Positive electrode active material, nonaqueous electrolyte secondary battery, and manufacturing method for these

Abstract

To provide a positive electrode active material with which the resistance of the positive electrode can be reduced.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 containing 75 mol% or more of Ni relative to the total mole number of metal elements excluding Li. 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. A crystallite size L1 of the first active material is 80,000 Å or more. A crystallite size L2 of the second active material is 2,000 Å or less. The ratio (L003 / L104) of the crystallite size of the first active material is 1.60 to 2.0.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a positive electrode active material, a non-aqueous electrolyte secondary battery, and methods for manufacturing these.

Background Art

[0002] In non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, it is known to use a lithium transition metal composite oxide as the positive electrode active material contained in the active material layer of the positive electrode (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As the active material contained in the active material layer of the positive electrode, two types of lithium transition metal composite oxides having different particle diameters may be used. When mixing two types of active materials having different particle diameters, in order to improve the packing property in the active material layer, an active material with a high sphericity (closer to a spherical shape) may be used. When an active material with a high sphericity is used for the positive electrode, the resistance such as the DC resistance and charge transfer resistance of the non-aqueous electrolyte secondary battery may increase.

[0005] An object of the present disclosure is to provide a positive electrode active material capable of reducing the resistance when used as a positive electrode, and a non-aqueous electrolyte secondary battery capable of reducing the resistance such as DC resistance and charge transfer resistance.

Means for Solving the Problems

[0006] 〔1〕 including 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 containing 75 mol% or more of Ni with respect to the total number of moles of metal elements excluding Li. The first active material is single particles or secondary particles formed by aggregation of 2 to 10 primary particles. The second active material is secondary particles formed by aggregation of 50 or more primary particles. The crystallite size L1 of the first active material is 80,000 Å or more. The crystallite size L2 of the second active material is 2,000 Å or less. The ratio (L 003 / L 104 ) of the crystallite sizes of the first active material is 1.60 to 2.0, a positive electrode active material. 〔2〕 The positive electrode active material according to 〔1〕, containing 20 to 55% by weight of the first active material. 〔3〕 The positive electrode active material according to 〔1〕 or 〔2〕, wherein the ratio (D250 / D150) of the average particle diameter (D250) of the second active material to the average particle diameter (D150) of the first active material is 2.4 to 8.5. 〔4〕 The positive electrode active material according to any one of 〔1〕 to 〔3〕, wherein the lithium transition metal composite oxide contains at least Ni, Co, and Mn as transition metals. 〔5〕 A non-aqueous electrolyte secondary battery having an active material layer containing the positive electrode active material according to any one of 〔1〕 to 〔4〕. 〔6〕 A method for producing the positive electrode active material according to any one of 〔1〕 to 〔4〕, including a step of producing the first active material, wherein the step includes a first firing step of obtaining a fired product by firing a mixture containing a lithium compound and a nickel-containing compound in the range of 900 to 1000 °C, and a second firing step of further firing the fired product at a firing temperature lower than the firing temperature of the first firing step and for a firing time 5 times or longer than the firing time of the first firing step. A method for producing a positive electrode active material. 〔7〕 The method for producing a positive electrode active material according to 〔6〕, wherein the second firing step is performed in an atmosphere having an oxygen concentration of 90% or more. 〔8〕The firing temperature of the second firing step is 80°C or more lower than the firing temperature of the first firing step, the method for producing a positive electrode active material according to 〔6〕or 〔7〕. 〔9〕A method for manufacturing a non-aqueous electrolyte secondary battery having an active material layer containing a positive electrode active material, 〔6〕~〔8〕The method for manufacturing a positive electrode active material according to any one of them is used to manufacture the positive electrode active material, and the method for manufacturing a non-aqueous electrolyte secondary battery.

Advantages of the Invention

[0007] According to the positive electrode active material of the present disclosure, the resistance when used as a positive electrode can be reduced, and the resistance such as the DC resistance and the charge transfer resistance of the non-aqueous electrolyte secondary battery using this positive electrode can be reduced.

Embodiments for Carrying Out the Invention

[0008] In this specification, a numerical range such as "x to y" includes 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 containing 75 mol% or more of Ni with respect to the total number of moles of metal elements excluding Li. 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 crystallite size L1 of the first active material is 80,000 Å or more. The crystallite size L2 of the second active material is 2,000 Å or less. The ratio of the crystallite size of the first active material (L 003 / L104 ) is from 1.60 to 2.0.

[0010] 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 improved. Thereby, the volumetric energy density of the positive electrode obtained using the positive electrode active material can be improved.

[0011] Both the first active material and the second active material are lithium transition metal composite oxides, and the content of Ni with respect to the total number of moles of metal elements excluding Li (hereinafter also referred to as "Ni content") is 75 mol% or more. 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 78 mol% or more, may be 80 mol% or more, may be 82 mol% or more, may be 75 to 98 mol%, may be 80 to 95 mol%, or may be 82 to 90 mol%. By the Ni content of the first active material and the second active material being respectively independently within the above range, a secondary battery with a high energy density can be obtained.

[0013] The lithium transition metal composite oxide only needs to 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 ≦ 0.3 and 0.75 ≦ x ≦ 1, and Me may contain one or more selected from the group consisting of Co, Mn, Al, 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 ≤ 0.25, or may be -0.20 ≤ a ≤ 0.20. x may be 0.78 ≤ x ≤ 0.99, or may be 0.80 ≤ x ≤ 0.95. Me may contain one or more selected from the group consisting of Co, Mn, Al, Zr, Ti, Mg, Mo, and Nb, preferably contains at least one of Co and Mn, and more preferably contains Co and Mn.

[0015] The compositions of the first active material and the second active material can be determined by ICP (Inductively Coupled Plasma) emission spectrometry.

[0016] 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 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. Other active materials may be primary particles or secondary particles.

[0017] (The first active material) The first active material is a single particle or a secondary particle in which 2 to 10 primary particles are aggregated. When the first active material is a secondary particle, the number of aggregated primary particles may be 2 to 8, or may be 2 to 5. The active material may crack due to compression during the production of the positive electrode and charge / discharge of the secondary battery. When the active material cracks, the specific surface area increases, so it becomes easy to react with the electrolyte, generating gas or becoming easy to expand due to charge / discharge of the secondary battery. Since the first active material is a single particle or a secondary particle with a small number of aggregated primary particles, it is less likely to crack by the above-described compression and charge / discharge than the second active material. Therefore, when the positive electrode active material contains the first active material, it is easy to suppress gas generation from the secondary battery and expansion of the secondary battery.

[0018] The crystallite size L1 of the first active material is 80,000 Å or more, may be 85,000 Å or more, and may be 90,000 Å or more. The crystallite size L1 of the first active material is, for example, 100,000 Å or less. When the crystallite size L1 is within the above range, it is easy to suppress the generation of a fresh surface after the durability test. The crystallite size L1 is the average value of the crystallite sizes at all diffraction peaks of the first active material confirmed by the X-ray diffraction method (hereinafter also referred to as the "XRD method"), and can be measured by the method described in the examples below. The crystallite size L1 can be adjusted by the production conditions (sintering conditions, grinding conditions) of the first active material.

[0019] The ratio of the crystallite sizes of the first active material (L 003 / L 104 ) is 1.60 to 2.0, may be 1.65 to 1.90, may be 1.70 to 1.85, and may be 1.71 to 1.80. The ratio of the crystallite sizes of the first active material (L 003 / L 104 ) is an index indicating the isotropy (sphericity) of the crystal structure of the crystallites in the first active material. It can be said that the crystallites of the first active material with the ratio of crystallite sizes (L 003 / L 104 ) within the above range have a relatively large anisotropic shape. The crystallite sizes L 003 and L 104 are respectively the crystallite sizes at the diffraction peaks of the (003) plane and the (104) plane measured by XRD of the first active material, and can be measured by the method described in the examples below. The ratio of the crystallite sizes of the first active material (L 003 / L 104 ) can be adjusted by the production conditions (sintering conditions, grinding conditions) of the first active material.

[0020] Since the first active material is secondary particles with few single particles or few aggregated primary particles, it is easy to reduce the unevenness on the surface of the first active material, and it tends to become particles with a smooth surface having a small surface roughness. When the first active material having such a smooth surface is mixed with a second active material having a different average particle size, the contact area tends to be small. When the contact area between the first active material and the second active material becomes small, the resistance of electron transfer in the active material layer of the positive electrode increases, which may cause an increase in various resistance components of the secondary battery. On the other hand, since the ratio (L 003 / L 104 ) of the crystallite size of the first active material is within the above range, the crystallites in the first active material are presumed to have a flat spherical shape. Thereby, since the contact area between the first active material and the second active material can be increased, it is considered that the resistance of electron transfer in the active material layer of the positive electrode can be reduced.

[0021] The average particle diameter (D150) of the first active material may be, for example, 1 to 10 μm, 2 to 9 μm, or 3 to 8 μm. In this specification, the average particle diameter is the particle diameter (D50) at which the cumulative frequency from the smaller particle diameter in the volume-based particle size distribution becomes 50%. The volume-based particle size distribution can be measured by a laser diffraction particle size distribution measuring device.

[0022] When the total weight of the positive electrode active material is 100% by weight, the content of the first active material in the positive electrode active material is preferably 20 to 55% by weight, 25 to 50% by weight, or 30 to 45% by weight.

[0023] (The 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, 500 or more, 1,000 or more, 5,000 or more, and is usually 5×10 6 pieces or less, and may be 5×10 5 pieces or less.

[0024] The crystallite size L2 of the second active material is 2,000 Å or less, may be 1,900 Å or less, and may be 1,800 Å or less. The crystallite size L2 of the second active material is preferably 800 to 2,000 Å, may be 1,000 to 1,900 Å, may be 1,200 to 1,800 Å, and may be 1500 to 1800 Å. Since the second active material is secondary particles in which a large number of primary particles are aggregated, when the crystallite size L2 becomes small, it is easy to reduce the unevenness on the surface of the second active material and the surface roughness tends to become small. Therefore, by mixing the second active material having the crystallite size L2 within the above range and the first active material having an average particle diameter smaller than that of the second active material, it is easy to increase the contact area between the first active material and the second active material. The crystallite size L2 is the average value of the crystallite sizes at all diffraction peaks of the second active material confirmed by XRD, and can be measured by the method described in the examples below. The crystallite size L2 can be adjusted by the production conditions (sintering conditions, pulverization conditions) of the second active material.

[0025] The average particle diameter (D250) of the second active material may be, for example, 5 to 25 μm, may be 10 to 22 μm, and may be 12 to 20 μm.

[0026] The ratio (D250 / D150) of the average particle diameter (D250) of the second active material to the average particle diameter (D150) of the first active material is preferably 2.4 to 8.5, may be 2 to 8, and may be 3 to 7. When the above ratio (D250 / D150) is within the above range, it is easy to improve the fillability (packing density) in the active material layer.

[0027] When the total weight of the positive electrode active material is 100% by weight, the content of the second active material in the positive electrode active material is preferably 45 to 80% by weight, 50 to 75% by weight, and may be 55 to 70% by weight.

[0028] The second active material preferably has a spherical shape or a shape close to spherical. Thereby, the fluidity of the positive electrode active material can be improved, and when a paste containing the positive electrode active material is applied on the positive electrode current collector, the occurrence of problems such as breakage of the positive electrode current collector can be suppressed.

[0029] Ratio (L 003 / L 104 ) of the crystallite sizes of the second active material may be 1.1 to 1.9, may be 1.2 to 1.85, or may be 1.3 to 1.8. The crystallite size L 003 and L 104 of the second active material are the crystallite sizes at the diffraction peaks of the (003) plane and the (104) plane measured by XRD, and can be measured by the method described in the examples below. The ratio (L 003 / L 104 ) of the crystallite sizes of the second active material can be adjusted according to the production conditions of the second active material.

[0030] (Method for producing a positive electrode active material) The method for producing the positive electrode active material of the present embodiment includes a step of producing the first active material, and may include a step of producing the second active material. According to this production method, the above-described first active material can be obtained. In this production method, the step of producing the first active material includes a first firing step of obtaining a fired product by firing a mixture containing a lithium compound and a nickel-containing compound within a temperature range of 900 to 1000°C, and a second firing step of further firing the fired product at a firing temperature lower than the firing temperature of the first firing step and for a firing time five times or longer than the firing time of the first firing step.

[0031] The step of producing the first active material may include pulverizing the fired product obtained in the first firing step and subjecting the pulverized fired product to the second firing step.

[0032] Examples of the lithium compound include lithium hydroxide and lithium carbonate. Examples of the nickel-containing compound include, in addition to Ni, composite oxides or composite hydroxides containing the metal element represented by Me in the above formula (I).

[0033] The firing temperature of the first firing step (hereinafter also referred to as the "first firing temperature") may be 920 to 980 °C, or may be 930 to 970 °C. By adjusting the first firing temperature, the size of single particles or primary particles of the first active material can be adjusted. The time of the first firing step (hereinafter also referred to as the "first firing time") is, for example, 1 to 100 hours, may be 1 to 50 hours, or may be 1 to 10 hours. The oxygen concentration in the first firing step is, for example, 90 to 100%, may be 92 to 98%, or may be 93 to 96%.

[0034] The firing temperature of the second firing step (hereinafter also referred to as the "second firing temperature") may be lower than the first firing temperature. The second firing temperature is preferably 80 °C or more lower than the first firing temperature, more preferably 100 °C or more lower, and even more preferably 120 °C or more lower. The temperature difference between the first firing temperature and the second firing temperature is, for example, 400 °C or less. The second firing temperature is, for example, 500 to 920 °C, may be 600 to 900 °C, or may be 700 to 850 °C. By adjusting the second firing temperature, the ratio of the crystallite size (L 003 / L 104 ) of the first active material can be adjusted.

[0035] The time of the second firing step (hereinafter also referred to as the "second firing time") may be 5 times or more the length of the first firing time. The second firing time may be 5.2 times or more, or 5.5 times or more the first firing time. The second firing time is, for example, 8 times or less the first firing time. The second firing time is, for example, 5 to 500 hours, may be 5 to 100 hours, may be 7 to 30 hours, or may be 7 to 20 hours. By adjusting the second firing time, the ratio of the crystallite size (L 003 / L 104 ) of the first active material can be adjusted.

[0036] The oxygen concentration in the second firing step is preferably 90% or more, may be 95% or more, or may be 100%. By adjusting the oxygen concentration in the second firing step, it becomes easier to obtain the first active material having the above-mentioned ratio of crystallite size.

[0037] The second active material can be obtained by firing a mixture containing a lithium compound and a nickel-containing compound. The firing of the mixture in the production of the second active material may be carried out in one step or in two or more steps. By adjusting the firing conditions such as the firing temperature and the firing time, the crystallite size L2 of the second active material and the ratio of the crystallite sizes (L 003 / L 104 ) can be adjusted.

[0038] The method for producing the positive electrode active material may include a step of mixing the first active material and the second active material produced above. The first active material and the second active material can be mixed using a mixer such as a blender.

[0039] (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, according to this battery, resistances such as the DC resistance and the charge transfer resistance can be reduced.

[0040] 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.

[0041] 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.

[0042] 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 Al alloys, and any metal foil that is stable within the potential range of the positive electrode may be used.

[0043] 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 to materials for forming the active material layer such as the positive electrode active material, a binder, and a conductive material, and kneading them.

[0044] 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 and polytetrafluoroethylene; 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).

[0045] 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. A known material may be used for the negative electrode current collector. The negative electrode active material layer may contain a known negative electrode active material, a conductive material, a binder, and the like.

[0046] The separator has a base material with a single-layer structure or a multi-layer structure, and may have functional layers such as an adhesive layer and a heat-resistant layer on at least one side of the base material. The base material is, for example, a porous sheet such as a film and a non-woven fabric made of a resin such as polyolefin such as polyethylene and polypropylene.

[0047] The non-aqueous electrolyte preferably contains an electrolyte in a non-aqueous solvent such as an organic solvent. Known materials can be used for the electrolyte and the non-aqueous solvent.

[0048] (Method for manufacturing a non-aqueous electrolyte secondary battery) The manufacturing method of this battery includes the step of manufacturing a positive electrode by the manufacturing method of the positive electrode active material described above. The manufacturing method of this battery may further include the step of obtaining an electrode body using this positive electrode, a negative electrode, and a separator, and the step of housing the electrode body and the non-aqueous electrolyte in a battery case.

Example

[0049] Hereinafter, the present disclosure will be described more specifically by showing examples and comparative examples. [Measurement of average particle diameter of active material] The average particle diameters (D150 and D250) of the first active material and the second active material were measured by a laser diffraction particle size distribution measuring device.

[0050] [Calculation of crystallite sizes L1 and L2] The crystallite sizes L1 and L2 of the first active material and the second active material were determined by obtaining an XRD profile of 15 to 110° using an X-ray diffraction (XRD) device (manufactured by Rigaku, "SmartLab"). Specifically, the value Δθ of the full width at half maximum (FWHM) of each diffraction peak of the XRD profile obtained for the active material was applied to the Scherrer equation, and a structural model corrected according to the value of 2θ / θ was constructed. The crystallite size of each diffraction peak was determined by WPPF analysis of the Rietveld analysis software. The average value of the crystallite sizes determined for all the diffraction peaks obtained from the XRD profile was taken as the crystallite size (L1, L2) of the active material.

[0051] [Ratio of crystallite sizes (L 003 / L 104 ) calculation] In the procedure described in the calculation of the crystallite sizes L1 and L2, the crystallite sizes L 003 and L 104 at the diffraction peaks of the (003) plane and the (104) plane among the diffraction peaks of the XRD profile were determined, and the ratio of the crystallite sizes (L 003 / L 104 ) was calculated.

[0052] 〔Example 1〕 (Production of the positive electrode active material) A mixture containing lithium hydroxide monohydrate as a lithium compound and nickel cobalt manganese hydroxide as a nickel-containing compound was calcined at 950 °C for 2 hours to obtain a calcined product (first calcination step). After pulverizing the calcined product, the pulverized calcined product was calcined at 750 °C for 12 hours in an atmosphere with an oxygen concentration of 94% (second calcination step) to obtain a first active material. The first active material contained 83 mol% of Ni with respect to the total number of moles of metal elements excluding Li, and was a lithium transition metal composite oxide containing Co and Mn. The first active material had an average particle diameter (D150), crystallite size L1, and ratio of crystallite sizes (L 003 / L 104 ) shown in Table 1. The first active material was single particles or secondary particles formed by aggregation of 2 to 10 primary particles.

[0053] As the second active material, a lithium transition metal composite oxide having an average particle diameter (D250), crystallite size L2, and ratio of crystallite sizes (L 003 / L 104 ) shown in Table 1, containing 81.5 mol% of Ni with respect to the total number of moles of metal elements excluding Li, and containing Co and Mn was used. The second active material was secondary particles formed by aggregation of 6,000 to 10,000 primary particles. The first active material in the positive electrode active material was 40% by weight, and the second active material was 60% by weight. The positive electrode active material was obtained by mixing using a blender at 50 rpm for 5 minutes.

[0054] (Production of the positive electrode) The positive electrode active material, conductive material, binder, etc. were mixed, an appropriate amount of solvent was added, and kneaded with a kneader to obtain a mixture. The mixture was applied to a positive electrode current collector and dried, and compressed to form an active material layer, thereby obtaining a positive electrode having an active material layer formed on the positive electrode current collector.

[0055] [Examples 2 to 5, Comparative Examples 1 to 5] Except for adjusting the conditions of the first calcination step and the second calcination step, etc., according to the procedure of Example 1, the average particle diameter (D150), crystallite size L1, and ratio of crystallite sizes (L 003 / L 104A first active material having 003 / L 104 ) was obtained. The first active material was either single particles or secondary particles formed by aggregation of 2 to 10 primary particles. Also, the average particle diameter (D250), crystallite size L2, and ratio of crystallite sizes (L 003 / L 104 ) shown in Tables 1 and 2 were prepared for a second active material. The second active material was secondary particles formed by aggregation of 6,000 to 10,000 primary particles. The first active material and the second active material contained 83 mol% and 81.5 mol% of Ni, respectively, with respect to the total number of moles of metal elements excluding Li. Both the first active material and the second active material were lithium transition metal composite oxides containing Co and Mn.

[0056] A positive electrode was fabricated in the same procedure as in Example 1, except that the first active material and the second active material shown in Table 1 were used.

[0057] [Measurement of the Compaction Resistance of the Positive Electrode Active Material] The resistance values measured by compressing the positive electrode active materials (mixed powder of the first active material and the second active material) obtained in the examples and comparative examples to 0.5 MPa were taken as the compaction resistance of the positive electrode active material. It is considered that the smaller the value of the compaction resistance, the larger the contact area between the first active material and the second active material. The results are shown in Tables 1 and 2.

[0058] [Measurement of the Resistance of the Cell (Measurement of DC Resistance R s and Charge Transfer Resistance R CT )] The positive electrodes and artificial graphite negative electrodes fabricated in the examples and comparative examples were opposed to each other through a separator and housed in a battery case. Then, a non-aqueous electrolyte was injected to fabricate a laminated cell. After charging the cell to 3.7 V, a Nyquist plot was obtained at a frequency of 0.05 mHz to 5 MHz using an impedance analyzer. The real component of the impedance was taken on the horizontal axis and the imaginary component of the impedance was taken on the vertical axis in the complex plane. The DC resistance R s of the cell was calculated from the value of the intercept on the high-frequency side of the real axis, and the charge transfer resistance R CT of the cell was calculated from the value corresponding to the radius of the semi-circle drawn on the low-frequency side. The results are shown in Tables 1 and 2.

[0059] [Measurement of the Resistance of the Positive Electrode] The positive electrode taken out by disassembling the cell fabricated for the cell resistance measurement was washed and dried. The resistance of the positive electrode was measured using an electric resistance measurement system (manufactured by Hioki, "RM2610"). It can be said that the smaller the resistance of the positive electrode, the larger the contact area between the first active material and the second active material in the active material layer even after the cell is charged. The results are shown in Table 1 and Table 2.

[0060] [Table 1]

[0061] [Table 2]

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 containing 75 mol% or more of Ni with respect to the total number of moles of metal elements excluding Li, wherein the first active material is a single particle or a secondary particle formed by aggregation of 2 to 10 primary particles, wherein the second active material is a secondary particle formed by aggregation of 50 or more primary particles, wherein the crystallite size L1 of the first active material is 80,000 Å or more, wherein the crystallite size L2 of the second active material is 2,000 Å or less, The ratio of the crystallite size of the first active material (L ００３ / L １０４ ) is 1.60 to 2.0, the positive electrode active material.

2. The positive electrode active material according to claim 1, comprising 20 to 55% by weight of the first active material.

3. The average particle diameter (D ２ 50) of the second active material and the average particle diameter (D １ 50) of the first active material, and the ratio (D ２ 50 / D １ 50) is 2.4 to 8.

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

4. The positive electrode active material according to claim 1, wherein the lithium transition metal composite oxide contains at least Ni, Co, and Mn as transition metals.

5. 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 4, a non-aqueous electrolyte secondary battery.

6. A method for producing a positive electrode active material according to any one of claims 1 to 4, comprising a step of producing the first active material, wherein the step includes a first firing step of obtaining a fired product by firing a mixture containing a lithium compound and a nickel-containing compound in a range of 900 to 1000 °C, and a second firing step of further firing the fired product at a firing temperature lower than the firing temperature of the first firing step and for a firing time 5 times or longer than the firing time of the first firing step, a method for producing a positive electrode active material.

7. The method for producing a positive electrode active material according to claim 6, wherein the second firing step is performed in an atmosphere with an oxygen concentration of 90% or more.

8. The method for producing a positive electrode active material according to claim 6, wherein the firing temperature of the second firing step is 80 °C or more lower than the firing temperature of the first firing step.

9. A method for producing a non-aqueous electrolyte secondary battery having an active material layer containing a positive electrode active material, wherein the positive electrode active material is produced by the method for producing a positive electrode active material according to claim 6, a method for producing a non-aqueous electrolyte secondary battery.

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