JP2021034142A - Production method of multiple oxide that is precursor of cathode active material for lithium ion secondary battery - Google Patents

Abstract

To provide a method for stably producing cathode active material capable of showing excellent output characteristics and cycle characteristics when evaluating as the battery characteristics of a secondary battery.SOLUTION: In a method of producing a nickel manganese composite oxide having the form of secondary particles of multilayer structure, as a precursor of cathode active material of multilayer structure composed of lithium nickel manganese composite oxide of hexagonal system, for the nickel manganese composite oxide having the form of secondary particles of multilayer structure where the compositional formula is shown by NixMnyCozMt(OH)2+β, atmospheric temperature is raised from room temperature to the surplus water removal temperature of 150°C-250°C at a rate of temperature increase of 1°C/min. or less in an oxidative atmosphere, thereafter raised from the surplus water removal temperature to the roasting temperature of 400°C-800°C at a rate of temperature increase of 1°C/min.-5°C/min., before being held at the roasting temperature for one hour or more thus roasting the nickel manganese composite oxide.SELECTED DRAWING: None

Description

The present invention relates to a method for producing a composite oxide which is a precursor of a positive electrode active material for a lithium ion secondary battery, a method for producing a positive electrode active material for a lithium ion secondary battery using this precursor as an intermediate raw material, and a positive electrode thereof. The present invention relates to a method for manufacturing a lithium ion secondary battery using an active material as a positive electrode material.

In recent years, with the spread of small information terminals such as smartphones and tablet PCs, the demand for small and lightweight secondary batteries having high energy density is increasing. Further, as a power source for electric vehicles such as hybrid electric vehicles, plug-in hybrid electric vehicles, and battery-powered electric vehicles, the development of high-output secondary batteries is strongly desired. As a secondary battery for the above application, a non-aqueous electrolyte secondary battery mainly composed of a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator is known. In addition, an all-solid-state secondary battery using a solid electrolyte is expected as a next-generation energy storage device.

Among the above secondary batteries, a lithium ion secondary battery that uses an active material composed of a layered or spinel-type lithium transition metal composite oxide as a positive electrode material and desorbs and inserts lithium by charging and discharging has already been put into practical use. ing. Lithium-ion secondary batteries can obtain 4V class voltage and have excellent characteristics such as energy density, but research and development are still being actively carried out to further improve the characteristics. As the lithium transition metal composite oxide used as the positive electrode active material of this lithium ion secondary battery, composite oxides having various compositions have been proposed.

For example, lithium cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel, which is cheaper than cobalt, and lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co). _1/3 Mn _1/3 O ₂ ), lithium manganese composite oxide using manganese (LiMn ₂ O ₄ ), lithium nickel manganese cobalt composite oxide (LiNi _0.5 Mn _0.5 O ₂ ), etc. Can be done. In addition, various forms of the positive electrode active material have been proposed.

For example, Patent Document 1 discloses a positive electrode active material composed of a hexagonal lithium-containing composite oxide having a layered structure and having the form of secondary particles having voids, and has an average particle size of 3 to 12 μm. It is described that a secondary battery having a large discharge capacity and a high output can be obtained by suppressing the particle size distribution to be narrow. Further, Patent Document 2 describes the form of secondary particles having a porous structure composed of lithium manganese-based composite oxide, lithium nickel-cobalt-manganese-based composite oxide, or lithium nickel-cobalt-aluminum-based composite oxide. The positive electrode active material having the above is disclosed, and it is stated that by suppressing the tap density within the range of 0.3 to 1.0 g / cc, a secondary battery having excellent life characteristics at the time of high output charge / discharge can be obtained. Has been done.

Japanese Unexamined Patent Publication No. 2013-229339 Japanese Unexamined Patent Publication No. 2015-023021

As disclosed in Patent Document 1, a lithium ion secondary battery having excellent cycle characteristics and output characteristics can be obtained by using a positive electrode active material having a relatively small particle size and a narrow particle size distribution, that is, a uniform particle size. It will be possible to obtain. The reason is that the smaller the particle size of the powder or granular material, the larger the specific surface area. Therefore, if the positive electrode active material has a small particle size, not only can a sufficient reaction area with the non-aqueous electrolyte be secured. This is because if the particle size is small, the positive electrode can be formed thin, so that the moving distance between the positive electrode and the negative electrode of lithium ions can be shortened, and as a result, the positive electrode resistance can be reduced. Further, if the positive electrode active material has a narrow particle size distribution, the voltage applied to each particle in the positive electrode can be made uniform, so that a high voltage is selectively applied to the fine particles that may occur when the particle size varies widely. This is because it is possible to suppress the problem of a decrease in battery capacity caused by deterioration.

However, there are cases where it cannot be said that a small particle size and a narrow particle size distribution are sufficient to develop even higher output characteristics. Therefore, in order to further improve the output characteristics, as disclosed in Patent Documents 1 and 2, voids are provided inside the secondary particles of the positive electrode active material composed of secondary particles, and at least a part of the voids are provided. It is effective to have a structure in which the portions communicate with the surface of the secondary particles. Since the reaction resistance of such a positive electrode active material having a hollow structure or a porous structure is reduced, higher output characteristics can be obtained. In addition, compared to a positive electrode active material having a dense solid structure having the same particle size and no voids, a large contact area with an electrolyte, especially a non-aqueous electrolyte solution, can be secured, so that lithium during charging and discharging can be secured. Desorption and insertion of ions are likely to occur, and the positive electrode resistance can be significantly reduced.

However, the positive electrode active material having a hollow structure or a porous structure has a problem that the particle strength tends to be low, contrary to its high output characteristics. Therefore, in the production methods disclosed in Patent Documents 1 and 2 described above, when a lithium nickel-cobalt-manganese composite oxide is produced by firing from a nickel-cobalt-manganese composite hydroxide, particle cracking occurs in the heating process of the firing step. Is thought to occur. When particle cracking occurs in the firing step in this way, fine particles are mixed in the obtained positive electrode active material active material, or cracks occur in the positive electrode active material particles. In the positive electrode active material containing fine particles, the fine particles may deteriorate at an accelerating rate during repeated charging and discharging. Further, the positive electrode active material particles having cracks are easily cracked during charging / discharging, and the new surface appearing at that time hardly contributes to charging / discharging, so that the cycle characteristics are deteriorated.

Therefore, there is a demand for a method for stably producing a positive electrode active material having a porous structure with high output and excellent cycle characteristics without causing particle cracking. The present invention has been made in view of the above circumstances, and stably a positive electrode active material having a porous structure capable of exhibiting excellent output characteristics and cycle characteristics when evaluated as the battery characteristics of a secondary battery. It is an object of the present invention to provide a method of manufacturing.

In order to achieve the above object, the method for producing a nickel-manganese composite oxide according to the present invention has a multi-layer structure as a precursor of a positive electrode active material having a porous structure composed of a hexagonal lithium nickel-manganese composite oxide. There is a method for producing a nickel-manganese composite oxide having the form of a next particle, and the composition formula is Ni _x Mn _y Co _z M _t (OH) _{2 + β} (x + y + z + t = 1, 0.3 ≦ x ≦ 0.95, 0. 05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, −0.20 ≦ β ≦ 0.20, M is Mg, Ca, Al, Ti, V, Cr, Oxidation of nickel-manganese composite hydroxide in the form of multi-layered secondary particles represented by (one or more additive elements selected from the group consisting of Zr, Nb, Mo, Hf, Ta, and W). In the atmosphere, the ambient temperature is raised from room temperature to a temperature for removing excess water of 150 ° C. or higher and 250 ° C. or lower at a heating rate of 1 ° C./min or less, and then at a heating rate of more than 1 ° C./min and 5 ° C./min or lower. It is characterized in that the temperature is raised from the excess water removal temperature to a roasting temperature of 400 ° C. or higher and 800 ° C. or lower, and the roasting is held at the roasting temperature for 1 hour or longer.

According to the present invention, a positive electrode active material having a porous structure capable of exhibiting excellent output characteristics and cycle characteristics when evaluated as the battery characteristics of a secondary battery can be easily produced on an industrial scale.

It is sectional drawing of the nickel-manganese composite oxide of embodiment of this invention by a scanning electron microscope. It is sectional drawing of the lithium nickel-manganese composite oxide of embodiment of this invention by a scanning electron microscope.

The present inventor has a positive electrode active material for a lithium ion secondary battery (hereinafter, also referred to as a "positive electrode active material") capable of exhibiting excellent output characteristics and cycle characteristics when used as a positive electrode material for a lithium ion secondary battery. As a result of diligent studies on the manufacturing method of (referred to as), when the hydroxide of the raw material is heat-treated to produce a positive electrode active material, the occurrence of particle cracking is suppressed by defining the conditions of the heat treatment, thereby suppressing the positive electrode activity. We have found that it is possible to produce a lithium ion secondary battery having excellent battery characteristics by drawing out the characteristics inherent in the substance, and have completed the present invention.

Specifically, the heat treatment is a step of roasting a nickel-manganese composite hydroxide to produce a nickel-manganese composite oxide which is a precursor of a positive electrode active material (hereinafter, "oxidation roasting step" or "primary firing"). (Referred to as), a step of calcining the obtained mixture by adding a lithium compound to the obtained nickel-manganese composite oxide and mixing to produce a lithium nickel-manganese composite oxide (hereinafter, "synthetic firing step" or "synthetic firing step" or ". It is divided into two steps (referred to as "secondary firing").

Then, in the former oxidative roasting step, the ambient temperature is preferably raised from room temperature to a dehydration temperature at which the removal of excess water is almost completed at a temperature rise rate of 1 ° C./min or less in an oxidizing atmosphere, and then this dehydration temperature. To a predetermined roasting temperature held for the oxidative roasting treatment, the temperature is raised at a heating rate of more than 1 ° C./min and 5 ° C./min or less. Then, it is held at the roasting temperature for 1 hour or more. As a result, nickel-manganese composite oxide can be produced by oxidative roasting with almost no particle cracking.

Next, in the latter synthetic firing step, a lithium compound prepared separately is added to the nickel-manganese composite oxide and mixed, and the obtained mixture is preferably calcined in an oxygen atmosphere at a firing temperature of 700 to 1000 ° C. for 2 to 10 hours. Baking is performed by holding. As a result, a lithium nickel-manganese composite oxide having a porous structure having a specific surface area of 1.5 to 4.0 m ^{2 / g can be produced.} Since the occurrence of particle cracking can be suppressed by performing the heat treatment in two steps as described above, the secondary battery produced by using the obtained lithium nickel-manganese composite oxide as the positive electrode active material has cycle characteristics. It is excellent and can greatly improve the output characteristics. Hereinafter, a method for producing a nickel-manganese composite oxide which is a precursor of the positive electrode active material according to the embodiment of the present invention and a method for producing a positive electrode active material using the precursor as an intermediate raw material will be described. In this specification, A to B, which is a numerical range of A or more and B or less, may be expressed as A to B.

1. 1. Method for producing nickel-manganese composite oxide (1) Oxidation roasting step In the method for producing nickel-manganese composite oxide according to the embodiment of the present invention, nickel-manganese composite hydroxide as a raw material is heat-treated to be a precursor of a positive electrode active material. The body nickel-manganese composite oxide is produced, and this heat treatment mainly removes excess water contained in the raw material nickel-manganese composite hydroxide, and the nickel-manganese composite after the water removal. The hydroxide is oxidatively roasted to produce a nickel-manganese composite oxide. It is divided into the latter stages of the reaction and treated separately under optimum conditions. As a result, the residual water content of the nickel-manganese composite oxide, which is a precursor of the positive electrode active material, can be reduced to a certain amount or less, and variations in the composition of the positive electrode active material precursor can be suppressed.

[Raising rate]
Specifically, in the first half of the reaction, the atmosphere temperature of the raw material nickel-manganese composite hydroxide is 150 to 150 to the dehydration temperature of excess water from room temperature at a heating rate of 1 ° C./min or less in an oxidizing atmosphere. The temperature is raised to 250 ° C., preferably 200 ° C. As a result, excess water contained in the nickel-manganese composite hydroxide can be efficiently removed. When this temperature rising rate exceeds 1 ° C./min, the water content in the nickel-manganese composite hydroxide rapidly evaporates and the pressure inside the particles increases, resulting in particle cracking in particles having a porous structure with weak particle strength. Is likely to occur. The lower limit of the temperature rising rate is not particularly limited, but is preferably 0.2 ° C./min or more from an economical point of view.

Next, in the latter stage of the reaction, the temperature of the nickel-manganese composite hydroxide from which the water was removed was raised to a temperature rising rate of more than 1 ° C./min and 5 ° C./min or less in a non-reducing atmosphere similar to the above. The temperature is raised from the above dehydration temperature to the roasting temperature described later. In the temperature range from the dehydration temperature to the roasting temperature, a composite oxide is generated from the composite hydroxide of nickel manganese. Therefore, when the temperature is raised at a heating rate exceeding 5 ° C./min, the composite oxide crystallizes. The structure is easily distorted, and the possibility of particle cracking increases. On the contrary, when the temperature rising rate is 1 ° C./min or less, the above-mentioned problem of particle cracking is less likely to occur, but the heat treatment takes too much time and the productivity is lowered, which is uneconomical.

[Roasting temperature]
The roasting temperature of the nickel-manganese composite hydroxide is in the range of 400 to 800 ° C. If the roasting temperature is less than 400 ° C., the formation of the nickel-manganese composite hydroxide from the nickel-manganese composite hydroxide becomes insufficient, and when the lithium nickel-manganese composite oxide as the positive electrode active material is finally formed, each of them is produced. The variation in the atomic number ratio of metal components and lithium becomes too large. On the contrary, if the roasting temperature exceeds 800 ° C., the energy efficiency for oxidative roasting decreases, the production cost increases, and the oxidative roasting equipment that can be used is limited. The roasting temperature can be obtained by measuring the temperature of the gas phase portion of the heat treatment furnace with a thermometer.

[Roasting retention time]
In this oxidative roasting step, in order to sufficiently promote the oxidative roasting of the nickel-manganese composite hydroxide, the nickel-manganese composite hydroxide is kept at the above-mentioned roasting temperature for 1 hour or more. If the holding time of this oxidative roasting is less than 1 hour, the formation from the nickel-manganese composite hydroxide to the nickel-manganese composite oxide becomes insufficient, and finally the lithium nickel-manganese composite oxide as the positive electrode active material is produced. Occasionally, the variation in the atomic number ratio of each metal component and lithium becomes too large. The upper limit of the holding time of the oxidative roasting is not particularly limited, but it is preferably less than 5 hours, more preferably less than 3 hours in consideration of productivity.

[Roasting atmosphere]
The atmosphere during the above-mentioned oxidative roasting step is not particularly limited as long as it is an oxidative atmosphere, but air is introduced into a heat treatment furnace charged with the raw material nickel-manganese composite hydroxide and oxidative roasting treatment is performed in an air stream. Is more preferable. The heat treatment furnace in this case is preferably one that does not generate gas from the viewpoint of keeping the atmospheric conditions in the furnace uniform. Examples of such a heat treatment furnace include an electric furnace, and either a batch type or a continuous type electric furnace can be preferably used. After the above-mentioned oxidative roasting, it may be cooled to about room temperature by natural cooling, but it is preferably cooled at a cooling rate of 2 to 10 ° C./min.

(2) Composition The nickel-manganese composite oxide produced by the method for producing a precursor according to the embodiment of the present invention has a composition formula A of Ni _x Mn _y Co _z M _t (OH) _{2 + β} (in the formula, x + y + z + t). = 1, 0.3 ≤ x ≤ 0.95, 0.05 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 ≤ t ≤ 0.1, -0.20 ≤ β ≤ 0.20 Yes, M is one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W).

(3) Particle Structure As the nickel-manganese composite hydroxide used as a raw material for the above-mentioned oxidative roasting step, those having the form of secondary particles having a multi-layer structure are used. Specifically, as shown in the cross-sectional view of FIG. 1 by the scanning electron microscope SEM, the central portion C in which the primary particles are densely present, the surface portion S in which the primary particles are densely present, and the central portion C thereof. It is preferably formed between the surface portion S and the intermediate portion M in which the primary particles are sparsely present. A nickel-manganese composite hydroxide having such a characteristic structure can be formed, for example, by adjusting the crystallization reaction conditions in the production step of the nickel-manganese composite hydroxide by crystallization. It can be produced by switching the atmosphere at the time of the crystallization reaction between a non-oxidizing atmosphere and an oxidizing atmosphere. In the above-mentioned oxidative roasting step, substantially the same multilayer structure is maintained even after the roasting treatment. That is, the nickel-manganese composite oxide obtained by the above-mentioned oxidative roasting is also located between the central portion C and the surface portion S in which the primary particles are densely present as shown in FIG. 1, and the primary particles are sparse. It is composed of an existing intermediate portion M.

2. Method for producing lithium nickel-manganese composite oxide (1) Mixing step In the method for producing a lithium nickel-manganese composite oxide, a separately prepared lithium compound is added to the nickel-manganese composite oxide produced by the above-mentioned precursor production method. First, a lithium mixture (mixed powder) is obtained. At the time of this mixing, the ratio of the amount of substance (Li) of lithium to the sum (Me) of the amounts of substances of nickel, manganese, cobalt and the additive element M, which are metal atoms other than lithium in the lithium mixture (hereinafter, Li / Me ratio). (Also referred to as), but preferably 0.95 to 1.5, more preferably 1.0 to 1.5, still more preferably 1.0 to 1.35, and most preferably 1.0 to 1. Mix so that it becomes 2. Since the Li / Me ratio hardly changes before and after the synthetic firing treatment described later, the nickel-manganese composite oxide and the lithium compound are mixed so that the Li / Me ratio of the positive electrode active material to be finally produced is within the above range. It may be mixed.

The type of the lithium compound is not particularly limited, but considering that it is easily available, easy to handle, and stable in quality, it is preferable to use lithium hydroxide, lithium carbonate, or a mixture thereof. In the mixing of the lithium compound and the nickel-manganese composite oxide, it is preferable that the nickel-manganese composite oxide having the form of secondary particles having a multilayer structure is sufficiently mixed with a strength that does not destroy the form of the nickel-manganese composite oxide. If this mixing is insufficient, the Li / Me ratio may vary among the individual particles of the finally produced positive electrode active material, and sufficient battery characteristics may not be obtained. A general mixer can be used for this mixing. For example, a shaker mixer, a lady gemixer, a julia mixer, a V blender, or the like can be used.

(2) Synthetic firing step The lithium mixture obtained in the above mixing step is fired by holding it at a predetermined firing temperature for a predetermined time, and the lithium nickel-manganese composite oxide is diffused into the nickel-manganese composite oxide. To generate. The type of heat treatment furnace for performing this firing treatment is not particularly limited as long as the heat treatment can be performed in a non-reducing atmosphere, but a heat treatment furnace capable of heat-treating the lithium mixture in an air atmosphere or an oxygen stream is preferable. Further, like the heat treatment furnace used in the above-mentioned oxidative roasting step, one that does not generate gas is preferable from the viewpoint of keeping the atmospheric conditions in the furnace uniform. Examples of such a heat treatment furnace include an electric furnace, and either a batch type or a continuous type electric furnace can be preferably used.

[Baking temperature]
The firing temperature for firing the above lithium mixture is preferably 700 to 1000 ° C. If the firing temperature is less than 700 ° C., lithium may not sufficiently diffuse into the nickel-manganese composite oxide particles during firing, and excess lithium or unreacted nickel-manganese composite oxide particles may remain. The crystallinity of the lithium nickel-manganese composite oxide particles obtained after the firing treatment may be insufficient. On the contrary, when the firing temperature exceeds 1000 ° C., the lithium nickel-manganese composite oxide particles are strongly sintered and abnormal grain growth is caused, so that the content ratio of the irregular and coarse particles is increased. It is not preferable because it increases. When the lithium nickel-manganese composite oxide of the composition formula B described later is produced, it is more preferable that the firing temperature is in the range of 800 to 950 ° C. The above firing temperature can be obtained by measuring the temperature of the gas phase portion of the heat treatment furnace with a thermometer.

The rate of temperature rise to the above firing temperature is preferably 1 to 15 ° C./min, and more preferably 5 to 10 ° C./min. When the temperature is raised across the melting point of the lithium compound at this stage of raising the temperature, it is preferable to keep the temperature at or near the melting point for preferably 1 to 5 hours, more preferably for 2 to 5 hours. .. Thereby, the nickel-manganese composite oxide particles and the lithium compound can be reacted more uniformly.

[Baking retention time]
In order to sufficiently promote the firing of the lithium mixture, it is preferable to hold the lithium mixture at the firing temperature for 2 hours or more, more preferably 4 to 24 hours, and most preferably 4 to 10 hours. If the holding time for this firing is less than 2 hours, lithium may not be sufficiently diffused into the nickel-manganese composite oxide particles, and excess lithium or unreacted nickel-manganese composite oxide particles may remain. In addition, the crystallinity of the lithium nickel-manganese composite oxide particles obtained after the firing treatment may be insufficient.

After the lapse of the holding time for firing, it is preferable to cool from the firing temperature to 200 ° C. at a cooling rate of 2 to 10 ° C./min, and at a cooling rate of 3.3 to 7.7 ° C./min. It is more preferable to cool. By keeping the cooling rate within this range, it is possible to prevent the problem that the equipment such as the bowl is damaged by quenching without impairing the productivity.

[Baking atmosphere]
The atmosphere at the time of the above synthetic firing is preferably a non-reducing atmosphere, and more preferably an oxidizing atmosphere. In the case of an oxidizing atmosphere, it is more preferable that the atmosphere has an oxygen concentration of 18 to 100% by volume, and it is particularly preferable to perform the treatment in an air stream of a mixed gas of oxygen adjusted to the oxygen concentration and an inert gas. If the oxygen concentration is less than 18% by volume, the crystallinity of the lithium nickel-manganese composite oxide particles may be insufficient. The crystallinity here means the degree of synthesis of the lithium composite oxide.

(3) Crushing Step The lithium nickel-manganese composite oxide produced by the above synthetic firing treatment may contain agglomerates or sintered bodies due to agglomeration or light sintering generated during heat treatment. Therefore, in order to adjust the average particle size and particle size distribution of the lithium nickel-manganese composite oxide as the positive electrode active material within a suitable range, it is possible to crush the aggregates or sintered bodies of these lithium nickel-manganese composite oxides. preferable.

Specifically, during synthetic firing, agglomerates or sintered bodies composed of a plurality of secondary particles may be formed by necking due to sintering of secondary particles. Therefore, after the synthetic firing, the powder or granular material is formed. It is put into a crushing means and an appropriate mechanical energy is applied to the powder or granular material to perform a crushing process. As a result, the secondary particles themselves can be separated to the original secondary particles state with almost no destruction, that is, aggregation and sintering can be loosened. A general crushing means can be used, for example, a pin mill or a hammer mill can be used. In order to prevent the secondary particles from being destroyed as much as possible, it is preferable to predetermine appropriate operating conditions of the crushing means using the sampled lithium nickel-manganese composite oxide.

3. 3. Positive Active Material for Lithium Ion Secondary Battery The positive positive active material produced by the above method for producing the lithium nickel-manganese composite oxide of the embodiment of the present invention includes lithium, nickel and manganese as essential elements and cobalt as an optional element. When Li: Ni: Mn: Co: M, which is the atomic number ratio of each metal element, is (1 + u): x: y: z: t, which is a lithium nickel-nickel-manganese composite oxide containing the additive element M and the additive element M. , X + y + z + t = 1, -0.05 ≦ u ≦ 0.50, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ It is 0.1. The above-mentioned additive element M is one or more elements selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta and W. This lithium nickel-manganese composite oxide has a hexagonal layered crystal structure.

[Particle structure]
The lithium nickel-manganese composite oxide produced by the method for producing a lithium nickel-manganese composite oxide according to the embodiment of the present invention described above has a multilayer structure which is a characteristic form of the nickel-manganese composite oxide which is a precursor thereof. Unlike this, as shown in the cross-sectional view of FIG. 2 by the scanning electron microscope SEM, it has a porous structure having innumerable voids as a whole. As a result, a wide contact area with the electrolytic solution can be secured while maintaining sufficient particle strength, so that high output characteristics can be obtained when used as the positive electrode active material of the secondary battery.

That is, when the lithium nickel-manganese composite oxide composed of secondary particles having a porous structure having innumerable voids as a whole is used as a positive electrode material, it is secondary through the grain boundaries between the primary particles or the voids. Since the electrolytic solution penetrates into the particles, lithium can be removed and inserted not only on the surface of the secondary particles but also inside the secondary particles. Moreover, since the lithium nickel-manganese composite oxide has a large number of electrically conductive paths inside the secondary particles, the electrical resistance inside the particles can be sufficiently reduced. Therefore, when the positive electrode of the secondary battery is formed by using this lithium nickel-manganese composite oxide, it is possible to significantly improve the output characteristics without impairing the capacity characteristics and the cycle characteristics.

[Volume average particle size]
The positive electrode active material produced by the above-mentioned method for producing a lithium nickel-manganese composite oxide according to the embodiment of the present invention is not particularly limited, but the volume average particle diameter (MV) may be, for example, 3 μm or more and 9 μm or less. it can. When this volume average particle size (MV) is within the above range, the battery capacity per unit volume of the secondary battery using the positive electrode active material can be increased, and the thermal stability and output characteristics are also improved. Can be done.

On the other hand, when the volume average particle diameter (MV) of the positive electrode active material is less than 3 μm, the filling property of the positive electrode active material is lowered, and it becomes difficult to increase the battery capacity per unit volume (volume). On the contrary, when the volume average particle diameter (MV) of the positive electrode active material exceeds 9 μm, the reaction area of the positive electrode active material may decrease and the output characteristics may become insufficient. The volume average particle size (MV) of the positive electrode active material can be obtained from, for example, a volume integrated value measured by a laser light diffraction / scattering type particle size analyzer. Further, the volume average particle diameter (MV) can be adjusted by appropriately changing the firing temperature and the firing holding time in the synthetic firing step.

[Particle size distribution]
The positive electrode active material produced by the above-mentioned method for producing a lithium nickel-manganese composite oxide according to the embodiment of the present invention has an index [(d90-d10) / MV] indicating the spread of the particle size distribution of 0.65 or less. be able to. When this [(d90-d10) / MV] is in the above range, the positive electrode active material can be composed of the lithium nickel-manganese composite oxide having a very narrow particle size distribution, so that the content ratio of fine particles and coarse particles is high. Therefore, the thermal stability, cycle characteristics, and output characteristics of the secondary battery using this positive electrode active material as the positive electrode can be improved.

On the other hand, when the above [(d90-d10) / MV] exceeds 0.65, the content ratio of fine particles and coarse particles in the positive electrode active material increases, so that the positive electrode active material having such a wide particle size distribution spreads. For example, the secondary battery using the above tends to generate heat due to the local reaction of fine particles, and the thermal stability is lowered. Further, since the fine particles are selectively deteriorated, the cycle characteristics are likely to be deteriorated. Further, since the secondary battery using the positive electrode active material having a wide particle size distribution has a high content ratio of coarse particles, it becomes difficult to secure a sufficient reaction area between the electrolytic solution and the positive electrode active material, and the output characteristics. May decrease.

Assuming industrial-scale production, it is not realistic to use a positive electrode active material having an excessively small [(d90-d10) / MV]. Therefore, in consideration of cost and productivity, the lower limit of [(d90-d10) / MV] in the positive electrode active material is preferably 0.25 or more. Note that d10 and d90 in [(d90-d10) / MV] are particle diameters at which the integrated volumes measured by, for example, a laser light diffraction / scattering type particle size analyzer are 10% and 90%, respectively. Further, the above [(d90-d10) / MV] can be adjusted by appropriately changing the firing temperature and the firing holding time in the synthetic firing step.

[Crystalline diameter]
The positive electrode active material produced by the above-mentioned method for producing a lithium nickel-manganese composite oxide according to the embodiment of the present invention has a crystallite diameter (hereinafter, (003)) determined by a Scheller formula from a (003) plane diffraction peak obtained by XRD measurement. ) Planar crystallite diameter) can be preferably 80 nm or more, and more preferably 100 nm or more. When the (003) plane crystallite diameter is 80 nm or more, the crystallinity is high, and the secondary battery using this lithium nickel-manganese composite oxide as the positive electrode has improved output characteristics because the positive electrode resistance is reduced. However, the thermal stability is also improved. On the other hand, when the crystallite diameter of the (003) plane is less than 80 nm, the crystallinity may be insufficient or the thermal stability of the secondary battery may be lowered. The (003) plane crystallite diameter can be adjusted by appropriately changing the firing temperature and the firing holding time in the synthetic firing step.

[Specific surface area]
The positive electrode active material produced by the above method for producing a lithium nickel-manganese composite oxide according to the embodiment of the present invention preferably has a BET specific surface area of 1.5 m ² / g or more and 4.0 m ² / g or less. Can be 2.0 m ² / g or more and 4.0 m ² / g or less, more preferably 2.5 m ² / g or more and 4.0 m ² / g or less. When this BET specific surface area is ^{within the range of 1.5 to 4.0 m 2} / g, a sufficient contact area with the electrolytic solution can be secured when used for the positive electrode of the secondary battery, so that the positive electrode resistance Can be reduced and sufficient output characteristics can be obtained. The BET specific surface area can be adjusted by appropriately changing the firing temperature and the firing holding time in the synthetic firing step.

[composition]
The above lithium-nickel-manganese composite oxide produced in the production method of the lithium-nickel-manganese composite oxide of the embodiment of the present invention, the composition formula B is _{Li 1 + u Ni x Mn y} Co z M t O 2 + α (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, −0. 2 ≦ α ≦ 0.2, M is represented by one or more additive elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W).

In the above composition formula B, the range of u indicating the amount of lithium (Li) is −0.05 or more and 0.50 or less, but 0 or more and 0.50 or less is preferable, and 0 or more and 0.35 or less is more. preferable. When the value of u is in the range of −0.05 or more and 0.50 or less, the output characteristics and capacity characteristics of the secondary battery using this positive electrode active material as the positive electrode material can be improved. On the other hand, when the value of u is less than −0.05, the positive electrode resistance of the secondary battery becomes large, and it becomes difficult to improve the output characteristics. On the contrary, when the value of u exceeds 0.50, the initial discharge capacity may decrease or the positive electrode resistance may increase.

In the above composition formula B, the range of x indicating the content of nickel (Ni) is 0.3 or more and 0.95 or less, but 0.3 or more and 0.9 or less is preferable. Nickel is an element that contributes to increasing the potential and capacity of the secondary battery. Therefore, when the value of x is less than 0.3, the capacity characteristics of the secondary battery using this positive electrode active material should be improved. Becomes difficult. On the contrary, when the value of x exceeds 0.95, the content of other elements is relatively reduced, and the effect of other elements cannot be obtained.

In the above composition formula B, the range of y indicating the content of manganese (Mn) is 0.05 or more and 0.55 or less, but it is preferably 0.10 or more and 0.40 or less. Since manganese is an element that contributes to the improvement of thermal stability, when the value of y is less than 0.05, it becomes difficult to improve the thermal stability of the secondary battery using this positive electrode active material. On the contrary, when the value of y exceeds 0.55, Mn may be eluted from the positive electrode active material during high temperature operation, and the charge / discharge cycle characteristics may be deteriorated.

In the above composition formula B, the range of z indicating the content of cobalt (Co) is 0 or more and 0.4 or less, but 0.10 or more and 0.35 or less is preferable. Since cobalt is an element that contributes to the improvement of charge / discharge cycle characteristics, when the value of z exceeds 0.4, the initial discharge capacity of the secondary battery using this positive electrode active material may be significantly reduced.

The above-mentioned positive electrode active material may contain an additive element M in addition to the above-mentioned metal element in order to further improve the durability and output characteristics of the secondary battery. Examples of such element M include magnesium (Mg), calcium (Ca), aluminum (Al), titanium (Ti), vanadium (V), chromium (Cr), zirconium (Zr), niobium (Nb), and molybdenum (Nb). One or more selected from Mo), hafnium (Hf), titanium (Ta), and tungsten (W) can be used. In the above composition formula B, the value of t indicating the content of the additive element M is 0 or more and 0.1 or less with respect to the total amount of substances of Ni, Co, Mn and M, but is 0.001 or more. 0.05 or less is preferable. When the value of t exceeds 0.1, the metal elements that contribute to the Redox reaction decrease, so that the battery capacity may decrease.

From the viewpoint of further improving the capacity characteristics of the secondary battery, the composition of the positive electrode active material is changed from the composition formula B to the composition formula B1: Li _{1 + u} Ni _x Mn _y Co _z W _a M _b O ₂ (-). 0.05 ≦ u ≦ 0.20, x + y + z = 1, 0.7 <x ≦ 0.95, 0.05 ≦ y ≦ 0.1, 0 ≦ z ≦ 0.2, 0 <a ≦ 0.1, 0 ≦ b ≦ 0.1 and M may be one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta). Above all, from the viewpoint of achieving both thermal stability and battery capacity, it is more preferable that the value of x in the composition formula B1 is 0.7 <x ≦ 0.9, and 0.7 <x ≦ 0. It is more preferably .85.

From the viewpoint of achieving further improvement of the thermal stability of the secondary battery, the composition of the positive electrode active material, a composition formula in place of the above-mentioned composition formula _{B B2: Li 1 + u Ni} x Mn y Co z W a M b O ₂ (−0.05 ≦ u ≦ 0.50, x + y + z = 1, 0.3 ≦ x ≦ 0.7, 0.1 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 <a ≦ 0 .1, 0 ≦ b ≦ 0.1, M is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, and Ta). Good.

4. Lithium-ion secondary battery (1) Non-aqueous electrolyte secondary battery A lithium-ion secondary battery produced by using the positive electrode active material produced by the above-mentioned method for producing a lithium nickel-manganese composite oxide according to the embodiment of the present invention is, for example. It has the same components as a general non-aqueous electrolyte secondary battery mainly composed of a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution. The shape of this non-aqueous electrolyte secondary battery is not limited, and can be various shapes such as a cylindrical shape and a laminated shape. Regardless of the shape, the electrode body consisting of the positive electrode and the negative electrode arranged via the separator is impregnated with the non-aqueous electrolyte solution, and between the current collector of the positive electrode and the positive electrode terminal leading to the outside, and A non-aqueous electrolyte secondary battery is manufactured by connecting the current collector of the negative electrode and the negative electrode terminal leading to the outside by using a current collecting lead or the like, and housing the battery in a battery case to seal the battery. Can be done. Hereinafter, each component will be described.

(A) Positive electrode First, a conductive agent and a binder are mixed with the powdered positive electrode active material produced by the above-mentioned method for producing a lithium nickel-manganese composite oxide according to the embodiment of the present invention, and further, if necessary, Activated carbon for increasing the electric double layer capacity and a solvent for adjusting the viscosity are added, and these are kneaded to prepare a positive electrode mixture paste. The blending ratio of the materials constituting the positive electrode mixture paste affects the performance of the non-aqueous electrolyte secondary battery, so the blending ratio should be appropriate. For example, when the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 60 to 95 parts by mass and the conductive agent is similar to the positive electrode of a general non-aqueous electrolyte secondary battery. The content of the binder is preferably 1 to 20 parts by mass, and the content of the binder is preferably 1 to 20 parts by mass.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of aluminum foil, for example, and the solvent is scattered by drying. In order to increase the electrode density, pressurization may be performed by a roll press or the like, if necessary. Thereby, after producing the sheet-shaped positive electrode, the positive electrode can be produced by cutting the positive electrode into an appropriate size according to the target battery. The method for producing the positive electrode is not limited to this, and other methods may be used for producing the positive electrode.

As the conductive agent used as the raw material of the positive electrode mixture paste, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black and Ketjen black can be used. The binder plays a role of binding the active material particles, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin and polyacrylic. Acids can be used. Further, the above-mentioned positive electrode active material, the conductive agent and the activated carbon to be added as needed may be dispersed, and a solvent having a role of dissolving the binder may be added to the positive electrode mixture. As this solvent, for example, an organic solvent such as N-methyl-2-pyrrolidone can be used.

(B) Negative electrode For the negative electrode, prepare a negative electrode active material that can occlude and desorb lithium ions, such as metallic lithium or lithium alloy, and add a binder and an appropriate solvent to the negative electrode and knead it to form a paste. Obtain the negative electrode mixture of. This negative electrode mixture paste is applied to the surface of a metal leaf current collector such as copper, dried, and compressed as necessary to increase the electrode density. Thereby, the negative electrode can be manufactured.

As described above, a substance containing lithium such as metallic lithium or a lithium alloy may be used for the negative electrode, or a calcined organic compound such as natural graphite, artificial graphite or phenol resin capable of occluding / desorbing lithium ions. Alternatively, a powder or granule of a carbon substance such as coke may be used. As with the positive electrode, a fluororesin such as PVDF can be used as the binder for the negative electrode, and N-methyl-2-pyrrolidone or the like can be used as the solvent for dispersing these active substances and the binder. Organic solvent can be used.

(C) Separator A separator having a function of separating the positive electrode and the negative electrode and holding an electrolyte by sandwiching the separator between the positive electrode and the negative electrode is used. The material of this separator is not particularly limited as long as it has the above-mentioned function, but it is preferable to use a thin film made of, for example, polyethylene or polypropylene, which has a large number of fine pores.

(D) Non-aqueous electrolyte solution As the non-aqueous electrolyte solution, for example, a solution in which a lithium salt as a supporting salt is dissolved in an organic solvent can be used. Alternatively, an ionic liquid in which a lithium salt is dissolved may be used. The ionic liquid is a salt that is composed of a click-on and an anion other than lithium ions and that is in a liquid state even at room temperature.

Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate, tetrahydrofuran and 2-methyltetrahydrofuran. One selected from ether compounds such as dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesulton, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more thereof may be mixed. Can be used.

Further, as the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , and a composite salt thereof can be used. The non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, or the like in order to improve the battery characteristics.

(2) All-solid-state secondary battery As the solid electrolyte used in the all-solid-state secondary battery, it is preferable to use one having a property of being able to withstand a high voltage. Examples of such a solid electrolyte include an inorganic solid electrolyte and an organic solid electrolyte. As the former inorganic solid electrolyte, an oxide-based solid electrolyte or a sulfide-based solid electrolyte is preferably used.

The oxide-based solid electrolyte is not limited, but preferably contains oxygen (O) and has lithium ion conductivity and electronic insulation. Specifically, lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO _{4- Li 3} PO ₄ , Li ₄ SiO _{4 -Li 3} VO ₄ , Li ₂ O-B ₂ O _3- P ₂ O ₅ , Li ₂ O-SiO ₂ , Li ₂ O-B ₂ O _3- ZnO, Li _{1 + x} Al _x Ti _2-x (PO) ₄ ) ₃ (0 ≦ x ≦ 1), Li _{1 + x} Al _x Ge _2-x (PO ₄ ) ₃ (0 ≦ x ≦ 1), LiTi ₂ (PO ₄ ) ₃ , Li _3x La _{2 / 3-x} TiO ₃ (0 ≦ x ≦ 2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O _4th grade can be mentioned.

Further, as the sulfide-based solid electrolyte, those containing sulfur (S) and having lithium ion conductivity and electron insulating property are preferably used, although not limited to the above. Specifically, Li ₂ SP ₂ S ₅ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li _{2 SP 2} S ₅ , LiI-Li _{2 SB 2} S _{3, Li 3 PO 4 -Li 2} S-Si 2 S, Li 3 PO 4 -Li 2 S-SiS 2, LiPO 4 -Li 2 S-SiS, LiI-Li 2 S-P 2 O 5, LiI-Li ₃ PO _4- P ₂ S _{5 and the} like can be mentioned.

Further, may be used an inorganic solid electrolyte other than the above, for _example, can be cited Li ₃ N, LiI, and Li 3 N-LiI-LiOH and the like. On the other hand, the latter organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof and the like can be used. The organic solid electrolyte may contain a supporting salt (lithium salt).

(3) Characteristics of Lithium Ion Secondary Battery As described above, the lithium ion secondary battery having the above structure uses the positive electrode active material produced by the production method of the embodiment of the present invention as the positive electrode material. Excellent capacitance characteristics, output characteristics and cycle characteristics. Moreover, it is excellent in thermal stability and safety even in comparison with a conventional secondary battery using a positive electrode active material composed of lithium nickel-based oxide particles.

(4) Applications Since the lithium ion secondary battery having the above structure is excellent in capacity characteristics, output characteristics and cycle characteristics as described above, a small portable electronic device (a small portable electronic device in which these characteristics are required at a high level) ( It can be suitably used as a power source for a notebook personal computer, a mobile phone terminal, etc.). Further, the non-aqueous electrolyte secondary battery produced by the manufacturing method of the embodiment of the present invention is excellent in safety, and not only can be miniaturized and increased in output, but also an expensive protection circuit is simplified. Therefore, it can be suitably used as a power source for transportation equipment whose mounting space is limited.

As described above, the method for producing a precursor of a positive electrode active material according to the embodiment of the present invention, the method for producing a positive electrode active material using the precursor as an intermediate raw material, and the method for producing a lithium ion secondary battery using the positive electrode active material. As described above, the present invention is not limited to the above-described embodiment, and includes various modified examples and alternative examples. That is, the scope of rights of the present invention extends to the scope of claims and the equivalent scope thereof. Next, the present invention will be described with reference to examples, but the present invention is not limited to the following examples.

(Example 1)
First, nickel-manganese-cobalt composite hydroxide particles were prepared by a wet method. At that time, a nickel-manganese-cobalt composite hydroxide having a multi-layer structure was prepared by switching the atmosphere in the reaction vessel during the crystallization reaction between a non-oxidizing atmosphere and an oxidizing atmosphere. By adjusting the mixing ratio of the raw materials, the substance amount ratio was set to nickel: manganese: cobalt = 5: 3: 2.

This composite hydroxide was placed in an alumina saggar and primary fired in a roller herskill simulator furnace (manufactured by Noritake Company, Inc.) in which the oxygen concentration was maintained at 20% by volume. As the temperature rise pattern of the atmospheric temperature during the primary firing, the temperature rise rate was set to 1 ° C./min from room temperature to 200 ° C. and 2 ° C./min from 200 ° C. to 700 ° C. Then, it was held at 700 ° C. for 3 hours to form a nickel-manganese-cobalt composite oxide. After holding for 3 hours, the mixture is cooled to room temperature by natural cooling, lithium hydroxide prepared separately is added, and the mixture is mixed using a shaker mixer device (TURBULA Type T2C manufactured by Willie et Bacoffen (WAB)). , A lithium mixture was obtained. The lithium hydroxide was blended so that the Li / Me ratio of the lithium mixture was 1.1.

The lithium mixture obtained above was placed in an alumina saggar and secondarily fired in a roller herskilln simulator furnace (manufactured by Noritake Company, Inc.) in which the oxygen concentration was maintained at 60% by volume or more. As a pattern for raising the ambient temperature during this secondary firing, the temperature was raised from room temperature to 900 at a rate of 5 ° C./min, and the temperature was maintained at 900 ° C. for 4 hours. In this way, the lithium nickel manganese cobalt composite oxide of Sample 1 was prepared. When the cross section of the obtained lithium nickel manganese cobalt composite oxide of Sample 1 was observed using SEM, it was confirmed that it had a porous structure.

Lithium nickel-manganese-cobalt composite oxides of Samples 2 to 16 were prepared in the same manner as in Sample 1 except that the heat treatment conditions for the primary firing and / or the secondary firing were variously changed. In order to evaluate the mechanical strength of the lithium nickel manganese cobalt composite oxides of these samples 1 to 16, the fine powder ratio was measured. Specifically, a flow-type particle image analyzer (FPIA-3000: manufactured by Maru Balloon Co., Ltd.) was charged with a lithium nickel-manganese-cobalt composite oxide of each sample for evaluation. In addition, the evaluation of the fine powder ratio is evaluated as "good" if the number of particles of 1 μm or less contained in 10,000 particles is less than 1% and "bad" if the number of particles is 1% or more by the counting method using the above device. did. The results are shown in Table 1 below.

From the results in Table 1 above, all of the lithium nickel-manganese-cobalt composite oxides of Samples 1 to 14 prepared by the method satisfying the requirements of the present invention had a good evaluation of the fine powder ratio. On the other hand, the lithium nickel-manganese-cobalt composite oxides of the samples 15 and 16 prepared by the method not satisfying the requirements of the present invention had poor evaluation of the fine powder ratio.

Claims (7)

There is a method for producing a nickel-manganese composite oxide having a multi-layered secondary particle form as a precursor of a positive electrode active material having a porous structure composed of a hexagonal lithium nickel-manganese composite oxide.
The composition formula is Ni _x Mn _y Co _z M _t (OH) _{2 + β} (x + y + z + t = 1, 0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, −0.20 ≦ β ≦ 0.20, M is selected from the group consisting of Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W. With respect to the nickel-manganese composite hydroxide having the form of secondary particles having a multilayer structure represented by (one or more kinds of additive elements), the ambient temperature is raised from room temperature to 150 at a heating rate of 1 ° C./min or less in an oxidizing atmosphere. After raising the temperature to the excess water removal temperature of ° C. or higher and 250 ° C. or lower, the temperature rises from the excess water removal temperature to the roasting temperature of 400 ° C. or higher and 800 ° C. or lower at a heating rate of more than 1 ° C./min and 5 ° C./min or lower. A method for producing a nickel-manganese composite oxide, which comprises heating and holding at the roasting temperature for 1 hour or more for roasting. The form of the secondary particles having the multilayer structure is composed of a central portion and a surface portion in which the primary particles are densely present, and an intermediate portion located between the central portion and the surface portion in which the primary particles are sparsely present. The method for producing a nickel-manganese composite oxide according to claim 1, wherein the nickel-manganese composite oxide is produced. A feature is that a lithium compound is mixed with a nickel-manganese composite oxide produced by the production method according to claim 1 or 2, and the obtained mixture is calcined at a calcining temperature of 700 to 1000 ° C. for 2 hours or more. A method for producing a lithium nickel-manganese composite oxide. The lithium-nickel-manganese composite oxide, a composition formula _{Li 1 + u Ni x Mn y} Co z M t O 2 + α (-0.05 ≦ u ≦ 0.50, x + y + z + t = 1,0.3 ≦ x ≦ 0.95, 0.05 ≦ y ≦ 0.55, 0 ≦ z ≦ 0.4, 0 ≦ t ≦ 0.1, −0.20 ≦ α ≦ 0.20, M is Mg, Ca, Al, Ti, V, The lithium nickel-manganese composite oxide according to claim 3, which is represented by (one or more additive elements selected from the group consisting of Cr, Zr, Nb, Mo, Hf, Ta, and W). Production method. The method for producing a lithium nickel-manganese composite oxide according to claim 3 or 4, wherein the lithium compound is lithium carbonate, lithium hydroxide, or a mixture thereof. The production of the lithium nickel-manganese composite oxide according to any one of claims 3 to 5, wherein the specific surface area of the lithium nickel-manganese composite oxide is 1.5 to 4.0 m ^{2 / g.} Method. A lithium ion secondary battery composed of at least a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode active material of the positive electrode is a lithium nickel manganese produced by the production method according to any one of claims 3 to 6. A method for manufacturing a lithium ion secondary battery, which comprises using a composite oxide.