Positive electrode active material for non-aqueous electrolyte secondary batteries and method for producing the same

Abstract

The present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery that can improve the output characteristics at low SOC when a non-aqueous electrolyte secondary battery is constructed. [Solution] A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a layered structure and secondary particles formed by the aggregation of multiple primary particles containing lithium and nickel-containing lithium transition metal composite oxides. The smoothness of the secondary particles is greater than 0.73, and the circularity of the secondary particles is greater than 0.83. The secondary particles contain cobalt and have a first region with a depth of 150 nm from the particle surface and a second region with a depth of 10 nm or less from the particle surface. The ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium is greater in the second region than in the first region, and the value obtained by dividing the ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium in the second region by the ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium in the first region is 0.03 or more and 0.9 or less.

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material for non-aqueous electrolyte secondary batteries and a method for producing the same. [Background technology]

[0002] High power output characteristics are required for electrode active materials in non-aqueous electrolyte secondary batteries used in large power equipment such as electric vehicles. To obtain high power output characteristics, positive electrode active materials having a structure of secondary particles formed by the aggregation of many primary particles are considered effective. In this regard, 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 1). 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 2).

[0003] On the other hand, a technique has been proposed to provide a coating layer containing Co on the surface of the positive electrode active material, which is said to improve storage stability (weather resistance) while maintaining battery characteristics (see, for example, Patent Document 3). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] International Publication No. 2013 / 183711 [Patent Document 2] International Publication No. 2016 / 180288 [Patent Document 3] Japanese Patent Publication No. 2018-14208 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] One aspect of this disclosure aims to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can improve the output characteristics in a low charge state (low SOC) when a non-aqueous electrolyte secondary battery is constructed. [Means for solving the problem]

[0006] The first embodiment is a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising secondary particles having a layered structure and composed of a plurality of primary particles comprising a lithium transition metal composite oxide containing lithium and nickel. The positive electrode active material for a non-aqueous electrolyte secondary battery has a smoothness of secondary particles greater than 0.73 and a circularity of secondary particles greater than 0.83. The secondary particles contain cobalt and have a first region with a depth of 150 nm from the particle surface and a second region with a depth of 10 nm or less from the particle surface, and the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium is greater in the second region than in the first region.

[0007] The second embodiment is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: preparing a positive electrode active material raw material having a layered structure and comprising secondary particles formed by a plurality of primary particles comprising a lithium transition metal composite oxide containing lithium and nickel, wherein the smoothness of the secondary particles is greater than 0.73 and the circularity of the secondary particles is greater than 0.83; contacting the positive electrode active material raw material with a cobalt compound to obtain a cobalt deposit; and heat-treating the cobalt deposit at a temperature of 500°C or higher and less than 1100°C to obtain a heat-treated product.

[0008] A third embodiment is a non-aqueous electrolyte lithium-ion secondary battery comprising a positive electrode containing the positive electrode active material for a non-aqueous electrolyte secondary battery, a negative electrode, and a non-aqueous electrolyte. [Effects of the Invention]

[0009] According to one aspect of this disclosure, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can improve the output characteristics at low SOC when a non-aqueous electrolyte secondary battery is constructed. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic cross-sectional view of secondary particles contained in the positive electrode active material. [Modes for carrying out the invention]

[0011] 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 refers to 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 described below are illustrative examples of positive electrode active materials for non-aqueous electrolyte secondary batteries and methods for producing them, in order to embody the technical concept of this disclosure, and this disclosure is not limited to the positive electrode active materials for non-aqueous electrolyte secondary batteries and methods for producing them described below.

[0012] Cathode active material for non-aqueous electrolyte secondary batteries The positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter also simply referred to as "positive electrode active material") has a layered structure and is composed of secondary particles formed by the aggregation of multiple primary particles containing lithium and nickel-containing lithium transition metal composite oxides. 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. The secondary particles contain cobalt in their composition, and for example, they have cobalt-containing deposits on their surface. The secondary particles having cobalt-containing deposits have a first region with a depth of 150 nm from the particle surface and a second region with a depth of 10 nm or less from the particle surface, and the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium in the composition is greater in the second region than in the first region.

[0013] 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 conductive additives within the positive electrode, thus reducing resistance at the interface between the secondary particles and the conductive additives. Furthermore, when deposits containing cobalt are applied to the surface of the secondary particles, the compound is more likely to adhere evenly, reducing the resistive component. Reducing the resistive component in the positive electrode active material improves the output characteristics of non-aqueous electrolyte secondary batteries. Additionally, it reduces cracking of secondary particles caused by pressure molding during positive electrode formation. This can be attributed, for example, to the uniform application of pressure molding across the entire particle. These effects derived from the shape of the secondary particles constituting the positive electrode active material are specifically described, for example, in International Publication No. 2021 / 020531.

[0014] In the secondary particles of lithium transition metal composite oxides that constitute the positive electrode active material, cobalt is unevenly distributed near the surface of the particles, resulting in a higher concentration of cobalt. This improves the power output characteristics when a battery is constructed using such a positive electrode active material. In particular, it can improve power output characteristics at low states of charge (SOC). The exact form of cobalt near the particle surface is not clear, but possible forms include solid solution of cobalt near the surface of the secondary particles of the lithium transition metal composite oxide, or a cobalt-containing compound coating the surface of the secondary particles of the lithium transition metal composite oxide that serves as the base material. The effect of uneven distribution of cobalt near the surface of the secondary particles on improving power output characteristics at low SOC tends to be more effective when the nickel content ratio in the composition of the lithium transition metal composite oxide is high. This is thought to be because, for example, the potential difference between the lithium transition metal compound that serves as the base material and the compound present near the surface allows lithium to move and diffuse without being inhibited even at low SOC.

[0015] 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.

[0016] The smoothness of the secondary particle may be greater than, for example, 0.73, preferably 0.74 or higher, more preferably 0.76 or higher, 0.80 or higher, or 0.83 or higher. The upper limit of the smoothness is 1. Here, the 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: Using the fitting function of image processing software, an approximate ellipse with the same area as the contour shape of the target secondary particle is found. From the major axis a and minor axis b of this approximate ellipse, the total circumference L of the approximate ellipse is calculated 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 shape of the secondary particle (L op The ratio of the total circumference (L) of the approximate ellipse to (L / L) op It is defined as follows. The magnification of the image used to calculate the smoothness of 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.

[0017] 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.

[0018]

Number

[0019] The circularity of the secondary particles may be, for example, greater than 0.83, preferably 0.84 or more, more preferably 0.86 or more, or 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 defined as the equivalent diameter of the circle.

[0020] Specifically, using a dry particle image analyzer (Morphologi G3S: manufactured by Malvern; lens magnification 20 times), the individual ratios (L1 / L0) are calculated for about 10,000 particles, and the circularity of the secondary particles is determined as the arithmetic mean value thereof.

[0021] The particle size distribution of the secondary particles may be, for example, less than 0.9, preferably 0.85 or less, more preferably 0.8 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 defined as the 10% particle diameter D 10 , 50% particle diameter D 50 and 90% particle diameter D 90 respectively. When taking D 90 and D 10 the difference between them is D 50The 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.

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

[0023] 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 The particle size may be, for example, 0.1 μm or more and 1.5 μm or less, preferably 0.12 μm or more, more preferably 0.15 μm or more, 0.2 μm or more, or 0.3 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, 0.6 μm or less, or 0.4 μm or less. When 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. Being able to identify the outline of a primary particle means that the entire outline of the primary particle can be traced on the image.

[0024] 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, more preferably 10 or more, or 15 or more. Also ratio D 50 / D SEM Preferably, it is 100 or less, more preferably 50 or less, 30 or less, or 20 or less.

[0025] The secondary particles containing lithium transition metal composite oxides that constitute the positive electrode active material have a first region near its surface with a depth of approximately 150 nm from the particle surface and a second region with a depth of 10 nm or less from the particle surface. In the positive electrode active material, the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium in its composition (hereinafter also simply referred to as the "cobalt ratio") is greater in the second region than in the first region. Here, the depth of the second region from the particle surface is, for example, 10 nm or less, but may be near 10 nm.

[0026] A method for selecting the first and second regions in a cross-sectional image of a secondary particle will be explained with reference to the drawings. Figure 1 is a schematic cross-sectional view of a secondary particle. The first region 10 is selected, for example, as follows: In the cross-sectional image of the secondary particle 100, a tangent line to the particle surface 30 is set, and then a perpendicular line is drawn through the point of tangency and perpendicular to the tangent line. The neighborhood of a point on this perpendicular line that is 150 nm in the direction of the particle interior from the particle surface 30 is defined as the first region 10. Similarly, the second region 20 is selected as the neighborhood of a point on the perpendicular line that is 10 nm in the direction of the particle interior from the particle surface 30. Here, "neighborhood" is intended to encompass the area required for compositional analysis. The depth of the first region from the particle surface may be, for example, 140 nm to 160 nm, and the depth of the second region from the particle surface may be, for example, 5 nm to 15 nm.

[0027] The cobalt ratio of the first region may be, for example, 0 or more, preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.025 or more, or 0.03 or more. The cobalt ratio of the first region may be, for example, 0.5 or less, preferably 0.3 or less, more preferably 0.2 or less, even more preferably 0.1 or less, or 0.05 or less. The cobalt ratio of the second region may be, for example, 0.03 or more, preferably 0.05 or more, more preferably 0.1 or more, and even more preferably 0.15 or more. The cobalt ratio of the second region may be, for example, 0.9 or less, preferably 0.8 or less, more preferably 0.5 or less, and especially preferably 0.3 or less, or 0.2 or less. The value obtained by subtracting the cobalt ratio of the first region from the cobalt ratio of the second region may be, for example, 0.02 or more, preferably 0.03 or more and 0.85 or 0.05 or more and 0.50 or 0.50 or 0.03. Furthermore, it is preferable that the cobalt ratio be 0.03 or higher, 0.05 or higher, or 0.1 or higher, and may be 0.85 or lower, 0.5 or lower, 0.3 or lower, or 0.2 or lower. Also, the value obtained by dividing the cobalt ratio of the second region by the cobalt ratio of the first region may be, for example, 2 or higher, preferably 2.2 or higher and 500 or lower, more preferably 2.5 or higher and 100 or lower, and even more preferably 3 or higher and 10 or lower. When the cobalt ratio in a particular composition is within the above range, the output characteristics at low SOC tend to be improved.

[0028] In the first region, where the depth from the particle surface is approximately 150 nm, the ratio of moles of nickel to the total number of moles of metal elements other than lithium (hereinafter also simply referred to as the "nickel ratio") may be, for example, 0.2 or more, preferably 0.33 or more, more preferably 0.6 or more, 0.8 or more, or 0.9 or more. The nickel ratio in the first region may be, for example, 1 or less, preferably 0.98 or less, more preferably 0.95 or less. Furthermore, in the second region, where the depth from the particle surface is 10 nm or less, the nickel ratio may be, for example, 0.06 or more, preferably 0.1 or more, more preferably 0.33 or more, 0.5 or more, or 0.6 or more. The nickel ratio in the second region may be, for example, 0.98 or less, preferably 0.95 or less, more preferably 0.9 or less, 0.85 or less, or 0.8 or less. In addition, the value obtained by dividing the nickel ratio in the second region by the nickel ratio in the first region may be, for example, less than 1, preferably 0.9 or less or 0.85 or less. Furthermore, the value obtained by dividing the nickel ratio of the second region by the nickel ratio of the first region may be, for example, 0.02 or more, preferably 0.03 or more, or 0.07 or more.

[0029] The nickel ratio and cobalt ratio in the first and second regions can be calculated by measuring SEM-EDX in the cross-section of lithium transition metal composite oxide particles.

[0030] In lithium transition metal composite oxide particles, the cobalt ratio may decrease continuously or discontinuously from the particle surface to the interior of the particle. The cobalt concentration gradient, which is the absolute value of the difference in the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium in the first and second regions divided by the difference in depth from the surface of the first and second regions, is, for example, 0.0000007 (nm). -1 ) is larger than 0.005 (nm -1 ) is less than 0.00005 (nm) -1 ) or more 0.003(nm -1 ) or less, or 0.0001 (nm) -1 ) or more 0.002(nm -1 ) or less. Preferably, 0.00005 (nm)-1 ) or more, 0.0001(nm -1 ) or greater, or 0.0005 (nm) -1 ) or more, and 0.004 (nm -1 ) or less, 0.003(nm -1 ) or less, or 0.002 (nm) -1 ) or less is acceptable. When the cobalt concentration gradient is within the above range, the output at low SOC tends to be improved. Specifically, the cobalt concentration gradient is obtained by subtracting the cobalt ratio in the first region from the cobalt ratio in the second region, and dividing that value by subtracting the depth from the surface of the second region from the depth from the surface of the first region.

[0031] The composition of the positive electrode active material can be considered to be the composition of the lithium transition metal composite oxide before the cobalt compound is attached, as described later in the manufacturing method, with the attached cobalt compound added.

[0032] The ratio of moles of nickel to the total number of moles of metal elements other than lithium in the composition of the positive electrode active material may be, for example, greater than 0 and less than 1, and preferably 0.3 or more and less than 1. The lower limit of the ratio of moles of nickel to the total number of moles of metal elements other than lithium may preferably be 0.33 or more, more preferably 0.6 or more, or 0.8 or more. The upper limit of the ratio of moles of nickel to the total number of moles of metal elements other than lithium may preferably be 0.98 or less, and more preferably 0.95 or less. When the ratio of moles of nickel is within the above range, it tends to be possible to achieve both high-voltage charge / discharge capacity and cycle characteristics in a non-aqueous electrolyte secondary battery.

[0033] The ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium in the composition of the positive electrode active material may be, for example, greater than 0 and 0.5 or less, preferably 0.01 or more and 0.4 or less, more preferably 0.02 or more and 0.3 or less, even more preferably 0.03 or more and 0.2 or less, and particularly preferably 0.04 or more and 0.1 or less, from the viewpoint of charge and discharge capacity. When the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium is within the above range, the output at low SOC tends to be further improved.

[0034] The composition of the positive electrode active material is at least one primary metallic element M selected from the group consisting of manganese (Mn) and aluminum (Al). 1 It may further contain the following: In the composition of the positive electrode active material, M is the total number of moles of metal elements other than lithium. 1 The ratio of the number of moles may be, for example, 0 or more and 0.5 or less, preferably 0.01 or more and 0.3 or less from the viewpoint of safety, more preferably 0.02 or more and 0.2 or less, and even more preferably 0.03 or more and 0.1 or less.

[0035] The composition of the positive electrode active material is at least one secondary metallic element M selected from the group consisting of boron (B), sodium (Na), magnesium (Mg), silicon (Si), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), zinc (Zn), gallium (Ga), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), tin (Sn), barium (Ba), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), gadollium (Gd), lutetium (Lu), tantalum (Ta), tungsten (W), bismuth (Bi), etc. 2 It may also contain secondary metallic elements M. 2may be at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W. In the composition of the positive electrode active material, M with respect to the total molar number of metal elements other than lithium 2 The molar ratio may be, for example, 0 or more and 0.1 or less, preferably 0.001 or more and 0.05 or less.

[0036] The molar ratio of lithium to the total molar number of metal elements other than lithium in the composition of the positive electrode active material may be, for example, 0.95 or more and 1.5 or less, preferably 1 or more and 1.3 or less, and more preferably 1.03 or more and 1.25 or less.

[0037] In the composition of the positive electrode active material, the molar ratio of nickel, cobalt, and manganese may be, for example, nickel:cobalt:manganese = (from 0.3 to less than 1):(from 0.01 to 0.4):(from 0.01 to 0.3), preferably (from 0.33 to 0.98):(from 0.02 to 0.3):(from 0.02 to 0.2), and more preferably (from 0.6 to 0.98):(from 0.03 to 0.2):(from 0.03 to 0.1).

[0038] The composition of the positive electrode active material may be represented by, for example, the following formula (1). Li p Ni x Co y M 1 z M 2 w O2(1) satisfies 0.95 ≦ p ≦ 1.5, 0 < x < 1, 0 < y ≦ 0.5, 0 ≦ z ≦ 0.5, 0 ≦ w ≦ 0.1, and x + y + z + w ≦ 1. M 1 is at least one selected from the group consisting of Al and Mn, and M 2x is at least one selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Lu, Ta, W, and Bi. x, y, z, and w may satisfy 0.3≦x<1, 0.01≦y≦0.4, 0.01≦z≦0.3, 0≦w≦0.1, 0.33≦x<0.98, 0.02≦y≦0.3, 0.02≦z≦0.2, 0≦w≦0.1, or 0.6≦x≦0.98, 0.03≦y≦0.2, 0.03≦z≦0.1, 0.001≦w≦0.05. p may satisfy 1≦p≦1.3.

[0039] From the viewpoint of initial efficiency in non-aqueous electrolyte secondary batteries, the nickel element disorder of the lithium transition metal composite oxide contained in the positive electrode active material is preferably 4.0% or less, more preferably 2.0% or less, and even more preferably 1.5% or less, as determined by X-ray diffraction. Here, nickel element disorder refers to the chemical disorder of the transition metal ions (nickel ions) that should occupy their original sites. In layered lithium transition metal composite oxides, a typical example is the swapping of alkali metal ions that should occupy the site represented by 3b in Wyckoff notation (3b site, hereafter the same) and transition metal ions that should occupy the 3a site. A smaller nickel element disorder is preferable because it improves initial efficiency.

[0040] The nickel disorder in lithium transition metal composite oxides can be determined by X-ray diffraction. X-ray diffraction spectra are measured for lithium transition metal composite oxides using CuKα radiation. The compositional model is (Li 1-d Ni d )(Ni x Co y Mn z The system is defined as O2(x+y+z=1), and structural optimization is performed by Rietveld analysis based on the obtained X-ray diffraction spectrum. The percentage of d calculated as a result of structural optimization is taken as the value of the nickel element disorder.

[0041] Method for manufacturing positive electrode active material A method for producing a positive electrode active material may include, for example, a positive electrode active material raw material preparation step of preparing a positive electrode active material raw material having a layered structure and comprising secondary particles formed by a plurality of primary particles comprising a lithium transition metal composite oxide containing lithium and nickel, wherein the smoothness of the secondary particles is greater than 0.73 and the circularity of the secondary particles is greater than 0.83; a cobalt deposition step of contacting the positive electrode active material raw material with a cobalt compound to obtain a cobalt deposit; and a deposit heat treatment step of heat treating the cobalt deposit at a temperature of 500°C or higher and less than 1100°C to obtain a heat treated product.

[0042] Furthermore, the preparation step for the positive electrode active material raw material in the method for producing the positive electrode active material may include, for example, a composite oxide preparation step of preparing a nickel composite oxide in which secondary particles are made up of a plurality of primary particles containing a nickel composite oxide, and the smoothness of the secondary particles is greater than 0.74; a lithium mixing step of mixing the nickel composite oxide and a lithium compound to obtain a lithium mixture; and a synthesis step of heat-treating the lithium mixture to obtain a lithium transition metal composite oxide containing nickel and having a layered structure. The prepared positive electrode active material raw 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.

[0043] Furthermore, the preparation step for the raw materials of the positive electrode active material in the method for producing the positive electrode active material may include: preparing a first solution containing nickel 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 nickel-containing composite hydroxide from the reaction solution; heat-treating the composite hydroxide to obtain a nickel composite oxide containing secondary particles formed by the aggregation of multiple primary particles containing the nickel-containing composite oxide; mixing the nickel composite oxide with a lithium compound to obtain a lithium mixture; and heat-treating the lithium mixture.

[0044] Cathode active material raw material preparation process Complex oxide preparation process In the composite oxide preparation step, a nickel composite oxide containing secondary particles formed by the aggregation of multiple primary particles containing nickel-containing composite oxides is prepared. The smoothness of the secondary particles containing nickel composite oxide may be greater than 0.74. The nickel composite oxide may be prepared by appropriately selecting from commercially available products, or it may be manufactured and prepared by the nickel composite oxide manufacturing method described later. Details of the prepared nickel composite oxide will be described later.

[0045] Lithium blending process In the lithium mixing process, the prepared nickel composite oxide and lithium compound are mixed to obtain a lithium mixture. Mixing methods include, for example, dry mixing of the nickel composite oxide and lithium compound using a stirrer or similar device, and wet mixing of a nickel composite oxide slurry using a ball mill or similar device. Examples of lithium compounds include lithium hydroxide, lithium nitrate, lithium carbonate, and mixtures thereof.

[0046] 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, 0.95 or more and 1.5 or less, and preferably 1.0 or more and 1.30 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 1.5 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.

[0047] Synthesis process In the synthesis process, a lithium mixture is heat-treated to obtain a lithium transition metal composite oxide containing nickel and having a layered structure. 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 cathode active material raw material. In the synthesis process, the lithium contained in the lithium compound may diffuse into the nickel composite oxide to obtain the lithium transition metal composite oxide.

[0048] The heat treatment temperature may be, for example, 600°C to 990°C, and preferably 650°C to 960°C. When the heat treatment temperature is 600°C or higher, the increase in unreacted lithium components tends to be suppressed. When the heat treatment temperature is 990°C or lower, the decomposition of the generated lithium transition metal composite oxide tends to be suppressed. The heat treatment time may be, for example, 4 hours or more, as the time for holding the maximum temperature. The heat treatment atmosphere may be in the presence of oxygen, and preferably an atmosphere containing 10% to 100% by volume of oxygen.

[0049] In the preparation process for the cathode active material raw materials, after the synthesis process, the resulting heat-treated material may be subjected to processing such as coarse crushing, pulverization, or dry sieving, if necessary.

[0050] The lithium transition metal composite oxide contained in the cathode active material raw material obtained in the cathode active material raw material preparation step may, for example, contain nickel in its composition and have a layered structure. The lithium transition metal composite oxide may contain at least Li and a transition metal such as Ni, and may further contain at least one primary metal element selected from the group consisting of Al and Mn. In addition, the lithium transition metal composite oxide may further contain at least one secondary metal element selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Lu, Ta, W, and Bi. The secondary metal element may be at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0051] In the composition of the lithium transition metal composite oxide contained in the positive electrode active material raw material, 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 0.3 or more. The ratio of moles of nickel to the total number of moles of metal elements other than lithium may be 0.33 or more, or 0.6 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 0.98 or less, more preferably 0.95 or less. When the ratio of moles of nickel is within the above range, it tends to be possible to achieve both high-voltage charge / discharge capacity and cycle characteristics in a non-aqueous electrolyte secondary battery.

[0052] In the composition of the lithium transition metal composite oxide contained in the positive electrode active material raw material, the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium is, for example, 0 or more, preferably 0.01 or more, more preferably 0.02 or more, even more preferably 0.03 or more, and particularly preferably 0.04 or more. Alternatively, the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium may be, for example, 0.5 or less, preferably 0.4 or less, more preferably 0.3 or less, even more preferably 0.2 or less, or 0.1 or less. When the ratio of the number of moles of cobalt is within the above range, the charge / discharge capacity can be increased at high voltages in a non-aqueous electrolyte secondary battery. Furthermore, when the ratio of the number of moles of cobalt is within the above range, there is a tendency to be able to further improve the output at low SOC.

[0053] In the composition of the lithium transition metal composite oxide contained in the positive electrode active material raw material, 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 or more, preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more. Also, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements other than lithium is, for example, 0.5 or less, preferably 0.3 or less, more preferably 0.2 or less, or 0.1 or less. When the ratio of the total number of moles of manganese and aluminum is within the above range, it tends to be easier to achieve both charge / discharge capacity and safety in a non-aqueous electrolyte secondary battery.

[0054] In the composition of the lithium transition metal composite oxide contained in the positive electrode active material raw material, the ratio of the number of moles of lithium to the total number of moles of metal elements 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. Also, the ratio of the number of moles of lithium to the total number of moles of metal elements 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 the number of moles of lithium is 0.95 or more, the interfacial resistance of the positive electrode surface in a non-aqueous electrolyte secondary battery using the positive electrode active material containing the obtained lithium transition metal composite oxide is suppressed, and the output of the non-aqueous electrolyte secondary battery tends to improve. On the other hand, when the ratio of the number of moles of lithium is 1.5 or less, the initial discharge capacity when the positive electrode active material is used as the positive electrode of a non-aqueous electrolyte secondary battery tends to improve.

[0055] In the composition of the lithium transition metal composite oxide contained in the positive electrode active material raw material, the ratio of the number of moles of nickel, cobalt, and manganese may be, for example, nickel:cobalt:manganese = (0.3 to less than 1):(0.01 to 0.4):(0.01 to 0.3), preferably (0.33 to 0.98):(0.02 to 0.3):(0.02 to 0.2), and more preferably (0.6 to 0.98):(0.03 to 0.2):(0.03 to 0.1). 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) = (0.3 to less than 1):(0.01 to 0.4):(0.01 to 0.4), preferably (0.33 to 0.98):(0.02 to 0.3):(0.02 to 0.2).

[0056] In the composition of the lithium transition metal composite oxide contained in the positive electrode active material raw material, the ratio of the total number of moles of secondary metal elements to the total number of moles of metal elements other than lithium is, for example, 0 or more, preferably 0.001 or more, and more preferably 0.003 or more. Furthermore, the ratio of the total number of moles of secondary metal elements to the total number of moles of metal elements other than lithium is, for example, 0.1 or less, preferably 0.05 or less, and more preferably 0.01 or less.

[0057] The lithium transition metal composite oxide contained in the positive electrode active material raw material can be represented by the following formula (2), for example. The lithium transition metal composite oxide may have a layered structure and may have a hexagonal crystal structure. Li p1 Ni x1 Co y1 M 1 z1 M 2 w1 O2(2)

[0058] Here, p1, x1, y1, z1, and w1 satisfy 0.95≦p1≦1.5, 0.3≦x1<1, 0≦y1≦0.5, 0≦z1≦0.5, 0≦w1≦0.1, and x1+y1+z1+w1≦1. Preferably, 0.33≦x1≦0.98, 0.01≦y1≦0.4, 0.01≦z1<0.3, and 0≦w1≦0.1, and more preferably, 0.6≦x1≦0.98, 0.03≦y1≦0.2, 0.03≦z1≦0.1, and 0.001≦w1≦0.05.

[0059] M 1 M may represent at least one of Mn and Al. 2 This may represent at least one selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Lu, Ta, W, and Bi, and may represent at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0060] 50% particle size D of positive electrode active material raw material50 For example, the particle size is 1 μm or more and 30 μm or less, preferably 1.5 μm or more, more preferably 3 μm or more, and from the viewpoint of power density, preferably 10 μm or less, and more preferably 5.5 μm or less.

[0061] 90% particle size D in the cumulative particle size distribution based on volume of positive electrode active material raw materials 90 10% particle size D 10 The ratio to indicates the extent of the particle size distribution; a smaller value indicates that the particle size is more uniform. 90 / D 10 For example, it may be 4 or less, and from the viewpoint of power density, it is preferably 3 or less, and more preferably 2.5 or less. 90 / D 10 The lower limit may be, for example, 1.2 or higher.

[0062] Cobalt deposition process In the cobalt deposition process, the prepared positive electrode active material raw material and a cobalt compound are brought into contact to obtain a cobalt deposit in which the cobalt compound adheres to the surface of the lithium transition metal composite oxide particles contained in the positive electrode active material raw material. The contact between the positive electrode active material raw material and the cobalt compound may be carried out dry or wet. In the case of dry contact, the positive electrode active material raw material and the cobalt compound can be mixed using, for example, a high-speed shear mixer, and then the contact can be carried out. Examples of cobalt compounds include cobalt hydroxide, cobalt oxide, and cobalt carbonate.

[0063] In the wet process, contact between the positive electrode active material raw material and the cobalt compound can be achieved by bringing the positive electrode active material raw material into contact with a liquid medium containing a cobalt compound. The liquid medium may be stirred as needed. The liquid medium containing the cobalt compound may be a solution of the cobalt compound or a dispersion of the cobalt compound. Alternatively, the positive electrode active material raw material may be suspended in a solution of the cobalt compound, and the cobalt compound may be precipitated in the solution by adjusting the pH, temperature, etc., thereby adhering the cobalt compound to the surface of the lithium transition metal composite oxide particles contained in the positive electrode active material raw material.

[0064] Examples of cobalt compounds in the solution include cobalt sulfate, cobalt nitrate, and cobalt chloride. Examples of cobalt compounds in the dispersion include cobalt hydroxide, cobalt oxide, and cobalt carbonate. The liquid medium may contain water, for example, or it may contain a water-soluble organic solvent such as alcohol in addition to water. The concentration of the cobalt compound in the liquid medium can be, for example, 1% by mass or more and 8.5% by mass or less.

[0065] The total amount of cobalt compound brought into contact with the positive electrode active material raw material is, for example, 1 mol% to 20 mol%, preferably 3 mol% to 15 mol%, relative to the lithium transition metal composite oxide contained in the positive electrode active material raw material, based on cobalt.

[0066] The contact temperature between the positive electrode active material raw material and the cobalt compound is, for example, 40°C to 80°C, preferably 40°C to 60°C. Alternatively, the contact temperature may be, for example, 20°C to 80°C. The contact time is, for example, 30 minutes to 180 minutes, preferably 30 minutes to 60 minutes.

[0067] After contact with a liquid medium containing a cobalt compound, the positive electrode active material raw material to which the cobalt compound has adhered may be subjected to treatments such as filtration, washing with water, and drying, if necessary. Alternatively, preliminary heat treatment may be performed depending on the type of cobalt compound adhering to it. If preliminary heat treatment is performed, the temperature is, for example, 100°C to 350°C, preferably 120°C to 320°C. The treatment time is, for example, 5 hours to 20 hours, preferably 8 hours to 15 hours. The atmosphere for the preliminary heat treatment may be, for example, an oxygen-containing atmosphere, or an atmospheric atmosphere.

[0068] Heat treatment process for deposited materials In the deposit heat treatment process, the cobalt deposit obtained in the cobalt deposit process is heat-treated at a predetermined temperature of 500°C to less than 1100°C to obtain a heat-treated product. The resulting heat-treated product is a positive electrode active material containing a lithium transition metal composite oxide with a high cobalt concentration near the particle surface, and can improve the output characteristics at low SOC in a non-aqueous electrolyte secondary battery constructed using this material.

[0069] The cobalt deposit subjected to heat treatment may be a mixture with a lithium compound. That is, the manufacturing method may include a mixing step of mixing the cobalt deposit and the lithium compound to obtain a mixture before the heat treatment step of the deposit. Heat treating the cobalt deposit together with the lithium compound at a predetermined temperature may further improve the output characteristics of the non-aqueous electrolyte secondary battery.

[0070] The heat treatment temperature for cobalt deposits is, for example, 500°C or more and less than 1100°C. The lower limit of the heat treatment temperature is preferably 550°C or more, more preferably 600°C or more, and particularly preferably 630°C or more. The upper limit of the heat treatment temperature is preferably 1000°C or less, more preferably 900°C or less, even more preferably 800°C or less, and particularly preferably 750°C or less. The heat treatment time is, for example, 1 hour or more and 20 hours or less, preferably 3 hours or more and 10 hours or less. The heat treatment atmosphere is, for example, an oxygen-containing atmosphere, and may be an air atmosphere.

[0071] After heat treatment, the heat-treated material may be subjected to further processing such as crushing, grinding, classification, and sizing, as needed.

[0072] The heat-treated material obtained as described above contains secondary particles formed by the aggregation of multiple primary particles containing lithium transition metal composite oxide, the smoothness of the secondary particles is greater than 0.73, the circularity of the secondary particles is greater than 0.83, and the cobalt concentration is higher near the surface of the secondary particles. In other words, in the secondary particles containing lithium transition metal composite oxide, the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium is greater in the second region, which is about 10 nm deep from the particle surface, than in the first region, which is about 150 nm deep from the particle surface.

[0073] Method for producing nickel complex oxides Nickel composite oxides used in the preparation process for cathode active material raw materials can be manufactured, for example, as follows. The method for manufacturing nickel composite oxides includes, for example, a first solution preparation step of preparing a first solution containing nickel 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 nickel-containing composite hydroxide 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-containing composite oxides. The smoothness of the produced nickel-containing secondary particles is greater than 0.74.

[0074] First solution preparation step In the first solution preparation step, a first solution containing nickel 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 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 in the first solution may be set appropriately according to the average particle size of the target nickel 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.

[0075] The first solution may further contain, in addition to nickel ions, at least one selected from the group consisting of cobalt ions, 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 boron, sodium, magnesium, silicon, phosphorus, sulfur, potassium, calcium, titanium, vanadium, chromium, iron, copper, zinc, gallium, strontium, yttrium, zirconium, niobium, molybdenum, indium, tin, barium, lanthanum, cerium, neodymium, samarium, europium, gadolium, lutetium, tantalum, tungsten, and bismuth. The secondary metallic element may be at least one selected from the group consisting of zirconium, titanium, magnesium, tantalum, niobium, molybdenum, and tungsten.

[0076] The concentration of metal ions such as nickel 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 concentration of metal ions is suppressed from exceeding the saturation concentration of the metal salt at room temperature, and the decrease in the metal ion concentration in the solution due to the precipitation of metal salt crystals is suppressed.

[0077] 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.

[0078] 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.

[0079] 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 nickel-containing composite hydroxide particles 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.

[0080] 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.

[0081] 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.

[0082] 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, which tends to result in nickel composite oxides with higher smoothness. If the supply time is 60 hours or less, productivity can be further improved.

[0083] The value obtained by taking the total number of moles of nickel, etc. supplied in the first solution throughout the entire crystallization process as the denominator and the total number of moles of nickel, etc. supplied in the first solution per hour as the numerator, may be, for example, 0.015 or more and 0.125 or less, preferably 0.020 or more and 0.10 or less. If it is 0.015 or more, productivity can be further improved. If it is 0.125 or less, there is a tendency to obtain nickel composite oxides with higher smoothness.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] 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 the supply of 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-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 the supply of 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.

[0092] 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.

[0093] A method for producing nickel composite oxides 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 nickel-containing composite hydroxide 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.

[0094] 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.

[0095] 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.

[0096] Composite hydroxide recovery process In the complex hydroxide recovery process, the nickel-containing complex hydroxide 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, or drying. The composition ratio of metal elements in the complex hydroxide may be approximately the same as the composition ratio of metal elements in lithium transition metal complex oxides obtained using these as raw materials.

[0097] 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 0.3 or greater, or 0.33 or greater. The ratio of the number of moles of nickel to the total number of moles of metal elements may also be 0.6 or greater. Furthermore, the ratio of the number of moles of nickel to the total number of moles of metal elements is preferably 0.98 or less, or 0.95 or less.

[0098] The resulting composite hydroxide may have a ratio of 0 to 0.5 moles of cobalt to the total number of moles of metal elements contained in the composite hydroxide. The ratio of 0.01 to 0.02 moles of cobalt to the total number of moles of metal elements is preferably 0.01 or higher, 0.02 or higher, 0.03 or higher, or 0.04 or higher. Furthermore, the ratio of 0.4 moles of cobalt to the total number of moles of metal elements is preferably 0.4 or lower. The ratio of 0.3 to 0.2 moles of cobalt to the total number of moles of metal elements may be 0.3 or lower, 0.2 or lower, or 0.1 or lower.

[0099] The composite hydroxide may contain at least one of manganese and aluminum in its composition. In the composite hydroxide, 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 or more, preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more. The ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements is also, for example, 0.5 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 0.3 or less, 0.2 or less, or 0.1 or less.

[0100] The composite hydroxide may contain at least one secondary metal element in its composition. In the composite hydroxide, 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 or more, 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, 0.1 or less, preferably 0.05 or less, and more preferably 0.01 or less.

[0101] 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)

[0102] In formula (3), M 1 M represents at least one of Mn and Al. 2 This represents at least one selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Lu, Ta, W, and Bi. j, k, m, n, and γ satisfy 0.3≦j<1, 0≦k≦0.5, 0≦m≦0.5, 0≦n≦0.1, and 0≦γ≦1. Preferably, 0.33≦j≦0.98, 0.01≦k≦0.4, 0.01≦m≦0.3, 0≦n≦0.1, more preferably 0.6≦j≦0.98, 0.03≦k≦0.2, 0.03≦m≦0.1, and 0.001≦n≦0.05. Also preferably, M 2 is at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0103] Composite hydroxide heat treatment process In the composite hydroxide heat treatment process, the resulting composite hydroxide is heat-treated to obtain a nickel composite oxide containing secondary particles formed by the aggregation of multiple primary particles containing nickel-containing composite oxides. By heat treatment, the composite hydroxide is dehydrated to produce nickel composite oxide. The nickel composite oxide may be a precursor of a lithium transition metal composite oxide, or it may be a precursor of a positive electrode active material.

[0104] The heat treatment temperature may be, for example, 105°C to 900°C, preferably 300°C to 500°C. The heat treatment time may be, for example, 5 hours to 30 hours, preferably 10 hours to 20 hours. The heat treatment atmosphere may be an oxygen-containing atmosphere or an air atmosphere.

[0105] The smoothness of the resulting secondary particles containing nickel 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 containing nickel 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 nickel composite oxide are measured in the same manner as those of the secondary particles constituting the positive electrode active material. Furthermore, the upper limits for the smoothness and circularity of the secondary particles are 1 or less, and may be less than 1.

[0106] The particle size distribution of secondary particles containing nickel composite oxides 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.

[0107] The volume-average particle diameter of the secondary particles containing nickel composite oxide is, for example, 1 μm or more and 30 μm or less, preferably 1.5 μm or more, more preferably 2 μm or more, still more preferably 3 μm or more, and also preferably 18 μm or less, more preferably 12 μm or less, still more preferably 8 μm or less. When the volume-average particle diameter of the secondary particles is within the above range, the fluidity is good, and the output may be further improved when constructing a secondary battery. Here, the volume-average particle diameter is the 50% particle diameter D corresponding to 50% cumulative from the smaller-diameter side in the volume-based cumulative particle size distribution. 50 is.

[0108] The secondary particles containing nickel composite oxide are formed by aggregation of a plurality of primary particles. The average particle diameter D based on electron microscope observation of the primary particles SEM is, for example, 0.1 μm or more and 1.5 μm or less, preferably 0.12 μm or more, more preferably 0.15 μm or more. Also, the average particle diameter D based on electron microscope observation of the primary particles SEM is preferably 1.2 μm or less, more preferably 1.0 μm or less. When the average particle diameter based on electron microscope observation of the primary particles is within the above range, the output may be improved when constructing a battery.

[0109] The ratio D of the average particle diameter D based on electron microscope observation of the 50% particle diameter D in the volume-based cumulative particle size distribution of the secondary particles containing nickel composite oxide 50 may be, for example, 2.5 or more. The ratio D SEM / 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. 50 / D SEM is preferably 100 or less, more preferably 50 or less.

[0110] In nickel composite oxides, the ratio of moles of nickel to the total number of moles of metal elements contained in the nickel composite oxide may be, for example, greater than 0 and less than 1. The ratio of moles of nickel to the total number of moles of metal elements is preferably 0.3 or more, or 0.33 or more. The ratio of moles of nickel to the total number of moles of metal elements may be 0.6 or more. Furthermore, the ratio of moles of nickel to the total number of moles of metal elements is preferably 0.98 or less, or 0.95 or less.

[0111] In nickel composite oxides, the ratio of the number of moles of cobalt to the total number of moles of metal elements contained in the nickel composite oxide may be 0 or more and 0.5 or less. Preferably, the ratio of the number of moles of cobalt to the total number of moles of metal elements is 0.01 or more, 0.02 or more, 0.03 or more, or 0.04 or more. Also, preferably, the ratio of the number of moles of cobalt to the total number of moles of metal elements is 0.4 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, 0.2 or less, or 0.1 or less.

[0112] Nickel composite oxides may contain at least one of manganese and aluminum in their composition. In nickel composite oxides, 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 or more, preferably 0.01 or more, more preferably 0.02 or more, and even more preferably 0.03 or more. Alternatively, the ratio of the total number of moles of manganese and aluminum to the total number of moles of metal elements may be, for example, 0.5 or less, 0.3 or less, 0.2 or less, or 0.1 or less.

[0113] Nickel composite oxides may contain at least one secondary metal element in their composition. In nickel composite oxides, 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 or more, 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, 0.1 or less, preferably 0.05 or less, and more preferably 0.01 or less.

[0114] Nickel composite oxides may have a composition represented by, for example, the following formula (4). Ni q Co r M 1 s M 2 t O2(4)

[0115] In formula (4), M 1 M represents at least one of Mn and Al. 2 This represents at least one selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Lu, Ta, W, and Bi. q, r, s, and t satisfy 0.3≦q<1, 0≦r≦0.5, 0≦s≦0.5, 0≦t≦0.1, and q+r+s+t≦1.1. Preferably, 0.33≦q≦0.98, 0.01≦r≦0.4, 0.01≦s≦0.3, 0≦t≦0.1, more preferably 0.6≦q≦0.98, 0.03≦r≦0.2, 0.03≦s≦0.1, and 0.001≦t≦0.05. Also preferably, M 2 is at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0116] [Non-aqueous electrolyte secondary battery electrode] The electrode for a non-aqueous electrolyte secondary battery comprises a current collector and a positive electrode active material layer disposed on the current collector and containing a positive electrode active material for a non-aqueous electrolyte secondary battery manufactured by the aforementioned manufacturing method. A non-aqueous electrolyte secondary battery equipped with such an electrode can improve output characteristics at low SOC.

[0117] Examples of materials for the current collector include aluminum, nickel, and stainless steel. The positive electrode active material layer can be formed by applying a positive electrode mixture, obtained by mixing the above-mentioned positive electrode active material, conductive material, binder, etc., with a solvent, onto the current collector, and then performing drying, pressurizing, etc. Examples of conductive materials include natural graphite, artificial graphite, and acetylene black. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, and polyamide acrylic resin.

[0118] [Non-aqueous electrolyte lithium-ion secondary battery] A non-aqueous electrolyte lithium-ion secondary battery comprises a positive electrode containing a positive electrode active material for non-aqueous electrolyte secondary batteries, a negative electrode, and a non-aqueous electrolyte. The positive electrode comprises a current collector and a positive electrode active material layer disposed on the current collector, which contains the aforementioned positive electrode active material for non-aqueous electrolyte secondary batteries. A non-aqueous electrolyte secondary battery having such a positive electrode can improve output characteristics, particularly at low states of charge (SOC).

[0119] Examples of materials for the current collector include aluminum, nickel, and stainless steel. The positive electrode active material layer can be formed by applying a positive electrode mixture, obtained by mixing the above-mentioned positive electrode active material, conductive material, binder, etc., with a solvent, onto the current collector, and then performing drying, pressurizing, etc. Examples of conductive materials include natural graphite, artificial graphite, and acetylene black. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, and polyamide acrylic resin.

[0120] A non-aqueous electrolyte secondary battery comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, a separator, and the like. For the negative electrode, electrolyte, separator, and the like in a non-aqueous electrolyte secondary battery, for example, those described in Japanese Patent Publication No. 2002-075367, Japanese Patent Publication No. 2011-146390, Japanese Patent Publication No. 2006-12433 (the entirety of which is incorporated herein by reference), etc., for non-aqueous electrolyte secondary batteries can be used as appropriate.

[0121] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and it goes without saying that any configuration that is substantially identical to the technical idea described in the claims of this disclosure and produces similar effects is included within the technical scope of this disclosure. [Examples]

[0122] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples.

[0123] Primary particle size, i.e., average particle size D based on electron microscope observation of primary particles. SEM The particle size was measured as follows: A scanning electron microscope (SEM) was used to observe the primary particles constituting the secondary particles at magnifications ranging from 1,000x to 15,000x, depending on the particle size. Fifty primary particles with discernible contours were selected. The contour length was determined by tracing the contours of the selected primary particles using image processing software. The spherical equivalent diameter was calculated from the contour length, and the average particle size D based on electron microscope observation of the primary particles was calculated as the arithmetic mean of the obtained spherical equivalent diameters. SEM They sought it.

[0124] 10% particle size D in volume-based cumulative particle size distribution 10 , 50% particle size D 50 and 90% particle size D 90 The 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 calculated 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

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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).

[0129] Example 1 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 9.2:0.4:0.4 for the metal elements, with a combined concentration of nickel, cobalt, and manganese of 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.

[0130] Preparation of the liquid medium 30 liters of water were prepared in the reaction vessel, and a 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.

[0131] 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.

[0132] 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.

[0133] 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 composite hydroxide).

[0134] Manufacturing of nickel complex oxides Nickel 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 composite oxide).

[0135] The obtained nickel 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 0.039 It was O2. When the physical properties of the obtained nickel composite oxide were evaluated as described above, the 50% particle size D 50 The diameter was 6.2 μm, the circularity was 0.89, and the smoothness was 0.76.

[0136] The two materials obtained above were dry-mixed to obtain a lithium mixture, with a molar ratio of lithium hydroxide to nickel composite oxide of 1.10. The obtained lithium mixture was heat-treated in an oxygen atmosphere (oxygen concentration 40 vol%) at 740°C for 5 hours to carry out the synthesis process. Subsequently, it was subjected to a dispersion treatment to obtain a lithium transition metal composite oxide as a raw material for the cathode active material.

[0137] 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 1.10 Ni 0.921 Co 0.040 Mn 0.039 It was O2. When the physical properties of the obtained lithium transition metal composite oxide were evaluated as described above, the 50% particle size D 50 The diameter was 6.26 μm, the circularity was 0.86, and the smoothness was 0.76.

[0138] To the obtained lithium transition metal composite oxide, 3 mol% cobalt oxide was added and mixed in a mixer to obtain a cobalt deposit. Subsequently, the cobalt deposit was heat-treated at 665°C for 5 hours in an oxygen atmosphere (oxygen concentration 40 vol%). The resulting heat-treated material was dispersed in a resin ball mill to the same volume-average particle size as the cathode active material raw material after the synthesis process, and then sieved dry to obtain a lithium transition metal composite oxide having a deposit containing Co on its surface as the cathode active material.

[0139] The obtained positive electrode active material was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy, revealing that its composition was Li 1.06 Ni 0.894 Co 0.068 Mn 0.038 It was O2. When the physical properties of the obtained lithium transition metal composite oxide were evaluated as described above, the 50% particle size D 50 The diameter was 6.35 μm, the circularity was 0.84, and the smoothness was 0.74.

[0140] Comparative Example 1 The lithium transition metal composite oxide used as the cathode active material raw material in Example 1 was used as the cathode active material in Comparative Example 1.

[0141] Evaluation of cobalt and nickel distribution The cobalt and nickel distributions within the particles of the positive electrode active material obtained above were evaluated. Specifically, the nickel and cobalt content in the first and second regions were evaluated as follows.

[0142] Composition analysis The positive electrode active materials obtained in Example 1 and Comparative Example 1 were dispersed in epoxy resin and solidified. Then, a cross-section polisher (manufactured by JEOL Ltd.) was used to create cross-sections of the secondary particles of the positive electrode active material to prepare measurement samples. At one point each in the first region (150 nm depth from the surface) and the second region (10 nm depth from the surface) of the measurement sample, the intensity ratios of each metal component other than lithium were determined using a scanning electron microscope (SEM) / energy dispersive X-ray spectrometer (EDX) (manufactured by Hitachi High-Technologies Corporation; acceleration voltage 3 kV). The cobalt ratio (Co ratio) was defined as the intensity ratio of cobalt to the sum of the intensity ratios of the metal components other than lithium, and the nickel ratio (Ni ratio) was defined as the intensity ratio of nickel to the sum of the intensity ratios of the metal components other than lithium. The results are shown in Table 1.

[0143] [Table 1]

[0144] In the positive electrode active material according to Example 1, the smoothness of the secondary particles constituting the positive electrode active material is greater than 0.73, and the circularity is greater than 0.83. From this, it is considered that the cobalt-containing deposits are evenly attached to the surface of the positive electrode active material, and that this tends to improve the output at low SOC.

[0145] Assembly of evaluation batteries The output characteristics of evaluation batteries equipped with positive electrodes containing the positive electrode active materials of Example 1 and Comparative Example 1 were evaluated by measuring the DC-IR (direct current internal resistance). The measurements were performed using evaluation batteries assembled as follows.

[0146] Fabrication of the positive electrode A positive electrode slurry was prepared by dispersing and dissolving 96.5 parts by mass of positive electrode active material, 1.5 parts by mass of acetylene black, and 2 parts by mass of PVDF (polyvinylidene fluoride) in NMP (N-methyl-2-pyrrolidone). The obtained positive electrode slurry was applied to a current collector made of aluminum foil, dried, and then pressed using a roll press to obtain a positive electrode active material layer density of 3.5 g / cm³. 3 It is compressed and molded to a size of 15cm. 2 The positive electrode was obtained by cutting it in that manner.

[0147] Fabrication of the negative electrode A negative electrode slurry was prepared by dispersing 97.5 parts by mass of artificial graphite, 1.5 parts by mass of CMC (carboxymethylcellulose), and 1.0 part by mass of SBR (styrene-butadiene rubber) in water. The obtained negative electrode slurry was coated onto copper foil, dried, and then compressed to obtain the negative electrode.

[0148] Preparation of non-aqueous electrolyte Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 to obtain a mixed solvent. Lithium hexafluoride phosphate (LiPF6) was dissolved in the resulting mixed solvent to a concentration of 1 mol / L to obtain a non-aqueous electrolyte.

[0149] Fabrication of evaluation batteries Lead electrodes were attached to the positive and negative electrode current collectors, and then vacuum-dried at 120°C. Next, a separator was placed between the positive and negative electrodes, and the components were placed in a laminated pouch. This pouch was then vacuum-dried at 60°C to remove any moisture adsorbed on each component. After that, a non-aqueous electrolyte was injected into the laminated pouch under an argon atmosphere, and the pouch was sealed to produce an evaluation battery.

[0150] aging The evaluation battery was subjected to constant voltage constant current charging (cutoff current 0.05C) with a charging voltage of 4.2V and a charging current of 0.1C (1C being the current at which discharge ends in 1 hour), and constant current discharge with a discharge termination voltage of 2.5V and a discharge current of 0.1C, allowing the non-aqueous electrolyte to permeate the positive and negative electrodes.

[0151] Measurement of DC internal resistance The evaluation batteries, after aging, were placed in a 25°C environment, and the DC-IR (DC-IR) was measured. After constant current charging to a state of charge (SOC) of 95% at a full charge voltage of 4.2V, the open-circuit potential at SOC 95% was measured. Subsequently, pulse discharge with a specific current value i was performed for 30 seconds, and the voltage V after 10 seconds was measured. The DC-IR (DC-IR) was calculated from the difference between the open-circuit potential and the voltage V after 10 seconds. This was then discharged with a constant current down to SOC 95%, 80%, 50%, 20%, 10%, and 5%, and the DC-IR at each SOC was measured. The current value i at SOC 95%, 10%, and 5% was set to 0.07A, and the current value i at SOC 80%, 50%, and 20% was set to 0.12A. Table 2 shows the relative resistance values ​​at each SOC, with the DC-IR at SOC 5% of Comparative Example 1 set to 1.

[0152] [Table 2]

[0153] As shown in Table 2, for materials with specific levels of smoothness and roundness, a difference in cobalt concentration between the surface and the interior above a certain level improves output at low SOC. [Explanation of Symbols]

[0154] 10 1st region, 20 2nd region, 30 particle surface, 100 secondary particle

Claims

1. It has a layered structure and contains secondary particles which are made up of multiple primary particles that contain lithium and nickel-containing lithium transition metal composite oxides, The smoothness of the secondary particle is greater than 0.73, and the circularity of the secondary particle is greater than 0.

83. The secondary particle contains cobalt and has a first region with a depth of 150 nm from the particle surface and a second region with a depth of 10 nm or less from the particle surface, and the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium is greater in the second region than in the first region. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium in the second region, divided by the ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium in the first region, is 0.03 or more and 0.9 or less.

2. The positive electrode active material according to claim 1, wherein the difference between the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium in the second region and the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium in the first region is 0.02 or more.

3. The positive electrode active material according to claim 1 or 2, wherein the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium in the second region, divided by the ratio of the number of moles of cobalt to the total number of moles of metal elements other than lithium in the first region, is 2 or more.

4. The positive electrode active material according to any one of claims 1 to 3, wherein the secondary particles have a volume-average particle size of 1 μm or more and 30 μm or less.

5. The aforementioned secondary particles are the 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 positive electrode active material according to any one of claims 1 to 4, wherein the value obtained by dividing by is less than 0.

9.

6. The ratio of the number of moles of nickel to the total number of moles of metal elements other than lithium is greater than 0 and less than 1. A positive electrode active material according to any one of claims 1 to 5, 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 0.5 or less.

7. A positive electrode active material according to any one of claims 1 to 6, having a composition represented by the following formula (1). Li ｐ Ni ｘ Co ｙ M １ ｚ M ２ ｗ O ２ (1) 0.95≦p≦1.5, 0<x<1, 0<y≦0.5, 0≦z≦0.5, 0≦w≦0.1, x+y+z+w≦1, M １ is at least one selected from the group consisting of Al and Mn, and M ２ It is at least one selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Lu, Ta, W, and Bi.

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