Positive electrode active material for lithium ion secondary battery

Abstract

The purpose of the present invention is to provide a positive electrode active material for a lithium ion secondary battery, which has high particle strength while maintaining excellent output characteristics when used for the lithium ion secondary battery.　This positive electrode active material for a lithium ion secondary battery is characterized in that: said positive electrode active material contains a lithium metal composite oxide composed of secondary particles that are obtained by aggregating primary particles that contain lithium, nickel, manganese, and cobalt; the particles of the lithium metal composite oxide are composed of a central part having a solid structure and an outer part having a serrated structure that extends to the outside of the central part and has a coating layer on the surface; the coating layer contains lithium and tungsten; the tungsten content is 0.01 to 5 at%; the chlorine content is 0.0005% by mass or greater; and the particle strength is 10 MPa or greater.

Description

Positive electrode active material for lithium ion secondary battery

[0001] The present invention relates to a positive electrode active material for a lithium ion secondary battery. More specifically, the present invention relates to a positive electrode active material for a lithium ion secondary battery that has high strength and excellent output characteristics (low resistance) when used in a lithium ion secondary battery.

[0002] Currently, lithium ion secondary batteries are used in a wide range of fields, including small and thin electronic devices such as smartphones, tablets, mobile personal computers, and wearable devices (next-generation terminals), in-vehicle batteries for hybrid electric vehicles (HEVs) and electric vehicles (EVs), and energy storage systems for residential solar power generation and wind power generation. Although about 30 years have passed since the practical application of lithium ion secondary batteries, their applications and the global market continue to expand, and further technological innovations in terms of performance and cost are expected.

[0003] By the way, among the positive electrode active materials used in such lithium ion secondary batteries, positive electrode active materials composed of lithium nickel cobalt aluminum composite oxide (NCA) containing nickel, cobalt, and aluminum in specific ratios, or lithium nickel manganese cobalt composite oxide (NMC) containing nickel, manganese, and cobalt in specific ratios, are attracting particular attention as materials that can provide high capacity, high output (low resistance), good cycle characteristics, and good thermal stability.

[0004] In the in-vehicle lithium ion secondary batteries installed in clean vehicles such as electric vehicles, as a technology related to the ease of extracting current, which is a particularly important characteristic, that is, a positive electrode active material excellent in output characteristics (low resistance), for example, the following are known.

[0005] Patent Document 1 describes a positive electrode active material in which composite hydroxide particles produced by the above crystallization reaction are obtained as a precursor, and the secondary particles have a space outside the center of the secondary particle where at least one primary particle is absent and an outer shell that is electrically conductive with the center. This is done by controlling the pH of a nucleation aqueous solution containing at least a transition metal and an ammonium ion supplier to 12.0 to 14.0 to perform nucleation (nucleation step), and then controlling the pH of a particle growth aqueous solution containing the nucleus to be lower than the pH of the nucleation step and to 10.5 to 12.0 to grow the particles (particle growth step). In this process, the initial stages of the nucleation step and the particle growth step are performed in a non-oxidizing atmosphere, and in the particle growth step, this non-oxidizing atmosphere is switched to an oxidizing atmosphere and then switched back to a non-oxidizing atmosphere at least once.

[0006] Patent Document 2 describes a transition metal-containing composite hydroxide obtained as a precursor, which is clearly separated into a nucleation step for nucleation and a particle growth step for growing the obtained nuclei, and manufactured by controlling the atmosphere by maintaining a non-oxidizing atmosphere in the initial and middle stages (70% to 90% of the particle growth step) of the nucleation step and particle growth step, and then switching from a non-oxidizing atmosphere to an oxidizing atmosphere in the later stages of the particle growth step, and then switching back to a non-oxidizing atmosphere, and having secondary particles formed by the aggregation of plate-like primary particles, and having a low-density layer formed by the aggregation of fine primary particles having a smaller particle size than the plate-like primary particles near the surface of the secondary particles, and having a tap density of 1.5 g / cm³. ３ The above describes a positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the surface roughness index value, which is the value obtained by dividing the measured specific surface area of ​​the secondary particle by the geometric surface area of ​​the secondary particle assuming that the secondary particle is a perfect sphere, is in the range of 3.6 to 10.

[0007] However, in positive electrode active materials employing the technologies described in Patent Documents 1 and 2, sufficient strength is not obtained in the spatial regions of the characteristic secondary particles, near the surface, and ultimately, in the overall strength of the secondary particles. As a result, durability issues remain unresolved, such as the tendency to collapse during the pressurization process in positive electrode manufacturing and during the battery's charge-discharge cycle.

[0008] International Publication No. 2014 / 181891, International Publication No. 2018 / 097137

[0009] This invention has been made in view of the problems of the prior art, and aims to provide a new positive electrode active material for lithium-ion secondary batteries that has high particle strength while maintaining excellent output characteristics when used in lithium-ion secondary batteries.

[0010] To solve the above problems, the inventors have diligently conducted research on lithium metal composite oxides used as positive electrode active materials for lithium-ion secondary batteries (hereinafter also simply referred to as "positive electrode active materials"). As a result, they have discovered that when manufacturing positive electrode active materials employing the technologies of Patent Documents 1 and 2, a higher particle strength can be obtained by changing the cobalt raw material from cobalt sulfate to inexpensive cobalt chloride (i.e., by adding chlorine to the raw material solution in the crystallization process) as a measure to reduce costs. Furthermore, they have discovered that superior output characteristics can be obtained when a coating layer containing lithium and tungsten is placed on the surface of the lithium metal composite oxide particles, thus completing the present invention.

[0011] In other words, according to one aspect of the present invention for solving the above problems, the first aspect of the present invention is a positive electrode active material for a lithium-ion secondary battery, characterized in that it contains lithium metal composite oxide particles composed of secondary particles formed by the aggregation of primary particles containing lithium, nickel, manganese, and cobalt, wherein the lithium metal composite oxide particles consist of a central part with a solid structure and an outer part with a sawtooth structure that extends outside the central part and has a coating layer on its surface, the coating layer contains lithium and tungsten, the tungsten content is 0.01 to 5 atomic percent and the chlorine content is 0.0005 mass percent or more, and the particle strength of the secondary particles is 10 MPa or more.

[0012] The second aspect of the present invention is a positive electrode active material for a lithium ion secondary battery, characterized in that the cross-sectional area of the serrated structure tissue in the first aspect is 1 to 60% of the total cross-sectional area of the secondary particles.

[0013] The third aspect of the present invention is a positive electrode active material for a lithium ion secondary battery, characterized in that the porosity at the center of the solid structure in the first aspect is 10% or less.

[0014] The fourth aspect of the present invention is a positive electrode active material for a lithium ion secondary battery, characterized in that the tap density of the particles of the lithium metal composite oxide in the first aspect is 1 to 3 g / cm ３ or less.

[0015] The fifth aspect of the present invention is a positive electrode active material for a lithium ion secondary battery, characterized in that the average particle size MV of the particles of the lithium metal composite oxide in the first aspect is 2 to 20 μm, and (D90 particle size - D10 particle size) / D50 particle size representing the particle size distribution is 1.2 or less.

[0016] The sixth aspect of the present invention is a positive electrode active material for a lithium ion secondary battery, characterized in that the specific surface area of the particles of the lithium metal composite oxide in the first aspect is 1 to 3 m ２ / g.

[0017] The seventh aspect of the present invention is a positive electrode active material for a lithium ion secondary battery, characterized in that the oil absorption amount of the particles of the lithium metal composite oxide in the first aspect is 25 to 50 ml / 100 g.

[0018] The eighth aspect of the present invention is that the component composition of the particles of the lithium metal composite oxide in the first aspect is represented by the general formula (A): Li ａ Ni １－ｘ－ｙ－ｚ Mn ｘ Co ｙ M ｚ W Ｓ O ２＋αThis is a positive electrode active material for lithium-ion secondary batteries, characterized by being represented by (a number satisfying 0.95 ≤ a ≤ 1.5, 0 < x ≤ 0.5, 0 < y ≤ 0.5, 0 ≤ z ≤ 0.2, 0.3 ≤ 1 - x - y - z ≤ 0.98, 0.0001 ≤ s ≤ 0.05, and -0.1 ≤ α ≤ 0.2, where M contains one or more elements selected from Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, S, Na, and K).

[0019] According to the present invention, it is possible to provide a positive electrode active material for lithium-ion secondary batteries that has high particle strength while maintaining excellent output characteristics when used in lithium-ion secondary batteries.

[0020] This is an example of a cross-sectional image of metal composite hydroxide particles (precursor), which are the main raw materials for lithium metal composite oxide particles (cathode active material), consisting of secondary particles composed of a solid structure in the center and a serrated structure on the outside. This is a tungsten mapping image of lithium metal composite oxide particles according to the present invention. This is a backscattered electron image of lithium metal composite oxide particles according to the present invention. This is a schematic cross-sectional view of an evaluation battery (coin-type battery CBA) used to evaluate the battery characteristics according to the present invention.

[0021] The positive electrode active material for lithium-ion secondary batteries of the present invention will be described in detail below in the following order of 1 and 2. The present invention is not limited to the embodiments described below, and the embodiments can be modified based on the knowledge of those skilled in the art without departing from the spirit of the invention. In the following description, "A to B" means "A or more and B or less," and "●, and / or ▲" means "either ●, ▲, or both."

[0022] 1. Cathode active material for lithium-ion secondary batteries 2. Evaluation of the cathode active material for lithium-ion secondary batteries

[0023] 1. Positive electrode active material for lithium-ion secondary batteries The present invention provides a positive electrode active material for lithium-ion secondary batteries that contains lithium metal composite oxide particles composed of secondary particles formed by the aggregation of primary particles made of lithium composite oxide containing lithium, nickel, manganese, and cobalt, wherein the lithium metal composite oxide particles are secondary particles composed of a central solid structure, a sawtooth structure extending outward therefrom, and a coating layer containing lithium and tungsten covering the surface of the sawtooth structure, characterized in that the tungsten content is 0.01 to 5 atomic percent, the chlorine content is 0.0005 mass percent or more, and the particle strength of the secondary particles is 10 MPa or more.

[0024] (1) The sawtooth structure of the lithium metal composite oxide that serves as the positive electrode active material according to the present invention, the metal composite hydroxide that serves as its precursor, and optionally the secondary particles of the metal composite oxide that serve as intermediates, is a unique structure with a jagged shape. By giving the particles this structure, the specific surface area of ​​the lithium metal composite oxide that is finally obtained increases. When this is incorporated into a battery as the positive electrode active material, the reaction area with the electrolyte is improved, the positive electrode resistance is reduced, and high output can be obtained.

[0025] The above-mentioned sawtooth structure can be identified, for example, by observing a cross-section of the particle with a scanning electron microscope (SEM). Figure 1 is an example of a cross-sectional SEM image showing the particle structure of a precursor metal composite hydroxide particle 4, where a jagged sawtooth structure 2 is formed, extending outward from the secondary particle 1 which has a solid structure in the central part 3. Furthermore, the cross-sectional area of ​​the sawtooth structure 2 is preferably 1 to 60%, more preferably 10 to 60%, and particularly preferably 20 to 60%.

[0026] Furthermore, the cross-sectional area of ​​the sawtooth structure 2 can be determined, for example, by the following method. That is, after embedding a group of particles (samples) of the lithium metal composite oxide, metal composite hydroxide, and any metal composite oxide to be analyzed in resin, the cross-section of the particle group is exposed by cutting with argon sputtering using a cross-section polisher (CP), and this cross-section is imaged with a scanning electron microscope or the like. Then, by analyzing the cross-sectional images of any 20 or more secondary particles 1 with image analysis software, the total cross-sectional area of ​​each secondary particle and the cross-sectional area of ​​the solid structure are calculated, and then the cross-sectional area of ​​each sawtooth structure is calculated from the following formula (1) and taken as the average value.

[0027]

[0028] If the cross-sectional area is 1% or more, particularly high output characteristics can be obtained, and if the cross-sectional area is 60% or less, the particle strength of secondary particles can be maintained more appropriately.

[0029] (2) Coating layer The lithium metal composite oxide that serves as the positive electrode active material according to the present invention has a coating layer containing lithium and tungsten (hereinafter also simply referred to as the "coating layer") on the surface of the aforementioned sawtooth structure. Such a coating layer has high lithium ion conductivity and promotes intercalation and deintercalation. When incorporated into a secondary battery, it forms a lithium ion conduction path at the interface with the electrolyte, thereby improving battery characteristics such as battery capacity and output characteristics.

[0030] The form of the coating layer described above is not particularly limited, but for example, at least a portion can be in the form of a film, and at least a portion can be in the form of parts, and a mixture of film-like and particulate materials is also acceptable. In the case of a film-like form, its thickness is preferably 1 to 20 nm. If the thickness is 1 nm or more, particularly high lithium-ion conductivity can be obtained, and if the thickness is 20 nm or less, the film is uniformly distributed on the surface of the aforementioned sawtooth-like structure, so the effects of high capacity and high power output can be better demonstrated.

[0031] On the other hand, in the case of particulate matter, the particle size is preferably 1 to 400 nm. If the particle size is 1 nm or larger, particularly high lithium-ion conductivity can be obtained, and if it is 400 nm or smaller, the specific surface area increases due to the fine particles, so the effects of increased capacity and increased power can be better demonstrated.

[0032] Furthermore, the above coating layer preferably contains lithium tungstate, Li ２ WO ４ Li ４ WO ５ Li ６ WO ６ Li ２ W ４ O １３ Li ２ W ２ O ７ Li ６ W ２ O ９ Li ２ W ５ O １６ Li ９ W １９ O ５５ Li ３ W １０ O ３０ Li １８ W ５ O １５ Preferably, it contains one or more selected from these hydrates. In particular, Li ２ WO ４ , and / or, Li ４ WO ５ It is preferable to include this, which further enhances lithium-ion conductivity and significantly reduces positive electrode resistance.

[0033] (3) Particle Morphology and Internal Structure of Particles The lithium metal composite oxide that serves as the positive electrode active material according to the present invention, the metal composite hydroxide that serves as its precursor, and optionally the metal composite oxide that serves as an intermediate thereof mostly have the form of secondary particles formed by the aggregation of multiple primary particles, but may also contain primary particles that do not aggregate as secondary particles. There are no particular limitations on the shape of the primary particles that make up the secondary particles, or the shape of primary particles that exist individually, and they can take various shapes such as spherical, plate-like, needle-like, rectangular parallelepiped, elliptical, and rhombohedral. Furthermore, there are no particular limitations on the aggregation form of multiple primary particles, and they can take various forms such as aggregation in random directions, or aggregation that is almost uniform and radial from the center, forming substantially spherical or ellipsoidal secondary particles.

[0034] The secondary particles of lithium metal composite oxides, metal composite hydroxides, and any metal composite oxides have a solid structure with virtually no voids, except for the aforementioned sawtooth structure, in the interior (or "central part") which is not hollow or porous. Here, a solid structure refers to a cross-sectional state in which the inside of the secondary particle is filled, and "virtually no voids" is defined as a case where the porosity measured in the cross-section of the secondary particle is preferably 10% or less, more preferably 8% or less, and particularly preferably 6% or less.

[0035] Furthermore, the porosity can be determined, for example, by the following method. That is, after embedding a group of particles of the lithium metal composite oxide, metal composite hydroxide, and any metal composite oxide to be analyzed in a resin, the cross-section of the particle group is exposed by cutting with argon sputtering using a cross-section polisher, and the cross-section of this exposed particle group is imaged with a scanning electron microscope or the like. Then, by analyzing the cross-sectional images of any 20 or more secondary particles with image analysis software, the void areas excluding the sawtooth structure are identified as black regions and the dense areas excluding the sawtooth structure are identified as white regions. The porosity of each is then calculated from the following formula (2) and the average value is obtained.

[0036]

[0037] As described above, lithium metal composite oxide particles, which have a solid structure with almost no internal voids, possess high strength. Therefore, when used as a positive electrode active material, they can ensure a sufficient contact area between the positive electrode active material and the electrolyte without excessively reducing the bulk density.

[0038] The shape of primary particles, the morphology of secondary particles, and the internal structure of secondary particles of lithium metal composite oxides, metal composite hydroxides, and any other metal composite oxides can be determined, for example, by observing a cross-section of the particles with a scanning electron microscope. As mentioned above, Figure 1 is an example of a cross-sectional SEM image showing the particle structure of a precursor metal composite hydroxide, and it can be seen that the central part of the secondary particles has a solid structure.

[0039] Furthermore, the particles of lithium metal composite oxides, metal composite hydroxides, and any metal composite oxides may contain a mixture of solid secondary particles, hollow secondary particles, and porous secondary particles. The mixing ratio of such solid, hollow, and porous structures can be controlled, for example, by appropriately adjusting the crystallization conditions of the metal composite hydroxide that serves as a source of transition metals such as nickel, manganese, and cobalt. The lithium metal composite oxide particles obtained in this way have the advantage of having less variation in composition and particle size compared to those produced by simply mixing solid, hollow, and porous particles prepared separately.

[0040] (4) Composition The component composition of the lithium metal composite oxide particles that will be used as the positive electrode active material according to the present invention is the general formula (A): Li ａ Ni １－ｘ－ｙ－ｚ Mn ｘ Co ｙ M ｚ W Ｓ O ２＋αIt is preferable that the number be controlled to be expressed as (a number satisfying 0.95 ≤ a ≤ 1.5, 0 < x ≤ 0.5, 0 < y ≤ 0.5, 0 ≤ z ≤ 0.2, 0.3 ≤ 1 - x - y - z ≤ 0.98, 0.0001 ≤ s ≤ 0.05, and -0.1 ≤ α ≤ 0.2, where M includes one or more elements selected from Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, S, Na, and K).

[0041] In the above general formula (A), the value of a, which represents the lithium (Li) content, is preferably 0.95 to 1.5, more preferably 0.95 to 1.4, and particularly preferably 0.95 to 1.3.

[0042] In the general formula (A) above, the value of 1-x-y-z, which indicates the nickel (Ni) content, is preferably 0.3 to 0.98. When used as a positive electrode active material, it is possible to increase the potential and capacity of lithium-ion secondary batteries. If 1-x-y-z is less than 0.3, the above-mentioned increase in potential and capacity cannot be sufficiently achieved. Conversely, if 1-x-y-z exceeds 0.98, the molar ratio of manganese (Mn) and cobalt (Co) decreases, and there is a risk that the effect cannot be fully obtained.

[0043] Furthermore, x, which indicates the manganese (Mn) content, is preferably greater than 0 and 0.5 or less, as using it as a positive electrode active material can improve the durability of lithium-ion secondary batteries. If x is 0, the above-mentioned effect of improving durability cannot be fully obtained, and conversely, if x exceeds 0.5, the amount of metal elements that contribute to the oxidation-reduction reaction (Redox reaction) decreases, which may lead to a decrease in battery capacity.

[0044] Furthermore, the cobalt (Co) content y is preferably greater than 0 and 0.5 or less. When used as a positive electrode active material, it can improve the cycle characteristics of lithium-ion secondary batteries and reduce the expansion and contraction behavior of the crystal lattice due to lithium insertion and deinsertion during charging and discharging. If y is 0, the effect of reducing the expansion and contraction behavior of the crystal lattice cannot be obtained, and conversely, if y exceeds 0.5, the amount of cobalt added is too much, resulting in a large decrease in initial discharge capacity and becoming disadvantageous in terms of cost.

[0045] Furthermore, by using additive elements M (hereinafter simply referred to as "element M" or "M") such as calcium (Ca) and magnesium (Mg), battery characteristics such as cycle characteristics and output characteristics can be further improved. However, if z, which indicates the M content, exceeds 0.2, the amount of metal elements contributing to the redox reaction decreases, which may reduce battery capacity. Note that the optionally added M can be added at either the time of manufacturing the metal composite hydroxide particles (precursor) or the time of manufacturing the lithium metal composite oxide particles (cathode active material).

[0046] Furthermore, the tungsten (W) content, s, which will be described later, is preferably 0.0001 ≤ s ≤ 0.05, and when used as a positive electrode active material, it is possible to further improve the output characteristics.

[0047] (5) Tap density The tap density of the lithium metal composite oxide particles that will be used as the positive electrode active material according to the present invention is preferably 1 to 3 g / cm³ ３ More preferably 1.2 to 2.8 g / cm³ ３ Particularly preferably 1.4 to 2.6 g / cm³ ３ Therefore, if the tap density is within the above range, incorporating lithium metal composite oxide particles as the positive electrode active material into a lithium-ion secondary battery can simultaneously improve the charge / discharge capacity per unit volume and the cycle characteristics of the battery.

[0048] In contrast, the tap density of lithium metal composite oxide particles is 1 g / cm³. ３ Below 3 g / cm³, the packing efficiency of the positive electrode active material is low, and therefore the charge / discharge capacity cannot be sufficiently improved. ３ If this value is exceeded, the specific surface area of ​​the positive electrode active material decreases, reducing the reaction area with the electrolyte, and thus preventing sufficient improvement in output characteristics.

[0049] (6) Average particle size MV The average particle size MV of the lithium metal composite oxide particles that serve as the positive electrode active material according to the present invention is preferably 2 to 20 μm, more preferably 3 to 19 μm, and particularly preferably 4 to 18 μm. If the average particle size MV is within the above range, when the lithium metal composite oxide particles are incorporated into a lithium-ion secondary battery as the positive electrode active material, the battery capacity per unit volume can be increased, safety is improved and cycle characteristics are improved. In contrast, if the average particle size MV is less than 2 μm, the packing density of the particles decreases when the positive electrode is manufactured, which may reduce the battery capacity per unit volume of the positive electrode. If it exceeds 20 μm, the specific surface area of ​​the positive electrode active material decreases, reducing the interface with the electrolyte of the secondary battery, which may result in an increase in the resistance of the positive electrode and a decrease in the output characteristics of the battery.

[0050] Furthermore, the average particle size MV of the lithium metal composite oxide particles can be controlled not only by the nucleation time in the crystallization process during the manufacturing process of the metal composite hydroxide particles, but also by the supply amount of the raw material solution (metal compound) and the pH. Specifically, if the average particle size MV is less than 2 μm, the supply amount of the raw material solution may be reduced to shorten the nucleation time in the crystallization process, or the pH may be controlled to a lower level. This reduces the amount of nuclei that serve as seed for the particles, thus increasing the particle size of the resulting metal composite hydroxide particles. Conversely, if the average particle size MV exceeds 20 μm, the supply amount of the raw material solution may be increased to lengthen the nucleation time in the crystallization process, or the pH may be controlled to a higher level. This increases the amount of nuclei that serve as seed for the particles, thus decreasing the particle size of the resulting metal composite hydroxide particles.

[0051] (7) Particle size distribution The particle size distribution of the lithium metal composite oxide particles that serve as the positive electrode active material according to the present invention can be calculated from the following formula (3) using the D10 particle size, D50 (median) particle size, and D90 particle size.

[0052]

[0053] This particle size distribution is preferably 1.2 or less, more preferably 1.0 or less, and particularly preferably 0.8 or less. If the particle size distribution is 1.2 or less, when lithium metal composite oxide particles are incorporated into a lithium-ion secondary battery as the positive electrode active material, the packing density of the positive electrode active material increases, and the energy density per unit volume can be improved. On the other hand, if the particle size distribution exceeds 1.2, the specific surface area of ​​the positive electrode active material decreases, reducing the interface with the electrolyte of the secondary battery, which can result in an increase in the resistance of the positive electrode and a decrease in the output characteristics of the battery.

[0054] (8) Specific surface area The specific surface area of ​​the lithium metal composite oxide particles that serve as the positive electrode active material according to the present invention is preferably 1 to 3 m². ２ / g, more preferably 1.1 to 2.9 m ２ / g, particularly preferably 1.2 to 2.8 m ２ The value is / g. If the specific surface area is within the above range, when lithium metal composite oxide particles are incorporated into a lithium-ion secondary battery as a positive electrode active material, a sufficient particle contact surface that can come into contact with the electrolyte can be secured, thereby improving the charge / discharge capacity as well as other battery characteristics. In contrast, if the specific surface area is 1 m² ２ Below 3m / g, the particle contact surface becomes too small, and sufficient charge / discharge capacity cannot be obtained. ２ If the value exceeds / g, the particle contact surface becomes excessive, potentially leading to excessively high surface activity and a decrease in the characteristics of each battery.

[0055] (9) Oil Absorption The oil absorption amount of the lithium metal composite oxide particles that serve as the positive electrode active material according to the present invention is preferably 25 to 50 ml / 100 g, more preferably 26 to 49 ml / 100 g, and particularly preferably 27 to 48 ml / 100 g. If the oil absorption amount is within the above range, when the lithium metal composite oxide particles are incorporated into a lithium-ion secondary battery as the positive electrode active material, a sufficient particle contact surface that can come into contact with the electrolyte can be secured, thereby improving the charge / discharge capacity as well as other battery characteristics. On the other hand, if the oil absorption amount is less than 25 ml / 100 g, the particle contact surface becomes too small, and sufficient charge / discharge capacity cannot be obtained. If it exceeds 50 ml / 100 g, the particle contact surface becomes excessive, and the surface activity becomes too high, which may lead to a decrease in each battery characteristic.

[0056] (10) Tungsten Content The tungsten content of the lithium metal composite oxide particles that serve as the positive electrode active material according to the present invention is preferably 0.01 to 5 atomic%, more preferably 0.02 to 4 atomic%, and particularly preferably 0.03 to 3 atomic%. If the tungsten content is within the above range, as shown in the tungsten mapping image in Figure 2, a film containing tungsten with high lithium ion conductivity is formed on the surface of the lithium metal composite oxide particles, and as shown in the backscattered electron image in Figure 3, particles containing tungsten with high lithium ion conductivity are formed. Therefore, when the lithium metal composite oxide particles are incorporated into a lithium-ion secondary battery as the positive electrode active material, the output characteristics can be further improved.

[0057] (11) Chlorine content The chlorine content of the lithium metal composite oxide particles that serve as the positive electrode active material according to the present invention is preferably 0.0005% by mass or more, more preferably 0.0008% by mass or more, and particularly preferably 0.001% by mass or more. The chlorine content of the metal composite hydroxide particles that serve as the precursor is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, and particularly preferably 0.003% by mass or more. The chlorine content of the metal composite oxide particles that can be optionally obtained as an intermediate is preferably 0.001% by mass or more, more preferably 0.002% by mass or more, and particularly preferably 0.003% by mass or more. If the chlorine content is within the above range, high-strength lithium metal composite oxide particles can be incorporated into a lithium-ion secondary battery as the positive electrode active material, and the durability of the battery can be improved while maintaining each battery characteristic.

[0058] (12) Particle strength The particle strength of the secondary particles according to the present invention is preferably 10 MPa or more, more preferably 15 MPa or more, and particularly preferably 20 MPa or more. If the particle strength is within the above range, high-strength lithium metal composite oxide particles can be incorporated into a lithium-ion secondary battery as a positive electrode active material, and the durability of the battery can be improved while maintaining each battery characteristic.

[0059] 2. Evaluation of Cathode Active Materials for Lithium-ion Secondary Batteries (1) Sample Evaluation Method 1) Sawtooth Structure and its Cross-sectional Area The sawtooth structure formed on the outside of secondary particles can be confirmed by scanning electron microscopy (SEM). In addition, in the analysis, a cross-section polisher (CP) IB-19530CP (manufactured by JEOL Ltd.) is used to process the sample, and the sawtooth structure in the obtained cross-sectional image can be observed using a Schottky field emission scanning electron microscope JSM-7001F (manufactured by JEOL Ltd.). Furthermore, using the image analysis and measurement software WinRoof 6.1.1 (manufactured by Mitani Corporation), cross-sectional images of 20 arbitrarily selected target particles can be analyzed, and after calculating the total cross-sectional area and the cross-sectional area of ​​the solid structure of each secondary particle, the cross-sectional area of ​​each sawtooth structure can be calculated from the above formula (1), and the average value can be used as the final cross-sectional area of ​​the sawtooth structure.

[0060] 2) Solid structure and its porosity. The solid structure of the central part of the secondary particle can be confirmed by scanning electron microscopy (SEM).

[0061] Furthermore, in the analysis, a cross-sectional sample of the particle processed using a cross-section polishing device (CP) IB-19530CP (manufactured by JEOL Ltd.) is used, and the solid structure in the resulting cross-sectional SEM image can be observed using a Schottky field emission scanning electron microscope (SEM) JSM-7001F (manufactured by JEOL Ltd.).

[0062] Furthermore, using the image analysis and measurement software WinRoof 6.1.1 (manufactured by Mitani Corporation), cross-sectional images of 20 arbitrarily selected target particles can be analyzed. For each cross-sectional image, the void areas excluding the sawtooth structure of the particle cross-section are identified as black regions, and the dense areas excluding the sawtooth structure of the particle cross-section are identified as white regions. Then, the porosity of each can be calculated using the aforementioned formula (2), and the average value can be used as the final porosity.

[0063] 3) Composition and tungsten content: The composition and tungsten content can be evaluated by acid decomposition-ICP (inductively coupled plasma) emission spectroscopy.

[0064] Furthermore, the analysis can utilize the ICPE-9000 multi-type ICP emission spectrometer (manufactured by Shimadzu Corporation). From the obtained results, the Li / Me ratio (the ratio of the number of lithium (Li) atoms to the sum of the number of transition metal elements (Ni, Mn, and Co) and element M contained in the lithium metal composite oxide (positive electrode active material), "the ratio value") can be determined.

[0065] 4) Tap density can be determined by taking 12 g of tap density sample into a 20 ml graduated cylinder, attaching this graduated cylinder to a shaking specific gravity measuring instrument, and repeating the operation of free-falling it from a height of 2 cm 500 times. Alternatively, the KRS-409 shaking specific gravity measuring instrument (manufactured by Kuramochi Scientific Instruments Co., Ltd.) can be used for the analysis.

[0066] 5) Particle size and particle size distribution of secondary particles: The average particle size MV, D10 particle size, D50 particle size (median particle size), D90 particle size, and particle size distribution ((D90 - D10) / D50) of secondary particles can be determined from the volume-referenced distribution measured using the laser diffraction / scattering method. In addition, the Microtrac MT3300EXII (manufactured by Microtrac Bell Co., Ltd.), a laser diffraction / scattering particle size distribution measuring device, can be used for the analysis.

[0067] 6) Specific surface area: The specific surface area can be determined by measuring it using the nitrogen gas adsorption and desorption method with the BET method.

[0068] Furthermore, the analysis can utilize the MacSorb 1200 series (manufactured by Mountec Co., Ltd.), a gas-flow type specific surface area measuring device.

[0069] 7) Oil Absorption The amount of oil absorbed (as DBP absorption) can be determined by using DBP (dibutyl phthalate, di-n-butyl phthalate) as a reagent liquid and following the procedure described in "JIS K 6217-4:2008 (Carbon black for rubber - Basic properties - Part 4: Method for determining oil absorption (including compressed samples))". However, since the procedure is complicated, the amount of oil absorbed is generally measured using an absorption measuring device that is commercially available in accordance with JIS. The measurement result is calculated as the amount absorbed per 100g of sample, so the unit is expressed as "ml / 100g".

[0070] Furthermore, the analysis can utilize the S-500 (manufactured by Asahi Research Institute Co., Ltd.), an absorption measurement device compliant with "JIS K 6217-4:2008".

[0071] 8) Coating layer compounds: Compounds contained in the coating layer can be identified by X-ray diffraction (XRD). Specifically, the sample collected in the sample holder is measured using CuKα radiation as the radiation source, with a measurement speed of 2° / min, a tube voltage of 45kV, a tube current of 40mA, and a measurement range of 2θ = 10 to 100°.

[0072] Furthermore, by comparing the standard diffraction pattern of a compound with the diffraction pattern of a sample using the PDF (Powder Diffraction File) database in the ICDD (International Centre for Diffraction Data), the compound can be identified.

[0073] Furthermore, the analysis can utilize an X-ray diffractometer (XRD) called X'PertPRO (manufactured by Spectris Corporation).

[0074] 9) The chlorine content can be determined by directly analyzing a chlorine-containing sample, or by separating chlorine in the form of silver chloride through distillation, and then measuring it using X-ray fluorescence (XRF) analysis. Furthermore, an X-ray fluorescence analyzer such as Axios (manufactured by Spectris Corporation) can be used for the analysis.

[0075] 10) Particle Strength: The sample particles (secondary particles) are placed on a silicon plate, and after fine-tuning the position to align with the center of the indenter of the analyzer, the indenter is brought into contact with the sample particles to the extent that no large load is applied. By measuring with a test force of 150 mN and a loading speed of 2.0 mN / second, the particle strength (average value of 10 particles) can be determined. In addition, the microstrength evaluation tester MCT-500 (manufactured by Shimadzu Corporation) can be used for the analysis.

[0076] (2) Battery Evaluation Method 1) Method for Manufacturing an Evaluation Battery An evaluation battery (coin-type battery CBA shown in Figure 4) can be manufactured by the following method. First, 52.5 mg of the above-mentioned positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene are weighed and mixed, and then press-molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm to manufacture a positive electrode PE (evaluation electrode). Next, the manufactured positive electrode PE is dried in a vacuum dryer at 120°C for 12 hours, and then an evaluation battery is manufactured using this positive electrode PE in a glove box with an argon gas atmosphere where the dew point is controlled to -80°C.

[0077] Furthermore, a metallic lithium electrode NE with a diameter of 17 mm and a thickness of 1 mm is used. The electrolyte is 1 mole of lithium perchlorate (LiClO2). ４ An equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Pharmaceutical Co., Ltd.) is used as the supporting electrolyte, and a polyethylene porous membrane with a thickness of 25 μm is used for the separator SE. The evaluation battery is assembled into a coin-type battery by placing the gasket GA and wave washer WW, and using the positive electrode can PC and negative electrode can NC.

[0078] 2) Discharge Capacity After preparing the evaluation battery described above, leave it for 24 hours until the open-circuit voltage (OCV) stabilizes, then set the current density to the positive electrode to 0.1 mA / cm². ２The discharge capacity can be determined by charging the battery to a cutoff voltage of 4.3V, allowing it to rest for one hour, and then discharging it to a cutoff voltage of 3.0V. A multi-channel voltage / current generator, the R6741A (manufactured by Advantest Corporation), can be used for the measurement.

[0079] 3) Positive electrode resistance: The evaluation battery described above is charged to a charging potential of 4.1V, and a Nyquist plot is obtained by measuring the AC impedance using a potentiostat / galvanostat and a frequency response analyzer. This Nyquist plot is represented as the sum of characteristic curves showing the solution resistance, negative electrode resistance and its capacitance, and positive electrode resistance and its capacitance. Based on the Nyquist plot, the positive electrode resistance can be determined by performing fitting calculations using an equivalent circuit. For measurement, a potentiostat / galvanostat 1287A (manufactured by Solartron Analytical) and a frequency response analyzer 1255B (manufactured by Solartron Analytical) can be used.

[0080] The present invention will be described in detail below using examples. Unless otherwise specified, the following examples use reagents manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., and preparations made from them. However, the present invention is not limited in any way by the following examples.

[0081] (1) Production of metal composite hydroxide particles (precursors) First, 14 L of water was placed in a 60 L reaction vessel, and the temperature inside the vessel was set to 40°C while stirring. Then, nitrogen gas was introduced into the vessel to control the gas phase inside the vessel to a non-oxidizing atmosphere with an oxygen concentration of 2% by volume or less. Next, appropriate amounts of alkaline solution (25% by mass sodium hydroxide aqueous solution) and ammonium ion solution (25% by mass aqueous ammonia) were added to the water in the vessel to prepare a reaction solution such that the pH (based on a liquid temperature of 25°C, the same applies below) was 12.8 and the ammonium ion concentration was 10 g / L.

[0082] On the other hand, nickel sulfate hexahydrate, manganese sulfate monohydrate, and cobalt chloride hexahydrate (a cobalt raw material for cost reduction and particle strength improvement) were weighed so that the composition (atomic percent) of nickel, manganese, and cobalt was Ni:Mn:Co = 34:33:33. These were then dissolved in water to prepare a raw material solution so that the total concentration of nickel, manganese, and cobalt was 2 mol / L and the concentration of chlorine was 1.35 mol / L.

[0083] Then, the raw material solution was added to the reaction solution in the tank at a rate of 100 ml / min, and at the same time, the alkaline solution and ammonium ion solution were also added to the reaction solution at a constant rate. Nucleation was carried out by performing crystallization for 1 minute while maintaining the pH of the reaction solution at 12.8 (nucleation process pH) and the ammonium ion concentration at 10 g / L.

[0084] After temporarily stopping the supply of the raw material solution, alkaline solution, and ammonium ion solution, sulfuric acid was added until the pH of the reaction solution reached 11.2 (particle growth process pH). Once the pH reached 11.2, the supply of the raw material solution, alkaline solution, and ammonium ion solution was resumed, and crystallization was carried out for 3 hours and 40 minutes while maintaining the pH at 11.2 and the ammonium ion concentration at 10 g / L (including 1 minute of crystallization for nucleation, the crystallization time reached 82% of the total crystallization time) to grow the particles.

[0085] Then, while maintaining the same conditions as crystallization under a non-oxidizing atmosphere for 20 minutes, except for being in an air (oxidizing) atmosphere, crystallization was carried out under an oxidizing atmosphere (including 1 minute of crystallization for nucleation, the crystallization time reached 89% of the total crystallization time). After that, the atmosphere was returned to the original non-oxidizing atmosphere to continue particle growth (total 4 hours and 30 minutes), completing the crystallization (including 1 minute of crystallization for nucleation, the crystallization time reached 100% of the total crystallization time), resulting in nickel-manganese-cobalt composite hydroxide (metal composite hydroxide) particles, Ni, which have a sawtooth structure on the outside and a solid structure in the center. ０．３４ Mn ０．３３ Co ０.３３ (OH) ２ A slurry containing the following was obtained.

[0086] The slurry containing the obtained metal composite hydroxide particles (before washing) was placed in a filter press and the metal composite hydroxide cake was recovered by pressure filtration. This metal composite hydroxide cake was returned to the reaction vessel, and after alkaline washing by filling the vessel with an alkaline washing solution (5% by mass sodium hydroxide aqueous solution) and stirring for 30 minutes, pressure filtration was performed again using the filter press to recover the alkaline-washed cake. This alkaline-washed cake was returned to the reaction vessel, and after final washing (water washing) by filling the vessel with water and stirring for 30 minutes, pressure filtration was performed once more using the filter press to recover the washed cake (metal composite hydroxide cake).

[0087] The recovered metal composite hydroxide cake was dried in an electric heating dryer at 150°C for 5 hours to obtain the metal composite hydroxide.

[0088] (2) Production of Lithium Calcined Products The obtained metal composite hydroxide particles (precursors) and lithium carbonate, a lithium compound, were weighed so that the ratio (Li / Me), which is the ratio of the number of lithium atoms (Li) to the number of atoms of other metals (Me), was 1.1, and they were thoroughly mixed to obtain a lithium mixture. This lithium mixture was calcined by heating it in an oxygen (oxygen concentration: 100 vol%) air stream at 450°C for 2 hours, and then calcined by heating it in an oxygen (oxygen concentration: 100 vol%) air stream at 900°C for 5 hours to obtain a lithium nickel manganese cobalt composite oxide (lithium calcined product) having a sawtooth structure on the outside and a solid structure inside. １．１ Ni ０．３４ Mn ０．３３ Co ０．３３ O ２ I obtained it.

[0089] (3) Production of lithium metal composite oxide particles (cathode active material) Lithium calcined material and water were supplied to the washing tank, and the mass ratio was controlled to be 1.25 for lithium calcined material and 1 for water. The slurry in the tank was stirred for 30 minutes (second water wash), and the slurry was subjected to pressure filtration using a filter press until the moisture content was 10% by mass or less, and the second wash cake (second water wash cake) was recovered.

[0090] To the recovered second-wash cake, tungsten trioxide, a tungsten compound, was added so that the atomic percentage of tungsten relative to the sum of nickel, manganese, and cobalt was 0.2. This mixture was then supplied to a mixer and mixed for 3 hours while maintaining a temperature of 30°C to obtain a tungsten mixture.

[0091] The obtained tungsten mixture is vacuum-dried at 0.1 kPa or less, 180°C, and maintained for 10 hours. The aggregates contained in the dried material are then crushed with a pin mill, resulting in a lithium nickel manganese cobalt tungsten composite oxide (lithium metal composite oxide (positive electrode active material)) having a sawtooth structure on the outside, a coating layer containing lithium and tungsten on the surface of the sawtooth structure, and a solid structure inside. １．０８ Ni ０．３４ Mn ０．３３ Co ０．３３ W ０．００２ O ２ I obtained it.

[0092] In the particle growth step of the crystallization process, the procedure was the same as in Example 1, except that crystallization was performed in a non-oxidizing atmosphere for 3 hours and 30 minutes (including 1 minute of crystallization for nucleation, the crystallization time reached 78% of the total crystallization time), followed by crystallization in an air atmosphere for 30 minutes (including 1 minute of crystallization for nucleation, the crystallization time reached 89% of the total crystallization time).

[0093] In the particle growth step of the crystallization process, the procedure was the same as in Example 1, except that crystallization was performed in a non-oxidizing atmosphere for 3 hours and 20 minutes (including 1 minute of crystallization for nucleation, the crystallization time reached 74% of the total crystallization time), followed by crystallization in an air atmosphere for 40 minutes (including 1 minute of crystallization for nucleation, the crystallization time reached 89% of the total crystallization time).

[0094] In the particle growth step of the crystallization process, the procedure was the same as in Example 1, except that crystallization was performed in a non-oxidizing atmosphere for 3 hours and 10 minutes (including 1 minute of crystallization for nucleation, until the crystallization time reached 70% of the total crystallization time), followed by crystallization in an air atmosphere for 50 minutes (including 1 minute of crystallization for nucleation, until the crystallization time reached 89% of the total crystallization time).

[0095] In the particle growth step of the crystallization process, the procedure was the same as in Example 1, except that crystallization was performed for 3 hours under a non-oxidizing atmosphere (including 1 minute of crystallization for nucleation, until the crystallization time reached 67% of the total crystallization time), followed by 1 hour of crystallization under an atmospheric atmosphere (including 1 minute of crystallization for nucleation, until the crystallization time reached 89% of the total crystallization time).

[0096] An oxidation roasting step is added between the crystallization and calcination steps. The metal composite hydroxide particles (precursors) are calcined by heating them in an airflow (oxygen concentration: 21% by volume) at 450°C for 2 hours, and then subjected to oxidation roasting by heating them in an airflow (oxygen concentration: 21% by volume) at 600°C for 5 hours, resulting in nickel-manganese-cobalt composite oxide (metal composite oxide) particles having a serrated structure on the outside and a solid structure in the center. ０．３４ Mn ０．３３ Co ０．３３ The procedure was the same as in Example 1, except that O was obtained and used for firing.

[0097] (Comparative Example 1) Following the procedure described in Example 1 of Patent Document 1, the final result is Li particles of lithium nickel manganese cobalt composite oxide (positive electrode active material) having a solid structure on the surface and a multilayer structure inside. １．１ Ni ０．３４ Mn ０．３３ Co ０．３３ O ２ The following was obtained. Specifically, conventional cobalt sulfate heptahydrate was used as the cobalt raw material, and the procedure was the same as in Example 1, except that in the particle growth of the crystallization process, crystallization was carried out in a non-oxidizing atmosphere for 1 hour and 8 minutes (including 1 minute of crystallization for nucleation, the crystallization time reached 25% of the total crystallization time), followed by crystallization in an air atmosphere for 22 minutes (including 1 minute of crystallization for nucleation, the crystallization time reached 33% of the total crystallization time).

[0098] (Comparative Example 2) Following the procedure described in Example 1 of Patent Document 2, Li obtained particles of lithium nickel manganese cobalt composite oxide (positive electrode active material) having a sawtooth structure on the outside and a solid structure on the inside. １．１ Ni ０．３４ Mn ０．３３Co ０．３３ O ２ The following was obtained. Specifically, conventional cobalt sulfate heptahydrate was used as the cobalt raw material, and the procedure was the same as in Example 1, except that in the particle growth of the crystallization process, crystallization was carried out in a non-oxidizing atmosphere for 3 hours and 46 minutes (including 1 minute of crystallization for nucleation, the crystallization time reached 83% of the total crystallization time), followed by crystallization in an air atmosphere for 22 minutes (including 1 minute of crystallization for nucleation, the crystallization time reached 92% of the total crystallization time).

[0099] The evaluation results for the metal composite hydroxide particles (precursors) and lithium metal composite oxide particles (positive electrode active material) obtained in Examples 1-6 and Comparative Examples 1 and 2, as well as the evaluation results for the metal composite oxide particles (intermediate) obtained in Example 6, are shown in Tables 1-3. Note that the positive electrode resistance results in Table 3 are shown as relative values ​​based on the value in Comparative Example 1.

[0100]

[0101]

[0102]

[0103] [Overall Assessment] When the lithium metal composite oxide particles (positive electrode active material) of Examples 1 to 6, which are within the scope of the present invention, were used in lithium-ion secondary batteries, they all exhibited equivalent or better discharge capacity and output characteristics (reduced resistance) compared to the lithium metal composite oxide particles of Comparative Examples 1 and 2, which deviated from the scope of the present invention, while also demonstrating an improvement in particle strength.

[0104] By giving the metal composite hydroxide particles, which are precursors to lithium metal composite oxide particles, a serrated structure on the outside, when the final lithium metal composite oxide particles are incorporated into a lithium-ion secondary battery, the reaction area with the electrolyte is improved, the positive electrode resistance is reduced, and high output is obtained. In addition, the present invention has found that by including chlorine in the raw material solution in the crystallization process, higher particle strength can be obtained, and by placing a coating layer containing lithium and tungsten on the surface of the lithium metal composite oxide, even better output characteristics can be obtained. The evaluation results shown in Table 1 are sufficient to support these findings.

[0105] Furthermore, the technical scope of the present invention is not limited to the embodiments described above. One or more of the requirements described above may be omitted. The requirements described above may be combined as appropriate. In addition, to the extent permitted by law, the contents of all documents cited herein are incorporated and used as part of the text.

[0106] 1. Secondary particles 2. Serrated structure 3. Central part 4. Metal composite hydroxide particles CBA Coin cell (evaluation battery) PE Positive electrode (evaluation electrode) NE Negative electrode SE Separator GA Gasket WW Wave washer PC Positive electrode can NC Negative electrode can

Claims

It contains lithium metal composite oxide particles, which are composed of secondary particles formed by the aggregation of primary particles containing lithium, nickel, manganese, and cobalt. The lithium metal composite oxide particles are composed of a central solid structure and an outer sawtooth structure that extends outside the central part and has a coating layer on its surface. The coating layer contains lithium and tungsten. The tungsten content is 0.01 to 5 atomic percent, and the chlorine content is 0.0005 mass percent or more. Furthermore, the positive electrode active material for lithium-ion secondary batteries is characterized in that the particle strength of the secondary particles is 10 MPa or more. 　 The positive electrode active material for lithium-ion secondary batteries according to claim 1, characterized in that the cross-sectional area of ​​the sawtooth structure is 1 to 60% of the total cross-sectional area of ​​the secondary particles. 　 The positive electrode active material for lithium-ion secondary batteries according to claim 1, characterized in that the porosity in the central part of the solid structure is 10% or less. 　 The tap density of the lithium metal composite oxide particles is 1 to 3 g / cm³. ３ The positive electrode active material for lithium-ion secondary batteries according to claim 1, characterized in that it is as follows: 　 The positive electrode active material for a lithium-ion secondary battery according to claim 1, characterized in that the average particle size MV of the lithium metal composite oxide particles is 2 to 20 μm, and the particle size distribution (D90 particle size - D10 particle size) / D50 particle size is 1.2 or less. 　 The specific surface area of ​​the lithium metal composite oxide particles is 1 to 3 m². ２ The positive electrode active material for lithium-ion secondary batteries according to claim 1, characterized in that it is / g. 　 The positive electrode active material for a lithium-ion secondary battery according to claim 1, characterized in that the oil absorption capacity of the lithium metal composite oxide particles is 25 to 50 ml / 100 g. 　 The component composition of the particles of the lithium metal composite oxide is represented by the general formula (A): Li ａ Ni １－ｘ－ｙ－ｚ Mn ｘ Co ｙ M ｚ W Ｓ O ２＋α (0.95 ≤ a ≤ 1.5, 0 < x ≤ 0.5, 0 < y ≤ 0.5, 0 ≤ z ≤ 0.2, 0.3 ≤ 1 - x - y - z ≤ 0.98, 0.0001 ≤ s ≤ 0.05, and a number satisfying -0.1 ≤ α ≤ 0.2, M contains one or more elements selected from Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, S, Na, and K), and the positive electrode active material for a lithium ion secondary battery according to claim 1 is characterized by this.

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