Positive electrode for lithium-ion secondary battery and lithium-ion secondary battery

Abstract

To provide a positive electrode for a lithium-ion secondary battery that enables obtaining a lithium-ion secondary battery capable of reducing gas generation, and a lithium-ion secondary battery using the same.SOLUTION: A positive electrode for a lithium-ion secondary battery includes a positive electrode active material layer. A positive electrode active material contained in the positive electrode active material layer includes a lithium composite oxide (X) having a layered rock salt crystal structure. The content of Li2CO3 in the positive electrode active material is 0.01 mass% or more and 0.15 mass% or less of the total positive electrode active material.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery. [Background technology]

[0002] Lithium composite oxides having a layered rock-salt crystal structure are known as positive electrode active materials for lithium ion secondary batteries. Patent Document 1, for example, describes a technology relating to lithium ion secondary batteries that use lithium composite oxides having a layered rock-salt crystal structure as the positive electrode active material.

[0003] Patent Document 1 describes a positive electrode for the purpose of providing a positive electrode that can impart high gas generation suppression performance during storage and high cycle characteristics to a non-aqueous electrolyte secondary battery, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector, the positive electrode active material layer containing first Ni-containing lithium composite oxide particles in the form of single particles and second Ni-containing lithium composite oxide particles in the form of secondary particles, the first Ni-containing lithium composite oxide particles and the second Ni-containing lithium composite oxide particles each having a layered crystal structure, the first Ni-containing lithium composite oxide particles having an average particle size (D50) of 2 μm to 6 μm, the second Ni-containing lithium composite oxide particles having an average primary particle size of 1.2 μm to 2.0 μm, and the second Ni-containing lithium composite oxide particles having an average particle size (D50) of 12 μm to 20 μm. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-91566 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention provides a positive electrode for a lithium ion secondary battery that can reduce the amount of gas generated from the resulting lithium ion secondary battery, and a lithium ion secondary battery that uses the positive electrode for a lithium ion secondary battery. [Means for solving the problem]

[0006] According to the present invention, there are provided the following positive electrode for a lithium ion secondary battery and the following lithium ion secondary battery.

[0007] [1] A positive electrode for a lithium ion secondary battery including a positive electrode active material layer, the positive electrode active material contained in the positive electrode active material layer contains a lithium composite oxide (X) having a layered rock salt crystal structure, A positive electrode for a lithium ion secondary battery, wherein the content of Li2CO3 in the positive electrode active material is 0.01% by mass or more and 0.15% by mass or less with respect to the total amount of the positive electrode active material. [2] The positive electrode for a lithium ion secondary battery according to [1], wherein the positive electrode active material comprises single-crystal particles (A) made of the lithium composite oxide (X) and polycrystalline particles (B) made of the lithium composite oxide (X). [3] The positive electrode for a lithium ion secondary battery according to [2], wherein the content of Li2CO3 in the single crystal particles (A) is 0.01% by mass or more and 0.18% by mass or less based on the entire single crystal particles (A). [4] The positive electrode for a lithium ion secondary battery according to [2] or [3], wherein the content of Li2CO3 in the polycrystalline particles (B) is 0.01 mass % or more and 0.30 mass % or less with respect to the entire polycrystalline particles (B). [5] The positive electrode for a lithium ion secondary battery according to any one of [2] to [4], wherein, when the content of the single crystal particles (A) in the positive electrode active material layer is W1 and the content of the polycrystalline particles (B) in the positive electrode active material layer is W2, the mass ratio (W1 / W2) of the single crystal particles (A) to the polycrystalline particles (B) is 0.1 or more and 10.0 or less. [6] The single crystal particles (A) have a specific surface area of ​​0.01 m as measured by a nitrogen adsorption BET method. 2 / g or more 3.0m 2 The positive electrode for a lithium ion secondary battery according to any one of [2] to [5], wherein the positive electrode has a value of not more than 1 / g. [7] The polycrystalline particles (B) have a specific surface area of ​​0.01 m as measured by a nitrogen adsorption BET method. 2 / g or more 3.0m 2 The positive electrode for a lithium ion secondary battery according to any one of [2] to [6], wherein the positive electrode has a viscosity of 1000 psi or less. [8] The particle diameter d of the single crystal particles (A) at which the cumulative value in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 10% 10 , 90% particle diameter d 90 and average particle diameter d 50 (d 90 -d 10 ) / d 50 The positive electrode for a lithium ion secondary battery according to any one of [2] to [7], wherein the value of is 0.1 or more and 10.0 or less. [9] The particle diameter d of the single crystal particles (A) at which the cumulative value in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 10% 10 The positive electrode for a lithium ion secondary battery according to any one of [2] to [8], wherein the average particle size is 0.1 μm or more and 5.0 μm or less.

[10] The average particle diameter d of the single crystal particles (A) at which the cumulative value reaches 50% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method 50 The positive electrode for a lithium ion secondary battery according to any one of [2] to [9], wherein the average particle size is 1.0 μm or more and 10.0 μm or less.

[11] The particle diameter d of the single crystal particles (A) is 90% of the cumulative value in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. 90 The positive electrode for a lithium ion secondary battery according to any one of [2] to

[10] , wherein the average particle size is 3.0 μm or more and 20.0 μm or less.

[12] The particle diameter d of the polycrystalline particles (B) at which the cumulative value in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 10% 10 , 90% particle diameter d 90 and average particle diameter d 50 (d 90 -d 10 ) / d 50 The positive electrode for a lithium ion secondary battery according to any one of [2] to

[11] , wherein the value of is 0.1 or more and 5.0 or less.

[13] The particle diameter d of the polycrystalline particles (B) at which the cumulative value in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 10% 10 The positive electrode for a lithium ion secondary battery according to any one of [2] to

[12] , wherein the average particle size is 0.5 μm or more and 15.0 μm or less.

[14] The polycrystalline particles (B) have an average particle diameter d at which the cumulative value reaches 50% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. 50 The positive electrode for a lithium ion secondary battery according to any one of [2] to

[13] , wherein the average particle size is 2.0 μm or more and 25.0 μm or less.

[15] The particle diameter d of the polycrystalline particles (B) at which the cumulative value in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 90% 90 The positive electrode for a lithium ion secondary battery according to any one of [2] to

[14] , wherein the average particle size is 3.0 μm or more and 40.0 μm or less.

[16] The positive electrode for a lithium ion secondary battery according to any one of [1] to

[15] , wherein the lithium composite oxide (X) contains one or more composite oxides selected from the group consisting of lithium-nickel composite oxides, lithium-cobalt composite oxides, lithium-nickel-aluminum composite oxides, and lithium-nickel-cobalt-manganese composite oxides.

[17] The positive electrode for a lithium ion secondary battery according to any one of [1] to

[16] , wherein the lithium composite oxide (X) contains a lithium-nickel-cobalt-manganese composite oxide.

[18] The positive electrode for a lithium ion secondary battery according to any one of [1] to

[17] , wherein the content of the positive electrode active material in the positive electrode active material layer is 50.0 parts by mass or more and 99.9 parts by mass or less, when the total amount of the positive electrode active material layer is 100.0 parts by mass.

[19] [1] to

[18] , and a positive electrode for a lithium ion secondary battery according to any one of [1] to

[18] . an electrolyte layer; a negative electrode including a negative electrode active material layer; A lithium-ion secondary battery comprising:

[20] The lithium ion secondary battery according to

[19] , wherein the negative electrode active material contained in the negative electrode active material layer comprises one or more negative electrode active materials selected from the group consisting of carbon materials, lithium-based metal materials, Si-based materials, and conductive polymer materials. [twenty one] The lithium ion secondary battery according to

[19] or

[20] , wherein the negative electrode active material contained in the negative electrode active material layer contains Si-C composite particles containing silicon and a carbon material. [twenty two] The lithium ion secondary battery according to any one of

[19] to

[21] , wherein the negative electrode active material contained in the negative electrode active material layer contains graphite particles. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a positive electrode for a lithium ion secondary battery that can produce a lithium ion secondary battery that can reduce the amount of gas generated, and a lithium ion secondary battery that uses the positive electrode for a lithium ion secondary battery. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing an example of a lithium ion secondary battery according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. To avoid complexity, when there are multiple identical components in the same drawing, only one of them may be labeled with a symbol, and not all of them. The drawings are for illustrative purposes only, and the shapes and dimensional ratios of the components in the drawings do not necessarily correspond to the actual products. In this embodiment, "A to B" indicating a numerical range means A or more and B or less unless otherwise specified.

[0011] <Positive electrodes for lithium-ion secondary batteries> The positive electrode for a lithium ion secondary battery of this embodiment is a positive electrode for a lithium ion secondary battery including a positive electrode active material layer, wherein the positive electrode active material included in the positive electrode active material layer includes a lithium composite oxide (X) having a layered rock salt crystal structure, and the content of Li2CO3 in the positive electrode active material is 0.01 mass% or more and 0.15 mass% or less with respect to the entire positive electrode active material. The content of Li2CO3 in the positive electrode active material is 0.01 mass % or more and 0.15 mass % or less, preferably 0.02 mass % or more and 0.14 mass % or less, more preferably 0.03 mass % or more and 0.13 mass % or less, and even more preferably 0.04 mass % or more and 0.12 mass % or less, from the viewpoint of further reducing the amount of gas generated from the resulting lithium ion secondary battery. The content of Li2CO3 in the positive electrode active material can be adjusted, for example, by washing the positive electrode active material in the positive electrode active material layer with an aqueous sodium sulfate solution and / or an aqueous lithium sulfate solution for a predetermined period of time.

[0012] In this embodiment, the content of Li2CO3 in the positive electrode active material can be measured by, for example, neutralization titration with hydrochloric acid.

[0013] As a result of investigations by the present inventors, it was found that there is a correlation between the content of Li2CO3 in a positive electrode active material and the amount of gas generated by a lithium-ion secondary battery. As a result of further intensive investigations based on the above findings, the present inventors found that by setting the content of Li2CO3 in a positive electrode active material within the above range, the amount of gas generated by the resulting lithium-ion secondary battery can be reduced, and thus completed the present invention. The reason why the amount of gas generated in the resulting lithium-ion secondary battery can be reduced when the Li2CO3 content in the positive electrode active material is within the above range is not clear, but it is speculated that the mechanism is that when the Li2CO3 content in the positive electrode active material is within the above range, the Li2CO3 content, which is thought to be one of the causes of gas generation during charge / discharge cycles, falls within an appropriate range, thereby reducing the amount of gas generated in the lithium-ion secondary battery.

[0014] From the viewpoint of further reducing the amount of gas generated from the resulting lithium ion secondary battery, the lithium composite oxide (X) having a layered rock salt crystal structure preferably contains one or more composite oxides selected from the group consisting of lithium-nickel composite oxides, lithium-cobalt composite oxides, lithium-nickel-aluminum composite oxides, and lithium-nickel-cobalt-manganese composite oxides, and more preferably contains lithium-nickel-cobalt-manganese composite oxides.

[0015] From the viewpoint of increasing capacity, the lithium-nickel-cobalt-manganese composite oxide of this embodiment preferably contains a composite oxide represented by the following formula (1).

[0016] Li a Ni b Co c Mn d M e O2(1) In the formula (1), M is one or more selected from the group consisting of Al, Mg, Na, Co, K, W, Cu, Fe, Ba, V, Cr, Ti, Zr, Zn, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and 0.5≦a≦1.5, 0.6≦b<1.0, 0 <c<0.2、0<d<0.2、0≦e<1.0である。

[0017] In the composite oxide of formula (1), 0.5≦a≦1.5, preferably 0.6≦a≦1.4, more preferably 0.7≦a≦1.3, even more preferably 0.8≦a≦1.2, even more preferably 0.9≦a≦1.1, and even more preferably a=1.0.

[0018] In the composite oxide of the formula (1), 0.6 ≦ b < 1.0, and from the viewpoint of reducing the gas generation amount of the resulting lithium ion secondary battery, preferably 0.65 ≦ b < 1.0, more preferably 0.7 ≦ b < 1.0, still more preferably 0.75 ≦ b < 1.0, and still more preferably 0.8 ≦ b ≦ 0.95.

[0019] In the composite oxide of the formula (1), 0 < c < 0.2, preferably 0.01 ≦ c ≦ 0.15, more preferably 0.02 ≦ c ≦ 0.15, and still more preferably 0.03 ≦ c ≦ 0.1.

[0020] In the composite oxide of the formula (1), 0 < d < 0.2, preferably 0.01 ≦ d ≦ 0.15, more preferably 0.02 ≦ d ≦ 0.15, and still more preferably 0.02 ≦ d ≦ 0.1.

[0021] In the composite oxide of the formula (1), 0 ≦ e < 1.0, preferably 0 ≦ e ≦ 0.5, more preferably 0 ≦ e ≦ 0.3, still more preferably 0 ≦ e ≦ 0.2, still more preferably 0 ≦ e ≦ 0.1, and still more preferably e = 0.

[0022] From the viewpoint of reducing the gas generation amount of the resulting lithium ion secondary battery, when the total amount of the positive electrode active material layer is 100.0 parts by mass, the content of the positive electrode active material in the positive electrode active material layer of the present embodiment is preferably 50.0 parts by mass or more and 99.9 parts by mass or less, more preferably 75.0 parts by mass or more and 99.5 parts by mass or less, still more preferably 85.0 parts by mass or more and 99.0 parts by mass or less, still more preferably 90.0 parts by mass or more and 98.5 parts by mass or less, and still more preferably 95.0 parts by mass or more and 98.0 parts by mass or less.

[0023] The positive electrode active material of the present embodiment preferably includes single crystal particles (A) composed of a lithium composite oxide (X) having a layered rock salt-type crystal structure and polycrystalline particles (B) composed of a lithium composite oxide (X) having a layered rock salt-type crystal structure. In this embodiment, a single-crystal particle is a particle that is composed of a single crystal grain and does not show grain boundaries when observed under an electron microscope at 1000 to 5000 magnifications. Even when multiple single-crystal particles are closely attached, they are also included in the category of single-crystal particles. On the other hand, in this embodiment, a polycrystalline particle is a particle in which multiple crystal grains with different crystal orientations and grain boundaries are observed within the solid when observed under an electron microscope at 1000 to 5000 magnifications.

[0024] The total content of the single-crystal particles (A) and the polycrystalline particles (B) in the positive electrode active material layer of this embodiment is preferably 50 parts by mass or more and 100 parts by mass or less, more preferably 60 parts by mass or more and 100 parts by mass or less, even more preferably 70 parts by mass or more and 100 parts by mass or less, still more preferably 80 parts by mass or more and 100 parts by mass or less, still more preferably 90 parts by mass or more and 100 parts by mass or less, and still more preferably 95 parts by mass or more and 100 parts by mass or less, when the content of the positive electrode active material in the positive electrode active material layer is taken as 100 parts by mass, from the viewpoint of further reducing the amount of gas generated in the resulting lithium-ion secondary battery. and more preferably 98 parts by mass or more and 100 parts by mass or less.

[0025] When the content of the single-crystal particles (A) in the positive electrode active material layer is W1 and the content of the polycrystalline particles (B) in the positive electrode active material layer is W2, the mass ratio (W1 / W2) of the content of the single-crystal particles (A) to the content of the polycrystalline particles (B) is preferably 0.1 or more and 10.0 or less, more preferably 0.5 or more and 9.0 or less, even more preferably 1.0 or more and 8.0 or less, even more preferably 1.5 or more and 7.0 or less, and even more preferably 2.0 or more and 6.0 or less, from the viewpoint of reducing the amount of gas generated from the obtained lithium-ion secondary battery.

[0026] The content of Li2CO3 in the single crystal particles (A) is preferably 0.01 mass % or more and 0.18 mass % or less, more preferably 0.02 mass % or more and 0.15 mass % or less, even more preferably 0.03 mass % or more and 0.14 mass % or less, and still more preferably 0.04 mass % or more and 0.13 mass % or less, based on the entire single crystal particles (A), from the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery.

[0027] In this specification, the particle size at which the cumulative value reaches 10% in the volume-based particle size distribution measured by the laser diffraction / scattering particle size distribution measurement device is defined as d 10 , 90% particle diameter is d 90 , and the particle diameter at which the cumulative value reaches 50% is the average particle diameter d 50 Let's say.

[0028] The particle diameter d of the single crystal particles (A) 10 From the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery, the average particle size is preferably 0.1 μm or more and 10.0 μm or less, more preferably 0.1 μm or more and 5.0 μm or less, even more preferably 0.3 μm or more and 4.0 μm or less, and even more preferably 0.5 μm or more and 3.5 μm or less.

[0029] Average particle diameter d of single crystal particles (A) 50 From the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery, the average particle size is preferably 1.0 μm or more and 10.0 μm or less, more preferably 1.3 μm or more and 8.0 μm or less, even more preferably 1.5 μm or more and 7.0 μm or less, even more preferably 1.8 μm or more and 6.0 μm or less, and even more preferably 2.0 μm or more and 5.5 μm or less.

[0030] The particle diameter d of the single crystal particles (A) 90From the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery, the average particle size is preferably 3.0 μm or more and 20.0 μm or less, more preferably 3.5 μm or more and 18.0 μm or less, even more preferably 4.0 μm or more and 15.0 μm or less, even more preferably 5.0 μm or more and 13.0 μm or less, and even more preferably 5.5 μm or more and 10.0 μm or less.

[0031] The specific surface area of ​​the single crystal particles (A) as measured by the nitrogen adsorption BET method is preferably 0.01 m from the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery. 2 / g or more 3.0m 2 / g or less, more preferably 0.05m 2 / g or more 2.8m 2 / g or less, more preferably 0.10m 2 / g or more 2.5m 2 / g or less, more preferably 0.15m 2 / g or more 2.2m 2 / g or less, more preferably 0.20m 2 / g or more 2.0m 2 / g or less, more preferably 0.25m 2 / g or more 1.8m 2 / g or less.

[0032] The particle diameter d of the single crystal particles (A) 10 , the particle diameter d 90 and the average particle diameter d 50 (d 90 -d 10 ) / d 50 From the viewpoint of further reducing the amount of gas generated from the resulting lithium ion secondary battery, the value of is preferably 0.1 or more and 10.0 or less, more preferably 0.2 or more and 5.0 or less, even more preferably 0.3 or more and 4.0 or less, even more preferably 0.5 or more and 3.5 or less, and even more preferably 0.7 or more and 3.0 or less.

[0033] The content of Li2CO3 in the polycrystalline particles (B) is preferably 0.01 mass % or more and 0.30 mass % or less, more preferably 0.02 mass % or more and 0.25 mass % or less, even more preferably 0.03 mass % or more and 0.23 mass % or less, even more preferably 0.03 mass % or more and 0.20 mass % or less, and still more preferably 0.04 mass % or more and 0.18 mass % or less, based on the entire polycrystalline particles (B), from the viewpoint of further reducing the amount of gas generated in the resulting lithium-ion secondary battery.

[0034] The particle diameter d of the polycrystalline particles (B) 10 From the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery, the average particle size is preferably 0.5 μm or more and 15.0 μm or less, more preferably 1.0 μm or more and 14.0 μm or less, even more preferably 3.0 μm or more and 13.0 μm or less, even more preferably 4.0 μm or more and 12.0 μm or less, and even more preferably 5.0 μm or more and 11.0 μm or less.

[0035] Average particle diameter d of polycrystalline particles (B) 50 From the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery, the average particle size is preferably 2.0 μm or more and 25.0 μm or less, more preferably 5.0 μm or more and 20.0 μm or less, even more preferably 7.0 μm or more and 18.0 μm or less, and even more preferably 8.0 μm or more and 15.0 μm or less.

[0036] The particle diameter d of the polycrystalline particles (B) 90 From the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery, the average particle size is preferably 3.0 μm or more and 40.0 μm or less, more preferably 4.0 μm or more and 35.0 μm or less, even more preferably 6.0 μm or more and 30.0 μm or less, even more preferably 8.0 μm or more and 25.0 μm or less, and even more preferably 10.0 μm or more and 20.0 μm or less.

[0037] The specific surface area of ​​the polycrystalline particles (B) as determined by the nitrogen adsorption BET method is preferably 0.01 m from the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery. 2 / g or more 3.0m 2 / g or less, more preferably 0.03m 2 / g or more 2.5m 2 / g or less, more preferably 0.05m 2 / g or more 2.0m 2 / g or less, more preferably 0.10m 2 / g or more 1.5m 2 / g or less, more preferably 0.15m 2 / g or more 1.0m 2 / g or less.

[0038] The particle diameter d of the polycrystalline particles (B) 10 , the particle diameter d 90 and the average particle diameter d 50 (d 90 -d 10 ) / d 50 From the viewpoint of further reducing the amount of gas generated from the resulting lithium ion secondary battery, the value of is preferably 0.1 or more and 5.0 or less, more preferably 0.2 or more and 3.0 or less, even more preferably 0.3 or more and 1.5 or less, even more preferably 0.4 or more and 1.0 or less, and even more preferably 0.4 or more and 0.7 or less.

[0039] The positive electrode active material of this embodiment may further contain a positive electrode active material other than the single crystal particles (A) and the polycrystalline particles (B). The positive electrode active material other than the single crystal particles (A) and the polycrystalline particles (B) is not particularly limited, and examples thereof include transition metal sulfides such as TiS2, FeS, and MoS2; MnO, VO5, and VO 13 The lithium iron phosphate battery preferably contains one or more materials selected from the group consisting of transition metal oxides such as TiO and olivine-type lithium iron phosphate, and preferably contains olivine-type lithium iron phosphate from the viewpoint of improving the working potential, capacity, durability, and energy density.

[0040] The lithium composite oxide (X) having a layered rock salt type crystal structure, the single crystal particles (A), and the polycrystalline particles (B) of the present embodiment are commercially available products, or may be prepared by a method including the following procedure. For example, Ni obtained by known coprecipitation methods w Cox Mn y M z By mixing oxide particles represented by O3 with lithium hydroxide and heat treating the mixture in the atmosphere, it is possible to obtain positive electrode active material particles composed of the composite oxide represented by the above-mentioned formula (1).

[0041] By adjusting the particle size of the oxide particles and the heat treatment temperature in air, the resulting positive electrode active material particles can be adjusted to be single crystal or polycrystalline, and the particle size can also be controlled. In single crystal particles, multiple particles aggregate when growing to a predetermined particle size by heat treatment. Therefore, single crystal particles of a predetermined particle size can be obtained by pulverizing the aggregated particles using a jet mill or the like. The composite oxide particles can be classified by sieving them through meshes with different openings and linearities.

[0042] The surfaces of the obtained positive electrode active material particles contain lithium carbonate, which is produced by the reaction of moisture and carbon dioxide in the air with lithium hydroxide. Here, in order to adjust the content of lithium carbonate in the positive electrode active material particles, it is preferable to wash the positive electrode active material particles. As a method for washing the positive electrode active material particles, for example, a method for washing the positive electrode active material particles with an aqueous lithium sulfate solution and / or an aqueous sodium sulfate solution can be mentioned, and by performing such washing, the content of lithium carbonate in the positive electrode active material particles can be adjusted. The lithium ion concentration of the lithium sulfate aqueous solution during washing is preferably 1 mol / L or less. By adjusting the lithium ion concentration of the lithium sulfate aqueous solution within the above range, it is possible to avoid excessive removal of lithium during washing and to easily control the lithium carbonate content in the positive electrode active material to an appropriate amount.

[0043] A coating layer may be formed on the surface of the washed positive electrode active material particles. For example, the coating layer can be formed by heat treatment or the like. The material of the coating layer is not particularly limited, but examples include an aluminum oxide layer (Al2O3) and a niobium oxide layer (Nb2O5). However, it is preferable to minimize the inclusion of boron oxide such as B2O3, as this can cause cracking of the polycrystalline particles during the production of lithium-ion secondary batteries.

[0044] The positive electrode active material layer of this embodiment preferably contains a conductive additive, and more preferably contains a conductive additive and a binder, from the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery.

[0045] Examples of the conductive additive in the positive electrode active material layer of this embodiment include carbon fibers such as carbon nanofibers, carbon blacks such as acetylene black and ketjen black, activated carbon, graphite, mesoporous carbon, fullerenes, and carbon nanotubes. From the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery, it is particularly preferable to use carbon nanotubes (CNTs). CNTs are substances in which a six-membered ring network of carbon atoms (graphene) has a single-layer or multi-layer coaxial tubular structure, and examples include single-wall carbon nanotubes (SWCNTs) and multi-wall carbon nanotubes (MWCNTs). Either type of CNT may be used. Furthermore, to support the conductivity of the positive electrode active material layer, carbon black may be used in addition to CNTs.

[0046] The content of the conductive additive in the positive electrode active material layer of this embodiment is preferably 0.05 to 10.0 parts by mass, more preferably 0.1 to 5.0 parts by mass, even more preferably 0.2 to 2.5 parts by mass, and even more preferably 0.5 to 2.0 parts by mass, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass, from the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery. When carbon nanotubes are used alone or in combination with other conductive additives, the content of the carbon nanotubes in the positive electrode active material layer of this embodiment is preferably 0.01 to 3 parts by mass, particularly preferably 0.03 to 2 parts by mass, and even more preferably 0.05 to 1.5 parts by mass, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass, from the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery.

[0047] Examples of the binder in the positive electrode active material layer of this embodiment include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), polyvinyl fluoride (PVF), and VdF-hexafluoropropylene copolymers; conductive polymers such as polyanilines, polythiophenes, polyacetylenes, and polypyrroles; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin. These may be used alone or in combination of two or more. Among these, from the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery, the binder in the positive electrode active material layer of the present embodiment preferably contains one or more selected from the group consisting of fluororesin, polycarboxylic acid polymer, and synthetic rubber, more preferably contains one or more selected from the group consisting of polyvinylidene fluoride, polycarboxylic acid polymer, and styrene butadiene rubber, and even more preferably contains polyvinylidene fluoride.

[0048] From the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery, the content of the binder in the positive electrode active material layer of this embodiment is preferably 0.05 parts by mass or more and 10.0 parts by mass or less, more preferably 0.1 parts by mass or more and 5.0 parts by mass or less, even more preferably 0.2 parts by mass or more and 2.5 parts by mass or less, and even more preferably 0.5 parts by mass or more and 2.0 parts by mass or less, when the total amount of the positive electrode active material layer is taken as 100.0 parts by mass.

[0049] In addition, the positive electrode active material layer may contain appropriate electrode additives that are generally used for forming electrodes, such as thickeners, dispersants, and stabilizers.

[0050] The thickness of the positive electrode active material layer of this embodiment is preferably 10 μm or more and 250 μm or less, more preferably 20 μm or more and 200 μm or less, and even more preferably 50 μm or more and 150 μm or less, from the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery.

[0051] The density of the positive electrode active material layer of this embodiment is preferably 0.5 g / cm from the viewpoint of further improving the battery performance of the resulting lithium ion secondary battery. 3 More than 5.0g / cm 3 or less, more preferably 1.0 g / cm 3 More than 4.5g / cm 3 More preferably 2.5 g / cm or less 3 More than 4.0g / cm 3 More preferably, 3.0 g / cm or less 3 More than 4.0g / cm 3 The following is the result.

[0052] The positive electrode current collector layer of this embodiment contains, for example, one or more selected from the group consisting of aluminum, stainless steel, nickel, titanium, and alloys thereof. The positive electrode current collector layer may be in the form of, for example, a foil, a flat plate, or a mesh. The thickness of the positive electrode current collector layer is not particularly limited, but is, for example, 1 μm to 50 μm.

[0053] <Lithium-ion secondary battery> The lithium ion secondary battery of this embodiment includes the positive electrode for lithium ion secondary batteries of this embodiment. By including the positive electrode for lithium ion secondary batteries of this embodiment, the amount of gas generation can be reduced.

[0054] The lithium ion secondary battery of this embodiment will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an example of the lithium ion secondary battery of this embodiment. As shown in FIG. 1, the lithium ion secondary battery 10 of this embodiment includes, for example, the positive electrode for the lithium ion secondary battery of this embodiment, an electrolyte layer, and a negative electrode including a negative electrode active material layer. A separator 5 can be provided between the positive electrode and the negative electrode. A plurality of electrode pairs of a positive electrode and a negative electrode can be provided.

[0055] The lithium-ion secondary battery 10 includes a positive electrode including a positive electrode current collector 3 made of a metal such as aluminum foil and a positive electrode active material layer 1 containing a positive electrode active material disposed thereon, and a negative electrode including a negative electrode current collector 4 made of a metal such as copper foil and a negative electrode active material layer 2 containing a negative electrode active material disposed thereon. The positive electrode and negative electrode are stacked, for example, with a separator 5 made of a nonwoven fabric, a polypropylene microporous film, or the like, interposed between them, so that the positive electrode active material layer 1 and the negative electrode active material layer 2 face each other. This electrode pair is housed in a container formed of exterior bodies 6 and 7 made of, for example, aluminum laminate film. A positive electrode tab 9 is connected to the positive electrode current collector 3, and a negative electrode tab 8 is connected to the negative electrode current collector 4, with these tabs extending outside the container. An electrolyte solution is poured into the container and sealed. Alternatively, a container may contain an electrode group in which multiple electrode pairs are stacked.

[0056] The lithium ion secondary battery 10 can be fabricated according to a known method. The electrodes can be, for example, laminates or wound bodies. The exterior can be a metal exterior or an aluminum laminate exterior. The battery can be in any shape, such as a coin, button, sheet, cylindrical, rectangular, or flat shape.

[0057] In the lithium-ion secondary battery of this embodiment, the negative electrode preferably includes a negative electrode active material layer containing a negative electrode active material and a negative electrode current collector. The negative electrode active material layer of this embodiment preferably includes a negative electrode active material and a binder, and more preferably includes a negative electrode active material, a binder, and a conductive additive.

[0058] From the viewpoint of further reducing the amount of gas generated from the resulting lithium-ion secondary battery, the negative electrode active material in the negative electrode active material layer of this embodiment preferably contains one or more negative electrode active materials selected from the group consisting of carbon materials, lithium-based metal materials, Si-based materials, and conductive polymer materials, more preferably contains one or more negative electrode active materials selected from the group consisting of carbon materials and Si-based materials, and even more preferably contains both an Si-based material and a carbon material.

[0059] The carbon material contained in the negative electrode active material of this embodiment may be, for example, graphite particles, hard carbon, soft carbon, carbon black, or any mixture thereof, and preferably contains graphite particles. Graphite particles are available from, for example, Nippon Graphite Industries Co., Ltd. and JFE Chemical Corporation.

[0060] Examples of the Si-based material contained in the negative electrode active material of this embodiment include silicon oxide and Si-C composite particles containing silicon and a carbon material, and preferably contains Si-C composite particles from the viewpoint of reducing the amount of gas generated from the resulting lithium ion secondary battery.

[0061] Silicon oxides available for use include those available from Sigma-Aldrich Corporation, Kojundo Chemical Laboratory Co., Ltd., Kanto Chemical Co., Ltd., Fujifilm Wako Pure Chemical Industries, Ltd., Osaka Titanium Co., Ltd., and the like.

[0062] The Si—C composite particles of this embodiment are particles in which the carbon material contains a porous carbon material, and silicon is present in at least some of the pores of the porous carbon material. In the present embodiment, the method for producing the Si-C composite particles is not particularly limited. For example, the Si-C composite particles may have a median diameter of 4.0 to 10.0 μm and a specific surface area of ​​1000 to 1800 m.2 / g of porous carbon material is placed in a tubular furnace, the inside of the furnace is replaced with argon gas, and then a mixed gas of silane gas containing 1 to 3 mol % of silane gas and nitrogen gas is flowed into the tubular furnace at a flow rate of 250 to 350 sccm, and the furnace is maintained under conditions of 450 to 550°C, 700 to 800 Torr, and treatment for 90 to 150 minutes. Examples of porous carbon materials constituting the Si-C composite particles of this embodiment include activated carbon, aggregates of carbon fibers, aggregates of carbon nanotubes, carbon obtained by heat treating resins or organic materials, etc. Porous carbon materials can be produced by methods for producing activated carbon or known methods for heat treating polymers, but commercially available products may also be purchased, and are not limited to these, as long as silicon can be produced or incorporated into the pores of the porous carbon.

[0063] In the lithium ion secondary battery of this embodiment, the content of graphite particles in the negative electrode active material layer is W A , the content of Si-C composite particles in the negative electrode active material layer is W B When we do this, W B W against A Ratio of W A / W B From the viewpoint of further improving the battery performance of the obtained lithium ion secondary battery, the value of is preferably 1.0 or more and 20.0 or less, more preferably 2.0 or more and 15.0 or less, even more preferably 2.5 or more and 10.0 or less, even more preferably 2.8 or more and 8.0 or less, even more preferably 3.0 or more and 5.5 or less, and even more preferably 3.5 or more and 5.0 or less.

[0064] In order to further improve the battery performance of the resulting lithium-ion secondary battery, the content of the negative electrode active material in the negative electrode active material layer of this embodiment is preferably 50.0 parts by mass or more and 100.0 parts by mass or less, more preferably 75.0 parts by mass or more and 99.0 parts by mass or less, even more preferably 85.0 parts by mass or more and 98.5 parts by mass or less, even more preferably 90.0 parts by mass or more and 98.0 parts by mass or less, and even more preferably 95.0 parts by mass or more and 97.5 parts by mass or less, when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass.

[0065] Examples of the conductive additive in the negative electrode active material layer of this embodiment include carbon fibers such as carbon nanofibers; carbon blacks such as acetylene black and ketjen black; and carbon materials such as activated carbon, mesoporous carbon, fullerenes, and carbon nanotubes. One of these may be used alone, or two or more may be used in combination.

[0066] In order to further improve the battery performance of the resulting lithium-ion secondary battery, the content of the conductive additive in the negative electrode active material layer of this embodiment is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, more preferably 0.03 parts by mass or more and 3.0 parts by mass or less, even more preferably 0.05 parts by mass or more and 1.0 parts by mass or less, and even more preferably 0.07 parts by mass or more and 0.5 parts by mass or less, when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass.

[0067] Examples of the binder in the negative electrode active material layer of this embodiment include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and polyvinyl fluoride (PVF); polycarboxylic acid-based polymers such as poly(meth)acrylic acid; conductive polymers such as polyaniline, polythiophene, polyacetylene, and polypyrrole; synthetic rubbers such as styrene butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), isoprene rubber (IR), and acrylonitrile butadiene rubber (NBR); and polysaccharides such as carboxymethyl cellulose (CMC), xanthan gum, guar gum, and pectin. These may be used alone or in combination of two or more.

[0068] In order to further improve the battery performance of the resulting lithium-ion secondary battery, the content of the binder in the negative electrode active material layer in this embodiment is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 1.0 parts by mass or more and 7.0 parts by mass or less, and even more preferably 2.0 parts by mass or more and 5.0 parts by mass or less, when the total amount of the negative electrode active material layer is taken as 100.0 parts by mass.

[0069] The negative electrode current collector of this embodiment contains, for example, one or more materials selected from the group consisting of copper, stainless steel, nickel, titanium, and alloys thereof. The negative electrode current collector may be in the form of, for example, a foil, a flat plate, or a mesh. The thickness of the negative electrode current collector is not particularly limited, but is, for example, 1 μm to 50 μm.

[0070] The electrolyte layer of this embodiment is a layer disposed between the positive electrode and the negative electrode, and includes a separator and an electrolyte solution, and examples of the electrolyte layer include a porous separator impregnated with a nonaqueous electrolyte solution and a solid electrolyte layer.

[0071] Examples of the electrolyte solution of this embodiment include organic solvents such as cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), and butylene carbonate (BC); chain carbonates such as ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and dipropyl carbonate (DPC); aliphatic carboxylic acid esters; γ-lactones such as γ-butyrolactone; chain ethers; and cyclic ethers, in which lithium salts such as lithium hexafluorophosphate (LiPF), lithium fluoroborate (LiBF), LiFSI, and lithium perchlorate (LiClO) are dissolved. These organic solvents may be used singly or in combination of two or more.

[0072] The separator of this embodiment is mainly made of a resin porous film, woven fabric, nonwoven fabric, etc., and the resin component can be, for example, a polyolefin resin such as polypropylene or polyethylene, a polyester resin, an acrylic resin, a styrene resin, a nylon resin, etc. If necessary, the separator may have a layer containing inorganic particles, and examples of the inorganic particles include insulating oxides, nitrides, sulfides, carbides, etc.

[0073] The exterior body of this embodiment can be a case or can case made of a flexible film, and from the viewpoint of reducing the weight of the battery, it is preferable to use a flexible film. The flexible film can be a metal layer serving as a base material, with resin layers provided on both sides. The metal layer can be selected from those with barrier properties, such as preventing leakage of the electrolyte solution and infiltration of moisture from the outside, and aluminum, stainless steel, etc. can be used. A heat-sealable resin layer, such as modified polyolefin, is provided on at least one side of the metal layer. The heat-sealable resin layers of the flexible films are placed opposite each other, and the periphery of the portion housing the electrode stack is heat-sealed to form the exterior body. A resin layer, such as a nylon film or polyester film, can be provided on the surface of the exterior body opposite the side on which the heat-sealable resin layer is formed.

[0074] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. [Example]

[0075] The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

[0076] (Method for cleaning positive electrode active material) The Li2CO3 content in the single crystal particles (A) and polycrystalline particles (B) used in the examples and comparative examples was adjusted to the values ​​shown in Table 1 by washing the single crystal particles (A) and polycrystalline particles (B) with an aqueous sodium sulfate solution and / or an aqueous lithium sulfate solution for a predetermined time, then dehydrating and drying them, and sintering them in an oxygen atmosphere at 900°C. The Li2CO3 content in the single crystal particles (A) and polycrystalline particles (B) can also be adjusted by adjusting the washing time.

[0077] Example 1 A lithium ion secondary battery was fabricated by the following method.

[0078] [I] Preparation of positive electrode A slurry of positive electrode active material, binder, and conductive additive dispersed in a solvent is applied to a current collector foil, which is then dried and pressed, resulting in an initial charge capacity per unit area of ​​4.1 mAh / cm. 2 The thickness of the positive electrode active material layer was adjusted so that In this example, the positive electrode active material layer contains Li(Ni 0.9 Co 0.05 Mn 0.05 The composite oxide contains 97.5 mass% of lithium-nickel-cobalt-manganese composite oxide represented by the formula (I)O2, 1.5 mass% of polyvinylidene fluoride (PVDF) as a binder, and 1.0 mass% of multi-walled carbon nanotubes (MWCNT) as a conductive additive. N-methyl-2-pyrrolidone was used as the solvent for slurrying, and a long foil with a thickness of 12 μm and mainly composed of aluminum was used as the current collector. The thickness of the positive electrode active material layer is such that the initial charge capacity per unit area is 4.1 mAh / cm 2 The dried active material layer was compressed together with the current collector using a roll press to form a positive electrode active material layer with a density of 3.5 g / cm. 3 The positive electrode was obtained by adjusting the composition so that

[0079] The positive electrode active material uses two types of lithium-nickel-cobalt-manganese composite oxides with different particle size distributions, and the above composition formula represents the composition of the mixture of the two types of lithium-nickel-cobalt-manganese composite oxides. The single crystal particles (A) of the positive electrode active material have an average particle diameter d 50 The particle size is 3.5 μm and is composed of a single crystal lithium-nickel-cobalt-manganese composite oxide. The other positive electrode active material, polycrystalline particles (B), has an average particle diameter d 50 The particle diameter is 10.1 μm and is composed of polycrystalline lithium-nickel-cobalt-manganese composite oxide. The mass ratio of the single crystal particles (A) to the polycrystalline particles (B) (SC / PC blending ratio) is 70:30.

[0080] [II] Preparation of negative electrode A slurry of negative electrode active material, binder, and conductive additive dispersed in a solvent is applied to a current collector foil, which is then dried and pressed, resulting in an initial charge capacity per unit area of ​​4.4 mAh / cm. 2 The thickness of the negative electrode active material layer was adjusted so that The negative electrode active material used was a mixture of artificial graphite and Si-C composite particles (Si:carbon mixture ratio of 45:55 (mass ratio)) containing silicon within the pores of porous carbon particles. The mixture ratio of Si-C composite particles to artificial graphite was 19:81 (mass ratio). The Si-C composite particles were created by exposing porous carbon particles to a mixture of silane gas and nitrogen gas in a high-temperature environment, thereby incorporating silicon into the pores of the porous carbon.

[0081] A slurry was prepared by dispersing in water 96.6% by mass of a mixed active material of Si-C composite particles and artificial graphite, 3.0% by mass of a polyacrylic acid binder as a binder, 0.1% by mass of carboxymethyl cellulose as a dispersant, and 0.3% by mass of single-walled carbon nanotubes (SWCNTs) as a conductive additive. The slurry was uniformly applied to a copper-based current collector with a thickness of 8 μm and then dried. The negative electrode active material layer had an initial charge capacity per unit area of ​​4.4 mAh / cm. 2 Then, the negative electrode active material layer is compressed and molded using a roll press to a density of 1.65 g / cm. 3 The negative electrode was fabricated so that

[0082] [III] Preparation of electrode stack The positive and negative electrodes were arranged facing each other with a separator interposed therebetween, and these were repeatedly stacked. The separator was a 10 μm-thick microporous polyethylene film with a ceramic coating on both sides.

[0083] [IV] Encapsulation in an outer packaging The electrode laminate obtained in the above [III] and a non-aqueous electrolyte solution were placed in a laminate outer casing, and the periphery of the laminate outer casing was sealed to prepare a lithium ion secondary battery. The non-aqueous electrolyte was prepared by mixing an organic solvent and a supporting salt. More specifically, the non-aqueous electrolyte was prepared by mixing a cyclic carbonate (EC) and a chain carbonate (DEC, EMC) in a volume ratio of 1:6, and then adding lithium hexafluorophosphate (LiPF6) and fluoroethylene carbonate (FEC) as supporting salts to the resulting mixture. One end of a positive electrode tab and one end of a negative electrode tab are connected to the positive electrode and the negative electrode, respectively, and the other ends are drawn out to the outside through a sealing portion around the laminate exterior body.

[0084] <Method for measuring particle size of positive electrode active material and negative electrode active material> The particle diameter d of the positive electrode active material and the negative electrode active material at which the cumulative volume is 10% in the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution measurement method 10 , the average particle diameter d in the volume-based particle size distribution 50 and the particle diameter d at which the cumulative volume in the volume-based particle size distribution is 90% 90 was measured using a laser diffraction / scattering particle size distribution analyzer (MT3000, manufactured by Microtrac). The positive electrode active material and the negative electrode active material were suspended in a dispersion medium, ultrasonically dispersed, and then measured. Each measurement was performed five times, and the average value was used.

[0085] <Method for measuring the specific surface area of ​​positive electrode active material and negative electrode active material> The specific surface area of ​​each positive electrode active material was determined by the nitrogen adsorption BET method using Quanta Sorb manufactured by Quantachrome Corporation.

[0086] <Measurement of lithium carbonate (Li2CO3) content in positive electrode active material> The lithium carbonate (Li2CO3) content in the single crystal particles (A) and polycrystalline particles (B) was measured by neutralization titration with hydrochloric acid. Specifically, 30 g of single-crystal particles (A) or polycrystalline particles (B) was added to 100 mL of pure water and stirred for 30 minutes, and then the single-crystal particles (A) or polycrystalline particles (B) was removed by filtration. Next, while measuring the pH of the obtained filtrate, a standard hydrochloric acid solution was added to the filtrate, and the content [mass%] of lithium carbonate (Li2CO3) in the single-crystal particles (A) or polycrystalline particles (B) was calculated from the neutralization point that appeared. The results are shown in Table 1 as the Li2CO3 content. The total Li2CO3 content in the positive electrode active material in each Example and Comparative Example was calculated from the Li2CO3 content in the single crystal particles (A), the Li2CO3 content in the polycrystalline particles (B), and the mass ratio of the single crystal particles (A) to the polycrystalline particles (B) in the positive electrode active material in each Example and Comparative Example, and the results are shown in Table 1.

[0087] <Evaluation of gas generation amount> The resulting lithium-ion secondary battery was placed in a thermostatic chamber at 45°C and charged at 30 mA. After the upper limit voltage reached 4.2 V, it was charged at a constant voltage until the total charging time reached 2.5 hours. It was then discharged at a constant current of 30 mA until the lower limit voltage reached 2.5 V. This charge / discharge cycle was repeated 300 times. For lithium-ion secondary batteries, the cell volume after 300 cycles was compared with the cell volume after the second cycle to determine the volume change rate, i.e., the amount of gas generated. Cell volume was measured using the Archimedes method, and the evaluation results are shown in Table 1. The evaluation was as follows: a volume change of less than 3% was rated A (good); a volume change of 3% to less than 5% was rated B (slightly poor); and a volume change of 5% or more was rated C (poor).

[0088] (Examples 2 to 5, Comparative Examples 1 to 4) Lithium ion secondary batteries were fabricated in the same manner as in Example 1, except that the types of positive electrode active material and negative electrode active material were changed as shown in Table 1, and evaluations were carried out in the same manner as in Example 1. The obtained results are shown in Table 1.

[0089] [Table 1]

[0090] The raw materials of the lithium ion secondary batteries of the examples and comparative examples are as follows. <Positive electrode> [Positive electrode active material (single crystal particles (A))] In each of the Examples and Comparative Examples, the following positive electrode active materials were used. Example 1, Example 2, Example 5, Comparative Example 1: Li(Ni) 0.9 Co 0.05 Mn 0.05 )O2 single crystal particle d 10 :2.3μm Average particle diameter d 50 :3.5μm d 90 :6.5μm Specific surface area: 0.6m 2 / g Example 3: Li(Ni) 0.9 Co 0.05 Mn 0.05 )O2 single crystal particle d 10 :3.5μm Average particle diameter d 50 :5.0μm d 90 :8.0μm Specific surface area: 0.3m 2 / g Example 4: Li(Ni) 0.9 Co 0.05 Mn 0.05 )O2 single crystal particle d 10 :1.0μm Average particle diameter d 50 :2.0μm d 90 :6.0μm Specific surface area: 1.7m 2 / g Comparative Example 2: Li(Ni) 0.9 Co 0.05 Mn 0.05 )O2 single crystal particle d 10 :4.0μm Average particle diameter d 50 :5.5μm d 90 :8.5μm Specific surface area: 0.3m 2 / g Comparative Examples 3 and 4: Li(Ni) 0.9 Co 0.05 Mn 0.05 )O2 single crystal particle d 10 :1.1μm Average particle diameter d 50 :2.3μm d 90 :5.0μm Specific surface area: 1.5m 2 / g

[0091] [Cathode active material (polycrystalline particles (B))] In each of the Examples and Comparative Examples, the following positive electrode active materials were used. Example 1, Example 2, Comparative Examples 1 to 4 Li(Ni) 0.9 Co 0.05 Mn 0.05 )O2 polycrystalline particles d 10 :6.7μm Average particle diameter d 50 : 10.1 μm d 90 :11.8μm Specific surface area: 0.7m 2 / g Example 3 Li(Ni) 0.9 Co 0.05 Mn 0.05 )O2 polycrystalline particles d 10 :6.5μm Average particle diameter d 50 :10.0μm d 90 :11.5μm Specific surface area: 0.7m 2 / g Example 4 Li(Ni) 0.9 Co 0.05 Mn 0.05 )O2 polycrystalline particles d 10 :7.0μm Average particle diameter d 50 :12.0μm d 90 :11.8μm Specific surface area: 0.6m 2 / g Example 5 Li(Ni) 0.9 Co 0.05 Mn 0.05 )O2 polycrystalline particles d 10 :10.0μm Average particle diameter d 50 :13.0μm d 90 :15.0μm Specific surface area: 0.2m 2 / g

[0092] [Other Materials for the Positive Electrode for Lithium-Ion Secondary Battery in the Present Embodiment] Binder: Polyvinylidene fluoride (PVDF) Conductive additive: Multi-wall carbon nanotubes (MWCNT)

[0093] <Negative electrode> [Negative electrode] In each of the Examples and Comparative Examples, the following negative electrode active materials were used. Examples and Comparative Examples Other Than Comparative Example 4: SiC / Graphite (a mixture of Si-C composite particles and artificial graphite) Mixture ratio of Si and carbon in Si-C composite particles: 45:55 (mass ratio) Mixing ratio of Si-C composite particles and artificial graphite: 19:81 (mass ratio) Average particle diameter of Si-C composite particles d 50 :8.0μm Specific surface area of ​​Si-C composite particles: 13.9m 2 / g Average particle diameter d of artificial graphite 50 :12.0μm Comparative Example 4: SiO / graphite (a mixture of SiO particles and artificial graphite) Mixing ratio of SiO particles to artificial graphite: 19:81 (mass ratio) Average particle size of SiO particles d 50 :9.0μm Average particle diameter d of artificial graphite 50 :12.0μm

[0094] [Other materials for negative electrodes of lithium-ion secondary batteries] Binder: Polyacrylic acid binder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) [Explanation of symbols]

[0095] 1 Cathode active material layer 2 Negative electrode active material layer 3 Positive electrode current collector 4 Negative electrode current collector 5 Separator 6. Exterior body 7. Exterior body 8 Negative electrode tab 9 Positive tab 10 Lithium-ion secondary battery

Claims

1. A positive electrode for a lithium ion secondary battery including a positive electrode active material layer, the positive electrode active material contained in the positive electrode active material layer contains a lithium composite oxide (X) having a layered rock salt crystal structure, Li in the positive electrode active material ２ CO ３ The content of the positive electrode active material is 0.01% by mass or more and 0.15% by mass or less based on the total amount of the positive electrode active material.

2. 2. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the positive electrode active material comprises single-crystal particles (A) composed of the lithium composite oxide (X) and polycrystalline particles (B) composed of the lithium composite oxide (X).

3. Li in the single crystal particles (A) ２ CO ３ The positive electrode for a lithium ion secondary battery according to claim 2, wherein the content of the single crystal particles (A) is 0.01% by mass or more and 0.18% by mass or less based on the total mass of the single crystal particles (A).

4. Li in the polycrystalline particles (B) ２ CO ３ The positive electrode for a lithium ion secondary battery according to claim 2 or 3, wherein the content of the polycrystalline particles (B) is 0.01 mass % or more and 0.30 mass % or less with respect to the entire polycrystalline particles (B).

5. The content of the single-crystal particles (A) in the positive electrode active material layer is W １ The content of the polycrystalline particles (B) is W ２ When the mass ratio of the single crystal particles (A) to the polycrystalline particles (B) is １ / W ２ 5. The positive electrode for a lithium ion secondary battery according to claim 2, wherein the value of (a) is 0.1 or more and 10.0 or less.

6. The single crystal particles (A) have a specific surface area of ​​0.01 m2 as measured by a nitrogen adsorption BET method. ２ / g or more 3.0m ２ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 5, wherein the SiO2 content is 0.1g or less.

7. The polycrystalline particles (B) have a specific surface area of ​​0.01 m2 as measured by the nitrogen adsorption BET method. ２ / g or more 3.0m ２ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 6, wherein the SiO2 content is 0.1g or less.

8. The particle diameter d of the single crystal particles (A) at which the cumulative value reaches 10% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method １０ , 90% particle diameter d ９０ and average particle diameter d ５０ (d ９０ -d １０ ) / d ５０ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 7, wherein the value of is 0.1 or more and 10.0 or less.

9. The particle diameter d of the single crystal particles (A) at which the cumulative value reaches 10% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method １０ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 8, wherein the average particle size is 0.1 μm or more and 5.0 μm or less.

10. The average particle diameter d of the single crystal particles (A) at which the cumulative value reaches 50% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method ５０ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 9, wherein the average particle size is 1.0 μm or more and 10.0 μm or less.

11. The particle diameter d of the single crystal particles (A) at which the cumulative value reaches 90% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method ９０ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 10, wherein the average particle size is 3.0 μm or more and 20.0 μm or less.

12. The particle diameter d of the polycrystalline particles (B) at which the cumulative value in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 10% １０ , 90% particle diameter d ９０ and average particle diameter d ５０ (d ９０ -d １０ ) / d ５０ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 11, wherein the value of is 0.1 or more and 5.0 or less.

13. The particle diameter d of the polycrystalline particles (B) at which the cumulative value in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 10% １０ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 12, wherein the average particle size is 0.5 μm or more and 15.0 μm or less.

14. The polycrystalline particles (B) have an average particle diameter d at which the cumulative value reaches 50% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. ５０ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 13, wherein the average particle size is 2.0 μm or more and 25.0 μm or less.

15. The particle diameter d of the polycrystalline particles (B) at which the cumulative value reaches 90% in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method ９０ The positive electrode for a lithium ion secondary battery according to any one of claims 2 to 14, wherein the average particle size is 3.0 μm or more and 40.0 μm or less.

16. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 15, wherein the lithium composite oxide (X) comprises one or more composite oxides selected from the group consisting of lithium-nickel composite oxides, lithium-cobalt composite oxides, lithium-nickel-aluminum composite oxides, and lithium-nickel-cobalt-manganese composite oxides.

17. 17. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the lithium composite oxide (X) contains a lithium-nickel-cobalt-manganese composite oxide.

18. 18. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the content of the positive electrode active material in the positive electrode active material layer is 50.0 parts by mass or more and 99.9 parts by mass or less, when the entire positive electrode active material layer is 100.0 parts by mass.

19. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 18, an electrolyte layer; a negative electrode including a negative electrode active material layer; A lithium-ion secondary battery comprising:

20. 20. The lithium ion secondary battery according to claim 19, wherein the negative electrode active material contained in the negative electrode active material layer comprises one or more negative electrode active materials selected from the group consisting of a carbon material, a lithium-based metal material, a Si-based material, and a conductive polymer material.

21. 21. The lithium ion secondary battery according to claim 19, wherein the negative electrode active material contained in the negative electrode active material layer comprises Si—C composite particles containing silicon and a carbon material.

22. The lithium ion secondary battery according to any one of claims 19 to 21, wherein the negative electrode active material contained in the negative electrode active material layer contains graphite particles.

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