KR20040032796A - Lithium Cobalt Composite Oxide, Method for preparing the Same and Nonaqueous Electrolyte Secondary Battery - Google Patents

Abstract

PURPOSE: Provided is a lithium secondary battery having improved discharging characteristic by anode activating material containing specified lithium-cobalt composite oxides. CONSTITUTION: The secondary battery comprises: an anode(3) containing lithium-cobalt composite oxide as anode activating material, a cathode(2), and a separator(1) equipped between the anode and the cathode. The lithium-cobalt composite oxide comprises 100ppm or less of Ni and is represented by formula of LixCo(1-y)MyO2N2 (wherein M means at least one element selected from transition metal elements, elements of groups II, XIII, XIV and XV among periodic table of elements except for Co and Ni; N is halogen element; x is 0.10<=x<=1.25, y is 0<=y<=0.05, and z is 0<=z<=0.05).

Description

Lithium Cobalt Composite Oxide and Method for Preparing the Same and Nonaqueous Electrolyte Secondary Battery

The present invention relates to a lithium cobalt composite oxide and a method of manufacturing the same, a nonaqueous electrolyte secondary battery, and a portable electronic device.

It is known that transition metal oxides having a hexagonal layered crystal structure can introduce suitable metal ions between the lattice sites and / or lattice of the crystal. In particular, the lithium interlayer compound can introduce lithium ions between the crystal lattice sites and / or lattice under a specific potential difference, and again take it out. Lithium secondary batteries using lithium cobalt composite oxide and LiCoO ₂ as a positive electrode active material have high volumetric energy density, which makes it possible to miniaturize and reduce the weight of portable electronic devices. It is rapidly spreading as a power source.

On the other hand, studies are also being made to replace expensive cobalt with other inexpensive transition metals such as nickel and manganese (for example, Japanese Patent Laid-Open No. 11-71114 and Japanese Patent Laid-Open). See 11-292550). Japanese Patent Laid-Open No. 11-292550 discloses a lithium composite oxide obtained from a raw material represented by the chemical formula of LiCo _x Ni _(1-x) O ₂ (0.05≤x <1). Even after the Co component of the lithium cobalt composite oxide (LiCoO ₂ ) is partially replaced with Ni, a stable crystal structure can be maintained. As described above, in the related art, expensive cobalt is attempted to be replaced with nickel.

However, as a result of diligent research by the present inventors, it was found that when the Co component of the lithium cobalt composite oxide (LiCoO ₂ ) serving as the positive electrode active material was partially replaced with Ni, the discharge characteristics of the lithium secondary battery deteriorated. Therefore, an object of the present invention is to provide a lithium secondary battery with improved discharge characteristics.

1 is a cross-sectional view of a nonaqueous electrolyte secondary battery of one embodiment of the present invention.

2 is a graph showing the relationship between the voltage and the discharge capacity of the nonaqueous electrolyte lithium secondary battery according to the present invention.

<Explanation of symbols for the main parts of the drawings>

1 separator

2 cathode

3 anode

4 current collector

5 Mounting Brackets

6 external terminals

7 electrolyte

More specifically, the present invention provides the following.

(1) A lithium cobalt composite oxide, wherein the Ni content is 100 ppm or less and is represented by the formula (1).

<Formula 1>

Li _x Co _1-y M _y O ₂ N _z

In the formula, M represents one or more elements selected from transition metal elements excluding Co and Ni, elements of Groups 2, 13, 14, and 15 of the periodic table, N represents a halogen atom, x is 0.10 ≦ x ≦ 1.25, y is 0 ≦ y ≦ 0.05, and z represents 0 ≦ z ≦ 0.05.

(2) The lithium cobalt composite oxide according to claim 1, wherein the lithium cobalt composite oxide contains a sulfate group.

(3) The lithium cobalt composite oxide according to claim 1 or 2, wherein the Ni content is 60 ppm or less.

(4) The lithium cobalt composite oxide according to any one of items 1 to 3, which is lithium cobalt oxide for a nonaqueous electrolyte secondary battery.

(5) A method for producing a lithium cobalt composite oxide, wherein a mixture of cobalt oxyhydroxide and a lithium compound having a Ni content of 100 ppm or less is heated to 700 to 1100 ° C.

(6) A lithium cobalt composite oxide characterized by further mixing at least one selected from a halogen compound and a sulfate compound into a mixture of cobalt oxyhydroxide and a lithium compound having a Ni content of 100 ppm or less and heating it at 700 to 1100 ° C. Manufacturing method.

(7) A non-aqueous electrolyte secondary battery, wherein the lithium cobalt composite oxide according to any one of items 1 to 3 is included in the positive electrode as the positive electrode active material.

(8) A portable electronic device comprising the nonaqueous electrolyte secondary battery according to (7).

<Embodiment of the invention>

Hereinafter, the positive electrode active material and the nonaqueous electrolyte secondary battery of the present invention will be further described.

<Lithium cobalt composite oxide>

Lithium cobalt composite oxide according to the present invention is a lithium cobalt composite oxide, characterized by the formula (1). That is, as the lithium cobalt composite oxide according to the present invention, for example, Ni _x 100 ppm or less Li _x CoO ₂ , LiCoO ₂ N _z , LiCo _1-y M _y O ₂ , or LiCo _1-y M _y O ₂ N _z may be mentioned, especially Ni is very low Li _x CoO ₂ and Li _x CoO _{2 z} N that contains the halogen element is preferably (and x is 0.10≤x≤1.25, y is 0≤y≤0.05, z Represents 0 ≦ z ≦ 0.05). These lithium cobalt composite oxides can be used suitably for the positive electrode active material for lithium ion non-aqueous electrolyte secondary batteries.

The lithium cobalt composite oxide according to the present invention includes other elements M, for example, Li, Na, B, Ca, Mg, Si, Cu, Ce, Y, Ti, V, Mn, Fe, Sn, Zr, Sb, Nb. One or more elements selected from the group consisting of Ru, Pb, Hf, Ta, La, Pr and Nd may be included. Examples of the halogen atom N include halogen atoms such as fluorine, chlorine, bromine and iodine, and fluorine is particularly preferable.

In the lithium cobalt composite oxide according to the present invention, the Ni content is 100 ppm or less. It is further more preferable that Ni content is 70 ppm or less, and Ni content is 60 ppm or less. Especially preferably, Ni content is 30 ppm or less.

Content of the sulfuric acid group in a lithium cobalt complex oxide is represented by (weight of sulfuric acid group quantified by analysis) / (weight of the positive electrode active material obtained by synthesis), and 0.01 weight% or more and 5 weight% or less are preferable. Moreover, 0.05 weight% or more and 2 weight% or less are more preferable, and 0.1 weight% or more and 1 weight% or less are especially preferable. Various methods can be used for the determination of sulfuric acid groups. For example, the sulfuric acid group can be quantified by ion chromatography after the sample is completely dissolved in nitric acid, hydrogen peroxide, or the like. In addition, sulfuric acid groups can be quantified by ICP emission spectrometry or titration. ICP emission spectrometry is a method in which a sample is dissolved with nitric acid and perchloric acid, sulfur is quantified by ICP emission analysis, and converted into a sulfate group. The titration method is to add barium chromate and dilute hydrochloric acid solution to the sample, neutralize with ammonia, filter, and titrate the sulfuric acid group indirectly by titrating CrO ₄ ^2- in the filtrate generated by substitution with sulfuric acid with iodine method. It is based on the method described in the Society Edition "Experimental Chemistry Lecture 15 Analytical Chemistry (Bottom)" (Maruzen Kabushiki Kaisha).

In addition, the halogen element contained in the lithium cobalt composite oxide has a content of 0.005 to 2.5% by weight, preferably 0.05 to 1.5% by weight.

In the lithium cobalt composite oxide contained in the positive electrode of the lithium secondary battery, as the Ni content in the lithium cobalt composite oxide decreases, the discharge capacity of the lithium secondary battery increases and the voltage is easily maintained. Therefore, the volume energy density of a lithium secondary battery increases, and a portable electronic device can be miniaturized and light weight. In addition, the fluorine compound and the sulfuric acid group are further present in the lithium cobalt composite oxide, whereby load characteristics, cycle characteristics, high temperature storage characteristics, low temperature characteristics and safety can be improved.

<Cobalt oxyhydroxide>

In the manufacturing method of this invention, cobalt oxyhydroxide (CoOOH) whose Ni content is 100 ppm or less is used. It is preferable to use cobalt oxyhydroxide (CoOOH) whose Ni content is 70 ppm or less, and it is more preferable to use cobalt oxyhydroxide which Ni content is 60 ppm or less. Especially preferably, it is cobalt oxyhydroxide which Ni content is 30 ppm or less. This is because the Ni content in the lithium cobalt composite oxide obtained by the production method of the present invention decreases as the nickel content in the reactant decreases. Cobalt oxyhydroxide may be thought of as a main component, but it is considered that CoOOH to the outside is included, such as Co ₃ O _4, CoCO _3.

It does not specifically limit about which manufacturing method the cobalt oxyhydroxide used for the manufacturing method of this invention was obtained. For example, a compound having a divalent cobalt such as cobalt nitrate, cobalt chloride or cobalt sulfate may be oxidized with an oxidizing agent and then neutralized with alkali.

It does not specifically limit as said oxidizing agent, For example, air, oxygen, ozone; Salts thereof represented by permanganic acid (HMnO ₄ ) and M ³ MnO ₄ ; Chromic acid (CrO ₃ ) and related compounds thereof represented by M ³ ₂ Cr ₂ O ₇ , M ³ ₂ CrO ₄ , M ³ CrO ₃ X, CrO ₂ X ₂ , and the like; Halogen such as F ₂ , Cl ₂ , Br ₂ , I ₂ and the like; Peroxides such as H ₂ O ₂ , Na ₂ O ₂ , BaO ₂ and the like; Compounds represented by peroxoic acid and M ³ ₂ S ₂ O ₈ , M ³ ₂ SO ₅ , H ₂ CO ₃ , CH ₃ CO ₃ H and the like; With oxygen acid and M ³ MClO, M ³ BrO, M ³ IO, M ³ ClO ₃ , M ³ BrO ₃ , M ³ IO ₃ , M ³ ClO ₄ , M ³ IO ₄ , Na ₃ H ₂ IO ₆ , KIO _4, etc. The compound or its salt etc. which are displayed are mentioned. In the formula, M ³ represents an alkali metal element. It does not specifically limit as said alkali metal element, For example, lithium, sodium, potassium, rubidium, etc. are mentioned. In addition, X represents a halogen element.

It does not specifically limit as alkali to neutralize, The aqueous solution of inorganic hydroxides, such as lithium hydroxide, sodium hydroxide, potassium hydroxide, magnesium hydroxide, calcium hydroxide, barium hydroxide, ammonium hydroxide, etc. can be used preferably.

The cobalt oxyhydroxide is obtained by dissolving a compound having a divalent cobalt such as cobalt nitrate, cobalt chloride, and cobalt sulfate in water to form an aqueous solution, and simultaneously performing neutralization and oxidation by adding the oxidizing agent and the alkali. Can be. Furthermore, the said cobalt oxyhydroxide can be obtained by adding the said alkali to the aqueous solution containing the compound which has the said divalent cobalt, synthesize | combining bivalent cobalt hydroxide, and then oxidizing by adding an oxidizing agent. Moreover, the said cobalt oxyhydroxide can be obtained by adding the said oxidizing agent to the aqueous solution containing the compound which has the said bivalent cobalt, and then neutralizing by adding the said alkali.

<Lithium compound>

In the production method of the present invention, a lithium compound is used. Although a lithium compound is not specifically limited, For example, inorganic lithium salts, such as lithium hydroxide, lithium carbonate, and a lithium nitrate, can be used preferably. As a lithium compound, lithium carbonate is preferable since it is industrially easy and inexpensive. It is preferable that the density | concentration of a lithium compound is high in purity.

<Sulfate Compound>

In the manufacturing method which concerns on this invention, a sulfate compound can be contained. Inorganic or organic sulfate compounds may be added and used, and inorganic salts include iron sulfate, cobalt sulfate, nickel sulfate, zinc sulfate, copper sulfate, lithium sulfate, potassium sulfate, magnesium sulfate, beryllium sulfate, strontium sulfate, barium sulfate, and These hydrates can be used. Moreover, as organic salts, tetrahydroammonium sulfate, trifluoromethanesulfonic acid, 1-naphthylamine-2-sulfonic acid, 1-naphthylamine-5-sulfonic acid, 1-naphthol-3,6- disulfonic acid, p -Bromobenzenesulfonic acid, p-anilinesulfonic acid, o-xylene-4-sulfonic acid, dimethylsulfone, o-sulfobenzoic acid, 5-sulfosalicylic acid and the like can be used. Among these, cobalt sulfate and magnesium sulfate are used preferably.

<Halogen Compound>

In the manufacturing method of this invention, a halogen compound can be contained. Examples of the halogen compound to be added include a combination of one or more metal elements selected from Li, Mg, Al, Ca, Ti, V, Cr, Mn, Fe, and Co, and halogen elements such as fluorine, chlorine, and bromine. this is possible, but among these, LiF, MgF ₂ is used as is preferred.

<Manufacturing method>

In the production method according to the present invention, for example, first, the above-described cobalt oxyhydroxide and a lithium compound, preferably lithium carbonate, are mixed to obtain a mixture. Mixing may be either dry or wet, but dry is preferred because it is easy to manufacture. In the case of dry mixing, it is preferable to use a mixer in order to uniformly mix the raw materials. The mixing ratio of the raw material lithium compound and cobalt oxyhydroxide in the mixing step is 0.99 to 1.06, preferably 0.99 to 1.02, of the molar ratio (Li / Co) of Co atoms and Li atoms.

In the manufacturing method which concerns on this invention, it is preferable to add further at least 1 sort (s) of compound chosen from a sulfate compound and a halogen compound to the mixture of cobalt oxyhydroxide and a lithium compound, and to mix by the same method as the above.

In addition, the average particle diameter of cobalt oxyhydroxide is although it does not specifically limit, For example, it is 1-20 micrometers, Preferably it is 8-15 micrometers. The average particle diameter of the lithium compound is not particularly limited as in cobalt oxyhydroxide, but is, for example, 1 to 100 µm, preferably 1 to 20 µm.

Next, the mixture is calcined. The firing temperature is preferably 700 to 1100 ° C, more preferably 850 to 1050 ° C. The firing time is 1 to 24 hours, preferably 2 to 10 hours. When the firing temperature is lower than 700 ° C, the lithium cobalt composite oxide cannot be sufficiently synthesized, and cobalt oxyhydroxide or a lithium compound as a raw material remains, which is not preferable. On the other hand, when the firing temperature is higher than 1100 ° C, decomposition of the intended lithium cobalt composite oxide begins, and battery characteristics of a lithium secondary battery using the lithium cobalt composite oxide as a positive electrode active material, in particular, capacity deterioration due to voltage at the end of discharge. It is not preferable because the cycle characteristics deteriorate.

Firing can be performed in either air or an oxygen atmosphere, and is not particularly limited. After baking, it is appropriately cooled and pulverized as necessary to obtain a lithium cobalt composite oxide. The pulverization carried out as necessary is appropriately performed in the case where the lithium cobalt composite oxide obtained by firing is in the form of a softly bonded block, but the particles themselves of the lithium cobalt composite oxide have a specific average particle size and a BET specific surface area. That is, the resulting lithium cobalt composite oxide has an average particle diameter of 1 to 30 µm, preferably 3 to 20 µm, particularly preferably 5 to 15 µm, and a BET specific surface area of 0.1 to 2.0 m 2 / g. , Preferably 0.2 to 1.5 m 2 / g, particularly preferably 0.2 to 1.0 m 2 / g.

The nickel content relative to the lithium cobalt composite oxide and cobalt oxyhydroxide is in excess of 100% by weight and no more than 100 ppm, particularly preferably 0 to 60 ppm. This is because the nickel atom in the lithium cobalt composite oxide is substituted at the same site as the cobalt atom, so that the number of cobalt atoms that contribute to charge and discharge capacity is reduced. In addition, since the nickel atom is substituted with cobalt by another valence, it is thought that there is less trivalent cobalt required for charging and discharging for charge guarantee. The lower limit of the nickel content is not particularly limited.

<Measurement method of Ni content>

After completely dissolving the lithium cobalt composite oxide (0.5 g) while boiling with perchloric acid, distilled water was added to 100 ml, and the amount of Ni in the solution was quantified by an ICP emission spectrometer (manufactured by SCI).

<Measuring method of sulfuric acid group>

Quantification of the sulfuric acid group was performed by the following method. 0.5 g of the sample is weighed into a 30 ml beaker, 6 ml of dilute nitric acid added with 1 part of water to 1 part of nitric acid and 4 ml of hydrogen peroxide added with 1 part of water to 1 part of hydrogen peroxide are heated on a hot plate and dissolved completely. . Subsequently, after cooling, the solution is transferred to a 100 ml volumetric flask and subjected to static. Furthermore, it diluted 10-fold and quantified the sulfuric acid group by the ion chromatograph (2000i / s type by the DIONEX company of USA).

<Method for Measuring Halogen Element>

[Quantification of Fluoride Ions]

Steam distillation was performed on the obtained LiCoO ₂ , and fluoride ions were quantified by applying the lanthanum-alizarin complexon absorbance method or the ion electrode method (according to JIS K 0102 34).

<Battery manufacturing method>

The lithium cobalt composite oxide is used for the lithium secondary battery positive electrode active material. The positive electrode active material is a raw material of a positive electrode mixture of a lithium secondary battery described later, that is, a mixture containing a positive electrode active material, a conductive agent, a binder, a filler, and the like as necessary. Since the lithium secondary battery positive electrode active material according to the present invention contains the lithium cobalt composite oxide, when mixing with other raw materials to prepare a positive electrode mixture, kneading is easy and when the obtained positive electrode mixture is applied to a positive electrode current collector, Ease of coating.

The lithium secondary battery according to the present invention uses the lithium cobalt composite oxide as the positive electrode active material. Nonaqueous electrolyte containing a positive electrode, a negative electrode, a separator, and a lithium salt. The positive electrode is formed by, for example, coating and drying a positive electrode mixture on a positive electrode current collector, and the positive electrode mixture includes a positive electrode active material, a conductive agent, a binder, a filler added as necessary, and the like.

The positive electrode current collector is not particularly limited as long as it is an electron conductor which does not cause chemical change in the battery constituted. For example, carbon, nickel, titanium, silver on the surface of stainless steel, nickel, aluminum, titanium, calcined carbon, aluminum or stainless steel The surface-treated thing etc. are mentioned.

Examples of the conductive agent include graphite such as natural graphite and artificial graphite, carbon black, acetylene black, carbon fiber, conductive materials such as carbon nanotubes, metals, and nickel powder. Examples of the natural graphite include, for example, Scale graphite, scale fragment graphite, earth graphite, etc. are mentioned. These can be used 1 type or in combination or 2 or more types. The blending ratio of the conductive agent is 1 to 50% by weight, preferably 2 to 30% by weight in the positive electrode mixture.

As the binder, for example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinylpyrrolidone, ethylene-propylene-diene terpolymer (EPDM), liquor Polysaccharides, such as fonned EPDM, styrene butadiene rubber, fluorine rubber, and polyethylene oxide, a thermoplastic resin, a polymer having rubber elasticity, etc. are mentioned, These can be used 1 type or in combination or 2 or more types. The blending ratio of the binder is 2 to 30% by weight, preferably 5 to 15% by weight in the positive electrode mixture.

The filler is to suppress volume expansion of the positive electrode in the positive electrode mixture, and is added as necessary. Any filler may be used as long as it is a fibrous material which does not cause chemical changes in the battery constituted. For example, fibers such as olefin-based polymers such as polypropylene and polyethylene, glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0-30 weight% is preferable in positive mix.

The negative electrode is formed by coating and drying a negative electrode material on a negative electrode current collector. The negative electrode current collector is not particularly limited as long as it is an electron conductor that does not cause chemical change in a battery composed of stainless steel, nickel, copper, titanium, aluminum, calcined carbon, carbon, nickel, titanium, The surface-treated silver, aluminum-cadmium alloy, etc. are mentioned.

Although it does not restrict | limit especially as a negative electrode material, For example, a carbonaceous material, a metal complex oxide, lithium metal, a lithium alloy, etc. are mentioned. As a carbonaceous material, a non-graphitizing carbon material, a graphite type carbon material, etc. are mentioned, for example. Examples of the metal complex oxide include Sn _p M ¹ -pM ² _q O _r (wherein M ¹ represents at least one element selected from Mn, Fe, Pb, and Ge, and M ² represents Al, B, P, Si, at least one element selected from group 1, group 2, group 3 and halogen elements of the periodic table, and represents 0 <p ≦ 1, 1 ≦ q ≦ 3, 1 ≦ r ≦ 8), and the like. The compound of the is mentioned.

As the separator, an insulating thin film having a large ion permeability and having a predetermined mechanical strength is used. In view of organic solvent resistance and hydrophobicity, a sheet or nonwoven fabric made from an olefin polymer such as polypropylene or glass fiber or polyethylene is used. As a pore size of a separator, it may be the range generally useful for a battery, for example, it is O1-10 micrometers. As thickness of a separator, it may be a general battery range, for example, 5-300 micrometers. In addition, when solid electrolytes, such as a polymer, are used as electrolyte mentioned later, a solid electrolyte may also serve as a separator. In addition, compounds such as pyridine, triethyl phosphite, triethanolamine and the like may be added to the electrolyte for the purpose of improving the discharge and charge / discharge characteristics.

The non-aqueous electrolyte containing a lithium salt consists of a non-aqueous electrolyte and a lithium salt. As the nonaqueous electrolyte, a nonaqueous electrolyte or an organic solid electrolyte is used. As the non-aqueous electrolyte, for example, N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, Tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, tri One kind of an aprotic organic solvent, such as methoxymethane, dioxolane derivative, sulfolane, 3-methyl-2-oxazodinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether and 1,3-propanesaltone Or the solvent which mixed 2 or more types is mentioned.

As an organic solid electrolyte, a polyethylene derivative or the polymer containing this, a polypropylene oxide derivative or the polymer containing the same, a phosphate ester polymer, etc. are mentioned, for example. As the lithium salt, those dissolved in the non-aqueous electrolyte can be used. For example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl _The salt which mixed 1 type (s) or 2 or more types, such as ₄ , lithium chloroborane, a lower aliphatic lithium carboxylate, and lithium tetraphenyl borate, is mentioned.

The shape of the lithium secondary battery according to the present invention can be applied to any shape such as a button shape, a sheet shape, a cylinder shape, and a shape. Although the use of the lithium secondary battery according to the present invention is not particularly limited, for example, electronic devices such as notebook personal computers, laptop personal computers, pocket word processors, mobile phones, separate wireless telephones, portable CD players, radios, etc. And civilian electronic devices such as automobiles, electric vehicles, and game machines. In addition, the lithium secondary battery is included in the nonaqueous electrolyte secondary battery.

<Portable electronic device>

In the present invention, a portable electronic device containing the nonaqueous electrolyte secondary battery is provided. Examples of portable electronic devices include notebook personal computers, pocket word processors, cellular phones, separate wireless telephones, portable CD players, radios, and gaming devices.

<Example>

Hereinafter, the lithium cobalt composite oxide and the nonaqueous electrolyte secondary battery of the present invention will be further described.

In the following examples and comparative examples, lithium carbonate (average particle diameter is preferably 10 to 15 µm, for example, 11.0 µm), and cobalt oxyhydroxide having a Ni content of 25, 49, 98, 205, or 502 ppm ( Chem Grade (manufactured by QNI) (average particle size of 10 to 15 µm is preferred, for example, 12.0 µm) was weighed so as to have an Li / Co atomic ratio of 0.99 to 1.060 and sufficiently mixed by induction to prepare a uniform mixture. . Subsequently, the mixture was charged into an alumina crucible, placed in an electric furnace, heated in an atmospheric atmosphere, held at a temperature of 700 to 1100 ° C. for 10 hours, and fired. Synthesized by classification.

<Example 1>

Firing at 950 ° C. for 10 hours yielded a lithium cobalt composite oxide (LiCoO ₂ ) having a Ni content of 28 ppm. The average particle diameter was 10.2 mu m.

<Example 2>

Firing at 800 ° C. for 10 hours yielded a lithium cobalt composite oxide (LiCoO ₂ ) having a Ni content of 45 ppm. The average particle diameter was 12.0 mu m.

<Example 3>

Baking at 1000 ° C. for 10 hours yielded a lithium cobalt composite oxide (LiCoO ₂ ) having a Ni content of 58 ppm. The average particle diameter was 11.2 mu m.

<Example 4>

Firing at 1050 ° C. for 10 hours yielded a lithium cobalt composite oxide (LiCoO ₂ ) having a Ni content of 96 ppm. The average particle diameter was 10.5 탆.

Example 5

Lithium carbonate, cobalt oxyhydroxide and lithium sulfate corresponding to Li / O molar ratio of 1.04 and calcium sulfate equivalent to 2000 ppm of SO ₄ per LiCoO ₂ were mixed and calcined at 1060 ° C. for 5 hours to obtain 40 ppm of Ni and SO ₄ , respectively. A lithium cobalt composite oxide (LiCoO ₂ ) of 1905 ppm was obtained. The average particle diameter was 12.5 μm.

<Example 6>

Lithium carbonate and cobalt oxyhydroxide having a Li / Co molar ratio of 1.04 are mixed with MgF ₂ having an equivalent of 3000 ppm of F per LiCoO ₂ and calcined at 1060 ° C. for 5 hours to obtain Ni and F contents of 40 ppm and 820 ppm, respectively. Phosphorus lithium cobalt composite oxide (LiCoO ₂ ) was obtained. The average particle diameter was 12.2 mu m.

<Example 7>

Lithium carbonate and cobalt oxyhydroxide with a Li / Co molar ratio of 1.04 are mixed with calcium sulfate having 1500 ppm of SO ₄ per LiCoO ₂ and MgF ₂ having 2000 ppm of F, and calcined at 1060 ° C. for 5 hours. The lithium cobalt composite oxide (LiCoO ₂ ) having 40 ppm, 540 ppm, and 1950 ppm of, F, and SO ₄ was obtained. The average particle diameter was 12.9 mu m.

Comparative Example 1

Firing at 1060 ° C. for 10 hours yielded a lithium cobalt composite oxide (LiCoO ₂ ) having a Ni content of 201 ppm. The average particle diameter was 10.7 µm.

Comparative Example 2

Firing at 820 ° C. for 10 hours yielded a lithium cobalt composite oxide (LiCoO ₂ ) having a Ni content of 490 ppm. The average particle diameter was 11.2 mu m.

<Particle size distribution measuring method>

The average particle diameter described in this specification shall show the value obtained by the laser scattering particle size distribution measuring apparatus. Although a measuring apparatus is not specifically limited, In this specification, the laser type particle size distribution measuring apparatus (Microtrac) by Nikkiso Corporation was used.

<Battery performance test>

(I) the manufacture of a lithium secondary battery;

91 wt% of lithium cobalt composite oxide, 6 wt% of graphite powder, and 3 wt% of polyvinylidene fluoride were mixed as examples 1 to 7 and Comparative Examples 1 to 2 prepared as described above to obtain a cathode agent, which was N-methyl. Kneading paste was prepared by dispersing in 2-pyrrolidinone. After apply | coating this kneading paste to aluminum foil, it dried and pressed, it punched in the disk of diameter 15mm, and obtained the positive electrode plate.

In FIG. 1, using this positive electrode plate, each member such as a separator 1, a negative electrode 2, a positive electrode 3, a current collector plate 4, a mounting bracket 5, an external terminal 6, an electrolyte solution 7, and the like To prepare a lithium secondary battery, that is, a non-aqueous electrolyte secondary battery. Among them, a metal lithium foil was used for the negative electrode, and an electrolyte solution in which 1 mol of LiPF ₆ was dissolved in 1 liter of a 1: 1 kneading solution of ethylene carbonate and diethyl carbonate was used.

(II) performance evaluation of the battery;

The produced lithium secondary battery was operated at room temperature, and the initial discharge capacity was measured to evaluate battery performance.

(III) evaluation method;

The discharge capacity was charged up to 4.3 V with CCCV (1.0 C) for the positive electrode, and then discharged to 2.7 V to measure the discharge capacity. In addition, the relationship between voltage and discharge capacity is shown in FIG. 2 for a lithium secondary battery prepared using lithium cobalt composite oxides prepared in Examples 1 to 7 and Comparative Examples 1 and 2 as a positive electrode active material.

<Experiment Result>

The active materials obtained in Examples 1 to 7 and Comparative Examples 1 and 2 were electrode-coated to conduct a constant current charge / discharge test at 2.7 V to 4.3 V (vs. Li / Li ⁺ ). His charge and discharge curves are shown. Charge-discharge current was performed at 0.2C. It was found that all of the active materials obtained in Examples 1 to 7 had an initial discharge capacity of 158 mAH / g or more, and a large discharge capacity was obtained compared to the active materials obtained in Comparative Examples 1 and 2. It is thought that this is because the Ni contained in the lithium cobalt composite oxide is substituted with Co to form a solid solution, so that the amount of Co used as a capacity decreases and a capacity decrease occurs. From these results, it was confirmed that the lithium composite oxide of Examples 1-7 was excellent as a nonaqueous electrolyte secondary battery.

In the present invention, a lithium secondary battery having improved discharge characteristics can be provided by using a lithium cobalt composite oxide having a Ni content of 100 ppm or less as a positive electrode active material. By using these lithium secondary batteries, it is possible to reduce the size and weight of a portable electronic device.

Claims (8)

A lithium cobalt composite oxide, wherein the Ni content is 100 ppm or less and represented by the formula (1). <Formula 1> Li _x Co _1-y M _y O ₂ N _z In the formula, M represents one or more elements selected from transition metal elements excluding Co and Ni, elements of Groups 2, 13, 14, and 15 of the periodic table, N represents a halogen atom, x is 0.10 ≦ x ≦ 1.25, y is 0 ≦ y ≦ 0.05, and z represents 0 ≦ z ≦ 0.05. The lithium cobalt composite oxide according to claim 1, wherein the lithium cobalt composite oxide contains a sulfate group. The lithium cobalt composite oxide according to claim 1 or 2, wherein the Ni content is 60 ppm or less. The lithium cobalt composite oxide according to any one of claims 1 to 3, which is lithium cobalt oxide for a nonaqueous electrolyte secondary battery. A method for producing a lithium cobalt composite oxide, wherein a mixture of cobalt oxyhydroxide and a lithium compound having a Ni content of 100 ppm or less is heated to 700 to 1100 ° C. A method for producing a lithium cobalt composite oxide, characterized by further mixing at least one selected from a halogen compound and a sulfate compound in a mixture of cobalt oxyhydroxide and a lithium compound having a Ni content of 100 ppm or less and heating it at 700 to 1100 ° C. . The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the lithium cobalt composite oxide is contained in the positive electrode as the positive electrode active material. A portable electronic device comprising the nonaqueous electrolyte secondary battery according to claim 7.