Method for regenerating cathode active material and cathode active material regenerated thereby

Abstract

The present invention relates to a method for regenerating a cathode active material and a regenerated cathode active material regenerated thereby and, more specifically, to a method for regenerating a cathode active material, comprising the steps of: detaching a cathode active material from a waste cathode through heat treatment at a predetermined temperature; and milling the recovered cathode active material. Accordingly, the regenerated cathode active material may have a reduced specific surface area and reduced impurities derived from a coating agent such as carbon, and excellent electrical conductivity, and may provide excellent coating properties by lowering the viscosity of an electrode slurry comprising the regenerated cathode active material. When applied to a secondary battery, the cathode active material provides excellent battery characteristics, does not use a strong acid or an organic solvent and is therefore eco-friendly, and greatly improves economic feasibility and productivity since, through a simple process, the cathode active material can be regenerated as it is without decomposition of the cathode active material.

Description

Method for regenerating a positive electrode active material and a positive electrode active material regenerated therefrom

[0001] [Cross-reference with application(s)]

[0002] The present application claims the benefit of priority based on Korean Patent Application No. 10-2025-0015611 filed on February 7, 2025, and Korean Patent Application No. 10-2026-0023525 re-filed on February 5, 2026, based thereon, and all contents disclosed in the documents of said Korean patent applications are incorporated as part of this specification.

[0003] The present invention relates to a method for regenerating an anode active material and an anode active material regenerated therefrom. More specifically, the invention relates to a method for regenerating an anode active material that includes steps such as heat-treating the anode active material from a waste anode at a predetermined temperature to detach and recover it, and milling it under predetermined conditions, thereby reducing the specific surface area and impurities derived from the coating agent, such as carbon, of the regenerated anode active material, and providing excellent electrical conductivity, and having excellent coating properties due to the low viscosity of the electrode slurry containing the anode, and providing excellent battery characteristics when applied to a secondary battery, and is environmentally friendly as it does not use strong acids or organic solvents during the regeneration process, and can directly regenerate the waste anode active material without decomposing it through a simple regeneration process, thereby greatly improving economic efficiency and productivity.

[0004] The demand for lithium-ion batteries has continuously increased since the 1990s alongside the portable electronic device market, and has recently surged globally due to the rapid growth of the electric vehicle market. This could lead to instability in the supply and demand of lithium resources in the near future, and the continuous accumulation of end-of-life waste batteries could also cause significant environmental problems. To address these issues, the recycling of waste lithium-ion batteries is a critical technical challenge.

[0005] A lithium secondary battery is largely composed of a positive electrode in which a positive active material layer is coated on a metal foil such as aluminum, a negative electrode in which a negative active material layer is coated on a metal foil such as copper, a separator that prevents the positive and negative electrodes from mixing with each other, and an electrolyte that enables the movement of lithium ions between the positive and negative electrodes. The positive electrode is manufactured by applying a positive electrode composition, which includes a positive active material, a binder, a conductive material, and a solvent, onto a current collector made of a metal foil such as aluminum, drying it, and then pressure-molding it.

[0006] The cathode accounts for more than 60% of the cost of a lithium-ion battery, and active cathode 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 being applied as a high-capacity lithium-ion battery for electric vehicles due to its low unit cost and supply stability. Accordingly, research is being conducted on regeneration processing technologies to selectively recover valuable metals or directly recover cathode active materials from cathodes of lithium-ion batteries that are discarded after use or cathode scrap generated during the lithium-ion battery manufacturing process (hereinafter referred to as "waste cathodes").

[0007] However, due to the characteristics of the regenerated cathode active material, the particle size distribution is uneven and the crystal structure is unstable. Consequently, fine particles are easily generated due to particle breakage during the electrode manufacturing process, and thermal stability is poor, leading to problems such as degradation of battery performance, including lifespan characteristics, in high-voltage environments.

[0008] Meanwhile, conventional technologies for recovering valuable metals from spent anodes mostly involve dissolving the spent anode with hydrochloric acid, sulfuric acid, or nitric acid, then extracting the valuable metals with an organic solvent to use as raw materials for synthesizing active anode materials. However, methods using strong acids or organic solvents present problems such as environmental pollution and increased process costs. Furthermore, when recycled into active anode materials, the recovered metal components must undergo a process to be restored back into the active anode material, which results in reduced process efficiency. In particular, for lithium iron phosphate (LiFePO4), a wet method is mainly used to obtain Li, Fe, and P as compounds by using high concentrations of strong acids or strong bases to break down its very stable hexahedral crystal structure in order to recover valuable metals. However, this process generates a large amount of toxic wastewater, making it difficult to avoid environmental pollution problems, and subsequent processes are required to treat it, which increases production costs.

[0009] Therefore, recently, a direct recycling method for regenerating the active material from waste anodes without decomposing it has been actively researched, and about four main methods have been introduced, including calcination, solvent dissolution, aluminum foil dissolution, and crushing and screening.

[0010] However, while the above solvent dissolution method can obtain regenerated cathode active materials with a relatively clean surface, it has the disadvantage of poor stability because the solvent used to dissolve the binder, such as N-methyl-2-pyrrolidone (NMP), is a toxic gas and poses an explosion risk, and a high-cost solvent recovery process is required.

[0011] In addition, while the above-mentioned aluminum foil melting method offers good process stability, low process costs, and easy binder removal, it has disadvantages such as the generation of difficult-to-remove foreign substances on the surface of the regenerated cathode active material and the risk of explosion due to the generation of hydrogen gas during the aluminum foil removal process.

[0012] The above crushing and screening method has the advantage of being the simplest process, but it is difficult to completely separate the current collector and the positive active material, and it has the disadvantage that the particle size distribution of the positive active material changes during the crushing process and the binder remains, causing the battery characteristics of the regenerated positive active material to deteriorate.

[0013] Finally, although the calcination method is a simple process, it has the disadvantages of generating foreign substances on the surface of the regenerated cathode active material that degrade the output performance of the battery, generating waste gas, and consuming a large amount of energy. However, compared to other methods, it has the advantages of not generating toxic gases, having no risk of explosion, and having excellent battery characteristics. However, the above calcination method has a problem in that the specific surface area of ​​the regenerated cathode active material is large, so the viscosity of the electrode slurry containing the regenerated cathode active material, conductive material, binder, solvent, and dispersion medium is high, resulting in non-uniformity when coated on the current collector, which degrades the battery characteristics of the secondary battery.

[0014] Therefore, there is a need to develop a method for regenerating cathode active materials that improves the battery characteristics of secondary batteries by improving the coating properties of the electrode slurry containing the material on the current collector, while regenerating the cathode active material from waste cathodes without decomposing it so that no metal elements are wasted.

[0015] In order to solve the problems of the prior art as described above, the present invention aims to provide a method for regenerating an anode active material that includes steps such as heat-treating the anode active material from a waste anode at a predetermined temperature to detach and recover it, and milling it under predetermined conditions, thereby reducing the specific surface area and impurities derived from the coating agent, such as carbon, of the regenerated anode active material and providing excellent electrical conductivity, lowering the viscosity of the electrode slurry containing it to provide excellent coating properties, and providing excellent battery characteristics when applied to a secondary battery, and is also environmentally friendly as it does not use strong acids or organic solvents, and directly regenerates the anode active material without decomposing it through a simple process, thereby greatly improving economic efficiency and productivity.

[0016] In addition, the present invention aims to provide a regenerated cathode active material that can provide excellent battery characteristics when applied to a secondary battery by reducing the specific surface area and impurities derived from the coating agent, such as carbon, and restoring the structure to a fresh cathode active material, and a secondary battery including the same.

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

[0018] To achieve the above objective, the present invention provides a method for regenerating an anode active material, characterized by comprising: (a) a step of heat-treating a waste anode, on which an anode active material layer comprising an olivine structure is coated on a current collector, at 450 to 740°C for 3 to 7 hours under an oxidizing atmosphere to detach the anode active material from the current collector; (b) a step of preparing an anode active material slurry by first milling the detached anode active material under the addition of a coating agent; (c) a step of drying and calcining the prepared anode active material slurry; and (d) a step of secondarily milling the calcined anode active material.

[0019] II) In the above I), the positive active material having the olivine structure may be a compound represented by the following chemical formula 1.

[0020] [Chemical Formula 1]

[0021]

[0022] (In the above chemical formula 1, M comprises one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are each -0.5≤a≤0.5, 0≤b≤0.5, and 0≤c≤0.1.)

[0023] III) In I) or II) above, the positive electrode active material having the olivine structure may include lithium iron phosphate.

[0024] IV) In the above I) to III), the anode active material detached after heat treatment in step (a) has a specific surface area (BET) of 3.6 m² 2 It may be less than / g.

[0025] V) In the above I) to IV), after the first milling in step (b), the anode active material has an average particle size (D 50 ) It can be 0.3 to 0.5 μm.

[0026] Average particle size (D of the positive active material in step (b) above) 50 ) is, for example, the average particle size (D) measured in the slurry state. 50 ) may be, in this case, the coating agent is in liquid form and the average particle size (D) of the positive electrode active material 50 ) does not affect the size.

[0027] VI) In the above I) to V), the primary milling in step (b) may be performed using a ball mill, a high-energy ball mill, a vibratory mill, or a roll mill.

[0028] VII) In the above I) to VI), the coating agent in step (b) may include one or more selected from the group consisting of metal, organometal, and carbon components.

[0029] VIII) In the above I) to VII), the above step (c) may include: a step (c1) of spray-drying the positive active material slurry of the above step (b); and a step (c2) of forming a coating layer on the positive active material by calcining the dried positive active material at 500 to 900 ℃ under a reducing atmosphere.

[0030] IX) In the above I) to VIII), after secondary milling in step (d), the positive active material has an average particle size (D 50 ) It can be 0.80 to 1.73㎛.

[0031] X) In the above I) to IX), the secondary milling in step (d) can be performed using a jet mill.

[0032] XI) In the above I) to X), the positive active material after secondary milling in step (d) may include single particles.

[0033] XII) In the above I) to XI), the positive active material after secondary milling in step (d) is I measured by Raman spectrum analysis D / I G The peak ratio may be 0.950 or less.

[0034] In addition, XIII) The present invention is based on the following chemical formula 1

[0035] [Chemical Formula 1]

[0036]

[0037] A compound represented by (in the above Chemical Formula 1, M comprises one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are each -0.5≤a≤0.5, 0≤b≤0.5, and 0≤c≤0.1), having an olivine structure, and I as measured by Raman spectrum analysis D / I G The present invention provides a regenerated cathode active material characterized by a peak ratio of 0.950 or less.

[0038] XIV) In the above XIII), the regenerated cathode active material has an a-axis lattice constant of 10.3275 to 10.3293 Å and a c-axis lattice constant of 4.6912 to 4.6920 Å as measured by X-ray diffraction analysis (XRD), and a cell volume of 291.00 to 291.15 Å. 3 and the grain size may be 118 to 170 nm.

[0039] XV) In the above XII) or XIV), the regenerated positive electrode active material may include a single particle.

[0040] XVI) In the above XII) or XV), the regenerated positive active material may have an area ratio of the positive active material peak to the total sum of the positive active material peak, D1 peak, D2 peak, D3 peak, and G peak areas obtained by fitting the Raman spectrum of the positive active material peak, which is 0.010 or less.

[0041] Additionally, XVII) The present invention provides a secondary battery characterized by comprising a regenerated positive electrode active material according to any one of claims I) to XVI).

[0042] According to the present invention, the positive electrode active material regenerated from the waste positive electrode has a reduced specific surface area and impurities derived from the coating agent, such as carbon, and has excellent electrical conductivity. It also has excellent coating properties for current collectors by lowering the viscosity of the electrode slurry containing it, and provides excellent battery characteristics when applied to a secondary battery. Furthermore, since the positive electrode active material is regenerated directly without decomposing it in a simple and eco-friendly manner, it has the effect of providing a method for regenerating a positive electrode active material that significantly improves economic efficiency and productivity.

[0043] In addition, it is environmentally friendly as it does not use acid, and process costs are reduced because neutralization and wastewater treatment are not required. Furthermore, it provides a method for regenerating cathode active materials that is directly regenerated without decomposing the waste material, thereby eliminating wasted metal elements, and does not use organic solvents, thus eliminating the generation of toxic gases and the risk of explosion.

[0044] In addition, the regenerated positive electrode active material has a reduced specific surface area and impurities derived from coating agents such as carbon, has excellent electrical conductivity, and lowers the viscosity of the electrode slurry containing it to provide excellent coating properties for current collectors, and provides excellent battery characteristics when applied to a secondary battery, and has the effect of providing a regenerated positive electrode active material and a secondary battery containing it.

[0045] Figure 1 is the result of pattern analysis through X-ray diffraction (XRD) of the regenerated cathode active material or fresh cathode active material prepared in Examples 1, 3, 4 and Reference Example.

[0046] FIG. 2 is a graph showing the viscosity of the regenerated cathode active material or fresh cathode active material prepared in Examples 1, 3, 4 and Reference Example.

[0047] Figure 3 is an SEM image of the regenerated cathode active material prepared in Example 1.

[0048] Figure 4 is an SEM image of the regenerated cathode active material prepared in Example 4.

[0049] Figure 5 is a graph showing the results of the Raman spectrum analysis of the fresh cathode active material prepared in the reference example.

[0050] Figure 6 is a graph showing the positive active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained by fitting the Raman spectrum of Figure 5 below.

[0051] Figure 7 is a graph measuring the CHC performance of the regenerated cathode active material or fresh cathode active material prepared in Example 4 and the reference example.

[0052] FIG. 8 is a graph showing the capacity of the regenerated cathode active material or fresh cathode active material according to the number of cycles prepared in Example 4 and the reference example.

[0053] While researching a method to directly regenerate a positive active material from a waste cathode containing a positive active material having an olivine structure without decomposing the positive active material, the inventors confirmed that when the method appropriately includes a step of heat-treating the waste cathode in an oxidizing atmosphere within a predetermined temperature and time range to detach the positive active material and a step of milling the recovered positive active material, the specific surface area of ​​the regenerated positive active material and impurities derived from the coating agent, such as carbon, are reduced, the electrical conductivity is excellent, and the viscosity of the electrode slurry containing it is lowered so that it is uniformly coated on the current collector, thereby improving battery characteristics when applied to a secondary battery. Based on this, they further devoted themselves to research and completed the present invention.

[0054]

[0055] Below, the method for regenerating the positive active material described herein is examined in detail, divided into steps.

[0056] However, terms and words used in this specification and claims cannot be interpreted as being limited to their ordinary or dictionary meanings, and must be interpreted in a meaning and concept consistent with the technical spirit of the invention, based on the principle that the inventor may appropriately define the concept of the terms to best describe his application. Accordingly, it should be understood that the embodiments described in this specification and the configurations illustrated in the drawings are merely one embodiment of the invention and do not represent all of the technical spirit of the invention, and that there may be various equivalents and modifications that can replace them, and that they may be arranged, replaced, combined, separated, or designed into various other configurations.

[0057] All technical and scientific terms used in this description have the same meaning as commonly understood by those skilled in the art to which the present invention belongs, unless otherwise defined.

[0058]

[0059] Method for regenerating positive electrode active material

[0060] The method for regenerating a positive electrode active material according to the present invention comprises: (a) a step of heat-treating a waste positive electrode, on which a layer of positive electrode active material including a positive electrode active material having an olivine structure is coated on a current collector, at 450 to 740°C for 3 to 7 hours under an oxidizing atmosphere to detach the positive electrode active material from the current collector; (b) a step of preparing a positive electrode active material slurry by first milling the detached positive electrode active material under the addition of a coating agent; (c) a step of drying and calcining the prepared positive electrode active material slurry; and (d) a step of secondarily milling the calcined positive electrode active material. In this case, the specific surface area of ​​the regenerated positive electrode active material and impurities derived from the coating agent, such as carbon, are reduced, and the electrical conductivity is excellent. Furthermore, the viscosity of the electrode slurry containing the same is lowered to provide excellent coating properties, and when applied to a secondary battery, it provides excellent battery characteristics. Additionally, since the positive electrode active material can be regenerated as is without decomposing it in a simple and eco-friendly manner, there are advantages that economic efficiency and productivity are greatly improved.

[0061]

[0062] In the above description, the positive active material layer of the waste positive electrode applied in step (a) may include a positive active material, a binder, and a conductive material.

[0063] In this description, "oxidizing atmosphere" may specifically be an air atmosphere or an atmosphere with an oxygen purity of 30% or more.

[0064] In this specification, "fresh" cathode active material refers to a cathode active material manufactured by novel synthesis, rather than one obtained by recovery and regeneration from spent batteries.

[0065] In the present invention, the electrode slurry is a liquid mixture comprising a positive active material, a conductive material, a binder, a solvent, and / or optionally a dispersant, and is applied to a current collector to form an electrode.

[0066]

[0067] (a) Heat treatment step

[0068] In the present invention, the method for recovering a positive active material comprises the step of (a) heat-treating a waste positive electrode coated with a layer of positive active material having an olivine structure on a current collector at 450 to 740°C for 3 to 7 hours in an oxidizing atmosphere to detach the positive active material from the current collector, wherein the specific surface area of ​​the recovered and detached positive active material and impurities derived from the coating agent, such as carbon, are reduced and the electrical conductivity is excellent, and the viscosity of the electrode slurry containing it is lowered so that the coating properties on the current collector are excellent and the battery characteristics of the secondary battery are excellent.

[0069]

[0070] The above-mentioned waste anode may preferably be an anode separated from a secondary battery that has been discarded after use, or an anode sheet or anode scrap discarded after cutting or defects generated during the secondary battery manufacturing process. For example, in the case of anode scrap generated during the manufacturing process, there is an advantage in that there is no loss of lithium ions within the anode active material, thereby enabling the realization of better battery characteristics.

[0071] The above secondary battery may preferably be a lithium secondary battery.

[0072]

[0073] In this description, the olivine structure is a type of crystal structure of the cathode active material, having a hexahedron-shaped lattice structure in a 3D form. Since PO (phosphorus-oxygen) is strongly bonded, the structure can be maintained even if all lithium ions are removed, resulting in minimal performance degradation due to charging and discharging and excellent thermal stability. Additionally, although the olivine structure has the disadvantages of having a lower energy density compared to other cathode active materials and low electrical conductivity and lithium ion diffusivity, it offers significant economic advantages because it uses inexpensive iron instead of expensive cobalt.

[0074] The above olivine structure can be verified by methods generally practiced in the technical field to which the present invention belongs, and as a specific example, can be verified through X-ray diffraction analysis (XRD).

[0075]

[0076] The positive electrode active material having the above olivine structure may be, for example, a compound represented by the following chemical formula 1, and in this case, it has excellent high-temperature stability and lifespan characteristics, and has the advantage of being economical since it does not need to contain expensive rare metals such as cobalt and nickel.

[0077] [Chemical Formula 1]

[0078]

[0079] (In the above chemical formula 1, M comprises one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are each -0.5≤a≤0.5, 0≤b≤0.5, and 0≤c≤0.1.)

[0080] The positive electrode active material having the above olivine structure may preferably include lithium iron phosphate (LiFePO4), in which case it has excellent high-temperature stability and lifespan characteristics, and has the advantage of being economical since it does not need to include expensive rare metals such as cobalt and nickel.

[0081]

[0082] The above conductive material may be, for example, a carbon-based conductive material, and preferably carbon black, CNT, or a mixture thereof.

[0083] 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.

[0084] The positive active material layer of the above-mentioned waste positive electrode may be manufactured by including, for example, a solvent, and the solvent may be a solvent generally used in the technical field to which the present invention belongs for mixing the positive active material, binder, and / or conductive material.

[0085] The above solvent may be, for example, one or more selected from the group consisting of dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methyl-2-pyrrolidone (NMP), acetone, and water.

[0086] The anode active material layer of the above-mentioned waste anode may be manufactured by further including, for example, a dispersant.

[0087] The above dispersant is, for example, a cellulose-based compound, polyalkylene oxide, polyvinyl alcohol, polyvinylpyrrolidone, polyvinyl acetal, polyvinyl ether, polyvinylsulfonic acid, polyvinyl chloride (PVC), polyvinylidene fluoride, chitosans, starch, amylose, 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) It may be one or more selected from the group consisting of copolymers and methyl methacrylate-acrylonitrile-butadiene-styrene (MABS) copolymers.

[0088]

[0089] The above heat treatment temperature may be, for example, 450 to 740 ℃, preferably 490 to 740 ℃, more preferably 510 to 740 ℃, even more preferably 560 to 720 ℃, particularly preferably 600 to 720 ℃, and particularly more preferably 650 to 710 ℃. Within this range, foreign substances such as binders and conductive materials contained in the positive active material of the waste positive electrode are removed, and the positive active material can be recovered through regeneration treatment to form a positive active material, which can be simply referred to as a 'de-removal process'. Furthermore, the positive active material recovered through the above heat treatment has a small specific surface area, impurities derived from coating agents such as carbon are cleanly removed, and has excellent electrical conductivity. It also lowers the viscosity of the electrode slurry containing it, resulting in excellent coating properties for the current collector and excellent battery characteristics when applied to a secondary battery.

[0090]

[0091] The above heat treatment time may be, for example, 3 to 7 hours, preferably 4 to 6 hours, and more preferably 4.5 to 5.5 hours. Within this range, the specific surface area, viscosity, and impurities derived from the coating agent, such as carbon, of the positive electrode active material are reduced, and the electrical conductivity is excellent. Additionally, the viscosity of the electrode slurry containing it is lowered, resulting in excellent coating properties for the current collector and providing the advantage of providing excellent battery characteristics when applied to a secondary battery.

[0092]

[0093] The positive active material in the above-mentioned waste cathode may be coated with a coating agent containing, for example, metal and / or carbon. In the field of secondary batteries, positive active materials are often coated with various coating agents containing metal and / or carbon to improve battery performance. However, if the structure of such coating layers is destroyed during the process of recovering the positive active material from the waste cathode and the material is reused in the battery without removing it, it may cause a degradation in battery performance. Therefore, if the positive active material in the above-mentioned waste cathode is coated with a coating agent, it is advantageous to remove it. In the heat treatment step according to the present invention, the coating agent, such as carbon, on the surface of the positive active material can be cleanly removed, and the specific surface area is reduced, so the electrode slurry containing it has a lower viscosity and is uniformly coated on the current collector, thereby providing the advantage of excellent battery performance in the secondary battery.

[0094]

[0095] The above heat treatment can be performed, for example, under an air or oxygen atmosphere, and in this case, foreign substances such as metal introduced from the binder, conductive material, and current collector are smoothly removed, which has the advantage of enabling the recovery of the desired regenerated cathode active material with high purity and high yield.

[0096] The above oxygen atmosphere may, for example, have a purity of oxygen of 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 to 99%, and within this range, there is an advantage of being able to recover the desired regenerated cathode active material with high purity and high yield.

[0097] The purity % of the above oxygen may be volume % or mol %.

[0098] The purity of the oxygen described herein is not particularly limited when measured by a measurement method commonly used in the technical field to which the present invention belongs.

[0099]

[0100] The heating rate to reach the above heat treatment temperature may be, for example, 1 to 10 ℃ / min, preferably 2 to 9 ℃ / min, and more preferably 3 to 7 ℃ / min, and within this range, there is an advantage of being able to recover the desired regenerated cathode active material with high purity and high yield.

[0101] The cathode material detached in the above heat treatment step can be recovered, for example, in the form of powder.

[0102]

[0103] The anode active material recovered after the above heat treatment is completed can be naturally cooled, for example, and in this case, there is an advantage in that it is easy to feed into a subsequent process.

[0104]

[0105] In the above (a) heat treatment step, for example, after the heat treatment is completed, foreign substances can be removed from the waste anode and high-purity anode active material powder can be obtained.

[0106]

[0107] The cathode active material recovered after the completion of the heat treatment step (a) above may preferably be composed of components capable of providing the above-mentioned chemical formula 1 or lithium iron phosphate (LFP)-based cathode active material, and as a specific example, may include Fe2O3 and Li3Fe2(PO4)3. In this case, through subsequent regeneration treatment, a high-purity regenerated cathode active material can be provided in which the residual amount of metallic impurities such as aluminum and carbon-based impurities is significantly reduced. The regenerated cathode active material has high purity and can provide good battery characteristics when applied as a cathode active material for a secondary battery.

[0108]

[0109] After the completion of the heat treatment step (a) above, the recovered cathode active material has, for example, a specific surface area (BET) of 3.6 m² 2 / g or less, preferably 3.2 m 2 / g or less, more preferably 3.0 m 2 / g or less, more preferably 2.5 m 2 / g or less, particularly preferably 2.0 m 2 It may be / g or less, and particularly more preferably 1.7 to 2.0 m 2 / g, most preferably 1.8 to 2.0 m 2 It can be / g, and within this range, when the positive active material is prepared as an electrode slurry, the interaction with the binder and solvent is reduced, resulting in lower viscosity and excellent coating properties on the current collector, and the secondary battery to which this is applied has the advantage of excellent battery characteristics.

[0110]

[0111] After the completion of the heat treatment step (a) above, the recovered positive active material may, for example, have a mean pore diameter of 32 nm or less, preferably 30 nm or less, more preferably 28 nm or less, even more preferably 26 nm or less, and even more preferably 22 to 26 nm. Within this range, the viscosity of the electrode slurry is lowered to provide excellent coating properties for the current collector, and the secondary battery to which this is applied has the advantage of having excellent battery characteristics.

[0112]

[0113] After the completion of the heat treatment step (a) above, the recovered cathode active material has, for example, a total pore volume of 0.027 cm 3 / g or less, preferably 0.025 cm 3 / g or less, more preferably 0.021 cm 3 / g or less, more preferably 0.017 to 0.021 cm 3 / g, more preferably 0.018 to 0.020 cm 3 It can be / g, and within this range, the viscosity of the electrode slurry is lowered to provide excellent coating properties on the current collector, and the secondary battery to which this is applied has the advantage of excellent battery characteristics.

[0114] In this description, the specific surface area (BET), mean pore diameter, and total pore volume can be measured using measurement methods commonly used in the technical field to which the present invention belongs, for example, by the BET (Brunauer-Emmett-Teller) method, and specifically, can be calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using BEL Japan's BELSORP-mino II.

[0115]

[0116] After the completion of the heat treatment step (a) above, the recovered cathode active material may, for example, have a carbon (C) element content of 1.0 wt% or less, preferably 0.7 wt% or less, more preferably 0.5 wt% or less, even more preferably 0.3 wt% or less, even more preferably 0.2 wt% or less, and particularly preferably 0.1 wt% or less. The lower limit thereof is not particularly limited, but may be 0.001 wt% or more or 0.01 wt% or more in terms of the balance between the purity and recovery rate of the cathode active material and process efficiency. In this case, it is possible to recover a high-purity cathode active material, and there is an advantage of lowering the viscosity of the electrode slurry.

[0117] In this description, the measurement of carbon element content is not particularly limited to methods commonly practiced in the technical field to which the present invention belongs, and as a specific example, it can be measured by quantitative analysis using a CS analyzer (Carbon / Sulfur Determinator).

[0118]

[0119] (b) 1st milling step

[0120] The method for regenerating a positive electrode active material according to the present invention includes the step of (b) milling the detached positive electrode active material under the addition of a coating agent to produce a positive electrode active material slurry, and by controlling the particle size within a predetermined range before introducing the positive electrode active material recovered by detachment in this manner into a subsequent regeneration process, the particle size and particle size distribution of the finally obtained regenerated positive electrode active material are evenly controlled, and the particles are controlled in a state favorable for restoring the crystal structure of the regenerated positive electrode active material in a subsequent step, thereby having the advantage of significantly improving battery characteristics.

[0121] The above first milling may be, for example, wet milling, in which case the coating agent is evenly dispersed in the positive active material by a solvent such as water, and spraying is facilitated, which has the advantage of uniformly coating the carbon component on the regenerated positive active material during the subsequent drying and firing stages.

[0122]

[0123] The milling in step (b) above can preferably be performed using a ball mill, a high-energy ball mill, a vibrating mill, or a roll mill, and more preferably a ball mill. In this case, it is easy to control the particle size distribution of the positive electrode active material and the average particle size of the finally obtained regenerated positive electrode active material, and there is an advantage in restoring the crystal structure of the regenerated positive electrode active material obtained in a subsequent step.

[0124]

[0125] The milling of step (b) above can be performed, for example, for 2 to 20 hours using a ball mill such as the one above, preferably for 4 to 18 hours, more preferably for 4.5 to 16 hours, even more preferably for 5 to 13 hours, even more preferably for 6 to 12 hours, and particularly preferably for 8 to 10 hours. Within this range, there is an advantage of suppressing the generation of fine particles and smoothly controlling the particle size distribution of the regenerated cathode active material within a narrow range.

[0126]

[0127] The milling of step (b) above can be performed, for example, under conditions of 100 to 500 rpm, preferably 150 to 450 rpm, more preferably 180 to 420 rpm, even more preferably 190 to 410 rpm, even more preferably 200 to 400 rpm, and particularly more preferably 250 to 320 rpm. In this case, there is an advantage that the desired effect can be sufficiently expressed while suppressing the generation of fine particles and maintaining the crystal structure of the positive active material.

[0128]

[0129] The average particle size (D of the positive active material powder obtained after milling in step (b) above) 50 The particle size can be, for example, 0.3 to 0.5 μm, preferably 0.3 to 0.45 μm, more preferably 0.34 to 0.40 μm, and even more preferably 0.36 to 0.40 μm. In this case, there is an advantage in that the particle size of the finally obtained regenerated cathode active material can be controlled within a desired range while suppressing the generation of fine particles and maintaining the crystal structure of the cathode active material.

[0130] In this description, the average particle size (D of the positive electrode active material) 50 The measurement method of ) is not particularly limited to measurement methods commonly practiced in the technical field to which the present invention belongs, and, for example, may be the average particle diameter at the cumulative 50% standard of the particle diameter distribution measured using laser diffraction.

[0131]

[0132] The average particle size of the positive active material powder obtained after milling in step (b) above can be measured using a slurry of detached positive active material and coating agent formed through milling in step (b). Since the slurry is a physical mixture of the positive active material and the liquid coating agent and a coating layer has not yet been formed on the surface of the positive material, the average particle size of the positive active material measured by taking a sample from the slurry can be considered as the particle size of the positive active material.

[0133]

[0134] In addition to the conditions described above, other milling conditions are not particularly limited as long as they are milling conditions commonly employed in the technical field to which the present invention belongs. For example, specific conditions that may affect particle size, such as whether various balls are mixed according to the size and material of the balls during ball milling, can be appropriately selected within the limits of being able to control the particle size of the cathode active material to the range described above. As a specific example, zirconia balls with a diameter of 0.5 to 2 mm and zirconia balls with a diameter of 4 to 6 mm are mixed in a weight ratio of 1:0.5 to 1.5, or as a more specific example, zirconia balls with a diameter of 1 mm and zirconia balls with a diameter of 5 mm are mixed in a weight ratio of 1:1, and ball milling is performed under the above milling time and speed. This has the advantage of being advantageous for controlling the particle size to the desired size, but it is not limited thereto.

[0135]

[0136] The above coating agent may, for example, include one or more selected from the group consisting of metal, organometallic, and carbon components, and as a specific example, may be used in a liquid state by mixing with a solvent, in which case the detached positive active material and the coating agent may be homogeneously mixed to form a slurry, and there is an advantage that a coating layer is uniformly formed on the surface of the positive active material through subsequent drying and calcination steps.

[0137] The above coating agent may preferably include a carbon component, in which case it has the advantage of having even better battery characteristics.

[0138] The carbon component is not particularly limited to carbon components commonly used in coating agents in the technical field to which the present invention belongs, and the carbon component may be one or more selected from the group consisting of sugars such as sucrose, glucose, and fructose, graphite, and polyvinylidene fluoride, and preferably may be sugars, and more preferably may be sucrose. In this case, coating is easy and economical, and there is an excellent effect of improving battery characteristics.

[0139] The above 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 may be boron (B), tungsten (W), or a mixture thereof, and even more preferably may be a mixture of boron (B) and tungsten (W), and a specific example may be tungsten boride (WB), in which case the resistance characteristics and lifespan characteristics of the battery are improved.

[0140] The above metal may be included in the form of, for example, a metal element, its oxide, or an acid.

[0141] The above organometallic is not particularly limited as long as it is an organometallic commonly used in coating agents in the technical field to which the present invention belongs, and specific examples may include metal alkoxides.

[0142] The above solvent is not particularly limited as long as it is a solvent commonly used in coating agents in the technical field to which the present invention belongs, and preferably may be an aqueous solvent, more preferably may be water, and even more preferably may be deionized water.

[0143] The above coating agent may be included in an amount of, for example, 20% by weight or less, preferably 1 to 10% by weight, more preferably 2 to 10% by weight, of the total weight of the coating solution including the coating agent and the solvent. In this case, the coating efficiency is excellent, and the subsequent drying and firing steps and the secondary milling step proceed smoothly, which has the advantage of uniformly forming a coating layer on the surface of the regenerated cathode active material particles.

[0144] In step (b) above, the mixing ratio of the coating agent and the positive electrode active material can be appropriately adjusted by considering the amount (weight% or thickness) of the coating layer to be formed on the surface of the regenerated positive electrode active material to be finally recovered. However, if the ratio of the solvent becomes excessively high, there is a possibility that lithium elements of the positive electrode active material may be lost, so it must be appropriately adjusted within a range that prevents the loss of lithium elements. When the particle size of the positive electrode active material detached by primary milling (wet milling) according to the present invention is controlled, it is more advantageous for preventing the formation of fine particles and controlling the particle size distribution, and there is also an advantage that temperature changes are suppressed during the primary milling process, thereby preventing the destruction of the crystal structure of the regenerated positive electrode active material.

[0145]

[0146] (c) Cathode active material slurry drying and calcination step

[0147] The method for regenerating a positive electrode active material according to the present invention includes (c) a step of drying and calcining the positive electrode active material slurry recovered in step (b). In this case, a coating layer is evenly formed on the particle surface of the regenerated positive electrode active material, and when applied to a secondary battery, the battery's output characteristics, charge / discharge performance, and lifespan performance are improved, thereby providing the advantage of providing good battery characteristics equivalent to or better than those of a fresh positive electrode active material. Additionally, the particle size and particle size distribution of the positive electrode active material are appropriately controlled before forming the coating layer, so that the coating layer can be uniformly formed on the particle surface, thereby providing the advantage of a more superior effect in improving battery characteristics.

[0148]

[0149] As a specific example, the above step (c) may include: (c1) a step of spray-drying the anode active material slurry milled in the above step (b) to form an anode active material coated with a coating agent (c1); and a step of calcining the anode active material coated with a coating agent at 500 to 900 ℃ under a reducing atmosphere (c2); in this case, the coating efficiency is excellent, particle aggregation of the anode active material is prevented, and the coating is evenly formed on the surface of the anode active material particles, which is advantageous for improving battery performance.

[0150]

[0151] The above spray drying can be used without particular limitation as long as it is spray drying equipment commonly used in the technical field to which the present invention belongs. Examples include ultrasonic spray drying devices, air nozzle spray drying devices, ultrasonic nozzle spray drying devices, filter expansion droplet generators, or electrostatic spray drying devices, but are not limited thereto.

[0152] In addition, the flow rate, spray pressure, and spray speed can be appropriately selected considering the amount of coating agent to be coated on the surface of the final regenerated cathode active material.

[0153]

[0154] Through the above spray drying, the solvent contained in the positive active material slurry formed in step (b) is dried, and the coating agent can be evenly applied to the surface of the positive active material. However, in order to firmly form a coating layer on the surface of the positive active material, the coating agent applied to the surface of the positive active material must be sufficiently solidified through heat treatment. In order to prevent the coating agent from being oxidized or degraded during this process, it is preferable to perform heat treatment under a reducing atmosphere.

[0155] After the above spray drying, the anode active material coated with the coating agent can be heat-treated, for example, at 500 to 900 ℃ under a reducing atmosphere, preferably at 600 to 850 ℃, more preferably at 650 to 850 ℃, even more preferably at 700 to 830 ℃, and even more preferably at 750 to 820 ℃. In this case, there is an advantage that the coating agent is stably coated on the surface of the regenerated anode active material while maintaining the inherent properties of the anode active material.

[0156] For example, the firing of step (c) above may have a heating rate of 1 to 20 ℃ / min to reach the firing temperature, preferably 1 to 10 ℃ / min, more preferably 2 to 7 ℃ / min, and there is an advantage that the desired firing effect can be sufficiently expressed within this range.

[0157] The firing of step (c) above can be carried out, for example, by heating at the firing temperature for 5 to 15 hours, preferably 7 to 13 hours, more preferably 8 to 12 hours, and there is an advantage that the desired firing effect can be sufficiently expressed within this range.

[0158] The above reducing atmosphere may include, for example, an inert atmosphere, and specifically, an argon (Ar) or nitrogen (N2) atmosphere.

[0159] As a preferred example, the nitrogen atmosphere may have a purity of 80% or more, preferably 90% or more, more preferably 90 to 99.8%, and even more preferably 95 to 99.8%. In this case, there is an advantage in that oxidation of the coating agent is prevented during the calcination process and a coating layer is stably formed on the surface of the anode active material.

[0160] The purity % of the above nitrogen may be volume % or mol %.

[0161] The purity of the nitrogen described herein is not particularly limited when measured by a measurement method commonly used in the technical field to which the present invention belongs.

[0162]

[0163] The amount of the coating layer formed on the surface of the regenerated positive electrode active material particles recovered after the above drying and calcination may be, for example, 0.1 to 15 weight%, preferably 0.2 to 10 weight%, more preferably 0.5 to 5 weight%, even more preferably 0.7 to 3 weight%, and even more preferably 0.8 to 2 weight% based on the total weight of the regenerated positive electrode active material including the weight of the coating layer, and there is an advantage that the desired coating effect can be sufficiently expressed within this range.

[0164] The amount of the coating layer formed on the surface of the above-mentioned regenerated cathode active material particles can be measured by methods conventionally practiced in the technical field to which the present invention belongs, and as a specific example, can be measured by quantitative analysis using thermogravimetric analysis (TGA) or a CS analyzer (Carbon / Sulfur Determinator).

[0165]

[0166] The thickness of the coating layer coated on the surface of the above-mentioned regenerated positive electrode active material particles can be appropriately controlled according to the desired coating amount. In this description, the thickness of the coating layer can be measured by methods commonly practiced in the technical field to which the present invention belongs, and, for example, can be obtained by measuring the long diameters of 5 to 100 positive electrode active material particles observed using a transmission electron microscope (TEM) or a scanning electron microscope (SEM) and then calculating the arithmetic mean.

[0167]

[0168] (d) Second milling step

[0169] The method for regenerating a positive electrode active material according to the present invention may, for example, include a step of (d) secondary milling the positive electrode active material recovered after drying and calcination in step (c). In this case, aggregation, particle breakage, and the generation of fine particles in the finally obtained regenerated positive electrode active material are prevented, and the particle size distribution is controlled to a narrow range, thereby providing the advantage of being able to manufacture the positive electrode active material as a single particle. From this, the degradation of battery performance due to fine particles is prevented, and the thermal stability and lifespan characteristics of the battery are further improved. Furthermore, when the regenerated positive electrode active material is ultimately applied to the positive electrode of a secondary battery, there is an advantage of being able to provide good battery characteristics equivalent to or better than those of the fresh positive electrode active material.

[0170] The positive active material recovered after drying and calcination in step (c) above is difficult to manufacture into an electrode because, for example, secondary particles are aggregated. Even if it is manufactured into an electrode, when applied to a secondary battery, cracks easily form within the particles due to repeated volume changes during charging and discharging, which reduces lifespan and safety. Therefore, this problem can be solved by making it into single particles through the secondary milling above.

[0171]

[0172] The above single particle may, for example, be a particle composed of 30 or fewer nodules, preferably 1 to 20 nodules, more preferably 1 to 10 nodules, even more preferably 1 to 5 nodules, and most preferably 1 nodule. In this case, the degradation of the battery's performance during the electrode manufacturing process is prevented, and there is an effect of providing a positive electrode active material with excellent thermal stability and lifespan characteristics.

[0173] In this description, a nodule refers to a particle unit body constituting a single particle, and may refer to a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which grain boundaries are not apparent when observed at a magnification of 5,000 to 20,000 times using a scanning electron microscope (SEM) or an electron backscatter diffraction (EBSD) analyzer.

[0174] In this description, the number of nodules refers to the average value of the number of nodules of the positive active material particles. For example, a positive electrode containing a positive active material is cut by ion milling, and a cross-sectional image in the thickness direction of the cut positive electrode is obtained using a scanning electron microscope (SEM). Then, at least 30 particles are selected for each of the largest particle size positive active material particles and the smallest particle size positive active material particles within the cross-sectional image, and the number of nodules in the cross-section of each positive active material particle is measured through SEM image analysis and calculated by arithmetically averaging them.

[0175] In this description, secondary particles refer to aggregates formed by the aggregation of multiple single particles, which contain more than 30 nodules.

[0176]

[0177] After the above secondary milling, the positive active material is, for example, an average particle size (D 50The depth may be 0.80 to 1.73 μm, preferably 1.00 to 1.70 μm, more preferably 1.20 to 1.67 μm, even more preferably 1.40 to 1.67 μm, even more preferably 1.50 to 1.67 μm, particularly preferably 1.55 to 1.65 μm, and particularly more preferably 1.60 to 1.65 μm, and there is an advantage that excellent battery characteristics are exhibited within this range.

[0178] Average particle size (D) of the positive active material after the above secondary milling 50 ) can be adjusted, for example, by the oxidation heat treatment temperature for detaching the positive active material from the current collector, primary milling conditions, coating layer content, and / or secondary milling conditions. For example, the higher the oxidation heat treatment temperature for detaching the positive active material from the current collector, the higher the average particle size (D) of the positive active material after secondary milling. 50 ) increases.

[0179]

[0180] The above secondary milling can be performed using a jet mill, for example. In this case, the crystal structure of the positive electrode active material can be easily converted into single particles while preventing damage, and the particle size and particle distribution of the finally obtained regenerated positive electrode active material can be precisely controlled within a narrow range. Additionally, the introduction of foreign substances that may occur during the milling process is prevented, which has the advantage of improving the purity of the regenerated positive electrode active material.

[0181] The above jet mill can be operated, for example, using an inert gas that does not react with the regenerated cathode active material, under conditions of a temperature of -30°C to 30°C, preferably -20°C to 20°C, and a pressure of 0.8 to 10 bar. More specifically, it can be operated under conditions where the pressure of the feeding line is 2 to 8 bar, preferably 2.5 to 6 bar, more preferably 3 to 5 bar, and the pressure of the grinding line is 0.8 to 2 bar, preferably 0.9 to 1.5 bar, more preferably 1 to 1.3 bar. Within this range, there is an advantage in preventing damage to the crystal structure of the cathode active material and in precisely controlling the particle size and particle distribution of the finally obtained regenerated cathode active material within a narrow range. The above inert gas may be, for example, argon (Ar) or nitrogen (N2).

[0182]

[0183] Average particle size (D) of the positive active material detached using a ball mill in the above first milling. 50 When the coated positive active material is milled using a jet mill in the second milling step after adjusting the particle size to 0.3 to 0.5 μm, it is possible to control the particle size distribution of the positive active material within a narrow range while suppressing the generation of fine particles, and at the same time, it is advantageous to restore the crystal structure of the positive active material to the crystal structure of the fresh positive active material. Furthermore, since it is possible to manufacture it as a single particle while suppressing damage to the coating layer formed in step (c), it is particularly advantageous for improving battery performance and stability and enhancing lifespan characteristics.

[0184] After performing the above second milling, the average particle size (D) of the positive active material 50 The average particle size (D) of the positive electrode active material after performing the first milling. 50 The increase compared to ) is due to the formation of a coating layer.

[0185]

[0186] The regenerated cathode active material recovered in step (d) above may have an a-axis lattice constant measured by X-ray diffraction analysis (XRD) of, for example, 10.3275 to 10.3293 Å, preferably 10.3278 to 10.3290 Å, more preferably 10.3281 to 10.3287 Å, and even more preferably 10.3282 to 10.3285 Å, and within this range, the regenerated cathode active material structure is restored to a fresh cathode active material structure and has the advantage of providing good battery characteristics without lithium loss in the lattice.

[0187]

[0188] The regenerated cathode active material recovered in step (d) above may have a c-axis lattice constant measured by X-ray diffraction analysis (XRD) of, for example, 4.6912 to 4.6920 Å, preferably 4.6914 to 4.6918 Å, more preferably 4.6916 to 4.6918 Å, and within this range, the regenerated cathode active material structure is restored to a fresh cathode active material structure and has the advantage of providing good battery characteristics without lithium loss in the lattice.

[0189]

[0190] The regenerated cathode active material finally recovered in step (d) above may have a b-axis lattice constant measured by X-ray diffraction analysis (XRD) of, for example, 6.0065 to 6.0075 Å, preferably 6.0067 to 6.0073 Å, and more preferably 6.0069 to 6.0071 Å, and within this range, the regenerated cathode active material structure is restored to a fresh cathode active material structure and has the advantage of providing good battery characteristics without lithium loss in the lattice.

[0191]

[0192] The regenerated cathode active material finally recovered in step (d) above has, for example, a cell volume of 291.00 to 291.15 Å as measured by X-ray diffraction (XRD).3 It may be, preferably 291.02 to 291.13 Å 3 , more preferably 291.05 to 291.12 Å 3 , more preferably 291.07 to 291.12 Å 3 This can be done, and within this range, the regenerated cathode active material structure is restored to a fresh cathode active material structure, and there is an advantage in that there is no lithium loss within the lattice, which can provide good battery characteristics.

[0193]

[0194] In addition, the regenerated cathode active material recovered in step (d) above may have a grain size measured by X-ray diffraction analysis (XRD) of, for example, 118 to 170 nm, preferably 118 to 165 nm, more preferably 120 to 160 nm, even more preferably 120 to 150 nm, even more preferably 120 to 140 nm, and particularly preferably 120 to 130 nm. In this case, the regenerated cathode active material structure is restored to a fresh cathode active material structure, which has the advantage of providing good battery characteristics.

[0195]

[0196] In this description, the a-axis lattice constant, the c-axis lattice constant, and the cell volume can be measured by measurement methods commonly used in the technical field to which this invention belongs, and specifically, can be measured using X-ray diffraction analysis (XRD). More specifically, the a-axis lattice constant, the b-axis lattice constant, and the c-axis lattice constant can be obtained by calculating the data obtained through X-ray diffraction analysis using Cu Kα rays as a source for the cathode active material using the XRD Rietveld refinement method, and the cell volume can be calculated as the product of the obtained a-axis lattice constant, the b-axis lattice constant, and the c-axis lattice constant. In addition, the crystallite size can be estimated using the peak broadening of the X-ray diffraction data obtained by X-ray diffraction analysis (XRD) and can be quantitatively calculated using the Scherrer Equation.

[0197]

[0198] The regenerated cathode active material finally recovered in step (d) above may include, for example, single particles, and more preferably, not include secondary particles. In this case, there is no particle breakage during the electrode manufacturing process, so there is no degradation of battery performance due to fine particles, and the internal structure is uniform so the movement of lithium ions is smooth, and there are excellent lifespan characteristics in a high voltage environment, high thermal stability, and low gas generation during charging and discharging.

[0199]

[0200] The regenerated cathode active material finally recovered in step (d) above may be, for example, an electrode slurry prepared by mixing the regenerated cathode active material, Super-C carbon black powder as a conductive material, and KF200 polyvinylidene fluoride as a binder in a ratio of 95 / 2 / 3, with a solid content of 58.5 wt%, and the viscosity measured at 2.5 / s under room temperature conditions using a rheometer may be, for example, 28,000 mPa·s or less, preferably 20,000 mPa·s or less, more preferably 16,000 mPa·s or less, even more preferably 15,500 mPa·s or less, even more preferably 13,000 to 15,500 mPa·s, and particularly preferably 14,000 to 15,000 mPa·s, within this range, excellent coating properties on the current collector and the advantages of the secondary battery to which it is applied have excellent battery characteristics.

[0201]

[0202] The regenerated cathode active material finally recovered in step (d) above may be, for example, an electrode slurry prepared by mixing the regenerated cathode active material, Super-C carbon black powder as a conductive material, and KF200 polyvinylidene fluoride as a binder in a ratio of 95 / 2 / 3, with a solid content of 58.5 wt%, and the viscosity measured at 1000 / s under room temperature conditions using a rheometer may be 2,000 mPa·s or less, preferably 1,600 mPa·s or less, more preferably 1,500 mPa·s or less, even more preferably 1,200 to 1,500 mPa·s, and even more preferably 1,300 to 1,400 mPa·s. Within this range, it has excellent coating properties on the current collector and has the advantage of excellent battery characteristics of the secondary battery to which it is applied.

[0203]

[0204] The regenerated cathode active material finally recovered in step (d) above is, for example, I measured by Raman spectrum analysis. D / IG The peak ratio may be 0.950 or less, preferably 0.940 or less, more preferably 0.930 or less, even more preferably 0.920 or less, even more preferably 0.916 or less, particularly preferably 0.860 to 0.916, and particularly more preferably 0.880 to 0.916, and within this range, the electrical conductivity is excellent, so when applied to a secondary battery, the battery characteristics are excellent.

[0205] I measured by the Raman spectrum analysis described herein D / I G The peak ratio is a measure indicating the relative degree of crystallinity, I D In Raman spectrum analysis, 1350 to 1380 cm⁻¹ -1 The peak in the absorption region, i.e., the intensity value of the D band, represents the peak of the amorphous region, and I G 1580 to 1600 cm⁻¹ in Raman spectrum analysis -1 The peak in the absorption region, that is, the intensity value of the G band, represents the peak of the crystalline portion. Specifically, in Raman spectrum analysis, the G band indicates carbon crystals without structural defects; the closer the crystallinity is to graphitic, the higher the G peak becomes, and since the D band peak increases when disorder or defects are generated within the carbonaceous material, I D / I G The smaller the ratio, the better the electrical conductivity.

[0206] In addition, I measured by the Raman spectrum analysis of this document D / I G The peak ratio can be obtained from the intensity values ​​of the D band and the G band in the raw data (spectrum) obtained from the Raman spectrum analysis results in Figure 5 below.

[0207]

[0208] The regenerated cathode active material finally recovered in step (d) above is measured through Raman spectrum analysis, and the ratio of the area of ​​the cathode active material peak to the total sum of the areas of the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained by fitting the Raman spectrum may be, for example, 0.010 or less, preferably 0.006 or less, more preferably 0.004 or less, even more preferably 0.0001 to 0.004, and even more preferably 0.001 to 0.004. Within this range, carbon coating, etc. is suitably performed on the regenerated cathode active material, and there is an advantage of excellent battery characteristics when applied to a secondary battery. A smaller ratio of the area of ​​the cathode active material peak to the total sum of the areas of the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak indicates that the area on the surface of the cathode active material where the coating agent is not applied is smaller.

[0209] In the Raman spectrum described herein, fitting is a data processing technique used to accurately analyze the position, width, intensity, shape, etc., of individual Raman peaks in a measured Raman spectrum, and primarily refers to separating overlapping peaks or extracting accurate peak information from a spectrum containing noise. As a specific example, Figure 5 below shows the raw data obtained from the Raman spectrum analysis of a fresh cathode active material, and Figure 6 shows the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained by fitting the Raman spectrum of Figure 5. In Figure 6, the yellow graph represents the raw data (spectrum) obtained from the Raman spectrum analysis, and by fitting it, the D1 peak (red), D2 peak (blue), D3 peak (green), G peak (purple), and LFP peak (black) can be obtained. These peaks are believed to indicate the regularity, stability, and / or state or degree of coating of the regenerated cathode active material particles.

[0210]

[0211] In this description, the positive active material peak can be obtained by fitting the spectrum resulting from Raman spectrum analysis, and at 950 to 970 cm⁻¹ in the Raman spectrum -1 It can mean the peak in the absorption region.

[0212]

[0213] The regenerated cathode active material finally recovered in step (d) above may have a ratio of the area of ​​the D1 peak to the total area of ​​the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained by fitting the spectrum measured through Raman spectrum analysis, for example, 0.235 or less, preferably 0.225 or less, more preferably 0.220 or less, even more preferably 0.215 or less, particularly preferably 0.200 to 0.215, and particularly more preferably 0.205 to 0.215, and within this range, the coating agent, etc., on the regenerated cathode active material is suitably adjusted, thereby improving the battery characteristics.

[0214] The D1 peak obtained by fitting the spectrum resulting from the Raman spectrum analysis of the above-mentioned positive electrode active material is at 1160 to 1180 cm⁻¹. -1 It may be a peak in the absorption region.

[0215]

[0216] The regenerated cathode active material finally recovered in step (d) above may have a ratio of the area of ​​the D2 peak to the total area of ​​the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained by fitting the spectrum measured through Raman spectrum analysis, for example, 0.425 or less, preferably 0.420 or less, more preferably 0.400 to 0.420, even more preferably 0.405 to 0.420, particularly preferably 0.410 to 0.420, and particularly more preferably 0.410 to 0.415, and within this range, the coating agent, etc., on the regenerated cathode active material is suitably adjusted, thereby having the effect of improving battery characteristics.

[0217] The D2 peak obtained by fitting the spectrum resulting from the Raman spectrum analysis of the above-mentioned positive electrode active material is at 1340 to 1360 cm⁻¹. -1 It may be a peak in the absorption region.

[0218]

[0219] The regenerated cathode active material finally recovered in step (d) above may have a ratio of the area of ​​the D3 peak to the total area of ​​the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained by fitting the spectrum measured through Raman spectrum analysis, for example, 0.185 or less, preferably 0.125 to 0.185, more preferably 0.133 to 0.185, even more preferably 0.150 to 0.185, particularly preferably 0.160 to 0.185, particularly more preferably 0.165 to 0.185, and most preferably 0.170 to 0.183, and within this range, the coating agent, etc., on the regenerated cathode active material is suitably adjusted, thereby improving the battery characteristics.

[0220] The D3 peak obtained by fitting the spectrum resulting from the Raman spectrum analysis of the above-mentioned positive electrode active material is at 1500 to 1520 cm⁻¹. -1It may be a peak in the absorption region.

[0221]

[0222] The regenerated cathode active material finally recovered in step (d) above is measured through Raman spectrum analysis, and the ratio of the area of ​​the G peak to the total sum of the areas of the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained by fitting the sample may be, for example, 0.210 or less, preferably 0.205 or less, more preferably 0.185 to 0.205, even more preferably 0.190 to 0.205, particularly preferably 0.190 to 0.200, and particularly more preferably 0.190 to 0.195, and within this range, the coating agent, etc., on the regenerated cathode active material is suitably adjusted, thereby having the effect of improving battery characteristics.

[0223] The D3 peak obtained by fitting the spectrum resulting from the Raman spectrum analysis of the above-mentioned positive electrode active material is at 1590 to 1610 cm⁻¹. -1 It may be a peak in the absorption region.

[0224]

[0225] The method for regenerating the positive electrode active material of the present invention can provide battery characteristics equivalent to those of a secondary battery manufactured with a fresh positive electrode active material by selectively recovering the positive electrode active material with high purity through the heat treatment step (a) as described above, and then regenerating the recovered positive electrode active material through the steps (b) to (d) above. As a result, the regenerated positive electrode active material of the present invention has the advantage of being able to replace the fresh positive electrode active material by reducing the specific surface area and impurities derived from the coating agent, such as carbon, and having excellent electrical conductivity, and by lowering the viscosity of the electrode slurry containing it to improve the coating properties on the current collector. Furthermore, by regenerating the positive electrode active material from the waste electrode without decomposing it by element, all metal elements of the positive electrode active material can be recovered from the waste electrode without waste, and since there is no need to replenish lithium, iron, or phosphorus during the regeneration process of the positive electrode active material, economic efficiency and productivity can be significantly improved.

[0226]

[0227] Regenerative cathode active material

[0228] The regenerated cathode active material of the present invention is characterized by being regenerated by the cathode active material regeneration method of the present invention. In this case, along with the environmentally friendly advantage, the specific surface area and impurities derived from the coating agent, such as carbon, are reduced, and the electrical conductivity is excellent. Furthermore, the electrode slurry containing this material has a lower viscosity, which improves the coating properties on the current collector. Consequently, when applied as a cathode active material for a secondary battery, the charge / discharge characteristics, cycle characteristics, and lifespan characteristics of the battery are excellent, and the thermal stability is superior, resulting in improved high-temperature performance. Additionally, since such a regenerated cathode active material can provide battery characteristics equivalent to or greater than those of a fresh cathode active material, it has the advantage of being able to replace a secondary battery containing a fresh cathode active material.

[0229]

[0230] The above-mentioned regenerative cathode active material may preferably be a compound represented by the following chemical formula 1, more preferably lithium iron phosphate (LFP), and even more preferably LiFePO4 with an olivine structure, in which case it has excellent high-temperature stability and lifespan characteristics and excellent economic efficiency.

[0231] [Chemical Formula 1]

[0232]

[0233] (In the above chemical formula 1, M comprises one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are each -0.5≤a≤0.5, 0≤b≤0.5, and 0≤c≤0.1.)

[0234]

[0235] The above-mentioned regenerated cathode active material may, for example, have an a-axis lattice constant measured by X-ray diffraction analysis (XRD) of 10.3275 to 10.3293 Å, preferably 10.3278 to 10.3290 Å, more preferably 10.3281 to 10.3287 Å, and even more preferably 10.3282 to 10.3285 Å, and in this case, there is an advantage of being able to provide excellent battery characteristics.

[0236]

[0237] The above-mentioned regenerated cathode active material may, for example, have a c-axis lattice constant measured by X-ray diffraction analysis (XRD) of 4.6912 to 4.6920 Å, preferably 4.6914 to 4.6918 Å, more preferably 4.6916 to 4.6918 Å, and in this case, there is an advantage of being able to provide excellent battery characteristics.

[0238]

[0239] The above-mentioned regenerated cathode active material may, for example, have a b-axis lattice constant measured by X-ray diffraction analysis (XRD) of 6.0065 to 6.0075 Å, preferably 6.0067 to 6.0073 Å, and more preferably 6.0069 to 6.0071 Å, and in this case, there is an advantage of being able to provide excellent battery characteristics.

[0240]

[0241] The above-mentioned regenerated cathode active material has, for example, a cell volume of 291.00 to 291.15 Å as measured by X-ray diffraction analysis (XRD). 3 It may be, preferably 291.02 to 291.13 Å 3 , more preferably 291.05 to 291.12 Å 3 , more preferably 291.07 to 291.12 Å 3 It can be, and in this case, there is an advantage in that it can provide excellent battery characteristics.

[0242]

[0243] The above-mentioned regenerated cathode active material may, for example, have a grain size of 118 to 170 nm as measured by X-ray diffraction analysis (XRD), preferably 118 to 165 nm, more preferably 120 to 160 nm, even more preferably 120 to 150 nm, even more preferably 120 to 140 nm, and particularly preferably 120 to 130 nm, and in this case, there is an advantage of being able to provide excellent battery characteristics.

[0244]

[0245] The above-mentioned regenerated positive electrode active material may include, for example, single particles, and more preferably, not include secondary particles. In this case, there is no particle breakage during the electrode manufacturing process, so there is no degradation of battery performance due to fine particles, and it has the effect of providing a positive electrode active material that has excellent lifespan characteristics in a high-voltage environment, high thermal stability, and low gas generation during charging and discharging.

[0246]

[0247] The above-mentioned regenerated cathode active material may be, for example, an electrode slurry prepared by mixing the regenerated cathode active material, Super-C carbon black powder as a conductive material, and KF200 polyvinylidene fluoride as a binder in a ratio of 95 / 2 / 3, with a solid content of 58.5 wt%, and the viscosity measured at 2.5 / s under room temperature conditions using a rheometer may be 28,000 mPa·s or less, preferably 20,000 mPa·s or less, more preferably 16,000 mPa·s or less, even more preferably 15,500 mPa·s or less, even more preferably 13,000 to 15,500 mPa·s, and particularly preferably 14,000 to 15,000 mPa·s. Within this range, the coating properties on the current collector are excellent, and there is an advantage that the battery characteristics of the secondary battery to which it is applied are excellent.

[0248] The above-mentioned regenerated cathode active material may be, for example, an electrode slurry prepared by mixing the regenerated cathode active material, carbon black powder Super-C as a conductive material, and polyvinylidene fluoride KF200 as a binder in a ratio of 95 / 2 / 3, with a solid content of 58.5 wt%, and the viscosity measured at 1000 / s under room temperature conditions using a rheometer may be 2,000 mPa·s or less, preferably 1,600 mPa·s or less, more preferably 1,500 mPa·s or less, even more preferably 1,200 to 1,500 mPa·s, and even more preferably 1,300 to 1,400 mPa·s. Within this range, the coating properties on the current collector are excellent, and there is an advantage that the battery characteristics of the secondary battery to which it is applied are excellent.

[0249]

[0250] The above-mentioned regenerated cathode active material is, for example, I measured by Raman spectrum analysis D / I GThe peak ratio may be 0.950 or less, preferably 0.940 or less, more preferably 0.930 or less, even more preferably 0.920 or less, even more preferably 0.916 or less, particularly preferably 0.860 to 0.916, and particularly more preferably 0.880 to 0.916, and within this range, the electrical conductivity is excellent, so when applied to a secondary battery, the battery characteristics are excellent.

[0251]

[0252] The above-mentioned regenerated cathode active material may, for example, have a spectrum measured through Raman spectrum analysis and fitted to obtain a ratio of the area of ​​the cathode active material peak to the total area of ​​the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak, such that the ratio is 0.010 or less, preferably 0.006 or less, more preferably 0.004 or less, even more preferably 0.0001 to 0.004, and even more preferably 0.001 to 0.004. Within this range, the coating agent is uniformly applied to the cathode active material, resulting in excellent electrical conductivity and the advantage of having excellent battery characteristics when applied to a secondary battery.

[0253]

[0254] The above-mentioned regenerated cathode active material may have a spectrum measured through Raman spectrum analysis and a ratio of the area of ​​the D1 peak to the total area of ​​the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained by fitting the spectrum, such that, for example, the ratio is 0.235 or less, preferably 0.225 or less, more preferably 0.220 or less, even more preferably 0.215 or less, particularly preferably 0.200 to 0.215, and particularly more preferably 0.205 to 0.215, and within this range, the coating agent, etc., is suitably adjusted on the regenerated cathode active material, thereby having the effect of improving battery characteristics.

[0255]

[0256] The above-mentioned regenerated cathode active material may have a spectrum of measuring through Raman spectrum analysis and fitting the area ratio of the D2 peak to the total area of ​​the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained as a result of fitting, for example, 0.425 or less, preferably 0.420 or less, more preferably 0.400 to 0.420, even more preferably 0.405 to 0.420, particularly preferably 0.410 to 0.420, and particularly more preferably 0.410 to 0.415, and within this range, the coating agent, etc., on the regenerated cathode active material is suitably adjusted, thereby having the effect of improving battery characteristics.

[0257]

[0258] The above-mentioned regenerated cathode active material may, for example, have a spectrum measured through Raman spectrum analysis and fitted to obtain a ratio of the area of ​​the D3 peak to the total area of ​​the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak, such that the ratio is, for example, 0.185 or less, preferably 0.125 to 0.185, more preferably 0.133 to 0.185, even more preferably 0.150 to 0.185, particularly preferably 0.160 to 0.185, particularly more preferably 0.165 to 0.185, and most preferably 0.170 to 0.183. Within this range, the coating agent, etc., is suitably adjusted on the regenerated cathode active material, thereby improving the battery characteristics.

[0259]

[0260] The above-mentioned regenerated cathode active material may, for example, have a spectrum measured through Raman spectrum analysis and fitted to obtain a ratio of the area of ​​the G peak to the total area of ​​the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak, such that, for example, the ratio is 0.210 or less, preferably 0.205 or less, more preferably 0.185 to 0.205, even more preferably 0.190 to 0.205, particularly preferably 0.190 to 0.200, and particularly more preferably 0.190 to 0.195. Within this range, the coating agent, etc., is suitably adjusted on the regenerated cathode active material, thereby having the effect of improving battery characteristics.

[0261]

[0262] secondary battery

[0263] The present invention provides a secondary battery characterized by including the above-mentioned positive active material, wherein the battery has excellent charge / discharge characteristics, cycle characteristics, and lifespan characteristics, excellent thermal stability, improved high-temperature performance, and excellent electrical conductivity.

[0264]

[0265] Hereinafter, preferred embodiments are presented to aid in understanding the present invention; however, the following embodiments are merely illustrative of the invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the invention, and that such variations and modifications fall within the scope of the appended claims.

[0266]

[0267] [Example]

[0268] Example 1

[0269] A waste anode coated with a layer of positive active material, comprising an LFP positive active material having an olivine structure, a binder, and a conductive material, on an aluminum current collector was heat-treated in a furnace under an air atmosphere at a rate of 5 °C / min and at 490 °C for 5 hours. At this time, the air supply rate was 3 L / min. During this process, the binder inside the waste anode was thermally decomposed, and the positive active material separated from the current collector was recovered as a powder. At this time, the average pore diameter, total pore volume, specific surface area (BET), and carbon (C) content of the recovered positive active material powder were measured.

[0270] After the above heat treatment, the heat supply was stopped to completely cool the recovered cathode active material powder to room temperature. The recovered cathode active material powder was then mixed with a coating agent prepared by mixing sucrose and deionized water. The mixture of 87.37 g of the recovered cathode active material and 10.03 g of the coating agent was fed into a ball mill device and milled for 9 hours at 300 rpm to recover a slurry of the cathode active material and coating agent (first milling). The average particle diameter (D) of the cathode active material powder was measured by taking a sample from the slurry. 50 ) was 0.30 μm.

[0271] The slurry recovered after the first milling above was dried by a spray drying method so that the residual solvent content was less than 0.1 wt%. At this time, the hot air temperature was set to 240 ℃ and the discharge temperature was maintained at 95~98 ℃.

[0272] The above-described dried slurry was heated in a furnace under a nitrogen atmosphere at a rate of 3 ℃ / min and calcined at 800 ℃ for 10 hours to form a carbon (C) coating layer on the surface of the cathode active material. At this time, the nitrogen supply rate during calcination was 3 L / min, and the coating amount was 1.43 wt% as a result of CS analysis after the completion of calcination. Specifically, for the CS analysis, a carbon standard was measured at least three times after measuring a blank for the calibration curve. A combustion promoter was added to a crucible containing 10 mg of the sample, placed on the lower electrode of a CS analyzer, and then the sample was injected from the top and combusted to measure the carbon content.

[0273] The above-mentioned coated cathode active material is subjected to secondary milling using a jet mill under a nitrogen (N2) atmosphere with a feeding line pressure of 4 bar and a grinding line pressure of 1 bar, thereby producing a particle diameter D 50 A regenerated positive electrode active material with a thickness of 1.33 μm was obtained.

[0274]

[0275] Example 2

[0276] The procedure was carried out in the same manner as Example 1, except that the heat treatment temperature was changed to 520 ℃. At this time, after the first milling, the anode active material had a particle diameter D 50 is 0.32 μm, and the particle diameter D of the regenerated cathode active material obtained after secondary milling 50 It was 1.42 µm.

[0277]

[0278] Example 3

[0279] The procedure was carried out in the same manner as Example 1, except that the heat treatment temperature was changed to 580 ℃. At this time, after the first milling, the anode active material had a particle diameter D 50 is 0.35 μm, and the particle diameter D of the regenerated cathode active material obtained after secondary milling 50It was 1.52 µm.

[0280]

[0281] Example 4

[0282] The procedure was carried out in the same manner as Example 1, except that the heat treatment temperature was changed to 700 ℃. At this time, after the first milling, the anode active material had a particle diameter D 50 is 0.38 μm, and the particle diameter D of the regenerated cathode active material obtained after secondary milling 50 It was 1.63 μm.

[0283]

[0284] Comparative Example 1

[0285] The above Example 1 was carried out in the same manner as Example 1, except that the heat treatment temperature was changed to 300 ℃.

[0286]

[0287] Comparative Example 2

[0288] The procedure was carried out in the same manner as Example 1, except that the heat treatment temperature was changed to 800 ℃. At this time, after the first milling, the anode active material had a particle diameter D 50 is 0.43 μm, and the particle diameter D of the regenerated cathode active material obtained after secondary milling 50 It was 1.85 µm.

[0289]

[0290] Reference Example

[0291] A fresh LFP-based cathode active material was used instead of a regenerated cathode active material. As a result of analyzing the fresh LFP-based cathode active material by ICP analysis, it was confirmed to be a LiFePO4 cathode active material having elemental ratios of Li / Fe : 1.06, Li / P : 1.00, and P / Fe : 1.06.

[0292]

[0293] [Test Example I: Measurement of Average Pore Diameter, Total Pore Volume, Specific Surface Area (BET), and Carbon Content]

[0294] In the above Examples 1 to 4 and Comparative Examples 1 and 2, the average pore diameter (D) of the anode active material obtained by delamination after heat treatment 50 The total pore volume, specific surface area, and carbon content were measured and are shown in Table 1 below.

[0295]

[0296] * Average particle size (D 50 ; μm): Measured using the laser diffraction method. Specifically, after dispersing the particles of the regenerated cathode active material in a dispersion medium, they were introduced into a commercially available laser diffraction particle size measuring device such as Microtrac MT 3000, irradiated with ultrasound of approximately 28 kHz at an output of 60 W, and the particle distribution was measured to analyze the average particle size at the cumulative 50% standard of the particle diameter distribution.

[0297] * Specific surface area (BET; m²) 2 / g), average pore diameter (nm) and total pore volume (cm²) 3 / g): Measured by the BET (Brunauer-Emmett-Teller) method. Specifically, it was calculated from the amount of nitrogen gas adsorbed at liquid nitrogen temperature (77K) using the BELSORP-mino II from BEL Japan.

[0298] * Carbon content (weight%): Quantitative analysis was performed using a CS analyzer (Carbon / Sulfur Determinator) with the cathode active material powder recovered after heat treatment. Specifically, after measuring the blank for the calibration curve, the carbon standard was measured at least three times. A combustion promoter was added to a crucible containing 10 mg of the sample, placed on the lower electrode of the CS analyzer, and then the sample was injected from the top and combusted to measure the carbon content (relative to 100 weight% of the input sample).

[0299]

[0300] Classification Heat Treatment Temperature (°C) Average Pore Diameter (nm) Total Pore Volume (cm²) 3 / g) Specific surface area (BET) (m² 2 / g) Carbon Content (Weight%) Example 1 490 29.34 0.026 3.55 0.7 Example 25 20 30.92 0.024 3.11 0.5 Example 3 580 27.04 0.0202 89 0.5 Example 4 700 25.81 0.019 1.88 0.1 Comparative Example 1 300----Comparative Example 2800 23.55 0.017 0.99 0.1 Reference Example-14.91 0.038 10.55 1.4

[0301] -: Unmeasurable

[0302] As shown in Table 1 above, it was confirmed that the cathode active material recovered by heat treatment from Examples 1 to 4 had a smaller total pore volume, specific surface area (BET), and carbon content, and a larger average pore diameter compared to the fresh cathode active material of the reference example.

[0303] However, in Comparative Example 1, the thermal decomposition of the conductive material and binder was insufficient, making it impossible to recover the positive active material from the current collector, and thus the physical properties could not be measured. In addition, in Comparative Example 2, the average pore diameter, total pore volume, and specific surface area decreased and the carbon content decreased compared to Examples 1 to 4 as a result of heat treatment at 800°C, but black foreign substances were found on the surface of the positive active material, which appears to be due to the surface of the positive active material melting during heat treatment at a very high temperature.

[0304] In the reference example, carbon coating was applied to the fresh cathode active material, so the specific surface area was higher than that of Examples 1 to 4.

[0305]

[0306] [Test Example II: Crystal Structure via X-ray Diffraction Analysis (XRD)]

[0307] The crystal structure of the regenerated or prepared positive electrode active material in Examples 1, 3, 4 and Reference Example was determined by X-ray diffraction analysis (XRD) to measure the a-axis lattice constant, b-axis lattice constant, c-axis lattice constant, cell volume, and grain size, and is shown in Table 2 below. Specifically, the measurement method was determined as follows from the main peak or the full width at half maximum of three or more peaks obtained by taking 5 g of positive electrode active material particles, placing them in an XRD measurement holder, and irradiating the particles with X-rays.

[0308] * a-axis / b-axis / c-axis lattice constants, and cell volume: Data obtained through X-ray diffraction analysis using CuKα rays as a source for the positive electrode active material was calculated using the XRD Rietveld refinement method, and the cell volume was obtained as the product of the a-axis lattice constant, the b-axis lattice constant, and the c-axis lattice constant.

[0309] * Crystallite size (mm): The crystallite size was estimated using the peak broadening of X-ray diffraction data obtained by X-ray diffraction analysis (XRD) and quantitatively calculated using the Scherrer Equation.

[0310]

[0311] Classificationa axis(Å)b axis(Å)c axis(Å)Cell Volume (Å 3 )Crystallite size (nm) Example 1 10.328 26.007 34.6918 291.11140 Example 3 10.327 96.006 94.6916 291.06167 Example 4 10.328 36.006 94.6918 291.10122 Reference Example 10.329 06.007 24.6917 291.11163

[0312] As shown in Table 2 above, Examples 1, 3, and 4 had a-axis lattice constant, b-axis lattice constant, c-axis lattice constant, cell volume, and grain size of the cathode active material crystals that were generally similar to the analysis results of the reference example, and from this, it was confirmed that lithium was not lost within the lattice structure.

[0313]

[0314] [Test Example III: Pattern Analysis via X-ray Diffraction Analysis (XRD)]

[0315] The characteristics of the regenerated or prepared cathode active materials in Examples 1, 3, 4 and Reference Example were measured through XRD pattern analysis as follows, and the results are shown in Figure 1 below.

[0316] * XRD pattern analysis: This was obtained using a standard X-ray diffraction device commonly used in laboratories. Specifically, the analysis was performed using the Rigaku XG-2100 X-ray diffraction analyzer.

[0317]

[0318] Figure 1 below shows the XRD patterns of the regenerated or prepared cathode active materials in Examples 1, 3, 4 and the Reference Example. In the XRD pattern, the horizontal axis is 2θ (Theta) (degree, degrees), and the vertical axis is intensity. As shown in Figure 1 below, it was confirmed that no additional materials were generated in Examples 1, 3, and 4 compared to the Reference Example. Through this, it was found that the regenerated cathode active material prepared by heat treatment at a high temperature according to the present invention showed no change in crystal structure compared to the fresh cathode active material.

[0319]

[0320] [Test Example IV: Viscosity Characteristics]

[0321] The viscosity characteristics of the regenerated or prepared positive electrode active materials in Examples 1, 3, 4 and Reference Example were measured as follows and are shown in Table 3 and Figure 2.

[0322] * Viscosity characteristics: An electrode slurry was prepared by mixing Super-C as the positive active material and conductive material and KF200 as the binder in a ratio of 95 / 2 / 3, with a solid content of 58.5 wt%. The viscosity of the prepared electrode slurry was measured using a rheometer at room temperature conditions while increasing the shear rate from 0.01 to 1000 / s at regular intervals. Table 3 below shows the viscosity values ​​at 2.5 / s and 1000 / s.

[0323] In this description, room temperature may be one point within the range of 20 ± 5 ℃.

[0324]

[0325] Classification Example 1 Example 3 Example 4 Reference Example Viscosity (2 nd ascending)2.5 / s27,87715,58114,76415,2821000 / s1,8541,5791,3422,069

[0326] As shown in Table 3 above, it was confirmed that the viscosity of the electrode slurry containing the regenerated positive active material in Examples 1, 3, and 4 was more similar to the reference example as the heat treatment temperature increased.

[0327] The low viscosity of the electrode slurry containing the cathode active material recovered through heat treatment according to the present invention is attributed to the fact that the specific surface area (BET) is reduced by heat treatment at a high temperature, as confirmed in Table 1 above, thereby reducing the interaction with the binder and solvent.

[0328]

[0329] In addition, as shown in Fig. 2 below, it was confirmed that the regenerated cathode active materials in Examples 1, 3, and 4 had higher viscosity than the reference example at a shear rate of 0.01 / s to 2.5 / s, and that the viscosity of Examples 3 and 4 was lower than the reference example at a shear rate of 2.5 / s or higher.

[0330] In addition, it was found that as the heat treatment temperature of the regenerated cathode active material according to the present invention increases, the viscosity of the electrode slurry containing it decreases to a level similar to or equivalent to that of the reference example, which is a fresh cathode active material, thereby uniformly coating the current collector and improving the battery performance of the secondary battery.

[0331]

[0332] [Test Example V: SEM Image]

[0333] SEM images of the regenerated cathode active materials in Examples 1 and 4 were analyzed and are shown in Figures 3 and 4 below, respectively.

[0334]

[0335] Figure 3 below is an SEM image of Example 1, and Figure 4 below is an SEM image of Example 4. As shown in Figures 3 and 4 below, it was confirmed that the regenerated cathode active material according to the present invention showed increased particle growth and reduced fine particles as the heat treatment temperature increased.

[0336]

[0337] [Test Example VI: Raman Spectrum Analysis]

[0338] Raman spectrum analysis was performed on the regenerated cathode active materials in Examples 1, 3, and 4 above. Specifically, for the Raman spectrum analysis, a Raman spectrum was obtained for the surface of the sample using a DXR3xi '532 nm laser, and peak analysis was performed based on the average spectrum of 625 points and is shown in Tables 4 and 5 below. The results of the Raman spectrum analysis for the fresh cathode active material prepared in the reference example above are shown in Figures 5 and 6 below.

[0339] I in Table 4 below D / I G The peak ratio is 1580 to 1600 cm⁻¹ in the raw data (spectrum) obtained from the Raman spectrum analysis. -1 I, the peak intensity of the absorption region G1350 to 1380 cm for -1 I, the peak intensity of the absorption region D It was calculated as a ratio of .

[0340] In Table 5 below, the area ratio was obtained from each peak obtained by fitting the raw data (spectrum) obtained by measuring the cathode active material with a Raman spectrum. Specifically, the LFP area ratio is the area ratio of the LFP peak to the total sum of the areas of the LFP peak, D1 peak, D2 peak, D3 peak, and G peak; the D1 area ratio is the area ratio of the D1 peak to the total sum of the areas of the LFP peak, D1 peak, D2 peak, D3 peak, and G peak; the D2 area ratio is the area ratio of the D2 peak to the total sum of the areas of the LFP peak, D1 peak, D2 peak, D3 peak, and G peak; and the D3 area ratio is the area ratio of the D3 peak to the total sum of the areas of the LFP peak, D1 peak, D2 peak, D3 peak, and G peak.

[0341]

[0342] In addition, the D1 peak obtained by fitting the spectrum obtained by measuring the cathode active material by Raman spectrum in Fig. 6 is at 1160 to 1180 cm⁻¹ in the Raman spectrum analysis. -1 It is the peak of the absorption region, and sp 2 -sp 3 It refers to CC and C=C stretching vibrations of polyene-like structure at the edge of a bond or carbon network, and the D2 peak is at 1340 to 1360 cm⁻¹ in Raman spectral analysis. -1It is a peak in the absorption region, representing the graphene layer edge at CC and C=C stretching vibrations of a polyene-like structure at the edge of the carbon network, and the D3 peak is at 1500 to 1520 cm⁻¹ in Raman spectrum analysis. -1 It is a peak in the absorption region, indicating amorphousness, and the G peak is at 1590 to 1610 cm⁻¹ in Raman spectrum analysis. -1 It is a peak in the absorption region and represents an ordered carbon crystal without structural defects.

[0343]

[0344] Classification Heat Treatment Temperature I D / I G ratio Example 1490 ℃ 0.919 Example 3580 ℃ 0.929 Example 4700 ℃ 0.915

[0345] As shown in Table 4 above, if the heat treatment temperature for detaching the positive active material from the current collector is carried out at 450 to 740 ℃, I D / I G As the ratio decreases, electrical conductivity is excellent, and furthermore, the higher the heat treatment temperature, the more I D / I G It was confirmed that the ratio was low. In Raman spectrum analysis, the G band indicates carbon crystals without structural defects; the closer the crystallinity is to graphitic, the higher the G peak, and since the D band peak increases when disorder or defects are generated within the carbonaceous material, I D / I G It can be seen that the smaller the ratio, the better the electrical conductivity.

[0346]

[0347] Classification Heat Treatment Temperature Area Ratio LF PD 1 D 2 D 3 G Example 1 490 ℃ 0.00 9 0.2 3 2 0.4 2 2 0.1 3 5 0.2 2 Example 3 580 ℃ 0.00 5 0.2 0 6 0.4 1 9 0.1 6 8 0.2 2 Example 4 700 ℃ 0.00 3 0.2 1 2 0.4 1 2 0.1 8 1 0.1 9 2

[0348] As shown in Table 5 above, the LFP area ratio is a factor indicating the uniformity of the coating agent applied to the surface of the positive electrode active material; a lower value indicates that the area of ​​the positive electrode active material without the coating agent applied is smaller. According to the present invention, when heat treatment is performed at a temperature of 450 to 740 ℃, it can be seen that the carbon coating on the positive electrode active material is uniformly formed as the LFP area ratio decreases, and it can be predicted that the battery performance will be excellent when applied to a secondary battery. Furthermore, it was found that the higher the heat treatment temperature according to the present invention, the lower the specific surface area (BET), resulting in a more uniform carbon coating.

[0349] In addition, Figure 5 below shows the raw data (spectrum) of the Raman spectrum analysis of the fresh cathode active material prepared in the reference example. In Figure 5 below, 1350 to 1380 cm⁻¹ -1 The peak intensity value of the absorption region is I D and 1580 to 1600 cm -1 The peak intensity value of the absorption region is I G by means of I D / I G The peak ratio was calculated. The above I D / I G The peak ratio is an indicator that measures the structural defects and disorder of the cathode active material.

[0350] In addition, Figure 6 below shows the Raman spectrum of the fresh cathode active material prepared in the reference example and the D1, D2, D3, and G peaks obtained by fitting the same. In Figure 6 below, the black graph represents the LFP peak, and it can be seen that the carbon coating on the cathode active material is more uniform as the area of ​​the LFP peak decreases.

[0351]

[0352] [Test Example VI: Coin Half-Sell Evaluation]

[0353] The characteristics of the positive electrode active material regenerated or prepared in Example 4 and Reference Example above were measured through a coin half cell (hereinafter referred to as 'CHC') evaluation as follows, and the results are shown in Figures 7 and 8 below.

[0354]

[0355] * CHC Manufacturing: 95 wt% of recycled or fresh cathode active material, 2 wt% of carbon black as a conductive material, and 3 wt% of PVdF as a binder were weighed and mixed with NMP to make a cathode composite slurry. This was applied to the top of an aluminum foil current collector with a thickness of 20 μm and dried at 130°C for 1 hour, then stamped to manufacture a cathode and a cell (CHC) was manufactured. As an electrolytic core, the capacity was measured using a mixed solvent of ethylene carbonate (EC):dimethyl carbonate (DMC):diethyl carbonate (DEC) = 1:2:1 (weight ratio) containing other additives, under the following conditions.

[0356] * Initial charge / discharge capacity (%) of CHC: The capacity was measured for each cycle while charging and discharging each cell for 7 cycles under the following conditions and is shown in Figure 7 below. The initial charge / discharge capacity measured at this time is also shown in Figure 7 below.

[0357] Charge: 0.33C, CC / CV, 3.65V, 0.05C cut-off

[0358] Discharge: 0.33C, CC, 2.5V

[0359]

[0360] As shown in Fig. 7 below, it was confirmed that the regenerated cathode active material of Example 4 according to the present invention has superior initial charge / discharge capacity compared to the fresh cathode active material of the reference example, and particularly superior discharge capacity, thus having excellent battery characteristics.

[0361] In addition, as shown in Fig. 8 below, the regenerated cathode active material of Example 4 exhibited a discharge capacity superior to that of the fresh cathode active material of the reference example during 7 cycles.

[0362]

[0363] From the above experimental results, it was confirmed that the positive electrode active material regenerated according to the method for regenerating the positive electrode active material according to the present invention has a reduced specific surface area and a reduced carbon content, which lowers the viscosity of the electrode slurry containing it, making it easy to coat onto a current collector, and can provide battery characteristics equivalent to or better than those of the fresh positive electrode active material.

[0364] Furthermore, from this, it was confirmed that the method for regenerating the positive electrode active material according to the present invention does not use strong acids or organic solvents, and that the positive electrode active material is regenerated to have good battery characteristics even without the replenishment of lithium, iron, and / or phosphorus.

Claims

1. (a) A step of heat-treating a waste anode coated with a positive active material layer comprising a positive active material having an olivine structure on a current collector at 450 to 740 ℃ for 3 to 7 hours under an oxidizing atmosphere to detach the positive active material from the current collector; (b) a step of preparing an anode active material slurry by primary milling the detached anode active material under the addition of a coating agent; (c) drying and calcining the manufactured cathode active material slurry; and (d) a step of secondary milling the calcined positive active material; characterized by including Method for regenerating positive electrode active material.

2. In Paragraph 1, The positive electrode active material having the above olivine structure is characterized as being a compound represented by the following chemical formula 1. Method for regenerating positive electrode active material. [Chemical Formula 1] (In the above chemical formula 1, M comprises one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are each -0.5≤a≤0.5, 0≤b≤0.5, and 0≤c≤0.1.) 3. In Paragraph 2, The positive electrode active material having the above-mentioned olivine structure is characterized by containing lithium iron phosphate. Method for regenerating positive electrode active material.

4. In Paragraph 1, The cathode active material debonted after heat treatment in step (a) above has a specific surface area (BET) of 3.6 m² 2 Characterized by being less than or equal to / g Method for regenerating positive electrode active material.

5. In Paragraph 1, After the first milling in step (b) above, the positive active material has an average particle size (D 50 Characterized by being 0.3 to 0.5 μm Method for regenerating positive electrode active material.

6. In Paragraph 1, The first milling in step (b) above is characterized by being performed using a ball mill, a high-energy ball mill, a vibratory mill, or a roll mill. Method for regenerating positive electrode active material.

7. In Paragraph 1, In the above step (b), the coating agent is characterized by comprising one or more selected from the group consisting of metals, organometals, and carbon components. Method for regenerating positive electrode active material.

8. In Paragraph 1, The above step (c) is characterized by comprising: a step (c1) of spray-drying the positive active material slurry of the above step (b); and a step (c2) of forming a coating layer on the positive active material by calcining the dried positive active material at 500 to 900 ℃ under a reducing atmosphere. Method for regenerating positive electrode active material.

9. In Paragraph 1, After secondary milling in step (d) above, the positive active material has an average particle size (D 50 Characterized by being 0.80 to 1.73 μm Method for regenerating positive electrode active material.

10. In Paragraph 1, The secondary milling in step (d) above is characterized by being performed using a jet mill. Method for regenerating positive electrode active material.

11. In Paragraph 1, The positive active material after secondary milling in step (d) above is characterized by containing single particles. Method for regenerating positive electrode active material.

12. In Paragraph 1, After secondary milling in step (d) above, the cathode active material is I as measured by Raman spectrum analysis D / I G Characterized by a peak ratio of 0.950 or less Method for regenerating positive electrode active material.

13. The following chemical formula 1 [Chemical Formula 1] A compound represented by (in the above chemical formula 1, M comprises one or more elements selected from the group consisting of Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, X comprises one or more elements selected from the group consisting of F, S, and N, and a, b, and c are each -0.5≤a≤0.5, 0≤b≤0.5, and 0≤c≤0.1), Having an olivine structure, I measured by Raman spectrum analysis D / I G Characterized by a peak ratio of 0.950 or less Regenerative positive electrode active material.

14. In Paragraph 13, The above-mentioned regenerated cathode active material has an a-axis lattice constant of 10.3275 to 10.3293 Å, a c-axis lattice constant of 4.6912 to 4.6920 Å, and a cell volume of 291.00 to 291.15 Å as measured by XRD analysis. 3 and characterized by having a grain size of 118 to 170 nm Regenerative positive electrode active material.

15. In Paragraph 13, The above-mentioned regenerative cathode active material is characterized by containing single particles. Regenerative positive electrode active material.

16. In Paragraph 13, The above-described regenerated cathode active material is characterized by having an area ratio of the cathode active material peak to the total sum of the areas of the cathode active material peak, D1 peak, D2 peak, D3 peak, and G peak obtained by fitting a Raman spectrum of 0.010 or less. Regenerative positive electrode active material.

17. Characterized by including a regenerated cathode active material according to any one of claims 12 to 16 Secondary battery.

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