JP4543156B2 - Lithium ferrite composite oxide and method for producing the same - Google Patents

Description

  The present invention relates to a lithium ferrite 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, most of the secondary batteries installed in portable devices such as mobile phones and notebook computers in Japan 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 and power load leveling systems in the future, 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.

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 rare metal cobalt, it is one of the causes of high material costs 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). There is a problem that the battery performance is significantly deteriorated, and the substitution to these materials is not so advanced.

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 _0.5 Mn _0.5 ) composed of lithium manganese oxide (Li ₂ MnO ₃ ) and lithium ferrite, which are inexpensive and resource-rich after iron. ) _1-x O ₂ or less iron-containing Li ₂ MnO ₃ ) has been found to have an average discharge voltage close to 4 V, comparable to lithium cobalt oxide, in charge and discharge tests at room temperature (see Patent Documents 3 and 4 below) ).

Furthermore, 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. Have already filed a patent application (Japanese Patent Application No. 2004-246085).

As described above, various reports have been made on lithium ferrite-based positive electrode materials that can replace lithium-cobalt-based positive electrode materials, but in order to further improve the charge / discharge characteristics, in order to find positive electrode materials with superior performance. In addition, 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 2002-68748 A Japanese Patent Laid-Open No. 2002-121026

  The present invention has been made in view of the current state of the prior art described above, and its main object is to maintain an average discharge voltage of 3 V or more in a long-term charge / discharge cycle, and a lithium cobalt oxide positive electrode material. The material can have a discharge capacity equivalent to or higher than that, can be obtained by using an inexpensive raw material with less resource restrictions, and compared with a known low-cost positive electrode material. An object of the present invention is to provide a novel material that can exhibit better charge / discharge characteristics.

The present inventor has intensively studied to achieve the above-described object. As a result, when a novel iron-aluminum-manganese oxide solid solution in which a specific amount of Al is further dissolved in iron-containing Li ₂ MnO ₃ is used as a positive electrode material for a lithium ion secondary battery, lithium-iron- It has been found that charge / discharge characteristics superior to those of the manganese composite oxide are exhibited, and the present invention has been completed.

That is, the present invention provides the following lithium ferrite composite oxide, a manufacturing method thereof, a lithium ion secondary battery positive electrode material and a lithium ion secondary battery comprising the lithium ferrite composite oxide.
1. Composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ (0 <x <1/3, 0.05 ≦ m ≦ 0.75, 0.01 ≦ n ≦ 0.5, 0.06 ≦ m + n <1 ) And a lithium ferrite composite oxide having a layered rock salt structure.
2. _2. The lithium ferrite composite oxide according to item 1, wherein n is 0.06 to 0.3 in the composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ .
3. A mixed aqueous solution containing a manganese compound and an iron compound is made alkaline to form a precipitate. The obtained precipitate is hydrothermally treated with an oxidizing agent and a water-soluble lithium compound under alkaline conditions, and then the hydrothermally treated product is converted to aluminum. Calcination in the presence of a compound and a lithium compound,
Composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ (0 <x <1/3, 0.05 ≦ m ≦ 0.75, 0.01 ≦ n ≦ 0.5, 0.06 ≦ m + n <1 ) And a method for producing a lithium ferrite composite oxide having a layered rock salt structure.
4). Composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ (0 <x <1/3, 0.05 ≦ m ≦ 0.75, 0.01 ≦ n ≦ 0.5, 0.06 ≦ m + n <1 4. Lithium ion secondary battery positive electrode material made of a lithium ferrite composite oxide having a layered rock salt structure. Composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ (0 <x <1/3, 0.05 ≦ m ≦ 0.75, 0.01 ≦ n ≦ 0.5, 0.06 ≦ m + n <1 ) And a lithium ion secondary battery comprising a lithium ion secondary battery positive electrode material made of a lithium ferrite composite oxide having a layered rock salt structure.

The lithium ferrite composite oxide of the present invention has a composition formula Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ (where 0 <x <1/3, 0.01 ≦ m ≦ 0.5, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n <1). The crystal structure is a layered rock salt structure similar to LiCoO ₂ which is a known substance.

FIG. 1 is a drawing schematically showing the structure of the lithium ferrite composite oxide of the present invention. The left side of FIG. 1 shows the elements contained in each layer of the crystal for LiCoO ₂ , and the right side of FIG. 1 shows the elements contained in each layer of the crystal for the composite oxide of the present invention.

As can be seen from FIG. 1, in LiCoO ₂ , Co ions and Li ions are two-dimensionally arranged along the a-axis direction at the positions between the octahedral lattices of the cubically packed oxide ions in the c-axis direction. It has a crystal structure laminated alternately. On the other hand, the crystal structure of the lithium ferrite oxide of the present invention is that Li ions, Fe ions, Al ions, and Mn ions are present in the Co layer of LiCoO ₂ and that Fe ions are partially in the Li layer. The feature is that it is replaced with.

Layered rock salt type LiFeO ₂ in which the Co layer of LiCoO ₂ is entirely replaced by Fe ions is known to have almost no charge / discharge capacity (K. Ado, M. Tabuchi , H. Kobayashi, H. Kageyama, O. Nakamura, Y. Inaba, R. Kanno, M. Takagi and Y. Takeda, J. Electochem. Soc., 144, [7], L177, (1997)).

In contrast, as described above, in the lithium ferrite composite oxide of the present invention, Fe ions are diluted in the Co layer due to the coexistence of Li ions, Al ions, and Mn ions. In order to obtain a complex oxide having a sufficient discharge capacity, such dilution of iron ions is an important requirement. In addition, Fe ions are often mixed in the Li layer, but this occurs because lithium ferrite tends to have a cubic rock salt structure (a structure corresponding to the assumption that all metal elements are the same ion in FIG. 1). Yes, these Fe ions do not contribute to charging and discharging.

In the composite oxide of the present invention, it is particularly important that a specific amount of Al ions is contained. In lithium-iron-manganese composite oxides in which no Al ions are present, spinel ferrite (compounds having an inverted spinel structure such as LiFe ₅ O ₈ or MnFe ₂ O ₄₎ is fired at a high temperature when the composite oxide is produced. ) Tend to be formed. Since this spinel ferrite is hardly charged / discharged in the 3-4V region, it may cause a decrease in charge / discharge performance. However, when Al is present, the formation of spinel ferrite is remarkably suppressed, contributing to charge / discharge. It is considered that the charge / discharge characteristics are further improved as compared with the lithium-iron-manganese composite oxide.

In the lithium ferrite composite oxide of the present invention, the amount of Fe ions to be dissolved (m value: Fe / (Fe + Mn + Al)) is 5 to 75 mol% (0.05 ≦ Fe / (Fe + Mn + Al) ≦ 0.75), preferably about 20 to 60 mol% (0.2 ≦ Fe / (Fe + Mn + Al) ≦ 0.6). In this case, not only is the Fe ion diluted insufficiently, but the Fe ions in the Li layer that are not involved in charge / discharge increase, which is not preferable in terms of battery characteristics. In some cases, the charge / discharge capacity is small, which is not preferable.

Al ions to be dissolved in the lithium ferrite composite oxide of the present invention are considered to be present in the layered rock salt structure in the form of replacing Mn ions in the same manner as Fe ions. Al ions are present in a trivalent state, and are thought to contribute to the refinement of composite oxide particles and the suppression of the formation of spinel ferrite as described above. The amount of Al ions dissolved in the composite oxide of the present invention (n value: Al / (Fe + Mn + Al)) is 1 to 50 mol% (0.01 ≦ Al / (Fe + Mn +) of the amount of metal ions other than Li ions. Al) ≦ 0.5), preferably about 6 to 30 mol% (0.06 ≦ Al / (Fe + Mn + Al) ≦ 0.3) When using a large amount of Al not involved in charge / discharge, This is not preferable because it causes a decrease in charge / discharge capacity and generation of impurities such as LiAlO _2. On the other hand, if the amount of Al ion solid solution is too small, effects such as spinel ferrite formation suppression effect and particle refinement are not sufficiently exhibited. So it is not preferable.

  The total amount of Fe ions and Al ions to be dissolved in the lithium ferrite composite oxide of the present invention is in the range of about 0.06 ≦ m + n <1 in the composition formula, preferably about 0.25 ≦ m + n ≦ 0.8. Is within the range.

In the lithium ferrite composite oxide of the present invention, as long as the layered rock salt type crystal structure can be maintained, _{x of} Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ is a transition metal. A value between 0 and 1/3 can be taken depending on the average valence of ions. Preferably it is the range of 0.05-0.30.

Furthermore, the composite oxide of the present invention is an impurity phase such as lithium hydroxide, lithium carbonate, aluminum compound (including hydrates thereof) in a range that does not significantly affect the charge / discharge characteristics (up to about 10 mol%). May be included.

  The composite oxide of the present invention can be produced by a conventional composite oxide synthesis method such as a hydrothermal reaction method or a solid phase reaction method. In particular, a production method using a hydrothermal reaction is preferable because a composite oxide having excellent charge / discharge performance can be easily formed.

In the production method using a hydrothermal reaction, first, a precipitate is formed by making a mixed solution obtained by dissolving a metal compound that is a source of generation of iron ions and manganese ions in water, a water / alcohol mixture or the like, alkaline. Next, an oxidant and a water-soluble lithium compound are added thereto, and hydrothermal treatment is performed under alkaline conditions to form a lithium-manganese-iron precursor. Next, a target lithium ferrite composite oxide can be obtained by adding a water-soluble aluminum compound and a lithium compound to the obtained precursor and baking it. Hereinafter, this manufacturing method will be specifically described.

  As an iron compound and a manganese compound, if it is a component which can form the mixed aqueous solution containing these compounds, it can use without limitation. 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, hydroxides and the like. These water-soluble compounds may be either anhydrides or hydrates. Further, even a water-insoluble compound such as an oxide can be used as an aqueous solution after being dissolved using an acid such as hydrochloric 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 the iron compound and manganese compound in this mixed aqueous solution become the element ratio similar to each element ratio in the target complex oxide.

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 iron compound and the manganese compound 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. By using a water-alcohol mixed solvent, a precipitate can be formed at a temperature lower than 0 ° C. The amount of alcohol used may be appropriately determined according to the target precipitation temperature, but it is usually appropriate to use about 50 parts by weight or less with respect to 100 parts by weight of water.

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.

  The method for making the mixed aqueous solution alkaline is not particularly limited, and usually an alkali or an aqueous solution containing an alkali may be added to the mixed aqueous solution. Moreover, a coprecipitate can be formed also by the method of adding this mixed aqueous solution to the aqueous solution containing an alkali.

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, 0.1
It can be used as an aqueous solution having a concentration of about ˜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.

  During precipitation, the temperature of the mixed aqueous solution is set to about -50 ° C to + 15 ° C, preferably about -40 ° C to + 10 ° C, so that spinel ferrite is generated due to the generation of heat of neutralization during the reaction. It is suppressed and a homogeneous coprecipitate is easily formed.

After making the mixed aqueous solution alkaline, the reaction solution is further blown with air at about 0 to 150 ° C. (preferably about 10 to 100 ° C.) for about 1 to 7 days (preferably about 2 to 4 days). In addition, it is preferable to oxidize and age the precipitate.

  The precipitate can be purified by washing the resulting precipitate with distilled water or the like to remove excess alkali components, residual raw materials, and the like, followed by filtration.

  Next, the precipitate obtained by the above method is subjected to hydrothermal treatment under alkaline conditions together with an oxidizing agent and a water-soluble lithium compound. Hydrothermal treatment can be performed by heating an aqueous solution containing the precipitate, the oxidizing agent, and the water-soluble lithium compound under alkaline conditions. Heating is usually performed in a sealed container.

In the aqueous solution used for the hydrothermal reaction, the content of the precipitate containing iron and manganese is preferably about 1 to 100 g, more preferably about 10 to 80 g per liter of water.

  As the water-soluble lithium compound, for example, a water-soluble lithium salt such as lithium chloride or lithium nitrate, lithium hydroxide, or the like can be used. These water-soluble lithium compounds can be used singly or in combination of two or more, and any of anhydrides and hydrates may be used.

  The amount of the water-soluble lithium compound used is preferably about Li / (Fe + Mn) = 1 to 10 as the molar ratio of lithium element to the total number of moles of Fe and Mn in the precipitation product, and about 3 to 7 More preferably.

The concentration of the water-soluble lithium compound is preferably about 0.1 to 10 mol / l, 1 to 8 mol / l
More preferably, it is about.

  The oxidizing agent can be used without particular limitation as long as it decomposes during the hydrothermal reaction to generate oxygen, and specific examples include potassium chlorate, lithium chlorate, sodium chlorate, hydrogen peroxide water, and the like. Can do.

The concentration of the oxidizing agent is preferably about 0.1 to 10 mol / l, and more preferably about 0.5 to 5 mol / l.

  About pH of the aqueous solution at the time of performing a hydrothermal reaction, it is usually preferable to set it as about pH8 or more, and it is more preferable to set it as about pH11 or more.

  When the aqueous solution containing the precipitate, the oxidizing agent and the aqueous lithium compound is under alkaline conditions, it may be heated as it is, but when the pH value is low, for example, an alkali metal such as potassium hydroxide or sodium hydroxide. What is necessary is just to raise pH value by adding a hydroxide, ammonia, etc.

  Hydrothermal reaction can be performed using a normal hydrothermal reaction apparatus (for example, a commercially available autoclave).

  Hydrothermal reaction conditions are not particularly limited, but may be usually about 100 to 300 ° C. and about 0.1 to 150 hours, preferably about 150 to 250 ° C. and about 1 to 100 hours.

After completion of the hydrothermal reaction, the reaction product is usually washed in order to remove the remaining lithium compound and the like. For example, water, water-alcohol, acetone or the like can be used for washing. Next, the product is filtered and dried at a temperature of 80 ° C. or higher (usually about 100 ° C.) to obtain a lithium-iron-manganese precursor.

  In the present invention, the target layered rock salt type lithium ferrite composite oxide can be obtained by firing the precursor obtained above together with an aluminum compound and a lithium compound.

The aluminum compound can be used without particular limitation as long as it is a compound containing an aluminum element. For example, aluminum oxide, aluminum hydroxide, aluminum nitrate, aluminum chloride, hydrates thereof, and the like can be used. The amount of the aluminum compound used may be appropriately set according to the Al / (Fe + Mn + Al) ratio (n value) in the composition formula of the target substance. In particular, it is preferable to use an X-ray diffraction pattern or the like so that ferrite, LiAlO _{2 and the} like, which are impurity phases not involved in charge / discharge, are not recognized.

In addition, since Al ³⁺ ions are amphoteric metal ions that are soluble in both acids and alkalis, Al ions may be eluted during the water washing treatment after firing, which will be described later. Usually, according to the production method of the present invention, a lithium ferrite composite oxide having an Al molar ratio of about 50% of the Al molar ratio in the raw material tends to be obtained. For this reason, in order to obtain a lithium ferrite composite oxide having an intended Al molar ratio, the Al molar ratio in the raw material may be appropriately increased or decreased according to the Al molar ratio in the product.

The lithium compound can be used without particular limitation as long as it contains a lithium element. Specific examples include lithium salts such as lithium chloride, lithium nitrate, and lithium acetate, lithium hydroxide, and hydrates thereof. it can. The amount of lithium compound used is lithium
What is necessary is just to set it as about 0.1-2 mol with respect to 1 mol of iron-manganese precursors.

  Usually, in order to improve the reactivity, it is preferable to pulverize and mix the lithium-iron-manganese precursor obtained by the above method, and then to fire. As for the degree of pulverization, it is sufficient that coarse particles are not included and the mixture has a uniform color tone.

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.

The firing atmosphere is not particularly limited, and any atmosphere such as the air, an oxidizing atmosphere, an inert atmosphere, or a reducing atmosphere can be selected. The firing temperature is preferably about 200 to 1000 ° C, more preferably about 300 to 800 ° C. The firing time is preferably about 1 to 100 hours, and more preferably about 20 to 60 hours.

After completion of the firing, the fired product is usually subjected to a water washing treatment, a solvent washing treatment or the like in order to remove excess lithium compound. Thereafter, filtration is performed, for example, a temperature of 80 ° C. or higher, preferably 100 ° C.
You may heat dry at the temperature of a grade.

Furthermore, if necessary, the heat-dried product is pulverized, a lithium compound is added, calcined, washed, and dried to repeat a series of operations, whereby the excellent properties of the lithium ferrite composite oxide ( Stable charge / discharge characteristics, high capacity, etc. in the operating voltage region as a positive electrode material for a lithium ion secondary battery can be further improved.

The lithium ion secondary battery using the lithium ferrite composite oxide according to the present invention can be manufactured by a known method. That is, the novel composite oxide according to the present invention is used as the positive electrode material, the known metal lithium, carbon-based material (activated carbon, graphite), etc. are used as the negative electrode material, and the known ethylene carbonate and dimethyl are used as the electrolyte. A lithium ion secondary battery can be assembled according to a conventional method using a solution in which a lithium salt such as lithium perchlorate or LiPF ₆ is dissolved in a solvent such as carbonate, and using other known battery components. That's fine.

  According to the present invention, using an inexpensive raw material and element, the average discharge voltage can be maintained at 3 V or more, and the discharge capacity (150 mAh / g or more) is equal to or higher than that of the lithium cobalt oxide-based positive electrode material. Thus, a novel composite oxide useful as a positive electrode material can be obtained.

  In particular, the composite oxide of the present invention has many components that contribute to charge / discharge because the formation of spinel ferrite is suppressed during heat treatment at high temperatures, and can exhibit excellent charge / discharge characteristics.

  The lithium ferrite composite oxide according to the present invention is extremely useful as a positive electrode material for a lithium ion secondary battery having a high capacity and a low cost.

  Hereinafter, examples and comparative examples will be shown to further clarify the features of the present invention.

Example 1
Add 50.50 g of iron (III) nitrate nonahydrate and 24.74 g of manganese (II) chloride tetrahydrate (total amount 0.25 mol, Fe: Mn molar ratio = 1: 1) to 500 ml of distilled water and dissolve completely. It was. An aqueous lithium hydroxide solution (a solution in which 50 g of lithium hydroxide monohydrate was dissolved in 500 ml of distilled water) was prepared in another beaker. This lithium hydroxide aqueous solution was put into a titanium beaker, 200 ml of ethanol was added and stirred, and then allowed to stand in a thermostatic bath, and the thermostatic bath was kept at −10 ° C. Next, the metal salt aqueous solution was gradually dropped into the lithium hydroxide aqueous solution over 2 to 3 hours to form an Fe-Mn precipitate. Make sure that the reaction solution is completely alkaline (pH 11 or higher), and under stirring, add the coprecipitate to the reaction solution at room temperature.
Oxidation treatment was performed by blowing air for days to age the precipitate.

The obtained precipitate was washed with distilled water and filtered, and the precipitated product was mixed with lithium hydroxide monohydrate 50.
g, 50 g of potassium chlorate, 309 g of potassium hydroxide and 600 ml of distilled water were placed in a polytetrafluoroethylene beaker and stirred well. The pH of this aqueous solution was 11 or more. Thereafter, it was placed in a hydrothermal reactor (autoclave) and hydrothermally treated at 220 ° C. for 8 hours.

  After the hydrothermal treatment is completed, the reaction furnace is cooled to near room temperature, the beaker containing the hydrothermal treatment reaction solution is taken out of the autoclave, the generated precipitate is washed with distilled water, and excess lithium hydroxide or the like is present. By removing the salts and filtering, a powdery product (lithium-iron-manganese precursor) was obtained.

The precursor obtained by filtration was mixed with lithium hydroxide aqueous solution in which 15.74 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water, and further 10.42 g of aluminum nitrate nonahydrate (Fe: Mn: Al An aqueous solution in which a molar ratio = 0.45: 0.45: 0.10) was dissolved in 50 ml of distilled water was added, and after stirring, dried overnight at 100 ° C. and pulverized to produce a powder.

Next, the obtained powder was calcined in an oxygen stream at 700 ° C. for 20 hours, and in order to remove excess lithium salt, the calcined product was washed with distilled water, filtered, dried, and the target products of iron and Aluminum-containing Li ₂ MnO ₃ was obtained as a powdered product.

Rietveld analysis of the X-ray diffraction pattern of this final product (program is RIETAN-2000
2 is shown in FIG. In FIG. 2, the actually measured X-ray diffraction pattern of the iron and aluminum-containing Li ₂ MnO ₃ is indicated by a (+) mark, and the calculated value is indicated by a solid line. In addition, the peak position of iron and aluminum-containing Li ₂ MnO ₃ is a vertical bar, and the difference between the measured value and the calculated value is displayed in the lower part of the pattern. All peaks are unit cells of layered rock salt type iron-containing Li ₂ MnO ₃ (Li _{1 + x} (Fe _0.5 Mn _0.5 ) _1-x O ₂ ) of Comparative Example 1 described later.

で指数付けすることができた。

I was able to index.

The lattice constant (a = 2.8769 (3) A, c = 14.2764 (13) A) calculated from each peak of the iron and aluminum-containing Li ₂ MnO ₃ obtained in Example 1 is the layered rock salt type of Comparative Example 1. Of iron-containing Li ₂ MnO ₃ (Li _{1 + x} (Fe _0.5 Mn _0.5 ) _1-x O ₂ ) % (m value) and 6 mol% (n value) are contained, and the x value calculated from the Li / (Mn + Fe + Al) value is 0.20. It was confirmed that the contained Li ₂ MnO ₃ (Li _1.20 (Fe _0.47 Mn _0.47 Al _0.06 ) _0.80 O ₂ ) was obtained.

From the Rietveld analysis results, it was found that the structural model corresponding to the crystal structure of FIG. 1 is expressed as (Li _0.9325 M _{0.0675 (18)} ) _3a [M _{0.707 (3)} Li _0.293 ] _3b O ₂ . Here, 3a and 3b indicate the occupied positions of metal ions in the Li layer and the Co layer of LiCoO ₂ in FIG. 1, respectively, and M indicates a metal ion other than lithium. The sum of the metal amounts M at positions 3a and 3b is 0.775, which is very close to 0.80 estimated from the above composition formula, and supports the above conclusion.

FIG. 3 shows the iron and aluminum-containing Li ₂ MnO ₃ obtained as the final product in Example 1.
It is drawing which electronically processed the electron micrograph of this. From FIG. 3, it is clear that, according to Example 1, iron and aluminum-containing Li ₂ MnO ₃ having a relatively uniform particle size of about 100 nm was formed.

Comparative Example 1
In the same manner as in Example 1, after forming a precipitate from the Fe-Mn mixed aqueous solution and aging, hydrothermal treatment,
A lithium-iron-manganese precursor was obtained by washing with water and filtering.

Next, a lithium hydroxide aqueous solution in which 15.74 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water and the precursor were mixed, dried at 100 ° C., and pulverized to obtain a powdered product. . The obtained powdery product was calcined at 700 ° C. for 20 hours in an oxygen stream, and the calcined product was washed with distilled water, filtered and dried to remove excess lithium salt, and the iron-containing Li ₂ MnO ₃ was obtained as a powder product.

The X-ray diffraction pattern of this final product is shown in FIG. In FIG. 4, the measured X-ray diffraction pattern of the iron-containing Li ₂ MnO ₃ is indicated by a (+) mark, and the calculated value is indicated by a solid line. The peak position of iron-containing Li ₂ MnO ₃ is a vertical bar, and the difference between the measured value and the calculated value is displayed in the lower part of the pattern.

  All sharp diffraction peaks are derived from layered rock salt structures

で指数付け可能であり、層状岩塩型を有するリチウム−鉄−マンガン複合酸化物が生成していることが確認できた。得られた格子定数値は、既に報告されているリチウム−鉄−マンガン複合酸化物の値（格子定数a=2.882A, c=14.287A）に近い値であった（M.Tabuchi, A.Nakashima, H.Shigemura, K.Ado, H.Kobayashi, H.Sakaebe, H.Kageyama, T.Nakamura,
M.Kohzaki, A.Hirano and R.Kanno, Journal of The Electrochemical Society, 149, A509-A524, 2002。）
一方、図中矢印で示されるブロードなピークは試料中に存在するスピネルフェライトの単位胞

Thus, it was confirmed that a lithium-iron-manganese composite oxide having a layered rock salt type was formed. The obtained lattice constant value was close to the value of the reported lithium-iron-manganese complex oxide (lattice constant a = 2.882A, c = 14.287A) (M. Tabuchi, A. Nakashima , H. Shigemura, K. Ado, H. Kobayashi, H. Sakaebe, H. Kageyama, T. Nakamura,
M. Kohzaki, A. Hirono and R. Kanno, Journal of The Electrochemical Society, 149, A509-A524, 2002. )
On the other hand, the broad peak indicated by the arrow in the figure is a unit cell of spinel ferrite present in the sample.

で指数付けできた。鉄含有Li₂MnO₃とスピネルフェライト両生成相の存在比は、78:22と見積もられた。比較例１において得られた鉄含有Li₂MnO₃の各ピークより計算される格子定
数(a= 2.86316(17)A, c=14.2430(9)A)が、上記文献の記載値に近いこと、化学分析(下記
表１)により、Feが仕込量通り50モル%(m値)含まれていること、Li/(Mn+Fe)値より計算さ
れるx値が0.15であることから、比較例１において、試料平均組成は(Li_1.15(Fe_0.5Mn_0.5)_0.85O₂)となる。またリートベルト解析結果より図1の結晶構造に対応する構造モデルが(Li_0.9784M_0.0216(19))_3a[M_0.673(4)Li_0.327]_3bO₂と表されることがわかった。ここで3a及
び3bはそれぞれ図１のLiCoO₂のLi層とCo層内の金属イオンの占有位置をそれぞれ示し、M
はリチウム以外の金属イオンを示す。3a及び3b位置の金属量Ｍの和は0.695となり上記組
成式から推定される0.85に比べかなり小さくなっている。これは鉄含有Li₂MnO₃に比べて
鉄イオンを多く含むスピネルフェライトの生成により鉄イオンが鉄含有Li₂MnO₃構造中よ
り遊離した結果として生じたものと判断できる。

I was able to index. The abundance ratio of both iron-containing Li ₂ MnO ₃ and spinel ferrite formation phases was estimated to be 78:22. The lattice constants (a = 2.86316 (17) A, c = 14.2430 (9) A) calculated from the peaks of the iron-containing Li ₂ MnO ₃ obtained in Comparative Example 1 are close to the values described in the above document, As a result of chemical analysis (Table 1 below), Fe contained 50 mol% (m value) as charged, and the x value calculated from the Li / (Mn + Fe) value was 0.15. 1, the sample average composition is (Li _1.15 (Fe _0.5 Mn _0.5 ) _0.85 O ₂ ). From the Rietveld analysis results, it was found that the structural model corresponding to the crystal structure of FIG. 1 is expressed as (Li _0.9784 M _{0.0216 (19)} ) _3a [M _{0.673 (4)} Li _0.327 ] _3b O ₂ . Here, 3a and 3b respectively indicate the occupied positions of metal ions in the Li layer and the Co layer of LiCoO ₂ in FIG.
Represents a metal ion other than lithium. The sum of the metal amounts M at the positions 3a and 3b is 0.695, which is considerably smaller than 0.85 estimated from the above composition formula. This can be determined to have occurred as a result of iron ions liberated from the iron-containing Li ₂ MnO ₃ structure by the formation of spinel ferrites containing more iron than the iron-containing Li ₂ MnO _3.

  From the above results, it is clear that in Comparative Example 1, a large amount of spinel ferrite phase was by-produced despite the production under the same production conditions as in Example 1 except that aluminum nitrate was added. From this result, it was confirmed that there was an effect of suppressing the formation of spinel ferrite by dissolving aluminum ions as in Example 1.

  The elemental analysis results in Example 1 and Comparative Example 1 are shown in Table 1 below.

Charge / discharge test Each composite oxide obtained in Example 1 and Comparative Example 1 is used as a positive electrode material, a carbon material is used as a negative electrode material, and a mixed salt of ethylene carbonate and diethyl carbonate is used as a supporting salt, LiPF. _A coin-type lithium battery was prepared using a 1M solution in which ₆ was dissolved as an electrolyte. The charge / discharge characteristics of this lithium battery were studied at the start of charging at 60 ° C. (potential range: 3.0-4.3 V, current density: 42 mA / g).

FIG. 5 is a graph showing charge / discharge characteristics of lithium batteries using the positive electrode materials of Example 1 and Comparative Example 1. In FIG. 5, the upward curve corresponds to the charge curve, and the downward curve corresponds to the discharge curve. From FIG. 5, the battery using the iron- and aluminum-containing Li ₂ MnO ₃ positive electrode material of Example 1 has a higher charge / discharge capacity than the battery using the iron-containing Li ₂ MnO ₃ positive electrode material of Comparative Example 1. It is clear.

FIG. 6 is a graph showing the dependency of the discharge capacity of each battery on the number of charge / discharge cycles. From this result, it can be seen that the lithium battery using the iron and aluminum-containing Li ₂ MnO ₃ positive electrode material of Example 1 has a high capacity over all the cycle numbers.

From the above results, the iron- and aluminum-containing Li ₂ MnO ₃ composite oxide of the present invention exhibits excellent charge / discharge characteristics in a charge / discharge test at a high temperature of 60 ° C., and is a lithium ferrite type for lithium ion secondary batteries. It was confirmed that the cathode material has excellent performance.

It is drawing which shows typically the crystal structure of the lithium ferrite type complex oxide of the present invention. . 1 is a drawing showing an X-ray diffraction pattern of a sample obtained in Example 1. An electron micrograph of the resulting iron and aluminum-containing Li ₂ MnO ₃ in Example 1 is an electronic image-processed drawings. 4 is a drawing showing an X-ray diffraction pattern of a sample obtained in Comparative Example 1. It is a graph which shows the charging / discharging characteristic in 60 degreeC of the coin-type lithium battery which each used the sample obtained in Example 1 and Comparative Example 1 as a positive electrode material. It is a graph which shows the charge-discharge cycle number dependence of the discharge capacity of the coin-type lithium battery which used the sample obtained in Example 1 and Comparative Example 1 as a positive electrode material, respectively.

Claims (5)

Composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ (0 <x <1/3, 0.05 ≦ m ≦ 0.75, 0.01 ≦ n ≦ 0.5, 0.06 ≦ m + n <1 ) And a lithium ferrite composite oxide having a layered rock salt structure. _2. The lithium ferrite composite oxide according to claim 1, wherein in the composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ , n is 0.06 to 0.3. A mixed aqueous solution containing a manganese compound and an iron compound is made alkaline to form a precipitate. The obtained precipitate is hydrothermally treated with an oxidizing agent and a water-soluble lithium compound under alkaline conditions, and then the hydrothermally treated product is converted to aluminum. Calcination in the presence of a compound and a lithium compound,
Composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ (0 <x <1/3, 0.05 ≦ m ≦ 0.75, 0.01 ≦ n ≦ 0.5, 0.06 ≦ m + n <1 ) And a method for producing a lithium ferrite composite oxide having a layered rock salt structure. Composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ (0 <x <1/3, 0.05 ≦ m ≦ 0.75, 0.01 ≦ n ≦ 0.5, 0.06 ≦ m + n <1 Lithium ion secondary battery positive electrode material comprising a lithium ferrite complex oxide having a layered rock salt type structure Composition formula: Li _{1 + x} (Mn _1-mn Fe _m Al _n ) _1-x O ₂ (0 <x <1/3, 0.05 ≦ m ≦ 0.75, 0.01 ≦ n ≦ 0.5, 0.06 ≦ m + n <1 ) And a lithium ion secondary battery comprising a lithium ion secondary battery positive electrode material made of a lithium ferrite composite oxide having a layered rock salt structure.

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