Positive electrode active material, electrode mixture, and battery

Abstract

This positive electrode active material contains a composite oxide that contains the element lithium (Li), the element nickel (Ni), and the element manganese (Mn). Designating W1 as the mass of the positive electrode active material at 400°C as measured by thermogravimetry of the positive electrode active material in an air atmosphere, W2 as the maximum mass of the positive electrode active material at a temperature of from 500°C (inclusive) to 600°C (inclusive) as measured by said thermogravimetry, and SA as the surface area of the positive electrode active material submitted to the thermogravimetric measurement, the ratio (W2-W1) / SA of the mass increase W2-W1 to the surface area SA is not greater than 0.25 g / cm2.

Description

Positive electrode active material, electrode mixture, and battery

[0001] This invention relates to a positive electrode active material, an electrode mixture, and a battery.

[0002] In recent years, rechargeable batteries have attracted attention as a means of preventing global warming by reducing carbon dioxide emissions. Among rechargeable batteries, lithium-ion batteries, which have high energy density and high voltage, are widely used.

[0003] Lithium manganese nickel oxide is known as one of the active materials included in the positive electrode of such batteries. However, a challenge in commercializing lithium manganese nickel oxide was that the metal elements contained in the oxide would dissolve into the electrolyte, generating gas within the cell and degrading battery performance.

[0004] For example, Patent Document 1 contains Li[Ni ｙ Mn2-(a+b)-y-zLi ａ Ti ｂ M ｚ ]O ４ A lithium manganese nickel oxide represented by the formula has been proposed. The literature states that a lithium manganese nickel oxide having this compositional formula can exhibit an operating potential of 5V while significantly suppressing gas generation during high-temperature cycling.

[0005] Re-table No. 2013-161949

[0006] Although the lithium manganese nickel oxide described in Patent Document 1 can suppress gas generation, there was a need to further reduce the amount of metal element leaching in order to further suppress the degradation of battery performance.

[0007] Therefore, the object of the present invention is to provide a positive electrode active material in which the amount of metal leaching is reduced.

[0008] The present invention relates to a positive electrode active material containing a composite oxide comprising lithium (Li), nickel (Ni), and manganese (Mn), wherein W1 is the mass of the positive electrode active material at 400°C as measured by thermogravimetric analysis of the positive electrode active material in an air atmosphere, W2 is the maximum mass of the positive electrode active material at a temperature of 500°C to 600°C as measured by the same thermogravimetric analysis, and SA is the surface area of ​​the positive electrode active material subjected to the thermogravimetric analysis, and the ratio of the mass increase W2-W1 to the surface area SA (W2-W1) / SA is 0.25 mg / m². ２ The following is a positive electrode active material.

[0009] Figure 1 is a graph showing the results of thermogravimetric measurements of the positive electrode active material of Example 1. Figure 2 is a graph showing the results of thermogravimetric measurements of the positive electrode active material of Example 2. Figure 3 is a graph showing the results of thermogravimetric measurements of the positive electrode active material of Example 3. Figure 4 is a graph showing the results of thermogravimetric measurements of the positive electrode active material of Comparative Example 1.

[0010] The present invention will be described below based on its preferred embodiments.

[0011] [Positive Electrode Active Material] The positive electrode active material of the present invention contains a composite oxide. This composite oxide contains lithium (Li) element, nickel (Ni) element, manganese (Mn) element and oxygen (O) element. The composite oxide contained in the positive electrode active material of the present invention is not particularly limited as long as it contains Li element, Ni element, Mn element and O element, and those having various crystal structures can be used. For example, as the composite oxide, a lithium transition metal composite oxide having a spinel structure, a lithium transition metal composite oxide having a layered rock salt type structure, etc. can be used. In particular, it is preferable to use a lithium transition metal composite oxide having a spinel structure as the composite oxide because it has an operating potential of 4.5 V or more based on the metal Li standard potential. "Having an operating potential of 4.5 V or more based on the metal Li standard potential" means that it is not necessary to have only an operating potential of 4.5 V or more as a plateau region, and it also includes the case where it has a part of an operating potential of 4.5 V or more. Therefore, the present invention is not limited to a positive electrode active material composed only of a 5V-class positive electrode active material having an operating potential of 4.5 V or more as a plateau region. For example, the positive electrode active material of the present invention may contain a positive electrode active material 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 occupies, for example, 30% by mass or more, preferably 50% by mass or more, and particularly preferably 80% by mass or more (including 100% by mass).

[0012] The lithium transition metal composite oxide having a spinel structure is, for example, represented by the general formula LiNi ｘ Mn ２－ｘ O ４ (x represents a number greater than 0 and less than 2). As another example of the composite oxide, a spinel-type lithium manganese-containing composite oxide having a crystal structure in which a part of the Mn site in spinel-type LiNi ｘ Mn ２－ｘ O ４ 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 )O４－δ Examples include spinel-type lithium manganese-containing composite oxides represented by formula (I). In formula (I), the M element is preferably one or more elements 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 improving its properties. By selecting the M element from the elements described above, the crystal structure can be stabilized and the amount of metal elements eluted can be reduced. From this viewpoint, the composite oxide preferably contains one or more elements selected from the group consisting of Mg, Al, and Ti as the M element, and more preferably contains the Ti element.

[0013] In formula (I), it is preferable that "x" is between 0.001 and 0.200, "y" is between 0.20 and 1.20, and "z" is between 0.000 and 0.500. Furthermore, "4-δ" indicates that oxygen deficiency may be present, and it is preferable that δ is between 0 and 0.2.

[0014] The types of metal elements contained in the composite oxide and their content can be analyzed, for example, by ICP emission spectroscopy.

[0015] The positive electrode active material of the present invention may contain components other than the composite oxide described above. However, from the viewpoint of sufficiently improving the various performances of a battery incorporating the positive electrode active material of the present invention, the positive electrode active material of the present invention preferably contains 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more of the composite oxide.

[0016] As a result of our investigations, we have found that if there is a deficiency of oxygen atoms in the crystal structure of the composite oxide constituting the positive electrode active material, the crystal structure becomes unstable, and the amount of metal elements leached from the positive electrode active material (particularly the amount of Mn leached) tends to increase. In contrast, in the positive electrode active material of the present invention, oxygen atoms are sufficiently contained in the crystal structure of the composite oxide, so the amount of metal elements leached from the positive electrode active material is reduced. This is advantageous from the viewpoint of further suppressing gas generation from the battery.

[0017] Whether or not a composite oxide crystal structure contains a sufficient number of oxygen atoms can be evaluated by thermogravimetric analysis. Specifically, when W1 is the mass of the positive electrode active material at 400°C as measured by thermogravimetric analysis, W2 is the maximum mass of the positive electrode active material at temperatures between 500°C and 600°C as measured by the same thermogravimetric analysis, and SA is the surface area of ​​the positive electrode active material subjected to the same thermogravimetric analysis, the ratio of the mass increase W2-W1 to the surface area SA, (W2-W1) / SA, is 0.25 mg / m². ２ The following is the result: (W2 - W1) / SA is 0.25 mg / m². ２ The following indicates that W2-W1 is sufficiently small, that is, the amount of oxygen atoms incorporated into the crystal structure of the composite oxide when heated to between 500°C and 600°C is sufficiently small. In other words, (W2-W1) / SA is 0.25 mg / m³. ２ The following indicates that the crystal structure of the composite oxide constituting the positive electrode active material of the present invention already contains a sufficient amount of oxygen atoms before heating. From this viewpoint, (W2-W1) / SA is 0.25 mg / m². ２ Preferably, it is 0.15 mg / m² ２ It is more preferable that the following is the case: 0.10 mg / m² ２ It is even more preferable that the following is the case: 0.05 mg / m² ２ The following is particularly preferable. Also, (W2-W1) / SA is typically 0 mg / m². ２ However, when actually performing measurements, negative values ​​may sometimes be obtained.

[0018] The reason for using 400°C instead of room temperature as the measurement temperature for mass W1 is to eliminate the influence of moisture adsorbed on the positive electrode active material.

[0019] The thermogravimetric analysis can be performed, for example, using a NETZSCH STA-2500 Regulus under air conditions and a heating rate of 5°C / min. The mass of the positive electrode active material used for thermogravimetric analysis can be, for example, 40 mg.

[0020] The surface area SA of the positive electrode active material used for thermogravimetric analysis is calculated as the product of the BET specific surface area SSA of the positive electrode active material and the mass of the positive electrode active material used for thermogravimetric analysis (e.g., 40 mg). The BET specific surface area SSA can be 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.), in accordance with "(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". The 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.

[0021] To set (W2 - W1) / SA within the above numerical range, for example, a positive electrode active material can be produced by calcining a mixture containing the composite hydroxide and Li compound described later.

[0022] Furthermore, it can sometimes be confirmed by X-ray diffraction measurement that the composite oxide constituting the positive electrode active material of the present invention contains a sufficient amount of oxygen atoms within its crystal structure. More specifically, it is preferable that the full width at half maximum (FWHM) of the diffraction peak originating from the (111) plane is 0.2 deg. or less, and the full width at half maximum (FWHM) of the diffraction peak originating from the (400) plane is 0.2 deg. or less, when the positive electrode active material of the present invention is subjected to X-ray diffraction measurement. The diffraction peak originating from the (111) plane is a diffraction peak originating from the Li-O bond in the spinel-type crystal structure, and the diffraction peak originating from the (400) plane is a diffraction peak originating from the M-O bond (M represents Ni or Mn) in the spinel-type crystal structure. Therefore, the fact that the full width at half maximum of the diffraction peak originating from the (111) plane is 0.2 deg. or less, and the full width at half maximum of the diffraction peak originating from the (400) plane is 0.2 deg. or less, indicates that the composite oxide having a spinel-type crystal structure has few oxygen vacancies and that the amount of oxygen atoms contained within the crystal structure is close to the stoichiometric amount.

[0023] From the above viewpoint, the full width at half maximum (FWHM) of the diffraction peak originating from the (111) plane is more preferably 0.15 deg. or less, and even more preferably 0.08 deg. or less. Similarly, the FWHM of the diffraction peak originating from the (400) plane is more preferably 0.15 deg. or less, and even more preferably 0.09 deg. or less. There is no particular limit to the lower limit of the FWHM of the diffraction peaks originating from the (111) plane and the (400) plane, but it is practical to set them independently to 0.05 deg. or more, or 0.06 deg. or more, respectively. The measurement conditions for X-ray diffraction measurement will be described in the examples below.

[0024] To set the full width at half maximum of the diffraction peaks originating from the (111) and (400) planes within the above-mentioned numerical range, the positive electrode active material can be manufactured, for example, by the manufacturing method described later.

[0025] 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 1.7 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, 3.0 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. A detailed method for measuring tap density will be described in the examples below.

[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 BET specific surface area (SSA) of the positive electrode active material of the present invention is 2.0 m². ２ It is preferable that the amount is less than or equal to 1.5 m ２ It is more preferable that it be less than or equal to 1.0 m ２It is even more preferable that the amount is less than or equal to / g. Furthermore, 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 0.1 m². 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 higher. To set SSA within the above range, for example, the temperature of the firing process in the manufacturing method described later can be appropriately controlled.

[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 tap density TD of the positive electrode active material of the present invention is 1.0 g / cm³. ３ Preferably, it should be 1.1 g / cm³ or more. ３ It is more preferable that the amount be greater than or equal to 1.2 g / cm³. ３ It is even more preferable that the above conditions are met. Furthermore, 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 TD should be 3.0 g / cm³. ３ Preferably, it is 2.5 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 firing temperature can be appropriately controlled in the manufacturing method described later.

[0028] The positive electrode active material of the present invention may be, for example, particulate. In this case, the particle size of the positive electrode active material of the present invention is 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 μm or more, and even more preferably 5 μm or more. This is because excessive aggregation of particles is suppressed, resulting in good dispersibility. On the other hand, the volume cumulative particle size D ５０The volume cumulative particle size D is preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 15 μm or less. This is because it ensures sufficient contact between the positive electrode active material particles and between the positive electrode active material particles and the electrolyte. ５０ The particle size may be 10 μm or less.

[0029] Here, volume cumulative particle size D ５０ This 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).

[0030] 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 D, the water-soluble solvent was passed through a 60 μm filter, the solvent refractive index was set to 1.33, the particle permeability condition to "permeable", the particle shape to "non-spherical", the particle refractive index to 2.46, the measurement range to 0.243 μm to 704.0 μm, and the measurement time to 30 seconds. The arithmetic mean of two measurements was taken. ５０ Let's assume that.

[0031] 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. The elements contained in the coating layer can be detected by analytical methods such as ICP emission spectrometry, X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES). For example, when detecting elements contained in the coating layer using ICP emission spectrometry, 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 the solvent are analyzed by ICP emission spectrometry. If an element is present in a higher concentration in the solution containing the particle surface than in the solution containing the remaining particles, it can be concluded that the element is contained in the coating layer. Alternatively, when detecting elements contained in the coating layer using XPS analysis, XPS analysis combined with ion sputtering is performed. Specifically, XPS analysis and ion sputtering are repeatedly performed on the sample. In the 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 this change in the detected elements, the elements contained in the coating layer can be confirmed. Even when using AES, elements contained in the coating layer can be detected in a similar manner to 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, the positive electrode active material is produced by calcining a mixture of a composite hydroxide containing nickel and manganese elements and a lithium compound. After describing the details of the composite hydroxide, the steps for preparing the composite hydroxide and the steps for producing 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 ｙ Examples 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 method ＯＨ 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: ＯＨThe density is sufficiently close to that of lithium carbonate, and the miscibility between them is high, so that composite hydroxides can be used to effectively produce, for example, spinel-type lithium transition metal composite oxides (hereinafter also referred to as "LNMOs"). 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 １０is preferably 1.5 or more, more preferably 1.8 or more, and still more preferably 2.0 or more. From the same perspective, D ９０ / D １０ is preferably 5.0 or less, more preferably 4.8 or less, and still more preferably 4.6 or less.

[0051] In the composite hydroxide, it is preferable that each particle size constituting the particle size distribution is within a predetermined range from the viewpoint of obtaining a composite hydroxide capable of obtaining a positive electrode active material capable of manufacturing a high-performance battery. 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% by volume in the cumulative volume measured by the laser diffraction scattering method of particle size distribution. ５０ (Hereinafter, simply referred to as "particle size D ５０ ").) is preferably 3.0 μm or more, more preferably 3.5 μm or more, still more preferably 4.0 μm or more, and even more preferably 7.5 μm or more. Also, from the viewpoint of output characteristics when used as a positive electrode active material, the particle size D of the composite hydroxide ５０ is preferably 20.0 μm or less, more preferably 19.0 μm or less, and still more preferably 18.0 μm or less.

[0052] Also, from the viewpoint of durability when used as a positive electrode active material, the particle size D of the composite hydroxide １０ is preferably 1.0 μm or more, more preferably 1.2 μm or more, 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 of the composite hydroxide １０ is preferably 10.0 μm or less, more preferably 9.5 μm or less, and still more preferably 9.0 μm or less.

[0053] Also, from the viewpoint of durability when used as a positive electrode active material, the particle size D of the composite hydroxide ９０ is preferably 6.0 μm or more, more preferably 6.5 μm or more, 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 of the composite hydroxide ９０is preferably 37.0 μm or less, more preferably 36.0 μm or less, and even more preferably 35.0 μm or less. The particle size D of the composite hydroxide ５０ , 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.

[0054] The particle size D ５０ , the particle size D ９０ and the particle size D １０ are preferably within the above ranges. To achieve this, 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 below.

[0055] The composite hydroxide preferably has a BET specific surface area within a predetermined range. Specifically, from the viewpoint 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, from the viewpoint of reducing the moisture content of the composite hydroxide during the drying process and lowering the energy cost associated with drying in the manufacturing method described below, 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 in the same manner as the BET specific surface area SSA of the positive electrode active material.

[0056] As described above, the composite hydroxide preferably has low packing property. Therefore, it is also preferable that the apparent density of the composite hydroxide is low. Specifically, from the viewpoint of reducing the packing property and firing the composite hydroxide in a state where oxygen permeates throughout, 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, and even more preferably 0.70 g / cm３ It is even more preferable that the following conditions be met: 0.50 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 apparent density of the composite hydroxide, the better. However, from the viewpoint of adjusting the reaction with oxygen when calcining the composite hydroxide, an apparent density of 0.30 g / cm³ of the composite hydroxide is preferable. ３ Preferably, it is 0.32 g / cm³ or more. ３ It is even more preferable that the concentration be greater than or equal to 0.34 g / cm³. ３ The above is even more preferable. The method for measuring apparent density will be explained in the examples described later.

[0057] 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.

[0058] 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.

[0059] <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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] In the process of producing complex hydroxides, water is added to 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.

[0071] 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 reaction solution may be stirred continuously or intermittently. When stirring the reaction solution intermittently, a period of time during which the reaction solution is not stirred can be set, as long as it is short enough that turbulence can be considered to be occurring in the liquid. 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 making it easier to generate 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 at a peripheral speed of 5.5 m / s or less, more preferably 5.0 m / s or less, even more preferably 4.5 m / s or less, even more preferably 4.2 m / s or less, and particularly preferably 4.0 m / s or less.

[0072] 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.

[0073] 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.

[0074] The addition of the metal ion aqueous solution to the water may be continuous or intermittent. When the metal ion aqueous solution is added intermittently, a short period of time without addition can be set, as long as it is short enough to be considered as continuous addition. From the viewpoint of successfully producing complex hydroxides, continuous addition of the metal ion aqueous solution is preferable. When the metal ion aqueous solution is added continuously, it is preferable to slow down the addition rate of the metal ion aqueous solution during the complex hydroxide formation reaction. This is because it allows for the successful production of 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 a slower addition rate of the metal ion aqueous solution, and a larger S / V value means a faster addition rate. 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)

[0075] 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.

[0076] 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.

[0077] 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)

[0078] 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.

[0079] 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.

[0080] 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. When the inert gas is blown in intermittently, the period during which the inert gas is not blown in can be set to a short enough time that it can be considered as if the inert gas is being blown in continuously. Only one type of inert gas may be blown into the reaction mixture, or two or more types of inert gas may be blown in. When two or more types of inert gas are blown into the reaction mixture, the value T mentioned above refers to the total amount of inert gas blown in.

[0081] 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 the complex hydroxide 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.

[0082] <Process for producing positive electrode active material using composite hydroxide> Once the composite hydroxide is obtained, it is then mixed with a lithium compound to obtain a mixture. Examples of lithium compounds to be mixed with the composite oxide include lithium hydroxide (LiOH) and lithium carbonate (LiOH). 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. 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. There are no particular restrictions on the method of mixing the composite hydroxide and the lithium compound; wet mixing or dry mixing is acceptable.

[0083] 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.

[0084] 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 ＬｉIt 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 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 d Ｌｉ 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.

[0085] 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.

[0086] Next, the mixture is calcined in an oxygen-containing atmosphere to produce a positive electrode active material having a desired crystalline structure (typically spinel type). 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 900°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 40 hours or less. The calcination atmosphere is not particularly limited as long as it is an oxygen-containing atmosphere, and for example, an air atmosphere or an oxygen atmosphere can be used. From the viewpoint of allowing the mixture and oxygen to react sufficiently, it is preferable to calcine the mixture while circulating the 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 becomes constant.

[0087] Calcination can be carried out, for example, with the mixture contained in a reaction vessel that is open at the top. As mentioned above, the complex hydroxides contained in the mixture contained in the reaction vessel have relatively low packing density. Therefore, the packing density of the mixture in the reaction vessel will be relatively small.

[0088] When a mixture is calcined, its volume gradually decreases. For example, if lithium carbonate is used as the lithium compound, carbon dioxide is gradually released from the lithium carbonate during calcination, causing the volume of the mixture to decrease. As the volume of the mixture decreases, multiple cracks develop in the mixture within the reaction vessel, due to the relatively low packing density of the mixture in the reaction vessel, as described above. These cracks typically extend from the top to the bottom of the mixture, allowing oxygen to be supplied to the entire mixture from above through these cracks. Therefore, the mixture reacts sufficiently with oxygen during calcination, and the resulting composite oxide crystal structure contains a sufficient amount of oxygen atoms. A composite oxide containing a sufficient amount of oxygen atoms in its crystal structure has increased crystal structure stability, thus reducing the amount of metal elements leached from the composite oxide.

[0089] 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. 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.

[0090] 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.

[0091] 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.

[0092] [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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] [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.

[0097] The present invention includes the following technical concept: [1] A positive electrode active material containing a composite oxide including lithium (Li), nickel (Ni), and manganese (Mn), wherein W1 is the mass of the positive electrode active material at 400°C as measured by thermogravimetric analysis of the positive electrode active material in an air atmosphere, W2 is the maximum mass of the positive electrode active material at a temperature of 500°C to 600°C as measured by thermogravimetric analysis, and SA is the surface area of ​​the positive electrode active material subjected to thermogravimetric analysis, wherein the ratio of the mass increase amount W2-W1 to the surface area SA (W2-W1) / SA is 0.25 mg / m² ２The following are positive electrode active materials: [2] The positive electrode active material according to [1], wherein the full width at half maximum of the diffraction peak originating from the (111) plane, as measured by X-ray diffraction, is 0.2 deg. or less, and the full width at half maximum of the diffraction peak originating from the (400) plane is 0.2 deg. or less. [3] The ratio of tap density TD to BET specific surface area SSA, TD / SSA, is 1.5 kg ２ / m ５ 3.0 kg ２ / m ５ The positive electrode active material described in [1] or [2] below. [4] The positive electrode active material described in any one of [1] to [3] 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). [5] An electrode mixture comprising the positive electrode active material described in any one of [1] to [4] and an electrolyte. [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 [1] to [4].

[0098] 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%".

[0099] <Preparation of Complex Hydroxides> [Production Example 1] 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 concentrations of nickel and manganese in the metal ion aqueous solution are shown in Table 1. 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 produce a complex 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 set so that S / V was as shown in Table 1. The amount of water V1, the amount of metal ion aqueous solution added V2, and the amount of sodium hydroxide aqueous solution added V3 are as shown in Table 1. The sodium hydroxide aqueous solution was added at an addition rate such that the pH of the reaction solution was maintained at the value shown in Table 1. The amount of nitrogen gas injected was as shown in Table 1, and the peripheral speed and temperature of the reaction mixture were also adjusted to the values ​​shown in the same table. The reaction mixture was separated into solid and liquid by decantation to separate the complex hydroxide. This was heated and dried under the conditions shown in Table 1 to obtain the desired complex hydroxide. X-ray diffraction (XRD) analysis of this complex hydroxide confirmed the presence of nickel and manganese elements in the form of hydroxides.

[0100] [Comparative Manufacturing Example 1] In Manufacturing Example 1, the conditions for generating the composite hydroxide were changed as shown in Table 1. Otherwise, the desired composite hydroxide was obtained in the same manner as in Manufacturing Example 1. XRD analysis of this composite hydroxide confirmed the presence of nickel and manganese elements in hydroxide form.

[0101] <Manufacturing of positive electrode active material> [Examples 1 to 3] The composite hydroxide prepared in Manufacturing Example 1 was measured by the gas displacement method and its density d Ｌｉ 2.20 g / cm³ ３A mixture was obtained by mixing the composite hydroxide with lithium carbonate and titanium(IV) oxide. The mixing ratio of the composite hydroxide, lithium carbonate, and titanium(IV) oxide was such 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 at the temperatures shown in Table 2. The calcination time was 37 hours, and the calcination atmosphere was an air atmosphere, with air circulating during the calcination of the mixture. Next, a re-oxidation treatment was performed at the temperatures and times shown in Table 2. The atmosphere for the re-oxidation treatment was an air atmosphere. The calcined material obtained by the re-oxidation treatment was crushed 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.

[0102] [Comparative Example 1] A positive electrode active material was obtained in the same manner as in Example 2, except that the composite oxide prepared in Comparative Production Example 1 was used instead of the composite hydroxide prepared in Production Example 1.

[0103] [Evaluation of Composite Hydroxides] For the composite hydroxides obtained in each production example and production comparison example, the oil absorption amount, density, and particle size D were evaluated according to the method described above. １０ , particle size D ５０ , particle size D ９０ The BET specific surface area was also measured. The composition of the composite hydroxide, the nickel and manganese content, the apparent density, and the tap density were measured according to the method described below. Furthermore, the miscibility of the composite hydroxide was evaluated according to the method described below. These results are shown in Table 3.

[0104] [Composition of the composite hydroxide, nickel and manganese content] The nickel content (%) and manganese content (%) were measured by ICP emission spectrometry in accordance with JIS K 0116:2014.

[0105] [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. ３ 50g 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.

[0106] [Tap Density] Tap density was measured in accordance with JIS Z2512 using a tapping machine (model: KSR-409, 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.

[0107] [Mixability of the Composite Hydroxide] Mixability was evaluated in accordance with JIS K 5600:1999. First, a sample was prepared by mixing 99 g of composite hydroxide and 21 g of lithium carbonate for 2000 seconds at setting 1 using an Extreme Mill (WARING MODEL MX1200XTSLJ). Approximately half a spatula-sized portion of the sample was placed on the deeper end of a grind gauge (maximum groove depth 100 μm, scale interval 10 μm). The long side of the scraper was made parallel to the width direction of the grind gauge, and the tip of the scraper was brought into contact with the aforementioned end of the grind gauge. The scraper was then pulled toward the shallower end of the groove on the grind gauge. The stretched sample was visually inspected, and the groove depth at which streaks appeared due to the aggregation of particles in the sample was read. A small value or no streaks observed indicates good mixability.

[0108] [Evaluation of positive electrode active material] The positive electrode active material obtained in each example and comparative example was evaluated by the method described above to determine the average particle size D ５０ The BET specific surface area (SSA) was also measured. Furthermore, the following evaluations were performed. These results are shown in Table 4.

[0109] [Thermogravimetric Analysis] Thermogravimetric analysis of the positive electrode active materials obtained in each example and comparative example was performed using a NETZSCH STA-2500 Regulus. The results are shown in Figures 1 to 4. The mass W0 of the positive electrode active material used in the measurement is as shown in Table 4. An amount of Al equal to that of the positive electrode active material was used as a reference. ２ O ３The following was used. The measurement was performed in an air atmosphere with an air flow rate of 100 mL / min, and the heating rate was set to 5°C / min. Based on this measurement, the difference between masses W1 and W0 at 400°C, W1-W0, and the difference between the maximum mass W2 and W0 at temperatures between 500°C and 600°C, W2-W0, were determined. Furthermore, the value of (W2-W1) / SA was calculated using the measurement results of the BET specific surface area SSA mentioned above. Here, SA is a value calculated based on the following formula: SA = SSA × W0

[0110] [X-ray Diffraction Measurement] X-ray diffraction measurements were performed on the positive electrode active materials obtained in the examples and comparative examples to identify the crystal structure and determine the full width at half maximum of the diffraction peaks originating from the (111) and (400) planes. The diffraction peak originating from the (111) plane was observed at 2θ = 18.7 ± 0.3 deg. The diffraction peak originating from the (400) plane was observed at 2θ = 44.2 ± 0.3 deg. The measurement conditions for the X-ray diffraction measurements were as follows. • Equipment name: Fully automated multi-purpose X-ray diffractometer D8 ADVANCE (manufactured by BRUKER) • Radiation source: CuKα1 • Tube voltage: 40kV • Tube current: 40mA • Measurement method: Focusing method (reflection method) • Optical system: Multilayer mirror optical system (DBO) • Detector: LYNXEYE XE-T • Incident solar slit: 2.5° • Receiver solar slit: 2.5° • Divergence slit: 0.5° • Receiver slit: (Open) • Measurement range: 2θ = 15 to 120° • Step size: 0.014° • Scan speed: 1.560° / min

[0111] [Measurement of Mn elution amount] 1 mol / L LiPF ６ One g of positive electrode active material was dispersed in 10 mL of an organic solvent (ethylene carbonate / dimethyl carbonate = 3 / 7) containing the specified substance, and left at 85°C for 144 hours. Subsequently, the amount of Mn element in the organic solvent (i.e., the amount of Mn element eluted from the positive electrode active material) was measured by ICP emission spectrometry. The above measurement was performed twice, and the arithmetic mean of the measured Mn element elution amounts is shown in Table 4.

[0112] [Tap Density] Tap density was measured in accordance with JIS Z2512 using a tapping machine (model: KSR-409, 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.

[0113]

[0114]

[0115]

[0116] As is clear from Table 4, the positive electrode active materials of each example, produced by calcining a bulky mixture containing complex hydroxides, showed a reduced amount of Mn elution compared to the positive electrode active material of Comparative Example 1. Although not shown in the table, X-ray diffraction measurements confirmed that the positive electrode active materials of each example have a spinel-type crystal structure.

[0117] The present invention provides a positive electrode active material with reduced metal leaching. The positive electrode active material according to the present invention is advantageous in that it can further suppress the degradation of battery performance by further reducing the amount of metal elements leached. As a result, it is possible to suppress the occurrence of product defects during battery manufacturing and the degradation of battery performance during repeated use. Consequently, waste can be reduced during battery manufacturing and use, and energy costs can also be reduced. In these respects, 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 the manufacturing and use of batteries.

Claims

1. A positive electrode active material containing a composite oxide including lithium (Li), nickel (Ni), and manganese (Mn), wherein W1 is the mass of the positive electrode active material at 400°C as measured by thermogravimetric analysis of the positive electrode active material in an air atmosphere, W2 is the maximum mass of the positive electrode active material at a temperature between 500°C and 600°C as measured by thermogravimetric analysis, and SA is the surface area of ​​the positive electrode active material subjected to thermogravimetric analysis, and the ratio of the mass increase W2 - W1 to the surface area SA (W2 - W1) / SA is 0.25 mg / m² ２ The positive electrode active material is as follows:

2. The positive electrode active material according to claim 1, wherein the full width at half maximum of the diffraction peak originating from the (111) plane, as measured by X-ray diffraction, is 0.2 degrees or less, and the full width at half maximum of the diffraction peak originating from the (400) plane is 0.2 degrees or less.

3. The ratio of tap density TD to BET specific surface area SSA, TD / SSA, is 1.5 kg ２ / m ５ 3.0 kg ２ / m ５ The positive electrode active material according to claim 1, which is as follows:

4. 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).

5. An electrode mixture comprising a positive electrode active material and an electrolyte according to any one of claims 1 to 4.

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 4.

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