Method for regenerating positive electrode active material and positive electrode active material regenerated using same

Abstract

The present invention relates to a method for regenerating a positive electrode active material and a positive electrode active material regenerated using the same, and more specifically, the present invention can provide a method for regenerating a positive electrode active material and a positive electrode active material regenerated using the same, the method includes the steps of: recovering a positive electrode active material by heat treating a waste positive electrode including a current collector and a positive electrode active material layer formed on a surface thereof in an oxidizing atmosphere; a coating agent is added into the recycled positive electrode active material and calcined in a reducing atmosphere to form a coating on the surface of the positive electrode active material, meanwhile, a ferric iron compound in the positive electrode active material is converted into a ferrous iron compound, and polycrystalline particles are converted into a single crystal positive electrode active material; and grinding the positive electrode active material on which the coating layer is formed and which is converted into a divalent iron compound to control the particle size of the positive electrode active material, thereby synthesizing a single crystal structure and simultaneously converting ferric iron into divalent iron in a regeneration process so that no ferric iron remains inside the regenerated positive electrode active material. Accordingly, deterioration of battery performance may be prevented, life characteristics may be excellent in a high voltage environment, thermal stability may be improved, and an amount of gas generated during charging and discharging may be reduced.

Description

Technical Field

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2024-0029457, filed on February 29, 2024, Korean Patent Application No. 10-2024-0029458, filed on February 29, 2024, and Korean Patent Application No. 10-2025-0001945, filed on January 7, 2025, based on the priority of the aforementioned patents, the disclosures of which are incorporated herein by reference.

[0003] This invention relates to a method for regenerating cathode active materials and the cathode active materials regenerated therefrom. According to the invention, by controlling the atmosphere and temperature conditions in the steps of desorbing and recovering the cathode active material from the waste cathode and in the steps of coating the recovered cathode active material with a coating agent and calcining it, a single-crystal structure is synthesized during the regeneration process, while ferric iron is converted to ferrous iron, resulting in no ferric iron residue in the regenerated cathode active material. Therefore, battery performance degradation can be prevented, lifetime characteristics can be excellent in high-voltage environments, thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced. Background Technology

[0004] Since the 1990s, the demand for lithium-ion batteries has increased with the growing market for portable electronic devices. More recently, the rapid growth of the electric vehicle market has led to a surge in global demand for lithium-ion batteries. This increased demand may result in instability in the supply and demand of lithium resources in the near future. Furthermore, the continuous accumulation of waste batteries can cause significant environmental problems. To address these issues, the regeneration of waste lithium-ion batteries presents a crucial technological challenge.

[0005] Typically, a lithium-ion secondary battery consists of: a positive electrode formed by coating a metal foil (e.g., aluminum) with a layer of positive electrode active material; a negative electrode formed by coating a metal foil (e.g., copper) with a layer of negative electrode active material; a separator to prevent mixing of the positive and negative electrodes; and an electrolyte that allows lithium ions to move between the positive and negative electrodes. The positive electrode is manufactured by coating a positive electrode composition, including a positive electrode active material, a binder, a conductive material, and a solvent, onto a current collector made of metal foil (e.g., aluminum), drying it, and then pressing it into shape.

[0006] The cathode accounts for over 60% of the cost of lithium-ion batteries. These cathode active materials include lithium cobalt oxide (LiCoO2), lithium nickel cobalt manganese oxide (LiNiMnCoO2), lithium manganese oxide (LiMnO2), and lithium iron phosphate (LiFePO4). Among these, lithium iron phosphate is increasingly used as a raw material for high-capacity lithium-ion batteries used in electric vehicles due to its low unit price and stable supply. Therefore, various researches are underway on recycling technologies to selectively recover valuable metals or directly recover cathode active materials from cathodes discarded after use or from cathode waste generated during lithium-ion battery manufacturing (hereinafter referred to as "waste cathodes").

[0007] A method for directly regenerating cathode active materials from waste cathodes without decomposing the cathode active material (direct regeneration method) is being investigated. There are four main methods for this: calcination, solvent dissolution, aluminum (Al) foil dissolution, and pulverization and sieving.

[0008] Calcination is a simple process, but it has drawbacks such as forming foreign matter on the surface of the regenerated positive electrode active material, which degrades the rate performance of the battery. Furthermore, due to these drawbacks, it also generates waste gas and consumes excessive energy.

[0009] Additionally, when using solvent dissolution, regenerated positive electrode active materials with relatively clean surfaces can be obtained. However, because the solvents used to dissolve the binder (e.g., N-methyl-2-pyrrolidone (NMP)) are toxic gases and pose an explosion risk, this method suffers from poor stability and requires an expensive solvent recovery process.

[0010] Furthermore, the aluminum foil dissolution method offers good process stability, low cost, and easy removal of the binder. However, it results in the formation of difficult-to-remove foreign matter on the surface of the recycled positive electrode active material, and poses an explosion risk due to the generation of hydrogen gas during aluminum foil removal.

[0011] Furthermore, among the methods described above, the pulverization and sieving method can be carried out through the simplest process. However, it is difficult to completely separate the current collector from the positive electrode active material, the particle size distribution of the positive electrode active material changes during the pulverization process, and the battery characteristics of the regenerated positive electrode active material deteriorate due to residual binders.

[0012] In particular, the disadvantage of waste cathodes containing lithium iron phosphate as the cathode active material is that during the regeneration process, polycrystalline particles are synthesized and trivalent iron particles are mixed into the lithium iron phosphate, which reduces battery performance.

[0013] [Existing Technical Documents]

[0014] [Patent Literature]

[0015] Japanese Patent Application Publication No. 2024-503575 Summary of the Invention

[0016] [Technical Issues]

[0017] Therefore, the present invention was made in view of the above-mentioned problems. One object of the present invention is to provide a method for regenerating a positive electrode active material and a positive electrode active material regenerated therefrom. According to the present invention, by controlling the atmosphere and temperature conditions in the steps of desorbing and recovering the positive electrode active material from the waste positive electrode and in the steps of coating the recovered positive electrode active material with a coating agent and calcining it, a single crystal structure is synthesized during the regeneration process, while ferric iron is converted to ferrous iron, so that no ferric iron residue remains in the regenerated positive electrode active material. Therefore, the degradation of battery performance can be prevented, the life characteristics in high-voltage environments can be excellent, thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced.

[0018] The above and other objectives can be achieved by the invention described below.

[0019] [Technical Solution]

[0020] (I) According to one aspect of the present invention, a method for regenerating a positive electrode active material is provided, the method comprising:

[0021] (a) Recovering positive electrode active material by heat treatment of waste positive electrode, including current collector and positive electrode active material layer formed on its surface, under an oxidizing atmosphere;

[0022] (b) Adding a coating agent to the recovered positive electrode active material and calcining it under a reducing atmosphere to form a coating on the surface of the positive electrode active material, converting the trivalent iron compound in the positive electrode active material into a divalent iron compound, and converting the polycrystalline particles into a single-crystal positive electrode active material; and

[0023] (c) The particle size of the positive electrode active material is controlled by grinding the coated positive electrode active material, in which the trivalent iron compound is converted into a divalent iron compound.

[0024] II) According to I), step (a) may include a first heat treatment at 300–500°C in an oxidizing atmosphere; and a second heat treatment at 500–700°C in an oxidizing atmosphere after the first heat treatment.

[0025] III) According to I) to II), a single heat treatment can be carried out for 30 minutes to 10 hours, and a second heat treatment can be carried out for 30 minutes to 10 hours.

[0026] IV) According to I) to III), step (b) may include adding the coating agent to the recovered positive electrode active material and pre-grinding it; spray-drying the pre-grinding positive electrode active material; and calcining the spray-dried positive electrode active material at 710 to 900°C in a reducing atmosphere.

[0027] V) According to I) to IV), the coating agent may contain one or more of a metal, organometallic and carbon component, preferably a carbon component, and more preferably one or more of a sucrose, glucose, graphite, polyvinylidene fluoride (PVDF), polyethylene glycol (PEG), citric acid, polyvinyl alcohol (PVA), graphene and fructose.

[0028] VI) According to I) to V), calcination can be carried out for 1 to 24 hours.

[0029] VII) According to I) to VI), the pre-grinding can be performed using a ball mill, a high-energy ball mill, a vibratory mill, or a roller mill.

[0030] VIII) According to I) to VII), pre-grinding can be carried out for 2 to 24 hours at a stirring speed of 50 to 500 rpm.

[0031] IX) According to I) to VIII), in step (c), the grinding can be performed using a jet mill.

[0032] X) According to I) to IX), in step (c), grinding can be carried out in air or an inert atmosphere.

[0033] XI) Based on I) to X), the positive electrode active material can be represented by the following chemical formula 1.

[0034] [Chemical Formula 1]

[0035] Li 1-a M a Fe 1-b N b P 1-c X c O 4-d Y d

[0036] Wherein, M includes one or more elements selected from the group consisting of Nb, Al, Na, Ti, Zr and K; N includes one or more elements selected from the group consisting of Mo, V, Mn, Sm, Eu, Yb, Cu, Mg, Ni and Co; X includes Si; Y includes one or more elements selected from the group consisting of F, S and N; and a, b, c and d are respectively 0≤a<1, 0≤b<1, 0≤c<1, 0≤d<4.

[0037] XII) According to I) to XI), the positive electrode active material may be composed of more than 99 mol% or 100 mol% single crystals.

[0038] XIII) According to I) to XII), based on XRD analysis or electron paramagnetic resonance (EPR) analysis, the positive electrode active material may contain less than 1 mol% or 0 mol% of trivalent iron compound, based on a total of 100 mol% of divalent iron compound and trivalent iron compound.

[0039] XIV) According to another aspect of the present invention, a regenerated positive electrode active material is provided, which is represented by the following chemical formula 1 and consists of 99 mol% or more or 100 mol% single crystals.

[0040] [Chemical Formula 1]

[0041] Li 1-a M a Fe 1-b N b P 1-c X c O 4-d Y d

[0042] Wherein, M includes one or more elements selected from the group consisting of Nb, Al, Na, Ti, Zr and K; N includes one or more elements selected from the group consisting of Mo, V, Mn, Sm, Eu, Yb, Cu, Mg, Ni and Co; X includes Si; Y includes one or more elements selected from the group consisting of F, S and N; and a, b, c and d are respectively 0≤a<1, 0≤b<1, 0≤c<1, 0≤d<4.

[0043] According to another aspect of the present invention, a secondary battery is provided, which includes the regenerated positive electrode active material.

[0044] [Beneficial Effects]

[0045] According to the present invention, a method for regenerating positive electrode active materials is provided. In the method according to the present invention, a single-crystal structure is synthesized during the regeneration process, while ferric iron is converted to ferrous iron, resulting in no residual ferric iron in the regenerated positive electrode active material. Therefore, battery performance degradation can be prevented, lifetime characteristics can be excellent in high-voltage environments, thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced.

[0046] Furthermore, the present invention has the effect of providing a method for regenerating cathode active materials that significantly improves economic efficiency and productivity by directly regenerating cathode active materials in a simple and environmentally friendly manner without decomposition. Attached Figure Description

[0047] Figure 1 This is a diagram of the regenerated positive electrode active material in Examples 2 and Comparative Examples 3 and 4 of the present invention.

[0048] Figure 2 TEM images of the positive electrode active material regenerated in Example 1 and Comparative Examples 1 and 2.

[0049] Figure 3 TEM images and electron diffraction (EDP) images of the regenerated positive electrode active materials in Example 2 and Comparative Example 3 are shown.

[0050] Figure 4 TEM images and TEM-EDS surface scan images of the regenerated positive electrode active material in Comparative Example 4 are shown.

[0051] Figure 5 XRD patterns of the positive electrode active materials regenerated in Example 2 and Comparative Examples 3 and 4 are shown.

[0052] Figure 6 XPS plots of the regenerated positive electrode active materials in Example 2 and Comparative Examples 3 and 4 are shown.

[0053] Figure 7 EPR diagrams of the regenerated positive electrode active materials in Example 2 and Comparative Examples 3 and 4 are shown.

[0054] Figure 8 The graph shows the electrochemical performance (including rated voltage, energy capacity, CHC capacity retention and lifetime capacity at 45°C) of the regenerated positive electrode active materials in Comparative Example 1 and Comparative Examples 1 and 2.

[0055] Figure 9 The graph shows the electrochemical performance (including energy capacity and CHC capacity retention) of the regenerated or newly prepared positive electrode active materials in Comparative Examples 2, 3, and 4.

[0056] In the accompanying drawings, respectively, Ref represents Comparative Example 1, 700C represents Comparative Example 2, 800C represents Example 1, a) represents Example 2, b) represents Comparative Example 3, and c) represents Comparative Example 4. Detailed Implementation

[0057] The inventors have investigated a method for directly regenerating waste cathode materials to obtain cathode materials with excellent battery performance without decomposing the waste cathode materials (direct regeneration method). In their research, the inventors confirmed that when the atmosphere and temperature conditions are controlled during the steps of desorption from the waste cathode and recovery of the cathode active material, and the steps of coating the recovered cathode active material with a coating agent and calcining, a single-crystal structure is synthesized during the regeneration process of the cathode active material. Simultaneously, trivalent iron is converted to divalent iron, resulting in no residual trivalent iron in the regenerated cathode active material. Therefore, battery performance degradation is prevented, lifetime characteristics in high-voltage environments are excellent, thermal stability is improved, and the amount of gas generated during charging and discharging is reduced. Based on these results, the inventors conducted further research to complete this invention.

[0058] In this invention, the active material layer of the waste positive electrode may include positive electrode active material, adhesive and conductive material.

[0059] In this invention, "oxidizing atmosphere" can specifically refer to air or an atmosphere having an oxygen purity of 30% or more.

[0060] In this invention, unless otherwise stated, "trivalent iron compound" may include, but is not limited to, Li3Fe(PO4)3 and Fe2O3.

[0061] In this invention, the newly prepared positive electrode active material refers to a newly prepared positive electrode active material that is not obtained from the recycling of waste batteries or through the regeneration of waste batteries.

[0062] The positive electrode active material, the method for regenerating the positive electrode active material, and the secondary battery of the present invention will be described in detail below.

[0063] The terms and words used in this specification and the appended claims should not be construed as limited to their ordinary or dictionary meanings, but rather should be interpreted as having meanings and concepts consistent with the technical spirit of the invention in order to best describe the invention. Furthermore, since the configurations shown in the embodiments and drawings of this specification are merely implementations of the invention and do not represent all the technical spirit of the invention, it should be understood that many equivalents and variations exist that can replace the above-described configurations, and the invention can be arranged, substituted, combined, separated, or designed into various other configurations.

[0064] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0065] Regeneration methods for positive electrode active materials

[0066] The method for regenerating the positive electrode active material of the present invention includes: step (a) recovering the positive electrode active material by heat-treating a waste positive electrode, including a current collector and a layer of positive electrode active material formed on its surface, under an oxidizing atmosphere; step (b) adding a coating agent to the recovered positive electrode active material and calcining it under a reducing atmosphere to form a coating on the surface of the positive electrode active material, converting the trivalent iron compound in the positive electrode active material into a divalent iron compound, and converting polycrystalline particles into monocrystalline positive electrode active material; and step (c) controlling the particle size of the positive electrode active material by grinding the positive electrode active material with the coating formed and the trivalent iron compound converted into a divalent iron compound. In this case, the monocrystalline crystal structure can be restored, and the trivalent iron generated during the regeneration process can be completely converted into divalent iron. Therefore, excellent charging capacity, resistance characteristics, and capacity characteristics can be achieved.

[0067] The following sections will describe in detail each step of the regeneration method for the positive electrode active material.

[0068] (a) Recycling positive electrode active materials

[0069] In this invention, the method for regenerating the positive electrode active material includes the step of heating a waste positive electrode comprising a current collector and a layer of positive electrode active material formed thereon under an oxidizing atmosphere. In this case, recycling can be easily carried out, and the purity of the recycled positive electrode active material can be improved.

[0070] The waste positive electrode can preferably be a positive electrode separated from a used and discarded secondary battery, a defective positive electrode sheet or waste positive electrode generated during the secondary battery manufacturing process, or a positive electrode sheet or waste positive electrode after cutting. For example, in the case of positive electrode waste generated during the manufacturing process, excellent battery characteristics can be achieved because there is no lithium ion loss in the positive electrode active material.

[0071] The preferred choice for secondary batteries is lithium-ion batteries.

[0072] In this invention, the olivine structure is a crystal structure of the positive electrode active material, which is a 3D hexahedral lattice structure. In this structure, PO (phosphorus-oxygen) is strongly bonded, allowing the structure to be maintained even when all lithium ions are lost. Therefore, performance degradation due to charging and discharging can be prevented, and thermal stability can be excellent. Compared with other positive electrode active materials, positive electrode active materials with an olivine structure have disadvantages such as low energy density, low conductivity, and low lithium-ion diffusion; however, this positive electrode active material has a significant economic advantage because it uses inexpensive iron instead of expensive cobalt.

[0073] The olivine structure can be confirmed by measurement methods commonly practiced in the technical field to which this invention pertains, specifically by X-ray diffraction analysis (XRD).

[0074] For example, positive electrode active materials with an olivine structure may include compounds represented by the following chemical formula 1. In this case, high-temperature stability, lifetime characteristics, and economic efficiency can be excellent.

[0075] [Chemical Formula 1]

[0076] Li 1-a M a Fe 1-b N b P 1-c X c O 4-d Y d

[0077] In chemical formula 1, M includes one or more elements selected from the group consisting of Nb, Al, Na, Ti, Zr and K; N includes one or more elements selected from the group consisting of Mo, V, Mn, Sm, Eu, Yb, Cu, Mg, Ni and Co; X includes Si; Y includes one or more elements selected from the group consisting of F, S and N; and a, b, c and d are 0≤a<1, 0≤b<1, 0≤c<1 and 0≤d<4, respectively.

[0078] In chemical formula 1, a, b, c, and d can be 0≤a≤0.5, 0≤b≤0.5, 0≤c≤0.5, and 0≤d≤0.1, respectively.

[0079] The compound represented by chemical formula 1 is preferably lithium iron phosphate. In this case, high-temperature stability, lifetime characteristics, and economic efficiency can be excellent.

[0080] Lithium iron phosphate may preferably include LiFePO4 with an olivine structure. In this case, high-temperature stability, lifetime characteristics, and economic efficiency can be excellent.

[0081] For example, the conductive material can be a carbon-based conductive material, preferably carbon black, CNT, or a mixture thereof.

[0082] For example, the adhesive may be a polymer adhesive, preferably polyvinylidene fluoride (PVDF), acrylonitrile-butadiene rubber (NBR) or a mixture thereof, more preferably polyvinylidene fluoride.

[0083] For example, the active material layer of a spent positive electrode may include a solvent. The solvent can be used to mix the positive electrode active material, binder, and / or conductive material, and can be a solvent commonly used in the technical field to which this invention pertains. For example, the solvent may include one or more selected from the group consisting of dimethyl sulfoxide (DMSO), isopropanol, N-methyl-2-pyrrolidone (NMP), acetone, and water.

[0084] For example, the active material layer of a waste cathode may further include a dispersant.

[0085] For example, dispersants may include one or more selected from the group consisting of cellulose compounds, polyoxyethylene, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl ether, polyvinyl sulfonic acid, polyvinyl chloride (PVC), polyvinylidene fluoride, chitosan, starch, linear starch, polyacrylamide, poly-N-isopropylacrylamide, poly-N,N-dimethylacrylamide, polyethyleneimine, polyoxyethylene, poly(2-methoxyethoxyethylene), poly(acrylamide-co-diallyldimethylammonium chloride), acrylonitrile-butadiene-styrene (ABS) copolymer, acrylate-styrene-acrylonitrile (ASA) copolymer, a mixture of acrylate-styrene-acrylonitrile (ASA) copolymer and propylene carbonate, styrene-acrylonitrile (SAN) copolymer and methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) copolymer.

[0086] For example, step (a) of recovering positive electrode active material may include: a step (a1) of performing a primary heat treatment at 300–440°C in an oxidizing atmosphere; and a step (a2) of performing a secondary heat treatment at 500–650°C in an oxidizing atmosphere after the primary heat treatment. In this case, foreign matter such as binders and conductive materials contained in the active material of the waste positive electrode can be easily removed, and the positive electrode active material precursor can be recovered in high yield, which can be simply referred to as the "desorption process".

[0087] In this invention, the positive electrode active material precursor is proposed to distinguish it from the final regenerated positive electrode active material after desorption and calcination and grinding processes, and it refers to a material that can provide the final regenerated positive electrode active material through calcination and grinding processes.

[0088] There are no particular limitations on the heat treatment method, as long as the heat treatment method is a method commonly implemented in the technical field to which this invention pertains, and the heating rate and heating time can be appropriately adjusted as needed.

[0089] As a preferred example, step (a) of recovering the positive electrode active material may include a step (a1) of performing a primary heat treatment at 350–440°C in an oxidizing atmosphere; and a step (a2) of performing a secondary heat treatment at 520–630°C in an oxidizing atmosphere after the primary heat treatment. In this case, the primary heat treatment temperature may be lower than the secondary heat treatment temperature. Under these conditions, binders and conductive materials can be easily removed during the recovery of the positive electrode active material from the waste positive electrode. Furthermore, foreign matter such as aluminum introduced from the current collector can be easily removed. Therefore, high-purity positive electrode active material can be recovered.

[0090] As a preferred example, according to the present invention, after pre-desorption by oxidizing and heat-treating the waste positive electrode in a low-temperature range, the positive electrode active material powder containing the pre-desorbed positive electrode active material can be oxidized and heat-treated again at a high temperature to complete the desorption process. In this case, the amount of residual metal flowing out of the current collector can be significantly reduced without the need for a separate pretreatment process to separate or remove the current collector. Therefore, the purity of the positive electrode active material can be increased, and the process can be simplified.

[0091] More specifically, in the recovery process for desorbing and recycling positive electrode active materials from waste positive electrodes, heat treatment can be performed in two stages under predetermined temperature conditions and higher temperature conditions as described above. In this case, metallic foreign matter that may flow out from the current collector during the primary heat treatment process (primary desorption process) can be removed. Furthermore, during the secondary oxidation heat treatment process at high temperature (desorption process), carbonaceous foreign matter such as binders, conductive materials, and coatings on the surface of the positive electrode active material can be removed. Therefore, the amount of residual foreign matter other than the components constituting the positive electrode active material can be significantly reduced, thereby enabling the recovery of high-purity positive electrode active materials through a simple process.

[0092] Furthermore, for example, the positive electrode active material within the waste positive electrode can be coated with a coating agent containing metals and / or carbon. Typically, positive electrode active materials are coated with various coating agents containing metals and / or carbon for the purpose of improving battery performance. During the recovery of positive electrode active material from waste positive electrodes, the structure of this coating is destroyed, and when the positive electrode active material is reused in a battery without removing the coating, it may lead to degradation of battery performance. Therefore, when positive electrode active material within waste positive electrodes is coated, it is advantageous to remove the coating. In the secondary heat treatment step (a2), the carbon coating on the surface of the positive electrode active material can be removed. In this case, the purity of the recovered positive electrode active material can be increased, and battery performance degradation can be prevented.

[0093] For example, primary and secondary heat treatments can be carried out in an oxidizing atmosphere, including air or oxygen. In this case, foreign metallic substances introduced from the binder, conductive material, and current collector can be successfully removed, allowing the desired positive electrode active material to be recovered with high purity and high yield.

[0094] For example, the purity of the oxygen atmosphere can be 30% or more, or 50% or more, preferably 70% or more, more preferably 80% or more, even more preferably 90% or more, and even more preferably 90-99%. Within this range, the desired positive electrode active material can be recovered with high purity and high yield.

[0095] The purity (%) of oxygen can be expressed as volume % or mole % .

[0096] In this invention, the purity of oxygen can be measured using commonly used measurement methods in the technical field to which this invention pertains, without any particular limitation.

[0097] The primary heat treatment can preferably be carried out at 330–440°C, more preferably at 350–440°C, even more preferably at 360–440°C, and even more preferably at 360–420°C. Within this range, the purity and recovery rate of the positive electrode active material precursor can be significantly increased without excessive energy consumption.

[0098] For example, the heating rate can be 1 to 10 °C / min, preferably 2 to 9 °C / min, and more preferably 3 to 7 °C / min, until the primary heat treatment temperature is reached. Within this range, the desired positive electrode active material can be recovered with high purity and high yield.

[0099] For example, the heat treatment time can be from 30 minutes to 10 hours, preferably from 40 minutes to 8.5 hours, more preferably from 1 to 8 hours, and even more preferably from 3 to 6 hours. Within this range, the desired positive electrode active material can be recovered with high purity and high yield.

[0100] For example, in a primary heat treatment step (a1), the active material layer of the waste positive electrode can be separated from the current collector. During this process, a portion of the binder and conductive material contained in the positive electrode active material layer can be removed; however, some of the remaining binder and conductive material may remain in the positive electrode material pre-desorbed in the primary heat treatment step (a1). Therefore, the positive electrode material recovered in the primary heat treatment step (a1) may include the positive electrode active material, residual binder, and residual conductive material.

[0101] In a single heat treatment step (a1), the pre-desorbed cathode material can be recovered in powder form.

[0102] For example, the step of recovering the positive electrode active material can include a cooling step of the positive electrode active material powder recovered in the primary heat treatment step between the primary heat treatment step (a1) and the secondary heat treatment step (a2). In this case, by minimizing the mixing ratio of the metals constituting the current collector, the positive electrode active material precursor can be recovered with high purity and high yield. Furthermore, the crystallinity of the regenerated positive electrode active material obtained after the regeneration process can be increased. Therefore, when the regenerated positive electrode active material is used in a secondary battery, battery characteristics can be improved.

[0103] As a concrete example, cooling can be achieved through natural cooling by stopping the heat supply to the furnace undergoing a heat treatment and allowing the furnace to reach room temperature. In this case, subsequent processes can be easily carried out without additional energy consumption.

[0104] In this invention, room temperature refers to a point within 20±5℃.

[0105] The secondary heat treatment can be carried out at 500–650°C, preferably 520–630°C, more preferably 530–620°C, and even more preferably 520–610°C. Within this range, the purity and recovery rate of the positive electrode active material precursor can be significantly increased without excessive energy consumption.

[0106] For example, the heating rate can be 1 to 10 °C / min, preferably 5 to 10 °C / min, and more preferably 7 to 9 °C / min, until the secondary heat treatment temperature is reached. Within this range, the desired positive electrode active material can be recovered with high purity and high yield.

[0107] For example, the secondary heat treatment time can be 30 minutes to 10 hours, preferably 40 minutes to 8.5 hours, more preferably 1 to 8 hours, and even more preferably 3 to 6 hours. Within this range, the desired positive electrode active material can be recovered with high purity and high yield.

[0108] For example, after the secondary heat treatment is completed, the recovered positive electrode active material can be naturally cooled. In this case, the recovered positive electrode active material can be easily introduced into subsequent processes.

[0109] For example, after step (a) of recycling the positive electrode active material is completed, the recycled positive electrode active material (positive electrode active material precursor) may include compounds represented by Chemical Formula 1, preferably LFP-type positive electrode active materials, with specific examples being Fe2O3 and Li3Fe2(PO4)3. In this case, the residual amount of metallic foreign matter such as aluminum and carbon-like foreign matter can be significantly reduced through subsequent regeneration treatment, thereby providing high-purity regenerated positive electrode active material. The regenerated positive electrode active material has high purity. Therefore, when the regenerated positive electrode active material is used as the positive electrode active material in a secondary battery, excellent battery characteristics can be achieved.

[0110] In this invention, any LFP-type positive electrode active material that is generally defined or used in the technical field to which this invention pertains can be used as the LFP-type positive electrode active material, without any particular limitation.

[0111] For example, after step (a) of recovering the positive electrode active material is completed, the content of residual metals introduced from the current collector in the recovered positive electrode active material precursor can be less than 390 ppm, preferably less than 250 ppm, more preferably less than 240 ppm, even more preferably less than 230 ppm, and even more preferably less than 225 ppm, and there is no particular limitation on the lower limit of the content. In terms of the balance between the purity and recovery rate of the positive electrode active material and the process efficiency, the content of residual metals can be more than 10 ppm, or more than 50 ppm. In this case, high-purity positive electrode active material can be recovered.

[0112] There are no particular restrictions on the metal introduced from the current collector, as long as the metal is a metal commonly used in current collectors in the technical field to which this invention pertains, and as a specific example, it can be aluminum.

[0113] In this invention, as a method for measuring the content of metal elements, methods commonly practiced in the technical field to which this invention pertains can be used without particular limitation. As a specific example, the content of metal elements can be measured by ICP (inductively coupled plasma) analysis.

[0114] For example, after step (a) of recovering the positive electrode active material is completed, the carbon (C) content of the recovered positive electrode active material precursor can be less than 1.0% by weight, preferably less than 0.5% by weight, more preferably less than 0.1% by weight, even more preferably less than 0.08% by weight, and even more preferably less than 0.06% by weight, and there is no particular limitation on the lower limit. In terms of the balance between the purity and recovery rate of the positive electrode active material and the process efficiency, the carbon (C) content can be more than 0.001% by weight, or more than 0.01% by weight. In this case, high-purity positive electrode active material can be recovered.

[0115] In this invention, as a method for measuring carbon content, any method commonly practiced in the technical field to which this invention pertains can be used without particular limitation. As a specific example, a carbon / sulfur (CS) analyzer can be used to quantitatively measure carbon content.

[0116] (b) Restoring the divalent structure of the positive electrode active material to contain no trivalent iron compounds.

[0117] In this invention, the method for regenerating the positive electrode active material includes steps (b) of adding a coating agent to the recycled positive electrode active material and calcining it under a reducing atmosphere to form a coating on the surface of the positive electrode active material, converting the trivalent iron compounds in the positive electrode active material into divalent iron compounds, and converting polycrystalline particles into monocrystalline positive electrode active material. In this case, a coating can be formed on the particle surface of the regenerated positive electrode active material. Therefore, when the regenerated positive electrode active material is applied to a secondary battery, the battery's output characteristics, charging and discharging performance, and lifespan performance can be improved, and battery characteristics comparable to those when using newly manufactured positive electrode active material can be provided. Furthermore, since the crystal structure is similar to that of newly manufactured positive electrode active material before coating formation, restoring a divalent structure free of trivalent iron compounds, the coating can be uniformly formed on the particle surface, preventing particle agglomeration of the positive electrode active material and improving battery performance.

[0118] Step (b) may include: adding a coating agent to the recovered positive electrode active material (precursor) and pre-grinding it; spray-drying the pre-grinded positive electrode active material; and calcining the spray-dried positive electrode active material at 710–900°C in a reducing atmosphere. In this case, a coating with uniform particle size and uniform thickness can be formed. Furthermore, since the positive electrode active material contains ferrous compounds but not ferric compounds, a structure similar to the crystal structure of newly prepared positive electrode active material can be restored.

[0119] For example, the coating agent can be one or more of metals, organometals, and carbon components, preferably a coating agent that includes carbon components configured to form a carbon coating. In this case, battery characteristics can be further improved.

[0120] As the carbon component, any carbon component commonly used in the technical field to which this invention pertains can be used without any particular limitation. As a specific example, the carbon component may include one or more selected from the group consisting of sugars (e.g., sucrose, glucose, and fructose), graphite, and polyvinylidene fluoride, preferably sugars, more preferably sucrose. In this case, coating can be easily performed, and economic efficiency can be improved. Furthermore, when applied to batteries, battery characteristics can be significantly improved.

[0121] The 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, Nb, 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 this case, the resistivity and lifetime characteristics can be improved.

[0122] For example, a metal can be an oxide or acid that includes the metal as an element in its molecule.

[0123] As a metal-containing coating agent, commonly used metal-containing coating agents in the art to which this invention pertains can be used, without particular limitation. As a specific example, metal alkoxides can be used.

[0124] For example, as a coating agent, a coating agent solution obtained by mixing a metal, organometallic, or carbon component with a suitable solvent can be used. In this case, any commonly used solvent can be used without any particular limitation. As a specific example, an aqueous solvent, more specifically deionized water, can be used. Based on the total weight of the coating agent solution, the solid content in the coating agent solution can be less than 20% by weight, preferably 1 to 15% by weight, more preferably 2 to 10% by weight. In this case, the coating efficiency can be excellent, and the subsequent grinding process can proceed smoothly. Therefore, the coating finally formed on the particle surface of the positive electrode active material can be uniform.

[0125] As a method for applying a coating agent to a recycled positive electrode active material (precursor), coating methods commonly used in the art to which this invention pertains can be used without particular limitation. Specific examples include: liquid methods involving mixing the positive electrode active material and a liquid coating agent; mechanochemical methods utilizing high mechanical energy such as ball milling; fluidized bed coating methods; spray drying methods; precipitation methods where the coating agent is deposited onto the surface of the positive electrode active material in an aqueous solution; methods utilizing the reaction between a vapor-phase coating agent and the positive electrode active material; and sputtering.

[0126] The preferred method for drying the positive electrode active material coated with the coating agent is spray drying. In this case, a uniform coating can be formed, the agglomeration of the positive electrode active material particles can be prevented, and the coating process can be carried out smoothly, thereby achieving excellent productivity.

[0127] Spray drying can be performed using commonly used spray drying apparatuses in the technical field to which this invention pertains, without any particular limitations. For example, ultrasonic spray drying apparatuses, air nozzle spray drying apparatuses, ultrasonic nozzle spray drying apparatuses, filter-expanded droplet generating apparatuses, or electrostatic spray drying apparatuses can be used. As a specific example, the PSD-05 device (manufactured by Eugene Tech Co., Ltd.) can be used, but the invention is not limited thereto.

[0128] In addition, the amount of coating agent applied to the surface of the regenerated positive electrode active material can be considered to appropriately select the spray pressure and the supply rate of the coating agent solution.

[0129] After spray drying, the calcination of the coated positive electrode active material can be carried out in a reducing atmosphere at a temperature of 710–900°C, preferably 710–850°C, more preferably 710–800°C, and even more preferably 710–750°C. Under these conditions, the coating agent can be stably coated on the surface of the positive electrode active material while maintaining the inherent properties of the positive electrode active material. According to Examples 1 and 2 below, it can be confirmed that the calcination atmosphere and temperature conditions are variables that can restore the divalent structure without trivalent iron compounds and recover the single-crystal state of the active material.

[0130] The interior of the regenerated positive electrode active material according to the present invention and the interior of the regenerated positive electrode active material not according to the present invention are shown below. Figure 1 It is shown schematically in the middle.

[0131] The following Figure 1 This is a schematic diagram illustrating the positive electrode active material regenerated in Example 2 according to the present invention and the positive electrode active material regenerated in Comparative Examples 3 and 4 not according to the present invention. Figure 1 As shown in Comparative Example 4 on the right, when heat treatment was performed in an oxidizing atmosphere followed by calcination without a reducing atmosphere, ferric compounds were present inside. Furthermore, even when calcination was performed in a reducing atmosphere, the calcination temperature conditions were unsuitable. Figure 1 In Comparative Example 3, some ferric compounds remained without being converted into divalent iron compounds. On the other hand, under the heat treatment conditions and calcination temperature conditions according to the present invention… Figure 1 In Example 2 on the left, it was confirmed that all ferric compounds were converted into ferrous compounds.

[0132] For example, during calcination, the heating rate can be 1 to 20 °C / min, preferably 1 to 10 °C / min, and more preferably 2 to 7 °C / min, until the calcination temperature is reached. Within this range, the desired calcination effect can be sufficiently achieved.

[0133] For example, calcination can be carried out at the calcination temperature for 1 to 24 hours, preferably 1 to 16 hours, and more preferably 3 to 16 hours. Within this range, the desired calcination effect can be fully achieved.

[0134] For example, the reducing atmosphere can be an argon (Ar) or nitrogen (N2) atmosphere. As a preferred example, in the reducing atmosphere, the purity of the nitrogen can be 80% or more, preferably 90% or more, more preferably 90% to 99.8%, and even more preferably 95% to 99.8%. In this case, oxidation of the coating agent can be prevented during calcination, and a coating can be stably formed on the surface of the positive electrode active material.

[0135] The purity (%) of nitrogen can be expressed as volume % or molar %.

[0136] In this specification, the purity of nitrogen can be measured using measurement methods commonly used in the technical field to which this invention pertains, without any particular limitations.

[0137] For example, based on the total weight of the recycled positive electrode active material, including the weight of the coating, the amount of coating formed on the surface of the recycled positive electrode active material particles can be 0.1 to 15% by weight, preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, even more preferably 0.7 to 3% by weight, and even more preferably 0.8 to 2% by weight. Within this range, the desired coating effect can be sufficiently achieved.

[0138] The amount of coating formed on the surface of the regenerated positive electrode active material particles can be measured using measurement methods commonly used in the technical field to which this invention pertains, and as a specific example, it can be quantitatively measured by thermogravimetric analysis (TGA) or a carbon / sulfur (CS) analyzer.

[0139] The thickness of the coating formed on the surface of the regenerated positive electrode active material particles can be appropriately controlled according to the required coating amount. In this invention, the coating thickness can be measured using measurement methods commonly practiced in the art to which this invention pertains. For example, the long side diameter of 5 to 100 positive electrode active material particles can be measured using transmission electron microscopy (TEM) or scanning electron microscopy (SEM), and the arithmetic mean of the measurements can then be calculated to obtain the coating thickness.

[0140] For example, step (b) may include a pre-grinding step. In this case, by controlling the particle size within a predetermined range before the recycled positive electrode active material undergoes a subsequent regeneration process, the particle size and particle size distribution of the finally obtained recycled positive electrode active material can be uniformly controlled. Furthermore, by controlling the particles in a state conducive to restoring the crystal structure of the positive electrode active material in subsequent steps, battery characteristics can be significantly improved.

[0141] For example, pre-grinding can be performed using a ball mill, high-energy ball mill, vibratory mill, or roller mill, with a ball mill being preferred. In this case, the particle size distribution of the regenerated positive electrode active material can be easily controlled, and the average particle size of the finally obtained regenerated positive electrode active material can be easily controlled, which can be advantageous for restoring the crystal structure of the positive electrode active material in subsequent steps.

[0142] For example, pre-grinding can be performed for 2 to 24 hours, preferably 2 to 20 hours, and more preferably 5 to 16 hours. Within this range, the generation of fine particles can be suppressed, and the particle size distribution of the regenerated positive electrode active material can be smoothly controlled within a narrow range.

[0143] For example, pre-grinding can be performed at 50 to 500 rpm, preferably 100 to 450 rpm, more preferably 150 to 420 rpm, even more preferably 180 to 410 rpm, even more preferably 200 to 400 rpm, and even more preferably 250 to 320 rpm. In this case, the generation of fine particles can be suppressed, and the desired effect can be fully achieved while maintaining the crystal structure of the positive electrode active material.

[0144] After pre-grinding, the average particle size (D) of the obtained positive electrode active material powder is... 50 The particle size can be 0.3 to 0.7 μm, preferably 0.3 to 0.65 μm, more preferably 0.35 to 0.65 μm, even more preferably 0.4 to 0.6 μm, and even more preferably 0.45 to 0.55 μm. In this case, the occurrence of fine particles can be suppressed, and the particle size of the finally obtained regenerated positive electrode active material can be controlled within the desired range while maintaining the crystal structure of the positive electrode active material.

[0145] (c) Synthesis of single crystal particles

[0146] For example, the method for regenerating the positive electrode active material of the present invention may include step (c) of grinding the positive electrode active material whose divalent structure is restored and which does not contain trivalent iron compounds. In this case, agglomeration and particle breakage of the finally obtained regenerated positive electrode active material can be prevented, and the generation of fine particles can be prevented. Furthermore, since the particle size distribution is controlled within a narrow range, the positive electrode active material can be prepared as single-crystal particles. Therefore, battery performance degradation due to fine particles can be prevented, and the thermal stability and lifespan characteristics of the battery can be further improved. Moreover, when the regenerated positive electrode active material is finally used as the positive electrode of a secondary battery, it can provide battery characteristics equivalent to or better than those of a freshly made positive electrode active material.

[0147] For example, a single particle can be a particle composed of 30 or fewer nodules, preferably a particle composed of 1 to 20 nodules, more preferably a particle composed of 1 to 10 nodules, even more preferably a particle composed of 1 to 5 nodules, and most preferably a particle composed of 1 nodule. In this case, a positive electrode material can be provided that prevents battery performance degradation during electrode manufacturing and imparts high thermal stability and excellent lifespan characteristics to the battery.

[0148] In this invention, a nodule refers to a particle unit that constitutes a single particle, and can be a single crystal without grain boundaries, or a polycrystalline material that does not appear to have grain boundaries when observed using a scanning electron microscope (SEM) or electron backscatter diffraction (EBSD) at a field of view of 5,000 to 20,000 times.

[0149] In this invention, the number of nodules refers to the average number of nodules in the positive electrode active material particles. The positive electrode containing the positive electrode active material is cut using an ion milling method, and a cross-sectional image in the thickness direction of the cut positive electrode is obtained using a scanning electron microscope (SEM). Then, within the cross-sectional image, at least 30 particles are selected for both large-diameter and small-diameter positive electrode active material particles. The number of nodules in the cross-section of each positive electrode active material particle is then measured by SEM image analysis, and the arithmetic mean is calculated.

[0150] In this invention, secondary particles are aggregates formed by the aggregation of multiple single particles, and refer to particles containing more than 30 nodules.

[0151] For example, in step (c), a jet mill can be used for grinding. In this case, the particle size and particle distribution of the finally obtained regenerated positive electrode active material can be precisely controlled within a narrow range while preventing damage to the crystal structure of the positive electrode active material. Furthermore, since the inflow of foreign matter that may occur during the grinding process is prevented, the purity of the regenerated positive electrode active material can be increased.

[0152] For example, jet mills can operate in air or inert gas at temperatures ranging from -30°C to 30°C, preferably from -20°C to 20°C, and pressures from 0.8 to 10 bar. In this configuration, the particle size and particle distribution of the final regenerated positive electrode active material can be precisely controlled within a narrow range while preventing damage to the crystal structure of the positive electrode active material. Furthermore, the purity of the regenerated positive electrode active material can be improved by preventing the inflow of foreign matter that may occur during the grinding process.

[0153] In particular, it is preferable to use an inert gas that does not react with the regenerated positive electrode active material for jet milling, as this prevents the regeneration of ferric compounds through jet milling energy. For example, the inert gas can be argon (Ar), nitrogen (N2), etc.

[0154] More specifically, jet milling can be performed for less than 5 minutes under the following conditions: a feed line pressure of 2 to 8 bar, preferably 2.5 to 6 bar, more preferably 3 to 5 bar, and a milling line pressure of 0.8 to 2 bar, preferably 0.9 to 1.5 bar, more preferably 1 to 1.3 bar. Within this range, damage to the crystal structure of the positive electrode active material can be prevented, the particle size and particle distribution of the finally obtained regenerated positive electrode active material can be precisely controlled within a narrow range, and a single-particle structure can be easily achieved.

[0155] For example, in step (c), the average particle size (D) of the finally recovered recycled positive electrode active material is... 50The micrometer diameter (μm) can be from 0.6 to 3.0 μm, preferably from 0.7 to 2.0 μm, more preferably from 0.8 to 1.5 μm, even more preferably from 0.9 to 1.2 μm, and even more preferably from 0.955 to 1.255 μm. In this case, excellent battery characteristics can be achieved.

[0156] In this invention, the average particle size (D) of the positive electrode active material is used for measurement. 50 The method can use measurement methods commonly used in the technical field to which this invention pertains, without particular limitation. For example, the average particle size can be the average particle size based on the cumulative 50% standard of the particle size distribution measured using a laser diffraction method.

[0157] For example, in step (c), the crystal size of the recovered and regenerated positive electrode active material, as measured by X-ray diffraction (XRD), can be 120 to 180 nm, preferably 125 to 170 nm, more preferably 130 to 167 nm, even more preferably 140 to 166 nm, and even more preferably 150 to 165 nm. In this case, the structure of the regenerated positive electrode active material can be restored to that of the newly manufactured positive electrode active material, thereby providing excellent battery characteristics.

[0158] Furthermore, for example, in step (c), the cell volume of the finally recovered regenerated positive electrode active material, as measured by XRD, can be 291.00 to... Preferred 291.02 to More preferably 291.15 to In this case, the structure of the regenerated positive electrode active material can be restored to that of the newly manufactured positive electrode active material, thereby providing excellent battery characteristics.

[0159] Regenerated positive electrode active material

[0160] The regenerated positive electrode active material of the present invention is prepared using the regeneration method of the positive electrode active material of the present invention. In this case, environmental friendliness can be achieved, and a single-crystal structure can be obtained. Furthermore, by converting trivalent iron to divalent iron, no trivalent iron compounds remain in the regenerated positive electrode active material. Therefore, when the regenerated positive electrode active material is used as the positive electrode active material of a secondary battery, the battery's charge-discharge characteristics, cycle characteristics, lifetime characteristics, and thermal stability can be excellent, and the battery's high-temperature performance can be improved. Ultimately, the regenerated positive electrode active material of the present invention can provide battery characteristics comparable to or better than those of a secondary battery using a freshly prepared positive electrode active material.

[0161] For example, the recycled cathode active material can be a compound represented by chemical formula 1, preferably a lithium iron phosphate (LFP) type cathode active material, and more preferably LiFePO4 with an olivine structure. In this case, high-temperature stability, lifetime characteristics, and economic efficiency can be excellent.

[0162] [Chemical Formula 1]

[0163] Li 1-a M a Fe 1-b N b P 1-c X c O 4-d Y d

[0164] In chemical formula 1, M includes one or more elements selected from the group consisting of Nb, Al, Na, Ti, Zr and K; N includes one or more elements selected from the group consisting of Mo, V, Mn, Sm, Eu, Yb, Cu, Mg, Ni and Co; X includes Si; Y includes one or more elements selected from the group consisting of F, S and N; and a, b, c and d are 0≤a<1, 0≤b<1, 0≤c<1 and 0≤d<4, respectively.

[0165] In chemical formula 1, a, b, c, and d can be 0≤a≤0.5, 0≤b≤0.5, 0≤c≤0.5, and 0≤d≤0.1, respectively.

[0166] For example, as measured by XRD, regenerated cathode active materials can have crystal sizes of 120 to 180 nm and 291.00 to... The cell volume is [specifically, the crystal size]. Preferably, the crystal size can be 125 to 170 nm, more preferably 130 to 167 nm, even more preferably 140 to 166 nm, and even more preferably 150 to 165 nm. Preferably, the cell volume can be 291.02 to [specifically, the crystal size]. More preferably 291.15 to In this case, excellent battery characteristics can be provided.

[0167] The regenerated positive electrode active material is preferably a single particle in which no boundary layer is observed within the particle, more preferably a single particle formed solely by a single crystal, and does not include secondary particles. In this case, during the electrode manufacturing process, the positive electrode active material is transformed into a positive electrode active material containing only divalent iron compounds. Therefore, battery performance degradation can be prevented, lifetime characteristics in high-voltage environments can be excellent, thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced.

[0168] For example, the regenerated cathode active material can be a cathode active material composed of 99 mol% or more, or 100 mol% single crystals, preferably a compound represented by Chemical Formula 1, and more preferably a lithium iron phosphate compound. In this case, by synthesizing single crystal particles during the cathode active material regeneration process, the degradation of battery performance can be prevented, the life characteristics in high-voltage environments can be excellent, thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced.

[0169] As measured by XRD analysis or electron paramagnetic resonance (EPR) analysis, the regenerated cathode active material may contain less than 1 mol% or 0 mol% of ferrous and ferric compounds, more preferably 0 mol% of ferric compounds, based on a total of 100 mol% of ferrous and ferric compounds. In this case, by synthesizing cathode active material particles containing only ferrous compounds during electrode manufacturing, battery performance degradation can be prevented, lifetime characteristics in high-voltage environments can be excellent, thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced.

[0170] In this invention, mole % may be referred to as volume % if necessary.

[0171] For example, the fluorine (F) content of the regenerated positive electrode active material can be less than 250 mg / kg, preferably less than 200 mg / kg, and more preferably 10 to 200 mg / kg. Within this range, particle strength can be improved, and therefore, charging capacity, resistance characteristics, and capacity characteristics can be excellent.

[0172] In this invention, the fluorine (F) content can be measured using an ICP analyzer. A general-purpose ICP analyzer widely used in laboratories can be used, but there is no deviation depending on the measuring device or method.

[0173] For example, the average crystal size of the regenerated positive electrode active material can be 50 to 500 nm, preferably 50 to 300 nm, and more preferably 50 to 200 nm. Within this range, the conductivity of the regenerated positive electrode active material can be improved, thereby increasing battery life.

[0174] In this invention, the average crystal size can be measured by XRD crystal analysis, and there is no deviation depending on the measuring device or method. Specifically, 5g of positive electrode active material particles are placed in a support, irradiated with X-rays, and the resulting diffraction lattice is analyzed to obtain the average crystal size. At this time, according to the calculation method, the average crystal size of the primary particles of the positive electrode active material can be obtained from the full width at half maximum (FWHM) of the main peak or three or more peaks.

[0175] Furthermore, the regenerated positive electrode active material of the present invention comprises a lithium iron phosphate compound coated with a carbon-containing coating agent, and is characterized by the absence of peaks for trivalent iron compounds in XRD and electron paramagnetic resonance (EPR) analyses. In this case, battery performance such as charging capacity, resistance characteristics, and capacity characteristics can be excellent.

[0176] Secondary batteries

[0177] The secondary battery of the present invention includes a regenerated positive electrode active material. In this case, by completely converting the trivalent iron compound inside the regenerated positive electrode active material into a divalent iron compound and achieving a single crystal structure, the degradation of battery performance can be prevented, the life characteristics in high-voltage environments can be excellent, thermal stability can be improved, and the amount of gas generated during charging and discharging can be reduced.

[0178] The description of the secondary battery of the present invention may include all the descriptions of the above-described regenerated positive electrode active material and the method for regenerating the positive electrode active material, therefore, repeated descriptions are omitted in this specification.

[0179] The manufacturing method of the secondary battery according to the present invention is not particularly limited, as long as the method is a commonly used method for manufacturing lithium secondary batteries in the technical field to which the present invention pertains.

[0180] The invention will now be described in more detail with reference to the following preferred embodiments. However, these embodiments are provided for illustrative purposes only and should not be construed as limiting the scope and spirit of the invention. Furthermore, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention, and such changes and modifications are also within the scope of the appended claims.

[0181] Example

[0182] Example 1

[0183] On an aluminum current collector coated with a positive electrode active material layer including an LFP with an olivine structure, a binder, and a conductive material, the remaining positive electrode waste after punching the positive electrode plate is prepared. Then, the positive electrode waste is crushed into 2cm × 2cm pieces.

[0184] Then, the temperature is increased at a rate of 5°C / min under an oxygen atmosphere, followed by a heat treatment at 390°C for 5 hours. During this process, 95% pure oxygen is supplied at a rate of 3 L / min. The binder within the waste positive electrode is thermally decomposed, and the positive electrode active material powder separated from the current collector is recovered.

[0185] After the first heat treatment, heating was stopped, and the recovered positive electrode active material powder was completely cooled at room temperature. Then, it was heated again in air at a rate of 8°C / min, and the recovered positive electrode active material powder was heated at 580°C for 5 hours for a second heat treatment. Oxygen was supplied at a rate of 3 L / min during this process.

[0186] After the secondary heat treatment, heating was stopped, and the material was cooled to room temperature. Then, a coating composition (solvent: water) obtained by mixing sucrose in deionized water to achieve a carbon content of 4.4 parts by weight per 100 parts by weight of the positive electrode active material was added as a coating agent to the recovered positive electrode active material (precursor) powder. The powder was pre-milled using a ball mill at 300 rpm for 12 hours, and then the coated positive electrode active material was dried by spray drying. The average particle size (D) of the spray-dried positive electrode active material powder was... 50 The value is 0.5 μm.

[0187] In a furnace, the spray-dried positive electrode active material was heated at a heating rate of 3 °C / min under a nitrogen atmosphere, and then calcined at 800 °C for 12 hours to form a carbon (C) coating on the surface of the positive electrode active material. During calcination, the nitrogen supply rate was 3 L / min, and the coating amount after calcination, based on CS analysis, was 1.43% by weight.

[0188] The coated positive electrode active material was milled in air atmosphere using a jet mill at a feed line pressure of 4 bar and a grinding line pressure of 1 bar to obtain regenerated positive electrode active material with a final particle size of 200 to 1500 nm.

[0189] Example 2

[0190] The regenerated positive electrode active material was prepared in the same manner as in Example 1, except that it was ground in an inert argon (Ar) atmosphere using a jet mill at a feed line pressure of 4 bar and a grinding line pressure of 1 bar.

[0191] Comparative Example 1

[0192] The newly prepared LFP cathode active material was used instead of the regenerated cathode active material. Analysis of the newly prepared LFP cathode active material using ICP analysis confirmed that it was an LFP (LiFePO4) cathode active material with elemental ratios of Li / Fe: 1.06, Li / P: 1.00, and P / Fe: 1.06.

[0193] Comparative Example 2

[0194] Except for calcination at 700°C after spray drying, the regenerated positive electrode active material was prepared in the same manner as in Example 1.

[0195] Comparative Example 3

[0196] Except for calcination at 600°C after spray drying, the regenerated positive electrode active material was prepared in the same manner as in Example 2.

[0197] Comparative Example 4

[0198] In Example 2, only a secondary heat treatment step was performed to prepare the regenerated positive electrode active material.

[0199] [Test Case I: TEM Analysis]

[0200] TEM analysis was performed on the regenerated or newly prepared positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 4.

[0201] Specifically, scanning electron microscopy (SEM) images of the positive electrode active material were obtained using a TITAN G2 800-200, and the images are shown below. Figure 1 and Figure 2 As shown in the image.

[0202] Figure 1 TEM images of the regenerated or newly prepared positive electrode active materials obtained in Example 1 and Comparative Example 1 of the present invention are shown.

[0203] as follows Figure 1 As shown, when observing the carbon coating and its interface, Example 1 and Comparative Example 2 appear similar. However, in the electron diffraction (EDP) pattern on the right, when observing the spot structure (corresponding to a single-particle crystal structure) and the ring structure (corresponding to a multi-particle crystal structure), in Comparative Example 2, both the ring structure as a single-particle crystal structure and the spot structure as a multi-particle crystal structure are clearly observed simultaneously, indicating the coexistence of single crystals and polycrystalline structures. In the case of Example 1, only the spot structure as a single-particle crystal structure is observed, indicating that particles composed solely of single crystals were manufactured.

[0204] Based on these results, it is confirmed that the regeneration method of the present invention synthesizes single-particle regenerated positive electrode active materials with a single-crystal structure.

[0205] [Test Case II: TEM Analysis]

[0206] TEM analysis was performed on the regenerated or newly prepared positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 4.

[0207] Specifically, TEM images of the positive electrode active material were obtained using a TEM (TITAN G2 800-20) device.

[0208] The following Figure 3 TEM images and electron diffraction (EDP) images of the regenerated positive electrode active material in Example 2 and Comparative Example 3 of the present invention are shown below. Figure 4 TEM images and TEM-EDS surface scan images of the regenerated positive electrode active material in Comparative Example 4 are shown.

[0209] as follows Figure 3 As shown, in Example 2 and Comparative Example 3, Fe 3+ The reduction reaction occurred appropriately and no grain boundaries were observed. On the other hand, in Figure 4 In Comparative Example 4, grain boundaries can be confirmed because trivalent iron compounds (Fe2O3 and Li3Fe2(PO4)3) are present within the particles of the regenerated positive electrode active material.

[0210] Here, the similarity between the images of Example 2 and Comparative Example 3 is inferred to be due to the presence of local foreign matter (ferric compound) in Comparative Example 3 that is difficult to observe in TEM images.

[0211] I am Figure 4 In the TEM-EDS surface scan image of Comparative Example 4, a large amount of P was observed inside, and a large amount of Fe was observed on the particle surface. Here, P indicates the presence of the trivalent iron compound Li3Fe2(PO4)3, and it is inferred that the Fe at the surface sites is Fe2O3.

[0212] Therefore, in Comparative Example 4, since no reduction calcination process was performed, most of the ferric compounds existed as ferric oxide compounds, and a core / shell form was observed. According to Figure 3 The TEM-EDS surface scan images in Example 2 and Comparative Example 3 both show mixed shapes of P and Fe, which is inferred to be because most of the trivalent iron compounds (Li3Fe2(PO4)3 and Fe2O3) are reduced to the divalent iron compound LFP form.

[0213] [Test Case III: XRD Analysis]

[0214] XRD analysis was performed on the regenerated or newly prepared positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 4, and XRD patterns were obtained.

[0215] Specifically, next Figure 5 The XRD patterns of the regenerated positive electrode active materials of Example 2 and Comparative Examples 3 and 4 of the present invention are shown.

[0216] as follows Figure 5 As shown, in Example 2 and Comparative Examples 3 and 4 of the present invention, the reduction reaction from ferric compound to ferrous compound was carried out appropriately, and an XRD pattern consistent with that of freshly prepared LFP was obtained.

[0217] On the other hand, in the case of Comparative Example 4, it was confirmed that the reduction reaction from ferric compound to ferrous compound did not occur well, and thus Fe2O3 and Li3Fe2(PO4)3 were observed.

[0218] [Test Case IV: XPS Analysis]

[0219] XPS analysis was performed on the regenerated or newly prepared positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 4, and XPS plots were obtained.

[0220] Specifically, the following Figure 6 XPS plots of the regenerated positive electrode active materials of Example 2 and Comparative Examples 3 and 4 of the present invention are shown. O was analyzed by XPS analysis. 1s The differences.

[0221] As shown below Figure 6 As shown, no difference was found between the reference (freshly prepared LFP) and Comparative Example 3, which was inferred to be because the oxygen elements present in the positive electrode active material are located in the same crystal.

[0222] However, in Comparative Example 4, a shoulder was observed at around 530 eV. This is believed to be due to, as Figure 3 As shown in the EDP image, in Comparative Example 4, the outer surface of the particle is in the form of Fe2O3, and the interior of the particle has a core / shell form containing many Li3Fe2(PO4)3.

[0223] and Figure 5 Similar to XRD, when trace amounts of trivalent iron compounds are present in the newly prepared positive electrode active material of Comparative Example 1, they will not be observed by XPS. Therefore, the XPS analysis results of Example 2 and Comparative Example 3 are similar.

[0224] [Test Case V: EPR Analysis]

[0225] EPR analysis was performed on the regenerated or newly prepared positive electrode active materials obtained in Examples 1 and 2 and Comparative Examples 1 to 4, and EPR diagrams were obtained.

[0226] Specifically, next Figure 7 EPR diagrams of the regenerated positive electrode active materials of Example 2 and Comparative Examples 3 and 4 of the present invention are shown.

[0227] as follows Figure 7As shown, in Comparative Example 4, peaks caused by trivalent iron compounds present in Li3Fe2(PO4)3 and Fe2O3 were clearly observed.

[0228] However, no corresponding peak was observed in Example 2 because all the ferric compounds were reduced and converted into ferrous compounds.

[0229] Furthermore, unlike the XRD and XPS results, the EPR analysis showed a different slope shape in Comparative Example 3 compared to Example 2. This is believed to be because trace amounts of ferric compounds, which were not observed in XRD and XPS, remained in Comparative Example 3, resulting in a different slope shape in the EPR graph.

[0230] Based on these results, unlike Comparative Examples 3 and 4, in Example 2, complete conversion of the ferric compound was confirmed, and a regenerated positive electrode active material containing only ferrous compounds was prepared.

[0231] [Test Case VI: CHC Battery Evaluation]

[0232] The electrochemical performance of the regenerated or newly prepared cathode active materials obtained from Examples 1 and 2 and Comparative Examples 1 to 4 was evaluated using the CHC battery as described below.

[0233] *CHC Battery Evaluation: A slurry was prepared by mixing 97.5% by weight of regenerated or virgin positive electrode active material, 1% by weight of carbon black as a conductive material, and 1.5% by weight of PVDF as a binder with LFP. The slurry was then coated with aluminum foil to fabricate the positive electrode, followed by the fabrication of a battery (coin half-cell, CHC). The voltage was then set from 3V to 4.3V, and the battery was charged and discharged at 0.1C / 0.1C. Electrochemical performance (charge capacity, discharge capacity, and efficiency) was evaluated under conditions containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a weight ratio of 3:7, along with other additives, as the electrolyte.

[0234] The evaluation results are respectively in Figure 8 and 9 As shown in the image.

[0235] Down Figure 8 This is a graph comparing the electrochemical performance (e.g., rated voltage, energy capacity, CHC capacity retention, and lifetime capacity at 45°C) of the regenerated or newly prepared positive electrode active materials obtained in Example 1 and Comparative Examples 1 and 2. (Below) Figure 9 This is a graph comparing the electrochemical performance (e.g., energy capacity and CHC capacity retention) of the regenerated or newly prepared positive electrode active materials obtained in Example 2 and Comparative Examples 3 and 4.

[0236] as follows Figure 8As shown in the upper right figure, Example 1, marked with blue ink, exhibits a charge and discharge capacity that is superior to or equal to that of the newly prepared positive electrode active material of Comparative Example 1, marked with black ink, and the regenerated positive electrode active material of Comparative Example 2, marked with red ink.

[0237] as follows Figure 9 As shown, Example 2, marked with blue ink, exhibits superior battery characteristics compared to Comparative Example 3, which is marked with black ink. In particular, as... Figure 9 As shown in the lower right figure, Example 2 exhibits excellent high-temperature (45°C) life characteristics. In contrast, in Comparative Example 4, the high-temperature (45°C) life characteristics are so poor that it is difficult to measure the battery characteristics.

Claims

1. A method for regenerating a positive electrode active material, comprising the following steps: (a) Recovering positive electrode active material by heat treatment of waste positive electrode, including current collector and positive electrode active material layer formed on its surface, under an oxidizing atmosphere; (b) Adding a coating agent to the recovered positive electrode active material and calcining it under a reducing atmosphere to form a coating on the surface of the positive electrode active material, converting the trivalent iron compound in the positive electrode active material into a divalent iron compound, and converting the polycrystalline particles into a single crystal positive electrode active material; as well as (c) The particle size of the positive electrode active material is controlled by grinding the coated positive electrode active material, in which the trivalent iron compound is converted into a divalent iron compound.

2. The method as described in claim 1, wherein, Step (a) includes performing a heat treatment at 300–440°C in an oxidizing atmosphere; and performing a secondary heat treatment at 500–650°C in an oxidizing atmosphere after the primary heat treatment.

3. The method as described in claim 1, wherein, In step (a), the first heat treatment is performed for 30 minutes to 10 hours, and the second heat treatment is performed for 30 minutes to 10 hours.

4. The method of claim 1, wherein, Step (b) includes: adding the coating agent to the recovered positive electrode active material and pre-grinding it; spray-drying the pre-grinding positive electrode active material; and calcining the spray-dried positive electrode active material at 710–900°C in a reducing atmosphere.

5. The method as described in claim 1 or 4, wherein, The coating agent contains one or more of the following: metal, organometallic, and carbon components.

6. The method of claim 1 or 4, wherein, In step (b), calcination is carried out for 1 to 24 hours.

7. The method of claim 4, wherein, The pre-grinding is performed using a ball mill, high-energy ball mill, vibratory mill, or roller mill.

8. The method of claim 7, wherein, The pre-grinding is carried out at a stirring speed of 50 to 500 rpm for 2 to 24 hours.

9. The method of claim 1, wherein, In step (c), the grinding is performed using a jet mill.

10. The method of claim 1, wherein, The positive electrode active material is represented by the following chemical formula 1. [Chemical Formula 1] Li 1-a M a Iron 1-b N b P 1-c X c O 4-d Y d Wherein, M includes one or more elements selected from the group consisting of Nb, Al, Na, Ti, Zr and K; N includes one or more elements selected from the group consisting of Mo, V, Mn, Sm, Eu, Yb, Cu, Mg, Ni and Co; X includes Si; Y includes one or more elements selected from the group consisting of F, S and N; and a, b, c and d are respectively 0≤a<1, 0≤b<1, 0≤c<1, 0≤d<4.

11. The method of claim 1, wherein, The positive electrode active material is composed of 99 mol% or more or 100 mol% single crystals.

12. The method of claim 1, wherein, Based on XRD analysis or electron paramagnetic resonance (EPR) analysis, the positive electrode active material contains less than 1 mol% or 0 mol% of trivalent iron compounds, based on a total of 100 mol% of divalent and trivalent iron compounds.

13. A regenerated positive electrode active material, represented by the following chemical formula 1, and composed of 99 mol% or more or 100 mol% single crystals. [Chemical Formula 1] Li 1-a M a Iron 1-b N b P 1-c X c O 4-d Y d in, M includes one or more elements selected from the group consisting of Nb, Al, Na, Ti, Zr, and K; N includes one or more elements selected from the group consisting of Mo, V, Mn, Sm, Eu, Yb, Cu, Mg, Ni, and Co; X includes Si; Y includes one or more elements selected from the group consisting of F, S, and N; and a, b, c, and d are respectively 0≤a≤0.5, 0≤b≤0.5, 0≤c≤0.5, and 0≤d≤0.

1.

14. A secondary battery comprising the recycled positive electrode active material as described in claim 13.

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