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

Abstract

This positive electrode for a lithium-ion secondary battery comprises a positive electrode current collector layer and a positive electrode active material layer, wherein: a positive electrode active material contained in the positive electrode active material layer includes single crystal particles (A) composed of a lithium composite oxide (X) having a layered rock salt-type crystal structure, and polycrystal particles (B) composed of a lithium composite oxide (X) having a layered rock salt-type crystal structure; the average particle diameter d50 of the single crystal particles (A) in the volume-based particle size distribution measured by a laser diffraction and scattering-type particle size distribution measurement method is less than 6.0 μm; the average particle diameter d50 of the polycrystal particles (B) in the volume-based particle size distribution measured by a laser diffraction and scattering-type particle size distribution measurement method is at least 6.0 μm and less than 15.0 μm; and when the content of the single crystal particles (A) in the positive electrode active material layer is W1, and the content of the polycrystal 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 polycrystal particles (B) is at least 0.85.

Description

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

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

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

[0003] Patent Document 1 describes a positive electrode having a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector, with the aim 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 active material layer contains 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, and the first Ni-containing lithium composite oxide particles and the second Ni-containing lithium composite oxide particles each have a layered crystal structure. The first Ni-containing lithium composite oxide particles have an average particle diameter (D50) of 2 μm to 6 μm, the second Ni-containing lithium composite oxide particles have an average primary particle diameter of 1.2 μm to 2.0 μm, and the second Ni-containing lithium composite oxide particles have an average particle diameter (D50) of 12 μm to 20 μm.

[0004] Japanese Patent Application Laid-Open No. 2023-91566

[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 can suppress breakage of the positive electrode current collector, and a lithium ion secondary battery using the positive electrode for a lithium ion secondary battery.

[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 current collector layer and a positive electrode active material layer, wherein the positive electrode active material included in the positive electrode active material layer 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 the lithium composite oxide (X) having a layered rock-salt type crystal structure, and the single-crystal particles (A) have an average particle diameter d ５０ the average particle diameter d of the polycrystalline particles (B) in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is less than 6.0 μm; ５０ is 6.0 μm or more and less than 15.0 μm, and the content of the single-crystal particles (A) in the positive electrode active material layer is W １ and the content of the polycrystalline particles (B) in the positive electrode active material layer is W ２ When the mass ratio of the content of the single crystal particles (A) to the content of the polycrystalline particles (B) is １ / W ２ ) is 0.85 or more. [2] The W １ / W ２ [3] The positive electrode for a lithium ion secondary battery according to [1], wherein the average particle diameter d ５０ D １ [μm], and the average particle diameter d ５０ D ２ When [μm], D １ and D ２ [4] The positive electrode for a lithium ion secondary battery according to [1] or [2], wherein the difference between the average particle diameter d ５０ [5] The positive electrode for a lithium ion secondary battery according to any one of [1] to [3], wherein the average particle diameter d of the polycrystalline particles (B) is more than 0.5 μm. ５０ [6] The positive electrode for a lithium ion secondary battery according to any one of [1] to [4], wherein the specific surface area of ​​the single crystal particles (A) measured by a nitrogen adsorption BET method is 0.25 m ２ / g or more 4.0m ２[7] The positive electrode for a lithium ion secondary battery according to any one of [1] to [5], wherein the specific surface area of ​​the polycrystalline particles (B) measured by a nitrogen adsorption BET method is less than 0.4 m ２ / g or more 1.8m ２ [8] The positive electrode for a lithium ion secondary battery according to any one of [1] to [6], wherein the particle diameter d of the single-crystal particles (A) at which a cumulative value of 10% in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is obtained is 10%. １０ , 90% particle diameter d ９０ and average particle diameter d ５０ (d ９０ -d １０ ) / d ５０ [9] The positive electrode for a lithium ion secondary battery according to any one of [1] to [7], wherein the value of the particle diameter d of the single-crystal particles (A) is greater than 0.8 and less than or equal to 10.0, where the cumulative value of the particle diameter d is 10% in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. １０

[10] The positive electrode for a lithium ion secondary battery according to any one of [1] to [8], wherein the particle diameter d of the single-crystal particles (A) at which a cumulative value of 90% in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is obtained is 0.2 μm or more and 4.0 μm or less. ９０

[11] The positive electrode for a lithium ion secondary battery according to any one of [1] to [9], wherein the particle diameter d of the polycrystalline particles (B) at which a cumulative value of 10% in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is obtained is 3.0 μm or more and 8.5 μm or less. １０ , 90% particle diameter d ９０ and average particle diameter d ５０ (d ９０ -d １０ ) / d ５０

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

[10] , wherein the value of the particle diameter d of the polycrystalline particles (B) at which the cumulative value of the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 10% is more than 0.3 and 1.0 or less. １０

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

[11] , wherein the particle diameter d of the polycrystalline particles (B) at which a cumulative value of 90% in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is obtained is 2.0 μm or more and 11.5 μm or less. ９０

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

[13] , 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.

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

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

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

[15] , 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.

[17] A lithium ion secondary battery comprising: the positive electrode for lithium ion secondary batteries according to any one of [1] to

[16] ; an electrolyte layer; and a negative electrode including a negative electrode active material layer.

[18] The lithium ion secondary battery according to

[17] , wherein the negative electrode active material included in the negative electrode active material layer includes 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.

[19] The lithium ion secondary battery according to

[17] or

[18] , wherein the negative electrode active material included in the negative electrode active material layer includes Si-C composite particles including silicon and a carbon material.

[20] The lithium ion secondary battery according to any one of

[17] to

[19] , wherein the negative electrode active material included in the negative electrode active material layer includes graphite particles.

[0008] According to the present invention, it is possible to provide 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 can suppress breakage of the positive electrode current collector, and a lithium ion secondary battery using the positive electrode for a lithium ion secondary battery.

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

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. To avoid complexity, when multiple identical components are present in the same drawing, only one of them may be labeled with a reference symbol, and not all of them. The drawings are for illustrative purposes only. The shape and dimensional ratios of each component in the drawings do not necessarily correspond to 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 electrode for lithium ion secondary battery> The positive electrode for lithium ion secondary battery of this embodiment is a positive electrode for lithium ion secondary battery including a positive electrode current collector layer and a positive electrode active material layer. The positive electrode active material included in the positive electrode active material layer includes single crystal particles (A) (hereinafter, also referred to as "single crystal particles (A)") composed of a lithium composite oxide (X) having a layered rock salt crystal structure, and polycrystalline particles (B) (hereinafter, also referred to as "polycrystalline particles (B)") composed of a lithium composite oxide (X) having a layered rock salt crystal structure. The average particle diameter d ５０ The average particle diameter d of the polycrystalline particles (B) in the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is less than 6.0 μm. ５０ The content of the single-crystal particles (A) in the positive electrode active material layer is W １ and the content of the polycrystalline particles (B) in the positive electrode active material layer is W ２ When the mass ratio of the content of the single crystal particles (A) to the content of the polycrystalline particles (B) is １ / W ２ ) is 0.85 or more.

[0012] According to the positive electrode for a lithium ion secondary battery of this embodiment, the amount of gas generated in the resulting lithium ion secondary battery can be reduced, and breakage of the positive electrode current collector can be suppressed.

[0013] In this embodiment, a single-crystal particle is a particle in which no grain boundaries are observed when observed under an electron microscope at 1000 to 5000 magnifications, and the particle is composed of a single crystal grain. Even when multiple single-crystal particles are closely attached, this also falls under the category of a single-crystal particle. 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.

[0014] The mass ratio (W) of the content of the single-crystal particles (A) to the content of the polycrystalline particles (B) １ / W ２ ) is 0.85 or more, preferably 1.0 or more, more preferably 1.5 or more, and even more preferably 2.0 or more, from the viewpoint of being able to reduce the amount of gas generated in the resulting lithium ion secondary battery and being able to suppress breakage of the positive electrode current collector. １ / W ２ From the viewpoint of further improving the energy density of the resulting lithium ion secondary battery, the mass ratio (W) of the content of the single-crystal particles (A) to the content of the polycrystalline particles (B) is preferably 8.5 or less, more preferably 7.5 or less, even more preferably 7.0 or less, and even more preferably 6.5 or less. １ / W ２ ) is preferably 0.85 or more and 8.5 or less, more preferably 1.0 or more and 7.5 or less, even more preferably 1.5 or more and 7.0 or less, and still more preferably 2.0 or more and 6.5 or less, from the viewpoint of being able to reduce the amount of gas generated in the resulting lithium ion secondary battery and being able to suppress breakage of the positive electrode current collector, and from the viewpoint of being able to further improve the energy density of the resulting lithium ion secondary battery.

[0015] From the viewpoints of being able to further reduce the amount of gas generated from the resulting lithium ion secondary battery and to further suppress breakage of the positive electrode current collector, 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.

[0016] The lithium-nickel-cobalt-manganese composite oxide of this embodiment preferably contains a composite oxide represented by the following formula (1) from the viewpoint of increasing capacity.

[0017] Li ａ Ni ｂ Co ｃ Mn ｄ M ｅ O ２ (1) In the formula (1), M represents one or more elements 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, and 0≦e<1.0.

[0018] 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.

[0019] In addition, in the composite oxide of formula (1), 0.6≦b<1.0 is satisfied, and from the viewpoint of further improving the capacity of the obtained lithium ion secondary battery, 0.65≦b<1.0 is preferred, 0.7≦b<1.0 is more preferred, 0.75≦b<1.0 is even more preferred, and 0.8≦b≦0.95 is even more preferred.

[0020] 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 even more preferably 0.03≦c≦0.1.

[0021] 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 even more preferably 0.02≦d≦0.1.

[0022] In the composite oxide of the formula (1), 0≦e<1.0, preferably 0≦e≦0.5, more preferably 0≦e≦0.3, even more preferably 0≦e≦0.2, even more preferably 0≦e≦0.1, and even more preferably e=0.

[0023] 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 may be, for example, TiS ２ , FeS, MoS ２ transition metal sulfides such as MnO, V ２ O ５ , V ６ O １３ , TiO ２ The lithium iron phosphate oxide preferably contains an olivine-type lithium iron phosphate, from the viewpoint of improving working potential, capacity, durability, and energy density. The olivine-type lithium phosphate oxide contains, for example, at least one element selected from the group consisting of Mn, Cr, Co, Cu, Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, Nb, and Fe, as well as lithium, phosphorus, and oxygen.

[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, still more preferably 95 parts by mass or more and 100 parts by mass or less, and still more preferably 98 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 from the obtained lithium-ion secondary battery and further suppressing breakage of the positive electrode current collector.

[0025] From the viewpoint of further improving the energy density of the resulting lithium-ion secondary battery, the content of the positive electrode active material in the positive electrode active material layer of this 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, even more preferably 85.0 parts by mass or more and 99.0 parts by mass or less, even 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, when the entire positive electrode active material layer is taken as 100.0 parts by mass.

[0026] 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 , and the particle diameter at 90% is d ９０ , and the particle diameter at which the cumulative value reaches 50% is the average particle diameter d ５０ Let's say.

[0027] Average particle diameter d of single crystal particles (A) ５０ is less than 6.0 μm from the viewpoint of being able to reduce the amount of gas generation in the resulting lithium ion secondary battery and being able to suppress breakage of the positive electrode current collector, and from the viewpoint of being able to further improve the battery performance of the resulting lithium ion secondary battery, is preferably more than 0.5 μm and less than 6.0 μm, more preferably 0.6 μm or more and 5.8 μm or less, even more preferably 0.7 μm or more and 5.5 μm or less, and still more preferably 0.8 μm or more and 5.2 μm or less.

[0028] Particle diameter d of single crystal particles (A) １０ is preferably more than 0 μm and less than 4.5 μm, more preferably 0.1 μm or more and 4.0 μm or less, from the viewpoint of being able to further reduce the amount of gas generation in the resulting lithium ion secondary battery and to further suppress breakage of the positive electrode current collector, and is even more preferably 0.2 μm or more and 4.0 μm or less, and still more preferably 0.5 μm or more and 3.8 μm or less, from the viewpoint of being able to further improve the battery performance of the resulting lithium ion secondary battery.

[0029] Particle diameter d of single crystal particles (A) ９０ is preferably 2.0 μm or more and less than 9.0 μm, more preferably 3.0 μm or more and 8.5 μm or less, and even more preferably 3.3 μm or more and 8.3 μm or less, from the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery and further suppressing breakage of the positive electrode current collector.

[0030] 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 in the resulting lithium ion secondary battery and further suppressing breakage of the positive electrode current collector, the value of is preferably more than 0.8 and 10.0 or less, more preferably 0.85 or more and 8.5 or less, and even more preferably 0.9 or more and 7.5 or less.

[0031] The specific surface area of ​​the single crystal particles (A) as measured by the nitrogen adsorption BET method is preferably 0.2 m from the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery and further suppressing breakage of the positive electrode current collector. ２ / g excess 10m ２ / g or less, more preferably 0.25m ２ / g or more 7.0m ２ / g or less, and from the viewpoint of improving the battery performance of the resulting lithium ion secondary battery, it is more preferably 0.25 m ２ / g or more 4.0m ２ / g, more preferably less than 0.25 m ２ / g or more 3.5m ２ / g or less, more preferably 0.25m ２ / g or more 3.0m ２ / g or less, more preferably 0.3m ２ / g or more 2.5m ２ / g or less.

[0032] Average particle diameter d of polycrystalline particles (B) ５０ is 6.0 μm or more and less than 15.0 μm from the viewpoint of being able to reduce the amount of gas generation in the resulting lithium ion secondary battery and being able to suppress breakage of the positive electrode current collector, and is preferably more than 6.0 μm and less than 15.0 μm, more preferably 6.5 μm or more and 14.0 μm or less, and even more preferably 7.0 μm or more and 13.0 μm or less, from the viewpoint of being able to further improve the capacity retention rate of the resulting lithium ion secondary battery.

[0033] Particle diameter d of polycrystalline particles (B) １０ is preferably 1.5 μm or more and less than 11.7 μm from the viewpoint of being able to further reduce the amount of gas generation in the resulting lithium ion secondary battery and to further suppress breakage of the positive electrode current collector, and is more preferably 2.0 μm or more and 11.5 μm or less, even more preferably 3.0 μm or more and 11.0 μm or less, and even more preferably 4.0 μm or more and 11.0 μm or less, from the viewpoint of being able to further improve the capacity retention rate of the resulting lithium ion secondary battery.

[0034] The particle diameter d of the polycrystalline particles (B) ９０ is preferably 6.5 μm or more and less than 16.8 μm from the viewpoint of being able to further reduce the amount of gas generation in the resulting lithium ion secondary battery and to further suppress breakage of the positive electrode current collector, and is more preferably 7.0 μm or more and 16.5 μm or less, even more preferably 8.0 μm or more and 16.2 μm or less, and even more preferably 9.0 μm or more and 16.0 μm or less from the viewpoint of being able to further improve the capacity retention rate of the resulting lithium ion secondary battery.

[0035] Particle diameter d of polycrystalline particles (B) １０ , the particle diameter d ９０ and the average particle diameter d ５０ (d ９０ -d １０ ) / d ５０The value of is preferably more than 0.3 and 1.0 or less, more preferably 0.4 or more and 0.9 or less, from the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery and further suppressing breakage of the positive electrode current collector.

[0036] The specific surface area of ​​the polycrystalline particles (B) as determined by the nitrogen adsorption BET method is preferably 0.3 m from the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery and further suppressing breakage of the positive electrode current collector. ２ / g excess 2.5m ２ / g or less, more preferably 0.4m ２ / g or more 2.0m ２ / g or less, and from the viewpoint of further improving the capacity retention rate of the obtained lithium ion secondary battery, it is more preferably 0.4 m ２ / g or more 1.8m ２ / g or less, more preferably 0.5m ２ / g or more 1.5m ２ / g or less.

[0037] The average particle diameter d of the single crystal particles (A) ５０ D １ [μm], and the average particle diameter d ５０ D ２ When [μm], D １ and D ２ From the viewpoint of being able to further reduce the amount of gas generation in the resulting lithium ion secondary battery and to further suppress breakage of the positive electrode current collector, the difference is preferably 2.0 μm or more and 11.4 μm or less, more preferably 2.3 μm or more and 11.3 μm or less, and from the viewpoint of being able to further improve the capacity retention rate of the resulting lithium ion secondary battery, it is even more preferably more than 2.5 μm and 11.2 μm or less, even more preferably 3.0 μm or more and 11.0 μm or less, and even more preferably 3.5 μm or more and 10.5 μm or less.

[0038] The single crystal particles (A) and polycrystalline particles (B) of this embodiment are commercially available products, or may be prepared by a method including the following procedure. For example, Ni particles obtained by a known coprecipitation method can be prepared by the following method. ｗ Co ｘ Mn ｙ M ｚ O３ and lithium hydroxide, and the resulting mixture is heat-treated in the atmosphere, whereby positive electrode active material particles constituted by the composite oxide represented by the above formula (1) can be obtained.

[0039] 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.

[0040] The surfaces of the obtained positive electrode active material particles contain lithium hydroxide used during synthesis and lithium carbonate produced by the reaction of lithium hydroxide with moisture and carbon dioxide in the air. Here, it is preferable to wash the positive electrode active material particles in order to adjust the content of lithium carbonate and lithium hydroxide in the positive electrode active material particles. Examples of methods for washing the positive electrode active material particles include washing the positive electrode active material particles with an aqueous lithium sulfate solution and / or an aqueous sodium sulfate solution. By performing such washing, the content of lithium carbonate and lithium hydroxide 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, excessive lithium is not removed during washing, making it easier to control the content of lithium carbonate and lithium hydroxide in the positive electrode active material to appropriate amounts.

[0041] 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 for example, an aluminum oxide layer (Al ２ O ３ ) and niobium oxide layer (Nb ２ O ５ However, since cracks in the polycrystalline particles occur when manufacturing lithium ion secondary batteries, B ２O ３ It is preferable to avoid the inclusion of boron oxide such as the above as much as possible.

[0042] 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.

[0043] 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). Any CNT may be used as the conductive additive. Furthermore, in order to support the conductivity of the positive electrode active material layer, carbon black may be used in combination with CNTs as a conductive additive.

[0044] The content of the conductive additive 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, 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 parts by mass or more and 3 parts by mass or less, particularly preferably 0.03 parts by mass or more and 2 parts by mass or less, and even more preferably 0.05 parts by mass or more and 1.5 parts by mass or less, 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.

[0045] 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), or 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.

[0046] 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 still 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.

[0047] 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.

[0048] 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.

[0049] 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 5.0g / cm or more ３ or less, more preferably 1.0 g / cm ３ 4.5g / cm or more ３ More preferably 2.5 g / cm or less ３ 4.0g / cm or more ３ More preferably, 3.0 g / cm or less ３ 4.0g / cm or more ３ The following is the result.

[0050] 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 or more and 50 μm or less.

[0051] <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, it is possible to reduce the amount of gas generation and suppress breakage of the positive electrode current collector.

[0052] 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 containing a negative electrode active material. 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.

[0053] 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 interposed between them, such as a nonwoven fabric or a microporous polypropylene film, 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.

[0054] 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.

[0055] 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.

[0056] 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 a carbon material, a lithium-based metal material, a Si-based material, and a conductive polymer material, more preferably contains one or more negative electrode active materials selected from the group consisting of a carbon material and a Si-based material, and even more preferably contains both a Si-based material and a carbon material.

[0057] 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., JFE Chemical Corporation, etc.

[0058] 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 from the viewpoint of further improving the capacity retention rate, it preferably contains Si-C composite particles.

[0059] Silicon oxides available for use include those available from Sigma-Aldrich, Kojundo Chemical Laboratory, Kanto Chemical Co., Ltd., Fujifilm Wako Pure Chemical Industries, Ltd., Osaka Titanium Co., Ltd., and the like.

[0060] 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 part of the pores of the porous carbon material. In this 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 The Si-C composite particles can be obtained by a manufacturing method in which a porous carbon material having a molecular weight of 1000 / g is placed in a tubular furnace, the inside of the furnace is purged with argon gas, and then a mixed gas of silane gas containing 1 to 3 mol% 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 at 450 to 550°C, 700 to 800 Torr, and 90 to 150 minutes. Examples of porous carbon materials that make up the Si-C composite particles of this embodiment include activated carbon, aggregates of carbon fibers, aggregates of carbon nanotubes, and carbon obtained by heat treating resins or organic materials. Porous carbon materials can be produced by methods such as manufacturing activated carbon or known manufacturing methods involving heat treatment of polymers. However, commercially available products may also be purchased, and are not limited to these, as long as silicon can be generated or incorporated into the pores of the porous carbon.

[0061] 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.

[0062] 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 still 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.

[0063] 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.

[0064] 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 still 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.

[0065] 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. 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 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.

[0067] The negative electrode current collector of this embodiment contains, for example, one or more selected from the group consisting of copper, stainless steel, nickel, titanium, and alloys thereof. The shape of the negative electrode current collector may be, 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 or more and 50 μm or less.

[0068] 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.

[0069] The electrolyte solution of this embodiment may be, for example, a solution of lithium hexafluorophosphate (LiPF) in an organic solvent 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. ６ ), lithium fluoride (LiBF ４ ), LiFSI, lithium perchlorate (LiClO ４ The organic solvent may be used alone or in combination of two or more kinds.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0074] Example 1 A lithium ion secondary battery was fabricated by the following method.

[0075] [I] Preparation of Positive Electrode A slurry in which a positive electrode active material, a binder, and a conductive additive are dispersed in a solvent is applied to a current collector foil, dried, and then pressed to obtain a positive electrode with an initial charge capacity of 4.1 mAh / cm ２ In this example, the thickness of the positive electrode active material layer was adjusted so that the positive electrode active material was Li (Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ The cathode active material layer contained 97.5 mass% of a lithium-nickel-cobalt-manganese composite oxide represented by the formula (I), 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 12 μm-thick long foil composed primarily of aluminum was used as the current collector. The thickness of the cathode active material layer was such that the initial charge capacity per unit area was 4.1 mAh / cm. ２ The dried active material layer was compressed together with the current collector by a roll press method to adjust the density of the positive electrode active material layer to 3.5 g / cm ３ The positive electrode was obtained by adjusting the composition so that

[0076] 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 is the composition of a mixture of the two types of lithium-nickel-cobalt-manganese composite oxides. The single crystal particles (A), which are one of the positive electrode active materials, have an average particle diameter d５０ The other positive electrode active material, polycrystalline particles (B), has an average particle diameter d ５０ The particles were composed of polycrystalline lithium-nickel-cobalt-manganese composite oxide, with a mean particle size of 10.1 μm. The mass ratio of the single-crystal particles (A) to the polycrystalline particles (B) (SC / PC blending ratio) was 70:30.

[0077] [II] Preparation of negative electrode A slurry in which a negative electrode active material, a binder, and a conductive additive are dispersed in a solvent is applied to a current collector foil, dried, and then pressed to obtain 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 thickness was 1 / 2 of the total thickness of the negative electrode active material layer. As the negative electrode active material, a mixture of Si-C composite particles (Si:carbon mixture ratio of 45:55 (mass ratio)) containing silicon in the pores of the porous carbon particles and artificial graphite was used. The mixture ratio of the Si-C composite particles to the artificial graphite was 19:81 (mass ratio). The Si-C composite particles were obtained by exposing porous carbon particles to a mixed gas of silane gas and nitrogen gas in a high-temperature environment, thereby incorporating silicon into the pores of the porous carbon.

[0078] A slurry was prepared by dispersing 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 in water. This slurry was uniformly applied to an 8 μm-thick copper-based current collector and 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 by a roll press method to have a density of 1.65 g / cm ３ The negative electrode was fabricated so that

[0079] [III] Preparation of Electrode Stacks 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.

[0080] [IV] Encapsulation in Exterior The electrode laminate obtained in [III] above and the non-aqueous electrolyte were placed in a laminate exterior, and the periphery of the laminate exterior was sealed to produce 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 adding lithium hexafluorophosphate (LiPF ) as a supporting salt to the resulting mixture. ６ The positive electrode and the negative electrode were connected at one end to a positive electrode tab and a negative electrode tab, respectively, and the other end was extended to the outside via a sealing portion around the laminate exterior body.

[0081] <Method for measuring particle diameter of positive electrode active material and negative electrode active material> The particle diameter d at which the cumulative volume becomes 10% in the volume-based particle size distribution of the positive electrode active material and the negative electrode active material is measured by a laser diffraction scattering particle size distribution measurement method. １０ , the average particle diameter d in the volume-based particle size distribution ５０ and a particle diameter d at which the cumulative volume in the volume-based particle size distribution becomes 90%. ９０ The particle size distributions were 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 each suspended in a dispersion medium (0.1% by mass sodium hexametaphosphate aqueous solution), ultrasonically dispersed, and then measured. Each measurement was performed five times, and the average value was used.

[0082] <Method for measuring the specific surface area of ​​the positive electrode active material and the negative electrode active material> The specific surface area of ​​each positive electrode active material was determined by the nitrogen adsorption BET method using QuantaSorb manufactured by Quantachrome Corporation.

[0083] <Cutting of the positive electrode current collector foil> An electrode laminate separately prepared as described in [I] to [III] above was pressed with a roll press at a linear pressure of 1.4 ton / cm. The cross section of the pressed electrode laminate was observed with a scanning electron microscope (SEM) to evaluate the presence or absence of cutting of the positive electrode current collector foil (fracture of the foil). The results are shown in Table 1.

[0084] <Amount of Positive Electrode Active Material Penetrated into Positive Electrode Current Collector Foil> An electrode laminate prepared separately as described in [I] to [III] above was pressed with a roll press at a linear pressure of 1.4 ton / cm. The cross section of the pressed electrode laminate was observed with a scanning electron microscope (SEM). For the portions of the positive electrode current collector foil where the positive electrode active material had penetrated (hereinafter referred to as recesses), the depth of the recesses in the y-axis direction was measured as the amount of penetration, with the surface of the positive electrode current collector foil in the x-axis direction. The results are shown in Table 1. The depth of the recesses was measured at a total of 10 locations, including the center of the pressed electrode laminate, and the average value was used.

[0085] <Energy Density> The lithium-ion secondary battery was charged at 7.2 mA, and after the upper limit voltage reached 4.2 V, it was charged at a constant voltage until the total charging time reached 12 hours. It was then discharged at a constant current of 7.2 mA until the lower limit voltage reached 2.5 V. It was charged again under the same conditions, left in a thermostatic chamber at 45°C for 3 days, and discharged again under the same conditions, and then charged and discharged once more. The capacity and average voltage at the final discharge were evaluated. After this evaluation, the thickness of the lithium-ion secondary battery (hereinafter sometimes simply referred to as "cell") was evaluated.

[0086] The thickness of the unit of the lithium-ion secondary battery, i.e., the sum of the thickness of the positive electrode active material layer, half the thickness of the positive electrode current collector, the thickness of the separator, the thickness of the negative electrode active material layer, and half the thickness of the negative electrode current collector, was calculated from the thickness of the cell. Specifically, the thickness was calculated by subtracting the thickness of the laminate exterior body, half the thickness of the positive electrode current collector, and half the thickness of the negative electrode current collector from the thickness of the cell.

[0087] The energy density of the unit part of the lithium-ion secondary battery was calculated from the following formula (2). The thickness of the current collector was calculated assuming that there was no penetration of the active material. (Capacity during cell discharge) × (Average voltage during cell discharge) / (Area of ​​electrode) / (Thickness of positive electrode active material layer + Half thickness of positive electrode current collector + Thickness of separator + Thickness of negative electrode active material layer + Half thickness of negative electrode current collector) (2)

[0088] <Capacity Retention Rate> The 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, the battery was charged at a constant voltage until the total charging time reached 2.5 hours. The battery 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, and the ratio of the 300th discharge capacity to the first discharge capacity was defined as the capacity retention rate after 300 cycles.

[0089] <Amount of Gas Generation> For the lithium-ion secondary battery, the cell volume after 300 charge / discharge cycles described in <Capacity Retention Rate> was compared with the cell volume after the second cycle to determine the volume change rate, i.e., the amount of gas generation. The cell volume was measured using the Archimedes method, and the evaluation results are shown in Table 1. The evaluation was as follows: A (good) if the volume change was less than 3%, B (fair) if the volume change was 3% or more but less than 5%, and C (unacceptable) if the volume change was 5% or more.

[0090] (Examples 2 to 11, Comparative Examples 1 to 3) Lithium ion secondary batteries were fabricated in the same manner as in Example 1, except that the type and blending ratio of the positive electrode active material and the type of the negative electrode active material were changed as shown in Table 1, and evaluations were performed in the same manner as in Example 1. The obtained results are shown in Table 1.

[0091]

[0092] The SC / PC blend ratio in Table 1 means the mass ratio of single crystal particles (SC) to polycrystalline particles (PC). １ / W ２ The content of single crystal particles in the positive electrode active material layer (W １ ) and the content of polycrystalline particles in the positive electrode active material layer (W ２ ) means the mass ratio to

[0093] The raw materials for the lithium ion secondary batteries of each Example and Comparative Example are as follows. <Positive Electrode> [Positive Electrode Active Material (Single Crystal Particles (A))] The following positive electrode active materials were used in each Example and Comparative Example. Example 1, Examples 4 to 8, Examples 10 and 11, Comparative Examples 2 and 3: Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Single crystal particle d １０ :2.0μm Average particle diameter d ５０ : 3.5 μm d ９０ : 6.5μm Specific surface area: 0.6m ２ / g Example 2: Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Single crystal particle d １０ :3.5μm Average particle diameter d ５０ : 5.0 μm d ９０ :8.0μm Specific surface area: 0.3m ２ / g Example 3: Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Single crystal particle d １０ :0.1μm Average particle diameter d ５０ : 1.0 μm d ９０ :3.5μm Specific surface area:2.5m ２ / g Example 9: Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Single crystal particle d １０ :0.1μm Average particle diameter d ５０ : 0.5 μm d ９０ :4.0μm Specific surface area:4.0m ２ / g ・Comparative example 1: Li (Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Single crystal particle d １０ :4.5μm Average particle diameter d ５０ : 6.0 μm d ９０ :9.0μm Specific surface area: 0.2m ２ / g

[0094] [Positive Electrode Active Material (Polycrystalline Particles (B))] The following positive electrode active materials were used in each of the Examples and Comparative Examples: Examples 1 to 3, Examples 6 to 9, Example 11, and Comparative Examples 1 and 3. Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Polycrystalline particles of d １０ :6.7μm Average particle diameter d ５０ : 10.1 μm d ９０ : 11.8μm Specific surface area: 0.7m ２ / g Example 4 Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Polycrystalline particles of d １０ :10.7μm Average particle diameter d ５０ : 12.0 μm d ９０ :15.8μm Specific surface area: 0.5m ２ / g Example 5 Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Polycrystalline particles of d １０ :4.6μm Average particle diameter d ５０ : 8.0 μm d ９０ :9.7μm Specific surface area: 1.1m ２ / g Example 10 Li(Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Polycrystalline particles of d １０ :1.7μm Average particle diameter d ５０ : 6.0 μm d ９０ :6.8μm Specific surface area: 1.9m ２ / g ・Comparative Example 2 Li (Ni ０．９ Co ０．０５ Mn ０．０５ ) O ２ Polycrystalline particles of d １０ :11.8μm Average particle diameter d ５０ : 15.0 μm d ９０ :16.8μm Specific surface area: 0.3m ２ / g

[0095] [Other Materials of the Positive Electrode for Lithium-Ion Secondary Battery in the Present Embodiment] Binder: Polyvinylidene fluoride (PVDF) Conductive additive: Multi-walled carbon nanotubes (MWCNT)

[0096] <Negative electrode> [Negative electrode active material] The following negative electrode active materials were used in each of the examples and comparative examples. Examples and comparative examples other than Example 8: SiC / graphite (mixture of Si-C composite particles and artificial graphite) Mixing ratio of Si to carbon in the Si-C composite particles: 45:55 (mass ratio) Mixing ratio of Si-C composite particles to artificial graphite: 19:81 (mass ratio) Average particle diameter d of the Si-C composite particles ５０ Specific surface area of ​​Si-C composite particles: 13.9 m ２ / g Average particle diameter d of artificial graphite ５０ Example 8: SiO / graphite (mixture of SiO particles and artificial graphite) Mixing ratio of SiO particles to artificial graphite: 19:81 (mass ratio) Average particle diameter d of SiO particles ５０ Average particle diameter d of artificial graphite: 9.0 μm ５０ : 12.0 μm [Other materials for negative electrodes for lithium ion secondary batteries] Binder: polyacrylic acid binder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0097] This application claims priority based on Japanese Patent Application No. 2024-054989, filed March 28, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0098] REFERENCE SIGNS LIST 1 Positive electrode 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 electrode tab 10 Lithium ion secondary battery

Claims

1. A positive electrode for a lithium ion secondary battery comprising a positive electrode current collector layer and a positive electrode active material layer, wherein the positive electrode active material contained in the positive electrode active material layer comprises 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 the lithium composite oxide (X) having a layered rock-salt type crystal structure, and the single-crystal particles (A) have an average particle diameter d ５０ the average particle diameter d of the polycrystalline particles (B) in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is less than 6.0 μm; ５０ is 6.0 μm or more and less than 15.0 μm, and the content of the single-crystal particles (A) in the positive electrode active material layer is W １ and the content of the polycrystalline particles (B) in the positive electrode active material layer is W ２ When the mass ratio of the content of the single crystal particles (A) to the content of the polycrystalline particles (B) is １ / W ２ ) is 0.85 or more.

2. The above W １ / W ２ 2. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the σ is 8.5 or less.

3. The average particle diameter d of the single crystal particles (A) ５０ D １ [μm], and the average particle diameter d ５０ D ２ When [μm], D １ and D ２ The positive electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the difference between the thickness and the thickness is 3.0 μm or more and 11.0 μm or less.

4. The average particle diameter d of the single crystal particles (A) ５０ The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the average particle diameter is greater than 0.5 µm.

5. The average particle diameter d of the polycrystalline particles (B) ５０ The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the average particle diameter exceeds 6.0 µm.

6. The single crystal particles (A) have a specific surface area of ​​0.25 m2 as measured by the nitrogen adsorption BET method. ２ / g or more 4.0m ２ The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the SiO2 content is less than 1 / g.

7. The specific surface area of ​​the polycrystalline particles (B) measured by the nitrogen adsorption BET method is 0.4 m ２ / g or more 1.8m ２ The positive electrode for a lithium ion secondary battery according to any one of claims 1 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 1 to 7, wherein the value of is more than 0.8 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 1 to 8, wherein the average particle size is 0.2 µm or more and 4.0 µm or less.

10. 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 1 to 9, wherein the average particle size is 3.0 µm or more and 8.5 µm or less.

11. The particle diameter d of the polycrystalline particles (B) 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 1 to 10, wherein the value of is more than 0.3 and 1.0 or less.

12. The particle diameter d of the polycrystalline particles (B) 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 1 to 11, wherein the average particle size is 2.0 µm or more and 11.5 µm or less.

13. 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 1 to 12, wherein the average particle size is 7.0 µm or more and 16.5 µm or less.

14. A positive electrode for a lithium ion secondary battery according to any one of claims 1 to 13, 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.

15. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 14, wherein the lithium composite oxide (X) includes a lithium-nickel-cobalt-manganese composite oxide.

16. A positive electrode for a lithium ion secondary battery according to any one of claims 1 to 15, 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 taken as 100.0 parts by mass.

17. A lithium ion secondary battery comprising: a positive electrode for a lithium ion secondary battery according to any one of claims 1 to 16; an electrolyte layer; and a negative electrode including a negative electrode active material layer.

18. The lithium ion secondary battery according to claim 17, 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.

19. The lithium ion secondary battery according to claim 17 or 18, 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.

20. The lithium ion secondary battery according to any one of claims 17 to 19, wherein the negative electrode active material contained in the negative electrode active material layer includes graphite particles.

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