Positive electrode active material recycling method

Abstract

A method for recycling active materials by recovering active materials from positive electrode waste is provided. The positive electrode active material recycling method according to the present invention comprises the following steps: (a-1) soaking positive electrode waste including a lithium composite transition metal oxide positive electrode active material layer on a current collector in an alkaline aqueous solution to separate the active material layer from the current collector; (a-2) recovering the active material in the active material layer by thermally decomposing a binder and a conductive material in the active material layer by heat-treating the active material layer in air; (b) washing the recovered active material with an alkaline lithium compound aqueous solution in an aqueous solution state, and drying the washed active material; and (c) adding a lithium precursor to the washed active material, and annealing the resulting mixture to obtain a reusable active material.

Description

Technical Field

[0001] The present disclosure relates to a method for recycling resources in the manufacturing process of lithium secondary batteries. More specifically, the present disclosure relates to a method for collecting and recycling positive electrode waste generated in the manufacturing process of lithium secondary batteries or positive electrode active materials of lithium secondary batteries discarded after use. This application claims priority to Korean Patent Application No. 10-2020-0067429 filed with the Korean Intellectual Property Office on June 4, 2020, the disclosure of which is incorporated herein by reference in its entirety. Background Art

[0002] Rechargeable lithium secondary batteries are gaining attention as an alternative to fossil energy. Such lithium secondary batteries are mainly used in traditional handheld devices such as mobile phones, cameras, and power tools. Recently, the scope of application tends to be gradually expanded to vehicles driven by electricity (EV, HEV, PHEV), large-capacity energy storage systems (ESS), and uninterruptible power supply systems (UPS).

[0003] A lithium secondary battery comprises: an electrode assembly, the electrode assembly comprising a unit cell, each unit cell comprising a positive plate and a negative plate, the positive plate and the negative plate comprising a current collector and an active material coated on the current collector, a separator being interposed between the positive plate and the negative plate; and a package or battery case, in which the electrode assembly is airtightly received together with an electrolyte solution. Lithium secondary batteries mainly include lithium-based oxides as positive electrode active materials and carbon-based materials as negative electrode active materials. Lithium-based oxides contain metals such as cobalt, nickel or manganese. In particular, cobalt, nickel and manganese are very expensive precious metals. Among them, cobalt is a strategic metal, and its supply is the focus of worldwide attention. Due to the limited number of cobalt producing countries, the global supply of cobalt is unstable. When the supply and demand of strategic metals are unbalanced, the cost of raw materials is likely to rise.

[0004] Research has been conducted on collecting and recovering precious metals from lithium secondary batteries (waste batteries) discarded after expiration. In addition to waste batteries, it is more preferable to collect resources from waste materials discarded after positive plates are punched out, or from positive plates that have defects or failures in the process.

[0005] Currently, if Figure 1 As shown in FIG, a lithium secondary battery is manufactured by coating a positive electrode slurry including a positive electrode active material, a conductive material, a binder and a solvent on a long sheet type positive electrode collector 10 (such as an aluminum (Al) foil) to form a positive electrode active material layer 20, manufacturing a positive electrode sheet 30, and punching out a positive electrode plate 40 in a predetermined size. The remainder after punching is discarded as a positive electrode waste 50. If the positive electrode active material is collected and reused from the positive electrode waste 50, it will be very ideal in terms of industrial economy and environment.

[0006] Most of the existing methods for collecting positive active materials include dissolving the positive electrode with hydrochloric acid, sulfuric acid, nitric acid, etc., extracting active material elements such as cobalt, nickel, and manganese, and using them as raw materials for the synthesis of positive active materials. However, the use of acid to extract active material elements adopts a non-environmentally friendly process to collect pure raw materials, and requires a neutralization process and a wastewater treatment process, resulting in an increase in process costs. In addition, such a process is unlikely to collect lithium (one of the key positive active material elements). In order to overcome these shortcomings, a direct recycling method that does not dissolve the positive active material and does not extract the active material in elemental form is needed.

[0007] Furthermore, since some electrolyte solution remains on the positive electrode waste obtained from positive electrodes damaged during processing, batteries determined to be defective or unqualified in quality tests, or waste batteries discarded after expiration, a method for collecting active materials by safely treating the electrolyte solution is required. Summary of the invention

[0008] Technical issues

[0009] The present disclosure is directed to providing a method for collecting and reusing active materials from cathode waste.

[0010] Technical Solution

[0011] In order to solve the above problems, the method for recycling positive electrode active materials disclosed in the present invention includes: (a-1) soaking positive electrode waste including a lithium composite transition metal oxide positive electrode active material layer located on a current collector in an alkaline solution to separate the active material layer from the current collector; (a-2) heat-treating the active material layer in air to thermally decompose the binder and conductive material in the active material layer, and collecting the active material in the active material layer; (b) washing the collected active material with a lithium compound solution that is alkaline in an aqueous solution, and drying it; and (c) annealing the washed active material with the addition of a lithium precursor to obtain a reusable active material.

[0012] In the present disclosure, the alkaline solution preferably includes LiOH or NaOH.

[0013] In the present disclosure, the method for recycling positive electrode active materials may further include: (d) performing surface coating on the annealed active material.

[0014] The heat treatment may be performed at 300°C to 800°C.

[0015] The heat treatment may be performed at 550° C. for 30 minutes with a temperature rise rate of 5° C. / minute.

[0016] The content of the lithium compound (preferably LiOH) in the lithium compound solution is greater than 0% and less than 15%. The washing may be performed within 1 hour.

[0017] The washing may be performed by stirring the collected active material while being immersed in the lithium compound solution.

[0018] The lithium precursor may be at least one of LiOH, Li2CO3, LiNO3 and Li2O.

[0019] The amount of addition of the lithium precursor may be used to adjust the ratio of lithium to other metals in the raw active material used in the active material layer by adding lithium at a ratio of lost lithium.

[0020] For example, the lithium precursor may be added in an amount to add lithium at a molar ratio of 0.001 to 0.4.

[0021] Furthermore, the amount of the lithium precursor added is preferably for adding more lithium in a molar ratio of 0.0001 to 0.1 based on a molar ratio of lithium:other metals of 1:1.

[0022] The annealing may be performed at 400° C. to 1000° C. in air.

[0023] The temperature of the annealing step may exceed the melting point of the lithium precursor.

[0024] The active material in the active material layer may be collected in a powder form, and carbon generated by carbonization of the binder or the conductive material may not remain on the surface.

[0025] The surface coating step may include coating at least one of a metal, an organic metal, and a carbon material on the surface through a solid phase or liquid phase treatment, and performing a heat treatment at 100° C. to 1200° C.

[0026] The recyclable active material may be represented by the following Formula 1:

[0027] [Formula 1]

[0028] Li a Ni x Mn y Co z M w O 2+δ

[0029] wherein M comprises at least one selected from the group consisting of B, W, Al, Ti and Mg, <a≤1.1,0≤x<0.95,0≤y<0.8,0≤z<1.0,0≤w≤0.1,-0.02≤δ≤0.02,x+y+z+w=1。

[0030] The reusable active material may have a fluorine (F) content of 150 ppm or less.

[0031] The cathode waste may contain residual electrolyte solution, and the electrolyte solution may be removed in the step (a-1), and the step (a-1) may further include filtering and washing after the soaking.

[0032] Beneficial Effects

[0033] According to the present disclosure, it is possible to reuse discarded positive electrode active materials (such as positive electrode waste generated in the lithium secondary battery manufacturing process) without using acid, thereby achieving environmental protection. The method according to the present disclosure does not require a neutralization process or a wastewater treatment process, thereby achieving environmental mitigation and process cost reduction.

[0034] According to the present disclosure, all metal elements of the positive electrode active material can be collected. The method does not use the extracted active material elements as raw materials for synthesizing the positive electrode active material, but directly reuses the active material collected in powder form, thereby achieving economic benefits.

[0035] According to the present disclosure, toxic and explosive solvents such as NMP, DMC, acetone, and methanol are not used, thereby achieving safety, and since simple processes such as heat treatment, washing, and annealing are used, it is easy to manage and suitable for large-scale production.

[0036] According to the present disclosure, since the residual electrolyte solution on the positive electrode waste of the discarded battery is removed in the step of using the alkaline solution, the subsequent heat treatment process can be safely carried out and the presence of impurities such as metal compounds caused by the residual electrolyte solution can be prevented, and since no expensive organic solvent is used, there is a cost advantage.

[0037] According to the present disclosure, good resistance characteristics and capacity characteristics can be ensured without degrading the electrochemical performance of the collected active materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The accompanying drawings illustrate embodiments of the present disclosure and, together with the following detailed description, help to further understand the technical aspects of the present disclosure. Therefore, the present disclosure should not be interpreted as being limited to the drawings.

[0039] Figure 1 The figure shows the positive electrode scraps discarded after punching out the positive electrode plates in the positive electrode sheets.

[0040] Figure 2 is a flow chart of an active material recycling method according to the present disclosure.

[0041] Figure 3 is shown with Figure 2 A diagram of a series of steps associated with the process of immersion in an alkaline solution.

[0042] Figure 4 is a picture showing a series of steps related to the process of immersing in an alkaline solution in an experimental example of the present disclosure.

[0043] Figure 5 and Figure 6 The results of battery evaluation using the active materials of Examples and Comparative Examples are shown.

[0044] Figure 7 and Figure 8 Scanning electron microscope (SEM) images of active materials of Examples and Comparative Examples are shown.

[0045] Fig. 9 It is a graph showing the particle size distribution of the active materials of Examples and Comparative Examples. DETAILED DESCRIPTION

[0046] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Before the description, it should be understood that the terms or words used in the specification and the appended claims should not be interpreted as being limited to the general and dictionary meanings, but are interpreted according to the meanings and concepts corresponding to the technical aspects of the present disclosure based on the principle that the inventor is allowed to appropriately define the terms to obtain the best interpretation. Therefore, the embodiments described herein and the illustrations in the drawings are only examples and do not fully describe the technical aspects of the present disclosure, so it should be understood that various other equivalents and modifications may be made to them when filing a patent application.

[0047] In the following description, reference is made to the accompanying drawings which form a part of the present disclosure. The embodiments described in the detailed description, drawings, and appended claims are not intended to be limiting. Other embodiments may be used, and modifications and changes may be made thereto, without departing from the technical aspects and scope of the subject matter disclosed herein. As generally described herein and illustrated in the accompanying drawings, aspects of the present disclosure may include arrangements, substitutions, combinations, separations, and designs of various different elements, and it will be immediately understood that all such elements are expressly contemplated.

[0048] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs (hereinafter referred to as "person skilled in the art").

[0049] The present disclosure is not limited to the specific embodiments described herein. It is obvious to those skilled in the art that many variations and changes may be made to the present disclosure without departing from the technical aspects and scope of the present disclosure. It is obvious to those skilled in the art that functionally equivalent methods within the scope of the present disclosure are apparent from the previous description, in addition to those methods listed herein. Such variations and changes fall within the scope of the appended claims. The scope of all equivalents to which the present disclosure and the appended claims are entitled will be defined by the appended claims. It should be understood that the present disclosure is not limited to specific variant methods. It should be further understood that the terms used herein are intended to describe specific embodiments, rather than to limit the present disclosure.

[0050] The traditional active material recycling process is mainly to extract the valuable metal (nickel, cobalt, manganese) elements in the lithium secondary battery active materials whose performance has deteriorated after use, and resynthesize the active materials. Compared with the traditional process, the feature of the present invention is to collect active materials from the positive electrode waste generated in the lithium secondary battery manufacturing process.

[0051] In addition, well-known active material recycling processes involve producing metals (direct reduction method) or resynthesizing active materials from valuable metals extracted by acid / base dissolution or melted using reducing agents / additives, which requires additional chemical methods, complicates the process, and causes additional economic expenditure. However, the present disclosure relates to a method for directly recycling positive electrode active materials without dissolving the positive electrode active materials.

[0052] In order to directly reuse the positive electrode active material, it is necessary to remove the current collector from the positive electrode. The current collector can be removed from the positive electrode by high temperature heat treatment to remove the binder, using a solvent to melt the binder, melting the current collector, and screening the active material by dry grinding and sieving.

[0053] When a solvent is used to melt the binder, the stability of the solvent is important. NMP is the most effective solvent, but its disadvantages are toxicity and high cost. Another disadvantage is that a waste solvent reprocessing or solvent collection process must be performed. The process cost required to melt the current collector is lower than that of using a solvent. However, it is difficult to remove impurities from the surface of the reusable active material, and hydrogen is produced in the process of removing the current collector, posing a risk of explosion. Dry grinding and screening cannot perfectly separate the current collector and active material. The particle size distribution of the active material changes during the grinding process, and it is difficult to remove the binder, resulting in a decrease in the characteristics of the battery including the reusable active material.

[0054] The present disclosure first uses an alkaline solution to separate the active material layer from the current collector, and uses a high temperature heat treatment to separate the binder in the active material layer from the current collector. In particular, since an alkaline solution is used first, the problem caused by the residual electrolyte solution is solved, and the heat treatment is performed in the air, so the process only requires heating without any special device configuration, so it is relatively simple and suitable for large-scale production and commercialization. Impurities should not remain on the surface of the reusable active material. The present disclosure proposes to remove impurities from the surface of the reusable active material.

[0055] In the following, reference will be made to Figure 2 An active material recycling method according to one embodiment of the present disclosure is described. Figure 2 is a flow chart of an active material recycling method according to the present disclosure.

[0056] refer to Figure 2 , first, discarded positive electrode waste is prepared ( S10 ).

[0057] As mentioned above Figure 1 The positive electrode waste can be what is left after manufacturing a positive electrode sheet including a lithium composite transition metal oxide positive electrode active material layer on a current collector and punching a positive electrode sheet. In addition, the positive electrode waste can be prepared by collecting positive electrodes that have defects or failures during the process. In addition, the positive electrode waste can be prepared by separating positive electrodes from lithium secondary batteries discarded after use.

[0058] For example, discarded positive electrode waste can be prepared, or positive electrode waste can be prepared from a positive electrode damaged in a secondary battery manufacturing process, the secondary battery manufacturing process including coating a slurry on a sheet-type current collector of an aluminum foil, drying in a vacuum oven at about 120° C. to make a positive electrode sheet, punching out a positive electrode plate in a predetermined size, assembling the positive electrode plate with a negative electrode plate and injecting an electrolyte solution, the slurry being prepared by adding N-methylpyrrolidone (NMP) to lithium cobalt oxide (LiCoO2 (LCo)) as an active material or a lithium-based active material including nickel, cobalt and manganese, carbon such as carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder and mixing.

[0059] The cathode waste has an active material layer on a current collector of a metal foil such as an aluminum foil. In the case where there is a residual electrolyte solution on the discarded cathode waste, it is necessary to safely remove the electrolyte solution.

[0060] Subsequently, the positive electrode waste is crushed to an appropriate size (S20). Crushing refers to cutting or chopping the positive electrode waste into an appropriate size for disposal. After switching or chopping, the size of the positive electrode waste is reduced to, for example, 1 cm×1 cm. Various dry milling equipment can be used for crushing, including hand mills, pin mills, disc mills, cutting mills and hammer mills, as well as high-speed cutters.

[0061] Cutting or shredding can be performed considering the characteristics required by the equipment used in the disposal and subsequent processes of the cathode waste. For example, when equipment that requires continuous processing is used to load and unload cathode waste, it is necessary to break up the oversized cathode waste to facilitate the movement of the cathode waste.

[0062] Subsequently, the positive electrode waste is soaked in an alkaline solution (S25). During the soaking process, mechanical force can be applied by, for example, ultrasonic treatment, stirring with a magnetic stirrer, or crushing with the aid of an appropriate tool. The concentration of the alkaline solution is between pH 7 and pH 14, preferably between pH 10 and pH 14, and more preferably between pH 12 and pH 14. Preferably, the alkaline solution includes LiOH or NaOH. The alkaline solution may include KOH or NaCl. In addition to the listed materials, the alkaline solution may also include chemical materials eluted with water or polar materials ionized.

[0063] When the positive electrode waste is put into an alkaline solution, the current collector dissolves. In this case, an external mechanical force can be applied, for example, by stirring, to make it easier to separate the active material layer from the current collector and remove the residual electrolyte solution on the active material layer. When the current collector is completely dissolved in the alkaline solution, or when the active material layer is separated, the current collector floats on the alkaline solution due to the difference in specific gravity, so only the active material layer can be collected by filtration after soaking. In this case, the active material layer may lose the continuity characterized by the layer and may be broken into pieces, but because the active material, binder and conductive material are still agglomerated in the active material layer, the active material layer exists in a sheet form, and in this case, the active material layer is indicated in this specification.

[0064] The current collector can be completely dissolved in the alkaline solution and then washed with water to remove it, or when the separated current collector floats on the alkaline solution due to the difference in specific gravity, the floating material can be separated and removed with a net. After filtering the active material sheet with a reduced pressure filter, it can be further washed to completely remove Na in the electrolyte solution and the alkaline solution.

[0065] Figure 3: is a diagram showing a series of steps related to the process of S25 of soaking in an alkaline solution. (a) shows that the positive electrode waste material broken into pieces is soaked in an alkaline solution and stirred, (b) shows that stirring is further performed, (c) shows that in some positive electrode waste materials, the active material layer is finally separated from the aluminum (Al) current collector, (d) shows that the current collector is completely dissolved or separated from the active material layer after soaking and stirring, (e) shows that the active material layer sinks due to the difference in specific gravity, and (f) shows the active material layer that has undergone washing and drying as an additional step. As shown in (f), through this step, the current collector and the electrolyte solution are removed, leaving only the sheet-like active material layer.

[0066] Then, refer to Figure 2 , the active material layer separated in S25 is heat-treated in air (S30). The active material layer is formed by coating a slurry including a mixture of an active material, a conductive material, a binder and a solvent, and after the solvent evaporates, the active material and the conductive material are combined with the binder. The active material layer is separated from the current collector by S25, but since the active material and the conductive material are bonded together with the binder, it is necessary to remove the binder to separate the active material.

[0067] In the present disclosure, heat treatment is performed to thermally decompose the binder in the active material layer. The heat treatment may be performed at 300°C to 800°C and may be referred to as high temperature heat treatment. At temperatures below 300°C, it may be difficult to remove the binder, while temperatures above 800°C are not necessary. If heat treatment is performed in the presence of a current collector, it is necessary to perform heat treatment at a temperature below the melting point of the current collector, but since the current collector according to the present disclosure has been separated, the heat treatment temperature is not limited by the current collector.

[0068] The heat treatment time is long enough to cause the binder to thermally decompose. For example, the heat treatment time is about 30 minutes. Preferably, the heat treatment time is more than 30 minutes. As the heat treatment time increases, the thermal decomposition time of the binder will be extended, but when the heat treatment time is equal to or longer than the predetermined time, there is no difference in the thermal decomposition effect. Preferably, the heat treatment time is more than 30 minutes and less than 5 hours.

[0069] The heat treatment equipment may include various types of furnaces. For example, the heat treatment equipment may be a box-type furnace, and in consideration of productivity, may be a rotary kiln capable of continuous processing.

[0070] After heat treatment, the product can be cooled quickly or slowly in air.

[0071] For example, the heat treatment may be performed at 550°C for 30 minutes with a temperature rise rate of 5°C / minute. For example, this temperature rise rate is within the allowable range of the box furnace and is sufficient to heat the positive electrode waste without generating thermal shock. When the heat treatment is performed at the above temperature for less than 10 minutes, thermal decomposition is insufficient, and therefore it is necessary to perform the heat treatment for more than 10 minutes, preferably more than 30 minutes.

[0072] Through the heat treatment in air, the binder and the conductive material in the active material layer are thermally decomposed to remove CO2 and H2O. Since the binder is removed, the active material to be collected can be screened out in the form of powder. Therefore, the active material in the active material layer can be collected by performing S30.

[0073] It is important to perform the heat treatment of S30 in air. When heat treated in a reducing or inert gas environment, the binder and the conductive material undergo carbonization rather than thermal decomposition. When carbonized, carbon remains on the surface of the active material and degrades the performance of the reusable active material. When heat treated in air, the carbon in the binder or conductive material is removed by generating CO, CO2 gas through a combustion reaction with oxygen, so the binder and conductive material do not remain and are almost all removed.

[0074] Therefore, according to the present disclosure, the active material is collected in a powder form, and carbon generated by carbonization of the binder or the conductive material does not remain on the surface.

[0075] In the case of residual electrolyte solution in the positive electrode waste, when S30 of the proposed method is performed without S25, a large amount of impurities (such as metal compounds) may be formed when the electrolyte solution, binder and conductive material are removed by heat treatment. In addition, when heat treatment is performed in the presence of an electrolyte solution, the electrolyte solution may make it impossible to stably maintain the heat treatment temperature. However, when the electrolyte solution is completely removed and the current collector is separated by the proposed S25, lithium metal impurities that may be formed by the electrolyte solution can be avoided.

[0076] Subsequently, the collected active material is washed and dried (S40). It is important to wash with a lithium mixture solution, which is alkaline in aqueous solution. The lithium mixture solution contains a lithium mixture, preferably LiOH, whose content is above 0% and below 15%. Preferably, the amount of LiOH is below 15%. When an excess of LiOH is included, the excess LiOH may remain on the surface of the active material after washing, which may affect the subsequent annealing process. In order to make the surface of the active material as clean as possible before annealing, it is not advisable to add excess LiOH, and the amount of LiOH is limited to below 15%.

[0077] Washing can be carried out by soaking the collected active material in a lithium mixture solution. Washing can be carried out within a week (preferably one day, more preferably 1 hour) after soaking. When washing for a week or longer, the capacity will be reduced due to excessive lithium dissolution. Therefore, it is expected to perform washing within 1 hour. Washing includes soaking the active material in an alkaline lithium mixture solution in an aqueous solution and stirring it under soaking. It is expected that soaking and stirring are carried out together. When the active material is soaked in a lithium mixture solution without stirring, the washing process is very slow, causing lithium dissolution. When stirring is carried out together, the process time is minimized, therefore, it is expected to stir while soaking in a lithium mixture solution. After filtering, it can be dried in air in a furnace (convection type).

[0078] Washing with a lithium mixture solution that is alkaline in an aqueous solution is performed to remove LiF and metal fluorides that may be present on the surface of the collected active material, and surface modification is performed. In the heat treatment process of S30, the binder and the conductive material in the active material layer are removed by evaporation of CO2 and H2O. In this process, CO2 and H2O react with lithium on the surface of the active material to produce Li2CO3 and LiOH, and fluorine (F) (such as PVdF) present in the binder reacts with the metal element of the positive electrode active material to produce LiF or metal fluoride. When LiF or metal fluoride remains, the characteristics of the battery including the reusable active material will decrease. The present disclosure adds a washing step of S40 to remove reactants that may be produced on the surface of the reusable active material in the heat treatment step (S30) to prevent impurities from remaining on the surface of the reusable active material.

[0079] In S40, it is important to wash with a lithium mixture solution that is alkaline in aqueous solution. When sulfuric acid or hydrochloric acid aqueous solution is used instead of a lithium mixture solution that is alkaline in aqueous solution, F on the surface of the active material is washed away, but the performance of the reusable positive active material may be reduced due to the dissolution of transition metals (Co, Mg) present in the active material. The role of the lithium mixture solution that is alkaline in aqueous solution used in the present disclosure is to remove trace amounts of binders that may remain after the thermal decomposition of S30, not to dissolve transition metals present in the active material, and to compensate for the amount of lithium dissolved during the washing process.

[0080] Through S40, the present disclosure can adjust the LiF content on the surface of the collected active material to less than 500 ppm, thereby improving the capacity. Preferably, the F content can be 150 ppm or less. More preferably, the F content can be 30 ppm or less.

[0081] Subsequently, the washed active material is annealed with the addition of a lithium precursor ( S50 ).

[0082] The loss of lithium in the active material may occur through the previous steps S30 and S40. S50 compensates for the loss of lithium.

[0083] Furthermore, in S50 , the crystal structure of the active material is restored by annealing, so that the characteristics of the reusable active material are restored or improved to the level of fresh active material that has not been used.

[0084] After the previous steps S30 and S40, structural transformation can be found in the surface of the active material. For example, the NCM-based lithium composite transition metal oxide as an active material may have a spinel structure, which is due to the conversion of nickel into rock salt [NiCO3·2Ni(OH)2)H20] when it is damp in S40. When the battery is manufactured in this state, the characteristics of the battery may decrease, such as a decrease in capacity. The present disclosure restores the crystal structure with the help of S50. For example, the NCM-based lithium composite transition metal oxide as an active material is restored to a hexagonal structure. Therefore, the initial characteristics can be restored or improved to a level similar to that of the fresh active material.

[0085] In addition, in the case of LCO active materials, Co3O4 may be generated on the surface by thermal decomposition. When a battery is manufactured without removing Co3O4, the characteristics of the battery may be degraded. The present disclosure can restore or improve the initial characteristics to a level similar to that of a fresh active material by restoring the crystal structure and removing Co3O4 through S50.

[0086] The lithium precursor in S50 may be at least one of LiOH, Li2CO3, LiNO3 and Li2O.

[0087] The amount of lithium precursor added is used to add lithium to the ratio of lithium to other metals in the raw material active material (i.e., fresh active material) used in the active material layer at the ratio of lithium loss. For example, when the ratio of lithium to other metals in the fresh active material is 1, the amount of lithium precursor added can be used to add lithium at a molar ratio of 0.001 to 0.4. It is suitable to add lithium at a molar ratio of 0.01 to 0.2. The addition of lithium precursor exceeds the lithium lost by washing, resulting in unreacted lithium precursor left on the reusable active material, so that the resistance during the active material reuse process increases, so it is necessary to supply lithium precursor in an appropriate amount.

[0088] In addition, based on a molar ratio of lithium: other metals of 1: 1, the amount of lithium precursor added is preferably used to add more lithium at a molar ratio of 0.001 to 0.1. Excess lithium is added to form a surface protective layer on the active material by surface coating, which will be described in detail below. When a secondary battery is manufactured using an active material, side reactions can be suppressed and life characteristics can be maintained with the help of an electrolyte solution.

[0089] Annealing can be performed at 400°C to 1000°C in air. The annealing temperature can be 600°C to 900°C. The temperature varies within a limited range, depending on the type of lithium precursor. The annealing time can be at least 1 hour. Preferably, the annealing time is about 5 hours. When the annealing time is long, the crystal structure may be fully restored, but long-term annealing does not have a great effect on the performance. For example, the annealing time is about 15 hours or less. The annealing equipment can be similar to or the same as the equipment of the heat treatment step S30.

[0090] For example, when Li2CO3 is used as a lithium precursor, the annealing temperature is preferably 700°C to 900°C, more preferably 710°C to 780°C. This is because the melting point of Li2CO3 is 723°C. Most preferably, annealing is performed at 750°C. 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. This is because the melting point of LiOH is 462°C.

[0091] Preferably, the annealing temperature is higher than the melting point of the lithium precursor. However, at a temperature higher than 1000°C, the positive electrode active material will undergo thermal decomposition and the performance of the active material will be reduced, so the annealing temperature should not exceed 1000°C.

[0092] Through S50, recyclable active materials can be obtained.

[0093] Optionally, S60 may be performed. In S60, the active material annealed in S50 is surface-coated.

[0094] The surface coating step may include coating at least one of a metal, an organic metal, and a carbon material on the surface by solid phase or liquid phase treatment, and heat treating at 100° C. to 1200° C. When heat treating at a temperature higher than 1200° C., performance degradation may occur due to thermal decomposition of the positive electrode active material. In the surface coating process, coating on the surface by solid phase or liquid phase treatment may use mixing, milling, spray drying, and grinding.

[0095] By surface coating, a surface protective layer of different metals is formed. In the case where the molar ratio of lithium in the positive active material: other metals is 1: 1, when the molar ratio of lithium in the positive active material: other metals is reduced to less than 1: 1 due to the reaction of lithium in the active material with the surface coating material, 100% capacity cannot be exhibited. Therefore, an excess of lithium is added to compensate for the lithium loss in the previous step S50, so that the molar ratio of lithium in the positive active material: other metals is 1: 1, and more lithium is included in the positive active material at a molar ratio of 0.0001 to 0.1 with other metals. Therefore, a surface protective layer can be formed so that the molar ratio of lithium in the positive active material: other metals in the surface coating is 1: 1.

[0096] In detail, when the active material is coated with a metal oxide such as B, W, BW and the like and subjected to heat treatment, a lithium boron oxide layer may be formed on the surface of the active material and used as a surface protective layer. The lithium additionally included at a molar ratio of 0.0001 to 0.1 in S50 reacts with the metal oxide such as B, W, BW and the like in S60, and the molar ratio of lithium: other metals in the positive electrode active material does not decrease to less than 1:1, so the capacity does not decrease.

[0097] The recyclable active material obtained by the above method can be represented by Formula 1.

[0098] [Formula 1]

[0099] Li a Ni x Mn y Co z M w O 2+δ

[0100] wherein M comprises at least one selected from the group consisting of B, W, Al, Ti and Mg, <a≤1.1,0≤x<0.95,0≤y<0.8,0≤z<1.0,0≤w≤0.1,-0.02≤δ≤0.02,x+y+z+w=1。

[0101] The F content of the recyclable active material may be 100 ppm or less. According to the present disclosure, an active material having a reduced F content may be collected, and when reused as an active material, may provide excellent resistance characteristics and capacity characteristics.

[0102] According to the present disclosure, LiF or metal fluoride is removed in the washing step of S40. Li2CO3 is removed in the annealing of S50. The steps of washing and drying using a lithium compound solution that is alkaline in an aqueous solution are safe and low-cost, and can remove LiF or metal fluoride without losing other elements, prevent the dissolution of transition metals, and compensate for the lithium loss that occurs during the process. The annealing step is also safe and low-cost, and can effectively remove Co3O4 and restore the crystal structure (i.e., improve crystallinity), thereby improving the battery characteristics of the reusable active material.

[0103] The reusable active material obtained according to the present disclosure can have a particle size distribution similar to that of the fresh active material, which eliminates the need for a separate treatment for adjusting the particle size distribution. Since the carbon generated by the carbonization of the binder or the conductive material does not remain on the surface, no carbon removal step is required. Figure 2 The active material obtained by the method can be used to manufacture the positive electrode without any treatment.

[0104] The recycled active material may be used 100% without composition adjustment or may be mixed with fresh active material and may be used to prepare a slurry together with a conductive material, a binder, and a solvent.

[0105] Hereinafter, experimental examples of the present disclosure will be described in detail.

[0106] <Experimental example>

[0107] The prepared positive electrode active materials were evaluated using the following method.

[0108] The experiments were mainly conducted in three categories. The first category was to analyze the changes in active material elements through immersion in alkaline solution at S25, heat treatment at S30, and washing and drying at S40; the second category was to detect the element loss of each process in LCO active materials with Al surface coating; and the third category was to verify the effect of the method according to the present disclosure in NCM active materials with BW surface coating.

[0109] The first type of experiment is shown below. The elemental analysis results are summarized in Table 1. ND means 30 ppm or less was measured.

[0110] [Table 1]

[0111] Li / Co ratio Al F Na Sample #1 0.98 0.30wt% 0.16wt% Sample #2 0.94 0.35wt% 0.27wt% ND Sample #3 0.96 0.37wt% 0.13wt% Sample #4 0.95 0.36wt% 150ppm

[0112] (Sample #1) Fresh positive active material. LCO positive active material with Al surface coating was selected. Analysis of the fresh LCO positive active material showed a Li / Co ratio of 0.98, Al of 0.30 wt%, and F of 0.15 wt%.

[0113] (Sample #2) After 96.25 wt% of Sample #1, 1.5 wt% of carbon black as a conductive material, 2.25 wt% of PVdF as a binder were measured and mixed with NMP to prepare a slurry for manufacturing a positive electrode, and then a positive electrode waste was obtained.

[0114] Figure 4 1 shows a series of steps related to the process of immersing in an alkaline solution in an experimental example of the present disclosure. Figure 4 As shown in , the positive electrode waste is soaked in 1M NaOH, then filtered and washed to obtain a sheet-like active material layer. That is, S25 of the method disclosed in the present invention is performed. Figure 4In the figure, (a) shows the positive electrode waste broken into pieces, and (b) shows the positive electrode waste broken into pieces immersed in 1M NaOH and stirred. (c) shows that after further stirring, the Al current collector is separated and floats on the NaOH. (d) shows that the Al current collector is almost completely separated and floats. (e) shows that after filtering out the NaOH and Al current collector, part of the active material sinks to the bottom.

[0115] The elemental analysis results showed that the Li / Co ratio was 0.94, Al was 0.35wt%, F was 0.27wt%, and Na was not detected. By comparing sample #1 and sample #2, it was found that the ratio of lithium to metal was reduced by immersion in an alkaline solution. In addition, it can be seen that when the positive electrode waste was immersed in a high concentration of NaOH, the current collector Al dissolved, but a result value similar to that of the fresh LCO positive electrode active material was obtained by washing. In the case of F, it can be seen that the binder PVdF was rarely decomposed in the alkaline solution and still remained. As a result of detecting whether there were any alkaline elements remaining as a result of immersing the positive electrode waste in the NaOH alkaline solution, most of the Na was removed by filtration and washing after immersion without being detected.

[0116] (Sample #3) The active material layer of Sample #2 was subjected to a heat treatment corresponding to S30 in the method disclosed herein to collect the active material. The heat treatment was performed at 800°C for 5 hours. The elemental analysis results showed that the Li / Co ratio was 0.96, Al was 0.37wt%, and F was 0.13wt%. The results showed that F was reduced by the heat treatment.

[0117] (Sample #4) The active material of Sample #3 was washed and dried in accordance with S40 in the method of the present disclosure. The washing was performed with LiOH for 10 minutes. By comparing Sample #3 and Sample #4, it can be seen that the F content was adjusted to 150 ppm or less by washing with LiOH. It can be seen that the washing with S40 is very effective in removing F.

[0118] Next is the experiment of the second category. The results of elemental analysis are summarized in Table 2. ICP analysis was performed on the LCO positive active material coated with Al on the surface to track the changes in the amount of the specific element Al.

[0119] [Table 2]

[0120] Al(wt%) Sample #5 0.33 Sample #6 0.33 Sample #7 0.33

[0121] (Sample #5) Fresh positive electrode active material The aluminum content of this active material is 0.33 wt%.

[0122] (Sample #6) After 96.25wt% of Sample #5, 1.5wt% of carbon black as a conductive material, 2.25wt% of PVdF as a binder, and NMP were mixed to prepare a slurry for manufacturing a positive electrode, and then a positive electrode waste was obtained. The positive electrode waste was soaked in 1M NaOH, and then filtered and washed to obtain an active material layer separated from the current collector. Subsequently, a heat treatment was performed at 550°C for 30 minutes to collect the active material. That is, S25 and S30 in the method of the present disclosure were performed, and the Al content was measured to be 0.33wt%, which did not change.

[0123] (Sample #7) The active material of Sample #6 was washed and dried corresponding to S40 in the method of the present disclosure. Washing with LiOH was performed for 10 minutes. The Al content was measured to be 0.33 wt%, with no change.

[0124] It can be seen that the Al content of sample #6 that has undergone heat treatment has not changed, and the Al content of sample #7 that further includes a subsequent process has not changed. Al tolerates relatively high temperatures, and since the heat treatment temperature of 550°C is lower than the melting point of Al, there is no loss of Al. According to the present disclosure, although heat treatment is performed, LiF or metal fluoride can be removed by temperature control without losing elements such as Al, and preventing the dissolution of transition metals. Accordingly, the present experiment shows that when active materials are collected by the method according to the present disclosure, reusable active materials can be obtained without loss of specific elements.

[0125] The following is an experiment of the third category.

[0126] Example 1: Recyclable active materials are collected by the active material recycling method of the present disclosure described above. A discarded positive electrode waste is prepared from an NCM-based active material and is subjected to S25 by immersion in 1M NaOH. The heat treatment of S30 is performed at 550°C for 30 minutes. Washing of S40 is performed with LiOH for 10 minutes. In S50, annealing is performed at 750°C for 15 hours, and a lithium precursor (Li2CO3) is added to this process according to the molar ratio of lithium and other metals in the raw active material (inductively coupled plasma (ICP) analysis), and the amount added is to add more lithium at a molar ratio of 0.09. In theory, in the case of fresh active materials, the molar ratio of lithium: other metals is 1:1, but since the average error of the ICP equipment for measuring the molar ratio is ±0.05 (preferably about ±0.02), the molar ratio of lithium: other metals in the raw active material may be 1±0.05:1 as measured by ICP. In this experiment, a lithium precursor was added based on the analysis ratio analyzed by ICP.

[0127] Example 2: Based on Example 1, an active material surface protection layer recovery process of S60 is performed.

[0128] Comparative Example 1: Fresh NCM-based lithium composite transition metal oxide was used instead of using recycled active materials.

[0129] Comparative Example 2: Only S25 and S30 in the above-mentioned active material recycling method of the present invention are performed to separate the Al current collector, remove the binder and the conductive material, and collect the NCM-based lithium active material. S25 and S30 are performed under the same conditions as Example 1. The surface modification process of S40, the crystal structure recovery process of S50, and the surface coating process of S60 in the active material recycling method of the present invention are not performed.

[0130] Comparative Example 3: On the basis of Comparative Example 2, the active material was collected by performing the surface modification of S40 in the active material recycling method disclosed in the present invention. That is, the surface modification was performed, but the crystal structure recovery process of S50 and the surface coating process of S60 in the active material recycling method disclosed in the present invention were not performed. S40 was performed under the same conditions as in Example 1.

[0131] Comparative Example 4: Based on Comparative Example 2, the NCM-based active material was collected by performing the crystal structure recovery of S50 of the active material recycling method disclosed above without performing the surface modification of S40. Unlike Example 1, annealing was performed to recover the crystal structure without adding a lithium precursor.

[0132] Comparative Example 5: S25, S30, S40 and S50 of the active material recycling method were performed in the same manner as in Example 1. In this case, unlike Example 1, annealing was performed for recovering the crystal structure without adding a lithium precursor.

[0133] ICP analysis was performed on the positive electrode active material collected or prepared in each of Examples and Comparative Examples to analyze the amount of residual LiF, the ratio of lithium and other metals in the active material, and the amount of specific elements such as B or W.

[0134] In addition, the electrochemical performance was evaluated using a battery (Coin Half Cell, CHC) manufactured by the following operation: 96.25 wt % of the positive electrode active material collected or prepared in each embodiment and comparative example, 1.5 wt % of carbon black as a conductive material and 2.25 wt % of PVdF as a binder were measured, mixed with NMP to prepare a slurry and manufacture a positive electrode.

[0135] In order to determine the amount of LiF remaining in the active materials collected in Comparative Examples 2 and 3, F detection and analysis were performed using ICP. The results are shown in Table 3 below.

[0136] [Table 3]

[0137] Comparative Example 2 Comparative Example 3 F content (mg / kg) 1450 ND

[0138] ND means that 30 ppm or less was measured. Referring to Table 3, it was found that the F content in the collected positive electrode active material was significantly reduced in Comparative Example 3 compared with Comparative Example 2. That is, it can be seen that LiF was completely dissolved in the lithium compound solution by washing, and thus completely removed, so that it could not be detected by ICP. Therefore, it can be seen that S40 has a very good removal effect on LiF.

[0139] In order to detect whether there is any change in lithium in the positive electrode active material during S30 and S40 of the present disclosure, the ratio of lithium to other metals in the active material was analyzed by ICP. The results are shown in Table 4 below.

[0140] [Table 4]

[0141]

[0142] Referring to Table 4, it can be seen that, compared with Comparative Example 1, Comparative Example 2 has a lithium / other metal ratio reduced by about 0.2 to 0.5 through the heat treatment of S30; and compared with Comparative Example 2, Comparative Example 3 has a lithium / other metal ratio reduced by about 0.2 to 0.5 through the washing and drying of S40. It seems that the ratio of lithium to other metals in the NCM-based active material is greatly reduced due to the relatively large specific surface area of ​​the particles and the conversion to the spinel structure. Therefore, it can be seen that it is necessary to compensate for the insufficient lithium.

[0143] Table 4 shows the values ​​measured by ICP analysis, and as described above, the error value of ICP analysis is about ±0.02. Therefore, in Comparative Example 1 of the fresh active material, the ratio of lithium to other metals may be less than 1. Therefore, the amount of lithium precursor added to compensate for the loss of lithium is the amount of lithium reduced based on the ratio of lithium to other metals in the raw material active material (i.e., fresh active material) used in the active material layer (i.e., the molar ratio by ICP analysis).

[0144] Figure 5 and Figure 6 Results of battery evaluation using active materials of Examples and Comparative Examples are shown. Rate performance was evaluated by evaluating capacity as a function of cycle number at different currents. The equipment used for evaluation was a charge / discharge tester commonly used in laboratories. There were no differences depending on the measuring device or method. Figure 5 and Figure 6 In the graph of , the horizontal axis represents the number of cycles and the vertical axis represents the capacity.

[0145] The voltage is 3V to 4.3V, and the initial formation charge / discharge is performed at 0.1C / 0.1C. The electrolyte solution of the battery is a carbonate-based electrolyte solution, and includes ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a ratio of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 3:7, and an additive is added.

[0146] First, refer to Figure 5 In the case of Comparative Example 2 before surface modification by S40 and Comparative Example 3 after surface modification, Comparative Example 3 after surface modification showed a rapid decrease in electrode capacity. This is because, as described above, the nickel in the NCM-based active material is converted into rock salt after being exposed to moisture, resulting in a decrease in capacity.

[0147] However, when annealing (750°C / 15 hours) was performed without surface modification, which corresponds to Comparative Example 4, the effect of capacity improvement was small compared with Comparative Example 2. This is due to the residual LiF on the surface of the active material when surface modification was not performed. As shown in Table 1 above, the degree of removal of LiF by washing was satisfactory.

[0148] When surface modification and annealing were performed after the primary heat treatment, the capacity increased as shown in Comparative Example 5. The reason is that, although the capacity decreased after surface modification as shown in Comparative Example 3, after LiF was removed by surface modification, Ni rock salt was reduced by annealing and its structure returned to a hexagonal shape.

[0149] Then, refer to Figure 6 , it is found that the capacity of Example 1 is improved compared to Comparative Example 5. Compared to Comparative Example 5, Example 1 involves adding a lithium precursor during annealing. It can be seen that the capacity is improved by adding a lithium precursor to compensate for the lithium lost in the previous step. Reference Table 4 describes the lithium lost by heat treatment and washing.

[0150] Based on the results of ICP analysis (Table 4), lithium compounds were added according to the ratio of lithium loss to the existing lithium content in the positive electrode active material. As can be seen from additional experiments, the addition at a molar ratio of 0.09 to 0.1 showed a capacity improvement effect comparable to that of Comparative Example 1.

[0151] According to the present disclosure, active materials can be collected from cathode waste at a directly usable level. Since no toxic and explosive solvents such as NMP, DMC, acetone and methanol are used, and since simple and safe processes such as heat treatment, washing and drying, and annealing are adopted, it is safe and suitable for large-scale production.

[0152] Figure 7 and Figure 8It is a scanning electron microscope (SEM) image of the active material of the embodiment and the comparative example. The SEM image is taken using a SEM device commonly used in the laboratory. For example, HITACHI s-4200 can be used for imaging. However, there is no difference depending on the measurement equipment or method.

[0153] Figure 7 (a) is a SEM image of a fresh active material of Comparative Example 1, and (b) is an enlarged image of (a). (c) shows the surface of a positive electrode scrap from a fresh active material, and (d) is an enlarged image of (c). The fresh active material has no particle cracking or disintegration, but the positive electrode scrap from the electrode shows pressed and cracked or disintegrated particles on the surface during the roll pressing process.

[0154] Figure 7 (e) is a SEM image of Comparative Example 2, and (f) is an enlarged image of (e). Referring to (e) and (f), no binder or conductive material was observed in the collected active material. That is, it can be seen that the binder or conductive material was removed during the high temperature heat treatment. Therefore, it can be seen that the binder or conductive material rarely remains on the surface of the active material through the heat treatment in air.

[0155] Figure 8 (a) is a SEM image of Comparative Example 3, and (b) is an enlarged image of (a). Figure 7 In (c) and (d), it can be seen that the particles are dispersed through the process.

[0156] Figure 8 (c) is a SEM image of Comparative Example 5, and (d) is an enlarged image of (c). (e) is a SEM image of Example 1, and (f) is an enlarged image of (e). It can be seen that the particles dispersed in the previous step form agglomerates by annealing. Figure 8 (f) and Figure 7 Compared with (a), it can be seen that the recyclable active material of Example 1 shows the same shape as the fresh active material.

[0157] Fig. 9 : is a particle size distribution diagram of the active materials of the embodiments and comparative examples. The particle size distribution can be obtained using a particle size analyzer commonly used in the laboratory. For example, it can be measured using a Horiba LA 950V2 particle size analyzer. However, there is no difference depending on the measurement equipment or method. Fig. 9 In the figure, the horizontal axis is the particle size (μm) and the vertical axis is the volume %.

[0158] Fig. 9 The particle size distribution chart results are similar to Figure 7 and Figure 8The SEM results are consistent. Since the NCM-based active material suffers severe particle cracking or disintegration due to rolling during the electrode formation process, a large number of small particles are observed in the particle size distribution of Comparative Example 2 after one heat treatment, while Comparative Example 3 shows a higher distribution of small particles after surface modification. However, when annealing is performed, as shown in the previous SEM results, the particle clusters increase, so that the particle size distribution of Comparative Example 5 or Example 1 is similar to that of Comparative Example 1 of the fresh active material. In particular, the particle size distribution of Example 1 is more similar to that of Comparative Example 1. The volume % of particles having the same particle size with a difference within the range of ±2% is defined as a similar particle size distribution. According to the present disclosure, the particle size distribution of the reusable active material is no different from that of the fresh active material, and the initial characteristics are almost maintained, and it is expected that the characteristics of the battery including the reusable active material will be at a similar level to the characteristics of the battery using fresh active materials.

[0159] The amount of specific elements was analyzed by ICP analysis of the positive electrode active material collected or prepared in each Example and Comparative Example. The results are shown in Table 5 below.

[0160] [Table 5]

[0161] B content (mg / kg) W content (mg / kg) Comparative Example 1 500 3100 Comparative Example 2 200 2700 Comparative Example 3 ND 200 Comparative Example 5 ND 200 Example 1 ND 200

[0162] As seen in Comparative Example 1, the fresh active material used in this experiment further includes B and W. In the case of Comparative Example 2, it can be seen that the contents of B and W are reduced by heat treatment, and the results of the remaining Comparative Examples reveal that B is almost completely removed in the subsequent process. In the case of W, it can be seen that a large amount of W is removed by washing in the surface modification process (as in Comparative Example 3).

[0163] Therefore, depending on the type of active material used initially, some may be susceptible to heat and moisture, so specific elements may be lost in this process, especially in the surface modification process, which may be completely removed or have a small amount of residue by washing, and in some cases, its characteristics may not be fully restored by performing annealing as in Example 1. In this case, it is desirable to perform an additional surface coating step as proposed. In this experimental embodiment, the surface coating step includes coating with B and W. Surface coating can serve as a surface protective layer for the positive active material. Surface coating can be a process for compensating for insufficient specific elements while restoring the surface protective layer in the fresh active material. In the case of the fresh active material used in this experiment, the surface protective layer includes BW, and the loss of lithium in this process is interpreted as (lithium in the active material itself + lithium used to form the surface protective layer): the ratio of other metals, rather than the ratio of lithium in the active material itself to other metals is 1:1. Therefore, in the above experiment, the molar ratio of lithium lost in Comparative Example 3 is 0.09, which can be interpreted as the sum of lithium in the positive active material and lithium used to form the surface protective layer. In this embodiment, the amount of lithium precursor added is to supplement lithium.

[0164] The surface coating step is subjected to a heat treatment process after a solid phase or liquid phase reaction.

[0165] When the recyclable active material is represented by the following Formula 1,

[0166] [Formula 1]

[0167] Li a Ni x Mn y Co z M w O 2+δ

[0168] wherein M comprises at least one selected from the group consisting of B, W, Al, Ti and Mg, <a≤1.1,0≤x<0.95,0≤y<0.8,0≤z<1.0,0≤w≤0.1,-0.02≤δ≤0.02,x+y+z+w=1。

[0169] It can be considered that M in Formula 1 is supplemented by surface coating.

[0170] When the surface coating layer includes B, BW, B-Ti, BW-Ti, the surface coating heat treatment can be performed at a temperature of 200°C to 500°C, and other metal materials, carbon materials and organic metal materials are used for coating at a temperature between 100°C and 1200°C.

[0171] According to the present disclosure, cathode waste can be recycled using a simple, environmentally friendly, and economical method, and a lithium secondary battery manufactured by recycling the prepared NCM-based lithium composite transition metal oxide cathode active material does not have problems with battery performance.

[0172] Although the present disclosure has been described herein with respect to limited embodiments and drawings, the present disclosure is not limited thereto, and it will be apparent to those skilled in the art that various modifications and changes may be made thereto within the technical aspects of the present disclosure and the scope of the appended claims and their equivalents.

Claims

1. A method for recycling positive electrode active materials, the method comprising the following steps: (a-1) soaking a positive electrode waste including a lithium composite transition metal oxide positive electrode active material layer on a current collector in an alkaline solution to separate the active material layer from the current collector; (a-2) heat-treating the active material layer in air to thermally decompose the fluorine-containing binder and the conductive material in the active material layer, and collecting the active material in the active material layer; (b) washing the collected active material with a solution of a basic lithium compound in aqueous solution and drying; as well as (c) The washed active material is annealed with the addition of a lithium precursor to obtain a reusable active material.

2. The method for recycling positive electrode active materials according to claim 1, wherein: The alkaline solution includes LiOH or NaOH.

3. The method for recycling positive electrode active materials according to claim 1, further comprising the following steps: (d) Surface coating of the annealed active material.

4. The method for recycling positive electrode active materials according to claim 1, wherein: The heat treatment is performed at 300°C to 800°C.

5. The method for recycling positive electrode active materials according to claim 1, wherein: The content of the lithium compound in the lithium compound solution is at most 15%, and the washing is performed within 1 hour.

6. The method for recycling positive electrode active materials according to claim 1, wherein: The washing is performed by stirring the collected active material while being immersed in the lithium compound solution.

7. The method for recycling positive electrode active materials according to claim 1, wherein: The lithium precursor used in the annealing is at least one of LiOH, Li2CO3, LiNO3 and Li2O.

8. The method for recycling positive electrode active materials according to claim 1, wherein: The amount of the lithium precursor added is for adding lithium at a ratio of lost lithium to the ratio of lithium to other metals in the raw active material used in the active material layer.

9. The method for recycling positive electrode active materials according to claim 8, wherein: The lithium precursor is added in an amount for adding lithium at a molar ratio of 0.001 to 0.

4.

10. The method for recycling positive electrode active materials according to claim 8, wherein: Based on a molar ratio of lithium to other metals of 1:1, the added amount of the lithium precursor is used to add more lithium at a molar ratio of 0.0001 to 0.

1.

11. The method for recycling positive electrode active materials according to claim 1, wherein: The annealing is performed at 400° C. to 1000° C. in air.

12. The method for recycling positive electrode active materials according to claim 1, wherein: The annealing temperature exceeds the melting point of the lithium precursor.

13. The method for recycling positive electrode active materials according to claim 12, wherein: The annealing temperature does not exceed 1000°C.

14. The method for recycling positive electrode active materials according to claim 1, wherein: The active material in the active material layer is collected in a powder form, and carbon generated by carbonization of the binder or the conductive material does not remain on the surface.

15. The method for recycling positive electrode active materials according to claim 3, wherein: The surface coating includes coating at least one of a metal, an organic metal, and a carbon material on the surface by solid phase or liquid phase treatment, and performing a heat treatment at 100° C. to 1200° C.

16. The method for recycling positive electrode active materials according to claim 1, wherein: The recyclable active material is represented by the following formula 1: [Formula 1] Li a Ni x Mr y Co z M w O 2+δ wherein M comprises at least one selected from the group consisting of B, W, Al, Ti and Mg, <a≤1.1,0≤x<0.95,0≤y<0.8,0≤z<1.0,0≤w≤0.1,-0.02≤δ≤0.02,x+y+z+w=1。 17. The method for recycling positive electrode active materials according to claim 1, wherein: The recyclable active material has a fluorine (F) content of 150 ppm or less.

18. The method for recycling positive electrode active materials according to claim 1, wherein: The positive electrode waste contains residual electrolyte solution, and the electrolyte solution is removed in the step (a-1), and The step (a-1) further comprises filtering and washing after the soaking.

Images