Positive electrode active material, positive electrode active material layer, positive electrode, lithium ion secondary battery, and lithium ion secondary battery module

Abstract

This positive electrode active material has a weight loss rate of 0.34% or less as determined by the method 1. Method 1: Using a simultaneous thermogravimetric differential thermal measurement device, 0.5 g of the positive electrode active material is subjected to simultaneous thermogravimetric differential thermal measurement from 100°C to 500°C in a nitrogen atmosphere with a temperature rise rate of 20°C / min; and the weight loss rate (%) at 500°C is determined. In the simultaneous thermogravimetric differential thermal measurement, an alumina container is used as a sample container, and the measurement is caried out at a nitrogen gas flow rate of 50 mL / min. The weight loss rate at 500°C is determined on the assumption that the weight of the positive electrode active material at 100°C is 100.00%.

Description

Positive electrode active material, positive electrode active material layer, positive electrode, lithium-ion secondary battery, and lithium-ion secondary battery module

[0001] The present invention relates to a positive electrode active material, a positive electrode active material layer, a positive electrode, a lithium-ion secondary battery, and a lithium-ion secondary battery module.

[0002] In some cases, the positive electrode active material is separated from the positive electrode active material layer and then regenerated.

[0003] Patent Document 1 describes a method for regenerating electronic functional materials that aims to improve the properties of recycled materials by reliably and industrially separating and removing foreign matter, impurities, fine powder, and coarse particles such as aggregated coarse clumps that are mixed in during various recovery and recycling processes. The method comprises a step of recovering electronic functional materials from waste materials or waste electronic components generated in the manufacturing process of electronic components, and a step of refining the recovered electronic functional materials to regenerate powdered electronic functional materials. The method is characterized in that, in the step of refining the recovered electronic functional materials, at least one of coarse particles and high-density particles is separated and removed from the powdered electronic functional materials by utilizing the difference in resistance force based on the particle size or density of the particles constituting the powdered electronic functional materials.

[0004] Japanese Patent Publication No. 2003-117535

[0005] The present invention provides a positive electrode active material that can suppress the deterioration of the battery characteristics of the resulting lithium-ion secondary battery, as well as a positive electrode active material layer, a positive electrode, a lithium-ion secondary battery, and a lithium-ion secondary battery module using the positive electrode active material.

[0006] The inventors diligently conducted research to solve the above problems. As a result, they discovered that a positive electrode active material with a weight reduction rate of 0.34% or less, determined by a specific method, can suppress the deterioration of the battery characteristics of the resulting lithium-ion secondary battery, thus completing the present invention.

[0007] According to the present invention, the following positive electrode active material, positive electrode active material layer, positive electrode, lithium-ion secondary battery, and lithium-ion secondary battery module are provided.

[0008] [1] A positive electrode active material having a weight reduction rate of 0.34% or less determined by the following Method 1. (Method 1) Using a simultaneous thermogravimetry-differential thermal analysis apparatus, 0.5 g of the positive electrode active material is subjected to simultaneous thermogravimetry-differential thermal measurement from 100°C to 500°C under a nitrogen atmosphere at a temperature increase rate of 20°C / min, and the weight reduction rate (%) at 500°C is determined. In the simultaneous thermogravimetry-differential thermal measurement, an alumina container is used as the sample container, and the measurement is performed under a condition of a nitrogen gas flow rate of 50 mL / min. Further, the weight reduction rate at 500°C is determined with the weight of the positive electrode active material at 100°C defined as 100.00%. [2] In a volume-based particle size distribution obtained by a laser diffraction scattering particle size distribution measurement method, the median diameter D ５０ is 1.0 µm or more and 30.0 µm or less, the positive electrode active material according to [1]. [3] In a volume-based particle size distribution obtained by a laser diffraction scattering particle size distribution measurement method, the particle diameter D at which the cumulative value is 10% １０ is 0.5 µm or more and 20.0 µm or less, the positive electrode active material according to [1] or [2]. [4] In a volume-based particle size distribution obtained by a laser diffraction scattering particle size distribution measurement method, the particle diameter D at which the cumulative value is 90% ９０ is 3.0 µm or more and 40.0 µm or less, the positive electrode active material according to any one of [1] to [3]. [5] In a volume-based particle size distribution obtained by a laser diffraction scattering particle size distribution measurement method, the particle diameter D at which the cumulative value is 10% １０ , the particle diameter D at which the cumulative value is 90% ９０ and the median diameter D ５０ determined from (D ９０ - D １０ ) / D ５０[1] to [4], wherein the value of is 0.50 or more and 2.00 or less. [6] The positive electrode active material according to any one of [1] to [5], wherein the positive electrode active material is a positive electrode active material taken from a positive electrode active material layer, and the positive electrode active material layer is a separation from the positive electrode including the positive electrode active material layer and the positive electrode current collector layer. [7] The positive electrode active material according to [6], wherein the positive electrode is a separation from one or more selected from the group consisting of waste batteries, waste positive electrodes, and positive electrode cuttings. [8] The positive electrode active material according to [6] or [7], wherein the electrolyte content in the positive electrode active material layer is 10.0 parts by mass or less when the total amount of the positive electrode active material layer is 100.0 parts by mass. [9] The positive electrode active material according to any one of [6] to [8], wherein the precipitated separation of the slurry containing the positive electrode active material layer and an organic solvent.

[10] The positive electrode active material according to [9], wherein the organic solvent contains a nitrogen-containing polar solvent.

[11] A positive electrode active material according to any one of [6] to

[10] , wherein the positive electrode active material layer comprises a binder, a conductive additive, and a positive electrode active material (a).

[12] A positive electrode active material according to

[11] , wherein the positive electrode active material (a) comprises one or more selected from the group consisting of lithium-transition metal composite oxides, transition metal sulfides, transition metal oxides, and olivine-type lithium phosphorus oxides.

[13] A positive electrode active material according to

[11] or

[12] , wherein the binder comprises one or more selected from the group consisting of fluorine-based polymers, fluorine-based ionomers, and fluororubber.

[14] A positive electrode active material according to any one of [1] to

[13] , wherein the conductive additive comprises one or more selected from the group consisting of carbon nanotubes, carbon nanohorns, graphene, carbon nanobrushes, and carbon black.

[15] A positive electrode active material according to any one of [1] to

[14] , wherein the cell capacity reduction amount ΔC determined by the method 2 below is 2.10% or less. (Method 2) 9.0 parts by mass of the positive electrode active material, NMC composite oxide (LiNi ０．５ Mn ０．３ Co ０．２ O ２ ) 56.7 parts by mass, lithium manganese composite oxide (LiMn ２ O ４A positive electrode active material slurry is prepared by adding 90 parts by mass of N-methyl-2-pyrrolidone to a solid component consisting of 24.3 parts by mass Next, the pressurized lithium-ion secondary battery is subjected to initial charge and discharge (Rate: 1 / 3C, Temperature: 25°C, Upper voltage limit: 4.15V, Lower voltage limit: 2.5V), and then a cell capacity confirmation test (Rate: 1 / 3C, Temperature: 25°C, Upper voltage limit: 4.15V, Lower voltage limit: 2.5V) is performed to measure the cell capacity C. Then, the cell capacity C is measured in the same manner as above, except that the solid content is changed to a solid content consisting of 63.0 parts by mass of the NMC composite oxide, 27.0 parts by mass of the lithium manganese composite oxide, 5.0 parts by mass of the carbon black, and 5.0 parts by mass of the polyvinylidene fluoride. Ｖ The following is measured. Next, the cell capacity reduction amount ΔC (%) is calculated using the following formula. Here, in the initial charge / discharge and cell capacity confirmation tests, constant current charging is performed up to the upper limit voltage, and then the constant voltage is maintained at the upper limit voltage until the current value drops to 0.05C. Cell capacity reduction amount ΔC = {(C Ｖ -C) / C ｖ} × 100

[16] A positive electrode active material layer containing the positive electrode active material described in any of [1] to

[15] .

[17] A positive electrode having the positive electrode active material layer described in

[16] and a positive electrode current collector layer.

[18] A lithium-ion secondary battery having the positive electrode described in

[17] and a negative electrode.

[19] A lithium-ion secondary battery module comprising the lithium-ion secondary battery described in

[18] .

[0009] According to the present invention, it is possible to provide a positive electrode active material that can suppress the deterioration of the battery characteristics of the resulting lithium-ion secondary battery, as well as a positive electrode active material layer using the positive electrode active material, a positive electrode, a lithium-ion secondary battery, and a lithium-ion secondary battery module.

[0010] This is a schematic cross-sectional view illustrating an example of a lithium-ion secondary battery according to this embodiment.

[0011] In this embodiment, "A to B" indicating a numerical range means A or greater and B or less, unless otherwise specified.

[0012] <Positive Electrode Active Material> The positive electrode active material of this embodiment has a weight loss rate of 0.34% or less, which can be determined by the following method 1. (Method 1) Using a thermogravimetric and differential thermal simultaneous measurement device, 0.5 g of the positive electrode active material is subjected to simultaneous thermogravimetric and differential thermal measurements from 100°C to 500°C under a nitrogen atmosphere and a heating rate of 20°C / min, and the weight loss rate (%) at 500°C is determined. Here, in the simultaneous thermogravimetric and differential thermal measurement, an alumina container is used as the sample container, and the measurement is performed under the condition of a nitrogen gas flow rate of 50 mL / min. The weight loss rate at 500°C is determined by setting the weight of the positive electrode active material at 100°C to 100.00%.

[0013] According to the inventors' research, a correlation was found between the weight loss rate of the positive electrode active material regenerated from the positive electrode active material layer and the battery characteristics of the resulting lithium-ion secondary battery. Based on the above findings, the inventors conducted further investigations and found that by using the weight loss rate obtained by Method 1 above as an indicator and setting the weight loss rate to 0.34% or less, the deterioration of the battery characteristics of the resulting lithium-ion secondary battery can be suppressed, thus completing the present invention.

[0014] From the viewpoint of further suppressing degradation of the battery characteristics of the obtained lithium ion secondary battery, the weight loss rate of the positive electrode active material of the present embodiment is 0.34% or less, preferably 0.33% or less, more preferably 0.32% or less, still more preferably 0.31% or less, still more preferably 0.30% or less, and still more preferably 0.28% or less. The lower limit of the weight loss rate is not particularly limited, and may be, for example, 0.01% or more, 0.10% or more, 0.15% or more, or 0.20% or more.

[0015] The weight loss rate of the positive electrode active material of the present embodiment may be 0.01% or more and 0.34% or less, may be 0.01% or more and 0.33% or less, may be 0.10% or more and 0.32% or less, may be 0.15% or more and 0.31% or less, may be 0.20% or more and 0.30% or less, or may be 0.20% or more and 0.28% or less.

[0016] The positive electrode active material of the present embodiment can be obtained by appropriately selecting production procedures, production conditions, and the like. Preferred examples of the production procedures and production conditions include taking out the positive electrode active material from the positive electrode active material layer under appropriate conditions, and performing a sedimentation separation treatment on the positive electrode active material under appropriate conditions. Details of these will be described later.

[0017] <Particle size distribution> In the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement for the positive electrode active material of the present embodiment, the median diameter D ５０ is preferably 1.0 μm or more and 30.0 μm or less, more preferably 3.0 μm or more and 20.0 μm or less, still more preferably 4.0 μm or more and 15.0 μm or less, and still more preferably 5.0 μm or more and 10.0 μm or less, from the viewpoint of further suppressing degradation of the battery characteristics of the obtained lithium ion secondary battery.

[0018] In the volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement for the positive electrode active material of the present embodiment, the particle diameter D at which the cumulative value is 10% １０is preferably 0.5 µm or more and 20.0 µm or less, more preferably 1.0 µm or more and 15.0 µm or less, even more preferably 2.0 µm or more and 10.0 µm or less, still more preferably 3.0 µm or more and 7.0 µm or less, from the viewpoint of further suppressing a decrease in the battery characteristics of the obtained lithium ion secondary battery.

[0019] In the volume-based particle size distribution measured by laser diffraction scattering particle size distribution analysis for the positive electrode active material of the present embodiment, the particle diameter D at which the cumulative value is 90% ９０ is preferably 3.0 µm or more and 40.0 µm or less, more preferably 5.0 µm or more and 30.0 µm or less, even more preferably 8.0 µm or more and 20.0 µm or less, still more preferably 10.0 µm or more and 15.0 µm or less, from the viewpoint of further suppressing a decrease in the battery characteristics of the obtained lithium ion secondary battery.

[0020] In the volume-based particle size distribution measured by laser diffraction scattering particle size distribution analysis for the positive electrode active material of the present embodiment, the particle diameter D at which the cumulative value is 10% １０ , the particle diameter D at which the cumulative value is 90% ９０ and the median diameter D ５０ obtained from (D ９０ -D １０ ) / D ５０ has a value of preferably 0.50 or more and 2.00 or less, more preferably 0.70 or more and 1.50 or less, even more preferably 0.80 or more and 1.30 or less, still more preferably 0.90 or more and 1.20 or less, and even more preferably 0.95 or more and 1.15 or less, from the viewpoint of further suppressing a decrease in the battery characteristics of the obtained lithium ion secondary battery.

[0021] In the present embodiment, the volume-based particle size distribution of the positive electrode active material measured by laser diffraction scattering particle size distribution analysis can be measured, for example, for the positive electrode active material using a particle size distribution measuring apparatus by the laser diffraction scattering method in accordance with JIS R1629:1997.

[0022] The positive electrode active material in this embodiment is preferably positive electrode active material extracted from a positive electrode active material layer. Furthermore, the positive electrode active material layer in this embodiment is preferably a separation from the positive electrode that includes a positive electrode active material layer and a positive electrode current collector layer, and more preferably a separation from the positive electrode in which the positive electrode active material layer and the positive electrode current collector layer are laminated.

[0023] The positive electrode current collector layer of this embodiment preferably comprises one or more materials selected from the group consisting of aluminum, stainless steel, nickel, titanium, and alloys thereof, and more preferably aluminum. The shape of the positive electrode current collector layer is not particularly limited, but for example, it may be foil-shaped with a thickness in the range of 0.1 to 500 μm.

[0024] In this embodiment, if the positive electrode active material layer is a material separated from the positive electrode, the positive electrode is preferably a material separated from one or more items selected from the group consisting of a waste battery, a waste positive electrode, and a positive electrode cutting. In this embodiment, the waste battery is preferably a waste battery that has not undergone charging or discharging.

[0025] The electrolyte content in the positive electrode active material layer of this embodiment is preferably 10.0 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 1.0 part by mass or less, and even more preferably 0.1 parts by mass or less, when the total amount of the positive electrode active material layer is 100.0 parts by mass. The lower limit of the electrolyte content in the positive electrode active material layer of this embodiment is not particularly limited, but it may be 0 parts by mass or more, when the total amount of the positive electrode active material layer is 100.0 parts by mass. The positive electrode active material layer of this embodiment may be a positive electrode active material layer that does not contain electrolyte.

[0026] The electrolyte content in the positive electrode active material layer of this embodiment may be, for example, 0 parts by mass or more and 10.0 parts by mass or less, 0 parts by mass or more and 5.0 parts by mass or less, 0 parts by mass or more and 1.0 part by mass or less, or 0 parts by mass or more and 0.1 parts by mass or less, when the total amount of the positive electrode active material layer is 100.0 parts by mass.

[0027] The positive electrode active material in this embodiment is preferably a precipitated separation product of a slurry containing a positive electrode active material layer and an organic solvent.

[0028] In this embodiment, if the positive electrode active material is a precipitated separation product of a slurry containing a positive electrode active material layer and an organic solvent, the organic solvent preferably includes nitrogen-containing polar solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide, N,N-dimethylacetamide, N,N-dimethyl sulfoxide, hexamethylphosphoamide, tetramethylurea, triethyl phosphate, and trimethyl phosphate, and more preferably includes N-methyl-2-pyrrolidone.

[0029] In this embodiment, when the positive electrode active material is the precipitated separation product of a slurry containing a positive electrode active material layer and an organic solvent, the content of the organic solvent in the slurry is preferably 100.0 parts by mass or more and 1000.0 parts by mass or less, more preferably 200.0 parts by mass or more and 800.0 parts by mass or less, even more preferably 300.0 parts by mass or more and 700.0 parts by mass or less, and even more preferably 400.0 parts by mass or more and 600.0 parts by mass or less, when the total amount of the positive electrode active material layer is 100.0 parts by mass.

[0030] The positive electrode active material layer of this embodiment preferably includes a binder, a conductive additive, and a positive electrode active material (a). The positive electrode active material (a) of this embodiment may or may not be recycled material.

[0031] The positive electrode active material (a) in the positive electrode active material layer of this embodiment preferably comprises one or more selected from the group consisting of lithium-transition metal composite oxides, transition metal sulfides, transition metal oxides, and olivine-type lithium phosphate oxides, and more preferably comprises one or more selected from the group consisting of lithium manganese composite oxides and NMC composite oxides.

[0032] The content of the positive electrode active material (a) in the positive electrode active material layer of this embodiment is preferably 70.0 parts by mass or more and 99.5 parts by mass or less, more preferably 80.0 parts by mass or more and 99.0 parts by mass or less, and even more preferably 85.0 parts by mass or more and 95.0 parts by mass or less, when the total amount of the positive electrode active material layer is 100.0 parts by mass.

[0033] The binder in the positive electrode active material layer of this embodiment preferably comprises one or more selected from the group consisting of fluorine-based polymers such as polyvinylidene fluoride (PVdF); fluorine-based ionomers; and fluororubber, more preferably comprising a fluorine-based polymer, and even more preferably comprising polyvinylidene fluoride.

[0034] The binder content in the positive electrode active material layer of this embodiment is preferably 0.1 parts by mass or more and 15.0 parts by mass or less, more preferably 0.5 parts by mass or more and 10.0 parts by mass or less, even more preferably 1.0 parts by mass or more and 7.0 parts by mass or less, and even more preferably 3.0 parts by mass or more and 6.5 parts by mass or less, when the total amount of the positive electrode active material layer is 100.0 parts by mass.

[0035] The conductive additive in the positive electrode active material layer of this embodiment preferably comprises one or more selected from the group consisting of carbon nanotubes; carbon nanohorns; graphene; carbon nanobrushes; and carbon black such as acetylene black, Ketjen black, furnace black, thermal black, and channel black, and more preferably comprises carbon black.

[0036] The content of the conductive additive in the positive electrode active material layer of this embodiment is preferably 0.1 parts by mass or more and 15.0 parts by mass or less, more preferably 0.5 parts by mass or more and 10.0 parts by mass or less, even more preferably 1.0 parts by mass or more and 7.0 parts by mass or less, and even more preferably 3.0 parts by mass or more and 6.5 parts by mass or less, when the total amount of the positive electrode active material layer is 100.0 parts by mass.

[0037] <Cell Capacity Reduction ΔC> The cell capacity reduction ΔC obtained by Method 2 of this embodiment is preferably 2.10% or less, more preferably 2.05% or less, even more preferably 2.00% or less, even more preferably 1.95% or less, even more preferably 1.90% or less, even more preferably 1.85% or less, and even more preferably 1.75% or less, from the viewpoint of further suppressing the deterioration of the battery characteristics of the obtained lithium-ion secondary battery. The lower limit of the cell capacity reduction ΔC is not particularly limited, but for example it may be 0.10% or more, 0.50% or more, 0.80% or more, 1.00% or more, or 1.30% or more. (Method 2) 9.0 parts by mass of positive electrode active material, NMC composite oxide (LiNi ０．５ Mn ０．３ Co ０．２ O ２ ) 56.7 parts by mass, lithium manganese composite oxide (LiMn ２ O ４A positive electrode active material slurry is prepared by adding 90 parts by mass of N-methyl-2-pyrrolidone to a solid component consisting of 24.3 parts by mass Next, the pressurized lithium-ion secondary battery undergoes initial charge-discharge (Rate: 1 / 3C, Temperature: 25°C, Upper voltage limit: 4.15V, Lower voltage limit: 2.5V), followed by a cell capacity confirmation test (Rate: 1 / 3C, Temperature: 25°C, Upper voltage limit: 4.15V, Lower voltage limit: 2.5V) to measure the cell capacity C. Then, the solid content is changed to consist of 63.0 parts by mass of NMC composite oxide, 27.0 parts by mass of lithium manganese composite oxide, 5.0 parts by mass of carbon black, and 5.0 parts by mass of polyvinylidene fluoride, and the cell capacity C is measured in the same manner as for the cell capacity C. Ｖ The following is measured. Next, the cell capacity reduction ΔC (%) is calculated using the formula below. Here, in the initial charge / discharge and cell capacity confirmation test, constant current charging is performed up to the upper limit voltage, and then the constant voltage is maintained at the upper limit voltage until the current value drops to 0.05C. Cell capacity reduction ΔC = {(C Ｖ -C) / C ｖ} × 100

[0038] The cell capacity reduction ΔC obtained by method 2 of this embodiment may be 0.10% or more and 2.10% or less, 0.10% or more and 2.05% or less, 0.10% or more and 2.00% or less, 0.50% or more and 1.95% or less, 0.80% or more and 1.90% or less, 1.00% or more and 1.85% or less, or 1.30% or more and 1.75% or less.

[0039] <Method for producing positive electrode active material> The positive electrode active material of this embodiment can be produced by a manufacturing method that includes, for example, the steps of: (A1) mixing a positive electrode active material layer containing positive electrode active material (a), a binder, and a conductive additive with an organic solvent to prepare a slurry; (B) separating the slurry into precipitate and supernatant liquid; and (C) removing the supernatant liquid to obtain precipitate containing positive electrode active material (a).

[0040] <Step (A1)> In step (A1) of this embodiment, a slurry is prepared by mixing a positive electrode active material layer containing positive electrode active material (a), a binder, and a conductive additive with an organic solvent.

[0041] In step (A1) of this embodiment, the method of mixing the positive electrode active material layer with the organic solvent is not particularly limited, but examples include mixing the organic solvent to which the positive electrode active material layer has been added using one or more mixers selected from the group consisting of a small mill mixer, a V-type mixer, a rocking mixer, a planetary motion mixer, a ball mill, and a vibrating mill.

[0042] <Step (B)> In step (B) of this embodiment, the slurry is separated into a precipitate and a supernatant liquid.

[0043] In step (B) of this embodiment, the precipitate mainly consists of positive electrode active material (a), and also contains a binder and a conductive additive. The binder contained in the precipitate includes the binder contained in the positive electrode active material layer that does not dissolve in the organic solvent and remains attached to the positive electrode active material (a) and the conductive additive. The conductive additive contained in the precipitate includes conductive additive particles contained in the positive electrode active material layer that are relatively large in size and prone to settling.

[0044] In step (B) of this embodiment, the supernatant liquid contains non-settling particles in an organic solvent in which a portion of the binder is dissolved. In step (B) of this embodiment, the non-settling particles include positive electrode active material (a), a binder, and a conductive additive. The positive electrode active material (a) contained in the non-settling particles includes relatively small particle sizes that are less likely to settle, such as particles that were crushed by pressing during the manufacture of the positive electrode, from among the positive electrode active material (a) particles contained in the positive electrode active material layer. The binder contained in the non-settling particles includes binder contained in the positive electrode active material layer that did not dissolve in the organic solvent and remained attached to the positive electrode active material (a) and the conductive additive. The conductive additive contained in the non-settling particles includes relatively small particle sizes that are less likely to settle, from among the conductive additive particles contained in the positive electrode active material layer.

[0045] In step (B) of this embodiment, the method for separating the slurry into precipitate and supernatant is preferably one or more selected from the group consisting of a method of letting the slurry stand, a method of centrifuging the slurry, and a method of diffusion separation of the slurry, and more preferably a method of letting the slurry stand.

[0046] In step (B) of this embodiment, if the method for separating the slurry into precipitate and supernatant is a method of letting the slurry stand, the time for letting the slurry stand is preferably 0.1 hours or more and 20.0 hours or less, more preferably 1.0 hour or more and 15.0 hours or less, even more preferably 1.5 hours or more and 10.0 hours or less, even more preferably 2.0 hours or more and 5.0 hours or less, and even more preferably 2.5 hours or more and 4.0 hours or less.

[0047] <Step (C)> In step (C) of this embodiment, the supernatant liquid is removed to obtain a precipitate containing the positive electrode active material (a).

[0048] In step (C) of this embodiment, the method for removing the supernatant liquid is not particularly limited, but one or more methods selected from the group consisting of, for example, a method of sucking up the supernatant liquid using a dropper, pump, or suction tube, a method of tilting the container to drain the supernatant liquid, and a method of removing the supernatant liquid by filtration can be used. Among these, the method of sucking up the supernatant liquid using a dropper, pump, or suction tube is preferred as the method for removing the supernatant liquid.

[0049] <Step (D)> The method for producing the positive electrode active material of this embodiment preferably includes, after step (A1), a step (D) in which the slurry is stirred at a temperature of 50°C or higher to perform a high-temperature washing treatment.

[0050] In step (D) of this embodiment, the method for performing the high-temperature washing treatment on the slurry is not particularly limited, but examples include using a hot stirrer, or using a combination of a heating device such as a hot plate or electric heater and a stirring device such as a stirring rod or propeller-type stirrer.

[0051] In step (D) of this embodiment, the processing temperature for the high-temperature washing treatment is preferably 50°C to 150°C, more preferably 70°C to 120°C, even more preferably 80°C to 110°C, and even more preferably 90°C to 100°C.

[0052] In step (D) of this embodiment, the processing time for the high-temperature washing treatment is preferably 0.1 hours or more and 10.0 hours or less, more preferably 0.3 hours or more and 5.0 hours or less, and even more preferably 0.5 hours or more and 2.0 hours or less.

[0053] In step (D) of this embodiment, the stirring speed for the high-temperature washing treatment is preferably 100 rpm or more and 800 rpm or less, more preferably 200 rpm or more and 600 rpm or less, and even more preferably 300 rpm or more and 500 rpm or less.

[0054] <Steps (A2), (B), and (C)> The method for producing the positive electrode active material of this embodiment preferably further comprises, in this order: Step (A2) of mixing the precipitate obtained in Step (C) with an organic solvent to prepare a slurry; Step (B) of separating the slurry obtained in Step (A2) into precipitate and supernatant liquid; and Step (C) of removing the supernatant liquid to obtain precipitate containing the positive electrode active material (a).

[0055] In the method for producing the positive electrode active material of this embodiment, it is more preferable to repeat steps (A2), (B), and (C) in this order two or more times, and even more preferable to repeat them three or more times.

[0056] In the method for producing the positive electrode active material of this embodiment, when the total amount of the positive electrode active material layer in step (A1) is 100.0 parts by mass, it is preferable to repeat steps (A2), (B), and (C) in this order until the amount of non-settling particles contained in the supernatant liquid is preferably 5.0 parts by mass or less, more preferably 4.5 parts by mass or less, and even more preferably 4.0 parts by mass or less.

[0057] The mass of non-settled particles in the supernatant can be determined, for example, by filtering the supernatant, drying the non-settled particles remaining on the filter, and measuring their mass.

[0058] In this specification, the process of performing steps (A1), (B), and (C) on the positive electrode active material layer in this order, and the process of performing steps (A2), (B), and (C) on the precipitate in this order, will also be referred to as the "sedimentation separation process."

[0059] In the method for producing the positive electrode active material of this embodiment, a preferred embodiment of step (A2) is the same as a preferred embodiment of step (A1) described above.

[0060] In the method for producing a positive electrode active material of this embodiment, preferred embodiments of steps (B) and (C) after step (A2) are the same as preferred embodiments of steps (B) and (C) after step (A1) described above.

[0061] <Step (E)> The method for producing the positive electrode active material of this embodiment preferably further includes step (E) of separating the positive electrode active material layer from the positive electrode which includes the positive electrode active material layer and the positive electrode current collector layer. In the method for producing the positive electrode active material of this embodiment, step (E) is preferably performed before step (A1).

[0062] In step (E) of this embodiment, the positive electrode is preferably impregnated with one or more substances selected from the group consisting of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, and N-methylpyrrolidone, more preferably with aqueous sodium hydroxide solution, and the positive electrode active material layer is separated from the positive electrode by removing the positive electrode current collector layer.

[0063] In step (E) of this embodiment, when the positive electrode is impregnated with an aqueous sodium hydroxide solution or an aqueous potassium hydroxide solution, the standing time after impregnating the positive electrode with the aqueous sodium hydroxide solution or potassium hydroxide solution is preferably 1 hour or more and 15 hours or less, more preferably 5 hours or more and 12 hours or less, and the concentration of the aqueous sodium hydroxide solution or potassium hydroxide solution used is preferably 1 M or more and 10 M or less, more preferably 3 M or more and 7 M or less.

[0064] In step (E) of this embodiment, it is preferable to impregnate the positive electrode with one or more substances selected from the group consisting of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, and N-methylpyrrolidone, then wash the positive electrode with water to remove the positive electrode current collector layer, and then impregnate the resulting positive electrode active material layer with one or more substances selected from the group consisting of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, and N-methylpyrrolidone under similar conditions, wash with water, and dry.

[0065] <Step (F)> The method for producing the positive electrode active material of this embodiment preferably further includes step (F) of recovering a positive electrode from one or more selected from the group consisting of waste batteries, waste positive electrodes, and positive electrode cuttings. In the method for producing the positive electrode active material of this embodiment, step (F) is preferably performed before step (E).

[0066] In the manufacturing process of lithium-ion secondary batteries, for example, a positive electrode is produced by coating a metal foil or the like with a positive electrode active material (a) together with a binder and a conductive additive. During this process, a large amount of waste batteries, waste positive electrodes, and positive electrode cuttings containing the positive electrode active material (a) are generated due to the need to determine the optimal conditions and cut the positive electrode to a specified size. Since the positive electrode active material (a) is very expensive, it is preferable to recover the positive electrode containing the positive electrode active material (a) from one or more types selected from the group consisting of waste batteries, waste positive electrodes, and positive electrode cuttings, in order to further improve yield.

[0067] <Step (G)> The method for producing the positive electrode active material of this embodiment preferably further includes step (G) of drying, crushing, and classifying the final precipitate.

[0068] In step (G) of this embodiment, the method for drying the final precipitate is not particularly limited, but examples include using a heating device such as a dryer, hot stirrer, hot plate, or electric heater. The drying conditions are also not particularly limited as long as the precipitate is sufficiently dried, but for example, they can be 70 to 150°C for 1 to 10 hours.

[0069] In step (G) of this embodiment, a method for crushing and classifying the dried sediment includes, for example, using one or more types selected from the group consisting of a sieve shaker, a centrifugal classifier, an inertial classifier, and a gravity classifier. Among these, the method using a sieve shaker is preferred.

[0070] Based on the above, it is preferable that the method for producing the positive electrode active material of this embodiment includes all of steps (F), (E), (A1), (D), (B), (C), (A2), (B), (C), and (G), and it is more preferable that all of the above steps are included in the above order. Furthermore, it is even more preferable that steps (A2), (B), and (C) be repeated two or more times in this order.

[0071] The method for producing the positive electrode active material of this embodiment preferably does not include a firing step of 500°C or higher, more preferably does not include a firing step of 400°C or higher, even more preferably does not include a firing step of 300°C or higher, and even more preferably does not include a firing step of 200°C or higher.

[0072] In the method for producing the positive electrode active material of this embodiment, the final yield of the positive electrode active material obtained is preferably 50.0 parts by mass or more and 100.0 parts by mass or less, more preferably 60.0 parts by mass or more and 95.0 parts by mass or less, even more preferably 70.0 parts by mass or more and 90.0 parts by mass or less, and even more preferably 80.0 parts by mass or more and 85.0 parts by mass or less, when the total amount of positive electrode active material (a) in the positive electrode active material layer is 100.0 parts by mass.

[0073] <Positive electrode active material layer (P)> The positive electrode active material layer (P) of this embodiment includes the positive electrode active material of this embodiment. Since the positive electrode active material of this embodiment can suppress the deterioration of the battery performance of the resulting lithium-ion secondary battery, the positive electrode active material layer (P) of this embodiment can suppress the deterioration of the battery characteristics of the resulting lithium-ion secondary battery.

[0074] The content of the positive electrode active material of this embodiment in the positive electrode active material layer (P) of this embodiment is preferably 0.1 parts by mass or more and 40.0 parts by mass or less, more preferably 1.0 part by mass or more and 35.0 parts by mass or less, even more preferably 5.0 parts by mass or more and 30.0 parts by mass or less, and even more preferably 7.0 parts by mass or more and 20.0 parts by mass or less, when the total amount of the positive electrode active material layer (P) is 100.0 parts by mass.

[0075] The positive electrode active material layer (P) of this embodiment preferably includes a positive electrode active material (a). The positive electrode active material (a) in the positive electrode active material layer (P) of this embodiment preferably includes one or more selected from the group consisting of lithium-transition metal composite oxides, transition metal sulfides, transition metal oxides, and olivine-type lithium phosphorus oxides, and more preferably includes one or more selected from the group consisting of lithium manganese composite oxides and NMC composite oxides.

[0076] The content of the positive electrode active material (a) in the positive electrode active material layer (P) of this embodiment is preferably 50.0 parts by mass or more and 99.0 parts by mass or less, more preferably 60.0 parts by mass or more and 95.0 parts by mass or less, even more preferably 70.0 parts by mass or more and 90.0 parts by mass or less, and even more preferably 75.0 parts by mass or more and 85.0 parts by mass or less, when the total amount of the positive electrode active material layer (P) is 100.0 parts by mass.

[0077] The positive electrode active material layer (P) of this embodiment preferably contains a binder. The binder in the positive electrode active material layer (P) of this embodiment preferably contains one or more selected from the group consisting of fluorine-based polymers such as polyvinylidene fluoride (PVdF); fluorine-based ionomers; and fluororubber, more preferably contains a fluorine-based polymer, and even more preferably contains polyvinylidene fluoride.

[0078] The binder content in the positive electrode active material layer (P) of this embodiment is preferably 0.1 parts by mass or more and 15.0 parts by mass or less, more preferably 0.5 parts by mass or more and 10.0 parts by mass or less, even more preferably 1.0 parts by mass or more and 7.0 parts by mass or less, and even more preferably 3.0 parts by mass or more and 6.5 parts by mass or less, when the total amount of the positive electrode active material layer (P) is 100.0 parts by mass.

[0079] The positive electrode active material layer (P) of this embodiment preferably contains a conductive additive. The conductive additive in the positive electrode active material layer (P) of this embodiment preferably contains one or more selected from the group consisting of carbon nanotubes; carbon nanohorns; graphene; carbon nanobrushes; and carbon black such as acetylene black, Ketjen black, furnace black, thermal black, and channel black, and more preferably contains carbon black.

[0080] The content of the conductive additive in the positive electrode active material layer (P) of this embodiment is preferably 0.1 parts by mass or more and 15.0 parts by mass or less, more preferably 0.5 parts by mass or more and 10.0 parts by mass or less, even more preferably 1.0 parts by mass or more and 7.0 parts by mass or less, and even more preferably 3.0 parts by mass or more and 6.5 parts by mass or less, when the total amount of the positive electrode active material layer (P) is 100.0 parts by mass.

[0081] The thickness of the positive electrode active material layer (P) in this embodiment is not particularly limited, but may be, for example, 0.1 μm or more and 1000 μm or less, 1 μm or more and 500 μm or less, or 5 μm or more and 100 μm or less.

[0082] <Positive Electrode> The positive electrode of this embodiment has a positive electrode active material layer (P) and a positive electrode current collector layer. The positive electrode active material layer (P) of this embodiment can suppress the deterioration of the battery performance of the resulting lithium-ion secondary battery, and therefore the positive electrode of this embodiment can suppress the deterioration of the battery characteristics of the resulting lithium-ion secondary battery.

[0083] The positive electrode current collector layer in this embodiment may be made of, for example, aluminum, stainless steel, nickel, titanium, or an alloy thereof. The shape of the positive electrode current collector layer may be, for example, foil, a flat plate, or a mesh. The thickness of the positive electrode current collector layer is not particularly limited, but is, for example, 1 μm or more and 50 μm or less.

[0084] <Lithium-ion secondary battery> The lithium-ion secondary battery of this embodiment has a positive electrode and a negative electrode. The positive electrode of this embodiment can suppress the deterioration of the battery performance of the resulting lithium-ion secondary battery, and therefore the lithium-ion secondary battery of this embodiment can suppress the deterioration of battery characteristics.

[0085] The lithium-ion secondary battery of this embodiment will be described with reference to the figures. Figure 1 is a schematic cross-sectional view showing an example of the lithium-ion secondary battery of this embodiment. As shown in Figure 1, the lithium-ion secondary battery 10 comprises the positive electrode, electrolyte, and negative electrode of this embodiment. A separator 5 can also be provided between the positive electrode and the negative electrode. Multiple pairs of positive and negative electrodes can be provided.

[0086] The lithium-ion secondary battery 10 has a positive electrode comprising a positive electrode current collector layer 3 made of a metal such as aluminum foil and a positive electrode active material layer 1 containing a positive electrode active material provided thereon, and a negative electrode comprising a negative electrode current collector layer 4 made of a metal such as copper foil and a negative electrode active material layer 2 containing a negative electrode active material provided thereon. The positive electrode and the negative electrode are laminated via a separator 5 made of a nonwoven fabric or a polypropylene microporous film, for example, so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. This electrode pair is housed in a container formed of an outer casing 6, 7 made of an aluminum laminate film, for example. A positive electrode tab 9 is connected to the positive electrode current collector layer 3 and a negative electrode tab 8 is connected to the negative electrode current collector layer 4, and these tabs are pulled out of the container. An electrolyte is injected into the container and sealed. A structure in which a group of electrodes, each consisting of multiple laminated electrode pairs, is housed in the container is also possible.

[0087] The lithium-ion secondary battery 10 can be manufactured according to known methods. For electrodes, for example, laminates or wound bodies can be used. For the outer casing, metal casings or aluminum laminate casings can be used as appropriate. The shape of the battery may be any shape, such as coin type, button type, sheet type, cylindrical type, prismatic type, or flat type.

[0088] In the lithium-ion secondary battery of this embodiment, the negative electrode preferably comprises a negative electrode active material layer containing a negative electrode active material and a negative electrode current collector layer. The negative electrode active material layer of this embodiment preferably contains a negative electrode active material and a binder.

[0089] Examples of negative electrode active materials in the negative electrode active material layer of this embodiment include carbon materials such as natural graphite, artificial graphite, amorphous carbon, diamond-like carbon, fullerene, carbon nanotubes, and carbon nanohorns; lithium-based metallic materials such as lithium metal and lithium alloys; Si-based materials such as Si, SiO2, SiOx (0 < x ≤ 2), and Si-containing composite materials; and conductive polymer materials such as polyacene, polyacetylene, and polypyrrole. One of these may be used alone, or two or more may be used in combination.

[0090] Examples of conductive additives in the negative electrode active material layer of this embodiment include carbon fibers such as carbon nanofibers; carbon blacks such as acetylene black and Ketjenblack; and carbon materials such as activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. One of these may be used alone, or two or more may be used in combination.

[0091] Examples of binders in the negative electrode active material layer of this embodiment include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF); polycarboxylic acid polymers such as poly(meth)acrylic acid; conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole; synthetic rubbers such as styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile-butadiene rubber (NBR); and polysaccharides such as carboxymethylcellulose (CMC), xanthan gum, guar gum, and pectin. One of these may be used alone, or two or more may be used in combination.

[0092] The negative electrode current collector layer in this embodiment may be made of, for example, copper, stainless steel, nickel, titanium, or an alloy thereof. The shape of the negative electrode current collector layer may be, for example, foil, a flat plate, or a mesh. The thickness of the negative electrode current collector layer is not particularly limited, but is, for example, 1 μm or more and 50 μm or less.

[0093] The electrolyte in this embodiment may include, for example, cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), and butylene carbonate (BC); linear carbonates such as ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and dipropyl carbonate (DPC); aliphatic carboxylic acid esters; γ-lactones such as γ-butyrolactone; linear ethers; and organic solvents such as cyclic ethers, to which lithium hexafluoride phosphate (LiPF) is added. ６ ), lithium borofluoride (LiBF ４), LiFSI, lithium perchlorate (LiClO ４ Examples include solutions of lithium salts such as ), and the organic solvent may be used alone or in combination of two or more.

[0094] The separator of this embodiment is, for example, mainly made of a porous membrane, woven fabric, nonwoven fabric, etc., and as the resin component, for example, polyolefin resins such as polypropylene and polyethylene, polyester resins, acrylic resins, styrene resins, or nylon resins can be used. In addition, if necessary, a layer containing inorganic particles may be formed in the separator, and examples of inorganic particles include insulating oxides, nitrides, sulfides, carbides, etc.

[0095] As the outer casing of this embodiment, for example, a case or can made of a flexible film can be used, and from the viewpoint of reducing the weight of the battery, it is preferable to use a flexible film. The flexible film can be one in which a resin layer is provided on both the front and back surfaces of a metal base layer. The metal layer can be selected to have barrier properties such as preventing leakage of electrolyte and intrusion of moisture from the outside, and can be made of aluminum, stainless steel, etc. A heat-sealable resin layer, such as a modified polyolefin, is provided on at least one surface of the metal layer. The outer casing is formed by facing the heat-sealable resin layers of the flexible film toward each other and heat-sealing the area around the part that houses the electrode laminate. A resin layer such as a nylon film or polyester film can be provided on the surface of the outer casing opposite to the surface on which the heat-sealable resin layer is formed.

[0096] <Lithium-ion secondary battery module> The lithium-ion secondary battery module of this embodiment is equipped with the lithium-ion secondary battery of this embodiment. Since the lithium-ion secondary battery of this embodiment can suppress the deterioration of battery characteristics, the lithium-ion secondary battery module of this embodiment can suppress the deterioration of battery characteristics.

[0097] The lithium-ion secondary battery module of this embodiment preferably includes two or more lithium-ion secondary batteries of this embodiment connected in series or in parallel. The lithium-ion secondary battery module of this embodiment more preferably includes a housing capable of housing two or more lithium-ion secondary batteries of this embodiment connected in series or in parallel. The lithium-ion secondary battery module of this embodiment more preferably includes one or more selected from the group consisting of a protection circuit to protect the lithium-ion secondary batteries from overcurrent, a balance circuit to equalize the voltage between the electrodes of the lithium-ion secondary batteries, a controller to control the lithium-ion secondary batteries, a cooler capable of cooling the lithium-ion secondary batteries, and a heater capable of heating the lithium-ion secondary batteries.

[0098] The lithium-ion secondary battery module of this embodiment can be used in a battery system comprising multiple electrically connected lithium-ion secondary battery modules and a battery control system. Examples of battery systems include battery packs, stationary battery systems, automotive power battery systems, automotive auxiliary battery systems, and emergency power supply battery systems.

[0099] Although embodiments of the present invention have been described above, these are merely examples, and various other configurations can be adopted. Furthermore, the present invention is not limited to the embodiments described above, and modifications and improvements that can achieve the objectives of the present invention are included within the scope of the present invention.

[0100] Embodiments of the present invention will be described in detail based on examples and comparative examples. However, the present invention is not limited to these examples.

[0101] <Fabrication of the positive electrode> As the positive electrode active material (a), NMC composite oxide (LiNi ０．５ Mn ０．３ Co ０．２ O ２ , average particle size 15 μm) 63.0 parts by mass, lithium manganese composite oxide (LiMn ２ O ４A solid component was prepared consisting of 27.0 parts by mass of ) 5.0 parts by mass of carbon black as a conductive additive and 5.0 parts by mass of polyvinylidene fluoride (PVdF) as a binder. Next, 90 parts by mass of N-methyl-2-pyrrolidone (NMP), a slurry viscosity adjusting solvent, was added to this solid component to prepare a positive electrode active material slurry. Then, the positive electrode active material slurry was applied to both sides of an aluminum foil (thickness 20 μm), which was to be the positive electrode current collector layer, using a die coater, and dried and pressed to produce a positive electrode with a positive electrode active material layer coating thickness of 70 μm on one side.

[0102] <Preparation of positive electrode active material regenerated from positive electrode active material layer> (Example 1) The obtained positive electrode was impregnated in a 5 M sodium hydroxide aqueous solution and left to stand for 9 hours to separate the positive electrode active material layer and the positive electrode current collector layer. Next, the separated positive electrode active material layer and positive electrode current collector layer were washed with water, the positive electrode current collector layer was removed, and the positive electrode active material layer was extracted. Next, the extracted positive electrode active material layer was impregnated again in a 5 M sodium hydroxide aqueous solution and left to stand for 9 hours, then washed with water and dried to obtain a positive electrode active material layer.

[0103] When the total amount of the obtained positive electrode active material layer was 100.0 parts by mass, 100.0 parts by mass of the positive electrode active material layer and 500.0 parts by mass of N-methyl-2-pyrrolidone were mixed to prepare a slurry. Next, the obtained slurry was subjected to a high-temperature washing treatment by stirring it with a hot stirrer at 95°C and 300 rpm for 1 hour, and the aluminum foil separated in the slurry was collected with a sieve. Next, the slurry was allowed to stand for 3 hours to separate the precipitate from the supernatant, and the supernatant was removed using a pipette to obtain a precipitate containing positive electrode active material (a). Next, the precipitate was subjected to a further settling separation treatment under the same conditions to obtain another precipitate. Finally, the obtained precipitate was dried using a hot plate at 80°C for 12 hours, then crushed and classified using an agate mortar to obtain the positive electrode active material of Example 1. The final yield of the positive electrode active material obtained in Example 1 was 84.2 parts by mass, when the total amount of positive electrode active material (a) in the positive electrode active material layer was 100.0 parts by mass. Furthermore, the mass of non-settled particles contained in the supernatant after the second sedimentation separation treatment was 2.4 parts by mass, when the total amount of positive electrode active material (a) in the positive electrode active material layer was 100.0 parts by mass.

[0104] (Example 2) The positive electrode active material of Example 2 was obtained in the same manner as in Example 1, except that the number of sedimentation separation treatments was changed to a total of three. The final yield of the positive electrode active material of Example 2 obtained was 82.0 parts by mass, when the total amount of positive electrode active material (a) in the positive electrode active material layer was 100.0 parts by mass. In addition, the mass of non-settled particles contained in the supernatant after the third sedimentation separation treatment was 2.2 parts by mass, when the total amount of positive electrode active material (a) in the positive electrode active material layer was 100.0 parts by mass.

[0105] (Example 3) The positive electrode active material of Example 3 was obtained in the same manner as in Example 1, except that the total number of sedimentation separation treatments was changed to four. The final yield of the positive electrode active material of Example 3 obtained was 78.5 parts by mass, when the total amount of positive electrode active material (a) in the positive electrode active material layer was 100.0 parts by mass. In addition, the mass of non-settled particles contained in the supernatant after the fourth sedimentation separation treatment was 3.5 parts by mass, when the total amount of positive electrode active material (a) in the positive electrode active material layer was 100.0 parts by mass.

[0106] (Comparative Example 1) The positive electrode active material of Comparative Example 1 was obtained in the same manner as in Example 1, except that the total number of sedimentation separation treatments was changed to one. The final yield of the positive electrode active material of Comparative Example 1 obtained was 86.6 parts by mass, when the total amount of positive electrode active material (a) in the positive electrode active material layer was 100.0 parts by mass. In addition, the mass of non-settled particles contained in the supernatant after the first sedimentation separation treatment was 13.4 parts by mass, when the total amount of positive electrode active material (a) in the positive electrode active material layer was 100.0 parts by mass.

[0107] <Particle Size Distribution> For each example and comparative example of the positive electrode active material, the volume frequency particle size distribution was measured using a particle size distribution analyzer (Partica LA-960, Horiba, Ltd.) and the laser diffraction scattering method in accordance with JIS R1629:1997. From the obtained volume frequency particle size distribution, the median diameter D ５０ , particle size D where the cumulative value is 10% １０ , particle size D where the cumulative value is 90% ９０ and (D ９０ -D １０ ) / D ５０ The values ​​were determined. The results are shown in Table 1. Here, the positive electrode active material (A) was suspended in a dispersion medium (0.1% by mass sodium hexametaphosphate aqueous solution), ultrasonically dispersed, and then measured. Five measurements were taken, and the average value was used for each measurement.

[0108] <Weight Loss Rate> For each example and comparative example, thermogravimetric and differential thermal simultaneous measurement device (STA7200, Hitachi High-Tech Science Corporation) was used to measure 0.5 g of positive electrode active material from 100°C to 500°C under a nitrogen atmosphere and a heating rate of 20°C / min, and the weight loss rate (%) at 500°C was determined. The results are shown in Table 1. Here, for the thermogravimetric and differential thermal simultaneous measurement, an alumina container was used as the sample container and the measurement was performed under the condition of a nitrogen gas flow rate of 50 mL / min. The weight loss rate at 500°C was calculated by setting the weight of the positive electrode active material at 100°C to 100.00%.

[0109] <Fabrication of Lithium-ion Secondary Batteries> For each example and comparative example, a solid component was prepared consisting of 9.0 parts by mass of positive electrode active material regenerated from the positive electrode active material layer, 56.7 parts by mass of the above-mentioned NMC composite oxide, 24.3 parts by mass of lithium manganese composite oxide, 5.0 parts by mass of carbon black as a conductive additive, and 5.0 parts by mass of polyvinylidene fluoride (PVdF) as a binder. Next, 90 parts by mass of N-methyl-2-pyrrolidone (NMP), a slurry viscosity adjusting solvent, was added to this solid component to prepare a positive electrode active material slurry. Then, the positive electrode active material slurry was applied to both sides of an aluminum foil (thickness 20 μm), which was the positive electrode current collector layer, using a die coater, and dried and pressed to produce a positive electrode with a coating thickness of 70 μm on one side of the positive electrode active material layer.

[0110] A solid component consisting of 95.0 parts by mass of natural graphite (average particle size 18 μm) as the negative electrode active material and 5.0 parts by mass of polyvinylidene fluoride as a binder was prepared. Next, an appropriate amount of N-methyl-2-pyrrolidone, a slurry viscosity adjusting solvent, was added to this solid component to prepare a negative electrode active material slurry. Then, the negative electrode active material slurry was coated onto both sides of a copper foil (10 μm) current collector using a die coater, and dried and pressed to produce a negative electrode with a single-sided coating thickness of 55 μm of the negative electrode active material layer.

[0111] A mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (50:50 (volume ratio)) was used as the solvent. In addition, 1.0 M lithium hexafluorophosphate (LiPF) was added. ６ ) was used as the lithium salt. Furthermore, to 100.0 parts by mass of the total amount of the above solvent and lithium salt, 1.0 part by mass of 1,3-propanesultone, 1.0 part by mass of vinylene carbonate, and 1.0 part by mass of fluoroethylene carbonate were added to prepare the electrolyte. Note that "1.0 M lithium hexafluorophosphate" means that the concentration of lithium hexafluorophosphate in the mixture of the mixed solvent and lithium salt is 1.0 M.

[0112] As a separator, a three-layer porous resin film (total thickness 18 μm) consisting of a polypropylene porous film (6 μm thick) / polyethylene porous film (6 μm thick) / polypropylene porous film (6 μm thick) was fabricated, with a 4 μm thick heat-resistant insulating layer placed on one side.

[0113] The positive electrode prepared as described above was cut into a 200 mm x 200 mm square, the negative electrode into a 210 mm x 210 mm square, and the separator into a 220 mm x 220 mm square (10 positive electrodes, 11 negative electrodes, and 20 separators). Next, these positive and negative electrodes were alternately stacked with separators in between to create a power generation element. Then, tabs were welded to the obtained power generation element and sealed together with the electrolyte in an outer casing made of 150 μm thick aluminum laminate film to produce lithium-ion secondary batteries for each example and comparative example.

[0114] <Cell Capacity Reduction ΔC> For each example and comparative example of lithium-ion secondary battery, the lithium-ion secondary battery was sandwiched between a urethane rubber sheet (3 mm thick) and an Al plate (5 mm thick) larger than the electrode area, and the lithium-ion secondary battery was appropriately pressed from both sides in the stacking direction. Next, the pressed lithium-ion secondary battery underwent initial charge and discharge (Rate: 1 / 3C, Temperature: 25°C, Upper Voltage Limit: 4.15V, Lower Voltage Limit: 2.5V), and then a cell capacity confirmation test (Rate: 1 / 3C, Temperature: 25°C, Upper Voltage Limit: 4.15V, Lower Voltage Limit: 2.5V) was performed to measure the cell capacity C. Next, in <Lithium-ion Secondary Battery Fabrication>, the cell capacity C was measured in the same manner as for cell capacity C, except that the solid content was changed to consist of 63.0 parts by mass of NMC composite oxide, 27.0 parts by mass of lithium manganese composite oxide, 5.0 parts by mass of carbon black, and 5.0 parts by mass of polyvinylidene fluoride. Ｖ The following was measured. Next, the cell capacity reduction ΔC (%) was calculated using the following formula. The results are shown in Table 1. Here, in the initial charge / discharge and cell capacity confirmation tests, constant current charging was performed up to the upper limit voltage, and then the constant voltage was maintained at the upper limit voltage until the current value dropped to 0.05C. Cell capacity reduction ΔC = {(C Ｖ -C) / C ｖ} × 100

[0115]

[0116] This application claims priority based on Japanese Patent Application No. 2025-056264, filed on 28 March 2025, and incorporates all of its disclosures herein.

[0117] 1. Positive electrode active material layer 2. Negative electrode active material layer 3. Positive electrode current collector layer 4. Negative electrode current collector layer 5. Separator 6. Outer casing 7. Outer casing 8. Negative electrode tab 9. Positive electrode tab 10. Lithium-ion secondary battery

Claims

1. A positive electrode active material having a weight loss rate of 0.34% or less, as determined by Method 1 below. (Method 1) Using a thermogravimetric and differential thermal simultaneous measurement device, 0.5 g of the positive electrode active material is subjected to simultaneous thermogravimetric and differential thermal measurements from 100°C to 500°C under a nitrogen atmosphere and a heating rate of 20°C / min, and the weight loss rate (%) at 500°C is determined. Here, in the simultaneous thermogravimetric and differential thermal measurement, an alumina container is used as the sample container, and the measurement is performed under the condition of a nitrogen gas flow rate of 50 mL / min. The weight loss rate at 500°C is determined by setting the weight of the positive electrode active material at 100°C to 100.00%.

2. In the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution method, the median diameter D ５０ The positive electrode active material according to claim 1, wherein the particle size is 1.0 μm or more and 30.0 μm or less.

3. In the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution method, the particle size D at which the cumulative value reaches 10% １０ The positive electrode active material according to claim 1 or 2, wherein the particle size is 0.5 μm or more and 20.0 μm or less.

4. In the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution method, the particle size D at which the cumulative value reaches 90% ９０ The positive electrode active material according to any one of claims 1 to 3, wherein the diameter is 3.0 μm or more and 40.0 μm or less.

5. In a volume-based particle size distribution measured by laser diffraction scattering particle size distribution measurement, the particle diameter D at which the cumulative value is 10% １０ , the particle diameter D at which the cumulative value is 90% ９０ and the median diameter D ５０ obtained from (D ９０ - D １０ ) / D ５０ has a value of 0.50 or more and 2.00 or less. The positive electrode active material according to any one of claims 1 to 4.

6. The positive electrode active material according to any one of claims 1 to 5, wherein the positive electrode active material is a positive electrode active material removed from a positive electrode active material layer, and the positive electrode active material layer is a separation from the positive electrode including the positive electrode active material layer and the positive electrode current collector layer.

7. The positive electrode active material according to claim 6, wherein the positive electrode is a separated material selected from one or more items from the group consisting of waste batteries, waste positive electrodes, and positive electrode cuttings.

8. The positive electrode active material according to claim 6 or 7, wherein the electrolyte content in the positive electrode active material layer is 10.0 parts by mass or less when the total amount of the positive electrode active material layer is 100.0 parts by mass.

9. The positive electrode active material according to any one of claims 6 to 8, which is a precipitated separation product of a slurry containing the positive electrode active material layer and an organic solvent.

10. The positive electrode active material according to claim 9, wherein the organic solvent includes a nitrogen-containing polar solvent.

11. The positive electrode active material according to any one of claims 6 to 10, wherein the positive electrode active material layer comprises a binder, a conductive additive, and a positive electrode active material (a).

12. The positive electrode active material according to claim 11, wherein the positive electrode active material (a) comprises one or more selected from the group consisting of lithium-transition metal composite oxides, transition metal sulfides, transition metal oxides, and olivine-type lithium phosphate oxides.

13. The positive electrode active material according to claim 11 or 12, wherein the binder comprises one or more selected from the group consisting of fluorine polymers, fluorine ionomers, and fluororubbers.

14. The positive electrode active material according to any one of claims 11 to 13, wherein the conductive additive comprises one or more selected from the group consisting of carbon nanotubes, carbon nanohorns, graphene, carbon nanobrushes, and carbon black.

15. The positive electrode active material according to any one of claims 1 to 14, wherein the cell capacity reduction ΔC determined by the method 2 below is 2.10% or less. (Method 2) 9.0 parts by mass of the positive electrode active material, NMC composite oxide (LiNi ０．５ Mn ０．３ Co ０．２ O ２ ) 56.7 parts by mass, lithium manganese composite oxide (LiMn ２ O ４ A positive electrode active material slurry is prepared by adding 90 parts by mass of N-methyl-2-pyrrolidone to a solid component consisting of 24.3 parts by mass Next, the pressurized lithium-ion secondary battery is subjected to initial charge and discharge (Rate: 1 / 3C, Temperature: 25°C, Upper voltage limit: 4.15V, Lower voltage limit: 2.5V), and then a cell capacity confirmation test (Rate: 1 / 3C, Temperature: 25°C, Upper voltage limit: 4.15V, Lower voltage limit: 2.5V) is performed to measure the cell capacity C. Then, the cell capacity C is measured in the same manner as above, except that the solid content is changed to a solid content consisting of 63.0 parts by mass of the NMC composite oxide, 27.0 parts by mass of the lithium manganese composite oxide, 5.0 parts by mass of the carbon black, and 5.0 parts by mass of the polyvinylidene fluoride. Ｖ The following is measured. Next, the cell capacity reduction amount ΔC (%) is calculated using the following formula. Here, in the initial charge / discharge and cell capacity confirmation tests, constant current charging is performed up to the upper limit voltage, and then the constant voltage is maintained at the upper limit voltage until the current value drops to 0.05C. Cell capacity reduction amount ΔC = {(C Ｖ -C) / C ｖ }×100 16. A positive electrode active material layer comprising the positive electrode active material according to any one of claims 1 to 15.

17. A positive electrode having a positive electrode active material layer and a positive electrode current collector layer as described in claim 16.

18. A lithium-ion secondary battery having a positive electrode and a negative electrode as described in claim 17.

19. A lithium-ion secondary battery module comprising the lithium-ion secondary battery described in claim 18.

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