Positive electrode active material, non-aqueous electrolyte secondary battery, and method for producing same

Abstract

The invention relates to a positive electrode active material, a non-aqueous electrolyte secondary battery, and a method for manufacturing the positive electrode active material and the non-aqueous electrolyte secondary battery. And a positive electrode active material including a first active material and a second active material having a larger average particle diameter than the first active material. Each of the first active material and the second active material is a lithium transition metal composite oxide containing at least 75 mol% of Ni with respect to the total number of moles of metal elements other than lithium. The first active material is a single particle or a secondary particle in which 2-10 primary particles are aggregated, and 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 # imgabs0 # or more. The crystallite size (L2) of the second active material is # imgabs 1 # or less. The crystallite size ratio (L003 / L104) of the first active material is 1.60 to 2.0.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material, a non-aqueous electrolyte secondary battery, and a method for manufacturing the same. 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 (for example, Japanese Patent Laid-Open No. 2021-114410) is known to be used. Summary of the Invention

[0003] 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 are sometimes used. When mixing two types of active materials having different particle diameters, in order to improve the filling property in the active material layer, an active material having a high sphericity (closer to a spherical shape) is sometimes used. When an active material having a high sphericity is used for the positive electrode, the resistance such as the DC resistance and the charge transfer resistance of the non-aqueous electrolyte secondary battery sometimes increases.

[0004] An object of the present disclosure is to provide a positive electrode active material capable of reducing the resistance when formed into a positive electrode, and a non-aqueous electrolyte secondary battery capable of reducing the resistance such as the DC resistance and the charge transfer resistance.

[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, wherein both the first active material and the second active material are lithium transition metal composite oxides containing Ni in an amount of 75 mol% or more based on the total molar amount of metal elements other than Li, 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 crystallite size L1 of the first active material is or more, the crystallite size L2 of the second active material is or less, and the ratio L 003 / L 104 of the crystallite size of the first active material is 1.60 to 2.0.

[0006] [2] The positive electrode active material according to [1], which contains 20 to 55% by weight of the first active material.

[0007] [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.

[0008] [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.

[0009] [5] 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 [4].

[0010] [6] A method for manufacturing the positive electrode active material according to any one of [1] to [4], which includes a step of manufacturing the first active material, the step including: a first firing step in which a mixture containing a lithium compound and a nickel-containing compound is fired in the range of 900 to 1000 °C to obtain a fired product; and a second firing step in which the fired product is further fired at a firing temperature lower than the firing temperature of the first firing step and for a firing time that is 5 times or more the length of the firing time of the first firing step.

[0011] [7] The method for manufacturing the 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.

[0012] [8] The method for manufacturing the positive electrode active material according to [6] or [7], wherein the firing temperature of the second firing step is lower than the firing temperature of the first firing step by 80 °C or more.

[0013] [9] A method for manufacturing a non-aqueous electrolyte secondary battery, which is a method for manufacturing a non-aqueous electrolyte secondary battery having an active material layer containing a positive electrode active material, wherein the positive electrode active material is manufactured by using the method for manufacturing the positive electrode active material according to any one of [6] 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 as long as there is no special description. 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 lower limit value. For example, by arbitrarily combining a value within the numerical range with a value described in other parts of this specification or in a table, 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 the 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 containing Ni at 75 mol% or more based on the total molar amount of metal elements other than Li. 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 crystallite size L1 of the first active material is or more. The crystallite size L2 of the second active material is or less. The ratio of the crystallite sizes of the first active material (L 003 / L 104 ) is 1.60 to 2.0.

[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. As a result, the volumetric energy density of the positive electrode obtained using the positive electrode active material can be increased.

[0019] Both the first active material and the second active material are lithium transition metal composite oxides, and the content of Ni based on the total molar amount of metal elements other than Li (hereinafter also referred to as "Ni content") is 75 mol% or more. The compositions of the first active material and the second active material may be the same as or different from each other.

[0020] The Ni content of the above 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%, may be 82 to 90 mol%. By the Ni content of the first active material and the second active material being independently within the above ranges, a secondary battery with a high 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 ≤ 0.3 and 0.75 ≤ x ≤ 1, and Me may include one or more selected from Co, Mn, Al, 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 ≤ 0.25, 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 include one or more selected from Co, Mn, Al, Zr, Ti, Mg, Mo, and Nb, preferably includes at least one of Co and Mn, and more preferably includes Co and Mn.

[0025] The compositions of the first active material and the second active material can be determined by ICP (Inductively Coupled Plasma) optical emission spectrometry.

[0026] 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 can be primary particles or secondary particles.

[0027] (The first active material)

[0028] 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 can be 2 to 8, or can be 2 to 5. The active material sometimes cracks due to compression during the manufacture of the positive electrode and charge and discharge of the secondary battery. If the active material cracks, the specific surface area increases, so it is easy to react with the electrolyte to generate gas, or it is easy to expand due to charge and discharge of the secondary battery. The first active material is single particles or secondary particles with a small number of aggregated primary particles, so it is less likely to crack due to the above-mentioned compression and charge and discharge compared with the second active material. Therefore, by including the first active material in the positive electrode active material, it is easy to suppress gas generation from the secondary battery and expansion of the secondary battery.

[0029] The crystallite size L1 of the first active material is or more, and can be or more, and can be or more. The crystallite size L1 of the first active material is, for example, As described below, when the crystallite size L1 is within the above range, it is easy to suppress the generation of new surfaces after the durability test. The crystallite size L1 is the average value of the crystallite sizes in all diffraction peaks of the first active material confirmed by the X-ray diffraction method (hereinafter also referred to as the "XRD method"). It can be measured by the method described in the examples below. The crystallite size L1 can be adjusted by the manufacturing conditions (sintering conditions, pulverization conditions) of the first active material.

[0030] The ratio of the crystallite sizes of the first active material (L 003 / L 104 ) is 1.60 to 2.0, can be 1.65 to 1.90, can be 1.70 to 1.85, and can 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 the crystallite sizes (L 003 / L 104 ) within the above range have a relatively large non-isotropic shape. The L 003 and L 104 of the crystallite sizes of the first active material are the crystallite sizes at the diffraction peaks of the (003) plane and (104) plane measured by XRD for the first active material, respectively, 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 manufacturing conditions (sintering conditions, pulverization conditions) of the first active material.

[0031] The first active material is single particles or secondary particles with a small number of aggregated primary particles. Therefore, it is easy to reduce the unevenness on the surface of the first active material and easily become particles with a smooth surface having a small surface roughness. When the first active material with such a smooth surface is mixed with the second active material having a different average particle size, the contact area tends to be small. If the contact area between the first active material and the second active material is small, the resistance to electron movement in the active material layer of the positive electrode is large, which can be a cause for an increase in various resistance components of the secondary battery. On the other hand, it is speculated that when the ratio of the crystallite sizes of the first active material (L 003 / L 104 ) is within the above range, the crystallites in the first active material have a flat spherical shape. Thus, the contact area between the first active material and the second active material can be increased, and it is considered that the resistance to electron movement in the active material layer of the positive electrode can be reduced.

[0032] The average particle diameter (D150) of the first active material may be, for example, 1 to 10 μm, may be 2 to 9 μm, and may be 3 to 8 μm. In this specification, the average particle diameter is the particle diameter (D50) at which the cumulative frequency becomes 50% from the smaller particle diameter side in the volume-based particle size distribution. The volume-based particle size distribution can be measured using a laser diffraction type particle size distribution measuring device.

[0033] When the total weight of the positive electrode active material is set to 100% by weight, the content of the first active material in the positive electrode active material is preferably 20 to 55% by weight, may be 25 to 50% by weight, and may be 30 to 45% by weight.

[0034] (Second active material)

[0035] The second active material is secondary particles formed by aggregation of 50 or more primary particles. In the second active material, the number of aggregated primary particles may be 100 or more, may be 500 or more, may be 1000 or more, may be 5000 or more, and is usually 5×10 6 pieces or less, and may be 5×10 5 pieces or less.

[0036] The crystallite size L2 of the second active material is or less, and may be or less, and may be or less. The crystallite size L2 of the second active material is preferably and may be and may be and may be Since the second active material is secondary particles formed by aggregation of a plurality of primary particles, if the crystallite size L2 becomes smaller, the unevenness on the surface of the second active material is likely to decrease, and the surface roughness tends to become smaller. Therefore, by mixing the second active material having the crystallite size L2 within the above range with the first active material having a smaller average particle diameter than 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 in all the 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 using the manufacturing conditions (sintering conditions, pulverization conditions) of the second active material.

[0037] 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.

[0038] The ratio (D250 / D150) of the average particle size (D250) of the second active material to the average particle size (D150) of the first active material is preferably 2.4 to 8.5, can be 2 to 8, and can be 3 to 7. By having the ratio (D250 / D150) within the above range, it is easy to improve the packing property (packing density) in the active material layer.

[0039] When the total weight of the positive electrode active material is set to 100% by weight, the content of the second active material in the positive electrode active material is preferably 45 to 80% by weight, can be 50 to 75% by weight, and can be 55 to 70% by weight.

[0040] The second active material is preferably spherical or near-spherical in shape. Thereby, the fluidity of the positive electrode active material can be improved, and thus when coating a mixture containing the positive electrode active material on the positive electrode current collector, adverse situations such as breakage of the positive electrode current collector can be suppressed.

[0041] The ratio of the crystallite sizes of the second active material (L 003 / L 104 ) can be 1.1 to 1.9, can be 1.2 to 1.85, and can be 1.3 to 1.8. The L 003 and L 104 of the crystallite sizes 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 of the crystallite sizes of the second active material (L 003 / L 104 ) can be adjusted by the manufacturing conditions of the second active material.

[0042] (Method for manufacturing positive electrode active material)

[0043] The method for manufacturing the positive electrode active material of the present embodiment includes a step of manufacturing the first active material, and may include a step of manufacturing the second active material. According to this manufacturing method, the above-mentioned first active material can be obtained. In this manufacturing method, the step of manufacturing the first active material includes: a first firing step in which a mixture containing a lithium compound and a nickel-containing compound is fired in the range of 900 to 1000 °C to obtain a fired product; and a second firing step in which the fired product is further fired at a firing temperature lower than the firing temperature of the first firing step and for a firing time 5 times or more the length of the firing time of the first firing step.

[0044] In the step of manufacturing the first active material, the fired product obtained in the first firing step may be pulverized, and the pulverized fired product may be supplied to the second firing step.

[0045] Examples of the lithium compound include lithium hydroxide and lithium carbonate. Examples of the nickel-containing compound include a composite oxide or a composite hydroxide containing, in addition to Ni, the metal element represented by Me in the above formula (I).

[0046] The firing temperature of the first firing step (hereinafter also referred to as "the first firing temperature") can be 920 to 980 °C, and can be 930 to 970 °C. By adjusting the first firing temperature, the size of the 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, can be 1 to 50 hours, and can be 1 to 10 hours. The oxygen concentration in the first firing step is, for example, 90 to 100%, can be 92 to 98%, and can be 93 to 96%.

[0047] The firing temperature of the second firing step (hereinafter also referred to as "the second firing temperature") only needs to 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 further 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, can be 600 to 900 °C, and can be 700 to 850 °C. By adjusting the second firing temperature, the ratio of the crystallite sizes (L 003 / L 104 ) of the first active material can be adjusted.

[0048] The time of the second firing step (hereinafter also referred to as "the second firing time") only needs to be 5 times or more the length of the first firing time. The second firing time can be 5.2 times or more the first firing time, and can be 5.5 times or more. 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, can be 5 to 100 hours, can be 7 to 30 hours, and can be 7 to 20 hours. By adjusting the second firing time, the ratio of the crystallite sizes (L 003 / L 104 ) of the first active material can be adjusted.

[0049] The oxygen concentration in the second firing step is preferably 90% or more, can be 95% or more, and can be 100%. By adjusting the oxygen concentration in the second firing step, it is easy to obtain the first active material having the above-mentioned ratio of crystallite sizes.

[0050] The second active material can be obtained by firing a mixture containing a lithium compound and a nickel-containing compound. Regarding the firing of the mixture when manufacturing the second active material, it can be carried out in one stage or in two or more stages. 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 )。

[0051] The method for manufacturing the positive electrode active material may include a step of mixing the first active material and the second active material manufactured above. The first active material and the second active material can be mixed using a mixer such as a blender.

[0052] (Non-aqueous electrolyte secondary battery)

[0053] 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 positive electrode active material. Therefore, according to this battery, it is possible to reduce resistances such as the DC resistance and the charge transfer resistance.

[0054] 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 can 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 can be disposed between the electrode body and the outer package.

[0055] 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 a wound type in which the positive electrode, the negative electrode, and the separator are wound into a laminate.

[0056] The positive electrode has a positive electrode current collector and an active material layer containing the above 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.

[0057] The active material layer can be formed, for example, by coating, drying, and compressing a binder on the positive electrode current collector. The binder can be prepared by adding a solvent to materials such as the positive electrode active material, a binder material, and a conductive material that form the active material layer and kneading them.

[0058] In addition to the above positive electrode active material, the active material layer may include a binder material and a conductive material, etc. As the binder material, for example, fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene; 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 material 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.

[0059] The negative electrode generally 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. For the negative electrode current collector, known materials can be used. The negative electrode active material layer may contain known negative electrode active materials, conductive materials, binders, and the like.

[0060] The separator has a substrate with a single-layer structure or a multi-layer structure, and functional layers such as an adhesive layer and a heat-resistant layer may be provided on at least one side of the substrate. The substrate is a porous sheet material such as a film and a non-woven fabric made of resins such as polyolefins such as polyethylene and polypropylene.

[0061] The non-aqueous electrolyte is preferably a product containing 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.

[0062] (Method for manufacturing a non-aqueous electrolyte secondary battery)

[0063] This battery has an active material layer containing a positive electrode active material, and the manufacturing method of this battery includes a step of manufacturing the positive electrode active material by using the above-described manufacturing method of the positive electrode active material. The manufacturing method of this battery may further include: a step of obtaining an electrode body using a positive electrode, a negative electrode, and a separator; and a step of housing the electrode body and the non-aqueous electrolyte in a battery case.

[0064] Examples

[0065] Examples and comparative examples are shown below to illustrate the present disclosure more specifically.

[0066] [Measurement of average particle size of active material]

[0067] The average particle sizes (D150 and D250) of the first active material and the second active material were measured using a laser diffraction particle size distribution measuring device.

[0068] [Calculation of crystallite sizes L1 and L2]

[0069] Regarding the crystallite sizes L1 and L2 of the first active material and the second active material, an XRD distribution from 15 to 110° was obtained using an X-ray diffraction (XRD) device (manufactured by RIGAKU, "SmartLab") to determine. Specifically, the value Δθ of the full width at half maximum (FWHM) of each diffraction peak of the XRD distribution obtained for the active material was substituted into the Scherrer formula, a structural model corrected according to the value of 2θ / θ was constructed, and the crystallite size of each diffraction peak was determined by the WPPF analysis of the Rietvelt analysis software. The average value of the crystallite sizes determined for all the diffraction peaks obtained from the XRD distribution was set as the crystallite size (L1, L2) of the active material.

[0070] [Ratio of crystallite sizes (L 003 / L 104Calculation of

[0071] Determine the crystallite sizes L at the diffraction peaks of the (003) plane and (104) plane in the XRD pattern according to the steps described in the calculation of crystallite sizes L1 and L2. 003 and L 104 , and calculate the ratio of crystallite sizes (L 003 / L 104 ).

[0072] [Example 1]

[0073] (Production of positive electrode active material)

[0074] 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 the calcined product was pulverized, 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 is a lithium transition metal composite oxide containing 83 mol% of Ni relative to the total molar amount of metal elements other than Li and containing Co and Mn. The first active material has an average particle size (D150), a crystallite size L1, and a ratio of crystallite sizes (L 003 / L 104 ) shown in Table 1. The first active material is a single particle or a secondary particle aggregated by 2 to 10 primary particles.

[0075] As the second active material, a lithium transition metal composite oxide having an average particle size (D250), a crystallite size L2, and a ratio of crystallite sizes (L 003 / L 104 ) shown in Table 1, containing 81.5 mol% of Ni relative to the total molar amount of metal elements other than Li and containing Co and Mn was used. The second active material is a secondary particle aggregated by 6000 to 10000 primary particles. The positive electrode active material was mixed at 50 rpm for 5 minutes using a blender so that the first active material in the positive electrode active material was 40% by weight and the second active material was 60% by weight to obtain a positive electrode active material.

[0076] (Production of positive electrode)

[0077] Mix the positive electrode active material, conductive material, binder material, etc., add an appropriate amount of solvent, and knead with a kneader to obtain a mixture. The mixture was coated on the positive electrode current collector, 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.

[0078] [Examples 2 to 5, Comparative Examples 1 to 5]

[0079] In addition to adjusting the conditions of the first firing process and the second firing process, etc., according to the steps of Example 1, the first active material having the average particle diameter (D150), the crystallite size L1, and the ratio of crystallite sizes (L 003 / L 104 ) shown in Tables 1 and 2 was obtained. The first active material is a single particle or a secondary particle formed by aggregation of 2 to 10 primary particles. In addition, a second active material having the average particle diameter (D250), the crystallite size L2, and the ratio of crystallite sizes (L 003 / L 104 ) shown in Tables 1 and 2 was prepared. The second active material is a secondary particle formed by aggregation of 6000 to 10000 primary particles. The first active material contains 83 mol% of Ni relative to the total molar amount of metal elements other than Li, and the second active material contains 81.5 mol% of Ni relative to the total molar amount of metal elements other than Li. Both the first active material and the second active material are lithium transition metal composite oxides containing Co and Mn.

[0080] Except for using the first active material and the second active material shown in Tables 1 and 2, a positive electrode was fabricated by the same steps as those of Example 1.

[0081] [Measurement of Pressing Resistance of Positive Electrode Active Material]

[0082] The resistance value measured by compressing the positive electrode active material (mixed powder of the first active material and the second active material) obtained in the examples and comparative examples to 0.5 MPa was defined as the pressing resistance of the positive electrode active material. It is considered that the smaller the value of the pressing 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.

[0083] [Measurement of Resistance of Battery Cell (Measurement of DC Resistance R S and Charge Transfer Resistance R CT )]

[0084] The positive electrode and artificial graphite negative electrode fabricated in the examples and comparative examples were opposed to each other via a separator, and after being housed in a battery case, a non-aqueous electrolyte was injected to fabricate a laminated battery cell (cell). After charging the battery cell to 3.7 V, a Nyquist curve was obtained using an impedance analyzer at a frequency of 0.05 mHz to 5 MHz. On the complex plane, the real part of the impedance was taken on the horizontal axis and the imaginary part of the impedance was taken on the vertical axis. The DC resistance R s of the battery 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 battery cell was calculated from the value corresponding to the radius of the semicircle drawn on the low-frequency side. The results are shown in Tables 1 and 2.

[0085] [Measurement of Resistance of Positive Electrode]

[0086] The battery cell fabricated for the resistance measurement of the battery cell was disassembled, and the removed positive electrode was washed and dried. The resistance of the positive electrode was measured using a 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 after charging the battery cell. The results are shown in Tables 1 and 2.

[0087] [Table 1]

[0088]

[0089] [Table 2]

[0090]

[0091] As described above, the embodiments of the present invention have been described. However, it should be considered that the embodiments disclosed this time 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 size 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 Ni at 75 mol% or more relative to the total number of moles of metal elements other than lithium, 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 crystallite size L1 of the first active substance is or more. The crystallite size L2 of the second active material is hereinafter The ratio L of the microcrystalline size of the first active substance 003 / L 104 is 1.60 to 2.

0.

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

3. The positive electrode active material according to claim 1, wherein, The ratio D250 / D150 of the average particle size D250 of the second active material to the average particle size D150 of the first active material is 2.4 to 8.

5.

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. 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 claims 1 to 4.

6. A method for manufacturing the positive electrode active material according to any one of claims 1 to 4, comprising a step of manufacturing the first active material, the step including: a first firing step in which a mixture containing a lithium compound and a nickel-containing compound is fired in the range of 900 to 1000 °C to obtain a fired product, and a second firing step in which the fired product is further fired at a firing temperature lower than the firing temperature of the first firing step and for a firing time 5 times or more the length of the firing time of the first firing step.

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

8. The method for manufacturing 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 manufacturing a non-aqueous electrolyte secondary battery, which is a method for manufacturing a non-aqueous electrolyte secondary battery having an active material layer containing a positive electrode active material, wherein, The positive electrode active material is manufactured by the method for manufacturing the positive electrode active material according to any one of claims 6 to 8.

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