Method for producing lithium nickel composite oxide

Abstract

The purpose of the present disclosure is to provide a method for producing a lithium-nickel complex oxide, the method being capable of suppressing a variation in crystallite size. The method for producing a lithium-nickel complex oxide according to an aspect of the present disclosure comprises: a filling step for filling a firing container (7) with a Ni-containing metal compound and a Li compound to obtain a filling material (5) including the Ni-containing metal compound and the Li compound; and a firing step for firing the filling material (5) that fills the firing container (7), wherein, in the filling step, when the filling material (5) that fills the firing container (7) is divided into two equal parts in the height direction, the molar ratio A of Li to metals other than Li in the filling material (5a) in the upper half region and the molar ratio B of Li to metals other than Li in the filling material (5b) in the lower half region satisfy 1<B / A<1.15.

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a lithium nickel composite oxide. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, have high energy densities and are already used as power sources for portable electronic devices. However, research and development is also underway to utilize non-aqueous electrolyte secondary batteries not only for such applications but also as large-scale power sources for hybrid vehicles, electric vehicles, and the like.

[0003] Lithium nickel composite oxide, which is used as a positive electrode active material for non-aqueous electrolyte secondary batteries, has advantages over the currently mainstream lithium cobalt composite oxide, such as a higher capacity, and the raw material nickel is less expensive and more stably available than cobalt, making it a promising next-generation positive electrode material.

[0004] As a method for producing a lithium nickel composite oxide, for example, a method is mentioned in which a powder of a positive electrode material precursor containing lithium and nickel is filled into a firing vessel and fired in an oxygen atmosphere and an air atmosphere for a predetermined time (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5916876 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional methods for producing lithium nickel composite oxides have a problem in that the reaction does not proceed sufficiently near the bottom of the firing vessel due to insufficient heat conduction during firing, resulting in large variations in the crystallite size of the resulting lithium nickel composite oxide. If a lithium nickel composite oxide with large variations in crystallite size is used as a positive electrode active material, there is a risk that the discharge rate characteristics of a non-aqueous electrolyte secondary battery will deteriorate, for example. Therefore, there is a need for a production method that reduces the variations in crystallite size of lithium nickel composite oxides.

[0007] Therefore, an object of the present disclosure is to provide a method for producing a lithium nickel composite oxide that can suppress variations in crystallite size. [Means for solving the problem]

[0008] A method for producing a lithium nickel composite oxide according to one embodiment of the present disclosure includes a filling step of filling a firing container with a Ni-containing metal compound and a Li compound to obtain a packing containing the Ni-containing metal compound and the Li compound, and a firing step of firing the packing packed in the firing container, wherein when the packing packed in the firing container in the filling step is divided into two equal parts in the height direction, a molar ratio A of Li to metals other than Li in the packing in the upper half region and a molar ratio B of Li to metals other than Li in the packing in the lower half region are 1 [Effects of the Invention]

[0009] According to one embodiment of the present disclosure, a lithium nickel composite oxide with reduced variation in crystallite size can be obtained. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic cross-sectional view of a firing vessel filled with a Ni-containing metal compound and a Li compound. [Figure 2] FIG. 2 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION​

[0011] Hereinafter, an example of an embodiment will be described in detail with reference to the drawings, but the drawings referred to in the description of the embodiment are schematic drawings.

[0012] The method for producing a lithium nickel composite oxide of this embodiment includes a filling step of filling a firing vessel with a Ni-containing metal compound and a Li compound to obtain a filling containing the Ni-containing metal compound and the Li compound, and a firing step of firing the filling containing the Ni-containing metal compound and the Li compound filled in the firing vessel.

[0013] <Filling process> The Ni-containing metal compound filled into the firing container is not particularly limited as long as it is a Ni-containing compound, but it may contain elements other than Ni. Examples of other elements include Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among these, it is preferable to contain at least one of Co, Mn, and Al. Suitable compounds include metal compounds containing Ni, Co, and Mn, and metal compounds containing Ni, Co, and Al. The Ni-containing metal compound may be in the form of, for example, hydroxide, oxyhydroxide, or oxide. Among these, hydroxide and oxyhydroxide are preferred because they are easy to combine with Ni and other elements and have high reactivity with Li compounds. Ni-containing metal hydroxides can be obtained by conventional methods such as crystallization, coprecipitation, and homogeneous precipitation. Ni-containing metal oxyhydroxides can be obtained by adding an oxidizing agent such as sodium hypochlorite or hydrogen peroxide to the Ni-containing metal hydroxide obtained by the above method. The Ni-containing metal oxide can be obtained by, for example, firing the hydroxide or oxyhydroxide in a non-reducing atmosphere. The firing temperature is not particularly limited as long as the non-reducing atmosphere can be maintained, but is preferably 850°C or lower, and more preferably in the range of 500°C to 750°C.

[0014] Examples of Li compounds to be filled into the firing container include hydroxides, oxyhydroxides, oxides, carbonates, nitrates, and halides of lithium. These may be used alone or in combination. Among these, lithium hydroxides are preferred, and lithium hydroxide is particularly preferred, due to their low melting point and high reactivity with Ni-containing metal compounds.

[0015] 1 is a schematic cross-sectional view of a firing vessel filled with a Ni-containing metal compound and a Li compound. When the filler 5 containing the Ni-containing metal compound and the Li compound filled in the firing vessel 7 in the filling step is divided into two equal parts in the height direction, the molar ratio A of Li to metals other than Li in the filler 5a in the upper half region and the molar ratio B of Li to metals other than Li in the filler 5b in the lower half region are 1.

[0016] ​Alternatively, for example, a mixture of Ni-containing metal compounds and Li compounds may be filled so that the molar ratio of Li to metals other than Li increases stepwise from the top to the bottom of the firing container 7. Specifically, a mixture A of Ni-containing metal compounds and Li compounds having a high molar ratio of Li to metals other than Li is filled to a predetermined height from the bottom of the firing container 7, and a mixture B of Ni-containing metal compounds and Li compounds having a lower molar ratio of Li to metals other than Li than mixture A is filled to a predetermined height on top of mixture A. Furthermore, a mixture C of Ni-containing metal compounds and Li compounds having a lower molar ratio of Li to metals other than Li than mixture B is filled to a predetermined height on top of mixture B. Then, mixtures having a lower molar ratio of Li to metals other than Li than the mixtures filled so far are continuously filled until the filling reaches the predetermined height. Note that the Li compounds in each mixture may be the same or different compounds. When different compounds are used, it is preferable that the Li compound in the mixture first filled into the firing container 7 be a Li compound with a low melting point, particularly a Li compound with a lower melting point than the Li compound in the mixtures filled subsequently. The above-mentioned filling method is an example, and the molar ratio A and the molar ratio B are 1

[0017] The molar ratio A and the molar ratio B are 1 ​​

[0018] The molar ratio A and the molar ratio B preferably satisfy the relationship 1.02≦B / A≦1.12, for example, in order to further suppress variations in crystallite size.

[0019] The molar ratio of Li to metals other than Li and the molar ratio of Ni to metals other than Li in the entire packing are appropriately set depending on the composition of the target lithium nickel composite oxide. However, from the viewpoint of, for example, thermal stability, the molar ratio of Li to metals other than Li in the entire packing is preferably 0.95 to 1.10. Furthermore, from the viewpoint of, for example, capacity, the molar ratio of Ni to metals other than Li in the entire packing is preferably 0.65 to 1.00.

[0020] In an industrial production process, a firing container 7 having inner dimensions ranging from 100 mm (L) × 100 mm (W) × 20 mm (H) to 500 mm (L) × 500 mm (W) × 100 mm (H) is used. The raw material is filled so that the height of the filler 5 containing the raw material Li compound and Ni-containing metal compound is in the range of 5 to 100 mm.

[0021] <Firing process> The filler 5 containing the Ni-containing metal compound and the Li compound packed in the firing vessel 7 is fired. The firing conditions are appropriately set in consideration of the reactivity between the Li compound and the Ni-containing metal compound, and include, for example, a one-stage firing in which firing is performed for a predetermined time at a temperature range of 650 to 850°C in an oxygen atmosphere, or a two-stage firing in which firing is performed for a predetermined time at a temperature range of 400 to 600°C in an oxygen atmosphere, followed by firing for a predetermined time at a temperature range of 650 to 850°C.

[0022] The device for firing the filler 5 filled in the firing vessel 7 is not particularly limited, but for example, firing furnaces such as an electric furnace, a kiln, a tubular furnace, and a pusher furnace can be used.

[0023] The fired filler (fired product) is washed to remove impurities, or pulverized to control the particle size to a predetermined size, as required.

[0024] The manufacturing method of this embodiment allows for the production of a lithium nickel composite oxide with reduced variation in crystallite size. The composition of the lithium nickel composite oxide can be changed by adjusting the amounts of raw materials charged, but from the standpoint of, for example, increasing the capacity of non-aqueous electrolyte secondary batteries, it is preferable to prepare a composite oxide represented by the following composition formula (1): Composition formula (1): Li a Ni 1-b M b O2 (wherein M represents a metal element other than Ni, a is 0.95≦a≦1.10, and b is 0.01≦b≦0.5).

[0025] FIG. 2 is a cross-sectional view of a nonaqueous electrolyte secondary battery according to an embodiment. The nonaqueous electrolyte secondary battery 10 shown in FIG. 2 includes a wound electrode assembly 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, a nonaqueous electrolyte, insulating plates 18 and 19 disposed above and below the electrode assembly 14, respectively, and a battery case 15 for accommodating the above components. The battery case 15 is composed of a cylindrical case body 16 with a bottom and a sealing member 17 that closes the opening of the case body 16. Note that, instead of the wound electrode assembly 14, other types of electrode bodies may be used, such as a laminated electrode body formed by alternately stacking positive and negative electrodes with separators interposed therebetween. Examples of the battery case 15 include cylindrical, prismatic, coin-shaped, or button-shaped metal outer cans, and pouch outer cans formed by laminating a resin sheet and a metal sheet.

[0026] Case body 16 is, for example, a cylindrical metal outer can with a bottom. A gasket 28 is provided between case body 16 and sealing body 17 to ensure airtightness inside the battery. Case body 16 has, for example, a protruding portion 22, which is a portion of the side surface that protrudes inward and supports sealing body 17. Protruding portion 22 is preferably formed in an annular shape along the circumferential direction of case body 16, and supports sealing body 17 on its upper surface.

[0027] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in this order from the electrode body 14 side. Each member constituting the sealing body 17 has, for example, a disk or ring shape, and each member except for the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected to one another at their respective centers, and the insulating member 25 is interposed between their respective peripheral edges. When the internal pressure of the nonaqueous electrolyte secondary battery 10 increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further increases, the upper valve body 26 ruptures, and gas is discharged from the opening of the cap 27.

[0028] 2, a positive electrode lead 20 attached to the positive electrode 11 passes through a through-hole in an insulating plate 18 and extends toward the sealing body 17, and a negative electrode lead 21 attached to the negative electrode 12 passes outside an insulating plate 19 and extends toward the bottom of the case body 16. The positive electrode lead 20 is connected to the underside of a filter 23, which is the bottom plate of the sealing body 17, by welding or the like, and a cap 27, which is the top plate of the sealing body 17 and is electrically connected to the filter 23, serves as the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the case body 16 by welding or the like, and the case body 16 serves as the negative electrode terminal.

[0029] Each component of the nonaqueous electrolyte secondary battery 10 will be described in detail below.

[0030] [Negative electrode] The negative electrode 12 includes, for example, a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0031] The negative electrode current collector may be, for example, a foil of a metal such as copper that is stable in the potential range of the negative electrode, or a film having such a metal disposed on the surface thereof.

[0032] The negative electrode active material layer contains a negative electrode active material. Preferably, the negative electrode active material layer also contains a binder, etc. The negative electrode 12 can be produced, for example, by preparing a negative electrode mixture slurry containing the negative electrode active material, the binder, etc., applying the negative electrode mixture slurry onto a negative electrode current collector, drying the slurry to form a negative electrode active material layer, and rolling the negative electrode active material layer.

[0033] The negative electrode active material is not particularly limited as long as it is a material that can absorb and release lithium ions, and examples thereof include carbonaceous materials such as natural graphite and artificial graphite, elements such as silicon, titanium, germanium, tin, lead, zinc, magnesium, sodium, aluminum, potassium, and indium, alloys, and oxides thereof.

[0034] Examples of binders include fluorine-based resins, PAN, polyimide-based resins, acrylic-based resins, polyolefin-based resins, styrene-butadiene rubber (SBR), nitrile-butadiene rubber (NBR), carboxymethyl cellulose (CMC) or a salt thereof, polyacrylic acid (PAA) or a salt thereof (PAA-Na, PAA-K, etc., or a partially neutralized salt), polyvinyl alcohol (PVA), etc. These may be used alone or in combination of two or more.

[0035] [Positive electrode] The positive electrode 11 is composed of, for example, a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode current collector can be a foil of a metal such as aluminum that is stable within the potential range of the positive electrode, or a film with such a metal disposed on the surface layer. The positive electrode active material layer includes, for example, a positive electrode active material, a binder, a conductive material, etc.

[0036] The positive electrode 11 can be produced, for example, by applying a positive electrode composite slurry containing a positive electrode active material, a binder, a conductive material, etc. onto a positive electrode current collector, drying the slurry to form a positive electrode active material layer, and then rolling the positive electrode active material layer.

[0037] The positive electrode active material is the lithium nickel composite oxide obtained by the manufacturing method of this embodiment. Note that the positive electrode active material may contain a composite oxide other than the lithium nickel composite oxide obtained by the manufacturing method of this embodiment, as long as the battery performance is not impaired. For example, a composite oxide that does not contain Ni may be used.

[0038] Examples of the conductive material include carbon particles such as carbon black (CB), acetylene black (AB), ketjen black, graphite, etc. These may be used alone or in combination of two or more.

[0039] Examples of binders include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide-based resins, acrylic-based resins, polyolefin-based resins, etc. These may be used alone or in combination of two or more.

[0040] [Non-aqueous electrolyte] The non-aqueous electrolyte includes, for example, a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The electrolyte is not limited to a liquid electrolyte, and may be a solid electrolyte using a gel polymer or the like. The non-aqueous solvent may be, for example, an ester, an ether, a nitrile such as acetonitrile, an amide such as dimethylformamide, or a mixed solvent of two or more of these. The non-aqueous solvent may contain a halogen-substituted compound in which at least a portion of the hydrogen atoms of these solvents are substituted with halogen atoms such as fluorine.

[0041] Examples of the esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone (GBL) and γ-valerolactone (GVL); and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate.

[0042] Examples of the ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methyl phenyl ether. and chain ethers such as ethyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0043] As the halogen-substituted compound, it is preferable to use a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC), a fluorinated chain carbonate, a fluorinated chain carboxylate such as methyl fluoropropionate (FMP), or the like.

[0044] The electrolyte salt is preferably a lithium salt. Examples of lithium salts include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), LiPF 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 、LiCl, LiBr, LiI, lithium chloroborane, lithium lower aliphatic carboxylic acid, borate salts such as Li2B4O7, Li(B(C2O4)F2), imide salts such as LiN(SO2CF3)2, LiN(C1F 2l+1 SO2)(C m F 2m+1 SO2){l, m are integers of 0 or more}, etc. The lithium salt may be used alone or in combination of multiple kinds. Among these, from the viewpoints of ionic conductivity, electrochemical stability, etc., it is preferable to use LiPF6. The concentration of the lithium salt is preferably 0.8 to 1.8 mol per 1 L of the non-aqueous solvent.

[0045] [Separator] For the separator 13, for example, a porous sheet having ion permeability and insulation is used. Specific examples of the porous sheet include microporous thin films, woven fabrics, non-woven fabrics, etc. As the material of the separator, olefin resins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin resin. Also, a multi-layer separator including a polyethylene layer and a polypropylene layer may be used, or a separator with a material such as an aramid resin or ceramic coated on the surface of the separator may be used.

Examples

[0046] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0047] Example 1 [Preparation of lithium nickel composite oxide] Urea was added to a mixed solution containing nickel sulfate, cobalt sulfate, and aluminum nitrate. The solution was stirred while the temperature was adjusted to between 80 and 100°C to control the crystal growth rate and obtain a precipitate. This precipitate was a Ni-Co-Al coprecipitated hydroxide (Ni) with an atomic ratio of Ni, Co, and Al of 0.91:0.045:0.045. 0.91 Co 0.045 Al 0.045 (OH)2).

[0048] Next, the Ni-Co-Al coprecipitated hydroxide was mixed with lithium hydroxide monohydrate (LiOH / H2O) to obtain a mixed powder M.

[0049] The bottom of an alumina firing container was filled with lithium hydroxide monohydrate, and mixed powder M was then filled on top of the lithium hydroxide monohydrate to form a packing inside the firing container. The ratio of lithium hydroxide monohydrate packed on the bottom of the firing container to mixed powder M packed on top of the lithium hydroxide monohydrate was 5:100 by mass. The mixing ratio of Ni-Co-Al coprecipitated hydroxide to lithium hydroxide monohydrate in mixed powder M was adjusted so that, when the packing was divided into two equal parts in the height direction, the molar ratio A of Li to metals other than Li in the packing in the upper half was 1.173, and the molar ratio B of Li to metals other than Li in the packing in the lower half was 1.314. In this case, the molar ratio B / molar ratio A was 1.12.

[0050] The firing container containing the packing was placed in an electric furnace and fired in an oxygen atmosphere at 750°C for 15 hours to obtain a lithium nickel composite oxide containing Co and Al (composition: LiNi 0.91 Co 0.045 Al 0.045 O2) This was used as the positive electrode active material.

[0051] [Preparation of positive electrode] The lithium-nickel composite oxide (positive electrode active material), acetylene black (conductive material), and polyvinylidene fluoride (average molecular weight: 1.1 million) (binder) were mixed in a mass ratio of 98:1:1 to prepare a positive electrode composite slurry with a solid content of 70%. This slurry was applied to both sides of a 15 μm-thick aluminum foil, the coating was dried, and then rolled with a rolling roller to produce a positive electrode with positive electrode active material layers formed on both sides of the positive electrode current collector.

[0052] [Preparation of negative electrode] Graphite powder (95 parts by mass) and silicon oxide (5 parts by mass) were mixed to form the negative electrode active material. 100 parts by mass of this negative electrode active material, 1 part by mass of carboxymethyl cellulose (CMC) as a binder, and an appropriate amount of water were mixed, and 1.2 parts by mass of styrene butadiene rubber (SBR) and an appropriate amount of water were added to this mixture to prepare a negative electrode composite slurry. This slurry was applied to both sides of an 8 μm-thick copper foil, the coating was dried, and then the coating was rolled using a rolling roller to produce a negative electrode with a negative electrode active material layer formed on both sides of the negative electrode current collector.

[0053] [Preparation of non-aqueous electrolyte] A non-aqueous electrolyte was prepared by adding 5 parts by mass of vinylene carbonate (VC) to 100 parts by mass of a mixed solvent consisting of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio of EC:DMC = 1:3), and dissolving LiPF6 at a concentration of 1 mol / L.

[0054] [Fabrication of non-aqueous electrolyte secondary battery] After attaching leads to the positive and negative electrodes, a separator consisting of a 3 μm alumina particle layer formed on a 12 μm polyethylene film was placed between the positive and negative electrodes, and the resulting structure was wound to produce a wound electrode assembly. This electrode assembly was inserted into a case body, and the negative electrode lead was welded to the bottom of the case body. Next, the positive electrode lead was welded to a sealing member. After pouring nonaqueous electrolyte into the case body, the open end of the case body was sealed with a sealing member via a gasket, resulting in a nonaqueous electrolyte secondary battery. The battery capacity of the nonaqueous electrolyte secondary battery was 2500 mAh.

[0055] <Example 2> A packing was formed in the packing container, with the ratio of lithium hydroxide monohydrate packed at the bottom of the packing container to the mixed powder M packed on top of the lithium hydroxide monohydrate being 0.1:100 in mass terms. The mixing ratio of the Ni-Co-Al coprecipitated hydroxide and lithium hydroxide monohydrate in the mixed powder M was adjusted so that, when the packing container was divided into two equal parts in the height direction, the molar ratio A of Li to metals other than Li in the packing container in the upper half region was 1.230, and the molar ratio B of Li to metals other than Li in the packing container in the lower half region was 1.255. At this time, the molar ratio B / molar ratio A was 1.02. A nonaqueous electrolyte secondary battery was fabricated under the same conditions as in Example 1.

[0056] Example 3 A packing was formed in the packing container, with the ratio of lithium hydroxide monohydrate packed on the bottom of the packing container to the mixed powder M packed on top of the lithium hydroxide monohydrate being 0.01:100 in mass terms. The mixing ratio of the Ni-Co-Al coprecipitated hydroxide and lithium hydroxide monohydrate in the mixed powder M was adjusted so that when the packing container was divided into two equal parts in the height direction, the molar ratio A of Li to metals other than Li in the packing container in the upper half region was 1.236, and the molar ratio B of Li to metals other than Li in the packing container in the lower half region was 1.248. At this time, the molar ratio B / molar ratio A was 1.01. A nonaqueous electrolyte secondary battery was fabricated under the same conditions as in Example 1.

[0057] <Comparative Example 1> Only the mixed powder M was filled into a firing container to form a packing in the firing container. The mixing ratio of lithium hydroxide monohydrate to Ni-Co-Al coprecipitated hydroxide in the mixed powder M was adjusted so that the molar ratio B of Li to metals other than Li in the packing in each of the upper half region and the lower half region when the packing was divided into two equal parts in the height direction was 1.242. At this time, the molar ratio B / molar ratio A was 1. A nonaqueous electrolyte secondary battery was fabricated under the same conditions as in Example 1.

[0058] <Comparative Example 2> A packing was formed in the packing container, with the ratio of lithium hydroxide monohydrate packed at the bottom of the packing container to the mixed powder M packed on top of the lithium hydroxide monohydrate being 7:100 in mass terms. The mixing ratio of the Ni-Co-Al coprecipitated hydroxide and lithium hydroxide monohydrate in the mixed powder M was adjusted so that when the packing container was divided into two equal parts in the height direction, the molar ratio A of Li to metals other than Li in the packing container in the upper half region was 1.160, and the molar ratio B of Li to metals other than Li in the packing container in the lower half region was 1.339. At this time, the molar ratio B / molar ratio A was 1.15. A nonaqueous electrolyte secondary battery was fabricated under the same conditions as in Example 1.

[0059] [Crystallite size measurement] The lithium nickel composite oxides obtained in each example and each comparative example were sampled from the top and bottom of the firing vessel, and the crystallite size of each sample was measured. Here, the crystallite size refers to the average size of the crystallites, and the crystallite refers to the region within the primary particle that can be considered as a single crystal. The crystallite size was obtained by Rietveld analysis using DIFFRAC plusTOPAS on data measured with high precision using an X-ray diffractometer from Bruker AXS Co., Ltd.

[0060] The variation in crystallite size was evaluated according to the following criteria from the absolute value of the difference between the crystallite size of the lithium nickel composite oxide sampled from near the bottom surface of the firing container and the crystallite size of the lithium nickel composite oxide sampled from near the top surface of the firing container. A: 0nm or more and less than 15nm B: 15nm or more and less than 20nm C:20nm or more C is poor, B is good, and A is better.

[0061] [Discharge rate characteristics] The nonaqueous electrolyte secondary batteries of each Example and Comparative Example were charged at a constant current of 0.2 C until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.02 C. Then, they were discharged at a constant current of 0.2 C until the voltage reached 2.5 V, and the 0.2 C discharge capacity was measured. Next, they were charged at a constant current of 0.2 C until the voltage reached 4.2 V, and then charged at a constant voltage of 4.2 V until the current reached 0.02 C. Then, they were discharged at a constant current of 1.0 C until the voltage reached 2.5 V, and the 1.0 C discharge capacity was measured. The discharge rate characteristics were then calculated using the following formula: Discharge rate characteristics = (0.2C discharge capacity / 1.0C discharge capacity) x 100

[0062] The discharge rate characteristics were evaluated according to the following criteria. A: 98.5% or more B: 98.0% or more but less than 98.5% C: Less than 98.0% C is poor, B is good, and A is better.

[0063] Table 1 shows the variation in crystallite size and discharge rate characteristics in each example and comparative example. The evaluation results are summarized below.

[0064] [Table 1]

[0065] When the packing packed in the firing vessel is divided into two equal parts in the height direction, the molar ratio A of Li to metals other than Li in the packing in the upper half region and the molar ratio B of Li to metals other than Li in the packing in the lower half region are 1 [Explanation of symbols]

[0066] 5, 5a, 5b Filler, 7 Firing container, 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 15 Battery case, 16 Case body, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Protruding portion, 23 Filter, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket.​

Claims

1. a filling step of filling a firing container with a Ni-containing metal compound and a Li compound to obtain a filler containing the Ni-containing metal compound and the Li compound; A firing step of firing the material filled in the firing container, a molar ratio A of Li to metals other than Li in the filling material in the upper half region and a molar ratio B of Li to metals other than Li in the filling material in the lower half region satisfying 1.02≦B / A≦1.12 when the filling material filled in the firing container in the filling step is divided into two equal parts in the height direction.

2. The method for producing a lithium nickel composite oxide according to claim 1 , wherein the Li compound includes lithium hydroxide.

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