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

A positive electrode for a non-aqueous electrolyte secondary battery according to the present disclosure includes a positive electrode mixture layer. The positive electrode mixture layer contains at least one compound selected from the group consisting of a carboxylic acid and a carboxylic acid anhydride, a positive electrode active material, a conductive material, a fluorine-containing polymer, and a dispersant. The positive electrode includes a positive electrode active material having a compositional formula of LiyNixM (1-x) O2-[delta] (in the formula, 0.6 < = x < = 1, 0 < y < = 1.2, 0 < = [delta] < = 0.05, and M including at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca, and B. ) A composite oxide represented by formula (1). The conductive material includes a carbon material. The dispersing agent comprises nitrile group-containing rubber.

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 (Patent No. 3540097) discloses "a positive electrode mixture for a non-aqueous battery, which is prepared by adding an organic acid to a mixture containing a positive electrode active material formed of a composite metal oxide, a conductive aid, a vinylidene fluoride polymer, and an organic solvent."

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 3540097 Summary of the invention

[0007] Problem that the invention aims to solve

[0008] 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.

[0009] Solutions for solving problems

[0010] 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: at least one compound selected from the group consisting of carboxylic acid and carboxylic anhydride, 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, 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, and the dispersant contains a nitrile-containing rubber.

[0011] 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.

[0012] Another 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: at least one compound selected from the group consisting of carboxylic acid and carboxylic anhydride, a positive electrode active material, a conductive material, a fluorine-containing polymer, a dispersant, and a liquid medium, 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, and the dispersant contains a nitrile-containing rubber.

[0013] Effects of the Invention

[0014] According to the present disclosure, a positive electrode for a nonaqueous electrolyte secondary battery having a high capacity and being easy to manufacture can be obtained. By using this positive electrode, a nonaqueous electrolyte secondary battery having a high capacity can be easily manufactured.

[0015] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] 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

[0017] 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 disclosure 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.

[0018] (Positive electrode for non-aqueous electrolyte secondary battery)

[0019] 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: at least one compound selected from the group consisting of carboxylic acid and carboxylic anhydride, 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 contains at least one element selected from the group consisting of Co, Mn, Al, Fe, Ti, Sr, Ca and B.) A composite oxide (composite metal oxide) represented by. The conductive material contains a carbon material. The dispersant contains a nitrile-containing rubber. Hereinafter, at least one compound selected from the group consisting of carboxylic acid and carboxylic anhydride is sometimes referred to as a "carboxylic acid compound".

[0020] 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 is easily 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, resulting in reduced battery performance.

[0021] By adding a carboxylic acid compound to the positive electrode slurry, the reaction of the fluorinated polymer and the alkaline impurities can be suppressed, and the gelation of the positive electrode slurry can be suppressed. However, as a result of the study, the inventors found that the following situation exists: the added carboxylic acid compound is decomposed at a high potential to produce gas. When gas is generated in the positive electrode mixture layer, the performance and safety of the battery are reduced according to its amount. In particular, when the internal potential of the positive electrode mixture layer is deviated, it becomes easy to produce a part with a high local potential, and the carboxylic acid compound present in the part particularly promotes decomposition and increases gas generation, thereby greatly reducing the performance of the battery.

[0022] As a result of the study, the inventors have newly discovered that by using a nitrile-containing rubber (nitrile-containing rubber) as a dispersant, the problem caused by the addition of a carboxylic acid compound can be solved. The present disclosure is based on this new insight. Through the present disclosure, a high-capacity and easily manufactured positive electrode for a non-aqueous electrolyte secondary battery can be obtained. Furthermore, through the present disclosure, gas generation in a secondary battery can be suppressed.

[0023] The reason why the problem caused by the addition of carboxylic acid compounds can be solved by using nitrile-containing rubber is not clear at present. However, it can be considered that by adding nitrile-containing rubber, the dispersibility of carbon material (conductive material) is improved and the deviation of the internal potential of the positive electrode mixture layer is reduced. Further, the affinity of nitrile-containing rubber and fluoropolymer represented by vinylidene fluoride polymer is particularly high. Therefore, it is found that these two kinds of polymer materials act as the effect of dispersant together, and the dispersibility of carbon material is further improved. Therefore, it can be considered that by using nitrile-containing rubber and fluoropolymer in combination with carbon material, a particularly high effect can be obtained.

[0024] (Positive electrode active material)

[0025] 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 composite oxide containing lithium and a transition metal is contained. The composite oxide may 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-mentioned composition formula can be used.

[0026] 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 molar ratio of lithium increases and decreases by charging and discharging. As a specific example of a composite oxide, lithium-nickel-cobalt-aluminum composite oxide (LiNi 0.9 Co 0.05 Al 0.05 O2, etc.)

[0027] 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), the battery capacity can be particularly increased. On the other hand, when x is set to 0.8 or more, gelation of the positive electrode slurry becomes more likely to occur, so it becomes particularly important to combine the carboxylic acid compound and the nitrile-containing rubber with the carbon material.

[0028] The composite oxide is usually used in the form of particles. The average particle size of the composite oxide may be 1 μm or more, 2 μm or more, or 5 μm or less, or 20 μm or less, or 15 μm or less, or 10 μm or less, or 6 μm or less, or 5 μm or less.

[0029] 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.

[0030] The positive electrode active material may include: a first particle of the composite oxide 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 particles.

[0031] When the average particle size of the composite oxide particles is large, the particles are easy to break during charging. When the particles break, it is easy to cause the generation of gas from the grain boundary and the dissolution of metal from the grain boundary, and the durability of the battery is reduced. On the other hand, when the average particle size of the composite oxide particles is small, the particles become easy to condense, so 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 average surface area of ​​the positive electrode active material in the mixture is increased, and the positive electrode active material, alkaline impurities and fluorinated polymers in the positive electrode slurry become easy to contact. Therefore, when two kinds of active material particles with different average particle sizes are made using a high Ni active material, gelation is particularly easy to occur when the positive electrode slurry is made. Therefore, it becomes particularly important to use a nitrile-containing polymer and a carboxylic acid compound in combination.

[0032] The ratio R1 of the mass M1 of the first particles in the composite oxide particles may be in the range of 10 to 40 mass % (e.g., 15 to 30 mass %). The ratio R2 of the mass M2 of the second particles in the composite oxide particles may be in the range of 60 to 90 mass % (e.g., 70 to 85 mass %).

[0033] 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).

[0034] (Conductive materials)

[0035] Examples of carbon materials (conductive materials) include conductive carbon particles such as carbon black, carbon nanotubes, and other conductive carbon materials. The carbon material preferably includes carbon nanotubes. By using carbon nanotubes as conductive materials, the deviation of the potential in the positive electrode can be particularly suppressed, and gas generation can be particularly suppressed. Furthermore, by using carbon nanotubes, the resistance of the positive electrode mixture layer can be reduced by adding a small amount. The proportion of carbon nanotubes in the total carbon material (conductive material) is, for example, 50% by mass or more, preferably in the range of 80 to 100% by mass (for example, in the range of 90 to 100% by mass).

[0036] In the positive electrode mixture layer, the amount of the carbon nanotubes 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, relative to 100 parts by mass of the positive electrode active material.

[0037] 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 a bundle state. 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.

[0038] From the viewpoint of improving the conductivity of 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 can be 1 μm or more or 5 μm or less, or 20 μm or less or 15 μm or less.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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 small amount of addition can suppress potential deviation inside the positive electrode mixture layer. 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.

[0044] (Carboxylic acid compounds)

[0045] The carboxylic acid compound may be a monocarboxylic acid, a polycarboxylic acid (e.g., a dicarboxylic acid or a tricarboxylic acid), or a carboxylic anhydride. Examples of carboxylic acids include formic acid, acetic acid, propionic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, maleic acid, fumaric acid, phthalic acid, aconitic acid, and the like. Examples of carboxylic anhydrides include acetic anhydride, propionic anhydride, oxalic anhydride, succinic anhydride, maleic anhydride, phthalic anhydride, malonic anhydride, and the like. Carboxylic acids can react with alkaline impurities. The carboxylic anhydride added to the positive electrode slurry can undergo a transformation to carboxylic acids and / or react with alkaline impurities.

[0046] In the positive electrode mixture layer, the amount of the carboxylic acid compound is 0.001 mass parts or more or 0.01 mass parts or more relative to 100 mass parts of the positive electrode active material, and can be 0.2 mass parts or less or 0.1 mass parts or less. For example, in the positive electrode mixture layer, the amount of the carboxylic acid compound can also be in the range of 0.001 to 0.2 mass parts relative to 100 mass parts of the positive electrode active material. By setting it in this range, the gelation of the positive electrode slurry can be particularly suppressed, and a high-performance positive electrode can be stably obtained.

[0047] (Rubber containing nitrile group)

[0048] The nitrile group-containing rubber contains a nitrile group. The nitrile group-containing rubber acts as a dispersant. In addition, the nitrile group-containing rubber may also act as a binder in the positive electrode mixture layer. Examples of nitrile group-containing rubbers include copolymers containing monomers of acrylonitrile and diene (e.g., butadiene). Specifically, examples of nitrile group-containing rubbers include acrylonitrile rubber (NBR), hydrogenated nitrile rubber (H-NBR), and modified bodies thereof. The weight average molecular weight of the nitrile group-containing rubber may be in the range of 5,000 to 500,000.

[0049] In the positive electrode mixture layer, the amount of the nitrile group-containing rubber 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, based on 100 parts by mass of the positive electrode active material.

[0050] (Fluoropolymer)

[0051] 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 containing monomers containing vinylidene fluoride. The fluorine-containing polymer may also be a combination of a vinylidene fluoride polymer and other fluorine-containing polymers. The vinylidene fluoride polymer may also be a copolymer of vinylidene fluoride and other monomers. Examples of vinylidene fluoride polymers include polyvinylidene fluoride (PVDF).

[0052] In the positive electrode mixture layer, the amount of the fluorinated polymer 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, based on 100 parts by mass of the positive electrode active material.

[0053] The weight average molecular weight of the fluorine-containing polymer may be 800,000 or more, 1,000,000 or more, or 1,200,000 or less, or 2,000,000 or less, and by setting the weight average molecular weight to 1,000,000 or more, a high effect as a binder can be obtained with a small amount.

[0054] The positive electrode mixture layer may also contain ingredients other than the above (e.g., thickeners) and compounds other than the above. For example, the positive electrode mixture layer may also contain polyvinyl pyrrolidone, cellulose derivatives (e.g., alkyl cellulose, carboxyalkyl cellulose, and salts thereof), etc. Polymer materials such as polyvinyl pyrrolidone and cellulose derivatives may function as dispersants and binders.

[0055] 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 other than the positive electrode active material to the conductive 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.

[0056] Positive electrode mixture layer (1 layer) per 1m 2 The mass of the positive electrode plate can be 200 g or more, preferably 250 g or more. By setting the mass to 250 g or more, a high capacity can be achieved as a lithium ion battery. As described above, by using the positive electrode plate disclosed in the present invention, the disadvantages caused by increasing the mass can be suppressed. The mass can be increased by thickening the positive electrode mixture layer or increasing the density of the positive electrode mixture layer.

[0057] 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 positive electrode mixture layer is thickened, an increase in internal resistance can be suppressed.

[0058] (Positive electrode collector)

[0059] 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, and the like.

[0060] (Positive electrode slurry and method for producing positive electrode)

[0061] 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.

[0062] 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 carboxylic acid compound, 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. As described above, repeated descriptions of each component are omitted. The positive electrode slurry may further contain any of the above-mentioned components (polyvinyl pyrrolidone, cellulose derivatives, etc.).

[0063] 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.

[0064] The ratio of the components contained in the positive electrode slurry is in principle reflected in the ratio of the components in the positive electrode mixture layer. 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.

[0065] 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, carboxylic acid compound, conductive material, fluorine-containing 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.

[0066] (Conductive material dispersion)

[0067] 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 carboxylic acid compound, a conductive material, a fluorine-containing polymer, a dispersant and a liquid medium. The conductive material contains a carbon material. The dispersant contains a nitrile-containing rubber. As described above, these components are omitted from repeated descriptions. The conductive material dispersion may also contain any component contained in the positive electrode mixture layer (e.g., any of the above-mentioned components).

[0068] 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.

[0069] 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.

[0070] (Non-aqueous electrolyte secondary battery)

[0071] 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 can be used. Examples of the constituent elements of the secondary battery are described below.

[0072] (positive electrode)

[0073] As the positive electrode, the positive electrode of this embodiment can be used.

[0074] (negative electrode)

[0075] 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.

[0076] 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.

[0077] 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.

[0078] (Negative electrode active material)

[0079] 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.

[0080] 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.

[0081] 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.

[0082] Metal foil can be used as the negative electrode current collector. The negative electrode current collector can be porous. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloys, copper, and copper alloys.

[0083] (Non-aqueous electrolyte)

[0084] 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.

[0085] 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.

[0086] Examples of lithium salts include lithium salts containing chloric acid (LiClO4, LiAlCl4, LiB 10 Cl 10 etc.), 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.

[0087] 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, an electrolyte having excellent ion conductivity and moderate viscosity can be obtained.

[0088] 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.

[0089] (Separator)

[0090] 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.

[0091] (Outer shell)

[0092] 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.

[0093] 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 .

[0094] 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. The periphery of the sealing plate 5 is engaged with the open end of the battery case 4, and the engaged portion is laser welded. That is, the positive electrode is electrically connected to the battery case 4 which also serves as the positive terminal. 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.

[0095] 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.

[0096] (Note)

[0097] The above description discloses the following technology.

[0098] (Technology 1)

[0099] A positive electrode for a non-aqueous electrolyte secondary battery,

[0100] It includes a positive electrode mixture layer,

[0101] The positive electrode mixture layer includes at least one compound selected from the group consisting of carboxylic acid and carboxylic anhydride, a positive electrode active material, a conductive material, a fluorine-containing polymer, and a dispersant.

[0102] 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.) A composite oxide represented by.

[0103] The conductive material comprises a carbon material,

[0104] The dispersant comprises a nitrile group-containing rubber.

[0105] (Technique 2)

[0106] The positive electrode according to technology 1, wherein the composition formula of the composite oxide satisfies 0.8≤x≤1.

[0107] (Technique 3)

[0108] The positive electrode according to technology 1 or 2, wherein the positive electrode active material includes: first particles of the composite oxide having an average particle size of 1 μm to 6 μm, and second particles of the composite oxide having an average particle size of 8 μm to 20 μm.

[0109] (Technique 4)

[0110] The positive electrode according to technology 1 or 2, wherein the conductive material further comprises carbon nanotubes.

[0111] (Technique 5)

[0112] The positive electrode according to Technology 4, wherein the average diameter of the carbon nanotubes is 20 nm or less.

[0113] (Technique 6)

[0114] The positive electrode according to any one of claims 1 to 5, wherein in the positive electrode mixture layer, the amount of the at least one compound is in the range of 0.001 to 0.2 parts by mass relative to 100 parts by mass of the positive electrode active material.

[0115] (Technique 7)

[0116] A non-aqueous electrolyte secondary battery comprising the positive electrode according to any one of techniques 1 to 6.

[0117] (Technology 8)

[0118] A positive electrode slurry for a positive electrode of a non-aqueous electrolyte secondary battery,

[0119] The invention comprises at least one compound selected from the group consisting of carboxylic acid and carboxylic anhydride, a positive electrode active material, a conductive material, a fluorine-containing polymer, a dispersant and a liquid medium.

[0120] 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

[0121] The conductive material comprises a carbon material,

[0122] The dispersant comprises a nitrile group-containing rubber.

[0123] (Technique 9)

[0124] The positive electrode slurry according to Technology 8, wherein the composition formula of the composite oxide satisfies 0.8≤x≤1.

[0125] (Technology 10)

[0126] The positive electrode according to technology 8 or 9, wherein the positive electrode active material includes: first particles of the composite oxide having an average particle size of 1 μm or more and 6 μm or less, and second particles of the composite oxide having an average particle size of 8 μm or more and 20 μm or less.

[0127] (Technology 11)

[0128] The positive electrode according to any one of Techniques 8 to 10, wherein the carbon material includes carbon nanotubes.

[0129] (Technology 12)

[0130] The positive electrode slurry according to Technology 11, wherein the average diameter of the carbon nanotubes is 20 nm or less.

[0131] (Technology 13)

[0132] The positive electrode slurry according to any one of claims 8 to 12, wherein the amount of the at least one compound is in the range of 0.001 to 0.2 parts by mass relative to 100 parts by mass of the positive electrode active material.

[0133] Example

[0134] 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.

[0135] (Production of Battery A1)

[0136] Battery A1 was produced in the following manner.

[0137] (1) Preparation of negative electrode

[0138] 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.

[0139] (2) Preparation of positive electrode

[0140] First, the positive electrode active material, polyvinylidene fluoride (binder), carbon nanotubes (conductive material), nitrile-containing rubber (dispersant), carboxylic acid compound, and N-methyl-2-pyrrolidone (dispersion medium) are mixed at a predetermined mass ratio to prepare a positive electrode slurry SA1. As the positive electrode active material, LiNi 0.80 Co 0.10 Mn 0.10 The composite oxide represented by O2. As the positive electrode active material (composite oxide), particles having an average particle size of 1 μm and particles having an average particle size of 8 μm were mixed and used.

[0141] The average length and average diameter of the carbon nanotubes are 1 μm and 10 nm, respectively. The amount of carbon nanotubes added is 0.5 parts by mass relative to 100 parts by mass of the positive electrode active material. The amount of polyvinylidene fluoride added is 1 part by mass relative to 100 parts by mass of the positive electrode active material. Maleic anhydride is used as the carboxylic acid compound. The amount of the carboxylic acid compound added is 0.05 parts by mass relative to 100 parts by mass of the positive electrode active material. The amount of the nitrile-containing rubber added is 0.1 parts by mass relative to 100 parts by mass of the positive electrode active material.

[0142] 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 PA1 including an aluminum foil and a positive electrode mixture layer formed on both sides of the aluminum foil is produced.

[0143] (3) Preparation of electrolyte (non-aqueous electrolyte)

[0144] 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.

[0145] (4) Production of secondary batteries

[0146] 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.

[0147] (Production of Batteries A2 to A6 and Batteries C1 to C5)

[0148] The types of components (conductive material, carboxylic acid compound, nitrile-containing rubber) contained in the positive electrode slurry, the composition of the positive electrode active material, and the particle size distribution of the positive electrode active material are changed as shown in Table 1. In addition, positive electrode slurries SA2 to SA6 and positive electrode slurries SC1 to SC5 are prepared according to the same method and conditions as the preparation method and conditions of positive electrode slurry SA1 of battery A1. As a composite oxide constituting the positive electrode active material, a composite oxide constituting the positive electrode active material used in positive electrode slurry SA1 is used. It should be noted that in Table 1, the particle size distribution of the active material particles becomes two kinds, and particles with an average particle size of 1 μm and particles with an average particle size of 8 μm are mixed and used in the same manner as positive electrode slurry SA1. In Table 1, the particle size distribution of the active material particles becomes one kind, and active material particles with an average particle size of 12 μm are used. Using these positive electrode slurries, positive electrodes PA2 to PA6 and positive electrodes PC1 to PC5 were produced under the same method and conditions as those for producing positive electrode PA1 of battery A1. Using these positive electrodes, batteries A2 to A6 and batteries C1 to C5 were produced under the same method and conditions as those for producing battery A1.

[0149] (Evaluation of Stability of Positive Electrode Slurry)

[0150] The stability of the prepared positive electrode slurry was evaluated by the following method. The viscosity of the slurry was measured on the day of preparation and after the prepared slurry was left to stand for 2 days, and the increase rate was taken as the viscosity increase rate of the slurry. The viscosity of the slurry was measured using a B-type viscometer.

[0151] (Battery capacity measurement)

[0152] The battery capacity of each of the above-mentioned batteries was measured according to the following steps. First, for each battery, the maximum current value was set to 0.3It under an environment of 25°C, and constant current charging was performed until the voltage reached 4.2V, and then constant voltage charging was performed at 4.2V until the current value dropped to 0.05It. Then, the discharge termination voltage was set to 2.5V, and constant current discharge was performed at a current of 0.2It. The discharge capacity at this time was measured. It should be noted that It(A) = rated capacity (Ah) / 1(h).

[0153] (Evaluation of gas generation amount)

[0154] The gas generation amount of the fabricated battery was evaluated by the following method: First, the fabricated battery was stored in a constant temperature chamber set at 80° C. in a charged state. Next, the battery was discharged and decomposed in a sealed container, and the generated gas amount was evaluated.

[0155] Table 1 shows a portion of the components included in the positive electrode mixture layer and the evaluation results. It should be noted that in Table 1, the slurry viscosity increase rate represents a relative value when the viscosity increase rate of slurry C1 is set to 100%, the battery capacity represents a relative value when the battery capacity of battery C1 is set to 100%, and the gas generation amount represents a relative value when the gas generation amount of battery C1 is set to 100%. In Table 1, "Ni ratio x in the composition of the active material" is the ratio of the positive electrode active material to the above-mentioned composition formula Li y Ni x M (1-x) O 2-δ Indicates the value of x when. In Table 1, "2 types of particle size distribution of active material particles" means that two positive electrode active materials with different average particle sizes are mixed and used, and 1 type means that two positive electrode active materials with different average particle sizes are not mixed and used. That is, the particle size distribution curve of the active material particles of "2 types of particle size distribution of active material particles" has two peaks, and the particle size distribution curve of "1 type of particle size distribution of active material particles" has one peak.

[0156] [Table 1]

[0157]

[0158] Batteries A1 to A6, and the positive electrode slurries and positive electrodes used in their production are the batteries, positive electrode slurries, and positive electrodes of the present embodiment. Batteries C1 to C5, and the positive electrode slurries and positive electrodes used in their production are comparative examples.

[0159] In Table 1, the slurry viscosity increase rate and the gas generation amount are preferably low, and the battery capacity is preferably high. As shown in Table 1, the viscosity increase of the positive electrode slurry disclosed in the present invention is small, and the positive electrode can be easily manufactured. In addition, the battery capacity of the battery disclosed in the present invention is high and the gas generation amount can be suppressed. In particular, when carbon nanotubes are used as the conductive material and hydrogenated nitrile rubber is used as the nitrile group-containing rubber, a good battery is obtained.

[0160] Industrial Applicability

[0161] 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.

[0162] 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.

[0163] Description of Reference Numerals

[0164] 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: at least one compound selected from the group consisting of carboxylic acid and carboxylic anhydride, 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 group-containing rubber.

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 The positive electrode active material includes first particles of the composite oxide having an average particle diameter of 1 μm or more and 6 μm or less, and second particles of the composite oxide having an average particle diameter of 8 μm or more and 20 μm or less.

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

5. The positive electrode according to claim 4, wherein The average diameter of the carbon nanotubes is less than 20 nm.

6. The positive electrode according to claim 1 or 2, wherein In the positive electrode mixture layer, the amount of the at least one compound is in the range of 0.001 to 0.2 parts by mass relative to 100 parts by mass of the positive electrode active material. 7 . A non-aqueous electrolyte secondary battery comprising the positive electrode according to claim 1 .

8. A positive electrode slurry for a positive electrode of a non-aqueous electrolyte secondary battery, The invention comprises: at least one compound selected from the group consisting of carboxylic acid and carboxylic anhydride, 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 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 includes a carbon material, and the dispersant includes a nitrile group-containing rubber.

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