Method for producing regenerated positive electrode active material

Abstract

To provide a technique for recovering a capacity in a deteriorated positive electrode active material and reducing a reaction resistance increased by deterioration without using a means of calcination SOLUTION: According to the technology disclosed herein, a method for producing a regenerated positive electrode active material is provided. The production method includes preparing a positive electrode active material and polishing 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 a surface of the core particle. In this production method, at least a part of the coating portion is separated from the core particle by polishing. The ratio (IB / IA) between the peak intensity IA at the 8341eV of the nickel (Ni) - K absorption edge measured by XAFS analysis for the positive electrode active material before polishing and the peak intensity IB at the 8341eV of the nickel (Ni) - K absorption edge measured by XAFS analysis for the positive electrode active material after polishing is 0.7 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a regenerated positive electrode active material. [Background technology]

[0002] An example of an electricity storage device is a secondary battery such as a lithium-ion secondary battery. In recent years, this type of secondary battery has been suitably used as a portable power source for personal computers, mobile terminals, etc., and as a power source for driving vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] The method for producing a positive electrode active material disclosed in JP 2022-82205 A includes a layer formation step and a heat treatment step. The layer formation step is a step of spraying a molten lithium-containing material onto an electrode raw material to form a lithium-containing material layer on the electrode raw material. The heat treatment step is a step of heating the electrode raw material on which the lithium-containing material layer has been formed, and introducing the lithium contained in the lithium-containing material into the electrode raw material to obtain a positive electrode active material. The publication states that with this configuration, the lithium sprayed onto the raw material particles of the positive electrode active material can be sufficiently introduced into the raw material particles as lithium ions, thereby further increasing the energy density and improving battery performance, and further shortening the production time and further improving productivity.

[0004] Japanese Patent Application Laid-Open No. 2017-79211 describes a method for producing a recycled electrode active material from a battery having an electrode composition including a coated active material in which at least a portion of the surface of the electrode active material is coated with a coating agent containing a coating resin, and an electrolyte. This production method includes an extraction step and a removal step. The extraction step is a step of removing the electrode composition from the battery. The removal step is a step of removing the coating resin from the coated active material contained in the electrode composition removed from the battery. The publication also describes that this configuration makes it possible to obtain a recycled electrode active material by recovering the electrode active material from the battery.

[0005] The lithium-ion secondary battery disclosed in Japanese Patent Application Laid-Open No. 2000-268878 includes a positive electrode and a negative electrode. The positive electrode contains, as a positive electrode active material, a lithium nickel composite oxide having a regular arrangement layered rock salt structure represented by the composition formula LiNi x M1 y M2 z O2 (where 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). The negative electrode contains, as a negative electrode active material, a carbon material composed of graphite particles and carbonaceous particles on the surface of which graphitization has not progressed and that cover at least a part of the surface of the graphite particles. The same publication describes that with such a configuration, a lithium-ion secondary battery excellent in cycle characteristics (particularly cycle characteristics in a high-temperature usage environment) and inexpensive can be provided without reducing the battery capacity.

[0006] Japanese Patent Application Laid-Open No. 2004-349210 discloses a method for regenerating a positive electrode active material for a lithium secondary battery. This regeneration method has a firing step and a cooling step. The firing step is a step of firing the positive electrode active material for a lithium secondary battery at a firing temperature of 750°C or higher and 1000°C or lower. The cooling step is a step of cooling from the firing temperature to a predetermined temperature at a rate of 0.2 to 2.0°C / min. The same publication describes that with such a configuration, the crystallite size of the positive electrode active material can be grown to a sufficient size under these conditions, so that the performance of the positive electrode active material can be dramatically regenerated.

[0007] Non-Patent Document 1 describes a study using XDS and Cs-STEM structural analysis and first-principles calculations to investigate the structural change process accompanying the migration of transition metal ions during charge / discharge of Li-excess layered oxide positive electrodes and their electrochemical degradation. This study revealed that Mn and Ni ions migrate from the transition metal layer to the Li layer, primarily in the surface region of the active material particles, during charge / discharge cycling, forming NaCl-type MnO and NiO. Based on the above study, this document infers a structural change reaction in which Mn and Ni ions irreversibly migrate between the transition metal layer and the Li layer in the active material surface layer, which contains oxygen vacancies, resulting in the formation of NaCl-type MnO and NiO. According to Non-Patent Document 1, the electrochemical degradation accompanied by a decrease in discharge potential due to charge / discharge cycling is thought to be caused by NiO and MnO formed on the active material surface. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2022-82205 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-79211 [Patent Document 3] Japanese Patent Application Laid-Open No. 2000-268878 [Patent Document 4] Japanese Patent Application Laid-Open No. 2004-349210 [Non-patent literature]

[0009] [Non-Patent Document 1] SUNBEAM Annual Report with Research Results, Part 2, Vol.9 (2019) Summary of the Invention [Problem to be solved by the invention]

[0010] Positive electrode active materials having a layered crystalline structure have been used as materials for the positive electrodes of energy storage devices. It is known that, for example, the layered crystalline structure on the surface of the positive electrode active material changes to a rock salt crystalline structure during charge-discharge cycles of the energy storage device. The relationship between such changes in the crystalline structure on the surface of the positive electrode active material and the charge-discharge cycle characteristics of the energy storage device has been studied.

[0011] As described in the aforementioned patent documents, calcination is one method for restoring a deteriorated positive electrode active material. However, calcination requires a large amount of energy and is costly. Furthermore, there is still room for improvement in achieving both the effect of restoring capacity and the effect of reducing the resistance increased due to deterioration. Therefore, the present inventors wanted to restore the capacity of a deteriorated positive electrode active material and reduce the reaction resistance increased due to deterioration without using calcination. [Means for solving the problem]

[0012] The technology disclosed herein provides a method for producing a recycled cathode active material. This method includes preparing a cathode active material and polishing the cathode active material. The cathode 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 coating portion is separated from the core particle by polishing. The peak intensity I at 8341 eV at the nickel (Ni) K absorption edge measured by XAFS analysis of the cathode active material before polishing is A and the peak intensity I at 8341 eV at the nickel (Ni) K absorption edge measured by XAFS analysis of the polished positive electrode active material. B and the ratio (I B / I A ) is 0.7 or less. According to this configuration, it is possible to recover the capacity of the deteriorated positive electrode active material without using a calcination method, and to reduce the reaction resistance that has increased due to deterioration. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a vertical cross-sectional view of a lithium-ion secondary battery 100. As shown in FIG. [Figure 2] FIG. 2 is a schematic diagram of the electrode body 20. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the energy storage device disclosed herein will be described below. The embodiment described herein does not particularly limit the technology disclosed herein. The technology disclosed herein is not limited to the embodiment described herein, unless otherwise specified. The drawings are schematic and do not necessarily reflect the actual product. Furthermore, members and parts that perform the same function are appropriately designated by the same reference numerals, and redundant explanations may be omitted. Furthermore, the notation "A to B" indicating a numerical range means "greater than or equal to A and less than or equal to B" unless otherwise specified, and also encompasses the meaning of "greater than A and less than B."

[0015] In this specification, the term "electricity storage device" refers to a device in which charging and discharging occur by the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. Electricity storage devices include secondary batteries such as lithium ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries; and capacitors such as lithium ion capacitors and electric double layer capacitors. Below, an embodiment in which the electricity storage device is a lithium ion secondary battery will be described.

[0016] The method for producing a regenerated cathode active material disclosed herein includes, for example, a preparation step, a first analysis step, a polishing step, a classification step, a second analysis step, and an evaluation step. Note that the production method disclosed herein may include any steps other than those described above, as necessary.

[0017] The preparation step is, for example, a step of preparing a deteriorated positive electrode active material. The positive electrode active material may be recovered from, for example, a used power storage device. The following describes a case where the used power storage device is a lithium ion secondary battery.

[0018] Fig. 1 is a longitudinal cross-sectional view of a lithium-ion secondary battery 100. Fig. 2 is a schematic diagram of an electrode assembly 20. The lithium-ion secondary battery 100 shown in Fig. 1 is a used lithium-ion secondary battery. As shown in Fig. 1, the lithium-ion secondary battery 100 includes the electrode assembly 20, a case 30, and a non-aqueous electrolyte solution 80.

[0019] 1 and 2, the electrode assembly 20 is a wound electrode assembly in which a long, sheet-like positive electrode 50 and a long, sheet-like negative electrode 60 are stacked together with a long, sheet-like separator 70 interposed therebetween and wound in the sheet longitudinal direction (hereinafter simply referred to as the "longitudinal direction"). In the electrode assembly 20, the exposed region 52a of the positive electrode 50 and the exposed region 62a of the negative electrode 60 protrude outward from both ends in the lateral direction perpendicular to the longitudinal direction.

[0020] As shown in FIGS. 1 and 2, the positive electrode 50 includes a long sheet-like positive electrode collector 52 and a positive electrode active material layer 54. The positive electrode collector 52 is, for example, aluminum foil. In this embodiment, the positive electrode collector 52 has a region where the positive electrode active material layer 54 is provided and an exposed region 52a where the positive electrode active material layer 54 is not provided and the surface of the positive electrode collector 52 is exposed. The positive electrode active material layer 54 is provided, for example, in a strip shape along the longitudinal direction on one or both sides (both sides here) of the positive electrode collector 52. The positive electrode active material layer 54 is not provided at an end (the left end in the drawing) in the short-side direction of the sheet (hereinafter simply referred to as the "short-side direction"). Here, the exposed region 52a is a strip-shaped region at the end (the left end in the drawing) in the short-side direction. As shown in FIG. 1, the current collector plate 42a is attached to the exposed region 52a.

[0021] The positive electrode active material layer 54 contains, for example, a positive electrode active material. In this embodiment, the positive electrode active material has a core particle and a coating portion on the surface of the core particle. The core particle here has a layered crystal structure. The core particle may be, for example, a lithium composite oxide. Although not particularly limited, it is preferable that the core particle be a single particle from the viewpoint of stability, taking into account the polishing step described below.

[0022] The lithium composite oxide is preferably a lithium transition metal composite oxide containing at least Ni as a transition metal element. Examples of the lithium transition metal composite oxide include lithium nickel composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt manganese composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium iron nickel manganese composite oxide. The core particle may be of one type, or two or more types may be combined.

[0023] In this specification, the term "lithium nickel cobalt manganese composite oxide" refers to oxides containing Li, Ni, Co, Mn, and O as constituent elements, as well as oxides containing one or more additional elements. Examples of the additional elements include transition metal elements and typical metal elements, such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. The additional elements may also be metalloid elements, such as B, C, Si, and P; or nonmetallic elements, such as S, F, Cl, Br, and I. This also applies to the lithium nickel composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium iron nickel manganese composite oxide described above.

[0024] The core particles may be, for example, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2 and the like can be preferably used.

[0025] The coating portion has, for example, a rock salt crystal structure. The coating portion with the rock salt crystal structure may include, for example, a coating portion formed when a transition metal of the core particle moves from a transition metal site to a lithium site due to charging and discharging of the lithium ion secondary battery 100. Therefore, the presence of a coating portion with a rock salt crystal structure in the positive electrode active material may indicate that the positive electrode active material has deteriorated. Although not particularly limited, examples of the coating portion include nickel oxide (NiO) and manganese oxide (MnO).

[0026] The average particle diameter of the positive electrode active material is generally 0.5 μm to 20 μm. The average particle diameter 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 diameter 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 diameter of the positive electrode active material here refers to the average particle diameter of the positive electrode active material comprising a core particle and a coating portion. In this specification, the "average particle diameter" of particles refers to the particle diameter (D 50 particle size).

[0027] The positive electrode active material layer 54 may contain, in addition to the positive electrode active material, a conductive material, a binder, and the like. 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, for example, preferably 70 mass % or more, and more preferably 85 mass % to 95 mass %. The content of the conductive material relative to the entire positive electrode active material layer 54 is, for example, 0.1 mass % to 20 mass %. The content of the binder relative to the entire positive electrode active material layer 54 is, for example, 0.5 mass % to 15 mass %. In this specification, the term "positive electrode mixture" refers to all of the materials constituting the positive electrode active material layer 54.

[0028] As shown in FIGS. 1 and 2, the negative electrode 60 includes a long, sheet-like negative electrode current collector 62 and a negative electrode active material layer 64. The negative electrode current collector 62 is, for example, copper foil. In this embodiment, the negative electrode current collector 62 has a region where the negative electrode active material layer 64 is provided and an exposed region 62a where the negative electrode active material layer 64 is not provided and the surface of the negative electrode active material layer 64 is exposed. The negative electrode active material layer 64 is provided, for example, in a strip shape along the longitudinal direction on one or both sides (both sides in this case) of the negative electrode current collector 62. The negative electrode active material layer 64 is not provided at the end in the short side direction (the end on the right side in the figure). Here, the exposed region 62a is a strip-shaped region at the end in the short side direction (the end on the right side in the figure). As shown in FIG. 1, a current collector 44a is attached to the exposed region 62a.

[0029] The negative electrode active material layer 64 contains, for example, a negative electrode active material. The negative electrode active material is not particularly limited, and any conventionally known negative electrode active material used for this type of application can be used. The negative electrode active material may be, for example, a carbon material such as graphite, hard carbon, or soft carbon; silicon (Si); or the like. The content of the negative electrode active material in the entire negative electrode active material layer 64 is, for example, preferably 70 mass % or more, and more preferably 85 mass % to 98 mass %.

[0030] The negative electrode active material layer 64 may contain a binder, a thickener, and the like in addition to the negative electrode active material. Examples of binders include styrene butadiene rubber (SBR). The content of the binder relative to the entire negative electrode active material layer 64 is not particularly limited, but is, for example, 0.1% by mass to 8% by mass. For example, carboxymethyl cellulose (CMC) can be preferably used as the thickener. The content of the thickener relative to the entire negative electrode active material layer 64 is not particularly limited, but is, for example, 0.3% by mass to 3% by mass.

[0031] The separator 70 may be a porous sheet (film) made of a resin material such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide. The porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator 70.

[0032] The case 30 is, for example, an outer container that houses the electrode assembly 20 and the nonaqueous electrolyte 80. Here, the case 30 is a flat, rectangular case. As shown in FIG. 1 , the case 30 has a positive electrode terminal 42, a negative electrode terminal 44, a safety valve 36, and an inlet (not shown). The positive electrode terminal 42 is, for example, a terminal for external connection on the positive electrode side. Here, the positive electrode terminal 42 is electrically connected to the positive electrode 50 of the electrode assembly 20 via a current collector 42a. The negative electrode terminal 44 is, for example, a terminal for external connection on the negative electrode side. Here, the negative electrode terminal 44 is electrically connected to the negative electrode 60 of the electrode assembly 20 via a current collector 44a. The safety valve 36 is, for example, a thin-walled portion that is configured to release internal pressure in the case 30 when the internal pressure rises above a predetermined level. The inlet is, for example, a portion through which the nonaqueous electrolyte 80 is injected into the case 30.

[0033] The nonaqueous electrolyte 80 includes, for example, a nonaqueous solvent and a supporting salt. Examples of the nonaqueous solvent include organic solvents such as various carbonates, ethers, esters, nitriles, sulfones, and lactones commonly used in this type of application. Among these, carbonates are preferred. Examples of carbonates include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC) (preferably monofluoroethylene carbonate), monofluoromethyl difluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC). As the nonaqueous solvent, one type of nonaqueous solvent may be used alone, or two or more types of nonaqueous solvents may be used in combination. Examples of the supporting salt include lithium salts such as LiPF6, LiBF4, and LiClO4. The concentration of the supporting electrolyte may be, for example, 0.7 mol / L to 1.4 mol / L. The nonaqueous electrolyte 80 may contain additives used in this type of application, as needed. Examples of additives include film-forming agents such as LiB(C2O4)2 (LiBOB) and LiBF2 (C2O4); gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB); thickeners; etc.

[0034] In the preparation step, in this embodiment, first, the deteriorated electricity storage device (here, the lithium ion secondary battery 100) is disassembled, and the electrode body 20 is removed from the inside of the case 30, and then the positive electrode 50 is removed. Next, the positive electrode active material layer 54 is scraped off from the positive electrode current collector 52 of the positive electrode 50, thereby obtaining a positive electrode mixture containing the positive electrode active material.

[0035] Although not particularly limited, the preparation step is preferably performed in an inert and dry atmosphere from the viewpoint of suppressing acceleration of deterioration. For example, the steps from disassembling the lithium-ion secondary battery 100 to obtaining the positive electrode mixture may be performed in a glove box, which is an inert and dry atmosphere.

[0036] 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, it is possible to analyze the degree to which the coating portion is formed, the composition of the coating portion, etc. In this embodiment, in the first analysis step, the peak intensity I at 8341 eV of the nickel (Ni) absorption edge measured by XAFS analysis of the positive electrode active material obtained in the preparation step is A Measure.

[0037] The presence of a peak at 8341 eV at the nickel (Ni) absorption edge indicates that, for example, nickel (Ni) ions in the positive electrode active material move from the transition metal site to the lithium site and are converted into a divalent state (Ni 2+ ) is observed. This may mean that nickel (Ni) ions migrate to the lithium site during charging of the lithium-ion secondary battery 100, changing their valence to divalent and unable to return to the transition metal site during discharge. The presence of a peak at 8341 eV indicates the presence of a coating containing a nickel compound with a rock salt crystal structure (e.g., NiO) on a portion of the surface of the positive electrode active material. Furthermore, nickel compounds with a rock salt crystal structure exhibit lithium insertion / extraction at a lower potential than positive electrode active materials with a layered crystal structure, lowering the discharge potential and contributing to degradation. Therefore, the presence of a peak at 8341 eV at the nickel (Ni) absorption edge can be used as an indicator of degradation of the lithium-ion secondary battery 100.

[0038] In this embodiment, XAFS analysis may be performed using a transmission method. The positive electrode active material subjected to XAFS analysis in the first analysis step may be the positive electrode mixture obtained in the preparation step, from the viewpoint of facilitating analysis. Commercially available measuring devices may be used without particular limitation in this step and the second analysis step. For example, the "QuantumLeap V210" manufactured by Canon Inc. may be used for such measurements. For example, the analysis software "Athena" may be preferably used to analyze the obtained data.

[0039] The polishing step is, for example, a step of polishing the positive electrode active material. By performing the polishing step, for example, the coating portion can be separated from the core particles. In this embodiment, the positive electrode mixture obtained in the preparation step is placed in a container containing an abrasive, and the container is rotated to polish the positive electrode active material. The abrasive (e.g., alumina abrasive grains) may be coated on the inner wall of the container. The rotation of the container is not particularly limited, but may be both rotation and revolution. The rotation speed and revolution speed may both be set to approximately 500 rpm to 3000 rpm (preferably 1000 rpm to 2500 rpm). The polishing time is, for example, 10 minutes to 120 minutes, preferably 30 minutes to 60 minutes. For example, a commercially available rotation-revolution mixer can be preferably used in the polishing step. An example of a commercially available rotation-revolution mixer is Thinky Corporation's "Awatori Rentaro."

[0040] The polishing step is preferably carried out in an inert and dry atmosphere, for example, from the viewpoint of efficiently separating the coating portion and suppressing unwanted chemical reactions during polishing.

[0041] The classification step is, for example, a step of classifying the polished positive electrode active material. By performing the classification step, for example, coating portions separated by polishing and minute debris generated by polishing can be removed, and particles of an appropriate size can be obtained. In this embodiment, the classification step obtains a particle group having the same particle size distribution as the positive electrode active material before polishing. Therefore, it is preferable to obtain a particle group having an average particle diameter of approximately 0.5 μm to 20 μm in the classification step. The average particle diameter of the particle group obtained in the classification step is, for example, 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more. The average particle diameter of the particle group obtained in the classification step is, for example, 15 μm or less, preferably 12 μm or less, and more preferably 10 μm or less.

[0042] The second analysis step is, for example, a step of performing XAFS analysis on the positive electrode active material after the polishing step. By performing the second analysis step, for example, it is possible to analyze the extent to which the coating portion remains on the core particle surface, the composition of the remaining coating portion, etc. In this embodiment, in the second analysis step, the peak intensity I at 8341 eV of the nickel (Ni) absorption edge measured by XAFS analysis of the positive electrode active material after the polishing step is B Measure.

[0043] The evaluation step is a step of evaluating whether the material can be used as a regenerated positive electrode active material based on the results obtained in the first analysis step and the results obtained in the second analysis step. In this embodiment, in the evaluation step, the peak intensity I A and peak intensity I B Ratio to (I B / I A If the ratio (I) is 0.7 or less, the positive electrode active material is evaluated as a "good product" and can be used as a recycled positive electrode active material. In this case, the positive electrode active material can be used, for example, as a positive electrode active material when manufacturing a new lithium ion secondary battery. B / I A ) is greater than 0.7, the positive electrode active material is evaluated as a "defective product" and is not usable as a regenerated positive electrode active material. In this case, the positive electrode active material may be subjected to the above-described polishing treatment again, for example.

[0044] From the viewpoint of realizing better battery performance of the battery using the recycled positive electrode active material, the ratio (I B / I A ) is preferably 0.65 or less, more preferably 0.6 or less, and even more preferably 0.55 or less, and the smaller the better. B / I A ) is generally 0.05 or more, for example 0.1 or more, or may be 0.2 or more or 0.3 or more.

[0045] The recycled positive electrode active material produced by the production method disclosed herein can be used, for example, in the production of lithium ion secondary batteries for various applications. Suitable applications include power sources for driving vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Lithium ion secondary batteries can be used, for example, as storage batteries for small power storage devices. Lithium ion secondary batteries can also be used, for example, in the form of assembled batteries in which multiple batteries are connected in series and / or parallel.

[0046] The method for producing a regenerated cathode active material disclosed herein includes preparing a cathode active material and polishing the cathode active material. The cathode 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 coating portion is separated from the core particle by polishing. The peak intensity I at 8341 eV at the nickel (Ni) K absorption edge measured by XAFS analysis of the cathode active material before polishing is A and the peak intensity I at 8341 eV at the nickel (Ni) K absorption edge measured by XAFS analysis of the polished positive electrode active material. B and the ratio (I B / I A ) is less than 0.7.

[0047] The cathode active material prepared by this manufacturing method is a cathode 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. As described above, the coating portion of the cathode active material is formed, for example, by the charge / discharge cycle of the lithium-ion secondary battery 100, and can be a cause of deterioration of the cathode active material. This manufacturing method includes polishing the cathode active material having the coating portion, thereby making it possible to separate the coating portion of the cathode active material. The degree of separation of the coating portion from the cathode active material by polishing is evaluated by XAFS analysis of the cathode active material before and after polishing. In the evaluation by XAFS analysis, the peak intensity I at 8341 eV of the nickel (Ni)-K absorption edge of the cathode active material before polishing was evaluated. A and the peak intensity I at 8341 eV of the nickel (Ni) K absorption edge for the polished active material. B Ratio to (I B / I A ) is 0.7 or less is evaluated as a good product. In other words, the manufacturing method disclosed herein can produce a regenerated positive electrode active material by polishing the positive electrode active material and evaluating the degree of separation of the coating portion of the positive electrode active material by polishing. Therefore, the manufacturing method disclosed herein can restore the capacity of a deteriorated positive electrode active material and reduce the reaction resistance increased by deterioration without using a calcination method.

[0048] In the manufacturing method disclosed herein, the positive electrode active material may be polished in a dry atmosphere, which can prevent lithium ions from being released from the core particles due to moisture content.

[0049] The manufacturing method disclosed herein may include performing XAFS analysis of the positive electrode active material before and after polishing. By performing XAFS analysis of the positive electrode active material before and after polishing, it is possible to produce a highly reliable regenerated positive electrode active material that recovers capacity and reduces reaction resistance that increases due to degradation.

[0050] The manufacturing method disclosed herein may include classifying the polished positive electrode active material. By classifying the polished positive electrode active material, it is possible to selectively obtain particles having an appropriate particle size from a mixture of particles having an appropriate particle size and coating pieces separated by polishing.

[0051] In the manufacturing method disclosed herein, it is preferable to obtain a positive electrode active material having an average particle size of 5 μm to 10 μm by classification, thereby obtaining a particle group having a particle size distribution suitable for a positive electrode active material used in an electricity storage device.

[0052] In the manufacturing method disclosed herein, the positive electrode active material may be a lithium transition metal composite oxide, thereby providing a preferable method for regenerating a positive electrode active material that is a lithium transition metal composite oxide.

[0053] Test examples relating to the technology disclosed herein will be described below, but it is not intended that the technology disclosed herein be limited to those shown in the following test examples.

[0054] [Deterioration of the positive electrode active material] The raw material is single particle LiNi 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 a conductive material, and polyvinylidene fluoride (PVdF) as a binder were prepared. These were mixed with N-methylpyrrolidone (NMP) as a solvent in a mass ratio of LNCM:AB:PVdF = 90:8:2 to prepare a positive electrode paste. The positive electrode paste was applied in strips to both sides of a long piece of aluminum foil, dried, and then pressed to obtain a positive electrode sheet.

[0055] Graphite was used as the negative electrode active material, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener. These were mixed with water as the solvent in a graphite:SBR:CMC mass ratio of 98:1:1 to prepare a negative electrode paste. The negative electrode paste was applied in strips to both sides of a long copper foil strip, dried, and then pressed to obtain a negative electrode sheet.

[0056] The separator was a porous polyolefin sheet with a three-layer structure (PP / PE / PP) and an HRL. The positive electrode sheet, negative electrode sheet, and two separator sheets were stacked and wound, and then pressed from the side to flatten the stack to produce a flat wound electrode assembly.

[0057] Next, the positive and negative electrode terminals were connected to the wound electrode body and housed in a rectangular case with an electrolyte injection hole. A nonaqueous electrolyte was then injected through the injection hole, which was then hermetically sealed. The nonaqueous electrolyte was prepared by dissolving LiPF6 as a supporting electrolyte 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. An aging treatment was then performed to produce a usable lithium-ion secondary battery.

[0058] The lithium ion secondary battery was placed in an environment of 40° C. The lithium ion secondary battery was subjected to constant current (CC) charging at a current value of 1 C to 4.3 V, and then CC discharging at a current value of 1 C to 3.0 V, thereby causing the lithium ion secondary battery to deteriorate. Note that, during this deterioration, 400 charge-discharge cycles were performed, with the above charge-discharge cycle being one cycle.

[0059] The deteriorated lithium-ion secondary battery was discharged until the voltage reached 2 V. The lithium-ion secondary battery was then disassembled to remove the positive electrode sheet, which was then crushed to recover the positive electrode mixture, which was then passed through a sieve with 500 μm openings to prepare a powder.

[0060] [Polishing and Classification of Cathode Active Material] <Examples 1 to 4, Comparative Examples 2 and 3> Next, the powder was polished. For the polishing of the powder, a rotation-revolution mixer ("Awatori Rentaro" manufactured by Shinki Co., Ltd.) was used. The powder was put into a container coated with an abrasive (particle size 80 (3.6 μm to 18 μm)) made of alumina on the inner wall, and the container was set on a holder inclined at 45° with respect to the revolution axis, and polishing was carried out. The revolution speed of the mixer was 1500 rpm. The number of revolutions of the container was 1500 rpm. The polishing time was set to 30 minutes to 60 minutes. The atmosphere for polishing was a nitrogen atmosphere and a dry atmosphere. Then, the polished powder was classified to obtain a particle group having an average particle diameter of 8 μm.

[0061] <Comparative Example 1> The cathode mixture obtained by crushing the cathode sheet was classified to obtain a particle group having an average particle diameter of 8 μm. This was taken as Comparative Example 1.

[0062] <Reference Example> The cathode active material as the above raw material was prepared as a reference example.

[0063] For the powders of each example after classification and the reference example, the average particle diameter D2 was measured using the above measuring device. And the following formula (X): Decrease (μm) = (Average particle diameter D1 before polishing) - (Average particle diameter D2 after polishing) (X) was used to obtain the decrease (μm) in the average particle diameter before and after polishing. The results are shown in the corresponding columns of Table 1. Here, the average particle diameter of Comparative Example 1 was taken as the average particle diameter D1.

[0064] [XAFS Analysis] The powders of each example and the reference example after classification were subjected to XAFS analysis using the transmission method. The XAFS analysis was performed according to the manual for the measurement device used, the "QuantumLeap V210" (manufactured by Canon Inc.). In the XAFS analysis, the incident energy was set to the manganese (Mn) K-absorption edge, the cobalt (Co) K-absorption edge, and the nickel (Ni) K-absorption edge, respectively, and the transmitted portion of each energy (transmission XAFS) was measured. The type of X-ray used in the measurement was hard X-ray. Simultaneously, the diffraction intensities for the (003) and (104) planes in the space group R-3m were acquired. The anomalous dispersion term f" (eu / site) was calculated 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 at the nickel (Ni) absorption edge was acquired. The XAFS spectrum was extracted using the analysis software "Athena," which is widely used for XAFS analysis. And, the peak intensity I A and the peak intensity I of other examples B and the ratio (I B / I A The results are shown in the corresponding columns in Table 1.

[0065] [Capacity retention rate evaluation] Seven types of test secondary batteries were fabricated using the classified powders of Examples 1 to 4 and Comparative Examples 1 to 3 according to the materials and procedures described above. Furthermore, a test secondary battery of a reference example was fabricated using the positive electrode active material as the raw material according to the materials and procedures described above. The eight types of test secondary batteries fabricated here were placed in an environment of 25°C. The test secondary batteries were CCCV charged to 4.3 V at a current value of 0.1 C (cut current: 0.01 C). Then, the test secondary batteries were CCCV discharged from 4.3 V to 3.0 V (cut current: 0.01 C). The capacity of each test secondary battery was measured when this CCCV charge and CCCV discharge constituted one cycle of charge and discharge. The capacity of the test secondary battery of each example was then calculated, assuming the capacity of the reference example test secondary battery to be 100%. The results are shown in the corresponding column in Table 1.

[0066] The test secondary batteries were charged in a temperature environment of -10°C until the SOC of the positive electrode reached 50%. Next, impedance measurements were performed under conditions of an amplitude of 5 mV and a measurement frequency range of 0.01 Hz to 10,000 Hz. A Cole-Cole plot was created from the obtained results, and the diameter of the semicircle was used as the resistance value. The resistance of the test secondary battery of each example was calculated, assuming the resistance value of the test secondary battery of the reference example to be 100%. The results are shown in the corresponding columns in Table 1.

[0067] [Table 1]

[0068] The manufacturing method performed in this test example included preparing a positive electrode active material and polishing the positive electrode active material. The positive electrode active material had core particles with a layered crystal structure and a coating portion with a rock salt crystal structure on the surface of the core particles. By polishing, at least a portion of the coating portion was separated from the core particles. As shown in Table 1, the peak intensity I at 8341 eV at the nickel (Ni) K absorption edge measured by XAFS analysis of the positive electrode active material before polishing was A and the peak intensity I at 8341 eV at the nickel (Ni) K absorption edge measured by XAFS analysis of the polished positive electrode active material. B and the ratio (I B / I A In the test secondary batteries fabricated using the positive electrode active materials of Examples 1 to 4 in which the ratio (%) was 0.7 or less, the capacity retention rate recovered and the reaction resistance that had increased due to degradation was reduced.

[0069] The techniques disclosed herein may include the techniques described in the following sections. Section 1: A method for producing a recycled positive electrode active material, a core particle having a layered crystal structure; a coating portion having a rock salt crystal structure on the surface of the core particle; preparing a positive electrode active material comprising: polishing the positive electrode active material; It encompasses Here, by the polishing, At least a portion of the coating is separated from the core particle, The peak intensity I at 8341 eV at the nickel (Ni) K absorption edge measured by X-ray absorption fine structure analysis of the positive electrode active material before polishing A and the peak intensity I at 8341 eV at the nickel (Ni) K absorption edge measured by X-ray absorption fine structure analysis of the polished positive electrode active material. B and the ratio (I B / I A ) is 0.7 or less, manufacturing method. Section 2: Item 2. The manufacturing method according to Item 1, wherein the polishing is performed in a dry atmosphere. Section 3: Item 3. The manufacturing method according to item 1 or 2, further comprising performing X-ray absorption fine structure analysis of the positive electrode active material before and after the polishing. Section 4: Item 4. The manufacturing method according to any one of items 1 to 3, further comprising classifying the positive electrode active material after the polishing. Section 5: Item 5. The manufacturing method according to Item 4, wherein the positive electrode active material having an average particle size of 5 μm or more and 10 μm or less is obtained by the classification. Item 6: Item 6. The method according to any one of Items 1 to 5, wherein the positive electrode active material is a lithium transition metal composite oxide.

[0070] Although the embodiments of the technology disclosed herein have been described above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Explanation of symbols]

[0071] 20 Electrode body 30 cases 42 Positive terminal 44 Negative terminal 50 positive electrode 60 negative electrode 70 Separator 80 Nonaqueous electrolyte 100 Lithium-ion secondary battery

Claims

1. A method for producing a recycled positive electrode active material, a core particle having a layered crystal structure; a coating portion having a rock salt crystal structure on the surface of the core particle; preparing a positive electrode active material comprising: polishing the positive electrode active material; It encompasses Here, by the polishing, At least a portion of the coating is separated from the core particle, The peak intensity I at 8341 eV at the nickel (Ni)-K absorption edge measured by X-ray absorption fine structure analysis of the positive electrode active material before polishing Ａ and the peak intensity I at 8341 eV at the nickel (Ni)-K absorption edge measured by X-ray absorption fine structure analysis of the polished positive electrode active material. Ｂ and the ratio (I Ｂ / I Ａ ) is 0.7 or less.

2. The manufacturing method according to claim 1 , wherein the polishing of the positive electrode active material is performed in a dry atmosphere.

3. The manufacturing method according to claim 1 , further comprising performing X-ray absorption fine structure analysis of the positive electrode active material before and after the polishing.

4. The method according to any one of claims 1 to 3, further comprising classifying the positive electrode active material after the polishing.

5. The method according to claim 4 , wherein the positive electrode active material obtained by the classification has an average particle size of 5 μm or more and 10 μm or less.

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

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