Positive electrode active material, positive electrode plate, and nonaqueous electrolyte secondary battery

Abstract

To provide a positive electrode active material capable of obtaining a nonaqueous electrolyte secondary battery excellent in both input / output characteristics and a capacity maintenance rate in a charge / discharge cycle.SOLUTION: A positive electrode active material comprising a first group of particles and a second group of particles, wherein the first group of particles comprises a plurality of first particles, the second group of particles comprises a plurality of second particles, the first particles comprise particles having a void, the second particles comprise secondary particles formed by aggregation of primary particles, the secondary particles have an integrated intensity ratio (I003 / I104) of 1.05 to 1.19, and the secondary particles have a crystallite size L003 of 1000 Å or more.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material, and further to a positive electrode plate and a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2013-93295 (Patent Document 1) discloses a positive electrode mixture containing at least two types of positive electrode active material particles having different average particle sizes.

[0003] Japanese Patent Application Laid-Open No. 2020-87879 (Patent Document 2) discloses a lithium metal composite oxide powder composed of secondary particles formed by aggregation of primary particles and single particles that exist independently of the secondary particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-93295 [Patent Document 2] Japanese Patent Application Publication No. 2020-87879 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide a positive electrode active material that allows for the production of a nonaqueous electrolyte secondary battery that is excellent in both input / output characteristics and capacity retention rate in charge / discharge cycles (hereinafter also referred to as cycle capacity retention rate). [Means for solving the problem]

[0006] [1] A particle composition comprising a first particle group and a second particle group, the first particle group includes a plurality of first particles, the second particle group includes a plurality of second particles, the first particles include particles having voids, The second particles include secondary particles formed by aggregation of primary particles, The integrated intensity ratio (I 003 / I 104 ) of the diffraction peak in the X-ray diffraction method of the secondary particles is 1.05 to 1.19, The crystallite size L 003 of the secondary particles is 1000 Å or more, a positive electrode active material. [2] The mass ratio (first particle group: second particle group) of the first particle group and the second particle group in the positive electrode active material is 8:2 to 5:5, the positive electrode active material according to [1]. [3] The first particles have a circularity of 0.92 or more, the positive electrode active material according to [1] or [2]. [4] The first particles have a core part, a void part outside the core part, and an outer structure part outside the void part, the positive electrode active material according to any one of [1] to [3]. [5] The average particle diameter of the first particle group is 8 to 20 μm, the positive electrode active material according to any one of [1] to [4]. [6] The average particle diameter of the second particle group is 2 to 7 μm, the positive electrode active material according to any one of [1] to [5]. [7] The second particles include a lithium transition metal composite oxide having a layered crystal structure, The lithium transition metal composite oxide is Li, Ni, Mn, Co, and M [M is one or more metal elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, and W.], and The molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M = a:x:y:z:t [a, x, y, z, and t are 1.0 ≦ a ≦ 1.3, x + y + z = 1, 0.25 ≦ x ≦ 0.9, 0 < y ≦ 0.6, 0 < z ≦ 0.6, and 0 < t ≦ 0.1.], the positive electrode active material according to any one of [1] to [6]. [8] A positive electrode plate including the positive electrode active material according to any one of [1] to [7]. [9] A non-aqueous electrolyte secondary battery including the positive electrode plate according to [7].

Advantages of the Invention

[0007] According to the present disclosure, it is possible to provide a positive electrode active material that allows a nonaqueous electrolyte secondary battery to be obtained that is excellent in both input / output characteristics and cycle capacity retention rate. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view of a particle having voids. [Figure 2] FIG. 2 is a schematic cross-sectional view illustrating a reaction vessel that generates a Taylor vortex reaction field. [Figure 3] FIG. 3 is a schematic cross-sectional view of the positive electrode plate in the thickness direction. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Cathode active material> The positive electrode active material of the present disclosure includes a first particle group and a second particle group. The first particle group includes a plurality of first particles. The second particle group includes a plurality of second particles. The first particles include particles having voids. The second particles include secondary particles formed by aggregation of primary particles. The integrated intensity ratio (I 003 / I 104 ) (hereinafter also referred to as the integrated intensity ratio) is 1.05 to 1.19. The crystallite size L of the secondary particles 003 (hereinafter also referred to as crystallite size) is 1000 Å or more.

[0010] In a positive electrode active material layer made of positive electrode active material particles containing two types of particles with different average particle sizes, the particles with a relatively large average particle size tend to have a longer lithium ion diffusion distance within the particles, resulting in a decrease in input / output characteristics. Furthermore, in a positive electrode active material layer made of positive electrode active material particles containing both single particles and agglomerated particles, which are secondary particles formed by agglomeration of multiple primary particles, the lithium ion diffusivity of the single particles is lower than that of the agglomerated particles, resulting in a longer lithium ion diffusion distance and a decrease in input / output characteristics. Furthermore, single particles tend to be relatively expensive to manufacture. Furthermore, excessive promotion of crystal growth of the primary particles of the agglomerated particles can easily cause particle cracking during rolling during the manufacturing process of the positive electrode active material layer, resulting in a decrease in cycle capacity retention. The positive electrode active material of the present disclosure, which contains first and second particles, enables the production of a nonaqueous electrolyte secondary battery (hereinafter also referred to as a battery) with excellent input / output characteristics and cycle capacity retention. The input / output characteristics and cycle capacity retention are evaluated according to the methods described in the Examples section below.

[0011] The first particle group includes a plurality of first particles. The content of the first particles in the first particle group is, for example, 70 to 100 mass%, or alternatively, 85 to 98 mass%, or 90 to 95 mass%, when the total amount of the first particle group is 100 mass%. The first particle group can include only a plurality of first particles.

[0012] The average particle diameter of the first particle group may be, for example, 2 to 20 μm, and preferably 8 to 20 μm. In this specification, the average particle diameter is 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 laser diffraction particle size analyzer. The average particle diameter of the first particle group can be controlled, for example, by adjusting the raw material composition and firing conditions (firing temperature, firing time, etc.), and by selecting the type and particle diameter of precursor particles used to produce the first particles.

[0013] The first particle includes a particle having a void portion. The first particle may include only particles having a void portion. The particle having a void portion will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view of a particle 10 having a void portion. The particle 10 having a void portion has a core portion 11, a void portion 12, and an outer structure portion 13. The particle 10 having a void portion may be a secondary particle (hereinafter also referred to as a first secondary particle) formed by aggregation of primary particles. The first secondary particle is a particle different from the second secondary particle described below that is contained in the second particle. The particle 10 having a void portion has one core portion and one layer of outer structure portion. The particle 10 having a void portion has improved Li diffusibility within the particle, and tends to be more likely to have excellent input / output characteristics due to the presence of the void portion.

[0014] The void portion 12 can be a space between the core portion 11 and the outer structure portion 13. The core portion 11 may be an aggregate of primary particles 14. The core portion 11 may have a solid structure or a hollow structure. If the core portion 11 is hollow, the hollow portion of the core portion 11 is not considered to be a void portion 12. The outer structure portion 13 may be an aggregate of primary particles 15. The core portion 11 and the outer structure portion 13 may be completely separated by the void portion 12, or in a particle 10 having a void portion, the primary particles 14 and the primary particles 15 may be in contact with each other, and there may be a portion where the core portion 11 and the outer structure portion 13 are in contact with each other. Only a portion of the primary particles 14 and the primary particles 15 is shown in FIG. 1.

[0015] The particle 10 having voids may further have one or more layers of additional outer structure outside the outer structure 13. When the particle 10 having voids has two or more layers of outer structure, the particle 10 having voids may have two layers of voids. The outer structure 13 may be formed so as to completely cover the core 11, or may be formed so as to partially cover it.

[0016] The circularity of the void-containing particles 10 may be, for example, 0.92 or more, preferably 0.93 or more, more preferably 0.94 or more, and may be, for example, 1.00 or less. The circularity of the void-containing particles 10 is the average of 50 void-containing particles 10. When the circularity of the void-containing particles 10 is 0.92 or more, the packing property tends to be easily improved. In this specification, the circularity is calculated by the following formula: Circularity = (perimeter of a circle equal to the projected area of ​​the particle) / (perimeter of the particle) The circularity of a voided particle is the average of 50 voided particles.

[0017] The average ratio (%) of the width (thickness) of the void portion 12 to the particle size (diameter) of the void portion 10 (hereinafter also referred to as the first ratio) may be, for example, 10% or more or 40% or more, or 80% or less or 70% or less. The particle size of the void portion 10 may be the diameter of the void portion 10 when the void portion 10 is considered to be a circle in its cross section. For example, in FIG. 1, the particle size of the void portion 10 is indicated by the line 16. The width (thickness) of the void portion 12 may be the dimension of the void portion 12 at the above-mentioned radius (line 16) of the void portion 10.

[0018] The particle 10 having voids may have an average ratio (%) of the thickness of the outer structure 13 to the particle size (diameter) of 3% to 50% (hereinafter also referred to as the second ratio). The thickness of the outer structure 13 may be the dimension of the outer structure 13 at the diameter (straight line 16) of the particle 10 having voids. The first ratio and the second ratio are averages for 50 particles 10 having voids. The first ratio and the second ratio are measured according to the method described in the Examples section below.

[0019] The proportion of voids 12 to the total volume of void-containing particle 10 may be, for example, 10% or more, 40% or more, or 60% or more, or 30% or less, 60% or less, or 80% or less. In this specification, the proportion of voids 12 to the total volume of void-containing particle 10 is determined by processing a cross-sectional SEM image of void-containing particle 10, distinguishing between the areas where primary particles 14 and 15 exist and voids 12, and calculating the proportion of the total area of ​​voids 12 to the area of ​​void-containing particle 10.

[0020] The BET specific surface area of ​​the particle 10 having voids is, for example, 0.5 to 2.8 m 2 The BET specific surface area may be measured according to the method described in the Examples section below.

[0021] The primary particle diameter of the void-containing particles 10 may be, for example, 0.1 to 1.0 μm. The primary particle diameter of the void-containing particles 10 is measured according to the method described in the Examples section below.

[0022] The particles 10 having voids have voids that are relatively uniform in cross section, and therefore when used in a positive electrode plate, can easily improve the output characteristics and capacity characteristics of a battery.

[0023] The void-containing particle 10 may be a particle made of a composite oxide containing Li and Ni, a particle made of a transition metal composite oxide containing Li, Ni, and Mn, or a particle made of a transition metal composite oxide containing Li, Ni, Co, and Mn.

[0024] The particle 10 having a void portion may be, for example, a particle having a void portion represented by the following formula (i): Li 1+a1 Ni 1-x-y-z Co x Mn y M z O2(i) [In formula (i), -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 composition of the first composite oxide may be determined by inductively coupled plasma (ICP) atomic emission spectroscopy (ICP-AES). Specifically, the composition can be determined in accordance with JIS K 0116:2014, General Rules for Optical Emission Spectroscopy. For example, the first composite oxide is dissolved by alkali fusion using a high-resolution ICP atomic emission spectroscopy analyzer (Hitachi High-Tech Science Corporation, model PS3500DDII) and then diluted to a predetermined volume with ultrapure water, tartaric acid, or hydrochloric acid. The wavelengths for each element measured by ICP-AES are Li: 670.784 nm, Co: 238.892 nm, Mn: 257.61 nm, and Ni: 231.604 nm.

[0025] The particles 10 having voids can be produced by a production method including, for example, a mixing step of mixing precursor particles with Li to obtain a mixture, and a firing step of firing the mixture.

[0026] The precursor particles may be particles that have, for example, a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion, and are made of a transition metal composite hydroxide that contains Ni.

[0027] The precursor particles can be produced by a production method including a crystallization step of generating a Taylor vortex reaction field, adding an aqueous solution containing a compound containing a transition metal (hereinafter also referred to as a raw metal aqueous solution), an ammonium donor, and an alkaline aqueous solution to the Taylor vortex reaction field, and crystallizing a transition metal composite hydroxide containing nickel (hereinafter also referred to as a first metal hydroxide).

[0028] The transition metal composite hydroxide containing Ni may be a composite hydroxide further containing Mn, or may be a nickel-cobalt-manganese composite hydroxide further containing Mn and Co. The transition metal composite hydroxide containing Ni is preferably a nickel-cobalt-manganese composite hydroxide (hereinafter also referred to as an NCM composite hydroxide).

[0029] 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.

[0030] 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).

[0031] 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 void-containing particles 10 are transition metal composite oxides containing Li, Ni, Co, and Mn, 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).

[0032] 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).

[0033] 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.

[0034] 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。

[0035] 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。

[0036] 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。

[0037] The ammonium donor may be, for example, an aqueous ammonia solution, the ammonia concentration of which may be, for example, 5 to 20 wt %.

[0038] 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 %.

[0039] 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).

[0040] The reaction layer that generates a Taylor vortex reaction field will be described with reference to FIG. 2. The reaction vessel 100 shown in FIG. 2 includes an outer cylinder 111 and an inner cylinder 112. The outer cylinder 111 is fixed. The inner cylinder 112 can be rotated by a motor 118. The outer cylinder 111 includes a first supply port 113 for supplying a raw metal aqueous solution, a second supply port 114 for supplying an ammonium supply, and a third supply port 115 for supplying an alkaline aqueous solution. The outer cylinder 111 further includes an outlet 116.

[0041] In the reaction tank 100, crystallization can be carried out, for example, by the following procedure. First, water is filled between the outer cylinder 111 and the inner cylinder 112 through the first supply port 113, and the inner cylinder 112 is rotated to generate a Taylor vortex flow between the outer cylinder 111 and the inner cylinder 112, thereby generating a Taylor vortex reaction field. The rotation speed of the inner cylinder 112 can be, for example, 500 to 2000 rpm.

[0042] Aqueous sodium hydroxide solution is supplied to the fluid from the third supply port 115, and the pH of the Taylor vortex reaction field at a liquid temperature of 25°C can be adjusted to 12.5 or less. The pH at a liquid temperature of 25°C can be controlled, for example, by adjusting the flow rate of the aqueous sodium hydroxide solution using a pH controller. The pH of the Taylor vortex reaction field at a liquid temperature of 25°C may be, for example, 10.7 or more. From the viewpoint of the circularity of the particles 10 having voids, the pH of the Taylor vortex reaction field at a liquid temperature of 25°C is preferably 11.0 or more and 12.5 or less.

[0043] The crystallization process can include, for example, first and second crystallizations. The first crystallization can be initiated by supplying the raw metal aqueous solution through the first supply port 113 and the ammonium supply through the second supply port 114. The raw metal aqueous solution and the ammonium supply can be supplied to the Taylor vortex reaction field at a molar ratio of 1:1. In the first crystallization, the oxygen concentration in the Taylor vortex reaction field can be maintained at 3.5 vol% or less. One method for maintaining the oxygen concentration in the Taylor vortex reaction field at 3.5 vol% or less is to inject nitrogen gas into the raw metal aqueous solution and the ammonium supply supplied to the Taylor vortex reaction field and bubble the gas. Hereinafter, the oxygen concentration in the Taylor vortex reaction field from the start of crystallization until the oxygen concentration in the Taylor vortex reaction field is changed as described below is also referred to as the "first oxygen concentration." The oxygen concentration in the Taylor vortex reaction field can be confirmed using a dissolved oxygen meter.

[0044] The time for which the first crystallization is performed (hereinafter also referred to as the first crystallization time) can be set so that the ratio of the time for which crystallization is performed to the total time for which crystallization is performed in the crystallization step (hereinafter also referred to as the first crystallization ratio) is, for example, 40% to 90%. When the first crystallization ratio is within the above range, it tends to be easier to produce precursor particles. When the first crystallization ratio is less than 40%, it tends to be difficult to form the core portion. When the first crystallization ratio is more than 90%, it tends to be difficult to form the outer structure portion.

[0045] Next, the oxygen concentration in the Taylor vortex reaction field can be changed to 5 vol% or more and 65 vol% or less, and the second crystallization can be performed while maintaining the oxygen concentration. The oxygen concentration in the Taylor vortex reaction field can be changed, for example, by changing the type of gas bubbled into the raw metal aqueous solution and the ammonium supplier. In the second crystallization, the type of gas used to maintain the oxygen concentration in the Taylor vortex reaction field from 5 vol% to 65 vol% or less can be, for example, a mixed gas of oxygen and nitrogen. To change the oxygen concentration in the Taylor vortex reaction field, the supply of the raw metal aqueous solution and the ammonium supplier is stopped, the oxygen concentration in the Taylor vortex reaction field is changed to 5 vol% to 65 vol% or less, and then the supply of the raw metal aqueous solution and the ammonium supplier is resumed, and crystallization can be performed. The time during which the supply of the raw metal aqueous solution and the ammonium supplier is stopped is not included in the overall crystallization time. Hereinafter, the oxygen concentration in the Taylor vortex reaction field in the second crystallization is also referred to as the second oxygen concentration. If the second oxygen concentration is less than 5 vol%, the formation of an external structure tends to be difficult. If the second oxygen concentration exceeds 65 vol %, the circularity of the first particles tends to be difficult to improve.

[0046] The time for which the second crystallization is performed (hereinafter also referred to as the second crystallization time) may be such that the proportion of the time for which the second crystallization is performed to the total time for which crystallization is performed in the crystallization step (hereinafter also referred to as the second crystallization proportion) is, for example, 10% to 60%. When the second crystallization proportion is within the above range, the first particles tend to be easily produced and the circularity tends to be easily improved. When the second crystallization proportion is less than 10%, the outer structure tends to be less easily formed. When the first crystallization proportion is more than 60%, the circularity tends to be less easily improved. From the viewpoints of the production and circularity of precursor particles, the second crystallization proportion is preferably 15% to 55%, more preferably 20% to 50%. The second crystallization time may be, for example, 3 to 30 minutes. During crystallization, the pH of the Taylor vortex reaction field at a liquid temperature of 25°C may be maintained at the pH adjusted before the start of crystallization. As a result, the precursor particles can be easily produced. The pH at a liquid temperature of 25°C in the Taylor vortex reaction field during crystallization is maintained at 12.5 or less, preferably 11.0 or more and 12.5 or less.

[0047] In the crystallization step, after the second crystallization, the oxygen concentration in the Taylor vortex reaction field may be changed from 5 vol% to 65 vol% to 3.5 vol% or less and a further crystallization (hereinafter referred to as third crystallization a) may be performed. Alternatively, the oxygen concentration in the Taylor vortex reaction field may be changed from 3.5 vol% or less to 5 vol% to 65 vol% or less and a further crystallization (hereinafter referred to as third crystallization b) may be performed. Third crystallization a and third crystallization b may each be performed one or more times. Performing third crystallization a and third crystallization b one or more times each makes it easier to produce precursor particles having two or more layers of voids.

[0048] The first ratio and the second ratio can be controlled, for example, by adjusting the pH, oxygen concentration, and timing of switching the oxygen concentration in the crystallization step, adjusting the rotation of the inner cylinder, and the like.

[0049] The ratio of the core portion 11 to the particle size (diameter) of the particle 10 having a void portion 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 during the crystallization process, or by adjusting the rotation speed of the inner cylinder.

[0050] After the crystallization step is completed, the solution containing the precursor particles can be taken out from the outlet 116 and collected in the container 17. The collected solution containing the precursor particles can be filtered, washed with water, and then dried to obtain the precursor particles.

[0051] In the mixing step, the precursor particles and Li can be mixed so that the ratio of the number of Li atoms to the total number of metal elements other than Li in the positive electrode active material particles (Li / Me ratio) is, for example, 1.0 to 1.3.

[0052] In the firing step, the temperature at which the mixture is fired may be, for example, 700 to 1000° C., preferably 700 to 850° C., and more preferably 710 to 850° C. The time for firing the mixture may be, for example, 3 to 10 hours. The firing step can be carried out in an oxidizing atmosphere.

[0053] The second particle group includes a plurality of second particles. The content of the second particles in the second particle group is, for example, 70 to 100 mass%, or alternatively, 85 to 98 mass%, or 90 to 95 mass%, when the total amount of the second particle group is 100 mass%. The second particle group can include only a plurality of second particles.

[0054] The second particle group can have a smaller average particle diameter than the first particle group. By having the second particle group have a smaller average particle diameter than the first particle group, the occurrence of particle cracking of the first particles due to pressing in the manufacturing process of the positive electrode active material layer is suppressed and the packing property of the positive electrode active material layer is improved, which tends to make the input / output characteristics and cycle capacity retention rate of the battery excellent.

[0055] The average particle diameter of the second particle group may be, for example, 2 to 20 μm, and preferably 2 to 7 μm. When the average particle diameter of the second particle group is within the above range, a battery with excellent cycle capacity retention is easily obtained. The average particle diameter of the second particle group can be controlled by adjusting production conditions such as precursor synthesis conditions (reaction time, pH, etc.) and firing conditions (firing temperature, firing time, etc.).

[0056] The second particle contains secondary particles formed by aggregation of primary particles (hereinafter also referred to as the second secondary particles). The second secondary particle is a lithium transition metal composite oxide having a layered crystal structure (hereinafter also referred to as the second composite oxide). The second composite oxide contains Li, Ni, Mn, Co, and M [M is one or more metal elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, and W.], and the molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M = a:x:y:z:t (a, x, y, z, and t satisfy 1.0 ≤ a ≤ 1.3, x + y + z = 1, 0.25 ≤ x ≤ 0.9, 0 < y ≤ 0.6, 0 < z ≤ 0.6, and 0 < t ≤ 0.1). That the second composite oxide contains Li, Ni, Mn, and Co means that it contains lithium element, nickel element, manganese element, and cobalt element. The composition of the second composite oxide can be determined by ICP (Inductively Coupled Plasma) optical emission spectrometry (ICP-AES).

[0057] In the second particle, the integrated intensity ratio (I 003 / I 104 ) of the diffraction peak in the X-ray diffraction method (hereinafter also referred to as the XRD method) of the second secondary particle is 1.05 to 1.19, and the crystallite size L 003 of the second secondary particle is 1000 Å or more. When the second secondary particle has the integrated intensity ratio (I 003 / I 104 ) and the crystallite size L 003 within the above ranges, the cycle capacity retention rate tends to be improved.

[0058] The second secondary particle is an aggregated particle formed by aggregation of primary particles. The number of aggregated primary particles in the second secondary particle is preferably 50 or more, may be 100 or more, may be 1000 or more, and is usually 5×10 6 or less, and 5×10 5The number of agglomerates of the second secondary particles may be less than 1000. The agglomeration number of the second secondary particles can be adjusted by adjusting the production conditions, such as the firing conditions (firing temperature, number of firings, firing time, etc.) when producing the second secondary particles. The agglomeration number of the primary particles contained in the second secondary particles can be confirmed, for example, by a scanning electron microscope (hereinafter also referred to as "SEM") image obtained by SEM. The second secondary particles may be agglomerated particles with a solid structure that does not have voids inside.

[0059] The second secondary particles are a second composite oxide, and it can be confirmed, for example, by X-ray diffraction measurement, that the second composite oxide has a layered crystal structure. Examples of the layered crystal structure of the second composite oxide include a hexagonal crystal structure (layered rock salt type) and a monoclinic crystal structure. The second composite oxide with a layered crystal structure can easily insert and extract lithium ions smoothly.

[0060] The metal element M contained in the second composite oxide may contain one or more of the above-mentioned metal elements, but preferably contains at least W (tungsten). When the metal element M contains W, the integrated intensity ratio (I 003 / I 104 ) and crystallite size L 003 It becomes easier to obtain a composite oxide having the above structure.

[0061] The molar ratio of Li is 1.0 ≤ a ≤ 1.3, and it may be 1.0 ≤ a ≤ 1.25, 1.01 ≤ a ≤ 1.2, 1.03 ≤ a ≤ 1.15, or 1.04 ≤ a ≤ 1.1. The molar ratio of Ni is 0.25 ≤ x ≤ 0.9, and it may be 0.3 ≤ x ≤ 0.9, 0.4 ≤ x ≤ 0.88, or 0.5 ≤ x ≤ 0.85. The molar ratio of Mn is 0 < y ≤ 0.6, and it may be 0.05 ≤ y ≤ 0.5, 0.08 ≤ y ≤ 0.3, or 0.10 ≤ y ≤ 0.2. The molar ratio of Co is 0 < z ≤ 0.6, and it may be 0 < z ≤ 0.5, 0.01 ≤ z ≤ 0.3, or 0.02 ≤ z ≤ 0.1. The molar ratio of M is 0 < t ≤ 0.1, and it may be 0 < t ≤ 0.08, 0.001 ≤ t ≤ 0.05, or 0.002 ≤ t ≤ 0.01. When the second complex oxide contains two or more metal elements M, the molar ratio of M refers to the total amount of two or more metal elements.

[0062] The integrated intensity ratio (I 003 / I 104 ) of the diffraction peaks of the second secondary particles is 1.05 to 1.19, and it may be 1.06 to 1.18, 1.08 to 1.17, or 1.10 to 1.15. The integrated intensity ratio (I 003 / I 104 ) is preferably 1.05 to 1.16, and more preferably 1.06 to 1.15. When the integrated intensity ratio (I 003 / I 104 ) exceeds the above range, the crystal growth of the primary particles is promoted during the process of manufacturing the secondary particles, making the secondary particles prone to cracking, so the cycle capacity retention rate is likely to decrease. The second secondary particles are difficult to crack because the integrated intensity ratio (I 003 / I 104 ) is within the above range. Therefore, by using the second secondary particles, it is easier to obtain a battery with excellent cycle retention rate.

[0063] The integrated intensity I 003 and I 104are the integrated intensities of the diffraction peaks on the (003) and (104) planes of the second secondary particles measured by XRD, respectively, and can be measured by the method described in the Examples below. The integrated intensity ratio (I 003 / I 104 ) can be adjusted by, for example, the amount of lithium added (compounding ratio) when producing the second secondary particles, the raw material composition, and production conditions such as firing conditions (firing temperature, number of firings, firing time, etc.).

[0064] Secondary particle crystallite size L 003 is 1000 Å or more, may be 1010 Å or more, may be 1020 Å or more, may be 1000 to 3000 Å, may be 1010 to 2500 Å, may be 1020 to 2000 Å, or may be 1020 to 1500 Å. 003 / I 104 If the crystallite size L of the second secondary particles is within the above range, the Li site occupancy rate in the transition metal layer of the secondary particles tends to be large, and the discharge capacity of the secondary battery tends to decrease. 003 By setting the value within the above range, the Li site occupancy rate can be reduced, and therefore, the decrease in the discharge capacity of the battery can be suppressed.

[0065] Secondary particle crystallite size L 003 The crystallite size L of the second secondary particles can be calculated from the half-width of the diffraction peak of the (003) plane measured by the XRD method, and can be calculated by the method described in the examples below. 003 can be adjusted by the manufacturing conditions such as the amount of lithium added (compounding ratio) when manufacturing the second secondary particles, the raw material composition, and the firing conditions (firing temperature, number of firings, firing time, etc.).

[0066] The second secondary particles can be obtained, for example, by mixing a compound containing Ni, Mn, and Co (hereinafter also referred to as a "NiMnCo-containing precursor"), a lithium compound, and, if necessary, an M-containing compound containing the metal element M to obtain a mixture, and then firing this mixture. Alternatively, the second secondary particles may be obtained by mixing a Ni-containing compound containing Ni, a Mn-containing compound containing Mn, a Co-containing compound containing Co, a lithium compound, and an M-containing compound containing the metal element M to obtain a mixture, and then firing this mixture. The Ni-containing compound, the Mn-containing compound, and the Co-containing compound may contain the metal element M.

[0067] Examples of NiMnCo precursors include composite oxides or composite hydroxides containing Ni, Mn, and Co. Examples of lithium compounds include lithium hydroxide and lithium carbonate. Examples of M-containing compounds include ammonium compounds containing the metal element M.

[0068] The mass ratio of the first particle group to the second particle group (first particle group:second particle group) in the positive electrode active material may be, for example, 8:2 to 5:5. This mass ratio tends to make it easier to obtain a battery with excellent input / output characteristics and cycle capacity retention. The positive electrode active material can be obtained by mixing the first particle group and the second particle group.

[0069] The positive electrode active material may contain, in addition to the first and second particles, positive electrode active material particles of a type different from the first and second particles. The positive electrode active material particles of a type different from the first and second particles that the positive electrode active material may contain may be single particles or secondary particles other than the first and second particles (hereinafter also referred to as other secondary particles). The single particles may be a lithium transition metal composite oxide having a layered crystal structure, and their composition may be within the range of the composition described for the first particle group and the second particle group, or may be outside this range. The other secondary particles may be secondary particles having a composition outside the range of the composition described for the second secondary particles, and may have a composition that is different from the integrated intensity ratio (I 003 / I 104) may be secondary particles outside the range of the crystallite size L 003 Other secondary particles may have a solid structure without voids, or may have a structure with voids.

[0070] <Positive electrode> The positive electrode plate of the present disclosure will be described with reference to FIG. 3. FIG. 3 is a schematic cross-sectional view of the positive electrode plate in the thickness direction (both sides). The positive electrode plate 20 has a positive electrode current collector 21 and a positive electrode active material layer 22 containing the above-described positive electrode active material, with the positive electrode active material layer 22 being formed on the positive electrode current collector 21. The positive electrode active material includes the above-described first particles 23 and second particles 24. The positive electrode active material layer 22 is formed on one or both sides of the positive electrode current collector 21. The positive electrode current collector 21 is 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 20 may be used.

[0071] The positive electrode active material layer 22 may contain, in addition to the positive electrode active material, a binder, a conductive material, and the like. 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).

[0072] The positive electrode active material layer 22 can be formed, for example, by applying a positive electrode mixture slurry onto the positive electrode current collector 21, 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 for forming the active material layer, such as the above-mentioned positive electrode active material, binder, and conductive material, and kneading the mixture.

[0073] The positive electrode active material layer 22 may have a thickness of, for example, 10 to 200 μm. The positive electrode active material layer may have a high density. The density of the positive electrode active material layer is, for example, 3.5 g / cm 3or more, for example, 4.0 g / cm 3 It may have the following densities:

[0074] <Nonaqueous electrolyte secondary battery> The battery of the present disclosure has the above-described positive electrode plate, and therefore tends to be excellent in both input / output characteristics and cycle capacity retention rate.

[0075] A battery typically includes an electrode assembly including a positive electrode plate 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] The present invention will be described in more detail below with reference to examples. [Example]

[0082] [Measuring average particle size] The average particle diameters (D50) of the first particles A and B, the second particles A and B, the particles C, and the particles D used in the examples and comparative examples were measured in accordance with JIS Z 8825:2022 Particle size analysis - Laser diffraction and scattering method. The laser diffraction particle size distribution measuring device used was the "MT3000II" manufactured by Microtrac. Isopropyl alcohol (IPA) was used as the solvent for wet dispersion.

[0083] [BET specific surface area measurement] The BET specific surface areas of the first particles A and B, the second particles A and B, the particles C and the particles D used in the examples and comparative examples were measured using a commercially available flow type gas adsorption specific surface area measuring device.

[0084] [Circularity measurement] The circularity of the first particles A and B, particles C and particles D used in the examples and comparative examples was measured using a commercially available particle shape image analyzer.

[0085] [Measurement of primary particle size, first ratio, and second ratio] The cross sections of the first particles A and B, particles C, and particles D used in the examples and comparative examples were extracted by ion milling. The cross sections were observed using a commercially available scanning electron microscope (SEM) to obtain SEM images. Regarding the primary particle diameter, 50 or more primary particles were extracted using image analysis software, and the average particle diameter was calculated. The void and outer structure regions were identified in the obtained images using image analysis software, and the first ratio (void width / particle diameter) and the second ratio (outer structure thickness / particle diameter) were calculated from the scale ratio.

[0086] [integrated intensity ratio (I 003 / I 104 ) and crystallite size L 003 Measurement of The second particles A and B, particles C, and particles D used in the examples and comparative examples were crushed in an agate mortar to an average particle size (D50) of 43 μm or less, and then subjected to X-ray diffraction measurement using an X-ray diffractometer (Rigaku "SmartLab"). The XRD profile obtained by the X-ray diffraction measurement confirmed that the lithium transition metal composite oxide had a layered crystal structure.

[0087] The integrated intensity ratio (I 003 / I 104 ) was calculated.

[0088] Intensity of the diffraction peak on the (003) plane in the XRD profile I 003 The value of the half-width of the diffraction peak is used as the broadening B of the diffraction peak in the Scherrer formula below, and the crystallite size L on the (003) plane is calculated. 003 was calculated. L 003 =Kλ / Bcosθ [In the formula, K is the Scherrer constant, λ is the wavelength of the X-ray [nm], B is the broadening of the diffraction peak [rad], and θ is the Flag angle [rad].]

[0089] [Battery construction] A negative electrode active material was prepared as a mixture of graphite and SiO. Styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used as binders. The negative electrode active material, SBR, and CMC were mixed in a mass ratio of 100:1:1 (negative electrode active material:SBR:CMC) and water to prepare a negative electrode slurry. The negative electrode slurry was applied to copper foil as a negative electrode current collector foil, dried, compressed, and then cut to the specified size to obtain a negative electrode plate. A separator having a three-layer structure of polypropylene / polyethylene / polypropylene was prepared. The positive electrode plate prepared in each of the examples and comparative examples was laminated with the negative electrode plate via a separator to obtain an electrode assembly. A positive electrode tab formed of aluminum foil in the region where the positive electrode active material layer of the positive electrode current collector foil was not formed, and a negative electrode tab formed of copper foil in the region where the negative electrode active material layer of the negative electrode current collector foil was not formed were exposed at both ends of the electrode assembly. The positive electrode tab was welded to the external positive electrode current collector, and the negative electrode tab was welded to the external negative electrode current collector, and then the electrode assembly was inserted into an exterior body made of aluminum laminate film, and the film was welded to form a liquid injection port. After pouring nonaqueous electrolyte through the liquid injection port, the liquid injection port was sealed to obtain a battery.

[0090] [Evaluation of input / output characteristics] The fabricated battery was charged to SOC 50%. After resting for 1 hour, it was rested for 6 hours in an environment at a temperature of -10°C. Then, it was discharged for 10 seconds at a current of 5C. The resistance was calculated by the following formula, where the OCV voltage immediately before discharge was V0 and the voltage at the time of 10-second discharge was V1. Resistance (Ω) = (V0-V1) / 5C current value The lower the resistance, the better the input / output characteristics are judged to be.

[0091] [Evaluation of cycle capacity retention rate] The fabricated battery was subjected to 300 cycles of 0.5C charge / discharge in a voltage range of 4.2V-3.0V at a temperature of 25°C. A 0.1C charge / discharge process was performed in a voltage range of 4.2V-3.0V at a temperature of 25°C, and the capacity obtained during discharge was defined as the post-cycle battery capacity. The cycle capacity retention rate was calculated using the following formula: Cycle capacity retention rate = Battery capacity after cycling / Initial battery capacity The higher the cycle capacity retention rate, the better the cycle capacity retention rate is judged to be.

[0092] Example 1 [Preparation of positive electrode plate] First particles A were prepared as first particles. SEM observation confirmed that first particles A were secondary particles formed by agglomeration of 50 or more primary particles, and that they were particles having a core, a void outside the core, and an outer structure outside the void. The composition, average particle diameter (D50), BET specific surface area, primary particle diameter, circularity, first ratio, and second ratio of first particles A are shown in Table 1.

[0093] Second particles A were prepared as second particles. SEM observation confirmed that second particles A were secondary particles formed by the aggregation of 50 or more primary particles, and that they had a solid structure with no voids inside the particles. The composition, average particle diameter (D50), BET specific surface area, and integrated intensity ratio (I 003 / I 104 ) and crystallite size L 003 is shown in Table 2.

[0094] A positive electrode mixture slurry was prepared by mixing 100 parts by mass of a positive electrode active material mixture in which the first particles A and the second particles A were mixed in a weight ratio of 8:2, 1 part by mass of graphite as a conductive material, and 1 part by mass of polyvinylidene fluoride powder as a binder, and then adding an appropriate amount of N-methyl-2-pyrrolidone (NMP).

[0095] The positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil and dried. The coating was then rolled using a rolling roller to produce a positive electrode plate in which a positive electrode active material layer was formed on both sides of the positive electrode current collector. The density of the positive electrode active material layer was 3.55 g / m 2 The results are shown in Table 4.

[0096] <Example 2> A positive electrode plate was produced in the same manner as in Example 1, except that first particles B and second particles B were used instead of first particles A and second particles A used in Example 1. SEM observation confirmed that first particles B were secondary particles formed by agglomeration of 50 or more primary particles, and that they were particles having a core portion, a void portion outside the core portion, and an outer structure portion outside the void portion. The composition, average particle diameter (D50), BET specific surface area, primary particle diameter, circularity, first ratio, and second ratio of first particles B are shown in Table 1. SEM observation confirmed that second particles B were secondary particles formed by agglomeration of 50 or more primary particles, and that they were particles with a solid structure with no void portion inside the particle. The composition, average particle diameter (D50), BET specific surface area, and integrated intensity ratio (I 003 / I 104 ) and crystallite size L 003 The results are shown in Table 2. The results are shown in Table 4.

[0097] <Examples 3 to 5> A positive electrode plate was produced in the same manner as in Example 1, except that the mixing ratio of the first particles A and the second particles A shown in Table 4 was used instead of the 8:2 mixing ratio of the first particles A and the second particles A in Example 1. The results are shown in Table 4.

[0098] <Comparative Example 1> A positive electrode plate was produced in the same manner as in Example 1, except that particles C and D were used instead of the first particles A and second particles A used in Example 1. SEM observation confirmed that particles C were secondary particles formed by agglomeration of 50 or more primary particles, and had a solid structure with no voids inside the particles. The composition, average particle diameter (D50), BET specific surface area, primary particle diameter, circularity, and integrated intensity ratio (I 003 / I 104 ) and crystallite size L 003 The results are shown in Table 3. Particle D was confirmed to be a single particle (a secondary particle consisting of one single particle or 2 to 10 primary particles) by SEM observation. The composition, average particle diameter (D50), BET specific surface area, circularity, and integrated intensity ratio (I 003 / I 104 ) and crystallite size L003 The results are shown in Table 3. The results are shown in Table 4.

[0099] <Comparative Example 2> A positive electrode plate was produced in the same manner as in Example 1, except that only the first particles A were used instead of the first particles A and the second particles A used in Example 1. The results are shown in Table 4.

[0100] <Comparative Example 3> A positive electrode plate was produced in the same manner as in Example 1, except that only the second particles A were used instead of the first particles A and the second particles A used in Example 1. The results are shown in Table 4.

[0101] <Comparative Example 4> A first positive electrode composite slurry was prepared by mixing 100 parts by mass of the first particles A as a positive electrode active material, 1 part by mass of graphite as a conductive material, and 1 part by mass of polyvinylidene fluoride powder as a binder, and then adding an appropriate amount of N-methyl-2-pyrrolidone (NMP). A second positive electrode composite slurry was prepared by mixing 100 parts by mass of the second particles A as a positive electrode active material, 1 part by mass of graphite as a conductive material, and 1 part by mass of polyvinylidene fluoride powder as a binder, and then adding an appropriate amount of N-methyl-2-pyrrolidone (NMP).

[0102] The second positive electrode composite slurry was applied to both sides of a positive electrode current collector made of aluminum foil and dried. Next, the first positive electrode composite slurry was applied to the coating film derived from the second positive electrode composite slurry and dried. The coating thickness ratio of the first positive electrode composite slurry to the second positive electrode composite slurry was 8:2. The coating film was then rolled using a rolling roller. This resulted in a positive electrode plate having a positive electrode active material layer formed on both sides of the positive electrode current collector, with a second layer containing second particles A on the positive electrode current collector side and a first layer containing first particles A on the side opposite the second layer from the positive electrode current collector. SEM observation of the cross section of the obtained positive electrode plate confirmed that the thickness ratio (first layer:second layer) of the first layer (upper layer) to the second layer (lower layer) was 8:2. The results are shown in Table 4.

[0103] [Table 1]

[0104] [Table 2]

[0105] [Table 3]

[0106] [Table 4]

[0107] In Examples 1, 3 to 5, a mixture of first particles with excellent input / output characteristics and second particles with excellent Li solid-phase diffusivity and low particle cracking was used, achieving both excellent input / output characteristics and cycle capacity retention. On the other hand, in Comparative Example 1, single particles with low particle cracking were used as the second particles, resulting in excellent cycle capacity retention. However, the use of solid-structured aggregated particles and single particles resulted in poor Li solid-phase diffusivity, and no input / output characteristics were achieved. In Comparative Example 2, only particles with voids were used, resulting in excellent input / output characteristics, but a cycle capacity retention rate inferior to that of Example 1 due to particle cracking caused by rolling during the positive electrode plate fabrication process. In Comparative Example 3, the cycle capacity retention rate was equivalent to that of Comparative Example 1, but the input / output characteristics were inferior to those of Example 1.

[0108] In Example 2, the mass ratio of the second particles to the first particles was higher than in Examples 1 and 3 to 5, and as a result, the input / output characteristics were lower than in Examples 1 and 3 to 5. However, compared to Comparative Example 1, which did not use the first particles or the second particles, and Comparative Examples 2 and 3, which used a single type of particle, both excellent input / output characteristics and cycle capacity retention rate were achieved.

[0109] In Comparative Example 4, although the input / output characteristics were excellent due to the first particles contained in the first layer (upper layer), the first particles with a large reaction area were contained on the first layer (upper layer) side where the reaction was likely to concentrate, which made the reaction more likely to proceed and resulted in greater deterioration, and therefore an excellent cycle capacity retention rate was not obtained. [Explanation of symbols]

[0110] 10 Particle having void portion, 11 Core portion, 12 Void portion, 13 Outer structure portion, 14, 15 Primary particle, 16 Straight line, 20 Positive electrode plate, 21 Positive electrode current collector, 22 Positive electrode active material layer, 23 First particle, 24 Second particle, 100 Reaction vessel, 111 Outer cylinder, 112 Inner cylinder, 113 First supply port, 114 Second supply port, 115 Third supply port, 116 Discharge port, 117 Container, 118 Motor.

Claims

1. The particle includes a first particle group and a second particle group, the first particle group includes a plurality of first particles, the second particle group includes a plurality of second particles, the first particles include particles having voids, the second particles include secondary particles formed by aggregation of primary particles, The integrated intensity ratio (I ００３ / I １０４ ) is 1.05 to 1.19, The crystallite size L of the secondary particles ００３ is 1000 Å or more.

2. 2. The positive electrode active material according to claim 1, wherein a mass ratio of the first particle group to the second particle group (first particle group:second particle group) in the positive electrode active material is 8:2 to 5:

5.

3. The positive electrode active material according to claim 1 , wherein the first particles have a circularity of 0.92 or more.

4. The positive electrode active material according to claim 1 , wherein the first particle has a core portion, the void portion outside the core portion, and an outer structure portion outside the void portion.

5. 3. The positive electrode active material according to claim 1, wherein the first particle group has an average particle diameter of 8 to 20 μm.

6. 3. The positive electrode active material according to claim 1, wherein the second particle group has an average particle diameter of 2 to 7 μm.

7. the second particles contain a lithium transition metal composite oxide having a layered crystal structure, The lithium transition metal composite oxide is Li, Ni, Mn, Co, and M (M is one or more metal elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, and W), and 3. The positive electrode active material according to claim 1 or 2, wherein the molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M=a:x:y:z:t, where a, x, y, z, and t are 1.0≦a≦1.3, x+y+z=1, 0.25≦x≦0.9, 0<y≦0.6, 0<z≦0.6, and 0<t≦0.

1.

8. A positive electrode plate comprising the positive electrode active material according to claim 1 or 2.

9. A non-aqueous electrolyte secondary battery comprising the positive electrode plate according to claim 8.

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