JP2005235416A - Lithium manganate for lithium secondary battery cathode sub active material, lithium secondary battery cathode active material, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium manganate for lithium secondary battery cathode sub active material, which provides a lithium secondary battery with excellent overcharge characteristics and battery preservation characteristics, and also to provide a lithium secondary battery cathode active material as well as a lithium secondary battery using the same. <P>SOLUTION: The lithium manganate for the lithium secondary battery cathode sub active material is expressed in a formula: Li<SB>x</SB>MnO<SB>2</SB>, with a pH of 9.0 or more, provided x satisfies 0.9≤x≤1.1, and the lithium secondary battery cathode material as well as the lithium secondary battery contain the same. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

  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)). Since then, research and development on lithium-based composite oxides has been actively promoted, and many proposals have been made so far.

  However, in a lithium secondary battery using a lithium-based composite oxide as a positive electrode active material, a copper foil used as a negative electrode current collector elutes in the electrolyte during overdischarge, and a part of it is deposited on the positive electrode. As a result, there is a problem that charge / discharge characteristics are easily deteriorated. For this reason, a method of preventing an overdischarge itself by providing an electric circuit for preventing overdischarge on the outside of the battery is used. Costs such as packs increase.

On the other hand, a method has also been proposed in which a lithium-based composite oxide such as LiCoO _{2 is} used as a main active material and LiMnO ₂ is added as a subsidiary active material thereto (for example, JP-A-6-349493). LiMnO ₂ used in JP-A-6-349493 is obtained by thoroughly mixing 1 mol of commercially available manganese dioxide and 0.5 mol of lithium carbonate and heat-treating at 800 ° C. for 8 hours in a nitrogen stream. It is what
JP-A-6-349493 (Claim 1, Example 1)

However, in the lithium secondary battery using LiMnO ₂ manufactured by the above method of JP-A-6-349493 as a cathode secondary active material, the overdischarge characteristics are improved to some extent, but the battery has an increase in the internal pressure of the battery due to gas generation. There is a problem that the storage characteristics deteriorate.

  Accordingly, an object of the present invention is to provide a lithium secondary battery positive electrode side active material lithium manganate capable of imparting excellent overdischarge characteristics and battery storage characteristics to a lithium secondary battery, and a lithium secondary battery positive electrode using the same. An object is to provide an active material and a lithium secondary battery.

  In such a situation, the present inventors have conducted extensive research on a positive electrode active material capable of imparting excellent performance to lithium secondary batteries, in particular, excellent overdischarge characteristics. A lithium secondary battery using a layered lithium manganate having a particle size of 9.0 or more and less than 11.0 as a secondary active material has excellent overdischarge characteristics, further suppresses gas generation, and has excellent battery storage characteristics. As a result, the present invention has been completed.

  That is, the first invention according to the present invention is the following general formula (1);

Li _x MnO ₂ (1)
(Wherein x represents 0.9 ≦ x ≦ 1.1), and a lithium manganate for a secondary active material for a positive electrode of a lithium secondary battery having a pH of 9.0 or more and less than 11 is provided. Is.

  Moreover, 2nd invention which concerns on this invention is lithium manganate for lithium secondary battery positive electrode side active materials of said 1st invention, following General formula (2);

Li _a M _{1- b} AbO _c (2)
(Wherein M is at least one transition metal element selected from Co and Ni, A is at least one transition metal element selected from Mg, Al, Mn, Ti, Zr, Fe, Cu, Zn, Sn, In) A metal element, a is 0.9 ≦ a ≦ 1.1, b is 0 ≦ b ≦ 0.4, and c is 1.8 ≦ c ≦ 2.2.) The present invention provides a positive electrode active material for a lithium secondary battery.

  The third invention according to the present invention provides a lithium secondary battery using the lithium secondary battery positive electrode active material.

  The lithium secondary battery using the positive electrode active material containing the lithium manganate of the present invention as a secondary active material has excellent overdischarge characteristics, further suppresses gas generation, and has excellent battery storage characteristics.

The lithium manganate according to the first aspect of the present invention is for a secondary active material used by being added to the positive electrode active material of a lithium secondary battery, and uses X-rays using Cu-Kα rays as the powder source. The following general formula (1) showing a single phase of LiMnO ₂ when diffraction analysis is performed;

Li _x MnO ₂ (1)
(Wherein x represents 0.9 ≦ x ≦ 1.1). It is distinguished from the conventional lithium manganate for lithium secondary battery positive electrode side active material by its pH value. That is, the conventional lithium manganate has a pH of 11 or more, while the lithium manganate of the present invention has a pH of 9.0 or more and less than 11, preferably 9.0 to 10.8. Since the pH of the lithium manganate of the present invention is in the above-mentioned range, the lithium secondary battery using the lithium manganate as a secondary active material is provided with excellent overdischarge characteristics, and further suppresses gas generation and has battery storage characteristics. Can be improved.

  In the present invention, this pH value is obtained by adding 100 g of pure water to 5 g of the lithium manganate powder, stirring the mixture at 25 ° C. for 5 minutes, and then measuring the pH of the supernatant with a pH meter.

Furthermore, the lithium manganate for a secondary active material for a positive electrode of a lithium secondary battery of the present invention has an average particle size determined by a laser diffraction method of 1 to 50 μm, preferably 4 to 20 μm, particularly preferably 4 to 5 in addition to the above pH characteristics. A thickness of 10 μm is preferable in that polarization and poor conduction can be suppressed. Further, BET specific surface area of 0.1~2.0m ² / g, preferably preferably in that it can suppress is the Mn elution with 0.3~1.0m ² / g.

Examples of a method for producing lithium manganate for a positive electrode secondary active material for a lithium secondary battery include a method of washing LiMnO ₂ obtained by a known method with water (water washing method), or a lithium compound and a manganese compound. A first baking in an oxygen-containing atmosphere, and then a second baking at a temperature higher than the first baking temperature in a substantially inert atmosphere (multistage baking). Method). In the water washing method, an alkaline component contained in a known LiMnO ₂ having a pH of 11 or more is washed away with water to obtain a pH of 9.0 or more and less than 11.0.

Specific examples of the multistage firing method include a lithium compound such as lithium carbonate and lithium hydroxide and a manganese compound such as manganese oxide and manganese carbonate in a molar ratio of Li atom to Mn atom (Li / Mn) of 0.9 to 1. .1, preferably 0.98 to 1.02, and then the mixture is brought to an atmosphere having an oxygen content of 1% by volume or more, preferably 5 to 21% by volume while supplying oxygen or air to the firing furnace. Li ₂ MnO ₃ having excellent reactivity with a lithium compound after firing at 400 to 750 ° C., preferably 550 to 650 ° C. for 1 hour or longer, preferably 3 hours or longer, particularly preferably 5 to 20 hours; a lithium-manganese composite oxide of LiMn ₂ O _4, 1 or more kinds of man selected from _MnO 2, _Mn 2 _{O 3} and _Mn 3 _{O 4} is irreversibly produced in this case the reaction A mixture with an oxide of oxide (hereinafter referred to as “reaction precursor”), and then an oxygen content such as inert gas or vacuum is 0.1% by volume, preferably 0.06% by volume. A method of converting the reaction precursor to lithium manganate represented by the general formula (1) by baking at 800 to 1100 ° C., preferably 900 to 1000 ° C. for 3 hours or more, preferably 5 to 20 hours in the following atmosphere: Is mentioned. In the present invention, among these methods for producing lithium manganate, a multi-stage firing method is easily obtained with a stable pH value in that lithium manganate obtained by the method does not cause an increase in the amount of adsorbed water. Particularly preferred in terms.

Next, the lithium secondary battery positive electrode active material according to the second invention of the present invention contains the lithium composite oxide represented by the general formula (2) and the secondary active material. The lithium composite oxide represented by the general formula (2) is not particularly limited. In the general formula (2), a preferable metal of M is Co, and a preferable metal of A is Mn. Examples include LiCoO ₂ , LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O _{2 and the} like, and these lithium composite oxides can be used alone or in combination. Of these, LiCoO ₂ is particularly preferred because it is widely used industrially and has a high synergistic effect with the lithium manganate of the present invention.

The physical properties and the like of the lithium composite oxide are not particularly limited, but the average particle size determined by the laser method is 1 to 50 μm, preferably 3 to 20 μm, particularly preferably 3 to 10 μm. An average particle size within this range is preferable in that polarization and poor conduction can be suppressed. Further, BET specific surface area of 0.1~2.0m ² / g, preferably from 0.2~1.0m ² / g. A BET specific surface area within this range is preferable in that elution of Mn can be suppressed.

  Further, the lithium composite oxide is obtained by adding 100 g of pure water to 5 g of the lithium composite oxide powder, stirring for 5 minutes at 25 ° C., and then measuring the pH of the supernatant with a pH meter, preferably less than 11. 9 to 10.8 is preferable in that gas generation during high-temperature storage can be further suppressed.

  The mixing ratio of the secondary active material of the present invention is 5 to 30 parts by weight, preferably 10 to 20 parts by weight with respect to 100 parts by weight of the lithium composite oxide. When the content ratio of the secondary active material is larger than 30 parts by weight, the discharge capacity is decreased. On the other hand, when the content is smaller than 5 parts by weight, the effect of suppressing overdischarge cannot be obtained sufficiently.

  The lithium secondary battery positive electrode active material of the present invention is produced by uniformly mixing a predetermined amount of the lithium composite oxide and the secondary active material. The mixing means is not particularly limited, and the mixing means is prepared by a mechanical means in which a strong shearing force is applied by a wet method or a dry method so as to obtain a uniform composition in the above ratio. The wet method is operated by an apparatus such as a ball mill, a disper mill, a homogenizer, a vibration mill, a sand grind mill, an attritor, and a powerful stirrer. On the other hand, in the dry method, apparatuses such as a high speed mixer, a super mixer, a turbo sphere mixer, a Henschel mixer, a nauter mixer, and a ribbon blender can be used. These uniform blending operations are not limited to the illustrated mechanical means. If desired, the particle size may be adjusted by grinding with a jet mill or the like.

  A lithium secondary battery according to a third aspect of 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 nonaqueous 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. The lithium secondary battery according to the present invention is obtained by uniformly applying the lithium composite oxide as the positive electrode active material and the lithium manganate as the secondary active material to the positive electrode. Is unlikely to occur.

  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 a configured battery. For example, graphite such as natural graphite and artificial graphite, carbon black, acetylene black, ketjen black, channel black, Carbon blacks such as furnace black, lamp black and thermal black, conductive fibers such as carbon fiber and metal fiber, metal powders such as carbon fluoride, aluminum and nickel powder, conductivity such as zinc oxide and potassium titanate Examples thereof include conductive materials such as whiskers, conductive metal oxides such as titanium oxide, and polyphenylene derivatives. Examples of natural graphite include scaly graphite, scaly graphite, and earthy graphite. These conductive agents 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. The filler is not particularly limited as long as it is a fibrous material that does not cause a chemical change in the constructed battery. For example, olefinic polymers such as polypropylene and polyethylene, 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 the constituted battery, but the positive electrode potential (about 3.5 V vs. Li / The present invention is most effective for those which are oxidized and dissolved by Li +). Further, the surface of the material may be oxidized and used, or the surface of the current collector 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 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. In addition, when solid electrolytes, such as a polymer, are used as electrolyte mentioned later, a solid electrolyte may 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 electrolyte, a nitride, halide, oxyacid salt, or the like of Li can be used. 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, Li 3 PO 4 -Li 2 S-SiS 2, and the like phosphorus sulfide compound.

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 configured in this manner is a lithium secondary battery that has excellent overdischarge characteristics, further suppresses gas generation, and has excellent battery storage characteristics. The shape of the battery may be any shape such as a button, a sheet, a cylinder, a corner, or a coin shape. In addition, the lithium secondary battery of the present invention includes, for example, a notebook 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, a video movie It can be suitably used for consumer electronic devices such as electronic devices such as automobiles, electric vehicles, and game devices.

  EXAMPLES Next, although an Example is given and this invention is demonstrated more concretely, this is only an illustration and does not restrict | limit this invention.

<Preparation of LiMnO ₂ >
・ Samples A, B, C
Electrolytic manganese dioxide (FMH, average particle size 6 μm; manufactured by Tosoh Corporation) was calcined in the atmosphere at 600 ° C. for 5 hours to prepare Mn ₂ O ₃ (average particle size 6 μm). Next, 40.0 g of Mn ₂ O ₃ prepared above and 18.7 g of lithium carbonate (average particle size 5 μm; manufactured by SQM) were dry-mixed in a household coffee mill, and an alumina crucible at a feed rate of 1 L / min. The temperature is raised to 600 ° C. at a temperature rising rate of 200 ° C./h while being fed into the inside, and then at a temperature rising rate of 200 ° C./h while feeding nitrogen gas into the alumina crucible at a feeding rate of 1 L / min. The temperature was raised to 800 ° C. and kept at 800 ° C. for 12 hours. Next, while introducing nitrogen gas into the alumina crucible at a supply rate of 1 L / min, the mixture was cooled to room temperature at a temperature decrease rate of 200 ° C./h and then pulverized to obtain a greenish brown powder. When the obtained green-brown powder was identified by a crystal phase by XRD, it was confirmed to be a LiMnO ₂ single phase (sample A).

Next, 100 g of pure water was added to 5 g of LiMnO ₂ powder, and after stirring at 120 rpm for 5 minutes at 25 ° C., the pH of the supernatant was measured with a pH meter. As a result, the pH was 11.5. Further, this LiMnO ₂ powder was washed with water to prepare LiMnO ₂ powder having a pH of 10.9 (sample C) and 11.2 (sample B), and various physical properties of these LiMnO ₂ samples are shown in Table 1.

・ Sample D
Electrolytic manganese dioxide (FMH, average particle size 6 μm; manufactured by Tosoh Corporation) was calcined in the atmosphere at 600 ° C. for 5 hours to prepare Mn ₂ O ₃ (average particle size 6 μm). Next, 40.0 g of Mn ₂ O ₃ prepared above and 18.7 g of lithium carbonate (average particle size 5 μm; manufactured by SQM) were dry-mixed in a household coffee mill, and the alumina crucible was fed at a feed rate of 1 L / min. The temperature is increased to 600 ° C. at a temperature increase rate of 200 ° C./h while being supplied into the inside, and then the air is switched to nitrogen gas and 200 ° C./h is supplied while being supplied into the alumina crucible at a supply rate of 1 L / min. The temperature was raised to 800 ° C. at a rate of temperature rise, and kept at 800 ° C. for 12 hours. Next, while introducing nitrogen gas into the alumina crucible at a supply rate of 1 L / min, the mixture was cooled to room temperature at a temperature decrease rate of 200 ° C./h and then pulverized to obtain a greenish brown powder. When the obtained green-brown powder was identified by a crystal phase by XRD, it was confirmed to be a LiMnO ₂ single phase (sample D). The main physical properties of the obtained LiMnO ₂ are shown in Table 1. The pH was measured by the same method as described above.

<Lithium composite oxide (preparation of main active material)>
40.0 g of Co ₃ O ₄ (average particle size 5 μm) and 8.38 g of Li ₂ CO ₃ (average particle size 5 μm) were weighed, thoroughly mixed by a dry process, and calcined at 1000 ° C. for 5 hours. The fired product was pulverized and classified to obtain LiCoO ₂ . Various physical properties of this product are shown in Table 2. The pH was measured by the above method.

Examples 1-2 and Comparative Examples 1-3
The various LiMnO ₂ (sub-active material) prepared above and the lithium composite oxide (main active material) prepared above were sufficiently mixed in a household coffee mill at the blending ratios shown in Table 3 to produce various positive electrode actives. The material was prepared.

<Preparation of lithium secondary battery>
<Battery performance test>
(1) Production of lithium secondary battery;
91% by weight of the positive electrode active material (main active material + secondary active material) of Examples 1-2 and Comparative Examples 1-3 prepared as described above, 6% by weight of graphite powder, and 3% by weight of polyvinylidene fluoride were mixed. A kneading paste was prepared by dispersing in N-methyl-2-pyrrolidinone as a positive electrode agent. The kneaded paste was applied to an aluminum foil, dried, pressed and punched into a disk having a diameter of 15 mm to obtain a positive electrode plate. Using this positive electrode plate, a 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. Of these, artificial graphite was used for the negative electrode, copper was used for the current collector, and 1 mol of LiPF ₆ was dissolved in 1 liter of a 1: 1 kneaded solution of ethylene carbonate and methyl ethyl carbonate as the electrolyte.

(2) Overdischarge test For the batteries of Examples 1 and 2 and Comparative Examples 1 to 3, the battery was charged to 4.2 V at a current of 1 CmA at 25 ° C., charged at a constant voltage of 4.2 V for 3 hours, and then 1 CmA. The discharge capacity (hereinafter referred to as “initial discharge capacity”) when discharged to 2.0 V at a current of 1 mm was measured. Next, the battery was allowed to stand for 2 days at a constant voltage of 0 V and overdischarged. After being left standing, it was recharged at a constant current and a constant voltage at 1 CmA and 4.2 V for 3 hours, and then a constant current was discharged at 1 CmA to 2.0 V, and a discharge capacity (hereinafter referred to as “recovery capacity”) was measured. For this recovery capacity, the ratio of the recovery capacity to the initial discharge capacity measured in the previous discharge test (hereinafter referred to as “capacity recovery rate”) was determined and shown in Table 4. Further, the battery after the test was disassembled and the positive electrode was observed to observe whether copper of the negative electrode current collector was deposited on the positive electrode. The results are shown in Table 4.

(3) Gas generation test In addition, after charging the lithium secondary battery prepared above to 4.2 V at a current of 1 CmA at 25 ° C., it was kept in a constant temperature bath at 4.2 ° C. while being held at a constant voltage of 4.2 V. Hold for 10 days. Next, the battery was disassembled, and the generated gas was collected in water in a cylinder and the amount of gas generated was measured. The results are shown in Table 4.

  From the results of Table 4, it can be seen that the lithium secondary battery using the lithium manganate of the present invention as a secondary active material has improved overdischarge characteristics, further reduced gas generation, and improved battery storage characteristics. .

Claims (9)

The following general formula (1);
Li _x MnO ₂ (1)
(Wherein x represents 0.9 ≦ x ≦ 1.1) and the pH is 9.0 or more and less than 11, manganese for lithium secondary battery positive electrode side active material Lithium acid. The lithium manganate for a secondary active material for a positive electrode of a lithium secondary battery according to claim 1, wherein the average particle size is 1 to 50 µm. The lithium manganate for a secondary active material for a positive electrode of a lithium secondary battery according to claim 1, wherein the BET specific surface area is 0.1 to 2.0 m ² / g. The lithium manganate for a lithium secondary battery positive electrode side active material according to any one of claims 1 to 3, and the following general formula (2);
Li _a M _{1- b} AbO _c (2)
(Wherein M is at least one transition metal element selected from Co and Ni, A is at least one transition metal element selected from Mg, Al, Mn, Ti, Zr, Fe, Cu, Zn, Sn, In) A metal element, a is 0.9 ≦ a ≦ 1.1, b is 0 ≦ b ≦ 0.4, and c is 1.8 ≦ c ≦ 2.2.) A positive electrode active material for a lithium secondary battery, comprising: The lithium secondary oxide positive electrode active material according to claim 4, wherein the lithium composite oxide has an average particle diameter of 1 to 50 μm. The lithium secondary oxide positive electrode active material according to claim 4 or 5, wherein the lithium composite oxide has a BET specific surface area of 0.1 to 2.0 m ² / g. The lithium secondary oxide positive electrode active material according to any one of claims 4 to 6, wherein the lithium composite oxide has a pH of 9.0 or more and less than 11. The lithium secondary battery positive electrode active material according to claim 4, wherein the lithium composite oxide is LiCoO ₂ . A lithium secondary battery using the lithium secondary battery positive electrode active material according to any one of claims 4 to 8.