Positive electrode active material and non-aqueous electrolyte secondary battery

Abstract

To provide a positive electrode active material for a nonaqueous electrolyte secondary battery in which output resistance is improved and a gas generation amount is suppressed, and a nonaqueous electrolyte secondary battery.SOLUTION: The first active material and the second active material contain lithium and nickel, a content of nickel is 80 mol% or more with respect to 100 mol% of a total amount of metal elements other than lithium, and an average particle size (D50) of the second active material is smaller than an average particle size (D50) of the first active material, 1.05 ≤ 800nm ≤ 1.20 and 0.80 ≤ 500cm ≤ 1.00 are satisfied, where Ib / Ia is a ratio of a maximum value Ib in a range of 500 to 600cm - 1 to a maximum value Ia in a range of 450 to s1 - 1 in a Raman spectrum measured by Raman spectrometry, and s1 and s2 are Ib / Ia of the first active material and the second active material, respectively. s2.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Japanese Patent Laid-Open Publication No. 2011-113825 (Patent Document 1) proposes a high-capacity, high-power, and highly safe positive electrode material for lithium-ion secondary batteries, which is a mixture of two types of positive electrode active materials.

[0003] Japanese Patent Application Laid-Open No. 2023-64746 (Patent Document 2) proposes a positive electrode active material that improves particle stability by providing a concentration gradient such that the cobalt concentration decreases from the surface to the center of the lithium composite oxide, thereby mitigating the occurrence of cracks and collapse or change in the crystal structure not only in the surface but also in the center. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-113825 [Patent Document 2] Japanese Patent Application Publication No. 2023-64746 Summary of the Invention [Problem to be solved by the invention]

[0005] To increase the capacity of non-aqueous electrolyte secondary batteries, development is underway using positive electrode active materials with a high nickel content. When a positive electrode active material with a highly reactive lithium cobalt oxide layer (also known as an LCO layer) formed on the particle surface is used, the output resistance of non-aqueous electrolyte secondary batteries tends to improve, but the number of reaction sites with the electrolyte also increases, which tends to increase the amount of gas generation. On the other hand, when particles with a relatively large crystallite size and little aggregation are used, the reaction area with the electrolyte is reduced, which tends to reduce the amount of gas generation, but tends to decrease the output resistance.

[0006] An object of the present disclosure is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery that have improved output resistance and reduced gas generation. [Means for solving the problem]

[0007] [1] A positive electrode active material comprising a first active material and a second active material, the first active material and the second active material contain lithium and nickel; the first active material and the second active material have a nickel content of 80 mol % or more relative to 100 mol % of the total amount of metal elements other than lithium; the average particle diameter (D50) of the second active material is smaller than the average particle diameter (D50) of the first active material; The crystallite size of the second active material is 800 nm or more, 450-500 cm in the Raman spectrum measured by Raman spectroscopy -1 500-600 cm for the maximum value Ia in the range -1 When the ratio of the maximum value Ib in the range is Ib / Ia and the Ib / Ia of the first active material and the second active material are s1 and s2, respectively, the following formula: (1) 1.05≦s1≦1.20 (2) 0.80≦s2≦1.00 A positive electrode active material that satisfies the above requirements. [2] The following formula: (3) 1.10≦s1 / s2≦1.30 The positive electrode active material according to [1], further satisfying the above. [3] The positive electrode active material according to [1] or [2], wherein the first active material has an average particle size (D50) of 12 to 20 μm, and the second active material has an average particle size (D50) of 2 to 8 μm. [4] The positive electrode active material according to any one of [1] to [3], wherein the mass ratio of the first active material to the second active material is 5 / 5 to 8 / 2. [5] The positive electrode active material according to any one of [1] to [4], wherein the molar ratio of lithium to the metal element other than lithium in the first active material is 1.02 to 1.05. [6] The positive electrode active material according to any one of [1] to [5], wherein the molar ratio of lithium to the metal element other than lithium in the second active material is 0.98 to 1.04. [7] A non-aqueous electrolyte secondary battery comprising the positive electrode active material according to any one of [1] to [6]. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery that have improved output resistance and reduced gas generation. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Cathode active material> The positive electrode active material of the present disclosure is used, for example, in a positive electrode active material layer of a positive electrode of a nonaqueous electrolyte secondary battery (hereinafter also referred to as a battery) such as a lithium ion battery. The positive electrode active material includes a first active material and a second active material. The first active material and the second active material contain lithium (Li) and nickel (Ni). The first active material and the second active material have a Ni content (hereinafter also referred to as Ni content) of 80 mol % or more relative to 100 mol % of the total amount of metal elements other than Li. The average particle diameter (D50) of the second active material is smaller than the average particle diameter (D50) of the first active material. The crystallite size of the second active material is 800 nm or more. The Raman spectrum measured by Raman spectroscopy has a peak width of 450 to 500 cm. -1 500-600 cm for the maximum value Ia in the range -1 When the ratio of the maximum value Ib in the range is Ib / Ia and the Ib / Ia of the first active material and the second active material are s1 and s2, respectively, the following formula: (1) 1.05≦s1≦1.20 (2) 0.80≦s2≦1.00 Meet the following.

[0010] The first active material and the second active material both have a Ni content of 80 mol % or more. The first active material and the second active material may each independently have a Ni content of, for example, 80 mol % to 98 mol %, 81 mol % to 95 mol %, or 82 mol % to 90 mol %. By using a first active material and a second active material with a Ni content within the above range, the capacity of a nonaqueous electrolyte secondary battery can be increased.

[0011] The first active material and the second active material may be a lithium-transition metal composite oxide containing a transition metal other than Li and Ni. The lithium-transition metal composite oxide is an oxide containing Li, Ni, and a transition metal. The transition metal other than Ni contained in the lithium-transition metal composite oxide may be one or more selected from the group consisting of manganese (Mn), cobalt (Co), aluminum (Al), titanium (Ti), boron (B), zirconium (Zr), magnesium (Mg), iron (Fe), copper (Cu), zinc (Zn), tin (Sn), sodium (Na), potassium (K), barium (Ba), strontium (Sr), calcium (Ca), tungsten (W), molybdenum (Mo), niobium (Nb), and silicon (Si). Preferably, the transition metal is one or more selected from the group consisting of Mn, Co, and Al, and more preferably, one or more selected from the group consisting of Mn and Co. The transition metals preferably include Mn and Co, and may include Ni, Mn, Co and Al.

[0012] The lithium transition metal composite oxide may be, for example, a compound represented by the following formula (i). Li 1-a Ni x Me 1-x O2(i) [In formula (i), -0.3≦a≦0.2 and 0.8≦x≦1, Me may include one or more elements selected from the group consisting of Mn, Co, Al, Ti, B, Zr, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, and Si.

[0013] In the above formula (i), a may be -0.25≦a≦0.15 or -0.20≦a≦0.10. x may be 0.80≦x≦0.98 or 0.82≦x≦0.90. Me may contain one or more elements selected from the group consisting of Co, Mn, Al, B, Zr, Ti, Mg, Mo, and Nb, and preferably contains at least one of Co and Mn, and more preferably contains Co and Mn. The compositions of the first active material and the second active material can be determined, for example, by ICP (inductively coupled plasma) optical emission spectroscopy.

[0014] The composition of the first active material and the composition of the second active material may be the same as or different from each other.

[0015] The molar ratio of Li to the total number of moles of metal elements other than Li in the first active material can be, for example, 1.02 to 1.05.

[0016] The molar ratio of Li to the total number of moles of metal elements other than Li in the second active material can be, for example, 0.98 to 1.04.

[0017] The first active material may be a particle group consisting of a plurality of particles. The average particle diameter (D50) of the first active material may be, for example, 12 to 20 μm, 13 to 19 μm, or 14 to 18 μm. In this specification, the average particle diameter (D50) is the particle diameter at which the cumulative frequency of particles with smaller diameters in a volume-based particle size distribution is 50%. The volume-based particle size distribution can be measured using a particle size distribution analyzer. The average particle diameter (D50) of the first active material can be adjusted, for example, by the manufacturing conditions of the first active material.

[0018] The first active material may be an aggregated particle. The first active material may contain a plurality of aggregated particles. In this specification, an aggregated particle refers to a secondary particle formed by the aggregation of 100 or more primary particles. In the first active material, the aggregation number of the primary particles may be 1,000 or more, or may be 10,000 or more, and is usually 5×10 6 5 x 10 or less 5It may be less than one.

[0019] The average particle size of the primary particles constituting the aggregated particles may be, for example, 0.8 to 6.0 μm. In this specification, the average particle size of the primary particles is a value determined from a scanning electron microscope (SEM) image of the surfaces of the secondary particles, and is calculated by analyzing SEM images of the surfaces of multiple secondary particles to determine the longest diameter of each primary particle and averaging these values ​​for multiple secondary particles.

[0020] The first active material (primary particles constituting the aggregated particles) usually consists of a plurality of crystallites. The crystallite size of the first active material may be, for example, 700 nm or less, and may be 500 to 700 nm. In this specification, the crystallite size is defined as the intensity I of the diffraction peak on the (104) plane in the XRD analysis of the active material. 104 The full width at half maximum of the diffraction peak is calculated by applying the Scherrer equation. 104 can be measured by the method described in the Examples below. The crystallite size of the first active material can be adjusted, for example, by the manufacturing conditions of the first active material. By using, as the first active material, particles that have a larger average particle diameter (D50), a smaller crystallite size, and more aggregates of primary particles than the second active material, the reaction area with the electrolyte increases, and output resistance tends to be improved.

[0021] The first active material can be produced, for example, by a production method including a first firing step of firing a first mixture containing a lithium compound and a transition metal-containing compound to obtain a fired product. The production method may further include a second firing step of firing a second mixture containing the fired product obtained in the first firing step and the metal-containing compound. The production method may include a step of crushing the fired product obtained in the first firing step or the second firing step.

[0022] Examples of lithium compounds include one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium chloride, and lithium fluoride. Examples of transition metal-containing compounds include composite oxides or composite hydroxides containing transition metals such as Ni, Co, and Mn among the metal elements other than Li in the above formula (i). The content of Li in the first mixture is preferably 0.7 to 1.2 mol% based on the total number of moles of metal elements contained in the first mixture.

[0023] The firing temperature in the first firing step may be, for example, 700 to 1000° C., and the firing time in the first firing step may be, for example, 5 to 15 hours.

[0024] Examples of the metal-containing compound include oxides or hydroxides containing a metal element represented by Me in formula (i), and may be, for example, oxides or hydroxides containing a metal element including a transition metal such as Co, or oxides or hydroxides containing a metal element other than transition metals such as Al and B.

[0025] The firing temperature in the second firing step may be, for example, 200 to 800° C., and the firing time in the second firing step may be, for example, 3 to 18 hours.

[0026] A first active material having the above-described properties can be obtained by adjusting the firing conditions in the first firing step and the second firing step, the conditions for crushing the fired product obtained in the first firing step or the second firing step, and the like.

[0027] The second active material can be a particle group consisting of a plurality of particles. The average particle diameter (D50) of the second active material is smaller than the average particle diameter (D50) of the first active material. This improves the packing of the positive electrode active material in the positive electrode active material layer, and tends to improve the volumetric energy density of the positive electrode obtained using the positive electrode active material. The average particle diameter (D50) of the second active material can be adjusted, for example, by the manufacturing conditions of the second active material.

[0028] The average particle size (D50) of the second active material may be, for example, 2.0 to 8.0 μm, 2.5 to 7.0 μm, or 3.0 to 6.0 μm.

[0029] The second active material may be a single particle. A single particle refers to a single particle or a secondary particle formed by agglomeration of 2 to 10 primary particles. When the first active material is a single secondary particle, the agglomeration number of the primary particles may be 2 to 8 or 2 to 5.

[0030] The average particle size of a single particle or the primary particles constituting a single particle may be, for example, 0.7 μm or more, 0.8 μm or more, or 1.0 μm or more, for example, 0.7 μm or more and 8.0 μm or less, or 0.8 μm or more and 6.0 μm or less.

[0031] The second active material (single particles and primary particles constituting the single particles) typically consists of multiple crystallites. The crystallite size of the second active material is 800 nm or more, for example, 900 to 1200 Å, 950 to 1150 Å, or 1000 to 1120 Å. The crystallite size of the second active material can be adjusted, for example, by the manufacturing conditions of the second active material. When the second active material particles consist of a single particle, the reaction between the second active material and the electrolyte typically occurs on the surface of the single particle. When the second active material particles are secondary particles consisting of multiple primary particles, the reaction occurs on the surface of the secondary particle. Therefore, by using particles with a smaller average particle diameter (D50), larger crystallite size, and less aggregation of primary particles compared to the first active material, the reaction area with the electrolyte tends to be reduced, and the amount of gas generation tends to be more easily suppressed.

[0032] The second active material can be produced, for example, through a two-stage sintering process, as explained in the method for producing the first active material. By adjusting the sintering conditions and crushing conditions, a second active material having the above-mentioned properties can be obtained. In the method for producing the second active material, the firing temperature in the first firing step may be, for example, 700 to 1000°C, and the firing time in the first firing step may be, for example, 5 to 15 hours. In the method for producing the second active material, the firing temperature in the second firing step may be, for example, 200 to 500°C, and the firing time in the second firing step may be, for example, 3 to 18 hours.

[0033] The positive electrode active material satisfies formula (1) and formula (2). By measuring the Raman spectrum by Raman spectroscopy, the composition near the surface of the particles of the first active material and the second active material (for example, to a depth of several tens of nanometers from the surface) can be analyzed. -1 The maximum value Ia in the range of 500-600 cm in the Raman spectrum measured by Raman spectroscopy represents the peak of the Co-O bond. -1 The maximum value Ib in this range represents the peak of the Ni-O bond. When the positive electrode active material satisfies formulas (1) and (2), the ratio of highly reactive Co (lithium cobalt oxide) to Ni on the surface of the second active material is higher than that of the first active material, thereby improving output resistance while suppressing gas generation. Furthermore, the ratio of Co (lithium cobalt oxide) to Ni on the surface of the first active material is lower than that of the second active material, thereby enabling suppression of gas generation while improving output resistance. As a result, it becomes easier to achieve both improved battery output characteristics and suppressed gas generation. Raman spectra measured by Raman spectroscopy can be measured according to the method described in the Examples section below. s1 and s2 can be controlled, for example, by adjusting the raw material composition of the first active material and the second active material and the manufacturing conditions (e.g., the number of firing steps, firing temperature, firing time, etc.).

[0034] The positive electrode active material is preferably a compound represented by the following formula (3): (3) 1.10≦s1 / s2≦1.30 Further satisfy.

[0035] The first active material and the second active material each have a compound represented by the following formula (ii) on the surface of the particle: Li m M n O l (ii) [In formula (ii), M represents at least one element selected from Ni, Mn, Co, Al, Ti, B, Zr, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, and Si; 0≦m≦10, 0≦n≦8, 2≦l≦13, except when both m and n are 0. The first active material may have a layer containing a compound represented by formula (ii). When the first active material has a layer containing a compound represented by formula (ii), the compound represented by formula (ii) preferably contains one selected from the group consisting of B, Al, and Ti as M. When the second active material has a layer containing a compound represented by formula (ii), the compound represented by formula (ii) preferably contains one selected from the group consisting of Co, B, Al, and W as M. The layer containing the compound represented by formula (ii) may be formed, for example, over the entire surface of the first active material and the second active material, or may be formed partially on the surface of the first active material and the second active material. For example, in the production process of the first active material and the second active material, when a lithium compound and a transition metal-containing compound or a metal-containing compound are mixed and fired, a compound containing the element represented by M may also be mixed. This may result in the formation of a layer containing the compound represented by formula (ii) on the surface of the first active material and the second active material. For example, after the lithium transition metal composite oxide is produced, the layer containing the compound represented by formula (ii) may be formed by coating the surface of the first active material and the second active material with the compound.

[0036] The mass ratio of the first active material to the second active material in the positive electrode active material (first active material / second active material) may be, for example, 5 / 5 to 8 / 2, and from the viewpoint of simultaneously improving the battery output characteristics and suppressing the amount of gas generation, is preferably 5 / 5 to 7 / 3, and more preferably 5 / 5 to 6 / 4.

[0037] The positive electrode active material may contain an active material other than the first active material and the second active material, as long as the object of the present disclosure is not impaired. Examples of the other active material include a lithium transition metal composite oxide having a Ni content outside the above range, or a compound other than a lithium transition metal composite oxide. The other active material may be primary particles (single particles) or secondary particles.

[0038] <Nonaqueous electrolyte secondary battery> The battery of this embodiment has a positive electrode, and the positive electrode has an active material layer containing the above-described positive electrode active material, which improves the packing of the positive electrode active material in the active material layer, thereby improving the volumetric energy density of the positive electrode and the output characteristics of the battery.

[0039] A battery typically includes an electrode assembly including a positive electrode and a non-aqueous electrolyte. The battery may have a battery case that houses the electrode assembly and the non-aqueous electrolyte. The battery case may include an exterior body having an opening and a sealing plate that seals the opening. The exterior body and the sealing plate may be formed using a metal such as Al, an Al alloy, iron, or an iron alloy, and may be formed using, for example, an Al laminate film. A resin sheet serving as an electrode holder may be disposed between the electrode assembly and the exterior body.

[0040] The electrode assembly may include a positive electrode, a negative electrode, and a separator. In the electrode assembly, the active material layer of the positive electrode and the negative electrode active material layer of the negative electrode face each other with the separator interposed therebetween. The electrode assembly may be a laminated type in which the positive electrode, the negative electrode, and the separator are laminated, or a wound type in which a laminate in which the positive electrode, the negative electrode, and the separator are laminated is wound.

[0041] The positive electrode has a positive electrode current collector and an active material layer containing the above-mentioned positive electrode active material, with the active material layer on the positive electrode current collector. The active material layer is formed on one or both sides of the positive electrode current collector. The positive electrode current collector is, for example, a metal foil made of an Al material such as Al or an Al alloy, and may be any metal foil that is stable within the potential range of the positive electrode.

[0042] The active material layer can be formed, for example, by applying a mixture to a positive electrode current collector, drying it, and compressing it. The mixture can be prepared by adding a solvent such as N-methyl-2-pyrrolidone (NMP) to materials that form the active material layer, such as a positive electrode active material, a binder, and a conductive material, and kneading the mixture.

[0043] The active material layer may contain, in addition to the positive electrode active material described above, a binder and a conductive material. Examples of binders include known materials such as fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE) and cellulose-based resins such as carboxymethyl cellulose (CMC). Examples of conductive materials include carbon materials. Examples of carbon materials include one or more selected from the group consisting of fibrous carbon, carbon black, coke, and activated carbon. Examples of fibrous carbon include carbon nanotubes (CNTs).

[0044] A negative electrode typically has 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] The present invention will be described in more detail below with reference to examples. [Example]

[0049] [Raman spectrum measurement] The Raman spectra of the first and second active materials were measured by Raman spectroscopy using Nanophoton's "RAMANtouch." Measurements were performed using a 100x objective lens with the laser focused on the positive electrode active material powder. The conditions were: wavelength 532 nm (ion argon laser), grating 300 gr / mm, exposure time 5 seconds, number of integrations 2, measurement wavelength 100 cm -1 ~4000cm -1 450-500 cm in the Raman spectrum -1Maximum values ​​in the range of Ia and 500-600 cm -1 From the maximum value Ib in this range, s1 (Ib / Ia of the first active material) and s2 (Ib / Ia of the second active material) were calculated.

[0050] [Measurement of average particle size (D50)] The average particle diameters (D50) of the first active material and the second active material were measured using a laser diffraction particle size distribution measuring device ("Mastersizer-3000", manufactured by Malvern Panalytical).

[0051] [Crystallite size measurement] The crystallite size was calculated from the peak intensity of the (104) plane using an X-ray diffractometer ("SmartLab", manufactured by Rigaku).

[0052] [Measurement of output resistance and gas increase] (Preparation of positive electrode plate) 97.5 parts by mass of the positive electrode active material of each of the examples and comparative examples, 1.5 parts by mass of carbon black as a conductive material, and 1.0 part by mass of polyvinylidene fluoride (PVdF) as a binder were mixed, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to obtain a slurry. The slurry was applied to an aluminum foil as a positive electrode current collector, dried, and rolled to a predetermined thickness using a rolling roller. As a result, a slurry with a density of 3.30 g / cm3 was formed on the aluminum foil. 3 The raw positive electrode plate was cut to a predetermined size, and an aluminum tab was attached to obtain a positive electrode plate.

[0053] (Preparation of Electrolyte) An electrolyte solution was prepared by adding lithium hexafluorophosphate (LiPF6) as a supporting salt to a mixed solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) as a non-aqueous solvent in a volume ratio of 30:70 (EC:EMC) to give a concentration of 1 mol / L per 1 L of the mixed solvent, and then adding vinylene carbonate (VC) to give a content of 0.3 mass% relative to the total mass of the mixed solvent.

[0054] (Preparation of test cell) The positive electrode plate obtained above and a lithium metal plate as a counter electrode of the positive electrode plate were laminated with a polyolefin separator interposed therebetween to obtain a laminated electrode body. The laminated electrode body was housed in a battery case made of an aluminum laminate sheet, and the prepared electrolyte solution was poured into the battery case, and the opening was sealed to obtain a test cell.

[0055] (Measurement of output resistance and gas increase) The output resistance (Ω) of the test cell was measured. The smaller the output resistance, the better the battery characteristics. The volume of the test cell was measured by Archimedes' method immediately after production and after storage for 30 days at 70°C and SOC 100%. The change in volume (volume after storage for 30 days at 70°C and SOC 100% minus the volume immediately after production) was taken as the gas increase. The smaller the gas increase, the more suppressed the amount of gas generation.

[0056] [Preparation of first active material] First active materials having the following different s1 (Ib / Ia ratios) were prepared via a one-stage or two-stage firing process. SEM observation confirmed that all of the prepared first active materials consisted of secondary particles (aggregated particles) consisting of 100 or more primary particles with particle diameters in the range of 0.8 to 6 μm. The crystallite sizes of all of the first active materials were confirmed to be in the range of 500 to 700 nm. [First active material (s1=1.26)] It was produced by the following first firing step. First firing step: By controlling the stirring speed, time, pH, etc. in the coprecipitation process, Ni agglomerated particles (secondary particles formed by agglomeration of several hundred primary particles) with an average particle diameter (D50) of about 17 μm are prepared as a precursor of the first active material. 0.80 Co 0.05 Mn 0.15 A transition metal compound represented by (OH)2 was prepared. The prepared transition metal compound was mixed with LiOH and baked at a temperature of 800°C for 12 hours to obtain a first active material (s1 = 1.26) which was a lithium transition metal composite oxide.

[0057] [First active material (s1=1.01)] It was produced by the above-mentioned first firing step and the following second firing step. Second firing step: Co(OH)2 was added to the first active material prepared in the first firing step and mixed, and then fired in a firing furnace under an O2 atmosphere at a temperature of 250°C for 6 hours [step (b)] to obtain the first active material (s1=1.01), which is a lithium transition metal composite oxide.

[0058] [First active material (s1=1.07)] It was produced by the above-mentioned first firing step and the following second firing step. Second firing step: Co(OH)2 was added to the first active material produced in the first firing step and mixed, and then the mixture was fired in a firing furnace under an O2 atmosphere at a temperature of 600°C for 12 hours to obtain the first active material (s1=1.07).

[0059] [First active material (s1=1.13)] It was produced by the above-mentioned first firing step and the following second firing step. Second firing step: Co(OH)2 was added to the first active material produced in the first firing step and mixed, and then the mixture was fired in a firing furnace under an O2 atmosphere at a temperature of 700°C for 15 hours to obtain the first active material (S1 = 1.13).

[0060] [Preparation of second active material] The following second active materials having different s1 (Ib / Ia ratios) were prepared by one-stage or two-stage firing processes. SEM observation confirmed that all of the prepared first active materials were single particles with primary particle diameters in the range of 0.8 to 6 μm. [Second active material (s2=1.19)] First firing step: By controlling the stirring speed, time, pH, etc. during the coprecipitation process, Ni was prepared as a precursor of the second active material. The Ni was then co-precipitated into a single particle (a single particle or a secondary particle formed by agglomeration of approximately 2 to 10 primary particles) with an average particle diameter (D50) of approximately 4 μm. 0.83 Co 0.12 Mn 0.05A transition metal compound represented by (OH)2 was prepared. The prepared transition metal compound was mixed with LiOH and baked at a temperature of 800°C for 12 hours to obtain a second active material (s2 = 1.19), which was a lithium transition metal composite oxide.

[0061] [Second active material (s2=0.75)] It was produced by the above-mentioned first firing step and the following second firing step. Second firing step: Co(OH)2 was added to the second active material produced in the first firing step and mixed, and then the mixture was fired in an O2 atmosphere in a firing furnace at a temperature of 250°C for 6 hours to obtain a second active material (s2 = 0.75).

[0062] [Second active material (s2=0.88)] It was produced by the above-mentioned first firing step and the following second firing step. Second firing step: Co(OH)2 was added to the second active material produced in the first firing step and mixed, and then the mixture was fired in a firing furnace at 300°C for 10 hours in an O2 atmosphere to obtain a second active material (s2 = 0.88).

[0063] [Second active material (s2=0.96)] It was produced by the above-mentioned first firing step and the following second firing step. Second firing step: Co(OH)2 was added to the second active material produced in the first firing step and mixed, and then the mixture was fired in an O2 atmosphere in a firing furnace at 400°C for 12 hours to obtain a second active material (s2 = 0.96).

[0064] <Examples 1 to 4 and Comparative Examples 1 to 6> The first active material and the second active material were mixed in a mass ratio of 6:4 (first active material:second active material) to prepare the positive electrode active materials of the examples and comparative examples. The output resistance and gas increase rate of the positive electrode active materials were measured. The results are shown in Table 1.

[0065] [Table 1]

[0066] As shown in Table 1, in Examples 1 to 4, the s1 of the first active material was 1.05 to 1.20, the s2 of the second active material was 0.80 to 1.00, the crystallite size of the second active material was 800 nm or larger, the average particle diameter (D50) of the second active material was smaller than that of the first active material, and the output resistance of the test cell was improved and the amount of gas generation was suppressed. This shows that by controlling the s1 and average particle diameter (D50) of the first active material and the s2, crystallite size, and average particle diameter (D50) of the second active material, the output resistance of the battery can be improved and the amount of gas generation can be suppressed.

Claims

1. A positive electrode active material including a first active material and a second active material, the first active material and the second active material contain lithium and nickel, the first active material and the second active material have a nickel content of 80 mol % or more relative to 100 mol % of the total amount of metal elements other than lithium; the average particle diameter (D50) of the second active material is smaller than the average particle diameter (D50) of the first active material; The crystallite size of the second active material is 800 nm or more, 450-500 cm in the Raman spectrum measured by Raman spectroscopy －１ 500 to 600 cm for the maximum value Ia in the range －１ When the ratio of the maximum value Ib in the range is Ib / Ia, and the Ib / Ia of the first active material and the second active material are s1 and s2, respectively, the following formula: (1) 1.05≦s1≦1.20 (2) 0.80≦s2≦1.00 A positive electrode active material that satisfies the above requirements.

2. The following formula: (3) 1.10≦s1 / s2≦1.30 The positive electrode active material according to claim 1 , further satisfying the following:

3. 3. 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, and the second active material has an average particle diameter (D50) of 2 to 8 μm.

4. 3. The positive electrode active material according to claim 1, wherein a mass ratio of the first active material to the second active material is 5 / 5 to 8 / 2.

5. 3. The positive electrode active material according to claim 1, wherein a molar ratio of lithium to metal elements other than lithium in the first active material is 1.02 to 1.

05.

6. 3. The positive electrode active material according to claim 1, wherein a molar ratio of lithium to metal elements other than lithium in the second active material is 0.98 to 1.

04.

7. A non-aqueous electrolyte secondary battery comprising the positive electrode active material according to claim 1 or 2.

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