JP2005060162A - Method for producing lithium-manganese-nickel composite oxide, and positive pole active material for nonaqueous electrolytic secondary battery using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a lithium-manganese-nickel composite oxide with a spinel crystal structure in which a spinel structure single phase wherein the entering of manganese and nickel into their solid solution is sufficiently progressed is realized, and also, a powder state capable of attaining high packing density is secured. <P>SOLUTION: A mixed aqueous solution of an aqueous lithium salt, manganese nitrate and nickel nitrate is admixed with a nonionic aqueous solution organic compound comprising no metallic ions so as to be 1/10M to 1/5M based on M as the total molar number of Li, Mn and Ni, thereafter, moisture and nitrate groups in the mixed aqueous solution are removed under heating at ≥150°C to synthesize a lithium-manganese-nickel composite oxide precursor, and further, the synthesized composite oxide precursor is heat-treated in an oxygen atmosphere. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a lithium manganese nickel composite oxide used for a positive electrode active material for a non-aqueous electrolyte secondary battery. The present invention also relates to a positive electrode active material for a non-aqueous secondary battery that can have a high charge / discharge capacity as a battery.

  In recent years, with the widespread use of portable devices such as mobile phones and laptop computers, there is an increasing demand for small and lightweight secondary batteries with high energy density. Lithium secondary batteries have a discharge potential as high as 4V compared to nickel-cadmium batteries and nickel-hydrogen batteries, which has the advantage of helping to reduce the weight of the equipment and prolong the life of the battery. It is rapidly spreading.

  A lithium ion secondary battery uses a positive electrode that uses a lithium-containing composite oxide as an active material and a material that can occlude and release lithium, such as lithium, a lithium alloy, a metal oxide, or carbon. A negative electrode and a separator or a solid electrolyte containing a non-aqueous electrolyte are the main components.

As a positive electrode material for a lithium secondary battery, lithium cobaltate (LiCoO ₂ ) is used, but since cobalt is limited in resources and expensive, recently, as an alternative to lithium cobaltate, Lithium and manganese compounds (LiMn ₂ O ₄ , LiMnO ₂ ), lithium and nickel compounds (LiNiO ₂ ) and the like have been developed.

Among them, lithium manganese oxide materials having a spinel crystal structure are attracting attention because they are inexpensive and have low toxicity. Examples of the spinel type lithium manganese oxide include Li ₂ Mn ₄ O ₉ , Li ₄ Mn ₅ O ₁₂ , and LiMn ₂ O ₄ .

By the way, in order to increase the energy density of the battery, one method is to use a positive electrode active material having a high potential. In addition, a high voltage of 300 V or higher is required as a power source for electric vehicles. Therefore, when LiCoO ₂ is used as the positive electrode active material, since the operating voltage is about 4.2 V, there is a problem that the number of connected batteries increases. Therefore, it is necessary to use a positive electrode active material having a voltage higher than that of LiCoO _2. However, the spinel type lithium manganese oxide as described above has an operating voltage of 4 V or less, and has a capacity higher than that in the case of using LiCoO _2. In addition, in order to obtain a high voltage of 300 V, there is a problem that the number of connected batteries is further increased than when LiCoO ₂ is used. Therefore, higher voltage is also being studied for spinel type lithium manganese composite oxide. Recently, Li [Mn _3/2 M _1/2 ] O ₄ (where M is Cr, Fe, Co, Ni, Cu, etc.) in which the atomic ratio of manganese to other metals is substantially 3: 1. It is known that the represented composite oxide has a potential around 5 V (Japanese Patent Laid-Open No. 9-147867), and is expected as a positive electrode active material for a 5 V class lithium ion secondary battery.

  However, the above materials are relatively difficult to synthesize, and it has been difficult to achieve both a single phase of the spinel structure and a high packing density by conventional synthesis methods. For example, if a method such as finely pulverized mixing that allows solid solution of manganese and nickel to progress sufficiently, a single phase of spinel structure can be realized, but it becomes difficult to handle due to the small particle size, and the composite after synthesis A high packing density could not be achieved with the oxide. On the other hand, by using a simple solid-phase method to synthesize a complex oxide having a suitable particle size that is suitable as a battery, that is, has a high packing density and is easy to handle, the solid solution of manganese and nickel is reduced. It became insufficient, and a different phase such as nickel oxide was generated, and a spinel structure single phase could not be realized. As a result, the capacity in the high potential region of 4.8 V is reduced, the flatness of the potential is lost, a shelf appears in the low potential region near 4 V, and the positive electrode material with high energy density is not obtained. There was a problem that the generation of gas was remarkable.

  The uniform mixing in the liquid-liquid mixed system represented by the complex polymerization method disclosed in JP-A-2001-185148 is characterized by uniform mixing in the liquid phase. The particle size is very fine and only a low tap density can be obtained. Japanese Patent Laid-Open No. 2001-146426 discloses a method in which lithium, manganese and nickel compounds are pulverized and mixed in a wet manner, and the resulting slurry is spray-dried. However, since the solution of manganese and nickel is inhibited, uniform solid solution does not progress, and as a result, there remains a problem that a shelf appears in a low potential region near 4 V in the charging curve.

  In JP 2002-158007 A, as a raw material of lithium manganese nickel composite oxide, a method of obtaining a manganese nickel composite hydroxide or composite oxide in which a mixed aqueous solution of a manganese salt and a nickel salt is reacted with an alkaline solution and coprecipitated is obtained. Proposed. In this method, ammonium ion donors (ammonium chloride, ammonium carbonate, ammonium fluoride, etc.), hydrazine, ethylenediamine quaternary, which can form complexes with manganese ions and nickel ions in aqueous solution to obtain spherical particles. A complexing agent such as acetic acid, nitritotriacetic acid, uracil diacetic acid or glycine is required, and a step of drying at a high temperature is required to remove the complexing agent. Further, when no complexing agent is added, it is difficult to obtain spherical particles in the range of pH 11 to 13, there are many fine particles, the filterability is poor, and the attached filtrate is difficult to wash and impurities increase. It had problems such as. In addition, molding and pulverizing the lithium manganese nickel composite oxide into pellets causes the spherical particles to collapse and the specific surface area to increase due to the generation of fine powder. Was necessary.

JP-A-9-147867 JP 2001-185148 A JP 2001-146426 A JP 2002-158007 A

  The present invention solves the above-mentioned problems, realizes a spinel structure single phase in which solid solution of manganese and nickel is sufficiently advanced, and secures a powder state capable of achieving a high packing density. A production method for obtaining a lithium manganese nickel composite oxide having the following is provided.

The method for producing a lithium manganese nickel composite oxide according to the present invention has a general formula: Li _{1 + X} Mn ₂ -YX Ni _Y O ₄ (where −0.05 ≦ X ≦ 0.10, 0.45 ≦ Y ≦ 0). .55) in the method for producing a lithium manganese nickel composite oxide having a spinel structure, water-soluble lithium salt, manganese nitrate (Mn (NO ₃ ) ₂ ) and nickel nitrate (Ni (NO ₃ ) ₂ ) are mixed with water. In a mixed aqueous solution obtained by dissolving in water, a nonionic water-soluble organic compound not containing metal ions is 1/10 M or more and 1/5 M or less with respect to the total M of the number of moles of lithium, manganese, and nickel. Then, the lithium manganese nickel composite oxide precursor is synthesized by heating and removing water and nitrate groups of the mixed aqueous solution at a temperature of 150 ° C. or higher, and further, the synthesized By heat treating the case oxide precursor in an oxygen atmosphere, characterized by obtaining a lithium-manganese-nickel composite oxide.

  The nonionic water-soluble organic compound not containing a metal ion is preferably an organic compound having a carboxylic acid group not containing a metal ion. In addition, the organic compound having a carboxylic acid group that does not contain the metal ion is selected from one or more of acetic acid, oxalic acid, and citric acid. Moreover, it is preferable to use lithium nitrate as a water-soluble lithium salt.

  The lithium manganese nickel composite oxide precursor is preferably heat-treated at a temperature of 500 ° C. or higher and lower than 800 ° C.

The positive electrode active material for a non-aqueous electrolyte secondary battery using the lithium manganese nickel composite oxide obtained by the above production method has a general formula: Li _{1 + X} Mn _2-YX Ni _Y O ₄ (however, −0.05 ≦ X ≦ 0.10, 0.45 ≦ Y ≦ 0.55), a spinel structure single phase can be realized, and a tap density of 0.2 to 1.0 m ² / g is obtained. It is done.

  According to the present invention, as a synthesis method for maintaining a uniform mixed state of a metal salt as a raw material of a lithium manganese nickel composite oxide and converting it to a composite oxide, citric acid is added to a metal nitrate mixed aqueous solution to form a gel By using the citric acid gelation combustion method, which is obtained by synthesizing the target compound by low-temperature reaction, the reaction of lithium ions, manganese, and nickel ions can be promoted in a liquid-liquid homogeneous mixed system. A spinel-type lithium manganese nickel composite oxide that achieves a spinel structure single phase with sufficiently advanced solid solution and secures a powder state that can achieve a high packing density can be obtained. A non-aqueous secondary battery active material that can be provided can be provided.

  As a synthesis method for maintaining a uniform mixed state of a metal salt as a raw material of a lithium manganese nickel composite oxide and converting it into a composite oxide, the present inventors added citric acid to a metal nitrate mixed aqueous solution, By using the citric acid gelation combustion method obtained by synthesizing the target compound by low temperature reaction, the reaction of lithium ion, manganese, and nickel ion can be promoted in a liquid-liquid homogeneous mixed system. The present inventors have found that a spinel-type lithium manganese nickel composite oxide that achieves a spinel structure single phase in which solid solution of nickel is sufficiently advanced and has a powder state capable of achieving a high packing density can be obtained. .

A feature of the present invention is a spinel structure represented by the general formula Li _{1 + X} Mn ₂ -YX Ni _Y O ₄ (where −0.05 ≦ X ≦ 0.10, 0.45 ≦ Y ≦ 0.55). In a method for producing a lithium manganese nickel composite oxide having water, a mixed aqueous solution of a water-soluble lithium salt, manganese nitrate (Mn (NO ₃ ) ₂ ) and nickel nitrate (Ni (NO ₃ ) ₂ ) does not contain metal ions. An ionic water-soluble organic compound, for example, an organic compound having a carboxylic acid group not containing metal ions, more specifically acetic acid, succinic acid, citric acid, etc. is added, and then the water and nitrate groups of the mixed aqueous solution are added to 150 The lithium manganese nickel composite oxide is synthesized by heating and removing at a temperature of ℃ or higher and further heat-treating the synthesized lithium manganese nickel compound oxide precursor in an oxygen atmosphere. Lies in the fact.

Citric acid is added to a mixed aqueous solution of water-soluble lithium salt, manganese nitrate (Mn (NO ₃ ) ₂ ) and nickel nitrate (Ni (NO ₃ ) ₂ ) as a nonionic water-soluble organic compound that does not contain metal ions, In this state, when the mixed aqueous solution is heated at a temperature of 150 ° C. or higher, both lithium ions, manganese ions, and nickel ions in the mixed aqueous solution undergo the following reaction as the water evaporates to form citrate and gel. As a result, the ions are fixed and easily reacted, and the ions are uniformly dispersed.

Reaction formula:
M (NO ₃ ) _X + C ₆ H ₈ O ₇ → C ₆ H _8−x O ₇ M _{x / 2} + xNO ₂ + x / 2H ₂ O
(M = Ni, Mn, Li; where x = 1 for Li, and x = 2 for Mn, Ni.)
The reason for using a nonionic water-soluble organic compound that does not contain metal ions in the production method of the present invention is that if metal ions such as potassium and sodium remain, other compounds than lithium manganese nickel composite oxide are synthesized. Because. That is, a nonionic water-soluble organic compound that does not contain metal ions acts as a cation carrier that supports and fixes metal ions. Prevents separation of manganese and nickel nitrate.

  Examples of nonionic water-soluble organic compounds that do not contain metal ions include citric acid and organic compounds having a carboxylic acid group that do not contain metal ions, specifically, acetic acid, oxalic acid, formic acid, tartaric acid, and the like. Of these, citric acid is most preferred. This is because citric acid has a function of rapidly carrying out a combustion reaction with a nitrate metal ion at the time of thermal decomposition of a nitro compound at a low temperature, and supporting and fixing the metal ion by a citrate complex polymerization reaction. Organic compounds having other carboxylic groups such as acetic acid and succinic acid can exhibit the same functions as citric acid, although their functions are inferior. Among these, acetic acid and succinic acid are more preferable.

The addition amount of the nonionic water-soluble organic compound not containing the metal ions is 1/10 M or more and 1/5 M or less with respect to the total M of the number of moles of Li, Mn, and Ni. If it is less than 1 / 10M, the function of supporting and fixing metal ions is not sufficiently exerted, and the ions are not uniformly dispersed. On the other hand, if it exceeds 1 / 5M, nitration does not proceed well. Spinel-type LiMn _1.5 Ni _0.5 O ₄ composite oxide precursor powder cannot be obtained.

  Examples of compounds that can be used as the water-soluble lithium salt include lithium nitrate, lithium hydroxide, lithium hydroxide monohydrate, lithium carbonate, and lithium oxide. However, in the production method according to the present invention, lithium nitrate is preferable in order to smoothly advance the reaction of the metal nitrate mixed aqueous solution and citric acid.

  When the above citric acid compound in the form of gel is heated at 150 ° C. or higher, it decomposes and burns to generate heat. When the generated heat reaches 300 to 350 ° C., synthesis of lithium ions, manganese ions and nickel ions A composite reaction occurs, and a lithium manganese nickel composite oxide precursor in which each element is uniformly dispersed is synthesized.

  The lithium manganese nickel composite oxide precursor is in the form of a sponge and a powder mixture having a broad particle size distribution. Here, when the heating temperature is less than 150 ° C., decomposition or combustion of the nitro compound does not occur, and the lithium manganese nickel composite oxide cannot be synthesized. The heating temperature is not particularly limited as long as moisture is evaporated and the nitro compound is decomposed. From the decomposition temperature of the nitro compound, about 200 ° C. is sufficient at the highest.

  The composite oxide precursor powder thus obtained contains C and N as impurities immediately after synthesis. Therefore, in order to use this composite oxide precursor powder as a positive electrode material for a high voltage / high energy density type lithium secondary battery, it is necessary to remove these impurities.

  Therefore, as a method for producing a spinel type lithium manganese nickel composite oxide from which impurities are removed, the present invention is characterized in that the above-described lithium manganese nickel composite oxide precursor is heat-treated in an oxygen atmosphere. The heat treatment temperature is desirably 500 ° C. or higher and 800 ° C. or lower. Thereby, a spinel type lithium manganese nickel composite oxide with improved discharge capacity and charge / discharge cycle characteristics can be produced. When the heat treatment temperature is lower than 500 ° C., the oxidation does not proceed sufficiently, which is not preferable. When the heat treatment temperature is 800 ° C. or higher, a heterogeneous phase such as NiO is easily generated.

  As described above, according to the production method of the present invention, it is possible to synthesize lithium manganese nickel composite oxide under heat treatment conditions in a lower temperature region than in the prior art.

The spinel type lithium nickel manganese composite oxide obtained by the above production method desirably has a cubic unit cell lattice constant of not less than 8.17Å and less than 8.18Å. The specific surface area of the composite oxide is preferably 0.2 m ² / g or more and 1.0 m ² / g or less. Furthermore, the powder filling density (tap density) is preferably 1.52 g / cm ³ or more. By satisfying these various characteristics, a lithium nickel manganese composite oxide having a spinel structure single phase substantially free of different phases and having a high packing density can be obtained, and the composite oxide can be used as a non-aqueous electrolyte secondary battery. In the nonaqueous electrolyte secondary battery used as the positive electrode active material for a battery, a positive electrode active material for a nonaqueous electrolyte secondary battery in which no shelf appears in the potential region at 3.5 to 4.5 V in the charge / discharge curve is obtained. Here, the shelf refers to a potential step in the 4V region that appears in the descending portion of the discharge curve.

Spinel type lithium nickel manganese composite represented by the general formula: Li _{1 + X} Mn ₂ -YX Ni _Y O ₄ (where −0.05 ≦ X ≦ 0.10, 0.45 ≦ Y ≦ 0.55) A positive electrode using an oxide as a positive electrode active material is, for example, appropriately mixed with the positive electrode active material, if necessary, with a conductive additive, a binder, etc., and made into a paste with a solvent (the binder is dissolved in the solvent in advance). And may be mixed with a positive electrode active material and the like), and the obtained positive electrode mixture-containing paste is applied to a positive electrode current collector made of aluminum foil or the like, and dried to form a positive electrode mixture layer. It is produced by undergoing a step of pressure molding as necessary. However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.

  In producing the positive electrode, as the conductive auxiliary agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black-based material such as acetylene black, ketjen black, or the like can be used. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluorine rubber, styrene butadiene, cellulose resin, polyacrylic acid, or the like can be used.

  Examples of the negative electrode active material that is a counter electrode with respect to the positive electrode containing the positive electrode active material include lithium, lithium alloys represented by lithium-aluminum, graphite, pyrolytic carbons, cokes, glassy carbons, Charged and discharged at a low potential close to carbon-based materials that can reversibly store and release lithium ions, such as fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, alloys such as Si, Sn, In, or Li Compounds such as oxides and nitrides that can be used can also be used as the negative electrode active material.

  When the negative electrode active material is lithium or a lithium alloy, the negative electrode is used as it is or by pressure bonding to a current collector. When the negative electrode active material is a carbon-based material, the negative electrode Add and mix the same binder as in the case, paste it into a paste using a solvent (the binder may be dissolved in the solvent in advance and then mixed with the negative electrode active material), and the obtained negative electrode mixture-containing paste Is applied to a negative electrode current collector made of copper foil or the like, dried to form a negative electrode mixture layer, and subjected to pressure molding as necessary. However, the method for manufacturing the negative electrode is not limited to the above-described examples, and other methods may be used.

  As the electrolyte, either a non-aqueous liquid electrolyte or a gel polymer electrolyte can be used. In the present invention, a liquid electrolyte called an electrolytic solution is usually used frequently. This liquid electrolyte (electrolytic solution) is prepared by, for example, dissolving an electrolyte salt such as a lithium salt in a non-aqueous solvent mainly composed of an organic solvent. Examples of the solvent include dimethyl carbonate and diethyl carbonate. , Chain esters such as methyl ethyl carbonate and methyl propionate, chain phosphate triesters such as trimethyl phosphate, 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, 2-methyl-tetrahydrofuran, diethyl ether, etc. Can be used. In addition, amine organic solvents, sulfur organic solvents such as sulfolane, and the like can also be used.

  Furthermore, it is preferable to use an ester having a high dielectric constant (conductivity of 30 or more) as another solvent component from the viewpoint of improving battery characteristics, particularly load characteristics. Specific examples of the ester having a high dielectric constant include, for example, Ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone and the like, and sulfur-based esters such as ethylene glycol sulfite can also be used, but cyclic esters are preferable, and cyclic carbonates such as ethylene carbonate are particularly preferable. Is preferred. These solvents can be used alone or in combination of two or more.

As an electrolyte salt such as lithium salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 ( SO ₃ ) ₂ , LiN (Rf ₁ SO ₂ ) (Rf ₂ SO ₂ ) [where Rf ₁ and Rf ₂ are substituents containing a fluoroalkyl group], LiN (Rf ₃ OSO ₂ ) (Rf ₄ OSO ₂ ) [where Rf ₃ and Rf ₄ are fluoroalkyl groups], LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiC (Rf ₅ SO ₂ ) ₂ , LiN (Rf ₆ OSO ₂ ) ₂ [Wherein Rf ₅ and Rf ₆ are fluoroalkyl groups], polymer type imidolithium salts and the like are used alone or in admixture of two or more. The concentration of the electrolyte salt in the electrolytic solution is not particularly limited, but the concentration is preferably 0.1 mol / l or more and 2.0 mol / l or less.

  The gel polymer electrolyte corresponds to the above electrolyte solution gelled by a gelling agent. For the gelation, for example, a linear polymer such as polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, or the like thereof is used. Copolymers, polyfunctional monomers that polymerize by irradiation with actinic rays such as ultraviolet rays and electron beams (for example, tetrafunctional or higher functional groups such as pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate, ethoxylated pentaerythritol tetraacrylate, dipentaerythritol hexaacrylate, etc. Acrylates and tetrafunctional or higher methacrylates similar to the above acrylates). However, in the case of a monomer, the monomer itself does not gel the electrolyte solution, but a polymer obtained by polymerizing the monomer acts as a gelling agent.

  When gelling an electrolyte solution using a polyfunctional monomer as described above, if necessary, as a polymerization initiator, for example, benzoyls, benzoin alkyl ethers, benzophenones, benzoylphenylphosphine oxides, acetophenones Thioxanthones, anthraquinones, aminoesters and the like can also be used.

  In the nonaqueous electrolyte secondary battery using the positive electrode active material obtained by the present invention, the discharge capacity is large, the flatness at a high potential is excellent, and the tap density is high. An electrolyte secondary battery can be realized.

(Example 1)
Commercially available lithium nitrate (LiNO ₃ : manufactured by Kanto Chemical), manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O: manufactured by Wako Pure Chemical Industries) and nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O: Wako Pure) Yakuhin Kogyo Co., Ltd.) was weighed in a molar ratio of Li: Mn: Ni = 1.0: 1.5: 0.5 and dissolved in 50 ml of pure water to obtain a mixed aqueous solution. 100 g of a 20% by mass citric acid aqueous solution was added and mixed uniformly as a raw material.

  At this time, the amount of citric acid added was 1/9 M, where M is the molar amount of metal. In addition, 20 mass% citric acid melt | dissolved the commercially available citric acid monohydrate (made by Wako Pure Chemical Industries) with a pure water so that it might become a predetermined mass%.

  The raw material was heated and held with a hot stirrer, and water was removed by heating at a temperature of about 150 ° C. to 200 ° C., whereby decomposition and combustion of nitrate occurred. Synthetic composite reaction of lithium ions, manganese ions, and nickel ions occurred at around 300 to 350 ° C. by the generated heat, and composite oxide precursor powder was obtained.

The obtained composite oxide precursor was analyzed by powder X-ray diffraction using Cu Kα ray. As a result, in addition to the peak attributed to cubic spinel type LiMn _1.5 Ni _0.5 O _4, there was a slight peak of NiO. confirmed.

The obtained composite oxide precursor was calcined at 500 ° C. for 2 hours in a muffle furnace (model KDF HR7: manufactured by Denken), and then calcined in an oxygen atmosphere at 600 ° C. for 20 hours, thereby spinel type LiMn _1.5 Ni _0.5 O _4. Was synthesized. The obtained powder was analyzed by powder X-ray diffraction using Cu Kα ray, and as shown in FIG. 1, it belonged to LiMn _1.5 Ni _0.5 O ₄ having a cubic spinel structure substantially free of different phases. It was a peak.

  Using the obtained active material, a battery was prepared as follows, and the charge / discharge capacity was measured. 52.5 mg of active material, 15 mg of acetylene black and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded to a diameter of 11 mmφ under a pressure of 100 MPa. The produced electrode was dried in a vacuum dryer at 120 ° C. for 10 hours.

The 2032 type button battery shown in FIG. 3 was assembled in a glove box in an Ar atmosphere. Lithium metal having a diameter of 17 mmφ and a thickness of 1 mm was used for the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) using 1M LiPF ₆ as an indicator salt was used for the electrolyte. As the separator, a polyethylene porous film having a film thickness of 25 μm was used. The button battery was allowed to stand for about 10 hours, and after the OCV was stabilized, a charge / discharge test was conducted with a current density of 0.5 mA / cm ² and a cut-off voltage of 4.9V. As a result, as shown in FIG. 2, a lithium ion secondary battery having a large discharge capacity, which has excellent flatness of the charge / discharge potential and eliminates a shelf having a potential of 3.5 to 4.5 V in the charge / discharge curve. I know that there is.

(Example 2)
Spinel type LiMn _1.5 Ni _0.5 O ₄ was synthesized in the same manner as in Example 1, and the obtained lithium manganese nickel composite oxide precursor powder was calcined at 500 ° C. for 2 hours in a muffle furnace (model KDF HR7: manufactured by Denken). Subsequently, spinel-type LiMn _1.5 Ni _0.5 O ₄ was synthesized by baking in an oxygen atmosphere at 700 ° C. for 20 hours. Thereafter, the battery was prepared and evaluated in the same manner as in Example 1. As a result, as shown in FIG. 2, a lithium ion secondary battery having a large discharge capacity, which has excellent flatness of the charge / discharge potential and eliminates a shelf having a potential of 3.5 to 4.5 V in the charge / discharge curve. I know that there is.

(Example 3)
As a nonionic water-soluble organic compound containing no metal ions, 94 g of a 20% by mass aqueous acetic acid solution from commercially available acetic acid CH ₃ COOH (manufactured by Wako Pure Chemical Industries, Ltd.) is added, and the amount of acetic acid added is 1 when the molar amount of metal is M. A spinel type LiMn _1.5 Ni _0.5 O ₄ was synthesized in the same manner as in Example 1 except that it was set to / 3M, and then the battery was produced and evaluated. As a result, in the same manner as in Example 1, the lithium-ion secondary battery having a large discharge capacity, which is excellent in flatness of the charge / discharge potential and in which the potential shelf in the region of 3.5 to 4.5 V is eliminated in the charge / discharge curve. there were.

Example 4
As a nonionic water-soluble organic compound containing no metal ions, 94 g of a 20% by mass aqueous oxalic acid solution is added from commercially available oxalic acid (COOH) ₂ · 2H ₂ O (manufactured by Wako Pure Chemical Industries, Ltd.). Spinel type LiMn _1.5 Ni _0.5 O ₄ was synthesized in the same manner as in Example 1 except that M was set to 1 / 6M, and then the battery was fabricated and evaluated. As a result, in the same manner as in Example 1, the lithium-ion secondary battery having a large discharge capacity, which is excellent in flatness of the charge / discharge potential and in which the potential shelf in the region of 3.5 to 4.5 V is eliminated in the charge / discharge curve. there were.

(Example 5)
Spinel-type LiMn _1.5 Ni _0.5 O ₄ was synthesized in the same manner as in Example 1 except that commercially available lithium oxalate (COOLi) ₂ (manufactured by Wako Pure Chemical Industries, Ltd.) was used as the water-soluble lithium salt. And evaluated. As a result, in the same manner as in Example 1, the lithium-ion secondary battery having a large discharge capacity, which is excellent in flatness of the charge / discharge potential and in which the potential shelf in the region of 3.5 to 4.5 V is eliminated in the charge / discharge curve. there were.

(Example 6)
The composite oxide precursor of lithium manganese nickel was synthesized in the same manner as in Example 1, and the obtained lithium manganese nickel composite oxide precursor powder was temporarily prepared at 500 ° C. for 2 hours in a muffle furnace (model KDF HR7: manufactured by Denken). After the firing, spinel type LiMn _1.5 Ni _0.5 O ₄ was synthesized by firing in an oxygen atmosphere at 800 ° C. for 20 hours. Thereafter, the battery was prepared and evaluated in the same manner as in Example 1. In some batteries, the evaluation was the same as in Example 1. However, as shown in FIG. 2, some batteries had potential shelves in the 3.5 to 4.5 V region.

(Example 7)
The composite oxide precursor of lithium manganese nickel was synthesized in the same manner as in Example 1, and the obtained lithium manganese nickel composite oxide precursor powder was temporarily prepared at 500 ° C. for 2 hours in a muffle furnace (model KDF HR7: manufactured by Denken). After the firing, spinel-type LiMn _1.5 Ni _0.5 O ₄ was synthesized by firing in an oxygen atmosphere for 20 hours at 900 ° C. Thereafter, the battery was prepared and evaluated in the same manner as in Example 1. In some batteries, the evaluation was the same as in Example 1. However, as shown in FIG. 2, some batteries had potential shelves in the 3.5 to 4.5 V region.

(Comparative Example 1)
Lithium (LiNO ₃ : manufactured by Kanto Chemical), manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O: manufactured by Wako Pure Chemical Industries) and nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O: manufactured by Wako Pure Chemical Industries) ) In a molar ratio of Li: Mn: Ni = 1.0: 1.5: 0.5 to prepare a mixed aqueous solution without adding a nonionic water-soluble organic compound containing no metal ions. When heated at 150 ° C. to 200 ° C., the decomposition reaction of nitrate ions did not occur, and the composite oxide precursor powder of spinel type LiMn _1.5 Ni _0.5 O ₄ was not obtained.

(Comparative Example 2)
Commercially available lithium nitrate (LiNO ₃ : manufactured by Kanto Chemical), manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O: manufactured by Wako Pure Chemical Industries) and nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O: Wako Pure) Yakuhin Kogyo Co., Ltd.) was weighed so that Li: Mn: Ni = 1.0: 1.5: 0.5 and dissolved in 50 ml of pure water to obtain an aqueous solution.

100 g of 5% by mass citric acid aqueous solution was added to this as a raw material. At this time, the amount of citric acid added was 1/36 M, where M is the molar amount of metal. In addition, 20 mass% citric acid melt | dissolved the commercially available citric acid monohydrate (made by Wako Pure Chemical Industries) with a pure water so that it might become a predetermined mass%. When heated at 150 ° C. to 200 ° C., decomposition reaction of nitrate ions did not occur, and spinel-type LiMn _1.5 Ni _0.5 O ₄ composite oxide precursor powder was not obtained.

(Comparative Example 3)
Commercially available lithium nitrate (LiNO ₃ : manufactured by Kanto Chemical), manganese nitrate (Mn (NO ₃ ) ₂ .6H ₂ O: manufactured by Wako Pure Chemical Industries) and nickel nitrate (Ni (NO ₃ ) ₂ .6H ₂ O: Wako Pure) Yakuhin Kogyo Co., Ltd.) was weighed so that Li: Mn: Ni = 1.0: 1.5: 0.5 and dissolved in 50 ml of pure water to obtain an aqueous solution.

100 g of a 60% by mass aqueous citric acid solution was added to this as a raw material. At this time, the amount of citric acid added was 1/3 M, where M is the metal molar amount. In addition, 20 mass% citric acid melt | dissolved the commercially available citric acid monohydrate (made by Wako Pure Chemical Industries) with a pure water so that it might become a predetermined mass%. When heated at 150 ° C. to 200 ° C., the decomposition reaction of nitrate ions was insufficient, and a spinel-type LiMn _1.5 Ni _0.5 O ₄ composite oxide precursor powder was not obtained.

2 is an X-ray diffraction pattern of a dry powder of lithium manganese nickel composite oxide obtained in Example 1. FIG. It is a figure which shows the charging / discharging test result of the lithium secondary battery produced by Example 1, Example 2, Example 6, Example 7. FIG. However, in Example 6 and Example 7, the thing where the shelf of the potential appeared in the 4V region was shown. It is a figure which shows the outline of the coin battery used for battery evaluation.

Explanation of symbols

1 Lithium metal anode 2 Separator (electrolyte impregnation)
3 Positive electrode (Evaluation electrode)
4 Gasket 5 Negative electrode can 6 Positive electrode can 7 Current collector

Claims (6)

Lithium manganese nickel having a spinel structure represented by the general formula: Li _{1 + X} Mn ₂ -YX Ni _Y O ₄ (where −0.05 ≦ X ≦ 0.10, 0.45 ≦ Y ≦ 0.55) In the method for producing a composite oxide, a mixed aqueous solution obtained by dissolving water-soluble lithium salt, manganese nitrate, and nickel nitrate in water is mixed with a nonionic water-soluble organic compound that does not contain metal ions. Lithium manganese nickel is added by adding 1 / 10M to 1 / 5M with respect to the total number of moles M, and then removing the moisture and nitrate groups of the mixed aqueous solution by heating at a temperature of 150 ° C. or higher. Production of lithium manganese nickel composite oxide characterized by synthesizing composite oxide precursor and further heat-treating the synthesized composite oxide precursor in an oxygen atmosphere Law.   The method for producing a lithium manganese nickel composite oxide according to claim 1, wherein the nonionic water-soluble organic compound not containing metal ions is an organic compound having a carboxylic acid group not containing metal ions.   The method for producing a lithium manganese nickel composite oxide according to claim 2, wherein the organic compound having a carboxylic acid group not containing metal ions is selected from acetic acid, oxalic acid, and citric acid.   The method for producing a lithium manganese nickel composite oxide according to claim 1, wherein lithium nitrate is used as the water-soluble lithium salt.   The method for producing a lithium manganese nickel composite oxide according to claim 1, wherein the lithium manganese nickel composite oxide precursor is heat-treated at a temperature of 500 ° C or higher and lower than 800 ° C. It is obtained by the method for producing a lithium manganese nickel composite oxide according to claim 1 and has a general formula: Li _{1 + X} Mn _{2 -YX} Ni _Y O ₄ (where -0.05 ≦ X ≦ 0. 10, 0.45 ≦ Y ≦ 0.55), a spinel structure, and a tap density of 0.2 to 1.0 m ² / g is used. A positive electrode active material for a non-aqueous electrolyte secondary battery.

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