Particles, cathode active material particles, method for producing them and nonaqueous electrolyte secondary battery

Abstract

To provide precursor particles capable of forming cathode active material particles which suppresses the reduction in capacity and capacity maintenance rate of a nonaqueous electrolyte secondary battery and particle cracking, a method for producing the same and a nonaqueous electrolyte secondary battery.SOLUTION: There is provided a method for producing particles composed of a transition metal composite hydroxide containing nickel, wherein crystallization is started by adding an aqueous solution containing a compound containing a transition metal, an ammonium ion supplying material and an alkaline aqueous solution in a Taylor vortex reaction field and setting the pH at 25°C of the Taylor vortex reaction field to 11.4 to 12.5 and the oxygen concentration of the Taylor vortex reaction field to 1.0 vol.% or less and the oxygen concentration of the Taylor vortex reaction field is switched so that the total number of the number of switching the oxygen concentration of the Taylor vortex reaction field from 1.0 vol.% or less to 10.0 vol% or more and the number of switching the oxygen concentration of the Taylor vortex reaction field from 10.0 vol.% or more to 1.0 vol.% is 3 times or more.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 Application Laid-Open No. 2019-21610 (Patent Document 1) discloses a positive electrode active material precursor capable of forming a positive electrode active material for a non-aqueous electrolyte secondary battery, the positive electrode active material including porous secondary particles formed by aggregation of multiple primary particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-21610 Summary of the Invention [Problem to be solved by the invention]

[0004] The positive electrode active material disclosed in JP 2019-21610 A is prone to particle cracking when compressed during the positive electrode plate manufacturing process. Positive electrode plates for high-capacity nonaqueous electrolyte secondary batteries require high density, making particle cracking due to compression even more likely to occur. In particular, nonaqueous electrolyte secondary batteries using high-nickel positive electrode active materials with a high nickel content are prone to particle cracking due to expansion and contraction during charge-discharge cycles. As a result, the capacity retention rate of nonaqueous electrolyte secondary batteries may decrease.

[0005] An object of the present disclosure is to provide precursor particles that can be used to produce positive electrode active material particles that suppress a decrease in the initial capacity and capacity retention rate of a non-aqueous electrolyte secondary battery and particle cracking, positive electrode active material particles produced using the precursor particles, methods for producing the same, and non-aqueous electrolyte secondary batteries. [Means for solving the problem]

[0006] [1] A method for producing particles, comprising: the particles are 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 ion 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 25°C is 11.4 to 12.5, crystallization is initiated by setting the oxygen concentration in the Taylor vortex reaction field to 1.0 vol% or less; The method for producing particles includes switching the oxygen concentration in the Taylor vortex reaction field so that the total number of times the oxygen concentration in the Taylor vortex reaction field is switched from 1.0 vol% or less to 10.0 vol% or more and from 10.0 vol% or more to 1.0 vol% or less is 3 or more. [2] The method for producing particles according to [1], wherein the total number of times that the oxygen concentration in the Taylor vortex reaction field is switched is four or more. [3] The method for producing particles according to [1] or [2], wherein the ratio of the time from the start of crystallization until the oxygen concentration in the Taylor vortex reaction field is first switched to 10.0 vol% or more to the total time for crystallization in the crystallization step is 15% to 50%. [4] The method for producing particles according to any one of [1] to [3], wherein the ratio of the time from switching the oxygen concentration in the Taylor vortex reaction field to the next switching of the oxygen concentration in the Taylor vortex reaction field to the total time for crystallization in the crystallization step is 5% or more. [5] The method for producing particles according to any one of [1] to [4], wherein the switching of the oxygen concentration in the Taylor vortex reaction field from 1.0 vol% or less to 10.0 vol% or more and the switching of the oxygen concentration in the Taylor vortex reaction field from 10.0 vol% or more to 1.0 vol% or less are respectively the switching of the oxygen concentration in the Taylor vortex reaction field from 1.0 vol% or less to 15.0 vol% or more and the switching of the oxygen concentration in the Taylor vortex reaction field from 15.0 vol% or more to 1.0 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 2000 rpm or less. [7] A particle made of a transition metal composite hydroxide containing nickel, which has a core portion inside the particle and at least two porous layers outside the core portion, with voids accounting for 70% or more. [8] The particles according to [7], wherein the average ratio of the diameter of the core portion to the particle diameter is 30% to 70%. [9] Particles according to [7] or [8], wherein the average ratio of the width of the void layer to the particle diameter is 1.5% or more.

[10] The particles according to any one of [7] to [9], which have an average particle size of 1 μm to 10 μm.

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

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

[12] Positive electrode active material particles made of a transition metal composite oxide containing lithium and nickel, the particles having a core portion inside the particles and at least two void layers outside the core portion, with voids accounting for 70% or more.

[13] The positive electrode active material particles according to

[12] , wherein the average ratio of the diameter of the core portion to the particle diameter is 30% to 70%.

[14] The positive electrode active material particles according to

[12] or

[13] , wherein the average ratio of the width of the void layer to the particle diameter is 1.5% or more.

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

[12] to

[14] , which have an average particle size of 1 μm to 10 μm.

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

[12] to

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

[17] 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.

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

[12] to

[15] . [Effects of the Invention]

[0007] The present disclosure provides precursor particles capable of forming positive electrode active material particles that suppress a decrease in the initial capacity and capacity retention rate of a non-aqueous electrolyte secondary battery and particle cracking; positive electrode active material particles manufactured using the precursor particles; methods for manufacturing the same; and a non-aqueous electrolyte secondary battery. [Brief explanation of the drawings]

[0008] [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 first particle. [Figure 3] FIG. 3 is a scanning electron microscope image showing an example of the overall appearance of the first particle. [Figure 4] FIG. 4 is a scanning electron microscope image showing another example of the overall appearance of the first particle. [Figure 5] FIG. 5 is a scanning electron microscope image showing an example of a cross section of a first particle. [Figure 6] FIG. 6 is a scanning electron microscope image showing another example of a cross section of a first particle. [Figure 7] FIG. 7 is a schematic cross-sectional view of a positive electrode active material particle. [Figure 8] FIG. 8 is a scanning electron microscope image showing an example of the overall appearance of positive electrode active material particles. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Particle manufacturing method> The method for producing particles disclosed herein includes a step of generating a Taylor vortex reaction field, adding an aqueous solution containing a transition metal compound, an ammonium ion donor, and an alkaline aqueous solution to the Taylor vortex reaction field to crystallize the nickel-containing transition metal composite hydroxide. In the crystallization step, the pH of the Taylor vortex reaction field is 11.4 to 12.5 at 25°C, and crystallization is initiated by setting the oxygen concentration in the Taylor vortex reaction field to 1.0 vol% or less. The oxygen concentration in the Taylor vortex reaction field is switched from 1.0 vol% or less to 10.0 vol% or more and from 10.0 vol% or more to 1.0 vol% or less three times in total. Switching the oxygen concentration in the Taylor vortex reaction field from 1.0 vol% or less to 10.0 vol% or more means adjusting the oxygen concentration in the Taylor vortex reaction field from 1.0 vol% or less to 10.0 vol% or more. Switching the oxygen concentration in the Taylor vortex reaction field from 10.0 vol% or more to 1.0 vol% or less means adjusting the oxygen concentration in the Taylor vortex reaction field from 10.0 vol% or more to 1.0 vol% or less.

[0010] (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 battery), such as a lithium ion battery. The particles are hereinafter also referred to as precursor particles. The precursor particles are made of a transition metal composite hydroxide containing Ni, and contain particles (hereinafter also referred to as first particles) that have a core portion and at least two or more void layers outside the core portion, with voids accounting for 70% or more. The first particles will be described later. The precursor particles preferably contain only first particles, from the viewpoint of suppressing a decrease in the initial capacity and capacity retention rate of the battery and particle cracking.

[0011] The content of Ni relative to the metal elements other than Ni in the first metal hydroxide may be, for example, 50 mol % or more, 70 mol % or more, 80 mol % or more, or 90 mol % or more. When the Ni content in the first metal hydroxide is within the above range, it is easy to increase the initial capacity of the battery.

[0012] 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.

[0013] 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.

[0014] (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).

[0015] 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).

[0016] 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).

[0017] 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.

[0018] 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。

[0019] 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。

[0020] 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。

[0021] As the ammonium donor, for example, an aqueous ammonia solution can be used, and the ammonia concentration in the aqueous ammonia solution may be, for example, 5 to 20 wt %.

[0022] 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 %.

[0023] The Taylor vortex reaction field can be a fluid in which a Taylor vortex flow is generated. A Taylor vortex flow is a row of two donut-shaped vortices rotating in opposite directions. For example, by filling the interior of two concentric cylinders, the difference between their radii being small compared to their diameters, with a fluid, and rotating the inner cylinder (hereinafter also referred to as the inner cylinder) while keeping the outer cylinder (hereinafter also referred to as the outer cylinder) stationary, two rows of vortices can be generated in a ring shape along the circumference between the outer and inner cylinders. Multiple rows of two vortices can be generated along the length direction of the two concentric cylinders (direction perpendicular to the diameter).

[0024] By conducting the crystallization reaction in a fluid containing Taylor vortices, the pH does not need to be adjusted during crystallization, allowing precursor particles to be produced at a constant pH. This simplifies the precursor particle production process and facilitates industrial-scale production. Furthermore, this process significantly reduces the time required compared to batch production methods, which tends to improve precursor particle productivity. Furthermore, by starting crystallization with a Taylor vortex reaction field pH of 11.4 to 12.5 at 25°C and an oxygen concentration of 1.0 vol% or less in the Taylor vortex reaction field, and by limiting the total number of times the oxygen concentration in the Taylor vortex reaction field is switched from 1.0 vol% or less to 10.0 vol% or more and from 10.0 vol% or more to 1.0 vol% or less to three or more, this tends to facilitate the production of precursor particles capable of forming positive electrode active material particles that suppress a decrease in the initial capacity and capacity retention rate of the battery and particle cracking. A commercially available Taylor vortex-generating reactor can be used in the particle production method.

[0025] 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.

[0026] 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 Taylor vortex flows 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 may be, for example, 2000 rpm or less, or 500 rpm or more.

[0027] 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 11.4 to 12.5. 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. When the pH of the Taylor vortex reaction field at a liquid temperature of 25°C is within the above range, it tends to be easier to produce precursor particles that can form positive electrode active material particles that suppress reductions in the initial capacity and capacity retention of the battery, and particle cracking. The pH of the Taylor vortex reaction field at a liquid temperature of 25°C is preferably 11.5 to 12.3.

[0028] 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. Crystallization is initiated with the oxygen concentration in the Taylor vortex reaction field at 1.0 vol% or less. A method for maintaining the oxygen concentration in the Taylor vortex reaction field at 1.0 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. Maintaining an oxygen concentration in the Taylor vortex reaction field at 1.0 vol% or less at the start of crystallization tends to facilitate the production of first particles. The oxygen concentration in the Taylor vortex reaction field can be confirmed using a dissolved oxygen meter. The oxygen concentration in the Taylor vortex reaction field at the start of crystallization should be 1.0 vol% or less, for example, 0.8 vol% or less, 0.5 vol% or less, or 0.1 vol% or more.

[0029] After crystallization begins, the oxygen concentration in the Taylor vortex reaction field is switched from 1.0 vol% or less to 10.0 vol% or more. Hereinafter, switching the oxygen concentration in the Taylor vortex reaction field from 1.0 vol% or less to 10.0 vol% or more is also referred to as the "first switching." Performing the first switching tends to facilitate the production of precursor particles capable of forming positive electrode active material particles that suppress a decrease in the initial capacity and capacity retention rate of the battery, as well as particle cracking. From the perspective of ease of forming the first particles, the first switching is preferably a switching of the oxygen concentration in the Taylor vortex reaction field from 1.0 vol% or less to 15.0 vol% or more. The oxygen concentration in the Taylor vortex reaction field after the first switching may be, for example, 35 vol% or less.

[0030] The ratio of the time from the start of crystallization until the first switching is performed to the total time for crystallization in the crystallization step may be, for example, 15% to 50%, or 25% to 47%. By performing the first first switching for a time that satisfies the ratio in the above range, first particles having cores of an appropriate size tend to be formed more easily.

[0031] The oxygen concentration in the Taylor vortex reaction field can be changed by, for example, changing the type of gas bubbled into the raw metal aqueous solution and the ammonium supplier. The type of gas used for the first changeover may be, for example, a mixed gas of oxygen and nitrogen. When changing the oxygen concentration in the Taylor vortex reaction field in the crystallization process, the supply of the raw metal aqueous solution and the ammonium supplier is stopped, and after changing the oxygen concentration in the Taylor vortex reaction field, the supply of the raw metal aqueous solution and the ammonium supplier is resumed to perform crystallization.

[0032] In the particle production method of the present disclosure, the oxygen concentration in the Taylor vortex reaction field in the crystallization step may be 1.0 vol% or less and 10.0 vol% or more, for example, 0.1 vol% to 1.0 vol% or more and 10.0 vol% to 35 vol% or less.

[0033] Next, the oxygen concentration in the Taylor vortex reaction field is switched from 10.0 vol% or more to 1.0 vol% or less. Hereinafter, switching the oxygen concentration in the Taylor vortex reaction field from 10.0 vol% or more to 1.0 vol% or less is also referred to as the second switching. Performing the second switching tends to facilitate the production of precursor particles capable of forming positive electrode active material particles that suppress a decrease in the initial capacity and capacity retention rate of the battery and particle cracking. From the perspective of ease of forming the first particles, the second switching is preferably a switching of the oxygen concentration in the Taylor vortex reaction field from 15.0 vol% or more to 1.0 vol% or less. The oxygen concentration in the Taylor vortex reaction field after the second switching may be, for example, 0.8 vol% or less or 0.5 vol% or less, or 0.1 vol% or more.

[0034] The ratio of the time from the first switching to the second switching to the total time for crystallization in the crystallization step may be, for example, 5% or more. The time from the second switching to the first switching may be, for example, 10% or more. Performing the first switching and the second switching within the above-mentioned range of ratios tends to facilitate the formation of void layers in the first particles.

[0035] In the crystallization step, the oxygen concentration in the Taylor vortex reaction field is switched so that the total number of first and second switching operations is 3 or more. This total number is preferably 4 or more. When the total number of first and second switching operations is within the above range, it tends to be easier to produce precursor particles that can form positive electrode active material particles that suppress a decrease in the initial capacity and capacity retention rate of the battery and particle cracking.

[0036] 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.

[0037] <1st particle> The first particles are particles made of a Ni-containing transition metal composite hydroxide and have a core portion inside the particle and at least two void layers outside the core portion, with voids accounting for 70% or more. The first particles are precursors of positive electrode active material particles used in an active material layer of a battery positive electrode. Positive electrode active material particles made using the first particles tend to more easily suppress decreases in the initial capacity and capacity retention rate of the battery, as well as particle cracking. This is presumably because the positive electrode active material particles made using the first particles have a core portion and two or more void layers with a specific width, which ensures initial capacity and allows stress applied to the particles to be released even when pressed during the positive electrode plate production process, thereby suppressing particle cracking. The Ni-containing transition metal composite hydroxide may be the first metal hydroxide described above. The first particles can be produced by the particle production method described above.

[0038] 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. Methods for adjusting the average particle diameter of the first particles to the above range include, for example, adjusting the pH, oxygen concentration, the number of times the oxygen concentration is switched, and the crystallization time in the crystallization step of the above-mentioned particle manufacturing method, and adjusting the rotation speed of the inner cylinder. The average particle diameter of the first particles may be, for example, 1 μm to 10 μm. When the average particle diameter of the first particles is within the above range, a decrease in the initial capacity and capacity retention rate of the battery and particle cracking tend to be more easily suppressed.

[0039] 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 therein, void layers 22 and 23, an inner structure portion 24, and an outer structure portion 25.

[0040] The core 21 may have a solid structure or a hollow structure. When the core 21 has a hollow structure, the hollow structure of the core 21 is not considered to be a void layer. The internal structure of the core 21 can be controlled, for example, by adjusting the pH, oxygen concentration, and the time from the start of crystallization to the first change in oxygen concentration in the crystallization step of the above-mentioned particle production method, adjusting the rotation speed of the inner cylinder, etc.

[0041] The first particle may have two or more void layers, or may have three or more void layers. The number of void layers in the first particle may be five or less, four or less, or three or less. The first particle preferably has two void layers. The first particle 20 has two void layers. The void layers 22, 23 are formed outside the core portion 21. An internal structure portion is formed between the void layers. The first particle 20 has an internal structure portion 24 between the void layer 22 and the void layer 23. The first particle has an external structure portion outside the outermost void layer. The first particle 20 has an external structure portion 25 outside the void layer 23. The first particle 20 has, in order from the center of the particle, the core portion 21, the void layer 22, the internal structure portion 24, the void layer 23, and the external structure portion 25. When the first particle has three void layers, the first particle has, in order from the center of the particle, a core portion, a void layer, an inner structure portion, a void layer, an inner structure portion, a void layer, and an outer structure portion.

[0042] A method for forming two or more void layers includes a method in which the crystallization step is performed in the particle production method described above so that the total number of first switching operations and second switching operations is at least 3. For example, when forming two void layers, the total number of operations can be 3 or 4, and when forming three void layers, the total number of operations can be 4 or 5.

[0043] The first particles 20 may be secondary particles formed by agglomeration of primary particles. The core portion 21, the interior portion 24, and the exterior portion 25 may be agglomerates of primary particles. In Figure 2, some of the primary particles are illustrated as primary particles 26. There may be locations where the primary particles are in contact with each other between the core portion and the interior portion, between the interior portions, and between the interior portion and the exterior portion.

[0044] The void layer can be a region formed between the core and the inner structure, between the inner structure and the inner structure, or between the inner structure and the outer structure when the core, inner structure, and outer structure regions are distinguished using image analysis software in a scanning electron microscope image of the cross section of a first particle, and the region determined to be void accounts for 70% or more of the area of ​​the region. The void layer can also include primary particles not contained in the core, inner structure, or outer structure, such as areas where the primary particles mentioned above contact each other. In this specification, regions with voids of less than 70%, such as regions formed between the core and the inner structure, between the inner structure and the inner structure, or between the inner structure and the outer structure, where the voids are less than 70% because the width between them is small, or regions with voids of less than 70% because they contain many areas where the primary particles mentioned above contact each other, are not considered to be void layers.

[0045] The inner structure and the outer structure may be formed so as to completely cover the core and the air gap layer, respectively, or may be formed so as to partially cover them.

[0046] Figures 3 and 4 are SEM observation images showing an example of the overall appearance of a first particle. The outer structure of the first particle shown in Figure 4 is formed so as to partially cover the void layer (inner structure). Figures 5 and 6 are SEM observation images showing an example of a cross section of a first particle. The core portion of the first particle shown in Figure 5 has a hollow structure. The core portion of the first particle shown in Figure 6 has a solid structure.

[0047] 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 30% to 70%. The particle diameter of the first particles 20 may be the diameter of the cross section of the first particles 20 when the first particles 20 are considered to be circular. For example, in FIG. 2, the particle diameter of the first particles 20 is indicated by line 27. The diameter of the core portion 21 is the diameter of the core portion 21 at the above diameter (line 27). When the first ratio is within the above range, a decrease in the initial capacity and capacity retention rate of the battery and particle cracking tend to be more easily suppressed. Examples of methods for setting the first ratio within the above range include adjusting the pH, oxygen concentration, and the time from the start of crystallization to the first change in oxygen concentration in the crystallization step of the above-mentioned particle production method, and adjusting the rotation speed of the inner cylinder.

[0048] The first particles may have an average ratio (%) of the width (thickness) of each of the void layers 22, 23 to the particle diameter (hereinafter also referred to as the second ratio) of 1.5% or more. In the first particles 20, the width (thickness) of the void layers 22 is the sum of the dimensions of the void layers 22 at the diameter (straight line 27) of the first particles 20. In the first particles 20, the width (thickness) of the void layers 23 is the sum of the dimensions of the void layers 23 at the diameter (straight line 27) of the first particles 20. The second ratio is preferably 2.0% or more. In the first particles 20, the second ratio for each of the void layers 22, 23 may be 1.5% or more. When the second ratio is within the above range, a decrease in the initial capacity and capacity retention rate of the battery and particle cracking tend to be more easily suppressed. Methods for setting the second ratio within the above range include, for example, adjusting the pH, oxygen concentration, and timing of switching the oxygen concentration (first switching and second switching) in the crystallization step of the above-mentioned particle manufacturing method, adjusting the rotation speed of the inner cylinder, etc.

[0049] The first ratio and the second ratio are averages of 50 first particles, and are measured according to the method described in the Examples section below.

[0050] The average particle diameter of the primary particles 26 may be, for example, 0.01 to less than 0.1 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.

[0051] <Cathode active material particles> The positive electrode active material particles of the present disclosure are particles made of a transition metal composite oxide containing Li and Ni, and have a core portion inside and at least two void layers outside the core portion, with voids accounting for 70% or more. The positive electrode active material particles can be a sintered product of a mixture of the above-mentioned first particles and lithium (Li). Batteries fabricated using the positive electrode active material tend to be more susceptible to decreases in initial capacity and capacity retention, and to particle cracking. This is presumably because the positive electrode active material particles have a core portion and two or more void layers with a specific width, which ensures initial capacity and allows stress applied to the particles to be released even when pressed during the positive electrode plate fabrication process, thereby suppressing particle cracking.

[0052] The content of Ni relative to the metal elements other than Ni in the positive electrode active material particles may be, for example, 50 mol % or more, or may be 70 mol % or more, 80 mol % or more, or 90 mol % or more. When the Ni content in the positive electrode active material particles is within the above range, it is easy to increase the initial capacity of the battery.

[0053] The average particle size of the positive electrode active material particles may be, for example, 1 μm to 10 μm. When the average particle size of the positive electrode active material particles is within this range, a decrease in the initial capacity and capacity retention rate of the battery and particle cracking tend to be easily suppressed. Methods for adjusting the average particle size of the positive electrode active material particles to be within this range include, for example, selecting the type of precursor particles used and adjusting the firing conditions.

[0054] The positive electrode active material particles may be particles made of a transition metal composite oxide containing Li and Ni, or may be particles made of a transition metal composite oxide containing Li, Ni, and Mn, or may be particles made of a transition metal composite oxide containing Li, Ni, Co, and Mn.

[0055] 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:

[0056] The positive electrode active material particle will be described with reference to FIG. 7. FIG. 7 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, void layers 32 and 33, an inner structure portion 34, and an outer structure portion 35 inside. The core portion 31 may have a solid structure or a hollow structure. When the core portion 31 has a hollow structure, the hollow structure of the core portion 31 is not considered to be a void layer. The internal structure of the core portion 31 can be controlled, for example, by selecting the type of precursor particles used, adjusting the firing conditions, etc.

[0057] The positive electrode active material particles may have two or more void layers, or may have three or more void layers. The number of void layers in the positive electrode active material particles may be five or less, four or less, or three or less. The positive electrode active material particles preferably have two void layers. The first particle 20 has two void layers. The positive electrode active material particles 30 have two void layers. The void layers 32 and 33 are formed outside the core portion 31. An internal structure portion is formed between the void layers. The positive electrode active material particles 30 have an internal structure portion 34 between the void layers 32 and 33. The positive electrode active material particles have an external structure portion outside the outermost void layer. The positive electrode active material particles 30 have an external structure portion 35 outside the void layer 33. The positive electrode active material particle 30 has, in order from the center of the particle, a core portion 31, a void layer 32, an inner structure portion 34, a void layer 33, and an outer structure portion 35. When the positive electrode active material particle has three void layers, the first particle has, in order from the center of the particle, a core portion, a void layer, an inner structure portion, a void layer, an inner structure portion, a void layer, and an outer structure portion. The number of void layers of the positive electrode active material particle can be controlled, for example, by selecting the type of precursor particle (first particle) used, adjusting the firing conditions, etc. For example, to produce a positive electrode active material particle having two void layers, a precursor particle (first particle) having two void layers can be used.

[0058] The positive electrode active material particles 30 may be secondary particles formed by aggregation of primary particles. The core portion 31, the inner structure portion 34, and the outer structure portion 35 may be aggregates of primary particles. In FIG. 7, the primary particles are partially illustrated as primary particle 36. There may be locations where the primary particles are in contact with each other between the core portion and the inner structure portion, between the inner structure portions, and between the inner structure portion and the outer structure portion.

[0059] The void layer can be a region formed between the core and the inner structure, between the inner structure and the outer structure, or between the inner structure and the outer structure when the core, inner structure, and outer structure regions are distinguished using image analysis software in a scanning electron microscope image of the cross section of a positive electrode active material particle, and the area of ​​the region determined to be void occupies 70% or more of the area of ​​the region. The void layer can also include primary particles not contained in the core, inner structure, or outer structure, such as areas where the primary particles mentioned above contact each other. In this specification, regions with a void ratio of less than 70%, such as regions formed between the core and the inner structure, between the inner structure and the inner structure, or between the inner structure and the outer structure, where the void ratio is less than 70% because the width between the particles is small, or regions with a void ratio of less than 70% because they contain many areas where the primary particles mentioned above contact each other, are not considered to be void layers.

[0060] The inner structure and the outer structure may be formed so as to completely or partially cover the core and the void layer, respectively. Fig. 8 is an SEM image showing an example of the appearance of the entire positive electrode active material particle.

[0061] The positive electrode active material particles 30 may have an average ratio (%) of the diameter of the core portion 31 to the particle diameter (hereinafter also referred to as the third ratio) of 30% to 70%. 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. 7, the particle diameter of the positive electrode active material particles 30 is indicated by line 37. The diameter of the core portion 31 is the diameter of the core portion 31 at the above diameter (line 37). When the third ratio is within the above range, a decrease in the initial capacity and capacity retention rate of the battery and particle cracking tend to be easily suppressed. Methods for setting the third ratio within the above range include, for example, selecting the type of precursor particles (first particles) used and adjusting the firing conditions.

[0062] The positive electrode active material particles 30 may have an average ratio (%) of the width (thickness) of each of the void layers 32, 33 to the particle diameter (hereinafter also referred to as the fourth ratio) of 1.5% or more. In the positive electrode active material particles 30, the width (thickness) of the void layer 32 is the sum of the dimensions of the void layer 32 at the diameter (straight line 37) of the positive electrode active material particles 30. In the positive electrode active material particles 30, the width (thickness) of the void layer 33 is the sum of the dimensions of the void layer 33 at the diameter (straight line 37) of the positive electrode active material particles 30. The fourth ratio is preferably 2.0% or more. In the positive electrode active material particles 30, the fourth ratio for each of the void layers 32, 33 may be 1.5% or more. When the fourth ratio is within the above range, a decrease in the initial capacity and capacity retention rate of the battery and particle cracking tend to be more easily suppressed. Methods for controlling the fourth ratio within the above range include, for example, selecting the type of precursor particles (first particles) used and adjusting the firing conditions.

[0063] The third ratio and the fourth ratio are averages for 50 positive electrode active material particles, and are measured according to the method described in the Examples section below.

[0064] <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-described particle production method, a mixing step of mixing the obtained particles with Li to obtain a mixture, and a firing step of firing the mixture.

[0065] 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.

[0066] 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 740 to 810° C. The time for firing the mixture may be, for example, 3 to 10 hours. The firing step can be carried out in an oxidizing atmosphere.

[0067] <Nonaqueous electrolyte secondary battery> The battery of the present disclosure (hereinafter also referred to as the present battery) has a positive electrode plate, and the positive electrode plate has a positive electrode active material layer containing the above-described positive electrode active material particles, which tends to easily suppress decreases in initial capacity and capacity retention rate and particle cracking.

[0068] The battery typically includes an electrode assembly including a positive electrode and a non-aqueous electrolyte. The battery may have a battery case that houses the electrode assembly and the non-aqueous electrolyte. The battery case may include an exterior body having an opening and a sealing plate that seals the opening. The exterior body and the sealing plate may be formed using a metal such as Al, an Al alloy, iron, or an iron alloy, and may be formed using, for example, an Al laminate film. A resin sheet serving as an electrode holder may be disposed between the electrode assembly and the exterior body.

[0069] The electrode assembly may include a positive electrode plate, a negative electrode plate, and a separator. In the electrode assembly, the active material layer of the positive electrode plate and the negative electrode active material layer of the negative electrode plate face each other via the separator. The electrode assembly may be a laminated type in which the positive electrode plate, the negative electrode plate, and the separator are stacked, or a wound type in which a laminate in which the positive electrode plate, the negative electrode plate, and the separator are stacked is wound.

[0070] The positive electrode plate has a positive electrode current collector and a positive electrode active material layer containing the above-mentioned positive electrode active material, with the positive electrode active material layer on the positive electrode current collector. The positive electrode active material layer is formed on one or both sides of the positive electrode current collector. The positive electrode current collector is, for example, a metal foil made of an Al material such as Al or an Al alloy, and any metal foil that is stable within the potential range of the positive electrode plate may be used.

[0071] The positive electrode active material layer can be formed, for example, by applying a positive electrode mixture slurry onto a positive electrode current collector, drying it, and compressing it. The positive electrode mixture slurry can be prepared by adding a solvent such as N-methyl-2-pyrrolidone (NMP) to materials that form the active material layer, such as a positive electrode active material, a binder, and a conductive material, and kneading the mixture.

[0072] The positive electrode active material layer may contain, in addition to the positive electrode active material described above, a binder and a conductive material. Examples of binders include known materials such as fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE) and cellulose-based resins such as carboxymethyl cellulose (CMC). Examples of conductive materials include carbon materials. Examples of carbon materials include one or more selected from the group consisting of fibrous carbon, carbon black, coke, and activated carbon. Examples of fibrous carbon include carbon nanotubes (CNTs).

[0073] The positive electrode active material layer may have a thickness of, for example, 10 μm to 200 μm. The positive electrode active material layer may have a high density. The density of the positive electrode active material layer may be, for example, 3.5 g / cm. 3 or more, for example, 4.0 g / cm 3 It may have the following densities:

[0074] A negative electrode plate typically includes a negative electrode current collector and a negative electrode active material layer formed on one or both sides of the negative electrode current collector. The negative electrode current collector is a metal foil made of a copper material such as copper or a copper alloy. The negative electrode active material layer contains a negative electrode active material and may further contain a conductive material, a binder, and the like.

[0075] Examples of the negative electrode active material include known materials, such as carbon-based active material particles such as graphite, and metal-based active material particles containing an element selected from the group consisting of Si, Sn, Sb, Bi, Ti, and Ge. Examples of the conductive material include those described above. Examples of the binder include cellulose-based resins such as CMC, methyl cellulose (MC), and hydroxypropyl cellulose; polyacrylic acid; and styrene-butadiene rubber (SBR). CMC can also be used as a thickener.

[0076] The separator may have a substrate with a single-layer or multi-layer structure and a functional layer on at least one side of the substrate. The substrate may be a film made of a resin such as a polyolefin (e.g., polyethylene or polypropylene), polyester, cellulose, or polyamide, or a porous sheet such as a nonwoven fabric. The functional layer may be, for example, an adhesive layer and / or a heat-resistant layer. The adhesive layer may be formed, for example, with an adhesive. The heat-resistant layer may contain, for example, a filler and a binder.

[0077] The non-aqueous electrolyte preferably contains an electrolyte in a non-aqueous solvent such as an organic solvent. Examples of the electrolyte include one or more of LiPF6, LiBF4, LiClO4, LiFSO3, and LiBOB. Examples of the non-aqueous solvent include one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), butylene carbonate (BC), and diethyl carbonate (DEC). The non-aqueous electrolyte may further contain additives such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), and fluoroethylene carbonate.

[0078] The present invention will be described in more detail below with reference to examples. [Example]

[0079] [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.

[0080] (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.

[0081] (Measurement of the first ratio, second ratio and number of void layers) 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 void and core regions were identified using image analysis software, the number of void regions was counted, and the first ratio (core diameter / particle diameter) and second ratio (void width / particle diameter) were calculated from the scale ratio.

[0082] [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.

[0083] (Measurement of the third ratio, fourth ratio and number of void layers) The positive electrode active material 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 void and core regions were identified using image analysis software, the number of voids was counted, and the third ratio (core diameter / particle diameter) and fourth ratio (void width / particle diameter) were calculated from the scale ratio.

[0084] [Fabrication of non-aqueous electrolyte secondary battery] (Preparation of positive electrode plate) Positive electrode mixture pastes were prepared by mixing the positive electrode active material particles of the examples and comparative examples with a conductive material (acetylene black (AB)), a binder (PVDF), and a solvent (NMP). The positive electrode mixture pastes were prepared so that the mass ratio of the positive electrode active material particles, conductive material, and binder (positive electrode active material particles:conductive material:binder) was 100:1:1 (wt%). The prepared paste was applied to a positive electrode current collector (15 μm thick Al foil), dried, pressed to a predetermined thickness, and processed to the predetermined dimensions to obtain a positive electrode plate.

[0085] (Preparation of negative electrode plate) Anode active material (graphite), binders (SBR and CBC), and water were mixed to prepare anode mixture slurry. The anode mixture slurry was prepared so that the mass ratio of anode active material to binder (graphite:SBR:CMC) was 100:1:1 (wt%). The mixture was applied to anode current collector (10 μm thick copper foil), dried, compressed to a specified thickness, and cut to a specified size to prepare anode plates.

[0086] (Preparation of electrode body) Leads were attached to the positive and negative electrode plates, respectively, and the positive and negative electrode plates were stacked with a separator interposed therebetween to prepare an electrode assembly.

[0087] (Preparation of test cell) The electrode assembly was inserted into an exterior body made of an aluminum laminate sheet, a non-aqueous electrolyte was poured into it, and the opening of the exterior body was sealed to prepare a test cell (laminate cell) for a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte used was 1M LiPF6 as the Li salt, and a solvent of EC / FEC / EMC / DMC = 15 / 5 / 40 / 40 (vol.%).

[0088] [Battery evaluation] (Initial capacity measurement) In a 25°C environment, the battery was charged at a current of C / 3 to 4.2 Vcccv and then discharged to 3 V at a current of C / 3. The discharge capacity at this time was taken as the initial capacity. The initial capacity (%) was calculated as a percentage of the initial capacity of Comparative Example 1, which was taken as 100.

[0089] (Measurement of cycle capacity retention rate) In a 25°C environment, the test cell was charged using a constant current-constant voltage (CC-CV) method (CC current = 1C, CV voltage = 4.2V, 0.1C cutoff), and then discharged using a constant current (CC) method (CC current = 1C, 2.5V cutoff). This was considered as one cycle, and the capacity at this time was defined as the initial capacity. Charging and discharging were repeated under the above conditions until 200 cycles were reached, and the capacity was obtained. The following formula: Capacity retention rate (%) = (capacity after 200 cycles) / (initial capacity) × 100 The capacity retention rate (%) was calculated according to the following formula.

[0090] (Evaluation of particle cracking rate) The test cell used to measure the cycle capacity retention rate was disassembled after 200 cycles, and the removed positive electrode plate was cut out and a cross section was obtained by ion milling. The cross section was observed using a commercially available scanning electron microscope to obtain an SEM image. 100 positive electrode active material particles were randomly selected from the obtained SEM image, and the outline area of ​​each positive electrode active material particle and the area of ​​the voids within the particle were calculated using the following formula: Particle cracking rate (%) = (area of ​​void layer in positive electrode active material particle) / (outline area) × 100 The particle cracking rate (%) of 100 positive electrode active material particles calculated according to the above was calculated as an average.

[0091] 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.

[0092] (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.

[0093] (Preparation of aqueous ammonia solution) A 10 wt % aqueous ammonia solution was prepared using 28 wt % aqueous ammonia.

[0094] (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 liquid temperature of 25°C. Crystallization continued for 10 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.

[0095] Thereafter, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 15.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.1 at a liquid temperature of 25°C.

[0096] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 0.5 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at a liquid temperature of 25°C at 12.1.

[0097] Subsequently, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 15.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.1 at a liquid temperature of 25°C.

[0098] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentration in the raw metal aqueous solution and the ammonia aqueous solution became 0.5 vol%, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 6 minutes while maintaining the pH at 12.1 at a liquid temperature of 25° C. Thereafter, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped to complete the crystallization.

[0099] After crystallization was completed, the product was filtered, washed, and dried to obtain precursor particles. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was sequentially changed from 0.5 vol% at the start of crystallization to (1) 15.0 vol%, (2) 0.5 vol%, (3) 15.0 vol%, and (4) 0.5 vol%. The number of times the oxygen concentration in the Taylor vortex reaction field was changed from 1.0 vol% or less to 10.0 vol% or more (first changeover) was two, and the number of times the oxygen concentration in the Taylor vortex reaction field was changed from 10.0 vol% or more to 1.0 vol% or less (second changeover) was two, for a total of four changes in the oxygen concentration in the Taylor vortex reaction field. SEM observation of the cross-section of the precursor particles confirmed that, from the center of the particle, the precursor particles had a core, a void layer outside the core, an inner structure, a void layer, and an outer structure. The results are shown in Table 1.

[0100] <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 pH was adjusted to 11.5 at a liquid temperature of 25°C.

[0101] (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.

[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) Nitrogen gas was introduced and bubbled to maintain the oxygen concentration of the raw metal aqueous solution and the ammonia aqueous solution below 0.4 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 the pH at 11.5 at a base liquid temperature of 25°C. Crystallization continued for 15 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.

[0104] Thereafter, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 32.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 11.5 at a liquid temperature of 25°C.

[0105] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 0.4 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 11.5 at a liquid temperature of 25°C.

[0106] Subsequently, 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 in the raw metal aqueous solution and the ammonia aqueous solution became 32.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 11.5 at a liquid temperature of 25°C.

[0107] Next, the supply of the raw metal aqueous solution and the aqueous ammonia solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentration in the raw metal aqueous solution and the aqueous ammonia solution became 0.4 vol%, after which the raw metal aqueous solution and the aqueous ammonia solution were supplied so that the molar ratio of the raw metal aqueous solution to the aqueous ammonia solution became 1:1, and crystallization was carried out for 10 minutes while maintaining the pH at 11.5 at a liquid temperature of 25° C. Thereafter, the supply of the raw metal aqueous solution and the aqueous ammonia solution was stopped to complete the crystallization.

[0108] After crystallization was completed, the product was filtered, washed, and dried to obtain precursor particles. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was sequentially changed from 0.4 vol% at the start of crystallization to (1) 32.0 vol%, (2) 0.4 vol%, (3) 32.0 vol%, and (4) 0.4 vol%. The number of times the oxygen concentration in the Taylor vortex reaction field was changed from 1.0 vol% or less to 10.0 vol% or more (first changeover) was two, and the number of times the oxygen concentration in the Taylor vortex reaction field was changed from 10.0 vol% or more to 1.0 vol% or less (second changeover) was two. The results are shown in Table 1.

[0109] 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 pH was adjusted to 12.3 at a liquid temperature of 25°C.

[0110] (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 79:10:10:1.

[0111] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0112] (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 0.8 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 the pH at 12.3 at a base liquid temperature of 25°C. Crystallization continued for 10 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.

[0113] Thereafter, 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 in the raw metal aqueous solution and the ammonia aqueous solution became 17.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.3 at a liquid temperature of 25°C.

[0114] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 0.8 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.3 at a liquid temperature of 25°C.

[0115] Subsequently, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 17.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.3 at a liquid temperature of 25°C.

[0116] Next, the supply of the raw metal aqueous solution and the aqueous ammonia solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentration in the raw metal aqueous solution and the aqueous ammonia solution became 0.8 vol%, after which the raw metal aqueous solution and the aqueous ammonia solution were supplied so that the molar ratio of the raw metal aqueous solution to the aqueous ammonia solution became 1:1, and crystallization was carried out for 6 minutes while maintaining the pH at 12.3 at a liquid temperature of 25° C. Thereafter, the supply of the raw metal aqueous solution and the aqueous ammonia solution was stopped to complete the crystallization.

[0117] After crystallization was completed, the product was filtered, washed, and dried to obtain precursor particles. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was sequentially changed from 0.8 vol% at the start of crystallization to (1) 17.0 vol%, (2) 0.8 vol%, (3) 17.0 vol%, and (4) 0.8 vol%. The number of times the oxygen concentration in the Taylor vortex reaction field was changed from 1.0 vol% or less to 10.0 vol% or more (first changeover) was two, and the number of times the oxygen concentration in the Taylor vortex reaction field was changed from 10.0 vol% or more to 1.0 vol% or less (second changeover) was two. The results are shown in Table 1.

[0118] 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 pH was adjusted to 12.1 at a liquid temperature of 25°C.

[0119] (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.

[0120] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0121] (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 liquid temperature of 25°C. Crystallization continued for 10 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.

[0122] Thereafter, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 19.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at a liquid temperature of 25°C at 12.1.

[0123] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 0.5 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at a liquid temperature of 25°C at 12.1.

[0124] Subsequently, the supply of the raw metal aqueous solution and the aqueous ammonia solution was stopped, and a mixed gas of oxygen and nitrogen was introduced and bubbled so that the oxygen concentration in the raw metal aqueous solution and the aqueous ammonia solution became 19.0 vol%, and then the raw metal aqueous solution and the aqueous ammonia solution were supplied so that the molar ratio of the raw metal aqueous solution to the aqueous ammonia solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.1 at a liquid temperature of 25° C. Thereafter, the supply of the raw metal aqueous solution and the aqueous ammonia solution was stopped to complete the crystallization.

[0125] After crystallization was completed, the product was filtered, washed, and dried to obtain precursor particles. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was sequentially changed from 0.5 vol% at the start of crystallization to (1) 19.0 vol%, (2) 0.5 vol%, and (3) 19.0 vol%. The oxygen concentration in the Taylor vortex reaction field was changed from 1.0 vol% or less to 10.0 vol% or more (first changeover) twice, and from 10.0 vol% or more to 1.0 vol% or less (second changeover) once. The total number of changes in the oxygen concentration in the Taylor vortex reaction field was three. The results are shown in Table 1.

[0126] <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.

[0127] (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.

[0128] (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.

[0129] (nucleus growth process) After the nucleation step was completed, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and sulfuric acid was gradually supplied so that the pH of the solution in the reaction tank at a liquid temperature of 25°C was 11.4. The supply of the raw metal aqueous solution and the ammonia aqueous solution to the reaction tank was then resumed. Crystallization was continued for 4 hours while maintaining the pH at a liquid temperature of 25°C at 11.4. The supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and crystallization was completed. 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.

[0130] <Comparative 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 pH was adjusted to 11.2 at a liquid temperature of 25°C.

[0131] (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.

[0132] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0133] (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 0.4 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 the pH at 11.2 at a base liquid temperature of 25°C. Crystallization continued for 10 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.

[0134] Thereafter, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 15.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 11.2 at a liquid temperature of 25°C.

[0135] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 0.4 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 11.2 at a liquid temperature of 25°C.

[0136] Subsequently, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 15.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at a standard liquid temperature of 25°C at 11.2.

[0137] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentration in the raw metal aqueous solution and the ammonia aqueous solution became 0.4 vol%, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 6 minutes while maintaining the pH at 11.2 at a liquid temperature of 25° C. Thereafter, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped to complete the crystallization.

[0138] After crystallization was completed, the product was filtered, washed, and dried to obtain precursor particles. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was sequentially changed from 0.4 vol% at the start of crystallization to (1) 15.0 vol%, (2) 0.4 vol%, (3) 15.0 vol%, and (4) 0.4 vol%. The number of times the oxygen concentration in the Taylor vortex reaction field was changed from 1.0 vol% or less to 10.0 vol% or more (first changeover) was two, and the number of times the oxygen concentration in the Taylor vortex reaction field was changed from 10.0 vol% or more to 1.0 vol% or less (second changeover) was two. The results are shown in Table 1.

[0139] <Comparative 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 pH was adjusted to 12.8 at a liquid temperature of 25°C.

[0140] (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.

[0141] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0142] (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 0.4 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 the pH at 12.8 at a liquid temperature of 25°C. Crystallization continued for 10 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.

[0143] Thereafter, 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 in the raw metal aqueous solution and the ammonia aqueous solution became 18.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.8 at a liquid temperature of 25°C.

[0144] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 0.4 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at a standard liquid temperature of 25°C at 12.8.

[0145] Subsequently, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 18.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.8 at a liquid temperature of 25°C.

[0146] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentration in the raw metal aqueous solution and the ammonia aqueous solution became 0.4 vol%, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 6 minutes while maintaining the pH at 12.8 at a liquid temperature of 25° C. Thereafter, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped to complete the crystallization.

[0147] After crystallization was completed, the product was filtered, washed, and dried to obtain precursor particles. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was sequentially changed from 0.4 vol% at the start of crystallization to (1) 18.0 vol%, (2) 0.4 vol%, (3) 18.0 vol%, and (4) 0.4 vol%. The number of times the oxygen concentration in the Taylor vortex reaction field was changed from 1.0 vol% or less to 10.0 vol% or more (first changeover) was two, and the number of times the oxygen concentration in the Taylor vortex reaction field was changed from 10.0 vol% or more to 1.0 vol% or less (second changeover) was two. The results are shown in Table 1.

[0148] <Comparative 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 pH was adjusted to 12.1 at a liquid temperature of 25°C.

[0149] (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.

[0150] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0151] (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 4.2 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 the pH at 12.1 at a base liquid temperature of 25°C. Crystallization continued for 15 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.

[0152] Thereafter, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 22.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at a liquid temperature of 25°C at 12.1.

[0153] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 4.2 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at a liquid temperature of 25°C at 12.1.

[0154] Subsequently, 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 in the raw metal aqueous solution and the ammonia aqueous solution became 22.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at a liquid temperature of 25°C at 12.1.

[0155] Next, the supply of the raw metal aqueous solution and the aqueous ammonia solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentration in the raw metal aqueous solution and the aqueous ammonia solution became 4.2 vol%, after which the raw metal aqueous solution and the aqueous ammonia solution were supplied so that the molar ratio of the raw metal aqueous solution to the aqueous ammonia solution became 1:1, and crystallization was carried out for 8 minutes while maintaining the pH at 12.1 at a liquid temperature of 25° C. Thereafter, the supply of the raw metal aqueous solution and the aqueous ammonia solution was stopped to complete the crystallization.

[0156] After crystallization was completed, the product was filtered, washed, and dried to obtain precursor particles. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was sequentially changed from 4.2 vol% at the start of crystallization to (1) 22.0 vol%, (2) 4.2 vol%, (3) 22.0 vol%, and (4) 4.2 vol%. The number of times the oxygen concentration in the Taylor vortex reaction field was changed from 1.0 vol% or less to 10.0 vol% or more (first changeover) was two, and the number of times the oxygen concentration in the Taylor vortex reaction field was changed from 10.0 vol% or more to 1.0 vol% or less (second changeover) was two. The results are shown in Table 1.

[0157] <Comparative Example 5> [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 pH was adjusted to 12.1 at a liquid temperature of 25°C.

[0158] (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.

[0159] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0160] (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 liquid temperature of 25°C. Crystallization continued for 10 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.

[0161] Thereafter, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 5.3 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.1 at a liquid temperature of 25°C.

[0162] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 0.5 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at a liquid temperature of 25°C at 12.1.

[0163] Subsequently, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 5.3 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.1 at a liquid temperature of 25°C.

[0164] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentration in the raw metal aqueous solution and the ammonia aqueous solution became 0.5 vol%, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 6 minutes while maintaining the pH at 12.1 at a liquid temperature of 25° C. Thereafter, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped to complete the crystallization.

[0165] After crystallization was completed, the product was filtered, washed, and dried to obtain precursor particles. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was sequentially changed from 0.5 vol% at the start of crystallization to (1) 5.3 vol%, (2) 0.5 vol%, (3) 5.3 vol%, and (4) 0.5 vol%. The number of times the oxygen concentration in the Taylor vortex reaction field was changed from 1.0 vol% or less to 10.0 vol% or more (first changeover) was two, and the number of times the oxygen concentration in the Taylor vortex reaction field was changed from 10.0 vol% or more to 1.0 vol% or less (second changeover) was two. The results are shown in Table 1.

[0166] <Comparative Example 6> [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 pH was adjusted to 12.1 at a liquid temperature of 25°C.

[0167] (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.

[0168] (Preparation of aqueous ammonia solution) In the same manner as in Example 1, a 10 wt % aqueous ammonia solution was prepared.

[0169] (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 liquid temperature of 25°C. Crystallization continued for 10 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.

[0170] Thereafter, 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 concentrations in the raw metal aqueous solution and the ammonia aqueous solution became 15.0 vol %, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 4 minutes while maintaining the pH at 12.1 at a liquid temperature of 25°C.

[0171] Next, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped, and nitrogen gas was introduced and bubbled so that the oxygen concentration in the raw metal aqueous solution and the ammonia aqueous solution became 0.5 vol%, and then the raw metal aqueous solution and the ammonia aqueous solution were supplied so that the molar ratio of the raw metal aqueous solution to the ammonia aqueous solution became 1:1, and crystallization was carried out for 8 minutes while maintaining the pH at 12.1 at a liquid temperature of 25° C. Thereafter, the supply of the raw metal aqueous solution and the ammonia aqueous solution was stopped to complete the crystallization.

[0172] After crystallization was completed, the product was filtered, washed, and dried to obtain precursor particles. During the crystallization process, the oxygen concentration in the Taylor vortex reaction field was sequentially changed from 0.5 vol% at the start of crystallization to (1) 15.0 vol% and (2) 0.5 vol%. The oxygen concentration in the Taylor vortex reaction field was changed from 1.0 vol% or less to 10.0 vol% or more (first change) once, and from 10.0 vol% or more to 1.0 vol% or less (second change) once. The total number of changes in the oxygen concentration in the Taylor vortex reaction field was two. The results are shown in Table 1.

[0173] <Example 5> [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 moles of lithium to the total 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.

[0174] <Examples 6 to 8 and Comparative Examples 7 to 12> 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.

[0175] [Table 1]

[0176] [Table 2]

[0177] The positive electrode active materials of Examples 5 to 8, which were prepared using the precursor particles of Examples 1 to 4, respectively, suppressed particle cracking and the decrease in initial capacity and capacity retention. In contrast, the positive electrode active material of Comparative Example 7, which was prepared using the precursor particles of Comparative Example 1, did not suppress particle cracking, resulting in a decrease in capacity retention. The positive electrode active material of Comparative Example 8, which was prepared using the precursor particles of Comparative Example 2, had a small core diameter, resulting in a low initial capacity, and the width of the void layer was large, resulting in a decrease in capacity retention. The positive electrode active material of Comparative Example 9, which was prepared using the precursor particles of Comparative Example 3, did not suppress particle cracking because the particles did not grow and no void layer was formed, resulting in a decrease in initial capacity and capacity retention. The positive electrode active material of Comparative Example 10, which was prepared using the precursor particles of Comparative Example 4, had a decrease in initial capacity because the cores of the precursor particles and positive electrode active material particles were too sparse. The positive electrode active material of Comparative Example 11, which was produced using the precursor particles of Comparative Example 5, had a small void layer width, so particle cracking was not suppressed, resulting in a reduced capacity retention rate.The positive electrode active material of Comparative Example 12, which was produced using the precursor particles of Comparative Example 6, had only one void layer, so particle cracking was not suppressed, resulting in a reduced capacity retention rate. [Explanation of symbols]

[0178] 10 Reaction tank, 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, 23 Void layer, 24 Inner portion, 25 Outer portion, 26 Primary particle, 27 Straight line, 30 Positive electrode active material particle, 31 Core portion, 32, 33 Void layer, 34 Inner portion, 35 Outer portion, 36 Primary particle, 37 Straight line.

Claims

1. A method for producing particles, comprising: the particles are 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 ion 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 25°C is 11.4 to 12.5, crystallization is initiated by setting the oxygen concentration in the Taylor vortex reaction field to 1.0 vol% or less; a total number of times that the oxygen concentration in the Taylor vortex reaction field is switched from 1.0 vol% or less to 10.0 vol% or more and from 10.0 vol% or more to 1.0 vol% or less is 3 or more;

2. The method for producing particles according to claim 1 , wherein the total number of times that the oxygen concentration in the Taylor vortex reaction field is switched is four or more.

3. 3. The method for producing particles according to claim 1, wherein a ratio of a time period from the start of crystallization until the oxygen concentration in the Taylor vortex reaction field is first switched to 10.0 vol% or more to a total time period for crystallization in the crystallization step is 15% to 50%.

4. 3. The method for producing particles according to claim 1, wherein a ratio of a time period from when the oxygen concentration in the Taylor vortex reaction field is switched until the next time the oxygen concentration in the Taylor vortex reaction field is switched to an entire time period during which crystallization is performed in the crystallization step is 5% or more.

5. 3. The method for producing particles according to claim 1 or 2, wherein the switching of the oxygen concentration in the Taylor vortex reaction field from 1.0 vol% or less to 10.0 vol% or more and the switching of the oxygen concentration in the Taylor vortex reaction field from 10.0 vol% or more to 1.0 vol% or less are respectively switching of the oxygen concentration in the Taylor vortex reaction field from 1.0 vol% or less to 15.0 vol% or more and the switching of the oxygen concentration in the Taylor vortex reaction field from 15.0 vol% or more to 1.0 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 2000 rpm or less.

7. A particle made of a transition metal composite hydroxide containing nickel, the particle having a core portion inside the particle and at least two porous layers outside the core portion, the voids of which account for 70% or more.

8. 8. The particles according to claim 7, wherein the average ratio of the diameter of the core portion to the particle diameter is 30% to 70%.

9. 9. The particle according to claim 7, wherein the average ratio of the width of the void layer to the particle diameter is 1.5% or more.

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

11. The particle according to claim 7 or 8, wherein the core has a solid or hollow structure.

12. A positive electrode active material particle is made of a transition metal composite oxide containing lithium and nickel, and has a core portion inside the particle and at least two or more void layers outside the core portion, with voids accounting for 70% or more.

13. 13. The positive electrode active material particles according to claim 12, wherein an average ratio of the diameter of the core portion to the particle diameter is 30% to 70%.

14. The positive electrode active material particles according to claim 12 or 13, wherein an average ratio of the width of the void layer to the particle diameter is 1.5% or more.

15. The positive electrode active material particles according to claim 12 or 13, having an average particle size of 1 μm to 10 μm.

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

17. 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.

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

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