Nickel-manganese composite hydroxide and method for producing the same, positive electrode active material and method for producing the same, and nonaqueous electrolyte secondary battery

Abstract

The present application provides a positive electrode active material capable of obtaining a nonaqueous electrolyte secondary battery having a high energy density, a nickel-manganese composite hydroxide suitable as a precursor thereof, and a production method capable of easily producing them on an industrial scale. A nickel-manganese composite hydroxide and a production method thereof, and the like are provided, the nickel-manganese composite hydroxide being represented by general formula (1): Ni x Mn y M z (OH) 2+α and composed of secondary particles aggregated from a plurality of primary particles, a half-value width of a diffraction peak of a (001) plane obtained by X-ray diffraction measurement being 0.10° or more and 0.40° or less, and a porosity expressed by 〔(a pore area inside the secondary particle / a cross-sectional area of the secondary particle) x 100〕 (%) being 0.5% or more and 10% or less.

Description

[0001] This application is a divisional application of the application filed on July 28, 2017, with application number 201780047264.4, entitled "Nickel-manganese composite hydroxide and its manufacturing method, positive electrode active material for non-aqueous electrolyte secondary battery and its manufacturing method, and non-aqueous electrolyte secondary battery". Technical Field

[0002] This invention relates to nickel-manganese composite hydroxide and its manufacturing method, positive electrode active material for non-aqueous electrolyte secondary batteries and its manufacturing method, and non-aqueous electrolyte secondary batteries. Background Technology

[0003] In recent years, with the widespread use of portable electronic devices such as mobile phones and laptop computers, there has been a strong demand for the development of non-aqueous electrolyte secondary batteries with high energy density, small size, and lightweight design. Lithium-ion secondary batteries are a representative example of such non-aqueous electrolyte secondary batteries. The negative electrode active material in lithium-ion secondary batteries uses lithium metal, lithium alloys, metal oxides, or carbon, among other materials. These materials are capable of lithium intercalation and deintercalation.

[0004] Research and development of lithium-ion secondary batteries are currently underway. Among these, lithium-ion secondary batteries using lithium transition metal composite oxides, particularly the relatively easy-to-synthesize lithium-cobalt composite oxide (LiCoO2), as the positive electrode active material can achieve high voltages in the 4V range, and are therefore expected to be practically applied as batteries with high energy density. Additionally, research is also progressing on lithium-nickel composite oxide (LiNiO2) and lithium-nickel-cobalt-manganese composite oxide (LiNiO2), which use nickel, which is cheaper than cobalt, as the positive electrode active material. 0.33 Co 0.33 Mn 0.33 The development of technologies such as O2 is underway. Among these, lithium nickel cobalt manganese composite oxides have attracted considerable attention due to their excellent balance in battery capacity, output characteristics, durability, and cost. However, their capacity is inferior to that of lithium nickel composite oxide systems, thus requiring sufficient output characteristics and further improvements in battery capacity (energy density).

[0005] Various solutions have been proposed to address the demand for increased battery capacity in positive electrode active materials. For example, Patent Document 1 proposes a positive electrode active material for non-aqueous electrolyte secondary batteries with an average particle size of 2–8 μm and a particle size distribution width index ((d90-d10) / average particle size) of 0.60 or less, in order to improve cycle characteristics and achieve high power. Such active materials are characterized by uniform electrochemical reactions, thus exhibiting high capacity and long lifetime. However, on the other hand, the fillability of the positive electrode active material is reduced, therefore, its volumetric energy density cannot be considered high.

[0006] Furthermore, for example, Patent Document 2 discloses a method for manufacturing a positive electrode active material for lithium-ion batteries. In this method, hydroxide raw material powder is pulverized to prepare a slurry containing pulverized raw material powder with a specific particle size distribution. Using this slurry, approximately spherical granulated powder is formed. A lithium compound is mixed in, and the granulated powder and lithium compound are reacted by calcination. This yields a positive electrode active material with high battery characteristics, a desired porosity, and a high open-pore ratio. However, the process of pulverizing the obtained hydroxide and then granulating it again to obtain the precursor presents a productivity problem. Additionally, while increasing the open-pore ratio improves battery characteristics, it also reduces the volumetric energy density.

[0007] Furthermore, for example, Patent Document 3 proposes a positive electrode active material for non-aqueous electrolyte secondary batteries, which is obtained by calcining a mixture of nickel-cobalt-manganese composite hydroxide and a lithium compound. The nickel-cobalt-manganese composite hydroxide is obtained by precipitating an aqueous solution containing nickel salt, cobalt salt, and manganese salt under an atmosphere of an inactive gas and oxygen at a volume ratio of 0.5% to 3.0% relative to the inactive gas, while maintaining the pH at 10 or higher and 13 or lower. This increases the tap density and bulk density of the nickel-cobalt-manganese composite hydroxide, allowing for a higher density of the positive electrode active material and its precursor, thereby further improving the capacity of the non-aqueous electrolyte secondary battery. However, while battery capacity has been studied, research on other battery characteristics is insufficient.

[0008] On the other hand, Patent Document 4 proposes a positive electrode active material for a non-aqueous electrolyte secondary battery, which consists of an outer shell and a hollow portion inside it. The average particle size of the outer shell is greater than 8 μm and less than 16 μm, and the index representing the width of the particle size distribution, i.e., [(d90-d10) / average particle size], is less than 0.60. This positive electrode active material has a uniform particle size distribution and good filling properties, which can reduce the value of the positive electrode resistance. However, for hollow particles, although high output characteristics can be obtained, there is a problem of reduced filling properties. In addition, although the primary particle shape of hydroxide can be controlled by changing the atmosphere during crystallization, the change takes time, thus reducing productivity.

[0009] Furthermore, Patent Document 5 proposes a method for manufacturing nickel-manganese composite hydroxide particles. In this method, an aqueous solution containing at least nickel and manganese, an aqueous solution containing an ammonium ion donor, and an alkaline solution are supplied to a reaction tank and mixed to form a reaction aqueous solution. During the crystallization of the aforementioned nickel-manganese composite hydroxide particles, the oxygen concentration in the reaction tank is maintained at 3.0% by capacity or less. The temperature of the reaction aqueous solution is controlled at 35°C to 60°C, and the nickel ion concentration is controlled at 1000 mg / L or more. This improves the sphericity of the nickel-manganese composite hydroxide particles and enhances the filling performance of the positive electrode active material using it as a precursor. However, this proposal only focuses on the improved filling performance through particle sphericity; the volumetric energy density remains to be discussed.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 2011-116580

[0013] Patent Document 2: Japanese Patent Application Publication No. 2015-76397

[0014] Patent Document 3: Japanese Patent Application Publication No. 2013-144625

[0015] Patent Document 4: International Publication No. WO2012 / 169274

[0016] Patent Document 5: International Publication No. WO2015 / 115547 Summary of the Invention

[0017] The problem the invention aims to solve

[0018] As mentioned above, higher energy density is required for non-aqueous electrolyte secondary batteries, and various positive electrode active materials have been proposed to meet this requirement. However, a positive electrode active material that satisfies both high volumetric energy density and sufficient output characteristics by appropriately controlling fillability and battery capacity has not yet been developed. Furthermore, it is known that the fillability and battery capacity of positive electrode active materials can be improved, for example, by using high-level composite hydroxides (precursors) that also possess high tap density and specific surface area. Although various methods for manufacturing composite hydroxides (precursors) have been studied, a method for manufacturing composite hydroxides (precursors) that can sufficiently improve the performance of lithium-ion secondary batteries on an industrial scale has not yet been developed. Therefore, there is a need to develop methods for the cheaper, mass production of positive electrode active materials with high volumetric energy density and sufficient output characteristics, as well as methods for manufacturing composite hydroxides that serve as their precursors.

[0019] In view of the above problems, the object of the present invention is to provide: a positive electrode active material for a non-aqueous electrolyte secondary battery that has high energy density and sufficient output characteristics as a secondary battery, and a nickel-manganese composite hydroxide suitable as a precursor thereof. Furthermore, the object of the present invention is to provide: a method for manufacturing a nickel-manganese composite hydroxide that can be easily manufactured on an industrial scale; and a method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery using the nickel-manganese composite hydroxide.

[0020] Solution for solving the problem

[0021] In the first aspect of the present invention, a nickel-manganese composite hydroxide is provided, characterized in that it is formulated using the general formula (1): Ni x Mn y M z (OH) 2+α (In formula (1), M is one or more elements selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe and W, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, and satisfies x+y+z=1.0, α is 0≤α≤0.4.) It is composed of secondary particles formed by the aggregation of multiple primary particles. The half-width of the diffraction peak of the (001) plane obtained by X-ray diffraction is 0.10° or more and 0.40° or less, and the sparsity expressed as [(pore area inside the secondary particle / cross-sectional area of ​​the secondary particle)×100] (%) is 0.5% or more and 10% or less.

[0022] Furthermore, the aforementioned nickel-manganese composite hydroxide preferably has a pore volume of 0.01 cm³, as determined by nitrogen adsorption. 3 / g or more and 0.04cm 3 / g or less. Furthermore, the nickel-manganese composite hydroxide preferably has a particle size distribution width index [(D90-D10) / average particle size] of 0.7 or more, and a volume average particle size MV of 5 μm or more and 20 μm or less. Additionally, the nickel-manganese composite hydroxide preferably has a specific surface area of ​​5 m² / g. 2 / g or more and 15m 2 / g or less. Furthermore, the preferred tap density of the above-mentioned nickel-manganese composite hydroxide is 1.8 g / cm³. 3 Above and 2.5g / cm 3 the following.

[0023] In the second aspect of the present invention, a method for manufacturing a nickel-manganese composite hydroxide is provided, wherein the nickel-manganese composite hydroxide is formulated using general formula (1): Ni x Mn y M z (OH) 2+α(In the aforementioned formula (1), M is at least one element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe and W, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, and satisfies x+y+z=1.0, α is 0≤α≤0.4.) indicates that it is composed of secondary particles formed by the aggregation of multiple primary particles, and the manufacturing method includes the following crystallization step: neutralizing at least salts containing nickel and manganese in the reaction aqueous solution to generate nickel-manganese composite hydroxide, in the crystallization step, adjusting the dissolved oxygen concentration in the reaction aqueous solution to a range of 0.2 mg / L or more and 4.6 mg / L or less, and adjusting the dissolved nickel concentration to a range of 700 mg / L or more and 1500 mg / L or less.

[0024] Furthermore, preferably, during the crystallization process, the stirring power of the reaction aqueous solution is adjusted to 3 kW / m. 3 Above and 15kW / m 3 The following ranges are preferred. Furthermore, it is preferable that, in the crystallization process, the temperature of the reaction aqueous solution is adjusted to a range of 35°C or higher and 60°C or lower. Additionally, it is preferable that, in the crystallization process, the pH value of the reaction aqueous solution, measured at a reference liquid temperature of 25°C, is adjusted to a range of 10.0 or higher and 13.0 or lower. Furthermore, for the crystallization process, it is preferable to overflow the slurry containing nickel-manganese composite hydroxide particles, thereby recovering the aforementioned secondary particles, which are generated by continuously adding and neutralizing a mixed aqueous solution containing nickel and manganese to the reaction tank.

[0025] In the third aspect of the present invention, a positive electrode active material for a non-aqueous electrolyte secondary battery is provided, which is composed of a lithium-nickel-manganese composite oxide, wherein the lithium-nickel-manganese composite oxide is of general formula (2): Li 1+t Ni x Mn y M z O 2+β (In formula (2), M is at least one added element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W, t is -0.05≤t≤0.5, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, and satisfies x+y+z=1.0, β is 0≤β≤0.5.) represents a secondary particle formed by the aggregation of primary particles, and the density of the positive electrode active material for the non-aqueous electrolyte secondary battery, expressed as [(pore area inside the secondary particle / cross-sectional area of ​​the secondary particle)×100] (%), is 0.5% or more and 12% or less, and the DBP absorption measured according to JIS K6217-4 is 12 cm⁻¹. 3 / 100g or more and 20cm 3 / less than 100g.

[0026] Additionally, a tap density of 2.0 g / cm³ is preferred. 3 Above and 2.7g / cm 3 Furthermore, it is preferable that the ratio of the diffraction peak intensity I(003) of the 003 plane to the peak intensity I(104) of the 104 plane, I(003) / I(104), obtained by X-ray diffraction, is 1.7 or higher. Additionally, it is preferable that when any radial direction outward from the center of the secondary particle's cross-section is defined as the x-axis direction, and a direction orthogonal to the aforementioned x-axis direction is defined as the y-axis direction, the orientation ratio of the crystal ab plane, measured by electron backscatter diffraction in both the x-axis and y-axis directions, is 55% or higher.

[0027] In the fourth aspect of the present invention, a method for manufacturing a positive electrode active material for a non-aqueous electrolyte secondary battery is provided, wherein the positive electrode active material for the non-aqueous electrolyte secondary battery is composed of a lithium nickel manganese composite oxide, and the lithium nickel manganese composite oxide is of general formula (2): Li 1+t Ni x Mn y M z O 2+β (In formula (2), M is at least one additive element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe and W, t is -0.05≤t≤0.5, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, and satisfies x+y+z=1.0, β is 0≤β≤0.5.) represents a secondary particle formed by the aggregation of primary particles, and the manufacturing method includes the following steps: a step of mixing the above nickel-manganese composite hydroxide and lithium compound to obtain a mixture; and a step of calcining the mixture to obtain lithium nickel-manganese composite oxide.

[0028] Preferably, the nickel-manganese composite hydroxide is obtained by the above-described method for manufacturing nickel-manganese composite hydroxide.

[0029] In the fifth aspect of the present invention, a non-aqueous electrolyte secondary battery is provided, wherein the above-mentioned non-aqueous electrolyte secondary battery positive electrode active material is used as the positive electrode.

[0030] The effects of the invention

[0031] According to the positive electrode active material of the present invention, a non-aqueous electrolyte secondary battery with high energy density and sufficient output characteristics as a secondary battery can be obtained. Furthermore, the nickel-manganese composite hydroxide of the present invention has excellent filler properties, making it suitable as a precursor for the aforementioned positive electrode active material. Moreover, the manufacturing method of the nickel-manganese composite hydroxide and the positive electrode active material of the present invention can be easily carried out on an industrial scale, and can be said to have extremely high industrial value. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating an example of the nickel-manganese composite hydroxide of this embodiment.

[0033] Figure 2 The figure illustrates an example of a method for manufacturing the nickel-manganese composite hydroxide according to this embodiment.

[0034] Figure 3 This is a schematic diagram illustrating an example of the lithium nickel manganese composite oxide of this embodiment.

[0035] Figure 4 The figure shows an example of a method for manufacturing the lithium nickel manganese composite oxide according to this embodiment.

[0036] Figure 5 A photograph showing an example of the appearance and cross-section of the nickel-manganese composite hydroxide of this embodiment.

[0037] Figure 6 A photograph showing an example of the appearance and cross-section of the positive electrode active material of this embodiment.

[0038] Figure 7 This diagram illustrates a method for evaluating the crystal orientation of positive electrode active materials using electron backscatter diffraction (EBSD).

[0039] Figure 8 A simplified cross-sectional diagram of a button cell used in the evaluation of battery characteristics.

[0040] Figure 9 This is a diagram illustrating an example of a Nyquist plot obtained by the AC impedance method.

[0041] Figure 10 A simplified diagram illustrating the equivalent circuit used in the analytical impedance evaluation. Detailed Implementation

[0042] Hereinafter, with reference to the accompanying drawings, a detailed description will be given of the nickel-manganese composite hydroxide and its manufacturing method, as well as the positive electrode active material for non-aqueous electrolyte secondary batteries and its manufacturing method. It should be noted that in the accompanying drawings, for ease of understanding of each component, some parts are emphasized or simplified, and the actual structure, shape, scale, etc., may sometimes differ.

[0043] (1) Nickel-manganese composite hydroxide

[0044] Figure 1 This is a schematic diagram illustrating an example of the nickel-manganese composite hydroxide of this embodiment. (As shown...) Figure 1 As shown, the nickel-manganese composite hydroxide 1 (hereinafter also referred to as "composite hydroxide 1") is composed of secondary particles 3 formed by the aggregation of multiple primary particles 2. The secondary particles 3 have pores 4 between the primary particles 2. It should be noted that the composite hydroxide 1 is mainly composed of secondary particles 3 formed by the aggregation of primary particles 2, but it may also contain, for example, a small amount of primary particles 2 such as primary particles 2 that are not aggregated in the form of secondary particles 3, or primary particles 2 that have detached from the secondary particles 3 after aggregation.

[0045] As described below, the composite hydroxide 1 of this embodiment, during the crystallization reaction, controls the crystallinity and density to a specific range by adjusting the dissolved oxygen concentration, dissolved nickel concentration, and preferred stirring power in the reaction aqueous solution. Therefore, the non-aqueous electrolyte secondary battery (hereinafter also referred to as "secondary battery") containing the positive electrode active material (hereinafter also referred to as "positive electrode active material") of the non-aqueous electrolyte secondary battery using the composite hydroxide 1 as a precursor can have a very high energy density and can have sufficient output characteristics as a secondary battery.

[0046] Complex hydroxide 1 is represented by general formula (1): Ni x Mn y M z (OH) 2+α In the above formula (1), M is at least one additive element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe and W, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, α is 0≤α≤0.4, and satisfies x+y+z=1.0. It should be noted that in the above formula (1), α is a coefficient that varies according to the valence of the metal element contained in the composite hydroxide 1.

[0047] In equation (1) above, when y, representing the Mn content in composite hydroxide 1, is within the above range, the morphology of primary particles 2 can be adjusted according to the dissolved oxygen concentration in the reaction aqueous solution during the crystallization process, thereby controlling the density to the desired range. Furthermore, from the viewpoint of more precisely controlling the density, y is preferably 0.1 ≤ y ≤ 0.8. When the value of y is 0.1 or higher, the density of secondary particles 3 can be controlled with a lower dissolved oxygen concentration, thus preventing excessive oxidation of the transition metal. Additionally, in equation (1) above, when z, representing the M content, is greater than 0, the requirements for various battery characteristics can be met. For example, when M contains Co, the battery capacity and output characteristics are superior. When M is Co, 0.1 ≤ z ≤ 0.4 is preferred.

[0048] The half-width at half-maximum (WWHM) of the (001) plane diffraction peak of the composite hydroxide 1, as determined by XRD, is 0.10° or more and 0.40° or less, preferably 0.20° or more and less than 0.40°. The WWHM of the (001) plane is a factor that influences the size and orientation of the microcrystals constituting the composite hydroxide 1. When the WWHM of the (001) plane is within the above range, it exhibits high crystallinity and the primary particles have moderate orientation. Therefore, the secondary particles can have a dense structure, maintaining high energy density and sufficient output characteristics as a secondary battery when forming the positive electrode active material. When the WWHM of the (001) plane is less than 0.10°, the crystallinity becomes too high, resulting in poor reactivity with Li compounds when obtaining the positive electrode active material, making it impossible to obtain a positive electrode active material with the desired characteristics. On the other hand, when the half-width of the (001) plane exceeds 0.40°, the positive electrode active material obtained by using composite hydroxide 1 is sometimes prone to becoming loose particles (secondary particles 3 with high sparsity), or the orientation of the primary particles of the positive electrode active material is reduced. It should be noted that the diffraction peak of the (001) plane appears around 2θ=19° (2θ=19±1°).

[0049] For composite hydroxide 1, the sparsity, as measured by scanning electron microscopy (SEM) images of its secondary particle cross-section, is 0.5% or more and 10% or less, preferably 0.5% or more and 8% or less. When the sparsity is within this range, the battery capacity and fillability are excellent, and a positive electrode active material with higher volumetric energy density and sufficient output characteristics can be obtained. On the other hand, when the sparsity is less than 0.5%, the penetration of Li compounds into the particles is insufficient when obtaining the positive electrode active material, and the reactivity with lithium compounds sometimes decreases. Furthermore, when the sparsity exceeds 10%, the volumetric energy density sometimes decreases.

[0050] Here, "density" refers to a value obtained from image analysis of the cross-section of the composite hydroxide 1 particles using a scanning electron microscope (SEM), expressed as [(area of ​​pores 4 inside secondary particles 3 / cross-sectional area of ​​secondary particles 3) × 100] (%). For example, in Figure 1 In the cross-section of the composite hydroxide 1 particle shown, the sparsity density is expressed as [(area of ​​pores 4) / (sum of cross-sectional area of ​​primary particle 2 and area of ​​pores 4) × 100]. That is, the higher the sparsity density, the more porous the internal structure of the secondary particle 3; the lower the sparsity density, the more dense the internal structure of the secondary particle 3. It should be noted that the sparsity density can be expressed as the average sparsity density by randomly selecting 20 cross-sections of secondary particles 3 that constitute more than 80% of the volume average particle size (MV), measuring the sparsity density of each of these cross-sections, and using this average as the mean sparsity density.

[0051] The composite hydroxide 1 preferably has a pore volume of 0.01 cm³, as determined by nitrogen adsorption. 3 / g or more and 0.04cm 3 / g or less. When the pore volume is less than 0.01 mL / g, the penetration of Li compounds into the particles is insufficient when obtaining the positive electrode active material, and the reactivity with lithium compounds is sometimes reduced. When the pore volume is within the above range, the filling performance is excellent, and it can have output characteristics suitable as the positive electrode active material 10.

[0052] The particle size of composite hydroxide 1 is not particularly limited and can be set to a desired range. However, when used as a precursor for positive electrode active materials, the volume average particle size MV is preferably 5 μm or more and 20 μm or less, more preferably 6 μm or more and 15 μm or less. When the average particle size is less than 5 μm, the filling capacity of composite hydroxide 1 particles is significantly reduced, and it is sometimes difficult to increase the battery capacity per unit volume when making positive electrode active materials. On the other hand, when the average particle size exceeds 20 μm, the specific surface area decreases. Therefore, when making positive electrode active materials, the reactivity with lithium raw materials decreases, and it is sometimes impossible to obtain positive electrode active materials with high battery characteristics. The interface between the obtained positive electrode active material and the electrolyte is reduced, so the resistance of the positive electrode increases, and the output characteristics of the battery may sometimes decrease.

[0053] The composite hydroxide 1 preferably has an index representing the width of the particle size distribution, namely [(D90-D10) / average particle size], of 0.7 or more. When [(D90-D10) / average particle size] is less than 0.7, the uniformity of particle size increases, and there is a tendency for the charge / discharge capacity per unit mass (hereinafter also referred to as "battery capacity") to increase, but the particle filling capacity decreases, and the volumetric energy density sometimes becomes lower. [(D90-D10) / average particle size] can be adjusted to the above range, for example, by mixing composite hydroxides 1 with different particle sizes, or by manufacturing composite hydroxide 1 using a continuous crystallization method. It should be noted that the upper limit of [(D90-D10) / average particle size] is not particularly limited, but from the viewpoint of suppressing the excessive mixing of microparticles or coarse particles into the positive electrode active material, for example, 1.2 or less, more preferably 1.0 or less.

[0054] In the above [(D90-D10) / average particle size], D10 refers to the particle size whose accumulated volume, starting from the smallest particle size, is 10% of the total volume of all particles; D90 refers to the particle size whose accumulated volume, similarly, is 90% of the total volume of all particles. Furthermore, the average particle size is the volume average particle size MV, which is the average particle size obtained by weighting by volume. The volume average particle size MV, D90, and D10 can be determined using a laser diffraction scattering particle size analyzer.

[0055] The specific surface area of ​​composite hydroxide 1 is preferably 2.5 m². 2 / g or more and 50m 2 The range below / g, more preferably 5m 2 / g or more and 15m 2 The specific surface area is below a certain range. When the specific surface area is within the above range, the battery characteristics and fillability of the positive electrode active material using composite hydroxide 1 as a precursor become more superior. It should be noted that the specific surface area can be set to the above range by adjusting the particle size distribution and density of composite hydroxide 1, including the average particle size MV.

[0056] In addition, the tap density of composite hydroxide 1 is preferably 1.8 g / cm³. 3 Above and 2.5g / cm 3 The following range, more preferably 1.9 g / cm 3 Above and 2.5g / cm 3 The following range applies. When the tap density is within the above range, the filling performance of the positive electrode active material using composite hydroxide 1 as a precursor is better, which can improve the battery capacity. It should be noted that the tap density can be set to the above range by adjusting the particle size distribution and density of composite hydroxide 1, including the average particle size MV.

[0057] (2) Manufacturing method of nickel-manganese composite hydroxide

[0058] Figure 2 The figure illustrates an example of a method for manufacturing the nickel-manganese composite hydroxide according to this embodiment. The following description will explain... Figure 2 In such cases, it is appropriate to refer to a schematic diagram illustrating an example of complex hydroxide 1. Figure 1 .

[0059] For example Figure 2 As shown, the method for manufacturing the composite hydroxide 1 in this embodiment includes a crystallization step: in a reaction aqueous solution within a crystallization reaction tank, salts containing at least nickel and manganese are neutralized and co-precipitated. In this embodiment, during this crystallization step, it is important to adjust the dissolved nickel concentration and dissolved oxygen concentration in the reaction aqueous solution to specific ranges. By adjusting these factors (parameters), the particle size d of the resulting secondary particles 3 and the density of the secondary particles 3 can be controlled respectively. Furthermore, by adjusting the stirring power loaded in the reaction aqueous solution, the crystallinity of the secondary particles 3 and the density of the secondary particles 3 can be controlled more precisely.

[0060] The inventors conducted in-depth research on the manufacturing conditions of composite hydroxide 1 and found that by adjusting the dissolved oxygen concentration and the dissolved nickel concentration in the reaction aqueous solution, the morphology of primary particles 2 and secondary particles 3 can be accurately controlled. That is, the manufacturing method of this embodiment adjusts the dissolved nickel concentration to a specific range based on the dissolved oxygen concentration, thereby enabling the manufacture of composite hydroxide 1, which can also be used as a precursor for positive electrode active materials. It should be noted that "morphology" refers to characteristics related to the morphology and structure of primary particles 2 and / or secondary particles 3, including particle shape, density, average particle size, particle size distribution, crystal structure, and tap density.

[0061] The method for manufacturing the composite hydroxide 1 in this embodiment is as follows: By adjusting the dissolved oxygen concentration in the reaction aqueous solution to a lower range and then adjusting the dissolved nickel concentration to a higher range, the precipitation rate of the primary particles 2 is reduced, and the thickness of the primary particles 2 is increased in a way that fills the pores 4 between the primary particles 2, thereby forming secondary particles 3 with a dense structure. In addition, when the dissolved nickel concentration is adjusted to a higher range, the coarsening of the particle size of the secondary particles 3 can be suppressed.

[0062] Furthermore, the method for manufacturing the composite hydroxide 1 in this embodiment controls the aggregation state of the primary particles 2 based on the stirring power in the reaction aqueous solution, thereby enabling more accurate control of the particle size of the secondary particles 2 within a wider range. Specifically, when the dissolved oxygen concentration is adjusted to a low range, by adjusting the stirring power to a high range, the coarse growth of the secondary particles 3 caused by the aggregation of the primary particles 2 can be suppressed. Additionally, by suppressing the coarsening of the secondary particles 3, the precipitation of the composite hydroxide within the secondary particles 3 is promoted, resulting in more compact secondary particles 3. The conditions in the method for manufacturing the composite hydroxide 1 of this embodiment will be described below.

[0063] (Dissolved oxygen concentration)

[0064] The dissolved oxygen concentration in the reaction aqueous solution is adjusted to a range of 0.2 mg / L or more and 4.6 mg / L or less. By controlling the dissolved oxygen concentration within this range, the density of the secondary particles 3 is also controlled within this range, resulting in a composite hydroxide suitable as a precursor for the positive electrode active material. Furthermore, during the crystallization process, the dissolved oxygen concentration is preferably controlled within a certain range. The variation range of the dissolved oxygen concentration is preferably set to within ±0.2 mg / L, and more preferably within ±0.1 mg / L.

[0065] When the dissolved oxygen concentration is within the above range, for example, it can be obtained that... Figure 5 A, Figure 5 As shown in Figure B, composite hydroxide 1 has a dense structure and a high packing density (tap density). The positive electrode active material manufactured using composite hydroxide 1 has a high packing density, and therefore exhibits a high secondary battery capacity. When the dissolved oxygen concentration is less than 0.2 mg / L, the oxidation of transition metals, particularly manganese, becomes essentially inactive, resulting in an extremely dense interior for the secondary particles 3. Furthermore, unusual surface shapes sometimes appear. The positive electrode active material obtained using such a composite hydroxide exhibits higher reaction resistance and lower output characteristics. On the other hand, when the dissolved oxygen concentration exceeds 4.6 mg / L, the generated secondary particles have a more porous structure.

[0066] It should be noted that dissolved oxygen concentration can be determined using methods such as the Winkler method (chemical analysis), membrane permeation method (electrochemical measurement), and fluorescence measurement. Furthermore, any of these methods can yield equivalent dissolved oxygen concentration values; therefore, any of these methods can be used. It should also be noted that the dissolved oxygen concentration in the reaction solution can be adjusted, for example, by introducing inert gases (such as N2, Ar, etc.), air, or oxygen into the reaction vessel, and controlling the flow rate and composition of these gases. These gases can flow into the space within the reaction vessel or be blown into the reaction solution. Additionally, by using a stirring device such as stirring blades, the reaction solution can be moderately stirred within the range described below, thereby making the overall dissolved oxygen concentration of the reaction solution more uniform.

[0067] (Dissolved nickel concentration)

[0068] Regarding the concentration of dissolved nickel in the reaction aqueous solution, for example, using the temperature of the reaction aqueous solution as a reference, it is adjusted to a range of 700 mg / L or more and 1500 mg / L or less, preferably to a range of 700 mg / L or more and 1200 mg / L or less. By appropriately adjusting the dissolved nickel concentration within the above range, the average particle size and density can be controlled within the desired range, and a nickel-manganese composite hydroxide with low density and high sphericity can be easily obtained as a precursor for the positive electrode active material. Furthermore, in the crystallization process, the dissolved nickel concentration is preferably controlled within a certain range. For example, the variation range of the dissolved nickel concentration is preferably set to within ±20 mg / L. It should be noted that the dissolved nickel concentration can be determined, for example, by chemical analysis of the amount of Ni in the liquid component of the reaction aqueous solution using ICP emission spectroscopy.

[0069] When the dissolved nickel concentration in the reaction aqueous solution is less than 700 mg / L, the growth rate of primary particles 2 is rapid, and nucleation tends to dominate over particle growth, making the density of secondary particles more likely to exceed the aforementioned range. On the other hand, when the dissolved nickel concentration exceeds 1500 mg / L, the formation rate of composite hydroxide 1 (secondary particles 3) slows down significantly, and nickel remains in the filtrate. The composition of the resulting composite hydroxide 1 sometimes deviates significantly from the target value. Furthermore, under conditions of excessively high dissolved nickel concentration, the amount of impurities in composite hydroxide 1 increases significantly, sometimes reducing the battery performance when the positive electrode active material obtained from the composite hydroxide is used in a battery.

[0070] (Stirring power)

[0071] The stirring power loaded on the reaction aqueous solution is preferably 3 kW / m 3 Above and 15kW / m 3 The following range is adjusted, and it is preferred to set it to 3kW / m.3 Above and 14kW / m 3 The following range is further preferably set at 4.5 kW / m 3 Above and 12kW / m 3 The following range applies. By maintaining the stirring power within the aforementioned range, excessive fineness or coarsening of secondary particles can be suppressed, resulting in a particle size of composite hydroxide 1 that is more suitable as a positive electrode active material. Furthermore, by suppressing the coarsening of secondary particles, the secondary particles can be made more compact. Additionally, during the crystallization process, the stirring power is preferably controlled within a certain range. For example, the variation range of the stirring power can be set to ±0.2 kW / m. 3 Within. Alternatively, it can be, for example, 7kW / m. 3 The stirring power can be adjusted within the following range; it can also be 6.5 kW / m³. 3 The stirring power is adjusted within the following range. It should be noted that the stirring power is controlled within the above range by adjusting the size and rotation speed of the stirring devices, such as the stirring blades, in the reaction vessel.

[0072] The stirring power is less than 3kW / m 3 At this time, primary particles 2 tend to aggregate, sometimes forming coarser secondary particles 3. Consequently, the filling capacity of the positive electrode active material sometimes decreases. On the other hand, exceeding 15kW / m 3 When this happens, it is easy to excessively inhibit the aggregation of primary particles, causing secondary particles 3 to become too small, and sometimes reducing the filling capacity of the positive electrode active material.

[0073] (Reaction temperature)

[0074] The temperature of the reaction aqueous solution in the crystallization reaction tank is preferably in the range of 35°C or higher and 60°C or lower, more preferably in the range of 38°C or higher and 50°C or lower. When the temperature of the reaction aqueous solution exceeds 60°C, nucleation takes precedence over particle growth in the reaction aqueous solution, and the shape of the primary particles 2 constituting the composite hydroxide 1 tends to become excessively fine. When using such a composite hydroxide 1, there is a problem of reduced filling capacity of the resulting positive electrode active material. On the other hand, when the temperature of the reaction aqueous solution is lower than 35°C, particle growth tends to take precedence over nucleation in the reaction aqueous solution, and therefore, the shape of the primary particles 2 and secondary particles 3 constituting the composite hydroxide 1 tends to become coarse. When a composite hydroxide with such coarse secondary particles 3 is used as a precursor for a positive electrode active material, there is a problem that a positive electrode active material containing very large coarse particles with unevenness can be formed during electrode fabrication. Furthermore, when the temperature of the reaction aqueous solution is lower than 35°C, not only is there a problem of high residual metal ions in the reaction aqueous solution and very poor reaction efficiency, but there is also a problem of easily forming a composite hydroxide containing a large number of impurity elements.

[0075] (pH value)

[0076] The pH of the reaction aqueous solution is preferably between 10.0 and 13.0 at a reference solution temperature of 25°C. When the pH is within this range, the density can be controlled by appropriately adjusting the size and shape of the primary particles 2, while simultaneously controlling the morphology of the secondary particles, thereby obtaining a composite hydroxide 1 that is more suitable as a precursor for the positive electrode active material. Furthermore, when the pH is less than 10.0, the formation rate of composite hydroxide 1 slows down significantly, nickel remains in the filtrate, and the composition of the resulting composite hydroxide 1 sometimes deviates significantly from the target value. On the other hand, when the pH exceeds 13.0, the particle growth rate is rapid, and nucleation becomes more likely, thus easily resulting in small-diameter particles with poor sphericity.

[0077] (other)

[0078] The manufacturing method of this embodiment includes the following crystallization step: in a reaction aqueous solution, salts containing at least nickel and manganese are neutralized to generate nickel-manganese composite hydroxide particles. As a specific embodiment of the crystallization step, for example, while stirring the mixed aqueous solution containing at least nickel (Ni) and manganese (Mn) in the reaction tank at a certain speed, a neutralizing agent (e.g., an alkaline solution) is added to control the pH, and composite hydroxide particles can be generated through co-precipitation. In the manufacturing method of this embodiment, either a batch crystallization method or a continuous crystallization method can be used. Here, the continuous crystallization method refers to a crystallization method in which the above-mentioned mixed aqueous solution is continuously supplied while a neutralizing agent is supplied to control the pH, and composite hydroxide particles generated due to overflow are recovered. Compared with the batch method, the continuous crystallization method can obtain particles with a wide particle size distribution and easily obtain particles with high filling capacity. In addition, the continuous crystallization method is suitable for mass production and will be an industrially advantageous manufacturing method. For example, when the composite hydroxide 1 of this embodiment is manufactured by the continuous crystallization method, the filling properties (tap density) of the resulting composite hydroxide 1 particles can be further improved, and composite hydroxide 1 with higher filling properties and density can be produced easily and in large quantities.

[0079] The mixed aqueous solution can be an aqueous solution containing at least nickel and manganese, that is, an aqueous solution containing at least nickel and manganese salts dissolved in it. Furthermore, the mixed aqueous solution can contain M, or an aqueous solution containing nickel salt, manganese salt, and a salt containing M can be used. As the nickel and manganese salts and the salt containing M, at least one selected from the group consisting of sulfates, nitrates, and chlorides can be used. From the viewpoints of cost and wastewater treatment, sulfates are preferred.

[0080] The concentration of the mixed aqueous solution, based on the total amount of dissolved metal salts, is preferably set to 1.0 mol / L or more and 2.4 mol / L or less, more preferably 1.2 mol / L or more and 2.2 mol / L or less. If the concentration of the mixed aqueous solution is less than 1.0 mol / L, the concentration is too low, and there is a concern that the primary particles 2 constituting the composite hydroxide 1 (secondary particles 3) may not grow sufficiently. On the other hand, if the concentration of the mixed aqueous solution exceeds 2.4 mol / L, it will exceed the saturation concentration at room temperature, and crystals may precipitate again, posing a risk of clogging pipes. Furthermore, in the above cases, the nucleus generation of primary particles 2 increases, raising concerns about an increased proportion of microparticles in the resulting composite hydroxide particles. Here, the composition of the metal elements contained in the aforementioned mixed aqueous solution is consistent with the composition of the metal elements contained in the resulting composite hydroxide 1. Therefore, the composition of the metal elements in the mixed aqueous solution can be adjusted in the same way as the composition of the target composite hydroxide 1.

[0081] Alternatively, a complexing agent can be added to the mixed aqueous solution along with a neutralizing agent. The complexing agent is not particularly limited, as long as it can combine with metal elements such as nickel ions and manganese ions in the aqueous solution to form a complex. For example, an ammonium ion donor can be used as a complexing agent. There are no particular limitations on the ammonium ion donor; for example, at least one selected from the group consisting of ammonia, ammonium sulfate aqueous solution, and ammonium chloride aqueous solution can be used. Ammonia is preferred for ease of operation. When using an ammonium ion donor, it is preferable that the concentration of ammonium ions is in the range of 5 g / L or more and 25 g / L or less.

[0082] As a neutralizing agent, an alkaline solution can be used, such as a common aqueous solution of alkali metal hydroxides like sodium hydroxide or potassium hydroxide. From the viewpoints of cost and ease of operation, an aqueous solution of sodium hydroxide is preferred. It should be noted that the alkali metal hydroxide can also be added directly to the reaction aqueous solution; however, from the perspective of ease of pH control, adding it in aqueous solution form is preferred. In the above cases, the concentration of the alkali metal hydroxide aqueous solution is preferably 12% by mass or more and 30% by mass or less, more preferably 20% by mass or more and 30% by mass or less. When the concentration of the alkali metal hydroxide aqueous solution is less than 12% by mass, the supply to the reaction tank increases, raising concerns about insufficient particle growth. On the other hand, when the concentration of the alkali metal hydroxide aqueous solution exceeds 30% by mass, the pH value at the point of addition of the alkali metal hydroxide will locally increase, raising concerns about the generation of particulate matter.

[0083] Furthermore, the manufacturing method of this embodiment preferably includes a cleaning step after the crystallization step. The cleaning step is a step of cleaning away impurities contained in the composite hydroxide 1 obtained in the crystallization step described above. Pure water is preferably used as the cleaning solution. Additionally, the amount of cleaning solution is preferably 1 L or more relative to 300 g of composite hydroxide 1. When the amount of cleaning solution is less than 1 L relative to 300 g of composite hydroxide 1, the cleaning becomes insufficient, and impurities may sometimes remain in the composite hydroxide 1. As a cleaning method, for example, simply passing a cleaning solution such as pure water through a filter press or similar filter is sufficient. When further cleaning away SO4 remaining in the composite hydroxide 1, sodium hydroxide, sodium carbonate, or the like is preferably used as the cleaning solution.

[0084] (3) Positive electrode active material for non-aqueous electrolyte secondary batteries

[0085] Figure 3 (A) is a schematic diagram showing an example of a lithium nickel manganese composite oxide 11 (hereinafter also referred to as "composite oxide 11") constituting the positive electrode active material 10 (hereinafter also referred to as "positive electrode active material 10") for a non-aqueous electrolyte secondary battery according to this embodiment. Furthermore, Figure 3 Figure (B) illustrates the configuration of primary particles 12 in the positive electrode active material 10 (secondary particles 13). The composite oxide 11 is represented by general formula (2): Li 1+t Ni x Mn y M z O 2+β (In formula (2), M is at least one added element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe and W, t is -0.05≤t≤0.5, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, and satisfies x+y+z=1.0, β is 0≤β≤0.5.) indicates that it is formed by the aggregation of primary particles 12 into secondary particles 13. It should be noted that in the above formula (2), β is the valence of the metal element other than lithium contained in the composite oxide 11, and is a coefficient that varies according to the atomic ratio of lithium to the metal element other than lithium.

[0086] As described later, composite oxide 11 is formed by mixing and calcining the aforementioned composite hydroxide 1 and a lithium compound. Thus, the composition of composite oxide 11 is substantially the same as that of composite hydroxide 1, except for lithium. Furthermore, for y and z in the above formula (2), for example for the same reasons as for y and z in the above formula (1), it is preferable that 0.1 ≤ y ≤ 0.8, and when M is Co, it is preferable that 0.1 ≤ z ≤ 0.4.

[0087] In this embodiment, the positive electrode active material 10 uses the aforementioned composite hydroxide 1 as a precursor, thereby obtaining a secondary battery with very high energy density and sufficient output characteristics. It should be noted that the composite oxide 11 is mainly composed of secondary particles 13 formed by the aggregation of primary particles 12, but similarly to the composite hydroxide 1, it may also contain a small amount of primary particles 12 (alone). Furthermore, the positive electrode active material 10 may contain other lithium metal composite oxides besides the composite oxide 11, to the extent that it does not impair the effects of the present invention. The characteristics of the positive electrode active material 10 will be described below.

[0088] The density of the positive electrode active material 10 is 0.5% or more and 12% or less, preferably 1.0% or more and 10% or less. When the density is within the above range, the electrolyte can fully penetrate into the secondary particles 13, thereby obtaining high battery capacity and output characteristics, and the secondary particles 13 can be in a dense state, resulting in high fillability. Therefore, when this composite oxide 11 is used as the positive electrode active material in a secondary battery, a secondary battery with high volumetric energy density and sufficient output characteristics can be obtained. It should be noted that when the density becomes less than 0.5%, the electrolyte penetration into the secondary particles is insufficient, and high battery capacity cannot be obtained. Therefore, even with high fillability into the battery container, the battery capacity of each particle will decrease, and thus the overall energy density of the active material will decrease.

[0089] Here, "density" refers to a value obtained from image analysis of the cross-section of the composite oxide 11 particles using a scanning electron microscope (SEM), expressed as [(area of ​​pores 14 inside secondary particles 13 / cross-sectional area of ​​secondary particles 13) × 100] (%). For example, in... Figure 3 In the cross-section of the composite hydroxide 11 particles shown, the sparsity is expressed as [(area of ​​pore 14) / (sum of cross-sectional area of ​​primary particle 12 and area of ​​pore 14) × 100]. It should be noted that, similarly to the composite hydroxide 1 particles, the sparsity of the cross-sections of 20 secondary particles 13 can be measured separately, and the average sparsity is used as the average value.

[0090] For the positive electrode active material 10, the DBP absorption (hereinafter also referred to as "oil absorption") measured according to JIS K6217-4:2008 is 12 cm⁻¹. 3 / 100g or more and 20cm 3 / 100g or less. When the oil absorption is within the above range, the secondary battery obtained by using the positive electrode active material 10 as the positive electrode can maintain a sufficient amount of electrolyte in the positive electrode. Since the movement of lithium ions in the electrolyte is not restricted, sufficient battery capacity can be obtained. Furthermore, the oil absorption becomes less than 12cm³. 3When the electrolyte content is 100g, the electrolyte level in the positive electrode is insufficient, resulting in reduced battery capacity and output characteristics.

[0091] For the positive electrode active material 10, the ratio of the diffraction peak intensity I(003) of the 003 plane to the peak intensity I(104) of the 104 plane (hereinafter also referred to as the "peak intensity ratio"), as measured by X-ray diffraction, is preferably 1.7 or more, more preferably 1.7 or more and 2.5 or less. When the peak intensity ratio is 1.7 or more, the crystallinity of the positive electrode active material 10 is high, and the battery capacity and output characteristics are excellent. In addition, when the peak intensity ratio is in the above range, the primary particles grow on specific crystal planes, and therefore, the orientation of the primary particles 12 in the secondary particles 13 becomes higher, resulting in a structure in which at least a portion of the primary particles 12 are arranged radially from the center C of the secondary particles 13 to the outer periphery (radial structure). By having a radial structure, the electrolyte can easily penetrate into the interior of the positive electrode active material 10, and the stress load generated by the expansion and contraction of the positive electrode active material 10 during charging and discharging is mitigated at the grain boundaries of the primary particles 12, thereby improving the cycle characteristics.

[0092] Regarding the primary particles 12 in the secondary particles 13 (positive electrode active material 10), it is preferred, for example, that the primary particles 12 are located within a radius R2 of 50% from the outer periphery of the secondary particles 13 toward the particle center C (refer to...). Figure 3 Within (B)), relative to the total number of primary particles 12 present in the aforementioned 50% range, more than 50% of the number of primary particles 12 are arranged radially from the center C of the secondary particles 13 outwards. As a result, the positive electrode active material 10 becomes a particle structure with a higher radial orientation (radial structure), which can further improve battery characteristics when used as a positive electrode in a secondary battery. To further improve battery characteristics, it is more preferable that more than 70% of the primary particles 12 are arranged radially within the aforementioned 50% radius range R2. Furthermore, regarding the arrangement of the primary particles 12, when the dissolved oxygen concentration is within the aforementioned range, for example, by adjusting the stirring power together with the dissolved nickel concentration, a higher ratio of radial arrangement can be formed. For example, the Ni concentration is adjusted to 700 mg / L or more and 1500 mg / L or less, and the stirring power is adjusted to 4.0 kW / m. 3 Above and 12.0kW / m 3 When the following ranges are equal, radial structures become easier and clearer to detect.

[0093] Here, radial arrangement means, for example, Figure 3As shown in (B), in the cross-section of the composite oxide 11, the major axis L of the primary particle 12 is oriented along the radial direction R1 from the center C of the secondary particle 13 outwards. Here, orientation along the radial direction R1 means that in the cross-section of the composite oxide 11, the angle difference θ between the major axis L of the primary particle 12 and the radial direction R1 is within 45°, preferably within 30°. The angle difference θ between the major axis L of the primary particle 12 and the radial direction R1 can be obtained, for example, as follows: Figure 3 As shown in (B), on the major axis of the primary particle 12, when the direction from one end near the center of the secondary particle 13 toward the other end is defined as the major axis direction L, the angle θ between the radial direction R1 passing through the center of the major axis in the radial direction from the center C of the secondary particle 13 toward the outer periphery and the major axis direction L can be obtained.

[0094] For the positive electrode active material 10, the preferred tap density is 2.0 g / cm³. 3 Above and 2.7g / cm 3 The following range, preferably 2.2 g / cm³ 3 Above and 2.5g / cm 3 The following range. When the tap density is within the above range, the positive electrode active material achieves a good balance between battery capacity and fillability, which can further improve the battery's energy density.

[0095] Furthermore, for the positive electrode active material 10, the volume average particle size MV is preferably 5 μm or more and 20 μm or less, more preferably 6 μm or more and 15 μm or less. When the volume average particle size MV is within the above range, while maintaining a high fillability, the reduction of specific surface area is suppressed. The battery using this positive electrode active material can achieve both high fill density and excellent output characteristics.

[0096] Furthermore, for the positive electrode active material 10, the fluctuation index [(D90-D10) / average particle size], which represents the particle size fluctuation, is preferably 0.70 or higher. When the fluctuation index of the positive electrode active material 10 is within the above range, the moderate mixing of microparticles and coarse particles can suppress the decrease in the cycle characteristics and output characteristics of the obtained positive electrode active material 10, and can further improve the particle filling properties. From the viewpoint of suppressing excessive mixing of microparticles or coarse particles into the positive electrode active material 10, the fluctuation index of the positive electrode active material 10 is preferably set to 1.2 or lower, and more preferably to 1.0 or lower.

[0097] Figure 7Figures (A) and (B) illustrate the method for evaluating the crystal orientation of the positive electrode active material 10 using electron backscatter diffraction (EBSD). EBSD is a method in which an electron beam is irradiated onto a sample using a scanning electron microscope (SEM), and the Kikuchi pattern generated by the diffraction of the electron beam on the measured surface of the sample is analyzed, thereby determining the crystal orientation of minute locations. By analyzing the crystal orientation determined by EBSD, the crystal orientation in a specific direction can be evaluated.

[0098] In this specification, the center C2 of the cross-section of the secondary particles 13 constituting the positive electrode active material 10 (refer to...) Figure 7 The crystal orientation is evaluated using EBSD by taking any radial direction (A) towards the outer periphery as the x-axis and the direction orthogonal to the x-axis as the y-axis. The following refers to... Figure 7 (A) provides an explanation of the directions of each axis.

[0099] For example, such as Figure 7 As shown in (A), regarding the x-axis direction in the cross-section of the secondary particle 13, when the observation section is set to the plane of the paper, it can be defined as the direction from the center C2 towards the horizontal direction within the observation section. Similarly, regarding the y-axis direction in the cross-section of the secondary particle 13, when the observation section is set to the plane of the paper, it can be defined as the direction from the center C2 towards the vertical direction within the observation section. It should be noted that when the observation section is set to the plane of the paper, the direction from the center C2 towards the vertical and forward direction relative to the observation section is called the z-axis direction.

[0100] For the positive electrode active material 10 of this embodiment, it is preferable that the orientation ratio of the crystal ab plane, measured by EBSD, is 55% or more, more preferably 58% or more, and even more preferably 60% or more in the x-axis direction and y-axis direction, respectively. When the orientation ratio of the crystal ab plane is within the above range, the battery capacity is further improved.

[0101] The lithium-nickel-manganese composite oxide (positive electrode active material 10) has a hexagonal crystal structure and a layered structure in which transition metal ion layers such as nickel and manganese are alternately stacked with lithium ion layers in the c-axis direction. Furthermore, during the charging and discharging of the secondary battery, lithium ions in the crystal constituting the positive electrode active material 10 move in the

[100] -axis direction or the

[110] -axis direction (ab plane), undergoing lithium ion insertion and extraction. Therefore, although the details are not yet clear, it is believed that when the orientation ratio of the crystal ab plane in the x-axis and y-axis directions is within the aforementioned range, lithium ion insertion and extraction will proceed more smoothly within the positive electrode active material 10, further improving the battery capacity.

[0102] On the other hand, for example, in a positive electrode active material having a structure formed by random aggregation of primary particles, the orientation ratio of the crystal ab plane in at least one of the x-axis and y-axis directions becomes less than 55%, while the orientation ratio in the c-axis direction increases. In the above case, the battery capacity of the positive electrode active material 10 in the secondary battery (positive electrode) is sometimes insufficient.

[0103] It should be noted that the EBSD-based evaluation can be performed as follows: In cross-sectional observation of secondary particles 13, three or more secondary particles 13 that constitute more than 80% of the volume average particle size (MV) are selected, and the orientation ratios of the crystal ab planes in the x-axis and y-axis directions of each particle are measured and averaged. Furthermore, for specific EBSD-based evaluation methods, the methods described in the examples below can be used.

[0104] (4) Manufacturing method of positive electrode active material for non-aqueous electrolyte secondary batteries

[0105] The method for manufacturing the positive electrode active material in this embodiment is a method for manufacturing a positive electrode active material (hereinafter also referred to as "positive electrode active material") for a non-aqueous electrolyte secondary battery, which is composed of a lithium nickel manganese composite oxide (hereinafter also referred to as "composite oxide"), wherein the lithium nickel manganese composite oxide is of general formula (2): Li 1+t Ni x Mn y M z O 2+β (In formula (2), M is at least one additive element selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W, t is -0.05≤t≤0.5, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, and satisfies x+y+z=1.0, β is 0≤β≤0.5.) indicates that it is formed by the aggregation of primary particles into secondary particles.

[0106] Figure 4 This diagram illustrates an example of a method for manufacturing the positive electrode active material 10 according to this embodiment. Figure 4 As shown, the method for manufacturing the positive electrode active material 10 includes the following steps: a step of mixing the aforementioned composite hydroxide 1 and a lithium compound to obtain a mixture; and a calcination step of calcining the mixture to obtain a composite oxide 11. The morphology of the composite oxide 11 is strongly influenced by the morphology of the composite hydroxide 1, which is the precursor. Therefore, by adjusting the powder characteristics of the composite hydroxide 1 to a specific range as described above, the powder characteristics of the composite oxide 11 can be controlled to the aforementioned specific range. Hereinafter, the method for manufacturing the positive electrode active material 10 will be described.

[0107] (Mixed Process)

[0108] First, the aforementioned composite hydroxide 1 and a lithium compound are mixed to form a lithium mixture. Composite hydroxide 1 is preferably obtained by the above-described manufacturing method. There are no particular limitations on the lithium compound; any known lithium compound can be used. For example, from the viewpoint of ease of acquisition, lithium hydroxide, lithium nitrate, lithium carbonate, or mixtures thereof are preferred. Among these, from the viewpoint of ease of handling and quality stability, lithium hydroxide or lithium carbonate are more preferred as the lithium compound. It should be noted that composite hydroxide 1 can also be oxidized to form a nickel-manganese composite oxide before the mixing step, and then mixed with the lithium compound.

[0109] The composite hydroxide 1 and the lithium compound are mixed such that the ratio (Li / Me) of the number of lithium atoms (Li) in the lithium mixture to the sum of the number of atoms of the metals other than lithium, i.e., nickel, cobalt, and the added elements (Me), is 0.95 or more and 1.50 or less, preferably 0.95 or more and 1.20 or less. That is, the Li / Me ratio does not change before and after calcination; therefore, the Li / Me ratio mixed in this mixing process becomes the Li / Me ratio in the positive electrode active material. Thus, the mixing is performed in such a way that the Li / Me ratio in the lithium mixture becomes the same as the Li / Me ratio in the desired positive electrode active material.

[0110] Alternatively, a general mixer can be used for mixing, such as a oscillating mixer, Loedige mixer, Julia mixer, or V-type mixer, as long as the mixture is thoroughly mixed to the extent that the shape of the composite hydroxide 1 is not damaged.

[0111] (Roasting process)

[0112] Next, the lithium mixture is calcined to obtain composite oxide 11. Calcination is carried out in an oxidizing atmosphere at a temperature between 700°C and 1100°C. When the calcination temperature is below 700°C, calcination is not complete, and the tap density sometimes decreases. Furthermore, when the calcination temperature is below 700°C, lithium diffusion is insufficient, leaving residual lithium. This results in an irregular crystal structure or an inability to achieve sufficient uniformity in the composition of nickel, manganese, etc., within the particles, sometimes leading to insufficient characteristics when used in batteries. On the other hand, when the temperature exceeds 1100°C, the sparse areas on the particle surface become denser. Additionally, rapid sintering may occur between the particles of composite oxide 11, causing abnormal particle growth. Therefore, the calcined particles become coarse, potentially losing their approximately spherical secondary particle morphology. This reduces the specific surface area of ​​the positive electrode active material, leading to increased resistance and reduced battery capacity when used in batteries. The calcination time is not particularly limited, but is approximately 1 hour to 24 hours.

[0113] It should be noted that, from the viewpoint of ensuring a uniform reaction between the composite hydroxide 1 or the composite oxide 11 obtained by oxidizing it and the lithium compound, it is preferable to raise the temperature to the aforementioned calcination temperature at a heating rate ranging from 1°C / min to 10°C / min. Furthermore, the temperature can be maintained at a level near the melting point of the lithium compound for approximately 1 to 10 hours before calcination. This allows for a more uniform reaction.

[0114] It should be noted that, in the manufacturing method of the positive electrode active material 10 of this embodiment, the composite hydroxide 1 used may include, in addition to the composite hydroxide 1 formed from secondary particles 3 aggregated from primary particles 2, individual primary particles 2 such as primary particles 2 that are not aggregated in the form of secondary particles 3 and primary particles 2 that detach from secondary particles 3 after aggregation. Furthermore, the composite hydroxide 1 used may include composite hydroxides manufactured by methods other than those described above or composite oxides formed by oxidizing the composite hydroxide, to the extent that it does not impair the effects of the present invention.

[0115] (5) Non-aqueous electrolyte secondary battery

[0116] For one example of the non-aqueous electrolyte secondary battery (hereinafter also referred to as "secondary battery") of this embodiment, each component will be described separately. The secondary battery of this embodiment includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of the same components as a general lithium-ion secondary battery. It should be noted that the embodiment described below is merely an example, and the non-aqueous electrolyte secondary battery is represented by the following embodiment. Based on the common knowledge of those skilled in the art, it can be implemented in various modified and improved forms. In addition, the application of the secondary battery is not particularly limited.

[0117] (positive electrode)

[0118] Using the above-mentioned positive electrode active material 10, a positive electrode for a non-aqueous electrolyte secondary battery is manufactured. An example of the manufacturing method for the positive electrode is described below. First, the above-mentioned positive electrode active material 10 (powdered), conductive material, and binder are mixed, and then, as needed, target solvents such as activated carbon and viscosity adjusters are added, and the mixture is kneaded to prepare a positive electrode composite paste.

[0119] The mixing ratio of the various materials in the cathode composite material becomes a key factor in determining the performance of the lithium secondary battery and can be adjusted according to the application. The mixing ratio of the materials can be set to be the same as that of the cathode of a known lithium secondary battery. For example, when the total mass of the solid components of the cathode composite material excluding the solvent is set to 100% by mass, it can contain 60-95% by mass of cathode active material, 1-20% by mass of conductive material, and 1-20% by mass of binder.

[0120] The obtained positive electrode composite paste is coated onto the surface of a current collector, such as aluminum foil, and dried to allow the solvent to disperse, thus forming a sheet-like positive electrode. Depending on the needs, pressure may be applied by rolling or other methods to increase electrode density. The resulting sheet-like positive electrode can then be cut to a suitable size according to the target battery for battery fabrication. However, the method for fabricating the positive electrode is not limited to the method described above, and other methods may also be used.

[0121] As conductive materials, carbon black materials such as graphite (natural graphite, artificial graphite, and expanded graphite), acetylene black, and Ketjen black can be used.

[0122] As a binder, it plays a role in fixing and connecting active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene rubber, styrene butadiene, cellulose resins and polyacrylic acid can be used.

[0123] As needed, the positive electrode active material, conductive material, and activated carbon are dispersed, and a solvent for dissolving the binder is added to the positive electrode composite material. Specifically, organic solvents such as N-methyl-2-pyrrolidone can be used as the solvent. Additionally, activated carbon can be added to the positive electrode composite material to increase the electrical double-layer capacitance.

[0124] (negative electrode)

[0125] The negative electrode can be made of metallic lithium, lithium alloys, etc. Alternatively, the negative electrode can be formed as follows: a binder is mixed with a negative electrode active material that can absorb, store, and extract lithium ions, and a suitable solvent is added to form a paste-like negative electrode composite material. The obtained negative electrode composite material is coated on the surface of a metal foil current collector such as copper and dried. It is then compressed as needed to increase the electrode density.

[0126] As the negative electrode active material, for example, calcined organic compounds such as natural graphite, artificial graphite, and phenolic resin, and powdered carbonaceous materials such as coke can be used. In the above cases, as the negative electrode binder, similarly to the positive electrode, fluorinated resins such as PVDF can be used, and as the solvent for dispersing these active materials and binders, organic solvents such as N-methyl-2-pyrrolidone can be used.

[0127] (Separator)

[0128] It is configured by sandwiching a separator between the positive and negative electrodes. The separator is used to separate the positive and negative electrodes and retain the electrolyte. For example, a thin membrane with a large number of tiny pores, such as polyethylene or polypropylene, can be used.

[0129] (Non-aqueous electrolyte)

[0130] Non-aqueous electrolytes are obtained by dissolving lithium salts, which serve as supporting electrolytes, in an organic solvent. The organic solvent can be one or a combination of two or more of the following: cyclic carbonates such as ethylene carbonate, propylene carbonate, butyl carbonate, and trifluoromethyl vinyl carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butyryl lactone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate.

[0131] As supporting electrolytes, LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and their composite salts can be used. Furthermore, non-aqueous electrolytes can contain free radical scavengers, surfactants, and flame retardants.

[0132] (Battery shape and structure)

[0133] The non-aqueous electrolyte secondary battery of the present invention, composed of the positive electrode, negative electrode, separator, and non-aqueous electrolyte as described above, can be manufactured in various shapes such as cylindrical and stacked. In the case of any shape, the positive and negative electrodes are stacked to form an electrode body using the separator, and the non-aqueous electrolyte is immersed in the resulting electrode body. Current-collecting leads are used to connect the positive current collector to the positive terminal connected to the outside, and the negative current collector to the negative terminal connected to the outside. The battery is then sealed in a battery casing to complete the non-aqueous electrolyte secondary battery.

[0134] Example

[0135] The following describes specific embodiments of the present invention. However, the present invention is not limited to these embodiments.

[0136] (Example 1)

[0137] [Preparation of Complex Hydroxides]

[0138] Add the specified amount of pure water to the reaction tank (60L), and adjust the stirring power to 6.0kW / m. 3Next, while stirring, the temperature (liquid temperature) of the reaction tank was set to 45°C. At this time, nitrogen gas (N2) was supplied to the reaction tank, and the N2 flow rate was adjusted to maintain a dissolved oxygen concentration of 2.8 mg / L in the reaction tank solution. Simultaneously, a 2.0 mol / L mixed aqueous solution containing nickel sulfate, cobalt sulfate, and manganese sulfate in a nickel:cobalt:manganese molar ratio of 35:35:30, a 25% (w / w) sodium hydroxide aqueous solution as an alkaline solution, and a 25% (w / w) ammonia solution as a complexing agent were continuously added to the reaction tank to carry out a neutralization and crystallization reaction. The pH value and ammonium ion concentration were adjusted to maintain a constant dissolved nickel concentration of 1080 mg / L. At this time, the ammonium ion concentration in the reaction tank was in the range of 12–15 g / L. Furthermore, the total flow rate of the mixed solution, sodium hydroxide aqueous solution, and ammonia solution was controlled to maintain a residence time of 8 hours for the metal salts contained in the mixed aqueous solution. At this time, the pH was 11.6 at a reference liquid temperature of 25°C, with a fluctuation range of 0.1. After the reaction tank stabilizes, the slurry containing nickel-cobalt-manganese composite hydroxide is recovered from the overflow port and then filtered to obtain a filter cake of nickel-cobalt-manganese composite hydroxide. After filtration, 1L of pure water is supplied to 140g of the nickel-cobalt-manganese composite hydroxide filter cake in the filter while the filter is being filtered and the liquid is being passed through to clean impurities. Then, the cleaned nickel-cobalt-manganese composite hydroxide filter cake is atmospherically dried at 120°C to obtain nickel-cobalt-manganese composite hydroxide (hereinafter also referred to as "composite hydroxide").

[0139] The particle size distribution of the obtained composite hydroxide was determined using a laser diffraction scattering particle size distribution analyzer. The results showed an average particle size (MV) of 10.1 μm and a [D90-D10) / average particle size ratio of 0.78. The pore volume was determined by nitrogen adsorption, and the result was 0.013 cm³. 3 / g. The tap density was determined using an impact apparatus (Seishin KYT3000), after 500 impacts, and calculated from the volume and weight of the sample. The result was a tap density of 2.12 g / cm³. 3 The specific surface area was determined by the BET method based on nitrogen adsorption. The result showed a specific surface area of ​​5.8 m². 2 / g.

[0140] The surface and cross-sectional structure of the obtained composite hydroxide were observed using a scanning electron microscope (SEM). Figure 5 A, Figure 5 B shows the surface of the resulting composite hydroxide ( Figure 5 A) and cross-sectional structure ( Figure 5(B). Surface observation confirmed the formation of highly spherical secondary particles composed of plate-shaped primary particles. Cross-sectional observation confirmed a very dense internal structure. Furthermore, to evaluate the density, the cross-sectional area and internal pore area of ​​the particles were calculated using image analysis software (WinRoof 6.1.1), and the density was calculated using the formula [(internal pore area) / (cross-sectional area of ​​particle) × 100] (%). Cross-sections of 20 randomly selected secondary particles representing more than 80% of the volume average diameter (MV) were measured, and their average density (average density) was calculated, resulting in a density of 1.8%.

[0141] The resulting composite hydroxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The composition was found to be Ni:Co:Mn = 0.35:0.35:0.30, confirming the acquisition of particles with the target composition. The properties of the obtained composite hydroxide are shown in Table 1.

[0142] [Preparation of positive electrode active material]

[0143] Weigh the above-mentioned composite hydroxide and lithium carbonate to make the Li / Me ratio 1.06, and then mix them thoroughly using a swing mixer (Willy A. Bachofen (WAB) TURBULA Type T2C) to maintain the shape of the precursor, so as to obtain a lithium mixture (mixing process).

[0144] The lithium mixture was inserted into a calcination vessel made of magnesium oxide and heated to 950°C in an atmospheric atmosphere with a flow rate of 12 L / min using a closed electric furnace. The temperature was maintained at 2.77°C / min for 10 hours, and the furnace was cooled to room temperature to obtain lithium nickel manganese composite oxide (hereinafter also referred to as "lithium transition metal composite oxide").

[0145] (Roasting process)

[0146] The surface and cross-sectional structure of the obtained lithium transition metal composite oxide were observed using a scanning electron microscope. The results, similar to those for the composite hydroxide, confirmed the formation of well-spherical particles. The particle size distribution of the obtained positive electrode active material was determined in the same manner as for the composite hydroxide. The average particle size D50 was confirmed to be 9.6 μm, and [(D90-D10) / average particle size] was 0.80. The oil absorption and tap density were measured, both showing a value of 15.6 cm⁻¹. 3 / 100g, 2.40g / cm 3 .

[0147] The surface and cross-sectional structure of the obtained positive electrode active material were observed using a scanning electron microscope (SEM). Figure 6 A' Figure 6B' shows the surface of the obtained positive electrode active material ( Figure 6 (A') and cross-sectional structure ( Figure 6 (B'). It was confirmed that secondary particles with high sphericity, consisting of plate-shaped primary particles, similar in shape to the composite hydroxide, were obtained. Cross-sectional observation confirmed that the internal structure of the particles was very dense. Based on the cross-sectional observation, the density was calculated in the same manner as for the composite hydroxide, and the result was 1.0%.

[0148] The obtained positive electrode active material was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The results confirmed that its composition was Li. 1.06 Ni 0.35 Co 0.35 Mn 0.30 O2 was used to obtain particles with the target composition. The characteristics of the obtained positive electrode active material are shown in Table 2.

[0149] [Orientation Evaluation]

[0150] The radial orientation of the resulting secondary particles of active material was evaluated using EBSD (electron backscatter diffraction). When the sample to be tested was placed in the testing device, it was fixed to the support using a conductive paste (colloidal carbon paste) from the viewpoint of maintaining the conductivity of the sample.

[0151] It should be noted that a scanning electron microscope (SEM) device (Carl Zeiss Takumar 55) equipped with a computer capable of resolving crystal orientation was used as the measuring apparatus. The accelerating voltage of the electron beam irradiating the sample was set to approximately 15 kV, and the current was set to approximately 20 nA.

[0152] In addition, in the cross section of the sample being tested, the orientation information in the x-axis and y-axis directions is obtained in the area (the surface being tested) where the crystal orientation is measured, in strips of 2.5μm×12.5μm, and the number of measurement points is set to a total of 250,000 points.

[0153] It should be noted that, in order to facilitate the capture of the scattered electron beam (Kikuchi line) by the camera set on the SEM device, the sample to be measured (more specifically, the measured surface as a cross section) is deviated from the horizontal by about 70°, and the scattered electron beam is set in such a way that it is irradiated towards the camera.

[0154] The crystal orientation of a material obtained in EBSD varies depending on the orientation of the observer as the reference axis. Typically, the crystal orientation map is represented using any one of the orthogonal coordinate axes formed by the x, y, and z axes as a reference. Hereinafter, the crystal orientation maps using the x, y, and z axes as references will be referred to as IPF-X, IPF-Y, and IPF-Z, respectively. Figure 7 (A) and Figure 7 (B) shows a schematic diagram representing the observer's perspective corresponding to the orientation distribution of each crystal. For example... Figure 7 As shown in (B), IPF-X is a crystal orientation based on the horizontal direction in the same plane when the viewing section is the paper. IPF-Y is based on the vertical direction in the same plane. On the other hand, IPF-Z is a crystal orientation based on the vertical direction relative to the viewing section.

[0155] In the case of cathode materials, when observing the ends of cathode particles that are involved in lithium ion donation and acceptance with the electrolyte from the particle surface, the crystal orientation information in the radial direction from the particle center outward, which serves as the path for lithium ions to detach from the particle, becomes important. Therefore, when evaluating the orientation in the x-axis direction of the particle's radial direction, the IPF-X analysis results corresponding to the crystal orientation observed from these directions are used for crystal orientation analysis; similarly, the IPF-Y analysis results are used for the orientation in the y-axis direction.

[0156] The scattered electron beam (Kikuchi line) is observed using a camera. The data of the Kikuchi pattern observed by the camera is input into a computer for analysis to determine the crystal orientation. The determined crystal orientation data of the sample is obtained by deriving coordinates (x and y) and Euler angles (φ1, Φ, and φ2) representing the crystal orientation from each measurement point.

[0157] Each measurement point, having the Euler angle value obtained from the evaluation of the sample, is divided into crystal orientations that serve as zone axes, according to the following conditions.

[0158] <001>Axis: φ1=0°±30°, φ=0°±30°, φ2=0°±30°

[0159] <100>Axis: φ1=0°±30°, φ=90°±30°, φ2=60°±30°

[0160] <110>Axis: φ1=0°±30°, φ=90°±30°, φ2=120°±30°

[0161] Based on the above rules, it can be determined in which crystal orientation each measurement point belongs.

[0162] After the above division, the ratio of each crystal orientation in the measured plane was calculated based on the number of measurement points for each crystal orientation. The results are shown in Table 2 below.

[0163] It should be noted that this process is performed using commercially available EBSD parsing software (Oxford Instruments' EBSD parsing software: Project Manager-Tango).

[0164] [Battery Making]

[0165] The obtained positive electrode active material (52.5 mg), acetylene black (15 mg), and polytetrafluoroethylene resin (PTFE) (7.5 mg) were mixed and pressurized at 100 MPa to form a shape with a diameter of 11 mm and a thickness of 100 μm. Figure 8 The positive electrode (evaluation electrode) shown is PE. After drying the prepared positive electrode PE in a vacuum dryer at 120°C for 12 hours, a 2032 type button cell CBA was fabricated using this positive electrode PE in a glove box under an Ar atmosphere with a dew point controlled at -80°C. The negative electrode NE uses lithium (Li) metal with a diameter of 17 mm and a thickness of 1 mm. The electrolyte is a mixture of equal parts ethylene carbonate (EC) and diethyl carbonate (DEC) with 1M LiClO4 as the supported electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.). The separator SE uses a 25 μm thick porous polyethylene membrane. Furthermore, the button cell has a gasket GA and a wave-shaped gasket WW, and is assembled into a button cell from the positive electrode container PC and the negative electrode container NC.

[0166] The initial discharge capacity is as follows: After the button cell CBA is fabricated and left to stand for approximately 24 hours, and the open-circuit voltage (OCV) stabilizes, the current density relative to the positive electrode (PE) is set to 0.1 mA / cm². 2 The battery was charged to a cutoff voltage of 4.3V, allowed to rest for one hour, and then discharged to a cutoff voltage of 3.0V. This discharge capacity was recorded as the current capacity. A multi-channel voltage / current generator (Advantest R6741A, Co., Ltd.) was used to measure the discharge capacity. The reaction resistance was measured as follows: a button cell CBA, with its temperature adjusted to the measurement temperature, was charged at a charging potential of 4.1V, and the resistance value was measured using the AC impedance method. A frequency induction analyzer and a Potentiostat Galvanostat (Solatron 1255B) were used for the measurement. Figure 9 The Nyquist plot shown uses Figure 10 The equivalent circuit shown was fitted to calculate the value of the positive electrode resistance (reaction resistance). Additionally, the discharge voltage was calculated from the charge-discharge measurement results. Using this value, the tap density, and the initial discharge capacity, the volumetric energy density was calculated according to the formula: Volumetric Energy Density (Wh / L) = Average Discharge Voltage (V) × Discharge Capacity (A / kg) × Tap Density (kg / L). The measured results of the initial charge-discharge capacity, positive electrode resistance, and volumetric energy density of the obtained active material are shown in Table 2.

[0167] (Example 2)

[0168] The stirring power in the crystallization process was adjusted to 5.8 kW / m. 3 The N2 flow rate and pH value were adjusted to achieve a dissolved nickel concentration of 970 mg / L and a dissolved oxygen concentration of 4.5 mg / L in the reaction tank. Otherwise, the composite hydroxide and positive electrode active material were prepared in the same manner as in Example 1. The characteristics of the resulting composite hydroxide are shown in Table 1. Figure 5 C, Figure 5 D shows the surface of the resulting composite hydroxide ( Figure 5 C) and cross-sectional structure ( Figure 5 Fly D). Figure 6 C' Figure 6 D' shows the surface of the obtained positive electrode active material ( Figure 6 C') and cross-sectional structure ( Figure 6 (D'). Additionally, Table 2 shows the evaluation results of the characteristics and electrochemical properties of the obtained positive electrode active material. It should be noted that each evaluation was performed in the same manner as in Example 1.

[0169] (Example 3)

[0170] [Preparation of Complex Hydroxides]

[0171] Add the specified amount of pure water to the reaction tank (60L), and adjust the stirring power to 6.0kW / m. 3Next, while stirring, the temperature (liquid temperature) in the reaction tank was set to 45°C. At this time, nitrogen gas (N2) was supplied to the reaction tank, and the N2 flow rate was adjusted to achieve a dissolved oxygen concentration of 3.5 mg / L in the reaction tank. Simultaneously, a 2.0 mol / L mixed aqueous solution containing nickel sulfate, cobalt sulfate, and manganese sulfate in a nickel:cobalt:manganese molar ratio of 60:20:20, a 25% (w / w) sodium hydroxide aqueous solution as an alkaline solution, and a 25% (w / w) ammonia solution as a complexing agent were continuously added to the reaction tank to carry out a neutralization and crystallization reaction. The pH value and ammonium ion concentration were adjusted to maintain a constant dissolved nickel concentration of 720 mg / L. At this time, the ammonium ion concentration in the reaction tank was in the range of 12–15 g / L. Furthermore, the total flow rate of the mixed solution, sodium hydroxide aqueous solution, and ammonia solution was controlled to allow the metal salts contained in the mixed aqueous solution to reside for 8 hours. At this time, the pH was 11.7 at a reference liquid temperature of 25°C, with a fluctuation range of 0.1. After the reaction tank stabilized, the slurry containing nickel-cobalt-manganese composite hydroxide was recovered from the overflow port and then filtered to obtain a filter cake of nickel-cobalt-manganese composite hydroxide. After filtration, 1L of pure water was supplied to 140g of the nickel-cobalt-manganese composite hydroxide filter cake in the filter press while filtration was performed and the liquid was passed through to clean impurities. The cleaned nickel-cobalt-manganese composite hydroxide filter cake was then atmospherically dried at 120°C to obtain nickel-cobalt-manganese composite hydroxide (hereinafter also referred to as "composite hydroxide"). The surface and cross-sectional structure of the obtained composite hydroxide were observed using a scanning electron microscope (SEM). Figure 5 E, Figure 5 F shows the surface of the resulting composite hydroxide ( Figure 5 E) and cross-sectional structure ( Figure 5 (F).

[0172] The resulting composite hydroxide was dissolved in an inorganic acid and then chemically analyzed by ICP emission spectroscopy. The results confirmed its composition as Ni:Co:Mn = 0.60:0.20:0.20, yielding particles with the target composition. The properties of the obtained composite hydroxide are shown in Table 1.

[0173] [Preparation of positive electrode active material]

[0174] After weighing the above-mentioned composite hydroxide and lithium carbonate to make the Li / Me ratio 1.03, the mixture was thoroughly mixed using a swing mixer (Willy A. Bachofen (WAB) TURBULA Type T2C) to maintain the shape of the precursor, in order to obtain a lithium mixture (mixing process).

[0175] The lithium mixture is inserted into a calcining vessel made of magnesium oxide, and heated to 900°C in a closed electric furnace at a flow rate of 12 L / min in an atmospheric atmosphere at a heating rate of 2.77°C / min. The temperature is maintained for 10 hours, and the furnace is cooled to room temperature to obtain lithium nickel manganese composite oxide (hereinafter also referred to as "lithium transition metal composite oxide") (calcination process).

[0176] The surface and cross-sectional structure of the obtained positive electrode active material were observed using a scanning electron microscope (SEM). Figure 6 E', Figure 6 F' shows the surface of the obtained positive electrode active material ( Figure 6 E') and cross-sectional structure ( Figure 6 The positive electrode active material obtained by dissolving it in an inorganic acid was then chemically analyzed by ICP emission spectroscopy, which confirmed its composition as Li. 1.03 Ni 0.60 Co 0.20 Mn 0.20 O2 was used to obtain particles with the target composition. The characteristics of the obtained positive electrode active material are shown in Table 2. It should be noted that the evaluations were performed in the same manner as in Example 1.

[0177] (Comparative Example 1)

[0178] The stirring power in the crystallization process was adjusted to 5.5 kW / m. 3 The N2 flow rate and pH value were adjusted to achieve a dissolved nickel concentration of 410 mg / L and a dissolved oxygen concentration of 5.8 mg / L in the reaction aqueous solution. Otherwise, the composite hydroxide and positive electrode active material were prepared in the same manner as in Example 1. The characteristics of the resulting composite hydroxide are shown in Table 1. Furthermore, the evaluation results of the characteristics and electrochemical properties of the resulting positive electrode active material are shown in Table 2. It should be noted that all evaluations were performed in the same manner as in Example 1.

[0179] (Comparative Example 2)

[0180] The stirring power in the crystallization process was adjusted to 5.2 kW / m. 3 Air was supplied to replace N2, and its flow rate and pH were adjusted to achieve a dissolved nickel concentration of 300 mg / L and a dissolved oxygen concentration of 6.2 mg / L in the reaction aqueous solution. Otherwise, the composite hydroxide and positive electrode active material were prepared in the same manner as in Example 1. The characteristics of the resulting composite hydroxide are shown in Table 1. Furthermore, the evaluation results of the characteristics and electrochemical properties of the resulting positive electrode active material are shown in Table 2. It should be noted that all evaluations were performed in the same manner as in Example 1.

[0181] (Comparative Example 3)

[0182] The stirring power in the crystallization process was adjusted to 5.8 kW / m. 3The N2 flow rate and pH value were adjusted to achieve a dissolved nickel concentration of 350 mg / L and a dissolved oxygen concentration of 5.8 mg / L in the reaction aqueous solution. Otherwise, the composite hydroxide and positive electrode active material were prepared in the same manner as in Example 3. The characteristics of the resulting composite hydroxide are shown in Table 1. Furthermore, the evaluation results of the characteristics and electrochemical properties of the resulting positive electrode active material are shown in Table 2. It should be noted that all evaluations were performed in the same manner as in Example 1.

[0183] [Table 1]

[0184]

[0185] [Table 2]

[0186]

[0187] (Evaluation Results)

[0188] For Examples 1-3, by optimizing the dissolved oxygen concentration, dissolved nickel concentration, and stirring power, a composite hydroxide with high reactivity with Li and a specific half-width region exhibiting dense particle characteristics can be obtained. Furthermore, the results of pore volume and average density also indicate that a high-density composite hydroxide with excellent particle filling properties can be obtained. The positive electrode active material synthesized from such a composite hydroxide exhibits similar high density and excellent particle filling properties as the composite hydroxide, thus possessing a high volumetric energy density. Additionally, for Examples 1-3, in the EBSD-based orientation evaluation, the orientation ratio of the crystal ab planes, which favors Li ion insertion / extraction in both the x-axis and y-axis directions, is 55% or higher, indicating a radial structure. The cross-sectional SEM images also show that in Example 1, the radius R2 (referring to the area from the outer periphery of the secondary particle (positive electrode active material) towards the particle center is within 50%. Figure 3 Within (B)), 60% of the primary particles in range R2 radiate outwards from the center of the secondary particles in a radial pattern (radial direction R1, reference). Figure 3 (B) configuration. Similarly, in Examples 2 and 3, 83% and 87% of the primary particles, respectively, are arranged radially.

[0189] On the other hand, for Comparative Examples 1-3, the dissolved oxygen concentration was higher than that of the Examples. Therefore, the composite hydroxides with a larger half-width than those of the Examples became porous particles with high pore volume and average density. Consequently, the particle filling capacity was lower compared to the Examples. The volumetric energy density of the positive electrode active material synthesized from such composite hydroxides was lower than that of the Examples. Furthermore, in Comparative Examples 1-3, the orientation ratio of the crystal ab plane in the y-axis direction was less than 55% in the EBSD-based orientation evaluation.

[0190] By optimizing the dissolved nickel concentration, dissolved oxygen concentration, and stirring power, a high-density composite hydroxide with excellent particle packing properties can be obtained. Furthermore, by using such a nickel-manganese composite hydroxide, a positive electrode active material with a very high volumetric energy density can be obtained.

[0191] It should be noted that the scope of protection of this invention is not limited to the solutions described in the above embodiments, etc. Sometimes, one or more features described in the above embodiments, etc. are omitted. In addition, the features described in the above embodiments, etc., can be appropriately combined. Furthermore, as long as permitted by law, the contents of Japanese Patent Application No. 2016-150505 and all documents cited in this specification may be incorporated into this description.

[0192] Explanation of reference numerals in the attached figures

[0193] 1…Nickel-manganese complex hydroxide

[0194] 2… Primary particles (nickel-manganese composite hydroxide)

[0195] 3… Secondary particles (nickel-manganese composite hydroxide)

[0196] 4…Porosity (Nickel-Manganese Composite Hydroxide)

[0197] d…Particle size of secondary particles

[0198] 10… Positive electrode active material

[0199] 11…Lithium-nickel-manganese composite oxide

[0200] 12… Primary particles (lithium-nickel-manganese composite oxide)

[0201] 13… Secondary particles (lithium-nickel-manganese composite oxide)

[0202] 14…Porosity (Lithium-Nickel-Manganese Composite Oxide)

[0203] C…The central portion of the secondary particles (lithium-nickel-manganese composite oxide)

[0204] L…the major axis of the primary particle

[0205] R1...radiation direction

[0206] R2…the range of 50% of the radius of the secondary particles from the outer periphery towards the particle center.

Claims

1. A method for manufacturing a nickel-manganese composite hydroxide, characterized in that, The nickel-manganese composite hydroxide is formulated using general formula (1): Ni x Mn y M z (OH) 2+α It indicates that it is composed of secondary particles formed by the aggregation of multiple primary particles. In the formula (1), M is one or more elements selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe and W, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, and satisfies x+y+z=1.0, α is 0≤α≤0.

4. The manufacturing method includes the following crystallization step: neutralizing salts containing nickel and manganese respectively in a reaction aqueous solution to generate a nickel-manganese composite hydroxide. In the crystallization process, the dissolved oxygen concentration in the reaction aqueous solution is adjusted to a range of 0.2 mg / L or higher and 4.6 mg / L or lower, and the dissolved nickel concentration is adjusted to a range of 700 mg / L or higher and 970 mg / L or lower. In the crystallization process, the stirring power of the reaction aqueous solution on which the catalyst is supported is adjusted to 3 kW / m 3 above and 15 kW / m 3 the following ranges, The half-width of the diffraction peak on the (001) plane of the nickel-manganese composite hydroxide, as determined by X-ray diffraction, is greater than 0.20° and less than 0.40°, and the sparsity, expressed as [(pore area inside the secondary particles / cross-sectional area of ​​the secondary particles) × 100] (%), is greater than 0.5% and less than 10%.

2. The method for producing a nickel-manganese composite hydroxide according to claim 1, characterized by, The pore volume of the nickel-manganese composite hydroxide, as determined by nitrogen adsorption, is 0.01 cm³. 3 / g or more and 0.04cm 3 / g or less.

3. The method for producing a nickel-manganese composite hydroxide according to claim 1 or 2, characterized by, The nickel-manganese composite hydroxide has a particle size distribution width index [(D90-D10) / average particle size] of 0.7 or higher, and a volume average particle size MV of 5 μm or higher and 20 μm or lower.

4. The method for producing a nickel-manganese composite hydroxide according to claim 1 or 2, characterized by, The specific surface area of ​​the nickel-manganese composite hydroxide is 5m². 2 / g or more and 15m 2 / g or less.

5. The method for producing a nickel-manganese composite hydroxide according to claim 1 or 2, characterized by, The tap density of the nickel-manganese composite hydroxide is 1.8 g / cm³. 3 Above and 2.5g / cm 3 the following.

6. The method for producing a nickel-manganese composite hydroxide according to claim 5, characterized by, In the crystallization process, the variation range of the stirring power of the reaction aqueous solution on which the catalyst is supported is set to ±0.2 kW / m 3 Within the above range.

7. The method for producing a nickel-manganese composite hydroxide according to claim 1 or 6, characterized by, In the crystallization process, the temperature of the reaction aqueous solution is adjusted to a range of 35°C or higher and 60°C or lower.

8. The method for producing a nickel-manganese composite hydroxide according to claim 1 or 6, characterized by, In the crystallization process, the pH value of the reaction aqueous solution, measured at a reference temperature of 25°C, is adjusted to a range of 10.0 or higher and 13.0 or lower.

9. The method for manufacturing nickel-manganese composite hydroxide according to claim 1 or 6, characterized in that, The crystallization process causes the slurry containing nickel-manganese composite hydroxide particles to overflow, thereby recovering the secondary particles, which are generated by continuously adding and neutralizing a mixed aqueous solution containing nickel and manganese in a reaction tank.

10. A positive electrode active material for a non-aqueous electrolyte secondary battery, characterized in that, Composed of lithium-nickel-manganese composite oxide, wherein the lithium-nickel-manganese composite oxide is of general formula (2): Li 1+t Ni x Mn y M z O 2+β It indicates that it is formed by the aggregation of plate-shaped primary particles into secondary particles. In formula (2), M is one or more additive elements selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe, and W, t is -0.05≤t≤0.5, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, and satisfies x+y+z=1.0, β is 0≤β≤0.

5. The positive electrode active material for the non-aqueous electrolyte secondary battery has a sparsity of 1.2% to 12% as expressed by [(pore area inside the secondary particles / cross-sectional area of ​​the secondary particles) × 100] (%), and its DBP uptake, measured according to JIS K6217-4, is 12 cm⁻¹. 3 / 100g or more and 20cm 3 Less than 100g When any radial direction from the center of the cross-section of the secondary particle outward is defined as the x-axis direction, and a direction orthogonal to the x-axis direction is defined as the y-axis direction, the orientation ratio of the crystal ab plane measured by electron backscatter diffraction in both the x-axis and y-axis directions is 60% or more.

11. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 10, characterized by tap density of 2.0 g / cm 3 above and 2.7 g / cm 3 below.

12. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 10 or claim 11, characterized by The ratio of the diffraction peak intensity I(003) to the peak intensity I(104) of the 003 plane obtained by X-ray diffraction measurement, I(003) / I(104), is greater than 1.

7.

13. The positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 10 or 11, characterized by Within a radius of 50% from the outer periphery of the secondary particles to the center of the particles, for more than 70% of the primary particles, the major axis direction of the primary particles is arranged along a radial direction from the center of the secondary particles toward the outer periphery.

14. The positive electrode active material for nonaqueous electrolyte secondary cells according to claim 12, characterized by Within a radius of 50% from the outer periphery of the secondary particles to the center of the particles, for more than 70% of the primary particles, the major axis direction of the primary particles is arranged along a radial direction from the center of the secondary particles toward the outer periphery.

15. A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, characterized by, The positive electrode active material of the non-aqueous electrolyte secondary battery is composed of lithium-nickel-manganese composite oxide, which uses the general formula (2): Li 1+t Ni x Mn y M z O 2+β It indicates that it is formed by the aggregation of primary particles into secondary particles. In formula (2), M is one or more additive elements selected from Co, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, Fe and W, t is -0.05≤t≤0.5, x is 0.1≤x≤0.9, y is 0.05≤y≤0.8, z is 0≤z≤0.8, and satisfies x+y+z=1.0, β is 0≤β≤0.

5. The manufacturing method includes the following steps: mixing the nickel-manganese composite hydroxide obtained by the manufacturing method of any one of claims 1 to 9 with a lithium compound to obtain a mixture; and calcining the mixture to obtain a lithium-nickel-manganese composite oxide.

16. A nonaqueous electrolyte secondary battery characterized by comprising: The positive electrode active material of any one of claims 10 to 14 for a non-aqueous electrolyte secondary battery is used as the positive electrode.

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