Particles, cathode active material particles, method for producing them and non-aqueous electrolyte secondary battery

Abstract

To provide a method for producing particles having a core portion, a gap portion and an outer shell portion, which reduces the number of atmosphere changes in the crystallization step without requiring pH changes and composition changes of a transition metal-containing compound during the crystallization step and to provide particles and cathode active material particles composed of a transition metal composite hydroxide containing nickel having high circularity.SOLUTION: There is provided a method for producing particles which have a core portion, a gap portion and an outer shell portion and include first particles composed of a transition metal composite hydroxide containing nickel, wherein a first crystallization is performed in which the crystallization is performed by setting the pH of the Taylor vortex reaction field at a liquid temperature of 25°C to 12.5 or less and setting the oxygen concentration of the Taylor vortex reaction field to 3.5 vol.% or less and a second crystallization is performed in which the crystallization is performed by changing the oxygen concentration of the Taylor vortex reaction field to 5 vol.% or more and 65 vol.% or less and the time of the first crystallization is 40% or more and 90% or less of the total crystallization time.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to particles and a method for producing the same, and further to positive electrode active material particles, a method for producing the same, and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2013-147416 (Patent Document 1) discloses a nickel composite hydroxide used to produce a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same, and discloses that the nickel composite hydroxide has a core and an outer shell.

[0003] Japanese Patent Laid-Open Publication No. 2016-154143 (Patent Document 2) discloses transition metal composite hydroxide particles that serve as a precursor for a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same, and discloses that the positive electrode active material has a center portion, a space portion, and an outer shell portion. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-147416 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-154143 Summary of the Invention [Problem to be solved by the invention]

[0005] In the manufacturing method described in JP 2013-147416 A, after an oxidizing atmosphere is used in the nucleation step, the pH is changed in the particle growth step, and the oxidizing atmosphere is switched to a mixed gas atmosphere of oxygen and an inert gas, and further the composition of the metal compound to be supplied must be changed.

[0006] In the manufacturing method described in JP 2016-154143 A, it is necessary to use a non-oxidizing atmosphere in the nucleation step, switch to an oxidizing atmosphere in the particle growth step, and then switch back to a non-oxidizing atmosphere.

[0007] In any of the above-mentioned production methods, the crystallization step is complicated, the porosity in the nickel composite hydroxide particles is difficult to control, and the particle shape tends to be non-uniform. As a result, it may be difficult to obtain improvements in the output characteristics and capacity characteristics of the non-aqueous electrolyte secondary battery.

[0008] The object of the present disclosure is to provide a method for producing particles made of a nickel-containing transition metal composite hydroxide, which have a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, wherein the method eliminates the need to change the pH and the composition of the transition metal-containing compound in the crystallization step, thereby reducing the number of times the atmosphere is changed in the crystallization step, and a method for producing positive electrode active material particles including the same; and to provide particles made of a nickel-containing transition metal composite hydroxide, which have a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, and have a circularity of 0.90 or more; positive electrode active material particles made of a metal composite oxide containing lithium and nickel, which have a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, and have a circularity of 0.90 or more; and a nonaqueous electrolyte secondary battery including the same. [Means for solving the problem]

[0009] [1] A method for producing particles, comprising: the particles include first particles each having a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, the first particles being made of a transition metal composite hydroxide containing nickel, a crystallization step of generating a Taylor vortex reaction field, adding an aqueous solution containing a compound containing a transition metal, an ammonium donor, and an alkaline aqueous solution to the Taylor vortex reaction field, and crystallizing a nickel-containing transition metal composite hydroxide; In the crystallization step, The pH of the Taylor vortex reaction field at a liquid temperature of 25°C is 12.5 or less, a first crystallization is performed in which the oxygen concentration in the Taylor vortex reaction field is set to 3.5 vol% or less; Next, a second crystallization is carried out by changing the oxygen concentration in the Taylor vortex reaction field to 5 vol% or more and 65 vol% or less, A method for producing particles, wherein the time for carrying out the first crystallization is 40% or more and 90% or less of the total crystallization time. [2] The method for producing particles according to [1], wherein in the crystallization step, the pH of the Taylor vortex reaction field at a liquid temperature of 25°C is 11.0 or higher. [3] The method for producing particles according to [1] or [2], wherein in the first crystallization, crystallization is carried out while maintaining the oxygen concentration in the Taylor vortex reaction field at 3.0 vol% or less. [4] The method for producing particles according to any one of [1] to [3], wherein the time for carrying out the first crystallization is 50% or more and 80% or less of the total crystallization time. [5] The method for producing particles according to any one of [1] to [4], wherein the second crystallization is carried out while maintaining the oxygen concentration in the Taylor vortex reaction field at 10 vol % or more and 60 vol % or less. [6] The method for producing particles according to any one of [1] to [5], wherein the rotation speed of the inner cylinder that generates the Taylor vortex reaction field is 500 to 2000 rpm. [7] A particle having a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, the particle being made of a transition metal composite hydroxide containing nickel, and having a circularity of 0.90 or more. [8] The particles according to [7], having an average particle size of 1 μm to 10 μm. [9] The particles according to [7] or [8], wherein the average ratio (%) of the diameter of the core to the particle diameter is 1% to 70%.

[10] The particles according to any one of [7] to [9], wherein the average ratio (%) of the thickness of the outer structure to the particle diameter is 3% to 50%.

[11] The particles according to any one of [7] to

[10] , wherein the average ratio (%) of the width of the void portion to the particle diameter is 10% or more.

[12] A positive electrode active material particle having a core portion, a void portion outside the core portion, and an outer portion outside the void portion, the positive electrode active material particle being made of a metal composite oxide containing lithium and nickel, and having a circularity of 0.90 or more.

[13] The positive electrode active material particles according to

[12] , wherein the core portion has a solid structure or a hollow structure.

[14] The positive electrode active material particles according to

[12] or

[13] , further comprising one or more inner structure layers between the outer structure portion and the core portion.

[15] The positive electrode active material particles according to any one of

[12] to

[14] , which have an average particle size of 2 μm to 10 μm.

[16] The positive electrode active material particles according to any one of

[12] to

[15] , wherein the average ratio (%) of the thickness of the outer structure to the particle diameter is 5% to 50%.

[17] The electrode active material particles according to any one of

[12] to

[16] , wherein the average ratio (%) of the width of the void portion to the particle diameter is 5% to 80%.

[18] BET specific surface area is 0.5–2.8 m 2 The positive electrode active material particles according to any one of

[12] to

[17] , wherein the positive electrode active material particles have a viscosity of 1000 MPa.

[19] The positive electrode active material particles according to any one of

[12] to

[18] , which are secondary particles made of primary particles, and have an average particle diameter of 0.1 to 1.0 μm.

[20] A method for producing positive electrode active material particles, comprising: a particle production step of producing particles by the particle production method according to [1] or [2]; a mixing step of mixing the obtained particles with lithium to obtain a mixture; and a firing step of firing the mixture.

[21] A non-aqueous electrolyte secondary battery comprising the positive electrode active material particles according to any one of

[12] to

[19] . [Effects of the Invention]

[0010] According to the present disclosure, there are provided a method for producing particles made of a nickel-containing transition metal composite hydroxide, which have a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, wherein the method eliminates the need to change the pH or the composition of the transition metal-containing compound in the crystallization step, thereby reducing the number of times the atmosphere is changed in the crystallization step, and a method for producing positive electrode active material particles including the same; particles made of a nickel-containing transition metal composite hydroxide, which have a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, and have a circularity of 0.90 or more; positive electrode active material particles made of a metal composite oxide containing lithium and nickel, which have a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, and have a circularity of 0.90 or more; and a nonaqueous electrolyte secondary battery including the same. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view illustrating a reaction vessel that generates a Taylor vortex reaction field. [Figure 2] FIG. 2 is a schematic cross-sectional view of a precursor particle. [Figure 3] FIG. 3 is a scanning electron microscope image showing an example of the overall appearance of precursor particles. [Figure 4] FIG. 4 is a scanning electron microscope image showing an example of a cross section of a precursor particle. [Figure 5] FIG. 5 is a scanning electron microscope image showing an example of a cross section of a precursor particle. [Figure 6] FIG. 6 is a schematic cross-sectional view of a positive electrode active material particle. [Figure 7] FIG. 7 is a scanning electron microscope image showing an example of the overall appearance of positive electrode active material particles. [Figure 8] FIG. 8 is a scanning electron microscope image showing an example of the overall appearance of positive electrode active material particles. [Figure 9] FIG. 9 is a scanning electron microscope image showing an example of a cross section of a positive electrode active material particle. DETAILED DESCRIPTION OF THE INVENTION

[0012] <Particle manufacturing method> The particle manufacturing method of the present disclosure includes a first particle having a core, a void outside the core, and an outer structure outside the void, and made of a transition metal composite hydroxide containing nickel (Ni) (hereinafter also referred to as a first metal hydroxide). The method includes a crystallization step of generating a Taylor vortex reaction field, adding an aqueous solution containing a transition metal compound (hereinafter also referred to as a raw metal aqueous solution), an ammonium donor, and an alkaline aqueous solution to the Taylor vortex reaction field, and crystallizing the transition metal composite hydroxide containing nickel. In the crystallization step, the pH of the Taylor vortex reaction field at 25°C is 12.5 or less. A first crystallization is performed by setting the oxygen concentration in the Taylor vortex reaction field to 3.5 vol% or less. Next, a second crystallization is performed by changing the oxygen concentration in the Taylor vortex reaction field to 5 vol% or more and 65 vol% or less. The time spent performing the first crystallization is 40% to 90% of the total crystallization time.

[0013] (particle) The particles can be precursors of a positive electrode active material used in an active material layer of a positive electrode of a non-aqueous electrolyte secondary battery (hereinafter also referred to as a secondary battery), such as a lithium ion battery. The particles are hereinafter also referred to as precursor particles. The precursor particles include first particles. The precursor particles may include particles other than the first particles. Examples of particles other than the first particles include particles with a solid structure that does not have voids or outer structures, and particles with a hollow structure that does not have a core. When the precursor particles include particles other than the first particles, the content of the first particles in the precursor particles can be, for example, 50% or more. The precursor particles preferably include only the first particles. The first particles will be described later.

[0014] The first metal hydroxide may be a composite hydroxide further containing manganese (Mn), or may be a nickel-cobalt-manganese composite hydroxide (hereinafter also referred to as an NCM composite hydroxide) further containing Mn and cobalt (Co). The first metal hydroxide is preferably an NCM composite hydroxide.

[0015] The NCM composite hydroxide may be, for example, a compound represented by the following formula (i): Ni 1-x-y-z Co x Mn y M z (OH)2(i) (In formula (i), 0≦x<0.5, 0≦y<0.5, 0≦z<0.05, M is one or more elements selected from the group consisting of Al, Ti, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Si, V, Cr, and Ge. The composition of the first metal hydroxide can be determined by, for example, ICP (inductively coupled plasma) emission spectrometry.

[0016] (Crystallization process) The transition metal-containing compound contained in the raw metal aqueous solution can be, for example, a transition metal sulfate, nitrate, or carbonate. The transition metal-containing compound includes a Ni-containing compound. Examples of Ni-containing compounds include nickel sulfate (NiSO4), nickel nitrate [Ni(NO3)2], and nickel carbonate (NiCO3).

[0017] When the first metal hydroxide is a composite hydroxide further containing Mn, the raw metal aqueous solution may further contain a compound containing Mn. Examples of the compound containing Mn include manganese sulfate (MnSO), manganese nitrate [Mn(NO)], and manganese carbonate (MnCO). When the first metal hydroxide is an NCM composite hydroxide, the raw metal aqueous solution may further contain a compound containing Mn and a compound containing Co. Examples of the compound containing Co include cobalt sulfate (CoSO), cobalt nitrate [Co(NO)], and cobalt carbonate (CoCO).

[0018] The aqueous raw metal solution may further contain at least one element (hereinafter also referred to as an additive element) selected from the group consisting of Al, Ti, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Si, V, Cr, and Ge. The additive element may be added to the aqueous raw metal solution as the element itself or in the form of a salt (for example, in the form of a sulfate, nitrate, or carbonate).

[0019] The molar ratio of the transition metal-containing compound in the raw metal aqueous solution can be the molar ratio of the transition metal contained in the first metal hydroxide. The metal content in the raw metal aqueous solution can be, for example, 1.0 to 3.0 mol / L.

[0020] When the raw metal aqueous solution contains Mn, the molar ratio of Ni to Mn (Ni:Mn) in the raw metal aqueous solution is, for example, 1-x:0. <x<0.5であってよく、1-x:0.1<x<0.5または1-x:0.2<x<0.4であってもよい。

[0021] When the raw metal aqueous solution contains Mn and Co, the molar ratio of Ni, Mn, and Co in the raw metal aqueous solution (Ni:Mn:Co) is, for example, 1-xy:0 <x<0.5:0<y<0.5であってよく、1-x-y:0.05<x<0.25:0.05<y<0.25または1-x-y:0.1<x<0.2:0.1<y<0.2であってもよい。

[0022] When the raw metal aqueous solution contains Mn, Co, and other additive elements, the molar ratio of Ni, Mn, Co, and other additive elements in the raw metal aqueous solution (Ni:Co:Mn:other additive elements) is, for example, 1-xyz:0 <x<0.5:0<y<0.5:0<z<0.05であってよく、1-x-y-z:0.05<x<0.25:0.05<y<0.25:0.001<z<0.01または1-x-y-z:0.1<x<0.2:0.1<y<0.2:0.001<z<0.005であってもよい。

[0023] The ammonium donor may be, for example, an aqueous ammonia solution, the ammonia concentration of which may be, for example, 5 to 20 wt %.

[0024] The alkaline aqueous solution may be, for example, an aqueous sodium hydroxide solution, the sodium hydroxide concentration of which may be, for example, 10 to 40 wt %.

[0025] The Taylor vortex reaction field can be a fluid in which Taylor vortices are generated. Taylor vortices are two rows of donut-shaped vortices rotating in opposite directions. For example, two concentric cylinders whose difference in radius is small compared to their diameters can be filled with a fluid. By rotating the inner cylinder (hereinafter referred to as the inner cylinder) while keeping the outer cylinder (hereinafter referred to as the outer cylinder) stationary, two rows of vortices can be generated in a circular pattern along the circumference between the outer and inner cylinders. Multiple rows of two vortices can be generated along the length of the two concentric cylinders (perpendicular to the diameter). Performing a crystallization reaction in a fluid in which Taylor vortices are generated eliminates the need to change the pH or the composition of the transition metal-containing compound during crystallization, simplifying the production method of precursor particles and facilitating industrial-scale production. Furthermore, this method significantly reduces the production time compared to batch production methods, tending to improve productivity. In addition, a solid core is formed in a non-oxidizing atmosphere, and then an oxidizing atmosphere is used to form an outer structure around the core, enabling the production of particles having a core, voids, and outer structure. Furthermore, the use of a Taylor vortex reaction field tends to facilitate uniform size of the outer structure. The manufacturing method of the present disclosure can use a commercially available reactor that generates Taylor vortices.

[0026] The reaction layer that generates a Taylor vortex reaction field will be described with reference to FIG. 1. The reaction vessel 10 shown in FIG. 1 includes an outer cylinder 11 and an inner cylinder 12. The outer cylinder 11 is fixed. The inner cylinder 12 can be rotated by a motor 18. The outer cylinder 11 includes a first supply port 13 for supplying a raw metal aqueous solution, a second supply port 14 for supplying an ammonium supply, and a third supply port 15 for supplying an alkaline aqueous solution. The outer cylinder 11 further includes an outlet 16.

[0027] Crystallization can be carried out in the reaction tank 10, for example, by the following procedure. First, water is filled between the outer cylinder 11 and the inner cylinder 12 through the first supply port 13, and the inner cylinder 12 is rotated to generate a Taylor vortex flow between the outer cylinder 11 and the inner cylinder 12, thereby generating a Taylor vortex reaction field. The rotation speed of the inner cylinder 12 can be, for example, 500 to 2000 rpm.

[0028] Aqueous sodium hydroxide solution is supplied to the fluid through the third supply port 15, and the pH of the Taylor vortex reaction field at a liquid temperature of 25°C is adjusted to 12.5 or less. The pH at a liquid temperature of 25°C can be controlled, for example, by adjusting the flow rate of the aqueous sodium hydroxide solution using a pH controller. The pH of the Taylor vortex reaction field at a liquid temperature of 25°C may be, for example, 10.7 or more. From the viewpoint of particle circularity and from the viewpoint of obtaining positive electrode active material particles described below, the pH of the Taylor vortex reaction field at a liquid temperature of 25°C is preferably 11.0 or more and 12.5 or less.

[0029] In the crystallization process, first and second crystallizations are performed. The first crystallization is initiated by supplying the raw metal aqueous solution through the first supply port 13 and the ammonium supply through the second supply port 14. The raw metal aqueous solution and the ammonium supply are supplied to the Taylor vortex reaction field at a molar ratio of 1:1. In the first crystallization, the oxygen concentration in the Taylor vortex reaction field is maintained at 3.5 vol% or less. A method for maintaining the oxygen concentration in the Taylor vortex reaction field at 3.5 vol% or less includes, for example, bubbling nitrogen gas into the raw metal aqueous solution and the ammonium supply supplied to the Taylor vortex reaction field. The oxygen concentration in the Taylor vortex reaction field from the start of crystallization until the oxygen concentration in the Taylor vortex reaction field is changed (described later) is also referred to as the first oxygen concentration. Setting the first oxygen concentration to 3.5 vol% or less tends to facilitate the production of first particles. If the first oxygen concentration exceeds 3.5 vol%, core formation tends to be difficult. From the viewpoint of producing the first particles, the first oxygen concentration is preferably 3.0 vol% or less, more preferably 2.0 vol% or less, and even more preferably 1.0 vol% or less. The first oxygen concentration may be, for example, 0.5 vol% or more. The oxygen concentration in the Taylor vortex reaction field can be confirmed with a dissolved oxygen meter.

[0030] The time for which the first crystallization is performed (hereinafter also referred to as the first crystallization time) is set so that the proportion of the time for which crystallization is performed to the total time for which crystallization is performed in the crystallization step (hereinafter also referred to as the first crystallization proportion) is 40% or more and 90% or less. When the first crystallization proportion is within the above range, the first particles tend to be produced more easily. When the first crystallization proportion is less than 40%, the core portion tends to be less easily formed. When the first crystallization proportion is more than 90%, the outer portion tends to be less easily formed. From the viewpoint of producing the first particles, the first crystallization proportion is preferably 45% or more and 85% or less, more preferably 50% or more and 80% or less. The first crystallization time may be, for example, 10 minutes to 60 minutes.

[0031] Next, the oxygen concentration in the Taylor vortex reaction field is changed to and maintained at 5 vol% to 65 vol% or less, and a second crystallization is performed while maintaining the oxygen concentration. In the manufacturing method of the present disclosure, the oxygen concentration in the Taylor vortex reaction field can be changed only once during the crystallization process. The oxygen concentration in the Taylor vortex reaction field can be changed, for example, by changing the type of gas flowing into the raw metal aqueous solution and the ammonium supplier for bubbling. In the second crystallization, the type of gas used to maintain the oxygen concentration in the Taylor vortex reaction field at 5 vol% to 65 vol% or less may be, for example, a mixed gas of oxygen and nitrogen. To change the oxygen concentration in the Taylor vortex reaction field, the supply of the raw metal aqueous solution and the ammonium supplier is stopped, and the oxygen concentration in the Taylor vortex reaction field is changed to 5 vol% to 65 vol% or less, after which the supply of the raw metal aqueous solution and the ammonium supplier is resumed, and crystallization is performed. The time during which the supply of the raw metal aqueous solution and the ammonium supplier is stopped is not included in the overall crystallization time. Hereinafter, the oxygen concentration in the Taylor vortex reaction field during the second crystallization is also referred to as the second oxygen concentration. When the second oxygen concentration is within the above range, the first particles tend to be easier to produce. When the second oxygen concentration is less than 5 vol%, the outer structure tends to be difficult to form. When the second oxygen concentration is more than 65 vol%, the circularity of the first particles tends to be difficult to improve. From the viewpoint of the production and circularity of the first particles, the second oxygen concentration is preferably 10 vol% or more and 60 vol% or less, and more preferably 15 vol% or more and 55 vol% or less.

[0032] The time for which the second crystallization is performed (hereinafter also referred to as the second crystallization time) may be a time such that the proportion of the time for which crystallization is performed to the total time for which crystallization is performed in the crystallization step (hereinafter also referred to as the second crystallization proportion) is, for example, 10% or more and 60% or less. When the second crystallization proportion is within the above range, the first particles tend to be easily produced and the circularity tends to be easily improved. When the second crystallization proportion is less than 10%, the outer structure tends to be difficult to form. When the first crystallization proportion is more than 60%, the circularity tends to be difficult to improve. From the viewpoint of the production and circularity of the first particles, the second crystallization proportion is preferably 15% or more and 55% or less, more preferably 20% or more and 50% or less. The second crystallization time may be, for example, 3 minutes to 30 minutes.

[0033] During crystallization, the pH of the Taylor vortex reaction field at a liquid temperature of 25°C may be maintained at the pH adjusted before the start of crystallization, and there is no need to change the pH of the Taylor vortex reaction field at a liquid temperature of 25°C from the first crystallization to the second crystallization. As a result, it is possible to easily produce the first particles. The pH of the Taylor vortex reaction field at a liquid temperature of 25°C during crystallization is maintained at 12.5 or less, preferably 11.0 or more and 12.5 or less.

[0034] In the production method of the present disclosure, the oxygen concentration may be changed twice in the crystallization step. For example, in the second crystallization, the oxygen concentration in the Taylor vortex reaction field may be changed to 5 vol% or more and 65 vol% or less to perform crystallization (hereinafter also referred to as second crystallization A), and then the oxygen concentration in the Taylor vortex reaction field may be changed to 3.5 vol% or less to perform crystallization (hereinafter also referred to as second crystallization B). Second crystallization A and second crystallization B may be performed so that the total time falls within the above-mentioned second crystallization time range.

[0035] After the crystallization step is completed, the solution containing the precursor particles can be taken out from the outlet 16 and collected in a container 17. The collected solution containing the precursor particles can be filtered, washed with water, and then dried to obtain the precursor particles.

[0036] <1st particle> The first particles are particles made of a first metal hydroxide and have a core, a void outside the core, and an outer structure outside the void. The first particles can be produced by the particle production method described above. The average particle diameter of the first particles may be, for example, 1 μm to 10 μm. In this specification, the average particle diameter refers to the particle diameter D50 at which the cumulative frequency of particles with smaller diameters in a volume-based particle size distribution reaches 50%. The volume-based particle size distribution can be measured using a particle size distribution analyzer.

[0037] The circularity of the first particles may be, for example, 0.70 or more, preferably 0.80 or more, more preferably 0.90 or more, and even more preferably 0.95 or more, and may be, for example, 1.00 or less. In this specification, the circularity is calculated by the following formula: Circularity = (perimeter of a circle equal to the projected area of ​​the particle) / (perimeter of the particle) The circularity of the first particles is the average of 50 first particles. When the circularity of the first particles is 0.90 or more, the packing property of the positive electrode active material particles tends to be improved, and the capacity characteristics of the secondary battery tends to be improved.

[0038] The first particle will be described with reference to FIG. 2. FIG. 2 is a schematic cross-sectional view of a first particle 20. The first particle 20 has a core portion 21, a void portion 22, and an outer structure portion 23. The first particle 20 may be a secondary particle formed by aggregation of primary particles. The core portion 21 may be an aggregate of primary particles 24. The core portion 21 may have a solid structure or a hollow structure. When the core portion 21 is hollow, the hollow portion of the core portion 21 is not considered to be a void portion 22.

[0039] The exterior structure 23 may be an aggregate of primary particles 25. The void 22 may be a space between the core 21 and the exterior structure 23, and the core 21 and the exterior structure 23 may be completely separated by the void 22, or there may be a portion in the first particle 20 where the primary particles 24 and 25 are in contact with each other, so that the core 21 and the exterior structure 23 are in contact with each other.

[0040] The proportion of the voids 22 to the total volume of the first particles 20 may be, for example, 10% or more, 40% or more, or 60% or more, or 30% or less, 60% or less, or 80% or less. In this specification, the proportion of the voids 22 to the total volume of the first particles 20 is a value determined by processing a cross-sectional SEM image of the first particles 20, distinguishing between the portions where the primary particles 24 exist and the voids 22, and calculating the proportion of the total area of ​​the voids to the area of ​​the particles.

[0041] 2, only a portion of the primary particles 24 and 25 is shown. The first particle 20 may further have one or more additional outer structure layers outside the outer structure portion 23. The outer structure portion 23 may be formed so as to completely cover the core portion 21, or may be formed so as to partially cover it.

[0042] Figure 3 is a scanning electron microscope (hereinafter also referred to as SEM) image showing an example of the overall appearance of a first particle. Figures 4 and 5 are SEM images showing examples of cross sections of a first particle. The core portion of the first particle shown in Figure 4 has a hollow structure. The core portion of the first particle shown in Figure 5 has a solid structure.

[0043] The first particles 20 may have an average ratio (%) of the diameter of the core portion 21 to the particle diameter (hereinafter also referred to as the first ratio) of 1% to 70%. The particle diameter of the first particles 20 may be the diameter of the cross section of the first particle 20 when the first particle 20 is considered to be a circle. For example, in FIG. 2, the particle diameter of the first particle 20 is indicated by a line 26. The diameter of the core portion 21 may be the dimension of the core portion 21 at the above diameter (line 26).

[0044] The first particle 20 may have an average ratio (%) of the thickness of the outer structure 23 to the particle diameter (hereinafter also referred to as the second ratio) of 3% to 50%. The thickness of the outer structure 23 may be the dimension of the outer structure 23 at the above-mentioned diameter (straight line 26) of the first particle 20.

[0045] The first particles 20 may have an average ratio (%) of the width (thickness) of the voids 22 to the particle size (diameter) (hereinafter also referred to as the third ratio) of, for example, 10% or more, 40% or more, or 60% or more. The third ratio may be, for example, 30% or less, 60% or less, or 80% or less. The width (thickness) of the voids 22 may be the dimension of the voids 22 at the above-mentioned diameter (straight line 26) of the first particles 20. The first ratio, second ratio, and third ratio are averages for 50 first particles. The first ratio, second ratio, and third ratio are measured according to the method described in the Examples section below.

[0046] The first particles 20 have high packing properties and have voids that are relatively uniform in cross section, and therefore when used in positive electrode active material particles, the output characteristics and capacity characteristics can be easily improved.

[0047] The average particle diameter of the primary particles 24 and 25 may be, for example, 0.01 to less than 0.5 μm. In this specification, the average particle diameter of primary particles refers to particles in which grain boundaries cannot be visually identified in an SEM image of the particles and which have a first maximum diameter of 0.01 μm or more. The first maximum diameter refers to the distance between the two most distant points on the particle's contour. In this embodiment, the "particle contour" may be identified in a two-dimensional projection image of the particle or in a cross-sectional image of the particle. The particle contour may be identified in, for example, an SEM image of the powder or in a cross-sectional SEM image of the particle. The average value of the first maximum diameter is calculated from the first maximum diameters of 100 particles. The 100 particles are randomly selected.

[0048] <Cathode active material particles> The positive electrode active material particles of the present disclosure include a fired product of a mixture of the first particles and lithium (Li). The positive electrode active material particles may have an average particle size of, for example, 1 μm to 10 μm. The positive electrode active material particles have a circularity of 0.90 or more, preferably 0.95 or more, and may be, for example, 1.00 or less. The circularity of the positive electrode active material particles is the average of 50 positive electrode active material particles. When the positive electrode active material particles have a circularity of 0.90 or more, the packing property tends to be improved, and the capacity characteristics of the secondary battery tend to be improved.

[0049] The positive electrode active material particles may be particles made of a composite oxide containing Li and Ni, may be particles made of a composite oxide containing Li, Ni, and Mn, or may be particles made of a composite oxide containing Li, Ni, Co, and Mn.

[0050] The positive electrode active material particles may be, for example, a compound represented by the following formula (ii): Li 1+a1 Ni 1-x-y-z Co x Mn y M z O2(ii) (In formula (ii), -0.1≦a1<0.3, 0≦x<0.5, 0≦y<0.5, 0≦z<0.05, M is one or more elements selected from the group consisting of Al, Ti, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Si, V, Cr, and Ge. The particles may be made of a layered metal oxide represented by the following formula:

[0051] The positive electrode active material particles will be described with reference to Fig. 6. Fig. 6 is a schematic cross-sectional view of a positive electrode active material particle 30. The positive electrode active material particle 30 has a core portion 31, a void portion 32, and an outer structure portion 33. The positive electrode active material particle 30 may be a secondary particle formed by aggregation of primary particles.

[0052] The core portion 31 may be an aggregate of primary particles 34. The core portion 31 may have a solid structure or a hollow structure. When the core portion 31 is hollow, the hollow portion of the core portion is not considered to be a void portion 32. The outer structure portion 33 may be an aggregate of primary particles 35. The void portion 32 may be a space between the core portion 31 and the outer structure portion 33. The core portion 31 and the outer structure portion 33 may be completely separated by the void portion 32, or there may be a portion in the positive electrode active material particle 30 where the primary particles 34 and the primary particles 35 are in contact with each other, and the core portion 31 and the outer structure portion 33 are in contact with each other.

[0053] The proportion of the voids 32 to the total volume of the positive electrode active material particles 30 may be, for example, 10% or more, 40% or more, or 60% or more, or 30% or less, 60% or less, or 80% or less. In this specification, the proportion of the voids 32 to the total volume of the positive electrode active material particles 30 is a value determined by processing a cross-sectional SEM image of the positive electrode active material particles 30, distinguishing between the portions where the primary particles 34 are present and the voids 32, and calculating the proportion of the total area of ​​the voids 32 to the area of ​​the positive electrode active material particles 30.

[0054] 6, only a portion of primary particles 34 and primary particles 35 is shown. Positive electrode active material particle 30 may further have one or more additional outer structure layers outside outer structure portion 33. Outer structure portion 33 may be formed so as to completely cover core portion 31, or may be formed so as to partially cover core portion 31.

[0055] Fig. 7 is an SEM image showing an example of the overall appearance of a positive electrode active material particle. As shown in Fig. 8, the outer structure portion may be formed so as to partially cover the core portion. Fig. 9 is an SEM image showing an example of a cross section of a positive electrode active material particle.

[0056] The positive electrode active material particles 30 may have an average ratio (%) of the thickness of the outer structure 33 to the particle diameter (hereinafter also referred to as a fourth ratio) of 3% to 50%. The particle diameter of the positive electrode active material particles 30 may be the diameter of the cross section of the positive electrode active material particles 30 when the positive electrode active material particles 30 are considered to be circular. For example, in FIG. 3, the particle diameter of the positive electrode active material particles 30 is indicated by a line 36. The thickness of the outer structure 33 may be the dimension of the outer structure 33 at the above diameter (line 36) of the positive electrode active material particles 30.

[0057] The positive electrode active material particles 30 may have an average ratio (%) of the width (thickness) of the voids 32 to the particle size (diameter) (hereinafter also referred to as the fifth ratio) of, for example, 10% or more, 40% or more, or 60% or more, or 30% or less, 60% or less, or 80% or less. It may be 5% to 80%. The width (thickness) of the voids 32 may be the dimension of the voids 32 at the above-mentioned diameter (straight line 36) of the positive electrode active material particles 30. The fourth ratio and the fifth ratio are averages for 50 positive electrode active material particles 30. The fourth ratio and the fifth ratio are measured according to the method described in the Examples section below.

[0058] The BET specific surface area of ​​the positive electrode active material particles 30 is, for example, 0.5 to 2.8 m 2 / g.

[0059] The average particle size of the primary particles 34 and 35 may be, for example, 0.1 to 1.0 μm.

[0060] The positive electrode active material particles 30 have high packing properties and have voids that are relatively uniform in cross section, and therefore when used in positive electrode active material particles, it is possible to easily improve the output characteristics and capacity characteristics.

[0061] <Method of manufacturing positive electrode active material particles> The method for producing positive electrode active material particles includes a particle production step of producing particles by the above-mentioned method for producing precursor particles, a mixing step of mixing the obtained particles with lithium (Li) to obtain a mixture, and a firing step of firing the mixture.

[0062] In the mixing step, the precursor particles and Li can be mixed so that the ratio of the total number of moles of Li to the total number of moles of metal elements other than Li in the positive electrode active material particles (Li / Me ratio) is, for example, 1.0 to 1.3.

[0063] In the firing step, the temperature at which the mixture is fired may be, for example, 700 to 1000° C., preferably 700 to 850° C., and more preferably 710 to 850° C. The time for which the mixture is fired may be, for example, 3 to 10 hours. The firing step can be carried out in an oxidizing atmosphere.

[0064] <Nonaqueous electrolyte secondary battery> The secondary battery of the present disclosure may be used in any application. For example, the secondary battery may be used as a main power source or a power source for power assist in an electric vehicle. A battery module or a battery pack may be formed by connecting multiple secondary batteries. The secondary battery may be a lithium-ion battery.

[0065] The secondary battery of the present disclosure includes an outer casing, an electrode assembly, and an electrolyte. The electrode assembly may be wound or stacked. The electrode assembly includes a positive electrode plate, a separator, and a negative electrode plate. The positive electrode plate has a positive electrode active material layer containing the above-described positive electrode active material particles. That is, the secondary battery of the present disclosure includes the above-described positive electrode active material particles. Therefore, the secondary battery of the present disclosure can easily improve its output characteristics and capacity characteristics. [Example]

[0066] The present invention will be described in more detail below with reference to examples. In the examples, "%" and "parts" are by mass % and mass parts unless otherwise specified.

[0067] [Evaluation method of precursor particles] (composition analysis) The composition of the transition metal composite hydroxide containing nickel in the precursor particles was analyzed using an ICP emission spectrometer. 0.8 Co 0.1 Mn 0.1 (OH)2 was confirmed.

[0068] (Measurement of average particle size) The average particle size of the precursor particles of the examples and comparative examples was measured using an integrated volume value measured with a commercially available laser light diffraction / scattering particle size analyzer.

[0069] (Circularity measurement) The circularity of the precursor particles of the examples and comparative examples was measured using a commercially available particle shape image analyzer.

[0070] (Grain structure and measurement of 1st, 2nd and 3rd ratios) The precursor particles were cross-sectioned by ion milling. The cross-sections were observed using a commercially available scanning electron microscope (SEM) to obtain SEM images. The particle structures of the precursor particles of the examples and comparative examples were observed from the obtained images. The first ratio (core diameter / particle diameter), second ratio (external thickness / particle diameter), and third ratio (void width / particle diameter) were calculated using image analysis software to distinguish between the regions where primary particles exist and the void regions in the cross-sectional SEM images, and then the particle diameter (diameter), core diameter, external thickness, and void width were determined and calculated from the scale ratio. The notations indicating particle structure in Table 1 refer to the following particle structures. [Solid + Hollow] A particle having a core, a void, and an outer structure. [Solid] Particles with a solid structure (particles without voids or external structures). [Hollow] Particles with a hollow structure (particles without a core). [Solid + Hollow / Solid] A state in which particles having a core portion, void portions, and outer structure portions are mixed with particles having a solid structure (approximately 50% are particles having a core portion, void portions, and outer structure portions, and the remaining approximately 50% are particles having a solid structure). [Solid + Hollow / Hollow] A state in which particles having a core portion, a void portion, and an outer structure are mixed with particles having a hollow structure (approximately 50% are particles having a core portion, a void portion, and an outer structure, and the remaining approximately 50% are particles having a hollow structure). The ratio of particles having a core, voids and an outer structure to particles having a solid structure and particles having a hollow structure was determined from SEM observation images of the cross sections of 50 particles.

[0071] [Evaluation method for positive electrode active material particles] (Measurement of average particle size) The average particle size of the positive electrode active material particles of the examples and comparative examples was measured using an integrated volume value measured with a commercially available laser light diffraction / scattering particle size analyzer.

[0072] (Circularity measurement) The circularity of the positive electrode active material particles of the examples and comparative examples was measured using a commercially available particle shape image analyzer.

[0073] (BET specific surface area measurement) The specific surface areas of the examples and comparative examples were measured using a commercially available flow-type gas adsorption specific surface area measuring device.

[0074] (Measurement of the average particle size of primary particles, the fourth ratio and the fifth ratio) The precursor was cross-sectioned using ion milling. The cross-section was observed using a commercially available scanning electron microscope (SEM) to obtain SEM images. The average particle size of the primary particles was calculated by extracting the primary particles using image analysis software. The fourth ratio (thickness of the outer structure / particle diameter) and fifth ratio (width of the void / particle diameter) were calculated using image analysis software to distinguish between the areas containing primary particles and the void areas in the cross-sectional SEM image, and the particle diameter (diameter), thickness of the outer structure, and width of the void were determined and calculated from the scale ratio.

[0075] Example 1 [Production of precursor particles] (Generation of Taylor vortex reaction field) Water was placed in a 1 L reactor capable of generating a Taylor vortex reaction field. The reactor consisted of an outer and inner cylinder. While stirring the inner cylinder at 1500 rpm, the temperature of the solution in the reactor was adjusted to 30°C. An appropriate amount of 30 wt% sodium hydroxide solution was then added to adjust the pH to 12.1 at a liquid temperature of 25°C, generating a Taylor vortex reaction field between the outer and inner cylinders.

[0076] (Preparation of raw metal aqueous solution) Next, nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water so that the molar ratio (nickel sulfate:cobalt sulfate:manganese sulfate) was 80:10:10, to prepare a 2.0 mol / L aqueous solution of the raw metals.

[0077] (Preparation of aqueous ammonia solution) A 10 wt % aqueous ammonia solution was prepared using 28 wt % aqueous ammonia.

[0078] (Crystallization process) Nitrogen gas was introduced and bubbled to maintain the oxygen concentration of the raw metal aqueous solution and the ammonia aqueous solution below 0.5 vol%. The raw metal aqueous solution and the ammonia aqueous solution were then supplied to the Taylor vortex reaction field at a molar ratio of 1:1. Crystallization was initiated while maintaining a pH of 12.1 at a base liquid temperature of 25°C. Crystallization continued for 18 minutes. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was monitored using a dissolved oxygen meter. The pH of the Taylor vortex reaction field was controlled by adjusting the flow rate of the sodium hydroxide aqueous solution using a pH controller.

[0079] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and a mixed gas of oxygen and nitrogen was introduced and bubbled so that the oxygen concentration of the raw metal aqueous solution and the ammonia aqueous solution became 15 vol%. The raw metal aqueous solution and the ammonia aqueous solution were then again supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1. Crystallization was carried out for 12 minutes while maintaining the pH at 12.1 at a liquid temperature of 25°C. The supply of the solution was then stopped, and crystallization was terminated. After crystallization was completed, the product was filtered, washed with water, and dried, in that order, to obtain precursor particles. The results are shown in Table 1.

[0080] <Example 2> [Production of precursor particles] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm and the pH was adjusted to 11.5 at a liquid temperature of 25°C.

[0081] (Preparation of raw metal aqueous solution) An aqueous ammonia solution of 2.0 mol / L of the raw metal solution was prepared in the same manner as in Example 1, except that in the preparation of the raw metal solution in Example 1, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate (nickel sulfate:cobalt sulfate:manganese sulfate) was changed to 60:20:20 instead of 80:10:10.

[0082] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0083] (Crystallization process) Precursor particles were obtained by carrying out the crystallization step in the same manner as in Example 1, except that the pH and second oxygen concentration in the crystallization step in Example 1 were set to the pH and second oxygen concentration shown in Table 1. The results are shown in Table 1.

[0084] Example 3 [Production of precursor particles] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm and the pH was adjusted to 11.2 at a liquid temperature of 25°C.

[0085] (Preparation of raw metal aqueous solution) An aqueous ammonia solution of 2.0 mol / L of the raw metal solution was prepared in the same manner as in Example 1, except that, in the preparation of the raw metal solution in Example 1, nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water so that the molar ratio (nickel sulfate:cobalt sulfate:manganese sulfate) was 80:10:10, but nickel sulfate, cobalt sulfate, manganese sulfate, and zirconium sulfate were dissolved in water so that the molar ratio (nickel sulfate:cobalt sulfate:manganese sulfate:zirconium sulfate) was 69:10:20:1.

[0086] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0087] (Crystallization process) Precursor particles were obtained by carrying out the crystallization step in the same manner as in Example 1, except that the pH, first oxygen concentration, second oxygen concentration, first crystallization time, and second crystallization time in the crystallization step of Example 1 were changed to the pH, first oxygen concentration, second oxygen concentration, first crystallization time, and second crystallization time shown in Table 1. The results are shown in Table 1.

[0088] Example 4 [Production of precursor particles] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm and the pH was adjusted to 12.4 at a liquid temperature of 25°C.

[0089] (Preparation of raw metal aqueous solution) An aqueous ammonia solution of 2.0 mol / L of a raw metal solution was prepared in the same manner as in Example 1, except that in the preparation of the raw metal solution in Example 1, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate (nickel sulfate:cobalt sulfate:manganese sulfate) was changed to 88:6:6, instead of 80:10:10.

[0090] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0091] (Crystallization process) Precursor particles were obtained by carrying out the crystallization step in the same manner as in Example 1, except that the pH, first oxygen concentration, second oxygen concentration, first crystallization time, and second crystallization time in the crystallization step of Example 1 were changed to the pH, first oxygen concentration, second oxygen concentration, first crystallization time, and second crystallization time shown in Table 1. The results are shown in Table 1.

[0092] <Example 5> [Precursor manufacturing method] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm and the pH was adjusted to 10.7 at a liquid temperature of 25°C.

[0093] (Preparation of raw metal aqueous solution) In the same manner as in Example 1, a 2.0 mol / L aqueous ammonia solution containing the raw metal solution was prepared.

[0094] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0095] (Crystallization process) Precursor particles were obtained by carrying out the crystallization step in the same manner as in Example 1, except that the pH, second oxygen concentration, first crystallization time, and second crystallization time in the crystallization step of Example 1 were changed to the pH, second oxygen concentration, first crystallization time, and second crystallization time shown in Table 1. The results are shown in Table 1.

[0096] Example 6 [Precursor manufacturing method] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm.

[0097] (Preparation of raw metal aqueous solution) In the same manner as in Example 1, a 2.0 mol / L aqueous ammonia solution containing the raw metal solution was prepared.

[0098] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0099] (Crystallization process) Precursor particles were obtained by carrying out the crystallization step in the same manner as in Example 1, except that the first oxygen concentration, second oxygen concentration, first crystallization time, and second crystallization time in the crystallization step of Example 1 were changed to the first oxygen concentration, second oxygen concentration, first crystallization time, and second crystallization time shown in Table 1. The results are shown in Table 1.

[0100] Example 7 [Precursor manufacturing method] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm and the pH was adjusted to 11.8 at a liquid temperature of 25°C.

[0101] (Preparation of raw metal aqueous solution) An aqueous ammonia solution of 2.0 mol / L of a raw metal solution was prepared in the same manner as in Example 1, except that in the preparation of the raw metal solution in Example 1, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate (nickel sulfate:cobalt sulfate:manganese sulfate) was changed to 88:6:6, instead of 80:10:10.

[0102] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0103] (Crystallization process) Precursor particles were obtained by carrying out the crystallization step in the same manner as in Example 1, except that the pH, second oxygen concentration, first crystallization time, and second crystallization time in the crystallization step of Example 1 were changed to the pH, second oxygen concentration, first crystallization time, and second crystallization time shown in Table 1. The results are shown in Table 1.

[0104] Example 8 [Precursor manufacturing method] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm and the pH was adjusted to 11.8 at a liquid temperature of 25°C.

[0105] (Preparation of raw metal aqueous solution) An aqueous ammonia solution of 2.0 mol / L of a raw metal solution was prepared in the same manner as in Example 1, except that in the preparation of the raw metal solution in Example 1, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate (nickel sulfate:cobalt sulfate:manganese sulfate) was changed to 50:20:30, instead of 80:10:10.

[0106] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0107] (Crystallization process) Precursor particles were obtained by carrying out the crystallization step in the same manner as in Example 1, except that the pH, second oxygen concentration, first crystallization time, and second crystallization time in the crystallization step of Example 1 were changed to the pH, second oxygen concentration, first crystallization time, and second crystallization time shown in Table 1. The results are shown in Table 1.

[0108] Example 9 [Precursor manufacturing method] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm.

[0109] (Preparation of raw metal aqueous solution) An aqueous ammonia solution of 2.0 mol / L of a raw metal solution was prepared in the same manner as in Example 1, except that in the preparation of the raw metal solution in Example 1, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate (nickel sulfate:cobalt sulfate:manganese sulfate) was changed to 88:6:6, instead of 80:10:10.

[0110] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0111] (Crystallization process) Precursor particles were obtained by carrying out the crystallization step in the same manner as in Example 1, except that the second oxygen concentration, the first crystallization time, and the second crystallization time in the crystallization step of Example 1 were changed to the second oxygen concentration, the first crystallization time, and the second crystallization time shown in Table 1. The results are shown in Table 1.

[0112] Example 10 [Precursor manufacturing method] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm.

[0113] (Preparation of raw metal aqueous solution) An aqueous ammonia solution of 2.0 mol / L of a raw metal solution was prepared in the same manner as in Example 1, except that in the preparation of the raw metal solution in Example 1, the molar ratio of nickel sulfate, cobalt sulfate, and manganese sulfate (nickel sulfate:cobalt sulfate:manganese sulfate) was changed to 88:6:6, instead of 80:10:10.

[0114] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0115] (Crystallization process) Precursor particles were obtained by carrying out the crystallization step in the same manner as in Example 1, except that the second oxygen concentration, the first crystallization time, and the second crystallization time in the crystallization step of Example 1 were changed to the second oxygen concentration, the first crystallization time, and the second crystallization time shown in Table 1. The results are shown in Table 1.

[0116] <Comparative Example 1> [Precursor particle production (batch method)] (Preparing the reactor) 2 L of ammonia water with an ammonium ion concentration of 11.5 g / L was prepared using 28 wt% ammonia water. The 2 L of ammonia water was placed in a 5 L reactor, and nitrogen gas was introduced to maintain an oxygen concentration of 1.0 vol% or less within the reactor, followed by stirring at 800 rpm. After adjusting the solution in the reactor to 40°C, an appropriate amount of 30 wt% aqueous sodium hydroxide solution was added, and the pH was adjusted to 13.0 at a liquid temperature of 25°C.

[0117] (Preparation of raw metal aqueous solution) Next, nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in water in a molar ratio of 80:10:10 to prepare a 1.5 mol / L aqueous solution of raw metals.

[0118] (Nucleation process) The raw metal aqueous solution and ammonia aqueous solution were supplied in a timely manner so that the molar ratio was 1:1, and crystallization was carried out for 60 minutes while maintaining the pH at 13.0 at a liquid temperature of 25°C. The pH was controlled by adjusting the flow rate of sodium hydroxide using a pH controller. During this time, the concentration of the supplied ammonia aqueous solution was adjusted so that the ammonium ion concentration in the reaction liquid was maintained at 11.5 g / L.

[0119] (nucleus growth process) After the nucleation step, sulfuric acid was gradually supplied to the reaction vessel so that the pH of the solution at a base temperature of 25°C was 10.7. At the same time, a mixed gas of oxygen and nitrogen was introduced to the reaction vessel so that the oxygen concentration was 40 vol% and stirred for 30 minutes. The supply of the raw metal aqueous solution and the aqueous ammonia solution to the reaction vessel was then resumed. Crystallization was continued for 4 hours while maintaining the pH at a base temperature of 25°C at 10.7. Nitrogen gas was then again introduced to the reaction vessel so that the oxygen concentration in the vessel was 1.0 vol% or less. After 2 hours of crystallization, the supply of the raw metal aqueous solution and the aqueous ammonia solution was stopped, and crystallization was terminated. After crystallization was completed, the product was filtered, washed with water, and dried, in that order, to obtain precursor particles of Comparative Example 1. The results are shown in Table 1.

[0120] <Comparative Example 2> [Precursor manufacturing method] (Generation of Taylor vortex reaction field) A Taylor vortex reaction field was generated in the same manner as in Example 1, except that the rotation speed of the inner cylinder was set to 2000 rpm and the pH was adjusted to 12.8 at a liquid temperature of 25°C.

[0121] (Preparation of raw metal aqueous solution) In the same manner as in Example 1, a 2.0 mol / L aqueous ammonia solution containing the raw metal solution was prepared.

[0122] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0123] (Crystallization process) Precursor particles were obtained by carrying out a crystallization step in the same manner as in Example 1, except that the pH, second oxygen concentration, first crystallization time, and second crystallization time at a liquid temperature of 25°C in Example 1 were changed to the pH, second oxygen concentration, first crystallization time, and second crystallization time at a liquid temperature of 25°C shown in Table 1. The results are shown in Table 1.

[0124] Example 11 [Production of positive electrode active material particles] The precursor particles of Example 1 were mixed with a lithium compound so that the ratio of the total number of moles of lithium to the total number of moles of metal elements other than lithium (hereinafter also referred to as the Li / Me ratio) was 1.10, and then the mixture was fired in an oxidizing atmosphere at a firing temperature of 760°C for 7 hours to obtain positive electrode active material particles. The results are shown in Table 2.

[0125] <Examples 12 to 18 and Comparative Examples 3 to 8> Positive electrode active material particles were obtained in the same manner as in Example 1, except that precursor particles shown in Table 1 were used and the Li / Me ratio and / or firing temperature shown in Table 1 were used. The results are shown in Table 2.

[0126] [Table 1]

[0127] [Table 2]

[0128] In Examples 1 to 10, particles having a core, voids, and an outer structure could be produced without changing the pH during the crystallization process and while reducing the number of times the atmosphere was changed during the crystallization process, compared to Comparative Example 1. In Comparative Example 2, the pH exceeded 12.5 at a liquid temperature of 25°C, so particles having a core, voids, and an outer structure could not be obtained.

[0129] The positive electrode active material particles of Examples 13 to 20 have a circularity of 0.90 or more, and are therefore understood to have excellent packing properties. The positive electrode active material particles of Comparative Examples 4 and 7 have a low circularity and are therefore understood to have insufficient packing properties. In Comparative Example 5, the firing temperature was not sufficiently high, and therefore unreacted precursor particles were present. In Comparative Example 6, the firing temperature was too high, and therefore primary particles grew excessively, resulting in the voids disappearing, and the particles had a solid structure. Furthermore, in Comparative Example 8, the particles had a solid structure and low circularity. [Explanation of symbols]

[0130] 10 reaction vessel, 11 outer cylinder, 12 inner cylinder, 13 first supply port, 14 second supply port, 15 third supply port, 16 discharge port, 17 container, 18 motor, 20 first particle, 21 core portion, 22 void portion, 23 outer structure portion, 24, 25 primary particle, 26 straight line, 30 positive electrode active material particle, 31 core portion, 32 void portion, 33 outer structure portion, 34, 35 primary particle, 36 straight line.

Claims

1. A method for producing particles, comprising: the particles include first particles each having a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, the first particles being made of a transition metal composite hydroxide containing nickel, a crystallization step of generating a Taylor vortex reaction field, adding an aqueous solution containing a compound containing a transition metal, an ammonium donor, and an alkaline aqueous solution to the Taylor vortex reaction field, and crystallizing a nickel-containing transition metal composite hydroxide; In the crystallization step, The pH of the Taylor vortex reaction field at a liquid temperature of 25°C is 12.5 or less, a first crystallization is performed in which the oxygen concentration in the Taylor vortex reaction field is set to 3.5 vol% or less; Next, a second crystallization is performed in which the oxygen concentration in the Taylor vortex reaction field is changed to 5 vol% or more and 65 vol% or less, and crystallization is performed; The method for producing particles, wherein the time period during which the first crystallization is carried out is 40% or more and 90% or less of the total crystallization time.

2. The method for producing particles according to claim 1 , wherein in the crystallization step, the pH of the Taylor vortex reaction field at a liquid temperature of 25° C. is 11.0 or higher.

3. The method for producing particles according to claim 1 or 2, wherein the first crystallization is carried out while maintaining an oxygen concentration in the Taylor vortex reaction field at 3.0 vol % or less.

4. The method for producing particles according to claim 1 or 2, wherein the time for carrying out the first crystallization is 50% or more and 80% or less of the total crystallization time.

5. 3. The method for producing particles according to claim 1, wherein the second crystallization is carried out while maintaining an oxygen concentration in the Taylor vortex reaction field at 10 vol% or more and 60 vol% or less.

6. The method for producing particles according to claim 1 or 2, wherein the rotation speed of the inner cylinder that generates the Taylor vortex reaction field is 500 to 2000 rpm.

7. A particle having a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, the particle being made of a transition metal composite hydroxide containing nickel, and having a circularity of 0.90 or more.

8. The particles according to claim 7, having an average particle size of 1 μm to 10 μm.

9. 9. The particles according to claim 7, wherein the average ratio (%) of the diameter of the core portion to the particle diameter is 1% to 70%.

10. 9. The particle according to claim 7, wherein the average ratio (%) of the thickness of the outer structure to the particle diameter is 3% to 50%.

11. 9. The particle according to claim 7, wherein the average ratio (%) of the width of the void portion to the particle diameter is 10% or more.

12. A positive electrode active material particle having a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, the positive electrode active material particle being made of a metal composite oxide containing lithium and nickel, and having a circularity of 0.90 or more.

13. The positive electrode active material particle according to claim 12 , wherein the core portion has a solid structure or a hollow structure.

14. The positive electrode active material particle according to claim 12 or 13, further comprising one or more inner structure layers between the outer structure portion and the core portion.

15. The positive electrode active material particles according to claim 12 or 13, having an average particle size of 2 μm to 10 μm.

16. 14. The positive electrode active material particles according to claim 12, wherein the average ratio (%) of the thickness of the outer structure to the particle diameter is 5% to 50%.

17. 14. The electrode active material particles according to claim 12, wherein an average ratio (%) of the width of the void portion to the particle diameter is 5% to 80%.

18. BET specific surface area: 0.5 to 2.8 m ２ The positive electrode active material particles according to claim 12 or 13, wherein the SiO 2 content is 1 / g.

19. 14. The positive electrode active material particles according to claim 12, wherein the secondary particles are made of primary particles, and the average particle diameter of the primary particles is 0.1 to 1.0 μm.

20. 3. A method for producing positive electrode active material particles, comprising: a particle production step of producing particles by the particle production method according to claim 1 or 2; a mixing step of mixing the obtained particles with lithium to obtain a mixture; and a firing step of firing the mixture.

21. A non-aqueous electrolyte secondary battery comprising the positive electrode active material particles according to claim 12 or 13.

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