JP2003020229A - Lithium cobalt composite oxide, method for preparing the same, positive pole active substance of lithium secondary cell, and lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce such a lithium cobalt composite oxide that, when the oxide is used as the positive pole active substance of a lithium secondary cell, the lithium secondary cell is excellent in the performance as a cell, particularly in the characteristics with respect to load an cycle characteristics. SOLUTION: The lithium cobalt composite oxide is prepared by coating the surface of particles of lithium cobaltate expressed by the general formula of Lix CoO2-a , wherein (x) ranges 0.9<=x<=1.1 and (a) ranges -0.1<=a<=0.1, with a sulfate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium cobalt-based composite oxide useful as a positive electrode active material for a lithium secondary battery, a method for producing the same, a lithium secondary battery positive electrode active material containing the same, and particularly load characteristics and cycles. The present invention relates to a lithium secondary battery having excellent characteristics.

[0002]

2. Description of the Related Art In recent years, portable electric appliances have been made portable.
With the rapid progress of cordless technology, 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. Regarding this lithium-ion secondary battery, it was reported by Mizushima et al. In 1980 that lithium cobalt oxide was useful as a positive electrode active material for the lithium-ion secondary battery (“Material Research Bulletin” vol 15, P783-789 (1980)). Since then, research and development on lithium-based composite oxides have been actively promoted, and many proposals have been made so far. Conventionally, as a technique for increasing the energy density of the positive electrode active material, for example, cobalt oxide was used. The composition of lithium is Lix
CoO ₂ (provided that 1.05 ≦ x ≦ 1.3) is lithium-rich (Japanese Patent Laid-Open No. 3-127454),
On the contrary, Lix CoO ₂ (where 0 <x ≦ 1) is cobalt-rich (Japanese Patent Laid-Open No. 3-134969) and metal ions such as Mn, W, Ni and La are doped (special characteristics). Japanese Patent Laid-Open No. 3-201368, JP-A-4-3282
77, JP-A-4-319259, etc.), those in which the residual Li ₂ CO ₃ in lithium cobalt oxide is 10 wt% or less (JP-A-4-56064), LixCoO ₂ (however, 0 <x ≦ 1.25) and the spin concentration at g = 2.15 by the electron spin resonance apparatus is 1 × 10
Those having a rate of ¹⁸ pieces / g or less (Japanese Patent Laid-Open No. 2000-12022) have been proposed.

Further, as a physical feature of the lithium cobalt oxide-based positive electrode active material, a particle diameter is required, for example, an average particle diameter of LiCoO ₂ of 10 to 150 μm (JP-A-1-304664), primary particles of Average particle size 0.5 μm
Below (JP-A-4-33260), the average particle size is 2-1.
0 μm, particle size distribution D (25%) 0.5 to 10 μm, D
(50%) 2 to 10 μm, D (75%) 3.5 to 30 μm
m (JP-A-5-94822), 10% cumulative particle diameter 3 to
Particle size distribution of 15 μm, 50% cumulative particle diameter 8 to 35 μm, 90% cumulative particle diameter 30 to 80 μm (JP-A-5-151998), average particle diameter 2 to 9 μm, 1 to 9 μm of which is 60% or more of the total volume. (Japanese Patent Laid-Open No. 6-243897) has been proposed.

[0004]

Further, it is prepared by adding a sulfate group at the time of mixing raw materials and then calcining the mixture, which has a general formula: Li _x M _{1
-y N y O 2-z X} ( wherein, M is Co or Ni, N is a transition metal element not the same, or a second group of the periodic table, Group 13,
One or more elements selected from Group 14 elements, X is a halogen element, and 0.2 <x ≦ 1.2, 0 ≦ y ≦
A positive electrode active material which is a lithium-containing composite oxide having a composition of 0.5, 0 ≦ z ≦ 1, 0 ≦ a ≦ 2z) and which contains a sulfate group has also been proposed (Japanese Patent Laid-Open No. 2000-21402). ).

However, none of the lithium secondary batteries using the conventionally proposed lithium cobalt-based composite oxide as a positive electrode active material have realized sufficiently satisfactory load characteristics and cycle characteristics.

Therefore, an object of the present invention is to provide a lithium-cobalt composite oxide useful as a positive electrode active material of a lithium secondary battery, which is particularly excellent in load characteristics and cycle characteristics when used as a positive electrode active material of a lithium secondary battery. An object, a method for producing the same, a positive electrode active material containing the same, and a lithium secondary battery using the positive electrode active material.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by coating the surface of lithium cobalt oxide particles with a sulfate. They have found that they can do so and have completed the present invention.

That is, the first invention of the present invention is represented by the general formula: L
i _x CoO _2-a (x is 0.9 ≦ x ≦ 1.1, a is −0.
It takes a value of 1 ≦ a ≦ 0.1. The present invention provides a lithium cobalt-based composite oxide, characterized in that the surface of lithium cobalt oxide particles represented by the formula (4) is coated with a sulfate. The coating amount of the sulfate is in the range of 0.01 to 1.0 mol% in terms of the mole percentage of the sulfate with respect to the Co atom in the lithium-cobalt-based composite oxide (mol of sulfate / mol of Co atom). And the sulfate is preferably at least one selected from MgSO _{4 and} Al ₂ (SO ₄ ) ₃ .

A second invention of the present invention provides a method for producing a lithium-cobalt composite oxide, which comprises the following first and second steps. First step; Lithium compound and cobalt compound are mixed and fired to give a general formula; Li _x CoO _2-a (x is 0.9 ≦ x ≦ 1.1,
a takes a value of −0.1 ≦ a ≦ 0.1. ) The process of obtaining lithium cobalt oxide represented by. Second step: Lithium cobalt oxide obtained in the first step is brought into contact with an aqueous sulfate solution to be dried to precipitate a sulfate on the surface of lithium cobalt oxide particles to form a sulfate-coated lithium-cobalt-based composite oxide. The process of obtaining.

A third invention of the present invention is to provide a positive electrode active material for a lithium secondary battery, which comprises the lithium cobalt-based composite oxide.

A fourth aspect of the present invention provides a lithium secondary battery characterized by using the positive electrode active material for the lithium secondary battery.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below.
The lithium-cobalt composite oxide according to the present invention is obtained by coating the surface of lithium cobalt oxide particles with a sulfate. In the present invention, the surface of lithium cobalt oxide particles includes primary particles or aggregated particles in which primary particles are aggregated.

The lithium cobalt oxide is represented by the general formula: Li
_x CoO _2-a , and the value of x in the formula showing the amount of lithium atoms in the lithium cobalt oxide is 0.9
˜1.1, preferably 0.95 to 1.05. The value of a in the formula showing the amount of oxygen atoms in the lithium cobalt oxide is -0.1 to 0.1, preferably -0.05 to.
It is 0.05.

Other physical properties of the lithium cobalt oxide are not particularly limited, but the average particle diameter determined by the laser method is 1 to 20 μm, preferably 1 to 15 μm, particularly preferably 2 to 10 μm, and the BET specific surface area is Is 0.1
˜2 m ² / g, preferably 0.2 to 1.5 m ² / g, particularly preferably 0.3 to 1.0 m ² / g.

Examples of the sulfate salt coating the lithium cobalt oxide particles include iron sulfate, cobalt sulfate, nickel sulfate, zinc sulfate, copper sulfate, lithium sulfate, potassium sulfate,
Examples thereof include magnesium sulfate, beryllium sulfate, strontium sulfate, aluminum sulfate, and calcium sulfate, and these are used alone or in combination of two or more. Of these, magnesium sulfate or aluminum sulfate is preferable, and it is particularly preferable that these sulfates of such coating components are anhydrous.

The coating amount of the sulfate is 0.01 to 1.0 mol%, preferably 0, in terms of mol percentage of the sulfate to the Co atom of lithium cobalt oxide (mol of sulfate / mol of Co atom). It is preferably set to 0.05 to 0.2 mol%. The reason for this is that if the coating amount is less than 0.01 mol%, the battery performance improving effect due to the coating is not sufficiently exerted, while if it exceeds 1.0 mol%, the coated sulfate becomes surface resistance and the battery It is not preferable because the performance is reduced. In the present invention, the amount of the sulfate salt of the coating component can be confirmed by the ICP emission analysis method.

As another physical property of the lithium-cobalt composite oxide of the present invention, the average particle diameter determined by a laser method is 1 to 20 μm, preferably 1 to 15 μm, and particularly preferably 2 to 10 μm. When the average particle diameter is within this range, a coating film having a uniform thickness can be formed, which is preferable. In addition to the average particle diameter of the lithium cobalt-based composite oxide according to the present invention being in the above range, an average particle diameter of 1 is obtained by collecting primary particles having an average particle diameter of 0.1 to 2.5 μm. A primary particle aggregate having a particle size of 0 to 20 μm is preferable because Li is quickly inserted and removed when the lithium cobalt-based composite oxide is used as a positive electrode active material. Furthermore, the primary aggregate has a total volume of 70% or more,
It is more desirable that 80% or more of the particles have a particle size of 1 to 20 μm because a coating film having a uniform thickness can be formed.
Further, the lithium cobalt-based composite oxide according to the present invention,
BET specific surface area is 0.1 to ² m ² / g, preferably 0.
^{2 to} 1.5 m ² / g, particularly preferably 0.3 to 1.0 m ²
/ G. When the BET specific surface area is within this range, the safety is good, which is preferable.

Next, a method for producing the lithium-cobalt composite oxide having the above-mentioned physical properties according to the present invention will be described. The lithium-cobalt composite oxide of the present invention is prepared by mixing a lithium compound and a cobalt compound and firing the mixture to obtain a compound represented by the general formula: Li _x CoO _2-a (x is 0.9 ≦ x ≦ 1.
1 and a have a value of −0.1 ≦ a ≦ 0.1. ) Represented by the first step of obtaining lithium cobalt oxide, then, the lithium cobalt oxide obtained in the first step is brought into contact with an aqueous solution of sulfate to perform drying to precipitate the sulfate on the surface of the lithium cobalt oxide particles. It can be produced by performing the second step of obtaining a lithium cobalt-based composite oxide coated with a sulfate.

The reaction in the first step can be carried out by mixing a lithium compound and a cobalt compound and firing the mixture. The lithium compound and the cobalt compound as raw materials are not particularly limited as long as they are industrially available, and examples thereof include oxides, hydroxides, carbonates, nitrates and organic acid salts of the respective metals. In particular,
As the cobalt compound, cobalt carbonate and cobalt oxide are preferable because they are industrially easily available and inexpensive. Further, as the lithium compound, lithium carbonate is preferable because it is industrially easily available and inexpensive. The production history of any of these raw materials is not limited, but in order to produce a high-purity lithium cobalt-based composite oxide, it is preferable that the content of impurities is as small as possible. The cobalt compound and the lithium compound may be used either individually or in combination of two or more.

The blending ratio of the raw material lithium compound and cobalt compound in the first step is 0.90 to 1.1, preferably 0.95 to 1.1, in terms of the molar ratio of Co atom to Li atom (Li / Co). It is preferably set to 05.

In the first step of the present invention, for example, first, a predetermined amount of the above-mentioned raw material cobalt compound and lithium compound are mixed. The mixing may be performed by either a dry method or a wet method, but the dry method is preferable because the production is easy. In the case of dry mixing, it is preferable to use a blender that allows the raw materials to be uniformly mixed.

Next, the mixture is fired. The firing conditions may be such that the lithium cobalt-based composite oxide can be produced, and the firing temperature is 600 to 1100 ° C., preferably 80.
The firing time is preferably 0 to 1050 ° C. and the firing time is 2 to 24 hours. The firing atmosphere may be, for example, the air, an oxygen atmosphere, or an inert atmosphere, and is not particularly limited. Further, these firings can be repeated as many times as necessary.

After firing, the lithium cobalt oxide represented by the above general formula (1) is obtained by appropriately cooling and pulverizing if necessary. The pulverization, if necessary, is appropriately performed in the case where the lithium cobalt oxide obtained by firing is in the form of a block that is brittle and bonded, but the particles of lithium cobalt oxide itself have the above specific average particle diameter, It has a BET specific surface area. That is, the obtained lithium cobalt oxide has an average particle size of 1.0 to 20 μm, preferably 1.0.
15 m, is more preferably 2.0~10μm, BET specific surface area of 0.1~2.0m ² / g, preferably 0.2~1.5m ² / g, more preferably 0.3
Is about 1.0 m ² / g.

In the second step, the lithium cobalt oxide obtained in the first step is brought into contact with an aqueous sulfuric acid salt solution and dried to deposit a sulfate salt on the surface of the lithium cobalt oxide particles to coat the lithium cobalt-based composite with the sulfate salt. This is a step of obtaining an oxide.

The sulfate aqueous solution is an aqueous solution in which sulfate is dissolved in water, and the sulfate that can be used is, for example, iron sulfate, cobalt sulfate, nickel sulfate, zinc sulfate, copper sulfate, lithium sulfate, as described above. Examples thereof include potassium sulfate, magnesium sulfate, beryllium sulfate, strontium sulfate, aluminum sulfate, and calcium sulfate. These are used alone or in combination of two or more, and these are preferably hydrates having a higher solubility in water than anhydrides. . Among them, magnesium sulfate hydrate (MgSO ₄ .7H ₂ O) or aluminum sulfate hydrate (Al ₂ (SO ₄ ) ₃ .18H ₂ O) is particularly preferable.

Deposition of the sulfate salt on the surface of lithium cobalt oxide particles is carried out by removing the solvent from the sulfate aqueous solution. As a method for precipitating a sulfate salt on the surface of lithium cobalt oxide particles, for example, lithium cobalt oxide is impregnated into a sulfate aqueous solution, and a sulfate slurry containing lithium cobalt oxide is directly dried by a spray dryer or the like to form cobalt. Method for precipitating sulfate on the surface of lithium oxide particles, impregnating lithium cobalt oxide in aqueous sulfate solution, and drying lithium cobalt oxide particles obtained after solid-liquid separation to precipitate sulfate on the surface of lithium cobalt oxide particles. The method, coating by introducing a lithium cobalt oxide and an aqueous solution of sulfate into a fluidized bed coating apparatus, and drying can be carried out by a method of depositing a sulfate on the surface of the lithium cobalt oxide particles, or the like. The fluidized bed coater has a stable composition and can form a sulfate film uniformly. Using grayed device, the particle surface of the lithium cobalt oxide preferably be precipitated sulfate.

Usually, a sulfate film is formed on the surface of the lithium cobalt oxide particles after drying. When a sulfate hydrate is present in the film, the lithium cobalt composite oxide is treated with lithium. When used as a positive electrode active material of a secondary battery, water generated by decomposition of a hydrate of a sulfate causes decomposition of an electrolytic solution of a lithium secondary battery. It is preferable that

The heating temperature is not particularly limited as long as it is a temperature at which sulfate can be converted to an anhydride, but in many cases,
When the heat treatment temperature exceeds 900 ° C., the load characteristics of the lithium secondary battery using the lithium cobalt-based composite oxide as a positive electrode active material tend to deteriorate, and therefore, the temperature is usually 100 to 900 ° C., preferably 300 to 900 ° C. It is preferable to perform heat treatment at 600 ° C.

After the completion of the second step, it is pulverized if necessary to obtain a lithium-cobalt-based composite oxide according to the present invention in which a sulfate film is formed on the surface of lithium cobalt oxide particles. The pulverization is appropriately performed when the lithium-cobalt-based composite oxide is brittle and block-shaped, but the particles themselves of the lithium-cobalt-based composite oxide have the above-mentioned specific average particle diameter and BET specific surface area even before pulverization. I have.

The lithium cobalt-based composite oxide of the present invention thus obtained is preferably used as a positive electrode active material of a lithium secondary battery comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte containing a lithium salt. You can

The lithium cobalt-based composite oxide is used as the positive electrode active material for the lithium secondary battery according to the present invention.
The positive electrode active material is a positive electrode mixture for a lithium secondary battery described later,
That is, it is one raw material of a mixture of a positive electrode active material, a conductive agent, a binder, and optionally a filler. The lithium secondary battery positive electrode active material according to the present invention is a lithium cobalt-based composite oxide having the preferable particle size characteristics as described above, and is mixed with other raw materials to prepare a positive electrode mixture. At that time, kneading is easy, and coatability at the time of applying the obtained positive electrode mixture to the positive electrode current collector becomes easy.

A lithium secondary battery according to the present invention uses the positive electrode active material of the above lithium secondary battery,
It is composed of a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt. The positive electrode is formed by, for example, applying and drying a positive electrode mixture on a positive electrode current collector, and the positive electrode mixture is a positive electrode active material, a conductive agent, a binder, and a filler added as necessary. Consists of. In the lithium secondary battery according to the present invention, the positive electrode is uniformly coated with the lithium cobalt-based composite oxide as the positive electrode active material. Therefore, the lithium secondary battery according to the present invention is unlikely to cause deterioration in load characteristics and cycle characteristics.

The positive electrode current collector is not particularly limited as long as it is an electron conductor that does not cause a chemical change in the constructed battery, and examples thereof include stainless steel, nickel, aluminum, titanium, calcined carbon, aluminum and the like. Examples include stainless steel whose surface is treated with carbon, nickel, titanium, or silver.

The conductive agent is not particularly limited as long as it is an electron conductive material that does not chemically change in the constructed battery. For example, graphite such as natural graphite and artificial graphite, carbon black, acetylene black, Ketjen black, conductive materials such as carbon fibers and metals, nickel powder, metal fibers or polyphenylene derivatives, natural graphite, for example, Examples include scaly graphite, flake graphite, and earthy graphite. These can be used alone or in combination of two or more. The compounding ratio of the conductive agent in the positive electrode mixture is 1 to 50% by weight, preferably 2 to 30% by weight.

Examples of the binder include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene. Examples include enter polymers (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, polysaccharides such as polyethylene oxide, thermoplastic resins, polymers having rubber elasticity, etc., and these may be used alone or in combination of two or more. You can When a compound containing a functional group that reacts with lithium, such as a polysaccharide, is used, it is preferable to add a compound such as an isocyanate group to deactivate the functional group. The compounding ratio of the binder is 1 to 50% by weight, preferably 5 to 15% in the positive electrode mixture.
% By weight.

The filler suppresses volume expansion and the like of the positive electrode in the positive electrode mixture, and is added if necessary. As the filler, any fibrous material that does not cause a chemical change in the constructed battery can be used. For example, olefin polymers such as polypropylene and polyethylene, fibers such as glass and carbon are used.
The addition amount of the filler is not particularly limited, in the positive electrode mixture,
0 to 30% by weight is preferable.

For the negative electrode, the negative electrode material is applied and dried on the negative electrode current collector.
It is formed by drying. As the negative electrode current collector,
If it is an electron conductor that does not cause chemical change in the battery
Although not particularly limited, for example, stainless steel,
Nickel, copper, titanium, aluminum, calcined carbon, copper
Carbon, nickel, titanium, silver on the surface of stainless steel
Surface-treated and aluminum-cadmium
Aluminum alloy and the like. The negative electrode material is not particularly limited.
However, for example, carbonaceous materials, metal complex acids
Compound, lithium metal, lithium alloy, silicon alloy, tin
Series alloys, metal oxides, conductive polymers, chalcogen compounds
Materials, Li-Co-Ni-based materials, and the like. Carbonaceous material
Examples of materials include non-graphitizable carbon materials and graphite-based carbon materials
Fees are included. As the metal complex oxide, for example,
Sn_p M¹ _1-pM² _qO_r (In the formula, M¹Is Mn, F
indicating one or more elements selected from e, Pb and Ge,
M²Is Al, B, P, Si, Group 1 and Group 2 of the periodic table,
One or more elements selected from Group 3 and halogen elements
0 <p ≦ 1, 1 ≦ q ≦ 3, 1 ≦ r ≦ 8
You ), LixFe₂O₃(0 ≦ x ≦ 1), LixWO₂
Examples of the compound include (0 ≦ x ≦ 1). With metal oxides
And then Ag₂ O, TiO₂, Fe₂O₃ , MgO, V
₂ O_Five , NiO, CuO, ZnO, Mo₂O₃ , In₂
O₃, SnSiO₃ , In₂Sn₂O₇, GeO, GeO
₂, SnO, SnO₂, PbO, PbO₂, Pb ₂O₃, P
b₃O_Four, Sb₂O₃, Sb₂O_Four, Sb₂O_Five, Bi₂O₃, B
i₂O_Four, Bi₂O_FiveEtc. As a conductive polymer
Include polyacetylene, poly-p-phenylene and the like.
Be done.

As the separator, an insulating thin film having a large ion permeability and a predetermined mechanical strength is used. A sheet or non-woven fabric made of an olefin polymer such as polypropylene or glass fiber or polyethylene is used because of its resistance to organic solvents and hydrophobicity. The pore size of the separator may be in a range generally useful for batteries, and for example, 0.01 to 10
μm. The thickness of the separator may be in the range for general batteries, and is, for example, 5 to 300 μm.
When a solid electrolyte such as a polymer is used as the electrolyte described below, the solid electrolyte may also serve as the separator.

The non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolytic solution, an organic solid electrolyte, or an inorganic solid electrolyte is used. Examples of the non-aqueous electrolytic solution include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran and 2-methyl. Tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2- Oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propanesultone, methyl propionate, ethyl propionate, etc. A mixed solvent of one or more aprotic organic solvents.

As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative or a polymer containing the same, a polypropylene oxide derivative or a polymer containing the same, a phosphoric acid ester polymer, a polymer containing an ionic dissociative group, an ionic dissociative group is used. Examples thereof include a mixture of the polymer containing the non-aqueous electrolyte and the like.

As the inorganic solid electrolyte, Li ₃ N, Li
_{I, Li 5 NI 2, Li} 3 N-LiI-LiOH, LiS
iO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ Si
Examples thereof include S ₃ and phosphorus sulfide compounds.

As the lithium salt, one which is soluble in the above non-aqueous electrolyte is used, and for example, LiCl, LiBr,
LiI, LiClO ₄ , LiBF ₆ , LiB ₁₀ C
l ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF _{3
CO 2, LiAsF 6, LiSbF 6} , LiB 10
Cl ₁₀ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ S
Examples thereof include salts of O ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lower aliphatic lithium carboxylate, lithium tetraphenylborate and the like, or a mixture of two or more thereof.

In addition, the non-aqueous electrolyte contains discharge, charge characteristics,
The following compounds can be added for the purpose of improving flame retardancy. For example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinoneimine dye, N-substituted oxazolidinone and N, N-substituted imidazolidine, ethylene glycol dialkyl ether. , Ammonium salt, polyethylene glycol, pyrrole, 2-methoxyethanol, aluminum trichloride, conductive polymer electrode active material monomer, triethylenephosphonamide, trialkylphosphine, morpholine, aryl compound having carbonyl group, hexamethylphosphine Holic triamide and 4-alkylmorpholine, bicyclic tertiary amine,
Examples thereof include oils, phosphonium salts and tertiary sulfonium salts, phosphazenes, carbonates and the like. Further, in order to make the electrolytic solution nonflammable, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride can be contained in the electrolytic solution. Further, the electrolytic solution may contain carbon dioxide gas in order to have suitability for high temperature storage.

The lithium secondary battery according to the present invention is a lithium secondary battery having excellent battery performance, particularly load characteristics and cycle characteristics. The shape of the battery may be any shape such as a button, a sheet, a cylinder, a corner, or a coin shape.

[0045] Conventional lithium secondary battery using LiCoO ₂ is the time of charge and discharge, or decomposition electrolyte solution LiCoO ₂ surface, it is known that the film is produced, as a result the cycle characteristic and load characteristic Is said to be low. On the other hand, the lithium cobalt-based composite oxide of the present invention stabilizes the surface of the lithium cobalt oxide particles by coating the surface of the lithium cobalt oxide particles with a sulfate, and suppresses the decomposition of the electrolytic solution in contact therewith. In addition, the formation of a surface coating is suppressed, and the sulfate having a high ionic conductivity makes the removal and insertion of Li from the surface of the lithium cobalt oxide particles smoother, resulting in excellent battery performance, particularly load characteristics and cycle characteristics. It is thought that it is supposed to be.

The use of the lithium secondary battery according to the present invention is as follows.
For example, a laptop computer, a laptop computer, a pocket word processor, a mobile phone, a cordless handset, a portable CD player, a radio, an LCD TV, a backup power supply, an electric shaver, a memory card, an electronic device such as a video movie, an automobile, etc. , Electric vehicles, game machines, and other consumer electronic devices.

[0047]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited thereto.

<Preparation of MgSO ₄ aqueous solution> MgSO ₄ .7H ₂ O
Dissolve 246.48 g in 500 ml of pure water, make up the solution to 1000 ml, and add 1 mol / L of MgSO _4.
The containing aqueous solution was prepared.

<Preparation of Al ₂ (SO ₄ ) ₃ Aqueous Solution> Al ₂
(SO ₄ ) ₃・ 18H ₂ O 342.15g was added to pure water 500ml
The resulting solution was diluted to 1000 ml to prepare an aqueous solution containing Al ₂ (SO ₄ ) ₃ at 1 mol / L.

Examples 1 to 6 <First step> 40 kg of Co ₃ O ₄ (average particle size 2 μm) and Li ₂ C
19.9 kg of O ₃ (average particle diameter 3 μm) was weighed, sufficiently mixed in a dry system, and then baked at 1000 ° C. for 5 hours. The calcined product was crushed and classified to obtain LiCoO ₂ . The physical properties of this product are shown in Table 1.

[0051]

[Table 1]

<Second step> Fine particle coating device (PO
20.45 ml, 40.91 of an aqueous solution containing 1 mol / L of MgSO ₄ prepared above in 2 kg of lithium cobalt oxide obtained in the first step in WREX, model; GPCG type)
Each ml was introduced and coating treatment was performed. Next, 20 g of each of the coated lithium cobalt oxides obtained above was extracted and heat-treated at 300 ° C., 600 ° C., and 900 ° C. for 5 hours to obtain a lithium cobalt-based composite oxide sample. . The operating conditions of the fine particle coating device are a spray rate of 1.5 g / min, an air supply temperature of 90 ° C., and an air supply air volume of 20 m ³ / H.

Table 2 shows the physical properties of the obtained lithium cobalt-based composite oxide. The amount of MgSO _{4 in} the lithium cobalt-based composite oxide was quantitatively determined by ICP emission spectrometry. Further, the coating amount of MgSO _{4 in} Table 2 was determined by the mol% of MgSO ₄ with respect to the Co atom in lithium cobalt oxide.

[0054]

[Table 2]

Examples 7 to 12 <First Step> Lithium cobalt oxide was synthesized in the same manner as in Examples 1 to 6. <Second step> 1 mol / L of Al ₂ (SO ₄ ) ₃ prepared above is added to 2 kg of lithium cobalt oxide obtained in the first step in a fine particle coating device (manufactured by POWREX, model: GPCG type). 20.45 ml and 40.90 ml of the contained aqueous solutions were introduced to perform coating treatment. Next, in each of the coated lithium cobalt oxides obtained above, 2
0 g was extracted and heat-treated at 300 ° C., 600 ° C., and 900 ° C. for 5 hours to obtain a lithium-cobalt-based composite oxide sample.

Table 3 shows the physical properties of the obtained lithium cobalt-based composite oxide. The amount of Al ₂ (SO ₄ ) _{3 in} the lithium cobalt-based composite oxide was quantitatively determined by ICP emission spectrometry. The coating amount of Al ₂ (SO ₄ ) _{3 in} Table 3 indicates the mol% of Al ₂ (SO ₄ ) ₃ with respect to Co atoms in lithium cobalt oxide.

[0057]

[Table 3]

<Battery Performance Test> (1) Preparation of Lithium 2 Battery; Lithium-cobalt composite oxides of Examples 1 to 12 produced as described above and lithium cobalt oxide obtained in the first step of Example 1 (Comparative Example 1) 91% by weight, 6% by weight of graphite powder, and 3% by weight of polyvinylidene fluoride were mixed to prepare a positive electrode agent, which was dispersed in N-methyl-2-pyrrolidinone to prepare a kneading paste. The kneading 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 separator, a negative electrode, a positive electrode,
A lithium secondary battery was manufactured using each member such as a current collector, a mounting bracket, an external terminal, and an electrolytic solution. Of these, a metal lithium foil was used for the negative electrode, and an electrolyte prepared by dissolving 1 mol of LiPF _{6 in} 1 liter of a 1: 1 kneading solution of ethylene carbonate and methyl ethyl carbonate was used.

(2) Evaluation of Battery Performance The prepared lithium secondary battery was operated at room temperature and the following battery performance was evaluated.・ Measurement of capacity retention ratio Charge the battery to 1.0V / cm ² at room temperature up to 4.3V, and then discharge to 2.7V at 0.5mA / cm ² for 1 cycle. And the energy density was measured. Next, 20 cycles of charge and discharge in the above discharge capacity measurement were performed, and the capacity retention rate was calculated by the following formula. The results are shown in Table 4. In addition, Example 1 and Example 7
1 and 2 and 3 show the discharge characteristics of the lithium secondary battery using the lithium cobalt-based composite oxide prepared in Comparative Example 1 as the positive electrode active material under these conditions.

[Equation 1] -Evaluation of load characteristics First, the positive electrode was charged to a constant current voltage (CCCV) at 1.0C for 5 hours to 4.3V, and then discharged to 2.7V at a discharge rate of 2C. ,
These operations were set as one cycle, and the discharge capacity and energy density were measured for each cycle. This cycle was repeated 3 times, and the arithmetic mean value of the discharge capacities and the arithmetic mean value of the energy density of each of the first to third cycles were obtained. The results are shown in Table 4. In addition, the above operation was similarly performed at a discharge rate of 0.2 C for a lithium secondary battery using the lithium cobalt-based composite oxide prepared in Example 1, Example 7 and Comparative Example 1 as a positive electrode active material.
Discharge characteristics at 0.2 C and 2 C are shown in FIGS. 4, 5 and 6, respectively. It should be noted that the higher the value of this energy density, the more energy can be utilized even during high load discharge, indicating that higher voltage discharge is possible with the same discharge capacity, that is, the load characteristics. Is superior.

[0060]

[Table 4]

From the results shown in Table 4, the lithium secondary battery using the lithium-cobalt composite oxide of the present invention as the positive electrode active material used the positive electrode active material which was not coated with the sulfate of Comparative Example 1. High capacity retention rate compared to
It can be seen that the load characteristics are excellent. Furthermore, FIGS.
From the results, it can be seen that a clear shoulder is seen at the end of the discharge curve as compared to the case where the one not coated with sulfate is used as the positive electrode active material, and the high voltage is maintained until the end of discharge. .

[0062]

As described above, the lithium-cobalt-based composite oxide of the present invention is a lithium-cobalt-based composite oxide obtained by coating the surface of lithium cobalt oxide particles with a sulfate. When used as a positive electrode active material of a lithium secondary battery, the lithium secondary battery has excellent load characteristics and cycle characteristics.

[Brief description of drawings]

FIG. 1 is a diagram showing discharge characteristics of a lithium secondary battery prepared by using the lithium cobalt-based composite oxide of Example 1 as a positive electrode active material.

FIG. 2 is a diagram showing discharge characteristics of a lithium secondary battery prepared by using the lithium cobalt-based composite oxide of Example 7 as a positive electrode active material.

FIG. 3 is a diagram showing discharge characteristics of a lithium secondary battery prepared by using the untreated lithium cobalt-based composite oxide of Comparative Example 1 as a positive electrode active material.

FIG. 4 is a diagram showing discharge characteristics at a discharge rate of 0.2 C and 2 C of a lithium secondary battery prepared by using the lithium cobalt-based composite oxide of Example 1 as a positive electrode active material.

FIG. 5 is a diagram showing discharge characteristics at a discharge rate of 0.2 C and 2 C of a lithium secondary battery prepared by using the lithium cobalt-based composite oxide of Example 7 as a positive electrode active material.

FIG. 6 is a diagram showing discharge characteristics at a discharge rate of 0.2 C and 2 C of a lithium secondary battery prepared by using the untreated lithium cobalt-based composite oxide of Comparative Example 1 as a positive electrode active material.

Continued front page    F-term (reference) 4G048 AA04 AB02 AB04 AB05 AC06                       AE05                 5H029 AJ02 AJ05 AK03 AL03 AL04                       AL06 AL07 AL08 AL11 AL12                       AL16 AM02 AM03 AM04 AM05                       AM07 CJ02 CJ22 HJ02 HJ14                 5H050 AA02 AA07 BA17 CA08 CA09                       CB03 CB05 CB07 CB08 CB09                       CB11 CB12 CB20 CB22 GA02                       GA22 HA02 HA14

Claims (8)

[Claims] 1. A general formula; Li _x CoO _2-a (x is 0.9
≦ x ≦ 1.1, a takes a value of −0.1 ≦ a ≦ 0.1. ) A lithium-cobalt composite oxide characterized in that the surface of lithium cobalt oxide particles represented by the formula (4) is coated with a sulfate. 2. The coating amount of the sulfate is 0.01 mol% of the sulfate with respect to the Co atom in the lithium-cobalt-based composite oxide (mol of sulfate / mol of Co atom).
The lithium cobalt-based composite oxide according to claim 1, which is in the range of 1.0 mol% to 1.0 mol%. 3. The sulfate is MgSO ₄ or Al ₂ (S
2. At least one selected from O ₄ ) _3.
Alternatively, the lithium-cobalt-based composite oxide according to 2. 4. A method for producing a lithium-cobalt-based composite oxide, which comprises the following first and second steps. First step; Lithium compound and cobalt compound are mixed and fired to give a general formula; Li _x CoO _2-a (x is 0.9 ≦ x ≦ 1.1,
a takes a value of −0.1 ≦ a ≦ 0.1. ) The process of obtaining lithium cobalt oxide represented by. Second step: Lithium cobalt oxide obtained in the first step is brought into contact with an aqueous sulfate solution to be dried to precipitate a sulfate on the surface of lithium cobalt oxide particles to form a sulfate-coated lithium-cobalt-based composite oxide. The process of obtaining. 5. The method for producing a lithium-cobalt composite oxide according to claim 4, further comprising heat treatment after completion of the second step. 6. The heat treatment after the second step is performed at a temperature of 10
The method for producing a lithium cobalt-based composite oxide according to claim 5, which is performed at 0 to 900 ° C. 7. A positive electrode active material for a lithium secondary battery, comprising the lithium-cobalt composite oxide according to any one of claims 1, 2 and 3. 8. A lithium secondary battery comprising the positive electrode active material of the lithium secondary battery according to claim 7.