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

Abstract

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

[0002] From a safety standpoint, all-solid-state lithium-ion secondary batteries that use inorganic solid electrolytes instead of flammable non-aqueous electrolytes are being considered. Improvements in output characteristics are required for all-solid-state lithium-ion secondary batteries. For example, Patent Document 1 proposes a technique for forming a lithium-ion conductive oxide layer on the surface of the positive electrode active material, which is said to have excellent high-power characteristics.

[0003] On the other hand, a technique has been proposed to narrow the particle size distribution of secondary particles formed by the aggregation of primary particles into a nearly spherical shape as a positive electrode active material, which is said to enable higher battery capacity (see, for example, Patent Document 2). Furthermore, a technique has been proposed to produce spherical nickel-cobalt-aluminum hydroxide precursor material by coprecipitation, which is said to improve cycle characteristics (see, for example, Patent Document 3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2007 / 004590 [Patent Document 2] International Publication No. 2013 / 183711 [Patent Document 3] International Publication No. 2016 / 180288 [Overview of the project] [Problems that the invention aims to solve]

[0005] There is a need for further improvements in the battery characteristics of lithium-ion secondary batteries. Furthermore, there is a need to improve the properties of the positive electrode active material and its precursors used in them. [Means for solving the problem]

[0006] The first embodiment is a method for producing 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 to 13.5; supplying the first solution and the second solution separately and simultaneously to the liquid medium, while supplying a polymer containing constituent units derived from (meth)acrylic acid, to obtain a reaction solution in which the pH is maintained in the range of 10 to 13.5; obtaining a composite hydroxide containing nickel and cobalt from the reaction solution; and heat-treating the obtained composite hydroxide to obtain secondary particles consisting of aggregates of primary particles containing the nickel-cobalt composite oxide. The smoothness of the secondary particles constituting the nickel-cobalt composite oxide may be greater than 0.74.

[0007] The second embodiment is a nickel-cobalt composite oxide containing secondary particles formed by the aggregation of multiple primary particles containing a composite oxide comprising nickel and cobalt. The smoothness of the secondary particles constituting the nickel-cobalt composite oxide is greater than 0.74.

[0008] The third embodiment is a positive electrode active material having a layered structure and containing secondary particles which are aggregates of primary particles containing a lithium transition metal composite oxide including 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] The fourth embodiment is a positive electrode for an all-solid-state lithium-ion secondary battery comprising a positive electrode active material and an active material layer containing a solid electrolyte material. The positive electrode active material includes secondary particles formed by the aggregation of multiple 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 embodiment is an all-solid-state lithium-ion secondary battery comprising the positive electrode, the negative electrode, and a solid electrolyte layer. [Effects of the Invention]

[0011] According to one aspect of this disclosure, a positive electrode capable of reducing the internal resistance of an all-solid-state lithium-ion secondary battery can be provided. [Brief explanation of the drawing]

[0012] [Figure 1] This is an equivalent circuit diagram of an all-solid-state secondary battery. [Figure 2A] This is an example of a scanning electron microscope (SEM) image of the nickel-cobalt composite oxide according to Example 3. [Figure 2B] This is a further enlarged SEM image of Figure 2A. [Figure 3A] This is an example of an SEM image of the nickel-cobalt composite oxide according to Example 7. [Figure 3B] This is a further enlarged SEM image of Figure 3A. [Figure 4A] This is an example of an SEM image of a nickel-cobalt composite oxide related to Comparative Example 2. [Figure 4B] This is a further enlarged SEM image of Figure 4A. [Modes for carrying out the invention]

[0013] In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved. Furthermore, the content of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if multiple substances corresponding to each component exist in the composition. Embodiments of this disclosure will now be described in detail. However, the embodiments shown below are examples of methods for producing nickel-cobalt composite metal oxides, nickel-cobalt composite oxides, positive electrode active materials, positive electrodes for all-solid-state lithium-ion secondary batteries, and all-solid-state lithium-ion secondary batteries, which embody the technical concept of this disclosure. This disclosure is not limited to the positive electrode active materials, positive electrodes, and all-solid-state lithium-ion secondary batteries shown below.

[0014] Positive electrode for all-solid-state lithium-ion secondary batteries The positive electrode for an all-solid-state lithium-ion secondary battery (hereinafter also simply referred to as the positive electrode) comprises an active material layer containing a positive electrode active material and a solid electrolyte material. The positive electrode active material contained in the active material layer is composed of secondary particles made up of multiple 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] The secondary particles constituting the positive electrode active material have a specific shape, defined by their smoothness and circularity. This increases the contact area between the secondary particles and the solid electrolyte material, thus reducing resistance at the interface between the secondary particles and the solid electrolyte. Furthermore, when deposits containing specific elements are applied to the surface of the secondary particles to improve cycle characteristics, the compound is more likely to adhere evenly, reducing the resistance component. Additionally, cracking of secondary particles due to pressure molding during positive electrode formation can be reduced. This can be attributed, for example, to the uniform application of pressure molding across the entire particle.

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

[0017] The smoothness of the secondary particle is, for example, greater than 0.73, preferably 0.80 or higher, and more preferably 0.83 or higher. The upper limit of the smoothness is 1. Smoothness is an index representing the degree of unevenness in the contour shape of the secondary particle; the smoother the shape, the closer it approaches 1, and the greater the degree of unevenness, the closer it approaches 0. The above smoothness is determined as follows: An approximate ellipse with the same area as the contour shape of the target secondary particle is found using the fitting function of image processing software. The total circumference L of the approximate ellipse is calculated from the major axis a and minor axis b of the approximate ellipse using the Gauss-Kummer formula. op If we assume that the total circumference of the approximated ellipse is L, then the smoothness is the total circumference of the contour of the particle image (L op The ratio of the total circumference (L) of the approximate ellipse to (L / L) op ) The magnification of the image used to calculate the smoothness of the secondary particles can 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 scanning electron microscope (SEM) is used to capture backscattered electron images (magnification: 4000x), and for 20 to 40 secondary particles whose contours can be confirmed, an approximate ellipse is determined for each to obtain the major axis a and minor axis b. The total circumference L of the contour shape is also determined. op Measure the following. Calculate the total circumference L of the approximated ellipse based on the following approximation formula using the major axis a and minor axis b, and then calculate the ratio (L / L) for each secondary particle. 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 diameter of a circle having the same area as the particle image area in the contour shape of the secondary particles to the total circumference (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 diameter of the circle.

[0021] Specifically, using a dry particle image analyzer (Morphologi G3S: 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 deposit is 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% of the 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 When they are used, the difference between D 90 and D 10 is D50 The value obtained by dividing by is defined as the particle size distribution in this specification. That is, the particle size distribution of secondary particles is defined by the following equation. 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, and 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, which corresponds to the cumulative 50% from the small diameter side in the volume-based cumulative particle size distribution. 50 That is the case.

[0024] Secondary particles are formed by the aggregation of multiple primary particles. The average particle size D is determined based on electron microscopy observation of primary particles. SEM For example, the particle size is 0.1 μm or more and 1.5 μm or less, preferably 0.12 μm or more, and more preferably 0.15 μm or more. Also, the average particle size D based on electron microscope observation of primary particles. SEMThe particle size is preferably 1.2 μm or less, more preferably 1.0 μm or less. If the average particle size based on electron microscope observation of 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 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 1000x to 15000x depending on the particle size. Fifty primary particles whose contours can be confirmed are selected, and the spherical equivalent diameter is calculated from the contours of the selected primary particles using image processing software. The average particle size based on electron microscope observation of primary particles is obtained as the arithmetic mean of the obtained spherical equivalent diameters. In one embodiment, primary particles may have particles with a smaller average particle size than the primary particles attached to their surface. In another embodiment, primary particles may be an aggregate of particles with a smaller average particle size than the primary particles. The average particle size of the particles with a smaller average particle size than the primary particles may be measured based on electron microscope observation in the same manner as above. Confirmation of the contour of a primary particle means that the entire contour of the primary particle can be traced on the image.

[0025] Secondary particles are defined as the 50% particle size D in the cumulative particle size distribution based on volume. 50 Average particle size D based on electron microscope observations SEM Ratio D 50 / D SEM For example, it may be 2.5 or higher. Ratio D 50 / D SEM For example, it is between 2.5 and 150, preferably 5 or more, and more preferably 10 or more. Also, ratio D 50 / D SEM It 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 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 primary metallic 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). Furthermore, lithium transition metal composite oxides may further contain, in addition to these, at least one secondary metallic 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 secondary metallic 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 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 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. Furthermore, the ratio 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 moles of nickel is within the above range, it is possible to achieve both high-voltage charge / discharge capacity and cycle characteristics in an all-solid-state lithium-ion secondary battery (hereinafter also simply referred to as an all-solid-state secondary battery).

[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, even more preferably 0.1 or more, and particularly preferably 0.15 or more. Furthermore, 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. The ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium may also 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 range, sufficient charge and discharge capacity at high voltage can be achieved in the all-solid-state secondary battery.

[0029] When a lithium transition metal composite oxide contains at least one of manganese and aluminum, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements other than lithium is, for example, greater than 0, preferably 0.01 or more, more preferably 0.05 or more, even more preferably 0.1 or more, and particularly preferably 0.15 or more. Furthermore, 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. Alternatively, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements other than lithium may be 0.33 or less, 0.3 or less, or 0.25 or less. When the ratio of the total number of moles of manganese and aluminum is within the above-mentioned range, both charge / discharge capacity and safety can be achieved in an all-solid-state secondary battery.

[0030] In lithium transition metal composite oxides, the ratio of moles of lithium to the total number of moles of metals other than lithium is, for example, 0.95 or more, preferably 1.0 or more, more preferably 1.03 or more, and even more preferably 1.05 or more. Furthermore, the ratio of moles of lithium to the total number of moles of metals other than lithium is, for example, 1.5 or less, preferably 1.3 or less, more preferably 1.25 or less, and even more preferably 1.2 or less. When the ratio of moles of lithium is 0.95 or more, the interfacial resistance generated at the interface between the positive electrode surface and the solid electrolyte in an all-solid-state secondary battery using the resulting lithium transition metal composite oxide-containing positive electrode active material is suppressed, thus tending to improve the output of the all-solid-state secondary battery. On the other hand, when the ratio of moles of lithium is 1.5 or less, the initial discharge capacity when the positive electrode active material is used as the positive electrode in an all-solid-state secondary battery tends to improve.

[0031] When the lithium transition metal composite oxide contains nickel, cobalt, and manganese, the ratio of moles 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 nickel, cobalt, manganese, and aluminum, the ratio of moles 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 those 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 ≤ .02, x + y + z + w = 1, and -0.1 ≤ β ≤ 0.1. x, y, z, and w may satisfy 0 < x < 1, 0 ≤ y ≤ 0.6, 0 ≤ z ≤ 0.6, 0 ≤ w ≤ 0.015, may satisfy 0.33 ≤ x ≤ 0.95, 0. .01 ≤ y ≤ 0.35, 0 ≤ z ≤ 0.35, 0 ≤ w ≤ 0.01, and may satisfy 0.33 ≤ x ≤ 0.95, 0.02 ≤ y ≤ 0.35, 0.05 ≤ z ≤ 0.35, 0 ≤ w ≤ 0.01.

[0035] M9] 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 deposits containing niobium on their surface. These niobium-containing deposits may be attached to the surface of the secondary particles, or to the grain boundaries of the secondary particles. Furthermore, these niobium-containing deposits may be attached to the surface of the primary particles constituting the secondary particles, or may be solid-dissolved in at least some of the primary particles. In addition to niobium-containing deposits, the secondary particles constituting the positive electrode active material may also have deposits containing ionic conductive compounds such as boron, silicon, and titanium.

[0037] The amount of niobium-containing deposits on the positive electrode active material is, for example, 0.1 mol% to 10 mol% in terms of niobium relative to the lithium transition metal composite oxide, preferably 0.2 mol% to 8 mol%. When the amount of niobium deposits is within this range, the resistance component can be reduced while maintaining good cycle characteristics.

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

[0039] The content of the positive electrode active material in the positive electrode active material layer is, for example, 60% by mass or more, preferably 70% by mass or more. Alternatively, the content of the positive electrode active material is, for example, 95% by mass or less, preferably 90% by mass or less. A positive electrode active material content of 60% by mass or more provides sufficient battery capacity. Furthermore, a positive electrode active material content of 95% by mass or less suppresses an increase in resistance.

[0040] solid electrolyte material The solid electrolyte material applied to the positive electrode can be any material that has lithium ion conductivity, and examples of inorganic solid electrolyte materials include 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 Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (wherein m and n are positive numbers. Z is at least one selected from the group consisting of Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (wherein x and y are positive numbers. M is at least one selected from the group consisting of P, Si, Ge, B, Al, Ga, and In), Li 10 GeP2S 12 These are some examples.

[0042] In particular, the sulfide solid electrolyte material preferably comprises an ionic conductor containing Li, A (where A is at least one selected from the group consisting of P, Si, Ge, Al, and B), and S. Furthermore, the ionic conductor has an ortho-composition anionic structure (e.g., PS4). 3- Structure, SiS4 4- Structure, GeS4 4- Structure, AlS3 3- Structure, BS3 3- It is preferable that the anion structure is the main component of the anion. This makes it possible to obtain a sulfide solid electrolyte material with high chemical stability. The proportion of the anion structure in the ortho composition is preferably 70 mol% or more, and more preferably 90 mol% or more, relative to the total anion structure in the ion conductor. The proportion of the anion structure in the ortho composition can be determined by Raman spectroscopy, NMR, XPS, etc.

[0043] The sulfide solid electrolyte material preferably contains, in addition to the ion conductor, at least one selected from the group consisting of LiI, LiBr, and LiCl. At least a portion of LiI, LiBr, and LiCl is usually considered to exist incorporated into the structure of the ion conductor as LiI, LiBr, and LiCl components, respectively. Furthermore, the sulfide solid electrolyte material may have a LiI peak in X-ray diffraction measurements, but it is preferable that it does not have a LiI peak. This results in higher Li ion conductivity. The same applies to LiBr and LiCl. The content of LiX (X=I,Cl,Br) in the sulfide solid electrolyte material is, for example, in the range of 10 mol% to 30 mol%, and preferably in the range of 15 mol% to 25 mol%. Here, the proportion of LiX refers to the total proportion of LiX contained in the sulfide solid electrolyte material.

[0044] Examples of oxide solid electrolyte materials include Li2O-B2O3-P2O5, Li2O-SiO2, and Li-La-Ta-O (e.g., Li5La3Ta2O). 12 ), Li-La-Zr-O (for example, Li7La3Zr2O) 12 ), Li-Ba-La-Ta-O (for example, Li6BaLa2Ta2O) 12 ), Li 1+x Si x P 1-x O4(0≦x<1, for example 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 Examples include (0≦x<1). Furthermore, examples of nitride solid electrolyte materials include Li3N, and examples of halide solid electrolyte materials include LiI.

[0045] The solid electrolyte material may be a crystalline material or an amorphous material. Furthermore, the solid electrolyte material may be glass or crystallized glass (glass ceramics). A method for producing glass includes, for example, a method of amorphous treatment of the raw material composition. Examples of amorphous treatments include the melt-and-cool method and the mechanical milling method. A method for producing crystallized glass includes, for example, a method of heating the glass to a temperature above its crystallization temperature. A method for producing crystalline materials includes, for example, a method of heating the raw material composition while it is still in solid form (solid-phase method).

[0046] The shape of the solid electrolyte material is not particularly limited, but for example, a roughly spherical shape can be given. The volume-average particle size (D) of the solid electrolyte material. 50 ) is, for example, 0.1 μm or larger, and may be 0.5 μm or larger. On the other hand, the volume-average particle size (D) of the solid electrolyte material 50 The particle size is, for example, 50 μm or less, and may also be 10 μm or less. Furthermore, the Li ion conductivity of the solid electrolyte material is, for example, 1 × 10⁻¹⁶ at 25°C. -5 S / cm or more, 1 × 10 -4 Preferably, S / cm or higher, 1 × 10 -3 A value of S / cm or higher is more preferable.

[0047] The content of the solid electrolyte material in the positive electrode active material layer is, for example, 1% by mass or more, preferably 5% by mass or more, and more preferably 10% by mass or more. When the content of the solid electrolyte material is 1% by mass or more, the Li ion conductivity of the positive electrode active material layer is sufficiently improved. On the other hand, the content of the solid electrolyte material in the positive electrode active material layer is, for example, 60% by mass or less, preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less. When the content of the solid electrolyte material is 60% by mass or less, the relative content of the positive electrode active material does not become too low, and sufficient battery capacity can be obtained. Furthermore, it is preferable that the content of the solid electrolyte material in the positive electrode active material layer is lower than the content of the positive electrode active material.

[0048] Furthermore, the ratio of the solid electrolyte material content to the positive electrode active material content in the positive electrode active material layer (solid electrolyte material / positive electrode active material) is, for example, 0.01 or more, preferably 0.1 or more. Also, the ratio of the solid electrolyte material content to the positive electrode active material content is, for example, 1.5 or less, preferably 1 or less.

[0049] In addition to the positive electrode active material and solid electrolyte material, the positive electrode may also contain a conductive additive in the active material layer. Further inclusion of a conductive additive can further improve the electronic conductivity of the positive electrode's active material layer. Examples of conductive additives include carbon materials such as acetylene black (AB), Ketjenblack (KB), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0050] When the active material layer of the positive electrode contains a conductive additive, the content of the conductive additive in the active material layer of the positive electrode may be, for example, 1% by mass or more, preferably 2% by mass or more. Alternatively, the content of the conductive additive in the active material layer of the positive electrode 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. The inclusion of a binder can further improve the moldability of the active material layer of the positive electrode. Examples of binders include polyvinylidene fluoride (PVDF), butylene rubber (BR), and styrene-butadiene rubber (SBR). The positive electrode may further contain a thickening agent in the active material layer.

[0052] The positive electrode may have a form comprising a current collector and a positive electrode active material layer placed on the current collector, or it may consist only of a positive electrode active material layer molded into a desired shape.

[0053] A method for manufacturing a positive electrode may include a preparation step of preparing a positive electrode mixture containing at least a positive electrode active material and a solid electrolyte material, and a molding step of shaping the prepared positive electrode mixture into a desired shape. The molding step may optionally include applying the positive electrode mixture onto a current collector and shaping the applied positive electrode mixture.

[0054] A method for manufacturing a positive electrode composite material may include mixing a positive electrode active material and a solid electrolyte material, and optionally mixing in a conductive additive. The mixing can be done by dry mixing, for example, using a mixer or the like. Another manufacturing method may include adding a dispersion medium to the mixture of the positive electrode active material and the solid electrolyte material to form a slurry, performing a dispersion-promoting treatment on the slurry, and removing the dispersion medium from the slurry. Examples of dispersion-promoting treatments include ultrasonic treatment and shaking treatment.

[0055] One possible method for forming the positive electrode composite material is compression molding. The compression molding pressure can be, for example, 50 MPa or higher, and can be between 50 MPa and 500 MPa, or between 100 MPa and 350 MPa. By forming the positive electrode active material layer by compression molding, the positive electrode active material and the solid electrolyte material can be brought into close contact, thereby reducing interfacial resistance.

[0056] All-solid-state lithium-ion secondary battery An all-solid-state lithium-ion secondary battery includes a positive electrode comprising a positive electrode active material layer containing a positive electrode active material and a solid electrolyte material, a negative electrode comprising 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 constructed.

[0057] positive electrode The positive electrode includes a form composed of a positive electrode composite material containing the positive electrode active material and solid electrolyte material described above. In the positive electrode, the positive electrode active material layer may be formed integrally with the positive electrode current collector that collects current, if necessary. The positive electrode active material is composed of secondary particles which are aggregates of multiple primary particles containing lithium transition metal composite oxide. The smoothness and circularity of the secondary particles are as previously described, and the same applies to the preferred embodiment. The thickness of the positive electrode active material layer is, for example, in the range of 0.1 μm to 1000 μm, and preferably in the range of 0.1 μm to 300 μm.

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

[0059] Examples of negative electrode active materials include carbon active materials, metallic active materials, and oxide active materials. Examples of carbon active materials include graphite, hard carbon, and soft carbon. Examples of metallic active materials include In, Al, Si, Sn, and alloys containing at least these. Examples of oxide active materials include niobium oxide (e.g., Nb2O5) and lithium titanate (e.g., Li4Ti5O5). 12 Examples include silicon dioxide (e.g., SiO₂). The thickness of the negative electrode active material layer is, for example, in the range of 0.1 μm to 1000 μm, and preferably in the range of 0.1 μm to 300 μm.

[0060] solid electrolyte layer The solid electrolyte layer is a layer positioned 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 as needed. The solid electrolyte material and binder are as previously described.

[0061] The solid electrolyte material content in the solid electrolyte layer is, for example, within the range of 10% by mass or more and 100% by mass or less, preferably within the range of 50% by mass or more and 100% by mass or less. The thickness of the solid electrolyte layer is, for example, within the range of 0.1 μm or more and 1000 μm or less, preferably within the range of 0.1 μm or more and 300 μm or less. As for the method of forming the solid electrolyte layer, for example, a method of compression molding of the solid electrolyte material can be mentioned.

[0062] Other configurations An all-solid-state lithium-ion secondary battery has at least the positive electrode, negative electrode, and solid electrolyte layer described above. Furthermore, it may have a positive electrode current collector for collecting current from the positive electrode active material layer and a negative electrode current collector for collecting current from the negative electrode active material layer. Examples of materials for the positive electrode current collector include stainless steel (SUS), Ni, Cr, Au, Pt, Al, Fe, Ti, and Zn. Examples of materials for the negative electrode current collector include stainless steel (SUS), Cu, Ni, Fe, Ti, Co, and Zn. The all-solid-state lithium-ion secondary battery may also be equipped with any battery case, such as a SUS battery case. Examples of shapes for the all-solid-state lithium-ion secondary battery include coin type, laminate type, cylindrical type, and prismatic type.

[0063] Nonaqueous electrolyte secondary battery A positive electrode active material obtained according to one aspect of this disclosure can also be used as a positive electrode for a non-aqueous electrolyte secondary battery (hereinafter referred to as a non-aqueous electrolyte secondary battery) using a non-aqueous electrolyte. Even when used in a non-aqueous electrolyte secondary battery, it is possible to reduce the cracking of secondary particles due to pressure molding during positive electrode formation. In addition to the positive electrode described above, a non-aqueous electrolyte secondary battery is composed of a negative electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte, a separator, etc. For the negative electrode, non-aqueous electrolyte, separator, etc. in a non-aqueous electrolyte secondary battery, for example, those for non-aqueous electrolyte secondary batteries described in Japanese Patent Application Publication No. 2002-075367, Japanese Patent Application Publication No. 2011-146390, Japanese Patent Application Publication No. 2006-12433 (the entire disclosures of these are incorporated herein by reference), etc., can be used as appropriate.

[0064] Method for manufacturing positive electrode active material A method for producing a positive electrode active material may include, for example, a composite oxide preparation step of preparing a nickel-cobalt composite oxide in which secondary particles are made up of a plurality of primary particles containing a composite oxide containing nickel and cobalt, and the smoothness of the secondary particles is greater than 0.74; a lithium mixing step of mixing the nickel-cobalt composite oxide with a lithium compound to obtain a lithium mixture; and a synthesis step of heat-treating the lithium mixture to obtain a lithium transition metal composite oxide containing nickel and cobalt and having a layered structure. The produced positive electrode active material includes secondary particles made up of a plurality of primary particles containing 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. A method for producing a positive electrode active material may be a method for producing a positive electrode active material that includes secondary particles made up of a plurality of primary particles containing a lithium transition metal composite oxide, in which the smoothness of the secondary particles is greater than 0.73 and the circularity of the secondary particles is greater than 0.83.

[0065] Complex oxide preparation process In the composite oxide preparation step, a nickel-cobalt composite oxide is prepared, which includes secondary particles formed by the aggregation of multiple primary particles containing a composite oxide comprising nickel and cobalt. The smoothness of the secondary particles constituting the nickel-cobalt composite oxide may be greater than 0.74. The nickel-cobalt composite oxide may be prepared by appropriately selecting from commercially available products, or it may be manufactured and prepared by the nickel-cobalt composite oxide manufacturing method described later. Details of the prepared nickel-cobalt composite oxide will be described later.

[0066] Lithium blending process In the lithium mixing process, the prepared nickel-cobalt composite oxide and lithium compound are mixed to obtain a lithium mixture. Mixing methods include, for example, dry mixing of the nickel-cobalt composite oxide and lithium compound using a stirring mixer, and wet mixing of a nickel-cobalt composite oxide slurry using a ball mill or other mixer. Examples of lithium compounds include lithium hydroxide, lithium nitrate, lithium carbonate, and mixtures thereof.

[0067] The ratio of moles of lithium to the total number of moles of metal elements other than lithium in a lithium mixture (also called the lithium ratio) may be, for example, 0.90 or more and 1.30 or less, and preferably 1.0 or more and 1.20 or less. When the lithium ratio is 0.90 or more, the formation of by-products tends to be suppressed. Furthermore, when the lithium ratio is 1.30 or less, the increase in the amount of alkaline components present on the surface of the lithium mixture is suppressed, and the adsorption of moisture due to the deliquescent properties of the alkaline components is suppressed, which tends to improve handling properties.

[0068] Synthesis process In the synthesis process, a lithium mixture is heat-treated to obtain a lithium transition metal composite oxide having a layered structure containing nickel and cobalt. The lithium transition metal composite oxide is contained in primary particles, and secondary particles, which are aggregates of multiple primary particles, are contained in the positive electrode active material. In the synthesis process, the lithium contained in the lithium compound may diffuse into the nickel-cobalt composite oxide to obtain the lithium transition metal composite oxide.

[0069] The heat treatment temperature may be, for example, 650°C to 990°C, and preferably 700°C to 960°C. When the heat treatment temperature is 650°C or higher, the increase in unreacted lithium tends to be suppressed. When the heat treatment temperature is 990°C or lower, the decomposition of the resulting 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 holding the highest temperature. The heat treatment atmosphere may be in the presence of oxygen, and preferably an atmosphere containing 10% to 100% by volume of oxygen.

[0070] In the method for producing the positive electrode active material, after the synthesis process, the heat-treated material obtained may be subjected to processing such as coarse crushing, pulverizing, or dry sieving as needed.

[0071] Method for producing nickel-cobalt composite oxide A method for producing 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 formation factor; a liquid medium preparation step of preparing a liquid medium having a pH in the range of 10 to 13.5; a crystallization step of supplying a polymer containing constituent units derived from (meth)acrylic acid to the liquid medium while supplying the first solution and the second solution separately and simultaneously to obtain a reaction solution in which the pH is maintained in the range of 10 to 13.5; a composite hydroxide recovery step of obtaining a composite hydroxide containing nickel and cobalt from the reaction solution; and a composite hydroxide heat treatment step of heat treating the obtained composite hydroxide to obtain secondary particles consisting of aggregates of primary particles containing nickel and cobalt composite oxide. The smoothness of the secondary particles containing nickel-cobalt composite oxide produced is greater than 0.74. A method for producing nickel-cobalt composite oxide may be a method for producing nickel-cobalt composite oxide that includes secondary particles formed by the aggregation of multiple primary particles containing a composite oxide comprising 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 salt containing each metal element in water, according to the composition of the target nickel-cobalt composite oxide. Examples of salts include nitrates, sulfates, and hydrochlorides. When preparing the first solution, an acidic substance (e.g., an aqueous sulfuric acid solution) may be added to the water. This may make it easier to dissolve the salts containing each metal element. In the preparation of the first solution, a basic substance may be added to adjust the pH. 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 if the first solution contains nickel and cobalt, and the total number of moles of nickel, cobalt, and manganese if the first solution contains nickel, cobalt, and manganese.

[0073] The first solution may further contain, in addition to nickel ions and cobalt ions, at least one of aluminum ions and manganese ions. Furthermore, the first solution may further contain, in addition to these, ions of at least one secondary metallic 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 secondary metallic 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, between 1.0 mol / L and 2.6 mol / L in total, and preferably between 1.5 mol / L and 2.2 mol / L. When the metal ion concentration of the first solution is 1.0 mol / L or higher, a sufficient amount of crystallized material can be obtained per reaction vessel, thus improving productivity. On the other hand, when the metal ion concentration of the first solution is 2.6 mol / L or lower, the saturation concentration of the metal salt at room temperature is suppressed, and the decrease in the metal ion concentration in the solution due to the 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 that can form complex ions with the metal ions contained in the first solution. For example, if the complex ion forming factor is ammonia, an aqueous ammonia solution can be used as the second solution. The ammonia content in the aqueous ammonia solution may be, for example, 5% by mass or more and 25% by mass or less, and preferably 10% by mass or more and 20% by mass or less.

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

[0077] Crystallization process In the crystallization step, the first and second solutions are supplied separately and simultaneously to the liquid medium while maintaining the pH of the reaction solution between 10 and 13.5. A polymer containing constituent units derived from (meth)acrylic acid is also supplied to the liquid medium. This allows for the production of composite hydroxide particles containing nickel and cobalt from the reaction solution. In addition to the first and second solutions, a basic solution may be supplied to the liquid medium simultaneously. This makes it easy to maintain the pH of the reaction solution between 10 and 13.5.

[0078] In the crystallization process, it is preferable to supply each solution in such a way that the pH of the reaction solution is maintained within the range of 10 to 13.5. For example, the pH of the reaction solution can be maintained within the range of 10 to 13.5 by adjusting the supply amount of the second solution according to the supply amount of the first solution. If the pH of the reaction solution is lower than 10, the amount of impurities contained in the resulting composite hydroxide (for example, sulfuric acid and nitric acid other than metals contained in the mixed solution) will increase, which may lead to a decrease in the capacity of the final product, the secondary battery. Also, if the pH is higher than 13.5, many fine secondary particles will be generated, which may make the handling of the resulting composite hydroxide difficult. Furthermore, the temperature of the reaction solution may be controlled to be within the range of 25°C to 80°C, for example.

[0079] In the crystallization step, the concentration of nickel ions in the reaction solution may be maintained in a range of, for example, 10 ppm to 1000 ppm, preferably 10 ppm to 100 ppm. If the nickel ion concentration is 10 ppm or higher, the complex hydroxide will precipitate sufficiently. If the nickel ion concentration is 1000 ppm or lower, the amount of nickel eluted will be small, thus suppressing deviation from the desired composition. The nickel ion concentration can be adjusted, for example, by supplying a complex ion-forming solution so that the ammonium ion concentration in the reaction solution is between 1000 ppm and 15000 ppm when an aqueous ammonia solution is used as the complex ion-forming solution.

[0080] The supply time for 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 the supply time is 6 hours or more, the deposition rate of the composite hydroxide slows down, so a nickel-cobalt composite oxide with higher smoothness tends to be obtained. If the supply time is 60 hours or less, productivity can be further improved.

[0081] The value obtained by dividing the total number of moles of nickel, cobalt, etc. supplied in the first solution throughout the entire crystallization process by the number of moles of nickel, cobalt, etc. supplied per hour by the number of moles of the first solution supplied per hour may be, for example, 0.015 or more and preferably 0.020 or more and 0.10 or less. A value of 0.015 or more can further improve productivity. A value of 0.125 or less tends to yield nickel-cobalt composite oxides with higher smoothness.

[0082] The polymer containing constituent units derived from (meth)acrylic acid supplied to the liquid medium may be an anionic polymer having carboxyl groups that can function as a surfactant, dispersant, etc. The inclusion of constituent units derived from (meth)acrylic acid in the polymer suppresses foaming of the reaction solution and improves at least one of the smoothness and circularity of the resulting composite hydroxide. For example, with nonionic dispersants, which are common as dispersants, foaming can occur in the reaction solution, making particle size control difficult.

[0083] The constituent units of the polymer derived from (meth)acrylic acid include constituent units derived from acrylic acid, constituent units derived from methacrylic acid, constituent units derived from acrylic acid esters, constituent units derived from methacrylic acid esters, constituent units derived from acrylamide, constituent units derived from methacrylate amide, and the like. In addition to the constituent units derived from (meth)acrylic acid, the polymer may further contain other constituent units. Examples of other constituent units include constituent units derived from unsaturated dibasic acids or their acid anhydrides.

[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 becomes easier to control the particle size of secondary particles and tends to result in higher smoothness.

[0085] The polymer may be supplied to the liquid medium as an alkali metal salt, organic amine salt, ammonium salt, etc., in which at least a portion of the carboxyl groups are neutralized with alkali metal ions such as sodium ions, organic ammonium ions, or neutralizing bases such as ammonium ions. Furthermore, the polymer may be used individually or in combination of two or more types. When using two or more polymers, the combination may have different compositions, different weight-average molecular weights, different neutralizing bases, or any combination thereof.

[0086] The polymer supplied to the liquid medium may also contain other surfactants in addition to polymers containing structural units derived from (meth)acrylic acid. Examples of other surfactants include anionic surfactants having phosphate groups, sulfonic acid groups, etc., cationic surfactants having quaternary ammonium groups, etc., and nonionic surfactants. The amount of other surfactants supplied may be, for example, 10% by mass or less relative to the amount of polymer containing structural units derived from (meth)acrylic acid, and preferably 1% by mass or less.

[0087] The amount of polymer supplied to the liquid medium may be, for example, 0.5% by mass or more and 5% by mass or less, and preferably 1% by mass or more and 3% by mass or less, relative to the total mass of the composite hydroxide produced. If the amount of polymer supplied is 0.5% by mass or more relative to the total mass of the composite hydroxide produced, at least one of the smoothness and circularity of the resulting composite hydroxide tends to improve. Furthermore, if the amount supplied is 5% by mass or less, aggregation of secondary particles in the crystallization process is suppressed, and at least one of the smoothness and circularity of the resulting composite hydroxide tends to improve even further.

[0088] The polymer may be supplied to the liquid medium by supplying the polymer solution containing the polymer independently of the first and second solutions, or by supplying it together with at least one of the first and second solutions. When supplied together with at least one of the first and second solutions, at least one of the first and second solutions may contain the polymer, or at least one of the first and second solutions may be mixed with the polymer solution before being supplied to the liquid medium. The polymer content in the solution used to supply the polymer to the liquid medium may be, for example, 0.05% by mass or more and 3.1% by mass or less, and preferably 0.1% by mass or more and 0.8% by mass or less, relative to the mass of the solution.

[0089] The crystallization step may include, in this order, supplying the first solution and the second solution to the liquid medium separately and simultaneously, supplying the polymer separately and simultaneously with the first solution and the second solution, or supplying the polymer together with at least one of the first solution and the second solution. In other words, prior to supplying the polymer, a portion of the first solution and the second solution may be supplied to the liquid medium separately and simultaneously. By supplying the first solution and the second solution to the liquid medium, the particle size of the nickel and cobalt-containing composite hydroxide generated in the liquid medium can be controlled to a desired size. Here, the composite hydroxide may be generated, for example, as a seed crystal. By generating composite hydroxide with a desired particle size in the liquid medium prior to supplying the polymer, aggregation of primary particles is suppressed, and at least one of the smoothness and circularity of the composite hydroxide generated as secondary particles tends to be improved.

[0090] In the crystallization step, if the first solution and the second solution are supplied separately and simultaneously 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% to 95% of the total supply time. Preferably, it is 3% to 40%, and more preferably 5% to 20%. 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, composite hydroxides having the desired particle size can be generated in the liquid medium, the aggregation of primary particles is suppressed, and at least one of the smoothness and roundness is further improved.

[0091] A method for producing nickel-cobalt composite oxide may include a seed crystal generation step prior to the crystallization step. In the seed crystal generation step, for example, a portion of the prepared first solution is supplied to a liquid medium to generate a composite hydroxide containing nickel and cobalt in the liquid medium, for example, as a seed crystal. That is, the liquid medium used in the crystallization step may be a seed solution containing the composite hydroxide.

[0092] Prior to the crystallization process, if composite hydroxide particles are generated in the liquid medium beforehand, one of the pre-generated composite hydroxide particles becomes a seed crystal that constitutes one of the composite hydroxide particles obtained after the crystallization process. This allows the total number of secondary composite hydroxide particles obtained after the crystallization process to be controlled by the number of pre-generated composite hydroxide particles. For example, supplying a large amount of the first solution beforehand increases the number of composite hydroxide particles generated, so the average particle size of the secondary composite hydroxide particles after the crystallization process tends to be smaller. Also, for example, if the pH of the initial liquid medium is higher than the pH of the resulting reaction solution, the generation of composite hydroxide particles takes precedence over the growth of composite hydroxide particles. This results in the generation of composite hydroxide particles with a more homogeneous particle size, and it is possible to obtain composite hydroxide particles with a narrower particle size distribution.

[0093] In the crystallization process, the first solution, the second solution, and the polymer solution may be supplied to the liquid medium continuously or intermittently. From the viewpoint of improving roundness 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 the solution is not supplied throughout the entire supply time. Furthermore, "almost no time during which the solution is not supplied" means that the time during which the solution is not supplied is less than 1% of the total supply time.

[0094] Composite hydroxide recovery process In the complex hydroxide recovery process, the complex hydroxide containing nickel and cobalt is separated and recovered from the reaction solution. The recovery of the complex hydroxide from the reaction solution can be carried out by commonly used separation methods, such as filtering or centrifugation of the resulting precipitate. The obtained precipitate may be subjected to treatments such as washing with water, filtration, and drying. The composition ratio of the metal elements in the complex hydroxide may be approximately the same as the composition ratio of the metal elements in lithium transition metal complex oxides obtained using these as raw materials.

[0095] The resulting composite hydroxide may have a ratio of the number of moles of nickel to the total number of moles of metal elements contained in the composite hydroxide, 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 higher. Alternatively, the ratio may be 0.4 or higher, or 0.55 or higher. Furthermore, the ratio of the number of moles of nickel to the total number of moles of metal elements is preferably 0.95 or lower, or 0.8 or lower.

[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 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. Furthermore, 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.

[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, even more preferably 0.1 or more, and particularly preferably 0.15 or more. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements is, for example, 0.6 or less, preferably 0.35 or less. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements may be 0.33 or less, 0.3 or less, or 0.25 or less.

[0098] The composite hydroxide may contain at least one secondary metal element in its composition. When the composite hydroxide contains at least one secondary metal element in its composition, the ratio of the total number of moles of the secondary metal element to the total number of moles of the metal element is, for example, greater than 0, preferably 0.001 or more, and more preferably 0.003 or more. The ratio of the total number of moles of the secondary metal element to the total number of moles of the metal element is, for example, 0.02 or less, preferably 0.015 or less, and more preferably 0.01 or less.

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

[0104] The particle size distribution of secondary particles containing nickel-cobalt composite oxide is the 90% particle size D in the volume-based cumulative particle size distribution. 90 and 10% particle size D 10 The difference is 50% particle size D 50 The value obtained by dividing by ((D 90 -D 10 ) / D 50 For example, it is less than 0.8, and 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 nickel-cobalt composite oxide is, for example, 1 μm to 30 μm, preferably 1.5 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, also preferably 18 μm or less, more preferably 12 μm or less, and even 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 corresponds to the 50% particle size D, which corresponds to the cumulative 50% from the small diameter side in the volume-based cumulative particle size distribution. 50 That is the case.

[0106] Secondary particles containing nickel-cobalt composite oxide are formed by the aggregation of multiple primary particles. The average particle size D is determined based on electron microscopy observation of the primary particles. SEM For example, the particle size is 0.1 μm or more and 1.5 μm or less, preferably 0.12 μm or more, and more preferably 0.15 μm or more. Also, the average particle size D based on electron microscope observation of primary particles. SEMはPreferably, it is 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 of 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] For 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] For 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 embodiments. The above embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present disclosure and exhibits the same 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 ranging from 1000 to 15000 times according to the particle size. Fifty primary particles whose contours could be confirmed were selected, and the spherical equivalent diameter was calculated from the contours of the selected primary particles using image processing software. 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 90The cumulative particle size distribution based on volume was measured under wet conditions using a laser diffraction particle size distribution analyzer (SALD-3100, manufactured by Shimadzu Corporation), and the particle size corresponding to 10%, 50%, and 90% of the cumulative distribution from the smallest diameter side was determined. The particle size distribution was also determined as D 90 and D 10 The difference is D 50 It was calculated by dividing by . In other words, the particle size distribution of secondary particles was obtained 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 allowing it to harden, a cross-sectional sample was prepared by performing cross-sectional processing. A backscattered electron image (magnification: 4000x) was taken using a scanning electron microscope (Hitachi High-Technologies SU8230; acceleration voltage 3kV). From the obtained backscattered electron images, 20 to 40 secondary particles in which the particle contour could be confirmed were selected, and the total circumference L of each particle was processed using image processing software (ImageJ). op The following measurements were taken. Furthermore, using image processing software (ImageJ), the most fitting (approximate) ellipse was determined for the contours of the selected particles, and the major axis a and minor axis b of the approximate ellipse were obtained for each particle. From the obtained major axis a and minor axis b, the total circumference L of the approximate ellipse was determined using the Gauss-Kummer formula. Total circumference (L) of the particle image contour op The ratio of the total circumference (L) of the approximated ellipse to (L / L) op The smoothness was calculated as follows: The smoothness of the secondary particle was calculated as the arithmetic mean of the smoothness of the individual particles.

[0119] Circularity was determined as the ratio (L1 / L0) of the circumference (L1) calculated from the equivalent circle diameter to the total circumference (L0) of the secondary particle's contour shape, where the equivalent circle diameter is defined as the diameter of a circle having the same area as the particle image area in the secondary particle's contour shape. Specifically, the circularity of approximately 10,000 particles was measured using a dry particle image analyzer (Morphologi G3S: Malvern; lens magnification 20x), and the arithmetic mean of these measurements was used to determine the circularity of the secondary particles.

[0120] Tap density was measured as follows: 20g of the sample was placed in a 20mL graduated cylinder, tapped 150 times from a height of 6.5cm, and the volume was measured. The resulting density was defined as the tap density. Bulk density was measured as follows: The sample, sieved through a 0.5mm mesh, was placed in a 30mL container until it was overflowing, and the piled-up portion of the sample was scraped off using a spatula. The weight of the sample remaining in the container was measured to determine the bulk density.

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

[0122] (Example 1) [Preparation of solid electrolytes] Under an argon atmosphere, lithium sulfide and phosphorus pentasulfide were weighed in a molar ratio of 7:3. The weighed materials were crushed and mixed in an agate mortar to obtain sulfide glass. This was used as a solid electrolyte.

[0123] [Fabrication of the positive electrode] Primary particle size is 0.42 μm, 50% particle size D 50 The tap density is 6.0 μm, smoothness is 0.84, roundness is 0.88, and tap density is 2.48 g / cm³. 3 , with a specific surface area (BET value) of 0.43 m² 2 / g, bulk density of 1.45 g / cm³ 3 A positive electrode active material with a particle size distribution of 0.52 was prepared.

[0124] A cathode composite material was obtained by mixing 70 parts by mass of the prepared cathode active material, 27 parts by mass of the solid electrolyte, and 3 parts by mass of VGCF (gas-phase carbon fiber).

[0125] [Assembly of evaluation batteries] 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 bottom of the outer mold. The upper end of the lower mold was fixed in the middle of the outer mold. In this state, 100 mg of solid electrolyte was poured from the top of the outer mold to the upper end of the lower mold. After pouring, a cylindrical upper mold with an outer diameter of 11 mm was inserted from the top of the outer mold. After insertion, a pressure of 100 MPa was applied from above the upper mold to mold the solid electrolyte into a solid electrolyte layer. After molding, the upper mold was withdrawn from the top of the outer mold, and 20 mg of positive electrode composite material was poured from the top of the outer mold to the top of the solid electrolyte layer. After pouring, the upper mold was inserted again, and this time a pressure of 100 MPa was applied to mold the positive electrode composite material into a positive electrode active material layer. After molding, the upper mold was fixed, the lower mold was released and withdrawn from the bottom of the outer mold, and LiAl alloy, which is the negative electrode active material, was poured from the bottom of the lower mold to the bottom of the solid electrolyte layer. After insertion, the lower mold was reinserted, and a pressure of 350 MPa was applied from below the lower mold to form the negative electrode active material layer. The lower mold was fixed under pressure, and the positive electrode terminals were attached to the upper mold and the negative electrode terminals to the lower mold to obtain an all-solid-state secondary battery for evaluation.

[0126] (Example 2) Primary particle size is 0.41 μm, 50% particle size D 50 The tap density is 6.3 μm, smoothness is 0.87, circularity is 0.91, and tap density is 2.55 g / cm³. 3 , with a specific surface area of ​​0.37 m² 2 / g, bulk density is 1.67 g / cm³ 3 An all-solid-state secondary battery for evaluation was prepared 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) Primary particle size is 0.66 μm, 50% particle size D 50 The tap density is 6.4 μm, smoothness is 0.73, circularity is 0.83, and tap density is 2.09 g / cm³. 3 , with a specific surface area of ​​0.51 m² 2 / g, bulk density of 1.07 g / cm³ 3 An all-solid-state secondary battery for evaluation was prepared 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] A solid-state secondary battery for evaluation was charged to a state of charge (SOC) of 50%. It was connected to an AC power source at 25°C, and resistance measurements were performed using the AC impedance method. The frequency of the AC power source was logarithmically varied from 1 MHz to 0.1 Hz. Assuming the equivalent circuit shown in Figure 1, the diameter of the arc appearing in the frequency range between 1000 Hz and 5000 Hz was defined as the resistance originating 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 ​​for Example 1 and Example 2 were significantly lower than those for Comparative Example 1. Thus, by increasing the smoothness of the secondary particles constituting the positive electrode active material to more than 0.73 and the circularity to more than 0.83, the internal resistance of an all-solid-state secondary battery can be reduced.

[0131] (Example 3) Preparation of each solution A mixed solution (first solution) was prepared by mixing nickel sulfate solution, cobalt sulfate solution, and manganese sulfate solution in a molar ratio of 1:1:1 for each metal element (combined concentration of nickel, cobalt, and manganese: 1.7 mol / L). The total number of moles of metal elements in the mixed solution was 474 moles. A 25% by mass sodium hydroxide aqueous solution was prepared as a basic aqueous solution. A 12.5% ​​by mass ammonia aqueous solution (second solution) was prepared as a complex ion forming solution. As a polymer solution, a blend of the surfactants Aron A-30SL (manufactured by Toagosei Co., Ltd.; 40% by mass aqueous solution of ammonium polyacrylate, weight-average molecular weight = 6000) and Aron A-210 (manufactured by Toagosei Co., Ltd.; 43% by mass aqueous solution of sodium polyacrylate, weight-average molecular weight = 3000) was prepared in a mass ratio of 1:1.

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

[0133] Seed crystal generation process While stirring the liquid medium, two moles of the first solution were added to the liquid medium, representing the total number of moles of metal elements, to precipitate a composite hydroxide containing nickel, cobalt, and manganese.

[0134] Crystallization process While stirring the prepared liquid medium containing the composite hydroxide, the remaining 472 moles of the first solution, the sodium hydroxide aqueous solution, and the ammonia aqueous solution (second solution) were supplied separately and simultaneously, maintaining a basic pH (11.3). The polymer solution was supplied starting 3 hours after the start of supplying the first solution, the second solution, and the sodium hydroxide aqueous solution, allowing the composite hydroxide containing nickel, cobalt, and manganese to precipitate. The amount of polymer solution supplied was 1% by mass relative to the theoretical yield of the generated composite hydroxide. The first solution was supplied continuously for 18 hours. During the crystallization process, the temperature of the liquid medium was controlled to approximately 50°C.

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

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

[0137] The obtained nickel-cobalt transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.338 Co 0.331 Mn 0.331The result was O2. When the physical properties of the obtained nickel-cobalt composite oxide were measured in the same manner as above, the 50% particle size D 50 The diameter was 5.8 μm, the circularity was 0.91, and the smoothness was 0.80.

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

[0139] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.335 Co 0.333 Mn 0.332 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 3.5 μm, the circularity was 0.85, and the smoothness was 0.84.

[0140] (Example 5) The procedure was carried out under the same conditions as in Example 3, except that the amount of first solution supplied in the seed crystal generation step was reduced compared to Example 3, and the amount of first solution supplied in the crystallization step was increased accordingly compared to Example 1.

[0141] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.335 Co 0.333 Mn 0.332 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 7.9 μm, the circularity was 0.85, and the smoothness was 0.89.

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

[0143] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.339 Co 0.331 Mn 0.330 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 6.1 μm, the circularity was 0.89, and the smoothness was 0.91.

[0144] (Example 7) The experiment was carried out under the same conditions as in Example 3, except that the polymer solution was replaced with the surfactant Frospers 5000 (manufactured by SNF Corporation; 44% aqueous solution of sodium polyacrylate, weight-average molecular weight = 6500 to 10000).

[0145] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.340 Co 0.333 Mn 0.328 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 5.9 μm, the circularity was 0.87, and the smoothness was 0.89.

[0146] (Example 8) The procedure was carried out under the same conditions as in Example 3, except that the polymer solution was replaced with the surfactant Frospers 9000 (manufactured by SNF Corporation; 40% aqueous solution of sodium polyacrylate, weight-average molecular weight = 10,000 to 17,000).

[0147] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.338 Co 0.333 Mn 0.330 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 5.3 μm, the circularity was 0.88, and the smoothness was 0.85.

[0148] (Example 9) The procedure was carried out under the same conditions as in Example 3, except that the polymer solution was changed to the surfactant Frospers 10000 (manufactured by SNF Corporation; 30% aqueous solution of sodium polyacrylate, weight-average molecular weight = 50,000 to 70,000).

[0149] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.341 Co 0.331 Mn 0.328 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 8.0 μm, the circularity was 0.87, and the smoothness was 0.88.

[0150] (Example 10) The procedure was carried out under the same conditions as in Example 3, except that the polymer solution was replaced with the surfactant Frospers 15000 (manufactured by SNF; 30% aqueous solution of sodium polyacrylate, weight-average molecular weight = 100,000 to 170,000).

[0151] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.339 Co 0.331 Mn 0.329 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 8.5 μm, the circularity was 0.87, and the smoothness was 0.85.

[0152] (Example 11) The procedure 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] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.921 Co 0.040 Mn 0.039It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 5.8 μm, the circularity was 0.89, and the smoothness was 0.76.

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

[0155] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.340 Co 0.330 Mn 0.329 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 6.2 μm, the circularity was 0.86, and the smoothness was 0.56.

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

[0157] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.920 Co 0.040 Mn 0.040 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 5.8 μm, the circularity was 0.86, and the smoothness was 0.67.

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

[0159] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.336 Co 0.333 Mn 0.331 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50The diameter was 6.5 μm, the circularity was 0.88, and the smoothness was 0.45.

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

[0161] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.335 Co 0.334 Mn 0.331 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 3.2 μm, the circularity was 0.83, and the smoothness was 0.58.

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

[0163] The obtained nickel-cobalt composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Ni 0.328 Co 0.338 Mn 0.335 It was O2. Furthermore, the obtained nickel-cobalt composite oxide had a 50% particle size of D 50 The diameter was 8.2 μm, the circularity was 0.82, and the smoothness was 0.74.

[0164] [Table 2]

[0165] (Example 12) In Example 3, lithium carbonate was dry-mixed with nickel-cobalt composite oxide obtained in Example 3 so that the molar ratio of lithium carbonate to nickel-cobalt composite oxide was 1.15 times. The obtained lithium mixture was heat-treated at 890°C for 10 hours in an air atmosphere. Subsequently, it was dispersed to obtain a lithium transition metal composite oxide. To 900 g of the obtained lithium transition metal composite oxide, 136 g of Nb2O5 sol manufactured by Taki Chemical Co., Ltd., with a concentration of 4.2 mass%, was used as a niobium source. The sol was added dropwise while stirring the lithium transition metal composite oxide in a mixer to obtain a niobium deposit. Subsequently, it was heat-treated at 350°C for 9 hours in air. The obtained heat-treated material was dispersed in a resin ball mill to the same volume-average particle size as the base material after the synthesis process, and then dry-sieved to obtain a positive electrode active material as a lithium transition metal composite oxide treated with Nb.

[0166] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Li 1.15 Ni 0.338 Co 0.331 Mn 0.331 The result was O2. The evaluation results are shown in Table 3.

[0167] (Example 13) Except for using the nickel-cobalt composite oxide obtained in Example 4, the other aspects are the same as in Example 4. 12 A lithium transition metal composite oxide was obtained in the same manner.

[0168] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Li 1.15 Ni 0.335 Co 0.333 Mn 0.332 The result was 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] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Li 1.15 Ni 0.335 Co 0.334 Mn 0.331 The result was 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] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Li 1.15 Ni 0.335 Co 0.333 Mn 0.332 The result was 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] The obtained lithium transition metal composite oxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Li 1.15 Ni 0.335 Co 0.334 Mn 0.331 The electrolyte was O2. The impedance was measured using the same method as in Example 1, except that a crystalline solid electrolyte containing chlorine was used. The relative impedance was calculated by setting the impedance value of Comparative Example 1 obtained by this method to 1. The evaluation results are shown in Table 3.

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

[0176] [Table 3]

[0177] As shown in Table 3, the obtained examples were confirmed to have improved smoothness and circularity compared to 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. In other words, it was confirmed that the improvement effect on relative impedance was greater as the particle size decreased.

[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 herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A positive electrode active material for lithium-ion secondary batteries, having a layered structure and containing secondary particles formed by the aggregation of multiple primary particles containing lithium transition metal composite oxides including lithium, nickel, and cobalt, The smoothness of the secondary particle is greater than 0.73 and less than 1, and the circularity of the secondary particle is greater than 0.83 and less than 1, The positive electrode active material for the lithium-ion secondary battery has a 90% particle size D in the volume-based cumulative particle size distribution. ９０ and 10% particle size D １０ The difference is 50% of the particle size D ５０ The value obtained by dividing by is less than 0.

61. The aforementioned secondary particles are positive electrode active materials for lithium-ion secondary batteries having deposits containing niobium on their surface.

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

3. The lithium transition metal composite oxide has a ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium that is greater than 0 and less than 1. The positive electrode active material for a lithium-ion secondary battery according to claim 1 or 2, having a composition in which 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 0.6 or less.

4. The lithium transition metal composite oxide has a composition represented by the following formula (2) as a positive electrode active material for a lithium-ion secondary battery according to any one of claims 1 to 3. 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 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. １ M represents at least one of Mn and Al. ２ This 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 aforementioned secondary particles are the 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 D ５０ / D ＳＥＭ The value is between 5 and 100. The average particle size D SEM based on electron microscope observation is obtained by using a scanning electron microscope to observe primary particles constituting secondary particles at a magnification in the range of 1,000 to 15,000 times, selecting 50 primary particles whose contours can be confirmed, calculating the spherical equivalent diameter from the contours of the selected primary particles using image processing software, and obtaining the average spherical equivalent diameter as the arithmetic mean of the obtained spherical equivalent diameters, as described in any one of claims 1 to 4.

6. The primary particles are defined by an average particle size D based on electron microscope observation. ＳＥＭ A positive electrode active material for a lithium-ion secondary battery according to any one of claims 1 to 5, wherein the particle size is 0.15 μm or more and 1.0 μm or less.

7. The active material layer comprises a positive electrode active material and a solid electrolyte material, The positive electrode active material includes secondary particles which are composed of a plurality of primary particles comprising 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 particle is greater than 0.83 and less than 1. The positive electrode active material has a 90% particle size D in the volume-based cumulative particle size distribution. ９０ and 10% particle size D １０ The difference is 50% of the particle size D ５０ The value obtained by dividing by is less than 0.

61. The aforementioned secondary particles are positive electrodes for all-solid-state lithium-ion secondary batteries, having deposits containing niobium on their surface.

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

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

10. Prepare a first solution containing nickel ions and cobalt ions, Prepare a second solution containing the complex ion forming factor, Prepare a liquid medium with a pH in the range of 10 to 13.5, The first solution and the second solution are supplied separately and simultaneously to the liquid medium, while a polymer containing constituent units derived from (meth)acrylic acid is supplied, to obtain a reaction solution in which the pH is maintained in the range of 10 to 13.

5. To obtain a composite hydroxide containing nickel and cobalt from the aforementioned reaction solution, The aforementioned composite hydroxide is heat-treated to obtain a nickel-cobalt composite oxide containing secondary particles formed by the aggregation of multiple primary particles containing a composite oxide comprising nickel and cobalt. The nickel-cobalt composite oxide and the lithium compound are mixed to obtain a lithium mixture, The lithium mixture is heat-treated to obtain a lithium transition metal composite oxide containing nickel and cobalt and having a layered structure. A method for producing a positive electrode active material for a lithium-ion secondary battery, comprising contacting the lithium transition metal composite oxide with a niobium source to obtain a positive electrode active material having a deposit containing niobium on its surface.

11. It comprises an active material layer containing a positive electrode active material, The positive electrode active material includes secondary particles which are composed of a plurality of primary particles comprising 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 particle is greater than 0.83 and less than 1. The positive electrode active material has a 90% particle size D in the volume-based cumulative particle size distribution. ９０ and 10% particle size D １０ The difference is 50% of the particle size D ５０ The value obtained by dividing by is less than 0.

61. The aforementioned secondary particles are positive electrodes for lithium-ion secondary batteries having deposits containing niobium on their surface.

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