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

Abstract

To provide a positive electrode active material which includes single particles and aggregate particles including a Hi-Ni-based NCM compound and which can achieve both energy density and cycling performance, a positive electrode plate and a nonaqueous electrolyte secondary battery including the positive electrode active material, and a method of producing a positive electrode active material.SOLUTION: There is provided a positive electrode active material including single particles and aggregate particles. The single particles and the aggregate particles include a nickel-cobalt-manganese-based compound. A nickel content ratio in the nickel-cobalt-manganese-based compound included in the single particles is 70 mol% or more, and a nickel content ratio in the nickel-cobalt-manganese-based compound included in the aggregate particles is 75 mol% or more. The aggregate particles further include a phosphoric acid compound and at least one selected from the group consisting of a lithium-containing metal oxide and lithium borate, and a molar ratio of the lithium-containing metal oxide and the lithium borate with respect to the phosphoric acid compound in the aggregate particles is 5.0 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material, and further to a positive electrode plate, a non-aqueous electrolyte secondary battery, and a method for manufacturing the positive electrode active material. [Background technology]

[0002] Patent Document 1 discloses a lithium metal composite oxide composed of secondary particles formed by aggregation of primary particles and single particles that exist independently of the secondary particles, and proposes improving the packing density by blending the single particles and secondary particles to make the circularity distribution of the active material bimodal (two-peak distribution). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-87879 Summary of the Invention [Problem to be solved by the invention]

[0004] Positive electrode plates containing single particles and agglomerated particles containing a high-nickel-content nickel-cobalt-manganese compound (hereinafter also referred to as Hi-Ni-NCM compound) as a positive electrode active material are prone to particle cracking of the agglomerated particles during the compression process in manufacturing, and the particle cracking may progress during cycle testing. On the other hand, while coating the particle surface with a different element has been investigated to suppress particle cracking, the coating may extract lithium from the bulk of the positive electrode active material, reducing the thermal stability of the positive electrode active material and degrading its cycle performance.

[0005] An object of the present disclosure is to provide a positive electrode active material that includes single particles and agglomerated particles containing a Hi-Ni-based NCM compound and that can achieve both good energy density and good cycle characteristics, a positive electrode plate that includes the same, a nonaqueous electrolyte secondary battery, and a method for producing the positive electrode active material. [Means for solving the problem]

[0006] The present disclosure provides the following positive electrode active material, positive electrode plate, nonaqueous electrolyte secondary battery, and method for producing the positive electrode active material. [1] A positive electrode active material comprising single particles and aggregated particles, the single particles and the agglomerated particles contain a nickel-cobalt-manganese compound, the nickel content in the nickel-cobalt-manganese compound contained in the single particle is 70 mol% or more; the nickel content in the nickel-cobalt-manganese compound contained in the agglomerated particles is 75 mol % or more; the agglomerated particles further contain a phosphate compound and at least one selected from the group consisting of a lithium-containing metal oxide and a lithium borate, a molar ratio of the total mass of the lithium-containing metal oxide and lithium borate to the phosphate compound in the aggregated particles is 5.0 or less. [2] The positive electrode active material according to [1], wherein the mass ratio of the single particles to the aggregated particles is 20:80 to 50:50. [3] The positive electrode active material according to [1] or [2], wherein the lithium-containing metal oxide contains at least one selected from the group consisting of lithium tungstate, lithium zirconate, lithium titanate, and lithium aluminate. [4] A positive electrode active material layer containing the positive electrode active material according to any one of [1] to [3], wherein the density of the positive electrode active material layer is 3.65 g / cm 3 That's it for the positive plate. [5] A non-aqueous electrolyte secondary battery comprising the positive electrode plate according to [4]. [6] A method for producing a positive electrode active material according to any one of [1] to [3], a first treatment step of coating the aggregated particles with a phosphoric acid compound; a second treatment step of heat-treating the aggregated particles obtained after the first treatment step using at least one selected from the group consisting of metal oxides and boric acid, and a lithium salt; and a mixing step of mixing the aggregated particles after the second treatment step with single particles; A method for producing a positive electrode active material, comprising: [Effects of the Invention]

[0007] The present disclosure provides a positive electrode active material that includes single particles and agglomerated particles containing a Hi-Ni-based NCM compound and that can achieve both good energy density and good cycle characteristics, a positive electrode plate that includes the same, a nonaqueous electrolyte secondary battery, and a method for producing the positive electrode active material. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic flowchart of a method for producing a positive electrode active material in this embodiment. [Figure 2] FIG. 2 is a schematic diagram showing an example of a battery according to this embodiment. [Figure 3] FIG. 3 is a schematic diagram showing an example of an electrode assembly in this embodiment. [Figure 4] FIG. 4 is a conceptual diagram showing the positive electrode plate in this embodiment. [Figure 5] FIG. 5 is a schematic flowchart of a method for manufacturing a positive electrode plate in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure.

[0010] In this specification, elements expressed in the singular include the plural unless otherwise specified. For example, a "particle" can mean not only "one particle" but also "an aggregate of particles (powder, powder, particle group)."

[0011] <Cathode active material> The positive electrode active material includes single particles and aggregated particles. This makes it easier to increase the packing density of the positive electrode active material layer of the positive electrode plate. The positive electrode active material may essentially consist of single particles and aggregated particles. The positive electrode active material of this embodiment can be used in a non-aqueous electrolyte secondary battery. Details of the non-aqueous electrolyte secondary battery will be described later.

[0012] The individual particles and aggregated particles may have any size. The average particle diameter D50 of the individual particles may be, for example, 1 μm to 20 μm, preferably 1 μm to 10 μm, and more preferably 1 μm to 5 μm. The average particle diameters D50, D70, and D30 of the aggregated particles may be, for example, all 1 μm to 40 μm, preferably all 1 μm to 30 μm, and more preferably all 1 μm to 20 μm. The average particle diameters D50, D70, and D30 represent particle diameters at which the cumulative particle volume from the small particle size side in the volume-based particle size distribution is 50%, 70%, and 30%, respectively, of the total particle volume. The average particle diameter can be measured by a laser diffraction / scattering method.

[0013] Agglomerated particles may be aggregates of primary particles. Primary particles are particles in which grain boundaries cannot be visually identified in an SEM image of the particles and which have an average primary particle diameter of less than 0.5 μm. The average primary particle diameter is the distance between the two most distant points on the outline of a primary particle. The average primary particle diameter of primary particles may be, for example, 0.05 μm to 0.2 μm or 0.1 μm to 0.2 μm. When 10 or more primary particles randomly sampled from an SEM image of a single agglomerated particle have an average primary particle diameter of 0.05 μm to 0.2 μm, all of the primary particles contained in the agglomerated particle are considered to have an average primary particle diameter of 0.05 μm to 0.2 μm. The primary particles may have an average primary particle diameter of, for example, 0.1 μm to 0.2 μm.

[0014] The single particles and agglomerated particles (primary particles) contain a nickel-cobalt-manganese compound (hereinafter also referred to as an NCM compound). The nickel content in the NCM compound contained in the single particles is 70 mol% or more, preferably 73 mol% or more, and more preferably 76 mol% or more. The nickel content in the NCM compound contained in the agglomerated particles (primary particles) is 75 mol% or more, preferably 78 mol% or more, and more preferably 81 mol% or more. The nickel content is the content ratio of nickel to metal elements excluding lithium.

[0015] The NCM compound preferably contains a nickel-cobalt-manganese composite hydroxide, more preferably a lithium-nickel-cobalt-manganese composite oxide. The nickel-cobalt-manganese composite hydroxide may be obtained by, for example, a coprecipitation method. The nickel-cobalt-manganese composite hydroxide may be, for example, a compound represented by the general formula: Ni x Co y Mn z It may be a compound represented by (OH)2 (wherein x+y+z=1). The lithium nickel cobalt manganese composite oxide may have a molar ratio of lithium to nickel, cobalt, and manganese, Li:(Ni+Co+Mn), of, for example, 1.0 to 1.2:1.0.

[0016] The single particle may be, for example, a particle represented by the following formula (1): Li 1-a1 Ni x1 Me 1 1-x1 O2(1) [In formula (1), "a1" satisfies the relationship -0.3≦a1≦0.3. "x1" satisfies the relationship 0.7≦x1<1.0. "Me 1 " represents at least one selected from the group consisting of Co, Mn, Al, Zr, Ti, V, Cr, Fe, Cu, Zn, Mo, Sn, Ge, Nb, and W. The layered metal oxide may contain one or more first layered metal oxides represented by the following formula:

[0017] The primary particles may be, for example, those represented by the following formula (2): Li 1-a2 Ni x2 Me 2 1-x2 O2(2) [In formula (2), "a2" satisfies the relationship of -0.3 ≤ a2 ≤ 0.3. "x2" satisfies the relationship of 0.75 ≤ x2 ≤ 1.0. "Me 2 " represents at least one selected from the group consisting of Co, Mn, Al, Zr, Ti, V, Cr, Fe, Cu, Zn, Mo, Sn, Ge, Nb, and W.] It may contain one or more of the second-layered metal oxides represented by the above formula.

[0018] In formulas (1) and (2), for example, the relationship of "x1 < x2" may be satisfied.

[0019] For example, the single particle may contain at least one selected from the group consisting of LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2O2, and LiNi 0.8 Co 0.1 Mn 0.1 O2. For example, the primary particle may contain at least one selected from the group consisting of LiNi 0.75 Co 0.15 Mn 0.1 O2, and LiNi 0.75 Co 0.1 Mn 0.15 O2, and LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0020] For example, both the single particle and the primary particle may consist essentially of LiNi 0.75 Co 0.15 Mn 0.1 O2. For example, both the single particle and the primary particle may consist essentially of LiNi 0.75 Co 0.1 Mn0.15 For example, both the single particles and the primary particles may consist essentially of LiNiO. 0.8 Co 0.1 Mn 0.1 For example, a single particle may consist essentially of LiNiO. 0.7 Co 0.2 Mn 0.1 O2, and the primary particles are essentially LiNi 0.75 Co 0.1 Mn 0.15 For example, a single particle may consist essentially of LiNiO. 0.7 Co 0.2 Mn 0.1 O2, and the primary particles are essentially LiNi 0.75 Co 0.15 Mn 0.1 It may consist of O2.

[0021] When the single particles contain a lithium-nickel-cobalt-manganese composite oxide, the single particles can be obtained by, for example, mixing a lithium source such as lithium hydroxide with the nickel-cobalt-manganese composite hydroxide, firing the mixture, wet-pulverizing the mixture using a ball mill or the like, and drying the mixture. The single particles may be surface-treated.

[0022] The agglomerated particles further contain a phosphate compound and at least one selected from the group consisting of lithium-containing metal oxides and lithium borate (Li3BO3). This suppresses particle cracking of the agglomerated particles, making it easier to achieve a desired energy density, and also suppresses extraction of lithium from the interior of the agglomerated particles, making it easier to suppress deterioration of cycle characteristics. The degree of extraction of lithium from the interior of the agglomerated particles can be evaluated by the DTG peak value of the TG curve obtained by differential thermogravimetry (DTG) measurement, which will be described in the Examples section.

[0023] The phosphate compound may include, for example, lithium phosphate (LiPO). The lithium-containing metal oxide may include, for example, at least one selected from the group consisting of lithium tungstate (LiWO), lithium zirconate (LiZrO), lithium titanate (LiTiO), and lithium aluminate (LiAlO). The agglomerated particles preferably include lithium borate from the viewpoints of energy density and cycle characteristics.

[0024] When the agglomerated particles are lithium-nickel-cobalt-manganese composite oxide, the agglomerated particles can be obtained by, for example, mixing a lithium source such as lithium hydroxide with a nickel-cobalt-manganese composite hydroxide and calcining the mixture to obtain an agglomerated lithium-nickel-cobalt-manganese composite oxide (hereinafter also referred to as lithium composite oxide), then surface-treating the agglomerated lithium composite oxide with a phosphate compound, and then heat-treating the agglomerated lithium composite oxide with at least one selected from the group consisting of metal oxides and boric acid, and a lithium salt. Typically, coating the surface of a Hi-Ni-based NCM active material with a metal oxide or boric acid extracts lithium from the interior of the agglomerated particles, converting them into compounds such as lithium-containing metal oxides or lithium borate. To suppress this reaction, the surface of the Hi-Ni-based NCM active material is subjected to mechanochemical treatment using a phosphate compound such as lithium phosphate, followed by heat treatment using a metal oxide, boric acid, and a lithium salt. This forms a barrier layer of the phosphate compound between the surface of the Hi-Ni-based NCM active material and the coating layer, which inhibits lithium diffusion. This prevents lithium from being extracted from inside the agglomerated particles, and is thought to help prevent a decrease in cycle performance.

[0025] Examples of methods for surface treating an aggregated lithium composite oxide with a phosphate compound include mechanochemical treatment. Mechanochemical treatment can facilitate the formation of a phosphate compound layer on the surface of the aggregated particles. Mechanochemical treatment can be, for example, a dry treatment in which a base material (particles made of an aggregated lithium composite oxide) and coating material particles (lithium phosphate) are rotated at high speed in a container together with media (zirconia beads), pulverizing the coating material particles and bonding them to the surface of the base material to coat them. The molar ratio of the coating material particles to the base material may be, for example, 0.01 mol% or more and 2.0 mol% or less.

[0026] A method for heat-treating an aggregated lithium composite oxide (also referred to as a surface-treated lithium composite oxide) surface-treated with a phosphate compound using at least one selected from the group consisting of metal oxides and boric acid (H3BO3) and a lithium salt includes, for example, mixing the surface-treated lithium composite oxide with at least one selected from the group consisting of metal oxides and boric acid and a lithium salt, and heating the mixture at a temperature of 200°C to 400°C for 3 to 120 minutes. Examples of lithium salts include lithium carbonate. Examples of metal oxides include tungstic acid (H3BO3), zirconate (H4O4Zr), titanate (H4TiO4), and aluminate (HAlO2). The heat treatment time is preferably 10 to 60 minutes from the viewpoints of energy density and cycle characteristics.

[0027] The molar ratio of the total mass of the lithium-containing metal oxide and lithium borate to the phosphate compound in the aggregated particles (hereinafter also referred to as the coating ratio) is 5.0 or less. The lower limit of the coating ratio may be, for example, 0.5 or more, 0.8 or more, or 1.0 or more. The upper limit of the coating ratio may be, for example, 4.0 or less, 3.0 or less, 2.0 or less, or 1.8 or less.

[0028] The mass ratio of the single particles to the aggregated particles in the positive electrode active material may be, for example, 20:80 to 50:50, and preferably 30:70 to 50:50. When the mass ratio of the single particles to the aggregated particles in the positive electrode active material is within the above range, the packing property tends to be easily improved.

[0029] The DTG peak value of the positive electrode active material may be, for example, less than 3.2% / min, preferably 3.0% / min or less, more preferably 2.0% / min or less, and even more preferably 1.5% / min or less. The DTG peak value of the positive electrode active material is measured according to the method described in the Examples section below.

[0030] <Method of manufacturing positive electrode active material> 1, the method for producing a positive electrode active material includes a first treatment step (A) of coating agglomerated particles with a phosphate compound by, for example, mechanochemical treatment, a second treatment step (B) of heat-treating the agglomerated particles after the first treatment step using at least one selected from the group consisting of metal oxides and boric acid and a lithium salt, and a mixing step (C) of mixing the agglomerated particles after the second treatment step with single particles. The above descriptions apply to the single particles, agglomerated particles, phosphate compound, mechanochemical treatment, and heat treatment.

[0031] <Nonaqueous electrolyte secondary battery> Fig. 2 is a schematic diagram showing an example of a nonaqueous electrolyte secondary battery according to this embodiment. The battery 100 shown in Fig. 2 may be a lithium ion battery such as a main power source or a power source for power assist of an electric vehicle.

[0032] The battery 100 includes an exterior housing 90. The exterior housing 90 houses an electrode assembly 50 and an electrolyte (not shown). The electrode assembly 50 is connected to a positive terminal 91 by a positive current collecting member 81. The electrode assembly 50 is connected to a negative terminal 92 by a negative current collecting member 82. FIG. 3 is a schematic diagram showing an example of an electrode assembly in this embodiment. The electrode assembly 50 is a wound type. The electrode assembly 50 includes a positive electrode plate 20, a separator 40, and a negative electrode plate 30. That is, the battery 100 includes the positive electrode plate 20. The positive electrode plate 20 includes a positive electrode active material layer 22 and a positive electrode substrate 21. The negative electrode plate 30 includes a negative electrode active material layer 32 and a negative electrode substrate 31.

[0033] <Positive electrode> As shown in FIG. 4, a positive electrode plate 20 may have a positive electrode active material layer 22 formed directly or indirectly on one or both sides of a positive electrode substrate 21. The positive electrode substrate 21 may be a conductive sheet made of, for example, an Al alloy foil, a pure Al foil, or the like. The positive electrode active material layer 22 contains a positive electrode active material including single particles 11 and agglomerated particles 12. The positive electrode active material layer 22 contains the above-mentioned positive electrode active material. The positive electrode active material layer 22 may further contain a conductive material, a binder, and the like.

[0034] The positive electrode active material layer 22 may have a thickness of, for example, 10 μm or more and 200 μm or less. The positive electrode active material layer 22 may have a high density. The density of the positive electrode active material layer 22 is, for example, 3.65 g / cm. 3 may be 3.7 g / cm or more, 3 or more than 3.8g / cm 3 The positive electrode active material layer 22 may have a density of, for example, 4.0 g / cm 3 It may have the following densities:

[0035] <Manufacturing method of positive electrode plate> The manufacturing method of the positive electrode plate 20 in this embodiment includes (A) preparation of a positive electrode slurry, (B) application, and (C) rolling, as shown in FIG. 5. In (A) preparation of the positive electrode slurry, a positive electrode slurry containing the above-described positive electrode active material is prepared. The positive electrode slurry is prepared by dispersing the positive electrode active material in a dispersion medium. The dispersion medium may be an organic solvent, such as N-methyl-2-pyrrolidone (NMP), tetrahydrofuran (THF), dimethylformamide (DMF), methyl ethyl ketone (MEK), and dimethyl sulfoxide (DMSO). The positive electrode slurry may contain a conductive material and a binder. Examples of the conductive material include carbon nanotubes, carbon black such as acetylene black (AB), and other carbon materials (e.g., graphite). Examples of binders include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide (PA), polyamideimide (PAI), butadiene rubber (BR), styrene butadiene rubber (SBR), nitrile-butadiene rubber (NBR), styrene-ethylene-butylene-styrene block copolymer (SEBS), carboxymethyl cellulose (CMC), or combinations thereof. The slurry may have a solids concentration of, for example, 40% to 80%. Any stirring, mixing, or dispersing device may be used for mixing.

[0036] In coating (B), the positive electrode slurry is coated on the surface of the positive electrode substrate 21 to form the positive electrode active material layer 22. In rolling (C), the positive electrode active material layer 22 and the positive electrode substrate 21 are rolled together to produce the positive electrode plate 20. A raw sheet of the positive electrode plate 20 is produced by rolling. The raw sheet can be cut to a predetermined planar size according to the specifications of the battery 100. [Example]

[0037] The present invention will be described in more detail below with reference to examples. In the examples, "%" and "parts" are by mass % and mass parts unless otherwise specified.

[0038] Example 1 [Single particle preparation] Co-precipitation of Ni 0.78 Co 0.11 Mn 0.11 Nickel-cobalt-manganese composite hydroxide (OH)2 was calcined at 500°C to obtain nickel-cobalt-manganese composite oxide (Z1). Next, lithium hydroxide and nickel-cobalt-manganese composite oxide (Z1) were mixed so that the molar ratio of Li to the total amount of Ni, Co, and Mn was 1.05:1. The mixture was calcined in an oxygen atmosphere at 900°C for 72 hours, wet-pulverized in a ball mill, dried, and then converted to a single-particle structure. This was then heat-treated again in an oxygen atmosphere at 750°C for 10 hours to obtain a lithium composite oxide (composite oxide A) with a single-particle structure. Measurement of the particle size distribution of composite oxide A revealed a particle diameter (D50) of 3.6 μm. Observation of its structure using an SEM revealed that composite oxide A consisted of particles with a nearly single-particle structure, with particle diameters ranging from 2.5 to 3.8 μm.

[0039] [Preparation of aggregated particles] Co-precipitation of Ni 0.83 Co 0.05 Mn 0.12 A nickel-cobalt-manganese composite hydroxide (OH)2 was calcined with lithium hydroxide in an oxygen atmosphere at 800°C for 10 hours and then crushed to obtain a lithium composite oxide. 0.2 mol% lithium phosphate was added to the mixture and mechanochemically treated for a predetermined time using a P5 planetary mill manufactured by Filitch Co., Ltd., with φ2 mm zirconia balls to obtain a lithium composite oxide (composite oxide B1) with an aggregated structure coated with lithium phosphate (first treatment step). Subsequently, composite oxide B1 was added with 0.6 wt% boric acid and an equal molar amount of lithium carbonate, and heat-treated at 300°C to obtain a lithium composite oxide B1 (composite oxide B) with an aggregated structure coated with lithium borate (Li3PO4) as a surface-coating compound (second treatment step). The coating ratio and heat treatment time are shown in Table 1.

[0040] The particle size distribution of composite oxide B was D50 12 μm, D70 14 μm, and D30 10 μm. The cross section of composite oxide B after CP processing was observed by SEM, and the average primary particle diameter of composite oxide B was found to be 0.13 μm.

[0041] [Preparation of positive electrode active material] The composite oxide A and the composite oxide B2 were mixed in a mass ratio of 1:1 (mixing step) to obtain the positive electrode active material of Example 1.

[0042] <Examples 2 to 10> A positive electrode active material was prepared in the same manner as in Example 1, except that the additive compounds and surface coating compounds shown in Table 1 were used in amounts to achieve the coating ratios shown in Table 1, and that the treatment time in the second treatment step was set to the time shown in Table 1.

[0043] <Comparative Example 1> A positive electrode active material was produced in the same manner as in Example 1, except that aggregated particles were produced by the following procedure. Co-precipitation of Ni 0.83 Co 0.05 Mn 0.12 A nickel-cobalt-manganese composite hydroxide (OH)2 was calcined with lithium hydroxide in an oxygen atmosphere at 800°C for 10 hours, and then crushed to obtain a lithium composite oxide. To this, a lithium composite oxide coated with lithium phosphate, 0.6 wt% boric acid, and an equal molar amount of lithium carbonate were added, and the mixture was heat-treated at 300°C for 5 minutes to obtain a lithium composite oxide coated with lithium borate (Li3PO4). The heat treatment time is shown in Table 1.

[0044] [Preparation of positive electrode plate] The positive electrode active materials obtained in the examples and comparative examples, acetylene black, and polyvinylidene fluoride (PVdF) were further mixed to a solid mass ratio of 96.3:2.5:1.2, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added, followed by kneading to prepare a positive electrode composite slurry. The positive electrode composite slurry was applied to both sides of a 1N30 aluminum foil core having a thickness of 13 μm, the coating film was dried, and then the coating film was rolled using a rolling mill until the composite density of the coating film reached 3.7 g / cm. 3 The resultant was compressed to a predetermined electrode size, and cut to obtain a positive electrode plate in which a positive electrode composite layer was formed on both sides of the positive electrode core.

[0045] [Fabrication and evaluation of small lithium-ion batteries] A separator was placed between the electrodes and the carbon anode, which was then placed in a laminate outer bag. An electrolyte solution was added and the bag was sealed to produce a small laminated battery. The following examples and comparative examples were produced, each with a different coating treatment for the cathode active material. The battery size was determined by stacking eight electrode layers to obtain a charge capacity of 600 mAh. The measurement results for charge capacity (mAh / g) and discharge capacity (mAh / g) are shown in Table 1.

[0046] [Evaluation of DTG peak value] After charging, the battery was disassembled, washed, and dried. The powder mixture was scraped off from the positive electrode plate, and 10 mg of the powder mixture was placed in an Al pan in an Ar atmosphere glove box. The thermogravimetric change was measured at a rate of 5°C / min up to 500°C using a TG-DTA device (Shimadzu DTA-60AH). The DTG peak value (% / min) associated with oxygen release from the active material was determined from the differential curve. The results are shown in Table 1.

[0047] [Table 1]

[0048] As shown in Table 1, the DTG peak values ​​were lower in Examples 1 to 10 than in Comparative Example 1. It is clear that the positive electrode active material of the present disclosure can achieve both good energy density and good cycle characteristics. [Explanation of symbols]

[0049] 11 single particle, 12 agglomerated particle, 20 positive electrode plate, 21 positive electrode substrate, 22 positive electrode active material layer, 30 negative electrode plate, 31 negative electrode substrate, 32 negative electrode active material layer, 40 separator, 50 electrode body, 81 positive electrode current collecting member, 82 negative electrode current collecting member, 90 exterior body, 91 positive electrode terminal, 92 negative electrode terminal, 100 battery.

Claims

1. A positive electrode active material including single particles and aggregated particles, the single particles and the agglomerated particles contain a nickel-cobalt-manganese compound, the nickel content in the nickel-cobalt-manganese compound contained in the single particle is 70 mol % or more; the nickel content in the nickel-cobalt-manganese compound contained in the agglomerated particles is 75 mol % or more; the agglomerated particles further contain a phosphate compound and at least one selected from the group consisting of a lithium-containing metal oxide and a lithium borate, the agglomerated particles have a phosphate compound layer on the surface of the agglomerated particles, and a layer containing at least one selected from the group consisting of a lithium-containing metal oxide and lithium borate on the phosphate compound layer; a molar ratio of the total mass of the lithium-containing metal oxide and lithium borate to the phosphate compound in the aggregated particles is 5.0 or less.

2. 2. The positive electrode active material according to claim 1, wherein a mass ratio of the single particles to the aggregated particles is 20:80 to 50:

50.

3. 2. The positive electrode active material according to claim 1, wherein the lithium-containing metal oxide comprises at least one selected from the group consisting of lithium tungstate, lithium zirconate, lithium titanate, and lithium aluminate.

4. A cathode active material layer containing the cathode active material according to claim 1, wherein the density of the cathode active material layer is 3.65 g / cm ３ That's it for the positive plate.

5. A non-aqueous electrolyte secondary battery comprising the positive electrode plate according to claim 4.

6. The method for producing a positive electrode active material according to claim 1, a first treatment step of coating the agglomerated particles with a phosphoric acid compound; a second treatment step of heat-treating the aggregated particles obtained after the first treatment step using at least one selected from the group consisting of metal oxides and boric acid, and a lithium salt; and a mixing step of mixing the aggregated particles obtained after the second treatment step with single particles; A method for producing a positive electrode active material, comprising:

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