Positive electrode active material and method for producing a positive electrode active material

Abstract

Reduction of initial resistance. [Solution] A positive electrode active material comprising a layered lithium transition metal composite oxide, wherein the volume-based particle size distribution of the positive electrode active material is 0.1

Description

Technical Field

[0001] The present disclosure relates to a positive electrode active material and a method for manufacturing the positive electrode active material.

Background Art

[0002] Japanese Patent Application Laid-Open No. 2024-65999 (Patent Document 1) discloses a positive electrode active material for a lithium ion secondary battery, in which the ratio of the content of boron (B) to the content of carbon (C) is within a predetermined range, and the variation in particle size is within a predetermined range.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The positive electrode active material of Patent Document 1 suppresses the content of compounds that cause an increase in resistance, such as lithium carbonate, by containing B at a predetermined ratio, and reduces the reaction resistance. Further, by making the variation in the particle size of the positive electrode active material within a predetermined range, the mixing of coarse particles and fine particles is suppressed, and the output resistance is increased. However, there is room for improvement in reducing the initial resistance.

[0005] An object of the present disclosure is to reduce the initial resistance.

Means for Solving the Problems

[0006] [1] A positive electrode active material, The positive electrode active material contains a layered lithium transition metal composite oxide, In the volume-based particle size distribution of the positive electrode active material, the relationship of 0.1 < f2 / f1 ≦ 25 is satisfied, The f1 is the maximum frequency in the range where the maximum Feret diameter is 1 μm or more and 3 μm or less, The aforementioned f2 is a positive electrode active material whose maximum frequency is in the range of 5 μm to 25 μm in terms of maximum Ferret diameter.

[0007] By using a positive electrode active material that satisfies the relationship described in [1] above, the contact between positive electrode active materials, i.e., the conductive path, can be increased. This is expected to reduce the initial resistance.

[0008] [2] The positive electrode active material according to [1], wherein the volume-based particle size distribution of the positive electrode active material satisfies the relationship 0.5 ≤ f2 / f1 ≤ 3.0.

[0009] By using a positive electrode active material that satisfies the relationship described in [2] above, in addition to reducing initial resistance, improved durability can also be expected.

[0010] [3] The positive electrode active material according to [1] or [2], comprising single crystal particles and polycrystalline particles formed by the association of the single crystal particles.

[0011] [4] The lithium transition metal composite oxide has the general formula: Li x Ni a Co b Mn c O y It has a composition represented by, A positive electrode active material described in any of [1] to [3] that satisfies the following relationships: 0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, and 1.5≦y≦2.1.

[0012] A method for producing a positive electrode active material as described in [5] [1], (a) Prepare the precursor, (b) Prepare a mixture by mixing the precursor and the lithium compound. (c) Preparing a calcined product by calcining the mixture, (d) Washing the calcined material and preparing the positive electrode active material, The precursor contains a transition metal compound, The transition metal compound contains at least nickel, A method for producing a positive electrode active material, wherein a ratio of the amount of lithium in the lithium compound to the total amount of the transition metal in the transition metal compound is more than 1.0 and less than 2.0.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a schematic flowchart showing a method for producing a positive electrode active material in this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a lithium ion secondary battery of this embodiment. [Figure 3] FIG. 3 is a table showing experimental results. [Figure 4] FIG. 4 is an example of a particle size distribution of a positive electrode active material based on volume.

Modes for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "this embodiment"), and examples of the present disclosure (hereinafter may be abbreviated as "this example") will be described. However, this embodiment and this example do not limit the technical scope of the present disclosure.

[0015] The chemical composition of the positive electrode active material can be measured by ICP-AES (Inductively coupled plasma atomic emission spectroscopy). A sample solution is prepared by dissolving 0.1 g of a sample (positive electrode active material) in a mixed acid (10 ml) of hydrochloric acid and sulfuric acid. The sample solution is diluted to an appropriate concentration with a volumetric flask. After dilution, a composition analysis is performed by an ICP-AES apparatus. For example, a product name such as "PS3520 UVDD II (manufactured by Hitachi High-Technologies Corporation)" may be used.

[0016] In this specification, when a compound is represented by a stoichiometric formula such as "LiCoO2", this formula is merely a representative example. For example, when lithium cobaltate is represented as "LiCoO2", unless otherwise specified, lithium cobaltate is not limited to the composition ratio of "Li / Co / O = 1 / 1 / 2", but may contain Li, Co, and O in any composition ratio. The composition ratio may also be non-stoichiometric.

[0017] In this specification, the volume-based particle size distribution can be measured by a laser diffraction particle size distribution analyzer. The measurement procedure may be as follows: The material to be measured (positive electrode active material) is prepared. The material to be measured and the dispersion medium are mixed to prepare a sample (particle dispersion). The sample is introduced into a laser diffraction particle size distribution analyzer to measure the volume-based particle size distribution.

[0018] In this specification, "maximum Ferret diameter" refers to the distance between the two furthest points on the particle's contour line. The maximum Ferret diameter is measured in scanning electron microscope (SEM) images.

[0019] <Cathode active material> The positive electrode active material of this embodiment can reversibly intercept and release lithium ions. The positive electrode active material includes a layered lithium transition metal composite oxide. The positive electrode active material may be a positive electrode active material consisting of a layered lithium transition metal composite oxide. The lithium transition metal composite oxide includes lithium (Li), a transition metal (TM), and oxygen (O). TM includes at least nickel (Ni). The lithium transition metal composite oxide may be at least one selected from the group consisting of LiNiO2, Li(NiCoMn)O2, and Li(NiCoAl)O2. Among these, Li(NiCoMn)O2 is preferred because it has particularly excellent resistance characteristics. Such a lithium transition metal composite oxide preferably has a composition represented by the following general formula. Li x Ni a Co b Mnc O y In the above formula, the relationships of 0.1 ≦ x ≦ 1.5, 0.5 ≦ a ≦ 1.0, 0 ≦ b ≦ 0.3, 0 ≦ c ≦ 0.3, a + b + c = 1.0, and 1.5 ≦ y ≦ 2.1 are satisfied.

[0020] In the particle size distribution based on the volume of the positive electrode active material, the relationship of 0.1 < f2 / f1 ≦ 25 is satisfied. f1 is the maximum frequency (%) in the range where the maximum Feret diameter is 1 μm or more and 3 μm or less, and f2 is the maximum frequency (%) in the range where the maximum Feret diameter is 5 μm or more and 25 μm or less.

[0021] By using a positive electrode active material that satisfies such a relationship, the contact between the positive electrode active materials, that is, the conductive path can be increased. Thereby, a reduction in the initial resistance is expected.

[0022] f2 / f1 may be, for example, 0.3 or more, 0.33 or more, 0.5 or more, 0.58 or more, 1.0 or more, 1.5 or more, or 2.0 or more. f2 / f1 may be, for example, 20.5 or less, 20 or less, 15 or less, 10 or less, 5.33 or less, 5.0 or less, or 3.0 or less. f2 / f1 may satisfy, for example, the relationship of 0.5 ≦ f2 / f1 ≦ 3.0. Thereby, in addition to the reduction in the initial resistance, an improvement in durability is also expected. f2 / f1 may satisfy, for example, the relationship of 2.0 ≦ f2 / f1 ≦ 3.0. Thereby, a further improvement in durability is expected.

[0023] f1 may be, for example, 0.3 or more, 0.5 or more, 1.0 or more, 1.5 or more, 1.98 or more, or 2.0 or more. f1 may be, for example, 7.0 or less, 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, or 3.5 or less. f2 may be, for example, 0.75 or more, 1.0 or more, 1.5 or more, 2.0 or more, 2.5 or more, 3.0 or more, 3.5 or more, or 4.0 or more. f2 may be, for example, 10 or less, 9.0 or less, 8.5 or less, 8.0 or less, 7.5 or less, 7.0 or less, 6.5 or less, or 6.0 or less.

[0024] In the volume-based particle size distribution of the positive electrode active material, one peak may appear. The peak may be in the range of 1 μm to 3 μm, or in the range of 5 μm to 25 μm.

[0025] In the volume-based particle size distribution of the positive electrode active material, two peaks may appear. One of the two peaks may be the main peak and the other the shoulder peak (subpeak). The peak top of the main peak is higher than the peak top of the shoulder peak. If the peak top of the main peak is in the range of 1 μm to 3 μm, the peak top of the shoulder peak may be in the range of 5 μm to 25 μm. If the peak top of the main peak is in the range of 5 μm to 25 μm, the peak top of the shoulder peak may be in the range of 1 μm to 3 μm.

[0026] The positive electrode active material may contain single-crystal particles and polycrystalline particles. Polycrystalline particles are formed by the association (assembly) of multiple single-crystal particles. Single-crystal particles and polycrystalline particles can be identified by SEM imaging. In this embodiment, the composition of the single-crystal particles and polycrystalline particles is the same.

[0027] Single-crystal particles are, so to speak, small particles. A single-crystal particle is an independent, unaggregated particle, essentially consisting of a single particle, and is a particle in which grain boundaries cannot be seen in SEM images. Single-crystal particles have a relatively smaller particle size compared to polycrystalline particles.

[0028] Polycrystalline particles are, so to speak, large particles. Polycrystalline particles are particles formed by the association (assembly) of multiple single-crystal particles. Polycrystalline particles have a relatively larger particle size compared to single-crystal particles.

[0029] Single-crystal grains may have a maximum Ferret diameter of 1 μm to 3 μm. That is, f1 may be the maximum frequency of single-crystal grains. Polycrystalline grains may have a maximum Ferret diameter of 5 μm to 25 μm. That is, f2 may be the maximum frequency of polycrystalline grains.

[0030] The polycrystalline particles in this embodiment differ from conventional polycrystalline particles. The two can be distinguished, for example, by the maximum Ferret diameter and aspect ratio of single-crystal particles observed from SEM images. For instance, single-crystal particles contained within the polycrystalline particles of this embodiment may have a maximum Ferret diameter equivalent to that of a single-crystal particle existing independently. On the other hand, single-crystal particles contained within conventional polycrystalline particles are thought to have a smaller maximum Ferret diameter than single-crystal particles existing independently.

[0031] When the positive electrode active material contains both single-crystal and polycrystalline particles, the positive electrode active material in this embodiment differs from conventional positive electrode active materials that are mixtures of single-crystal and polycrystalline particles. The two can be distinguished, for example, by the maximum Ferret diameter of the single-crystal particles as seen in SEM images. For example, the average value of the maximum Ferret diameter of the single-crystal particles contained in the polycrystalline particles and the average value of the maximum Ferret diameter of the single-crystal particles existing independently fall within a range of ±10%. On the other hand, in conventional positive electrode active materials, the maximum Ferret diameter of the single-crystal particles contained in the polycrystalline particles and the single-crystal particles existing independently are not considered to fall within the above range.

[0032] When the positive electrode active material contains single-crystal particles and polycrystalline particles, the ratio of single-crystal particles to polycrystalline particles in the positive electrode active material is not particularly limited. The mass ratio (single-crystal particles:polycrystalline particles) may be, for example, 10:90 to 90:10, 20:80 to 80:20, 30:70 to 70:30, or 40:60 to 60:40. The positive electrode active material may consist only of single-crystal particles and polycrystalline particles.

[0033] <Method for manufacturing positive electrode active material> Figure 1 is a schematic flowchart of the method for producing the positive electrode active material in this embodiment. Hereinafter, the method for producing the positive electrode active material in this embodiment may be abbreviated as "this method". This method includes "(a) preparation of precursors", "(b) mixing", "(c) calcination", and "(d) washing".

[0034] (a) Preparation of the precursor This method includes preparing a precursor. The precursor may be synthesized by, for example, a coprecipitation method or a hydrothermal synthesis method. The precursor contains a transition metal compound. The transition metal compound contains at least Ni. The precursor may also contain, for example, a transition metal hydroxide containing Ni. For example, a raw material solution is prepared by dissolving the transition metal compound in water. A precipitate of the transition metal hydroxide may be formed by adding the raw material solution dropwise to an alkaline aqueous solution. For example, the precipitate (transition metal hydroxide) may be washed with water. After washing with water, the transition metal hydroxide may be recovered by filtration. After filtration, the transition metal hydroxide may be dried.

[0035] After the precipitation reaction is complete, the transition metal hydroxide may be subjected to calcination. Calcination can dehydrate the transition metal hydroxide and remove impurities. Any calcination apparatus or furnace can be used in this method. For example, a muffle furnace or electric furnace may be used. Calcination may be carried out, for example, under an oxygen atmosphere.

[0036] The calcination temperature may be, for example, 120°C or higher, or 150°C or higher. The calcination temperature may be, for example, 220°C or lower, or 200°C or lower. The calcination time may be, for example, 4 hours or more, or 6 hours or more. The calcination time may be, for example, 10 hours or less, or 8 hours or less. The calcination pressure may be, for example, 0.2 MPa or higher, or 0.5 MPa or higher. The calcination pressure may be, for example, 1.0 MPa or lower, or 0.8 MPa or lower.

[0037] ((b) mixture) This manufacturing method includes preparing a mixture by mixing a precursor and a lithium compound. For example, grinding and mixing may be carried out in a mortar and pestle. The lithium compound refers to a compound containing Li. The lithium compound may contain, for example, at least one selected from the group consisting of LiOH and Li2CO3. The lithium compound is the lithium source of the lithium transition metal composite oxide. The ratio of the amount of Li in the lithium compound to the total amount of TM in the precursor (transition metal compound) (hereinafter simply abbreviated as "charging ratio") is greater than 1.0 and less than 2.0. The charging ratio may be, for example, 1.05 or more, 1.1 or more, or 1.2 or more. The charging ratio may be, for example, 1.8 or less, 1.6 or less, or 1.4 or less.

[0038] ((c) firing) This manufacturing method includes preparing a calcined product by subjecting the mixture to calcination (hereinafter also referred to as "main calcination"). The same calcination apparatus and furnace as for the pre-calcination may be used. Main calcination may be carried out, for example, under an oxygen atmosphere.

[0039] The main firing temperature may be, for example, 650°C or higher, or 700°C or higher. The main firing temperature may be, for example, 1100°C or lower, or 1000°C or lower. The main firing temperature is higher than the pre-firing temperature. The main firing time may be, for example, 5 hours or more, 7 hours or more, or 10 hours or more. The main firing time may be, for example, 15 hours or less, 12 hours or less, or 10 hours or less. The main firing time is longer than the pre-firing time.

[0040] (d) Cleaning This manufacturing method includes washing the calcined material and preparing the positive electrode active material (lithium transition metal composite oxide). For example, the calcined material may be washed with water. For example, the calcined material may be crushed in a mortar and then washed. After washing, the calcined material may be filtered and dried. Excess Li can be removed by washing.

[0041] ((e) Decomposition) This manufacturing method may include crushing the positive electrode active material (lithium transition metal composite oxide). Any type of grinder (e.g., mortar and pestle, lab mill, etc.) can be used. By crushing, the particle size of the positive electrode active material (lithium transition metal composite oxide) can be adjusted.

[0042] <Lithium-ion rechargeable battery> Figure 2 is a schematic diagram showing a lithium-ion secondary battery (hereinafter abbreviated as "battery") in this embodiment. The battery 100 includes a power generation element 50 and an electrolyte (not shown). The battery 100 may include an outer casing. The outer casing may house the power generation element 50 and the electrolyte. The outer casing may be, for example, a metal case or a pouch made of Al laminate film.

[0043] The power generation element 50 may have any form. For example, the power generation element 50 may be a wound type, a laminated type, etc. The power generation element 50 may have a monopolar structure or a bipolar structure. The power generation element 50 includes a positive electrode 10, a negative electrode 20, and a separator 30. The separator 30 is placed between the positive electrode 10 and the negative electrode 20. Electrolyte permeates the gaps between each component and the gaps within each component. Each component may be, for example, in the form of a sheet.

[0044] (positive electrode) The positive electrode 10 includes a positive electrode active material. That is, the battery 100 includes a positive electrode active material. For example, the positive electrode 10 may include a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector supports the positive electrode active material layer. The positive electrode current collector may include, for example, aluminum foil.

[0045] The positive electrode active material layer contains the positive electrode active material. Details of the positive electrode active material are as described above.

[0046] The positive electrode active material layer may further contain, for example, a conductive material, a binder, etc. The conductive material may contain, for example, acetylene black (AB). The binder may contain, for example, PVDF. The conductive material and binder may be present in amounts of, for example, 0.1% by mass or more and 10% by mass or less relative to the positive electrode active material layer.

[0047] (Negative electrode) The negative electrode 20 may include a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector may include, for example, copper (Cu) foil. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material may include, for example, at least one selected from the group consisting of graphite, soft carbon, and hard carbon. The negative electrode active material layer may further include, for example, a conductive material, a binder, etc.

[0048] The conductive material may include, for example, carbon nanotubes (CNTs). The binder may include, for example, carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), etc. The amount of conductive material and binder blended may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of negative electrode active material.

[0049] 《Separator》 The separator 30 is porous. The separator 30 is permeable to the electrolyte. The separator 30 separates the positive electrode 10 and the negative electrode 20. The separator 30 is electrically insulating. The separator 30 may contain, for example, a polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 30 may have, for example, a single-layer structure or a multi-layer structure. The separator 30 may consist substantially of a PE layer, or it may be formed by laminating a PP layer, a PE layer, and a PP layer in that order. A heat-resistant layer may be formed on the surface of the separator 30.

[0050] 《Electrolyte》 The electrolyte contains a solvent and a lithium salt. The solvent is aprotic. The solvent may contain any components. For example, the solvent may contain at least one selected from the group consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0051] The lithium salt is a supporting electrolyte. The lithium salt is dissolved in the solvent. The lithium salt may contain, for example, at least one selected from the group consisting of LiPF6 and LiBF4. The lithium salt may have a molar concentration of, for example, 0.5 mol / L or more and 2.0 mol / L or less.

[0052] The electrolyte may further contain any additives. For example, the electrolyte may contain additives in an amount of 0.01% to 5% by mass. The additive may include at least one selected from the group consisting of vinylene carbonate (VC) and vinylethylene carbonate (VEC), etc. A solid electrolyte may be used instead of the electrolyte. [Examples]

[0053] <Manufacturing of positive electrode active material> (No.1~No.7) The raw material solution was formed by dissolving NiSO4, CoSO4, and MnSO4 in deionized water. In the raw material solution, the mixing ratio (mole ratio) of Ni, Co, and Mn was "Ni / Co / Mn = 90 / 5 / 5". The molar concentration of the raw material solution was 0.2%.

[0054] Ammonia water was added to the reaction vessel. The ammonia water was stirred with a stirrer, and the inside of the reaction vessel was replaced with nitrogen. Then, NaOH was added to the reaction vessel to form the reaction mixture. Starting material solution and ammonia water were added dropwise to the reaction mixture to maintain a pH within a certain range, and a precipitate of transition metal hydroxide was formed.

[0055] In a muffle furnace, the metal hydroxide was calcined. The calcination temperature was 120-220°C, the calcination time was 4-10 hours, and the calcination pressure was 0.2-1.0 MPa. After calcination, the transition metal hydroxide was dispersed in deionized water to form a dispersion. The dispersion was thoroughly stirred with a spatula, that is, the transition metal hydroxide was washed with water. After washing, the transition metal hydroxide was recovered by filtration. The precursor (transition metal hydroxide) was prepared by drying the transition metal hydroxide at 110°C for 12 hours.

[0056] In a mortar, the precursor (transition metal hydroxide) and LiOH were mixed to prepare the mixture. The mixing ratio was adjusted to the values ​​shown in Figure 3.

[0057] In a muffle furnace, the mixture was subjected to a final firing to prepare the fired product. The firing temperature was 650-1100°C, and the firing time was 5-15 hours.

[0058] In an agate mortar, the calcined material was crushed until the particle size was 0.2 mm or less, forming a crushed material. The crushed material was dispersed in 500 mL of pure water to form a slurry. The slurry was vigorously stirred for 1 minute. The slurry was filtered using filter paper and a Buchner funnel. The residue was rinsed with 500 mL of pure water to form a cake. The cake was vacuum-dried at 90°C. After drying, the cake was crushed using an agate mortar to adjust it to the desired particle size. Thus, cathode active materials (lithium transition metal composite oxides) No. 1 to No. 7 were manufactured.

[0059] (analysis) The composition of each positive electrode active material was confirmed using an ICP emission spectrometer (PS3520UVDD, manufactured by Hitachi High-Tech Science Corporation). All positive electrode active materials were "LiNi 0.90 Co 0.05 Mn 0.05The composition was confirmed to be "O2". Furthermore, upon examination of the crystal structure of each No., it was confirmed that all positive electrode active materials have a layered crystal structure.

[0060] The volume-based particle size distribution of each positive electrode active material was measured using a laser diffraction particle size distribution analyzer (WingSALD-2300, manufactured by Shimadzu Corporation). Figure 3 shows the f1, f2, and f2 / f1 for each positive electrode active material. As an example, Figure 4 shows the volume-based particle size distribution of positive electrode active materials No. 1, 2, 5, and 7.

[0061] <Rating> (Manufacturing of laminated cells) Laminate cells have been manufactured. The composition of the laminate cells is as follows:

[0062] Positive electrode: Positive electrode active material (lithium transition metal composite oxide), conductive material (AB) Negative electrode: Negative electrode active material (natural graphite) Electrolytes: LiPF6 (1 ml / L), EC / DMC / EMC = 3 / 4 / 3 (volume ratio)

[0063] The positive and negative electrodes were manufactured by coating the surface of a substrate (metal foil) with slurry. An Allgood film applicator (with film thickness adjustment function) was used as the coating apparatus. After coating with slurry, the coating film was dried at 80°C for 5 minutes.

[0064] A cycle test was conducted on the laminated cells under the following conditions. Ambient temperature: 60℃ Number of cycles: 100 Current rate: 0.3C Voltage range: 4.25V to 2.5V

[0065] Before the above cycle test and after the cycle test, each laminated cell was charged to 50% SOC (State of Charge), and then discharged and charged at 25°C at rates of 0.3C, 0.5C, 0.7C, and 1C. The average resistance estimated from the potential drop and rise after 0.1 seconds was taken as the IV resistance. The results are shown in Figure 3. In Figure 3, the IV resistance before the cycle test is referred to as the "initial resistance", and the IV resistance after the cycle test is referred to as the "post-cycle resistance". Note that "1C" indicates the current rate at which the SOC reaches 100% from 0% by charging in 1 hour.

[0066] <Result> In Figure 3, when the relationship of "0.1 < f2 / f1 ≤ 25" is satisfied, there is a tendency for the initial resistance to decrease. Also, when the relationship of "0.5 ≤ f2 / f1 ≤ 3.0" is satisfied, in addition to the reduction of the initial resistance, there is a tendency for the post-cycle resistance to decrease, that is, the durability improves. Furthermore, when the relationship of "2.0 ≤ f2 / f1 ≤ 3.0" is satisfied, there is a tendency for the durability to further improve.

Explanation of Symbols

[0067] 10 Positive electrode, 20 Negative electrode, 30 Separator, 50 Power generation element, 100 Lithium-ion secondary battery.

Claims

1. It is a positive electrode active material, The positive electrode active material includes a layered lithium transition metal composite oxide, In the volume-based particle size distribution of the positive electrode active material, 0.1 < f ２ / f １ Satisfying the relationship ≤ 25, Said f １ This is the maximum frequency in the range where the maximum Ferret diameter is between 1 μm and 3 μm. Said f ２ This refers to a positive electrode active material whose maximum frequency is in the range of 5 μm to 25 μm in terms of maximum Ferret diameter.

2. In the volume-based particle size distribution of the positive electrode active material, 0.5 ≤ f ２ / f １ The positive electrode active material according to claim 1, satisfying the relationship ≤ 3.

0.

3. The positive electrode active material according to claim 1 or claim 2, wherein the positive electrode active material comprises single crystal particles and polycrystalline particles formed by the association of the single crystal particles.

4. The lithium transition metal composite oxide has the general formula: Li ｘ Ni ａ Co ｂ Mn ｃ O ｙ It has a composition represented by, The positive electrode active material according to claim 1 or claim 2, wherein the following relationships are satisfied: 0.1 ≤ x ≤ 1.5, 0.5 ≤ a ≤ 1.0, 0 ≤ b ≤ 0.3, 0 ≤ c ≤ 0.3, a + b + c = 1.0, and 1.5 ≤ y ≤ 2.

1.

5. A method for producing a positive electrode active material according to claim 1, (a) Prepare the precursor, (b) Prepare a mixture by mixing the precursor and the lithium compound. (c) Preparing a calcined product by calcining the mixture, and (d) Washing the calcined material and preparing the positive electrode active material, The precursor comprises a transition metal compound, The transition metal compound comprises at least nickel, A method for producing a positive electrode active material, wherein the ratio of the amount of substance of lithium in the lithium compound to the total amount of substance of the transition metal in the transition metal compound is greater than 1.0 and less than 2.0.

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