JP7367336B2 - Nickel composite hydroxide, method for producing nickel composite hydroxide, positive electrode active material for lithium ion secondary batteries, method for manufacturing positive electrode active material for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Description

The present invention relates to a nickel composite hydroxide that is a precursor of a positive electrode active material for lithium ion secondary batteries, a method for producing the same, a positive electrode active material for secondary batteries using this nickel composite hydroxide as a raw material, a method for producing the same, and The present invention relates to a lithium ion secondary battery using a positive electrode active material for a lithium ion secondary battery as a positive electrode material.

In recent years, with the spread of mobile devices such as mobile phones and notebook computers, there is a strong desire to develop small and lightweight secondary batteries with high energy density. Examples of such secondary batteries include lithium ion secondary batteries that use lithium, lithium alloys, metal oxides, or carbon as a negative electrode.

Lithium composite oxide is used as a positive electrode active material for a lithium ion secondary battery. Lithium cobalt composite oxide is relatively easy to synthesize and has a high energy density because a high voltage of 4V class can be obtained in a lithium ion secondary battery using lithium cobalt composite oxide as a positive electrode material. It is expected to be a material for making secondary batteries practical. Regarding lithium-cobalt composite oxide, research and development is underway to achieve excellent initial capacity characteristics and cycle characteristics in secondary batteries, and various results have already been obtained.

However, the lithium cobalt composite oxide uses a rare and expensive cobalt compound as a raw material, which causes an increase in the costs of positive electrode materials and secondary batteries. A lithium ion secondary battery using a lithium cobalt composite oxide has a unit price per capacity that is about four times that of a nickel metal hydride battery, so its applicable uses are very limited. Therefore, from the viewpoint of realizing further weight reduction and miniaturization of portable devices, it is necessary to reduce the cost of the positive electrode active material and to make it possible to manufacture cheaper lithium ion secondary batteries.

Examples of positive electrode active materials that can be substituted for lithium cobalt composite oxide include lithium nickel composite oxide (LiNiO ₂ ) and lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ). Can be mentioned. Lithium-nickel composite oxide exhibits a high electrical voltage similar to that of lithium-cobalt composite oxide, but also a lower electrical potential than lithium-cobalt composite oxide, making it less likely that problems caused by oxidation of the electrolyte will be a problem. It is expected to be used as a positive electrode active material that enables high capacity batteries.

For example, Patent Document 1 proposes having a manganese-rich layer in the outer shell to reduce the alkalinity of the active material and suppress gelation during electrode production.

Furthermore, Patent Document 2 proposes nickel-manganese composite hydroxide particles and nickel-cobalt-manganese composite hydroxide particles, which are precursors of positive electrode active materials for non-aqueous electrolyte secondary batteries, and have high capacity and high output. It is possible.

JP2012-256435A Japanese Patent Application Publication No. 2011-116580

However, in Patent Document 1, no voids are introduced between the manganese-rich layer of the outer shell and the center layer, and elemental diffusion during firing cannot be sufficiently suppressed, and further improvement in cycle characteristics is required. Furthermore, as a positive electrode for a secondary battery, it is required to improve cycle characteristics at a higher level than conventional ones.

Therefore, in view of the above-mentioned problems, the present invention provides a nickel composite hydroxide that is a precursor of a positive electrode active material for lithium ion secondary batteries that prevents elemental diffusion in a manganese-rich layer and has excellent cycle characteristics. The purpose is to Another object of the present invention is to provide a method for easily producing the nickel composite hydroxide with high productivity. Another object of the present invention is to provide a positive electrode active material for a lithium ion secondary battery with excellent cycle characteristics, a method for producing the same, and a lithium ion secondary battery.

The nickel composite hydroxide according to one embodiment of the present invention is a nickel composite hydroxide composed of secondary particles in which a plurality of primary particles aggregate with each other, and in which nickel, cobalt, manganese, and element M are combined into Ni:Co:Mn :M=1-x1-y1-z1:x1:y1:z1 (M is at least one member selected from the group consisting of transition metal elements other than Ni, Co, and Mn, group 2 elements, and group 13 elements) , x1 is 0.15≦x1≦0.25, y1 is 0.15≦y1≦0.25, z1 is within the range of 0≦z1≦0.1, and 0.3≦x1+y1+z1≦ 0.5), and a manganese-rich layer is formed from the particle surface of the secondary particle toward the inside of the particle, and a layer is formed between the high-density central part of the secondary particle and the manganese-rich layer. The manganese-rich layer has a low density layer of nickel, cobalt, manganese, and element M such that Ni:Co:Mn:M=1-x2-y2-z2:x2:y2:z2 (where 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 x2 and y2 satisfy x2=0 and y2=1, or The manganese-rich layer has an atomic ratio of y2/((1-x2-y2-z2)+x2)≧1, and z2 is in the range of 0≦z2≦0.1), and the thickness of the manganese-rich layer is The thickness of the low density layer is 1% or more and less than 10% with respect to the diameter of the secondary particles, and the thickness of the low density layer is 1% or more and 10% or less with respect to the diameter of the secondary particles. do.

In this way, it is possible to provide a nickel composite hydroxide which is a precursor of a positive electrode active material for a lithium ion secondary battery with excellent cycle characteristics.

At this time, 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, and the cumulative 90 volume % diameter (D90) and the cumulative 10 volume % diameter (D10) are as follows. The particle size dispersion index [(D90-D10)/Mv] calculated from the volume average particle diameter (Mv) may be 0.60 or less.

In this way, excellent cycle characteristics can be obtained.

At this time, in one aspect of the present invention, there is provided a method for producing a nickel composite hydroxide comprising secondary particles in which a plurality of primary particles aggregate with each other, the method comprising: A nucleation step in which the mixed aqueous solution of No. 1 is adjusted to have a pH value of 12.5 or more based on a liquid temperature of 25° C. in a non-oxidizing atmosphere with an oxygen concentration of less than 5% by volume to generate nuclei. , Adjust the pH value of the slurry containing the nuclei formed in the nucleation step to a range of 10.5 to 12.5 and lower than the pH value in the nucleation step, based on the liquid temperature of 25 ° C. and a particle growth step of performing particle growth, the particle growth step includes a first particle growth step, a second particle growth step, and a third particle growth step, and the particle growth step includes a first particle growth step, a second particle growth step, and a third particle growth step. In the step, the first mixed aqueous solution is supplied to the mixed aqueous solution obtained in the nucleation step in a non-oxidizing atmosphere with an oxygen concentration of less than 5% by volume to form a high-density particle center. In the second particle growth step, the oxygen concentration is switched to an oxidizing atmosphere of 5% by volume or more, and the first mixed aqueous solution is supplied to the mixed aqueous solution obtained in the first particle growth step. to form a layered low-density layer, and in the third particle growth step, the oxygen concentration is switched to an oxidizing atmosphere of less than 5% by volume, and the mixed aqueous solution obtained in the second particle growth step is Nickel, cobalt, manganese, and element M are Ni:Co:Mn:M=1-x2-y2-z2:x2:y2:z2 (However, M is a transition metal element other than Ni, Co, or Mn, or a group 2 element. , and at least one element selected from the group consisting of Group 13 elements, and x2 and y2 satisfy x2=0 and y2=1, or y2/((1-x2-y2-z2)+x2) A second mixed aqueous solution containing an atomic ratio of 1) is supplied to form a manganese-rich layer, and the thickness of the manganese-rich layer is 1% or more and 10% of the diameter of the secondary particles. It is characterized by being less than or equal to

In this way, it is possible to provide a manufacturing method that can easily produce a nickel composite hydroxide with high productivity, which is a precursor of a positive electrode active material for a lithium ion secondary battery with excellent cycle characteristics.

At this time, in one aspect of the present invention, ammonia adjusted to a concentration of 5 g/L or more and 20 g/L or less may be added to the slurry in the particle growth step.

In this way, since ammonia acts as a complexing agent, it is possible to keep the solubility of metal ions constant, make the primary particles uniform, and prevent variations in the particle size of the nickel composite hydroxide. Furthermore, deviations in the composition of the nickel composite hydroxide can be prevented.

At this time, in one embodiment of the present invention, a positive electrode active material for a lithium ion secondary battery is composed of a lithium nickel composite oxide that is composed of secondary particles in which a plurality of primary particles aggregate with each other and has a hexagonal layered structure. The lithium-nickel composite oxide contains lithium, nickel, cobalt, manganese, and element M in the form of Li:Ni:Co:Mn:M=1+u:1-x1-y1-z1:x1:y1:z1 (however, , u is −0.05≦u≦0.50, 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, x1 is 0.15≦x1≦0.25, y1 is 0.15≦y1≦0.25, z1 is 0≦z1≦0.1), and from the particle surface of the secondary particle to the inside of the particle a manganese-rich layer, and a layered void layer between the high-density central part of the secondary particles and the manganese-rich layer, and the manganese-rich layer contains lithium, nickel, cobalt, manganese, and the element M. Li:Ni:Co:Mn:M=1+u:1-x2-y2-z2:x2:y2:z2 (where, u is -0.05≦u≦0.50, M is Ni, Co, Mn is at least one element selected from the group consisting of transition metal elements, group 2 elements, and group 13 elements, and x2 and y2 satisfy x2=0 and y2=1, or y2/((1 −x2−y2−z2)+x2)≧1, and z2 is within the range of 0≦z2≦0.1), and the thickness of the manganese-rich layer is equal to the diameter of the secondary particles. The thickness of the void layer is 1% or more and less than 10% with respect to the diameter of the secondary particle, and the thickness of the (003) plane is 1% or more and less than 10% with respect to the diameter of the secondary particle. It is characterized in that the crystallite diameter calculated from the peak is 100 nm or more and 150 nm or less.

In this way, a positive electrode active material for a lithium ion secondary battery with excellent cycle characteristics can be provided.

At this time, in one aspect of the present invention, in the particle size distribution measured by a laser diffraction scattering method, the volume average particle diameter (Mv) is 4 μm or more and 10 μm or less, and the cumulative 90 volume % diameter (D90) and the cumulative 10 volume % The particle size variation index [(D90-D10)/Mv] calculated from the diameter (D10) and the volume average particle size (Mv) may be 0.60 or less.

In this way, excellent cycle characteristics can be obtained.

At this time, in one embodiment of the present invention, a positive electrode active material for a lithium ion secondary battery is composed of a lithium nickel composite oxide that is composed of secondary particles in which a plurality of primary particles aggregate with each other and has a hexagonal layered structure. The manufacturing method includes a lithium mixing step of mixing a nickel composite hydroxide and a lithium compound to form a lithium mixture, and firing the lithium mixture at a temperature of 800°C or higher and 950°C or lower in an oxidizing atmosphere. The nickel composite hydroxide is produced by combining nickel, cobalt, manganese, and element M with Ni:Co:Mn:M=1-x1-y1-z1:x1:y1:z1 (however, M is , Ni, Co, at least one element selected from the group consisting of transition metal elements other than Mn, Group 2 elements, and Group 13 elements, x1 is 0.15≦x1≦0.25, and y1 is 0.15≦x1≦0.25. 15≦y1≦0.25, z1 is within the range of 0≦z1≦0.1, and satisfies 0.3≦x1+y1+z1≦0.5), and the nickel composite hydroxide has an atomic ratio of: The secondary particles have a manganese-rich layer from the particle surface toward the inside of the particles, and a laminar low-density layer between the central part of the secondary particles and the manganese-rich layer, and the manganese-rich layer includes nickel and nickel. Cobalt, manganese, and the element M are Ni:Co:Mn:M=1-x2-y2-z2:x2:y2:z2 (where M is a transition metal element other than Ni, Co, or Mn, a group 2 element, and At least one element selected from the group consisting of Group 13 elements, and x2 and y2 satisfy x2=0 and y2=1, or y2/((1-x2-y2-z2)+x2)≧1 and z2 is in the range of 0≦z2≦0.1), and the thickness of the manganese-rich layer is 1% or more and less than 10% with respect to the diameter of the secondary particles. and the thickness of the low density layer is 1% or more and 10% or less of the diameter of the secondary particles.

In this way, it is possible to provide a method for producing a positive electrode active material for a lithium ion secondary battery with excellent cycle characteristics.

In one aspect of the present invention, a lithium ion secondary battery may be provided that includes a positive electrode containing the positive electrode active material for a lithium ion secondary battery.

In this way, it is possible to provide a lithium ion secondary battery including a positive electrode containing a positive electrode active material for a lithium ion secondary battery with excellent cycle characteristics.

According to the present invention, it is possible to provide a nickel composite hydroxide that is a precursor of a positive electrode active material for a lithium ion secondary battery that prevents elemental diffusion in a manganese-rich layer and has excellent cycle characteristics. Furthermore, it is possible to provide a method for easily producing the nickel composite hydroxide with high productivity. Further, it is possible to provide a positive electrode active material for a lithium ion secondary battery with excellent cycle characteristics, a method for producing the same, and a lithium ion secondary battery.

FIG. 1 is a process diagram schematically showing a method for producing a nickel composite hydroxide according to an embodiment of the present invention. FIG. 2 is a process diagram schematically showing a method for manufacturing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention.

In order to solve the above problems, the present inventors conducted intensive studies on positive electrode active materials for lithium ion secondary batteries with excellent cycle characteristics, and found that the positive electrode active material had a gradient composition so that the manganese content near the surface was higher than that inside the interior. In addition, we found that by introducing a layered void layer between the particle center and the manganese-rich layer, excellent positive electrode resistance can be achieved. Furthermore, we found that by introducing a void layer between layers of different compositions, compositional diffusion inside the particles during firing is suppressed, and a positive electrode active material with a gradient composition can be obtained without limiting the firing temperature. , has completed the present invention. Hereinafter, preferred embodiments of the present invention will be described.

Note that the present embodiment described below does not unduly limit the content of the present invention described in the claims, and changes can be made without departing from the gist of the present invention. Furthermore, not all of the configurations described in this embodiment are essential as a solution to the present invention. The nickel composite hydroxide and the like according to one embodiment of the present invention will be explained in the following order.
1. Nickel composite hydroxide 2. Method for producing nickel composite hydroxide 3. Positive electrode active material for lithium ion secondary batteries 4. Manufacturing method of positive electrode active material for lithium ion secondary battery 5. Lithium ion secondary battery

<1. Nickel composite hydroxide>
The nickel composite hydroxide according to an embodiment of the present invention is composed of secondary particles in which a plurality of primary particles aggregate with each other, and a manganese-rich layer is formed from the particle surface of the secondary particles toward the inside of the particles. It has a layered low-density layer between the central part and the manganese-rich layer. This will be explained in detail below.

(composition)
The composition of the nickel composite hydroxide (the entire secondary particles) is Ni:Co:Mn:M=1-x1-y1-z1:x1:y1:z1 (where M is , Ni, Co, at least one element selected from the group consisting of transition metal elements other than Mn, Group 2 elements, and Group 13 elements, x1 is 0.15≦x1≦0.25, and y1 is 0.15≦x1≦0.25. 15≦y1≦0.25, z1 is within the range of 0≦z1≦0.1, and satisfies 0.3≦x1+y1+z1≦0.5).

The nickel content is expressed as 1-x1-y1-z1, and the range is 0.50≦1-x1-y1-z1≦0.70. When the lithium metal composite oxide has a layered rock salt type crystal structure and the nickel content is within the above range, the finally obtained lithium metal composite oxide can realize a high battery capacity when used in a secondary battery.

In the above general formula, x1 indicating the content of cobalt is 0.15≦x1≦0.25. When the cobalt content is within the above range, the lithium metal composite oxide finally obtained has high crystal structure stability and excellent cycle characteristics.

In the above general formula, y1 indicating the manganese content is 0.15≦y1≦0.25. When the manganese content is within the above range, the finally obtained lithium metal composite oxide can have high thermal stability.

The nickel composite hydroxide according to one embodiment of the present invention may contain additional elements M other than nickel, cobalt, and manganese as long as they do not affect the effects of the present invention. For example, it may contain transition metal elements other than nickel, cobalt, and manganese, group 2 elements, and group 13 elements. M(z1) satisfies 0≦z1≦0.1.

The compositional distribution inside the particles of the nickel composite hydroxide strongly influences the compositional distribution inside the particles of the positive electrode active material obtained using the same. In particular, as will be described later, by controlling the conditions in the firing process, it is possible to maintain the compositional distribution and particle size distribution inside the particles of the nickel composite hydroxide up to the positive electrode active material. Therefore, it is important to control the composition distribution inside the particles of the nickel composite hydroxide to be similar to that inside the particles of the positive electrode active material. By controlling in this way, the manganese-rich layer of the nickel composite hydroxide is maintained even in the positive electrode active material.

As described later, the nickel composite hydroxide is mixed with a lithium compound (lithium mixing step S30) and then fired (baking step S40) to form a positive electrode active material. The compositional distribution of the nickel composite hydroxide is inherited to the positive electrode active material. Therefore, the composition distribution of the entire nickel composite hydroxide can be made similar to the composition distribution of metals other than lithium in the positive electrode active material to be obtained.

(manganese rich layer)
The nickel composite hydroxide according to one embodiment of the present invention has a manganese-rich layer from the particle surface of the secondary particle toward the inside of the particle. The manganese-rich layer has a composition of nickel, cobalt, manganese, and element M such as Ni:Co:Mn:M=1-x2-y2-z2:x2:y2:z2 (where M is any element other than Ni, Co, or Mn). is at least one element selected from the group consisting of transition metal elements, group 2 elements, and group 13 elements, and x2 and y2 satisfy x2=0 and y2=1, or y2/((1- x2-y2-z2)+x2)≧1, and z2 is in the range of 0≦z2≦0.1. Here, y2 is in the range of 0.5≦y2≦1.

The manganese-rich layer may contain, for example, at least one of Ni and Co as a metal other than Mn. In this case, the manganese-rich layer contains Mn equal to or more than the total (mol) of Ni and Co. Further, the manganese-rich layer may contain Mn alone as a metal, and its composition may be Mn(OH) ₂ , for example. In this case, x2=0 and y2=1. Note that the composition of the manganese-rich layer can be determined, for example, by quantitative analysis using energy dispersive X-ray analysis (EDX) during cross-sectional observation using a scanning electron microscope. Further, the composition of the manganese-rich layer can be adjusted to a desired range by, for example, controlling the metal composition of the second mixed aqueous solution in the particle growth step (S20) described below. Note that the manganese-rich layer may also contain additive elements M other than nickel, cobalt, and manganese as long as they do not affect the effects of the present invention. For example, it may contain transition metal elements other than nickel, cobalt, and manganese, group 2 elements, and group 13 elements. M(z2) satisfies 0≦z2≦0.1.

Moreover, the thickness t of the manganese-rich layer is 1% or more and 10% or less with respect to the diameter d of the secondary particles. Note that the thickness t of the manganese-rich layer can be determined by composition mapping using EDX or line analysis. Further, the diameter d of the secondary particles can be determined by observing the cross section of the secondary particles using a scanning electron microscope. Since the thickness of the manganese-rich layer and the diameter d of the secondary particles may vary between secondary particles, it is preferable to measure a plurality of secondary particles and obtain the average value. It can be determined from the average value when 30 secondary particles are measured.

(low density layer)
The nickel composite hydroxide according to one embodiment of the present invention has a layered low-density layer between the central part of the secondary particles and the manganese-rich layer. Regarding the internal structure of the nickel composite hydroxide particles, by introducing a layered low-density layer between the particle center and the manganese-rich layer, compositional diffusion inside the particles during firing is suppressed and the firing temperature is limited. It is possible to maintain the compositional distribution inside the particles.

Further, the thickness s of the low density layer is 1% or more and 10% or less of the diameter d of the secondary particles. When the low-density layer is less than 1%, no void layer is formed in the subsequent firing process, and no manganese-rich layer is formed due to compositional diffusion. Moreover, when it exceeds 10%, the particle density and filling property of the finally obtained positive electrode active material are greatly reduced. Note that the thickness s of the low-density layer can be determined by observing the cross section of the secondary particles using a scanning electron microscope. Since the thickness s of the low-density layer and the diameter d of the secondary particles may vary between secondary particles, it is preferable to measure a plurality of secondary particles and obtain the average value. It can be determined from the average value when 30 selected secondary particles are measured.

The composition and structure inside the particles of the nickel composite hydroxide affect the composition and structure inside the particles of the positive electrode active material. Therefore, by setting the composition of the manganese-rich layer and the structure having a layered low-density layer within the above range, a manganese-rich layer containing lithium is formed in the resulting positive electrode active material, and when used as a battery positive electrode. Shows excellent cycle characteristics.

(Average particle size, particle size distribution)
The nickel composite hydroxide preferably has a volume average particle diameter (Mv) of 4 μm or more and 10 μm or less in the particle size distribution measured by a laser diffraction scattering method. When the volume average particle size of the nickel composite hydroxide is within the above range, the volume average particle size of the resulting positive electrode active material can be controlled within the range of 4 μm or more and 10 μm or less, and a battery using this positive electrode active material can be , excellent cycle characteristics can be obtained.

Nickel composite hydroxide is calculated by the cumulative 90 volume % diameter (D90), cumulative 10 volume % diameter (D10), and volume average particle diameter (Mv) in the particle size distribution measured by laser diffraction scattering method. , [(D90-D10)/Mv], which indicates the particle size variation index, is preferably 0.60 or less. When the dispersion index of the nickel composite hydroxide is within the above range, there is little incorporation of fine particles or coarse particles, and the cycle characteristics of the resulting positive electrode active material can be improved. The particle size distribution of the positive electrode active material is strongly influenced by the nickel composite hydroxide, so if the dispersion index of the nickel composite hydroxide exceeds 0.60 and the particle size distribution is wide, the positive electrode active material also contains fine particles. Or coarse particles may become present. Since it is difficult to completely suppress variations in particle size, the practical lower limit of the variation index is about 0.30 or more.

In the above [(D90-D10)/Mv], D10 means the particle size at which the number of particles at each particle size is accumulated from the smallest particle size and the cumulative volume is 10% of the total volume of all particles. ing. Moreover, D90 means a particle size at which the number of particles is accumulated and the cumulative volume is 90% of the total volume of all particles. The volume average particle diameter Mv, D90 and D10 can be measured using a laser beam diffraction scattering particle size analyzer.

<2. Method for producing nickel composite hydroxide>
A method for producing a nickel composite hydroxide according to an embodiment of the present invention includes supplying an aqueous solution containing a nickel salt, a cobalt salt, and a manganese salt, a neutralizing agent, and a complexing agent to a reaction vessel while stirring. Then, a nickel composite hydroxide is produced by a crystallization reaction. The method for producing nickel composite hydroxide includes a two-step crystallization process. That is, it includes a nucleation step S10 in which a nucleus that grows into a secondary particle is generated, and a particle growth step S20 in which the nucleus obtained in the nucleation step is grown.

Further, the particle growth step S20 includes a first particle growth step S21 in which a first mixed aqueous solution is supplied to the slurry containing the nuclei formed in the nucleation step S10 to grow the particles. After the growth step, the atmosphere is changed to an oxidizing atmosphere with an oxygen concentration of 5% by volume or more to perform particle growth, and the atmosphere is changed to a non-oxidizing atmosphere with an oxygen concentration of less than 5% by volume, and the atmosphere is changed to a non-oxidizing atmosphere with an oxygen concentration of less than 5% by volume. A third particle growth step S23 is included in which particle growth is performed by supplying a second mixed aqueous solution containing a metal salt having a molar ratio similar to that of Ni, Co, and Mn in the rich layer.

The method for producing nickel composite hydroxide including such a two-step batch crystallization process is disclosed in, for example, Patent Document 2 and Patent Document 3, and for detailed conditions, please refer to these documents. You can refer to it and adjust the conditions as appropriate. The method for producing a nickel composite oxide includes a two-step crystallization process, thereby making it possible to obtain a composite hydroxide having a narrow and uniform particle size distribution. Note that the following explanation is an example of a method for producing a nickel composite hydroxide, and is not limited to this method.

(Nucleation step S10)
First, in the nucleation step S10, a first mixed aqueous solution containing at least one of a nickel salt, a cobalt salt, and a manganese salt is heated at a liquid temperature of 25° C. in a non-oxidizing atmosphere with an oxygen concentration of less than 5% by volume. By adjusting the pH value to 12.5 or more, nuclei are preferentially generated in the formed aqueous solution for nucleation. In addition, when adding elements other than nickel, cobalt, and manganese, it is preferable to add a salt of the added element to the mixed aqueous solution.

In the nucleation step S10, the pH value of the nucleation aqueous solution is 12.5 or more, preferably 12.5 or more and 14.0 or less, more preferably 12.5 or more and 13.5 or less, based on a liquid temperature of 25°C. Control within the range. When the pH value of the aqueous solution for nucleation is controlled within the above range, nuclei can be sufficiently generated. When the pH value is less than 12.5 based on the liquid temperature of 25° C., although nuclei are generated, the nuclei themselves become large, so that secondary particles in which primary particles are aggregated cannot be obtained in the subsequent particle growth step. On the other hand, the higher the pH value, the finer the crystal nuclei can be obtained, but if it exceeds 14.0, the reaction solution may gel, making crystallization difficult, or the plate forming the secondary particles of the nickel composite hydroxide may Problems such as primary particles becoming too small may occur.

The pH can be controlled by adding an inorganic alkaline solution as a neutralizing agent. The inorganic alkaline solution is not particularly limited, and for example, common alkali metal hydroxide aqueous solutions such as sodium hydroxide and potassium hydroxide can be used. Although the alkali metal hydroxide can be added directly to the mixed aqueous solution, it is preferably added as an aqueous solution for ease of 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, more preferably 20% by mass or more and 25% by mass or less. If the concentration of the alkali metal hydroxide aqueous solution is low, the slurry concentration may decrease and productivity may deteriorate, so it is preferable to increase the concentration. % or more is preferable. On the other hand, if the concentration of the alkali metal hydroxide exceeds 30% by mass, the pH at the addition site becomes locally high and fine particles may be generated.

In the nucleation step S10, for example, a pre-reaction aqueous solution whose pH value is adjusted to 12.5 or higher by adding water to an inorganic alkaline aqueous solution is prepared in advance, and while stirring this pre-reaction aqueous solution in a reaction tank, For nucleation, the pH value is maintained in the above range by supplying a first mixed aqueous solution containing a nickel salt, a cobalt salt, and a manganese salt, and adding an inorganic alkaline aqueous solution (neutralizing agent) such as sodium hydroxide. Form an aqueous solution and perform nucleation. This method of supplying the mixed aqueous solution while maintaining the pH value of the nucleation aqueous solution is preferable because it allows strict control of the pH value and facilitates the generation of nuclei. Note that an ammonia aqueous solution (complexing agent) may be added to the nucleation aqueous solution together with an inorganic alkali aqueous solution (neutralizing agent). The concentration of ammonium ions in the aqueous solution for nucleation is preferably, for example, 3 g/L or more and 25 g/L or less.

The first mixed aqueous solution used in the nucleation step S10 contains a nickel salt, a cobalt salt, and a manganese salt. As these metal salts, sulfates, nitrates, chlorides, etc. can be used, and it is preferable to use sulfates from the viewpoints of cost, impurities, and waste liquid treatment. In addition, when adding elements other than nickel, cobalt, and manganese, it is preferable to add a salt of the added element to the mixed aqueous solution.

The concentration of the first mixed aqueous solution is preferably 1.0 mol/L to 2.2 mol/L, more preferably 1.5 mol/L to 2.0 mol/L in total of each metal salt. . If the concentration of the first mixed aqueous solution is low, the amount of the first mixed aqueous solution added will be large, and nucleation cannot be performed efficiently. Further, if the concentration of the first mixed aqueous solution is high, the concentration will be close to the saturated concentration at room temperature, so there is a risk that crystals will re-precipitate and clog the piping of the equipment.

The composition of the first mixed aqueous solution is appropriately determined in consideration of the composition of the manganese-rich layer so that the composition of the nickel composite hydroxide finally obtained has a desired composition.

The temperature of the aqueous solution for nucleation in the nucleation step S10 is preferably maintained at 40° C. or higher and 70° C. or lower, respectively. When the temperature is within the above range, the particle size of the nickel composite hydroxide can be grown to a target range.

(Particle growth step S20)
Next, in the particle growth step S20, after the completion of the nucleation step S10, the slurry containing the nuclei formed in the nucleation step S10 (slurry for particle growth) is adjusted to a pH value of 10.5 based on a liquid temperature of 25°C. The pH value is adjusted to be within the above range of 12.5 or less and lower than the pH value in the nucleation step S10.

The pH value of the particle growth slurry is controlled to be in the range of 10.5 to 12.5, preferably 11.0 to 12.0, and lower than the pH in the nucleation step S10, based on the liquid temperature of 25 ° C. be done. When the pH value of the slurry for particle growth is controlled within the above range, only the growth and aggregation of the nuclei generated in the nucleation step S10 can occur preferentially, new nucleation can be suppressed, and the resulting nickel composite The hydroxide can be made homogeneous, have a narrow particle size distribution range, and have a controlled shape. When the pH value based on the liquid temperature of 25° C. is less than 10.5, impurities contained in the obtained nickel composite hydroxide, such as anion constituent elements contained in the metal salt, increase. Moreover, if the pH value exceeds pH 12.5, new nuclei will be generated in the particle growth process, and the particle size distribution will also deteriorate. Further, from the viewpoint of more clearly separating the nucleation step S10 and the particle growth step S20, it is preferable to control the pH value of the particle growth slurry to be lower than the pH in the nucleation step by 0.5 or more, and 1.0 or more. It is more preferable to control it low.

The temperature of the particle growth slurry in the particle growth step S20 is preferably maintained at 40° C. or higher and 70° C. or lower, respectively. When the temperature is within the above range, the particle size of the nickel composite hydroxide can be grown to a target range. If the temperature is less than 40° C., the solubility of the metal salt in the mixed aqueous solution is low and the salt concentration is low, so that in the particle growth step S20, many fine particles are generated and the particle size distribution may be deteriorated. Moreover, when the temperature of the mixed aqueous solution exceeds 70° C., a large amount of ammonia volatilizes, and the nickel ammine complex concentration becomes unstable.

Note that it is preferable to add ammonia as a complexing agent to the particle growth slurry. At this time, 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, if the ammonia concentration is less than 5 g/L, the solubility of metal ions cannot be maintained constant, and the primary particles developed from the nucleus become uneven, resulting in nickel composite hydroxide. This may cause the particle size range to vary. If 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 deviations may occur. Furthermore, if the ammonia concentration fluctuates, the solubility of metal ions will fluctuate and a uniform nickel composite hydroxide will not be formed, so it is preferable to maintain it at a constant value. For example, it is preferable to maintain the ammonia concentration at a desired concentration by increasing or decreasing the ammonia concentration by about 5 g/L with respect to the set concentration.

Ammonia is added using an ammonium ion donor, but the ammonium ion donor is not particularly limited, and for example, ammonia, ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc. can be used.

The particle growth step S20 is divided into the following three stages depending on the atmosphere and the combination of the mixed aqueous solution to be added.

(First particle growth step S21)
The first particle growth step S21 corresponds to a step of forming the center part of the particles of nickel composite hydroxide. In the first particle growth step S21, the first mixed aqueous solution is supplied to the slurry containing nuclei in a non-oxidizing atmosphere with an oxygen concentration of less than 5% by volume. By setting the oxygen concentration to less than 5% by volume, unnecessary oxidation can be suppressed and a high-density central part of the particles can be obtained. The first mixed aqueous solution has been explained in the above nucleation step S10, so it will be omitted here. The first mixed solution used in the nucleation step S10 and the first mixed solution used in the first particle growth step S21 are used so that the composition of the finally obtained nickel composite hydroxide has the desired composition. You can change it if you can control it. However, from the viewpoint of simplifying the process, it is preferable that they have the same composition.

(Second particle growth step S22)
The second particle growth step S22 corresponds to a step of forming a low-density layer of nickel composite hydroxide. The second particle growth step S22 is performed by changing the atmosphere from the first particle growth step S21 to an oxidizing atmosphere with an oxygen concentration of 5% by volume or more and crystallizing the first mixed aqueous solution. Thereby, a layered low-density layer can be introduced into the nickel composite hydroxide.

The timing of switching can be adjusted depending on the thickness of the low-density layer, but for example, if the 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 an oxidizing atmosphere after introducing a total of 12.5 atom % or more and 80 atom % or less of manganese and M, and more preferably 50 atom % or more and 70 atom % or less. After switching to an oxidizing atmosphere, it is preferable to add nickel, cobalt, manganese, and M in a total amount of 2.5 atomic % or more and 10 atomic % or less. Furthermore, if the concentration and supply rate of the mixed aqueous solution are constant, they can be changed depending on the crystallization time. That is, it is preferable to switch the atmosphere after 12.5% to 80% of the crystallization time from the start of crystallization to the end of crystallization has elapsed, and in the case of an oxidizing atmosphere, the atmosphere should be maintained for 2.5% to 10% of the time. is preferred. As a result, a low-density layer with a desired thickness is formed at a desired position.

(Third particle growth step S23)
The third particle growth step S23 corresponds to a step of forming a manganese-rich layer of nickel composite hydroxide. The third particle growth step S23 is performed by switching the atmosphere from the second particle growth step S22 to a non-oxidizing atmosphere with an oxygen concentration of less than 5% by volume, and switching the mixed aqueous solution to be supplied to the second mixed solution. . Since the second mixed solution contains a large amount of cobalt, a manganese-rich layer is formed.

The second mixed aqueous solution used in the third particle growth step S23 contains at least a manganese salt, and may also contain a nickel salt or a cobalt salt. As the metal salt, sulfates, nitrates, chlorides, etc. can be used, and sulfates are preferably used from the viewpoints of cost, impurities, and waste liquid treatment. In addition, when adding elements other than nickel, cobalt, and manganese, it is preferable to add a salt of the added element to the mixed aqueous solution.

The composition of the second mixed aqueous solution is Ni:Co:Mn:M=1-x2-y2-z2:x2:y2:z2 (where M is Ni, Co, Mn). is at least one element selected from the group consisting of transition metal elements, group 2 elements, and group 13 elements, and x2 and y2 satisfy x2=0 and y2=1, or y2/((1 −x2−y2−z2)+x2)≧1, and z2 is within the range of 0≦z2≦0.1. Since the composition of the manganese-rich layer formed in the third particle growth step is inherited by the composition of the manganese-rich layer of the finally obtained positive electrode active material, the composition of the manganese-rich layer of the finally obtained positive electrode active material Together, the composition of the second mixed aqueous solution is determined.

The concentration of the second mixed aqueous solution is preferably 1.0 mol/L to 2.2 mol/L, more preferably 1.5 mol/L to 2.1 mol/L in total of each metal salt. . If the concentration of the second mixed aqueous solution is low, the amount of the first mixed aqueous solution to be added will be large, and nucleation cannot be performed efficiently. Further, if the concentration of the second mixed aqueous solution is high, the concentration will be close to the saturated concentration at room temperature, so there is a risk that crystals will re-precipitate and clog the pipes of the equipment.

From the above, according to the method for producing a nickel composite hydroxide according to an embodiment of the present invention, general formula (1): Ni _1-x1-y1-z1 Co _x1 Mn _y1 M _z1 (OH) _2+α1 (the above formula In (1), 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 x1 is 0.15≦x1≦0. .25, y1 is 0.15≦y1≦0.25, z1 is within the range of 0≦z1≦0.1, satisfies 0.3≦x1+y1+z1≦0.5, α1 is -0.2≦α1 ≦0.2), a manganese-rich layer from the particle surface of the secondary particle toward the inside of the particle, and a layered low-density layer between the center of the secondary particle and the manganese-rich layer. The manganese-rich layer has the general formula (2): Ni _1-x2-y2-Z2 Co _x2 Mn _y2 M _z2 (OH) _2+α2 (In the above formula (2), M is Ni, Co, Mn is at least one element selected from the group consisting of transition metal elements, group 2 elements, and group 13 elements, and x2 and y2 satisfy x2=0 and y2=1, or y2/((1 -x2-y2-z2)+x2)≧1, z2 is within the range of 0≦z2≦0.1, α2 is -0.2≦α2≦0.2), and the above The thickness of the manganese-rich layer is 1% or more and 10% or less with respect to the diameter of the secondary particles, and the thickness of the low-density layer is 1% or more and 10% or less with respect to the diameter of the secondary particles. % or less can be obtained.

<3. Cathode active material for lithium ion secondary batteries>
The positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention has a manganese-rich layer formed from the particle surface of the secondary particles toward the inside of the particles, and a layer formed between the central part of the secondary particles and the manganese-rich layer. It has a void layer of A positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is a mixture of a nickel composite hydroxide having a layered low-density layer between the manganese-rich layer and the center of the particles, and a lithium compound. By firing under specific conditions, the surface layer (manganese-rich layer) maintains a manganese-rich layer, and the low-density layer is absorbed into the center of the particle and becomes a void layer, while secondary lithium is generated. It is manufactured by dispersing it inside particles. The positive electrode active material for a lithium ion secondary battery has a manganese-rich layer containing lithium, and, as described later, can obtain higher durability by obtaining particles with high crystallinity.

A positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is composed of secondary particles in which a plurality of primary particles aggregate with each other, and is composed of a lithium-nickel composite oxide having a hexagonal layered structure. . In addition, lithium-nickel composite oxide is made by combining lithium, nickel, cobalt, manganese, and element M into Li:Ni:Co:Mn:M=1+u:1-x1-y1-z1:x1:y1:z1 (however, u is −0.05≦u≦0.50, 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 x1 is 0 .15≦x1≦0.25, y1 is 0.15≦y1≦0.25, and z1 is contained in an atomic ratio of 0≦z1≦0.1).

u, which indicates the excess amount of lithium, is −0.05 or more and 0.50 or less, preferably −0.05 or more and 0.20 or less. When u is less than −0.05, the reaction resistance of the positive electrode in a lithium ion secondary battery using the obtained positive electrode active material increases, and the output of the secondary battery decreases. On the other hand, when u exceeds 0.50, the initial discharge capacity of a secondary battery using this positive electrode active material decreases, and the reaction resistance of the positive electrode also increases. From the viewpoint of increasing capacity, it is more preferable that u is set to -0.02 or more and 0.10 or less. Note that the composition of the positive electrode active material can be determined by ICP emission spectrometry.

The manganese-rich layer in the positive electrode active material for a lithium ion secondary battery contains lithium, nickel, cobalt, manganese, and element M as Li:Ni:Co:Mn:M=1+u:1-x2-y2-z2:x2: y2:z2 (where u is -0.05≦u≦0.50, 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) x2 and y2 satisfy x2=0 and y2=1, or y2/((1-x2-y2-z2)+x2)≧1, and z2 satisfies 0≦z2≦0.1 (within the range of ). Note that y2 satisfies 0.5≦y2≦1.

The manganese-rich layer in the positive electrode active material for lithium ion secondary batteries does not contain nickel and cobalt (x2=0, y2=1), or the manganese-rich layer with respect to nickel and cobalt [y2/((1-x2- y2-z2)+x2)] is 1 or more.

The thickness of the manganese-rich layer in the positive electrode active material for a lithium ion secondary battery is 1% or more and 10% or less of the diameter of the secondary particles. Thereby, cycle characteristics can be improved. When the thickness of the manganese-rich layer is less than 1%, sufficient improvement in durability cannot be obtained due to the influence of the composition inside the particles. On the other hand, if the thickness exceeds 10%, the composition of the entire secondary particle becomes manganese-rich, resulting in a decrease in battery capacity, or the manganese composition ratio y2 of the manganese-rich layer becomes less than 0.5, resulting in insufficient improvement in cycle characteristics. effect cannot be obtained. Further, the thickness of the manganese-rich layer in the positive electrode active material can be determined by composition mapping using EDX or line analysis. Further, the diameter of the secondary particles can be determined by observing the secondary particles using a scanning electron microscope. The thickness of the manganese-rich layer and the diameter of the secondary particles may vary between secondary particles, so it is preferable to measure multiple secondary particles and find the average value (the above-mentioned nickel composite hydroxide (see description). The composition of the manganese-rich layer can be determined, for example, by quantitative analysis using energy-dispersive A manganese-rich layer can be determined when the composition ratio/(nickel composition ratio+cobalt composition ratio)) is 1 or more.

The thickness of the layered void layer in the positive electrode active material for a lithium ion secondary battery is 1% or more and 10% or less of the diameter of the secondary particles. This makes it possible to suppress compositional diffusion inside the particles even at the firing temperature required to obtain highly crystalline particles, making it possible to maintain a manganese-rich layer on the surface of the positive electrode active material particles, improving cycle characteristics. . If a void layer is not formed, a manganese-rich layer will not be formed due to compositional diffusion. On the other hand, when the thickness of the void layer exceeds 10%, the particle density and filling properties of the secondary particles are significantly reduced.

The positive electrode active material for a lithium ion secondary battery has a crystallite diameter of 100 nm or more and 150 nm or less, calculated from the peak of the (003) plane by X-ray diffraction measurement. This makes it possible to achieve both high battery capacity and excellent durability. If it is less than 100 nm, there is a high possibility that the crystallinity is not sufficient, making it difficult to obtain high output characteristics. Moreover, when the thickness exceeds 150 nm, deterioration of various battery characteristics is observed due to over-firing.

The positive electrode active material for a lithium ion secondary battery preferably has a volume average particle diameter (Mv) of 4 μm or more and 10 μm or less in a particle size distribution measured by a laser diffraction scattering method. Thereby, high output characteristics can be obtained.

The positive electrode active material for a lithium ion secondary battery has a particle size variation index calculated from a cumulative 90 volume % diameter (D90), a cumulative 10 volume % diameter (D10), and the volume average particle diameter (Mv). [(D90-D10)/Mv] is preferably 0.60 or less. Thereby, it is possible to reduce the contamination of fine particles and coarse particles, and to obtain high output characteristics with less variation. Note that the volume average particle diameter (Mv), D90, and D10 can be determined in the same manner as for the nickel composite hydroxide.

<4. Manufacturing method of positive electrode active material for lithium ion secondary battery>
A method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention includes a lithium mixing step S30 in which a nickel composite hydroxide and a lithium compound are mixed to form a lithium mixture; A firing step S40 is performed in which firing is performed at a temperature of 800° C. or higher and 950° C. or lower in an oxidizing atmosphere. Each process will be explained below.

(Lithium mixing step S30)
In the lithium mixing step S30, the above-described nickel composite hydroxide and lithium compound are mixed to form a lithium mixture. The lithium compound is not particularly limited and any known lithium compound can be used. For example, from the viewpoint of easy availability, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferably used. Among these, lithium hydroxide or lithium carbonate is more preferably used as the lithium compound from the viewpoint of ease of handling and stability of quality.

Nickel composite hydroxide and lithium compound are based on 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 additional elements (Me), and the number of atoms of lithium (Li). The ratio (Li/Me) is 0.95 to 1.50, preferably 0.95 to 1.20, more preferably 0.98 to 1.10. That is, since Li/Me does not change before and after the firing process, the Li/Me mixed in this lithium mixing step S30 becomes the Li/Me in the positive electrode active material, so that the Li/Me in the lithium mixture becomes the positive electrode to be obtained. They are mixed to be the same as Li/Me in the active material.

Further, for mixing, a general mixer can be used, such as a shaker mixer, Loedige mixer, Julia mixer, V blender, etc., to the extent that the skeleton of the nickel composite hydroxide is not destroyed. It suffices if they are mixed.

(Firing step S40)
In the firing step S40, the lithium mixture is fired at a temperature of 800° C. or more and 950° C. or less in an oxidizing atmosphere. The firing is preferably performed at a temperature of 800° C. or higher and 950° C. or lower in an oxidizing atmosphere. If the firing temperature is less than 800° C., high crystallinity cannot be obtained, and high output characteristics cannot be obtained when used in a battery. On the other hand, when the temperature exceeds 950° C., cation mixing occurs in which various transition metals enter lithium sites due to overfiring, and various battery characteristics deteriorate. Further, the firing time is not particularly limited, but is preferably about 1 hour or more and 24 hours or less.

In addition, from the viewpoint of uniformly performing the reaction between the nickel composite hydroxide or nickel composite oxide and the lithium compound, it is preferable to raise the temperature to the above temperature at a heating rate of 1 ° C / min to 5 ° C / min. . Furthermore, the reaction can be carried out more uniformly by maintaining the temperature near the melting point of the lithium compound for about 1 hour or more and 10 hours or less.

As described above, according to the method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention, the lithium nickel composite oxide has the general formula (3): Li _1+u Ni _{1-x1-y1- z1} Co _x1 Mn _y1 M _z1 O _2+β1 (In the above formula (3), 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) , u is -0.05≦u≦0.50, x1 is 0.15≦x1≦0.25, y1 is 0.15≦y1≦0.25, z1 is 0≦z1≦0.1. (within the range of 0.3≦x1+y1+z1≦0.5, and β1 is −0.2≦β1≦0.2), from the particle surface of the secondary particle toward the inside of the particle. The manganese-rich layer has a layered void layer between the central part of the secondary particles and the manganese-rich layer, and the manganese-rich layer has a general formula (4): Li _1+u Ni _1-x2-y2-z2 Co _x2 Mn _y2 M _z2 O _2+β2 (In the above formula (4), 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) Yes, u is expressed as -0.05≦u≦0.50, and x2 and y2 satisfy x2=0 and y2=1, or y2/((1-x2-y2-z2)+x2)≧ 1, z2 is within the range of 0≦z2≦0.1, and β2 is -0.2≦β2≦0.2), and the thickness of the manganese-rich layer is The thickness of the void layer is 1% or more and 10% or less with respect to the diameter of the secondary particles, and the thickness of the void layer is 1% or more and 10% or less with respect to the diameter of the secondary particles, and the thickness is determined by X-ray diffraction measurement. It is possible to obtain a positive electrode active material for a lithium ion secondary battery characterized in that the crystallite diameter calculated from the peak of the 003) plane is 100 nm or more and 150 nm or less.

<5. Lithium ion secondary battery>
A lithium ion secondary battery according to an embodiment of the present invention is characterized by including a positive electrode containing a positive electrode active material for a lithium ion secondary battery. Further, the lithium ion secondary battery can be configured with the same components as a general lithium ion secondary battery, and includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. Note that the embodiment described below is merely an example, and the lithium ion secondary battery of this embodiment can be modified in various ways based on the embodiment described in this specification and based on the knowledge of those skilled in the art. It can be implemented in an improved form. Moreover, the lithium ion secondary battery of this embodiment is not particularly limited in its use.

(a) Positive electrode A positive electrode for a lithium ion secondary battery is produced, for example, in the following manner using the positive electrode active material for a lithium ion secondary battery described above. First, a powdered positive electrode active material, a conductive material, and a binder are mixed, and if necessary, activated carbon and a solvent for purposes such as viscosity adjustment are added, and the mixture is kneaded to prepare a positive electrode composite paste. The mixing ratio of each component in the positive electrode composite paste is, for example, assuming that the total solid content of the positive electrode composite excluding the solvent is 100 parts by mass. It is preferable that the content of the 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 aluminum foil, for example, and dried to scatter the solvent. If necessary, pressure may be applied using 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 depending on the intended battery and used for battery production. However, the method for producing the positive electrode is not limited to the exemplified method, 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-based materials such as acetylene black, Ketjen black (registered trademark), etc. can be used.

The binder plays a role in binding the active material particles, and includes, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, polyacrylic resin, etc. An acid etc. can be used.

Note that, if necessary, a solvent for dispersing the positive electrode active material, conductive material, and activated carbon and dissolving 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. Furthermore, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(b) Negative electrode The negative electrode is made of metal lithium, lithium alloy, etc., or a negative electrode composite made by mixing a binder with a negative electrode active material that can absorb and desorb lithium ions, and adding an appropriate solvent to form a paste. is applied onto the surface of a metal foil current collector made of copper or the like, dried, and compressed to increase the electrode density if necessary.

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

(c) Separator A separator is placed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and can be a thin film made of polyethylene, polypropylene, etc., and has many minute pores.

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

Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, linear carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, and also tetrahydrofuran, 2- One type selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more types may be used in combination. It can be used as

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , complex salts thereof, and the like can be used. Furthermore, the nonaqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

Furthermore, a solid electrolyte may be used as the non-aqueous electrolyte. A solid electrolyte has the property of being able to withstand high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

As the inorganic solid electrolyte, oxide-based solid electrolytes, sulfide-based solid electrolytes, etc. are used.

The oxide-based solid electrolyte is not particularly limited, and any material that contains oxygen (O) and has lithium ion conductivity and electronic insulation can be used. Examples _of oxide-based _solid electrolytes include lithium phosphate _{( Li 3} PO _{4 ) , Li 3} PO ₄ N _X , LiBO _{2 N} PO ₄ , Li ₄ SiO ₄ -Li ₃ VO ₄ , Li ₂ O-B ₂ O ₃ -P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O ₃ -ZnO, Li _1+X Al _X Ti _2-X (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO _{4 ) 3} (0≦X≦1), LiTi ₂ (PO ₄ ) ₃ , Li _{3 3-X} TiO ₃ (0≦X≦2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 Examples include P _0.4 O ₄ and the like.

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

Note that as the inorganic solid electrolyte, other than those mentioned above may be used, for example, Li ₃ N, LiI, Li ₃ N-LiI-LiOH, etc. may be used.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound that exhibits ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof, etc. can be used. Moreover, the organic solid electrolyte may contain a supporting salt (lithium salt).

(e) Shape and configuration of battery A lithium ion secondary battery according to an embodiment of the present invention is configured of, for example, the above-described positive electrode, negative electrode, separator, and non-aqueous electrolyte. Further, the shape of the lithium ion secondary battery is not particularly limited, and can be various shapes such as a cylindrical shape and a stacked type. Regardless of the shape, the positive electrode and negative electrode are laminated with a separator in between to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte, and communicated with the positive electrode current collector to 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 lithium ion secondary battery.

A lithium ion secondary battery according to an embodiment of the present invention has excellent cycle characteristics by including a positive electrode made of the above-described positive electrode active material.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples in any way. The manufacturing conditions of the nickel composite hydroxide and the positive electrode active material for lithium ion secondary batteries are explained in each example and comparative example, and the manufacturing conditions of the nickel composite hydroxide and the positive electrode active material for lithium ion secondary batteries are explained in each example and comparative example. , volume average particle diameter and particle size distribution measurement, composition, SEM and EDX analysis, battery manufacturing, and positive electrode resistance will be described first.

(Volume average particle diameter and particle size distribution measurement)
The volume average particle diameter and particle size distribution were measured using a laser diffraction particle size analyzer (manufactured by Nikkiso Co., Ltd., trade name: Microtrac), and the tap density was measured using a shaking specific gravity meter (manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd., KRS-). 409). Compositional analysis was performed using an ICP emission spectrometer (manufactured by Shimadzu Corporation, ICPS-8100).

(composition)
The composition of the entire particle was confirmed using an ICP emission spectrometer (ICPE-9000, manufactured by Shimadzu Corporation, Shimadzu Corporation).

(SEM and EDX analysis)
Regarding the structure of the particles, nickel composite hydroxide powder or lithium nickel composite oxide powder was embedded in resin, and the cross section of the particles could be observed using focused ion beam processing. (trade name: S-4700) manufactured by M. Co., Ltd.).

The composition of the manganese-rich layer in the nickel composite hydroxide powder or the lithium-nickel composite oxide powder was analyzed using an energy dispersive X-ray spectrometer (EDX; manufactured by JEOL Ltd., trade name: JED2300). The EDX detector had a resolution of 137 eV, and the measurement conditions were a tube voltage of 20 kV, a tube current of 20 μA, a magnification of 5000 times, a WD of 15 mm, a process time of 4, and a count of 4 million or more.

(Manufacturing of batteries)
The obtained positive electrode active material for a lithium ion secondary battery was evaluated by producing and evaluating a battery as follows. 52.5 mg of positive electrode active material for lithium ion secondary batteries, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm to obtain a positive electrode PE ( An evaluation electrode) was prepared. The produced positive electrode was dried in a vacuum dryer at 120° C. for 12 hours. Then, using this positive electrode, a 2032 type coin-shaped battery was fabricated in a glove box in an Ar atmosphere with a dew point controlled at -80°C.

The Li metal negative electrode uses a negative electrode sheet in which graphite powder with an average particle size of approximately 20 μm punched out into a disk shape of 14 mm in diameter and polyvinylidene fluoride is coated on copper foil, and the electrolyte supports 1M LiPF ₆ . A 3:7 mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Pharmaceutical Co., Ltd.) was used as an electrolyte. A polyethylene porous membrane with a thickness of 25 μm was used as the separator. Further, the coin-shaped battery has a gasket and a wave washer, and is assembled into a coin-shaped battery with a positive electrode can and a negative electrode can. The cycle characteristics indicating the performance of the manufactured coin-type battery were evaluated as follows.

(Cycle characteristics)
Using the above 2032 type coin battery, CC charge to 4.1V at a rate of 2C, rest for 10 minutes, then CC discharge to 3.0V at the same rate, and rest for 10 minutes, for 500 charge/discharge cycles. The capacity retention rate for 500 cycles was calculated by repeatedly measuring the 500th discharge capacity with respect to the initial discharge capacity.

Manufacturing conditions for each example and comparative example will be explained below.

(Example 1)
The first mixed aqueous solution (raw material solution) contains nickel sulfate (nickel concentration: 78.3 g/L), cobalt sulfate (cobalt concentration: 39.1 g/L), and manganese sulfate (manganese concentration: 0.3 g/L). ) was prepared, and a composite solution of nickel sulfate (nickel concentration: 58.7 g/L) and manganese sulfate (manganese concentration: 55.0 g/L) was prepared as a second mixed aqueous solution (raw material solution). Prepared. The metal concentration of each mixed aqueous solution was 2 mol/L.

Put 25L of pure water into a reaction tank (60L), set the temperature inside the tank to 42℃ while stirring in a nitrogen atmosphere (oxygen concentration in the reaction tank below 2% by volume), and add 25L of pure water to it. % sodium hydroxide aqueous solution and 25% by mass aqueous ammonia to adjust the pH value of the liquid in the tank to 12.8 based on the liquid temperature of 25°C and the ammonia concentration in the liquid to 10 g/L, and then react. It was made into a pre-aqueous solution. Here, the first mixed aqueous solution was added at a rate of 130 ml/min, and at the same time, 25% by mass ammonia water and 25% by mass aqueous sodium hydroxide solution were added at a constant rate, and the pH value was adjusted to 12.8 (nucleation Crystallization was performed for 2 minutes and 30 seconds while controlling the pH (nucleation step S10).

After that, only the supply of the 25 mass% sodium hydroxide aqueous solution was temporarily stopped until the pH value reached 11.6 (nucleus growth pH) based on the liquid temperature of 25°C, and after the pH value reached 11.6, it was restarted again. The supply of the 25% by mass sodium hydroxide aqueous solution was restarted, and the pH value was controlled at 11.6 for 2.2 hours in a non-oxidizing atmosphere (first particle growth step S21), in an oxidizing atmosphere (atmospheric atmosphere). After continuing crystallization for 0.2 hours (second particle growth step S22), the atmosphere was switched to a non-oxidizing atmosphere, and the first mixed solution (raw material solution) was switched to the second mixed aqueous solution. Crystallization was continued for 6 hours (third particle growth step S23) and then terminated. After the crystallization was completed, the product was washed with water, filtered, and dried to obtain nickel-cobalt-manganese composite hydroxide particles containing a manganese-rich layer.

The overall composition of the obtained nickel cobalt manganese composite hydroxide particles was measured using an emission spectrometer, and it was confirmed that Ni:Co:Mn=60:20:20. Further, the composition of the manganese-rich layer was confirmed by EDX to be Ni:Co:Mn=50:0:50.

Furthermore, the cross section of the nickel cobalt manganese composite hydroxide particles including the manganese-rich layer was observed by SEM, and the thicknesses of the low-density layer and the manganese-rich layer were measured. The results are shown in Table 1.

Next, the obtained nickel-cobalt-manganese composite hydroxide particles containing a manganese-rich layer and lithium carbonate weighed so that Li/Me = 1.04 were mixed in a shaker mixer device (Willi & Bacchofen (WAB)). A lithium mixture was obtained by thoroughly mixing the mixture using a TURBULA Type T2C (manufactured by Co., Ltd.). This lithium mixture was held and fired at 880° C. for 10 hours in an air stream (oxygen: 21% by volume), and then crushed to obtain lithium nickel cobalt manganese composite oxide particles containing a manganese-rich layer.

The composition of the entire lithium nickel cobalt manganese composite oxide particles including the obtained manganese-rich layer was measured using an emission spectrometer, and it was confirmed that Li:Ni:Co:Mn=104:60:20:20. Further, the composition of the manganese-rich layer was confirmed by EDX to be Li:Ni:Co:Mn=104:50:0:50.

Further, a cross section of the lithium nickel cobalt manganese composite oxide particles including a manganese-rich layer was observed by SEM, and the thicknesses of the void layer and the manganese-rich layer were measured. In addition, a battery was produced as described above, and its cycle characteristics were evaluated. The evaluation results are shown in Table 2.

(Example 2)
The first mixed aqueous solution (raw material solution) is made of nickel sulfate (nickel concentration: 79.5 g/L), cobalt sulfate (cobalt concentration: 36.4 g/L), and manganese sulfate (manganese concentration: 1.5 g/L). , the second mixed aqueous solution (raw material solution) was mixed with nickel sulfate (nickel concentration: 23.5 g/L), cobalt sulfate (cobalt concentration: 17.7 g/L), and manganese sulfate (manganese concentration: 71.5 g/L). ) Nickel-cobalt-manganese composite hydroxide particles containing a manganese-rich layer were obtained in the same manner as in Example 1, except for the following. Lithium-nickel-cobalt-manganese composite oxide particles containing a manganese-rich layer were obtained in the same manner as in Example 1 except that the nickel-cobalt-manganese composite hydroxide particles containing the manganese-rich layer were used. The evaluation results are shown in Tables 1 and 2.

(Example 3)
Lithium nickel cobalt manganese composite oxide particles containing a manganese-rich layer were obtained in the same manner as in Example 1 except that the firing temperature was 830°C. The evaluation results are shown in Table 2.

(Example 4)
Lithium nickel cobalt manganese composite oxide particles containing a manganese-rich layer were obtained in the same manner as in Example 1 except that the firing temperature was 930°C. The evaluation results are shown in Table 2.

(Comparative example 1)
As the raw material solution used, only a composite solution of nickel sulfate (nickel concentration: 70.4 g/L), cobalt sulfate (cobalt concentration: 23.6 g/L), and manganese sulfate (manganese concentration: 22.0 g/L) was used. The nucleation step was performed in a nitrogen atmosphere for 2.5 minutes, and the first, second, and third particle growth steps were performed in a nitrogen atmosphere for 4 hours without using the second mixed aqueous solution. Nickel cobalt manganese composite hydroxide particles were obtained in the same manner as in Example 1 except for the above. Lithium nickel cobalt manganese composite oxide particles were obtained in the same manner as in Example 1 except that these nickel cobalt manganese composite hydroxide particles were used. The evaluation results are shown in Tables 1 and 2.

(Comparative example 2)
A positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that the second particle growth step was performed in a nitrogen atmosphere. The evaluation results are shown in Tables 1 and 2.

(Comparative example 3)
The first mixed aqueous solution (raw material solution) contains nickel sulfate (nickel concentration: 75.5 g/L), cobalt sulfate (cobalt concentration: 26.2 g/L), and manganese sulfate (manganese concentration: 14.7 g/L). ) was prepared, and after 3.4 hours in a non-oxidizing atmosphere before switching the raw material solutions for the nucleation process and particle growth process, switching to an oxidizing atmosphere and continuing crystallization for 0.2 hours, the non-oxidizing atmosphere The atmosphere was changed, and nickel sulfate (nickel concentration: 23.5 g/L) and manganese sulfate (manganese concentration: 87.9 g/L) were crystallized for 0.4 hours as a second mixed aqueous solution (composite solution). Nickel cobalt manganese composite hydroxide particles containing a manganese-rich layer were obtained in the same manner as in Example 1 except for this. Lithium-nickel-cobalt-manganese composite oxide particles containing a manganese-rich layer were obtained in the same manner as in Example 1 except that the nickel-cobalt-manganese composite hydroxide particles containing the manganese-rich layer were used. The evaluation results are shown in Tables 1 and 2.

(Comparative example 4)
The first mixed aqueous solution (raw material solution) contains nickel sulfate (nickel concentration: 87.6 g/L), cobalt sulfate (cobalt concentration: 29.3 g/L), and manganese sulfate (manganese concentration: 0.6 g/L). ) was prepared, and crystallization was continued for 1.4 hours in a non-oxidizing atmosphere before switching the raw material solution for the nucleation process and particle growth process, and then for 0.2 hours after switching to an oxidizing atmosphere. Switch to a neutral atmosphere, and combine nickel sulfate (nickel concentration: 58.7 g/L), cobalt sulfate (cobalt concentration: 19.7 g/L), and manganese sulfate (manganese concentration: 33.6 g/L). Nickel cobalt manganese composite hydroxide particles containing a manganese-rich layer were obtained in the same manner as in Example 1, except that the solution was used as a second mixed aqueous solution (raw material solution) and crystallized for 2.4 hours. Lithium-nickel-cobalt-manganese composite oxide particles containing a manganese-rich layer were obtained in the same manner as in Example 1 except that the nickel-cobalt-manganese composite hydroxide particles containing the manganese-rich layer were used. The evaluation results are shown in Tables 1 and 2.

(evaluation)
It can be seen that Examples 1 to 4 have high cycle characteristics and high durability by having a manganese-rich layer and a layered void layer inside the particles. On the other hand, it can be seen that Comparative Example 1 did not have a manganese-rich layer, and Comparative Example 2 did not have high durability because the manganese-rich layer disappeared due to compositional diffusion inside the particles due to firing. Although Comparative Example 3 has a manganese-rich layer, it can be seen that the durability improvement effect is small because the thickness of the low-density layer and the void layer is less than 1% of the secondary particle diameter. Although Comparative Example 4 has a manganese-rich layer, the thickness of the manganese-rich layer exceeds 10% of the secondary particle diameter, so it can be seen that the effect of improving cycle characteristics is small.

As described above, according to the present invention, it was possible to provide a nickel composite hydroxide, which is a precursor of a positive electrode active material for lithium ion secondary batteries, which prevents elemental diffusion in a manganese-rich layer and has excellent cycle characteristics. . Furthermore, it was possible to provide a method for easily producing the nickel composite hydroxide with high productivity. Furthermore, it was possible to provide a positive electrode active material for a lithium ion secondary battery with excellent cycle characteristics, a method for producing the same, and a lithium ion secondary battery.

Although each embodiment and each example of the present invention has been described in detail as above, those skilled in the art will appreciate that many modifications can be made without substantially departing from the novelty and effects of the present invention. , it will be easy to understand. Therefore, all such modifications are included within the scope of the present invention.

For example, a term that appears at least once in the specification or drawings together with a different term with a broader or synonymous meaning may be replaced by that different term anywhere in the specification or drawings. The book also includes nickel composite hydroxide, methods for producing nickel composite hydroxide, positive electrode active materials for lithium ion secondary batteries, methods for manufacturing positive electrode active materials for lithium ion secondary batteries, and the structure and operation of lithium ion secondary batteries. The present invention is not limited to those described in each embodiment and each example, and various modifications can be made.

S10 nucleation step, S20 particle growth step, S21 first particle growth step, S22 second particle growth step, S23 third particle growth step, S30 lithium mixing step, S40 firing step

Claims (8)

A nickel composite hydroxide consisting of secondary particles in which a plurality of primary particles aggregate with each other,
Nickel, cobalt, manganese, and element M are Ni:Co:Mn:M=1-x1-y1-z1:x1:y1:z1 (However, M is a transition metal element other than Ni, Co, or Mn, or a group 2 element. , and at least one element selected from the group consisting of Group 13 elements, x1 is 0.15≦x1≦0.25, y1 is 0.15≦y1≦0.25, and z1 is 0≦z1≦0. .1 and satisfies 0.3≦x1+y1+z1≦0.5),
The secondary particle has a manganese-rich layer from the particle surface toward the inside of the particle, and a layered low-density layer between the high-density center part of the secondary particle and the manganese-rich layer,
The manganese-rich layer contains nickel, cobalt, manganese, and the element M Ni:Co:Mn:M=1-x2-y2-z2:x2:y2:z2 (where M is a transition other than Ni, Co, or Mn). At least one element selected from the group consisting of metal elements, Group 2 elements, and Group 13 elements, and x2 and y2 satisfy x2=0 and y2=1, or y2/((1-x2- y2-z2)+x2)≧1, and z2 is within the range of 0≦z2≦0.1),
The thickness of the manganese-rich layer is 1% or more and less than 10% with respect to the diameter of the secondary particles, and the thickness of the low-density layer is 1% or more with respect to the diameter of the secondary particles. A nickel composite hydroxide characterized by having a content of 10% or less. In the particle size distribution measured by laser diffraction scattering method, the volume average particle diameter (Mv) is 4 μm or more and 10 μm or less,
The particle size dispersion index [(D90-D10)/Mv] is calculated from the cumulative 90 volume % diameter (D90), the cumulative 10 volume % diameter (D10), and the volume average particle diameter (Mv). The nickel composite hydroxide according to claim 1, characterized in that it is 0.60 or less. A method for producing a nickel composite hydroxide comprising secondary particles in which a plurality of primary particles aggregate with each other,
The first mixed aqueous solution containing at least one of a nickel salt, a cobalt salt, and a manganese salt is heated to a pH value of 12.5 or more based on a liquid temperature of 25° C. in a non-oxidizing atmosphere with an oxygen concentration of less than 5% by volume. a nucleation step in which nuclei are generated by adjusting the
Adjust the pH value of the slurry containing the nuclei formed in the nucleation step to a range of 10.5 to 12.5, based on a liquid temperature of 25° C., and lower than the pH value in the nucleation step. a particle growth step of performing particle growth;
The particle growth step includes a first particle growth step, a second particle growth step, and a third particle growth step,
In the first particle growth step, the first mixed aqueous solution is supplied to the mixed aqueous solution obtained in the nucleation step in a non-oxidizing atmosphere with an oxygen concentration of less than 5% by volume, to form a high-density particle . form the center of the particle,
In the second particle growth step, the oxygen concentration is switched to an oxidizing atmosphere of 5% by volume or more, and the first mixed aqueous solution is supplied to the mixed aqueous solution obtained in the first particle growth step, Forms a layered low-density layer,
In the third particle growth step, the oxygen concentration is switched to an oxidizing atmosphere of less than 5% by volume, and nickel, cobalt, manganese, and element M are added to the mixed aqueous solution obtained in the second particle growth step. Co:Mn:M=1-x2-y2-z2:x2:y2:z2 (where M is selected from the group consisting of Ni, Co, transition metal elements other than Mn, group 2 elements, and group 13 elements) is at least one element, and x2 and y2 satisfy x2=0 and y2=1, or satisfy an atomic ratio of y2/((1-x2-y2-z2)+x2)≧1). Supplying a mixed aqueous solution of 2 to form a manganese-rich layer,
A method for producing a nickel composite hydroxide, wherein the thickness of the manganese-rich layer is 1% or more and less than 10% of the diameter of the secondary particles. 4. The method for producing a nickel composite hydroxide according to claim 3, wherein in the particle growth step, ammonia whose concentration is adjusted to 5 g/L or more and 20 g/L or less is added to the slurry. A positive electrode active material for a lithium ion secondary battery composed of a lithium nickel composite oxide consisting of secondary particles in which a plurality of primary particles aggregate with each other and having a hexagonal layered structure,
The lithium-nickel composite oxide contains lithium, nickel, cobalt, manganese, and element M as Li:Ni:Co:Mn:M=1+u:1-x1-y1-z1:x1:y1:z1 (where u is - 0.05≦u≦0.50, 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 x1 is 0. 15≦x1≦0.25, y1 is 0.15≦y1≦0.25, z1 is included in an atomic ratio of 0≦z1≦0.1),
The secondary particles have a manganese-rich layer from the particle surface toward the inside of the particles, and a layered void layer between the central part of the secondary particles and the manganese-rich layer,
The manganese-rich layer contains lithium, nickel, cobalt, manganese, and element M in a manner that Li:Ni:Co:Mn:M=1+u:1-x2-y2-z2:x2:y2:z2 (where u is -0. 05≦u≦0.50, 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 x2 and y2 are x2 =0 and y2=1, or y2/((1-x2-y2-z2)+x2)≧1, and z2 is within the range of 0≦z2≦0.1). ,
The thickness of the manganese-rich layer is 1% or more and less than 10% with respect to the diameter of the secondary particles, and the thickness of the void layer is 1% or more and less than 10% with respect to the diameter of the secondary particles. % or less,
A positive electrode active material for a lithium ion secondary battery, characterized in that the crystallite diameter calculated from the peak of the (003) plane by X-ray diffraction measurement is 100 nm or more and 150 nm or less. In the particle size distribution measured by laser diffraction scattering method, the volume average particle diameter (Mv) is 4 μm or more and 10 μm or less,
The particle size dispersion index [(D90-D10)/Mv] is calculated from the cumulative 90 volume % diameter (D90), the cumulative 10 volume % diameter (D10), and the volume average particle diameter (Mv). The positive electrode active material for a lithium ion secondary battery according to claim 5, wherein the positive electrode active material is 0.60 or less. A method for producing a positive electrode active material for a lithium ion secondary battery composed of a lithium nickel composite oxide consisting of secondary particles in which a plurality of primary particles aggregate with each other and having a hexagonal layered structure, the method comprising:
a lithium mixing step of mixing a nickel composite hydroxide and a lithium compound to form a lithium mixture;
a firing step of firing the lithium mixture at a temperature of 800°C or more and 950°C or less in an oxidizing atmosphere,
The nickel composite hydroxide contains nickel, cobalt, manganese, and the element M as Ni:Co:Mn:M=1-x1-y1-z1:x1:y1:z1 (however, M is other than Ni, Co, and Mn). is at least one element selected from the group consisting of transition metal elements, group 2 elements, and group 13 elements, x1 is 0.15≦x1≦0.25, and y1 is 0.15≦y1≦0.25. , z1 is within the range of 0≦z1≦0.1 and satisfies 0.3≦x1+y1+z1≦0.5.)
The nickel composite hydroxide includes a manganese-rich layer from the particle surface of the secondary particle toward the inside of the particle, and a layered low-density layer between the high-density central part of the secondary particle and the manganese-rich layer. have,
The manganese-rich layer contains nickel, cobalt, manganese, and the element M Ni:Co:Mn:M=1-x2-y2-z2:x2:y2:z2 (where M is a transition other than Ni, Co, or Mn). At least one element selected from the group consisting of metal elements, Group 2 elements, and Group 13 elements, and x2 and y2 satisfy x2=0 and y2=1, or y2/((1-x2- y2-z2)+x2)≧1, and z2 is within the range of 0≦z2≦0.1),
The thickness of the manganese-rich layer is 1% or more and less than 10% with respect to the diameter of the secondary particles, and the thickness of the low-density layer is 1% or more with respect to the diameter of the secondary particles. A method for producing a positive electrode active material for a lithium ion secondary battery, characterized in that the content is 10% or less. A lithium ion secondary battery comprising at least a positive electrode comprising the positive electrode active material for a lithium ion secondary battery according to claim 5 or 6.

Images