JP2017210395A - Nickel composite hydroxide and manufacturing method therefor, cathode active material for nonaqueous electrolyte secondary cell and manufacturing method therefor and nonaqueous electrolyte secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cathode active material for nonaqueous electrolyte secondary cell achieving both of high filling density and high specific surface area and exhibiting high cell capacity and high output characteristics when used for a cathode of a cell, nickel composite hydroxide which is a precursor thereof, or the like.SOLUTION: There is provided nickel composite hydroxide consisting of secondary particles obtained by aggregating a plurality of primary particles and represented by general formula (1):NiCoMn(OH), where x is in a range of 0.20≤x≤0.35, y is in a range of 0.20≤y≤0.35 and they satisfy 0.4≤x+y≤0.7, having an outer shell layer from a particle surface to particle inside of the secondary particles and the outer shell layer has a thickness of 10% to 30% of the secondary particle diameter and the content of the cobalt is 5 atom% or less based on the total of metal elements contained in the outer shell layer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a nickel composite hydroxide and a manufacturing method thereof, a positive electrode active material for a non-aqueous electrolyte secondary battery, a manufacturing method thereof, and a non-aqueous electrolyte secondary battery.

  In recent years, with the widespread use of portable devices such as mobile phones and notebook computers, development of small and lightweight secondary batteries having high energy density is strongly desired. As such a secondary battery, there is a non-aqueous electrolyte secondary battery using lithium, a lithium alloy, a metal oxide, or carbon as a negative electrode.

  For example, lithium composite oxide is used as the positive electrode active material for the positive electrode material of the non-aqueous electrolyte secondary battery. Lithium-cobalt composite oxide is relatively easy to synthesize, and a non-aqueous electrolyte secondary battery using lithium-cobalt composite oxide as a positive electrode material can obtain a high voltage of 4V, so that it has a high energy density. It is expected as a material for putting the secondary battery to practical use. With regard to lithium cobalt composite oxide, research and development for realizing excellent initial capacity characteristics and cycle characteristics in secondary batteries has been advanced, and various results have already been obtained.

  However, since the lithium cobalt composite oxide uses a rare and expensive cobalt compound as a raw material, it causes a cost increase of the positive electrode material and the secondary battery. Since the unit price per capacity of the non-aqueous electrolyte secondary battery using the lithium cobalt composite oxide is about four times that of the nickel metal hydride battery, applicable applications are considerably limited. Therefore, from the viewpoint of realizing further reduction in weight and size of the portable device, it is necessary to reduce the cost of the positive electrode active material and enable the manufacture of a cheaper non-aqueous electrolyte secondary battery.

  One of the positive electrode active materials that can be substituted for the lithium cobalt composite oxide is a lithium nickel composite oxide using nickel that is cheaper than cobalt. Lithium-nickel composite oxide exhibits the same high battery voltage as lithium-cobalt composite oxide, has a lower electrochemical potential than lithium-cobalt composite oxide, and is less prone to decomposition due to oxidation of the electrolyte. It is expected as a positive electrode active material that can increase the capacity of secondary batteries. For this reason, research and development of lithium-nickel composite oxides are also actively conducted.

  Here, it is known that the battery capacity is closely related to the filling property. If the packing density is increased, more positive electrode active materials can be filled in the same volume of electrodes, so that the battery capacity increases. When the particle density is equivalent, it is effective to increase the particle size in order to increase the packing density.

  On the other hand, in order to improve the output characteristics, it is effective to form a space in which the electrolytic solution can enter the positive electrode active material. Such a positive electrode active material can increase the reaction area with the electrolytic solution compared with a solid positive electrode active material having the same particle size, so that the positive electrode resistance can be greatly reduced. It becomes.

  However, for example, when the particle size is increased to increase the packing density in order to improve the battery capacity, the particle size may be too large, the specific surface area may decrease, and the output characteristics may decrease. In addition, when the specific surface area is increased to improve the output characteristics, the packing density may decrease and the battery capacity may decrease. As described above, it has been difficult to obtain a secondary battery having both a high packing density (tap density) and a high specific surface area and high battery capacity and high output characteristics.

  By the way, it is known that the positive electrode active material inherits the properties of the transition metal composite hydroxide particles as the precursor. That is, in order to obtain the positive electrode active material described above, it is necessary to appropriately control the particle size, particle size distribution, particle structure and the like of the transition metal hydroxide particles that are the precursors.

  For example, in Patent Documents 1 to 3, a precursor of a positive electrode active material is obtained by a crystallization reaction that is clearly separated into two stages: a nucleation process that mainly performs nucleation and a particle growth process that mainly performs particle growth. A method for producing transition metal composite hydroxide particles is disclosed. In these methods, by adjusting the pH value and reaction atmosphere in the nucleation step and the particle growth step as appropriate, the particle size distribution is narrow, the particle size distribution is narrow, and the low-density central part composed of fine primary particles and the high-density The transition metal composite hydroxide particles composed of the outer shell portion are obtained.

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

  However, in the manufacturing methods described in Patent Documents 1 to 3, there is a problem in productivity because it is necessary to temporarily stop the supply of the raw material aqueous solution to control the atmosphere. Further, in the positive electrode active material produced from the obtained particles, the output characteristics are improved, but the hollow energy is provided at the center of the particle, and hence the volume energy density cannot be improved.

  In view of such problems, the present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery and a precursor thereof that can achieve both a high packing density and a high specific surface area, and can obtain a high volumetric energy density and high output characteristics. It aims at providing the nickel composite hydroxide which is a body. It is another object of the present invention to provide a method for easily producing the nickel composite hydroxide and the positive electrode active material with high productivity.

  As a result of intensive studies on the filling property and specific surface area of the positive electrode active material using nickel composite hydroxide as a precursor, the present inventors have controlled the composition inside the secondary particles of the nickel composite hydroxide to control the vicinity of the particle surface. By reducing the cobalt content of the composition, the positive electrode active material obtained has the knowledge that the particle size is uniform, the packing density is high, and the surface area is high, and the present invention has been completed.

In a first aspect of the present invention consists of secondary particles in which a plurality of primary particles are aggregated, the general formula _{(1): Ni 1-x} -y Co x Mn y (OH) 2 + α ( the formula (1) of x is 0.20 ≦ x ≦ 0.35, y is 0.20 ≦ y ≦ 0.35, α is in the range of 0 ≦ α ≦ 0.5, and satisfies 0.4 ≦ x + y ≦ 0.7. )), Which has an outer shell layer from the particle surface of the secondary particle to the inside of the particle, and the outer shell layer is 10% or more and 30% or less of the diameter of the secondary particle. The nickel composite hydroxide is provided with a nickel composite hydroxide having a thickness of ≦ 5 atomic% with respect to the total amount of metal elements contained in the outer shell layer.

  In the particle size distribution measured by the laser diffraction scattering method, the volume average particle diameter (Mv) is 4 μm or more and 10 μm or less, the cumulative 90 volume% diameter (D90), the cumulative 10 volume% diameter (D10), and the volume It is preferable that [(D90−D10) / Mv] indicating a particle size variation index calculated by the average particle size (Mv) is 0.60 or less.

In a second aspect of the present invention consists of secondary particles in which a plurality of primary particles are aggregated, the general formula _{(1): Ni 1-x} -y Co x Mn y (OH) 2 + α ( the formula (1) of x is 0.20 ≦ x ≦ 0.35, y is 0.20 ≦ y ≦ 0.35, α is in the range of 0 ≦ α ≦ 0.5, and satisfies 0.4 ≦ x + y ≦ 0.7. )) In a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less so that the pH value is 12.5 or more based on a liquid temperature of 25 ° C. To a nucleation step for generating nuclei, and a slurry containing the nuclei formed in the nucleation step in a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less based on a liquid temperature of 25 ° C. The pH value is adjusted to 10.5 or more and 12.5 or less and lower than the pH value in the nucleation step, A first particle growth step for supplying a first mixed aqueous solution containing at least one of a nickel salt, a cobalt salt, and a manganese salt; and the first mixed aqueous solution includes 5 atoms with respect to all metal atoms in the secondary particles. A second particle growth step of switching to a second mixed aqueous solution containing cobalt in an amount of not more than% and supplying the slurry to the slurry. In the second particle growth step, 10% of the diameter from the secondary particle surface to the inside of the particle A nickel composite hydroxide that has a thickness of 30% or less and that forms an outer shell layer having a cobalt content of 5 atomic percent or less with respect to the total of metal elements contained in the outer shell layer. A manufacturing method is provided.

  In the first and second particle growth steps, the ammonia concentration of the slurry is preferably adjusted to 5 g / L or more and 20 g / L or less.

In the third aspect of the present invention, it is composed of secondary particles in which a plurality of primary particles are aggregated, and is represented by the general formula (2): Li _{1 + u} Ni _1-xy Co _x Mn _y O ₂ (in the formula (2) u is in the range of −0.05 ≦ u ≦ 0.50, x is in the range of 0.20 ≦ x ≦ 0.35, y is in the range of 0.20 ≦ y ≦ 0.35, and 0.4 ≦ x + y ≦ 0. .7) and a positive electrode active material for a non-aqueous electrolyte secondary battery including a lithium nickel composite oxide having a hexagonal layered structure, wherein the lithium nickel composite oxide has a specific surface area. 1.0 m ² / g or more and 3.0 m ² / g or less, the tap density is 2.0 g / ml or more and 3.0 g / ml or less, and the product of the specific surface area and the tap density is 3.0 or more. A positive electrode active material for a non-aqueous electrolyte secondary battery is provided.

  The lithium nickel composite oxide has a volume average particle size (Mv) of 4 μm or more and 10 μm or less in a particle size distribution by a laser diffraction scattering method, and a cumulative 90 volume% diameter (D90) and a cumulative 10 volume% diameter (D10). [(D90−D10) / Mv], which indicates a particle size variation index, calculated by the volume average particle size (Mv), is preferably 0.60 or less. Further, the lithium nickel composite oxide has an outer shell layer from the particle surface of the secondary particle to the inside of the particle, the outer shell layer has a thickness of 10% to 30% of the diameter of the secondary particle, and It is preferable that the content of cobalt in the outer shell layer is less than the content of cobalt inside.

In the fourth aspect of the present invention, general formula (2): Li _{1 + u} Ni _1-xy Co _x Mn _y O ₂ (in the formula (2), u is −0.05 ≦ u ≦ 0.50). , X is 0.20 ≦ x ≦ 0.35, and y is in the range of 0.20 ≦ y ≦ 0.35, and satisfies 0.4 ≦ x + y ≦ 0.7. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium-nickel composite oxide having a crystalline layered structure, wherein the nickel composite hydroxide and a lithium compound are mixed to form lithium There is provided a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: forming a mixture; and firing the lithium mixture at a temperature of 850 ° C. to 1100 ° C. in an oxidizing atmosphere. The

  The mixing of the nickel composite hydroxide and the lithium compound is such that the ratio (Li / Me) of the number of lithium atoms (Li) to the sum of the number of atoms of metals other than lithium (Me) contained in the lithium mixture is (Li / Me). It is preferable to mix so that it may become 0.95 or more and 1.5 or less.

  According to a fifth aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the positive electrode includes the positive electrode active material for the non-aqueous electrolyte secondary battery. Is done.

  The positive electrode active material of the present invention has both a high packing density and a high specific surface area. When used as a positive electrode material for a secondary battery, the secondary battery has a high energy density and high output characteristics. can get. In addition, the nickel composite hydroxide of the present invention has a controlled composition inside the particles and is suitably used as a precursor of the positive electrode active material. Moreover, the manufacturing method of the nickel composite hydroxide and the positive electrode active material using the same according to the present invention is a method for manufacturing the nickel composite hydroxide and the positive electrode active material using the same easily and with high productivity. I will provide a. Therefore, it can be said that the industrial value of the present invention is extremely high.

FIG. 1 is a schematic view showing an example of the nickel composite hydroxide of the present embodiment. FIG. 2 is a flowchart showing an example of the method for producing the nickel composite hydroxide of the present embodiment. FIG. 3 is a flowchart showing an example of a method for producing the positive electrode active material of the present embodiment. FIG. 4 is a schematic diagram showing an evaluation coin-type battery (2032 type) used in the examples. FIG. 5 is a schematic explanatory diagram of an impedance evaluation measurement example and an equivalent circuit used for analysis.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 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.

[Nickel composite hydroxide]
FIG. 1 is a schematic diagram showing an example of secondary particles 1 constituting the nickel composite hydroxide according to the present embodiment. As shown in FIG. 1, the secondary particle 1 has an outer shell layer 2 that does not contain cobalt or has a very low content. A central portion 3 is disposed inside the outer shell layer 2. The nickel composite hydroxide is suitably used as a precursor of a positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter also referred to as “positive electrode active material”). A positive electrode active material obtained from a nickel composite hydroxide can obtain excellent battery characteristics when used as a positive electrode material for a non-aqueous secondary battery.

(Composition of nickel composite hydroxide)
Nickel composite hydroxide of the present embodiment, the general formula _{(1): Ni 1-x} -y Co x Mn y (OH) 2 + α ( In the formula (1), x is 0.20 ≦ x ≦ 0. 35, y is in the range of 0.20 ≦ y ≦ 0.35, and α is in the range of 0 ≦ α ≦ 0.5). Further, the above x and y satisfy 0.4 ≦ x + y ≦ 0.7. Further, the nickel composite hydroxide 1 may contain a small amount of other additive elements. In this case, the nickel composite hydroxide 1, for example, the general formula _{(1-2): Ni 1-x} -y _{over z Co x Mn y M z (} OH) 2 + α (M in formula (1-2) Is at least one element selected from the group consisting of transition metal elements other than Ni, Co, and Mn, Group 2 elements, and Group 13 elements, x is 0.20 ≦ x ≦ 0.35, and y is 0 20 ≦ y ≦ 0.35, z is in the range of 0 ≦ z ≦ 0.1, and α is in the range of 0 ≦ α ≦ 0.5, and satisfies 0.4 ≦ x + y + z ≦ 0.7. The

(Particle structure of nickel composite hydroxide)
The nickel composite hydroxide is composed of secondary particles 1 in which a plurality of primary particles are aggregated. The outer shell layer 2 has a thickness of 10% or more and 30% or less of the diameter of the secondary particle from the particle surface of the secondary particle 1 to the inside of the particle (particle center), and the content of cobalt is The layer is 5 atomic% or less with respect to the total of metal elements contained in the outer shell layer. Moreover, the minimum of content of cobalt is 0 atomic% or more. The nickel composite hydroxide has an outer shell layer 2 whose composition is controlled from the particle surface to the inside of the secondary particle 1, thereby increasing the specific surface area while maintaining the tap density of the obtained positive electrode active material. This makes it possible to achieve both output characteristics and volume energy density. The cobalt content of the outer shell layer 2 can be measured, for example, by quantitative analysis of energy dispersive X-ray analysis (EDX) in cross-sectional observation with a scanning electron microscope. Further, the cobalt content of the outer shell layer 2 can be adjusted to a desired range by controlling the metal composition of the second liquid mixture in the second particle growth step (step S3) described later, for example.

  The particle morphology of the positive electrode active material is strongly influenced by the particle morphology of the precursor. For this reason, by controlling the powder characteristics of the precursor, similar powder characteristic grains exist in the positive electrode active material. That is, the secondary particle 1 has a surface (outer shell layer) of acicular primary particles found in hydroxide particles having a high nickel content by setting the cobalt content of the outer shell layer 2 to 5 atomic% or less. 2) and secondary particles having on the surface (outer shell layer 2) plate-like primary particles found in hydroxide particles having a high manganese content can be obtained. A hexagonal lithium nickel composite oxide (positive electrode active material) having a layered structure is prepared by mixing and firing a nickel composite hydroxide composed of secondary particles 1 having a controlled internal structure of the particles and a lithium compound. In the case of forming a positive active material composed of secondary particles having a particle structure with a dense center and a sparse surface near the surface due to the difference in morphology of the nickel composite hydroxide (precursor), the tap density of the positive active material It is possible to increase the specific surface area while maintaining the above, and when used in a secondary battery, both the output characteristics and the volume energy density can be achieved at a high level.

  On the other hand, in the case of a nickel composite hydroxide represented by the general formula (1) and composed of secondary particles having a uniform composition inside the particles, the primary particles constituting the secondary particles are needle-like primary particles or plates. In comparison with the primary particles (rich in Ni or Mn), since the Co content is high and the form is thick, the specific surface area of the resulting positive electrode active material tends to decrease, and the high tap density and high specific surface area It is difficult to achieve both.

  The form of the primary particles constituting the outer shell layer 2 and the central portion 3 is particularly limited as long as the positive electrode active material obtained as described later has both a high tap density and a high specific surface area. For example, an intermediate form between plate-like primary particles and needle-like primary particles may be used.

  The thickness t of the outer shell layer 2 is 10% or more and 30% or less, preferably 10% or more, with respect to the diameter d of the secondary particle from the particle surface of the secondary particle to the inside of the particle (particle central part). 20% or less. When the thickness t of the outer shell layer 2 is in the above range, the balance between the tap density and the specific surface area of the obtained positive electrode active material is excellent. The thickness t of the outer shell layer 2 can be obtained by composition mapping by EDX or line analysis. Further, the diameter d of the secondary particle 1 can be obtained by observing a cross section of the secondary particle 1 using a scanning electron microscope. Since the thickness t of the outer shell layer 2 and the diameter d of the secondary particles may vary among the secondary particles 1 constituting the nickel composite hydroxide, a plurality of secondary particles 1 are measured and averaged. It is preferable to obtain the value, for example, it can be obtained from an average value when arbitrary 10 secondary particles 1 are measured.

The composition of the outer shell layer 2 is not particularly limited if it meets the above characteristics, for example, the outer shell layer 2, the general formula _{(3): Ni 1-x} -y Co x Mn y (OH) 2 ( where formula X in the range is 0 ≦ x ≦ 0.05, y is in the range of 0 ≦ y ≦ 0.6, and 0 ≦ x + y ≦ 0.6 is satisfied. In the general formula (3), x = 0 may be _satisfied , that is, the outer shell layer 2 is represented by Ni _1-y Mn _y (OH) ₂ (0 ≦ y ≦ 0.6). For example, it may be Ni (OH) ₂ or Ni _0.5 Mn _0.5 (OH) ₂ . Further, a part of Ni may be further substituted with another additive element. For example, the outer shell layer 2 has a general formula (3-2): Ni _1-xyZ Co _x Mn _y M _z ( OH) ₂ (wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co, and Mn, group 2 elements, and group 13 elements, and x is 0 ≦ x ≦ 0. .05, y is in the range of 0 ≦ y ≦ 0.6, and z is in the range of 0 ≦ z ≦ 0.1, and satisfies 0 ≦ x + y + y ≦ 0.6.

(Dispersion of average particle size and particle size of nickel composite hydroxide)
The nickel composite hydroxide preferably has a volume average particle size (Mv) of 4 μm or more and 10 μm or less in a particle size distribution by a laser diffraction scattering method. Further, the nickel composite hydroxide has a particle size variation index [(D90−D10) / Mv] calculated by D90 and D10 in the particle size distribution by the laser diffraction scattering method and the volume average particle size (Mv). It is preferable that it is 0.60 or less. By setting [(D90-D10) / Mv] within the above range, the dispersion index of the obtained positive electrode active material can be reduced, and cycle characteristics and output characteristics can be improved.

  Since the particle size distribution of the positive electrode active material is strongly influenced by the nickel composite hydroxide that is the precursor, if fine particles or coarse particles are mixed in the nickel composite hydroxide, similar particles are also present in the positive electrode active material. It comes to exist. That is, when the dispersion index of nickel composite hydroxide exceeds 0.60 and the particle size distribution is wide, fine particles or coarse particles may be present in the positive electrode active material. If the variation index is small, the characteristics of the positive electrode active material can be improved. However, since it is difficult to completely suppress the variation in particle size, the practical lower limit of the variation index is 0.30 or more. Degree.

  In addition, in [(D90-D10) / Mv] indicating the particle size variation index, D10 accumulates the number of particles in each particle size from the smaller particle size side, and the accumulated volume is 10 of the total volume of all particles. % Means the particle size. D90 means the particle size in which the number of particles is similarly accumulated and the accumulated volume is 90% of the total volume of all particles. Volume average particle diameter (Mv), D90 and D10 can be measured using a laser light diffraction / scattering particle size analyzer.

[Method for producing nickel composite hydroxide]
FIG. 2 is a flowchart showing an example of a method for producing a nickel composite hydroxide according to the present embodiment. When the flowchart of FIG. 2 is described, FIG. 1 is referred to as appropriate. The nickel composite hydroxide is produced by supplying an aqueous solution containing at least nickel, cobalt, and a manganese salt and a neutralizing agent, preferably a complexing agent, to a reaction vessel while stirring, and then performing a crystallization reaction. A nickel composite hydroxide composed of the secondary particles 1 is produced. As shown in FIG. 2, the nickel composite hydroxide production method divides crystallization into three stages and supplies an aqueous solution containing nickel, cobalt and manganese salts and a neutralizing agent, preferably a complexing agent. Then, a nucleation step (Step S1) for generating crystal nuclei while filling the reaction vessel, and first and second particle growth steps (Step S2, Step S3) for growing the crystal nuclei obtained in the nucleation step ). Hereinafter, each step will be described in detail.

[Nucleation process]
In the nucleation step (step S1), the composition of the first mixed aqueous solution (nucleation solution) containing at least one of a predetermined amount of nickel salt, cobalt salt and manganese salt used as the raw material aqueous solution is changed to a desired composition. Then, in a non-oxidizing atmosphere with an oxygen concentration of 5% by volume or less, the pH value is adjusted to be 12.5 or more at a liquid temperature of 25 ° C., thereby generating nuclei preferentially. Hereinafter, each condition of the nucleation process (step 1) will be described.

(PH control)
In the nucleation step (step S1), it is necessary to control the pH value of the first mixed aqueous solution (nucleation aqueous solution) to be in the range of 12.5 or more on the basis of the liquid temperature of 25 ° C. When the pH value based on the liquid temperature of 25 ° C. is less than 12.5, nuclei are generated, but the nuclei themselves grow and become larger. Therefore, the subsequent first and second particle growth steps (steps S2 and S3). ), Secondary particles having a high particle size uniformity cannot be obtained, and it becomes difficult to control the thickness t of the outer shell layer 2. On the other hand, finer nuclei are obtained as the pH value is higher. However, when the pH value exceeds 14.0, the reaction solution gels and crystallization is difficult, or the nuclei of the nickel composite hydroxide become too small. Problems may occur. That is, in the nucleation step (step S1), the pH value of the first mixed aqueous solution (nucleation aqueous solution) is 12.5 or more, preferably 12.5 or more and 14.0 or less, more preferably 12. By setting it within the range of 5 or more and 13.5 or less, nuclei can be generated sufficiently.

(Neutralizer)
The pH can be controlled by adding an alkaline solution that is a neutralizing agent. The alkali solution is not particularly limited, and for example, a general alkali metal hydroxide aqueous solution such as sodium hydroxide or potassium hydroxide can be used. The alkali metal hydroxide can be directly added to the mixed 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 12.5% by mass or more and 30% by mass or less, and more preferably 20% by mass or more and 25% by mass or less. When the concentration of the alkali metal hydroxide aqueous solution is low, the slurry concentration may decrease and the productivity may deteriorate. Therefore, it is preferable to increase the concentration. Specifically, the concentration of the alkali metal hydroxide is 20 masses. % Or more is preferable. On the other hand, when the concentration of the alkali metal hydroxide exceeds 30% by mass, the pH at the addition position is locally increased and fine particles may be generated.

(Reaction temperature)
The temperature of the aqueous solution for nucleation in the nucleation step (step S1) is preferably maintained at 40 ° C. or higher and 70 ° C. or lower. When temperature is the said range, the fine nucleus of nickel composite hydroxide can fully be produced | generated.

  In the nucleation step (step S1), specifically, a solution prepared by adding water to an inorganic alkaline aqueous solution in advance to have a pH value of 12.5 or more is used as a reaction aqueous solution, and the reaction aqueous solution is stirred in the reaction vessel. While supplying the first mixed aqueous solution (aqueous solution for nucleation) and adding an inorganic alkaline aqueous solution (neutralizing agent) to maintain the pH value, nuclei can be generated to obtain a slurry containing the nuclei. . The method of supplying the first mixed aqueous solution (nucleation aqueous solution) while maintaining the pH value of the reaction aqueous solution is preferable because the pH value can be controlled strictly and nucleation is easy.

[First grain growth step]
Next, in the first particle growth step (step S2), first, after completion of the nucleation step (step S1), the slurry containing the nuclei in the reaction vessel is placed in a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less. Then, the pH is adjusted so that the pH value is 10.5 or more and 12.5 or less on the basis of the liquid temperature of 25 ° C. and lower than the pH in the nucleation step (step S1), and the pH adjusted slurry (for particle growth) Slurry). The pH value is controlled, for example, by adjusting the supply amount of the inorganic alkaline aqueous solution (neutralizing agent) while supplying the first mixed aqueous solution as described above. Moreover, you may adjust pH by adding the inorganic acid which comprises the salt contained in mixed aqueous solution.

  In the first particle growth step (step S2), a first mixed aqueous solution containing at least one of a nickel salt, a cobalt salt, and a manganese salt is supplied to the pH-adjusted slurry (particle growth slurry). Then, grain growth is performed. The first mixed aqueous solution contains a metal compound containing nickel, cobalt, and manganese as necessary so that a nickel composite hydroxide having a predetermined composition can be obtained. In this step, the central portion 3 of the secondary particle 1 is mainly formed.

(PH control)
In the first particle growth step (step S2), the pH value of the particle growth slurry is in the range of 10.5 to 12.5, preferably 11.0 to 12.0, based on the liquid temperature of 25 ° C., and It controls so that it may become lower than pH in a nucleation process. When the pH value based on the liquid temperature of 25 ° C. is less than 10.5, there arises a problem that impurities contained in the obtained nickel composite hydroxide, for example, anionic constituent elements contained in the metal salt increase. Moreover, the metal component which remains in the liquid component of a slurry increases, and the problem that a composition shift and a yield fall arises. On the other hand, when the pH exceeds 12.5, new nuclei are generated in the particle growth generation step, the particle size distribution is deteriorated, and the thickness t of the outer shell layer 2 formed in the subsequent step cannot be controlled. That is, in the particle growth process, by controlling the pH value of the particle growth slurry within the above range, the growth of nuclei generated in the nucleation process (step S1) is preferentially caused, and new nucleation is suppressed. The resulting nickel composite hydroxide can be homogeneous, have a narrow particle size distribution range, and a controlled shape. In order to more clearly separate nucleation and particle growth, it is preferable to control the pH value of the particle growth slurry to be 0.5 or more lower than the pH in the nucleation step (step S1), and 1.0 or more. It is more preferable to control it low.

(Complexing agent)
In the first and second particle growth steps, it is preferable to add ammonia as a complexing agent. In this case, the ammonia concentration in the particle growth slurry is preferably controlled to 5 g / L or more and 20 g / L or less. Since ammonia acts as a complexing agent, when the ammonia concentration is less than 5 g / L, the solubility of metal ions cannot be kept constant, and the primary particles with developed crystals become non-uniform, resulting in a nickel composite hydroxide. The width of the particle diameter may vary, and the thickness t of the outer shell layer 2 may vary. When the ammonia concentration exceeds 20 g / L, the solubility of metal ions becomes too high, the amount of metal ions remaining in the slurry for particle growth increases, and compositional deviation may occur. Further, when the ammonia concentration varies, the solubility of metal ions varies, and a uniform nickel composite hydroxide is not formed. Therefore, it is preferable to maintain a constant value. For example, it is preferable to keep the fluctuation of the ammonia concentration at a desired concentration with an increase or decrease range of about 5 g / L with respect to the set concentration. In the nucleation step, a complexing agent may be added under the same conditions.

  The addition of ammonia can be performed by an ammonium ion supplier. Although an ammonium ion supply body is not specifically limited, For example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride etc. can be used.

(Reaction temperature)
The temperature of the aqueous reaction solution in the first particle growth step (step S2) is preferably maintained at 40 ° C to 70 ° C. Thereby, it is possible to grow the nickel composite hydroxide to a target range. If the temperature is lower than 40 ° C., the solubility of the metal salt in the liquid component of the particle growth slurry is low and the salt concentration is low. Therefore, in the particle growth process, there are many nucleations and fine particles increase, and the particle size distribution may deteriorate. Further, there is a high possibility that the volume average particle size ratio is out of the range of 0.2 to 0.6. When the temperature of the mixed aqueous solution exceeds 70 ° C., when ammonia is used, the volatilization is large, the concentration of the nickel ammine complex is not stable, and the particle size varies. Moreover, about a neutralizing agent, the thing similar to a nucleation process can be used.

(Raw material aqueous solution)
The first mixed aqueous solution that is a raw material aqueous solution contains at least one of a nickel salt, a cobalt salt, and a manganese salt. As these metal salts, sulfates, nitrates, chlorides and the like can be used, and sulfates are preferably used from the viewpoint of cost, impurities and waste liquid treatment. In the first mixed aqueous solution, a metal compound containing nickel, cobalt, manganese, and additive element M is included as necessary so that a nickel composite hydroxide having a predetermined composition ratio can be obtained. In addition, the content of nickel, cobalt, manganese, and element M in the first mixed solution is particularly limited as long as the nickel composite hydroxide 1 represented by the above formula (1) is finally obtained. Not. The first mixed solution used in the nucleation step (step S1) and the first mixed solution used in the first particle growth step (step S2) may have the same composition. May be different. In the first particle growth step (Step 2), as in the nucleation step (Step 1), the oxygen concentration can be performed in a non-oxidizing atmosphere of 5% by volume or less. It is not necessary to temporarily stop the supply of the raw material aqueous solution (for example, the first mixed aqueous solution).

[Second grain growth step]
Next, in the second particle growth step (step S3), the first mixed aqueous solution, which is the raw material aqueous solution, is added to the total of the metal elements contained in the outer shell layer while the pH conditions are the same except for the switching of the raw material aqueous solution On the other hand, the slurry is switched to the second mixed aqueous solution containing 5 atomic% or less of cobalt and supplied to the slurry. In the second particle growth step (step S3), it is necessary to reduce the cobalt content in the reaction aqueous solution in order to form the outer shell layer 2 described above. Therefore, the first mixed aqueous solution used in the first particle growth step is switched to the second mixed aqueous solution having a cobalt content lower than that of the first mixed aqueous solution. Thereby, nickel composite hydroxide particles having a low cobalt content on the target particle surface can be obtained.

  The timing of switching may be adjusted according to the thickness of the outer shell layer. For example, nickel and cobalt in all mixed aqueous solutions (including the first and second mixed aqueous solutions) supplied from the start of crystallization to the end of crystallization. It is preferable to switch to the second mixed aqueous solution having a metal composition corresponding to the composition of the outer shell layer 2 after adding 10 atomic% or more and 65 atomic% or less in total of manganese and M. Moreover, if the supply amount of the mixed aqueous solution is constant, it can be switched depending on the crystallization time. That is, the mixed aqueous solution may be switched when 10% to 65% of the crystallization time from the start of crystallization to the end of crystallization has elapsed.

  In the first and second particle growth steps (step S2 and step S3), the metal composition ratio of the secondary particles grown from the nuclei obtained in the nucleation step (step S1) is the first and second particles. This is the same as the composition ratio of each metal in the first mixed aqueous solution and the second mixed aqueous solution used as the raw material aqueous solution in the growth process (step S2 and step S3), respectively. Also in the nucleation step (step S1), the composition ratio of the metal in the nucleus is the same as the composition ratio of each metal in the first mixed aqueous solution (nucleation aqueous solution) used as the raw material aqueous solution. Therefore, the total of the metal salt in the raw material aqueous solution used in the nucleation step (step S1) and the metal salt in the raw material aqueous solution used in the first and second particle growth steps (step S2 and step S3) is the nickel composite water. It adjusts so that it may become a composition ratio of each metal of an oxide.

  Respective salts of the first mixed aqueous solution used in the nucleation step (step S1) and the first particle growth step (step S2) and the second mixed aqueous solution used in the second particle growth step (step 2) The total concentration of each salt is preferably 1.0 mol / L or more and 2.2 mol / L or less, and more preferably 1.5 mol / L or more and 2.0 mol / L or less. If the salt concentration of these mixed aqueous solutions is less than 1.0 mol / L, the salt concentration may be too low and the nickel composite hydroxide crystals may not grow sufficiently. In order to increase productivity, it is more preferable that the salt concentration of these mixed aqueous solutions is 1.5 mol / L or more. On the other hand, if the salt concentration of these mixed aqueous solutions exceeds 2.2 mol / L, it exceeds the saturation concentration at room temperature, so there is a risk of crystals reprecipitating and clogging the piping, and there is an opportunity for nucleation. Increases, resulting in an increase in fine particles.

[Positive electrode active material for non-aqueous electrolyte secondary battery]
The positive electrode active material of the present embodiment is composed of secondary particles in which a plurality of primary particles are aggregated with each other. The general formula (2): Li _{1 + u} Ni _1-xy Co _x Mn _y O ₂ (wherein the formula (2) ) In the range of −0.05 ≦ u ≦ 0.50, x is in the range of 0.20 ≦ x ≦ 0.35, y is in the range of 0.20 ≦ y ≦ 0.35, and 0.4 ≦ x + y. ≦ 0.7.) And includes a lithium nickel composite oxide having a hexagonal layered structure, and can achieve both a high specific surface area and a high tap density. Hereinafter, characteristics of the lithium nickel composite oxide will be described.

(Specific surface area)
The lithium nickel composite oxide has a specific surface area of 1.0 m ² / g or more and 3.0 m ² / g or less, and preferably 1.2 m ² / g or more and 2.5 m ² / g or less. When the specific surface area is in the above range, the output characteristics of the obtained secondary battery can be improved. The specific surface area can be measured by the BET method.

(Tap density)
The lithium nickel composite oxide has a tap density of 2.0 g / ml or more and 3.0 g / ml or less, and preferably 2.0 g / ml or more and 2.5 g / ml or less. When the tap density is in the above range, the battery capacity of the obtained secondary battery can be improved. The tap density can be measured by, for example, a shaking specific gravity measuring device (KRS-409, manufactured by Kuramochi Scientific Instruments).

(Relationship between specific surface area and tap density)
The lithium nickel composite oxide has a product of specific surface area and tap density (specific surface area × tap density) of 3 or more. Generally, the relationship between the specific surface area and the tap density is contradictory, but when the product of the specific surface area and the tap density is 3 or more, the high output characteristics due to the high specific surface area and the high filling into the battery due to the high tap density. Sex can be made compatible. By using the product of the specific surface area and the tap density for evaluation, it is possible to select a material having a large balance between both. When the product of the specific surface area and the tap density is less than 3, the specific surface area is low and high output characteristics cannot be obtained, or the tap density is low and the filling property into the battery is lowered. The upper limit of the product of the specific surface area and the tap density is not particularly limited, but is about 6 or less, more preferably about 5 or less.

(Average particle size and variation in particle size)
The lithium nickel composite oxide preferably has a volume average particle size (Mv) of 4 μm or more and 10 μm or less in a particle size distribution measured by a laser diffraction scattering method. Thereby, the high filling density in a battery and the outstanding output characteristic can be made to make compatible.

  Further, the lithium nickel composite oxide exhibits a particle size variation index calculated by the cumulative 90 volume% diameter (D90), the cumulative 10 volume% diameter (D10), and the volume average particle diameter (Mv). (D90-D10) / Mv] is preferably 0.60 or less. Thereby, mixing of fine particles and coarse particles can be reduced, and further excellent durability and output characteristics can be obtained. The volume average particle diameter (Mv) and D90 and D10 can be obtained in the same manner as the nickel composite hydroxide.

(composition)
The lithium nickel composite oxide has the general formula (2): Li _{1 + u} Ni _1-xy Co _x Mn _y O ₂ (wherein u in the formula (2) is −0.05 ≦ u ≦ 0.50, x Is in the range of 0.20 ≦ x ≦ 0.35, and y is in the range of 0.20 ≦ y ≦ 0.35, and satisfies 0.4 ≦ x + y ≦ 0.7.

  In the above formula (2), u indicating an excess amount of lithium is −0.05 or more and 0.50 or less, and preferably −0.05 or more and 0.20 or less. When the excess amount u of lithium is less than −0.05, the reaction resistance of the positive electrode in the non-aqueous electrolyte secondary battery using the obtained positive electrode active material increases, and the output of the secondary battery decreases. On the other hand, when the excessive amount u of lithium exceeds 0.50, the initial discharge capacity of the secondary battery using this positive electrode active material is lowered and the reaction resistance of the positive electrode is also increased. Note that the composition of the positive electrode active material can be obtained by ICP emission analysis.

  The composition ratio of the nickel composite hydroxide is maintained as it is as the composition ratio of the metal elements other than lithium. On the other hand, the composition ratio between the central part of the secondary particles and the outer shell layer tends to be homogenized during firing during the manufacturing process, but by leaving the difference in composition ratio, the surface state of the secondary particles becomes less sparse. And a high specific surface area. Therefore, like the nickel composite hydroxide, the positive electrode active material has an outer shell layer from the particle surface of the secondary particle to the inside of the particle, and the outer shell layer is 10% or more of the diameter of the secondary particle. It is preferable that it has a thickness of 30% or less and that the cobalt content is less than the internal cobalt content.

Further, the lithium nickel composite oxide may contain a small amount of additive elements in order to improve battery characteristics. In this case, the lithium nickel composite oxide, for example, the general formula _{(2-2): Li 1 + u} Ni 1-x-y Co x Mn y M z O 2 (M in the formula (2-2), Ni , Co, and Mn are at least one element selected from the group consisting of transition metal elements, group 2 elements, and group 13 elements, u is −0.05 ≦ u ≦ 0.50, and x is 0.20. ≦ x ≦ 0.35, y is in the range of 0.20 ≦ y ≦ 0.35, and z is in the range of 0 ≦ z ≦ 0.1, and satisfies 0.4 ≦ x + y + z ≦ 0.7. The

[Method for producing positive electrode active material for non-aqueous electrolyte secondary battery]
FIG. 3 is a flowchart showing an example of a method for producing a positive electrode active material according to the present embodiment. The production method of the present embodiment has a general formula (2): Li _{1 + u} Ni _1-xy Co _x Mn _y O ₂ (wherein u is −0.05 ≦ u ≦ 0.50, x Is 0.20 ≦ x ≦ 0.35, y is 0.20 ≦ y ≦ 0.35), and is a non-aqueous electrolyte composed of a lithium nickel composite oxide having a hexagonal layered structure It is a manufacturing method of the positive electrode active material for secondary batteries. Hereinafter, a method for producing the positive electrode active material will be described with reference to FIG.

  As shown in FIG. 3, the method for producing a positive electrode active material includes mixing the nickel composite hydroxide and the lithium compound to form a lithium mixture (step S4), and oxidizing the lithium mixture into an oxidizing atmosphere. And firing at a temperature of 850 ° C. to 1100 ° C. (step S5). Hereinafter, each step will be described.

(Mixing process)
First, the nickel composite hydroxide and the lithium compound are mixed to form a lithium mixture (step S4). The lithium compound is not particularly limited, and a known lithium compound can be used. For example, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferably used from the viewpoint of easy availability. . Among these, as the lithium compound, lithium oxide or lithium carbonate is more preferable from the viewpoint of easy handling and quality stability. Prior to the mixing step, the nickel composite hydroxide may be oxidized to form a nickel composite oxide and then mixed.

  The nickel composite hydroxide and the lithium compound are the number of atoms of metals other than lithium in the lithium mixture, that is, the sum of the number of atoms of nickel, cobalt and additive elements (Me) and the number of atoms of lithium (Li). Mixing is performed so that the ratio (Li / Me) is 0.95 to 1.50, preferably 0.95 to 1.20. That is, since Li / Me does not change before and after firing, the Li / Me ratio mixed in this mixing step (step S4) becomes the Li / Me ratio in the positive electrode active material, so that Li / Me in the lithium mixture can be obtained. To be the same as Li / Me in the positive electrode active material.

  In addition, a general mixer can be used for mixing, and a shaker mixer, a Roedige mixer, a Julia mixer, a V blender, and the like can be used. What is necessary is just to be mixed.

(Baking process)
Next, the lithium mixture is fired to obtain a lithium nickel composite oxide (step S5). Firing is performed at 850 ° C. or higher and 1100 ° C. or lower in an oxidizing atmosphere. When the firing temperature is lower than 850 ° C., the firing is not sufficiently performed, and the tap density may be lowered. In addition, when the firing temperature is less than 850 ° C., the diffusion of lithium does not proceed sufficiently, surplus lithium remains, the crystal structure is not aligned, and the nickel, cobalt, and manganese composition inside the particles is sufficiently uniform In some cases, sufficient characteristics cannot be obtained when used in a battery. On the other hand, when the temperature exceeds 1100 ° C., the sparse part of the particle surface is densified. In addition, intense sintering may occur between the composite oxide particles and abnormal grain growth may occur. For this reason, the particles after firing may be coarse and cannot maintain a substantially spherical particle form. . Since such a positive electrode active material has a reduced specific surface area, when used in a battery, there arises a problem that the resistance of the positive electrode increases and the battery capacity decreases. Moreover, although baking time is not specifically limited, It is about 1 to 24 hours.

  From the viewpoint of uniformly performing the reaction between the nickel composite hydroxide or the nickel composite oxide obtained by oxidizing it and the lithium compound, the rate of temperature rise is, for example, 1 ° C./min to 5 ° C./min. It is preferable to raise the temperature to the above firing temperature within a range of min or less. Furthermore, the reaction can be carried out more uniformly by maintaining at a temperature near the melting point of the lithium compound for about 1 hour to 10 hours before firing.

[Nonaqueous electrolyte secondary battery]
The non-aqueous electrolyte secondary battery of this embodiment can be comprised by the component similar to a general non-aqueous electrolyte secondary battery, for example, contains a positive electrode, a negative electrode, and a non-aqueous electrolyte. Note that the embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present embodiment can be variously modified based on the knowledge of those skilled in the art based on the embodiment described in the present specification. It can be implemented in an improved form. Further, the use of the nonaqueous electrolyte secondary battery of the present embodiment is not particularly limited.

(Positive electrode)
Using the positive electrode active material for a non-aqueous electrolyte secondary battery described above, for example, a positive electrode of a non-aqueous electrolyte secondary battery is produced as follows. First, a powdered positive electrode active material, a conductive material, and a binder are mixed, and, if necessary, a target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare a positive electrode mixture paste. The mixing ratio of each component in the positive electrode mixture paste is, for example, when the total solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, like the positive electrode of a general non-aqueous electrolyte secondary battery, It is preferable that the content of the positive electrode active material is 60 to 95 parts by mass, the content of the conductive material is 1 to 20 parts by mass, and the content of the binder is 1 to 20 parts by mass.

  The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, an 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 or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the illustrated one, and other methods may be used.

  As the conductive agent for the positive electrode, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black (registered trademark), and the like 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, polyacrylic. An acid or the like can be used.

  If necessary, a positive electrode active material, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. 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, lithium alloy, or the like, or a negative electrode active material capable of occluding and desorbing lithium ions, a binder mixed with a binder, and an appropriate solvent added to form a paste, copper or the like It is applied to the surface of the metal foil current collector, dried, and compressed to increase the electrode density as necessary.

  As the negative electrode active material, for example, natural graphite, artificial graphite, a fired organic compound such as phenol resin, or a powdery carbon material such as coke can be used. In this case, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used as in the case of the positive electrode, and as a solvent for dispersing these active materials and the binder, N-methyl-2-pyrrolidone or the like can be used. Organic solvents can be used.

(Separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte. For example, a thin film such as polyethylene or polypropylene and a film having many minute holes can be used.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte, for example, a solution obtained by dissolving a lithium salt as a supporting salt in an organic solvent is used. Examples of the organic solvent used 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, A single compound selected from ether compounds such as 2-methyltetrahydrofuran and 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. Can be used.
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 non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(Battery shape and configuration)
The nonaqueous electrolyte secondary battery of the present embodiment includes, for example, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte solution as described above. Further, the shape of the non-aqueous electrolyte secondary battery is not particularly limited, and can be various types such as a cylindrical type and a laminated type. 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. Connect between the positive electrode terminal and between the negative electrode current collector and the negative electrode terminal leading to the outside using a current collecting lead, etc., and seal the battery case to complete the non-aqueous electrolyte secondary battery. .

(Characteristics of non-aqueous electrolyte secondary battery)
The non-aqueous electrolyte secondary battery of the present embodiment has the above-described configuration and has a positive electrode using the positive electrode active material described above, so that a high packing density and a high specific surface area can be obtained, and a volume energy density and output characteristics are obtained. And it will be excellent.

(Use of secondary battery)
Since the secondary battery of this embodiment has the above properties, it is suitable for the power source of small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require high capacity.
Further, the secondary battery of the present embodiment is also suitable for a battery as a motor driving power source that requires high charge / discharge characteristics. When a battery becomes large, it becomes difficult to ensure safety, and an expensive protection circuit is indispensable. However, since the secondary battery of the present invention has excellent safety, safety can be ensured. Not only is this easy, but the expensive protection circuit can be simplified and the cost can be reduced. And since it can be reduced in size and increased in output, it is suitable as a power source for transportation equipment subject to restrictions on the mounting space.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these Examples. In this example, unless otherwise specified, each reagent grade sample manufactured by Wako Pure Chemical Industries, Ltd. was used for the production of the composite hydroxide, the positive electrode active material, and the production of the secondary battery.

(Evaluation method)
In the following examples and comparative examples, volume average particle size and particle size distribution were measured with a laser diffraction particle size distribution meter (trade name: Microtrack, manufactured by Nikkiso Co., Ltd.).

  The tap density was measured with a shaking specific gravity measuring instrument (KRS-409, manufactured by Kuramochi Scientific Instruments).

  The specific surface area was measured by a flow method gas adsorption method specific surface area measuring device (manufactured by Yuasa Ionics Co., Ltd., Multisorb).

  The appearance of the particles was observed with a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation, trade name: S-4700). The composition of the outer shell layer was analyzed by an energy dispersive X-ray spectrometer (EDX; manufactured by JEOL Ltd., trade name: JED2300). The resolution of the EDX detector was 137 eV, and the measurement conditions were tube voltage 20 kV, tube current 20 μA, magnification 5000 times, WD 15 mm, process time 4, counting 4 million counts or more. The Co content of the outer shell layer was determined by composition analysis by EDX in the scanning electron microscope observation of the secondary particle cross section. The thickness of the outer shell layer was determined by changing the accelerating voltage in the scanning electron microscope observation of the cross section of the secondary particles, selecting secondary particles capable of observing the cross section near the center of the secondary particles, and The outer shell layer was judged from EDX mapping of Ni, Co, and Mn of the particle cross section, the thickness of the outer shell layer was measured with respect to the diameter of the cross section of the secondary particle, and the average value of 20 secondary particles was obtained. . The diameter of the secondary particle cross section is obtained as the longest distance between any two points on the outer periphery of the secondary particle cross section, and the thickness of the outer shell layer is determined from any point on the outer periphery of the secondary particle cross section. Using the shortest distance of the boundary between the layer and the central portion as the thickness, each secondary particle was measured at five locations and averaged.

  The composition analysis of the positive electrode active material was performed using an ICP emission analyzer (ICPS-8100, manufactured by Shimadzu Corporation).

(Manufacture of secondary batteries for evaluation)
Evaluation of the obtained positive electrode active material for a non-aqueous electrolyte secondary battery was performed by producing and evaluating a coin-type battery CBA shown in FIG. 4 as follows. 52.5 mg of a positive electrode active material for a non-aqueous electrolyte secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed, and press molded to a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa. The positive electrode PE (electrode for evaluation) shown in FIG. The produced positive electrode PE was dried at 120 ° C. for 12 hours in a vacuum dryer. And using this positive electrode PE, 2032 type coin-type battery CBA was produced in the glove box of Ar atmosphere where the dew point was controlled at -80 degreeC.

As the negative electrode NE, a negative electrode sheet in which graphite powder punched into a disk shape with a diameter of 14 mm and an average particle diameter of about 20 μm and polyvinylidene fluoride are applied to a copper foil is used, and 1 M LiPF ₆ is used as the electrolyte for the electrolyte. A 3: 7 mixed solution (manufactured by Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) was used. As the separator SE, a polyethylene porous film having a film thickness of 25 μm was used. The coin-type battery CBA has a gasket GA and a wave washer WW, and was assembled into a coin-shaped battery by the positive electrode can PC and the negative electrode can NC. The initial discharge capacity and the positive electrode resistance (output characteristics) showing the performance of the manufactured coin-type battery CBA were evaluated as follows.

(Initial discharge capacity)
The initial discharge capacity is left for about 24 hours after the coin-type battery CBA is manufactured. After the open circuit voltage OCV (Open Circuit Voltage) is stabilized, the current density with respect to the positive electrode is set to 0.1 mA / cm ² and the cut-off voltage 4 The capacity when the battery was charged to 3 V, discharged after a pause of 1 hour to a cutoff voltage of 3.0 V was defined as the initial discharge capacity. A multi-channel voltage / current generator (Fujitsu Access Co., Ltd.) was used to measure the charge / discharge capacity.

(Reaction resistance)
Moreover, resistance value was measured by the alternating current impedance method using a 2032 type coin battery charged at a charging potential of 4.1V. For measurement, when a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron) are used to measure by the AC impedance method, a Nyquist plot shown in FIG. 5 is obtained. Since the Nyquist plot is represented as the sum of a characteristic curve indicating solution resistance, negative electrode resistance and capacity, and positive electrode resistance and capacity, fitting calculation was performed using an equivalent circuit to calculate a positive resistance value.

Example 1
As the first mixed aqueous solution, a composite solution of nickel sulfate (concentration: 38.8 g / L), cobalt sulfate (concentration: 39.0 g / L), and manganese sulfate (concentration: 36.3 g / L) was prepared. A nickel sulfate (concentration: 115.9 g / L) solution was prepared as the second mixed aqueous solution.

  25 L of pure water was put into the reaction tank (60 L) and the temperature in the tank was increased to 42 ° C. while stirring in a nitrogen atmosphere (oxygen concentration of 5% by volume or less; oxygen concentration in the reaction tank of 2% by volume or less). Set. Add appropriate amounts of 25% by mass aqueous sodium hydroxide and 25% by mass ammonia water into the reaction tank, and adjust the pH value of the liquid in the tank to 12.8 based on the liquid temperature of 25 ° C. Adjusted to 10 g / L. A mixed aqueous solution of nickel sulfate, cobalt sulfate, and manganese sulfate (first mixed aqueous solution) was added thereto at a rate of 130 ml / min to obtain a reaction aqueous solution. At the same time, 25% by mass aqueous ammonia and 25% by mass aqueous sodium hydroxide solution were added at a constant rate, and crystallization was carried out for 2 minutes and 30 seconds while controlling the pH value to 12.8 (nucleation pH) (nucleation) Process).

  Thereafter, until the pH value reaches 11.6 (particle growth pH) on the basis of the liquid temperature of 25 ° C., only the supply of the 25 mass% sodium hydroxide aqueous solution is temporarily stopped, and after the pH value reaches 11.6, again The crystallization was continued for 2.4 hours while the supply of the 25% by mass aqueous sodium hydroxide solution was resumed, the pH value was controlled at 11.6, and the ammonia concentration in the liquid was controlled at 10 g / L. Particle growth process).

  Thereafter, crystallization was continued for 1.6 hours (second particle growth step) under the same conditions as in the particle growth step except that the raw material solution was switched to a nickel sulfate aqueous solution (second mixed aqueous solution). Was terminated.

After completion of crystallization, the product was washed with water, filtered and dried, and nickel composite hydroxide represented by Ni _0.60 Co _0.20 Mn _0.20 (OH) _{2 + α} (0 ≦ α ≦ 0.5) Particles were obtained. Table 1 shows the evaluation results of the obtained nickel composite hydroxide particles (precursor).

  The obtained nickel composite hydroxide particles and lithium carbonate weighed so as to be Li / Me = 1.04 are sufficiently used using a shaker mixer device (TURBULA Type T2C manufactured by Willy et Bacofen (WAB)). Mixed to obtain a lithium mixture. This lithium mixture was calcined by holding at 870 ° C. for 10 hours in an air (oxygen: 21 vol%) airflow, and then crushed to obtain a lithium nickel composite oxide (positive electrode active material) and evaluated. Table 2 shows the physical property evaluation of the obtained positive electrode active material, and Table 3 shows the battery evaluation.

(Example 2)
The first mixed aqueous solution is a composite solution of nickel sulfate (concentration: 78.3 g / L) and cobalt sulfate (concentration: 39.3 g / L), and the second mixed aqueous solution is nickel sulfate (concentration: 58.7 g). / L) A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that a composite solution of a solution and manganese sulfate (concentration: 54.9 g / L) was used. The evaluation results are shown in Tables 1 and 2.

(Example 3)
The first mixed aqueous solution is a composite solution of nickel sulfate (concentration: 39.1 g / L), cobalt sulfate (concentration: 58.9 g / L), and manganese sulfate (concentration: 18.3 g / L). The mixed aqueous solution of No. 2 was made into a composite solution of nickel sulfate (concentration: 58.7 g / L) and manganese sulfate (concentration: 54.9 g / L), and the firing temperature was 950 ° C. Similarly, a positive electrode active material was obtained and evaluated. The evaluation results are shown in Tables 1 and 2.

Example 4
Using the precursor obtained in Example 1, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the firing temperature was 900 ° C. The evaluation results are shown in Table 2.

(Comparative Example 1)
The mixed aqueous solution used was a composite solution (first raw material solution) of nickel sulfate (concentration: 70.4 g / L), cobalt sulfate (concentration: 23.6 g / L) and manganese sulfate (concentration: 22.0 g / L). The precursor and the positive electrode active material were obtained and evaluated in the same manner as in Example 1 except that the crystallization was performed only with). The evaluation results are shown in Tables 1 and 2.

(Comparative Example 2)
The first mixed aqueous solution is a composite solution of nickel sulfate (concentration: 65.2 g / L) and cobalt sulfate (concentration: 26.2 g / L), and the second mixed aqueous solution is nickel sulfate (concentration: 24. g). 4 g / L) solution and nickel sulfate (concentration: 115.9 g / L) in the same manner as in Example 1 except that the particle growth crystallization time was 3.6 hours and 0.4 hours. Thus, a precursor and a positive electrode active material were obtained and evaluated. The evaluation results are shown in Tables 1 and 2.

(Comparative Example 3)
The first mixed aqueous solution is a composite solution of nickel sulfate (concentration: 78.3 g / L) and manganese sulfate (concentration: 36.6 g / L), and the second mixed aqueous solution is nickel sulfate (concentration: 58. g). A precursor and a positive electrode active material were obtained and evaluated in the same manner as in Example 1 except that a composite solution of 7 g / L) and cobalt sulfate concentration: 58.9 g / L) was used. The evaluation results are shown in Tables 1 and 2.

(Comparative Example 4)
Using the precursor obtained in Example 1, a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that the firing temperature was 800 ° C. The evaluation results are shown in Table 2.

(Evaluation results)
The nickel composite hydroxide (precursor) of the example has a certain amount of a layer (outer shell layer) having a low cobalt content from the surface of the precursor particle to the inside. Moreover, the positive electrode active material obtained from the precursor of the example maintained a high tap density as compared with the positive electrode active material prepared from a precursor having a uniform composition inside the particles as in Comparative Example 1, for example. It was shown that particles having a high specific surface area can be obtained. Furthermore, it was shown that the secondary battery using the obtained positive electrode material had higher initial discharge capacity, reduced reaction resistance, and improved electrical characteristics as compared with Comparative Example 1.

  Further, in Comparative Example 2 in which the thickness of the outer shell layer of the precursor is less than 10% with respect to the particle diameter, the specific surface area is small and the reaction resistance is high as compared with the Examples. Further, in Comparative Example 3 where the Co content in the outer shell layer is large, the tap density is similar to that in the example, but the specific surface area is small and the reaction resistance is also high. Furthermore, in Comparative Example 4 where the firing temperature is less than 850 ° C., the capacity per unit weight does not decrease, but the capacity per unit volume of the battery decreases because the tap density is low and the chargeability to the battery decreases.

1 ... Secondary particles (nickel composite hydroxide)
2 ... outer shell layer 3 ... central portion t ... outer shell layer thickness d ... secondary particle diameter CBA ... coin cell battery PC ... positive electrode can NC ... negative electrode can GA ... gasket PE ... positive electrode NE ... negative electrode SE ... separator WW ... Wave washer

Claims (10)

It consists of secondary particles in which a plurality of primary particles are aggregated, and has the general formula (1): Ni _1-xy Co _x Mn _y (OH) _{2 + α} (wherein x in the formula (1) is 0.20 ≦ x ≦ 0. .35, y is 0.20 ≦ y ≦ 0.35, α is in the range of 0 ≦ α ≦ 0.5, and satisfies 0.4 ≦ x + y ≦ 0.7. An oxide,
From the particle surface of the secondary particle to the inside of the particle, having an outer shell layer,
The outer shell layer has a thickness of 10% to 30% of the secondary particle diameter, and the cobalt content is 5 atomic% or less with respect to the total of metal elements contained in the outer shell layer. Nickel composite hydroxide.   In the particle size distribution measured by the laser diffraction scattering method, the volume average particle diameter (Mv) is 4 μm or more and 10 μm or less, the cumulative 90 volume% diameter (D90) and the cumulative 10 volume% diameter (D10), and the volume average particle 2. The nickel composite hydroxide according to claim 1, wherein [(D90−D10) / Mv] indicating a particle size variation index calculated by the diameter (Mv) is 0.60 or less. It consists of secondary particles in which a plurality of primary particles are aggregated, and has the general formula (1): Ni _1-xy Co _x Mn _y (OH) _{2 + α} (wherein x in the formula (1) is 0.20 ≦ x ≦ 0. .35, y is 0.20 ≦ y ≦ 0.35, α is in the range of 0 ≦ α ≦ 0.5, and satisfies 0.4 ≦ x + y ≦ 0.7. A method for producing an oxide comprising:
A nucleation step for generating nuclei by adjusting the pH value to be 12.5 or higher in a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less based on a liquid temperature of 25 ° C .;
The slurry containing nuclei formed in the nucleation step is a non-oxidizing atmosphere having an oxygen concentration of 5% by volume or less, and a pH value of 10.5 or more and 12.5 or less on the basis of a liquid temperature of 25 ° C., and A first particle growth step of adjusting the pH to be lower than the pH value in the nucleation step, and supplying a first mixed aqueous solution containing at least one of a nickel salt, a cobalt salt and a manganese salt to the slurry;
A second particle growth step of switching the first mixed aqueous solution to a second mixed aqueous solution containing 5 atomic% or less of cobalt with respect to all metal atoms in the secondary particles and supplying the second mixed aqueous solution to the slurry; Including
In the second particle growth step, the total of metal elements having a thickness of 10% to 30% of the diameter from the surface of the secondary particles to the inside of the particles and having a cobalt content in the outer shell layer A method for producing a nickel composite hydroxide, wherein an outer shell layer of 5 atomic% or less is formed.   The method for producing a nickel composite hydroxide according to claim 3, wherein the ammonia concentration of the slurry is adjusted to 5 g / L or more and 20 g / L or less in the first and second particle growth steps. It consists of secondary particles in which a plurality of primary particles are aggregated, and has the general formula (2): Li _{1 + u} Ni _1-xy Co _x Mn _y O ₂ (wherein u in the formula (2) is −0.05 ≦ u ≦ 0.50, x is in the range of 0.20 ≦ x ≦ 0.35, and y is in the range of 0.20 ≦ y ≦ 0.35, and satisfies 0.4 ≦ x + y ≦ 0.7. A positive electrode active material for a non-aqueous electrolyte secondary battery comprising a lithium nickel composite oxide having a hexagonal layered structure,
The lithium nickel composite oxide has a specific surface area of 1.0 m ² / g to 3.0 m ² / g, a tap density of 2.0 g / ml to 3.0 g / ml, and a specific surface area and tap. A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the product with the density is 3.0 or more.   The lithium nickel composite oxide has a volume average particle size (Mv) of 4 μm or more and 10 μm or less in a particle size distribution by a laser diffraction scattering method, and a cumulative 90 volume% diameter (D90) and a cumulative 10 volume% diameter (D10). The non-aqueous electrolyte secondary according to claim 5, wherein [(D90−D10) / Mv] indicating a particle size variation index calculated by the volume average particle size (Mv) is 0.60 or less. Positive electrode active material for batteries.   The positive electrode active material has an outer shell layer from the particle surface of the secondary particle to the inside of the particle, the outer shell layer has a thickness of 10% to 30% of the secondary particle diameter, and The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5, wherein the content of cobalt is less than the content of internal cobalt. General formula (2): Li _{1 + u} Ni _1-xy Co _x Mn _y O ₂ (in the formula (2), u is −0.05 ≦ u ≦ 0.50, x is 0.20 ≦ x. ≦ 0.35, y is in the range of 0.20 ≦ y ≦ 0.35, and satisfies 0.4 ≦ x + y ≦ 0.7.) And has a hexagonal layered structure A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery composed of a composite oxide,
Mixing the nickel composite hydroxide of claim 1 or claim 2 and a lithium compound to form a lithium mixture;
Firing the lithium mixture formed in the mixing step at a temperature of 850 ° C. to 1100 ° C. in an oxidizing atmosphere, and producing a positive electrode active material for a non-aqueous electrolyte secondary battery Method.   In the mixing of the nickel composite hydroxide and the lithium compound, the ratio (Li / Me) of the number of lithium atoms (Li) to the sum of the number of atoms of metals other than lithium (Me) contained in the lithium mixture is The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries of Claim 8 mixed so that it may become 0.95 or more and 1.5 or less. A non-aqueous electrolyte comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the positive electrode includes the positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 5 or 6. Secondary battery.

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