Cathode active material and non-aqueous electrolyte secondary battery

Abstract

To provide a cathode active material that enables the production of a non-aqueous electrolyte secondary battery with high capacity and excellent thermal stability.SOLUTION: The cathode active material includes a first active material and a second active material. The first active material is a lithium transition metal composite oxide containing 75 mol% or more Ni and 0.5 to 2.8 mol% Ti, relative to the total moles of metal elements excluding Li. The second active material is a lithium transition metal composite oxide containing 75 mol% or more Ni, relative to the total moles of metal elements excluding Li. The Ti content in the second active material is 0.1 mol% or less relative to the total moles of metal elements excluding Li. The disorder of Ni in the first active material is 2.1 to 2.6%, and the disorder of Ni in the second active material is 2.0% or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] It is known that in order to increase the capacity of a battery, two types of Ni-containing lithium composite oxides having a high Ni content and different average particle sizes are used as the positive electrode active material. For example, Patent Document 1 discloses that the Ni disorder of the Ni-containing lithium composite oxide is adjusted in order to obtain good output characteristics and durability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 003642 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even if the Ni disorder of the Ni-containing lithium composite oxide is adjusted, the thermal stability of the secondary battery may be reduced.

[0005] An object of the present disclosure is to provide a positive electrode active material that enables the production of a nonaqueous electrolyte secondary battery that has high capacity and excellent thermal stability, and a nonaqueous electrolyte secondary battery using the same. [Means for solving the problem]

[0006] [1] A battery comprising a first active material and a second active material having an average particle diameter (D50) smaller than that of the first active material, the first active material is a secondary particle formed by agglomeration of 50 or more primary particles, the second active material is at least one of a single particle and a secondary particle formed by agglomeration of 2 to 10 primary particles, the first active material is a lithium transition metal composite oxide containing 75 mol % or more of Ni and 0.5 to 2.8 mol % of Ti relative to the total number of moles of metal elements excluding Li, the second active material is a lithium transition metal composite oxide containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, the content of Ti in the second active material is 0.1 mol% or less based on the total number of moles of metal elements excluding Li, The disorder of Ni in the first active material is 2.1 to 2.6%, A positive electrode active material, wherein the disorder of Ni in the second active material is 2.0% or less. [2] The positive electrode active material according to [1], wherein the content of Ti in the first active material is 1 to 2.5 mol % based on the total number of moles of metal elements excluding Li. [3] The positive electrode active material according to [1] or [2], wherein the mass ratio of the first active material to the second active material is first active material:second active material=7:3 to 5:5. [4] The positive electrode active material according to any one of [1] to [3], wherein the first active material has an average particle diameter (D50) of 12 to 20 μm. [5] The positive electrode active material according to any one of [1] to [4], wherein the second active material has an average particle size (D50) of 2 to 6 μm. [6] The positive electrode active material according to any one of [1] to [5], wherein the particle size distribution of the first active material ({average particle size (D90) - average particle size (D10)} / average particle size (D50)) is 0.2 to 0.8. [7] The positive electrode active material according to any one of [1] to [6], wherein the particle size distribution of the second active material ({average particle size (D90) - average particle size (D10)} / average particle size (D50)) is 0.7 to 1.5. [8] The positive electrode active material according to any one of [1] to [7], wherein the content of Co relative to the total number of moles of metal elements excluding Li in the first active material is smaller than the content of Co relative to the total number of moles of metal elements excluding Li in the second active material. [9] A battery having a positive electrode plate, The positive electrode plate of a non-aqueous electrolyte secondary battery has an active material layer containing the positive electrode active material according to any one of [1] to [8]. [Effects of the Invention]

[0007] The positive electrode active material of the present disclosure can provide a nonaqueous electrolyte secondary battery that achieves both high capacity and good thermal stability. DETAILED DESCRIPTION OF THE INVENTION

[0008] In this specification, unless otherwise specified, a numerical range such as "x to y" includes both the upper and lower limits. That is, "x to y" represents a numerical range of "greater than or equal to x and less than or equal to y." A numerical value arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described elsewhere in this specification, in a table, or in a figure.

[0009] (Cathode active material) The positive electrode active material of this embodiment (hereinafter also referred to as "the present positive electrode active material") is used in the positive electrode plate of a non-aqueous electrolyte secondary battery (hereinafter also referred to as "secondary battery") such as a lithium ion battery.

[0010] The positive electrode active material includes a first active material and a second active material. The second active material has a smaller average particle diameter (D50) than the first active material. The first active material is a secondary particle (hereinafter also referred to as "first secondary particle") formed by agglomeration of 50 or more primary particles. The second active material is at least one of a single particle and a secondary particle (hereinafter also referred to as "second secondary particle") formed by agglomeration of 2 to 10 primary particles.

[0011] The first active material is a lithium transition metal composite oxide containing 75 mol% or more of Ni and 0.5 to 2.8 mol% of Ti relative to the total number of moles of metal elements excluding Li. The second active material is a lithium transition metal composite oxide containing 75 mol% or more of Ni relative to the total number of moles of metal elements excluding Li. The Ti content of the second active material is 0.1 mol% or less relative to the total number of moles of metal elements excluding Li. The disorder of Ni in the first active material is 2.1 to 2.6%. The disorder of Ni in the second active material is 2.0% or less.

[0012] By using a cathode active material containing a first active material and a second active material having a Ni content within the above range and different average particle diameters (D50) and particle aggregation morphologies, it is easy to increase the capacity of a secondary battery, but the thermal stability of the secondary battery may be reduced. This cathode active material contains Ti in the above-mentioned content of the first active material, and the Ni disorder is within the above-mentioned range, thereby improving the thermal stability of the secondary battery. On the other hand, using the above-mentioned first active material to improve the thermal stability of a secondary battery may result in a decrease in the capacity of the secondary battery. However, in this cathode active material, the second active material does not contain Ti or contains only a trace amount of Ti, and the Ni disorder is within the above-mentioned range, thereby also achieving a high capacity of the secondary battery. This cathode active material allows for the production of a secondary battery that achieves both high capacity and good thermal stability.

[0013] The first active material is a first secondary particle formed by agglomeration of 50 or more primary particles. The agglomeration number of the primary particles in the first secondary particle may be 100 or more, or may be 1000 or more, and is usually 5×10 6 5 x 10 or less 5 In this specification, the aggregation number of primary particles can be confirmed, for example, by a scanning electron microscope (hereinafter also referred to as "SEM") image obtained by SEM.

[0014] The first active material is a lithium transition metal composite oxide (hereinafter also referred to as "first composite oxide") containing 75 mol% or more of Ni and 0.5 to 2.8 mol% of Ti relative to the total number of moles of metal elements excluding Li. The Ni content of the first composite oxide is preferably 80 mol% or more, and may be 82 mol% or more, 75 to 96 mol%, 80 to 93 mol%, or 82 to 90 mol%, relative to the total number of moles of metal elements excluding Li. The Ti content of the first composite oxide may be 0.8 to 2.8 mol%, and preferably 1 to 2.5 mol%, or may be 1.3 to 2.2 mol%, relative to the total number of moles of metal elements excluding Li. The Ti contained in the first active material is preferably solid-dissolved throughout the first active material. The range of the Ni content of the first composite oxide and the range of the Ti content of the first composite oxide can be set by any combination from the ranges described above. The range of the Ni content in the first composite oxide and the range of the Ti content in the first composite oxide can be set by any combination from the ranges described above.

[0015] The Ni disorder of the first active material is 2.1 to 2.6%, and may be 2.2 to 2.6%, 2.3 to 2.6%, or 2.1 to 2.5%. The Ni disorder of the first active material represents the mixing rate of Ni element (cation mixing amount) at lithium sites in the crystal structure of the first active material. The range of Ni disorder of the first active material can be set in any combination with the above-mentioned range of the Ni and / or Ti content of the first composite oxide, i.e., the first active material. When the Ti content and Ni disorder of the first active material are within the above-mentioned ranges, the thermal stability of the secondary battery can be improved.

[0016] The first active material, i.e., the first composite oxide, preferably contains Co. The Co content [mol %] relative to the total number of moles of metal elements excluding Li in the first active material is preferably smaller than the Co content [mol %] relative to the total number of moles of metal elements excluding Li in the second active material described below. This makes it easier to obtain a secondary battery that has high capacity and excellent thermal stability. The Co content of the first active material may be, for example, 2 to 15 mol %, 2 to 10 mol %, or 3 to 7 mol % relative to the total number of moles of metal elements excluding Li.

[0017] The first composite oxide may have, for example, a structure represented by formula (I). Li x1 (Ni (1-y1-z1) Co y1 Me1 z1 )O2(I) [In formula (I), 0.8≦x1≦1.3, 0.02≦y1≦0.15, and 0.01≦z1≦0.18; Me1 contains Ti, and may also contain one or more elements selected from the group consisting of Mn, Al, Mg, Mo, Nb, W, B, and Zr.

[0018] In formula (I), x1 may be 1≦x1≦1.2, 1≦x1≦1.1, or 1.01≦x1≦1.08. In formula (I), y1 may be 0.02≦y1≦0.12, 0.03≦y1≦0.10, or 0.04≦y1≦0.08. In formula (I), z1 may be 0.01≦z1≦0.15, 0.02≦z1≦0.12, or 0.03≦z1≦0.1. In formula (I), Me1 preferably contains Ti and one or more elements selected from the group consisting of Mn and Al, and more preferably contains Ti and Mn. The ranges of x1, y1, z1, and M1 can be set by any combination from the ranges described above.

[0019] The second active material is at least one of a single particle and a second secondary particle formed by agglomeration of 2 to 10 primary particles. The second active material may be a single particle, a second secondary particle, or a mixture of a single particle and a second secondary particle. The number of agglomerated primary particles in the second secondary particle may be 2 to 8, 2 to 5, or 3 to 5.

[0020] The second active material is a lithium transition metal composite oxide (hereinafter also referred to as "second composite oxide") containing 75 mol% or more of Ni relative to the total number of moles of metal elements excluding Li. The second composite oxide may or may not contain Ti. The Ni content of the second composite oxide is preferably 80 mol% or more, and may be 82 mol% or more, 75 to 96 mol%, 80 to 93 mol%, or 82 to 90 mol%, relative to the total number of moles of metal elements excluding Li. The Ti content of the second composite oxide is 0.1 mol% or less, 0.05 mol% or less, or 0.01 mol% or less, relative to the total number of moles of metal elements excluding Li. When the second active material contains Ti, it may be present as a solid solution in the entire second active material. The range of the Ni content of the second composite oxide and the range of the Ti content of the second composite oxide can be set by any combination from the ranges described above.

[0021] The Ni disorder of the second active material is 2.0% or less, and may be 0.1 to 2.0%, 0.5 to 1.8%, or 0.8 to 1.7%. The Ni disorder of the second active material represents the mixing rate of Ni element (cation mixing amount) at lithium sites in the crystal structure of the second active material. The range of Ni disorder of the second active material can be set in any combination with the above-mentioned range of the Ni and / or Ti content of the second composite oxide, i.e., the second active material. By keeping the Ti content and Ni disorder of the second active material within the above-mentioned ranges, the capacity of the secondary battery can be increased.

[0022] The second active material, i.e., the second composite oxide, preferably contains Co. The Co content [mol %] relative to the total number of moles of metal elements excluding Li in the second active material is preferably greater than the Co content [mol %] relative to the total number of moles of metal elements excluding Li in the first active material. This makes it easier to obtain a secondary battery that has both high capacity and excellent thermal stability. The Co content of the second active material may be, for example, 2 to 20 mol %, 5 to 18 mol %, or 8 to 15 mol % relative to the total number of moles of metal elements excluding Li.

[0023] The second composite oxide may have, for example, a structure represented by formula (II). Li x2 (Ni (1-y2-z2) Co y2 Me2 z2 )O2(II) [In formula (I), 0.8≦x2≦1.2, 0.02≦y2≦0.2, and 0.001≦z2≦0.15; Me1 may contain one or more elements selected from the group consisting of Ti, Mn, Al, Mg, Mo, Nb, W, B, and Zr.

[0024] In formula (II), x2 may be 1≦x2≦1.1 or 1.01≦x2≦1.08. In formula (II), y2 may be 0.02≦y2≦0.12, 0.03≦y2≦0.10, or 0.04≦y2≦0.08. In formula (II), z2 may be 0.005≦z2≦0.12, 0.01≦z2≦0.1, or 0.02≦z2≦0.08. In formula (II), Me2 preferably contains one or more elements selected from the group consisting of Mn and Al, and more preferably contains Mn. The ranges of x2, y2, z2, and M2 can be set by any combination from the ranges described above.

[0025] The Ni and Ti contents of the first and second composite oxides can be adjusted by the amounts of Ni and Ti contained in the raw materials (Ni source and Ti source) used in their production. The compositions of the first and second composite oxides can be determined by dissolving them in nitric acid or the like and subjecting them to ICP (inductively coupled plasma) atomic emission spectrometry.

[0026] The disorder of Ni in the first active material and the second active material can be adjusted by the Ti content of the first active material and the second active material, and by the firing conditions, such as the firing temperature, number of firings, and firing time, when producing the first composite oxide and the second composite oxide. The disorder of Ni in the first active material and the second active material can be determined by Rietveld analysis of measurement data obtained by X-ray diffraction.

[0027] The aggregation number of the primary particles in the first secondary particles constituting the first active material and the aggregation number of the primary particles in the second secondary particles constituting the second active material can be adjusted by the firing conditions, etc., when producing the first composite oxide and the second composite oxide, respectively.

[0028] The first active material has an average particle size (D50) of preferably 12 to 20 μm, or alternatively 14 to 18 μm, or alternatively 15 to 17 μm. The first active material has a particle size distribution of preferably 0.2 to 0.8, or alternatively 0.2 to 0.6, or alternatively 0.3 to 0.5. In this specification, the particle size distribution is calculated by the following formula: Particle size distribution ={Average particle diameter (D90)-Average particle diameter (D10)} / Average particle diameter (D50)

[0029] In this specification, the average particle size (D10), average particle size (D50), and average particle size (D90) are particle sizes at which the cumulative frequency of the smaller particle sizes in a volume-based particle size distribution is 10%, 50%, and 90%, respectively. The volume-based particle size distribution can be measured using a laser diffraction particle size distribution analyzer.

[0030] The average primary particle diameter of the first secondary particles constituting the first active material is preferably 0.5 to 1.5 μm, and may be 0.7 to 1.2 μm. The average primary particle diameter of the first secondary particles is calculated as the average distance between the two most distant points on the contour lines of 10 or more primary particles randomly sampled from an SEM image of the particle surface of the first active material.

[0031] The second active material has an average particle size (D50) of preferably 2 to 6 μm, or alternatively 2.5 to 5 μm, or alternatively 3 to 4.5 μm. The particle size distribution of the second active material is preferably 0.7 to 1.5, or alternatively 1 to 1.4, or alternatively 1.1 to 1.3.

[0032] The average particle size (hereinafter also referred to as "average particle size") of the single particles and primary particles constituting the second secondary particles of the second active material is preferably 1 to 3 μm, and may be 1 to 2 μm. The average particle size of the second active material is calculated as the average distance between the two most distant points on the outline of a total of 10 or more single particles and primary particles randomly extracted from an SEM image of the particle surface of the second active material.

[0033] When the average particle diameter (D50) and particle distribution of the first active material and the second active material are within the above ranges, it is easy to form an active material layer (described later) using this positive electrode active material with high density, and it is easy to increase the capacity of the secondary battery. The ranges of the average particle diameter and particle size distribution of the first active material and the second active material can be set by any combination from the above ranges.

[0034] The various physical properties of the first active material and the second active material described above, such as the aggregation morphology, the content of elements such as Ti, Ni, and Co, the disorder of Ni, the average particle size (D50), the particle size distribution, the average primary particle size, and the average particle size, can be set in any combination within the above-mentioned ranges.

[0035] The first active material can be obtained, for example, by mixing a Ni-containing compound containing Ni, a lithium compound, and a Ti-containing compound containing Ti, followed by firing. The Ni-containing compound may contain metal elements other than Ni, such as Co and Mn. The Ni-containing compound may be a hydroxide or an oxide. Examples of the Ni-containing compound include NiCoMn composite hydroxide. Examples of the lithium compound include lithium hydroxide and lithium carbonate. Examples of the Ti-containing compound include titanium oxide.

[0036] The second active material can be obtained, for example, by mixing a Ni-containing compound and a lithium compound, followed by firing the mixture. Examples of the Ni-containing compound and the lithium compound include those described above.

[0037] The mass ratio of the first active material to the second active material in the present positive electrode active material is preferably first active material:second active material=7:3 to 5:5, and may be 6.5:3.5 to 5.5:4.5. When the mass ratio is within the above range, an active material layer (described below) formed using the present positive electrode active material can be easily formed at a high density, and the capacity of the secondary battery can be easily increased.

[0038] The present positive electrode active material may contain only the first active material and the second active material, or may further contain an active material other than the first active material and the second active material. The total content of the first active material and the second active material in the present positive electrode active material may be 85 to 100 mass%, 90 to 100 mass%, 92 to 99 mass%, or 95 to 98 mass% of the total amount of the present positive electrode active material.

[0039] (Nonaqueous electrolyte secondary battery) The nonaqueous electrolyte secondary battery of this embodiment (hereinafter also referred to as "the battery") has a positive electrode plate having an active material layer (hereinafter also referred to as "the positive electrode active material layer") containing the positive electrode active material. Because the battery has a positive electrode plate having a positive electrode active material layer, it can achieve both high capacity and good thermal stability.

[0040] The battery may include an electrode assembly including a positive electrode plate and a non-aqueous electrolyte, and may also include a battery case that accommodates 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 are preferably made of metal and can be formed using aluminum, an aluminum alloy, iron, an iron alloy, or the like. A resin sheet serving as an electrode holder may be disposed between the electrode assembly and the exterior body. The battery case may also be a laminate film. The laminate film has a layered structure in which, for example, a metal layer and a resin layer are stacked. A pouch-shaped battery case can be formed by overlapping and welding the edges of the laminate film.

[0041] The electrode assembly may include a negative electrode plate and a separator in addition to a positive electrode plate. In the electrode assembly, the positive electrode 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 a positive electrode plate, a negative electrode plate, and a separator are stacked, or a wound type in which a long laminate in which a positive electrode plate, a negative electrode plate, and a separator are stacked is wound. The wound type electrode assembly may have a flat shape obtained by pressing a long laminate after winding it.

[0042] The positive electrode plate can have a positive electrode active material layer on one or both sides of a positive electrode current collector foil. The positive electrode current collector foil is a metal foil made of an aluminum material such as aluminum or an aluminum alloy. In addition to the positive electrode active material, the positive electrode active material layer can further include at least one of a conductive additive and a binder.

[0043] Examples of the binder include fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide, acrylic resin, polyolefin, cellulose resins such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl cellulose, polyethylene oxide (POE), etc. The binder may contain one or more of the above-mentioned binders.

[0044] The conductive additive may be, for example, a carbon material. The carbon material may be, for example, one or more selected from the group consisting of fibrous carbon, carbon black (acetylene black, ketjen black, etc.), coke, and activated carbon. The fibrous carbon may be, for example, carbon nanotubes (CNT). The CNT may be a single-walled carbon nanotube (SWCNT) or a multi-walled carbon nanotube such as a double-walled carbon nanotube (DWCNT). The conductive additive may contain one or more of the conductive additives described above.

[0045] The positive electrode plate can be obtained, for example, by forming a positive electrode active material layer on a positive electrode current collector foil. For example, a positive electrode mixture slurry containing the present positive electrode active material is applied to the positive electrode current collector foil, dried, and compressed to form a positive electrode active material layer, thereby obtaining a positive electrode plate. In addition to the present positive electrode active material, the positive electrode mixture slurry can contain a binder, a conductive additive, and a solvent such as N-methyl-2-pyrrolidone (NMP).

[0046] The negative electrode plate typically includes a negative electrode current collector foil and a negative electrode active material layer. The negative electrode plate may include a negative electrode active material layer on one or both sides of the negative electrode current collector foil. The negative electrode current collector foil is, for example, a metal foil made of a copper material such as copper or a copper alloy. The negative electrode active material layer includes a negative electrode active material and may further include a conductive additive, a binder, and the like.

[0047] Examples of negative electrode active materials include carbon-based active material particles and metal-based active material particles. Examples of carbon-based active material particles include one or more particles selected from the group consisting of graphite (e.g., natural graphite and artificial graphite), hard carbon, soft carbon, and carbon (C) such as amorphous coated graphite. Examples of metal-based active material particles include particles of metal elements such as simple metals or metal oxides containing elements selected from the group consisting of silicon (Si), tin (Sn), antimony (Sb), bismuth (Bi), titanium (Ti), and germanium (Ge). Examples of metal-based active material particles include one or more particles selected from the group consisting of Si, SiOx (x=0.5 to 1.5), a composite of Si and C (hereinafter also referred to as "SiC composite"), and Sn.

[0048] Examples of the binder include cellulose-based resins such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl cellulose; polyacrylic acid; and styrene butadiene rubber (SBR). The binder may contain one or more of these. Examples of the conductive aid include those listed above, and the binder may contain one or more of the conductive aids listed above.

[0049] The negative electrode plate can be obtained, for example, by forming a negative electrode active material layer on a negative electrode current collector foil. For example, a negative electrode mixture slurry containing the negative electrode active material is applied to the negative electrode current collector foil, dried, and compressed to form a negative electrode active material layer, thereby obtaining a negative electrode plate. The negative electrode mixture slurry can contain, in addition to the negative electrode active material, a conductive additive, a binder, and a solvent such as water.

[0050] The separator may have a substrate and a functional layer on at least one side of the substrate. The substrate may be a film or a porous sheet such as a nonwoven fabric made of a resin such as a polyolefin (e.g., polyethylene or polypropylene), polyester, cellulose, or polyamide. The substrate may have a single-layer structure or a multi-layer structure. Examples of the functional layer include an adhesive layer and a heat-resistant layer, and the separator may have one or both of these. The adhesive layer may be formed, for example, with an adhesive. The heat-resistant layer may contain, for example, a filler and a binder.

[0051] The non-aqueous electrolyte preferably contains an electrolyte in a non-aqueous solvent such as an organic solvent. Examples of the electrolyte include LiPF6, LiBF4, LiClO4, LiFSO3, and LiBOB (lithium bis(oxalato)borate). The non-aqueous electrolyte may contain one or more of these electrolytes. Examples of the non-aqueous solvent include 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 contain one or more of these non-aqueous solvents. The non-aqueous electrolyte may further contain an additive such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), or fluoroethylene carbonate. [Example]

[0052] Hereinafter, the present disclosure will be described more specifically with reference to examples and comparative examples.

[0053] [Examples 1 to 4, Comparative Examples 1 to 4] (Preparation of positive electrode active material) A NiCoMn composite hydroxide, a lithium compound, and titanium oxide were mixed and fired at a temperature range of 700 to 900°C to obtain a first active material. The first active material is a secondary particle formed by aggregation of 50 or more primary particles. The first active material was dissolved in nitric acid, and the composition of the first active material was determined by ICP (inductively coupled plasma) atomic emission spectroscopy. The first active material contained 83 mol% Ni and Ti with the contents shown in Table 1, based on the total number of moles of metal elements excluding Li.

[0054] A NiCoMn composite hydroxide and a lithium compound were mixed and fired at a temperature range of 800 to 900°C to obtain a second active material. The second active material was at least one of single particles and secondary particles formed by aggregation of 2 to 10 primary particles. The second active material was dissolved in nitric acid, and the composition of the second active material was determined by ICP emission spectroscopy. The second active material contained 83 mol% of Ni relative to the total number of moles of metal elements excluding Li. The Ti content of the second active material was 0.1 mol% or less.

[0055] (Preparation of positive electrode plate) The first active material, the second active material, carbon black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder were mixed in a mass ratio of 58.5:39:1.5:1.0 (first active material: second active material: conductive additive: binder), and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum foil as a positive electrode current collector foil, dried, compressed to a predetermined thickness using a rolling roller, cut to a predetermined size, and then an aluminum tab was attached to obtain a positive electrode plate.

[0056] (Preparation of test cell) A lithium metal foil was prepared as a counter electrode for the positive electrode plate, and a polyolefin separator was prepared. The positive electrode plate, separator, and lithium metal foil were laminated to obtain a laminated electrode assembly. The electrode assembly was inserted into an aluminum laminate film exterior body, and a non-aqueous electrolyte solution was poured into it. The opening of the exterior body was then sealed to obtain a test cell. The non-aqueous electrolyte solution was prepared by dissolving lithium hexafluorophosphate (LiPF6) as an electrolyte at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in an EC:EMC ratio of 30:70 (volume ratio), and adding vinylene carbonate (VC) as an additive so that the amount was 0.3 mass% relative to the total amount of the mixed solvent.

[0057] [Calculation of Ni disorder in the first active material and the second active material] Using a fully automated multipurpose X-ray diffractometer (Rigaku, "SmartLab"), X-ray diffraction measurements were performed on the first and second active materials packed in a dedicated folder using the reflection method, with a Cu tube (target element), a tube voltage of 45 kV, and a tube current of 200 mA. The Ni disorder in the first and second active materials was determined by Rietveld analysis of the measurement data. The results are shown in Table 1.

[0058] [Measurement of average particle size and particle size distribution of first active material and second active material] The average particle diameter (D10), average particle diameter (D50), and average particle diameter (D90) of the first active material and the second active material were measured using a particle size distribution analyzer (Malvern Panalvtical, "Mastersizer-3000"). The particle size distribution was calculated using the following formula. The results are shown in Table 1. Particle size distribution ={Average particle diameter (D90)-Average particle diameter (D10)} / Average particle diameter (D50)

[0059] [Evaluation of thermal stability] The test cell was charged at 0.2 mA / cm 2 At a current density of 4.3V vs. Li / Li + Charge at a constant current until it reaches 4.3V vs. Li / Li +and the current density is 0.04mA / cm 2 After constant-voltage charging until the positive electrode mixture reached 300°C, the positive electrode mixture constituting the positive electrode active material layer was removed from the positive electrode plate. Using a differential thermogravimetry device (Shimadzu, "DTG-60A"), the positive electrode mixture was heated to 300°C at a rate of 5°C / min, and the minimum value of the DTG curve, which is the differential curve of the obtained TG curve, was determined. The results are shown in Table 1. The minimum value of the DTG curve represents the rate of weight loss of the positive electrode mixture, with a higher value indicating better thermal stability.

[0060] [Evaluation of discharge capacity] At a temperature of 25°C, the test cell was driven at 0.2 mA / cm 2 At a current density of 4.3V vs. Li / Li + Charge at a constant current until it reaches 4.3V vs. Li / Li + and the current density is 0.04mA / cm 2 The test cell was charged at a constant voltage of 0.04 mA / cm 2 At a current density of 3.0V vs. Li / Li + The discharge capacity was measured by discharging at a constant current until the battery reached 0. The results are shown in Table 1.

[0061] [Table 1]

Claims

1. a first active material and a second active material having an average particle diameter (D50) smaller than that of the first active material; the first active material is a secondary particle formed by agglomeration of 50 or more primary particles, the second active material is at least one of a single particle and a secondary particle formed by agglomeration of 2 to 10 primary particles, the first active material is a lithium transition metal composite oxide containing 75 mol % or more of Ni and 0.5 to 2.8 mol % of Ti relative to the total number of moles of metal elements excluding Li, the second active material is a lithium transition metal composite oxide containing 75 mol % or more of Ni relative to the total number of moles of metal elements excluding Li, the content of Ti in the second active material is 0.1 mol % or less based on the total number of moles of metal elements excluding Li, The Ni disorder of the first active material is 2.1 to 2.6%, The positive electrode active material, wherein the second active material has a Ni disorder of 2.0% or less.

2. 2. The positive electrode active material according to claim 1, wherein the content of Ti in the first active material is 1 to 2.5 mol % based on the total number of moles of metal elements excluding Li.

3. 2. The positive electrode active material according to claim 1, wherein a mass ratio of the first active material to the second active material is first active material:second active material=7:3 to 5:

5.

4. 2. The positive electrode active material according to claim 1, wherein the first active material has an average particle diameter (D50) of 12 to 20 μm.

5. 5. The positive electrode active material according to claim 4, wherein the second active material has an average particle diameter (D50) of 2 to 6 μm.

6. 5. The positive electrode active material according to claim 4, wherein the particle size distribution of the first active material ({average particle size (D90) - average particle size (D10)} / average particle size (D50)) is 0.2 to 0.

8.

7. 6. The positive electrode active material according to claim 5, wherein the particle size distribution of the second active material ({average particle size (D90) - average particle size (D10)} / average particle size (D50)) is 0.7 to 1.

5.

8. 2. The positive electrode active material according to claim 1, wherein a content of Co relative to a total number of moles of metal elements excluding Li in the first active material is smaller than a content of Co relative to a total number of moles of metal elements excluding Li in the second active material.

9. A positive electrode plate is provided. A non-aqueous electrolyte secondary battery, wherein the positive electrode plate has an active material layer containing the positive electrode active material according to any one of claims 1 to 8.

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