JP2022161973A - Particle of transition metal complex hydroxide, positive pole active material for lithium-ion secondary battery, and lithium-ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive pole active material which can have a more improved battery property level, or the like.

SOLUTION: A particle of a transition metal complex hydroxide including a transition metal and an added element having an unbalanced distribution in the particle includes a secondary particle formed by aggregating of a plurality of primary particles. The secondary particle includes: a center part positioned at a site including a center of the secondary particle and formed by aggregating of a plurality of fine primary particles; and an outer peripheral part positioned on an outside of the center part, larger than the fine primary particles, and formed by aggregating of plate-shaped primary particles. The fine primary particle of the center part contains a higher concentration of the added element therein than the plate-shaped primary particle of the outer peripheral part. The particle of the transition metal complex hydroxide has an average particle diameter of 1 μm or more and 15 μm or less.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

The present invention provides transition metal composite hydroxide particles, a method for producing the same, a positive electrode active material for a lithium ion secondary battery using the transition metal composite hydroxide particles as a precursor, a method for producing the same, and the lithium ion The present invention relates to a lithium ion secondary battery using a positive electrode active material for secondary batteries as a positive electrode material.

In recent years, with the spread of mobile electronic devices such as smart phones and tablet PCs, there is a strong demand for development of small, lightweight non-aqueous electrolyte secondary batteries with high energy density. Also, there is a strong demand for the development of high-output secondary batteries as power sources for electric vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles.

As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery, which is a type of non-aqueous electrolyte secondary battery. This lithium-ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of desorbing and intercalating lithium is used as an active material used as a material for the negative electrode and the positive electrode. As the electrolyte, a non-aqueous electrolytic solution obtained by dissolving a lithium salt, which is a supporting salt, in an organic solvent, or a non-aqueous electrolyte such as a nonflammable solid electrolyte having ion conductivity is used.

Among these lithium-ion secondary batteries, a lithium-ion secondary battery using a layered or spinel-type lithium-transition metal composite oxide as a positive electrode active material can obtain a voltage of 4V class, and thus has a high energy density. As a battery, research and development are currently actively carried out, and some of them are also being put to practical use.

As a positive electrode active material for such a lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, lithium Nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), lithium nickel manganese composite oxide (LiNi _0.5 Particles of lithium transition metal composite oxides such as Mn _0.5 O ₂ ) have been proposed.

Also, in a lithium ion secondary battery, a technique for controlling the particle structure of the lithium-transition metal composite oxide has been proposed for the purpose of obtaining a positive electrode having high battery characteristics (high cycle characteristics, high output characteristics, etc.). there is

For example, in Patent Documents 1 to 3, the precursor of the positive electrode active material is formed by a crystallization reaction that is clearly separated into two stages, a nucleation step in which nucleation is mainly performed and a particle growth step in which particles are mainly grown. A method for producing particles of transition metal composite hydroxide is disclosed. In these methods, by appropriately adjusting the pH value and the reaction atmosphere in the nucleation step and the particle growth step, the particle size is small, the particle size distribution is narrow, and a low-density central portion composed of fine primary particles and a plate-like particle Alternatively, transition metal composite hydroxide particles are obtained which are composed of high-density outer shells composed of acicular primary particles.

On the other hand, in order to obtain a positive electrode with high battery characteristics (high cycle characteristics, high output characteristics, etc.), several techniques have been proposed for adding elements other than lithium, nickel, cobalt, and manganese to the lithium-transition metal composite oxide. ing.

For example, in Patent Document 4, general formula: Ni _1-xy Co _x Mn _y M _z (OH) _2+a (where 0.10≦x≦0.35, 0≦y≦0.35, 0<z ≤ 0.05, 0 ≤ a ≤ 0.5, M is Al, Mg, Ca, Ti, Zr, Nb, Ta, Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm , Er, Ce, Nd, La, Cd, and at least one element selected from the group consisting of Lu), wherein the nickel-cobalt composite hydroxide has a plurality of aggregates of primary particles The secondary particles consist of a first layer in which the ratio of the depth in the radial direction to the radius of the secondary particles is less than 5% from the surface, and the ratio of the depth in the radial direction is 5% or more. A second layer present inside the secondary particles from the first layer less than 50%, and a third layer present inside the secondary particles from the second layer having a depth ratio of 50% or more in the radial direction and wherein the SEM-EDX spectrum for the element M with respect to the radial depth of the secondary particles has a peak in the second layer. The positive electrode active material obtained from this composite hydroxide has a first layer existing on the surface of the secondary particles, a second layer existing inside the secondary particles from the first layer, and a secondary layer from the second layer. The SEM-EDX spectrum of the element M with respect to the depth in the radial direction of the secondary particle has a peak in the second layer, and has excellent low-temperature output characteristics and high discharge capacity. It is said that the battery characteristics of

JP 2012-246199 A JP 2013-147416 A WO2012/131881 JP 2016-210674 A

For example, as in Patent Documents 1 to 3, when the positive electrode active material is composed of particles having a small particle size and a narrow particle size distribution, cycle characteristics and output characteristics can be improved. This is because particles with a small particle size have a large specific surface area, and when used as a positive electrode active material, not only can a sufficient reaction area with the electrolyte be ensured, but also the positive electrode can be formed thin, and lithium ions can be produced. This is because the movement distance within the positive electrode plate can be shortened, and thus the positive electrode resistance can be reduced. In addition, particles with a narrow particle size distribution can uniformize the voltage applied to the particles in the electrode, so it is possible to suppress the decrease in battery capacity caused by the selective deterioration of the particles when charging and discharging are repeated. That's why.

Further, as in Patent Documents 1 to 3, by forming a space into which the electrolytic solution can enter inside the positive electrode active material particles, the output characteristics can be further improved. Such a positive electrode active material can have a larger reaction area with the electrolyte than a positive electrode active material with a solid structure having a similar particle size, so the positive electrode resistance can be significantly reduced. becomes. It is known that the particle properties of the positive electrode active material greatly depend on the particle properties of the precursor transition metal composite hydroxide. That is, the positive electrode active material described above can be obtained by appropriately controlling the particle size, particle size distribution, particle structure, etc. of the transition metal composite hydroxide, which is the precursor thereof.

However, as described in Patent Documents 1 to 3, there is a limit to improving battery characteristics (eg, high cycle characteristics, output characteristics, etc.) only by controlling the particle structure, and further improvement of battery characteristics is difficult. It has been demanded.

Further, for example, according to Patent Document 4, the element M has a specific distribution inside the secondary particles, thereby improving the battery characteristics, but there is a demand for further improvement in the battery characteristics.

In view of the above problems, the present invention provides a positive electrode active material that can further improve battery characteristics when a secondary battery is constructed, and a transition metal composite hydroxide that is suitably used as a precursor thereof. The purpose is to provide particles. Another object of the present invention is to provide a secondary battery having high battery characteristics.

According to the first aspect of the present invention, particles of a transition metal composite hydroxide containing a transition metal and an additive element having an uneven distribution within the particles, formed by aggregation of a plurality of primary particles The secondary particles include a central portion and an outer peripheral portion disposed outside the central portion, the central portion being formed by aggregating a plurality of fine primary particles, and the outer peripheral portion is larger than the fine primary particles and is formed by aggregation of plate-like primary particles, the additive element is contained at a higher concentration in the central portion than in the outer peripheral portion, and has an average particle size of 1 μm or more and 15 μm or less. Transition Particles of metal composite hydroxide are provided.

Further, nickel (Ni), manganese (Mn), an additive element (M), and cobalt (Co) are included, and the material amount ratio (molar ratio) of each element is Ni:Mn:Co: M=x:y:z:t (x+y+z+t=1, 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0<t≦0.1, M may be represented by one or more additive elements selected from Nb, Mo, Ta, Ti, Zr, and W). Further, the surface of the secondary particles may have a coating layer, and the coating layer may contain a compound containing an additive element. In addition, the outer peripheral portion has a region containing additive elements in a range of 50% or more and 80% or less with respect to the thickness of the outer peripheral portion from the surface to the inside of the particle, and a region other than that containing no additive elements. may

According to a second aspect of the present invention, a positive electrode active material containing particles of a lithium-transition metal composite oxide containing lithium, a transition metal, and an additive element other than the transition metal, wherein a plurality of primary particles are Secondary particles formed by agglomeration are included, the secondary particles comprise an outer shell portion and a hollow portion inside the outer shell portion, the hollow portion does not contain primary particles, and the secondary particles are Provided is a positive electrode active material for a lithium ion secondary battery, which has an average particle diameter of 1 μm or more and 15 μm or less and has a concentrated layer in which an additive element is concentrated on the surface of primary particles.

Further, the ratio of the concentration of the additive element contained in the concentrated layer to the concentration inside the primary particles may be 5 or more. Also, the BET specific surface area may be 0.7 m ² /g or more and 5.0 m ² /g or less. Further, the particles of the lithium-transition metal composite oxide contain lithium (Li), nickel (Ni), manganese (Mn), an additive element (M), and optionally cobalt (Co), and each The material amount ratio (molar ratio) of the elements is Li:Ni:Mn:Co:M=(1+u):x:y:z:t (−0.05≦u≦0.50, x+y+z+t=1, 0. 3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 < t ≤ 0.1, M is Nb, Mo, Ta, Ti, Zr, and W one or more additive elements selected from) and may have a hexagonal crystal structure having a layered structure.

According to a third aspect of the present invention, the lithium ion battery comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and the positive electrode active material for a lithium ion secondary battery is used as the positive electrode material of the positive electrode. A secondary battery is provided.

When the transition metal composite hydroxide of the present invention is used as a precursor of a positive electrode active material for a secondary battery, it is possible to obtain a secondary battery in which the effect of the additive element (eg, improvement of output characteristics, etc.) is further improved. can be done. When the positive electrode active material of the present invention is used in a secondary battery, it is possible to obtain a secondary battery in which the effect of the additive element is further improved. In addition, the lithium ion secondary battery of the present invention has excellent battery characteristics in which the effect of the additive element is further improved. Therefore, the industrial significance of the present invention is extremely large.

FIG. 1(A) and FIG. 1(B) are schematic diagrams showing examples of transition metal composite hydroxide particles. FIGS. 2A and 2B are schematic diagrams showing other examples of transition metal composite hydroxide particles. FIGS. 3A and 3B are schematic diagrams showing examples of positive electrode active materials. FIG. 4 is a diagram showing an example of a method for producing transition metal composite hydroxide particles. FIG. 5 is a diagram showing an example of a method for producing transition metal composite hydroxide particles. FIG. 6 is a diagram showing an example of a method for producing transition metal composite hydroxide particles. FIG. 7 is a diagram showing an example of a method for producing a positive electrode active material. FIG. 8 is a diagram showing an example of a method for producing a positive electrode active material. FIG. 9 is a schematic cross-sectional view of a coin-type battery used for battery evaluation. FIG. 10 is a schematic explanatory diagram of an example of impedance evaluation measurement and an equivalent circuit used for analysis. FIG. 11(A) is a diagram illustrating a TEM observation image of a part of the outer shell portion of the outer shell portion of the secondary particles of the positive electrode active material obtained in the example, and FIG. 11(B) is a TEM observation image. 11(C) is a photograph of a TEM-EDX image (photograph substituting for a drawing).

Hereinafter, transition metal composite hydroxide particles, a method for producing the same, a positive electrode active material for a lithium ion secondary battery, a method for producing the same, and a lithium ion secondary battery according to embodiments will be described with reference to the drawings. It should be noted that the present invention is not limited to the embodiments described below. In addition, in the drawings, in order to make each configuration easy to understand, some parts are emphasized or some parts are simplified, and the actual structure, shape, scale, etc. may differ.

1. Particles of Transition Metal Composite Hydroxide The particles of the transition metal composite hydroxide according to the present embodiment contain a transition metal and an additive element having a biased distribution within the particles. When the particles of the transition metal composite hydroxide according to the present embodiment are used as a precursor of a positive electrode active material for lithium ion secondary batteries, it is possible to obtain a positive electrode active material in which the effect of the additive element is further improved.

FIGS. 1(A) to (B) and FIGS. 2(A) to (B) are schematic diagrams showing examples of transition metal composite hydroxide particles according to the present embodiment. FIGS. 3A and 3B are schematic diagrams showing an example of a positive electrode active material obtained using transition metal composite hydroxide particles as a precursor.

As shown in FIG. 1(A), the transition metal composite hydroxide particles 10 have a central portion 3 and an outer peripheral portion 4 arranged outside the central portion 3 . As shown in FIG. 1B, transition metal composite hydroxide particles 10 are secondary particles 2 formed by aggregation of a plurality of primary particles 1 (fine primary particles 1a, plate-like primary particles 1b). including. As shown in FIG. 1B, the central portion 3 is formed by agglomerating a plurality of fine primary particles 1a. The peripheral portion 4 is larger than the fine primary particles 1a and is formed by aggregation of the plate-like primary particles 1b. Moreover, the average particle diameter of the particles 10 (secondary particles 2) of the transition metal composite hydroxide is preferably 1 μm or more and 15 μm or less.

The particles 10 of the transition metal composite hydroxide are mainly composed of the secondary particles 2, but may contain the primary particles 1 alone. The details of the transition metal composite hydroxide particles 10 will be described below.

[Particle structure]
(Secondary particles)
Particles 10 of transition metal composite hydroxide include substantially spherical secondary particles 2 formed by aggregation of a plurality of primary particles 1 (including fine primary particles 1a and plate-like primary particles 1b). More specifically, the transition metal composite hydroxide particles 10 have a central portion 3 composed of fine primary particles 1a, and plate-like primary particles 1b larger than the fine primary particles 1a outside the central portion 3. It comprises a structure with a perimeter 4 . By producing the positive electrode active material 100 using the transition metal composite hydroxide particles 10 as a precursor, lithium is sufficiently diffused into the particles in the later-described firing step (step S50, see FIG. 7). Thus, the positive electrode active material 100 with uniform lithium distribution and good quality can be obtained.

The central portion 3 has, for example, a structure with many gaps in which fine primary particles 1a are connected. Therefore, when compared with the outer peripheral portion 4 made of plate-shaped primary particles 1b that are larger and thicker than the fine primary particles 1a, the central portion 3 shrinks due to sintering in the firing step (step S50, see FIG. 7) at a lower temperature. generated from Therefore, as the sintering progresses, the fine primary particles 1a present in the central portion 3 shrink from the center of the secondary particles 2 toward the outer peripheral portion 4 where sintering progresses more slowly, and finally the outer periphery It is absorbed by the portion 4 and constitutes an outer shell portion as indicated by reference numeral "24" in FIG. 3(A). On the other hand, due to such contraction of the fine primary particles 1a and absorption into the outer peripheral portion 4, a space is generated in the central portion 3. As shown in FIG. Since the central portion 3 is considered to have a low density and the contraction rate of the fine primary particles 1a present in the central portion 3 is large, the central portion 3 is reduced in the presence of the primary particles 1 as the sintering progresses. It becomes a space having a size large enough to prevent the formation of a hollow portion 23 (see FIGS. 3A and 3B) in the positive electrode active material 100 .

(Distribution of additive elements)
The fine primary particles 1a present in the central portion 3 contain the additive element at a higher concentration than in the outer peripheral portion 4 . When the fine primary particles 1a contain a high-concentration additive element, shrinkage of the fine primary particles 1a in the firing step (step S50, see FIG. 7) concentrates the additive element, and the outer shell portion of the positive electrode active material 100 An additive element is diffused on the surface of the primary particles 21 forming 24 . Then, in the positive electrode active material 100 obtained, a concentrated layer C in which the additive element is concentrated is formed on the surfaces of the primary particles 21 present in the outer shell portion 24 . The distribution of the additive elements in the particles 10 of the transition metal composite hydroxide can be confirmed, for example, by detecting the additive elements by surface analysis of the cross section of the particles using an energy dispersive X-ray analyzer (EDX). can be done.

Moreover, as shown in FIG. 2(A), the transition metal composite hydroxide particles 10 may be further coated with a coating layer 5 containing a compound containing an additive element. By having such a particle structure, in the obtained positive electrode active material 100, the concentrated layer C is formed more uniformly on the surface of the primary particles 21 in the entire secondary particles 22, and the battery characteristics can be further improved. (See FIGS. 3A and 3B).

Moreover, the additive element may be contained only in the central portion 3 or may be contained in both the central portion 3 and the outer peripheral portion 4 . When the outer peripheral portion 4 contains the additive element, as shown in FIG. 2B, it is preferable to have a layer 4a containing the additive element at a higher concentration than the inner side of the outer peripheral portion 4 on the surface side of the outer peripheral portion 4. . When the transition metal composite hydroxide particles 10 have such a particle structure, the obtained positive electrode active material 100 has a more uniform concentration layer C on the surface of the primary particles 21 over the entire secondary particles 22. formed, and the battery characteristics can be further improved. Moreover, in the outer peripheral portion 4 , the thickness of the layer 4 a containing the additive element at a higher concentration than the inner side is preferably 50% or more and 80% or less of the thickness t of the outer peripheral portion 4 . When the thickness of the layer 4a containing the additive element at a high concentration is within the above range, the resulting positive electrode active material 100 has a more uniform concentrated layer C formed on the surfaces of the primary particles 21 throughout the secondary particles 22. , it becomes possible to further improve the battery characteristics.

(Type of additive element)
The type of additive element is not particularly limited, but from the viewpoint of further improving the durability and output characteristics of the lithium ion secondary battery, magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), One selected from vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), lanthanum (La), and tungsten (W) It preferably includes the above. Among these, from the viewpoint of further improving the output characteristics, it is more preferable to contain one or more elements selected from Nb, Mo, Ta, Ti, Zr, and W. For example, additive elements containing W may include One type of additive element may be included, or two or more types may be included. The additive element is contained inside the primary particles 1 described above.

(fine primary particles)
The fine primary particles 1a forming the central portion 3 preferably have an average particle diameter of 0.01 μm or more and 0.3 μm or less, more preferably 0.1 μm or more and 0.3 μm or less. When the average particle size of fine primary particles 1a is within the above range, a space (hollow portion 23) having a sufficient size can be formed. On the other hand, when the average particle size of the fine primary particles 1a is less than 0.01 μm, the central portion 3 having a sufficient size may not be formed. Also, if it exceeds 0.3 μm, the temperature at which sintering starts and shrinkage are not sufficient in the firing step (step S50), and a sufficiently large space (hollow portion 23) cannot be obtained after firing (step S50). Sometimes.

Also, the shape of the fine primary particles 1a is not particularly limited, but is preferably plate-like and/or needle-like. When the fine primary particles 1a have these shapes, the central portion 3 has a sufficiently low density, and a large amount of space (hollow portion 23) can be formed by large shrinkage due to firing (step S50). can.

(plate-shaped primary particles)
It is preferable that the plate-like primary particles 1b forming the outer peripheral portion 4 aggregate in random directions. When the plate-like primary particles 1b aggregate in random directions, gaps are generated substantially uniformly between the primary particles 1 in the outer peripheral portion 4, and the lithium compound and the transition metal composite oxide particles 10 are mixed (step S40). Then, when firing (step S50), the molten lithium compound spreads inside the secondary particles 2, and lithium can be sufficiently diffused.

In addition, since the plate-like primary particles 1b are aggregated in random directions, the shrinkage of the central portion 3 in the firing step (step S50) also occurs more evenly. A space (hollow portion 23) having a depth can be formed.

The plate-shaped primary particles 1b preferably have an average particle diameter of 0.3 μm or more and 3 μm or less, more preferably 0.4 μm or more and 1.5 μm or less, and 0.4 μm or more and 1.0 μm or less. is particularly preferred. When the average particle size of the plate-shaped primary particles 1b is less than 0.3 μm, the temperature at which sintering starts in the firing step (step S50) is lowered, and a sufficiently large space may not be obtained after firing. If it exceeds 3 μm, it is necessary to increase the firing temperature in order to obtain sufficient crystallinity of the obtained positive electrode active material, and sintering occurs between the secondary particles, resulting in the deterioration of the obtained positive electrode active material. The particle size may exceed the above range.

The particle sizes of fine primary particles 1a and plate-like primary particles 1b can be measured by observing the cross section of transition metal composite hydroxide particles 10 using a scanning electron microscope (SEM). For example, a plurality of secondary particles 2 (transition metal composite hydroxide particles 10) are embedded in a resin or the like, and a cross-section of the plurality of secondary particles 2 can be observed by processing such as a cross-section polisher. The particle size of each of the fine primary particles 1a and the plate-like primary particles 1b is the maximum diameter (maximum length) of the cross section of preferably 10 or more primary particles 1a and 1b in the secondary particles 2. It can be obtained by measuring and calculating the average value.

(The outer periphery)
The thickness t (see FIG. 1A) of the outer peripheral portion 4 is preferably 5% or more and 45% or less, more preferably 7% or more and 35% or less, of the particle size (diameter) of the secondary particles 2. It is more preferable to have Here, the thickness of the outer shell portion 24 of the positive electrode active material 100 is generally maintained at the thickness of the outer peripheral portion 4 of the transition metal composite hydroxide particles 10 . Therefore, when the thickness t of the outer peripheral portion 4 is within the above range, sufficient hollow portions 23 can be formed in the lithium metal composite oxide particles (positive electrode active material 100). On the other hand, when the thickness of the outer peripheral portion 4 is less than 5%, the outer peripheral portion 4 becomes too thin, and the overall shrinkage of the transition metal composite hydroxide particles 10 increases in the firing step (step S50), and , sintering may occur between the secondary particles 22 of the positive electrode active material 100 to be obtained, and the particle size distribution of the positive electrode active material 100 may deteriorate. Moreover, when the thickness of the outer peripheral portion 4 exceeds 45%, the central portion 3 having a sufficient size may not be formed.

In addition, the thickness t of the outer peripheral portion 4 can be measured by the following method. First, from a plurality of secondary particles 2 in the resin, secondary particles 2 that can be observed in cross section at the center of the particle are selected, and at three or more arbitrary locations, the outer periphery of the outer peripheral portion 4 and the central portion 3 The average thickness of the outer peripheral portion 4 for each particle is obtained by measuring the distance between the two points on the inner peripheral surface of the side where the distance is the shortest. Then, the distance between any two points with the maximum distance on the outer circumference of the secondary particle 2 is the particle size (diameter) of the secondary particle 2, and the particle size (diameter) of the secondary particle 2 is the above average By dividing the thickness (average thickness of outer peripheral portion 4 / particle size (diameter) of secondary particles 2 ), the thickness (%) of outer peripheral portion 4 for each secondary particle 2 is obtained. Furthermore, the thickness (%) of each secondary particle 2 obtained for 10 or more secondary particles 2 is averaged, and the thickness (%) of the outer peripheral portion 4 with respect to the particle size (diameter) of the secondary particle 2 can be asked for.

(Average particle size)
The transition metal composite hydroxide particles 10 have an average particle size of 1 μm or more and 15 μm or less, preferably 3 μm or more and 12 μm or less, and more preferably 3 μm or more and 10 μm or less. The average particle size of the transition metal composite hydroxide particles 10 correlates with the average particle size of the positive electrode active material 100 obtained by using the transition metal composite hydroxide particles 10 as a precursor. Therefore, by controlling the average particle diameter within the above range, the average particle diameter of the positive electrode active material 100 can be controlled within a predetermined range. The average particle diameter of the transition metal composite hydroxide particles 10 means the volume-based average particle diameter (MV), which can be obtained from the volume integrated value measured by a laser beam diffraction scattering particle size analyzer, for example. can.

(particle size distribution)
In addition, the transition metal composite hydroxide particles 10 have an index [(d90-d10)/average particle diameter], which is an index showing the spread of the particle size distribution, is preferably 0.65 or less, more preferably 0.55 or less, More preferably, it is 0.50 or less.

The particle size distribution of the positive electrode active material 100 is strongly influenced by the transition metal composite hydroxide particles 10 that are its precursor. Therefore, when transition metal composite hydroxide particles containing many fine and coarse particles are used as a precursor, the positive electrode active material also contains many fine and coarse particles. It becomes impossible to sufficiently improve the safety, cycle characteristics and output characteristics of the secondary battery. On the other hand, if the [(d90-d10)/average particle diameter] is adjusted to 0.65 or less at the stage of the particles 10 of the transition metal composite hydroxide, this can be obtained as a precursor. The particle size distribution of the positive electrode active material 100 obtained can also be narrowed, and the problems described above can be avoided.

Assuming industrial-scale production, it is not realistic to use transition metal composite hydroxide particles 10 with an excessively small [(d90-d10)/average particle diameter]. . Therefore, in consideration of cost and productivity, the lower limit of [(d90-d10)/average particle diameter] in the transition metal composite hydroxide particles 10 is preferably about 0.25.

Note that d10 is the number of particles in each particle size accumulated from the smaller particle size side, and the particle size at which the cumulative volume is 10% of the total volume of all particles, and d90 is the number of particles. It means the particle size whose cumulative volume is 90% of the total volume of all particles. d10 and d90 can be obtained from volume integrated values measured with a laser light diffraction/scattering particle size analyzer in the same manner as the average particle size.

(composition)
The composition of the transition metal composite hydroxide particles 10 is not particularly limited as long as it has the structure, average particle diameter and particle size distribution described above. The transition metal composite hydroxide particles 10 may contain, for example, one or more metal elements selected from nickel, cobalt, and manganese, and additive elements other than these metal elements. In addition, the transition metal composite hydroxide particles 10 may contain, for example, nickel, manganese, and additional elements, and may contain nickel, manganese, cobalt, and additional elements.

For example, the transition metal composite hydroxide particles 10 contain nickel (Ni), manganese (Mn), an additive element (M), and optionally cobalt (Co), and the substance amount ratio of each element (molar ratio) is Ni: Mn: Co: M = x: y: z: t (x + y + z + t = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0<t≦0.1, M is preferably one or more additional elements selected from Nb, Mo, Ta, Ti, Zr, and W). When the transition metal composite hydroxide particles 10 having such a composition are used as the precursor of the positive electrode active material, a secondary battery having high output characteristics and cycle characteristics can be obtained.

Further, the particles 10 of the transition metal composite hydroxide are represented by the general formula (1): NixMnyCozMt(OH) _2+a ( _x + _y + _z + _t =1, 0.3≤x≤0.95, 0.05≤ y≦0.55, 0≦z≦0.4, 0<t≦0.1, 0≦a≦0.5, M is selected from Nb, Mo, Ta, Ti, Zr and W one or more additional elements). By using such particles of transition metal composite hydroxide as a precursor, it is possible to easily obtain a positive electrode active material represented by the general formula (2) described later, and to have high output characteristics and cycle characteristics. You can get the following batteries.

The above molar ratio of the transition metal composite hydroxide particles 10 and the preferable composition range of nickel, manganese, cobalt and additive elements constituting the particles in the general formula (1) are the positive electrode active material 100 described later. and the preferred composition range of each element in the general formula (2). Therefore, description of these matters is omitted here.

The method for producing the transition metal composite hydroxide particles 10 is not particularly limited as long as it has the above specific structure, average particle diameter, etc., but can be easily obtained by the production method described below. can.

2. Method for Producing Particles of Transition Metal Composite Hydroxide FIGS. 4 to 6 are diagrams showing an example of a method for producing the particles 10 of transition metal composite hydroxide according to the present embodiment. The production method according to the present embodiment is a method for producing transition metal composite hydroxide particles 10 by a crystallization reaction. As shown in FIGS. is supplied to form a reaction aqueous solution, the pH value of the reaction aqueous solution at a liquid temperature of 25 ° C. is adjusted to a range of 12.0 or more and 14.0 or less, and nucleation is performed (step S10); , The pH value of the reaction aqueous solution containing nuclei obtained in the nucleation step at a liquid temperature of 25 ° C. is controlled to be lower than the pH value of the nucleation step and 10.5 or more and 12.0 or less. and a particle growth step (step S20) for growing nuclei.

In the crystallization reaction, a nucleation step (step S10) mainly for nucleation and a grain growth step (step S20) for grain growth are clearly distinguished into two stages, thereby having a narrow particle size distribution, A transition metal composite hydroxide having a more uniform particle size can be obtained.

In the nucleation step (step S10), nuclei are generated in an acidic atmosphere with an oxygen concentration exceeding 5% by volume. In addition, the grain growth step (step S20) includes a first grain growth step (step S21) in which the nuclei are grown in an acidic atmosphere, and an oxidizing atmosphere in the first grain growth step (step S21) with an oxygen concentration of and a second grain growth step (step S22) of switching to a non-oxidizing atmosphere of 5% by volume or less and further growing the nuclei in the non-oxidizing atmosphere.

In the manufacturing method according to the present embodiment, the nucleation step (step S10) and the grain growth step (step S20) are separated into two stages, and by switching the reaction atmosphere in the grain growth step (step S20), The transition metal composite hydroxide particles 10 having the above-described particle structure can be easily produced on an industrial scale with high productivity.

Further, in the particle growth step (step S20), a raw material aqueous solution containing additive elements other than the transition metal contained in the reaction aqueous solution is added to the reaction aqueous solution in an oxidizing atmosphere, and the additive element is added in a non-oxidizing atmosphere. Stops the addition of the raw material aqueous solution containing to the reaction aqueous solution, or reduces the supply amount of the additive element to the reaction aqueous solution. In the nucleation step (step S10), the raw material aqueous solution containing the additive element may or may not be supplied to the reaction aqueous solution.

The inventors of the present invention have made intensive studies in order to further improve the battery characteristics based on the technology described in Patent Document 2 and the like. As a result, in the oxidizing atmosphere, the raw material aqueous solution containing the additive element is supplied, and in the non-oxidizing atmosphere, the supply of the raw material aqueous solution containing the additive element is stopped, or the amount of the additive element supplied to the reaction aqueous solution is reduced. By increasing the I got some insight. In the secondary battery, when the additive element is present at a high concentration on the surfaces of the primary particles 21 that come into contact with the electrolyte, the effect of adding the additive element can be more efficiently exhibited, and the battery characteristics are further improved. Each step will be described below.

(1) Crystallization Reaction [Nucleation Step (Step S10)]
In the nucleation step (step S10), the reaction aqueous solution containing the raw material aqueous solution containing the transition metal and the ammonium ion donor has a pH value in the range of 12.0 or more and 14.0 or less at a liquid temperature of 25 ° C. The nuclei are generated in an acidic atmosphere with an oxygen concentration exceeding 5% by volume. An example of a method for producing a reaction aqueous solution (hereinafter also referred to as "aqueous solution for nuclear generation") in the nuclear generation step (step S10) will be described below.

First, a compound containing a transition metal as a raw material is dissolved in water to prepare an aqueous raw material solution. Further, an aqueous solution containing an alkaline aqueous solution and an ammonium ion donor is supplied and mixed into the reaction vessel, and the pH value measured at a liquid temperature of 25 ° C. is in the range of 12.0 to 14.0. A pre-reaction aqueous solution is prepared. The ammonium ion concentration of the pre-reaction aqueous solution is preferably 3 g/L or more and 25 g/L or less. The pH value of the pre-reaction aqueous solution can be measured with a pH meter, and the ammonium ion concentration can be measured with an ion meter.

Next, while stirring the pre-reaction aqueous solution, the raw material aqueous solution is supplied. As a result, an aqueous solution for nucleation is formed in the reaction tank. Since the pH value of the aqueous solution for nucleation is within the above-described range, nucleation occurs preferentially with little growth of nuclei in the nucleation step (step S10).

In the nucleation step (step S10), the pH value and the concentration of ammonium ions in the aqueous solution for nucleation change along with the nucleation. Therefore, the alkaline aqueous solution and the ammonia aqueous solution are supplied at appropriate times, and the pH value of the aqueous solution for nucleation (liquid in the reaction tank) is controlled to be in the range of pH 12.0 or more and 14.0 or less based on the liquid temperature of 25°C. Moreover, it is preferable to adjust the concentration of ammonium ions to a range of 3 g/L or more and 25 g/L or less.

In addition, in the nucleation step (step S10), the reaction atmosphere is adjusted to an oxidizing atmosphere in which the oxygen concentration exceeds 5% by volume. As a result, the central portion 3 formed by aggregation of the fine primary particles 1 can be formed inside the transition metal composite hydroxide particles 10, and the transition metal composite hydroxide particles 10 are used as a precursor. By using it, it is possible to finally obtain a positive electrode active material having a hollow structure, so that the reaction area with the electrolytic solution can be further increased.

In the nucleation step (step S10), new nuclei are continuously generated by supplying an aqueous solution containing a raw material aqueous solution, an alkaline aqueous solution and an ammonium ion donor to the nucleating aqueous solution. Then, when a predetermined amount of nuclei is generated in the nucleation aqueous solution, the nucleation step (step S10) is terminated.

At this time, the amount of nuclei generated can be determined from the amount of the metal compound contained in the raw material aqueous solution supplied to the nucleation aqueous solution. The amount of nuclei generated in the nucleation step is not particularly limited, but in order to obtain transition metal composite hydroxide particles with a narrow particle size distribution, It is preferably 0.1 atomic % or more and 2 atomic % or less, more preferably 0.1 atomic % or more and 1.5 atomic % or less, relative to the metal element in the metal compound contained.

[Particle Growth Step (Step S20)]
In the particle growth step (step S20), the reaction aqueous solution containing the nuclei obtained in the nucleation step (step S10) has a pH value at a liquid temperature of 25° C. that is lower than the pH value of the reaction aqueous solution in the nucleation step. In addition, the nuclei are grown by controlling the range of 10.5 or more and 12.0 or less. An example of a method for adjusting the reaction aqueous solution (hereinafter also referred to as "aqueous solution for particle growth") in the particle growth step (step S20) will be described below.

The pH value of the aqueous solution for particle growth can be adjusted, for example, by stopping the supply of the alkaline aqueous solution. It is preferred to stop the feed and adjust the pH value. Specifically, after stopping the supply of all aqueous solutions, it is preferable to adjust the pH value by supplying the same inorganic acid as the acid that constitutes the transition metal compound as a raw material to the aqueous solution for nucleation. .

Then, while stirring the particle growth aqueous solution, supply of the raw material aqueous solution is restarted. At this time, since the pH value of the aqueous solution for particle growth is within the range described above, almost no new nuclei are generated, nuclei (particles) grow, and transition metal composite hydroxide particles having a predetermined particle size are produced. is formed. In the particle growth step (step S20) as well, the pH value and ammonium ion concentration of the aqueous solution for particle growth change as the particles grow. Maintain within the above range.

As described above, the aqueous solution for particle growth may be the same reaction aqueous solution as the aqueous solution for nuclear generation except for adjusting the pH value. , which may be used. For example, separately from the nucleation aqueous solution, a component-adjusting aqueous solution adjusted to a pH value and an ammonium ion concentration suitable for the particle growth step (step S20) is prepared, and this component-adjusting aqueous solution is added to the nucleation step (step S10 ) Add and mix the aqueous solution for nucleation after the nucleation step, preferably the aqueous solution for nucleation after removing a part of the liquid component after the nucleation step, and use this as the aqueous solution for particle growth to perform the particle growth step. may

When an aqueous solution for particle growth (aqueous solution for component adjustment) is prepared separately from the aqueous solution for nucleation, the separation of the nucleation step (step S10) and the particle growth step (step S20) can be performed more reliably. The reaction aqueous solution in each step can be controlled to an optimum state. In particular, since the pH value of the aqueous solution for particle growth can be controlled within the optimum range from the start of the particle growth step (step S20), the resulting transition metal composite hydroxide particles 10 can have a narrower particle size distribution. can be

Also, the grain growth step (step S20) includes the first grain growth step (step S21) and the second grain growth step (step S22), as described above. Each step in the grain growth step (step S20) will be described below.

[First Particle Growth Step (Step S21)]
In the first grain growth step (step S21), nuclei are grown in an acidic atmosphere following the nucleation step (step S10). In the first particle growth step (step S21), the particle growth is performed in an oxidizing atmosphere, thereby forming the central portion 3 in which the fine primary particles 1a are agglomerated.

The concentration of oxygen in the oxidizing atmosphere exceeds 5% by volume, and is preferably twice or more, more preferably five times the concentration of oxygen in the non-oxidizing atmosphere in the second grain growth step (step S22). That's it.

Also, in an oxidizing atmosphere, a raw material aqueous solution containing an additive element different from the transition metal is supplied to the reaction aqueous solution. Thereby, the additive element can be contained in the central portion 3 . The additive element contained in the central portion 3 is finally distributed in the concentrated layer C present on the surfaces of the primary particles 21 in the positive electrode active material 100 .

[Second Grain Growth Step (Step S22)]
Next, in the second grain growth step (step S22), the oxidizing atmosphere in the first grain growth step (step S21) is switched to a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less. and grow the nucleus. In the second particle growth step (step S22), it is possible to form the peripheral portion 4 in which the plate-like primary particles 1b are aggregated.

In the middle of the particle growth step (step S20), by switching the reaction atmosphere from an oxidizing atmosphere to a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less, transition metal composite hydroxide particles 10 having the above-described particle structure are obtained. can be obtained.

In addition, in a non-oxidizing atmosphere, the supply of the raw material aqueous solution containing the additive element to the reaction aqueous solution is stopped, or the amount of the additive element supplied to the reaction aqueous solution in the raw material aqueous solution containing the additive element is reduced. As a result, the additive element can be contained at a higher concentration in the central portion 3 than in the outer peripheral portion 4 .

For example, the concentration of the additive element with respect to elements (including transition metals) other than the additive element in the raw material aqueous solution is such that the concentration in the oxidizing atmosphere is higher than the concentration in the non-oxidizing atmosphere. The concentration of the additive element in the oxidizing atmosphere is preferably two times or more, more preferably five times or more, the concentration of the additive element in the non-oxidizing atmosphere. Particularly preferably, the raw material aqueous solution containing the additive element is added in the oxidizing atmosphere, and the addition of the raw material aqueous solution containing the additive element is stopped in the non-oxidizing atmosphere.

The central portion 3 (fine primary particles 1a) formed in the oxidizing atmosphere shrinks inside the outer peripheral portion 4 formed in the non-oxidizing atmosphere to form the hollow portion 23 when the positive electrode active material 100 is manufactured. do. Therefore, the additive element added in the oxidizing atmosphere diffuses to the outer peripheral portion 4 in the firing step (step S50), and is present largely on the surfaces of the primary particles 21 that finally form the outer shell portion 24 of the positive electrode active material 100. Then, the concentrated layer C of the additive element is formed. By forming the concentrated layer C on the surfaces of the primary particles 21 that come into contact with the electrolytic solution, the effect of adding the additive element can be more efficiently exhibited. For example, when adding an additive element (e.g., tungsten, niobium, molybdenum, tantalum, etc.) that has the effect of improving the output characteristics, it is possible to improve the output characteristics more effectively than with conventional techniques. .

The additive element added in the oxidizing atmosphere exists mostly on the surface (concentrated layer C) of the primary particles 21, whereas the additive element added in the non-oxidizing atmosphere exists mostly inside the primary particles 21. become. Therefore, the amount (mole) of the additive element supplied to the aqueous solution for particle growth per unit time is By adjusting the ratio of the amount (mole) of the substance to be higher in the oxidizing atmosphere than in the non-oxidizing atmosphere, the additive element can be present at a high concentration on the surface of the primary particles 21 (enriched layer C). .

When the amount of the additive element supplied to the reaction aqueous solution contained in the raw material aqueous solution containing the additive element is reduced, the supply amount of the additive element to the reaction aqueous solution per unit time is set to a non-oxidizing atmosphere rather than an oxidizing atmosphere. Adjustments can be made by reducing the atmosphere. For example, when the supply rate of the raw material aqueous solution containing the additive element to the reaction aqueous solution is constant, the concentration of the additive element in the raw material aqueous solution containing the additive element may be decreased in a non-oxidizing atmosphere rather than in an oxidizing atmosphere. good. Further, for example, when the concentration of the raw material aqueous solution containing the additive element is kept constant, the supply amount of the raw material aqueous solution containing the additive element per unit time may be decreased in the non-oxidizing atmosphere rather than in the oxidizing atmosphere.

Further, in the second particle growth step (step S22), after stopping the supply of the raw material aqueous solution containing the additive element to the aqueous solution for particle growth, or after reducing the amount of additive element supplied to the reaction aqueous solution, As shown in FIG. 6, it is preferable to restart the supply of the raw material aqueous solution containing the additive element to the grain growth aqueous solution.

When the supply of the raw material aqueous solution containing the additive element to the aqueous solution for particle growth is stopped, the timing of resuming the supply of the raw material aqueous solution containing the additive element is determined based on the total time for grain growth during the crystallization reaction. It is preferable to restart when 50% or more and 80% or less have passed.

In addition, in the second grain growth step (step S22), when the amount of the additive element supplied to the reaction aqueous solution is reduced, the total time for grain growth during the crystallization reaction is 35% or more and 75% After the lapse of time, the amount of the additive element supplied to the reaction aqueous solution may be further increased.

As described above, when the supply of the raw material aqueous solution containing the additive element is restarted or the supply amount of the additive element is increased, the thickness from the surface of the outer peripheral portion 4 to the inside of the particle is 50% or more and 80% or less with respect to the thickness. (on the surface side) can be made higher than on the inner side (inside the surface side) of the outer peripheral portion 4 . By forming such a layer containing the additive element at a higher concentration than the inner side on the surface side of the outer peripheral portion 4, the formation of the concentrated layer C in the positive electrode active material 100 can be made more uniform and the battery characteristics can be improved. It becomes possible.

In the nucleation step (step S10) and the particle growth step (step S20), metal ions such as transition metals in the reaction aqueous solution precipitate as nuclei or primary particles 1 . Therefore, as the crystallization reaction progresses, the ratio of the liquid component to the metal component in the aqueous solution for nucleation and the aqueous solution for particle growth increases. As a result, the concentration of the raw material aqueous solution is apparently lowered, and particularly in the particle growth step (step S20), the growth of the transition metal composite hydroxide particles 10 (primary particles 1 and secondary particles 2) stagnates. Sometimes. Therefore, in order to suppress the increase of the liquid component, part of the liquid component of the aqueous solution for particle growth is discharged out of the reaction tank after the end of the nucleation step (step S10) and during the particle growth step (step S20). is preferred.

As a method for discharging part of the liquid component of the aqueous solution for particle growth to the outside of the reaction tank, for example, the supply and stirring of the aqueous solution containing the raw material aqueous solution, the alkaline aqueous solution, and the ammonium ion donor are temporarily stopped, and the It is preferable to settle the nuclei of the transition metal composite hydroxide particles 10 and discharge the supernatant liquid of the aqueous solution for particle growth. By such an operation, the relative concentration of the mixed aqueous solution in the aqueous solution for particle growth can be increased, so that the stagnation of particle growth can be prevented, and the particle size distribution of the obtained transition metal composite hydroxide particles 10 can be adjusted to a suitable value. Not only can the range be controlled, but the density of the secondary particles 2 as a whole can also be improved. The timing of discharging part of the liquid component of the aqueous solution for particle growth to the outside of the reaction tank is not particularly limited, and can be appropriately adjusted according to the degree of growth of the transition metal composite hydroxide particles 10 .

[Particle size control of transition metal composite hydroxide particles]
The particle size of the transition metal composite hydroxide particles 10 to be obtained is not particularly limited, but is preferably 1 μm or more and 15 μm or less. The particle size of the transition metal composite hydroxide particles 10 is controlled by the time and pH value of the nucleation step (step S10), the time and pH value of the particle growth step (step S20), the supply amount of the raw material aqueous solution, and the like. can do.

For example, by performing the nucleation step (step S10) at a high pH value, or by prolonging the time of the particle generation step (step S20), in the nucleation step (step S10), the By increasing the amount of the metal element contained in the raw material aqueous solution, the amount of nuclei generated can be increased, and the particle size of the resulting transition metal composite hydroxide particles 10 can be reduced.

Conversely, by suppressing the amount of nuclei generated in the nucleation step (step S10), the particle size of the obtained transition metal composite hydroxide particles 10 can be increased. Further, for example, if the particle growth step (step S20) is continued until the particles grow to a desired particle size, transition metal composite hydroxide particles 10 having a desired particle size can be obtained.

Hereinafter, each raw material and conditions preferably used in the crystallization step will be described.
[material]
As the raw material aqueous solution containing a transition metal, an aqueous solution obtained by dissolving a compound containing a transition metal in water may be used. The compound containing a transition metal is not particularly limited, but it is preferable to use a water-soluble compound for ease of handling, and it is more preferable to use a water-soluble nitrate, sulfate, hydrochloride, or the like. From the viewpoint of preventing contamination, it is more preferable to suitably use a sulfate.

As the raw material aqueous solution containing the additive element different from the transition metal (raw material aqueous solution), an aqueous solution obtained by dissolving a compound containing the desired additive element in water may be used. Although the compound containing the additive element is not particularly limited, it is preferable to use a water-soluble compound. For example, when the additive element is one or more elements selected from Nb, Mo, Ta, Ti, Zr, and W, water-soluble compounds are preferred, such as niobium oxalate, ammonium molybdate, tantalum Sodium tungstate, sodium tungstate, ammonium tungstate and the like can be preferably used.

In the production method according to the present embodiment, the ratio of each metal element in the raw material aqueous solution (whole) is generally the composition ratio of the transition metal composite hydroxide particles 10 obtained. Therefore, the content of each metal element in the raw material aqueous solution may be appropriately adjusted according to the composition of the target transition metal composite hydroxide particles 10 .

For example, when trying to obtain the transition metal composite hydroxide particles 10 represented by the general formula (1) described above, the ratio of each metal element in the raw material aqueous solution (whole) is changed to Ni:Mn:Co : M = x: y: z: t (however, x + y + z + t = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 < t ≤ 0 .1, M is one or more elements selected from Nb, Mo, Ta, Ti, Zr, and W).

The concentration of the raw material aqueous solution is preferably 1 mol/L or more and 2.6 mol/L or less, more preferably 1.5 mol/L or more and 2.2 mol/L or less, in terms of the total concentration of the compounds containing each metal element as the raw material. If the concentration of the raw material aqueous solution is less than 1 mol/L, the amount of crystallized material per reaction tank is small, resulting in a decrease in productivity. On the other hand, when the concentration of the mixed aqueous solution exceeds 2.6 mol/L, it exceeds the saturated concentration at normal temperature, and crystals of the compound containing each metal element re-precipitate, which may clog pipes.

A plurality of compounds containing different metal elements may be supplied to the reaction tank as one type of raw material aqueous solution, or may be supplied to the reaction tank as a plurality of raw material aqueous solutions each containing a different metal element. For example, when a compound containing a plurality of metal elements is mixed with water and reacts with each other to produce a compound other than the target compound, an aqueous solution (raw material aqueous solution) of the compound containing the metal element is individually prepared. is preferred. When using a plurality of raw material aqueous solutions each containing a different metal element, the plurality of raw material aqueous solutions are adjusted so that the total concentration of the metal element in all the raw material aqueous solutions is within the above range, and the reaction vessel is filled at a predetermined ratio. may be supplied to

In addition, the supply amount of the raw material aqueous solution is such that the concentration of the product in the aqueous solution for particle growth is preferably 30 g/L or more and 200 g/L or less, more preferably 80 g/L or more and 150 g/L or less at the end of the particle growth step. so that If the product concentration is less than 30 g/L, the aggregation of primary particles may be insufficient. On the other hand, when it exceeds 200 g/L, the aqueous solution for nucleation or the aqueous solution for particle growth does not sufficiently diffuse in the reaction tank, and uneven particle growth may occur.

(alkaline aqueous solution)
The alkaline aqueous solution for adjusting the pH value in the reaction aqueous solution is not particularly limited, and a general alkaline metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. Although the alkali metal hydroxide can be added directly to the reaction aqueous solution, it is preferable to add it as an aqueous solution for ease of pH control. In this case, the concentration of the aqueous alkali metal hydroxide solution is preferably 20% by mass or more and 50% by mass or less, more preferably 20% by mass or more and 30% by mass or less. By regulating the concentration of the alkali metal aqueous solution within such a range, it is possible to suppress the amount of solvent (water amount) supplied to the reaction system and prevent the pH value from locally increasing at the addition position. , it becomes possible to efficiently obtain transition metal composite hydroxide particles with a narrow particle size distribution.

The method of supplying the alkaline aqueous solution is not particularly limited as long as the pH value of the reaction aqueous solution does not become locally high and is maintained within a predetermined range. For example, while sufficiently stirring the reaction aqueous solution, it may be supplied by a pump capable of controlling the flow rate such as a metering pump.

(Aqueous solution containing ammonium donor)
The aqueous solution containing the ammonium ion donor is also not particularly limited, and for example, ammonia water or an aqueous solution of ammonium sulfate, ammonium chloride, ammonium carbonate or ammonium fluoride can be used.

When aqueous ammonia is used as the ammonium ion donor, its concentration is preferably 20% by mass or more and 30% by mass or less, more preferably 22% by mass or more and 28% by mass or less. By regulating the concentration of ammonia water within such a range, the loss of ammonia due to volatilization can be minimized, and thus production efficiency can be improved.

The aqueous solution containing the ammonium ion donor can also be supplied by a pump whose flow rate can be controlled in the same manner as the alkaline aqueous solution.

(pH value)
In the nucleation step (step S10), the pH value of the reaction aqueous solution at a liquid temperature of 25° C. is within the range of 12.0 or more and 14.0 or less, and in the particle growth step (step S20), the reaction aqueous solution is adjusted at a liquid temperature of 25° C. The pH value in is controlled within the range of 10.5 to 12.0. In any step, it is preferable to control the fluctuation range of the pH value during the crystallization reaction within ±0.2. If the fluctuation range of the pH value is large, the ratio of the amount of nucleation and particle growth will not be constant, and it may be difficult to obtain transition metal composite hydroxide particles with a narrow particle size distribution.

In the nucleation step (step S10), the pH value of the reaction aqueous solution (nucleation aqueous solution) is adjusted to 12.0 or more and 14.0 or less, preferably 12.3 or more and 13.5 or less at a liquid temperature of 25°C. More preferably, it is controlled within the range of 12.5 or more and 13.3 or less. This makes it possible to suppress the growth of nuclei and give priority to nucleation, so that the nuclei generated in the nucleation step (step S10) can be uniform and have a narrow particle size distribution. On the other hand, if the pH value is less than 12.0, the growth of nuclei (particles) proceeds along with nucleation, so that the particle size of the resulting transition metal composite hydroxide particles becomes non-uniform and the particle size distribution deteriorates. . On the other hand, when the pH value exceeds 14.0, the generated nuclei become too fine, which causes a problem of gelation of the reaction aqueous solution (nucleation aqueous solution).

In the particle growth step (step S20), the pH value of the reaction aqueous solution (particle growth aqueous solution) is adjusted to 10.5 or more and 12.0 or less, preferably 11.0 or more and 12.0 or less, at a liquid temperature of 25°C. Preferably, it is controlled within the range of 11.5 or more and 12.0 or less. As a result, the generation of new nuclei is suppressed, it becomes possible to give priority to particle growth, and the resulting transition metal composite hydroxide particles 10 can be made homogeneous and have a narrow particle size distribution. On the other hand, if the pH value is less than 10.5, the concentration of ammonium ions increases and the solubility of metal ions increases, which not only slows down the crystallization reaction but also reduces the amount of metal ions remaining in the reaction aqueous solution. increase and productivity deteriorates. In addition, when the pH value exceeds 12.0, the amount of nuclei generated during the particle growth step (step S20) increases, the particle size of the resulting transition metal composite hydroxide particles 10 becomes non-uniform, and the particle size distribution becomes uneven. Getting worse.

When the pH value of the aqueous reaction solution (aqueous solution for particle growth) is 12.0, this is a boundary condition between nucleation and nucleus growth. It can be any condition. That is, when the pH value of the nucleation step (step S10) is set higher than 12.0 to generate a large amount of nuclei, and then the pH value of the particle growth step (step S20) is set to 12.0, a large amount of Since the nuclei exist, particle growth occurs preferentially, and transition metal composite hydroxide particles 10 having a narrow particle size distribution can be obtained.

On the other hand, when the pH value of the nucleation step (step S10) is set to 12.0, since there are no growing nuclei in the reaction aqueous solution, nucleation occurs preferentially, and the pH value of the particle growth step (step S20) is set to By making it smaller than 12.0, the generated nuclei grow and good transition metal composite hydroxide particles 10 can be obtained. In any case, the pH value in the grain growth step (step S20) may be controlled to be lower than the pH value in the nucleation step (step S10). In order to clearly separate nucleation and grain growth, The pH value in the particle growth step (step S20) is preferably lower than the pH value in the nucleation step (step S10) by 0.5 or more, more preferably by 1.0 or more.

(reaction atmosphere)
In the manufacturing method of the present embodiment, after controlling the pH value in each step as described above, the reaction atmosphere in the nucleation step (step S10) and the first grain growth step (step S21) is changed to an oxidizing atmosphere. adjust. As a result, the central portion 3 in which the fine primary particles 1a are aggregated is formed. Further, in the middle of the grain growth step (step S20), the atmosphere is switched from the oxidizing atmosphere to the non-oxidizing atmosphere, and a second grain growth step (step S22) is performed in which the grains are grown in the non-oxidizing atmosphere. Outside the portion 3, an outer peripheral portion 4 is formed in which plate-like primary particles 1b are aggregated.

When the reaction atmosphere is controlled as described above, the fine primary particles 1a constituting the central portion 3 may be, for example, plate-like and/or needle-like as shown in FIG. It may be in any other shape. Other shapes may be, for example, a rectangular parallelepiped shape, an elliptical shape, or a rhombohedral shape. The shape of the fine primary particles 1a can be adjusted by the composition of the particles 10 of the transition metal composite hydroxide. Similarly, the plate-like primary particles 1b forming the outer peripheral portion 4 may also have other shapes. In addition, in the production method according to the present embodiment, it is preferable to appropriately control the reaction atmosphere in each stage according to the composition of the target transition metal composite hydroxide particles 10 .

In the first particle growth step (step S21), the reaction atmosphere is controlled to an oxidizing atmosphere to form the central portion 3 of the transition metal composite hydroxide particles 10 . Specifically, the oxygen concentration in the reaction atmosphere is controlled so as to exceed 5% by volume, preferably 10% by volume or more, more preferably an atmospheric atmosphere (oxygen concentration: 21% by volume). By controlling the oxygen concentration in the reaction atmosphere within the above range, it is possible to form fine primary particles 1a having an average particle diameter in the range of 0.01 μm to 0.3 μm.

The upper limit of the oxygen concentration in the reaction atmosphere in the first particle growth step (step S21) is not particularly limited. The thickness is less than 01 μm, and the layer (peripheral portion 4) having a low density of the additive element may not have a sufficient size. Therefore, the oxygen concentration in the first grain growth step (step S21) is preferably 30% by volume or less.

On the other hand, in the second particle growth step (step S22), the atmosphere is controlled to a weakly oxidizing atmosphere or a non-oxidizing atmosphere to form the outer peripheral portion of the transition metal composite hydroxide particles 10 . Specifically, the mixed atmosphere of oxygen and inert gas is controlled so that the oxygen concentration in the reaction atmosphere is 5% by volume or less, preferably 2% by volume or less, more preferably 1% by volume or less. As a result, the nuclei generated in the nucleation step (step S10) can grow to a certain range while suppressing unnecessary oxidation. It is possible to form a structure in which plate-like primary particles 1b aggregate. Therefore, it is possible to form the outer peripheral portion 4 having a sufficient difference in particle size between the primary particles 1 and the central portion 3 described above.

The particle size of each of the fine primary particles 1a and the plate-like primary particles 1b is preferably the maximum diameter (maximum length) of the cross section of each of the primary particles 1a and 1b of 10 or more in the secondary particles 2. It can be obtained by measuring the diameter and calculating the average value.

(Change atmosphere)
The switching from the oxidizing atmosphere to the non-oxidizing atmosphere in the particle growth step (step S20) is performed at an appropriate timing so that the transition metal composite hydroxide particles 10 having the above-described particle structure are formed. An example of atmosphere switching will be described below.

The timing of switching the atmosphere can be determined in consideration of the size of the central portion 3 so that the hollow portion 23 can be obtained in the positive electrode active material 100 to the extent that fine particles are not generated and the cycle characteristics are not deteriorated. preferable. The atmosphere may be switched, for example, after 0.5% or more and 40% or less, preferably 0.5% or more and 30%, of the entire time for grain growth during the crystallization reaction. After 0.5% or more and 25% or less have passed, it is carried out. If the atmosphere is switched at more than 40% of the total grain growth time, the central portion 3 becomes large, and the thickness of the outer peripheral portion 4 becomes too thin with respect to the diameter of the secondary particles 2. There is On the other hand, if the atmosphere is switched at less than 0.5% of the total grain growth time, the central part 3 becomes too small, or the two parts comprising the central part 3 and the outer peripheral part 4 are formed. Secondary particles 2 may not be formed.

The method for switching the atmosphere is not particularly limited, but from the viewpoint of shortening the time for switching the atmosphere, it is preferable to use an air diffuser. Conventionally, the reaction atmosphere is switched by circulating the atmosphere gas in the reaction tank or by inserting a conduit having an inner diameter of about 1 mm to 50 mm into the reaction aqueous solution and bubbling the atmosphere gas. However, since it takes a long time to switch the reaction atmosphere in these methods, it was necessary to stop the supply of the raw material aqueous solution during the switching of the atmosphere. On the other hand, the air diffuser is composed of a conduit having a large number of fine holes on its surface, and can release a large number of fine gases (bubbles) into the liquid. Therefore, when the atmosphere is switched using an air diffuser, it is possible to switch the reaction atmosphere in a short time, and there is no need to stop the supply of the raw material aqueous solution when switching the atmosphere, improving production efficiency. can be achieved.

As the diffuser pipe, it is preferable to use a ceramic diffuser from the viewpoint of excellent resistance in a high pH environment. In addition, the smaller the pore size of the air diffusion pipe, the better. When the pore size of the diffuser tube is sufficiently small, fine air bubbles can be discharged, so that the reaction atmosphere can be switched with high efficiency.

(ammonium ion concentration)
The ammonium ion concentration in the reaction aqueous solution is preferably 3 g/L or more and 25 g/L or less, more preferably 5 g/L or more and 20 g/L or less. Ammonium ions function as a complexing agent in the aqueous reaction solution. If the ammonium ion concentration is less than 3 g/L, the solubility of the metal ions in the reaction aqueous solution cannot be kept constant, or the reaction aqueous solution tends to gel, resulting in a well-ordered transition of shape and particle size. It becomes difficult to obtain the metal composite hydroxide particles 10 . On the other hand, when the ammonium ion concentration exceeds 25 g/L, the solubility of the metal ions in the reaction aqueous solution becomes too large, and the amount of metal ions remaining in the reaction aqueous solution increases, which may cause composition deviation. .

Moreover, it is preferable to maintain the ammonium ion concentration in the reaction aqueous solution at a constant value within the above range. When the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of metal ions fluctuates, and uniform transition metal composite hydroxide particles 10 may not be formed. Therefore, it is preferable to control the fluctuation range of the ammonium ion concentration within a certain range through the nucleation step (step S10) and the particle growth step (step S20). Control is preferred.

(reaction temperature)
The temperature of the reaction aqueous solution (reaction temperature) is preferably controlled in the range of 20° C. or higher, more preferably 20° C. or higher and 60° C. or lower throughout the nucleation step (step S10) and the particle growth step (step S20). When the reaction temperature is lower than 20° C., the solubility of the reaction aqueous solution is low, and nucleation tends to occur. It becomes difficult to control within a narrow range. The upper limit of the reaction temperature is not particularly limited, but if it exceeds 60° C., volatilization of ammonia is accelerated, and an aqueous solution containing an ammonium ion donor is supplied to control the ammonium ions in the reaction aqueous solution within a certain range. Quantities will increase and production costs will increase.

(manufacturing device)
The crystallizer (reaction tank) used for the crystallization reaction is not particularly limited, but it is preferable that the reaction atmosphere can be switched by the air diffuser described above. Moreover, it is preferable to use a batch-type crystallizer in which the precipitated product is not recovered until the crystallization reaction is completed. When a batch-type crystallizer is used, unlike a continuous crystallizer that collects the product by an overflow method, the growing particles are not collected at the same time as the overflow liquid, so transition metals with a narrow particle size distribution The composite hydroxide particles 10 can be easily obtained. From the viewpoint of appropriately controlling the reaction atmosphere during the crystallization reaction, it is preferable to use a closed crystallizer.

(2) Covering step (step S30)
In the manufacturing method according to the present embodiment, as shown in FIG. 6, a coating step (step S30) of coating the crystallized product obtained after the second grain growth step (step S20) with a compound containing an additive element. may be further provided. By including the coating step (step S30), the concentrated layer C in the positive electrode active material 100 can be formed more uniformly, and the battery characteristics can be further improved.

The coating method is not particularly limited as long as the transition metal composite hydroxide particles 10 can be uniformly coated with the compound containing the additive element. An example of the covering step (step S30) will be described below.

For example, the crystallized product obtained after the second grain growth step (step S22) is slurried, the pH value thereof is controlled within a predetermined range, and then an aqueous solution (aqueous solution for coating) in which a compound containing an additive element is dissolved is added. By adding, a compound containing the additive element is precipitated on the surface of the crystallized material (particles of the transition compound hydroxide). As a result, transition metal composite hydroxide particles 10 uniformly coated with the compound containing the additive element can be obtained. In this case, instead of the aqueous solution for coating, an alkoxide solution of the additive element may be added to the slurried crystallized product. Alternatively, instead of slurrying the crystallized product, the surface of the crystallized product may be coated by spraying an aqueous solution or slurry in which a compound containing an additive element is dissolved onto the crystallized product and drying the solution. Alternatively, for example, the coating may be carried out by spray-drying a slurry in which the crystallized product and the compound containing the additive element are suspended. For example, the crystallized product and the compound containing the additive element are mixed by a solid-phase method. You may coat|cover by methods, such as.

When the surface of the crystallized product (particles of the transition composite hydroxide) is coated with the additive element, the composition of the particles 10 of the transition metal composite hydroxide obtained after coating is the desired transition metal composite water. The compositions of the raw material aqueous solution and the coating aqueous solution are appropriately adjusted so as to match the composition of the oxide particles 10 . Further, the coating step (step S30) may be performed on the heat-treated particles after heat-treating the crystallized product (particles of the transition metal composite hydroxide). At least part of the heat-treated particles may contain transition metal composite oxide particles obtained by oxidizing crystallized substances (transition metal composite hydroxide particles).

(Particles of transition metal composite hydroxide)
The production method according to the present embodiment is not limited by the composition of the obtained transition metal composite hydroxide particles 10 as long as the structure, average particle diameter and particle size distribution described above can be achieved. The transition metal composite hydroxide particles 10 may contain, for example, one or more metal elements selected from nickel, cobalt, and manganese, and additional elements other than these metal elements. element may be included, and nickel, manganese, cobalt, and additional elements may be included.

For example, the transition metal composite hydroxide particles 10 contain nickel (Ni), manganese (Mn), cobalt (Co), and an additive element (M), and the material amount ratio (molar ratio) of each element is , Ni: Mn: Co: M = x: y: z: t (x + y + z + t = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 <t≦0.1, M is one or more additive elements selected from Nb, Mo, Ta, Ti, Zr, and W).

Moreover, the production method according to the present embodiment can be suitably applied to particles 10 of transition metal composite hydroxide represented by the following general formula (1).
General formula (1): NixMnyCozMt(OH) _2+a ( _x + _y + _z + _t =1, 0.3≤x≤0.95, 0.05≤y≤0.55, 0≤z≤0.4 , 0 < t ≤ 0.1, 0 ≤ a ≤ 0.5, M is one or more additional elements selected from Nb, Mo, Ta, Ti, Zr, and W)

The preferable range of each element is the same as the preferable range of each element in the positive electrode active material 100 described later.

3. Positive Electrode Active Material for Lithium Ion Secondary Battery As shown in FIGS. It can be suitably used as a positive electrode material for secondary batteries.

Particles 20 (positive electrode active material 100) of lithium-transition metal composite oxide are composed of secondary particles 22 formed by aggregation of a plurality of primary particles 21 . Further, the secondary particles 22 each include an outer shell portion 24 and a hollow portion 23 arranged inside the outer shell portion 24 . Moreover, the average particle size of the positive electrode active material 100 is 1 μm or more and 15 μm or less.

The lithium-transition metal composite oxide particles 20 are mainly composed of secondary particles 22 , but may contain primary particles 21 alone. Details of the positive electrode active material 100 will be described below.

[Particle structure]
(Secondary particles)
As shown in FIG. 3A, the lithium-transition metal composite oxide particles 20 include an outer shell portion 24 and a hollow portion 23 inside the outer shell portion 24 and free of primary particles. As shown in FIG. 3B, the lithium-transition metal composite oxide particles 20 include secondary particles 22 formed by agglomeration of a plurality of primary particles 21 . In the positive electrode active material 100 having such a particle structure, the electrolytic solution penetrates through the grain boundaries or voids between the primary particles 21, and lithium is intercalated and deintercalated even at the reaction interface on the surface of the primary particles 21 on the side of the hollow portion 23 inside the particles. Since the input is performed, the movement of Li ions and electrons is not hindered, and the output characteristics can be improved.

(Outer shell)
The thickness of the outer shell portion 24 is preferably 5% or more and 45% or less, more preferably 8% or more and 38% or less, in terms of the ratio of the particle size of the secondary particles 22 . If the thickness ratio of the outer shell portion 24 is less than 5%, the strength of the secondary particles 22 is reduced, and the secondary particles 22 are destroyed when the powder is handled and when it is used as the positive electrode of the battery, resulting in fine particles. may occur and deteriorate the battery characteristics. On the other hand, when the thickness ratio of the outer shell portion 24 exceeds 45%, the grain boundaries or voids in which the electrolytic solution can enter the hollow portion 23 inside the secondary particles 22 are reduced, and the electrolytic solution that penetrates into the inside of the particles is reduced. Since the surface area that contributes to the battery reaction becomes smaller, the positive electrode resistance increases and the output characteristics may deteriorate. The ratio of the thickness of the outer shell portion 24 to the secondary particle diameter can be obtained in the same manner as for the outer peripheral portion 4 of the transition metal composite hydroxide particles 10 described above. The thickness (absolute value) of the outer shell portion 24 is, for example, in the range of 0.5 μm or more and 2.5 μm or less, and preferably in the range of 0.4 μm or more and 2.0 μm or less.

(Concentrated layer)
The positive electrode active material 100 has a concentrated layer C in which the additive element is concentrated on the surfaces of the primary particles 21 (see FIG. 3B). When the positive electrode active material 100 has the concentrated layer C, the effect of the additive element can be exhibited more efficiently. In particular, when an additive element that contributes to the improvement of output characteristics is contained, the resistance (internal resistance) inside the lithium-transition metal composite oxide particles 20 can be significantly reduced due to the interaction with the hollow structure. Therefore, when a secondary battery is constructed using this positive electrode active material 100, the output characteristics can be further improved without impairing the battery capacity and cycle characteristics.

The concentration of the additive element contained in the concentrated layer C is the ratio of the concentration of the additive element contained in the interior of the primary particles 21 (the portion other than the concentrated layer C) (the concentration of the additive element contained in the concentrated layer C/ The concentration of additive elements contained inside the primary particles 21) is preferably 2 or more, more preferably 5 or more. This makes it possible to further improve the effect of the additive element (eg, output characteristics). The concentration of the additive element on the surface of the primary particles 21 can be obtained by analyzing the composition from the surface to the inside of the primary particles 21 by cross-sectional observation with a transmission electron microscope (TEM) (eg, TEM- EDX analysis, see Examples). The concentrated layer C can be detected as a high-concentration peak on the surface side of the primary particles 21 from the concentration profile of the primary particles 21 of the additive element. Further, the concentration ratio of the additive element between the concentrated layer C and the inside of the primary particle 21 is the ratio of the highest concentration peak on the surface side in the primary particle 21 to the lowest concentration inside the concentrated layer C. can be obtained by

The additive element is mainly present on the surface side of the primary particles 21 to form the concentrated layer C, and the additive element is present in solid solution in the crystal of the lithium-transition metal composite oxide. may exist as fine particles of a compound of lithium and additional elements at grain boundaries.

[Average particle diameter]
The positive electrode active material 100 has an average particle size of 1 μm or more and 15 μm or less, preferably 3 μm or more and 12 μm or less, more preferably 3 μm or more and 10 μm or less. When the average particle size of the positive electrode active material 100 is within the above range, not only can the battery capacity per unit volume of the secondary battery using the positive electrode active material 100 be increased, but also thermal stability and output characteristics are improved. can do. On the other hand, when the average particle diameter of the positive electrode active material 100 is less than 1 μm, the filling property of the positive electrode active material is deteriorated, and the battery capacity per unit volume cannot be increased. Further, when the average particle size of the positive electrode active material 100 exceeds 15 μm, the reaction area of the positive electrode active material 100 is reduced, and the interface with the electrolyte is reduced, making it difficult to improve the output characteristics.

Note that the average particle size of the positive electrode active material 100 means the volume-based average particle size (MV), like the average particle size of the particles 10 of the transition metal composite hydroxide described above. It can be obtained from the volume integrated value measured with a type particle size analyzer.

[Particle size distribution]
[(d90-d10)/average particle diameter], which is an index showing the spread of the particle size distribution of the positive electrode active material 100, is not particularly limited, but is preferably 0.70 or less, more preferably 0.60 or less, and still more preferably 0.55 or less. When [(d90-d10)/average particle size] is within the above range, it indicates that the particles are composed of particles with an extremely narrow particle size distribution. Such a positive electrode active material 100 has a low ratio of fine particles and coarse particles, and a secondary battery using this has better thermal stability, cycle characteristics, and output characteristics.

On the other hand, when [(d90-d10)/average particle size] of the positive electrode active material 100 exceeds 0.70, the ratio of fine particles and coarse particles in the positive electrode active material 100 increases. For example, in a secondary battery using the positive electrode active material 100 with a high proportion of fine particles, the secondary battery tends to generate heat due to the local reaction of the fine particles, and not only does the thermal stability decrease, but also , the selective deterioration of fine particles may result in poor cycle characteristics. In addition, in a secondary battery using the positive electrode active material 100 with a large proportion of coarse particles, a sufficient reaction area between the electrolyte and the positive electrode active material cannot be ensured, and the output characteristics may be inferior. .

Assuming industrial-scale production, it is not realistic to use a material with an excessively small [(d90-d10)/average particle diameter] as the positive electrode active material 100 . Therefore, when considering cost and productivity, the lower limit of [(d90-d10)/average particle size] in the positive electrode active material 100 is preferably about 0.25.

Note that the meanings of d10 and d90 in [(d90-d10)/average particle diameter] and how to obtain them are the same as those of the transition metal composite hydroxide particles 10 described above, so the description here is omitted.

[composition]
The composition of the positive electrode active material 100 is not particularly limited as long as it has the structure described above. The positive electrode active material 100 may contain, for example, lithium, one or more metal elements selected from nickel, cobalt, and manganese, and additive elements other than these metal elements. Moreover, the positive electrode active material 100 may contain lithium, nickel, manganese, and additional elements, and may contain lithium, nickel, manganese, cobalt, and additional elements.

For example, the positive electrode active material 100 includes lithium (Li), nickel (Ni), manganese (Mn), an additional element (M), and optionally cobalt (Co), and the material amount ratio (molar ratio) is Li:Ni:Mn:Co:M=(1+u):x:y:z:t (−0.05≦u≦0.50, x+y+z+t=1, 0.3≦x≦0.95 , 0.05≦y≦0.55, 0≦z≦0.4, 0<t≦0.1, M is one or more selected from Nb, Mo, Ta, Ti, Zr, and W is preferably represented by the additional element). When the positive electrode active material 100 having such a composition is used, a secondary battery having higher output characteristics and cycle characteristics can be obtained.

In addition, the positive electrode active material 100 has a general formula (2): Li _1+u Ni _{x Mny} Co _z M _t O _2+b (−0.05≦u≦0.50, x+y+z+t=1, 0.3≦x≦0. 95, 0.05≦y≦0.55, 0≦z≦0.4, 0<t≦0.1, 0≦b≦0.5, M is Nb, Mo, Ta, Ti, Zr, and one or more additional elements selected from W).

In the molar ratio or the general formula (2), the value of u indicating the excess amount of lithium (Li) is preferably -0.05 or more and 0.50 or less, more preferably 0 or more and 0.50 or less, It is more preferably 0 or more and 0.35 or less. When the value of u is within the above range, it is possible to further improve the output characteristics and battery capacity of a secondary battery using the positive electrode active material 100 as a positive electrode material. On the other hand, when the value of u is less than -0.05, the positive electrode resistance of the secondary battery increases, and the output characteristics may not be improved. Moreover, when the value of u exceeds 0.50, the initial discharge capacity may decrease, or the positive electrode resistance may increase.

Nickel (Ni) is an element that contributes to increasing the potential and capacity of secondary batteries. In the molar ratio or the general formula (2), the value of x indicating the nickel content is preferably 0.3 or more and 0.95 or less, more preferably 0.3 or more and 0.9 or less. . When the value of x is less than 0.3, it becomes difficult to improve the secondary battery capacity using the positive electrode active material 100 . On the other hand, if the value of x exceeds 0.95, the content of other elements is reduced, so that effect cannot be obtained.

Manganese (Mn) is an element that contributes to improving thermal stability. In the molar ratio or the general formula (2), the value of y indicating the manganese content is preferably 0.05 or more and 0.55 or less, more preferably 0.10 or more and 0.40 or less. . When the value of y is less than 0.05, it becomes difficult to improve the thermal stability of the secondary battery using the positive electrode active material 100 . On the other hand, if the value of y exceeds 0.55, Mn may be eluted from the positive electrode active material 100 during operation at high temperatures, deteriorating charge-discharge cycle characteristics.

Cobalt (Co) is an element that contributes to the improvement of charge-discharge cycle characteristics. In the above molar ratio or the general formula (2), the value of z indicating the content of cobalt is preferably 0 or more and 0.4 or less, more preferably 0.10 or more and 0.35 or less. When the value of z exceeds 0.4, the initial discharge capacity of the secondary battery using the positive electrode active material 100 may be significantly reduced.

The positive electrode active material 100 contains additive elements in addition to the metal elements described above in order to further improve the battery characteristics. Examples of additive elements include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum (Mo ), hafnium (Hf), tantalum (Ta), lanthanum (La), and tungsten (W). Among these, one or more selected from Nb, Mo, Ta, Ti, Zr, and W is preferable as the additive element. When these additive elements are contained, battery characteristics (eg, durability, output characteristics, etc.) can be improved.

Among these, from the viewpoint of further improving the output characteristics, it is more preferable to contain one or more elements selected from Nb, Mo, Ta, Ti, Zr, and W. For example, additive elements containing W may include One type of additive element may be included, or two or more types may be included. Note that the additive element is preferably present in the concentrated layer C formed on the surface of the primary particles 21 .

In the molar ratio or the general formula (2), the value of t indicating the content of the additive element M is preferably greater than 0 and 0.1 or less, more preferably 0.001 or more and 0.05 or less. be. On the other hand, if the value of t exceeds 0.1, the metal elements that contribute to the Redox reaction decrease, resulting in a decrease in battery capacity.

In order to further improve the battery capacity of a secondary battery using the positive electrode active material 100, the composition is represented by the general formula (3): Li _1+u Ni _{x Mny} Co _{z Mt} O ₂ ( −0.05≦u≦0.20, x+y+z+t=1, 0.7<x≦0.95, 0.05≦y≦0.1, 0≦z≦0.2, 0<t≦0.1 , M are one or more additive elements selected from Nb, Mo, Ta, Ti, Zr, and W). In particular, in order to achieve both thermal stability, the value of x in general formula (3) is more preferably 0.7<x≦0.9, and 0.7<x≦0.85. It is more preferable that

Further, in order to further improve the thermal stability of the positive electrode active material 100, the composition thereof is represented by the general formula (4): Li _1+u Ni _{x Mny} Co _z M _t O ₂ (−0.05≦u≦ 0.50, x + y + z + t = 1, 0.3 ≤ x ≤ 0.7, 0.1 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 < t ≤ 0.1, M is Nb, Mo , Ta, Ti, Zr, and one or more additive elements selected from W).

[Specific surface area]
Further, the positive electrode active material 100 preferably has a specific surface area of 0.7 m ² /g or more and 5.0 m ² /g or less, and is 1.8 m ² /g or more and 5.0 m ² /g or less. is more preferable. When the specific surface area of the positive electrode active material 100 is within the above range, the contact area with the electrolyte is large, and the output characteristics of the secondary battery using this can be greatly improved. On the other hand, when the specific surface area of the positive electrode active material is less than 0.7 m ² /g, the reaction area with the electrolyte cannot be secured when the secondary battery is configured, and the output characteristics are sufficiently obtained. It becomes difficult to improve On the other hand, when the specific surface area of the positive electrode active material exceeds 5.0 m ² /g, the reactivity with the electrolytic solution becomes too high, and the thermal stability may decrease.

The specific surface area of the positive electrode active material 100 can be measured, for example, by the BET method using nitrogen gas adsorption.

[Tap density]
2. Description of the Related Art In recent years, in order to extend the usage time of portable electronic devices and the traveling distance of electric vehicles, there is a demand for higher capacity secondary batteries. On the other hand, the thickness of the electrode of the secondary battery is required to be about several microns from the viewpoint of the packing and electronic conductivity of the battery as a whole. Therefore, the positive electrode active material is required to have a high capacity and a high filling property, thereby increasing the capacity of the secondary battery as a whole. From this point of view, the positive electrode active material 100 preferably has a tap density of 1.0 g/cm ³ or more, more preferably 1.3 g/cm ³ or more, which is an index of fillability. If the tap density is less than 1.0 g/cm ³ , the fillability may be low, and the overall battery capacity of the secondary battery may not be sufficiently improved. On the other hand, the upper limit of the tap density is not particularly limited, but the upper limit under normal manufacturing conditions is about 3.0 g/cm ³ .

The tap density indicates the bulk density after tapping a sample powder collected in a container 100 times based on JIS Z-2504, and can be measured using a shaking specific gravity meter.

The manufacturing method of the positive electrode active material 100 is not particularly limited as long as it has the above specific structure, average particle diameter, etc., but it can be easily obtained by the manufacturing method described below.

4. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery FIGS. 7 and 8 are diagrams showing an example of production of the positive electrode active material 100 according to the present embodiment. The manufacturing method according to the present embodiment is a method for manufacturing the positive electrode active material 100 for a lithium ion secondary battery, and as shown in FIG. and a mixing step (step S40) of forming a lithium mixture, and a firing step (step S50) of firing the lithium mixture at 650° C. or higher and 980° C. or lower in an oxidizing atmosphere. According to such a manufacturing method, the positive electrode active material 100 described above can be easily obtained.

As shown in FIG. 8, if necessary, a heat treatment step (step S35), a calcining step (step S45), a crushing step (step S55), or the like may be added to the above-described steps. . Each step will be described below.

[Heat Treatment Step (Step S35)]
In the method for manufacturing the positive electrode active material 100 according to this embodiment, a heat treatment step (step S35) may be provided before the mixing step (step S40). In this step (step S35), the transition metal composite hydroxide particles 10 are heat-treated to obtain heat-treated particles. Here, the particles after the heat treatment are the particles 10 of the transition metal composite hydroxide from which at least part of the excess moisture has been removed, and the particles of the transition metal composite oxide converted to the oxide by the heat treatment step (step S35). , or mixtures thereof.

In the heat treatment step (step S35), excess moisture contained in the transition metal composite hydroxide particles 10 is removed by heating the transition metal composite hydroxide particles 10 for heat treatment. As a result, the amount of water remaining until after the baking step (step S50) can be reduced to a certain amount, and variations in the composition of the obtained positive electrode active material 100 can be suppressed.

The heating temperature in the heat treatment step is preferably 105°C or higher and 750°C or lower. If the heating temperature is lower than 105° C., excess moisture in the particles 10 of the transition metal composite hydroxide cannot be removed, and variations may not be sufficiently suppressed. On the other hand, if the heating temperature exceeds 700° C., no further effect can be expected, and the production cost may increase.

In the heat treatment step (step S35), the number of atoms of each metal component in the obtained positive electrode active material 100 and the number of atoms of Li may be removed to the extent that there is no variation in the number of atoms. It is not necessary to convert the metal composite hydroxide particles 10 into transition metal composite oxide particles. However, in order to reduce the variation in the number of atoms of each metal component and the ratio of the number of Li atoms, all the particles 10 of the transition metal composite hydroxide are heated to 400° C. or higher to remove the transition metal Conversion to composite oxide particles is preferred.

It should be noted that the above-described variation can be further suppressed by determining the metal components contained in the particles 10 of the transition metal composite hydroxide according to the heat treatment conditions in advance by analysis and determining the mixing ratio with the lithium compound. can be done.

The atmosphere of the heat treatment is not particularly limited, and may be a non-reducing atmosphere, but it is preferable to perform the heat treatment in an air stream, which can be easily performed.

In addition, the heat treatment time is not particularly limited, but from the viewpoint of sufficiently removing excess moisture in the transition metal composite hydroxide particles 10, it is preferably at least 1 hour, and 5 hours or more and 15 hours or less. is more preferred.

[Mixing step (step S40)]
In the mixing step (step S40), the transition metal composite hydroxide particles 10 or the heat-treated particles (hereinafter collectively referred to as "precursor particles") are mixed with a lithium compound. to obtain a lithium mixture.

In the mixing step (step S40), the sum of the number of metal atoms other than lithium in the lithium mixture, such as nickel, cobalt, manganese, and the additive element M (N _Me ), and the number of lithium atoms (N _Li ) ratio (N _Li /N _Me ) is 0.95 or more and 1.5 or less, preferably 1.0 or more and 1.5 or less, more preferably 1.0 or more and 1.35 or less, further preferably 1.0 or more The precursor particles and the lithium compound are mixed so that the ratio is 1.2 or less. That is, since N _Li /N _Me does not change before and after the firing step (step S50), N Li /N _Me in the mixing step (step S40) is _adjusted to N _Li /N _Me of the desired positive electrode active material. First, it is necessary to mix the precursor particles with the lithium compound.

Although the lithium compound used in the mixing step (step S40) is not particularly limited, it is preferable to use lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture of these in terms of availability. In particular, considering ease of handling and stability of quality, it is preferable to use lithium hydroxide or lithium carbonate.

It is preferable that the precursor particles and the lithium compound are sufficiently mixed to the extent that fine powder is not generated. Insufficient mixing may result in variations in N _Li /N _Me between individual particles, making it impossible to obtain sufficient battery characteristics. In addition, a general mixer can be used for mixing. As a mixer, a shaker mixer, a Loedige mixer, a Julia mixer, a V blender, or the like can be used.

[Temporary Firing Step (Step S45)]
When lithium hydroxide or lithium carbonate is used as the lithium compound, as shown in FIG. good too.

The calcining step (step S45) is a step of calcining the lithium mixture at a temperature lower than the calcining temperature in the calcining step (step S50), and at a temperature of 350° C. or higher and 800° C. or lower, preferably 450° C. or higher and 780° C. or lower. . When the calcination step (step S45) is provided, lithium can be sufficiently diffused in the precursor particles, and finally, more uniform lithium-transition metal composite oxide particles 20 can be obtained.

The holding time at the calcination temperature is preferably 1 hour or more and 10 hours or less, and preferably 3 hours or more and 6 hours or less. In addition, the atmosphere in the calcining step (step S45) is preferably an oxidizing atmosphere, similar to the later-described firing step (step S50), and the atmosphere should have an oxygen concentration of 18% by volume or more and 100% by volume or less. is more preferred.

[Baking step (step S50)]
The firing step (step S50) is a step of firing the lithium mixture at 650° C. or higher and 980° C. or lower in an oxidizing atmosphere. By firing the lithium mixture, lithium is diffused into the precursor particles to obtain particles 20 (positive electrode active material 100) of lithium-transition metal composite oxide.

In the firing step (step S50), the primary particles 1 present in the central portion 3 and the outer peripheral portion 4 of the precursor particles (transition metal composite hydroxide particles 10) undergo sintering shrinkage while the primary particles in the positive electrode active material 100 Particles 21 are formed. Since the central portion 3 is composed of the fine primary particles 1a, sintering starts at a lower temperature than the peripheral portion 4 composed of the larger plate-like primary particles 1b. Furthermore, the central portion 3 has a larger amount of contraction than the outer peripheral portion 4 . For this reason, the fine primary particles 1a forming the central portion 3 shrink toward the outer peripheral portion 4, where sintering progresses slowly, and a hollow portion 23 having a space of an appropriate size is formed. Further, the outer peripheral portion 4 absorbs the fine primary particles 1a while shrinking during sintering to form the outer shell portion 24 . As a result, the internal resistance of the positive electrode active material 100 is significantly reduced, and when a secondary battery is constructed, it becomes possible to improve the output characteristics without impairing the battery capacity and cycle characteristics.

The particle structure of the positive electrode active material 100 is basically determined according to the particle structure of the transition metal composite hydroxide particles 10 as a precursor, but may be affected by the composition, firing conditions, and the like. Therefore, it is preferable to adjust each condition appropriately so as to obtain a desired structure after performing a preliminary test.

The furnace used in the firing step (step S50) is not particularly limited as long as it can heat the lithium mixture in the atmosphere or in an oxygen stream. However, from the viewpoint of maintaining a uniform atmosphere in the furnace, an electric furnace that does not generate gas is preferable, and either a batch type or a continuous type electric furnace can be suitably used. The same applies to the furnace used in the heat treatment step (step S35) and the calcining step (step S45).

(firing temperature)
The baking temperature in the baking step (step S50) is 650° C. or higher and 980° C. or lower. If the firing temperature is less than 650° C., lithium does not sufficiently diffuse into the precursor particles, leaving excess lithium or unreacted precursor particles, or causing the resulting lithium-transition metal composite oxide particles 20 to deteriorate. Crystallinity may be insufficient. On the other hand, if the firing temperature exceeds 980° C., the particles 20 of the lithium-transition metal composite oxide are violently sintered, causing abnormal grain growth and increasing the proportion of irregularly shaped coarse particles.

In addition, when trying to obtain the positive electrode active material 100 represented by the general formula (4) described above, the firing temperature is preferably 650° C. or higher and 900° C. or lower. On the other hand, when trying to obtain the positive electrode active material represented by the general formula (5), the firing temperature is preferably 800° C. or higher and 980° C. or lower.

In addition, the heating rate in the firing step (step S50) is preferably 2° C./min or more and 10° C./min or less, more preferably 5° C./min or more and 10° C./min or less. Furthermore, during the firing step (step S50), before heating to the above firing temperature, at a temperature near the melting point of the lithium compound (eg, about ±50 ° C. of the melting point), preferably for 1 hour or more and 5 hours or less, more preferably is preferably held for 2 hours or more and 5 hours or less. Thereby, the precursor particles and the lithium compound can be reacted more uniformly. For example, when the lithium compound is lithium hydroxide (melting point: 462° C.), it is preferable to maintain the temperature at around the melting point of 400° C. to 500° C. before raising the temperature to the firing temperature during the firing step (step S50). .

(Baking time)
Of the firing time, the holding time at the firing temperature described above is preferably at least 2 hours or more, more preferably 4 hours or more and 24 hours or less. If the holding time at the firing temperature is less than 2 hours, lithium does not sufficiently diffuse into the precursor particles, leaving excess lithium or unreacted precursor particles, or resulting in a lithium-transition metal composite oxide. The crystallinity of the particles 20 may become insufficient.

After the holding time is over, the cooling rate from the firing temperature to at least 200° C. is preferably 2° C./min or more and 10° C./min or less, more preferably 3° C./min or more and 7° C./min or less. preferable. When the cooling rate is controlled within such a range, it is possible to prevent equipment such as a sagger from being damaged by rapid cooling while ensuring productivity.

(firing atmosphere)
The atmosphere during firing is preferably an oxidizing atmosphere, more preferably an atmosphere with an oxygen concentration of 18% by volume or more and 100% by volume or less, and a mixed atmosphere of oxygen having the above oxygen concentration and an inert gas. is particularly preferred. That is, the calcination is preferably carried out in the atmosphere or in an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium-transition metal composite oxide particles 20 may be insufficient.

[Crushing step (step S55)]
After the firing step (step S50), a crushing step (step S55) of crushing the aggregates or sintered bodies of the lithium-transition metal composite oxide particles 10 may be provided. The lithium-transition metal composite oxide particles 10 (positive electrode active material 100) obtained after the firing step (step S50) may be aggregated or slightly sintered. When the pulverization step (step S55) is provided, the average particle size and particle size distribution of the obtained positive electrode active material 100 can be adjusted to a suitable range. In addition, crushing refers to applying mechanical energy to aggregates composed of multiple secondary particles generated by sintering necking between secondary particles during firing, and almost without destroying the secondary particles themselves. It means the operation of separating and loosening aggregates.

As a crushing method, known means can be used, for example, a pin mill or a hammer mill can be used. At this time, it is preferable to adjust the crushing force to an appropriate range so as not to destroy the secondary particles.

3. Lithium Ion Secondary Battery A lithium ion secondary battery (hereinafter also referred to as a “secondary battery”) according to the present embodiment includes a positive electrode containing the positive electrode active material 100 described above, a negative electrode, and a non-aqueous electrolyte. A secondary battery includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. A secondary battery may also include, for example, a positive electrode, a negative electrode, and a solid electrolyte. In addition, the secondary battery may be a secondary battery that charges and discharges by desorption and insertion of lithium ions. For example, it may be a non-aqueous electrolyte secondary battery, or an all-solid lithium secondary battery. There may be. Note that the embodiments described below are merely examples, and the secondary battery according to the present embodiment is applied to various modifications and improvements based on the embodiments described herein. may

[Components]
(positive electrode)
First, the positive electrode active material 100, a conductive material, and a binder are mixed, and if necessary, activated carbon and a solvent for viscosity adjustment are added, and the mixture is kneaded to prepare a positive electrode mixture paste. . At that time, the mixing ratio of each component in the positive electrode mixture paste can be appropriately adjusted according to the intended performance of the secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass or more and 95 parts by mass or less, and the content of the conductive material is 1 part by mass or more and 20 parts by mass or less. and the content of the binder may be 1 part by mass or more and 20 parts by mass or less.

As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black can be used.

The binder plays a role of binding the active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin and polyacrylic. Acids can be used.

If necessary, the positive electrode active material, the conductive material, and the activated carbon may be dispersed, and a solvent that dissolves the binder may be added to the positive electrode mixture. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon may be added to the positive electrode mixture in order to increase the electric double layer capacity.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil, and dried to scatter the solvent. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. Thus, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size depending on the intended battery, and used for manufacturing the battery. The method for producing the positive electrode is not limited to the method described above, and other methods may be used.

(negative electrode)
Metallic lithium, a lithium alloy, or the like may be used as the negative electrode. In addition, as a negative electrode, a negative electrode active material capable of intercalating and deintercalating lithium ions is mixed with a binder, and an appropriate solvent is added to form a paste. It may be applied to the surface, dried, and compressed to increase the electrode density as necessary.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the binder for the negative electrode in the same manner as the binder for the positive electrode. Solvents can be used.

(separator)
Between the positive electrode and the negative electrode, a separator is interposed and arranged as necessary. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and may be a thin film of polyethylene, polypropylene, or the like, having a large number of minute pores.

(Non-aqueous electrolyte)
A non-aqueous electrolytic solution can be used as the non-aqueous electrolyte. The non-aqueous electrolytic solution may be, for example, one obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Further, as the non-aqueous electrolytic solution, an ionic liquid in which a lithium salt is dissolved may be used. The ionic liquid refers to a salt composed of cations and anions other than lithium ions and exhibiting a liquid state even at room temperature.

Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more may be mixed. can be used as

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , composite salts thereof, and the like can be used. Furthermore, the non-aqueous electrolytic solution may contain radical scavengers, surfactants, flame retardants, and the like.

A solid electrolyte may be used as the non-aqueous electrolyte. Solid electrolytes have the property of withstanding high voltages. Solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

As the inorganic solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or the like is used.

The oxide-based solid electrolyte is not particularly limited, and can be used as long as it contains oxygen (O) and has lithium ion conductivity and electronic insulation. Examples of oxide-based solid electrolytes include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li ₃ PO4, _{Li4SiO4 - Li3VO4} , Li2O _{- B2O3 - P2O5 ,} Li2O _{- SiO2} , Li2O _{- B2O3 -} ZnO, _{Li1 + X AlXTi 2-X} (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ (0≦X≦1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2/ 3-X} TiO ₃ (0≦X≦2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ and the like.

The sulfide-based solid electrolyte is not particularly limited, and any solid electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Li ₂ SP ₂ S ₅ , LiI—Li ₂ S—B ₂ S ₃ , Li ₃ PO ₄ —Li ₂ S—Si ₂ S, Li ₃ PO ₄ —Li ₂ S—SiS ₂ , LiPO ₄ —Li ₂ S—SiS, LiI—Li ₂ S—P ₂ O ₅ , LiI—Li ₃ PO ₄ —P ₂ S ₅ and the like.

Inorganic solid electrolytes other than those described above may be used, such as Li ₃ N, LiI, Li ₃ N--LiI--LiOH, and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, and the like can be used. Moreover, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may also be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(Battery shape and configuration)
The configuration of the secondary battery is not particularly limited, and may be composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, etc. as described above, or may be composed of a positive electrode, a negative electrode, a solid electrolyte, etc. Moreover, the shape of the secondary battery is not particularly limited, and various shapes such as a cylindrical shape and a laminated shape can be used.

For example, when the secondary battery is a non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte, and the positive electrode collection is performed. A current collecting lead or the like is used to connect between a current collector and a positive electrode terminal that communicates with the outside, and between a negative electrode current collector and a negative electrode terminal that communicates with the outside, and the secondary battery is sealed in a battery case. complete the

(3) Characteristics of Lithium-Ion Secondary Battery Since the lithium-ion secondary battery according to the present embodiment uses the positive electrode active material 100 as a positive electrode material, as described above, the effect of the additive element is more efficient than before. It is possible to express it in the battery, and the battery characteristics (eg, battery capacity, output characteristics, cycle characteristics, etc.) are excellent.

(4) Applications The secondary battery according to the present embodiment has excellent battery characteristics as described above, and small portable electronic devices (notebook personal computers, mobile phones, etc.) that require these characteristics at a high level. can be suitably used as a power supply for In addition, when an additive element effective for thermal stability is contained, an expensive protection circuit can be simplified, so that it can be suitably used as a power supply for transportation equipment that is limited in mounting space.

The present invention will be described in detail below using examples and comparative examples. In the following examples and comparative examples, reagent special grade samples manufactured by Wako Pure Chemical Industries, Ltd. were used to prepare transition metal composite hydroxide particles and positive electrode active materials, unless otherwise specified. In addition, throughout the nucleation step and the particle growth step, the pH value of the reaction aqueous solution is measured by a pH controller (Nisshin Rika NPH-690D), and based on this measured value, the supply amount of the sodium hydroxide aqueous solution is adjusted. Thus, the variation range of the pH value of the reaction aqueous solution in each step was controlled within a range of ±0.2.

(Example 1)
[Production of particles of transition metal composite hydroxide]
(Nucleation step)
First, the temperature in the tank was set to 40° C. while half the amount of water was put into the reaction tank (34 L) and stirred. At this time, the inside of the reaction tank was set to an air atmosphere (oxygen concentration: 21% by volume). Appropriate amounts of 25% by mass aqueous sodium hydroxide solution and 25% by mass aqueous ammonia are added to the water in the reaction tank to adjust the pH value of the reaction solution in the tank to 13.0 at a liquid temperature of 25°C. did. Further, the concentration of ammonia in the reaction solution was adjusted to 10 g/L to prepare an aqueous pre-reaction solution.

At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were mixed with water so that the molar ratio of each metal element was Ni:Mn:Co:Zr=33.1:33.1:33.1:0.2. to prepare a 1.8 mol/L raw material aqueous solution.

This raw material aqueous solution was added to the pre-reaction aqueous solution in the reaction vessel at a rate of 88 ml/min to obtain a reaction aqueous solution (aqueous solution for nucleation). At the same time, 25% by mass ammonia water and 25% by mass aqueous sodium hydroxide solution were also added to this aqueous reaction solution at a constant rate, and the pH value was adjusted to 13.0 ( Nucleation was performed by crystallization for 2 minutes and 30 seconds while controlling the nucleation pH value).

(Particle growth step)
(i) First particle growth step After nucleation is completed, the supply of all the aqueous solution is temporarily stopped, and sulfuric acid is added to adjust the pH value to 11.6 based on the liquid temperature of 25°C. to form a reaction aqueous solution (aqueous solution for particle growth). The raw material aqueous solution and the 25% by mass aqueous sodium hydroxide solution were again supplied to the reaction aqueous solution, and the sodium tungstate aqueous solution was additionally supplied as the raw material aqueous solution containing the additive element (W). was maintained at the above value (10 g/L), and the pH value was maintained at the above value (11.6), crystallization was continued, and grain growth (first grain growth step) was performed for 30 minutes. The concentration and flow rate of the sodium tungstate aqueous solution were adjusted so as to match the finally obtained composition.

(ii) Second particle growth step After the first particle growth step, the liquid supply is temporarily stopped, and nitrogen gas is supplied until the oxygen concentration in the space inside the reaction vessel becomes a non-oxidizing atmosphere of 0.2% by volume or less. The flow rate was 5 L/min (reaction atmosphere switching). After that, the supply of only the raw material aqueous solution not containing the additive element (W) was restarted (after 12.5% of the entire grain growth time had elapsed), and the ammonia concentration and pH value were maintained and the growth was started. In addition, crystallization was performed for 2 hours.

When the inside of the reactor became full, the crystallization was stopped, and the stirring was stopped and the mixture was allowed to stand, thereby facilitating the precipitation of the product. After that, half of the supernatant liquid was extracted from the reaction vessel, crystallization was restarted, and after 2 hours of crystallization (total of 4 hours), the crystallization was terminated.

(washing, filtration, drying)
Then, the product was washed with water, filtered and dried to obtain particles of transition metal composite hydroxide. It should be noted that the switching from the air atmosphere to the nitrogen atmosphere was performed at a time point of 12.5% of the entire grain growth process time from the start of the grain growth process.

In the above crystallization, the pH was controlled by adjusting the supply flow rate of the aqueous sodium hydroxide solution using a pH controller, and the variation range was within the range of 0.2 above and below the set value.

[Analysis of transition metal composite hydroxide particles]
A sample of the obtained particles of the transition metal composite hydroxide was dissolved in an inorganic acid and then chemically analyzed by _{ICP emission} spectroscopy _{. 33} 1Zr _0.002 W _0.005 (OH) _2+a (0≦a≦0.5).

In addition, for the particles of this transition metal composite hydroxide, the value [(d90-d10)/average particle size] indicating the average particle size and particle size distribution was measured by a laser diffraction scattering type particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., Micro It was obtained by calculating from the volume integrated value measured using the track HRA). As a result, the average particle diameter was 5.2 μm, and the [(d90−d10)/average particle diameter] value was 0.48.

Next, when the particles of the obtained transition metal composite hydroxide were observed by SEM (scanning electron microscope S-4700 manufactured by Hitachi High-Technologies Corporation) (magnification: 1000 times), this transition metal composite hydroxide It was confirmed that the particles of the material were substantially spherical and had a substantially uniform particle size.

In addition, a sample of the particles of the obtained transition metal composite hydroxide was embedded in a resin and subjected to cross-section polisher processing. The composite hydroxide particles are composed of secondary particles, and the secondary particles are composed of needle-like and flake-like fine primary particles (particle size of about 0.3 μm) in the center and outside the center. It was confirmed that the outer peripheral portion was composed of plate-like primary particles (particle diameter of about 0.6 μm) larger than the fine primary particles. The thickness of the outer peripheral portion with respect to the diameter of the secondary particles was 12%, as determined from the SEM observation of the cross section. In addition, it was confirmed from the concentration profile of tungsten (W) obtained by EDX analysis of the cross section of the particle using TEM that tungsten (W) was mainly present in the central part.

[Production of positive electrode active material]
(Heat treatment process)
The particles of the transition metal composite oxide were heat-treated at 700° C. for 6 hours in an air stream (oxygen: 21% by volume) to convert them into particles of the transition metal composite oxide and recover them.

(lithium mixing process)
Lithium hydroxide was weighed so that N _Li /N _Me =1.12, and mixed with the composite oxide particles to prepare a lithium mixture. Mixing was performed using a shaker-mixer device (TURBULA Type T2C manufactured by Willie & Bachoffen (WAB)).

(Baking process)
The resulting lithium mixture was calcined at 500° C. for 4 hours in the air (oxygen: 21% by volume), then calcined at 950° C. for 4 hours, cooled, and then pulverized to obtain a positive electrode active material. .

[Analysis of positive electrode active material]
The particle size distribution of the obtained positive electrode active material was measured in the same manner as the transition metal composite hydroxide particles, and the average particle size was 4.7 μm, and the [(d90−d10)/average particle size] value was 0.48.

In addition, SEM observation and cross-sectional SEM observation of the positive electrode active material were performed in the same manner as the transition metal composite hydroxide particles. It was confirmed that they were aligned. On the other hand, through cross-sectional SEM observation, it was confirmed that this positive electrode active material had a hollow structure including an outer shell portion formed by sintering primary particles and a hollow portion inside the outer shell portion. The ratio of the thickness of the outer shell to the particle size of the positive electrode active material obtained from this observation was 11%.

Furthermore, EDX (TEM-EDX) analysis of the cross section of the particles of the positive electrode active material was performed using a TEM. The results are shown in FIGS. 11(A) to 11(C). FIG. 11(A) is a diagram schematically showing a cross section of a part of the outer shell portion of the secondary particles of the positive electrode active material subjected to TEM-EDX analysis, and FIG. 11(B) is a TEM observation image. FIG. 11C is a photograph of a TEM-EDX image. As shown in FIGS. 11A to 11C, from the tungsten (W) concentration profile obtained by TEM-EDX analysis, the W concentration is around 0.1 μm from the surface in the primary particle toward the inside of the particle. A high peak was identified (enriched layer). It was also confirmed that the ratio of the concentration of this peak to the minimum concentration inside the thickened layer (peak concentration/minimum concentration inside) in the analyzed primary particles was 5 or more.

For the obtained positive electrode active material, the specific surface area was measured by a flow-type gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multisorb), and the tap density was measured by a tapping machine (Kuramochi Scientific Instruments Manufacturing Co., Ltd., KRS-406). , respectively, were measured. As a result, it was confirmed that the specific surface area was 1.5 m ² /g and the tap density was 1.31 g/cm ³ .

Further, when the obtained positive electrode active material was analyzed by powder X-ray diffraction using Cu—Kα rays using an X-ray diffractometer (manufactured by PANalytical, X'Pert PRO), the crystal structure of the positive electrode active material was was confirmed to consist of a single phase of hexagonal layered crystal lithium-nickel-manganese composite oxide.

Furthermore, according to analysis using an ICP emission spectrometer, this positive electrode active material is represented by the general formula: Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ It was confirmed that

[Manufacture of coin-type battery and evaluation of battery characteristics]
52.5 mg of the positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm, and the positive electrode PE shown in FIG. (Evaluation electrode) was produced. The produced positive electrode PE was dried in a vacuum dryer at 120° C. for 12 hours. Then, using this positive electrode PE, a 2032-type coin-type battery CBA was produced in an Ar atmosphere glove box in which the dew point was controlled at -80°C.

For the negative electrode NE, a negative electrode sheet in which graphite powder with an average particle size of about 20 μm and polyvinylidene fluoride, which are punched into a disk shape with a diameter of ₁₄ mm, and polyvinylidene fluoride are coated on a copper foil is used. A mixture of equal amounts of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Tomiyama Pharmaceutical Co., Ltd.) was used. A polyethylene porous film having a film thickness of 25 μm was used as the separator 3 . Also, the coin-type battery CBA has a gasket GA and a wave washer WW, and is assembled into a coin-shaped battery with a positive electrode can PC and a negative electrode can NC. The initial discharge capacity and positive electrode resistance, which indicate the performance of the manufactured coin-type battery CBA, were evaluated as follows.

[Initial discharge capacity]
For the initial discharge capacity, the coin-type battery CBA was left for about 24 hours after production, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was 0.1 mA / cm ² and the cutoff voltage was 4. The battery was charged to 3 V, rested for 1 hour, and then discharged to a cut-off voltage of 3.0 V. The capacity was taken as the initial discharge capacity.

[Positive resistance]
In addition, the positive electrode resistance was measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B) after charging the coin-type battery CBA at 25° C. with a charging potential of 4.1 V. A Nyquist plot shown in is obtained. Since this Nyquist plot is expressed as the sum of characteristic curves showing the solution resistance, the negative electrode resistance and its capacity, and the positive electrode resistance and its capacity, a fitting calculation is performed using an equivalent circuit based on this Nyquist plot, and the positive electrode resistance was calculated.

Table 1 shows the properties of the particles of the transition metal composite hydroxide obtained in this example, and Table 2 shows the properties of the positive electrode active material and evaluation of the coin-type battery CBA produced using this positive electrode active material. show. In addition, Tables 1 and 2 show the same contents for Examples 2 to 5 and Comparative Example 1 below.

(Example 2)
In the second grain growth step, the flow rate of the sodium tungstate aqueous solution is adjusted so that the concentration of tungsten in the non-oxidizing atmosphere is 20% with respect to the concentration of the additive element (tungsten) in the raw material aqueous solution in the oxidizing atmosphere. A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1 except that the positive electrode active material was obtained. _It was _confirmed that the composition of the obtained positive electrode active _{material was represented by Li1.12Ni0.331Mn0.331Co0.331Zr0.002W0.005O2 .}

(Example 3)
In the grain growth step, the same procedure as in Example 1 was performed, except that the reaction atmosphere was switched from the air atmosphere to the nitrogen atmosphere when 6.25% of the entire grain growth time had elapsed. , a positive electrode active material, etc., were obtained and evaluated. The compositions of the obtained transition metal composite hydroxide particles and the positive electrode active material are the same as in Example 1, and the transition metal composite hydroxide particles are needle-like fine primary particles as in Example 1. (particle diameter of approximately 0.2 μm) and an outer peripheral portion consisting of plate-like primary particles (particle diameter of 0.8 μm) larger than the fine primary particles outside the central portion.

(Example 4)
In the grain growth step, sodium tungstate is added so that the concentration (addition ratio) of the additive element (W) in the non-oxidizing atmosphere is 10% with respect to the concentration of the additive element (W) in the raw material aqueous solution in the oxidizing atmosphere. A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that the flow rate of the aqueous solution was adjusted. _It was _confirmed that the composition of the obtained positive electrode active _{material was represented by Li1.12Ni0.331Mn0.331Co0.331Zr0.002W0.005O2 .}

(Example 5)
Same as Example 1, except that in the grain growth step, the sodium tungstate aqueous solution was adjusted to the same amount as the flow rate in the oxidizing atmosphere when 50% of the entire grain growth time elapsed. Then, a positive electrode active material and the like were obtained and evaluated. _It was _confirmed that the composition of the obtained positive electrode active _{material was represented by Li1.12Ni0.331Mn0.331Co0.331Zr0.002W0.005O2 .}

(Comparative example 1)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that a constant amount of the sodium tungstate aqueous solution was supplied during the entire grain growth process, that is, the M addition ratio was set to 100%. . _It was _confirmed that the composition of the obtained positive electrode active _{material was represented by Li1.12Ni0.331Mn0.331Co0.331Zr0.002W0.005O2 .}

(evaluation)
The transition metal composite hydroxide particles of Examples 1 to 5 have a structure consisting of a central portion composed of fine primary particles and an outer peripheral portion composed of plate-like primary particles. Moreover, it was confirmed that the central portion contained an additive element. In addition, the positive electrode active materials of Examples 1 to 5 have a structure consisting of an outer shell portion in which aggregated primary particles are sintered and a hollow portion inside thereof, and a concentrated layer of additive elements on the surface of the primary particles. have. The coin-type battery CBA using these positive electrode active materials had a high initial discharge capacity and a low positive electrode resistance, demonstrating excellent battery characteristics.

Reference Signs List 1 Primary particles 1a Fine primary particles 1b Plate-like primary particles 2 Secondary particles 3 Central portion 4 Peripheral portion 4a Layer containing high-concentration additive element (peripheral portion)
5... Coating layer 10... Particles of transition metal composite hydroxide 20... Particles of lithium transition metal composite oxide 21... Primary particles (positive electrode active material)
22 Secondary particles (positive electrode active material)
23 Hollow portion 24 Outer shell portion 100 Positive electrode active material t Thickness of outer peripheral portion C Concentrated layer CBA Coin battery PE Positive electrode (evaluation electrode)
NE... Negative electrode SE... Separator GA... Gasket WW... Wave washer PC... Positive electrode can NC... Negative electrode can

Claims (9)

Particles of a transition metal composite hydroxide containing a transition metal and an additive element having an uneven distribution within the particle,
including secondary particles formed by aggregation of a plurality of primary particles,
The secondary particles are
a center portion disposed at a site including the center of the secondary particles and formed by aggregation of a plurality of fine primary particles;
an outer peripheral portion disposed outside the central portion and formed by aggregation of plate-shaped primary particles that are larger than the fine primary particles;
The additive element is contained at a higher concentration in the fine primary particles in the central portion than in the plate-like primary particles in the outer peripheral portion,
The average particle size is 1 μm or more and 15 μm or less,
Particles of transition metal composite hydroxide. Nickel (Ni), manganese (Mn), the additive element (M), and cobalt (Co) are included, and the material amount ratio (molar ratio) of each element is Ni:Mn:Co:M = x: y: z: t (x + y + z + t = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 < t ≤ 0.1, M is one or more additional elements selected from Nb, Mo, Ta, Ti, Zr, and W), the transition metal composite hydroxide particles according to claim 1. 3. The particles of transition metal composite hydroxide according to claim 1, having a coating layer on the surface of said secondary particles, said coating layer containing said compound containing said additive element. The outer peripheral portion includes a region containing the additive element in a range of 50% or more and 80% or less with respect to the thickness of the outer peripheral portion from the surface to the inside of the particle, and a region other than the additive element. 3. The transition metal composite hydroxide particles according to claim 1 or 2, comprising: A positive electrode active material containing particles of a lithium-transition metal composite oxide containing lithium, a transition metal, and an additive element other than the transition metal,
including secondary particles formed by aggregation of a plurality of primary particles,
The secondary particles have an outer shell and a hollow inside the outer shell,
The hollow portion does not contain the primary particles,
The secondary particles have an average particle size of 1 μm or more and 15 μm or less, and have a concentrated layer in which the additive element is concentrated on the surface of the primary particles.
Positive electrode active material for lithium ion secondary batteries. 6. The positive electrode active material for a lithium ion secondary battery according to claim 5, wherein the ratio of the concentration of the additive element contained in the concentrated layer to the concentration inside the primary particles is 5 or more. The cathode active material for a lithium ion secondary battery according to claim 5 or 6, having a BET specific surface area of 0.7 m ² /g or more and 5.0 m ² /g or less. The lithium-transition metal composite oxide particles contain lithium (Li), nickel (Ni), manganese (Mn), an additional element (M), and optionally cobalt (Co), and each element The amount ratio (molar ratio) of Li: Ni: Mn: Co: M = (1 + u): x: y: z: t (-0.05 ≤ u ≤ 0.50, x + y + z + t = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 < t ≤ 0.1, M is Nb, Mo, Ta, Ti, Zr, and W The positive electrode active for a lithium ion secondary battery according to any one of claims 5 to 7, which is represented by one or more selected additive elements) and has a hexagonal crystal structure having a layered structure. material. A positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte are provided, and the positive electrode active material for a lithium ion secondary battery according to any one of claims 5 to 8 is used as the positive electrode material of the positive electrode. , lithium-ion secondary battery.

Images