JP2023040082A - Metal complex hydroxide and production method therefor, cathode active material for lithium-ion secondary battery and production method therefor, and lithium-ion secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode active material having a high output and a high tap density when a secondary battery is formed, and a complex hydroxide as a precursor thereof.

SOLUTION: Provided is a method of producing a metal complex hydroxide, including a first crystallization step and a second crystallization step. The first crystallization step includes supplying a first aqueous raw material solution containing metallic elements and an ammonium ion feeder to a reaction tank, and adjusting the pH of an aqueous reaction solution in the reaction tank to obtain first metal complex hydroxide particles. The second crystallization step includes supplying a second aqueous raw material solution containing metal elements and more tungsten than the first aqueous raw material solution and an ammonium ion feeder to the aqueous reaction solution containing the first metal complex hydroxide particles, adjusting the pH of the aqueous reaction solution, and forming a tungsten-concentrated layer on surfaces of the first metal complex hydroxide particle to obtain second metal complex hydroxide particles having a tapped density of 1.7 g/cm³ or more and 2.3 g/cm³ or less and containing secondary particles having a solid medium structure consisting of a plurality of primary particles aggregated together.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2023,JPO&INPIT

Description

TECHNICAL FIELD The present invention relates to a metal composite hydroxide and its manufacturing method, a positive electrode active material for a lithium ion secondary battery and its manufacturing method, and a lithium ion secondary battery using the same.

In recent years, with the spread of portable electronic devices such as mobile phones and laptop computers, there is a strong demand for the development of small, lightweight lithium-ion secondary batteries with high energy density. In addition, there is a strong demand for the development of high-output secondary batteries as power sources for driving vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles.

As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery, which is a type of lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of desorbing and intercalating lithium is used as an active material used as a material for the negative electrode and the positive electrode.

Among lithium-ion secondary batteries, lithium-ion secondary batteries using a layered or spinel-type lithium metal composite oxide as a positive electrode active material can obtain a voltage of 4V class, so they are currently used as batteries with high energy density. , research and development are being actively carried out, and some are even being put to practical use.

As a positive electrode active material for such a lithium ion secondary battery, lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, Lithium-nickel-cobalt-manganese composite oxide (LiNi1 _{/ 3Co1} / _{3Mn1/ 3O2 )} , lithium-manganese composite oxide using manganese ( _LiMn2O4 ), lithium-nickel-manganese composite oxide (LiNi0 _{. 5} Mn _0.5 O ₂ ) have been proposed.

By the way, in order to further improve the output characteristics of the lithium ion secondary battery, a method of increasing the specific surface area of the positive electrode active material is generally known. When the specific surface area of the positive electrode active material is increased, a sufficient reaction area with the electrolytic solution can be ensured when the positive electrode active material is incorporated in the secondary battery. Accordingly, several techniques have been proposed for improving the output characteristics by controlling the particle structure of the positive electrode active material.

For example, Patent Literatures 1 to 3 propose a method of producing a positive electrode active material using a composite hydroxide obtained by a two-step crystallization process as a precursor. The positive electrode active materials described in these patent documents have a small particle size and a narrow particle size distribution, and have a hollow structure or a space inside the particles, so that they have a high specific surface area and are said to have excellent output characteristics. . However, for example, as a power source for driving a vehicle such as a hybrid automobile, a positive electrode active material having higher output characteristics is required.

On the other hand, addition of a different element to the lithium-metal composite oxide that constitutes the positive electrode active material is being studied as a means of realizing a positive electrode active material having higher output characteristics by further reducing the reaction resistance. As such dissimilar elements, for example, transition metals such as Mo, Nb, W, and Ta, which can take high numbers, have been proposed.

For example, in Patent Document 4, the main component is a lithium transition metal compound having a function of intercalating and deintercalating lithium ions, and the main component raw material contains an additive that suppresses grain growth and sintering during firing. Lithium-transition metal-based compound powder obtained by adding at least one or more at a ratio of 0.01 mol% or more and less than 2 mol% with respect to the total molar amount of transition metal elements in the raw material of the main component, followed by firing. body is described. In addition, the additive is an oxide containing at least one element selected from Mo, W, Nb, Ta, and Re, and the total of metal elements other than Li on the surface portion of the primary particles and the additive element It is described that the total atomic ratio of the additive elements to the grain is at least 5 times the atomic ratio of the entire grain.

Further, in Patent Document 5, a step of dispersing W on the surfaces of the primary particles of the powder by adding and mixing an alkaline aqueous solution in which a tungsten compound is dissolved in a specific proportion to a lithium metal composite oxide powder; Li ₂ WO ₄ , Li ₄ WO ₅ , or Li ₆ W ₂ O ₉ by heat-treating the alkaline aqueous solution in which the mixed tungsten compound is dissolved and the lithium metal composite oxide powder in the range of 100 to 700 ° C. A manufacturing method has been proposed in which fine particles containing lithium tungstate obtained from the above are formed on the surface of the lithium metal composite oxide powder or on the surface of the primary particles of the powder.

Further, in Patent Document 6, a positive electrode active material made of a lithium metal composite oxide is composed of primary particles and secondary particles formed by agglomeration of the primary particles, and voids through which an electrolytic solution can permeate are formed in the secondary particles. A positive electrode active material has been proposed, which has a compound layer having a layer thickness of 20 nm or less containing lithium in which tungsten is concentrated on the surface or grain boundary of the lithium metal composite oxide, and which has a layer thickness of 20 nm or less. As a preferred method for obtaining the powder, a lithium metal composite oxide can be obtained by mixing a composite hydroxide or a tungsten compound together when mixing a composite oxide and a lithium compound, followed by firing. However, in this method, it is said that the particle size of the tungsten compound is preferably 1/5 times or less the average particle size of the manganese composite hydroxide or the manganese composite hydroxide.

Further, in Patent Document 7, in the crystallization reaction, the nucleation step and the particle growth step are separated by pH control to produce composite hydroxide particles, and tungsten is added to the surface of the obtained composite hydroxide particles. A method for producing a transition metal composite hydroxide comprising a coating step of forming a coating containing and a positive electrode active material using the hydroxide as a precursor have been proposed.

Further, in Patent Document 8, a layer of a first positive electrode active material represented by Li _x1 Ni _a1 Mn _b1 Co _c1 O ₂ is provided on the surface of a current collector, and A positive _electrode for a lithium secondary battery has been proposed, _{which is} provided with a layer of a second positive electrode active _material represented by _{Lix2Nia2Mnb2Coc2MdO2} (M is Mo, W _, and Nb).

In addition, Patent Document 9 discloses a method for producing a nickel-cobalt composite hydroxide, wherein a solution containing nickel, cobalt and manganese, a complex ion forming agent and a basic solution are separately and simultaneously placed in one reaction vessel. a first crystallization step for obtaining nickel-cobalt composite hydroxide particles by supplying a solution containing nickel, cobalt and manganese, a complex ion forming agent, and a basic solution after the first crystallization step. and a solution containing the element M are supplied separately and simultaneously, thereby supplying the nickel-cobalt composite hydroxide particles with nickel, cobalt, manganese and the element M (Al, Mg, Ca, Ti, Zr, Nb, Ta , Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and Lu. including a second crystallization step of crystallizing oxide particles, wherein the total moles of nickel, cobalt and manganese supplied in the first crystallization step are MOL (1), nickel supplied in the second crystallization step; A manufacturing method has been proposed in which 0.30≦MOL(1)/{MOL(1)+MOL(2)}<0.95, where MOL(2) is the total mole of cobalt and manganese.

JP 2012-246199 A JP 2013-147416 A JP 2016-094307 A JP 2008-305777 A JP 2013-125732 A JP 2014-197556 A JP 2012-252844 A JP 2012-079608 A JP 2016-210674 A

However, in the method described in Patent Document 4, some of the additive elements such as Mo, Ta, and W are substituted with Ni arranged in layers in the crystal, and battery capacity, cycle characteristics, etc. There was a problem that the battery characteristics deteriorated.

In addition, the lithium metal composite oxide produced by the production method described in Patent Document 5 has improved output characteristics, but the cycle characteristics are not sufficient when the thickness of the tungsten fine particles formed on the particle surface is not uniform. was there.

In addition, the method described in Patent Document 6 is not industrially suitable because it is necessary to pulverize the tungsten compound once in order to obtain a nano-order tungsten compound, and it is not easy to handle. In addition, since the thickness of the compound layer varies due to non-uniformity in the particle size of the obtained fine particles, the reaction resistance is insufficiently reduced, and the effect of improving the output characteristics is limited. In addition, it is also described that tungsten is contained as an additive element in manganese composite hydroxide in order to obtain the powder, but it is difficult to form a compound layer in which tungsten is concentrated in nano order by this method.

In addition, the method described in Patent Document 7 is industrially unpreferable because the step of coating with tungsten is added, which increases the number of steps. In addition, although tungsten is deposited by controlling the pH in the coating process, the thickness of the coating layer is not uniform due to fluctuations in the controlled pH, so uniform coating is difficult. In addition, when a lithium metal composite oxide obtained by mixing a metal composite hydroxide coated with tungsten unevenly with lithium is used, the coating layer becomes a resistance, and the output decreases rather. there were.

In addition, in the positive electrode active material formed by the method described in Patent Document 8, since the first positive electrode active material and the second positive electrode active material are in different phases, when used in a secondary battery, charging and discharging There was a problem that the structural change at the time of reaction was different, cracks were generated during repeated charging and discharging, and the cycle characteristics were deteriorated.

In addition, the composite hydroxide and the positive electrode active material obtained by the method described in Patent Document 9 have a depth ratio of 5% or more and less than 50% in the radial direction. It is described that the spectrum has a peak of the element M, and the positive electrode active material contains the element M containing tungsten inside the surface layer of the secondary particles, so that the crystallinity is reduced and used for secondary batteries. battery characteristics may deteriorate.

In view of such problems, the present invention provides a positive electrode active material having high crystallinity and high tap density when used for the positive electrode of a secondary battery, and when used for the positive electrode of the secondary battery, the positive electrode resistance An object of the present invention is to provide a positive electrode active material with reduced (reaction resistance) and capable of obtaining high output, and a metal composite hydroxide that is a precursor thereof.

A first embodiment of the invention comprises nickel, manganese and tungsten and optionally cobalt and the element M, and the atomic ratio of the respective metal elements is Ni:Mn:Co: W: M = x: y: z: a: b (x + y + z = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 < a ≤ 0.1, 0 ≤ b ≤ 0.1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta) A method for producing a metal composite hydroxide in which a first raw material aqueous solution containing a metal element and an ammonium ion donor are supplied to a reaction tank, the pH of the reaction aqueous solution in the reaction tank is adjusted, and crystallization is performed. a first crystallization step of obtaining first metal composite hydroxide particles by performing a precipitation reaction; and a reaction aqueous solution containing the first metal composite hydroxide particles containing a metal element and By supplying a second raw material aqueous solution containing more tungsten than the raw material aqueous solution of 1 and an ammonium ion donor, adjusting the pH of the reaction aqueous solution, and performing a crystallization reaction, the first metal composite hydroxide and a second crystallization step of forming a tungsten-concentrated layer on the surface of the substance particles to obtain second metal composite hydroxide particles, and the metal composite hydroxide obtained after the second crystallization step. is a metal composite hydroxide containing secondary particles having a tap density of 1.7 g/cm ³ or more and 2.3 g/cm ³ or less and having a solid structure formed by aggregating a plurality of primary particles. A manufacturing method is provided.

Further, the first crystallization step includes a nucleation step for generating nuclei and a grain growth step for grain growth, and the second crystallization step includes grain growth following the grain growth step. The first crystallization step and the second crystallization step are performed in a non-oxidizing atmosphere with an oxygen concentration of 1% by volume or less, and the first crystallization step and the second crystallization step For particle growth in , the pH of the reaction aqueous solution is preferably adjusted to be lower than the pH value of the reaction aqueous solution in the nucleation step.

In addition, the metal element in the first raw material aqueous solution is added in the reaction tank in a range of 50% by mass or more and 95% by mass or less with respect to the total amount of metal added in the first crystallization step and the second crystallization step. It is preferable to supply the second raw material aqueous solution in the second crystallization step after supplying to . In addition, the second crystallization step preferably includes forming the tungsten-concentrated layer to a thickness of 100 nm or less in the direction from the surface toward the center of the second metal composite hydroxide. . In addition, the addition of the second raw material aqueous solution in the second crystallization step is performed when 50% or more and 95% or less of the entire grain growth time has passed in the first and second crystallization steps. preferably. Moreover, it is preferable to supply the second raw material aqueous solution by separately supplying the first raw material aqueous solution and the tungsten-containing aqueous solution to the reaction aqueous solution. Moreover, the concentration of tungsten in the aqueous solution containing tungsten is preferably 18% by mass or more with respect to the entire aqueous solution containing tungsten.

A second embodiment of the present invention comprises nickel, manganese and tungsten and optionally cobalt and the element M, and the atomic ratio of the respective metal elements is Ni:Mn:Co:W : M = x: y: z: a: b (x + y + z = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 < a ≤ 0 .1, 0 ≤ b ≤ 0.1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta) A metal composite hydroxide having a tungsten-concentrated layer on the surface, a tap density of 1.7 g/cm ³ or less and 2.3 g/cm ³ or more, and a plurality of primary particles aggregated Provided is a composite metal hydroxide containing secondary particles having a solid structure of

Also, the average thickness of the tungsten-concentrated layer is preferably 100 nm or less. In addition, the average particle size of the composite hydroxide is 4.0 μm or more and 9.0 μm or less, and [(d90−d10)/MV], which is an index showing the spread of the particle size distribution, is 0.65 or less. is preferred.

In the third embodiment of the present invention, at least one of the metal composite hydroxide obtained by the above production method and the metal composite oxide obtained by heat-treating the metal composite hydroxide is mixed with a lithium compound. and sintering the lithium mixture to obtain a lithium metal composite oxide.

In addition, the value of (d50 of the positive electrode active material/d50 of the metal composite hydroxide), which is an index indicating the degree of aggregation between particles of the lithium metal composite oxide, is 0.95 or more and 1.05 or less. Adjusting is preferred.

A fourth embodiment of the present invention comprises lithium, nickel, manganese and tungsten and optionally cobalt and the element M, wherein the atomic ratio of the respective metal elements is Li:Ni:Co: Mn: W: M = 1 + u: x: y: z: a: b (x + y + z = 1, -0.05 ≤ u ≤ 0.50, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0 .55, 0≦z≦0.4, 0<a≦0.1, 0≦b≦0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and one or more elements selected from Ta), and the lithium metal composite oxide is a secondary particle having a solid structure in which a plurality of primary particles are aggregated A compound containing tungsten and lithium is concentrated in the surface layer of the primary particles present on the surface or inside the secondary particles and the grain boundaries between the primary particles, and the tap density is 1.8 g / cm ³ A positive electrode active material for a lithium ion ^secondary battery is provided, which has a BET specific surface area of 0.6 m ² /g or more and 1.2 m ² /g or less.

Also, the crystallite size of the (003) plane obtained by powder X-ray diffraction measurement is preferably 120 nm or more.

In a fifth embodiment of the present invention, a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and using the positive electrode active material for a lithium ion secondary battery as the positive electrode material of the positive electrode. A second battery is provided.

According to the present invention, a positive electrode active material having high crystallinity and high tap density is used for the positive electrode of a secondary battery, the positive electrode resistance (reaction resistance) is reduced, and high output can be obtained. It is possible to provide a positive electrode active material capable of and a metal composite hydroxide that is a precursor thereof. Further, according to the present invention, it is possible to provide a secondary battery containing such a positive electrode active material. Furthermore, according to the present invention, it is possible to provide a method for easily producing such positive electrode active material and metal composite hydroxide on an industrial scale. Therefore, the industrial significance of the present invention is extremely large.

1(A) and 1(B) are schematic diagrams showing an example of a metal composite hydroxide, and FIG. 1(C) is a cross-sectional SEM image showing a metal composite hydroxide having a solid structure. An example. FIG. 2 is a diagram showing an example of a method for producing a metal composite hydroxide. FIG. 3 is a diagram showing an example of a method for producing a metal composite hydroxide. FIGS. 4(A) and 4(B) are diagrams for explaining the start point of addition of an aqueous solution containing tungsten. FIGS. 5A and 5B are schematic diagrams showing examples of lithium metal composite oxides. FIG. 6 is a diagram showing an example of a method for producing a lithium metal composite oxide. FIG. 7 is a schematic diagram showing a coin-type battery for evaluation used in Examples. FIGS. 8(A) and 8(B) show a drawing-substituting photograph (upper diagram) showing the distribution of W by surface analysis using EDX of a metal composite hydroxide, and a tungsten-enriched layer in the drawing-substituting photograph. It is an explanatory diagram (lower diagram) for

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

1. Metal composite hydroxide FIGS. 1A and 1B are schematic diagrams showing an example of the metal composite hydroxide according to the present embodiment, and FIG. It is an example of a cross-sectional SEM image showing a composite hydroxide. As shown in FIG. 1A, composite metal hydroxide 10 includes secondary particles 2 formed by aggregation of a plurality of primary particles 1 . The shape of the primary particles 1 constituting the secondary particles 2 is not particularly limited, but may be, for example, plate-like, needle-like, or fine primary particles smaller than these. In addition, the particle structure of the secondary particles 2 is not particularly limited. It is possible to have a void structure having a plurality of voids inside the particles 2, a multilayer structure having layered voids inside the secondary particles 2, etc. Among these, the obtained positive electrode active material has a higher particle strength. and a high tap density, a solid structure is preferred.

In this specification, the secondary particles 2 having a solid structure means that the plurality of primary particles 1 are distributed relatively uniformly and densely throughout the secondary particles 2, and It means having a structure in which one or more clear hollow portions (for example, occupying 10% or more of the cross-sectional area of the secondary particles 2) do not exist (see FIG. 1(C)). Further, when the metal composite hydroxide 10 has a solid structure, the porosity of the metal composite hydroxide 10 (the void area inside the secondary particles 2 with respect to the cross-sectional area of the secondary particles 2) is, for example, 20% or less. and preferably 10% or less.

In addition, the metal composite hydroxide 10 may be composed of the secondary particles 2 only, or may be composed of the secondary particles 2 and the primary particles 1 alone.

(Tungsten concentrated layer)
The metal composite hydroxide 10 (secondary particles 2) has a tungsten-concentrated layer 3 in which tungsten is concentrated on its surface layer, as shown in FIG. 1(B). The tungsten-concentrated layer 3 is formed on the surface of the metal composite hydroxide 10 and refers to a layered region in which tungsten is more concentrated than inside the secondary particles 2 . The positive electrode active material using the metal composite hydroxide 10 with the tungsten-concentrated layer 3 formed thereon as a precursor has high crystallinity and reduced positive electrode resistance (reaction resistance). A secondary battery can obtain a high output. The tungsten-enriched layer 3 can be confirmed, for example, by detecting the W distribution by surface analysis using an energy dispersive X-ray spectrometer (EDX), as shown in FIG. Note that the primary particles 1 are not shown in FIG. 1(B).

As will be described later, the tungsten-concentrated layer 3 is a compound 23 containing tungsten and lithium (for example, tungsten Lithium oxide, etc.) is formed (see FIG. 5).

For example, as shown in FIGS. 5A and 5B, in the lithium metal composite oxide 20 (positive electrode active material), the compound 23 containing tungsten and lithium is the surface layer of the primary particles 21, or the primary particles It is formed at the grain boundary between 21 . Since the compound 23 containing tungsten and lithium has high ionic conductivity, when the lithium metal composite oxide 20 (positive electrode active material) is used for the positive electrode of the secondary battery, the surface layer of the primary particles 21 in contact with the electrolyte, Alternatively, the presence of the compound 23 containing tungsten and lithium at the grain boundaries between the primary particles 21 can reduce the positive electrode resistance of the positive electrode active material and greatly contribute to improving the output characteristics of the secondary battery.

Note that when a conventional method for producing a metal composite hydroxide is used, the tungsten contained in the metal composite hydroxide 10 (precursor) suppresses sintering inside the secondary particles 2 during firing. there were. Therefore, in the conventional precursor containing tungsten, the tungsten in the positive electrode active material obtained contributes to the reduction of the positive electrode resistance, while the crystallinity of the lithium metal composite oxide constituting the positive electrode active material is reduced. had a problem. Therefore, it has been difficult to achieve high output characteristics and high crystallinity in a secondary battery in a positive electrode active material containing tungsten obtained using a conventional manufacturing method. However, since the metal composite hydroxide 10 according to the present embodiment forms the tungsten-concentrated layer 3 on the surface layer, the effect of suppressing the sintering of tungsten inside the secondary particles 2 during firing hardly occurs. It is possible to reduce the positive electrode resistance and improve the crystallinity of the lithium metal composite oxide 20 obtained.

The average thickness of the tungsten-concentrated layer 3 can be, for example, 200 nm or less, preferably 100 nm or less, more preferably 10 nm or more and 100 nm or less in the direction from the surface to the center of the metal composite hydroxide 10. and more preferably 20 nm or more and 50 nm or less. When the thickness of the tungsten-concentrated layer 3 is 100 nm or less, the crystallinity of the lithium metal composite oxide 20 can be further increased, and when the lithium metal composite oxide 20 is used for the positive electrode of the secondary battery, It is possible to further reduce the positive electrode resistance and improve the output characteristics.

The average thickness of the tungsten-concentrated layer 3 is obtained by cutting a metal composite hydroxide 10 embedded in a resin or the like to prepare a sample of the cross section of the secondary particle 2, and using EDX to measure the W distribution surface. Analyze and measure. Specifically, in the sample of the secondary particle 2 cross section, the secondary particle 2 cross section that is 80% or more of the volume average particle diameter (MV) measured using a laser light diffraction scattering particle size analyzer is randomly selected. 20 selected secondary particles 2, in the direction from the surface of the metal composite hydroxide 10 toward the center C, in the direction from the surface of the metal composite hydroxide 10 toward the center C, the thickness of the site (tungsten concentrated layer 3) where W is detected ( width) are measured at five or more locations, and the average thickness of the tungsten-concentrated layer 3 for each secondary particle 2 is obtained. By calculating the average thickness of each of the selected 20 secondary particles 2, the average thickness of the tungsten-concentrated layer 3 can be obtained.

If the average thickness of the tungsten-concentrated layer 3 exceeds 100 nm, the effect of suppressing sintering due to tungsten increases during firing, and the growth of the primary particles 21 may be hindered. Therefore, in the obtained lithium metal composite oxide 20, a large number of primary particles having a small crystallite diameter are formed, and many crystal grain boundaries are generated, which may increase the reaction resistance in the positive electrode. In addition, the crystallinity of the lithium metal composite oxide 20 may be lowered as the growth of the primary particles 21 is suppressed.

On the other hand, when the average thickness of the tungsten-concentrated layer 3 is less than 10 nm, the specific surface area increases, and the metal composite hydroxide 10 easily aggregates during firing, so the packing density of the resulting positive electrode active material decreases. As a result, the battery capacity per volume (volume) may decrease. In addition, the compound 23 containing tungsten and lithium may not be sufficiently formed in the lithium metal composite oxide 20, resulting in insufficient lithium ion conductivity.

Further, the average thickness of the tungsten-concentrated layer 3 is, with respect to the volume average particle diameter (MV) of the metal composite hydroxide 10, in the direction from the surface of the secondary particles 2 to the center C of the secondary particles 2, for example , 3% or less. The average thickness of the tungsten-concentrated layer 3 is preferably 2% or less, more preferably 0.1, from the viewpoint of further improving the crystallinity of the lithium metal composite oxide 20 and further reducing the reaction resistance. % or more and 2% or less, more preferably 0.1% or more and 1% or less, and still more preferably 0.1% or more and 0.5% or less.

(Volume average particle size)
The volume average particle diameter (MV) of the metal composite hydroxide 10 is not particularly limited, but is preferably 4.0 μm or more, more preferably 4 μm or more and 9.0 μm or less, and preferably 4.0 μm or more and 7 μm or less. is. The volume average particle diameter (MV) of the metal composite hydroxide 10 correlates with the volume average particle diameter (MV) of the lithium metal composite oxide 20 (positive electrode active material) using the metal composite hydroxide 10 as a precursor. Therefore, by controlling the volume average particle size (MV) of the metal composite hydroxide 10 within the above range, the lithium metal composite oxide 20 (see FIG. 5) using the metal composite hydroxide 10 as a precursor can be obtained. The volume average particle diameter (MV) can also be controlled within the above range.

When the volume average particle diameter (MV) of the metal composite hydroxide 10 is less than 4 μm, the specific surface area is high, and in the baking step (step S40, see FIG. 6) for producing the positive electrode active material, the metal composite water Particles of the oxide 10 easily agglomerate, and the packing density of the obtained positive electrode active material is lowered, and the battery capacity per volume (volume) may be lowered. In addition, the volume average particle diameter (MV) can be obtained, for example, from a volume integrated value measured by a laser beam diffraction/scattering particle size analyzer.

(Spread of particle size distribution)
The composite metal hydroxide 10 has an index [(d90-d10)/MV] of 0.65 or less, which is an index showing the spread of the particle size distribution. The particle size distribution of the lithium metal composite oxide 20 (positive electrode active material) is strongly influenced by the metal composite hydroxide 10 that is its precursor. Therefore, when the metal composite hydroxide 10 containing many fine particles and coarse particles is used as the precursor, the lithium metal composite oxide 20 also contains many fine particles and coarse particles. In a secondary battery using such a lithium metal composite oxide 20 as a positive electrode active material, battery characteristics such as thermal stability, cycle characteristics, and output characteristics may deteriorate. Therefore, when [(d90-d10)/MV] of the metal composite hydroxide 10 is adjusted to the above range, the particle size distribution of the lithium metal composite oxide 20 obtained by using this as a precursor is narrowed so that fine particles and Mixing of coarse particles can be suppressed.

The lower limit of [(d90-d10)/MV] of the metal composite hydroxide 10 is not particularly limited, but it is preferably about 0.25 or more from the viewpoint of cost and productivity. Assuming industrial-scale production, it is not realistic to use a metal composite hydroxide 10 with an excessively small [(d90-d10)/MV].

In addition, d10 means the particle size at which particles in each particle size are accumulated from the smaller particle size side, and the cumulative volume is 10% of the total volume of all particles, It means the particle size whose cumulative volume is 90% of the total volume of all particles. In addition, d10 and d90 can be obtained from volume integrated values measured with a laser beam diffraction scattering particle size analyzer in the same manner as the volume average particle diameter (MV).

(tap density)
The tap density of the metal composite hydroxide 10 is preferably 1.7 g/cm ³ or more and 2.3 g/cm 3 or less, more preferably 1.8 g/cm ^{3 or} more and 2.2 g/cm ³ or less, More preferably, it is 1.9 g/cm ³ or more and 2.1 g/cm ³ or less.

The tap density of the metal composite hydroxide 10 correlates with the tap density of the lithium metal composite oxide 20 (positive electrode active material) using the metal composite hydroxide 10 as a precursor, and the metal composite hydroxide 10 has a solid structure. , the tap density of the obtained lithium metal composite oxide 20 tends to be slightly higher than that of the metal composite hydroxide 10 . Therefore, by controlling the tap density of the metal composite hydroxide 10 within the above range, the tap density of the lithium metal composite oxide 20 (see FIG. 5) using this metal composite hydroxide 10 as a precursor is It is possible to control within the range described later. When the metal composite hydroxide 10 has a tap density within the above range, the obtained lithium metal composite oxide 20 also has a high tap density. Therefore, when the lithium metal composite oxide 20 is used for the positive electrode, a secondary battery having a high volumetric energy density can be obtained.

The positive electrode active material obtained by using the metal composite hydroxide 10 as a precursor has a tungsten-concentrated layer 3, and by setting the above [(d90-d10) / MV] to the preferable range, in the secondary battery , thermal stability, cycle characteristics, and output characteristics can be further improved, and by setting the tap density within the above range, a higher energy density can be obtained. In addition, when the metal composite hydroxide 10 has a solid structure, the positive electrode active material obtained has high particle strength, so that the energy density per volume can be increased, and during charge-discharge cycles Cycle characteristics can be improved by suppressing cracking of the positive electrode active material.

(composition)
The composition of the metal composite hydroxide 10 is not particularly limited, but for example, the metal composite hydroxide 10 contains Ni, Co and W, and optionally Mn and M, and the number of atoms of each metal element The ratio (A) is Ni:Co:Mn:W:M=x:y:z:a:b (x+y+z=1, 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0<a≦0.1, 0≦b≦0.1, M is Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta one or more metal elements selected from).

In addition, since the atomic ratio (A) of each metal element in the metal composite hydroxide 10 is maintained in the lithium metal composite oxide 20, the metal composite represented by the ratio (A) of the metal elements In the hydroxide 10, the composition range and critical significance of nickel, manganese, cobalt, tungsten and the element M constituting the hydroxide 10 are the same as those of the positive electrode active material represented by the ratio (B), which will be described later. Therefore, description of these matters is omitted here.

Further, the metal composite hydroxide 10 has the general formula (A1 ₎ : _{NixMnyCozWaMb ( OH ) 2+α} (x+y+z=1, 0.3≦x≦0.95, 0.05≦y ≤0.55, 0≤z≤0.4, 0<a≤0.1, 0≤b≤0.1, 0≤α≤0.5, M is Mg, Ca, Al, Ti, V, one or more metal elements selected from Cr, Zr, Nb, Mo, Hf, and Ta).

In the general formula (A1), from the viewpoint of further improving the capacity characteristics of the secondary battery using the obtained positive electrode active material, the composition is represented by the general formula (A2): Ni _{x Mny} Co _z W _a M _b (OH)2+α(x+y+z=1, 0.7<x≦0.95, 0.05≦y≦0.1, 0≦z≦0.2, 0<a≦0.1, 0≦b≦ 0.1, 0≦α≦0.5, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, and Mo). Furthermore, from the viewpoint of achieving both thermal stability and battery capacity, the value of x in the general formula (A2) is more preferably 0.7 < x ≤ 0.9, and 0.7 < More preferably, x≦0.85.

In the general formula (A1), from the viewpoint of further improving the thermal stability of the secondary battery using the obtained positive electrode active material, the composition is represented by the general formula (A3): Ni _{x Mny} Co _z W _a M _b (OH) _2+α (x+y+z=1, 0.3≦x≦0.7, 0.1≦y≦0.55, 0≦z≦0.4, 0<a≦0.1, 0≦b ≤ 0.1, 0 ≤ α ≤ 0.5, M is one or more elements selected from Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta). .

2. Method for Producing Metal Composite Hydroxide FIGS. 2 and 3 are diagrams showing an example of a method for producing a metal composite hydroxide according to the present embodiment. The production method according to the present embodiment contains nickel, manganese, tungsten, optionally cobalt, and the element M by a crystallization reaction, and the atomic ratio of the respective metal elements is Ni: Mn: Co: W: M = x: y: z: a: b (x + y + z = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0<a≦0.1, 0≦b≦0.1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta) A method for producing a metal composite hydroxide represented by By the production method according to the present embodiment, the metal composite hydroxide 10 having the properties described above can be easily produced on an industrial scale.

[Crystallization reaction]
As shown in FIG. 2, in the method for producing the metal composite hydroxide 10, nickel (Ni) and manganese (Mn), and optionally cobalt (Co) and/or metal elements are placed in the reaction tank. A first crystallization step (step S10) of supplying a first raw material aqueous solution containing (M) and an ammonium ion donor to carry out a crystallization reaction to obtain first metal composite hydroxide particles. and supplying a second raw material aqueous solution containing more tungsten than the first raw material aqueous solution and an ammonium ion donor to the reaction aqueous solution containing the first metal composite hydroxide particles to initiate a crystallization reaction. and a second crystallization step (step S20) of forming a tungsten-concentrated layer on the surface of the first metal composite hydroxide particles to obtain second metal composite hydroxide particles.

In the method for producing a metal composite hydroxide according to the present embodiment, in the second crystallization step (step S20), the surfaces of the first composite hydroxide particles obtained in the first crystallization step (step S10) Then, by forming the tungsten-concentrated layer 3, the second metal composite hydroxide particles can be obtained. Since the inside of the second metal composite hydroxide particles does not contain tungsten or is composed of the first metal composite hydroxide particles with a low tungsten content, lithium metal obtained using this as a precursor The composite oxide 20 (positive electrode active material) has high crystallinity inside the particles, and the compound 23 containing tungsten and lithium derived from the tungsten-concentrated layer 3 is the surface of the primary particles 21 or the grain boundary between the primary particles 21. , the secondary battery has excellent output characteristics.

As shown in FIG. 3, the first crystallization step (step S10) further includes a nucleation step (step S11) mainly for nucleation and a grain growth step (step S12) for mainly grain growth. is preferred. The nucleation step (step S11) and the particle growth step (step S12) can be clearly separated, for example, by controlling the pH of the reaction aqueous solution, and the metal composite having a narrow particle size distribution and a uniform particle size Hydroxide 10 can be obtained. The second crystallization step (step S20) is a step in which grain growth is mainly performed following the grain growth step (step S12).

A method for producing a nickel composite hydroxide including such a two-stage crystallization process is disclosed, for example, in Patent Documents 2 and 3, and for detailed conditions, refer to these documents. conditions can be adjusted accordingly. In addition, as described later, the method for producing a metal composite hydroxide according to the present embodiment can form the tungsten-concentrated layer 3 having a desired film thickness using the conditions of a known crystallization method. , can be easily applied to industrial scale production.

Each step of the manufacturing method including the nucleation step (step S11) and the grain growth step (step S12) will be described below with reference to FIG. Note that the following description is an example of a method for producing the metal composite hydroxide 10, and is not limited to this method.

(1) First crystallization step (step S10)
(Nucleation step)
First, the first raw material aqueous solution and the ammonium ion donor are supplied, and the pH of the reaction aqueous solution (nucleation aqueous solution) in the reaction vessel is controlled within a predetermined range to generate nuclei (step S11). The first raw material aqueous solution is prepared, for example, by dissolving a compound containing a transition metal as a raw material in water. In the method for producing a metal composite hydroxide described below, the composition ratio of the metal composite hydroxide formed by crystallization in each step is the same as the composition ratio of each metal in the raw material aqueous solution. The composition ratio of each metal in the raw material aqueous solution can be the composition ratio of the transition metals of the desired composite metal hydroxide. Also, the first raw material aqueous solution may contain a small amount of tungsten, or may contain no tungsten.

First, an alkaline aqueous solution and an aqueous solution containing an ammonium ion donor are supplied and mixed in a reaction vessel, and the pH value measured at a liquid temperature of 25 ° C. is 12.0 or more and 14.0 or less, and the ammonium ion concentration is A pre-reaction aqueous solution having a concentration of 3 g/L or more and 25 g/L or less is prepared.

When mainly obtaining metal composite hydroxide particles having a solid structure with a tap density of 1.7 g/cm ³ or more and 2.3 g/cm ³ or less, the reaction atmosphere in the reaction vessel is, for example, oxygen concentration is A non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less is preferable, and an atmosphere with an oxygen concentration of 1% by volume or less is more preferable. The atmosphere is controlled by, for example, introducing nitrogen gas. 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.

Then, while stirring the pre-reaction aqueous solution in the reaction vessel, the first raw material aqueous solution is supplied into the reaction vessel to form the reaction aqueous solution (nucleation-use aqueous solution). In the nucleation step (step S11), the pH value and ammonium ion concentration of the aqueous solution for nucleation change with the nucleation in the reaction aqueous solution. It is preferable to control the pH value of the liquid in the range of pH 12.0 or more and 14.0 or less and the concentration of ammonium ions in the range of 3 g/L or more and 25 g/L or less based on the liquid temperature of 25°C. When the pH value of the reaction aqueous solution (nucleation aqueous solution) is within the above range, nucleation occurs preferentially with little growth of nuclei.

The pH value of the reaction aqueous solution (nucleation aqueous solution) measured at a liquid temperature of 25° C. is preferably 12.0 or more and 14.0 or less, more preferably 12.3 or more and 13.5 or less, and still more preferably 12.5. It is in the range of 5 or more and 13.3 or less. When the pH is within the above range, the growth of nuclei can be suppressed, nucleation can be prioritized, and the nuclei generated in the nucleation step can be 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) progresses along with nucleation, so that the particle size of the metal composite hydroxide particles obtained becomes non-uniform and the particle size distribution deteriorates. On the other hand, if the pH value exceeds 14.0, the generated nuclei may become too fine, and the aqueous reaction solution (aqueous solution for nucleation) may gel.

The variation range of the pH value in the reaction aqueous solution (nucleation aqueous solution) is preferably within ±0.2. If the fluctuation range of the pH value is large, the ratio of the amount of nucleation and particle growth will not be constant, making it difficult to obtain metal composite hydroxide particles with a narrow particle size distribution.

The ammonium ion concentration of the reaction aqueous solution (nucleation aqueous solution) is preferably adjusted within the range of 3 g/L or more and 25 g/L or less, more preferably 5 g/L or more and 20 g/L or less. Since ammonium ions function as a complexing agent in the reaction aqueous solution, when the ammonium ion concentration is less than 3 g/L, the solubility of metal ions cannot be kept constant, and the reaction aqueous solution tends to gel. As a result, it becomes difficult to obtain metal composite hydroxide particles having a uniform shape and particle size. On the other hand, when the ammonium ion concentration exceeds 25 g/L, the solubility of the metal ions becomes too high, so that the amount of metal ions remaining in the reaction aqueous solution increases, which may cause composition deviation.

If the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of the metal ions fluctuates and uniform metal composite hydroxide particles are no longer formed. Therefore, it is preferable to control the fluctuation range of the ammonium ion concentration within a certain range through the nucleation step (step S11) and the particle growth step (step S12). Specifically, the fluctuation range is ±5 g/L. Control is preferred.

In the nucleation step (step S11), new nuclei are continuously generated by supplying an aqueous solution containing the first raw material aqueous solution, an alkaline aqueous solution, and an ammonium ion donor to the reaction aqueous solution (nucleation aqueous solution). be done. Then, when a predetermined amount of nuclei is generated in the nucleation aqueous solution, the nucleation step is terminated. At this time, the amount of nuclei generated can be determined from the amount of the metal compound contained in the raw material aqueous solution supplied to the nucleation aqueous solution.

The amount of nuclei generated in the nucleation step (step S11) is not particularly limited, but from the viewpoint of obtaining metal composite hydroxide particles with a narrow particle size distribution, the crystallization step (first crystallization step and It is preferably 0.1 atomic % or more and 2 atomic % or less, and 0.1 atomic % or more and 1.5 atomic % with respect to the metal element in the metal compound contained in the raw material aqueous solution supplied through the (including the precipitation step). More preferably:

Moreover, in the nucleation step, the upper limit of the temperature of the reaction aqueous solution (the aqueous solution for nucleation) is not particularly limited, but for example, it is preferably 60° C. or lower, more preferably 50° C. or lower. This is because, if the temperature of the reaction aqueous solution (the aqueous solution for nucleation) exceeds 60° C., the primary crystals may be distorted and the tap density may begin to decrease. In addition, the lower limit of the temperature of the reaction aqueous solution (the aqueous solution for nucleation) is, for example, 20° C. or higher.

(Particle growth step)
Next, the particles are grown in a reaction aqueous solution (aqueous solution for particle growth) whose pH is adjusted to a specific range (step S12). The aqueous reaction solution (aqueous solution for particle growth) is formed by supplying the aqueous reaction solution containing the generated nuclei with the first raw material aqueous solution, the alkaline aqueous solution, and the aqueous solution containing the ammonium ion donor. The reaction aqueous solution (aqueous solution for particle growth) preferably has a pH value of 10.5 or more and 12.0 or less and an ammonium ion concentration of 3 g/L or more and 25 g/L or less, measured at a liquid temperature of 25°C. As a result, particle growth takes precedence over nucleation in the aqueous reaction solution (aqueous solution for particle growth).

When mainly obtaining metal composite hydroxide particles having a solid structure with a tap density of 1.7 g/cm ³ or more and 2.3 g/cm ³ or less, the reaction atmosphere in the reaction vessel is, for example, oxygen concentration is A non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less is preferable, and an atmosphere with an oxygen concentration of 1% by volume or less is more preferable. When the oxygen concentration of the reaction atmosphere in the reaction vessel is 1% by volume or less, the secondary particles 2 having a solid structure in which the primary particles 1 are densely arranged can be easily obtained, and the obtained positive electrode active material crystallinity can be further improved. The atmosphere is controlled by, for example, introducing nitrogen gas.

Specifically, after the nucleation step is completed, the pH value of the nucleation aqueous solution in the reaction tank is adjusted to 10.5 or more and 12.0 or less based on the liquid temperature of 25 ° C., and the reaction aqueous solution in the particle growth step An aqueous solution for grain growth is formed. The pH value can be adjusted by stopping the supply of only the alkaline aqueous solution, but from the viewpoint of improving the uniformity of the particle size, the pH value can be adjusted by temporarily stopping the supply of all the aqueous solution. preferable. In addition, the adjustment of the pH value is performed when the reaction aqueous solution (nucleation aqueous solution) contains an inorganic acid of the same kind as the acid constituting the compound containing the transition metal as a raw material, for example, a transition metal sulfate as a raw material. may be performed by supplying sulfuric acid.

Next, the supply of the first raw material aqueous solution is resumed while stirring the reaction aqueous solution (aqueous solution for particle growth). At this time, since the pH value of the aqueous solution for particle growth is within the range described above, almost no new nuclei are generated, the nuclei (particles) grow, and the first metal composite hydroxide having a predetermined particle size is obtained. Particles can be formed. In the particle growth step (step S12) as well, the pH value and the ammonium ion concentration of the aqueous solution for particle growth change as the particles grow. It is necessary to maintain the above range.

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, more preferably 11.5 or more and 11.9 or less, at a liquid temperature of 25°C. control within the range of When the pH is within the above range, generation of new nuclei can be suppressed, particle growth can be prioritized, and the resulting metal composite hydroxide can be homogeneous and have a narrow particle size distribution. On the other hand, if the pH value is less than 10.5, the concentration of ammonium ions increases and the solubility of metal ions increases, which not only slows down the crystallization reaction but also reduces the amount of metal ions remaining in the reaction aqueous solution. may increase and productivity may deteriorate. On the other hand, if the pH value exceeds 12.0, the amount of nuclei generated during the particle growth step increases, the particle size of the metal composite hydroxide particles obtained becomes non-uniform, and the particle size distribution deteriorates.

The variation range of the pH value in the reaction aqueous solution (particle growth aqueous solution) is preferably within ±0.2. If the fluctuation range of the pH value is large, the ratio of the amount of nucleation and particle growth will not be constant, making it difficult to obtain a metal composite hydroxide with a narrow particle size distribution.

In addition, the pH value in the grain growth step (step S12) is preferably adjusted to a lower value than the pH value in the nucleation step (step S11). The pH value in the step (step S12) is preferably lower than the pH value in the nucleation step (step S11) by 0.5 or more, more preferably by 0.8 or more.

For example, when the pH value of the reaction aqueous solution (the nucleation step and/or the particle growth step) is 12.0, this is a boundary condition between nucleation and nucleation growth. It can be the condition of either the production process or the grain growth process. That is, when the pH value of the nucleation step is set higher than 12.0 to generate a large amount of nuclei, and then the pH value of the particle growth step is set to 12.0, a large amount of nuclei are present in the reaction aqueous solution. Particle growth occurs preferentially, and metal composite hydroxide particles with a narrow particle size distribution can be obtained. On the other hand, when the pH value of the nucleation step is set to 12.0, since there are no growing nuclei in the reaction aqueous solution, nucleation occurs preferentially. Then, the generated nuclei grow and good metal composite hydroxide particles can be obtained.

The ammonium ion concentration of the aqueous reaction solution (aqueous solution for particle growth) can be set in the same range as the preferred range of the ammonium ion concentration in the aqueous reaction solution (aqueous solution for nucleation). Also, the fluctuation range of the ammonium ion concentration can be the same as the preferable range in the reaction aqueous solution (nucleation aqueous solution).

(2) Second crystallization step (step S20)
Next, a second raw material aqueous solution containing a metal element and containing more tungsten than the first raw material aqueous solution, and an ammonium ion donor are supplied to the reaction aqueous solution containing the first metal composite hydroxide particles. , a crystallization reaction is performed (step S20). As a result, second metal composite hydroxide particles are obtained in which a tungsten-concentrated layer is formed on the surface of the first metal composite hydroxide particles.

Particles grow with secondary particles, which are agglomeration of a plurality of primary particles, as nuclei. A second crystallization step (step S20) may be performed by supplying a second raw material aqueous solution containing more tungsten and an ammonium ion donor to the reaction aqueous solution containing the first metal composite hydroxide particles. can. As a result, a tungsten-concentrated layer is formed on the peripheral portion of the secondary particles that constitute the first composite oxide particles.

In the method for producing a metal composite hydroxide of the present embodiment, for example, by adjusting the timing of starting the addition of the second raw material aqueous solution (that is, the timing of starting the second crystallization step), the first metal The thickness of the tungsten-enriched layer formed around the composite hydroxide particles can be easily controlled.

In the second crystallization reaction (step S20), the metal element in the first raw material aqueous solution is reduced by, for example, 10 It can be started by supplying the second raw material aqueous solution at the time when it is supplied to the reaction vessel in a mass % or more. Thereby, a tungsten-concentrated layer can be easily formed on the surface of the first metal composite hydroxide particles.

In addition, from the viewpoint of obtaining a positive electrode active material that has higher crystallinity and further reduces the reaction resistance when used for the positive electrode of a secondary battery, the metal element in the first raw material aqueous solution is added to the first crystallization. Supply to the reaction tank preferably in the range of 50% by mass to 95% by mass, more preferably in the range of 75% by mass to 90% by mass, based on the total amount of metal added in the step and the second crystallization step At this point, the second raw material aqueous solution can be supplied, and the second crystallization step (step S20) can be started.

Since the second crystallization step (step S20) is a step in which grain growth is performed in the same manner as the grain growth step (step S12), the pH, temperature, and ammonium ion concentration of the reaction aqueous solution and the atmosphere in the reaction vessel etc. can be the same conditions as in the particle growth step (step S12). By continuously performing the second crystallization step (step S20) under the same conditions as the particle growth step (step S12), it is possible to easily produce tungsten on the surface of the first metal composite hydroxide particles with high productivity. Concentrated layer formation can be carried out.

Also, the supply of the second raw material aqueous solution may be performed by separately preparing a raw material aqueous solution containing a metal element other than tungsten and an aqueous solution containing tungsten, and supplying the respective aqueous solutions to the reaction vessel. By separately supplying an aqueous solution containing tungsten, a tungsten-concentrated layer can be formed more easily and uniformly. Moreover, as shown in FIG. 2, the second raw material aqueous solution may include the first raw material aqueous solution and an aqueous solution containing tungsten (W), and the respective aqueous solutions may be separately supplied to the reaction aqueous solution. As a result, by changing the concentration of the aqueous solution containing tungsten and the flow rate when supplying the aqueous solution containing tungsten to the reaction tank, a tungsten concentrated layer can be uniformly formed, and tungsten can be easily concentrated. It is possible to adjust the layer thickness.

An aqueous solution containing tungsten can be prepared, for example, by dissolving a tungsten compound in water. The tungsten compound to be used is not particularly limited, and a compound containing tungsten without containing lithium can be used, but preferably sodium tungstate can be used.

The tungsten (W) concentration of the aqueous solution containing tungsten is not particularly limited, but is, for example, 0.1 mol/l or more and 0.5 mol/l or less, preferably 0.2 mol/l or more and 0.4 mol/l or less. The addition flow rate of the aqueous solution containing tungsten is not particularly limited, but is, for example, 5 L/min or more and 20 L/min or less, preferably 10 L/min or more and 15 L/min or less.

The thickness of the tungsten-concentrated layer can also be controlled by adjusting the concentration of the tungsten-containing aqueous solution or by adjusting the addition flow rate of the aqueous solution. For example, when the concentration and addition flow rate of the aqueous solution containing tungsten are constant, the thickness and concentration of the tungsten-concentrated layer to be formed can be adjusted more accurately and easily by adjusting the time point at which the addition of the aqueous solution containing tungsten is started. be able to.

FIG. 4 is a diagram showing a preferred example of the manufacturing method of this embodiment. In FIG. 4, the first crystallization step (step S10) includes the nucleation step (step S11) and the grain growth step (step S12) separately, and the grain growth step (step S12) Continuously, when the second crystallization step (step S20) is performed by supplying the aqueous solution containing tungsten together with the first aqueous raw material solution, the time point at which the aqueous solution containing tungsten is added (second crystallization step is a diagram for explaining the disclosure point of time).

FIG. 4(A) shows that after 75% of the entire grain growth time from the start of grain growth to the end of grain growth (the end of the crystallization process), the amount of tungsten compound It is a figure which shows an example at the time of adding aqueous solution. In this case, as shown in the lower part of FIG. 4A, a tungsten-concentrated layer 3 can be formed on the surface layer (periphery) of the secondary particles (first metal composite hydroxide particles). In addition, when the aqueous solution of the tungsten compound is added in the whole process from the start point of grain growth to the end point, the tungsten concentrated layer is not formed.

FIG. 4(B) shows that the tungsten compound is It is a figure which shows an example at the time of adding aqueous solution of. In this case, as shown in the lower part of FIG. 4(B), the surface layer (periphery) of the secondary particles (first metal composite hydroxide particles) is compared with the case where addition is started after 75% of the time has passed. to form a more concentrated tungsten-enriched layer.

When the second crystallization step (step S20) is performed by supplying the tungsten-containing aqueous solution together with the first raw material aqueous solution as described above, the supply of the tungsten-containing aqueous solution (second raw material aqueous solution) is For example, when 10% or more of the entire time from the start to the end of the grain growth in the second crystallization step has passed, preferably when 50% or more and 95% or less, more preferably 75% or more and 90% of the time has passed. It can be done after 10% or less. When the supply time is within the above range, a tungsten-concentrated layer can be easily obtained with high productivity. Further, within the above range, when the timing of starting the addition of the aqueous solution containing tungsten is later, there is a tendency that the crystallite size of the obtained positive electrode active material can be increased. The addition of the aqueous solution containing tungsten is continued until the crystallization reaction is completed.
Hereinafter, each raw material and conditions preferably used in the crystallization step will be described.

(First and second raw material aqueous solutions)
The first aqueous raw material solution and the second aqueous raw material solution contain nickel and manganese and optionally cobalt, element M and tungsten. Also, the first raw material aqueous solution may not contain tungsten. In the second crystallization step, when the first raw material aqueous solution and the tungsten-containing aqueous solution are used as the second raw material aqueous solution, the ratio of the metal elements in the first raw material aqueous solution is the metal composite finally obtained. It becomes the composition ratio of hydroxides (excluding tungsten). Therefore, the content of each metal element in the first raw material aqueous solution can be appropriately adjusted according to the desired composition of the metal composite hydroxide. For example, when trying to obtain metal composite hydroxide particles represented by the ratio (A) described above, the ratio of the metal elements in the raw material aqueous solution is changed to Ni:Mn:Co:M=x:y:z:b (However, x + y + z = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 ≤ b ≤ 0.1) can be done. The compositions of the first aqueous raw material solution and the second aqueous raw material solution used in the first crystallization step and the second crystallization step may be different. In this case, the total content of each metal element in the raw material aqueous solution used in each crystallization step can be the composition ratio of the resulting metal composite hydroxide.

The compounds of metal elements (transition metals) used for the preparation of the first aqueous raw material solution and the second aqueous raw material solution are not particularly limited, but water-soluble nitrates, sulfates, hydrochlorides, etc. are used for ease of handling. is preferably used, and from the viewpoint of cost and prevention of halogen contamination, it is particularly preferable to use sulfate.

In addition, the element M (M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) in the metal composite hydroxide is preferably contained, the compound for supplying the element M is similarly a water-soluble compound, such as magnesium sulfate, calcium sulfate, aluminum sulfate, titanium sulfate, ammonium peroxotitanate, potassium titanium oxalate, sulfuric acid Vanadium, ammonium vanadate, chromium sulfate, potassium chromate, zirconium sulfate, niobium oxalate, ammonium molybdate, hafnium sulfate, sodium tantalate, sodium tungstate, ammonium tungstate and the like can be preferably used.

The concentrations of the first raw material aqueous solution and the second raw material aqueous solution are 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, in total of the metal compounds. Below. If the concentration of the raw material aqueous solution is less than 1 mol/L, the amount of crystallized material per reaction tank is small, resulting in low productivity. On the other hand, when the concentration of the mixed aqueous solution exceeds 2.6 mol/L, it exceeds the saturated concentration at normal temperature, and crystals of each metal compound re-precipitate, which may clog pipes and the like.

It should be noted that the metal compounds described above do not necessarily have to be supplied to the reaction tank as one type of raw material aqueous solution. For example, when performing a crystallization reaction using a metal compound that reacts to produce a compound other than the target compound when mixed, the total concentration of the aqueous solution of all metal compounds is within the above range. An aqueous solution of the metal compound may be prepared and supplied to the reaction vessel at a predetermined ratio as an aqueous solution of individual metal compounds.

In addition, the supply amounts of the first raw material aqueous solution and the second raw material aqueous solution are the product (second metal composite hydroxide particles) in the reaction solution (particle growth aqueous solution) at the end of the crystallization step. 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. If the concentration of the product is less than 30 g/L, the aggregation of primary particles may be insufficient. On the other hand, if the concentration of the product exceeds 200 g/L, the aqueous solution for nucleation or the aqueous solution for particle growth may not sufficiently diffuse into the reaction tank, resulting in uneven particle growth.

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

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

(Aqueous solution containing ammonium ion donor)
Aqueous solutions containing ammonium ion donors are not particularly limited either, and for example, ammonia water or aqueous solutions of ammonium sulfate, ammonium chloride, ammonium carbonate or ammonium fluoride can be used.

When aqueous ammonia is used as the ammonium ion donor, its concentration is preferably 20% to 30% by mass, more preferably 22% to 28% by mass. By limiting the concentration of ammonia water to such a range, loss of ammonia due to volatilization or the like can be minimized, and production efficiency can be improved.
The aqueous solution containing the ammonium ion donor can also be supplied by a pump whose flow rate can be controlled in the same manner as the alkaline aqueous solution.

(reaction atmosphere)
By controlling the atmosphere in the reaction vessel to be an oxidizing atmosphere or a non-oxidizing atmosphere, the particle structure and tap density of the metal composite hydroxide are controlled. When mainly obtaining metal composite hydroxide particles having a solid structure with a tap density of 1.7 g/cm ³ or more and 2.3 g/cm ³ or less, a nucleation step (step S11) and a particle growth step ( In steps S12 and S20), for example, the atmosphere is preferably a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less, and more preferably an atmosphere with an oxygen concentration of 1% by volume or less. For example, when the oxygen concentration in the reaction atmosphere is 1% by volume or less, it is preferable to control the atmosphere to be a mixture of oxygen and an inert gas.

(reaction temperature)
The temperature of the reaction aqueous solution (reaction temperature) is preferably 20° C. or higher, more preferably 20° C. or higher and 60° C. or lower throughout the crystallization process (nucleation process, particle growth process, and second crystallization process). Control. If the reaction temperature is lower than 20° C., the solubility of the reaction aqueous solution becomes low, and nucleation tends to occur, making it difficult to control the average particle size and particle size distribution of the resulting metal composite hydroxide. There is The upper limit of the reaction temperature is not particularly limited, but if it exceeds 60° C., volatilization of ammonia is accelerated, and an ammonium ion supplier is supplied to control the ammonium ions in the reaction aqueous solution within a certain range. The amount of aqueous solution containing is increased, and the production cost is increased. If the reaction temperature exceeds 60° C., the primary crystal may be distorted in the nucleation step (step S11) and the tap density may be lowered.

(Manufacturing equipment)
In the method for producing a metal composite hydroxide according to the present embodiment, it is preferable to use an apparatus that does not collect the product until the reaction is completed, such as a batch reactor. With such an apparatus, growing particles are not recovered at the same time as the overflow liquid, unlike a continuous crystallizer that recovers the product by an overflow method, so metal composite hydroxides with a narrow particle size distribution Particles can be obtained easily.

In addition, in the method for producing a metal composite hydroxide of the present embodiment, it is preferable to control the reaction atmosphere during the crystallization reaction, so it is preferable to use an apparatus capable of controlling the atmosphere, such as a closed type apparatus. With such an apparatus, the reaction atmosphere in the nucleation step and the particle growth step can be appropriately controlled, so metal composite hydroxide particles having the above-described particle structure and a narrow particle size distribution can be easily produced. can get to

The composition of the metal composite hydroxide 10 obtained by the production method of the present embodiment is not particularly limited as long as the particle structure, average particle size and particle size distribution described above can be realized. ) can be preferably applied to the metal composite hydroxide represented by

3. Positive electrode active material for lithium ion secondary battery The positive electrode active material according to the present embodiment contains lithium, nickel, manganese, and tungsten, optionally cobalt, and the element M, and the number of atoms of each metal element The ratio is Li:Ni:Mn:Co:W:M=(1+u):x:y:z:a:b (x+y+z=1, −0.05≦u≦0.50, 0.3≦x≦ 0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0<a≦0.1, 0≦b≦0.1, M is Mg, Ca, Al, Ti, V , Cr, Zr, Nb, Mo, Hf, and Ta)). In addition, the lithium metal composite oxide has a hexagonal layered crystal structure.

FIGS. 5A and 5B are schematic diagrams showing an example of the lithium metal composite oxide according to this embodiment. The lithium metal composite oxide 20 contains secondary particles 22 formed by agglomeration of a plurality of primary particles 21, as shown in FIG. 5(A). The lithium metal composite oxide 20 may be composed of the secondary particles 22 only, or may be composed of the secondary particles 22 and the primary particles 21 alone. Details of the lithium metal composite oxide 20 will be described below with reference to FIGS. 5(A) and 5(B).

(Compound containing tungsten and lithium)
Lithium metal composite oxide 20, as shown in FIG. Compound 23 containing is present in a concentrated form. The location of the compound 23 containing tungsten and lithium can be confirmed, for example, by detecting the W distribution by area analysis using an energy dispersive X-ray spectrometer (EDX), as shown in FIG. In addition, it is preferable that more of the compound 23 containing tungsten and lithium exists on the surface (surface layer) of the secondary particle 22 than on the inside.

When the surface layer of the positive electrode active material is coated with a different compound, the movement (intercalation) of lithium ions is greatly restricted. be. On the other hand, the compound 23 containing tungsten and lithium (for example, lithium tungstate) has a high lithium ion conductivity and thus has the effect of promoting the movement of lithium ions. The substance 20 forms a conductive path of Li at the interface with the electrolyte by forming a compound 23 containing tungsten and lithium on the surface layer of the primary particles 21 near the surface and on the grain boundaries between the primary particles 21. By doing so, the reaction resistance of the positive electrode active material can be reduced and the output characteristics can be improved. The compound 23 containing tungsten and lithium can exist, for example, in the form of fine particles near the surface of the lithium metal composite oxide 20 .

The compound 23 containing tungsten and lithium is not particularly limited, and examples thereof include lithium tungstates such as Li ₂ WO ₄ , Li ₄ WO ₅ and Li ₂ W ₂ O ₇ . These lithium tungstates are concentrated on the surface layer of the primary particles 21 existing on the surface or inside the secondary particles 22 and on the grain boundaries between the primary particles 21, thereby forming the lithium metal composite oxide 20. The lithium ion conductivity is further increased, and when used in the positive electrode of a secondary battery, the reduction in reaction resistance becomes even greater.

(particle structure)
The structure of the secondary particles 22 of the lithium metal composite oxide 20 is not particularly limited. A void structure having a plurality of voids 24 or a hollow structure having a hollow portion 25 may be used. The structure of the secondary particles 22 of the lithium metal composite oxide 20 is preferably a solid structure from the viewpoint of having higher particle strength and higher tap density.

In this specification, that the secondary particles 22 have a solid structure means that the plurality of primary particles 1 are uniformly and densely distributed throughout the secondary particles 2 and that a distinct single particle is formed inside the secondary particles 2. Alternatively, it means having a structure in which a plurality of hollow portions (for example, occupying 10% or more of the cross-sectional area of the secondary particles 2) do not exist. Further, when the metal composite hydroxide 10 has a solid structure, the porosity of the metal composite hydroxide 10 (the void area inside the secondary particles 2 with respect to the cross-sectional area of the secondary particles 22) is, for example, 20% or less. and preferably 10% or less.

When the lithium metal composite oxide 20 inherits the solid structure, which is a feature of the metal composite hydroxide described above, and has a solid structure, there are few voids inside the secondary particles 22, so compared with other structures and has the highest particle strength. In addition, when the lithium metal composite oxide 20 has high particle strength, the energy density per volume can be increased, and the occurrence of cracking of the positive electrode active material during charge-discharge cycles can be suppressed. characteristics can be improved.

When producing the secondary particles 22 (metal composite hydroxide) having a multilayer structure including the hollow portion 25 and the space portion 26, the positive electrode active material according to the present embodiment is continuously subjected to a conventionally known particle growth process, By adding the second crystallization step of adding an aqueous solution containing tungsten as described above, the metal composite hydroxide 10 in which the tungsten-concentrated layer 3 is formed on the surface layer, and lithium using this as a precursor A metal composite oxide 20 can be obtained. The lithium metal composite oxide 20 has a multilayer structure including hollow portions 25 and space portions 26 due to the presence of the compound 23 containing lithium and tungsten in the surface layer of the primary particles 21 and the grain boundaries between the primary particles 21. The output characteristics can be further improved while maintaining the crystallinity of the positive electrode active material containing the secondary particles 22 .

(Volume average particle size)
Although the volume average particle diameter (MV) of the positive electrode active material is not particularly limited, it can be, for example, 3 μm or more and 9 μm or less. When the volume average particle diameter (MV) is within the above range, the battery capacity per unit volume of the secondary battery using the positive electrode active material can be increased, and thermal stability and output characteristics can also be improved. can. On the other hand, when the volume average particle diameter (MV) of the positive electrode active material is less than 4 μm, the filling property of the positive electrode active material is deteriorated, and it is difficult to increase the battery capacity per unit volume (volume). Moreover, when the volume average particle diameter (MV) of the positive electrode active material exceeds 9 μm, the reaction area of the positive electrode active material starts to decrease, so the output characteristics may not be sufficient.

Note that the volume average particle diameter (MV) of the positive electrode active material can be obtained, for example, from the volume integrated value measured with a laser beam diffraction scattering particle size analyzer, similarly to the metal composite hydroxide 10 described above.

(particle size distribution)
[(d90-d10)/MV], which is an index showing the spread of the particle size distribution, of the positive electrode active material is preferably 0.65 or less. When [(d90−d10)/MV] is within the above range, the positive electrode active material is composed of the lithium metal composite oxide 20 with a very narrow particle size distribution. Such a positive electrode active material has a low ratio of fine particles and coarse particles, and a secondary battery using this positive electrode active material for the positive electrode is excellent in thermal stability, cycle characteristics and output characteristics.

On the other hand, when [(d90-d10)/MV] exceeds 0.65, the ratio of fine particles and coarse particles in the positive electrode active material increases. A secondary battery using a positive electrode active material with a wide particle size distribution, for example, generates heat due to local reactions of fine particles, lowers thermal stability, and selectively deteriorates fine particles. , the cycle characteristics may deteriorate. In addition, secondary batteries using a positive electrode active material with a wide particle size distribution have a large proportion of coarse particles, so it is not possible to secure a sufficient reaction area between the electrolyte and the positive electrode active material, resulting in a decrease in output characteristics. I have something to do.

Assuming industrial-scale production, it is not realistic to use a material with an excessively small [(d90-d10)/MV] as the positive electrode active material. Therefore, considering cost and productivity, the lower limit of [(d90-d10)/MV] in the positive electrode active material is preferably 0.25 or more. The meanings of d10 and d90 in [(d90-d10)/MV] and the method for measuring them are the same as for the metal composite hydroxide described above.

(sintering aggregation)
The positive electrode active material has a [lithium metal composite oxide d50/metal composite hydroxide d50] (hereinafter referred to as “d50 ratio”), which is an index indicating sintering and aggregation, in the range of 0.95 to 1.05. Preferably. When the d50 ratio is within the above range, the positive electrode active material can be composed of the lithium metal composite oxide 20 in which aggregation of secondary particles due to sintering and aggregation is suppressed. Such a positive electrode active material has high fillability in the positive electrode of the secondary battery, and when used in the positive electrode of the secondary battery, has a high capacity, little variation in characteristics, and a secondary battery with excellent uniformity. can be obtained.

On the other hand, when the d50 ratio exceeds 1.05, the specific surface area may decrease and the filling property may decrease due to aggregation during sintering. A secondary battery using such a positive electrode active material may have lower output characteristics and lower battery capacity due to lower reactivity. In addition, when the secondary battery using such a positive electrode active material is repeatedly charged and discharged, the positive electrode selectively collapses from the weak strength portion where the secondary particles are agglomerated, so the cycle characteristics can be a factor that greatly impairs

In addition, when the d50 ratio is less than 1.0, by pulverizing the lithium metal composite oxide 20, some of the primary particles 21 are missing from the secondary particles 22, resulting in a decrease in particle size. In particular, when the d50 ratio is less than 0.95, there are many missing primary particles 21, resulting in a large amount of fine powder and a wide particle size distribution.

Note that the metal composite hydroxide d50 means the d50 of the metal composite hydroxide 10 used as a precursor when producing the lithium metal composite oxide 20 . In addition, the d50 of each particle can be measured with a laser light diffraction scattering particle size analyzer. % means the particle size.

(Crystallite diameter)
The positive electrode active material according to the present embodiment is compared with a positive electrode active material using as a precursor a metal composite hydroxide obtained by uniformly adding tungsten throughout the crystallization process as in the conventional manufacturing method. , the crystallite size of the (003) plane obtained by powder X-ray diffraction measurement can be made larger. The crystallite diameter of the (003) plane of the positive electrode active material may be, for example, 110 nm or more, may be 115 nm or more, and preferably is 120 nm or more. When the crystallite diameter of the (003) plane of the positive electrode active material is 120 nm or more, the crystallinity is high, and the secondary battery using this positive electrode active material for the positive electrode has a reduced positive electrode resistance, so the output characteristics is improved, and the thermal stability is also improved. On the other hand, when the crystallite size of the (003) plane of the positive electrode active material is less than 120 nm, the crystallinity may not be sufficient, and the thermal stability of the secondary battery may deteriorate.

Although the upper limit of the crystallite size of the (003) plane of the positive electrode active material is not particularly limited, it can be, for example, 200 nm or less, preferably 120 nm or more and 150 nm or less. In the positive electrode active material of the present embodiment, high crystallinity can be maintained by using the metal composite hydroxide 10 having the tungsten-concentrated layer 3 on the surface as described above, so that the crystallites of the (003) plane The diameter can be within the above range.

(tap density)
The tap density of the positive electrode active material is preferably 1.8 g/cm ³ or more and 2.4 g/cm ³ or less, more preferably 2.0 g/cm ³ or more and 2.2 g/cm ³ or less. When the tap density of the positive electrode active material is within the above range, a secondary battery having a higher volumetric energy density can be obtained. On the other hand, when the tap density is less than 1.8 g/cm ³ , there are many void portions in the grain structure, and the strength of the grains is lowered, resulting in poor cycle characteristics. In addition, the fillability of the positive electrode active material deteriorates, making it difficult to increase the battery capacity per unit volume.

When the particle size distribution of the positive electrode active material is wide, the tap density tends to increase. In this case, the fine particles may selectively deteriorate, resulting in deterioration of the cycle characteristics. Therefore, [(d90-d10) / MV], which is an index indicating the spread of the particle size distribution of the positive electrode active material, is within the above range (e.g., 0.65 or less), and the tap density is within the above range (e.g., 1.8 g/cm ³ or more and 2.4 g/cm ³ or less), high volume energy density and excellent cycle characteristics can be obtained.

(Specific surface area)
The BET specific surface area of the positive electrode active material is preferably 0.6 m ² /g or more and 1.2 m ² /g or less, more preferably 0.7 m ² /g or more and 1.1 m ² /g or less, still more preferably It is 0.8 m ² /g or more and 1.0 m ² /g or less. When the BET specific surface area is within the above range, the contact area with the electrolytic solution can be made sufficient when using the positive electrode of the secondary battery, so the positive electrode resistance can be reduced and sufficient output characteristics can be obtained. can.

(composition)
_The composition _of the positive _electrode active material of the present _embodiment is _not particularly limited as long as it has the properties described _{above .} .05≦u≦0.50, x+y+z=1, 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0<a≦0.1, 0 ≦b≦0.1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta).

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

In the above general formula (B), the value of x indicating the content of nickel (Ni) is preferably 0.3 or more and 0.95 or less, more preferably 0.3 or more and 0.9 or less. Nickel is an element that contributes to increasing the potential and capacity of secondary batteries. If the value of x is less than 0.3, the capacity characteristics of the secondary battery using this positive electrode active material cannot be improved. On the other hand, when the value of x exceeds 0.95, the contents of other elements are reduced, and the effects of other elements cannot be obtained.

In the general formula (B), the value of y indicating the content of manganese (Mn) is preferably 0.05 or more and 0.55 or less, more preferably 0.10 or more and 0.40 or less. Manganese is an element that contributes to improving thermal stability. If the value of y is less than 0.05, the thermal stability of the secondary battery using this positive electrode active material cannot be improved. On the other hand, if the value of y exceeds 0.55, Mn may be eluted from the positive electrode active material during high-temperature operation, degrading charge-discharge cycle characteristics.

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

In the above general formula (B), the value of a indicating the content of tungsten (W) is more than 0 and 0.1 or less when the total number of moles of Ni, Co and Mn is 1, preferably 0.001 or more and 0.01 or less, more preferably 0.0045 or more and 0.006 or less. When the value of a is within the above range, the positive electrode active material has excellent output characteristics and cycle characteristics while maintaining high crystallinity. In addition, as described above, W is mainly contained in the surface layer of the primary particles 21 near the surface of the secondary particles 22 or in the grain boundaries between the primary particles 21 in the positive electrode active material.

In order to further improve the durability and output characteristics of the secondary battery, the positive electrode active material of the present embodiment may contain the element M in addition to the metal elements described above. Such elements M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum ( Mo), hafnium (Hf), and tantalum (Ta) can be used.

In the general formula (B), the value of b indicating the content of the element M is preferably 0 or more and 0.1 or less, more preferably 0.1 when the sum of the number of moles of Ni, Co and Mn is 1. 001 or more and 0.05 or less. If the value of b exceeds 0.1, the metal element that contributes to the Redox reaction is reduced, so the battery capacity may decrease.

In the positive electrode active material represented by the general formula (B), from the viewpoint of further improving the capacity characteristics of the secondary battery, the composition is represented by the general formula (B1): Li _1+u Ni _{x Mny} Co _z W _a M _b O ₂ (−0.05≦u≦0.20, x+y+z=1, 0.7<x≦0.95, 0.05≦y≦0.1, 0≦z≦0.2, 0< a ≤ 0.1, 0 ≤ b ≤ 0.1, M is one or more selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta element). Among them, from the viewpoint of achieving both thermal stability and battery capacity, the value of x in the general formula (B1) is more preferably 0.7 < x ≤ 0.9, and 0.7 < x More preferably, ≦0.85.

Further, from the viewpoint of further improving thermal stability, the composition is represented by the general formula (B2): Li _1+u Ni _{x Mny} Co _z W _{a Mb} O ₂ (−0.05≦u≦0.50, x+y+z=1, 0.3≦x≦0.7, 0.1≦y≦0.55, 0≦z≦0.4, 0<a≦0.1, 0≦b≦0.1, M is , Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta).

4. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery FIG. 6 is a diagram showing an example of a method for producing a positive electrode active material according to the present embodiment. The production method of the present embodiment can easily produce a positive electrode active material containing the lithium metal composite oxide 20 described above on an industrial scale. The positive electrode active material containing the lithium metal composite oxide 20 is not particularly limited as long as it has the specific structure, average particle diameter and particle size distribution described above, and can be obtained using a known manufacturing method.

As shown in FIG. 6, the method for producing a positive electrode active material according to the present embodiment includes a step (step S30) and firing the lithium mixture to obtain a lithium metal composite oxide (step S40). In addition to the above-described steps, steps such as a heat treatment step and a calcining step may be added as necessary.

Tungsten in the tungsten-concentrated layer 3 formed on the surface layer of the metal composite hydroxide 10 reacts with the lithium compound in the step of mixing with the lithium compound (step S30) and the step of firing (step S40) to form a lithium metal composite. A compound 23 containing tungsten and lithium is formed on the surface layers of the primary particles in the oxide 20 and on the grain boundaries between the primary particles. Hereinafter, a method for manufacturing a positive electrode active material according to this embodiment will be described with reference to FIG.

(Mixing process)
First, at least one of a metal composite hydroxide and a metal composite oxide obtained by heat-treating a metal composite hydroxide (hereinafter collectively referred to as "precursor") is mixed with a lithium compound. to obtain a lithium mixture (step S30).

In step S30, the ratio (Li /Me) is 0.95 or more and 1.5 or less, preferably 1.0 or more and 1.5 or less, more preferably 1.0 or more and 1.35 or less, further preferably 1.0 or more and 1.2 or less. As such, the precursor and lithium compound are mixed. That is, since Li/Me does not change before and after the firing process, the precursor and the lithium compound are mixed so that Li/Me in the mixing process becomes Li/Me of the desired positive electrode active material. Li/Me may exceed 1 or may exceed 1.1 from the viewpoint of sufficiently forming the compound 23 containing tungsten and lithium.

The lithium compound used for mixing is not particularly limited, but lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferably used from the viewpoint of availability. In particular, considering ease of handling and stability of quality, it is preferable to use lithium hydroxide or lithium carbonate.

It is preferable that the precursor and the lithium compound are sufficiently mixed to the extent that fine powder is not generated. Insufficient mixing may cause variations in Li/Me among individual particles, making it impossible to obtain sufficient battery characteristics. In addition, a general mixer can be used for mixing. For example, shaker mixers, Loedige mixers, Julia mixers, V-blenders, etc. can be used.

(Heat treatment process)
A step of heat-treating the metal composite hydroxide (heat treatment step) may optionally be provided before the mixing step (step S30). The precursor obtained by heat treatment may be mixed with a lithium compound (not shown). Here, the precursor obtained after the heat treatment includes a metal composite hydroxide from which at least part of excess water has been removed in the heat treatment step, and a precursor in which the metal composite hydroxide has been converted to an oxide by the heat treatment step ( metal composite oxides), or mixtures thereof.

The heat treatment step is a step of heating and heat-treating the metal composite hydroxide to remove at least part of the moisture contained in the metal composite hydroxide. As a result, the amount of water remaining until after the baking step (step S40) can be reduced to a certain amount, and variation in the composition of the obtained positive electrode active material can be suppressed.

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

In the heat treatment step, the number of atoms of each metal component in the positive electrode active material and the number of atoms of Li may be removed to the extent that there is no variation in the number of atoms. It doesn't have to be converted into something. However, from the viewpoint of reducing the variation in the number of atoms of each metal component and the ratio of the number of Li atoms, heat treatment is performed at 400 ° C. or higher to convert all metal composite hydroxides into composite oxides. is preferred. Note that the number of atoms of the metal component contained in the metal composite hydroxide under the heat treatment conditions is determined in advance by analysis, and the mixing ratio with the lithium compound is determined, so that the above-described variations can be further suppressed. .
The atmosphere in which the heat treatment is performed is not particularly limited as long as it is a non-reducing atmosphere.

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

(Baking process)
The lithium mixture is then fired to obtain lithium metal composite oxide 20 (step S40). This step is a step of sintering under predetermined conditions to diffuse lithium into the precursor to obtain the lithium metal composite oxide 20 . The obtained lithium metal composite oxide 20 may be used as it is as a positive electrode active material, or may be used as a positive electrode active material after adjusting the particle size distribution by a pulverization step, as described later.

[Firing temperature]
The firing temperature is preferably 650° C. or higher and 980° C. or lower. If the firing temperature is less than 650° C., lithium does not sufficiently diffuse into the precursor, leaving excess lithium (including unreacted lithium compounds) and unreacted metal composite hydroxides or metal composite oxides. Otherwise, the resulting lithium metal composite oxide may have insufficient crystallinity. On the other hand, if the firing temperature exceeds 980° C., intense sintering occurs between the lithium composite oxide particles, causing abnormal grain growth and increasing the proportion of amorphous coarse particles.

Moreover, when manufacturing the positive electrode active material represented by the general formula (B1) described above, the firing temperature is preferably 650° C. or higher and 900° C. or lower. Moreover, when producing the positive electrode active material represented by the general formula (B2), the firing temperature is preferably 800° C. or higher and 980° C. or lower.

[Temperature rising rate]
The heating rate to the firing temperature is preferably 2° C./min or more and 10° C./min or less, and may be 5° C./min or more and 9° C./min or less. Furthermore, in the firing step (step S40), the lithium compound used may be held at a temperature near the melting point for preferably 1 to 5 hours, more preferably 2 to 5 hours. Thereby, the precursor and the lithium compound can be reacted more uniformly.

[Baking time]
The holding time (firing time) at the above firing temperature is preferably at least 2 hours or more, more preferably 4 hours or more and 24 hours or less. Moreover, the holding time of the firing temperature (firing time) may be 2 hours or more and 15 hours or less, or may be 2 hours or more and 10 hours or less. If the holding time at the firing temperature is less than 2 hours, lithium does not sufficiently diffuse into the precursor, leaving excess lithium or unreacted metal composite hydroxide or metal composite oxide, or resulting lithium The crystallinity of the metal composite oxide may not be sufficient.

[Cooling rate]
After the firing time (holding time) is completed, the cooling rate from the firing temperature to at least 200°C is preferably 2°C/min or more and 10°C/min or less, and 3°C/min or more and 7°C/min or less. is more preferred. By controlling the cooling rate within the above range, it is possible to prevent equipment such as a sagger from being damaged by rapid cooling while ensuring productivity.

[Firing atmosphere]
The atmosphere at the time of 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 particularly preferably oxygen having an oxygen concentration in the above range and an inert gas. It is a mixed atmosphere. That is, the calcination is preferably carried out in the atmosphere or in an oxygen stream. If the oxygen concentration in the atmosphere is less than 18% by volume, the lithium metal composite oxide may not have sufficient crystallinity.

[Firing furnace]
The furnace used in the firing step (step S40) is not particularly limited as long as it can heat the lithium mixture in the atmosphere or in an oxygen stream. From the viewpoint of maintaining a uniform atmosphere in the furnace, an electric furnace that does not generate gas is preferable, and a batch-type or continuous-type electric furnace may be used. Further, from the viewpoint of maintaining a uniform atmosphere in the furnace, a similar furnace can be selected for the furnace used in the heat treatment process and the calcining process.

(calcination process)
When lithium hydroxide or lithium carbonate is used as the lithium compound, calcination may be performed after the mixing step (step S30) and before the firing step (step S40). The calcination is a step of calcining the lithium mixture at a temperature lower than the calcination temperature described later, 350° C. or more and 800° C. or less, preferably 450° C. or more and 780° C. or less. Thereby, lithium can be sufficiently diffused in the precursor, and more uniform lithium composite oxide particles can be obtained.

The holding time at the above temperature is preferably 1 hour or more and 10 hours or less, and preferably 3 hours or more and 6 hours or less. The atmosphere in the calcining step is preferably an oxidizing atmosphere, more preferably an atmosphere with an oxygen concentration of 18% by volume or more and 100% by volume or less, as in the firing step (step S40) described above.

(Crushing process)
Agglomeration or mild sintering may occur in the lithium metal composite oxide 20 obtained by the firing step (step S40). In such a case, it is preferable to pulverize the aggregates or sintered bodies of the secondary particles 22 of the lithium metal composite oxide 20 . Thereby, the volume average particle size (MV) and particle size distribution of the positive electrode active material to be obtained can be adjusted to a suitable range. In addition, crushing means that mechanical energy is applied to aggregates composed of a plurality of secondary particles 22 generated by sintering necking between secondary particles 22 during firing, and most of the secondary particles 22 themselves are destroyed. It means an operation to separate agglomerates without breaking them apart.

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

5. Lithium Ion Secondary Battery A lithium ion secondary battery (hereinafter also referred to as a “secondary battery”) according to the present embodiment includes a positive electrode containing a positive electrode active material, a negative electrode, and an electrolyte. A lithium ion secondary battery can be composed of the same components as conventionally known lithium ion secondary batteries, and includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. Also, the secondary battery may be, for example, an all-solid secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte. Each component other than the positive electrode will be described below.

The embodiments described below are merely examples, and the lithium ion secondary battery of the present invention is applied to various modifications and improvements based on the embodiments described herein. is also possible.

(positive electrode)
A positive electrode for a secondary battery is produced using the positive electrode active material described above. An example of the method for producing the positive electrode will be described below. First, the positive electrode active material (powder), conductive agent, and binder are mixed, and if necessary, activated carbon and a solvent for viscosity adjustment are added, and the mixture is kneaded. A positive electrode mixture paste is prepared.

Since the mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium secondary battery, it can be adjusted according to the application. The mixture ratio of the materials can be the same as that of the positive electrode of a known lithium secondary battery. The content of the conductive agent may be 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.

The obtained positive electrode mixture paste is applied, for example, to the surface of a current collector made of aluminum foil, and dried to scatter the solvent, thereby producing a sheet-like positive electrode. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. The sheet-shaped positive electrode thus obtained can be cut into a size suitable for the intended battery, and used for the manufacture of the battery. However, the method for producing the positive electrode is not limited to the above-exemplified method, and other methods may be used.

Examples of conductive agents that can be used include graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black.

Binders play a role in binding active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, and cellulose resin. and polyacrylic acid can be used.

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

(negative electrode)
Metallic lithium, a lithium alloy, or the like can be used for the negative electrode. In addition, the negative electrode is prepared by mixing a negative electrode active material capable of intercalating and deintercalating lithium ions with a binder, adding an appropriate solvent to make a paste, and applying the negative electrode mixture to the surface of a metal foil current collector such as copper. It may be applied, dried, and compressed to increase the electrode density as necessary.

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

(separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and a known one can be used. For example, a thin film such as polyethylene or polypropylene having a large number of fine pores can be used. can.

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

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

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

Moreover, when the lithium ion secondary battery is an all-solid secondary battery, a solid electrolyte may be used as the non-aqueous electrolyte. Solid electrolytes have the property of withstanding high voltages. Solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

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

The oxide-based solid electrolyte is not particularly limited, and can be used as long as it contains oxygen (O) and has lithium ion conductivity and electronic insulation. Examples of oxide-based solid electrolytes include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li _{3 PO4} , _Li4SiO4 - _Li3VO4 , _{Li2O - B2O3 - P2O5} , _{Li2O - SiO2 , Li2O} - _{B2O3 -} ZnO, Li1 _{+X AlXTi 2-X} (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ (0≦X≦1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2/ 3-X} TiO ₃ (0≦X≦2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ and the like.

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

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

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

(Shape and configuration of secondary battery)
The lithium ion secondary battery according to the present embodiment, which is composed of the positive electrode, the negative electrode, the separator, the non-aqueous electrolyte solution, the positive electrode, the negative electrode, and the solid electrolyte described above, has a cylindrical shape, a laminated shape, and the like. Various shapes are possible.

When a non-aqueous electrolytic solution is used as the non-aqueous electrolyte, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, and the obtained electrode body is impregnated with the non-aqueous electrolytic solution. A lead for current collection is used to connect between the connected positive electrode terminal and between the negative electrode current collector and the negative electrode terminal connected to the outside, and the battery case is sealed to complete the lithium ion secondary battery. .

[Characteristics of lithium ion secondary battery]
As described above, the lithium-ion secondary battery according to the present invention uses the positive electrode active material obtained by using the metal composite hydroxide 10 as a precursor, and therefore has excellent capacity characteristics, output characteristics and cycle characteristics. Moreover, when compared with a secondary battery using a positive electrode active material composed of conventional lithium-nickel-based oxide particles, it is also superior in thermal stability.

As described above, the lithium-ion secondary battery according to the present invention is excellent in capacity characteristics, output characteristics and cycle characteristics. (telephone terminal, etc.). In addition, the lithium-ion secondary battery of the present invention is excellent in thermal stability, and not only can it be made smaller and higher in output, but it can also simplify the expensive protection circuit, so it can be installed in less space. It can also be suitably used as a power source for transportation equipment subject to restrictions.

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

(Example 1)
(a) Production of metal composite hydroxide [nucleation step]
First, 1.2 L of water was put into the reactor, and the temperature in the reactor was set to 40° C. while stirring at 790 rpm. At this time, nitrogen gas was introduced into the reaction tank to make the reaction atmosphere a non-oxidizing atmosphere with an oxygen concentration of 1% by volume or less. Subsequently, appropriate amounts of 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water were supplied into the reaction tank so that the pH value was 12.5 at a liquid temperature of 25° C. and the ammonium ion concentration was 10 g/L. to form a pre-reaction aqueous solution.

At the same time, nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were dissolved in water so that the molar ratio of each metal element was Ni:Mn:Co:Zr=38:30:32:0.2, and 2 mol/ A first raw material aqueous solution of L was prepared.

Next, the first raw material aqueous reaction solution was supplied to the pre-reaction aqueous solution at 13 ml/min to form an aqueous solution for the nucleation step, and nucleation was performed for 2.5 minutes. At this time, a 25% by mass aqueous sodium hydroxide solution and a 25% by mass aqueous ammonia solution were supplied at appropriate times to maintain the pH value and the ammonium ion concentration of the aqueous solution for nucleation within the ranges described above.

[Particle growth step]
After the nucleation was completed, the supply of all the aqueous solution was temporarily stopped, and sulfuric acid was added to the reaction tank to adjust the pH value to 11.6 based on the liquid temperature of 25°C, thereby causing particle growth. An aqueous solution was formed. After confirming that the pH value reached a predetermined value, the first raw material aqueous solution was supplied to the reaction tank to grow the nuclei (particles) generated in the nucleation step. Nitrogen gas was introduced into the reaction atmosphere, and a non-oxidizing atmosphere with an oxygen concentration of 1% by volume or less was continuously maintained.

[Second crystallization step]
As the second raw material aqueous solution, the first raw material aqueous solution and an aqueous solution containing tungsten were used. Sodium tungstate dihydrate was used as an aqueous solution containing tungsten, and the molar ratio of each metal element in the resulting hydroxide was Ni:Co:Mn:Zr:W=38:30:32:0.2:0. 6 to prepare an aqueous sodium tungstate solution.

After 19/20 hours (95%) of the entire grain growth time, the first aqueous solution was supplied, and the sodium tungstate aqueous solution was started to be supplied to the reaction vessel (addition range: 5%). The grain growth process was terminated by stopping the supply of all aqueous solutions. After that, the obtained product was washed with water, filtered and dried to obtain a powdery metal composite hydroxide.

In addition, in the particle growth step in the first crystallization step and the second crystallization step, 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water are supplied as appropriate through these steps to allow particle growth. The pH value and ammonium ion concentration of the aqueous solution were maintained within the ranges described above. Nitrogen gas was introduced into the reaction atmosphere to adjust the atmosphere to a non-oxidizing atmosphere with an oxygen concentration of 1% by volume or less, and switching between the non-oxidizing atmosphere and the oxidizing atmosphere was performed four times. The supply rate of the first raw material aqueous solution was kept constant (13 ml/min) throughout the crystallization process.

(b) Evaluation of metal composite hydroxide By analysis using an ICP emission spectrometer (manufactured by Shimadzu Corporation, ICPE-9000ICPE-9000), this metal composite hydroxide has the general formula: Ni _0.38 Mn _{0.30Co0.32Zr0.002W0.005 (} OH _{) 2 .}

In addition, using a laser light diffraction scattering particle size analyzer (manufactured by Nikkiso Co., Ltd., Microtrac HRA), the average particle size of the metal composite hydroxide is measured, and d10 and d90 are measured to determine the spread of the particle size distribution. [(d90-d10)/MV], which is an index to show, was calculated. As a result, it was confirmed that the average particle size of the metal composite hydroxide was 5.4 μm and [(d90−d10)/MV] was 0.43.

In addition, in order to confirm the presence or absence of a tungsten-concentrated layer in the metal composite hydroxide and its thickness, an energy mounted on a scanning transmission electron microscope (manufactured by Hitachi High-Technologies Co., Ltd., HD-2300A) Using a dispersive X-ray spectrometer (EDX), surface analysis of the cross section of the metal composite hydroxide was performed. As a result, formation of a portion (tungsten-concentrated layer) where tungsten is concentrated in the surface layer of the metal composite hydroxide was confirmed, and the thickness thereof was confirmed to be 3 to 8 m.

In addition, the tap density was measured using a shaking specific gravity meter (KRS-409, manufactured by Kuramochi Scientific Instruments Co., Ltd.). The measurement was carried out after dense packing by a method of repeating free fall from a depth of 2 cm 500 times. The evaluation results are shown in .

(c) Preparation of positive electrode active material The metal composite hydroxide obtained as described above was mixed with a shaker mixer device (TURBULA Type T2C manufactured by Willie & Bakkofen (WAB)) so that Li / Me became 1.14. ) was used to thoroughly mix with lithium carbonate to obtain a lithium mixture.

This lithium mixture is heated to 900° C. at a temperature elevation rate of 2.52.5° C./min in an air stream (oxygen concentration: 21% by volume), calcined by holding at this temperature for 4 hours, and cooled. Cool to room temperature at a rate of about 4°C/min. Aggregation or mild sintering occurred in the positive electrode active material thus obtained. Therefore, the positive electrode active material was pulverized to adjust the average particle size and particle size distribution.

(d) Evaluation of positive electrode active material By analysis using an ICP emission spectrometer, this positive electrode active material has the general formula: Li _1.14 Ni _0.38 Mn _0.30 Co _0.32 Zr _0.002 W ₀ It was confirmed to be expressed in _0.005 O ₂ . Also, using a laser light diffraction scattering particle size analyzer, the average particle size of the lithium metal composite oxide is measured, and d10 and d90 are measured, which is an index showing the spread of the particle size distribution [(d90-d10). /MV] was calculated. As a result, it was confirmed that the average particle size of the lithium metal composite oxide was 5.3 μm, [(d90−d10)/MV] was 0.43, and the d50 ratio was 1.04.

Also, the crystallite size of the (003) plane was measured using an X-ray diffractometer (X'Pert PRO manufactured by Spectris Co., Ltd.) and found to be 1,433 Å (143.3 nm).

In addition, in order to confirm the distribution of tungsten in the lithium metal composite oxide using a scanning transmission electron microscope, an energy dispersive X-ray spectrometer (EDX) was used to perform surface analysis of the cross section of the lithium metal composite oxide. . As a result, it was confirmed that a large amount of tungsten was contained in the surface layer of the primary particles near the surface of the secondary particles and in the grain boundaries between the primary particles in the lithium metal composite oxide.

In addition, the tap density is evaluated under the same conditions as for the metal composite hydroxide, and the BET specific surface area is evaluated by a specific surface area measuring device (manufactured by Mountec Co., Ltd., Macsorb 1200 series) that adopts the flow method-nitrogen gas adsorption method. bottom. Evaluation results are shown in Table 2.

(e) Fabrication of Secondary Battery FIG. 7 is a diagram showing a 2032-type coin battery CBA used for evaluation of battery characteristics. A method for manufacturing a secondary battery will be described below with reference to FIGS.

The obtained positive electrode active material: 52.5 mg, acetylene black: 15 mg, and PTEE: 7.5 mg were mixed and press-molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. A positive electrode PE was prepared by drying at °C for 12 hours.

Next, using this positive electrode PE, a 2032 type coin battery CBA was produced in an Ar atmosphere glove box with a controlled dew point of -80°C. Lithium metal with a diameter of 17 mm and a thickness of 1 mm is used for the negative electrode NE of this 2032 type coin battery, and the electrolytic solution is ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiClO ₄ as the supporting electrolyte. A mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. A polyethylene porous film having a film thickness of 25 μm was used as the separator SE. The 2032-type coin battery CBA has a gasket GA and is assembled into a coin-shaped battery with a positive electrode can PC and a negative electrode can NC.

(f) Battery evaluation [Resistance]
Using the coin battery CBA assembled as described above, the resistance value by the AC impedance method at SOC 20% was measured, and the relative value based on Comparative Example 1 was obtained from Ref. It was calculated as a resistance value for The results are shown in Table 2.

(Examples 2-8)
As shown in Table 1, a metal composite hydroxide was obtained under the same conditions as in Example 1, except that the timing (addition time) of adding the tungsten-containing aqueous solution during grain growth was changed. Table 1 shows the evaluation results of the obtained metal composite hydroxide.

In addition, using an energy dispersive X-ray spectrometer (EDX) mounted on a scanning transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, HD-2300A), the metal composite hydroxides obtained in Examples 2 to 8 A surface analysis of the cross section of was performed, and the obtained distribution of W was analyzed. As a result, in the metal composite hydroxides obtained in Examples 2 to 8, a portion (tungsten concentrated layer) where tungsten is concentrated in the surface layer of the secondary particles was detected, and the thickness thereof was 20 nm or more and 160 nm. It was confirmed that:

Next, a positive electrode active material and a secondary battery were obtained under the same conditions as in Example 1, except that the obtained metal composite hydroxide was used as a precursor. Table 2 shows the evaluation results of the obtained metal composite hydroxide and positive electrode active material. In addition, using an energy dispersive X-ray spectrometer (EDX) mounted on a scanning transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, HD-2300A), the lithium metal composite oxides obtained in Examples 2 to 8 A surface analysis of the cross section of was performed, and the obtained distribution of W was analyzed. As a result, in the lithium metal composite oxides obtained in Examples 2 to 8, it was confirmed that a large amount of tungsten was present in the surface layer of the primary particles near the surface of the secondary particles and in the grain boundaries between the primary particles. was done.

(Comparative example 1)
A metal composite hydroxide was obtained under the same conditions as in Example 1, except that the tungsten compound was added from the start of the grain growth step (addition range was 100%). Table 1 shows the evaluation results of the obtained metal composite hydroxide. Next, a positive electrode active material and a secondary battery were produced under the same conditions as in Example 1, except that the obtained metal composite hydroxide was used as a precursor. Tables 1 and 2 show the evaluation results of the obtained positive electrode active material and secondary battery.

(Comparative example 2)
Using a metal composite hydroxide (Ni _0.38 Mn _0.30 Co _0.32 Zr _0.002 (OH) ₂ ) that does not contain tungsten, and when mixing the metal composite hydroxide and lithium carbonate Then, tungsten oxide was _{added and} mixed to obtain a lithium mixture (external addition). _0.30 Co _0.32 Zr _0.002 W _0.005 O ₂ ) and a secondary battery were fabricated. Tables 1 and 2 show the evaluation results of the obtained positive electrode active material and secondary battery.

(Comparative Example 3)
A metal composite hydroxide, a positive electrode active material, and a secondary battery were produced under the same conditions as in Example 1, except that the sodium tungstate aqueous solution was not supplied in the second crystallization step during the crystallization step. Tables 1 and 2 show the evaluation results of the obtained metal composite hydroxide, positive electrode active material, and secondary battery.

(Evaluation results)
It was confirmed that the metal composite hydroxide obtained in the example forms a tungsten-concentrated layer on its surface. In addition, the positive electrode active material obtained in Example has a larger crystallite diameter than Comparative Example 1 in which tungsten is added throughout the crystallization process, and when used as a positive electrode of a secondary battery, , showed a low positive electrode resistance (resistance value).

In addition, the metal composite hydroxides obtained in Examples 1 to 6 formed a tungsten-concentrated layer with a thickness of 100 nm or less, and the positive electrode active materials obtained using these metal composite hydroxides as precursors were Compared to Comparative Example 2 in which a tungsten compound was externally added, it had a larger crystallite diameter and exhibited a lower resistance value when used as the positive electrode of a secondary battery.

On the other hand, the positive electrode active material obtained in Comparative Example 3, in which tungsten is not added, has a relatively large crystallite diameter as compared with the other examples and comparative examples in which tungsten is added, but can be used as a positive electrode of a secondary battery. It was shown that the resistance value was large and the output characteristics were poor.

DESCRIPTION OF SYMBOLS 10... Metal composite hydroxide 1... Primary particle 2... Secondary particle 3... Tungsten concentration layer 20... Lithium metal composite oxide 21... Primary particle 22... Secondary particle 23... Compound containing tungsten and lithium 24... Void 25... Hollow part 26 Space part CBA Coin battery CA Case PC Positive electrode can NC Negative electrode can GA Gasket PE Positive electrode NE Negative electrode SE Separator

Claims (14)

Ni:Mn:Co:W:M=x:y:z: a: b (x+y+z=1, 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4, 0<a≦0.1, 0≦b≦0. 1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta. There is
A first raw material aqueous solution containing the metal element and an ammonium ion donor are supplied to a reaction tank, the pH of the reaction aqueous solution in the reaction tank is adjusted, and a crystallization reaction is performed to obtain the first metal. a first crystallization step for obtaining composite hydroxide particles;
A second raw material aqueous solution containing the metal element and containing more tungsten than the first raw material aqueous solution, and an ammonium ion supplier are supplied to the reaction aqueous solution containing the first metal composite hydroxide particles. Then, by adjusting the pH of the reaction aqueous solution and performing a crystallization reaction, a tungsten-concentrated layer is formed on the surface of the first metal composite hydroxide particles, and the second metal composite hydroxide particles are obtained. a second crystallization step of obtaining
The first crystallization step includes a nucleation step for generating nuclei and a grain growth step for grain growth, and the second crystallization step includes grain growth following the grain growth step. including
The metal element in the first raw material aqueous solution is added in the range of 50% by mass or more and 95% by mass or less with respect to the total amount of metal added in the first crystallization step and the second crystallization step. After supplying to the reaction tank, supplying the second raw material aqueous solution in the second crystallization step,
The metal composite hydroxide obtained after the second crystallization step has a tap density of 1.7 g/cm ³ or more and 2.3 g/cm ³ or less, and is a solid formed by aggregating a plurality of primary particles. including secondary particles having a structure,
A method for producing a metal composite hydroxide. The first crystallization step and the second crystallization step are performed in a non-oxidizing atmosphere with an oxygen concentration of 1% by volume or less,
3. The pH of the reaction aqueous solution is adjusted so as to be lower than the pH value of the reaction aqueous solution in the nucleation step in the grain growth in the first crystallization step and the second crystallization step. 2. The method for producing a metal composite hydroxide according to 1. The second crystallization step includes forming the tungsten-concentrated layer to a thickness of 100 nm or less in the direction from the surface to the center of the second metal composite hydroxide particle, The method for producing a metal composite hydroxide according to claim 1 or 2. The addition of the second raw material aqueous solution in the second crystallization step is performed when 50% or more and 95% or less of the entire grain growth time has elapsed in the first and second crystallization steps. The method for producing a metal composite hydroxide according to any one of claims 1 to 3, wherein the metal composite hydroxide is produced. The supply of the second raw material aqueous solution is performed by separately supplying the first raw material aqueous solution and an aqueous solution containing tungsten to the reaction aqueous solution according to any one of claims 1 to 4. A method for producing a metal composite hydroxide. The method for producing a metal composite hydroxide according to claim 5, wherein the concentration of tungsten in the aqueous solution containing tungsten is 18% by mass or more with respect to the entire aqueous solution containing tungsten. nickel, manganese and tungsten and optionally cobalt and the element M, and the atomic ratio of the respective metal elements is Ni:Mn:Co:W:M=x:y:z:a : b (x + y + z = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 < a ≤ 0.1, 0 ≤ b ≤ 0.1 , M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta),
The metal composite hydroxide contains secondary particles in which a plurality of primary particles are aggregated,
Having a tungsten-concentrated layer on the surface of the secondary particles, and
Containing secondary particles having a tap density of 1.7 g/cm ³ or less and 2.3 g/cm ³ or more and having a solid structure formed by aggregating a plurality of primary particles,
Metal composite hydroxide. 8. The metal composite hydroxide according to claim 7, wherein the tungsten-concentrated layer has an average thickness of 100 nm or less. Claim 7, wherein the volume average particle diameter (MV) is 4.0 μm or more and 9.0 μm or less, and [(d90−d10)/MV], which is an index showing the spread of the particle size distribution, is 0.65 or less. Or the metal composite hydroxide according to claim 8. At least one of the metal composite hydroxide obtained by the production method according to any one of claims 1 to 6 and the metal composite oxide obtained by heat-treating the metal composite hydroxide, and a lithium compound to obtain a lithium mixture;
and calcining the lithium mixture to obtain a lithium metal composite oxide. The value of (d50 of the positive electrode active material/d50 of the metal composite hydroxide), which is an index indicating the degree of aggregation between particles of the lithium metal composite oxide, is 0.95 or more and 1.05 or less. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 10, wherein the adjustment is performed. Lithium, Nickel, Manganese, and Tungsten, optionally Cobalt, and the element M, wherein the atomic ratio of each metal element is Li:Ni:Co:Mn:W:M=1+u:x: y:z:a:b (x+y+z=1, −0.05≦u≦0.50, 0.3≦x≦0.95, 0.05≦y≦0.55, 0≦z≦0.4 , 0<a≦0.1, 0≦b≦0.1, M is one or more selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta element) containing a lithium metal composite oxide represented by
The lithium metal composite oxide contains secondary particles having a solid structure formed by aggregation of a plurality of primary particles,
A compound containing tungsten and lithium is concentrated and present in the surface layer of the primary particles present on the surface or inside the secondary particles and in the grain boundaries between the primary particles,
The tap density is 1.8 g/cm ³ or less and 2.4 g/cm ³ or more, and
BET specific surface area is 0.6 m ² /g or more and 1.2 m ² /g or less,
Positive electrode active material for lithium ion secondary batteries. 13. The positive electrode active material for a lithium ion secondary battery according to claim 12, wherein the crystallite size of the (003) plane obtained by powder X-ray diffraction measurement is 120 nm or more. A lithium ion secondary comprising 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 claim 12 or 13 is used as the positive electrode material of the positive electrode battery.

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