JP2019189489A - Metal composite hydroxide and manufacturing method therefor, cathode active material for nonaqueous electrolyte secondary battery and manufacturing method therefor, and nonaqueous electrolyte secondary battery manufactured using the same - Google Patents

Abstract

To provide a cathode active material having high crystallinity and constituting a secondary battery having high output, and to provide a composite hydroxide containing a particle having a multilayer structure, which is a precursor of the cathode active material, and a manufacturing method for the composite hydroxide.SOLUTION: There is provided the manufacturing method for metal composite hydroxide including nickel, manganese, and tungsten, optionally cobalt, and an element M. The manufacturing method for metal composite hydroxide comprises: a first crystallization step of supplying a first raw material solution including the metal element and an ammonium ion supply body to a reaction tank, adjusting pH of reaction solution in the reaction tank, and performing a crystallization reaction to obtain a first metal composite hydroxide particle; and a second crystallization step of supplying second raw material solution including the metal element and more tungsten than the first raw material solution, and ammonium ion supply body to a reaction solution including the first metal composite hydroxide particle, adjusting pH of the reaction solution, and performing a crystallization reaction to form a tungsten concentrated layer on a surface of the first metal composite hydroxide particle to thereby obtain a second metal composite hydroxide particle.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a metal composite hydroxide and a production method thereof, a positive electrode active material for a non-aqueous electrolyte secondary battery, a production method thereof, and a non-aqueous electrolyte secondary battery using the same.

  In recent years, with the widespread use of portable electronic devices such as smartphones, tablet terminals, and notebook personal computers, development of small and lightweight non-aqueous electrolyte secondary batteries having high energy density is strongly desired. In addition, development of a high output secondary battery is strongly desired as a power source for driving a hybrid electric vehicle, a plug-in hybrid electric vehicle, a battery-powered electric vehicle, and the like.

  As a secondary battery satisfying such requirements, there is a lithium ion secondary battery which is a kind of non-aqueous electrolyte secondary battery. A lithium ion secondary battery includes a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of desorbing and inserting lithium is used as an active material used as a material for the negative electrode and the positive electrode.

  Among lithium ion secondary batteries, a lithium ion secondary battery using a layered or spinel type lithium metal composite oxide as a positive electrode active material can obtain a voltage of 4 V class, and is currently used as a battery having a high energy density. Research and development has been actively conducted, and some have been put into practical use.

As a positive electrode active material of such a lithium ion secondary battery, a lithium cobalt composite oxide (LiCoO ₂ ) that is relatively easy to synthesize, a lithium nickel composite oxide (LiNiO ₂ ) using nickel that is cheaper than cobalt, Lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese, lithium nickel manganese composite oxide (LiNi _{0. 5} Mn _0.5 O ₂₎ lithium metal composite oxide such as have been proposed.

  By the way, a method of increasing the specific surface area of the positive electrode active material is generally known in order to further improve the output characteristics of the lithium ion secondary battery. 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 into the secondary battery. Therefore, several techniques for improving output characteristics by controlling the particle structure of the positive electrode active material have been proposed.

  For example, Patent Documents 1 to 3 propose a method for producing a positive electrode active material using a composite hydroxide obtained by a crystallization process performed in two stages as a precursor. The positive electrode active materials described in these patent documents are said to have a high specific surface area and excellent output characteristics by having a small particle size, a narrow particle size distribution, and a hollow structure or space inside the particles. . 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 constituting the positive electrode active material has been studied as a means for realizing a positive electrode active material having a higher output characteristic by further reducing the reaction resistance. As such dissimilar elements, for example, transition metals capable of taking an expensive number such as Mo, Nb, W, and Ta have been proposed.

  For example, in Patent Document 4, a lithium transition metal compound having a function capable of inserting / extracting lithium ions is a main component, and an additive for suppressing grain growth and sintering during firing is added to the main component material. Lithium transition metal-based compound powder obtained by adding at least one or more of them in a proportion of 0.01 mol% or more and less than 2 mol% with respect to the total molar amount of transition metal elements in the main component raw material, and then firing The body is listed. Further, the additive is an oxide containing at least one element selected from Mo, W, Nb, Ta, and Re, and is a total of Li in the surface portion of the primary particles and metal elements other than the additive element. It is described that the total atomic ratio of the additive elements to is not less than 5 times the atomic ratio of the entire particle.

In Patent Document 5, a step of dispersing W on the surface of primary particles of the powder by adding and mixing an alkaline aqueous solution in which a specific proportion of a tungsten compound is dissolved in the lithium metal composite oxide powder; 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 less than 700 ° C., any of Li ₂ WO ₄ , Li ₄ WO ₅ and Li ₆ W ₂ O ₉ is used. There has been proposed a production method in which fine particles containing lithium tungstate represented are formed on the surface of the lithium metal composite oxide powder or the primary particles of the powder.

  Further, in Patent Document 6, a positive electrode active material composed of a lithium metal composite oxide, which is composed of primary particles and secondary particles formed by agglomeration of primary particles, and the voids through which the electrolyte can permeate are formed as secondary particles. A positive electrode active material having a compound layer having a layer thickness of 20 nm or less containing lithium enriched in tungsten on the surface or grain boundary of a lithium metal composite oxide is proposed. As a preferred method for obtaining the powder, a lithium metal composite oxide can be obtained by mixing and baking a composite compound or a tungsten compound when mixing the composite oxide and the lithium compound. However, in this method, the particle size of the tungsten compound is preferably 1/5 times or less than the average particle size of the manganese composite hydroxide or manganese composite hydroxide.

  In Patent Document 7, in the crystallization reaction, a nucleation step and a particle growth step are separated by pH control to produce composite hydroxide particles, and tungsten is formed on the surface of the obtained composite hydroxide particles. A transition metal composite hydroxide production method including a coating step for forming a coating containing a cathode active material using the hydroxide as a precursor has been proposed.

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 attached to the surface of the current collector, and the surface of the first positive electrode active material is attached to the surface of the first positive electrode active material. There has been proposed a positive electrode for a lithium secondary battery to which a layer of a second positive electrode active material represented by Li _x2 Ni _a2 Mn _b2 Co _c2 M _d O ₂ (M is Mo, W, and Nb) is attached.

  Patent Document 9 discloses a method for producing a nickel-cobalt composite hydroxide, in which a solution containing nickel, cobalt, and manganese, a complex ion forming agent, and a basic solution are separately and simultaneously provided in one reaction vessel. A first crystallization step of obtaining nickel-cobalt composite hydroxide particles, 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 element M separately and simultaneously, nickel, cobalt, manganese and element M (Al, Mg, Ca, Ti, Zr, Nb, Ta) are added to the nickel-cobalt composite hydroxide particles. , Cr, Mo, W, Fe, Cu, Si, Sn, Bi, Ga, Y, Sm, Er, Ce, Nd, La, Cd, and at least one selected from the group consisting of Lu A second crystallization step of crystallizing composite hydroxide particles containing the upper element), and the total moles of nickel, cobalt and manganese supplied in the first crystallization step are MOL (1) and the second crystal Production method wherein 0.30 ≦ MOL (1) / {MOL (1) + MOL (2)} <0.95, where MOL (2) is the total mole of nickel, cobalt and manganese supplied in the deposition step Has been proposed.

JP 2012-246199 A JP 2013-147416 A JP 2006-094307 A JP 2008-305777 A JP 2013-125732 A JP 2014-197556 A JP 2012-252844 A JP 2012-079608 A Japanese Patent Laid-Open No. 2016-210684

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

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

  Further, the method described in Patent Document 6 is not industrially suitable because the tungsten compound needs to be pulverized once in order to obtain a nano-order tungsten compound, and is not easy to handle. Further, since the thickness of the compound layer can vary due to nonuniformity in the particle size of the resulting fine particles, the reaction resistance is not sufficiently 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 the manganese composite hydroxide in order to obtain the powder, but it is difficult to form a compound layer enriched with tungsten on the nano order by this method.

  Moreover, since the process described in Patent Document 7 adds a step of coating tungsten, the number of steps increases, which is not industrially preferable. Moreover, although tungsten is deposited by controlling the pH in the coating step, it is difficult to uniformly coat the coating layer because the thickness of the coating layer is not uniform due to fluctuations in the controlled pH. In addition, in the case of using a composite oxide obtained by mixing lithium with a composite hydroxide in which tungsten is coated non-uniformly, there is a problem in that the output is lowered because of resistance.

  Moreover, since the positive electrode active material comprised by the method of patent document 8 is a different phase from a 1st positive electrode active material and a 2nd positive electrode active material, when it uses for a secondary battery, it is charging / discharging. There was a discrepancy in the structural change during the reaction, and cracks occurred during repeated charging and discharging, resulting in deterioration of cycle characteristics.

  Further, the composite hydroxide and the positive electrode active material obtained by the method described in Patent Document 9 are formed on the second layer in which the ratio of the depth in the radial direction is 5% or more and less than 50% by SEM-EDX. It is described that it has a peak of element M by spectrum, and in the positive electrode active material, element M containing tungsten is contained inside from the surface layer of the secondary particles, so that the crystallinity is lowered and used for the secondary battery. Battery characteristics may be reduced.

  In view of the above problems, the present invention reduces the reaction resistance when used in the positive electrode of a secondary battery, has a higher output, and has a higher crystallinity, and a metal composite that is a precursor thereof. The object is to provide hydroxides.

In the first embodiment of the present invention, nickel, manganese, and tungsten, and optionally cobalt and the element M, and the atomic ratio of each metal element 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, where 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, comprising: supplying a first raw material aqueous solution containing a metal element to a reaction tank and an ammonium ion supplier; adjusting the pH of the reaction aqueous solution in the reaction tank; A first crystallization step of obtaining first metal composite hydroxide particles by performing a crystallization reaction; and a first metal composite hydroxide Supplying a second raw material aqueous solution containing metal elements and containing more tungsten than the first raw material aqueous solution to the reaction aqueous solution containing the product particles, and an ammonium ion supplier, and adjusting the pH of the reaction aqueous solution Performing a crystallization reaction to form a tungsten concentrated layer on the surface of the first metal composite hydroxide particles to obtain second metal composite hydroxide particles, and a second crystallization step. In the grain growth in the first crystallization step and the second crystallization step, any of a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less and an oxidizing atmosphere having an oxygen concentration exceeding 1% by volume Including switching the reaction atmosphere to one of the atmospheres a plurality of times, the metal composite hydroxide includes secondary particles in which a plurality of primary particles are aggregated, and the secondary particles are moved from the center of the particles to the surface. The primary particles are densely arranged Tap density of a genus composite hydroxide having a multi-layer structure including a central part, a void part in which primary particles are arranged more sparsely than the central part, and a solid part in which primary particles are densely arranged There is provided a method for producing a metal composite hydroxide, wherein is 0.75 g / cm ³ or more and 1.35 g / cm ³ or less.

  The first crystallization step includes a nucleation step for nucleation and a particle growth step for particle growth, and the second crystallization step performs particle growth following the particle growth step. The nucleation in the first crystallization step is performed in a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less, and the particle growth in the first crystallization step and the second crystallization step is a reaction. The pH of the aqueous solution is adjusted to be lower than the pH value of the reaction aqueous solution in the nucleation step, and any of a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less and an oxidizing atmosphere having an oxygen concentration exceeding 1% by volume It is preferable to include switching to the one atmosphere to the reaction atmosphere four times.

  In addition, the reaction vessel in which the metal element in the first raw material aqueous solution is in the range of 50% by mass to 95% by mass 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 the supply. Moreover, it is preferable that a 2nd crystallization process includes forming a tungsten concentration layer so that thickness may be set to 100 nm or less in the direction which goes to the center part from the surface of a 2nd metal composite hydroxide. . 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 time during which particle growth is performed in the first and second crystallization steps. Preferably it is done. The second raw material aqueous solution is preferably supplied by supplying the first raw material aqueous solution and the aqueous solution containing tungsten separately to the reaction aqueous solution. Moreover, it is preferable that the tungsten concentration in the aqueous solution containing tungsten is 18 mass% or more with respect to the whole aqueous solution containing tungsten.

In the second embodiment of the present invention, nickel, manganese, tungsten, and optionally cobalt and element M are included, and the atomic ratio of each metal element 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 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 comprising secondary particles in which a plurality of primary particles are aggregated, wherein the secondary particles have a central portion in which the primary particles are densely arranged from the center of the secondary particles toward the surface; A multilayer including at least a void portion in which primary particles are arranged sparser than a central portion and a solid portion in which primary particles are densely arranged Has a concrete, having a tungsten concentration layer on the surface of the secondary particles, the tap density is less than 0.75 g / cm ³ or more 1.35 g / cm ^3, a metal complex hydroxide is provided.

  Moreover, it is preferable that the thickness of a tungsten concentration layer is 100 nm or less. Further, the average particle size of the metal composite hydroxide is 4.0 μm or more and 9.0 μm or less, and [(d90−d10) / average particle size] which is an index indicating the spread of the particle size distribution is 0.65 or less. It is preferable that

  In the third embodiment of the present invention, lithium is mixed with 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, and lithium. There is provided a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a step of obtaining a mixture; and a step of firing a lithium mixture to obtain a lithium metal composite oxide.

  Moreover, the manufacturing method of the said positive electrode active material is a parameter | index (d50 of positive electrode active material / d50 of metal composite hydroxide) which is a parameter | index which shows the degree of aggregation of lithium metal complex oxide particle | grains, and is 0.95. It is preferable to adjust to be 1.05 or less.

In the fourth embodiment of the present invention, lithium, nickel, manganese, and tungsten, and optionally cobalt and the element M, 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 Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, 1 or more elements selected from Ta), and the lithium metal composite oxide includes secondary particles in which a plurality of primary particles are aggregated. From the center of the secondary particles to the surface, the central part where the primary particles are densely arranged, and the primary particles are arranged sparser than the central part The surface layer of the primary particles present on the surface or inside of the secondary particles, and the grains between the primary particles, and having a multilayer structure including at least a void portion and a solid portion in which the primary particles are densely arranged the field, there are compounds containing tungsten and lithium are concentrated, the tap density of less 1.00 g / cm ³ or more 2.00 g / cm ^3, and, BET specific surface area of 1.45 m ² / g or more 5 Provided is a positive electrode active material for a non-aqueous electrolyte secondary battery that is .40 m ² / g or less.

  The positive electrode active material preferably has a (003) plane crystallite diameter of 120 nm or more obtained by powder X-ray diffraction measurement.

  In the fourth embodiment of the present invention, a nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, and the positive electrode includes the positive electrode active material for a nonaqueous electrolyte secondary battery. Provided.

  According to the present invention, when used for a positive electrode of a secondary battery, a positive electrode active material having reduced reaction resistance, high output and high crystallinity, and a metal composite hydroxide as a precursor thereof. Can be provided. Moreover, according to this invention, the secondary battery containing such a positive electrode active material can be provided. Furthermore, according to the present invention, it is possible to provide a method by which such a positive electrode active material and a metal composite hydroxide can be easily produced on an industrial scale. For this reason, the industrial significance of the present invention is extremely large.

1A to 1B are schematic views illustrating an example of a metal composite hydroxide, and FIG. 1C is an example of a cross-sectional SEM image of the metal composite hydroxide. FIG. 2 is a diagram illustrating an example of a method for producing a metal composite hydroxide. FIG. 3 is a diagram illustrating an example of a method for producing a metal composite hydroxide. FIG. 4 is a diagram for explaining a disclosure time point of adding an aqueous solution containing tungsten. 5A to 5D are schematic views illustrating an example of a lithium metal composite oxide. FIG. 6 is a diagram illustrating an example of a method for producing a lithium metal composite oxide. FIG. 7 is a schematic diagram illustrating the evaluation coin-type battery used in the examples. FIG. 8 is a drawing-substituting photograph (upper figure) showing an example of W distribution by surface analysis using EDX of a metal composite hydroxide having a tungsten-concentrating layer, and an explanation for explaining the tungsten-concentrating layer in the drawing-substituting photograph It is a figure (lower figure).

  Hereinafter, with reference to the drawings, a metal composite hydroxide and a production method thereof, a positive electrode active material for a non-aqueous electrolyte secondary battery, a production method thereof, and a non-aqueous electrolyte secondary battery will be described. The present invention is not limited to the embodiments described below. Further, in the drawings, in order to make each configuration easy to understand, a part of the structure is emphasized or a part of the structure is simplified, and an actual structure, shape, scale, or the like may be different.

(Tungsten enriched layer)
FIG. 1A is a schematic diagram showing an example of a metal composite hydroxide according to the present embodiment. As shown in FIG. 1A, the metal composite hydroxide 10 (secondary particles 2) has a tungsten enriched layer 3 in which tungsten is concentrated on the surface layer. The tungsten enriched layer 3 is formed on the surface of the metal composite hydroxide 10 and refers to a layered region in which tungsten is enriched from inside the particles. When the metal composite hydroxide 10 on which the tungsten enriched layer 3 is formed is used as a precursor, a positive electrode active material with high crystallinity and reduced reaction resistance can be obtained. For example, as shown in FIG. 8, the tungsten enriched layer 3 can be confirmed by detecting the W distribution by surface analysis using an energy dispersive X-ray analyzer (EDX). In addition, in FIG. 1 (A), the primary particle 1 is not illustrated.

  As will be described later, the tungsten enriched layer 3 forms a compound 23 (for example, lithium tungstate) containing tungsten and lithium in the lithium metal composite oxide 20 (see FIG. 5). The compound 23 containing tungsten and lithium is formed in a step of mixing the metal composite hydroxide 10 (precursor) and the lithium compound and firing to obtain the lithium metal composite oxide 20 (see FIG. 5).

  In the lithium metal composite oxide 20 (positive electrode active material), the compound 23 containing tungsten and lithium is formed on the surface layer of the primary particles 21 or at the grain boundaries between the primary particles 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 that come into contact with the electrolytic solution, Alternatively, the presence of the compound 23 containing tungsten and lithium at the grain boundaries between the primary particles 21 can reduce the reaction resistance of the positive electrode active material and can greatly contribute to the output improvement.

  In addition, when using the conventional method for producing a metal composite hydroxide, tungsten contained in the metal composite hydroxide (precursor) may suppress sintering during firing. Therefore, the conventional precursor containing tungsten is contradictory to the fact that tungsten in the obtained positive electrode active material contributes to the reduction of reaction resistance, while the crystallinity of the lithium metal composite oxide constituting the positive electrode active material is lowered. There was a problem, and it was difficult to realize a lithium metal composite oxide having excellent output characteristics and high crystallinity. However, since the metal composite hydroxide 10 according to the present embodiment forms the tungsten concentrated layer 3 on the surface layer, the reaction resistance can be reduced with little effect of suppressing the sintering of tungsten during firing. And the crystallinity of the obtained lithium metal composite oxide 20 can be improved.

  In the direction from the surface of the metal composite hydroxide 10 toward the central portion C, the thickness of the tangsugten enriched layer 3 can be, for example, 200 nm, preferably 100 nm or less, more preferably 10 nm or more and 100 nm or less. More preferably, they are 20 micrometers or more and 50 micrometers or less. When the thickness of the tungsten enriched 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, The reaction resistance can be further reduced and the output characteristics can be improved.

  The thickness of the tungsten enriched layer 3 is determined by cutting a material in which the composite hydroxide 10 is embedded in a resin or the like, preparing a sample of the secondary particle 2 cross section, and performing surface analysis of W distribution using EDX. Go and measure. Specifically, in a sample having a secondary particle 2 cross section, a secondary particle 2 cross section that is 80% or more of the volume average particle diameter (MV) measured using a laser diffraction diffraction particle size analyzer is randomly selected. In the selected secondary particles 2, the thickness of the portion (tungsten enriched layer 3) where W is detected deeply in the direction from the surface of the metal composite hydroxide 10 toward the center C in each selected secondary particle 2 ( Width) is measured at five or more locations, and the average thickness of the tungsten concentrated layer 3 in each secondary particle 2 is determined. And the thickness of the tungsten concentration layer 3 can be obtained by calculating the average value of the thickness of each of the selected 20 secondary particles 2.

When the thickness of the tungsten enriched layer 3 exceeds 100 nm, the effect of suppressing the sintering by tungsten is increased during firing, and the growth of primary particles may be inhibited. Therefore, in the obtained lithium metal composite oxide, a large number of primary particles having a small crystallite diameter are formed, and many crystal grain boundaries are generated, so that the reaction resistance at the positive electrode may increase. In addition, the crystallinity of the lithium metal composite oxide 20 may decrease as the growth of primary particles is suppressed.
On the other hand, when the thickness of the tungsten enriched layer 3 is less than 10 nm, the specific surface area is increased, and the metal composite hydroxides 10 are easily aggregated during firing, so that the packing density of the obtained positive electrode active material is reduced. The battery capacity per volume may decrease. In addition, tungsten and lithium-containing compound 23 may not be sufficiently formed in lithium metal composite oxide 20, and lithium ion conductivity may not be sufficient.

  Further, the thickness of the tungsten enriched layer 3 is, for example, 3% or less in the direction from the surface of the secondary particle 2 toward the center C of the secondary particle 2 with respect to the average particle size of the metal composite hydroxide 10. can do. The thickness of the tungsten enriched 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. It is 2% or less, more preferably 0.1% or more and 1% or less, and further preferably 0.1% or more and 0.5% or less. In addition, the average particle diameter of the metal composite hydroxide 10 means a volume average particle diameter (MV).

(Particle structure)
FIG. 1B is a schematic diagram illustrating an example of a metal composite hydroxide according to the present embodiment, and FIG. 1C illustrates an example of a cross-sectional SEM image of the metal composite hydroxide according to the present embodiment. is there. As shown in FIG. 1C, the metal composite hydroxide 10 includes secondary particles 2 formed by aggregating a plurality of primary particles 1. Although the shape of the primary particle 1 which comprises the secondary particle 2 is not specifically limited, For example, shapes, such as plate shape and needle shape, may be sufficient as fine primary particles smaller than these. The metal composite hydroxide 10 may include single primary particles 1 in addition to the secondary particles 2. The particle structure of the secondary particles 2 is not particularly limited, and includes a solid structure in which almost no voids are observed in the particles, a hollow structure having a hollow portion at the center of the particle, and a void structure having a plurality of voids. Although it may have a conventionally known particle structure, as shown in FIGS. 1 (B) and 1 (C), it has a multilayer structure having a layered void portion 5 and a layered solid portion 6. preferable. Hereinafter, preferred examples of the particle structure will be described with reference to FIGS.

  As shown in FIG. 1B, the secondary particle 2 according to this embodiment includes a central portion 4 in which the primary particles 1 are densely arranged from the center C of the secondary particle 2 toward the surface, and the primary particles. It is preferable to have a multilayer structure including at least a void portion 5 in which 1 is arranged more sparsely than the central portion 4 and a solid portion 6 in which primary particles are densely arranged. Note that a structure in which primary particles are densely arranged is also referred to as a solid structure.

  Moreover, the secondary particle 2 should just have the space | gap part 5 and the solid part 6 at least one layer toward the surface from the center C of the secondary particle 2, FIG.1 (B) and FIG. As shown in C), two layers may be provided alternately. When the secondary particles 2 have a multilayer structure, the specific surface area of the obtained lithium metal composite oxide 20 (positive electrode active material) can be increased to improve the output characteristics.

  Further, the tungsten enriched layer 3 may be formed not only on the surface of the secondary particle 2 but also in the void portion 5 and the solid portion 6 existing therein, It is preferably formed on the surface portion of the solid portion 6 disposed on the outermost surface.

  The particle structure of the secondary particles 2 can be a multilayer structure by switching the reaction atmosphere in the particle growth step a plurality of times in the crystallization reaction, as will be described later.

(Tap density)
The tap density of the metal composite hydroxide 10 is not particularly limited. For example, when the secondary particle 2 has a multilayer structure, it is preferably 0.75 g / cm ³ or more and 1.35 g / cm ³ or less, more preferably Is 1 g / cm ³ or more and 1.35 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 composite hydroxide 10 as a precursor, and the metal composite hydroxide 10 has a multilayer structure. When it has, the tap density of the obtained lithium metal composite oxide 20 tends to be higher than the tap density 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 the composite hydroxide 10 as a precursor will be described later. It becomes possible to control the range. When this lithium metal composite oxide 20 is used for the positive electrode, a secondary battery having a high battery capacity can be obtained. On the other hand, when the tap density of the metal composite hydroxide 10 is less than 0.75 g / cm ³ , for example, in the baking process (see step S40, FIG. 6) when manufacturing the positive electrode active material, In some cases, the height is increased, and the crystallinity may be lowered without being sufficiently fired.

(Average particle size)
The average particle size 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. The average particle diameter of the metal composite hydroxide 10 correlates with the average particle diameter of the lithium metal composite oxide 20 (positive electrode active material) having the composite hydroxide 10 as a precursor. Therefore, by controlling the average particle size of the metal composite hydroxide 10 within the above range, the average particle size of the lithium metal composite oxide 20 (see FIG. 5) having the composite hydroxide 10 as a precursor is also reduced. It becomes possible to control to the said range.

  When the average particle diameter of the metal composite hydroxide 10 is less than 4 μm, the specific surface area becomes high, and in the firing step (see step S40, FIG. 6) when producing the positive electrode active material, the metal composite hydroxide 10 The particles may easily aggregate together, resulting in a decrease in the packing density of the resulting positive electrode active material, resulting in a decrease in battery capacity per volume. In the present specification, the average particle diameter of the secondary particles 2 means a volume average particle diameter (MV), and can be obtained from, for example, a volume integrated value measured by a laser light diffraction / scattering particle size analyzer. .

In the metal composite hydroxide 10, [(d90-d10) / average particle diameter], which is an index indicating the spread of the particle size distribution, is 0.65 or less. The particle size distribution of the lithium metal composite oxide 20 (positive electrode active material) is strongly influenced by the composite hydroxide 10 that is a precursor thereof. For this reason, when the composite hydroxide 10 containing many fine particles and coarse particles is used as a 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) / average particle size] of the metal composite hydroxide 10 is adjusted to the above range, the particle size distribution of the lithium metal composite oxide 20 obtained using this as a precursor is narrowed to be fine. Mixing of particles and coarse particles can be suppressed.
The lower limit value of [(d90-d10) / average particle diameter] of the composite hydroxide 10 is not particularly limited, but is preferably about 0.25 or more from the viewpoint of cost and productivity. When assuming production on an industrial scale, it is not realistic to use the composite hydroxide 10 having an excessively small [(d90−d10) / average particle diameter].

  In addition, d10 means the particle size in which the number of particles in each particle size is accumulated from the smaller particle size, and the accumulated volume is 10% of the total volume of all particles, and d90 is similarly accumulated in the number of particles. In addition, it means a particle size whose cumulative volume is 90% of the total volume of all particles. Moreover, d10 and d90 can be calculated | required from the volume integrated value measured with the laser beam diffraction scattering type particle size analyzer similarly to an average particle diameter.

(composition)
The composition of the metal composite hydroxide 10 is not particularly limited. For example, the metal composite hydroxide 10 includes 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 It is preferable that it is 1 or more types of metal elements selected from these.

In addition, since the ratio (A) of the number of atoms of each metal element in the metal composite hydroxide 10 is maintained also in the lithium metal composite oxide 20, the composite water represented by the ratio (A) of the metal element is used. In the oxide 10, the composition range of nickel, manganese, cobalt, tungsten, and the element M constituting the oxide 10 and the critical significance thereof are the same as those of the positive electrode active material represented by the ratio (B) described later. For this reason, description of these matters is omitted here.
The metal complex hydroxide 10 is represented by the general formula _{(A1): Ni x Mn y} Co z W a M b (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, And 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 expressed by the general formula (A2): NixMnyCozWaMb (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 preferably 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.

From the viewpoint of further improving the thermal stability of the secondary battery using the obtained positive electrode active material in the general formula (A1), the composition is expressed by the general formula (A3): Ni _x Mn _y 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, and M is preferably 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 to 3 are diagrams illustrating an example of a method for producing a metal composite hydroxide according to the present embodiment. The manufacturing method according to the present embodiment includes nickel, manganese, and tungsten, and optionally cobalt and the element M by a crystallization reaction, and the atomic ratio of each metal element 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, Ta) It is the method of manufacturing the metal composite hydroxide shown by these. With the manufacturing method according to the present embodiment, the metal composite hydroxide 10 having the above characteristics can be easily manufactured on an industrial scale.

[Crystalling 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 a metal element are contained in the reaction vessel. A first crystallization process (step S10) in which a first raw material aqueous solution containing (M) and an ammonium ion supplier are supplied to perform a crystallization reaction to obtain first metal composite hydroxide particles. And a second raw material aqueous solution containing more tungsten than the first raw material aqueous solution and an ammonium ion supplier to the reaction aqueous solution containing the first metal composite hydroxide particles, And performing a second crystallization step (step S20) to obtain a second metal composite hydroxide particle by forming a tungsten concentrated layer on the surface of the first metal composite hydroxide particle.

  In the method for producing a metal composite hydroxide according to the present embodiment, the surface of the first composite hydroxide particles obtained by the first crystallization process (step S10) in the second crystallization process (step S20). In addition, by forming the tungsten enriched layer 3, the second metal composite hydroxide particles can be obtained. Since the inside of the second metal composite hydroxide particles is composed of the first metal composite hydroxide particles that do not contain tungsten or have a low content of tungsten, the lithium metal obtained using this as the 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 present on the surface of the primary particles or at the grain boundaries between the primary particles. The output characteristics are excellent.

  As shown in FIG. 3, the first crystallization step (step S10) further includes a nucleation step (step S11) mainly for nucleation and a particle growth step (step S12) mainly for particle growth. It is preferable. 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 uniform particle size with a narrow particle size distribution. Hydroxide 10 can be obtained. Note that the second crystallization step (step S20) is a step of mainly performing particle growth following the particle growth step (step S12).

  In addition, about the manufacturing method of nickel composite hydroxide including such a two-step crystallization process, it is disclosed by patent document 2, patent document 3, etc., for these conditions, refer to these documents. Thus, the conditions can be adjusted as appropriate. Moreover, since the manufacturing method of the metal composite hydroxide which concerns on this embodiment can form the tungsten concentration layer 3 which has a desired film thickness using the conditions of a well-known crystallization method so that it may mention later. Can be easily applied to industrial scale production.

  Hereafter, with reference to FIG. 3, each process of the manufacturing method including a nucleation process (step S11) and a particle growth process (step S12) is demonstrated. In addition, the following description is an example of the manufacturing method of the metal composite hydroxide 10, Comprising: It does not limit to this method.

(1) First crystallization step (step S10)
(Nucleation process)
First, the first raw material aqueous solution and the ammonium ion supplier are supplied, and the pH of the reaction aqueous solution (nucleation aqueous solution) in the reaction tank is controlled within a predetermined range to perform nucleation (step S11). The first raw material aqueous solution is prepared by, for example, 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 metal of the target metal composite hydroxide. The first raw material aqueous solution may contain a small amount of tungsten or may not contain tungsten.

  First, an aqueous solution containing an alkaline aqueous solution and an ammonium ion supplier is supplied and mixed in the reaction vessel, and the pH value measured on the basis of the liquid temperature of 25 ° C. is 12.0 or higher and 14.0 or lower, and the ammonium ion concentration is A pre-reaction aqueous solution of 3 g / L or more and 25 g / L or less is prepared. The reaction atmosphere in the reaction vessel is preferably a non-oxidizing atmosphere when the particle central portion has a solid structure (when the primary particles 1 are densely arranged). The atmosphere is controlled by introducing, for example, nitrogen gas. The pH value of the aqueous solution before reaction can be measured with a pH meter, and the ammonium ion concentration can be measured with an ion meter.

  Next, while stirring the pre-reaction aqueous solution in the reaction tank, the first raw material aqueous solution is supplied into the reaction tank to form a reaction aqueous solution (nucleation aqueous solution). In the nucleation step (step S11), the pH value of the nucleation aqueous solution and the concentration of ammonium ions change with the nucleation in the reaction aqueous solution. It is preferable to control so that the pH value of the liquid is maintained in the range of pH 12.0 to 14.0 on the basis of the liquid temperature of 25 ° C., and the ammonium ion concentration is maintained in the range of 3 g / L to 25 g / L. When the pH value of the aqueous reaction solution (aqueous solution for nucleation) is in the above range, nucleation occurs preferentially with almost no growth of nuclei.

  The pH value measured on the basis of the liquid temperature of the reaction aqueous solution (nucleation aqueous solution) at 25 ° C. is preferably 12.0 to 14.0, more preferably 12.3 to 13.5, and still more preferably 12. The range is from 5 to 13.3. When the pH is in the above range, the growth of nuclei can be suppressed and nucleation can be prioritized, and the nuclei generated in the nucleation step can be homogeneous and have a narrow particle size distribution. On the other hand, when the pH value is less than 12.0, the growth of nuclei (particles) proceeds with nucleation, so that the obtained metal composite hydroxide particles have non-uniform particle sizes, and the particle size distribution deteriorates. Moreover, when pH value exceeds 14.0, the produced | generated nucleus becomes too fine and reaction aqueous solution (aqueous solution for nucleation) may gelatinize.

  It should be noted that the fluctuation range of the pH value in the aqueous reaction solution (nucleation aqueous solution) is preferably within ± 0.2. When the fluctuation range of the pH value is large, the nucleation amount and the rate of particle growth are not constant, and it becomes difficult to obtain metal composite hydroxide particles having a narrow particle size distribution.

  The ammonium ion concentration in the aqueous reaction solution (nucleation aqueous solution) is preferably adjusted within a range of 3 g / L to 25 g / L, more preferably 5 g / L to 20 g / L. Since ammonium ions function as a complexing agent in the aqueous reaction solution, when the ammonium ion concentration is less than 3 g / L, the solubility of the metal ions cannot be kept constant, or the aqueous reaction solution tends to gel. Thus, 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 metal ions becomes too high, so that the amount of metal ions remaining in the reaction aqueous solution increases, which may cause a composition shift or the like.

  If the ammonium ion concentration fluctuates during the crystallization reaction, the solubility of metal ions fluctuates, and uniform metal composite hydroxide particles are not formed. Therefore, it is preferable to control the fluctuation range of the ammonium ion concentration within a certain range through the nucleation process (step S11) and the particle growth process (step S12). Specifically, the fluctuation range is ± 5 g / L. It is preferable to control.

In the nucleation step (step S11), new nuclei are continuously generated by supplying the reaction aqueous solution (nucleation aqueous solution) with the first raw material aqueous solution, the alkaline aqueous solution and the aqueous solution containing the ammonium ion supplier. Is done. Then, when a predetermined amount of nuclei is generated in the aqueous solution for nucleation, the nucleation step is finished. At this time, the amount of nucleation can be determined from the amount of the metal compound contained in the raw material aqueous solution supplied to the nucleation aqueous solution.
The generation amount of nuclei in the nucleation step (step S11) is not particularly limited, but from the viewpoint of obtaining metal composite hydroxide particles having a narrow particle size distribution, the crystallization step (first crystallization step and second crystallization step). Preferably 0.1 atomic percent or more and 2 atomic percent or less, and preferably 0.1 atomic percent or more and 1.5 atomic percent based on the metal element in the metal compound contained in the raw material aqueous solution supplied through More preferably, it is as follows.

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

(Particle growth process)
Next, particle growth is performed in a reaction aqueous solution (aqueous solution for particle growth) whose pH is adjusted to a specific range (step S12). The reaction aqueous solution (particle growth aqueous solution) is formed by supplying a first raw material aqueous solution, an alkaline aqueous solution, and an aqueous solution containing an ammonium ion supplier to the reaction aqueous solution containing the produced nuclei. The reaction aqueous solution (particle growth aqueous solution) is preferably adjusted to have 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 as measured on the basis of a liquid temperature of 25 ° C. Thereby, in the reaction aqueous solution (aqueous solution for particle growth), particle growth is performed preferentially over nucleation.

Regarding the reaction atmosphere in the reaction vessel, when mainly forming secondary particles having a multilayer structure in which the tap density of the metal composite hydroxide is 0.75 g / cm ³ or more and 1.35 g / cm ³ or less, the oxygen concentration is It is preferable to switch between a non-oxidizing atmosphere of 1% by volume or less and an oxidizing atmosphere in which the oxygen concentration exceeds 1% by volume as appropriate. The atmosphere is controlled by introducing, for example, nitrogen gas.

  Specifically, after completion of the nucleation step, the pH value of the aqueous solution for nucleation in the reaction vessel is adjusted to 10.5 or more and 12.0 or less on the basis of the liquid temperature of 25 ° C., and the reaction aqueous solution in the particle growth step. An aqueous solution for particle growth is formed. The pH value can be adjusted by stopping the supply of only the alkaline aqueous solution. However, from the viewpoint of enhancing the uniformity of the particle size, the supply of all aqueous solutions can be temporarily stopped to adjust the pH value. preferable. The pH value is adjusted when the reaction aqueous solution (nucleation aqueous solution) uses an inorganic acid of the same type as the acid constituting the compound containing the transition metal as the raw material, for example, a transition metal sulfate as the raw material. May be performed by supplying sulfuric acid.

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

  The pH value of the aqueous reaction 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, based on a liquid temperature of 25 ° C. Control to the range. When the pH is in the above range, generation of new nuclei is suppressed, particle growth can be prioritized, and the resulting metal composite hydroxide can be made homogeneous and have a narrow particle size distribution. On the other hand, when the pH value is less than 10.5, the ammonium ion concentration increases and the solubility of metal ions increases, so that not only does the rate of crystallization reaction slow, but also the amount of metal ions remaining in the reaction aqueous solution. May increase and productivity may deteriorate. Moreover, when pH value exceeds 12.0, the amount of nucleation in a particle growth process will increase, the particle size of the metal composite hydroxide particle obtained may become non-uniform | heterogenous, and particle size distribution may deteriorate.

  Note that the fluctuation range of the pH value in the reaction aqueous solution (particle growth aqueous solution) is preferably within ± 0.2. When the fluctuation range of the pH value is large, the amount of nucleation and the rate of particle growth are not constant, and it becomes difficult to obtain a metal composite hydroxide having a narrow particle size distribution.

  The pH value of the particle growth step (step S12) is preferably adjusted to a value lower than the pH value of the nucleation step (step S11). In order to clearly separate nucleation and particle growth, particle growth The pH value of the step (Step S12) is preferably 0.5 or more lower than the pH value of the nucleation step (Step S11), more preferably 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, it is a boundary condition between nucleation and nucleation growth. The conditions can be either the production step or the particle growth step. That is, when the pH value of the nucleation step is higher than 12.0 to cause nucleation in a large amount, and the pH value of the particle growth step is set to 12.0, a large amount of nuclei exist in the reaction aqueous solution. Particle growth occurs preferentially, and metal composite hydroxide particles having a narrow particle size distribution can be obtained. On the other hand, when the pH value in the nucleation step is 12.0, there is no nucleus that grows in the reaction aqueous solution, so nucleation takes precedence and the pH value in the particle growth step is made smaller than 12.0. Thus, the generated nucleus grows and good metal composite hydroxide particles can be obtained.

  The ammonium ion concentration of the reaction aqueous solution (particle growth aqueous solution) can be made the same as the preferable range of the ammonium ion concentration in the reaction aqueous solution (nucleation aqueous solution). In addition, the fluctuation range of the ammonium ion concentration can be the same as the preferable range in the reaction aqueous solution (nucleation aqueous solution).

  The reaction atmosphere of the particle growth step (step S12) may be switched by adjusting the oxygen concentration. For example, when the central part of the secondary particle has a solid structure, the reaction is continued from the nucleation step (step S11). After growing the particles in a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less, switching to an oxidizing atmosphere in which the oxygen concentration exceeds 1% by volume (the first switching), the particles are grown, and the oxygen concentration is further increased. However, the grain growth may be performed by switching to a non-oxidizing atmosphere of 1% by volume or less (second switching). By switching the reaction atmosphere, secondary particles having the multilayer structure described above can be obtained.

  Further, when producing secondary particles having a multilayer structure, the reaction atmosphere may be switched multiple times in the particle growth step (whole) in the first crystallization step and the second crystallization step. Without switching the reaction atmosphere in the growth process (step S12), the reaction atmosphere may be switched multiple times in the second crystallization process, and the reaction atmosphere is switched multiple times in the particle growth process (step S12). You may go. In the particle growth step (step S12), the reaction atmosphere may be switched two or more times or four or more times.

(2) Second crystallization step Next, a second raw material aqueous solution containing a metal element and containing more tungsten than the first raw material aqueous solution in the reaction aqueous solution containing the first metal composite hydroxide particles, Ammonium ion supplier is supplied to perform a crystallization reaction (step S20). Thereby, the 2nd metal compound hydroxide particle which formed the tungsten concentration layer on the surface of the 1st metal compound hydroxide particle is obtained.
In the second crystallization step, the first raw material aqueous solution is continuously formed from the particle growth step (step S12) because the particle growth is performed using secondary particles in which a plurality of primary particles are aggregated as nuclei. A second raw material aqueous solution containing more tungsten containing more tungsten and an ammonium ion supplier are supplied to the reaction aqueous solution containing the first metal composite hydroxide particles, and the second crystallization step (step S20). It can be performed. Thereby, a tungsten concentrated layer is formed on the outer peripheral portion of the secondary particles constituting the first composite oxide particles.

  In the method for producing a metal composite hydroxide of the present embodiment, for example, the first metal is adjusted by adjusting the timing at which the second raw material aqueous solution starts to be added (that is, the timing at which the second crystallization step is disclosed). The thickness of the tungsten concentrated layer formed on the outer periphery of 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, for example, 10% of the total amount of metal added in the first crystallization step and the second crystallization step. It can be started by supplying the second raw material aqueous solution when it is supplied to the reaction tank of mass% or more. Thereby, a tungsten concentrated layer can be easily formed on the surface of the first metal composite hydroxide particles.

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

  Since the second crystallization step (step S20) is a step in which particle growth is performed as in the particle growth step (step S12), the pH, temperature, ammonium ion concentration of the reaction aqueous solution, and the atmosphere in the reaction tank The conditions can be the same as in the particle growth step (step S12). By continuously performing the second crystallization step (Step S20) under the same conditions as in the particle growth step (Step S12), tungsten is easily formed on the surface of the first metal composite hydroxide particles with high productivity. A concentrated layer can be formed.

  The second raw material aqueous solution may be supplied by separately preparing a raw material aqueous solution containing a metal element other than tungsten and an aqueous solution containing tungsten, and supplying each to a reaction vessel. By separately supplying an aqueous solution containing tungsten, a tungsten enriched layer can be formed more easily and uniformly. Further, as shown in FIG. 2, the second raw material aqueous solution may include a first raw material aqueous solution and an aqueous solution containing tungsten (W), and each aqueous solution may be separately supplied to the reaction aqueous solution. Thus, by changing the concentration of the aqueous solution containing tungsten and the flow rate at the time of supplying the aqueous solution containing tungsten to the reaction tank, a tungsten concentrated layer can be formed uniformly and the tungsten can be easily concentrated. It becomes possible to adjust the thickness of the layer.

  The aqueous solution containing tungsten can be prepared by, for example, dissolving a tungsten compound in water. The tungsten compound to be used is not particularly limited, and a compound containing tungsten can be used without containing lithium, but sodium tungstate can be preferably 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 aqueous solution containing tungsten or adjusting the addition flow rate of the aqueous solution. For example, when the concentration and the addition flow rate of an 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 start point of the addition of the aqueous solution containing tungsten. be able to.

  FIG. 4 is a view showing a preferred example of the manufacturing method of the present embodiment. In FIG. 4, the first crystallization step (step S10) includes a nucleation step (step S11) and a particle growth step (step S12) separately, and the particle growth step (step S12). When the second crystallization step (step S20) is performed by supplying an aqueous solution containing tungsten together with the first raw material aqueous solution, the disclosure time point of the addition of the aqueous solution containing tungsten (second crystallization step) FIG.

  FIG. 4 (A) shows the tungsten compound from the time when 75% of the entire time from the start of the particle growth to the end of the particle growth (the end of the crystallization process) is obtained. 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, the tungsten concentrated layer 3 can be formed on the surface layer (outer periphery) of the secondary particles (first metal composite hydroxide particles). Note that the tungsten concentrated layer 3 is not formed when an aqueous solution of a tungsten compound is added in the entire process from the start point to the end point of particle growth.

  FIG. 4 (B) shows a tungsten compound from the time when 87.5% has elapsed with respect to the entire time during which particle growth is performed from the start time of particle growth to the end time of particle growth (end of crystallization step). It is a figure which shows an example at the time of adding the aqueous solution of this. In this case, as shown in the lower part of FIG. 4B, compared with the case where the addition is started from the point when 75% has elapsed on the surface layer (outer periphery) of the secondary particles (first metal composite hydroxide particles). Thus, a more concentrated tungsten enriched layer can be formed.

When supplying the aqueous solution containing tungsten together with the first raw material aqueous solution as described above to perform the second crystallization step (Step S20), the supply of the aqueous solution containing tungsten (second raw material aqueous solution) For example, when 10% or more has elapsed, preferably 50% or more and 95% or less has elapsed, and more preferably 75% or more and 90% of the entire time from the start to the end of the particle growth in the second crystallization step. % Can be performed when less than%. When the time for disclosing supply is in the above range, the tungsten enriched layer can be easily obtained with good productivity. In addition, within the above range, when the time point at which the addition of the aqueous solution containing tungsten is disclosed later, the crystallite diameter of the obtained positive electrode active material tends to be increased. Note that 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 raw material aqueous solution and the second raw material aqueous solution contain nickel, manganese, and optionally cobalt, element M, and tungsten. Further, the first raw material aqueous solution may not contain tungsten. In the second crystallization step, when the first raw material aqueous solution and the aqueous solution containing tungsten 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. The composition ratio of hydroxide (excluding tungsten). Therefore, the content of each metal element in the first aqueous raw material solution can be appropriately adjusted according to the composition of the target metal composite hydroxide. For example, when trying to obtain the metal composite hydroxide particles represented by the ratio (A) described above, the ratio of the metal element in the raw material aqueous solution is set 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 do. The compositions of the first raw material aqueous solution and the second raw material aqueous 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 obtained metal composite hydroxide.

  Although the compound of the metal element (transition metal) used for adjustment of the 1st raw material aqueous solution and the 2nd raw material aqueous solution is not specifically limited, From ease of handling, water-soluble nitrate, sulfate, hydrochloride, etc. From the viewpoint of cost and prevention of halogen contamination, it is particularly preferable to use sulfate.

  Further, element M in the metal composite hydroxide (M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W) In the case where the element M is contained, the compound for supplying the element M is preferably a water-soluble compound, for example, magnesium sulfate, calcium sulfate, aluminum sulfate, titanium sulfate, ammonium peroxotitanate, potassium potassium 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 suitably used.

  The concentration of the first raw material aqueous solution and the second raw material aqueous solution is the sum of the metal compounds, 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. The following. When the concentration of the raw material aqueous solution is less than 1 mol / L, the amount of crystallized material per reaction tank is reduced, and thus the productivity is lowered. On the other hand, if the concentration of the mixed aqueous solution exceeds 2.6 mol / L, it exceeds the saturation concentration at normal temperature, so that crystals of each metal compound may reprecipitate and clog piping and the like.

In addition, the metal compound mentioned above does not necessarily need to be supplied to a reaction tank as one type of raw material aqueous solution. For example, when a crystallization reaction is performed using a metal compound that reacts when mixed to produce a compound other than the target compound, individually such that the total concentration of the aqueous solution of all metal compounds falls within the above range. An aqueous solution of a metal compound may be prepared and supplied into the reaction vessel at a predetermined ratio as an aqueous solution of individual metal compounds.
In addition, the supply amount of the first raw material aqueous solution and the second raw material aqueous solution is 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. When the concentration of the product is less than 30 g / L, the aggregation of primary particles may be insufficient. On the other hand, when the concentration of the product exceeds 200 g / L, the aqueous solution for nucleation or the aqueous solution for particle growth does not sufficiently diffuse in the reaction tank, and the particle growth may be biased.

(Alkaline aqueous solution)
The aqueous alkali solution for adjusting the pH value in the aqueous reaction solution is not particularly limited, and a general aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide can be used. The alkali metal hydroxide can be directly added to the reaction aqueous solution, but it is preferably added as an aqueous solution in view of easy pH control. In this case, the concentration of the aqueous alkali metal hydroxide solution is preferably 20% by mass or more and 50% by mass or less, and more preferably 20% by mass or more and 30% by mass or less. By regulating the concentration of the alkali metal aqueous solution to such a range, it is possible to prevent the pH value from being locally increased at the addition position while suppressing the amount of solvent (water amount) supplied to the reaction system. In addition, metal composite hydroxide particles having a narrow particle size distribution can be obtained efficiently.

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

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

  When ammonia water is used as the ammonium ion supplier, the concentration is preferably 20% by mass to 30% by mass, more preferably 22% by mass to 28% by mass. By restricting the ammonia water concentration to such a range, loss of ammonia due to volatilization or the like can be suppressed to a minimum, so that production efficiency can be improved.

  In addition, the supply method of the aqueous solution containing an ammonium ion supply body can also be supplied by a pump capable of controlling the flow rate, similarly to the alkaline aqueous solution.

(Reaction atmosphere)
In the nucleation step, the reaction atmosphere in the manufacturing method of the present embodiment is a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less when the central part of the particle has a solid structure in which primary particles are densely arranged. It is preferable to control. In order to mainly form secondary particles having a metal composite hydroxide tap density of 0.75 g / cm ^{3 to} 1.35 g / cm ³ and having a multilayer structure, the first crystallization step In the particle growth (step S12, step S20) in the second crystallization step, a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less and an oxidizing atmosphere having an oxygen concentration of more than 1% by volume, It is preferable to carry out switching appropriately. In the non-oxidizing atmosphere, specifically, it is necessary to control the mixed atmosphere of oxygen and inert gas so that the oxygen concentration in the reaction atmosphere is preferably 1% by volume or less. The oxidizing atmosphere may be an atmosphere in which the oxygen concentration in the reaction atmosphere exceeds 1% by volume. For example, the oxygen concentration may exceed 5% by volume or may be an air atmosphere.

  As described above, by controlling the atmosphere in the reaction vessel to an oxidizing atmosphere or a non-oxidizing atmosphere, and controlling the number of times the reaction atmosphere is switched, the particle structure of the metal composite hydroxide, the specific surface area And the tap density is controlled. The number of times of switching of the reaction atmosphere in the entire particle growth (step S12 and step S20) in the first crystallization step and the second crystallization step may be, for example, two times or more. It may be 4 times or more. From the viewpoint of obtaining a positive electrode active material having a large BET specific surface area, the switching of the reaction atmosphere is preferably 4 times or more, and preferably 4 times from the viewpoint of productivity. In addition, the switching timing of the reaction atmosphere can be appropriately adjusted according to the desired thickness of each layer in the multilayer structure.

(Reaction temperature)
The temperature of the aqueous reaction 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 and particle growth process, second crystallization process). Control. When the reaction temperature is less than 20 ° C., nucleation is likely to occur due to low solubility of the aqueous reaction solution, and it becomes 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 when it exceeds 60 ° C., the volatilization of ammonia is promoted, and an ammonium ion supplier that is supplied to control ammonium ions in the aqueous reaction solution within a certain range. As a result, the amount of the aqueous solution containing increases the production cost. Further, when the temperature exceeds 60 ° C., as described above, in the nucleation step, there is a possibility that the primary crystal is distorted and the tap density starts to be lowered.

(Manufacturing equipment)
In the method for producing a metal composite hydroxide according to this embodiment, it is preferable to use an apparatus that does not recover the product until the reaction is completed, for example, a batch reaction tank. With such an apparatus, unlike the continuous crystallization apparatus that recovers the product by the overflow method, the growing particles are not recovered simultaneously with the overflow liquid, so that the metal composite hydroxide having a narrow particle size distribution is obtained. Particles can be easily obtained.

  Further, in the method for producing a metal composite hydroxide of the present embodiment, since it is preferable to control the reaction atmosphere during the crystallization reaction, it is preferable to use an apparatus capable of controlling the atmosphere such as a sealed apparatus. With such an apparatus, the reaction atmosphere in the nucleation process and the particle growth process can be appropriately controlled, so that the metal composite hydroxide particles having the above-described particle structure and having a narrow particle size distribution can be easily obtained. 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 above-described particle structure, average particle diameter, and particle size distribution can be realized. For example, the composition ratio (A It can apply suitably with respect to the metal composite hydroxide represented by.

3. Positive electrode active material for non-aqueous electrolyte secondary battery The positive electrode active material according to the present embodiment includes lithium, nickel, manganese, and tungsten, and optionally cobalt and element M, and the atoms of the respective metal elements The number 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, A lithium metal composite oxide (hereinafter referred to as “lithium metal composite oxide”) represented by V, Cr, Zr, Nb, Mo, Hf, or Ta. The lithium metal composite oxide has a hexagonal layered crystal structure.

  FIG. 5A is a schematic diagram illustrating an example of a lithium metal composite oxide according to the present embodiment. As shown in FIG. 5A, the lithium metal composite oxide 20 includes secondary particles 22 formed by aggregating a plurality of primary particles 21. The lithium metal composite oxide 20 may contain a small amount of single primary particles 21. Hereinafter, the details of the lithium metal composite oxide 20 will be described with reference to FIGS. 5 (A) and 5 (B).

(Compounds containing tungsten and lithium)
As shown in FIG. 5B, the lithium metal composite oxide 20 contains tungsten and lithium at the surface layer of the primary particles 21 existing on the surface or inside of the secondary particles 22 and the grain boundaries between the primary particles 21. Containing compound 23 is present in concentrated form. For example, as shown in FIG. 9, the presence site of the compound 23 containing tungsten and lithium can be confirmed by detecting the W distribution by surface analysis using an energy dispersive X-ray analyzer (EDX). Further, it is preferable that the compound 23 containing tungsten and lithium is present more on the surface (surface layer) than inside the secondary particles 22.

  When the surface layer of the positive electrode active material is coated with a heterogeneous compound, the movement (intercalation) of lithium ions is greatly limited, and as a result, the advantage of the high capacity of the lithium metal composite oxide cannot be fully exhibited. is there. On the other hand, the compound 23 containing tungsten and lithium (for example, lithium tungstate) has an effect of accelerating the movement of lithium ions because of high conductivity of lithium ions, and therefore, the lithium metal composite oxidation according to the present embodiment. The object 20 forms a Li conduction path at the interface with the electrolytic solution by forming a compound 23 containing tungsten and lithium in the surface layer of the primary particles 21 near the surface and 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 in the form of fine particles near the surface of the lithium metal composite oxide 20, for example.

The compound 23 containing tungsten and lithium, is not particularly limited, for _example, lithium tungstate, such as _{Li 2 WO 4, Li 4 WO} 5, Li 2 W 2 O 7. These lithium tungstates are concentrated on the surface layer of the primary particles 21 present on the surface or inside of the secondary particles 22 and the grain boundaries between the primary particles 21, thereby forming the lithium metal composite oxide 20. When the lithium ion conductivity is further increased and the lithium ion conductivity is used for the positive electrode of the secondary battery, the reaction resistance is further reduced.

(Particle structure)
The lithium metal composite oxide in the present embodiment inherits the multilayer structure that is characteristic of the metal composite hydroxide, increases the contact area with the electrolyte while maintaining sufficient particle strength, and provides output characteristics. Is also excellent.

  The structure of the secondary particles 22 of the lithium metal composite oxide 20 is not particularly limited. For example, the secondary particles 22 may have a solid structure formed by agglomerating primary particles relatively without gaps. However, as shown in FIG. 5A, the secondary particle 22 has a central portion 24 that is a solid structure. Further, outside the central portion 24, a void portion 26 in which the primary particles 21 are arranged more sparsely than the central portion 24, and a substantial portion in which the primary particles 21 are densely arranged and can be electrically connected to the central portion. And a multi-layer structure having 21. When the lithium metal composite oxide 20 composed of secondary particles having voids 26 in the secondary particles 22 is used as the positive electrode of the secondary battery, the electrolyte penetrates into the secondary particles, and the secondary particles Since the contact area between the primary particles 21 inside the electrolyte 22 and the electrolyte increases, the resistance inside the secondary particles 22 can be reduced and the output characteristics can be improved. A plurality of substantial portions 21 may exist, and for example, as described in Patent Document 3, may be configured by an outer shell portion or an outer shell portion and an inner shell portion. Moreover, the center part 24 may have a hollow structure.

  Further, in the lithium composite oxide, it may be formed in a layered shape between the central portion 24 and the substantial portion 21 or between the plurality of substantial portions 21 or may be partially formed. The central portion may be in a state where a plurality of aggregated portions formed by aggregating plate-like primary particles are connected. In this specification, “electrically conductive” means that the high-density portions of the lithium metal composite oxide are directly structurally connected and electrically conductive. means.

  When the lithium metal composite oxide 20 including the secondary particles 22 having the multilayer structure as described above is used as the positive electrode, the interior of the secondary particles 22 is interposed through the grain boundaries or voids 26 between the primary particles 21. Therefore, the lithium can be desorbed and inserted not only on the surface of the secondary particles 22 but also inside the secondary particles 22. Moreover, since the lithium metal composite oxide 20 has a large number of electrically conductive paths inside the secondary particles 22, the resistance inside the particles can be made sufficiently small. Therefore, when the positive electrode of the secondary battery is configured using the lithium metal composite oxide 20, the output characteristics can be greatly improved without impairing the capacity characteristics and the cycle characteristics.

  The secondary particles having a multilayer structure including the hollow portion 25 and the space portion 26 are formed by appropriately adjusting the respective conditions in the nucleation step (step S11) and the particle growth step (step S12). For example, the conditions described in Patent Documents 2 and 3 may be used.

  The positive electrode active material according to the present embodiment is an aqueous solution containing tungsten as described above in succession to a conventionally known particle growth step during the production of secondary particles 22 (metal composite hydroxide) having a multilayer structure. By adding a second crystallization step of adding the metal composite hydroxide 10 having the tungsten concentrated layer 3 formed on the surface layer (surface), and the lithium metal composite oxide 20 using this as a precursor Obtainable. The lithium metal composite oxide 20 includes a secondary particle 22 having a multilayer structure because the compound 23 containing lithium and tungsten is present at the grain boundary between the surface layer of the primary particle 21 and the primary particle 21. The output characteristics can be further improved while maintaining the crystallinity.

(BET specific surface area)
Although the BET specific surface area of the positive electrode active material is not particularly limited, for example, it is preferably 1.45 m ² / g or more and 5.40 m ² / g or less, and preferably 2 m ² / g or more and 5.40 m ² / g or less. it is more preferable, and further preferably 2.5 m ² / g or more 5.40m ² / g or less. When the BET specific surface area is in the above range, when the positive electrode of the secondary battery is used, the contact area with the electrolytic solution can be increased, the positive electrode resistance can be reduced, and the output characteristics can be improved.

(Tap density)
The tap density of the positive electrode active material is not particularly limited, for example, when the secondary particles 2 having a multi-layer structure, is preferably 1.00 g / cm ³ or more 2.00 g / cm ³ or less, more preferably 1. It is 2 g / cm ³ or more and 2.00 g / cm ³ or less. When the tap density of the positive electrode active material is in the above range, the output characteristics are improved by increasing the contact area with the electrolytic solution while improving the battery capacity per unit volume. On the other hand, when the tap density exceeds 2.00 g / cm ³ , there are few portions having voids in the particle structure, and there is a tendency that the average particle size tends to increase, and the output characteristics decrease as the reaction area decreases. . In addition, when the spread of the particle size distribution is large, the tap density tends to increase, but in this case, the fine particles may be selectively deteriorated to deteriorate the cycle characteristics. On the other hand, when the tap density is less than 1.00 g / cm ³ , the portion having voids increases in the particle structure, and the particle strength is lowered, so that the cycle characteristics may be lowered. Moreover, the filling property of the positive electrode active material is lowered, and it is difficult to increase the battery capacity per unit volume.

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

  The average particle diameter of the positive electrode active material means a volume-based average particle diameter (MV) as in the case of the metal composite hydroxide described above. For example, the volume integration measured with a laser light diffraction / scattering particle size analyzer It can be obtained from the value.

(Particle size distribution)
The positive electrode active material of the present embodiment preferably has [(d90−d10) / average particle size], which is an index indicating the spread of the particle size distribution, of 0.65 or less. When [(d90-d10) / average particle size] is in the above range, the lithium metal composite oxide 20 can be constituted by a very narrow particle size distribution. Such a positive electrode active material has a small proportion of fine particles and coarse particles, and a secondary battery using this for the positive electrode has excellent thermal stability, cycle characteristics, and output characteristics.

  On the other hand, when [(d90−d10) / average particle diameter] 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 having a large particle size distribution, for example, generates heat due to a local reaction of fine particles, reduces thermal stability, and selectively degrades fine particles. The cycle characteristics may be deteriorated. In addition, secondary batteries using a positive electrode active material with a large particle size distribution have a large proportion of coarse particles, so that a sufficient reaction area between the electrolyte and the positive electrode active material cannot be secured, resulting in a decrease in output characteristics. There are things to do.

  Note that, on the assumption of industrial scale production, it is not realistic to use a material having an excessively small [(d90-d10) / average particle size] as the positive electrode active material. Therefore, in consideration of cost and productivity, the lower limit of [(d90−d10) / average particle diameter] is preferably about 0.25. In addition, the meanings of d10 and d90 in [(d90−d10) / average particle diameter] and how to obtain them are the same as those of the metal composite hydroxide described above.

(Sintered aggregation)
The positive electrode active material of the present embodiment has an index indicating sintering aggregation [lithium metal composite oxide d50 / metal composite hydroxide d50 (hereinafter referred to as “d50 ratio”)] of 0.95 to 1.05. The following range is preferable. When the d50 ratio is in the above range, the positive electrode active material can be composed of the lithium metal composite oxide 20 with little aggregation of secondary particles accompanying sintering aggregation. A secondary battery using such a positive electrode active material has a high filling property, a high capacity, a small variation in characteristics, and an excellent uniformity.

  On the other hand, when the d50 ratio is 1.05 or more, the specific surface area may decrease with the aggregation of sintering, and the filling property may decrease. A secondary battery using such a positive electrode active material may have reduced output characteristics and reduced capacity due to a decrease in reactivity. In addition, when a secondary battery using such a positive electrode active material is repeatedly charged and discharged, the secondary battery selectively collapses from a weak portion where the secondary particles are aggregated in the positive electrode. May be a factor that greatly impairs.

In addition, when the d50 ratio is less than 1.0, by crushing the lithium metal composite oxide 20, a part of the primary particles 21 are missing from the secondary particles 22 and the particle size is reduced. In particular, when the d50 ratio is less than 0.95, a large amount of fine particles are generated due to the large number of missing primary particles 21, and the particle size distribution may be broadened.
The metal composite hydroxide d50 means d50 of the metal composite hydroxide 10 used as a precursor when the lithium metal composite oxide 20 is produced. The d50 of each particle can be measured with a laser light diffraction / scattering particle size analyzer, and the number of particles in each particle size is accumulated from the smaller particle size side, and the accumulated volume is the total volume of all particles. It means a particle size of 50%.

(Crystallite diameter)
The positive electrode active material according to the present embodiment is compared with a positive electrode active material using a metal composite hydroxide as a precursor obtained by uniformly adding tungsten throughout the crystallization process as in the conventional manufacturing method. The crystallite diameter of the (003) plane obtained by powder X-ray diffraction measurement can be further increased. The crystallite diameter of the (003) plane of the positive electrode active material can be, for example, 110 nm or more, and is preferably adjusted to 120 nm or more. When the crystallite diameter of the (003) plane of the positive electrode active material is 120 nm or more, the secondary battery using this positive electrode active material as the positive electrode has high output characteristics because the reaction resistance is low. The thermal stability is also improved. On the other hand, when the crystallite diameter of the (003) plane is less than 120 nm, the thermal stability of the secondary battery may be lowered. The upper limit of the (003) plane crystallite diameter is not particularly limited, but may be, for example, 200 nm or less, and preferably 120 nm or more and 150 nm or less. In the positive electrode active material of this embodiment, as described above, high crystallinity can be maintained by using the metal composite hydroxide 10 having the tungsten enriched layer 3 on the surface as a precursor. The diameter can be within the above range.

(composition)
The composition of the positive electrode active material of the present embodiment is not particularly limited as long as it has the above-described characteristics. 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).
In the 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, and further preferably 0 or more and 0.35. It is as follows. When the value of u is in the above range, the output characteristics and capacity characteristics of a secondary battery using this positive electrode active material as a positive electrode material can be improved. 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 or the positive electrode resistance may increase.

  In the general formula (B), the value x indicating the nickel (Ni) content 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 higher potential and higher capacity of the secondary battery. When 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 content of other elements decreases, and the effects of other elements cannot be obtained.

  In the general formula (B), the value 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 the improvement of thermal stability. When 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, when the value of y exceeds 0.55, Mn is eluted from the positive electrode active material during high temperature operation, and the charge / discharge cycle characteristics may be deteriorated.

  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, and 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 the 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 not more than 0.1 when the total number of moles of Ni, Co and Mn is 1, preferably It is 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 in the above range, the positive electrode active material is more excellent in output characteristics and cycle characteristics while maintaining high crystallinity. As described above, W is mainly included in the surface layer of the primary particles 21 in the vicinity of the surface of the secondary particles 22 or the grain boundary between the primary particles 21 in the positive electrode active material.

  In the positive electrode active material of the present embodiment, in order to further improve the durability and output characteristics of the secondary battery, the element M may be contained in addition to the metal element described above. Examples of such element M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), molybdenum ( One or more selected from 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. 0, when the total 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 contributing to the Redox reaction decreases, and the battery capacity may be reduced.

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 expressed by the general formula (B1): Li _{1 + u} Ni _x Mn _y Co _z W _a MbO 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 elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta) It is preferable. Among these, 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.

From the viewpoint of achieving further improvement of the thermal stability, the composition, the general formula _{(B2): Li 1 + u} Ni x Mn y Co z W a M b 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 are preferably used.

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

  As shown in FIG. 6, the method for producing a positive electrode active material according to the present embodiment is a step of obtaining a lithium mixture by mixing a metal composite hydroxide obtained by the above production method and a lithium compound (step S30). And a step of baking the lithium mixture to obtain a lithium metal composite oxide (step S40). In addition to the steps described above, steps such as a heat treatment step and a calcination step may be added as necessary.

  Tungsten in the tungsten enriched layer formed on the surface of the metal composite hydroxide reacts with the lithium compound in the mixing step (step S30) and the firing step (step S40) with the lithium compound, and thereby the lithium metal composite oxide. A compound 23 containing tungsten and lithium is formed in the surface layer of the primary particles and the grain boundaries between the primary particles. Hereinafter, with reference to FIG. 6, the manufacturing method of the positive electrode active material which concerns on this embodiment is demonstrated.

(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”) and a lithium compound are mixed. Thus, a lithium mixture is obtained (step S30).

  In the mixing step (step S30), a metal atom other than lithium in the lithium mixture, specifically, the sum of the number of atoms of nickel, cobalt, manganese and the element M (Me), and the number of lithium atoms (Li) The ratio (Li / Me) is 0.95 to 1.5, preferably 1.0 to 1.5, more preferably 1.0 to 1.35, and still more preferably 1.0 to 1. A precursor and a lithium compound are mixed so that it may become 2 or less. That is, since Li / Me does not change before and after the firing step, the precursor and the lithium compound are mixed so that Li / Me in the mixing step becomes Li / Me of the target positive electrode active material.

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

  It is preferable that the precursor and the lithium compound are sufficiently mixed so that no fine powder is generated. Insufficient mixing may cause variation in Li / Me among individual particles, and may not provide sufficient battery characteristics. In addition, a general mixer can be used for mixing. For example, a shaker mixer, a Laedige mixer, a Julia mixer, a V blender, or the like can be used.

(Heat treatment process)
In the method for producing the positive electrode active material of the present embodiment, a heat treatment step is optionally provided before the mixing step (step S30), and the metal composite hydroxide is heat treated and then mixed with the lithium compound. Good (not shown). Here, the particles obtained after the heat treatment include not only the metal composite hydroxide particles from which excess water has been removed in the heat treatment step, but also transition metal composite oxides converted to oxides by the heat treatment step (hereinafter referred to as “ Also included are particles of a “metal composite oxide” or mixtures thereof.

  The heat treatment step is a step of removing excess moisture contained in the metal composite hydroxide by heating the metal composite hydroxide to 105 ° C. or more and 750 ° C. or less and performing heat treatment. Thereby, the water | moisture content which remains after a baking process can be reduced to a fixed amount, and the dispersion | variation in the composition of the positive electrode active material obtained can be suppressed.

  The heating temperature in the heat treatment step is 105 ° C. or higher and 750 ° C. or lower. When the heating temperature is less than 105 ° C., excess moisture in the metal composite hydroxide cannot be removed, and variation may not be sufficiently suppressed. On the other hand, even if the heating temperature exceeds 700 ° C., not only a further effect cannot be expected, but the production cost increases.

  Note that in the heat treatment step, it is sufficient that water can be removed to such an extent that the number of atoms of each metal component in the positive electrode active material and the ratio of the number of Li atoms do not vary. There is no need to convert it into a thing. However, in order to reduce the variation in the number of atoms of each metal component and the number of Li atoms, all metal composite hydroxides are converted into composite oxides by heating to 400 ° C. or higher. It is preferable. In addition, the above-mentioned dispersion | variation can be suppressed more by calculating | requiring beforehand the metal component contained in the metal complex hydroxide by heat processing conditions by analysis, and determining the mixing ratio with a lithium compound.

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

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

(Baking process)
Next, the lithium mixture obtained in the mixing step (step S30) is baked to obtain a lithium metal composite oxide (step S40). In this step, firing is performed under predetermined conditions, and lithium is diffused in the precursor to obtain a lithium metal composite oxide. The obtained lithium metal composite oxide 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 crushing step as described later.

[Baking temperature]
The firing temperature of the lithium mixture is preferably 650 ° C. or higher and 980 ° C. or lower. When the firing temperature is less than 650 ° C., lithium does not sufficiently diffuse into the precursor, and surplus lithium, unreacted metal composite hydroxide or metal composite oxide remains, or the resulting lithium metal composite oxidation The crystallinity of the object becomes insufficient. On the other hand, when the firing temperature is higher than 980 ° C., the lithium composite oxide particles are vigorously sintered, abnormal grain growth is caused, and the proportion of irregular coarse particles may increase.

  In addition, when it is going to obtain the positive electrode active material represented with the general formula (B1) mentioned above, it is preferable that a calcination temperature shall be 650 degreeC or more and 900 degrees C or less. On the other hand, when the positive electrode active material represented by the general formula (B2) is to be obtained, the firing temperature is preferably 800 ° C. or higher and 980 ° C. or lower.

  In addition, the rate of temperature increase in the firing step is preferably 2 ° C./min to 10 ° C./min, and more preferably 5 ° C./min to 10 ° C./min. Further, during the firing step (step S40), it is preferably maintained at a temperature near the melting point of the lithium compound used, preferably 1 hour or more and 5 hours or less, more preferably 2 hours or more and 5 hours or less. Thereby, a precursor and a lithium compound can be made to react more uniformly.

[Baking time]
The holding time (baking time) at the baking temperature is preferably at least 2 hours, more preferably 4 hours or more and 24 hours or less. When the holding time at the firing temperature is less than 2 hours, lithium is not sufficiently diffused in the precursor, and surplus lithium, unreacted metal composite hydroxide particles or heat-treated particles remain, or the obtained lithium composite oxide The crystallinity of the particles may be insufficient.

  After the holding time, the cooling rate from the firing temperature to at least 200 ° C. is preferably 2 ° C./min to 10 ° C./min, more preferably 33 ° C./min to 77 ° C./min. preferable. By controlling the cooling rate within such a range, it is possible to prevent the facilities such as the mortar from being damaged by the rapid cooling while securing the productivity.

[Baking atmosphere]
The firing atmosphere is preferably an oxidizing atmosphere, more preferably an oxygen concentration of 18% by volume to 100% by volume, and a mixed atmosphere of oxygen having the above oxygen concentration and an inert gas. Is particularly preferred. That is, firing is preferably performed in the air or in an oxygen stream. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium composite oxide particles may be insufficient.

  In addition, the furnace used for a baking process (step S40) is not restrict | limited in particular, What is necessary is just what can heat a lithium mixture in air | atmosphere or oxygen stream. However, from the viewpoint of keeping the atmosphere in the furnace uniform, an electric furnace that does not generate gas is preferable, and either a batch type or a continuous type electric furnace can be suitably used. The same applies to the furnace used in the heat treatment step and the calcining step.

(Calcination process)
In addition, when using lithium hydroxide and lithium carbonate as a lithium compound, you may perform a calcination process after a mixing process (step S30) and before a baking process (step S40). The calcination step is a step of calcination of the lithium mixture at a temperature lower than the firing temperature described later and at 350 to 800 ° C., preferably 450 to 780 ° C. Thereby, lithium can fully be 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 calcination step 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, as in the baking step described later.

(Crushing process)
The lithium metal composite oxide obtained by the firing step (Step S40) may be aggregated or slightly sintered. In such a case, it is preferable to crush the aggregate or sintered body of the lithium composite oxide particles. Thereby, the average particle diameter and particle size distribution of the positive electrode active material obtained can be adjusted to a suitable range. Note that pulverization means that mechanical energy is applied to an aggregate composed of a plurality of secondary particles generated by sintering necking between secondary particles during firing, and the secondary particles themselves are hardly destroyed. It means an operation of separating and loosening the aggregates.

  As a crushing method, a 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. Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present embodiment includes the same components as a general non-aqueous electrolyte secondary battery, such as a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. Note that the embodiments described below are merely examples, and the nonaqueous electrolyte secondary battery of the present invention is applied to various modified and improved embodiments based on the embodiments described in the present specification. It is also possible to do.

(1) Component (positive electrode)
Using the positive electrode active material for a nonaqueous electrolyte secondary battery obtained by the present embodiment, for example, a positive electrode of a nonaqueous electrolyte secondary battery is produced as follows.

  First, a conductive material and a binder are mixed with the obtained powdery positive electrode active material, and activated carbon and a solvent such as viscosity adjustment are added as necessary, and these are kneaded to prepare a positive electrode mixture paste. Make it. At that time, the mixing ratio in the positive electrode mixture paste is also an important factor for determining the performance of the nonaqueous electrolyte secondary battery. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 parts by mass or more and 95 parts by mass or less, like the positive electrode of a general nonaqueous electrolyte secondary battery. The content of the conductive material can be 1 part by mass or more and 20 parts by mass or less, and the content of the binder can be 1 part by mass or more and 20 parts by mass or less.

  The obtained positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.

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

  The binder plays a role of anchoring the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin, and polyacrylic are used. An acid can be used.

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

(Negative electrode)
For the negative electrode, metallic lithium or lithium alloy, or a negative electrode active material that can occlude and desorb lithium ions is mixed with a binder, and an appropriate solvent is added into a paste to form a negative electrode mixture such as copper. It is applied to the surface of the metal foil current collector, dried, and compressed to increase the electrode density as necessary.

  Examples of the negative electrode active material include lithium-containing materials such as metallic lithium and lithium alloys, natural graphite capable of occluding and desorbing lithium ions, sintered organic compounds such as artificial graphite and phenolic resins, and carbon materials such as coke. A powdery body can be used. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder, as in the case of the positive electrode, and an organic material such as N-methyl-2-pyrrolidone can be used as a solvent for dispersing these active materials and the binder. A solvent can be used.

(Separator)
The separator is disposed between the positive electrode and the negative electrode, and has a function of separating the positive electrode and the negative electrode and holding the electrolyte. As such a separator, for example, a thin film such as polyethylene or polypropylene and a film having many fine pores can be used. However, the separator is not particularly limited as long as it has the above function.

(Non-aqueous electrolyte)
The nonaqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.
Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, and tetrahydrofuran, 2-methyltetrahydrofuran. And one kind selected from ether compounds such as dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, or a mixture of two or more kinds. it can.
As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and complex salts thereof can be used.

  Furthermore, the nonaqueous electrolytic solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(2) Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present invention composed of the above positive electrode, negative electrode, separator and non-aqueous electrolyte can be made into various shapes such as a cylindrical shape and a laminated shape. it can.

  In any case, the positive electrode and the negative electrode are laminated through a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like, and sealed in a battery case to complete a nonaqueous electrolyte secondary battery. .

(3) Characteristics of Nonaqueous Electrolyte Secondary Battery Since the nonaqueous electrolyte secondary battery of the present invention uses the positive electrode active material of the present invention as a positive electrode material as described above, capacity characteristics, output characteristics, and cycle characteristics. Excellent. Moreover, it can be said that the thermal stability is also excellent in comparison with a secondary battery using a positive electrode active material made of conventional lithium nickel oxide particles.

(4) Applications The nonaqueous electrolyte secondary battery of the present invention is excellent in capacity characteristics, output characteristics, and cycle characteristics as described above, and is a small portable electronic device (notebook type) that requires these characteristics at a high level. It can be suitably used as a power source for personal computers and prefectural telephone terminals. Further, the nonaqueous electrolyte secondary battery of the present invention is excellent in thermal stability, and not only can be downsized and increased in output, but also can simplify an expensive protection circuit, so that a mounting space can be reduced. It can also be suitably used as a power source for transportation equipment that is restricted by the above.

  Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. In the following examples and comparative examples, unless otherwise specified, special grades of reagents manufactured by Wako Pure Chemical Industries, Ltd. were used for the production of the metal composite hydroxide and the positive electrode active material. Further, the pH value of the reaction aqueous solution is measured by a pH controller (manufactured by Nisshin Rika, NPH-690D) through the nucleation step and the particle growth step, and the supply amount of the sodium hydroxide aqueous solution is adjusted based on this measurement value. Thus, the fluctuation range of the pH value of the aqueous reaction solution in each step was controlled within a range of ± 0.2.

(Example 1)
(A) Production of metal composite hydroxide [nucleation process]
First, 1.2 L of water was put in the reaction tank, and the temperature in the tank was set to 40 ° C. while stirring at 790 rpm. At this time, nitrogen gas was introduced into the reaction vessel and allowed to flow for 30 minutes, and the reaction atmosphere was a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less. Subsequently, an appropriate amount of 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water is supplied into the reaction tank so that the pH value is 12.5 based on the liquid temperature of 25 ° C. and the ammonium ion concentration is 10 g / L. Was adjusted to form an aqueous solution before reaction.

  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. A first raw material aqueous solution of L was prepared.

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

[Particle growth process]
After the nucleation is completed, once the supply of all aqueous solutions is stopped, sulfuric acid is added to the reaction vessel, and the pH value is adjusted to 11.6 based on the liquid temperature of 25 ° C. An aqueous solution was formed. After confirming that the pH value became a predetermined value, the first raw material aqueous solution was supplied to the reaction vessel, and the nuclei (particles) generated in the nucleation step were grown.

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

  The first aqueous solution was supplied at the time when 19/20 hours (95%) had elapsed with respect to the entire time for particle growth, and the supply of the sodium tungstate aqueous solution to the reaction vessel was started (addition range: 5%). The particle growth process was completed by stopping the supply of all aqueous solutions. Thereafter, the resulting product was washed with water, filtered and dried to obtain a powdered metal composite hydroxide.

  Note that switching between the non-oxidizing atmosphere and the oxidizing atmosphere was performed four times in the particle growth process of the first crystallization process and the second crystallization process. Specifically, after switching from the non-oxidizing atmosphere to the oxidizing atmosphere (first time), switching to the non-oxidizing atmosphere (second time). Further, after switching to an oxidizing atmosphere (third time), switching to a non-oxidizing atmosphere (fourth time) was performed. Nitrogen gas was introduced as the non-oxidizing atmosphere, an atmosphere having an oxygen concentration of 1% by volume or less was used, and the atmospheric atmosphere was used as the oxidizing atmosphere. The timing of switching the reaction atmosphere was performed when 20%, 40%, 60%, and 80% had elapsed with respect to the entire time during which particle growth was performed.

  In addition, in the particle growth step in the first crystallization step and the second crystallization step, through these steps, a 25% by mass sodium hydroxide aqueous solution and 25% by mass ammonia water are supplied in a timely manner, and the particle growth. The pH value and ammonium ion concentration of the aqueous solution were maintained in the ranges described above. The supply rate of the first aqueous raw material solution was constant (13 ml / min) throughout the crystallization process.

(B) Evaluation of metal composite hydroxide By analysis using an ICP emission spectroscopic analyzer (ICPE-9000ICPE-9000, manufactured by Shimadzu Corporation, Shimadzu Corporation), this metal composite hydroxide has a general formula: Ni _0. It was confirmed that it is represented by ₃₈ Mn _0.30 Co _0.32 Zr _0.002 W _0.005 (OH) ₂ .

  In addition, the average particle size of the metal composite hydroxide was measured using a laser light diffraction / scattering particle size analyzer (Microtrack Bell Co., Ltd., Microtrack MT3300EX2), d10 and d90 were measured, and the particle size distribution was measured. [(D90−d10) / average particle diameter], which is an index indicating the spread of the particle size, was calculated. As a result, it was confirmed that the metal composite hydroxide had an average particle size of 5.4 μm and [(d90−d10) / average particle size] of 0.45.

  Moreover, in order to confirm the presence or absence and the thickness of the tungsten enriched layer in the metal composite hydroxide, the energy mounted on the scanning transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, HD-2300A) A surface analysis of the cross section of the metal composite hydroxide was performed using a distributed X-ray analyzer (EDX). As a result, formation of a portion where tungsten was concentrated in the surface layer of the metal composite hydroxide (tungsten concentrated layer) was confirmed, and the thickness was confirmed to be 3 m or more and 8 m or less.

Moreover, tap density is high about this graduated cylinder after filling the obtained metal complex hydroxide into a 20 ml graduated cylinder using a shaking specific gravity measuring instrument (KRS-409, manufactured by Kuramochi Scientific Instruments Co., Ltd.). The measurement was performed after the free fall from 2 cm was densely packed by a method of repeating 500 times. As a result, it was confirmed that the tap density was 0.75 g / cm ³ or more and 1.35 g / cm ³ or less.

(C) Preparation of positive electrode active material Shaker mixer device (TURBULA Type T2C manufactured by Willy et Bacofen (WAB) Co., Ltd.) was used so that the metal composite hydroxide obtained as described above had Li / Me of 1.14. ) And thoroughly mixed with lithium carbonate to obtain a lithium mixture.
The lithium mixture was fired by heating to 900 ° C. in a stream of air (oxygen concentration: 21% by volume) at a rate of temperature increase of 2.52.5 ° C./min and holding at this temperature for 4 hours, cooling Cooled to room temperature at a rate of about 4 ° C./min. The positive electrode active material thus obtained had agglomerated or slightly sintered. For this reason, this positive electrode active material was crushed and the average particle size and particle size distribution were adjusted.

(D) Evaluation of positive electrode active material By analysis using an ICP emission spectroscopic analyzer, this positive electrode active material has a general formula: Li _1.14 Ni _0.38 Mn _0.30 Co _0.32 Zr _0.002 W ₀ It was confirmed to be represented by _0.005 O ₂ . In addition, the average particle size of the lithium metal composite oxide is measured using a laser light diffraction / scattering type particle size analyzer, and d10 and d90 are measured to indicate the spread of the particle size distribution [(d90-d10). / Average particle size] was calculated. As a result, it was confirmed that the lithium metal composite oxide had an average particle size of 5.3 μm, [(d90−d10) / average particle size] of 0.45, and a d50 ratio of 1.04.

  Further, when the crystallite diameter of the (003) plane was measured using an X-ray diffractometer (Spectris Co., Ltd., X'Pert PRO), it was 1385 mm (138.5 nm).

  Moreover, in order to confirm the distribution of tungsten in the lithium metal composite oxide, an energy dispersive X-ray analyzer (EDX) mounted on a scanning transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, HD-2300A) is used. Surface analysis of the cross section of the lithium metal composite oxide was performed. As a result, it was confirmed that the lithium metal composite oxide contained a large amount of tungsten 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 addition, the tap density is evaluated under the same conditions as the metal composite hydroxide, and the BET specific surface area is evaluated by a specific surface area measuring apparatus (manufactured by Mountec Co., Ltd., MacSorve 1200 series) employing a flow method-nitrogen gas adsorption method. did.

(E) Production of Secondary Battery FIG. 7 is a view showing a 2032 type coin battery CBA used for evaluation of battery characteristics. Hereinafter, a method for manufacturing a secondary battery will be described with reference to FIGS.

  The positive electrode active material obtained as described above: 52.5 mg, acetylene black: 15 mg, and PTEE: 7.5 mg were mixed and pressed at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm. A positive electrode PE was produced by drying at 120 ° C. for 12 hours in a dryer.

Next, using this positive electrode PE, a 2032 type coin battery CBA was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C. The negative electrode NE of the 2032 type coin battery uses lithium metal having a diameter of 17 mm and a thickness of 1 mm, and the electrolyte is made of ethylene carbonate (EC), diethyl carbonate (DEC), or the like using 1M LiClO ₄ as a supporting electrolyte. A quantity mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) was used. The separator SE was a polyethylene porous film having a film thickness of 25 μm. The 2032 type coin battery CBA has a gasket GA and is assembled into a coin-shaped battery by the positive electrode can PC and the 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 determined as Ref. The calculated resistance value was 93%. These results are shown in Table 1.

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

  In addition, the metal composite hydroxides obtained in Examples 2 to 8 using an energy dispersive X-ray analyzer (EDX) mounted on a scanning transmission electron microscope (Hitachi High-Technologies HD-2300A) A surface analysis of the cross section was performed, and the distribution of W obtained was analyzed. As a result, in the metal composite hydroxides obtained in Examples 2 to 8, a portion (tungsten enriched layer) where tungsten was concentrated on 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 the positive electrode active material. Moreover, the lithium metal composite oxide obtained in Examples 2-8 using an energy dispersive X-ray analyzer (EDX) mounted on a scanning transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, HD-2300A) A surface analysis of the cross section was performed, and the distribution of W obtained was analyzed. As a result, it was confirmed that the lithium metal composite oxides obtained in Examples 2 to 8 contained a large amount of tungsten in the surface layer of the primary particles near the surface of the secondary particles and the grain boundaries between the primary particles. It 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 process (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. The evaluation results of the obtained positive electrode active material and secondary battery are shown in Tables 1 and 2.

(Comparative Example 2)
When using a metal composite hydroxide not containing tungsten (Ni _0.38 Mn _0.30 Co _0.32 Zr _0.002 (OH) ₂ ) and mixing the metal composite hydroxide and lithium carbonate In addition, tungsten oxide was added together and mixed to obtain a lithium mixture (external addition). The following are the same conditions as in Example 1 except that the positive electrode active material (Li _1.14 Ni _0.38 Mn _0.30 Co _0.32 Zr _0.002 W _0.005 O ₂ ) and a secondary battery were manufactured. The evaluation results of the obtained positive electrode active material and secondary battery are shown in Tables 1 and 2.

(Comparative Example 3)
During the crystallization step, 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 aqueous sodium tungstate solution was not supplied in the second 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 the surface thereof. In addition, the positive electrode active material obtained in the example has a larger crystallite diameter than that of Comparative Example 1 in which tungsten is added throughout the crystallization process, and when used as a positive electrode of a secondary battery. The resistance value was low.

  Moreover, the metal composite hydroxides obtained in Examples 1 to 6 were formed with a tungsten concentrated layer having a thickness of 100 nm or less, and the positive electrode active material obtained using these metal composite hydroxides as precursors, Even when compared with 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 a positive electrode of a secondary battery.

  On the other hand, the positive electrode active material obtained in Comparative Example 3 to which tungsten is not added is used as a positive electrode for a secondary battery, although the crystallite diameter is relatively large compared to other examples and comparative examples to which tungsten is added. The resistance value was large and the output characteristics were inferior.

DESCRIPTION OF SYMBOLS 10 ... Metal composite hydroxide 1 ... Primary particle 2 ... Secondary particle 3 ... Tungsten concentration layer 4 ... Center part 5 ... Cavity part 6 ... Substantial part C ... Center 20 ... Lithium metal composite oxide 21 ... Primary particle 22 ... Secondary Next particle 23 ... Compound containing tungsten and lithium 24 ... Central part 25 ... Substantial part 26 ... Cavity 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 (15)

It contains nickel, manganese and tungsten, optionally cobalt, and element M, and the atomic ratio of each metal element 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 a method for producing a metal composite hydroxide represented by Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta. There,
By supplying a first raw material aqueous solution containing the metal element to the reaction tank and an ammonium ion supplier, adjusting the pH of the reaction aqueous solution in the reaction tank, and performing a crystallization reaction, the first metal A first crystallization step to obtain composite hydroxide particles;
A second 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 Obtaining a second crystallization step,
In the particle growth in the first crystallization step and the second crystallization step, any of a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less and an oxidizing atmosphere having an oxygen concentration exceeding 1% by volume Including switching the reaction atmosphere to one atmosphere multiple times,
The metal composite hydroxide includes secondary particles in which a plurality of primary particles are aggregated,
The secondary particles, from the center of the secondary particles toward the surface, a central portion where the primary particles are densely arranged, a void portion where the primary particles are arranged more sparsely than the central portion, and A multilayer structure including a solid portion in which primary particles are closely arranged;
The tap density of the genus composite hydroxide is 0.75 g / cm ³ or more and 1.35 g / cm ³ or less,
A method for producing a metal composite hydroxide. The first crystallization step includes a nucleation step for performing nucleation and a particle growth step for performing particle growth, and the second crystallization step performs particle growth following the particle growth step. Including
Nucleation in the first crystallization step is performed in a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less,
The particle growth in the first crystallization step and the second crystallization step is such that the pH of the reaction aqueous solution is adjusted to be lower than the pH value of the reaction aqueous solution in the nucleation step, and The method includes four times switching the reaction atmosphere to any one of a non-oxidizing atmosphere having an oxygen concentration of 1% by volume or less and an oxidizing atmosphere having an oxygen concentration exceeding 1% by volume. The manufacturing method of the metal complex hydroxide as described in 1 .. The metal element in the first raw material aqueous solution is in the range of 50% by mass to 95% by mass with respect to the total amount of metal added in the first crystallization step and the second crystallization step. After supplying to the reaction vessel, supplying the second raw material aqueous solution in the second crystallization step,
The manufacturing method of the metal composite hydroxide of Claim 1 or Claim 2.   The second crystallization step includes forming the tungsten enriched layer so as to have a thickness of 100 nm or less in a direction from the surface of the second metal composite hydroxide toward the center. The manufacturing method of the metal composite hydroxide as described in any one of Claims 1-3.   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 time during which particle growth is performed in the first and second crystallization steps. The manufacturing method of the metal composite hydroxide as described in any one of Claims 1-4 performed.   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. A method for producing a metal composite hydroxide.   The method for producing a metal composite hydroxide according to claim 6, wherein a tungsten concentration in the aqueous solution containing tungsten is 18% by mass or more with respect to the entire aqueous solution containing tungsten. Nickel, manganese, tungsten, and optionally cobalt and the element M, and the atomic ratio of each metal element 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), and is a metal composite hydroxide,
Including secondary particles in which a plurality of primary particles are aggregated,
The secondary particles, from the center of the secondary particles toward the surface, a central portion where the primary particles are densely arranged, a void portion where the primary particles are arranged more sparsely than the central portion, and Having a multilayer structure including at least a solid portion in which primary particles are closely arranged,
Having a tungsten enriched layer on the surface of the secondary particles;
The tap density is 0.75 g / cm ³ or more and 1.35 g / cm ³ or less,
Metal composite hydroxide.   The metal composite hydroxide according to claim 8, wherein the tungsten concentrated layer has a thickness of 100 nm or less.   The composite hydroxide particles have an average particle size of 4.0 μm or more and 9.0 μm or less, and [(d90−d10) / average particle size] which is an index indicating the spread of the particle size distribution is 0.65 or less. The metal composite hydroxide according to claim 8 or 9, wherein Mixing at least one of the metal composite hydroxide obtained by the production method according to any one of claims 1 to 7 and the metal composite oxide obtained by heat-treating the metal composite hydroxide with a lithium compound. And obtaining a lithium mixture;
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: baking the lithium mixture to obtain a lithium metal composite oxide.   The value (d50 of the positive electrode active material / d50 of the metal composite hydroxide), which is an index indicating the degree of aggregation of particles of the lithium metal composite oxide, is 0.95 or more and 1.05 or less. The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 11 to adjust. Lithium, nickel, manganese, tungsten, and optionally cobalt and the element M, and 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 elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta A lithium metal composite oxide represented by
The lithium metal composite oxide includes secondary particles in which a plurality of primary particles are aggregated,
The secondary particles, from the center of the secondary particles toward the surface, a central portion where the primary particles are densely arranged, a void portion where the primary particles are arranged more sparsely than the central portion, and Having a multilayer structure including at least a solid portion in which primary particles are closely arranged,
A surface layer of primary particles present on the surface or inside of the secondary particles, and a grain boundary between the primary particles, a compound containing tungsten and lithium is present in a concentrated state,
Tap density is at 1.00 g / cm ³ or more 2.00 g / cm ³ or less, and,
The BET specific surface area is 1.45 m ² / g or more and 5.40 m ² / g or less,
Positive electrode active material for non-aqueous electrolyte secondary battery.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 13, wherein the (003) plane crystallite diameter obtained by powder X-ray diffraction measurement is 120 nm or more.   A nonaqueous electrolyte comprising a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, wherein the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 13 or 14 is used as a positive electrode material of the positive electrode. Secondary battery.