Metal composite compound and positive electrode active material using the metal composite compound as a precursor

Abstract

A metal composite compound from which a positive electrode active material having an excellent capacity retention rate can be obtained, and a positive electrode active material using the metal composite compound as a precursor are provided. [Solution] A metal complex compound in which the relative standard deviation of the volume-based crystallite size distribution calculated from the diffraction peaks within the range of 2θ=38±1° in powder X-ray diffraction measurement using CuKα radiation is 0.70 or more.

Description

[Technical Field]

[0001] The present invention relates to a metal composite compound and a positive electrode active material having a metal composite compound as a precursor, and particularly to a metal composite compound and a positive electrode active material having a metal composite compound as a precursor that can provide a positive electrode active material having an excellent capacity retention rate. [Background technology]

[0002] In recent years, in order to reduce environmental impact, secondary batteries have been used in a wide range of fields, such as portable devices such as mobile phones and portable personal computers, and vehicles that use or combine electricity as a power source. Examples of secondary batteries include secondary batteries using non-aqueous electrolytes, such as lithium-ion secondary batteries. Secondary batteries using non-aqueous electrolytes, such as lithium-ion secondary batteries, are suitable for miniaturization and weight reduction, and have properties such as a high capacity retention rate and a high utilization rate.

[0003] To improve the battery characteristics of lithium-ion secondary batteries, high battery capacity and high output characteristics are required. Therefore, a nickel-based hydroxide has been proposed for use as a positive electrode active material for lithium composite oxides, which have a peak half width at around 19° in the range of 0.1° to 0.60°, a peak half width at around 38° in the range of 0.1° to 0.50°, and a peak half width at around 52° in the range of 0.1° to 0.65° in an X-ray diffraction profile using CuKα radiation (Patent Document 1).

[0004] Patent Document 1 describes that, based on the finding that the discharge capacity of a lithium composite oxide depends on the half-value width of a peak in a specific X-ray diffraction profile of a raw material hydroxide, a high-capacity lithium composite oxide for a positive electrode active material can be obtained by using, as a raw material, a hydroxide containing nickel as its main component and having a relatively low half-value width.

[0005] On the other hand, for example, in portable devices such as mobile phones and portable personal computers, electric vehicles that use electricity as a power source, or hybrid vehicles that also use electricity as a power source, the nonaqueous electrolyte secondary batteries that serve as power sources are required to have properties with an even improved capacity retention rate. However, the precursor of the positive electrode active material in Patent Document 1 leaves room for improvement in the capacity retention rate of nonaqueous electrolyte secondary batteries. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-310433 Summary of the Invention [Problem to be solved by the invention]

[0007] In view of the above circumstances, an object of the present invention is to provide a metal composite compound that can provide a positive electrode active material having an excellent capacity retention rate, and a positive electrode active material that uses the metal composite compound as a precursor. [Means for solving the problem]

[0008] In the metal composite compound of the present invention, the relative standard deviation of the volume-based crystallite size distribution calculated from the diffraction peaks in the range of 2θ=38±1° in powder X-ray diffraction measurement using CuKα radiation is adjusted to 0.70 or more. Therefore, in the metal composite compound of the present invention, the volume-based crystallite size distribution calculated from the diffraction peaks in the range of 2θ=38±1° has a large variation. In addition, the metal composite compound of the present invention is a precursor of a positive electrode active material.

[0009] The gist of the configuration of the present invention is as follows. [1] A metal complex compound having a relative standard deviation of 0.70 or more in the volume-based crystallite size distribution calculated from the diffraction peaks within the range of 2θ=38±1° in powder X-ray diffraction measurement using CuKα radiation. [2] The metal complex compound according to [1], having a tap density of more than 1.5 g / mL. [3] The following composition formula (I) Ni 1-x-y Co x M y O z (OH) 2-α Formula (I) The metal complex compound according to [1] or [2], represented by formula (I), wherein 0≦x≦0.4, 0≦y≦0.4, 0≦x+y<0.5, 0≦z≦3, −0.5≦α≦2, and α−z<2 are satisfied, and M is one or more additive elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si. [4] The metal complex compound according to any one of [1] to [3], wherein the particle diameter at a cumulative volume percentage of 50% by volume (D50) is 7.0 μm or more and 20.0 μm or less. [5] The metal complex compound according to any one of [1] to [4], wherein the mode of the crystallite size in the crystallite size distribution is 20 Å or more and 200 Å or less. [6] The metal complex compound according to any one of [1] to [5], wherein the relative standard deviation is 1.20 or less. [7] A positive electrode active material for a non-aqueous electrolyte secondary battery, obtained by baking the metal composite compound according to any one of [1] to [6] with a lithium compound. [Effects of the Invention]

[0010] According to the metal composite compound of the present invention, in powder X-ray diffraction measurement using CuKα rays, the relative standard deviation of the volume-based crystallite size distribution calculated from the diffraction peaks in the range of 2θ=38±1° is 0.70 or more, and therefore a positive electrode active material having excellent capacity retention can be obtained.

[0011] According to the metal composite compound of the present invention, since the tap density is more than 1.5 g / mL, a more excellent capacity retention rate can be obtained.

[0012] According to the metal composite compound of the present invention, the particle diameter (D50) at a cumulative volume percentage of 50% by volume is 7.0 μm or more and 20.0 μm or less, which makes it easy to adjust the relative standard deviation of the volume-based crystallite size distribution calculated from the diffraction peaks within the range of 2θ=38±1° to 0.70 or more. DETAILED DESCRIPTION OF THE INVENTION

[0013] The metal complex compound of the present invention will be described in detail below.

[0014] The metal composite compound of the present invention is a secondary particle formed by aggregation of a plurality of primary particles. The particle shape of the metal composite compound of the present invention is not particularly limited and may be a wide variety of shapes, such as a substantially spherical shape or a substantially elliptical shape.

[0015] The metal composite compound of the present invention has a relative standard deviation of the volume-based crystallite size distribution calculated from diffraction peaks within the range of 2θ=38±1° in powder X-ray diffraction measurement using CuKα radiation adjusted to 0.70 or more.

[0016] The metal composite compound of the present invention has a relative standard deviation of 0.70 or more in the volume-based crystallite size distribution calculated from the diffraction peaks in the range of 2θ=38±1° in powder X-ray diffraction measurement using CuKα radiation, and therefore a positive electrode active material using the metal composite compound of the present invention as a precursor has an excellent capacity retention rate.

[0017] The relative standard deviation of the crystallite size distribution of the metal composite compound of the present invention can be obtained by the following method. First, a powdered metal composite compound is subjected to powder X-ray diffraction measurement using CuKα as a radiation source and within a measurement range of a diffraction angle 2θ of 10° to 90°, to obtain a diffraction peak within the range of 2θ = 38 ± 1°. An example of an X-ray diffractometer used for the powder X-ray diffraction measurement is Ultima IV manufactured by Rigaku Corporation.

[0018] The obtained diffraction peak data is read into analytical software, analyzed using the FP method, and the analytical data is output as a log-normal distribution to obtain the relative standard deviation of the volume-based crystallite size distribution. For example, the integrated powder X-ray analysis software PDXL2 manufactured by Rigaku Corporation can be used as the analytical software.

[0019] A metal composite compound having a relative standard deviation of 0.70 or more has a wide crystallite size distribution, i.e., the crystallite size variation is increased. A positive electrode active material obtained by firing a mixture of a metal composite compound and a lithium compound having an increased crystallite size variation grows during firing, with larger crystallites incorporating smaller crystallites, thereby promoting the crystal growth of the positive electrode active material. As a result, the crystalline structure of the positive electrode active material is prevented from collapsing during charging and discharging, improving durability and exhibiting an excellent capacity retention rate.

[0020] The relative standard deviation is not particularly limited as long as it is 0.70 or more, but the lower limit of the relative standard deviation is preferably 0.71 or more, and particularly preferably 0.72 or more, from the viewpoint of further improving the capacity retention rate of the positive electrode active material using the metal composite compound of the present invention as a precursor. On the other hand, the upper limit of the relative standard deviation is, for example, 1.20 or less.

[0021] The upper and lower limits of the relative standard deviation can be arbitrarily combined. The relative standard deviation is preferably 0.71 or more and 1.20 or less, and particularly preferably 0.72 or more and 1.20 or less.

[0022] The mode of the crystallite size in the crystallite size distribution can be determined by analyzing the crystallite size distribution determined by the above method using the above analysis software.

[0023] The mode of the crystallite size in the crystallite size distribution is not particularly limited, but its lower limit is preferably 20 Å or more, particularly preferably 30 Å or more, from the viewpoint of contributing to the promotion of crystal growth of the positive electrode active material when the mixture of the metal composite compound and the lithium compound is fired. On the other hand, the upper limit of the mode of the crystallite size in the crystallite size distribution is preferably 200 Å or less, more preferably 150 Å or less, particularly preferably 130 Å or less, from the viewpoint of contributing to the improvement of the capacity retention rate by the expansion and contraction of the crystallites due to charge and discharge.

[0024] The lower limit and upper limit of the mode can be arbitrarily combined. The mode is preferably 20 Å or more and 200 Å or less, more preferably 30 Å or more and 150 Å or less, and particularly preferably 30 Å or more and 130 Å or less.

[0025] The tap density of the metal composite compound of the present invention is not particularly limited, but from the viewpoint of improving the packing density of the positive electrode active material and obtaining an even better capacity retention rate, the lower limit is preferably more than 1.5 g / mL, more preferably 1.7 g / mL or more, and particularly preferably 1.9 g / mL or more. On the other hand, from the viewpoint of suppressing particle cracking due to an increase in particle density, the upper limit of the tap density is preferably 2.4 g / mL or less, more preferably 2.3 g / mL or less, and particularly preferably 2.2 g / mL or less.

[0026] The tap density may be set to any desired lower and upper limits, and is preferably greater than 1.5 g / mL and equal to or less than 2.4 g / mL, more preferably equal to or greater than 1.7 g / mL and equal to or less than 2.3 g / mL, and particularly preferably equal to or greater than 1.9 g / mL and equal to or less than 2.2 g / mL, from the viewpoint of suppressing particle cracking while obtaining a high packing density of the positive electrode active material and an even more excellent capacity retention rate.

[0027] The particle diameter (D50) at a cumulative volume percentage of 50% by volume of the metal composite compound of the present invention (hereinafter sometimes simply referred to as "D50") is not particularly limited, but the lower limit is preferably 7.0 μm or more, more preferably 8.0 μm or more, and particularly preferably 10.0 μm or more, from the viewpoint of improving the packing density of the positive electrode active material in the positive electrode. On the other hand, the upper limit of D50 of the metal composite compound of the present invention is preferably 20.0 μm or less, more preferably 19.0 μm or less, and particularly preferably 18.0 μm or less, from the viewpoint of improving contact with the electrolyte. The above-mentioned lower limit and upper limit can be combined arbitrarily.

[0028] Among these, from the viewpoint of facilitating adjustment of the relative standard deviation of the volume-based crystallite size distribution calculated from diffraction peaks within the range of 2θ=38±1° to 0.70 or more, 7.0 μm to 20.0 μm is preferred, 8.0 μm to 19.0 μm is more preferred, and 10.0 μm to 18.0 μm is particularly preferred. The above-mentioned D50 refers to the particle size measured with a particle size distribution analyzer using a laser diffraction / scattering method.

[0029] The composition of the metal composite compound of the present invention may be, for example, the following composition formula (I): Ni 1-x-y Co x M y O z (OH) 2-α Formula (I) (wherein formula (I) satisfies 0≦x≦0.4, 0≦y≦0.4, 0≦x+y<0.5, 0≦z≦3, −0.5≦α≦2, and α−z<2, and M is one or more additional elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si), i.e., nickel-containing hydroxide or nickel-containing oxide.

[0030] Among these, the value of x is preferably 0.05≦x≦0.35, more preferably 0.07≦x≦0.30, and particularly preferably 0.10≦x≦0.25. The value of y is preferably 0.01≦y≦0.25, more preferably 0.02≦y≦0.20, and particularly preferably 0.03≦y≦0.17. The value of x+y is preferably 0.06≦x+y≦0.45, more preferably 0.10≦x+y≦0.32, and particularly preferably 0.12≦x+y≦0.30.

[0031] The metal composite compound of the present invention can be used as a precursor (hydroxide or oxide) of a positive electrode active material for a non-aqueous electrolyte secondary battery.

[0032] Next, a positive electrode active material for a non-aqueous electrolyte secondary battery using the metal composite compound of the present invention as a precursor (hereinafter, sometimes simply referred to as "the positive electrode active material of the present invention") will be described. The positive electrode active material of the present invention is in a form in which the metal composite compound of the present invention, which is a precursor, is calcined with, for example, a lithium compound. By calcining the metal composite compound of the present invention with a lithium compound, a non-aqueous electrolyte secondary battery having an excellent capacity retention rate can be obtained.

[0033] The positive electrode active material of the present invention has a layered crystal structure, and from the viewpoint of obtaining a secondary battery with a high capacity retention rate, it is preferably a trigonal crystal structure, a hexagonal crystal structure, or a monoclinic crystal structure. The positive electrode active material of the present invention can be used, for example, as a positive electrode active material for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries.

[0034] Next, a method for producing a metal composite compound of the present invention will be described. The method for producing a metal composite compound of the present invention includes a reaction step in which a metal-containing aqueous solution containing nickel, a complexing agent, and an alkaline aqueous solution are continuously supplied to a reaction vessel to cause a crystallization reaction to obtain a metal composite compound. The reaction step is preferably carried out in a batch-type reaction vessel or a continuous reaction vessel.

[0035] <Reaction process for obtaining metal complex compound> The reaction process for obtaining a metal composite compound is a crystallization process in which a metal-containing aqueous solution containing nickel, a pH adjuster which is an alkaline aqueous solution, and a complexing agent are added and mixed in a reaction tank, and a coprecipitation reaction occurs in the reaction solution to obtain a metal composite compound.

[0036] Specifically, by coprecipitation, a metal-containing aqueous solution containing nickel, which contains a nickel salt (e.g., sulfate) and an optional cobalt salt (e.g., sulfate) and a salt of the additional element M (e.g., sulfate), an alkaline aqueous solution, and a complexing agent are added to a reaction vessel, whereby a neutralization reaction occurs in the reaction vessel to cause crystallization, thereby preparing a metal composite compound and obtaining a slurry-like suspension containing the metal composite compound. Water, for example, is used as the solvent for the suspension.

[0037] The complexing agent is not particularly limited as long as it can form a complex with nickel, the optional cobalt, and the added element M in an aqueous solution, and examples thereof include ammonium ion donors (ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.).

[0038] The alkaline aqueous solution is not particularly limited as long as it adjusts the pH value of the aqueous solution in the reaction tank during coprecipitation, and examples thereof include aqueous solutions of alkali metal hydroxides (for example, sodium hydroxide, potassium hydroxide).

[0039] When the nickel-containing metal-containing aqueous solution, alkaline aqueous solution, and complexing agent are continuously supplied to a reaction vessel, nickel, the optional cobalt, and the additional element M undergo a crystallization reaction, producing a metal composite compound. The pH value of the nickel-containing metal-containing aqueous solution is, for example, pH 2 to pH 6, based on a liquid temperature of 40°C. During the crystallization reaction, the temperature in the reaction vessel is controlled, for example, within a range of 10°C to 80°C, preferably 20°C to 70°C; the pH value in the reaction vessel is controlled, for example, within a range of pH 9 to pH 13, preferably pH 10 to pH 12, based on a liquid temperature of 40°C; the ammonium ion concentration per liter of slurry in the reaction vessel is controlled within a range of 1 g / L to 20 g / L; and the solids concentration of the slurry containing the metal composite compound in the reaction vessel is controlled within a range of 50 g / L to 300 g / L, while the materials in the reaction vessel are appropriately stirred.

[0040] In the method for producing a metal composite compound of the present invention, the ratio of the ammonium ion concentration per 1 L of slurry in the reaction tank to the solids concentration of the slurry (ammonium ion concentration per 1 L of slurry in the reaction tank / solids concentration of the slurry in the reaction tank) is adjusted to 0.130 or less. Furthermore, in the method for producing a metal composite compound of the present invention, the ratio of the pH value of the reaction tank slurry at a standard liquid temperature of 40°C to the pH value of the nickel-containing metal-containing aqueous solution at a standard liquid temperature of 40°C (pH value of the reaction tank slurry at a standard liquid temperature of 40°C / pH value of the nickel-containing metal-containing aqueous solution at a standard liquid temperature of 40°C) is adjusted to more than 2.00. By adjusting the ammonium ion concentration per 1 L of slurry in the reaction tank / solids concentration of the slurry in the reaction tank to 0.130 or less and the pH value of the reaction tank slurry at a standard liquid temperature of 40°C / pH value of the nickel-containing metal-containing aqueous solution at a standard liquid temperature of 40°C to more than 2.00, a metal composite compound having a relative standard deviation of 0.70 or more can be obtained.

[0041] The value of the ammonium ion concentration per 1 L of the slurry in the reaction tank / the solids concentration of the slurry in the reaction tank is not particularly limited as long as it is 0.130 or less, but is preferably 0.100 or less, more preferably 0.070 or less, and particularly preferably 0.050 or less, from the viewpoint of obtaining a metal composite compound having the relative standard deviation of 0.70 or more. The lower limit of the value of the ammonium ion concentration per 1 L of the slurry in the reaction tank / the solids concentration of the slurry in the reaction tank is, for example, 0.015 or more.

[0042] The pH value of the reaction tank slurry at a liquid temperature of 40°C / pH value of the metal-containing aqueous solution containing nickel at a liquid temperature of 40°C is not particularly limited as long as it is greater than 2.00, but is preferably 2.05 or more, and particularly preferably 2.10 or more, from the viewpoint of obtaining a metal composite compound having the relative standard deviation of 0.70 or more.

[0043] When the reaction process is a continuous process, the prepared metal complex compound is continuously discharged from the reaction vessel by overflowing from the overflow pipe of the reaction vessel. When the reaction process is a batch process, the reaction is stopped after a predetermined time, and the metal complex compound in the reaction vessel is completely discharged from the system using a pump or the like.

[0044] The obtained slurry containing the metal complex compound may be subjected to solid-liquid separation, in which a solid phase and a liquid phase are separated by filtration to obtain a solid phase containing the metal complex compound. Furthermore, during the solid-liquid separation, the solid phase may be washed with an alkaline aqueous solution. Thereafter, the solid phase containing the metal complex compound may be dried.

[0045] Next, a method for producing the positive electrode active material of the present invention will be described. For example, in the method for producing the positive electrode active material of the present invention, a lithium compound is first added to the metal composite compound of the present invention to prepare a mixture of the metal composite compound and the lithium compound. The lithium compound is not particularly limited as long as it is a compound containing lithium, and examples thereof include lithium carbonate and lithium hydroxide.

[0046] The mixing ratio of the lithium compound and the metal composite compound may be, for example, such that the molar ratio of lithium in the lithium compound to the total amount of metals contained in the metal composite compound (total amount of nickel, cobalt as an optional component, and additional element M) is in the range of 1.00 or more and 1.10 or less.

[0047] Next, the mixture is fired to produce a positive electrode active material. Examples of firing conditions include a firing temperature of 600°C to 1000°C, a temperature rise rate of 50°C / h to 300°C / h, and a firing time of 5 hours to 20 hours. The firing atmosphere is not particularly limited, but examples include air and oxygen. The firing furnace used for firing is not particularly limited, but examples include a stationary box furnace and a roller hearth continuous furnace.

[0048] Next, a positive electrode using the positive electrode active material of the present invention will be described. The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector and using the positive electrode active material of the present invention. The positive electrode active material layer contains the positive electrode active material of the present invention, a binder, and, if necessary, a conductive additive. The conductive additive is not particularly limited as long as it can be used for non-aqueous electrolyte secondary batteries, and for example, a carbon-based material can be used. Examples of carbon-based materials include graphite powder, carbon black (e.g., acetylene black), and fibrous carbon materials. Examples of binders include, but are not limited to, thermoplastic resins. Examples of thermoplastic resins include polyvinylidene fluoride (PVdF), butadiene rubber (BR), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), and the like, as well as combinations thereof. Examples of positive electrode current collectors include, but are not limited to, conductive metal materials such as aluminum foil, nickel foil, and stainless steel.

[0049] In a method for producing a positive electrode, for example, a positive electrode active material, a conductive additive, and a binder are mixed to prepare a positive electrode active material slurry, which is then filled into a positive electrode current collector by a known filling method, dried, and then rolled and fixed by a press or the like.

[0050] A nonaqueous electrolyte secondary battery can be assembled by preparing a positive electrode using the positive electrode active material obtained as described above, a negative electrode, an electrolytic solution containing a predetermined electrolyte, and a separator by a known method.

[0051] The negative electrode may be an electrode in which a negative electrode active material layer using a negative electrode active material is supported on a negative electrode current collector, or an electrode made of the negative electrode active material alone. The negative electrode active material is not particularly limited as long as it is a commonly used material, and examples thereof include graphite such as natural graphite and artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fiber, and organic polymer compound sintered bodies. The negative electrode current collector is not particularly limited, and examples thereof include metal materials such as copper foil, nickel foil, and stainless steel.

[0052] Furthermore, the negative electrode active material layer may further contain, as necessary, a conductive additive, a binder, etc. Examples of the conductive additive and binder include the same ones as those used in the positive electrode active material layer.

[0053] In a method for producing a negative electrode, for example, a negative electrode active material, an optional conductive additive and binder, and water are mixed to prepare a negative electrode active material slurry, which is then filled into a negative electrode current collector by a known filling method, dried, and then rolled and fixed by a press or the like.

[0054] The electrolytes contained in non-aqueous electrolytes include LiClO4, LiPF6, LiAsF6, LiSbF6, LiBF4, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(COCF3), Li(C4F9SO3), LiC(SO2CF3)3, Li2B 10 Cl 10Examples of the lithium salt include LiBOB (here, BOB is bis(oxalato)borate), LiFSI (here, FSI is bis(fluorosulfonyl)imide), lithium salts of lower aliphatic carboxylic acids, and lithium salts such as LiAlCl4. These may be used alone or in combination of two or more.

[0055] Examples of the dispersion medium for the electrolyte include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran. Examples of suitable organic solvents include ethers such as methyl formate, methyl acetate, and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone; and organic solvents containing fluoro groups (organic solvents in which one or more hydrogen atoms have been replaced with fluorine atoms). These may be used alone or in combination of two or more.

[0056] Alternatively, a solid electrolyte may be used instead of an electrolyte-containing electrolytic solution. Examples of solid electrolytes that can be used include organic polymer electrolytes such as polyethylene oxide polymer compounds, polymer compounds containing at least one of a polyorganosiloxane chain and a polyoxyalkylene chain. Also usable are so-called gel-type solid electrolytes in which a nonaqueous electrolytic solution is held in a polymer compound. Examples of inorganic solid electrolytes that contain sulfides include Li2S-SiS2, Li2S-GeS2, Li2S-P2S5, Li2S-B2S3, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li2SO4, and Li2S-GeS2-P2S5. These may be used alone or in combination of two or more.

[0057] The separator is not particularly limited, but may be, for example, a material in the form of a porous film, nonwoven fabric, woven fabric, etc., made of a polyolefin resin such as polyethylene or polypropylene, a fluororesin, a nitrogen-containing aromatic polymer, etc. These may be used alone or in combination of two or more types. [Example]

[0058] Next, examples of the metal complex compound of the present invention will be described, but the present invention is not limited to these examples as long as they do not depart from the spirit of the invention.

[0059] Production of metal complex compounds of Examples and Comparative Examples Preparation of metal complex compound of Example 1 Water was placed in a reaction vessel equipped with a rotary stirrer with stirring blades and an overflow pipe, and the temperature inside the reaction vessel was then raised to 70°C. A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed to obtain a predetermined molar ratio of nickel:cobalt:manganese to produce a metal-containing aqueous solution containing nickel. Next, the nickel-containing metal-containing aqueous solution, an ammonium sulfate aqueous solution as a complexing agent, and a sodium hydroxide aqueous solution were continuously added to the reaction vessel under stirring to obtain a slurry containing a metal complex compound. While maintaining the temperature inside the reaction vessel, the ratio of the ammonium ion concentration per 1 L of slurry in the reaction vessel to the solids concentration of the slurry in the reaction vessel was adjusted to 0.019, and the pH value of the reaction vessel slurry at a liquid temperature of 40°C to the pH value of the nickel-containing metal-containing aqueous solution at a liquid temperature of 40°C was adjusted to 2.24. The resulting slurry containing the metal complex compound was then overflowed and withdrawn from the overflow pipe of the reaction vessel. The extracted slurry containing the metal complex compound was subjected to solid-liquid separation, and the solid phase was washed with an alkaline aqueous solution and then dried to obtain the metal complex compound.

[0060] Preparation of metal complex compound of Example 2 Water was placed in a reaction vessel equipped with a rotary stirrer with stirring blades and an overflow pipe, and the temperature inside the reaction vessel was then raised to 60°C. A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed to achieve a predetermined molar ratio of nickel:cobalt:manganese to prepare a metal-containing aqueous solution containing nickel. Next, the nickel-containing metal-containing aqueous solution, an ammonium sulfate aqueous solution as a complexing agent, and a sodium hydroxide aqueous solution were continuously added to the reaction vessel under stirring to obtain a slurry containing a metal composite compound. While maintaining the temperature inside the reaction vessel, the ammonium ion concentration per liter of the slurry in the reaction vessel / solids concentration of the slurry in the reaction vessel was adjusted to 0.019, and the pH value of the reaction vessel slurry at a liquid temperature of 40°C / pH value of the nickel-containing metal-containing aqueous solution at a liquid temperature of 40°C was adjusted to 2.10. The produced slurry was overflowed from the overflow pipe of the reaction tank and supplied to a settling tank having a predetermined volume, where the metal composite compound was allowed to settle for a predetermined time to produce a concentrated slurry. After the predetermined time had elapsed, the concentrated slurry was returned from the settling tank to the reaction tank. After the above steps were continuously carried out for a predetermined time, the slurry was extracted from the reaction tank and the settling tank using a pump or the like, and the slurry containing the metal composite compound was removed from the system. The subsequent steps were carried out in the same manner as in Example 1, and the metal composite compound of Example 2 was obtained.

[0061] Preparation of metal complex compound of Example 3 Water was placed in a reaction vessel equipped with a rotary stirrer with stirring blades and an overflow pipe, and the temperature inside the reaction vessel was then raised to 60°C. A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed to obtain a predetermined molar ratio of nickel:cobalt:manganese to prepare a metal-containing aqueous solution containing nickel. Next, the nickel-containing metal-containing aqueous solution, an ammonium sulfate aqueous solution as a complexing agent, and a sodium hydroxide aqueous solution were continuously added to the reaction vessel under stirring to obtain a slurry containing a metal composite compound. While maintaining the temperature inside the reaction vessel, the ratio of the ammonium ion concentration per 1 L of slurry in the reaction vessel to the solids concentration of the slurry in the reaction vessel was adjusted to 0.018, and the pH value of the reaction vessel slurry at a liquid temperature of 40°C to the pH value of the nickel-containing metal-containing aqueous solution at a liquid temperature of 40°C was adjusted to 2.24. Subsequent steps were carried out in the same manner as in Example 1, and the metal composite compound of Example 3 was obtained.

[0062] Preparation of metal complex compound of Example 4 Water was placed in a reaction vessel equipped with a rotary stirrer with stirring blades and an overflow pipe, and the temperature inside the reaction vessel was then raised to 71°C. A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed to obtain a predetermined molar ratio of nickel:cobalt:manganese to prepare a metal-containing aqueous solution containing nickel. Next, the nickel-containing metal-containing aqueous solution, an ammonium sulfate aqueous solution as a complexing agent, and a sodium hydroxide aqueous solution were continuously added to the reaction vessel under stirring to obtain a slurry containing a metal composite compound. While maintaining the temperature inside the reaction vessel, the ratio of the ammonium ion concentration per 1 L of slurry in the reaction vessel to the solids concentration of the slurry in the reaction vessel was adjusted to 0.022, and the pH value of the reaction vessel slurry at a liquid temperature of 40°C to the pH value of the nickel-containing metal-containing aqueous solution at a liquid temperature of 40°C was adjusted to 2.24. Subsequent steps were carried out in the same manner as in Example 1, and the metal composite compound of Example 4 was obtained.

[0063] Preparation of metal composite compound of Comparative Example 1 Water was placed in a reaction vessel equipped with a rotary stirrer with stirring blades and an overflow pipe, and the temperature inside the reaction vessel was then raised to 70°C. A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed to achieve a predetermined molar ratio of nickel:cobalt:manganese to produce a metal-containing aqueous solution containing nickel. Next, the nickel-containing metal-containing aqueous solution, an ammonium sulfate aqueous solution as a complexing agent, and a sodium hydroxide aqueous solution were continuously added to the reaction vessel under stirring to obtain a slurry containing a metal composite compound. While maintaining the temperature inside the reaction vessel, the ratio of the ammonium ion concentration per 1 L of slurry in the reaction vessel to the solids concentration of the slurry in the reaction vessel was adjusted to 0.076, and the ratio of the pH value of the reaction vessel slurry at a liquid temperature of 40°C to the pH value of the nickel-containing metal-containing aqueous solution at a liquid temperature of 40°C was adjusted to 2.00. The resulting slurry containing the metal composite compound was overflowed and removed from the overflow pipe of the reaction vessel. Subsequent steps were carried out in the same manner as in Example 1, and a metal composite compound of Comparative Example 1 was obtained.

[0064] Preparation of metal composite compound of Comparative Example 2 Water was placed in a reaction vessel equipped with a rotary stirrer with stirring blades and an overflow pipe, and the temperature inside the reaction vessel was then raised to 70°C. A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed to achieve a predetermined molar ratio of nickel:cobalt:manganese to produce a metal-containing aqueous solution containing nickel. Next, the nickel-containing metal-containing aqueous solution, an ammonium sulfate aqueous solution as a complexing agent, and a sodium hydroxide aqueous solution were continuously added to the reaction vessel under stirring to obtain a slurry containing a metal composite compound. While maintaining the temperature inside the reaction vessel, the ratio of the ammonium ion concentration per 1 L of slurry in the reaction vessel to the solids concentration of the slurry in the reaction vessel was adjusted to 0.138, and the ratio of the pH value of the reaction vessel slurry at a liquid temperature of 40°C to the pH value of the nickel-containing metal-containing aqueous solution at a liquid temperature of 40°C was adjusted to 1.93. The resulting slurry containing the metal composite compound was overflowed and removed from the overflow pipe of the reaction vessel. Subsequent steps were carried out in the same manner as in Example 1, and a metal composite compound of Comparative Example 2 was obtained.

[0065] Preparation of metal composite compound of Comparative Example 3 Water was placed in a reaction vessel equipped with a rotary stirrer with stirring blades and an overflow pipe, and the temperature inside the reaction vessel was then raised to 70°C. A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution were mixed to achieve a predetermined molar ratio of nickel:cobalt:manganese to produce a metal-containing aqueous solution containing nickel. Next, the nickel-containing metal-containing aqueous solution, an ammonium sulfate aqueous solution as a complexing agent, and a sodium hydroxide aqueous solution were continuously added to the reaction vessel under stirring to obtain a slurry containing a metal composite compound. While maintaining the temperature inside the reaction vessel, the ratio of the ammonium ion concentration per 1 L of slurry in the reaction vessel to the solids concentration of the slurry in the reaction vessel was adjusted to 0.154, and the ratio of the pH value of the reaction vessel slurry at a liquid temperature of 40°C to the pH value of the nickel-containing metal-containing aqueous solution at a liquid temperature of 40°C was adjusted to 2.12. The resulting slurry containing the metal composite compound was overflowed and removed from the overflow pipe of the reaction vessel. Subsequent steps were carried out in the same manner as in Example 1 to obtain a metal composite compound of Comparative Example 3.

[0066] The evaluation items for the physical properties of the metal composite compounds of the examples and comparative examples are as follows.

[0067] (1) Composition analysis of metal complex compounds The composition analysis was carried out by dissolving the obtained metal composite compound in hydrochloric acid and then using an inductively coupled plasma emission spectrometer (Optima 8300, manufactured by PerkinElmer Japan Co., Ltd.).

[0068] (2) Relative standard deviation of volume-based crystallite size distribution calculated from diffraction peaks within the range of 2θ=38±1° The obtained metal complex compound was subjected to powder X-ray diffraction measurement (X-ray diffractometer: "Ultima IV", manufactured by Rigaku Corporation) using CuKα as the radiation source and a diffraction angle 2θ measurement range of 10° to 90°, and a diffraction peak was obtained within the range of 2θ = 38 ± 1°. The obtained diffraction peak data was read into analysis software (integrated powder X-ray analysis software "PDXL2", manufactured by Rigaku Corporation), analyzed using the FP method, and the analysis data was output as a normal logarithmic distribution. The relative standard deviation of the volume-based crystallite size distribution calculated from the diffraction peaks within the range of 2θ = 38 ± 1° was obtained.

[0069] (3) Tap density (g / mL) Measurement was carried out using a tap denser (KYT-4000, manufactured by Seishin Co., Ltd.) by the constant mass measurement method described in JIS R1628.

[0070] The evaluation results of the physical properties of the metal composite compounds of the examples and comparative examples are shown in Table 1 below.

[0071] Production of positive electrode active materials using metal composite compounds of Examples and Comparative Examples as precursors Lithium hydroxide powder was added to and mixed with the metal composite compounds of the examples and comparative examples so that the Li / (Ni+Co+Mn) molar ratio was 1.05, to obtain a mixture of the metal composite compound and lithium hydroxide. The resulting mixture was subjected to a calcination treatment to obtain a lithium metal composite oxide, which was used as the positive electrode active material. The calcination conditions were an oxygen atmosphere, a temperature increase rate of 175°C / h, a calcination temperature of 790°C, and a calcination time of 5 hours. A roller hearth kiln was used for the calcination.

[0072] Manufacturing of positive electrodes using positive electrode active materials A positive electrode was fabricated using the positive electrode active material obtained as described above, and a battery for evaluation was assembled using the fabricated positive electrode. Specifically, the positive electrode active material obtained, a conductive additive (acetylene black), and a binder (PVdF) were mixed in a weight ratio of 92:5:3, respectively, and the resulting mixture was applied to a positive electrode current collector (aluminum foil), dried, and pressed to adhere to the positive electrode current collector, thereby forming a positive electrode.

[0073] A lithium secondary battery was fabricated using the positive electrode obtained as described above, a negative electrode (metallic lithium), an electrolyte solution containing an electrolyte (LiPF6) (a mixed solution of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate in a volume ratio of 30:35:35), and a separator (made of polypropylene).

[0074] Evaluation items for lithium secondary batteries Capacity retention rate after 50 cycles (%) A charge-discharge test was conducted on the lithium secondary battery. The battery was charged at a constant current and voltage of 0.2 C at 25°C until the battery voltage reached 4.3 V, and then discharged at a constant current of 0.2 C until the battery voltage reached 2.5 V. This charge-discharge cycle was repeated four times, and the discharge capacity at the fourth cycle was designated as the initial capacity. Furthermore, a constant current charge-discharge cycle test was conducted at 25°C, with a charge rate of 0.5 C and a discharge rate of 1 C, with a charge cut-off voltage of 4.3 V and a discharge cut-off voltage of 2.5 V. The discharge capacity at the 50th cycle relative to the initial capacity, expressed as a percentage, was calculated as the capacity retention rate, and a capacity retention rate of 95% or higher was designated as acceptable.

[0075] The evaluation results of the lithium secondary batteries of the Examples and Comparative Examples are shown in Table 1 below.

[0076] [Table 1]

[0077] As can be seen from Table 1, the metal composite compounds of Examples 1 to 4, which were produced by adjusting the ammonium ion concentration per 1 L of slurry in the reaction tank / solid concentration of the slurry in the reaction tank to 0.130 or less and the pH value of the reaction tank slurry at a liquid temperature of 40°C / pH value of the nickel-containing metal-containing aqueous solution at a liquid temperature of 40°C to more than 2.00, and had a relative standard deviation of 0.70 or more, had a capacity retention rate of 98.0% or more after 50 cycles, and obtained excellent capacity retention rates.

[0078] Furthermore, the metal composite compounds of Examples 1 to 4 had tap densities of 2.0 g / mL to 2.1 g / mL.

[0079] On the other hand, as can be seen from Table 1, the metal composite compounds of Comparative Examples 1 to 3, which were produced with a relative standard deviation of less than 0.70, in which the ammonium ion concentration per 1 L of the slurry in the reaction tank / solid concentration of the slurry in the reaction tank was greater than 0.130 and / or the pH value of the reaction tank slurry based on a liquid temperature of 40°C / pH value of the nickel-containing metal-containing aqueous solution based on a liquid temperature of 40°C was 2.00 or less, had a capacity retention rate of less than 95% after 50 cycles, and did not achieve an excellent capacity retention rate.

[0080] Furthermore, the metal composite compounds of Comparative Examples 1 to 3 had tap densities of 1.0 g / mL to 1.5 g / mL. [Industrial Applicability]

[0081] When a positive electrode active material using the metal composite compound of the present invention as a precursor is used in a secondary battery, an excellent capacity retention rate can be achieved, and therefore the positive electrode active material can be used in a wide range of secondary battery fields, such as portable devices and vehicles.

Claims

1. A metal composite compound having a relative standard deviation of 0.70 or more in volume-based crystallite size distribution calculated from diffraction peaks within the range of 2θ=38±1° in powder X-ray diffraction measurement using CuKα radiation.

2. The metal complex compound according to claim 1, having a tap density of more than 1.5 g / mL.

3. The following composition formula (I) Ni １－ｘ－ｙ Co ｘ M ｙ O ｚ (OH) ２－α ... Formula (I) (In formula (I), 0≦x≦0.4, 0≦y≦0.4, 0≦x+y<0.5, 0≦z≦3, −0.5≦α≦2, and α−z<2 are satisfied, and M is one or more additive elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Nb, Ga, W, Mo, B, and Si.) The metal complex compound according to claim 1 or 2, represented by the formula (I).

4. 3. The metal complex compound according to claim 1, wherein the particle diameter at a cumulative volume percentage of 50% by volume (D50) is 7.0 μm or more and 20.0 μm or less.

5. 3. The metal complex compound according to claim 1, wherein the mode of the crystallite size in the crystallite size distribution is 20 Å or more and 200 Å or less.

6. 3. The metal complex compound according to claim 1, wherein the relative standard deviation is 1.20 or less.

7. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising the metal complex compound according to claim 1 or 2, fired with a lithium compound.

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