Positive electrode active material and nonaqueous electrolyte secondary battery

Abstract

To provide a positive electrode active material that can improve the output characteristic of a nonaqueous electrolyte secondary battery while improving the fluidity of a first active material.SOLUTION: A 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. Both the first active material and the second active material are lithium transition metal complex oxide. The first active material is a single particle or a secondary particle in which two to ten primary particles are aggregated. 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) obtained from a scanning type electron microscope image of the single particle or the primary particle of the first active material to the average particle diameter of the first active material (D150) is 0.80 or more. A diffraction peak intensity ratio (I003 / I104) of the first active material in the X-ray diffraction method is 1.6 or more.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 Art

[0002] In non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, it is known to use lithium transition metal composite oxides as the positive electrode active material contained in the active material layer of the positive electrode. As the active material contained in the active material layer of the positive electrode, two types of active materials having different particle diameters may be mixed and used (see Patent Document 1, etc.). It is also known to use single particles and particles with a small number of aggregated primary particles (hereinafter also referred to as "single particles, etc.") as the active material used for the positive electrode (see Patent Document 2, etc.).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since single particles, etc. have a small particle diameter and a distorted particle shape, they tend to have poor fluidity. When forming an active material layer by mixing two types of active materials having different particle diameters, the active material with poor fluidity can cause a decrease in the filling property of the active material layer. In order to improve the filling property of the active material layer, it is conceivable to improve the fluidity of single particles, etc. However, when forming an active material layer containing two types of active materials having different particle diameters, using single particles, etc. with excellent fluidity sometimes results in a decrease in the output characteristics of the non-aqueous electrolyte secondary battery.

[0005] The present disclosure aims 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 that is a single particle or a secondary particle formed by aggregation of 2 to 10 primary particles, and a non-aqueous electrolyte secondary battery using the same.

Means for Solving the Problems

[0006] 〔1〕 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 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) obtained from a scanning electron microscope image of the single particle or primary particle of the first active material to the average particle diameter (D150) of the first active material is 0.80 or more, the intensity ratio (I 003 / I 104 ) of the diffraction peak in the X-ray diffraction method of the first active material is 1.6 or more, a positive electrode active material. 〔2〕 The positive electrode active material according to 〔1〕, wherein the ratio (R / D150) is 0.84 or more. 〔3〕 The positive electrode active material according to 〔1〕 or 〔2〕, wherein the intensity ratio (I 003 / I 104 ) is 1.7 or more. 〔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. 〔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. 〔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. 〔7〕 The specific surface area of the second active material is 0.13 to 0.27 m 2The positive electrode active material according to any one of [1] to [6], which is / g. 〔8〕 The first active material and the second active material are both lithium transition metal composite oxides containing 50 to 70 mol% of Ni with respect to the total number of moles of metal elements excluding Li, and the positive electrode active material according to any one of [1] to [7]. 〔9〕 A non-aqueous electrolyte secondary battery having an active material layer containing the positive electrode active material according to any one of [1] to [8].

Advantages of the Invention

[0007] According to the positive electrode active material of the present disclosure, the output characteristics of the non-aqueous electrolyte secondary battery can be improved while improving the fluidity of the first active material.

Mode for Carrying Out the Invention

[0008] 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 numerical value arbitrarily selected from within the numerical range may be used as a new upper limit value or lower limit value. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described in another part of this specification, in a table, or in a figure, etc.

[0009] (Positive electrode active material) The positive electrode active material of the present embodiment is used, for example, in an active material layer of 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 diameter 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 in which 2 to 10 primary particles are aggregated. 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) obtained from a scanning electron microscope (hereinafter also referred to as "SEM") image of a single particle or a primary particle of the first active material to the average particle diameter (D150) of the first active material is 0.80 or more. The intensity ratio (I of the diffraction peak in the X-ray diffraction (hereinafter also referred to as "XRD") method of the first active material003 / I 104 ) is 1.6 or more.

[0010] Since the positive electrode active material contains the first active material and the second active material, the packing property of the positive electrode active material in the active material layer can be improved, so that the volume energy density of the positive electrode obtained using the positive electrode active material can be improved. By using the first active material having a relatively small average particle diameter as single particles or secondary particles in which 2 to 10 primary particles are aggregated, the cycle characteristics of the secondary battery can be improved.

[0011] 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") with respect to the total number of moles of metal elements excluding 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 may be different from each other.

[0012] The Ni content of the 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 greater than the Ni content of the second active material. By the Ni contents of the first active material and the second active material being independently within the above ranges, a secondary battery with improved volume energy density can be obtained.

[0013] The lithium transition metal composite oxide may contain Li and Ni, but preferably contains at least Ni, Co, and Mn as transition metals. 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 0.5 ≦ x ≦ 0.7, and Me may contain one or more selected from the group consisting of Co, Mn, Al, B, Zr, Ti, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, and Si.

[0014] In the above formula (i), a may be -0.25 ≤ a ≤ 0.15, or -0.20 ≤ a ≤ 0.10. x may be 0.52 ≤ x ≤ 0.68, or 0.55 ≤ x ≤ 0.65, or 0.55 ≤ x ≤ 0.60. Me may contain one or more selected from the group consisting of Co, Mn, Al, B, Zr, Ti, Mg, Mo, and Nb, 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) emission spectrometry.

[0015] The positive electrode active material may contain other active materials 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 materials include lithium transition metal composite oxides in which the Ni content is outside the above range, or compounds other than lithium transition metal composite oxides. The other active material may be primary particles (single particles) or secondary particles.

[0016] (The first active material) The first active material is single particles or secondary particles in which 2 to 10 primary particles are aggregated. When the first active material is secondary particles, the number of aggregated primary particles may be 2 to 8, or 2 to 5. By including the first active material in which the positive electrode active material is single particles or secondary particles with a small number of aggregated primary particles, the cycle characteristics of the secondary battery can be improved.

[0017] 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.

[0018] It can be said that the above ratio (R / D150) is an index indicating that the first active material is single particles. It can be said that the larger the value, the larger the content ratio of single particles. On the other hand, the smaller the above ratio (R / D150), the larger the content ratio of aggregated particles (secondary particles), and it can be said that the primary particles are likely to aggregate. In the first active material with a small particle size, the aggregability of the particles easily affects the fluidity. Therefore, when the ratio (R / D150) is within the above range, the fluidity of the first active material can be improved. Thereby, it is considered that the filling property of the positive electrode active material in the active material layer can be improved, and the volume energy density of the positive electrode obtained using the positive electrode active material can be improved.

[0019] The average particle diameter (R) may be, for example, 1.7 to 6 μm, may be 2 to 5 μm, or may be 2.5 to 4.5 μm. The average particle diameter (R) is a value obtained from the SEM image of the single particles or primary particles of the first active material by observing the surface of the first active material with SEM. As described in the examples below, the SEM images of the surfaces of a plurality of first active materials are subjected to image analysis to determine the longest diameter of the single particles or primary particles of each first active material, and this is the average value of a plurality of first active materials.

[0020] The average particle diameter (D150) is preferably 2 to 6 μm, may be 3 to 5 μm, or may be 4 to 5 μm. In this specification, the average particle diameter (D50) is the particle diameter at which the cumulative frequency from the smaller particle diameter in the volume-based particle size distribution reaches 50%, and the average particle diameter (D150) is the average particle diameter (D50) of the first active material. The volume-based particle size distribution can be measured by a particle size distribution measuring device.

[0021] The intensity ratio (I 003 / I 104 ) of the diffraction peaks in the XRD method of the first active material is 1.6 or more, preferably 1.7 or more, and may be 1.75 or more. The intensity ratio (I 003 / I 104 ) may be 1.6 to 2, may be 1.7 to 1.9, or may 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 crystallites in the first active material. When the intensity ratio (I 003 / I 104 ) increases, the crystal structure of the crystallites of the first active material becomes more anisotropic, and it is considered that the region contributing to the insertion and desorption of Li ions increases. The intensities I 003 and I 104 of the diffraction peaks of the first active material are the intensities of the diffraction peaks on the (003) plane and the (104) plane measured by the XRD method of the first active material, respectively, and can be measured by the method described in the examples below. The intensity ratio (I 003 / I 104 ) can be adjusted, for example, by the manufacturing conditions of the first active material described below.

[0022] Increasing the above ratio (R / D150) of the first active material can improve the fluidity of the first active material, but since the content ratio of the secondary particles in which the primary particles are aggregated becomes small, the specific surface area of the first active material tends to become small. When the specific surface area of the first active material becomes small, the output characteristics of the secondary battery tend to deteriorate. On the other hand, by setting the intensity ratio (I 003 / I 104 ) of the first active material within the above range, it is considered that the region contributing to the insertion and desorption of Li ions can be increased, and thus the output characteristics of the secondary battery can be improved.

[0023] The crystallite size L1 of the first active material is preferably 900 to 1200 Å, may be 950 to 1150 Å, or may be 1000 to 1120 Å. The crystallite size L1 is calculated by applying the value of the full width at half maximum of the intensity I 104 of the diffraction peak of the first active material to the Scherrer equation.

[0024] When the total mass of the positive electrode active material is 100% by mass, the content of the first 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.

[0025] The first active material can be produced 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, and a second firing step of firing a second mixture containing the fired product and a metal-containing compound. The production 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.

[0026] 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 transition metal-containing compound include a composite oxide or composite hydroxide containing a transition metal 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% with respect to the total number of moles of the metal elements contained in the first mixture.

[0027] The firing temperature of the first firing step is preferably 700 to 1000 °C, and the firing time of the first firing step is preferably 3 to 7 hours.

[0028] Examples of the metal-containing compound include an oxide or hydroxide containing the metal element represented by Me in the formula (i), and preferably an oxide or hydroxide containing a metal element other than transition metals such as Al and B. The metal-containing compound may be an oxide or hydroxide containing a metal element including a transition metal.

[0029] The firing temperature of the second firing step is preferably 300 to 600 °C, and the firing time of the second firing step is preferably 3 to 10 hours.

[0030] By adjusting the firing conditions in the first firing step and the second firing step, the crushing conditions of the fired product obtained in the first firing step or the second firing step, etc., the ratio (R / D150) and strength ratio (I 003 / I 104 ) etc. of the first active material can be adjusted.

[0031] (Second active material) The second active material is secondary particles in which 50 or more primary particles are aggregated. In the second active material, the number of aggregated primary particles may be 100 or more, may be 1000 or more, may be 10000 or more, and is usually 5×10 6 pieces or less, and may be 5×10 5 pieces or less.

[0032] The average particle diameter (D250) of the second active material is preferably 12 to 20 μm, may be 13 to 19 μm, or may be 14 to 18 μm.

[0033] 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, may be 1:3 to 1:8, may be 1:3.5 to 1:7, or may be 1:3.5 to 1:8. When the ratio (D150:D250) is within the above range, the packing property of the positive electrode active material in the active material layer can be improved, and the volume energy density of the positive electrode can be improved.

[0034] The specific surface area (BET) of the second active material is preferably 0.13 to 0.27 m 2 / g, may be 0.15 to 0.25 m 2 / g, or may be 0.17 to 0.23 m 2 / g. The specific surface area can be measured using a specific surface area measuring device. When the specific surface area of the second active material is within the above range, it is easy to improve the output characteristics of the secondary battery.

[0035] The crystallite size L2 of the second active material is preferably 400 to 900 Å, may be 500 to 880 Å, or may be 600 to 850 Å. The crystallite size L2 is the intensity I of the diffraction peak of the second active material 104 calculated by applying the value of the full width at half maximum to the Scherrer equation.

[0036] 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 when the total mass of the positive electrode active material is 100% by mass.

[0037] The second active material can be produced, for example, through a two-step sintering process as described in the production method of the first active material. By adjusting the sintering conditions and crushing conditions, a second active material having the above-described characteristics can be obtained.

[0038] (Non-aqueous electrolyte secondary battery) 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 volume energy density of the positive electrode can be improved, and the output characteristics of this battery can be improved.

[0039] This battery usually 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 can include an exterior body having an opening and a sealing plate that seals the opening. The exterior body and the sealing plate can be formed using a metal such as Al, an Al alloy, iron, or an iron alloy, and can be formed using, for example, an Al laminate film. A resin sheet as an electrode holder may be disposed between the electrode body and the exterior body.

[0040] The electrode body may include a positive electrode, a negative electrode, and a 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 with the separator interposed therebetween. 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.

[0041] 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, for example, a metal foil composed of an Al material such as Al and an Al alloy, and any metal foil that is stable within the potential range of the positive electrode may be used.

[0042] The active material layer can be formed, for example, by applying a binder on the 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 the positive electrode active material, a binder, and a conductive material, and kneading them.

[0043] In addition to the above-described positive electrode active material, the active material layer may contain a binder and a conductive material, etc. Examples of the binder 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 the conductive material include carbon materials. The carbon material includes, for example, one or more selected from the group consisting of fibrous carbon, carbon black, coke, and activated carbon. Examples of the fibrous carbon include carbon nanotubes (CNT).

[0044] 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 composed of a Cu material such as copper and a copper alloy. The negative electrode active material layer contains a negative electrode active material and may further contain a conductive material, a binder, etc.

[0045] Known materials can be used as the negative electrode active material. Examples include carbon-based active material particles such as graphite, and metal-based active material particles containing elements 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; styrene butadiene rubber (SBR). CMC can also be used as a thickening agent.

[0046] The separator may have a substrate with a single-layer structure or a multilayer structure, and may have a functional layer on at least one side of the substrate. The substrate may be a porous sheet such as a film and a nonwoven fabric made of a resin such as polyolefin, polyester, cellulose, and polyamide, such as polyethylene and polypropylene. Examples of the functional layer include an adhesive layer and / or a heat-resistant layer. The adhesive layer can be formed by, for example, an adhesive. The heat-resistant layer can 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.

Examples

[0048] Hereinafter, the present disclosure will be described more specifically by showing examples and comparative examples. [Measurement of average particle diameters (D150 and D250) of active materials] The average particle diameters (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).

[0049] [Measurement of the average particle diameter (R) of the first active substance and calculation of the ratio (R / D150)] Using a scanning electron microscope (SEM), SEM images of the particle surfaces of the first active substance were obtained. Using image analysis software Mac-View (manufactured by MOUNTECH), more than 10 of the first active substances in the SEM images were randomly selected. When the first active substance is a secondary particle, the outer shape of the primary particle was specified, and for all the primary particles contained in each first active substance, the length of the longest part (longest length) of the diameter was determined, and the average value of the longest lengths of each primary particle was taken as the longest diameter of the first active substance. When the first active substance is a single particle, the longest diameter was determined after specifying the outer shape of the single particle and taken as the longest diameter of the first active substance. The longest diameters of each first active substance determined in this way were averaged for the above-mentioned more than 10 first active substances selected, and this was taken as the average particle diameter (R) of the first active substance. From the average particle diameter (R) of the first active substance and the average particle diameter (D150) obtained above, the ratio (R / D150) was calculated.

[0050] [Intensity ratio (I 003 / I 104 ), calculation of crystallite sizes L1 and L2] 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 measurements of the first active substance filled in a dedicated folder were performed by the reflection method. In the XRD profile obtained by the XRD measurement, the intensity I 003 of the diffraction peak of the (003) plane that appears at 2θ = 18~19°, and the intensity I 104 of the diffraction peak of the (104) plane that appears at 2θ = 44~45°, from which the intensity ratio (I 003 / I 104 ) was calculated.

[0051] The intensity I 104The value of the full width at half maximum (FWHM) was applied to Scherrer's equation to calculate the crystallite size L1 of the first active material. In the same procedure as above, XRD measurement was performed on the second active material, and the crystallite size L2 was calculated from the intensity I 104 of the diffraction peak.

[0052] [Measurement of Specific Surface Area of Second Active Material] The specific surface area of the second active material was measured using a specific surface area measuring device (manufactured by MOUNTECH, Macsorb HM model-1208).

[0053] [Examples 1 and 2, Comparative Examples 1 to 4] [Fabrication of Positive Electrode] As the first active material, a lithium transition metal composite oxide having an average particle diameter (D150), a ratio of average particle diameters (R / D150), an intensity ratio (I 003 / I 104 ), and a crystallite size L1 shown in Table 1, containing at least Ni, Co, and Mn, and having a Ni:Co:Mn = 60:20:20 (mol% ratio) was prepared. The first active material was single particles or secondary particles in which 2 to 5 primary particles were aggregated.

[0054] As the second active material, a lithium transition metal composite oxide having an average particle diameter (D250), a specific surface area (BET), and a crystallite size L2 shown in Table 1, containing at least Ni, Co, and Mn, and having a Ni:Co:Mn = 55:20:25 (mol% ratio) was prepared. The second active material was secondary particles in which 100 or more primary particles were aggregated.

[0055] 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 applied to an aluminum foil as a positive electrode current collector, dried, and rolled using a rolling roller to form an active material layer, and then cut to the electrode size and an aluminum tab was attached to obtain a positive electrode.

[0056] (Fabrication of Negative Electrode) 98 parts by mass of the negative electrode active material, 1 part by mass of CMC as a thickener, 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 applied to a copper foil as a negative electrode current collector, dried, and rolled using a rolling roller to form a negative electrode active material layer. Then, it was cut to the electrode size, and a nickel tab was attached to obtain a negative electrode.

[0057] (Fabrication of a non-aqueous electrolyte secondary battery) The positive electrode and the negative electrode prepared above were laminated through a separator made of polyolefin to obtain a laminated electrode body. The laminated electrode body was housed in a battery case composed of an aluminum laminate sheet, and after injecting a non-aqueous electrolyte, the opening of the battery case was sealed to obtain a test cell as a secondary battery. The non-aqueous electrolyte was prepared by adding LiPF6 as an electrolyte at a concentration of 1 mol / L to a mixed solvent of EC and EMC mixed at EC:EMC = 30:70 (volume ratio), and adding vinylene carbonate so as to be 0.3% by mass based on the mass of the mixed solvent.

[0058] [Evaluation of the fluidity of the first active material] 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). The results are shown in Table 1.

[0059] [Evaluation of the output characteristics of the test cell] To evaluate the output characteristics of the test cell, the internal resistance (DCIR) of the test cell was measured at 25 °C when the state of charge (SOC) of the test cell prepared above was 50% (the charge capacity relative to the initial discharge capacity was 50%). The results are shown in Table 1.

[0060]

Table 1

[0061] As shown in Table 1, in Examples 1 and 2, the angle of repose of the first active material is 45° or less, and the internal resistance of the test cell is 0.080 Ω or less. From this, it can be seen that by controlling the ratio of the average particle diameter (R / D150) and the intensity ratio of the diffraction peak (I 003 / I 104 ) of the first active material, it is possible to improve the output characteristics of the test cell while improving the fluidity of the first active material contained in the positive electrode active material.

Claims

1. 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 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 / D １ 50) of the average particle diameter (R) obtained from a scanning electron microscope image of single particles or primary particles of the first active material to the average particle diameter (D １ 50) of the first active material is 0.80 or more, １ and １ 50) is The intensity ratio (I ００３ / I １０４ ) of the diffraction peak in the X-ray diffraction method of the first active material is 1.6 or more, and it is a positive electrode active material.

2. The ratio (R / D １ 50) is 0.84 or more, and the positive electrode active material according to claim 1.

3. The strength ratio (I ００３ / I １０４ ) is 1.7 or more. The positive electrode active material according to claim 1.

4. The average particle diameter (D １ 50) of the first active material is 2 to 6 μm, and the positive electrode active material according to claim 1.

5. The average particle diameter (D ２ 50) of the second active material is 12 to 20 μm, and the positive electrode active material according to claim 1.

6. The average particle diameter (D １ 50) of the first active material and the average particle diameter (D ２ 50) of the second active material, and the ratio (D １ 50:D ２ 50) is 1:2 to 1:

10. The positive electrode active material according to claim 1.

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

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 50 to 70 mol% of Ni with respect to the total number of moles of metal elements excluding Li.

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

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