Positive electrode active material and non-aqueous electrolyte secondary battery

Abstract

The invention relates to a positive electrode active material and a nonaqueous electrolyte secondary battery. The positive electrode active material includes a first active material and a second active material having a larger average particle diameter than the first active material. The first active material and the second active material are both lithium transition metal composite oxides. The first active material is a single particle or a secondary particle formed by aggregation of 2-10 primary particles. The second active material is a secondary particle in which 50 or more primary particles are aggregated. The ratio (R / D150) of the average particle diameter (R) of single particles or primary particles of the first active material to the average particle diameter (D150) of the first active material is 0.80 or more, said average particle diameter (R) being determined from a scanning electron microscope image. The intensity ratio (I003 / I104) of diffraction peaks of the first active material in X-ray diffraction is 1.6 or more.

Description

Technical Field

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

[0002] In non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, as the positive electrode active material contained in the active material layer of the positive electrode, a lithium transition metal composite oxide is known to be used. As the active material contained in the active material layer of the positive electrode, sometimes two kinds of active materials having different particle diameters are mixed and used (Japanese Patent Laid-Open No. 2011-113825, etc.). As the active material for the positive electrode, particles having a small number of single particles and primary particle aggregates (hereinafter also referred to as "single particles, etc.") are also known (Japanese Patent Laid-Open No. 2017-188445, etc.). Summary of the Invention

[0003] Single particles (individual particles), etc. tend to have poor fluidity because of their small particle size and irregular particle shape (deformation). In the case of mixing two kinds of active materials having different particle diameters to form an active material layer, the active material with poor fluidity can cause a decrease in the packing property of the active material layer. In order to improve the packing property of the active material layer, improving the fluidity of single particles, etc. is considered. However, when forming an active material layer containing two kinds of active materials having different particle diameters, if single particles, etc. with excellent fluidity are used, sometimes the output characteristics of the non-aqueous electrolyte secondary battery decrease.

[0004] An object of the present disclosure is to provide a positive electrode active material capable of improving the output characteristics of a non-aqueous electrolyte secondary battery while improving the fluidity of a first active material (single particles or secondary particles formed by aggregation of 2 to 10 primary particles), and a non-aqueous electrolyte secondary battery using the same.

[0005] [1] A positive electrode active material comprising a first active material and a second active material having an average particle diameter larger than that of the first active material, both the first active material and the second active material being lithium transition metal composite oxides, the first active material being single particles or secondary particles formed by aggregation of 2 to 10 primary particles, the second active material being secondary particles formed by aggregation of 50 or more primary particles, the ratio (R / D150) of the average particle diameter (R) of the single particle or primary particle of the first active material obtained from a scanning electron microscope image to the average particle diameter (D150) of the first active material being 0.80 or more, and the intensity ratio (I 003 / I 104 ) of the diffraction peak in the X-ray diffraction method of the first active material being 1.6 or more.

[0006] [2] The positive electrode active material according to [1], wherein the ratio (R / D150) is 0.84 or more.

[0007] [3] The positive electrode active material according to [1] or [2], wherein the intensity ratio (I 003 / I 104 ) is 1.7 or more.

[0008] [4] The positive electrode active material according to any one of [1] to [3], wherein the average particle diameter (D150) of the first active material is 2 to 6 μm.

[0009] [5] The positive electrode active material according to any one of [1] to [4], wherein the average particle diameter (D250) of the second active material is 12 to 20 μm.

[0010] [6] The positive electrode active material according to any one of [1] to [5], wherein the ratio (D150:D250) of the average particle diameter (D150) of the first active material to the average particle diameter (D250) of the second active material is 1:2 to 1:10.

[0011] [7] The positive electrode active material according to any one of [1] to [6], wherein the specific surface area of the second active material is 0.13 to 0.27 m 2 / g.

[0012] [8] The positive electrode active material according to any one of [1] to [7], wherein both the first active material and the second active material are lithium transition metal composite oxides containing Ni in an amount of 50 to 70 mol% based on the total number of moles of metal elements other than Li.

[0013] [9] A non-aqueous electrolyte secondary battery having a positive electrode, the positive electrode having an active material layer containing the positive electrode active material according to any one of [1] to [8].

[0014] The above and other objects, features, aspects and advantages of the present invention will become clear from the following detailed description related to the present invention. Detailed Description

[0015] In this specification, numerical ranges such as "x to y" include the upper limit value and the lower limit value unless otherwise specified. That is, "x to y" represents a numerical range of "x or more and y or less". A value arbitrarily selected from within the numerical range can be set as a new upper limit value or a new lower limit value. For example, by arbitrarily combining the values within the numerical range with the values described in other parts of this specification or in tables, etc., a new numerical range can be set.

[0016] (Positive Electrode Active Material)

[0017] The positive electrode active material of the present embodiment is, for example, an active material layer included in a positive electrode of a non-aqueous electrolyte secondary battery such as a lithium ion battery (hereinafter also referred to as "secondary battery"). The positive electrode active material includes a first active material and a second active material having an average particle size larger than that of the first active material. Both the first active material and the second active material are lithium transition metal composite oxides. The first active material is a single particle or a secondary particle formed by aggregation of 2 to 10 primary particles. The second active material is a secondary particle formed by aggregation of 50 or more primary particles. The ratio (R / D150) of the average particle size (R) of the single particle or primary particle of the first active material obtained from a scanning electron microscope (hereinafter also referred to as "SEM") image to the average particle size (D150) of the first active material is 0.80 or more. The intensity ratio (I 003 / I 104 ) in the X-ray diffraction (hereinafter also referred to as "XRD") method of the first active material is 1.6 or more.

[0018] By including the first active material and the second active material in the positive electrode active material, the packing density of the positive electrode active material in the active material layer can be increased, and thus the volume energy density of the positive electrode obtained by using the positive electrode active material can be increased. By using a single particle or a secondary particle formed by aggregation of 2 to 10 primary particles as the first active material having a relatively small average particle size, the cycle characteristics of the secondary battery can be improved.

[0019] Both the first active material and the second active material are preferably lithium transition metal composite oxides in which the content of Ni (hereinafter also referred to as "Ni content") relative to the total molar number of metal elements other than Li is 50 to 70 mol%. The composition of the first active material and the composition of the second active material may be the same as each other or different from each other.

[0020] The Ni content of the above lithium transition metal composite oxide may be 52 to 68 mol%, may be 55 to 65 mol%, or may be 55 to 60 mol%. The Ni content of the first active material may be larger than the Ni content of the second active material. By the Ni content of the first active material and the second active material being independently within the above ranges, a secondary battery with an increased volume energy density can be obtained.

[0021] The above lithium transition metal composite oxide only needs to contain Li and Ni. Preferably, as the transition metal, it preferably contains at least Ni, Co, and Mn. The above lithium transition metal composite oxide may be, for example, a compound represented by the following formula (i).

[0022] Li 1-a Ni x Me 1-x O2(i)

[0023] [In formula (i), -0.3 ≤ a ≤ 0.2 and 0.5 ≤ x ≤ 0.7, and Me may include one or more selected from Co, Mn, Al, B, Zr, Ti, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, and Si.]

[0024] In the above formula (i), a may be -0.25 ≤ a ≤ 0.15, or may be -0.20 ≤ a ≤ 0.10. x may be 0.52 ≤ x ≤ 0.68, or may be 0.55 ≤ x ≤ 0.65, or may be 0.55 ≤ x ≤ 0.60. Me may include one or more selected from Co, Mn, Al, B, Zr, Ti, Mg, Mo, and Nb, preferably includes at least one of Co and Mn, and more preferably includes 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 spectrometry.

[0025] Within the scope that does not impair the object of the present disclosure, the positive electrode active material may include other active materials in addition to the first active material and the second active material. As other active materials, lithium transition metal composite oxides with Ni content outside the above range, or compounds other than lithium transition metal composite oxides can be cited. The other active material may be primary particles (single particles) or secondary particles.

[0026] (The first active material)

[0027] The first active material is single particles or secondary particles formed by aggregation of 2 to 10 primary particles. When the first active material is secondary particles, the number of aggregated primary particles may be 2 to 8, or may be 2 to 5. By including the first active material which is single particles or secondary particles with a small number of aggregated primary particles in the positive electrode active material, the cycle characteristics of the secondary battery can be improved.

[0028] The above ratio (R / D150) of the first active material is 0.80 or more, preferably 0.83 or more, more preferably 0.84 or more, and may be 0.85 or more. The ratio (R / D150) may be 0.80 to 1.0, may be 0.83 to 0.95, may be 0.84 to 0.92, or may be 0.85 to 0.90. The ratio (R / D150) can be adjusted, for example, by the manufacturing conditions of the first active material described later.

[0029] The above ratio (R / D150) can be said to be an index indicating that the first active material is single particles. The larger the value, the larger the proportion of single particles. On the other hand, the smaller the above ratio (R / D150), the larger the proportion of aggregated particles (secondary particles), and the easier it is for primary particles to aggregate. When the particle size of the first active material is small, the aggregability of the particles easily affects the fluidity. Therefore, by setting the ratio (R / D150) within the above range, the fluidity of the first active material can be improved. Thereby, the filling property of the positive active material in the active material layer can be improved, and it is considered that the volume energy density of the positive electrode obtained using the positive active material can be improved.

[0030] The average particle size (R) can be, for example, 1.7 to 6 μm, can be 2 to 5 μm, and can be 2.5 to 4.5 μm. The average particle size (R) is a value obtained by observing the surface of the first active material using SEM and determining the longest diameter of the single particles or primary particles of the first active material from the SEM image. As described in the examples below, it is a value obtained by image analysis of the SEM images of the surfaces of multiple first active materials to determine the longest diameter of the single particles or primary particles of each first active material, and then averaging the values obtained for multiple first active materials.

[0031] The average particle size (D150) is preferably 2 to 6 μm, can be 3 to 5 μm, and can be 4 to 5 μm. In this specification, the average particle size (D50) is the particle size at which the cumulative frequency from the smaller particle size side in the volume-based particle size distribution becomes 50%, and the average particle size (D150) is the average particle size (D50) of the first active material. The volume-based particle size distribution can be measured using a particle size distribution measuring device.

[0032] The intensity ratio (I 003 / I 104 ) of the diffraction peak in the XRD method of the first active material is 1.6 or more, preferably 1.7 or more, and can be 1.75 or more. The intensity ratio (I 003 / I 104 ) can be 1.6 to 2, can be 1.7 to 1.9, and can be 1.75 to 1.85. The intensity ratio (I 003 / I 104 ) of the first active material is an index indicating the isotropy of the crystal structure of the microcrystals in the first active material. If the intensity ratio (I 003 / I 104 ) increases, the crystal structure of the microcrystals in the first active material becomes more anisotropic, and it is considered that the region contributing to the insertion and extraction of Li ions increases. The intensity I 003 and I 104The intensities of the diffraction peaks at the (003) plane and the (104) plane of the first active material measured by the XRD method can be measured by the method described in the following examples. The intensity ratio (I 003 / I 104 ) can be adjusted, for example, by the manufacturing conditions of the first active material described later.

[0033] If the above ratio (R / D150) of the first active material is increased, the fluidity of the first active material can be improved. However, since the content ratio of the secondary particles formed by aggregation of the primary particles becomes small, the specific surface area of the first active material tends to become small. If the specific surface area of the first active material becomes small, the output characteristics of the secondary battery are likely to decrease. On the other hand, by making the intensity ratio (I 003 / I 104 ) of the first active material within the above range, the region contributing to the insertion and extraction of Li ions can be increased, and it is considered that the output characteristics of the secondary battery can be improved.

[0034] The crystallite size L1 of the first active material is preferably It can be It can be The crystallite size L1 is calculated by substituting the value of the full width at half maximum of the diffraction peak intensity I 104 of the first active material into the Scherrer formula.

[0035] When the total mass of the positive electrode active material is set to 100% by mass, the content of the first active material in the positive electrode active material can be 20 to 80% by mass, can be 30 to 70% by mass, and can be 40 to 60% by mass.

[0036] The first active material can be manufactured, for example, by the following manufacturing method, which includes: a first firing step of firing a first mixture containing a lithium compound and a compound containing a transition metal to obtain a fired product; and a second firing step of firing a second mixture containing the fired product and a compound containing a metal. The manufacturing method of the first active material may include a step of crushing the fired product obtained in the first firing step or the second firing step.

[0037] Examples of the lithium compound include one or more of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium chloride, and lithium fluoride. Examples of the compound containing a transition metal include a composite oxide or composite hydroxide containing transition metals such as Ni, Co, and Mn among the metal elements represented by Me in the above formula (i). The content of Li in the first mixture is preferably 0.7 to 1.2 mol% relative to the total molar amount of the metal elements contained in the first mixture.

[0038] The firing temperature in the first firing process is preferably 700 to 1000 °C, and the firing time in the first firing process is preferably 3 to 7 hours.

[0039] As the metal-containing compound, oxides or hydroxides containing the metal element represented by Me in the formula (i) can be cited. Preferably, oxides or hydroxides containing metal elements other than transition metals such as Al and B can be cited. The metal-containing compound can also be an oxide or hydroxide containing a metal element containing a transition metal.

[0040] The firing temperature in the second firing process is preferably 300 to 600 °C, and the firing time in the second firing process is preferably 3 to 10 hours.

[0041] By adjusting the firing conditions in the first firing process and the second firing process, the crushing conditions of the fired product obtained in the first firing process or the second firing process, etc., the ratio (R / D150) and strength ratio (I 003 / I 104 ) etc. of the first active material can be adjusted.

[0042] (Second active material)

[0043] The second active material is secondary particles aggregated by 50 or more primary particles. In the second active material, the number of aggregated primary particles can be 100 or more, can be 1000 or more, can be 10000 or more, and is usually 5×10 6 pieces or less, and can be 5×10 5 pieces or less.

[0044] The average particle diameter (D250) of the second active material is preferably 12 to 20 μm, can be 13 to 19 μm, and can be 14 to 18 μm.

[0045] The ratio (D150:D250) of the average particle diameter (D150) of the first active material to the average particle diameter (D250) of the second active material is preferably 1:2 to 1:10, can be 1:3 to 1:8, can be 1:3.5 to 1:7, and can be 1:3.5 to 1:8. By the ratio (D150:D250) being within the above range, the filling property of the positive active material in the active material layer can be improved, and the volumetric energy density of the positive electrode can be improved.

[0046] The specific surface area (BET) of the second active material is preferably 0.13 to 0.27 m 2 / g, can be 0.15 to 0.25 m 2 / g, and can be 0.17 to 0.23 m 2 / g. The specific surface area can be measured using a specific surface area measuring device. By the specific surface area of the second active material being within the above range, it is easy to improve the output characteristics of the secondary battery.

[0047] The crystallite size L2 of the second active material is preferably It may be It may be The crystallite size L2 is calculated by substituting the value of the full width at half maximum of the intensity I of the diffraction peak of the second active material into the Scherrer formula. 104 into the Scherrer formula.

[0048] When the total mass of the positive electrode active material is set to 100% by mass, the content of the second active material in the positive electrode active material may be 20 to 80% by mass, may be 30 to 70% by mass, or may be 40 to 60% by mass.

[0049] The second active material can be manufactured, for example, through a two-stage sintering process as described in the manufacturing method of the first active material. By adjusting the sintering conditions and crushing conditions, a second active material having the above-described various characteristics can be obtained.

[0050] (Non-aqueous electrolyte secondary battery)

[0051] The non-aqueous electrolyte secondary battery of the present embodiment (hereinafter also referred to as "this battery") has a positive electrode, and the positive electrode has an active material layer containing the above-described positive electrode active material. Therefore, the filling property of the positive electrode active material in the active material layer can be improved, the volumetric energy density of the positive electrode can be increased, and at the same time, the output characteristics of this battery can be improved.

[0052] This battery generally includes an electrode body containing a positive electrode and a non-aqueous electrolyte. This battery may have a battery case that houses the electrode body and the non-aqueous electrolyte. The battery case may include an outer package having an opening and a sealing plate that seals the opening. The outer package and the sealing plate can be formed of a metal such as Al, an Al alloy, iron, or an iron alloy, and can be formed of an Al laminated film, for example. A resin sheet as an electrode support may be disposed between the electrode body and the outer package.

[0053] The electrode body may include a positive electrode, a negative electrode, and a separator (separator). In the electrode body, the active material layer of the positive electrode and the negative electrode active material layer of the negative electrode face each other via the separator. The electrode body may be a laminated type in which the positive electrode, the negative electrode, and the separator are laminated, or may be a wound type in which a laminate of the positive electrode, the negative electrode, and the separator is wound.

[0054] The positive electrode has a positive electrode current collector and an active material layer containing the above-described positive electrode active material, and the active material layer is provided 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 a metal foil made of an Al material such as Al and an Al alloy, and any metal foil that is stable in the potential range of the positive electrode may be used.

[0055] The active material layer can be formed, for example, by coating a binder on a positive electrode current collector, drying, and compressing. The binder can be prepared by adding a solvent such as N-methyl-2-pyrrolidone (NMP) to materials for forming the active material layer such as positive electrode active material, binder material, and conductive material, and kneading them.

[0056] In addition to the above-mentioned positive electrode active material, the active material layer may include a binder material, a conductive material, etc. As the binder material, for example, fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE); well-known materials such as cellulose-based resins such as carboxymethyl cellulose (CMC) can be cited. As the conductive material, for example, carbon materials can be cited. The carbon materials can be, for example, one or more selected from fibrous carbon, carbon black, coke, and activated carbon. As the fibrous carbon, carbon nanotubes (CNT) can be cited.

[0057] The negative electrode usually 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, for example, a metal foil made of copper materials such as copper and copper alloys. The negative electrode active material layer contains a negative electrode active material and may further contain a conductive material, an adhesive, etc.

[0058] As the negative electrode active material, well-known materials can be cited, for example, carbon-based active material particles such as graphite; and metal-based active material particles containing elements selected from Si, Sn, Sb, Bi, Ti, Ge, etc. Regarding the conductive material, the above-mentioned conductive materials can be cited. Regarding the adhesive, cellulose-based resins such as CMC, methyl cellulose (MC), and hydroxypropyl cellulose; polyacrylic acid; styrene-butadiene rubber (SBR), etc. can be cited. CMC can also be used as a thickener.

[0059] The separator has a substrate with a single-layer structure or a multi-layer structure, and a functional layer may be provided on at least one side of the substrate. The substrate can be a porous sheet such as a film and non-woven fabric made of resins such as polyolefins such as polyethylene and polypropylene, polyester, cellulose, polyamide, etc. The functional layer can be, for example, an adhesive layer and / or a heat-resistant layer. The adhesive layer can be formed, for example, by using an adhesive. The heat-resistant layer can contain, for example, a filler and an adhesive.

[0060] The non-aqueous electrolyte preferably contains an electrolyte in a non-aqueous solvent such as an organic solvent. As the electrolyte, one or more of LiPF6, LiBF4, LiClO4, LiFSO3, and LiBOB, etc. can be cited. As the non-aqueous solvent, one or more of ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), butylene carbonate (BC), and diethyl carbonate (DEC), etc. can be cited. The non-aqueous electrolyte may further contain additives such as vinylene carbonate (VC), ethylene vinyl carbonate (VEC), and fluoroethylene carbonate.

[0061] Example

[0062] Examples and comparative examples are shown below to illustrate the present disclosure more specifically.

[0063] [Measurement of average particle size (D150 and D250) of active substances]

[0064] The average particle sizes (D150 and D250) of the first active substance and the second active substance were measured using a particle size distribution measuring device (Mastersizer-3000, manufactured by Malvern Panalytical).

[0065] [Measurement of average particle size (R) of the first active substance and calculation of ratio (R / D150)]

[0066] SEM images of the particle surface of the first active substance were obtained using a scanning electron microscope (SEM). Using image analysis software Mac-View (manufactured by MOUNTECH), more than 10 first active substances were randomly selected from the SEM images. In the case where the first active substance is a secondary particle, the shape of the primary particle was determined. For all the primary particles contained in each first active substance, the length of the longest part of the diameter (longest length) was determined, and the average value of the longest lengths of the respective primary particles was set as the longest diameter of the first active substance. In the case where the first active substance is a single particle, after determining the shape of the single particle, the longest diameter was determined and set as the longest diameter of the first active substance. The average value of the longest diameters of the respective first active substances thus determined was averaged for the above-mentioned more than 10 first active substances and set as the average particle size (R) of the first active substance. From the average particle size (R) of the first active substance and the average particle size (D150) obtained above, the ratio (R / D150) was calculated.

[0067] [Intensity ratio of diffraction peaks (I 003 / I 104 ), calculation of crystallite sizes L1 and L2]

[0068] Using a fully automatic multi-purpose X-ray diffractometer (SmartLab, manufactured by Rigaku), with the tube target (target element) being Cu, the tube voltage being 45 kV, and the tube current being 200 mA, XRD measurement of the first active substance filled in a dedicated sample holder (holder) was performed using the reflection method. In the XRD distribution obtained from the XRD measurement, from the intensity I 003 of the diffraction peak of the (003) plane appearing at 2θ = 18 - 19° and the intensity I 104 of the diffraction peak of the (104) plane appearing at 2θ = 44 - 45°, the intensity ratio (I 003 / I 104 ) was calculated.

[0069] Substitute the value of the full width at half maximum (FWHM) of the diffraction peak intensity I obtained above into the Scherrer formula to calculate the crystallite size L1 of the first active material. Using the same steps as above, perform XRD measurement on the second active material, and calculate the crystallite size L2 from the diffraction peak intensity I 104 104

[0070] [Measurement of Specific Surface Area of Second Active Material]

[0071] The specific surface area of the second active material was measured using a specific surface area measurement device (manufactured by MOUNTECH Co., Ltd., Macsorb HM model-1208).

[0072] [Examples 1 and 2, Comparative Examples 1 to 4]

[0073] [Fabrication of Positive Electrode]

[0074] As the first active material, a lithium transition metal composite oxide having an average particle size (D150), ratio of average particle sizes (R / D150), intensity ratio (I 003 / I 104 ) and crystallite size L1 shown in Table 1, and containing at least Ni, Co, and Mn with Ni:Co:Mn = 60:20:20 (mol% ratio) was prepared. The first active material is single particles or secondary particles aggregated by 2 to 5 primary particles.

[0075] As the second active material, a lithium transition metal composite oxide having an average particle size (D250), specific surface area (BET), and crystallite size L2 shown in Table 1, and containing at least Ni, Co, and Mn with Ni:Co:Mn = 55:20:25 (mol% ratio) was prepared. The second active material is secondary particles aggregated by 100 or more primary particles.

[0076] 50 parts by mass of the first active material and 50 parts by mass of the second active material were mixed to obtain a positive electrode active material. 97.5 parts by mass of the positive electrode active material, 1.5 parts by mass of carbon black as a conductive material, and 1.0 part by mass of PVdF as a binder were mixed, and an appropriate amount of NMP as a solvent was added to prepare a slurry-like mixture. The mixture was coated on an aluminum foil as a positive electrode current collector, dried, rolled using a rolling mill, and after forming an active material layer, it was cut into electrode sizes and an aluminum electrode tab was installed to obtain a positive electrode.

[0077] [Fabrication of Negative Electrode]

[0078] ​​98 parts by mass of a negative electrode active material, 1 part by mass of CMC as a thickening agent, and 1 part by mass of SBR as a binder were dispersed in water to prepare a slurry-like negative electrode mixture. The negative electrode mixture was coated on a copper foil serving as a negative electrode current collector, dried, and rolled using a rolling mill. After forming a negative electrode active material layer, it was cut into electrode sizes, and a nickel electrode plate was installed to obtain a negative electrode.

[0079] (Fabrication of a non-aqueous electrolyte secondary battery)

[0080] The positive electrode and the negative electrode fabricated above were laminated via a polyolefin-based separator to obtain a laminated electrode body. The laminated electrode body was housed in a battery case composed of an aluminum laminate sheet, a non-aqueous electrolyte was injected, and then the opening of the battery case was sealed to obtain a test battery cell as a secondary battery. The non-aqueous electrolyte was prepared by adding LiPF6 as an electrolyte at a concentration of 1 mol / L in a mixed solvent in which EC and EMC were mixed at a volume ratio of EC:EMC = 30:70, and adding vinylene carbonate in such a manner that the mass relative to the mixed solvent became 0.3 mass%.

[0081] [Evaluation of the fluidity of the first active material]

[0082] To evaluate the fluidity of the first active material, the angle of repose of the first active material was measured using a powder tester PT-X (manufactured by Hosokawa Micron Corporation). The results are shown in Table 1.

[0083] [Evaluation of the output characteristics of the test battery cell]

[0084] To evaluate the output characteristics of the test battery cell, the internal resistance (DCIR) of the test battery cell fabricated above was measured at 25 °C at the time when the state of charge (SOC) was 50% (the charge capacity relative to the initial discharge capacity was 50%). The results are shown in Table 1.

[0085]

Table 1

[0086]

[0087] As shown in Table 1, in Examples 1 and 2, the angle of repose of the first active material was 45° or less, and the internal resistance of the test battery cell was 0.080 Ω or less. From this, it can be understood that by controlling the ratio of the average particle size (R / D150) and the intensity ratio of the diffraction peaks (I 003 / I 104 ) of the first active material, it is possible to improve the fluidity of the first active material contained in the positive electrode active material and at the same time improve the output characteristics of the test battery cell.

[0088] The above describes the embodiments of the present invention. However, it should be considered that the disclosed embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is represented by the claims and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A positive electrode active material comprising a first active material and a second active material having an average particle diameter larger than that of the first active material, wherein both the first active material and the second active material are lithium transition metal composite oxides, the first active material is a single particle or a secondary particle formed by aggregation of 2 to 10 primary particles, the second active material is a secondary particle formed by aggregation of 50 or more primary particles, the ratio R / D150 of the average particle diameter R of the single particle or primary particle of the first active material determined from a scanning electron microscope image to the average particle diameter D150 of the first active material is 0.80 or more, The intensity ratio I of the diffraction peaks in the X-ray diffraction method of the first active substance 003 / I 104 is 1.6 or more.

2. The positive electrode active material according to claim 1, wherein the ratio R / D150 is 0.84 or more.

3. The positive electrode active material according to claim 1, wherein, The intensity ratio I 003 / I 104 is 1.7 or more.

4. The positive electrode active material according to claim 1, wherein, The average particle diameter D150 of the first active material is 2 to 6 μm.

5. The positive electrode active material according to claim 1, wherein, The average particle diameter D250 of the second active material is 12 to 20 μm.

6. The positive electrode active material according to claim 1, wherein The ratio D150:D250 of the average particle diameter D150 of the first active material to the average particle diameter D250 of the second active material is 1:2 to 1:

10.

7. The positive electrode active material according to claim 1, wherein The specific surface area of the second active substance is 0.13 to 0.27 m 2 / g.

8. The positive electrode active material according to claim 1, wherein, Both the first active material and the second active material are lithium transition metal composite oxides containing Ni in an amount of 50 to 70 mol% based on the total number of moles of metal elements other than Li.

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

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