Method for producing regenerated positive electrode active material

Abstract

The present disclosure relates to a method for manufacturing a regenerated positive electrode active material. Provided is a technique for restoring the capacity in a degraded positive electrode active material and reducing the reaction resistance increased due to degradation without using a firing means. According to the technology disclosed herein, a method for producing a regenerated positive electrode active material is provided. The manufacturing method comprises the following steps: preparing a positive electrode active material; and grinding the positive electrode active material. The positive electrode active material includes a core particle having a layered crystal structure, and a coating portion having a rock salt crystal structure on the surface of the core particle. In this production method, at least a portion of the coated portion is separated from the core particles by grinding. The ratio (IB / IA) of the peak intensity IA at 8341 eV of the nickel (Ni)-K absorption edge as measured in XAFS analysis of the positive electrode active material before polishing to the peak intensity IB at 8341 eV of the nickel (Ni)-K absorption edge as measured in XAFS analysis of the positive electrode active material after polishing is 0.7 or less.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing regenerated positive electrode active materials. Background Technology

[0002] Examples of energy storage devices include secondary batteries such as lithium-ion batteries. In recent years, these secondary batteries have been used in portable power supplies for personal computers, mobile terminals, etc., and as power sources for vehicle propulsion in battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] Japanese Patent Application Publication No. 2022-82205 discloses a method for manufacturing a positive electrode active material, which includes a layer formation step and a heat treatment step. The layer formation step involves spraying molten lithium-containing material onto an electrode raw material to form a lithium-containing material layer. The heat treatment step involves heating the electrode raw material to which the lithium-containing material layer has been formed, introducing lithium contained in the lithium-containing material into the interior of the electrode raw material, and obtaining the positive electrode active material. This publication describes how, using this configuration, by fully introducing lithium as lithium ions into the interior of the raw material particles sprayed onto the positive electrode active material, energy density can be further improved, battery performance can be enhanced, manufacturing time can be further shortened, and productivity can be further increased.

[0004] Japanese Patent Application Publication No. 2017-79211 discloses a method for manufacturing regenerated electrode active material from a battery having an electrode composition, wherein the electrode composition comprises: a coated active material on which at least a portion of the surface of the electrode active material is coated with a coating agent comprising a coating resin, and an electrolyte. The manufacturing method includes a removal step and a removal step. The removal step is the step of removing the electrode composition from the battery. The removal step is the step of removing the coating active material contained in the electrode composition removed from the battery from the coating resin. This publication describes how, using this configuration, regenerated electrode active material can be obtained by recovering the electrode active material from the battery.

[0005] The lithium-ion secondary battery disclosed in Japanese Patent Application Publication No. 2000-268878 includes a positive electrode and a negative electrode. Regarding the positive electrode, the active material comprises a material with the formula LiNi. x M1 y M2 zA lithium-nickel composite oxide with a regularly arranged layered rock salt structure, represented by O2 (M1 is at least one selected from Co and Mn; M2 is at least one selected from Al, B, Fe, Cr, and Mg; x+y+z=1; 0.5<x<0.95; 0.01<y<0.4; 0.001<z<0.2). Regarding the negative electrode, the active material comprises a carbon material consisting of graphitic particles and ungraphitized carbonaceous particles whose surfaces are at least partially coated. This publication describes a lithium-ion secondary battery using this structure that provides excellent cycle characteristics (especially under high-temperature operating conditions) and is inexpensive without reducing battery capacity.

[0006] Japanese Patent Application Publication No. 2004-349210 discloses a method for regenerating positive electrode active material for lithium-ion batteries. This regeneration method includes a firing step and a cooling step. The firing step involves firing the positive electrode active material for lithium-ion batteries at a firing temperature of 750°C or higher and 1000°C or lower. The cooling step involves cooling the material from the firing temperature to a specified temperature at a rate of 0.2 to 2.0°C / min. The publication describes that using this configuration, the crystallite size of the positive electrode active material can grow to a sufficient size under these conditions, thus enabling a significant improvement in the performance of the positive electrode active material during regeneration.

[0007] Non-Patent Literature 1 describes the structural changes and electrochemical degradation associated with the migration of transition metal ions during charge-discharge cycles in a Li-excess layered oxide cathode, investigated using structural analysis and first-principles calculations employing XDS and Cs-STEM. According to this study, during charge-discharge cycling, Mn and Ni ions migrate from the transition metal layer to the Li layer, primarily in the surface region of the active material particles, generating NaCl-type MnO and NiO. In this literature, based on the aforementioned research, it is inferred that the irreversible migration of Mn and Ni ions between the transition metal / Li layers occurs in the oxygen-deficient surface of the active material, leading to the formation of NaCl-type MnO and NiO, a structural change reaction. Furthermore, according to Non-Patent Literature 1, the main reason for the electrochemical degradation associated with the decrease in discharge potential during charge-discharge cycling is the formation of NiO and MnO on the surface of the active material.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2022-82205

[0011] Patent Document 2: Japanese Patent Application Publication No. 2017-79211

[0012] Patent Document 3: Japanese Patent Application Publication No. 2000-268878

[0013] Patent Document 4: Japanese Patent Application Publication No. 2004-349210

[0014] Non-patent literature

[0015] Non-patent literature 1: SUNBEAM Annual Report with Research Results, Part 2, Vol.9 (2019) Summary of the Invention

[0016] The problem that the invention aims to solve

[0017] Currently, layered crystal structures are sometimes used as positive electrode materials for energy storage devices. It is known that, through charge-discharge cycles of energy storage devices, the layered crystal structure can change towards a rock salt crystal structure on the surface of the positive electrode active material. The correlation between this change in the surface crystal structure of the positive electrode active material and the charge-discharge cycle characteristics of the energy storage device has been investigated.

[0018] As described in the aforementioned patent documents, firing is one method for regenerating degraded positive electrode active material. However, firing consumes a large amount of energy, is costly, and there is still room for improvement in achieving both capacity recovery and reduction of resistance increased due to deterioration. Therefore, the inventors sought to restore the capacity of degraded positive electrode active material and reduce the reaction resistance increased due to deterioration without using firing.

[0019] Methods for solving problems

[0020] According to the technology disclosed herein, a method for manufacturing a regenerated positive electrode active material is provided. The method includes: preparing a positive electrode active material; and grinding the positive electrode active material. The positive electrode active material includes: core particles having a layered crystal structure, and a coating portion having a rock salt crystal structure on the surface of the core particles. In this manufacturing method, grinding is used to separate at least a portion of the coating portion from the core particles. The peak intensity I at 8341 eV of the nickel (Ni)-K absorber end of the positive electrode active material before grinding is determined by XAFS analysis. A The peak intensity I at 8341 eV of the nickel (Ni)-K absorber end, as determined by XAFS analysis of the milled positive electrode active material. B The ratio (I) B / I A The capacitance becomes 0.7 or less. Based on this configuration, it is possible to restore the capacity of the degraded positive electrode active material without using firing methods, and to reduce the reaction resistance increased due to deterioration. Attached Figure Description

[0021] Figure 1 This is a longitudinal cross-sectional view of a lithium-ion secondary battery 100.

[0022] Figure 2 This is a schematic diagram of electrode body 20. Detailed Implementation

[0023] The following describes one embodiment of the energy storage device disclosed herein. The embodiment described herein is not specifically limited to the technology disclosed herein. Unless otherwise specified, the technology disclosed herein is not limited to the embodiment described herein. The accompanying drawings are schematic descriptions and do not necessarily reflect the actual object. Furthermore, components / parts that perform the same function are sometimes labeled with the same reference numerals, and repeated descriptions are sometimes omitted. Additionally, unless otherwise specified, the designation "A~B" indicating a numerical range means "A or more and B or less," and also includes the meaning of "greater than A and less than B."

[0024] In this specification, the term "energy storage device" refers to a device that generates charge and discharge through the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. Energy storage devices include secondary batteries such as lithium-ion batteries, nickel-metal hydride batteries, and nickel-cadmium batteries; and capacitors such as lithium-ion capacitors and double-layer capacitors. The following describes an implementation method where the energy storage device is a lithium-ion secondary battery.

[0025] The method for manufacturing regenerated positive electrode active material disclosed herein includes, for example, a preparation step, a first analytical step, a grinding step, a classification step, a second analytical step, and an evaluation step. It should be noted that, in addition to the steps described above, the manufacturing method disclosed herein may include any other steps as needed.

[0026] The preparation process is, for example, the process of preparing degraded positive electrode active material. This positive electrode active material can be recycled, for example, from a used energy storage device. The following explanation is for the case where the used energy storage device is a lithium-ion secondary battery.

[0027] Figure 1 This is a longitudinal cross-sectional view of a lithium-ion secondary battery 100. Figure 2 This is a schematic diagram of electrode body 20. Figure 1 The lithium-ion secondary battery 100 shown is a used lithium-ion secondary battery. For example... Figure 1 As shown, the lithium-ion secondary battery 100 includes an electrode body 20, a casing 30, and a non-aqueous electrolyte 80.

[0028] like Figure 1 and Figure 2As shown, the electrode body 20 is a wound electrode body formed by overlapping a strip-shaped positive electrode 50 and a strip-shaped negative electrode 60 through a strip-shaped separator 70 and winding them along the length direction of the sheet (hereinafter also referred to as the "length direction"). In the electrode body 20, the exposed area 52a in the positive electrode 50 and the exposed area 62a in the negative electrode 60 extend outward from both ends in the width direction orthogonal to the length direction.

[0029] like Figure 1 and Figure 2 As shown, the positive electrode 50 includes a strip-shaped positive current collector 52 and a positive active material layer 54. The positive current collector 52 is, for example, an aluminum foil. In this embodiment, the positive current collector 52 has a region where the positive active material layer 54 is disposed, and an exposed region 52a where the surface of the positive current collector 52 is exposed due to the absence of the positive active material layer 54. The positive active material layer 54 is, for example, a strip-shaped portion along the length direction on one or both sides (in this case, both sides) of the positive current collector 52. The positive active material layer 54 is not disposed at the end (left end in the figure) in the width direction (hereinafter also referred to as "width direction"). The exposed region 52a is, here, a strip-shaped region at the end in the width direction (left end in the figure). Figure 1 As shown, a collector plate 42a is installed in the exposed area 52a.

[0030] The positive electrode active material layer 54, for example, contains a positive electrode active material. In this embodiment, the positive electrode active material has core particles and a coating on the surface of the core particles. The core particles here have a layered crystal structure. The core particles may be, for example, lithium composite oxides. There are no particular limitations, but considering the implementation of the grinding process described later, from the viewpoint of stability, the core particles are preferably single particles.

[0031] The lithium composite oxide is preferably a lithium transition metal composite oxide that contains at least Ni as a transition metal element. Examples of lithium transition metal composite oxides include lithium-nickel composite oxides, lithium-nickel-manganese composite oxides, lithium-nickel-cobalt-manganese composite oxides, lithium-nickel-cobalt-aluminum composite oxides, and lithium-iron-nickel-manganese composite oxides. The nucleus can be of one type or a combination of two or more types.

[0032] It should be noted that in this specification, the term "lithium-nickel-cobalt-manganese composite oxide" refers not only to oxides with Li, Ni, Co, Mn, and O as constituent elements, but also to oxides containing one or more additional elements. Examples of these additional elements include transition metals and typical metallic elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. Additional elements may be half-metallic elements such as B, C, Si, and P; and non-metallic elements such as S, F, Cl, Br, and I. This also applies to the aforementioned lithium-nickel composite oxides, lithium-nickel-manganese composite oxides, lithium-nickel-cobalt-aluminum composite oxides, and lithium-iron-nickel-manganese composite oxides.

[0033] As a nuclear particle, LiNi can be preferably used, for example. 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.

[0034] The coating may have, for example, a rock salt crystal structure. This rock salt crystal structure coating may, for example, contain material generated during the charging and discharging of the lithium-ion secondary battery 100, resulting from the migration of transition metal nuclei from transition metal sites to lithium sites. Therefore, the presence of a rock salt crystal structure coating in the positive electrode active material can indicate degradation of the positive electrode active material. While not particularly limited, the coating may, for example, contain nickel oxide (NiO) or manganese oxide (MnO).

[0035] The average particle size of the positive electrode active material is approximately 0.5 μm to 20 μm. The average particle size of the positive electrode active material is, for example, 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more. The average particle size of the positive electrode active material is, for example, 15 μm or less, preferably 12 μm or less, and more preferably 10 μm or less. The average particle size of the positive electrode active material referred to herein refers to the average particle size of the positive electrode active material including the core particles and the coating. It should be noted that, in this specification, regarding particles, the term "average particle size" refers to the particle size (D0) that represents the cumulative 50% of the particle size from the microparticle side in the volume-based particle size distribution determined by particle size distribution measurement based on laser diffraction-light scattering method. 50 Particle size).

[0036] In addition to the positive electrode active material, the positive electrode active material layer 54 may include conductive materials, binders, etc. Examples of conductive materials include carbon black such as acetylene black (AB) and other carbon materials such as graphite. Examples of binders include polyvinylidene fluoride (PVDF). The content of the positive electrode active material relative to the entire positive electrode active material layer 54 is preferably 70% by mass or more, more preferably 85% to 95% by mass. The content of the conductive material relative to the entire positive electrode active material layer 54 is, for example, 0.1% to 20% by mass. The content of the binder relative to the entire positive electrode active material layer 54 is, for example, 0.5% to 15% by mass. It should be noted that in this specification, "positive electrode binder" refers to the entirety of the materials constituting the positive electrode active material layer 54.

[0037] like Figure 1 and Figure 2 As shown, the negative electrode 60 includes a strip-shaped negative electrode current collector 62 and a negative electrode active material layer 64. The negative electrode current collector 62 is, for example, a copper foil. In this embodiment, the negative electrode current collector 62 has a region where the negative electrode active material layer 64 is disposed, and an exposed region 62a where the surface of the negative electrode active material layer 64 is exposed. The negative electrode active material layer 64 is, for example, a strip-shaped region along the length direction on one or both sides (in this case, both sides) of the negative electrode current collector 62. The negative electrode active material layer 64 is not disposed at its width-direction end (the right end in the figure). The exposed region 62a is, in this case, a strip-shaped region at the width-direction end (the right end in the figure). Figure 1 As shown, a collector plate 44a is installed in the exposed area 62a.

[0038] The negative electrode active material layer 64 contains, for example, a negative electrode active material. There are no particular limitations on the negative electrode active material, and conventionally known negative electrode active materials used in this application can be used. The negative electrode active material can be, for example, carbon materials such as graphite, hard carbon, and soft carbon; or silicon (Si). The content of the negative electrode active material relative to the entire negative electrode active material layer 64 is preferably 70% by mass or more, more preferably 85% to 98% by mass.

[0039] In addition to the negative electrode active material, the negative electrode active material layer 64 may contain binders, thickeners, etc. Examples of binders include styrene-butadiene rubber (SBR). The content of the binder relative to the total negative electrode active material layer 64 is not particularly limited, and may be, for example, 0.1% to 8% by mass. As a thickener, carboxymethyl cellulose (CMC) is preferably used, for example. The content of the thickener relative to the total negative electrode active material layer 64 is not particularly limited, and may be, for example, 0.3% to 3% by mass.

[0040] As the separator 70, examples include porous sheets (membranes) made of resin materials such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. The porous sheet can be a single-layer structure or a multi-layered structure (e.g., a three-layer structure with PP layers laminated on both sides of a PE layer). A heat-resistant layer (HRL) can be provided on the surface of the separator 70.

[0041] The housing 30 is, for example, an outer container housing the electrode body 20 and the non-aqueous electrolyte 80. Here, the housing 30 is a flat, square-shaped housing. Figure 1 As shown, the housing 30 has a positive terminal 42, a negative terminal 44, a safety valve 36, and an injection port (not shown). The positive terminal 42 is, for example, an external connection terminal on the positive side. The positive terminal 42 is electrically connected to the positive electrode 50 of the electrode body 20 via a current collector 42a. The negative terminal 44 is, for example, an external connection terminal on the negative side. The negative terminal 44 is electrically connected to the negative electrode 60 of the electrode body 20 via a current collector 44a. The safety valve 36 is, for example, a thin-walled portion designed to release internal pressure when the internal pressure of the housing 30 rises above a predetermined level. The injection port is, for example, a portion for injecting a non-aqueous electrolyte 80 into the housing 30.

[0042] The non-aqueous electrolyte 80 includes, for example, a non-aqueous solvent and a supporting salt. Examples of non-aqueous solvents used in this application include various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones. Carbonates are preferred. Examples of carbonates include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), fluoroethylene carbonate (FEC) (preferably monofluoroethylene carbonate), monofluoromethyl difluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC). One non-aqueous solvent can be used alone, or two or more non-aqueous solvents can be used in combination. Examples of supporting salts include lithium salts such as LiPF6, LiBF4, and LiClO4. The concentration of the supporting salt can be, for example, from 0.7 mol / L to 1.4 mol / L. The non-aqueous electrolyte 80 may, as needed, contain additives used in this application. As an additive, it may contain, for example, film-forming agents such as LiB(C2O4)2 (LiBOB) and LiBF2 (C2O4); gas generators such as biphenyl (BP) and cyclohexylbenzene (CHB); thickeners, etc.

[0043] In the preparation process, in this embodiment, firstly, the deteriorated energy storage device (here, a lithium-ion secondary battery 100) is disassembled, the electrode body 20 is removed from inside the casing 30, and then the positive electrode 50 is removed. Secondly, the positive electrode active material layer 54 can be scraped off from the positive electrode current collector 52 of the positive electrode 50 to obtain a positive electrode mixture containing the positive electrode active material.

[0044] While there are no particular limitations, from the viewpoint of suppressing accelerated degradation, the preparation process is preferably carried out in an inactive and dry atmosphere. For example, from the disassembly of the lithium-ion secondary battery 100 to obtaining the positive electrode mixture, it is preferable to carry out the process in a glove box with an inactive and dry atmosphere.

[0045] The first analysis step is, for example, a step of performing X-ray absorption fine structure (XAFS) analysis on the prepared positive electrode active material. By performing the first analysis step, for example, the degree of coating formation and the composition of the coating can be analyzed. In this embodiment, in the first analysis step, the peak intensity I at 8341 eV of the nickel (Ni) absorption end, as measured in the XAFS analysis of the positive electrode active material obtained in the preparation step, is determined. A .

[0046] The presence of the peak at 8341 eV at the nickel (Ni) absorber end indicates, for example, that during the charging and discharging of the lithium-ion secondary battery 100, nickel (Ni) ions in the positive electrode active material migrate from the transition metal site to the lithium site and become divalent (Ni). 2+ This means that during charging of the lithium-ion secondary battery 100, nickel (Ni) ions move to lithium sites and their valence becomes divalent, while during discharge, they no longer return to transition metal sites. It is known that due to the presence of the peak at 8341 eV, a portion of the surface of the positive electrode active material contains a coating of nickel compounds (e.g., NiO) with a rock-salt crystal structure. Furthermore, in the rock-salt crystal structure of the nickel compound, lithium insertion / deposition occurs at a lower potential than in the layered crystal structure of the positive electrode active material, thus lowering the discharge potential and becoming a major cause of degradation. Therefore, the presence of the peak at 8341 eV at the nickel (Ni)-absorber end can be used as an indicator of the degradation of the lithium-ion secondary battery 100.

[0047] In this embodiment, XAFS analysis using the permeation method is preferable. From the viewpoint of facilitating analysis, the positive electrode active material used for XAFS analysis in the first analysis step can be the positive electrode mixture obtained in the preparation step. Commercially available measuring devices are not particularly limited in their use in this and second analysis steps. For example, the "QuantumLeap V210" manufactured by Canon Corporation can be cited as an example. For the analysis of the obtained data, the analysis software "Athena" is preferred, for example.

[0048] The grinding process is, for example, the process of grinding the positive electrode active material. By performing the grinding process, it is possible, for example, to separate the coated portion from the nuclei. In this embodiment, the positive electrode active material is ground by adding the positive electrode mixture obtained in the preparation process into a container containing the grinding material and rotating the container. The grinding material (e.g., alumina abrasive particles) is preferably coated on the inner wall of the container. There is no particular limitation on the rotation of the container; it can be both rotation and revolution. The number of rotations and revolutions can both be set to approximately 500 rpm to 3000 rpm (preferably 1000 rpm to 2500 rpm). The grinding time is, for example, 10 minutes to 120 minutes, preferably set to 30 minutes to 60 minutes. In the grinding process, a commercially available spin-revolution mixer can be preferably used, for example. As a commercially available spin-revolution mixer, THINKY's "Defoaming Rentaro" is an example.

[0049] Regarding the grinding process, from the viewpoint of efficiently separating the coated parts while suppressing unwanted chemical reactions during grinding, it is preferable to carry out the process in an inactive and dry atmosphere.

[0050] The grading process is, for example, a process of grading the ground positive electrode active material. By performing the grading process, for example, the coating portion separated due to grinding, and the small fragments generated due to grinding, can be removed to obtain particles of a suitable size. In this embodiment, in the grading process, a particle group having the same particle size distribution as the positive electrode active material before grinding is obtained. Therefore, it is preferable to obtain a particle group with an average particle size of approximately 0.5 μm to 20 μm in the grading process. The average particle size of the particle group obtained in the grading process is, for example, 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more. The average particle size of the particle group obtained in the grading process is, for example, 15 μm or less, preferably 12 μm or less, and more preferably 10 μm or less.

[0051] The second analysis step is, for example, a step of performing XAFS analysis on the positive electrode active material after the grinding process. By performing the second analysis step, it is possible to analyze, for example, the degree of residual coating on the surface of the nuclear particles and the composition of the residual coating. In this embodiment, in the second analysis step, the peak intensity I at 8341 eV of the nickel (Ni) absorption end, as measured in the XAFS analysis of the positive electrode active material after the grinding process, is determined. B .

[0052] The evaluation process, for example, is a process of evaluating whether a material can be used as a regenerated positive electrode active material based on the results obtained in the first analysis process and the results obtained in the second analysis process. In this embodiment, in the evaluation process, at peak intensity I... A With peak intensity I B The ratio (I) B / I AWhen the ratio (I) is below 0.7, it is rated as "good" and deemed suitable for use as a regenerated positive electrode active material. In this case, the positive electrode active material can be used, for example, as a positive electrode active material in the manufacture of new lithium-ion secondary batteries. B / I A If the particle size is greater than 0.7, it is evaluated as a "defective product" and deemed unsuitable for use as a regenerated positive electrode active material. In this case, the positive electrode active material can be subjected to the aforementioned grinding process again, for example.

[0053] From the perspective of better realizing the battery performance of batteries using regenerated positive electrode active materials, compared to (I B / I A Preferably, it is 0.65 or less, more preferably 0.6 or less, and even more preferably 0.55 or less; the smaller the better. While there are no particular limitations, it is more than (I B / I A It is approximately 0.05 or higher, for example, 0.1 or higher, or 0.2 or 0.3 or higher.

[0054] The regenerated positive electrode active material manufactured using the manufacturing method disclosed herein can be used, for example, in the manufacture of lithium-ion secondary batteries for various applications. Preferred applications include drive power supplies installed in vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Lithium-ion secondary batteries can also be used, for example, as batteries in small energy storage devices. Lithium-ion secondary batteries can also be used, for example, in the form of battery packs composed of multiple batteries connected in series and / or in parallel.

[0055] The method for manufacturing regenerated positive electrode active material disclosed herein includes: preparing a positive electrode active material; and grinding the positive electrode active material. The positive electrode active material includes: core particles having a layered crystal structure, and a coating portion having a rock salt crystal structure on the surface of the core particles. In this manufacturing method, at least a portion of the coating portion is separated from the core particles by grinding. The peak intensity I at 8341 eV of the nickel (Ni)-K absorber, measured in XAFS analysis of the positive electrode active material before grinding, is... A The peak intensity I at 8341 eV of the nickel (Ni)-K absorber, as determined by XAFS analysis of the milled positive electrode active material. B The ratio (I) B / I A It becomes below 0.7.

[0056] The positive electrode active material prepared using this manufacturing method comprises: core particles having a layered crystal structure, and a coating portion having a rock salt crystal structure on the surface of the core particles. As mentioned above, the coating portion of the positive electrode active material is formed, for example, through charge-discharge cycles of a lithium-ion secondary battery 100, and can be a major cause of degradation of the positive electrode active material. In this manufacturing method, by including grinding the positive electrode active material having the coating portion, the coating portion of the positive electrode active material can be separated. The degree of separation from the coating portion of the positive electrode active material caused by grinding is evaluated by XAFS analysis of the positive electrode active material before and after grinding. In the evaluation using XAFS analysis, the peak intensity I at 8341 eV of the nickel (Ni)-K absorber end of the positive electrode active material before grinding is used. A The peak intensity I at 8341 eV for the nickel (Ni)-K absorption end of the polished active material B The ratio (I) B / I A Substances with a strength of 0.7 or less are evaluated as good products. In other words, in the manufacturing method disclosed herein, regenerated positive electrode active materials can be manufactured by grinding the positive electrode active material and evaluating the degree of separation of the coating portion of the positive electrode active material caused by grinding. Therefore, by using the manufacturing method disclosed herein, the capacity in degraded positive electrode active materials can be restored without using firing methods, and the reaction resistance increased due to deterioration can be reduced.

[0057] In the manufacturing method disclosed herein, the positive electrode active material is ground in a dry atmosphere during the grinding process. This suppresses the removal of lithium ions from the nucleus particles caused by the presence of moisture.

[0058] The manufacturing method disclosed herein may include performing XAFS analysis of the positive electrode active material before and after grinding. By performing XAFS analysis of the positive electrode active material before and after grinding, it is possible to manufacture a regenerated positive electrode active material with high reliability in terms of capacity recovery and reduction of reaction resistance increased due to degradation.

[0059] The manufacturing method disclosed herein may include classifying the milled positive electrode active material. By classifying the milled positive electrode active material, it is possible to selectively obtain a particle group with a suitable particle size from a mixture of particle groups with suitable particle size and coated sheets, etc., separated by milling.

[0060] In the manufacturing method disclosed herein, positive electrode active material with an average particle size of 5 μm to 10 μm can be obtained through grading. This allows for the acquisition of a particle group with a preferred particle size distribution as a positive electrode active material for energy storage devices.

[0061] In the manufacturing method disclosed herein, the positive electrode active material can be a lithium transition metal composite oxide. Therefore, a preferred regeneration method for the positive electrode active material, which is a lithium transition metal composite oxide, can be provided.

[0062] The following description of test examples related to the technology disclosed herein is not intended to limit the technology disclosed herein to the content shown in the test examples below.

[0063] [Deterioration of the positive electrode active material]

[0064] Single-particle LiNi is prepared as a raw material to serve as the positive electrode active material. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (LNCM) (average particle size: 8 μm), acetylene black (AB) as the conductive material, and polyvinylidene fluoride (PVdF) as the binder are mixed with N-methylpyrrolidone (NMP) as the solvent in a mass ratio of LNCM:AB:PVdF = 90:8:2 to prepare a positive electrode paste. The positive electrode paste is coated onto both sides of a long strip of aluminum foil to form a strip, dried, and then pressed to obtain the positive electrode sheet.

[0065] Graphite, used as the negative electrode active material, styrene-butadiene rubber (SBR), used as the binder, and carboxymethyl cellulose (CMC), used as the thickener, are prepared. These are mixed with water as a solvent in a mass ratio of graphite:SBR:CMC = 98:1:1 to prepare a negative electrode paste. The negative electrode paste is coated onto both sides of a long strip of copper foil to form a strip, dried, and then pressed to obtain the negative electrode sheet.

[0066] As a separator, HRL separator sheets are prepared on a porous polyolefin sheet with a three-layer structure of PP / PE / PP. The positive electrode sheet, negative electrode sheet and two separator sheets are stacked, wound, and then pressed flat from the side to create a flat wound electrode body.

[0067] Next, the positive and negative terminals are connected to the wound electrode body and housed in a square casing with an electrolyte injection port. Then, a non-aqueous electrolyte is injected through the injection port, and the injection port is sealed airtight. It should be noted that the non-aqueous electrolyte is prepared by dissolving LiPF6, as the supporting salt, at a concentration of 1.1 mol / L in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC:DMC:EMC = 3:3:4. Then, an aging process is performed to produce a usable lithium-ion secondary battery.

[0068] The lithium-ion secondary battery was placed in an environment of 40°C. For the lithium-ion secondary battery, it was charged with a constant current (CC) of 1C until 4.3V, and then discharged with a CC of 1C until 3.0V, thus degrading the lithium-ion secondary battery. It should be noted that this degradation involved 400 charge-discharge cycles, with the above charge-discharge cycle considered as one cycle.

[0069] The degraded lithium-ion secondary battery is discharged until the voltage reaches 2V. Then, the lithium-ion secondary battery is disassembled, the positive electrode is removed, the positive electrode is crushed, the positive electrode flux is recovered, and then powder is prepared by sieving through a sieve with a mesh size of 500μm.

[0070] [Grinding and Classification of Positive Electrode Active Materials]

[0071] <Examples 1 to 4, Comparative Example 2, Comparative Example 3>

[0072] Next, the powder was ground. A rotation-revolution mixer (THINKY's "Defoaming Rentaro") was used for grinding the powder. The powder was placed in a container coated with alumina abrasive material (particle size 80 (3.6μm~18μm)) on the inner wall, and the container was placed on a support tilted at 45° relative to the revolution axis for grinding. The mixer's revolution speed was 1500 rpm. The container's rotation speed was 1500 rpm. The grinding time was set to 30 to 60 minutes. The grinding atmosphere was a nitrogen atmosphere and a dry atmosphere. Then, the ground powder was classified to obtain a particle group with an average particle size of 8μm.

[0073] <Comparative Example 1>

[0074] The positive electrode mixture obtained by crushing the positive electrode sheet was fractionated to obtain a particle group with an average particle size of 8 μm. This was used as Comparative Example 1.

[0075] <Reference example>

[0076] The positive electrode active material prepared as the above raw material is used as a reference example.

[0077] For the graded powder samples and the reference sample, the average particle size D2 was measured using the aforementioned measuring apparatus. Then, the following mathematical formula (X) was used:

[0078] Reduction in size (μm) = (Average particle size D1 before grinding) - (Average particle size D2 after grinding) (X)

[0079] The reduction in average particle size (μm) before and after grinding was obtained. The results are shown in this column of Table 1. It should be noted that the average particle size of Comparative Example 1 is set as the average particle size D1.

[0080] [XAFS Analysis]

[0081] For the graded powders and reference examples, XAFS analysis using the transmission method was performed. The XAFS analysis was performed according to the manual of the measuring device "QuantumLeap V210" (manufactured by Canon Corporation) used in the analysis. In the XAFS analysis, the incident energy was set to the manganese (Mn)-K absorption end, the cobalt (Co)-K absorption end, and the nickel (Ni)-K absorption end, and the transmission amount (transmission XAFS) of each energy was measured. The type of X-ray measured was hard X-ray. At the same time, the diffraction intensities of the (003) plane and the (104) plane in the space group R-3m were obtained simultaneously. The anomalous dispersion term f""eu / site" was obtained from the obtained diffraction intensities, and the XAFS spectrum corresponding to the anomalous dispersion term f" was extracted. Next, the peak intensity at 8341 eV of the nickel (Ni) absorption end was obtained. For the extraction of the XAFS spectrum, the analysis software "Athena" which is widely used in XAFS analysis was used. Then, the peak intensity I of Comparative Example 1 was calculated. A Peak intensity I compared to other examples B The ratio (I) B / I A The results are shown in this column of Table 1.

[0082] [Evaluation of Capacity Maintenance Rate]

[0083] Using the graded powders from Examples 1 to 4 and Comparative Examples 1 to 3, and following the materials and steps described above, seven types of test secondary batteries were prepared. Furthermore, using the positive electrode active material as the aforementioned raw material, and following the materials and steps described above, test secondary batteries for reference examples were prepared. Eight test secondary batteries prepared therein were placed in an environment of 25°C. The test secondary batteries were subjected to CCCV charging (cutoff current: 0.01C) at a current of 0.1C to 4.3V. Then, the test secondary batteries were subjected to CCCV discharging (cutoff current: 0.01C) from 4.3V to 3.0V. The capacity of each test secondary battery was measured when the CCCV charging and discharging cycle was considered as one cycle. Furthermore, the capacity of each example's test secondary battery was calculated when the capacity of the test secondary battery for the reference example was set to 100%. The results are shown in this column of Table 1.

[0084] The test secondary battery was charged at -10°C until the state of charge (SOC) of the positive electrode reached 50%. Next, impedance measurements were performed at an amplitude of 5mV and a frequency range of 0.01Hz to 10000Hz. A Cole-Cole diagram was created using the results, with the diameter of the semicircle defined as the resistance value. The resistance of each test secondary battery was calculated when the resistance of the reference example's test secondary battery was set to 100%. The results are shown in this column of Table 1.

[0085] Table 1

[0086] Table 1

[0087]

[0088] The manufacturing method implemented in this experimental example includes: preparing a positive electrode active material; and grinding the positive electrode active material. The positive electrode active material includes: core particles having a layered crystal structure, and a coating portion having a rock salt crystal structure on the surface of the core particles. By grinding, at least a portion of the coating portion is separated from the core particles. Then, as shown in Table 1, the peak intensity I at 8341 eV of the nickel (Ni)-K absorber end is measured using XAFS analysis of the positive electrode active material before grinding. A The peak intensity I at 8341 eV of the nickel (Ni)-K absorber, as determined by XAFS analysis of the milled positive electrode active material. B The ratio (I) B / I A In the test secondary batteries made from the positive electrode active materials of Examples 1 to 4 with a value of 0.7 or less, the capacity retention rate was restored and the reaction resistance that had increased due to deterioration was reduced.

[0089] The technology disclosed herein may include the technology described in the following items.

[0090] Item 1:

[0091] A method for manufacturing regenerated positive electrode active material, comprising: preparing a positive electrode active material, said positive electrode active material comprising: core particles having a layered crystal structure, and a coating portion having a rock salt crystal structure on the surface of said core particles; and

[0092] The positive electrode active material is ground.

[0093] In this process, at least a portion of the coating is separated from the nuclear particles through the grinding, and the peak intensity I at 8341 eV of the nickel (Ni)-K absorption end is determined in the X-ray absorption microstructure analysis of the positive electrode active material before grinding. AThe peak intensity I at 8341 eV at the nickel (Ni)-K absorption end, as determined in the X-ray absorption microstructure analysis of the ground positive electrode active material, is... B The ratio (I) B / I A It becomes below 0.7.

[0094] Item 2:

[0095] According to the manufacturing method of item 1, the positive electrode active material is ground in a dry atmosphere during the grinding process.

[0096] Item 3:

[0097] The manufacturing method according to item 1 or 2 includes, before and after the grinding, performing X-ray absorption microstructure analysis of the positive electrode active material.

[0098] Item 4:

[0099] The manufacturing method according to any one of claims 1 to 3 includes classifying the ground positive electrode active material.

[0100] Item 5:

[0101] According to the manufacturing method described in item 4, the positive electrode active material with an average particle size of 5 μm or more and 10 μm or less is obtained by means of the grading.

[0102] Item 6:

[0103] The manufacturing method according to any one of items 1 to 5, wherein the positive electrode active material is a lithium transition metal composite oxide.

[0104] The embodiments of the technology disclosed herein have been described above, but these are merely illustrative and do not limit the scope of the patent claims. The technology described in the patent claims includes technical solutions that are various modifications and alterations to the specific examples described above.

[0105] Explanation of reference numerals in the attached figures

[0106] 20 Electrode Body

[0107] 30. Housing

[0108] 42 Positive extremes

[0109] 44 Negative extremes

[0110] 50 Positive Electrode

[0111] 60 Negative electrode

[0112] 70 Separator

[0113] 80 Non-aqueous electrolyte

[0114] 100 Lithium-ion Secondary Battery

Claims

1. A method for manufacturing regenerated positive electrode active material, comprising: Prepare a positive electrode active material, the positive electrode active material comprising: core particles having a layered crystal structure, and a coating portion having a rock salt crystal structure on the surface of the core particles; and The positive electrode active material is ground. In this process, at least a portion of the coating is separated from the nuclear particles through the grinding, and the peak intensity I at 8341 eV of the nickel (Ni)-K absorption end is determined in the X-ray absorption microstructure analysis of the positive electrode active material before grinding. A The peak intensity I at 8341 eV at the nickel (Ni)-K absorption end, as determined in the X-ray absorption microstructure analysis of the ground positive electrode active material, is... B The ratio (I) B / I A It becomes below 0.

7.

2. The manufacturing method according to claim 1, wherein, In the grinding process, the positive electrode active material is ground in a dry atmosphere.

3. The manufacturing method according to claim 1, wherein, Before and after the grinding process, the process includes performing X-ray absorption microstructure analysis of the positive electrode active material.

4. The manufacturing method according to any one of claims 1 to 3, wherein, This includes classifying the ground positive electrode active material.

5. The manufacturing method according to claim 4, wherein, By employing the aforementioned grading method, the positive electrode active material with an average particle size of 5 μm or more and 10 μm or less is obtained.

6. The manufacturing method according to claim 1, wherein, The positive electrode active material is a lithium transition metal composite oxide.

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