JP4411157B2 - Lithium manganese nickel composite oxide, method for producing the same, and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a method for producing a lithium manganese nickel-based composite oxide. The lithium manganese nickel-based composite oxide obtained by the production method of the present invention is particularly useful as a positive electrode active material for a lithium secondary battery.

The present applicant has previously proposed a method for producing a lithium manganese composite oxide useful as a positive electrode active material of a lithium secondary battery (see Patent Documents 1 and 2). The lithium manganese composite oxide obtained by this production method has an advantage that the storage capacity characteristics of the lithium secondary battery are improved because the elution amount of manganese ions is small even when contacting with the non-aqueous electrolyte. However, in a lithium secondary battery using the lithium manganese composite oxide as a positive electrode active material, charging and discharging cycle characteristics are greatly deteriorated when charging is performed at a voltage exceeding 4.3 V to increase the discharge capacity. was there.
Therefore, for the purpose of improving charge / discharge cycle characteristics, a lithium manganese nickel composite oxide in which a part of manganese in the lithium manganese composite oxide is replaced with another transition metal element such as nickel has been proposed (Patent Documents 3 to 3). 5). Among these lithium manganese nickel composite oxides, a lithium secondary battery using a Li [Mn _3/2 Ni _1/2 ] O ₄ composition as a positive electrode active material has excellent charge / discharge cycle characteristics. There are advantages such as being able to generate a high voltage.

JP 2001-122626 A JP 2002-226213 A JP 2001-185148 A JP 2002-158007 A JP 2003-81637 A

However, in a lithium secondary battery using a conventional lithium manganese nickel-based composite oxide as a positive electrode active material, the coulomb efficiency, the discharge capacity retention ratio, and the ratio of 5 V discharge capacity region / (5 V discharge capacity region + 4 V discharge capacity region) are low. The battery performance as expected was not obtained.
Accordingly, an object of the present invention is to provide excellent charge / discharge cycle characteristics when used as a positive electrode active material of a lithium secondary battery, and to provide Coulomb efficiency, discharge capacity retention ratio, and 5V discharge capacity region / (5V discharge capacity region + 4V discharge). An object of the present invention is to provide a lithium manganese nickel-based composite oxide that can be a lithium secondary battery having a high capacity region ratio, a method for producing the same, and a lithium secondary battery using the same.

Therefore, as a result of intensive studies on composite oxides obtained by changing starting materials and reaction temperatures, the present inventors have obtained a mixture containing a specific metal element by firing twice in a specific temperature range. By using lithium manganese nickel-based composite oxide as a positive electrode active material of a lithium secondary battery, it has excellent charge / discharge cycle characteristics, coulomb efficiency, discharge capacity retention ratio, 5V discharge capacity region / (5V discharge capacity region + 4V discharge capacity The present inventors have found that the ratio of (region) can be improved and have completed the present invention.
That is, the present invention is a method for producing a lithium manganese nickel-based composite oxide represented by the following general formula (1):
Li _x Mn _1.5-y Ni _{0.5-z My + z} O _4-w (1)
(Wherein 0.9 <x <1.1, y> 0, z> 0, 0 <y + z <0.1, 0 ≦ w <2, M is selected from magnesium, aluminum, titanium and zirconium) Represents at least one metal element.)
The lithium manganese nickel characterized by firing a mixture containing lithium, manganese, nickel and M at 950 to 1050 ° C., cooling to obtain a precursor, and then re-firing the precursor at 550 to 650 ° C. It is a manufacturing method of a system complex oxide.

The present invention also provides a lithium manganese nickel-based composite oxide characterized in that the mixture containing lithium, manganese, nickel and M comprises a lithium compound, a composite compound of manganese and nickel, and a compound containing M. Is the method.
The present invention also provides a method for producing a lithium manganese nickel-based composite oxide, wherein the precursor has a BET specific surface area of 0.2 to 0.6 m ² / g.
Moreover, this invention is a manufacturing method of the lithium manganese nickel type complex oxide characterized by the average particle diameter of the said precursor being 5-15 micrometers.
The present invention also provides the method for producing a lithium manganese nickel-based composite oxide, wherein M is magnesium or titanium.

  Moreover, this invention is a lithium manganese nickel type complex oxide manufactured by the said method.

  Moreover, this invention is a lithium secondary battery provided with the positive electrode containing the said lithium manganese nickel type complex oxide.

  In the present invention, the molar ratio 1.5 of Mn in the formula of the lithium manganese nickel composite oxide includes an error range of ± 0.05, and the molar ratio 0.5 of Ni is an error range of ± 0.05. Is included.

  ADVANTAGE OF THE INVENTION According to this invention, it can be set as the lithium secondary battery which is excellent in charging / discharging cycling characteristics, and whose ratio of Coulomb efficiency, discharge capacity maintenance factor, and 5V discharge capacity area / (5V discharge capacity area + 4V discharge capacity area) is high. A lithium manganese nickel composite oxide can be provided.

Hereinafter, the present invention will be described based on preferred embodiments thereof.
The lithium manganese nickel composite oxide produced according to the present invention is a spinel type oxide represented by the following general formula (1).
Li _x Mn _1.5-y Ni _{0.5-z My + z} O _4-w (1)
(Wherein 0.9 <x <1.1, y> 0, z> 0, 0 <y + z <0.1, 0 ≦ w <2, M is selected from magnesium, aluminum, titanium and zirconium) Represents at least one metal element.)

  This lithium manganese nickel-based composite oxide is a step of firing a mixture containing lithium, manganese, nickel and M at 950 to 1050 ° C. and cooling to obtain a precursor (hereinafter sometimes referred to as a first firing step), The precursor obtained in the first firing step can be produced by a method including a step of re-baking at 550 to 650 ° C. (hereinafter sometimes referred to as a second firing step).

The starting material used in the present invention is a mixture containing lithium, manganese, nickel and M. Examples of the mixture as the starting material include the following, and can be arbitrarily selected.
(A) A mixture comprising a complex compound of manganese and nickel, a lithium compound and a compound containing M.
(B) A mixture comprising a compound containing a manganese compound, a nickel compound, a lithium compound and M.
Examples of the composite compound of manganese and nickel in the above (a) include a composite hydroxide of manganese and nickel, a composite oxyhydroxide, a composite carbonate, and a composite oxide. Alternatively, two or more kinds can be used in combination. More specifically, the composite hydroxide and the composite oxyhydroxide can be used in combination. Among these complex compounds, it is preferable to use a complex hydroxide or a complex oxyhydroxide from the viewpoint of suppressing by-products. In these composite compounds, the atomic ratio of manganese to nickel is preferably Mn: Ni = 72.5: 27.5 to 77.5: 22.5, and Mn: Ni = 75: 25 Is more preferable. This is because, when the proportion of manganese is too small, the discharge capacity per unit weight of the positive electrode active material decreases, and when the proportion of nickel is too small, the 4V discharge capacity region (undesirable discharge) increases.

The complex compound can be prepared, for example, by a coprecipitation method. More specifically, the composite hydroxide is prepared by coprecipitation of the composite hydroxide by mixing a mixed aqueous solution containing a manganese compound and a nickel compound, a complexing agent aqueous solution, and an alkaline aqueous solution. can do. At that time, the mixing ratio of the manganese compound and the nickel compound in the mixed aqueous solution is preferably the atomic ratio of manganese and nickel in the obtained composite hydroxide, preferably Mn: Ni = 72.5: 27.5-77.5. : 22.5, more preferably Mn: Ni = 75: 25.
Examples of the manganese compound used here include water-soluble salts of manganese such as manganese sulfate, manganese nitrate, and manganese chloride. Examples of the nickel compound include water-soluble salts of nickel such as nickel sulfate, nickel nitrate, and nickel chloride.
As the complexing agent, those capable of forming a complex with manganese and nickel are used. For example, ammonium ion sources (ammonia, ammonium chloride, ammonium carbonate, ammonium fluoride), hydrazine, ethylenediaminetetraacetate, glycine and the like can be mentioned.
During the coprecipitation operation, the pH of the reaction solution is maintained in the range of about 9-13. The pH can be maintained, for example, by adding an aqueous alkali solution such as sodium hydroxide or potassium hydroxide.

Moreover, as another method for preparing the composite hydroxide, for example, a method described in JP-A-2002-201028 can be used. More specifically, a nickel salt containing a cobalt salt (cobalt (II) ion) and a manganese salt (manganese (II) ion) in an inert gas atmosphere or in the presence of a reducing agent while sufficiently stirring the reaction vessel. It can be prepared by continuously supplying an aqueous solution, a complexing agent and an alkali metal hydroxide, continuously growing crystals, and continuously taking out the resulting precipitate.
It is preferable to keep the salt concentration in the reaction vessel within ± 5 mS / cm in the range of 50 to 200 mS / cm and the ammonium ion concentration within ± 0.5 g / L in the range of 1 to 10 g / L. Further, it is preferable that the reaction pH is maintained within ± 0.05 in the range of 11.0 to 13.0, and the reaction temperature is maintained within ± 0.5 ° C within the range of 25 to 80 ° C. Examples of the salt concentration regulator include sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, ammonium hydrochloride, and ammonium sulfate. Examples of calcium salts include nitrates, acetates and oxalates.

  The composite oxyhydroxide can be prepared by obtaining a composite hydroxide precipitate according to the above-described method, and then blowing air into the reaction solution to oxidize the composite hydroxide.

  The composite oxide can be prepared by obtaining a precipitate of the composite hydroxide according to the above-described method and then heat-treating the precipitate at, for example, 200 to 500 ° C.

  The composite carbonate is prepared by coprecipitation of the composite carbonate by mixing a mixed aqueous solution containing a manganese compound and a nickel compound, an aqueous solution of a complexing agent, and an aqueous solution of an alkali carbonate or hydrogen carbonate. Can do. The composite carbonate can also be prepared by introducing carbon dioxide into the mixed aqueous solution. At that time, the mixing ratio of the manganese compound and the nickel compound in the mixed aqueous solution is preferably the atomic ratio of manganese and nickel in the obtained composite carbonate, preferably Mn: Ni = 72.5: 27.5-77.5: 22.5, more preferably Mn: Ni = 75: 25. Examples of the alkali carbonate or hydrogen carbonate alkali used here include sodium carbonate, potassium carbonate, sodium hydrogen carbonate and the like.

  On the other hand, examples of the manganese compound in (b) include manganese oxides, hydroxides, oxyhydroxides, and carbonates, and these may be used alone or in combination of two or more. it can. Examples of nickel compounds include nickel oxides, hydroxides, oxyhydroxides, and carbonates, and these can be used alone or in combination of two or more. However, it is preferable to use the same type of manganese compound and nickel compound. For example, when an oxide is used as the manganese compound, it is preferable to use an oxide as the nickel compound. A particularly preferred combination is a combination of manganese dioxide and nickel oxide.

  Examples of the lithium compound used in (a) and (b) include lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxide. Among these, industrially easily available and inexpensive. To lithium carbonate is preferred.

  Further, the compound containing M used in (A) and (B) is a compound containing at least one metal element selected from magnesium, aluminum, titanium and zirconium, and a specific compound containing M is M An oxide, carbonate, organic acid salt, etc. are mentioned, These can be used individually or in combination of 2 or more types.

  Any of these compounds may have any production history, but it is preferable that the content of impurities is small in order to produce a high-purity lithium manganese nickel-based composite oxide. In order to improve the reactivity, it is preferable to use a fine compound. In many cases, the average particle size obtained from the laser particle size distribution measurement method is 5 to 15 μm, and 8 to 12 μm. Is preferred. If the average particle diameter of the compound is within the above range, a mixture in which the compound is uniformly dispersed can be obtained, whereby a single-phase lithium manganese nickel-based composite oxide can be obtained by X-ray diffraction, which is preferable.

  In the production method according to the present invention, it is possible to use a mixture of (a) as a starting material in a lithium secondary battery using a lithium manganese nickel-based composite oxide as a positive electrode active material. It is preferable because cycle characteristics can be obtained.

In the production method according to the present invention, first, (b) a compound containing manganese and nickel, a compound containing lithium compound and M, or (b) a compound containing manganese compound, nickel compound, lithium compound and M is mixed, A mixture in which these compounds are uniformly dispersed is obtained. This mixing may be either a dry method or a wet method, but a dry method is preferred because it is easy to produce.
The compounding ratio of each compound in the mixture is such that the molar ratio of Li / (Mn + Ni + M) is 0.45 to 0.55, preferably 0.495 to 0.505, and the stoichiometric ratio is 0.5. It is particularly preferable to set the values as close as possible. Further, the molar ratio of M / (Mn + Ni) is 0.0005 to 0.05, preferably 0.001 to 0.025. The reason for this is that when the ratio is less than 0.0005, the effect of adding a compound containing M is reduced. On the other hand, when the ratio exceeds 0.05, the effect of adding a compound containing M is not only saturated but also the discharge capacity tends to decrease. Because.

Next, the first firing step will be described.
In the first firing step, the mixture containing lithium, manganese, nickel and M is fired at 950 to 1050 ° C, preferably 975 to 1025 ° C, more preferably 975 to 1000 ° C. The first firing step is generally performed in the atmosphere. And this mixture turns into a precursor by this baking. This precursor has the same composition as the spinel type lithium manganese nickel composite oxide represented by the general formula (1). In the present invention, the lithium manganese nickel composite obtained in the first firing step is used. The oxide is called a precursor, and is distinguished from a lithium manganese nickel-based composite oxide obtained in the second firing step described later.
The reason why the firing temperature in the first firing step is within the above range is that if the temperature is less than 950 ° C., the charge / discharge cycle characteristics are good, but the amount of manganese elution increases rapidly, while if the temperature exceeds 1050 ° C., the charge / discharge This is because the cycle characteristics deteriorate. In addition, the temperature increase rate and the temperature decrease rate in the first firing step are preferably 30 ° C./h to 300 ° C./h. If the rate of temperature increase and the rate of temperature decrease is less than 30 ° C./h, the production efficiency may be reduced. If the rate exceeds 300 ° C./h, not only the desired battery performance will be difficult to obtain, but also cracks in the firing pot (furnace) Is likely to occur.

In the first firing step, controlling the specific surface area of the obtained precursor is advantageous in obtaining a lithium manganese nickel-based composite oxide with a small amount of manganese elution. Specifically, the BET specific surface area of the starting material, that is, a mixture containing lithium, manganese, nickel and M is generally 10 to 15 m ² / g, and this is calcined in the above temperature range, whereby the precursor BET it is preferable that the specific surface area and 0.2~0.6m ² / g, and more preferably set to 0.2-0.4 m ² / g. In order to obtain a precursor having a BET specific surface area in such a range, the firing time may be appropriately adjusted at a temperature within the above range, more specifically 8 to 30 hours, particularly 12 to 20 hours. It is preferable.

Furthermore, in addition to the BET specific surface area, the precursor preferably has an average particle size determined by a laser particle size distribution measurement method of 5 to 15 μm, more preferably 8 to 12 μm. If the average particle diameter of the precursor is within the above range, it is particularly preferable since it falls within the range of suitable electrode density, TAP density and specific surface area, and further battery performance such as charge / discharge cycle characteristics is improved. In order to obtain a precursor having an average particle size in such a range, a starting material within the range of the average particle size may be used and the reaction may be performed at the baking temperature and baking time.
The precursor obtained here is once cooled. Cooling temperature shall be 50 degrees C or less, and it cools to room temperature simply.

Next, a 2nd baking process is demonstrated.
In the second firing step, the precursor obtained in the first firing step is fired at 550 to 650 ° C, preferably 600 to 650 ° C. Compared with the precursor obtained in the first firing step by this firing, the elution amount of manganese is reduced, and 5 V discharge capacity in a lithium secondary battery using the obtained lithium manganese nickel-based composite oxide as a positive electrode active material The ratio of region / (5V discharge capacity region + 4V discharge capacity region) can be improved. This is probably because the structure of oxygen deficiency in the spinel is repaired, and trivalent manganese, which is considered to be the cause of elution, is changed to tetravalent manganese, which is considered to be difficult to elute. Moreover, the coulomb efficiency improves by changing trivalent manganese into tetravalent manganese. That is, it is considered that the irreversible capacity is reduced.
The reason for setting the firing temperature in the second firing step to be in the above range is that if the temperature is less than 550 ° C. or exceeds 650 ° C., the trivalent manganese that forms the 4V discharge region changes to the tetravalent manganese that forms the 5V discharge region. This is because the existence ratio of the 4V discharge region is increased. Moreover, as for the temperature increase rate and temperature decrease rate in a 2nd baking process, 30 to 300 degreeC / h is preferable. If the rate of temperature increase and the rate of temperature decrease is less than 30 ° C./h, the production efficiency may decrease. If the rate exceeds 300 ° C./h, not only the desired battery performance will be difficult to obtain, but also the firing furnace (pot) cracks, etc. Is likely to occur.

This second firing step is generally performed in the air or in an oxygen atmosphere having an oxygen concentration of 20 wt% or more. The firing time is a time for sufficiently repairing the structure of oxygen vacancies in the spinel. The longer the time, the more effective, but considering the balance between the structure repair of oxygen vacancies and the production efficiency, it is 10 to 100 hours. It is preferably 15 to 50 hours.
After completion of the firing, the mixture is cooled and, if necessary, pulverized and classified to obtain the lithium manganese nickel-based composite oxide represented by the general formula (1), which is the target product.

A preferable physical property of the lithium manganese nickel-based composite oxide is that the BET specific surface area is 0.2 to 0.6 m ² / g, particularly 0.2 to 0.4 m ² / g, from the viewpoint of reducing the manganese elution amount. Is particularly preferred. In addition, the lithium manganese nickel-based composite oxide has an average particle size of 5 to 15 μm, particularly 8 to 12 μm, determined from the laser particle size distribution measurement method from the viewpoint of electrode density and TAP density, and further battery performance. Is preferred.

  The lithium manganese nickel-based composite oxide thus obtained has reduced manganese elution and is particularly useful as a positive electrode active material in a lithium secondary battery. Therefore, when this lithium manganese nickel-based composite oxide is used as a positive electrode active material of a lithium secondary battery, it has excellent charge / discharge cycle characteristics, and has a Coulomb efficiency, a discharge capacity retention ratio, and a 5V discharge capacity region / (5V discharge capacity region). A lithium secondary battery having a high ratio of (+4 V discharge capacity region) can be provided. In particular, it is preferable to use magnesium as M in the general formula (1) because the above-described effect becomes higher.

  The lithium secondary battery has a non-aqueous electrolyte containing a positive electrode, a negative electrode, a separator, and a lithium salt. The positive electrode is formed, for example, by applying and drying a positive electrode mixture on a positive electrode current collector. The positive electrode mixture includes a positive electrode active material composed of a lithium manganese nickel composite oxide obtained by the production method of the present invention, a conductive agent, a binder, and a filler added as necessary.

  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 a configured battery. For example, stainless steel, nickel, aluminum, titanium, calcined carbon, aluminum or stainless steel Examples of the surface include carbon, nickel, titanium, and silver surface-treated.

  Examples of the conductive agent include graphite such as natural graphite and artificial graphite, carbon black, acetylene black, conductive materials such as carbon fiber, metal, and nickel powder. Examples of natural graphite include scaly graphite and scaly graphite. Examples thereof include graphite and earthy graphite, and 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 polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, regenerated cellulose, diacetyl cellulose, polyvinyl pyrrolidone, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber, Polysaccharides such as fluororubber and polyethylene oxide, thermoplastic resins, polymers having rubber elasticity, and the like can be mentioned, and these can be used alone or in combination of two or more. The blending ratio of the binder is 2 to 30% by weight, preferably 5 to 15% by weight in the positive electrode mixture.

  The filler 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 a negative electrode current collector, for example. 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 constructed 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.

Although it does not restrict | limit especially as a negative electrode material, For example, a carbonaceous material, a metal complex oxide, lithium metal, a lithium alloy etc. are mentioned. 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 O _r (wherein M ¹ represents one or more elements selected from Mn, Fe, Pb and Ge, and M ² represents 1 or more elements selected from Al, B, P, Si, Periodic Table Group 1, Group 2, Group 3 and halogen elements, 0 <p ≦ 1, 1 ≦ q ≦ 3, 1 ≦ a compound such as r ≦ 8).

  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 general battery range, and is, for example, 5 to 300 μm. In the case where a solid electrolyte such as a polymer is used as the electrolyte described later, the solid electrolyte may also serve as a separator. In addition, for the purpose of improving discharge and charge / discharge characteristics, a compound such as pyridine, triethyl phosphite, triethanolamine or the like may be added to the electrolyte.

  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 or an organic 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, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, 3-methyl-2- One or more aprotic organic solvents such as oxazodinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone Mixed solvents thereof.

Examples of the organic solid electrolyte include a polyethylene derivative or a polymer containing the same, a polypropylene oxide derivative or a polymer containing the same, and a phosphate ester polymer. The lithium salt, which is soluble in the non-aqueous electrolyte is used, for _{example, LiClO 4, LiBF 4, LiPF} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, LiAlCl ₄ , salts obtained by mixing one or more of chloroborane lithium, lower aliphatic lithium carboxylate, lithium tetraphenylborate and the like.

  The battery shape can be applied to any of buttons, sheets, cylinders, corners, and the like. The use of the lithium secondary battery according to the present invention is not particularly limited. For example, the electronic device such as a notebook computer, a laptop computer, a pocket word processor, a mobile phone, a cordless cordless handset, a portable CD player, a radio, an automobile, and an electric vehicle. And consumer electronic devices such as game machines.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[Preparation of complex oxide of manganese and nickel]
300 mL of a mixed salt aqueous solution (volume ratio 1: 1) of 0.4 mol / L NiSO ₄ .6H ₂ O and 1.2 mol / L MnSO ₄ .5H ₂ O was prepared. Separately, 100 mL of a 1.5 mol / L aqueous ammonia solution and 200 mL of a 6 mol / L aqueous NaOH solution were prepared as complexing agents. These three aqueous solutions were simultaneously added dropwise to a 1 L capacity beaker containing 200 mL of water. During the dropping, the dropping rate of each aqueous solution was adjusted so that the pH of the reaction solution was 11. The dropping speed was 60 mL / min for the mixed salt aqueous solution, 20 mL / min for the ammonia aqueous solution, and 40 mL / min for the NaOH aqueous solution. The temperature of the reaction solution was kept at 50 ° C. As a result, Mn and Ni hydroxides were coprecipitated. The coprecipitate was aged by stirring for 9 hours. During this time, the amount of liquid in the reaction system was controlled by the overflow method, and the overflowed liquid was replaced every 3 hours. The hydroxide produced by precipitation after filtration was repulped and washed. Washing was performed thoroughly while judging the cleaning effect with a conductivity meter. After drying, the precipitated product was analyzed by X-ray diffraction. As a result, the precipitated product is not amorphous, but is a eutectic of Mn and Ni in which Mn and Ni are solid-solved with each other, and the composition is almost represented by Mn _0.75 Ni _0.25 (OH) _2. It was confirmed that The precipitated product had a BET specific surface area of 12.2 m ² / g, and the average particle size determined from the laser particle size distribution measurement method was 9.7 μm.

[Example 1]
<Preparation of starting materials>
The complex oxide of manganese and nickel obtained above, lithium carbonate (manufactured by Nippon Chemical Industry Co., Ltd., average particle size 14 μm) and MgO (manufactured by Ube Materials Co., Ltd., average particle size 1 μm) were mixed with Li: Mn: Ni: Weigh so that the Mg molar ratio is 0.5: 0.75: 0.25: 0.005, and then uniformly mix with a blender to obtain a mixture containing Li, Mn, Ni and Mg as starting materials. Obtained.
<First firing step>
Next, the obtained mixture was calcined in the atmosphere at 1000 ° C. for 12 hours to obtain a precursor. The rate of temperature increase until reaching the maximum temperature zone was 100 ° C./h. Thereafter, the temperature was lowered naturally to room temperature (20 ° C.) at a rate of 100 ° C./h. After cooling, the precursor was lightly pulverized using a home mixer. The BET specific surface area of the precursor was 0.39 m ² / g, and the average particle size determined from the laser particle size distribution measurement method was 10.5 μm.
<Second firing step>
The precursor obtained in the first firing step was refired at 600 ° C. for 15 hours in the air. The rate of temperature increase until reaching the maximum temperature zone was 100 ° C./h. After firing, the _mixture was cooled to room temperature (20 ° C.) at a temperature drop rate of 100 ° C./h, then pulverized and classified, and represented by the composition formula Li _1.000 Mn _1.4925 Ni _0.4975 Mg _0.01 O _3.9925 . Lithium manganese nickel composite oxide was obtained. The composite oxide had a BET specific surface area of 0.38 m ² / g, and the average particle size determined by the laser particle size distribution measurement method was 10.6 μm.
Main preparation conditions are shown in Table 1, and various physical properties of the obtained lithium manganese nickel-based composite oxide are shown in Table 2.

[Example 2]
Lithium manganese represented by the composition formula Li _1.000 Mn _1.4925 Ni _0.4975 Mg _0.01 O _3.9925 in the same manner as in Example 1 except that the firing temperature in the first firing step was 950 ° C. A nickel-based composite oxide was obtained. The composite oxide had a BET specific surface area of 0.46 m ² / g and an average particle size determined by the laser particle size distribution measurement method of 10.4 μm.
The BET specific surface area of the precursor was 0.48 m ² / g, and the average particle size determined from the laser particle size distribution measurement method was 10.5 μm.
Main preparation conditions are shown in Table 1, and various physical properties of the obtained lithium manganese nickel-based composite oxide are shown in Table 2.

Example 3
TiO ₂ (manufactured by Showa Denko KK, average particle size 0.5 μm) was used instead of MgO, and the molar ratio of Li: Mn: Ni: Ti in the starting material was 0.5: 0.75: 0.25: 0.005. A lithium manganese nickel-based composite oxide represented by the composition formula Li _1.000 Mn _1.4925 Ni _0.4975 Ti _0.01 O _3.9925 was obtained in the same manner as in Example 1. The composite oxide had a BET specific surface area of 0.37 m ² / g, and the average particle size determined by the laser particle size distribution measurement method was 10.9 μm.
Main preparation conditions are shown in Table 1, and various physical properties of the obtained lithium manganese nickel-based composite oxide are shown in Table 2.

Example 4
In the same manner as in Example 1 except that the starting material was prepared so that the molar ratio of Li: Mn: Ni: Mg was 0.475: 0.75: 0.25: 0.005, the composition formula Li _0.95 A lithium manganese nickel composite oxide represented by Mn _1.4925 Ni _0.4975 Mg _0.01 O _3.9925 was obtained. The composite oxide had a BET specific surface area of 0.40 m ² / g, and the average particle size determined by the laser particle size distribution measurement method was 10.6 μm.
In addition, Table 2 shows various physical properties of the obtained lithium manganese nickel-based composite oxide.

Example 5
The composition formula Li _1.05 was obtained in the same manner as in Example 1 except that the starting material was prepared so that the molar ratio of Li: Mn: Ni: Mg was 0.525: 0.75: 0.25: 0.005. A lithium manganese nickel composite oxide represented by Mn _1.4925 Ni _0.4975 Mg _0.01 O _3.9925 was obtained. The composite oxide had a BET specific surface area of 0.38 m ² / g, and the average particle size determined by the laser particle size distribution measurement method was 10.3 μm.
In addition, Table 2 shows various physical properties of the obtained lithium manganese nickel-based composite oxide.

Example 6
Lithium carbonate (manufactured by Nippon Chemical Industry Co., Ltd., average particle size 14 μm), manganese dioxide (manufactured by Junsei Chemical Co., Ltd., average particle size 5 μm), nickel oxide (manufactured by Wako Pure Chemical Industries, Ltd., average particle size 7 μm) and MgO (Ube Materials Co., Ltd.) Manufactured, average particle diameter 1 μm), Li: Mn: Ni: Mg molar ratio is weighed to be 0.5: 0.75: 0.25: 0.005, and then uniformly mixed by a blender, The composition formula Li _1.000 Mn _1.4925 Ni _0.4975 Mg _0.01 O _3.9925 was obtained in the same manner as in Example 1 except that a mixture containing Li, Mn, Ni and Mg as starting materials was obtained. Lithium manganese nickel-based composite oxide represented by The composite oxide had a BET specific surface area of 0.48 m ² / g, and the average particle size determined by the laser particle size distribution measurement method was 8.2 μm.
In addition, Table 2 shows various physical properties of the obtained lithium manganese nickel-based composite oxide.

[Comparative Example 1]
<Preparation of starting materials>
The same composite oxide of manganese and nickel and lithium carbonate (average particle size: 14 μm) as used in Example 1 is set so that the Li: Mn: Ni molar ratio is 0.5: 0.75: 0.25. And then uniformly mixed with a blender to obtain a mixture containing Li, Mn and Ni as starting materials.
<First firing step>
Next, the obtained mixture was calcined in the atmosphere at 1000 ° C. for 12 hours to obtain a precursor. The rate of temperature increase until reaching the maximum temperature zone was 100 ° C./h. Thereafter, the temperature was lowered naturally to room temperature (20 ° C.) at a rate of 100 ° C./h. After cooling, the precursor was lightly pulverized using a home mixer. The BET specific surface area of the precursor was 0.41 m ² / g, and the average particle size obtained from the laser particle size distribution measurement method was 10.8 μm.
<Second firing step>
The precursor obtained in the first firing step was fired at 600 ° C. for 15 hours in the air. The rate of temperature increase until reaching the maximum temperature zone was 100 ° C./h. After firing, the mixture is cooled to room temperature (20 ° C.) at a rate of temperature decrease of 100 ° C./h, pulverized and classified, and lithium manganese nickel represented by the composition formula Li _1.0 Mn _1.5 Ni _0.5 O _4.0 A system complex oxide was obtained. The composite oxide had a BET specific surface area of 0.40 m ² / g, and the average particle size determined by the laser particle size distribution measurement method was 10.7 μm.
Main preparation conditions are shown in Table 1, and various physical properties of the obtained lithium manganese nickel-based composite oxide are shown in Table 2.

[Performance evaluation]
Manganese elution amount of lithium manganese nickel composite oxide obtained in Examples and Comparative Examples, initial discharge capacity of lithium secondary battery using these composite oxides as positive electrode active material, Coulomb efficiency at 10th cycle, 20 The energy retention rate at the cycle, the maximum average operating voltage, and the discharge capacity ratio of 4.5 to 5.0 V / 3.0 to 5.0 V were measured by the following methods. The results of manganese elution amount are shown in Table 2, and the other results are shown in Table 3.
In addition, initial discharge capacity curves for Examples 1, 2, 3 and Comparative Example 1 are shown in FIGS. 1, 2, 3, and 4, respectively.

<Manganese elution amount>
1 g of lithium manganese nickel composite oxide was put in a sealable Teflon (registered trademark) container. The container was placed in a vacuum dryer heated to 120 ° C. overnight to remove moisture. After the container was taken out from the vacuum dryer, 5 g of the electrolytic solution was put into a Teflon (registered trademark) container in a dry air atmosphere and the container was covered. The electrolytic solution was obtained by dissolving 1 mol of LiPF _{6 in} 1 liter of a 1: 2 volume ratio of ethylene carbonate and diethyl carbonate. The container was shaken up and down to thoroughly mix the composite oxide and the electrolyte, and then the container was placed in a thermostat at 80 ° C. and left for 1 week. During this time, the container was shaken once every 2-3 days to mix them. After one week, the container was taken out from the thermostat, and the electrolytic solution in the container was filtered with a 0.1 μm filter. 1 g of the filtrate was put into a 100 mL volumetric flask, and a mixed solvent of ultrapure water: ethanol = 80: 20 (weight ratio) was added to the volumetric flask to dilute to constant volume. After shaking the volumetric flask well, the manganese concentration was quantified by atomic absorption spectrometry. Based on the quantitative value, the amount of manganese elution was determined by converting how much manganese was dissolved in 5 g of the electrolyte.

<Initial discharge capacity>
5.7 g of lithium manganese nickel composite oxide, 0.15 g of conductive agent (conductive carbon, Super P manufactured by Erachem) and 0.15 g of binder (polyvinylidene fluoride) were mixed. Next, about 5 ml of N-methylpyrrolidinone was added, and a uniform paint was prepared with a stirrer. A positive electrode sheet was obtained by applying a paint to an aluminum sheet and drying at 120 ° C. for 2 hours. The coating thickness was 120 μm. The positive electrode sheet was pressed and then punched out to a size of φ15 mm to obtain a positive electrode plate. Using this positive electrode plate, a lithium secondary battery was produced using each member such as a separator, a negative electrode, a current collector plate, a mounting bracket, an external terminal, and an electrolytic solution. As the negative electrode, a metal lithium foil was used, and as the electrolyte, 1 mol of LiPF ₆ was dissolved in 1 liter of a mixed solution of ethylene carbonate and diethyl carbonate in a volume ratio of 1: 2. With respect to this lithium secondary battery, the initial discharge capacity was measured at 25 ° C. Charging was performed at CCCV up to 5.0 V at a current value of 0.5 C (charging was terminated when the current value reached 0.05 C), and discharging was performed at CC up to 3.0 V at a current value of 0.2 C.

<10th cycle coulomb efficiency>
For the lithium secondary battery used for the measurement of the initial discharge capacity, the discharge capacity at the 10th cycle and the charge capacity at the 10th cycle were measured, and the discharge capacity at the 10th cycle / the charge capacity at the 10th cycle × 100 to 10 The coulombic efficiency at the cycle was calculated.

<20th cycle discharge capacity maintenance rate>
For the lithium secondary battery used for the measurement of the initial discharge capacity, the discharge capacity at the first cycle and the charge capacity at the 20th cycle are measured, and the discharge capacity at the 20th cycle / the discharge capacity at the first cycle × 100 to 20 The discharge capacity retention rate at the cycle was calculated.

<20th cycle energy maintenance rate>
About the lithium secondary battery used for the measurement of the above-mentioned initial discharge capacity, the energy density of the first cycle (discharge capacity × voltage) and the energy density of the 20th cycle are obtained, and the energy density of the 20th cycle / the energy of the 1st cycle. The energy retention rate at the 20th cycle was calculated from density × 100.

<Maximum average operating voltage>
Regarding the lithium secondary battery used for the measurement of the initial discharge capacity described above, the voltage of the cycle when the operating voltage during discharge was the highest among the measured cycles was defined as the maximum average operating voltage.

<Discharge capacity ratio of 4.5-5.0V / 3.0-5.0V>
In order to confirm the ratio of 5V discharge capacity region / (5V discharge capacity region + 4V discharge capacity region) for the lithium secondary battery used for the measurement of the initial discharge capacity described above, the cut voltage at the time of discharge was 4.5V. The discharge capacity ratio was calculated from discharge capacity of 4.5 to 5.0 V / discharge capacity of 3.0 to 5.0 V × 100 as 0V.

  As is clear from the results shown in Table 3, the lithium secondary battery using the lithium manganese nickel-based composite oxide obtained in Examples 1 to 6 as the positive electrode active material was compared with that of Comparative Example 1, It can be seen that Coulomb efficiency, capacity maintenance rate and energy maintenance rate are high. Further, as is clear from the results of the discharge capacity ratios in Table 3 and FIGS. 1, 2, 3, and 4, the lithium manganese nickel composite oxides obtained in Examples 1, 2, and 3 were used for the positive electrode active. It can be seen that the lithium secondary battery used as the material has a small voltage change (plateau) in the vicinity of 4V and a large proportion of the 5V region compared to that of Comparative Example 1.

It is a figure showing the initial stage discharge capacity curve of the lithium secondary battery which used the complex oxide obtained in Example 1 as a positive electrode active material. It is a figure showing the initial stage discharge capacity curve of the lithium secondary battery which used the complex oxide obtained in Example 2 as a positive electrode active material. It is a figure showing the initial stage discharge capacity curve of the lithium secondary battery which used the complex oxide obtained in Example 3 as a positive electrode active material. It is a figure showing the initial stage discharge capacity curve of the lithium secondary battery which used the complex oxide obtained by the comparative example 1 as a positive electrode active material.

Claims (7)

A method for producing a lithium manganese nickel-based composite oxide represented by the following general formula (1):
Li _x Mn _1.5-y Ni _{0.5-z My + z} O _4-w (1)
(Wherein 0.9 <x <1.1, y> 0, z> 0, 0 <y + z <0.1, 0 ≦ w <2, M is selected from magnesium, aluminum, titanium and zirconium) Represents at least one metal element.)
The lithium manganese nickel characterized by firing a mixture containing lithium, manganese, nickel and M at 950 to 1050 ° C., cooling to obtain a precursor, and then re-firing the precursor at 550 to 650 ° C. Method for producing a composite oxide.   2. The lithium manganese nickel composite oxide according to claim 1, wherein the mixture containing lithium, manganese, nickel, and M is composed of a lithium compound, a composite compound of manganese and nickel, and a compound containing M. Method. ^{2. The} method for producing a lithium manganese nickel-based composite oxide according to claim 1, wherein the precursor has a BET specific surface area of 0.2 to 0.6 m ² / g.   The method for producing a lithium manganese nickel-based composite oxide according to claim 3, wherein the precursor has an average particle size of 5 to 15 μm.   The method for producing a lithium manganese nickel-based composite oxide according to claim 1, wherein M is magnesium or titanium.   A lithium manganese nickel composite oxide produced by the method according to claim 1.   A lithium secondary battery comprising a positive electrode comprising the lithium manganese nickel-based composite oxide according to claim 6.

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