[0311]

[0312] Comparative Example 1-2

[0313] The same procedure as Example 1-1 was followed, except that the positive electrode active material layer powder obtained in Manufacturing Example 1 was heat-treated in air at 550°C for 2 hours to recover the positive electrode active material.

[0314]

[0315] Comparative Example 1-3

[0316] The positive electrode active material layer powder obtained in the above Manufacturing Example 2 was heat-treated in air at 480°C for 3 hours to recover the positive electrode active material. Here, the temperature increase rate until reaching the heat treatment temperature was 5°C / min.

[0317]

[0318] [Test Example III: Residual Lithium Content]

[0319] The residual lithium content of the positive electrode active materials obtained from Examples 1-1 to 1-4 and Comparative Examples 1-1 and 1-2 was measured as follows, and the results are shown in Table 1 below.

[0320] * Residual lithium content: Measured using a pH titrator T5 (Mettler Toledo). Specifically, 5 g of the positive electrode active material was dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, filtered to remove the active material, and the resulting solution was titrated with a 0.1 M HCl solution, while measuring 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.

[0321] Classification Li2CO3 (wt%) LiOH (wt%) Total (wt%) Example 1-10.1150.9581.073 Example 1-20.1750.9821.157 Example 1-30.3760.8921.268 Example 1-40.1230.9571.08 Comparative Example 1-10.7840.8991.683 Comparative Example 1-20.5020.9141.416

[0322] As shown in Table 1 above, it was confirmed that the contents of LiOH and Li2CO3 remaining in the positive electrode active material of Examples 1-1 to 1-4 according to the present invention were significantly reduced compared to Comparative Example 1-1 corresponding to the prior art, and that the contents of LiOH and Li2CO3 remaining in the positive electrode active material were also reduced compared to Comparative Example 1-2, which was outside the heat treatment temperature range of the present invention.

[0323]

[0324] Example 2-1

[0325] The positive electrode active material recovered in Example 1-1 was annealed in air at 650°C for 5 hours, with LiOH added as a lithium precursor, without a washing process. At this time, the lithium precursor was added in an amount corresponding to 5 mol% when the total lithium in the raw positive electrode active material used in the positive electrode active material layer is 100 mol%.

[0326] The above annealed positive electrode active material and distilled water were mixed in a weight ratio of 1:2, stirred at 300 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. Here, air was supplied at a rate of 3 L / min.

[0327] The above-mentioned washed positive electrode active material was coated with boric acid and then heated at 300°C for 5 hours to produce a final regenerated positive electrode active material. Here, the temperature increase rate until reaching the heat treatment temperature was 2°C / min, and air was supplied at 3 L / min.

[0328]

[0329] Example 2-2

[0330] In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and annealing was performed by adding LiOH as a lithium precursor in an amount corresponding to 7 mol% when the total lithium in the positive electrode active material used in the positive electrode active material layer is 100 mol%, and the same procedure as in Example 2-1 was repeated except that the annealing was performed.

[0331]

[0332] Example 2-3

[0333] In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and annealing was performed by adding LiOH as a lithium precursor in an amount corresponding to 10 mol% when the total lithium in the positive electrode active material used in the positive electrode active material layer is 100 mol%, except that the same procedure as in Example 2-1 was repeated.

[0334]

[0335] Example 2-4

[0336] In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and annealing was performed by adding LiOH as a lithium precursor in an amount corresponding to 12 mol% when the total lithium in the positive electrode active material used in the positive electrode active material layer is 100 mol%, and the same procedure as in Example 2-1 was repeated except that the annealing was performed.

[0337]

[0338] Example 2-5

[0339] In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and annealing was performed by adding LiOH as a lithium precursor in an amount corresponding to 13 mol% when the total lithium in the positive electrode active material used in the positive electrode active material layer is 100 mol%, and the same procedure as in Example 2-1 was repeated except that the annealing was performed.

[0340]

[0341] Example 2-6

[0342] In Example 2-1, the positive electrode active material was changed to the positive electrode active material recovered in Example 1-4, and annealing was performed by adding LiOH as a lithium precursor in an amount corresponding to 14 mol% when the total lithium in the positive electrode active material used in the positive electrode active material layer is 100 mol%, and the same procedure as in Example 2-1 was repeated except that the annealing was performed.

[0343]

[0344] Example 2-7

[0345] In Example 2-1, the positive electrode active material was annealed in the same manner as in Example 2-1, except that LiOH was added as a lithium precursor to the positive electrode active material recovered in Example 1-1 in an amount corresponding to 15 mol% when the total lithium in the raw positive electrode active material used in the positive electrode active material layer is 100 mol%.

[0346]

[0347] Comparative Example 2-1

[0348] LiOH was added as a lithium precursor to the positive electrode active material recovered in Comparative Example 1-1, and annealed in air at 650°C for 5 hours. At this time, the lithium precursor was added in an amount corresponding to 15 mol% when the total lithium in the raw positive electrode active material used in the positive electrode active material layer is 100 mol%.

[0349] The above annealed positive electrode active material and distilled water were mixed in a weight ratio of 1:2, stirred at 300 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. Here, air was supplied at a rate of 3 L / min.

[0350] The above-mentioned washed positive electrode active material was coated with boric acid and then heated at 300°C for 5 hours to produce a final regenerated positive electrode 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 reaching the heat treatment temperature was 2°C / min, and air was supplied at 3 L / min.

[0351]

[0352] Comparative Example 2-2

[0353] LiOH was added as a lithium precursor to the positive electrode active material recovered in Comparative Example 1-3, and annealed in air at 650°C for 5 hours. At this time, the lithium precursor was added in an amount corresponding to 15 mol% when the total lithium in the raw positive electrode active material used in the positive electrode active material layer is 100 mol%.

[0354] The above annealed positive electrode active material and distilled water were mixed in a weight ratio of 1:2, stirred at 300 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. Here, air was supplied at a rate of 3 L / min.

[0355] The above-mentioned washed positive electrode active material was coated with boric acid and then heated at 300°C for 5 hours to produce a final regenerated positive electrode active material. Here, the temperature increase rate until reaching the heat treatment temperature was 2°C / min, and air was supplied at 3 L / min.

[0356]

[0357] Comparative Example 2-3

[0358] LiOH was added as a lithium precursor to the positive electrode active material recovered in Comparative Example 1-1, and annealed in air at 650°C for 5 hours. At this time, the lithium precursor was added in an amount corresponding to 10 mol% when the total lithium in the raw positive electrode active material used in the positive electrode active material layer is 100 mol%.

[0359] The above annealed positive electrode active material and distilled water were mixed in a weight ratio of 1:2, stirred at 300 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. Here, air was supplied at a rate of 3 L / min.

[0360] The above-mentioned washed positive electrode active material was coated with boric acid and then heated at 300°C for 5 hours to produce a final regenerated positive electrode 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 reaching the heat treatment temperature was 2°C / min, and air was supplied at 3 L / min.

[0361]

[0362] Reference example

[0363] Fresh NCMA-based lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio of 88:7:4:1) rather than a regenerative cathode active material was used.

[0364]

[0365] [Experimental Example IV: SEM Analysis]

[0366] The results of SEM analysis of the regenerated positive electrode active materials manufactured from Example 2-3, Comparative Example 2-1, and Comparative Example 2-2 are shown in Figures 4 to 6 below.

[0367]

[0368] FIG. 4 below is a cross-section of a regenerated positive electrode active material manufactured from Example 2-3 pulverized with a pin mill, FIG. 5 below is a regenerated positive electrode active material manufactured from Comparative Example 2-1 according to the prior art, and FIG. 6 below is a regenerated positive electrode active material manufactured from Comparative Example 2-2 pulverized with a blender. FIG. 4 below shows that a positive electrode active material layer in which a current collector was separated from positive electrode scrap by pin mill pulverization was obtained, and it was confirmed that the regenerated positive electrode active material layer manufactured therefrom maintained the shape of small particles without being broken, compared to FIG. 5 below. On the other hand, in FIG. 6 below, which was pulverized with a blender, separation of the current collector from the positive electrode scrap was not completely achieved, so that a portion of the aluminum current collector was mixed into the positive electrode active material layer, and the aluminum current collector was present in the regenerated positive electrode active material manufactured therefrom.

[0369]

[0370] [Experimental Example V: XRD Analysis]

[0371] The regenerated positive electrode active materials obtained in Examples 2-1 to 2-7 and Comparative Example 2-1 were each subjected to XRD analysis to measure the a-axis length, c-axis length, cell volume, and crystal size of the crystal structure, which are shown in Table 2 below.

[0372]

[0373] Classification a axis (Å)c axis (Å)Cell Volume (Å 3 )Crystallite size (nm)Example 2-12.87714.209101.8173Example 2-22.87614.207101.7572Example 2-32.87514.205101.6672Example 2-42.87314.201101.5479Example 2-52.87314.201101.5279Example 2-62.87314.201101.4779Example 2-72.87314.201101.4979Comparative Example 2-12.87414.205101.6576Reference Example 2.87414.204101.5885

[0374] As shown in Table 2 above, Examples 2-1 to 2-7 had crystal structures of a-axis length, c-axis length, and cell volume at levels similar to those of the reference examples, and it was expected that the crystal size would be reduced, thereby improving battery characteristics.

[0375]

[0376] [Experimental Example VI: CHC Cell Evaluation]

[0377] The electrochemical performance of the regenerated positive electrode active materials manufactured in Examples 2-1 to 2-7, Comparative Example 2-1, and Comparative Example 2-3 was measured through the CHC cell evaluation as follows, and the results are shown in Figures 7 and 8 and Table 3 below.

[0378] * CHC cell manufacturing: 96 wt% of the regenerated cathode active material, 2 wt% of the conductive material carbon black, and 2 wt% of the binder PVdF were weighed and mixed in NMP to make a slurry. This was coated on aluminum foil to manufacture the cathode, and then a cell (Coin Half Cell, CHC) was manufactured. The electrochemical performance (charge capacity, discharge capacity, and efficiency) and cycle life characteristics were evaluated under the conditions of ethylene carbonate (EC): dimethyl methyl carbonate (DMC) = 3:7 (weight ratio) as the electrolyte and other additives included.

[0379] * Initial capacity evaluation of the cell: At 25 ℃, one charge / discharge cycle was performed on each cell under the following conditions.

[0380] Charge: 0.2C, CC / CV, 4.5V, 0.05C cut-off

[0381] Discharge: 0.2C, CC, 3.0V, cut-off

[0382] * Charge / discharge efficiency of the cell: The charge / discharge efficiency was calculated using the following mathematical formula 1 using the charge capacity and discharge capacity obtained from the initial capacity evaluation of the cell, and is shown in Table 3 below.

[0383] [Mathematical Formula 1]

[0384] Charge / discharge efficiency (%) = [Discharge capacity (mAh / g) / Charge capacity (mAh / g)] * 100

[0385] * Evaluation of high-temperature life characteristics of cells: At 45 ℃, 20 cycles of charge and discharge were performed on each cell under the following conditions, and the capacity retention rate and resistance increase rate (△DCIR) for each cycle were calculated using the following mathematical formulas 2 and 3, respectively, and are shown in Figure 8.

[0386] Charge: 0.33C, CC / CV, 4.5V, 0.05C cut-off

[0387] Discharge: 0.33C, CC, 3.0V, 0.05C cut-off

[0388] [Equation 2]

[0389] Capacity retention rate (%) = (discharge capacity after N cycles / discharge capacity after 1 cycle) * 100

[0390] [Equation 3]

[0391] △DCIR = {(Resistance after N cycles / Resistance after 1 cycle) * 100} - 100

[0392]

[0393] The following Figure 7 is a graph showing the initial charge / discharge capacity as a result of coin cell evaluation for each of the regenerated positive electrode active materials manufactured in Examples 2-1 to 2-7 and Comparative Example 2-3.

[0394] As shown in FIG. 7 below, the regenerative positive electrode active material according to the present invention thermally decomposes the binder and the conductive agent at a lower temperature than the prior art, thereby reducing lithium loss in the positive electrode active material compared to the prior art, thereby reducing the amount of lithium precursor required for the crystal structure recovery process. Specifically, in Example 2-3 and Comparative Example 2-3, in which 10 mol% of the lithium precursor was added at the same content, Example 2-3 showed a superior initial capacity evaluation result compared to Comparative Example 2-3. In addition, Example 2-2, in which 7 mol% of the lithium precursor was added, showed a similar initial capacity evaluation result to Comparative Example 2-3, in which 10 mol% of the lithium precursor was added.

[0395]

[0396] Comparison Example 2-3 Example 2-1 Example 2-2 Example 2-3 Example 2-4 Example 2-5 Example 2-6 Example 2-7 Charge / discharge efficiency (%) 90.388.590.891.792.092.592.392.3

[0397] As shown in Table 3 above, the regenerative positive electrode active materials according to the present invention (Examples 2-1 to 2-7) had charge / discharge efficiencies similar to or higher than those of Comparative Example 2-3 according to the prior art.

[0398]

[0399] In addition, the following Figure 8 is a graph showing the capacity retention rate and resistance increase rate for 20 cycles as a result of evaluating the coin cell for each of the regenerated positive electrode active materials manufactured in Examples 2-1 to 2-7 and Comparative Example 2-1. Referring to this, it was confirmed that the regenerated positive electrode active materials according to the present invention (Examples 2-1 to 2-7) had a superior capacity retention rate and a lower resistance increase rate than Comparative Example 2-1 even at high temperatures compared to Comparative Example 2-1 according to the prior art. Example 2-5 had a lower capacity retention rate than Comparative Example 2-1, but a lower resistance increase rate, and Example 2-1 had a lower resistance increase rate than Comparative Example 2-1, but a better capacity retention rate than Comparative Example 2-1.

[0400]

[0401] [Explanation of symbols]

[0402] 10: Whole house

[0403] 20: Active material layer

[0404] 30: Bipolar sheet

[0405] 40: Bipolar plate

[0406] 50: Bipolar scrap

Claims

1. (a) A step of grinding a waste cathode including a current collector and a cathode active material layer coated thereon using a pin mill under dry conditions to obtain a cathode active material layer in the form of powder; (b) a step of recovering the positive electrode active material by heat-treating the obtained positive electrode active material layer powder in air at 460 to 530°C; (c) a step of adding a lithium precursor to the recovered positive electrode active material and annealing at 400 to 1000°C; and (d) a step of washing the annealed positive electrode active material with a washing solution; characterized in that it comprises; Method for regenerating positive electrode active material.

2. In paragraph 1, In the above step (a), the grinding by the pin mill is characterized in that it is performed under conditions of 5000 to 10000 rpm. Method for regenerating positive electrode active material.

3. In paragraph 1, The above step (a) is characterized in that it includes a pretreatment step of shredding or cutting the positive electrode. Method for regenerating positive electrode active material.

4. In paragraph 1, Characterized in that the positive electrode active material recovered after heat treatment in the above step (b) is provided to the annealing in the above step (c) without washing. Method for regenerating positive electrode active material.

5. In paragraph 1, The above step (b) is characterized in that the total amount of surface residual LiOH and Li2CO3 of the positive electrode active material recovered after heat treatment is controlled to 1.35 wt% or less. Method for regenerating positive electrode active material.

6. In paragraph 1, The above cathode active material is at least one selected from the group consisting of 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, characterized in that it contains 60 mol% or more of Ni based on 100 mol% of the total of the remaining metals excluding Li. Method for regenerating positive electrode active material.

7. In paragraph 1, In the above step (b), the heat treatment is characterized in that it is performed for 1.5 to 6 hours. Method for regenerating positive electrode active material.

8. In paragraph 1, The lithium precursor is characterized in that it is added in an amount corresponding to 3 to 17 mol% when the total lithium in the raw material positive electrode active material used in the positive electrode active material layer is 100 mol%. Method for regenerating positive electrode active material.

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

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

11. In paragraph 1, The above detergent is characterized in that it is water. Method for regenerating positive electrode active material.

12. In paragraph 1, The method for regenerating the positive electrode active material is characterized in that it includes the step of e) surface coating the washed positive electrode active material. Method for regenerating positive electrode active material.

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

14. Characterized in that it is manufactured by a method for regenerating a positive electrode active material according to Articles 1 to 13. Regenerated cathode active material.

15. At least one selected from the group consisting of 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, containing at least 60 mol% of Ni based on 100 mol% of the total of the remaining metals excluding Li. The total amount of residual LiOH and Li2CO3 is 1.35 wt% or less, and the a-axis measured by XRD is 2.871 to 2.888 Å, the c-axis is 14.200 to 14.210 Å, and the cell volume is 101.45 to 101.82 Å. 3 and characterized by a crystal size of 72 to 84 nm. Regenerated cathode active material.

16. In paragraph 15, The above regenerative positive electrode active material is characterized in that the surface is coated with a coating agent containing metal or carbon. Regenerated cathode active material.

17. Characterized in that it comprises the regenerative positive electrode active material of clause 15 or clause 16. Secondary battery. 18.(a) A step of applying an impact force of 5.1 to 10.2 N (Newton) and a centrifugal force of 2600 to 10700 N (Newton) to a waste cathode including a current collector and a cathode active material layer coated thereon under dry conditions to obtain a cathode active material layer in the form of a powder; (b) a step of recovering the positive electrode active material by heat-treating the obtained positive electrode active material layer powder in air at 460 to 530°C; (c) a step of adding a lithium precursor to the recovered positive electrode active material and annealing at 400 to 1000°C; and (d) a step of washing the annealed positive electrode active material with a washing solution; characterized in that it comprises; Method for regenerating positive electrode active material.

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