Positive electrode active material for lithium-ion secondary battery, positive electrode for lithium-ion secondary battery, and lithium-ion secondary battery

Abstract

This positive electrode active material for a lithium-ion secondary battery contains a lithium nickel composite oxide having a hexagonal layered structure. The positive electrode active material for a lithium ion secondary battery includes one or more types of particles selected from particles composed of primary particles and secondary particles in which a plurality of primary particles are aggregated, and contains Li, Ni, an element M, Ti, and Zr at a molar ratio of Li : Ni : M : Ti : Zr = d : 1-a-b-c : a: b : c. The ratio of a diffraction peak intensity I(003) of a (003) plane to a diffraction peak intensity I(104) of a (104) plane of 1.9 or more, the ratio being determined from X-ray diffraction measured using Cu-Kα radiation as an X-ray source and a flat plate sample holder of a Bragg-Brentano optical system. The specific surface area as determined by a nitrogen adsorption method is 0.50 m2 / g-1.6 m2 / g.

Description

Positive electrode active material for lithium-ion secondary batteries, positive electrode for lithium-ion secondary batteries, lithium-ion secondary battery

[0001] This invention relates to a positive electrode active material for lithium-ion secondary batteries, a positive electrode for lithium-ion secondary batteries, and a lithium-ion secondary battery.

[0002] In recent years, with the widespread use of portable electronic devices such as mobile phones and laptop computers, there has been a strong demand for the development of small, lightweight rechargeable batteries with high energy density and durability. Furthermore, there is a strong demand for high-output rechargeable batteries for use in power tools and electric vehicles, including hybrid cars. In addition to the above-mentioned required characteristics, there is also a growing need for rechargeable batteries with high durability that do not degrade easily even after repeated use.

[0003] Lithium-ion batteries are a type of secondary battery that meets these requirements. A lithium-ion battery consists of a negative electrode, a positive electrode, and an electrolyte, and the active materials of the negative and positive electrodes are materials that can detach and insert lithium. As mentioned above, lithium-ion batteries have high energy density, power output characteristics, and durability.

[0004] Various studies have been conducted on the active material of the positive electrode to improve the performance of lithium-ion secondary batteries.

[0005] For example, Patent Document 1 discloses a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which includes: mixing composite oxide particles containing nickel having predetermined particle size characteristics with a lithium compound to obtain a first mixture; heat-treating the first mixture at a first temperature and a second temperature higher than the first temperature to obtain a first heat-treated product; and dispersing the first heat-treated product. Patent Document 1 also discloses that the first temperature is 850°C or higher and 950°C or lower, and the second temperature is 980°C or higher and 1100°C or lower.

[0006] According to the method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery disclosed in Patent Document 1, it is possible to obtain a positive electrode active material that consists of a single particle or contains lithium transition metal oxide particles such that the number of primary particles constituting one secondary particle is reduced.

[0007] Japanese Patent Application Publication No. 2017-188443

[0008] Regarding the positive electrode active material for lithium-ion secondary batteries, there has been conventional research into using single particles composed of primary particles, or positive electrode active materials containing secondary particles with a reduced number of constituent primary particles. This is because using single particles or positive electrode active materials containing secondary particles with a reduced number of constituent primary particles can prevent particle breakage during positive electrode manufacturing and charging / discharging, thereby improving durability during repeated charging and discharging.

[0009] When using a positive electrode active material that consists of single particles or secondary particles with a reduced number of constituent primary particles, attempts are being made to increase the size of the primary particles in order to lower the specific surface area of ​​the positive electrode active material and reduce the contact area between the particles contained in the positive electrode active material and the electrolyte.

[0010] This is because increasing the size of the primary particles contained in the positive electrode active material reduces the contact area between the particles and the electrolyte, thereby avoiding performance degradation and gas generation due to reactions between the particles and the electrolyte.

[0011] Conventionally, in order to increase the size of the primary particles contained in the positive electrode active material, the temperature at which the raw material mixture is calcined during the manufacturing process of the positive electrode active material has been raised to a high temperature of 850°C or higher. However, raising the heat treatment temperature during the manufacturing of the positive electrode active material causes problems such as cation mixing, which reduces the battery capacity per unit surface area.

[0012] In other words, conventionally, no positive electrode active material for lithium-ion secondary batteries was known that could reduce the specific surface area while also being excellent in battery capacity per unit area when used in lithium-ion secondary batteries.

[0013] Therefore, in view of the problems of the above-mentioned conventional technology, one aspect of the present invention aims to provide a positive electrode active material for lithium-ion secondary batteries that reduces the specific surface area while also being excellent in terms of the ratio of battery capacity per specific surface area when used in lithium-ion secondary batteries.

[0014] To solve the above problems, according to one aspect of the present invention, a positive electrode active material for a lithium-ion secondary battery comprising a lithium nickel composite oxide having a hexagonal layered structure, comprising one or more types selected from particles consisting of primary particles and secondary particles formed by the aggregation of multiple primary particles, The material contains lithium (Li), nickel (Ni), element M (M), titanium (Ti), and zirconium (Zr) in a molar ratio of Li:Ni:M:Ti:Zr = d:1-a-b-c:a:b:c (wherein element M is at least one element selected from Co, Mn, Al, W, Mo, Mg, Ca, Cr, Ta, Nb, Si, F, and B, and a, b, c, and d satisfy 0.001 ≤ a < 0.60, 0.0003 ≤ b < 0.02, 0.0003 ≤ c < 0.02, 0.92 ≤ d ≤ 1.20, and 0.35 ≤ b / c ≤ 5.0). Using Cu-kα rays as the X-ray source, the X-ray diffraction pattern measured using a flat plate sample holder of a Bragg-Brentano optical system shows that the ratio of the diffraction peak intensity I(003) of the (004) plane to the diffraction peak intensity I(104) of the (104) plane is 1.8 or greater, and the specific surface area determined by the nitrogen adsorption method is 0.50 m². ２ / g or more 1.6m ２ The present invention provides a positive electrode active material for lithium-ion secondary batteries that is less than or equal to / g.

[0015] According to one aspect of the present invention, it is possible to provide a positive electrode active material for lithium-ion secondary batteries that reduces the specific surface area while also exhibiting excellent battery capacity per unit area when used in lithium-ion secondary batteries.

[0016] Figure 1 is an explanatory diagram of the configuration of coin-type batteries fabricated in the examples and comparative examples. Figure 2 is an explanatory diagram of the configuration of laminate-type batteries fabricated in the examples and comparative examples. Figure 3 is a schematic cross-sectional view of a positive electrode active material for a lithium-ion secondary battery according to one aspect of the present disclosure.

[0017] The following describes embodiments for carrying out the present invention, but the present invention is not limited to the embodiments described below, and various modifications and substitutions can be made to the embodiments described below without departing from the scope of the present invention. [Positive electrode active material for lithium-ion secondary batteries] The positive electrode active material for lithium-ion secondary batteries of this embodiment (hereinafter also simply referred to as "positive electrode active material") may include a lithium nickel composite oxide having a hexagonal layered structure. The positive electrode active material of this embodiment may also consist only of a lithium nickel composite oxide having a hexagonal layered structure, but this does not exclude the inclusion of unavoidable impurities. (1) Particles The positive electrode active material of this embodiment may include one or more types selected from particles consisting of primary particles and secondary particles formed by the aggregation of multiple primary particles.

[0018] A particle composed of primary particles is a single particle made up of only one primary particle; it means that a single particle consists of only one primary particle.

[0019] Furthermore, a secondary particle formed by the aggregation of multiple primary particles means that two or more primary particles have aggregated to form a single secondary particle.

[0020] The positive electrode active material of this embodiment may contain secondary particles, but it is preferable that the number of primary particles constituting the secondary particles be small. The average number of primary particles constituting the secondary particles may be, for example, 20 or less, 10 or less, or 5 or less. The lower limit of the average number of primary particles constituting the secondary particles is not particularly limited and may be, for example, 2 or more.

[0021] The method for measuring the average number of primary particles constituting secondary particles of the positive electrode active material is not particularly limited, but can be carried out, for example, by the following procedure.

[0022] First, the positive electrode active material of this embodiment is embedded in a resin, and a cross-section polishing process is performed to prepare a sample for cross-sectional observation. The sample for cross-sectional observation can be prepared by performing a cross-section polishing process so that the cross-sections of the particles contained in the positive electrode active material of this embodiment, embedded in the resin, are exposed.

[0023] Next, the prepared cross-sectional observation sample is observed using a Scanning Electron Microscope (SEM), and the number of primary particles constituting the secondary particles in the positive electrode active material of this embodiment can be measured. In the following description, the secondary particles and primary particles contained in the positive electrode active material of this embodiment will also be referred to simply as "secondary particles" and "primary particles."

[0024] When measuring and calculating the number of primary particles that constitute secondary particles, five to twenty secondary particles of average size are selected from the secondary particles to be evaluated within the SEM observation field of view of the cross-sectional observation sample. If the number of secondary particles in the field of view is less than five, all secondary particles can be included in the evaluation.

[0025] The SEM observation field of view (hereinafter also referred to as "observation field of view") for a sample used for cross-sectional observation is the observation field of view when the SEM magnification is selected so that a total of 100 to 200 particles contained in the positive electrode active material of this embodiment can be observed. The number of particles when selecting the SEM magnification is the total number of particles consisting of primary particles and secondary particles.

[0026] An average-sized secondary particle refers to a secondary particle whose secondary particle diameter is within ±10% of the average secondary particle diameter of all secondary particles present within the observation field, using the average secondary particle diameter of the secondary particles within the observation field as the reference value.

[0027] In calculating the average secondary particle diameter, for 5 to 10 secondary particles present within the observation field, the diameter of the smallest inclusion circle for each secondary particle can be used as the secondary particle diameter. Then, the average value of the secondary particle diameters of the evaluated 5 to 10 secondary particles can be used as the average secondary particle diameter of the secondary particles present within the observation field.

[0028] Then, for a selected secondary particle of average size, the number of constituent primary particles can be measured.

[0029] Using the same procedure, the number of primary particles constituting secondary particles in a total of three fields of view, selected to avoid overlap, is determined. The average value (arithmetic mean) of the number of primary particles constituting secondary particles measured in the three fields of view can then be used as the average value of the number of primary particles constituting secondary particles in the positive electrode active material.

[0030] The positive electrode active material of this embodiment can also have a higher proportion of primary particles among the particles it contains. By increasing the proportion of primary particles in the positive electrode active material of this embodiment, it is possible to prevent the particles from breaking during electrode fabrication or when repeated charging and discharging is performed, thereby improving durability. Durability here can also be referred to as cycle characteristics, and improving durability and cycle characteristics means that when the positive electrode active material of this embodiment is applied to a lithium-ion secondary battery and repeated charging and discharging is performed, the rate of decrease in discharge capacity can be reduced.

[0031] The positive electrode active material of this embodiment may have a particle number ratio of 60% or more consisting of primary particles, or 70% or more. By setting the particle number ratio of primary particles to 60% or more for the positive electrode active material of this embodiment, durability can be particularly enhanced. The positive electrode active material of this embodiment can also be composed only of particles consisting of primary particles, so the particle number ratio of primary particles may be 100% or less. In the positive electrode active material of this embodiment, the particle number ratio of primary particles can be adjusted, for example, by crushing the raw material mixture after firing, but it is difficult to completely prevent the inclusion of secondary particles, which may lead to a decrease in productivity. For this reason, the particle number ratio of primary particles in the positive electrode active material of this embodiment may be 99% or less, or 90% or less. (Cobalt coating layer) For example, as shown in Figure 3, the particles 30 of the positive electrode active material of this embodiment may have a cobalt coating layer 31 containing cobalt at one or more selected locations on the surface of the particles consisting of primary particles and the surface of the secondary particles.

[0032] By having a cobalt coating layer on the particles of the positive electrode active material, the resistance at the particle surface of the positive electrode active material can be reduced, thereby improving the output characteristics. Therefore, by having a cobalt coating layer on the particles of the positive electrode active material of this embodiment, it is possible to provide a positive electrode active material for lithium-ion secondary batteries that has a low specific surface area while reducing resistance and exhibiting excellent output.

[0033] The cobalt coating layer 31 refers to a region in the cross-section of the positive electrode active material particles 30 where, when line analysis is performed along a straight line L from the center O of the positive electrode active material particles toward the outer surface 30A, the cobalt concentration is locally higher than in other parts. For this reason, the cobalt coating layer may be formed from cobalt alone, or it may further contain one or more elements other than cobalt, such as nickel contained in lithium nickel composite oxide, or elements M, titanium, zirconium, etc. The cobalt coating layer may be a region where the cobalt content is 2% or more higher in terms of amount of substance compared to the parts other than the cobalt coating layer. For line analysis, for example, SEM-EDS may be used. EDS stands for Energy Dispersive Spectroscopy. When performing line analysis, the center of the positive electrode active material particles is the center of the minimum inclusion circle of the positive electrode active material particles, and line analysis can be performed along the radius of the minimum inclusion circle.

[0034] The cobalt coating layer may be one or more selected from a layer formed by the uneven distribution of cobalt within the particles of the positive electrode active material, and a coating layer covering the surface of the particles of the positive electrode active material. (2) Composition The positive electrode active material of this embodiment may contain lithium (Li), nickel (Ni), element M (M), titanium (Ti), and zirconium (Zr) in the ratio Li:Ni:M:Ti:Zr = d:1-a-b-c:a:b:c.

[0035] The positive electrode active material of this embodiment is, for example, a material with the general formula: Li ｄ Ni １－ａ－ｂ－ｃ M ａ Ti ｂ Zr ｃ O ２＋αIt can be expressed as follows. (2-1) Regarding element M, the positive electrode active material of this embodiment may also contain element M. Element M can be at least one element selected from, for example, cobalt (Co), manganese (Mn), aluminum (Al), tungsten (W), molybdenum (Mo), magnesium (Mg), calcium (Ca), chromium (Cr), tantalum (Ta), niobium (Nb), silicon (Si), fluorine (F), and boron (B). In particular, from the viewpoint of improving the thermal stability of lithium nickel composite oxide and reducing, for example, the thermal decomposition of lithium nickel composite oxide, element M may also contain at least one or more selected from cobalt (Co) and manganese (Mn).

[0036] The value of 'a', which indicates the content of element M, can be set, for example, to 0.001 ≤ a < 0.60.

[0037] Furthermore, if the lithium nickel composite oxide contains multiple types of element M, it is preferable that the sum of the content ratios of the multiple types of element M satisfies the above range. (Regarding magnesium and fluorine) Element M may contain one or more selected from magnesium (Mg) and fluorine (F). One or more selected from magnesium and fluorine may be added in addition to titanium and zirconium.

[0038] The presence of magnesium in element M can promote the growth of primary particles. Furthermore, the presence of fluorine in element M can also promote the growth of primary particles.

[0039] If the positive electrode active material of this embodiment contains magnesium, the molar ratio of magnesium content a1 may satisfy the condition 0.0003 ≤ a1 < 0.02. By setting the magnesium content a1 to 0.0003 or higher, the growth of primary particles can be particularly promoted.

[0040] Furthermore, if the positive electrode active material of this embodiment contains fluorine, the condition 0.0003 ≤ a2 < 0.02 may be satisfied when a2 is the molar ratio of fluorine content. By setting the fluorine content a2 to 0.0003 or higher, the growth of primary particles can be particularly promoted.

[0041] However, excessive addition of magnesium or fluorine may saturate the effect of promoting primary particle growth and may even inhibit it. Therefore, the molar ratio of magnesium and fluorine may be less than 0.02 each.

[0042] The magnesium and fluorine described so far are contained in element M. Since d, which indicates the content of element M, corresponds to the sum of the content ratios of element M in terms of molar mass, a1 and a2, which indicate the content ratios of magnesium and fluorine, are included in a, which indicates the content ratio of element M. For example, if element M contains only magnesium or only zirconium, then a = a1 and a = a2, respectively.

[0043] Element M may contain only magnesium and / or fluorine, or it may contain both magnesium and / or fluorine.

[0044] Element M may contain cobalt (Co). The cobalt may be contained in a cobalt coating layer that can be positioned at one or more selected locations on the surface of the particles consisting of primary particles and on the surface of the secondary particles.

[0045] Furthermore, cobalt may be included in the lithium nickel composite oxide as an element that forms the lithium nickel composite oxide.

[0046] Therefore, cobalt may be dispersed inside the lithium nickel composite oxide particles, or it may be unevenly distributed on the surface of the lithium nickel composite oxide particles, either on the surface portion of the lithium nickel composite oxide particles or contained in the coating. (2-2) Regarding titanium and zirconium, according to the inventors' studies of the present invention, by including zirconium (Zr) as an additive element in the positive electrode active material, the growth of primary particles contained in the positive electrode active material can be promoted. However, in order to improve battery characteristics such as battery capacity while sufficiently lowering the specific surface area when the lithium nickel composite oxide is crushed to include, for example, particles consisting of primary particles, a further primary particle growth promotion effect is required.

[0047] Therefore, the inventors of the present invention conducted further studies. As a result, they discovered that titanium (Ti), which was thought to inhibit the growth of primary particles when included alone as an additive element, can promote the growth of primary particles when included together with zirconium, compared to when zirconium is included alone, thus completing the present invention.

[0048] Therefore, the lithium nickel composite oxide of this embodiment can contain zirconium and titanium, as represented by the above general formula.

[0049] In the above general formula, b, which represents the content of titanium among elements other than lithium and oxygen, and c, which represents the content of zirconium, can satisfy 0.0003 ≤ b < 0.02 and 0.0003 ≤ c < 0.02, respectively.

[0050] By setting the titanium content (b) and the zirconium content (c) to 0.0003 or higher, the growth of primary particles can be promoted. As a result, it is possible to produce sufficiently large primary particles without raising the calcination temperature to 850°C or higher, and to sufficiently reduce the specific surface area of ​​the pulverized material obtained by grinding after calcination.

[0051] However, since the effect of promoting primary particle growth will saturate even with excessive addition of titanium and zirconium, the titanium content (b) and the zirconium content (c) can each be set to less than 0.02.

[0052] The ratio of titanium to zirconium content is not particularly limited, but for example, b, which represents the titanium content, and c, which represents the zirconium content, can satisfy the condition 0.35 ≤ b / c ≤ 5.0. By setting b / c within the above range, the primary particles of the positive electrode active material can be made particularly large, and the variation in particle size of the positive electrode active material can be reduced. In addition, the specific surface area of ​​the positive electrode active material can be made particularly small.

[0053] When the ratio of titanium and zirconium content satisfies 0.35 ≤ b / c ≤ 5.0, the growth of primary particles of the positive electrode active material can be particularly promoted. In this embodiment, it is preferable that titanium and zirconium are detected when, for example, a sample for cross-sectional observation of the positive electrode active material is prepared and compositional analysis is performed at the center and surface of the primary particles of the positive electrode active material using EDS or the like. It is even more preferable that titanium and zirconium are detected at both the center and the surface. EDS is an abbreviation for Energy Dispersive X-ray Spectroscopy.

[0054] For cross-sectional observation of the positive electrode active material, a sample prepared for evaluating the number of primary particles constituting secondary particles, or a sample prepared using the same procedure, can be used. The center of the primary particle refers to the center of the smallest inclusion circle of the primary particle observed in the cross-sectional observation sample.

[0055] By performing a compositional analysis of the positive electrode active material of this embodiment using ICP (Inductively Coupled Plasma), etc., it is possible to identify that the positive electrode active material of this embodiment contains titanium or zirconium. (2-3) Regarding nickel, in lithium nickel composite oxide, the higher the nickel content, the higher the capacity that can be achieved when used as a positive electrode material for lithium-ion secondary batteries.

[0056] The nickel content can be such that the total content of nickel with elements M, titanium, and zirconium is 1. In other words, the nickel content can be 1-a-b-c.

[0057] The nickel content ratio 1-a-b-c may be 0.50 ≤ 1-a-b-c ≤ 0.99, 0.80 ≤ 1-a-b-c ≤ 0.99, or 0.90 ≤ 1-a-b-c ≤ 0.98. By increasing the nickel content ratio, the battery capacity can be increased when the positive electrode active material of this embodiment is used in a lithium-ion secondary battery. Furthermore, the capacity retention rate can be increased by keeping the nickel content ratio within the above range. (2-4) For lithium, the lithium content ratio d can be 0.92 ≤ d ≤ 1.20. (For oxygen) The oxygen content ratio is not particularly limited and can be selected according to the composition of lithium, nickel, element M, titanium, zirconium, etc. contained in the positive electrode active material of this embodiment. For example, in the positive electrode active material of this embodiment, α in 2 + α, which is the oxygen content ratio in the general formula described above, may be -0.20 ≤ α ≤ 0.20. (3) Regarding the concentration ratio of titanium and zirconium in the primary particles, the ratio R1 (R1 = Ti2 ÷ Ti1) of the titanium concentration Ti1 inside the primary particles and the titanium concentration Ti2 on the surface of the primary particles in the positive electrode active material of this embodiment may be 0.8 or more and 2.0 or less, i.e., 0.8 ≤ R1 ≤ 2.0. The ratio R1 of the titanium concentration Ti1 inside the primary particles and the titanium concentration Ti2 on the surface of the primary particles in the positive electrode active material of this embodiment may be 1.0 or more and 1.9 or less, or 1.2 or more and 1.8 or less.

[0058] Furthermore, the ratio R2 (R2 = Zr2 ÷ Zr1) of the zirconia concentration Zr1 inside the primary particles of the positive electrode active material of this embodiment to the zirconia concentration Zr2 on the surface of the primary particles may be 1.5 or greater, i.e., 1.5 ≤ R2. The ratio R2 of the zirconia concentration Zr1 inside the primary particles of the positive electrode active material of this embodiment to the zirconia concentration Zr2 on the surface of the primary particles may be 1.5 or greater and 5.0 or less, 2.0 or greater and 5.0 or less, or 2.5 or greater and 4.5 or less.

[0059] When measuring the concentrations of titanium and zirconium, a sample for cross-section observation of the positive electrode active material is prepared, and observation can be performed using, for example, a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The magnification of the observation field is not particularly limited, but for example, in order to observe the surface and interior of the primary particles to be evaluated, it is preferably 10,000 times or more, and more preferably 30,000 times or more. In the obtained observation image of the primary particle, point analysis is performed using EDS (Energy dispersive X-ray spectroscopy) on the outermost surface of the primary particle and the center of the primary particle, whereby the concentrations of titanium and zirconium can be measured. (4) X-ray diffraction pattern In the positive electrode active material of the present embodiment, the ratio of the diffraction peak intensity I(003) of the (003) plane to the diffraction peak intensity I(104) of the (104) plane (I(003) / I(104)) obtained from the X-ray diffraction pattern may be 1.8 or more, and may also be 1.9 or more.

[0060] The above X-ray diffraction pattern can be measured using Cu-Kα radiation as the X-ray source and a flat plate sample holder of Bragg-Brentano optical system.

[0061] When I(003) / I(104) is 1.8 or more, it means that the positive electrode active material of the present embodiment contains lithium nickel composite oxide particles including single primary particles or secondary particles in which the number of contained primary particles is sufficiently reduced at a particularly suitable ratio. Therefore, when producing a positive electrode or the like using the positive electrode active material of the present embodiment, the packing property of the positive electrode can be improved, and the battery characteristics of a lithium ion secondary battery using the positive electrode can be enhanced.

[0062] The upper limit of I(003) / I(104) is not particularly limited, but may be, for example, 5.0 or less, or 3.0 or less. Accordingly, I(003) / I(104) may be 1.8 or more and 5.0 or less, or may be 1.9 or more and 3.0 or less. (5) Specific surface area In the positive electrode active material of the present embodiment, the specific surface area determined by the nitrogen adsorption method is 0.50 m ２ / g or more and 1.6 m ２ / g or less, or may be 0.7 m ２ / g or more 1.4m ２ It may be less than / g.

[0063] The positive electrode active material of this embodiment has a specific surface area of ​​0.50 m². ２ By setting the amount to 1g or more, an adequate contact area with the electrolyte can be secured, thereby increasing the battery capacity.

[0064] The positive electrode active material of this embodiment has a specific surface area of ​​1.6 m². ２ By making it less than / g, the contact area with the electrolyte can be reduced, thereby reducing the reaction with the electrolyte, improving durability, and also reducing the generation of gas due to the reaction with the electrolyte. (6) Particle size characteristics (6-1) Volume average particle size The volume average particle size of the positive electrode active material in this embodiment is not particularly limited, but the volume average particle size MV determined from the volume-based particle size distribution by laser diffraction and scattering method may be 0.5 μm or more and 6.0 μm or less, or 1.5 μm or more and 5.0 μm or less.

[0065] By setting the volume-average particle size MV of the positive electrode active material in this embodiment to 0.5 μm or more, the particles of the positive electrode active material in this embodiment become sufficiently large, reducing the contact area with the electrolyte. This reduces the reaction with the electrolyte, improves durability, and also reduces the generation of gas due to the reaction with the electrolyte.

[0066] Furthermore, by setting the volume-average particle size MV of the positive electrode active material in this embodiment to 6.0 μm or less, it is possible to prevent the particles of the positive electrode active material in this embodiment from becoming excessively large and to ensure an appropriate contact area with the electrolyte, thereby increasing the battery capacity. (6-2) Particle size variation index The particle size variation index PDW (Particle size Distribution Width), which is obtained from the volume-based particle size distribution of the positive electrode active material in this embodiment by the following formula (1) may be 0.40 or more and 1.2 or less, or 0.6 or more and 1.0 or less.

[0067] PDW = (D90 - D10) / MV ... (1) In equation (1), D90, D10, and MV represent the 90% cumulative volume particle size (D90), which is the 90% diameter of the volume-based particle size distribution obtained by the laser diffraction and scattering method, the 10% cumulative volume particle size (D10), which is the 10% diameter of the volume-based particle size distribution, and the volume-average particle size MV.

[0068] By keeping the particle size variation index (PDW) within the above range, it means that the particle size distribution of the positive electrode active material in this embodiment is not excessively narrow or excessively wide, thus particularly enhancing energy density and cycle characteristics. [Method for manufacturing positive electrode active material for lithium-ion secondary batteries] The method for manufacturing the positive electrode active material for lithium-ion secondary batteries in this embodiment will now be described. According to the method for manufacturing the positive electrode active material in this embodiment, a positive electrode active material according to one aspect of the present disclosure can be manufactured. For this reason, some explanations of matters already described will be omitted. Note that the method for manufacturing the positive electrode active material according to one aspect of the present disclosure is not limited to the following method for manufacturing the positive electrode active material.

[0069] The method for producing the positive electrode active material of this embodiment may include a raw material mixing step, a calcination step, and a pulverization step.

[0070] In the raw material mixing process, a nickel composite compound, a lithium compound, a titanium element source, and a zirconium element source can be mixed to prepare a raw material mixture.

[0071] In the firing process, the raw material mixture prepared in the raw material mixing process is fired to obtain a fired product.

[0072] In the grinding process, the calcined material obtained in the calcination process is ground up to obtain a positive electrode active material.

[0073] The following describes each step. (1) Raw material mixing step In the raw material mixing step, as described above, a nickel composite compound, a lithium compound, a titanium element source, and a zirconium element source can be mixed to prepare a raw material mixture. In the raw material mixing step, in addition to the above raw materials, one or more elements selected from the element M source may be added and mixed to prepare a raw material mixture. The raw materials used will be described below. (Nickel composite compound) The nickel composite compound used in the raw material mixing step may contain nickel, which is an element other than lithium, oxygen, titanium, and zirconium among the elements contained in the target lithium nickel composite oxide particles, and element M.

[0074] While not particularly limited, nickel composite compounds can be used, such as nickel composite hydroxides or roasted nickel composite hydroxides. Examples of roasted nickel composite hydroxides include nickel composite oxides and mixtures of nickel composite oxides and nickel composite hydroxides.

[0075] Furthermore, the nickel composite compound may be a material having a coating layer containing element M on the surface of nickel oxide or nickel hydroxide, or a mixture of nickel oxide, nickel hydroxide, etc., with element M alone or a compound of element M.

[0076] The nickel composite compound can contain, for example, nickel (Ni) and element M (M) in a molar ratio of Ni:M = x:y. In the above formula, x and y can satisfy the relationship x:y = 1-a-b-c:a with 1-a-b-c and a in the general formula of the positive electrode active material of this embodiment.

[0077] Since element M has already been explained in the section on the positive electrode active material, we will omit its explanation here.

[0078] If the nickel composite compound is a nickel composite oxide, for example, the general formula is: Ni ｘ M ｙ O １＋β It can be expressed as follows.

[0079] If the nickel complex compound is a nickel complex hydroxide, for example, the general formula is: Ni ｘ M ｙ (OH) ２＋γ It can be expressed as follows.

[0080] Note that x, y, and element M have already been explained, so their explanations will be omitted. β and γ can be defined, for example, as -0.2 ≤ β ≤ 0.2 and -0.2 ≤ γ ≤ 0.2.

[0081] When using nickel composite hydroxide as the nickel composite compound, the method for producing the nickel composite hydroxide is not particularly limited. For example, nickel composite hydroxide obtained by crystallization methods such as coprecipitation or homogeneous precipitation can be used.

[0082] In the raw material mixing process, the nickel composite hydroxide described above can be used as is as the nickel composite compound, or it may be used after being oxidized and roasted to form a roasted product.

[0083] The conditions for oxidative roasting of nickel composite hydroxides are not particularly limited, but nickel composite hydroxides can be oxidative roasted, for example, in an oxidizing atmosphere at a temperature of 500°C to 800°C. The oxidative roasting temperature may be 550°C to 750°C.

[0084] When a roasted nickel complex hydroxide is used as the nickel complex compound, the composition ratio of lithium to elements other than lithium and oxygen in the lithium nickel complex oxide can be made particularly stable when a raw material mixture mixed with lithium compounds, etc., is calcined to obtain a lithium nickel complex oxide.

[0085] The atmosphere used for oxidative roasting is not particularly limited and can be carried out in an oxidizing atmosphere as described above, or in an air atmosphere or in an airflow for easier implementation. (Lithium compound) The lithium compound is not particularly limited and any compound containing lithium can be used. As a lithium compound, for example, one or more selected from lithium carbonate, lithium hydroxide, and lithium nitrate can be used. Among these, one or more selected from lithium carbonate and lithium hydroxide can be preferably used from the viewpoint of having less influence from residual impurities and dissolving at the calcination temperature. Furthermore, lithium hydroxide can be more preferably used from the viewpoint of obtaining a lithium nickel composite acid with high crystallinity. (Titanium element source) The titanium element source is a component containing titanium, and as a titanium element source, one or more selected from elemental titanium and titanium-containing compounds can be used.

[0086] The titanium element source is not particularly limited, but from the viewpoint of ease of handling, availability, and prevention of contamination with impurities, one or more types selected from titanium oxide, titanium hydroxide, titanium hydride, titanium chloride, titanium nitrate, etc. can be suitably used, and titanium oxide can be used more suitably. (Zirconium element source) The zirconium element source is a component containing zirconium, and as the zirconium element source, one or more types selected from elemental zirconium and zirconium-containing compounds can be used.

[0087] The zirconium element source is not particularly limited, but from the viewpoint of ease of handling, availability, and prevention of contamination with impurities, one or more types selected from zirconium oxide, zirconium hydroxide, zirconium hydride, zirconium nitrate, zirconium chloride, zirconium acetate, etc., can be suitably used, with zirconium oxide being particularly suitably used.

[0088] (Element M source) As explained earlier, element M can also contain magnesium or fluorine. Therefore, a magnesium source or a fluorine source may be added as an element M source.

[0089] The magnesium element source is not particularly limited, but from the viewpoint of ease of handling, availability, and prevention of contamination with impurities, one or more types selected from magnesium oxide, magnesium hydroxide, magnesium hydride, magnesium sulfate, magnesium chloride, etc., can be suitably used.

[0090] The fluorine element source is not particularly limited, but from the viewpoint of ease of handling, availability, and prevention of contamination with impurities, one or more types selected from ammonium fluoride, lithium fluoride, sodium fluoride, etc., can be suitably used. (Mixing ratio) The mixing ratio of the nickel composite compound, lithium compound, titanium element source, zirconium element source, and element M source is not particularly limited. However, the composition ratio of lithium and elements other than lithium and oxygen in the calcined product obtained after calcination is kept approximately the same as the composition ratio in the raw material mixture.

[0091] Therefore, it is preferable to adjust the amount of lithium (Li) in the raw material mixture so that the amount of substance ratio (Li / Me) is 0.92 or more and 1.20 or less relative to the total amount (Me) of nickel, element M, titanium, and zirconium in the raw material mixture.

[0092] Furthermore, if a washing process is carried out after the firing process, the proportion of lithium in the raw material mixture may be adjusted to be higher than the Li / Me ratio mentioned above, taking into account the amount of excess lithium removed in the washing process.

[0093] Furthermore, for titanium, zirconium, and element M sources, each raw material can be weighed and mixed so that the composition ratio of nickel and element M contained in the raw material mixture matches the desired composition.

[0094] The apparatus and method for mixing the nickel composite compound, lithium compound, titanium element source, zirconium element source, and element M source are not particularly limited, as long as they can uniformly mix the two. For example, dry mixers or mixing and granulation devices such as shaker mixers, Redigge mixers, Julia mixers, and V blenders can be used. (2) Firing process In the firing process, the raw material mixture can be fired in an oxidizing atmosphere to obtain a fired product. When the raw material mixture is fired in the firing process, lithium from the lithium compound diffuses into the nickel composite compound and reacts, so a lithium nickel composite oxide is formed. In addition, when the raw material mixture is fired, it is thought that titanium, zirconium, and element M contained in the titanium element source, zirconium element source, and element M source are also diffused into the nickel composite compound.

[0095] In the firing process, the firing temperature for firing the raw material mixture is not particularly limited, but it can be, for example, 600°C or higher and less than 850°C.

[0096] By setting the firing temperature to 600°C or higher, the diffusion of lithium into the nickel composite compound can be sufficiently promoted.

[0097] Furthermore, by keeping the firing temperature below 850°C, it is possible to prevent sintering from progressing between the particles of the generated positive electrode active material. In addition, it is possible to prevent the occurrence of abnormal grain growth and the coarsening of the particles contained in the fired product.

[0098] The holding time at the firing temperature is not particularly limited, but it can be, for example, 3 hours or more, or 5 hours or more and 24 hours or less.

[0099] During the process of raising the temperature to the firing temperature, the mixture can be held in a temperature range from near the melting point of the lithium compound used to the firing temperature, for example, between 400°C and 550°C, for about 1 to 5 hours. Holding the mixture in this temperature range allows the reaction to proceed particularly uniformly.

[0100] The atmosphere during firing can be, for example, an oxidizing atmosphere. The oxidizing atmosphere is not particularly limited, but an oxygen-containing gas atmosphere can be used, for example, an atmosphere with an oxygen concentration of 18% to 100% by volume.

[0101] By maintaining an oxygen concentration of 18% by volume or higher in the atmosphere during firing, the reaction between components in the raw material mixture can be promoted, thereby increasing the crystallinity of the positive electrode active material.

[0102] When an oxygen-containing gas atmosphere is used, the gas constituting the atmosphere can be, for example, air, oxygen, or a mixture of oxygen and an inert gas.

[0103] Furthermore, when using a mixed gas of oxygen and an inert gas as the gas constituting the oxygen-containing gas atmosphere, for example, as described above, it is preferable that the oxygen concentration in the mixed gas satisfies the above-mentioned range.

[0104] The firing process may be carried out in an oxygen-containing gas stream, or in air or an oxygen stream. Performing the firing process in an oxygen stream can particularly improve battery characteristics.

[0105] The furnace used for firing is not particularly limited and can be any furnace capable of firing the raw material mixture in a predetermined atmosphere. As for the furnace used for firing, an electric furnace that does not generate gas can be preferably used from the viewpoint of maintaining a uniform atmosphere inside the furnace, and either a batch type or a continuous type furnace can be used. (3) Grinding process Although intersintering of particles is prevented in the fired product obtained after the firing process, coarse particles may be formed due to weak sintering or aggregation. In addition, the fired product obtained after the firing process contains secondary particles formed by the aggregation of primary particles.

[0106] Therefore, in the grinding process, the calcined material obtained after the calcination process is ground to produce particles consisting of primary particles or secondary particles formed by the aggregation of multiple primary particles. The secondary particles can be ground in such a way that the number of primary particles they contain is reduced.

[0107] In the grinding process, the equipment used for grinding and the grinding conditions can be selected to achieve the required degree of aggregation and particle size for the positive electrode active material.

[0108] Grinding can be carried out using grinding equipment such as a jet mill, ball mill, or wet ball mill.

[0109] Furthermore, the grinding process can be carried out in multiple stages using multiple grinding devices.

[0110] After grinding, sieving, classification, etc., can be performed as needed, and particle size characteristics such as particle size distribution can be further adjusted and selected.

[0111] The method for producing the positive electrode active material of this embodiment may also include a water washing step as needed. (4) Water washing step The method for producing the positive electrode active material of this embodiment may also include a washing step after the calcination step or the pulverization step in which the calcined product or pulverized product is washed with water as needed. By performing the water washing step, excess lithium remaining on the particle surface can be removed.

[0112] The washing process can be carried out by mixing the calcined or pulverized material with water to be used for washing to form a slurry, stirring it for a predetermined time, and then performing solid-liquid separation. After solid-liquid separation, drying can also be performed.

[0113] When forming a cobalt coating layer on one or more selected locations on the surface of primary particles or secondary particles of the positive electrode active material, a cobalt-containing compound may be added to the water used for washing. The cobalt coating layer can be formed by washing with water containing the cobalt-containing compound and then drying.

[0114] Any water-soluble salt can be used as the cobalt-containing compound, such as cobalt sulfate or cobalt acetate. The thickness of the cobalt coating layer can be selected by adjusting the amount of cobalt-containing compound added, the washing time, and the drying conditions. [Positive electrode for lithium-ion secondary battery, lithium-ion secondary battery] The positive electrode for lithium-ion secondary battery of this embodiment (hereinafter also referred to as "positive electrode") may include a positive electrode active material according to one aspect of this disclosure.

[0115] Furthermore, the lithium-ion secondary battery of this embodiment (hereinafter also referred to as "secondary battery") may have a positive electrode, a negative electrode, and an electrolyte. The positive electrode may include a positive electrode active material according to one aspect of this disclosure.

[0116] The following describes an example of the configuration of the positive electrode and secondary battery of this embodiment, with each component explained separately. The secondary battery of this embodiment includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of components similar to those of a general lithium-ion secondary battery. Note that the positive electrode for lithium-ion secondary batteries and lithium-ion secondary batteries of the embodiments described below are merely examples. The positive electrode for lithium-ion secondary batteries and lithium-ion secondary batteries of this embodiment can be implemented in various modified and improved forms based on the knowledge of those skilled in the art, including the embodiments described below. Furthermore, the secondary battery does not particularly limit its use. (Positive Electrode) The positive electrode of the secondary battery of this embodiment may include a positive electrode active material according to one aspect of this disclosure.

[0117] An example of a method for manufacturing a positive electrode is described below. First, the positive electrode active material (in powder form), conductive material, and binder are mixed to form a positive electrode mixture. Then, activated carbon and solvents for purposes such as viscosity adjustment are added as needed, and this mixture is kneaded to produce a positive electrode mixture paste.

[0118] The mixing ratio of each material in the positive electrode composite is a factor that determines the performance of the lithium-ion secondary battery, and therefore can be adjusted according to the application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium-ion secondary battery. For example, if the total mass of the solid content of the positive electrode composite, excluding the solvent, is 100% by mass, the positive electrode active material can be contained in a ratio of 60% to 95% by mass, the conductive material in a ratio of 1% to 20% by mass, and the binder in a ratio of 1% to 20% by mass.

[0119] The resulting positive electrode composite paste is applied to the surface of a current collector, for example, made of aluminum foil, and dried to remove the solvent, thereby producing a sheet-like positive electrode. If necessary, it can be pressurized using a roll press or the like to increase the electrode density. The sheet-like positive electrode thus obtained can be cut to an appropriate size according to the intended battery and used in the manufacture of the battery.

[0120] As conductive materials, for example, graphite (natural graphite, artificial graphite, and expanded graphite, etc.) and carbon black-based materials such as acetylene black and Ketjenblack (registered trademark) can be used.

[0121] The binder serves to hold the active material particles together, and one or more of the following can be used: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resins, and polyacrylic acid.

[0122] If necessary, a solvent that dissolves the binder and disperses the positive electrode active material, conductive material, etc., can be added to the positive electrode mixture. Specifically, organic solvents such as N-methyl-2-pyrrolidone can be used as the solvent. In addition, activated carbon can be added to the positive electrode mixture to increase the electrical double layer capacitance.

[0123] The method for manufacturing the positive electrode is not limited to the examples given above, and other methods may be used. For example, the positive electrode composite material can be press-molded and then dried in a vacuum atmosphere. (Negative electrode) Lithium metal, lithium alloy, etc. can be used for the negative electrode. Alternatively, the negative electrode may be formed by mixing a binder with a negative electrode active material that can intercept and deintercept lithium ions, adding a suitable solvent to make a paste, coating the surface of a metal foil current collector such as copper with the negative electrode composite material, drying it, and compressing it to increase the electrode density as needed.

[0124] As the negative electrode active material, for example, natural graphite, artificial graphite, and calcined organic compounds such as phenolic resin, and powdered carbon materials such as coke can be used. In this case, as with the positive electrode, a fluororesin such as PVDF can be used as the negative electrode binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing these active materials and binders. (Separator) A separator can be placed between the positive electrode and the negative electrode as needed. The separator separates the positive electrode and the negative electrode and holds the electrolyte, and known separators can be used, for example, a thin film of polyethylene or polypropylene having many minute pores can be used. (Non-aqueous electrolyte) As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used.

[0125] As a non-aqueous electrolyte, for example, a lithium salt dissolved in an organic solvent can be used as a supporting salt. Alternatively, a lithium salt dissolved in an ionic liquid may be used as a non-aqueous electrolyte. An ionic liquid is a salt composed of cations and anions other than lithium ions, and is liquid at room temperature.

[0126] As the organic solvent, one of the following may be used alone or in combination: cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butanesultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate.

[0127] LiPF is used as a supporting salt. ６ LiBF ４ LiClO ４ LiAsF ６ ,LiN(CF ３ SO ２ ) ２These, and their combined salts, can be used. Furthermore, the non-aqueous electrolyte may contain radical scavengers, surfactants, and flame retardants.

[0128] Furthermore, solid electrolytes may be used as non-aqueous electrolytes. Solid electrolytes have the property of being able to withstand high voltages. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

[0129] Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0130] The oxide-based solid electrolyte is not particularly limited, and for example, one containing oxygen (O) and having lithium ion conductivity and electronic insulation properties can be suitably used. For example, lithium phosphate (Li ３ PO ４ ), Li ３ PO ４ N Ｘ LiBO ２ N Ｘ LiNbo ３ , LiTaO ３ Li ２ SiO ３ Li ４ SiO ４ -Li ３ PO ４ Li ４ SiO ４ -Li ３ VO ４ Li ２ O-B ２ O ３ -P ２ O ５ Li ２ O-SiO ２ Li ２ O-B ２ O ３ -ZnO, Li １＋Ｘ Al Ｘ Ti ２－Ｘ (PO ４ ) ３ (0≦X≦1), Li １＋Ｘ Al Ｘ Ge ２－Ｘ (PO ４ ) ３(0≦X≦1), LiTi ２ (PO ４ ) ３ , Li ３Ｘ La ２／３－Ｘ TiO ３ (0≦X≦2 / 3), Li ５ La ３ Ta ２ O １２ , Li ７ La ３ Zr ２ O １２ , Li ６ BaLa ２ Ta ２ O １２ , Li ３．６ Si ０．６ P ０．４ O ４ One or more types selected from the above can be used.

[0131] The sulfide-based solid electrolyte is not particularly limited, and for example, one containing sulfur (S) and having lithium ion conductivity and electronic insulation can be preferably used. As the sulfide-based solid electrolyte, for example, Li ２ S-P ２ S ５ , Li ２ S-SiS ２ , LiI-Li ２ S-SiS ２ , LiI-Li ２ S-P ２ S ５ , LiI-Li ２ S-B ２ S ３ , Li ３ PO ４ -Li ２ S-Si ２ S, Li ３ PO ４ -Li ２ S-SiS ２ , LiPO ４ -Li ２ S-SiS, LiI-Li ２ S-P ２ O ５ , LiI-Li ３ PO ４ -P ２ S ５You may use one or more types selected from the above.

[0132] Note that other inorganic solid electrolytes may be used besides those mentioned above, for example, Li ３ N, LiI, Li ３ N-LiI-LiOH, etc., may also be used.

[0133] The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, or copolymers thereof can be used. The organic solid electrolyte may also contain a supporting salt (lithium salt). (Shape and structure of the secondary battery) The lithium-ion secondary battery of this embodiment, as described above, can be made into various shapes such as cylindrical or stacked. In any case, if the secondary battery of this embodiment uses a non-aqueous electrolyte, the positive electrode and negative electrode can be stacked with a separator in between to form an electrode body, and the resulting electrode body can be impregnated with a non-aqueous electrolyte. The positive electrode current collector and the positive electrode terminal that is open to the outside, and the negative electrode current collector and the negative electrode terminal that is open to the outside can be connected using current collecting leads, and the structure can be sealed in a battery case.

[0134] As previously described, the secondary battery of this embodiment is not limited to a form using a non-aqueous electrolyte solution as the non-aqueous electrolyte; for example, a secondary battery using a solid non-aqueous electrolyte, i.e., an all-solid-state battery, can also be used. In the case of an all-solid-state battery, the components other than the positive electrode active material can be changed as necessary.

[0135] The secondary battery of this embodiment can be used for various applications, but because it can be a high-capacity, high-output secondary battery, it is suitable for powering small portable electronic devices (such as notebook computers and mobile phone terminals) that always require high capacity. The secondary battery of this embodiment is also suitable for powering electric vehicles that require high output.

[0136] Furthermore, since the secondary battery of this embodiment can be miniaturized and have a high output, it is suitable as a power source for electric vehicles where mounting space is limited. Moreover, the secondary battery of this embodiment can be used not only as a power source for electric vehicles that are driven purely by electrical energy, but also as a power source for so-called hybrid vehicles that are used in conjunction with combustion engines such as gasoline engines and diesel engines.

[0137] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0138] First, we will explain the evaluation methods for the positive electrode active material and secondary battery obtained in the following examples and comparative examples. (1) Evaluation Method (1-1) Evaluation Method for Positive Electrode Active Material The following evaluations were performed on the obtained positive electrode active material.

[0139] (a) Composition The composition of the positive electrode active material was evaluated by analysis using an ICP emission spectrometer (VARIAN, 725ES). The evaluation results are shown in the "Monetary Ratio" column of Table 1. Table 1 also shows the molar ratio (Ti / Zr) of titanium to zirconium contained in the positive electrode active material.

[0140] (b) Concentration ratio of titanium and zirconium in primary particles First, the positive electrode active materials prepared in the following examples and comparative examples were embedded in resin, and cross-section polishing was performed to prepare samples for cross-sectional observation.

[0141] The prepared samples for cross-sectional observation were examined using a transmission electron microscope (TEM).

[0142] In this process, point analysis was performed on the surface and interior of primary particles using EDS (Electron Diode) on the samples used for cross-sectional observation, and the concentrations of titanium and zirconium were measured.

[0143] The magnification of the observation field was set to between 30,000x and 40,000x in order to observe the surface and interior of the primary particles to be evaluated. Point analysis using EDS was then performed on the surface and interior of the primary particles in the obtained observation images. Through point analysis, the titanium concentration Ti1 inside the primary particle, the titanium concentration Ti2 on the surface of the primary particle, the zirconia concentration Zr1 inside the primary particle, and the zirconia concentration Zr2 on the surface of the primary particle were determined.

[0144] The measurement points on the surface of the primary particle were defined as the intersections of a straight line along the major axis of the primary particle being evaluated and the contour line of the outermost surface of the primary particle. Since two intersection points can occur between the straight line along the major axis of the primary particle and the contour line of the outermost surface of the primary particle, one point was selected for evaluation.

[0145] Furthermore, the measurement point inside the primary particle was defined as any single point located on the major axis of the primary particle, within 25% of the major axis diameter from the center of the major axis.

[0146] Then, the ratio R1 (R1 = Ti2 ÷ Ti1) between the titanium concentration Ti1 inside the primary particle and the titanium concentration Ti2 on the surface of the primary particle was calculated. In addition, the ratio R2 (R2 = Zr2 ÷ Zr1) between the zirconia concentration Zr1 inside the primary particle and the zirconia concentration Zr2 on the surface of the primary particle was calculated.

[0147] Ten different primary particles were selected, and the ratio R1 of the titanium concentration Ti1 inside the primary particle to the titanium concentration Ti2 on the surface of the primary particle, and the ratio R2 of the zirconia concentration Zr1 inside the primary particle to the zirconia concentration Zr2 on the surface of the primary particle were calculated using the procedure described above.

[0148] Then, the arithmetic mean of the above ratio R1 for the 10 primary particles that were evaluated was taken as the ratio R1 of the titanium concentration Ti1 inside the primary particle and the titanium concentration Ti2 on the surface of the primary particle for the primary particle of the positive electrode active material that was subjected to evaluation.

[0149] Furthermore, the arithmetic mean of the above ratio R2 for the 10 primary particles that were evaluated was defined as the ratio R2 of the zirconia concentration Zr1 inside the primary particle and the zirconia concentration Zr2 on the surface of the primary particle for the primary particle of the positive electrode active material used for evaluation.

[0150] The evaluation results are shown in the "Concentration Ratio of Titanium and Zirconium in Primary Particles" column of Table 1, with the concentration ratio R1 for titanium shown in the "Ti (R1)" column and the concentration ratio R2 for zirconium shown in the "Zr (R2)" column.

[0151] (c) Particle number ratio consisting of primary particles First, the positive electrode active material prepared in the following examples and comparative examples was embedded in resin, and cross-section polishing was performed to prepare a sample for cross-sectional observation.

[0152] The prepared cross-sectional observation samples were observed using a scanning electron microscope (SEM, Hitachi High-Technologies Corporation, Scanning Electron Microscope S-4700).

[0153] In this process, the magnification of the SEM was selected so that a total of 100 to 200 particles of the positive electrode active material were included within the first field of view of the sample used for cross-sectional observation.

[0154] Then, the number of primary particles among all particles contained within the first observation field was counted, and the ratio of primary particles to all particles contained within the first observation field was calculated and defined as the ratio R1 of primary particles in the first observation field.

[0155] In the obtained observation images, particles in which no grain boundaries were observed within the particle were defined as particles consisting of primary particles. In the obtained observation images, particles in which grain boundaries were observed within the particle were defined as secondary particles formed by the aggregation of multiple primary particles.

[0156] The observation field of view was changed, and the cross-sectional sample was observed under the same conditions in the second and third observation fields, in addition to the first observation field of view described above. For the second and third observation fields, positions were selected that did not overlap with the other observation fields for the same cross-sectional sample, and the SEM magnification was selected under the same conditions as for the first observation field of view.

[0157] Then, the number ratio R2 of particles consisting of primary particles in the second observation field and the number ratio R3 of particles consisting of primary particles in the third observation field were calculated.

[0158] Next, the average value of the number ratio of particles consisting of primary particles in the three fields of view, i.e., (R1 + R2 + R3) / 3, was calculated and used as the number ratio of particles consisting of primary particles for the observed cathode active material. The evaluation results are shown in the "Primary Particle Ratio" column of Table 1. (d) Volume-average particle size MV, particle size variation index (Particle size variation index: PDW) For the cathode active materials prepared in the following examples and comparative examples, the volume-based particle size distribution was obtained by the laser diffraction and scattering method using a laser diffraction scattering particle size analyzer (model: Microtrac HRA, manufactured by Nikkiso Co., Ltd.).

[0159] The volume-based particle size distribution was obtained, and the volume-average particle size (MV) was calculated.

[0160] Furthermore, from the obtained volume-based particle size distribution, the 90% cumulative volume particle size (D90) and the 10% cumulative volume particle size (D10) were determined, and together with the volume-average particle size MV, the particle size variation index PDW was calculated using the previously described formula (1).

[0161] The evaluation results are shown in the "Volume Average Particle Size MV" and "Particle Size Variation Index" columns of Table 1, respectively. (e) Specific Surface Area The specific surface area of ​​the positive electrode active materials prepared in the following examples and comparative examples was measured by nitrogen adsorption using a fluidized gas adsorption specific surface area measuring device (MultiSorb, manufactured by Yuasa Ionics Co., Ltd.).

[0162] The evaluation results are shown in the "Specific Surface Area" column of Table 1. (f) Diffraction peak intensity of the (10⁴) plane I （１０４） Diffraction peak intensity I of the (003) plane （００３） For the positive electrode active materials prepared in the examples and comparative examples with ratios below the given ratio, an X-ray diffractometer (BRUKER, D8 DISCOVER) was used to analyze monochromatized CuKα as the X-ray source. １ The XRD pattern was measured using the Bragg-Brentano optical system's flat sample holder. From the obtained XRD pattern, the intensity I(003) of the peak in the (003) plane located around 2θ = 18° and the intensity I(104) of the peak in the (104) plane located around 2θ = 44° were determined, and I(003) / I(104) was calculated.

[0163] The evaluation results are shown in the "I(003) / I(104)" column of Table 1.

[0164] From the obtained XRD patterns, it was confirmed that the lithium nickel composite oxide contained in the positive electrode active material manufactured in the following examples has a hexagonal layered structure. (1-2) Method for evaluating battery characteristics (a) Discharge capacity The discharge capacity was evaluated using the coin-type batteries shown in Figure 1, which were manufactured in the following examples and comparative examples.

[0165] After preparing the coin-type batteries described in the following examples and comparative examples, leave them for about 12 hours until the open-circuit voltage (OCV) stabilizes, then set the current density to 0.1 mA / cm² for the positive electrode. ２ The battery was charged to a cutoff voltage of 4.3V. After charging, it was left idle for one hour, and the discharge capacity at which it was discharged to a cutoff voltage of 2.5V was defined as the discharge capacity.

[0166] The evaluation results are shown in the "Discharge Capacity" column under "Battery Characteristics" in Table 1. The ratio of discharge capacity to specific surface area of ​​the positive electrode active material is also calculated and shown in the "Discharge Capacity / Specific Surface Area" column. (b) Impedance Measurement The coin-type batteries prepared in the following examples and comparative examples were first conditioned. Conditioning was performed in a constant temperature bath maintained at 25°C with a current density of 0.3 mA / cm². ２ The test was performed by charging the battery to a cutoff voltage of 4.2V, letting it rest for 10 minutes, and then discharging it to a cutoff voltage of 2.5V. This cycle was repeated five times. The initial discharge capacity was defined as the capacity at which the battery was discharged to 2.5V after one cycle under the same conditions following the conditioning.

[0167] After measuring the initial discharge capacity, the coin-type battery was charged to 50% of its initial discharge capacity, allowed to rest for 10 minutes, and then discharged at a 1C rate for 10 seconds. The change in voltage during this 10-second discharge at the 1C rate was then measured.

[0168] According to Ohm's law, the voltage change was divided by the current to calculate the resistance (DC-IR), which was used as the reaction resistance, representing the DC resistance of the battery at SOC 50%, 1C, 10 seconds, and 25°C. In this case, since the coin-type batteries prepared in the following examples and comparative examples use the same components other than the positive electrode active material, the above DC resistance of the battery is considered to be an evaluation of the resistance of the positive electrode active material. The evaluation results are shown in the "Impedance Measurement" column under "Battery Characteristics" in Table 1. (c) Volume Expansion Rate The volume of the laminate-type batteries shown in Figure 2, prepared in the following examples and comparative examples, was measured by the Archimedes method and was used as the pre-cycle volume.

[0169] Next, the device was left in a constant temperature chamber maintained at 25°C for about 12 hours. After the open-circuit voltage (OCV) stabilized, conditioning was performed by repeating charge and discharge cycles five times with a cutoff voltage of 2.5V-4.3V.

[0170] Next, the batteries were charged at 60°C using constant current constant voltage (CCCV) charging up to 4.2V. While maintaining the voltage at 4.2V, they were stored in a constant temperature chamber set to 60°C for 14 days using float charging. After 14 days, the batteries were discharged to 2.5V. After discharge, the volume of the laminated batteries was measured using the Archimedes method and recorded as the post-cycle volume.

[0171] The volume expansion coefficient was calculated from the volume before and after the cycle using the following formula.

[0172] (Volume expansion coefficient) = (Volume after cycling) / (Volume before cycling) × 100 (2) Manufacturing conditions for positive electrode active material Below, the manufacturing conditions and evaluation results for positive electrode active material, etc. in the examples and comparative examples will be described. [Example 1] (Manufacturing of positive electrode active material) (Raw material mixing process) A nickel composite oxide in which the molar ratio of nickel to cobalt is Ni:Co = 95:5 was mixed with lithium hydroxide, titanium oxide and zirconium oxide to prepare a raw material mixture. The nickel composite oxide was obtained by heat treatment of nickel composite hydroxide obtained by crystallization.

[0173] Lithium hydroxide was weighed out so that the ratio of the number of lithium (Li) atoms to the number of other metals (Me) contained in the raw material mixture, i.e., was 1.01.

[0174] Titanium oxide and zirconium oxide were added in such a way that the amount of titanium and zirconium was 0.1 mol% each relative to the total amount of nickel and cobalt. The addition ratio of titanium to zirconium (Ti / Zr) was 1.

[0175] A shaker mixer (Willi e Bakkofen (WAB) model: TURBULA Type T2C) was used for mixing. (Castration process) The raw material mixture obtained in the mixing process was calcined at 780°C under an oxygen atmosphere. (Grinding process) The calcined product obtained in the calcination process was ground using a jet mill (Nippon Pneumatic Co., Ltd., model: PJM100). The grinding conditions were selected in prior tests to ensure that the proportion of primary particles was sufficiently high.

[0176] The positive electrode active material obtained after the crushing process was evaluated. The evaluation results are shown in Table 1. (Fabrication of secondary battery) A coin-type battery, which is a lithium-ion secondary battery, was fabricated according to the procedure shown in Figure 1. The charge and discharge capacity of the obtained coin-type battery was also evaluated. The evaluation results are shown in Table 1. (Coin-type battery) As shown in Figure 1, the coin-type battery 10 has a case 11 and an electrode 12 housed inside the case 11.

[0177] The case 11 includes a hollow positive electrode can 111 with one end open, and a negative electrode can 112 positioned at the opening of the positive electrode can 111. The case 11 is shaped such that when the negative electrode can 112 is positioned at the opening of the positive electrode can 111, a space for housing the electrode 12 is formed between the negative electrode can 112 and the positive electrode can 111.

[0178] The electrode 12 has a positive electrode 121, a separator 122, and a negative electrode 123, which are stacked in this order, and is housed in the case 11 such that the positive electrode 121 is in contact with the inner surface of the positive electrode can 111 and the negative electrode 123 is in contact with the inner surface of the negative electrode can 112.

[0179] The case 11 is equipped with a gasket 113, which restricts relative movement between the positive electrode can 111 and the negative electrode can 112, maintaining a non-contact state, i.e., an electrically insulated state, and thus fixing them in place. The gasket 113 also has the function of sealing the gap between the positive electrode can 111 and the negative electrode can 112, thereby creating an airtight and liquid-tight barrier between the inside and outside of the case 11.

[0180] This coin-type battery 10 was manufactured using the following procedure. First, 52.5 mg of the obtained positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene (PTFE) resin were mixed and pelletized to a size of approximately 75 mg with a diameter of 11 mm to produce the positive electrode 121. Then, the prepared positive electrode was dried in a vacuum dryer at 100°C for 12 hours.

[0181] Using this positive electrode 121, negative electrode 123, separator 122, and electrolyte, a coin-type battery 10 was fabricated in a glove box with an Ar atmosphere where the dew point was controlled to -60°C.

[0182] The negative electrode 123 used lithium metal punched out in the shape of a 13 mm diameter disc.

[0183] A polyethylene porous membrane with a thickness of 25 μm was used for the separator 122. The electrolyte was 1 M LiClO ４ A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1 (manufactured by Toyama Pharmaceutical Co., Ltd.) was used as the supporting electrolyte.

[0184] (Laminated Battery) As shown in Figure 2, the laminated battery 20 has a structure in which an electrolyte is impregnated into a laminate of a positive electrode film 21, a separator 22, and a negative electrode film 23, and then sealed with a laminate 24. A positive electrode tab 25 is connected to the positive electrode film 21, and a negative electrode tab 26 is connected to the negative electrode film 23, with the positive electrode tab 25 and negative electrode tab 26 exposed outside the laminate 24.

[0185] A slurry was prepared by dispersing 20.0 g of the obtained positive electrode active material, 0.638 g of acetylene black, and 0.638 g of polyvinylidene fluoride in N-methyl-2-pyrrolidone (NMP) and spreading it on aluminum foil to a depth of 1 cm. ２ The positive electrode active material was coated so that 19.0 mg was present per aluminum foil. Next, the slurry containing the positive electrode active material was coated onto the aluminum foil and dried in air at 120°C for 30 minutes to remove NMP. The aluminum foil coated with the positive electrode active material was cut into strips 66 mm wide and roll-pressed with a load of 4.0 t to produce a positive electrode film. The positive electrode film was then cut into a rectangle of 50 mm x 30 mm and dried in a vacuum dryer at 120°C for 12 hours, and used as the positive electrode film 21 of the laminate-type battery 20.

[0186] Furthermore, a negative electrode film 23 was prepared by coating copper foil with a negative electrode composite paste, which is a mixture of graphite powder with an average particle size of about 20 μm and polyvinylidene fluoride. For the separator 22, a polyethylene porous film with a thickness of 20 μm was used, and for the electrolyte, 1 M LiPF was used. ６ A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 3:7 (manufactured by Ube Industries, Ltd.) was used as the supporting electrolyte.

[0187] In a dry room controlled to a dew point of -60°C, the laminate of the positive electrode film 21, separator 22, and negative electrode film 23 was impregnated with an electrolyte, and then sealed with a laminate 24 to produce a laminate-type battery 20.

[0188] The evaluation results are shown in Table 1. [Examples 2 to 6] The cathode active material was manufactured under the same conditions as in Example 1, except that the molar ratio of lithium, titanium, and zirconium contained in the raw material mixture was changed in the raw material mixing process, and the amount of lithium hydroxide, titanium oxide, and zirconium oxide added was selected according to the desired composition.

[0189] For example, in Example 2, titanium oxide and zirconium oxide were added such that the amounts of titanium and zirconium were 0.2 mol% each relative to the total amount of nickel and cobalt, and the addition ratio of titanium to zirconium (Ti / Zr) was 1.

[0190] Furthermore, coin-type and laminate-type lithium-ion secondary batteries were manufactured and evaluated under the same conditions as in Example 1, except that the obtained positive electrode active material was used. The evaluation results are shown in Table 1. [Example 7] The positive electrode active material was manufactured under the same conditions as in Example 1, except that the firing temperature was set to 800°C in the firing process.

[0191] Furthermore, coin-type and laminate-type lithium-ion secondary batteries were fabricated and evaluated under the same conditions as in Example 1, except for the use of the obtained positive electrode active material. The evaluation results are shown in Table 1. [Example 8] In the raw material mixing process, a nickel composite oxide was used in which the molar ratio of nickel, manganese, and cobalt was Ni:Mn:Co = 93:2:5. In addition, in the raw material mixing process, titanium oxide and zirconium oxide were added in such a way that the amount of titanium and zirconium was 0.1 mol% and 0.1 mol% respectively relative to the total amount of nickel, manganese, and cobalt.

[0192] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Example 1. Furthermore, the positive electrode active material was manufactured under the same conditions as in Example 1, except that the positive electrode active material obtained in this example was used.

[0193] Furthermore, coin-type and laminate-type lithium-ion secondary batteries were fabricated and evaluated using the obtained positive electrode active material. The evaluation results are shown in Table 1. [Example 9] In the raw material mixing process, a nickel composite oxide was used in which the molar ratio of nickel, manganese, and cobalt was Ni:Mn:Co = 96:1:3. In addition, in the raw material mixing process, titanium oxide and zirconium oxide were added in such a way that the amount of titanium and zirconium was 0.1 mol% each relative to the total amount of nickel, manganese, and cobalt.

[0194] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Example 1. In addition, coin-type and laminate-type lithium-ion secondary batteries were manufactured and evaluated under the same conditions as in Example 1, except that the positive electrode active material obtained in this example was used. The evaluation results are shown in Table 1. [Example 10] In the raw material mixing process, titanium oxide and zirconium oxide were added so that the amounts of titanium and zirconium were 0.1 mol% and 0.1 mol%, respectively, relative to the total amount of nickel, manganese, and cobalt. In addition, ammonium fluoride was added in the raw material mixing process so that the amount of fluorine added was 0.5 mol%, relative to the total amount of nickel, manganese, and cobalt. Element M is manganese and cobalt.

[0195] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Example 9. [Example 11] In the raw material mixing process, titanium oxide and zirconium oxide were added so that the amounts of titanium and zirconium were 0.1 mol% and 0.1 mol%, respectively, relative to the total amount of nickel, manganese, and cobalt. In addition, magnesium oxide was added in the raw material mixing process so that the amount of magnesium added was 0.5 mol%, relative to the total amount of nickel, manganese, and cobalt. Element M is manganese and cobalt.

[0196] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Example 9. [Example 12] In the raw material mixing process, titanium oxide and zirconium oxide were added so that the amounts of titanium and zirconium were 0.1 mol% and 0.1 mol%, respectively, relative to the total amount of nickel, manganese, and cobalt. In addition, in the raw material mixing process, magnesium oxide and ammonium fluoride were added so that the amounts of magnesium and fluorine were 0.25 mol%, respectively, relative to the total amount of nickel, manganese, and cobalt. Element M is manganese and cobalt.

[0197] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Example 9. [Example 13] After the calcination process, 100 g of the calcined product obtained in the calcination process was mixed with a 0.1 mol / L cobalt sulfate solution, stirred for 15 minutes, and then filtered and dried to prepare the positive electrode active material in the same manner as in Example 2, except that it was washed with water and coated with cobalt.

[0198] Furthermore, coin-type and laminate-type lithium-ion secondary batteries were fabricated and evaluated under the same conditions as in Example 1, except for the use of the obtained positive electrode active material. The evaluation results are shown in Tables 1 to 3.

[0199] In the cross-section of the lithium nickel composite oxide particles contained in the positive electrode active material prepared in this embodiment, line analysis was performed by SEM-EDS from the center toward the outer surface along the radius of the smallest inclusion circle of the lithium nickel composite oxide particles. As a result, it was confirmed that a cobalt coating layer was formed on the surface of the lithium nickel composite oxide particles, in terms of the amount of cobalt, which was 2% or more higher in terms of the amount of substance compared to other parts. [Comparative Example 1, Comparative Example 2] In the raw material mixing process, the raw material mixture was weighed and mixed so that the amount of substance ratio of each element contained in the raw material mixture was as shown in Table 1, and titanium oxide and zirconium oxide were not added.

[0200] Furthermore, the firing temperature in the firing process was set to 780°C (Comparative Example 1) and 800°C (Comparative Example 2). Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Example 1.

[0201] The firing temperature is set higher than the typical temperature used when manufacturing positive electrode active materials of the same composition, so that the primary particles contained in the resulting positive electrode active material grow to a sufficiently large size. In Comparative Examples 3 to 6 below, the firing temperature is also selected so that the primary particles contained in the resulting positive electrode active material grow to a sufficiently large size.

[0202] Furthermore, coin-type and laminate-type lithium-ion secondary batteries were fabricated and evaluated under the same conditions as in Example 1, except for the use of the obtained positive electrode active material. The evaluation results are shown in Table 1. [Comparative Example 3] In the raw material mixing process, titanium oxide was added so that the amount of titanium was 0.1 mol% relative to the total amount of nickel and cobalt. In Comparative Example 3, zirconium oxide was not added.

[0203] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Example 1.

[0204] Furthermore, coin-type and laminate-type lithium-ion secondary batteries were fabricated and evaluated under the same conditions as in Example 1, except for the use of the obtained positive electrode active material. The evaluation results are shown in Table 1. [Comparative Example 4] In the raw material mixing process, zirconium oxide was added so that the amount of zirconium was 0.1 mol% relative to the total amount of nickel and cobalt. In Comparative Example 4, titanium oxide was not added.

[0205] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Example 1.

[0206] Furthermore, a coin-type lithium-ion secondary battery was fabricated and evaluated under the same conditions as in Example 1, except that the obtained positive electrode active material was used. The evaluation results are shown in Table 1. [Comparative Example 5] Titanium oxide and zirconium oxide were not added in the raw material mixing process.

[0207] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Example 8.

[0208] Furthermore, a coin-type lithium-ion secondary battery was manufactured and evaluated under the same conditions as in Example 1, except that the obtained positive electrode active material was used. The evaluation results are shown in Table 1. [Comparative Example 6] The positive electrode active material was manufactured under the same conditions as in Comparative Example 1, except that the firing temperature was set to 850°C in the firing process.

[0209] Furthermore, coin-type and laminate-type lithium-ion secondary batteries were fabricated and evaluated under the same conditions as in Example 1, except for the use of the obtained positive electrode active material. The evaluation results are shown in Table 1. [Comparative Example 7] In the raw material mixing process, a nickel composite oxide was used in which the molar ratio of nickel, manganese, and cobalt was Ni:Mn:Co = 96:1:3.

[0210] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Comparative Example 1. [Comparative Example 8] In the raw material mixing process, in addition to lithium hydroxide and nickel composite oxide, only ammonium fluoride was added so that the amount of fluorine added was 0.5 mol% relative to the total amount of nickel, manganese, and cobalt.

[0211] Except for the points mentioned above, the positive electrode active material was manufactured under the same conditions as in Comparative Example 7. [Comparative Example 9] In the raw material mixing process, in addition to lithium hydroxide and nickel composite oxide, only magnesium oxide was added, such that the amount of magnesium added was 0.5 mol% relative to the total amount of nickel, manganese, and cobalt.

[0212] Except for the points mentioned above, the cathode active material was manufactured under the same conditions as in Comparative Example 7.

[0213] [Comparative Example 10] In the raw material mixing process, in addition to lithium hydroxide and nickel composite oxide, only magnesium oxide and ammonium fluoride were added, such that the amount of magnesium and fluorine added was 0.25 mol% each relative to the total amount of nickel, manganese, and cobalt.

[0214] Except for the points mentioned above, the cathode active material was manufactured under the same conditions as in Comparative Example 7.

[0215] According to the results shown in Table 1, the specific surface area in Examples 1 to 13 was 1.6 m². ２ The value was less than / g, confirming that the specific surface area had been reduced.

[0216] Furthermore, as shown in Table 1, it was confirmed that in Examples 1 to 13, the value of discharge capacity / specific surface area, which is the electrical capacity per specific surface area of ​​the lithium-ion secondary battery, was also higher compared to the corresponding comparative examples.

[0217] Furthermore, when comparing battery characteristics, it is possible to compare experimental examples with corresponding compositions of positive electrode active material. For this reason, Examples 1 to 7 and Example 13 can be compared with Comparative Examples 1 to 4 and Comparative Example 6. Also, Example 8 can be compared with Comparative Example 5. Examples 9 to 12 will be compared with Comparative Examples 7 to 10. [Note] The embodiments of the present disclosure are, for example, as follows.

[0218] <1> A positive electrode active material for a lithium-ion secondary battery comprising a lithium nickel composite oxide having a hexagonal layered structure, comprising one or more types selected from particles consisting of primary particles and secondary particles formed by the aggregation of multiple primary particles, The material contains lithium (Li), nickel (Ni), element M (M), titanium (Ti), and zirconium (Zr) in a molar ratio of Li:Ni:M:Ti:Zr = d:1-a-b-c:a:b:c (wherein element M is at least one element selected from Co, Mn, Al, W, Mo, Mg, Ca, Cr, Ta, Nb, Si, F, and B, and a, b, c, and d satisfy 0.001 ≤ a < 0.60, 0.0003 ≤ b < 0.02, 0.0003 ≤ c < 0.02, 0.92 ≤ d ≤ 1.20, and 0.35 ≤ b / c ≤ 5.0). Using Cu-kα rays as the X-ray source, the X-ray diffraction pattern measured using a flat plate sample holder of a Bragg-Brentano optical system shows that the ratio of the diffraction peak intensity I(003) of the (004) plane to the diffraction peak intensity I(104) of the (104) plane is 1.8 or greater, and the specific surface area determined by the nitrogen adsorption method is 0.50 m². ２ / g or more 1.6m ２ A positive electrode active material for lithium-ion secondary batteries with a density of less than / g.

[0219] <2> The positive electrode active material for lithium-ion secondary batteries according to <1>, wherein the element M comprises one or more selected from magnesium and fluorine.

[0220] <3> A positive electrode active material for a lithium-ion secondary battery according to <1> or <2>, wherein the number ratio of particles consisting of the primary particles is 60% or more.

[0221] <4> A positive electrode active material for a lithium-ion secondary battery according to any one of <1> to <3>, wherein the particle made up of the primary particle and one or more locations selected from the surface of the secondary particle have a cobalt coating layer containing cobalt.

[0222] <5> A positive electrode active material for a lithium-ion secondary battery according to any one of <1> to <4>, wherein the volume-average particle size MV, determined from the volume-based particle size distribution by laser diffraction and scattering method, is 0.5 μm or more and 6.0 μm or less, and the particle size variation index [(D90 - D10) / MV] calculated by D90, which is the 90% diameter based on volume, D10, which is the 10% diameter based on volume, and the volume-average particle size MV, is 0.40 or more and 1.2 or less.

[0223] <6> A positive electrode active material for a lithium-ion secondary battery according to any one of <1> to <5>, wherein the ratio of the titanium concentration Ti1 inside the primary particle to the titanium concentration Ti2 on the surface of the primary particle (Ti2 ÷ Ti1) is 0.8 or more and 2.0 or less, and the ratio of the zirconia concentration Zr1 inside the primary particle to the zirconia concentration Zr2 on the surface of the primary particle (Zr2 ÷ Zr1) is 1.5 or more.

[0224] <7> A positive electrode containing the positive electrode active material for lithium-ion secondary batteries described in any of <1> to <6>.

[0225] <8> A lithium-ion secondary battery having a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode contains a positive electrode active material for lithium-ion secondary batteries as described in any of <1> to <6>.

[0226] This application claims priority based on Japanese Patent Application No. 2025-057194, filed with the Japan Patent Office on 28 March 2025, and the entire contents of Japanese Patent Application No. 2025-057194 are incorporated herein by reference.

[0227] 10 Coin-type battery 11 Case 111 Positive electrode can 112 Negative electrode can 113 Gasket 12 Electrode 121 Positive electrode 122 Separator 123 Negative electrode 30 Particles of positive electrode active material 30A Outer surface 31 Cobalt coating layer O Center L Straight line

Claims

1. A positive electrode active material for a lithium-ion secondary battery comprising a lithium nickel composite oxide having a hexagonal layered structure, comprising one or more types selected from particles consisting of primary particles and secondary particles formed by the aggregation of multiple primary particles, The material contains lithium (Li), nickel (Ni), element M (M), titanium (Ti), and zirconium (Zr) in a molar ratio of Li:Ni:M:Ti:Zr = d:1-a-b-c:a:b:c (wherein element M is at least one element selected from Co, Mn, Al, W, Mo, Mg, Ca, Cr, Ta, Nb, Si, F, and B, and a, b, c, and d satisfy 0.001 ≤ a < 0.60, 0.0003 ≤ b < 0.02, 0.0003 ≤ c < 0.02, 0.92 ≤ d ≤ 1.20, and 0.35 ≤ b / c ≤ 5.0). Using Cu-kα rays as the X-ray source, the X-ray diffraction pattern measured using a flat plate sample holder of a Bragg-Brentano optical system shows that the ratio of the diffraction peak intensity I(003) of the (004) plane to the diffraction peak intensity I(104) of the (104) plane is 1.8 or greater, and the specific surface area determined by the nitrogen adsorption method is 0.50 m². ２ / g or more 1.6m ２ A positive electrode active material for lithium-ion secondary batteries with a density of less than / g.

2. The positive electrode active material for a lithium-ion secondary battery according to claim 1, wherein the element M comprises one or more selected from magnesium and fluorine.

3. The positive electrode active material for a lithium-ion secondary battery according to claim 1 or 2, wherein the number ratio of particles consisting of the primary particles is 60% or more.

4. A positive electrode active material for a lithium-ion secondary battery according to any one of claims 1 to 3, wherein the surface of the particles made up of the primary particles and one or more locations selected from the surface of the secondary particles have a cobalt-containing cobalt coating layer.

5. A positive electrode active material for a lithium-ion secondary battery according to any one of claims 1 to 4, wherein the volume-average particle size MV, determined from the volume-based particle size distribution by laser diffraction and scattering method, is 0.5 μm or more and 6.0 μm or less, and the particle size variation index [(D90 - D10) / MV] calculated by D90, which is the 90% diameter based on volume, D10, which is the 10% diameter based on volume, and the volume-average particle size MV, is 0.40 or more and 1.2 or less.

6. A positive electrode active material for a lithium-ion secondary battery according to any one of claims 1 to 5, wherein the ratio of the titanium concentration Ti1 inside the primary particle to the titanium concentration Ti2 on the surface of the primary particle (Ti2 ÷ Ti1) is 0.8 or more and 2.0 or less, and the ratio of the zirconia concentration Zr1 inside the primary particle to the zirconia concentration Zr2 on the surface of the primary particle (Zr2 ÷ Zr1) is 1.5 or more.

7. A positive electrode for a lithium-ion secondary battery comprising the positive electrode active material for a lithium-ion secondary battery described in any one of claims 1 to 6.

8. A lithium-ion secondary battery having a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode contains a positive electrode active material for a lithium-ion secondary battery as described in any one of claims 1 to 6.

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