Positive electrode active material and method for producing same

Abstract

The present invention addresses the problem of providing a positive electrode active material having improved quantitative properties in a feeder. The positive electrode active material contains a composite oxide containing a lithium (Li) element, a nickel (Ni) element, and a manganese (Mn) element. The positive electrode active material has an angle-of-repose of 55.0-65.0 degrees and a collapse angle of 43.0-60.0 degrees. The positive electrode active material preferably has an angle-of-difference of less than 13.0 degrees. In addition, the arithmetic average peripheral length of the primary particles of the positive electrode active material is preferably 8.0 μm or less. The positive electrode active material also preferably has a spinel-type crystal structure and an a-axis length of 8.150-8.200 Å.

Description

Positive electrode active material and method for manufacturing the same

[0001] The present invention relates to a positive electrode active material for a battery and a method for producing the same.

[0002] In recent years, secondary batteries have attracted attention as an initiative to prevent global warming by reducing carbon dioxide emissions. Among secondary batteries, lithium secondary batteries, which have high energy density and high voltage, are widely used. Lithium manganese composite oxide (hereinafter also referred to as "LMO") is known as one of the active materials used in the positive electrode of lithium secondary batteries. In particular, lithium secondary batteries that use spinel-type lithium nickel manganese composite oxide (see Patent Documents 1 to 3, hereinafter also referred to as "LNMO"), in which some of the manganese in LMO is replaced with other transition metal elements such as nickel, as the positive electrode active material have better cycle characteristics compared to those that use LMO as the positive electrode active material. Another advantage is that LNMO has an electromotive force in the 5V range, while LMO has an electromotive force in the 4V range.

[0003] Japanese Patent Publication No. 2001-185148, Japanese Patent Publication No. 2002-158007, Japanese Patent Publication No. 2003-81637

[0004] When manufacturing batteries industrially using LNMO as a positive electrode active material, it is common practice to supply a fixed amount of LNMO from a hopper using a feeder to the downstream process. In this case, if the fluidity of the LNMO is excessively high, it is difficult to accurately measure the amount in the feeder. Therefore, the object of the present invention is to provide a positive electrode active material with appropriate fluidity and a method for producing the same.

[0005] The present invention provides a positive electrode active material containing a composite oxide comprising lithium (Li), nickel (Ni), and manganese (Mn), having an angle of repose of 55.0 degrees or more and 65.0 degrees or less, and a collapse angle of 43.0 degrees or more and 60.0 degrees or less.

[0006] The present invention also provides a method for producing a positive electrode active material, comprising mixing a composite hydroxide containing nickel (Ni) and manganese (Mn) elements, a lithium compound, and a sintering aid to obtain a mixture, and then firing the mixture in an oxygen-containing atmosphere, wherein the composite hydroxide has an oil absorption capacity of 3.0 mL / 5 g or more and 6.5 mL / 5 g or less as measured in accordance with JIS K 5101:2004, and the oxygen-containing atmosphere contains more than 21.0 volume percent of oxygen.

[0007] The present invention will be described below based on its preferred embodiments.

[0008] [Positive Electrode Active Material] The positive electrode active material of the present invention is a powder composed of a plurality of particles. The positive electrode active material of the present invention contains a composite oxide. This composite oxide contains lithium (Li), nickel (Ni), manganese (Mn), and oxygen (O). The composite oxide may be, for example, a lithium transition metal composite oxide having a layered rock salt type crystal structure or a spinel type crystal structure. When the composite oxide has a spinel type crystal structure, it is preferable that the composite oxide has an operating potential of 4.5 V or higher at a metallic Li reference potential. "Having an operating potential of 4.5 V or higher at a metallic Li reference potential" does not mean that it is necessary to have only an operating potential of 4.5 V or higher as a plateau region, but also includes cases where it has an operating potential of 4.5 V or higher in part. Therefore, the present invention is not limited to positive electrode active materials consisting only of 5V class positive electrode active materials having an operating potential of 4.5 V or higher as a plateau region. For example, the positive electrode active material of the present invention may include positive electrode active materials having an operating potential of less than 4.5 V as a plateau region. Specifically, it is preferable that the 5V class positive electrode active material accounts for, for example, 30% by mass or more, preferably 50% by mass or more, and among these, a positive electrode active material that accounts for 80% by mass or more (including 100% by mass) is permitted.

[0009] Composite oxides having a spinel-type crystal structure include, for example, those with the general formula LiNi ｘ Mn ２－ｘ O ４(x represents a number greater than 0 and less than 2.) It can be represented as such. Further, as another example of the composite oxide, a spinel-type LiNi ｘ Mn ２－ｘ O ４ A spinel-type lithium manganese-containing composite oxide having a crystal structure in which a part of the Mn sites in is substituted with Li, Ni element, and other M elements (details of the M element will be described later) can also be mentioned. In addition, formula (I): Li １＋ｘ (Ni ｙ M ｚ Mn ２－ｘ－ｙ－ｚ )O ４－δ The spinel-type lithium manganese-containing composite oxide represented by can also be mentioned. The M element in formula (I) is preferably one or a combination of two or more selected from the group consisting of Na, Mg, B, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. The M element is a substitution element that mainly contributes to stabilizing the crystal structure and enhancing the properties. By selecting the M element from the above-described elements, the crystal structure can be stabilized and the elution amount of the metal element can be reduced. From this viewpoint, the M element is preferably Mg, Al, or Ti, and more preferably contains the Ti element.

[0010] In formula (I), "x" is preferably 0.001 or more and 0.200 or less, "y" is preferably 0.20 or more and 1.20 or less, and "z" is preferably 0.000 or more and 0.500 or less. Further, "4 - δ" indicates that it may contain oxygen deficiency, and δ is preferably 0 or more and 0.2 or less.

[0011] The types and contents of the metal elements contained in the composite oxide can be analyzed by, for example, ICP emission spectrometry.

[0012] The positive electrode active material of the present invention may contain other components other than the above-described composite oxide. However, from the viewpoint of sufficiently enhancing various performances of the battery in which the positive electrode active material of the present invention is incorporated, the positive electrode active material of the present invention preferably contains the composite oxide at 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more.

[0013] In the industrial manufacture of batteries, the positive electrode active material is generally supplied to the downstream process by a feeder in a quantitative amount from a hopper. In this case, if the fluidity of the positive electrode active material is excessively high, it is difficult to accurately quantify it in the feeder. Therefore, the inventors diligently studied how to control the fluidity of the positive electrode active material and found that the fluidity of the positive electrode active material particles can be successfully controlled by appropriately controlling the angle of repose of the positive electrode active material particles. Specifically, the positive electrode active material of the present invention preferably has an angle of repose of 55.0 degrees or more, more preferably 56.0 degrees or more, and even more preferably 57.0 degrees or more. Furthermore, the positive electrode active material of the present invention preferably has an angle of repose of 65.0 degrees or less, more preferably 64.0 degrees or less, and even more preferably 62.0 degrees or less.

[0014] The angle of repose of the positive electrode active material is automatically measured using a PT-X powder tester (registered trademark) manufactured by Hosokawa Micron Corporation. The measurement conditions are as follows: <Measurement conditions for the angle of repose> - Sieve vibration setting: 1.5 - Vibration time: 170 seconds - Sample amount: 100 g

[0015] In addition to the angle of repose of the positive electrode active material of the present invention satisfying the above-mentioned range, it is preferable that the collapse angle range is also controlled. By setting the collapse angle of the positive electrode active material to a specific range, the flow in response to vibration can also be controlled, and consequently, the fluidity of the positive electrode active material can be successfully controlled. From this viewpoint, it is preferable that the collapse angle of the positive electrode active material of the present invention is 43.0 degrees or more, more preferably 45.0 degrees or more, and even more preferably 47.0 degrees or more. Furthermore, it is preferable that the collapse angle of the positive electrode active material of the present invention is 60.0 degrees or less, more preferably 59.0 degrees or less, and even more preferably 57.0 degrees or less.

[0016] The collapse angle of the positive electrode active material is measured using a PT-X powder tester (registered trademark) manufactured by Hosokawa Micron Corporation. The measurement conditions are as follows: <Measurement conditions for collapse angle> After automatic measurement of the angle of repose, the collapse angle is calculated by automatic measurement of three collapse impacts.

[0017] In relation to the angle of repose and collapse angle described above, the difference angle of the positive electrode active material of the present invention is preferably less than 13.0 degrees, more preferably 12.5 degrees or less, and even more preferably 12.0 degrees or less, from the viewpoint of improving the fluidity of the positive electrode active material in the battery manufacturing equipment. From a similar viewpoint, the difference angle of the positive electrode active material is preferably 1.0 degree or more, more preferably 2.5 degrees or more, and even more preferably 4.0 degrees or more.

[0018] The angle difference of the positive electrode active material is the angle calculated by subtracting the collapse angle from the angle of repose of the positive electrode active material.

[0019] In order to set the angle of repose, collapse angle, and difference angle of the positive electrode active material within the above-mentioned numerical range, for example, in the manufacturing method described later, a specific nickel-manganese composite hydroxide can be used as the raw material, and a calcination atmosphere containing more than 21.0% by volume of oxygen can be used.

[0020] The particle size of the positive electrode active material of the present invention is determined by the cumulative volume particle size D at 50% of the cumulative volume, as measured by laser diffraction scattering particle size distribution analysis. ５０ (Hereinafter also referred to as "average particle diameter") is preferably 0.5 μm or more, more preferably 3.0 μm or more, even more preferably 5.0 μm or more, and even more preferably 7.0 μm or more. On the other hand, the volume cumulative particle size D ５０ The volume cumulative particle size D of the positive electrode active material is preferably 30.0 μm or less, more preferably 20.0 μm or less, even more preferably 15.0 μm or less, and even more preferably 12.0 μm or less. ５０ By keeping the range described above, the fluidity of the positive electrode active material particles can be controlled with greater precision.

[0021] Here, volume cumulative particle size D ５０This has meaning as a substitute value for the average diameter of particles, including primary and secondary particles. "Primary particle" refers to the smallest unit particle surrounded by a grain boundary when observed with an SEM (scanning electron microscope, e.g., 500 to 5000x magnification). On the other hand, in this invention, "secondary particle" refers to a particle that is independent of other particles, formed by the aggregation of multiple primary particles sharing a portion of their outer circumference (grain boundary).

[0022] Volume cumulative particle size D ５０ The volume cumulative particle size D is measured by the following method: Using an automated sample feeder for laser diffraction particle size distribution analyzers (Microtrac SDC, manufactured by Microtrac-Bell Corporation), the positive electrode active material powder is placed in a 20% by mass ethanol solvent, and after irradiating with 40W ultrasound for 360 seconds at a flow rate of 40%, the particle size distribution is measured using the Microtrac-Bell Corporation laser diffraction particle size distribution analyzer MT3300EX, and the volume cumulative particle size D is obtained from the volume-based particle size distribution chart. ５０ Measure D ５０ When measuring the particle size, the water-soluble solvent was passed through a 60 μm filter, with the solvent refractive index set to 1.33, particle permeability set to "permeable," particle shape set to "non-spherical," particle refractive index set to 2.46, measurement range set to 0.243 μm to 704.0 μm, and measurement time set to 30 seconds. The average of two measurements was used to determine the particle size D. １０ , particle size D ５０ and particle size D ９０ Let's assume that.

[0023] Generally, the fluidity of a powder is influenced by the degree of contact between the particles constituting the powder. Therefore, by appropriately controlling the fluidity of the positive electrode active material of the present invention, the arithmetic mean perimeter of the primary particles of the positive electrode active material is preferably 8.0 μm or less, more preferably 7.9 μm or less, and even more preferably 7.8 μm or less. From a similar viewpoint, the arithmetic mean perimeter of the primary particles of the positive electrode active material is preferably 2.0 μm or more, more preferably 4.0 μm or more, and even more preferably 6.0 μm or more. In order to set the arithmetic mean perimeter of the primary particles of the positive electrode active material within the above numerical range, for example, the temperature and time of the calcination treatment of the mixture can be appropriately controlled in the manufacturing method described later.

[0024] Similarly, from the viewpoint of appropriately controlling the fluidity of the positive electrode active material of the present invention, the circularity coefficient of the primary particles of the positive electrode active material is preferably 0.40 or higher, more preferably 0.45 or higher, and even more preferably 0.50 or higher. From a similar viewpoint, the circularity coefficient of the primary particles of the positive electrode active material is preferably 0.65 or lower, more preferably 0.63 or lower, and even more preferably 0.60 or lower. In order to set the circularity coefficient of the primary particles of the positive electrode active material within the above numerical range, for example, the temperature and time of the calcination treatment of the mixture can be appropriately controlled in the manufacturing method described later.

[0025] The arithmetic mean perimeter and circularity coefficient of the primary particles of the positive electrode active material are calculated by the following method: Scanning electron microscope images of the positive electrode active material are taken, and 80 non-overlapping particles are randomly selected. The perimeter L of the two-dimensional projection image of the particles is measured, and this arithmetic mean value is taken as the arithmetic mean perimeter. In addition, the area S of the two-dimensional projection image of the particles is measured, and the circularity coefficient of the particle is calculated as 4πS / L. ２ It is calculated from the formula shown. The arithmetic mean of the circularity coefficients of each particle is taken as the circularity coefficient mentioned above. For these image analyses, for example, the image analysis particle size distribution measurement software MAC-View (manufactured by Mountec Co., Ltd.) can be used. If the two-dimensional projection image of the particle is a perfect circle, the circularity coefficient of the particle is 1.

[0026] From the viewpoint of reducing the contact area with the electrolyte and suppressing the elution of metal elements from the positive electrode active material, the ratio TD / SSA of the tap density TD to the BET specific surface area SSA of the positive electrode active material of the present invention is 1.5 kg ２ / m ５ Preferably, it should be 1.8 kg or more. ２ / m ５ It is more preferable that the amount be greater than or equal to 2.0 kg. ２ / m ５ It is even more preferable that the above conditions are met. Furthermore, the upper limit of TD / SSA is not particularly limited, but for example, 4.0 kg ２ / m ５ The following is particularly true for 3.9 kg ２ / m ５ The following, in particular, is 3.7 kg ２ / m ５ The following is the most practical approach. In this specification, tap density refers to the value measured in accordance with JIS Z2512. Detailed measurement methods for tap density and BET specific surface area will be described in the examples below.

[0027] From the viewpoint of reducing the contact area with the electrolyte and suppressing the elution of metal elements from the positive electrode active material, the BET specific surface area (SSA) of the positive electrode active material of the present invention is 3.0 m². ２ It is preferable that the amount is less than or equal to 2.0 m ２ It is more preferable that it be less than or equal to 1.5 m ２ It is even more preferable that it be less than or equal to 1.0 m ２ It is even more preferable that the amount is less than or equal to / g. Also, from a similar viewpoint, the BET specific surface area SSA of the positive electrode active material of the present invention is 0.1m². ２ It is preferable that the amount be 0.2 m or more. ２ It is more preferable that it be 0.3 m or more per gram. ２ It is even more preferable that the SSA is 1 / g or more. In order to set SSA within the above range, for example, the temperature and time of the calcination treatment of the mixture can be appropriately controlled in the manufacturing method described later.

[0028] From the viewpoint of increasing the electrode density of the positive electrode incorporating the positive electrode active material of the present invention and the energy density of the battery, the tap density TD of the positive electrode active material of the present invention is 1.3 g / cm³. ３ Preferably, it is 1.4 g / cm³ or more. ３ It is more preferable that the amount be greater than or equal to 1.5 g / cm³. ３ It is even more preferable that the above is true. There is no particular limit on the upper limit of TD, but from the same viewpoint as above, TD should be 2.5 g / cm³. ３ Preferably, it is 2.3 g / cm³. ３ It is more preferable that the following is the case: 2.0 g / cm³ ３ It is even more preferable that the following conditions are met. In order to set TD within the above range, for example, the temperature and time of the calcination treatment of the mixture can be appropriately controlled in the manufacturing method described later.

[0029] As described above, the positive electrode active material of the present invention preferably has a spinel-type crystal structure. When X-ray diffraction measurement is performed on the positive electrode active material, the a-axis length of the crystal measured is preferably 8.150 Å or more, more preferably 8.160 Å or more, and even more preferably 8.170 Å or more. Furthermore, the a-axis length is preferably 8.200 Å or less, more preferably 8.197 Å or less, and even more preferably 8.194 Å or less. By setting the a-axis length within this range, the elution of metal elements from the crystal structure can be further suppressed. In order to set the a-axis length within the above range, for example, one or more transition metal elements other than nickel and manganese can be included in the composite oxide. Titanium is an example of such a transition metal element. A detailed method for measuring the a-axis length will be described in the examples described later.

[0030] For the purpose of improving various properties of the positive electrode active material of the present invention, part or all of the surface of the positive electrode active material may be coated with another substance. As a coating layer for the positive electrode active material, for example, a coating layer containing the element Li (lithium), element A (where A represents one or more elements selected from the group consisting of Ti, B, P, Zr, Ta, Nb, Zn, W, La, and Al), and element O (oxygen) can be used. Specifically, for the purpose of suppressing the increase in reaction resistance and deterioration of cycle characteristics during high-temperature storage, the surface of the positive electrode active material can be coated with one or more substances selected from the group consisting of, for example, lithium niobate, lithium titanate, lithium lanthanuzirconate, lithium tantalate, and lithium tungstate.

[0031] Elements contained in the coating layer can be detected by analytical techniques such as ICP emission spectroscopy, X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). For example, when detecting elements in the coating layer using ICP emission spectroscopy, a solution obtained by dissolving the particle surface of the positive electrode active material in a solvent and a solution obtained by dissolving the remaining particles after removing the particle surface in a solvent are analyzed by ICP emission spectroscopy. If an element is present in a higher amount in the solution obtained by dissolving the particle surface than in the solution obtained by dissolving the remaining particles, it can be concluded that the element is contained in the coating layer. Furthermore, when detecting elements in the coating layer using XPS analysis, XPS analysis is performed in combination with ion sputtering. Specifically, XPS analysis and ion sputtering are repeatedly performed on the measurement sample. In XPS analysis before ion sputtering, elements contained in the coating layer are detected. In contrast, as ion sputtering is repeated, the coating layer is gradually removed, and finally, elements contained in the part of the positive electrode active material that is inside the coating layer are detected by XPS analysis. By observing these changes in detected elements, the elements contained in the coating layer can be identified. Even when using AES, the elements in the coating layer can be detected using a method similar to that of XPS.

[0032] [Method for Manufacturing the Positive Electrode Active Material] Next, a preferred method for manufacturing the positive electrode active material of the present invention will be described. In this manufacturing method, a composite hydroxide containing nickel and manganese elements, a lithium compound, and a sintering aid are mixed to obtain a mixture, and then the mixture is calcined to produce the positive electrode active material. After describing the details of the composite hydroxide, the steps for preparing the composite hydroxide and the steps for manufacturing the positive electrode active material using the composite hydroxide will be described in order.

[0033] <Composite Hydroxides> In this specification, "composite hydroxide" refers to a compound consisting of hydroxides of two or more metal elements. With such composite hydroxides, for example, a positive electrode active material with reduced elution of metal elements can be obtained by the manufacturing method described later.

[0034] The composite hydroxide contains metal elements, and more preferably, at least nickel and manganese. This makes it possible to obtain a composite hydroxide that can be used to obtain a positive electrode active material capable of manufacturing high-performance batteries. In the composite hydroxide, it is desirable that the nickel and manganese elements exist in the form of hydroxides, but some of the nickel and / or manganese elements may exist in a state other than hydroxide, for example, in the form of oxides.

[0035] From the viewpoint of obtaining a positive electrode active material that can manufacture high-performance batteries, the nickel element content in the composite hydroxide is preferably 12.0% by mass or more, more preferably 13.0% by mass or more, and even more preferably 14.0% by mass or more. From a similar viewpoint, the nickel element content in the composite hydroxide is preferably 20.0% by mass or less, more preferably 19.0% by mass or less, and even more preferably 18.0% by mass or less.

[0036] Furthermore, from the viewpoint of obtaining a positive electrode active material that can manufacture high-performance batteries, the manganese element content in the composite hydroxide is preferably 40.0% by mass or more, more preferably 41.0% by mass or more, and even more preferably 42.0% by mass or more. From a similar viewpoint, the manganese element content in the composite hydroxide is preferably 50.0% by mass or less, more preferably 49.0% by mass or less, and even more preferably 48.0% by mass or less.

[0037] Furthermore, from the viewpoint of obtaining a positive electrode active material that can manufacture high-performance batteries, the molar ratio of manganese element to nickel element in the composite hydroxide is preferably 2.60 or higher, more preferably 2.65 or higher, and even more preferably 2.70 or higher. Similarly, from the viewpoint of obtaining a positive electrode active material that can manufacture high-performance batteries, the molar ratio of manganese element to nickel element in the composite hydroxide is preferably 3.40 or lower, more preferably 3.35 or lower, and even more preferably 3.30 or lower.

[0038] In order to set the nickel and manganese content within the above-mentioned ranges, it is preferable to adjust the concentration of nickel ions or manganese ions in the metal ion aqueous solution in the manufacturing method described later.

[0039] The composite hydroxide may contain other elements in addition to nickel and manganese. This makes it possible to obtain a positive electrode active material that can successfully manufacture high-performance batteries. Examples of other elements include Na, Mg, B, Al, P, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce. One or more of these other elements may be used. When the composite hydroxide contains other elements, there are no particular restrictions on the state in which these other elements exist. The other elements may exist, for example, in the form of hydroxides and oxides. Alternatively, the other elements may exist together with nickel and manganese in the form of a composite hydroxide.

[0040] If the composite hydroxide contains other elements, it is preferable that their content be within a predetermined range. Specifically, from the viewpoint of obtaining a positive electrode active material that can successfully manufacture high-performance batteries, it is preferable that the content of other elements in the composite hydroxide be 0.1% by mass or more, more preferably 0.2% by mass or more, and even more preferably 0.3% by mass or more. From a similar viewpoint, it is preferable that the content of other elements in the composite hydroxide be 8.0% by mass or less, more preferably 7.5% by mass or less, and even more preferably 7.0% by mass or less.

[0041] The presence and content of nickel, manganese, and other elements can be measured, for example, by ICP emission spectroscopy.

[0042] A preferred compositional formula for the composite hydroxide is, for example, formula (II): Ni ｘ Mn ｙExamples include OOH (where x + y = 1). In equation (II), "x" is preferably 0.23 or more and 0.28 or less, and more preferably 0.24 or more and 0.27 or less. "y" is preferably 0.72 or more and 0.77 or less, and more preferably 0.73 or more and 0.76 or less.

[0043] It is preferable that the composite hydroxide has many voids in its aggregate, i.e., low packing capacity. Compounds with low packing capacity are more easily exposed to oxygen throughout the compound compared to compounds with high packing capacity. This is particularly advantageous when calcining the compound. For example, when calcining a composite hydroxide, it is possible to calcine it with a sufficient amount of oxygen permeating not only the outside but also the inside of the composite hydroxide, and as a result, a positive electrode active material that can successfully manufacture high-performance batteries can be obtained. The degree of packing capacity of a composite hydroxide can be evaluated by the amount of oil absorbed, measured in accordance with JIS K 5101:2004. A higher amount of oil absorbed means that the composite hydroxide has low packing capacity. Specifically, from the viewpoint of reducing packing capacity and calcining the composite hydroxide with oxygen permeating throughout, it is preferable that the amount of oil absorbed by the composite hydroxide is 3.0 mL / 5 g or more, more preferably 3.2 mL / 5 g or more, even more preferably 3.4 mL / 5 g or more, and even more preferably 4.0 mL / 5 g or more. Furthermore, from the viewpoint of adjusting the reaction with oxygen when calcining the composite hydroxide, the oil absorption of the composite hydroxide is preferably 6.5 mL / 5 g or less, more preferably 6.3 mL / 5 g or less, even more preferably 6.0 mL / 5 g or less, and even more preferably 5.5 mL / 5 g or less.

[0044] The oil absorption of the composite hydroxide is measured by the following method. First, 5 g of the composite hydroxide is placed on a stainless steel plate. Then, using a burette, commercially available boiled linseed oil is dropped little by little onto the plate, and the mixture is spread evenly using a spatula. This spreading process is repeated until the small particles in the mixture of composite hydroxide and boiled linseed oil aggregate and form clumps of the sample. After the clumps of the sample are formed, one more drop of boiled linseed oil is added and mixed until a uniform putty-like consistency is achieved. This putty should be spreadable without cracking or crumbling, and should adhere lightly to the stainless steel plate. The value on the burette is read, and the amount of boiled linseed oil used is taken as the oil absorption amount.

[0045] It is preferable that complex hydroxides have high miscibility with other compounds (e.g., solids). Since substances with high miscibility with other compounds also have high dispersibility themselves, the degree of miscibility can be evaluated by the degree of dispersibility. A positive correlation is known to exist between high dispersibility and high oil absorption. Therefore, complex hydroxides have high miscibility with other compounds because their oil absorption falls within the aforementioned range.

[0046] In order to keep the oil absorption within the above-mentioned range, it is preferable to generate turbulence in the liquid or adjust the pH of the reaction solution or the rate of addition of the metal ion aqueous solution in the manufacturing method described later.

[0047] It is preferable that the density of the composite hydroxide is within a predetermined range. This makes it easier to mix the composite hydroxide with other compounds, for example, when using other compounds with a density close to that of the composite hydroxide as raw materials for the positive electrode active material. As a result, the miscibility of these mixtures is improved, and a positive electrode active material that can successfully manufacture high-performance batteries can be obtained. From the viewpoint of making this effect even more pronounced, the density d of the composite hydroxide measured by the gas displacement method is ＯＨ 4.00 g / cm³ ３ Preferably, it is 4.05 g / cm³ or more. ３ It is even more preferable that the amount be greater than or equal to 4.10 g / cm³. ３ The above is even more preferable. From a similar viewpoint, the density d of the composite hydroxide measured by the gas displacement methodＯＨ It is 4.99 g / cm³ ３ Preferably, it is 4.95 g / cm³. ３ It is even more preferable that the following conditions be met: 4.90 g / cm³ ３ It is even more preferable that the following conditions be met: 4.45 g / cm³ ３ It is even more preferable that the following conditions are met: The density of lithium carbonate measured by the gas displacement method is approximately 2.00 g / cm³. ３ 2.40g / cm or more ３ The density d of the composite hydroxide is as follows: ＯＨ Since the density is sufficiently close to that of lithium carbonate, and their miscibility is high, composite hydroxides can be used to effectively produce, for example, spinel-type lithium transition metal composite oxides. In this specification, when there are no closed pores in the composite hydroxide and lithium carbonate, the density d ＯＨ This refers to true density, and if closed pores exist, the density d ＯＨ This refers to apparent density.

[0048] density d of complex hydroxide ＯＨ The density is measured using a density measuring device (BELPycno Ver1.04A, manufactured by Microtrac-Bell Co., Ltd.) by the gas displacement method. Pretreatment is performed by purging three times. The measurement is performed in true density mode. The composite hydroxide is measured as is without grinding. For density measurement, the attached dedicated sample basket is used, and approximately 2 g of composite hydroxide is filled into the sample basket for measurement. In this way, the density d of the composite hydroxide is measured. ＯＨ (g / cm ３ ) Measure.

[0049] density d ＯＨ To achieve the above-mentioned range, it is preferable to adjust the pH of the reaction solution or the rate of addition of the metal ion aqueous solution.

[0050] It is preferable for the composite hydroxide to have a broad particle size distribution. This is because a broad particle size distribution allows for high mixability of the composite hydroxide. The degree of broad particle size distribution of the composite hydroxide is determined by the cumulative particle size at a cumulative volume of 10% by laser diffraction scattering particle size distribution measurement method, D １０ (Hereafter simply referred to as "particle size D")１０ It is also called ". ) and the cumulative volume particle size D at 90% of the cumulative volume, as measured by laser diffraction scattering particle size distribution analysis. ９０ (Hereafter simply referred to as "particle size D") ９０ It is also called ". ) When D ９０ / D １０ It can be defined by the following. Specifically, from the viewpoint of improving the miscibility of the complex hydroxide, D ９０ / D １０ It is preferable that it is 1.5 or higher, more preferably 1.8 or higher, and even more preferably 2.0 or higher. From a similar viewpoint, D ９０ / D １０ It is preferable that the value is 5.0 or less, more preferably 4.8 or less, and even more preferably 4.6 or less.

[0051] In a composite hydroxide, it is preferable from the viewpoint of obtaining a composite hydroxide capable of producing a positive electrode active material that can manufacture a high-performance battery, such that the individual particle sizes constituting its particle size distribution are within a predetermined range. Specifically, from the viewpoint of durability when used as a positive electrode active material, the composite hydroxide has a volume cumulative particle size D at 50% cumulative volume as measured by laser diffraction scattering particle size distribution analysis. ５０ (Hereafter simply referred to as "particle size D") ５０ It is also called ". The particle size D of the composite hydroxide is preferably 3.0 μm or larger, more preferably 3.5 μm or larger, even more preferably 4.0 μm or larger, and even more preferably 7.5 μm or larger. Furthermore, from the viewpoint of the output characteristics when used as a positive electrode active material, the particle size D of the composite hydroxide is also preferable. ５０ The particle size is preferably 20.0 μm or less, more preferably 19.0 μm or less, and even more preferably 18.0 μm or less.

[0052] Particle size D ５０It has the meaning as an alternative value of the average diameter of particles including primary particles and secondary particles. The "primary particle" means the smallest unit particle surrounded by grain boundaries when observed with a SEM (scanning electron microscope, for example, 500 to 5000 times magnification). On the other hand, in this specification, the "secondary particle" means a particle in which a plurality of primary particles aggregate so as to share a part of their outer peripheries (grain boundaries) and is independent from other particles.

[0053] Also, from the viewpoint of durability when used as a positive electrode active material, the particle size D １０ of the composite hydroxide is preferably 1.0 μm or more, more preferably 1.2 μm or more, and still more preferably 1.4 μm or more. Also, from the viewpoint of output characteristics when used as a positive electrode active material, the particle size D １０ of the composite hydroxide is preferably 10.0 μm or less, more preferably 9.5 μm or less, and still more preferably 9.0 μm or less.

[0054] From the viewpoint of durability when used as a positive electrode active material, the particle size D ９０ of the composite hydroxide is preferably 6.0 μm or more, more preferably 6.5 μm or more, and still more preferably 7.0 μm or more. Also, from the viewpoint of output characteristics when used as a positive electrode active material, the particle size D ９０ of the composite hydroxide is preferably 37.0 μm or less, more preferably 36.0 μm or less, and still more preferably 35.0 μm or less. The particle size D ５０ of the composite hydroxide, the particle size D １０ and the particle size D ９０ can be measured in the same manner as the average particle size D ５０ of the positive electrode active material.

[0055] The particle size D ５０ of the composite hydroxide, the particle size D ９０ and the particle size D １０ To make them within the above ranges, it is preferable to adjust the concentration of the basic aqueous solution, the concentration of the metal ion aqueous solution, or the peripheral speed of the stirring device in the manufacturing method described later.

[0056] The composite hydroxide preferably has a BET specific surface area within a predetermined range. Specifically, from the perspective of increasing the packing property and mixing property of the composite hydroxide by increasing the oil absorption amount, the BET specific surface area of the composite hydroxide is preferably 15.0 m ２ / g or more, more preferably 16.0 m ２ / g or more, and even more preferably 17.0 m ２ / g or more. Also, in the manufacturing method described later, from the perspective of reducing the moisture content of the composite hydroxide during the drying process and lowering the energy cost related to drying, the BET specific surface area of the composite hydroxide is preferably 65.0 m ２ / g or less, more preferably 64.0 m ２ / g or less, and even more preferably 63.0 m ２ / g or less. The BET specific surface area of the composite hydroxide can be measured by the same method as the BET specific surface area SSA of the positive electrode active material.

[0057] As described above, the composite hydroxide preferably has a low packing property. Therefore, it is also preferable that the apparent density of the composite hydroxide is low. Specifically, from the perspective of reducing the packing property and firing in a state where oxygen permeates throughout the composite hydroxide, the apparent density of the composite hydroxide is preferably 0.90 g / cm ３ or less, more preferably 0.80 g / cm ３ or less, even more preferably 0.70 g / cm ３ or less, and even more preferably 0.50 g / cm ３ or less. From the perspective of making the above effects more remarkable, the lower the apparent density of the composite hydroxide, the better. However, from the perspective of adjusting the reaction with oxygen when firing the composite hydroxide, the apparent density of the composite hydroxide is preferably 0.30 g / cm ３ or more, more preferably 0.32 g / cm ３ or more, and even more preferably 0.34 g / cm ３ or more. The method for measuring the apparent density will be described in the examples below.

[0058] Because composite hydroxides have low packing properties, a low tap density is also desirable. Specifically, from the viewpoint of reducing packing properties and ensuring oxygen is distributed throughout the composite hydroxide during firing, a tap density of 1.30 g / cm³ for the composite hydroxide is preferable. ３ Preferably, it is 1.20 g / cm³. ３ It is even more preferable that the following is the case: 1.10 g / cm³ ３ It is even more preferable that the concentration be less than 1.00 g / cm³. ３ It is even more preferable that the following conditions are met. From the viewpoint of making the above-mentioned effects even more pronounced, the lower the tap density of the composite hydroxide, the better. However, from the viewpoint of adjusting the reaction with oxygen when calcining the composite hydroxide, a tap density of 0.50 g / cm³ of the composite hydroxide is preferable. ３ Preferably, it is 0.52 g / cm³ or more. ３ It is even more preferable that the concentration be greater than or equal to 0.54 g / cm³. ３ The above is even more preferable. A detailed method for measuring tap density will be described in the examples below.

[0059] In order to set the BET specific surface area, apparent density, and tap density within the above-mentioned range, it is preferable to adjust the pH of the reaction solution, the rate of addition of the metal salt, or the peripheral speed of the stirring device in the manufacturing method described later.

[0060] <Process for preparing the complex hydroxide> Next, the process for preparing the complex hydroxide will be explained. This process is carried out by adding a metal ion aqueous solution and a basic aqueous solution while stirring water to generate the complex hydroxide.

[0061] First, a basic aqueous solution is prepared. A basic aqueous solution can be prepared by mixing a basic compound with water. Examples of basic compounds include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, as well as ammonia. One basic compound or two or more basic compounds can be used. In the complex hydroxide formation reaction described later, from the viewpoint of successfully obtaining the desired complex hydroxide by minimizing the coprecipitation of nickel and manganese, it is preferable that the basic compound is at least one of sodium hydroxide and ammonia, and more preferably sodium hydroxide. This is because the coprecipitation of nickel and manganese tends to increase the packing density of the desired complex hydroxide.

[0062] There are no particular restrictions on the method of mixing the basic compound with water. For example, one method is to stir the water and then add the basic compound to it and mix. When using two or more basic compounds in combination, they may be added simultaneously or sequentially.

[0063] From the viewpoint of successfully obtaining complex hydroxides, the concentration of the basic compound in the basic aqueous solution is preferably adjusted to 10.0 mol / L or higher, more preferably 11.0 mol / L or higher, and even more preferably 12.0 mol / L or higher. From a similar viewpoint, the concentration of the basic compound in the basic aqueous solution is preferably adjusted to 15.0 mol / L or lower, more preferably 14.0 mol / L or lower, and even more preferably 13.0 mol / L or lower.

[0064] Prepare a metal ion aqueous solution along with a basic aqueous solution. The metal ion aqueous solution can be prepared by mixing a metal ion source with water. As the metal ion source, a water-soluble salt of a metal element can be used. At least nickel and manganese are used as metal elements. In addition, other metal elements such as Na, Mg, B, Al, K, Ca, Ti, V, Cr, Fe, Co, Cu, Ga, Y, Zr, Nb, Mo, In, Ta, W, Re, and Ce may be used. As water-soluble salts of these metal elements, for example, salts, complexes, and chlorides of nickel, manganese, and other metal elements can be used. These can be used individually or in combination of two or more. As salts of nickel, manganese, and other metal elements, for example, oxo salts such as sulfates, nitrates, phosphates, and phosphates, and organic salts such as oxalates and acetates can be used. As complexes of nickel, manganese, and other metal elements, for example, ammine complex salts, as well as complexes and complex salts with other organic ligands can be used. From the viewpoint of successfully obtaining complex hydroxides, the metal ion source is preferably at least one of nickel and manganese sulfates, nitrates, and ammine complex salts, and more preferably nickel and manganese sulfates.

[0065] There are no particular restrictions on the method of mixing the metal ion source with water. For example, one method is to stir the water and then add the metal ion source and mix it. When using two or more metal ion sources in combination, they may be added together or simultaneously. This prepares an aqueous metal ion solution containing at least nickel ions and manganese ions.

[0066] It is preferable to use a metal ion source such that the concentrations of various metal ions in the metal ion aqueous solution are within a predetermined range. Specifically, from the viewpoint of successfully obtaining complex hydroxides, it is preferable to prepare the metal ion aqueous solution so that the concentration of nickel ions is 25.0 g / L or more, more preferably 25.5 g / L or more, and even more preferably 26.0 g / L or more. From a similar viewpoint, it is preferable to prepare the metal ion aqueous solution so that the concentration of nickel ions is 33.0 g / L or less, more preferably 32.5 g / L or less, and even more preferably 32.0 g / L or less. Furthermore, from the viewpoint of successfully obtaining complex hydroxides, it is preferable to prepare the metal ion aqueous solution so that the concentration of manganese ions is 80.0 g / L or more, more preferably 81.0 g / L or more, and even more preferably 82.0 g / L or more. From a similar viewpoint, it is preferable to prepare the metal ion aqueous solution so that the concentration of manganese ions is 88.0 g / L or less, more preferably 87.0 g / L or less, and even more preferably 86.0 g / L or less.

[0067] Furthermore, from the viewpoint of successfully obtaining complex hydroxides, the molar ratio of manganese ions to nickel ions in the metal ion aqueous solution is preferably 2.60 or higher, more preferably 2.65 or higher, and even more preferably 2.70 or higher. From a similar viewpoint, the molar ratio of nickel ions to manganese ions in the metal ion aqueous solution is preferably 3.40 or lower, more preferably 3.35 or lower, and even more preferably 3.30 or lower.

[0068] When using other metal elements as a metal ion source, from the viewpoint of successfully obtaining complex hydroxides, it is preferable to prepare the aqueous metal ion solution so that the concentration of other metal ions is 1 g / L or more, more preferably 2 g / L or more, and even more preferably 3 g / L or more. From a similar viewpoint, it is preferable to prepare the aqueous metal ion solution so that the concentration of other metal ions is 15 g / L or less, more preferably 12 g / L or less, and even more preferably 10 g / L or less.

[0069] Along with the above aqueous solutions, a reaction vessel is prepared, which serves as the reaction site for the basic aqueous solution and the metal ion aqueous solution. The reaction vessel used in this manufacturing method has a distinctive feature in the shape of its inner surface. Normally, when a reaction is carried out in the liquid phase, stirring of the liquid can cause vortices to be generated in the liquid. In this case, the crystal nuclei produced by the reaction rotate in the reaction vessel with the swirling water flow, making it difficult for the crystal nuclei to come into contact with each other. While the crystal nuclei can grow easily due to the reduced contact between them, aggregation caused by contact is less likely to occur, resulting in crystals with fewer voids, i.e., high packing efficiency. In contrast, this manufacturing method controls the water flow generated in the liquid during the reaction in the liquid phase. This allows for appropriate contact between the crystal nuclei produced by the reaction, enabling both crystal nucleus growth and aggregation. As a result, crystals with low packing efficiency can be obtained. The inventors have discovered for the first time that controlling the water flow can reduce the packing efficiency of composite hydroxides.

[0070] The water flow can be controlled by combining multiple planes to form the inner surface of the reaction vessel. For example, in a reaction vessel where the inner surface is integrally curved, water flow tends to occur along the inner surface, easily creating vortices. In contrast, in the reaction vessel of this embodiment, where the inner surface is a combination of planes, turbulence is more likely to occur due to changes in the angle of the inner surface. In this specification, "turbulence" refers to water flow with a Reynolds number of 2310 or higher. Specifically, from the viewpoint of generating turbulence in the liquid and achieving both nucleation growth and aggregation during the complex hydroxide formation reaction, it is preferable that the inner surface of the reaction vessel has a combination of three or more planes. From the viewpoint of effectively generating turbulence, it is preferable that the planes in the reaction vessel are connected in a series of three or more planes. In this case, the part where three or more planes are connected only needs to be at least a part of the inner surface, and the other parts may be curved. This part may be in any part of the reaction vessel, for example, the upper, middle, and lower parts of the inner surface of the reaction vessel. From the above viewpoint, it is even more preferable that the inner surface of the reaction vessel has a combination of four or more planes. Furthermore, from a similar viewpoint, it is preferable that the inner surface of the reaction vessel has a combination of seven or fewer surfaces, more preferably six or fewer surfaces, and even more preferably five or fewer surfaces. From the viewpoint of making the above-mentioned effects even more pronounced, it is particularly preferable that the inner surface of the reaction vessel consists only of a combination of flat surfaces.

[0071] In the process of producing complex hydroxides, water is placed in a reaction vessel, and while stirring the water in the reaction vessel, a metal ion aqueous solution and a basic aqueous solution are added to the water. This produces a complex hydroxide containing at least nickel and manganese elements in the reaction solution. In this process, the addition times of the metal ion aqueous solution and the basic aqueous solution may be different, as long as there is a period of time when they are added simultaneously. Specifically, (i) the start and end times of adding the metal ion aqueous solution and the basic aqueous solution to the water may be the same, (ii) the start times of adding the metal ion aqueous solution and the basic aqueous solution to the water may be the same, but the end times may be different, (iii) the start times of adding the metal ion aqueous solution and the basic aqueous solution to the water may be different, but the end times may be the same, and (iv) the start and end times of adding the metal ion aqueous solution and the basic aqueous solution to the water may be different.

[0072] There are no particular restrictions on the method of stirring the reaction solution in the reaction vessel, and known stirring devices can be used. The stirring of the reaction solution may be continuous or intermittent. Even when the reaction solution is stirred intermittently, if there is a short period of time during which the reaction solution is not stirred, such that turbulence can be considered to be generated in the liquid, it shall be considered as continuous stirring. From the viewpoint of effectively generating turbulence in the liquid and further achieving both nucleation growth and aggregation during the complex hydroxide formation reaction, it is preferable to stir the reaction solution continuously. When stirring the reaction solution using a stirring device, it is preferable to set the peripheral speed of the device within a predetermined range. Specifically, from the viewpoint of causing the reaction solution to collide with the inner surface of the reaction vessel and facilitating the generation of turbulence, it is preferable to stir the reaction solution with a peripheral speed of 2.5 m / s or more, more preferably 2.8 m / s or more, and even more preferably 3.0 m / s or more. From a similar viewpoint, it is preferable to stir the reaction solution with a peripheral speed of 4.5 m / s or less, more preferably 4.2 m / s or less, and even more preferably 4.0 m / s or less.

[0073] During the complex hydroxide formation reaction, it is preferable to set the temperature of the reaction solution within a predetermined range. Specifically, from the viewpoint of successfully obtaining complex hydroxides by achieving an appropriate reaction rate, it is preferable to set the temperature of the reaction solution to 50°C or higher, more preferably 55°C or higher, and even more preferably 60°C or higher. From a similar viewpoint, it is preferable to set the temperature of the reaction solution to 80°C or lower, more preferably 75°C or lower, and even more preferably 70°C or lower.

[0074] During the complex hydroxide formation reaction, it is preferable to maintain the pH of the reaction solution in the reaction vessel within a predetermined range. Specifically, it is preferable to maintain the pH of the reaction solution at 9.0 or higher, more preferably 9.1 or higher, and even more preferably 9.2 or higher, from the viewpoint of successfully obtaining complex hydroxides, within a pH range where the basic aqueous solution and the metal ion aqueous solution can react. Furthermore, if the pH is too high, the rate of complex hydroxide formation is fast, very fine particles are generated, and these particles strongly aggregate, resulting in high packing density. Therefore, from the viewpoint of successfully obtaining complex hydroxides with low packing density, it is preferable to maintain the pH of the reaction solution at 9.5 or lower, more preferably 9.4 or lower, and even more preferably 9.3 or lower. pH adjustment can be performed, for example, by adjusting the addition rate of the metal ion aqueous solution or the basic aqueous solution. More specifically, for example, by adding the metal ion aqueous solution at a constant rate while appropriately adjusting the addition rate of the basic aqueous solution to match the pH of the reaction solution, the pH of the reaction solution can be controlled within the above range. Alternatively, the pH of the reaction solution can be controlled within the above range by adding the basic aqueous solution at a constant rate while appropriately adjusting the rate of addition of the metal ion aqueous solution to match the pH of the reaction solution. The addition of the basic aqueous solution or the metal ion aqueous solution may be continuous or intermittent. From the viewpoint of successfully adjusting the pH of the reaction solution, it is preferable to add the metal ion aqueous solution at a constant rate while continuously or intermittently adding the basic aqueous solution.

[0075] The addition of the metal ion aqueous solution to the water may be continuous or intermittent. Even if the metal ion aqueous solution is added intermittently, if the duration is short enough to be considered as continuous addition, it will be treated as continuous addition. From the viewpoint of successfully producing complex hydroxides, it is preferable to continuously add the metal ion aqueous solution. When continuously adding the metal ion aqueous solution, it is preferable to slow down the rate of addition of the metal ion aqueous solution during the complex hydroxide formation reaction. This is because it is possible to successfully produce complex hydroxides with low packing density. The addition rate is determined by the value of S / V ((L / hr) / L) defined by the following formula (1). A smaller S / V value means that the rate of addition of the metal ion aqueous solution is slower, and a larger S / V value means that the rate of addition of the metal ion aqueous solution is faster. S / V (1) V: Total volume of liquid in the reaction vessel at the end of the reaction (L) S: Addition rate of metal ion aqueous solution (L / hr)

[0076] From the viewpoint of successfully setting the rate of addition of the metal ion aqueous solution, it is preferable to calculate the value of V in equation (1) before the start of the reaction. The value of V is defined by the following equation (2): V = V1 + V2 + V3 (2) In equation (2), V1 is the amount of water (L) added to the reaction vessel before the formation reaction of the complex hydroxide. V2 is the amount of metal ion aqueous solution added to the water (L). V3 is the amount of basic aqueous solution added to the water (L). The value of V2 can be set appropriately according to the desired amount of complex hydroxide to be produced. For example, the ratio of the amount of water to the amount of metal ion aqueous solution added, V1 / V2, can be set to 1 / 3 or more and 3 or less. The value of V3 is the amount of basic aqueous solution required to precipitate all of the metal ions in the metal ion aqueous solution.

[0077] From the perspective of successfully obtaining low-packing composite hydroxides by balancing the formation and aggregation of crystal nuclei, an S / V value of 0.50hr －１ Preferably, the following is true: 0.40hr －１ It is even more preferable that the following conditions apply: 0.35hr －１The following is even more preferable. From the viewpoint of making the above-mentioned effects even more pronounced, the smaller the S / V value, the better. However, from the viewpoint of obtaining a composite hydroxide with low packing properties, the S / V value should be 0.08hr. －１ Preferably, it is 0.09hr －１ It is even more preferable that the above be true, and 0.10hr －１ It is even more preferable that the above conditions are met.

[0078] It is preferable to add the metal ion aqueous solution to the reaction mixture in the reaction vessel while blowing in an inert gas. This suppresses the unintended oxidation of the generated complex hydroxide. Examples of inert gases include helium, nitrogen, neon, and argon. One or more inert gases can be used. From the viewpoint of simplicity and effectively suppressing the oxidation of the complex hydroxide, it is preferable to use at least nitrogen gas. From the viewpoint of effectively suppressing the oxidation of the complex hydroxide, it is preferable to blow in a predetermined amount of inert gas. The amount blown in is determined by the value of T / V ((L / min) / L) defined by the following formula (3). A smaller value of T / V means that less inert gas is blown in, and a larger value of T / V means that more inert gas is blown in. T / V (3) V: Total volume of liquid in the reaction vessel at the end of the reaction (L) T: Amount of inert gas blown in (L / min)

[0079] From the viewpoint of successfully setting the amount of inert gas to be blown in, it is preferable to calculate the value of V in equation (3) before the reaction starts. The value of V is defined by equation (2) above.

[0080] From the perspective of effectively suppressing the oxidation of complex hydroxides, the T / V value is 0.08 min. －１ Preferably, it is 0.09 min －１ It is even more preferable that the above be true, and 0.10 min －１ It is even more preferable that the above is true. From a similar viewpoint, the value of T / V is 0.25 min. －１ Preferably, the following: 0.24 min －１ It is even more preferable that the following conditions be met: 0.23 min －１The following is even more preferable:

[0081] The inert gas may be blown into the reaction mixture from one location in the reaction vessel, or from multiple locations simultaneously, depending on the volume of the reaction vessel. The inert gas may be blown into the reaction mixture continuously or intermittently. Even if the inert gas is blown in intermittently, if the duration is short enough to be considered as continuous blowing, it will be treated as continuous blowing. Only one type of inert gas may be blown into the reaction mixture, or two or more types of inert gases may be blown in. When two or more types of inert gases are blown into the reaction mixture, the value T mentioned above refers to the total amount of inert gas blown in.

[0082] Once the complex hydroxide is formed in the reaction solution, the reaction solution is then separated into solid and liquid components by decantation and filtration to remove the complex hydroxide from the reaction solution. After that, the complex hydroxide is washed with water and dried. From the viewpoint of successfully removing moisture from the complex hydroxide and obtaining a positive electrode active material that can easily manufacture high-performance batteries with high thermal efficiency, it is preferable to dry the complex hydroxide at 80°C or higher, more preferably at 90°C or higher, and even more preferably at 100°C or higher. From a similar viewpoint, it is preferable to dry the complex hydroxide at 200°C or lower, more preferably at 190°C or lower, and even more preferably at 180°C or lower. Furthermore, from the viewpoint of successfully removing moisture from the complex hydroxide and obtaining a positive electrode active material that can easily manufacture high-performance batteries with high thermal efficiency, it is preferable to dry it for 1 hour or more, more preferably at 8 hours or more, even more preferably at 10 hours or more, and even more preferably at 12 hours or more. From a similar viewpoint, it is preferable to dry the composite hydroxide for 1000 hours or less, more preferably 150 hours or less, even more preferably 120 hours or less, and even more preferably 100 hours or less. In this way, the desired composite hydroxide can be obtained.

[0083] <Process for producing positive electrode active material using composite hydroxide> Once the composite hydroxide is obtained, it is then mixed with a lithium compound and a sintering aid to obtain a mixture. Examples of lithium compounds include lithium hydroxide (LiOH) and lithium carbonate (Li ２ CO ３ ), lithium nitrate (LiNO) ３ ), LiOH・H ２ O, Lithium oxide (Li ２ Examples include lithium fatty acids and lithium halides. Among these, lithium carbonate is preferred. Boron compounds are preferred as sintering aids. Specifically, for example, lithium tetraborate, (Li ２ B ４ O ７ ), boric acid (H ３ BO ３ ), Lithium metaborate (LiBO ２ ), lithium pentaborate (LiB ５ O ８ ) and lithium perborate (Li ２ B ２ O ５ ) etc. can be used.

[0084] The mixing ratio of the composite hydroxide and the lithium compound can be appropriately adjusted according to the elemental composition of the desired composite oxide. The amount of sintering aid mixed in can preferably be 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.2% by mass or more, relative to the total amount of the composite hydroxide, lithium compound, and sintering aid. By using such an amount of sintering aid, the sintering temperature of the mixture in the next firing step can be sufficiently reduced. Furthermore, from the viewpoint of obtaining a positive electrode active material having the desired properties while sufficiently reducing the sintering temperature, the amount of sintering aid mixed in is preferably 1.4% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less, relative to the total amount of the composite hydroxide, lithium compound, and sintering aid.

[0085] There are no particular restrictions on the order in which the composite hydroxide, lithium compound, and sintering aid are mixed; any two components may be mixed first, followed by the remaining components, or all three components may be mixed simultaneously. There are no particular restrictions on the method of mixing the composite hydroxide, lithium compound, and sintering aid; wet mixing or dry mixing may be used.

[0086] The mixture may contain other components besides the composite hydroxide, lithium compound, and sintering aid described above. Examples of such components include titanium(IV) oxide. By including titanium(IV) oxide in the mixture, the crystal structure of the resulting composite oxide can be reinforced, and the elution of metal elements from the composite oxide can be suppressed. From this viewpoint, the titanium(IV) oxide content in the mixture is preferably 3% by mass or more, more preferably 4% by mass or more, and even more preferably 5% by mass or more. On the other hand, from the viewpoint of ensuring a balance between reinforcing the crystal structure and the battery characteristics due to the amount of composite oxide, the content of other components such as titanium(IV) oxide in the mixture is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less.

[0087] From the viewpoint of facilitating smoother mixing of the complex hydroxide and the lithium compound, it is preferable that the density of the complex hydroxide and the density of the lithium compound do not differ significantly. Specifically, when mixing the complex hydroxide and the lithium compound, the density of the lithium compound d Ｌｉ The density d of the complex hydroxide relative to ＯＨ ratio d ＯＨ / d Ｌｉ It is preferable to mix the two so that the ratio is 2.10 or less, more preferably 2.00 or less, and even more preferably 1.90 or less. Also, the density ratio d ＯＨ / d Ｌｉ A value closer to 1 is preferable, but a value of 1.80 or higher, or 1.82 or higher, is more practical. Ｌｉ is, d ＯＨ Similarly, this is the density measured by the gas displacement method. Therefore, d Ｌｉ This refers to the apparent density when closed pores exist in the lithium compound, and the true density when closed pores do not exist. d ＯＨ The value and dＬｉ The value of the ratio d varies depending on the state of each substance. ＯＨ / d Ｌｉ The measured d ＯＨ The maximum value and d Ｌｉ This is the value obtained by comparing the maximum values ​​of the two values.

[0088] The composite hydroxide produced by the method described above has a density d as described above. ＯＨ Preferably 4.00 g / cm³ ３ 4.99g / cm or more ３ The following is true: By using a composite hydroxide having such density in a mixture with a lithium compound, the density ratio of the two is d ＯＨ / d Ｌｉ This can be easily set within the above-mentioned numerical range.

[0089] Next, the mixture is calcined in an oxygen-containing atmosphere to produce a positive electrode active material having a spinel-type crystalline structure. The calcination temperature is preferably 600°C or higher, more preferably 700°C or higher, and even more preferably 750°C or higher. Alternatively, the calcination temperature is preferably 1000°C or lower, more preferably 950°C or lower, and even more preferably 870°C or lower. The calcination time is preferably 0.5 hours or more, more preferably 3 hours or more, and even more preferably 5 hours or more. Alternatively, the calcination time is preferably 50 hours or less, more preferably 45 hours or less, and even more preferably 35 hours or less.

[0090] The firing atmosphere preferably contains more than 21% by volume of oxygen, more preferably 50% by volume or more, and even more preferably 80% by volume or more. By firing the mixture in an atmosphere with such an oxygen content, a positive electrode active material having the angle of repose and collapse angle within the above-mentioned numerical range, the above-mentioned tap density TD and BET specific surface area SSA, and the above-mentioned crystalline structure can be easily obtained. There is no particular upper limit on the oxygen content in the firing atmosphere, and firing may be carried out in an atmosphere of 100% oxygen gas. There is no particular limit on components other than oxygen in the firing atmosphere, and inert gases such as nitrogen and argon can be used, for example.

[0091] From the viewpoint of ensuring a sufficient reaction between the mixture and oxygen, it is preferable to calcine the mixture while circulating the calcination atmosphere. During the heating process until the target calcination temperature is reached, the temperature may be continuously increased over time, or a period of time may be provided during the heating process when the temperature remains constant.

[0092] After calcining the mixture, a re-oxidation treatment may be performed as needed. By performing a re-oxidation treatment, the amount of oxygen deficiency in the composite oxide constituting the positive electrode active material can be reduced. By reducing the amount of oxygen deficiency, the elution of metal elements from the composite oxide can be suppressed. The re-oxidation treatment is carried out by heat-treating the composite oxide after calcination. The temperature of the re-oxidation treatment is preferably 300°C or higher, more preferably 400°C or higher, and even more preferably 500°C or higher. Alternatively, the temperature of the re-oxidation treatment is preferably 900°C or lower, more preferably 850°C or lower, and even more preferably 800°C or lower. In particular, performing the re-oxidation treatment at a high temperature tends to further promote sintering between particles, resulting in a decrease in the BET specific surface area (SSA) of the resulting positive electrode active material. The duration of the re-oxidation treatment is preferably 0.5 hours or more, more preferably 2 hours or more, and even more preferably 5 hours or more. Alternatively, the duration of the re-oxidation treatment is preferably 50 hours or less, more preferably 45 hours or less, and even more preferably 40 hours or less. The atmosphere for the re-oxidation treatment can be an air atmosphere or an oxygen-containing atmosphere such as an oxygen atmosphere.

[0093] The re-oxidation treatment may be carried out by firing the mixture at the firing temperature and then lowering the temperature to the re-oxidation treatment temperature, or by firing the mixture at the firing temperature, cooling it to room temperature, and then raising the temperature again to the re-oxidation treatment temperature. In either case, during the process of reaching the target temperature, the temperature may be continuously changed over time, or a period of time may be provided during the temperature change when the temperature becomes constant.

[0094] The positive electrode active material obtained by the above manufacturing method can be transformed into a powder with a desired particle size by crushing or classifying, if necessary.

[0095] [Electrode Mixture] The positive electrode active material of the present invention can be used, for example, in the form of an electrode mixture containing the positive electrode active material and an electrolyte. The electrolyte may be solid or liquid. When a solid electrolyte is used as the electrolyte, the content of the positive electrode active material in the electrode mixture may be 30% by mass or more, 40% by mass or more, or 50% by mass or more, when the total solid content is considered to be 100% by mass. Alternatively, the content of the positive electrode active material may be, for example, 98% by mass or less, 90% by mass or less, or 85% by mass or less. By having the content of the positive electrode active material within the above range, the electrode can fully exhibit its function.

[0096] The electrolyte that can be used in the present invention can be the same as the electrolyte used in general liquid-type batteries, and may be a non-aqueous electrolyte or an aqueous electrolyte. For example, organic electrolytes, polymer solid electrolytes, molten salts, etc. can be used. Examples of organic electrolytes as solvents include esters such as propylene carbonate, ethylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, substituted tetrahydrofurans such as tetrahydrofuran and 2-methyltetrahydrofuran, ethers such as dioxolane, diethyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, dimethyl sulfoxide, sulfolane, methylsulfolane, acetonitrile, methyl formate, methyl acetate, etc., and one or more of these as mixed solvents can be used. In addition, examples of electrolyte salts that dissolve in organic solvents include lithium perchlorate, lithium borofluoride, lithium hexafluoride phosphate (hereinafter referred to as "LiPF") ６ Examples include lithium salts such as lithium hexafluoride, lithium trifluoromethanesulfonate, lithium halides, and lithium aluminate chloride.

[0097] The solid electrolyte that can be used in the present invention can be the same as the solid electrolyte used in general solid batteries, as long as it has lithium ion conductivity. Examples include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, and halide solid electrolytes, but sulfide solid electrolytes are preferred. The sulfide solid electrolyte may contain lithium (Li) and sulfur (S) and have lithium ion conductivity, or it may contain lithium (Li), phosphorus (P), and sulfur (S) and have lithium ion conductivity. The sulfide solid electrolyte may be a crystalline material, glass ceramic, or glass. The sulfide solid electrolyte may have a crystalline phase with an argyrodite structure. Examples of such sulfide solid electrolytes include Li ２ S-P ２ S ５ Li ２ S-P ２ S ５ - LiX (where "X" indicates one or more halogen elements), Li ２ S-P ２ S ５ -P ２ O ５ Li ２ S-Li ３ PO ４ -P ２ S ５ Li ３ PS ４ Li ４ P ２ S ６ Li １０ GeP ２ S １２ Li ３．２５ Ge ０．２５ P ０．７５ S ４ Li ７ P ３ S １１ Li ３．２５ P ０．９５ S ４ Li ａ PS ｂ X ｃExamples include compounds represented by (X is at least one halogen element; a represents a number between 3.0 and 6.0; b represents a number between 3.5 and 4.8; c represents a number between 0.1 and 3.0). In addition, examples include sulfide solid electrolytes described in WO2013 / 099834A1 and WO2015 / 001818A1.

[0098] The positive electrode active material contained in the electrode mixture may consist solely of the positive electrode active material of the present invention, or it may be a combination of the positive electrode active material of the present invention and other positive electrode active materials. Examples of other positive electrode active materials include particles made of known lithium transition metal composite oxides. When using the positive electrode active material of the present invention in combination with other positive electrode active materials, it is preferable that the positive electrode active material of the present invention is contained in an amount of 50% by mass or more, and particularly 70% by mass or more, relative to the total positive electrode active material.

[0099] [Battery] The positive electrode active material of the present invention can be suitably used as a positive electrode active material for a battery. The battery may be a primary battery or a secondary battery. The battery of the present invention may, for example, have a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer and containing an electrolyte. The positive electrode layer contains the positive electrode active material of the present invention. The positive electrode active material of the present invention is particularly suitably used as a positive electrode active material for a non-aqueous electrolyte secondary battery in which the electrolyte is liquid.

[0100] The present invention includes the following technical concepts: [1] A positive electrode active material containing a composite oxide comprising lithium (Li), nickel (Ni), and manganese (Mn), wherein the angle of repose is 55.0 degrees or more and 65.0 degrees or less, and the collapse angle is 43.0 degrees or more and 60.0 degrees or less. [2] The positive electrode active material according to [1], wherein the difference angle is less than 13.0 degrees. [3] The positive electrode active material according to [1] or [2], wherein the arithmetic mean perimeter of the primary particles is 8.0 μm or less. [4] The positive electrode active material according to any one of [1] to [3], having a spinel-type crystal structure and an a-axis length of 8.150 Å or more and 8.200 Å or less. [5] A positive electrode active material according to any one of [1] to [4], having a coating layer on its surface containing the element Li (lithium), the element A (where A represents one or more elements selected from the group consisting of Ti, B, P, Zr, Ta, Nb, Zn, W, La, and Al), and the element O (oxygen). [6] A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer and containing an electrolyte, wherein the positive electrode layer contains the positive electrode active material according to any one of [1] to [5]. [7] A method for producing a positive electrode active material, comprising mixing a composite hydroxide containing nickel (Ni) and manganese (Mn) elements, a lithium compound, and a sintering aid to obtain a mixture, and then firing the mixture in an oxygen-containing atmosphere, wherein the composite hydroxide has an oil absorption amount of 3.0 mL / 5 g or more and 6.5 mL / 5 g or less as measured in accordance with JIS K 5101:2004, and the oxygen-containing atmosphere contains more than 21.0 volume percent of oxygen. [8] The method according to [7], wherein a boron compound is used as the sintering aid. [9] The method according to [8], wherein lithium tetraborate is used as the boron compound.

[0101] The present invention will be described in more detail below with reference to examples. However, the scope of the present invention is not limited to these examples. Unless otherwise specified, "%" means "mass%".

[0102] [Example 1] <Preparation of Composite Hydroxide> 9600 g of nickel sulfate hexahydrate and 19400 g of manganese sulfate monohydrate were added to 75 L of pure water and stirred to prepare a metal ion aqueous solution. The total molar concentration of nickel and manganese in the metal ion aqueous solution was 2.0 mol / L. Water was added to a reaction vessel consisting of a combination of four flat inner surfaces (i.e., a reaction vessel with a rectangular cross-section), and the water was stirred to generate turbulence. While continuously blowing nitrogen gas into this reaction vessel, the metal ion aqueous solution and a 12.5 mol / L sodium hydroxide aqueous solution were added simultaneously to generate a composite hydroxide. Subsequently, the addition of the metal ion aqueous solution and the sodium hydroxide aqueous solution was stopped simultaneously. The metal ion aqueous solution was added continuously, and the addition rate S was S / V of 0.11hr －１ The rate at which the reaction was performed was as follows: The amount of water V1 was 5.3 L, the amount of metal ion aqueous solution added V2 was 5.3 L, and the amount of sodium hydroxide aqueous solution added V3 was 1.7 L. The sodium hydroxide aqueous solution was added at a rate that maintained the pH of the reaction solution at 9.3. The nitrogen gas injection rate T / V was 0.12 min. －１ The reaction mixture was stirred at a peripheral speed of 3.1 m / s and at a temperature of 65°C. The reaction mixture was separated into solid and liquid by decantation to separate the composite hydroxide. This was heated and dried at 120°C for 12 hours to obtain the target composite hydroxide. X-ray diffraction (XRD) analysis of this composite hydroxide confirmed the presence of nickel and manganese elements in the form of hydroxides. The nickel and manganese content in the composite hydroxide was measured by ICP emission spectrometry in accordance with JIS K 0116:2014, and it was found that the composite hydroxide had the compositional formula Ni ０．２５ Mn ０．７５ The compound was represented as OOH. The oil absorption capacity of this complex hydroxide was 4.75 mL / 5 g, and the density measured by gas displacement was 4.37 g / cm³. ３ The apparent density is 0.40 g / cm³. ３ The tap density is 0.76 g / cm³. ３ Particle size D ５０ It was 11.4 μm.

[0103] <Manufacturing of positive electrode active material> The composite hydroxide prepared by the method described above has a density d measured by the gas displacement method. Ｌｉ 2.20 g / cm³ ３ A mixture was obtained by mixing the composite hydroxide with lithium carbonate, titanium dioxide, and lithium tetraborate. The mixing ratio of the composite hydroxide, lithium carbonate, and titanium dioxide was set so that the molar ratio of Li, Ni, Mn, and Ti in the resulting positive electrode active material was Li:Ni:Mn:Ti = 1:0.4:1.2:0.2. This mixture was calcined under the conditions shown in Table 1. The calcination atmosphere was 100% by volume of oxygen, and the mixture was calcined while this atmosphere was circulated. Next, a re-oxidation treatment was performed at the temperature and time shown in Table 1. The atmosphere for the re-oxidation treatment was the same as the calcination atmosphere. The calcined material obtained by the re-oxidation treatment was pulverized using a pin mill, and then classified using a sieve with a mesh size of 53 μm, and the sieved material was collected to obtain the positive electrode active material.

[0104] [Example 2] The same procedure as in Example 1 was followed, except that titanium oxide was not used in the preparation of the mixture. The mixing ratio of the composite hydroxide and lithium carbonate was set to a ratio such that the molar ratio of Li, Ni, and Mn in the resulting positive electrode active material was Li:Ni:Mn = 1:0.5:1.4. The positive electrode active material was obtained in the same manner as in Example 1.

[0105] [Examples 3 and 4] Positive electrode active material was obtained in the same manner as in Example 1, except that the firing conditions and re-oxidation treatment conditions shown in Table 1 were used.

[0106] [Comparative Example 1] In the preparation of the composite hydroxide in Example 1, instead of a reaction vessel consisting of a combination of flat inner surfaces, a reaction vessel with an integrally curved inner surface (i.e., a reaction vessel with a circular cross-section) was used. Also, the addition rate S of the metal ion aqueous solution was set to S / V = 0.03hr －１ The reaction rate was set to achieve the desired result. The sodium hydroxide solution was added at a rate that maintained the pH of the reaction solution at 10.0. The nitrogen gas injection rate T / V was 0.12 min. －１The reaction mixture was stirred at a peripheral speed of 1.0 m / s and at a temperature of 40°C. The resulting composite hydroxide was dried at 80°C for 24 hours. The oil absorption of this composite hydroxide was 1.75 mL / 5 g, and the density measured by gas displacement was 4.50 g / cm³. ３ Therefore, the apparent density is 1.00 g / cm³. ３ The tap density is 1.79 g / cm³. ３ Particle size D ５０ The particle size was 10.5 μm. The composite hydroxide obtained in this manner was subjected to the calcination and re-oxidation treatment conditions shown in Table 1 to obtain a positive electrode active material. Except for the points mentioned above, the procedure was the same as in Example 1.

[0107]

[0108] [Evaluation] For the positive electrode active materials obtained in the examples and comparative examples, the angle of repose and collapse angle were measured using the method described above, and the difference angle was calculated. In addition, the particle size D was measured using the method described above. ５０ The arithmetic mean perimeter and circularity of the primary particles were also measured. Furthermore, the BET specific surface area (SSA), apparent density, tap density (TD), and a-axis length of the crystal were measured using the following method. In addition, the quantitative accuracy during discharge from the feeder was evaluated using the following method. The results are shown in Table 2 below.

[0109] [BET Specific Surface Area SSA] The specific surface area was measured using a nitrogen-helium mixed gas containing 30% by volume of nitrogen as the adsorbent gas and 70% by volume of helium as the carrier gas, and a specific surface area measuring device (e.g., Macorb manufactured by Mountec Co., Ltd.), according to "(3.5) Single-point method" of "6.2 Flow method" in JIS R 1626 "Method for measuring the specific surface area of ​​fine ceramic powder by gas adsorption BET method". Preliminary degassing conditions were 10 minutes at 250°C under atmospheric pressure. Degassing was also performed at 250°C for 1 minute before the main measurement.

[0110] [Apparent Density] The apparent density was measured in accordance with JIS Z2512 using a tapping machine (model: KSR-406, manufactured by Kuramochi Kagaku Kikai Seisakusho Co., Ltd.). In detail, a volume of 150 cm³ was measured. ３50g of composite hydroxide was placed in a graduated cylinder. The tap stroke was set to 6cm and the number of taps to 100 for measurement.

[0111] [Tap Density TD] Tap density was measured in accordance with JIS Z2512 using a tapping machine (model: KSR-406, manufactured by Kuramochi Kagaku Kikai Seisakusho Co., Ltd.). In detail, a volume of 150 cm³ was measured. ３ 50 g of composite hydroxide was placed in a graduated cylinder. The tap stroke was set to 6 cm and the number of taps to 510 for measurement.

[0112] [Crystal a-axis length] Measurements were taken using a fully automated multi-purpose X-ray diffractometer D8 ADVANCE (manufactured by BRUKER), and the a-axis length was calculated using TOPAS-version 6 software.

[0113] [Quantitative accuracy during discharge from the feeder] A feeder consisting of a coil feeder and a small motor (Oriental Motor: M590-502C) was installed at the bottom of the hopper. The discharge rate of the positive electrode active material from the feeder was set to 2 kg / min. After the discharge operation stopped, the amount of positive electrode active material that collapsed and was discharged from the feeder was measured to evaluate the quantitative accuracy. Specifically, if the amount of positive electrode active material discharged after the discharge operation stopped exceeded 5% of the supply amount, it was evaluated as "×" because the fluidity was high and the quantitative accuracy of the measurement was lost. On the other hand, if the amount of positive electrode active material discharged after the discharge operation stopped was 5% or less of the supply amount, it was evaluated as "○" because the quantitative accuracy was good.

[0114]

[0115] As is clear from the results shown in Table 2, the positive electrode active material in each example exhibits good quantitative accuracy when discharged from the feeder.

[0116] The present invention provides a positive electrode active material that has appropriate fluidity, thereby improving quantitative accuracy in feeders. The present invention also provides a method for easily producing such a positive electrode active material. The positive electrode active material of the present invention is advantageous in that particle aggregation is less likely to occur even when wet coating is performed, and a highly uniform coating layer can be formed by the coating process. As a result, the occurrence of defective products and battery degradation can be suppressed when manufacturing batteries using the positive electrode active material of the present invention. Consequently, waste can be reduced and energy costs can be reduced during battery manufacturing and use. Due to these advantages, the positive electrode active material of the present invention enables the sustainable management and efficient use of natural resources, and promotes decarbonization (carbon neutrality) in battery manufacturing and use.

Claims

1. A positive electrode active material containing a composite oxide comprising lithium (Li), nickel (Ni), and manganese (Mn), having an angle of repose of 55.0 degrees or more and 65.0 degrees or less, and a collapse angle of 43.0 degrees or more and 60.0 degrees or less.

2. The positive electrode active material according to claim 1, wherein the angle of difference is less than 13.0 degrees.

3. The positive electrode active material according to claim 1, wherein the arithmetic mean circumference of the primary particles is 8.0 μm or less.

4. The positive electrode active material according to claim 1, having a spinel-type crystal structure and an a-axis length of 8.150 Å or more and 8.200 Å or less.

5. The positive electrode active material according to claim 1, having a coating layer on its surface containing the elements Li (lithium), A (where A represents one or more elements selected from the group consisting of Ti, B, P, Zr, Ta, Nb, Zn, W, La, and Al), and O (oxygen).

6. A battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer and containing an electrolyte, wherein the positive electrode layer contains the positive electrode active material described in any one of claims 1 to 5.

7. A method for producing a positive electrode active material, comprising mixing a composite hydroxide containing nickel (Ni) and manganese (Mn) elements, a lithium compound, and a sintering aid to obtain a mixture, and then firing the mixture in an oxygen-containing atmosphere, wherein the composite hydroxide has an oil absorption capacity of 3.0 mL / 5 g or more and 6.5 mL / 5 g or less as measured in accordance with JIS K 5101:2004, and the oxygen-containing atmosphere contains more than 21.0 volume percent of oxygen.

8. The manufacturing method according to claim 7, wherein a boron compound is used as the sintering aid.

9. The manufacturing method according to claim 8, wherein lithium tetraborate is used as the boron compound.

Images