Method for manufacturing 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

To provide a positive electrode active material for a lithium ion secondary battery which can reduce the internal resistance of an all-solid-state lithium ion secondary battery.SOLUTION: A positive electrode active material for a lithium ion secondary battery has a layered structure and includes secondary particles formed of collected primary particles containing a lithium transition metal composite oxide containing lithium, nickel, and cobalt. The smoothness of the secondary particles is larger than 0.73 and is smaller than 1 and the roundness of the secondary particles is larger than 0.83 and is smaller than 1. The positive electrode active material for a lithium-ion secondary battery has a value obtained by dividing the difference between the 90% particle diameter (D90) and the 10% particle diameter (D10) in the cumulative particle size distribution on a volume basis by the 50% particle diameter (D50), and the value is less than 0.61.SELECTED DRAWING: Figure 2A

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing 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 Art

[0002] From the viewpoint of safety and the like, all-solid-state lithium ion secondary batteries using an inorganic solid electrolyte instead of a flammable non-aqueous electrolyte have been studied. In all-solid-state lithium ion secondary batteries, improvement of output characteristics is required. For example, Patent Document 1 proposes a technique of forming a lithium ion conductive oxide layer on the surface of a positive electrode active material, and it is said to be excellent in high output characteristics.

[0003] On the other hand, as a positive electrode active material, a technique of narrowing the particle size distribution of secondary particles formed by aggregation of primary particles into a substantially spherical shape has been proposed, and it is said that the battery can be made to have a higher capacity (see, for example, Patent Document 2). Furthermore, a technique of manufacturing a spherical nickel cobalt aluminum hydroxide precursor material by a coprecipitation method has been proposed, and it is said that cycle characteristics are improved (see, for example, Patent Document 3).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0005] Further improvement in battery characteristics is required for lithium-ion secondary batteries. Further improvement in the characteristics of the positive electrode active material and its precursor used therein is also required.

Means for Solving the Problems

[0006] A first aspect is a method for producing a nickel cobalt composite oxide. The production method includes preparing a first solution containing nickel ions and cobalt ions, preparing a second solution containing a complex ion forming factor, preparing a liquid medium having a pH in the range of 10 or more and 13.5 or less, and supplying the first solution and the second solution separately and simultaneously to the liquid medium while supplying a polymer containing a structural unit derived from (meth)acrylic acid to obtain a reaction solution maintained at a pH in the range of 10 or more and 13.5 or less, obtaining a composite hydroxide containing nickel and cobalt from the reaction solution, and heat-treating the obtained composite hydroxide to obtain secondary particles formed by aggregation of a plurality of primary particles containing 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.

[0007] A second aspect is 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 smoothness of the secondary particles constituting the nickel cobalt composite oxide is greater than 0.74.

[0008] A third aspect is a positive electrode active material containing secondary particles formed by aggregation of a plurality of primary particles containing a lithium transition metal composite oxide having a layered structure and containing lithium, nickel, and cobalt. The smoothness of the secondary particles constituting the positive electrode active material is greater than 0.73, and the circularity of the secondary particles is greater than 0.83.

[0009] A fourth aspect is a positive electrode for an all-solid-state lithium-ion secondary battery including 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 aggregation of a plurality of primary particles containing a lithium transition metal composite oxide. The secondary particles have a smoothness greater than 0.73 and a circularity greater than 0.83.

[0010] The fifth aspect is an all-solid-state lithium-ion secondary battery including the positive electrode, the negative electrode, and the solid electrolyte layer.

Effects of the Invention

[0011] According to one aspect of the present disclosure, it is possible to provide a positive electrode capable of reducing the internal resistance of an all-solid-state lithium-ion secondary battery.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2A

Figure 2B

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Modes for Carrying Out the Invention

[0013] In this specification, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved. In addition, the content of each component in the composition means the total amount of the plurality of substances corresponding to each component in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. Hereinafter, embodiments of the present disclosure will be described in detail. However, the embodiments shown below are examples of 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 for embodying the technical idea of the present disclosure, and the present disclosure is not limited to the positive electrode active material, positive electrode, and all-solid-state lithium-ion secondary battery for an all-solid-state lithium-ion secondary battery shown below.

[0014] Positive electrode for all-solid-state lithium-ion secondary battery A positive electrode for an all-solid-state lithium-ion secondary battery (hereinafter, also simply referred to as a positive electrode) includes 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 aggregation of a plurality of primary particles containing a lithium transition metal composite oxide. The secondary particles constituting the positive electrode active material have a smoothness greater than 0.73 and a circularity greater than 0.83.

[0015] Since the secondary particles constituting the positive electrode active material have a specific shape specified by smoothness and circularity, for example, the contact area between the secondary particles and the solid electrolyte material increases, so it is considered that the resistance at the interface between the secondary particles and the solid electrolyte is reduced. Also, when an adherend containing a specific element is adhered to the surface of the secondary particles for the purpose of improving cycle characteristics, the compound to be adhered is likely to adhere evenly, and the resistance component can be reduced. Furthermore, cracking of the secondary particles due to pressure molding during positive electrode formation can be reduced. This can be considered, for example, because the pressure of the pressure molding is evenly applied to the entire particle.

[0016] Positive electrode active material The positive electrode active material is composed of secondary particles formed by aggregation of 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 aggregation of, for example, 50 or more primary particles. The positive electrode active material may be manufactured by the method for manufacturing a positive electrode active material described later.

[0017] The smoothness of the secondary particles is, for example, greater than 0.73, preferably 0.80 or more, and more preferably 0.83 or more. The upper limit of the smoothness is 1. The smoothness is an index representing the degree of unevenness in the contour shape of the secondary particles, and approaches 1 as the shape is smoother and approaches 0 as the degree of unevenness increases. The above smoothness is obtained as follows. For the contour shape of the target secondary particles, an approximate ellipse having the same area as the contour shape of the target secondary particles is obtained using the fitting function of image processing software. From the major axis a and minor axis b of the approximate ellipse, the total perimeter L of the approximate ellipse is calculated using Gauss-Kummer's formula. Let the total perimeter of the contour shape of the secondary particles be L op and, assuming that the total perimeter of the approximated ellipse is L, the smoothness is the ratio (L / L op ) of the total perimeter (L) of the approximate ellipse to the total perimeter (L op ) of the contour of the particle image. The magnification of the image used for calculating the smoothness of the secondary particles may be appropriately selected according to the particle size of the secondary particles. The magnification may be, for example, 1000 times or more and 10000 times or less, preferably 1000 times or more and 6000 times or less, and more preferably 2000 times or more and 6000 times or less.

[0018] Specifically, a backscattered electron image (magnification: 4000 times) is taken using a scanning electron microscope (SEM), and for 20 to 40 secondary particles whose contours can be confirmed, approximate ellipses are obtained respectively to obtain the major axis a and minor axis b. Also, the total perimeter L op of the contour shape is measured. Based on the following approximate formula, the total perimeter L of the approximated ellipse is calculated from the major axis a and minor axis b, and the ratio (L / L op) is obtained, and the smoothness of the secondary particles is calculated as the arithmetic mean value thereof. Note that being able to confirm the contour of the secondary particles means that the entire contour of the secondary particles can be traced on the image.

[0019]

Number

[0020] The circularity of the secondary particles is, for example, greater than 0.83, preferably 0.86 or more, more preferably 0.90 or more. Note that the upper limit of the circularity is 1. The circularity is an index representing the roundness of the contour shape of the secondary particles, and the closer it is to 1, the closer the shape is to a circle. The circularity is defined as the ratio (L1 / L0) of the circumference (L1) calculated from the equivalent circle diameter to the total perimeter (L0) of the contour shape of the secondary particles when the diameter of the circle having the same area as the particle image area in the contour shape of the secondary particles is taken as the equivalent circle diameter.

[0021] Specifically, using a dry particle image analyzer (Morphologi G3S: manufactured by Malvern; lens magnification 20 times), the individual ratios (L1 / L0) were calculated for about 10,000 particles, and the circularity of the secondary particles was determined as the arithmetic mean value thereof.

[0022] The particle size distribution of the secondary particles is, for example, less than 0.61, preferably 0.60 or less, more preferably 0.58 or less, still more preferably 0.54 or less, and particularly preferably 0.50 or less. The particle size distribution is an index indicating the variation in the particle diameters of the individual secondary particles in the secondary particle group, and the smaller the value, the smaller the variation in the particle diameters. When the particle size distribution of the secondary particles is within the above range, when attaching another element to the surface of the secondary particles, the deposits are more likely to adhere uniformly. In this specification, the particle size distribution is defined as follows. The particle diameters corresponding to 10%, 50%, and 90% cumulative from the small diameter side in the volume-based cumulative particle size distribution are respectively the 10% particle diameter D 10 , 50% particle diameter D 50 and 90% particle diameter D 90 In the case of using, D 90 and D 10 The difference between is D50 The value divided by [ID] is defined as the particle size distribution in this specification. That is, the particle size distribution of the 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 analyzer.

[0023] The volume-average particle size 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 also preferably 12 μm or less, more preferably 8 μm or less. When the volume-average particle size of the secondary particles is within the above range, the fluidity is good, and the output may be further improved when constructing a secondary battery. Here, the volume-average particle size is the 50% particle size D 50 corresponding to the cumulative 50% from the small-diameter side in the volume-based cumulative particle size distribution.

[0024] The secondary particles are formed by aggregation of a plurality of primary particles. The average particle size D SEM based on the electron microscope observation of the primary particles is, for example, 0.1 μm or more and 1.5 μm or less, preferably 0.12 μm or more, more preferably 0.15 μm or more. Also, the average particle size D SEMis preferably 1.2 μm or less, more preferably 1.0 μm or less. If the average particle size based on electron microscope observation of the primary particles is within the above range, the output may be improved when constructing a battery. Here, the average particle size based on electron microscope observation of the primary particles is measured as follows. Using a scanning electron microscope (SEM), the primary particles constituting the secondary particles are observed at a magnification ranging from 1000 times to 15000 times depending on the particle size. 50 primary particles whose outlines can be confirmed are selected, and the spherical equivalent diameter is calculated from the outlines of the selected primary particles using image processing software, and the average particle size based on electron microscope observation of the primary particles is obtained as the arithmetic average value of the obtained spherical equivalent diameters. In one embodiment, the primary particles may have particles having 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 having an average particle size smaller than the primary particles. The average particle size of the particles having an average particle size smaller than the primary particles may be measured based on electron microscope observation in the same manner as above. The outline of the primary particles being able to be confirmed means that the entire outline of the primary particles can be traced on the image.

[0025] 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 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.

[0026] The lithium transition metal composite oxide contained in the primary particles constituting the secondary particles may, for example, contain nickel in its composition and may 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 contains lithium (Li), nickel (Ni), and cobalt (Co), and may further contain at least one of aluminum (Al) and manganese (Mn). In addition to these, 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).

[0027] 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 more. 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 more or 0.55 or more. Also, 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, more preferably 0.8 or less. When the ratio of the number of moles of nickel is within the above-described range, in a all-solid-state lithium-ion secondary battery (hereinafter, also simply referred to as an all-solid-state secondary battery), it is possible to achieve both high-voltage charge-discharge capacity and cycle characteristics.

[0028] 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, still more preferably 0.1 or more, and particularly preferably 0.15 or more. Also, 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, and more preferably 0.35 or less. Further, 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-described range, a sufficient charge-discharge capacity at high voltage can be achieved in the all-solid-state secondary battery.

[0029] 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, still more preferably 0.1 or more, and particularly preferably 0.15 or more. Also, 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. Further, 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-described range, both charge-discharge capacity and safety can be achieved in the all-solid-state secondary battery.

[0030] 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 still more preferably 1.05 or more. Also, 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 still more preferably 1.2 or less. When the ratio of the number 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 the all-solid-state secondary battery using the positive electrode active material containing the obtained lithium transition metal composite oxide is suppressed, so that the output of the all-solid-state secondary battery tends to improve. On the other hand, when the ratio of the number of moles of lithium is 1.5 or less, the initial discharge capacity tends to improve when the positive electrode active material is used for the positive electrode of the all-solid-state secondary battery.

[0031] 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).

[0032] When the lithium transition metal composite oxide contains at least one second metal element, the ratio of the total molar number of the second metal element to the total molar number of the metal elements other than lithium 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 other than lithium is, for example, 0.02 or less, preferably 0.015 or less, more preferably 0.01 or less.

[0033] When represented by composition, examples of the lithium transition metal composite oxide include the lithium transition metal composite oxide represented by the following formula (2). The lithium transition metal composite oxide may have a layered structure and may have a hexagonal crystal structure. Li p Ni x Co y M 1 z M 2 w O 2+β (2)

[0034] 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, and 0 ≤ w ≤ 0.015, may satisfy 0.33 ≤ x ≤ 0.95, 0.01 ≤ y ≤ 0.35, 0 ≤ z ≤ 0.35, and 0 ≤ w ≤ 0.01, and may satisfy 0.33 ≤ x ≤ 0.95, 0.02 ≤ y ≤ 0.35, 0.05 ≤ z ≤ 0.35, and 0 ≤ w ≤ 0.01.

[0035] 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.

[0036] The secondary particles constituting the positive electrode active material may have an attachment containing niobium on their surfaces. 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 a part 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, or the like.

[0037] The amount of the attachment containing niobium in the positive electrode active material is, for example, 0.1 mol% or more and 10 mol% or less in terms of niobium relative 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.

[0038] Examples of the attachment containing niobium include niobium-containing compounds such as lithium niobate. The attachment containing niobium may be obtained by mixing a solution or dispersion of a niobium compound or a solid niobium compound with the secondary particles, and may also be obtained by heat-treating the mixture as necessary.

[0039] The content of the positive electrode active material in the active material layer of the positive electrode is, for example, 60% by mass or more, and preferably 70% by mass or more. Further, the content of the positive electrode active material is, for example, 95% by mass or less, and preferably 90% by mass or less. When the content of the positive electrode active material is 60% by mass or more, a sufficient battery capacity can be obtained. Further, when the content of the positive electrode active material is 95% by mass or less, an increase in resistance can be suppressed.

[0040] Solid electrolyte material The solid electrolyte material applied to the positive electrode may be a 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.

[0041] Examples of sulfide solid electrolyte materials include, for example, 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, 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 (where 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 GeP2S 12 and the like.

[0042] In particular, the sulfide solid electrolyte material preferably includes 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. Further, the ion conductor preferably has an ortho-composed anion structure (for example, PS4 3- structure, SiS4 4- structure, GeS4 4- structure, AlS3 3- structure, BS3 3- structure) as the main component of the anion. Thereby, a sulfide solid electrolyte material with high chemical stability can be obtained. The proportion of the ortho-composed anion structure is preferably 70 mol% or more, more preferably 90 mol% or more, based on the total anion structure in the ion conductor. The proportion of the ortho-composed anion structure can be determined by Raman spectroscopy, NMR, XPS, etc.

[0043] The sulfide solid electrolyte material preferably contains at least one selected from the group consisting of LiI, LiBr, and LiCl in addition to the ion conductor. At least a part of LiI, LiBr, and LiCl is generally considered to exist in a state incorporated into the structure of the ion conductor as an LiI component, an LiBr component, and an LiCl component, respectively. Further, the sulfide solid electrolyte material may have a peak of LiI in X-ray diffraction measurement, but preferably does not have a peak of LiI. Thereby, the Li ion conductivity becomes higher. The same applies to LiBr and LiCl in this regard. The content of LiX (X = I, Cl, Br) in the sulfide solid electrolyte material is, for example, in the range of 10 mol% or more and 30 mol% or less, and preferably in the range of 15 mol% or more and 25 mol% or less. Here, the ratio of LiX refers to the total ratio of LiX contained in the sulfide solid electrolyte material.

[0044] Examples of the oxide solid electrolyte material include Li2O-B2O3-P2O5, Li2O-SiO2, Li-La-Ta-O (e.g., Li5La3Ta2O 12 )), Li-La-Zr-O (e.g., Li7La3Zr2O 12 ), Li-Ba-La-Ta-O (e.g., Li6BaLa2Ta2O 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 the nitride solid electrolyte material include Li3N, etc., and examples of the halide solid electrolyte material include LiI, etc.

[0045] The solid electrolyte material may be a crystalline material or an amorphous material. Further, the solid electrolyte material may be glass or crystallized glass (glass ceramics). Examples of the method for producing glass include a method of performing an amorphization treatment on a raw material composition. Examples of the amorphization treatment include a melt quenching method, a mechanical milling method, and the like. Examples of the method for producing crystallized glass include a method of heating glass to a temperature equal to or higher than the crystallization temperature. Further, examples of the method for producing a crystalline material include a method of heating a raw material composition while it is in a solid state (solid phase method).

[0046] The shape of the solid electrolyte material is not particularly limited, and examples thereof include a substantially spherical shape. The volume average particle diameter (D 50 ) of the solid electrolyte material 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 ) of the solid electrolyte material is, for example, 50 μm or less, and may be 10 μm or less. Further, the Li-ion conductivity of the solid electrolyte material is, at 25°C, for example, 1×10 -5 S / cm or more, preferably 1×10 -4 S / cm or more, and more preferably 1×10 -3 S / cm or more.

[0047] The content of the solid electrolyte material in the active material layer of the positive electrode 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 active material layer of the positive electrode is sufficiently improved. On the other hand, the content of the solid electrolyte material in the active material layer of the positive electrode 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 a sufficient battery capacity can be obtained. Further, in the active material layer of the positive electrode, the content of the solid electrolyte material is preferably lower than the content of the positive electrode active material.

[0048] 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. Also, the ratio of the content of the solid electrolyte material to the content of the positive electrode active material may be, for example, 1.5 or less, preferably 1 or less.

[0049] In addition to the positive electrode active material and the solid electrolyte material, the positive electrode may contain a conductive auxiliary material in the active material layer. By further including the conductive auxiliary material, the electron conductivity in the positive electrode active material layer can be further improved. Examples of the conductive auxiliary material include carbon materials such as acetylene black (AB), ketjen black (KB), vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), and carbon nanofiber (CNF).

[0050] When the positive electrode active material layer of the positive electrode contains a conductive auxiliary material, the content rate of the conductive auxiliary material in the positive electrode active material layer may be, for example, 1% by mass or more, preferably 2% by mass or more. Also, the content rate of the conductive auxiliary material in the positive electrode active material layer may be, for example, 10% by mass or less, preferably 5% by mass or less.

[0051] The positive electrode may further contain a binder in the active material layer. By including the binder, the moldability of the positive electrode active material layer can be further improved. Examples of the binder include polyvinylidene fluoride (PVDF), butylene rubber (BR), styrene-butadiene rubber (SBR), and the like. The positive electrode may further contain a thickening material in the active material layer.

[0052] The form of the positive electrode may be a form having a current collector and a positive electrode active material layer disposed on the current collector, or may be a form consisting only of the positive electrode active material layer formed into a desired shape.

[0053] As a method for manufacturing a positive electrode, it may include a preparation step of preparing a positive electrode composite material containing at least a positive electrode active material and a solid electrolyte material, and a forming step of forming the prepared positive electrode composite material into a desired shape. The forming step may include, if necessary, applying the positive electrode composite material onto a current collector and forming the applied positive electrode composite material.

[0054] Examples of the method for manufacturing a positive electrode composite material include a method including mixing a positive electrode active material and a solid electrolyte material, and, if necessary, also mixing a conductive auxiliary material therewith. The mixing can be, for example, dry mixing and can be performed using a mixer or the like. Also, as a manufacturing method, there can be mentioned a method including adding a dispersion medium to a mixture of a positive electrode active material and a solid electrolyte material to form a slurry, performing a dispersion promotion treatment on the slurry, and removing the dispersion medium from the slurry. Examples of the dispersion promotion treatment include ultrasonic treatment, shaking treatment, and the like.

[0055] Examples of the method for forming a positive electrode composite material include compression molding. The pressure for compression molding can be, for example, 50 MPa or more, and can be 50 MPa or more and 500 MPa or less, or 100 MPa or more and 350 MPa or less. By forming the active material layer of the positive electrode by compression molding, the positive electrode active material and the solid electrolyte material can be brought into close contact, and the interfacial resistance can be reduced.

[0056] All-solid-state lithium-ion secondary battery An 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. By having the secondary particles constituting the positive electrode active material have the specific configuration described above, an all-solid-state lithium-ion secondary battery with reduced internal resistance can be configured.

[0057] Positive electrode The positive electrode includes a form composed of a positive electrode mixture containing the above-described positive electrode active material and solid electrolyte material. In the positive electrode, if necessary, the positive electrode active material layer may be integrally formed with the positive electrode current collector that conducts current collection. The positive electrode active material is composed of secondary particles formed by aggregation of a plurality of primary particles containing a lithium transition metal composite oxide. The smoothness and roundness of the secondary particles are as described above, and the preferred embodiments are the same. The thickness of the positive electrode active material layer is, for example, in the range of 0.1 μm or more and 1000 μm or less, preferably in the range of 0.1 μm or more and 300 μm or less.

[0058] Negative electrode The negative electrode includes a negative electrode active material layer containing at least a negative electrode active material. In the negative electrode, if necessary, the negative electrode active material layer may be integrally formed with the negative electrode current collector that conducts current collection. The negative electrode active material layer may further contain at least one of a solid electrolyte material, a conductive auxiliary material, and a binder, if necessary. The solid electrolyte material, conductive auxiliary material, and binder are as described above.

[0059] 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 (e.g., SiO), etc. The thickness of the negative electrode active material layer is, for example, in the range of 0.1 μm or more and 1000 μm or less, preferably in the range of 0.1 μm or more and 300 μm or less.

[0060] 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 or the like, if necessary. The solid electrolyte material and the binder are as described above.

[0061] The content ratio of the solid electrolyte material contained in the solid electrolyte layer is, for example, in the range of 10% by mass or more and 100% by mass or less, preferably in the range of 50% by mass or more and 100% by mass or less. The thickness of the solid electrolyte layer is, for example, in the range of 0.1 μm or more and 1000 μm or less, preferably in the range of 0.1 μm or more and 300 μm or less. Further, examples of the method for forming the solid electrolyte layer include a method of compression molding the solid electrolyte material.

[0062] Other configurations The all-solid-state lithium-ion secondary battery has at least the positive electrode, negative electrode, and solid electrolyte layer described above. Further, it may have a positive electrode current collector for collecting current of the positive electrode active material layer and a negative electrode current collector for collecting current of the negative electrode active material layer. Examples of the material of the positive electrode current collector include stainless steel (SUS), Ni, Cr, Au, Pt, Al, Fe, Ti, Zn, etc. Examples of the material of the negative electrode current collector include stainless steel (SUS), Cu, Ni, Fe, Ti, Co, Zn, etc. The all-solid-state lithium-ion secondary battery may include an arbitrary battery case such as a battery case made of SUS. Examples of the shape of the all-solid-state lithium-ion secondary battery include coin type, laminate type, cylindrical type, and square type.

[0063] Non-aqueous electrolyte secondary battery The positive electrode active material obtained according to one aspect of the present disclosure can also be used for the positive electrode of a non-aqueous electrolyte secondary battery (hereinafter, non-aqueous electrolyte solution secondary battery) using a non-aqueous electrolyte. Even when used in a non-aqueous electrolyte secondary battery, cracking of secondary particles due to pressure molding during positive electrode formation can be reduced. The non-aqueous electrolyte secondary battery includes, in addition to the positive electrode described above, a negative electrode for non-aqueous electrolyte secondary battery, a non-aqueous electrolyte, a separator, etc. For the negative electrode, non-aqueous electrolyte, separator, etc. in the non-aqueous electrolyte secondary battery, for example, those for non-aqueous electrolyte secondary batteries described in JP-A-2002-075367, JP-A-2011-146390, JP-A-2006-12433 (the entire disclosure contents of these are incorporated herein by reference) can be appropriately used.

[0064] Method for manufacturing positive electrode active material The method for manufacturing a positive electrode active material may include, for example, a composite oxide preparation step of preparing a nickel cobalt composite oxide including secondary particles formed by aggregation of a plurality of primary particles including a composite oxide containing nickel and cobalt, and having a smoothness of the secondary particles greater than 0.74; a lithium mixing step of mixing the nickel cobalt composite oxide and 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 manufactured positive electrode active material includes secondary particles formed by aggregation of a plurality of primary particles including a 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 manufacturing a positive electrode active material may be a method for manufacturing a positive electrode active material including secondary particles formed by aggregation of a plurality of primary particles including a lithium transition metal composite oxide, having a smoothness of the secondary particles greater than 0.73, and having a circularity of the secondary particles greater than 0.83.

[0065] Composite oxide preparation step In the composite oxide preparation step, a nickel cobalt composite oxide including secondary particles formed by aggregation of a plurality of primary particles including a composite oxide containing nickel and cobalt is prepared. 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 appropriately selected from commercially available products for preparation, or may be prepared by the method for manufacturing a nickel cobalt composite oxide described below. Details of the prepared nickel cobalt composite oxide will be described below.

[0066] Lithium mixing step In the lithium mixing step, the prepared nickel cobalt composite oxide and the 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 with a stirring mixer or the like, and a method of preparing a slurry of the nickel cobalt composite oxide and wet mixing it with a mixer such as a ball mill. Examples of the lithium compound include lithium hydroxide, lithium nitrate, lithium carbonate, and mixtures thereof.

[0067] 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, 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. When the lithium ratio is 1.30 or less, an increase in the amount of alkali components present on the surface of the lithium mixture is suppressed, moisture adsorption due to the deliquescence of the alkali components is suppressed, and the handleability tends to be improved.

[0068] Synthesis step 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 aggregation of a plurality of primary particles are contained in the positive electrode active material. In the synthesis step, the lithium transition metal composite oxide may be obtained by diffusion of lithium contained in the lithium compound into the nickel cobalt composite oxide.

[0069] The heat treatment temperature may be, for example, 650 °C or more and 990 °C or less, preferably 700 °C or more and 960 °C or less. When the heat treatment temperature is 650 °C or more, an increase in the unreacted lithium content tends to be suppressed. When the heat treatment temperature is 990 °C or less, decomposition of the generated lithium transition metal composite oxide tends to be suppressed. The heat treatment time may be, for example, 10 hours or more as the time for maintaining the maximum temperature. The atmosphere for the heat treatment may be in the presence of oxygen, preferably an atmosphere containing 10 vol% or more and 100 vol% or less of oxygen.

[0070] In the method for producing a positive electrode active material, after the synthesis step, the heat-treated product obtained as necessary may be subjected to treatments such as coarse crushing, pulverization, and dry sieving.

[0071] Method for producing nickel cobalt composite oxide The 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 factor, a liquid medium preparation step of preparing a liquid medium having a pH in the range of 10 or more and 13.5 or less, and while separately and simultaneously supplying the first solution and the second solution to the liquid medium, supplying a polymer containing a structural unit derived from (meth)acrylic acid to obtain a reaction solution maintained at a pH in the range of 10 or more and 13.5 or less; 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 formed by aggregation of a plurality of primary particles containing a composite oxide containing nickel and cobalt. The smoothness of the secondary particles containing the produced nickel cobalt composite oxide is 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 containing a composite oxide containing nickel and cobalt, wherein the smoothness of the secondary particles is greater than 0.74.

[0072] 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 a salt containing each metal element in water according to the composition of the target nickel cobalt composite oxide. Examples of the types of salts include nitrates, sulfates, and hydrochlorides. Further, when preparing the first solution, an acidic substance (e.g., sulfuric acid aqueous solution) may be added to the water. This may make it easier for the salts containing each metal element to dissolve. In the preparation of the first solution, a basic substance may be further added to adjust the pH. Also, 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 means the total number of moles of nickel and cobalt when the first solution contains nickel and cobalt, and the total number of moles of nickel, cobalt, and manganese when the first solution contains nickel, cobalt, and manganese.

[0073] In addition to nickel ions and cobalt ions, the first solution may further contain at least one of aluminum ions and manganese ions. Further, in addition to these, the first solution may further 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 selected from the group consisting of zirconium, titanium, magnesium, tantalum, niobium, molybdenum, and tungsten.

[0074] The concentration of metal ions such as nickel and cobalt in the first solution may be, for example, 1.0 mol / L or more and 2.6 mol / L or less in total for each metal ion, preferably 1.5 mol / L or more and 2.2 mol / L or less. When the metal ion concentration of the first solution is 1.0 mol / L or more, the productivity is improved because a sufficient amount of crystallized product per reaction tank can be obtained. On the other hand, when the metal ion concentration of the first solution is 2.6 mol / L or less, exceeding the saturation concentration of the metal salt at room temperature is suppressed, and a decrease in the metal ion concentration in the solution due to precipitation of metal salt crystals is suppressed.

[0075] 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 a complex ion with the metal ion 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, preferably 10% by mass or more and 20% by mass or less.

[0076] Liquid medium preparation step In the liquid medium preparation step, a liquid medium having a pH in the range of 10 or more and 13.5 or less is prepared. The liquid medium is adjusted to a solution having a pH of 10 or more and 13.5 or less, for example, by using a predetermined amount of water and a basic solution such as an aqueous sodium hydroxide solution in a reaction vessel. By adjusting the pH of the solution to 10 or more and 13.5 or less, fluctuations in the pH of the reaction solution at the initial stage of the reaction can be suppressed.

[0077] Crystallization step In the crystallization process, while maintaining the pH of the reaction solution to be formed within the range of 10 or more and 13.5 or less, the first solution and the second solution are separately and simultaneously supplied to the liquid medium. Further, a polymer containing a structural unit derived from (meth)acrylic acid is supplied to the liquid medium. Thereby, composite hydroxide particles containing nickel and cobalt can be obtained from the reaction solution. To the liquid medium, in addition to the first solution and the second solution, a basic solution may be simultaneously supplied. Thereby, the pH of the reaction solution can be easily maintained within the range of 10 or more and 13.5 or less.

[0078] In the crystallization process, it is preferable to supply each solution so that the pH of the reaction solution is maintained within the range of 10 or more and 13.5 or less. For example, according to the supply amount of the first solution, by adjusting the supply amount of the second solution, the pH of the reaction solution can be maintained within the range of 10 or more and 13.5 or less. When the pH of the reaction solution is lower than 10, the amount of impurities (for example, sulfuric acid content and nitric acid content other than metals contained in the mixed solution) contained in the obtained composite hydroxide increases, which may cause a decrease in the capacity of the secondary battery as the final product. Further, when the pH is higher than 13.5, a large number of minute secondary particles are generated, and the handleability of the obtained composite hydroxide may deteriorate. Also, the temperature of the reaction solution may be controlled to be, for example, within the range of 25°C or more and 80°C or less.

[0079] In the crystallization process, the concentration of nickel ions in the reaction solution may be maintained, for example, within the range of 10 ppm or more and 1000 ppm or less, preferably within the range of 10 ppm or more and 100 ppm or less. If the concentration of nickel ions is 10 ppm or more, the composite hydroxide is sufficiently precipitated. If the concentration of nickel ions is 1000 ppm or less, since the amount of eluted nickel is small, deviation from the target composition is suppressed. The nickel ion concentration can be adjusted, for example, when an aqueous ammonia solution is used for the complex ion formation solution, by supplying the complex ion formation solution so that the ammonium ion concentration in the reaction solution is within the range of 1000 ppm or more and 15000 ppm or less.

[0080] 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 becomes slow, so that a nickel cobalt composite oxide with higher smoothness tends to be obtained. If it is 60 hours or less, productivity can be further improved.

[0081] 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, the value may be, for example, 0.015 or more and 0.125 or less, preferably 0.020 or more and 0.10 or less. If it is 0.015 or more, productivity can be further improved. If it is 0.125 or less, a nickel cobalt composite oxide with higher smoothness tends to be obtained.

[0082] 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, a dispersant, or the like. By the polymer containing structural units derived from (meth)acrylic acid, foaming of the reaction solution is suppressed, and at least one of the smoothness and roundness of the obtained composite hydroxide is improved. For example, in the case of a general nonionic dispersant as a dispersant, foaming may occur in the reaction solution, making it difficult to control the particle size.

[0083] 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 acrylamide, structural units derived from methacrylamide, and the like. In addition to the structural units derived from (meth)acrylic acid, the polymer may further contain other structural units. Examples of the other structural units include structural units derived from an unsaturated dibasic acid or its acid anhydride.

[0084] The weight average molecular weight of the polymer may be, for example, 50,000 or less, 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, more preferably 6,000 or more. When the weight average molecular weight of the polymer is within the above range, it tends to be easier to control the particle size of the secondary particles and the smoothness becomes higher.

[0085] The polymer may be supplied to the liquid medium as an alkali metal salt, an organic amine salt, an ammonium salt, etc. in which at least a part of the carboxy group is neutralized with a neutralizing base such as an alkali metal ion such as sodium ion, an organic ammonium ion, or an ammonium ion. Further, one kind of polymer may be used alone, or two or more kinds may be used in combination. When two or more kinds of polymers are used, any combination of different compositions, different weight average molecular weights, different neutralizing bases, or a combination of these may be used.

[0086] Other surfactants other than the polymer containing a structural unit derived from (meth)acrylic acid may be used in combination with the polymer supplied to the liquid medium. Examples of other surfactants include anionic surfactants having a phosphate group, a sulfonic acid group, etc., cationic surfactants having a quaternary ammonium group, etc., and nonionic surfactants. The supply amount of other surfactants may be, for example, 10% by mass or less, preferably 1% by mass or less, based on the supply amount of the polymer containing a structural unit derived from (meth)acrylic acid.

[0087] The supply amount of the polymer to the liquid medium may be, for example, 0.5% by mass or more and 5% by mass or less, preferably 1% by mass or more and 3% by mass or less, based on the total mass of the composite hydroxide to be produced. If the supply amount of the polymer is 0.5% by mass or more based on the total mass of the composite hydroxide to be produced, at least one of the smoothness and the circularity of the obtained composite hydroxide tends to be improved. Further, 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 the circularity of the obtained composite hydroxide tends to be further improved.

[0088] The supply of the polymer to the liquid medium may be independent of the first solution and the second solution by supplying a polymer solution containing the polymer, or may be supplied together with at least one of the first solution and the second solution. When 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 a polymer, or at least one of the first solution and the second solution and the polymer solution may be mixed and then supplied to the liquid medium. The content of the polymer in the solution used for supplying the polymer to the liquid medium may be, for example, 0.05% by mass or more and 3.1% by mass or less, preferably 0.1% by mass or more and 0.8% by mass or less, based on the mass of the solution.

[0089] The crystallization step may include, in this order, separately and simultaneously supplying the first solution and the second solution to the liquid medium, and separately and simultaneously supplying the polymer separately from 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 other words, prior to the supply of the polymer, a part of the first solution and the second solution may be separately and simultaneously supplied 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 formed in the liquid medium can be controlled to a desired size. Here, the composite hydroxide may be formed, for example, as seed crystals. By generating a composite hydroxide having a desired particle size in the liquid medium prior to the supply of the polymer, aggregation of primary particles is suppressed, and at least one of the smoothness and roundness of the composite hydroxide formed as secondary particles tends to be further improved.

[0090] In the crystallization process, when the first solution and the second solution are separately and simultaneously supplied to the liquid medium prior to the supply of the polymer, the supply time of the first solution and the second solution prior to the supply of the polymer may be 2% or more and 95% or less of the total supply time. Preferably, it is 3% or more and 40% or less, and more preferably 5% or more and 20% or less. By setting the supply time of the first solution and the second solution prior to the supply of the polymer within this range, as described above, a composite hydroxide having a desired particle size can be generated in the liquid medium, aggregation of primary particles can be suppressed, and at least one of smoothness and roundness is further improved.

[0091] 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, by supplying a part of the prepared first solution to the liquid medium, a composite hydroxide containing nickel and cobalt is generated in the liquid medium as, for example, a seed crystal. That is, the liquid medium used in the crystallization step may be a seed solution containing a composite hydroxide.

[0092] If composite hydroxide particles are generated in advance in the liquid medium prior to the crystallization step, one particle of the pre-generated composite hydroxide becomes a seed crystal that constitutes one particle of the composite hydroxide obtained after the crystallization step. Thereby, the total number of secondary particles of the composite hydroxide obtained after the crystallization step can be controlled by the number of the pre-generated composite hydroxide particles. For example, when a large amount of the first solution is supplied in advance, the number of generated composite hydroxide particles increases, so the average particle size of the secondary particles of the composite hydroxide after the crystallization step tends to decrease. Also, for example, when the pH of the initial liquid medium is made higher than the pH of the resulting reaction solution, the generation of composite hydroxide particles is prioritized over the growth of composite hydroxide particles. Thereby, composite hydroxide particles having a more uniform particle size can be generated, and composite hydroxide particles having a narrower particle size distribution can be obtained.

[0093] In the crystallization process, the first solution, the second solution, and the polymer solution may each be supplied continuously or intermittently to the liquid medium. From the viewpoint of improving circularity and smoothness, it is preferable that the first solution is supplied continuously throughout the entire supply time of the first solution in the crystallization process. Here, "continuously throughout the entire supply time" means that there is almost no time during which it is not supplied throughout the entire supply time. Also, having almost no supply time means that the time during which it is not supplied is less than 1% of the total supply time.

[0094] Composite hydroxide recovery step In the composite hydroxide recovery step, a composite hydroxide containing nickel and cobalt is separated and recovered from the reaction solution. The recovery of the composite hydroxide from the reaction solution can be carried out by commonly used separation means such as filtering the generated precipitate and centrifugation. Treatments such as washing with water, filtration, and drying may be performed on the obtained precipitate. The composition ratio of the metal elements in the composite hydroxide may be substantially the same as the composition ratio of the metal elements in the lithium transition metal composite oxide obtained using these as raw materials.

[0095] The obtained 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, 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 more. Also, the ratio of the number of moles of nickel to the total number of moles of metal elements may be 0.4 or more, or 0.55 or more. Also, 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.

[0096] 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 more 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 more, 0.05 or more, 0.1 or more, or 0.15 or more. Also, the ratio of the number of moles of cobalt to the total number of moles of metal elements is preferably not more than 0.35. The ratio of the number of moles of cobalt to the total number of moles of metal elements may be not more than 0.3 or not more than 0.25.

[0097] 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, still more preferably 0.1 or more, and particularly preferably 0.15 or more. Also, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements is, for example, not more than 0.6, preferably not more than 0.35. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements may be not more than 0.33, not more than 0.3, or not more than 0.25.

[0098] 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 number of moles of the second metal element to the total number of moles of 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 number of moles of the second metal element to the total number of moles of metal elements is, for example, not more than 0.02, preferably not more than 0.015, and more preferably not more than 0.01.

[0099] The composite hydroxide may have a composition represented by, for example, the following formula (3). Ni j Co k M 1 m M 2 n (OH)2+γ (3)

[0100] 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, and 0 ≤ γ ≤ 2. Preferably, 0.33 ≤ j ≤ 0.95, 0.02 ≤ k ≤ 0.35, 0.01 ≤ m ≤ 0.35, 0 ≤ n ≤ 0.015, and 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.

[0101] Composite hydroxide heat treatment step In the composite hydroxide heat treatment step, the obtained 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. By heat treatment, the composite hydroxide is dehydrated to form a nickel-cobalt composite oxide. The nickel-cobalt composite oxide may be a precursor of a lithium transition metal composite oxide or may be a precursor of a positive electrode active material.

[0102] The heat treatment temperature may be, for example, 105°C or higher and 900°C or lower, preferably 300°C or higher and 500°C or lower. The heat treatment time may be, for example, 5 hours or longer and 30 hours or shorter, preferably 10 hours or longer and 20 hours or shorter. The heat treatment atmosphere may be an atmosphere containing oxygen or may be an air atmosphere.

[0103] The smoothness of the secondary particles containing the nickel-cobalt composite oxide may be greater than, for example, 0.74, preferably 0.80 or more, or 0.85 or more. The circularity of the secondary particles constituting the nickel-cobalt composite oxide is, for example, 0.80 or more, preferably 0.85 or more, or 0.87 or more. Here, the smoothness and circularity of the secondary particles containing the nickel-cobalt composite oxide are measured in the same manner as those in the secondary particles constituting the positive electrode active material. Further, the upper limit of the smoothness and circularity of the secondary particles is 1 or less, and may be less than 1.

[0104] The particle size distribution of the secondary particles containing the nickel-cobalt composite oxide is the difference between the 90% particle size D 90 and the 10% particle size D 10 in the volume-based cumulative particle size distribution, divided by the 50% particle size D 50 ((D 90 -D 10 ) / D 50 ), and is, for example, less than 0.8, preferably 0.7 or less, 0.6 or less, or 0.5 or less.

[0105] The volume average particle size of the secondary particles containing the 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, still more preferably 3 μm or more, and also preferably 18 μm or less, more preferably 12 μm or less, and still more preferably 8 μm or less. When the volume average particle size of the secondary particles is within the above range, the fluidity is good, and the output may be further improved when forming a secondary battery. Here, the volume average particle size is the 50% particle size D 50 corresponding to the cumulative 50% from the small-diameter side in the volume-based cumulative particle size distribution.

[0106] The secondary particles containing the nickel-cobalt composite oxide are formed by aggregation of a plurality of primary particles. The average particle size D SEM based on electron microscope observation of the primary particles is, for example, 0.1 μm or more and 1.5 μm or less, preferably 0.12 μm or more, more preferably 0.15 μm or more. Also, the average particle size D SEMは, preferably 1.2 μm or less, more preferably 1.0 μm or less. When the average particle size based on the electron microscope observation of the primary particles is within the above range, the output may be improved when constructing a battery. Here, the average particle size based on the electron microscope observation of the primary particles is synonymous with the average particle size in the positive electrode active material.

[0107] The secondary particles containing nickel cobalt composite oxide have a 50% particle size D in the cumulative particle size distribution based on volume 50 The average particle size D based on the electron microscope observation SEM The ratio D to 50 / D SEM May be, for example, 2.5 or more. The ratio D 50 / D SEM Is, for example, 2.5 or more and 150 or less, preferably 5 or more, more preferably 10 or more. Also, the ratio D 50 / D SEM Is preferably 100 or less, more preferably 50 or less.

[0108] 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 more. The ratio of the number of moles of nickel to the total number of moles of metal elements may be 0.4 or more, or 0.55 or more. Also, 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.

[0109] In the nickel cobalt composite oxide, the ratio of the number of moles of cobalt to the total number of moles of metal elements contained in the nickel cobalt composite oxide may be greater than 0 and 0.6 or less. The ratio of the number of moles of cobalt to the total number of moles of metal elements is preferably 0.02 or more, 0.05 or more, 0.1 or more, or 0.15 or more. Also, 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.

[0110] 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 molar number of manganese and aluminum to the total molar number of metal elements is, for example, greater than 0, preferably 0.01 or more, more preferably 0.05 or more, still more preferably 0.1 or more, and particularly preferably 0.15 or more. Also, the ratio of the total molar number of manganese and aluminum to the total molar number of metal elements is, for example, 0.6 or less, preferably 0.35 or less. The ratio of the total molar number of manganese and aluminum to the total molar number of metal elements may be 0.33 or less, 0.3 or less, or 0.25 or less.

[0111] 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 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 metal elements is, for example, 0.02 or less, preferably 0.015 or less, and more preferably 0.01 or less.

[0112] The nickel-cobalt composite oxide may have a composition represented by the following formula (1), for example. Ni q Co r M 1 s M 2 t O 2+α (1)

[0113] In formula (1), M 1 represents at least one of Mn and Al. M 2represents 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.

[0114] Note that the present disclosure is not limited to the above-described embodiments. The above-described 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 operational effects is, of course, included in the technical scope of the present disclosure.

Examples

[0115] Hereinafter, the present disclosure will be specifically described by way of examples, but the present disclosure is not limited to these examples.

[0116] The primary particle size, that is, the average particle size based on the electron microscope observation of the primary particles, was measured as follows. Using a scanning electron microscope (SEM), the primary particles constituting the secondary particles were observed at magnifications in the range of 1000 to 15000 times according to the particle size. 50 primary particles whose outlines could be confirmed were selected, and the spherical equivalent diameter was calculated from the outlines of the selected primary particles using image processing software, and the average particle size based on the electron microscope observation of the primary particles was determined as the arithmetic mean value of the obtained spherical equivalent diameters.

[0117] The 10% particle size D in the volume-based cumulative particle size distribution 10 , the 50% particle size D 50 and the 90% particle size D 90Using a laser diffraction particle size distribution analyzer (SALD-3100 manufactured by Shimadzu Corporation), the volume-based cumulative particle size distribution was measured under wet conditions, and the particle sizes corresponding to 10%, 50%, and 90% cumulative from the smaller diameter side were determined. Also, the particle size distribution was calculated by dividing the difference between D 90 and D 10 by D 50 . That is, the particle size distribution of the secondary particles was determined by the following formula. Particle size distribution = (D 90 - D 10 ) / D 50

[0118] The smoothness was measured as follows. After filling the positive electrode active material with epoxy and curing it, cross-section processing was performed to prepare a cross-section sample. Using a scanning electron microscope (Hitachi High-Technologies SU8230; acceleration voltage 3 kV), a backscattered electron image (magnification; 4000 times) was taken. For the obtained backscattered electron image, 20 to 40 secondary particles whose particle contours could be confirmed were selected, and for each particle, the total perimeter L op was measured using image processing software (ImageJ). Also, for the contours of the selected particles, the most fitting (approximate) ellipse was obtained using image processing software (ImageJ), and the major axis a and minor axis b of the approximate ellipse were obtained for each particle. Using an approximate formula of Gauss-Kummer's formula from the obtained major axis a and minor axis b, the total perimeter L of the approximate ellipse was determined. The smoothness was determined as the ratio (L / L op ) of the total perimeter (L) of the approximate ellipse to the total perimeter (L op ) of the contour of the particle image. The smoothness of the secondary particles was calculated as the arithmetic mean of the smoothness of individual particles.

[0119] The circularity was determined as the ratio (L1 / L0) of the circumference (L1) calculated from the equivalent circle diameter to the total perimeter (L0) of the contour shape of the secondary particles when the diameter of the circle having the same area as the particle image area in the contour shape of the secondary particles is defined as the equivalent circle diameter. Specifically, using a dry particle image analyzer (Morphologi G3S: Malvern; lens magnification 20 times), the individual circularities of about 10,000 particles were measured, and the circularity of the secondary particles was determined as the arithmetic mean value thereof.

[0120] The tap density was measured as follows. 20 g of the sample was put into a 20 mL graduated cylinder, and after tapping 150 times from a height of 6.5 cm, the volume was measured, and the obtained density was taken as the tap density. The bulk density was measured as follows. The sample passed through a sieve (mesh size 0.5 mm) was put into a 30 mL container until it became a heap, and the top part of the sample heap was scraped off using a spatula. The bulk density was determined by measuring the weight of the sample remaining in the container.

[0121] The specific surface area was measured by the nitrogen gas adsorption method (one-point method) using a BET specific surface area measuring device (Macsorb Model-1201 manufactured by Mountech Co., Ltd.).

[0122] (Example 1) [Fabrication of Solid Electrolyte] Under an argon atmosphere, lithium sulfide and phosphorus pentasulfide were weighed so that the molar ratio thereof was 7:3. The weighed substances were pulverized and mixed in an agate mortar to obtain a sulfide glass. This was used as the solid electrolyte.

[0123] [Fabrication of Positive Electrode] A positive electrode active material having a primary particle size of 0.42 μm, a 50% particle size D 50 of 6.0 μm, a smoothness of 0.84, a circularity of 0.88, a tap density of 2.48 g / cm 3 , a specific surface area (BET value) of 0.43 m 2 / g, a bulk density of 1.45 g / cm 3 , and a particle size distribution of 0.52 was prepared.

[0124] 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 to obtain a positive electrode mixture.

[0125] [Assembly of Evaluation Battery] A cylindrical lower mold with an outer diameter of 11 mm was inserted into a cylindrical outer mold with an inner diameter of 11 mm from the lower part of the outer mold. The upper end of the lower mold was fixed at the middle position of the outer mold. In this state, 100 mg of solid electrolyte was introduced from the upper part of the outer mold to the upper end of the lower mold. After the introduction, a cylindrical upper mold with an outer diameter of 11 mm was inserted from the upper part of the outer mold. After the insertion, a pressure of 100 MPa was applied from above the upper mold to form the solid electrolyte into a solid electrolyte layer. After the forming, the upper mold was pulled out from the upper part of the outer mold, and 20 mg of positive electrode composite material was introduced from the upper part of the outer mold to the upper part of the solid electrolyte layer. After the introduction, the upper mold was inserted again, and this time a pressure of 100 MPa was applied to form the positive electrode composite material into a positive electrode active material layer. After the forming, the upper mold was fixed, the fixing of the lower mold was released and it was pulled out from the lower part of the outer mold, and LiAl alloy which is a negative electrode active material was introduced from the lower part of the lower mold to the lower part of the solid electrolyte layer. After the introduction, 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 into a negative electrode active material layer. With the pressure applied, the lower mold was fixed, a positive electrode terminal was attached to the upper mold, and a negative electrode terminal was attached to the lower mold to obtain an all-solid-state secondary battery for evaluation.

[0126] (Example 2) The primary particle size is 0.41 μm, and the 50% particle size D 50 is 6.3 μm, the smoothness is 0.87, the circularity is 0.91, and the tap density is 2.55 g / cm 3 , the specific surface area is 0.37 m 2 / g, the bulk density is 1.67 g / cm 3 , and 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 with a particle size distribution of 0.43 was used.

[0127] (Comparative Example 1) The primary particle size is 0.66 μm, and the 50% particle size D 50 is 6.4 μm, the smoothness is 0.73, the circularity is 0.83, and the tap density is 2.09 g / cm 3 , the specific surface area is 0.51 m 2 / g, the bulk density is 1.07 g / cm 3 , and 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 with a particle size distribution of 0.61 was used.

[0128] [Impedance Measurement] The all-solid-state secondary battery for evaluation was charged and set to a state of 50% state of charge (SOC). It was connected to an AC power supply at 25°C, and resistance measurement was performed by the AC impedance method. The frequency of the AC power supply was logarithmically changed from 1 MHz to 0.1 Hz. Assuming an equivalent circuit as shown in Fig. 1, the diameter of the arc appearing in the frequency range of 1000 Hz or more and 5000 Hz or less was taken as the resistance derived from the positive electrode active material (the resistance component in the impedance at the positive electrode / electrolyte interface) by fitting using the least squares method. The results are shown in Table 1.

[0129]

Table 1

[0130] As shown in Table 1, the measured impedance values of Example 1 and Example 2 were significantly reduced compared to Comparative Example 1. Thus, by making the smoothness of the secondary particles constituting the positive electrode active material greater than 0.73 and the circularity greater than 0.83, the internal resistance of the all-solid-state secondary battery can be reduced.

[0131] (Example 3) Preparation of each solution A mixed solution (nickel, cobalt, and manganese combined concentration of 1.7 mol / L; first solution) was prepared by mixing a nickel sulfate solution, a cobalt sulfate solution, and a manganese sulfate solution so that the molar ratio of the metal elements was 1:1:1. The total number of moles of metal elements in the mixed solution was 474 moles. As a basic aqueous solution, a 25% by mass sodium hydroxide aqueous solution was prepared. As a complex ion forming solution, a 12.5% by mass aqueous ammonia solution (second solution) was prepared. As a polymer solution, a blend of 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) with a mass ratio of 1:1 was prepared.

[0132] Preparation of the liquid medium 30 liters of water was prepared in a reaction vessel, and a sodium hydroxide solution was added to adjust the pH to 12.5. Nitrogen gas was introduced to replace the inside of the reaction vessel with nitrogen to prepare a liquid medium.

[0133] Seed crystal formation step While stirring the liquid medium, 2 moles of the first solution in terms of the total number of moles of metal elements was added to the liquid medium to precipitate a composite hydroxide containing nickel, cobalt, and manganese.

[0134] Crystallization step While stirring the liquid medium containing the prepared composite hydroxide, 472 moles of the remaining first solution, an aqueous sodium hydroxide solution, and an aqueous ammonia solution (second solution) were separately and simultaneously supplied while maintaining the basicity (pH 11.3). The polymer solution was supplied starting 3 hours after the start of the supply of the first solution, the second solution, and the aqueous sodium hydroxide solution to precipitate a composite hydroxide containing nickel, cobalt, and manganese. The supply amount of the polymer solution was 1% by mass as the supply amount of the polymer with respect to the theoretical yield of the produced composite hydroxide. In addition, the supply of the first solution was continuously supplied over 18 hours. In the crystallization step, the temperature of the liquid medium was controlled to be about 50°C.

[0135] The precipitate was recovered, followed by washing with water, filtration, and drying to obtain a composite hydroxide containing nickel, cobalt, and manganese (hereinafter also referred to as nickel-cobalt composite hydroxide).

[0136] Production of nickel-cobalt composite oxide The nickel-cobalt composite hydroxide was heat-treated at 320°C for 16 hours in an air atmosphere and recovered as a transition metal composite oxide containing nickel, cobalt, and manganese (hereinafter also referred to as nickel-cobalt composite oxide).

[0137] After dissolving the obtained nickel-cobalt transition metal composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.338 Co 0.331 Mn 0.331It was O2. Regarding the obtained nickel-cobalt composite oxide, when the physical properties were measured in the same manner as above, the 50% particle size D 50 was 5.8 μm, the circularity was 0.91, and the smoothness was 0.80.

[0138] (Example 4) The amount of the first solution supplied in the seed crystal formation step was increased compared to Example 1, and accordingly, the amount of the first solution supplied in the crystallization step was decreased compared to Example 1, and the amount of the polymer solution was changed so that the supply amount of the polymer was 1.4% by mass based on the theoretical yield of the produced composite hydroxide, and the same conditions as in Example 3 were carried out except for this.

[0139] After dissolving the obtained nickel-cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.335 Co 0.333 Mn 0.332 O2. Also, for the obtained nickel-cobalt composite oxide, the 50% particle size D 50 was 3.5 μm, the circularity was 0.85, and the smoothness was 0.84.

[0140] (Example 5) The amount of the first solution supplied in the seed crystal formation step was decreased compared to Example 3, and accordingly, the amount of the first solution supplied in the crystallization step was increased compared to Example 1, and the same conditions as in Example 3 were carried out except for this.

[0141] After dissolving the obtained nickel-cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.335 Co 0.333 Mn 0.332 O2. Also, for the obtained nickel-cobalt composite oxide, the 50% particle size D 50 was 7.9 μm, the circularity was 0.85, and the smoothness was 0.89.

[0142] (Example 6) The same conditions as in Example 3 were carried out except that the amount of the polymer solution was changed so that the supply amount of the polymer was 2% by mass based on the theoretical yield of the produced composite hydroxide.

[0143] After dissolving the obtained nickel-cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.339 Co 0.331 Mn 0.330 O2. Also, the obtained nickel-cobalt composite oxide had a 50% particle size D 50 of 6.1 μm, a circularity of 0.89, and a smoothness of 0.91.

[0144] (Example 7) The procedure was carried out under the same conditions as in Example 3, except that the polymer solution was changed to Fluosperse 5000 (manufactured by SNF; 44% aqueous solution of sodium polyacrylate, weight average molecular weight = 6500 to 10000), which is a surfactant.

[0145] After dissolving the obtained nickel-cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.340 Co 0.333 Mn 0.328 O2. Also, the obtained nickel-cobalt composite oxide had a 50% particle size D 50 of 5.9 μm, a circularity of 0.87, and a smoothness of 0.89.

[0146] (Example 8) The procedure was carried out under the same conditions as in Example 3, except that the polymer solution was changed to Fluosperse 9000 (manufactured by SNF; 40% aqueous solution of sodium polyacrylate, weight average molecular weight = 10000 to 17000), which is a surfactant.

[0147] After dissolving the obtained nickel-cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.338 Co 0.333 Mn 0.330 O2. Also, the obtained nickel-cobalt composite oxide had a 50% particle size D 50 of 5.3 μm, a circularity of 0.88, and a smoothness of 0.85.

[0148] (Example 9) The experiment was carried out under the same conditions as in Example 3, except that the polymer solution was changed to Fluosperse 10000 (manufactured by SNF; 30% aqueous solution of sodium polyacrylate, weight average molecular weight = 50000 to 70000), which is a surfactant.

[0149] After dissolving the obtained nickel cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.341 Co 0.331 Mn 0.328 O2. Also, the obtained nickel cobalt composite oxide had a 50% particle size D 50 of 8.0 μm, a circularity of 0.87, and a smoothness of 0.88.

[0150] (Example 10) The experiment was carried out under the same conditions as in Example 3, except that the polymer solution was changed to Fluosperse 15000 (manufactured by SNF; 30% aqueous solution of sodium polyacrylate, weight average molecular weight = 100000 to 170000), which is a surfactant.

[0151] After dissolving the obtained nickel cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.339 Co 0.331 Mn 0.329 O2. Also, the obtained nickel cobalt composite oxide had a 50% particle size D 50 of 8.5 μm, a circularity of 0.87, and a smoothness of 0.85.

[0152] (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.

[0153] After dissolving the obtained nickel cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.921 Co 0.040 Mn 0.039It was O2. Also, the obtained nickel cobalt composite oxide had a 50% particle size D 50 of 5.8 μm, a circularity of 0.89, and a smoothness of 0.76.

[0154] (Comparative Example 2) It was carried out under the same conditions as in Example 3 except that the polymer solution was not supplied.

[0155] After dissolving the obtained nickel cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.340 Co 0.330 Mn 0.329 O2. Also, the obtained nickel cobalt composite oxide had a 50% particle size D 50 of 6.2 μm, a circularity of 0.86, and a smoothness of 0.56.

[0156] (Comparative Example 3) It was carried out under the same conditions as in Example 11 except that the polymer solution was not supplied.

[0157] After dissolving the obtained nickel cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.920 Co 0.040 Mn 0.040 O2. Also, the obtained nickel cobalt composite oxide had a 50% particle size D 50 of 5.8 μm, a circularity of 0.86, and a smoothness of 0.67.

[0158] (Comparative Example 4) It was carried out under the same conditions as in Example 3 except that a 40 mass% citric acid solution was supplied instead of the polymer solution.

[0159] After dissolving the obtained nickel cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.336 Co 0.333 Mn 0.331 O2. Also, the obtained nickel cobalt composite oxide had a 50% particle size D 50It was 6.5 μm in particle size, 0.88 in circularity, and 0.45 in smoothness.

[0160] (Comparative Example 5) It was carried out under the same conditions as in Example 4 except that the polymer solution was not supplied.

[0161] After dissolving the obtained nickel-cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.335 Co 0.334 Mn 0.331 O2. Also, the obtained nickel-cobalt composite oxide had a 50% particle size D 50 of 3.2 μm, a circularity of 0.83, and a smoothness of 0.58.

[0162] (Comparative Example 6) It was carried out under the same conditions as in Example 5 except that the polymer solution was not supplied.

[0163] After dissolving the obtained nickel-cobalt composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Ni 0.328 Co 0.338 Mn 0.335 O2. Also, the obtained nickel-cobalt composite oxide had a 50% particle size D 50 of 8.2 μm, a circularity of 0.82, and a smoothness of 0.74.

[0164]

Table 2

[0165] (Example 12) The nickel cobalt composite oxide obtained in Example 3 and lithium carbonate were dry-mixed so that the molar ratio of lithium carbonate to the nickel cobalt composite oxide was 1.15 times to obtain a lithium mixture. The obtained lithium mixture was heat-treated at 890 °C for 10 hours in an air atmosphere. Thereafter, a dispersion treatment was performed to obtain a lithium transition metal composite oxide. With respect to 900 g of the obtained lithium transition metal composite oxide, using an Nb2O5 sol manufactured by Takaki Chemical Co., Ltd. having a concentration of 4.2% by mass as a niobium source, 136 g of the sol was dropped while stirring the lithium transition metal composite oxide with a mixer to obtain a niobium deposit. Thereafter, heat treatment was performed at 350 °C for 9 hours in the air. The obtained heat-treated product was subjected to a dispersion treatment using a resin ball mill so as to have the same volume average particle diameter as that of the base material after the synthesis step, and was sieved dry to obtain a positive electrode active material as a lithium transition metal composite oxide subjected to Nb treatment.

[0166] After dissolving the obtained lithium transition metal composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Li 1.15 Ni 0.338 Co 0.331 Mn 0.331 O2. The evaluation results are shown in Table 3.

[0167] (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.

[0168] After dissolving the obtained lithium transition metal composite oxide in an inorganic acid and performing chemical analysis by ICP emission spectrometry, its composition was Li 1.15 Ni 0.335 Co 0.333 Mn 0.332 O2. The evaluation results are shown in Table 3.

[0169] (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.

[0170] After dissolving the obtained lithium transition metal composite oxide in an inorganic acid, chemical analysis was performed by ICP emission spectrometry. As a result, its composition was Li 1.15 Ni 0.335 Co 0.334 Mn 0.331 O2. The evaluation results are shown in Table 3.

[0171] (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.

[0172] After dissolving the obtained lithium transition metal composite oxide in an inorganic acid, chemical analysis was performed by ICP emission spectrometry. As a result, its composition was Li 1.15 Ni 0.335 Co 0.333 Mn 0.332 O2. The evaluation results are shown in Table 3.

[0173] (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.

[0174] After dissolving the obtained lithium transition metal composite oxide in an inorganic acid, chemical analysis was performed by ICP emission spectrometry. As a result, its composition was Li 1.15 Ni 0.335 Co 0.334 Mn 0.331 O2. Regarding the impedance, it was measured in the same manner as in Example 1, except that a solid electrolyte containing chlorine in its composition and being crystalline was used. When the impedance value of Comparative Example 1 obtained by this method was set to 1, the relative value was calculated as the relative impedance. The evaluation results are shown in Table 3.

[0175] The nickel-cobalt composite oxide particles obtained in Example 3, Example 7, and Comparative Example 2 were observed at an acceleration voltage of 1.5 kV using the above-described scanning electron microscope (Hitachi High-Technologies SU8230). FIGS. 2A and 2B are examples of SEM images of the nickel-cobalt composite oxide particles obtained in Example 3, FIGS. 3A and 3B are examples of SEM images of the nickel-cobalt composite oxide particles obtained in Example 7, and FIGS. 4A and 4B are examples of SEM images of the nickel-cobalt composite oxide particles obtained in Comparative Example 2. Also, FIGS. 2A, 3A, and 4A are SEM images observed at a magnification of 15,000 times, and FIGS. 2B, 3B, and 4B are SEM images observed at a magnification of 50,000 times. As shown in FIGS. 2B, 3B, and 4B, it can be seen that in Example 3 prepared using the polymer solution, the growth of primary particles is suppressed and dense secondary particles are formed as compared with Comparative Example 2 in which the polymer solution was not used.

[0176]

Table 3

[0177] As shown in Table 3, it was confirmed that the obtained examples were improved in both smoothness and roundness as compared with the comparative examples, and a reduction in resistance was confirmed. The ratio of the relative impedance of Example 12 to Comparative Example 1 was smaller than the ratio of the relative impedance of Example 14 to Comparative Example 8, and the ratio of the relative impedance of Example 13 to Comparative Example 7 was even smaller. That is, it was confirmed that the smaller the particle size, the greater the improvement effect of the relative impedance.

[0178] 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 in this specification are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually stated to be incorporated by reference.

Claims

1. A positive electrode active material for a lithium ion secondary battery, comprising secondary particles having a layered structure and formed by aggregation of a plurality of primary particles including a lithium transition metal composite oxide containing lithium, nickel, and cobalt, the smoothness of the secondary particles is greater than 0.73 and less than 1, and the circularity of the secondary particles is greater than 0.83 and less than 1; The positive electrode active material for a lithium ion secondary battery has a 90% particle size D ９０ and 10% particle size D １０ The difference between this and 50% particle size D ５０ The value divided by is less than 0.61, The secondary particles have a niobium-containing deposit on their surfaces.

2. 2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the secondary particles have a volume average particle size of 1 μm or more and 30 μm or less.

3. In the lithium transition metal composite oxide, the ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium is greater than 0 and less than 1; 3. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium is greater than 0 and not greater than 0.

6.

4. 4. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the lithium transition metal composite oxide has a composition represented by the following formula (2): Li ｐ Ni ｘ Co ｙ M １ ｚ M ２ ｗ O ２＋β (2) Here, p, x, y, z, w, and β satisfy the following conditions: 1.0≦p≦1.3, 0<x<1, 0<y≦0.6, 0≦z≦0.6, 0≦w≦0.02, x+y+z+w=1, −0.1≦β≦0.

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.

5. The secondary particles have a 50% particle size D ５０ Average particle size D based on electron microscope observation ＳＥＭ Ratio D to ５０ / D ＳＥＭ The positive electrode active material for a lithium ion secondary battery according to claim 1 , wherein the value of σ is 5 or more and 100 or less.

6. The primary particles have an average particle size D ＳＥＭ The positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the average particle size is 0.15 µm or more and 1.0 µm or less.

7. an active material layer including a positive electrode active material and a solid electrolyte material; the positive electrode active material includes secondary particles formed by aggregation of a plurality of primary particles including a lithium transition metal composite oxide containing lithium, nickel, and cobalt, the smoothness of the secondary particles is greater than 0.73 and less than 1; the circularity of the secondary particles is greater than 0.83 and less than 1; The positive electrode active material has a 90% particle size D ９０ and 10% particle size D １０ The difference between this and 50% particle size D ５０ The value divided by is less than 0.61, The secondary particles have a surface on which a deposit containing niobium is formed.

8. 8. The positive electrode according to claim 7, wherein the secondary particles have a volume average particle size of 1 μm or more and 30 μm or less.

9. An all-solid-state lithium ion secondary battery comprising the positive electrode according to claim 7 or 8, a negative electrode, and a solid electrolyte layer.

10. 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; heat-treating the composite hydroxide 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; mixing the nickel-cobalt composite oxide with a lithium compound to obtain a lithium mixture; and heat-treating the lithium mixture to obtain a lithium transition metal composite oxide containing nickel and cobalt and having a layered structure.

11. an active material layer containing a positive electrode active material; the positive electrode active material includes secondary particles formed by aggregation of a plurality of primary particles including a lithium transition metal composite oxide containing lithium, nickel, and cobalt, the smoothness of the secondary particles is greater than 0.73 and less than 1; the circularity of the secondary particles is greater than 0.83 and less than 1; The positive electrode active material has a 90% particle size D ９０ and 10% particle size D １０ The difference between this and 50% particle size D ５０ The value divided by is less than 0.61, The secondary particles have a surface on which a deposit containing niobium is formed.

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