Positive electrode for secondary battery, method for manufacturing same, and nonaqueous electrolyte secondary battery

Abstract

Disclosed is a positive electrode for a secondary battery, the positive electrode including a positive electrode mixture that contains a positive electrode active material and a binder. The positive electrode active material contains a lithium-containing composite oxide that contains at least Ni. The lithium-containing composite oxide has the proportion of Ni in the metal elements other than Li is 80 atom% or more, and contains 0.2 mass% to 0.5 mass% inclusive of an alkali component. The binder contains a fluorine-containing polymer, and the fluorine-containing polymer has a degree of polyene formation of 0.2 or less.

Description

Positive electrode for secondary battery, method of manufacturing the same, and non-aqueous electrolyte secondary battery CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims the benefit of priority to Japanese Patent Application No. 2024-005064, filed on January 17, 2024 in the Japan Patent Office, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a positive electrode for a secondary battery, a method for producing the same, and a non-aqueous electrolyte secondary battery.

[0003] Patent Document 1 proposes "a sodium ion secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte having sodium ion conductivity, the positive electrode comprising positive electrode active material particles, a conductive additive, and a binder, the positive electrode active material particles comprising oxide particles that occlude and release sodium ions and a coating layer that coats the oxide particles, the oxide particles comprising oxide A containing Ni and Mn, the coating layer comprising at least one material B selected from the group consisting of ceramics and carbonaceous materials, and the binder comprising a fluororesin."

[0004] Patent Document 2 proposes "a positive electrode for a sodium ion secondary battery, comprising a positive electrode active material that absorbs and releases sodium ions, a conductive additive, a binder, and a carboxylic acid, wherein the binder comprises a vinylidene fluoride polymer, and the carboxylic acid has at least one of a boiling point and a thermal decomposition point, the lower of which exceeds 150°C."

[0005] Patent Document 3 describes a layered lithium nickel composite oxide in which the nickel ratio in metals other than lithium is 80 mol % or more, LiOH, Li ２ CO ３ and a positive electrode having a positive electrode mixture layer containing a chlorine-containing polyvinylidene fluoride polymer, ２ CO ３ The contents of LiOH and Li in the positive electrode mixture layer are 0.1% by weight or more and 2.1% by weight or less,２ CO ３ The document proposes a lithium ion secondary battery in which the total content of chlorine in the positive electrode mixture layer is 0.2% by weight or more and 4.2% by weight or less, and the chlorine content in the positive electrode mixture layer is 30 μg / g or more and 120 μg / g or less.

[0006] JP 2017-107713 A International Publication No. 2016 / 021405 International Publication No. 2019 / 088171

[0007] Because lithium-containing composite oxides with a high Ni content are highly alkaline, when they are mixed with a liquid medium, alkaline components are eluted from the lithium-containing composite oxide during preparation of the positive electrode slurry. The alkaline components react with the fluorine-containing polymer contained as a binder in the positive electrode mixture, thickening the positive electrode slurry obtained by dispersing the positive electrode mixture in the liquid medium. The thickening of the positive electrode slurry can lead to reduced productivity due to poor liquid delivery, increased material loss, and variations in positive electrode quality.

[0008] It is possible to partially remove the alkaline component by washing the lithium-containing composite oxide with water. However, washing with water causes deterioration of the lithium-containing composite oxide. From the viewpoint of avoiding deterioration as much as possible, it is difficult to sufficiently remove the alkaline component by washing with water.

[0009] It is conceivable to form a "coating layer that coats the oxide particles" as in Patent Document 1, but there is room for improvement because the coating layer increases the resistance of the positive electrode.

[0010] One aspect of the present disclosure relates to a positive electrode for a secondary battery, including a positive electrode composite including a positive electrode active material and a binder, wherein the positive electrode active material includes a lithium-containing composite oxide including at least Ni, and in the lithium-containing composite oxide, a proportion of Ni among metal elements other than Li is 80 atomic % or more, the lithium-containing composite oxide includes 0.2 mass % or more and 0.5 mass % or less of an alkaline component, and the binder includes a fluorine-containing polymer, and the fluorine-containing polymer has a degree of polyenization of 0.2 or less.

[0011] Another aspect of the present disclosure relates to a non-aqueous electrolyte secondary battery including the above-described positive electrode for a secondary battery, a negative electrode, a separator, and a non-aqueous electrolyte.

[0012] Yet another aspect of the present disclosure relates to a method for producing a positive electrode for a secondary battery, the method including: preparing a positive electrode slurry including a liquid medium and a positive electrode composite dispersed in the liquid medium; preparing a positive electrode current collector and forming a coating film of the positive electrode slurry on a surface of the positive electrode current collector; and heating and drying the coating film at 200°C or less, wherein the positive electrode composite includes a positive electrode active material, a binder, and an organic additive including a heteroatom, the positive electrode active material includes a lithium-containing composite oxide including at least Ni, and in the lithium-containing composite oxide, a proportion of Ni among metal elements other than Li is 80 atomic % or more, the lithium-containing composite oxide includes an alkali component of 0.2 mass % or more and 0.5 mass % or less, and the binder includes a fluorine-containing polymer.

[0013] According to the present disclosure, it is possible to suppress both the deterioration of the lithium-containing composite oxide and the thickening of the positive electrode slurry. The novel features of the present invention are set forth in the appended claims, but the present invention, both in terms of its configuration and content, together with other objects and features of the present invention, will be better understood from the following detailed description taken in conjunction with the drawings.

[0014] 1 is a partially cutaway schematic perspective view of a nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure.

[0015] The following describes embodiments of the present disclosure using examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials may be exemplified, but other numerical values ​​and materials may be applied as long as the effects of the present disclosure are obtained. In this specification, the term "numerical value A to numerical value B" includes numerical value A and numerical value B and can be read as "numerical value A or greater and numerical value B or less." In the following description, when lower and upper limits for specific physical properties or conditions are exemplified, any of the exemplified lower limits and any of the exemplified upper limits can be arbitrarily combined, as long as the lower limit is not greater than the upper limit. In the following description, when examples of components or methods are listed, only one of the listed examples may be used, or multiple of the listed examples may be used in combination, unless otherwise specified.

[0016] The present disclosure encompasses any combination of two or more claims arbitrarily selected from the appended claims, i.e., any combination of two or more claims arbitrarily selected from the appended claims may be combined unless a technical contradiction arises.

[0017] Non-aqueous electrolyte secondary batteries include lithium ion secondary batteries that use a liquid non-aqueous electrolyte, solid state batteries that include a gel electrolyte, and all-solid state batteries that use a solid electrolyte.

[0018] A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and a separator is usually disposed between the positive electrode and the negative electrode.

[0019] (Positive Electrode) The positive electrode according to the present disclosure comprises a positive electrode mixture containing a positive electrode active material and a binder. The positive electrode mixture may further contain a conductive material. The positive electrode mixture is usually supported on a positive electrode current collector to form a positive electrode mixture layer. The positive electrode mixture layer is formed on the surface of the positive electrode current collector.

[0020] The positive electrode current collector is made of a sheet-like conductive material. A non-porous conductive substrate (such as a metal foil) or a porous conductive substrate (such as a mesh, net, or punched sheet) is used as the positive electrode current collector. The positive electrode composite layer is supported in the form of a film on one or both surfaces of the positive electrode current collector. The material of the positive electrode current collector is not particularly limited, but examples thereof include stainless steel, aluminum, aluminum alloys, and titanium.

[0021] The positive electrode active material includes a lithium-containing composite oxide containing at least Ni. From the viewpoint of increasing capacity, in the lithium-containing composite oxide, the proportion of Ni to metal elements other than Li is 80 atomic % or more. Among them, the lithium-containing composite oxide is preferably a lithium nickel oxide (hereinafter also referred to as "composite oxide N") that contains Li and Ni, the proportion of Ni to metal elements other than Li is 80 atomic % or more, and has a layered rock salt crystal structure. The proportion of Ni to metal elements other than Li may be 88 atomic % or more, 90 atomic % or more, or 95 atomic % or more. In the composite oxide N, the proportion of Ni to metal elements other than Li is less than 100 atomic %, may be 99 atomic % or less, or may be 98 atomic % or less.

[0022] The positive electrode active material may contain other materials, but the proportion of the composite oxide N in the positive electrode active material is, for example, 70% by mass or more, 90% by mass or more, 95% by mass or more, or even 100%.

[0023] The complex oxide N with a high Ni content contains alkaline components. The complex oxide N in which the proportion of Ni among the metal elements other than Li is 90 atomic % or more is particularly alkaline. If the alkalinity of the synthesized complex oxide N (before washing with water) is higher than the allowable range, some of the alkaline components may be removed by washing with water to an extent that allows for acceptable deterioration. However, the complex oxide N with a high Ni content may contain alkaline components regardless of whether it is before or after washing with water. The alkaline components include, for example, LiOH, Li ２ CO ３ However, it is mostly strong alkali (mainly LiOH) that causes thickening of the positive electrode slurry.

[0024] When the composite oxide N is mixed with a liquid medium (dispersion medium), an alkaline component dissolves into the liquid medium. When the composite oxide N contains 0.2 mass % or more of an alkaline component, the cathode slurry typically undergoes a significant thickening during preparation. This thickening occurs when a fluorine-containing polymer contained as a binder in the cathode mixture reacts with the alkaline component to form a polyenation. Polyenation is a phenomenon in which a fluorine-containing polymer generates double bonds, and the polyenated fluorine-containing polymer promotes gelation of the cathode slurry over time. To avoid significant thickening due to gelation of the cathode slurry, conventional cathode mixtures do not contain an alkaline component of 0.2 mass % or more.

[0025] In contrast, the composite oxide N contained in the positive electrode mixture according to the present disclosure contains 0.2% by mass or more and 0.5% by mass or less of an alkaline component. The thickening of the positive electrode slurry is suppressed by the organic additive containing a heteroatom contained in the positive electrode mixture in the positive electrode slurry. The organic additive containing a heteroatom (hereinafter also referred to simply as "organic additive") adheres to the surface of the composite oxide N via the heteroatom. As a result, contact between the surface of the composite oxide N and the liquid medium is suppressed, the elution of the alkaline component is suppressed, and the reaction between the fluorine-containing polymer and the alkaline component is suppressed. Therefore, the polyenation degree of the fluorine-containing polymer contained in the positive electrode mixture layer (positive electrode mixture) peeled from the positive electrode current collector is small, 0.2 or less. The polyenation degree of the fluorine-containing polymer is preferably 0.17 or less, more preferably 0.15 or less.

[0026] The content of the alkaline component contained in the composite oxide N may be, for example, 0.25 mass % or more and 0.4 mass % or less, or 0.25 mass % or more and 0.35 mass % or less. When the composite oxide N contains more than 0.5 mass % of the alkaline component, it becomes difficult to suppress the increase in viscosity of the positive electrode slurry even when an organic additive is used.

[0027] The degree of polyenation of the fluorine-containing polymer can be determined by the following method. A 20 g sample of the positive electrode composite layer (positive electrode composite) peeled from the positive electrode current collector is weighed and mixed with 10 mL of N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP") to obtain a mixed solution. The mixed solution is centrifuged at 8,000 rpm for 0.5 hours to remove the positive electrode active material. Next, the conductive agent is removed by ultracentrifugation at 80,000 rpm for 11 hours and then at 80,000 rpm for 4 hours to obtain an NMP solution of the fluorine-containing polymer. A fluorine-containing polymer film is obtained from the NMP solution of the fluorine-containing polymer by a casting method. The film is dried under reduced pressure at 60°C for 2 hours. The obtained film is measured using a Raman spectrometer. After baseline correction, the peak intensity at 1,130 cm －１ The peak P1 due to the C═C bond observed near 2980 cm －１ CH observed nearby ２ The intensity ratio (P1 / P2) of the peak P1 derived from the polyenation product to the peak P2 derived from the polyenation product is calculated as the degree of polyenation.

[0028] The content of the alkaline component contained in the composite oxide N can be determined by the following method. A 1.0 g sample of the positive electrode composite layer (positive electrode composite) peeled from the positive electrode current collector is weighed, mixed with 30 mL of ion-exchanged water, and dissolved by shaking for 30 seconds to obtain a sample solution in which the alkaline component has been eluted. Thereafter, the sample solution is filtered, and N ２ The sample is titrated with 1 mol / L hydrochloric acid under atmospheric pressure until the pH reaches 8.4. The mass of LiOH, which is an alkaline component, is calculated from the amount of hydrochloric acid required for the titration, and the ratio of the mass of LiOH to the total mass of the complex oxide N and the alkaline component contained in the sample is calculated. Note that the pH range below 8.4 is determined by the LiOH content. ２ CO ３ This is the titration range for weak alkalis such as

[0029] Because the organic additive has a flexible organic chain, it is unlikely to inhibit the battery reaction even when attached to the surface of the composite oxide N. Therefore, the organic additive has little effect on the resistance of the positive electrode. Furthermore, because the organic additive has low heat resistance, it can be removed from the positive electrode composite by thermal decomposition or the like during the manufacturing process of the positive electrode. The positive electrode composite layer (positive electrode composite) peeled off from the positive electrode current collector may or may not contain an organic additive containing a heteroatom. From the viewpoint of significantly suppressing an increase in the resistance of the positive electrode, the smaller the content of the organic additive contained in the positive electrode composite, the more preferable.

[0030] When the positive electrode composite layer (positive electrode composite) peeled off from the positive electrode current collector contains an organic additive, the ratio of the mass of the organic additive to the mass of the composite oxide N is preferably 0.1 mass% or less, more preferably 0.07 mass% or less, still more preferably 0.05 mass% or less or 0.03 mass% or less, and may be 0.01 mass% or less. The ratio of the mass of the organic additive to the mass of the composite oxide N may be, for example, 0.005 mass% or more.

[0031] The ratio of the mass of the organic additive to the mass of the composite oxide N can be calculated from the measurement results of thermogravimetric analysis (TGA) of a sample of the positive electrode composite layer (positive electrode composite) peeled from the positive electrode current collector and the mass of the composite oxide N contained in the sample. TGA may be performed in air at a rate of 5°C / min.

[0032] The decomposition temperature (thermal decomposition temperature) of the organic additive is preferably 200°C or lower, more preferably 180°C or lower. The decomposition temperature can be measured by TGA under atmospheric conditions at a rate of 5°C / min. Organic additives with a decomposition temperature of 200°C or lower are easily removed from the positive electrode composite by thermal decomposition or the like during the manufacturing process of the positive electrode. This makes it easy to reduce the ratio of the mass of the organic additive to the mass of the complex oxide N contained in the positive electrode composite layer in the completed positive electrode.

[0033] The organic additive may be a Lewis base. Among Lewis bases, Lewis bases having nitrogen (N) as a heteroatom are particularly preferred. It is believed that the unshared electron pair of nitrogen adsorbs to the Lewis acid site on the surface of the composite oxide N. Lewis bases having multiple nitrogen atoms with unshared electron pairs in the molecule are particularly preferred because they increase the number of reaction sites. Among Lewis bases having nitrogen as a heteroatom, Lewis bases having a nitrogen-containing heterocycle are particularly preferred. The nitrogen-containing heterocycle is preferably, for example, a 5-membered ring, a 6-membered ring, or a 7-membered ring, and preferably has two or more nitrogen atoms. The heteroatom is not limited to N, but may also be S, P, O, etc. The organic additive may contain N and heteroatoms other than N as heteroatoms.

[0034] The nitrogen-containing heterocycle may be a saturated ring without a double bond, but preferably has aromaticity. The aromatic nitrogen-containing heterocycle may contain one or more nitrogen atoms in the ring, but may also contain two or more nitrogen atoms. Preferred examples of the nitrogen-containing heterocycle include a pyrazole ring, an imidazole ring, a diazine ring, a triazine ring, and a diazepine ring.

[0035] The organic additive preferably has a chain organic group to effectively prevent contact between the liquid medium and the surface of the composite oxide N. For example, the organic additive may have a chain organic group bonded to a ring-constituting atom of the nitrogen-containing heterocycle. The number of carbon atoms in such an organic group may be, for example, 1 to 50, or 5 to 20.

[0036] The molecular weight of the organic additive may be, for example, from 50 to 1,000, from 100 to 800, or from 100 to 500. An organic additive having such a molecular weight has a low thermal decomposition temperature and a size sufficient to effectively suppress contact between the liquid medium and the surface of the composite oxide N.

[0037] The composite oxide N may further contain Co and Mn. Co and Mn contribute to stabilizing the crystal structure of the composite oxide N. The role of the organic additive is particularly important because the composite oxide N containing Co and Mn is very alkaline and is significantly deteriorated by washing with water.

[0038] From the viewpoint of reducing costs and increasing capacity, the proportion of Co in the metal elements other than Li contained in the composite oxide N is preferably 0 atomic % or more and 20 atomic % or less, and more preferably more than 0 atomic % and 5 atomic % or less.

[0039] From the viewpoint of cost reduction, the ratio of Mn to the metal elements other than Li contained in the composite oxide N may be 1 atomic % or more and 10 atomic % or less, 2 atomic % or more and 5 atomic % or less, or 3 atomic % or more and 5 atomic % or less.

[0040] The composite oxide N may further contain Al. Al contributes to stabilizing the crystal structure of the composite oxide N. The composite oxide N containing Co, Mn, and Al is highly alkaline, so the role of the organic additive is particularly important.

[0041] The proportion of Al in the metal elements other than Li contained in the composite oxide N may be 0.1 atomic % or more and 5 atomic % or less, 0.2 atomic % or more and 3 atomic % or less, or 0.5 atomic % or more and 1 atomic % or less.

[0042] The composite oxide N is, for example, a compound represented by the formula: Li ｙ Ni ｘ M （１－ｘ） O ２－δ (0.8≦x≦1, 0<y≦1.2, and −0.05≦δ≦0.05). Here, the element M may include at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W, and B. x, which indicates the atomic ratio of Ni, may be 0.98 or less, or 0.95 or less. x increases or decreases due to charging and discharging of the secondary battery.

[0043] The element M is represented by the formula: Co １－ｘ－ａ－ｂ Mn ａ Al ｂ (0<a<0.05 and 0<b<0.05).

[0044] The thickness of the positive electrode composite layer is not particularly limited, but may be, for example, 50 μm to 150 μm, or 75 μm to 125 μm. A single positive electrode active material layer may be formed by a plurality of layers having different morphologies. For example, two or more layers containing positive electrode active materials with different average particle sizes may be stacked, or two or more layers containing positive electrode active materials of different types or compositions may be stacked.

[0045] The average particle size (D50) of the composite oxide N particles is, for example, 1 μm or more and 50 μm or less, and may be 5 μm or more and 25 μm or less. The average particle size (D50) refers to the median diameter at which the cumulative volume is 50% in a volume-based particle size distribution. The volume-based particle size distribution can be measured using a commercially available laser diffraction / scattering particle size distribution measuring device.

[0046] The average particle size of the composite oxide N may be measured from the cross section of the positive electrode composite layer by taking an SEM image of the cross section so that 10 or more particles of the composite oxide N are observed, and the diameters of the circles having the same area as the cross sections of the 10 or more particles of the composite oxide N are determined by image processing, and the average value thereof may be used as the average particle size.

[0047] Fluorine-containing polymers that function as binders include vinylidene fluoride polymers. Examples of vinylidene fluoride polymers include polymers of monomers containing vinylidene fluoride. The fluorine-containing polymer may be a combination of a vinylidene fluoride polymer and another fluorine-containing polymer. The vinylidene fluoride polymer may be a copolymer of vinylidene fluoride and another monomer. Examples of vinylidene fluoride polymers include polyvinylidene fluoride (PVDF) and vinylidene fluoride-hexafluoropropylene copolymer. The vinylidene fluoride polymer preferably contains 90 mol % or more of monomer units derived from vinylidene fluoride. The degree of polyenization of the fluorine-containing polymer before being mixed with the positive electrode slurry is usually 0.1 or less.

[0048] In the positive electrode mixture, the amount of the fluorine-containing polymer per 100 parts by mass of the positive electrode active material may be 0.1 parts by mass or more, or 0.5 parts by mass or more, and may be 2.0 parts by mass or less, or 1.2 parts by mass or less.

[0049] The weight-average molecular weight of the fluorine-containing polymer may be 800,000 or more, 1,000,000 or more, or 1,200,000 or more, or may be 2,000,000 or less, or 1,800,000 or less. By making the weight-average molecular weight 1,000,000 or more, a high effect as a binder can be obtained with a small amount.

[0050] The conductive material that may be optionally contained in the positive electrode composite layer is not particularly limited, and known conductive materials may be used. Among them, conductive carbonaceous materials are preferred. Examples of conductive carbonaceous materials include conductive carbon particles such as carbon black and graphite, carbon nanotubes (CNTs), and carbon fibers other than CNTs.

[0051] The positive electrode slurry may contain other components as needed. For example, the positive electrode slurry may contain a binder other than the fluorine-containing polymer. Examples of such binders include hydrogenated nitrile butadiene rubber.

[0052] (Method for Manufacturing Positive Electrode) An example of a method for manufacturing a positive electrode for a secondary battery according to the present disclosure (hereinafter also referred to as "manufacturing method (M)") will be described. The manufacturing method (M) includes a first step of preparing a positive electrode slurry and a second step of forming a positive electrode mixture layer on a positive electrode current collector using the positive electrode slurry. The second step includes a step of preparing a positive electrode current collector, forming a coating film of the positive electrode slurry on the surface of the positive electrode current collector, and a step of heating and drying the coating film.

[0053] The positive electrode slurry prepared in the first step of manufacturing method (M) includes a liquid medium and a positive electrode composite dispersed in the liquid medium. The positive electrode composite is the same as the positive electrode composite described above. For example, the positive electrode slurry can be prepared by mixing a positive electrode active material, a fluorine-containing polymer, an organic additive, a liquid medium, and a conductive material. The positive electrode active material includes composite oxide N. The positive electrode slurry can be prepared by mixing the positive electrode composite with the liquid medium. The organic additive may be dissolved in the liquid medium in advance as a solution and then mixed with other components. The mixing method is not particularly limited, and known mixing methods may be used.

[0054] The liquid medium may be an organic solvent or water. As the organic solvent, N-methyl-2-pyrrolidone (NMP) is preferred, but alcohols such as ethanol, ethers such as tetrahydrofuran, amides such as dimethylformamide, ketones such as cyclohexanone, etc. may also be used.

[0055] The organic additive is used to suppress thickening of the positive electrode slurry. Therefore, it is sufficient that the organic additive is contained in the positive electrode slurry, and it is not necessary that the organic additive is contained in the positive electrode composite layer. In order to effectively suppress thickening of the positive electrode slurry, the mass ratio of the organic additive to the mass of the lithium-containing composite oxide in the positive electrode slurry is, for example, preferably 0.002 mass% or more and 0.3 mass% or less, more preferably 0.02 mass% or more and 0.3 mass% or less, and may be 0.1 mass% or more and 0.25 mass% or less.

[0056] In the second step, the step of forming a coating film of the positive electrode slurry on the surface of the positive electrode current collector can be performed using a coating device such as a bar coater, a gravure coater, a blade coater, a roll coater, a comma coater, a die coater, a lip coater, etc. Multiple positive electrode slurries with different compositions may be prepared, and two or more layers of these slurries may be coated one on top of the other.

[0057] In the second step, the coating film is preferably dried at 200° C. or lower, and may be dried at a temperature of, for example, 150° C. or higher, or even 180° C. or higher. The coating film drying step vaporizes the liquid medium to form an unrolled coating film. At least a portion of the organic additives can be decomposed or vaporized during the coating film drying step and removed from the unrolled coating film.

[0058] Typically, the unrolled coating film is then rolled to form a positive electrode composite layer. The conditions for the rolling are not particularly limited. The density of the positive electrode active material in the positive electrode composite layer is, for example, 3.3 g / cm ３ Above, 4.0g / cm ３ or less, and 3.5 g / cm ３ 4.0g / cm or more ３ The following is also acceptable.

[0059] The positive electrode mixture layer may be formed on only one surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector, depending on the structure of the battery.

[0060] (Non-aqueous electrolyte secondary battery) A battery (hereinafter also referred to as "secondary battery (B)") that is an example of a non-aqueous electrolyte secondary battery according to the present disclosure will be described. The secondary battery (B) includes the above-described positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte.

[0061] The positive electrode mixture layer provided in the positive electrode of the secondary battery (B) may contain an organic additive attached to the surface of the complex oxide N, but the amount is very small. The ratio of the mass of the organic additive to the mass of the complex oxide N is, for example, 0.1 mass% or less. Therefore, the organic additive remaining in the positive electrode mixture layer hardly increases the resistance of the positive electrode.

[0062] The components other than the positive electrode are not particularly limited, and components used in known non-aqueous electrolyte secondary batteries may be applied. Examples of the components of the secondary battery (B) are described below.

[0063] (Positive Electrode) The positive electrode described above is used as the positive electrode.

[0064] (Negative electrode) The negative electrode may have at least a negative electrode current collector. In the case of a lithium metal secondary battery, a negative electrode current collector on which lithium metal or a lithium alloy can be deposited is used as the negative electrode. In the case of a lithium ion secondary battery, the negative electrode typically includes a negative electrode composite containing a negative electrode active material. The negative electrode composite is supported on the negative electrode current collector to form a negative electrode composite layer. The negative electrode composite layer is formed on the surface of the negative electrode current collector.

[0065] The negative electrode mixture contains a negative electrode active material as an essential component. The negative electrode mixture may contain optional components such as a binder, a thickener, and a conductive material. These optional components may include the components exemplified as the components of the positive electrode.

[0066] The negative electrode composite layer may be formed by applying a negative electrode slurry, in which the components of the negative electrode composite are dispersed in a liquid medium (dispersion medium), to the surface of the negative electrode current collector and drying the applied film. The dried coating may be rolled as necessary. The liquid medium may be any of the liquid media exemplified for the positive electrode slurry.

[0067] (Negative electrode active material) The negative electrode active material is selected depending on the type of secondary battery (B). An example of the negative electrode active material is a material capable of absorbing and releasing lithium ions. Examples of such materials include carbonaceous materials, Si-containing materials, and the like. The negative electrode active material may contain or be a Si-containing material. Metallic lithium, a lithium alloy, or the like may be used as the negative electrode active material. The negative electrode may contain one type of negative electrode active material or a combination of two or more types.

[0068] Examples of carbonaceous materials include graphite, easily graphitizable carbon (soft carbon), and hardly graphitizable carbon (hard carbon). One type of carbonaceous material may be used alone, or two or more types may be used in combination. Graphite is preferred because it has excellent charge / discharge stability and a small irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0069] Examples of Si-containing materials include simple Si, silicon alloys, silicon compounds (such as silicon oxides), and composite materials in which a silicon phase is dispersed in a lithium ion conductive phase (matrix). Examples of silicon oxides include SiO ｘ The lithium ion conductive phase may include SiO particles. For example, x is 0.5≦x<2, and may be 0.8≦x≦1.6. ２ At least one selected from the group consisting of a silicate phase, a silicate phase, and a carbon phase may be used.

[0070] The negative electrode current collector may be a metal foil. The negative electrode current collector may be porous. Examples of materials for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy.

[0071] (Non-aqueous electrolyte) The non-aqueous electrolyte includes a solvent (non-aqueous solvent) and a solute dissolved in the solvent. Examples of the solute include a lithium salt. Various additives may be added to the non-aqueous electrolyte.

[0072] Known materials can be used as the solvent. Examples of solvents that can be used include cyclic carbonates, chain carbonates, cyclic carboxylic acid esters, and chain carboxylic acid esters. Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC). Examples of chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). Examples of cyclic carboxylic acid esters include γ-butyrolactone (GBL) and γ-valerolactone (GVL). Examples of chain carboxylic acid esters include non-aqueous solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP). One type of non-aqueous solvent may be used alone, or two or more types may be used in combination.

[0073] Examples of lithium salts include lithium salts of chlorine-containing acids (LiClO ４ , LiAlCl ４ , LiB １０ Cl １０ etc.), lithium salts of fluorine-containing acids (LiPF ６ , LiPF ２ O ２ , LiBF ４ , LiSbF ６ , LiAsF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ etc.), lithium salt of fluorine-containing acid imide (LiN(FSO ２ ) ２ , LiN(CF ３ SO ２ ) ２ , LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ ), LiN(C ２ F ５ SO ２ ) ２and lithium halides (LiCl, LiBr, LiI, etc.). The lithium salts may be used alone or in combination of two or more.

[0074] The concentration of the lithium salt in the nonaqueous electrolyte may be 1 mol / L or more and 2 mol / L or less, or 1 mol / L or more and 1.5 mol / L or less. By setting the lithium salt concentration within this range, an electrolyte solution having excellent ionic conductivity and appropriate viscosity can be obtained.

[0075] The non-aqueous electrolyte may contain known additives, examples of which include 1,3-propane sultone, methylbenzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, and fluorobenzene.

[0076] (Separator) The separator is disposed between the positive electrode and the negative electrode. The separator preferably has high ion permeability and adequate mechanical strength and insulating properties. The separator may be made of a microporous thin film, woven fabric, nonwoven fabric, or the like. Examples of separator materials include polyolefins (polypropylene, polyethylene, etc.) and other resins.

[0077] (Exterior Body) The exterior body (battery case) houses the electrode group and the non-aqueous electrolyte. The exterior body is not particularly limited, and a known exterior body may be used. The electrode group is composed of a positive electrode, a negative electrode, and a separator. The configuration of the electrode group is not particularly limited, and may be a wound type or a laminated type. A wound type electrode group is formed by winding a positive electrode and a negative electrode with a separator interposed therebetween. A laminated type electrode group is formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween. The shape of the non-aqueous electrolyte secondary battery is not particularly limited, and may be cylindrical, prismatic, coin-shaped, button-shaped, laminate-shaped, etc.

[0078] Fig. 1 is a schematic perspective view with a portion cut away of a secondary battery 10 according to an embodiment of the present disclosure. Fig. 1 shows a prismatic nonaqueous electrolyte battery as an example. The secondary battery 10 shown in Fig. 1 includes a battery case 4 in the shape of a rectangular cylinder with a bottom, and an electrode group 1 and a nonaqueous electrolyte (not shown) housed in the battery case 4.

[0079] The electrode group 1 includes a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator disposed therebetween. The positive electrode is the same as the positive electrode described above. The negative electrode current collector of the negative electrode is electrically connected to a negative electrode terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode current collector of the positive electrode is electrically connected to the back surface of the sealing plate 5 via a positive electrode lead 2. In other words, the positive electrode is electrically connected to the battery case 4, which also serves as the positive electrode terminal. The periphery of the sealing plate 5 is fitted into the open end of the battery case 4, and the fitting is laser welded. The sealing plate 5 has an injection hole for a non-aqueous electrolyte. The injection hole is closed with a sealing plug 8 after the non-aqueous electrolyte is injected.

[0080] (Additional Notes) The above description discloses the following technologies. (Technology 1) A positive electrode for a secondary battery, comprising a positive electrode mixture including a positive electrode active material and a binder, wherein the positive electrode active material includes a lithium-containing composite oxide including at least Ni, wherein in the lithium-containing composite oxide, a ratio of Ni to metal elements other than Li is 80 atomic % or more, the lithium-containing composite oxide includes 0.2 mass % or more and 0.5 mass % or less of an alkaline component, and the binder includes a fluorine-containing polymer, and the degree of polyenization of the fluorine-containing polymer is 0.2 or less. (Technology 2) A positive electrode for a secondary battery according to Technology 1, wherein the lithium-containing composite oxide further includes Co and Mn. (Technology 3) A positive electrode for a secondary battery according to Technology 1 or 2, wherein the lithium-containing composite oxide further includes Al. (Technology 4) A positive electrode for a secondary battery, wherein the lithium-containing composite oxide has a structure represented by the formula: Li ｙ Ni ｘ M （１－ｘ） O ２－δ(0.8≦x≦1, 0<y≦1.2 and −0.05≦δ≦0.05), and M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W, and B. (Technology 5) A positive electrode for a secondary battery according to any one of Techniques 1 to 3, wherein M is represented by the formula: Co １－ｘ－ａ－ｂ Mn ａ Al ｂ(Technology 6) The positive electrode for a secondary battery according to any one of Technologies 1 to 5, wherein the positive electrode mixture further contains an organic additive containing a heteroatom, and the ratio of the mass of the organic additive to the mass of the lithium-containing composite oxide is 0.1 mass% or less. (Technology 7) The positive electrode for a secondary battery according to Technology 6, wherein the decomposition temperature of the organic additive is 200°C or less. (Technology 8) The positive electrode for a secondary battery according to Technology 6 or 7, wherein the organic additive is a Lewis base. (Technology 9) The positive electrode for a secondary battery according to any one of Technologies 6 to 8, wherein the molecular weight of the organic additive is 50 or more and 1000 or less. (Technology 10) A non-aqueous electrolyte secondary battery comprising the positive electrode for a secondary battery according to any one of Technologies 1 to 9, a negative electrode, a separator, and a non-aqueous electrolyte. (Technology 11) A method for manufacturing a positive electrode for a secondary battery, comprising the steps of: preparing a positive electrode slurry including a liquid medium and a positive electrode composite dispersed in the liquid medium; preparing a positive electrode current collector and forming a coating film of the positive electrode slurry on a surface of the positive electrode current collector; and heating and drying the coating film at 200°C or less, wherein the positive electrode composite includes a positive electrode active material, a binder, and an organic additive including a heteroatom, wherein the positive electrode active material includes a lithium-containing composite oxide including at least Ni, wherein a ratio of Ni to metal elements other than Li in the lithium-containing composite oxide is 80 atomic % or more, the lithium-containing composite oxide includes an alkaline component of 0.2 mass % to 0.5 mass % or less, and the binder includes a fluorine-containing polymer. (Technology 12) A method for manufacturing a positive electrode for a secondary battery according to Technology 11, wherein the decomposition temperature of the organic additive is 200°C or less. (Technology 13) The method for producing a positive electrode for a secondary battery according to Technology 11 or 12, wherein the organic additive is a Lewis base. (Technology 14) The method for producing a positive electrode for a secondary battery according to any one of Technology 11 to 13, wherein the molecular weight of the organic additive is 50 or more and 1000 or less. (Technology 15) The method for producing a positive electrode for a secondary battery according to any one of Technology 11 to 14, wherein the ratio of the mass of the organic additive to the mass of the lithium-containing composite oxide is 0.002 mass% or more and 0.3 mass% or less.

[0081] The present disclosure will be specifically described below based on examples, but the present disclosure is not limited to the following examples.

[0082] (Preparation of Positive Electrode Slurry A1) Positive electrode active material, polyvinylidene fluoride (PVDF, fluorine-containing polymer), pyrazole derivative having a chain organic group with 10 carbon atoms (PZ1, Lewis base), acetylene black (conductive material), and NMP (liquid medium) were mixed in a predetermined mass ratio to prepare positive electrode slurry A1. The positive electrode active material, PVDF, PZ1, and conductive material are the components of the positive electrode mixture. The positive electrode active material was a fluorine-containing polymer having the composition formula LiNi ０．９ Co ０．０４ Mn ０．０５ Al ０．０１ O ２ In the positive electrode composite, the positive electrode active material, PVDF, PZ1, and conductive material were mixed in a mass ratio of positive electrode active material:PVDF:PZ:conductive material=100:0.6:0.02:0.75.

[0083] The weight-average molecular weight of PVDF was 1.4 million. The molecular weight of the pyrazole derivative (PZ1) was about 200, and the thermal decomposition temperature of PZ1 was about 180°C.

[0084] (Preparation of Positive Electrode Slurries A2 to A4, C1 and C2) Positive electrode slurries A2 to A3, C1 and C2 were prepared by the same method and under the same conditions as for preparing positive electrode slurry A1, except that the type of organic additive and its mass ratio relative to the composite oxide N were changed to change the mass ratio relative to the composite oxide N contained in the positive electrode mixture layer in the completed positive electrode as shown in Table 1.

[0085] Neither positive electrode slurry C1 nor C2 contained any organic additives. Furthermore, positive electrode slurry C2 used a composite oxide NX that was different from the other positive electrode slurries. The composite oxide NX was thoroughly washed with water, allowing some deterioration of the composite oxide NX, in order to thoroughly remove the alkaline components in advance.

[0086] In the positive electrode slurry A4, the organic additive was changed from PZ1 to an amine derivative (PZ2, Lewis base) with a molecular weight of about 20,000 and a thermal decomposition temperature of about 400°C.

[0087] For each positive electrode slurry prepared, the viscosity μ0 on the day of preparation and the viscosity μ1 7 days after preparation were measured. The viscosity increase rate was calculated using the following formula. The viscosity increase rate for each positive electrode slurry is shown in Table 2. The lower the viscosity increase rate, the better the positive electrode slurry.

[0088] "Viscosity increase rate (%) = 100 × μ1 / μ0"

[0089] (1) Preparation of Positive Electrode The above-described positive electrode slurry was applied to the surface of an aluminum foil (positive electrode current collector) to form a coating film, thereby obtaining a laminate of the aluminum foil and the coating film. Next, the coating film was dried at 180°C, and the laminate was then rolled. In this manner, a positive electrode including an aluminum foil and a positive electrode composite layer formed on both sides of the aluminum foil was prepared. The positive electrodes prepared using the positive electrode slurries A1 to A4 are referred to as positive electrodes A1 to A4, respectively, and the positive electrodes prepared using the positive electrode slurries C1 to C2 are referred to as positive electrodes C1 to C2, respectively.

[0090] <Measurement of Polyenation Degree> For each positive electrode, the positive electrode composite layer (positive electrode composite) was peeled off from the positive electrode current collector, and a 20 g sample of the positive electrode composite was weighed and mixed with 10 mL of NMP. From the mixed solution, an NMP solution of a fluorine-containing polymer (PVDF) was obtained by the method described above. A fluorine-containing polymer film was formed from the NMP solution of PVDF by the method described above, and the film was analyzed by Raman spectroscopy at 1130 cm －１ The peak P1 due to the C═C bond observed near 2980 cm －１ CH observed nearby ２ The intensity ratio (P1 / P2) of the peak P1 derived from the positive electrode to the peak P2 derived from the positive electrode was calculated as the degree of polyenization. The degree of polyenization of PVDF before being mixed into the positive electrode slurry was less than 0.01. The degree of polyenization of PVDF contained in each positive electrode is shown in Table 1.

[0091] <Measurement of Alkaline Component Content of Complex Oxide N> For each positive electrode, the positive electrode composite layer (positive electrode composite) was peeled from the positive electrode current collector, and a 1.0 g sample of the positive electrode composite was weighed and mixed with 30 mL of ion-exchanged water. The alkaline component was eluted using the method described above to prepare a sample solution, and the mass of the alkaline component was calculated by titration. The alkaline component content was calculated as the ratio of the mass of the alkaline component to the total mass of the complex oxide N and the alkaline component contained in the sample, and was found to be 0.31 mass%. The alkaline component content of the complex oxide N contained in each positive electrode is shown in Table 1.

[0092] <Measurement of Peel Strength> The peel strength of the positive electrode composite layer from the positive electrode current collector was determined using a measuring device conforming to JIS Z0237 (2009). Specifically, the positive electrode was formed into a strip-shaped sample having a width of 10 mm and a length of 50 mm or more, and one side of a 20 mm wide x 130 mm long double-sided tape (No. 5606 manufactured by Nitto Denko Corporation) was attached to the positive electrode composite layer of the sample. The other side of the double-sided tape was attached to a horizontal table having a flat surface, and one end of the positive electrode current collector in the longitudinal direction was fixed with a force gauge and pulled vertically at a rate of 50 mm / min to peel the positive electrode composite layer attached to the double-sided tape from the positive electrode current collector. The tension at this time was measured for 15 seconds or more, and the average tension over a continuous 15-second period was calculated. The peel strength of each positive electrode is shown in Table 2 as a relative value, with the peel strength of positive electrode C1 being 100. The larger the relative value, the higher the peel strength and the higher the positive electrode performance.

[0093] (2) Preparation of Negative Electrode A negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), and water were mixed in a predetermined mass ratio to prepare a negative electrode slurry. Graphite was used as the negative electrode active material. Next, the negative electrode slurry was applied to the surface of copper foil (negative electrode current collector) to form a laminate including the copper foil and a coating film formed on the copper foil. Next, the coating film was dried, and the laminate was rolled. In this way, a negative electrode including copper foil and a negative electrode mixture layer formed on both sides of the copper foil was formed.

[0094] (3) Preparation of electrolyte (non-aqueous electrolyte) LiPF ６ The electrolyte solution was prepared by adding LiPF (lithium salt). ６The concentration of was 1.0 mol / L. As the non-aqueous solvent, a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of EC:EMC=3:7 was used.

[0095] (4) Fabrication of Secondary Batteries Leads were attached to each of the positive and negative electrodes. Next, an electrode group was fabricated by spirally winding the positive and negative electrodes, with the separator disposed between the positive and negative electrodes. This electrode group and a nonaqueous electrolyte were then housed in a cylindrical battery case. In this manner, cylindrical batteries A1 to A4 of the example, each equipped with positive electrodes A1 to A4, and comparative batteries C1 to C2, each equipped with positive electrodes C1 to C2, were fabricated.

[0096] [Evaluation] The discharge capacity, internal resistance, and capacity degradation rate of each battery were measured. The relative values, with the evaluation result of Battery C1 set to 100, are shown in Table 2. The larger the discharge capacity value, the better the performance, and the smaller the internal resistance and capacity degradation rate, the better the performance.

[0097] <Discharge Capacity> Each battery was charged at a constant current equivalent to 0.5 It in a 25° C. environment until the battery voltage reached 4.2 V, and then continuously charged at a constant voltage of 4.2 V until the current value reached 0.05 It. After a 10-minute rest period following charging, the battery was discharged at a constant current equivalent to 0.2 It until the battery voltage reached 2.5 V, and the capacity was determined.

[0098] <Capacity Deterioration Rate> The above charge / discharge cycle was repeated 300 times, and the rate of decrease in the discharge capacity at the 300th cycle relative to the discharge capacity at the 5th cycle was determined.

[0099] <Internal Resistance> In a temperature environment of 25°C, the battery was charged at a constant current of 0.3 It until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.05 It. Next, the battery was discharged at a constant current of 0.3 It for 100 minutes to bring the state of charge (SOC) to 50%.

[0100] The voltage value was measured when a battery with an SOC of 50% was discharged for 10 seconds at currents of 0 A, 0.1 A, 0.5 A, and 1.0 A. The internal resistance (DCIR) was calculated from the absolute value of the slope when the relationship between the discharge current value and the voltage value after 10 seconds was approximated to a straight line by the least squares method.

[0101]

[0102]

[0103] As is clear from a comparison between Examples 1 to 4 and Comparative Example 1, the viscosity increase rate was significantly reduced by including an organic additive in the positive electrode slurry. Furthermore, although the viscosity increase rate decreased as the amount of organic additive increased, it can be seen that from the viewpoint of battery performance, such as discharge capacity and capacity degradation rate, it is desirable that the amount of organic additive not be too large. Furthermore, from the viewpoint of peel strength, it can be seen that it is desirable that the organic additive not have an excessively high thermal decomposition temperature and not too large a molecular weight. Furthermore, as shown by Battery C2, it is possible to remove the alkaline component of the composite oxide N to a certain extent by washing with water, but it can be seen that washing the composite oxide N with water increases the internal resistance of the battery and also increases the capacity degradation rate.

[0104] The positive electrode for a secondary battery according to the present disclosure can be used in a high-performance non-aqueous electrolyte secondary battery.

[0105] While the present invention has been described in terms of presently preferred embodiments, such disclosure is not to be interpreted as limiting. Various changes and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains upon reading the above disclosure. It is therefore intended that the appended claims be interpreted to cover all changes and modifications that do not depart from the true spirit and scope of the invention.

[0106] 1: electrode group, 2: positive electrode lead, 3: negative electrode lead, 4: battery case, 5: sealing plate, 6: negative electrode terminal, 7: gasket, 8: sealing plug, 10: secondary battery (nonaqueous electrolyte secondary battery)

Claims

1. The positive electrode for a secondary battery includes a positive electrode composite material containing a positive electrode active material and a binder, the positive electrode active material includes a lithium-containing composite oxide containing at least Ni, in the lithium-containing composite oxide, the proportion of Ni in metal elements other than Li is 80 atomic% or more, the lithium-containing composite oxide contains an alkali component of 0.2 mass% or more and 0.5 mass% or less, the binder includes a fluorine-containing polymer, and the degree of polyene of the fluorine-containing polymer is 0.2 or less.

2. The positive electrode for a secondary battery according to claim 1, wherein the lithium-containing composite oxide further includes Co and Mn.

3. The positive electrode for a secondary battery according to claim 2, wherein the lithium-containing composite oxide further includes Al.

4. The lithium-containing composite oxide has the formula: Li ｙ Ni ｘ M （１－ｘ） O ２－δ (0.8 ≤ x ≤ 1, 0 < y ≤ 1.2 and -0.05 ≤ δ ≤ 0.05), where M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W, and B. The positive electrode for a secondary battery according to any one of claims 1 to 3.

5. M is of the formula: Co １－ｘ－ａ－ｂ Mn ａ Al ｂ (0 < a < 0.05 and 0 < b < 0.05), the positive electrode for a secondary battery according to claim 4.

6. The positive electrode for a secondary battery according to any one of claims 1 to 3, wherein the positive electrode composite material further includes an organic additive containing a heteroatom, and the proportion of the mass of the organic additive to the mass of the lithium-containing composite oxide is 0.1 mass% or less.

7. The positive electrode for a secondary battery according to claim 6, wherein the decomposition temperature of the organic additive is 200 °C or lower.

8. The positive electrode for a secondary battery according to claim 6, wherein the organic additive is a Lewis base.

9. The positive electrode for a secondary battery according to claim 6, wherein the molecular weight of the organic additive is 50 or more and 1000 or less.

10. A non-aqueous electrolyte secondary battery including the positive electrode for a secondary battery according to any one of claims 1 to 3, a negative electrode, a separator, and a non-aqueous electrolyte.

11. A method for manufacturing a positive electrode for a secondary battery, comprising: preparing a positive electrode slurry including a liquid medium and a positive electrode composite material dispersed in the liquid medium; preparing a positive electrode current collector and forming a coating film of the positive electrode slurry on the surface of the positive electrode current collector; and heating and drying the coating film at 200 °C or lower. The positive electrode composite material includes a positive electrode active material, a binder, and an organic additive containing a heteroatom. The positive electrode active material includes a lithium-containing composite oxide containing at least Ni. In the lithium-containing composite oxide, the proportion of Ni in metal elements other than Li is 80 atomic% or more. The lithium-containing composite oxide contains an alkali component of 0.2 mass% or more and 0.5 mass% or less. The binder includes a fluorine-containing polymer.

12. The method for manufacturing a positive electrode for a secondary battery according to claim 11, wherein the decomposition temperature of the organic additive is 200 °C or lower.

13. The method for manufacturing a positive electrode for a secondary battery according to claim 11, wherein the organic additive is a Lewis base.

14. The method for manufacturing a positive electrode for a secondary battery according to any one of claims 11 to 13, wherein the molecular weight of the organic additive is 50 or more and 1000 or less.

15. The method for manufacturing a positive electrode for a secondary battery according to any one of claims 11 to 13, wherein the ratio of the mass of the organic additive to the mass of the lithium-containing composite oxide is 0.002% by mass or more and 0.3% by mass or less.

Images