JP7252174B2 - Positive electrode active material for lithium secondary battery, method for producing the same, and lithium secondary battery - Google Patents

Description

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

2. Description of the Related Art In recent years, as home appliances have rapidly become portable and cordless, lithium ion secondary batteries have been put to practical use as power sources for small electronic devices such as laptop computers, mobile phones, and video cameras. Since Mizushima et al. reported 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. has been advanced, and many proposals have been made so far.

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

Patent Literature 1 below proposes a lithium secondary battery in which a lithium cobalt-based composite oxide in which the proportion of titanium present on the particle surfaces of lithium cobaltate is 20% or more is used as a positive electrode active material. Further, Patent Document 2 below describes a positive electrode active material for a lithium secondary battery comprising a lithium transition metal composite oxide containing 0.20 to 2.00% by weight of Ti atoms, wherein the Ti atoms are lithium transition metals. It has been proposed to use a lithium-cobalt-based composite oxide, which exists in the depth direction from the particle surface of the composite oxide and has a maximum concentration gradient on the particle surface, as a positive electrode active material. Patent Documents 3 and 4 below propose that a lithium-cobalt-based composite oxide containing Sr atoms and Ti atoms be used as a positive electrode active material.

Japanese Patent Application Laid-Open No. 2005-123111 International publication WO2011/043296 pamphlet JP 2013-182758 A JP 2013-182757 A

In recent years, there has been a demand for further improvement in the energy density of lithium-ion batteries. One of the means for achieving this is to increase the voltage, such as increasing the end-of-charge voltage of the battery. However, even with these prior art methods, there is a problem that cycle characteristics deteriorate when charging and discharging voltages are repeated under a high voltage.

Accordingly, an object of the present invention is to provide a positive electrode for a lithium secondary battery that, when used as a positive electrode active material for a lithium secondary battery, exhibits less cycle deterioration even when charging and discharging are repeated under high voltage, and has a high energy density retention rate. An object of the present invention is to provide an active material, and a lithium secondary battery that exhibits little deterioration in cycles even when charging and discharging are repeated under high voltage and has a high energy density retention rate.

As a result of intensive 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, attaches a Ti-containing compound to the surface of the particles, and , Mg-containing lithium-cobalt-based composite oxide particles containing cobalt oxide ( _Co3O4 ) inside or on _the surface of the particles. The inventors have found that a lithium secondary battery having a high energy density retention rate with little cycle deterioration even after repeating the above has been found, and has completed the present invention.

That is, the present invention (1) consists 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. (Co ₃ O ₄ ), and the Ti- _containing compound is one or more selected from oxides of Ti and composite oxides _of Ti and Li. A diffraction peak near 2θ = 36.8° is observed, and the content of cobalt oxide (Co ₃ O ₄ ) in the Mg-containing lithium-cobalt-based composite oxide containing cobalt oxide (Co ₃ O ₄ ) is When the Mg-containing lithium-cobalt-based composite oxide containing cobalt oxide (Co ₃ O ₄ ) was subjected to X-ray diffraction analysis using CuKα rays as a radiation source , it was found that 2θ = 37.4° due to LiCoO ₂ was observed. The ratio of the intensity (A) of the diffraction peak near 2θ=36.8° due to Co 3 O 4 to the intensity (B) of the diffraction peak ((A/B)×100) is greater than 0.60 _% and ₅ A positive electrode active material for a lithium secondary battery is provided, wherein the content is 0% or less .

Further, in the present invention ( 2 ), the Mg content in the Mg-containing lithium-cobalt _{- based} composite oxide containing cobalt oxide ( _Co3O4 ) contains cobalt oxide ( _Co3O4 ) in terms of atoms. The positive electrode active material for a lithium secondary battery according to (1 ) , characterized in that Mg is 0.01 to 5.00 mol% with respect to Co in the Mg-containing lithium-cobalt-based composite oxide. is.

Further, the present invention ( 3 ) provides the positive electrode active material for a lithium secondary battery according to (1) or (2), wherein the Ti-containing compound is an oxide containing titanium.

Further, according to the present invention ( 4 ), any one of (1) to ( 3 ), wherein the average particle size of the primary particles of the Ti-containing compound obtained from a scanning electron micrograph is 2.0 μm or less. The present invention provides the positive electrode active material for a lithium secondary battery according to the above item.
Further, in the present invention ( 5 ), _{the adhesion amount of the Ti-containing compound is, in terms of atoms, as Ti in terms of Co in the Mg-containing lithium-cobalt-based composite oxide containing cobalt oxide (Co O )} . Provided is a positive electrode active material for a lithium secondary battery according to any one of (1) to ( 4 ), wherein the content is 0.01 to 5.00 mol %.

In the present invention ( 6 ), the Mg-lithium-cobalt-based composite oxide particles contain, in addition to Li, Co, Mg and O, one or more M elements (M is Al, Ti, Zr, Cu , Fe, Sr, Ca, V, Mo, Bi, Nb, Si, Zn, Ga, Ge, Sn, Ba, W, Na, K, Ni or Mn) (1 ) to ( 5 ) to provide a positive electrode active material for a lithium secondary battery.

In addition, the present invention ( 7 ) is obtained by dry-mixing Mg-containing lithium-cobalt-based composite oxide particles containing cobalt oxide (Co ₃ O ₄ ) and a Ti-containing compound to obtain cobalt oxide (Co ₃ O ₄ ) containing Mg-containing lithium-cobalt-based composite oxide particles and a Ti-containing compound are obtained, and then the mixed product is heat-treated at 400 to 1000 ° C. to obtain a lithium secondary battery. The present invention provides a method for producing a positive electrode active material for a lithium secondary battery according to (1), characterized by obtaining a positive electrode active material.
Further, the present invention ( 8 ) is the positive electrode for a lithium secondary battery according to (7) , wherein the Ti-containing compound has an average particle size of 0.01 to 10.0 μm as determined by a laser diffraction/scattering method. A method for producing an active material is provided.

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 ( 6 ).

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 exhibits little cycle deterioration even when charging and discharging are repeated under high voltage, and has a high energy density retention rate. , and a lithium secondary battery having a high energy density retention rate with little cycle deterioration even when charging and discharging are repeated under high voltage.

3 is a charge-discharge characteristic diagram of a lithium secondary battery using the positive electrode active material sample obtained in Example 1. FIG. 3 is a charge-discharge characteristic diagram of a lithium secondary battery using the positive electrode active material sample obtained in Example 2. FIG. 3 is a charge-discharge characteristic diagram of a lithium secondary battery using the positive electrode active material sample obtained in Comparative Example 1. FIG. 4 is a charge-discharge characteristic diagram of a lithium secondary battery using the positive electrode active material sample obtained in Comparative Example 2. FIG. 3 is a charge-discharge characteristic diagram of a lithium secondary battery using the positive electrode active material sample obtained in Comparative Example 3. FIG. 4 is a charge-discharge characteristic diagram of a lithium secondary battery using the positive electrode active material sample obtained in Comparative Example 4. FIG. 3 is a charge-discharge characteristic diagram of a lithium secondary battery using the positive electrode active material sample obtained in Comparative Example 5. FIG.

A positive electrode active material for a lithium secondary battery of the present invention comprises Mg-containing lithium-cobalt-based composite oxide particles having a Ti-containing compound attached to at least a portion of the particle surface, and the Mg-containing lithium-cobalt-based composite oxide. is a positive electrode active material for a lithium secondary battery 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 adheres to the particle surfaces of the 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, the positive electrode active material for a lithium secondary battery of the present invention allows Mg to exist inside the lithium cobalt composite oxide particles, attaches a Ti-containing compound to the surface of the lithium cobalt composite oxide particles, and , Cobalt oxide (Co ₃ O ₄ ) is present inside the lithium-cobalt-based composite oxide particles and/or on the surface of the lithium-cobalt-based composite oxide particles.

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

The Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles according to the positive electrode active material for lithium secondary batteries of the present invention contain Mg inside 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 a lithium _secondary battery of the present invention, Mg exists. In the present invention, the presence of Mg inside the particles of the Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles means that Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles are obtained by using CuKα rays as a radiation source. It means that substantially no diffraction peak due to MgO is detected when the composite oxide particles are subjected to X-ray diffraction analysis. The phrase "substantially no diffraction peak due to MgO is detected" means that the peak intensity of the diffraction peak due to MgO is less than the lower detection limit of the analyzer.

In the lithium-cobalt-based composite oxide, when Mg is present on the particle surface, the Mg element present on the particle surface is present on the particle surface in the form of MgO, so Mg is present on the particle surface. When the lithium-cobalt-based composite oxide is subjected to X-ray diffraction analysis, peaks attributed to MgO are observed.

In the positive electrode active material for a lithium secondary battery of the present invention, cobalt oxide (Co ₃ O ₄ ) is contained inside and/or on the particle surface of the Co ₃ O ₄ and Mg-containing lithium-cobalt composite oxide particles. In the present invention, containing cobalt oxide ( _Co3O4 ) inside the particles of the _Co3O4- and Mg _- containing lithium-cobalt- _{based composite oxide particles means the Co3O4- and} Mg _- containing lithium-cobalt-based composite oxide particles. contains Co present in the state of Co ₃ O ₄ inside the grains of In addition, the content of cobalt oxide ( _Co3O4 ) on the particle surface of the _{Co3O4- and} Mg _- containing lithium-cobalt-based _{composite oxide particles means that the particles of the Co3O4- and} Mg-containing lithium-cobalt-based composite oxide particles It means that it contains Co that is attached to the surface and exists in the form of Co ₃ O ₄ . That is, in the positive electrode active material for a 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 the Co It is present in the positive electrode active material for lithium secondary batteries in a state of adhering to the particle surfaces of the ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles.

In the present invention, the fact that the Mg-containing lithium-cobalt-based composite oxide particles contain cobalt oxide (Co ₃ O ₄ ) is determined by X-ray diffraction analysis of the Mg-containing lithium-cobalt-based composite oxide using CuKα rays as a radiation source. This is confirmed by the detection of a diffraction peak due to Co ₃ O ₄ when this is done. Detecting a diffraction peak due to Co ₃ O ₄ means that the peak intensity of the diffraction peak due to Co ₃ O ₄ is equal to or higher than the detection lower limit of the analyzer.
In the present invention, the fact that the peak intensity of the diffraction peak due to Co ₃ O ₄ is equal to or higher than the lower detection limit of the analyzer means that the Mg-containing lithium-cobalt-based composite oxide containing cobalt oxide (Co ₃ O ₄ ) of the present invention When X-ray diffraction analysis is performed using CuKα rays as a radiation source, the intensity (B) of the diffraction peak near 2θ = 37.4 ° (37.4 ± 0.2 °) due to LiCoO ₂ is compared with Co ₃ The ratio of the intensity (A) of the diffraction peak near 2θ = 36.8 ° (36.8 ± 0.2 °) due to O ₄ ((A / B) × 100) is preferably more than 0.60% Show big.

In the positive electrode active material for a lithium secondary battery of the present invention, the Ti-containing compound adheres to a part of the particle surface of the Co ₃ O ₄ and Mg-containing lithium-cobalt composite oxide particles, or the entire particle surface is covered. A Ti-containing compound adheres to the surface. In addition, the state that the Ti-containing compound adheres 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.

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

In the positive electrode active material for lithium secondary batteries of the present invention (that is, in the entire positive electrode active material for lithium secondary batteries of the present invention), the atomic ratio of Li to Co (Li/Co) is preferably 0.0. 90 to 1.20, particularly preferably 0.95 to 1.15. When the molar ratio of Li to Co (Li/Co) in terms of atoms in the lithium-cobalt-based composite oxide is within the above range, the energy density of the positive electrode active material for a lithium secondary battery is increased.

In the positive electrode active material for lithium secondary batteries of the present invention (that is, in the entire positive electrode active material for lithium secondary batteries of the present invention), the atomic conversion mol% of Mg with respect to Co ((Mg/Co) × 100) is It is preferably 0.01 to 5.00 mol %, particularly preferably 0.05 to 2.00 mol %. The mol% ((Mg/Co) x 100) in terms of atoms of Mg relative to Co in the positive electrode active material for lithium secondary batteries is within the above range, so that the positive electrode active material for lithium secondary batteries has high cycle characteristics. .

In the positive electrode active material for lithium secondary batteries of the present invention (that is, in the entire positive electrode active material for lithium secondary batteries of the present invention), the atomic conversion mol% of Ti relative to Co ((Ti/Co) × 100) is It is preferably 0.01 to 5.00 mol %, particularly preferably 0.10 to 2.00 mol %. Battery characteristics such as high charge/discharge capacity, cycle characteristics, and safety due to the atomic conversion mol% of Ti with respect to Co in the positive electrode active material for lithium secondary batteries being in the above range ((Ti/Co) × 100) 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, an oxide of Ti, a composite oxide of Ti and Li, or a composite of Ti and M element. oxides, composite oxides of Ti, element M and Li, composite oxides of Ti and Mg, and the like.

Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles contain any one or more of the M elements shown below as necessary for the purpose of improving performance or physical properties. can do. The M element optionally contained in the Mg-containing lithium-cobalt-based composite oxide is 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 composite oxide particles contain the M element, the atomic conversion mol% of the M element with respect to Co in the Co ₃ O ₄ and Mg containing lithium cobalt composite oxide ((M /Co)×100) is preferably 0.01 to 5.00 mol %, particularly preferably 0.05 to 2.00 mol %. In the case where the Co ₃ O ₄ and Mg-containing lithium cobalt composite oxide particles contain the M element, the atomic conversion mol% of the M element with respect to Co in the Co ₃ O ₄ and Mg containing lithium cobalt composite oxide particles ( When (M/Co)×100) is within the above range, battery characteristics can be improved without impairing charge/discharge capacity. When the Co ₃ O ₄ and Mg-containing lithium cobalt-based composite oxide particles contain two or more M elements, the number of moles of the M element in terms of atoms, which is the basis for calculating the above mol %, is Refers to the total number of moles of an element.

The M element may be present inside the Co ₃ O ₄ and Mg-containing lithium cobalt composite oxide particles, or may be present on the surface of the 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 composite oxide particles, the M element is present in the form of an oxide, composite oxide, sulfate, phosphate, or the like. good too.

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

Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles are produced by, 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 process to

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

The cobalt compound for the raw material mixing step is not particularly limited as long as it is a cobalt compound that is usually used as a raw material for producing a lithium-cobalt-based composite oxide. Carbonates, nitrates, sulfates, organic acid salts and the like can be mentioned.

The magnesium compound used in the raw material mixing step is generally not particularly limited as long as Mg atoms can be present inside the particles of the Mg-containing lithium-cobalt-based composite oxide. Magnesium oxides, hydroxides, Carbonates, organic acid salts, and the like can be mentioned.

In the raw material mixing step, the mixing ratio of the lithium compound and the cobalt compound is such that, in terms of atoms, 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, or more. The mixing ratio is preferably 0.950 to 1.000, particularly preferably 0.960 to 0.999. When the mixing ratio of the lithium compound and the cobalt compound is within the above range, Mg-containing lithium-cobalt-based composite _oxide particles ( _{Co 3 O 4} and Mg-containing lithium-cobalt-based composite oxide particles) are 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 with respect to Co ((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 within the above range, the cycle characteristics of the positive electrode active material for lithium secondary batteries are improved.

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

Compounds 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 the M element may be used.

The raw material lithium compound, cobalt compound, magnesium compound and compound containing element M may have any production history. It is preferable that the content is small.

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, a now A mixing method using a turmixer or the like can be mentioned. At the laboratory level, a home-use mixer is sufficient as a mixing method.

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

In the firing step, the firing temperature for firing the raw material mixture to react the raw materials is 800 to 1150°C, preferably 900 to 1100°C, and particularly preferably higher than 1000°C and not higher than 1100°C. When the firing temperature is within the above range, the generation of overheated decomposition products of the Co ₃ O ₄ and Mg-containing lithium cobalt composite oxide particles can be reduced, and cobalt oxide (Co ₃ O ₄ ) is reduced to the above range. It can be contained while remaining within the range.

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

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 diameter of the Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles before the Ti-containing compound is attached is the particle diameter (D50) at 50% of the volume in the particle size distribution obtained by the laser diffraction/scattering method. , 0.5 to 30.0 μm, preferably 3.0 to 25.0 μm, particularly preferably 7.0 to 25.0 μm. In addition, 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. ˜0.60 m ² /g. When the average particle size 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, the positive electrode mixture can be easily prepared and coated. and an electrode with high fillability can be obtained.

In the positive electrode active material for a lithium secondary battery of the present invention, a Ti-containing compound adheres to at least 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 lithium secondary batteries of the present invention, the Ti-containing compound may adhere to a part of the surface of the Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles, or the Co ₃ It may adhere to cover the entire surface of the _O4- and Mg-containing lithium-cobalt-based composite oxide particles. In the positive electrode active material for a lithium secondary battery of the present invention, the Ti-containing compound is attached to at least a part of the surface of the Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide particles. less energy and higher energy retention.

Examples of the Ti-containing compound related to the positive electrode active material for lithium secondary batteries 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 in terms of atoms is 0.01 as Ti relative to Co in the Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide. to 5.00 mol %, preferably 0.10 to 2.00 mol %. When the amount of the Ti-containing compound attached 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 diameter of the positive electrode active material for a lithium secondary battery of the present invention is 0.5 to 30.0 μm, preferably 0.5 to 30.0 μm, as a particle diameter (D50) at 50% volume accumulation in the particle size distribution obtained by a laser diffraction/scattering method. 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 lithium secondary batteries of the present invention is preferably 0.05 to 1.0 m ² /g, particularly preferably 0.15 to 0.6 m ² /g. When the average particle size or 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 positive electrode mixture can be easily prepared and coated, and an electrode with high fillability can be obtained. be done.

The positive electrode active material for lithium secondary batteries 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 lithium secondary batteries according to the present invention. It is preferable from the viewpoint of obtaining a lithium secondary battery having a high energy density retention rate with little cycle deterioration even when charging and discharging are repeated under a high voltage.

In the method for producing a positive electrode active material for a lithium secondary battery according to the present invention, Mg-containing lithium-cobalt-based composite oxide particles containing cobalt oxide (Co ₃ O ₄ ) and a Ti-containing compound are dry-mixed. Thereby, a mixed product of Mg-containing lithium-cobalt-based composite oxide particles containing cobalt oxide (Co ₃ O ₄ ) and a Ti-containing compound is obtained, and then the mixed 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, characterized by 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 used for the lithium secondary battery according to the present invention. It 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.

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

In the method for producing a lithium secondary positive electrode active material of the present invention, the amount of the Ti-containing compound mixed 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. A mixing amount of 0.01 to 5.00 mol%, preferably 0.10 to 2.00 mol% as Ti with respect to Co in the cobalt-based composite oxide provides high charge/discharge capacity and cycle performance. It is preferable from the viewpoint of achieving compatibility between battery performance such as characteristics, load characteristics, and safety.

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

Apparatuses used in the mixing process include, for example, high-speed mixers, super mixers, turbosphere mixers, Henschel mixers, Nauta mixers, ribbon blenders, and V-type mixers. Note that these mixing operations are not limited to the exemplified mechanical means. Also, at the laboratory level, a home mixer or a laboratory mill will suffice.

The mixed product of Co ₃ O ₄ and Mg-containing lithium cobalt composite oxide particles and Ti-containing compound obtained in this way is fine particles of Ti _- containing compound produced by pulverizing into fine particles during dry mixing. It adheres to the surface of the _O4- and Mg-containing lithium-cobalt-based composite oxide particles.

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

In the method for producing the positive electrode active material for lithium secondary of the present invention, the heat treatment time is not critical, and is usually 1 hour or more, preferably 2 to 10 hours. 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 or oxygen gas.

The lithium secondary battery of the present invention uses the positive electrode active material for lithium secondary batteries of the present invention as a positive electrode active material. A 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 of the lithium secondary battery of the present invention is formed, for example, by coating and drying a positive electrode material mixture on a positive electrode current collector. The positive electrode mixture is composed of 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 a lithium secondary battery of the present invention is uniformly applied to the positive electrode. For this reason, the lithium secondary battery of the present invention has high battery performance, in particular, even if charging and discharging are repeated under high voltage, there is little deterioration in (charge-discharge) capacity, and the energy density retention rate is high.

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

The positive electrode current collector for 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 constructed battery. Examples include stainless steel, nickel, aluminum, and titanium. , calcined carbon, aluminum or stainless steel surface-treated with carbon, nickel, titanium or silver. The surface of these materials may be oxidized before use, or the surface of the current collector may be roughened by surface treatment. Examples of the form of the current collector include foil, film, sheet, net, punched material, lath, porous material, foam, fiber group, non-woven fabric, and the like. Although the thickness of the current collector is not particularly limited, it is preferably 1 to 500 μm.

The conductive agent for the lithium secondary battery of the present invention is not particularly limited as long as it is an electronically conductive material that does not cause chemical changes in the constructed 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, and thermal black, conductive fibers such as carbon fiber and metal fiber, Metal powders such as carbon fluoride, aluminum and nickel powders; 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 flake graphite, flake graphite, earthy graphite, and the like. These can be used singly 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 binders for the lithium secondary battery of the present invention include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, diacetylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, and polypropylene. , ethylene-propylene-diene terpolymer (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-perfluoromethyl vinyl ether-tetra Fluoroethylene copolymer, ethylene-acrylic acid copolymer or its (Na ⁺ ) ion crosslinked product, ethylene-methacrylic acid copolymer or its (Na ⁺ ) ion crosslinked product, ethylene-methyl acrylate copolymer or its (Na ⁺ ) ion cross-linked products, ethylene-methyl methacrylate copolymers or (Na ⁺ ) ion cross-linked products thereof, polysaccharides such as polyethylene oxide, thermoplastic resins, polymers having rubber elasticity, and the like. species or a combination of two or more species can be used. When using a compound containing a functional group that reacts with lithium, such as a polysaccharide, it is preferable to deactivate the functional group by adding a compound such as an isocyanate 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 for the lithium secondary battery of the present invention suppresses volume expansion of the positive electrode in the positive electrode mixture, and is added as necessary. As the filler, any fibrous material can be used as long as it does not cause a chemical change in the constructed battery. The amount of the filler to be added is not particularly limited, but is preferably 0 to 30% by mass in the positive electrode mixture.

The negative electrode of the lithium secondary battery of the present invention is formed by coating and drying a negative electrode material on a negative electrode current collector. The negative electrode current collector for 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 constructed battery. Examples include stainless steel, nickel, copper, and titanium. , aluminum, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, or silver, and an aluminum-cadmium alloy. Further, the surface of these materials may be oxidized before use, or the surface of the current collector may be roughened by surface treatment. Examples of the form of the current collector include foil, film, sheet, net, punched material, lath, porous material, foam, fiber group, non-woven fabric, and the like. Although the thickness of the current collector is not particularly limited, it is preferably 1 to 500 μm.

The negative electrode material for the lithium secondary battery of the present invention is not particularly limited. materials, conductive polymers, chalcogen compounds, Li—Co—Ni materials, Li ₄ Ti ₅ O ₁₂ , lithium niobate, silicon oxide (SiOx: 0.5≦x≦1.6), and the like. Examples of carbonaceous materials include non-graphitizable carbon materials and graphite-based carbon materials. Examples of metal composite oxides include Sn _p (M ¹ ) _1-p (M ² ) _q O _r (wherein 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, Groups 1, 2 and 3 of the periodic table and halogen elements, 0<p≦1, 1≦q≦3 , 1≦r≦8.), Li _t Fe ₂ O ₃ (0≦t≦1), and Li _t WO ₂ (0≦t≦1). As metal oxides _, GeO, _GeO2 , _SnO , _SnO2 , PbO, _{PbO2 , Pb2O3} , _Pb3O4 , _{Sb2O3 , Sb2O4 , Sb2O5 , Bi2O3} , Bi ₂ O ₄ , Bi ₂ O ₅ and the like. Examples of conductive polymers include polyacetylene and poly-p-phenylene.

As the separator for the lithium secondary battery of the present invention, an insulating thin film having a high ion permeability and a predetermined mechanical strength is used. Sheets and non-woven fabrics made of olefin polymers such as polypropylene, glass fibers, or polyethylene are used because of their organic solvent resistance and hydrophobicity. The pore size of the separator may generally be within a useful range for batteries, for example, 0.01 to 10 μm. The thickness of the separator may be within the range for general batteries, for example, 5 to 300 μm. In addition, 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 lithium salt-containing non-aqueous electrolyte of the lithium secondary battery of the present invention comprises a non-aqueous electrolyte and a lithium salt. Non-aqueous electrolytes, organic solid electrolytes, and inorganic solid electrolytes are used as the non-aqueous electrolyte for the lithium secondary battery of the present invention. Non-aqueous electrolytes include, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyl Tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methylsulfolane, 3-methyl -Aprotic organic solvents such as 2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether, 1,3-propanesultone, methyl propionate, and ethyl propionate One type or a mixture of two or more types may be used.

Examples of the organic solid electrolyte for the lithium secondary battery of the present invention include polyethylene derivatives, polyethylene oxide derivatives or polymers containing these, polypropylene oxide derivatives or polymers containing these, phosphate ester polymers, polyphosphazenes, polyaziridines, and polyethylenes. Examples thereof include polymers containing ionic dissociation groups such as sulfide, polyvinyl alcohol, polyvinylidene fluoride, and polyhexafluoropropylene, and mixtures of polymers containing ionic dissociation groups and the above non-aqueous electrolytes.

Li nitrides, halides, _oxysalts , sulfides and the like can be _used as _the inorganic solid electrolyte for the lithium secondary battery of the present invention. _3N —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 _{2S5 , Li2S -- SiS2 ,} Li2S _-- GeS2, _Li2S -- _{Ga2S3 , Li2S} -- _{B2S3 , Li2SP2S5} - _X , _Li2S -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, where X is LiI, B ₂ S ₃ , or at least one selected from Al ₂ S ₃ ), and the like.

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 ), phosphorus oxide (P ₂ O ₅ ), compounds containing oxygen such _as lithium borate ( _Li3BO3 ), _{Li3PO4 -} uN2u _/3 (u is 0<u<4), _{Li4SiO4 -} uN2u _/3 (u is 0<u<4), _{Li4GeO4 - uN2u/3} (where u is 0<u<4), and _{Li3BO3 -} uN2u _/3 (where u is 0<u<3). The containing compound can be contained in the inorganic solid electrolyte. The addition of this oxygen-containing compound or nitrogen-containing compound widens the gaps in the formed amorphous skeleton, reduces hindrance to the movement of lithium ions, and further improves the ionic conductivity.

As _the lithium _salt for _the lithium secondary _battery of the present invention, one that dissolves in the above non _- aqueous electrolyte is used _{. SO3 , LiCF3CO2 , LiAsF6} , _{LiSbF6 , LiB10Cl10} , _{LiAlCl4 , CH3SO3Li} , _CF3SO3Li , ( _CF3SO2 ) _2NLi , lithium chloroborane, lower _aliphatic One or a mixture of two or more of lithium carboxylate, lithium tetraphenylborate, and imides may be used.

In addition, the following compounds can be added to the non-aqueous electrolyte for the purpose of improving discharge and charge characteristics and flame retardancy. For example, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones and N,N-substituted imidazolidines, ethylene glycol dialkyl ethers. , ammonium salt, polyethylene glycol, pyrrole, 2-methoxyethanol, aluminum trichloride, monomer of conductive polymer electrode active material, triethylenephosphonamide, trialkylphosphine, morpholine, aryl compound with carbonyl group, hexamethylphosphine Holic triamides and 4-alkylmorpholines, bicyclic tertiary amines, oils, phosphonium salts and tertiary sulfonium salts, phosphazenes, carbonates and the like. Moreover, in order to make the electrolyte nonflammable, the electrolyte may contain a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride. In addition, carbon dioxide gas can be contained in the electrolytic solution in order to make it suitable for high-temperature storage.

The lithium secondary battery of the present invention is a lithium secondary battery that has a high energy density retention rate with little deterioration in cycles even when charging and discharging are repeated, especially under high voltage. , a coin shape, or the like.

Applications of the lithium secondary battery of the present invention are not particularly limited. 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.

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

<Preparation of lithium cobalt composite oxide particles (LCO) sample>
<LCO sample 1>
Lithium carbonate (average particle size 5.7 μm), tricobalt tetroxide (average particle size 2.5 μm) and magnesium oxide (average particle size 3.6 μm) were weighed, thoroughly mixed in a laboratory mill, and Li/Co was 0.997 and the molar ratio of Mg to Co was 1.00 mol %.
The resulting raw material mixture was then fired in an alumina pot at 1070° C. for 5 hours in the air. After firing, the fired product was pulverized and classified to obtain Co ₃ O ₄ and Mg-containing lithium-cobalt composite oxide particles shown in Table 1.
The Mg content was 1.00 mol % with respect to Co in the Co ₃ O ₄ and Mg-containing lithium-cobalt composite oxide.
The obtained Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide was subjected to X _- ray diffraction analysis using CuKα rays as a radiation source. 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 determined as the ratio of the heights of the diffraction peaks. Moreover, the diffraction peak due to MgO was below the lower limit of detection and was not substantially detected.

<LCO sample 2>
Lithium carbonate (average particle size: 5.7 μm) and tricobalt tetroxide (average particle size: 2.5 μm) were weighed and thoroughly mixed in a laboratory mixer to obtain a raw material mixture with a Li/Co molar ratio of 0.997. got
The resulting raw material mixture was then fired in an alumina pot at 1070° C. for 5 hours in the air. After firing, the fired product was pulverized and classified to obtain Co ₃ O ₄ and Mg-containing lithium-cobalt composite oxide particles shown in Table 1.
The obtained Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide was subjected to X _- ray diffraction analysis using CuKα rays as a radiation source. 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 determined as the ratio of the heights of the diffraction peaks.

<LCO sample 3>
Lithium carbonate (average particle size 5.7 μm), tricobalt tetroxide (average particle size 2.5 μm) and magnesium oxide (average particle size 3.6 μm) were weighed, thoroughly mixed with a home mixer, and Li/Co A raw material mixture having a molar ratio of 1.02 and a molar ratio of Mg to Co of 0.01 mol % was obtained.
The resulting raw material mixture was then fired in an alumina pot at 1070° C. for 5 hours in the air. After firing, the fired product was pulverized and classified to obtain Co ₃ O ₄ and Mg-containing lithium-cobalt composite oxide particles shown in Table 1.
The Mg content was 1.00 mol % with respect to Co in the Co ₃ O ₄ and Mg-containing lithium-cobalt composite oxide.
The obtained Co ₃ O ₄ and Mg-containing lithium-cobalt-based composite oxide was subjected to X-ray diffraction analysis using CuKα radiation _as a radiation _source . , was below the lower limit of detection and was virtually undetectable. Moreover, the diffraction peak due to MgO was below the lower limit of detection and was not substantially detected.

・ Measurement of diffraction peak intensity ratio ((A / B) × 100) X-ray diffraction analysis of the measurement sample is performed using an X-ray diffraction analyzer (manufactured by Rigaku, SmartLab Studio II), analysis software (Rigaku basic data processing software), the intensity (A) of the diffraction peak near 2θ = 36.8 ° due to Co ₃ O ₄ and the diffraction peak near 2θ = 37.4 ° due to LiCoO ₂ Intensity (B) was obtained. Then, from the intensities of the obtained diffraction peaks, the diffraction peak near 2θ = 36.8° 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 ratio of the intensity (A) of ((A/B) × 100) was calculated.
The measurement conditions for the X-ray diffractometer are as follows.
X-ray source: CuKα ray Tube voltage: 45 kV
Current: 200mA
Scan speed: 1°/min
Step: 0.02°
Measurement method: continuous measurement

(Example 1)
30 g of LCO sample 1 was sampled, 0.245 g of titanium oxide (TiO ₂ ) was added thereto, thoroughly mixed in a laboratory mill, and the resulting mixed product was fired at 800° C. for 5 hours. , heat treatment was performed to obtain a positive electrode active material sample to which 1.00 mol % of titanium oxide in terms of Ti atoms adhered to Co in the LCO sample.
Further, the Ti atoms on the particle surface were mapped by SEM-EDX analysis of the obtained positive electrode active material sample, and it was confirmed that Ti was present on part of the particle surface of the LCO sample 1.
Agglomerates composed of secondary particles of aggregated primary particles were used as titanium oxide. 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 randomly extracting 100 particles from a scanning electron microscope.

(Example 2)
30 g of LCO sample 1 was sampled, 0.061 g of titanium oxide (TiO ₂ ) was added thereto, thoroughly mixed in a laboratory mill, and the resulting mixed product was fired at 800° C. for 5 hours. , heat treatment was performed to obtain a positive electrode active material sample to which 0.25 mol % of titanium oxide in terms of Ti atoms adhered to Co in the LCO sample.
Further, the Ti atoms on the particle surface were mapped by SEM-EDX analysis of the obtained positive electrode active material sample, and it was confirmed that Ti was present on part of the particle surface of the LCO sample 1.

(Comparative example 1)
The LCO sample 1 was sintered as it was at 800° C. for 5 hours and subjected to heat treatment to obtain a positive electrode active material sample.

(Comparative example 2)
The LCO sample 2 was sintered as it was at 800° C. for 5 hours and subjected to heat treatment to obtain a positive electrode active material sample.

(Comparative Example 3)
30 g of LCO sample 2 was sampled, 0.245 g of titanium oxide (TiO ₂ ) was added thereto, thoroughly mixed in a laboratory mill, and the resulting mixed product was fired at 800° C. for 5 hours. , heat treatment was performed to obtain a positive electrode active material sample to which 1.00 mol % of titanium oxide in terms of Ti atoms adhered to Co in the LCO sample.
Further, the obtained positive electrode active material sample was subjected to SEM-EDX analysis to perform mapping of Ti atoms on the particle surface, and it was confirmed that Ti was present on part of the particle surface of the LCO sample 2.

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

(Comparative Example 5)
30 g of LCO sample 3 was sampled, 0.245 g of titanium oxide (TiO ₂ ) was added thereto, thoroughly mixed in a laboratory mill, and the resulting mixed product was fired at 800° C. for 5 hours. , heat treatment was performed to obtain a positive electrode active material sample to which 1.00 mol % of titanium oxide in terms of Ti atoms adhered to Co in the LCO sample.
Further, the Ti atoms on the particle surface were mapped by SEM-EDX analysis of the obtained positive electrode active material sample, and it was confirmed that Ti was present on part of the particle surface of the LCO sample 3.

Then, a battery performance test was conducted as follows.

<Production of lithium secondary battery>
95% by mass of the positive electrode active material obtained in Examples and Comparative Examples, 2.5% by mass of graphite powder, and 2.5% by mass of polyvinylidene fluoride were mixed to form a positive electrode agent, which was added to N-methyl-2-pyrrolidinone. A kneaded paste was prepared by dispersing. The kneaded paste was applied to an aluminum foil, dried, 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 members such as a separator, a negative electrode, a positive electrode, a collector plate, a mounting bracket, an external terminal, and an electrolytic solution. Among them, a metal lithium foil was used as the negative electrode, and a solution prepared by dissolving 1 mol of LiPF ₆ in 1 liter of a 1:1 mixed solution of ethylene carbonate and methyl ethyl carbonate was used as the electrolyte.
Next, performance evaluation of the obtained lithium secondary battery was performed. The results are shown in Table 4.

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

(1) Test Conditions for Evaluation of 4.6 V Cycle Characteristics Lithium secondary batteries using positive electrode active material samples obtained in Examples and Comparative Examples were subjected to the following tests.
First, the battery was charged at 0.5 C to 4.6 V over 2 hours, and then subjected to constant current/constant voltage charging (CCCV charging) to keep the voltage at 4.6 V for 3 hours. After that, charge and discharge were performed by constant current discharge (CC discharge) to 2.7 V at 0.2 C, and these operations were regarded as one cycle, and the discharge capacity was measured for each cycle. This cycle was repeated for 20 cycles.
1 to 7 show charge-discharge characteristics of lithium secondary batteries using positive electrode active material samples obtained in Examples and Comparative Examples.

(2) Initial capacity (per weight of active material), initial charge/discharge efficiency The charge and discharge capacity of the first cycle in the cycle characteristic evaluation is the initial charge capacity and the initial discharge capacity, and the efficiency calculated by the following formula is the initial charge/discharge efficiency. Efficient.
Initial charge/discharge efficiency (%) = (1st cycle charge capacity/1st cycle discharge capacity) x 100

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

(4) Energy Density Retention Rate The energy density retention rate was calculated by the following formula from the Wh capacity (per active material weight) during discharge at the 1st cycle and the 20th cycle in the cycle characteristic evaluation.
Energy density maintenance rate (%) = (Discharge Wh capacity at 20th cycle/Discharge Wh capacity at 1st cycle) x 100

Claims (9)

It consists 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 ). , The Ti-containing compound _is one or more selected from oxides of Ti and composite oxides of Ti and Li, and in X _- ray diffraction analysis, A diffraction peak was observed , and the content of cobalt oxide (Co ₃ O ₄ ) in the Mg-containing lithium-cobalt-based composite oxide containing cobalt oxide (Co ₃ O ₄ ) was determined using CuKα rays as a radiation source. When the Mg-containing lithium-cobalt-based composite oxide containing cobalt oxide (Co ₃ O ₄ ) is subjected to X-ray diffraction analysis, the intensity of the diffraction peak near 2θ = 37.4° due to LiCoO ₂ (B) The ratio of the intensity (A) of the diffraction peak near 2θ = 36.8° due to 3 O 4 ((A/B) × 100) is greater than 0.60% and 5.0% _or less _. A positive electrode active material for lithium secondary batteries. The Mg content in the Mg-containing lithium cobalt-based composite oxide containing cobalt oxide (Co ₃ O ₄ ) is an Mg-containing lithium cobalt-based composite oxide containing cobalt oxide (Co ₃ O ₄ ) in terms of atoms. 2. The positive electrode active material for a lithium secondary battery according to claim 1 , wherein Mg is 0.01 to 5.00 mol % with respect to Co therein. 3. The positive electrode active material for a lithium secondary battery according to claim 1, wherein said Ti-containing compound is an oxide containing titanium. The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 3 , wherein the average particle size of the primary particles of the Ti-containing compound obtained from a scanning electron micrograph is 2.0 µm or less. . The adhesion amount of the Ti-containing compound is 0.01 to 5.00 mol% as Ti in terms of atoms with respect to Co in the Mg-containing lithium-cobalt-based composite oxide containing cobalt oxide (Co ₃ O ₄ ). The positive electrode active material for a lithium secondary battery according to any one of claims 1 to 4 , characterized in that: The Mg-lithium-cobalt-based composite oxide particles contain, in addition to Li, Co, Mg and O, one or more M elements (M is Al, Ti, Zr, Cu, Fe, Sr, Ca, V, Mo, Bi, Nb, Si, Zn, Ga, Ge, Sn, Ba, W, Na, K, Ni or Mn ). Positive electrode active material for lithium secondary batteries. Mg-containing lithium containing cobalt oxide (Co ₃ O ₄ ) is obtained by dry mixing Mg-containing lithium cobalt-based composite oxide particles containing cobalt oxide (Co ₃ O ₄ ) and a Ti-containing compound. 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. The method for producing a positive electrode active material for a lithium secondary battery according to claim 1. 8. The method for producing a positive electrode active material for a lithium secondary battery according to claim 7 , wherein the Ti-containing compound has an average particle size of 0.01 to 10.0 μm as determined by a laser diffraction/scattering method. A lithium secondary battery using the positive electrode active material for a lithium secondary battery according to any one of claims 1 to 6 .

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