Regenerated positive electrode active material, method for regenerating the same, and secondary battery containing the same

Abstract

The present invention relates to a regenerated positive electrode active material, a regenerating method thereof, and a secondary battery including the same, and more particularly to a regenerated positive electrode active material which is at least one selected from the group consisting of a lithium nickel oxide (LNO)-based positive electrode active material, a nickel cobalt manganese (NCM)-based positive electrode active material, a nickel cobalt aluminum (NCA)-based positive electrode active material, and a nickel cobalt manganese aluminum (NCMA)-based positive electrode active material, and which is characterized in that it contains 60 mol % or more of Ni, has a fluorine (F) content of 250 mg / kg or less, and has an average crystal size of 122 nm or less, a regenerating method thereof, and a secondary battery including the same. According to the present invention, a waste positive electrode using a high-nickel (High-Ni) positive electrode material is subjected to an oxidative heat treatment by introducing oxygen, and then the waste positive electrode is washed for the first time. Then, a lithium precursor is added, annealed, and then washed for the second time, so that the fluorine (F) content on the surface of the regenerated positive electrode active material is reduced. Furthermore, by dividing the oxidative heat treatment step into two steps, the binder is burned cleanly, and the fluorine (F) and residual lithium generated in the heat treatment step are reduced, and the crystal size is reduced, thereby providing a positive electrode active material with excellent charging capacity, resistance characteristics, and capacity characteristics. In addition, since no acid is used in the recovery and regeneration process, it is environmentally friendly, and since there is no need for neutralization and wastewater treatment, the process cost is reduced. Since the positive electrode active material is regenerated as it is without being decomposed, there are no metal elements to be discarded, and since no organic solvent is used, there is no risk of toxic gas generation or explosion. In particular, since the water washing process is omitted, there is an effect of providing a method for regenerating a positive electrode active material with greatly improved economic efficiency and productivity.

Description

[Technical Field]

[0001] [Cross-reference with related applications] This application claims the benefit of priority under Korean Patent Application No. 10-2023-0081265, which was refiled on June 23, 2023, based on Korean Patent Application No. 10-2022-0082984 dated July 6, 2022, and Korean Patent Application No. 10-2022-0082985 dated July 6, 2022, and all content disclosed in the documents of said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a regenerated positive electrode active material, a method for regenerating the same, and a secondary battery containing the same. More specifically, the present invention relates to a method for regenerating a positive electrode active material in which a waste positive electrode using high-nickel (High-Ni) positive electrode material is subjected to oxidation heat treatment by introducing oxygen, followed by primary washing, then lithium precursor is added, annealing is performed, and then secondary washing is performed to remove fluorine (F) and lithium precursor that did not participate in the reaction from the surface of the regenerated positive electrode active material. Furthermore, by dividing the oxidation heat treatment step into two steps, the binder is cleanly burned, the amount of fluorine (F) and residual lithium generated in the heat treatment step is reduced, and the crystallite size becomes smaller, resulting in a positive electrode active material with excellent charging capacity, resistance characteristics, and capacitance characteristics. The recovery and regeneration process does not use acid, making it environmentally friendly, and since neutralization and wastewater treatment are not required, process costs are reduced. Since the positive electrode active material is regenerated without decomposition, there are no discarded metal elements, and since organic solvents are not used, there is no risk of generating toxic gases or explosion. In particular, the water washing step is omitted, resulting in a method for regenerating a positive electrode active material that greatly improves economy and productivity. [Background technology]

[0003] Lithium-ion batteries generally consist of a positive electrode with a positive electrode active material layer coated on a metal foil such as aluminum, a negative electrode with a negative electrode active material layer coated on a metal foil such as copper, a separation membrane to prevent the positive and negative electrodes from mixing, and an electrolyte that allows lithium ions to move between the positive and negative electrodes.

[0004] The positive electrode active material layer mainly uses lithium-based oxides as the active material, and the negative electrode active material layer mainly uses carbon material as the active material. However, since lithium-based oxides generally contain rare metals such as cobalt, nickel, or manganese, much research is being conducted on recovering and reusing rare metals from the positive electrodes of lithium secondary batteries that are discarded after use, or from positive electrode scrap generated in the manufacturing process of lithium secondary batteries (hereinafter referred to as "waste positive electrodes").

[0005] Conventional techniques for recovering rare metals from waste cathodes mostly involve dissolving the waste cathode in hydrochloric acid, sulfuric acid, or nitric acid, then extracting cobalt, manganese, nickel, etc., with an organic solvent, and using these as raw materials again for the synthesis of cathode active materials.

[0006] However, the extraction method of rare metals using acids has environmental pollution problems, as it requires neutralization and wastewater treatment processes, which significantly increases process costs, and it has the drawback of not being able to recover lithium, which is the main metal in the cathode active material.

[0007] To overcome these drawbacks, recent research has focused on methods for directly recycling positive electrode active materials from waste positive electrodes without decomposing them (direct recycling methods). Four main types of such methods have been introduced: calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

[0008] However, although the aforementioned firing method is simple in its process, it has the disadvantages of generating foreign matter on the surface of the recycled positive electrode active material that reduces the output performance of the battery, generating waste gas, and consuming a large amount of energy.

[0009] Furthermore, while the aforementioned solvent dissolution method can produce a regenerated cathode active material with a relatively clean surface, it has the disadvantage of poor stability and the need for an expensive solvent recovery process because the solvent used to dissolve the binder, such as N-methyl-2-pyrrolidone (NMP), is a toxic gas and poses an explosion risk.

[0010] Furthermore, while the aluminum foil melting method has good process stability, low process costs, and easy binder removal, it has the disadvantages of generating foreign matter that is difficult to remove on the surface of the regenerated positive electrode active material, and generating hydrogen gas during the aluminum foil removal process, which poses a risk of explosion.

[0011] Finally, while the aforementioned crushing and screening method has the advantage of being the simplest process, it has the disadvantages of being difficult to completely separate the current collector and the positive electrode active material, the particle size distribution of the positive electrode active material changing during the crushing process, and the binder remaining, which degrades the battery characteristics of the regenerated positive electrode active material.

[0012] Therefore, there is an urgent need to develop methods for safely and environmentally friendly recycling cathode active materials with improved output performance, using fewer processes and at lower costs, without discarding metal elements from waste cathodes. [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] To solve the problems of the conventional technology described above, the present invention aims to provide a method for regenerating positive electrode active material in which, after oxidative heat treatment of a waste positive electrode using high-nickel (High-Ni) positive electrode material by introducing oxygen, a primary wash is performed, then a lithium precursor is added, annealing is performed, and a secondary wash is performed to remove fluorine (F) and lithium precursor that did not participate in the reaction from the surface of the regenerated positive electrode active material. Furthermore, by dividing the oxidation heat treatment step into two steps, the binder is cleanly burned, the amount of fluorine (F) and residual lithium generated in the heat treatment step is reduced, and the crystallite size is reduced, thereby providing a positive electrode active material with excellent charging capacity, resistance characteristics, and capacitance characteristics. In addition, since no acid is used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly, and process costs are reduced because neutralization and wastewater treatment are not required. Furthermore, since the positive electrode active material is regenerated without decomposition, there are no discarded metal elements, and since no organic solvents are used, there is no risk of generating toxic gases or explosion. In particular, the water washing step is omitted, so the economy and productivity are greatly improved.

[0014] Furthermore, the present invention aims to provide a secondary battery with excellent initial discharge capacity, output performance (rate performance), and capacity characteristics.

[0015] The above-mentioned and other objectives of the present invention can all be achieved by the present invention as described below. [Means for solving the problem]

[0016] To achieve the above objectives, the present invention provides a positive electrode active material that is selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, characterized in that it contains 60 mol% or more of Ni, has a fluorine (F) content of 250 mg / kg or less, and has an average crystallite size of 122 nm or less.

[0017] II) In the above I), the positive electrode active material may have a surface coated with a coating agent containing metal or carbon.

[0018] III) In the above I) or II), the metal may be boron (B), tungsten (W), or a mixture thereof.

[0019] IV) In the above I) to III), the positive electrode active material may be a recycled positive electrode active material.

[0020] Further, the present invention provides a method for recycling a positive electrode active material, comprising: V) subjecting a used positive electrode having a positive electrode active material layer containing 60 mol% or more of Ni formed on a current collector to oxidative heat treatment by introducing oxygen, and separating the current collector from the positive electrode active material layer by thermally decomposing a binder and a conductive material in the positive electrode active material layer to recover the positive electrode active material in the positive electrode active material layer; VI) a step of performing primary washing on the recovered positive electrode active material; VII) a step of adding a lithium precursor to the primarily washed positive electrode active material and annealing; VIII) a step of performing secondary washing on the annealed positive electrode active material.

[0021] VI) In the above V), the oxidative heat treatment can be performed at 300 to 650 °C.

[0022] VII) In the above V) or VI), the oxidative heat treatment can be performed by performing a primary heat treatment at 300 to 450 °C and then a secondary heat treatment at 500 to 650 °C.

[0023] VIII) In the above V) to VII), the primary heat treatment can be performed for 10 minutes to 3 hours, and the secondary heat treatment can be performed for 10 minutes to 2 hours.

[0024] IX) In the above V) to VIII), the oxygen may have a purity of 59% or more.

[0025] X) In V) to IX) above, the primary cleaning can be performed by immersing the recovered positive electrode active material in water or an aqueous solution of a basic lithium compound as a cleaning solution, or by stirring it while immersed.

[0026] XI) In V) to X) above, the aqueous solution of the basic lithium compound may contain more than 0% by weight and 15% by weight or less of the lithium compound.

[0027] XII) In the above V) to XI), the method of adding a lithium precursor to the primary washed positive electrode active material in the annealing step is to mix the primary washed positive electrode active material with a lithium precursor solution and spray dry it.

[0028] XIII) In V) to XII) above, the secondary cleaning may include the steps of mixing the annealed positive electrode active material with water as a cleaning solution, filtering it, and drying the solid portion of the positive electrode active material obtained after filtering.

[0029] XIV) In V) to XIII) above, the lithium precursor may include one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0030] XV) In V) to XIV) above, the lithium precursor may be added in an amount corresponding to 1 mol% to 40 mol%, when the total amount of lithium in the positive electrode active material of the raw materials used in the positive electrode active material layer is 100 mol%.

[0031] XVI) In V) to XV) above, the annealing can be carried out at 400 to 1000°C.

[0032] XVII) In V) to XVI), the method for regenerating the positive electrode active material may further include the step of surface coating the secondary cleaned positive electrode active material to obtain a reusable positive electrode active material.

[0033] XVIII) In the above V) to XVII), the surface coating can be applied to the surface by coating one or more of metals, organometallics, and carbon components in a solid-phase or liquid-phase manner, and then heat-treated at 100 to 1200°C.

[0034] Furthermore, the present invention can provide a regenerated positive electrode active material characterized by being manufactured by the method for regenerating positive electrode active material described in XIX) V) to XVIII).

[0035] Furthermore, the present invention provides a positive electrode active material that is selected from the group consisting of XX) lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, characterized in that it contains 60 mol% or more of Ni, has a fluorine (F) content of 305 mg / kg or less, and has an average crystallite size of 139 nm or less.

[0036] XXI) In XX) above, the positive electrode active material may have a residual Li2CO3 content of 0.16% by weight or less.

[0037] XXII) In XX) or XXI) above, the positive electrode active material may be a regenerated positive electrode active material.

[0038] Furthermore, the present invention provides a secondary battery characterized by containing a positive electrode active material as described in any one of the above items XXIII), I) to IV), XIX), XX), and XXII). [Effects of the Invention]

[0039] According to the present invention, a waste cathode using high-nickel (High-Ni) cathode material is subjected to oxidation heat treatment by introducing oxygen, followed by primary washing, then lithium precursor is added, followed by annealing, and finally secondary washing. This removes fluorine (F) and lithium precursor that did not participate in the reaction from the surface of the regenerated cathode active material, reducing the crystal size. Furthermore, by dividing the oxidation heat treatment step into two steps, the binder is cleanly burned, reducing the fluorine (F) and residual lithium generated in the heat treatment step, and reducing the crystal size (crystallite size). This provides a cathode active material with excellent charging capacity, resistance characteristics, and capacitance characteristics. In addition, since no acid is used in the recovery and regeneration process of the cathode active material, it is environmentally friendly, and since neutralization and wastewater treatment are not required, process costs are reduced. Since the cathode active material is regenerated without decomposition, no metal elements are discarded, and since no organic solvents are used, there is no risk of generating toxic gases or explosion. In particular, the water washing step is omitted, thus providing a method for regenerating cathode active material that greatly improves economy and productivity. [Brief explanation of the drawing]

[0040] The following drawings accompanying this specification illustrate embodiments of the present invention and, together with the detailed description below, serve to further illustrate the technical concept of the present invention. Therefore, the present invention should not be construed as being limited to the matters described in these drawings. [Figure 1] This figure shows positive electrode scrap that is discarded after the electrode plates are cut from the positive electrode sheet. [Figure 2] These are SEM images of the cathode active material regenerated in Example 1 and Comparative Examples 1-3. [Figure 3] This graph shows the results of the charging capacity of coin cells to which the regenerated positive electrode active material from Example 1 and Comparative Examples 1-3 was applied. [Figure 4] This graph shows the results of charge-discharge cycles performed on monocells to which the regenerated positive electrode active material from Example 1 and Comparative Examples 1-3 was applied, illustrating the changes in capacity retention rate (%) and resistance increase rate (%) with respect to the number of cycles. [Figure 5] This graph shows the results of the charging capacity of coin cells to which the regenerated positive electrode active material from Additional Examples 1-3 and Additional Comparative Examples 1 and 2 was applied. [Figure 6] This graph shows the change in capacity retention rate (%) as the number of cycles performed on a monocell to which the regenerated positive electrode active material from Additional Examples 1-3 and Additional Comparative Examples 1 and 2 was applied. [Figure 7] This is a flowchart of the regeneration process for the positive electrode active material according to the present invention. [Modes for carrying out the invention]

[0041] The inventors of the present invention were researching a direct recycled method for directly regenerating a positive electrode active material with superior battery performance from a waste positive electrode without decomposing the positive electrode active material. They found that when a waste positive electrode using high-nickel (High-Ni) positive electrode material is subjected to oxidation heat treatment with oxygen, followed by primary washing, then annealing with the addition of a lithium precursor, and finally secondary washing, fluorine (F) and lithium precursor that did not participate in the reaction are removed from the surface of the regenerated positive electrode active material, resulting in a smaller crystal size. Furthermore, when the oxidation heat treatment step is divided into two steps, the binder is burned cleanly, reducing the fluorine (F) and residual lithium generated in the heat treatment step, and thus reducing the crystal size (crystallite size), improving the battery characteristics of the regenerated positive electrode active material. Based on this, they continued their research and completed the present invention.

[0042] The following describes in detail the regenerated positive electrode active material, its regeneration method, and the secondary battery containing it.

[0043] However, the terms and words used in this specification and in the claims shall not be interpreted to be limited to their ordinary or dictionary meanings, but rather to be interpreted in a sense and concept consistent with the technical idea of ​​the present invention, based on the principle that inventors may appropriately define the concepts of terms in order to best describe their invention. Accordingly, it should be understood that the embodiments and configurations shown in the drawings described herein are merely embodiments of the present invention and do not represent the entire technical idea of ​​the present invention, and that there may be various equivalents and modifications that can substitute for them, and that they may be arranged, substituted, combined, separated or designed in various other configurations.

[0044] All technical and scientific terms used herein have the same meaning as those commonly understood by those with ordinary skill in the art to which this invention pertains, unless otherwise defined.

[0045] positive electrode active material The positive electrode active material of the present invention is one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, characterized in that it contains 60 mol% or more of Ni, has a fluorine (F) content of 250 mg / kg or less, and has an average crystal size of 122 nm or less. In this case, it has the effect of being excellent in charge capacity, resistance characteristics, and capacitance characteristics.

[0046] The positive electrode active material preferably includes one or more selected from the group consisting of lithium cobalt oxides such as LiCoO2 (hereinafter referred to as "LCO"); lithium manganese oxides such as LiMnO2 or LiMn2O4; lithium iron phosphate compounds such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA; lithium nickel cobalt aluminum oxide); lithium nickel oxides such as LiNiO2; nickel manganese-based lithium composite metal oxides in which part of nickel (Ni) in the lithium nickel oxide is replaced by manganese (Mn); and NCM-based lithium composite transition metal oxides in which part of nickel (Ni) in the lithium nickel oxide is replaced by manganese (Mn) and cobalt (Co). In this case, there is an effect of being excellent in electrochemical performance, resistance characteristics, capacity characteristics, etc.

[0047] Specific examples of the positive electrode active material include the following Chemical Formula 1 [Chemical Formula 1] Li a Ni x Mn y Co z M w O 2+δ (In the Chemical Formula 1, M includes one or more selected from the group consisting of B, W, Al, Ti, and Mg, and 1 < a ≤ 1.1, 0 < x < 0.95, 0 < y < 0.8, 0 < z < 1.0, 0 ≤ w ≤ 0.1, -0.02 ≤ δ ≤ 0.02, and x + y + z + w = 1). It can include a compound represented by this, and in this case, there is an effect of being excellent in electrochemical performance, resistance characteristics, capacity characteristics, etc.

[0048] The positive electrode active material preferably contains 80 mol% or more of Ni, more preferably 81 mol% or more, and still more preferably 81 to 95 mol%. Within this range, there is an effect of being excellent in charge capacity, resistance characteristics, and capacity characteristics.

[0049] In this description, the Ni content is not particularly limited when measured using methods such as IC (Ion Chromatography) commonly used in the art to which the present invention pertains. For example, it can be measured using an IC-ICP (Inductively Coupled Plasma) analyzer, an IC-ICP-MS analyzer, or an IC-ICP-AEC analyzer.

[0050] The positive electrode active material may, for example, have a fluorine (F) content of 250 mg / kg or less, preferably 200 mg / kg or less, and more preferably 10 to 200 mg / kg, and within this range, it has the advantage of having excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0051] In this description, the fluorine (F) content can be measured using an ICP analyzer, and this can be done using a general ICP analyzer commonly used in laboratories. However, there is no deviation depending on the measuring device or method.

[0052] The positive electrode active material may, for example, have an average crystal size of 122 nm or less, preferably 115 to 122 nm, and more preferably 120 to 122 nm. Within this range, reducing the crystal size reduces strain and minimizes cycle cracks, which has the advantage of extending the battery life.

[0053] In this description, the average crystal size can be measured by XRD crystallography, and there is no deviation due to the measurement device or method. Specifically, it can be determined by placing 5g of positive electrode active material particles in a holder and analyzing the diffraction grating produced when the particles are irradiated with X-rays. The method of determination can be based on the main peak or the full width at half maximum of three or more peaks, which can be considered to correspond to the average crystal size of the primary particles of the positive electrode active material.

[0054] As an example, the positive electrode active material may have a surface LiOH content of 0.32% by weight or less, preferably 0.31% by weight or less, and more preferably 0.01 to 0.31% by weight, and within this range, it has the advantage of having excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0055] The positive electrode active material may, for example, have a surface content of 0.19% by weight or less of Li2CO3, preferably 0.01 to 0.19% by weight, and within this range, it has the advantage of having excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0056] As an example, the positive electrode active material may have a total sum of LiOH and Li2CO3 remaining on its surface of 0.51% by weight or less, preferably 0.50% by weight or less, and more preferably 0.01 to 0.50% by weight. Within this range, there is an advantage in that it exhibits excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0057] In this description, the residual amounts of LiOH and Li2CO3 on the surface of the positive electrode active material can be measured using a pH titrator (T5, manufactured by Mettler Toledo). Specifically, 5 g of positive electrode active material is dispersed in 100 ml of distilled water, mixed at 300 rpm for 5 minutes, and then filtered to remove the active material. The resulting filtrate is titrated with a 0.1 M HCl solution, and the change in pH value is measured to obtain a pH titration curve. Using the obtained pH titration curve, the residual amounts of LiOH and Li2CO3 in the positive electrode active material are calculated.

[0058] Furthermore, the positive electrode active material of the present invention is one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, and is characterized by containing 60 mol% or more of Ni, having a fluorine (F) content of 305 mg / kg or less, and having a crystallite size of 139 nm or less. In this case, it has the effect of having excellent capacity characteristics and lifetime characteristics.

[0059] The positive electrode active material preferably contains 80 mol% or more of Ni, more preferably 81 mol% or more, and even more preferably 81 to 95 mol%, and within this range, it has the effect of having excellent charging capacity, resistance characteristics and capacitance characteristics.

[0060] The positive electrode active material may, for example, have a fluorine (F) content of 305 mg / kg or less, preferably 250 mg / kg or less, more preferably 200 mg / kg or less, and even more preferably 10 to 200 mg / kg, and within this range, it has the advantage of having excellent capacity characteristics.

[0061] The positive electrode active material may, for example, have an average crystal size of 139 nm or less, preferably 120 to 139 nm, more preferably 130 to 139 nm, even more preferably 133 to 139 nm, and even more preferably 133 to 136 nm. Within this range, reducing the crystal size reduces strain and minimizes cycle cracks, which has the advantage of extending the battery life.

[0062] The positive electrode active material may, for example, have a surface content of 0.16% by weight or less, preferably 0.14% by weight or less, more preferably 0.1% by weight or less, and even more preferably 0.01 to 0.1% by weight of Li2CO3. Within this range, there is an advantage in that it has excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0063] The positive electrode active material may, for example, have a surface LiOH content of 0.32% by weight or less, preferably 0.3% by weight or less, more preferably 0.01 to 0.3% by weight, and even more preferably 0.01 to 0.28% by weight. Within this range, there is an advantage in that it exhibits excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0064] As an example, the positive electrode active material may have a total sum of LiOH and Li2CO3 remaining on its surface of 0.45% by weight or less, preferably 0.42% by weight or less, more preferably 0.40% by weight or less, and even more preferably 0.01 to 0.4% by weight. Within this range, there is an advantage in that it exhibits excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0065] The positive electrode active material may, for example, have its surface coated with metal or carbon, preferably with metal. In this case, the structural stability of the positive electrode active material is improved without any chemical or physical changes to the positive electrode active material itself, thereby improving electrochemical properties such as output performance, life characteristics, and capacity. Furthermore, the physicochemical properties are also improved by the effect of regulating the amount of residual lithium and reducing pH through substitution with a different element on the surface of the positive electrode active material.

[0066] The aforementioned metal is preferably 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; even more preferably boron (B), tungsten (W), or a mixture thereof; and even more preferably tungsten (W) and boron (B). A specific example is tungsten boride (WB), in which case there is an effect of improving resistance characteristics and lifetime characteristics.

[0067] The coating agent may, for example, be present in an amount of 0.001 to 0.3 mol% relative to 1 mol% of metal in the positive electrode active material before coating treatment, preferably 0.01 to 0.3 mol%, more preferably 0.01 to 0.15 mol%, even more preferably 0.01 to 0.1 mol%, and even more preferably 0.01 to 0.05 mol%. Within this range, the structural stability and electrochemical performance are improved while maintaining the properties of the positive electrode active material itself.

[0068] Preferably, the surface coating involves coating the surface with a coating agent containing one or more of metals, organometallics, and carbon components using a solid-phase or liquid-phase method, followed by heat treatment at 100 to 1200°C. In this case, the structural stability and electrochemical performance are improved while maintaining the properties of the positive electrode active material itself.

[0069] The positive electrode active material may preferably be a regenerated positive electrode active material, which has the advantage of being economical and highly productive.

[0070] Method for regenerating positive electrode active material The present invention provides a method for regenerating positive electrode active material, comprising the steps of: separating the current collector from the positive electrode active material layer and recovering the positive electrode active material from the positive electrode active material layer by introducing oxygen to an oxidation heat treatment on a waste positive electrode having a positive electrode active material layer containing 60 mol% or more of Ni formed on it; thermally decomposing the binder and conductive material in the positive electrode active material layer by the current collector; primary washing the recovered positive electrode active material; adding a lithium precursor to the primary washed positive electrode active material and annealing it; and secondary washing the annealed positive electrode active material. In this case, fluorine (F) and lithium precursors that could not participate in the reaction are removed from the surface of the regenerated positive electrode active material, resulting in a smaller crystallite size, which in turn provides the effect of achieving excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0071] The following is a detailed explanation of the regeneration method for the positive electrode active material, broken down into stages.

[0072] (a) Step of recovering the positive electrode active material from the waste positive electrode. The step (a) of recovering positive electrode active material from a waste positive electrode according to the present invention may preferably be a step of oxidizing the waste positive electrode, which includes a current collector and a positive electrode active material layer coated thereon, by introducing oxygen to recover the positive electrode active material. In this case, the process is simple and has the effect of thoroughly removing the binder, conductive material and current collector.

[0073] The waste positive electrode may preferably be a positive electrode separated from a lithium secondary battery that has been discarded after use, a defective positive electrode sheet generated in the manufacturing process of a lithium secondary battery, or positive electrode scrap, and more preferably it may be positive electrode scrap remaining after punching out a positive electrode plate from a positive electrode sheet.

[0074] The positive electrode active material layer in step (a) above may preferably include a positive electrode active material, a binder, and a conductive material.

[0075] The positive electrode active material may, as an example, include one or more selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material.

[0076] The positive electrode active material is preferably at least one selected from the group consisting of lithium cobalt oxides such as LiCoO2 (hereinafter referred to as "LCO"); lithium manganese oxides such as LiMnO2 or LiMn2O4; lithium iron phosphate compounds such as LiFePO4; lithium nickel cobalt aluminum oxide (NCA); lithium nickel oxides such as LiNiO2; nickel manganese-based lithium composite metal oxides in which part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn); and NCM-based lithium composite transition metal oxides in which part of nickel (Ni) in the lithium nickel oxide is substituted with manganese (Mn) and cobalt (Co), and can contain 60 mol% or more of Ni, more preferably, it is a nickel manganese-based lithium composite metal oxide, an NCM-based lithium composite transition metal oxide, or a mixture thereof, and in this case, there is an effect of excellent reversible capacity and thermal stability.

[0077] As still another specific example, the positive electrode active material has the following Chemical Formula 1 [Chemical Formula 1] Li a Ni x Mn y Co z M w O 2+δ (In Chemical Formula 1, M contains at least one 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.) It may be a compound represented by this.

[0078] The positive electrode active material preferably contains 80 mol% or more of Ni, more preferably 81 mol% or more, and still more preferably 81 to 95 mol%, and within this range, there is an effect of excellent initial discharge capacity, output performance, capacity characteristics, and resistance characteristics.

[0079] The conductive material may, for example, be a carbon-based conductive material, and preferably may be carbon black, CNTs, or a mixture thereof.

[0080] The binder may be, for example, a polymer binder, preferably polyvinylidene fluoride (PVdF), acrylonitrile-butadiene rubber (NBR), or a mixture thereof, and more preferably polyvinylidene fluoride.

[0081] The oxidation heat treatment temperature is preferably 400 to 600°C, more preferably 500 to 600°C, and even more preferably 530 to 580°C. Within this range, the current collector does not melt, and the carbon material in the binder and conductive material reacts with oxygen and is burned off as CO and CO2 gases, thus having the advantage that almost all of the binder and conductive material can be easily removed without any residue.

[0082] The aforementioned oxidation heat treatment time may preferably be 10 minutes to 5 hours, more preferably 30 minutes to 5 hours, even more preferably 30 minutes to 2 hours, and even more preferably 30 minutes to 1 hour. Within this range, the current collector does not melt, and only the binder and the like are removed, which has the advantage of easily separating the positive electrode active material from the current collector.

[0083] In this description, the oxidation heat treatment time refers to the time spent at the oxidation heat treatment temperature, and the time it takes to reach that temperature is not included in the calculation.

[0084] The aforementioned oxidation heat treatment can be carried out in two steps, for example. Preferably, a primary heat treatment is performed at 300-450°C, followed by a secondary heat treatment at 500-650°C. In this case, the process is simple, and it has the effect of thoroughly removing the binder, conductive material, and current collector, reducing fluorine (F) and residual lithium generated during the thermal decomposition process, and reducing the crystallite size.

[0085] The primary heat treatment temperature may more preferably be 300 to 430°C, and even more preferably 320 to 400°C, which has the advantage that thermal decomposition of the binder and organic matter occurs smoothly within this range.

[0086] The primary heat treatment time is preferably 10 minutes to 3 hours, more preferably 20 minutes to 160 minutes. Within this range, the current collector does not melt, and only the binder and the like are removed, which has the advantage of easily separating the positive electrode active material from the current collector.

[0087] The secondary heat treatment temperature may more preferably be 510 to 630°C, and even more preferably 520 to 630°C. Within this range, the binder and conductive material are completely combusted, reducing the amount of fluorine (F) and residual lithium generated during the thermal decomposition process, and resulting in a smaller crystal size.

[0088] The aforementioned secondary heat treatment time may preferably be 10 minutes to 2 hours, more preferably 20 minutes to 100 minutes. Within this range, the current collector does not melt, and only the binder and the like are removed, which has the advantage of easily separating the positive electrode active material from the current collector.

[0089] The sum of the primary and secondary heat treatment times may be, for example, 20 minutes to 5 hours, preferably 30 minutes to 4 hours. Within this range, the current collector does not melt, and only the binder is removed, allowing for easy separation of the positive electrode active material from the current collector. This has the advantage of reducing fluorine (F) and residual lithium generated during the thermal decomposition process, and resulting in smaller crystal size.

[0090] The oxygen used in the aforementioned oxidation heat treatment may, for example, have a purity of 59% or higher, preferably 70% or higher, more preferably 80% or higher, even more preferably 90% or higher, and even more preferably 90-99%. Within this range, the binder and conductive material are removed without residue, and the stability of Ni in the active material increases, resulting in a smaller crystal size.

[0091] The purity percentage of the oxygen may be in volume percentage or mol%.

[0092] The purity of the oxygen described herein is not particularly limited and can be measured by measurement methods commonly used in the art to which the present invention pertains.

[0093] Figure 1 shows the positive electrode scrap that is discarded after the positive electrode plate is cut from the positive electrode sheet.

[0094] Referring to Figure 1, a positive electrode sheet 30 is manufactured by coating a long sheet-shaped positive electrode current collector, aluminum foil 10, with a positive electrode active material layer 20 containing positive electrode active material, conductive material, binder, etc. Then, this is punched out to a certain size to produce a positive electrode plate 40, and positive electrode scrap 50 is generated from the remaining portion. The punching is one means of cutting the positive electrode sheet.

[0095] Furthermore, the positive electrode active material layer 20 is formed by coating the aluminum foil 10 with a slurry containing a mixture of positive electrode active material, conductive material, binder, and solvent. Since the slurry is very sensitive to environmental factors such as temperature, it is extremely difficult to determine the coating conditions. As a result, waste positive electrode sheets are generated before the conditions for producing a positive electrode sheet 30 of the desired quality are found through predetermined tests.

[0096] For reference, in the embodiment described below, positive electrode scrap was used as the waste positive electrode.

[0097] (b) A step of primary cleaning the recovered positive electrode active material. The method for regenerating positive electrode active material of the present invention includes (b) a step of primary washing the recovered positive electrode active material, which has the advantage of removing metal fluorides such as LiF that may be present on the surface of the regenerated positive electrode active material and modifying the surface.

[0098] During the aforementioned oxidation heat treatment, CO2 and H2O from the binder and conductive material in the active material layer may react with lithium on the surface of the active material to form Li2CO3 and LiOH, or fluorine (F) present in binders such as PVdF may react with the metal elements constituting the positive electrode active material to form LiF or metal fluorides. If LiF or metal fluorides remain, the battery characteristics will deteriorate when the active material is reused.

[0099] For the aforementioned primary washing, the washing solution can, for example, be water or an aqueous solution of a basic lithium compound, and more preferably water.

[0100] The water may preferably be distilled water or deionized water, and more preferably distilled water. In this case, metal fluorides such as LiF, which tend to remain on the surface of the positive electrode active material, are removed, resulting in an excellent surface modification effect.

[0101] The basic lithium compound aqueous solution may preferably contain more than 0% by weight and up to 15% by weight of the lithium compound, and more preferably more than 0% by weight and up to 10% by weight of the lithium compound. In this case, metal fluorides such as LiF, which tend to remain on the surface of the positive electrode active material, are removed, thereby not only modifying the surface but also preventing the dissolution of transition metals present in the positive electrode active material and replenishing lithium that may dissolve during the washing process. If the solution contains an excess amount of lithium compound beyond the aforementioned range, an excess amount of LiOH may remain on the surface of the active material even after washing, which may affect the subsequent annealing process.

[0102] The lithium compound may, for example, be LiOH, LiNO3, or a mixture thereof, preferably LiOH. In this case, there is an effect of removing fluorine (F) from the surface of the positive electrode active material and lithium precursors that were unable to participate in the reaction.

[0103] In the aforementioned primary cleaning, the weight ratio of the recovered positive electrode active material to the cleaning solution may be, for example, 1:1 to 1:40, preferably 1:1 to 1:35, more preferably 1:1 to 1:30, and even more preferably 1:1 to 1:20. Within this range, there is the advantage that metal fluorides such as LiF are effectively removed.

[0104] The primary cleaning can be carried out, for example, by immersing the recovered positive electrode active material in a cleaning solution. The immersion can be carried out, for example, for one week, preferably within one day, more preferably within one hour, and even more preferably for 10 to 50 minutes. If the immersion time is one week or longer, there is a risk of a decrease in capacity due to excessive dissolution of lithium.

[0105] The aforementioned primary cleaning may preferably include stirring the positive electrode active material while it is immersed in the cleaning solution. In this case, the rapid cleaning process can suppress the elution of lithium, thus shortening the process time.

[0106] The primary cleaning may preferably include the steps of filtering the positive electrode active material and cleaning solution after cleaning, and drying the solid portion of the positive electrode active material obtained after filtering, in which case metal fluorides such as LiF are removed more effectively.

[0107] The filtration may preferably be reduced-pressure filtration using a filter.

[0108] The drying may be carried out preferably at 100 to 500°C, more preferably at 120 to 400°C, even more preferably at 120 to 300°C, and even more preferably at 120 to 200°C.

[0109] The drying may preferably be carried out under vacuum.

[0110] In this description, vacuum drying is not particularly limited as long as it is a vacuum drying method commonly used in the art to which the present invention pertains.

[0111] (c) Add lithium precursor to the primary washed positive electrode active material and perform annealing. The method for regenerating a positive electrode active material of the present invention includes the step of (c) adding a lithium precursor to the primary washed positive electrode active material and annealing it, in which case the crystal structure of the positive electrode active material is restored, thereby restoring the properties of the reused active material to the level of a new active material that has never been used, or further improving them.

[0112] The (c) annealing step may preferably be a step of adding a lithium precursor to the primary washed positive electrode active material and annealing in air or oxygen at 400 to 1000°C, preferably a step of annealing in air at 400 to 1000°C. In this case, there is an effect of improving the battery characteristics of the regenerated positive electrode active material by improving the crystallinity, such as by increasing crystallinity or restoring the crystal structure.

[0113] The lithium precursor may preferably be one or more selected from the group consisting of LiOH, Li2CO3, LiNO3, and Li2O.

[0114] Preferably, the lithium precursor can be added in an amount equal to the amount of lithium that has decreased from the molar ratio of lithium in the positive electrode active material in step (a) above, based on the amount of lithium in the recovered positive electrode active material, and more preferably in an amount of lithium that is in a molar ratio of 0.0001 to 0.2 relative to the molar ratio of lithium in the positive electrode active material in step (a). Within this range, the deficient lithium in the regenerated positive electrode active material is replenished, and the crystallinity is improved, such as by increasing crystallinity or restoring the crystal structure, thereby improving the battery characteristics of the regenerated positive electrode active material.

[0115] The lithium precursor may preferably be added in an amount corresponding to 1 to 40 mol%, more preferably 1 to 15 mol%, and even more preferably 1 to 10 mol%, when the total lithium in the positive electrode active material of the raw materials used in the positive electrode active material layer is 100 mol%, and within this range, no residual precursor that can increase the resistance of the regenerated positive electrode active material remains, which is very useful for improving battery characteristics.

[0116] The annealing temperature can be adjusted within a limited range depending on the melting point of the lithium precursor. For example, in the case of LiCO3, since the melting point is 723°C, annealing can preferably be performed at 700-900°C, more preferably at 710-780°C. In the case of LiOH, since the melting point is 462°C, annealing can preferably be performed at 400-600°C, more preferably at 450-480°C. Within this range, the crystal structure is restored, which has the effect of improving the output performance of the battery.

[0117] The annealing temperature may preferably be higher than the melting point of the lithium precursor; however, if it exceeds 1000°C, thermal decomposition of the positive electrode active material may occur, which may lead to a decrease in battery performance; therefore, a temperature of 1000°C or lower is preferred.

[0118] In the annealing step (c) described above, the method for adding the lithium precursor to the primary washed positive electrode active material may involve drying the washed positive electrode active material and then adding the lithium precursor in a solid or liquid phase. As another example, the lithium precursor solution can be added to the washed positive electrode active material and spray-dried, thereby performing drying and lithium precursor addition in a single step. In this case, particle aggregation due to drying is reduced, the process of mixing the solid-phase lithium precursor can be omitted, and spray drying has the advantage of producing the product in powder form rather than in lumps.

[0119] The lithium precursor solution can, as an example, be a lithium compound soluble in an aqueous solution or an organic solvent.

[0120] (d) Step of secondary cleaning of the annealed positive electrode active material. The method for regenerating a positive electrode active material of the present invention includes (d) a step of secondary cleaning of the annealed positive electrode active material, in which case lithium precursors that exist on the surface of the positive electrode active material in the form of LiOH, Li2CO3, etc., without being able to participate in the reaction after the addition of lithium precursors are removed, which has the advantage of preventing a decrease in battery performance and the generation of gas due to the subsequent reaction between residual lithium precursors and the electrolyte.

[0121] The aforementioned secondary washing may be carried out using water as the washing solution, for example, and preferably distilled water or deionized water. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain due to the excess lithium added in step (c) annealing, are effectively removed.

[0122] The secondary washing may preferably include the steps of mixing the annealed positive electrode active material with the washing solution in a weight ratio of 1:1 to 1:20, filtering the mixture, and drying the solid positive electrode active material obtained after filtering. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain due to excess lithium added in the annealing step, are effectively removed.

[0123] The annealed active material and the washing solution may be mixed in a weight ratio of preferably 1:1 to 1:20, more preferably 1:1 to 1:15, even more preferably 1:1 to 1:10, and even more preferably 1:1 to 1:5. In this case, (c) lithium precursors such as LiOH and Li2CO3, which tend to remain due to excess lithium added in the annealing step, are effectively removed.

[0124] The aforementioned secondary cleaning may include the steps of mixing the annealed positive electrode active material with a cleaning solution, filtering it, and drying the solid portion of the positive electrode active material obtained after filtering. In this case, excellent charging capacity, resistance characteristics, and capacitance characteristics are achieved.

[0125] (e) A step of surface coating the second-cleaned positive electrode active material to obtain a reusable positive electrode active material. The method for regenerating positive electrode active material of the present invention includes (e) the step of surface coating the second-cleaned positive electrode active material to obtain a reusable positive electrode active material, which has the effect of improving structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0126] Preferably, the surface coating involves coating the surface with a coating agent containing one or more of metals, organometallics, and carbon components using a solid-phase or liquid-phase method, followed by heat treatment at 100 to 1200°C. In this case, the structural stability and electrochemical performance are improved while maintaining the properties of the positive electrode active material itself.

[0127] The aforementioned metal-containing coating agent is preferably a coating agent containing 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 a coating agent containing one or more selected from the group consisting of B, W, Al, Ti, and Mg; even more preferably a coating agent containing boron (B), tungsten (W), or a mixture thereof; and even more preferably a coating agent containing tungsten (W) and boron (B). A specific example is a coating agent containing tungsten boride (WB), in which case there is an effect of improving resistance characteristics and life characteristics.

[0128] The coating agent containing the metal may, for example, be an oxide or acid containing the metal as an element within its molecule.

[0129] The aforementioned organometallic coating agent is not particularly limited as long as it is a coating agent commonly used in the art to which the present invention pertains and contains an organometallic compound containing the aforementioned metal, and specific examples include metal alkoxides.

[0130] The coating agent containing the carbon component is not particularly limited as long as it is a coating agent containing a carbon component that is commonly used in the art to which the present invention belongs, and may include sugars such as sucrose as specific examples.

[0131] As an example, the coating agent may be present in an amount of 0.001 to 0.3 mol%, preferably 0.01 to 0.3 mol%, more preferably 0.01 to 0.15 mol%, even more preferably 0.01 to 0.1 mol%, and even more preferably 0.01 to 0.05 mol%, based on the component that is actually coated on the surface of the positive electrode active material excluding the solvent, relative to 1 mol% of the metal in the positive electrode active material before coating treatment. Within this range, the structural stability and electrochemical performance are improved while maintaining the properties of the positive electrode active material itself.

[0132] The heat treatment temperature is preferably 100 to 1000°C, more preferably 200 to 1000°C, and even more preferably 200 to 500°C. Within this range, performance degradation due to thermal decomposition of the positive electrode active material does not occur, and structural stability and electrochemical performance are improved.

[0133] The heat treatment time can preferably be 1 to 16 hours, more preferably 3 to 7 hours. Within this range, it is possible to improve the structural stability and electrochemical performance while maintaining the properties of the positive electrode active material itself.

[0134] The coating method is not particularly limited as long as it is a coating method commonly used in the art to which the present invention belongs. For example, it may be a liquid-phase method in which a liquid coating agent is manufactured and mixed with the positive electrode active material, a mechanochemical method using the high mechanical energy of ball milling, a fluidized bed coating method, a spray drying method, a precipitation method in which the coating agent is precipitated on the surface of the positive electrode active material in an aqueous solution, a method that utilizes the reaction between the gas-phase coating agent and the positive electrode active material, or a sputtering method.

[0135] The aforementioned metal, organometallic, and carbon components may, for example, be spherical, plate-shaped, angular, or needle-shaped, and such shapes can be adjusted by changing process conditions during the manufacturing process. The definitions of each shape are not particularly limited, as long as they conform to definitions generally accepted in the art to which this invention belongs.

[0136] The coating agent preferably has an average diameter of 1 to 1000 nm and a specific surface area of ​​10 to 100 m². 2 It may also be / g, and more preferably the average diameter is 10 to 100 nm and the specific surface area is 20 to 100 m 2 The concentration may be as low as / g, and within this range, it can uniformly adhere to the surface of the positive electrode active material, thereby imparting structural stability to the positive electrode active material and improving problems such as deterioration of lifetime characteristics and electrochemical performance due to lattice deformation and collapse of the crystal structure of the positive electrode active material.

[0137] In this description, the average diameter can be measured by a measurement method commonly used in the art to which the present invention pertains. For example, it can be measured using the laser diffraction method. Specifically, particles of the positive electrode active material are dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer such as the Microtrac MT 3000. Ultrasound at approximately 28 kHz is irradiated at an output of 60 W, and the average particle size (D50) based on the 50% reference of the particle size distribution in the measuring device can be calculated.

[0138] In this description, the specific surface area can be measured by a measurement method commonly used in the art to which the present invention pertains. For example, it can be measured by the BET (Brunauer-Emmett-Teller) method, and specifically, it can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BELSORP-mino II from BEL Japan.

[0139] The positive electrode active material produced by the positive electrode active material regeneration method of the present invention may, for example, have a fluorine (F) content of 250 mg / kg or less, preferably 200 mg / kg or less, and more preferably 10 to 200 mg / kg, and within this range, it has the advantage of being excellent in charge capacity, resistance characteristics and capacitance characteristics.

[0140] As an example, the positive electrode active material may have a surface LiOH content of 0.32% by weight or less, preferably 0.31% by weight or less, and more preferably 0.01 to 0.31% by weight, and within this range, it has the advantage of having excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0141] The positive electrode active material may, for example, have a surface content of 0.19% by weight or less of Li2CO3, preferably 0.01 to 0.19% by weight, and within this range, it has the advantage of having excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0142] As an example, the positive electrode active material may have a total sum of LiOH and Li2CO3 remaining on its surface of 0.51% by weight or less, preferably 0.50% by weight or less, and more preferably 0.01 to 0.50% by weight. Within this range, there is an advantage in that it exhibits excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0143] The positive electrode active material may, for example, have an average crystal size of 122 nm or less, preferably 115 to 122 nm, and more preferably 120 to 122 nm. Within this range, reducing the crystal size reduces strain and minimizes cycle cracks, which has the advantage of extending the battery life.

[0144] Furthermore, the positive electrode active material produced by the positive electrode active material regeneration method of the present invention may, for example, have a fluorine (F) content of 305 mg / kg or less, preferably 250 mg / kg or less, more preferably 200 mg / kg or less, and even more preferably 10 to 200 mg / kg, and within this range, it has the advantage of having excellent capacity characteristics.

[0145] The positive electrode active material may, for example, have a surface content of 0.16% by weight or less, preferably 0.14% by weight or less, more preferably 0.10% by weight or less, and even more preferably 0.01 to 0.10% by weight of Li2CO3. Within this range, there is an advantage in that it has excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0146] The positive electrode active material may, for example, have a surface LiOH content of 0.32% by weight or less, preferably 0.30% by weight or less, more preferably 0.01 to 0.30% by weight, and even more preferably 0.01 to 0.28% by weight. Within this range, there is an advantage in that it exhibits excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0147] As an example, the positive electrode active material may have a total sum of LiOH and Li2CO3 remaining on its surface of 0.45% by weight or less, preferably 0.42% by weight or less, more preferably 0.40% by weight or less, and even more preferably 0.01 to 0.40% by weight. Within this range, there is an advantage in that it exhibits excellent charging capacity, resistance characteristics, and capacitance characteristics.

[0148] The positive electrode active material may, for example, have an average crystal size of 139 nm or less, preferably 120 to 139 nm, more preferably 130 to 139 nm, even more preferably 133 to 139 nm, and even more preferably 133 to 136 nm. Within this range, reducing the crystal size reduces strain and minimizes cycle cracks, which has the advantage of extending the battery life.

[0149] Figure 7 is a flowchart illustrating one embodiment of the present invention, showing the regeneration process for the positive electrode active material.

[0150] Referring to Figure 7, first, cathode scrap is prepared as waste cathode (step S10). For example, a slurry prepared by mixing NCM-based lithium composite transition metal oxide, carbon black, and polyvinylidene fluoride with NMP (N-methyl pyrrolidone) is coated onto aluminum foil and dried in a vacuum oven at approximately 120°C to produce a cathode sheet. After punching out cathode plates of a certain size from this, the remaining cathode scrap can be prepared.

[0151] In particular, the present invention can be effectively applied to a waste positive electrode in which a positive electrode active material containing 60 mol% or more Ni was used, preferably a positive electrode active material containing 80 mol% or more Ni, more preferably a positive electrode active material containing 81 mol% or more Ni, and even more preferably a positive electrode active material containing 81 to 95 mol% Ni.

[0152] The aforementioned positive electrode scrap has a positive electrode active material layer on aluminum foil. After the solvent evaporates, the positive electrode active material layer has a structure in which a binder binds the positive electrode active material and the conductive material. Therefore, when the binder is removed, the positive electrode active material is separated from the aluminum foil.

[0153] Next, the prepared positive electrode scrap is crushed to an appropriate size (step S20). Here, crushing includes cutting or shredding the positive electrode scrap to a size that is easy to handle. Specifically, the crushed positive electrode scrap may be 1 cm x 1 cm in size. For the crushing, various dry grinding equipment such as a hand mill, pin mill, disc mill, cutting mill, or hammer mill may be used as an example, and a high-speed cutting machine may be used to increase productivity.

[0154] Preferably, the crushing process can be decided by considering the handling of the positive electrode scrap and the characteristics required by the equipment used in subsequent processes, such as whether or not to crush the scrap and the size of the pieces. However, if equipment capable of continuous processing is used, the positive electrode scrap must be crushed into even smaller pieces because good fluidity is required.

[0155] Next, oxygen is introduced into the positive electrode scrap to perform oxidation heat treatment and recover the positive electrode active material (step S30). Here, the heat treatment is performed to thermally decompose the binder in the active material layer.

[0156] The aforementioned oxidation heat treatment is preferably carried out with oxygen of 80% purity or higher, and more preferably with oxygen of 90% purity or higher. In this case, the stability of Ni can be ensured in the waste cathode in which high-nickel (High-Ni) cathode material was used, and the binder and conductive material are cleanly removed. When heat treatment is performed in a reducing gas or inactive gas atmosphere, the binder and conductive material carbonize without thermal decomposition. When carbonization occurs, carbon components remain on the surface of the cathode active material, and the performance of the reused cathode active material deteriorates. In contrast, when oxidation heat treatment is performed with oxygen, the carbon components in the binder and conductive material react with oxygen and disappear as gases such as CO and CO2, so both the binder and conductive material are removed.

[0157] The aforementioned oxidation heat treatment is preferably carried out at 300 to 650°C, and specifically at 590°C. However, if the temperature is below 300°C, it is difficult to remove the binder, making it impossible to separate the current collector, and if it exceeds 650°C, the current collector melts, resulting in the problem that it cannot be separated.

[0158] The aforementioned oxidation heat treatment preferably has a temperature rise rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, it can be implemented without putting undue strain on the heat treatment equipment and has the advantage of not causing thermal shock to the positive electrode scrap.

[0159] The aforementioned oxidation heat treatment can be carried out for a period of time sufficient to adequately decompose the binder, preferably 30 minutes or more, more preferably 30 minutes to 5 hours, and specifically around 30 minutes. Within this range, the binder is adequately decomposed, and the decomposition efficiency is excellent.

[0160] In this document, "high-nickel cathode active material" refers to a cathode active material containing 60 mol% or more nickel.

[0161] The oxidation heat treatment step can preferably be carried out in two steps, and more preferably, a primary oxidation heat treatment can be performed at 300-430°C followed by a secondary heat treatment at 510-630°C. In this case, the heat treatment in two steps has the advantage of reducing fluorine (F) and residual lithium generated during the thermal decomposition process, and reducing the crystal size.

[0162] The primary oxidation heat treatment temperature may more preferably be 320 to 400°C.

[0163] The primary heat treatment time may preferably be 10 minutes to 3 hours, and more preferably 20 minutes to 160 minutes.

[0164] The secondary oxidation heat treatment temperature may more preferably be 520 to 630°C. Within this range, the binder and conductive material are sufficiently thermally decomposed, and the fluorine (F) and residual lithium generated during the thermal decomposition process are reduced, resulting in the advantage of smaller crystal size.

[0165] The aforementioned secondary heat treatment time may preferably be 10 minutes to 2 hours, more preferably 20 minutes to 100 minutes. Within this range, the current collector does not melt, and only the binder and the like are removed, which has the advantage of easily separating the positive electrode active material from the current collector.

[0166] The aforementioned oxidation heat treatment preferably has a temperature rise rate of 1 to 20°C / min, more preferably 3 to 10°C / min, and specifically 5°C / min. Within this range, it can be implemented without putting undue strain on the heat treatment equipment and has the advantage of not causing thermal shock to the positive electrode scrap.

[0167] The aforementioned oxidation heat treatment can be carried out using various types of furnaces, for example, a box-type furnace, or, considering productivity, a rotary kiln capable of continuous processing.

[0168] After the aforementioned oxidation heat treatment, the cooling can be carried out slowly or rapidly in the atmosphere.

[0169] Next, the recovered positive electrode active material is subjected to primary washing (step S40).

[0170] Since fluorine (F) and lithium remain on the surface of the positive electrode active material recovered in the oxidation heat treatment step S30, a washing step is necessary to remove them.

[0171] The aforementioned primary washing step involves washing the recovered positive electrode active material with water or an aqueous solution of a basic lithium compound, preferably water, as the washing solution.

[0172] The water may preferably be distilled water or deionized water, which has the advantage of modifying the surface by removing metal fluorides such as LiF.

[0173] The basic aqueous solution of lithium compound contains more than 0% by weight and up to 15% by weight, preferably more than 0% by weight and up to 10% by weight of the lithium compound. In this case, there is an advantage that the surface is modified by removing metal fluorides such as LiF that may be present on the surface of the regenerated positive electrode active material. If the lithium compound exceeds 15% by weight, an excess amount of lithium compounds such as LiOH and LiNO3 may remain on the surface of the positive electrode active material even after washing, which may affect the subsequent annealing process.

[0174] The lithium compound may specifically be LiOH.

[0175] The primary washing described above can be carried out by immersing the recovered active material in the washing solution. After immersion, washing can be performed within one week, preferably within one day, and more preferably within one hour. If washing is performed for more than one week, there is a risk of a decrease in capacity due to excessive dissolution of lithium. Therefore, it is preferable to perform the washing within one hour. Primary washing includes immersing the active material in the washing solution and stirring while immersed. It is preferable to perform stirring in parallel as much as possible. When using an aqueous lithium compound solution as the washing solution, if only immersion is performed without stirring, the washing process will be slow and may cause lithium to dissolve. Since stirring in parallel can minimize the process time, it is preferable to stir at the same time as impregnation with the aqueous lithium compound solution.

[0176] After the initial washing, further steps such as filtration and air drying in a convection oven can be performed.

[0177] In the aforementioned primary cleaning, the weight ratio of the recovered positive electrode active material to the cleaning solution may be 1:1 to 1:40, preferably 1:1 to 1:35, and more preferably 1:1 to 1:30. Within this range, there is the advantage that metal fluorides such as LiF are effectively removed.

[0178] The primary cleaning may preferably include the steps of filtering the positive electrode active material and cleaning solution after cleaning, and drying the solid portion of the positive electrode active material obtained after filtering.

[0179] The filtration is preferably reduced-pressure filtration using a filter, and the drying is vacuum drying at 120-140°C.

[0180] Next, a lithium precursor is added to the primary washed positive electrode active material and annealing is performed (step S50).

[0181] In the annealing step S50, it is important to add a lithium precursor to the primary-washed positive electrode active material and perform annealing. While lithium loss may occur in the positive electrode active material during the preceding steps S30 and S40, step S50 replenishes such lithium loss.

[0182] Furthermore, in step S50, the crystal structure of the active material is restored through annealing, thereby restoring or further improving the properties of the reused active material to the level of a new, unused active material.

[0183] During steps S30 and S40, a deformed structure may form on the surface of the positive electrode active material. For example, in the case of an NCM-based lithium composite transition metal oxide active material, in step S40, Ni may be converted into rock salt [NiCO3·2Ni(OH)2)H2O] by moisture, forming a spinel structure. If a battery is manufactured in this state, the battery's characteristics may deteriorate, such as a decrease in capacity. In this invention, the crystal structure is restored through step S50. For example, the positive electrode active material, which is an NCM-based lithium composite transition metal oxide, is restored to a hexagonal crystal structure. This makes it possible to restore or improve the initial characteristics to a level similar to that of an unused positive electrode active material.

[0184] The lithium precursor in step S50 may be one or more of LiOH, Li2CO3, LiNO3, and Li2O.

[0185] A method for adding a lithium precursor to a primary washed active material may involve drying the washed positive electrode active material and then adding the lithium precursor in a solid or liquid phase. Alternatively, the lithium precursor solution can be added to the washed positive electrode active material and spray-dried, thereby performing drying and lithium precursor addition in a single step. The lithium precursor solution can be an aqueous solution or a lithium compound soluble in an organic solvent.

[0186] If the cathode active material particles are dried immediately in an oven or similar device after the surface modification process by primary washing, they may aggregate and form clumps. Mixing the lithium precursor into these aggregated particles may require grinding the clumps, making the process complex and difficult to implement as a continuous process. Furthermore, especially with NCM-based cathode active materials, if the lithium precursor and powder are mixed or milled in the presence of moisture, the cathode active material absorbs the moisture, causing severe aggregation. Therefore, if the cathode active material is mixed into a lithium precursor solution after primary washing, dispersed, and then spray-dried, the aggregation of particles due to drying and the hassle of mixing solid-phase lithium precursor can be eliminated. In other words, spray drying offers the advantage of producing the material in powder form rather than clumps.

[0187] During spray drying, the lithium precursor solution dries immediately after spraying, and the lithium precursor components coat or come into contact with the surface of the positive electrode active material. At this time, there is also the advantage that the particles aggregate due to capillary force as the lithium precursor solution, which is the solvent, dries, thus adjusting the particle size. In the case of positive electrode scrap made from electrodes, the particles on the surface are compressed during the rolling process, which can cause cracking or fracture. In particular, NCM-based positive electrode active materials experience greater particle fracture due to rolling during electrode formation compared to LCO, resulting in a problem of uneven particle size in recovered positive electrode active material compared to unused positive electrode active material.

[0188] Furthermore, NCM-based active materials use large particles that are formed by the aggregation of primary particles having a size of tens to hundreds of nanometers into secondary particles. When a cathode manufactured from such an active material is rolled to adjust the porosity within the electrode, the secondary particles may break and become primary particles, or they may be broken down into smaller particles that are larger but smaller than the large particles.

[0189] The more particles that are broken by rolling, the greater the specific surface area of ​​the active material. Therefore, in the case of reusable active material obtained from rolled electrodes, problems can arise where it negatively affects the slurry properties, electrode adhesion, and electrode performance during reuse.

[0190] As explained above, through the spray drying step, the lithium precursor is coated onto the surface of the positive electrode active material, and the positive electrode active material is obtained with controlled particle size. Since the addition of the lithium precursor, particleization, and drying are performed in a single step, it has the effect of simplifying the process. Furthermore, spray drying is special in that it is not simply a means of obtaining active material, but a means of re-particleizing particles that have already been used and broken by rolling or other processes.

[0191] Furthermore, since it is only necessary to mix and disperse the positive electrode active material particles, which were washed in the previous step, into a lithium precursor solution of a certain concentration, washing and spray drying have the advantage of being a continuous process. Thus, the method for regenerating positive electrode active material according to this embodiment has the advantage of process continuity, and the coating, drying, and particleization (in other words, particle readjustment) of the lithium precursor are performed simultaneously in a single step.

[0192] Furthermore, since lithium is lost from the positive electrode active material during steps S30 and S40, step S50 replenishes this lost lithium. In addition, since deformation structures (for example, Co3O4 in the case of LCO active material) may form on the surface of the positive electrode active material during the previous steps, step S50 improves the battery characteristics of the regenerated positive electrode active material by restoring the crystal structure of the positive electrode active material through annealing, restoring it to the level of a newly produced positive electrode active material. Here, "newly produced" is the opposite concept of "regenerated," meaning it is made for the first time, and is the same word as "raw material" used in the examples.

[0193] As a specific example of the lithium precursor, LiOH is used.

[0194] The lithium precursor is preferably added in an amount equal to at least the molar ratio of the lost lithium, compared to the molar ratio of lithium to other metals in the newly generated positive electrode active material used in the positive electrode active material layer. Adding an excessive amount of lithium precursor compared to the amount of lost lithium will leave unreacted lithium precursor in the regenerated positive electrode active material, which increases resistance, so it is necessary to add an appropriate amount of lithium precursor. For example, if the molar ratio of lithium to other metals in the newly generated positive electrode active material is 1, an amount of lithium precursor can be added such that the lithium molar ratio is 0.001 to 0.4, and preferably an amount of lithium precursor can be added such that the lithium molar ratio is 0.01 to 0.2.

[0195] As a specific example, when a lithium precursor is added at a molar ratio of 0.09 to 0.1 (based on lithium metal), which is the ratio of the lost lithium content to the lithium content in the newly generated cathode active material based on the results of ICP analysis, it shows a capacity improvement effect equivalent to that of the newly generated cathode active material. Here, the results of the ICP analysis have an error value of approximately ±0.02.

[0196] Specifically, the lithium precursor may be added in an amount of lithium corresponding to 1 mol% to 40 mol%, more preferably 1 to 15 mol%, and even more preferably 1 to 10 mol%, when the total amount of lithium in the positive electrode active material of the raw materials used in the positive electrode active material layer is 100 mol%.

[0197] The annealing is carried out, for example, in air under conditions of 400 to 1000°C, preferably under conditions of 600 to 900°C, and this temperature must be modified within a limited range depending on the type of lithium precursor.

[0198] The annealing temperature is preferably above the melting point of the lithium precursor. However, temperatures exceeding 1000°C will cause thermal decomposition of the positive electrode active material, leading to a decrease in performance, so the temperature should not exceed 1000°C. For example, when Li2CO3 is used as the lithium precursor, an annealing temperature of 700 to 900°C is appropriate, more preferably 710 to 780°C, and most preferably 750 to 780°C. When LiOH is used as the lithium precursor, an annealing temperature of 400 to 600°C is appropriate, more preferably 450 to 480°C, and most preferably 470 to 480°C.

[0199] The annealing time is often one hour or more, preferably 15 hours or less, and more preferably 4 to 6 hours. A longer annealing time allows for sufficient recovery of the crystal structure, but even with long annealing times, there is no significant impact on performance. In this case, the annealing equipment can be the same as or similar to that used in the heat treatment step S30.

[0200] Next, the annealed positive electrode active material is subjected to secondary cleaning (step S60).

[0201] In the annealing step S50, lithium precursors that did not participate in the reaction remain on the surface of the positive electrode active material in the form of LiOH and Li2CO3, so a residual lithium removal step is necessary to remove them. In particular, high-nickel (High-Ni) positive electrode active materials require an excess amount of Li due to the cation mixing phenomenon, which makes it easy for lithium impurities such as lithium carbonate (Li2CO3) to remain on the surface. Such impurities can later react with the electrolyte, degrade the performance of the battery, and generate gas, so they must be thoroughly removed.

[0202] In the aforementioned secondary cleaning, distilled water can preferably be used as the cleaning solution. In this case, it has the advantage of being safe and inexpensive, while not leaching out transition metals present in the positive electrode active material.

[0203] The washing process may preferably include the steps of mixing the annealed positive electrode active material with the washing solution in a weight ratio of 1:1 to 1:10, more preferably 1:1 to 1:5, followed by filtration, and drying the solid positive electrode active material obtained after filtration. In this case, lithium precursors such as LiOH and Li2CO3, which tend to remain due to the excess lithium added in step S50, are effectively removed.

[0204] The mixing of the annealed positive electrode active material and distilled water is preferably carried out by stirring, and the stirring is not particularly limited, but may be mechanical stirring or ultrasonic stirring.

[0205] The filtration is preferably reduced-pressure filtration using a filter, and the drying is vacuum drying at 120-140°C.

[0206] Next, as a selective step, the cleaned positive electrode active material can be surface coated (step S70).

[0207] The aforementioned surface coating involves, for example, applying a coating agent containing a metal, organometallic, or carbon component to the surface using a solid-phase or liquid-phase method, followed by heat treatment. If the heat treatment temperature is too low, the desired surface protective layer of dissimilar metals will not be formed, and if the heat treatment temperature is too high, the performance of the battery will deteriorate due to the thermal decomposition of the positive electrode active material.

[0208] Specifically, when a metal oxide or acid containing B, W, BW, etc. is coated onto a cleaned positive electrode active material and then heat-treated, a surface protective layer, such as a lithium boron oxide layer, is formed on the surface of the positive electrode active material.

[0209] The solid-phase or liquid-phase method for the surface coating may, for example, be a method such as mixing, milling, spray drying, or grinding.

[0210] If the annealing step S50 is performed so that the molar ratio of lithium to other metals in the positive electrode active material is 1:1, the lithium in the positive electrode active material reacts with the coating agent in the surface coating step S70, causing the molar ratio of lithium to other metals in the positive electrode active material to fall below 1:1. As a result, such a regenerated positive electrode active material will not be able to fully utilize its 100% battery capacity. However, if the lithium precursor is added in excess in the annealing step S50 to a ratio of 0.0001 to 0.1 more molars relative to the other metals in the positive electrode active material, the surface protective layer is formed in the surface coating step S70, and the molar ratio of lithium to other metals in the positive electrode active material becomes 1:1, thus preventing a decrease in battery capacity.

[0211] secondary battery The secondary battery of the present invention includes the positive electrode active material, and in this case, fluorine (F) and lithium precursors that could not participate in the reaction are removed from the surface of the positive electrode active material, resulting in a smaller crystallite size, which provides excellent charging capacity, resistance characteristics, and capacity characteristics. Furthermore, since acids and organic solvents are not used in the recovery and regeneration process of the positive electrode active material, it is environmentally friendly, and in particular, the initial water washing process is omitted, resulting in excellent economic efficiency and productivity.

[0212] The secondary battery of the present invention may include all of the above-described positive electrode active material and regeneration method. Therefore, redundant descriptions thereof are omitted here.

[0213] The following are preferred embodiments to aid in understanding the present invention. However, these embodiments are merely illustrative of the present invention, and it will be obvious to those skilled in the art that various changes and modifications are possible within the scope of the present invention and the technical concept, and that such changes and modifications fall within the scope of the appended claims.

[0214] [Examples] Example 1 The positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide with nickel content of 85 mol%) discarded after punching out the positive electrode plates was crushed, and then subjected to oxidation heat treatment at 590°C for 30 minutes with 95% pure oxygen to remove the binder and conductive material, separate the current collector and positive electrode active material, and then recover the positive electrode active material. Here, the temperature rise rate to reach the heat treatment temperature was 5°C / min, and oxygen (O2) was supplied at 10 L / min.

[0215] The recovered positive electrode active material was subjected to primary washing by immersion in distilled water and simultaneous stirring. At this time, the weight ratio of the recovered positive electrode active material to distilled water was set to 1:30, and after stirring at 500 rpm for 10 minutes, only the active material was extracted by vacuum filtration using a filter. Compared to the raw material, the positive electrode active material after primary washing showed a decrease of 0.11 moles of lithium, based on 1 mole of lithium in the positive electrode active material.

[0216] The primary washed positive electrode active material was dried overnight at 100°C, and then LiOH was added as a lithium precursor. The mixture was then annealed in air at 750°C for 5 hours. The air was supplied at a rate of 3 L / min. At this time, the lithium precursor was added in an amount corresponding to 18 mol%, when the total lithium content in the positive electrode active material was assumed to be 100 mol%.

[0217] The annealed positive electrode active material and distilled water were mixed in a 1:1 weight ratio, stirred for 5 minutes under 500 rpm conditions for secondary washing, and then filtered under reduced pressure to obtain the solids. The solids were vacuum dried at 100°C for 12 hours to obtain the washed positive electrode active material.

[0218] The cleaned positive electrode active material was coated with boric acid and then heated at 300°C for 5 hours to produce the final regenerated positive electrode active material. Here, the amount of boric acid added was equivalent to 1000 ppm of boron lost in the previous step, the temperature rise rate until the heat treatment temperature was reached was 2°C / min, and air was supplied at 3 L / min.

[0219] In this document, the molar ratio of lithium to other metals in the positive electrode active material, the remaining amount of LiF, etc., were measured using an ICP analyzer. While these measurements can be performed using a standard ICP analyzer commonly used in laboratories, there is no deviation due to the measurement device or method.

[0220] Comparative Example 1 The regenerated cathode active material was produced in the same manner as in Example 1, except that in the step of oxidation heat treatment in Example 1, air (containing 21% oxygen) was introduced instead of oxygen during the heat treatment.

[0221] Comparative Example 2 In this example, a regenerated cathode active material was produced in the same manner as in Example 1, except that in the oxidative heat treatment step, air (containing 21% oxygen) was introduced instead of oxygen during the heat treatment, and the primary cleaning step was omitted.

[0222] Comparative Example 3 In this example, the regenerated cathode active material was produced in the same manner as in Example 1, except that the primary cleaning step was omitted.

[0223] [Example Test I: SEM Analysis] The regenerated cathode active materials obtained in Example 1 and Comparative Examples 1-3 were imaged using a scanning electron microscope (SEM) and are shown in Figure 2. The SEM images were taken using a general-purpose SEM commonly used in laboratories. Specifically, a Hitachi S-4200 was used. However, there was no deviation due to the measurement equipment or method.

[0224] As can be seen in Figure 2, the regenerated positive electrode active material produced in Example 1 was found to have broken into small particles, and these broken particles were found to be in contact with or dispersed among larger particles. On the other hand, in Comparative Examples 1 to 3, it was found that the particles were aggregated without breaking into smaller particles.

[0225] [Test Example II: XRD Analysis] The crystal size of the regenerated cathode active material obtained in Example 1 and Comparative Examples 1-3 was measured by XRD crystallography.

[0226] Specifically, 5g of the regenerated cathode active material particles obtained in Example 1 and Comparative Examples 1-3 were placed in a holder, and the diffraction grating generated by irradiating the particles with X-rays was analyzed to determine the crystal size. The method used was to determine the main peak or the full width at half maximum of three or more peaks, which corresponded to the average crystal size of the primary particles of the regenerated cathode active material. The average crystal size of the primary particles of the regenerated cathode active material based on these results is shown in Table 1 below.

[0227] [Table 1]

[0228] As shown in Table 1 above, it can be confirmed that the crystal size of the regenerated positive electrode active material produced in Example 1 was smaller than that of Comparative Examples 1 to 3. When the crystal size is reduced in this way, strain can be reduced and cycle cracks can be minimized, which has the advantage of extending the battery life.

[0229] [Test Example III: Residual Fluorine (F) Content] The fluorine (F) content remaining in the regenerated positive electrode active material obtained in Example 1 and Comparative Examples 1-3 was measured using an ICP analyzer, and the results are shown in Table 2 below. While this can be measured using a general ICP analyzer commonly used in laboratories, there is no deviation due to the measuring device or method.

[0230] [Table 2]

[0231] As can be seen from Table 2 above, it was found that Example 1 according to the present invention had a significantly reduced residual fluorine content compared to Comparative Examples 1 to 3.

[0232] [Test Example IV: Residual Lithium Content] The residual lithium content of the regenerated cathode active materials obtained in Example 1 and Comparative Examples 1-3 was measured as follows, and the results are shown in Table 3 below. *Residual lithium content: 5 g of positive electrode active material was dispersed in 100 ml of distilled water and mixed at 300 rpm for 5 minutes. The active material was then filtered, and the resulting filtrate was titrated with a 0.1 M HCl solution while measuring the change in pH to obtain a pH titration curve. Using the obtained pH titration curve, the residual amounts of LiOH and Li2CO3 in the positive electrode active material were calculated.

[0233] [Table 3]

[0234] As shown in Table 3 above, it was confirmed that the residual lithium content of the regenerated cathode active material in Example 1 was reduced compared to Comparative Examples 1 to 3.

[0235] [Test Example V: Evaluation of CHC Cells] The electrochemical performance of the regenerated cathode active materials obtained in Example 1 and Comparative Examples 1-3 was measured through evaluation of the CHC cell as described below, and the results are shown in Figure 3. *Evaluation of CHC cells: 97.5 wt% recycled cathode active material, 1 wt% carbon black (a conductive material), and 1.5 wt% PVdF (a binder) were weighed and mixed with NMP to produce a slurry. This slurry was coated onto aluminum foil to produce a cathode, and then a cell (Coin Half Cell, CHC) was manufactured. The electrochemical performance (charging capacity, discharging capacity, and efficiency) was evaluated under conditions of a voltage of 3 to 4.3 V, charging and discharging at 0.1 C / 0.1 C, and an electrolyte of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 3:7 (by weight ratio), along with other additives.

[0236] Figure 3 shows the results of evaluating coin cells for each of the regenerated cathode active materials manufactured or prepared in Example 1 and Comparative Examples 1 to 3. It was confirmed that the regenerated cathode active material according to the present invention (Example 1) had superior charging capacity compared to Comparative Examples 1 to 3.

[0237] [Test Example VI: Evaluation of Monocell] The capacity retention rate and resistance increase rate of monocells produced using the regenerated cathode active materials obtained in Example 1 and Comparative Examples 1-3 were measured through the following monocell evaluation, and the results are shown in Figure 4. *Manufacturing of monocells: A cathode active material slurry identical to that used for coin cells was applied to 20 μm thick aluminum foil, dried at 130°C for 1 hour, and then punched out to a size of 30 mm x 42 mm to produce the cathode.

[0238] On the other hand, a slurry of negative electrode active material was prepared by mixing 95.6% by weight of a mixture of natural graphite and artificial graphite in a 5:5 weight ratio with 3.3% by weight of conductive material and 1.1% by weight of binder. This slurry was then applied to a 10 μm thick copper foil, rolled and dried, and then punched out to a size of 31 mm × 43 mm to produce the negative electrode.

[0239] After joining the manufactured positive and negative electrodes to a separation membrane, an electrolyte solution with a weight ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) = 3:7 was injected, and then the cell was vacuum-sealed to produce a monocell. After 10 hours of aging, electrochemical evaluation was performed.

[0240] *Measurement of capacity retention rate at high temperature (45°C): Each monocell manufactured from the regenerated positive electrode active material obtained in Example 1 and Comparative Examples 1-3 was formed at a rate of 0.1C, and then the gas inside the battery was removed (degassing process). Subsequently, 4.2V, 1C, 0.05C cut-off CC / CV charging and 2.5V, 0.5C CC discharge were performed 200 times each at high temperature (45°C). The discharge capacity after one cycle and the discharge capacity after 200 cycles were measured using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 6A), and the discharge capacity after one cycle was set as the initial capacity. Then, the capacity retention rate was calculated by comparing the discharge capacity after 200 cycles with the initial capacity (100%) using the following formula 1, and the results are shown in Figure 4.

[0241] [Formula 1] Capacity retention rate (%) = (Discharge capacity after high-temperature cycle / Initial discharge capacity) × 100

[0242] *Measurement of resistance increase rate at high temperature (45°C): Each monocell manufactured from the regenerated positive electrode active material obtained in Example 1 and Comparative Examples 1-3 was formed at a rate of 0.1C, and then the gas inside the battery was removed (degassing process). After the lithium secondary battery from which the gas had been removed was transferred to a charger / discharger at room temperature (25°C), it was charged to 4.2V at a rate of 0.33C under constant current / constant voltage conditions and 0.05C cutoff charging, and then discharged at 0.33C 2.5V. Based on the discharge capacity after three charge / discharge cycles, the State of Charge (SOC) was adjusted to 50%. At this time, the DC internal resistance was measured using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 6A) through the voltage drop that appeared when a discharge pulse was applied at 2.5C for 10 seconds, and this resistance was set as the initial resistance.

[0243] Subsequently, 200 cycles each of 4.2V, 1C, and 0.05C cutoff CC / CV charging and 2.5V, 0.5C CC discharge were performed at a high temperature (45°C). After that, the lithium secondary battery was transferred to a room temperature (25°C) charge / discharge unit. Then, after adjusting the SOC (State of Charge) to 50%, the DC internal resistance was measured using a PNE-0506 charge / discharge unit (manufacturer: PNE Solutions Co., Ltd., 5V, 6A) through the voltage drop observed when a discharge pulse (2.5C) was applied for 10 seconds. This was compared to the initial resistance (0%), and the resistance increase rate (%) was calculated using Equation 2 below. The results are shown in Figure 4.

[0244] [Formula 2] Resistance increase rate (%) = {(Resistance after high-temperature cycle - Initial resistance) / Initial resistance} × 100

[0245] As shown in Figure 4, it was confirmed that as the number of cycles increased, Example 1 had a higher capacitance retention rate and a lower resistance increase rate compared to Comparative Examples 1-3.

[0246] [Additional Examples] Additional Example 1 The positive electrode scrap (current collector: aluminum foil, positive electrode active material: NCM-based lithium composite transition metal oxide with nickel content of 86 mol%) discarded after punching out the positive electrode plates was crushed, and then subjected to primary heat treatment at 350°C for 2 hours with 95% pure oxygen. After that, the temperature was raised to 590°C for secondary heat treatment for 30 minutes to remove the binder and conductive material, separate the current collector and positive electrode active material, and then the positive electrode active material was recovered. The rate of temperature rise to reach the heat treatment temperature was 5°C / min, and oxygen (O2) was supplied at 10 L / min.

[0247] The recovered positive electrode active material was subjected to primary washing by immersion in distilled water as a washing solution and simultaneous stirring. At this time, the weight ratio of the recovered positive electrode active material to the washing solution was set to 1:30, and after stirring at 500 rpm for 10 minutes, only the active material was extracted by vacuum filtration using a filter. Compared to the raw material, the amount of lithium in the positive electrode active material after primary washing was reduced by 0.11 moles.

[0248] The primary washed positive electrode active material was dried overnight at 100°C, then LiOH was added as a lithium precursor, and the mixture was annealed in air at 750°C for 5 hours. Air was supplied at a rate of 3 L / min. The lithium precursor added was in an amount corresponding to 18 mol%, assuming a total lithium content of 100 mol% in the positive electrode active material used as the raw material for the positive electrode active layer.

[0249] The annealed positive electrode active material and distilled water were mixed in a 1:10 weight ratio, stirred for 5 minutes under 500 rpm conditions for secondary washing, and then filtered under reduced pressure to obtain the solids. The solids were vacuum-dried at 100°C for 12 hours to obtain the washed positive electrode active material.

[0250] The cleaned positive electrode active material was coated with boric acid and then heated at 300°C for 5 hours to produce the final regenerated positive electrode active material. Here, the amount of boric acid added was equivalent to 1000 ppm of boron lost in the previous step, the temperature rise rate until the heat treatment temperature was reached was 2°C / min, and air was supplied at 3 L / min.

[0251] In this document, the molar ratio of lithium to other metals in the positive electrode active material, the remaining amount of LiF, etc., were measured using an ICP analyzer. While these measurements can be performed using a standard ICP analyzer commonly used in laboratories, there is no deviation due to the measurement device or method.

[0252] In this document, ppm refers to a weight-based unit unless otherwise defined.

[0253] Additional Example 2 In the above-mentioned Additional Example 1, the regenerated cathode active material was produced in the same manner as in Additional Example 1, except that a primary heat treatment was performed at 350°C for 30 minutes, followed by a secondary heat treatment at 590°C for 30 minutes.

[0254] Additional Example 3 In the above-mentioned Additional Example 1, the regenerated cathode active material was produced in the same manner as in Additional Example 1, except that a primary heat treatment was performed at 350°C for 30 minutes, followed by a secondary heat treatment at 570°C for 30 minutes.

[0255] Additional Comparative Example 1 In the above-mentioned Additional Example 1, the regenerated cathode active material was produced in the same manner as in Additional Example 1, except that the primary and secondary heat treatment steps were performed at 550°C for 30 minutes.

[0256] Additional Comparative Example 2 In the above-mentioned Additional Example 1, the recovered positive electrode active material was immediately provided to the annealing step without primary washing, except that the regenerated positive electrode active material was produced in the same manner as in Additional Example 1.

[0257] [Test Example I: XRD Analysis] The crystal sizes of the regenerated positive electrode active materials obtained in Additional Examples 1 to 3 and Additional Comparative Example 1 were measured by XRD crystal analysis.

[0258] Specifically, 5 g of the regenerated positive electrode active material particles obtained in Additional Examples 1 to 3 and Additional Comparative Example 1 were placed in a holder respectively, and the diffraction grating emitted by irradiating the particles with X-rays was analyzed to obtain the result. The method of obtaining was from the half-value width of the main peak or three or more peaks, which corresponded to the average crystal size of the primary particles of the regenerated positive electrode active material particles. The average crystal size of the primary particles of the regenerated positive electrode active material according to this result is shown in Table 4 below.

[0259] [Table 4]

[0260] As shown in Table 4 above, it can be confirmed that the crystal sizes of the regenerated positive electrode active materials produced in Additional Examples 1 to 3 were smaller than those in Additional Comparative Example 1. When the crystal size becomes smaller in this way, the strain can be reduced to minimize the cycle crack, and the battery has the advantage of extended life.

[0261] [Test Example II: Content of Residual Fluorine (F)] The content of fluorine (F) remaining in the regenerated positive electrode active materials obtained in Additional Examples 1 to 3, Additional Comparative Examples 1 and 2 was measured using an ICP analyzer, and the results are shown in Table 5 below. At this time, it can be measured with a general ICP analyzer commonly used in the laboratory, and there is no deviation due to the measuring device or method. <00​​​​​​​​​​As can be confirmed from Table 5 above, it was confirmed that in Additional Examples 1 to 3 according to the present invention, the content of residual fluorine decreased as compared with Additional Comparative Examples 1 and 2. In particular, it was found that in Additional Comparative Example 2 where primary washing was not performed, the content of residual fluorine was very high.

[0264] [Test Example III: Content of Residual Lithium] The content of residual lithium in the regenerated cathode active materials obtained in Additional Examples 1 to 3, Additional Comparative Examples 1 and 2 was measured as follows, and the results are shown in Table 6 below. * Content of residual lithium: 分散(disperse) 5 g of the cathode active material in 100 ml of distilled water, mix at 300 rpm for 5 minutes, then filter to filter the active material, and measure the change in pH value while titrating the obtained filtrate with a 0.1 M HCl solution to obtain a pH titration curve. Using the obtained pH titration curve, the residual amount of LiOH and the residual amount of Li2CO3 in the cathode active material were calculated.

[0265]

Table 6

[0266] As shown in Table 6 above, it was confirmed that in Additional Examples 1 to 3, the content of residual lithium in the regenerated cathode active material decreased as compared with Additional Comparative Examples 1 and 2.

[0267] [Test Example IV: Evaluation of CHC Cell] The electrochemical performance of the regenerated cathode active materials obtained in Additional Examples 1 to 3, Additional Comparative Examples 1 and 2 was measured through the evaluation of a CHC cell as follows, and the results are shown in FIG. 5. *Evaluation of CHC cells: 97.5% by weight of recycled positive electrode active material, 1% by weight of carbon black as a conductive material, and 1.5% by weight of PVdF as a binder were weighed and mixed with NMP to produce a slurry. This slurry was coated onto aluminum foil to produce a positive electrode, and a cell (Coin Half Cell, CHC) was manufactured by adding ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 3:7 (by weight ratio) as the electrolyte, along with other additives. The manufactured coin cell was charged to 4.3V at 25°C with a constant current of 0.1C and a 0.05C cutoff. Then, it was discharged to 3.0V with a constant current of 0.1C. The charge capacity at this time was measured and is shown in Figure 5.

[0268] Figure 5 shows the results of evaluating coin cells for each of the regenerated cathode active materials produced in Additional Examples 1-3 and Additional Comparative Examples 1 and 2. It was confirmed that the regenerated cathode active materials according to the present invention (Additional Examples 1-3) have superior charging capacity compared to Additional Comparative Examples 1 and 2.

[0269] [Test Example V: Evaluation of Monocell] The capacity retention rate of monocells produced using the regenerated cathode active materials obtained in the above-mentioned Additional Examples 1-3 and Additional Comparative Examples 1 and 2 was measured through the following monocell evaluation, and the results are shown in Figure 6. *Manufacturing of monocells: A cathode active material slurry identical to that used for coin cells was applied to 20 μm thick aluminum foil, dried at 130°C for 1 hour, and then punched out to a size of 30 mm x 42 mm to produce the cathode.

[0270] On the other hand, a slurry of negative electrode active material was prepared by mixing 95.6% by weight of a mixture of natural graphite and artificial graphite in a 5:5 weight ratio with 3.3% by weight of conductive material and 1.1% by weight of binder. This slurry was then applied to a 10 μm thick copper foil, rolled and dried, and then punched out to a size of 31 mm × 43 mm to produce the negative electrode.

[0271] After joining the manufactured positive and negative electrodes to a separation membrane, an electrolyte solution with a weight ratio of ethylene carbonate (EC) to ethyl methyl carbonate (EMC) = 3:7 was injected, and then the cell was vacuum-sealed to produce a monocell. After 10 hours of aging, electrochemical evaluation was performed.

[0272] *Measurement of capacity retention rate at high temperature (45°C): Each monocell manufactured from the regenerated positive electrode active material obtained in the above-mentioned Additional Examples 1-3 and Additional Comparative Examples 1 and 2 was formed at a rate of 0.1C, and then the gas inside the battery was removed (degassing process). Subsequently, 4.2V, 1C, 0.05C cut-off CC / CV charging and 2.5V, 0.5C CC discharge were performed 100 times each at high temperature (45°C). The discharge capacity after one cycle and the discharge capacity after 100 cycles were measured using a PNE-0506 charger / discharger (manufacturer: PNE Solutions Co., Ltd., 5V, 6A), and the discharge capacity after one cycle was set as the initial capacity. Then, the capacity retention rate was calculated by comparing the discharge capacity after 100 cycles with the initial capacity (100%) using the following formula 1, and the results are shown in Figure 6.

[0273] [Formula 1] Capacity retention rate (%) = (Discharge capacity after high-temperature cycle / Initial discharge capacity) × 100

[0274] As shown in Figure 6, it was confirmed that additional examples 1 to 3 had a higher capacity retention rate compared to additional comparative examples 1 and 2 as the number of cycles increased. [Explanation of Symbols]

[0275] 10 Current collector 20 Active material layer 30 Positive electrode sheets 40 Positive plate 50 Positive electrode scrap

Claims

1. A positive electrode active material selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, wherein it contains 60 mol% or more of Ni, has a fluorine (F) content of 250 mg / kg or less, and has an average crystal size of 115 to 122 nm, The aforementioned positive electrode active material is a regenerated positive electrode active material. The positive electrode active material is characterized in that the total sum of LiOH and Li₂CO₃ remaining on the surface is 0.51% by weight or less.

2. The positive electrode active material according to claim 1, characterized in that the surface of the positive electrode active material is coated with a coating agent containing boron (B), tungsten (W), or a mixture thereof, or a coating agent containing carbon.

3. The positive electrode active material according to claim 2, characterized in that the surface of the positive electrode active material is coated with a coating agent containing boron and tungsten (W).

4. A positive electrode active material selected from the group consisting of lithium nickel oxide (LNO)-based positive electrode active material, nickel-cobalt-manganese (NCM)-based positive electrode active material, nickel-cobalt-aluminum (NCA)-based positive electrode active material, and nickel-cobalt-manganese-aluminum (NCMA)-based positive electrode active material, wherein it contains 60 mol% or more of Ni, has a fluorine (F) content of 305 mg / kg or less, and has an average crystal size of 120 to 139 nm, The aforementioned positive electrode active material is a regenerated positive electrode active material. The positive electrode active material is characterized in that the total sum of LiOH and Li₂CO₃ remaining on the surface is 0.45% by weight or less.

5. The positive electrode active material is residual Li ２ CO ３ The positive electrode active material according to claim 4, characterized in that the content of is 0.16% by weight or less.

6. A secondary battery characterized by containing the positive electrode active material described in any one of claims 1 to 5.

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