Metal composites

Abstract

Providing metal composite compounds that can be used to manufacture lithium secondary batteries with high initial charge-discharge efficiency. [Solution] A metal composite compound containing at least Ni, obtained by measuring the powder of the metal composite compound using scanning electron microscopy-energy dispersive X-ray spectroscopy, wherein in a scatter plot with the projected area circle equivalent diameter (μm) of the particles of the metal composite compound on the horizontal axis and the Ni content (mol%) of the particles of the metal composite compound on the vertical axis, the slope S of the approximate straight line calculated by the least squares method is between -0.2 and 0.2, and in the volume-based particle size distribution, the particle diameter D is such that the cumulative volume percentage from the smallest particle side is 10%. 10 When (μm), the above D 10 A metal composite compound in which X, the standard deviation of the Ni content (mol%) in particles with a projected area equivalent diameter of (μm) or less, is 2.0 mol% or less.

Description

Technical Field

[0001] The present invention relates to a metal composite compound.

Background Art

[0002] The positive electrode active material contained in the positive electrode of a lithium secondary battery is obtained, for example, by mixing and firing a lithium compound and a metal composite compound containing a metal element other than Li.

[0003] As the applications of lithium secondary batteries expand, improvement of the battery performance of lithium secondary batteries is demanded. As a technique for improving the battery performance of lithium secondary batteries, attempts have been made to control the physical properties of the metal composite compound used as a raw material for the positive electrode active material.

[0004] For example, Patent Document 1 discloses that lithium metal oxide powder produced using a precursor defined by D 10 and D 90 as a raw material can provide a lithium secondary battery with high safety and high output.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] As the application fields of lithium secondary batteries expand, further improvement of the initial charge-discharge efficiency is demanded. An object of the present invention is to provide a metal composite compound capable of manufacturing a lithium secondary battery with high initial charge-discharge efficiency.

Means for Solving the Problems

[0007] The present invention includes the following [1] to [5]. [1] A metal composite compound containing at least Ni, wherein in a scatter diagram with the equivalent circle diameter of the projected area (μm) of the particles of the metal composite compound on the horizontal axis and the Ni content ratio (mol%) of the particles of the metal composite compound on the vertical axis, which is obtained by measuring the powder of the metal composite compound by scanning electron microscope - energy dispersive X - ray spectroscopy, the slope S of the approximate straight line calculated by the least - squares method is - 0.2 or more and 0.2 or less, and in the volume - based particle size distribution, when the particle diameter at which the cumulative volume ratio from the small - particle side is 10% is D 10 (μm), X, which is the standard deviation of the Ni content ratio (mol%) in particles with an equivalent circle diameter of the projected area of D 10 (μm) or less, is 2.0 mol% or less. A metal composite compound [2] In the particle size distribution, when the particle diameter at which the cumulative volume ratio from the small - particle side is 50% is D 50 (μm), the ratio of X to Y, which is the standard deviation of the Ni content ratio (mol%) in particles with an equivalent circle diameter of the projected area of D 50 (μm) or more, is 7.0 or less. The metal composite compound according to [1] [3] In the particle size distribution, D 50 (μm), which is the particle diameter at which the cumulative volume ratio from the small - particle side is 50%, is 4 μm or more and 20 μm or less, and the ratio of D 50 (μm) to D 10 (μm), D 10 / D 50 is 0.3 or more and 0.8 or less, and in the volume - based cumulative particle size distribution, when the particle diameter at which the cumulative volume ratio from the small - particle side is 90% is D 90 (μm), the ratio of D 50 (μm) to D 90 (μm), D 90 / D 50 is 1.4 or more and 1.8 or less. The metal composite compound according to [1] or [2] [4] The metal composite compound according to any one of [1] to [3], which is represented by the following formula (I) Ni (1-x-y) M1 x M2 y O z (OH) 2-α (I) (In formula (I), 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 0.2, 0 < x + y < 1, 0 ≦ z ≦ 3, -0.5 ≦ α ≦ 2, and α - z < 2, M1 is one or more elements selected from the group consisting of Co, Mn, and Al, and M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.) [5] The metal composite compound according to any one of [1] to [4], wherein S does not contain 0. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide a metal composite compound capable of manufacturing a lithium secondary battery with high initial charge-discharge efficiency. [Modes for Carrying Out the Invention]

[0009] In the present specification, the metal composite compound (Metal Composite Compound) is hereinafter referred to as "MCC", and the cathode active material for lithium secondary batteries (Cathode Active Material for lithium secondary batteries) is hereinafter referred to as "CAM". In addition, when "MCC particles" are described, it means one MCC particle, and when "MCC" is described, it means MCC powder which is an aggregate of MCC particles.

[0010] "Ni" does not refer to nickel metal but to nickel atoms. Similarly, "Co", "Li", etc. refer to cobalt atoms, lithium atoms, etc., respectively.

[0011] When a numerical range is described, for example, as "1 - 10 μm" or "1~10 μm", it means a range from 1 μm to 10 μm, and a numerical range including the lower limit value of 1 μm and the upper limit value of 10 μm.

[0012] [Measurement of Initial Charge-Discharge Efficiency] A lithium secondary battery is produced by the following method, and the initial charge-discharge efficiency is measured.

[0013] 1. Manufacturing of lithium secondary batteries (CAM fabrication) MCC and lithium hydroxide monohydrate powder are weighed and mixed in such a ratio that the molar ratio of Li in the lithium hydroxide monohydrate powder to the total amount of elements other than oxygen atoms in the MCC (e.g., Ni, element M1 or element M2 described later) is 1.02 to obtain a mixture. The obtained mixture is calcined at 650°C for 5 hours under an oxygen atmosphere, and then calcined at 750°C for 5 hours under an oxygen atmosphere to obtain CAM.

[0014] (Fabrication of positive electrodes for lithium secondary batteries) The obtained CAM, conductive material (acetylene black), and binder (PVdF) are added and kneaded in a ratio of CAM:conductive material:binder = 92:5:3 (mass ratio) to prepare a paste-like positive electrode mixture. N-methyl-2-pyrrolidone is used as the organic solvent when preparing the positive electrode mixture.

[0015] The resulting positive electrode mixture is applied to a 40 μm thick aluminum foil, which will serve as the current collector, and vacuum-dried at 150°C for 8 hours to obtain a positive electrode for a lithium secondary battery. The electrode area of ​​this lithium secondary battery positive electrode is 1.65 cm². 2 Let's assume that.

[0016] (Manufacturing of lithium secondary batteries) Perform the following operations inside a glove box under an argon atmosphere. (Fabrication of positive electrode for lithium secondary battery) The positive electrode for the lithium secondary battery, fabricated in the above step, is placed with the aluminum foil side facing down on the bottom cover of a coin-type battery R2032 part (for example, manufactured by Hosen Co., Ltd.), and a separator (porous polyethylene film) is placed on top of it. 300 μL of electrolyte is then injected. The electrolyte is a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35, to which LiPF6 is dissolved at a ratio of 1.0 mol / L.

[0017] Next, using metallic lithium as the negative electrode, the negative electrode is placed on top of the separator, the top cover is closed with a gasket, and the battery is crimped with a crimping machine to produce a lithium secondary battery (half-cell of coin-type R2032).

[0018] 2. Charge / Discharge Test Using the lithium secondary battery manufactured by the method described above, the test will be conducted as described in (Measurement Method) below.

[0019] (Measurement method) First, the lithium secondary battery prepared as described above is left to stand at room temperature for 12 hours to allow the separator and positive electrode mixture layer to be sufficiently impregnated with the electrolyte. Next, at a test temperature of 25°C, both charging and discharging are performed with a current setting of 0.2CA, and constant current constant voltage charging and constant current constant voltage discharging are performed, respectively. The maximum charging voltage is 4.3V, and the minimum discharging voltage is 2.5V. The charging capacity is measured, and the obtained value is defined as the "initial charging capacity" (mAh / g). Furthermore, the discharging capacity is measured, and the obtained value is defined as the "initial discharging capacity" (mAh / g).

[0020] Then, using the obtained values ​​for the initial discharge capacity and the initial charge capacity, the initial charge-discharge efficiency is calculated using the following formula (a). Initial charge / discharge efficiency (%) = Initial discharge capacity (mAh / g) / Initial charge capacity (mAh / g) × 100 (a)

[0021] In this embodiment, scanning electron microscopy-energy-dispersive X-ray spectroscopy is referred to as "SEM-EDX". As the scanning electron microscope-energy-dispersive X-ray spectrometer, for example, a Schottky field emission scanning electron microscope (manufactured by JEOL Ltd., product name JSM-7900F) equipped with Oxford Instruments' X-Max 150 as the EDX detector can be used. Furthermore, SEM-EDX analysis is performed using SEM-EDX with an acceleration voltage of 15kV and a resolution of 119nm.

[0022] <Metal composite compounds> This embodiment is an MCC containing at least Ni. An example of an MCC is a hexagonal compound having a layered structure. Examples of MCCs include metal composite oxides, metal composite hydroxides, or mixtures thereof. Metal composite hydroxides may also include partially oxidized compounds. One form of MCC particles is a secondary particle, which is an aggregate of primary particles.

[0023] MCC is defined as a scatter plot obtained by measuring MCC using SEM-EDX, where the horizontal axis represents the equivalent circle diameter (μm) of the projected area of ​​the MCC particle and the vertical axis represents the Ni content ratio (mol%) of the MCC particle relative to the projected area. The slope of the approximate straight line calculated using the least squares method is between -0.2 and 0.2. Hereafter, this slope may be abbreviated as "S". Furthermore, in the volume-based particle size distribution of MCC, the particle size at which the cumulative volume proportion from the smallest particles is 10% is defined as D 10 When the diameter is (μm), the equivalent diameter of the projected area circle of the MCC particle is D 10 The standard deviation X of the Ni content in particles with a diameter of (μm) or less is 2.0 mol% or less.

[0024] [Measurement of S, X, and Y] When measuring MCCs with SEM-EDX, MCC particles that fall within the measurement field are randomly selected using the automatic extraction function of the SEM-EDX instrument, and the projected area equivalent diameter and Ni content of the MCC particles are calculated. At this time, the measurement field is changed until at least 50 MCC particles satisfying the following conditions (i) to (iii) are measured for each condition, and a total of at least 300 particles are measured, and the automatic extraction of particles and the measurement of the projected area equivalent diameter and Ni content of the MCC particles are repeated. (i) Particles with a projected area equivalent diameter of 7 μm or less. (ii) Particles with a projected area equivalent diameter greater than 7 μm and less than or equal to 10 μm. (iii) Particles with a projected area equivalent diameter greater than 10 μm.

[0025] Regarding the measurement of MCC particles, for example, if 50 particles of type (i), 150 particles of type (ii), and 100 particles of type (iii) are extracted and the Ni content ratio of each particle is measured, this can be used to calculate S, X, and Y. Furthermore, if a predetermined number of MCC particles satisfying the above conditions (i) to (iii) do not appear even after a total of 5000 particles have been extracted, it will be considered that no MCC particles satisfying the above conditions (i) to (iii) have been detected, and the sample will not fall under the scope of this invention.

[0026] When MCC particles are extracted based on the projected area equivalent diameter criteria described in (i) to (iii) above, the entire MCC can be roughly divided into large particles, medium particles, and small particles, and the characteristics obtained in each division can be determined as characteristics for each particle size.

[0027] The surface of the MCC is measured using SEM-EDX to obtain the projected area equivalent diameter of the MCC particles contained in the MCC, and the Ni content (mol%) of the MCC particles. Furthermore, in the volume-based particle size distribution of MCC, the particle size at which the cumulative volume proportion from the smallest particles is 10% is defined as D 10 When the diameter is (μm), the equivalent diameter of the projected area circle of the MCC particle is D 10 The standard deviation of the Ni content in particles with a diameter of (μm) or less, X (mol%), is obtained. Furthermore, in the volume-based particle size distribution of MCC, the particle size at which the cumulative volume proportion from the smallest particles is 50% is defined as D 50 When the diameter is (μm), the equivalent diameter of the projected area circle of the MCC particle is D 50 The standard deviation of the Ni content in particles larger than (μm) is obtained as Y (mol%).

[0028] To obtain S, a scatter plot is created with the projected area equivalent diameter (μm) on the horizontal axis and the Ni content ratio (mol%) relative to the projected area equivalent diameter on the vertical axis. In the resulting scatter plot, we obtain S, which is the slope of the approximate straight line calculated using the least squares method.

[0029] In this embodiment, S is -0.2 to 0.2, preferably -0.15 to 0.15, and more preferably -0.1 to 0.1. MCCs where S satisfies the above range mean that the Ni content (mol%) is uniform regardless of particle size. When S is 0, it means that the Ni content (mol%) is the same regardless of particle size. Since it is unlikely that all particles would have the same Ni content (mol%), 0 is practically excluded from S.

[0030] Furthermore, X is 2.0 mol% or less, preferably 1.8 mol% or less, and more preferably 1.6 mol% or less. The lower limit of X is not particularly limited, but for example, it can be 0.1 mol% or more, 0.2 mol% or more, or 0.3 mol% or more. The upper and lower limits for X can be combined in any way. Examples of combinations include 0.1-2.0 mol%, 0.2-1.8 mol%, and 0.3-1.6 mol%. If X satisfies the above range, D 10 This means that the Ni content (mol%) is uniform in particles smaller than (μm), i.e., in the small particle region.

[0031] MCCs where S and X satisfy the above ranges mean that the Ni content (mol%) is uniform regardless of particle size, and that the Ni content (mol%) is uniform in the small particle region. CAM produced using such MCC as a precursor maintains the Ni content (mol%) defined by S and X. That is, CAM produced using the MCC of this embodiment as a precursor has a uniform Ni content (mol%) regardless of particle size, and the Ni content (mol%) is uniform in the small particle region. In such CAM, Ni is uniformly distributed within the particles, resulting in an electrode with a uniform composition when used as an electrode, which suppresses variations in current values. This makes it possible to produce lithium secondary batteries with low resistance and high initial charge-discharge efficiency.

[0032] The MCC preferably has a ratio of X to Y, [X / Y], of 7.0 or less, more preferably 6.5 or less, even more preferably 6.0 or less, and particularly preferably 5.5 or less. The lower limit of [X / Y] is not particularly limited, and is, for example, 1.0 or more, 1.1 or more, 1.2 or more, or 1.3 or more. The above upper and lower limits of [X / Y] can be arbitrarily combined. Examples of combinations include, for example, 1.0 to 7.0, 1.1 to 6.5, 1.2 to 6.0, and 1.3 to 5.5.

[0033] X and [X / Y] being within the above ranges means that, in 10 the following small particle region and 50 the above large particle region, the difference in the standard deviation (mol%) of the Ni content ratio is small and the Ni content ratio (mol%) is uniform. The CAM produced using the MCC of this embodiment as a precursor maintains [X / Y]. That is, the CAM produced using such an MCC as a precursor has a uniform Ni content ratio (mol%) in the small particle region and the large particle region. Such a CAM has Ni uniformly present in the particles, and when used as an electrode, the electrode has a uniform composition, and the variation in the current value is easily suppressed. Therefore, it becomes an MCC that can produce a lithium secondary battery with low resistance and high initial charge-discharge efficiency.

[0034] The MCC is preferably represented by the following formula (I). Ni (1-x-y) M1 x M2 y O z (OH) 2-α (I) (In formula (I), 0 ≦ x ≦ 0.8, 0 ≦ y ≦ 0.2, 0 < x + y < 1, 0 ≦ z ≦ 3, -0.5 ≦ α ≦ 2, and α - z < 2, M1 is one or more elements selected from the group consisting of Co, Mn, and Al, and M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.)

[0035] (x) x is preferably 0.05 or greater, and more preferably 0.1 or greater. x is preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.3 or less. The above lower and upper limits for x can be combined in any way. From the viewpoint of improving the initial charge-discharge efficiency of the battery, x is preferably 0-0.5, more preferably 0.05-0.4, and even more preferably 0.1-0.3.

[0036] (y) y is preferably 0.15 or less, more preferably 0.1 or less, and even more preferably 0.05 or less. The above lower and upper limits for y can be combined in any way. From the viewpoint of improving the initial charge-discharge efficiency of the battery, y is preferably 0-0.15, more preferably 0-0.1, and even more preferably 0-0.05.

[0037] (x+y) x+y is preferably greater than 0, more preferably 0.03 or greater, and even more preferably 0.05 or greater. x+y is preferably 0.7 or less, more preferably 0.6 or less, even more preferably 0.4 or less, and particularly preferably 0.3 or less. The above lower and upper limits for x+y can be combined in any way. From the viewpoint of improving the initial charge-discharge efficiency of the battery, x+y is preferably greater than 0 and 0.7 or less, more preferably greater than 0 and 0.6 or less, even more preferably between 0.03 and 0.4, and particularly preferably between 0.05 and 0.3.

[0038] From the viewpoint of obtaining a lithium secondary battery with high initial charge-discharge efficiency, it is preferable that element M2 is one or more elements selected from the group consisting of Ti, Mg, W, Nb, and Zr.

[0039] [Composition analysis] The composition of MCC is measured using an ICP emission spectrometer after dissolving the MCC in hydrochloric acid. For example, an Optima 8300 (manufactured by PerkinElmer Corporation) can be used as an ICP emission spectrometer.

[0040] [Particle size distribution measurement] The volume-based particle size distribution of MCC is measured by laser diffraction scattering. 250 μL of a 10% by mass sodium hexametaphosphate aqueous solution is added as a dispersant to a Microtrac MT3300EXII manufactured by Microtrac-Bell Corporation, and the particle size distribution is measured to obtain a volume-based particle size distribution curve. MCC is added so that the transmittance during measurement is 85 ± 5%.

[0041] In the obtained particle size distribution curve, the particle size at which the cumulative volume percentage from the smallest particle side reaches 10% is defined as D. 10 (μm), the particle size at which the cumulative volume percentage from the smallest particle side reaches 50% is D. 50 (μm), the particle size at which the cumulative volume percentage from the smallest particle side reaches 90% is D. 90 Let it be (μm).

[0042] MCC's D 50 The particle size is preferably 4 μm or larger, more preferably 7 μm or larger, and even more preferably 9 μm or larger. 50 The particle size is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less. MCC's D 50 The above lower and upper limits can be combined in any way. As an example of a combination, see MCC's D 50 These are 4-20 μm, 7-18 μm, and 9-15 μm.

[0043] MCC's D 50 D 10 The ratio of D 10 / D 50 A value of 0.3 or higher is preferred, 0.35 or higher is more preferred, and 0.40 or higher is even more preferred. 10 / D 50 It is preferably 0.8 or less, more preferably 0.75 or less, and even more preferably 0.70 or less. D 10 / D 50 The above lower and upper limits can be combined in any way. As an example of a combination, MCC's D 10 / D 50These ranges from 0.3 to 0.8, 0.35 to 0.75, and 0.40 to 0.70.

[0044] MCC's D 50 D 90 The ratio of D 90 / D 50 A value of 1.4 or higher is preferred, 1.45 or higher is more preferred, and 1.50 or higher is even more preferred. 90 / D 50 It is preferably 1.8 or less, more preferably 1.75 or less, and even more preferably 1.70 or less. D 90 / D 50 The above lower and upper limits can be combined in any way. As an example of a combination, MCC's D 90 / D 50 These ranges from 1.4 to 1.8, 1.45 to 1.75, and 1.50 to 1.70.

[0045] ≪Method of manufacturing MCC≫ MCCs can be manufactured by batch coprecipitation or continuous coprecipitation. The manufacturing method will be described in detail below, using a metal composite hydroxide containing Ni and element M1 as an example.

[0046] First, using a coprecipitation method, particularly the continuous coprecipitation method described in JP-A-2002-201028, a nickel salt solution, a metal salt solution of element M1, an alkaline aqueous solution, and a complexing agent as needed are mixed in a reaction vessel to produce a metal composite hydroxide containing Ni and element M1.

[0047] As the nickel salt solute in the nickel salt solution, one or more of the following can be used: nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate.

[0048] Examples of metal salts that can be used as the solute in a metal salt solution of element M1 include cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt acetate, manganese sulfate, manganese nitrate, manganese chloride, manganese acetate, aluminum sulfate, and sodium aluminate.

[0049] The above metal salts are used in proportions corresponding to the composition ratio of the above composition formula (I). Water is used as the solvent.

[0050] When a nickel salt solution, a metal salt solution of element M1, an alkaline aqueous solution, and a complexing agent as needed are continuously supplied to the reaction vessel, Ni and element M1 react, and Ni (1-x) M1 x (OH) 2-α Nuclei for the crystals are formed. Furthermore, by continuously supplying these raw materials, the nuclei grow. At this time, the nickel salt solution and the metal salt solution of element M1 may be mixed to prepare a mixed solution before supplying it to the reaction vessel, and this mixed solution may be supplied to the reaction vessel. Alternatively, the nickel salt solution, the metal salt solution of element M1, and the mixed solution may each be supplied to the reaction vessel from multiple supply ports.

[0051] Here, the reaction slurry refers to a mixture of solids and liquids present in the reaction vessel, specifically a mixture containing a nickel salt solution, a metal salt solution of element M1, a mixed solution, a complexing agent, an alkaline aqueous solution, and solid components including precipitates formed by the reaction.

[0052] The complexing agent is a compound capable of forming complexes with Ni and element M1 ions in aqueous solution. Examples include ammonium ion suppliers, hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine.

[0053] Examples of ammonium ion suppliers include ammonium salts such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride.

[0054] The reaction slurry does not necessarily have to contain a complexing agent. If a complexing agent is included, the amount of the complexing agent in the reaction slurry should, for example, have a molar ratio to the total number of moles of metal salts in the reaction slurry that is greater than 0 and 2.0 or less.

[0055] In the coprecipitation method, an alkaline aqueous solution is added to the reaction slurry before its pH changes from alkaline to neutral in order to adjust the pH value of the reaction slurry. Sodium hydroxide aqueous solution or potassium hydroxide aqueous solution can be used as the alkaline aqueous solution.

[0056] In this specification, the pH value is defined as the value measured when the reaction slurry temperature is 40°C. If the temperature of the reaction slurry sampled from the reaction vessel is not 40°C, the reaction slurry should be heated or cooled to 40°C before measuring the pH.

[0057] During the reaction, the ratio [C1 / C2] of the solid content concentration (mass%) of the reaction slurry (C1) to the nickel concentration (mass%) of the nickel salt solution (C2) is controlled to be between 1.01 and 1.3. Here, nickel concentration refers to the weight ratio of nickel element contained in a certain weight of solution. Furthermore, the ratio [P1 / P2] of the pH of the nickel salt solution (P1) to the pH of the reaction slurry (P2) is controlled to 0.440 or higher. In this case, if the nickel salt solution and the metal salt solution of element M1 are mixed before supplying them to the reaction vessel and supplied as a mixed solution, C2 is the nickel concentration (mass%) of the mixed solution, and P1 is the pH of the mixed solution.

[0058] The solid content concentration (mass%) of a reaction slurry can be calculated, for example, by taking a certain weight of reaction slurry from the reaction vessel, filtering and drying the slurry, and then calculating the ratio of the dry weight of the solid content to the weight of the slurry taken out. Specifically, the solid content concentration (mass%) of the reaction slurry can be calculated as follows: Dry weight of solid content (g) / Weight of slurry taken out (g) × 100. When [C1 / C2] and [P1 / P2] are within the above ranges, nickel is consumed in a balanced manner during nucleation and growth, respectively, and an MCC satisfying S, X and [X / Y] is obtained.

[0059] The substances in the reaction vessel should be stirred and mixed as needed. For the reaction vessel used in the continuous coprecipitation method, an overflow type reaction vessel can be used to separate the formed reaction precipitate.

[0060] To control the atmosphere inside the reaction vessel to the desired level, a specific gas can be passed through the vessel, or the reaction slurry can be directly bubbled into it.

[0061] After the above reaction, the neutralized reaction precipitate is washed with water and then isolated. For isolation, methods such as dehydrating the slurry containing the reaction precipitate (i.e., the co-precipitate slurry) by centrifugation or suction filtration are used. The isolated reaction precipitate is washed, dehydrated, dried, and sieved as needed to obtain the metal complex hydroxide.

[0062] After drying the MCC, classification may be performed as appropriate.

[0063] Washing of the reaction precipitate is preferably carried out with water, weakly acidic water, or an alkaline washing solution. In this embodiment, washing with an alkaline washing solution is preferred, and washing with an aqueous solution of sodium hydroxide or potassium hydroxide is more preferred. It is preferable to wash the reaction precipitate with water, weak acid water, or an alkaline washing solution in an amount of 10 times or more by mass relative to the precipitate's mass, and it is preferable that the temperature of the weak acid water or alkaline washing solution be 30°C or higher. Furthermore, it is preferable to perform the washing at least once. Furthermore, after washing with a solution other than water, it is preferable to wash again with water to ensure that no compounds derived from the washing solution remain in the reaction precipitate.

[0064] The drying temperature is preferably 80 to 250°C, and more preferably 90 to 230°C. The drying time is preferably 0.5 to 30 hours, and more preferably 1 to 25 hours. The drying pressure may be either atmospheric pressure or reduced pressure.

[0065] When producing metal composite oxides as MCCs, metal composite hydroxides can be heated to produce metal composite oxides. Multiple heating steps may be performed if necessary. In this specification, heating temperature refers to the set temperature of the heating device. If there are multiple heating steps, it refers to the temperature at which each heating step is performed at the highest holding temperature.

[0066] The heating temperature is preferably 300 to 700°C, and more preferably 350 to 680°C. When the heating temperature is 300 to 700°C, a metal composite oxide is obtained in which the metal composite hydroxide is sufficiently oxidized.

[0067] The holding time at the heating temperature can range from 0.1 to 20 hours, with 0.5 to 10 hours being preferred. The heating rate to reach the heating temperature is, for example, 50 to 400°C / hour. The heating atmosphere can be air, oxygen, nitrogen, argon, or a mixture thereof.

[0068] The heating device may have an atmosphere with an appropriate amount of oxygen. This oxygen-containing atmosphere may be a mixed gas atmosphere of an inert gas and an oxidizing gas, or it may be an inert gas atmosphere with an oxidizing agent present. By having an atmosphere with an appropriate amount of oxygen inside the heating device, the transition metal contained in the metal composite hydroxide is appropriately oxidized, making it easier to control the morphology of the metal composite oxide.

[0069] In an oxygen-containing atmosphere, the oxygen and oxidizing agent only need to be present in sufficient quantities to oxidize the transition metal. If the oxygen-containing atmosphere is a mixed gas atmosphere of an inert gas and an oxidizing gas, the atmosphere inside the heating device can be controlled by methods such as passing the oxidizing gas through the heating device. As oxidizing agents, peroxides such as hydrogen peroxide, peroxide salts such as permanganate, perchlorates, hypochlorites, nitric acid, halogens, or ozone can be used.

[0070] <Method for manufacturing positive electrode active material for lithium secondary batteries> CAM can be manufactured using the aforementioned MCC as a raw material.

[0071] The method for manufacturing CAM includes a firing step in which a mixture of MCC and a lithium compound is fired. The method for manufacturing CAM may include a mixing step in which MCC and a lithium compound are mixed before the firing step, and a washing step in which the obtained fired product is washed after the firing step.

[0072] [Mixing process] Mix MCC with a lithium compound. As the lithium compound, one or more selected from the group consisting of lithium carbonate, lithium hydroxide, and lithium hydroxide monohydrate can be used.

[0073] The lithium compound and MCC are mixed, taking into consideration the composition ratio of the final product, to obtain a mixture of the lithium compound and MCC.

[0074] [Firing process] The resulting mixture is calcined. The calcination process promotes the growth of CAM crystals. The calcination process is carried out, for example, in an oxygen-containing atmosphere at a calcination temperature of 500-1000°C.

[0075] In this specification, firing temperature refers to the temperature of the atmosphere inside the firing furnace, and means the maximum temperature at which the firing temperature is maintained (maximum holding temperature). If the firing process has multiple firing stages, the firing temperature refers to the temperature at the stage where the firing was performed at the highest holding temperature among all stages.

[0076] The firing temperature is preferably 550-900°C, and more preferably 600-800°C.

[0077] Furthermore, the holding time at the firing temperature can range from 0.1 to 30 hours, with 0.5 to 20 hours being preferred.

[0078] Furthermore, it is preferable to perform the firing in an oxygen-containing atmosphere. Specifically, it is preferable to introduce oxygen gas to create an oxygen-containing atmosphere inside the firing furnace.

[0079] [Washing process] In this embodiment, the fired product may be washed with a cleaning solution such as pure water or an alkaline cleaning solution. The fired product after washing may be dried as appropriate.

[0080] The calcined material, after being fired and washed as appropriate, is crushed and sieved as appropriate to obtain CAM.

[0081] According to the MCC configuration described above, it is possible to manufacture a CAM that can achieve high initial charge-discharge efficiency for lithium secondary batteries.

[0082] Furthermore, by using the above-described method for manufacturing CAM, it is possible to suitably manufacture CAM with high initial charge-discharge efficiency for lithium secondary batteries by using the aforementioned MCC as a raw material.

[0083] <Lithium-ion secondary battery> A suitable positive electrode for lithium secondary batteries when using the above-mentioned CAM will be described below. Hereafter, the positive electrode for lithium secondary batteries may be referred to simply as the positive electrode. Furthermore, we will describe lithium secondary batteries that are suitable for use as a positive electrode.

[0084] A suitable example of a lithium secondary battery using CAM includes a positive electrode and a negative electrode, a separator sandwiched between the positive and negative electrodes, and an electrolyte placed between the positive and negative electrodes.

[0085] <All-solid-state lithium secondary battery> The above CAM can be used as the CAM for an all-solid-state lithium secondary battery.

[0086] An example of an all-solid-state lithium secondary battery includes a laminate having a positive electrode, a negative electrode, and a solid electrolyte layer, and an outer casing that houses the laminate. Alternatively, the all-solid-state lithium secondary battery may have a bipolar structure in which the CAM and negative electrode active material are arranged on both sides of the current collector. A specific example of a bipolar structure is the structure described in JP-A-2004-95400. [Examples]

[0087] Next, the present invention will be described in more detail with reference to examples.

[0088] <Composition analysis> The composition of MCC was analyzed by the method described in the above <Composition analysis>.

[0089] <Measurement of S, X, and Y> S, X, and Y were measured by the method described in the above <Measurement of S, X, and Y>. Furthermore, [X / Y] was calculated from the obtained results.

[0090] <Measurement of initial charge-discharge efficiency> The initial charge-discharge efficiency was measured by the method described in the above <Measurement of initial charge-discharge efficiency>.

[0091] <Example 1> After water was put into a reaction tank equipped with a rotary stirring device having a stirring blade and an overflow pipe, an aqueous sodium hydroxide solution was added. An aqueous nickel sulfate solution and an aqueous cobalt sulfate solution were mixed at a molar ratio of Ni:Co of 95.5:4.5 to prepare a mixed solution 1. Next, into the reaction tank, while stirring, the above mixed solution 1, an aqueous ammonium sulfate solution as a complexing agent, and an aqueous sodium hydroxide solution were continuously added to obtain a reaction slurry 1. At this time, while maintaining the temperature of the reaction slurry 1 at 70°C, each solution was added at a ratio such that the slurry concentration of the reaction slurry 1 / the Ni concentration of the mixed solution 1 (C1 / C2) was 1.14 and the pH of the mixed solution 1 / the pH of the reaction slurry 1 (P1 / P2) was 0.446 to obtain a reaction precipitate 1. The obtained reaction precipitate 1 was subjected to isolation, washing, dehydration, drying, and sieving to obtain a metal composite hydroxide 1.

[0092] <Example 2> After water was put into a reaction tank equipped with a rotary stirring device having a stirring blade and an overflow pipe, an aqueous sodium hydroxide solution was added. Mixed solution 2 was prepared by mixing nickel sulfate aqueous solution, cobalt sulfate aqueous solution, and aluminum sulfate aqueous solution in a ratio of Ni:Co:Al of 93.0:4.0:3.0. Next, the above mixed solution 2, along with aqueous ammonium sulfate and aqueous sodium hydroxide as complexing agents, were continuously added to the reaction vessel under stirring to obtain reaction slurry 2. At this time, while maintaining the temperature of reaction slurry 2 at 70°C, each solution was added in a ratio such that the slurry concentration of reaction slurry 2 / Ni concentration of mixed solution 2 (C1 / C2) was 1.23 and the pH of mixed solution 2 / pH of reaction slurry 2 (P1 / P2) was 0.489 to obtain reaction precipitate 2. The resulting reaction precipitate 2 was isolated, washed, dehydrated, dried, and sieved to obtain metal composite hydroxide 2.

[0093] <Example 3> After adding water to a reaction vessel equipped with a rotary stirring device having a stirring blade and an overflow pipe, an aqueous sodium hydroxide solution was added. Mixed solution 3 was prepared by mixing nickel sulfate aqueous solution, cobalt sulfate aqueous solution, and manganese sulfate aqueous solution in a ratio of Ni:Co:Mn of 95.0:3.0:2.0. Next, the mixed solution 3, along with aqueous ammonium sulfate and aqueous sodium hydroxide as complexing agents, were continuously added to the reaction vessel under stirring to obtain reaction slurry 3. At this time, while maintaining the temperature of reaction slurry 3 at 70°C, each solution was added in a ratio such that the slurry concentration of reaction slurry 3 / Ni concentration of mixed solution 3 (C1 / C2) was 1.08 and the pH of mixed solution 3 / pH of reaction slurry 3 (P1 / P2) was 0.447 to obtain reaction precipitate 3. The resulting reaction precipitate 3 was isolated, washed, dehydrated, dried, and sieved to obtain metal composite hydroxide 3.

[0094] <Comparative Example 1> After adding water to a reaction vessel equipped with a rotary stirring device having a stirring blade and an overflow pipe, an aqueous sodium hydroxide solution was added. Mixed solution 4 was prepared by mixing nickel sulfate aqueous solution, cobalt sulfate aqueous solution, and aluminum sulfate aqueous solution in a ratio of Ni:Co:Al of 88.0:9.0:3.0. Next, the mixed solution 4, along with aqueous ammonium sulfate and aqueous sodium hydroxide as complexing agents, were continuously added to the reaction vessel under stirring to obtain reaction slurry 4. At this time, while maintaining the temperature of reaction slurry 4 at 40°C, each solution was added in a ratio such that the slurry concentration of reaction slurry 4 / Ni concentration of mixed solution 4 (C1 / C2) was 1.02 and the pH of mixed solution 4 / pH of reaction slurry 4 (P1 / P2) was 0.433 to obtain reaction precipitate 4. The resulting reaction precipitate 4 was isolated, washed, dehydrated, dried, and sieved to obtain metal composite hydroxide 4.

[0095] <Comparative Example 2> After adding water to a reaction vessel equipped with a rotary stirring device having a stirring blade and an overflow pipe, an aqueous sodium hydroxide solution was added. Mixed solution 5 was prepared by mixing nickel sulfate aqueous solution, cobalt sulfate aqueous solution, and manganese sulfate aqueous solution in a ratio of Ni:Co:Mn of 83.0:5.0:12.0. Next, the mixed solution 5, an aqueous solution of ammonium sulfate as a complexing agent, and an aqueous solution of sodium hydroxide were successively added to the reaction vessel under stirring to obtain a reaction slurry 5. At this time, while maintaining the temperature of the reaction slurry 5 at 70°C, each solution was added in a ratio such that the slurry concentration of the reaction slurry 5 / Ni concentration of the mixed solution 5 (C1 / C2) was 1.35 and the pH of the mixed solution 5 / pH of the reaction slurry 5 (P1 / P2) was 0.436 to obtain a reaction precipitate 5. The resulting reaction precipitate 5 was isolated, washed, dehydrated, dried, and sieved to obtain the metal composite hydroxide 5.

[0096] Table 1 below shows the composition, S, X, X / Y, and D of MCC1-3 produced in Examples 1-3 and MCC11-12 produced in Comparative Examples 1-2. 50 , D 10 / D 50 , D 90 / D 50 This indicates. Furthermore, the results of the initial charge-discharge efficiency of lithium secondary batteries using positive electrode active materials made from MCC1-3 produced in Examples 1-3 and MCC11-12 produced in Comparative Examples 1-2 are shown.

[0097] [Table 1]

[0098] As shown in Table 1, Examples 1 to 3, in which S was between -0.2 and 0.2 and X was 2.0 mol% or less, all showed high initial charge-discharge efficiencies of 85% or more.

Claims

1. A metal composite compound containing at least Ni, obtained by measuring the powder of the metal composite compound using scanning electron microscopy-energy-dispersive X-ray spectroscopy, has a scatter plot on which the projected area circle equivalent diameter (μm) of the particles of the metal composite compound is on the horizontal axis and the Ni content (mol%) of the particles of the metal composite compound is on the vertical axis, wherein the slope S of the approximate straight line calculated by the least squares method is between -0.2 and 0.2, and in the volume-based particle size distribution, the particle size D is such that the cumulative volume percentage from the smallest particle side is 10%. １０ When (μm), the above D １０ A metal composite compound in which X, the standard deviation of the Ni content (mol%) in particles with a projected area equivalent diameter of (μm) or less, is 2.0 mol% or less.

2. In the particle size distribution described above, the particle size at which the cumulative volume ratio from the smallest particle side becomes 50% is D. ５０ When (μm), the above X and the above D ５０ The metal composite compound according to claim 1, wherein the ratio of Y, which is the standard deviation of the Ni content (mol%) in particles with a projected area equivalent diameter of (μm) or more, to 7.0 or less.

3. In the particle size distribution, D is the particle diameter at which the cumulative volume ratio from the small particle side is 50%. ５０ (μm) is 4 μm or more and 20 μm or less, and the ratio of D ５０ (μm) to D １０ (μm), D １０ / D ５０ is 0.3 or more and 0.8 or less. In the cumulative particle size distribution based on volume, when the particle diameter at which the cumulative volume ratio from the small particle side is 90% is D ９０ (μm), the ratio of D ５０ (μm) to D ９０ (μm), D ９０ / D ５０ is 1.4 or more and 1.8 or less. The metal composite compound according to claim 1 or 2.

4. A metal composite compound according to claim 1 or 2, represented by the following formula (I). Ni （１－ｘ－ｙ） M1 ｘ M2 ｙ O ｚ (OH) ２－α (I) (In equation (I), 0 ≤ x ≤ 0.8, 0 ≤ y ≤ 0.2, 0 < x + y < 1, 0 ≤ z ≤ 3, -0.5 ≤ α ≤ 2, and α - z < 2, where M1 is one or more elements selected from the group consisting of Co, Mn, and Al, and M2 is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.)

5. The metal composite compound according to claim 1 or 2, wherein S does not contain 0.

Images