JP2013212959A - Lithium manganese-based composite oxide and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new material capable of exhibiting more superior charging/discharging characteristics in a lithium manganese-based composite oxides expected as positive electrode material replacing a lithium cobalt-based positive-electrode material.SOLUTION: After a precipitate is formed through a coprecipitation method and subjected to wet oxidation, firing is carried out in two stages to obtain a new lithium manganese-based composite oxide having a monoclinic layered rock salt type structure represented by the composition formula: Li(MnFeNi)O(where x, m and n satisfy 0≤x≤1/3, 0≤m≤0.6, and 0≤n≤0.3), the composite oxide having superior charging/discharging characteristics such that (1) the mol ratio of three components of Mn, Fe and Ni is within a specific range and (2) the average oxidation number of Mn, Fe and Ni is 3.4 to 3.6.

Description

  The present invention relates to a lithium manganese composite oxide useful as a positive electrode material for a next-generation low-cost lithium ion secondary battery and a method for producing the same.

  Currently, in Japan, most of secondary batteries installed in portable devices such as mobile phones and notebook computers are lithium ion secondary batteries. In addition, lithium ion secondary batteries are expected to be put into practical use as large batteries for electric vehicles, power load leveling systems, and the like, and their importance is increasing.

Currently, in lithium ion secondary batteries, a lithium cobalt oxide (LiCoO ₂ ) material is mainly used as a positive electrode material, and a carbon material such as graphite is used as a negative electrode material. When these electrode materials are used, Li is desorbed while the cobalt in the lithium cobalt oxide is oxidized from trivalent to tetravalent by charging, and Li is supplied to the negative electrode. Desorbs, tetravalent cobalt is reduced to trivalent, and Li is inserted into the positive electrode to operate as a battery.

In such a lithium ion secondary battery, the amount of lithium ions reversibly desorbed (equivalent to charging) and inserted (equivalent to discharging) in the positive electrode material determines the capacity of the battery, and the voltage at the time of desorption / insertion is the battery. LiCoO ₂ as a positive electrode material is an important battery constituent material related to battery performance. For this reason, the demand for lithium cobalt oxide is expected to increase further with the future expansion and enlargement of lithium ion secondary batteries.

However, since lithium cobalt oxide contains a large amount of cobalt, which is a rare metal, it is one of the factors that increase the material cost of lithium ion secondary batteries. Furthermore, considering that about 20% of cobalt resources are currently used in the battery industry, it is considered difficult to meet future demand growth with only the cathode material made of LiCoO ₂ .

Currently, lithium nickel oxide (LiNiO ₂ ) and lithium manganese oxide (LiMn ₂ O ₄ ) have been reported as cheaper and less resource-constrained positive electrode materials, and some have been put into practical use as alternative materials. Yes. However, lithium nickel oxide has the problem of reducing the safety of the battery during charging, and lithium manganese oxide elutes trivalent manganese into the electrolyte during charge and discharge at high temperatures (about 60 ° C). Due to the problem of significantly degrading battery performance, substitution for these materials has not progressed much. Among lithium manganese oxides, a positive electrode material called LiMnO ₂ has also been proposed, but this material gradually has a spinel crystal structure typified by the above LiMn ₂ O _{4 due} to its original structure. Since the shape of the charge / discharge curve changes greatly with the progress of the charge / discharge cycle, it has not been put into practical use.

Further, lithium ferrite (LiFeO ₂ ) containing iron, which is more abundant in resources, less toxic, and cheaper than manganese and nickel, has been studied as a potential electrode material. However, since lithium ferrite obtained by a normal manufacturing method, that is, by mixing an iron source and a lithium source and firing at high temperature, hardly charges or discharges, it cannot be used as a positive electrode material for a lithium ion secondary battery.

On the other hand, LiFeO ₂ obtained by the ion exchange method has been reported to be chargeable / dischargeable (see Patent Documents 1 and 2 below), but the average discharge voltage of these materials is 2.5 V or less and the value of LiCoO ₂ Since it is significantly lower than (approximately 3.7V), it is difficult to replace LiCoO ₂ .

The present inventors have already described a layered rock salt type solid solution (Li _{1 + x} (Fe _y Mn ₁ ) composed of lithium manganese oxide (Li ₂ MnO ₃ ) and lithium ferrite, which are cheaper and resource-rich after iron. _-y ) _1-x O ₂ (0 <x <1/3, 0 <y <1), hereinafter referred to as “iron-containing Li ₂ MnO ₃ ”) is a lithium cobalt oxide in the charge / discharge test at room temperature. It has been found that it has an average discharge voltage close to 4V (see Patent Documents 3 and 4 below).

In addition, the present inventors show that a lithium-iron-manganese composite oxide satisfying specific conditions exhibits a higher capacity (150 mAh / g) and stable charge / discharge cycle characteristics than LiMn ₂ O ₄ during a high-temperature cycle test. (See Patent Document 5 below).

Furthermore, the present inventors have also reported that a positive electrode material in which Ni is further dissolved in Li ₂ MnO ₃ containing iron is a material with little cycle deterioration (see Patent Documents 6 and 7 below).

  As described above, various reports have been made on lithium manganese-based positive electrode materials that can be substituted for lithium cobalt-based positive electrode materials. However, a positive electrode material having further excellent charge / discharge characteristics is desired, and in order to improve the characteristics, optimization of the chemical composition and manufacturing conditions of the positive electrode material is desired.

Japanese Patent Laid-Open No. 10-120421 JP-A-8-295518 JP 2002-068748 A Japanese Patent Laid-Open No. 2002-121026 JP 2005-154256 A JP2003-48718 JP 2006-36621 A

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is more excellent in lithium manganese-based composite oxides expected as a positive electrode material that can replace a lithium cobalt-based positive electrode material. It is to provide a novel material capable of exhibiting charge / discharge characteristics.

  The present inventor has intensively studied to achieve the above-described object. As a result, in the lithium manganese based composite oxide in which iron and nickel are dissolved, when using a raw material having a specific composition range and adopting a coprecipitation method from an aqueous solution, when using specific manufacturing conditions, It has been found that a novel composite oxide which has not been known so far can be obtained in which the average oxidation numbers of iron, nickel and manganese are within a specific range. The novel composite oxide thus obtained has a higher charge / discharge capacity than a conventionally known lithium manganese composite oxide having the same composition. It has been found that by using it as a positive electrode material for a secondary battery, a lithium ion secondary battery having excellent performance can be produced using an inexpensive raw material, and the present invention has been completed here.

That is, the present invention provides the following lithium manganese composite oxide, a production method thereof, a lithium ion secondary battery positive electrode material and a lithium ion secondary battery comprising the lithium manganese composite oxide.
Item 1. Compositional _{formula: Li 1 + x (Mn 1} -mn Fe m Ni n) 1-x O 2 ( wherein, x, a range of m and n, 0 ≦ x ≦ 1/3 ,
A composite oxide having a monoclinic layered rock salt structure represented by 0 ≦ m ≦ 0.6, 0 ≦ n ≦ 0.3,
(1) The molar ratio of the three components of Mn, Fe, and Ni is point A (Mn: Fe: Ni = 60: 40: 0), point in the molar ratio triangular composition diagram with Mn, Fe, and Ni as vertices. B (Mn: Fe: Ni = 40: 60: 0), point C (Mn: Fe
: Ni = 70: 0: 30) and the point D (Mn: Fe: Ni = 80: 0: 20) within the range of a quadrangle with the four points as vertices,
(2) A lithium manganese composite oxide characterized in that the average oxidation number of Mn, Fe, and Ni is 3.4 to 3.6.
Item 2. Item ^2. The lithium manganese composite oxide according to Item 1, having a specific surface area of 10 to 50 m ² / g and a spontaneous magnetization of 0.005 emu / g or less.
Item 3. A mixed aqueous solution containing a manganese compound, an iron compound, and a nickel compound is made alkaline to form a precipitate, a lithium compound is added to the formed precipitate and wet oxidation treatment is performed, followed by firing in an oxidizing atmosphere, Item 3. The method for producing a lithium manganese composite oxide according to Item 1 or 2, wherein the firing is performed in an active gas atmosphere.
Item 4. Item 4. The method for producing a lithium manganese composite oxide according to Item 3, wherein the temperature of the mixed aqueous solution during precipitation is 30 to 80 ° C.
Item 5. Item 3 or 4 wherein the method of wet-oxidizing the precipitate is a method of blowing an oxidizing gas while stirring the aqueous solution containing the precipitate, or a method of adding an oxidizing compound while stirring the aqueous solution containing the precipitate. A method for producing the lithium manganese composite oxide according to 1.
Item 6. Item 6. The lithium manganese based composite oxidation according to any one of Items 3 to 5, wherein firing in an oxidizing atmosphere is performed at 400 to 600 ° C, and firing in an inert gas atmosphere is performed at 600 to 850 ° C. Manufacturing method.
Item 7. Item 3. A positive electrode material for a lithium ion secondary battery comprising the lithium manganese composite oxide according to Item 1 or 2.
Item 8. A lithium ion secondary battery comprising a positive electrode material for a lithium ion secondary battery comprising the lithium manganese composite oxide according to Item 1 or 2.

  Hereinafter, the lithium manganese composite oxide and the method for producing the same of the present invention will be specifically described.

Lithium manganese composite oxide of lithium manganese-based composite oxide of the present invention, the composition _{formula: Li 1 + x (Mn 1} -mn Fe m Ni n) 1-x O 2 ( wherein, x, a range of m and n Is a composite oxide having a monoclinic layered rock salt structure represented by 0 ≦ x ≦ 1/3, 0 ≦ m ≦ 0.6, 0 ≦ n ≦ 0.3,
(1) The molar ratio of the three components of Mn, Fe, and Ni is point A (Mn: Fe: Ni = 60: 40: 0), point in the molar ratio triangular composition diagram with Mn, Fe, and Ni as vertices. B (Mn: Fe: Ni = 40: 60: 0), point C (Mn: Fe
: Ni = 70: 0: 30) and the point D (Mn: Fe: Ni = 80: 0: 20) within the range of a quadrangle with the four points as vertices,
(2) The average oxidation number of Mn, Fe and Ni is 3.4 to 3.6.

The above-described lithium manganese composite oxide is based on a rock salt structure, which is a general crystal structure of oxide, and has a space group similar to the known substance Li ₂ MnO ₃

Based on the crystal phase of a monoclinic layered rock-salt structure with a predetermined amount of Ni and Fe in solid solution, the average oxidation number of the transition metal element consisting of Mn, Ni and Fe is 3. It is controlled within the range of 4 to 3.6. The composite oxide of the present invention having such characteristics has a higher charge / discharge capacity than the known composite oxide in which the average oxide of the transition metal element is outside the above-described range. It has excellent characteristics as a positive electrode active material for secondary batteries.

  The amount of Fe to be dissolved in the composite oxide is in the range of 0 to 60 mol% based on the total amount of transition metal elements composed of Mn, Fe and Ni, that is, 0 ≦ Fe / (Mn + Ni + Fe) must be in the range of ≦ 0.6, preferably in the range of 10 to 30%. The amount of Ni is in the range of 0 to 30 mol%, that is, in the range of 0 ≦ Ni / (Mn + Ni + Fe) ≦ 0.3, based on the total amount of transition metal elements composed of Mn, Fe and Ni. It must be present and is preferably in the range of 5-25%.

Further, the molar ratio of the transition metal element composed of Mn, Ni, and Fe is indicated by a point A (Mn: Fe: Ni = 60: 40 in the molar ratio triangular composition diagram having Mn, Fe, and Ni as vertices shown in FIG. : 0), Point B (Mn: Fe: Ni = 40: 60: 0), Point C (Mn: Fe: Ni = 70: 0: 30), and Point D (Mn: Fe: Ni = 80: 0: 20) It must be within the range of a quadrangle with 4 vertices. The composition represented by the above composition formula: Li _{1 + x} (Mn _1-mn Fe _m Ni _n ) _1-x O ₂ and the molar ratio of the three components of Mn, Fe, and Ni are shown in FIG. In the triangular composition diagram shown, when it is within the range of a quadrangle having points A, B, C, and D as vertices, Mn, Ni, and Fe are produced by producing a composite oxide by the method described later. A composite oxide in which the average oxidation number of the transition element consisting of is in the range of 3.4 to 3.6 can be obtained.

Method for Producing Lithium Manganese Composite Oxide Hereinafter, a method for producing the lithium manganese composite oxide of the present invention will be described.

  The lithium manganese based composite oxide of the present invention forms a precipitate containing Mn, Fe and Ni from an aqueous solution containing Mn ions, Fe ions and Ni ions by a coprecipitation method, and a lithium compound is added to the formed precipitate. After wet oxidation, the wet oxide of the precipitate may be mixed with a lithium compound as necessary, fired in an oxidizing atmosphere, and then fired in an inert gas atmosphere. Hereinafter, each step will be described.

(I) Formation of precipitate In the step of forming a precipitate by the coprecipitation method, a mixed aqueous solution in which a metal compound as a raw material of Mn, Fe and Ni is dissolved in water, a water / alcohol mixture or the like is made alkaline, and Mn, Fe and A precipitate containing Ni is formed.

  The manganese compound, iron compound, and nickel compound that are constituent metal sources can be used without particular limitation as long as they can form a mixed aqueous solution containing these compounds. Usually, a water-soluble compound may be used. Specific examples of such water-soluble compounds include water-soluble salts such as chlorides, nitrates, sulfates, oxalates and acetates. In the case of manganese, permanganate can also be used. These water-soluble compounds may be either anhydrides or hydrates. In addition, even a water-insoluble compound such as a metal itself, an oxide, or a hydroxide can be used as an aqueous solution by being dissolved using an acid such as hydrochloric acid or nitric acid. Each of these raw material compounds may be used alone or in combination of two or more for each metal source.

What is necessary is just to make it the mixing ratio of each said metal compound in this mixed aqueous solution become an element ratio similar to each element ratio in the target complex oxide. That is, in the composition formula: Li _{1 + x} (Mn _1-mn Fe _m Ni _n ) _1-x O ₂ , m and n are in the range of 0 ≦ m ≦ 0.6, 0 ≦ n ≦ 0.3, and each transition Each raw material may be mixed so that the molar ratio of the metal elements is within a range surrounded by a rectangle having points A, B, C and D as vertices in the triangular composition diagram shown in FIG.

The concentration of each compound in the mixed aqueous solution is not particularly limited, and may be determined as appropriate so that a uniform mixed aqueous solution can be formed and a coprecipitate can be smoothly formed. Usually, the total concentration of the constituent metal compounds may be about 0.01 to 5 mol / l, preferably about 0.1 to 2 mol / l.

  As a solvent for the mixed aqueous solution, water may be used alone, or a water-alcohol mixed solvent containing a water-soluble alcohol such as methanol or ethanol may be used.

  In order to generate a precipitate (coprecipitate) from the mixed aqueous solution, the mixed aqueous solution may be made alkaline. Conditions for forming a good precipitate vary depending on the type and concentration of each compound contained in the mixed aqueous solution, and thus cannot be defined unconditionally. However, it is usually preferable to set the pH to about 8 or more, and to about pH 11 or more. More preferred.

  There is no particular limitation on the method of making the mixed aqueous solution alkaline. Usually, the mixed aqueous solution may be added to an alkali or an aqueous solution containing an alkali. Moreover, a coprecipitate can be formed also by the method of adding the aqueous solution containing an alkali to this mixed aqueous solution. Examples of the alkali used to make the mixed aqueous solution alkaline include alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, and lithium hydroxide, ammonia, and the like. When these alkalis are used as an aqueous solution, for example, they can be used as an aqueous solution having a concentration of about 0.1 to 20 mol / l, preferably about 0.3 to 10 mol / l. Further, the alkali may be dissolved in a water-alcohol mixed solvent containing a water-soluble alcohol, similarly to the mixed aqueous solution of the metal compound described above.

  The liquid temperature of the mixed aqueous solution during the formation of the precipitate is preferably about 30 to 80 ° C, more preferably about 40 to 75 ° C. By forming a precipitate under such heating, the reaction rate at the time of forming a precipitate as a hydroxide can be improved, and a massive secondary particle in which fine primary particles are aggregated can be obtained. Such massive secondary particles have a large specific surface area and high oxidation reactivity, and have an advantage that the electrode plate density is easily improved when a coating electrode described later is used.

  After forming a precipitate under such conditions, a composite oxidation in which the average oxidation number of the target transition metal element is within the range of 3.4 to 3.6 by performing wet oxidation, firing, or the like by a method described later. You can get things.

  Next, a lithium compound is added to the slurry obtained by dispersing the precipitate obtained by the above-described method in water, and wet oxidation is performed.

  Prior to wet oxidation, it is preferable to purify the precipitate formed under heating by removing excess alkali components, residual raw materials and the like by a method such as washing with water. The purified precipitate may be separated by a method such as decantation or filtration, and then dispersed again in water to form a slurry, followed by wet oxidation by adding a lithium compound.

  When performing wet oxidation, the amount of the precipitate contained in the slurry is preferably about 50 to 300 g / L, and more preferably about 100 to 250 g / L. As the lithium compound added to the slurry, lithium hydroxide, lithium chloride, lithium nitrate, lithium acetate, or the like can be used. The addition amount of the lithium compound is preferably about 1 to 3 mol, and more preferably about 1.5 to 2 mol, with respect to 1 mol of the transition metal contained in the precipitate.

The wet oxidation method is not particularly limited. For example, an oxidizing gas such as oxygen or air may be blown while uniformly dispersing the slurry containing the precipitate in the reaction vessel. The degree of stirring is not particularly limited, and stirring may be performed so that a uniform slurry state is obtained. For example, the stirring may be performed at a rotational speed of about 200 to 800 rpm, preferably about 300 to 500 rpm.

  The amount of the oxidizing gas blown is not particularly limited, but is preferably about 0.3 to 5 L / min, and preferably about 0.5 to 2 L / min per liter of the slurry containing the precipitate. More preferred. At this time, in order to efficiently perform the oxidation reaction, it is preferable to use a device for making bubbles fine, such as a diffuser, and to blow in a fine oxidizing gas.

Further, wet oxidation can also be performed by a method of adding an oxidizing compound such as H ₂ O ₂ while stirring the slurry containing the precipitate in a uniform state. The method for adding the oxidizing compound and the amount of the oxidizing compound are not particularly limited. For example, about 5 to 10% by weight of a H ₂ O ₂ aqueous solution is used, and about 100 to 150 mL is dropped at a flow rate of about 1 to 5 ml / min. Wet oxidation can also be performed by the method.

  The liquid temperature during wet oxidation is not particularly limited, but may be, for example, about 10 to 60 ° C., preferably about 20 to 50 ° C. The wet oxidation time is usually about 8 hours to 3 days, preferably about 12 to 36 hours.

  After forming a precipitate from a mixed aqueous solution containing a raw material having a specific blending ratio by the above-described method, by adding a lithium compound to the formed precipitate and performing wet oxidation, manganese, iron, and the like contained in the coprecipitate Lithium manganese composite in which the oxidation can proceed and the average oxidation number of the transition metal element composed of Mn, Ni and Fe is in the range of 3.4 to 3.6 by combining with the two-stage firing method described later An oxide can be obtained. Furthermore, by performing wet oxidation, the specific surface area of the composite oxide obtained after the baking treatment described later can be increased.

  Next, the slurry containing the precipitate after wet oxidation is dried to obtain a dry powder. Although there is no limitation in particular about the drying method, Evaporation to dryness by a shelf type dryer, a slurry dryer, a spray dryer, etc. can be used. The powder temperature during drying is preferably about 60 to 200 ° C, and more preferably about 70 to 120 ° C.

(Ii) Calcination Treatment Next, the wet oxide of the precipitate obtained before the hydrothermal treatment is subjected to a two-stage calcination treatment under the conditions described later, whereby the average oxidation number of the transition metal element is 3.4 to 3. It can be controlled within a range of 6.

  In the firing treatment, the amount of lithium element contained in the wet oxide of the precipitate is preferably about 1.3 to 2.2 mol with respect to 1 mol of the transition metal element. Therefore, a composition analysis is performed before the firing treatment, and based on this result, a lithium compound is added as necessary so that the amount of lithium element contained in the wet oxide is within the above-described preferred range. That's fine. However, the addition amount of the lithium compound added at this stage is preferably within a range of about 0.01 to 2 mol with respect to 1 mol of the transition metal element contained in the wet oxide.

  The lithium compound that can be added before the firing treatment can be used without particular limitation as long as it contains a lithium element. Specific examples include lithium salts such as lithium carbonate, lithium chloride, lithium nitrate, and lithium acetate, lithium hydroxide, and the like. Can be mentioned. These lithium compounds can be used singly or in combination of two or more. The lithium compound can be used in the form of a powder, an aqueous solution, or the like, but is preferably used in the form of an aqueous solution in order to ensure the uniformity of the reaction. In this case, the concentration of the aqueous solution is usually about 0.1 to 10 mol / l.

  Usually, in order to improve the reactivity, it is preferable to add a lithium compound to the raw material for baking, pulverize and mix, and then fire. As for the degree of pulverization, it is sufficient that coarse particles are not included and the mixture has a uniform color tone.

  As the firing treatment, first, firing is performed in an oxidizing atmosphere as a first step. As a method for firing in an oxidizing atmosphere, for example, heating in an atmosphere of an oxygen-containing gas such as air or oxygen is preferably performed at about 400 to 600 ° C., more preferably about 450 to 550 ° C. In this step, it is considered that, by firing in an oxidizing atmosphere, oxidation of manganese mainly proceeds to form tetravalent manganese.

  The firing time in an oxidizing atmosphere is preferably about 1 to 10 hours including the time to reach the firing temperature, and more preferably about 2 to 7 hours. Next, as a second stage baking, baking is performed in an inert gas atmosphere. The method for firing in an inert gas atmosphere is not particularly limited. For example, in an inert atmosphere such as an inert gas stream such as nitrogen or argon gas, the temperature is about 600 to 850 ° C., preferably 700 to 800. What is necessary is just to heat to about degreeC.

In this case, the firing temperature is within the above-mentioned range from the firing temperature in an oxidizing atmosphere.
The temperature is preferably about 200 to 300 ° C. higher.

  The firing time in an inert gas atmosphere is preferably about 1 to 48 hours including the time to reach the firing temperature, and more preferably about 10 to 30 hours.

  By firing in an inert gas atmosphere under such conditions, a monoclinic layered rock-salt crystal structure can be grown without changing the oxidation number of transition metal elements formed by firing in an oxidizing atmosphere. Thus, the target composite oxide can be obtained. As a result, the average oxidation number of the transition metal element composed of Mn, Ni, and Fe contained in the formed complex oxide can be controlled within the range of 3.4 to 3.6. In this case, although the oxidation number of each element is not necessarily clear, it is considered that Mn becomes almost tetravalent, Fe becomes almost trivalent, and Ni becomes almost divalent through the above-described manufacturing process.

Moreover, according to the above-described two-stage firing method, the specific surface area of the formed complex oxide can be increased. This is considered to be due to the fact that carbon dioxide gas is generated during firing by firing in an inert atmosphere, whereby pores develop in the fired product and the specific surface area increases. According to the method of the present invention, a complex oxide having a high specific surface area of about 10 m ² / g or more can be obtained. The upper limit of the specific surface area is not particularly limited, but the above-described method can usually obtain a complex oxide having a specific surface area of up to about 50 m ² / g. The composite oxide of the present invention has such a high specific surface area, so that the Li insertion / desorption cross-sectional area becomes large, and it is considered that the charge / discharge reaction proceeds smoothly. In the present specification, the specific surface area is a BET specific surface area determined by an N ₂ gas adsorption method.

Furthermore, according to the two-step firing method described above, the oxidation of iron contained in the composite oxide is difficult to proceed and the formation of spinel ferrite components such as LiFe ₅ O ₈ and MnFe ₂ O ₄ that do not contribute to the charge / discharge reaction Is suppressed, thereby having a high charge / discharge capacity. The content of the spinel ferrite component can be indirectly evaluated by measuring spontaneous magnetization. According to the present invention, since the generation of the spinel ferrite component is suppressed, a composite oxide having a very low spontaneous magnetization of 0.005 emu / g or less can be obtained.

Furthermore, in the above-described firing step, the Li content, powder characteristics, and the like of the formed lithium manganese composite oxide can be controlled. For example, the lithium content in the lithium manganese composite oxide can be adjusted by appropriately setting the amount of the lithium compound added during firing. Moreover, the particle size of the lithium manganese composite oxide can be increased by increasing the firing temperature.

  After obtaining the lithium manganese composite oxide by the above-described firing step, the fired product is usually subjected to a water washing treatment or a solvent washing treatment in order to remove excess lithium compounds, impurities and the like. Thereafter, filtration may be performed and, for example, heat drying may be performed at a temperature of 80 ° C. or higher, preferably about 100 ° C.

Lithium Ion Secondary Battery A lithium ion secondary battery using the lithium manganese composite oxide of the present invention as a positive electrode material can be produced by a known method. For example, a novel composite oxide according to the present invention is used as a positive electrode material, a known metal lithium, a carbon-based material (activated carbon, graphite), silicon, silicon oxide, or the like is used as a negative electrode material, and a known electrolyte solution is used. Using a solution (organic electrolyte) in which a lithium salt such as lithium perchlorate or LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, etc., and other known battery configurations What is necessary is just to assemble a lithium ion secondary battery using an element according to a conventional method.

  According to the present invention, in the lithium manganese composite oxide containing iron and nickel, the novel composite oxide in which the average oxidation number of the transition metal element composed of manganese, iron and nickel is controlled to 3.4 to 3.6. Can be obtained.

  The obtained composite oxide has a large specific surface area, suppresses the generation of a ferrite component that does not contribute to the charge / discharge reaction, and is a highly useful oxide as a positive electrode material having a high charge / discharge capacity.

  Therefore, by using the composite oxide of the present invention as the positive electrode material, a lithium ion secondary battery having excellent performance can be obtained using a relatively inexpensive raw material.

The triangular composition figure which shows the molar ratio of the transition metal element contained in the lithium manganese complex oxide of this invention. The schematic block diagram of the reaction apparatus used by the Example and the comparative example. The schematic diagram of the evaluation cell used for the charging / discharging test in an Example and a comparative example.

  EXAMPLES Hereinafter, examples and comparative examples will be shown to further clarify the features of the present invention, but the present invention is not limited to the following examples and comparative examples.

Example 1
Using the reaction apparatus shown in FIG. 2, a lithium manganese composite oxide was produced by the following method.

  First, 3 L of water is placed in a 5 L SUS cylindrical reactor 2 equipped with a stirrer 1, then 150 g of ammonium sulfate is added, and a 37% sodium hydroxide aqueous solution is added until the pH reaches 11.0. The temperature was kept at 45 ° C. using an electric heater (not shown).

Then, iron (II) sulfate heptahydrate, manganese (II) sulfate pentahydrate and nickel (II) sulfate hexahydrate (iron: manganese: nickel metal (molar ratio) = 2: 6: 2) In addition to distilled water, it was completely dissolved. The metal ion concentrations at that time were 26.0 g / L for manganese, 9.25 g / L for nickel, and 8.76 g / L for iron. This was continuously supplied from the metal ion-containing solution preparation tank 4 through the pipe 3 to the reaction tank 2 at a constant rate over 4 hours. Moreover, the pH of the solution in the said reaction tank 2 was hold | maintained at 11.0 by adding 37% sodium hydroxide aqueous solution intermittently through the pipe | tube 6 from the solution tank 5 containing hydroxide ions. A pH sensor 7 was used to control the pH of the solution. By the above reaction operation, a coprecipitate composed of Fe—Mn—Ni composite hydroxide was obtained.

  Subsequently, the obtained composite hydroxide was washed with water by a decantation method to remove excessive salts such as sulfate and filtered, and an Fe—Mn—Ni composite hydroxide was obtained. This was put into a 2 L reaction vessel, and 141.9 g of lithium hydroxide monohydrate and distilled water were added to make a total slurry of 1.5 liters. Under stirring at 400 rpm, the slurry containing Fe-Mn-Ni composite hydroxide was subjected to an oxidation treatment by blowing air at 5 liters / min at room temperature for 1 day to mature the precipitate. They were dried with a spray dryer together with the slurry so that the powder temperature was 80 ° C.

  The obtained powder was fired at 500 ° C. for 3 hours in an air stream, and then the fired product was fired at 750 ° C. for 20 hours in a nitrogen stream. Subsequently, in order to remove excess lithium salt, the fired product was washed with distilled water, filtered and dried to obtain a powdery product.

X-ray diffraction (XRD) was performed on the obtained powdery product. As a result, the previously reported unit cell of Li ₂ MnO ₃ with monoclinic layered rock-salt structure: space group

The same measurement pattern was obtained. From this result, it was confirmed that the powdery product obtained in Example 1 was only a monoclinic layered rock salt type crystal phase.

Furthermore, the powdery product obtained in Example 1 was subjected to composition analysis, specific surface area measurement, spontaneous magnetization measurement, transition metal element average oxidation number measurement, and charge / discharge characteristic evaluation by the following methods. The results are shown in Table 1 below.
(I) Composition analysis The metal atom content (mass%) of each positive electrode active material powder was melt | dissolved with hydrochloric acid, and measured by ICP-AES (Perkin Elmer optima7300DV).
(Ii) Specific surface area measurement B. Measured by measuring the amount of adsorbed N ₂ gas using Maxsorb manufactured by Mountec. E. T. The specific surface area was determined by the method.
(Iii) using the spontaneous magnetization measurement Riken Denshi Co., Ltd. vibrating _{magnetometer, (NH 4) 2 Mn (} SO 4) 2 .6H after calibration the ₂ O as the magnetization standard sample, ranging from -1 + 1T Measure the magnetic field dependence of the magnetization of a sample with a known weight, and perform linear regression analysis of the magnetic field dependence of the magnetization for each of the +0.5 to + 1T range and the -0.5 to -1T range. Spontaneous magnetization was determined by averaging the absolute values.
(Iv) Measurement of average oxidation number of transition metal elements The average valence of transition metals was determined by a redox titration method utilizing the fact that iron, manganese and nickel become divalent cations in hydrochloric acid solution.

First, 1 g of potassium iodide is put into a 50 ml Erlenmeyer flask, and then the positive electrode active material powder 0.2
10 g of 6M hydrochloric acid and 10 ml of distilled water were added and dissolved. As a result, iron, manganese, and nickel having a valence of 2 or more generate iodine by a redox reaction that takes electrons from iodine ions to become divalent cations.

The amount of iodine produced by this reaction was measured by an oxidation-reduction titration method using thiosulfate, thereby measuring the number of electrons taken from iodine ions by iron, manganese and nickel. Since iron, manganese, and nickel are divalent in the solution state, the average oxidation numbers of iron, manganese, and nickel were obtained by calculating the number of moles from the amounts of iron, manganese, and nickel contained in each positive electrode active material powder. .
(V) Evaluation of charge / discharge characteristics Using the powdered product obtained in Example 1 as a positive electrode active material, a lithium ion secondary battery (TOM cell) was produced, and a charge / discharge test was conducted under the following battery configuration and charge / discharge conditions. went.
<Battery configuration and charge / discharge test conditions>
Positive electrode: The powdered product obtained in Example 1 was used as a positive electrode active material, a conductive material (acetylene black (AB) and a binder (polyvinylidene fluoride (PVDF)), an active material: AB: PVDF (weight ratio). ) = 85: 10: 5 was mixed in N-methyl-2-pyrrolidone (NMP) to form a slurry, which was then applied to an aluminum plate having a thickness of 20 μm. After drying, a positive electrode active material layer was formed on the surface of the aluminum plate, and then the aluminum plate on which the positive electrode active material layer was formed was pressure-molded at a pressure of 100 MPa to form a sheet-like sheet having a total thickness of 80 μm. The sheet-like molded product was punched out to 18 mm to obtain a positive electrode plate.
Negative electrode: Lithium metal electrolyte: LiPF ₆ dissolved at 1.0 mol / L in a mixed solvent of ethylene carbonate and dimethyl carbonate Test temperature: 25 ° C
Current density (per electrode plate): 0.21 mA
Potential range: 2.0-4.8 V (vs. Li)
Evaluation cell: TOM cell (manufactured by Nippon Tomcell) shown in FIG.

Examples 2-6
A powdery product was obtained in the same manner as in Example 1 except that the ratios of iron (II) sulfate heptahydrate, manganese (II) sulfate pentahydrate and nickel (II) sulfate hexahydrate were changed. It was.

  As a result of confirming the crystal structure of the obtained powdery product in the same manner as in Example 1, it was confirmed that all were monoclinic layered rock salt type crystal phases.

  Further, in the same manner as in Example 1, the product was subjected to composition analysis, specific surface area measurement, spontaneous magnetization measurement, transition metal element average oxidation number measurement, and charge / discharge characteristic evaluation. The results are shown in Tables 1 and 2 below.

Example 7
As raw materials, iron nitrate (III), nonahydrate, manganese chloride (II), tetrahydrate, and nickel chloride (II), hexahydrate (iron: manganese: nickel (molar ratio of metal components) = 2) A powdery product was obtained in the same manner as in Example 1 except that: 6: 2) was used.

  As a result of confirming the crystal structure of the obtained powdery product in the same manner as in Example 1, it was confirmed that it was only a monoclinic layered rock salt type crystal phase.

  Further, in the same manner as in Example 1, the product was subjected to composition analysis, specific surface area measurement, spontaneous magnetization measurement, transition metal element average oxidation number measurement, and charge / discharge characteristic evaluation. The results are shown in Table 2 below.

Example 8
A powdery product was obtained in the same manner as in Example 1 except that oxygen was blown instead of blowing air into the slurry solution containing the Fe—Mn—Ni composite hydroxide.

  As a result of confirming the crystal structure of the obtained powdery product in the same manner as in Example 1, it was confirmed that it was only a monoclinic layered rock salt type crystal phase.

  Further, in the same manner as in Example 1, the product was subjected to composition analysis, specific surface area measurement, spontaneous magnetization measurement, transition metal element average oxidation number measurement, and charge / discharge characteristic evaluation. The results are shown in Table 2 below.

Example 9
Instead of the operation of blowing air into the slurry solution containing the Fe-Mn-Ni composite hydroxide, 120 ml of 9 wt% H ₂ O ₂ solution was dropped into the slurry solution at a flow rate of 2 ml / min.
A powdery product was obtained in the same manner as in Example 1 except for the addition.

  As a result of confirming the crystal structure of the obtained powdery product in the same manner as in Example 1, it was confirmed that it was only a monoclinic layered rock salt type crystal phase.

  Further, in the same manner as in Example 1, the product was subjected to composition analysis, specific surface area measurement, spontaneous magnetization measurement, transition metal element average oxidation number measurement, and charge / discharge characteristic evaluation. The results are shown in Table 2 below.

Comparative Examples 1-3
A powdery product was obtained in the same manner as in Example 1 except that the ratios of iron (II) sulfate heptahydrate, manganese (II) sulfate pentahydrate and nickel (II) sulfate hexahydrate were changed. It was.

  As a result of confirming the crystal structure of the obtained powdery product in the same manner as in Example 1, it was confirmed that all were monoclinic layered rock salt type crystal phases.

  Further, in the same manner as in Example 1, the product was subjected to composition analysis, specific surface area measurement, spontaneous magnetization measurement, transition metal element average oxidation number measurement, and charge / discharge characteristic evaluation. The results are shown in Table 3 below.

Comparative Example 4
A powdered product was obtained in the same manner as in Example 1 except that air was not blown into the slurry solution containing the Fe—Mn—Ni composite hydroxide.

  As a result of confirming the crystal structure of the obtained powdery product in the same manner as in Example 1, it was confirmed that it was only a monoclinic layered rock salt type crystal phase.

  Further, in the same manner as in Example 1, the product was subjected to composition analysis, specific surface area measurement, spontaneous magnetization measurement, transition metal element average oxidation number measurement, and charge / discharge characteristic evaluation. The results are shown in Table 3 below.

Comparative Example 5
A powdery product was obtained in the same manner as in Example 1 except that the step of baking the powder after the wet oxidation treatment in an air stream was omitted.

The obtained powdery product was subjected to powder X-ray diffraction measurement. As a result, in addition to Li ₂ MO ₃ , a LiFeO ₂ peak was confirmed and it was considered that phase separation occurred.

  Further, in the same manner as in Example 1, the product was subjected to composition analysis, specific surface area measurement, spontaneous magnetization measurement, transition metal element average oxidation number measurement, and charge / discharge characteristic evaluation. The results are shown in Table 1 below.

Comparative Example 6
Instead of firing at 750 ° C. for 20 hours in a nitrogen stream, a powdery product was obtained in the same manner as in Example 1 except that firing was performed at 750 ° C. for 20 hours in an air stream.

  As a result of confirming the crystal structure of the obtained powdery product in the same manner as in Example 1, it was confirmed that it was only a monoclinic layered rock salt type crystal phase.

  Further, in the same manner as in Example 1, the product was subjected to composition analysis, specific surface area measurement, spontaneous magnetization measurement, transition metal element average oxidation number measurement, and charge / discharge characteristic evaluation. The results are shown in Table 1 below.

  As is clear from the above results, the powder products obtained by the methods of Examples 1 to 9 all have an average valence of the transition metal element in the range of 3.4 to 3.6. Compared with the powdery products of Comparative Examples 1 to 6 outside this range, the initial discharge capacity was a high value and had excellent charge / discharge characteristics.

  Furthermore, according to the methods of Examples 1 to 9, it was confirmed that a complex oxide having a large specific surface area and low spontaneous magnetization composed of a monoclinic layered rock salt type crystal phase single phase was obtained.

Claims (8)

Composition formula: Li _{1 + x} (Mn _1-mn Fe _m Ni _n ) _1-x O ₂ (where x, m and n are in the range of 0 ≦ x ≦ 1/3, 0 ≦ m ≦ 0.6, 0 A composite oxide having a monoclinic layered rock salt structure represented by ≦ n ≦ 0.3,
(1) The molar ratio of the three components of Mn, Fe, and Ni is point A (Mn: Fe: Ni = 60: 40: 0), point in the molar ratio triangular composition diagram with Mn, Fe, and Ni as vertices. B (Mn: Fe: Ni = 40: 60: 0), point C (Mn: Fe
: Ni = 70: 0: 30) and the point D (Mn: Fe: Ni = 80: 0: 20) within the range of a quadrangle with the four points as vertices,
(2) A lithium manganese composite oxide characterized in that the average oxidation number of Mn, Fe, and Ni is 3.4 to 3.6. ^2. The lithium manganese based composite oxide according to claim 1, wherein the specific surface area is 10 to 50 m ² / g and the spontaneous magnetization is 0.005 emu / g or less. A mixed aqueous solution containing a manganese compound, an iron compound, and a nickel compound is made alkaline to form a precipitate, a lithium compound is added to the formed precipitate and wet oxidation treatment is performed, followed by firing in an oxidizing atmosphere, The method for producing a lithium manganese composite oxide according to claim 1, wherein the firing is performed in an active gas atmosphere. The method for producing a lithium manganese composite oxide according to claim 3, wherein the temperature of the mixed aqueous solution at the time of precipitation formation is 30 to 80 ° C. The method of wet-oxidizing the precipitate is a method of blowing an oxidizing gas while stirring the aqueous solution containing the precipitate, or a method of adding the oxidizing compound while stirring the aqueous solution containing the precipitate. 4. The method for producing a lithium manganese composite oxide according to 4. 6. The lithium manganese composite according to claim 3, wherein firing in an oxidizing atmosphere is performed at 400 to 600 ° C., and firing in an inert gas atmosphere is performed at 600 to 850 ° C. 6. Production method of oxide. The positive electrode material for lithium ion secondary batteries which consists of a lithium manganese type complex oxide of Claim 1 or 2. The lithium ion secondary battery which uses the positive electrode material for lithium ion secondary batteries which consists of a lithium manganese type complex oxide of Claim 1 or 2 as a component.

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