Positive electrode active material for lithium ion secondary battery and manufacturing method thereof

Abstract

To provide a positive electrode active material for obtaining a lithium ion secondary battery having excellent battery capacity and coulombic efficiency, and a manufacturing method thereof.SOLUTION: In a lithium metal composite oxide containing lithium and nickel, when the molar ratio of lithium to a metal other than lithium is 0.95 to 1.30, a lithium ion secondary battery is assembled using a positive electrode containing a lithium metal composite oxide and a negative electrode containing metallic lithium, and a dQ / dV curve is created, the charge peak intensity obtained at a voltage of 4.10 to 4.30 V is 500 to 1100 mAh / g / V, and the discharge peak intensity obtained at a voltage of 3.35 to 3.55 V is 150 to 300 mAh / g / V.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a positive electrode active material for a lithium ion secondary battery and a method for producing the same, and more particularly to a positive electrode active material for a lithium ion secondary battery that, when used in a lithium ion secondary battery, has excellent battery capacity (charge / discharge capacity) and coulombic efficiency (charge / discharge efficiency), and a method for producing the same. [Background technology]

[0002] Although some time has passed since global warming came into the spotlight due to the increase in greenhouse gases such as CO2 in the atmosphere, it is difficult to say that the situation has improved, and various efforts to reduce greenhouse gas emissions are still being made on a global scale.

[0003] Among them, cars that run on fossil fuels, such as gasoline and diesel cars, emit not only CO2 but also NO X , SO X Because lithium-ion batteries have been considered particularly problematic as a source of air pollutants due to their emissions of hydrocarbons, hybrid vehicles, plug-in hybrid vehicles, and electric vehicles that use electricity stored in lithium-ion secondary batteries have attracted attention as environmentally friendly next-generation vehicles, and research and development toward their practical application has been progressing from early on. The lithium-ion secondary batteries installed in these next-generation vehicles are required to have even higher energy density, longer life, and lower cost, and research into improving battery characteristics is becoming increasingly active.

[0004] Furthermore, thermal power plants, which convert thermal energy obtained by burning fossil fuels into electrical energy, also emit large amounts of CO2, making it extremely difficult to build new thermal power plants. To address this growing demand for electricity, one effective way to utilize power is to store potentially surplus electricity at night in lithium-ion secondary batteries installed in homes and use this during the daytime, when electricity consumption is high, thereby leveling the load. Furthermore, efforts to use home storage batteries made of lithium-ion secondary batteries together with solar power generation systems are gradually gaining popularity. This allows the stored clean electricity to be used not only during the day but also at night, and is also expected to serve as an emergency power source in the event of power outages caused by disasters such as earthquakes and typhoons.

[0005] Lithium-ion secondary batteries are composed of a positive electrode, a negative electrode, a non-aqueous electrolyte, or a solid electrolyte, and the active materials used for the positive and negative electrodes are materials capable of desorbing and inserting lithium. The non-aqueous electrolyte includes a non-aqueous electrolyte solution obtained by dissolving a lithium salt, which serves as a supporting salt, in an organic solvent, and the solid electrolyte includes inorganic or organic solid electrolytes that are non-flammable and have lithium ion conductivity.

[0006] Among lithium-ion secondary batteries, those that use lithium metal-containing composite oxides with a layered rock salt or spinel structure as the positive electrode material can obtain a voltage of 4 V, and therefore are being researched, developed, and commercialized as batteries with high energy density.

[0007] Positive electrode materials for lithium-ion secondary batteries include lithium cobalt composite oxide (lithium cobalt oxide, LiCoO2, also known as LCO), which is relatively easy to manufacture, lithium nickel composite oxide (lithium nickel oxide, LiNiO2, also known as LNO), which uses nickel, which is cheaper than cobalt, lithium manganese composite oxide (lithium manganese oxide, LiMn2O4, also known as LMO), and lithium nickel manganese composite oxide (LiNi 0.5Mn 0.5 O2, also known as LNMO), lithium nickel manganese cobalt composite oxide (e.g., LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2, also known as NMC), lithium nickel cobalt aluminum composite oxide (e.g., LiNi 0.75 Co 0.15 Al 0.10 Positive electrode active materials made of lithium metal composite oxides such as lithium ion batteries (also called NCA or O2) have been proposed.

[0008] Among lithium metal composite oxides, positive electrode active materials made from lithium nickel manganese cobalt composite oxide (NMC), which contains nickel, manganese, and cobalt, and lithium nickel cobalt aluminum composite oxide (NCA), which contains nickel, cobalt, and aluminum, are expected to be materials that have excellent thermal stability, high capacity, good cycle characteristics, and can provide high output with low resistance.

[0009] For example, in Patent Document 1, the general formula: Li x (Ni 1-y Co y ) 1-z M z The document discloses a positive electrode active material that is a lithium nickel oxide having a composition represented by the formula: 0.98≦x≦1.1, 0.05≦y≦0.4, 0.01≦z≦0.2, where M is one or more selected from the group consisting of Al, Mn, Ti, and Mg, and that has at least one structural characteristic of (1) an a-axis of 2.8 Å or more, (2) a lattice volume of 99.6 Å or more, (3) a Ni-O bond distance of 1.8 Å or more, (4) a Ni-Ni bond distance of 2.8 Å or more, (5) a Ni-O Debye-Waller factor of 0.065 or more, and (6) a Ni-Ni Debye-Waller factor of 0.066 or less, when the SOC is at least 50%. The document also describes a positive electrode active material that has excellent structural stability (thermal stability) and a high discharge capacity (high energy density).

[0010] Patent Document 2 discloses a positive electrode active material for a lithium ion battery prepared by a coprecipitation method, the coprecipitation method comprising a step of adding ammonia water to an aqueous solution of a mixture of nickel sulfate, manganese sulfate, and cobalt sulfate, and adding lithium hydroxide while stirring to obtain a metal hydroxide, and the positive electrode active material for a lithium ion battery is prepared by a step of mixing the metal hydroxide obtained by the coprecipitation method with lithium carbonate to obtain a mixed powder of the metal hydroxide and the lithium carbonate, and then firing the mixed powder, and the positive electrode active material for a lithium ion battery is prepared by a step of mixing the metal hydroxide obtained by the coprecipitation method with lithium carbonate to obtain a mixed powder of the metal hydroxide and the lithium carbonate, and the positive electrode active material has a composition formula: Li a Ni x Co y Mn 1-x-y The document discloses a positive electrode active material for lithium ion batteries, which is represented by the formula O2 (where 0.9≦a≦1.2, 0.7≦x≦0.9, and 0.1≦y≦0.3) and has a sodium content of 100 ppm or less. It also discloses that by carrying out a coprecipitation reaction using lithium hydroxide, a coprecipitate that does not contain sodium, which acts as an impurity, can be produced, which suppresses polarization in the battery and, as a result, significantly improves the cycle characteristics of the battery. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-332713 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-162601 Summary of the Invention [Problem to be solved by the invention]

[0012] However, the positive electrode active material described in Patent Document 1 is not sufficiently capable of meeting the demand for higher battery capacity, which requires further improvement. Furthermore, while different elements are added to the lithium metal composite oxide to improve battery characteristics, the reliance on the addition of different elements is excessive, and no mention is made of improvements to the lithium metal composite oxide itself, such as the aforementioned LNO, NCA, or NMC, and it cannot be said that the advantages of lithium metal composite oxides, such as high capacity and low cost, are fully utilized. Furthermore, the positive electrode active material described in Patent Document 2 only shows improvements in cycle characteristics, and makes little mention of increasing battery capacity.

[0013] In view of these problems, the present invention aims to provide a positive electrode active material for a lithium ion secondary battery, which is capable of obtaining a lithium ion secondary battery having excellent battery capacity (charge / discharge capacity) and coulombic efficiency (charge / discharge efficiency) by improving and optimizing the lithium metal composite oxide itself, and a method for producing the same. [Means for solving the problem]

[0014] That is, a first aspect of the present invention that solves the above-mentioned problems is a lithium metal composite oxide comprising secondary particles formed by agglomeration of primary particles containing lithium and nickel, or a lithium metal composite oxide comprising both the primary particles and the secondary particles, wherein the lithium metal composite oxide has a molar ratio of lithium to a metal other than lithium of 0.95 to 1.30, and a lithium ion secondary battery is assembled using a positive electrode containing the lithium metal composite oxide and a negative electrode containing metallic lithium. The battery is charged to a voltage of 4.30 V and then discharged to a voltage of 3.00 V, and when a graph (dQ / dV curve) is created with voltage on the horizontal axis and dQ / dV, which is the value obtained by differentiating battery capacity with voltage, on the vertical axis, the charge peak intensity obtained at a voltage of 4.10 to 4.30 V is 500 to 1100 mAh / g / V, and the discharge peak intensity obtained at a voltage of 3.35 to 3.55 V is 150 to 300 mAh / g / V.

[0015] According to the first aspect of the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery, which is used to obtain a lithium ion secondary battery having excellent battery capacity (charge / discharge capacity) and coulombic efficiency (charge / discharge efficiency).

[0016] At this time, the lithium metal composite oxide has a specific surface area of 0.25 to 1.50 m 2 / g, the (003) crystallite diameter may be 800 to 1600 Å, and the metal (Me) site occupancy may be 97.2 to 100%.

[0017] This makes it possible to increase the crystallinity of the lithium nickel composite oxide constituting the positive electrode active material, thereby increasing the battery capacity of the lithium ion secondary battery.

[0018] In this case, when the lithium ion secondary battery is assembled using a positive electrode containing the lithium metal composite oxide and a negative electrode containing metallic lithium, and is charged to a voltage of 4.30 V and then discharged to a voltage of 3.00 V, the resulting discharge capacity may be 232 to 240 mAh / g and the resulting coulombic efficiency may be 90.0 to 95.0%.

[0019] In this way, it is possible to provide a positive electrode active material for a lithium ion secondary battery, which is capable of obtaining a lithium ion secondary battery having excellent discharge capacity and coulombic efficiency (charge and discharge efficiency).

[0020] In this case, the lithium metal composite oxide is represented by the general formula (B): Li s Ni 1-x M x O 2+α (wherein s, x, and α are in the ranges of 0.95≦s≦1.30, 0≦x≦0.2, and −0.1≦α≦0.2, and M is at least one metal element selected from the group consisting of Co, Mn, W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, and S).

[0021] In this way, it is possible to provide a positive electrode active material for a lithium ion secondary battery, which is used to obtain a lithium ion secondary battery having excellent battery capacity (charge / discharge capacity) and coulomb efficiency (charge / discharge efficiency).

[0022] A second aspect of the present invention is a method for producing secondary particles formed by agglomeration of primary particles containing lithium and nickel, or a lithium metal composite oxide comprising both the primary particles and the secondary particles, the method comprising: a crystallization step of mixing a raw material aqueous solution containing nickel, an alkaline aqueous solution containing sodium hydroxide, and an ammonium aqueous solution containing ammonium ions to prepare a reaction solution, and controlling the pH of the reaction solution (based on a liquid temperature of 25°C) to be 11.0 to 12.5 to obtain a metal composite hydroxide cake; and a drying step of washing the metal composite hydroxide cake and then drying it at 120 to 200°C for 1 to 10 hours. ,gold a mixing step of mixing the metal composite hydroxide with a lithium compound to obtain a lithium mixture; a calcination step of calcining the lithium mixture at 300 to 500°C for 1 to 10 hours to react in a state free of the metal composite oxide to obtain a lithium calcined product; and a firing step of calcining the lithium calcined product at 650 to 900°C for 1 to 20 hours to react in a state free of the metal composite oxide to obtain a lithium metal composite oxide, wherein the method further comprises, between the calcination step and the firing step, a cooling step of cooling the lithium calcined product to room temperature, and a first crushing step of crushing the lithium calcined product.

[0023] According to a second aspect of the present invention, it is possible to provide a method for producing a positive electrode active material for a lithium ion secondary battery, which can obtain a lithium ion secondary battery excellent in battery capacity (charge / discharge capacity) and coulombic efficiency (charge / discharge efficiency). Furthermore, the generation of a metal composite oxide (intermediate) can be more reliably suppressed in the first crushing step, and the generation of agglomerates or sintered bodies of the resulting lithium metal composite oxide can be reduced in the firing step that follows the first crushing step.

[0024] In this case, the production method may be such that the metal composite hydroxide, which is a raw material for the lithium metal composite oxide, reacts directly with the lithium compound without passing through the form of the metal composite oxide during the production process.

[0025] In this way, it is possible to provide a method for producing a positive electrode active material for a lithium ion secondary battery, which enables to obtain a lithium ion secondary battery having excellent battery capacity (charge / discharge capacity) and coulomb efficiency (charge / discharge efficiency).

[0026] At this time ,before After the calcination step, the lithium metal composite oxide is crushed in a second crushing step. The process It may have.

[0027] Do it like this If, The average particle size and particle size distribution of the positive electrode active material obtained after the second crushing step can be controlled within a suitable range.

[0028] In this case, the lithium metal composite oxide is represented by the general formula (B): Li s Ni 1-x M x O 2+α (wherein s, x, and α are in the ranges of 0.95≦s≦1.30, 0≦x≦0.2, and −0.1≦α≦0.2, and M is at least one metal element selected from the group consisting of Co, Mn, W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, and S).

[0029] In this way, it is possible to provide a method for producing a positive electrode active material for a lithium ion secondary battery, which enables to obtain a lithium ion secondary battery having excellent battery capacity (charge / discharge capacity) and coulomb efficiency (charge / discharge efficiency).

[0030] In this case, the metal composite hydroxide may have a trigonal crystal structure, the metal composite oxide may have a cubic crystal structure, and the lithium metal composite oxide may have a rhombohedral crystal structure.

[0031] In this way, the lithium metal composite oxide (positive electrode active material) can be produced from the metal composite hydroxide (precursor) without going through a metal composite oxide (intermediate) with a different crystal system.

[0032] In this case, the lithium compound may be lithium hydroxide and / or lithium carbonate.

[0033] These lithium compounds are easy to handle, have a constant quality, and contain little impurities such as sulfate, chloride, and nitrate. [Effects of the Invention]

[0034] According to the present invention, it is possible to provide a positive electrode active material for a lithium ion secondary battery that has excellent battery capacity (charge / discharge capacity) and coulombic efficiency (charge / discharge efficiency) when used in a lithium ion secondary battery, and a method for producing the same. [Brief explanation of the drawings]

[0035] [Figure 1] Figure 1 is an explanatory diagram showing an example of crystal structure change in a conventional process. Figure 1(A) is a schematic diagram of the crystal structure of a metal composite hydroxide (precursor) with space group P3-m1 (trigonal), Figure 1(B) is a schematic diagram of the crystal structure of a metal composite oxide (intermediate) with space group Fm3m (cubic), and Figure 1(C) is a schematic diagram of the crystal structure of a lithium metal composite oxide (cathode active material) with space group R3-m (rhombohedral). [Figure 2] FIG. 2 is a process diagram showing an outline of a method for producing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention. [Figure 3] 2 is a graph showing the results of compound identification of the lithium calcined product obtained by X-ray diffraction (XRD) according to the present invention. [Figure 4] 1 is a graph showing charge / discharge curves obtained by evaluation of a lithium ion secondary battery according to the present invention. [Figure 5] 1 is a graph showing a dQ / dV curve obtained by evaluation of a lithium ion secondary battery according to the present invention. [Figure 6] 1 is a graph showing the (003) peak and (104) peak of a lithium metal composite oxide obtained by X-ray diffraction (XRD) according to the present invention. [Figure 7]2 is an observation image showing the particle shape of the lithium metal composite oxide according to the present invention, obtained by a scanning electron microscope (SEM). [Figure 8] 1 is a graph showing the particle size distribution of a lithium metal composite oxide according to the present invention, obtained by a laser diffraction / scattering method. [Figure 9] FIG. 1 is an explanatory diagram of a coin battery used in evaluation of a lithium ion secondary battery according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0036] The positive electrode active material for a lithium ion secondary battery (hereinafter also simply referred to as "positive electrode active material") of the present invention and its manufacturing method will be described in detail below in the order of 1 to 5. The present invention is not limited to the embodiments described below, and modifications to the embodiments can be made based on the knowledge of those skilled in the art without departing from the spirit of the present invention. 1. Crystal matching between precursor and positive electrode active material 2. Manufacturing method of positive electrode active material for lithium-ion secondary batteries 3. Positive electrode active material for lithium-ion secondary batteries 4. Lithium-ion secondary batteries Ratings 5.1-4

[0037] 1. Crystal matching between precursor and positive electrode active material In the positive electrode active material for lithium ion secondary batteries and the manufacturing method thereof, there is a method in which a metal composite hydroxide (e.g., Ni(OH)2, (NiMnCo)(OH)2, (NiCoAl)(OH)2, etc.), which is a raw material of a lithium metal composite oxide, is first converted into a form containing a metal composite oxide (e.g., NiO, (NiMnCo)O, (NiCoAl)O, etc.), and then calcined together with a lithium compound (e.g., LiOH, Li2CO3, etc.) to obtain a lithium metal composite oxide (e.g., LNO, NMC, NCA, etc.).

[0038] However, in this conventional process, as shown in the example in Figure 1, when focusing on the crystal structures of the metal composite hydroxide (precursor) (hereinafter also referred to as the "precursor"), the metal composite oxide (hereinafter also referred to as the "intermediate"), and the lithium metal composite oxide (hereinafter also referred to as the "cathode active material"), the process starts with Ni(OH)2, a metal composite hydroxide (precursor) with a space group P3-ml (trigonal), and goes through the metal composite oxide (intermediate) NiO, which has a significantly different crystal system, with the space group Fm3m (cubic), and then returns to a structure similar to that of the metal composite hydroxide (precursor), to obtain the lithium metal composite oxide (cathode active material) LiNiO2 with a space group R3-m (rhombohedral). This puts a large strain on the crystal structure of the final lithium metal composite oxide (cathode active material). Here, Figure 1(A) is a schematic diagram of the crystal structure of the metal composite hydroxide (precursor) having space group P3-m1 (trigonal), Figure 1(B) is a schematic diagram of the crystal structure of the metal composite oxide (intermediate) having space group Fm3m (cubic), and Figure 1(C) is a schematic diagram of the crystal structure of the lithium metal composite oxide (cathode active material) having space group R3-m (rhombohedral).

[0039] The adverse effect that this change in crystal structure has on lithium metal composite oxide (positive electrode active material) is thought to be the occurrence of cation mixing, in which transition metals migrate to lithium ion sites. This inhibits the diffusion of lithium ions within the solid phase, increases diffusion resistance, and raises concerns about a decrease in battery capacity (charge / discharge capacity) and coulombic efficiency (charge / discharge efficiency).

[0040] Therefore, if it were possible to produce a lithium metal composite oxide (positive electrode active material) directly from a metal composite hydroxide (precursor), it would be possible to significantly reduce the burden on the crystalline structure of the lithium metal composite oxide (positive electrode active material).

[0041] The present inventors have conducted extensive research into further increasing the capacity of positive electrode active materials for lithium ion secondary batteries, and as a result have discovered that it is possible to provide a new positive electrode active material for lithium ion secondary batteries (hereinafter simply referred to as "secondary battery" or "battery") that has excellent battery capacity (charge / discharge capacity) and coulombic efficiency (charge / discharge efficiency) by allowing a metal composite hydroxide, which is a raw material for lithium metal composite oxide, to react directly with a lithium compound in a state that does not contain a metal composite oxide during the manufacturing process, i.e., without passing through the form of a metal composite oxide, and thus to provide a new method for manufacturing the same, which has led to the completion of the present invention.

[0042] 2. Manufacturing method of positive electrode active material for lithium-ion secondary batteries Hereinafter, a method for producing a positive electrode active material for a lithium ion secondary battery will be described with reference to the drawings. As shown in Fig. 2, a method for producing a positive electrode active material for a lithium ion secondary battery according to one embodiment of the present invention comprises a crystallization step S1, a drying step S2, a mixing step S3, a calcination step S4, and a firing step S7. Hereinafter, a cooling step S5 and a first crushing step S6 may be included between the calcination step S4 and the firing step S7, and a second crushing step S8 may be included after the firing step S7. Hereinafter, each step will be described in the order of (2-1) to (2-3). (2-1) Preparation of metal composite hydroxide (precursor) (2-2) Preparation of lithium calcined product (2-3) Production of lithium metal composite oxide (positive electrode active material)

[0043] (2-1) Preparation of metal composite hydroxide (precursor) In the production of the metal composite hydroxide (precursor), the following 1) crystallization step S1 and 2) drying step S2 are carried out to produce 3) the metal composite hydroxide (precursor).

[0044] 1) Crystallization process S1 First, an aqueous solution of a metal compound containing nickel and an optionally added element M (M) is prepared as a raw material solution. The aqueous solution of the metal compound can be easily prepared by dissolving the metal compound in water at a temperature of about 30°C. From the viewpoint of cost and preventing the inclusion of halogens, examples of the metal compound include metal sulfates and hydrates, but the present invention is not limited to these examples. The concentration of the metal compound in the aqueous solution of the metal compound is not particularly limited, but is usually 1.0 to 2.6 mol / L. Unless otherwise specified, the symbol "to" in the specification indicates a range from above to below.

[0045] Next, the aqueous solution of the metal compound is added to the water at 40 to 60°C that has been poured into the reaction vessel, and as will be described later, the pH and ammonium ion (NH4 + ) concentration is adjusted to crystallize the particles. Furthermore, when the particles are crystallized, the generation of secondary particles due to aggregation of the primary particles proceeds in parallel. The temperature during crystallization is preferably 40°C or higher from the viewpoint of suppressing coarsening of the metal composite hydroxide (precursor), and is preferably 60°C or lower from the viewpoint of suppressing miniaturization of the metal composite hydroxide (precursor). Note that during crystallization, it is preferable to thoroughly stir the contents in the reaction tank from the viewpoint of efficiently crystallizing the particles.

[0046] The atmosphere (reaction atmosphere) during crystallization is an inert atmosphere, and preferably has an oxygen concentration of 2% by volume or less, more preferably 1% by volume or less. That is, it is preferable to use an atmosphere consisting of an inert gas such as nitrogen or argon that contains almost no oxygen, and it is particularly preferable to spray this inert gas onto the surface of the contents in the reaction vessel to completely block contact between the contents and oxygen. By controlling the atmosphere during crystallization to such an inert atmosphere, secondary particles with a high density and an appropriate particle size can be obtained. Furthermore, while adjusting the pH of the water in the reaction vessel to 11.0 to 12.5 with a pH adjuster such as an aqueous solution of sodium hydroxide, the aqueous solution of the metal compound and the ammonium ion (NH4 +It is preferable to add aqueous ammonia to the reaction vessel to adjust the concentration of ammonium ions (NH4 + ) concentration is preferably 5 to 30 g / L, more preferably 10 to 20 g / L, from the viewpoint of stabilizing the crystallization treatment.

[0047] 2) Drying process S2 The slurry containing the metal composite hydroxide (precursor) cake obtained in the crystallization step S1 is subjected to solid-liquid separation using a filtering device such as a filter press, and the recovered solid metal composite hydroxide (precursor) cake is washed with wash water, thereby removing impurities from the metal composite hydroxide (precursor) cake.

[0048] Since moisture adheres to the surface of the water-washed metal composite hydroxide (precursor) cake, it is preferable to dry the metal composite hydroxide (precursor) cake in a dryer. Examples of dryers include a static dryer, a fluidized bed dryer, and an airflow dryer, but the present invention is not limited to these examples. When a heating dryer is used as the dryer, it is preferably an electrically heated dryer that does not generate carbon gas in a dry atmosphere.

[0049] The drying temperature for the metal composite hydroxide (precursor) cake is preferably 100°C or higher, more preferably 120°C or higher, from the viewpoint of increasing drying efficiency, and is preferably 200°C or lower, more preferably 180°C or lower, from the viewpoint of suppressing deterioration of the metal composite hydroxide (precursor). The drying time for the metal composite hydroxide (precursor) cake differs depending on the drying temperature of the metal composite hydroxide (precursor) cake and cannot be determined in general terms. Therefore, it is preferable to determine the drying time appropriately depending on the drying temperature of the metal composite hydroxide (precursor) cake and other factors, but it is usually about 1 to 10 hours.

[0050] 3) Metal composite hydroxide (precursor) The average particle size of the metal composite hydroxide (precursor) obtained in the drying step S2 is preferably 3 μm or more, more preferably 4 μm or more, from the viewpoint of increasing the packing density of the metal composite hydroxide (precursor) and thereby increasing the battery capacity (charge / discharge capacity per volume), and is preferably 20 μm or less, more preferably 15 μm or less, from the viewpoint of increasing the specific surface area of the positive electrode active material and improving the output characteristics of the battery.

[0051] The composition of the metal composite hydroxide (precursor) is, from the viewpoint of obtaining a positive electrode active material for a lithium ion secondary battery represented by general formula (B) described later, which has excellent battery characteristics such as battery capacity (charge / discharge capacity) and coulomb efficiency (charge / discharge efficiency) when used in a lithium ion secondary battery, the general formula (A): Ni 1-x M x It is preferably a metal composite hydroxide (precursor) represented by the formula (OH)2 (wherein x is 0≦x≦0.2, and M is at least one metal element selected from the group consisting of Co, Mn, W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, and S).

[0052] In the metal composite hydroxide (precursor) represented by general formula (A), the composition range of nickel and the additive element M constituting it and their critical meaning are the same as those of the lithium metal composite oxide (positive electrode active material) represented by general formula (B) described below, and therefore a description of these matters will be omitted here.

[0053] As shown in FIG. 1, the metal composite hydroxide (precursor) has a crystal structure of space group P3-ml (trigonal). A metal composite oxide (intermediate) obtained by subjecting the metal composite hydroxide (precursor) to oxidative roasting or the like has a crystal structure of space group Fm3m (cubic), which is a different crystal structure from the metal composite hydroxide (precursor). The element M in the general formula (B) is located at the Ni position in the trigonal crystal, and when the molar ratio "x" of the element M in the general formula (B) is 0.20 or less, the metal composite hydroxide (precursor) has a crystal structure of space group P3-ml (trigonal). The metal composite oxide (intermediate) to which the element M has been added has a crystal structure of space group Fm3m (cubic).

[0054] Metal composite hydroxide (precursor) particles are obtained by the crystallization step S1 and drying step S2.

[0055] (2-2) Preparation of lithium calcined product The lithium calcined product is produced by carrying out the following steps: 1) mixing step S3 and 2) calcining step S4. 2) Calcining step S4 can also be followed by 3) cooling step S5 and 4) first crushing step S6.

[0056] As raw materials for the lithium metal composite oxide (cathode active material), a metal composite hydroxide (precursor) and a lithium compound are used. In the present invention, the metal composite hydroxide (precursor) reacts directly with the lithium compound to obtain a lithium calcined product, without passing through the form of a metal composite oxide (intermediate). That is, in the present invention, the metal composite hydroxide (precursor) is not converted into a metal composite oxide (intermediate) by roasting. In the production of the lithium calcined product, a first-stage heat treatment is performed in a calcination step S4 without the metal composite oxide (intermediate) present, in order to obtain the lithium metal composite oxide (cathode active material) described below.

[0057] 1) Mixing process S3 In the mixing step S3, the metal composite hydroxide (precursor) and a lithium compound are mixed together to produce a lithium mixture.

[0058] (a) Lithium compounds Examples of lithium compounds include lithium carbonate (Li2CO3, melting point: 723°C), lithium hydroxide (LiOH, melting point: 462°C), lithium nitrate (LiNO3, melting point: 261°C), lithium chloride (LiCl, melting point: 613°C), and lithium sulfate (Li2SO4, melting point: 859°C), but the present invention is not limited to these examples. These lithium compounds may be used alone or in combination of two or more. Among these lithium compounds, lithium hydroxide and lithium carbonate are preferred because they are easy to handle, have stable quality, and contain little impurities such as sulfate, chloride, and nitrate, but lithium hydroxide is more preferred. Lithium hydroxide is also preferred from the viewpoint of the calcination temperature, which will be described later. The maximum particle size of the lithium compound is preferably 10 μm or less, and the average particle size of the lithium compound is preferably 5 μm or less.

[0059] (b) Preparation of lithium mixture As described above, in the mixing step S3, the metal composite hydroxide (precursor) and the lithium compound are mixed to obtain a lithium mixture. As the mixing device, a shaker mixer or the like can be used.

[0060] The metal composite hydroxide (precursor) and the lithium compound are preferably mixed so that the ratio between the total number of atoms of metal elements contained in the lithium metal composite oxide (cathode active material) and the number of lithium atoms (hereinafter simply referred to as the "ratio"; that is, Li / Me, as described below) is 0.95 to 1.30. From the viewpoints of suppressing coarsening of particle size and crystallite size and improving cycle characteristics, the upper limit of the "ratio" is more preferably 0.97 to 1.20, and particularly preferably 0.98 to 1.05. When the metal composite hydroxide (precursor) and the lithium compound are mixed at this "ratio," lithium atoms are incorporated into the 3a site, which is the lithium site, thereby improving battery characteristics.

[0061] Here, the above-mentioned sites refer to crystallographically equivalent lattice positions. When an atom exists at a lattice position, it is said that the site is occupied, and the occupied site is called an "occupied site." Taking lithium-nickel composite oxide (lithium nickel oxide, LiNiO2, LNO) as an example, LiNiO2 has three occupied sites. The three occupied sites are called the lithium site, nickel site, and oxygen site, respectively, or the 3a site, 3b site, and 6c site.

[0062] 2) Pre-firing step S4 In the calcination step S4, the lithium mixture obtained in the mixing step S3 is calcined in an air atmosphere or an oxidizing atmosphere to obtain a calcined lithium product containing secondary particles formed by aggregation of primary particles. In the calcination step S4, the metal composite hydroxide (precursor) and the lithium mixture are directly reacted to produce a lithium metal composite oxide (cathode active material). The lithium metal composite oxide (cathode active material) with a similar crystal structure can be produced from the metal composite hydroxide (precursor) without passing through a metal composite oxide (intermediate) with a different crystal system. In this way, the calcination step S4 aligns the crystal structures of the metal composite hydroxide (precursor) and the lithium metal composite oxide (cathode active material) before and after the reaction, thereby significantly reducing the stress on the crystal structure of the lithium metal composite oxide (cathode active material).

[0063] The oxygen concentration in the oxidizing atmosphere is preferably 18 to 100% by volume. The calcination temperature of the lithium mixture is preferably 300 to 500°C, more preferably 400 to 480°C, so that the metal composite hydroxide (precursor) reacts directly with the lithium compound without passing through a metal composite oxide (intermediate) with a significantly different crystal system to produce a lithium metal composite oxide (cathode active material) with a similar crystal system to that of the metal composite hydroxide (precursor). Calcination is preferably performed near the melting point or reaction temperature of the lithium compound, which allows sufficient diffusion of lithium into the metal composite hydroxide (precursor) and promotes the reaction between the metal composite hydroxide (precursor) and the lithium compound. At temperatures below 300°C, decomposition of the metal composite hydroxide (precursor) is difficult to proceed, potentially inhibiting the reaction between the metal composite hydroxide (precursor) and the lithium compound. At temperatures above 500°C, the metal composite hydroxide (precursor) is converted to a metal composite oxide (intermediate), potentially inhibiting the reaction between the metal composite hydroxide (precursor) and the lithium compound. The calcination time of the lithium mixture varies depending on the calcination temperature of the lithium mixture and cannot be determined in general, and therefore should be determined appropriately depending on the calcination temperature of the lithium mixture and other factors. However, the calcination time is usually preferably about 1 to 10 hours, and more preferably about 2 to 8 hours.

[0064] 3) Cooling process S5 Furthermore, since the metal composite hydroxide (precursor) reacts directly with the lithium compound without passing through the metal composite oxide (intermediate), it is preferable to cool the mixture to room temperature after the calcination step S4 when transferring from the calcination step S4 to the subsequent calcination step S7. By performing this cooling step S5, it is possible to more reliably suppress the generation of the metal composite oxide (intermediate). Furthermore, although the detailed reason is unknown, it is possible to more gently proceed with the reaction in the calcination step S7 described below.

[0065] 4) First crushing process S6 The lithium calcined product obtained in the calcination step S4 may be agglomerated or slightly sintered. In such cases, it is preferable to crush the agglomerates or sintered bodies of the lithium calcined product. By performing this first crushing step S6, the reactivity between lithium and transition metals such as nickel can be improved in the subsequent calcination step S7, thereby more reliably suppressing the formation of metal composite oxides (intermediates). This also reduces the generation of agglomerates or sintered bodies of the lithium metal composite oxide obtained in the subsequent calcination step S7. Crushing refers to the operation of applying mechanical energy to agglomerates consisting of multiple secondary particles that are formed during calcination due to sintering necking between secondary particles, thereby separating the agglomerates without substantially destroying the secondary particles themselves, thereby loosening the agglomerates. Known methods, such as a pin mill or hammer mill, can be used for crushing. In this case, it is preferable to control the crushing force within an appropriate range so as not to destroy the secondary particles.

[0066] A lithium metal composite oxide (positive electrode active material) is obtained by the above-mentioned mixing step S3 and calcining step S4, or by the mixing step S3, calcining step S4, cooling step S5, and first crushing step S6.

[0067] (2-3) Production of lithium metal composite oxide (positive electrode active material) In the production of the lithium metal composite oxide (positive electrode active material), the following 1) firing step S7 is carried out to produce the lithium metal composite oxide (positive electrode active material). After 1) firing step S7, 2) second crushing step S8 can also be carried out.

[0068] 1) Firing process S7 In the firing step S7, the lithium calcined product is fired in an air atmosphere or an oxidizing atmosphere to obtain a lithium metal composite oxide (cathode active material) containing secondary particles formed by aggregation of primary particles. That is, in the present invention, in order to obtain the lithium metal composite oxide (cathode active material), a second-stage heat treatment is performed in the firing step S7 without containing the metal composite oxide (intermediate).

[0069] The oxygen concentration in the oxidizing atmosphere is preferably 18 to 100% by volume. The firing temperature of the lithium calcined product is preferably 650°C or higher, more preferably 700°C or higher, from the viewpoint of reducing the amount of unreacted excess lithium and improving crystallinity, and is preferably 900°C or lower, from the viewpoint of suppressing excessive sintering between particles of the lithium metal composite oxide (positive electrode active material). The firing time of the lithium calcined product varies depending on the firing temperature of the lithium calcined product and cannot be determined in general, so it is determined appropriately depending on the firing temperature of the lithium calcined product and other factors, but is usually preferably about 1 to 20 hours, more preferably about 5 to 15 hours.

[0070] By firing the lithium calcined product in the above manner, primary particles of a lithium metal composite oxide (cathode active material) containing lithium and nickel are formed, and lithium metal composite oxide (cathode active material) particles containing secondary particles formed by aggregation of the primary particles are obtained. The secondary particles are usually spherical or ellipsoidal in shape.

[0071] 2)Second crushing process S8 The lithium metal composite oxide (cathode active material) obtained in the calcination step S7 may be agglomerated or slightly sintered. In such cases, it is preferable to crush the agglomerates or sintered body of the lithium metal composite oxide (cathode active material). This allows the average particle size and particle size distribution of the resulting cathode active material to be controlled within a suitable range. Crushing refers to the process of applying mechanical energy to agglomerates consisting of multiple secondary particles that are formed during calcination due to sintering necking between secondary particles, thereby separating the agglomerates without substantially destroying the secondary particles themselves, thereby loosening the agglomerates. Known methods, such as a pin mill or hammer mill, can be used for crushing. It is preferable to control the crushing force within an appropriate range so as not to destroy the secondary particles.

[0072] By the above-mentioned firing step S7, or by the firing step S7 and the second crushing step S8, lithium metal composite oxide (positive electrode active material) particles are obtained.

[0073] 3. Positive electrode active material for lithium-ion secondary batteries A positive electrode active material for a lithium-ion secondary battery according to one embodiment of the present invention is a lithium metal composite oxide comprising secondary particles formed by agglomeration of primary particles containing lithium and nickel, or a lithium metal composite oxide comprising both primary and secondary particles, wherein the lithium metal composite oxide has a molar ratio of lithium to a metal other than lithium of 0.95 to 1.30. A lithium-ion secondary battery is assembled using a positive electrode containing the lithium metal composite oxide and a negative electrode containing metallic lithium. The battery is charged to a voltage of 4.30 V and then discharged to a voltage of 3.00 V. When a graph (dQ / dV curve) is plotted, with voltage on the horizontal axis and dQ / dV, which is the value obtained by differentiating battery capacity with voltage, on the vertical axis, the battery exhibits a charge peak intensity of 500 to 1100 mAh / g / V at voltages of 4.10 to 4.30 V and a discharge peak intensity of 150 to 300 mAh / g / V at voltages of 3.35 to 3.55 V. Details are described below.

[0074] 1) Composition The composition of the lithium metal composite oxide (positive electrode active material) according to one embodiment of the present invention is represented by the general formula (B): Li s Ni 1-x M x O 2+α (wherein s, x, and α are in the ranges of 0.95≦s≦1.30, 0≦x≦0.2, and −0.1≦α≦0.2, and M is at least one metal element selected from the group consisting of Co, Mn, W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, and S). When a positive electrode active material having the above composition is used in a lithium ion secondary battery, a lithium ion secondary battery with excellent battery characteristics such as battery capacity (charge / discharge capacity) can be obtained. The molar ratios (contents) of nickel and the optionally added element M (M), as well as the critical significance, are as follows:

[0075] Nickel (Ni) is an element that contributes to increasing the potential and capacity of lithium-ion secondary batteries, and in order to fully obtain this effect, the value of "1-x", which indicates the molar ratio, is preferably set within the range of 0.80 to 1.00, more preferably 0.85 to 1.00, and particularly preferably 0.90 to 1.00. If the value of "1-x" is less than 0.80, it is not possible to improve the charge / discharge capacity of the lithium-ion secondary battery.

[0076] The element M (M) is an element that contributes to the output characteristics, cycle characteristics, thermal stability, safety, etc. of a lithium-ion secondary battery, and is added as desired. The value of "x," which indicates the molar ratio of the element M, may be 0, but in order to fully obtain the above-mentioned effects, the value of "x" is preferably set within a range of more than 0 and not more than 0.20, more preferably more than 0 and not more than 0.15, and particularly preferably more than 0 and not more than 0.10. If the value of "x" is 0, the output characteristics, cycle characteristics, thermal stability, safety, etc. of the lithium-ion secondary battery cannot be improved. On the other hand, if the value of "x" exceeds 0.20, the molar ratio of nickel decreases, and the effects cannot be fully obtained. As such an element M (M), one or more elements selected from the group consisting of cobalt (Co), manganese (Mn), tungsten (W), molybdenum (Mo), vanadium (V), calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), titanium (Ti), chromium (Cr), zirconium (Zr), aluminum (Al), niobium (Nb), tantalum (Ta), silicon (Si), phosphorus (P), boron (B), and sulfur (S) can be used.

[0077] The Li content, s, is 0.95≦s≦1.30. Furthermore, s is preferably 0.97≦s≦1.20, and more preferably 0.98≦s≦1.05. By setting the Li content within this range, it is possible to suppress coarsening of the particle size and crystallite size of the positive electrode active material. Furthermore, in a lithium-ion secondary battery using this positive electrode active material, it is possible to improve battery characteristics such as cycle characteristics.

[0078] In the general formula (B), α represents the excess or deficiency of oxygen relative to the stoichiometric ratio of Li(Ni,M)O2. If α is within the above range, the crystal structure has few defects, and the appropriate crystal structure allows for high charge / discharge capacity and output characteristics.

[0079] 2) Peak characteristics of the dQ / dV curve A lithium-ion secondary battery was assembled using a positive electrode containing a lithium-metal composite oxide and a negative electrode containing metallic lithium, and was charged to a voltage of 4.30 V and then discharged to a voltage of 3.00 V. When a graph (dQ / dV curve) was created with voltage on the horizontal axis and dQ / dV, which is the value obtained by differentiating battery capacity with voltage, on the vertical axis, the charge peak intensity obtained at voltages of 4.10 to 4.30 V was 500 to 1100 mAh / g / V, and the discharge peak intensity obtained at voltages of 3.35 to 3.55 V was 150 to 300 mAh / g / V. Through various investigations, the present inventors found that the charge peak intensity and discharge peak intensity of the positive electrode active material are related to excellent battery capacity (charge / discharge capacity) and Coulombic efficiency (charge / discharge efficiency), leading to the completion of the present invention.

[0080] 3) Particle size and particle structure The particle size of the primary particles in the lithium metal composite oxide (positive electrode active material) is not particularly limited, but is usually about 0.2 to 1 μm. The particle size of the secondary particles is not particularly limited, but is usually about 3 to 30 μm. The lithium metal composite oxide (positive electrode active material) is essentially composed of secondary particles, but may contain a small amount of primary particles in addition to the secondary particles.

[0081] 4) Crystallite size The crystallite diameter of the positive electrode active material, as determined from the X-ray diffraction peak of the (003) plane, is preferably 800 Å or more and 1600 Å or less. By setting the crystallite diameter to 800 Å or more and 1600 Å or less, the crystallinity of the lithium nickel composite oxide constituting the positive electrode active material can be increased. This increases the battery capacity of the lithium ion secondary battery. If the crystallite diameter of the positive electrode active material is less than 800 Å, the crystal growth may be insufficient, resulting in reduced capacity and output. On the other hand, if the crystallite diameter exceeds 1600 Å, the battery characteristics may be reduced due to cation mixing.

[0082] 5) Li seat occupancy rate The Li site occupancy of the positive electrode active material is preferably 97% or more. Such a high lithium site occupancy can suppress the occurrence of cation mixing in a lithium ion secondary battery using this lithium metal composite oxide as a positive electrode active material, and can achieve a high charge / discharge capacity. Furthermore, if the Li site occupancy is less than 97%, there is a possibility that cation mixing may occur.

[0083] 6) Me seat occupancy rate The Me site occupancy of the positive electrode active material is preferably 97.2% or more. The Me site occupancy correlates with battery characteristics, and a higher Me site occupancy leads to better battery characteristics. The upper limit of the Me site occupancy is not particularly limited, and a Me site occupancy of 100%, i.e., a state in which all Me sites are occupied by Me, is also included in the scope of the present invention. If the Me site occupancy is less than 97.2%, cation mixing may occur.

[0084] 7) Specific surface area The specific surface area of the positive electrode active material is 0.25 to 1.50 m 2 / g or less is preferable. A positive electrode active material having a specific surface area in this range has a large contact area with the electrolyte, and can improve the charge / discharge capacity of a lithium ion secondary battery using the positive electrode active material. In contrast, 2If the specific surface area of the positive electrode active material is less than 1.50 m / g, when a lithium ion secondary battery is constructed, the reaction area with the electrolyte cannot be secured, and sufficient charge / discharge capacity may not be obtained. 2 If the solubility exceeds 1 / g, the reactivity with the electrolyte becomes too high, which may result in a decrease in thermal stability.

[0085] 8) Crystal structure The positive electrode active material has a rhombohedral crystal structure of space group R3-m as shown in Figure 1(C). Furthermore, element M in the general formula (B) is present at the Ni position in the rhombohedral crystal structure, and when the value of the molar ratio "x" of element M in the general formula (B) is 0.20 or less, the positive electrode active material has a rhombohedral crystal structure of space group R3-m. If the value of the molar ratio "x" of element M in the general formula (B) exceeds 0.20, a second phase such as a spinel structure may be formed depending on the type (combination) of element M. Therefore, from the viewpoint of matching the crystallinity of the metal composite hydroxide (precursor) and the lithium metal composite oxide (positive electrode active material), the value of "x" is preferably 0.20 or less.

[0086] 9) Lattice constant The positive electrode active material preferably has an a-axis lattice constant of 2.8450 Å or more and a c-axis lattice constant of 14.170 Å or more. By setting the a-axis and c-axis lattice constants within the above ranges, it is possible to prevent the distortion of the crystal lattice from becoming too large and maintain a high battery capacity. From the viewpoint of battery capacity, the a-axis lattice constant is more preferably 2.8756 to 2.8900 Å, and the c-axis lattice constant is more preferably 14.198 to 14.250 Å.

[0087] 4. Lithium-ion secondary batteries The lithium ion secondary battery of the present invention is characterized by having a positive electrode containing the above-mentioned positive electrode active material for lithium ion secondary batteries.

[0088] The components of the lithium ion secondary battery of the present invention are not particularly limited as long as they are similar to the components of commonly used lithium ion secondary batteries. For example, if the lithium ion secondary battery of the present invention is a non-aqueous electrolyte lithium ion secondary battery, it includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution. Furthermore, if the lithium ion secondary battery of the present invention is an all-solid-state lithium ion secondary battery, it includes a positive electrode, a negative electrode, and a solid electrolyte.

[0089] The embodiments of the lithium ion secondary battery of the present invention described below are merely examples, and embodiments in which various changes or improvements have been made to the embodiments based on the knowledge of those skilled in the art are included within the scope of the present invention.

[0090] (4-1) Non-aqueous electrolyte secondary battery 1) Positive electrode In addition to the above-mentioned positive electrode active material for lithium-ion secondary batteries, a conductive agent and a binder are mixed to form a positive electrode mixture, and activated carbon or an organic solvent is added as needed for viscosity adjustment, and the mixture is further kneaded to form a positive electrode mixture paste. The mixing ratio of each material in the positive electrode mixture is also an important factor in determining the performance of a lithium-ion secondary battery. While there are no particular limitations on the mixing ratio of each material in the positive electrode mixture, it is preferable that the positive electrode mixture contain 60 to 95 mass% of the positive electrode active material, 1 to 20 mass% of the conductive agent, and 1 to 20 mass% of the binder, relative to 100 mass% of the total mass of the solids of the positive electrode mixture excluding the organic solvent, similar to the positive electrodes of general lithium secondary batteries.

[0091] The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, aluminum foil, and dried to volatilize (evaporate) the organic solvent. If necessary, pressure may be applied using a roll press or the like to increase the electrode density. In this manner, a sheet-shaped positive electrode is produced. The sheet-shaped positive electrode can be cut to an appropriate size as needed and used to manufacture a battery under desired conditions. However, the method for producing the positive electrode is not limited to the above, and other methods may also be used.

[0092] In preparing the positive electrode, the conductive agent can be graphite (natural graphite, artificial graphite, expanded graphite, etc.), acetylene black, Ketjen black, or other carbon black-based materials. The binder, which serves to bind the particles of the positive electrode active material, can be, for example, polyvinylidene fluoride (PVDF), fluorine-containing resins such as polytetrafluoroethylene, ethylene propylene diene rubber, and fluororubber, or thermoplastic resins such as styrene butadiene, cellulose-based resins, polyacrylic acid, polypropylene, and polyethylene. If necessary, the positive electrode active material, conductive agent, and activated carbon can be dispersed, and an organic solvent that dissolves the binder can be added to the positive electrode mixture and kneaded to prepare a positive electrode mixture paste. Examples of the organic solvent that can be added include N-methyl-2-pyrrolidone (NMP). Activated carbon can also be added to the positive electrode mixture to increase the capacity of the electric double layer.

[0093] 2) Negative electrode The negative electrode is made by mixing metallic lithium, lithium alloys, or other negative electrode active materials capable of absorbing and desorbing lithium ions with a binder, adding an appropriate organic solvent to form a paste. This paste is then applied to the surface of a metal foil current collector such as copper, dried, and, if necessary, pressed using a roll press to increase electrode density. Negative electrode active materials can include natural graphite, artificial graphite, sintered organic compounds such as phenolic resin, and powdered carbon materials such as coke. In this case, the negative electrode binder is a fluorine-containing resin such as polyvinylidene fluoride (PVDF), as in the positive electrode, and an organic solvent such as N-methyl-2-pyrrolidone (NMP) can be used to disperse the negative electrode active material and binder.

[0094] 3) Separator A separator is placed between the positive and negative electrodes to separate them and retain the electrolyte, and can be a thin membrane made of polyethylene or polypropylene with many tiny holes.

[0095] 4) Non-aqueous electrolyte The non-aqueous electrolyte solution is prepared by dissolving a lithium salt as a supporting electrolyte in an organic solvent. The organic solvent may be selected from the group consisting of cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and trifluoropropylene carbonate (TFPC), chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and dipropyl carbonate (DPC), ether compounds such as tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), and dimethoxyethane (DME), sulfur compounds such as ethyl methyl sulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate, either singly or in combination. The supporting electrolyte may be lithium hexafluorophosphate (LiPF), lithium tetrafluoroborate (LiBF), lithium perchlorate (LiClO), lithium hexafluoroarsenate (LiAsF), lithium bis(trifluoromethanesulfonyl)imide (LiN(CFSO)), or a composite salt thereof. Furthermore, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, or the like.

[0096] 5) Shape and configuration The lithium ion secondary battery of the present invention, which is composed of the positive electrode, negative electrode, separator, and non-aqueous electrolyte solution described above, can have various shapes, such as a cylindrical shape or a laminated shape. Regardless of the shape, the positive electrode and negative electrode are laminated with a separator interposed therebetween to form an electrode body, and this electrode body is impregnated with a non-aqueous electrolyte solution. A current collector lead or the like is used to connect the positive electrode current collector to a positive electrode terminal connected to the outside, and the negative electrode current collector to a negative electrode terminal connected to the outside. The battery can be completed by sealing the above-mentioned configuration in a battery case.

[0097] (4-2) All-solid-state battery 1) Positive electrode The above positive electrode active material powder and Li2S-P2S5-based glass or Li10 GeP2S 12 These sulfide-based lithium ion conductive solid electrolyte powders are mixed in an appropriate ratio (for example, 7:3 by weight), and this mixture is used as the positive electrode.

[0098] 2) Negative electrode The negative electrode is made of a mixture of metallic lithium, a lithium-indium alloy, or a negative electrode active material capable of absorbing and desorbing lithium ions, and the sulfide-based lithium ion conductive solid electrolyte powder in an appropriate ratio (for example, 7:3 by weight). Examples of the negative electrode active material that can be used include natural graphite, artificial graphite, baked organic compounds such as phenolic resins, and powders of carbonaceous materials such as coke.

[0099] 3) Solid electrolyte As a solid electrolyte, the ionic conductivity is 10 -4 There is no particular limitation as long as the lithium ion conductor has a valence of 0.05 S / cm or more. For example, sulfide-based lithium ion conductive solid electrolytes include Li2S-P2S5-based glass, Li 10 GeP2S 12 , Li3PO4-Li2S-SiS2-based glass, etc. can be used.

[0100] 4) Shape and configuration The all-solid-state battery of this embodiment, which is composed of the positive electrode, negative electrode, and solid electrolyte described above, can have various shapes, such as a circular shape, a sheet shape, etc. Regardless of the shape, the positive electrode and negative electrode are formed into an electrode body with the solid electrolyte interposed therebetween, and the obtained electrode body is connected between the positive electrode current collector and a positive electrode terminal connected to the outside, and between the negative electrode current collector and a negative electrode terminal connected to the outside, using current collecting leads or the like, and then sealed in a battery case to complete the all-solid-state battery.

[0101] (4-3) Characteristics of Lithium-ion Secondary Batteries As described above, the lithium ion secondary battery according to one embodiment of the present invention uses the positive electrode active material of the present invention as a positive electrode material, and therefore has excellent battery capacity (charge / discharge capacity) and coulombic efficiency (charge / discharge efficiency).

[0102] Ratings 5.1-4 (5-1) Sample evaluation method 1) Composition The composition can be evaluated by any method, including, for example, chemical analysis using acid decomposition-ICP (inductively coupled plasma) atomic emission spectroscopy. Measurements can be performed using, for example, a multi-type ICP atomic emission spectroscopy analyzer, ICPE-9000 (Shimadzu Corporation). From the results obtained, Li / Me (the ratio of the total number of metal element atoms (Me) contained in the lithium metal composite oxide (positive electrode active material) to the number of lithium atoms (Li)) can be determined.

[0103] 2) Compound identification The method for identifying a compound is not particularly limited, but for example, the compound can be identified by X-ray diffraction (XRD). For measurement, for example, an X-ray diffractometer (XRD) such as X'PertPRO (manufactured by Spectris Inc.) can be used. Specifically, a sample placed on a sample holder is measured using CuKα radiation as the radiation source under conditions of a measurement speed of 2° / min, a tube voltage of 45 kV, a tube current of 40 mA, and a measurement range of 2θ = 10 to 100°. The compound can then be identified by comparing the standard diffraction pattern of the compound with the diffraction pattern of the sample using the PDF (Powder Diffraction File) database in the ICDD (International Centre for Diffraction Data).

[0104] 3) Seat occupancy rate The method for evaluating the site occupancy (Li, Me) is not particularly limited, and the site occupancy can be determined, for example, by X-ray diffraction (XRD). For the measurement, for example, an X-ray diffractometer (XRD) such as X'PertPRO (manufactured by Spectris Inc.) can be used. That is, the Li site occupancy indicates the proportion of lithium (Li) in the lithium metal composite oxide in the lithium layer (Li site) of the layered structure, and the metal (Me) site occupancy indicates the proportion of metal element (Me site) in the nickel of the lithium metal composite oxide and the optionally added element M (M) in the metal layer (Me site) of the layered structure. The site occupancy can be determined by Rietveld analysis of the measured diffraction pattern using, for example, the widely used RIETAN-FP, High_Score_Plus (manufactured by Spectris Inc.), JADE_PRO (manufactured by Materials_Data), or other analysis programs.

[0105] 4) Lattice constant The method for evaluating the lattice constants (a-axis length, c-axis length) is not particularly limited, but for example, the lattice constants (a-axis length, c-axis length) can be determined by X-ray diffraction (XRD). For the measurement, for example, an X-ray diffractometer (XRD) such as X'PertPRO (manufactured by Spectris Inc.) can be used. That is, the measured diffraction pattern can be subjected to Rietveld analysis using an analysis program such as the commonly used RIETAN-FP, High_Score_Plus (manufactured by Spectris Inc.), or JADE_PRO (manufactured by Materials_Data).

[0106] 5) Oxygen coordinate Z The method for evaluating the oxygen coordinate Z is not particularly limited, but for example, the oxygen coordinate Z can be determined by X-ray diffraction (XRD). For the measurement, for example, an X-ray diffractometer (XRD) such as X'PertPRO (manufactured by Spectris Inc.) can be used. That is, the oxygen coordinate Z can be determined by performing Rietveld analysis on the measured diffraction pattern using an analysis program such as the commonly used RIETAN-FP, High_Score_Plus (manufactured by Spectris Inc.), or JADE_PRO (manufactured by Materials_Data).

[0107] 6) Slab thickness The method for evaluating the slab thickness (Li-O, Me-O) is not particularly limited, but for example, the slab thickness (Li-O, Me-O) can be determined by X-ray diffraction (XRD). For the measurement, for example, an X-ray diffractometer (XRD) such as X'PertPRO (manufactured by Spectris Inc.) can be used. That is, the measured diffraction pattern can be subjected to Rietveld analysis using an analysis program such as RIETAN-FP, which is widely used, or High_Score_Plus (manufactured by Spectris Inc.) or JADE_PRO (manufactured by Materials_Data).

[0108] 7) Crystallite size The method for evaluating the crystallite diameter ((003), (104)) is not particularly limited, but for example, the crystallite diameter ((003), (104)) can be determined by X-ray diffraction (XRD). For the measurement, for example, an X-ray diffractometer (XRD) such as X'PertPRO (manufactured by Spectris Inc.) can be used. That is, the measured diffraction pattern can be subjected to Rietveld analysis using an analysis program such as the commonly used RIETAN-FP, High_Score_Plus (manufactured by Spectris Inc.), or JADE_PRO (manufactured by Materials_Data Inc.), to determine the crystallite diameter.

[0109] 8) Average particle size The method for evaluating the average particle size is not particularly limited, but for example, the average particle size can be determined from the volume-based distribution measured using a laser diffraction / scattering method. For the measurement, for example, a laser diffraction / scattering particle size distribution analyzer, Microtrac MT3300EXII (manufactured by Microtrac BELL Co., Ltd.), can be used.

[0110] 9) Specific surface area The specific surface area can be measured by any method, including, but not limited to, a nitrogen gas adsorption-desorption method using the BET multipoint method or the BET single-point method. The measurement can also be performed using a specific surface area measuring device, such as a Macsorb 1200 series (manufactured by Mountec Co., Ltd.).

[0111] 10) Particle shape The method for evaluating the particle shape is not particularly limited, but for example, the particle shape can be confirmed by image observation using a scanning electron microscope (SEM). For measurement, for example, a scanning electron microscope (SEM) JSM-6360LA (manufactured by JEOL Ltd.) can be used.

[0112] 11) First-principles simulation Using first-principles simulations, we performed structural calculations for cases in which cation mixing did not occur and did occur, and calculated the lattice constants (a-axis length, c-axis length), oxygen coordinate Z, and slab thickness (Li-O, Me-O). These were then compared with the lattice constants (a-axis length, c-axis length), oxygen coordinate Z, and slab thickness (Li-O, Me-O) measured for samples prepared using the above method to confirm the occurrence of cation mixing. For the simulations, we used the first-principles electronic structure calculation program MedeA-VASP (Materials_Design) and the plane wave pseudopotential method (PAW method, Projector_Augmented_Wave_Methods) based on density functional theory (DFT).

[0113] (5-2) Battery evaluation method 1) Battery capacity (charging / discharging capacity) The method for evaluating the battery capacity (charge / discharge capacity) is not particularly limited. For example, a test battery (coin-type battery 10 shown in FIG. 9) is prepared as described below and left for about 24 hours. After the open circuit voltage (OCV) stabilizes, the current density to the positive electrode is set to 0.1 mA / cm. 2 The charge capacity can be determined by charging the battery up to a cutoff voltage of 4.30 V, and then by discharging the battery down to a cutoff voltage of 3.00 V after a one-hour rest, the discharge capacity can be determined. Measurements can be performed using, for example, a multi-channel voltage / current generator, the R6741A (manufactured by Advantest Corporation). From the results obtained, a graph (dQ / dV curve) can be created, showing voltage on the horizontal axis and dQ / dV, which is the value obtained by differentiating battery capacity with voltage, on the vertical axis. Furthermore, the coulombic efficiency (charge / discharge efficiency), which is the ratio of discharge capacity to charge capacity, can be determined. [Example]

[0114] The present invention will be specifically described below using Reference Examples, Examples, and Comparative Examples. In the following Examples and Comparative Examples, reagents manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. were used unless otherwise specified. Furthermore, the present invention is not limited in any way by the following Reference Examples, Examples, and Comparative Examples.

[0115] Furthermore, in order to confirm the tendency when cation mixing occurs in a lithium metal composite oxide (positive electrode active material), a simulation based on first-principles calculation was carried out as a reference example, and the results were compared with the examples and comparative examples.

[0116] (Reference example 1) Using the first-principles electronic structure calculation program MedeA-VASP (Materials_Design), we performed simulations using the plane wave-pseudopotential method (PAW method, Projector_Augmented_Wave_Methods) based on density functional theory (DFT) to predict the X-ray diffraction (XRD) profile of lithium nickel composite oxide (lithium nickel oxide, LiNiO2, LNO), a lithium metal composite oxide with space group R3-m (rhombohedral).

[0117] (Reference example 2) In a lithium nickel composite oxide (lithium nickel oxide, LiNiO, LNO) of the space group R3-m (rhombohedral), when nickel is mixed into the lithium (3a) site, that is, when cation mixing occurs, a structural calculation was carried out in the same manner as in Reference Example 1, except that 8% of the lithium atoms in the lithium (3a) site were replaced with nickel atoms.

[0118] Example 1 (1) Production of metal complex hydroxide (precursor) First, water was supplied into the reaction vessel, and while stirring at a stirring speed of 120 rpm, the temperature was controlled to 50°C, and nitrogen gas was introduced to create an inert atmosphere with an oxygen concentration of 0.7% by volume or less. In this state, an aqueous solution containing nickel sulfate was supplied into the reaction vessel at a constant flow rate using a pump. At this time, the pH of the contents (reaction aqueous solution) in the reaction vessel at a liquid temperature of 25°C was adjusted to 11.6, and the ammonium ion (NH4 + 25 mass% aqueous sodium hydroxide solution and 25 mass% aqueous ammonia were supplied at appropriate times so that the concentration of the metal composite hydroxide (precursor) was maintained at 10 g / L, and metal composite hydroxide (precursor) particles were crystallized. After that, the slurry containing the metal composite hydroxide (precursor) that overflowed from the reaction tank was charged into a filter press and filtered under pressure to recover a metal composite hydroxide (precursor) cake.

[0119] To this metal composite hydroxide (precursor) cake, a 5% by mass aqueous solution of sodium hydroxide was added in an amount ten times its mass, and the mixture was stirred. The mixture was then again placed in the filter press, and water in an amount equal to the 5% by mass aqueous solution of sodium hydroxide was added, followed by pressure filtration to wash the metal composite hydroxide (precursor) cake. The washed metal composite hydroxide (precursor) cake was dried at 150°C for 5 hours using an electrically heated dryer, yielding a metal composite hydroxide (precursor). Furthermore, a portion of the metal composite hydroxide (precursor) was sampled, and its composition was analyzed by acid decomposition-ICP (inductively coupled plasma) atomic emission spectroscopy, revealing that it contained Ni. 1.00 It was confirmed to be (OH)2.

[0120] (2) Manufacturing of lithium metal composite oxide (positive electrode active material) The metal composite hydroxide (precursor) and lithium hydroxide (lithium compound) were weighed out so that the ratio (Li / Me) of the number of lithium atoms (Li) to the number of non-lithium metal atoms (Me) was 1.03, and then thoroughly mixed to obtain a lithium mixture. This lithium mixture was calcined (first heat treatment) by heating it at 480°C for 3 hours in an oxygen (oxygen concentration: 100% by volume) stream. It was then cooled to room temperature and subjected to the first crushing step to crush any agglomerates contained in the resulting lithium calcined product. Furthermore, a portion of the lithium calcined product was sampled and subjected to compound identification by X-ray diffraction (XRD). As shown in Figure 3, peaks attributable to R3-m LiNiO2 and unreacted Li (Li2CO3) were detected, but no Fm-3m NiO was detected.

[0121] This lithium calcined product was calcined (second heat treatment) by heating it in an oxygen (oxygen concentration: 100% by volume) stream at 710°C for 10 hours, and then cooled to room temperature. A second crushing process was carried out to crush the aggregates contained in the calcined product, and finally a lithium metal composite oxide (positive electrode active material) was obtained. Furthermore, a portion of the lithium metal composite oxide (positive electrode active material) was sampled and analyzed for its composition by acid decomposition-ICP (inductively coupled plasma) atomic emission spectroscopy. The results showed that Li 1.03 Ni1.00 It was confirmed to be O2.

[0122] (3) Analysis of positive electrode active material The obtained positive electrode active material was subjected to X-ray diffraction measurement. For the measurement, an X-ray diffraction analyzer X'PertPRO (manufactured by Spectris Inc.) was used. Using the obtained X-ray diffraction pattern, Rietveld analysis was performed to determine the Li site occupancy, Me site occupancy, lattice constant, oxygen coordinate Z, slab thickness, and crystallite diameter. For the Rietveld analysis, the analytical software "RIETAN-FP" (freeware) was used. The crystallite diameter was determined based on the (003) peak and (104) peak of the lithium metal composite oxide shown in Figure 6.

[0123] (Average particle size) The average particle size of the obtained positive electrode active material was determined from the volume-based distribution measured using the laser diffraction / scattering method. The measurement was performed using a Microtrac MT3300EXII (Microtrac BEL Corporation), a particle size distribution measuring device that uses the laser diffraction / scattering method. Figure 8 shows the particle size distribution of the lithium metal composite oxide.

[0124] (Shape of positive electrode active material particles) Furthermore, a sample of the obtained positive electrode active material particles was embedded in resin and subjected to cross-section polishing, and the results of SEM observation at a magnification of 10,000 times were then taken. Figure 7 shows the particle shape of the lithium metal composite oxide obtained by scanning electron microscopy (SEM).

[0125] (specific surface area) The specific surface area of the obtained positive electrode active material was measured by the BET single-point method and the nitrogen gas adsorption-desorption method using a specific surface area measuring device, Macsorb 1200 series (manufactured by Mountec Co., Ltd.).

[0126] (4) Manufacturing of coin-cell batteries 52.5 mg of the positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene were weighed and mixed, and then press-molded at a pressure of 100 MPa to a diameter of 11 mm and a thickness of 100 μm to produce a positive electrode 1 (electrode for evaluation) shown in FIG. 9. The produced positive electrode 1 was dried in a vacuum dryer at 120°C for 12 hours. Then, using this positive electrode 1, a 2032-type coin battery 10 was produced in a glove box in an Ar atmosphere with a dew point controlled at -80°C.

[0127] The negative electrode 2 was made of metallic lithium with a diameter of 17 mm and a thickness of 1 mm, and the electrolyte was a mixture of equal parts of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 mol of LiClO4 as the supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.). The separator 3 was made of a 25 μm thick polyethylene porous film. The coin-type battery 10 was assembled with a positive electrode can 6 and a negative electrode can 7, with a gasket 4 and a wave washer 5 arranged in place.

[0128] (5) Measurement of battery capacity (charge / discharge capacity) and coulomb efficiency (charge / discharge efficiency) The fabricated battery was left for about 24 hours, and after the open circuit voltage (OCV) had stabilized, the current density to the positive electrode was increased to 0.1 mA / cm. 2 The capacity when the battery was charged to a cutoff voltage of 4.30 V was taken as the charge capacity. After a one-hour rest, the battery was discharged to a cutoff voltage of 3.0 V, and the capacity was taken as the discharge capacity. The coulomb efficiency (charge / discharge efficiency), which is the ratio of the discharge capacity to the charge capacity, was then calculated. The measurements were performed using a multi-channel voltage / current generator, R6741A (manufactured by Advantest Corporation).

[0129] The charge / discharge curves obtained during the measurements are shown in Figure 4. The charge / discharge curves obtained were then differentiated with respect to potential to obtain the dQ / dV curves shown in Figure 5. The positions and intensities of the charge and discharge peaks were determined from the obtained dQ / dV curves.

[0130] Example 2 The same operations as in Example 1 were carried out, except that the metal composite hydroxide (precursor) and lithium hydroxide, which is a lithium compound, were weighed so that the ratio (Li / Me), which is the ratio of the number of lithium atoms (Li) to the number of atoms of metals other than lithium (Me), was 1.00. Furthermore, a portion of the obtained lithium metal composite oxide (positive electrode active material) was sampled and its composition was analyzed by acid decomposition-ICP (inductively coupled plasma) atomic emission spectroscopy. As a result, Li 1.00 Ni 1.00 It was confirmed to be O2.

[0131] (Comparative Example 1) According to the conventional process of using a metal composite oxide (intermediate), the above metal composite hydroxide (precursor) was heated in an air stream (oxygen concentration: 21% by volume) at 600°C for 2 hours to perform oxidative roasting (heat treatment without containing lithium compounds), thereby obtaining a metal composite oxide (intermediate). Furthermore, a portion of the metal composite oxide (intermediate) was sampled and its composition was analyzed by acid decomposition-ICP (inductively coupled plasma) atomic emission spectroscopy. As a result, Ni 1.00 It was confirmed that O.

[0132] The same procedure as in Example 1 was carried out, except that the obtained metal composite oxide (intermediate) was mixed with lithium hydroxide, which is a lithium compound, and then calcined to produce a lithium metal composite oxide (positive electrode active material). Furthermore, a portion of the obtained lithium metal composite oxide (positive electrode active material) was sampled and analyzed for its composition by acid decomposition-ICP (inductively coupled plasma) atomic emission spectrometry. As a result, Li 1.03 Ni 1.00 It was confirmed to be O2.

[0133] The conditions for the Reference Examples, Examples, and Comparative Examples are shown in Table 1. Table 1 also shows the Li / Me, Li site occupancy, Me site occupancy, lattice constants (a-axis length, c-axis length), oxygen coordinate Z, slab thickness (Li-O, Me-O), crystallite diameter ((003), (104)), average particle diameter, and specific surface area for the Reference Examples, Examples, and Comparative Examples.

[0134] Regarding the conditions in Table 1, "LiNO2" in Reference Example 1 indicates the simulation conditions when nickel is not mixed into the lithium (3a) site, and "8% cation mixing" in Reference Example 2 indicates the simulation conditions when 8% of the lithium atoms in the lithium (3a) site are replaced with nickel atoms. Furthermore, "Ni(OH)2 precursor" in Examples 1 and 2 indicates the conditions under which a metal composite hydroxide (precursor) and a lithium compound were mixed and reacted, and "NiO intermediate" in Comparative Example 1 indicates the conditions under which a metal composite oxide (intermediate) and a lithium compound were mixed and reacted.

[0135] [Table 1]

[0136] Table 2 also shows the charge peak intensity between 4.10 and 4.30 V in the dQ / dV curve, the discharge peak intensity between 3.35 and 3.55 V, the charge capacity, the discharge capacity, and the coulombic efficiency for the examples and comparative examples.

[0137] [Table 2]

[0138] As shown in Table 1, the calculated values of Reference Examples 1 and 2, which were obtained by performing simulations using first-principles calculations, show that when cation mixing occurs, (1) the lattice constants (a-axis length, c-axis length) become smaller, both a and c, (2) the oxygen coordinate Z becomes larger, and (3) the slab thickness (Li-O, Me-O) becomes larger for Li-O and smaller for Me-O.

[0139] In contrast, when the experimental values of Example 1 and Comparative Example 1, which have the same Li / Me value, are compared, it is found that Comparative Example 1 is more consistent with the trends of (1) to (3) above. From this result, it is considered that cation mixing occurs more significantly in Comparative Example 1 than in Example 1, or in other words, cation mixing can be suppressed more significantly in Example 1 than in Comparative Example 1.

[0140] Furthermore, in Example 1, both the site occupancy rates (Li, Me) were increased compared to Comparative Example 1, and the battery characteristics such as the battery capacity (charge / discharge capacity) and the coulomb efficiency (charge / discharge efficiency) were improved compared to Comparative Example 1. These results are believed to support the effect of suppressing cation mixing.

[0141] Furthermore, as shown in Table 2, in the dQ / dV curves created in the battery evaluation, in Examples 1 and 2, compared to Comparative Example 1, (a) the charge peak intensity around 4.20 V (including around 3.70 V in the case of Example 1 alone) was smaller and shifted to the higher voltage side, and (b) the discharge peak intensity around 3.50 V was larger. In particular, it can be determined that the characteristic (b) is the cause of the improved discharge capacity.

[0142] Furthermore, it can be seen from Table 1 that the specific surface areas of the lithium metal composite oxides (positive electrode active materials) in Examples 1 and 2 are larger than the specific surface area of Comparative Example 1.

[0143] Furthermore, it can be seen from Table 1 that the crystallite diameter obtained from the X-ray diffraction peak of the (003) plane in Comparative Example 1 is longer than those in Examples 1 and 2.

[0144] The (003) peak and (104) peak of the lithium metal composite oxide obtained by X-ray diffraction (XRD) in the examples and comparative examples are shown in Figure 6. From these peaks, it can be seen that the (003) peak position of the examples is located on the lower angle side compared to the (003) peak position of the comparative examples. It can also be seen that the (003) / (104) peak intensity ratio of Example 1 is smaller than the (003) / (104) peak intensity ratio of Comparative Example 1.

[0145] Observation images showing the particle shapes of the lithium metal composite oxides in the examples and comparative examples, obtained by scanning electron microscopy (SEM), are shown in Figure 7. These images show that the secondary particle shapes are similar in the examples and comparative examples, but the particle surfaces of the examples are not smooth like the particle surfaces of the comparative examples, and are uneven.

[0146] Although the embodiments and examples of the present invention have been described in detail above, it will be readily apparent to those skilled in the art that many modifications are possible without substantially departing from the novel features and effects of the present invention. Therefore, all such modifications are intended to be included within the scope of the present invention.

[0147] For example, a term described at least once in the specification or drawings together with a different term having a broader or equivalent meaning can be replaced with that different term anywhere in the specification or drawings. Furthermore, the configurations and operations of the positive electrode active material for a lithium ion secondary battery and the manufacturing method thereof are not limited to those described in the embodiments and examples of the present invention, and various modifications are possible. [Explanation of symbols]

[0148] S1 crystallization process, S2 drying process, S3 mixing process, S4 calcination process, S5 cooling process, S6 first crushing process, S7 firing process, S8 second crushing process, 1 positive electrode (electrode for evaluation), 2 negative electrode, 3 separator, 4 gasket, 5 wave washer, 6 positive electrode can, 7 negative electrode can, 10 coin battery (for evaluation)

Claims

1. A lithium metal composite oxide comprising secondary particles formed by agglomeration of primary particles containing lithium and nickel, or both the primary particles and the secondary particles, The lithium metal composite oxide has a molar ratio of lithium to a metal other than lithium of 0.95 to 1.30, A lithium ion secondary battery was assembled using a positive electrode containing the lithium metal composite oxide and a negative electrode containing metallic lithium, and the battery was charged to a voltage of 4.30 V and then discharged to a voltage of 3.00 V. When a graph (dQ / dV curve) was prepared, with voltage on the horizontal axis and dQ / dV, which is the value obtained by differentiating battery capacity with voltage, on the vertical axis, the charge peak intensity obtained at a voltage of 4.10 to 4.30 V was 500 to 1100 mAh / g / V, and the discharge peak intensity obtained at a voltage of 3.35 to 3.55 V was 150 to 300 mAh / g / V. A positive electrode active material for a lithium ion secondary battery.

2. The lithium metal composite oxide has a specific surface area of 0.25 to 1.50 m ２ / g, (003) crystallite diameter is 800 to 1600 Å, and metal (Me) site occupancy is 97.2 to 100%.

3. 3. The positive electrode active material for lithium ion secondary batteries according to claim 1, wherein when the lithium ion secondary battery is assembled using a positive electrode containing the lithium metal composite oxide and a negative electrode containing the metallic lithium, and the battery is charged to a voltage of 4.30 V and then discharged to a voltage of 3.00 V, the resulting discharge capacity is 232 to 240 mAh / g and the resulting coulombic efficiency is 90.0 to 95.0%.

4. The lithium metal composite oxide is represented by the general formula (B): Li ｓ Ni １－ｘ M ｘ O ２＋α (wherein s, x, and α are in the ranges of 0.95≦s≦1.30, 0≦x≦0.2, and −0.1≦α≦0.2, and M is at least one metal element selected from the group consisting of Co, Mn, W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, and S).

5. 1. A method for producing secondary particles formed by agglomeration of primary particles containing lithium and nickel, or a lithium metal composite oxide comprising both the primary particles and the secondary particles, comprising: a crystallization step of mixing the raw material aqueous solution containing nickel, an alkaline aqueous solution containing sodium hydroxide, and an ammonium aqueous solution containing ammonium ions to prepare a reaction solution, and controlling the pH of the reaction solution (based on a liquid temperature of 25°C) to be 11.0 to 12.5 to obtain a metal composite hydroxide cake; a drying step of washing the metal composite hydroxide cake and then drying it at 120 to 200°C for 1 to 10 hours to obtain a metal composite hydroxide; a mixing step of mixing the metal composite hydroxide with a lithium compound to obtain a lithium mixture; a calcination step of calcining the lithium mixture at 300 to 500°C for 1 to 10 hours to react in a state free from the metal composite oxide, thereby obtaining a lithium calcined product; a calcination step of calcining the lithium calcined product at 650 to 900°C for 1 to 20 hours to react the product in a state not containing the metal composite oxide, thereby obtaining a lithium metal composite oxide; and a cooling step of cooling the lithium calcined product to room temperature and a first crushing step of crushing the lithium calcined product between the calcination step and the firing step;

6. 6. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5, wherein the metal composite hydroxide, which is a raw material of the lithium metal composite oxide, reacts directly with the lithium compound without passing through the form of the metal composite oxide during the production process.

7. 7. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5, further comprising a second crushing step of crushing the lithium metal composite oxide after the firing step.

8. The lithium metal composite oxide is represented by the general formula (B): Li ｓ Ni １－ｘ M ｘ O ２＋α (wherein s, x, and α are in the ranges of 0.95≦s≦1.30, 0≦x≦0.2, and −0.1≦α≦0.2, and M is at least one metal element selected from the group consisting of Co, Mn, W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, and S).

9. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 5 to 8, characterized in that the metal composite hydroxide has a trigonal crystal structure, the metal composite oxide has a cubic crystal structure, and the lithium metal composite oxide has a rhombohedral crystal structure.

10. 10. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 5, wherein the lithium compound is lithium hydroxide and / or lithium carbonate.

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