Method for manufacturing metal composite hydroxides and positive electrode active materials for lithium secondary batteries

Abstract

The present invention relates to a composite metal hydroxide that is used as the precursor for a positive electrode active substance of a lithium secondary battery. The composite metal hydroxide contains Ni, Co, and Mn and satisfies requirements (1) through (4). (1) The average particle strength is 10 MPa or greater but less than 45 MPa. (2) The molar ratio (Mn / Co) of manganese to cobalt is greater than 1.0. (3) The BET specific surface area is less than 40 m2 / g. (4) The average particle diameter D50 is 4.0 μm or less.

Description

[Technical Field]

[0001] This invention relates to a method for producing metal composite hydroxides and positive electrode active materials for lithium secondary batteries. This application claims priority based on Japanese Patent Application No. 2022-114311, filed in Japan on July 15, 2022, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] One method for producing positive electrode active materials for lithium secondary batteries is to mix a lithium compound with a metal composite compound containing metal elements other than Li and then calcine the mixture.

[0003] In order to improve the performance of lithium secondary batteries, the aforementioned metal composite compounds are being investigated. For example, Patent Document 1 discloses a nickel-manganese-cobalt-containing composite hydroxide as a precursor for a positive electrode active material for lithium-ion secondary batteries, comprising a plurality of plate-shaped primary particles and secondary particles formed by the aggregation of fine primary particles smaller than the plate-shaped primary particles. It has been disclosed that lithium-ion secondary batteries manufactured using the nickel-manganese-cobalt-containing composite hydroxide as a precursor exhibit high durability and excellent power output characteristics. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] JP-A-2020-177860 [Overview of the project] [Problems that the invention aims to solve]

[0005] As applications for lithium-ion batteries expand, further improvements in initial efficiency are required. The present invention has been made in view of the above circumstances, and an object thereof is to provide a metal composite hydroxide used as a precursor of a positive electrode active material for a lithium secondary battery, which can obtain a lithium secondary battery having high initial efficiency, and a method for producing a positive electrode active material for a lithium secondary battery using the metal composite hydroxide. **Means for Solving the Problems**

[0006] The present invention is as follows [1] to [4]. [1] A metal composite hydroxide used as a precursor of a positive electrode active material for a lithium secondary battery, which contains Ni, Co, and Mn and satisfies all of the following requirements (1) to (4). (1) The average particle strength is 10 MPa or more and less than 45 MPa. (2) The molar ratio of manganese to cobalt (Mn / Co) is more than 1.0. (3) The BET specific surface area is less than 40 m , 2+α , y , w , 1-x-y-w , x , 2 , , 50 , , , , , , / g. (4) The average particle diameter D 50 is 4.0 μm or less. [2] The metal composite hydroxide according to [1], which is represented by the following composition formula (I). Ni 1-x-y-w Co x Mn y M w (OH) 2+α ··· Formula (I) (In the composition formula (I), 0 < x < 0.5, 0 < y ≤ 0.5, 0 ≤ w ≤ 0.5, x < y, 0 < x + y + w < 1, 0 ≤ α are satisfied, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.) [3] The metal composite hydroxide according to [1] or [2], wherein the standard deviation of the particle strength is​​​[Effects of the Invention]

[0007] According to the present invention, it is possible to provide a metal composite hydroxide that can be used as a precursor for a positive electrode active material for a lithium secondary battery, which can be obtained from a lithium secondary battery with high initial efficiency, and a method for producing a positive electrode active material for a lithium secondary battery using the metal composite hydroxide. [Modes for carrying out the invention]

[0008] The definitions of terms used in this specification are as follows: Metal composite hydroxides are also referred to as "MCH" below. Cathode Active Material for lithium secondary batteries is also referred to as "CAM" below. "Ni" indicates the element Ni, not the metal nickel. The same applies to the notation of other elements such as Co and Mn. A "primary particle" refers to a particle that, when observed using a scanning electron microscope or similar device at a field of view between 10,000x and 30,000x magnification, does not exhibit visible grain boundaries. A "secondary particle" is a particle formed by the aggregation of primary particles. In other words, a secondary particle is an aggregate of primary particles. Regarding numerical ranges, "A or greater and B or less" is expressed as "A~B". For example, if a numerical range is written as "1~10MPa", it means a range from 1MPa to 10MPa, including the lower limit of 1MPa and the upper limit of 10MPa.

[0009] The methods for measuring each parameter of MCH in this specification are as follows:

[0010] (average particle strength) The average particle strength (unit: MPa) of MCH can be measured and calculated as follows. First, 20 secondary particles are randomly selected from MCH. Using a micro compression tester (for example, MCT-510 manufactured by Shimadzu Corporation), the particle diameter and particle strength are measured for each of the selected secondary particles. Here, the particle strength Cs (unit: MPa) is obtained by the following formula (A). In the following formula (A), P is the test force (unit: N), and d is the particle diameter (unit: mm). P is the pressure value at which the displacement amount becomes maximum while the test pressure remains almost constant when the test pressure is gradually increased. d is the value obtained by measuring the diameters in the X direction and Y direction in the observation image of the micro compression tester and calculating their average value). Cs = 2.8P / πd 2 ···(A) The average value of Cs of the obtained 20 secondary particles is the average particle strength. Since the particle strength is normalized by the particle diameter, if the structures of each particle are the same, particles with different particle diameters will have the same (average particle strength ± 5%) particle strength. On the other hand, if the particle strengths are different between particles, it can be said that the structures of each particle are different.

[0011] (Standard deviation of particle strength) The standard deviation of the particle strength of MCH can be calculated from the average particle strength obtained above (average particle strength) and Cs of 20 secondary particles.

[0012] (Average particle diameter D 50 ) The average particle diameter D of MCH or CAM 50The particle size (in μm) can be determined from the particle size distribution of MCH or CAM measured by laser diffraction scattering. Specifically, 0.1 g of the powder to be measured, for example, MCH or CAM, is added to 50 mL of a 0.2 mass% sodium hexametaphosphate aqueous solution to obtain a dispersion. Next, the particle size distribution of the obtained dispersion is measured using a laser diffraction scattering particle size distribution analyzer (for example, Microtrac MT3300EXII manufactured by Microtrac-Bell Co., Ltd.) to obtain a volume-based cumulative particle size distribution curve. In the obtained cumulative particle size distribution curve, the particle diameter value at 50% accumulation from the fine particle side is the average particle diameter (hereinafter, D 50 (This is sometimes written as follows.)

[0013] (BET specific surface area) BET specific surface area of ​​MCH (unit: m²) 2 The specific surface area ( / g) can be measured by the BET (Brunauer, Emmett, Teller) method. Nitrogen gas is used as the adsorption gas in the BET specific surface area measurement. For example, 1 g of the powder to be measured can be dried in a nitrogen atmosphere at 105°C for 30 minutes, and then measured using a BET specific surface area meter (e.g., Macsorb®, manufactured by Mountec).

[0014] (composition) The composition of each metallic element in MCH can be measured by inductively coupled plasma emission spectrometry (ICP). For example, after dissolving MCH in hydrochloric acid, the amount of each metallic element can be measured using an inductively coupled plasma emission spectrometer (e.g., SPS3000, manufactured by SII Nanotechnology Co., Ltd.).

[0015] The evaluation method for CAM in this specification is as follows:

[0016] (First-time efficiency) A lithium secondary battery is manufactured using CAM by the method described in the examples below. An initial efficiency test is performed using the manufactured lithium secondary battery by the following method, and the initial efficiency is calculated.

[0017] • Initial efficiency test Allow the lithium secondary battery 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 were performed with a current setting of 0.2CA, and constant current constant voltage charging and constant current constant voltage discharging were performed, respectively. The maximum charging voltage was 4.3V, and the minimum discharging voltage was 2.5V. The charging time was 6 hours, and the discharging time was 5 hours. The charging capacity was measured, and the obtained value was defined as the "initial charging capacity" (mAh / g). Furthermore, the discharging capacity was measured, and the obtained value was defined as the "initial discharging capacity" (mAh / g). Using the values ​​of the initial discharge capacity and the initial charge capacity, the initial efficiency is calculated using the following formula. Initial efficiency (%) = Initial discharge capacity (mAh / g) / Initial charge capacity (mAh / g) × 100

[0018] Metal composite hydroxides The MCH of this embodiment can be used as a precursor of CAM. The MCH contains Ni, Co, and Mn and satisfies all of the following requirements (1) to (4). (1) The average particle strength is 10 MPa or more and less than 45 MPa. (2) The molar ratio of manganese to cobalt (Mn / Co) is greater than 1.0. (3) BET specific surface area is 40m 2 It is less than / g. (4) Average particle diameter D 50 However, it is 4.0 μm or smaller.

[0019] MCH is an aggregate of multiple particles. In other words, MCH is in powder form. The aggregate of multiple particles may contain only secondary particles, or it may be a mixture of primary and secondary particles.

[0020] <Requirement (1)> The average particle strength of MCH is 10 MPa or more and less than 45 MPa. The average particle strength is 10 MPa or more, preferably 15 MPa or more, and more preferably 20 MPa or more. The average particle strength is less than 45 MPa, and preferably 44 MPa or less. The aforementioned lower and upper limits can be combined in any way. For example, the average particle strength is preferably 15 to 44 MPa, and more preferably 20 to 44 MPa. When the average particle strength is within the above range, it is easier to create a suitable electrode structure for the resulting lithium secondary battery positive electrode, and as a result, the initial efficiency of the resulting lithium secondary battery tends to improve.

[0021] When manufacturing CAM from MCH, the average particle size can change significantly. Since changes in average particle size greatly affect the particle design of CAM, it is also desirable that the average particle size of the particles remain stable when manufacturing CAM from MCH. If the average particle strength is within the aforementioned range, changes in average particle size are suppressed when manufacturing CAM from MCH. MCH's D 50 CAM's D 50 The ratio of MCH is preferably 0.8 or higher, more preferably 0.9 or higher, and even more preferably 1.0 or higher. 50 CAM's D 50 The ratio is preferably 1.4 or less, more preferably 1.3 or less, and even more preferably 1.2 or less. The aforementioned lower and upper limits can be combined in any way. For example, MCH's D 50 CAM's D 50 The ratio is preferably 0.8 to 1.4, more preferably 0.9 to 1.3, and even more preferably 1.0 to 1.2.

[0022] MCH that satisfies requirement (1) is MCH with low particle strength. Particle strength is thought to be determined by several factors related to the aggregation state of primary particles, such as the density of primary particles in secondary particles, the orientation of primary particles, the contact area between primary particles, and the strength of adhesion between primary particles. Furthermore, these factors are also influenced by properties originating from primary particles, such as the size and shape of primary particles. For example, even in MCH with a low density of primary particles in secondary particles, depending on the other factors mentioned above, the average particle strength of the MCH may exceed 45 MPa, thus failing to satisfy requirement (1).

[0023] As primary particles, primary particles having a sufficiently grown anisotropic shape are preferred. "Anisotropic shape" refers to a shape obtained as a result of growth biased in the direction of at least one of the crystal axes, the a-axis, b-axis, and c-axis. An example of anisotropic shape is a rod-shaped shape obtained as a result of growth biased in the direction of one axis. When primary particles grow sufficiently, they become relatively large. Larger primary particles have a smaller outer surface area per unit volume compared to smaller primary particles. Therefore, it is thought that when primary particles aggregate, the contact area between primary particles is smaller for larger primary particles compared to smaller primary particles. In addition, when primary particles have an anisotropic shape, it is thought that the density of primary particles in secondary particles is lower compared to primary particles with an isotropic shape. "Isotropic shape" refers to a shape obtained as a result of growth that is relatively equal with respect to the directions of the crystal axes, the a-axis, b-axis, and c-axis. In secondary particles, it is preferable that the aggregation state of primary particles is such that the density of primary particles is low, the orientation of the primary particles is uniform, the contact area between primary particles is small, and the adhesion strength between primary particles is low. Such secondary particles tend to have low particle strength and tend to satisfy requirement (1) above. Furthermore, it is preferable that the primary particles in the secondary particles are aligned in their orientation. In such cases, adjacent primary particles tend to slide against each other, making it easier for the secondary particles to crack. Therefore, such secondary particles tend to have low particle strength and are more likely to satisfy requirement (1) above. The aggregation state of primary particles and primary particles within secondary particles can be confirmed by observation using a scanning electron microscope.

[0024] <Requirement (2)> The molar ratio of manganese to cobalt in MCH (hereinafter also referred to as "Mn / Co") is greater than 1.0, preferably 1.1 or higher, and more preferably 1.2 or higher. Mn / Co may be 4.0 or lower, 3.0 or lower, or 2.0 or lower. The aforementioned lower and upper limits can be combined in any way. The Mn / Co ratio is preferably greater than 1.0 and less than or equal to 4.0, more preferably between 1.1 and 3.0, and even more preferably between 1.2 and 2.0. When the Mn / Co ratio exceeds (or is above) the aforementioned lower limit, the amount of relatively expensive cobalt used relative to relatively inexpensive manganese can be reduced, making it economical. Furthermore, when the Mn / Co ratio exceeds (or is above) the aforementioned lower limit, the initial efficiency of the resulting lithium secondary battery tends to improve. In addition, when the Mn / Co ratio is within the aforementioned range, changes in the average particle size are suppressed when manufacturing CAM from MCH.

[0025] <Requirement (3)> The BET specific surface area of ​​MCH is 40m². 2 Less than / g, 38m 2 It is preferable that the amount be less than or equal to 30m 2 It is more preferable that it be less than or equal to / g, 20m 2 It is even more preferable that the BET specific surface area is 5m² or less. 2 It may be more than / g, 7m 2 It may be more than / g, 9m 2 It may be more than / g. The aforementioned lower and upper limits can be combined in any way. The BET specific surface area of ​​MCH is 5m². 2 / g or more 40m 2 It is preferable that the amount be less than / g, and 5 to 38m 2 It is more preferable that the amount be / g, which is 7-30m 2It is more preferably 9-20m / g 2 It is particularly preferable that the value be / g. If the BET specific surface area is above the lower limit, it suppresses excessive crystallinity and makes it easier to satisfy requirement (1). If the BET specific surface area is below the upper limit, changes in average particle size are suppressed when manufacturing CAM from MCH.

[0026] <Requirement (4)> MCH's D 50 The particle size is 4.0 μm or less, preferably 1.0 to 4.0 μm, more preferably 1.5 to 4.0 μm, and even more preferably 2.0 to 4.0 μm. D 50 If the value is above the lower limit of the range, the increase in the BET specific surface area can be suppressed when manufacturing CAM from MCH, and gas generation due to side reactions with the electrolyte can be suppressed. 50 When the value is below the upper limit of the aforementioned range, the change in average particle size is suppressed when manufacturing CAM from MCH.

[0027] In addition to the requirements (1) to (4) above, MCH preferably satisfies the following physical properties.

[0028] The standard deviation of the particle strength of MCH is preferably 2 to 12 MPa. The standard deviation is preferably 2 MPa or higher, more preferably 3 MPa or higher, and even more preferably 4 MPa or higher. The standard deviation is preferably 12 MPa or lower, and more preferably 11 MPa or lower. The aforementioned lower and upper limits can be combined in any way. For example, the standard deviation is more preferably 3 to 11 MPa, and even more preferably 4 to 11 MPa. If the standard deviation of particle strength is above the lower limit of the above range, particle cracking due to contact between particles is less likely to occur, and handling is likely to be improved. If the standard deviation of particle strength is below the upper limit of the above range, the uniformity of the precursor is improved, and the cycle characteristics of the battery using the resulting CAM tend to be improved.

[0029] The MCH of this embodiment has Mn / Co exceeding 1.0. In an MCH with Mn / Co exceeding 1.0, it is known that it is likely to be oxidized during the production of MCH, and accordingly, the crystallinity decreases. In the MCH of this embodiment, by optimizing the production conditions as described later, even when Mn / Co exceeds 1.0, the crystallinity is maintained high. When the crystallinity of an MCH with Mn / Co exceeding 1.0 increases, the inventors of the present application have found that the primary particles grow into a rod-like shape. As described above, when the primary particles have an anisotropic shape such as a rod-like shape, it is considered that the density of the primary particles in the secondary particles is lower than that of the primary particles having an isotropic shape. In the MCH of this embodiment, it is considered that the high crystallinity is one of the factors satisfying the above requirement (1).

[0030] ≪Composition formula≫ MCH is preferably a compound represented by the following composition formula (I). Ni 1-x-y-w Co x Mn y M w (OH) 2+α ···Formula (I) In the composition formula (I), 0 < x < 0.5, 0 < y ≤ 0.5, 0 ≤ w ≤ 0.5, x < y, 0 < x + y + w < 1, 0 ≤ α are satisfied, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.

[0031] When w exceeds 0, from the viewpoint that the cycle characteristics of the battery using the obtained CAM are likely to be high, M is preferably one or more elements selected from the group consisting of Ti, Mg, Al, Zr, Nb, W, Mo, B, and Si, and more preferably one or more elements selected from the group consisting of Al, Zr, Nb, and W.

[0032] x is preferably 0.01 or more, more preferably 0.02 or more, and particularly preferably 0.03 or more. x is preferably 0.44 or less, more preferably 0.42 or less, and particularly preferably 0.40 or less.

[0033] The above upper and lower limits for x can be combined in any way. The above compositional formula (I) preferably satisfies 0.01 ≤ x ≤ 0.44, more preferably 0.02 ≤ x ≤ 0.42, and particularly preferably 0.03 ≤ x ≤ 0.40.

[0034] y is preferably 0.02 or higher, more preferably 0.03 or higher, and particularly preferably 0.04 or higher. y is preferably 0.45 or less, more preferably 0.43 or less, and particularly preferably 0.41 or less.

[0035] The above upper and lower limits for y can be combined in any way. The above compositional formula (I) preferably satisfies 0.02 ≤ y ≤ 0.45, more preferably 0.03 ≤ y ≤ 0.43, and particularly preferably 0.04 ≤ y ≤ 0.41.

[0036] x+y+w is preferably 0.20 or greater, more preferably 0.30 or greater, and particularly preferably 0.40 or greater. x+y+w is preferably 0.70 or less, more preferably 0.66 or less, and particularly preferably 0.60 or less. The above upper and lower limits for x+y+w can be combined in any way.

[0037] The above compositional formula (I) preferably satisfies 0 ≤ α ≤ 1.2. α is appropriately adjusted according to the possible chemical compositions of the hydroxides of each metal element.

[0038] <Method for producing metal composite hydroxides> The method for producing MCH in this embodiment includes a reaction step in which a solution of a metal salt of Ni, a solution of a metal salt of Co, a solution of a metal salt of Mn, a complexing agent, and an alkaline solution are supplied to a reaction vessel to carry out a coprecipitation reaction. MCH can be produced by known batch coprecipitation methods or continuous coprecipitation methods.

[0039] The following describes a method for producing MCH containing Ni, Co, and Mn as an example. Specifically, a nickel salt solution, a cobalt salt solution, a manganese salt solution, a complexing agent, and an alkaline solution are reacted using the continuous coprecipitation method described in JP-A-2002-201028, thereby producing Ni (1-x’-y’) Co x’ Mn y’ MCH represented by (OH)2 is produced. For example, when producing MCH represented by the composition formula (I), x' and y' correspond to x and y in the composition formula (I), respectively.

[0040] The nickel salt used as the solute in the nickel salt solution is not particularly limited, but for example, at least one of nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate can be used.

[0041] As the cobalt salt solute in the cobalt salt solution, at least one of the following can be used: cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate.

[0042] As the solute of the manganese salt solution, at least one of the following can be used: manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate.

[0043] Furthermore, when producing MCH containing metals other than Ni, Co, and Mn, sulfates, nitrates, chlorides, or acetates of those metals can be used as solutes.

[0044] The metal salt is the aforementioned Ni (1-x’-y’) Co x’ Mn y’ The amounts of each metal salt are specified so that the molar ratio of Ni, Co, and Mn in the mixed solution containing the above metal salts corresponds to (1-x'-y'):x':y' in the composition formula. Water is used as the solvent.

[0045] Examples of complexing agents include those capable of forming complexes with nickel ions, cobalt ions, and manganese ions in aqueous solution, such as ammonium ion suppliers such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, or ammonium fluoride, as well as hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine, with ammonium ion suppliers being preferred.

[0046] Preferably, the amount of complexing agent in a mixture containing a nickel salt solution, a cobalt salt solution, a manganese salt solution, and a complexing agent is such that its molar ratio to the total number of moles of the metal salts (nickel salt, cobalt salt, and manganese salt) is greater than 0 and 2.0 or less.

[0047] When an ammonium ion supplier is used as a complexing agent, the ammonia concentration relative to the total volume of solution in the reaction vessel is preferably 0.8 to 3.9 g / L, more preferably 1.0 to 3.9 g / L, and even more preferably 1.0 to 3.0 g / L. When the ammonia concentration is within the above range, requirements (1) and (4) are more easily satisfied.

[0048] In the coprecipitation method, to adjust the pH of the mixture containing the nickel salt solution, cobalt salt solution, manganese salt solution, and complexing agent, an alkaline solution is added to the mixture before its pH changes from alkaline to neutral. Examples of alkaline solutions include aqueous solutions of alkali metal hydroxides. Examples of alkali metal hydroxides include sodium hydroxide or potassium hydroxide.

[0049] In this specification, the pH value is defined as the value measured when the temperature of the mixture is 40°C. The pH of the mixture is measured when the temperature of the mixture sampled from the reaction vessel reaches 40°C. If the sampled mixture is below 40°C, the mixture is heated to 40°C and the pH is measured. If the sampled mixture is above 40°C, the mixture is cooled to 40°C and the pH is measured.

[0050] When the above nickel salt solution, cobalt salt solution, and manganese salt solution, along with a complexing agent, are continuously supplied to the reaction vessel, Ni, Co, and Mn react, and Ni (1-x’-y’) Co x’ Mn y’ (OH)2 is produced.

[0051] The reaction temperature is preferably 50 to 80°C, more preferably 50 to 75°C, and even more preferably 65 to 75°C. If the reaction temperature is above the lower limit, the MCH crystals grow easily, the crystallinity improves, and as a result, requirement (1) is more easily satisfied. If the reaction temperature is below the upper limit, the reaction is easier to control.

[0052] The pH value in the reaction vessel is preferably 10.0 to 12.1, more preferably 10.0 to 11.9, even more preferably 11.5 to 11.9, and still more preferably 11.5 to 11.8. When the pH is within the above range, the crystallinity and anisotropy of the MCH are controlled, and as a result, requirement (1) is more easily satisfied.

[0053] The reaction precipitate formed in the reaction vessel is neutralized while being stirred. The neutralization time for the reaction precipitate is, for example, 1 to 24 hours.

[0054] In the continuous coprecipitation method, a reaction vessel of the type that allows for overflow to separate the formed reaction precipitate can be used.

[0055] When producing MCH by batch coprecipitation, examples of reaction vessels include a reaction vessel without an overflow pipe, and a device equipped with a concentration tank connected to an overflow pipe, which concentrates the overflowed reaction precipitate in the concentration tank and circulates it back to the reaction vessel.

[0056] It is preferable to supply an oxygen-containing gas to the solution in the reaction vessel. When an oxygen-containing gas is supplied to the solution in the reaction vessel, primary particles grow while a portion of the MCH is oxidized. While primary particles of MCH are generally known to grow isotropically, when primary particles grow while a portion of the MCH is oxidized, the primary particles grow anisotropically. On the other hand, if too much oxygen is supplied, excessive oxidation proceeds, and the crystallinity of MCH decreases. The oxygen concentration relative to the total volume of the oxygen-containing gas is preferably 0.01 to 1.0 volume%. If the oxygen concentration is above the lower limit, anisotropic growth of primary particles is promoted. If the oxygen concentration is below the upper limit, the decrease in crystallinity is suppressed. As a result, requirement (1) is more easily satisfied.

[0057] The temperature and pH in the reaction vessel, the ammonia concentration relative to the total volume of the solution in the reaction vessel, and the oxygen concentration of the gas supplied to the solution in the reaction vessel, including oxygen gas, greatly affect the particle strength, BET specific surface area, and particle size of the resulting MCH. This effect is particularly large when the composition satisfies requirement (2). For this reason, it is preferable to adjust various conditions as appropriate in order to satisfy requirements (1), (3), and (4). In particular, when the composition satisfies requirement (2), it is known that the crystallinity of MCH decreases, as described above. When the crystallinity decreases, it becomes particularly difficult to satisfy requirement (1). In the manufacturing method of this embodiment, by optimizing various conditions, the crystallinity and anisotropy are maintained at a high level even when the composition satisfies requirement (2), and as a result, it becomes easier to satisfy requirement (1).

[0058] In this embodiment, it is preferable to set the reaction temperature to 50-80°C, the pH to 10.0-11.9, the ammonia concentration relative to the total volume of solution in the reaction vessel to 0.8-3.9 g / L, and the oxygen concentration of the oxygen-containing gas supplied to the solution in the reaction vessel to 0.01-1.0 volume%, and more preferably to set the reaction temperature to 65-75°C, the pH to 11.5-11.8, the ammonia concentration relative to the total volume of solution in the reaction vessel to 1.0-3.0 g / L, and the oxygen concentration of the oxygen-containing gas supplied to the solution in the reaction vessel to 0.02-0.05 volume%. By using these reaction conditions, it becomes easier to obtain MCH that satisfies the above requirements (1), (3), and (4).

[0059] After the above reaction, the neutralized reaction precipitate is washed 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.

[0060] The isolated reaction precipitate is washed, dehydrated, dried, and sieved to obtain MCH containing Ni, Co, and Mn.

[0061] 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 sodium hydroxide solution or an aqueous potassium hydroxide solution is more preferred. It is preferable to wash the reaction precipitate with water, weakly acidic water, or an alkaline washing solution in an amount of 10 times or more by mass relative to the precipitate's mass. Furthermore, it is preferable that the temperature of the water, weakly acidic water, or alkaline washing solution used be 30°C or higher. In addition, 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 aforementioned solution remain in the reaction precipitate.

[0062] 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 atmospheric pressure or reduced pressure.

[0063] Through the above process, MCH can be manufactured.

[0064] ≪Method for manufacturing positive electrode active material for lithium secondary batteries≫ The method for producing CAM comprises a mixing step of mixing MCH and a lithium compound, and a firing step of firing the resulting mixture in an oxygen-containing atmosphere at a temperature of 500°C to 1000°C. CAM, a lithium metal composite oxide, can be produced by this method.

[0065] The manufacturing method for CAM uses the MCH described above.

[0066] [Mixing process] Mix MCH with a lithium compound. The lithium compound used in this embodiment can be at least one of the following: lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide (including hydrate), lithium oxide, lithium chloride, and lithium fluoride. Among these, lithium hydroxide and lithium carbonate, or a mixture thereof, are preferred. Furthermore, if the raw material (reagent, etc.) containing lithium hydroxide also contains lithium carbonate, the lithium carbonate content in the lithium hydroxide is preferably 5% by mass or less.

[0067] A lithium compound and MCH are mixed, taking into consideration the composition ratio of the final product, to obtain a mixture of the lithium compound and MCH. The amount of lithium (molar ratio) to the total amount of metal contained in MCH is preferably 0.98 to 1.20, more preferably 1.04 to 1.10, and particularly preferably 1.05 to 1.10.

[0068] [Firing process] The resulting mixture is calcined in an oxygen-containing atmosphere at a calcination temperature between 500°C and 1000°C. By calcining the mixture, crystals of lithium metal composite oxide grow.

[0069] 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 which the material is heated to the highest holding temperature among all firing stages.

[0070] The firing temperature is preferably, for example, 650 to 900°C, more preferably 680 to 850°C, and particularly preferably 700 to 820°C. If the firing temperature is above the lower limit of the above range, a CAM with a strong crystalline structure can be obtained. If the firing temperature is below the upper limit of the above range, the volatilization of lithium on the particle surface of the CAM can be reduced.

[0071] The holding time during firing is preferably 3 to 50 hours, and more preferably 4 to 20 hours. If the holding time during firing is below the upper limit of the above range, lithium volatilization is suppressed, and the deterioration of battery performance is suppressed. If the holding time during firing is above the lower limit of the above range, crystal development is promoted, and the deterioration of battery performance is suppressed.

[0072] In this embodiment, the heating rate in the firing process to reach the maximum holding temperature is preferably 80°C / hour or more, more preferably 100°C / hour or more, and particularly preferably 150°C / hour or more. The heating rate in the heating process to reach the maximum holding temperature is calculated in the firing apparatus from the time from when heating is started until the holding temperature is reached.

[0073] The firing process preferably has multiple firing stages with different firing temperatures. For example, it is preferable to have a first firing stage and a second firing stage that is fired at a higher temperature than the first firing stage. Furthermore, there may be firing stages with different firing temperatures and firing times.

[0074] Depending on the desired composition, the firing atmosphere may be air, oxygen, nitrogen, argon, or a mixture thereof, and multiple firing steps may be performed if necessary. An oxygen-containing atmosphere is preferred for the firing atmosphere.

[0075] A mixture of MCH and a lithium compound may be calcined in the presence of an inert flux. The inert flux may be added in an amount that does not impair the initial capacity of the battery using CAM, and may remain in the calcined product. As an inert flux, for example, those described in WO2019 / 177032A1 can be used.

[0076] The firing apparatus used during firing is not particularly limited, and for example, either a continuous firing furnace or a fluidized firing furnace may be used. Examples of the continuous firing furnace include a tunnel furnace or a roller hearth kiln. As the fluidized firing furnace, a rotary kiln may be used.

[0077] As described above, CAM can be obtained by firing a mixture of MCH and a lithium compound.

[0078] The D of CAM 50 is preferably from 3.0 to 6.0 μm, more preferably from 3.0 to 5.0 μm, and even more preferably from 3.5 to 5.0 μm.

Examples

[0079] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

[0080] <Measurement of various parameters of MCH and CAM> The measurement of various parameters of MCH and CAM produced by the method described below was carried out by the measurement methods described above, such as (average particle strength), (standard deviation of particle strength), (average particle diameter D 50 ), (composition), and (BET specific surface area).

[0081] <Production of positive electrode for lithium secondary battery> CAM obtained by the production method described below, a conductive material (acetylene black), and a binder (PVdF) were added and kneaded so that the composition was CAM:conductive material:binder = 92:5:3 (mass ratio) to prepare a paste-like positive electrode mixture. When preparing the positive electrode mixture, N-methyl-2-pyrrolidone was used as an organic solvent.

[0082] The obtained positive electrode mixture was applied to an Al foil with a thickness of 40 μm serving as a 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 positive electrode for a lithium secondary battery was 1.65 cm 2 as such.

[0083] <Manufacturing of lithium-ion secondary batteries (coin-type half-cells)> The following operations were performed inside a glove box under an argon atmosphere. The positive electrode for the lithium secondary battery described above was placed with the aluminum foil side facing down on the bottom cover of a part for the coin-type battery R2032 (manufactured by Hosen Co., Ltd.), and a laminated film separator (16 μm thick) consisting of a heat-resistant porous layer laminated on top of a porous polyethylene film was placed on top of it. 300 μl of electrolyte was injected into this. The electrolyte used was a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35, to which LiPF6 was dissolved to a concentration of 1 mol / l. Next, metallic lithium was used as the negative electrode and placed on top of the separator. The top cover was then closed with a gasket and crimped using a crimping machine to fabricate a lithium secondary battery (coin-type half-cell R2032; hereinafter sometimes referred to as "coin-type half-cell").

[0084] <Measurement of initial efficiency> The initial discharge capacity and initial efficiency of the lithium secondary batteries produced using the method described above were determined using the measurement methods explained in (Initial Efficiency) above. An initial efficiency of over 90.0% is considered high.

[0085] [Example 1] After adding water to a reaction vessel equipped with a stirrer and overflow pipe, an aqueous sodium hydroxide solution was added, and the liquid temperature was maintained at 70°C.

[0086] Mixed raw material solution 1 was prepared by mixing nickel sulfate aqueous solution, cobalt sulfate aqueous solution, and manganese sulfate aqueous solution so that the molar ratio of Ni:Co:Mn was 0.5:0.2:0.3.

[0087] While circulating an oxygen-containing gas, the mixed raw material solution 1 and an aqueous ammonium sulfate solution were continuously added to the reaction vessel under stirring. An aqueous sodium hydroxide solution was added dropwise as needed to maintain a pH of 11.8 (measurement temperature: 40°C) in the solution within the reaction vessel. The dropping rate of the aqueous ammonium sulfate solution was adjusted to achieve an ammonium concentration of 2.5 g / L in the vessel, thereby obtaining reaction precipitate 1. The oxygen concentration relative to the total volume of the oxygen-containing gas was set to 0.04 vol%.

[0088] Reaction precipitate 1 was washed with a 5% by mass aqueous sodium hydroxide solution at a volume 20 times its mass relative to the precipitate 1. After washing, it was dehydrated using a centrifuge, washed with water, dehydrated, isolated, and dried at 105°C for 20 hours to obtain MCH1 containing Ni, Co, and Mn. The various parameters of MCH1 are shown in Table 1 (the same applies to Examples 2 and 3, and Comparative Examples 1 and 2). Note that 1-xyw, x, y, and w in the composition of Table 1 correspond to the values ​​in formula (I) above.

[0089] Lithium carbonate was weighed out so that the amount of Li (molar ratio) to the total amount of Ni, Co, and Mn contained in MCH1 was 1.07. MCH1 and lithium carbonate were mixed to obtain mixture 1.

[0090] Next, the obtained mixture 1 was calcined at 750°C for 6 hours under an oxygen atmosphere to obtain lithium metal composite oxide powder. The obtained powder and pure water adjusted to a liquid temperature of 5°C were mixed so that the powder mass was 0.3 of the total volume, and the slurry was stirred for 20 minutes, then dehydrated, and further rinsed with pure water adjusted to a liquid temperature of 5°C in an amount twice the mass of the powder, then isolated and dried at 150°C to obtain CAM1. The various parameters of CAM1 are shown in Table 1 (the same applies to Examples 2 and 3 and Comparative Examples 1 and 2 below).

[0091] A lithium secondary battery was fabricated using the obtained CAM1, and its initial efficiency was measured. The results are shown in Table 1 (the same applies to Examples 2 and 3, and Comparative Examples 1 and 2).

[0092] [Example 2] MCH2 and CAM2 were obtained in the same manner as in Example 1, except that the pH of the solution in the reaction vessel during MCH production was set to 11.55 (measurement temperature: 40°C) and the ammonium concentration in the vessel was set to 1.1 g / L. A lithium secondary battery was fabricated using the obtained CAM2, and the initial efficiency was measured.

[0093] [Example 3] In the production of MCH, nickel sulfate aqueous solution, cobalt sulfate aqueous solution, manganese sulfate aqueous solution, and zirconium sulfate aqueous solution were mixed so that the molar ratio of Ni:Co:Mn:Zr was 0.548:0.199:0.248:0.005, the liquid temperature in the reaction vessel was 50°C, the pH of the solution in the reaction vessel was 11.94 (measurement temperature: 40°C), and the ammonium concentration in the vessel was 2.6 g / L. MCH3 and CAM3 were obtained in the same manner as in Example 1. A lithium secondary battery was fabricated using the obtained CAM3, and the initial efficiency was measured.

[0094] [Comparative Example 1] Except for setting the liquid temperature in the reaction vessel to 30°C, the pH in the reaction vessel to 11.95 (measurement temperature: 40°C), and the ammonium concentration in the vessel to 4.0 g / L during MCH production, MCH4 and CAM4 were obtained in the same manner as in Example 1. A lithium secondary battery was fabricated using the obtained CAM4, and the initial efficiency was measured.

[0095] [Comparative Example 2] MCH5 and CAM5 were obtained in the same manner as in Example 1, except that during the production of MCH, nickel sulfate aqueous solution, cobalt sulfate aqueous solution, and manganese sulfate aqueous solution were mixed so that the molar ratio of Ni:Co:Mn was 0.6:0.2:0.2, the liquid temperature in the reaction vessel was 60°C, the pH in the reaction vessel was 12.2 (measurement temperature: 40°C), and the ammonium concentration in the vessel was 5.0 g / L. Using the obtained CAM5, a lithium secondary battery was fabricated, and its initial efficiency was measured.

[0096] [Table 1]

[0097] It was found that lithium secondary batteries using CAM for lithium secondary batteries, in which MCH of Examples 1 to 3 satisfies requirements (1) to (4), have high initial efficiency. In addition, in Examples 1 to 3, D 50 (CAM) / D 50 The (MCH) value falls within the range of 1.1 to 1.2, indicating that changes in average particle size are suppressed when manufacturing CAM from MCH.

Claims

1. A metal composite hydroxide used as a precursor for positive electrode active material in lithium secondary batteries, Includes Ni, Co, and Mn, A metal composite hydroxide that satisfies all of the following requirements (1) to (4). (1) The average particle strength is 10 MPa or more and less than 45 MPa. (2) The molar ratio of manganese to cobalt (Mn / Co) is greater than 1.

0. (3) BET specific surface area is 40 m ２ It is less than / g. (4) Average particle diameter D ５０ However, it is 4.0 μm or less.

2. A metal composite hydroxide according to claim 1, represented by the following compositional formula (I). Ni １－ｘ－ｙ－ｗ Co ｘ Mn ｙ M ｗ (OH) ２＋α ...Formula (I) (In the above compositional formula (I), the following conditions are satisfied: 0 < x < 0.5, 0 < y ≤ 0.5, 0 ≤ w ≤ 0.5, x < y, 0 < x + y + w < 1, 0 ≤ α, and M is one or more elements selected from the group consisting of Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.)

3. The metal composite hydroxide according to claim 1 or 2, wherein the standard deviation of the particle strength is 2 MPa or more and 12 MPa or less.

4. A method for producing a positive electrode active material for a lithium secondary battery, comprising a mixing step of mixing a metal composite hydroxide described in claim 1 or 2 with a lithium compound, and a firing step of firing the obtained mixture in an oxygen-containing atmosphere at a temperature of 500°C to 1000°C.

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