Positive electrode for lithium ion secondary batteries, lithium ion secondary battery, and lithium ion secondary battery module

Abstract

This positive electrode for lithium ion secondary batteries includes a positive electrode active material layer. A positive electrode active material included in the positive electrode active material layer contains active material particles composed of a lithium composite oxide (X) having a layered rock-salt type crystal structure. The average particle diameter d50 of the active material particles in a volume-based particle size distribution obtained by using a laser diffraction scattering particle size distribution measurement method is 5.0 μm or less. The ratio (d90 / DSEM) between the particle diameter d90 of the active material particles that has a cumulative value of 90% in the volume-based particle size distribution, which is obtained by using the laser diffraction scattering particle size distribution measurement method, and the average particle diameter DSEM based on electron microscope observation of the active material particles is 3.1 or less.

Description

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

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

[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 produce a lithium ion secondary battery with reduced gas generation, as well as a lithium ion secondary battery and a lithium ion secondary battery module that can produce reduced gas generation.

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

[0007] [1] 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 active material particles composed of a lithium composite oxide (X) having a layered rock salt crystal structure, and the active material particles have an average particle diameter d in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. ５０ The particle diameter d at which the cumulative value reaches 90% in the volume-based particle size distribution of the active material particles measured by a laser diffraction / scattering particle size distribution measurement method is 5.0 μm or less. ９０ and an average particle diameter D based on electron microscope observation of the active material particles. ＳＥＭ The ratio (d ９０ / D ＳＥＭ [2] The average particle diameter D of the active material particles as determined by electron microscope observation is 3.1 or less. ＳＥＭ [3] The positive electrode for a lithium ion secondary battery according to [1], wherein the particle diameter d at which a cumulative value reaches 10% in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 0.5 μm or more and 5.0 μm or less. １０ [4] The positive electrode for a lithium ion secondary battery according to [1] or [2], wherein the particle diameter d at which a cumulative value of 90% of the volume-based particle size distribution of the active material particles is measured by a laser diffraction / scattering particle size distribution measurement method is 0.5 μm or more and 5.0 μm or less. ９０ [5] The positive electrode for a lithium ion secondary battery according to any one of [1] to [3], wherein the particle diameter d at which a cumulative value reaches 10% in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method is 1.0 μm or more and 10.0 μm or less. １０ and the average particle diameter D ＳＥＭ The ratio (d １０ / D ＳＥＭ) is 0.9 or more. [6] The positive electrode for a lithium ion secondary battery according to any one of [1] to [5], wherein the lithium composite oxide (X) contains one or more composite oxides selected from the group consisting of lithium-nickel composite oxides, lithium-nickel-aluminum composite oxides, and lithium-nickel-cobalt-manganese composite oxides. [7] The positive electrode for a lithium ion secondary battery according to any one of [1] to [6], wherein the lithium composite oxide (X) contains a lithium-nickel-cobalt-manganese composite oxide. [8] The positive electrode for a lithium ion secondary battery according to any one of [1] to [7], 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. [9] The positive electrode for a lithium ion secondary battery according to any one of [1] to [8], wherein the Ni content relative to the metal atoms other than lithium contained in the lithium composite oxide (X) is 85 mol % or more.

[10] The positive electrode for a lithium ion secondary battery according to any one of [1] to [9], wherein the positive electrode active material layer further contains a binder.

[11] The positive electrode for a lithium ion secondary battery according to

[10] , wherein the binder contains one or more binders selected from the group consisting of fluorine-based binders and aqueous binders.

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

[11] , wherein the positive electrode active material layer further contains a conductive additive.

[13] The positive electrode for a lithium ion secondary battery according to

[12] , wherein the conductive additive contains one or more binders selected from the group consisting of carbon black, activated carbon, graphite, mesoporous carbon, fullerenes, carbon nanotubes, carbon nanohorns, carbon nanofibers, and carbon brushes.

[14] The positive electrode for a lithium ion secondary battery according to

[12] or

[13] , wherein the conductive additive contains carbon nanotubes.

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

[14] , an electrolyte layer, and a negative electrode including a negative electrode active material layer.

[16] The lithium ion secondary battery according to

[15] , wherein the anode active material contained in the anode active material layer comprises one or more anode active materials selected from the group consisting of carbon materials, lithium-based metal materials, Si-based materials, and conductive polymer materials.

[17] The lithium ion secondary battery according to

[15] or

[16] , wherein the anode active material contained in the anode active material layer comprises Si-C composite particles containing silicon and a carbon material.

[18] The lithium ion secondary battery according to any of

[15] to

[17] , wherein the anode active material contained in the anode active material layer comprises graphite particles.

[19] A lithium ion secondary battery module comprising the lithium ion secondary battery according to any of

[15] to

[18] .

[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 can reduce the amount of gas generated.

[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 active material layer, and the positive electrode active material included in the positive electrode active material layer includes active material particles formed of a lithium composite oxide (X) having a layered rock salt crystal structure. The active material particles have an average particle diameter d ５０ The particle diameter d at which the cumulative value reaches 90% in the volume-based particle size distribution of the active material particles measured by a laser diffraction / scattering particle size distribution measurement method is 5.0 μm or less.９０ and an average particle diameter D based on electron microscope observation of the active material particles. ＳＥＭ The ratio (d ９０ / D ＳＥＭ ) is 3.1 or less.

[0012] According to the positive electrode for a lithium ion secondary battery of this embodiment, the amount of gas generated from the resulting lithium ion secondary battery can be reduced.

[0013] 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.

[0014] In this specification, the average particle diameter based on electron microscope observation is referred to as D ＳＥＭ Specifically, single crystal particles are observed using a scanning electron microscope (e.g., SU3500, manufactured by Hitachi High-Technologies Corporation), and 100 particles that do not overlap with each other and whose particle outlines can be confirmed are randomly selected. The projected area circle equivalent diameter (Heywood diameter) of the selected particles is calculated using image processing software (e.g., ImageJ), and the arithmetic mean value of the obtained projected area circle equivalent diameters is calculated to determine the average particle diameter D ＳＥＭ can be obtained.

[0015] 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.

[0016] The average particle diameter d ５０From the viewpoint of reducing the amount of gas generated in the resulting lithium ion secondary battery, the average particle size is 5.0 μm or less, preferably 1.0 μm or more and 5.0 μm or less, more preferably 2.0 μm or more and 5.0 μm or less, even more preferably 2.5 μm or more and 5.0 μm or less, even more preferably 2.8 μm or more and 4.8 μm or less, and even more preferably 3.0 μm or more and 4.5 μm or less.

[0017] The average particle diameter d ９０ and the average particle diameter D ＳＥＭ The ratio (d ９０ / D ＳＥＭ ) is 3.1 or less, preferably 0.5 or more and 3.0 or less, more preferably 1.0 or more and 3.0 or less, even more preferably 1.5 or more and 3.0 or less, even more preferably 2.0 or more and 3.0 or less, even more preferably 2.1 or more and 2.8 or less, and even more preferably 2.2 or more and 2.8 or less, from the viewpoint of being able to reduce the amount of gas generation in the resulting lithium ion secondary battery.

[0018] 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-manganese composite oxides, lithium-nickel-manganese composite oxides, lithium-nickel-cobalt composite oxides, lithium-nickel-aluminum composite oxides, lithium-nickel-cobalt-aluminum composite oxides, lithium-nickel-manganese-aluminum composite oxides, lithium-nickel-cobalt-manganese-aluminum composite oxides, and lithium-nickel-cobalt-manganese composite oxides, more preferably contains one or more composite oxides selected from the group consisting of lithium-nickel composite oxides, lithium-nickel-aluminum composite oxides, and lithium-nickel-cobalt-manganese composite oxides, and even more preferably contains lithium-nickel-cobalt-manganese composite oxides.

[0019] 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.

[0020] 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.

[0021] 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, and still more preferably 0.9≦a≦1.1.

[0022] 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 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] The Ni content relative to metal atoms other than lithium contained in the lithium composite oxide (X) is preferably 75 mol% or more, more preferably 75 mol% or more and 99.9 mol% or less, even more preferably 80 mol% or more and 97.5 mol% or less, and still more preferably 85 mol% or more and less than 94 mol%, from the viewpoint of further reducing the amount of gas generated from the resulting lithium ion secondary battery.

[0027] The active material particles of this embodiment, which are made of the lithium composite oxide (X) having a layered rock salt crystal structure, may include single-crystal particles or polycrystalline particles. The active material particles preferably include single-crystal particles.

[0028] In this embodiment, the content of the active material particles in the positive electrode active material layer 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, even more preferably 80 parts by mass or more and 100 parts by mass or less, even more preferably 90 parts by mass or more and 100 parts by mass or less, even more preferably 95 parts by mass or more and 100 parts by mass or less, and even 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 resulting lithium ion secondary battery.

[0029] Particle diameter d of active material particles 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 5.0 μm or less, more preferably 1.5 μm or more and 4.5 μm or less, even more preferably more than 2.0 μm and less than 4.0 μm, even more preferably 2.3 μm or more and 3.8 μm or less, and even more preferably 2.5 μm or more and 3.7 μm or less.

[0030] Particle diameter d of active material particles ９０From 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 2.0 μm or more and less than 9.5 μm, even more preferably 3.0 μm or more and 9.0 μm or less, even more preferably 4.0 μm or more and 8.5 μm or less, even more preferably 5.0 μm or more and 8.3 μm or less, and even more preferably 5.5 μm or more and 8.1 μm or less.

[0031] Average particle diameter D of active material particles ＳＥＭ 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 5.0 μm or less, more preferably 1.0 μm or more and 4.5 μm or less, even more preferably 1.5 μm or more and 4.0 μm or less, and still more preferably 2.0 μm or more and 3.7 μm or less.

[0032] The particle diameter d of the active material particles １０ and the average particle diameter D ＳＥＭ The ratio (d １０ / D ＳＥＭ ) is preferably 0.9 or more, more preferably 0.9 or more but less than 2.0, even more preferably 0.9 or more but less than 1.5, and still more preferably 0.9 or more but less than 1.3, from the viewpoint of further reducing the amount of gas generated from the resulting lithium ion secondary battery.

[0033] The active material particles of this embodiment can be commercially available, or may be prepared by a method including the following procedure. For example, Ni obtained by a known coprecipitation method ｗ Co ｘ Mn ｙ M ｚ O ３ and lithium hydroxide, and the mixture is heat-treated in the atmosphere, whereby active material particles constituted by the composite oxide represented by the formula (1) can be obtained.

[0034] Here, by adjusting the particle size of the oxide particles and the heat treatment temperature in air, the obtained 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 they are grown to a predetermined particle size by heat treatment, so 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.

[0035] The surfaces of the obtained 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, washing the active material particles is preferable to adjust the contents of lithium carbonate and lithium hydroxide in the active material particles. Examples of methods for washing the active material particles include washing the active material particles with an aqueous lithium sulfate solution and / or an aqueous sodium sulfate solution. By performing such washing, the contents of lithium carbonate and lithium hydroxide in the active material particles can be adjusted. The lithium ion concentration of the aqueous lithium sulfate solution during washing is preferably 1 mol / L or less. By adjusting the lithium ion concentration of the aqueous lithium sulfate solution within the above range, excessive lithium is not removed during washing, making it easier to control the contents of lithium carbonate and lithium hydroxide in the positive electrode active material to appropriate amounts.

[0036] A coating layer may be formed on the surface of the washed 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 ２ O ３ It is preferable to avoid the inclusion of boron oxide such as the above as much as possible.

[0037] The positive electrode active material of this embodiment may further contain a positive electrode active material other than the active material particles (active material particles composed of a lithium composite oxide (X) having a layered rock salt type crystal structure). The positive electrode active material other than the active material particles 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.

[0038] From the viewpoint of further reducing the amount of gas generated from 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.

[0039] The positive electrode active material layer of this embodiment preferably further contains a binder, from the viewpoint of further reducing the amount of gas generated from the resulting lithium ion secondary battery.

[0040] 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.

[0041] The binder in the positive electrode active material layer of the present embodiment preferably contains one or more binders selected from the group consisting of fluorine-based binders and water-based binders, from the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery.

[0042] Examples of fluorine-based binders include fluororesins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyhexafluoropropylene (PHFP), polyvinyl fluoride (PVF), or VdF-hexafluoropropylene copolymers. Examples of aqueous binders include polytetrafluoroethylene-based resins, polycarboxylic acid-based polymers, styrene-butadiene rubber, and polyimide-based resins. One of these may be used alone, or two or more may be used in combination. Among these, the binder in the positive electrode active material layer of this embodiment preferably contains one or two selected from the group consisting of polyvinylidene fluoride and styrene-butadiene rubber, and more preferably contains polyvinylidene fluoride, from the viewpoint of further improving the battery performance of the resulting lithium-ion secondary battery.

[0043] In this embodiment, the aqueous binder refers to a binder that can be dispersed or dissolved in water to form an emulsion or aqueous solution. When using an aqueous binder, a thickener can also be used. The thickener is not particularly limited, but examples thereof include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, and hydroxypropyl cellulose, and their ammonium salts and alkali metal salts; polycarboxylic acids; polyethylene oxide; polyvinylpyrrolidone; polyacrylates such as sodium polyacrylate; and water-soluble polymers such as polyvinyl alcohol.

[0044] 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.

[0045] The positive electrode active material layer of this embodiment preferably further contains a conductive additive, from the viewpoint of further reducing the amount of gas generated in the resulting lithium ion secondary battery.

[0046] Examples of the conductive additive in the positive electrode active material layer of this embodiment include carbon materials such as carbon black, activated carbon, graphite, mesoporous carbon, fullerenes, carbon nanotubes (CNT), carbon nanohorns, carbon nanofibers, and carbon brushes. Among these, the conductive additive in the positive electrode active material layer of this embodiment preferably includes one or more materials selected from the group consisting of carbon black, activated carbon, graphite, mesoporous carbon, fullerenes, carbon nanotubes (CNT), carbon nanohorns, carbon nanofibers, and carbon brushes, from the viewpoint of further reducing the amount of gas generated in the resulting lithium-ion secondary battery. More preferably, the conductive additive includes one or more materials selected from the group consisting of carbon black and carbon nanotubes (CNTs). Even more preferably, the conductive additive includes carbon nanotubes (CNTs). CNTs are substances in which a six-membered ring network (graphene) of carbon atoms has a single-layer or multi-layer coaxial tubular structure, and examples thereof include single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Any CNT may be used as the conductive additive. Furthermore, in order to support the conductivity in the positive electrode active material layer, carbon black may be used in combination with the CNT as the conductive additive.

[0047] 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, more 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.

[0048] 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.

[0049] 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 reducing the amount of gas generated in the resulting lithium ion secondary battery.

[0050] 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.

[0051] 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.

[0052] <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.

[0053] 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. 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] From the viewpoint of further reducing the amount of gas generated from the resulting lithium-ion secondary battery, the negative electrode active material contained in the negative electrode active material layer of the present 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.

[0058] 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.

[0059] 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 further reducing the amount of gas generated from the resulting lithium ion secondary battery.

[0060] 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.

[0061] 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. ２The 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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 fluoroborate (LiBF ４ ), LiFSI, lithium perchlorate (LiClO ４ The organic solvent may be used alone or in combination of two or more kinds.

[0071] 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.

[0072] 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.

[0073] <Lithium-ion secondary battery module> The lithium-ion secondary battery module of this embodiment includes the lithium-ion secondary battery of this embodiment. Since the lithium-ion secondary battery of this embodiment can reduce the amount of gas generated, the lithium-ion secondary battery module of this embodiment can also reduce the amount of gas generated.

[0074] The lithium-ion secondary battery module of this embodiment preferably includes two or more lithium-ion secondary batteries of this embodiment connected in series or parallel. The lithium-ion secondary battery module of this embodiment more preferably includes a housing capable of accommodating two or more lithium-ion secondary batteries of this embodiment connected in series or parallel. The lithium-ion secondary battery module of this embodiment further preferably includes one or more components selected from the group consisting of a protection circuit that protects the lithium-ion secondary batteries from overcurrent, a balancing circuit that equalizes the voltage between the electrodes of the lithium-ion secondary batteries, a controller that controls the lithium-ion secondary batteries, a cooler that can cool the lithium-ion secondary batteries, and a heater that can heat the lithium-ion secondary batteries.

[0075] The lithium-ion secondary battery module of this embodiment can be used in a battery system including a plurality of electrically connected lithium-ion secondary battery modules and a battery control system. Examples of battery systems include battery packs, stationary storage battery systems, automotive power storage battery systems, automotive auxiliary storage battery systems, and emergency power storage battery systems.

[0076] 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.

[0077] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0078] Example 1 A lithium ion secondary battery was fabricated by the following method.

[0079] [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 layer contained Li as the positive electrode active material. １．００ Ni ０．９０ Co ０．０７ Mn ０．０３ 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 ３The positive electrode was obtained by adjusting the composition so that

[0080] [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.

[0081] 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

[0082] [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.

[0083] [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.

[0084] <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 were measured using a laser diffraction / scattering particle size distribution analyzer (MT3000, manufactured by Microtrac). For the positive electrode active material, a powder of the positive electrode active material was suspended in a dispersion medium (0.1% by mass aqueous sodium hexametaphosphate solution), ultrasonically dispersed, and then measured. For the graphite, the graphite was suspended in a dispersion medium (0.1% by mass aqueous sodium hexametaphosphate solution), ultrasonically dispersed, and then measured. For the Si—C composite particles, the Si—C composite particles were suspended in a dispersion medium (0.1% by mass aqueous sodium hexametaphosphate solution), ultrasonically dispersed, and then measured. Each measurement was performed five times, and the average value was used.

[0085] <Average particle diameter D of the positive electrode active material based on electron microscope observation ＳＥＭ Measurement method of the average particle diameter D of the positive electrode active material based on electron microscope observation ＳＥＭwas measured and calculated as follows. First, a scanning electron microscope (SU3500, manufactured by Hitachi High-Tech Corporation) was used to observe the positive electrode active material at a magnification of 1000 times in multiple areas of 60 μm × 60 μm, and 100 particles were randomly selected that did not overlap with each other and whose particle outlines could be confirmed. The projected area circle equivalent diameter (Heywood diameter) of the selected particles was calculated using image processing software (ImageJ), and the arithmetic mean value of the obtained projected area circle equivalent diameters was determined as the average particle diameter D ＳＥＭ The results are shown in Table 1.

[0086] <Method for Measuring Specific Surface Area of ​​Negative Electrode Active Material> The specific surface area of ​​each negative electrode active material was determined by the nitrogen adsorption BET method using QuantaSorb manufactured by Quantachrome Corporation.

[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 charge 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. The cell volume of the lithium-ion secondary battery 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 generation. The cell volume was measured using the Archimedes method. The evaluation results are shown in Table 1. 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 and 3, Comparative Examples 1 and 2 Lithium ion secondary batteries were fabricated in the same manner as in Example 1, except that the type of positive electrode active material was 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.

[0089]

[0090] In Table 1, d １０ / D ＳＥＭ is the average particle diameter D based on electron microscope observation ＳＥＭThe particle diameter d at which the cumulative volume becomes 10% in the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution measurement method １０ Also, d ９０ / D ＳＥＭ The average particle size D ＳＥＭ The particle diameter d at which the cumulative volume in the volume-based particle size distribution becomes 90% ９０ is the ratio of

[0091] The raw materials of the lithium ion secondary batteries of each example and comparative example are as follows. <Positive electrode> [Positive electrode active material] The following positive electrode active material was used in each example and comparative example. Example 1: Li １．００ Ni ０．９０ Co ０．０７ Mn ０．０３ O ２ Single crystal particle d １０ :2.6μm Average particle diameter d ５０ : 4.2 μm d ９０ : 6.2 μm D ＳＥＭ : 2.3 μm Example 2: Li １．０５ Ni ０．９２ Co ０．０５ Mn ０．０３ O ２ Single crystal particle d １０ :3.1μm Average particle diameter d ５０ : 3.0 μm d ９０ : 8.0 μm D ＳＥＭ : 2.7 μm Example 3: Li １．００ Ni ０．９０ Co ０．０７ Mn ０．０３ O ２ Single crystal particle d １０ :3.5μm Average particle diameter d ５０ : 5.0 μm d ９０ : 7.0 μm D ＳＥＭ :3.4μm ・Comparative example 1: Li １．００ Ni ０．９０ Co ０．０７ Mn ０．０３ O ２ Single crystal particle d １０ :4.0μm Average particle diameter d ５０ : 6.0 μm d ９０ : 11.0 μm D ＳＥＭ:2.7μm ・Comparative example 2: Li １．０３ Ni ０．９４ Co ０．０５ Mn ０．０１ O ２ Single crystal particle d １０ :2.0μm Average particle diameter d ５０ : 4.0 μm d ９０ : 9.5 μm D ＳＥＭ : 3.0 μm

[0092] [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)

[0093] <Negative electrode> The following materials were used in each example and comparative example. Negative electrode active material: 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 : 12.0 μm Binder: Polyacrylic acid binder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)

[0094] This application claims priority based on Japanese Patent Application No. 2024-054992, filed March 28, 2024, the disclosure of which is incorporated herein by reference in its entirety.

[0095] 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 including a positive electrode active material layer, wherein the positive electrode active material included in the positive electrode active material layer includes active material particles composed of a lithium composite oxide (X) having a layered rock salt crystal structure, and the active material particles have an average particle diameter d in a volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution measurement method. ５０ The particle diameter d at which the cumulative value reaches 90% in the volume-based particle size distribution of the active material particles measured by a laser diffraction / scattering particle size distribution measurement method is 5.0 μm or less. ９０ and an average particle diameter D based on electron microscope observation of the active material particles. ＳＥＭ The ratio (d ９０ / D ＳＥＭ ) is 3.1 or less.

2. The average particle diameter D of the active material particles as determined by electron microscope observation ＳＥＭ 2. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the average particle size is 0.5 μm or more and 5.0 μm or less.

3. The particle diameter d of the active material particles 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 3. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the average particle size is 0.5 μm or more and 5.0 μm or less.

4. The particle diameter d of the active material particles at which the cumulative value is 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 3, wherein the average particle size is 1.0 µm or more and 10.0 µm or less.

5. The particle diameter d of the active material particles 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 and the average particle diameter D ＳＥＭ The ratio (d １０ / D ＳＥＭ 5. The positive electrode for a lithium ion secondary battery according to claim 1, wherein the value of (a) is 0.9 or more.

6. A positive electrode for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the lithium composite oxide (X) comprises one or more composite oxides selected from the group consisting of lithium-nickel composite oxides, lithium-nickel-aluminum composite oxides, and lithium-nickel-cobalt-manganese composite oxides.

7. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 6, wherein the lithium composite oxide (X) includes a lithium-nickel-cobalt-manganese composite oxide.

8. A positive electrode for a lithium ion secondary battery according to any one of claims 1 to 7, 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.

9. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 8, wherein the content of Ni relative to the metal atoms other than lithium contained in the lithium composite oxide (X) is 85 mol % or more.

10. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 9, wherein the positive electrode active material layer further contains a binder.

11. The positive electrode for a lithium ion secondary battery according to claim 10, wherein the binder comprises one or more binders selected from the group consisting of fluorine-based binders and water-based binders.

12. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 11, wherein the positive electrode active material layer further contains a conductive additive.

13. The positive electrode for a lithium ion secondary battery according to claim 12, wherein the conductive additive comprises one or more selected from the group consisting of carbon black, activated carbon, graphite, mesoporous carbon, fullerenes, carbon nanotubes, carbon nanohorns, carbon nanofibers, and carbon brushes.

14. The positive electrode for a lithium ion secondary battery according to claim 12 or 13, wherein the conductive additive comprises carbon nanotubes.

15. A lithium ion secondary battery comprising: a positive electrode for a lithium ion secondary battery according to any one of claims 1 to 14; an electrolyte layer; and a negative electrode including a negative electrode active material layer.

16. The lithium ion secondary battery according to claim 15, 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.

17. The lithium ion secondary battery according to claim 15 or 16, 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.

18. The lithium ion secondary battery according to any one of claims 15 to 17, wherein the negative electrode active material contained in the negative electrode active material layer includes graphite particles.

19. A lithium ion secondary battery module comprising the lithium ion secondary battery according to any one of claims 15 to 18.

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