JP2003002661A - Method for producing lithium cobalt composite oxide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery, excellent in a high temperature storage stability, a cyclic characteristic, a weight capacity density, a volume capacity density, safetiness, and an easy mass-production. SOLUTION: An oxy-hydroxy cobalt powder having a weight average particle diameter of 1-20 μm and a specific surface area of 2-200 m<2> /g, and a lithium carbonate powder having a weight average particle diameter of 1-50 μm and a specific surface area of 0.1-10 m<2> /g are mixed and the mixture is calcined in an oxygen-containing atmosphere, thus producing the hexagonal lithium cobalt composite oxide for the lithium secondary battery, having a weight average particle diameter of 5-15 μm, a specific surface area of 0.15-0.60/gm<2> and an alkali content of <0.03 wt.%.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel method for producing a hexagonal lithium cobalt composite oxide having excellent properties as a positive electrode active material for a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, with the progress of portable and cordless devices, there is an increasing demand for a non-aqueous electrolyte secondary battery which is further compact, lightweight and has a high energy density. The active material for the non-aqueous electrolyte secondary battery includes LiCo
_{O 2, LiNiO 2, LiNi 0.} 8 Co 0.2 O 2, LiMn 2
Composite oxides of lithium and transition metals such as O ₄ and LiMnO ₂ are known.

Among them, a lithium secondary battery using a lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material and a lithium alloy, carbon such as graphite or carbon fiber as a negative electrode has a high voltage of 4V class. Since it can be obtained, it is widely used as a battery having a high energy density.

However, after the battery is stored in a charged state at a relatively high temperature, the capacity of the battery decreases, resulting in deterioration of high temperature storage, and deterioration of the cycle characteristic that the discharge capacity of the battery gradually decreases due to repeated charge and discharge cycles. There were problems, such as insufficient safety.
Further, in terms of weight capacity density and volume capacity density, further densification is required.

In order to improve these battery characteristics, Japanese Patent Laid-Open No. 10-1316 discloses a cobalt hydroxide in which the valence of cobalt is trivalent in order to improve cycle characteristics and the like.
A manufacturing method has been proposed in which cobalt oxyhydroxide or the like is dispersed in a lithium hydroxide aqueous solution and then heat-treated.

Further, in JP-A-10-279315 and JP-A-11-49519, cobalt oxyhydroxide in which cobalt has a valence of 3 is fired with a lithium compound at 250 to 1000 ° C. It has been proposed to use an active material having good capacity and good cycle characteristics.

Further, in WO9949528, a specific shape of LiCoO ₂ produced by mixing and firing a specific shape of cobalt oxyhydroxide with a lithium salt is used as a positive electrode active material, so that the tap density is high and the initial capacity is high. It has been proposed to obtain a battery having a good capacity retention rate or discharge characteristics.

[0008] The present inventors have also found that WO0127032.
No. 2θ = cobalt oxyhydroxide powder and lithium carbonate powder are dry-mixed and then fired in an oxygen-containing atmosphere, represented by the formula LiCoO ₂ and measured by X-ray diffraction using CuKα as a radiation source. 66.5 ± 1 ° (11
A method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery, which is characterized in that the half width of 0) plane diffraction peak is 0.070 to 0.110 °, was proposed.

[0009]

However, LiC
In lithium secondary batteries using oO ₂ as a positive electrode active material, these conventional technologies are currently used in terms of high temperature storage stability, cycle characteristics, weight capacity density, volume capacity density, safety, and ease of mass production. The fact is that what has been sufficiently satisfied has not yet been obtained, and the present invention further improves these, and a novel method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery having excellent characteristics. The purpose is to provide.

[0010]

Therefore, the present inventors have
As a result of diligent study, using specific raw materials,
A hexagonal lithium cobalt composite oxide having specific physical properties, which is preferably produced by mixing and firing under specific conditions, has a large capacity density when used as a positive electrode active material of a lithium secondary battery. It has been found that particularly excellent high temperature storage stability, cycle characteristics, weight capacity density, volume capacity density and safety can be obtained.

That is, the present invention has the following gist. (1) Weight average particle diameter is 1 to 20 μm and specific surface area is 2
Cobalt oxyhydroxide powder of 200 m ² / g, weight average particle diameter of 1 to 50 μm and specific surface area of 0.1 to 10
m ² / g of lithium carbonate powder is mixed and the mixture is fired in an oxygen-containing atmosphere.
15. A method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery, which has a specific surface area of 15 μm, a specific surface area of 0.15 to 0.60 m ² / g, and an alkali content of less than 0.03 wt%. (2) The hexagonal lithium cobalt composite oxide is C
2θ = measured by X-ray diffraction using uKα as a radiation source
The half value width of the (110) plane diffraction peak at 66.5 ± 1 ° is 0.
The method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery according to (1) above, which has an angle of 070 to 0.120 °. (3) Among the above-mentioned alkali contents, the lithium hydroxide content is less than 0.005 mass% (1) and (2) above.
Alternatively, the method for producing a hexagonal lithium cobalt composite oxide for a secondary battery according to (3). (4) Any one of the above (1) to (3), wherein 1% or less of the cobalt contained in the lithium cobalt composite oxide is replaced by an element of Group 4 or Group 5 of the periodic table in atomic ratio. The method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery according to 1. (5) The filling press density of the lithium cobalt composite oxide is 2.90 to 3.35 g / cm ³ (1) to
(4) The method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery according to any one of (4). (6) 970 to calcination of the mixture in an oxygen-containing atmosphere
The method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery according to any one of (1) to (5) above, which is performed at 1070 ° C. for 4 to 60 hours.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The hexagonal lithium cobalt composite oxide obtained by the production method of the present invention has a weight average particle diameter of 5
˜15 μm, specific surface area 0.15 to 0.60 m ² / g,
The feature is that the alkali content is less than 0.03 mass%. In particular, in the present invention, the hexagonal lithium cobalt composite oxide has a weight average particle diameter in a specific range, and the combination of the residual alkali content and the specific surface area of the composite oxide is low, the composite oxide It was found that when used as the positive electrode of a lithium battery, it contributes to the effect of reducing the capacity retention rate after high temperature storage. The mechanism of action is not clear, but due to the increase in the amount of residual alkali in the hexagonal lithium-cobalt composite oxide, the cobalt atoms in the positive electrode partly become highly oxidized, and the reaction area also increases due to the increase in the specific surface area. It is considered that the capacity retention rate is lowered by increasing the number of positive electrodes, the surface of the positive electrode in a charged state becomes more active, the solvent in the electrolytic solution is decomposed on the positive electrode, and carbon dioxide gas is generated.

In the present invention, the weight average particle diameter is the particle diameter at the point where the cumulative curve is 50% in the cumulative curve in which the particle size distribution is determined on the mass basis and the total mass is 100%. This is also referred to as a mass-based cumulative 50% diameter (for example, Chemical Engineering Handbook “Revised 5th Edition” (Chemical Engineering Society), p220-2.
21). The particle size is measured by sufficiently dispersing it in a medium such as water by ultrasonication or the like and measuring the particle size distribution (for example, using Microtrac HRAX-100 manufactured by Nikkiso Co., Ltd.).

The weight average particle diameter of the hexagonal lithium cobalt composite oxide in the present invention is 5 to 15 μm as described above.
have m. When the weight average particle diameter is less than 5 μm, it becomes difficult to form a dense and strong electrode layer, while
When it exceeds 15 μm, it becomes difficult to maintain the smoothness of the electrode surface, which is not preferable. A particularly preferable weight average particle size is 7
-12 μm.

In the present invention, the specific surface area means the numerical value of the positive electrode powder obtained by the BET method by nitrogen adsorption. The specific surface area of the hexagonal lithium cobalt composite oxide in the present invention is 0.15 to 0.60 m ² / g as described above. When the specific surface area is less than 0.15 m ² / g, the charge / discharge cycle durability is deteriorated and the high-current charge / discharge characteristics are deteriorated, which is not preferable. When the specific surface area exceeds 0.6 m ² / g, safety and storage stability at high temperature are deteriorated, which is not preferable. Particularly preferred specific surface area is 0.2 to 0.4 m ² / g
Is.

The residual alkali content of the hexagonal lithium cobalt composite oxide in the present invention is an equivalent amount obtained by pouring the composite oxide active material powder into pure water and neutralizing and titrating the extracted alkali content with hydrochloric acid. It is obtained from the number and means the total mass-based content of lithium hydroxide and lithium carbonate per unit weight of the composite oxide. It should be noted that the lithium hydroxide mentioned here also includes an alkali existing as lithium oxide. Each content rate can be quantified by the sequential titration method known as the so-called Warder method.
Specifically, about 10 g of a dried sample was precisely weighed, put in a 100 ml beaker, 50 ml of pure water was added, the inside of the beaker was replaced with nitrogen gas, and the mixture was stirred with a magnetic stirrer for about 1 hour. After leaving for 30 minutes, 3500
Centrifuge to settle by spinning, sample 30 ml of the supernatant, and extract from the acid equivalents required to neutralize to pH 8.0 with 1/10 N hydrochloric acid and the acid equivalents required to further neutralize to pH 4.0. Then, the lithium carbonate equivalent and the lithium hydroxide equivalent are determined, and the total of lithium hydroxide and lithium carbonate is determined as the weight content rate from the alkali equivalent numbers of both.

In the present invention, the above-mentioned residual alkali content is
It is controlled by the weight average particle size and the specific surface area of the cobalt oxyhydroxide powder and the lithium carbonate powder used in the method for producing the lithium-cobalt composite oxide, the mixing ratio thereof, the firing temperature of the mixture, the time, and the like. When the amount of residual alkali is 0.03% by mass or more, the capacity retention rate after high temperature storage is lowered and the charge / discharge cycle durability under high temperature becomes poor, which is not preferable. Neutralization up to pH 8.0 is not preferable because residual lithium hydroxide and lithium carbonate cannot be separated and quantified and the correlation with battery performance is poor. In the present invention, the preferred residual alkali content is less than 0.02% by mass, and the particularly preferred residual alkali content is less than 0.01% by mass. In the present invention, it was found that the capacity retention after high temperature storage and the charge / discharge cycle durability at high temperature are greatly affected by the residual amount of lithium hydroxide even with the residual alkali amount. The remaining amount of lithium hydroxide is 0.005% by mass or less, especially 0.001% by mass
The following are preferred. The amount of lithium carbonate is preferably 0.02% by mass or less, and more preferably 0.01% by mass or less.

The hexagonal lithium cobalt composite oxide produced according to the present invention has a half value width of the (110) plane diffraction peak of 2θ = 66.5 ± 1 ° measured by X-ray diffraction using CuKα as a radiation source. The range of 0.070 to 0.120 ° is particularly preferable because it exhibits excellent characteristics as a positive electrode active material of a lithium battery. The half width of the (110) plane diffraction peak reflects the crystallite diameter in a specific direction of the lithium-containing composite oxide, and it is considered that the smaller the crystallite diameter, the larger the half width. In the present invention, the full width at half maximum means the peak width at half the peak height.

The half width of the (110) plane diffraction peak of the hexagonal lithium cobalt composite oxide is the weight average particle diameter of the cobalt oxyhydroxide powder and the lithium carbonate powder used in the method for producing the lithium cobalt composite oxide. And the specific surface area, the mixing ratio thereof, the firing temperature of the mixture, the time, and the like. When the full width at half maximum of the (110) plane diffraction peak is less than 0.070 °, the charge / discharge cycle durability, initial capacity, average discharge voltage, or safety of the secondary battery used as the positive electrode active material decreases, which is preferable. Absent. In addition, the diffraction peak half width of the (110) plane is 0.12.
If the angle exceeds 0 °, the initial capacity and safety of the secondary battery decrease, which is not preferable. A particularly preferable half width of the diffraction peak is 0.080 to 0.110 °.

The hexagonal lithium cobalt composite oxide according to the present invention having the above-mentioned characteristics is prepared by mixing a cobalt oxyhydroxide powder having a specific weight average particle diameter and a specific surface area with a lithium carbonate powder, and mixing the mixture. Is baked in an oxygen-containing atmosphere. That is, the cobalt oxyhydroxide powder has a weight average particle diameter of 1 to 20 μm and a specific surface area of ² to 200 m ² / g, and the lithium carbonate powder has a weight average particle diameter of 1 to 50 μm and a specific surface area of 0.1 to 0.1 μm.
Having 10 m ² / g.

In the present invention, when the weight average particle diameter of cobalt oxyhydroxide is less than 1 μm, the safety of the battery is lowered and the packing density of the positive electrode layer is lowered, resulting in a decrease in capacity per volume. It is not preferable. Further, if the weight average particle diameter of cobalt oxyhydroxide exceeds 20 μm, the initial capacity is lowered and the discharge characteristics of the secondary battery at a large current are lowered, which is not preferable. A particularly preferred weight average particle size of cobalt oxyhydroxide is 4 to 15 μm.

In the present invention, when the specific surface area of cobalt oxyhydroxide is less than 2 m ² / g, the discharge capacity at a large current is reduced, which is not preferable. Further, when the specific surface area of cobalt oxyhydroxide exceeds 200 m ² / g, the packing density of the positive electrode layer decreases, resulting in a decrease in capacity per volume, which is not preferable. A particularly preferred specific surface area of cobalt oxyhydroxide is 20 to 100 m ² / g.

Although cobalt oxyhydroxide may be obtained in a water-containing state, in such a case, it is difficult to measure the specific surface area. Therefore, in the case of hydrous cobalt oxyhydroxide, the specific surface area of the cobalt oxyhydroxide in the present invention means the specific surface area of the powder after the water-containing material is dried and dehydrated at 120 ° C. for 16 hours. Further, in the present invention, when hydrous cobalt oxyhydroxide is used, it is preferably dried in advance and used, for example, 120 ° C.
It is preferable to use the powder after drying for 16 hours.

In the present invention, if the weight average particle diameter of lithium carbonate is less than 1 μm, the bulk density of the powder is lowered and the productivity during mass production is lowered, which is not preferable. Further, when the weight average particle diameter of lithium carbonate exceeds 50 μm, the initial capacity decreases, which is not preferable. A particularly preferable weight average particle size of lithium carbonate is 5 to 30 μm. Further, if the specific surface area of lithium carbonate is less than 0.1 m ² / g, the initial discharge capacity per unit weight will decrease, which is not preferable. Further, if the specific surface area of lithium carbonate exceeds 10 m ² / g, the packing density of the positive electrode layer decreases, resulting in a decrease in capacity per volume, which is not preferable. A particularly preferable specific surface area of lithium carbonate is 0.3 to ³ m ² / g.

In the present invention, the cobalt oxyhydroxide powder and the lithium carbonate powder are dry-mixed and then preferably baked at 970 to 1070 ° C. for 4 to 60 hours in an oxygen-containing atmosphere. In this case, wet mixing is not preferable because of low productivity. If the firing temperature is lower than 970 ° C., the safety is lowered and the charge / discharge cycle durability is lowered, which is not preferable. If the firing temperature exceeds 1070 ° C., the initial capacity is lowered and the safety is lowered, which is not preferable. A particularly preferable firing temperature is 1000 to 1050 ° C. Further, if the firing time is less than 4 hours, the firing state becomes non-uniform during mass production, and the characteristics tend to vary, which is not preferable. On the other hand, if it is 60 hours or more, the productivity is lowered, which is not preferable. Particularly preferably, a firing time of 10 to 30 hours is adopted.

This firing needs to be performed in an oxygen-containing atmosphere. The oxygen concentration is 10 to 100% by volume,
It is particularly preferably 19 to 50% by volume. When the oxygen concentration is low, the battery performance of the active material is deteriorated, which is not preferable.

The manufactured lithium secondary battery of the present invention is superior in safety and charge / discharge cycle durability to conventional active materials while maintaining the initial capacity. Among the lithium-cobalt composite oxides according to the present invention, the active material having a lithium composite oxide with a filling press density of 2.90 to 3.35 g / cm ³ has a high capacity density per unit volume in the electrode layer of the positive electrode. It is preferable because it is possible. In the present invention, the filling press density is 0.3 t / c of the lithium composite oxide powder.
It means the apparent density of a press-formed product when pressed under a load of m ² .

The filling press density is 2.90 g / cm ^3.
When it is less than the above range, the density of the positive electrode layer during coating / pressing decreases, resulting in a decrease in capacity per volume, which is not preferable. When the filling press density exceeds 3.35 g / cm ³ , the capacity developability at a high current density of the battery decreases, which is not preferable. The filling press density of the lithium composite oxide is particularly preferably 3.05 to 3.25 g / cm ³ .

In the above, cobalt trioxide was used as a raw material for the hexagonal lithium cobalt composite oxide, and this was mixed with lithium carbonate, and this was mixed at 850 ° C. to 107 ° C.
Lithium cobalt oxide was synthesized by firing at 0 ° C., and a lithium cobalt oxide having the same weight average particle diameter, specific surface area, residual alkalinity, and half-width of 110-side diffraction peak as that of the present invention was also synthesized. No active material was obtained that simultaneously satisfied all of the initial capacity, high temperature storage stability, 25 ° C charge / discharge cycle durability, and packing density. Although the reason for this is not clear, perhaps by mixing and burning the nearly amorphous cobalt oxyhydroxide directly with lithium carbonate, the lithiation reaction of cobalt oxyhydroxide with lithium carbonate was initiated at a lower temperature than cobalt trioxide. It seems to be the result.

Further, in the hexagonal lithium cobalt composite oxide of the present invention, 1 mol% or less, preferably 0.05 to 0.5 mol% of the atomic ratio of cobalt contained therein is added to Group 4 or Periodic Table. Substitution with a Group 5 element is also possible. In such a case, the internal resistance of the lithium battery using the obtained hexagonal lithium cobalt composite oxide as the positive electrode active material is reduced, and the charge / discharge characteristics at large current can be improved, which is preferable for batteries for large current discharge. . Ti, Nb, Ta and Zr are particularly preferable as the elements of Group 4 or Group 5 of the periodic table. When the above substitution is 1 mol% or more, the initial capacity of the battery decreases, which is not preferable.

In the present invention, examples of the raw material compounds used when adding the element compounds of Group 4 or Group 5 of the periodic table include hydroxides, oxides, chlorides, nitrates, sulfates and organic acids. Salt etc. are mentioned. When the compound is a water-soluble salt, it can be mixed and added to the powder mixture of cobalt oxyhydroxide and lithium carbonate by spraying the metal salt aqueous solution in the process of production as described above. In the case of a sparingly water-soluble compound such as a hydroxide or an oxide, a fine powder of a hydroxide or an oxide of an element of Group 4 or 5 of the periodic table may be mixed.

When a positive electrode for a lithium electrode is produced from the hexagonal system lithium cobalt composite oxide of the present invention obtained as described above, the powder of the composite oxide is mixed with a carbon system such as acetylene black, graphite or Ketchen black. The positive electrode mixture is formed by mixing the conductive material and the binder. Polyvinylidene fluoride, polytetrafluoroethylene, polyamide, carboxymethyl cellulose, acrylic resin or the like is used as the binder. A slurry or a kneaded product composed of the positive electrode mixture and the solvent or dispersion medium of the binder in the mixture is applied / supported on a positive electrode current collector such as an aluminum foil or a stainless foil to form a positive electrode plate. A porous polyethylene film, a porous polypropylene film or the like is used for the separator.

In a lithium battery using the hexagonal lithium cobalt composite oxide of the present invention as a positive electrode active material,
Carbonic acid ester is preferable as the solvent of the electrolyte solution. The carbonic acid ester may be cyclic or linear. Examples of the cyclic carbonic acid ester include propylene carbonate and ethylene carbonate (EC). Examples of the chain carbonic acid ester include dimethyl carbonate, diethyl carbonate (DEC), ethylmethyl carbonate (EMC), methylpropyl carbonate, methylisopropyl carbonate and the like.

In the present invention, the carbonate ester may be used alone or in combination of two or more kinds. Moreover, you may use it, mixing with another solvent. Further, depending on the material of the negative electrode active material, the combined use of a chain carbonic acid ester and a cyclic carbonic acid ester may improve the discharge characteristics, cycle durability, and charge / discharge efficiency.

Further, vinylidene fluoride is added to these solvents.
A gel polymer electrolyte may be prepared by adding a hexafluoropropylene copolymer (for example, Kainer manufactured by Atchem Co., Ltd.) or a vinylidene fluoride-perfluoropropyl vinyl ether copolymer and adding the following solutes.

As the solute of the electrolyte solution or the polymer electrolyte, ClO ₄ −, CF ₃ SO ₃ −, BF ₄ −, PF are used.
_{6 -, AsF 6 -, SbF} 6 -, CF 3 CO 2 -, (CF 3 S
Any one of lithium salts having O ₂ ) ₂ N- or the like as an anion 1
It is preferred to use more than one species. The solute (for example, the lithium salt described above) in the electrolyte solution or polymer electrolyte is preferably at a concentration of 0.2 to 2.0 mol / l (liter). If it deviates from this range, the ionic conductivity will decrease, and the electric conductivity of the electrolyte will decrease. More preferably, 0.5 to 1.5 mol / l is selected. Also,
A so-called lithium ion conductive room temperature molten salt may be used as the electrolytic solution. The room temperature molten salt, a trimethyl propyl ammonium - bis (trifluoromethane - sulfonyl) imide - and a lithium salt, 1-ethyl-3-imidazolium -BF ₄ salts, and the like.

In the secondary battery using the positive electrode active material of the present invention, a material capable of inserting and extracting lithium ions is used as the negative electrode active material. The material forming the negative electrode active material is not particularly limited as long as it has this property, and examples thereof include lithium metal, lithium alloys, carbon materials, oxides and carbon compounds mainly containing metals of Groups 14 and 15 of the periodic table. , Silicon carbide compounds, silicon oxide compounds, titanium sulfide, boron carbide compounds and the like.

As the carbon material, those obtained by thermally decomposing organic matter under various thermal decomposition conditions, artificial graphite, natural graphite, soil graphite, expanded graphite, scaly graphite and the like can be used. Further, as the oxide, a compound mainly containing tin oxide can be used. Copper foil, nickel foil, or the like is used as the negative electrode current collector.

The positive electrode and the negative electrode in the secondary battery using the positive electrode active material of the present invention are obtained by kneading the active material with an organic solvent to form a slurry, and applying the slurry to a metal foil current collector, drying and pressing. Is preferred. The shape of the lithium battery of the present invention is not particularly limited. A sheet shape (so-called film shape), a folding shape, a winding type bottomed cylindrical shape, a button shape, and the like are preferable, and the shape is selected according to the application.

[0040]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Example 1 A weight average particle size of 15 μm and a specific surface area of 60
m ² / g of cobalt oxyhydroxide powder was mixed with lithium carbonate powder having a weight average particle diameter of 15 μm and a specific surface area of 1.2 m ² / g. The mixing ratio was such that LiCoO ₂ was obtained after firing. After dry mixing these two powders,
The mixture was fired at 1040 ° C. for 16 hours in an atmosphere having an oxygen concentration of 28% by volume by adding oxygen gas to the air and pulverized.

The weight average particle diameter of the obtained fired pulverized product is 1
It was 1.5 μm and the specific surface area was 0.25 m ² / g. The residual alkali amount was 0.014% by mass, the residual lithium hydroxide amount was 0.001% by mass, and the residual thylium carbonate amount was 0.013% by mass.

An X-ray diffraction spectrum of the powder after pulverization was obtained by using an X-ray diffractometer (RINT 2100 manufactured by Rigaku Denki). In this powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (110) plane near 2θ = 66.5 ± 1 ° was 0.090 °. This lithium cobalt composite oxide powder was pressed at 0.3 t / cm ² , and the filling press density was calculated from the volume and weight, and it was 3.25 g / cm ³ . The LiCoO ₂ powder thus obtained, acetylene black and polytetrafluoroethylene powder were mixed in a weight ratio of 80/16/4, kneaded while adding toluene and dried to obtain a thickness of 15
A 0 μm positive electrode plate was prepared.

An aluminum foil having a thickness of 20 μm was used as a positive electrode current collector, and a porous polypropylene having a thickness of 25 μm was used as a separator. A 500 μm thick metallic lithium foil is used for the negative electrode, a nickel foil of 20 μm is used for the negative electrode current collector, and the electrolyte is 1M LiPF ₆ / EC + DEC.
Two (1: 1) stainless steel simple closed cell batteries were assembled in an argon glove box.

One of the batteries had a voltage of 4.3 V at a load current of 75 mA / g of positive electrode active material at 25 ° C.
Was charged up to 2.5 V at a load current of 75 mA per 1 g of the positive electrode active material, and the initial discharge capacity was determined. Further, this battery was further subjected to a charge / discharge cycle test 30 times. As a result, 25 ℃, 2.5 ~ 4.3V
The initial discharge capacity at 150 mAh / g was 30
The capacity retention rate after 9 charge / discharge cycles was 96.7%.

For the other battery, the positive electrode area is 1
Charge to 4.3V with a constant current of 0.2 mA per cm ² ,
Disassemble in an argon glove box, take out the positive electrode sheet after charging, wash the positive electrode sheet, and then the diameter is 3 m.
punched out in m, sealed in an aluminum capsule with EC,
The exothermic start temperature was measured by raising the temperature at a rate of 5 ° C./min with a scanning differential calorimeter. As a result, the heat generation start temperature is 162 ° C.
Met.

Also, spherical graphite (M
CMB) and polyvinylidene fluoride (PVDF) binder in a weight ratio of 90:10, MNP as a solvent and ball mill mixing to form a slurry, which was applied to a copper foil having a thickness of 20 μm by a doctor blade method, and at 70 ° C. 1
It was heated and dried for 0 hours to remove NMP, and then rolled and rolled to obtain a negative electrode sheet.

80/16 / LiCoO ₂ powder, acetylene black and polytetrafluoroethylene powder
The mixture was mixed at a weight ratio of 4 and kneaded while adding toluene and dried to prepare a positive electrode plate having a thickness of 150 μm, an aluminum foil having a thickness of 20 μm was used as a positive electrode current collector, and a separator having a thickness of 25 μm was made of a porous material. Polypropylene was used. Using 1M LiPF ₆ / EC + EMC (1: 1) as the electrolytic solution, a lithium ion type stainless steel coin cell having a thickness of 3 mm and a diameter of 20 mm was assembled in an argon glove box.
This cell was charged at 4.2V for 10 hours at 25 ° C, then 0.1C
Discharge at 4.2V to obtain the initial discharge capacity, and again at 4.2V for 10
After charging for an hour, it was stored at 70 ° C. for 7 days, charged again at 25 ° C. at 4.2 V and discharged by 0.1 C to obtain the initial capacity retention rate. As a result, the capacity retention rate after storage at 70 ° C is 85%.
Met.

[0048] and [Example 2] The weight average particle size 8μm and a specific surface area of 50 m ² / g of cobalt oxyhydroxide powder, the weight average particle size 15μm and a specific surface area of lithium carbonate powder of 1.2 m ² / g Mixed. The mixing ratio is LiCo after firing
It was blended so as to be O ₂ . After dry-mixing these two kinds of powders, oxygen gas was added to the air to obtain an oxygen concentration of 28% by volume at 1010 ° C.
Burned and ground for hours.

The weight average particle diameter of the obtained fired product was 9.6μ.
m, and the specific surface area was 0.36 m ² / g. An X-ray diffraction spectrum of the powder after pulverization was obtained using the same X-ray diffraction apparatus as in Example 1. In this powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (110) plane near 2θ = 66.5 ± 1 ° was 0.095 °. The alkali content in the active material determined in the same manner as in Example 1 was 0.018% by mass. The residual lithium hydroxide content was 0.002% by mass, and the residual thylium carbonate content was 0.016% by mass. Also, the filling press density of this lithium cobalt composite oxide powder was determined in the same manner as in Example 1 above, and it was 3.18 g / cm ³ .

_Two simple closed cell batteries were assembled in an argon glove box in the same manner as in Example 1 except that the LiCoO ₂ powder thus obtained was used.
For one of them, the initial capacity of the battery and the capacity after 30 cycles were determined in the same manner as in Example 1 above.
The initial discharge capacity at a temperature of 2.5 to 4.3 V is 151 m.
It was Ah / g, and the capacity retention ratio after 30 charge / discharge cycles was 96.8%.

When the reactivity of the charged positive electrode active material with the electrolytic solution was determined in the same manner as in Example 1 above, the heat generation starting temperature was 161 ° C.
Further, as a result of evaluating the lithium ion type coin cell in the same manner as in Example 1, the capacity retention rate after storage at 70 ° C. was 78%.

Example 3 Cobalt oxyhydroxide powder having a weight average particle diameter of 12 μm and a specific surface area of 66 m ² / g,
Weight average particle diameter 28 μm and specific surface area 0.43 m ² / g
Of lithium carbonate powder. Mixing ratio is Li after firing
It was blended so as to be CoO ₂ . These two kinds of powders were dry-mixed and then fired and pulverized at 1010 ° C. for 40 hours in an atmosphere having an oxygen concentration of 25% by volume by adding oxygen gas to air.

The weight average particle diameter of the obtained calcined and ground product is 1
It was 0.5 μm and the specific surface area was 0.28 m ² / g. An X-ray diffraction spectrum of the powder after pulverization was obtained using the same X-ray diffraction apparatus as in Example 1. In this powder X-ray diffraction using CuKα ray, 2θ = 66.5 ± 1
The half value width of the diffraction peak of the (110) plane near 0 ° is 0.093.
It was °.

The alkali content in the active material determined in the same manner as in Example 1 was 0.010% by mass. The residual lithium hydroxide content was less than 0.001% by mass and the residual thylium carbonate content was 0.010% by mass. Further, the filling press density of this lithium cobalt composite oxide powder was determined in the same manner as in Example 1 above, and was 3.22 g / c.
It was m ³ .

_Two simple sealed cell type batteries were assembled in an argon glove box in the same manner as in Example 1 except that the LiCoO ₂ powder thus obtained was used.
For one of them, the initial capacity of the battery and the capacity after 30 cycles were determined in the same manner as in Example 1 above.
The initial discharge capacity at a temperature of 2.5 to 4.3 V is 151 m.
It was Ah / g, and the capacity retention ratio after 30 charge / discharge cycles was 96.8%.

When the reactivity of the charged positive electrode active material with the electrolytic solution was determined in the same manner as in Example 1 above, the exothermic onset temperature was 165 ° C.
Further, as a result of evaluating the lithium ion coin cell in the same manner as in Example 1, the capacity retention rate after storage at 70 ° C. was 79%.

Example 4 Cobalt oxyhydroxide powder having a weight average particle diameter of 11 μm and a specific surface area of 55 m ² / g,
Lithium carbonate powder having a weight average particle diameter of 13 μm and a specific surface area of 1.4 m ² / g and niobium oxide Nb ₂ O ₅ powder having a weight average particle diameter of 0.15 μm and a specific surface area of 5.3 m ² / g were mixed. . After dry-mixing these three kinds of powders, the mixture was fired at 1010 ° C. for 16 hours in an atmosphere in which oxygen gas was added to the air so that the oxygen concentration was 28% by volume, and then pulverized.

The weight average particle diameter of the powder after firing and pulverization was 10.2 μm, and the specific surface area determined in the same manner as in Example 1 was 0.42 m ² / g. Example 1
An X-ray diffraction spectrum was obtained using the same X-ray diffractometer. In this powder X-ray diffraction using CuKα ray,
The half value width of the diffraction peak of the (110) plane near 2θ = 66.5 ± 1 ° was 0.110 °. The alkali content in the active material determined in the same manner as in Example 1 was 0.022% by mass. The residual lithium hydroxide content was 0.002% by mass, and the residual thylium carbonate content was 0.020% by mass. The filling press density of this lithium cobalt composite oxide powder was determined in the same manner as in Example 1 above, and it was 3.13 g / cm ³ . 80/16 of the LiCo _0.998 Nb _0.002 O ₂ powder thus obtained, acetylene black and polytetrafluoroethylene powder
The mixture was mixed at a weight ratio of / 4, kneaded while adding toluene, and dried to prepare a positive electrode plate having a thickness of 150 μm.

An aluminum foil having a thickness of 20 μm was used as a positive electrode current collector, a porous polypropylene having a thickness of 25 μm was used as a separator, a metallic lithium foil having a thickness of 500 μm was used as a negative electrode, and a nickel foil was used as a negative electrode current collector. 20 μm is used, and the electrolyte is 1 M LiPF ₆ / EC + DEC
A simple stainless steel closed cell was assembled using (1: 1) in an argon glove box.

First, 7 g per 1 g of the positive electrode active material at 25 ° C.
Charged up to 4.3V with a load current of 5mA, positive electrode active material 1
The initial discharge capacity was obtained by discharging to 2.5 V at a load current of 75 mA / g. Further charge / discharge cycle test
I went there. The initial discharge capacity at 2.5 to 4.3 V at 25 ° C. was 150 mAh / g, and the capacity retention rate after 30 charge / discharge cycles was 97.1%. Further, as a result of evaluating a stainless steel simple closed cell type battery using a lithium metal negative electrode in the same manner as in Example 1, the heat generation starting temperature was 160 ° C., and the capacity of the lithium ion type stainless coin cell after storing at 70 ° C. The maintenance rate was 80%.

Example 5 Cobalt oxyhydroxide powder having a weight average particle diameter of 11 μm and a specific surface area of 55 m ² / g,
Lithium carbonate powder having a weight-average particle diameter of 13μm and a specific surface area of 1.4 m ² / g, weight average particle size 0.22μm and specific surface area was mixed with anatase type titanium dioxide powder of 9m ² / g. After dry-mixing these three powders, oxygen gas was added to the air to adjust the oxygen concentration to 28% by volume.
In the atmosphere described above, the product was fired at 1010 ° C. for 16 hours and then pulverized.

The weight average particle diameter of the powder after firing and pulverization was 11.5 μm, and the specific surface area determined in the same manner as in Example 1 was 0.42 m ² / g. An X-ray diffraction spectrum was obtained using the same X-ray diffraction apparatus as in Example 1.
In this powder X-ray diffraction using CuKα ray, 2θ
The half value width of the diffraction peak of the (110) plane near = 66.5 ± 1 ° was 0.109 °. The alkali content in the active material determined in the same manner as in Example 1 was 0.0024% by mass.
Met. The residual lithium hydroxide content was 0.003% by mass and the residual thylium carbonate content was 0.021% by mass. Further, the filling press density of this lithium cobalt composite oxide powder was determined in the same manner as in Example 1 above, and it was 3.15 g / cm ³ .

LiCo _0.998 Ti thus obtained
_0.002 O ₂ powder, acetylene black, and polytetrafluoroethylene powder were mixed at a weight ratio of 80/16/4, kneaded while adding toluene, and dried to a thickness of 150 μm.
m positive electrode plate was produced. Then, an aluminum foil having a thickness of 20 μm was used as a positive electrode current collector, and a separator having a thickness of 25 μm was used.
m of porous polypropylene, 500 μm thick metallic lithium foil was used for the negative electrode, and nickel foil 2 was used as the negative electrode current collector.
0 μm is used, and the electrolyte is 1M LiPF6 / EC +
A simple stainless closed cell made of stainless steel was assembled in an argon glove box using DEC (1: 1).

First, 7 g per 1 g of the positive electrode active material at 25 ° C.
Charged up to 4.3V with a load current of 5mA, positive electrode active material 1
The initial discharge capacity was obtained by discharging to 2.5 V at a load current of 75 mA / g. Further charge / discharge cycle test
I went there. The initial discharge capacity at 2.5 to 4.3 V at 25 ° C. was 150 mAh / g, and the capacity retention rate after 30 charge / discharge cycles was 97.3%. Further, as a result of evaluating a stainless steel simple closed cell type battery using a lithium metal negative electrode in the same manner as in Example 1, the heat generation starting temperature was 160 ° C., and the capacity of the lithium ion type stainless coin cell after storing at 70 ° C. The maintenance rate was 82%.

Comparative Example 1 The same as Example 1 except that the particle size and specific surface area of the cobalt oxyhydroxide powder and the lithium carbonate powder were changed and the firing temperature was 940 ° C. for 8 hours. Lithium-cobalt composite oxide was synthesized and the physical properties of the active material and the battery performance were evaluated. The specific surface area of the lithium cobalt composite oxide is 1.0 m ² / g,
The weight average particle diameter was 9.6 μm. An X-ray diffraction spectrum of the powder after pulverization was obtained using the same X-ray diffraction apparatus as in Example 1. In this powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of the (110) plane near 2θ = 66.5 ± 1 ° was 0.128 °.

The alkali content in the active material determined in the same manner as in Example 1 was 0.045% by mass. The residual lithium hydroxide content was 0.009% by mass, and the residual thylium carbonate content was 0.036% by mass. When the filling press density of this lithium cobalt composite oxide powder was determined,
It was 3.14 g / cm ³ .

As a result of evaluating a stainless steel simple closed cell type battery using a lithium metal negative electrode in the same manner as in Example 1, the initial discharge capacity was 151 mAh / g, and the capacity retention rate after 30 charge / discharge cycles was It was 96.1%. In the same manner as in Example 1, a stainless steel simple closed cell battery using a lithium metal negative electrode was evaluated. As a result, the heat generation starting temperature was 160 ° C. In the same manner as in Example 1, the capacity retention of the lithium ion type coin cell made of stainless steel after storage at 70 ° C. was 71%.

[Comparative Example 2] A lithium-cobalt composite was prepared in the same manner as in Example 2 except that the firing temperature was 1030 ° C. for 28 hours, and the mixing ratio of the raw material lithium oxyhydroxide and lithium carbonate was changed. The oxide was synthesized and the physical properties of the active material and the battery performance were evaluated. The specific surface area of the lithium-cobalt composite oxide was 0.37 m ² / g. The weight average particle diameter was 9.7 μm. Regarding the powder after crushing,
An X-ray diffraction spectrum was obtained using the same X-ray diffraction apparatus as in Example 1. In this powder X-ray diffraction using CuKα ray, the half value width of the diffraction peak of (110) plane near 2θ = 66.5 ± 1 ° was 0.090 °. In addition, Example 1
The alkali content in the active material obtained in the same manner as above is 0.03.
It was 8% by mass. Residual lithium hydroxide content is 0.00
4% by mass, the content of residual thylium carbonate was 0.034% by mass.

When the filling press density of this lithium cobalt composite oxide powder was determined, it was 3.17 g / cm ³ . The filling press density of this lithium cobalt composite oxide powder was determined to be 3.17 g / cm ³ .
As a result of evaluating a stainless steel simple closed cell battery using a lithium metal negative electrode in the same manner as in Example 1, the initial discharge capacity was 151 mAh / g, and the capacity retention rate after 30 charge / discharge cycles was 96.3. %Met. As a result of evaluating a stainless steel simple closed cell battery using a lithium metal negative electrode in the same manner as in Example 1, the heat generation start temperature was 161 ° C.
Met. In the same manner as in Example 1, the lithium ion type stainless coin cell had a capacity retention rate of 6 after storage at 70 ° C.
It was 6%.

[0070]

INDUSTRIAL APPLICABILITY By using the hexagonal lithium cobalt composite oxide obtained by the production method of the present invention as a positive electrode active material for a lithium secondary battery, it can be used in a wide voltage range and has a weight capacity density. Characteristics such as large electric capacity such as volumetric capacity density, excellent storage stability at high temperature, charge / discharge cycle durability and safety can be obtained.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Megumi Yukawa             3-10 Chigasaki, Chigasaki City, Kanagawa Prefecture             Seimi Chemical Co., Ltd. (72) Inventor Kazuo Sunahara             3-10 Chigasaki, Chigasaki City, Kanagawa Prefecture             Seimi Chemical Co., Ltd. F-term (reference) 4G048 AA04 AB01 AB05 AC06 AD04                       AD06 AE05                 5H050 AA07 AA08 AA10 AA15 AA19                       BA15 CA08 CB02 CB07 CB12                       FA17 FA19 GA02 GA05 GA10                       GA12 GA27 HA01 HA02 HA05                       HA07 HA08 HA13 HA14 HA20

Claims (6)

[Claims] 1. A cobalt oxyhydroxide powder having a weight average particle diameter of 1 to 20 μm and a specific surface area of ² to 200 m ² / g, and a weight average particle diameter of 1 to 50 μm and a specific surface area of 0.1.
-10 m ² / g of lithium carbonate powder is mixed and the mixture is fired in an oxygen-containing atmosphere, the weight average particle diameter is 5 to 15 μm, and the specific surface area is 0.15 to 0.60 m ² /
g, an alkali content of less than 0.03% by weight, a method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery. 2. The half width of the (110) plane diffraction peak at 2θ = 66.5 ± 1 ° of the hexagonal lithium cobalt composite oxide measured by X-ray diffraction using CuKα as a radiation source is 0.070. The method for producing a hexagonal lithium cobalt complex oxide for a lithium secondary battery according to claim 1, wherein the hexagonal lithium cobalt composite oxide is about 0.120 °. 3. The lithium hydroxide content of the alkali content is less than 0.005% by mass.
Alternatively, the method for producing a hexagonal lithium cobalt composite oxide for a secondary battery according to Item 3. 4. The cobalt contained in the lithium cobalt composite oxide according to claim 1, wherein 1% or less in atomic ratio of cobalt is substituted with an element of Group 4 or Group 5 of the periodic table. A method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery as described above. 5. The hexagonal lithium for a lithium secondary battery according to claim 1, wherein a filling press density of the lithium cobalt composite oxide is 2.90 to 3.35 g / cm ^3. Method for producing cobalt composite oxide. 6. The firing of the mixture in an oxygen-containing atmosphere is performed 9
The method for producing a hexagonal lithium cobalt composite oxide for a lithium secondary battery according to claim 1, which is performed at 70 to 1070 ° C. for 4 to 60 hours.