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

Abstract

A positive electrode for a secondary battery, comprising a positive electrode mixture containing a positive electrode active material and a binder, the positive electrode active material containing a lithium-containing composite oxide containing at least Ni, the proportion of Ni among metal elements other than Li in the lithium-containing composite oxide being 80 atomic % or greater, the lithium-containing composite oxide containing 0.2 mass % or greater and 0.5 mass % or less of an alkali component, the binder containing a fluorine-containing polymer, the polyene degree of the fluorine-containing polymer being 0.2 or less.

Description

[0001] Cross-reference of related applications

[0002] This application claims priority to Japanese Patent Application No. 2024-005064, filed on January 17, 2024, with the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to a positive electrode for secondary batteries and a method for manufacturing the same, as well as a non-aqueous electrolyte secondary battery. Background Technology

[0004] Patent document 1 proposes "a sodium-ion secondary battery comprising a positive electrode, a negative electrode, a spacer between the positive electrode and the negative electrode, and a non-aqueous electrolyte having sodium ion conductivity, wherein the positive electrode comprises positive electrode active material particles, a conductive additive and a binder, the positive electrode active material particles having oxide particles that absorb and release sodium ions, and a coating layer covering the oxide particles, wherein the oxide particles comprise an oxide A containing Ni and Mn, the coating layer comprises at least one material B selected from ceramic and carbonaceous materials, and the binder comprises a fluororesin."

[0005] Patent document 2 proposes "a positive electrode for a sodium-ion secondary battery, comprising a positive electrode active material for absorbing and releasing sodium ions, a conductive additive, a binder, and a carboxylic acid, wherein the binder comprises a vinylidene fluoride-based polymer, and the carboxylic acid has at least one of a boiling point and a thermal decomposition point, wherein the lower of the boiling point and the thermal decomposition point exceeds 150°C".

[0006] Patent document 3 proposes "a lithium-ion secondary battery comprising a positive electrode having a positive electrode compound layer, wherein the positive electrode compound layer comprises a layered lithium-nickel composite oxide having a nickel ratio of 80 mol% or more in a metal other than lithium, LiOH, Li2CO3, and a chlorine-containing polyvinylidene fluoride polymer, wherein the content of LiOH in the positive electrode compound layer and the content of Li2CO3 in the positive electrode compound layer are 0.1 wt% or more and 2.1 wt% or less, respectively, the total content of LiOH and Li2CO3 in the positive electrode compound layer is 0.2 wt% or more and 4.2 wt% or less, and the chlorine content in the positive electrode compound layer is 30 μg / g or more and 120 μg / g or less."

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2017-107713

[0010] Patent Document 2: International Publication No. 2016 / 021405

[0011] Patent Document 3: International Publication No. 2019 / 088171 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] Because lithium-containing composite oxides with high Ni content are highly alkaline, the alkaline components dissolve from the lithium-containing composite oxides during the preparation of the cathode slurry when mixed with a liquid medium. These alkaline components react with the fluorinated polymers contained in the cathode binder, causing the cathode slurry, which is then dispersed in the liquid medium, to thicken. This thickening of the cathode slurry contributes to reduced productivity, increased material loss, and cathode quality deviations due to poor liquid delivery.

[0014] Alkaline components can be partially removed by washing lithium-containing composite oxides with water. However, washing leads to the degradation of lithium-containing composite oxides. From the perspective of minimizing degradation, it is difficult to completely remove alkaline components by washing with water.

[0015] Alternatively, a "coating layer of coated oxide particles" could be formed, as in Patent Document 1, but the coating layer would cause the resistance of the positive electrode to increase, so there is room for improvement.

[0016] Methods for solving problems

[0017] One aspect of this application relates to a positive electrode for a secondary battery, comprising a positive electrode compound containing a positive electrode active material and a binder, wherein the positive electrode active material comprises a lithium-containing composite oxide containing at least Ni, wherein Ni accounts for 80 atomic% or more of the metal elements other than Li in the lithium-containing composite oxide, the lithium-containing composite oxide contains 0.2% by mass and 0.5% by mass of an alkaline component, and the binder comprises a fluorinated polymer, wherein the degree of polyolefination of the fluorinated polymer is 0.2 or less.

[0018] Another aspect of this application relates to a non-aqueous electrolyte secondary battery, which includes the aforementioned positive electrode, negative electrode, spacer, and non-aqueous electrolyte for a secondary battery.

[0019] Another aspect of this application relates to a method for manufacturing a positive electrode for a secondary battery, comprising: a step of preparing a positive electrode slurry comprising a liquid medium and a positive electrode mixture dispersed in the liquid medium; a step of 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 a step of drying the coating film by heating it at a temperature below 200°C, wherein the positive electrode mixture comprises a positive electrode active material, a binder, and an organic additive containing heteroatoms, the positive electrode active material comprises a lithium-containing composite oxide containing at least Ni, wherein in the lithium-containing composite oxide, Ni accounts for 80 atomic% or more of the metal elements other than Li, the lithium-containing composite oxide comprises 0.2% by mass or more and 0.5% by mass or less of an alkaline component, and the binder comprises a fluorinated polymer.

[0020] Invention Effects

[0021] According to this application, it is possible to simultaneously suppress the degradation of lithium-containing composite oxides and the thickening of cathode slurry.

[0022] While novel features of the invention are described in the appended technical solutions, both the structure and content of the invention, along with its other objects and features, can be better understood from the following detailed description taken in conjunction with the accompanying drawings. Attached Figure Description

[0023] Figure 1 This is a schematic perspective view of a portion of a non-aqueous electrolyte secondary battery according to one embodiment of this application. Detailed Implementation

[0024] The following examples illustrate embodiments of this application, but this application is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes shown, but other numerical values ​​and materials can be applied as long as the effect of this application is achieved. In this specification, the phrase "numerical value A to numerical value B" includes both numerical value A and numerical value B, and can be replaced with "numerical value A or higher and numerical value B or lower." In the following description, when lower and upper limits of numerical values ​​related to specific physical properties, conditions, etc., are shown, any of the shown lower limits and any of the shown upper limits can be arbitrarily combined, as long as the lower limit is not higher than the upper limit. In the following description, when examples of constituent elements or methods are listed, unless specifically stated otherwise, only one of the listed examples can be used, or multiple of the listed examples can be used together.

[0025] This application includes a combination of matters described in any two or more technical solutions selected from the plurality of technical solutions described in the appended claims. That is, as long as no technical contradiction arises, a combination of matters described in any two or more technical solutions selected from the plurality of technical solutions described in the appended claims is permissible.

[0026] Non-aqueous electrolyte secondary batteries include lithium-ion secondary batteries that use liquid non-aqueous electrolytes, solid batteries that contain gel electrolytes, and all-solid batteries that use solid electrolytes.

[0027] Non-aqueous electrolyte secondary batteries have a positive electrode, a negative electrode, and a non-aqueous electrolyte. A spacer is usually placed between the positive and negative electrodes.

[0028] (positive electrode)

[0029] The positive electrode of this application comprises a positive electrode binder containing a positive electrode active material and a binder. The positive electrode binder may further contain a conductive material. The positive electrode binder is typically supported on a positive electrode current collector, forming a positive electrode binder layer. The positive electrode binder layer is formed on the surface of the positive electrode current collector.

[0030] The positive current collector is composed of a sheet-like conductive material. As a positive current collector, a non-porous conductive substrate (such as metal foil) or a porous conductive substrate (such as a mesh, perforated sheet, or punched sheet) can be used. A positive flux layer is supported as a film on one or both surfaces of the positive current collector. The material of the positive current collector is not particularly limited; stainless steel, aluminum, aluminum alloys, titanium, etc., can be used.

[0031] The positive electrode active material comprises a lithium-containing composite oxide containing at least Ni. From the viewpoint of high capacity, in the lithium-containing composite oxide, the proportion of Ni in the metal elements other than Li is 80 atomic% or more. Ideally, the lithium-containing composite oxide is a lithium-nickel oxide (hereinafter also referred to as "composite oxide N") containing Li and Ni, with Ni accounting for 80 atomic% or more of the metal elements other than Li, and having a layered rock salt-type crystal structure. The proportion of Ni in the metal elements other than Li can be 88 atomic% or more, 90 atomic% or more, or 95 atomic% or more. In the composite oxide N, the proportion of Ni in the metal elements other than Li is less than 100 atomic%, which can be 99 atomic% or less or 98 atomic% or less.

[0032] The positive electrode active material may contain other materials. The proportion of composite oxide N in the positive electrode active material may be, for example, 70% or more by mass, 90% or more by mass, 95% or more by mass, or even 100%.

[0033] High-Ni-content composite oxides (N) contain alkaline components. Composite oxides where Ni constitutes more than 90 atomic percent of the metals other than Li exhibit particularly high alkalinity. When the alkalinity of the synthesized composite oxide (before washing) exceeds the permissible range, some of the alkaline components can be removed by washing with water to a degree that allows for acceptable degradation. However, high-Ni-content composite oxides (N) can contain alkaline components both before and after washing. These alkaline components can be, for example, LiOH, Li₂CO₃, etc., but the thickening of the cathode slurry is mostly caused by strong bases (primarily LiOH).

[0034] When composite oxide N is mixed with a liquid medium (dispersion medium), the alkaline component dissolves into the liquid medium. When the composite oxide N contains 0.2% by mass or more of an alkaline component, the cathode slurry typically thickens significantly during preparation. This thickening occurs due to the polyolefination of fluorinated polymers, which act as binders in the cathode binder, with the alkaline component. Polyolefination refers to the formation of double bonds in the fluorinated polymers, and the polyolefinated fluorinated polymers promote the gelation of the cathode slurry over time. Because significant thickening due to gelation of the cathode slurry needs to be avoided, conventional cathode binders do not contain 0.2% by mass or more of an alkaline component.

[0035] In contrast, the composite oxide N contained in the cathode agent of this application contains 0.2% by mass and 0.5% by mass of an alkaline component. Thickening of the cathode slurry is suppressed by the heteroatom-containing organic additive contained in the cathode agent of the cathode slurry. The heteroatom-containing organic additive (hereinafter also simply referred to as "organic additive") adheres to the surface of the composite oxide N via heteroatoms. As a result, contact between the surface of the composite oxide N and the liquid medium is suppressed, dissolution of the alkaline component is suppressed, and reaction between the fluorinated polymer and the alkaline component is suppressed. Therefore, the polyolefin degree of the fluorinated polymer contained in the cathode agent layer (cathode agent) stripped from the cathode current collector is low, below 0.2. The polyolefin degree of the fluorinated polymer is preferably below 0.17, more preferably below 0.15.

[0036] The content of alkali in the composite oxide N can be, for example, 0.25% by mass or more and 0.4% by mass or less, or 0.25% by mass or more and 0.35% by mass or less. When the composite oxide N contains more than 0.5% by mass of alkali, it is difficult to suppress the thickening of the cathode slurry even when using organic additives.

[0037] The degree of polyolefination of fluorinated polymers can be determined by the following method.

[0038] A sample equivalent to 20 g of the positive electrode additive layer (positive electrode additive) stripped from the positive electrode current collector was weighed and mixed with 10 mL of N-methyl-2-pyrrolidone (hereinafter also referred to as "NMP") to obtain a mixture. The mixture was centrifuged at 8000 rpm for 0.5 hours to remove the positive electrode active material. Next, the conductive agent was removed by ultracentrifugation at 80000 rpm for 11 hours and then by ultracentrifugation at 80000 rpm for 4 hours, yielding an NMP solution of a fluorinated polymer. A fluorinated polymer membrane was obtained from the NMP solution of the fluorinated polymer by casting. The membrane was dried under reduced pressure at 60°C for 2 hours. The obtained membrane was measured using a Raman spectroscopy apparatus. After baseline correction, the value was calculated at 1130 cm⁻¹. -1 The peak P1, originating from the C=C bond, observed nearby is at 2980 cm⁻¹ -1 The intensity ratio (P1 / P2) of the CH2-originating peak P2 observed nearby is used as the degree of polyolefination.

[0039] The content of alkali components in the composite oxide N can be determined by the following method.

[0040] Weigh a sample equivalent to 1.0 g of the positive electrode binder layer (positive electrode binder) stripped from the positive electrode current collector, mix it with 30 mL of deionized water, and shake to dissolve for 30 seconds to obtain a sample solution in which the alkaline component is dissolved. Then, filter the sample solution and titrate it to pH 8.4 with 1 mol / L hydrochloric acid under a nitrogen atmosphere. Calculate the mass of LiOH (the alkaline component) based on the amount of hydrochloric acid required for titration, and then calculate the ratio of the mass of LiOH to the total mass of the N-oxide complex in the sample and the total mass of the alkaline component. It should be noted that the region with pH less than 8.4 is the titration region for weak bases such as Li₂CO₃.

[0041] Because organic additives have flexible organic chains, they do not easily hinder battery reactions even when attached to the surface of composite oxide N. Therefore, organic additives have little impact on the resistance of the positive electrode. Furthermore, organic additives have low heat resistance, so they can be removed from the positive electrode compound during the manufacturing process through thermal decomposition or similar methods. The positive electrode compound layer (positive electrode compound) stripped from the positive electrode current collector may or may not contain organic additives containing heteroatoms. From the viewpoint of significantly suppressing the increase in resistance of the positive electrode, a lower content of organic additives in the positive electrode compound is preferred.

[0042] When the positive electrode additive layer (positive electrode additive) stripped from the positive electrode current collector contains an organic additive, the mass ratio of the organic additive to the composite oxide N is preferably 0.1% by mass or less, more preferably 0.07% by mass or less, even more preferably 0.05% by mass or less or 0.03% by mass or less, and may also be 0.01% by mass or less. The mass ratio of the organic additive to the composite oxide N may, for example, be 0.005% by mass or more.

[0043] The ratio of the mass of the organic additive to the mass of the composite oxide N can be calculated based on the thermogravimetric analysis (TGA) results of a sample of the cathode compound layer (cathode compound) stripped from the cathode current collector and the mass of the composite oxide N contained in that sample. The TGA can be performed at atmospheric conditions at 5°C / min.

[0044] The decomposition temperature (thermal decomposition temperature) of the organic additive is preferably below 200°C, more preferably below 180°C. The decomposition temperature can be determined by TGA under atmospheric conditions at a rate of 5°C / min. Organic additives with a decomposition temperature below 200°C are easily removed from the cathode agent during cathode manufacturing through thermal decomposition or similar processes. Therefore, it is easier to reduce the mass ratio of the organic additive to the mass of the composite oxide N contained in the cathode agent layer of the finished cathode.

[0045] Organic additives can be Lewis bases. Among Lewis bases, those having nitrogen (N) as a heteroatom are particularly preferred. It is believed that the non-shared electron pairs of nitrogen are adsorbed on Lewis acid sites on the surface of the composite oxide N. Lewis bases having multiple nitrogen atoms with non-shared electron pairs in the molecule are particularly preferred in terms of increasing reaction sites. Among Lewis bases having nitrogen as a heteroatom, Lewis bases having nitrogen-containing heterocycles are particularly preferred. Nitrogen-containing heterocycles are preferably, for example, 5-membered, 6-membered, or 7-membered rings, and preferably have two or more nitrogen atoms. It should be noted that the heteroatom is not limited to N, and can also be S, P, O, etc. Organic additives can contain N and heteroatoms other than N as heteroatoms.

[0046] Nitrogen-containing heterocycles can be saturated rings without double bonds, but are preferably aromatic. Aromatic nitrogen-containing heterocycles only need to contain one or more nitrogen atoms, and may contain two or more. Preferred examples of nitrogen-containing heterocycles include pyrazole rings, imidazole rings, diazine rings, triazine rings, and diazapyridine rings.

[0047] To effectively suppress contact between the liquid medium and the surface of the composite oxide N, the organic additive preferably has chain-like organic groups. For example, it may have chain-like organic groups bonded to cyclic atoms of nitrogen-containing heterocycles. The number of carbon atoms in such organic groups may be, for example, 1 to 50, or 5 to 20.

[0048] The molecular weight of the organic additive can be, for example, 50 or more and 1000 or less, 100 or more and 800 or less, or 100 or more and 500 or less. Organic additives with such molecular weights have low thermal decomposition temperatures and sufficient size to effectively suppress contact between the liquid medium and the surface of the composite oxide N.

[0049] The N-complex oxide can be further enriched with Co and Mn. Co and Mn contribute to the stabilization of the crystal structure of the N-complex oxide. The N-complex oxide containing Co and Mn is very basic and deteriorates significantly due to water washing; therefore, the role of organic additives is particularly important.

[0050] From the perspective of cost reduction and high capacity, the proportion of Co in the composite oxide N to metal elements other than Li is preferably 0 atomic% or more and 20 atomic% or less, more preferably greater than 0 atomic% and less than 5 atomic%.

[0051] From the perspective of cost reduction, the proportion of Mn contained in the composite oxide N in the metal elements other than Li can be more than 1 atomic% and less than 10 atomic%, more than 2 atomic% and less than 5 atomic%, or more than 3 atomic% and less than 5 atomic%.

[0052] The N-complex oxide can further contain Al. Al contributes to the stabilization of the crystal structure of the N-complex oxide. The N-complex oxide containing Co, Mn, and Al is very basic, therefore the role of organic additives is particularly important.

[0053] The proportion of Al in the composite oxide N relative to the metal elements other than Li can 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.

[0054] Composite oxide N can be derived, for example, from 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) represents this. Here, element M can include at least one element selected from Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W and B. The atomic ratio of Ni, x, can be less than 0.98 or less than 0.95. x increases or decreases due to the charging and discharging of the secondary battery.

[0055] Element M can be represented by the formula: Co 1-x-a-b Mn a Al b(0 < a < 0.05 and 0 < b < 0.05) represents this.

[0056] The thickness of the positive electrode agent layer is not particularly limited; for example, it can be 50 μm or more and 150 μm or less, or 75 μm or more and 125 μm or less. A single positive electrode active material layer can be formed from multiple layers with different morphologies. For example, two or more layers containing positive electrode active materials with different average particle sizes can be stacked, or two or more layers containing positive electrode active materials of different types or compositions can be stacked.

[0057] The average particle size (D50) of the composite oxide N is, for example, greater than 1 μm and less than 50 μm, or greater than 5 μm and less than 25 μm. The average particle size (D50) refers to the median particle size at which the cumulative volume reaches 50% in a volume-based particle size distribution. The volume-based particle size distribution can be determined using a commercially available laser diffraction scattering particle size distribution measuring device.

[0058] The average particle size of the composite oxide N can be determined from the cross-section of the cathode compound layer. SEM images of the cross-section can be taken with more than 10 composite oxide N particles visible. Through image processing, the diameters of equivalent circles with the same area as the cross-section of each of the 10 or more composite oxide N particles are calculated, and their average value is taken as the average particle size.

[0059] Fluorinated polymers that function as binders include vinylidene fluoride (PVDF)-based polymers. Examples of PVDF-based polymers include polymers containing monomers of vinylidene fluoride. Fluorinated polymers can be combinations of PVDF-based polymers with other fluorinated polymers. PVDF-based polymers can be copolymers of vinylidene fluoride with other monomers. Examples of PVDF-based polymers include polyvinylidene fluoride (PVDF), PVDF-hexafluoropropylene copolymers, etc. PVDF-based polymers preferably contain monomer units derived from vinylidene fluoride in a proportion of 90 mol% or more. The degree of polyolefination of the fluorinated polymer before mixing into the positive electrode slurry is typically 0.1 or less.

[0060] In the positive electrode mixture, relative to 100 parts by mass of the positive electrode active material, the amount of fluorinated polymer can be more than 0.1 parts by mass, or more than 0.5 parts by mass, or less than 2.0 parts by mass, or less than 1.2 parts by mass.

[0061] Fluorinated polymers can have a weight-average molecular weight of 800,000 or more, 1 million or more, or 1.2 million or more, or less than 2 million or less than 1.8 million. By setting the weight-average molecular weight to 1 million or more, high performance as an adhesive can be achieved with a small amount.

[0062] The conductive material can be included as any component in the positive electrode layer; there are no particular limitations, and known conductive materials can 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.

[0063] The cathode slurry may contain components other than those mentioned above, as needed. For example, the cathode slurry may contain binders other than fluorinated polymers. Examples of such binders include hydrogenated nitrile rubber.

[0064] (The manufacturing method of the positive electrode)

[0065] An example method (hereinafter also referred to as "manufacturing method (M)") for manufacturing the positive electrode for a secondary battery according to this application will be described. Manufacturing method (M) includes a first step of preparing a positive electrode slurry and a second step of forming a positive electrode flux 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.

[0066] The positive electrode slurry prepared in the first step of manufacturing method (M) comprises a liquid medium and a positive electrode agent dispersed in the liquid medium. The positive electrode agent used is one already described. For example, the positive electrode slurry can be prepared by mixing a positive electrode active material, a fluorinated polymer, an organic additive, a liquid medium, and a conductive material. The positive electrode active material comprises a composite oxide N. The positive electrode slurry can be prepared by mixing the positive electrode agent with the liquid medium. The organic additive can be mixed with other components in the form of a solution pre-dissolved in the liquid medium. The mixing method is not particularly limited, and known mixing methods can be used.

[0067] The liquid medium can be an organic solvent or water. As an 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., can also be used.

[0068] Organic additives are used to suppress thickening of the cathode slurry. Therefore, they only need to be included in the cathode slurry and do not need to be included in the cathode binder layer. In order to effectively suppress thickening of the cathode slurry, it is preferable to set the mass ratio of the organic additive in the cathode slurry to the mass of the lithium-containing composite oxide to, for example, 0.002% by mass or more and 0.3% by mass or less, more preferably 0.02% by mass or more and 0.3% by mass or less, and it can also be set to 0.1% by mass or more and 0.25% by mass or less.

[0069] In the second step, the process of forming a coating film of the positive electrode slurry on the surface of the positive electrode current collector can be performed using coating equipment such as a rod coater, gravure coater, blade coater, roller coater, comma coater, die coater, and lip coater. Alternatively, multiple positive electrode slurries with different compositions can be prepared and coated in two or more layers.

[0070] In the second step, the drying process of the coating film is preferably carried out at a temperature below 200°C, for example, at a temperature above 150°C, and further above 180°C. Through the drying process of the coating film, the liquid medium evaporates to form an uncalendered coating film. At least a portion of the organic additives can be decomposed or evaporated during the drying process of the coating film and removed from the uncalendered coating film.

[0071] Typically, a calendering process is then performed after the coating is not calendered, forming the positive electrode additive layer. The calendering conditions are not particularly limited. The density of the positive electrode active material in the positive electrode additive layer is, for example, 3.3 g / cm³. 3 Above and 4.0 g / cm 3 The following can also be 3.5 g / cm³. 3 Above and 4.0 g / cm 3 the following.

[0072] Depending on the battery structure, the positive electrode flux layer can be formed on only one side of the positive electrode current collector, or it can be formed on both sides of the positive electrode current collector.

[0073] (Non-aqueous electrolyte secondary battery)

[0074] An example of a non-aqueous electrolyte secondary battery of this application (hereinafter also referred to as "secondary battery (B)") will be described. The secondary battery (B) includes the positive electrode, negative electrode, spacer and non-aqueous electrolyte described above.

[0075] The positive electrode of the secondary battery (B) may contain an organic additive attached to the surface of the composite oxide N in a trace amount. The mass ratio of the organic additive to the composite oxide N is, for example, less than 0.1% by mass. Therefore, the organic additive remaining in the positive electrode mixture layer hardly increases the resistance of the positive electrode.

[0076] There are no particular limitations on the components other than the positive electrode, and the components used in known non-aqueous electrolyte secondary batteries can also be used. Below, examples of the components of a secondary battery (B) will be explained.

[0077] (positive electrode)

[0078] The positive electrode uses the aforementioned positive electrode.

[0079] (negative electrode)

[0080] The negative electrode only needs to have a negative current collector. In the case of lithium metal secondary batteries, the negative electrode uses a negative current collector capable of depositing lithium metal or lithium alloy. In the case of lithium-ion secondary batteries, the negative electrode typically contains a negative electrode additive containing negative electrode active material. The negative electrode additive is supported on the negative current collector, forming a negative electrode additive layer. The negative electrode additive layer is formed on the surface of the negative current collector.

[0081] The negative electrode mixture contains a negative electrode active substance as an essential component. The negative electrode mixture may also contain binders, thickeners, conductive materials, etc., as optional components. These optional components can be those exemplified as components used in the positive electrode.

[0082] The negative electrode mixture layer can be formed by coating a negative electrode slurry, which disperses the components of the negative electrode mixture in a liquid medium (dispersion medium), onto the surface of the negative electrode current collector and then drying it. The dried coating can be calendered as needed. The liquid medium can be any liquid medium used as the positive electrode slurry, as exemplified.

[0083] (Negative electrode active material)

[0084] The negative electrode active material is selected based on the type of secondary battery (B). An example of a negative electrode active material is one capable of absorbing and releasing lithium ions. Examples of such materials include carbonaceous materials, Si-containing materials, etc. The negative electrode active material can contain Si-containing materials or be any material containing Si. Metallic lithium, lithium alloys, etc., can be used as negative electrode active materials. The negative electrode can contain one type of negative electrode active material or a combination of two or more.

[0085] Examples of carbonaceous materials include graphite, easily graphitized carbon (soft carbon), and difficult-to-graphitize carbon (hard carbon). A single carbonaceous material can be used, or two or more can be used in combination. Graphite is preferred due to its excellent charge-discharge stability and low irreversible capacity. Examples of graphite include natural graphite, synthetic graphite, and graphitized mesophase carbon particles.

[0086] Examples of Si-containing materials include elemental Si, silicon alloys, silicon compounds (silicon oxides, etc.), and composite materials in which a silicon phase is dispersed within a lithium-ion conductive phase (matrix). Examples of silicon oxides include SiO₂. x Particles. x can be, for example, 0.5 ≤ x < 2, or 0.8 ≤ x ≤ 1.6. As the lithium-ion conducting phase, at least one selected from SiO2 phase, silicate phase and carbon phase can be used.

[0087] For the negative current collector, metal foil can be used. The negative current collector can be porous. Examples of materials for the negative current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.

[0088] (Non-aqueous electrolyte)

[0089] Non-aqueous electrolytes consist of a solvent (a non-aqueous solvent) and a solute dissolved in the solvent. Examples of solutes include lithium salts. Various additives can be added to non-aqueous electrolytes.

[0090] Known materials can be used as solvents. Examples of solvents 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). 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 non-aqueous solvent can be used alone, or two or more can be used in combination.

[0091] Examples of lithium salts include lithium salts of chlorinated acids (LiClO4, LiAlCl4, LiB). 10 Cl 10 Lithium salts include those containing fluorine acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts containing fluorine imides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), and lithium halides (LiCl, LiBr, LiI, etc.). A single lithium salt can be used, or two or more can be used in combination.

[0092] The concentration of lithium salt in non-aqueous electrolytes can be above 1 mol / L and below 2 mol / L, or above 1 mol / L and below 1.5 mol / L. By setting the concentration of lithium salt within the above range, an electrolyte with excellent ionic conductivity and moderate viscosity can be obtained.

[0093] Non-aqueous electrolytes may contain known additives. Examples of additives include 1,3-propanesulfonate lactone, methyl benzenesulfonate, cyclohexylbenzene, biphenyl, diphenyl ether, fluorobenzene, etc.

[0094] (spacer)

[0095] A spacer is disposed between the positive and negative electrodes. The spacer preferably has high ion permeability and moderate mechanical strength and insulation. Microporous membranes, woven fabrics, nonwoven fabrics, etc., can be used as spacers. Examples of spacer materials include polyolefins (polypropylene, polyethylene, etc.) and other resins.

[0096] (outer body)

[0097] The electrode assembly and non-aqueous electrolyte are housed within the outer casing (battery housing). The outer casing is not particularly limited and can use any known type. The electrode assembly consists of a positive electrode, a negative electrode, and a spacer. The configuration of the electrode assembly is not particularly limited; it can be either wound or stacked. A wound electrode assembly is formed by winding the positive and negative electrodes together with the spacer in between. A stacked electrode assembly is formed by stacking the positive and negative electrodes together with the spacer in between. The shape of the non-aqueous electrolyte secondary battery is not particularly limited and can be cylindrical, square, coin-shaped, button-shaped, laminated, etc.

[0098] Figure 1 This is a schematic perspective view showing a section cut across a portion of a secondary battery 10 according to one embodiment of this application. Figure 1 As an example, a square non-aqueous electrolyte battery is shown. Figure 1 The secondary battery 10 shown includes a bottom-shaped cylindrical battery casing 4, and an electrode assembly 1 and a non-aqueous electrolyte (not shown) housed within the battery casing 4.

[0099] Electrode assembly 1 includes a strip-shaped negative electrode, a strip-shaped positive electrode, and spacers disposed between them. The positive electrode is the aforementioned positive electrode. The negative current collector of the negative electrode is electrically connected to the negative terminal 6 disposed on the sealing plate 5 via a negative lead 3. The negative terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive current collector of the positive electrode is electrically connected to the back side of the sealing plate 5 via a positive lead 2. That is, the positive electrode is electrically connected to the battery casing 4, which also serves as the positive terminal. The periphery of the sealing plate 5 is fitted into the open end of the battery casing 4, and this fitting is laser welded. The sealing plate 5 has an injection hole for a non-aqueous electrolyte. After the non-aqueous electrolyte is injected, the injection hole is blocked by a sealing plug 8.

[0100] (Postscript)

[0101] The following technologies are disclosed through the above description.

[0102] (Technology 1)

[0103] A positive electrode for a secondary battery, comprising a positive electrode compound containing a positive electrode active material and a binder.

[0104] The aforementioned positive electrode active material contains at least a lithium-containing composite oxide with Ni.

[0105] In the aforementioned lithium-containing composite oxides, Ni accounts for more than 80 atomic percent of the metal elements other than Li.

[0106] The aforementioned lithium-containing composite oxide contains 0.2% by mass and less than 0.5% by mass of an alkaline component.

[0107] The aforementioned adhesive contains fluorinated polymers.

[0108] The degree of polyolefination of the above-mentioned fluorinated polymers is below 0.2.

[0109] (Technology 2)

[0110] According to the positive electrode for a secondary battery described in Technology 1, the aforementioned lithium-containing composite oxide further comprises Co and Mn.

[0111] (Technology 3)

[0112] According to the positive electrode for a secondary battery described in Technique 1 or 2, the aforementioned lithium-containing composite oxide further comprises Al.

[0113] (Technology 4)

[0114] According to any one of the techniques 1 to 3, the positive electrode for a secondary battery, wherein the aforementioned lithium-containing composite oxide is derived from 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) means that

[0115] M contains at least one element selected from Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W, and B.

[0116] (Technology 5)

[0117] According to the positive electrode for a secondary battery described in Technology 4, M is derived from the formula: Co 1-x-a-b Mn a Al b (0 < a < 0.05 and 0 < b < 0.05) represents this.

[0118] (Technology 6)

[0119] According to any one of the techniques 1 to 5, the positive electrode for a secondary battery further comprises an organic additive containing heteroatoms.

[0120] The mass ratio of the above-mentioned organic additive to the mass of the above-mentioned lithium-containing composite oxide is less than 0.1% by mass.

[0121] (Technology 7)

[0122] According to the positive electrode for a secondary battery described in Technology 6, the decomposition temperature of the aforementioned organic additive is below 200°C.

[0123] (Technology 8)

[0124] According to the positive electrode for a secondary battery described in Technique 6 or 7, the aforementioned organic additive is a Lewis base.

[0125] (Technology 9)

[0126] According to any one of the techniques 6 to 8, the positive electrode for a secondary battery has a molecular weight of 50 or more and 1000 or less for the aforementioned organic additive.

[0127] (Technology 10)

[0128] A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a spacer, and a non-aqueous electrolyte as described in any one of claims 1 to 9.

[0129] (Technology 11)

[0130] A method for manufacturing a positive electrode for a secondary battery, comprising:

[0131] A process for preparing a positive electrode slurry comprising a liquid medium and a positive electrode agent dispersed in the liquid medium;

[0132] The process of preparing a positive current collector and forming a coating of the positive current collector slurry on the surface of the positive current collector; and

[0133] The process of drying the above coating by heating it at a temperature below 200°C.

[0134] The aforementioned positive electrode mixture contains positive electrode active material, binder, and organic additives containing heteroatoms.

[0135] The aforementioned positive electrode active material contains at least a lithium-containing composite oxide with Ni.

[0136] In the aforementioned lithium-containing composite oxides, Ni accounts for more than 80 atomic percent of the metal elements other than Li.

[0137] The aforementioned lithium-containing composite oxide contains 0.2% by mass and less than 0.5% by mass of an alkaline component.

[0138] The aforementioned adhesive contains fluorinated polymers.

[0139] (Technology 12)

[0140] According to the manufacturing method of the positive electrode for a secondary battery described in Technology 11, the decomposition temperature of the aforementioned organic additive is below 200°C.

[0141] (Technology 13)

[0142] According to the manufacturing method of the positive electrode for a secondary battery as described in Technique 11 or 12, the aforementioned organic additive is a Lewis base.

[0143] (Technology 14)

[0144] According to any one of the methods for manufacturing a positive electrode for a secondary battery as described in technical techniques 11 to 13, the molecular weight of the aforementioned organic additive is 50 or more and 1000 or less.

[0145] (Technology 15)

[0146] According to any one of the methods for manufacturing a positive electrode for a secondary battery as described in technical art 11 to 14, the mass ratio of the organic additive to the lithium-containing composite oxide is 0.002% by mass or more and 0.3% by mass or less.

[0147] Example

[0148] The present application is described in detail below based on the embodiments, but the present application is not limited to the following embodiments.

[0149] (Preparation of positive electrode slurry A1)

[0150] Positive electrode slurry A1 is prepared by mixing positive electrode active material, polyvinylidene fluoride (PVDF, a fluorinated polymer), a pyrazole derivative (PZ1, a Lewis base) with 10 carbon atoms, acetylene black (conductive material), and NMP (liquid medium) in a specified mass ratio. The positive electrode active material, PVDF, PZ1, and conductive material are the constituent components of the positive electrode mixture. The positive electrode active material uses the formula LiNi. 0.9 Co 0.04 Mn 0.05 Al 0.01 The particles of composite oxide N shown in O2. In the positive electrode mixture, the positive electrode active material, PVDF, PZ1 and conductive material are mixed in a mass ratio of positive electrode active material:PVDF:PZ:conductive material = 100:0.6:0.02:0.75.

[0151] The weight-average molecular weight of PVDF is 1.4 million. The molecular weight of the pyrazole derivative (PZ1) is approximately 200, and the thermal decomposition temperature of PZ1 is approximately 180°C.

[0152] (Preparation of positive electrode slurry A2-A4, C1-C2)

[0153] By changing the type of organic additive and its mass ratio relative to the composite oxide N, as shown in Table 1, the mass ratio of the positive electrode additive layer in the completed positive electrode relative to the composite oxide N is changed. Otherwise, positive electrode slurries A2 to A3 and C1 to C2 are prepared using the same method and conditions as the preparation of positive electrode slurry A1.

[0154] Neither cathode slurry C1 nor C2 contains organic additives. Furthermore, cathode slurry C2 uses a composite oxide NX, which is different from other cathode slurries. For the composite oxide NX, thorough water washing is performed to allow for a certain degree of degradation in order to fully remove alkaline components beforehand.

[0155] In the positive electrode slurry A4, PZ1 is replaced by an amine derivative (PZ2, Lewis base) with a molecular weight of about 20,000 and a thermal decomposition temperature of about 400°C, instead of PZ1, as an organic additive.

[0156] For the prepared cathode slurry, the viscosity μ0 on the day of preparation and the viscosity μ1 after 7 days were measured. Then, the viscosity rise rate was calculated according to the following formula. The viscosity rise rate of each cathode slurry is shown in Table 2. The lower the viscosity rise rate, the better the cathode slurry.

[0157] "Viscosity increase rate (%) = 100 × μ1 / μ0"

[0158] (1) Production of the positive electrode

[0159] A coating film is formed by coating the surface of an aluminum foil (positive current collector) with the aforementioned positive electrode paste, resulting in a laminate of the aluminum foil and the coating film. Next, the coating film is dried at 180°C, and the laminate is calendered. This produces a positive electrode comprising an aluminum foil and positive electrode binder layers formed on both sides of the aluminum foil. Positive electrodes made using positive electrode pastes A1 to A4 are designated as positive electrodes A1 to A4, and positive electrodes made using positive electrode pastes C1 to C2 are designated as positive electrodes C1 to C2.

[0160] <Determination of Polyene Degree>

[0161] In each positive electrode, the positive electrode flux layer (positive electrode flux) is peeled off from the positive electrode current collector. A sample equivalent to 20g of the positive electrode flux is weighed and mixed with 10mL of NMP. Using the above method, an NMP solution of a fluorinated polymer (PVDF) is obtained from the mixture. A fluorinated polymer film is formed from the PVDF NMP solution using the above method. The Raman spectroscopy measurement at 1130cm⁻¹ is then performed. -1 The peak P1, originating from the C=C bond, observed nearby is at 2980 cm⁻¹ -1 The intensity ratio (P1 / P2) of the CH2-originating peak P2 observed nearby is used as the polyolefin degree. It should be noted that the polyolefin degree of PVDF before being mixed into the cathode slurry is less than 0.01. The polyolefin degree of PVDF contained in each cathode is shown in Table 1.

[0162] <Determination of the alkaline content of N-complex oxides>

[0163] In each positive electrode, the positive electrode agent layer (positive electrode agent) was peeled off from the positive electrode current collector. A sample equivalent to 1.0 g of the positive electrode agent was weighed and mixed with 30 mL of deionized water. A sample solution was prepared by dissolving the alkaline component using the above method, and the mass of the alkaline component was calculated by titration. The content of the alkaline component was calculated as the ratio of the mass of the alkaline component in the sample to the total mass of the composite oxide N and the alkaline component, which was 0.31% by mass. The content of the alkaline component of the composite oxide N in each positive electrode is shown in Table 1.

[0164] <Determination of peel strength>

[0165] The peel strength of the positive electrode binder layer from the positive electrode current collector was determined using a testing apparatus according to JIS Z0237 (2009). Specifically, the positive electrode was shaped into a strip sample with a width of 10 mm × a length of 50 mm or more. One side of a double-sided adhesive tape (No. 5606, manufactured by Nitto Denko Corporation) with a width of 20 mm × a length of 130 mm was attached to the positive electrode binder layer of the sample. The other side of the double-sided adhesive tape was attached to a horizontal platform with a flat surface. One end of the positive electrode current collector in the longitudinal direction was fixed with a force gauge, and the tape was stretched vertically at a speed of 50 mm / min to peel the positive electrode binder layer attached to the double-sided adhesive tape from the positive electrode current collector. The tension was measured for at least 15 seconds, and the average tension over a continuous 15-second interval 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 set as 100. The larger the relative value, the higher the peel strength and the higher the performance of the positive electrode.

[0166] (2) Fabrication of the negative electrode

[0167] A negative electrode slurry is prepared by mixing a negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), and water in a specified mass ratio. Graphite is used as the negative electrode active material. Next, the negative electrode slurry is coated onto the surface of a copper foil (negative electrode current collector) to form a laminate containing the copper foil and a coating film formed on the copper foil. After the coating film is dried, the laminate is calendered. This forms a negative electrode containing the copper foil and negative electrode binder layers formed on both sides of the copper foil.

[0168] (3) Preparation of electrolyte (non-aqueous electrolyte)

[0169] The electrolyte was prepared by adding LiPF6 (lithium salt) to a non-aqueous solvent. The concentration of LiPF6 in the electrolyte was set to 1.0 mol / L. The non-aqueous solvent used was a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of EC:EMC = 3:7.

[0170] (4) Manufacturing of secondary batteries

[0171] Leads are installed on the positive and negative electrodes respectively. Next, the positive electrode, negative electrode, and spacer are wound into a spiral shape with a spacer between them to create an electrode assembly. Then, the electrode assembly and non-aqueous electrolyte are housed in a cylindrical battery casing. Thus, cylindrical batteries A1-A4 of the embodiments with positive electrodes A1-A4 and comparative batteries C1-C2 with positive electrodes C1-C2 were manufactured.

[0172] [evaluate]

[0173] The discharge capacity, internal resistance, and capacity degradation rate of each battery were measured. The relative values ​​when the evaluation result for battery C1 was set to 100 are shown in Table 2. A higher discharge capacity value indicates better performance, while lower internal resistance and capacity degradation rate values ​​indicate better performance.

[0174] <Discharge Capacity>

[0175] Each battery was charged at 25°C with a constant current equivalent to 0.5 It until the battery voltage reached 4.2V. Then, it was charged at a constant voltage of 4.2V until the current value reached 0.05 It. After charging, the battery was allowed to rest for 10 minutes, and then discharged with a constant current equivalent to 0.2 It until the voltage reached 2.5V. The capacity was then calculated.

[0176] <Capacity degradation rate>

[0177] Repeat the above charge-discharge cycle 300 times, and calculate the reduction ratio of the discharge capacity in the 300th cycle to the discharge capacity in the 5th cycle.

[0178] <Internal Resistance>

[0179] At 25°C, the battery was charged at a constant current of 0.3 It until the voltage reached 4.2V. Then, it was charged at a constant voltage of 4.2V until the current reached 0.05 It. Next, it was discharged at a constant current of 0.3 It for 100 minutes to bring the State of Charge (SOC) to 50%.

[0180] For a battery with a state of charge (SOC) of 50%, the voltage values ​​were measured when discharged for 10 seconds at currents of 0A, 0.1A, 0.5A, and 1.0A, respectively. The internal resistance (DCIR) was calculated based on the absolute value of the slope of the relationship between the discharge current and the voltage value after 10 seconds, which is approximated as a straight line using the least squares method.

[0181]

[0182]

[0183] A comparison of Examples 1-4 with Comparative Example 1 shows that including organic additives in the positive electrode slurry significantly reduces the viscosity rise rate. Furthermore, it is understood that the more organic additives are used, the lower the viscosity rise rate; however, from the viewpoint of battery performance such as discharge capacity and capacity degradation rate, it is ideal that the amount of organic additives is not excessive. Additionally, it is understood that from the viewpoint of peel strength, it is ideal that the thermal decomposition temperature of the organic additives is not too high and the molecular weight is not too large. Furthermore, it is understood that, as shown in battery C2, although the alkaline components of the composite oxide N can be removed to some extent by washing with water, the internal resistance of the battery increases due to the washing of the composite oxide N, and the capacity degradation rate also increases.

[0184] Industrial availability

[0185] The positive electrode for secondary batteries described in this application can be used in high-performance non-aqueous electrolyte secondary batteries.

[0186] Preferred embodiments of the present invention have been described, but such disclosure should not be interpreted as restrictive. Various modifications and alterations will be readily apparent to those skilled in the art upon reading the above disclosure. Therefore, the scope of the appended claims should be interpreted as including all modifications and alterations without departing from the true spirit and scope of the invention.

[0187] Explanation of reference numerals in the attached figures

[0188] 1: Electrode assembly, 2: Positive lead, 3: Negative lead, 4: Battery casing, 5: Sealing plate, 6: Negative terminal, 7: Gasket, 8: Sealing plug, 10: Secondary battery (non-aqueous electrolyte secondary battery)

Claims

1. A positive electrode for a secondary battery, comprising a positive electrode compound containing a positive electrode active material and a binder. The positive electrode active material comprises a lithium-containing composite oxide containing at least Ni. In the lithium-containing composite oxide, Ni accounts for more than 80 atomic percent of the metal elements other than Li. The lithium-containing composite oxide contains 0.2% by mass and less than 0.5% by mass of an alkaline component. The adhesive comprises a fluorinated polymer. The degree of polyolefination of the fluorinated polymer is below 0.

2.

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

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

4. The positive electrode for a secondary battery according to any one of claims 1 to 3, wherein, The lithium-containing composite oxide is derived from the formula: Li y Ni x M （1-x） O 2-δ This indicates that 0.8 ≤ x ≤ 1, 0 < y ≤ 1.2, and -0.05 ≤ δ ≤ 0.

05. M contains at least one element selected from Co, Mn, Al, Fe, Ti, Sr, Ca, Zr, W, and B.

5. The positive electrode for a secondary battery according to claim 4, wherein, M is derived from: Co 1-x-a-b Mn a Al b This indicates that 0 < a < 0.05 and 0 < b < 0.

05.

6. The positive electrode for a secondary battery according to any one of claims 1 to 3, wherein, The positive electrode mixture also contains organic additives containing heteroatoms. The mass ratio of the organic additive to the lithium-containing composite oxide is less than 0.1% by mass.

7. The positive electrode for a secondary battery according to claim 6, wherein, The organic additive decomposes at a temperature below 200°C.

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 organic additive has a molecular weight of 50 or higher and 1000 or lower.

10. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a spacer, and a non-aqueous electrolyte as described in any one of claims 1 to 3.

11. A method for manufacturing a positive electrode for a secondary battery, comprising: A process for preparing a positive electrode slurry comprising a liquid medium and a positive electrode agent dispersed in the liquid medium; The steps of preparing a positive current collector and forming a coating film of the positive current collector slurry on the surface of the positive current collector; and The process of drying the coating by heating it at a temperature below 200°C. The positive electrode mixture comprises a positive electrode active material, a binder, and an organic additive containing heteroatoms. The positive electrode active material comprises a lithium-containing composite oxide containing at least Ni. In the lithium-containing composite oxide, Ni accounts for more than 80 atomic percent of the metal elements other than Li. The lithium-containing composite oxide contains 0.2% by mass and less than 0.5% by mass of an alkaline component. The adhesive comprises a fluorinated polymer.

12. The method for manufacturing a positive electrode for a secondary battery according to claim 11, wherein, The organic additive decomposes at a temperature below 200°C.

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. A method for manufacturing a positive electrode for a secondary battery according to any one of claims 11 to 13, wherein, The organic additive has a molecular weight of 50 or higher and 1000 or lower.

15. A 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 more than 0.002% by mass and less than 0.3% by mass.

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