阅读说明：本技术 镍复合氢氧化物、镍复合氢氧化物的制造方法、锂离子二次电池用正极活性物质、锂离子二次电池用正极活性物质的制造方法及锂离子二次电池 (Nickel composite hydroxide, method for producing nickel composite hydroxide, positive electrode active material for lithium ion secondary battery, method for producing positive electrode active materi) 是由 山内充 伊藤泰 小向哲史 于 2020-04-24 设计创作，主要内容包括：本发明的目的在于提供作为正极电阻或循环特性优异的锂离子二次电池用正极活性物质的前体的镍复合氢氧化物。以Ni:Co:Mn:M＝1-x1-y1-z1:x1:y1:z1(其中,M为选自由Ni、Co、Mn以外的过渡金属元素、第2族元素以及第13族元素组成的组中的至少一种元素,x1为0.15≤x1≤0.25,y1为0.15≤y1≤0.25,z1为0≤z1≤0.1)的原子比包含镍、钴、锰和元素M,从二次粒子的粒子表面朝向粒子内部具有富钴层或富锰层且在二次粒子的中央部与富钴层或富锰层之间具有层状的低密度层,富钴层或富锰层的厚度相对于二次粒子的直径为1％以上10％以下,并且低密度层的厚度相对于二次粒子的直径为1％以上10％以下。(The purpose of the present invention is to provide a nickel composite hydroxide which is a precursor of a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance and cycle characteristics. The atomic ratio of Ni to Co to Mn to M is 1-x1-y1-z1 to x1 to y1 to z1 (wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co and Mn, group 2 elements and group 13 elements, x1 is 0.15. ltoreq. x 1. ltoreq.0.25, y1 is 0.15. ltoreq. y 1. ltoreq.0.25, and z1 is 0. ltoreq. z 1. ltoreq.0.1), contains nickel, cobalt, manganese and the element M, and has a cobalt-rich layer or 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 central portion of the secondary particle and the cobalt-rich layer or the manganese-rich layer, the thickness of the cobalt-rich layer or the manganese-rich layer being 1% or more and 10% or less with respect to the diameter of the secondary particle, and the thickness of the low-density layer being 1% or more and 10% or less with respect to the diameter of the secondary particle.)

1. A nickel composite hydroxide comprising secondary particles obtained by aggregating a plurality of primary particles, characterized in that,

the atomic ratio of Ni, Co, Mn and M is 1-x1-y1-z1, x1, y1 and z1 comprises nickel, cobalt, manganese and an element M, wherein M is at least one element selected from the group consisting of transition metal elements except Ni, Co and Mn, group 2 elements and group 13 elements, x1 is 0.15-0.25 of x1, y1 is 0.15-0.25 of y1, z1 is 0-0.1 of z1,

a low-density layer having a cobalt-rich layer or a manganese-rich layer from the particle surface of the secondary particle toward the inside of the particle and having a layer shape between the central portion of the secondary particle and the cobalt-rich layer or the manganese-rich layer,

the cobalt-rich layer contains nickel, cobalt, manganese and an element M in an atomic ratio of Ni: Co: Mn: M ═ 1-x2-y2-z2: x2: y2: z2, wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, group 2 elements and group 13 elements, x2 and y2 satisfy x2 ═ 1 and y2 ═ 0 or satisfy x2/((1-x2-y2-z2) + y2) ≥ 1, z2 is in a range of 0. ltoreq. z 2. ltoreq.0.1,

The manganese-rich layer contains nickel, cobalt, manganese and an element M in an atomic ratio of Ni: Co: Mn: M ═ 1-x2-y2-z2: x2: y2: z2, wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, group 2 elements and group 13 elements, x2 and y2 satisfy x2 ═ 0 and y2 ═ 1 or satisfy y2/((1-x2-y2-z2) + x2) ≥ 1, z2 is in a range of 0. ltoreq. z 2. ltoreq.0.1,

the thickness of the cobalt-rich layer or the manganese-rich layer is 1% or more and 10% or less with respect to the diameter of the secondary particle, and the thickness of the low-density layer is 1% or more and 10% or less with respect to the diameter of the secondary particle.

2. The nickel composite hydroxide according to claim 1, wherein the volume average particle diameter Mv is 4 μm or more and 10 μm or less in a particle size distribution measured by a laser diffraction scattering method,

the [ (D90-D10)/Mv ] which is calculated from the cumulative 90 vol% diameter D90, the cumulative 10 vol% diameter D10 and the volume average particle diameter Mv and which indicates the deviation index of the particle diameter is 0.60 or less.

3. A method for producing a nickel composite hydroxide, which is a method for producing a nickel composite hydroxide comprising secondary particles in which a plurality of primary particles are aggregated, comprising:

A nucleus generation step of adjusting a pH value of a first mixed aqueous solution containing at least one of a nickel salt, a cobalt salt, and a manganese salt to 12.5 or more in a non-oxidizing atmosphere having an oxygen concentration of less than 5% by volume based on a liquid temperature of 25 ℃ to generate nuclei; and

a particle growth step of adjusting a pH value of the slurry containing the nuclei formed in the nuclei production step to a range of 10.5 to 12.5 inclusive with respect to a liquid temperature of 25 ℃ and lower than the pH value in the nuclei production step to thereby grow particles,

the particle growth step includes a first particle growth step, a second particle growth step, and a third particle growth step of forming a cobalt-rich layer or a manganese-rich layer from the particle surface of the secondary particle toward the inside of the particle,

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 having an oxygen concentration of less than 5% by volume to form a particle center portion,

in the second particle growth step, the oxygen concentration is switched to an oxidizing atmosphere of 5 vol% or more, the first mixed aqueous solution is supplied to the mixed aqueous solution obtained in the first particle growth step, and a layered low-density layer is formed,

In the third particle growth step for forming the cobalt-rich layer, the oxygen concentration is switched to an oxidizing atmosphere of less than 5% by volume, and a second mixed aqueous solution containing nickel, cobalt, manganese and an element M in an atomic ratio of Ni: Co: Mn: M1-x 2-y2-z2: x2: y2: z2 is supplied to the mixed aqueous solution obtained in the second particle growth step to form the cobalt-rich layer, wherein M is at least one element selected from the group consisting of Ni, Co, and Mn, a transition metal element other than Mn, a group 2 element and a group 13 element, x2 and y2 satisfy x 2-1 and y 2-0, or satisfy x2 ((1-x2-y2-z2) + y2) ≥ 1, and z2 is in the range of 0.1 or 0.42 ≤ z2, or in the range of 0.1

In the third particle growth step for forming the manganese-rich layer, the oxygen concentration is switched to an oxidizing atmosphere of less than 5% by volume, and a second mixed aqueous solution containing nickel, cobalt, manganese and an element M in an atomic ratio of Ni: Co: Mn: M ═ 1-x2-y2-z2: x2: y2: z2 is supplied to the mixed aqueous solution obtained in the second particle growth step to form the manganese-rich layer, wherein M is at least one element selected from the group consisting of Ni, Co, a transition metal element other than Mn, a group 2 element and a group 13 element, and x2 and y2 satisfy x2 ═ 0 and y2 ═ 1 or satisfy y2 ((1-x2-y2-z2) + x2) ≥ 1.

4. The method of producing a nickel composite hydroxide according to claim 3, wherein ammonia is added to the slurry in a concentration of 5g/L to 20g/L in the particle growth step.

5. A positive electrode active material for a lithium ion secondary battery, which is a positive electrode active material for a lithium ion secondary battery comprising a lithium nickel composite oxide, wherein the lithium nickel composite oxide comprises secondary particles in which a plurality of primary particles are aggregated with each other, and has a hexagonal layered structure,

the lithium-nickel composite oxide contains lithium, nickel, cobalt, manganese and an element M in an atomic ratio of Li, Ni, Co, Mn, M being 1+ u:1-x1-y1-z1: x1: y1: z1, wherein u is-0.05 or more and u is 0.50 or less, 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 or more and x1 or less and 0.25, y1 is 0.15 or more and y1 or less and 0.25 or less, z1 is 0 or more and z1 or less and 0.1,

a cobalt-rich layer or a manganese-rich layer is provided from the particle surface of the secondary particle toward the inside of the particle, and a layered void layer is provided between the central portion of the secondary particle and the cobalt-rich layer or the manganese-rich layer,

the cobalt-rich layer contains lithium, nickel, cobalt, manganese and an element M in an atomic ratio of Li: Ni: Co: Mn: M ≦ 1+ u:1-x2-y2-z2: x2: y2: z2, wherein 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 ≦ 1 and y2 ≦ 0, or satisfy x2/((1-x2-y2-z2) + y2 ≦ 1), z2 is in a range of 0 ≦ z2 ≦ 0.1,

The manganese-rich layer contains lithium, nickel, cobalt, manganese and an element M in an atomic ratio of Li: Ni: Co: Mn: M ≦ 1+ u:1-x2-y2-z2: x2: y2: z2, wherein 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 satisfy y2/((1-x2-y2-z2) + x2 ≦ 1), z2 is in a range of 0 ≦ z2 ≦ 0.1,

the thickness of the cobalt-rich layer or the manganese-rich layer is 1% or more and 10% or less with respect to the diameter of the secondary particle, and the thickness of the void layer is 1% or more and 10% or less with respect to the diameter of the secondary particle,

the crystal grain diameter calculated from the peak of the (003) plane obtained by X-ray diffraction measurement is 100nm to 150 nm.

6. The positive electrode active material for a lithium ion secondary battery according to claim 5, wherein the volume average particle diameter Mv in the particle size distribution measured by a laser diffraction/scattering method is 4 μm or more and 10 μm or less,

the [ (D90-D10)/Mv ] which is calculated from the cumulative 90 vol% diameter D90, the cumulative 10 vol% diameter D10 and the volume average particle diameter Mv and which indicates the deviation index of the particle diameter is 0.60 or less.

7. A method for producing a positive electrode active material for a lithium ion secondary battery, the positive electrode active material being composed of a lithium nickel composite oxide, the lithium nickel composite oxide being composed of secondary particles in which a plurality of primary particles are aggregated with each other and having a hexagonal layered structure, the method comprising:

a lithium mixing step of mixing a nickel composite hydroxide with a lithium compound to form a lithium mixture; and

a firing step of firing the lithium mixture in an oxidizing atmosphere at a temperature of 800 ℃ to 950 ℃,

the nickel composite hydroxide comprises nickel, cobalt, manganese and an element M in an atomic ratio of Ni, Co, Mn, M being 1-x1-y1-z1: x1: y1: z1, wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co and Mn, group 2 elements and group 13 elements, x1 is 0.15-x 1-0.25, y1 is 0.15-y 1-0.25, z1 is 0-z 1-0.1,

the nickel composite hydroxide has a cobalt-rich layer or a manganese-rich layer from the particle surface of the secondary particle toward the inside of the particle, and has a layered low-density layer between the central portion of the secondary particle and the cobalt-rich layer or the manganese-rich layer,

The cobalt-rich layer contains nickel, cobalt, manganese and an element M in an atomic ratio of Ni: Co: Mn: M ═ 1-x2-y2-z2: x2: y2: z2, wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, group 2 elements and group 13 elements, x2 and y2 satisfy x2 ═ 1 and y2 ═ 0 or satisfy x2/((1-x2-y2-z2) + y2) ≥ 1, z2 is in a range of 0. ltoreq. z 2. ltoreq.0.1,

the manganese-rich layer contains nickel, cobalt, manganese and an element M in an atomic ratio of Ni: Co: Mn: M ═ 1-x2-y2-z2: x2: y2: z2, wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, group 2 elements and group 13 elements, x2 and y2 satisfy x2 ═ 0 and y2 ═ 1 or satisfy y2/((1-x2-y2-z2) + x2) ≥ 1, z2 is in a range of 0. ltoreq. z 2. ltoreq.0.1,

the thickness of the cobalt-rich layer or the manganese-rich layer is 1% or more and 10% or less with respect to the diameter of the secondary particle, and the thickness of the low-density layer is 1% or more and 10% or less with respect to the diameter of the secondary particle.

8. A lithium ion secondary battery comprising at least a positive electrode containing the positive electrode active material for a lithium ion secondary battery according to claim 5 or 6.

Technical Field

The present invention relates to a nickel composite hydroxide which is a precursor of a positive electrode active material for a lithium ion secondary battery, a method for producing the same, a positive electrode active material for a secondary battery using the nickel composite hydroxide as a raw material, a method for producing the same, and a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery as a positive electrode material. The present application claims priority on the basis of japanese patent application No. 2019-086217, which was filed in japan on 2019, month 4 and 26, and japanese patent application No. 2019-086218, which was filed in japan on 2019, month 4 and 26, which is incorporated by reference into the present application.

Background

In recent years, with the spread of portable devices such as mobile phones and notebook-size personal computers, development of small-sized and lightweight secondary batteries having high energy density has been strongly desired. As such a secondary battery, there is a lithium ion secondary battery using lithium, a lithium alloy, a metal oxide, or carbon as a negative electrode.

In a positive electrode material for a lithium ion secondary battery, a lithium composite oxide is used as a positive electrode active material. Lithium cobalt composite oxides are relatively easy to synthesize, and lithium ion secondary batteries using lithium cobalt composite oxides as the positive electrode material can obtain a high voltage of 4V class, and therefore, are expected as materials for practical use in secondary batteries having a high energy density. As for the lithium cobalt composite oxide, research and development for achieving excellent initial capacity characteristics, cycle characteristics in a secondary battery have been performed, and various results have been obtained.

However, since the lithium cobalt composite oxide uses a rare and expensive cobalt compound as a raw material, it causes an increase in the cost of a positive electrode material and a secondary battery. The unit price per capacity of a lithium ion secondary battery using the lithium cobalt composite oxide is about 4 times that of a nickel-hydrogen battery, and thus applicable uses are very limited. Therefore, from the viewpoint of further weight reduction and size reduction of portable devices, it is necessary to reduce the cost of the positive electrode active material and to manufacture a lithium ion secondary battery that is cheaper.

Examples of the positive electrode active material that can replace the lithium cobalt composite oxide include lithium nickel composite oxide (LiNiO)₂) Lithium nickel cobalt manganese composite oxide (LiNi)_1/3Co_1/3Mn_1/3O₂) And the like. Lithium nickel composite oxides exhibit a high voltage similar to that of lithium cobalt composite oxides and a lower potential than lithium cobalt composite oxides, and thus are less likely to cause problems due to oxidation of an electrolytic solution, and therefore, are expected as positive electrode active materials capable of realizing a high capacity of a secondary battery.

For example, patent document 1 proposes a method having an empirical formula: li_xM’_zNi_1-yM”_yO₂The core of (3) and the composition having a coating layer with a cobalt/nickel ratio larger than that of the core are excellent in thermal safety and cycle efficiency.

Further, patent document 2 proposes that the basicity of the active material is reduced and gelation at the time of forming the electrode is suppressed by providing a manganese-rich layer in the case.

Further, patent documents 2 and 3 propose nickel manganese composite hydroxide particles and nickel cobalt manganese composite hydroxide particles as precursors of positive electrode active materials for nonaqueous electrolyte secondary batteries, which have high capacity and can achieve high output.

Documents of the prior art

Patent document

Patent document 1: japanese Kokai publication Hei-2004-533104

Patent document 2: japanese patent laid-open No. 2012 and 256435

Patent document 3: japanese patent laid-open publication No. 2011-116580

Disclosure of Invention

Problems to be solved by the invention

However, patent document 1 does not describe the positive electrode resistance, and does not describe the amount of composition tilt. In patent document 2, no gap is introduced between the manganese-rich layer of the outer shell and the core layer, and element diffusion during firing cannot be sufficiently suppressed, and further improvement in cycle characteristics is required. Further, as a positive electrode of a secondary battery, output characteristics having a low positive electrode resistance and higher than a conventional level are required, or as a positive electrode of a secondary battery, improvement of cycle characteristics at higher than a conventional level is required.

In view of the above-described problems, an object of the present invention is to provide a nickel composite hydroxide which is a precursor of a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance, to improve output characteristics, or to provide a nickel composite hydroxide which is a precursor of a positive electrode active material for a lithium ion secondary battery having excellent cycle characteristics by preventing diffusion of an element in a manganese-rich layer. Further, it is an object to provide a method for easily producing the above 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 having excellent positive electrode resistance, a method for producing the same, and a lithium ion secondary battery.

Means for solving the problems

The nickel composite hydroxide according to one embodiment of the present invention is a nickel composite hydroxide including secondary particles in which a plurality of primary particles are aggregated with each other, wherein the nickel, cobalt, manganese, and element M are contained in an atomic ratio of Ni: Co: Mn: M1-x 1-y1-z1: x1: y1: z1 (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, x1 is 0.15. ltoreq. x 1. ltoreq. 0.25, y1 is 0.15. ltoreq. y 1. ltoreq. 0.25, and z1 is 0. ltoreq. z 1. ltoreq. 0.1), the cobalt-rich layer or the manganese-rich layer is provided from the particle surface of the secondary particles toward the particle interior of the particle, and the cobalt-rich layer or the manganese-rich layer is provided between the central portion of the secondary particle and the cobalt-rich layer or the manganese-rich layer, and the cobalt-rich layer is provided with Ni: Co: Mn: x 39 2 6: z2: z 3: z 4626, m is at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, group 2 elements, and group 13 elements, x2 and y2 satisfy x2 ≧ 1 and y2 ≧ 0, or satisfy x2/((1-x2-y2-z2) + y2) ≧ 1, and z2 is in the range of 0 ≦ z2 ≦ 0.1), including nickel, cobalt, manganese, and element M, the aforementioned manganese-rich layer includes Ni: Co: Mn: 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, Mn, group 2 elements, and group 13 elements, and x2 and y2 satisfy x2 ≧ 0 and y2 ≦ 1, or y2 ≦ 2 (x 2 — 2) ((x 361-x 2). ) The atomic ratio of (a) includes nickel, cobalt, manganese, and an element M, the thickness of the cobalt-rich layer or the manganese-rich layer is 1% or more and 10% or less with respect to the diameter of the secondary particle, and the thickness of the low-density layer is 1% or more and 10% or less with respect to the diameter of the secondary particle.

Thus, a nickel composite hydroxide which is a precursor of a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance and cycle characteristics can be provided.

In this case, in the particle size distribution measured by the laser diffraction scattering method, the volume average particle diameter (Mv) is 4 μm to 10 μm, and [ (D90-D10)/Mv ] indicating the deviation index of the particle diameter calculated from the cumulative 90 vol% diameter (D90), the cumulative 10 vol% diameter (D10) and the volume average particle diameter (Mv) may be 0.60 or less.

Thus, high output characteristics with little variation and excellent cycle characteristics can be obtained.

In this case, one aspect of the present invention is a method for producing a nickel composite hydroxide including secondary particles in which a plurality of primary particles are aggregated with each other, the method including: a nucleus generation step of adjusting a pH value of a first mixed aqueous solution containing at least one of a nickel salt, a cobalt salt, and a manganese salt to 12.5 or more in a non-oxidizing atmosphere having an oxygen concentration of less than 5% by volume based on a liquid temperature of 25 ℃ to generate nuclei; and a particle growth step of performing particle growth by adjusting a pH value of the slurry containing the nuclei formed in the nucleus formation step based on a liquid temperature of 25 ℃ to a range of 10.5 to 12.5 inclusive and lower than the pH value in the nucleus formation step, wherein the particle growth step includes a first particle growth step of forming a cobalt-rich layer or a manganese-rich layer from particle surfaces of the secondary particles toward particle interiors, a second particle growth step of supplying the first mixed aqueous solution to the mixed aqueous solution obtained in the nucleus formation step in a non-oxidizing atmosphere having an oxygen concentration of less than 5% by volume to form a particle center portion, and a third particle growth step of switching the oxygen concentration to an oxidizing atmosphere having an oxygen concentration of 5% by volume or higher in the second particle growth step, supplying the first mixed aqueous solution to the mixed aqueous solution obtained in the first particle growth step to form a layered low-density layer, switching the oxygen concentration to an oxidizing atmosphere of less than 5% by volume in the third particle growth step to form the cobalt-rich layer, supplying the mixed aqueous solution obtained in the second particle growth step with Ni: Co: Mn: M: 1-x2-y2-z2: x2: y2: z2 (where M is at least one element selected from the group consisting of Ni, Co, Mn, transition metal elements other than Ni, Co, Mn, group 2 elements, and group 13 elements, x2 and y2 satisfy x2 ═ 1 and y2 ═ 0, or satisfy x2/((1-x2-y2-z2) + y2) ≥ 1, z2 is in the range of 0.1.6763), cobalt and a second mixed aqueous solution containing nickel and M, where z contains manganese and z2, in the third particle growth step for forming the manganese-rich layer, 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 supplied with a second mixed aqueous solution containing nickel, cobalt, manganese, and an element M at an atomic ratio of 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 satisfy y2/((1-x2-y2-z2) + x2) ≥ 1), to form the manganese-rich layer.

Thus, a method for producing a nickel composite hydroxide that is a precursor of a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance and cycle characteristics can be provided with high productivity and with ease.

In this case, in one embodiment of the present invention, ammonia may be added to the slurry in a concentration adjusted to a range of 5g/L to 20g/L in the particle growth step.

In this way, since ammonia functions as a complexing agent, the solubility of the metal ions is kept constant, primary particles are uniformized, and variation in particle size of the nickel composite hydroxide can be prevented. In addition, the composition of the nickel composite hydroxide can be prevented from deviating.

In this case, one embodiment of the present invention is a positive electrode active material for a lithium ion secondary battery comprising a lithium nickel composite oxide having a hexagonal layered structure and comprising secondary particles in which a plurality of primary particles are aggregated, wherein the lithium nickel composite oxide comprises Li, Ni, Co, Mn, M, 1+ u, 1-x1-y1-z1, x1, y1, z1 (wherein u is-0.05. ltoreq. u.ltoreq.0.50, M is at least one element selected from the group consisting of Ni, Co, transition metal elements other than Mn, group 2 elements, and group 13 elements, x1 is 0.15. ltoreq. x 1. ltoreq.0.25, y1 is 0.15. ltoreq. y 1. ltoreq.0.25, z1 is 0 z 1. ltoreq.1), and the lithium, nickel, manganese and M are contained in an atomic ratio such that the lithium, cobalt, manganese and M are contained in the secondary particles from the surface layer or the inner part of the secondary particles, and the cobalt-rich layer or the cobalt-rich layer of the secondary particles A layered void layer, wherein the cobalt-rich layer contains Li, Ni, Co, Mn, M, 1+ u:1-x2-y2-z2: x2: y2: z2 (wherein u is-0.05. ltoreq. u.ltoreq.0.50, M is at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, group 2 elements, and group 13 elements, x2 and y2 satisfy x 2. 1 and y 2. ltoreq.0, or satisfy x2/((1-x2-y2-z2) + y 2. gtoreq.1, z2 is in the range of 0. ltoreq. z 2. ltoreq.0.1) and an element M, wherein the manganese-rich layer contains Li, Ni, Co, Mn, M, 1+ u:1-x2-y 2: 24. ltoreq.24: 24. y.9, z 639, and at least one element selected from the group 13 elements other than Ni, z 639, z 599, and z 599, x2 and y2 satisfy X2 and y2 are 1, or satisfy y2/((1-X2-y2-z2) + X2) ≥ 1, z2 is in the range of 0 ≤ z2 ≤ 0.1) an atomic ratio including lithium, nickel, cobalt, manganese, and an element M, a thickness of the cobalt-rich layer or the manganese-rich layer is 1% or more and 10% or less with respect to a diameter of the secondary particle, a thickness of the void layer is 1% or more and 10% or less with respect to a diameter of the secondary particle, and a crystal grain diameter calculated from a peak of a (003) plane obtained by X-ray diffraction measurement is 100nm or more and 150nm or less.

Thus, a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance and cycle characteristics can be provided.

In this case, 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 [ (D90-D10)/Mv ] indicating the deviation index of the particle diameter calculated from the cumulative 90 vol% diameter (D90), the cumulative 10 vol% diameter (D10) and the volume average particle diameter (Mv) may be 0.60 or less.

Thus, high output characteristics with little variation and excellent cycle characteristics can be obtained.

In this case, one aspect of the present invention is a method for producing a positive electrode active material for a lithium ion secondary battery, the positive electrode active material being composed of a lithium nickel composite oxide having a hexagonal layered structure and being composed of secondary particles in which a plurality of primary particles are aggregated with each other, the method comprising: a lithium mixing step of mixing a nickel composite hydroxide with a lithium compound to form a lithium mixture; and a firing step of firing the lithium mixture in an oxidizing atmosphere at a temperature of 800 ℃ to 950 ℃, wherein the nickel composite hydroxide contains nickel, cobalt, manganese, and an element M in an atomic ratio of Ni: Co: Mn: M1-x 1-y1-z1: x1: y1: z1 (wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co, and Mn, group 2 elements, and group 13 elements, x1 is 0.15. ltoreq. x 1. ltoreq. 0.25, y1 is 0.15. ltoreq. y 1. ltoreq. 0.25, and z1 is 0. ltoreq. z 1. ltoreq. 0.1) and has a cobalt-rich layer or a manganese-rich layer from the particle surface of the secondary particle toward the particle interior and a layered low-density layer between the central portion of the secondary particle and the cobalt-rich layer or the manganese-rich layer, and the cobalt-rich layer is Ni: Mn: x 395961-y 2: z2, m is at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, group 2 elements, and group 13 elements, x2 and y2 satisfy x2 ≧ 1 and y2 ≧ 0, or satisfy x2/((1-x2-y2-z2) + y2) ≧ 1, and z2 is in the range of 0 ≦ z2 ≦ 0.1), including nickel, cobalt, manganese, and element M, the aforementioned manganese-rich layer includes Ni: Co: Mn: 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, Mn, group 2 elements, and group 13 elements, and x2 and y2 satisfy x2 ≧ 0 and y2 ≦ 1, or y2 ≦ 2 (x 2 — 2) ((x 361-x 2). ) The atomic ratio of (a) includes nickel, cobalt, manganese, and an element M, the thickness of the cobalt-rich layer or the manganese-rich layer is 1% or more and 10% or less with respect to the diameter of the secondary particle, and the thickness of the low-density layer is 1% or more and 10% or less with respect to the diameter of the secondary particle.

Thus, a method for producing a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance and cycle characteristics can be provided.

In one aspect of the present invention, a lithium ion secondary battery including a positive electrode containing the positive electrode active material for a lithium ion secondary battery can be produced.

Thus, a lithium ion secondary battery including a positive electrode containing a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance and cycle characteristics can be provided.

Effects of the invention

According to the present invention, a nickel composite hydroxide which is a precursor of a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance and cycle characteristics can be provided. Further, a method for easily producing the above nickel composite hydroxide with high productivity can be provided. Further, a positive electrode active material for a lithium ion secondary battery excellent in positive electrode resistance and cycle characteristics, a method for producing the same, and a lithium ion secondary battery can be provided.

Drawings

Fig. 1 is a process diagram showing an overview of a method for producing a nickel composite hydroxide according to an embodiment of the present invention.

Fig. 2 is a process diagram showing an overview of a method for producing a positive electrode active material for a lithium-ion secondary battery according to an embodiment of the present invention.

Detailed Description

In order to solve the above problems, the present inventors have made intensive studies on a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance, and as a result, have obtained the following findings: the positive electrode active material has an inclined composition, so that the cobalt content in the vicinity of the surface is higher than that in the inside, and a layered void layer is introduced between the particle center and the cobalt-rich layer, whereby the positive electrode has excellent resistance. Further, as a result of intensive studies on a positive electrode active material for a lithium ion secondary battery having excellent cycle characteristics, the following findings were obtained: the positive electrode active material has an inclined composition, so that the manganese content in the vicinity of the surface is higher than that in the inside, and a layered void layer is introduced between the particle center and the manganese-rich layer, thereby providing excellent cycle characteristics. Further, the present inventors have obtained an insight that by introducing a void layer between layers having different compositions, diffusion of the composition inside the particles during firing can be suppressed, and a positive electrode active material having an inclined composition can be obtained without limiting the firing temperature, and have completed the present invention. Hereinafter, preferred embodiments of the present invention will be described.

The embodiments described below are not unreasonably limited to the contents of the present invention described in the scope of the claims, and may be modified within a range not departing from the gist of the present invention. Note that all the configurations described in the present embodiment are not essential as a solution of the present invention. The nickel composite hydroxide and the like according to one embodiment of the present invention will be described in the following order.

1. Nickel composite hydroxide

2. Method for producing nickel composite hydroxide

3. Positive electrode active material for lithium ion secondary battery

4. Method for producing positive electrode active material for lithium ion secondary battery

5. Lithium ion secondary battery

< 1. Nickel composite hydroxide >

The nickel composite hydroxide according to one embodiment of the present invention is composed of secondary particles in which a plurality of primary particles are aggregated, and has a cobalt-rich layer from the particle surface of the secondary particles toward the inside of the particles, and a layered low-density layer between the central portion of the secondary particles and the cobalt-rich layer. The nickel composite hydroxide according to an embodiment of the present invention is composed of secondary particles in which a plurality of primary particles are aggregated, and has a manganese-rich layer from the particle surface of the secondary particles toward the inside of the particles, and a low-density layer in the form of a layer between the central portion of the secondary particles and the manganese-rich layer. The details are as follows.

(composition)

In the composition of the nickel composite hydroxide (secondary particle bulk), nickel, cobalt, manganese and an element M are represented by an atomic ratio of Ni: Co: Mn: M: 1-x1-y1-z1: x1: y1: z1 (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, x1 is 0.15. ltoreq. x 1. ltoreq.0.25, y1 is 0.15. ltoreq. y 1. ltoreq.0.25, and z1 is 0. ltoreq. z 1. ltoreq.0.1). Further, 0.3. ltoreq. x1+ y1+ z 1. ltoreq.0.5 may be set.

The nickel content is represented by 1-x1-y1-z1, and the range of the nickel content is 0.50 to less than or equal to 1-x1-y1-z1 to less than or equal to 0.70. In the case where the lithium metal composite oxide has a crystal structure of a layered rock-salt type structure and the nickel content is in 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 representing the cobalt content is 0.15. ltoreq. x 1. ltoreq.0.25. When the cobalt content is in the above range, the finally obtained lithium metal composite oxide has high crystal structure stability and is more excellent in cycle characteristics.

In the above general formula, y1 indicating the manganese content is 0.15. ltoreq. y 1. ltoreq.0.25. In the case where the manganese content is in the above range, the finally obtained lithium metal composite oxide can obtain high thermal stability.

The nickel composite hydroxide according to an embodiment of the present invention may contain an additive element M other than nickel, cobalt, and manganese, as long as the effects of the present invention are not impaired. For example, a transition metal element other than nickel, cobalt, and manganese, a group 2 element, and a group 13 element may be included. M (z1) is more than or equal to 0 and less than or equal to z1 and less than or equal to 0.1.

The composition distribution of the nickel composite hydroxide within the particles strongly influences the composition distribution of the positive electrode active material obtained using the same within the particles. In particular, as will be described later, the composition distribution and particle size distribution of the nickel composite hydroxide inside the particles can be maintained as the positive electrode active material by controlling the conditions in the firing step. Therefore, it is important to control the composition distribution inside the particles of the nickel composite hydroxide so as to be the same as the composition distribution inside the particles of the positive electrode active material. By controlling in this manner, the cobalt-rich layer or the manganese-rich layer of the nickel composite hydroxide can be maintained also in the positive electrode active material.

The nickel composite hydroxide is mixed with a lithium compound as described later (lithium mixing step S30), and then fired (firing step S40) to form a positive electrode active material. The composition 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 set to be the same as the composition distribution of the metal other than lithium of the desired positive electrode active material. The cobalt-rich layer and the manganese-rich layer will be described below.

(cobalt-rich layer)

The nickel composite hydroxide according to one embodiment of the present invention has a cobalt-rich layer from the particle surface of the secondary particles toward the inside of the particles. The cobalt-rich layer contains nickel, cobalt, manganese, and an element M in an atomic ratio of Ni: Co: Mn: M1-x 2-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, Mn, group 2 elements, and group 13 elements, and x2 and y2 satisfy x 2-1 and y 2-0 or satisfy x2/((1-x2-y2-z2) + y2) ≥ 1, and z2 is in a range of 0. ltoreq. z 2. ltoreq.0.1). Wherein x2 is in the range of 0.5 ≦ x2 ≦ 1.

The cobalt-rich layer may contain Ni, Mn, for exampleAs a metal other than Co. In this case, the Co content in the cobalt-rich layer is 1 time or more of the total (mole) of Ni and Mn. The cobalt-rich layer may contain, for example, Co alone as a metal, and may have a composition of Co (OH) ₂. In this case, y2 is 0, and x2 is 1. The composition of the cobalt-rich layer can be determined by quantitative analysis of energy dispersive X-ray analysis (EDX) in cross-sectional observation using a scanning electron microscope, for example. The composition of the cobalt-rich layer can be adjusted to a desired range by controlling the metal composition of the second mixed aqueous solution in the particle growth step (S20) described later, for example. The cobalt-rich layer may contain an additive element M other than nickel, cobalt, and manganese, as long as the effect of the present invention is not impaired. For example, a transition metal element other than nickel, cobalt, and manganese, a group 2 element, and a group 13 element may be included. M (z2) is more than or equal to 0 and less than or equal to z2 and less than or equal to 0.1.

The thickness t of the cobalt-rich layer is 1% to 10% of the diameter d of the secondary particles. The thickness t of the cobalt-rich layer can be determined by composition mapping (mapping) using EDX and line analysis. The diameter d of the secondary particle can be determined by observing the cross section of the secondary particle using a scanning electron microscope. Since the thickness of the cobalt-rich layer and the diameter d of the secondary particles may vary among the secondary particles, it is preferable to measure a plurality of secondary particles and obtain the average value, for example, the average value can be obtained by measuring 30 randomly selected secondary particles.

(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 particles toward the inside of the particles. The manganese-rich layer contains nickel, cobalt, manganese and an element M in an atomic ratio of Ni: Co: Mn: M1-x 2-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, Mn, group 2 elements, and group 13 elements, and x2 and y2 satisfy x 2-0 and y 2-1 or satisfy y2/((1-x2-y2-z2) + x2) ≥ 1, and z2 is in a range of 0. ltoreq. z 2. ltoreq.0.1). Wherein y2 is in the range of 0.5. ltoreq. y 2. ltoreq.1.

The manganese-rich layer may contain at least one of Ni and MnA metal other than Mn. In this case, the Mn content of the manganese-rich layer is 1 time or more of the total (mole) of Ni and Co. Further, the manganese-rich layer may contain, for example, Mn alone as a metal and may have a composition of Mn (OH)₂. In this case, x2 is 0, and y2 is 1. The composition of the manganese-rich layer can be determined by quantitative analysis such as energy dispersive X-ray analysis (EDX) in cross-sectional observation with a scanning electron microscope, for example. The composition of the manganese-rich layer can be adjusted to a desired range by controlling the metal composition of the second mixed aqueous solution in the particle growth step (S20) described later, for example. The manganese-rich layer may contain an additive element M other than nickel, cobalt, and manganese, as long as the effect of the present invention is not impaired. For example, a transition metal element other than nickel, cobalt, and manganese, a group 2 element, and a group 13 element may be included. M (z2) is more than or equal to 0 and less than or equal to z2 and less than or equal to 0.1.

The thickness t of the manganese-rich layer is 1% to 10% of the diameter d of the secondary particles. The thickness t of the manganese-rich layer can be determined by drawing the composition of EDX and line analysis. The diameter d of the secondary particle can be determined by observing the cross section of the secondary particle using a scanning electron microscope. Since the thickness of the manganese-rich layer and the diameter d of the secondary particles may vary among the secondary particles, it is preferable to measure a plurality of secondary particles and determine the average value, for example, the average value can be determined by measuring 30 randomly selected secondary particles.

(Low Density layer)

The nickel composite hydroxide according to an embodiment of the present invention has a layered low-density layer between the center portion of the secondary particle and the cobalt-rich layer or the manganese-rich layer. In the structure of the inside of the particle of the nickel composite hydroxide, by introducing a layered low-density layer between the central part of the particle and the cobalt-rich layer or the manganese-rich layer, the diffusion of the composition inside the particle during firing can be suppressed, and the composition distribution inside the particle can be maintained without limiting the firing temperature.

The thickness s of the low-density layer is 1% to 10% of the diameter d of the secondary particles. When the low-density layer is less than 1%, a void layer is not formed in the subsequent firing step, and a cobalt-rich layer or a manganese-rich layer is not formed due to composition diffusion. If the amount is more than 10%, the particle density and filling property of the finally obtained positive electrode active material are greatly reduced. The thickness s of the low-density layer can be determined by observing the cross section of the secondary particle using a scanning electron microscope. Since the thickness s of the low-density layer and the diameter d of the secondary particles may vary among the secondary particles, it is preferable to measure a plurality of secondary particles and determine the average value, for example, the average value can be determined by measuring 30 randomly selected secondary particles.

The composition and structure of the inside of the particles of the nickel composite hydroxide affect the composition and structure of the inside of the particles of the positive electrode active material. Therefore, by setting the composition of the cobalt-rich layer and the structure of the low-density layer having a layered structure to the above ranges, the obtained positive electrode active material also forms a cobalt-rich layer containing lithium, and thus exhibits low positive electrode resistance when used in a positive electrode of a battery. In addition, by setting the composition of the manganese-rich layer and the structure of the low-density layer having a layered structure to the above ranges, the manganese-rich layer containing lithium is formed also in the obtained positive electrode active material, and excellent cycle characteristics are exhibited when used for a positive electrode of a battery.

(average particle diameter, 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 a particle size distribution measured by a laser diffraction scattering method. When the volume average particle diameter of the nickel composite hydroxide is within the above range, the volume average particle diameter of the obtained positive electrode active material can be controlled within a range of 4 μm to 10 μm, and a battery using the positive electrode active material can obtain excellent output characteristics and cycle characteristics.

In the particle size distribution of the nickel composite hydroxide measured by the laser diffraction scattering method, [ (D90-D10)/Mv ] indicating the deviation index of the particle diameter, which is calculated from the cumulative 90 vol% diameter (D90), the cumulative 10 vol% diameter (D10) and the volume average particle diameter (Mv), is preferably 0.60 or less. When the deviation index of the nickel composite hydroxide is within the above range, the mixing of fine particles and coarse particles is small, and the cycle characteristics and output characteristics of the obtained positive electrode active material can be improved. Since the particle size distribution of the positive electrode active material is strongly influenced by the nickel composite hydroxide, when the particle size distribution is in a wide state with a deviation index of the nickel composite hydroxide of more than 0.60, fine particles or coarse particles may be present in the positive electrode active material. Since it is difficult to completely suppress the variation in particle size, the lower limit of the variation index is practically about 0.30 or more.

In the above [ (D90-D10)/Mv ], D10 means a particle diameter obtained by integrating the number of particles in each particle diameter from the side having a smaller particle diameter and making the integrated volume thereof 10% of the total volume of all the particles. Similarly, D90 means a particle size obtained by integrating the number of particles and making the integrated volume 90% of the total volume of all the particles. The volume average particle diameters Mv, D90, and D10 can be measured using a laser diffraction scattering particle size analyzer.

< 2. method for producing nickel composite hydroxide

In the method for producing a nickel composite hydroxide according to an embodiment of the present invention, an aqueous solution containing a nickel salt, a cobalt salt, and a manganese salt is supplied to a reaction vessel while stirring a neutralizer and a complexing agent, and a crystallization reaction is performed to produce a nickel composite hydroxide. The method for producing a nickel composite hydroxide includes 2 crystallization steps. That is, the method includes a nucleus generation step S10 of generating nuclei that grow into secondary particles, and a particle growth step S20 of growing the nuclei obtained in the nucleus generation step.

Further, the particle growth step S20 includes: a first particle growth step S21 of supplying the first mixed aqueous solution to the slurry containing the nuclei formed in the nucleus formation step S10 to grow particles; a second particle growth step S22 of performing particle growth by switching the atmosphere to an oxidizing atmosphere having an oxygen concentration of 5% by volume or more after the first particle growth step S21; and a third particle growth step S23 of performing particle growth by switching the atmosphere to a non-oxidizing atmosphere having an oxygen concentration of less than 5% by volume and supplying a second mixed aqueous solution containing a metal salt in the same molar ratio as the molar ratio of Ni, Co, and Mn in the cobalt-rich layer or the manganese-rich layer. That is, in the third particle growth step, the cobalt-rich layer or the manganese-rich layer is formed from the particle surface of the secondary particle toward the inside of the particle.

As for the method for producing a nickel composite hydroxide including such a 2-stage batch crystallization step, for example, patent documents 2 and 3 disclose that the conditions can be appropriately adjusted with reference to these documents for the detailed conditions. The method for producing a nickel composite oxide can obtain a composite hydroxide having a narrow particle size distribution and a uniform particle size by including a 2-stage crystallization step. The following description is an example of a method for producing a nickel composite hydroxide, and is not limited to this method.

(nucleus formation step S10)

First, in the nucleus formation step S10, the first mixed aqueous solution containing at least one of a nickel salt, a cobalt salt, and a manganese salt is adjusted to a pH of 12.5 or more in a non-oxidizing atmosphere having an oxygen concentration of less than 5% by volume based on a liquid temperature of 25 ℃. When an element other than nickel, cobalt, and manganese is added, a salt of the added element is preferably added to the mixed aqueous solution.

In the nucleus-forming step S10, the pH of the aqueous solution for nucleus formation is controlled so as to be in the range of 12.5 or more, preferably 12.5 or more and 14.0 or less, and more preferably 12.5 or more and 13.5 or less, based on the liquid temperature of 25 ℃. When the pH of the aqueous solution for nucleus formation is controlled to the above range, nuclei can be sufficiently formed. When the pH value based on the liquid temperature of 25 ℃ is less than 12.5, nuclei are generated but the nuclei themselves become large, and therefore, secondary particles in which the primary particles are aggregated cannot be obtained in the subsequent particle growth step S20. On the other hand, the higher the pH, the more minute crystal nuclei are obtained, but if the pH is more than 14.0, the following problems may occur: the reaction solution is gelled and crystallization becomes difficult, or the plate-like primary particles constituting the secondary particles of the nickel composite hydroxide become too small.

The pH can be controlled by adding an inorganic base solution as a neutralizing agent. The inorganic alkaline solution is not particularly limited, and for example, a general aqueous alkali metal hydroxide solution such as sodium hydroxide or potassium hydroxide can be used. The alkali metal hydroxide may be added directly to the mixed aqueous solution, but is preferably added as an aqueous solution from the viewpoint of ease of pH control. In this case, the concentration of the alkali metal hydroxide aqueous solution is preferably 12.5 mass% or more and 30 mass% or less, and more preferably 20 mass% or more and 25 mass% or less. When the concentration of the alkali metal hydroxide aqueous solution is low, the slurry concentration may decrease to deteriorate the productivity, and therefore, it is preferable to increase the concentration, specifically, it is preferable to set the concentration of the alkali metal hydroxide to 20 mass% or more. On the other hand, if the concentration of the alkali metal hydroxide is more than 30 mass%, the pH at the addition site becomes locally high, and fine particles may be generated.

In the nucleus-forming step S10, for example, a pre-reaction aqueous solution is prepared by adding water to an inorganic alkali aqueous solution in advance to adjust the pH to 12.5 or more, and a first mixed aqueous solution containing a nickel salt, a cobalt salt, and a manganese salt is supplied to the pre-reaction aqueous solution in a reaction tank while stirring the pre-reaction aqueous solution, and an inorganic alkali aqueous solution (neutralizing agent) such as sodium hydroxide is added to form an aqueous solution for nucleus formation in which the pH is maintained in the above range, thereby forming nuclei. The method of supplying the mixed aqueous solution while maintaining the pH of the aqueous solution for generating nuclei in this manner is preferable because the pH can be strictly controlled and the generation of nuclei can be easily performed. The aqueous solution for forming nuclei may be added with an aqueous solution of an inorganic alkali (neutralizing agent) and an aqueous ammonia solution (complexing agent). The concentration of ammonium ions in the aqueous solution for generating nuclei is preferably, for example, 3g/L to 25 g/L.

The first mixed aqueous solution used in the nucleus formation step S10 contains a nickel salt, a cobalt salt, and a manganese salt. As the metal salt, sulfate, nitrate, chloride, and the like can be used, and sulfate is preferably used from the viewpoint of cost, impurities, and waste liquid treatment. When an element other than nickel, cobalt, and manganese is added, a salt of the added element is preferably added to the mixed aqueous solution.

The concentration of the first mixed aqueous solution is preferably 1.0 to 2.2mol/L, more preferably 1.5 to 2.0mol/L, based on the total amount of the metal salts. If the concentration of the first mixed aqueous solution is low, the amount of the first mixed aqueous solution to be added increases, and nucleus formation cannot be efficiently performed. Further, if the concentration of the first mixed aqueous solution is high, the concentration may be close to the saturation concentration at room temperature, and thus there is a risk that crystals may re-precipitate to block the piping of the facility.

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

The temperatures of the aqueous solutions for generating nuclei in the nucleation step S10 are preferably maintained at 40 ℃ to 70 ℃. When the temperature is in 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 nucleus formation step S10, the pH of the slurry (particle growth slurry) containing the nuclei formed in the nucleus formation step S10 is adjusted to be in the range of 10.5 to 12.5 with respect to the liquid temperature of 25 ℃ and lower than the pH in the nucleus formation step S10.

The pH of the slurry for particle growth 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 nucleus formation step S10, based on the liquid temperature of 25 ℃. When the pH of the slurry for particle growth is controlled to be within the above range, the growth and aggregation of the nuclei generated in the nucleus generation step S10 can be preferentially caused, new nucleus formation can be suppressed, and the obtained nickel composite hydroxide can be made homogeneous and has a narrow particle size distribution range and a controlled shape. When the pH value based on the liquid temperature of 25 ℃ is less than 10.5, impurities contained in the obtained nickel composite hydroxide, for example, anion constituent elements contained in the metal salt, increase. When the pH is higher than pH12.5, new nuclei are generated in the particle growth step, and the particle size distribution is also deteriorated. In addition, from the viewpoint of more clearly separating the nucleus formation step S10 and the particle growth step S20, the pH of the slurry for particle growth is preferably controlled to be lower by 0.5 or more, more preferably lower by 1.0 or more than the pH in the nucleus formation step.

The temperature of the slurry for particle growth in the particle growth step S20 is preferably maintained at 40 ℃ to 70 ℃. When the temperature is in the above range, the particle size of the nickel composite hydroxide can be grown to a target range. When the temperature is less than 40 ℃, the solubility of the metal salt in the mixed aqueous solution is low and the salt concentration is low, so that the amount of nuclei generated and the number of fine particles increase in the particle growth step S20, and the particle size distribution may deteriorate. In addition, if the temperature of the mixed aqueous solution is higher than 70 ℃, the volatilization of ammonia is high, and the concentration of the nickel-ammonia complex is unstable.

It is preferable to add ammonia as a complexing agent to the slurry for particle growth. The concentration of ammonia in the slurry for particle growth is preferably controlled to be 5g/L to 20 g/L. Since ammonia functions as a complexing agent, when the ammonia concentration is less than 5g/L, the solubility of the metal ions cannot be kept constant, and primary particles generated by nucleus growth become non-uniform, which may cause variation in the range of particle size of the nickel composite hydroxide. When the ammonia concentration is more than 20g/L, the solubility of the metal ions becomes too high, and the amount of the metal ions remaining in the slurry for particle growth increases, which may cause a deviation in the composition. Further, if the ammonia concentration fluctuates, the solubility of the metal ions fluctuates, and a uniform nickel composite hydroxide is not formed, so that it is preferable to maintain a constant value. For example, it is preferable to maintain the ammonia concentration at a desired concentration by increasing or decreasing the concentration to about 5g/L with respect to the set concentration.

The ammonia is added by 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, or the like can be used.

The particle growth step S20 can be divided into the following 3 stages depending on the atmosphere and the combination of the added mixed aqueous solution.

(first particle growth step S21)

The first particle growth step S21 corresponds to a step of forming the central portion of the particles of the 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 having 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 particle center portion can be obtained. The first mixed aqueous solution is already described in the nucleus formation step S10, and thus is 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 may be changed as long as the composition of the finally obtained nickel composite hydroxide can be controlled to a desired composition. However, from the viewpoint of simplification of the process, the same composition is preferable.

(second particle growth step S22)

The second particle growth step S22 corresponds to a step of forming a low-density layer of the nickel composite hydroxide. The second particle growth step S22 is performed by switching the atmosphere from the first particle growth step S21 to an oxidizing atmosphere having an oxygen concentration of 5% by volume or more and crystallizing the first mixed aqueous solution. This makes it possible to introduce a layered low-density layer into the nickel composite hydroxide.

The timing of switching may be adjusted according to the thickness of the low-density layer, and for example, it is preferable to switch to an oxidizing atmosphere after charging 12.5 at% or more and 80 at% or less, and more preferably 50 at% or more and 70 at% or less, of the total of nickel, cobalt, manganese, and M in all the mixed aqueous solutions (including the first and second mixed aqueous solutions) supplied from the start of crystallization to the end of crystallization. After switching to the oxidizing atmosphere, it is preferable to add 2.5 at% to 10 at% in total of nickel, cobalt, manganese and M. Further, if the concentration and the feeding rate of the mixed aqueous solution are fixed, switching can be performed according to the crystallization time. That is, the atmosphere may be switched at a time point of 12.5% to 80% of the crystallization time from the start of crystallization to the end of crystallization, and kept in an oxidizing atmosphere for a time of 2.5% to 10%. Whereby a low-density layer of a desired thickness can be formed at a desired position.

(third particle growth step S23)

The third particle growth step S23 corresponds to a step of forming a cobalt-rich layer or a manganese-rich layer of the 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 having an oxygen concentration of less than 5% by volume and switching the supplied mixed aqueous solution to the second mixed solution. The second mixed solution contains more cobalt or manganese, and thus a cobalt-rich layer or a manganese-rich layer is formed.

The second mixed aqueous solution used in the third particle growth step S23 for forming a cobalt-rich layer contains at least a cobalt salt, and may contain a nickel salt or a manganese salt. As the metal salt, sulfate, nitrate, chloride, and the like can be used, and sulfate is preferably used from the viewpoint of cost, impurities, and waste liquid treatment. The second mixed aqueous solution used in the third particle growth step S23 for forming the manganese-rich layer contains at least a manganese salt, and may contain a nickel salt or a cobalt salt. As the metal salt, sulfate, nitrate, chloride, and the like can be used, and sulfate is preferably used from the viewpoint of cost, impurities, and waste liquid treatment. When an element other than nickel, cobalt, and manganese is added, a salt of the added element is preferably added to the mixed aqueous solution.

The second mixed aqueous solution used in the third particle growth step S23 for forming a cobalt-rich layer contains nickel, cobalt, manganese and an element M in an atomic ratio of Ni: Co: Mn: M1-x 2-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, Mn, group 2 elements, and group 13 elements, x2 and y2 satisfy x2 ═ 1 and y2 ≥ 0, or satisfy x2/((1-x2-y2-z2) + y2) ≥ 1, and z2 falls within a range of 0. ltoreq. z 2. ltoreq.0.1). Since the composition of the cobalt-rich layer formed in the third particle growth step S23 is inherited to the composition of the cobalt-rich layer of the finally obtained positive electrode active material, the composition of the second mixed aqueous solution is determined in accordance with the composition of the cobalt-rich layer of the finally obtained positive electrode active material.

In the composition of the second mixed aqueous solution used in the third particle growth step S23 for forming the manganese-rich layer, the atomic ratio of Ni: Co: Mn: M is 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, Mn, group 2 elements, and group 13 elements, x2 and y2 satisfy x2 is 0 and y2 is 1, or satisfy y2/((1-x2-y2-z2) + x2) is 1 or more, and z2 is in the range of 0. ltoreq. z 2. ltoreq.0.1) includes nickel, cobalt, manganese, and an element M. The composition of the manganese-rich layer formed in the third particle growth step is inherited to the composition of the manganese-rich layer of the finally obtained positive electrode active material, and therefore the composition of the second mixed aqueous solution is determined in accordance with the composition of the manganese-rich layer of the finally obtained positive electrode active material.

The concentration of the second mixed aqueous solution used in the third particle growth step S23 for forming the cobalt-rich layer or the manganese-rich layer is preferably 1.0mol/L to 2.2mol/L, and more preferably 1.5mol/L to 2.0mol/L, based on the total of the metal salts. If the concentration of the second mixed aqueous solution is low, the amount of the first mixed aqueous solution to be added increases, and thus nucleus formation cannot be efficiently performed. Further, if the concentration of the second mixed aqueous solution is high, the concentration may be close to the saturated concentration at room temperature, and therefore, there is a risk that crystals may re-precipitate to block the piping of the facility.

From the above, according to the method for producing a nickel composite hydroxide according to an embodiment of the present invention, a nickel composite hydroxide can be obtained, which is characterized by using Ni: Co: Mn: M ═ 1-x1-y1-z1: x1: y1: z1 (general formula: Ni: Mn: M ═ 1-x1-y1-z 1)_1-x1-y1-z1Co_x1Mn_y1M_z1(OH)_2+α1) (wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co and Mn, group 2 elements and group 13 elements, x1 satisfies 0.15. ltoreq. x 1. ltoreq.0.25, y1 satisfies 0.15. ltoreq. y 1. ltoreq.0.25, z1 satisfies 0. ltoreq. z 1. ltoreq.0.1, and α 1 is-0.2. ltoreq. α 1. ltoreq.0.2) contains nickel, cobalt, manganese and an element M, and has a cobalt-rich layer or 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 central part of the secondary particle and the cobalt-rich layer or manganese-rich layer, and the cobalt-rich layer is formed by mixing Ni: Mn: M: 1-x2-y2-z2: x2: y2: z2 (general formula: ni _1-x2-y2-Z2Co_x2Mn_y2M_z2(OH)_2+α2) (wherein M is selected from the group consisting of Ni and Co, at least one element selected from the group consisting of transition metal elements other than Mn, group 2 elements, and group 13 elements, x2 and y2 satisfy x2 ═ 1 and y2 ═ 0, or satisfy x2/((1-x2-y2-z2) + y2) ≥ 1, z2 is in the range of 0. ltoreq. z2 ≤ 0.1, and α 2 is in the range of-0.2. ltoreq. α 2 ≤ 0.2) and contains nickel, cobalt, manganese, and an element M, and the manganese-rich layer contains Ni: Co: Mn: M ═ 1-x2-y2-z2: x2: y2: z2 (general formula: ni_1-x2-y2-Z2Co_x2Mn_y2M_z2(OH)_2+α2) (wherein M is at least one element selected from the group consisting of transition metal elements other than Ni, Co and Mn, group 2 elements and group 13 elements, and x2 and y2 satisfy x2 ═ 0 and y2 ═ 1, or satisfy y2/((1-x2-y2-z2) + x2) ≥ 1, z2 is in the range of 0. ltoreq. z 2. ltoreq.0.1, and α 2 is in the range of-0.2. ltoreq. α 2. ltoreq.0.2. ) The atomic ratio of (a) includes nickel, cobalt, manganese, and an element M, and the thickness of the cobalt-rich layer or the manganese-rich layer is 1% or more and 10% or less with respect to the diameter of the secondary particle, and the thickness of the low-density layer is 1% or more and 10% or less with respect to the diameter of the secondary particle.

< 3. Positive electrode active Material for lithium ion Secondary Battery

The positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention has a cobalt-rich layer or a manganese-rich layer from the particle surface of the secondary particles toward the inside of the particles, and has a layered void layer between the central portion of the secondary particles and the cobalt-rich layer or the manganese-rich layer. A positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is produced by: by mixing the nickel composite hydroxide having the layered low-density layer between the cobalt-rich layer or the manganese-rich layer and the particle central portion and the lithium compound, and firing the mixture under specific conditions, the surface layer portion (cobalt-rich layer or manganese-rich layer) maintains the rich layer of the cobalt-rich layer or manganese-rich layer, and the low-density layer is absorbed by the particle central portion to become a void layer, and lithium is dispersed in the secondary particles in this state. The positive electrode active material for a lithium ion secondary battery has a cobalt-rich layer containing lithium, and can obtain particles having high crystallinity as described later, thereby obtaining a lower positive electrode resistance. Further, the positive electrode active material for a lithium ion secondary battery has a manganese-rich layer containing lithium, and can obtain particles having high crystallinity as described later, thereby achieving higher durability.

A positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is composed of a lithium nickel composite oxide that is composed of secondary particles in which a plurality of primary particles are aggregated with each other and has a hexagonal layered structure. The lithium-nickel composite oxide contains lithium, nickel, cobalt, manganese and an element M in an atomic ratio of Li, Ni, Co, Mn, M, 1+ u:1-x1-y1-z1: x1: y1: z1 (where u is-0.05. ltoreq. u.ltoreq.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. ltoreq. x 1. ltoreq.0.25, y1 is 0.15. ltoreq. y 1. ltoreq.0.25, and z1 is 0. ltoreq. z 1. ltoreq.0.1).

U, which represents the excess amount of lithium, is in the range of-0.05 to 0.50, preferably-0.05 to 0.20. When u is less than-0.05, the reaction resistance of the positive electrode in the lithium ion secondary battery using the obtained positive electrode active material becomes large, and the output of the secondary battery becomes low. On the other hand, when u is greater than 0.50, the initial discharge capacity of the secondary battery using the positive electrode active material decreases, and the reaction resistance of the positive electrode also increases. From the viewpoint of increasing the capacity, it is more preferable to set u to-0.02 to 0.10. The composition of the positive electrode active material can be determined by ICP emission spectrometry.

The cobalt-rich layer in the positive electrode active material for a lithium ion secondary battery contains lithium, nickel, cobalt, manganese, and an element M at an atomic ratio of Li, Ni, Co, Mn, M, 1+ u:1-x2-y2-z2: x2: y2: z2 (where u is-0.05. ltoreq. u.ltoreq.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 satisfy x 2. ltoreq.1 and y 2. ltoreq.0, or satisfy x2/((1-x2-y2-z2) + y 2). gtoreq.1, and z2 is in the range of 0. ltoreq. z 2. ltoreq.0.1). Further, x2 is 0.5. ltoreq. x 2. ltoreq.1.

The cobalt-rich layer in the positive electrode active material for a lithium-ion secondary battery contains no nickel and manganese (x2 is 1, y2 is 0), or the cobalt ratio [ x2/((1-x2-y2-z2) + y2) ] with respect to nickel and manganese is 1 or more.

The manganese-rich layer in the positive electrode active material for a lithium-ion secondary battery contains lithium, nickel, cobalt, manganese, and an element M at an atomic ratio of Li, Ni, Co, Mn, M, 1+ u:1-x2-y2-z2, x2: y2: z2 (where u is-0.05. ltoreq. u.ltoreq.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 satisfy x 2. ltoreq.0 and y 2. ltoreq.1, or satisfy y2/((1-x2-y2-z2) + x 2. gtoreq.1), and z2 is in a range of 0. ltoreq. z 2. ltoreq.0.1). Y2 is 0.5. ltoreq. y 2. ltoreq.1.

The manganese-rich layer in the positive electrode active material for a lithium-ion secondary battery is free of nickel and cobalt (x2 is 0 and y2 is 1), or has a manganese ratio [ y2/((1-x2-y2-z2) + x2) ] to nickel and cobalt of 1 or more.

The thickness of the cobalt-rich layer or the manganese-rich layer in the positive electrode active material for a lithium ion secondary battery is 1% or more and 10% or less with respect to the diameter of the secondary particles. This can improve the battery output or cycle characteristics. If the thickness of the cobalt-rich layer or the manganese-rich layer is less than 1%, the output characteristics or the cycle characteristics cannot be sufficiently improved due to the composition inside the particles. On the other hand, if the thickness is more than 10%, the composition of the entire secondary particles becomes rich in cobalt or manganese, and the battery capacity decreases, or the manganese composition ratio y2 of the manganese-rich layer becomes less than 0.5, and a sufficient effect of improving the cycle characteristics cannot be obtained. The thickness of the cobalt-rich layer or the manganese-rich layer in the positive electrode active material can be determined by composition mapping using EDX and line analysis. The diameter of the secondary particles can be determined by observing the secondary particles using a scanning electron microscope. Since the thickness of the cobalt-rich layer and the diameter of the secondary particles may vary among the secondary particles, it is preferable to measure a plurality of secondary particles and obtain the average value (see the description of the nickel composite hydroxide). The composition of the cobalt-rich layer or the manganese-rich layer can be determined by, for example, quantitative analysis by energy dispersive X-ray analysis (EDX) in cross-sectional observation with a scanning electron microscope, and the cobalt-rich layer can be determined by making the cobalt ratio (cobalt ratio ═ cobalt composition ratio/(nickel composition ratio + manganese composition ratio)) to the total of nickel and manganese 1 or more. The manganese-rich layer can be determined by setting the manganese ratio (manganese ratio: manganese composition ratio/(nickel composition ratio + cobalt composition ratio)) to the total of nickel and cobalt to 1 or more.

The thickness of the layered void layer in the positive electrode active material for a lithium ion secondary battery is 1% to 10% with respect to the diameter of the secondary particles. This suppresses diffusion of the composition in the particles even at a firing temperature for obtaining particles having high crystallinity, and can maintain a cobalt-rich layer or a manganese-rich layer on the surface of the positive electrode active material particles, thereby improving the output characteristics or the cycle characteristics. If the thickness of the void layer is less than 1%, the suppression of the composition diffusion becomes insufficient, and the improvement of the output characteristics or the cycle characteristics cannot be sufficiently obtained. On the other hand, if the thickness of the void layer is more than 10%, the particle density and filling property of the secondary particles are greatly reduced.

The crystal grain diameter of the positive electrode active material for a lithium ion secondary battery calculated from the peak of the (003) plane obtained by X-ray diffraction measurement is 100nm to 150 nm. This can achieve both high battery capacity and excellent durability. When the average particle diameter is less than 100nm, the crystallinity is likely to be insufficient, and high output characteristics are not easily obtained. In addition, in the case of more than 150nm, deterioration of various battery characteristics due to over firing can be seen.

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 preferably has [ (D90-D10)/Mv ] which is a deviation index of particle diameter and is calculated from a cumulative 90 vol% diameter (D90), a cumulative 10 vol% diameter (D10) and the volume average particle diameter (Mv) and is preferably 0.60 or less. This reduces the mixing of fine particles and coarse particles, and provides high output characteristics with little variation. The volume average particle diameter (Mv), D90, and D10 can be determined in the same manner as for the nickel composite hydroxide.

< 4. method for producing positive electrode active material for lithium ion secondary battery

The method for producing a positive electrode active material for a lithium ion secondary battery according to one 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, and a firing step S40 in which the lithium mixture is fired at a temperature of 800 ℃ to 950 ℃ in an oxidizing atmosphere. The respective steps will be explained below.

(lithium mixing step S30)

In the lithium mixing step S30, the nickel composite hydroxide is mixed with a lithium compound to form a lithium mixture. The lithium compound is not particularly limited, and a known lithium compound can be used, and for example, lithium hydroxide, lithium nitrate, lithium carbonate, or a mixture thereof is preferably used from the viewpoint of easy acquisition. Among them, lithium hydroxide and lithium carbonate are more preferably used as the lithium compound from the viewpoints of ease of handling and stability of quality.

The nickel composite hydroxide and the lithium compound have a ratio (Li/Me) of the number of atoms of a metal other than lithium in the lithium mixture, that is, the number of atoms of lithium (Li) to the sum (Me) of the number of atoms of nickel, cobalt and an additive element, of 0.95 to 1.50, preferably 0.95 to 1.20, and more preferably 0.98 to 1.10. That is, since Li/Me does not change before and after the firing step, Li/Me mixed in this lithium mixing step S30 becomes Li/Me in the positive electrode active material, and therefore Li/Me in the lithium mixture is mixed in the same manner as Li/Me in the obtained positive electrode active material.

In addition, a general mixer may be used for the mixing, and a swing mixer, a Lodige (Lodige) mixer, a Julia mixer, a V blender or the like may be used as long as the mixing is sufficiently performed to the extent that the skeleton of the nickel composite hydroxide is not broken.

(firing Process S40)

In the firing step S40, the lithium mixture is fired at a temperature of 800 ℃ to 950 ℃ in an oxidizing atmosphere. The firing is preferably performed in an oxidizing atmosphere at 800 ℃ to 950 ℃. When the firing temperature is less than 800 ℃, high crystallinity cannot be obtained, and when the composition is used in a battery, high output characteristics cannot be obtained. On the other hand, if it exceeds 950 ℃, the cations of various transition metals entering into the lithium site are mixed due to overburning, and various battery characteristics are deteriorated. The firing time is not particularly limited, but is preferably about 1 hour to 24 hours.

In addition, from the viewpoint of uniformly proceeding 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 with a temperature raising rate of 1 ℃/min to 5 ℃/min. Further, the reaction can be more uniformly performed by maintaining the temperature near the melting point of the lithium compound for about 1 hour to 10 hours.

As described above, according to the method for producing a positive electrode active material for a lithium ion secondary battery of one embodiment of the present invention, a positive electrode active material for a lithium ion secondary battery can be obtained, which is characterized by containing Li, Ni, Co, Mn, M, 1+ u, 1-x1-y1-z1, x1, y1, z1 (general formula: Li: y: M_1+uNi_1-x1-y1-z1Co_x1Mn_y1M_z1O_2+β1) (wherein u is-0.05. ltoreq. u.ltoreq.0.50, M is at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, group 2 elements, and group 13 elements, x1 is 0.15. ltoreq. x 1. ltoreq.0.25, y1 is 0.15. ltoreq. y 1. ltoreq.0.25, z1 is 0. ltoreq. z 1. ltoreq.0.1, and β 1 is-0.2. ltoreq. β 1. ltoreq.0.2). The atomic ratio of lithium, nickel, cobalt, manganese, and the element M is as follows.A cobalt-rich layer or a manganese-rich layer is provided from the particle surface of the secondary particle toward the particle interior, and a layered void layer is provided between the central portion of the secondary particle and the cobalt-rich layer or the manganese-rich layer, and the cobalt-rich layer is formed by mixing Li, Ni, Co, Mn: M: 1+ u:1-x2-y2-z 5: x2: y2: z 48325 (general formula: li _{1+ u}Ni_1-x2-y2-z2Co_x2Mn_y2M_z2O_2+β2) (wherein u is-0.05. ltoreq. u.ltoreq.0.50, M is at least one element selected from the group consisting of transition metal elements other than Ni, Co, Mn, group 2 elements, and group 13 elements, x2 and y2 satisfy x 2. ltoreq.1 and y 2. ltoreq.0, or satisfy x2/((1-x2-y2-z2) + y2) or more 1, z2 is in the range of 0. ltoreq. z 2. ltoreq.0.1, and β 2 is in the range of-0.2. ltoreq. β 2. ltoreq.0.2) contains lithium, nickel, cobalt, manganese, and an element M, and the manganese-rich layer contains Ni: Co: Mn: M: 1-x2-y2-z2: x2: y2: z2 (general formula: li_1+uNi_1-x2-y2-z2Co_x2Mn_y2M_z2O_2+β2) (wherein M is selected from the group consisting ofAt 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, wherein x2 and y2 satisfy x2 ═ 0 and y2 ═ 1, or satisfy y2/((1-x2-y2-z2) + x2) ≥ 1, z2 is in the range of-0.2 ≤ z2 ≤ 0.1, and β 2 is in the range of-0.2 ≤ β 2 ≤ 0.2. ) The atomic ratio of (a) includes nickel, cobalt, manganese, and an element M, and the thickness of the cobalt-rich layer or the manganese-rich layer is 1% or more and 10% or less with respect to the diameter of the secondary particle, and the thickness of the void layer is 1% or more and 10% or less with respect to the diameter of the secondary particle.

< 5. lithium ion secondary battery

The 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. The lithium ion secondary battery may be configured with the same components as those of a general lithium ion secondary battery, and includes, for example, a positive electrode, a negative electrode, and a nonaqueous electrolytic solution. The embodiments described below are merely examples, and the lithium-ion secondary battery of the present embodiment may be implemented in various forms, which are modified and improved based on the embodiments described in the present specification, based on the knowledge of those skilled in the art. The lithium ion secondary battery of the present embodiment is not particularly limited in its application.

(a) Positive electrode

Using the positive electrode active material for a lithium ion secondary battery described above, a positive electrode for a lithium ion secondary battery is produced, for example, as follows. First, a positive electrode active material in powder form, a conductive material, and a binder are mixed, and further, activated carbon, a solvent for the purpose of viscosity adjustment, and the like are added as necessary, and these are kneaded to prepare a positive electrode material mixture paste. Regarding the mixing ratio of the components in the positive electrode material paste, for example, when the total mass of the solid components of the positive electrode material excluding the solvent is 100 parts by mass, it is preferable that the content of the positive electrode active material is 60 to 95 parts by mass, the content of the conductive material is 1 to 20 parts by mass, and the content of the binder is 1 to 20 parts by mass, as in the case of a positive electrode of a general lithium ion secondary battery.

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, pressurization is also performed by a roll press or the like to increase the electrode density. In this manner, a sheet-like positive electrode can be produced. The sheet-shaped positive electrode may be cut into a suitable size according to a target battery, and the cut positive electrode may be used for manufacturing the battery. However, the method for producing the positive electrode is not limited to the example, and other methods may be used.

As the conductive material of the positive electrode, for example, carbon black materials such as graphite (natural graphite, artificial graphite, expanded graphite, and the like), acetylene black, ketjen black (registered trademark), and the like can be used.

The binder plays a role of binding the active material particles, and for example, polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, polyacrylic acid, or the like can be used.

A solvent for dispersing the positive electrode active material, the conductive material, and the activated carbon and dissolving the binder is added to the positive electrode material as necessary. As the solvent, an organic solvent such as N-methyl-2-pyrrolidone can be specifically used. In addition, activated carbon may be added to the positive electrode material to increase the electric double layer capacity.

(b) Negative electrode

As the negative electrode, one formed as follows was used: a binder is mixed with a negative electrode active material capable of absorbing and desorbing lithium ions such as metal lithium, a lithium alloy, or the like, a suitable solvent is added to prepare a negative electrode mixture in a paste form, and the negative electrode mixture is applied to the surface of a metal foil current collector such as copper, dried, and compressed as necessary to increase the electrode density, thereby forming a negative electrode.

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

(c) Diaphragm

The positive electrode and the negative electrode are disposed with a separator interposed therebetween. The separator separates the positive electrode from the negative electrode, and holds the electrolyte, and for example, a thin film of polyethylene, polypropylene, or the like, having a large number of minute pores, may be used.

(d) Nonaqueous electrolyte

As the nonaqueous electrolyte, a nonaqueous electrolytic solution can be used. The nonaqueous electrolyte solution may be a solution obtained by dissolving a lithium salt as a supporting salt in an organic solvent, for example. As the nonaqueous electrolytic solution, a solution obtained by dissolving a lithium salt in an ionic liquid may be used. The ionic liquid is a salt that is composed of a cation other than lithium ions and an anion and that is liquid at normal temperature.

As the organic solvent, one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and propylene trifluorocarbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane, sulfur compounds such as methyl ethyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more thereof may be used in combination.

As supporting salt, LiPF may be used₆、LiBF₄、LiClO₄、LiAsF₆、LiN(CF₃SO₂)₂And complex salts thereof, and the like. Further, the nonaqueous electrolytic solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

As the nonaqueous electrolyte, a solid electrolyte may be used. The solid electrolyte has a property of withstanding high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

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

The oxide-based solid electrolyte is not particularly limited as long as it contains oxygen (O) and has lithium ion conductivity and electronic insulation propertiesThe application is as follows. Examples of the oxide-based solid electrolyte include lithium phosphate (Li)₃PO₄)、Li₃PO₄N_X、LiBO₂N_X、LiNbO₃、LiTaO₃、Li₂SiO₃、Li₄SiO₄-Li₃PO₄、Li₄SiO₄-Li₃VO₄、Li₂O-B₂O₃-P₂O₅、Li₂O-SiO₂、Li₂O-B₂O₃-ZnO、Li_1+XAl_XTi_2-X(PO₄)₃(0≤X≤1)、Li_1+XAl_XGe_2-X(PO₄)₃(0≤X≤1)、LiTi₂(PO₄)₃、Li_3XLa_2/3-XTiO₃(0≤X≤2/3)、Li₅La₃Ta₂O₁₂、Li₇La₃Zr₂O₁₂、Li₆BaLa₂Ta₂O₁₂、Li_3.6Si_0.6P_0.4O₄And the like.

The sulfide-based solid electrolyte is not particularly limited as long as it contains sulfur (S), and has lithium ion conductivity and electronic insulation properties. As the sulfide-based solid electrolyte, for example, Li may be mentioned₂S-P₂S₅、Li₂S-SiS₂、LiI-Li₂S-SiS₂、LiI-Li₂S-P₂S₅、LiI-Li₂S-B₂S₃、Li₃PO₄-Li₂S-Si₂S、Li₃PO₄-Li₂S-SiS₂、LiPO₄-Li₂S-SiS、LiI-Li₂S-P₂O₅、LiI-Li₃PO₄-P₂S₅And the like.

In addition, as the inorganic solid electrolyte, other substances than the above-mentioned ones may be used, and for example, Li may be used₃N、LiI、Li₃N-LiI-LiOH and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity, and for example, polyethylene oxide, polypropylene oxide, a copolymer thereof, or the like can be used. In addition, the organic solid electrolyte may also contain a supporting salt (lithium salt).

(e) Shape and constitution of battery

The lithium ion secondary battery according to one embodiment of the present invention is composed of, for example, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolytic solution described above. The shape of the lithium ion secondary battery is not particularly limited, and various shapes such as a cylindrical shape and a laminated shape can be used. In any of these shapes, an electrode assembly is formed by laminating a positive electrode and a negative electrode with a separator interposed therebetween, the obtained electrode assembly is impregnated with a nonaqueous electrolyte, and a positive electrode current collector and a negative electrode terminal leading to the outside are connected to each other and a negative electrode current collector and a negative electrode terminal leading to the outside by using a current collecting lead, and the electrode assembly is sealed in a battery case, thereby completing a lithium ion secondary battery.

The lithium ion secondary battery according to one embodiment of the present invention includes a positive electrode made of the positive electrode active material, and has low positive electrode resistance and excellent cycle characteristics.

Examples

The present invention will be described in further detail below with reference to examples and comparative examples, but the present invention is not limited to these examples at all. First, the volume average particle diameter and particle size distribution measurement, composition, SEM and EDX analysis, battery production, and positive electrode resistance of the obtained nickel composite hydroxide and positive electrode active material for a lithium ion secondary battery will be described.

(measurement of volume average particle diameter and particle size distribution)

The volume average particle diameter and the particle size distribution were measured by a laser diffraction particle size distribution meter (trade name: MICROTRAC, manufactured by NIKO JASCO Co., Ltd.), and the tap density was measured by an oscillation specific gravity measuring instrument (KRS-409, manufactured by KANYO scientific instruments, Ltd.). The composition analysis was carried out using an ICP emission spectrometer (ICPS-8100, product of Shimadzu corporation).

(composition)

The composition of the whole particles was confirmed by using an ICP emission spectrometer (ICPE-9000, product of Shimadzu corporation).

(SEM and EDX analysis)

The structure of the particles was observed by a scanning electron microscope (trade name: S-4700, manufactured by Hitachi Kagaku K.K.) in a state in which a nickel composite hydroxide powder or a lithium nickel composite oxide powder was embedded in a resin and the cross section of the particles was observed by focused ion beam processing.

The composition of the cobalt-rich layer or the manganese-rich layer in the nickel composite hydroxide powder or the lithium nickel composite oxide powder was analyzed by an energy dispersive X-ray spectrometer (EDX; product name: JED2300, manufactured by Nippon electronics Co., Ltd.). The EDX detector had a resolution of 137eV, and the measurement conditions were: tube voltage 20kV, tube current 20 muA, magnification 5000 times, WD15mm, processing time 4, and count 400 ten thousand or more.

(production of Battery)

The obtained positive electrode active material for a lithium ion secondary battery was evaluated by producing and evaluating the battery as follows. A positive electrode PE (electrode for evaluation) was produced by mixing 52.5mg of a positive electrode active material for a lithium ion secondary battery, 15mg of acetylene black, and 7.5mg of polytetrafluoroethylene resin (PTFE), and pressure-molding the mixture at a pressure of 100MPa to a diameter of 11mm and a thickness of 100 μm. The fabricated positive electrode was dried in a vacuum dryer at 120 ℃ for 12 hours. Then, using the positive electrode, a 2032 type coin cell was produced in a glove box in which the dew point was controlled to-80 ℃ in an Ar atmosphere.

As the Li metal negative electrode, a negative electrode sheet was used which was punched out into a disk shape having a diameter of 14mm and which had graphite powder having an average particle diameter of about 20 μ M and polyvinylidene fluoride coated on a copper foil, and as the electrolyte, 1M LiPF was used₆A mixture of Ethylene Carbonate (EC) and diethyl carbonate (DEC) at a ratio of 3:7 (manufactured by Fushan chemical industries, Ltd.) was used as a supporting electrolyte. As the separator, a film was usedA polyethylene porous film having a thickness of 25 μm. Further, the button type battery has a gasket and a wave washer, and a button-shaped battery is assembled from a positive electrode can and a negative electrode can. The positive electrode resistance (output characteristic) and cycle characteristics indicating the performance of the manufactured coin cell were evaluated as follows.

(Positive electrode resistance)

The resistance value was measured by an ac impedance method using a 2032 type coin cell charged at a charging potential of 4.1V. In the measurement, a nyquist diagram can be obtained by measuring with an ac impedance method using a frequency response analyzer and a potentiostat (Solartron). Since the nyquist diagram is expressed as the sum of characteristic curves showing the solution resistance, the negative electrode resistance and capacity, and the positive electrode resistance and capacity, the value of the positive electrode resistance was calculated by performing fitting calculation using an equivalent circuit.

(characteristics of cycle)

Further, using the above-mentioned 2032 type coin cell, the charge and discharge cycles were repeated 500 cycles after charging to 4.1V at a rate CC of 2C and resting for 10 minutes, discharging to 3.0V at the same rate CC and resting for 10 minutes, and the 500 th discharge capacity with respect to the initial discharge capacity was measured to calculate the capacity retention rate at 500 cycles.

The production conditions of each of examples and comparative examples of the nickel composite hydroxide and the positive electrode active material for a lithium ion secondary battery having a cobalt-rich layer or a manganese-rich layer are described below.

Examples and comparative examples of nickel composite hydroxide having cobalt-rich layer and positive electrode active material for lithium ion secondary battery

(example 1)

A composite solution of nickel sulfate (nickel concentration: 84.0g/L) and manganese sulfate (manganese concentration: 31.0g/L) was prepared as a first mixed aqueous solution (raw material solution), and a composite solution of nickel sulfate (nickel concentration: 38.0g/L) and cobalt sulfate (cobalt concentration: 79.0g/L) was prepared as a second mixed aqueous solution (raw material solution).

25L of pure water was charged into a reaction tank (60L) and stirred in a nitrogen atmosphere (the oxygen concentration in the reaction tank was 2% by volume or less), and an appropriate amount of 25% by mass aqueous sodium hydroxide solution and 25% by mass aqueous ammonia was added thereto with the temperature in the tank set at 42 ℃ to adjust the pH of the liquid in the tank to 12.8 based on the liquid temperature of 25 ℃ and the ammonia concentration in the liquid to 10g/L, thereby preparing a pre-reaction aqueous solution. To this, the first mixed aqueous solution was added at a rate of 130 ml/min, and at the same time, 25 mass% aqueous ammonia and 25 mass% aqueous sodium hydroxide solution were added at fixed rates, and crystallization was performed for 2 minutes and 30 seconds while controlling the pH at 12.8 (nucleation pH) (nucleation step S10).

Then, the supply of the 25 mass% sodium hydroxide aqueous solution was suspended until the pH reached 11.6 (nuclear growth pH) based on the liquid temperature of 25 ℃, and after the pH reached 11.6, the supply of the 25 mass% sodium hydroxide aqueous solution was restarted, and crystallization was continued for 2.2 hours in a non-oxidizing atmosphere with the pH being kept unchanged at 11.6 (first particle growth step S21), and after the crystallization was continued for 0.2 hours by switching to an oxidizing atmosphere (second particle growth step S22), the crystallization was continued for 1.0 hour by switching to a non-oxidizing atmosphere and switching the first mixed solution (raw material solution) to the second mixed aqueous solution (third particle growth step S23), and the process was ended. After the crystallization is completed, the product is washed with water, filtered and dried to obtain nickel-cobalt-manganese composite hydroxide particles containing a cobalt-rich layer.

The composition of the entire nickel-cobalt-manganese composite hydroxide particles was measured by a luminescence spectroscopic analyzer, and it was confirmed that Ni: Co: Mn was 60:20: 20. Further, it was confirmed by EDX that the composition of the cobalt-rich layer was 33:67:0 in terms of Ni: Co: Mn.

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

Next, the obtained nickel-cobalt-manganese composite hydroxide particles including a cobalt-rich layer were thoroughly mixed with lithium carbonate weighed so that Li/Me was 1.04 using a swing mixer apparatus (turbo type T2C manufactured by Willy a. bachofen (WAB)). The lithium mixture was baked in a stream of air (oxygen: 21 vol%) at 880 ℃ for 10 hours, and then pulverized to obtain lithium nickel cobalt manganese composite oxide particles including a cobalt-rich layer.

The composition of the entire lithium nickel cobalt manganese composite oxide particle including the cobalt-rich layer was measured by a luminescence spectroscopic analyzer, and it was confirmed that Li: Ni: Co: Mn was 104:60:20: 20. Further, the composition of the cobalt-rich layer was confirmed by EDX that Li was Ni, Co, Mn was 104:33:67: 0.

Further, the cross section of the lithium nickel cobalt manganese composite oxide particles including the cobalt-rich layer was observed by SEM, and the thicknesses of the void layer and the cobalt-rich layer were measured. Further, a battery was produced as described above, and the positive electrode resistance was measured. The evaluation results are shown in table 2.

(example 2)

Nickel cobalt manganese composite hydroxide particles including a cobalt-rich layer were obtained in the same manner as in example 1, except that the first mixed aqueous solution (raw material solution) was nickel sulfate (nickel concentration: 97.3g/L) and manganese sulfate (manganese concentration: 18.3g/L), the second mixed aqueous solution (raw material solution) was nickel sulfate (nickel concentration: 29.3g/L), cobalt sulfate (cobalt concentration: 58.9g/L), and manganese sulfate (manganese concentration: 27.5g/L), and the third particle growth step was performed for 1.6 hours. Lithium nickel cobalt manganese composite oxide particles including a cobalt-rich layer were obtained in the same manner as in example 1, except that the nickel cobalt manganese composite hydroxide particles including a cobalt-rich layer were used. The evaluation results are shown in tables 1 and 2.

(example 3)

Lithium nickel cobalt manganese composite oxide particles including a cobalt-rich layer were obtained in the same manner as in example 1, except that the firing temperature was set to 830 ℃. The evaluation results are shown in table 2.

(example 4)

Lithium nickel cobalt manganese composite oxide particles including a cobalt-rich layer were obtained in the same manner as in example 1, except that the firing temperature was 930 ℃. The evaluation results are shown in table 2.

Comparative example 1

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

A cobalt-rich layer-containing nickel-cobalt-manganese composite hydroxide particle was obtained in the same manner as in example 1, except that a composite solution of nickel sulfate (nickel concentration: 75.6g/L), cobalt sulfate (cobalt concentration: 15.7g/L), and manganese sulfate (manganese concentration: 24.5g/L) was prepared as the first mixed aqueous solution (raw material solution), a nucleation step was performed for 2.5 minutes in a non-oxidizing atmosphere, a particle growth step was performed before switching the raw material solution for 3.4 hours, crystallization was continued for 0.2 hours while switching the oxidizing atmosphere to the oxidizing atmosphere, and then, crystallization was performed for 0.4 hours while using a second mixed aqueous solution (composite solution) of nickel sulfate (nickel concentration: 23.5g/L) and cobalt sulfate (cobalt concentration: 94.3 g/L). Lithium nickel cobalt manganese composite oxide particles including a cobalt-rich layer were obtained in the same manner as in example 1, except that the nickel cobalt manganese composite hydroxide particles including a cobalt-rich layer were used. The evaluation results are shown in tables 1 and 2.

Comparative example 4

A composite solution of nickel sulfate (nickel concentration: 87.6g/L) and manganese sulfate (manganese concentration: 27.3g/L) was prepared as a first mixed aqueous solution (raw material solution), a nucleation step was performed for 2.5 minutes in a non-oxidizing atmosphere and a particle growth step was performed before switching the raw material solution for 1.4 hours, crystallization was continued for 0.2 hours while switching the raw material solution to an oxidizing atmosphere, and after switching the raw material solution to a non-oxidizing atmosphere, a composite solution of nickel sulfate (nickel concentration: 58.4g/L), cobalt sulfate (cobalt concentration: 38.7g/L) and manganese sulfate (concentration: 18.6g/L) was crystallized as a second mixed aqueous solution (raw material solution) for 2.4 hours, except that nickel-cobalt-manganese composite hydroxide particles including a cobalt-rich layer were obtained in the same manner as in example 1. In the same manner as in example 1 except that the nickel-cobalt-manganese composite hydroxide particles were used, lithium nickel-cobalt-manganese composite oxide particles including a cobalt-rich layer were obtained. The evaluation results are shown in tables 1 and 2.

[ Table 1]

[ Table 2]

Examples and comparative examples for nickel composite hydroxide having manganese-rich layer and positive electrode active material for lithium ion secondary battery

(example 5)

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

25L of pure water was charged into a reaction tank (60L) and stirred in a nitrogen atmosphere (the oxygen concentration in the reaction tank was 2% by volume or less), and an appropriate amount of 25% by mass aqueous sodium hydroxide solution and 25% by mass aqueous ammonia was added thereto with the temperature in the tank set at 42 ℃ to adjust the pH of the liquid in the tank to 12.8 based on the liquid temperature of 25 ℃ and the ammonia concentration in the liquid to 10g/L, thereby preparing a pre-reaction aqueous solution. To this, the first mixed aqueous solution was added at a rate of 130 ml/min, and at the same time, 25 mass% aqueous ammonia and 25 mass% aqueous sodium hydroxide solution were added at fixed rates, and crystallization was performed for 2 minutes and 30 seconds while controlling the pH at 12.8 (nucleation pH) (nucleation step S10).

Then, the supply of the 25 mass% sodium hydroxide aqueous solution was suspended until the pH reached 11.6 (nucleus growth pH) based on the liquid temperature of 25 ℃, and after the pH reached 11.6, the supply of the 25 mass% sodium hydroxide aqueous solution was restarted, and the crystallization was continued for 0.2 hours in a non-oxidizing atmosphere with the pH being kept constant at 11.6 (first particle growth step S21) and the oxidizing atmosphere (atmospheric atmosphere) being switched (second particle growth step S22), and after that, the crystallization was continued for 1.6 hours with the first mixed solution (raw material solution) switched to the second mixed aqueous solution (third particle growth step S23) and the process was ended. After the crystallization is finished, the product is washed with water, filtered and dried to obtain the nickel-cobalt-manganese composite hydroxide particles containing the manganese-rich layer.

The composition of the entire nickel-cobalt-manganese composite hydroxide particles was measured by a luminescence spectroscopic analyzer, and it was confirmed that Ni: Co: Mn was 60:20: 20. Further, the composition of the manganese-rich layer was confirmed by EDX that Ni, Co, and Mn were 50:0: 50.

Further, 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 3.

Next, the nickel-cobalt-manganese composite hydroxide particles including the manganese-rich layer thus obtained were thoroughly mixed with lithium carbonate weighed so that Li/Me was 1.04 using a swing mixer apparatus (turbo type T2C manufactured by Willy a. The lithium mixture was baked at 880 ℃ for 10 hours in a stream of air (oxygen: 21 vol%) and then pulverized to obtain lithium nickel cobalt manganese composite oxide particles including a manganese-rich layer.

The composition of the entire lithium nickel cobalt manganese composite oxide particle including the manganese-rich layer was measured by a luminescence spectroscopic analyzer, and it was confirmed that Li: Ni: Co: Mn was 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, the cross section of the lithium nickel cobalt manganese composite oxide particles including the manganese-rich layer was observed by SEM, and the thicknesses of the void layer and the manganese-rich layer were measured. Further, a battery was produced as described above, and the cycle characteristics were evaluated. The evaluation results are shown in table 4.

(example 6)

Nickel cobalt manganese composite hydroxide particles including a manganese-rich layer were obtained in the same manner as in example 5, except that the first mixed aqueous solution (raw material solution) was nickel sulfate (nickel concentration: 79.5g/L), cobalt sulfate (cobalt concentration: 36.4g/L), and manganese sulfate (manganese concentration: 1.5g/L), and the second mixed aqueous solution (raw material solution) was nickel sulfate (nickel concentration: 23.5g/L), cobalt sulfate (cobalt concentration: 17.7g/L), and manganese sulfate (manganese concentration: 71.5 g/L). Lithium nickel cobalt manganese composite oxide particles including a manganese-rich layer were obtained in the same manner as in example 5, except that the nickel cobalt manganese composite hydroxide particles including a manganese-rich layer were used. The evaluation results are shown in tables 3 and 4.

(example 7)

Lithium nickel cobalt manganese composite oxide particles including a manganese-rich layer were obtained in the same manner as in example 5, except that the firing temperature was set to 830 ℃. The evaluation results are shown in table 4.

(example 8)

Lithium nickel cobalt manganese composite oxide particles including a manganese-rich layer were obtained in the same manner as in example 5, except that the firing temperature was 930 ℃. The evaluation results are shown in table 4.

Comparative example 5

The nucleation step was performed for 2.5 minutes in a nitrogen atmosphere using only a composite solution of nickel sulfate (nickel concentration: 70.4g/L), cobalt sulfate (cobalt concentration: 23.6g/L) and manganese sulfate (manganese concentration: 22.0g/L) as a raw material solution without using the second mixed aqueous solution, and the first, second and third particle growth steps were performed for 4 hours in a nitrogen atmosphere. Otherwise, nickel-cobalt-manganese composite hydroxide particles were obtained in the same manner as in example 5. Lithium nickel cobalt manganese composite oxide particles were obtained in the same manner as in example 5, except that the nickel cobalt manganese composite hydroxide particles were used. The evaluation results are shown in tables 3 and 4.

Comparative example 6

A positive electrode active material was obtained and evaluated in the same manner as in example 5, except that the second particle growth step was performed in a nitrogen atmosphere. The evaluation results are shown in tables 3 and 4.

Comparative example 7

A nickel-cobalt-manganese composite hydroxide particle including a manganese-rich layer was obtained in the same manner as in example 5, except that a composite solution of nickel sulfate (nickel concentration: 75.5g/L), cobalt sulfate (cobalt concentration: 26.2g/L), and manganese sulfate (manganese concentration: 14.7g/L) was prepared as the first mixed aqueous solution (raw material solution), the nucleation step and the particle growth step before the switching of the raw material solution were performed in a non-oxidizing atmosphere, the crystallization was continued for 0.2 hours while switching to an oxidizing atmosphere, the crystallization was continued for 0.2 hours, and then the crystallization was performed for 0.4 hours while switching to a non-oxidizing atmosphere, and nickel sulfate (nickel concentration: 23.5g/L) and manganese sulfate (manganese concentration: 87.9g/L) were used as the second mixed aqueous solution (composite solution). Lithium nickel cobalt manganese composite oxide particles including a manganese-rich layer were obtained in the same manner as in example 5, except that the nickel cobalt manganese composite hydroxide particles including a manganese-rich layer were used. The evaluation results are shown in tables 3 and 4.

Comparative example 8

A composite solution of nickel sulfate (nickel concentration: 87.6g/L), cobalt sulfate (cobalt concentration: 29.3g/L) and manganese sulfate (manganese concentration: 0.6g/L) was prepared as a first mixed aqueous solution (raw material solution), a nucleation step and a particle growth step before switching the raw material solution for 1.4 hours were performed in a non-oxidizing atmosphere, crystallization was continued for 0.2 hours while switching to an oxidizing atmosphere, and after switching to a non-oxidizing atmosphere, crystallization was performed for 2.4 hours while using a composite solution of nickel sulfate (nickel concentration: 58.7g/L), cobalt sulfate (cobalt concentration: 19.7g/L) and manganese sulfate (manganese concentration: 33.6g/L) as a second mixed aqueous solution (raw material solution), to obtain nickel-cobalt-manganese composite hydroxide particles including a manganese-rich layer, in the same manner as in example 5. Lithium nickel cobalt manganese composite oxide particles including a manganese-rich layer were obtained in the same manner as in example 5, except that the nickel cobalt manganese composite hydroxide particles including a manganese-rich layer were used. The evaluation results are shown in tables 3 and 4.

[ Table 3]

[ Table 4]

Examples and comparative examples of nickel composite hydroxide containing cobalt-rich layer and positive electrode active material for lithium ion secondary battery

(evaluation)

It is understood that in examples 1 to 4, since the particles have a cobalt-rich layer and a layered void layer inside the particles, the positive electrode resistance is low, and high output characteristics are obtained. On the other hand, it is found that comparative example 1 has no cobalt-rich layer, and in comparative example 2, the cobalt-rich layer disappears due to diffusion of the composition in the particles caused by firing, and therefore the positive electrode resistance becomes high, and high output characteristics cannot be obtained. It is understood that in comparative example 3, although having a cobalt-rich layer, the positive electrode resistance is high and the effect of improving the output characteristics is small because the thicknesses of the low-density layer and the void layer are less than 1% of the secondary particle diameter. It is understood that comparative example 4 has a cobalt-rich layer, but the thickness of the cobalt-rich layer is greater than 10% of the secondary particle diameter, and therefore the positive electrode resistance is high and the effect of improving the output characteristics is small.

Examples and comparative examples for nickel composite hydroxide containing manganese-rich layer and positive electrode active material for lithium ion secondary battery

(evaluation)

It is understood that in examples 5 to 8, since the manganese-rich layer was provided and the lamellar void layer was provided in the particle interior, the cycle characteristics were improved and high durability was obtained. On the other hand, it is understood that comparative example 5 has no manganese-rich layer, and in comparative example 6, high durability cannot be obtained because the manganese-rich layer disappears due to diffusion of the composition in the particles caused by firing. It is understood that comparative example 7 has a manganese-rich layer, but the low-density layer and the void layer have thicknesses less than 1% relative to the secondary particle diameter, and therefore the durability improvement effect is small. It is understood that comparative example 8 has a manganese-rich layer, but the effect of improving the cycle characteristics is small because the thickness of the manganese-rich layer is larger than 10% with respect to the secondary particle diameter.

Based on the above, the present invention can provide a nickel composite hydroxide as a precursor of a positive electrode active material for a lithium ion secondary battery having excellent positive electrode resistance and cycle characteristics. Further, a method for easily producing the nickel composite hydroxide with high productivity can be provided. Further, a positive electrode active material for a lithium ion secondary battery excellent in positive electrode resistance and cycle characteristics, a method for producing the same, and a lithium ion secondary battery can be provided.

While the embodiments and examples of the present invention have been described in detail, those skilled in the art will readily understand that many modifications can be made without substantially departing from the novel aspects and effects of the present invention. Therefore, such modifications are included in the scope of the present invention.

For example, in the specification or the drawings, a term described at least once together with a different term having a broader meaning or the same meaning may be replaced with the different term anywhere in the specification or the drawings. The nickel composite hydroxide, the method for producing the nickel composite hydroxide, the positive electrode active material for a lithium ion secondary battery, the method for producing the positive electrode active material for a lithium ion secondary battery, and the configuration and operation of the lithium ion secondary battery are not limited to the description of the embodiments and examples of the present invention, and various modifications can be made.

Description of the symbols

S10: nucleus generation 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: and (5) a firing process.