JP4754209B2 - Method for producing lithium cobalt composite oxide powder - Google Patents

Description

  The present invention relates to a lithium cobalt composite oxide powder useful as a positive electrode active material of a lithium secondary battery, a method for producing the same, a lithium secondary battery positive electrode active material containing the same, and a lithium secondary battery particularly excellent in cycle characteristics It is.

  In recent years, as home appliances have become portable and cordless, lithium ion secondary batteries have been put to practical use as power sources for small electronic devices such as laptop computers, mobile phones, and video cameras. Regarding this lithium ion secondary battery, in 1980, Mizushima et al. Reported that lithium cobalt oxide was useful as a positive electrode active material for lithium ion secondary batteries (“Material Research Bulletin” vol15, P783-789 (1980)). ) Has been actively researched and developed on lithium-based composite oxides, and many proposals have been made so far.

  However, a lithium secondary battery using lithium cobaltate has a problem of deterioration of cycle characteristics due to elution of cobalt atoms.

Further, lithium cobalt composite oxides in which Co atoms of lithium cobaltate are partially substituted with Mg atoms have been proposed as positive electrode active materials (see, for example, Patent Documents 1 to 3).
Mg sources for including Mg atoms in lithium cobalt based composite oxides including Patent Documents 1 to 3 are magnesium oxide and magnesium carbonate, and as far as the applicant knows, Al, Zr, Ca and Ti sources. Among these compounds, there are no oxides or carbonates of these metals that actually use the phosphates or hydrogen phosphates of these metals, and even when these conventional methods are used, cycle characteristics are still not achieved. The problem of deterioration was left.

In addition, the present applicant has previously proposed lithium cobalt-based composite oxides containing these metal atoms obtained by treating the surface of lithium cobalt oxide particles with oxides or sulfates of these metals (Patent Documents 4 to 5). ).
JP-A-5-54889, page 1, page 8. JP 2000-11993 A, page 2, page 3. JP, 2004-79386, A, 2nd page, 7th page. JP2003-20229A. JP2003-221234A.

  According to the method proposed by the present applicant, the cycle characteristics can be improved. However, after producing lithium cobaltate, a separate process of surface-treating the lithium cobaltate must be provided. It is not industrially advantageous from the standpoint of the manufacturer.

  Accordingly, an object of the present invention is to provide a lithium-cobalt composite oxide powder that can improve the cycle characteristics of a lithium secondary battery, particularly when used as a positive electrode active material of a lithium secondary battery, and an industrially advantageous production thereof. It is an object to provide a method, a positive electrode active material for a lithium secondary battery containing the same, and a lithium secondary battery excellent in cycle characteristics using the positive electrode active material.

  As a result of intensive studies to solve these problems, the present inventors have obtained a lithium cobalt-based composite oxide containing a specific range of at least one metal atom selected from Mg, Al, Zr, Ca and Ti. Further, a lithium cobalt composite oxide powder containing these metal atoms obtained by an industrially advantageous method using the metal phosphate or / and hydrogen phosphate as the compound containing the metal atom is used as the positive electrode. The lithium secondary battery used as the active material has been found to be particularly excellent in cycle characteristics, and the present invention has been completed.

That is, inventions present invention you attempt to provide a lithium compound, a cobalt compound及beauty M g, Al, Zr, mixed by firing a compound containing at least one metal atom selected from Ca and Ti In the method for producing a lithium cobalt composite oxide, a metal phosphate or hydrogen phosphate is used as the metal atom-containing compound, and the molar ratio of the lithium compound, the cobalt compound, and the metal atom-containing compound to the Co atom. Then, Li is mixed with 0.90 to 1.20 Li atoms and 0.001 to 0.04 metal atoms, and the resulting mixture is fired.

  The lithium cobalt composite oxide powder of the present invention is useful as a positive electrode active material of a lithium secondary battery, and a lithium secondary battery using the lithium cobalt composite oxide as a positive electrode active material particularly has cycle characteristics. It will be excellent.

Hereinafter, the present invention will be described based on preferred embodiments thereof.
The lithium cobalt composite oxide powder according to the present invention has at least one metal atom selected from Mg, Al, Zr, Ca, and Ti (hereinafter abbreviated as “metal atom”) in an amount of 0.025 to 0.025. One or more metals selected from lithium compounds, cobalt compounds, and phosphates or hydrogen phosphates of the above-mentioned lithium cobalt-based composite oxides containing 1.0% by weight, preferably 0.025 to 0.5% by weight The lithium-cobalt composite oxide powder of the present invention having such a structure is produced by mixing a compound containing atoms and firing the mixture. Compared to those using oxides or carbonates of these metals as compounds containing lithium, the lithium secondary battery using the lithium cobalt composite oxide powder as a positive electrode active material has an excellent cycle. It is possible to impart the characteristics.

  In the present invention, the reason why the metal atom content falls within the above range is that when the metal atom content is less than 0.025% by weight, the cycle characteristics of the lithium secondary battery are not improved. This is because if the content exceeds 0% by weight, the capacity of the lithium secondary battery tends to decrease.

  In the present invention, it is particularly preferable that the metal atom is an Mg atom in that the metal atom to be contained is an Mg atom, so that the cycle characteristics of the lithium secondary battery can be further improved.

  As other physical properties of the lithium cobalt based composite oxide powder according to the present invention, the average particle size determined from the laser particle size distribution measurement method is 0.5 to 30 μm, preferably 10 to 25 μm, and the average particle size is When the thickness is within the range, it is preferable because a coating film having a uniform thickness can be formed. Particularly preferably, when the thickness is 10 to 20 μm, the safety of the lithium secondary battery using the lithium cobalt-based composite oxide powder as the positive electrode active material The property can be further improved.

The lithium cobalt composite oxide powder according to the present invention has a BET specific surface area of 0.05 to ¹ m ² / g, preferably 0.15 to 0.6 m ² / g. It is preferable that the BET specific surface area be within this range because safety is good.

In the lithium-cobalt composite oxide powder of the present invention, the metal phosphate or / and hydrogen phosphate is obtained by firing a lithium compound and a cobalt compound so that the metal component is oxidized by the action of the phosphate, etc. On the other hand, it is considered that the phosphoric acid content is preferentially present on the particle surface of the product as a oxide, while the phosphoric acid component reacts with lithium and is immobilized on the particle surface as a lithium phosphate by a chemical bond. Lithium acid acts as an impurity and leads to an increase in the impedance of the lithium secondary battery, which causes deterioration of charge / discharge cycle characteristics. Therefore, in the lithium cobalt composite oxide powder of the present invention, the amount of PO ₄ ²⁻ eluted in water derived from this lithium phosphate is 1% by weight or less, preferably 0.2% by weight or less. The battery performance is not particularly deteriorated, and it is particularly preferable in that excellent cycle characteristics can be imparted to the lithium secondary battery.
In the present invention, PO in the dispersion when the amount of PO ₄ ^2-eluting in water is dispersed in 5 minutes 25 ° C. The lithium cobalt composite oxide powder 30g of pure water 100 ml ₄ ^2- Is determined by ion chromatography.

Next, a method for producing the lithium cobalt composite oxide powder of the present invention will be described.
The method for producing a lithium cobalt composite oxide powder according to the present invention is performed by mixing a lithium compound, a cobalt compound, and a compound containing at least one metal atom selected from Mg, Al, Zr, Ca, and Ti, and firing. In the method for producing a lithium-cobalt-based composite oxide, a phosphate or hydrogen phosphate of the metal is used as the compound containing the metal atom, and the lithium compound, the cobalt compound, and the compound containing the metal atom are in a molar ratio to the Co atom, It mixes with Li atom 0.90-1.20 and metal atom 0.001-0.04, and the obtained mixture is baked.

  Examples of the first raw material lithium compound that can be used include lithium oxide, hydroxide, carbonate, nitrate, and organic acid salt. Among these, industrially inexpensive lithium carbonate is used. preferable. Further, this lithium compound has an average particle size determined by a laser particle size distribution measurement method of 0.1 to 200 μm, preferably 2 to 50 μm, because the reactivity is good, and thus it is particularly preferable.

Examples of the second raw material cobalt compound that can be used include cobalt oxides, hydroxides, carbonates, nitrates, and organic acid salts, which are industrially inexpensive, reactive, and calcined. It is particularly preferable to use tricobalt tetroxide (Co ₃ O ₄ ) or cobalt oxyhydroxide (CoOOH) in terms of safety of by-products generated as by-products therein. Further, this cobalt compound is particularly preferred when the average particle size determined by the laser particle size distribution measurement method is 0.1 to 20 μm, preferably 1 to 15 μm, since a uniform raw material mixture can be obtained.

  A compound containing at least one metal atom selected from Mg, Al, Zr, Ca and Ti as a third raw material that can be used is a phosphate or / and hydrogen phosphate of these metals, and the hydrogen phosphate The salt may be monohydrogen phosphate or dihydrogen phosphate. In particular, in the present invention, a magnesium secondary phosphate is particularly preferably used in that a lithium secondary battery using a lithium cobalt based composite oxide powder obtained using magnesium phosphate as a positive electrode active material exhibits improved high cycle characteristics. In addition, the compound containing the metal atom used may be a hydrate or an anhydride. The compound containing a metal atom has an average particle size determined by a laser particle size distribution measurement method of 0.1 to 20 μm, and preferably 2 to 15 μm, because the reactivity is good.

  The lithium compound, cobalt compound, and compound containing metal atoms as the first to third raw materials are not limited in production history, but in order to produce high purity lithium cobalt based composite oxide powder as much as possible. It is preferable that the impurity content is low.

  In the reaction operation, first, a predetermined amount of the lithium compound, the cobalt compound, and the compound containing metal atoms as the first to third raw materials are mixed. The mixing may be either a dry method or a wet method, but a dry method is preferred because the production is easy. In the case of dry mixing, it is preferable to use a blender or the like that uniformly mixes the raw materials.

  The compounding ratio of the lithium compound, cobalt compound and metal atom-containing compound as the first to third raw materials described above is a molar ratio with respect to Co atom, and Li atom is 0.90 to 1.20, preferably 0.98 to 1. 10 and metal atoms 0.001 to 0.04, preferably 0.01 to 0.02, and the above-mentioned metal is obtained with respect to the lithium cobalt based composite oxide obtained by firing described later at this blending ratio. A lithium cobalt based composite oxide powder containing 0.025 to 1.0% by weight, preferably 0.025 to 0.5% by weight of atoms can be obtained.

  Next, the mixture in which the first to third raw materials are uniformly mixed is fired. In the present invention, the firing temperature is 800 to 1150 ° C., preferably 900 to 1100 ° C. The reason for setting the firing temperature in the range is that if it is less than 800 ° C., the raw material cobalt compound may remain and cause a decrease in capacity. On the other hand, if the temperature exceeds 1150 ° C., the lithium cobalt composite oxide tends to decompose and the capacity tends to decrease.

  The firing time is 1 to 30 hours, preferably 1 to 5 hours. Firing may be performed in the air or in an oxygen atmosphere, and is not particularly limited. Moreover, these baking can be performed as many times as necessary.

After firing, the mixture is appropriately cooled and pulverized as necessary to obtain a lithium cobalt composite oxide powder.
In addition, the pulverization performed as necessary is appropriately performed when the lithium cobalt composite oxide powder obtained by firing is in a brittlely bonded block shape, etc., but the lithium cobalt composite oxide particles themselves are It has a specific average particle size and BET specific surface area. That is, the obtained lithium cobalt composite oxide powder has an average particle size of 0.5 to 30 μm, preferably 10 to 25 μm, and a BET specific surface area of 0.05 to ¹ m ² / g, preferably 0.15 to 5. 0.6 m ² / g.

The lithium cobalt composite oxide powder thus obtained contains 0.025 to 1% by weight, preferably 0.025 to 0.5% by weight, of at least one metal atom selected from Mg, Al, Zr, Ca and Ti. In addition to having the above-mentioned particle size characteristics, the amount of PO ₄ ²⁻ eluted in water is 1% by weight or less, preferably 0.5% by weight or less. Such a lithium cobalt composite oxide powder of the present invention can be suitably used as a positive electrode active material for a lithium secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt.

  The lithium cobalt composite oxide powder is used for the positive electrode active material of the lithium secondary battery according to the present invention. The positive electrode active material is a raw material of a mixture of a positive electrode mixture of a lithium secondary battery, which will be described later, that is, a positive electrode active material, a conductive agent, a binder, and, if necessary, a filler. The lithium secondary battery positive electrode active material according to the present invention is a lithium cobalt composite oxide powder having the above-mentioned preferable particle size characteristics and mixed with other raw materials to prepare a positive electrode mixture. In this case, kneading is easy, and the coating property when the obtained positive electrode mixture is applied to the positive electrode current collector becomes easy.

The lithium secondary battery according to the present invention uses the above-described lithium secondary battery positive electrode active material, and includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte containing a lithium salt. The positive electrode is formed, for example, by applying 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, and a filler added as necessary. Consists of. In the lithium secondary battery according to the present invention, the lithium cobalt composite oxide, which is a positive electrode active material, is uniformly applied to the positive electrode.
For this reason, especially the lithium secondary battery which concerns on this invention does not produce a fall of a load characteristic and cycling characteristics easily.

  The positive electrode current collector is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in the constituted battery. For example, stainless steel, nickel, aluminum, titanium, calcined carbon, aluminum, and stainless steel Examples of the surface include carbon, nickel, titanium, and silver surface-treated. The surface of these materials may be oxidized and used, or the current collector surface may be provided with irregularities by surface treatment. Examples of the current collector include foils, films, sheets, nets, punched ones, lath bodies, porous bodies, foam bodies, fiber groups, nonwoven fabric molded bodies, and the like. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

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

  Examples of the binder include starch, polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, regenerated cellulose, diacetylcellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer ( EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, fluorinated Vinylidene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene Oroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetra Fluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer or its (Na +) ionic crosslinked product, ethylene-methacrylic acid copolymer or its (Na + ) Ionic crosslinked body, ethylene-methyl acrylate copolymer or its (Na +) ionic crosslinked body, ethylene-methyl methacrylate copolymer or its (Na +) ionic crosslinked body, polysaccharide such as polyethylene oxide, thermoplastic resin Polymers having rubber elasticity, and these may be used individually or in combination. In addition, when using the compound containing a functional group which reacts with lithium like a polysaccharide, it is preferable to add the compound like an isocyanate group and to deactivate the functional group, for example. The blending ratio of the binder is 1 to 50% by weight, preferably 5 to 15% by weight in the positive electrode mixture.

  The filler suppresses the volume expansion of the positive electrode in the positive electrode mixture, and is added as necessary. As the filler, any fibrous material can be used as long as it does not cause a chemical change in the constructed battery. For example, olefinic polymers such as polypropylene and polyethylene, and fibers such as glass and carbon are used. Although the addition amount of a filler is not specifically limited, 0-30 weight% is preferable in a positive mix.

  The negative electrode is formed by applying and drying a negative electrode material on the negative electrode current collector. The negative electrode current collector is not particularly limited as long as it is an electronic conductor that does not cause a chemical change in a configured battery. For example, stainless steel, nickel, copper, titanium, aluminum, calcined carbon, copper or stainless steel Examples of the steel surface include carbon, nickel, titanium, silver surface-treated, and an aluminum-cadmium alloy. Further, the surface of these materials may be used after being oxidized, or the surface of the current collector may be used with surface roughness by surface treatment. Examples of the current collector include foils, films, sheets, nets, punched ones, lath bodies, porous bodies, foam bodies, fiber groups, nonwoven fabric molded bodies, and the like. The thickness of the current collector is not particularly limited, but is preferably 1 to 500 μm.

The negative electrode material is not particularly limited, and examples thereof include carbonaceous materials, metal composite oxides, lithium metals, lithium alloys, silicon-based alloys, tin-based alloys, metal oxides, conductive polymers, and chalcogen compounds. And Li—Co—Ni-based materials. Examples of the carbonaceous material include non-graphitizable carbon materials and graphite-based carbon materials. Examples of the metal composite oxide include Sn _p M ¹ _1-p M ² _{q Or} (wherein M ¹ represents one or more elements selected from Mn, Fe, Pb and Ge, and M ² represents Al. , B, P, Si, one or more elements selected from Group 1, Group 2, Group 3 of the periodic table and halogen elements, 0 <p ≦ 1, 1 ≦ q ≦ 3, 1 ≦ r ≦ 8.), LixFe ₂ O ₃ (0 ≦ x ≦ 1), LixWO ₂ (0 ≦ x ≦ 1) and the like. As the metal _{oxide, GeO, GeO 2, SnO,} SnO 2, PbO, PbO 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, Bi 2 O 3 Bi ₂ O ₄ , Bi ₂ O _{5 and the} like. Examples of the conductive polymer include polyacetylene and poly-p-phenylene.

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

  The non-aqueous electrolyte containing a lithium salt is composed of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolyte, an organic solid electrolyte, or an inorganic solid electrolyte is used. Examples of the non-aqueous electrolyte 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 derivatives, sulfolane, methylsulfolane, 3-methyl -2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3- Ropansaruton, methyl propionate, and a solvent obtained by mixing one or more aprotic organic solvents such as ethyl propionate.

  Examples of the organic solid electrolyte include a polyethylene derivative, a polyethylene oxide derivative or a polymer containing the same, a polypropylene oxide derivative or a polymer containing the same, a phosphate ester polymer, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, Examples thereof include a polymer containing an ionic dissociation group such as polyhexafluoropropylene, and a mixture of a polymer containing an ionic dissociation group and the above non-aqueous electrolyte.

As the inorganic solid electrolytes, nitrides Li, halides, oxygen acid salts, can be used sulfides, for _{example, Li 3 N, LiI, Li} 5 NI 2, Li 3 N-LiI-LiOH, LiSiO 4 _{, LiSiO 4 -LiI-LiOH, Li} 2 SiS 3, Li 4 SiO 4, Li 4 SiO 4 -LiI-LiOH, P 2 S 5, Li 2 S or _{Li 2 S-P 2 S 5} , Li 2 S-SiS ₂ , Li ₂ S—GeS ₂ , Li ₂ S—Ga ₂ S ₃ , Li ₂ S—B ₂ S ₃ , Li ₂ S—P ₂ S ₅ —X, Li ₂ S—SiS ₂ —X, Li ₂ S -GeS in _{2 -X, Li 2 S-Ga} 2 S 3 -X, Li 2 S-B 2 S 3 -X, ( wherein at least X is selected LiI, B ₂ S _3, or from Al ₂ S ₃ One or more).

Further, when the inorganic solid electrolyte is amorphous (glass), lithium phosphate (Li ₃ PO ₄ ), lithium oxide (Li ₂ O), lithium sulfate (Li ₂ SO ₄ ), phosphorus oxide (P ₂ O ₅₎ ), Compounds containing oxygen such as lithium borate (Li ₃ BO ₃ ), Li ₃ PO _4-x N _{2x / 3} (x is 0 <x <4), Li ₄ SiO _4-x N _{2x / 3} (x is Nitrogen such as 0 <x <4), Li ₄ GeO _4-x N _{2x / 3} (x is 0 <x <4), Li ₃ BO _3-x N _{2x / 3} (x is 0 <x <3) The compound to be contained can be contained in the inorganic solid electrolyte. By adding the compound containing oxygen or the compound containing nitrogen, the gap between the formed amorphous skeletons can be widened, the hindrance to movement of lithium ions can be reduced, and ion conductivity can be further improved.

As the lithium salt, those dissolved in the non-aqueous electrolyte are used. For example, LiCl, LiBr, LiI, LiClO ₄ , LiBF ₄ , LiB ₁₀ Cl ₁₀ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate, Examples thereof include salts in which one kind or two or more kinds such as imides are mixed.

  Moreover, the compound shown below can be added to a nonaqueous electrolyte for the purpose of improving discharge, a charge characteristic, and a flame retardance. For example, pyridine, triethyl phosphite, 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 compounds with carbonyl group, hexamethylphosphine Examples include hollic triamide and 4-alkylmorpholine, bicyclic tertiary amines, oils, phosphonium salts and tertiary sulfonium salts, phosphazenes, and carbonates. That. In order to make the electrolyte nonflammable, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride can be included in the electrolyte. In addition, carbon dioxide gas can be included in the electrolytic solution in order to make it suitable for high-temperature storage.

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

  The use of the lithium secondary battery according to the present invention is not particularly limited. For example, a laptop computer, a laptop computer, a pocket word processor, a mobile phone, a cordless cordless handset, a portable CD player, a radio, an LCD TV, a backup power source, and an electric shaver. And electronic devices such as memory cards and video movies, and consumer electronic devices such as automobiles, electric vehicles, and game machines.

In the lithium secondary battery using the lithium cobalt-based composite oxide powder of the present invention as the positive electrode active material, it is not clear why the cycle characteristics are particularly improved. However, as a conventional compound containing the metal atom, oxides of these metals are used. Lithium-cobalt composite oxide powder obtained by using a metal salt or carbonate is considered to be present in which the metal is uniformly dissolved in the interior of the lithium-cobalt composite oxide particles. As a compound containing an atom, a phosphoric acid salt or / and hydrogen phosphate of these metals is used, and a mixture of the compound containing the metal atom, a lithium compound and a cobalt compound is baked. It presents as preferentially oxide on the particle surfaces of the lithium-cobalt composite oxide by the action or the like of PO ₄ in the other components, further of content with this It believed to effectively suppress the elution of Co ⁴⁺ in a lithium-cobalt composite oxide of the causes of deterioration in cycle characteristics of the lithium secondary battery by delicate balance of the amount of the metal atoms that.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to these.
Examples 1 to 3 and Comparative Example 1
Co ₃ O ₄ (average particle size 2 μm) and Li ₂ CO ₃ (average particle size 7 μm) were weighed so that the molar ratio of Co atoms to Li atoms shown in Table 1 was reached, and Mg atoms shown in Table 1 were further measured. Then, commercially available Mg ₃ (PO ₄ ) ₂ · 8H ₂ O (average particle size 10.6 μm) was thoroughly mixed in a dry method so as to have a molar ratio of 5 and then fired at the temperature and time shown in Table 1. The fired product was pulverized and classified to obtain a lithium cobalt composite oxide containing Mg atoms.

Comparative Example 2
Co ₃ O ₄ (average particle size 2 μm) and Li ₂ CO ₃ (average particle size 9 μm) were weighed so that the molar ratio of Co atoms to Li atoms shown in Table 1 was obtained. Commercially available MgO (average particle size 8 μm) was thoroughly mixed in a dry manner so as to obtain an atomic molar ratio, and then fired at the temperatures and times shown in Table 1. The fired product was pulverized and classified to obtain a lithium cobalt composite oxide containing Mg atoms.

Comparative Example 3
Co ₃ O ₄ (average particle size 4.3 μm) and Li ₂ CO ₃ (average particle size 13 μm) were weighed so that the molar ratio of Co atoms to Li atoms shown in Table 1 was obtained. Commercially available MgCO ₃ (average particle size 5.2 μm) was thoroughly mixed in a dry manner so as to obtain a molar ratio of Mg atoms, and then fired at the temperature and time shown in Table 1. The fired product was pulverized and classified to obtain a lithium cobalt composite oxide containing Mg atoms.

Comparative Example 4
Co ₃ O ₄ (average particle size 12.1 μm) and Li ₂ CO ₃ (average particle size 13 μm) were weighed so as to have the molar ratio of Co atom to Li atom shown in Table 1, and thoroughly mixed by dry method. Thereafter, it was baked at 1080 ° C. for 5 hours. The fired product was pulverized and classified to obtain LiCoO ₂ .

(Physical property evaluation of lithium cobalt complex oxide)
The lithium cobalt composite oxide powders obtained in Examples 1 to 3 and Comparative Examples 1 to ₄ were measured for average particle diameter, BET specific surface area and eluted PO ₄ ^2- amount, and the results are shown in Table 2. It was. The average particle size was determined by a laser particle size distribution measurement method, and the amount of PO ₄ ²⁻ eluted was determined by the following method.

(1) Measurement of the amount of PO ₄ ^{2- to be} eluted 30 g of lithium cobalt complex oxide powder is dispersed in 100 ml of pure water at 25 ° C. for 5 minutes to elute PO ₄ ^2- from the particle surface, and the PO in the solution The amount of ₄ ^2- was quantified by ion chromatography.

注）表中のＭｇ含有量は試料を酸で溶解し、その溶解液をＩＣＰにより測定して求めた値である。

Note) The Mg content in the table is a value obtained by dissolving a sample with an acid and measuring the dissolved solution by ICP.

<Battery performance test>
(1) Production of lithium secondary battery;
91% by weight of the lithium cobalt composite oxide powder obtained in Examples 1 to 3 and Comparative Examples 1 to 4, 6% by weight of graphite powder, and 3% by weight of polyvinylidene fluoride were mixed to obtain a positive electrode agent. A kneaded paste was prepared by dispersing in methyl-2-pyrrolidinone. The kneaded paste was applied to an aluminum foil, dried, pressed and punched into a disk with a diameter of 15 mm to obtain a positive electrode plate.
Using this positive electrode plate, a lithium secondary battery was manufactured using each member such as a separator, a negative electrode, a positive electrode, a current collector plate, a mounting bracket, an external terminal, and an electrolytic solution. Among these, a metal lithium foil was used for the negative electrode, and 1 mol of LiPF ₆ dissolved in 1 liter of a 1: 1 kneaded solution of ethylene carbonate and methyl ethyl carbonate was used for the electrolyte.

(2) Battery performance evaluation The produced lithium secondary battery was operated at room temperature under the following conditions, and the following battery performance was evaluated.

<Evaluation of cycle characteristics>
The active materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were applied with an electrode and subjected to a constant current charge / discharge test at 2.7 V to 4.3 V (vs. Li / Li +). The resulting discharge characteristics are shown in FIGS. The charge / discharge current was 0.2 C.
From the results of FIGS. 1 to 7, it can be seen that the active materials obtained in Examples 1 to 3 have better cycle characteristics than the active materials obtained in Comparative Examples 1 to 4. This is presumably because Mg contained in lithium cobaltate remains on the surface as an oxide and coats the surface to suppress elution of Co ions that adversely affect cycle characteristics.

The discharge characteristic figure of the lithium secondary battery which used the lithium cobalt type complex oxide powder obtained in Example 1 as a positive electrode active material. The discharge characteristic figure of the lithium secondary battery which used the lithium cobalt type complex oxide powder obtained in Example 2 as a positive electrode active material. The discharge characteristic figure of the lithium secondary battery which used the lithium cobalt type complex oxide powder obtained in Example 3 as a positive electrode active material. The discharge characteristic view of the lithium secondary battery which used the lithium cobalt type complex oxide powder obtained by the comparative example 1 as a positive electrode active material. The discharge characteristic figure of the lithium secondary battery which used the lithium cobalt type complex oxide powder obtained by the comparative example 2 as a positive electrode active material. The discharge characteristic figure of the lithium secondary battery which used the lithium cobalt type complex oxide powder obtained by the comparative example 3 as a positive electrode active material. The discharge characteristic figure of the lithium secondary battery which used the lithium cobalt type complex oxide powder obtained by the comparative example 4 as a positive electrode active material.

Claims (3)

A lithium compound, a cobalt compound及beauty M g, Al, Zr, in the method for producing a lithium cobalt composite oxide for mixing and firing a compound containing at least one metal atom selected from Ca and Ti, the metal Using the metal phosphate or hydrogen phosphate as the compound containing atoms, the lithium compound, the cobalt compound, and the compound containing the metal atom in a molar ratio to Co atoms, Li atoms 0.90 to 1.20, metal atoms A method for producing a lithium cobalt based composite oxide powder, comprising mixing at 0.001 to 0.04 and firing the resulting mixture. The sintering method for producing a lithium cobalt composite oxide powder of claim 1 wherein performing at 800 to 1,150 ° C.. The method for producing a lithium cobalt composite oxide powder according to claim 1 or 2, wherein the compound containing a metal atom is magnesium phosphate.

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