Positive electrode active material and lithium-ion secondary battery

Abstract

Improved rate characteristics. [Solution] The positive electrode active material is, The positive electrode active material comprises single-crystal particles and polycrystalline particles, the polycrystalline particles being formed by the association of a plurality of single-crystal particles, each of the single-crystal particles and the polycrystalline particles containing a layered lithium nickel composite oxide, and the single-crystal particles satisfy all of the following relationships from formulas (1) to (3). D10 ≤ 2.5 (1) D50≦5.0 (2) (D90-D10) / D50≧3.0 (3) In the above formulas (1) to (3), D10, D50, and D90 represent the particle diameters at which the cumulative value becomes 10%, 50%, and 90% of the volume-based particle size distribution of the single crystal particles, respectively, and D10, D50, and D90 each have units of μm.

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material and a lithium-ion secondary battery. [Background technology]

[0002] Japanese Patent Publication No. 2023-36062 (Patent Document 1) discloses a positive electrode active material which is a metal oxide containing single crystal particles with a particle size of 1 to 8 μm and having a predetermined particle size distribution. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2023-36062 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The positive electrode active material described in Patent Document 1 has a narrow particle size distribution, and when the density of the positive electrode active material layer is increased by pressing, the frequency of contact between positive electrode active material particles decreases. As a result, the discharge capacity may be low and the rate characteristics may deteriorate.

[0005] The purpose of this disclosure is to improve rate characteristics. [Means for solving the problem]

[0006] [1] A positive electrode active material, The positive electrode active material includes single-crystal particles and polycrystalline particles. The polycrystalline particles are formed by the association of a plurality of single-crystal particles. Each of the single-crystal particles and the polycrystalline particles contains a layered lithium nickel composite oxide, The aforementioned single crystal particles are a positive electrode active material that satisfies all of the following relationships from equation (1) to (3). D10 ≤ 2.5 (1) D50≦5.0 (2) (D90-D10) / D50≧3.0 (3) In the above formulas (1) to (3), D10, D50, and D90 represent the particle diameters at which the cumulative value becomes 10%, 50%, and 90% of the volume-based particle size distribution of the single crystal particles, respectively, and D10, D50, and D90 each have units of μm.

[0007] In single-crystal particles, the diffusion distance of lithium (Li) within the single-crystal particle is long, resulting in a low utilization rate of Li within the single-crystal particle. Therefore, as shown in (1) and (2) above, reducing the particle size of the single-crystal particle is expected to improve the utilization rate of Li.

[0008] Furthermore, the "(D90-D10) / D50" shown in (3) above is also referred to as, for example, the "span value." The span value is an indicator of the breadth of the particle size distribution. The smaller the span value, the sharper the particle size distribution is considered to be. Conventional single-crystal particle type cathode active materials tend to have low packing efficiency because their particle size distribution is sharp. Therefore, as shown in (3) above, by broadening the particle size distribution of the single crystal particles, it is expected that packing efficiency will be improved and the frequency of contact between single crystal particles will increase. It is then thought that the discharge capacity will be improved and the rate characteristics will be improved due to these synergistic effects.

[0009] [2] The single crystal particles are the positive electrode active material described in [1] that satisfies all of the following relationships from formula (4) to (6). 0.1 ≤ D10 (4) 1.0 ≤ D50 (5) 12 ≥ (D90 - D10) / D50 (6)

[0010] [3] The single crystal particles are the positive electrode active material described in [1] or [2], satisfying the relationship in formula (7) below. 3.0 ≤ D90 / D50 ≤ 12 (7)

[0011] [4] The lithium nickel composite oxide has the general formula: Li x Nia Co b Mn c O y and having a composition represented by a positive electrode active material according to any one of [1] to [3], in which the 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 are satisfied.

[0012] [5] A lithium ion secondary battery comprising the positive electrode active material according to any one of [1] to [4].

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a schematic flowchart showing a method for manufacturing a positive electrode active material in the present embodiment. [Figure 2] FIG. 2 is a schematic diagram showing the lithium ion secondary battery of the present embodiment. [Figure 3] FIG. 3 is a schematic diagram showing the positive electrode of the present embodiment. [Figure 4] FIG. 4 is a table showing the manufacturing conditions and evaluation results of the positive electrode active materials of Nos. 1 to 6 in the examples. [Figure 5] FIG. 5 is a table showing the analysis results of the positive electrode active materials of Nos. 1 to 6 in the examples and the evaluation results of the evaluation cells.

Modes for Carrying Out the Invention

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

[0015] 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.

[0016] In this specification, "at least one of single-crystal particles and polycrystalline particles" may be collectively referred to as "positive electrode active material." A "single-crystal particle" is a single, independent particle that is not aggregated, consists of substantially a single particle, and has no visible grain boundaries in a scanning electron microscope (SEM) image. A "polycrystalline particle" is a particle formed by the association (aggregation) of multiple single-crystal particles.

[0017] In this specification, "particle size distribution" is defined as follows: D10 represents the particle size at which the cumulative frequency of the smallest particle size accounts for 10% in the volume-based particle size distribution. D50 represents the particle size at which the cumulative frequency of the smallest particle size accounts for 50% in the volume-based particle size distribution. D90 represents the particle size at which the cumulative frequency of the smallest particle size accounts for 90% in the volume-based particle size distribution. D10, D50, and D90 each have units of μm.

[0018] 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.

[0019] <Cathode active material> The cathode active material of this embodiment can reversibly intercalate and release lithium ions. The cathode active material includes single crystal particles and polycrystalline particles. The polycrystalline particles are formed by the aggregation of a plurality of single crystal particles. Each of the single crystal particles and the polycrystalline particles contains a layered lithium nickel composite oxide. Each of the single crystal particles and the polycrystalline particles may be a cathode active material composed of a layered lithium nickel composite oxide. As the lithium nickel composite oxide, for example, at least one selected from the group consisting of LiNiO2, Li(NiCoMn)O2, and Li(NiCoAl)O2 may be used. Among them, Li(NiCoMn)O2 is preferred because of its particularly excellent resistance characteristics. Such a lithium nickel composite oxide preferably has a composition represented by the following general formula. In this embodiment, the compositions of the single crystal particles and the polycrystalline particles are the same. The chemical composition of the cathode active material can be identified by, for example, inductively coupled plasma atomic emission spectroscopy (ICP-AES). Li x Ni a Co b Mn c 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] (Single crystal particles) Single crystal particles are so-called small particles. Single crystal particles have a relatively small particle size compared to polycrystalline particles. Single crystal particles can form a conductive path between polycrystalline particles. Single crystal particles have a volume-based particle size distribution. Single crystal particles satisfy all of the following relationships (1) to (3). D10≦2.5 (1) [[ID=好的,我将继续翻译。请告诉我你是否还有其他需求。]] D50≦5.0 (2) (D90 - D10) / D^50≧3.0 (3)

[0021] Single-crystal particles have a long diffusion distance for Li, resulting in low utilization of Li within the single-crystal particles. Therefore, as shown in (1) and (2) above, reducing the particle size of the single-crystal particles is expected to improve the utilization of Li.

[0022] Furthermore, conventional single-crystal particle type cathode active materials tend to have poor packing due to their sharp particle size distribution. Therefore, as shown in (3) above, broadening the particle size distribution of the single crystal particles is expected to improve packing and increase the frequency of contact between the single crystal particles. It is believed that these synergistic effects will improve the discharge capacity and rate characteristics.

[0023] Single crystal particles may satisfy all of the following relationships from equation (4) to (6). 0.1 ≤ D10 (4) 1.0 ≤ D50 (5) 12 ≥ (D90 - D10) / D50 (6)

[0024] D10 may be, for example, 0.2 μm or larger, or 0.3 μm or larger. D10 may also be, for example, 2.0 μm or smaller, or 1.5 μm or smaller.

[0025] D50 may be, for example, 1.2 μm or larger, or 1.5 μm or larger. D50 may be, for example, 4.5 μm or smaller, or 4.0 μm or smaller.

[0026] D90 may be, for example, 7.0 μm or more, or 10 μm or more. D90 may be, for example, 30 μm or less, or 28 μm or less.

[0027] (D90-D10) / D50 may be, for example, 3.5 or higher, or 4.0 or higher. (D90-D10) / D50 may be, for example, 11.5 or lower, or 11 or lower.

[0028] Single crystal particles may satisfy the relationship shown in equation (7) below. 3.0 ≤ D90 / D50 ≤ 12 (7)

[0029] D90 / D50 may be, for example, 3.2 or higher, or 3.5 or higher. D90 / D50 may be, for example, 11.5 or lower, or 11 or lower.

[0030] Single crystal particles may satisfy the relationship shown in equation (8) below. 1.0 ≤ D50 / D10 ≤ 6.0 (8)

[0031] D50 / D10 may be, for example, 1.5 or higher, or 1.8 or higher. D50 / D10 may be, for example, 5.5 or lower, or 5.0 or lower.

[0032] Single crystal particles may satisfy the relationship shown in equation (9) below. 1.8 ≤ D90 / (D10 + D50) ≤ 10 (9)

[0033] D90 / (D10+D50) may be, for example, 2.0 or greater, or 2.3 or greater. D90 / (D10+D50) may be, for example, 9.5 or less, or 9.0 or less.

[0034] (polycrystalline particles) Polycrystalline particles are, so to speak, large particles. Polycrystalline particles have a relatively larger particle size compared to single-crystal particles. Polycrystalline particles have a volume-based particle size distribution. The D50 of polycrystalline particles may be, for example, between 5 μm and 20 μm.

[0035] The polycrystalline particles in this embodiment are formed by the association of multiple single-crystal particles, and differ from conventional polycrystalline particles formed by the aggregation of single-crystal particles. The two can be distinguished, for example, by the maximum Ferret diameter and aspect ratio of the single-crystal particles as observed from SEM images. For example, the single-crystal particles contained in 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, it is thought that the single-crystal particles contained in conventional polycrystalline particles may have a maximum Ferret diameter smaller than that of a single-crystal particle existing independently. Note that "maximum Ferret diameter" refers to the distance between the two furthest points on the contour line of the particle.

[0036] (Content ratio) 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.

[0037] The positive electrode active material in this embodiment differs from conventional positive electrode active materials that are mixtures of single-crystal particles and polycrystalline particles. The two can be distinguished, for example, by the maximum Ferret diameter of the single-crystal particles as confirmed by SEM imaging. For example, the average value of the maximum Ferret diameter of the single-crystal particles contained in polycrystalline particles and the average value of the maximum Ferret diameter of 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 polycrystalline particles and the single-crystal particles existing independently are not considered to fall within the above range.

[0038] (others) The positive electrode active material may include other active materials other than the single-crystal particles and polycrystalline particles described above, to the extent that it does not impair the purpose of this embodiment. The other active materials may be single-crystal particles or polycrystalline particles.

[0039] <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", "(d) washing", and "(e) crushing".

[0040] (a) Preparation of the precursor This method includes preparing a precursor. The precursor may include, for example, a metal hydroxide. The metal hydroxide may be synthesized, for example, by a coprecipitation method. For example, a sulfate may be prepared. The sulfate may include, for example, at least one selected from the group consisting of NiSO4, CoSO4, MnSO4, and Al2(SO4)3. A raw material solution is prepared by dissolving the sulfate in water. The concentration of the raw material solution may be, for example, 10 to 50% by mass fraction. A precipitate of metal hydroxide may be formed by adding the raw material solution dropwise to an alkaline aqueous solution. For example, the precipitate (metal hydroxide) may be washed with water. After washing with water, the metal hydroxide may be recovered by filtration. After filtration, the metal hydroxide may be dried.

[0041] After the precipitation reaction is complete, the metal hydroxide may be subjected to calcination. Calcination can dehydrate the 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.

[0042] 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.

[0043] ((b) mixture) This manufacturing method involves forming a mixture by mixing a precursor with 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 nickel composite oxide. The ratio of the amount of Li to the amount of metal hydroxide may be, for example, greater than 1.2, 1.3 or more, 1.5 or more, 1.75 or more, or 2.0 or more. The ratio may also be, for example, 4.0 or less, 3.5 or less, or 3.0 or less.

[0044] ((c) firing) This method involves synthesizing lithium nickel composite oxide by subjecting a mixture to calcination (hereinafter also referred to as "main calcination"). The same calcination apparatus and furnace used for pre-calcination may be used. Main calcination may be carried out, for example, under an oxygen atmosphere.

[0045] 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, less than 850°C, or 800°C or lower. The main firing temperature is higher than the pre-firing temperature. The main firing time may be, for example, 8 hours or more, 9 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.

[0046] (d) Cleaning This manufacturing method includes washing the lithium nickel composite oxide. For example, the lithium nickel composite oxide may be washed with water. For example, the lithium nickel composite oxide may be crushed in a mortar and then washed. After washing with water, the lithium nickel composite oxide may be filtered and dried.

[0047] ((e) Decomposition) This method involves crushing lithium nickel composite oxide. Any type of grinder (e.g., mortar and pestle, lab mill, etc.) can be used. The particle size of the lithium nickel composite oxide can be adjusted by crushing.

[0048] <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.

[0049] 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.

[0050] (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 11 and a positive electrode active material layer 12. The positive electrode current collector 11 supports the positive electrode active material layer 12. The positive electrode current collector 11 may include, for example, aluminum foil.

[0051] Figure 3 is a schematic diagram showing the positive electrode of this embodiment. The positive electrode active material layer 12 contains positive electrode active material. The positive electrode active material contains single crystal particles 1 and polycrystalline particles 2. Details of single crystal particles 1 and polycrystalline particles 2 are as described above.

[0052] The positive electrode active material layer 12 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 12.

[0053] (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.

[0054] 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.

[0055] 《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.

[0056] 《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).

[0057] 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.

[0058] 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]

[0059] <Manufacturing of positive electrode active material> (No.1~No.6) The raw material solution was formed by dissolving NiSO4, CoSO4, and MnSO4 in deionized water. In the raw material solution, the molar ratio of Ni, Co, and Mn was "Ni / Co / Mn = 18 / 1 / 1". The concentration of the raw material solution was 0.2 ml.

[0060] 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. The starting material solution and ammonia water were added dropwise to the reaction mixture to maintain a pH within a certain range, and a precipitate (metal hydroxide) was formed.

[0061] In a muffle furnace, the metal hydroxide was calcined. The calcination temperature was 120°C, the calcination time was 5 hours, and the calcination pressure was 0.3 MPa. After calcination, the metal hydroxide was dispersed in deionized water to form a dispersion. The dispersion was thoroughly stirred with a spatula, that is, the metal hydroxide was washed with water. After washing, the metal hydroxide was recovered by filtration. The metal hydroxide was dried at 110°C for 12 hours to form a dried product.

[0062] In a mortar, the dried material and the lithium compound were mixed to form a mixture. The lithium compound used and its mass fraction are shown in Figure 4. The ratio of the amount of Li to the amount of metal hydroxides (Ni, Co, and Mn) is also shown in Figure 4.

[0063] In a muffle furnace, the mixture was subjected to a final calcination to synthesize a lithium nickel composite oxide (cathode active material). The conditions for the final calcination are shown in Figure 4.

[0064] In a mortar, the lithium nickel composite oxide was crushed. After crushing, the lithium nickel composite oxide was dispersed in pure water to form a dispersion. The dispersion was thoroughly stirred (washed with water) using a spatula. After washing, the lithium nickel composite oxide was recovered by filtration. The lithium nickel composite oxide was rinsed with pure water. After rinsing, the lithium nickel composite oxide was vacuum-dried at 90°C.

[0065] After vacuum drying, the particle size of the lithium nickel composite oxide was adjusted using a mortar and pestle.

[0066] (analysis) The composition of each No. positive electrode active material was confirmed using an ICP emission spectrometer (Hitachi High-Tech Science Corporation, PS3520UVDD). 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.

[0067] The volume-based particle size distribution of each No. single crystal particle was measured using a laser diffraction particle size distribution analyzer (WingSALD-2300, manufactured by Shimadzu Corporation). The particle size distribution for each No. single crystal particle is shown in Figure 5.

[0068] <Rating> (Manufacturing of evaluation cells) A cylindrical lithium-ion secondary battery (evaluation cell) has been manufactured. The configuration of the evaluation cell is as follows:

[0069] Power generation element: wound type Positive electrode: Positive electrode active material / AB / PVDF=88 / 10 / 2 (mass ratio) Negative electrode: Negative electrode active material (natural graphite), CMC, SBR Electrolytes: LiPF6 (1 ml / L), EC / DMC / EMC = 3 / 4 / 3 (volume ratio)

[0070] The positive and negative electrodes were manufactured by coating the surface of a substrate (metal foil) with a slurry. An Allgood film applicator (with film thickness adjustment function) was used as the coating device. After coating with the slurry, the coating was dried at 80°C for 5 minutes.

[0071] (Initial discharge capacity) Under a temperature of 25°C, charging and discharging were performed with a constant current of 0.1C within a voltage range of 3.0 to 4.1V, and the discharge capacity was measured as the initial discharge capacity. The results are shown in Figure 5. "C" is a symbol representing the rate. At a rate of 1C, the rated capacity is supplied over one hour.

[0072] (Rate characteristics) Under a temperature environment of 25°C, the discharge capacity of the evaluation cell was measured at both a 0.1C rate and a 1C rate. The "1C discharge capacity / 0.1C discharge capacity" was calculated by dividing the discharge capacity at the 1C rate (1C discharge capacity) by the discharge capacity at the 0.1C rate (0.1C discharge capacity). A larger "1C discharge capacity / 0.1C discharge capacity" indicates better rate characteristics.

[0073] <Result> As shown in Figure 5, when the conditions of this disclosure are met, there is a tendency for the rate characteristics to improve. [Explanation of symbols]

[0074] 1 single crystal particle, 2 polycrystalline particle, 10 positive electrode, 11 positive electrode current collector, 12 positive electrode active material layer, 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 single-crystal particles and polycrystalline particles. The polycrystalline particles are formed by the association of a plurality of single-crystal particles. Each of the single-crystal particles and the polycrystalline particles contains a layered lithium nickel composite oxide, The aforementioned single crystal particles are a positive electrode active material that satisfies all of the following relationships from equation (1) to (3). D10 ≤ 2.5 (1) D50 ≤ 5.0 (2) (D90-D10) / D50≧3.0 (3) In the above formulas (1) to (3), D10, D50, and D90 represent the particle diameters at which the cumulative value becomes 10%, 50%, and 90% of the volume-based particle size distribution of the single crystal particles, respectively, and D10, D50, and D90 each have units of μm.

2. The positive electrode active material according to claim 1, wherein the single crystal particles satisfy all of the following relationships from formula (4) to (6). 0.1 ≤ D10 (4) 1.0 ≤ D50 (5) 12≧(D90-D10) / D50 (6)

3. The positive electrode active material according to claim 1, wherein the single crystal particles satisfy the relationship shown in formula (7) below. 3.0 ≤ D90 / D50 ≤ 12 (7)

4. The aforementioned lithium nickel 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, 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 lithium-ion secondary battery comprising the positive electrode active material according to any one of claims 1 to 4.

Images