Method for regenerating positive electrode active material, regenerated positive electrode active material prepared using same, 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 prepared using the method, and a secondary battery comprising the same. More specifically, the present invention relates to a method for regenerating a positive electrode active material, a regenerated positive electrode active material prepared using the method, and a secondary battery comprising the same, the method comprising: a step (a) of regenerating a positive electrode active material; crushing the waste positive electrode containing a current collector and a positive electrode active material layer coated on the current collector under a dry condition by using a needle mill to obtain a positive electrode active material layer in a powder form; (b) heat-treating the obtained positive electrode active material layer powder in air at 460 DEG C to 530 DEG C to recover a positive electrode active material; a step (c) of adding a lithium precursor to the recovered positive electrode active material and annealing at 400 DEG C to 1000 DEG C; and (d) washing the annealed positive electrode active material with a washing solution. According to the present invention, the method for regenerating the positive electrode active material has the following advantages: the binder and the conductive material can be easily removed even at a heat treatment temperature lower than that of a conventional method, thereby minimizing damage to the positive electrode active material due to washing; and recovering the crystal structure with a small amount of lithium precursor due to the reduction of lithium loss in the positive electrode active material; a positive electrode active material having excellent battery characteristics can be provided; acid is not used in the process of recycling and regenerating the positive electrode active material, so that the method is environment-friendly; the requirements of neutralization and wastewater treatment are eliminated without using acid, so that the process cost can be reduced; discarding of metal elements can be prevented by regenerating the positive electrode active material without decomposing the positive electrode active material; and can prevent the generation of toxic gas or explosion by not using an organic solvent.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the priority of Korean Patent Application No. 10-2023-0078759 filed on June 20, 2023, in the Korean Intellectual Property Office, and Korean Patent Application No. 10-2024-0005347 filed again on January 12, 2024 based on the priority of the above patent, and the disclosures of each of them are incorporated herein by reference. Technical Field

[0003] The present invention relates to a method for regenerating a positive electrode active material, a regenerated positive electrode active material prepared by the method, and a secondary battery comprising the regenerated positive electrode active material. More specifically, the present invention relates to a method for regenerating a positive electrode active material, wherein the method comprises crushing a waste positive electrode under dry conditions using a pin mill before heat treatment to obtain a positive electrode active material layer in powder form, heat treating the positive electrode active material layer at a temperature lower than that of a conventional method to recover the positive electrode active material, immediately adding a lithium precursor to the recovered positive electrode active material without washing, and then annealing, thereby being able to easily remove a binder and a conductive material even at a heat treatment temperature lower than that of a conventional method, minimizing damage to the positive electrode active material due to washing, restoring a crystal structure with a small amount of lithium precursor due to a reduction in lithium loss in the positive electrode active material; being able to provide a positive electrode active material having excellent capacity characteristics and life characteristics; being environmentally friendly by not using an acid in the process of recovering and regenerating the positive electrode active material; being able to reduce process costs by eliminating the need for neutralization and wastewater treatment by not using an acid; being able to prevent the discarding of metal elements by regenerating the positive electrode active material without decomposing the positive electrode active material; being able to prevent the generation or explosion of toxic gases by not using an organic solvent; and being able to greatly improve economic efficiency and productivity. Background Art

[0004] Generally, a lithium secondary battery is composed of a positive electrode formed by coating a metal foil such as aluminum with a positive electrode active material layer, a negative electrode formed by coating a metal foil such as copper with a negative electrode active material layer, a separator for preventing the positive electrode from mixing with the negative electrode, and an electrolyte solution that allows lithium ions to migrate between the positive electrode and the negative electrode.

[0005] In the positive electrode active material layer, lithium oxides are mainly used as active materials. In the negative electrode active material layer, carbon materials are mainly used as active materials. Generally, lithium oxides contain rare metals, such as cobalt, nickel or manganese. Therefore, it is actively studied to recover and regenerate rare metals from the positive electrode of a lithium secondary battery discarded after use or from the positive electrode waste (hereinafter referred to as "waste positive electrode") generated when manufacturing a lithium secondary battery.

[0006] According to the related art of recovering rare metals from waste positive electrodes, after the waste positive electrodes are dissolved using hydrochloric acid, sulfuric acid or nitric acid, rare metals such as cobalt, manganese and nickel are extracted using an organic solvent, and then the extracted metals are used as raw materials for synthesizing positive electrode active materials.

[0007] However, in the case of the method of extracting rare metals using acid, due to environmental pollution problems, a neutralization process and a wastewater treatment process are required, which greatly increases the process cost. In addition, the main metal of the positive electrode active material, namely lithium, cannot be recovered by the above method.

[0008] In order to solve these shortcomings, a method of directly regenerating the positive electrode active material from the waste positive electrode without decomposing the positive electrode active material (direct regeneration method) is being studied. As such methods, there are mainly the following four methods: calcination, solvent dissolution, aluminum (Al) foil dissolution and crushing and screening.

[0009] The calcination method can be performed with a simple process, but has disadvantages such as the formation of foreign matter on the surface of the regenerated positive electrode active material, which reduces the rate performance of the battery. In addition to the above disadvantages, waste gas is generated and energy consumption is excessive.

[0010] In addition, when the solvent dissolution method is used, a regenerated positive electrode active material with a relatively clean surface can be obtained. However, since the solvent used to dissolve the binder (e.g., N-methyl-2-pyrrolidone (NMP)) is a toxic gas and has an explosion risk, this method has poor stability and requires an expensive solvent recovery process.

[0011] In addition, in the case of the aluminum foil dissolution method, the process stability is good, the process cost is low, and the binder is easy to remove. However, foreign matter that is difficult to remove is formed on the surface of the regenerated positive electrode active material, and there is an explosion risk due to the generation of hydrogen in the process of removing the aluminum foil.

[0012] In addition, among the above methods, the crushing and screening method can be performed by the simplest process. However, it is difficult to completely separate the current collector and the positive electrode active material, the particle size distribution of the positive electrode active material will change during the crushing process, and the battery characteristics of the regenerated positive electrode active material will deteriorate due to the residual binder.

[0013] Therefore, there is an urgent need to develop methods to safely regenerate cathode active materials with improved battery performance from spent cathodes through simple processes at low cost in an environmentally friendly manner without losing metal elements. Summary of the invention

[0014] [Technical issues]

[0015] Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to provide a method for regenerating a positive electrode active material, which method comprises crushing a waste positive electrode using a pin mill under dry conditions before firing the waste positive electrode to obtain a positive electrode active material layer in a powder form, heat-treating the positive electrode active material layer at a temperature lower than that of a conventional method to recover the positive electrode active material, immediately adding a lithium precursor to the recovered positive electrode active material without washing, and then annealing, thereby making it possible to easily remove a binder and a conductive material even at a heat treatment temperature lower than that of a conventional method, so that the positive electrode active material is not damaged by washing. Damage to the material is minimized, and the crystal structure is restored with a small amount of lithium precursor due to the reduction of lithium loss in the positive electrode active material; it is possible to provide a positive electrode active material with excellent capacity characteristics and life characteristics; it is environmentally friendly because no acid is used in the process of recovering and regenerating the positive electrode active material; the need for neutralization and wastewater treatment is eliminated without using acid, thereby reducing process costs; it is possible to prevent the discarding of metal elements by regenerating the positive electrode active material without decomposing the positive electrode active material; it is possible to prevent the generation or explosion of toxic gases by not using organic solvents; and it is possible to greatly improve economic efficiency and productivity.

[0016] Another object of the present invention is to provide a secondary battery having excellent initial charge / discharge capacity and life characteristics.

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

[0018] [Technical solution]

[0019] I) According to one aspect of the present invention, a method for regenerating a positive electrode active material is provided, the method comprising: step (a), using a pin mill to crush a waste positive electrode comprising a current collector and a positive electrode active material layer coated on the current collector under dry conditions to obtain a positive electrode active material layer in powder form; step (b), heat-treating the obtained positive electrode active material layer powder at 460°C to 530°C in air to recover the positive electrode active material; step (c), adding a lithium precursor to the recovered positive electrode active material and annealing it at 400°C to 1000°C; and step (d), washing the annealed positive electrode active material with a washing solution.

[0020] II) According to I), in step (a), pulverization by a pin mill may be performed at 5000 rpm to 10000 rpm.

[0021] III) According to I) or II), step (a) may include a pretreatment step of shredding or cutting the waste positive electrode.

[0022] IV) According to I) to III), the positive electrode active material recovered after the heat treatment in step (b) may be subjected to the annealing of step (c) without washing.

[0023] V) According to I) to IV), in step (b), LiOH and Li as surface residues of the positive electrode active material recovered after heat treatment may be 2 CO 3 The total amount is adjusted to an amount of 1.35 wt % or less.

[0024] VI) According to I) to V), the positive electrode active material may include one or more selected from the group consisting of nickel·cobalt·manganese (NCM)-based positive electrode active materials, nickel·cobalt·aluminum (NCA)-based positive electrode active materials and nickel·cobalt·manganese·aluminum (NCMA)-based positive electrode active materials, and the content of Ni is 60 mol% or more based on 100 mol% of the total amount of other metals other than Li.

[0025] VII) According to I) to VI), in step (b), the heat treatment may be performed for 1.5 hours to 6 hours.

[0026] VIII) According to I) to VII), the added amount of the lithium precursor may be 3 mol% to 17 mol% based on 100 mol% of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer.

[0027] IX) According to I) to VIII), the lithium precursor may include LiOH, Li 2 CO 3 、LiNO 3 and Li 2 One or more of O.

[0028] X) According to I) to IX), annealing may be performed at 400° C. to 1000° C. in an oxygen atmosphere or in air.

[0029] XI) According to I) to X), the washing solution may be water.

[0030] XII) According to 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.

[0031] XIII) According to I) to XII), the surface coating may be performed by coating the surface with one or more of metal, organic metal and carbon components in a solid or liquid form and heat treating the surface at 100°C to 1200°C.

[0032] XIV) According to another aspect of the present invention, there is provided a regenerated positive electrode active material prepared using the methods of I) to XIII).

[0033] XV) According to another aspect of the present invention, there is provided a regenerated positive electrode active material, comprising one or more 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 based on 100 mol % of the total amount of other metals other than Li, the content of Ni is 60 mol % or more, wherein the residual LiOH and Li in the regenerated positive electrode active material 2 CO 3 The total amount of is 1.35 wt % or less, and the a-axis length of the crystal structure of the regenerated positive active material measured by XRD is The length of the c-axis is The unit cell volume is And the grain size is 72nm to 84nm.

[0034] XVI) According to XV), the surface of the regenerated positive electrode active material may be coated with a coating agent containing metal or carbon.

[0035] XVII) According to another aspect of the present invention, there is provided a secondary battery comprising the regenerated positive electrode active material of XV) or XVI).

[0036] XVIII) According to another aspect of the present invention, a method for regenerating a positive electrode active material is provided, the method comprising: step (a), applying an impact force of 5.1 to 10.2 Newtons (N) and a centrifugal force of 2600 to 10700 Newtons (N) to a waste positive electrode comprising a current collector and a positive electrode active material layer coated on the current collector under dry conditions to obtain the positive electrode active material layer in powder form; step (b), heat treating the obtained positive electrode active material layer powder at 460°C to 530°C in air to recover the positive electrode active material; step (c), adding a lithium precursor to the recovered positive electrode active material and annealing it at 400°C to 1000°C; and step (d), washing the annealed positive electrode active material with a washing solution.

[0037] [Beneficial Effects]

[0038] According to the present invention, the effect of the present invention is to provide a positive electrode active material, which uses a pin mill to pulverize a waste positive electrode under dry conditions before heat treatment to obtain a positive electrode active material layer in powder form, heat treats the positive electrode active material layer at a temperature lower than that of a conventional method to recover the positive electrode active material, immediately adds a lithium precursor to the recovered positive electrode active material without washing, and then anneals, so that the binder and the conductive material can be easily removed even at a heat treatment temperature lower than that of the conventional method, the damage to the positive electrode active material due to washing is minimized, the occurrence of cracks in the active material is minimized by maintaining the shape of the basic particles without breaking and reducing the grain size and strain, the crystal structure is restored with a small amount of lithium precursor due to the reduction of lithium loss in the positive electrode active material, and excellent capacity characteristics and life characteristics are provided.

[0039] In addition, the effects of the present invention are to provide a positive electrode active material that is environmentally friendly by not using acid during the recovery and regeneration of the positive electrode active material; by eliminating the need for neutralization and wastewater treatment without using acid, the process cost can be reduced; by regenerating the positive electrode active material without decomposing the positive electrode active material, the discarding of metal elements can be prevented; and by not using an organic solvent, the generation or explosion of toxic gases can be prevented. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The following drawings attached to this specification illustrate embodiments of the present invention, and the technical concept of the present invention is further understood in conjunction with the detailed description described below. Therefore, the present invention is not limited to these drawings.

[0041] Figure 1 The figure shows the positive electrode scraps which are discarded after the electrode plates are cut from the positive electrode sheets.

[0042] Figure 2 : is a result showing the weight change rate according to the heat treatment time, which is obtained by analyzing the positive electrode active material layer powder obtained after pulverization using a pin mill by thermogravimetric analysis (TGA).

[0043] Figure 3 : is a result showing the weight change rate according to the heat treatment temperature, which is obtained by analyzing the positive electrode active material layer powder obtained after pulverization using a pin mill by thermogravimetric analysis (TGA).

[0044] Figure 4 The SEM cross section of the regenerated positive electrode active material prepared in Example 2-3 is shown.

[0045] Figure 5 A SEM cross section of the regenerated positive electrode active material prepared in Comparative Example 2-1 is shown.

[0046] Figure 6A SEM cross section of the regenerated positive electrode active material prepared in Comparative Example 2-2 is shown.

[0047] Figure 7 : is a graph showing the initial capacity according to charge and discharge, which shows the evaluation results of the coin cells of each of the regenerated positive electrode active materials prepared in Examples 2-1 to 2-7 and Comparative Example 2-3.

[0048] Figure 8 is a graph showing high temperature life characteristics, which shows the evaluation results of coin cells of each of the regenerated positive electrode active materials prepared in Examples 2-1 to 2-7 and Comparative Example 2-1.

[0049] Fig. 9 1 is a flow chart illustrating a regeneration process of a positive electrode active material according to an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The inventors have confirmed that when the waste positive electrode is crushed under dry conditions using a pin mill before heat treatment to obtain a positive electrode active material layer in powder form, the positive electrode active material layer is heat treated to recover the positive electrode active material, the lithium precursor is immediately added to the recovered positive electrode active material without washing, and annealing is performed, the binder and the conductive material are easily removed even at a heat treatment temperature lower than that of the conventional method, minimizing the damage to the positive electrode active material due to washing, maintaining the shape of the basic particles without breaking, reducing the grain size, reducing strain, and minimizing the occurrence of cracks in the positive electrode active material. In addition, the crystal structure is restored with a small amount of lithium precursor, thereby obtaining an economic advantage. In addition, the battery characteristics of the regenerated positive electrode active material are further improved. Based on these results, the inventors conducted further research to complete the present invention.

[0051] Hereinafter, a method for regenerating a cathode active material of the present invention, a regenerated cathode active material prepared using the method, and a secondary battery including the regenerated cathode active material will be described in detail.

[0052] The terms and words used in this specification and the appended claims should not be interpreted as limited to the ordinary meaning or dictionary meaning, but should be interpreted as having meanings and concepts that match the technical spirit of the present invention, so as to describe the present invention in the best way. In addition, since the configurations shown in the embodiments and drawings of this specification are only embodiments of the present invention and do not represent all the technical spirits of the present invention, it should be understood that there are many equivalents and variations that can replace the above configurations, and the present invention can be arranged, replaced, combined, separated or designed into various other configurations.

[0053] Unless defined otherwise, all technical and scientific terms used in the specification have the same meaning as commonly understood by one of ordinary skill in the art to which the invention belongs.

[0054] Regeneration method of positive electrode active material

[0055] The method for regenerating a positive electrode active material of the present invention comprises: step (a), using a pin mill to pulverize a waste positive electrode including a current collector and a positive electrode active material layer coated on the current collector under dry conditions to obtain a positive electrode active material layer in powder form; step (b), heat-treating the obtained positive electrode active material layer powder at 460° C. to 530° C. in air to recover the positive electrode active material; step (c), adding a lithium precursor to the recovered positive electrode active material and annealing at 400° C. to 1000° C.; and step (d), washing the annealed positive electrode active material with a washing solution. In this case, by performing heat treatment at a temperature lower than that in conventional cases, the amount of lithium residue generated during the thermal decomposition of the binder and the conductive material can be reduced, the shape of the basic particles in the positive electrode active material can be maintained, the grain size can be reduced, and the strain can be reduced, thereby minimizing the occurrence of cracks. In addition, the amount of lithium precursor required for the crystal structure recovery process can be reduced. In addition, by immediately annealing the recovered positive electrode active material without washing, damage to the positive electrode active material can be minimized, and battery characteristics can be improved.

[0056] Hereinafter, each step of the method for regenerating the positive electrode active material will be described in detail.

[0057] (a) Obtaining a powdered positive electrode active material layer from a discarded positive electrode

[0058] The method for regenerating the positive electrode active material of the present invention comprises: step (a), using a pin mill to crush the waste positive electrode comprising a current collector and a positive electrode active material layer coated on the current collector under dry conditions to obtain a positive electrode active material layer in powder form. In this case, the positive electrode active material layer and the current collector can be easily separated, and the positive electrode active material layer can be obtained in powder form. In addition, in the subsequent heat treatment process, the binder and the conductive material can be removed at a temperature lower than that of the conventional method. At this time, when different types of pulverizers such as blenders, mixers or disc mills other than pin mills are used, since the positive electrode active material layer and the current collector are not completely separated from the waste positive electrode, a portion of the current collector is mixed into the positive electrode active material layer, and a portion of the current collector remains in the regenerated positive electrode active material, thereby deteriorating the battery characteristics.

[0059] The pin mill commonly used in the technical field to which the present invention belongs can be used for the present invention without any particular limitation. Specifically, the pin mill can be composed of a rotor with a pin (impact column) attached radially and a stator configured to mesh with the rotor. The raw material is supplied to the center of the rotor and the stator and diffused together with the air flow generated during rotation, which in turn increases the circumferential speed of the pin. Therefore, the raw material is constantly subjected to a strong impact force, crushed, and then passed through the screen again and discharged. The pin mill can be crushed to a desired particle size by adjusting the shape, number and screen size of the pin. When the positive electrode waste is crushed with a pin mill, the collector sheet is shredded and the positive electrode active material layer is separated from the collector sheet. The collector sheet remains inside the screen, and the positive electrode active material layer passing through the screen is discharged as powder. The positive electrode active material layer powder is a mixture of positive electrode active material, binder and conductive material. In this way, the positive electrode active material layer and the collector can be separated by crushing with a pin mill under dry conditions.

[0060] For example, the pulverization by the pin mill can be carried out at 5000rpm to 10000rpm, preferably 5000rpm to 8000rpm, more preferably 5000rpm to 7000rpm, and even more preferably 5500rpm to 6500rpm. Within this range, the positive electrode active material layer and the current collector can be easily separated, thereby allowing only the positive electrode active material layer powder to be separated. Specifically, when the condition is less than the above range, the positive electrode active material layer and the current collector may not be separated and the productivity may be reduced. When the above conditions exceed the above range, there is a problem that the current collector is mixed into the positive electrode active material layer powder.

[0061] Preferably, the pulverization by the pin mill can be performed in a drying chamber under a nitrogen atmosphere. In this case, the heat generated during the pulverization process can inhibit the conversion of lithium carbonate present in the positive electrode active material layer into lithium hydroxide, and the positive electrode active material layer can be easily separated from the current collector.

[0062] In the present disclosure, a drying chamber refers to a room having a temperature of 20°C to 22°C and a wet-bulb temperature maintained at -60 to -50°C.

[0063] Preferably, the average particle size of the positive electrode active material layer obtained in the form of powder may be the same as or similar to the average particle size of the raw material positive electrode active material layer. In this case, the battery characteristics of the regenerated positive electrode active material may be excellent.

[0064] For example, before the waste positive electrode is pulverized using a pin mill, a pre-treatment step of shredding or cutting may be included. In this case, the positive electrode active material layer and the current collector can be easily separated.

[0065] For example, shredding or cutting can be carried out using various dry pulverization devices (such as hand mills, disk mills, cutting mills, and hammer mills). Additionally, in order to improve productivity, a high-speed cutting machine can be used.

[0066] In the present disclosure, the dry conditions are not particularly limited as long as they are the dry conditions commonly defined in the technical field to which the present invention pertains. For example, the dry conditions can be conditions without adding a solvent and / or drying conditions and / or conditions using dry pulverization devices.

[0067] The discarded positive electrode can preferably be a positive electrode separated from a lithium secondary battery discarded after use, or a defective positive electrode sheet or positive electrode waste generated during the manufacturing process of a lithium secondary battery, and more preferably be positive electrode waste remaining after blanking a positive electrode sheet to obtain a positive electrode plate.

[0068] The positive electrode active material layer in step (a) can preferably include a positive electrode active material, a binder, and a conductive material.

[0069] Preferably, the positive electrode active material can contain one or more selected from the group consisting of nickel-cobalt-manganese (NCM)-based positive electrode active materials, nickel-cobalt-aluminum (NCA)-based positive electrode active materials, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active materials, and based on 100 mol% of the total amount of other metals except Li, the content of Ni can be 60 mol% or more. In this case, the reversible capacity and thermal stability can be excellent.

[0070] As another specific example, the positive electrode active material can be a compound represented by the following Chemical Formula 1. In this case, the electrochemical performance, resistance characteristics, and capacity characteristics can be excellent.

[0071] [Chemical Formula 1]

[0072] Li a Ni x Mn y Co z M w O 2+δ

[0073] In Chemical Formula 1, M includes one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1.

[0074] For example, based on 100 mol% of the total amount of other metals other than Li, the positive electrode active material may contain Ni in an amount of 60 mol% or more, preferably 80 mol% or more, more preferably 81 mol% or more, and still more preferably 81 mol% to 95 mol%. Within this range, the charge capacity, resistance characteristics, and capacity characteristics may be excellent.

[0075] In the present disclosure, the Ni content can be measured by ion chromatography (IC) commonly used in the technical field to which the present invention belongs. As a specific example, an inductively coupled plasma (IC-ICP) analyzer, an IC-ICP-MS analyzer or an IC-ICP-AEC analyzer can be used.

[0076] For example, the conductive material may be a carbon-based conductive material, preferably carbon black, CNTs or a mixture thereof.

[0077] For example, the binder may be a polymer binder, preferably polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR) or a mixture thereof, more preferably polyvinylidene fluoride.

[0078] (b) Heat treatment of the obtained positive electrode active material layer powder

[0079] The method for regenerating a positive electrode active material of the present invention comprises: step (b), heat-treating the obtained positive electrode active material layer powder at 460°C to 530°C in air to recover the positive electrode active material. In this case, since the binder and the conductive material can be removed at a temperature lower than that of the conventional method, the damage to the positive electrode active material can be minimized. In addition, the amount of lithium residue generated by the thermal decomposition of the binder and the conductive material can be reduced, and the shape of the basic particles in the positive electrode active material can be maintained. In addition, the grain size and strain can be reduced, thereby minimizing the occurrence of cracks. In addition, the battery characteristics of the regenerated positive electrode active material can be improved.

[0080] The heat treatment temperature may be preferably 480° C. to 530° C., more preferably 480° C. to 500° C. Within this range, damage to the positive electrode active material may be minimized, and the amount of lithium residue generated by thermal decomposition of the binder and the conductive material may be reduced. In addition, the shape of the basic particles may be maintained without breaking, and the grain size and strain may be reduced, thereby minimizing the occurrence of cracks in the positive electrode active material. In addition, battery characteristics may be improved.

[0081] For example, the heat treatment time may be 1.5 hours to 6 hours, preferably 2 hours to 5.5 hours, more preferably 2 hours to 5 hours, still more preferably 2.5 hours to 5 hours, still more preferably 3 hours to 5 hours. Within this range, thermal decomposition of the binder and the conductive material can be actively performed, damage to the positive electrode active material can be minimized, the amount of lithium residue generated during the decomposition of the binder and the conductive material can be reduced, the shape of the basic particles can be maintained without breaking, the grain size and strain can be reduced, and the occurrence of cracks in the positive electrode active material can be reduced, thereby improving battery characteristics.

[0082] In the present disclosure, the heat treatment time is the time for heat treatment at the corresponding heat treatment temperature, excluding the time required to reach the corresponding heat treatment temperature.

[0083] The heat treatment may be performed at a temperature increase rate of 1 to 20°C / min, preferably 1 to 10°C / min, more preferably 3 to 8°C / min, and still more preferably 4 to 6°C / min. Within this range, the heat treatment may be performed without causing a burden on the heat treatment equipment, and thermal shock to the positive electrode active material layer powder may be prevented.

[0084] For example, the heat treatment equipment commonly used in the technical field to which the present invention belongs can be used in the present invention without particular limitation. For example, various types of furnaces, particularly box furnaces or rotary kilns can be used.

[0085] The rotary kiln has the advantage of being able to perform continuous processing and thus having excellent productivity.

[0086] In step (b), LiOH and Li 2 CO 3 The total amount of can 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 wt % to 1.10 wt %. Within this range, a positive electrode active material having excellent initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics can be provided.

[0087] In step (b), the Li 2 CO 3 The amount of may be, for example, 0.40 wt % or less, preferably 0.32 wt % or less, more preferably 0.25 wt % or less, still more preferably 0.20 wt % or less, still more preferably 0.15 wt % or less, still more preferably 0.05 wt % to 0.15 wt %. Within this range, a positive electrode active material having excellent initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics can be provided.

[0088] In step (b), the amount of LiOH remaining in the surface of the positive electrode active material recovered after heat treatment may be, for example, 0.99 wt % or less, preferably 0.96 wt % or less, more preferably 0.05 wt % to 0.96 wt %. Within this range, a positive electrode active material having excellent initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics can be provided.

[0089] In the present disclosure, the LiOH and Li 2 CO 3 The amount of can be measured using a pH titrator (T5, Mettler Toledo Co.). Specifically, 5 g of the positive electrode active material was dispersed in 100 ml of distilled water and mixed at 300 rpm for 5 minutes, and then filtered to filter out the active material and obtain a filtrate. The change in pH was measured while titrating the filtrate with a 0.1 M HCl solution. Based on the measurement results, a pH titration curve was obtained. Using the pH titration curve, the LiOH and Li 2 CO 3 of residual amount.

[0090] The positive electrode active material recovered in step (b) may preferably be subjected to annealing in step (c) without washing. In this case, damage to the surface of the positive electrode active material can be minimized, and the agglomerates of the positive electrode active material composed of secondary particles and the basic particles can be prevented from loosening and becoming primary particles.

[0091] In the present disclosure, “primary particle” refers to a primary structure of a single particle, and “secondary particle” refers to an aggregate or assembly of primary particles formed by physical or chemical bonds between primary particles, that is, a secondary structure.

[0092] (c) Adding lithium precursor to the recovered positive electrode active material and annealing

[0093] The regeneration method of the positive electrode active material of the present invention comprises: step (c), adding a lithium precursor to the recovered positive electrode active material and annealing at 400°C to 1000°C. In this case, a positive electrode active material having excellent initial discharge capacity, rate performance, capacity characteristics and resistance characteristics can be provided. In addition, since the washing process of the recovered active material is omitted, the economic efficiency and productivity can be greatly improved. In addition, the damage to the positive electrode active material can be minimized.

[0094] The annealing step (c) may preferably be to add the lithium precursor to the recovered positive electrode active material without washing and to anneal in oxygen (O 2) atmosphere or air at 400° C. to 1000° C. In this case, the crystallinity of the positive electrode active material can be increased or its crystal structure can be restored, thereby improving its crystallinity and improving the battery characteristics of the regenerated positive electrode active material.

[0095] The lithium precursor may preferably include a material selected from the group consisting of LiOH, Li 2 CO 3 、LiNO 3 and Li 2 One or more of the group consisting of O.

[0096] The amount of lithium precursor added may preferably correspond to the amount of lithium reduced relative to the amount of lithium in the positive active material of step (b) in the raw positive active material. As a specific example, when the positive active material recovered in step (b) is a positive active material represented by Chemical Formula 1, the amount of lithium precursor added may correspond to a lithium molar ratio of 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, even more preferably 0.009 to 0.013, based on the lithium molar ratio in the positive active material. Within this range, the crystallinity can be increased by supplementing the lithium in the regenerated positive active material, or the crystal structure can be restored to improve the crystallinity. Therefore, the battery characteristics of the regenerated positive active material can be improved.

[0097] Based on the total amount of lithium contained in the raw positive electrode active material 100 mol%, the amount of lithium precursor added may correspond to preferably 3 mol% to 17 mol%, more preferably 5 mol% to 15 mol%, and even more preferably 8 mol% to 13 mol%. Within this range, since there is no residual precursor that causes the resistance of the regenerated positive electrode active material to increase, the battery characteristics can be improved. Since the crystal structure can be restored with a smaller amount of lithium precursor than in conventional cases, an economic advantage can be obtained.

[0098] The annealing temperature can be adjusted within a limited range depending on the melting point of the lithium precursor. For example, in LiCO 3 In the case of a lithium precursor, its melting point is 723° C., so annealing can be performed at preferably 700° C. to 900° C., more preferably 710° C. to 780° C. In the case of LiOH as a lithium precursor, its melting point is 462° C., so annealing can be performed at preferably 400° C. to 600° C., more preferably 450° C. to 480° C. In this range, the crystal structure can be restored, so the rate performance of the battery can be excellent.

[0099] The annealing temperature may preferably be a temperature exceeding the melting point of the lithium precursor. However, when the annealing temperature exceeds 1000° C., thermal decomposition of the positive electrode active material may occur, resulting in degradation of battery performance. Therefore, the annealing temperature is preferably 1000° C. or less.

[0100] (d) Washing the annealed positive electrode active material with a washing solution

[0101] The method for regenerating the positive electrode active material of the present invention comprises: step (d), washing the annealed positive electrode active material with a washing solution. In this case, a small amount of washing solution can be used to remove the lithium precursor remaining on the positive electrode active material. Therefore, in the subsequent process, the battery performance degradation and gas generation caused by the reaction between the residual lithium precursor and the electrolyte solution can be prevented, and the wastewater treatment can be omitted.

[0102] The washing may preferably include the steps of mixing the annealed positive electrode active material and the washing solution and then filtering the mixed positive electrode active material and drying the solid positive electrode active material obtained after filtering. In this case, the excess lithium remaining in the positive electrode active material can be effectively removed.

[0103] Drying may be performed at preferably 100° C. to 500° C., more preferably 120° C. to 400° C., still more preferably 120° C. to 300° C., still more preferably 120° C. to 200° C. Within this range, residual Li may be effectively removed.

[0104] Drying may preferably be vacuum drying.

[0105] In the present disclosure, a vacuum drying method commonly practiced in the technical field to which the present invention belongs can be used in the present invention without particular limitation.

[0106] The washing may preferably include the steps of mixing the annealed positive electrode active material and the washing solution at a weight ratio of 1:1.5 to 1:5.5 and filtering, and drying the solid positive electrode active material obtained after filtering. In this case, an excess of lithium is added to suppress the cation mixing phenomenon that is easily occurred in the high nickel positive electrode active material. At this time, the lithium precursors such as LiOH and Li remaining due to the excess lithium can be effectively removed. 2 CO 3 The cation mixing phenomenon occurs due to the similar particle sizes of nickel and lithium.

[0107] In the present disclosure, the high-nickel 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 amount of other metals except Li.

[0108] The annealed active material and the washing solution may be mixed in a weight ratio of preferably 1:1.5 to 1:4, more preferably 1:1.5 to 1:3, and still more preferably 1:1.5 to 1:2.5. In this case, an excess of lithium is added to suppress the cation mixing phenomenon that easily occurs in the high nickel positive electrode active material. At this time, the lithium precursors such as LiOH and Li remaining due to the excess lithium can be effectively removed. 2CO 3 .

[0109] In particular, when the annealed active material and the washing solution are mixed in a weight ratio of 1:1.5 to 1:3, preferably 1:1.5 to 2.5, the initial discharge capacity (DCH) and efficiency of the regenerated positive active material may be further improved.

[0110] In addition, in the conventional method of washing and annealing the positive electrode active material recovered after heat treatment of the waste positive electrode, in order to remove the residual lithium during the washing step, 30 times more washing solution than the positive electrode active material is required. However, according to the present invention, since the recovered positive electrode active material is washed after annealing, a small amount of washing solution is used, wastewater treatment is not required, and the residual lithium removal efficiency can be excellent compared with the conventional method.

[0111] For example, the washing solution may be water or an alkaline lithium compound aqueous solution, preferably water. In this case, the lithium precursors such as LiOH, Li 2 CO 3 It can be completely removed with a small amount of washing solution. Therefore, no wastewater treatment is required and the rate performance of the battery can be greatly improved.

[0112] The water is more preferably distilled water or deionized water. In this case, the lithium precursors such as LiOH, Li 2 CO 3 It can be completely removed with a small amount of washing solution. Therefore, no wastewater treatment is required and the rate performance of the battery can be greatly improved.

[0113] The alkaline lithium compound aqueous solution may preferably contain a lithium compound in an amount greater than 0 wt % and less than 15 wt %, more preferably greater than 0 wt % and less than 10 wt %. In this case, the lithium precursor such as LiOH, Li 2 CO 3 It can be completely removed with a small amount of washing solution. Therefore, no wastewater treatment is required and the rate performance of the battery can be greatly improved.

[0114] The mixing of the annealed positive electrode active material and the washing solution is preferably performed by stirring, and the stirring is not particularly limited but may be mechanical or ultrasonic stirring.

[0115] The stirring may be performed for preferably 30 minutes, more preferably 20 minutes, still more preferably 15 minutes, still more preferably 5 to 10 minutes. Within this range, residual lithium can be effectively removed.

[0116] (e) Obtaining a reusable positive electrode active material by surface coating the washed positive electrode active material

[0117] The method for regenerating the positive electrode active material of the present invention optionally includes: step (e), obtaining a reusable positive electrode active material by surface coating the washed positive electrode active material. In this case, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0118] In the surface coating, preferably, the surface may be coated with a coating agent containing one or more of metal, organic metal and carbon components in a solid or liquid manner, and then heat-treated at 100° C. to 1200° C., more preferably 200° C. to 1000° C., and even more preferably 250° C. to 800° C. In this case, structural stability and electrochemical performance may be improved while maintaining the inherent properties of the positive electrode active material.

[0119] The coating agent containing metal may preferably contain one or more coating agents 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 contain one or more coating agents selected from the group consisting of B, W, Al, Ti and Mg, still more preferably contain boron (B), tungsten (W) or a mixture thereof, still more preferably contain tungsten (W) and boron (B), as a specific example, a coating agent containing tungsten boride (WB). In this case, the resistance characteristics and life characteristics can be improved.

[0120] For example, the coating agent containing a metal may be an oxide or an acid containing a metal as an element in its molecule.

[0121] As the coating agent containing an organic metal, a coating agent containing an organic metal compound containing a metal commonly used in the technical field to which the present invention belongs may be used without particular limitation. As a specific example, a metal alkoxide may be used.

[0122] As the coating agent containing a carbon component, a coating agent containing a carbon component commonly used in the technical field to which the present invention belongs can be used without particular limitation. As a specific example, sugars such as sucrose can be used.

[0123] For example, based on the components other than the solvent coated on the surface of the positive electrode active material, the content of the coating agent can be 0.001 mol % to 0.3 mol %, preferably 0.01 mol % to 0.3 mol %, more preferably 0.01 mol % to 0.15 mol %, still more preferably 0.01 mol % to 0.1 mol %, and still more preferably 0.01 mol % to 0.05 mol %. Within this range, structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0124] The heat treatment time may be preferably 1 to 16 hours, more preferably 3 to 7 hours. Within this range, structural stability and electrochemical performance may be improved while maintaining inherent properties of the positive electrode active material.

[0125] The coating method commonly used in the technical field to which the present invention belongs can be used as the coating method of the present invention without particular limitation. For example, a liquid method of mixing a positive electrode active material and a liquid coating agent, a mechanochemical method using high mechanical energy of ball milling, a fluidized bed coating method, a spray drying method, a precipitation method of precipitating a coating agent on the surface of a positive electrode active material in an aqueous solution, a method using a reaction between a gas phase coating agent and a positive electrode active material, or sputtering can be used.

[0126] For example, the metal, organometallic and carbon components can have a spherical, plate-like, square or needle-like shape. For example, such shapes can be controlled by changing the process conditions during the preparation process. Each shape is not particularly limited as long as the shape follows the definition generally accepted in the technical field to which the present invention belongs.

[0127] The coating agent may preferably have an average diameter of 1 nm to 1000 nm and a diameter of 10 nm. 2 / g to 100m 2 / g specific surface area, more preferably an average diameter of 10nm to 100nm and 20m 2 / g to 100m 2 / g specific surface area. Within this range, the coating agent can be uniformly adhered to the surface of the positive electrode active material, thereby improving the structural stability of the positive electrode active material. Therefore, the reduction in the life of the positive electrode active material and the degradation of its electrochemical performance due to lattice distortion or disintegration of the crystal structure can be prevented.

[0128] In the present disclosure, the average diameter can be measured by a measurement method commonly used in the technical field to which the present invention belongs. For example, the average diameter can be measured by a laser diffraction method. Specifically, the positive electrode active material particles are dispersed in a dispersion medium, the dispersed particles are placed in a commercially available laser diffraction particle size measuring device such as Microtrac MT 3000, and the particles are irradiated with an ultrasonic wave of about 28kHz at an output of 60W. Then, the average particle diameter (D50) is calculated based on 50% of the particle size distribution in the measuring device.

[0129] In the present disclosure, 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, the specific surface area can be measured by the Brunauer-Emmett-Teller (BET) method. Specifically, the specific surface area can be calculated based on the nitrogen adsorption amount at liquid nitrogen temperature (77K) using BELSORP-mino II manufactured by BEL Japan Co.

[0130] As another example, the regeneration method of the positive electrode active material of the present invention includes: step (a), applying an impact force of 5.1 to 10.2 Newtons (N) and a centrifugal force of 2600 to 10700 Newtons (N) to a waste positive electrode including a current collector and a positive electrode active material layer coated on the current collector under dry conditions to obtain a positive electrode active material layer in powder form; step (b), heat-treating the obtained positive electrode active material layer powder at 460° C. to 530° C. in air to recover the positive electrode active material; step (c), adding a lithium precursor to the recovered positive electrode active material and annealing at 400° C. to 1000° C.; and step (d), washing the annealed positive electrode active material with a washing solution. In this case, by performing heat treatment at a temperature lower than that in conventional cases, the amount of lithium residue generated during the thermal decomposition of the binder and the conductive material can be reduced, the shape of the basic particles in the positive electrode active material can be maintained, the grain size can be reduced, and the strain can be reduced, thereby minimizing the occurrence of cracks. In addition, the amount of lithium precursor required for the crystal structure recovery process can be reduced. In addition, by immediately annealing the recovered positive electrode active material without washing, damage to the positive electrode active material can be minimized and battery characteristics can be improved.

[0131] In step (a), the impact force may preferably be 5.1 to 8.1 Newtons (N), more preferably 5.1 to 7.1 Newtons (N), and even more preferably 5.6 to 6.6 Newtons (N). Within this range, the positive electrode active material layer and the current collector can be easily separated, thereby allowing only the positive electrode active material layer powder to separate. Specifically, when the condition is less than the above range, the positive electrode active material layer and the current collector may not be separated and the productivity may be reduced. When the above conditions exceed the above range, there is a problem of the current collector being mixed into the positive electrode active material layer powder.

[0132] In step (a), the centrifugal force may preferably be 2600N to 6900N, more preferably 2600N to 5300N, and even more preferably 3200N to 4500N. Within this range, the positive electrode active material layer and the current collector can be easily separated, thereby allowing only the positive electrode active material layer powder to be separated. Specifically, when the condition is less than the above range, the positive electrode active material layer and the current collector may not be separated and the productivity may be reduced. When the above conditions exceed the above range, there is a problem that the current collector is mixed into the positive electrode active material layer powder.

[0133] Specifically, the waste positive electrode can be crushed with an impact force of 5.1 to 10.2 Newtons (N) using a grinder under dry conditions, and can be discharged with a centrifugal force of 2600 to 10700 Newtons (N).

[0134] In the present disclosure, the measurement methods of impact force and centrifugal force commonly used in the technical field to which the present invention belongs can be used in the present invention without particular limitation. For example, the impact force and centrifugal force can be calculated using equations 1 and 3. At this time, the mass (kg) of the waste positive electrode, the revolutions per minute (rpm) of the pin mill, and the radius (m) of the pin mill follow the relationship in equations 1 and 3. At this time, the crushing time is 1 second, and the speed of the waste positive electrode after hitting the pin is 0.

[0135] [Equation 1]

[0136] Centrifugal force (N) = m × v 2 / r

[0137] In Equation 1, m is the mass of the waste positive electrode (kg), v is a value obtained by converting the revolutions per minute (rpm) of the pin mill into a speed (m / s) using the following Equation 2, and r is the radius (m) of the pin mill.

[0138] [Equation 2]

[0139] Speed ​​(m / s) = (2r × π × rpm) / 60

[0140] In Equation 2, r is the radius of the pin mill (m), π is the circumference of a circle, and rpm is the revolutions per minute (rpm) of the pin mill.

[0141] [Equation 3]

[0142] Impact force (N) = m × (v 1 -v 2 ) / △t

[0143] In Equation 3, m is the mass of the spent cathode (kg), v 1 is the velocity of the discarded positive electrode immediately before it collides with the needle (m / s), v 2 is the speed of the discarded positive electrode after collision with the needle (m / s), and Δt is the collision time (seconds), i.e., the crushing time, which is the time taken from v1 to v2.

[0144] In the present invention, v 2 is 0, and the collision time is 1 second.

[0145] Steps (b), (c) and (d) share all technical features of steps (b), (c) and (d) of the above-mentioned method for regenerating the positive electrode active material, so their repeated description will be omitted.

[0146] Regeneration of positive electrode active materials

[0147] The regenerated positive active material of the present invention is prepared using the regeneration method of the aforementioned positive active material. In this case, by heat treating at a temperature lower than the conventional case, the amount of lithium residue generated during the thermal decomposition of the binder and the conductive material can be reduced, the shape of the basic particles in the positive active material can be maintained, the grain size can be reduced, and the strain can be reduced, thereby minimizing the occurrence of cracks. In addition, the amount of lithium precursor required for the crystal structure recovery process can be reduced. In addition, by immediately annealing the recovered positive active material without washing, the damage to the positive active material can be minimized, and the battery characteristics can be improved.

[0148] In addition, the regenerated positive electrode active material of the present invention may include one or more selected from the group consisting of nickel·cobalt·manganese (NCM)-based positive electrode active materials, nickel·cobalt·aluminum (NCA)-based positive electrode active materials, and nickel·cobalt·manganese·aluminum (NCMA)-based positive electrode active materials, and the content of Ni may be 60 mol% or more based on 100 mol% of the total amount of other metals other than Li. Residual LiOH and Li in the regenerated positive electrode active material 2 CO 3 The total amount of may be 1.35 wt % or less, and the a-axis length of the crystal structure of the regenerated positive active material measured by XRD may be The length of the c-axis is The unit cell volume is And the grain size is 72nm to 80nm. In this case, by performing heat treatment at a temperature lower than that of the conventional method, damage to the positive electrode active material can be minimized, the amount of lithium residue generated during the decomposition of the binder and the conductive material can be reduced, the shape of the basic particles can be maintained without breaking, and the grain size and strain can be reduced, thereby minimizing the occurrence of cracks in the positive electrode active material. In addition, by annealing the recovered positive electrode active material without washing, damage to the positive electrode active material can be reduced, and battery characteristics can be improved.

[0149] As another specific example, the regenerated positive electrode active material may be a compound represented by the following Chemical Formula 1.

[0150] [Chemical formula 1]

[0151] Li a Ni x Mn y Co z M w O 2+δ

[0152] In Chemical Formula 1, M includes one or more selected from the group consisting of B, W, Al, Ti, and Mg, 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1. In this case, the electrochemical performance, resistance characteristics, and capacity characteristics can be excellent.

[0153] Based on 100 mol% of the total amount of metals other than Li, the recycled positive electrode active material may preferably contain 80 mol% or more, more preferably 81 mol% or more, still more preferably 81 mol% to 95 mol% of Ni. Within this range, the charge capacity, resistance characteristics, and capacity characteristics can be excellent.

[0154] For example, in the recycled positive electrode active material, the residual amount of Li 2 CO 3 may be 0.40 wt% or less, preferably 0.32 wt% or less, more preferably 0.25 wt% or less, still more preferably 0.20 wt% or less, still more preferably 0.15 wt% or less, still more preferably 0.05 wt% to 0.15 wt%. Within this range, a positive electrode active material having excellent initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics can be provided.

[0155] For example, in the recycled positive electrode active material, the residual amount of LiOH may be 0.99 wt% or less, preferably 0.96 wt% or less, more preferably 0.05 wt% to 0.96 wt%. Within this range, a positive electrode active material having excellent initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics can be provided.

[0156] For example, in the recycled positive electrode active material, the total residual amount of Li 2 CO 3 and LiOH may be 1.35 wt% or less, preferably 1.28 wt% or less, more preferably 1.10 wt% or less, still more preferably 0.1 wt% to 1.10 wt%. Within this range, a positive electrode active material having excellent initial discharge capacity, rate performance, capacity characteristics, and resistance characteristics can be provided.

[0157] For example, the a-axis length of the crystal structure of the recycled positive electrode active material measured by XRD may be preferably more preferably Within this range, the recycled positive electrode active material can be restored to a lattice structure similar to that of the raw material positive electrode active material.

[0158] For example, the c-axis length of the crystal structure of the recycled positive electrode active material measured by XRD may be Best Within this range, the regenerated positive electrode active material can be restored to a lattice structure similar to that of the raw positive electrode active material.

[0159] For example, the unit cell volume of the regenerated positive electrode active material measured by XRD can be Best Within this range, the regenerated positive electrode active material can be restored to a lattice structure similar to that of the raw positive electrode active material.

[0160] For example, the grain size of the regenerated positive electrode active material measured by XRD can be 72nm to 84nm, preferably 72nm to 82nm, more preferably 72nm to 80nm, still more preferably 72nm to 78nm, and still more preferably 72nm to 74nm. Within this range, the regenerated positive electrode active material can be restored to a lattice structure similar to that of the raw positive electrode active material.

[0161] For example, the surface of the regenerated positive electrode active material may be coated with metal or carbon, preferably metal. In this case, the structural stability of the positive electrode active material can be improved without chemical or physical changes in the positive electrode active material, and electrochemical properties such as rate performance, life characteristics and capacity can be improved. In addition, by replacing the surface of the positive electrode active material with a foreign element, the amount of residual lithium can be reduced and the pH can be lowered, thereby improving the physicochemical properties.

[0162] The metal may preferably include one or more selected from the group consisting of B, W, Al, Ti, Mg, Ni, Co, Mn, Si, Zr, Ge, Sn, Cr, Fe, V and Y, more preferably one or more selected from the group consisting of B, W, Al, Ti and Mg, still more preferably boron (B), tungsten (W) or a mixture thereof, still more preferably tungsten (W) and boron (B), and as a specific example, tungsten boride (WB). In this case, the resistance characteristics and life characteristics can be improved.

[0163] For example, based on 1 mol % of the metal in the positive electrode active material before coating, the content of the coating agent can be 0.001 mol % to 0.3 mol %, preferably 0.01 mol % to 0.3 mol %, more preferably 0.01 mol % to 0.15 mol %, still more preferably 0.01 mol % to 0.1 mol %, and still more preferably 0.01 mol % to 0.05 mol %. Within this range, structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0164] The surface coating may be preferably performed by coating the surface with a coating agent containing one or more of metal, organic metal and carbon components in a solid or liquid manner and heat treating the surface at 100° C. to 1200° C., more preferably 200° C. to 1000° C., and still more preferably 250° C. to 800° C. In this case, the structural stability and electrochemical performance can be improved while maintaining the inherent properties of the positive electrode active material.

[0165] the following Fig. 9 1 is a flowchart for explaining a regeneration process of a positive electrode active material according to one embodiment of the present invention.

[0166] refer to Fig. 9 First, a positive electrode waste as a discarded positive electrode is prepared (step S10). For example, an aluminum foil is coated with a slurry prepared by adding N-methylpyrrolidone (NMP) to an NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride and mixing, and then dried in a vacuum oven set at about 120° C. to obtain a positive electrode sheet. Then, the positive electrode sheet is punched out to obtain a positive electrode plate of a specific size. In this process, positive electrode waste is generated.

[0167] The positive electrode waste includes an aluminum foil and a positive electrode active material layer formed on the aluminum foil. After the solvent is volatilized, the positive electrode active material layer has a structure in which the positive electrode active material and the conductive material are combined by a binder.

[0168] Next, the prepared positive electrode waste is crushed into pieces of appropriate size (step S20). Here, crushing includes cutting or chopping the positive electrode waste into a size that is easy to handle. As a specific example, the size of the crushed positive electrode waste can be 1 cm×1 cm. For example, crushing can be performed using dry crushing equipment such as a hand grinder, a disc grinder, a cutting mill, and a hammer mill. In order to improve productivity, a high-speed cutter can be used.

[0169] Preferably, whether to perform crushing or the size of the fragments can be determined in consideration of the processing of the positive electrode waste and the characteristics of the equipment used in the subsequent process. For example, when using equipment capable of continuous processing, the positive electrode waste must be crushed into smaller fragments because these fragments must have good fluidity.

[0170] Next, the crushed cathode scrap is pulverized using a pin mill under dry conditions to obtain a cathode active material layer in a powder form (step S30 ).

[0171] The pin mill consists of a rotor with a needle (impact column) attached radially and a stator configured to mesh with the rotor. The raw material is supplied to the center of the rotor and the stator and diffused with the air flow generated during rotation, which in turn increases the circumferential speed of the needle. Therefore, the raw material is constantly subjected to a strong impact force, crushed, and then passed through the screen again and discharged. The pin mill can be crushed to the desired particle size by adjusting the shape, number and screen size of the needle. When the positive electrode waste is crushed with a pin mill, the collector sheet is shredded and the positive active material layer is separated from the collector sheet. The collector sheet remains inside the screen, and the positive active material layer passing through the screen is discharged as powder. The positive active material layer powder is a mixture of positive active material, binder and conductive material. In this way, the positive active material layer and the collector can be separated by crushing with a pin mill under dry conditions.

[0172] For example, the pulverization by the pin mill can be carried out at 5000rpm to 10000rpm, preferably 5000rpm to 8000rpm, more preferably 5000rpm to 7000rpm, still more preferably 5500rpm to 6500rpm, and as a specific example, 6000rpm. Within this range, since the positive electrode active material layer and the current collector are effectively separated, only the positive electrode active material layer powder can be separated. When the pulverization speed is less than 5000rpm, the positive electrode active material layer and the current collector may not be easily separated, and the pulverization must be carried out for a long time. When the pulverization speed exceeds 10000rpm, the current collector may be mixed with the positive electrode active material layer powder.

[0173] Next, the obtained positive electrode active material layer powder is heat-treated at 460° C. to 530° C. in air to recover the positive electrode active material (step S40 ). Here, the heat treatment is performed to thermally decompose the binder and the conductive material in the active material layer.

[0174] As described above, by heat treatment in air, the binder and the conductive material in the active material layer are thermally decomposed into CO 2 and H 2 O and is removed. Since the binder is removed, the positive electrode active material is separated from the positive electrode active material layer.

[0175] It is important that the heat treatment is performed in an air atmosphere. When the heat treatment is performed in a reducing gas or inert gas atmosphere, the binder and the conductive material are carbonized rather than thermally decomposed. When the binder and the conductive material are carbonized, the carbon component remains on the surface of the positive electrode active material, resulting in deterioration in the performance of the regenerated positive electrode active material. In contrast, when the heat treatment is performed in air, the carbon component in the binder and the conductive material reacts with oxygen and is converted into CO and CO. 2 The gases evaporate and disappear, so both the adhesive and the conductive material are removed.

[0176] Since the current collector is separated in the previous process, the heat treatment can be performed at a temperature lower than that of the conventional method, as a specific example, at 460°C to 530°C, preferably 480°C to 530°C, and more preferably 480°C to 500°C. When the heat treatment is performed at a temperature lower than 460°C, the thermal decomposition of the binder and the conductive material may not be effective. When the heat treatment is performed at a temperature exceeding 530°C, the amount of lithium residue generated by the thermal decomposition of the binder and the conductive material may be increased, the shape of the basic particles may be destroyed, the grain size and strain may be increased, and cracks may appear in the positive electrode active material. In addition, by removing the binder and the conductive material by heat treatment at a temperature lower than that of the conventional method, the cost can be reduced.

[0177] The heat treatment is preferably performed at a temperature increase rate of 1 to 20°C / min, more preferably 1 to 10°C / min, still more preferably 3 to 8°C / min, still more preferably 4 to 6°C / min, and as a specific example, 5°C / min. Within this range, the heat treatment can be performed without causing a burden on the heat treatment equipment, and thermal shock to the positive electrode active material layer powder can be prevented.

[0178] The heat treatment can be performed until the adhesive is completely thermally decomposed. For example, the heat treatment can be performed preferably for 1.5 hours to 6 hours, preferably 2 hours to 5.5 hours, more preferably 3 hours to 5 hours, and even more preferably 4 hours to 5 hours. Within this range, the adhesive can be completely thermally decomposed, and the thermal decomposition efficiency can be excellent.

[0179] For example, the heat treatment can be performed using various types of furnaces. For example, a box furnace can be used. Considering productivity, a rotary kiln capable of continuous treatment can be used.

[0180] After heat treatment, slow cooling or rapid cooling can be carried out in air.

[0181] Next, a lithium precursor is added to the recovered positive electrode active material and annealing is performed (step S50 ).

[0182] In the annealing step, it is important to immediately add the lithium precursor to the recovered positive active material and perform annealing without a washing process. In this case, since the crystallized LiF generated on the surface of the positive active material in the previous heat treatment step S40 is contained in the regenerated positive active material, when the regenerated positive active material is applied to a secondary battery, the battery characteristics can be improved, and the damage to the positive active material due to washing can be minimized.

[0183] In addition, lithium in the positive electrode active material is lost during the previous step S40. In step S50, the lost amount of lithium is replenished. In addition, during the previous step, a distorted structure (for example, Co in the case of the LCO active material) may be formed on the surface of the positive electrode active material. 3 O 4 ). In step S50, the crystal structure of the positive electrode active material can be restored by annealing, thereby improving the battery characteristics of the regenerated positive electrode active material, or restoring the battery characteristics of the regenerated positive electrode active material to the battery characteristics level of the newly made positive electrode active material. Here, "newly made" is a concept relative to "regenerated", and the newly made material means that the material is manufactured for the first time, and the newly made material is the same word as the "raw material" used in the embodiment.

[0184] The lithium precursor may include LiOH, Li 2 CO 3 、LiNO 3 and Li 2 One or more kinds of O, a specific example of which is LiOH.

[0185] Based on the molar ratio of lithium to other metals in the newly made positive active material contained in the positive active material layer, the lithium precursor is preferably added in a minimum amount corresponding to the molar ratio of the lost lithium. When an excess of lithium precursor is added relative to the amount of lithium loss, unreacted lithium precursor may remain in the regenerated positive active material, which results in an increase in resistance. Therefore, it is necessary to add an appropriate amount of lithium precursor. For example, when the molar ratio of lithium to other metals in the newly made positive active material is 1, the amount of lithium precursor added can be such that the molar ratio of lithium is 0.001 to 0.4, preferably 0.01 to 0.2.

[0186] As a specific example, when a lithium precursor is added at a molar ratio of 0.09 to 0.1 (in terms of lithium metal, which is a loss ratio relative to the lithium content in the fresh positive electrode active material) based on the ICP analysis results, the capacity can be increased to a level comparable to that of the fresh positive electrode active material. Here, the error value of the ICP analysis results is about ±0.02.

[0187] In the previous step S40, since the loss of lithium is reduced by performing heat treatment at a temperature lower than that of the conventional method, the added amount of the lithium precursor may be preferably 3 mol % to 17 mol %, more preferably 5 mol % to 15 mol %, and even more preferably 8 mol % to 13 mol %, based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer.

[0188] For example, annealing may be performed in air at 400° C. to 1000° C., preferably 600° C. to 900° C. In this case, the temperature should be determined within a limited range depending on the type of the lithium precursor.

[0189] The annealing temperature is preferably a temperature exceeding the melting point of the lithium precursor. However, at a temperature exceeding 1000°C, performance degradation occurs due to thermal decomposition of the positive electrode active material, so the annealing temperature should not exceed 1000°C. When using Li 2 CO 3 When used as a lithium precursor, the annealing temperature is preferably 700° C. to 900° C., more preferably 710° C. to 780° C., and even more preferably 750° C. to 780° C. In addition, when LiOH is used as a lithium precursor, the annealing temperature is preferably 400° C. to 600° C., more preferably 450° C. to 480° C., and even more preferably 470° C. to 480° C.

[0190] For example, the annealing time is preferably 1 hour or more, more preferably 15 hours or less, and even more preferably 4 to 6 hours. When the annealing time is long, the crystal structure can be fully restored, but even long-term annealing will not significantly affect the performance. In this case, the same or similar equipment as in step S40 for performing heat treatment can be used as the annealing equipment.

[0191] Next, the annealed positive active material is washed with a washing solution (step S60 ).

[0192] Since the lithium precursor that does not participate in the reaction in the annealing step S50 is LiOH and Li 2 CO 3 The residual lithium removal process is required to remove LiOH and Li 2 CO 3 LiOH and Li 2 CO 3 Impurities in the form of ions can react with the electrolyte solution, deteriorating battery performance and generating gas, so these impurities must be thoroughly removed.

[0193] The annealed positive electrode active material and the washing solution can be mixed in a weight ratio of preferably 1:1.5 to 1:5.5, more preferably 1:1.5 to 1:4, still more preferably 1:1.5 to 1:3, still more preferably 1:1.5 to 1:2.5. In this case, residual lithium can be removed with a small amount of washing solution. Therefore, wastewater treatment is not required, and a positive electrode active material having excellent initial discharge capacity, rate performance and capacity characteristics can be obtained.

[0194] The washing solution is preferably water. In this case, safety can be ensured, cost can be reduced, and dissolution of transition metals contained in the positive electrode active material can be prevented.

[0195] Washing may be preferably performed by mixing and filtering the annealed positive electrode active material and a washing solution, and then drying the obtained solid positive electrode active material.

[0196] The mixing of the annealed positive electrode active material and the washing solution may be preferably performed by stirring. The stirring is not particularly limited, but may be mechanical stirring or ultrasonic stirring.

[0197] The mechanical stirring may be preferably performed at 100 to 1000 RPM for 5 to 30 minutes, more preferably at 250 to 350 RPM for 5 to 10 minutes.

[0198] The filtration is preferably vacuum filtration using a filter, and the drying is preferably vacuum drying at 50°C to 140°C.

[0199] Next, as an optional step, the washed positive electrode active material may be surface coated (step S70 ).

[0200] For example, in surface coating, a coating agent containing metal, organic metal or carbon is used to coat the surface in a solid phase or a liquid phase and heat-treated. When the heat treatment temperature is too low, the desired surface protective layer may not be formed by the heterogeneous metal. When the heat treatment temperature is too high, the battery performance may deteriorate due to the thermal decomposition of the positive electrode active material.

[0201] Specifically, when the washed positive electrode active material is coated with a metal oxide such as B, W, and BW or an acid and heat-treated, a surface protective layer such as a lithium boron oxide layer is formed on the surface of the positive electrode active material.

[0202] Surface coating can be performed using solid phase or liquid phase methods such as mixing, grinding, spray drying or attrition.

[0203] When the molar ratio of lithium to other metals in the positive electrode active material in the annealing step S50 is 1:1, in the surface coating step S70, the lithium in the positive electrode active material reacts with the coating agent, and the molar ratio of lithium to other metals in the positive electrode active material is less than 1:1. In this case, the capacity of the battery containing the regenerated positive electrode active material may not be fully (reaching 100%) expressed. However, in the annealing step S50, when an excess of lithium precursor is added so that the molar ratio of lithium contained in the positive electrode active material is 0.0001 to 0.1 higher than that of other metals, in the surface coating step S70, a surface protective layer is formed, and the molar ratio of lithium to other metals in the positive electrode active material becomes 1:1, thereby preventing the battery capacity from deteriorating.

[0204] Secondary battery

[0205] The secondary battery of the present invention comprises the above-mentioned regenerated positive electrode active material. In this case, by heat treatment at a temperature lower than the conventional case, the amount of lithium residue generated during the thermal decomposition of the binder and the conductive material can be reduced, the shape of the basic particles in the positive electrode active material can be maintained, the grain size can be reduced, and the strain can be reduced, thereby minimizing the occurrence of cracks. In addition, the battery characteristics can be improved. In addition, by completely removing the residual lithium with a small amount of washing solution, there is no need for wastewater treatment. In addition, since no acid and organic solvent are used in the process of recovering and regenerating the positive electrode active material, environmental friendliness can be ensured, and economic efficiency and productivity can be excellent.

[0206] The description of the secondary battery of the present invention may include all the descriptions of the above-mentioned positive electrode active material and the method for regenerating the positive electrode active material, and thus repeated descriptions are omitted in this specification.

[0207] Hereinafter, the present invention will be described in more detail with reference to the following preferred embodiments. However, these embodiments are provided for illustrative purposes only and should not be construed as limiting the scope and spirit of the present invention. In addition, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention, and such changes and modifications are also within the scope of the appended claims.

[0208] [Example]

[0209] Preparation Example 1

[0210] After punching the positive electrode plate, the discarded positive electrode waste (current collector: aluminum foil, positive electrode active material: NCM-type lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio of 88:7:4:1)) was shredded and cut into a size of 2cm×2cm, and then ground in a dry state using a pin mill to obtain a positive electrode active material layer. At this time, the grinding by the pin mill was carried out at 6000rpm. After grinding, the average particle size (D50) of the obtained positive electrode active material layer powder was 8.9μm, and the average particle size (D50) of the raw positive electrode active material was 8.4μm.

[0211] The average diameter of the positive electrode active material layer powder can be measured by a laser diffraction method. Specifically, the positive electrode active material particles are dispersed in a dispersion medium, the dispersed particles are placed in a commercially available laser diffraction particle size measurement device such as Microtrac MT 3000, and the particles are irradiated with an ultrasonic wave of about 28 kHz at an output of 60 W. Then, the average particle diameter (D50) is calculated based on 50% of the particle size distribution in the measuring device.

[0212] Preparation Example 2

[0213] After punching the positive electrode plate, the discarded positive electrode waste (current collector: aluminum foil, positive electrode active material: NCM-type lithium composite transition metal oxide (Ni: Co: Mn: Al molar ratio of 88: 7: 4: 1)) was shredded and cut, and then ground for 1 minute in a dry state using a blender (WARING COMMERCIAL Co., BLENDER 8010S, model: HGBTWTS3) to obtain a positive electrode active material layer. At this time, the average particle size (D50) of the obtained positive electrode active material layer powder was 8.9 μm, and the average particle size (D50) of the raw positive electrode active material was 8.4 μm.

[0214] [Test Example I: Analysis of Heat Treatment Temperature Using TGA]

[0215] For the positive electrode active material layer powder obtained in Preparation Example 1, the weight change rate according to the heat treatment time was analyzed using TGA, and the results are shown below. Figure 2 For TGA analysis, the temperature was increased from 50°C to 480°C at a heating rate of 5°C / min, held for 5 hours, and then increased to 900°C at a heating rate of 5°C / min.

[0216] as follows Figure 2 As shown, before the heat treatment time was 210 minutes, the weight decreased due to the thermal decomposition of the binder and the conductive material. From 210 minutes to 510 minutes, the weight did not change, but after 510 minutes, the weight increased slightly. Based on these results, it was found that the binder and the conductive material were no longer thermally decomposed even if the thermal decomposition time exceeded 510 minutes.

[0217] [Test Example II: Analysis of Thermal Decomposition Temperature of Adhesive and Conductive Material Using TGA]

[0218] For the positive electrode active material layer powder obtained in Preparation Example 1, the weight change rate according to the heat treatment temperature was analyzed using TGA, and the results are shown below. Figure 3 At this time, the temperature range is 50°C to 900°C, and the heating rate is 5°C / min.

[0219] as follows Figure 3 As shown in FIG. 1 , thermal decomposition of the binder in the positive electrode active material layer powder starts at around 360° C., and thermal decomposition of the conductive material starts at around 450° C. Based on these results, it was found that even when the positive electrode active material layer powder obtained after separating the current collector from the positive electrode waste by pulverizing with a pin mill was heat-treated at a temperature lower than that of the conventional method, a positive electrode active material from which the binder and the conductive material had been sufficiently removed could be obtained.

[0220] In addition, refer to Figure 3, below 460° C., which is the temperature at which the binder thermally decomposes and loses weight, the thermal decomposition of the binder is insufficient, making it difficult to remove the binder and the conductive material from the positive electrode active material layer powder.

[0221] Example 1-1

[0222] The positive electrode active material layer powder obtained in Preparation Example 1 was heat-treated in air at 480° C. for 3 hours to recover the positive electrode active material. Here, the heating rate was 5° C. / min until the temperature reached the heat treatment temperature.

[0223] Example 1-2

[0224] The same procedure as in Example 1-1 was performed, except that the cathode active material layer powder obtained in Preparation Example 1 was heat-treated in air at 500° C. for 2 hours to recover the cathode active material.

[0225] Examples 1-3

[0226] The same procedure as in Example 1-1 was performed, except that the positive electrode active material layer powder obtained in Preparation Example 1 was heat-treated in air at 520° C. for 2 hours to recover the positive electrode active material.

[0227] Examples 1-4

[0228] The same procedure as in Example 1-1 was performed, except that the cathode active material layer powder obtained in Preparation Example 1 was heat-treated in air at 480° C. for 5 hours to recover the cathode active material.

[0229] Comparative Example 1-1

[0230] After punching the positive electrode plate, the discarded positive electrode waste (current collector: aluminum foil, positive electrode active material: NCM-type lithium composite transition metal oxide (Ni:Co:Mn:Al molar ratio of 88:7:4:1)) was shredded and cut, and then heat-treated at 590°C in air for 2 hours to obtain the positive electrode active material. At this time, the heating rate was 5°C / min until the heat treatment temperature was reached.

[0231] Comparative Example 1-2

[0232] The same procedure as in Example 1-1 was performed, except that the cathode active material layer powder obtained in Preparation Example 1 was heat-treated in air at 550° C. for 2 hours to recover the cathode active material.

[0233] Comparative Examples 1-3

[0234] The positive electrode active material layer powder obtained in Preparation Example 2 was heat-treated in air at 480° C. for 3 hours to recover the positive electrode active material. Here, the heating rate was 5° C. / min until the temperature reached the heat treatment temperature.

[0235] [Test Example III: Residual Lithium Content]

[0236] The residual lithium contents of the positive electrode active materials obtained in Examples 1-1 to 1-4 and Comparative Examples 1-1 and 1-2 were measured, and the results are shown in Table 1 below.

[0237] *Residual lithium content: The residual lithium content was measured using a pH titrator (T5, Mettler Toledo Co.). Specifically, 5 g of the positive electrode active material was dispersed in 100 ml of distilled water and mixed at 300 rpm for 5 minutes, and then filtered to filter out the active material and obtain a filtrate. The change in pH was measured while the filtrate was titrated with a 0.1 M HCl solution. Based on the measurement results, a pH titration curve was obtained. Using the pH titration curve, the LiOH and Li 2 CO 3 of residual amount.

[0238] [Table 1]

[0239]

[0240] As shown in Table 1, in the case of Examples 1-1 to 1-4 of the present invention, the LiOH and Li 2 CO 3 In addition, compared with Comparative Example 1-2 which exceeds the heat treatment temperature range of the present invention, the LiOH and Li 2 CO 3 The content is reduced.

[0241] Example 2-1

[0242] LiOH as a lithium precursor was immediately added to the positive electrode active material recovered in Example 1-1 without a washing process, and annealed in air at 650° C. for 5 hours. At this time, the amount of the lithium precursor added was 5 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer.

[0243] The annealed positive electrode active material was mixed with distilled water at 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° C. to 130° C. for 12 hours to obtain a washed positive electrode active material. At this time, air was supplied at a rate of 3 L / min.

[0244] The washed positive electrode active material was coated with boric acid and heated at 300°C for 5 hours to obtain a regenerated positive electrode active material as a final product. At this time, the amount of boric acid added corresponded to 1000 ppm of boron lost in the previous process, the temperature was increased to the heat treatment temperature at a heating rate of 2°C / min, and air was supplied at a rate of 3 L / min.

[0245] Example 2-2

[0246] The same procedure as in Example 2-1 was performed, except that the positive electrode active material recovered in Example 1-4 was used instead of the positive electrode active material of Example 2-1, LiOH as a lithium precursor was added in an amount of 7 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer, and annealing was performed.

[0247] Example 2-3

[0248] The same procedure as in Example 2-1 was performed, except that the positive electrode active material recovered in Example 1-4 was used instead of the positive electrode active material of Example 2-1, LiOH as a lithium precursor was added in an amount of 10 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer, and annealing was performed.

[0249] Embodiment 2-4

[0250] The same procedure as in Example 2-1 was performed, except that the positive electrode active material recovered in Example 1-4 was used instead of the positive electrode active material of Example 2-1, LiOH as a lithium precursor was added in an amount of 12 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer, and annealing was performed.

[0251] Embodiment 2-5

[0252] The same procedure as in Example 2-1 was performed, except that the positive electrode active material recovered in Example 1-4 was used instead of the positive electrode active material of Example 2-1, LiOH as a lithium precursor was added in an amount of 13 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer, and annealing was performed.

[0253] Embodiment 2-6

[0254] The same procedure as in Example 2-1 was performed, except that the positive electrode active material recovered in Example 1-4 was used instead of the positive electrode active material of Example 2-1, LiOH was added as a lithium precursor in an amount of 14 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer, and annealing was performed.

[0255] Embodiment 2-7

[0256] The same procedure as in Example 2-1 was performed, except that the positive electrode active material recovered in Example 1-1 was used instead of the positive electrode active material of Example 2-1, LiOH as a lithium precursor was added in an amount of 15 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer, and annealing was performed.

[0257] Comparative Example 2-1

[0258] LiOH was added as a lithium precursor to the positive electrode active material recovered in Comparative Example 1-1, and annealing was performed in air at 650° C. for 5 hours. At this time, the amount of the lithium precursor added was 15 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer.

[0259] The annealed positive electrode active material was mixed with distilled water at 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° C. to 130° C. for 12 hours to obtain a washed positive electrode active material. At this time, air was supplied at a rate of 3 L / min.

[0260] The washed positive electrode active material was coated with boric acid and heated at 300°C for 5 hours to obtain a regenerated positive electrode active material as a final product. At this time, the amount of boric acid added corresponded to 1000 ppm of boron lost in the previous process, the temperature was increased to the heat treatment temperature at a heating rate of 2°C / min, and air was supplied at a rate of 3 L / min.

[0261] Comparative Example 2-2

[0262] LiOH was added as a lithium precursor to the positive electrode active material recovered in Comparative Example 1-3, and annealing was performed in air at 650° C. for 5 hours. At this time, the amount of the lithium precursor added was 15 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer.

[0263] The annealed positive electrode active material was mixed with distilled water at 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° C. to 130° C. for 12 hours to obtain a washed positive electrode active material. At this time, air was supplied at a rate of 3 L / min.

[0264] The washed positive active material was coated with boric acid and heated at 300° C. for 5 hours to obtain a regenerated positive active material as a final product. At this time, the temperature was increased to the heat treatment temperature at a temperature increase rate of 2° C. / min, and air was supplied at a rate of 3 L / min.

[0265] Comparative Example 2-3

[0266] LiOH was added as a lithium precursor to the positive electrode active material recovered in Comparative Example 1-1, and annealing was performed in air at 650° C. for 5 hours. At this time, the amount of the lithium precursor added was 10 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer.

[0267] The annealed positive electrode active material was mixed with distilled water at 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° C. to 130° C. for 12 hours to obtain a washed positive electrode active material. At this time, air was supplied at a rate of 3 L / min.

[0268] The washed positive electrode active material was coated with boric acid and heated at 300°C for 5 hours to obtain a regenerated positive electrode active material as a final product. At this time, the amount of boric acid added corresponded to 1000 ppm of boron lost in the previous process, the temperature was increased to the heat treatment temperature at a heating rate of 2°C / min, and air was supplied at a rate of 3 L / min.

[0269] Reference example

[0270] Instead of the recycled positive electrode active material, a freshly prepared NCM-based lithium composite transition metal oxide (the molar ratio of Ni:Co:Mn:Al is 88:7:4:1) was used.

[0271] [Test Example IV: SEM Analysis]

[0272] The regenerated positive active materials prepared in Example 2-3, Comparative Example 2-1 and Comparative Example 2-2 were analyzed using SEM, and the results are shown below. Figures 4 to 6 middle.

[0273] Down Figure 4 The SEM cross section of the regenerated positive electrode active material prepared by pin milling in Example 2-3 is shown, Figure 5The regenerated positive electrode active material prepared in Comparative Example 2-1 according to the prior art is shown, and Figure 6 The regenerated positive electrode active material prepared by pulverizing in a mixer in Comparative Example 2-2 is shown. Figure 4 As shown in FIG. 1 , a positive electrode active material layer is obtained by separating a current collector from a positive electrode waste by pulverizing using a pin mill. In the regenerated positive electrode active material layer prepared using the positive electrode active material layer, the positive electrode active material layer is Figure 5 Compared with the conventional method, the shape of the basic particles is maintained without breaking. On the other hand, in the case of pulverization using a mixer, Figure 6 In the case of the positive electrode waste, the current collector is not completely separated from the positive electrode waste, and part of the aluminum current collector is incorporated into the positive electrode active material layer. Therefore, the aluminum current collector is present in the regenerated positive electrode active material prepared using the positive electrode active material layer.

[0274] [Test Example V: XRD analysis]

[0275] XRD analysis was performed on the regenerated positive electrode active materials obtained in Examples 2-1 to 2-7 and Comparative Example 2-1, and the a-axis length, c-axis length, unit cell volume and grain size of the crystal structure were measured, and the results are shown in Table 2 below.

[0276] [Table 2]

[0277]

[0278] As shown in Table 2, Examples 2-1 to 2-7 showed a-axis length, c-axis length, and unit cell volume of the crystal structure at similar levels to those of the Reference Example, and the grain size was reduced. These results indicate that the battery characteristics were further improved.

[0279] [Test Case VI: CHC Cell Evaluation]

[0280] The electrochemical properties of the regenerated positive active materials prepared in Examples 2-1 to 2-7, Comparative Example 2-1 and Comparative Example 2-3 were measured by the following CHC cell evaluation, and the results are shown below. Figure 7 and 8 And Table 3.

[0281] *Manufacture of CHC battery cells: 96 wt% of regenerated positive electrode active material, 2 wt% of carbon black as a conductive material, and 2 wt% of PVdF as a binder were prepared and mixed in NMP to obtain a slurry, which was used to coat aluminum foil to make a positive electrode. Then, a battery cell (button half cell, CHC) was manufactured. The electrochemical performance (charge capacity, discharge capacity and efficiency) and life characteristics were evaluated under the conditions of containing ethylene carbonate (EC) and dimethyl carbonate (DMC) as an electrolyte solution (ethylene carbonate (EC) : dimethyl carbonate (DMC) = 3:7 (weight ratio)) and other additives.

[0282] * Initial capacity evaluation of battery cells: Each battery cell is charged and discharged once under the following conditions at 25°C.

[0283] Charging: 0.2C, CC / CV, 4.5V, 0.05C cutoff

[0284] Discharge: 0.2C, CC, 3.0V, cut-off

[0285] *Charge / discharge efficiency of the cell: The charge capacity and discharge capacity obtained in the evaluation of the initial capacity of the cell were substituted into the following equation 1, the charge / discharge efficiency was calculated, and the results are shown in the following Table 3.

[0286] [Equation 1]

[0287] Charge / discharge efficiency (%) = [discharge capacity (mAh / g) / charge capacity (mAh / g)] × 100

[0288] *Evaluation of high temperature life characteristics of battery cells: At 45°C, under the following conditions, each battery cell was charged and discharged 20 times, and the capacity retention rate and resistance increase rate (△DCIR) of each cycle were calculated by equations 2 and 3, respectively, and the results are shown below Figure 8 middle.

[0289] Charging: 0.33C, CC / CV, 4.5V, 0.05C cutoff

[0290] Discharge: 0.33C, CC, 3.0V, 0.05C cutoff

[0291] [Equation 2]

[0292] Capacity retention rate (%) = (discharge capacity after N cycles / discharge capacity after 1 cycle) × 100

[0293] [Equation 3]

[0294] △DCIR={(resistance after N cycles / resistance after 1 cycle)×100}-100

[0295] Down Figure 7 The evaluation results of the coin cells of each of the regenerated positive electrode active materials prepared in Examples 2-1 to 2-7 and Comparative Example 2-3 are shown, and a graph showing the initial charge / discharge capacity is shown.

[0296] as follows Figure 7As shown, in the case of the regenerated positive electrode active material of the present invention, the thermal decomposition of the binder and the conductive material is carried out at a temperature lower than that of the prior art, so the lithium loss in the positive electrode active material is reduced compared with the prior art. Therefore, the amount of lithium precursor required in the process of restoring the crystal structure is reduced. Specifically, in Example 2-3 and Comparative Example 2-3 in which 10 mol% of lithium precursor is added at the same content, the initial capacity evaluation result of Example 2-3 is better than that of Comparative Example 2-3. In addition, Example 2-2 in which 7 mol% of lithium precursor is added shows an initial capacity evaluation result similar to that of Comparative Example 2-3 in which 10 mol% of lithium precursor is added.

[0297] [Table 3]

[0298]

[0299] As shown in Table 3, the regenerated positive electrode active materials of the present invention (Examples 2-1 to 2-7) exhibited charge / discharge efficiencies similar to or better than those of Comparative Example 2-3 according to the prior art.

[0300] in addition, Figure 8 The evaluation results of button cells of regenerated positive active materials prepared in Examples 2-1 to 2-7 and Comparative Example 2-1 are shown, and a graph showing the capacity retention rate and resistance increase rate after 20 cycles is shown. In the case of the regenerated positive active materials (Examples 2-1 to 2-7) of the present invention, the capacity retention rate of the cell is excellent at high temperature, and the resistance increase rate is lower than that of Comparative Example 2-1 according to the prior art. The capacity retention rate of Example 2-5 is lower than that of Comparative Example 2-1, but the resistance increase rate is low. The resistance increase rate of Example 2-1 is lower than that of Comparative Example 2-1, but the capacity retention rate is excellent compared with Comparative Example 2-1.

[0301] [Explanation of Reference Numerals]

[0302] 10: Current collector

[0303] 20: Active material layer

[0304] 30: Positive electrode

[0305] 40: Positive plate

[0306] 50: Positive electrode waste

Claims

1. A method for regenerating a positive electrode active material, comprising: Step (a), using a pin mill to grind a waste positive electrode comprising a current collector and a positive electrode active material layer coated on the current collector under dry conditions to obtain a positive electrode active material layer in a powder form; Step (b), heat-treating the obtained positive electrode active material layer powder at 460° C. to 530° C. in air to recover the positive electrode active material; Step (c), adding a lithium precursor to the recovered positive electrode active material and annealing at 400° C. to 1000° C.; as well as Step (d), washing the annealed positive electrode active material with a washing solution.

2. The method according to claim 1, wherein: In the step (a), pulverization by a pin mill is performed at 5000 rpm to 10000 rpm.

3. The method according to claim 1, wherein: Step (a) includes a pretreatment step of shredding or cutting the waste positive electrode.

4. The method according to claim 1, wherein: The positive electrode active material recovered after the heat treatment in step (b) is subjected to annealing in step (c) without washing.

5. The method according to claim 1, wherein: In step (b), the total amount of LiOH and Li2CO3 as surface residues of the positive electrode active material recovered after the heat treatment is adjusted to an amount of 1.35 wt% or less.

6. The method according to claim 1, wherein: The positive electrode active material includes one or more 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 the content of Ni is 60 mol% or more based on 100 mol% of the total amount of other metals except Li.

7. The method according to claim 1, wherein: In step (b), the heat treatment is performed for 1.5 hours to 6 hours.

8. The method according to claim 1, wherein: The amount of the lithium precursor added is 3 mol % to 17 mol % based on 100 mol % of the total amount of lithium in the raw positive electrode active material used in the positive electrode active material layer.

9. The method according to claim 1, wherein: The lithium precursor includes one or more of LiOH, Li2CO3, LiNO3 and Li2O.

10. The method according to claim 1, wherein: The annealing is performed at 400° C. to 1000° C. in an oxygen atmosphere or in air.

11. The method according to claim 1, wherein: The washing solution is water. 12 . The method according to claim 1 , comprising step (e) of surface coating the washed positive electrode active material.

13. The method according to claim 12, wherein: The surface coating is performed by coating the surface with one or more of metal, organic metal and carbon components in a solid or liquid form and then heat-treating the surface at 100°C to 1200°C.

14. A regenerated positive electrode active material prepared using the method of any one of claims 1 to 13.

15. A regenerated positive electrode active material, comprising one or more 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 based on 100 mol % of the total amount of other metals other than Li, the content of Ni is 60 mol % or more, in, The total amount of residual LiOH and Li2CO3 in the regenerated positive electrode active material is less than 1.35 wt %, and the a-axis length of the crystal structure of the regenerated positive electrode active material measured by XRD is to The length of the c-axis is to The unit cell volume is to And the grain size is 72nm to 84nm.

16. The regenerated positive electrode active material according to claim 15, wherein: The surface of the regenerated positive electrode active material is coated with a coating agent containing metal or carbon. 17 . A secondary battery comprising the regenerated positive electrode active material according to claim 15 .

18. A method for regenerating a positive electrode active material, comprising: Step (a), applying an impact force of 5.1 to 10.2 Newtons (N) and a centrifugal force of 2600 to 10700 Newtons (N) to a waste positive electrode comprising a current collector and a positive electrode active material layer coated on the current collector under dry conditions to obtain a positive electrode active material layer in a powder form; Step (b), heat-treating the obtained positive electrode active material layer powder at 460° C. to 530° C. in air to recover the positive electrode active material; Step (c), adding a lithium precursor to the recovered positive electrode active material and annealing at 400° C. to 1000° C.; as well as Step (d), washing the annealed positive electrode active material with a washing solution.

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