Positive electrode for nonaqueous electrolyte secondary battery, nonaqueous electrolyte secondary battery using same, and positive electrode slurry for positive electrode of nonaqueous electrolyte secondary battery

Abstract

The positive electrode of the present disclosure is a positive electrode for a non-aqueous electrolyte secondary battery. The positive electrode includes a positive electrode mixture layer. The positive electrode mixture layer contains a positive electrode active material, a conductive material, a fluorine-containing polymer, and a dispersant. The positive electrode active material contains a composite oxide represented by the compositional formula LiyNixM (1-x) O2-[delta] (in the formula, 0.6 < = x < = 1, 0 < y < = 1.2, 0 < = [delta] < = 0.05, and M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, and B. The conductive material includes a carbon material. The dispersant contains a nitrile group-containing rubber. The fluorine-containing polymer has a weight-average molecular weight of 1,000,000 or more.

Description

Technical Field

[0001] The present application relates to a positive electrode for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte secondary battery using the positive electrode, and a positive electrode slurry for the positive electrode of the nonaqueous electrolyte secondary battery. Background Art

[0002] Non-aqueous electrolyte secondary batteries have high power and high energy density, and are therefore used in a variety of fields, including consumer applications and automotive applications. In recent years, non-aqueous electrolyte secondary batteries have been sought to achieve higher performance, and various proposals have been made for non-aqueous electrolyte secondary batteries.

[0003] Patent Document 1 (Japanese Patent No. 7055476) discloses in Claim 1 "a positive electrode comprising a current collector and a positive electrode active material layer disposed on the current collector, wherein the positive electrode active material layer comprises a positive electrode active material, carbon nanotubes and a binder, wherein the binder comprises polyvinylidene fluoride having a weight average molecular weight of 720,000 to 980,000, and the carbon nanotubes have a BET specific surface area of ​​140 m 2 / g~195m 2 / g, the positive electrode satisfies the following formula 1:

[0004] [Formula 1] 1.3 ≤ B / A ≤ 3.4

[0005] In Formula 1, B is the content (weight %) of the polyvinylidene fluoride in the positive electrode active material layer, and A is the content (weight %) of the carbon nanotubes in the positive electrode active material layer.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent No. 7055476 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] One of the objects of the present disclosure is to provide a positive electrode for a nonaqueous electrolyte secondary battery that has a high capacity and is easily manufactured.

[0011] The novel features of the present invention are described in the appended claims, but the present invention can be better understood with reference to the following detailed description of the accompanying drawings in conjunction with other objects and features of the present invention, both in terms of structure and content.

[0012] Solutions for solving problems

[0013] One aspect of the present disclosure relates to a positive electrode for a non-aqueous electrolyte secondary battery. The positive electrode comprises a positive electrode mixture layer, wherein the positive electrode mixture layer comprises a positive electrode active material, a conductive material, a fluorine-containing polymer, and a dispersant, wherein the positive electrode active material comprises a composition formula of Li y Ni x M (1-x) O 2-δ (wherein, 0.6≤x≤1, 0<y≤1.2, 0≤δ≤0.05, and M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca and B.) The conductive material contains a carbon material, the dispersant contains a nitrile-containing rubber, and the weight average molecular weight of the fluorine-containing polymer is greater than 1 million.

[0014] Another aspect of the present disclosure relates to a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery includes the positive electrode of the present disclosure.

[0015] One aspect of the present disclosure relates to a positive electrode slurry for a positive electrode of a non-aqueous electrolyte secondary battery. The positive electrode slurry comprises a positive electrode active material, a conductive material, a fluorine-containing polymer, a dispersant, and a liquid medium. The positive electrode active material comprises a composition formula of Li y Ni x M (1-x) O 2-δ (wherein, 0.6≤x≤1, 0<y≤1.2, 0≤δ≤0.05, and M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca and B.) The conductive material contains a carbon material, the dispersant contains a nitrile-containing rubber, and the weight average molecular weight of the fluorine-containing polymer is greater than 1 million.

[0016] Effects of the Invention

[0017] According to the present disclosure, a positive electrode for a nonaqueous electrolyte secondary battery with high capacity and easy production can be obtained. By using this positive electrode, a nonaqueous electrolyte secondary battery with high capacity can be easily produced. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic perspective view of a partially cutaway nonaqueous electrolyte secondary battery according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0019] Hereinafter, the embodiments of the present disclosure are described with examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes exemplified, but other numerical values ​​and materials may also be applied as long as the effects of the present invention can be obtained. In this specification, a description such as "numerical value A to numerical value B" includes numerical value A and numerical value B, and may be renamed as "numerical value A or above and numerical value B or below". In the following description, when the lower limit and upper limit of numerical values ​​related to specific physical properties, conditions, etc. are exemplified, as long as the lower limit is not above the upper limit, any of the exemplified lower limits may be arbitrarily combined with any of the exemplified upper limits. In the following description, when examples of constituent elements and examples of methods are listed, as long as there is no special description, only one of the listed examples may be used, or a plurality of the listed examples may be used in combination.

[0020] (Positive electrode for non-aqueous electrolyte secondary battery)

[0021] The positive electrode of this embodiment is a positive electrode for a non-aqueous electrolyte secondary battery. The positive electrode includes a positive electrode mixture layer. The positive electrode mixture layer includes a positive electrode active material, a conductive material, a fluorine-containing polymer, and a dispersant. The positive electrode active material includes a composition formula of Li y Ni x M (1-x) O 2-δ (wherein, 0.6≤x≤1, 0<y≤1.2, 0≤δ≤0.05, M comprises at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca and B.) A composite oxide represented by. The conductive material comprises a carbon material. The dispersant comprises a nitrile-containing rubber. The weight average molecular weight of the fluorine-containing polymer is 1 million or more.

[0022] Now, the high capacity of non-aqueous electrolyte secondary batteries is sought. By using a high Ni active material (a composite oxide with a high Ni content) as a positive electrode active material, the capacity of the secondary battery can be increased. However, the high Ni active material has the following problem: during the manufacturing process, a large amount of alkaline impurities (such as potassium hydroxide) are contained. As a result, when a positive electrode slurry is prepared using a high Ni active material, the alkaline impurities contained therein react with the fluorine of the fluorinated polymer (binder), so that the slurry tends to become gelled. As a result, the formation of the positive electrode mixture layer becomes difficult, or the dispersibility of the positive electrode mixture layer components is reduced. When the dispersibility of the positive electrode mixture layer components is reduced, the internal resistance increases, or the utilization efficiency of the positive electrode active material is reduced, thereby causing the performance of the battery to decrease.

[0023] As a result of the study, the inventors have newly discovered that by combining a high-Ni active material, a carbon material (conductive material), a nitrile-containing rubber and a specific fluorine-containing polymer, it is possible to achieve a higher capacity than that achieved by using a high-Ni active material, and the manufacture of the positive electrode is also facilitated. The present invention is based on this new insight.

[0024] The reason for obtaining the above effect is not clear at present. However, the rubber containing nitrile groups has high affinity with carbon materials and fluoropolymers, so in the positive electrode slurry, there is the possibility that they are well dispersed and become one. As a result, it can be considered that the side reaction of the fluoropolymer is suppressed and gelation is suppressed. Such an effect is obtained because of the synergistic effect of the combination of carbon materials, nitrile-containing rubbers and fluoropolymers with large weight-average molecular weights.

[0025] Furthermore, by using a fluorinated polymer with a large weight average molecular weight, the amount of fluorinated polymer added can be reduced and the content of the positive electrode active material can be increased. Therefore, it becomes possible to increase the capacity beyond that achievable by using a high Ni active material.

[0026] (Positive electrode active material)

[0027] As the positive electrode active material, a material capable of absorbing and releasing lithium ions can be used. As an example of a positive electrode active material, a lithium transition metal composite oxide containing lithium and a transition metal is included. The composite oxide may also have a layered structure (e.g., a rock salt type crystal structure). As the positive electrode active material, a composite oxide represented by the above composition formula can be used.

[0028] In the above composition formula, M can be at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, Si, Nb, Zr, Mo, Zn, W and B. Or M can also be at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, and B. M preferably contains at least one element selected from the group consisting of Co, Mn, Al and Fe. It should be noted that in the above composition formula, the y value representing the composition ratio of lithium increases and decreases by charging and discharging. As a specific example of a composite oxide, lithium-nickel-cobalt-manganese composite oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.)

[0029] In the composition formula of the composite oxide, by setting x to 0.6 or more, the battery capacity can be increased. In the composition formula, 0.8≤x≤1 may also be satisfied. By setting x to 0.8 or more (e.g., 0.85 or more, 0.9 or more), the battery capacity can be particularly increased. On the other hand, when x is set to 8 or more, gelation of the positive electrode slurry becomes more likely to occur, so it becomes particularly important to combine the carbon material, the nitrile-containing rubber, and the specified fluorine-containing polymer.

[0030] The composite oxide is usually used in the form of particles. The average particle size of the composite oxide as a whole may be 1 μm or more, 5 μm or more, or 20 μm or less, 15 μm or less, 10 μm or less, or 6 μm or less.

[0031] In this specification, unless otherwise specified, the average particle size is the median particle size (D50) at which the cumulative volume becomes 50% in the volume-based particle size distribution. The median particle size can be obtained using a laser diffraction / scattering particle size distribution measuring device. In addition, by observing the cross section of the positive electrode mixture, the particle size of the particles contained in the positive electrode mixture can also be evaluated.

[0032] The positive electrode active material may include particles of the above-mentioned composite oxide having an average particle size of 1 μm or more and 6 μm or less. When the particle size of the composite oxide is large, the particles are easily broken during charging. When the particles are broken, it is easy to cause the generation of gas from the grain boundary and the dissolution of the metal from the grain boundary, and the durability of the battery is reduced. Therefore, the positive electrode active material preferably includes particles with a small particle size.

[0033] The positive electrode active material may include: a first particle having an average particle size of 1 μm or more and 6 μm or less, and a second particle of the composite oxide having an average particle size of 8 μm or more and 20 μm or less. In this case, a peak in the range of about 1 to 6 μm (particle size) and a peak in the range of about 8 to 20 μm (particle size) may appear in the particle size distribution curve (volume basis) of the entire composite oxide particle.

[0034] When the average particle size of the composite oxide particles is small, the particles become easy to condense, so sometimes there is a need to add a large amount of binder and conductive material, and the battery capacity is reduced. In addition, when they are added in large quantities, the stability of the positive electrode slurry is significantly reduced. By using two kinds of active material particles with different average particle sizes, the capacity and durability of the battery can be improved. However, by using two kinds of active material particles with different average particle sizes, the area of ​​contact between the positive electrode active material and the solvent in the positive electrode slurry is increased. Therefore, sometimes the alkaline impurities derived from the positive electrode active material become easy to contact with the fluoropolymer. Therefore, when two kinds of high Ni active material particles with different average particle sizes are used to make the positive electrode slurry, gelation is likely to occur. Therefore, it is particularly important to use the above-mentioned specific combination (fluoropolymer, nitrile-containing rubber, carbon material).

[0035] When the positive electrode active material includes the first particle and the second particle, the ratio R1 of the mass M1 of the first particle in the above-mentioned composite oxide particles can be in the range of 10 to 40 mass % (for example, in the range of 15 to 30 mass %). The ratio R2 of the mass M2 of the second particle in the above-mentioned composite oxide particles can be in the range of 60 to 90 mass % (for example, in the range of 70 to 85 mass %).

[0036] The content of elements constituting the composite oxide can be measured by an inductively coupled plasma atomic emission spectroscopy (ICP-AES), an electron probe microanalyzer (EPMA), or an energy dispersive X-ray spectroscopy (EDX).

[0037] (Conductive materials)

[0038] As examples of such carbon materials (conductive materials), conductive carbon particles such as carbon black, carbon nanotubes and other conductive carbon materials are included. The carbon material preferably includes carbon nanotubes, or may be carbon nanotubes. By using carbon nanotubes, the resistance of the positive electrode mixture layer can be reduced by adding a small amount. Further, it can be considered that by using carbon nanotubes, the effect brought about by the above-mentioned specific combination becomes particularly high.

[0039] The ratio of the carbon nanotubes in the entire carbon material (conductive material) is, for example, 50% by mass or more, and preferably in the range of 80 to 100% by mass (for example, in the range of 90 to 100% by mass).

[0040] In the positive electrode mixture layer, the amount of the carbon material (eg, carbon nanotube) per 100 parts by mass of the positive electrode active material may be 0.01 parts by mass or more and 1 part by mass or less, or 0.02 parts by mass or more and 0.5 parts by mass or less.

[0041] The average length of the carbon nanotubes can be more than 1 μm. In this case, the aspect ratio of the carbon nanotubes (the ratio of the length of the fiber to the diameter) becomes extremely large. Carbon nanotubes with a large aspect ratio become easy to contact the positive electrode active material and the collector linearly. Furthermore, the conductivity of the carbon nanotubes is excellent. Therefore, by using carbon nanotubes, the direct current resistance (DCR) of the battery can be greatly reduced. For the carbon nanotubes present in the positive electrode, sometimes a plurality of carbon nanotubes also exist in the form of bundles. In the calculation of the above-mentioned average length, the length of a single carbon nanotube present in the carbon nanotubes that form a bundle is used.

[0042] From the viewpoint of improving the conductivity in the composite layer, the average length of the carbon nanotubes is preferably 1 μm or more. On the other hand, there is no particular upper limit on the length of the carbon nanotubes, but the length of the carbon nanotubes is preferably not extremely large compared to the particle size of the positive electrode active material. The average length of the carbon nanotubes may be 1 μm or more or 5 μm or less, or 20 μm or less or 10 μm or less.

[0043] The average length of the carbon nanotubes can be obtained by image analysis using a scanning electron microscope (SEM). The average length of the carbon nanotubes can be obtained by measuring the lengths of 100 carbon nanotubes selected at random and calculating the arithmetic average of the lengths. In addition, the length refers to the length of the carbon nanotubes when they are extended in a straight line.

[0044] The average diameter of the carbon nanotubes may be 20 nm or less, 15 nm or less, or 1 nm or more. By setting the average diameter to 20 nm or less, a high effect can be obtained with a small amount.

[0045] The average diameter of carbon nanotubes is obtained by image analysis using a transmission electron microscope (TEM). The average diameter of carbon nanotubes can be measured by the following method. First, 100 carbon nanotubes are randomly selected and the diameter (outer diameter) of each of them is measured at any one point. Then, the measured diameters are arithmetic averaged to obtain the average diameter.

[0046] The carbon nanotubes may be any of single-layer carbon nanotubes (SWCNT) and multilayer carbon nanotubes (MWCNT). Examples of multilayer carbon nanotubes include double-layer carbon nanotubes, triple-layer carbon nanotubes, and carbon nanotubes with more than four layers. The positive electrode mixture layer preferably includes single-layer carbon nanotubes and / or multilayer carbon nanotubes. The multilayer carbon nanotubes included in the positive electrode mixture layer may be one type of multilayer carbon nanotubes or multiple types of multilayer carbon nanotubes with different numbers of layers.

[0047] The BET specific surface area of ​​carbon nanotubes can be 200 m 2 / g or more, 250m 2 There is no particular upper limit on the BET specific surface area, but it can be 2000 m / g or more. 2 / g or less. By setting the BET specific surface area to 200m 2 / g or more, even a smaller amount of carbon nanotubes can improve battery performance. The BET specific surface area of ​​carbon nanotubes can be measured by the BET method (nitrogen adsorption method) described in JIS (Japanese Industrial Standard) R1626.

[0048] (Rubber containing nitrile group)

[0049] The rubber containing nitrile groups contains nitrile groups. The rubber containing nitrile groups acts as a dispersant. In addition, the rubber containing nitrile groups also acts as a binder in the positive electrode mixture layer. As an example of the rubber containing nitrile groups, a copolymer of a monomer containing acrylonitrile and a diene (such as butadiene) is contained. Specifically, as an example of the rubber containing nitrile groups, acrylonitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), and their modified bodies are contained.

[0050] The weight average molecular weight of the nitrile group-containing rubber may also be in the range of 5000 to 500000. The weight average molecular weight of the nitrile group-containing rubber may also be 40000 or more. By setting the weight average molecular weight of the nitrile group-containing rubber to 40000 or more, it becomes easy to achieve both the effect of improving the dispersibility of carbon materials such as carbon nanotubes and reducing the viscosity of the positive electrode slurry.

[0051] In the positive electrode mixture layer, the amount of the nitrile group-containing rubber per 100 parts by mass of the positive electrode active material may be 0.01 parts by mass or more, or 0.05 parts by mass or more, or 1 part by mass or less, or 0.5 parts by mass or less.

[0052] (Fluoropolymer)

[0053] The fluorine-containing polymer acts as a binder in the positive electrode mixture layer. The fluorine-containing polymer is a polymer containing fluorine. Examples of fluorine-containing polymers 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 other fluorine-containing polymers. The vinylidene fluoride polymer may be a copolymer of vinylidene fluoride and other monomers. Examples of vinylidene fluoride polymers include polyvinylidene fluoride (PVDF).

[0054] The fluorine-containing polymer may be polyvinylidene fluoride in which a part is modified. Examples of the modified polyvinylidene fluoride include polyvinylidene fluoride to which polar functional groups such as various acidic groups are added.

[0055] In the positive electrode mixture layer, the amount of the fluorinated 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, or 2.0 parts by mass or less, or 1.2 parts by mass or less.

[0056] The weight average molecular weight of the fluorinated polymer can be more than 1 million, or more than 1.2 million or more than 1.3 million. By setting the weight average molecular weight to more than 1.3 million, even if the amount of binder added is reduced, the adhesion of the positive electrode can be maintained. Moreover, instead of reducing the amount of binder added, the amount of positive electrode active material is increased, and the battery capacity can be increased as a result. On the other hand, when the weight average molecular weight is increased, the gelation of the positive electrode slurry becomes easy to occur. Therefore, it is particularly important to use the above-mentioned specific combination.

[0057] The upper limit of the weight average molecular weight of the fluorine-containing polymer is not particularly limited, but may be 2 million or less or 1.8 million or less.

[0058] In the positive electrode mixture layer, the total content of the fluorinated polymer and the content of the nitrile-containing rubber can be less than 1.0 mass %. By setting the total to less than 1.0 mass %, the proportion of the positive electrode active material can be increased, and the high capacity of the battery becomes possible. In the positive electrode mixture layer of the present embodiment, the above-mentioned specific combination is used, so it is possible to set the total to less than 1.0 mass %. The total can also be more than 0.5 mass %.

[0059] The positive electrode mixture layer may contain a cellulose derivative. When the positive electrode mixture layer contains a cellulose derivative, the dispersibility of carbon is further improved, and the battery performance is improved.

[0060] In the positive electrode mixture layer, the cellulose derivative also acts as a binder. In addition, in the positive electrode slurry, the cellulose derivative also acts as a dispersant. Examples of cellulose derivatives include alkyl cellulose, hydroxyalkyl cellulose, carboxyalkyl cellulose and their salts (alkali metal salts, ammonium salts, etc.). Examples of alkyl cellulose include methyl cellulose, ethyl cellulose, ethyl methyl cellulose, etc. Examples of hydroxyalkyl cellulose include hydroxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, etc. Examples of carboxyalkyl cellulose include carboxymethyl cellulose, carboxyethyl cellulose, etc. Examples of alkali metals that form alkali metal salts include potassium and sodium, etc. Among them, methyl cellulose, ethyl cellulose, and hydroxypropyl methyl cellulose are preferred. The weight average molecular weight of the cellulose derivative can be in the range of 1000 to 1000000 (for example, in the range of 10000 to 1000000). Based on the viewpoint of the improved effect brought about by the configuration disclosed in the present invention, the weight average molecular weight of the cellulose derivative can be in the range of 10000 to 500000.

[0061] The positive electrode mixture layer may contain components other than the above (eg, thickener) or compounds other than the above. For example, the positive electrode mixture layer may contain polyvinyl pyrrolidone or the like.

[0062] The proportion of the positive electrode active material in the positive electrode mixture layer is determined using a mixture sample. The mixture sample is obtained according to the following steps. First, the secondary battery in the discharged state is disassembled to take out the positive electrode. Next, the positive electrode is cleaned with an organic solvent and then vacuum dried. After that, only the positive electrode mixture layer is taken out, and the taken out positive electrode mixture layer is used as a mixture sample. By performing TG-DTA, NMR, thermal decomposition GC-MS and other analyses on the mixture sample, the ratio of the binder and the conductive material other than the positive electrode active material can be calculated. In the case where the conductive material contains a plurality of carbon materials, the proportion of carbon nanotubes in the conductive material can be calculated by performing micro-Raman spectroscopy analysis on the cross section of the positive electrode mixture layer.

[0063] Positive electrode mixture layer (1 layer) per 1m 2 The mass of the positive electrode mixture layer can be 200 g or more, preferably 250 g or more. By setting the mass to 250 g or more, a high capacity lithium ion battery can be achieved. 2 When the quality of the positive electrode increases, it becomes difficult to maintain its adhesion, so it becomes necessary to use a binder with excellent adhesion. As described above, the positive electrode plate disclosed in the present invention can suppress the disadvantages caused by increasing the quality. The quality can be increased by thickening the positive electrode mixture layer or increasing the density of the positive electrode mixture layer.

[0064] The thickness of the positive electrode mixture layer is not particularly limited, and may be in the range of 50 μm to 250 μm. According to this embodiment, even if the thickness of the positive electrode mixture layer is increased, an increase in internal resistance can be suppressed.

[0065] (Positive electrode slurry and method for producing positive electrode)

[0066] The positive electrode slurry of this embodiment is a slurry for the positive electrode of a non-aqueous electrolyte secondary battery. The slurry is used to manufacture the above-mentioned positive electrode. Since the matters described for the positive electrode are applicable to the positive electrode slurry, repeated descriptions are sometimes omitted.

[0067] The positive electrode slurry contains the components of the positive electrode mixture layer and a liquid medium (dispersion medium) in which they are dispersed. Specifically, the positive electrode slurry contains a positive electrode active material, a conductive material, a fluorine-containing polymer, a dispersant, and a liquid medium. The positive electrode active material contains a composition formula of Li y Ni x M (1-x) O 2-δ (Wherein, 0.6≤x≤1, 0<y≤1.2, 0≤δ≤0.05, M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca and B.) A composite oxide represented by. The conductive material contains a carbon material. The dispersant contains a nitrile-containing rubber. The weight average molecular weight of the fluorine-containing polymer is greater than 1 million. For each component, as described above, repeated descriptions are omitted. The positive electrode slurry may further contain any component as needed. For example, the positive electrode slurry may contain a cellulose derivative.

[0068] There is no particular limitation on the liquid medium (dispersion medium), and water, an organic solvent, and a mixed solvent thereof may be used. Examples of organic solvents include alcohols (ethanol, etc.), ethers (tetrahydrofuran, etc.), amides (dimethylformamide, etc.), N-methyl-2-pyrrolidone (NMP), etc.

[0069] The ratio of the components contained in the positive electrode slurry is reflected in the ratio of the components in the positive electrode mixture layer in principle. Therefore, by changing the ratio of the components contained in the positive electrode slurry, the ratio of the components in the positive electrode mixture layer can be changed. The ratio of the components exemplified for the positive electrode mixture layer can also be applied to the ratio of the components in the positive electrode slurry. In the components other than the liquid medium, the total content of the fluorinated polymer and the content of the nitrile-containing rubber can be less than 1.0 mass %.

[0070] There is no particular limitation on the method for manufacturing the positive electrode, and a known method can be used. For example, the positive electrode can be formed by the following method. First, prepare a positive electrode slurry obtained by dispersing the materials of the positive electrode mixture layer (positive electrode active material, conductive material, fluorinated polymer, dispersant and other arbitrary components as needed) in a liquid medium. Then, after the positive electrode slurry is applied to the surface of the positive electrode collector to form a coating, the coating is dried to form a positive electrode mixture layer. The dried coating can also be rolled as needed. The positive electrode mixture layer can be formed on one surface of the positive electrode collector or on two surfaces.

[0071] (Conductive material dispersion)

[0072] The present disclosure provides a conductive material dispersion. The conductive material dispersion can be applied to the preparation of positive electrode slurry. The conductive material dispersion contains a conductive material, a nitrile-containing rubber, a fluorine-containing polymer and a liquid medium. The conductive material contains a carbon material. As described above, the carbon material (conductive material), the nitrile-containing rubber and the fluorine-containing polymer are omitted. The conductive material dispersion may also contain any component contained in the positive electrode mixture layer (for example, any of the above-mentioned components).

[0073] As the liquid medium of the conductive material dispersion, the liquid medium described as the liquid medium of the positive electrode slurry can be used, or a liquid medium different therefrom can be used. The conductive material dispersion does not substantially contain a positive electrode active material. By adding a positive electrode active material to the conductive material dispersion, a positive electrode slurry can be prepared. It is also possible to add any component and a liquid medium of the positive electrode mixture layer to the conductive material dispersion together with the positive electrode active material.

[0074] By changing the ratio of the components contained in the conductive material dispersion, the ratio of the components in the positive electrode mixture layer can be changed. The ratio of the components exemplified for the positive electrode mixture layer is applicable to the ratio of the components in the conductive material dispersion. Specifically, the ratio between the components can be obtained from the ratio of each component relative to 100 parts by mass of the positive electrode active material exemplified in the description of the positive electrode mixture layer.

[0075] (Non-aqueous electrolyte secondary battery)

[0076] The non-aqueous electrolyte secondary battery of the present embodiment includes the positive electrode of the present embodiment. The secondary battery at least further includes a negative electrode and a non-aqueous electrolyte on the basis of the positive electrode. The secondary battery may also include a positive electrode, a negative electrode, a non-aqueous electrolyte, a separator and an outer shell. Examples of the secondary battery include lithium ion secondary batteries, lithium metal secondary batteries, etc. There are no particular limitations on the constituent elements other than the positive electrode mixture layer, and known constituent elements may also be used. Examples of the constituent elements of the secondary battery are described below.

[0077] (positive electrode)

[0078] As the positive electrode, the positive electrode of this embodiment can be used.

[0079] (Positive electrode collector)

[0080] The positive electrode may also include a positive electrode collector. The positive electrode mixture layer may be disposed on the positive electrode collector. The shape and thickness of the positive electrode collector may be selected according to the application, and may be selected in a manner corresponding to the shape and thickness of the negative electrode collector. Examples of the material of the positive electrode collector include stainless steel, aluminum, aluminum alloy, titanium, etc. The positive electrode mixture layer may be formed only on one side of the positive electrode collector, or may be formed on both sides of the positive electrode collector.

[0081] (negative electrode)

[0082] The negative electrode typically includes a negative electrode mixture layer containing a negative electrode active material. The negative electrode may also include a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector. In the case of a lithium metal secondary battery, a negative electrode current collector capable of precipitating lithium metal or a lithium alloy may be used as the negative electrode.

[0083] The negative electrode mixture layer contains a negative electrode active material as an essential component. The negative electrode mixture layer may also contain a binder, a thickener, a conductive material, etc. as an optional component. As these optional components, the components exemplified as positive electrode components may also be used.

[0084] The negative electrode mixture layer can be formed by applying the negative electrode slurry obtained by dispersing the constituent components of the negative electrode mixture layer in a liquid medium (dispersion medium) to the surface of the negative electrode collector and drying it. The dried coating film can also be rolled as needed. As the liquid medium, the liquid medium exemplified as the liquid medium of the positive electrode slurry can also be used. The negative electrode mixture layer can be formed only on one side of the negative electrode collector, or on both sides of the negative electrode collector.

[0085] (Negative electrode active material)

[0086] The negative electrode active material can be selected according to the type of secondary battery. An example of a negative electrode active material is a material that can adsorb and release lithium ions. Examples of such materials include carbon materials, Si-containing materials, etc. The negative electrode active material can include Si-containing materials, or it can be Si-containing materials. As the negative electrode active material, metallic lithium, lithium alloys, etc. can be used. The negative electrode can include one negative electrode active material, or it can include a combination of two or more negative electrode active materials.

[0087] Examples of carbon materials include graphite, easily graphitized carbon (soft carbon), and difficultly graphitized carbon (hard carbon). One carbon material may be used alone or in combination of two or more. Graphite is preferred from the viewpoint of excellent charge and discharge stability and low irreversible capacity. Examples of graphite include natural graphite, artificial graphite, and graphitized mesophase carbon particles.

[0088] Examples of Si-containing materials include Si monomers, 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 particles. x is, for example, 0.5≤x<2, or 0.8≤x≤1.6. As the lithium ion conductive phase, at least one selected from the group consisting of a SiO2 phase, a silicate phase, and a carbon phase can be used.

[0089] The negative electrode current collector may be made of metal foil. The negative electrode current collector may be porous. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.

[0090] (Non-aqueous electrolyte)

[0091] The non-aqueous electrolyte (non-aqueous electrolytic solution) contains a solvent (non-aqueous solvent) and a solute dissolved in the solvent. Examples of the solute include lithium salts. Various additives may be added to the electrolytic solution.

[0092] As the solvent, known materials can be used. As the solvent, for example, cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, etc. can be used. As examples of cyclic carbonates, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethylene carbonate (VC), etc. can be listed. As chain carbonates, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. are included. As examples of cyclic carboxylates, γ-butyrolactone (GBL), γ-valerolactone (GVL), etc. are included. As examples of chain carboxylates, non-aqueous solvents such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), etc. are included. The non-aqueous solvent can be used alone or in combination of two or more.

[0093] Examples of lithium salts include lithium salts containing chloric acid (LiClO4, LiAlCl4, LiB 10 Cl 10etc.), lithium salts of fluorinated acids (LiPF6, LiPF2O2, LiBF4, LiSbF6, LiAsF6, LiCF3SO3, LiCF3CO2, etc.), lithium salts of fluorinated acid amides (LiN(FSO2)2, LiN(CF3SO2)2, LiN(CF3SO2)(C4F9SO2), LiN(C2F5SO2)2, etc.), lithium halides (LiCl, LiBr, LiI, etc.), etc. The lithium salts may be used alone or in combination of two or more.

[0094] The concentration of the lithium salt in the electrolyte may be 1 mol / L to 2 mol / L, or 1 mol / L to 1.5 mol / L. By setting the concentration of the lithium salt within the above range, a nonaqueous electrolyte having excellent ion conductivity and moderate viscosity can be obtained.

[0095] The electrolyte solution may contain a known additive, and examples of the additive include 1,3-propane sultone, toluenesulfonic acid, cyclohexylbenzene, biphenyl, diphenyl ether, fluorobenzene, and the like.

[0096] (Separator)

[0097] The separator is arranged between the positive electrode and the negative electrode. The separator preferably has high ion permeability and has appropriate mechanical strength and insulation. As the separator, a microporous film, a woven fabric, a non-woven fabric, etc. can be used. Examples of separator materials include polyolefins (polypropylene, polyethylene, etc.) and other resins.

[0098] (Outer shell)

[0099] The outer shell (battery shell) contains an electrode group and a non-aqueous electrolyte. There is no particular limitation on the outer shell, and a known outer shell can be used. The electrode group is composed of a positive electrode, a negative electrode and a separator. There is no particular limitation on the composition of the electrode group, and it can be a winding type or a stacked type. The wound electrode group is formed by winding the positive electrode and the negative electrode with a separator between them. The stacked electrode group is formed by stacking the positive electrode and the negative electrode with a separator between them. There is no particular limitation on the shape of the non-aqueous electrolyte secondary battery, and it can be cylindrical, square, coin-shaped, button-shaped, laminated, etc.

[0100] Figure 1 This is a schematic perspective view in which a portion of the secondary battery 10 according to one embodiment of the present disclosure is cut away. Figure 1 2 shows a square non-aqueous electrolyte battery as an example. Figure 1 The secondary battery 10 shown includes a battery case 4 having a bottom-square cylindrical shape, and an electrode group 1 and a non-aqueous electrolyte (not shown) accommodated in the battery case 4 .

[0101] The electrode group 1 has: a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator arranged therebetween. The negative electrode collector of the negative electrode is electrically connected to the negative terminal 6 provided on the sealing plate 5 via the negative electrode lead 3. The resin gasket 7 insulates the negative terminal 6 from the sealing plate 5. The positive electrode collector of the positive electrode is electrically connected to the back of the sealing plate 5 via the positive electrode lead 2. That is, the positive electrode is electrically connected to the battery case 4 which also serves as the positive terminal. The periphery of the sealing plate 5 is fitted with the open end of the battery case 4, and the fitting portion is laser welded. The sealing plate 5 has an injection hole for a non-aqueous electrolyte. The injection hole is plugged by a plug 8 after the non-aqueous electrolyte is injected.

[0102] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. As the positive electrode mixture layer, the above-mentioned positive electrode mixture layer is used.

[0103] (Note)

[0104] The above description discloses the following technology.

[0105] (Technology 1)

[0106] A positive electrode for a non-aqueous electrolyte secondary battery,

[0107] It includes a positive electrode mixture layer,

[0108] The positive electrode mixture layer comprises a positive electrode active material, a conductive material, a fluorine-containing polymer and a dispersant.

[0109] The positive electrode active material comprises a composition formula of Li y Ni x M (1-x) O 2-δ (wherein, 0.6≤x≤1, 0<y≤1.2, 0≤δ≤0.05, M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca and B.) a composite oxide represented by

[0110] The conductive material comprises a carbon material,

[0111] The dispersant comprises a nitrile-containing rubber,

[0112] The weight average molecular weight of the fluorine-containing polymer is 1,000,000 or more.

[0113] (Technique 2)

[0114] The positive electrode according to technology 1, wherein the composition formula of the composite oxide satisfies 0.8≤x≤1.

[0115] (Technique 3)

[0116] The positive electrode according to the technique 1 or 2, wherein in the positive electrode mixture layer, the total of the content of the fluorine-containing polymer and the content of the nitrile group-containing rubber is 1.0 mass % or less.

[0117] (Technique 4)

[0118] The positive electrode according to any one of techniques 1 to 3, wherein the positive electrode active material includes the composite oxide having an average particle diameter of 1 μm or more and 6 μm or less.

[0119] (Technique 5)

[0120] The positive electrode according to any one of Techniques 1 to 4, wherein the positive electrode mixture layer contains a cellulose derivative.

[0121] (Technique 6)

[0122] The positive electrode according to any one of techniques 1 to 5, wherein the weight average molecular weight of the fluorinated polymer is 1,300,000 or more.

[0123] (Technique 7)

[0124] The positive electrode according to any one of Techniques 1 to 6, wherein the fluorine-containing polymer is partially modified polyvinylidene fluoride.

[0125] (Technology 8)

[0126] The positive electrode according to any one of Techniques 1 to 7, wherein the carbon material includes carbon nanotubes.

[0127] (Technique 9)

[0128] The positive electrode according to any one of techniques 1 to 8, wherein the weight average molecular weight of the nitrile group-containing rubber is 40,000 or more.

[0129] (Technology 10)

[0130] A non-aqueous electrolyte secondary battery comprising the positive electrode according to any one of techniques 1 to 9.

[0131] (Technology 11)

[0132] A positive electrode slurry for a positive electrode of a non-aqueous electrolyte secondary battery,

[0133] It contains positive electrode active material, conductive material, fluorine-containing polymer, dispersant and liquid medium.

[0134] The positive electrode active material comprises a composition formula of Li y Ni x M (1-x) O 2-δ(wherein, 0.6≤x≤1, 0<y≤1.2, 0≤δ≤0.05, M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca and B.) a composite oxide represented by

[0135] The conductive material comprises a carbon material,

[0136] The dispersant comprises a nitrile-containing rubber,

[0137] The weight average molecular weight of the fluorine-containing polymer is 1,000,000 or more.

[0138] (Technology 12)

[0139] The positive electrode slurry according to Technology 11, wherein the composition formula of the composite oxide satisfies 0.8≤x≤1.

[0140] (Technology 13)

[0141] The positive electrode slurry according to technology 11 or 12, wherein the total content of the fluorine-containing polymer and the content of the nitrile group-containing rubber in the components other than the liquid medium is 1.0 mass % or less.

[0142] (Technology 14)

[0143] The positive electrode slurry according to any one of Techniques 11 to 13, wherein the positive electrode active material includes the composite oxide having an average particle diameter of 1 μm or more and 6 μm or less.

[0144] (Technology 15)

[0145] The positive electrode slurry according to any one of Techniques 11 to 14, further comprising a cellulose derivative.

[0146] (Technology 16)

[0147] The positive electrode slurry according to any one of Techniques 11 to 15, wherein the weight average molecular weight of the fluorine-containing polymer is 1.3 million or more.

[0148] (Technology 17)

[0149] The positive electrode slurry according to any one of Techniques 11 to 16, wherein the fluorine-containing polymer is a partially modified polyvinylidene fluoride.

[0150] (Technology 18)

[0151] The positive electrode slurry according to any one of Techniques 11 to 17, wherein the carbon material contains carbon nanotubes.

[0152] (Technology 19)

[0153] The positive electrode slurry according to any one of Techniques 11 to 18, wherein the weight average molecular weight of the nitrile group-containing rubber is 40,000 or more.

[0154] Example

[0155] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to the following examples. In this example, a plurality of nonaqueous electrolyte secondary batteries having different positive electrodes were prepared and evaluated.

[0156] (Production of Battery A1)

[0157] Battery A1 was produced in the following manner.

[0158] (1) Preparation of negative electrode

[0159] The silicon composite material and graphite are mixed in a mass ratio of silicon composite material: graphite = 5:95 and used as a negative electrode active material. The negative electrode active material, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR) and water are mixed in a specified mass ratio to prepare a negative electrode slurry. Next, the negative electrode slurry is applied to the surface of the copper foil (negative electrode collector) to form a laminate comprising copper foil and a coating formed on the copper foil. Then, after the coating is dried, the laminate is rolled. Thus, a negative electrode comprising a copper foil and a negative electrode mixture layer formed on both sides of the copper foil is formed.

[0160] (2) Preparation of positive electrode

[0161] First, the positive electrode active material, carbon nanotubes (conductive material), polyvinylidene fluoride (fluorinated polymer), hydrogenated nitrile rubber (rubber containing nitrile groups) and N-methyl-2-pyrrolidone (liquid medium) are mixed at a predetermined mass ratio to prepare a positive electrode slurry SA1. As the positive electrode active material, LiNi 0.85 Co 0.10 Mn 0.05 Composite oxide particles represented by O2. The composite oxide particles are used by mixing particles A having an average particle size (D50) of 14 μm and particles B having an average particle size (D50) of 4 μm in a mass ratio of 7:3. As a fluorine-containing polymer, a modified polyvinylidene fluoride having a weight average molecular weight (Mw) of 1.4 million is used. As a modified polyvinylidene fluoride, polyvinylidene fluoride to which an acidic group is attached is used. The average length and average diameter of the carbon nanotubes are 1 μm and 10 nm, respectively.

[0162] The amount of carbon nanotube added was 0.5 parts by mass relative to 100 parts by mass of the positive electrode active material. The amount of polyvinylidene fluoride added was 0.8 parts by mass relative to 100 parts by mass of the positive electrode active material. The amount of hydrogenated nitrile rubber (H-NBR) added was 0.2 parts by mass relative to 100 parts by mass of the positive electrode active material.

[0163] Next, the positive electrode slurry is applied to the surface of the aluminum foil (positive electrode current collector) to form a coating film, thereby obtaining a laminate of the aluminum foil and the coating film. Next, after the coating film is dried, the laminate is rolled. In this way, a positive electrode including the aluminum foil and the positive electrode mixture layer formed on both sides of the aluminum foil is produced.

[0164] (3) Preparation of electrolyte (non-aqueous electrolyte)

[0165] The electrolyte solution was prepared by adding LiPF6 (lithium salt) to a non-aqueous solvent. The concentration of LiPF6 in the electrolyte solution was set to 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.

[0166] (4) Production of secondary batteries

[0167] Leads are installed on the positive electrode and negative electrode respectively. Next, the positive electrode, the negative electrode and the separator are wound into a spiral shape in a manner that a separator is arranged between the positive electrode and the negative electrode, thereby preparing an electrode group. Next, the electrode group is inserted into the outer casing. As the outer casing, an outer casing made of a laminated film containing an aluminum foil (barrier layer) is used. Next, after the outer casing with the electrode group inserted is vacuum dried at 105°C for 2 hours, a non-aqueous electrolyte is injected into the outer casing, and the opening of the outer casing is sealed. In this way, a secondary battery A1 is produced.

[0168] (Production of Batteries A2 to A6 and Batteries C1 to C9)

[0169] The components contained in the positive electrode slurry were changed as shown in Table 1. Positive electrode slurries SA1 to SA6 and positive electrode slurries SC1 to SC9 were prepared according to the same method and conditions as the preparation method and conditions of positive electrode slurry SA1 of battery A1. As the composite oxide constituting the positive electrode active material, the composite oxide constituting the positive electrode active material used in positive electrode slurry SA1 was used. Using these positive electrode slurries, positive electrodes PA1 to PA6 and positive electrodes PC1 to PC9 were prepared under the same method and conditions as the preparation method and conditions of positive electrode PA1 of battery A1. Using these positive electrodes, batteries A2 to A6 and batteries C1 to C9 were prepared under the same method and conditions as the preparation method and conditions of battery A1.

[0170] In Table 1, “Active material Ni / Co / Mn (composition ratio)” indicates that the following active materials were used: LiNi 0.85 Co 0.10 Mn 0.05 The ratio of Ni / Co / Mn in the active material of O2 is changed as shown in the table. It should be noted that when Ni / Co / Mn=85 / 10 / 5, the composition formula Li y Ni x M (1-x) O 2-δ Where x=0.85.

[0171] In Table 1, the presence or absence of particles B refers to the presence or absence of particles B having an average particle size of 4 μm. “Presence” of particles B means that particles A and particles B are mixed and used. “Absence” of particles B means that only particles A are used.

[0172] In Table 1, the values ​​in the column "Protective material, etc." represent the amount relative to 100 parts by mass of the positive electrode active material. For example, positive electrode slurry SA6 contains 0.2 parts by mass of hydrogenated nitrile rubber (H-NBR) and 0.1 parts by mass of ethyl cellulose (EC) relative to 100 parts by mass of the positive electrode active material.

[0173] (Evaluation of Stability of Positive Electrode Slurry)

[0174] The stability of the positive electrode slurry was evaluated by the following method. The viscosity V0 on the day of slurry preparation and the viscosity V1 after the slurry was left to stand for 5 days were measured. The viscosity of the slurry was measured using a B-type viscometer. Then, the rate of change of viscosity was calculated by the following formula.

[0175] Viscosity change rate (%) = (V1 / V0) × 100

[0176] (Battery Evaluation)

[0177] The battery capacity and DC resistance of the manufactured battery were determined in the following order. First, the capacity of the manufactured battery was determined by repeating two operations A and B under a temperature environment of 25°C. The operation A was constant current charging at a constant current of 0.2It until the battery cell voltage reached 4.2V, and constant voltage charging at 4.2V until the current value reached 1 / 50It; and the operation B was constant current discharging at a constant current of 0.2It until the battery cell voltage reached 2.5V. Then, for the test battery cell whose capacity was confirmed, constant current charging was performed at a constant current of 0.2It until the battery cell voltage reached 4.2V, constant voltage charging was performed at 4.2V until the current value reached 1 / 50It, and then constant current discharging was performed at a constant current of 0.2It until the capacity reached 50% of the capacity (SOC50%) under a temperature environment of 25°C. A constant current of 0.5It was passed through the obtained battery for 10 seconds. The DC resistance (DCR) was determined by dividing the potential difference generated at this time by the current value. It should be noted that It(A)=rated capacity(Ah) / 1(h).

[0178] Some of the production conditions and evaluation results are shown in Table 1. In addition, the viscosity change rate of the slurry, the battery capacity, and the DC resistance of the battery are all relative values ​​with the result of Battery A1 being 100.

[0179] [Table 1]

[0180]

[0181] Batteries A1 to A6, and the positive electrode slurry and positive electrode used in their manufacture, are the batteries, positive electrode slurry and positive electrode of this embodiment. Batteries C1 to C9, and the positive electrode slurry and positive electrode used in their manufacture are comparative examples. The DC resistance and battery capacity of batteries C3 to C5 could not be measured because the battery manufacturing was interrupted during the battery manufacturing due to the peeling of the electrode plate.

[0182] In Table 1, the battery capacity is preferably high, and the viscosity change rate and DC resistance of the slurry are preferably low. The positive electrode slurry of this embodiment has high stability and can easily produce a positive electrode. The battery of this embodiment has low internal resistance and high battery capacity.

[0183] Industrial Applicability

[0184] The present disclosure can be used for a positive electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery. The secondary battery of the present disclosure can be used for various applications, and is preferably used as a main power source for mobile communication equipment, portable electronic equipment, and the like.

[0185] The present invention has been described with respect to the currently preferred embodiments, but such disclosure is not interpreted as limiting. By reading the above disclosure, various modifications and changes should undoubtedly be obvious to those skilled in the art in the technical field of the present invention. Therefore, it should be interpreted that the attached claims include all modifications and changes without departing from the true spirit and scope of the present invention.

[0186] Description of Reference Numerals

[0187] 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 (non-aqueous electrolyte secondary battery)

Claims

1. A positive electrode for a non-aqueous electrolyte secondary battery, It includes a positive electrode mixture layer, The positive electrode mixture layer comprises a positive electrode active material, a conductive material, a fluorine-containing polymer and a dispersant. The positive electrode active material comprises a composition formula of Li y Ni x M (1-x) O 2-δ The composite oxide represented by the formula, wherein 0.6≤x≤1, 0<y≤1.2, 0≤δ≤0.05, M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca and B, The conductive material comprises a carbon material, The dispersant comprises a nitrile-containing rubber, The weight average molecular weight of the fluorine-containing polymer is 1,000,000 or more.

2. The positive electrode according to claim 1, wherein In the composition formula of the composite oxide, 0.8≤x≤1 is satisfied.

3. The positive electrode according to claim 1 or 2, wherein In the positive electrode mixture layer, the total content of the fluorine-containing polymer and the nitrile group-containing rubber is 1.0 mass % or less.

4. The positive electrode according to claim 1 or 2, wherein The positive electrode active material includes the composite oxide having an average particle size of 1 μm or more and 6 μm or less.

5. The positive electrode according to claim 1 or 2, wherein The positive electrode mixture layer contains a cellulose derivative.

6. The positive electrode according to claim 1 or 2, wherein The weight average molecular weight of the fluorine-containing polymer is 1.3 million or more.

7. The positive electrode according to claim 1 or 2, wherein The fluorine-containing polymer is polyvinylidene fluoride which has been partially modified.

8. The positive electrode according to claim 1 or 2, wherein The carbon material includes carbon nanotubes.

9. The positive electrode according to claim 1 or 2, wherein The weight average molecular weight of the nitrile group-containing rubber is 40,000 or more. 10 . A non-aqueous electrolyte secondary battery comprising the positive electrode according to claim 1 or 2.

11. A positive electrode slurry for a positive electrode of a non-aqueous electrolyte secondary battery, It contains positive electrode active material, conductive material, fluorine-containing polymer, dispersant and liquid medium. The positive electrode active material comprises a composition formula of Li y Ni x M (1-x) O 2-δ The composite oxide represented by the formula, wherein 0.6≤x≤1, 0<y≤1.2, 0≤δ≤0.05, M contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca and B, The conductive material comprises a carbon material, The dispersant comprises a nitrile-containing rubber, The weight average molecular weight of the fluorine-containing polymer is 1,000,000 or more.

12. The positive electrode slurry according to claim 11, wherein: In the composition formula of the composite oxide, 0.8≤x≤1 is satisfied.

13. The positive electrode slurry according to claim 11 or 12, wherein: In the components other than the liquid medium, the total content of the fluorine-containing polymer and the nitrile group-containing rubber is 1.0 mass % or less.

14. The positive electrode slurry according to claim 11 or 12, wherein: The positive electrode active material includes the composite oxide having an average particle size of 1 μm or more and 6 μm or less. 15 . The positive electrode slurry according to claim 11 , further comprising a cellulose derivative.

16. The positive electrode slurry according to claim 11 or 12, wherein: The weight average molecular weight of the fluorine-containing polymer is 1.3 million or more.

17. The positive electrode slurry according to claim 11 or 12, wherein: The fluorine-containing polymer is polyvinylidene fluoride which has been partially modified.

18. The positive electrode slurry according to claim 11 or 12, wherein: The carbon material includes carbon nanotubes.

19. The positive electrode slurry according to claim 11 or 12, wherein: The weight average molecular weight of the nitrile group-containing rubber is 40,000 or more.

Images