JP2020001935A - Transition metal composite hydroxide particles and production method thereof, positive electrode active material for lithium ion secondary battery and production method thereof, and lithium ion secondary battery - Google Patents

Abstract

To provide a positive electrode active material or the like capable of further improving battery characteristics.SOLUTION: There is provided a method for producing transition metal composite hydroxide particles by a crystallization reaction. The method comprises: a nucleation step of producing nuclei under an acidic atmosphere by controlling a pH value to be in the range of 12 to 14; and a particle growth step of growing nuclei by controlling the obtained reaction aqueous solution containing nuclei so that the pH value is lower than that of the nucleation step and is in the range of 10.5 to 12.0. The particle growth step comprises: a first step of growing nuclei under an acidic atmosphere; and a second step of further growing nuclei under a non-oxidizing atmosphere. Included therein is that under an oxidizing atmosphere, a raw aqueous solution containing an additive element different from the transition metal is supplied; and under a non-oxidizing atmosphere, the supply of the raw aqueous solution to the reaction aqueous solution is stopped or the supply amount of the additive element to the reaction aqueous solution is reduced as compared with that under an oxidizing atmosphere.SELECTED DRAWING: Figure 1

Description

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

  2. Description of the Related Art In recent years, with the spread of portable electronic devices such as smartphones and tablet PCs, development of a small and lightweight non-aqueous electrolyte secondary battery having a high energy density has been strongly desired. Also, there is a strong demand for the development of a high-output secondary battery as a power source for electric vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles.

  As a secondary battery satisfying such requirements, there is a lithium ion secondary battery which is a kind 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. As an active material used as a material of the negative electrode and the positive electrode, a material capable of removing and inserting lithium is used. As the electrolyte, a non-aqueous electrolyte such as a non-aqueous electrolyte obtained by dissolving a lithium salt as a supporting salt in an organic solvent or a non-flammable solid electrolyte having ionic 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 4 V class, and thus has a high energy density secondary battery. Currently, research and development are being actively carried out as batteries, and some of them are being put to practical use.

As a positive electrode active material of such a lithium ion secondary battery, a lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, a lithium nickel composite oxide (LiNiO ₂ ) using nickel 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 a lithium transition metal composite oxide such as Mn _0.5 O ₂ ) have been proposed.

  In addition, in order to obtain a positive electrode having high battery characteristics (high cycle characteristics, high output characteristics, etc.) in a lithium ion secondary battery, a technique for controlling the particle structure of the lithium transition metal composite oxide has been proposed. I have.

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

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

For example, Patent Document 4, the general _{formula: Ni 1-x-y 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), the nickel-cobalt composite hydroxide is composed of a plurality of primary particles The secondary particles are composed 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. Less than 50% of the second layer present on the inner side of the secondary particles than the first layer, and a radial depth And a third layer present on the inner side of the secondary particles from the second layer having a ratio of 50% or more, wherein the spectrum of SEM-EDX for the element M with respect to the radial depth of the secondary particles in the second layer A nickel cobalt composite hydroxide having a peak is disclosed. The positive electrode active material obtained from the composite hydroxide has a first layer present on the surface of the secondary particles, a second layer present on the inner side of the secondary particles from the first layer, and a secondary layer present on the second layer. 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, and has excellent low-temperature output characteristics and high discharge capacity. It is said that the following battery characteristics can be obtained.

JP 2012-246199 A JP 2013-147416 A WO2012 / 131881 JP 2016-210675 A

  For example, when the positive electrode active material is composed of particles having a small particle size and a narrow particle size distribution as in Patent Documents 1 to 3, the cycle characteristics and output characteristics can be improved. This is because particles having a small particle diameter have a large specific surface area, and when used as a positive electrode active material, not only can a sufficient reaction area with an electrolytic solution be secured, but also the positive electrode can be made thin and lithium ions can be formed. This is because the moving distance in the positive electrode plate can be shortened, so that the positive electrode resistance can be reduced. In addition, since particles with a narrow particle size distribution can equalize the voltage applied to the particles in the electrode, it is possible to suppress a decrease in battery capacity due to selective deterioration of the particles when charge and discharge are repeated. That's why.

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

  However, as described in Patent Documents 1 to 3, merely controlling the particle structure has a limitation in improving battery characteristics (eg, high cycle characteristics, output characteristics, and the like), and further improving battery characteristics. It has been demanded.

  According to Patent Document 4, for example, although the element M has a specific distribution inside the secondary particles, the battery characteristics are improved, but further improvement in the battery characteristics is required.

  The present invention has been made in view of the above problems, and when a secondary battery is configured, a cathode active material capable of further improving battery characteristics, and a transition metal composite hydroxide suitably used as a precursor thereof. It is intended to provide particles. Another object of the present invention is to provide a method for easily producing the above-mentioned positive electrode active material and particles of the transition metal composite hydroxide with high productivity on an industrial scale. 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, a raw material aqueous solution containing a transition metal and an ammonium ion donor are supplied to form a reaction aqueous solution, and a transition metal composite hydroxide particle is produced by a crystallization reaction. A nucleus is formed in an acidic atmosphere in which the oxygen concentration exceeds 5% by volume by controlling the pH value at a liquid temperature of 25 ° C. to be in a range of 12.0 or more and 14.0 or less. 11. The pH value of the nucleation step and the reaction aqueous solution containing nuclei obtained in the nucleation step is lower than the pH value of the reaction aqueous solution in the nucleation step at a liquid temperature of 25 ° C., and 10.5 or more. A particle growth step of growing nuclei while controlling the particle growth to be 0 or less, wherein the particle growth step is a first particle growth step of growing nuclei in an acidic atmosphere, and a first particle growth step. Oxidizing atmosphere in the process, the oxygen concentration is 5 volumes A second particle growth step of further growing nuclei under a non-oxidizing atmosphere by switching to the following non-oxidizing atmosphere, wherein the raw material aqueous solution containing an additional element different from the transition metal under the oxidizing atmosphere To the reaction aqueous solution, and stopping the supply of the raw material aqueous solution containing the additive element to the reaction aqueous solution under a non-oxidizing atmosphere, or reducing the supply amount of the additive element to the reaction aqueous solution under the oxidizing atmosphere. And a method for producing particles of a transition metal composite hydroxide, the method comprising reducing the amount of the transition metal composite hydroxide.

  The switching from the oxidizing atmosphere to the non-oxidizing atmosphere in the second particle growth step is performed when 0.5% or more and 30% or less have elapsed with respect to the entire time during which the grain growth is performed during the crystallization reaction. May be performed. The particles of the transition metal composite hydroxide include nickel (Ni), manganese (Mn), cobalt (Co), and an additional element (M), and the material ratio (molar ratio) of each element is as follows: 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 additional elements selected from Nb, Mo, Ta, Ti, Zr, and W). Further, the method may further include a coating step of coating the crystallized product obtained after the second particle growth step with a compound containing an additional element. In the case where the supply of the raw material aqueous solution containing the additional element to the reaction aqueous solution is stopped in the second particle growth step, 50% or more and 80% or less with respect to the entire time during which the particle growth is performed during the crystallization reaction. At this point, the addition of the raw material aqueous solution containing the additional element to the reaction aqueous solution may be restarted.

  According to the second aspect of the present invention, there is provided a transition metal composite hydroxide particle including a transition metal and an additive element having an uneven distribution in the particle, wherein a plurality of primary particles are formed by aggregation. The secondary particles include a central portion and an outer peripheral portion disposed outside the central portion, and the central portion is formed by aggregating a plurality of fine primary particles, and the outer peripheral portion Is larger than the fine primary particles, the plate-like primary particles are formed by agglomeration, the additive element is contained at a higher concentration in the center than in the outer periphery, and the average particle diameter is 1 μm or more and 15 μm or less. A metal composite hydroxide particle is provided.

  Further, nickel (Ni), manganese (Mn), and an additional element (M), and cobalt (Co) are contained, and the material 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 additional elements selected from Nb, Mo, Ta, Ti, Zr, and W). Further, a coating layer may be provided on the surface of the secondary particles, and the coating layer may contain a compound containing an additive element. Further, the outer peripheral portion has, from the surface to the inside of the particle, a region containing the additive element in a range of 50% or more and 80% or less with respect to the thickness of the peripheral portion, and another region not containing the additive element. You may.

  According to the third aspect of the present invention, the particles of the transition metal composite hydroxide or the particles obtained by heat-treating the particles of the transition metal composite hydroxide are mixed with a lithium compound to form a lithium compound. A method for producing a positive electrode active material for a lithium ion secondary battery, comprising: a mixing step of forming a mixture; and a firing step of firing the lithium mixture formed in the mixing step at 650 ° C. or higher and 980 ° C. or lower in an oxidizing atmosphere. Provided.

  In the mixing step, the ratio of the sum of the number of atoms of metals other than lithium (NAMe) contained in the lithium mixture (NAMe) to the number of atoms of lithium (NALi) (NALi / NAMe) is 0.95 or more. The adjustment may be made to be 1.5 or less. Before the mixing step, a heat treatment step of heat-treating the transition metal composite hydroxide particles at 105 ° C. or more and 750 ° C. or less may be provided. Further, the positive electrode active material contains lithium (Li), nickel (Ni), manganese (Mn), an additional element (M), and optionally cobalt (Co), and a material ratio of each element. (Molar ratio) 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 1 selected from Nb, Mo, Ta, Ti, Zr, and W Or more kinds of additional elements).

  According to the fourth aspect of the present invention, a positive electrode active material containing lithium, a transition metal, and particles of a lithium transition metal composite oxide containing an additional element other than the transition metal, wherein the plurality of primary particles are Including secondary particles formed by aggregation, the secondary particles include an outer shell portion, a hollow portion inside the outer shell portion, the hollow portion does not include the primary particles, the secondary particles are: Provided is a positive electrode active material for a lithium ion secondary battery having an average particle diameter of 1 μm or more and 15 μm or less and having a concentrated layer in which an additional element is concentrated on the surface of primary particles.

Further, the ratio of the concentration of the additional element contained in the concentrated layer to the concentration inside the primary particles may be 5 or more. Further, the BET specific surface area may be 0.7 m ² / g or more and 5.0 m ² / g or less. The particles of the lithium transition metal composite oxide contain lithium (Li), nickel (Ni), manganese (Mn), an additional element (M), and optionally cobalt (Co). When the substance 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 And one or more additional elements selected from the group consisting of :), and may have a hexagonal crystal structure having a layered structure.

  According to a fifth aspect of the present invention, there is provided a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein 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 of a secondary battery, it is possible to obtain a secondary battery in which the effect of an additional element (eg, improvement in output characteristics, etc.) is further improved. Can be. When the positive electrode active material of the present invention is used in a secondary battery, a secondary battery in which the effect of the additional element is further improved can be obtained. Further, the production method of the present invention can easily produce the transition metal composite hydroxide particles and the positive electrode active material with high productivity on an industrial scale. Further, the lithium ion secondary battery of the present invention has excellent battery characteristics in which the effect of the added element is further improved. Therefore, the industrial significance of the present invention is extremely large.

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

  Hereinafter, the transition metal composite hydroxide particles according to the embodiment, a method for producing the same, a positive electrode active material for a lithium ion secondary battery and a method for producing the same, and a lithium ion secondary battery according to the embodiment will be described with reference to the drawings. The present invention is not limited to the embodiments described below. In the drawings, some components are emphasized or some components are simplified for easy understanding, and actual structures, shapes, scales, and the like may be different.

1. Transition Metal Composite Hydroxide Particles The transition metal composite hydroxide particles according to the present embodiment include a transition metal and an additive element having a distribution uneven in 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 a lithium ion secondary battery, a positive electrode active material in which the effect of an additional element is further improved can be obtained.

  1 (A) and 1 (B) and FIGS. 2 (A) and 2 (B) are schematic diagrams showing an example of particles of the transition metal composite hydroxide 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. 1A, the transition metal composite hydroxide particles 10 include a central portion 3 and an outer peripheral portion 4 arranged outside the central portion 3. As shown in FIG. 1 (B), a transition metal composite hydroxide particle 10 is composed of a plurality of primary particles 1 (fine primary particles 1a, plate-like primary particles 1b), and secondary particles 2 formed by agglomeration. including. As shown in FIG. 1B, the central portion 3 is formed by agglomeration of a plurality of fine primary particles 1a. The outer peripheral portion 4 is larger than the fine primary particles 1a, and is formed by aggregating the plate-like primary particles 1b. The average particle size of the transition metal composite hydroxide particles 10 (secondary particles 2) is preferably 1 μm or more and 15 μm or less.

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

[Particle structure]
(Secondary particles)
The transition metal composite hydroxide particles 10 include substantially spherical secondary particles 2 formed by aggregating a plurality of primary particles 1 (including fine primary particles 1a and plate-like primary particles 1b). More specifically, the particles 10 of the transition metal composite hydroxide have a central portion 3 composed of the fine primary particles 1a, and are formed outside the central portion 3 by plate-like primary particles 1b larger than the fine primary particles 1a. A structure having an outer peripheral portion 4 is provided. By manufacturing the positive electrode active material 100 using the transition metal composite hydroxide particles 10 as a precursor, lithium can be sufficiently diffused into the particles in a firing step (step S50, see FIG. 7) described later. Thus, a favorable positive electrode active material 100 having a uniform lithium distribution can be obtained.

  The central portion 3 has, for example, a structure with many gaps in which the fine primary particles 1a are continuous. Therefore, when compared with the outer peripheral portion 4 composed of the plate-like primary particles 1b having a thickness larger than the fine primary particles 1a, the central portion 3 has a lower shrinkage due to sintering in the firing step (step S50, see FIG. 7). Arising from Therefore, as the sintering progresses, the fine primary particles 1a present in the central portion 3 contract from the center of the secondary particles 2 to the outer peripheral portion 4 where sintering progresses more slowly, and finally the outer peripheral portion 4a. The shell 4 is absorbed by the portion 4 to form an outer shell portion indicated by reference numeral “24” in FIG. On the other hand, due to the contraction of the fine primary particles 1a and the absorption to the outer peripheral portion 4, a space is generated in the central portion 3. Since the central portion 3 is considered to have a low density and the contraction rate of the fine primary particles 1a existing in the central portion 3 is large, the central portion 3 The hollow space 23 (see FIGS. 3A and 3B) is formed in the positive electrode active material 100.

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

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

  Further, 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 an additional element, as shown in FIG. 2B, it is preferable that the outer peripheral portion 4 has a layer 4a containing an additional element at a higher concentration than the inner side of the outer peripheral portion 4 on the surface side. . When the particles 10 of the transition metal composite hydroxide have such a particle structure, the obtained positive electrode active material 100 has a concentrated layer C on the surface of the primary particles 21 more uniformly in the entire secondary particles 22. Thus, the battery characteristics can be further improved. In the outer peripheral portion 4, the thickness of the layer 4 a containing the additional element in a higher concentration than the inner side is preferably 50% or more and 80% or less with respect to the thickness t of the outer peripheral portion 4. When the thickness of the layer 4 a containing the high concentration of the additional element is within the above range, the obtained positive electrode active material 100 has the concentrated layer C formed more uniformly on the surface of the primary particles 21 in the entire secondary particles 22. In addition, the battery characteristics can be further improved.

(Type of additive element)
The type of the added 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 is preferable to include the above. Among these, from the viewpoint of further improving the output characteristics, it is more preferable to include one or more elements selected from Nb, Mo, Ta, Ti, Zr, and W. For example, an additive element containing W May be included. The additive element may include one type or two or more types. Note that the additional element is included in the primary particles 1.

(Fine primary particles)
The fine primary particles 1a constituting the central portion 3 preferably have an average particle size 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 diameter of the 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 diameter of the fine primary particles 1a is less than 0.01 μm, the central portion 3 having a sufficient size may not be formed. On the other hand, when the thickness exceeds 0.3 μm, the lowering of the temperature and the shrinkage at the start of sintering in the firing step (Step S50) are not sufficient, and a sufficiently large space (hollow portion 23) cannot be obtained after firing (Step S50). Sometimes.

  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 due to large shrinkage due to firing (step S50). it can.

(Plate-shaped primary particles)
It is preferable that the plate-like primary particles 1b constituting the outer peripheral portion 4 aggregate in random directions. When the plate-like primary particles 1b agglomerate in random directions, voids are generated almost uniformly between the primary particles 1 of the outer peripheral portion 4, and the lithium compound and the particles 10 of the transition metal composite oxide are mixed (Step S40). Then, at the time of firing (step S50), the molten lithium compound can reach inside the secondary particles 2 and the diffusion of lithium can be sufficiently performed.

  In addition, since the plate-like primary particles 1b are agglomerated in random directions, the shrinkage of the central portion 3 in the firing step (step S50) is more evenly generated. The space (hollow portion 23) having a height can be formed.

  The plate-like primary particles 1b preferably have an average particle size 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 diameter of the plate-like primary particles 1b is less than 0.3 μm, the start of sintering in the firing step (step S50) is reduced in temperature, and a sufficiently large space may not be obtained after firing. If it exceeds 3 μm, it is necessary to raise the sintering temperature in order to obtain sufficient crystallinity of the obtained positive electrode active material, and sintering occurs between the secondary particles, and the obtained positive electrode active material The particle size may exceed the above range.

  The particle diameters of the fine primary particles 1a and the plate-like primary particles 1b can be measured by observing the cross section of the transition metal composite hydroxide particles 10 using a scanning electron microscope (SEM). For example, a plurality of secondary particles 2 (particles 10 of the transition metal composite hydroxide) are embedded in a resin or the like, and a cross-section polisher process or the like is performed to enable observation of a cross section of the plurality of secondary particles 2. The particle diameter of each of the fine primary particles 1a and the plate-like primary particles 1b is preferably the maximum diameter (maximum length) of a cross section of each of the primary particles 1a and 1b in the secondary particles 2, preferably 10 or more. 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, with respect to the particle diameter (diameter) of the secondary particles 2. More preferably, there is. Here, as for the thickness of the outer shell portion 24 in the positive electrode active material 100, the thickness of the outer peripheral portion 4 in the transition metal composite hydroxide particles 10 is substantially maintained. Therefore, when the thickness t of the outer peripheral portion 4 is within the above range, a sufficient hollow portion 23 can be formed in the lithium metal composite oxide particles (the 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 entire transition metal composite hydroxide particles 10 shrink in the firing step (step S50), and In addition, sintering may occur between the secondary particles 22 of the obtained positive electrode active material 100, and the particle size distribution of the positive electrode active material 100 may be deteriorated. When the thickness of the outer peripheral portion 4 exceeds 45%, the central portion 3 having a sufficient size may not be formed.

  Note that the thickness t of the outer peripheral portion 4 can be measured by the following method. First, the secondary particles 2 from which the cross section of the particle center can be observed are selected from the plurality of secondary particles 2 in the resin, and the outer periphery of the outer peripheral portion 4 and the central portion 3 are selected at three or more arbitrary positions. The distance between two points where the distance on the inner circumference of the side is the shortest is measured, and the average thickness of the outer circumference 4 for each particle is determined. Next, the distance between any two points at which the distance is maximum on the outer periphery of the secondary particle 2 is defined as the particle diameter (diameter) of the secondary particle 2, and the above-described average is obtained by the particle diameter (diameter) of the secondary particle 2. By dividing the thickness (average thickness of outer peripheral portion 4 / particle diameter (diameter) of secondary particles 2), the thickness (%) of outer peripheral portion 4 for each secondary particle 2 is determined. Further, the thickness (%) of each secondary particle 2 obtained for ten or more secondary particles 2 is averaged, and the thickness (%) of the outer peripheral portion 4 with respect to the particle diameter (diameter) of the secondary particle 2 is obtained. Can be requested.

(Average particle size)
The average particle size of the transition metal composite hydroxide particles 10 is 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. The average particle diameter of the transition metal composite hydroxide particles 10 correlates with the average particle diameter of the positive electrode active material 100 obtained using the transition metal composite hydroxide particles 10 as a precursor. Therefore, by controlling the average particle size in the above range, the average particle size of the positive electrode active material 100 can be controlled in a predetermined range. In addition, the average particle diameter of the particles 10 of the transition metal composite hydroxide means a volume-based average particle diameter (MV), and can be determined from, for example, a volume integrated value measured by a laser light diffraction / scattering particle size analyzer. it can.

(Particle size distribution)
In addition, the transition metal composite hydroxide particle 10 is an index indicating the spread of the particle size distribution [(d90−d10) / average particle size], 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 affected by the transition metal composite hydroxide particles 10 as its precursor. For this reason, when the transition metal composite hydroxide particles containing a large number of fine particles and coarse particles are used as the precursor, the positive electrode active material also contains many fine particles and coarse particles. The safety, cycle characteristics and output characteristics of the secondary battery cannot be sufficiently improved. On the other hand, if ((d90−d10) / average particle size) is adjusted to be 0.65 or less at the stage of the transition metal composite hydroxide particles 10, this can be obtained as a precursor. The particle size distribution of the resulting positive electrode active material 100 can also be narrowed, and the above-described problem can be avoided.

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

  In addition, d10 accumulates the number of particles in each particle size from the smaller particle size side, and a particle size whose accumulated volume becomes 10% of the total volume of all particles, d90 similarly accumulates 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 determined from the volume integrated value measured by the laser light diffraction / scattering particle size analyzer in the same manner as the average particle diameter.

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

  For example, the particles 10 of the transition metal composite hydroxide include nickel (Ni), manganese (Mn), an additional element (M), and optionally cobalt (Co), and a material amount ratio of each element. (Molar ratio) 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, and M is preferably represented by 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 a precursor of a positive electrode active material, a secondary battery having high output characteristics and cycle characteristics can be obtained.

Furthermore, particles 10 of the transition metal complex hydroxide represented by the general formula _{(1): Ni x Mn y} Co z M t (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, and M is selected from Nb, Mo, Ta, Ti, Zr, and W (At least one additional element). By using such transition metal composite hydroxide particles as a precursor, a positive electrode active material represented by the following general formula (2) can be easily obtained, and a secondary electrode having high output characteristics and cycle characteristics can be obtained. The following battery can be obtained.

  The above molar ratio of the transition metal composite hydroxide particles 10 and the preferable composition range of nickel, manganese, cobalt, and the additional element constituting the particles in the general formula (1) are determined by the positive electrode active material 100 described later. And the preferable composition range of each element in the general formula (2). Therefore, a 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-mentioned specific structure, average particle size, and the like, but can be easily obtained by the production method described below. it can.

2. Method for Producing Transition Metal Composite Hydroxide Particles FIGS. 4 to 6 are diagrams illustrating an example of a method for producing the transition metal composite hydroxide particle 10 according to the present embodiment. The production method according to the present embodiment is a method for producing the transition metal composite hydroxide particles 10 by a crystallization reaction. As shown in FIGS. 4 to 6, a raw material aqueous solution containing a transition metal and an ammonium ion supplier To form a reaction aqueous solution, adjust the pH value of the reaction aqueous solution based on a liquid temperature of 25 ° C. to a range of 12.0 or more and 14.0 or less, and perform nucleation (step S10). Controlling the pH value of the reaction aqueous solution containing nuclei obtained in the nucleation step at a liquid temperature of 25 ° C. so as to be lower than the pH value in the nucleation step and to be 10.5 or more and 12.0 or less. And a step of growing a nucleus (step S20).

  The crystallization reaction has a narrow particle size distribution by clearly distinguishing a nucleation step (step S10) of mainly performing nucleation and a particle growth step (step S20) of mainly performing particle growth into two stages, 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 in which the oxygen concentration exceeds 5% by volume. The particle growth step (step S20) includes a first particle growth step (step S21) for growing the nucleus in an acidic atmosphere and an oxidizing atmosphere in the first particle growth step (step S21). A second particle growth step (step S22) of switching to a non-oxidizing atmosphere of 5% by volume or less and further growing the nucleus under the non-oxidizing atmosphere.

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

  In the particle growth step (step S20), a raw material aqueous solution containing an additional element 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. Is stopped, or the supply amount of the added element to the reaction aqueous solution is reduced. In the nucleation step (step S10), the raw material aqueous solution containing the additional element may or may not be supplied to the reaction aqueous solution.

  The present inventors have conducted intensive studies based on the technology described in Patent Document 2 and the like in order to further improve battery characteristics. As a result, in the oxidizing atmosphere, the raw material aqueous solution containing the additional element is supplied, and in the non-oxidizing atmosphere, the supply of the raw material aqueous solution containing the additional element is stopped, or the supply amount of the additional element to the reaction aqueous solution is reduced. By doing so, the amount of the additional element that forms a solid solution in the crystal of the positive electrode active material 100 decreases, and the surface of the primary particles 21 of the obtained positive electrode active material 100 can contain more additional element. Obtained knowledge. In the secondary battery, when the additive element is present at a high concentration on the surface of the primary particles 21 that comes into contact with the electrolytic solution, the effect of the additive element can be more efficiently exhibited, and the battery characteristics are further improved. Hereinafter, each step will be described.

(1) Crystallization reaction [nucleation step (step S10)]
In the nucleation step (Step S10), the reaction aqueous solution containing the transition metal-containing raw material aqueous solution and the ammonium ion donor has a pH value of 12.0 or more and 14.0 or less based on a liquid temperature of 25 ° C. With such control, nucleation is performed in an acidic atmosphere having an oxygen concentration exceeding 5% by volume. Hereinafter, an example of a method of producing a reaction aqueous solution (hereinafter, also referred to as “nucleus generation aqueous solution”) in the nucleation step (step S10) will be described.

  First, a compound containing a transition metal as a raw material is dissolved in water to prepare a raw material aqueous solution. Further, an aqueous solution containing an alkaline aqueous solution and an ammonium ion donor is supplied and mixed into the reaction tank, and the pH value measured at a liquid temperature of 25 ° C. is in the range of 12.0 to 14.0. Is prepared. The ammonium ion concentration of the aqueous solution before the reaction 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, a raw material aqueous solution is supplied while stirring the pre-reaction aqueous solution. Thereby, an aqueous solution for nucleation is formed in the reaction tank. Since the pH value of the aqueous solution for nucleation is in the range described above, in the nucleation step (Step S10), nuclei hardly grow, and nucleation occurs preferentially.

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

  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, it is possible to form the central portion 3 formed by aggregating the fine primary particles 1 inside the particles 10 of the transition metal composite hydroxide, and using the particles 10 of the transition metal composite hydroxide as a precursor. By using this, a positive electrode active material having a hollow structure can be finally obtained, so that the reaction area with the electrolytic solution can be further increased.

  In the nucleation step (step S10), a new nucleus is continuously generated by supplying an aqueous solution containing a raw material aqueous solution, an aqueous alkali solution and an ammonium ion donor to the aqueous solution for nucleation. Then, when a predetermined amount of nuclei have been generated in the aqueous solution for nucleation, the nucleation step (step S10) is ended.

  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 particles of the transition metal composite hydroxide having a narrow particle size distribution, the raw material aqueous solution supplied through the nucleation step and the particle growth step is required. The content is preferably from 0.1 atomic% to 2 atomic%, more preferably from 0.1 atomic% to 1.5 atomic%, based on the metal element in the contained metal compound.

[Particle Growth Step (Step S20)]
In the particle growth step (Step S20), the pH value of the reaction solution containing nuclei obtained in the nucleation step (Step S10) at a liquid temperature of 25 ° C. is lower than the pH value of the reaction aqueous solution in the nucleation step, At the same time, the nucleus is grown under the control of 10.5 or more and 12.0 or less. Hereinafter, an example of a method of 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.

  The pH value of the aqueous solution for particle growth can be adjusted, for example, by stopping the supply of the alkaline aqueous solution.However, in order to obtain particles of the transition metal composite hydroxide having a narrow particle size distribution, the pH value of all aqueous solutions must be once determined. It is preferable to stop the supply and adjust the pH value. Specifically, after stopping the supply of all the aqueous solutions, it is preferable to adjust the pH value by supplying the same inorganic acid as the acid constituting the transition metal compound to be the raw material to the nucleation aqueous solution. .

  Next, the supply of the raw material aqueous solution is restarted while stirring the particle growth aqueous solution. At this time, since the pH value of the aqueous solution for particle growth is in the above-described range, almost no new nuclei are generated, nucleus (particle) growth proceeds, and particles of the transition metal composite hydroxide having a predetermined particle size are obtained. Is formed. In the particle growth step (step S20), the pH value and the ammonium ion concentration of the aqueous solution for particle growth change as the particles grow, so that an alkaline aqueous solution and an aqueous ammonia solution are supplied at appropriate times to adjust the pH value and the ammonium ion concentration. Maintain in the above range.

  The aqueous solution for particle growth may use the same reaction aqueous solution as the aqueous solution for nucleation, except for adjusting the pH value, as described above. , May be used. For example, separately from the nucleation aqueous solution, a component adjustment aqueous solution adjusted to a pH value and an ammonium ion concentration suitable for the particle growth step (step S20) is prepared, and the component adjustment aqueous solution is added to the nucleation step (step S10). The nucleation aqueous solution after the nucleation, preferably the nucleation aqueous solution after the nucleation step, in which a part of the liquid component is removed, is added and mixed, and this is used as a particle growth aqueous solution to perform the particle growth step. You may.

  When an aqueous solution for particle growth (aqueous solution for component adjustment) is prepared separately from the aqueous solution for nucleation, the separation between 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 optimal state. In particular, since the pH value of the aqueous solution for particle growth can be controlled to an optimal range from the start of the particle growth step (step S20), the particle size distribution of the obtained transition metal composite hydroxide particles 10 is narrower. It can be.

  As described above, the particle growing step (Step S20) includes the first particle growing step (Step S21) and the second particle growing step (Step S22). Hereinafter, each step in the particle growth step (Step S20) will be described.

[First Particle Growth Step (Step S21)]
In the first particle 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 central portion 3 in which the fine primary particles 1a are aggregated can be formed by growing the particles in an oxidizing atmosphere.

  The oxygen concentration in the oxidizing atmosphere exceeds 5% by volume, and is preferably at least twice, more preferably 5 times, the oxygen concentration in the non-oxidizing atmosphere in the second particle growth step (step S22). That is all.

  Further, a raw material aqueous solution containing an additional element different from the transition metal is supplied to the reaction aqueous solution under an oxidizing atmosphere. Thereby, the central part 3 can contain an additional element. The additional element contained in the central part 3 is finally distributed in the concentrated layer C existing on the surface of the primary particles 21 in the positive electrode active material 100.

[Second Particle Growth Step (Step S22)]
Next, in the second particle growth step (Step S22), the oxidizing atmosphere in the first particle growing step (Step S21) is switched to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less, and the non-oxidizing atmosphere is changed to a non-oxidizing atmosphere. Then grow the nucleus further. In the second particle growth step (Step S22), the outer peripheral portion 4 in which the plate-like primary particles 1b are aggregated can be formed.

  By switching the reaction atmosphere from an oxidizing atmosphere to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less in the course of the particle growing step (step S20), the transition metal composite hydroxide particles 10 having the above-described particle structure are changed. Can be obtained.

  In a non-oxidizing atmosphere, supply of the raw material aqueous solution containing the additional element to the reaction aqueous solution is stopped, or the amount of the additional element in the raw material aqueous solution containing the additional element supplied to the reaction aqueous solution is reduced. This allows the central portion 3 to contain the added element at a higher concentration than the outer peripheral portion 4.

  For example, the concentration of the additional element with respect to the elements (including transition metals) other than the additional element in the raw material aqueous solution is set to be higher in an oxidizing atmosphere than in a non-oxidizing atmosphere. The concentration of the additive element in the oxidizing atmosphere is preferably at least twice, more preferably at least five times the concentration of the additive element in the non-oxidizing atmosphere. Particularly preferably, the raw material aqueous solution containing the additional element is added in an oxidizing atmosphere, and the addition of the raw material aqueous solution containing the additional element is stopped in a non-oxidizing atmosphere.

  The central portion 3 (fine primary particles 1a) formed in the oxidizing atmosphere contracts 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. I do. Therefore, a large amount of the additional element added in the oxidizing atmosphere is diffused to the outer peripheral portion 4 in the firing step (Step S50) and finally present on the surface of the primary particles 21 forming the outer shell 24 of the positive electrode active material 100. Thus, a concentrated layer C of the additional element is formed. By forming the concentrated layer C on the surface of the primary particles 21 that comes into contact with the electrolytic solution, the effect of adding the additional element can be more efficiently exhibited. For example, when an additional element (eg, tungsten, niobium, molybdenum, tantalum, or the like) having an effect of improving the output characteristics is added, the output characteristics can be more effectively improved as compared with the related art. .

  The additive element added in the oxidizing atmosphere is present in a large amount on the surface of the primary particles 21 (concentrated layer C), whereas the additive element added in the non-oxidizing atmosphere is present in the primary particles 21 in a large amount. become. Therefore, with respect to the amount (mol) of a metal element (eg, transition metal) per unit time other than the additional element supplied to the aqueous solution for particle growth per unit time of the additional element supplied to the aqueous solution for particle growth. By adjusting the ratio of the amount of the substance (mol) higher in an oxidizing atmosphere than in a non-oxidizing atmosphere, a high concentration of the additional element can be present on the surface of the primary particles 21 (concentrated layer C). .

  When the supply amount of the additional element contained in the raw material aqueous solution containing the additional element to the reaction aqueous solution is reduced, the supply amount of the additional element to the reaction aqueous solution per unit time is set to be more non-oxidizing than the oxidizing atmosphere. It can be adjusted by reducing it in the atmosphere. For example, when the supply rate of the raw material aqueous solution containing the additional element to the reaction aqueous solution is constant, the concentration of the additional element in the raw material aqueous solution containing the additional element may be reduced in a non-oxidizing atmosphere than in an oxidizing atmosphere. Good. Further, for example, when the concentration of the raw material aqueous solution containing the additional element is constant, the supply amount of the raw material aqueous solution containing the additional element per unit time may be reduced in a non-oxidizing atmosphere rather than an oxidizing atmosphere.

  Further, in the second particle growth step (Step S22), after the supply of the raw material aqueous solution containing the additional element to the aqueous solution for particle growth is stopped, or after the amount of the additional element to be supplied to the reaction aqueous solution is reduced, As shown in FIG. 6, it is preferable to restart the supply of the raw material aqueous solution containing the additional element to the aqueous solution for particle growth.

  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 particles of the raw material aqueous solution containing the additional element is determined based on the entire time during which the particle growth during the crystallization reaction is performed. Therefore, it is preferable to restart when 50% or more and 80% or less have elapsed.

  Also, in the second particle growth step (step S22), when the amount of the additional element supplied to the reaction aqueous solution is reduced, 35% or more and 75% or more of the entire time during which the crystal growth is performed during the crystallization reaction. At the time when the following has passed, the amount of the additional 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 additional element is restarted or when the supply amount of the additional element is increased, from the surface of the outer peripheral portion 4 to the inside of the particle, 50% or more and 80% or less with respect to the thickness. The concentration of the additional element in the range (surface side) can be higher than the concentration inside the outer peripheral portion 4 (the portion inside the surface side). By forming such a layer containing a higher concentration of the additional element 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 further uniformed 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 proceeds, the ratio of the liquid component to the metal component in the nucleation aqueous solution and the particle growth aqueous solution increases. As a result, apparently, the concentration of the raw material aqueous solution decreases, and in particular, in the particle growth step (Step S20), the growth of the transition metal composite hydroxide particles 10 (primary particles 1, 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 nucleation step (step S10) is completed and during the particle growth step (step S20). Is preferred.

  As a method of discharging a part of the liquid component of the aqueous solution for particle growth out 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 It is preferable to settle the nucleus and the particles 10 of the transition metal composite hydroxide 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 stagnation of the particle growth is prevented, and the particle size distribution of the obtained transition metal composite hydroxide particles 10 is preferably adjusted. Not only can it be controlled within the range, but also the density of the secondary particles 2 as a whole can be improved. The timing of discharging a 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 depending on the degree of growth of the transition metal composite hydroxide particles 10.

[Control of particle size of transition metal composite hydroxide particles]
The particle size of the obtained transition metal composite hydroxide particles 10 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 extending the time of the particle generation step (step S20), the nucleus is supplied to the reaction aqueous solution in the nucleation step (step S10). The amount of the metal element contained in the raw material aqueous solution can be increased, 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 resulting 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, particles 10 of the transition metal composite hydroxide 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 is preferably a water-soluble compound from the viewpoint of ease of handling, more preferably a water-soluble nitrate, sulfate, hydrochloride, or the like. It is further preferable to use a sulfate from the viewpoint of preventing the contamination of sulfide.

  As the raw material aqueous solution containing the additional element different from the transition metal (raw material aqueous solution), an aqueous solution obtained by dissolving a compound containing the target additional element in water may be used. The compound containing the additional element is not particularly limited, but 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, a water-soluble compound is preferable. For example, niobium oxalate, ammonium molybdate, tantalum Sodium acid, sodium tungstate, ammonium tungstate and the like can be suitably used.

  In the production method according to the present embodiment, the ratio of each metal element in the raw material aqueous solution (entire) is approximately the composition ratio of the obtained transition metal composite hydroxide particles 10. For this reason, in the raw material aqueous solution, the content of each metal element may be appropriately adjusted according to the desired composition of the 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), the ratio of each metal element in the raw material aqueous solution (total) is set to Ni: Mn: Co. : M = x: y: z: t (where x + y + z + t = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <t ≦ 0 .1, M are adjusted to be 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 total of the compounds containing each metal element as the raw material. When the concentration of the raw material aqueous solution is less than 1 mol / L, the amount of the crystallized substance per reaction vessel decreases, and the productivity decreases. On the other hand, when the concentration of the mixed aqueous solution exceeds 2.6 mol / L, the concentration of the compound containing each metal element is re-precipitated because the concentration exceeds the saturation concentration at normal temperature, which may cause clogging of pipes and the like.

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

  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 concentration of the product is less than 30 g / L, the aggregation of the primary particles may be insufficient. On the other hand, if it exceeds 200 g / L, the aqueous solution for nucleation or the aqueous solution for particle growth may not be sufficiently diffused in the reaction tank, and the particle growth may be biased.

(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. The alkali metal hydroxide can be directly added to the reaction aqueous solution, but is preferably added as an aqueous solution because of easy 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 aqueous alkali metal solution in such a range, it is possible to prevent the pH value from locally increasing at the addition position while suppressing the amount of the solvent (the amount of water) supplied to the reaction system. In addition, it is possible to efficiently obtain particles of the transition metal composite hydroxide having a narrow particle size distribution.

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

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

  When ammonia water is used as the ammonium ion supplier, 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 the ammonia water in such a range, the loss of ammonia due to volatilization or the like can be suppressed to a minimum, so that the production efficiency can be improved.

  In addition, the supply method of the aqueous solution containing the ammonium ion supplier can also be supplied by a pump whose flow rate can be controlled, similarly to the alkaline aqueous solution.

(PH value)
In the nucleation step (step S10), the pH value of the reaction aqueous solution based on the liquid temperature of 25 ° C. is in the range of 12.0 or more and 14.0 or less. Is controlled in the range from 10.5 to 12.0. In any step, the fluctuation range of the pH value during the crystallization reaction is preferably controlled within ± 0.2. When the fluctuation range of the pH value is large, the nucleation amount and the ratio of the particle growth are not constant, and it may be difficult to obtain particles of the transition metal composite hydroxide having a narrow particle size distribution.

  In the nucleation step (Step S10), the pH value of the reaction aqueous solution (nucleation aqueous solution) is 12.0 or more and 14.0 or less, preferably 12.3 or more and 13.5 or less, based on a liquid temperature of 25 ° C. More preferably, it is controlled in the range of 12.5 to 13.3. This makes it possible to suppress the growth of nuclei and give priority to nucleation, and to make the nuclei generated in the nucleation step (step S10) uniform and have a narrow particle size distribution. On the other hand, when the pH value is less than 12.0, the growth of nuclei (particles) proceeds along with the nucleation, so that the resulting transition metal composite hydroxide particles have non-uniform particle sizes, and the particle size distribution deteriorates. . When the pH value exceeds 14.0, nuclei to be formed are too fine, and a problem arises in that the reaction aqueous solution (nucleus generation aqueous solution) gels.

  In the particle growth step (Step S20), the pH value of the reaction aqueous solution (particle growth aqueous solution) is 10.5 or more and 12.0 or less, preferably 11.0 or more and 12.0 or less, based on a liquid temperature of 25 ° C. Preferably, it is controlled in the range of 11.5 or more and 12.0 or less. Thereby, generation of new nuclei is suppressed, and it becomes possible to give priority to particle growth, and it is possible to make the obtained transition metal composite hydroxide particles 10 uniform and have a narrow particle size distribution. On the other hand, when the pH value is less than 10.5, the concentration of ammonium ions increases, and the solubility of metal ions increases, so that not only the rate of the crystallization reaction decreases, but also the amount of metal ions remaining in the reaction aqueous solution. Increases and productivity decreases. When the pH value exceeds 12.0, the amount of nucleation 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 increases. Getting worse.

  When the pH value of the reaction aqueous solution (particle growth aqueous solution) is 12.0, which is a boundary condition between nucleation and nucleus growth, the nucleation or particle growth depends on the presence or absence of nuclei present in the reaction aqueous solution. Either condition can be set. That is, if the pH value in the nucleation step (step S10) is higher than 12.0 to generate a large amount of nuclei and then the pH value in the particle growth step (step S20) is 12.0, a large amount Nuclei exist, so that particle growth occurs preferentially, and particles 10 of the transition metal composite hydroxide having a narrow particle size distribution can be obtained.

  On the other hand, if the pH value in the nucleation step (step S10) is 12.0, there is no nucleus to grow in the reaction aqueous solution, so nucleation occurs preferentially, and the pH value in the particle growth step (step S20) is increased. By making it smaller than 12.0, the generated nucleus grows and good transition metal composite hydroxide particles 10 can be obtained. In any case, the pH value in the particle growth step (step S20) may be controlled to a value lower than the pH value in the nucleation step (step S10). In order to clearly separate nucleation and particle 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 1.0 or more.

(Reaction atmosphere)
In the manufacturing method of the present embodiment, the reaction atmosphere in the nucleation step (step S10) and the first particle growth step (step S21) is changed to an oxidizing atmosphere after controlling the pH value in each step as described above. adjust. Thereby, the central part 3 where the fine primary particles 1a are aggregated is formed. In the middle of the particle growth step (step S20), the oxidizing atmosphere is switched to the non-oxidizing atmosphere, and the second particle growing step (step S22) of growing the particles in the non-acidifying atmosphere is performed. An outer peripheral portion 4 in which the plate-like primary particles 1b are aggregated is formed outside the portion 3.

  When controlling the reaction atmosphere as described above, the fine primary particles 1a constituting the central portion 3 may be plate-like and / or needle-like, for example, as shown in FIG. Other shapes may be used. As other shapes, for example, a rectangular parallelepiped shape, an elliptical shape, a ridge shape, or the like may be used. The shape of the fine primary particles 1a can be adjusted by the composition of the transition metal composite hydroxide particles 10 and the like. Similarly, the plate-shaped primary particles 1b constituting the outer peripheral portion 4 may have other shapes. In the manufacturing 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 be an oxidizing atmosphere, and the central portion 3 of the transition metal composite hydroxide particle 10 is formed. Specifically, control is performed so that the oxygen concentration in the reaction atmosphere exceeds 5% by volume, preferably 10% by volume or more, and more preferably the air atmosphere (oxygen concentration: 21% by volume). By controlling the oxygen concentration in the reaction atmosphere within the above range, fine primary particles 1a having an average particle size in a range of 0.01 μm to 0.3 μm can be formed.

  The upper limit of the oxygen concentration in the reaction atmosphere in the first particle growth step (step S21) is not particularly limited. However, if the oxygen concentration is excessively high, the average particle size of the fine primary particles 1a is 0.1. When the thickness is less than 01 μm, the layer (the outer peripheral portion 4) having a low density of the additive element may not be sufficiently large. For this reason, it is preferable that the oxygen concentration in the first particle growth step (step S21) be 30% by volume or less.

  On the other hand, in the second particle growth step (Step S22), the outer periphery of the transition metal composite hydroxide particles 10 is formed by controlling the atmosphere to a weakly oxidizing atmosphere or a non-oxidizing atmosphere. Specifically, the mixed atmosphere of oxygen and an 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 be grown to a certain range while suppressing unnecessary oxidation, so that the outer peripheral portion 4 has an average particle diameter of 0.3 μm or more and 3 μm or less. Within this range, a plate-like primary particle 1b can be formed to have a structure in which the primary particles 1b are aggregated. Therefore, it is possible to form the outer peripheral portion 4 having a sufficient difference between the central portion 3 and the primary particles 1 described above.

  In addition, the particle diameter 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 the secondary particles 2, preferably 10 or more of each of the primary particles 1a and 1b. It can be obtained by measuring as a diameter and calculating an average value.

(Change of 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. Hereinafter, an example of switching the atmosphere will be described.

  The timing of the switching of the atmosphere may be determined in consideration of the size of the central portion 3 so that the hollow portion 23 in which the fine particles are not generated and the cycle characteristics are not deteriorated in the positive electrode active material 100 is obtained. preferable. The switching of the atmosphere may be performed, for example, at the time when 0.5% or more and 40% or less have elapsed with respect to the entire time during which the grain growth is performed during the crystallization reaction, and preferably 0.5% to 30%. This is performed at the time when the following has elapsed, more preferably at the time when 0.5% or more and 25% or less have elapsed. When the atmosphere is switched at a time point exceeding 40% of the entire time during which the particle growth is performed, the central portion 3 becomes large, and the thickness of the outer peripheral portion 4 with respect to the particle size of the secondary particles 2 becomes too thin. There is. On the other hand, when the atmosphere is switched at a time point of less than 0.5% with respect to the entire time during which the grain growth is performed, the central portion 3 becomes too small, or the central portion 3 and the outer peripheral portion 4 are provided. The secondary particles 2 may not be formed.

  The method for switching the atmosphere is not particularly limited, but is preferably performed using an air diffuser from the viewpoint of reducing the time for switching the atmosphere. Conventionally, the reaction atmosphere has been switched by flowing an atmosphere gas into 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 with the atmosphere gas. However, in these methods, it takes a long time to switch the reaction atmosphere, and thus it is 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 constituted by a conduit having a large number of fine holes on its surface, and can discharge a large number of fine gases (bubbles) into a liquid. Therefore, when the atmosphere is switched using an air diffuser, it is possible to switch the reaction atmosphere in a short time, and it is not necessary to stop the supply of the raw material aqueous solution at the time of switching the atmosphere, thereby improving the production efficiency. Can be achieved.

  It is preferable to use a ceramic air diffuser from the viewpoint of excellent resistance under a high pH environment. The air diffuser preferably has a smaller pore size, and has a pore size of 100 μm or less, more preferably 50 μm or less. When the pore diameter of the air diffuser is sufficiently small, fine bubbles can be released, and thus 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. The ammonium ion functions as a complexing agent in the reaction aqueous solution. When 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, and the transition in which the shape and particle size are well-ordered. It is 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 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 a composition deviation or the like. .

  Further, it is preferable that the ammonium ion concentration in the reaction aqueous solution is kept at a constant value within the above range. If the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of the metal ion fluctuates, and the uniform transition metal composite hydroxide particles 10 may not be formed. For this reason, it is preferable that the fluctuation range of the ammonium ion concentration be controlled within a certain range through the nucleation step (step S10) and the particle growth step (step S20), and specifically, the fluctuation range of ± 5 g / L. It is preferable to control.

(Reaction temperature)
The temperature (reaction temperature) of the reaction aqueous solution is preferably controlled to 20 ° C. or higher, more preferably 20 ° C. to 60 ° C., throughout the nucleation step (Step S10) and the particle growth step (Step S20). When the reaction temperature is lower than 20 ° C., nucleation is likely to occur due to the low solubility of the reaction aqueous solution, and the average particle size and particle size distribution of the resulting transition metal composite hydroxide particles 10 are suitable. It is difficult to control the range. The upper limit of the reaction temperature is not particularly limited. However, when the temperature exceeds 60 ° C., volatilization of ammonia is promoted, and the aqueous solution containing an ammonium ion supplier supplied to control the ammonium ion in the reaction aqueous solution within a certain range is controlled. The amount increases and the production cost increases.

(manufacturing device)
The crystallization apparatus (reaction tank) used for the crystallization reaction is not particularly limited, but a crystallization apparatus that can switch the reaction atmosphere by the above-described aeration tube is preferable. Further, it is preferable to use a batch-type crystallization apparatus that does not collect the precipitated product until the crystallization reaction is completed. When a batch type crystallizer is used, unlike a continuous crystallizer that collects products by the overflow method, the growing particles are not collected at the same time as the overflow liquid, so transition metal with a narrow particle size distribution is used. The composite hydroxide particles 10 can be easily obtained. Further, from the viewpoint of appropriately controlling the reaction atmosphere during the crystallization reaction, it is preferable to use a closed crystallization apparatus.

(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 a crystallized substance obtained after the second particle growth step (Step S20) with a compound containing an additional element. May be further provided. By providing 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 particles 10 of the transition metal composite hydroxide can be uniformly coated with the compound containing the additive element. Hereinafter, for example, an example of the coating step (Step S30) will be described.

  For example, the crystallized product obtained after the second particle growth step (step S22) is slurried, the pH value is controlled within a predetermined range, and then an aqueous solution (a coating aqueous solution) in which the compound containing the additional element is dissolved is used. In addition, a compound containing the additional element is precipitated on the surface of the crystallized product (transition composite hydroxide particles). Thereby, the particles 10 of the transition metal composite hydroxide uniformly coated with the compound containing the additional element can be obtained. In this case, instead of the coating aqueous solution, an alkoxide solution of the additional element may be added to the slurry crystallized product. Alternatively, the surface of the crystallized product may be coated by spraying an aqueous solution or a slurry in which the compound containing the additive element is dissolved or by spraying the slurry on the crystallized product without drying the crystallized product. Further, for example, the slurry in which the crystallized substance and the compound containing the additional element are suspended may be coated by a method of spray drying, for example, the crystallized substance and the compound containing the additional element are mixed by a solid phase method. Or the like.

  When the surface of the crystallized substance (particles of the transition composite hydroxide) is coated with the additional element, the composition of the transition metal composite hydroxide particles 10 obtained after the coating is changed to the target transition metal composite hydroxide. The compositions of the raw material aqueous solution and the coating aqueous solution are appropriately adjusted to match the composition of the oxide particles 10. Further, the coating step (Step S30) may be performed on the heat-treated particles after the crystallization (particles of the transition metal composite hydroxide) are heat-treated. In addition, at least a part of the heat-treated particles may include transition metal composite oxide particles obtained by oxidizing a crystallized substance (transition metal composite hydroxide particles).

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

  For example, the particles 10 of the transition metal composite hydroxide include nickel (Ni), manganese (Mn), cobalt (Co), and an additive element (M), and the material 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 preferably represented by one or more additional elements selected from Nb, Mo, Ta, Ti, Zr, and W).

Further, the production method according to the present embodiment can be suitably applied to the transition metal composite hydroxide particles 10 represented by the following general formula (1).
Formula _{(1): Ni x Mn y} Co z M t (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, and M is one or more additional elements selected from Nb, Mo, Ta, Ti, Zr, and W)

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

3. As shown in FIGS. 3A and 3B, the positive electrode active material 100 according to the present embodiment includes particles 20 of a lithium transition metal composite oxide, and includes lithium ion It can be suitably used as a positive electrode material of a secondary battery.

  The lithium transition metal composite oxide particles 20 (positive electrode active material 100) are composed of secondary particles 22 formed by aggregating a plurality of primary particles 21. The secondary particles 22 include an outer shell 24 and a hollow 23 disposed inside the outer shell 24. The average particle size of the positive electrode active material 100 is 1 μm or more and 15 μm or less.

  The particles 20 of the lithium transition metal composite oxide are mainly composed of the secondary particles 22, but may include the single primary particles 21. Hereinafter, the details of the positive electrode active material 100 will be described.

[Particle structure]
(Secondary particles)
As shown in FIG. 3A, the particles 20 of the lithium transition metal composite oxide include an outer shell portion 24 and a hollow portion 23 inside the outer shell portion 24 where no primary particles exist. As shown in FIG. 3B, the particles 20 of the lithium transition metal composite oxide include secondary particles 22 formed by aggregating a plurality of primary particles 21. In the positive electrode active material 100 having such a particle structure, the electrolytic solution intrudes from the grain boundaries or voids between the primary particles 21, and lithium is inserted and removed at the reaction interface on the surface of the primary particles 21 on the hollow portion 23 side inside the particles. Since the transfer 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, as a ratio to the particle size of the secondary particles 22. When the ratio of the thickness of the outer shell portion 24 is less than 5%, the strength of the secondary particles 22 is reduced, so that the secondary particles 22 are destroyed during powder handling and when used as a positive electrode of a battery, and fine particles are reduced. This may cause deterioration of battery characteristics. On the other hand, when the ratio of the thickness of the outer shell portion 24 exceeds 45%, the above-mentioned grain boundaries or voids where the electrolytic solution can enter the hollow portion 23 inside the secondary particles 22 are reduced, and the electrolytic solution entering the inside of the particles is reduced. And the surface area contributing to the battery reaction decreases, so that the positive electrode resistance may increase and output characteristics may decrease. The ratio of the thickness of the outer shell portion 24 to the secondary particle size can be determined in the same manner as the outer peripheral portion 4 of the transition metal composite hydroxide particle 10 described above. The thickness (absolute value) of the outer shell 24 is, for example, in the range of 0.5 μm to 2.5 μm, and preferably in the range of 0.4 μm to 2.0 μm.

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

  The concentration of the additive element contained in the concentrated layer C is a ratio of the concentration of the additive element contained inside 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 the additional element contained inside the primary particles 21) is preferably 2 or more, and more preferably 5 or more. As a result, the effect of the additional element (eg, output characteristics) can be further improved. The concentration of the additional element on the surface of the primary particles 21 can be determined 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 added element between the concentrated layer C and the inside of the primary particle 21 is a ratio between the highest concentration peak on the surface side in the primary particle 21 and the lowest concentration inside the concentrated layer C. Can be obtained by

  Note that the additive element mainly exists on the surface side in the primary particles 21 to form the concentrated layer C, and the additive element exists as a solid solution in the crystal of the lithium transition metal composite oxide. May be present as fine particles of a compound of lithium and an additive element at the grain boundary.

[Average particle size]
The positive electrode active material 100 has an average particle diameter 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. When the average particle diameter of the positive electrode active material 100 is in 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 the 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 decreases, and the battery capacity per unit volume cannot be increased. When the average particle diameter of the positive electrode active material 100 exceeds 15 μm, the reaction area of the positive electrode active material 100 decreases, and the interface with the electrolyte decreases, so that it becomes difficult to improve the output characteristics.

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

[Particle size distribution]
The index [(d90−d10) / average particle diameter], which is an index indicating 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 diameter] is in the above range, it indicates that the particles are composed of particles having an extremely narrow particle size distribution. Such a positive electrode active material 100 has a small proportion of fine particles and coarse particles, and a secondary battery using the same has more excellent thermal stability, cycle characteristics, and output characteristics.

  On the other hand, when [(d90−d10) / average particle diameter] 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 having a large proportion of fine particles, due to local reaction of the fine particles, the secondary battery is likely to generate heat, and not only is thermal stability reduced. In addition, the cycle characteristics may be inferior due to the selective deterioration of the fine particles. Further, in a secondary battery using the positive electrode active material 100 having a large proportion of coarse particles, the reaction area between the electrolyte and the positive electrode active material cannot be sufficiently secured, and the output characteristics may be poor. .

  In addition, on the assumption of production on an industrial scale, it is not realistic to use a material having an excessively small [(d90−d10) / average particle diameter] as the positive electrode active material 100. Therefore, in consideration of cost and productivity, the lower limit of [(d90−d10) / average particle size] in the positive electrode active material 100 is preferably set to about 0.25.

  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. Omitted.

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

  For example, the positive electrode active material 100 includes lithium (Li), nickel (Ni), manganese (Mn), an additional element (M), and optionally cobalt (Co), and a substance amount ratio (molar) of each element. Ratio: 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, and M is at least one selected from Nb, Mo, Ta, Ti, Zr, and W Is preferable. 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.

Also, the positive electrode active material 100, the general formula _{(2): Li 1 + u} Ni x Mn y 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 Or one or more additional elements selected from W).

  In the above molar ratio or the general formula (2), the value of u indicating the excess amount of lithium (Li) is preferably -0.05 to 0.50, more preferably 0 to 0.50, More preferably, it is 0 or more and 0.35 or less. When the value of u is within the above range, the output characteristics and battery capacity of a secondary battery using the positive electrode active material 100 as a positive electrode material can be further improved. On the other hand, when the value of u is less than -0.05, the positive electrode resistance of the secondary battery becomes large, and the output characteristics may not be improved. 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 higher potential and higher capacity of the secondary battery. In the above 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 is difficult to improve the battery capacity of the secondary battery using the positive electrode active material 100. On the other hand, when the value of x exceeds 0.95, the effect cannot be obtained because the content of other elements decreases.

  Manganese (Mn) is an element that contributes to improvement in thermal stability. In the above molar ratio or 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. . If 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, when the value of y exceeds 0.55, Mn is eluted from the positive electrode active material 100 during high-temperature operation, and the charge / discharge cycle characteristics may be deteriorated.

  Cobalt (Co) is an element that contributes to improvement of charge / discharge cycle characteristics. In the above molar ratio or the general formula (2), the value of z indicating the cobalt content is preferably from 0 to 0.4, more preferably from 0.10 to 0.35. If 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 an additional element in addition to the above-described metal element in order to further improve the battery characteristics. Examples of the additional element include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), and molybdenum (Mo). ), Hafnium (Hf), tantalum (Ta), lanthanum (La), and tungsten (W). Among these, the additive element is preferably at least one selected from Nb, Mo, Ta, Ti, Zr, and W. When these additional elements are included, battery characteristics (eg, durability, output characteristics, and the like) can be improved.

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

  In the above molar ratio or the general formula (2), the value of t indicating the content of the additional element M is preferably more than 0 and 0.1 or less, more preferably 0.001 or more and 0.05 or less. is there. On the other hand, when the value of t exceeds 0.1, the metal element contributing to the Redox reaction decreases, and the battery capacity decreases.

Note that in the positive electrode active material 100, when to achieve further improvement of the battery capacity of the secondary battery using this, its composition formula _{(3): Li 1 + u} Ni x Mn y Co z M t 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 And M are preferably adjusted to be represented by one or more additional elements selected from Nb, Mo, Ta, Ti, Zr, and W). In particular, when achieving compatibility with thermal stability, the value of x in the general formula (3) is more preferably set to 0.7 <x ≦ 0.9, and 0.7 <x ≦ 0.85. More preferably,

Further, in the positive electrode active material 100, when to achieve further improvement of thermal stability, the composition, the general formula _{(4): Li 1 + u} Ni x Mn y 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 W).

[Specific surface area]
Further, the positive electrode active material 100 preferably has a specific surface area of, for example, 0.7 m ² / g or more and 5.0 m ² / g or less, and 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 in the above range, the contact area with the electrolytic solution is large, and the output characteristics of a secondary battery using the same 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, when a secondary battery is formed, a reaction area with the electrolyte cannot be secured, and the output characteristics are insufficient. It is difficult to improve the quality. 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, so that the thermal stability may decrease.

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

[Tap density]
In recent years, in order to extend the usage time of portable electronic devices and the mileage of electric vehicles, further increase in capacity of secondary batteries is required. On the other hand, the thickness of the electrode of the secondary battery is required to be about several microns due to packing of the whole battery and problems of electron conductivity. For this reason, it is required that the positive electrode active material has a high capacity and a high filling property so that the secondary battery as a whole has a high capacity. From such a viewpoint, in the positive electrode active material 100, the tap density, which is an index of the filling property, is preferably 1.0 g / cm ³ or more, and more preferably 1.3 g / cm ³ or more. When the tap density is less than 1.0 g / cm ³ , the filling property is low, and the battery capacity of the entire 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 represents the bulk density of a sample powder collected in a container after tapping 100 times based on JIS Z-2504, and can be measured using a shaking specific gravity measuring device.

  The method for producing the positive electrode active material 100 is not particularly limited as long as it has the above-described specific structure, average particle size, and the like, but can be easily obtained by the production method described below.

4. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery FIGS. 7 and 8 are views 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. As shown in FIG. 7, the particles 10 of the transition metal composite hydroxide and the lithium compound are mixed. Then, 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 more and 980 ° C. or less in an oxidizing atmosphere are provided. According to such a manufacturing method, the above-described positive electrode active material 100 can be easily obtained.

  Note that, as shown in FIG. 8, if necessary, steps such as a heat treatment step (step S35), a calcining step (step S45), and a crushing step (step S55) may be added to the above-described steps. . Hereinafter, each step will be described.

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

  In the heat treatment step (step S35), excess water contained in the transition metal composite hydroxide particles 10 is removed by heating the transition metal composite hydroxide particles 10 and performing a heat treatment. This makes it possible to reduce the amount of water remaining until after the firing step (step S50) to a certain amount, and to suppress a variation in the composition of the obtained positive electrode active material 100.

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

  Note that the heat treatment step (Step S35) is not limited to all transitions, since it is only necessary to remove water to such an extent that the number of atoms of each metal component in the obtained positive electrode active material 100 and the ratio of the number of Li atoms do not vary. It is not necessary to convert the metal composite hydroxide particles 10 into transition metal composite oxide particles. However, in order to reduce the dispersion of the number of atoms of each metal component and the ratio of the number of atoms of Li, the particles 10 of all the transition metal composite hydroxides are heated to 400 ° C. or more, Conversion to composite oxide particles is preferred.

  The above-described variation can be further suppressed by previously determining the metal component contained in the transition metal composite hydroxide particles 10 by analysis under the heat treatment conditions and determining the mixing ratio with the lithium compound. Can be.

  The atmosphere of the heat treatment is not particularly limited and may be a non-reducing atmosphere, but is preferably performed in an air stream that can be easily performed.

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

[Mixing Step (Step S40)]
In the mixing step (step S40), a lithium compound is mixed with the transition metal composite hydroxide particles 10 or the particles after the heat treatment (hereinafter, these are collectively referred to as “precursor particles”). To obtain a lithium mixture.

In the mixing step (step S40), the sum of the number of atoms of metal atoms other than lithium in the lithium mixture, for example, nickel, cobalt, manganese, and the additional element M (N _Me ), and the number of lithium atoms (N _Li ) (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, and still more preferably 1.0 or more. The precursor particles and the lithium compound are mixed so as to be 1.2 or less. That is, since before and after the firing step (step S50) is _N Li _{/ N Me} does not change, so _{that N} Li _{/ N Me} in the mixing step (step S40) becomes the _N Li _{/ N Me} of the positive electrode active substance of interest In addition, it is necessary to mix the precursor particles and 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 thereof from the viewpoint of easy availability. Particularly, 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 so that fine powder is not generated. If the mixing is insufficient, variations in N _Li / N _Me occur between the individual particles, and sufficient battery characteristics may not be obtained. Note that a general mixer can be used for mixing. As the mixer, a shaker mixer, a Reedige mixer, a Julia mixer, a V blender, or the like can be used.

[Calcination process (Step S45)]
When lithium hydroxide or lithium carbonate is used as the lithium compound, as shown in FIG. 8, a calcining step (step S45) is provided after the mixing step (step S40) and before the firing step (step S50). Is also good.

  The calcining step (Step S45) is a step of calcining the lithium mixture at a temperature lower than the firing temperature in the firing step (Step S50) and at 350 ° C to 800 ° C, preferably 450 ° C to 780 ° C. . When the calcination step (Step S45) is provided, lithium can be sufficiently diffused into 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 more preferably 3 hours or more and 6 hours or less. Further, the atmosphere in the calcining step (step S45) is preferably an oxidizing atmosphere, as in the later-described baking step (step S50), and the oxygen concentration is preferably 18% by volume or more and 100% by volume or less. Is more preferred.

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

  In the firing step (step S50), the primary particles 1 existing in the central portion 3 and the outer peripheral portion 4 of the precursor particles (particles 10 of the transition metal composite hydroxide) undergo primary shrinkage while sintering and shrinking. The particles 21 are formed. Since the central portion 3 is composed of the fine primary particles 1a, it starts to sinter from a lower temperature region than the outer peripheral portion 4 composed of the larger plate-like primary particles 1b. Further, the central portion 3 has a larger contraction amount than the outer peripheral portion 4. For this reason, the fine primary particles 1a constituting the central portion 3 shrink toward the outer peripheral portion 4 where sintering progresses slowly, and the 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 by sintering, and forms 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 configured, the output characteristics can be improved without impairing the battery capacity or 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 that are precursors, but may be affected by the composition, firing conditions, and the like. Therefore, it is preferable to perform a preliminary test and appropriately adjust each condition so as to obtain a desired structure.

  The furnace used in the firing step (Step S50) is not particularly limited, and may be any furnace that can heat the lithium mixture in the air or in an oxygen stream. However, from the viewpoint of keeping the atmosphere in the furnace uniform, an electric furnace without gas generation is preferable, and any of a batch type or a continuous type electric furnace can be suitably used. This is the same for the furnace used in the heat treatment step (step S35) and the calcining step (step S45).

(Firing temperature)
The firing temperature in the firing step (Step S50) is from 650 ° C to 980 ° C. When the calcination temperature is lower than 650 ° C., lithium does not sufficiently diffuse into the precursor particles, so that surplus lithium and unreacted precursor particles remain, or the obtained lithium transition metal composite oxide particles 20 Crystallinity may be insufficient. On the other hand, when the calcination temperature exceeds 980 ° C., the particles 20 of the lithium transition metal composite oxide sinter violently, causing abnormal grain growth and increasing the proportion of irregularly shaped coarse particles.

  In the case where the positive electrode active material 100 represented by the general formula (4) is to be obtained, it is preferable that the firing temperature be 650 ° C. or more and 900 ° C. or less. On the other hand, when obtaining the positive electrode active material represented by the general formula (5), the firing temperature is preferably set to 800 ° C. or more and 980 ° C. or less.

  Further, the rate of temperature rise in the firing step (step S50) is preferably 2 ° C./min to 10 ° C./min, more preferably 5 ° C./min to 10 ° C./min. Furthermore, during the firing step (step S50), before raising the temperature 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 1 hour to 5 hours, more preferably Is preferably maintained for 2 hours to 5 hours. Thereby, the precursor particles and the lithium compound can be more uniformly reacted. For example, when the lithium compound is lithium hydroxide (melting point: 462 ° C.), it is preferable to maintain the temperature near the melting point at 400 ° C. to 500 ° C. before raising the temperature to the firing temperature during the firing step (Step S50). .

(Firing time)
Among the firing times, the holding time at the above-described firing temperature is preferably at least 2 hours or more, more preferably 4 hours or more and 24 hours or less. When the holding time at the firing temperature is less than 2 hours, lithium does not sufficiently diffuse into the precursor particles, and surplus lithium and unreacted precursor particles remain or the obtained lithium transition metal composite oxide The crystallinity of the particles 20 may be insufficient.

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

(Firing atmosphere)
The atmosphere during the firing is preferably an oxidizing atmosphere, more preferably an atmosphere having 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, firing is preferably performed in the air 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) for crushing the aggregate or the sintered body of the lithium transition metal composite oxide particles 10 may be provided. The particles 10 (positive electrode active material 100) of the lithium transition metal composite oxide obtained after the firing step (Step S50) may have undergone aggregation or slight sintering. When a crushing 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 is a method of applying mechanical energy to an aggregate composed of a plurality of secondary particles generated by sintering necking between the secondary particles during firing and hardly destroying the secondary particles themselves. It means an operation of separating and loosening aggregates.

  Known methods can be used as the crushing method. For example, a pin mill, a hammer mill, or the like 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 The lithium-ion secondary battery (hereinafter, also referred to as “secondary battery”) according to this embodiment includes a positive electrode including the above-described positive electrode active material 100, a negative electrode, and a nonaqueous electrolyte. The secondary battery includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. In addition, the secondary battery may include, for example, a positive electrode, a negative electrode, and a solid electrolyte. Further, the secondary battery may be a secondary battery that performs charging and discharging by desorption and insertion of lithium ions, for example, may be a non-aqueous electrolyte secondary battery, and may be an all-solid lithium secondary battery. There may be. The embodiment described below is merely an example, and the secondary battery according to this embodiment is applied to a form in which various changes and improvements are made based on the embodiment described in this specification. May be.

[Components]
(Positive electrode)
First, the above-described positive electrode active material 100, a conductive material and a binder are mixed, and if necessary, activated carbon or a solvent for viscosity control or the like is added, and the mixture is kneaded to prepare a positive electrode mixture paste. . At this time, the respective mixing ratios 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, or the like) or a carbon black-based material such as acetylene black or Ketjen black can be used.

  The binder plays a role of retaining the active material particles, and is, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluoro rubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, and polyacryl. Acids can be used.

  If necessary, a positive electrode active material, a conductive material and activated carbon may be dispersed, and a solvent for dissolving the binder may be added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. 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 to the surface of a current collector made of, for example, aluminum foil, dried, and the solvent is scattered. If necessary, pressure may be applied by a roll press or the like to increase the electrode density. Thus, a sheet-shaped positive electrode can be manufactured. The sheet-shaped positive electrode can be cut to an appropriate size according to the intended battery and used for battery production. Note that the method for manufacturing the positive electrode is not limited to the above method, but may be another method.

(Negative electrode)
As the negative electrode, metallic lithium, a lithium alloy, or the like may be used. In addition, as a negative electrode, a negative electrode mixture obtained by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions and adding an appropriate solvent to form a paste is formed on the surface of a metal foil current collector such as copper. May be applied, dried, and, if necessary, compressed to increase the electrode density.

  As the negative electrode active material, for example, fired organic compounds such as natural graphite, artificial graphite and phenolic resin, and powdered carbon materials such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder similarly to the positive electrode, and an organic material such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing the active material and the binder. Solvents can be used.

(Separator)
A separator is interposed between the positive electrode and the negative electrode as necessary. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and may be a thin film such as polyethylene or polypropylene having a large number of fine pores.

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

  Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, and linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, and further, tetrahydrofuran, 2-hydrogen carbonate, and the like. One compound selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone or as a mixture of two or more. Can be used.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and a composite salt thereof can be used. Further, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

  Further, a solid electrolyte may be used as the non-aqueous electrolyte. The solid electrolyte has a property that can withstand a high voltage. Examples of the solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte.

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

The oxide solid electrolyte is not particularly limited, and any oxide containing oxygen (O) and having lithium ion conductivity and electronic insulation can be used. The oxide-based solid electrolyte, for example, 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 PO ₄ , Li ₄ SiO ₄ —Li ₃ VO ₄ , Li ₂ O—B ₂ O ₃ —P ₂ O ₅ , Li ₂ O—SiO ₂ , Li ₂ O—B ₂ O ₃ —ZnO, Li _{1 + X} Al _X Ti _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 etc. I can do it.

The sulfide-based solid electrolyte is not particularly limited, and any electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. The sulfide-based solid electrolyte, for _{example, Li 2 S-P 2 S} 5, Li 2 S-SiS 2, LiI-Li 2 S-SiS 2, LiI-Li 2 S-P 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.

In addition, as the inorganic solid electrolyte, one other than the above may be used. For example, Li ₃ N, LiI, Li ₃ N—LiI—LiOH, or the like may be used.

  The organic solid electrolyte is not particularly limited as long as it is a polymer compound having ion conductivity, and examples thereof include polyethylene oxide, polypropylene oxide, and copolymers thereof. Further, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, a solid electrolyte may 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 configured with a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, or the like as described above, or may be configured with a positive electrode, a negative electrode, a solid electrolyte, or the like. The shape of the secondary battery is not particularly limited, and may be various shapes such as a cylindrical shape and a stacked shape.

  For example, when the secondary battery is a non-aqueous electrolyte secondary battery, a positive electrode and a negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte solution to form a positive electrode. Connect between the current collector and the positive terminal connected to the outside, and between the negative electrode current collector and the negative terminal connected to the outside using a current collecting lead or the like, and seal the battery case to the secondary battery. To complete.

(3) Characteristics of Lithium-ion Secondary Battery As described above, the lithium-ion secondary battery according to the present embodiment uses the positive electrode active material 100 as a positive electrode material, so that the effect of the additional element is more efficient than before. And excellent in battery characteristics (eg, battery capacity, output characteristics, cycle characteristics, etc.).

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

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In the following Examples and Comparative Examples, samples of a special grade reagent manufactured by Wako Pure Chemical Industries, Ltd. were used for preparing transition metal composite hydroxide particles and a positive electrode active material unless otherwise specified. During the nucleation step and the particle growth step, the pH value of the reaction aqueous solution is measured by a pH controller (Nippon Rika, NPH-690D), and the supply amount of the aqueous sodium hydroxide solution is adjusted based on the measured values. Thus, the fluctuation 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 transition metal composite hydroxide particles]
(Nucleation process)
First, the temperature inside the reaction tank (34 L) was set to 40 ° C. while stirring half of the water and stirring. At this time, the inside of the reaction tank was set to an air atmosphere (oxygen concentration: 21% by volume). An appropriate amount of a 25% by mass aqueous solution of sodium hydroxide and 25% by mass aqueous ammonia are added to the water in the reaction tank, and the pH of the reaction liquid in the tank is adjusted to 13.0 based on a liquid temperature of 25 ° C. did. Further, the ammonia concentration in the reaction solution was adjusted to 10 g / L to obtain an aqueous solution before the reaction.

  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 (nucleus generation aqueous solution). At the same time, a 25% by mass aqueous ammonia solution and a 25% by mass aqueous sodium hydroxide solution are also added to the reaction aqueous solution at a constant rate, and while maintaining the ammonia concentration in the reaction aqueous solution at the above value, the pH value is increased to 13.0 ( While controlling the nucleation pH value, crystallization was performed for 2 minutes and 30 seconds to perform nucleation.

(Grain growth process)
(I) First Particle Growth Step After the nucleation, the supply of all aqueous solutions is temporarily stopped, and sulfuric acid is added to adjust the pH value to 11.6 based on a liquid temperature of 25 ° C. Thus, an aqueous reaction solution (aqueous solution for particle growth) was formed. To the reaction aqueous solution, the supply of the raw material aqueous solution and the 25% by mass aqueous sodium hydroxide solution was restarted, and an aqueous solution of sodium tungstate was additionally supplied as the raw material aqueous solution containing the additional element (W). Was maintained at the above value (10 g / L), 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 aqueous solution of sodium tungstate 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 reaction tank space becomes a non-oxidizing atmosphere of 0.2% by volume or less. It was circulated at 5 L / min (switching of reaction atmosphere). Thereafter, the supply of only the raw material aqueous solution containing no added element (W) was restarted (after 12.5% of the entire time during which the particle growth was performed), and the ammonia concentration and the pH value were maintained and the growth was started. Crystallization was performed for 2 hours in total.

  When the inside of the reaction tank became full, crystallization was stopped, stirring was stopped, and the mixture was allowed to stand, thereby promoting precipitation of the product. Then, after half of the supernatant was taken out of the reaction tank, crystallization was restarted, crystallization was performed for 2 hours (total 4 hours), and crystallization was terminated.

(Washing, filtration, drying)
The product was washed with water, filtered, and dried to obtain transition metal composite hydroxide particles. Note that the switching from the air atmosphere to the nitrogen atmosphere is performed at the time of 12.5% of the entire grain growth process time from the start of the grain growth process.

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

[Analysis of transition metal composite hydroxide particles]
The resulting particles of the transition metal complex hydroxide was, after dissolving the sample by an inorganic acid, was subjected to chemical analysis by ICP emission spectroscopy, the composition _may, Ni _{0.331 Mn} 0.33 1Co _{0. 33} 1Zr _0.002 W _0.005 (OH) _{2 + a} (0 ≦ a ≦ 0.5).

  Further, for the particles of the transition metal composite hydroxide, [(d90−d10) / average particle size] values indicating the average particle size and the particle size distribution were measured using a laser diffraction / scattering type particle size distribution analyzer (Nikkiso Co., Ltd. (Track HRA). As a result, the average particle size was 5.2 μm, and the value of [(d90−d10) / average particle size] was 0.48.

  Next, the obtained transition metal composite hydroxide particles were observed by an SEM (manufactured by Hitachi High-Technologies Corporation, scanning electron microscope S-4700) (magnification: 1000 times). The particles of the product were substantially spherical, and it was confirmed that the particle sizes were substantially uniform.

  In addition, a sample of the obtained transition metal composite hydroxide particles embedded in resin and subjected to cross section polisher processing was subjected to SEM observation with a magnification of 10,000 times. The particles of the composite hydroxide are composed of secondary particles, and the secondary particles have a central portion composed of fine needle-like or flaky primary particles (having a particle diameter of about 0.3 μm) and a central portion outside the central portion. It was confirmed that it was composed of plate-shaped primary particles (diameter: about 0.6 μm) larger than the fine primary particles and an outer peripheral portion. The thickness of the outer peripheral portion with respect to the secondary particle diameter, determined from SEM observation of the cross section, was 12%. Further, from the concentration profile of tungsten (W) obtained by EDX analysis of the particle cross section using a TEM, it was confirmed that tungsten (W) was mainly present in the central portion.

[Manufacture of positive electrode active material]
(Heat treatment process)
The particles of the transition metal composite hydroxide were subjected to a heat treatment at 700 ° C. for 6 hours in a stream of air (oxygen: 21% by volume) to be converted into transition metal composite oxide particles and collected.

(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. The mixing was performed using a shaker mixer (TURBULA Type T2C, manufactured by Willy & Bacoffen (WAB)).

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

[Analysis of positive electrode active material]
When the particle size distribution of the obtained positive electrode active material was measured in the same manner as the particles of the transition metal composite hydroxide, the average particle size was 4.7 μm, and the value of [(d90−d10) / average particle size] value was obtained. 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, and the obtained positive electrode active material was substantially spherical, and the particle size was substantially uniform. It was confirmed that they were complete. On the other hand, cross-sectional SEM observation confirmed that the positive electrode active material had a hollow structure having a shell portion formed by sintering primary particles and a hollow portion inside. The ratio of the thickness of the outer shell to the particle diameter of the positive electrode active material, determined from this observation, was 11%.

  Further, EDX (TEM-EDX) analysis of the cross section of the particles of the positive electrode active material was performed using TEM. The results are shown in FIGS. FIG. 11A is a diagram schematically showing a partial cross section of the outer shell of the secondary particle of the positive electrode active material subjected to TEM-EDX analysis, and FIG. 11B is a TEM observation image. FIG. 11C is a photograph of a TEM-EDX image. As shown in FIGS. 11A to 11C, from the concentration profile of tungsten (W) obtained by the TEM-EDX analysis, the W concentration was found to be around 0.1 μm from the surface in the primary particles to the inside of the particles. A high peak was confirmed (concentrated layer). In addition, it was confirmed that the ratio of the concentration of this peak to the lowest concentration inside the concentrated 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 fluid surface 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 (Kuramo Scientific Instruments, KRS-406). , Respectively. 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, the obtained cathode active material was analyzed by powder X-ray diffraction using Cu-Kα ray using an X-ray diffractometer (X'Pert PRO, manufactured by PANalytical), and the crystal structure of the cathode active material was determined. Consisted of a single phase of hexagonal layered crystal lithium nickel manganese composite oxide.

Further, by analysis using an ICP emission spectrometer, this positive electrode active material was represented by a 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 it was done.

[Manufacture of coin-type battery and evaluation of battery characteristics]
The above positive electrode active material (52.5 mg), acetylene black (15 mg), and polytetrafluoroethylene resin (PTFE) (7.5 mg) were mixed and press-molded under a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm. (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 a glove box in an Ar atmosphere where the dew point was controlled at -80 ° C.

For the negative electrode NE, a negative electrode sheet formed by applying a graphite powder having an average particle diameter of about 20 μm and a polyvinylidene fluoride coated on a copper foil and punched into a disk having a diameter of 14 mm, and 1 M LiPF ₆ as an electrolyte is used as a supporting electrolyte. A mixed solution (equivalent to Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) was used. As the separator 3, a polyethylene porous film having a thickness of 25 μm was used. The coin-type battery CBA had a gasket GA and a wave washer WW, and was assembled into a coin-shaped battery with the positive electrode can PC and the negative electrode can NC. The initial discharge capacity and the positive electrode resistance indicating the performance of the manufactured coin-type battery CBA were evaluated as follows.

[Initial discharge capacity]
After the coin-type battery CBA was manufactured, the initial discharge capacity was allowed to stand for about 24 hours after the open-circuit voltage OCV (Open Circuit Voltage) was stabilized. After that, the current density with respect to the positive electrode was 0.1 mA / cm ² , and the cut-off voltage was 4 The capacity when the battery was charged to 0.3 V, discharged for 1 hour, and then discharged to a cutoff voltage of 3.0 V was defined as the initial discharge capacity.

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

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

(Example 2)
In the second particle growth step, the flow rate of the aqueous solution of sodium tungstate is adjusted such that the concentration of tungsten in the non-oxidizing atmosphere is 20% of the concentration of the additional element (tungsten) in the aqueous solution of the raw material in the oxidizing atmosphere. Except that, a positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1. It was confirmed that the composition of the obtained positive electrode active material was represented by Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ .

(Example 3)
In the particle growth step, the reaction atmosphere was switched from the air atmosphere to the nitrogen atmosphere in the same manner as in Example 1 except that 6.25% of the entire time during which the particle growth was performed was performed. And a positive electrode active material were obtained and evaluated. The obtained transition metal composite hydroxide particles and the composition of the positive electrode active material were the same as in Example 1, and the transition metal composite hydroxide particles were needle-like fine primary particles as in Example 1. (A particle diameter of about 0.2 μm) and an outer peripheral part of plate-like primary particles (particle diameter 0.8 μm) larger than the fine primary particles outside the central part.

(Example 4)
In the particle growth step, sodium tungstate is adjusted so that the concentration (addition ratio) of the additive element (W) in the non-oxidizing atmosphere is 10% of the concentration of the additional 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 Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ .

(Example 5)
In the particle growth step, the same as Example 1 except that the aqueous solution of sodium tungstate was adjusted to have the same flow rate as the flow rate in the oxidizing atmosphere when 50% had elapsed with respect to the entire time during which the particle growth was performed. In this way, 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 Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ .

(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 fixed amount of an aqueous solution of sodium tungstate was supplied, that is, the M addition ratio was set to 100% during the entire time of the particle growth step. . It was confirmed that the composition of the obtained positive electrode active material was represented by Li _1.12 Ni _0.331 Mn _0.331 Co _0.331 Zr _0.002 W _0.005 O ₂ .

(Evaluation)
The particles of the transition metal composite hydroxide of Examples 1 to 5 have a structure including a central portion composed of fine primary particles and an outer peripheral portion composed of plate-like primary particles. In addition, it was confirmed that the central portion contained an additional element. Further, the positive electrode active materials of Examples 1 to 5 each have a structure including an outer shell portion in which aggregated primary particles are sintered and a hollow portion inside the shell portion, and a concentrated layer of an additive element 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, indicating that it had excellent battery characteristics.

DESCRIPTION OF SYMBOLS 1 ... Primary particle 1a ... Fine primary particle 1b ... Plate-like primary particle 2 ... Secondary particle 3 ... Central part 4 ... Peripheral part 4a ... Layer containing high concentration additive element (peripheral part)
5 ... Coating layer 10 ... Transition metal composite hydroxide particles 20 ... Lithium transition metal composite oxide particles 21 ... Primary particles (positive electrode active material)
22 Secondary particles (positive electrode active material)
23 hollow part 24 outer shell 100 positive electrode active material t outer peripheral thickness C concentrated layer CBA coin cell 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 (18)

A method of producing particles of a transition metal composite hydroxide by supplying a raw material aqueous solution containing a transition metal and an ammonium ion donor to form a reaction aqueous solution, and by performing a crystallization reaction,
A nucleation step of performing nucleation in an acidic atmosphere having an oxygen concentration exceeding 5% by volume by controlling the pH value at a liquid temperature of 25 ° C. to be in a range of 12.0 to 14.0;
The reaction aqueous solution containing a nucleus obtained in the nucleation step, the pH value at a liquid temperature of 25 ° C. is lower than the pH value of the reaction aqueous solution in the nucleation step, and 10.5 or more and 12.0 or less. A particle growth step of growing the nucleus by controlling to be in a range,
The particle growing step,
A first particle growing step of growing the nucleus under the acidic atmosphere;
A second particle growth step of switching the oxidizing atmosphere in the first particle growing step to a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less and further growing the nucleus under the non-oxidizing atmosphere; ,
Supplying a raw material aqueous solution containing an additional element different from the transition metal to the reaction aqueous solution under the oxidizing atmosphere;
In the non-oxidizing atmosphere, the supply of the raw material aqueous solution containing the additional element to the reaction aqueous solution may be stopped, or the supply amount of the additional element to the reaction aqueous solution may be reduced from that in the oxidizing atmosphere. Including causing
A method for producing particles of a transition metal composite hydroxide.   The switching from the oxidizing atmosphere to the non-oxidizing atmosphere in the second grain growth step has elapsed from 0.5% to 30% with respect to the entire time during which grain growth is performed during the crystallization reaction. The method for producing transition metal composite hydroxide particles according to claim 1, which is performed at a time point.   The particles of the transition metal composite hydroxide include nickel (Ni), manganese (Mn), cobalt (Co), and the additive element (M), and a substance 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 < 3. The transition metal according to claim 1, wherein t ≦ 0.1 and M is represented by one or more additional elements selected from Nb, Mo, Ta, Ti, Zr, and W). 4. A method for producing composite hydroxide particles.   The transition metal composite according to any one of claims 1 to 3, further comprising a coating step of coating a crystallized substance obtained after the second particle growth step with a compound containing the additional element. A method for producing hydroxide particles.   In the second particle growth step, when the supply of the raw material aqueous solution containing the additional element to the reaction aqueous solution is stopped, 50% or more and 80% or less with respect to the entire time during which the particle growth is performed during the crystallization reaction. The method for producing transition metal composite hydroxide particles according to any one of claims 1 to 3, wherein the addition of the raw material aqueous solution containing the additional element to the reaction aqueous solution is restarted at a point in time when the elapsed time has elapsed. Transition metal, and an additive element having an uneven distribution in the particles, transition metal composite hydroxide particles containing,
Including secondary particles formed by aggregation of a plurality of primary particles,
The secondary particles have a central portion and an outer peripheral portion disposed outside the central portion,
The central portion is formed by aggregating a plurality of fine primary particles,
The outer peripheral portion is larger than the fine primary particles, and is formed by aggregating plate-like primary particles,
The additive element is contained in the central portion at a higher concentration than the outer peripheral portion,
The average particle size is 1 μm or more and 15 μm or less;
Transition metal composite hydroxide particles.   It contains nickel (Ni), manganese (Mn), the additive element (M), and cobalt (Co), and the material 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 represented by one or more additional elements selected from Nb, Mo, Ta, Ti, Zr, and W).   The transition metal composite hydroxide particles according to claim 6, further comprising a coating layer on a surface of the secondary particles, wherein the coating layer contains a compound containing the additive element.   The outer peripheral portion includes, from the surface to the inside of the particle, a region containing the additive element in a range of 50% or more and 80% or less with respect to the thickness of the peripheral portion, and a region not containing the additive element and other regions. The particles of the transition metal composite hydroxide according to claim 6, wherein the particles have: The particles of the transition metal composite hydroxide according to any one of claims 6 to 9 or the particles obtained by heat-treating the particles of the transition metal composite hydroxide are mixed with a lithium compound. A mixing step of forming a lithium mixture;
A method for producing a positive electrode active material for a lithium ion secondary battery, comprising a firing step of firing the lithium mixture formed in the mixing step at 650 ° C. or more and 980 ° C. or less in an oxidizing atmosphere. In the mixing step, the lithium mixture has a ratio (NA _Li / NA _Me ) of the sum of the number of atoms of metals other than lithium (NA _Me ) contained in the lithium mixture to the number of atoms of lithium (NA _Li ). The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 10, wherein the positive electrode is adjusted to be 0.95 or more and 1.5 or less.   The positive electrode active material for a lithium ion secondary battery according to claim 10 or 11, further comprising a heat treatment step of subjecting the transition metal composite hydroxide particles to a heat treatment at 105 ° C or more and 750 ° C or less before the mixing step. Manufacturing method.   The positive electrode active material contains lithium (Li), nickel (Ni), manganese (Mn), an additional element (M), and optionally cobalt (Co), and a material amount ratio of each element ( (Molar ratio) 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 selected from Nb, Mo, Ta, Ti, Zr, and W The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 10 to 12, which is represented by the above-mentioned additional elements). Lithium, a transition metal, containing particles of a lithium transition metal composite oxide containing an additional element other than the transition metal, a positive electrode active material,
Including secondary particles formed by aggregation of a plurality of primary particles,
The secondary particles include an outer shell portion and a hollow portion inside the outer shell portion,
The hollow portion does not include the primary particles,
The secondary particles have an average particle diameter of 1 μm or more and 15 μm or less, and have a concentrated layer in which the additive element is present on the surface of the primary particles.
Positive electrode active material for lithium ion secondary batteries.   15. The positive electrode active material for a lithium ion secondary battery according to claim 14, wherein a ratio of a concentration of the additional element contained in the concentrated layer to a concentration inside the primary particles is 5 or more. The positive electrode active material for a lithium ion secondary battery according to claim 14, wherein the BET specific surface area is 0.7 m ² / g or more and 5.0 m ² / g or less.   The particles of the lithium transition metal composite oxide include lithium (Li), nickel (Ni), manganese (Mn), an additional element (M), and optionally cobalt (Co), and each element includes Is a material 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 from Nb, Mo, Ta, Ti, Zr, and W 17. The positive electrode active material for a lithium ion secondary battery according to claim 14, wherein the positive electrode active material has a hexagonal crystal structure having a layered structure and is represented by one or more selected additional elements. 18. material.   A positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode active material for a lithium ion secondary battery according to any one of claims 14 to 17 is used as a positive electrode material of the positive electrode. , Lithium ion secondary battery.