Method for producing nickel-cobalt composite oxide, nickel-cobalt composite oxide, positive electrode active material, positive electrode for all-solid-state lithium-ion secondary battery, and all-solid-state lithium-ion secondary battery

Abstract

Provided is a positive electrode which is for an all-solid lithium-ion secondary battery, and can reduce the internal resistance of the all-solid-state lithium-ion secondary battery. The positive electrode is provided with an active material layer including a positive electrode active material and a solid electrolyte material. The positive electrode active material comprises secondary particles formed by agglomerating a plurality of primary particles each containing a lithium transition metal composite oxide. The smoothness of the secondary particles is greater than 0.73 and the circularity of the secondary particles is greater than 0.83.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a nickel-cobalt composite oxide, a nickel-cobalt composite oxide, a positive electrode active material, a positive electrode for an all-solid-state lithium-ion secondary battery, and an all-solid-state lithium-ion secondary battery. [Background technology]

[0002] From the viewpoint of safety, etc., all-solid-state lithium ion secondary batteries that use inorganic solid electrolytes instead of flammable non-aqueous electrolytes are being studied. Improvement in output characteristics is required for all-solid-state lithium ion secondary batteries. For example, International Publication No. 2007 / 004590 proposes a technology for forming a lithium ion conductive oxide layer on the surface of a positive electrode active material, which is said to have excellent high-output characteristics.

[0003] Meanwhile, a technique for narrowing the particle size distribution of secondary particles formed by aggregation of primary particles into approximately spherical shapes has been proposed as a positive electrode active material, which is said to enable higher battery capacity (see, for example, WO 2013 / 183711).Furthermore, a technique for producing spherical nickel cobalt aluminum hydroxide precursor material by coprecipitation has been proposed, which is said to improve cycle characteristics (see, for example, WO 2016 / 180288). Summary of the Invention [Problem to be solved by the invention]

[0004] Further improvements in the battery characteristics of lithium-ion secondary batteries are being sought, as are improvements in the characteristics of the positive electrode active materials and their precursors used therein. [Means for solving the problem]

[0005] The first aspect is a method for producing a nickel-cobalt composite oxide. The method includes preparing a first solution containing nickel ions and cobalt ions, preparing a second solution containing a complex ion-forming agent, and preparing a liquid medium having a pH in the range of 10 to 13.5. While separately and simultaneously supplying the first and second solutions to the liquid medium, a polymer containing structural units derived from (meth)acrylic acid is supplied to obtain a reaction solution having a pH maintained in the range of 10 to 13.5. Obtaining a composite hydroxide containing nickel and cobalt from the reaction solution, and heat-treating the obtained composite hydroxide to obtain secondary particles consisting of an aggregate of multiple primary particles comprising a composite oxide containing nickel and cobalt. The secondary particles constituting the nickel-cobalt composite oxide may have a smoothness greater than 0.74.

[0006] The second aspect is a nickel-cobalt composite oxide containing secondary particles formed by aggregation of a plurality of primary particles including a composite oxide containing nickel and cobalt. The smoothness of the secondary particles constituting the nickel-cobalt composite oxide is greater than 0.74.

[0007] The third aspect is a cathode active material comprising secondary particles having a layered structure and formed by aggregation of a plurality of primary particles each including a lithium transition metal composite oxide containing lithium, nickel, and cobalt, wherein the smoothness of the secondary particles constituting the cathode active material is greater than 0.73 and the circularity of the secondary particles is greater than 0.83.

[0008] A fourth aspect is a positive electrode for an all-solid-state lithium-ion secondary battery, comprising an active material layer containing a positive electrode active material and a solid electrolyte material. The positive electrode active material contains secondary particles formed by aggregating a plurality of primary particles containing a lithium transition metal composite oxide. The secondary particles have a smoothness of greater than 0.73 and a circularity of greater than 0.83.

[0009] A fifth aspect is an all-solid-state lithium ion secondary battery including the positive electrode, a negative electrode, and a solid electrolyte layer. [Effects of the Invention]

[0010] According to one aspect of the present disclosure, it is possible to provide a positive electrode that can reduce the internal resistance of an all-solid-state lithium-ion secondary battery. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an equivalent circuit diagram of an all-solid-state secondary battery. [Figure 2A] 1 is an example of a scanning electron microscope (SEM) image of the nickel-cobalt composite oxide according to Example 3. [Figure 2B] This is a further enlarged SEM image of FIG. 2A. [Figure 3A] 10 is an example of an SEM image of the nickel-cobalt composite oxide according to Example 7. [Figure 3B] This is a further enlarged SEM image of FIG. 3A. [Figure 4A] 1 is an example of an SEM image of a nickel-cobalt composite oxide according to Comparative Example 2. [Figure 4B] This is a further enlarged SEM image of FIG. 4A. DETAILED DESCRIPTION OF THE INVENTION

[0012] As used herein, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, the content of each component in a composition refers to the total amount of the multiple substances present in the composition when multiple substances corresponding to each component are present in the composition, unless otherwise specified. Hereinafter, embodiments of the present disclosure will be described in detail. However, the embodiments described below exemplify a method for producing a nickel-cobalt composite metal oxide, a nickel-cobalt composite oxide, a positive electrode active material, a positive electrode for an all-solid-state lithium-ion secondary battery, and an all-solid-state lithium-ion secondary battery, in order to embody the technical concept of the present disclosure. However, the present disclosure is not limited to the positive electrode active material for an all-solid-state lithium-ion secondary battery, the positive electrode, and the all-solid-state lithium-ion secondary battery described below.

[0013] Positive electrode for all-solid-state lithium-ion secondary batteries The positive electrode for an all-solid-state lithium-ion secondary battery (hereinafter simply referred to as the positive electrode) comprises an active material layer containing a positive electrode active material and a solid electrolyte material. The positive electrode active material contained in the active material layer is composed of secondary particles formed by aggregating a plurality of primary particles containing a lithium transition metal composite oxide. The secondary particles constituting the positive electrode active material have a smoothness of greater than 0.73 and a circularity of greater than 0.83.

[0014] The secondary particles constituting the positive electrode active material have a specific shape determined by smoothness and circularity. For example, the area of contact between the secondary particles and the solid electrolyte material is increased, which is thought to reduce the resistance at the interface between the secondary particles and the solid electrolyte. Furthermore, even when a substance containing a specific element is attached to the secondary particle surface to improve cycle characteristics, the attached compound is more likely to adhere evenly, reducing the resistance component. Furthermore, cracking of the secondary particles due to pressure molding during positive electrode formation can be reduced. This can be attributed to, for example, the pressure applied during pressure molding being uniform across the particles.

[0015] positive electrode active material The positive electrode active material is composed of secondary particles formed by aggregating a plurality of primary particles containing a lithium transition metal composite oxide. The smoothness of the secondary particles constituting the positive electrode active material may be greater than 0.73, and the circularity of the secondary particles may be greater than 0.83. The secondary particles are formed by aggregating, for example, 50 or more primary particles. The positive electrode active material may be manufactured by a method for manufacturing a positive electrode active material described below.

[0016] The smoothness of the secondary particles is, for example, greater than 0.73, preferably 0.80 or greater, and more preferably 0.83 or greater. The upper limit of the smoothness is 1. The smoothness is an index that represents the degree of unevenness in the contour shape of the secondary particle; the smoother the shape, the closer it is to 1, and the greater the degree of unevenness, the closer it is to 0. The smoothness is determined as follows: For the contour shape of the target secondary particle, a fitting function of image processing software is used to determine an approximation ellipse that has the same area as the contour shape of the target secondary particle. From the major axis a and minor axis b of this approximation ellipse, the total perimeter L of the approximation ellipse is calculated using the Gauss-Kummer formula. The total perimeter L of the contour shape of the secondary particle is determined as L op Let L be the total perimeter of the approximated ellipse. The smoothness is calculated by multiplying the total perimeter of the particle image outline (L op ) to the total perimeter of the approximate ellipse (L) ratio (L / L op ) The magnification of the image used to calculate the smoothness of the secondary particles may be appropriately selected depending on the particle size of the secondary particles. The magnification may be, for example, 1000 times or more and 10,000 times or less, preferably 1000 times or more and 6,000 times or less, and more preferably 2000 times or more and 6,000 times or less.

[0017] Specifically, a backscattered electron image (magnification: 4000x) is taken using a scanning electron microscope (SEM), and for 20 to 40 secondary particles whose outlines can be confirmed, an approximate ellipse is calculated to obtain the major axis a and the minor axis b. The total perimeter L of the outline shape is also calculated. op The total perimeter L of the approximate ellipse is calculated from the major axis a and the minor axis b based on the following approximation formula, and the ratio (L / L op ) is calculated, and the smoothness of the secondary particles is calculated as the arithmetic mean value of these. Note that being able to confirm the outline of the secondary particles means that the entire outline of the secondary particles can be traced on the image.

[0018]

number

[0019] The circularity of the secondary particles is, for example, greater than 0.83, preferably 0.86 or greater, and more preferably 0.90 or greater. The upper limit of the circularity is 1. The circularity is an index that represents the circularity of the outline shape of the secondary particles, and the closer it is to a circle, the closer it is to 1. The circularity is defined as the ratio (L1 / L0) of the circumferential length (L1) calculated from the circle-equivalent diameter to the total circumferential length (L0) of the outline shape of the secondary particle, where the diameter of a circle having the same area as the particle image area in the outline shape of the secondary particle is taken as the circle-equivalent diameter.

[0020] Specifically, a dry particle image analyzer (Morphologi G3S: Malvern; lens magnification 20x) was used to calculate the individual ratios (L1 / L0) for approximately 10,000 particles, and the circularity of the secondary particles was calculated as the arithmetic mean value of these ratios.

[0021] The particle size distribution of the secondary particles is, for example, smaller than 0.61, preferably 0.60 or less, more preferably 0.58 or less, even more preferably 0.54 or less, and particularly preferably 0.50 or less. The particle size distribution is an index that indicates the variation in particle size of individual secondary particles in a secondary particle group, and the smaller the value, the smaller the variation in particle size. If the particle size distribution of the secondary particles is within the above range, when another element is attached to the surface of the secondary particles, the attachment is more likely to be uniform. In this specification, the particle size distribution is defined as follows: The particle sizes corresponding to the cumulative 10%, 50%, and 90% from the small diameter side in the volume-based cumulative particle size distribution are respectively referred to as the 10% particle size D 10 , 50% particle size D 50 and 90% particle size D 90 In this case, D 90 and D 10 The difference between 50 The value obtained by dividing by this is the particle size distribution in this specification. That is, the particle size distribution of secondary particles is defined by the following formula. Particle size distribution=(D 90 -D 10 ) / D 50 Here, the volume-based cumulative particle size distribution is measured under wet conditions using a laser diffraction particle size distribution measuring device.

[0022] The volume average particle diameter of the secondary particles is, for example, 1 μm or more and 30 μm or less, preferably 2 μm or more, more preferably 3 μm or more, and preferably 12 μm or less, more preferably 8 μm or less. When the volume average particle diameter of the secondary particles is within the above range, the fluidity is good, and the output power may be further improved when forming a secondary battery. Here, the volume average particle diameter is the 50% particle diameter D corresponding to the cumulative 50% from the small diameter side in the cumulative particle size distribution based on volume. 50 is.

[0023] Secondary particles are formed by the aggregation of multiple primary particles. The average particle size D based on electron microscope observation of primary particles SEM is, for example, 0.1 μm or more and 1.5 μm or less, preferably 0.12 μm or more, and more preferably 0.15 μm or more. SEM is preferably 1.2 μm or less, more preferably 1.0 μm or less. If the average particle size of the primary particles based on electron microscopy is within this range, the output of the battery may be improved when it is constructed. Here, the average particle size of the primary particles based on electron microscopy is measured as follows. Using a scanning electron microscope (SEM), the primary particles constituting the secondary particles are observed at a magnification ranging from 1,000x to 15,000x depending on the particle size. Fifty primary particles whose outlines can be confirmed are selected, and the equivalent sphere diameter is calculated from the outlines of the selected primary particles using image processing software. The average particle size of the primary particles based on electron microscopy is determined as the arithmetic mean of the obtained equivalent sphere diameters. In one embodiment, the primary particles may have particles with an average particle size smaller than the primary particles attached to their surfaces. In another embodiment, the primary particles may be an aggregate of particles with an average particle size smaller than the primary particles. The average particle size of the particles with an average particle size smaller than the primary particles may be measured based on electron microscopy in the same manner as above. "The outlines of the primary particles can be confirmed" means that the entire outline of the primary particles can be traced on the image.

[0024] Secondary particles are those with a 50% particle size D in the cumulative particle size distribution based on volume. 50 Average particle size D based on electron microscope observation SEM Ratio to D50 / D SEM may be, for example, 2.5 or more. 50 / D SEM is, for example, 2.5 or more and 150 or less, preferably 5 or more, and more preferably 10 or more. 50 / D SEM is preferably 100 or less, more preferably 50 or less.

[0025] The lithium transition metal composite oxide contained in the primary particles constituting the secondary particles may, for example, contain nickel in its composition and have a layered structure. The lithium transition metal composite oxide may contain at least lithium (Li) and a transition metal such as nickel (Ni), and may further contain at least one first metal element selected from the group consisting of aluminum (Al), cobalt (Co), and manganese (Mn). The lithium transition metal composite oxide may contain lithium (Li), nickel (Ni), and cobalt (Co), and may further contain at least one of aluminum (Al) and manganese (Mn). In addition, the lithium transition metal composite oxide may further contain at least one second metal element selected from the group consisting of magnesium (Mg), calcium (Ca), titanium (Ti), zirconium (Zr), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), tungsten (W), iron (Fe), copper (Cu), silicon (Si), tin (Sn), bismuth (Bi), gallium (Ga), yttrium (Y), samarium (Sm), erbium (Er), cerium (Ce), neodymium (Nd), lanthanum (La), cadmium (Cd), and lutetium (Lu). The second metal element may be at least one selected from the group consisting of zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb), molybdenum (Mo), and tungsten (W).

[0026] When the lithium transition metal composite oxide contains nickel, the ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium is, for example, greater than 0, preferably 0.33 or greater. The ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium may be 0.4 or greater, or 0.55 or greater. Furthermore, the ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium is, for example, less than 1, preferably 0.95 or less, and more preferably 0.8 or less. When the ratio of the number of moles of nickel is within the above-mentioned range, it is possible to achieve both good charge / discharge capacity at high voltage and good cycle characteristics in an all-solid-state lithium ion secondary battery (hereinafter simply referred to as an all-solid-state secondary battery).

[0027] When the lithium transition metal composite oxide contains cobalt, the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium is, for example, greater than 0, preferably 0.02 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and particularly preferably 0.15 or more. The ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium is, for example, less than 1, preferably 0.6 or less, more preferably 0.35 or less. The ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium may be 0.33 or less, 0.3 or less, or 0.25 or less. When the ratio of the number of moles of cobalt is within the above-mentioned range, sufficient charge / discharge capacity at high voltages can be achieved in the all-solid-state secondary battery.

[0028] When the lithium transition metal composite oxide contains at least one of manganese and aluminum, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements other than lithium is, for example, greater than 0, preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and particularly preferably 0.15 or more. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements other than lithium is, for example, 0.6 or less, preferably 0.35 or less. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements other than lithium may be 0.33 or less, 0.3 or less, or 0.25 or less. When the ratio of the total number of moles of manganese and aluminum is within the above-mentioned range, both charge / discharge capacity and safety can be achieved in the all-solid-state secondary battery.

[0029] In the lithium transition metal composite oxide, the ratio of the number of moles of lithium to the total number of moles of metals other than lithium is, for example, 0.95 or more, preferably 1.0 or more, more preferably 1.03 or more, and even more preferably 1.05 or more. The ratio of the number of moles of lithium to the total number of moles of metals other than lithium is, for example, 1.5 or less, preferably 1.3 or less, more preferably 1.25 or less, and even more preferably 1.2 or less. When the ratio of moles of lithium is 0.95 or more, the interfacial resistance generated at the interface between the positive electrode surface and the solid electrolyte in an all-solid-state secondary battery using a positive electrode active material containing the resulting lithium transition metal composite oxide is suppressed, which tends to improve the output of the all-solid-state secondary battery. On the other hand, when the ratio of moles of lithium is 1.5 or less, the initial discharge capacity tends to improve when the positive electrode active material is used in the positive electrode of an all-solid-state secondary battery.

[0030] When the lithium transition metal composite oxide contains cobalt and manganese in addition to nickel, the molar ratio of nickel, cobalt, and manganese is, for example, nickel:cobalt:manganese=(0.33 to 0.95):(0.02 to 0.35):(0.01 to 0.35), preferably (0.33 to 0.8):(0.05 to 0.35):(0.05 to 0.35). When the lithium transition metal composite oxide contains cobalt, manganese, and aluminum in addition to nickel, the molar ratio of nickel, cobalt, and (manganese+aluminum) is, for example, nickel:cobalt:(manganese+aluminum)=(0.33 to 0.95):(0.02 to 0.35):(0.01 to 0.35), preferably (0.33 to 0.8):(0.05 to 0.35):(0.05 to 0.35).

[0031] When the lithium transition metal composite oxide contains at least one second metal element, the ratio of the total number of moles of the second metal element to the total number of moles of metal elements other than lithium is, for example, greater than 0, preferably 0.001 or more, more preferably 0.003 or more. The ratio of the total number of moles of the second metal element to the total number of moles of metal elements other than lithium is, for example, 0.02 or less, preferably 0.015 or less, more preferably 0.01 or less.

[0032] When the lithium transition metal composite oxide is expressed as a composition, for example, the lithium transition metal composite oxide is represented by the following formula (2): The lithium transition metal composite oxide may have a layered structure or a hexagonal crystal structure. Li p Ni x Co y M 1 z M 2 w O 2+β (2)

[0033] Here, p, x, y, z, w, and β satisfy 1.0 ≤ p ≤ 1.3, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 ≤ w ≤ 0.02, x + y + z + w = 1, and -0.1 ≤ β ≤ 0.1. x, y, z, and w may satisfy 0 < x < 1, 0 ≤ y ≤ 0.6, 0 ≤ z ≤ 0.6, 0 ≤ w ≤ 0.015, may satisfy 0.33 ≤ x ≤ 0.95, 0.01 ≤ y ≤ 0.35, 0 ≤ z ≤ 0.35, 0 ≤ w ≤ 0.01, and may satisfy 0.33 ≤ x ≤ 0.95, 0.02 ≤ y ≤ 0.35, 0.05 ≤ z ≤ 0.35, 0 ≤ w ≤ 0.01.

[0034] M 1 may represent at least one of Mn and Al. M 2 may represent at least one selected from the group consisting of Mg, Ca, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu, and may represent at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0035] The secondary particles constituting the positive electrode active material may have an attachment containing niobium on their surface. The attachment containing niobium may be attached to the surface of the secondary particles or may be attached to the grain boundaries of the secondary particles. Further, the attachment containing niobium may be attached to the surface of the primary particles constituting the secondary particles or may be dissolved in at least some of the primary particles. Further, the secondary particles constituting the positive electrode active material may have, in addition to the attachment containing niobium, an attachment containing a compound having ionic conductivity containing boron, silicon, titanium, etc.

[0036] The amount of the attachment containing niobium in the positive electrode active material is, in terms of niobium, for example, 0.1 mol% or more and 10 mol% or less with respect to the lithium transition metal composite oxide, and preferably 0.2 mol% or more and 8 mol% or less. When the amount of niobium attachment is within the above range, the resistance component can be reduced while maintaining good cycle characteristics.

[0037] Examples of the niobium-containing deposit include a niobium-containing compound such as lithium niobate. The niobium-containing deposit may be obtained by mixing a solution or dispersion of a niobium compound or a solid niobium compound with secondary particles, and may also be obtained by heat-treating the mixture as needed.

[0038] The content of the positive electrode active material in the positive electrode active material layer is, for example, 60% by mass or more, preferably 70% by mass or more. The content of the positive electrode active material is, for example, 95% by mass or less, preferably 90% by mass or less. When the content of the positive electrode active material is 60% by mass or more, sufficient battery capacity can be obtained. When the content of the positive electrode active material is 95% by mass or less, an increase in resistance can be suppressed.

[0039] solid electrolyte material The solid electrolyte material applied to the positive electrode may be any material having lithium ion conductivity, and examples thereof include inorganic solid electrolyte materials such as sulfide solid electrolyte materials, oxide solid electrolyte materials, nitride solid electrolyte materials, and halide solid electrolyte materials.

[0040] Examples of sulfide solid electrolyte materials include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (where m and n are positive numbers. Z is at least one selected from the group consisting of Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (wherein x and y are positive numbers; M is at least one selected from the group consisting of P, Si, Ge, B, Al, Ga, and In), Li 10 GeP2S12 etc.

[0041] In particular, the sulfide solid electrolyte material preferably comprises an ion conductor containing Li, A (A is at least one selected from the group consisting of P, Si, Ge, Al, and B), and S. Furthermore, the ion conductor preferably has an anion structure of ortho composition (e.g., PS4 3- Structure, SiS4 4- Structure, GeS4 4- Structure, AlS3 3- Structure, BS3 3- It is preferable that the anion structure has an ortho-composition as the main anion component. This allows for a sulfide solid electrolyte material with high chemical stability. The proportion of the anion structure with an ortho-composition is preferably 70 mol % or more, and more preferably 90 mol % or more, of the total anion structures in the ionic conductor. The proportion of the anion structure with an ortho-composition can be determined by Raman spectroscopy, NMR, XPS, etc.

[0042] The sulfide solid electrolyte material preferably contains, in addition to the ionic conductor, at least one selected from the group consisting of LiI, LiBr, and LiCl. It is generally believed that at least a portion of LiI, LiBr, and LiCl is present in the structure of the ionic conductor as a LiI component, a LiBr component, and a LiCl component, respectively. Furthermore, the sulfide solid electrolyte material may have a LiI peak in X-ray diffraction measurement, but preferably does not have a LiI peak. This results in higher Li-ion conductivity. The same applies to LiBr and LiCl. The content of LiX (X = I, Cl, Br) in the sulfide solid electrolyte material is, for example, in the range of 10 mol% to 30 mol%, preferably 15 mol% to 25 mol%. Here, the LiX content refers to the total content of LiX contained in the sulfide solid electrolyte material.

[0043] Examples of oxide solid electrolyte materials include Li2O-B2O3-P2O5, Li2O-SiO2, and Li-La-Ta-O (e.g., Li5La3Ta2O12 ), Li-La-Zr-O (e.g., Li7La3Zr2O 12 ), Li-Ba-La-Ta-O (e.g., LiBaLaTaO 12 ), Li 1+x Si x P 1-x O4 (0≦x<1, e.g., Li 3.6 Si 0.6 P 0.4 O4), Li 1+x Al x Ge 2-x (PO4)3(0≦x≦2), Li 1+x Al x Ti 2-x (PO4)3(0≦x≦2), Li3PO (4-3 / 2x) N x (0≦x<1), etc. Examples of nitride solid electrolyte materials include Li3N, and examples of halide solid electrolyte materials include LiI.

[0044] The solid electrolyte material may be a crystalline material or an amorphous material. The solid electrolyte material may be glass or crystallized glass (glass ceramics). Examples of methods for producing glass include a method of subjecting a raw material composition to an amorphization treatment. Examples of amorphization treatment include a melt quenching method and a mechanical milling method. Examples of methods for producing crystallized glass include a method of heating glass to a temperature equal to or higher than the crystallization temperature. Examples of methods for producing crystalline materials include a method of heating a raw material composition in a solid state (solid-phase method).

[0045] The shape of the solid electrolyte material is not particularly limited, but may be, for example, a substantially spherical shape. 50 ) is, for example, 0.1 μm or more, and may be 0.5 μm or more. On the other hand, the volume average particle diameter (D 50 ) is, for example, 50 μm or less, and may be 10 μm or less. The Li ion conductivity of the solid electrolyte material at 25° C. is, for example, 1×10-5 S / cm or more, 1×10 -4 S / cm or more is preferable, and 1×10 -3 It is more preferable that the viscosity is S / cm or more.

[0046] The content of the solid electrolyte material in the positive electrode active material layer is, for example, 1% by mass or more, preferably 5% by mass or more, and more preferably 10% by mass or more. When the content of the solid electrolyte material is 1% by mass or more, the Li-ion conductivity of the positive electrode active material layer is sufficiently improved. On the other hand, the content of the solid electrolyte material in the positive electrode active material layer is, for example, 60% by mass or less, preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When the content of the solid electrolyte material is 60% by mass or less, the content of the positive electrode active material does not become too low relatively, and sufficient battery capacity can be obtained. Furthermore, in the positive electrode active material layer, the content of the solid electrolyte material is preferably lower than the content of the positive electrode active material.

[0047] Furthermore, the ratio of the content of the solid electrolyte material to the content of the positive electrode active material in the positive electrode active material layer (solid electrolyte material / positive electrode active material) may be, for example, 0.01 or more, preferably 0.1 or more, and the ratio of the content of the solid electrolyte material to the content of the positive electrode active material is, for example, 1.5 or less, preferably 1 or less.

[0048] In addition to the positive electrode active material and the solid electrolyte material, the positive electrode may contain a conductive additive in the active material layer. The inclusion of the conductive additive further improves the electronic conductivity of the positive electrode active material layer. Examples of the conductive additive include carbon materials such as acetylene black (AB), ketjen black (KB), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0049] When the positive electrode active material layer contains a conductive additive, the content of the conductive additive in the positive electrode active material layer may be, for example, 1% by mass or more, preferably 2% by mass or more, and the content of the conductive additive in the positive electrode active material layer may be, for example, 10% by mass or less, preferably 5% by mass or less.

[0050] The positive electrode may further contain a binder in the active material layer. By including a binder, the moldability of the positive electrode active material layer can be further improved. Examples of binders include polyvinylidene fluoride (PVDF), butylene rubber (BR), and styrene butadiene rubber (SBR). The positive electrode may further contain a thickener in the active material layer.

[0051] The positive electrode may have a configuration including a current collector and a positive electrode active material layer disposed on the current collector, or may have a configuration consisting of only a positive electrode active material layer formed into a desired shape.

[0052] The method for manufacturing a positive electrode may include a preparation step of preparing a positive electrode composite containing at least a positive electrode active material and a solid electrolyte material, and a forming step of forming the prepared positive electrode composite into a desired shape. The forming step may include, as necessary, applying the positive electrode composite onto a current collector and forming the applied positive electrode composite.

[0053] Examples of methods for producing a positive electrode composite include mixing a positive electrode active material and a solid electrolyte material, and optionally adding a conductive additive. The mixing can be dry mixing, for example, using a mixer or the like. Another example of a production method includes adding a dispersion medium to a mixture of the positive electrode active material and the solid electrolyte material to form a slurry, subjecting the slurry to a dispersion promoting treatment, and removing the dispersion medium from the slurry. Examples of dispersion promoting treatments include ultrasonic treatment and shaking treatment.

[0054] The positive electrode composite can be formed, for example, by compression molding. The pressure of compression molding is, for example, 50 MPa or more, and can be 50 MPa to 500 MPa, or 100 MPa to 350 MPa. By forming the positive electrode active material layer by compression molding, the positive electrode active material and the solid electrolyte material are closely attached to each other, thereby reducing the interface resistance.

[0055] All-solid-state lithium-ion secondary battery The all-solid-state lithium-ion secondary battery includes a positive electrode including a positive electrode active material layer containing a positive electrode active material and a solid electrolyte material, a negative electrode including a negative electrode active material layer containing a negative electrode active material, and a solid electrolyte layer disposed between the positive electrode active material layer and the negative electrode active material layer. When the secondary particles constituting the positive electrode active material have the above-described specific structure, an all-solid-state lithium-ion secondary battery with reduced internal resistance can be constructed.

[0056] positive electrode The positive electrode may be formed from a positive electrode composite containing the above-described positive electrode active material and solid electrolyte material. In the positive electrode, the positive electrode active material layer may be integrally formed with a positive electrode current collector, if necessary. The positive electrode active material is formed from secondary particles formed by aggregating multiple primary particles containing a lithium transition metal composite oxide. The smoothness and circularity of the secondary particles are as described above, and preferred embodiments are also similar. The thickness of the positive electrode active material layer is, for example, in the range of 0.1 μm to 1000 μm, preferably in the range of 0.1 μm to 300 μm.

[0057] negative electrode The negative electrode includes a negative electrode active material layer containing at least a negative electrode active material. In the negative electrode, the negative electrode active material layer may be integrally formed with a negative electrode current collector that collects current, as necessary. The negative electrode active material layer may further contain at least one of a solid electrolyte material, a conductive additive, and a binder, as necessary. The solid electrolyte material, the conductive additive, and the binder are as described above.

[0058] Examples of the negative electrode active material include carbon active materials, metal active materials, and oxide active materials. Examples of the carbon active material include graphite, hard carbon, and soft carbon. Examples of the metal active material include In, Al, Si, Sn, and alloys containing at least these. Examples of the oxide active material include niobium oxide (e.g., Nb2O5), lithium titanate (e.g., Li4Ti5O 12 ), silicon oxide (for example, SiO), etc. The thickness of the negative electrode active material layer is, for example, in the range of 0.1 μm to 1000 μm, and preferably in the range of 0.1 μm to 300 μm.

[0059] solid electrolyte layer The solid electrolyte layer is a layer disposed between the positive electrode active material layer and the negative electrode active material layer. The solid electrolyte layer is a layer containing at least a solid electrolyte material, and may further contain a binder, etc., as necessary. The solid electrolyte material and the binder are as described above.

[0060] The content of the solid electrolyte material in the solid electrolyte layer is, for example, in the range of 10% by mass to 100% by mass, and preferably in the range of 50% by mass to 100% by mass. The thickness of the solid electrolyte layer is, for example, in the range of 0.1 μm to 1000 μm, and preferably in the range of 0.1 μm to 300 μm. In addition, the solid electrolyte layer can be formed, for example, by compression molding the solid electrolyte material.

[0061] Other configurations The all-solid-state lithium-ion secondary battery has at least the above-described positive electrode, negative electrode, and solid electrolyte layer. It may further have a positive electrode current collector that collects current from the positive electrode active material layer and a negative electrode current collector that collects current from the negative electrode active material layer. Examples of materials for the positive electrode current collector include stainless steel (SUS), Ni, Cr, Au, Pt, Al, Fe, Ti, and Zn. Examples of materials for the negative electrode current collector include stainless steel (SUS), Cu, Ni, Fe, Ti, Co, and Zn. The all-solid-state lithium-ion secondary battery may also include any battery case, such as a SUS battery case. Examples of shapes for the all-solid-state lithium-ion secondary battery include coin-type, laminate-type, cylindrical, and prismatic types.

[0062] Nonaqueous electrolyte secondary battery The positive electrode active material obtained according to one embodiment of the present disclosure can also be used in a positive electrode for a nonaqueous electrolyte secondary battery (hereinafter referred to as a nonaqueous electrolyte secondary battery) using a nonaqueous electrolyte. When used in a nonaqueous electrolyte secondary battery, cracking of secondary particles due to pressure molding during positive electrode formation can also be reduced. A nonaqueous electrolyte secondary battery is configured to include, in addition to the above-described positive electrode, a negative electrode for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte, a separator, and the like. For the negative electrode, nonaqueous electrolyte, separator, and the like in the nonaqueous electrolyte secondary battery, those for nonaqueous electrolyte secondary batteries described in, for example, JP 2002-075367 A, JP 2011-146390 A, and JP 2006-12433 A (the entire disclosures of which are incorporated herein by reference) can be appropriately used.

[0063] Method for producing positive electrode active material The method for producing a positive electrode active material may include, for example, a composite oxide preparation step of preparing a nickel-cobalt composite oxide, the nickel-cobalt composite oxide including secondary particles formed by aggregation of a plurality of primary particles containing a composite oxide containing nickel and cobalt, the secondary particles having a smoothness of greater than 0.74; a lithium mixing step of mixing the nickel-cobalt composite oxide with a lithium compound to obtain a lithium mixture; and a synthesis step of heat-treating the lithium mixture to obtain a lithium transition metal composite oxide containing nickel and cobalt and having a layered structure. The produced positive electrode active material includes secondary particles formed by aggregation of a plurality of primary particles containing the lithium transition metal composite oxide. The smoothness of the secondary particles may be greater than 0.73. The circularity of the secondary particles may be greater than 0.83. The method for producing a positive electrode active material may include a positive electrode active material including secondary particles formed by aggregation of a plurality of primary particles containing the lithium transition metal composite oxide, the secondary particles having a smoothness of greater than 0.73 and a circularity of greater than 0.83.

[0064] Complex oxide preparation process In the composite oxide preparation step, a nickel-cobalt composite oxide is prepared, which includes secondary particles formed by aggregation of a plurality of primary particles including a composite oxide containing nickel and cobalt. The smoothness of the secondary particles constituting the nickel-cobalt composite oxide may be greater than 0.74. The nickel-cobalt composite oxide may be prepared by appropriately selecting it from commercially available products, or may be prepared by manufacturing it using the method for manufacturing a nickel-cobalt composite oxide described below. Details of the nickel-cobalt composite oxide to be prepared will be described later.

[0065] Lithium mixing process In the lithium mixing step, the prepared nickel-cobalt composite oxide and a lithium compound are mixed to obtain a lithium mixture. Examples of the mixing method include a method of dry-mixing the nickel-cobalt composite oxide and the lithium compound using a stirring mixer or the like, and a method of preparing a slurry of the nickel-cobalt composite oxide and wet-mixing it using a mixer such as a ball mill. Examples of the lithium compound include lithium hydroxide, lithium nitrate, lithium carbonate, and mixtures thereof.

[0066] The ratio of the number of moles of lithium to the total number of moles of metal elements other than lithium in the lithium mixture (also referred to as the lithium ratio) may be, for example, 0.90 or more and 1.30 or less, and preferably 1.0 or more and 1.20 or less. When the lithium ratio is 0.90 or more, the generation of by-products tends to be suppressed. Furthermore, when the lithium ratio is 1.30 or less, the increase in the amount of alkaline components present on the surface of the lithium mixture is suppressed, and water adsorption due to the deliquescence of the alkaline components is suppressed, which tends to improve handleability.

[0067] Synthesis process In the synthesis step, the lithium mixture is heat-treated to obtain a lithium transition metal composite oxide containing nickel and cobalt and having a layered structure. The lithium transition metal composite oxide is contained in primary particles, and secondary particles formed by aggregations of multiple primary particles are contained in the positive electrode active material. In the synthesis step, the lithium contained in the lithium compound may diffuse into the nickel-cobalt composite oxide, thereby obtaining the lithium transition metal composite oxide.

[0068] The heat treatment temperature may be, for example, 650°C or higher and 990°C or lower, and preferably 700°C or higher and 960°C or lower. When the heat treatment temperature is 650°C or higher, an increase in the amount of unreacted lithium tends to be suppressed. When the heat treatment temperature is 990°C or lower, decomposition of the lithium transition metal composite oxide that is produced tends to be suppressed. The heat treatment time, as the time during which the maximum temperature is maintained, may be, for example, 10 hours or longer. The heat treatment may be performed in an atmosphere in the presence of oxygen, preferably an atmosphere containing 10% by volume or higher and 100% by volume or lower of oxygen.

[0069] In the method for producing a positive electrode active material, after the synthesis step, the heat-treated product obtained may be subjected to treatment such as crushing, pulverization, dry sieving, etc., as needed.

[0070] Method for producing nickel-cobalt composite oxide A method for producing a nickel-cobalt composite oxide includes, for example, a first solution preparation step of preparing a first solution containing nickel ions and cobalt ions, a second solution preparation step of preparing a second solution containing a complex ion-forming agent, a liquid medium preparation step of preparing a liquid medium having a pH in the range of 10 to 13.5, a crystallization step of supplying the first and second solutions separately and simultaneously to the liquid medium while supplying a polymer containing structural units derived from (meth)acrylic acid to obtain a reaction solution maintained at a pH in the range of 10 to 13.5, a composite hydroxide recovery step of obtaining a composite hydroxide containing nickel and cobalt from the reaction solution, and a composite hydroxide heat treatment step of heat-treating the obtained composite hydroxide to obtain secondary particles consisting of an aggregate of multiple primary particles containing a composite oxide containing nickel and cobalt. The secondary particles containing the nickel-cobalt composite oxide produced have a smoothness greater than 0.74. The method for producing a nickel-cobalt composite oxide may be a method for producing a nickel-cobalt composite oxide containing secondary particles formed by aggregation of a plurality of primary particles including a composite oxide containing nickel and cobalt, wherein the smoothness of the secondary particles is greater than 0.74.

[0071] First solution preparation step In the first solution preparation step, a first solution containing nickel ions and cobalt ions is prepared. The first solution is prepared by dissolving a predetermined amount of salt containing each metal element in water according to the composition of the target nickel-cobalt composite oxide. Examples of salts include nitrates, sulfates, and hydrochlorides. An acidic substance (e.g., a sulfuric acid solution) may be added to the water when preparing the first solution. This may facilitate the dissolution of the salt containing each metal element. A basic substance may also be added to adjust the pH when preparing the first solution. The total number of moles of metal elements, such as nickel and cobalt, in the first solution may be appropriately set according to the average particle size of the target nickel-cobalt composite oxide. Here, the total number of moles of metal elements refers to the total number of moles of nickel and cobalt when the first solution contains nickel and cobalt, or the total number of moles of nickel, cobalt, and manganese when the first solution contains nickel, cobalt, and manganese.

[0072] The first solution may further contain at least one of aluminum ions and manganese ions in addition to nickel ions and cobalt ions. The first solution may also contain ions of at least one second metal element selected from the group consisting of magnesium, calcium, titanium, zirconium, niobium, tantalum, chromium, molybdenum, tungsten, iron, copper, silicon, tin, bismuth, gallium, yttrium, samarium, erbium, cerium, neodymium, lanthanum, cadmium, and lutetium. The second metal element may be at least one element selected from the group consisting of zirconium, titanium, magnesium, tantalum, niobium, molybdenum, and tungsten.

[0073] The concentration of metal ions such as nickel and cobalt in the first solution may be, for example, 1.0 mol / L to 2.6 mol / L, preferably 1.5 mol / L to 2.2 mol / L, in total. When the metal ion concentration in the first solution is 1.0 mol / L or higher, a sufficient amount of crystallized material can be obtained per reaction vessel, improving productivity. On the other hand, when the metal ion concentration in the first solution is 2.6 mol / L or lower, the metal salt concentration is prevented from exceeding its saturation concentration at room temperature, and a decrease in the metal ion concentration in the solution due to the precipitation of metal salt crystals is suppressed.

[0074] Second solution preparation step In the second solution preparation step, a second solution containing a complex ion-forming factor is prepared. The second solution contains a complex ion-forming factor capable of forming complex ions with the metal ions contained in the first solution. For example, when the complex ion-forming factor is ammonia, an aqueous ammonia solution can be used as the second solution. The content of ammonia contained in the aqueous ammonia solution may be, for example, 5% by mass or more and 25% by mass or less, and preferably 10% by mass or more and 20% by mass or less.

[0075] Liquid medium preparation process In the liquid medium preparation step, a liquid medium having a pH in the range of 10 to 13.5 is prepared. The liquid medium is adjusted to a pH of 10 to 13.5 by, for example, adding a predetermined amount of water and a basic solution such as an aqueous sodium hydroxide solution to a reaction vessel. Adjusting the pH of the solution to 10 to 13.5 can suppress pH fluctuations in the reaction solution at the initial stage of the reaction.

[0076] Crystallization process In the crystallization step, the first solution and the second solution are supplied separately and simultaneously to the liquid medium while maintaining the pH of the resulting reaction solution in the range of 10 to 13.5. A polymer containing structural units derived from (meth)acrylic acid is also supplied to the liquid medium. This allows composite hydroxide particles containing nickel and cobalt to be obtained from the reaction solution. In addition to the first solution and the second solution, a basic solution may also be supplied to the liquid medium simultaneously. This makes it easy to maintain the pH of the reaction solution in the range of 10 to 13.5.

[0077] In the crystallization step, it is preferable to supply each solution so that the pH of the reaction solution is maintained in the range of 10 to 13.5. For example, the pH of the reaction solution can be maintained in the range of 10 to 13.5 by adjusting the supply amount of the second solution according to the supply amount of the first solution. If the pH of the reaction solution is lower than 10, the amount of impurities (e.g., sulfuric acid and nitric acid components other than metals contained in the mixed solution) contained in the resulting composite hydroxide will increase, which may lead to a decrease in the capacity of the final product, the secondary battery. Furthermore, if the pH is higher than 13.5, many fine secondary particles will be generated, which may deteriorate the handleability of the resulting composite hydroxide. Furthermore, the temperature of the reaction solution may be controlled, for example, to be in the range of 25°C to 80°C.

[0078] In the crystallization step, the nickel ion concentration in the reaction solution may be maintained, for example, in the range of 10 ppm to 1000 ppm, and is preferably maintained in the range of 10 ppm to 100 ppm. If the nickel ion concentration is 10 ppm or more, the composite hydroxide is sufficiently precipitated. If the nickel ion concentration is 1000 ppm or less, the amount of nickel eluted is small, thereby preventing deviation from the target composition. For example, when an aqueous ammonia solution is used as the complex ion-forming solution, the nickel ion concentration can be adjusted by supplying the complex ion-forming solution so that the ammonium ion concentration in the reaction solution is 1000 ppm to 15000 ppm.

[0079] The time for supplying the first solution may be, for example, 6 hours or more and 60 hours or less, preferably 8 hours or more and 60 hours or less, and more preferably 10 hours or more and 42 hours or less. If it is 6 hours or more, the precipitation rate of the composite hydroxide will be slow, and therefore a nickel-cobalt composite oxide with higher smoothness will tend to be obtained. Furthermore, if it is 60 hours or less, productivity can be further improved.

[0080] The value obtained by taking the total number of moles of nickel, cobalt, etc. in the first solution supplied throughout the crystallization process as the denominator and the total number of moles of nickel, cobalt, etc. in the first solution supplied per hour as the numerator may be, for example, 0.015 or more and 0.125 or less, and preferably 0.020 or more and 0.10 or less. If it is 0.015 or more, productivity can be further improved. Also, if it is 0.125 or less, a nickel-cobalt composite oxide with higher smoothness tends to be obtained.

[0081] The polymer containing structural units derived from (meth)acrylic acid supplied to the liquid medium may be, for example, an anionic polymer having a carboxy group that can function as a surfactant, dispersant, etc. When the polymer contains structural units derived from (meth)acrylic acid, foaming of the reaction solution is suppressed, and at least one of the smoothness and circularity of the resulting composite hydroxide is improved. For example, when a nonionic dispersant, which is commonly used as a dispersant, is used, foaming occurs in the reaction solution, making it difficult to control the particle size.

[0082] The structural units derived from (meth)acrylic acid constituting the polymer include structural units derived from acrylic acid, structural units derived from methacrylic acid, structural units derived from acrylic acid esters, structural units derived from methacrylic acid esters, structural units derived from acrylic acid amides, structural units derived from methacrylic acid amides, etc. The polymer may further contain other structural units in addition to the structural units derived from (meth)acrylic acid. Examples of other structural units include structural units derived from unsaturated dibasic acids or their acid anhydrides.

[0083] The weight-average molecular weight of the polymer may be, for example, 50,000 or less, and preferably 40,000 or less, 30,000 or less, or 20,000 or less. The lower limit of the weight-average molecular weight of the polymer may be, for example, 1,000 or more, preferably 3,000 or more, and more preferably 6,000 or more. When the weight-average molecular weight of the polymer is within the above range, it becomes easier to control the particle size of the secondary particles, and smoothness tends to be higher.

[0084] The polymer may be supplied to the liquid medium as an alkali metal salt, an organic amine salt, an ammonium salt, or the like, in which at least a portion of the carboxyl groups are neutralized with a neutralizing base such as an alkali metal ion (e.g., sodium ion), an organic ammonium ion, or an ammonium ion. One type of polymer may be used alone, or two or more types may be used in combination. When two or more types of polymers are used, they may be combined in any combination having different compositions, different weight-average molecular weights, or different neutralizing bases, or any combination thereof.

[0085] The polymer supplied to the liquid medium may contain a surfactant other than the polymer containing structural units derived from (meth)acrylic acid. Examples of the surfactant include anionic surfactants having a phosphate group, sulfonic acid group, etc., cationic surfactants having a quaternary ammonium group, etc., and nonionic surfactants. The amount of the surfactant supplied may be, for example, 10% by mass or less, and preferably 1% by mass or less, relative to the amount of the polymer containing structural units derived from (meth)acrylic acid supplied.

[0086] The amount of polymer supplied to the liquid medium may be, for example, 0.5% by mass or more and 5% by mass or less, and preferably 1% by mass or more and 3% by mass or less, based on the total mass of the composite hydroxide produced. If the amount of polymer supplied is 0.5% by mass or more based on the total mass of the composite hydroxide produced, at least one of the smoothness and circularity of the resulting composite hydroxide tends to be improved. Furthermore, if the supply amount is 5% by mass or less, aggregation of secondary particles in the crystallization step is suppressed, and at least one of the smoothness and circularity of the resulting composite hydroxide tends to be further improved.

[0087] The polymer may be supplied to the liquid medium as a polymer solution containing the polymer, either separately from the first solution and the second solution or together with at least one of the first solution and the second solution. When the polymer is supplied together with at least one of the first solution and the second solution, at least one of the first solution and the second solution may contain the polymer, or at least one of the first solution and the second solution may be mixed with the polymer solution and then supplied to the liquid medium. The polymer content in the solution used to supply the polymer to the liquid medium may be, for example, 0.05% by mass or more and 3.1% by mass or less, and preferably 0.1% by mass or more and 0.8% by mass or less, based on the mass of the solution.

[0088] The crystallization step may include, in this order, supplying the first solution and the second solution separately and simultaneously to the liquid medium, and supplying a polymer separately and simultaneously with the first solution and the second solution, or supplying a polymer together with at least one of the first solution and the second solution. In other words, prior to supplying the polymer, portions of the first solution and the second solution may be supplied separately and simultaneously to the liquid medium. By supplying the first solution and the second solution to the liquid medium, the particle size of the composite hydroxide containing nickel and cobalt produced in the liquid medium can be controlled to a desired size. Here, the composite hydroxide may be produced, for example, as seed crystals. By producing a composite hydroxide having a desired particle size in the liquid medium prior to supplying the polymer, aggregation of primary particles is suppressed, and at least one of the smoothness and circularity of the composite hydroxide produced as secondary particles tends to be further improved.

[0089] When the crystallization step includes separately and simultaneously supplying the first and second solutions to the liquid medium prior to supplying the polymer, the supply time of the first and second solutions prior to supplying the polymer may be 2% to 95% of the total supply time, preferably 3% to 40%, and more preferably 5% to 20%. By setting the supply time of the first and second solutions prior to supplying the polymer within this range, as described above, a composite hydroxide having a desired particle size can be produced in the liquid medium, aggregation of primary particles is suppressed, and at least one of smoothness and circularity is further improved.

[0090] The method for producing a nickel-cobalt composite oxide may include a seed crystal generation step prior to the crystallization step. In the seed crystal generation step, for example, a part of the prepared first solution is supplied to a liquid medium to generate a composite hydroxide containing nickel and cobalt in the liquid medium, for example, as seed crystals. In other words, the liquid medium supplied to the crystallization step may be a seed solution containing the composite hydroxide.

[0091] If composite hydroxide particles are generated in advance in a liquid medium prior to the crystallization step, each composite hydroxide particle generated in advance serves as a seed crystal that constitutes one composite hydroxide particle obtained after the crystallization step. This allows the total number of composite hydroxide secondary particles obtained after the crystallization step to be controlled by the number of composite hydroxide particles generated in advance. For example, if a large amount of the first solution is supplied in advance, the number of composite hydroxide particles generated increases, which tends to result in a smaller average particle size of the composite hydroxide secondary particles after the crystallization step. Furthermore, for example, if the pH of the initial liquid medium is made higher than the pH of the resulting reaction solution, the generation of composite hydroxide particles takes precedence over the growth of composite hydroxide particles. This allows the generation of composite hydroxide particles with a more uniform particle size and a narrower particle size distribution to be obtained.

[0092] In the crystallization step, the first solution, the second solution, and the polymer solution may each be continuously or intermittently supplied to the liquid medium. From the viewpoint of improving circularity and smoothness, it is preferable that the first solution is continuously supplied throughout the entire supply time of the first solution in the crystallization step. Here, "continuously throughout the entire supply time" means that there is almost no time during which the solution is not supplied throughout the entire supply time. Furthermore, "almost no time during which the solution is not supplied" means that the time during which the solution is not supplied is less than 1% of the entire supply time.

[0093] Complex hydroxide recovery process In the composite hydroxide recovery step, a composite hydroxide containing nickel and cobalt is separated and recovered from the reaction solution. The composite hydroxide can be recovered from the reaction solution by, for example, filtering the resulting precipitate or centrifuging it, which are commonly used separation means. The resulting precipitate may be subjected to treatments such as washing with water, filtering, and drying. The composition ratio of the metal elements in the composite hydroxide may be approximately the same as the composition ratio of the metal elements in the lithium transition metal composite oxide obtained using these as raw materials.

[0094] The resulting composite hydroxide may have a ratio of the number of moles of nickel to the total number of moles of metal elements contained in the composite hydroxide that is, for example, greater than 0 and less than 1. The ratio of the number of moles of nickel to the total number of moles of metal elements is preferably 0.33 or greater. The ratio of the number of moles of nickel to the total number of moles of metal elements may be 0.4 or greater, or 0.55 or greater. The ratio of the number of moles of nickel to the total number of moles of metal elements is preferably 0.95 or less, or 0.8 or less.

[0095] The resulting composite hydroxide may have a ratio of the number of moles of cobalt to the total number of moles of metal elements contained in the composite hydroxide that is greater than 0 and not greater than 0.6. The ratio of the number of moles of cobalt to the total number of moles of metal elements is preferably 0.02 or greater, 0.05 or greater, 0.1 or greater, or 0.15 or greater. The ratio of the number of moles of cobalt to the total number of moles of metal elements is preferably 0.35 or less. The ratio of the number of moles of cobalt to the total number of moles of metal elements may be 0.3 or less, or 0.25 or less.

[0096] The composite hydroxide may contain at least one of manganese and aluminum in its composition. When the composite hydroxide contains at least one of manganese and aluminum in its composition, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements is, for example, greater than 0, preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and particularly preferably 0.15 or more. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements is, for example, 0.6 or less, preferably 0.35 or less. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements may be 0.33 or less, 0.3 or less, or 0.25 or less.

[0097] The composite hydroxide may contain at least one second metal element in its composition. When the composite hydroxide contains at least one second metal element in its composition, the ratio of the total molar number of the second metal element to the total molar number of the metal elements is, for example, greater than 0, preferably 0.001 or more, more preferably 0.003 or more. Also, the ratio of the total molar number of the second metal element to the total molar number of the metal elements is, for example, 0.02 or less, preferably 0.015 or less, more preferably 0.01 or less.

[0098] The composite hydroxide may have, for example, a composition represented by the following formula (3). Ni j Co k M 1 m M 2 n (OH) 2+γ (3)

[0099] In formula (3), M 1 represents at least one of Mn and Al. M 2 represents at least one selected from the group consisting of Ca, Zr, Ti, Mg, Ta, Nb, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd and Lu. j, k, m, n and γ satisfy 0 < j < 1, 0 < k ≤ 0.6, 0 ≤ m ≤ 0.6, 0 ≤ n ≤ 0.02, 0 ≤ γ ≤ 2. Preferably, 0.33 ≤ j ≤ 0.95, 0.02 ≤ k ≤ 0.35, 0.01 ≤ m ≤ 0.35, 0 ≤ n ≤ 0.015, 0 ≤ γ ≤ 1. Also preferably, M 2 is at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo and W.

[0100] Composite hydroxide heat treatment step In the composite hydroxide heat treatment step, the resulting composite hydroxide is heat treated to obtain a nickel-cobalt composite oxide containing secondary particles formed by aggregation of a plurality of primary particles containing a composite oxide containing nickel and cobalt. The heat treatment dehydrates the composite hydroxide to produce a nickel-cobalt composite oxide. The nickel-cobalt composite oxide may be a precursor of a lithium transition metal composite oxide or a positive electrode active material precursor.

[0101] The heat treatment temperature may be, for example, 105° C. or higher and 900° C. or lower, and preferably 300° C. or higher and 500° C. or lower. The heat treatment time may be, for example, 5 hours or higher and 30 hours or lower, and preferably 10 hours or higher and 20 hours or lower. The heat treatment atmosphere may be an oxygen-containing atmosphere or an air atmosphere.

[0102] The smoothness of the resulting secondary particles containing nickel-cobalt composite oxide may be, for example, greater than 0.74, preferably 0.80 or greater, or 0.85 or greater. The circularity of the secondary particles constituting the nickel-cobalt composite oxide is, for example, 0.80 or greater, preferably 0.85 or greater, or 0.87 or greater. The smoothness and circularity of the secondary particles containing nickel-cobalt composite oxide are measured in the same manner as those of the secondary particles constituting the positive electrode active material. The upper limits of the smoothness and circularity of the secondary particles are 1 or less, and may be less than 1.

[0103] The particle size distribution of secondary particles containing nickel-cobalt composite oxide is the 90% particle size D 90 and 10% particle size D 10 The difference between the particle size D and the particle size D is 50%. 50 The value divided by ((D 90 -D 10 ) / D 50 ) is, for example, less than 0.8, preferably 0.7 or less, 0.6 or less, or 0.5 or less.

[0104] The volume average particle diameter of the secondary particles containing nickel-cobalt composite oxide is, for example, 1 μm or more and 30 μm or less, preferably 1.5 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, and preferably 18 μm or less, more preferably 12 μm or less, and even more preferably 8 μm or less. When the volume average particle diameter of the secondary particles is within the above range, the fluidity is good, and the output power may be further improved when forming a secondary battery. Here, the volume average particle diameter is the 50% particle diameter D corresponding to the cumulative 50% from the small diameter side in the cumulative particle size distribution based on volume. 50 is.

[0105] Secondary particles containing nickel-cobalt composite oxide are formed by the aggregation of multiple primary particles. The average particle size D based on electron microscope observation of the primary particles SEM is, for example, 0.1 μm or more and 1.5 μm or less, preferably 0.12 μm or more, and more preferably 0.15 μm or more. SEMは , preferably 1.2 μm or less, and more preferably 1.0 μm or less. If the average particle size of the primary particles as determined by electron microscope observation is within the above range, the output power of a battery may be improved when the battery is constructed. Here, the average particle size of the primary particles as determined by electron microscope observation is synonymous with the average particle size of the positive electrode active material.

[0106] The secondary particles containing nickel-cobalt composite oxide have a 50% particle size D in the cumulative particle size distribution based on volume. 50 Average particle size D based on electron microscope observation SEM Ratio to D 50 / D SEM may be, for example, 2.5 or more. 50 / D SEM is, for example, 2.5 or more and 150 or less, preferably 5 or more, and more preferably 10 or more. 50 / D SEM is preferably 100 or less, more preferably 50 or less.

[0107] In the nickel-cobalt composite oxide, the ratio of the number of moles of nickel to the total number of moles of metal elements contained in the nickel-cobalt composite oxide may be, for example, greater than 0 and less than 1. The ratio of the number of moles of nickel to the total number of moles of metal elements is preferably 0.33 or greater. The ratio of the number of moles of nickel to the total number of moles of metal elements may be 0.4 or greater, or 0.55 or greater. Furthermore, the ratio of the number of moles of nickel to the total number of moles of metal elements is preferably 0.95 or less, or 0.8 or less.

[0108] The nickel-cobalt composite oxide may have a ratio of the number of moles of cobalt to the total number of moles of metal elements contained in the nickel-cobalt composite oxide that is greater than 0 and not greater than 0.6. The ratio of the number of moles of cobalt to the total number of moles of metal elements is preferably 0.02 or greater, 0.05 or greater, 0.1 or greater, or 0.15 or greater. The ratio of the number of moles of cobalt to the total number of moles of metal elements is preferably 0.35 or less. The ratio of the number of moles of cobalt to the total number of moles of metal elements may be 0.3 or less, or 0.25 or less.

[0109] The nickel-cobalt composite oxide may contain at least one of manganese and aluminum in its composition. When the nickel-cobalt composite oxide contains at least one of manganese and aluminum in its composition, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements is, for example, greater than 0, preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and particularly preferably 0.15 or more. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements is, for example, 0.6 or less, preferably 0.35 or less. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements may be 0.33 or less, 0.3 or less, or 0.25 or less.

[0110] The nickel-cobalt composite oxide may contain at least one second metal element in its composition. When the nickel-cobalt composite oxide contains at least one second metal element in its composition, the ratio of the total molar number of the second metal element to the total molar number of the metal elements is, for example, greater than 0, preferably 0.001 or more, and more preferably 0.003 or more. Also, the ratio of the total molar number of the second metal element to the total molar number of the metal elements is, for example, 0.02 or less, preferably 0.015 or less, and more preferably 0.01 or less.

[0111] The nickel-cobalt composite oxide may have, for example, a composition represented by the following formula (1). Ni q Co r M 1 s M 2 t O 2+α (1)

[0112] In formula (1), M 1 represents at least one of Mn and Al. M 2 represents at least one selected from the group consisting of Ca, Zr, Ti, Mg, Ta, Nb, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu. q, r, s, t, and α satisfy 0 < q < 1, 0 < r ≤ 0.6, 0 ≤ s ≤ 0.6, 0 ≤ t ≤ 0.02, -0.1 ≤ α ≤ 1.1, and q + r + s + t = 1. Preferably, 0.33 ≤ q ≤ 0.95, 0.02 ≤ r ≤ 0.35, 0.01 ≤ s ≤ 0.35, and 0.01 ≤ t ≤ 0.015. Also preferably, M 2 is at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0113] Note that the present disclosure is not limited to the above embodiments. The above embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits the same effects is naturally included in the technical scope of the present disclosure.

Examples

[0114] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples.

[0115] Primary particle size, i.e., the average particle size based on electron microscope observation of primary particles, was measured as follows. Using a scanning electron microscope (SEM), the primary particles that make up the secondary particles were observed at magnifications ranging from 1,000x to 15,000x depending on the particle size. 50 primary particles whose particle outlines could be confirmed were selected, and the equivalent sphere diameter was calculated from the outlines of the selected primary particles using image processing software. The average particle size based on electron microscope observation of the primary particles was determined as the arithmetic mean of the equivalent sphere diameters obtained.

[0116] 10% particle size D in the volume-based cumulative particle size distribution 10 , 50% particle size D 50 and 90% particle size D 90 The cumulative particle size distribution on a volume basis was measured under wet conditions using a laser diffraction particle size distribution analyzer (SALD-3100 manufactured by Shimadzu Corporation), and the particle size distribution was calculated as the particle size corresponding to the cumulative 10%, 50%, and 90% from the smallest diameter side. 90 and D 10 The difference between 50 That is, the particle size distribution of secondary particles was calculated using the following formula: Particle size distribution=(D 90 -D 10 ) / D 50

[0117] The smoothness was measured as follows. The positive electrode active material was filled into epoxy and cured, and then cross-sectional processing was performed to prepare a cross-sectional sample. A scanning electron microscope (Hitachi High-Technologies SU8230; accelerating voltage 3 kV) was used to take a backscattered electron image (magnification: 4000 times). From the obtained backscattered electron image, 20 to 40 secondary particles whose particle outlines could be confirmed were selected, and for each particle, the total perimeter L was calculated using image processing software (ImageJ). opThe outline of the selected particles was then used to determine the best fitting (approximate) ellipse using image processing software (ImageJ), and the major axis a and minor axis b of the approximate ellipse were obtained for each particle. The total perimeter L of the approximate ellipse was calculated using the Gauss-Kummer formula from the obtained major axis a and minor axis b. The total perimeter L of the outline of the particle image (L op ) to the total perimeter of the approximated ellipse (L) ratio (L / L op The smoothness of the secondary particles was calculated as the arithmetic mean of the smoothness of the individual particles.

[0118] The circularity was calculated as the ratio (L1 / L0) of the circumference (L1) calculated from the equivalent circle diameter to the total circumference (L0) of the secondary particle's contour shape, where the diameter of a circle having the same area as the particle image area in the contour shape of the secondary particle is the equivalent circle diameter. Specifically, the circularity of approximately 10,000 particles was measured using a dry particle image analyzer (Morphologi G3S: Malvern; lens magnification 20x), and the circularity of the secondary particles was calculated as the arithmetic average value.

[0119] Tap density was measured as follows: 20 g of sample was placed in a 20 mL measuring cylinder and tapped 150 times from a height of 6.5 cm, after which the volume was measured and the density obtained was taken as the tap density. Bulk density was measured as follows: A sample that had been passed through a sieve (0.5 mm opening) was placed in a 30 mL container until it was heaped, and the heaped portion of the sample was scraped off using a spatula. The weight of the sample remaining in the container was measured to determine the bulk density.

[0120] The specific surface area was measured by the nitrogen gas adsorption method (single point method) using a BET specific surface area measuring device (Macsorb Model-1201 manufactured by Mountec Co., Ltd.).

[0121] Example 1 [Preparation of solid electrolyte] Lithium sulfide and phosphorus pentasulfide were weighed out in an argon atmosphere at a mass ratio of 7:3. The weighed materials were ground and mixed in an agate mortar to obtain sulfide glass, which was used as a solid electrolyte.

[0122] [Preparation of positive electrode] Primary particle size is 0.42 μm, 50% particle size D 50 6.0 μm, smoothness 0.84, circularity 0.88, tap density 2.48 g / cm 3 , specific surface area (BET value) is 0.43m 2 / g, bulk density 1.45g / cm 3 A positive electrode active material having a particle size distribution of 0.52 was prepared.

[0123] 70 parts by mass of the prepared positive electrode active material, 27 parts by mass of the solid electrolyte, and 3 parts by mass of VGCF (vapor grown carbon fiber) were mixed together to obtain a positive electrode mixture.

[0124] [Assembling the evaluation battery] A cylindrical lower die with an outer diameter of 11 mm was inserted from the bottom of a cylindrical outer die with an inner diameter of 11 mm. The upper end of the lower die was fixed in a position halfway between the outer die. In this state, 100 mg of solid electrolyte was poured into the upper end of the lower die from the top of the outer die. After pouring, a cylindrical upper die with an outer diameter of 11 mm was inserted from the top of the outer die. After insertion, a pressure of 100 MPa was applied from above the upper die to form the solid electrolyte into a solid electrolyte layer. After molding, the upper die was removed from the top of the outer die, and 20 mg of positive electrode composite was poured into the top of the solid electrolyte layer from the top of the outer die. After pouring, the upper die was inserted again, and this time a pressure of 100 MPa was applied to form the positive electrode composite into a positive electrode active material layer. After molding, the upper die was fixed, the lower die was released, and the lower die was pulled out from the bottom of the outer die. The negative electrode active material, LiAl alloy, was poured into the bottom of the solid electrolyte layer from the bottom of the lower die. After the charging, the lower mold was inserted again, and a pressure of 350 MPa was applied from below the lower mold to form the negative electrode active material layer. The lower mold was fixed in place under pressure, and a positive electrode terminal was attached to the upper mold and a negative electrode terminal to the lower mold, to obtain an all-solid-state secondary battery for evaluation.

[0125] Example 2 Primary particle size is 0.41 μm, 50% particle size D50 6.3 μm, smoothness 0.87, circularity 0.91, tap density 2.55 g / cm 3 , specific surface area is 0.37m 2 / g, bulk density 1.67g / cm 3 An all-solid-state secondary battery for evaluation was fabricated in the same manner as in Example 1, except that a positive electrode active material having a particle size distribution of 0.43 was used.

[0126] (Comparative Example 1) Primary particle size is 0.66 μm, 50% particle size D 50 6.4 μm, smoothness 0.73, circularity 0.83, tap density 2.09 g / cm 3 , specific surface area is 0.51m 2 / g, bulk density 1.07g / cm 3 An all-solid-state secondary battery for evaluation was fabricated in the same manner as in Example 1, except that a positive electrode active material having a particle size distribution of 0.61 was used.

[0127] [Impedance measurement] The all-solid-state secondary battery for evaluation was charged to a state of charge (SOC) of 50%. It was connected to an AC power source at 25°C, and resistance was measured using the AC impedance method. The frequency of the AC power source was logarithmically varied from 1 MHz to 0.1 Hz. An equivalent circuit was assumed as shown in Figure 1, and the diameter of the arc appearing in the frequency range of 1000 Hz to 5000 Hz was determined by fitting using the least squares method to determine the resistance derived from the positive electrode active material (the resistance component in the impedance of the positive electrode / electrolyte interface). The results are shown in Table 1.

[0128] [Table 1]

[0129] As shown in Table 1, the measured impedance values of Example 1 and Example 2 were significantly reduced compared to Comparative Example 1. In this way, by increasing the smoothness of the secondary particles constituting the positive electrode active material to more than 0.73 and the circularity to more than 0.83, the internal resistance of the all-solid-state secondary battery can be reduced.

[0130] Example 3 Preparation of each solution A mixed solution (1.7 mol / L of nickel, cobalt, and manganese combined; first solution) was prepared by mixing a nickel sulfate solution, a cobalt sulfate solution, and a manganese sulfate solution in a molar ratio of 1:1:1. The total number of moles of metal elements in the mixed solution was 474 moles. A 25% by mass aqueous solution of sodium hydroxide was prepared as a basic aqueous solution. A 12.5% by mass aqueous solution of ammonia (second solution) was prepared as a complex ion-forming solution. A 1:1 blend of surfactants, Aron A-30SL (manufactured by Toagosei Co., Ltd.; 40% by mass aqueous solution of ammonium polyacrylate, weight-average molecular weight = 6000) and Aron A-210 (manufactured by Toagosei Co., Ltd.; 43% by mass aqueous solution of sodium polyacrylate, weight-average molecular weight = 3000), was prepared as a polymer solution.

[0131] Liquid medium preparation 30 liters of water was prepared in a reaction vessel, and sodium hydroxide solution was added so that the pH was 12.5. Nitrogen gas was introduced to replace the atmosphere in the reaction vessel with nitrogen, and a liquid medium was prepared.

[0132] Seed crystal generation process While stirring the liquid medium, the first solution was added to the liquid medium in an amount of 2 moles in terms of the total number of moles of metal elements, to precipitate a composite hydroxide containing nickel, cobalt, and manganese.

[0133] Crystallization process While stirring the prepared liquid medium containing the composite hydroxide, the remaining 472 moles of the first solution, the aqueous sodium hydroxide solution, and the aqueous ammonia solution (second solution) were fed separately and simultaneously while maintaining basicity (pH 11.3). The polymer solution was fed three hours after the first solution, second solution, and aqueous sodium hydroxide solution were fed, and a composite hydroxide containing nickel, cobalt, and manganese was precipitated. The polymer solution was fed in an amount that resulted in 1% by mass of the polymer feed relative to the theoretical yield of the produced composite hydroxide. The first solution was fed continuously for 18 hours. The temperature of the liquid medium during the crystallization process was controlled to be approximately 50°C.

[0134] The precipitate was collected, washed with water, filtered, and dried to obtain a composite hydroxide containing nickel, cobalt, and manganese (hereinafter also referred to as nickel-cobalt composite hydroxide).

[0135] Production of nickel-cobalt composite oxide The nickel-cobalt composite hydroxide was subjected to heat treatment in an air atmosphere at 320°C for 16 hours, and recovered as a transition metal composite oxide containing nickel, cobalt, and manganese (hereinafter also referred to as nickel-cobalt composite oxide).

[0136] The obtained nickel-cobalt transition metal composite oxide was dissolved in inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.338 Co 0.331 Mn 0.331 The physical properties of the obtained nickel-cobalt composite oxide were measured in the same manner as above, and the 50% particle size D 50 The diameter was 5.8 μm, the circularity was 0.91, and the smoothness was 0.80.

[0137] Example 4 The same conditions as in Example 3 were used except that the amount of the first solution supplied in the seed crystal production step was increased compared to that in Example 1, and the amount of the first solution supplied in the crystallization step was correspondingly decreased compared to that in Example 1, and the amount of the polymer solution supplied was changed so that the amount of polymer supplied was 1.4 mass% of the theoretical yield of the produced composite hydroxide.

[0138] The obtained nickel-cobalt composite oxide was dissolved in inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.335 Co 0.333 Mn 0.332 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 3.5 μm, the circularity was 0.85, and the smoothness was 0.84.

[0139] Example 5 The same conditions as in Example 3 were used except that the amount of the first solution supplied in the seed crystal production step was reduced compared to Example 3, and the amount of the first solution supplied in the crystallization step was increased accordingly compared to Example 1.

[0140] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.335 Co 0.333 Mn 0.332 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 7.9 μm, the circularity was 0.85, and the smoothness was 0.89.

[0141] Example 6 The same conditions as in Example 3 were used except that the amount of polymer solution supplied was changed so that the amount of polymer supplied was 2% by mass relative to the theoretical yield of the produced composite hydroxide.

[0142] The obtained nickel-cobalt composite oxide was dissolved in inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.339 Co 0.331 Mn 0.330The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 6.1 μm, the circularity was 0.89, and the smoothness was 0.91.

[0143] Example 7 The experiment was carried out under the same conditions as in Example 3, except that the polymer solution was changed to a surfactant, Frosperse 5000 (manufactured by SNF; 44% aqueous solution of sodium polyacrylate, weight average molecular weight = 6500 to 10000).

[0144] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.340 Co 0.333 Mn 0.328 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 5.9 μm, the circularity was 0.87, and the smoothness was 0.89.

[0145] Example 8 The experiment was carried out under the same conditions as in Example 3, except that the polymer solution was changed to a surfactant, Frosperse 9000 (manufactured by SNF; 40% aqueous solution of sodium polyacrylate, weight average molecular weight = 10,000 to 17,000).

[0146] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.338 Co 0.333 Mn 0.330 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 5.3 μm, the circularity was 0.88, and the smoothness was 0.85.

[0147] Example 9 The experiment was carried out under the same conditions as in Example 3, except that the polymer solution was changed to a surfactant, Frosperse 10000 (manufactured by SNF; 30% aqueous solution of sodium polyacrylate, weight average molecular weight = 50,000 to 70,000).

[0148] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.341 Co 0.331 Mn 0.328 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 8.0 μm, the circularity was 0.87, and the smoothness was 0.88.

[0149] Example 10 The experiment was carried out under the same conditions as in Example 3, except that the polymer solution was changed to a surfactant, Frosperse 15000 (manufactured by SNF; 30% aqueous solution of sodium polyacrylate, weight average molecular weight = 100,000 to 170,000).

[0150] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.339 Co 0.331 Mn 0.329 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 8.5 μm, the circularity was 0.87, and the smoothness was 0.85.

[0151] Example 11 The experiment was carried out under the same conditions as in Example 3, except that the molar ratio of nickel, cobalt, and manganese in the first solution was changed to 9.2:0.4:0.4.

[0152] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.921 Co 0.040 Mn 0.039 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 5.8 μm, the circularity was 0.89, and the smoothness was 0.76.

[0153] (Comparative Example 2) The procedure was carried out under the same conditions as in Example 3, except that the polymer solution was not supplied.

[0154] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.340 Co 0.330 Mn 0.329 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 6.2 μm, the circularity was 0.86, and the smoothness was 0.56.

[0155] (Comparative Example 3) The procedure was carried out under the same conditions as in Example 11, except that the polymer solution was not fed.

[0156] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.920 Co 0.040 Mn 0.040 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 5.8 μm, the circularity was 0.86, and the smoothness was 0.67.

[0157] Comparative Example 4 The experiment was carried out under the same conditions as in Example 3, except that a 40% by mass citric acid solution was fed instead of the polymer solution.

[0158] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.336 Co 0.333 Mn 0.331 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 6.5 μm, the circularity was 0.88, and the smoothness was 0.45.

[0159] (Comparative Example 5) The procedure was carried out under the same conditions as in Example 4, except that the polymer solution was not supplied.

[0160] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.335 Co 0.334 Mn 0.331 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 3.2 μm, the circularity was 0.83, and the smoothness was 0.58.

[0161] (Comparative Example 6) The procedure was carried out under the same conditions as in Example 5, except that the polymer solution was not supplied.

[0162] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni 0.328 Co 0.338 Mn 0.335 The obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 8.2 μm, the circularity was 0.82, and the smoothness was 0.74.

[0163] [Table 2]

[0164] Example 12 The nickel-cobalt composite oxide obtained in Example 3 was dry-mixed with lithium carbonate at a molar ratio of 1.15 to obtain a lithium mixture. The resulting lithium mixture was heat-treated in an air atmosphere at 890°C for 10 hours. A dispersion treatment was then performed to obtain a lithium transition metal composite oxide. To 900 g of the obtained lithium transition metal composite oxide, 136 g of Nb2O5 sol (manufactured by Taki Chemical Co., Ltd.) with a 4.2 mass% concentration was added dropwise while stirring the lithium transition metal composite oxide in a mixer to obtain a niobium deposit. This was then heat-treated in air at 350°C for 9 hours. The heat-treated product was then dispersed in a resin ball mill to obtain the same volume average particle size as the base material after the synthesis process, and then dry-sieved to obtain a Nb-treated lithium transition metal composite oxide as a positive electrode active material.

[0165] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Li 1.15 Ni 0.338 Co 0.331 Mn 0.331 The evaluation results are shown in Table 3.

[0166] Example 13 A lithium transition metal composite oxide was obtained in the same manner as in Example 13, except that the nickel-cobalt composite oxide obtained in Example 4 was used.

[0167] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Li 1.15 Ni 0.335 Co 0.333 Mn 0.332 The evaluation results are shown in Table 3.

[0168] (Comparative Example 7) A lithium transition metal composite oxide was obtained in the same manner as in Example 12, except that the nickel-cobalt composite oxide obtained in Comparative Example 5 was used.

[0169] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Li 1.15 Ni 0.335 Co 0.334 Mn 0.331 The evaluation results are shown in Table 3.

[0170] Example 14 A lithium transition metal composite oxide was obtained in the same manner as in Example 12, except that the nickel-cobalt composite oxide obtained in Example 5 was used.

[0171] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Li 1.15 Ni 0.335 Co0.333 Mn 0.332 The evaluation results are shown in Table 3.

[0172] (Comparative Example 8) A lithium transition metal composite oxide was obtained in the same manner as in Example 12, except that the nickel-cobalt composite oxide obtained in Comparative Example 6 was used.

[0173] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Li 1.15 Ni 0.335 Co 0.334 Mn 0.331 The impedance was O2. The impedance was measured in the same manner as in Example 1, except that a crystalline solid electrolyte further containing chlorine in its composition was used. The impedance value of Comparative Example 1 obtained by this method was set to 1, and the relative value was calculated as the relative impedance. The evaluation results are shown in Table 3.

[0174] The nickel-cobalt composite oxide particles obtained in Examples 3, 7, and Comparative Example 2 were observed using the aforementioned scanning electron microscope (Hitachi High-Technologies SU8230) at an accelerating voltage of 1.5 kV. Figures 2A and 2B are example SEM images of the nickel-cobalt composite oxide particles obtained in Example 3, Figures 3A and 3B are example SEM images of the nickel-cobalt composite oxide particles obtained in Example 7, and Figures 4A and 4B are example SEM images of the nickel-cobalt composite oxide particles obtained in Comparative Example 2. Figures 2A, 3A, and 4A are SEM images observed at a magnification of 15,000x, and Figures 2B, 3B, and 4B are SEM images observed at a magnification of 50,000x. As shown in Figures 2B, 3B, and 4B, it can be seen that the growth of primary particles was suppressed and dense secondary particles were formed in Example 3, which was produced using a polymer solution, compared to Comparative Example 2, which did not use a polymer solution.

[0175] [Table 3]

[0176] As shown in Table 3, it was confirmed that the obtained Examples had improved smoothness and circularity compared to the Comparative Examples, and a reduction in resistance was confirmed. Compared to the ratio of relative impedance of Example 14 to Comparative Example 8, the ratio of relative impedance of Example 12 to Comparative Example 1 was smaller, and the ratio of relative impedance of Example 13 to Comparative Example 7 was even smaller. In other words, it was confirmed that the smaller the particle size, the greater the effect of improving the relative impedance.

[0177] The disclosure of Japanese Patent Application No. 2019-141366 (filing date: July 31, 2019) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. providing a first solution containing nickel ions and cobalt ions; providing a second solution containing a complex ion forming agent; Preparing a liquid medium having a pH in the range of 10 to 13.5; supplying a polymer containing structural units derived from (meth)acrylic acid to the liquid medium while separately and simultaneously supplying the first solution and the second solution to obtain a reaction solution whose pH is maintained in the range of 10 to 13.5; obtaining a composite hydroxide containing nickel and cobalt from the reaction solution; and heat-treating the composite hydroxide to obtain secondary particles composed of an aggregate of a plurality of primary particles comprising a composite oxide containing nickel and cobalt, the smoothness of the secondary particles is greater than 0.74 and less than 1; The circularity of the secondary particles is 0.85 or more and less than 1. A method for producing nickel-cobalt composite oxides for use as precursors of positive electrode active materials for lithium-ion secondary batteries.

2. The reaction solution is separately and simultaneously supplying the first solution and the second solution; supplying the polymer separately from and simultaneously with the first solution and the second solution, or supplying the polymer together with at least one of the first solution and the second solution, in this order.

3. The method according to claim 1 or 2, wherein the liquid medium contains a composite hydroxide containing nickel and cobalt.

4. The method according to any one of claims 1 to 3, wherein the nickel ion concentration in the reaction solution is maintained at 10 ppm or more and 1000 ppm or less.

5. The method according to claim 1 , wherein the first solution is supplied for a period of time of 6 hours or more and 60 hours or less.

6. The secondary particles are composed of a plurality of primary particles each including a composite oxide containing nickel and cobalt, the smoothness of the secondary particles is greater than 0.74 and less than 1; The nickel-cobalt composite oxide for use as a precursor for a positive electrode active material for a lithium ion secondary battery has a circularity of the secondary particles of 0.85 or more and less than 1.

7. the ratio of the number of moles of nickel to the total number of moles of metal elements is greater than 0 and less than 1; 7. The nickel-cobalt composite oxide according to claim 6, wherein the ratio of the number of moles of cobalt to the total number of moles of said metal elements is greater than 0 and not greater than 0.

6.

8. 8. The nickel-cobalt composite oxide according to claim 6, having a composition represented by the following formula (1): Ni ｑ Co ｒ M １ ｓ M ２ ｔ O ２＋α (1) In formula (1), M １ represents at least one of Mn and Al. ２ represents at least one selected from the group consisting of Ca, Zr, Ti, Mg, Ta, Nb, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu. q, r, s, t, and α satisfy the following conditions: 0<q<1, 0<r≦0.6, 0≦s≦0.6, 0≦t≦0.02, −0.1≦α≦1.1, and q+r+s+t=1.

Images