JP2020053383A - Positive electrode active material for lithium ion secondary battery and method for producing the same, positive electrode mixture paste for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

To provide a positive electrode active material with which gelation of a positive electrode mixture paste is suppressed and a secondary battery having excellent battery characteristics can be obtained.SOLUTION: There are provided a positive electrode active material for a lithium ion secondary battery and the like. The material mass ratio of elements other than niobium contained in the positive electrode active material 20 is represented by Li:Ni:Co:Mn:M=s:(1-x-y-z):x:y:z (where, 0≤x≤0.35, 0≤y≤0.35, 0≤z≤0.10 and 0.95<s<1.30 are satisfied, and M represents at least one selected from among V, Mg, Mo, Nb, Ti, W, Zr and Al). A lithium metal composite oxide 10 includes a secondary particle 2 formed by the aggregation of primary particles 1, 1a, 1b, and at least part of the surface of each primary particle is covered with a compound 3 containing lithium and niobium. The lithium hydroxide amount dissolving when the positive electrode active material is eluted into water, the amount being measured by a neutralization titration method, is 0.003 mass% or more and 0.15 mass% or less relative to the entire positive electrode active material.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a lithium ion secondary battery, a method for producing the same, a positive electrode mixture paste for a lithium ion secondary battery, and a lithium ion secondary battery.

  In recent years, with the spread of small information terminals such as smartphones and tablet PCs, development of small and lightweight secondary batteries having high energy density has been strongly desired. Further, there is a strong demand for the development of a secondary battery having excellent output characteristics and charge / discharge cycle characteristics as a power source for an electric vehicle such as a hybrid vehicle.

  A non-aqueous electrolyte secondary battery is a secondary battery that satisfies such requirements, and a lithium ion secondary battery is a typical non-aqueous electrolyte secondary battery. This lithium ion secondary battery includes a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of removing and inserting lithium is used as an active material of the negative electrode and the positive electrode.

  Such lithium ion secondary batteries are currently being actively researched and developed.Among them, lithium ion secondary batteries using a layered or spinel type lithium metal composite oxide as a positive electrode material are: Since a high voltage of 4V class can be obtained, the battery has been put to practical use as a battery having a high energy density.

Materials mainly proposed so far include lithium cobalt composite oxide (LiCoO ₂ ) which is relatively easy to synthesize, lithium metal composite oxide (LiNiO ₂ ) using nickel which is cheaper than cobalt, and lithium nickel. Examples thereof include a cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and a lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ).

  Techniques for improving battery characteristics (output characteristics, cycle characteristics, etc.) in the positive electrode active material include, for example, coating the positive electrode active material with a layer containing a different element other than the metal element contained in the lithium metal composite oxide. Some have been proposed.

  For example, Patent Document 1 discloses a positive electrode active material for a nonaqueous electrolyte secondary battery having at least a layered structure lithium transition metal composite oxide, wherein the lithium transition metal composite oxide is a primary particle and an aggregate thereof. Present in the form of particles comprising one or both of the primary particles, the primary particles having an aspect ratio of 1 to 1.8, and at least the surface of the particles is selected from the group consisting of molybdenum, vanadium, tungsten, boron, and fluorine A positive electrode active material for a non-aqueous electrolyte secondary battery having at least one compound has been proposed. According to Patent Literature 1, the conductivity is improved by having a compound having at least one selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine on the surface of the primary particles.

  Patent Document 2 discloses a compound containing, as a main component, a lithium transition metal compound having a function capable of inserting and removing lithium ions, and the main component material containing at least one element selected from B and Bi. And a compound containing at least one element selected from Mo, W, Nb, Ta and Re, each of which is added in combination, and then fired, the lithium transition metal-based compound powder for a positive electrode material of a lithium ion secondary battery. The body has been proposed. According to Patent Literature 2, after addition of an additional element, firing is performed to obtain a lithium transition metal-based compound powder including fine particles in which grain growth and sintering are suppressed, and the rate and output characteristics are improved. It is said that a lithium-containing transition metal-based compound powder which can be improved and easily handled and prepared for an electrode can be obtained.

Patent Document 3, the general formula _{Li a Ni 1-x-y} Co x M1 y W z M 2 wO 2 (1.0 ≦ a ≦ 1.5,0 ≦ x ≦ 0.5,0 ≦ y ≦ 0 0.5, 0.002 ≦ z ≦ 0.03, 0 ≦ w ≦ 0.02, 0 ≦ x + y ≦ 0.7, M1 is at least one selected from the group consisting of Mn and Al, M2 is Zr, Ti, Non-aqueous electrolyte secondary battery containing a lithium transition metal composite oxide represented by at least one selected from the group consisting of Mg, Ta, Nb and Mo) and a boron compound containing at least a boron element and an oxygen element. Positive electrode compositions have been proposed. According to Patent Document 3, by using a positive electrode composition containing a lithium transition metal composite oxide essentially containing nickel and tungsten and a specific boron compound, a positive electrode composition using a lithium transition metal composite oxide It is said that output characteristics and cycle characteristics can be improved.

  Patent Literature 4 discloses a lithium-transition metal oxide powder composed of lithium-transition metal oxide particles, the surface of which is partially or entirely coated with a coating layer containing lithium niobate, wherein the carbon content is 0. Lithium-transition metal oxide powders of not more than 0.03% by mass have been proposed. According to Patent Literature 4, by forming a coating layer containing lithium niobate on part or all of the surface of a lithium transition metal oxide particle, a lithium transition metal oxide powder having a low green compact resistance can be obtained. And

  Patent Literature 5 discloses an aqueous solution containing lithium ions and particles A, which are niobium sources and have a mode diameter (mode particle diameter) of 5 to 200 nm by a dynamic light scattering method, and a lithium secondary battery. Forming a lithium niobate layer on the surface of the particles B of the lithium secondary battery active material by adhering to a lithium secondary battery active material. According to Patent Literature 5, a lithium-niobium solution is used to form a lithium niobate layer on the surface of particles of an active material, thereby suppressing a decrease in discharge capacity and producing lithium secondary battery electrodes and materials thereof. It says that efficiency can be improved.

  By the way, the positive electrode of a lithium ion secondary battery is prepared by mixing, for example, a positive electrode active material, a binder such as polyvinylidene fluoride (PVDF), and a solvent such as N-methyl-2-pyrrolidone (NMP). It is produced by preparing a paste and applying it to a current collector such as an aluminum foil. At this time, when lithium is released from the positive electrode active material in the positive electrode mixture paste, it may react with moisture contained in the binder or the like to generate lithium hydroxide. The produced lithium hydroxide reacts with the binder, and the positive electrode mixture paste may gel. The gelation of the positive electrode mixture paste deteriorates the coating property on the current collector and the yield of the positive electrode. This tendency becomes remarkable when lithium in the positive electrode active material is in excess of the stoichiometric ratio and the ratio of nickel is high.

  Therefore, some attempts have been made to suppress the gelation of the positive electrode mixture paste. For example, Patent Document 6 proposes a positive electrode composition for a non-aqueous electrolyte secondary battery including a positive electrode active material composed of a lithium transition metal composite oxide and additional particles composed of acidic oxide particles. In this positive electrode composition, lithium hydroxide generated by reacting with water contained in the binder reacts preferentially with the acidic oxide, and suppresses the reaction between the generated lithium hydroxide and the binder. It is said to suppress gelation. The acid oxide also plays a role as a conductive agent in the positive electrode, lowers the resistance of the entire positive electrode, and contributes to improving the output characteristics of the battery.

  Patent Literature 7 describes a method for manufacturing a lithium ion secondary battery, in which a lithium transition metal oxide containing LiOH is prepared as a positive electrode active material in addition to a composition; it is contained per 1 g of the positive electrode active material. Grasping the molar amount P of LiOH; preparing 0.05 mol or more of tungsten oxide in terms of tungsten atom per mol of LiOH with respect to the molar amount P of LiOH; and preparing the positive electrode active material and tungsten oxide. There has been proposed a method for producing a lithium ion secondary battery, which includes kneading an organic solvent together with a conductive agent and a binder to prepare a positive electrode paste.

JP 2005-251716 A JP 2011-108554 A JP 2013-239434 A JP 2012-074240 A JP 2018-067474 A JP 2012-028313 A JP 2013-084395 A

  Patent Documents 1 to 5 all state that the battery characteristics such as output characteristics are improved. However, gelation of the positive electrode mixture paste during electrode production may occur, and the output characteristics and battery capacity may be improved. Along with the improvement of battery characteristics such as the above, further improvement for suppressing gelation is desired.

  For example, Patent Literatures 4 and 5 disclose a positive electrode active material having a coating layer containing lithium niobate. However, when producing a positive electrode, regarding the effect of suppressing gelation of a positive electrode mixture paste, Not at all.

  Further, in the method of Patent Document 6, there is a possibility that the separator of the acidic oxide may remain in the battery and the separator may be damaged, and the thermal stability may be reduced accordingly. It cannot be said that. Furthermore, the suppression of gelation can be improved by increasing the amount of the acidic oxide added to the positive electrode composition.However, by adding the acidic oxide, the weight of the positive electrode increases, and the weight per unit mass increases. Battery capacity deteriorates, and raw material costs increase.

  Also, the method of Patent Document 7 does not solve the problem of the possibility of breakage of the separator due to the residual acidic oxide and the problem of suppressing the gelation. In addition, there is a problem in that the addition of tungsten, which is a heavy element that does not contribute to charge and discharge, causes a large decrease in battery capacity per weight.

  In view of the above-described problems, the present invention suppresses gelling of a positive electrode mixture paste when producing a positive electrode, and provides excellent battery characteristics (high battery capacity, high charge / discharge efficiency, and low positive electrode resistance). It is an object to provide a positive electrode active material capable of obtaining a secondary battery having the same. Another object of the present invention is to provide a positive electrode mixture paste using the above positive electrode active material, and a lithium ion secondary battery. Another object of the present invention is to provide a method for producing the above positive electrode active material simply and with high productivity.

  In a first aspect of the present invention, a lithium metal composite oxide containing lithium (Li), nickel (Ni), and optionally cobalt (Co), manganese (Mn) and an element M, lithium and niobium ( A compound containing Nb) and a positive electrode active material for a lithium ion secondary battery, wherein the ratio (molar ratio) of each element other than niobium contained in the positive electrode active material is Li: Ni: Co. : Mn: M = s: (1-x-y-z): x: y: z (where 0 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0) .95 <s <1.30, M is at least one element selected from V, Mg, Mo, Nb, Ti, W, Zr and Al), and the lithium metal composite oxide has primary particles Including secondary particles formed by aggregation, at least a part of the surface of the primary particles is lithium. The amount of lithium hydroxide eluted when the positive electrode active material was dispersed in water, which was coated with a compound containing niobium and niobium and measured by a neutralization titration method, was 0.003% by mass based on the whole positive electrode active material. Provided is a positive electrode active material for a lithium ion secondary battery having a content of 0.15% by mass or less.

Further, the amount of niobium contained in the compound containing lithium and niobium is preferably 0.5 mol% or more and 2 mol% or less based on the total of Ni, Co, Mn, and M in the positive electrode active material. Further, the compound containing lithium and niobium preferably contains at least lithium niobate. In addition, the lithium niobate preferably contains at least one of Li ₃ NbO ₄ , LiNbO ₃ , LiNb ₃ O _8, and Li ₈ Nb ₂ O ₉ . Further, the compound containing lithium and niobium is preferably amorphous.

  According to a second aspect of the present invention, there is provided a method for producing a positive electrode active material for a lithium ion secondary battery, comprising lithium (Li), nickel (Ni), and optionally cobalt (Co), manganese (Mn) and an element. M and a niobium compound not containing lithium and capable of reacting with lithium, to obtain a mixture, and heat-treating the mixture to obtain a lithium metal composite oxide. In the powder of the product, the ratio (molar ratio) of the substance amounts of the respective elements is Li: Ni: Co: Mn: M = s: (1-x-y-z): x: y: z (where 0 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 <s <1.30, M is V, Mg, Mo, Nb, Ti, W, Zr and Al At least one element selected from the group consisting of: Secondary particles formed by agglomeration of primary particles and primary particles, and the amount of the niobium compound mixed is determined by a neutralization titration method, and the amount of lithium hydroxide eluted when the positive electrode active material is dispersed in water. Is provided in an amount of 0.003% by mass or more and 0.15% by mass or less based on the whole positive electrode active material, thereby providing a method for producing a positive electrode active material for a lithium ion secondary battery.

  Further, after the mixture is obtained, before the heat treatment, a solvent capable of dissolving the niobium compound is mixed in a range of 1% by mass or more and 40% by mass or less with respect to the lithium metal composite oxide powder. Is preferred.

  Further, the heat treatment is preferably performed at a heat treatment temperature of 80 ° C or higher and 450 ° C or lower. Further, the heat treatment may include a first heat treatment at a heat treatment temperature of 80 ° C. or more and 300 ° C. or less, and a second heat treatment performed at a temperature higher than the temperature of the first heat treatment. Further, the heat treatment may include a third heat treatment in which the heat treatment is performed at a temperature higher than the temperature of the second heat treatment. Further, the maximum temperature in the heat treatment may be 300 ° C. or more and 450 ° C. or less.

  Further, it is preferable that the surface of the primary particles of the positive electrode active material is coated with a compound containing lithium and niobium. Further, the niobium compound preferably contains at least one of a niobium oxide powder and a sol containing niobium oxide. The niobium compound preferably has a secondary particle diameter of 20 nm or less. Further, the amount of niobium contained in the niobium compound is preferably 0.5 mol% or more and 2.0 mol% or less based on the total amount of Ni, Co, Mn and M in the lithium metal composite oxide powder.

  According to a third aspect of the present invention, there is provided a positive electrode mixture paste for a lithium ion secondary battery, comprising the positive electrode active material for a lithium ion secondary battery of the first aspect.

  According to a fourth aspect of the present invention, there is provided a lithium ion secondary battery having a positive electrode including the positive electrode active material for a lithium ion secondary battery of the first aspect.

  According to the present invention, a positive electrode active material having a high battery capacity when used in a secondary battery, and a high charge / discharge efficiency, and in which the gelation of a positive electrode mixture paste when producing a positive electrode is suppressed. Can be provided. Furthermore, the production method is easy and suitable for production on an industrial scale, and its industrial value is extremely large.

FIG. 1A is a diagram illustrating an example of a positive electrode active material for a lithium ion secondary battery, and FIG. 1B is a diagram illustrating an example of a process of forming a compound containing lithium and niobium. 2A and 2B are diagrams illustrating an example of a method for manufacturing a positive electrode active material for a lithium ion secondary battery. FIG. 3 is a diagram illustrating an example of a method for producing a positive electrode active material for a lithium ion secondary battery. FIG. 4 is a diagram illustrating an example of a method for producing a positive electrode active material for a lithium ion secondary battery. FIG. 5 is a schematic explanatory diagram of a measurement example of impedance evaluation and an equivalent circuit used for analysis. FIG. 6 is a schematic sectional view of a coin-type battery used for battery evaluation.

  Hereinafter, a positive electrode active material for a lithium ion secondary battery, a method for producing the same, a positive electrode mixture paste for a lithium ion secondary battery, and a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, some components are emphasized or some components are simplified for easy understanding, and the actual structure, shape, scale, and the like may be different.

1. Positive electrode active material [Form of positive electrode active material]
First, a positive electrode active material for a lithium ion secondary battery (hereinafter, also referred to as “positive electrode active material”) according to the present invention will be described with reference to FIGS. FIG. 1A is a diagram schematically illustrating an example of the positive electrode active material according to the present embodiment, and FIG. 1B is an example of a process of forming a compound including lithium and niobium according to the present embodiment. It is a figure which shows typically.

  As shown in FIG. 1A, the positive electrode active material 20 includes a lithium metal composite oxide 10 containing at least lithium and nickel, and a compound 3 containing lithium and niobium (hereinafter, also referred to as “LiNb compound 3”). And The lithium metal composite oxide 10 includes the secondary particles 2 formed by aggregating the primary particles 1, and at least a part of the surface of the primary particles 1 is coated with the LiNb compound 3.

  The lithium metal composite oxide 10 is obtained, for example, by calcining a nickel composite hydroxide or a nickel composite oxide obtained by oxidizing and roasting a nickel composite hydroxide, and a lithium compound. On the surfaces of the secondary particles 2 and the primary particles 1 of the obtained lithium metal composite oxide 10, an unreacted lithium compound mainly derived from the raw material is present. The unreacted lithium compound may elute into the positive electrode mixture paste and react with a binder or an organic solvent to gel the positive electrode mixture paste. In addition, the excess lithium present in the lithium metal composite oxide 10 (crystal structure) may be eluted into the positive electrode mixture paste and cause the positive electrode mixture paste to gel. The present inventors have found that among these unreacted lithium and lithium (excess lithium) eluted from the composite oxide (crystal structure), lithium hydroxide ( Lithium (excess lithium hydroxide) eluted as LiOH) was found to contribute to the gelation of the positive electrode mixture paste. It is important to control the amount of lithium hydroxide eluted.

  As shown in FIG. 1B, the positive electrode active material 20 according to the present embodiment reacts at least a part of surplus lithium including surplus lithium hydroxide present on the surface of the primary particles 1 with a niobium compound described later. As a result, LiNb compound 3 is immobilized on the surface of primary particles 1. As a result, at least a part of the surface of the primary particles 1 is coated with the LiNb compound 3, and the amount of excess lithium hydroxide eluted into the paste is controlled to a specific range, thereby suppressing gelation of the positive electrode mixture paste. It is considered possible.

  In the positive electrode active material 20 in which the surface of the primary particles 1 of the lithium metal composite oxide 10 is coated with the LiNb compound 3, the LiNb compound 3 functions as a protective film and suppresses the deterioration of the lithium metal composite oxide 10 in the positive electrode. Thus, the charging and discharging efficiency of the secondary battery is improved. Further, the LiNb compound 3 formed in an appropriate step has a high lithium ion conductivity, and has an effect of promoting the movement of lithium ions during charging and discharging of the secondary battery. Therefore, the LiNb compound 3 forms a Li conduction path at the interface between the positive electrode active material 20 and the electrolyte, thereby suppressing a significant increase in the positive electrode resistance of the secondary battery.

  Here, the surface of the primary particles 1 of the lithium metal composite oxide 10 is, as shown in FIG. 1A, the primary particles 1 (e.g., FIG. 1A) exposed on the outer surface (surface) of the secondary particles 2. 1 (A), not only the surface portion of 1a) but also the primary particles 1 exposed in the vicinity of the surface of the secondary particles 2 through which the electrolyte can penetrate through the outside of the secondary particles 2 and in the internal voids. (Example: 1b of FIG. 1A). Furthermore, even the grain boundaries between the primary particles 1 are included if the bonding of the primary particles 1 is incomplete and the electrolyte is permeable. That is, since the elution of surplus lithium (including surplus lithium hydroxide) occurs at the contact surface with the electrolytic solution, the surplus lithium, the niobium compound and the niobium compound at the contact surface with the electrolytic solution (that is, the surface of the primary particles 1). Is reacted to form the LiNb compound 3, whereby the elution of surplus lithium (including surplus lithium hydroxide) can be suppressed.

  Further, the LiNb compound 3 may be formed on the entire surface of the primary particles 1 that is in contact with the electrolytic solution, or may be partially formed on the surface of the primary particles 1. Even when the LiNb compound 3 is partially formed on the surface of the primary particles 1, the effect of suppressing the gelation of the positive electrode mixture paste can be obtained.

  The presence of the LiNb compound 3 on the surface of the primary particle 1 exposed on the surface of the secondary particle 2 can be confirmed by, for example, X-ray photoelectron spectroscopy (XPS). The presence of niobium (Nb) on the surface of the primary particles 1 inside the secondary particles 2 is determined, for example, by an energy dispersive X-ray spectrometer (Energy) attached to a scanning transmission electron microscope (STEM). Dispersive x-ray Spectroscopy (EDS) can be confirmed.

  In the positive electrode active material 20, it is difficult to directly confirm the existence form of the trace amount of niobium present inside the secondary particles 2. However, (i) lithium is an element forming a compound with niobium. Considering what is considered and (ii) that at least a part of niobium is present in the form of the LiNb compound 3 on the surface of the primary particle 1 exposed on the surface of the secondary particle 2, It is presumed that the LiNb compound 3 (for example, lithium niobate) is also formed on the surface of the primary particles 1 in the inside.

  In addition, the positive electrode active material 20 may have the LiNb compound 3 formed on the surface of the primary particles 1, and may or may not have Nb inside the primary particles 1. . When Nb exists inside the primary particles 1, the concentration of Nb may have a concentration gradient from the surface to the inside of the primary particles 1. When the LiNb compound 3 is formed on the surface of the primary particles 1 and the amount of Nb contained in the interior of the primary particles 1 is small, the positive electrode mixture is maintained while maintaining the high battery capacity inherent in the lithium metal composite oxide 10. Gelation of the paste can be suppressed.

[Amount of lithium hydroxide eluted from positive electrode active material]
The amount of lithium hydroxide (LiOH) eluted when the positive electrode active material 20 is dispersed in water (sometimes abbreviated as “amount of eluted lithium hydroxide”) in the positive electrode active material 20 is the entire positive electrode active material 20. To 0.15 mass%, preferably 0.003 mass% to 0.15 mass%, more preferably 0.005 mass% to 0.13 mass%. When the amount of lithium hydroxide eluted (the amount of excess lithium hydroxide) is in the above range, gelation of the positive electrode mixture paste is extremely suppressed, and a secondary battery having excellent battery characteristics can be obtained. The amount of lithium hydroxide eluted is measured by neutralization titration, and when the obtained positive electrode active material 20 is dispersed in water, a lithium compound eluted from the positive electrode active material 20 (however, lithium derived from carbonate) (Excluding compounds) means the Li amount calculated from the amount of acid used up to the first neutralization point by neutralization titration.

  When the amount of the eluted lithium hydroxide exceeds 0.15% by mass, a large amount of the eluted lithium hydroxide is produced when producing the positive electrode, and it is difficult to suppress the gelation of the positive electrode mixture paste. On the other hand, when the amount of the eluted lithium hydroxide is less than 0.003% by mass, it is considered that the niobium compound generates the LiNb compound 3 while extracting lithium excessively from the lithium metal composite oxide 10, and the battery characteristics are deteriorated. May worsen. In addition, the lower limit of the amount of lithium hydroxide eluted is preferably 0.01% by mass or more, and more preferably 0.1% by mass or more, from the viewpoint of improving battery characteristics.

  The amount of lithium hydroxide eluted was determined by mixing 2 g of the positive electrode active material with 125 mL of pure water, stirring and dispersing for 1 minute, adding 5 mL of a 10% by mass barium chloride solution, and using 1.0 mol / L hydrochloric acid. It can be determined from the amount of hydrochloric acid up to the first neutralization point at the time of neutralization titration. By measuring the amount of lithium hydroxide eluted, the degree (degree) of elution of lithium hydroxide into the paste can be evaluated.

[Compound containing lithium and niobium]
In the lithium metal composite oxide 10 of the present embodiment, the LiNb compound 3 is formed on the surface of the primary particles 1. The LiNb compound 3 is a compound containing a Li atom and a Nb atom, and preferably contains at least lithium niobate. The lithium niobate preferably contains, for example, at least one of Li ₃ NbO ₄ , LiNbO ₃ , LiNb ₃ O ₈ and Li ₈ Nb ₂ O ₉ . Further, the LiNb compound 3 may be amorphous (amorphous) or may have a crystal structure. When the LiNb compound 3 is amorphous, lithium ion conductivity is improved, and the positive electrode resistance in the secondary battery can be reduced.

[Composition of lithium metal composite oxide]
The lithium metal composite oxide 10 has a layered crystal structure and includes lithium (Li), nickel (Ni), and optionally, cobalt (Co), manganese (Mn), and the element M. Further, the ratio (molar ratio) of the amount of each element other than niobium in the entire positive electrode active material is Li: Ni: Co: Mn: M = s: (1-x-y-z): x: y: z (where 0 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 <s <1.30, M is V, Mg, Mo, Nb, Ti , W, Zr and Al). As the composition of Ni, Co, Mn, and M in the lithium metal composite oxide 10, a known composition of the lithium metal composite oxide can be used within the above range, depending on the characteristics required for the secondary battery. The composition can be appropriately selected.

  In the above molar ratio, s indicating the Li content is more than 0.95 and less than 1.30, and may be 1.0 or more and 1.10 or less, or more than 1.0 and 1.10 or less. There may be. If the value of s is too small, other elements may occupy the portion of the lithium metal composite oxide 10 that should be occupied by lithium in the crystal of the particles, and the charge / discharge capacity of the secondary battery may decrease. On the other hand, when the value of s is 1.3 or more, there is an excess lithium compound that does not contribute to charge and discharge, and the positive electrode resistance (reaction resistance) may increase or the battery capacity may decrease.

  In the above molar ratio, (1-xyz) indicating the content of nickel (Ni) is 0.2 or more and 1.0 or less, and may be 0.3 or more and 1.0 or less. Further, from the viewpoint of high battery capacity, (1-xyz) is preferably 0.55 or more, more preferably 0.6 or more, and further preferably 0.8 or more. preferable. When the content of nickel (1-xy) exceeds 0.55, a high battery capacity can be obtained.

  Lithium-nickel composite oxides containing a large amount of nickel (Ni) tend to increase the viscosity of the positive electrode mixture paste at the time of electrode preparation, and to easily cause gelation. However, in the positive electrode active material 20 according to the present embodiment, even when the nickel content is in the above range, the surface of the primary particles 1 of the lithium metal composite oxide 10 is coated with the LiNb compound 3 to obtain the positive electrode mixture paste. Can be prevented from increasing in viscosity.

  In the above molar ratio, x indicating the content of cobalt (Co) is 0 ≦ x ≦ 0.35, may be 0.05 ≦ x ≦ 0.35, or 0.1 ≦ x ≦ 0. It may be three. When cobalt is contained within the above range, the battery has a high battery capacity and excellent cycle characteristics.

  In the above molar ratio, y indicating the content of manganese (Mn) is 0 ≦ y ≦ 0.35, and may be 0 ≦ y ≦ 0.10. When manganese is contained in the above range, it is excellent in thermal stability.

  In the above molar ratio, z indicating the content of the element M is, for example, 0 ≦ z ≦ 0.10. M can be selected from a plurality of elements according to required characteristics. Further, M preferably contains Al. When M contains Al and the content of Al in the above molar ratio is z1 and the content of M other than Al is z2 (where z1 + z2 = z), the value of z1 is preferably 0.01 or more and 0 or more. .1 or less. Further, the value of y2 may be 0 or more and 0.1 or less, or may be 0. Note that the positive electrode active material 20 may contain a small amount of elements other than the above-described Ni, Co, Mn, and the element M as long as the effects of the present invention are not impaired.

Incidentally, the lithium metal composite oxide 10 represented by the general _{formula: Li s Ni 1-x-} y-z Co x Mn y M z O 2 + α ( although, 0 ≦ x ≦ 0.35,0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 <s <1.30, 0 ≦ α ≦ 0.2, M is at least one selected from V, Mg, Mo, Nb, Ti, W, Zr and Al Element). The composition ratio of each metal element other than niobium in the whole positive electrode active material is the same as the above range. In the above general formula, α is a coefficient that changes according to the valence of a metal element other than lithium contained in the lithium metal composite oxide and the atomic ratio of lithium to the metal element other than lithium.

[Niobium content]
In addition, the amount of niobium contained in the LiNb compound 3 is preferably 0.5 mol% or more and 2.0 mol% or less with respect to the total of Ni, Co, Mn, and M in the lithium metal composite oxide 10. In addition, the amount of niobium contained in the LiNb compound 3 is more preferably 0.6 mol% or more and 1.8 mol% or less from the viewpoint of further improving battery characteristics and suppressing gelation.

[Volume average particle size Mv]
The volume average particle size Mv of the positive electrode active material 20 is, for example, 5 μm or more and 30 μm or less, and preferably 5 μm or more and 20 μm or less. When the volume average particle size Mv is less than 5 μm, a high output can be obtained when a secondary battery is obtained by increasing the specific surface area of the positive electrode active material 20, but the packing density of the positive electrode decreases and the charge per volume increases. While the discharge capacity is reduced, the dispersibility of the conductive agent and the positive electrode active material may be deteriorated when preparing the electrode paste. In addition, since the voltage applied to the individual positive electrode active material particles in the electrode becomes non-uniform, the particles to which a high voltage is applied deteriorate as charge and discharge are repeated, and the charge and discharge capacity of the secondary battery is reduced. descend. Conversely, when the volume average particle size Mv exceeds 30 μm, the specific surface area of the positive electrode active material decreases, and the interface with the electrolyte decreases, so that the number of paths for lithium ions to enter and exit decreases. It may rise and the output characteristics of the battery may decrease. The volume average particle size Mv is a value measured by a laser diffraction scattering method.

[Expansion of particle size distribution]
[(D90−d10) / volume average particle size Mv], which is an index indicating the spread of the particle size distribution, is not particularly limited, but is preferably 0.70 or more from the viewpoint of high filling property. More preferably, it is 70 or more and 1.2 or less. By using the method for producing the positive electrode active material 20 described below, the surface of the primary particles 1 can be uniformly coated with the LiNb compound 3 even when the particle size distribution of the positive electrode active material 20 is relatively large.

  Note that d10 is the particle size at which the number of particles at each particle size is accumulated from the smaller particle size side, and the accumulated volume is 10% of the total volume of all the particles. And the particle size whose cumulative volume is 90% of the total volume of all particles. Further, d10 and d90 can be determined from the integrated value of the volume measured by a laser light diffraction / scattering particle size analyzer similarly to the average particle diameter.

[Average primary particle size]
The average particle size of the primary particles 1 is not particularly limited, but is preferably, for example, 0.2 μm or more and 1.0 μm or less, and more preferably 0.3 μm or more and 0.7 μm or less. As a result, higher output characteristics, higher battery capacity, and higher cycle characteristics when used for the positive electrode of the secondary battery can be obtained. When the average particle size of the primary particles 1 is less than 0.2 μm, the sintering may be insufficient and sufficient battery performance may not be obtained. If the average particle size of the primary particles 1 exceeds 0.7 μm, high output characteristics and high cycle characteristics may not be obtained.

  In addition, the positive electrode active material 20 may have a hollow structure in which the secondary particles 2 form a hollow portion in the particle. When the secondary particles 2 have a hollow structure, the penetration of the electrolyte into the particles of the secondary particles 2 is further facilitated, and high output characteristics are more easily obtained. In addition, the number of hollow portions may be one or more. In addition, the positive electrode active material 20 may have a porous structure having a large number of voids in the secondary particles 2.

  Note that the lithium metal composite oxide 10 includes the secondary particles 2 formed by aggregating the plurality of primary particles 1. However, the lithium metal composite oxide 10 is, for example, a primary particle that is not aggregated as the secondary particles 2. It may contain a small amount of single primary particles 1 such as particles 1 and primary particles 1 dropped from secondary particles 2 after aggregation. Further, the positive electrode active material 20 may include a lithium metal composite oxide other than the above-described lithium metal composite oxide 10 as long as the effects of the present invention are not impaired.

  The method for manufacturing the positive electrode active material 20 is not particularly limited as long as the method can obtain the positive electrode active material 20 having the above characteristics. However, it is preferable to use a method for manufacturing a positive electrode active material described later.

2. Next, a method for manufacturing a positive electrode active material according to the present embodiment will be described with reference to FIG. FIG. 2A is a diagram illustrating an example of a method for manufacturing a positive electrode active material according to the present embodiment. The positive electrode active material 20 described above can be easily manufactured on an industrial scale with high productivity by a method for manufacturing a positive electrode active material as shown in FIG.

  As shown in FIG. 2A, a method for manufacturing the positive electrode active material 20 includes a lithium metal composite oxide powder having a layered crystal structure and a niobium compound (Nb containing no lithium and capable of reacting with lithium). Compound) (Step S10) and heat-treating (drying) the mixture obtained by mixing (Step S20). Hereinafter, each step will be described.

[Step S10 (mixing step)]
First, a mixture of a lithium metal composite oxide powder (base material) and a niobium compound not containing lithium and capable of reacting with lithium is obtained (step S10).

  At this time, the mixing amount of the niobium compound is measured by the neutralization titration method described above, and the amount of lithium hydroxide eluted when the obtained cathode active material 20 is dispersed in water is based on the entire cathode active material 20. Therefore, the amount is 0.15% by mass or less, preferably 0.003% by mass or more and 0.15% by mass or less, and more preferably 0.005% by mass or more and 0.13% by mass or less. From the viewpoint of improving the battery characteristics, the lower limit of the amount of lithium hydroxide eluted is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and further preferably 0% by mass. The amount may be adjusted to be at least 1% by mass.

  As described above, when the obtained positive electrode active material 20 is dispersed in water, the amount of lithium hydroxide (LiOH) eluted from the positive electrode active material 20 (however, lithium compound derived from carbonate Ex), the Li amount calculated from the amount of acid used up to the first neutralization point by neutralization titration. The amount of lithium hydroxide is determined, for example, by mixing 2 g of the positive electrode active material with 125 ml of pure water, stirring and dispersing for 1 minute, adding 5 ml of a 10% by mass barium chloride solution, and using 1.0 mol / l hydrochloric acid. After the neutralization titration, it can be calculated from the amount of hydrochloric acid used up to the first neutralization point.

  The niobium compound is not limited as long as it does not contain lithium and can react with lithium. Examples of the niobium compound include niobate, niobium oxide, niobium nitrate, niobium pentachloride, and niobium nitrate. Of these, niobium oxide is preferable. The niobium compound may be used alone or as a mixture of two or more.

  The niobium compound may be a powder, a sol (colloidal solution) in which the niobium compound is dispersed in an aqueous solution (dispersion medium), an aqueous solution in which the niobium compound is dissolved, or a mixture thereof. In light of the above, at least one of a powder and a sol is preferable, and a sol is more preferable.

  The niobium compound may be composed of at least one of primary particles and secondary particles including a plurality of primary particles. The volume average particle size Mv (secondary particle size) of the niobium compound is not particularly limited, but may be 1 μm or less, or 100 nm or less, preferably from the viewpoint of improving the dispersibility of the niobium compound. It is 20 nm or less. The lower limit of the volume average particle diameter Mv (secondary particle diameter) of the niobium compound is not particularly limited, and may be 5 nm or more, or 10 nm or more. The primary particle size of the niobium compound may be 5 nm or less.

  For example, when a niobium oxide sol having a volume average particle size Mv (secondary particle size) of 20 nm or less is used as the niobium compound, the primary particle size is as fine as several nm, and the niobium oxide is dispersed in a dispersion medium. Therefore, the LiNb compound 3 is extremely excellent in reactivity with lithium and can form a more uniform LiNb compound 3 on the surface of the positive electrode active material 20.

  The dispersion medium of the niobium oxide sol is not particularly limited, and a known aqueous solution can be used, but an aqueous solution containing ammonia is preferable.

  In the mixing step (Step S10), the amount of niobium added is adjusted and mixed so that the amount of lithium hydroxide eluted from the positive electrode active material 20 falls within the above range. A niobium compound such as a niobium oxide sol undergoes a neutralization reaction to form a LiNb compound 3 as a hydrate, and moisture is evaporated in a subsequent heat treatment (drying) step (step S20) to form an anhydrous LiNb compound 3. It is considered that the action of the LiNb compound 3 suppresses the elution of lithium into the positive electrode mixture paste.

  The amount of lithium hydroxide eluted from the positive electrode active material 20 depends on the atomic ratio (Li / Me) of Li to the total of Ni, Co, Mn, and M in the lithium metal composite oxide 10, or the production conditions of the powder. fluctuate. Therefore, the addition amount of the niobium compound such as niobium may be an amount that can form the LiNb compound 3 with the excess lithium and control the amount of lithium hydroxide eluted from the positive electrode active material 20 within the above range.

  As described above, the mixing amount of the niobium compound is appropriately adjusted according to the amount of lithium hydroxide eluted from the positive electrode active material 20, but the amount of niobium contained in the niobium compound is, for example, lithium metal composite. It is 0.5 mol% or more and 2.0 mol% or less, preferably 0.6 mol% or more and 1.8 mol% or less based on the total of Ni, Co, Mn and M in the oxide powder (base material). Thereby, the amount of the LiNb compound 3 to be formed is set to a suitable range, the amount of lithium hydroxide eluted from the positive electrode active material 20 is controlled to a specific range, and the battery characteristics such as the battery capacity are improved. Can be. In the manufacturing method according to the present embodiment, the amount of niobium with respect to the total of Ni, Co, Mn, and M is maintained in the obtained positive electrode active material 20.

  Since the powder characteristics and particle structure of the powder (base material) of the titanium metal composite oxide are inherited to the positive electrode active material 20, the composition, powder characteristics, and particle structure of the powder do not include the LiNb compound 3. Except for the above, the same positive electrode active material as described above can be used. The powder (base material) of the lithium metal composite oxide is selected according to the desired positive electrode active material.

  In the powder (base material) of the lithium metal composite oxide, for example, the ratio (molar ratio) of the amount of each element is Li: Ni: Co: Mn: M = s: (1-x-y-z): x: y: z (where 0 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 <s <1.30, M is V, Mg, Mo , Nb, Ti, W, Zr and Al) and has a layered crystal structure. The powder (base material) of the lithium metal composite oxide contains secondary particles formed by agglomeration of primary particles.

  The method for producing the lithium metal composite oxide powder (base material) is not particularly limited. For example, a nickel composite hydroxide obtained by a crystallization method, or a roasting of the nickel composite hydroxide The nickel composite oxide obtained as described above and a lithium compound may be mixed and then fired. As a method for producing the nickel composite hydroxide, either a batch method or a continuous method can be applied. From the viewpoint of cost and from the viewpoint of obtaining a nickel composite hydroxide having a wider particle size distribution, a continuous method of continuously collecting nickel composite hydroxide particles overflowing from the reaction vessel is more preferable.

  The amount of lithium hydroxide eluted from the positive electrode active material 20 contained in the lithium metal composite oxide powder (base material) is preferably 0.05% by mass or more and 1.0% by mass or less, preferably 0.1% by mass or more. 0.7 mass% or less. When the amount of lithium hydroxide eluted from the positive electrode active material 20 of the lithium metal composite oxide powder is in the above range, the LiNb compound 3 formed by reacting with the added niobium compound can be in a suitable amount. The suppression of gelation of the mixture paste and the battery characteristics (battery capacity, output characteristics, etc.) can be compatible at a high level.

  The amount of lithium hydroxide eluted from the positive electrode active material 20 is determined by measuring the amount of lithium hydroxide eluted when the lithium metal composite oxide powder is dispersed in water by neutralization titration with an acid, as described above. You can ask.

  On the other hand, when the amount of lithium hydroxide eluted from the lithium metal composite oxide powder (base material) is less than 0.05% by mass, the LiNb compound 3 to be formed is insufficient and battery characteristics may be deteriorated. . Further, when the amount of lithium hydroxide eluted from the positive electrode active material 20 exceeds 1.0% by mass, the amount of surplus lithium hydroxide remaining becomes large even when reacting with the niobium compound, and the amount of lithium hydroxide mixed when the positive electrode is manufactured is increased. The agent paste may gel.

  Further, the amount of lithium hydroxide eluted from the positive electrode active material 20 obtained after the heat treatment (Step S20) is preferably smaller than the amount of lithium hydroxide eluted from the base material (base material) of the lithium metal composite oxide. The amount of lithium hydroxide eluted from the base material (base material) of the lithium metal composite oxide may be at least 0.05% by mass or less than 0.1% by mass. When the amount of lithium hydroxide eluted from the positive electrode active material 20 is smaller than the amount of lithium hydroxide eluted from the base material, it indicates that the LiNb compound 3 is suitably formed on the surface of the primary particles 1.

[Step S11]
Further, as shown in FIG. 2 (B), after the above mixture is obtained, a solvent capable of dissolving the niobium compound is mixed with a lithium metal composite oxide powder (base) before heat treatment (step S20) described later. (Material) to be mixed with the mixture in a range of 1% by mass or more and 40% by mass or less (Step S11). When step S11 is provided, the niobium compound can be dispersed more uniformly on the surface of the lithium metal composite oxide powder (base material).

  The solvent that can dissolve the niobium compound is not particularly limited, and a known solvent can be used. However, water is preferably used from the viewpoint of reducing impurities.

  The mixing amount of the solvent capable of dissolving the niobium compound is preferably from 1% by mass to 40% by mass, and more preferably from 5% by mass to 20% by mass, based on the powder (base material) of the lithium metal composite oxide. You may. The mixing amount of the solvent capable of dissolving the niobium compound can be appropriately adjusted depending on the structure of the powder (base material) of the lithium metal composite oxide.

[Step S20 (heat treatment step)]
Next, the mixture obtained by mixing is heat-treated (dried) (Step S20). In this step, the mixture of the niobium compound and the powder of the lithium metal composite oxide is dried, and the excess lithium in the particles of the lithium metal composite oxide and excess lithium dissolved in the water in the mixture; In this step, a LiNb compound 3 is formed on the surface of the primary particles 1 by reacting with a niobium compound.

  The heat treatment temperature is preferably 450 ° C. or lower, and may be 80 ° C. or higher and 450 ° C. or lower. When the heat treatment temperature exceeds 450 ° C., the generated LiNb compound 3 may be decomposed, or niobium (Nb) may diffuse into the lithium metal composite oxide particles, and the LiNb compound 3 may decrease. On the other hand, when the heat treatment temperature is too low, the LiNb compound 3 having high lithium ion conductivity is not sufficiently formed, and the battery characteristics may not be improved.

  From the viewpoint of sufficiently drying the obtained mixture and preventing release of lithium from the lithium metal composite oxide, the heat treatment temperature is preferably from 100 ° C to 450 ° C, and is preferably from 100 ° C to 300 ° C. Good.

  The heat treatment time in the entire heat treatment step (Step S20) is not particularly limited, but is, for example, 1 hour or more and 24 hours or less.

  The atmosphere during the heat treatment is preferably a decarboxylation atmosphere, an inert atmosphere, or a vacuum atmosphere in order to avoid a reaction between moisture or carbonic acid in the atmosphere and lithium on the surface of the lithium metal composite oxide particles. In the case where the heat treatment is performed at 200 ° C. or more, the heat treatment may be performed in an oxygen atmosphere. Further, the pressure of the atmosphere during the heat treatment is preferably 1 atm or less. If the pressure is higher than 1 atm, the water content of the positive electrode active material may not be sufficiently reduced.

  The moisture content of the lithium metal composite oxide particles after the heat treatment is not particularly limited, but is preferably 0.2% by mass or less, more preferably 0.15% by mass or less. The lower limit of the water content is, for example, 0% by mass or more, and may be 0.01% by mass or more. When the water content of the powder exceeds 0.2% by mass, a gaseous component containing carbon and sulfur in the air may be absorbed to generate a lithium compound on the surface. The measured value of the moisture content is a value measured by a Karl Fischer moisture meter at a vaporization temperature of 300 ° C.

  Further, the heat treatment step (step S20) may be performed at a plurality of different temperatures. The heat treatment (step S20) includes, for example, a first heat treatment (step S21) and a second heat treatment (step S22) for performing a heat treatment at a temperature higher than the first heat treatment temperature, as shown in FIG. Good. Further, for example, as shown in FIG. 4, a third heat treatment (step S23) of performing a heat treatment at a temperature higher than the second heat treatment temperature may be included. Hereinafter, each step will be described.

[First heat treatment step (Step S21)]
The first heat treatment step (Step S21) is a step of drying the mixture to remove at least a part of the moisture in the mixture. When heat treatment is performed at a high temperature in a state where the mixture contains a large amount of moisture, aggregation and decomposition of the lithium metal composite oxide (base material) are likely to occur. Therefore, it is possible to form the LiNb compound 3 on the surface of the lithium metal composite oxide (base material) reliably by gradually increasing the temperature to remove most of the water and then performing a heat treatment at a higher temperature. it can.

  The heat treatment condition in the first heat treatment step (Step S21) may be a condition under which at least a part of the moisture in the mixture is removed, and the heat treatment temperature is preferably 80 ° C or more and 300 ° C or less, more preferably 80 ° C or more. The temperature may be 200 ° C or lower, or may be 80 ° C or higher and 150 ° C or lower.

[Second heat treatment step (Step S22)]
The second heat treatment step (Step S22) is a step of heat-treating the mixture at a higher temperature than the first heat treatment step (Step S21). When step S22 is provided, the reaction between (Li) and niobium (Nb) on the surface of the lithium metal composite oxide (base material) can be promoted to form LiNb compound 3 having high lithium ion conductivity. .

  The heat treatment temperature in the second heat treatment step (Step S22) may be higher than that of the first heat treatment step (Step S21) and 450 ° C. or less. For example, as described later, when a third heat treatment step (step S23) is further provided, the heat treatment temperature of the second heat treatment step (step S22) may be 100 ° C or higher and 300 ° C or 150 ° C or higher and 250 ° C or higher. C. or lower. The heat treatment time is not particularly limited, but is, for example, 1 hour or more and 12 hours or less.

[Third heat treatment step (Step S23)]
The third heat treatment step (Step S23) is a step of heat-treating the mixture at a higher temperature than the second heat treatment step (Step S22). When the step S23 is provided, the reaction between (Li) and niobium (Nb) on the surface of the lithium metal composite oxide (base material) is further promoted, and the LiNb compound 3 having high lithium ion conductivity is more reliably formed. can do.

  The heat treatment temperature in the third heat treatment step (Step S23) may be higher than that of the second heat treatment step (Step S22) and 450 ° C or lower, preferably 200 ° C or higher and 450 ° C or lower, more preferably 200 ° C or higher. 350 ° C. or lower is more preferable. The heat treatment time is not particularly limited, but is, for example, 1 hour or more and 12 hours or less.

  In the entire heat treatment step (Step S20), the maximum temperature of the heat treatment may be, for example, 100 ° C to 450 ° C, 150 ° C to 450 ° C, or 200 ° C to 450 ° C. The temperature may be 300 ° C. or higher and 450 ° C. or lower. In the above temperature range, the higher the maximum temperature of the heat treatment, the higher the lithium ion conductivity of the formed LiNb compound 3 tends to be.

  In the heat treatment step (step S20), heat treatment may be performed at a single temperature, or may be performed at a plurality of temperatures as described above. When heat treatment is performed at a plurality of temperatures, heat treatment may be performed in a pattern other than the above.

[Positive electrode mixture paste for non-aqueous secondary batteries]
Next, a method for producing the positive electrode mixture paste for a non-aqueous secondary battery according to the present invention (hereinafter, also referred to as “positive electrode mixture paste”) will be described. In the positive electrode mixture paste of the present embodiment, elution of lithium from the positive electrode active material is reduced, and gelation of the paste is suppressed. Therefore, even when stored for a long period of time, there is little change in the viscosity of the paste, and the paste has high stability. By manufacturing a positive electrode using such a paste, the positive electrode also has excellent characteristics stably, and the characteristics of the finally obtained battery can be stably improved.

The positive electrode mixture paste contains a positive electrode active material. The constituent material of the positive electrode mixture paste is not particularly limited, and a material equivalent to a known positive electrode mixture paste can be used. The positive electrode mixture paste contains, for example, a positive electrode active material, a conductive agent, and a binder. The positive electrode mixture paste may further contain a solvent. The positive electrode mixture paste has a positive electrode active material content of 60 to 95 parts by mass and a conductive agent content of 1 to 20 parts by mass when the total solid content of the positive electrode mixture excluding the solvent is 100 parts by mass. It is preferable that the binder be used in an amount of 1 to 20 parts by mass.
As the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, or the like), or a carbon black-based material such as acetylene black or Ketjen black can be used.

  The binder (binder) plays a role of binding the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluoro rubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin And polyacrylic acid.

  If necessary, a solvent for dispersing a positive electrode active material, a conductive agent, and activated carbon and dissolving a binder (binder) may be added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone (NMP) can be used as the solvent. Activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity. The positive electrode mixture paste is prepared by mixing a powdered positive electrode active material, a conductive agent, and a binder, and further adding a desired solvent such as activated carbon and viscosity adjustment if necessary, and kneading the mixture to form a positive electrode mixture paste. Can be produced.

  Since the viscosity ratio of the positive electrode mixture paste before and after storage for 76 hours (paste viscosity after storage for 76 hours / paste viscosity immediately after preparation) changes depending on characteristics of the lithium metal composite oxide used as the lithium metal composite oxide powder, Although not particularly limited, it can be, for example, 0.5 or more and 2.3 or less, preferably 0.5 or more and 1.9 or less, and more preferably 0.5 or more and 1.5 or less. The viscosity ratio before and after storage for 76 hours was such that 25.0 g of the positive electrode active material, 1.5 g of carbon powder as the conductive agent, and 2.9 g of polyvinylidene fluoride (PVDF) were mixed by a planetary motion kneader to prepare a positive electrode mixture paste. After being obtained, the obtained paste is stored in an air atmosphere for 76 hours, and can be evaluated by measuring the viscosity ratio before and after storage (paste viscosity after storage for 76 hours / paste viscosity immediately after preparation). The viscosity can be measured, for example, with a vibration type viscometer (VM10A manufactured by Sekonic).

[Lithium ion secondary battery]
The lithium ion secondary battery (hereinafter, also referred to as “secondary battery”) according to the present embodiment includes a positive electrode including the above-described positive electrode active material 20, a negative electrode, and an electrolyte. Lithium ion secondary batteries can be configured with the same components as conventionally known lithium ion secondary batteries, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte secondary battery including a non-aqueous electrolyte. It may be. The secondary battery may be, for example, an all-solid secondary battery including a positive electrode, a negative electrode, and a solid electrolyte. Hereinafter, each component will be described.

  The embodiment described below is merely an example, and the lithium ion secondary battery of the present embodiment is based on the embodiment described in the present specification, based on the knowledge of those skilled in the art, various changes, It can be implemented in an improved form. The use of the lithium ion secondary battery of the present embodiment is not particularly limited.

(Positive electrode)
Using the positive electrode mixture paste containing the positive electrode active material 20, for example, a positive electrode of a lithium ion secondary battery may be manufactured as follows.

  The positive electrode mixture paste is applied to, for example, the surface of a current collector made of aluminum foil, dried, and the solvent is scattered. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. Thus, a sheet-shaped positive electrode can be manufactured. The sheet-shaped positive electrode can be cut to an appropriate size according to the intended battery and used for the production of the battery. However, the method of manufacturing the positive electrode is not limited to the example, and another method may be used.

(Negative electrode)
For the negative electrode, a negative electrode mixture made into a paste by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions, or a negative electrode active material capable of absorbing and desorbing lithium ions, is used as a negative electrode. Is applied to the surface of the metal foil current collector, dried, and compressed if necessary to increase the electrode density.

  As the negative electrode active material, for example, natural graphite, artificial graphite, fired organic compounds such as phenolic resins, and powdered carbon materials such as coke can be used. In this case, as the negative electrode binder, similarly to the positive electrode, a fluorine-containing resin such as PVDF can be used, and as a solvent for dispersing these active materials and the binder, N-methyl-2-pyrrolidone or the like can be used. Organic solvents can be used.

(Separator)
A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and may be a thin film of polyethylene, polypropylene, or the like, which has a large number of minute holes.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte, a non-aqueous electrolyte, a solid electrolyte, or the like is used.

  The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Examples of the organic solvent include ethylene carbonate, propylene carbonate, butylene carbonate, cyclic carbonates such as trifluoropropylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, chain carbonates such as dipropyl carbonate, and further, tetrahydrofuran, 2-hydrogen carbonate, and the like. One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate are used alone or in combination of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) _{2 and the} like, and a composite salt thereof can be used. Further, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

  As the solid electrolyte, an oxide solid electrolyte, a sulfide solid electrolyte, or the like is used.

The oxide solid electrolyte is not particularly limited, and any oxide containing oxygen (O) and having lithium ion conductivity and electronic insulation can be used. The oxide-based solid electrolyte, 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 etc. I can do it.

The sulfide-based solid electrolyte is not particularly limited, and any electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. 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 5 , and the like.

In addition, as the inorganic solid electrolyte, one other than the above may be used. For example, Li ₃ N, LiI, Li ₃ N—LiI—LiOH, or the like may be used.

  The organic solid electrolyte is not particularly limited as long as it is a polymer compound having ion conductivity, and examples thereof include polyethylene oxide, polypropylene oxide, and copolymers thereof. Further, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(Battery shape and configuration)
The shape of the lithium ion secondary battery of the present embodiment composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte described above can be various shapes such as a cylindrical type and a stacked type. In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolytic solution, and communicates with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like, and sealed in a battery case to complete a lithium ion secondary battery.

  When a solid electrolyte is used, the positive electrode and the negative electrode are stacked with the solid electrolyte interposed between the positive electrode current collector and the positive electrode terminal communicating with the outside, and the negative electrode current collector and the negative electrode terminal communicating with the outside. Is connected using a current collecting lead or the like, and sealed in a battery case to complete a lithium ion secondary battery.

(Characteristic)
The secondary battery according to the present embodiment is manufactured using the above-described positive electrode active material, and can have a high battery capacity. A secondary battery using the positive electrode active material obtained in the preferred embodiment has a high initial discharge of 190 mAh / g or more when used for a positive electrode of a 2032 type coin-type battery CBA as shown in FIG. 3, for example. The capacity is obtained. In addition, the coin-type battery CBA can have an initial charge / discharge efficiency of 90% or more.

The initial charge / discharge efficiency was determined by setting the current density with respect to the positive electrode after the open-circuit voltage OCV (Open Circuit Voltage) was stabilized for about 24 hours after the coin-type battery CBA used in the example was manufactured. This is a value obtained by measuring the capacity when the battery was charged to a cutoff voltage of 4.3 V at 1 mA / cm ² , and was discharged to a cutoff voltage of 3.0 V after a one-hour pause.

  For example, the positive electrode active material obtained in the preferred embodiment may have a positive electrode resistance of 4Ω or less, or 3Ω or less, measured using a coin-type battery CBA. The measurement of the positive electrode resistance was performed by the method described in Examples.

  An example of a method for measuring the positive electrode resistance using the coin-type battery CBA is as follows. When the frequency dependence of the battery reaction is measured by a general AC impedance method as an electrochemical evaluation method, a Nyquist diagram based on the solution resistance, the negative electrode resistance and the negative electrode capacity, and the positive electrode resistance and the positive electrode capacity is shown in FIG. Obtained as follows. The battery reaction at the electrode consists of a resistance component due to charge transfer and a capacitance component due to the electric double layer. When these are represented by an electric circuit, a parallel circuit of resistance and capacitance is formed. Are represented by an equivalent circuit in which the parallel circuits are connected in series. A fitting calculation is performed on the Nyquist diagram measured using this equivalent circuit, and each resistance component and capacitance component can be estimated. The positive electrode resistance is equal to the diameter of the semicircle on the low frequency side of the obtained Nyquist diagram. Therefore, the AC impedance of the positive electrode PE is measured, and the resistance of the positive electrode can be estimated by performing fitting calculation on the obtained Nyquist diagram by using an equivalent circuit.

  Hereinafter, the present invention will be described specifically with reference to examples, but the present invention is not limited to these examples. The performance of the positive electrode active material obtained by the present embodiment, the positive electrode mixture paste using the positive electrode active material, and the secondary battery were measured. In this example, samples of the special grade reagent manufactured by Wako Pure Chemical Industries, Ltd. were used for the production of the composite hydroxide, the production of the positive electrode active material, and the production of the secondary battery.

(Amount of lithium hydroxide)
After mixing 2 g of the obtained positive electrode active material with 125 ml of pure water and stirring and dispersing for 1 minute, 5 ml of a 10% by mass barium chloride solution was added, and neutralization titration was performed using 1.0 mol / l hydrochloric acid. The amount of lithium hydroxide eluted in pure water was calculated from the amount of hydrochloric acid up to the first neutralization point.

(Moisture percentage)
The measurement was performed with a Karl Fischer moisture meter under the conditions of a vaporization temperature of 300 ° C.

(Viscosity stability of positive electrode mixture paste)
25.0 g of the positive electrode active material, 1.5 g of carbon powder as a conductive agent, and 2.9 g of polyvinylidene fluoride (PVDF) were mixed by a planetary kneader to obtain a positive electrode mixture paste. The obtained paste was stored in an air atmosphere for 76 hours, and the viscosity ratio before and after storage (paste viscosity after storage for 76 hours / paste viscosity immediately after preparation) was evaluated. The viscosity was measured with a vibration type viscometer (VM10A manufactured by Sekonic).

(Method of manufacturing and evaluating batteries)
The obtained positive electrode active material for lithium ion secondary batteries was evaluated by preparing a 2032 type coin-type battery CBA shown in FIG. 3 and measuring the charge / discharge capacity as described below. 52.5 mg of a positive electrode active material for a lithium ion secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed, and pressed under a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm. (Evaluation electrode) was produced. The produced positive electrode PE was dried in a vacuum dryer at 120 ° C. for 12 hours. Then, using this positive electrode PE, a coin-type battery CBA was produced in a glove box in an Ar atmosphere where the dew point was controlled at -80 ° C.

For the negative electrode NE, a negative electrode sheet in which a graphite powder having a volume average particle size of about 20 μm and a polyvinylidene fluoride coated on a copper foil and having a volume average particle diameter of about 20 μm, which is punched into a disk having a diameter of 14 mm, is used, and 1 M of LiPF ₆ is supported as an electrolytic solution. A mixed solution (equivalent to Toyama Pharmaceutical Co., Ltd.) of ethylene carbonate (EC) and diethyl carbonate (DEC) was used as an electrolyte. A polyethylene porous film having a thickness of 25 μm was used as the separator SE. The coin-type battery CBA had a gasket GA and a wave washer WW, and was assembled into a coin-shaped battery with the positive electrode can PC and the negative electrode can NC.

  Using the manufactured coin-type battery CBA, the initial discharge capacity and the positive electrode resistance were evaluated as follows.

(Initial discharge capacity)
After the coin-type battery CBA was manufactured, it was left standing for about 24 hours after the coin-type battery CBA was manufactured. After the open circuit voltage (OCV) was stabilized, the current density with respect to the positive electrode was 0.1 mA / cm ² and the cut-off voltage was 4 The capacity at the time when the battery was charged to 0.3 V, and after a one-hour pause was discharged to a cutoff voltage of 3.0 V was defined as the initial discharge capacity.

(Initial charge / discharge efficiency)
The initial charge / discharge efficiency was calculated by measuring the initial charge / discharge capacity by the method described in the preceding section and calculating as initial discharge capacity / initial charge capacity × 100.

(Positive electrode resistance)
The positive electrode resistance was measured by charging the coin-type battery CBA at a charging potential of 4.1 V and measuring the negative electrode resistance by an AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B). A plot is obtained. Since this Nyquist plot is represented as the sum of characteristic curves indicating solution resistance, negative electrode resistance and its capacity, and positive electrode resistance and its capacity, fitting calculation is performed using an equivalent circuit based on this Nyquist plot, and positive electrode resistance is calculated. Was calculated.

[Example 1]
(Manufacture of positive electrode active material)
After mixing a hydroxide powder mainly composed of Ni and lithium hydroxide, the mixture was fired to obtain a lithium metal composite oxide powder. The obtained lithium metal composite oxide is represented by Li _1.025 Ni _0.82 Co _0.15 Al _0.03 O ₂ , has a volume average particle diameter Mv of 6.2 μm, and [(d90−d10) / volume. Average particle size Mv] was 0.74. The obtained lithium metal composite oxide was used as a base material.

  Niobium oxide sol (manufactured by Taki Chemical Co., Ltd., Viral Nb-G6000) was mixed with the lithium metal composite oxide powder (base material). The niobium oxide sol was mixed in an amount of 0.5 mol% as niobium in the niobium oxide sol with respect to the total of Ni, Co and Al (total of metal elements other than Li) contained in the powder of the lithium metal composite oxide. . Thereafter, water was added to the lithium metal composite oxide powder (base material) in an amount of 10% by mass and further mixed.

  Thereafter, the obtained mixture is heated in a vacuum atmosphere from room temperature to 100 ° C. and heat-treated (first heat treatment) for 12 hours, and then further heated to 190 ° C. for 10 hours and heat-treated (second heat treatment). To obtain a positive electrode active material.

  When the obtained cathode active material was subjected to XRD measurement, no clear niobium compound peak was obtained. Therefore, it is considered that the niobium compound present on the surface of the positive electrode active material is in an amorphous state. Table 1 shows the evaluation results of the amount of lithium hydroxide, the water content, and the viscosity stability of the positive electrode mixture paste of the obtained positive electrode active material.

  In addition, the battery characteristics of a coin-type battery having a positive electrode manufactured using the obtained positive electrode active material were evaluated. Table 1 shows the evaluation results of the initial discharge capacity, the initial charge / discharge efficiency, and the positive electrode resistance of the coin-type battery.

[Example 2]
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that niobium oxide sol was mixed in a lithium metal composite oxide powder (base material) with niobium oxide in an amount of 1.0 mol%. Table 1 shows the evaluation results.

[Example 3]
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that niobium oxide sol was mixed in an amount of 1.5 mol% in niobium with a lithium metal composite oxide powder (base material). Table 1 shows the evaluation results.

[Example 4]
Niobium oxide sol was mixed with the lithium metal composite oxide powder (base material) in an amount of 1.5 mol% in niobium amount, and heat treatment was performed at 300 ° C. for 5 hours (third heat treatment) after the second heat treatment step. A positive electrode active material was obtained and evaluated in the same manner as in Example 1. Table 1 shows the evaluation results.
[Example 5]
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that niobium oxide sol was mixed in an amount of 2.0 mol% in niobium with a lithium metal composite oxide powder (base material). Table 1 shows the evaluation results.
[Example 6]
As a lithium metal composite oxide powder (base material), a composition was obtained by mixing a hydroxide powder mainly composed of Ni and lithium hydroxide, followed by firing, and having a composition of Li _1.025 Ni _0.82 Mn. A lithium metal composite oxide represented by _0.15 Al _0.03 O ₂ having a volume average particle size Mv of 6.5 μm and [(d90−d10) / volume average particle size Mv] of 0.75 was used. A positive electrode active material was obtained and evaluated in the same manner as in Example 2 except for the difference. Table 1 shows the evaluation results.
[Example 7]
A positive electrode active material was obtained and evaluated in the same manner as in Example 4, except that the third heat treatment was performed at 100 ° C. for 5 hours. Table 1 shows the evaluation results.
Example 8
A positive electrode active material was obtained and evaluated in the same manner as in Example 4, except that the third heat treatment was performed at 500 ° C. for 5 hours. Table 1 shows the evaluation results.

[Comparative Example 1]
A positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that niobium oxide sol was not mixed into the lithium metal composite oxide powder (base material). Table 1 shows the evaluation results.

[Comparative Example 2]
A positive electrode active material was obtained and evaluated in the same manner as in Example 1, except that 0.3 mol% of niobium oxide sol was added to the lithium metal composite oxide powder (base material). Table 1 shows the evaluation results.

[Comparative Example 3]
A commercially available niobium (V) oxide powder (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) obtained by pulverizing a lithium metal composite oxide powder (base material) to an average particle size of 1.0 μm with a ball mill was used in an amount of niobium. A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that 0 mol% was mixed. Table 1 shows the evaluation results.
[Comparative Example 4]
A positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that a separately prepared Li-Nb compound was mixed with a lithium metal composite oxide powder (base material) in an amount of 1.0 mol% in niobium. Table 1 shows the evaluation results. The Li-Nb compound was prepared by mixing 5.0 g of lithium hydroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) and 27.75 g of niobium (V) oxide powder (same as above) and calcining the mixture at 1000 ° C. for 10 hours in an electric furnace in an oxygen atmosphere. After that, the product was pulverized with a ball mill to an average particle size of 1 μm.
[Comparative Example 5]
After mixing the niobium oxide sol with the lithium metal composite oxide powder (base material), a positive electrode active material was obtained and evaluated in the same manner as in Example 1 except that water was not added. Table 1 shows the evaluation results.

(Evaluation)
In the secondary battery using the positive electrode active material of the example, good results were obtained in both the initial discharge capacity and the positive electrode resistance. Further, the viscosity ratio of the positive electrode mixture paste was 2 or less, and it was confirmed that the viscosity of the positive electrode mixture paste was stable. It was also confirmed that the secondary batteries of the examples had high initial charge / discharge efficiency. Further, with the positive electrode active materials of Examples 4 and 8 obtained by performing the third heat treatment step, the secondary batteries using the same were obtained under the same conditions except that the third heat treatment step was not performed. As compared with the obtained positive electrode active material of Example 3, the initial discharge capacity was higher and the positive electrode resistance was reduced. This is probably because the third heat treatment improved the lithium ion conductivity of the LiNb compound formed on the surface of the base material. In the positive electrode active materials of Examples 4 and 8 in which the third heat treatment was performed at a temperature higher than the temperature of the second heat treatment, the positive electrode active material of Example 7 in which the heat treatment was performed at a temperature lower than the temperature of the second heat treatment was used. The initial discharge capacity was higher than the material.

  On the other hand, since the positive electrode active material of Comparative Example 1 did not contain niobium, the amount of lithium hydroxide exceeded 0.150% by mass with respect to the positive electrode active material. The positive electrode mixture paste using the positive electrode active material of Comparative Example 1 had a large increase in viscosity. In the positive electrode active material of Comparative Example 2, since the amount of niobium added was small, the amount of lithium hydroxide eluted from the positive electrode active material by titration exceeded 0.15% by mass, and gelation of the positive electrode mixture paste could be suppressed. And the increase in viscosity was large. Further, in the positive electrode active materials of Comparative Examples 3, 4, and 5, since a good LiNb compound was not sufficiently formed, the amount of lithium hydroxide eluted from the positive electrode active material was large, the paste viscosity ratio was high, and the positive electrode resistance was large. Was.

  From the above results, it was shown that the positive electrode active material according to the present embodiment can achieve both a high initial discharge capacity, and a high initial charge / discharge efficiency, and suppression of gelation of the positive electrode mixture paste during electrode production. .

1, 1a, 1b: Primary particles 2: Secondary particles 3: LiNb compound 10: Lithium metal composite oxide 20: Positive electrode active material CBA: Coin cell 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 (17)

Contains lithium metal composite oxide containing lithium (Li), nickel (Ni), and optionally cobalt (Co), manganese (Mn) and element M, and a compound containing lithium and niobium (Nb) Positive electrode active material for a lithium ion secondary battery,
The ratio (molar ratio) of the amount of each element other than niobium contained in the positive electrode active material is Li: Ni: Co: Mn: M = s: (1-xyz): x: y: z (However, 0 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 <s <1.30, M is V, Mg, Mo, Nb, Ti, W, at least one element selected from Zr and Al)
The lithium metal composite oxide includes secondary particles formed by aggregation of primary particles, at least a part of the surface of the primary particles is coated with the compound including lithium and niobium,
The amount of lithium hydroxide eluted when the positive electrode active material is dispersed in water, measured by a neutralization titration method, is 0.003% by mass or more and 0.15% by mass or less based on the whole positive electrode active material. A positive electrode active material for a lithium ion secondary battery.   The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the positive electrode active material is a conductive agent contained in the compound containing lithium and niobium.   The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the compound containing lithium and niobium contains at least lithium niobate. The lithium _niobate, Li ₃ NbO _4, LiNbO 3, LiNb ₃ containing at least one of the positive electrode active material for a lithium ion secondary battery according to claim 3 of the O ₈ and _Li 8 _Nb 2 _{O 9.}   The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein the compound containing lithium and niobium is amorphous. A method for producing a positive electrode active material for a lithium ion secondary battery,
Powder of lithium metal composite oxide containing lithium (Li), nickel (Ni), and optionally cobalt (Co), manganese (Mn) and element M; niobium that does not contain lithium and can react with lithium Mixing the compound with to obtain a mixture;
Heat treating the mixture,
In the powder of the lithium metal composite oxide, the ratio (molar ratio) of the amount of each element is Li: Ni: Co: Mn: M = s: (1-xyz): x: y: z (However, 0 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, 0 ≦ z ≦ 0.10, 0.95 <s <1.30, M is V, Mg, Mo, Nb, Ti, W, at least one element selected from Zr and Al), and includes a primary particle and secondary particles formed by agglomeration of primary particles,
The mixing amount of the niobium compound is determined by a neutralization titration method. The amount of lithium hydroxide eluted when the positive electrode active material is dispersed in water is 0.003% by mass based on the whole positive electrode active material. At least 0.15 mass%.
A method for producing a positive electrode active material for a lithium ion secondary battery.   After obtaining the mixture and before performing the heat treatment, mixing a solvent capable of dissolving the niobium compound in a range of 1% by mass or more and 40% by mass or less with respect to the powder of the lithium metal composite oxide; The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 6, comprising:   The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 6, wherein the heat treatment has a heat treatment temperature of 80 ° C. or more and 450 ° C. or less.   9. The lithium according to claim 8, wherein the heat treatment includes a first heat treatment at a heat treatment temperature of 80 ° C. or more and 300 ° C. or less, and a second heat treatment performed at a temperature higher than the temperature of the first heat treatment. 10. A method for producing a positive electrode active material for an ion secondary battery.   The method of manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 9, wherein the heat treatment includes a third heat treatment in which the heat treatment is performed at a temperature higher than the temperature of the second heat treatment.   The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 6 to 10, wherein a maximum temperature in the heat treatment is 300C or more and 450C or less.   The production of the positive electrode active material for a lithium ion secondary battery according to any one of claims 6 to 11, wherein the surface of the primary particles is coated with a compound containing lithium and niobium. Method.   The manufacturing of the positive electrode active material for a lithium ion secondary battery according to any one of claims 6 to 12, wherein the niobium compound includes at least one of a powder of niobium oxide and a sol containing niobium oxide. Method.   The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 6 to 13, wherein the niobium compound has a secondary particle diameter of 20 nm or less.   The amount of niobium contained in the niobium compound is 0.5 mol% or more and 2.0 mol% or less based on the total amount of Ni, Co, Mn, and M in the powder of the lithium metal composite oxide. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 14.   A positive electrode mixture paste for a lithium ion secondary battery, comprising the positive electrode active material for a lithium ion secondary battery according to claim 1.   A lithium ion secondary battery having a positive electrode including the positive electrode active material for a lithium ion secondary battery according to claim 1.

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