WO2021246215A1 - Positive electrode active material for lithium secondary batteries, method for producing same, and lithium secondary battery - Google Patents

Abstract

The present invention provides: a positive electrode active material for lithium secondary batteries, said positive electrode active material being suppressed in cycle deterioration even if charging and discharging are repeated at a high voltage, while having a high energy density retention rate if used as a positive electrode active material for a lithium secondary battery; and a lithium secondary battery which is suppressed in cycle deterioration even if charging and discharging are repeated at a high voltage, while having a high energy density retention rate.　A positive electrode active material for lithium secondary batteries, said positive electrode active material being characterized by being composed of Mg-containing lithium-cobalt composite oxide particles, each having a particle surface, to at least a part of which a Ti-containing compound adheres, and being also characterized in that the Mg-containing lithium-cobalt composite oxide contains cobalt oxide (Co₃O₄).

Description

Positive electrode active material for lithium secondary battery, its manufacturing method and lithium secondary battery

The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery using the positive electrode active material.

In recent years, as household appliances have become more portable and cordless, lithium-ion secondary batteries have been put into practical use as a power source for small electronic devices such as laptop computers, mobile phones, and video cameras. Regarding this lithium-ion secondary battery, since it was reported by Mizushima et al. In 1980 that lithium cobalt oxide is useful as a positive electrode active material for lithium-ion secondary batteries, research and development on lithium-based composite oxides has been active. Many proposals have been made so far.

However, the lithium secondary battery using lithium cobalt oxide has a problem of deterioration of cycle characteristics due to elution of cobalt atoms and the like.

The following Patent Document 1 proposes a lithium secondary battery using a lithium cobalt-based composite oxide having a lithium cobalt oxide content of 20% or more on the particle surface of lithium cobalt oxide as a positive electrode active material. Further, Patent Document 2 below describes a positive electrode active material for a lithium secondary battery made of a lithium transition metal composite oxide containing 0.20 to 2.00% by weight of a Ti atom, wherein the Ti atom is a lithium transition metal. It has been proposed to use a lithium cobalt-based composite oxide that exists in the depth direction from the particle surface of the composite oxide and has the maximum concentration gradient on the particle surface as the positive electrode active material. Further, Patent Document 3 and Patent Document 4 below propose that a lithium cobalt-based composite oxide containing an Sr atom and a Ti atom is used as a positive electrode active material.

Japanese Unexamined Patent Publication No. 2005-123111 International Publication WO2011 / 043296 Pamphlet Japanese Unexamined Patent Publication No. 2013-182758 Japanese Unexamined Patent Publication No. 2013-182757

In recent years, there has been a demand for further improvement in the energy density of lithium-ion batteries. One of the means is to increase the voltage such as raising the charge termination voltage of the battery. However, even with these conventional methods, there is a problem that the cycle characteristics deteriorate when the charge / discharge voltage is repeated under a high voltage.

Therefore, an object of the present invention is that when used as a positive electrode active material for a lithium secondary battery, the positive electrode for a lithium secondary battery has a high energy density retention rate with little cycle deterioration even after repeated charging and discharging under a high voltage. It is an object of the present invention to provide a lithium secondary battery which is an active material and has a high energy density maintenance rate with little deterioration of the cycle even after repeated charging and discharging under a high voltage.

As a result of diligent research in view of the above circumstances, the present invention uses Mg-containing lithium-cobalt-based composite oxide particles as lithium-cobalt-based composite oxide particles, and attaches a Ti-containing compound to the surface of the particles. _{, A lithium secondary battery that uses a positive electrode active material containing cobalt oxide (Co 3} O ₄ ) inside or on the surface of Mg-containing lithium cobalt-based composite oxide particles as the positive electrode active material is charged and discharged under high voltage. We have found that the lithium secondary battery has a high energy density maintenance rate with little deterioration of the cycle even if the above steps are repeated, and have completed the present invention.

That is, the present invention (1) is composed of Mg-containing lithium cobalt-based composite oxide particles having a Ti-containing compound attached to at least a part of the particle surface, and the Mg-containing lithium cobalt-based composite oxide is cobalt oxide. It provides a positive electrode active material for a lithium secondary battery, which is characterized by containing (Co ₃ O _4).

Further, in the present invention (2), the _{content of cobalt oxide (Co 3} O ₄ ) in the Mg-containing lithium cobalt-based composite oxide containing the cobalt oxide (Co ₃ O ₄ ) is CuKα ray as a radiation source. When the Mg-containing lithium cobalt-based composite oxide containing cobalt oxide (Co ₃ O ₄ ) was subjected to X-ray diffraction analysis, the intensity of the diffraction peak near 2θ = 37.4 ° due to _{LiCoO 2 (B).} The ratio ((A / B) × 100) of the intensity (A) of the diffraction peak near 2θ = 36.8 ° due to Co ₃ O _{4 to) is larger than 0.6 and 5.0% or less.} (1) Provided is a positive electrode active material for a lithium secondary battery.

Further, the present invention (3) is, Mg content of Mg-containing lithium-cobalt composite oxide containing the cobalt oxide _(Co 3 _{O 4)} is, in terms of atom, cobalt oxide _(Co 3 _{O 4)} The positive electrode active material for the lithium secondary battery according to (1) or (2), which is 0.01 to 5.00 mol% as Mg with respect to Co in the Mg-containing lithium cobalt-based composite oxide. Is to provide.

Further, the present invention (4) provides the positive electrode active material for a lithium secondary battery according to any one of (1) to (3), wherein the Ti-containing compound is an oxide containing titanium. be.

Further, in the present invention (5), the amount of the Ti-containing compound adhered is as Ti with respect to Co in the Mg-containing lithium cobalt-based composite oxide containing cobalt _{oxide (Co 3} O _{4) in terms of atoms.} It provides a positive electrode active material for a lithium secondary battery according to any one of (1) to (4), which is characterized by having a content of 0.01 to 5.00 mol%.

Further, in the present invention (6), the Mg lithium cobalt-based composite oxide particles contain one or more M elements (M is Al, Ti, Zr, Cu) in addition to Li, Co, Mg and O. , Fe, Sr, Ca, V, Mo, Bi, Nb, Si, Zn, Ga, Ge, Sn, Ba, W, Na, K, Ni or Mn). )-(5) Provided is a positive electrode active material for a lithium secondary battery.

Further, the present invention (7), and Mg-containing lithium-cobalt composite oxide particles containing cobalt oxide _(Co 3 _{O 4),} a Ti-containing compound, by mixing treated with dry and cobalt oxide (Co ₃ It _{shall be obtained by obtaining a mixed product of Mg-containing lithium cobalt-based composite oxide particles containing O 4} ) and a Ti-containing compound, and then heat-treating the mixed product at 400 to 1000 ° C. The present invention provides a positive electrode active material for a lithium secondary battery according to any one of (1) to (6).

Further, the present invention (8), and Mg-containing lithium-cobalt composite oxide particles containing cobalt oxide _(Co 3 _{O 4),} a Ti-containing compound, by mixing treated with dry and cobalt oxide (Co ₃ A mixed treatment of Mg-containing lithium cobalt-based composite oxide particles containing O ₄ ) and a Ti-containing compound is obtained, and then the mixed treatment is heat-treated at 400 to 1000 ° C. for a lithium secondary battery. The present invention provides a method for producing a positive electrode active material for a lithium secondary battery, which comprises obtaining a positive electrode active material.

Further, the present invention (9) provides a lithium secondary battery characterized by using the positive electrode active material for a lithium secondary battery according to any one of (1) to (7).

According to the present invention, when used as a positive electrode active material for a lithium secondary battery, the positive electrode active material for a lithium secondary battery has a high energy density retention rate with little cycle deterioration even after repeated charging and discharging under high voltage. , And it is possible to provide a lithium secondary battery having a high energy density maintenance rate with little deterioration of the cycle even if charging and discharging are repeated under a high voltage.

The charge / discharge characteristic figure of the lithium secondary battery using the positive electrode active material sample obtained in Example 1. FIG. The charge / discharge characteristic figure of the lithium secondary battery using the positive electrode active material sample obtained in Example 2. FIG. The charge / discharge characteristic figure of the lithium secondary battery using the positive electrode active material sample obtained in the comparative example 1. FIG. The charge / discharge characteristic figure of the lithium secondary battery using the positive electrode active material sample obtained in the comparative example 2. FIG. The charge / discharge characteristic figure of the lithium secondary battery using the positive electrode active material sample obtained in the comparative example 3. FIG. The charge / discharge characteristic figure of the lithium secondary battery using the positive electrode active material sample obtained in the comparative example 4. FIG. The charge / discharge characteristic figure of the lithium secondary battery using the positive electrode active material sample obtained in the comparative example 5. FIG.

The positive electrode active material for a lithium secondary battery of the present invention is composed of Mg-containing lithium cobalt-based composite oxide particles having a Ti-containing compound attached to at least a part of the particle surface, and the Mg-containing lithium cobalt-based composite oxide. Is a positive electrode active material for a lithium secondary battery, which is characterized by containing cobalt oxide (Co ₃ O _4).

In the positive electrode active material for a lithium secondary battery of the present invention, a Ti-containing compound is attached to the particle surface of a Mg-containing lithium cobalt-based composite oxide containing cobalt _{oxide (Co 3} O _4). The positive electrode active material for a lithium secondary battery of the present invention is a "Mg-containing lithium cobalt-based composite oxide containing cobalt _{oxide (Co 3} O _{4)" to which a Ti-containing compound is attached.} Hereinafter, the Mg-containing lithium cobalt-based composite oxide containing cobalt oxide (Co ₃ O _{4 ) is also referred to as Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles.

That is, in the positive electrode active material for a lithium secondary battery of the present invention, Mg is present inside the particles of the lithium cobalt-based composite oxide particles, and the Ti-containing compound is adhered to the particle surface of the lithium cobalt-based composite oxide particles. _{Cobalt oxide (Co 3} O ₄ ) is present inside the particles of the lithium-cobalt-based composite oxide particles and / or on the surface of the particles of the lithium-cobalt-based composite oxide particles.

In other words, the positive electrode active material for the lithium secondary battery of the present invention adheres to the lithium cobalt-based composite oxide particles containing Mg inside and at least a part of the particle surface of the lithium cobalt-based composite oxide particles. It is an aggregate of lithium cobalt oxide composite oxide particles composed of the above Ti-containing compound and having cobalt oxide (Co ₃ O _{4) present inside and / or on the particle surface of the lithium cobalt oxide composite oxide particles.} be.

_{The Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles according to the positive electrode active material for a lithium secondary battery of the present invention contain Mg inside the particles of the lithium cobalt-based composite oxide particles. _{That is, in the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles according to the positive electrode active material for the lithium secondary battery of the present invention, _{Mg is contained inside the particles of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles. Exists. In the present invention, the Mg is present in the particle inside the _Co 3 _{O 4} and Mg-containing lithium-cobalt composite oxide particles, using a CuKα ray as a radiation source, _Co 3 _{O 4} and Mg-containing lithium-cobalt This means that when the composite oxide particles are subjected to X-ray diffraction analysis, the diffraction peak due to MgO is substantially not detected. The fact that the diffraction peak caused by MgO is not substantially detected means that the peak intensity of the diffraction peak caused by MgO is less than the lower limit of detection of the analyzer.

In the lithium cobalt-based composite oxide, when Mg is present on the particle surface, the Mg element existing on the particle surface is present on the particle surface in the state of MgO, so Mg is present on the particle surface. When the lithium-cobalt-based composite oxide is subjected to X-ray diffraction analysis, a peak due to MgO is observed.

The positive electrode active material for a lithium secondary battery of the present invention _{contains cobalt oxide (Co 3} O ₄ ) _{inside and / or on the surface of the particles of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles. In the present invention, _Co 3 _{O 4} and inside the particles Mg-containing lithium-cobalt composite oxide particles, and contains cobalt oxide _{(Co 3 O 4), Co} 3 O 4 and Mg-containing lithium-cobalt composite oxide particles It means that Co that exists in the state of _{Co 3} O ₄ is contained in the particles of Co. Further, the particle surface of the _Co 3 _{O 4} and Mg-containing lithium-cobalt composite oxide particles, and containing cobalt oxide _(Co 3 _{O 4),} the particles of _Co 3 _{O 4} and Mg-containing lithium-cobalt composite oxide particles It means that it contains Co that adheres to the surface and _{exists in the state of Co 3} O _4. That is, in the positive electrode active material for the lithium secondary battery of the present invention, cobalt oxide (Co ₃ O ₄ ) is _{present inside the particles of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles and / or Co. ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles are present in the positive electrode active material for a lithium secondary battery in a state of being attached to the particle surface.

In the present invention, the fact that the Mg-containing lithium cobalt-based composite oxide particles contain cobalt oxide (Co ₃ O ₄ ) means that the Mg-containing lithium cobalt-based composite oxide is analyzed by X-ray diffraction using CuKα rays as the radiation source. When this is done, it is confirmed by detecting the diffraction peak caused by _{Co 3} O _4. A diffraction peak due to Co ₃ O ₄ is detected, refers to the peak intensity of the diffraction peaks due to Co ₃ O ₄ is greater than or equal to the detection limit of the analyzer.
In the present invention, Co ₃ peak intensity of the diffraction peaks due to O ₄ is more than the detection limit of the analyzer A, cobalt oxide (Co 3 _{O 4)} Mg-containing lithium-cobalt composite oxide containing the present invention When X-ray diffraction analysis was performed using CuKα beam as a radiation source, _{Co 3 with} respect to the intensity (B) of the diffraction peak near 2θ = 37.4 ° (37.4 ± 0.2 °) caused by _{LiCoO 2.} the ratio of the intensity of the diffraction peak (a) of 2 [Theta] = 36.8 near ° due to _{O 4 (36.8 ± 0.2 °)} ((a / B) × 100) is more preferably 0.60% Indicates that it is large.

In the positive electrode active material for a lithium secondary battery of the present invention _{, a Ti-containing compound is attached to a part of the particle surface of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles, or the entire particle surface is covered. Therefore, Ti-containing compounds are attached. The term "Ti-containing compound attached to a part of the particle surface" means that the particle surface has a portion where the surface of the object to be coated is exposed in addition to the Ti-containing compound.

The cathode active material for a lithium secondary battery of the present invention, using CuKα-ray as a radiation source, Co ₃ O ₄ and Mg-containing lithium-cobalt composite oxide, i.e., a positive electrode active material for a lithium secondary battery of the present invention When X-ray diffraction analysis is performed, a diffraction peak having an intensity equal to or higher than the lower limit of detection is observed in the vicinity of 2θ = 36.8 ° caused by _{Co 3} O _4. In the positive electrode active material for the lithium secondary battery of the present invention, the _{content of cobalt oxide (Co 3} O _{4 ) in the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles uses CuKα ray as the radiation source. When the Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles, that is, the positive electrode active material for the lithium secondary battery of the present invention were subjected to X-ray diffraction analysis, 2θ = 37.4 due to _{LiCoO 2 was used.} Intensity of diffraction peak near ° (37.4 ± 0.2 °) Intensity of diffraction peak near 2θ = 36.8 ° (36.8 ± 0.2 °) due to _{Co 3} O _{4 with respect to (B).} The content of the ratio (A) ((A / B) × 100) is preferably greater than 0.60% and 5.00% or less, and particularly preferably 0.80 to 2.50%. It is preferable in that even if charging and discharging are repeated under a high voltage, the deterioration of the cycle is small and the effect of increasing the energy retention rate is high. In the present invention, the intensity ratio of the diffraction peak is a value obtained by the height ratio of the diffraction peak.

In the positive electrode active material for a lithium secondary battery of the present invention (that is, in the entire positive electrode active material for a lithium secondary battery of the present invention), the atomic equivalent molar ratio (Li / Co) of Li to Co is preferably 0. It is 90 to 1.20, particularly preferably 0.95 to 1.15. When the molar ratio (Li / Co) of Li to Co in the lithium cobalt-based composite oxide is in the above range, the energy density of the positive electrode active material for a lithium secondary battery becomes high.

In the positive electrode active material for a lithium secondary battery of the present invention (that is, in the entire positive electrode active material for a lithium secondary battery of the present invention), the atomic equivalent mol% of Mg with respect to Co ((Mg / Co) × 100) is. It is preferably 0.01 to 5.00 mol%, and particularly preferably 0.05 to 2.00 mol%. When the atomic equivalent mol% ((Mg / Co) × 100) of Mg with respect to Co in the positive electrode active material for a lithium secondary battery is in the above range, the cycle characteristics of the positive electrode active material for a lithium secondary battery are enhanced. ..

In the positive electrode active material for a lithium secondary battery of the present invention (that is, in the entire positive electrode active material for a lithium secondary battery of the present invention), the atomic equivalent mol% of Ti with respect to Co ((Ti / Co) × 100) is It is preferably 0.01 to 5.00 mol%, and particularly preferably 0.10 to 2.00 mol%. When the atomic equivalent mol% ((Ti / Co) × 100) of Ti with respect to Co in the positive electrode active material for a lithium secondary battery is in the above range, the battery characteristics such as high charge / discharge capacity, cycle characteristics, and safety are obtained. Can be compatible.

The _{Ti-containing compound adhering to the particle surface of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles is, for example, a Ti oxide, a Ti and Li composite oxide, or a Ti and M element composite. Examples thereof include oxides, composite oxides of Ti, M element and Li, composite oxides of Ti and Mg, and the like.

The Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles contain one or more of the following M elements, if necessary, for the purpose of improving performance or physical properties. can do. The M elements contained in the Mg-containing lithium cobalt-based composite oxide as required are Al, Ti, Zr, Cu, Fe, Sr, Ca, V, Mo, Bi, Nb, Si, Zn, Ga, Ge, Sn, Ba, W, Na, K, Ni or Mn.

When the Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles contain M element, the atomic equivalent mol% of M element with respect to _{Co in Co 3} O _{4 and Mg-containing lithium cobalt-based composite oxide ((M).} / Co) × 100) is preferably 0.01 to 5.00 mol%, particularly preferably 0.05 to 2.00 mol%. When the Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles contain M element, the atomic equivalent mol% of M element with respect to Co _{in Co 3} O _{4 and Mg-containing lithium cobalt-based composite oxide particles (} When (M / Co) × 100) is in the above range, the battery characteristics can be improved without impairing the charge / discharge capacity. When Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles contain two or more types of M elements, the number of moles of the atomically converted M element, which is the basis for calculating the above mol%, is each M. Refers to the total number of moles of elements.

M element is also present on the surface of the Co ₃ O ₄ and Mg-containing lithium-cobalt may be present in the interior of the composite oxide particles, Co ₃ O ₄ and Mg-containing lithium-cobalt composite oxide particles It may be present both inside and on the surface of the Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles.

When the _{M element is present on the particle surface of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles, the M element is present in the form of an oxide, a composite oxide, a sulfate, a phosphate, or the like. May be good.

The Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles are granules of the Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide.

The Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles are lithium cobalt-based composite oxides before the Ti-containing compound is attached to the particle surface.

The Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles are, for example, a raw material mixing step of preparing a raw material mixture containing a lithium compound, a cobalt compound, and a magnesium compound, and then firing the obtained raw material mixture. It is manufactured by performing a firing step.

The lithium compound involved in the raw material mixing step is not particularly limited as long as it is a lithium compound usually used as a raw material for producing a lithium cobalt-based composite oxide, and lithium oxides, hydroxides, carbonates, nitrates, etc. Examples thereof include sulfates and organic acid salts.

The cobalt compound involved in the raw material mixing step is not particularly limited as long as it is a cobalt compound usually used as a raw material for producing a lithium cobalt-based composite oxide, and is not particularly limited. Examples thereof include carbonates, nitrates, sulfates and organic acid salts.

The magnesium compound involved in the raw material mixing step is not particularly limited as long as the Mg atom can be present inside the particles of the Mg-containing lithium cobalt-based composite oxide, and magnesium oxides, hydroxides, and the like are not particularly limited. Examples thereof include carbonates and organic acid salts.

In the raw material mixing step, the mixing ratio of the lithium compound and the cobalt compound is such that the ratio of the number of moles of Li to the number of moles of Co (Li / Co molar ratio) is preferably 0.900 to 1.000 in terms of atoms. The mixing ratio is preferably 0.950 to 1.000, and particularly preferably 0.960 to 0.999. When the mixing ratio of the lithium compound and the cobalt compound is within the above range, the Mg-containing lithium cobalt-based composite oxide particles (Co ₃ O ₄ and _{) containing cobalt oxide (Co 3} O _{4) inside and / or on the particle surface are contained.} Mg-containing lithium-cobalt-based composite oxide particles) can be obtained.

In the raw material mixing step, the mixing ratio of the magnesium compound and the cobalt compound is, in terms of atoms, mol% of Mg in terms of atoms ((Mg / Co) × 100), preferably 0.01 to 5.00 mol%. Particularly preferably, the mixing ratio is 0.05 to 2.00 mol%. When the mixing ratio of the magnesium compound and the cobalt compound is in the above range, the cycle characteristics of the positive electrode active material for the lithium secondary battery are improved.

In the raw material mixing step, a compound containing M element can be mixed with the raw material mixture.

Examples of the compound containing the M element include oxides, hydroxides, carbonates, nitrates, sulfates, fluorides and organic acid salts containing the M element. As the compound containing the M element, a compound containing two or more kinds of M elements may be used.

The raw material lithium compound, cobalt compound, magnesium compound and compound containing M element are not limited in production history, but are impurities as much as possible in order to produce high-purity lithium cobalt-based composite oxide particles. It is preferable that the content is low.

In the raw material mixing step, as a method of mixing the lithium compound, the cobalt compound, the magnesium compound, and the compound containing the M element used as necessary, for example, a ribbon mixer, a henschel mixer, a super mixer, and now. A mixing method using a tar mixer or the like can be mentioned. At the laboratory level, a household mixer is sufficient as a mixing method.

The firing step is a step of obtaining a lithium cobalt-based composite oxide by firing the raw material mixture obtained by performing the raw material mixing step.

In the firing step, the firing temperature when the raw material mixture is fired and the raw materials are reacted is 800 to 1150 ° C., preferably 900 to 1100 ° C., particularly preferably higher than 1000 ° C. and 1100 ° C. or lower. When the firing temperature is within the above range, it is possible to reduce the _{production of superheated decomposition products of Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles, and cobalt oxide (Co ₃ O ₄ ) can be used as described above. It can be contained in a range that remains.

The firing time in the firing step is 1 to 30 hours, preferably 5 to 20 hours. Further, the firing atmosphere in the firing step is an oxidizing atmosphere of air, oxygen gas, or the like.

The Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles thus obtained may be subjected to a plurality of firing steps, if necessary.

_{The average particle size of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles before the Ti-containing compound is attached is a particle size (D50) with a volume integration of 50% in the particle size distribution obtained by the laser diffraction / scattering method. The thickness is 0.5 to 30.0 μm, preferably 3.0 to 25.0 μm, and particularly preferably 7.0 to 25.0 μm. _{The BET specific surface area of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles before the Ti-containing compound is attached ^{is preferably 0.05 to 1.0 m 2} / g, particularly preferably 0.15. It is ~ 0.60 m ² / g. _{When the average particle diameter or BET specific surface area of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles before the Ti-containing compound is attached is within the above range, it is easy to prepare and coat the positive electrode mixture. Further, an electrode having a high filling property can be obtained.

In the positive electrode active material for a lithium secondary battery of the present invention, a Ti-containing compound is attached to at least a part of the particle surface of _{the Co 3} O _{4 and Mg-containing lithium cobalt-based composite oxide particles.}

In the positive electrode active material for the lithium secondary battery of the present invention, the Ti-containing compound may _{be attached to a part of the surface of the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles, or Co ₃ O ₄ and may be attached over the entire surface of the Mg-containing lithium-cobalt composite oxide particles. In the positive electrode active material for a lithium secondary battery of the present invention, the cycle deterioration is caused by the Ti-containing compound adhering to at least a part of the surface of _{the Co 3} O _{4 and Mg-containing lithium cobalt-based composite oxide particles.} Less, higher energy retention rate.

Examples of the Ti-containing compound according to the positive electrode active material for a lithium secondary battery of the present invention include oxides containing titanium.

In the positive electrode active material for a lithium secondary battery of the present invention, the Ti-containing compound has high stability even when the oxide containing titanium is in a charged state, and can contribute to the improvement of battery characteristics.

In the positive electrode active material for a lithium secondary battery of the present invention, the amount of the Ti-containing compound attached is _{0.01 as Ti with respect to Co in Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide in terms of atoms. It is preferably ~ 5.00 mol%, preferably 0.10 to 2.00 mol%. When the amount of the Ti-containing compound adhered is within the above range, it is possible to achieve both high charge / discharge capacity and battery characteristics such as cycle characteristics, load characteristics, and safety.

The average particle size of the positive electrode active material for a lithium secondary battery of the present invention is a particle size (D50) with a volume integration of 50% in the particle size distribution obtained by the laser diffraction / scattering method, and is preferably 0.5 to 30.0 μm. It is 3.0 to 25.0 μm, particularly preferably 7.0 to 25.0 μm. The BET specific surface area of the positive electrode active material for a lithium secondary battery of the present invention is preferably 0.05 to 1.0 m ² / g, and particularly preferably 0.15 to 0.6 m ² / g. When the average particle size or the BET specific surface area of the positive electrode active material for a lithium secondary battery of the present invention is within the above range, the preparation and coatability of the positive electrode mixture can be facilitated, and an electrode having high filling property can be obtained. Be done.

The positive electrode active material for a lithium secondary battery according to the present invention may be produced by any production method, but is produced by the following method for producing a positive electrode active material for a lithium secondary battery according to the present invention. It is preferable from the viewpoint of making a lithium secondary battery having a high energy density maintenance rate with little deterioration of the cycle even if the battery is repeatedly charged and discharged under a high voltage.

In the method for producing a positive electrode active material for a lithium secondary battery according to the present invention, _{a Mg-containing lithium cobalt-based composite oxide particle containing cobalt oxide (Co 3} O ₄ ) and a Ti-containing compound are mixed and treated in a dry manner. Thereby, a mixed treatment product of the Mg-containing lithium cobalt-based composite oxide particles containing cobalt oxide (Co ₃ O ₄ ) and the Ti-containing compound is obtained, and then the mixed treatment product is heat-treated at 400 to 1000 ° C. This is a method for producing a positive electrode active material for a lithium secondary battery, which comprises obtaining a positive electrode active material for a lithium secondary battery.

_{The Mg-containing lithium cobalt-based composite oxide particles containing cobalt oxide (Co 3} O ₄ ) according to the method for producing a positive electrode active material for a lithium secondary battery according to the present invention are for the above-mentioned lithium secondary battery according to the present invention. This is the same as the Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles related to the positive electrode active material.

Examples of the Ti-containing compound according to the method for producing a positive electrode active material for a lithium secondary battery according to the present invention include an oxide containing titanium. Examples of the oxide containing titanium include an oxide of Ti.
The average particle size of the Ti-containing compound is the average particle size determined by the laser diffraction / scattering method, and is 30.0 μm or less, preferably 0.01 to 10.0 μm, which is efficient for the surface of the lithium cobalt-based composite oxide. It is preferable from the viewpoint that the Ti-containing compound can be attached.
The Ti-containing compound may be an agglomerate in which primary particles are aggregated to form secondary particles. In the method for producing a positive electrode active material for a secondary lithium of the present invention, Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles and a Ti-containing compound are mixed and treated in a dry manner, so that agglomerated inorganic Ti is contained. The compound can be crushed to the primary particles during mixing, and the Ti-containing compound can be attached to the particle surface of _{the Co 3} O _{4 and Mg-containing lithium cobalt-based composite oxide.}
When the aggregated Ti-containing compound is used, the primary particle size of the Ti-containing compound is the average particle size of the primary particles obtained from the scanning electron micrograph, and is 2.0 μm or less, preferably 0.01 to 0.5 μm. This is preferable from the viewpoint that the Ti-containing compound can be efficiently adhered to the surface of _{the Co 3} O _{4 and Mg-containing lithium cobalt-based composite oxide.}

In the method for producing a positive electrode active material for lithium secondary of the present invention, _{the mixing amount of the Ti-containing compound with the Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide is, in terms of atoms, Co ₃ O ₄ and Mg-containing lithium. The high charge / discharge capacity and cycle should be such that the mixing amount of Ti in the cobalt-based composite oxide is 0.01 to 5.00 mol%, preferably 0.10 to 2.00 mol%. It is preferable from the viewpoint of achieving both battery performance such as characteristics, load characteristics, and safety.

In the method for producing a positive electrode active material for lithium secondary of the present invention, Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles and a Ti-containing compound are mixed and treated in a dry manner to obtain Co ₃ O ₄ and Co 3 O 4 and A mixed product of Mg-containing lithium cobalt-based composite oxide particles and a Ti-containing compound can be obtained.

Examples of the device used in the mixing process include devices such as a high speed mixer, a super mixer, a turbosphere mixer, a Henschel mixer, a Nauter mixer and a ribbon blender, and a V-type mixer. It should be noted that these mixing operations are not limited to the exemplified mechanical means. At the laboratory level, home mixers and laboratory mills are sufficient.

In _{the mixed product of Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles and Ti-containing compound thus obtained, the fine particles of the Ti-containing compound produced by being pulverized into fine particles during dry mixing are Co ₃ O ₄ and Mg-containing lithium-cobalt is obtained by adhering to the surface of the composite oxide particles.

In the method for producing a positive electrode active material for lithium secondary of the present invention, _{a mixed treatment of Co 3} O ₄ and Mg-containing lithium cobalt-based composite oxide particles and a Ti-containing compound is then mixed at 400 to 1000 ° C., preferably 600 to 600. The heat treatment is carried out at 1000 ° C., particularly preferably 750 to 950 ° C. By performing this heat treatment, the Ti-containing compound can be firmly adhered to the surface of _{the Co 3} O ₄ of the surface-treated particles and the Mg-containing lithium cobalt-based composite oxide particles.

In the method for producing a positive electrode active material for a lithium secondary of the present invention, the heat treatment time is not critical, and if it is usually 1 hour or more, preferably 2 to 10 hours, the lithium secondary has satisfactory performance. A positive electrode active material for a battery can be obtained. The atmosphere of the heat treatment is preferably an oxidizing atmosphere such as air and oxygen gas.

The lithium secondary battery of the present invention uses the positive electrode active material for a lithium secondary battery of the present invention as the positive electrode active material. The lithium secondary battery of the present invention comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

The positive electrode according to the lithium secondary battery of the present invention is formed, for example, by applying and drying a positive electrode mixture on a positive electrode current collector. The positive electrode mixture comprises a positive electrode active material, a conductive agent, a binder, a filler added as necessary, and the like. In the lithium secondary battery of the present invention, the positive electrode active material for the lithium secondary battery of the present invention is uniformly coated on the positive electrode. Therefore, the lithium secondary battery of the present invention has high battery performance, and in particular, even if charging / discharging is repeated under a high voltage (charging / discharging), the capacity is less deteriorated and the energy density maintenance rate is high.

The content of the positive electrode active material contained in the positive electrode mixture according to the lithium secondary battery of the present invention is preferably 70 to 100% by mass, preferably 90 to 98% by mass.

The positive electrode current collector according to the lithium secondary battery of the present invention is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the configured battery, but is not particularly limited, and is, for example, stainless steel, nickel, aluminum, or titanium. , Calcined carbon, aluminum, stainless steel surface treated with carbon, nickel, titanium, silver and the like. The surface of these materials may be oxidized and used, or the surface of the current collector may be made uneven by surface treatment. Examples of the form of the current collector include foil, film, sheet, net, punched body, lath body, porous body, foam body, fiber group, non-woven fabric molded body and the like. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

The conductive agent according to the lithium secondary battery of the present invention is not particularly limited as long as it is an electronic conductive material that does not cause a chemical change in the configured battery. For example, graphite such as natural graphite and artificial graphite, carbon black such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and conductive fibers such as carbon fiber and metal fiber. Examples thereof include metal powders such as carbon fluoride, aluminum and nickel powder, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and conductive materials such as polyphenylene derivatives. Examples of graphite include scaly graphite, scaly graphite, earthy graphite and the like. These can be used alone or in combination of two or more. The blending ratio of the conductive agent is 1 to 50% by mass, preferably 2 to 30% by mass in the positive electrode mixture.

Examples of the binder according to the lithium secondary battery of the present invention include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene and polypropylene. , Ethylene-propylene-dienter polymer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluororubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-per Fluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-penta Fluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethylvinyl ether-tetra Fluoroethylene copolymer, ethylene-acrylic acid copolymer or its (Na ⁺ ) ion cross-linked polymer, ethylene-methacrylic acid copolymer or its (Na ⁺ ) ion cross-linked polymer, ethylene-methyl acrylate copolymer or its Examples thereof include (Na ⁺ ) ion cross-linking products, ethylene-methyl methacrylate copolymers or their (Na ⁺ ) ion cross-linking products, polysaccharides such as polyethylene oxide, thermoplastic resins, polymers having rubber elasticity, and the like. It can be used as a species or in combination of two or more. When a compound containing a functional group that reacts with lithium such as a polysaccharide is used, it is preferable to add a compound such as an isocyanate group to inactivate the functional group. The blending ratio of the binder is 1 to 50% by mass, preferably 5 to 15% by mass in the positive electrode mixture.

The filler according to the lithium secondary battery of the present invention suppresses the volume expansion of the positive electrode in the positive electrode mixture, and is added as necessary. As the filler, any fibrous material that does not cause a chemical change in the constructed battery can be used, and for example, olefin polymers such as polypropylene and polyethylene, and fibers such as glass and carbon are used. The amount of the filler added is not particularly limited, but is preferably 0 to 30% by mass in the positive electrode mixture.

The negative electrode according to the lithium secondary battery of the present invention is formed by applying and drying a negative electrode material on a negative electrode current collector. The negative electrode current collector according to the lithium secondary battery of the present invention is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the configured battery, but is not particularly limited, and is, for example, stainless steel, nickel, copper, or titanium. , Aluminum, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, aluminum-cadmium alloy and the like. Further, the surface of these materials may be oxidized and used, or the surface of the current collector may be made uneven by surface treatment. Examples of the form of the current collector include foil, film, sheet, net, punched body, lath body, porous body, foam body, fiber group, non-woven fabric molded body and the like. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

The negative electrode material according to the lithium secondary battery of the present invention is not particularly limited, but for example, a carbonaceous material, a metal composite oxide, a lithium metal, a lithium alloy, a silicon alloy, a tin alloy, and metal oxidation. Examples thereof include materials, conductive polymers, chalcogen compounds, Li—Co—Ni-based materials, Li ₄ Ti ₅ O ₁₂ , lithium niobate, silicon oxide (SiOx: 0.5 ≦ x ≦ 1.6) and the like. Examples of the carbonaceous material include graphitized carbon materials and graphite-based carbon materials. As the metal composite oxide, for example, Sn _p (M ¹ ) _1-p (M ² ) _{q Or} (in the formula, M ¹ represents one or more elements selected from Mn, Fe, Pb and Ge. M ² represents one or more elements selected from Al, B, P, Si, Group 1, Group 2, Group 3 and halogen elements of the Periodic Table, and 0 <p≤1, 1≤q≤3. ,. showing a _{1 ≦ r ≦ 8), Li} t Fe 2 O 3 (0 ≦ t ≦ 1), Li t WO 2 (0 ≦ t ≦ 1) compound of the like. Examples of the metal oxide include GeO, GeO ₂ , SnO, SnO ₂ , PbO, PbO ₂ , Pb ₂ O ₃ , Pb ₃ O ₄ , Sb ₂ O ₃ , Sb ₂ O ₄ , Sb ₂ O ₅ , and Bi ₂ O _3. , Bi ₂ O ₄ , Bi ₂ O _{5, and the} like. Examples of the conductive polymer include polyacetylene and poly-p-phenylene.

As the separator according to the lithium secondary battery of the present invention, an insulating thin film having a large ion transmittance and a predetermined mechanical strength is used. Sheets and non-woven fabrics made of olefin polymers such as polypropylene, glass fibers, polyethylene, etc. are used because of their organic solvent resistance and hydrophobicity. The pore diameter of the separator may be in a range generally useful for batteries, and is, for example, 0.01 to 10 μm. The thickness of the separator may be in the range for a general battery, and is, for example, 5 to 300 μm. When a solid electrolyte such as a polymer is used as the electrolyte described later, the solid electrolyte may also serve as a separator.

The non-aqueous electrolyte containing a lithium salt according to the lithium secondary battery of the present invention comprises a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte according to the lithium secondary battery of the present invention, a non-aqueous electrolyte solution, an organic solid electrolyte, and an inorganic solid electrolyte are used. Examples of the non-aqueous electrolyte solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran and 2-methyl. Tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxorane derivative, sulfolane, methylsulfolane, 3-methyl Of aprotic organic solvents such as -2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propanesarton, methyl propionate, ethyl propionate, etc. Examples thereof include a solvent obtained by mixing one kind or two or more kinds.

Examples of the organic solid electrolyte according to the lithium secondary battery of the present invention include a polyethylene derivative, a polyethylene oxide derivative or a polymer containing the same, a polypropylene oxide derivative or a polymer containing the same, a phosphoric acid ester polymer, polyphosphazene, polyaziridine, and polyethylene. Examples thereof include a polymer containing an ionic dissociation group such as sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene, and a mixture of a polymer containing an ionic dissociation group and the above-mentioned non-aqueous electrolytic solution.

As the inorganic solid electrolyte according to the lithium secondary battery of the present invention, Li nitrides, halides, oxidates, sulfides and the like can be used, for example, Li ₃ N, Li I, Li ₅ NI ₂ , Li. ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO _4- LiI-LiOH, P ₂ S ₅ , Li ₂ S or Li _{2 SP 2 S 5, Li 2 S-} SiS 2, Li 2 S-GeS 2, Li 2 S-Ga 2 S 3, Li 2 S-B 2 S 3, Li 2 S-P 2 S 5 -X, Li 2 S _{-SiS 2 -X, Li 2 S-} GeS 2 -X, Li 2 S-Ga 2 S 3 -X, Li 2 S-B 2 S 3 -X, ( wherein, X is LiI, B ₂ S _3, Alternatively, _{at least one selected from Al 2} S ₃ ) and the like can be mentioned.

Furthermore, when the inorganic solid electrolyte is amorphous (glass), lithium phosphate (Li ₃ PO ₄ ), lithium oxide (Li ₂ O), lithium sulfate (Li ₂ SO ₄ ), and phosphorus oxide (P ₂ O ₅₎ ), Lithium borate (Li ₃ BO ₃ ) and other oxygen-containing compounds, Li ₃ PO _4-u N _{2u / 3} (u is 0 <u <4), Li ₄ SiO _4-u N _{2u / 3} (u is Nitrogen such as 0 <u <4), Li ₄ GeO _4-u N _{2u / 3} (u is 0 <u <4), Li ₃ BO _3-u N _{2u / 3} (u is 0 <u <3), etc. The containing compound can be contained in the inorganic solid electrolyte. By adding the oxygen-containing compound or the nitrogen-containing compound, it is possible to widen the gaps of the formed amorphous skeleton, reduce the hindrance of the movement of lithium ions, and further improve the ionic conductivity.

As the lithium salt according to the lithium secondary battery of the present invention, those that are soluble in the above non-aqueous electrolyte are used, for example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , _{LiAsF 6} , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, chloroborane lithium, lower fatty group Examples thereof include a salt obtained by mixing one or more of lithium carboxylate, lithium tetraphenylborate, imides and the like.

In addition, the following compounds can be added to the non-aqueous electrolyte for the purpose of improving discharge, charging characteristics, and flame retardancy. For example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glime, hexaphosphate triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone and N, N-substituted imidazolidine, ethylene glycol dialkyl ether. , Ammonium salt, polyethylene glucol, pyrrole, 2-methoxyethanol, aluminum trichloride, monomer of conductive polymer electrode active material, triethylenephosphonamide, trialkylphosphine, morpholine, aryl compound with carbonyl group, hexamethylphos Examples include holictriamide and 4-alkylmorpholine, dicyclic tertiary amines, oils, phosphonium salts and tertiary sulfonium salts, phosphazene, carbonates and the like. Further, in order to make the electrolytic solution nonflammable, a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride can be contained in the electrolytic solution. In addition, carbon dioxide gas can be contained in the electrolytic solution in order to have suitability for high temperature storage.

The lithium secondary battery of the present invention is a lithium secondary battery in which cycle deterioration is small even when charging and discharging are repeated under high voltage and the energy density maintenance rate is high, and the shape of the battery is a button, a seat, a cylinder, and a corner. , Coin type, etc. may be any shape.

The use of the lithium secondary battery of the present invention is not particularly limited, but for example, a laptop computer, a laptop computer, a pocket word processor, a mobile phone, a cordless handset, a portable CD player, a radio, an LCD TV, a backup power supply, an electric shaver, and the like. Examples include electronic devices such as memory cards and video movies, and consumer electronic devices such as automobiles, electric vehicles, drones, game devices, and electric tools.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

<Preparation of lithium cobalt oxide composite oxide particles (LCO) sample>
<LCO sample 1>
Lithium carbonate (average particle size 5.7 μm), tricobalt tetraoxide (average particle size 2.5 μm) and magnesium oxide (average particle size 3.6 μm) are weighed, mixed well with an experimental mill, and Li / Co. A raw material mixture having a molar ratio of 0.997 and a mol% of Mg with respect to Co of 1.00 mol% was obtained.
The resulting raw material mixture was then calcined in an alumina pot at 1070 ° C. for 5 hours in the air. After completion of firing, the fired product was pulverized and classified to obtain Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles shown in Table 1.
The Mg content was 1.00 mol% with respect to Co in Co ₃ O ₄ and the Mg-containing lithium cobalt-based composite oxide.
As a result of X-ray diffraction analysis using CuKα beam using the obtained Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide as a radiation source, the intensity of the diffraction peak near 2θ = 37.4 ° due to LiCo _{O 2 (} The ratio ((A / B) × 100) of the intensity (A) of the diffraction peak near 2θ = 36.8 ° due to Co ₃ O _{4 to B) was 0.90%.} The intensity of the diffraction peak was obtained as a ratio of the heights of the diffraction peaks. Further, the diffraction peak caused by MgO was less than the lower limit of detection, and was not substantially detected.

<LCO sample 2>
Lithium carbonate (average particle size 5.7 μm) and tricobalt tetraoxide (average particle size 2.5 μm) were weighed and mixed sufficiently with an experimental mixer to prepare a raw material mixture having a Li / Co molar ratio of 0.997. Got
The resulting raw material mixture was then calcined in an alumina pot at 1070 ° C. for 5 hours in the air. After completion of firing, the fired product was pulverized and classified to obtain Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles shown in Table 1.
As a result of X-ray diffraction analysis using CuKα beam using the obtained Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide as a radiation source, the intensity of the diffraction peak near 2θ = 37.4 ° due to LiCo _{O 2 (} The ratio ((A / B) × 100) of the intensity (A) of the diffraction peak near 2θ = 36.8 ° due to Co ₃ O _{4 to B) was 1.90%.} The intensity of the diffraction peak was obtained as a ratio of the heights of the diffraction peaks.

<LCO sample 3>
Lithium carbonate (average particle size 5.7 μm), tricobalt tetraoxide (average particle size 2.5 μm) and magnesium oxide (average particle size 3.6 μm) are weighed, mixed well with a household mixer, and Li / Co. A raw material mixture having a molar ratio of 1.02 and a mol% of Mg with respect to Co of 0.01 mol% was obtained.
The resulting raw material mixture was then calcined in an alumina pot at 1070 ° C. for 5 hours in the air. After completion of firing, the fired product was pulverized and classified to obtain Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles shown in Table 1.
The Mg content was 1.00 mol% with respect to Co in Co ₃ O ₄ and the Mg-containing lithium cobalt-based composite oxide.
As a result of X-ray diffraction analysis using CuKα rays using the obtained Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide as a radiation source, the diffraction peak near 2θ = 36.8 ° caused by _{Co 3} O _{4 was found.} , It was less than the lower limit of detection and was not substantially detected. Further, the diffraction peak caused by MgO was less than the lower limit of detection, and was not substantially detected.

-Measurement of intensity ratio of diffraction peak ((A / B) x 100) X-ray diffraction analysis of the measured sample is performed using an X-ray diffraction analyzer (SmartLab Studio II, manufactured by Rigaku), and analysis software (Rigaku basics). Analysis using data processing software), the intensity (A) of the diffraction peak near 2θ = 36.8 ° caused by _{Co 3} O ₄ and the diffraction peak near 2θ = 37.4 ° caused by LiCo _{O 2} Strength (B) was obtained. Then, from the intensity of the diffraction peak obtained, the diffraction peak around 2 [Theta] = 36.8 ° attributed to _Co 3 _{O 4} to the intensity of the diffraction peak near 2 [Theta] = 37.4 ° attributed to LiCoO ₂ (B) The ratio of the intensity (A) of ((A / B) × 100) was calculated.
The measurement conditions of the X-ray diffractometer are as follows.
X-ray source: CuKα ray Tube voltage: 45kV
Current: 200mA
Scan speed: 1 ° / min
Step: 0.02 °
Measurement method: Continuous measurement

(Example 1)
30 g of LCO sample 1 was collected, _{0.245 g of titanium oxide (TiO 2} ) was added thereto, and the mixture was sufficiently mixed with an experimental mill, and the obtained mixed product was baked at 800 ° C. for 5 hours. , Heat treatment was carried out to obtain a positive electrode active material sample in which 1.00 mol% of titanium oxide was attached to Co in the LCO sample in terms of Ti atoms.
Further, the obtained positive electrode active material sample was mapped with Ti atoms on the particle surface by SEM-EDX analysis, and it was confirmed that Ti was present on a part of the particle surface of the LCO sample 1.
As titanium oxide, an aggregate composed of secondary particles in which primary particles were aggregated was used. The average particle size determined by the laser diffraction / scattering method was 0.4 μm, and the average particle size of the primary particles determined by the SEM photograph was 0.05 μm. The average particle size of the primary particles was determined by arbitrarily extracting 100 particles from a scanning electron microscope.

(Example 2)
30 g of LCO sample 1 was collected, _{0.061 g of titanium oxide (TiO 2} ) was added thereto, and the mixture was sufficiently mixed with an experimental mill, and the obtained mixed product was baked at 800 ° C. for 5 hours. , Heat treatment was carried out to obtain a positive electrode active material sample in which 0.25 mol% of titanium oxide was attached to Co in the LCO sample in terms of Ti atoms.
Further, the obtained positive electrode active material sample was mapped with Ti atoms on the particle surface by SEM-EDX analysis, and it was confirmed that Ti was present on a part of the particle surface of the LCO sample 1.

(Comparative Example 1)
The LCO sample 1 was calcined as it was at 800 ° C. for 5 hours and heat-treated to obtain a positive electrode active material sample.

(Comparative Example 2)
The LCO sample 2 was calcined as it was at 800 ° C. for 5 hours and heat-treated to obtain a positive electrode active material sample.

(Comparative Example 3)
30 g of LCO sample 2 was collected, _{0.245 g of titanium oxide (TiO 2} ) was added thereto, and the mixture was sufficiently mixed in an experimental mill, and the obtained mixed product was baked at 800 ° C. for 5 hours. , Heat treatment was carried out to obtain a positive electrode active material sample in which 1.00 mol% of titanium oxide was attached to Co in the LCO sample in terms of Ti atoms.
Further, the obtained positive electrode active material sample was mapped with Ti atoms on the particle surface by SEM-EDX analysis, and it was confirmed that Ti was present on a part of the particle surface of the LCO sample 2.

(Comparative Example 4)
The LCO sample 3 was calcined as it was at 800 ° C. for 5 hours and heat-treated to obtain a positive electrode active material sample.

(Comparative Example 5)
30 g of LCO sample 3 was collected, _{0.245 g of titanium oxide (TiO 2} ) was added thereto, and the mixture was sufficiently mixed in an experimental mill, and the obtained mixed product was baked at 800 ° C. for 5 hours. , Heat treatment was carried out to obtain a positive electrode active material sample in which 1.00 mol% of titanium oxide was attached to Co in the LCO sample in terms of Ti atoms.
In addition, the obtained positive electrode active material sample was mapped with Ti atoms on the particle surface by SEM-EDX analysis, and it was confirmed that Ti was present on a part of the particle surface of the LCO sample 3.

Next, a battery performance test was conducted as follows.

<Manufacturing of lithium secondary battery>
95% by mass of the positive electrode active material, 2.5% by mass of graphite powder, and 2.5% by mass of polyvinylidene fluoride obtained in Examples and Comparative Examples were mixed to prepare a positive electrode agent, which was used as N-methyl-2-pyrrolidinone. A kneaded paste was prepared by dispersing. The kneaded paste was applied to an aluminum foil, dried and pressed, and punched into a disk having a diameter of 15 mm to obtain a positive electrode plate.
Using this positive electrode plate, a coin-type lithium secondary battery was manufactured using each member such as a separator, a negative electrode, a positive electrode, a current collector plate, a mounting bracket, an external terminal, and an electrolytic solution. Among these, the negative electrode using metallic lithium foil, the electrolytic solution 1 of ethylene carbonate and methylethyl carbonate were used: a solution obtained by dissolving LiPF 6 ₁ mol per kneading liquid 1 liter.
Next, the performance of the obtained lithium secondary battery was evaluated. The results are shown in Table 4.

<Battery performance evaluation>
The produced coin-type lithium secondary battery was operated at room temperature under the following test conditions, and the following battery performance was evaluated.

(1) Test conditions for 4.6V cycle characteristic evaluation The following tests were performed on a lithium secondary battery using the positive electrode active material samples obtained in Examples and Comparative Examples.
First, charging was performed at 0.5 C for 2 hours to 4.6 V, and then constant current / constant voltage charging (CCCV charging) was performed at 4.6 V for holding the voltage for 3 hours. After that, charging and discharging were performed by constant current discharging (CC discharging) up to 2.7V at 0.2C, and the discharge capacity was measured for each cycle with these operations as one cycle. This cycle was repeated 20 cycles.
In addition, the charge / discharge characteristic diagrams of the lithium secondary batteries using the positive electrode active material samples obtained in Examples and Comparative Examples are shown in FIGS. 1 to 7, respectively.

(2) Initial capacity (per active material weight), initial charge / discharge efficiency The charge and discharge capacity of the first cycle in the cycle characteristic evaluation are the initial charge capacity and the initial discharge capacity, and the efficiency calculated by the following formula is the initial charge / discharge capacity. It was made efficient.
Initial charge / discharge efficiency (%) = (charge capacity in the first cycle / discharge capacity in the first cycle) ×
100

(3) Capacity retention rate The capacity retention rate was calculated from the discharge capacities (per active material weight) of the first cycle and the 20th cycle in the cycle characteristic evaluation by the following formula.
Capacity retention rate (%) = (discharge capacity in the 20th cycle / discharge capacity in the 1st cycle) x 100

(4) Energy density maintenance rate The energy density maintenance rate was calculated by the following formula from the Wh capacity (per active material weight) at the time of each discharge in the first cycle and the 20th cycle in the cycle characteristic evaluation.
Energy density maintenance rate (%) = (Discharge Wh capacity in the 20th cycle / Discharge Wh capacity in the 1st cycle) × 100

 

Claims (9)

1. It is composed of Mg-containing lithium cobalt-based composite oxide particles having a Ti-containing compound attached to at least a part of the particle surface, and the Mg-containing lithium cobalt-based composite oxide contains cobalt oxide (Co ₃ O ₄ ). A positive electrode active material for lithium secondary batteries.
2. The content of cobalt oxide _(Co 3 _{O 4)} cobalt oxide in Mg-containing lithium-cobalt composite oxide containing _(Co 3 _{O 4),} using the CuKα ray as a radiation source, cobalt oxide _(Co 3 O _When the Mg-containing lithium cobalt-based composite oxide containing _{4) is analyzed by X-ray diffraction, it is caused by Co 3} O ₄ with respect to the intensity (B) of the diffraction peak near 2θ = 37.4 ° caused by _{LiCoO 2.} The first aspect of claim 1, wherein the ratio ((A / B) × 100) of the intensity (A) of the diffraction peak near 2θ = 36.8 ° is larger than 0.60% and 5.0% or less. Positive active material for lithium secondary batteries.
3. The Mg content of the cobalt oxide _(Co 3 _{O 4)} Mg-containing lithium-cobalt composite oxide containing found in terms of atom, cobalt oxide _(Co 3 _{O 4)} Mg-containing lithium-cobalt composite oxide containing The positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein the amount of Mg is 0.01 to 5.00 mol% with respect to Co inside.
4. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3, wherein the Ti-containing compound is an oxide containing titanium.
5. The amount of the Ti-containing compound attached is 0.01 to 5.00 mol% as Ti with respect to Co in the Mg-containing lithium cobalt-based composite oxide containing cobalt _{oxide (Co 3} O _{4) in terms of atoms.} The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4, wherein the positive electrode active material is characterized by the above.
6. In addition to Li, Co, Mg and O, the Mg lithium cobalt-based composite oxide particles contain one or more M elements (M is Al, Ti, Zr, Cu, Fe, Sr, Ca, V, The invention according to any one of claims 1 to 5, wherein Mo, Bi, Nb, Si, Zn, Ga, Ge, Sn, Ba, W, Na, K, Ni or Mn are contained. Positive active material for lithium secondary batteries.
7. Mg-containing lithium cobalt oxide composite oxide particles containing cobalt oxide (Co ₃ O ₄ ) and a Ti-containing compound are mixed and treated in a dry manner to contain Mg-containing lithium containing _{cobalt oxide (Co 3} O _4). Claims 1 to 6 are obtained by obtaining a mixed product of cobalt-based composite oxide particles and a Ti-containing compound, and then heat-treating the mixed product at 400 to 1000 ° C. The positive electrode active material for a lithium secondary battery according to any one of the above.
8. Mg-containing lithium cobalt oxide composite oxide particles containing cobalt oxide (Co ₃ O ₄ ) and a Ti-containing compound are mixed and treated in a dry manner to contain Mg-containing lithium containing _{cobalt oxide (Co 3} O _4). A mixed product of cobalt-based composite oxide particles and a Ti-containing compound is obtained, and then the mixed product is heat-treated at 400 to 1000 ° C. to obtain a positive electrode active material for a lithium secondary battery. A method for manufacturing a positive electrode active material for a lithium secondary battery.
9. A lithium secondary battery according to any one of claims 1 to 7, wherein the positive electrode active material for a lithium secondary battery is used.
   

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