JP2006036620A - Lithium ferrite-based multiple oxide and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new material which can stably charge and discharge in an operating voltage region (about 4 V) equivalent to that of existing lithium cobalt oxide-based positive electrode material, by using inexpensive raw materials having little restriction on resources. <P>SOLUTION: This lithium ferrite-based multiple oxide having a layered rock salt-type structure is expressed by the compositional formula: Li<SB>1+x</SB>(Mn<SB>1-m-n</SB>Fe<SB>n</SB>Co<SB>m</SB>)<SB>1-x</SB>O<SB>2</SB>, where 0<x<1/3; 0.01≤m≤0.50; 0.05≤n≤0.75; 0.06≤m+n<1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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.

  In Japan, most of the 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 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 particular, LiCoO ₂ as the positive electrode material has a battery operating voltage (difference between the redox potential of the transition metal in the positive electrode and the redox potential of the negative electrode element), charge / discharge capacity (the amount of Li that can be desorbed and inserted from the positive electrode). ) And other important materials related to battery performance, and demand is expected to increase further in the future. However, since this compound contains a large amount of cobalt, which is a rare metal, it is one of the high cost factors of a lithium ion secondary battery. Furthermore, considering that about 20% of the world's global cobalt production is already used in the battery industry, it is unclear whether only the positive electrode material made of LiCoO ₂ can meet future demand growth. is there.

Currently, as a cheaper and more cathode material less resource limitations, lithium nickel oxide (LiNiO _2), lithium manganese oxide and (LiMn ₂ O ₄₎ or the like are known, some are replaced in LiCoO ₂ practical It has become. However, these materials have problems such as safety problems during battery charging (LiNiO ₂ ) and significant characteristic degradation due to manganese dissolution at 50 ° C. or higher (LiMn ₂ O ₄ ). Replacement of LiCoO ₂ with these materials has not progressed as expected.

In addition, lithium ferrite (LiFeO ₂ ) containing iron, which is more abundant in resources, less toxic, and cheaper than manganese and nickel, is being investigated as a potential electrode material. However, since lithium ferrite obtained by high-temperature firing using a normal iron source and Li source hardly charges and discharges, it does not have activity as a positive electrode material for a lithium ion secondary battery.

On the other hand, as a starting material alpha-NaFeO ₂ or FeOOH, LiFeO ₂ obtained using the H / Li ion exchange or Na / Li ion exchange method, although a charge flat potential in the vicinity of 4V, discharge potential Is less than 3V. (See Patent Document 1 and Patent Document 2 below). The discharge potential of LiFeO ₂ obtained by this ion exchange method is about 1 V or more lower than the discharge potential of LiCoO ₂ , and substitution of the latter material with the former material is quite difficult. As described above, a production technique for lithium ferrite reaching a practical level has not yet been established.

In the lithium secondary battery, as a criterion for determining whether or not lithium ferrite-based oxide is a positive electrode material that can replace LiCoO ₂ , the discharge flat potential associated with 3 + / 4 + redox of iron is present in the vicinity of 4V. There is a point whether or not. The present inventors have prepared a solid solution of lithium ferrite and lithium manganese oxide (Li ₂ MnO ₃ ) (Li _{1 + x} (Fe _0.5 Mn _0.5 ) _1-x O ₂ , 0 ≦ x ≦ 1/3. It has been found that a compound having a discharge flat potential accompanying 3 + / 4 + redox of iron in the 4V region can be obtained by forming (containing Li ₂ MnO ₃ ) (abbreviated as “Li ₂ MnO ₃ ”) (Patent Document 3 and Patent below) Reference 4). However, there is a problem that the charge / discharge capacity in the 4V region of this material deteriorates with an increase in the number of charge / discharge test cycles. At present, the above method has a high capacity necessary for practical use and Since a material with little cycle deterioration has not been obtained, further technical improvement is necessary (see Non-Patent Document 1 below).

In addition, the present inventors have found that by changing the nickel ions in the iron-containing Li ₂ MnO ₃ phase, changes due to an increase in the number of cycles of the charge / discharge curve can be suppressed under a low current density (7.5 mA / g). (See Patent Document 5 below). However, in order to put the iron-containing Li ₂ MnO ₃ positive electrode material into practical use, it has a high capacity (90 mAh / g or more) at a higher current density (for example, 40 mA / g or more).
Is extremely important. Accordingly, there is a strong demand for the development of a positive electrode material having such characteristics.

Furthermore, in order to put a new material into practical use as a positive electrode for a lithium ion secondary battery, a cathode material that has been put into practical use at low cost and has few resource constraints, such as lithium manganese spinel (Li _{1 + δ} Mn ₂₋ Having an advantage over _δ O ₄ (0 <δ <0.33) is also an important requirement.
Japanese Patent Laid-Open No. 10-120421 JP-A-8-295518 JP 2002-68748 A Japanese Patent Laid-Open No. 2002-121026 JP2003-48718 Mitsuharu Tabuchi et al., “Examination of charge / discharge characteristics improvement method for iron-containing Li2MnO3”, The 68th Annual Meeting of the Electrochemical Society of Japan, Kobe, April 2001

  The present invention has been made in view of the current state of the prior art as described above, and its main purpose is to stably charge and discharge in an operating voltage range (about 4 V) equivalent to that of a lithium cobalt oxide-based positive electrode material. Can be obtained by using inexpensive raw materials with less resource constraints, and more excellent compared to existing low-priced cathode materials that are in practical use. It is another object of the present invention to provide a novel material capable of exhibiting excellent charge / discharge characteristics.

The present inventor has intensively studied in view of the above problems of the prior art. As a result, in addition to finding a novel iron-cobalt-containing solid solution in which a specific amount of Co is further dissolved in iron-containing Li ₂ MnO ₃ , and using this solid solution as a positive electrode material for a lithium ion secondary battery, It has been found that high capacity can be achieved while maintaining good cycle characteristics in the target operating voltage range of about 4V. Furthermore, this solid solution has a high capacity under high-temperature charge / discharge conditions of, for example, about 60 ° C. using a carbon negative electrode when compared with an existing positive electrode material using a relatively inexpensive raw material such as lithium manganese spinel. I found out that it was. The present invention has been completed based on these findings.

That is, the present invention provides a lithium ferrite composite oxide, a manufacturing method thereof, a positive electrode material for a lithium ion secondary battery comprising the lithium ferrite composite oxide, and a lithium ion secondary battery described below.
1. Composition formula Li _{1 + x} (Mn _1-mn Fe _n Co _m ) _1-x O ₂ (However, 0 <x <1/3, 0.01 ≦ m ≦ 0.50, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n < A lithium ferrite complex oxide represented by 1) and having a layered rock salt structure.
2. The above-mentioned item is characterized in that a mixed aqueous solution containing a manganese compound, an iron compound and a cobalt compound is made alkaline to form a precipitate, and the obtained precipitation product is hydrothermally treated under alkaline conditions together with an oxidizing agent and a water-soluble lithium compound. 1. A method for producing a lithium ferrite composite oxide described in 1.
3. 3. The method for producing a lithium ferrite composite oxide according to item 1, wherein the product obtained after hydrothermal treatment by the method of item 2 is fired together with a lithium compound.
4). Composition formula Li _{1 + x} (Mn _1-mn Fe _n Co _m ) _1-x O ₂ (However, 0 <x <1/3, 0.01 ≦ m ≦ 0.50, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n < A positive electrode material for a lithium ion secondary battery represented by 1) and comprising a lithium ferrite composite oxide having a layered rock salt structure.
5. Composition formula Li _{1 + x} (Mn _1-mn Fe _n Co _m ) _1-x O ₂ (However, 0 <x <1/3, 0.01 ≦ m ≦ 0.50, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n < A lithium ion secondary battery comprising as a constituent element a positive electrode material comprising a lithium ferrite composite oxide represented by 1) having a layered rock salt structure.

Lithium ferrite composite oxide of the present invention, the composition formula _{Li 1 + x (Mn 1-} mn Fe n Co m) 1-x O 2 ( where, 0 <x <1 / 3,0.01 ≦ m ≦ 0.50,0.05 ≦ 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-based oxide of the present invention is that Li ions, Fe ions, and Mn ions partially replace the Co layer of LiCoO ₂ , and Fe ions are partially in the Li layer. The feature is that it is replaced with.

Conventionally, the layered rock salt type LiFeO ₂ in which the Co layer of LiCoO ₂ is completely 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)).

On the other hand, as described above, in the lithium ferrite composite oxide of the present invention, Fe ions are diluted by the coexistence of Li ions and Mn ions in the Co layer. 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 is because the lithium ferrite has a cubic rock salt structure (
This occurs because all the metal elements in FIG. 1 are assumed to have the same ion), and this Fe ion does not contribute to charge / discharge.

In the lithium ferrite composite oxide of the present invention, the amount of Fe ions to be dissolved (n value: Fe / (Fe + Mn + Co)) is 5 to 75 mol% (0.05 ≦ Fe / (Fe + Mn + Co) ≦ 0.75), preferably 20 to 60 mol% (0.20 ≦ Fe / (Fe + Mn + Co) ≦ 0.60) .When the amount of Fe ion solid solution is excessive Is not preferable in terms of battery characteristics because the Fe ions in the Li layer that do not participate in charge / discharge increase, whereas the charge / discharge capacity decreases when the amount of Fe ions dissolved is too small. It is not preferable.

Co ions dissolved in the lithium ferrite composite oxide of the present invention are basically present in the layered rock salt structure in the form of replacing Mn ions in the same manner as Fe ions (K. Numata, C. Sasaki, and S. Yamanaka, Solid State Ionics, 117, 257-263, (1999).). Co ions are presumed to exist in a trivalent state, and contribute to the reduction of the Fe ion content in the Li layer by improving the electronic conductivity of the composite oxide and stabilizing the layered rock salt structure. Seem. The amount of Co ions (m value: Co / (Fe + Mn + Co)) to be dissolved in the composite oxide of the present invention is 1 to 50 mol% (0.01 ≦ Co / (Fe + Mn +) of the amount of metal ions other than Li ions. Co) ≦ 0.50), preferably 5-30 mol% (0.05 ≦ Co / (Fe + Mn + Co) ≦ 0)
.30). When a large amount of Co, which is more expensive than Mn and Fe, is used, it is economically disadvantageous. On the other hand, when the amount of Co ions dissolved is too small, effects such as improvement of electron conductivity and stabilization of the layered rock salt structure are not sufficiently exhibited.

Further, the total amount of Fe ions and Co ions to be dissolved in the lithium ferrite composite oxide of the present invention is 0.06 ≦ m + n <1 in the above composition formula, preferably within the range of 0.3 ≦ m + n ≦ 0.8. It is in.

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

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

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, from the viewpoint of uniform mixing, using a mixed solution in which a metal compound that is a source of each ion is dissolved in water, a water / alcohol mixture,
It is preferable to produce by a hydrothermal reaction method. Hereinafter, a production method using a hydrothermal reaction will be specifically described.

  The composite oxide of the present invention using hydrothermal reaction is prepared by forming a precipitate by making a mixed aqueous solution containing an iron compound, a manganese compound and a cobalt compound alkaline, and the resulting precipitation product is converted into an oxidant and water-soluble lithium. It can be carried out by hydrothermal treatment with the compound under alkaline conditions.

  As an iron compound, a manganese compound, and a cobalt 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, manganese compound, and cobalt compound in this mixed aqueous solution become an 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, manganese compound and cobalt 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 coprecipitate from the mixed aqueous solution, the mixed aqueous solution may be made alkaline. Conditions for forming good coprecipitates vary depending on the type and concentration of each compound contained in the mixed aqueous solution, and thus cannot be defined unconditionally. However, the pH is preferably about 8 or more, and preferably about 11 or more. Is more preferable.

  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 for making 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.

  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.

  When the precipitate is formed, the temperature of the mixed aqueous solution is set to about −50 ° C. to + 15 ° C., preferably about −40 ° C. to + 10 ° C., whereby a homogeneous coprecipitate is easily formed.

  After forming the precipitate by making the mixed aqueous solution alkaline, the reaction solution is further air-cooled at about 0 to 150 ° C. (preferably about 10 to 100 ° C.) for about 1 to 7 days (preferably about 2 to 4 days). The coprecipitate is preferably oxidized and aged while blowing.

  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 precipitation product obtained by the above-described 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 the aqueous solution containing the precipitation product, the oxidizing agent and the water-soluble lithium compound under alkaline conditions.

In the aqueous solution used for the hydrothermal reaction, the content of the precipitation product containing Fe, Mn and Co 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 + Co) = 1 to 10 as a molar ratio of lithium element to the total number of moles of Fe, Mn and Co in the precipitation product, More preferably, it is about 3-7.

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 precipitation product, oxidizing agent and water-soluble lithium compound is under alkaline conditions, it may be heated as it is, but when the pH value is low, for example, potassium hydroxide, sodium hydroxide, for example The pH value may be increased by adding an alkali metal hydroxide such as ammonia or ammonia.

  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. The product is then filtered and dried at a temperature of 80 ° C. or higher (usually about 100 ° C.) to obtain a desired layered rock salt type lithium ferrite composite oxide.

  In the present invention, if necessary, the crystallinity of the layered rock salt type lithium ferrite composite oxide can be further improved by firing the composite oxide obtained above together with the lithium compound.

  As a lithium compound, if it is a compound containing a lithium element, it can be used without particular limitation, and specific examples include lithium salts such as lithium chloride, lithium nitrate, and lithium acetate, lithium hydroxide, and the like. The usage-amount of a lithium compound should just be about 0.1-2 mol with respect to 1 mol of said layered rock salt type lithium ferrite type complex oxides.

  Usually, in order to improve the reactivity, it is preferable that the lithium ferrite composite oxide obtained by the above method is pulverized and then fired. 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.

There is no particular limitation on the firing atmosphere, and any atmosphere such as an oxidizing atmosphere such as the air or an oxygen stream, 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, added with a lithium compound, calcined, washed and dried. Stable charge / discharge characteristics, high capacity, etc. in the operating voltage region as a positive electrode material for ion secondary batteries 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. Assembling a lithium ion secondary battery 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 Can do.

  According to the present invention, it is possible to obtain a novel material that can be stably charged and discharged in an operating voltage range (about 4 V) equivalent to that of an existing lithium cobalt oxide-based positive electrode material by using an inexpensive raw material. .

  In addition, this material can exhibit excellent performance as a positive electrode material even in a high temperature environment. For example, under high-temperature charge / discharge conditions (for example, about 60 ° C.), it has a higher capacity when compared with lithium manganese spinel, which is a typical low-cost positive electrode material in practical use.

  Therefore, the lithium ferrite-based composite oxide of the present invention is extremely useful as a positive electrode material for a lithium ion secondary battery with a high capacity and low cost, and further, for example, in a high temperature environment such as an in-vehicle secondary battery. As a positive electrode for a lithium ion secondary battery that may be used in, it can exhibit excellent performance.

  Examples and comparative examples are shown below to further clarify the features of the present invention. The present invention is not limited to these examples.

Iron (III) nitrate nonahydrate 50.50 g, manganese (II) chloride tetrahydrate 14.84 g and cobalt nitrate (II) hexahydrate 14.55 g (total amount 0.25 mol, Fe: Mn: Co molar ratio = 5: 3: 2) was added to 500 ml of distilled water and completely dissolved. 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 aqueous solution was placed in a titanium beaker and allowed to stand in a thermostat and kept in the thermostat at + 5 ° C. The metal salt aqueous solution was gradually dropped into the lithium hydroxide aqueous solution to form an Fe-Mn-Co precipitate. It was confirmed that the reaction solution was completely alkaline (pH 11 or more), and the reaction solution containing the coprecipitate was stirred for 2 days at room temperature with air to oxidize the precipitate.

The obtained precipitate was washed with distilled water and filtered, and 25 g of this precipitate was placed in a polytetrafluoroethylene beaker together with 50 g of lithium hydroxide monohydrate, 50 g of potassium chlorate and 600 ml of distilled water, and stirred well. 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, and the generated precipitate is washed with distilled water to remove excess lithium hydroxide and the like. Salts were removed, filtered and dried to obtain a powdery product (iron and cobalt containing Li ₂ MnO ₃ ).

Next, in order to improve the crystallinity of the obtained product, 25 g of the product powder and a lithium hydroxide aqueous solution in which 5.25 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water were mixed, and the temperature was 100 ° C. The powder obtained after drying and pulverization was calcined at 650 ° C. for 20 hours in the air. The calcined product is then washed with distilled water, filtered and dried to remove excess lithium salt, and the desired powdered product containing iron and cobalt containing Li ₂ MnO ₃ (i.e., Li _{1+ x} (Fe _0.5 Mn _0.3 Co _0.2 ) _1-x O ₂ ) was obtained.

で指数付けすることができた。 The X-ray diffraction pattern of this final product is shown in FIG. All peaks are shown in “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, A509-524, (2002). "Unit cell of layered rock salt type iron-containing Li ₂ MnO ₃ (ie Li _1.26 Fe _0.22 Mn _0.52 O ₂ )

I was able to index.

The composition of the final product was evaluated by inductively coupled high-frequency plasma spectroscopy (ICP) and atomic absorption analysis. The elemental analysis results are shown in Table 1.

The lattice constant (a = 2.8787 (4) A, c = 14.3116 (17) A) calculated from each peak of the iron and cobalt-containing Li ₂ MnO ₃ obtained in this example is more than the value described in the above document. According to chemical analysis (Table 1 below), Fe and Co are included in the amount of 50 mol% (n value) and 20 mol% (m value), respectively, and Li / (Mn + Fe Since the x value calculated from the (+ Co) value is 0.13, in this example, iron- and cobalt-containing Li ₂ MnO ₃ (that is, Li _1.13 (Fe _0.5 Mn _0.3 Co _0.2 ) _0.87 O ₂ ) is obtained. I was able to confirm.

FIG. 3 is a drawing obtained by electronically processing an electron micrograph of iron- and cobalt-containing Li ₂ MnO ₃ obtained as a final product in this example. FIG. 3 clearly shows that iron and cobalt-containing Li ₂ MnO ₃ having a particle diameter of about 100 nm and relatively uniform are formed according to this example.

The process is the same as in Example 1 until the step of obtaining the co-precipitate from the Fe-Mn-Co mixed aqueous solution, hydrothermally treating it, washing with water, filtering and drying to obtain the powdered product iron- and cobalt-containing Li ₂ MnO _3. is there.

  Next, in order to improve the crystallinity of the obtained product, 25 g of the product powder and a lithium hydroxide aqueous solution in which 5.25 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water were mixed, and the temperature was 100 ° C. The powder obtained after drying and pulverization was calcined at 700 ° C. for 20 hours in the air.

The calcined product is then washed with distilled water, filtered and dried to remove excess lithium salt, and the desired powdered product containing iron and cobalt containing Li ₂ MnO ₃ (i.e., Li _{1+ x} (Fe _0.5 Mn _0.3 Co _0.2 ) _1-x O ₂ ) was obtained.

で指数付けすることができた。また、実施例1に比べて各回折ピークがシャープであり本
実施例の試料が実施例1の試料に比べ結晶性が高いことがわかる。 The X-ray diffraction pattern of this final product is shown in FIG. All peaks are shown in “M. Tabuchi, A. Nakashima, H. Shigemura, K. Ado, H. Kobayashi, H. Sakaebe, H. Kageyama, T. Nakamura, MK.
ohzaki, A.Hirano and R.Kanno, Journal of the Electrochemical Society, 149, A509-524, (2002). "The layered rock salt-type iron-containing Li ₂ MnO ₃ (ie Li _1.26 Fe _0.22 Mn _0.52 O ₂ ) unit cell

I was able to index. In addition, each diffraction peak is sharper than that of Example 1, indicating that the sample of this example has higher crystallinity than the sample of Example 1.

The composition of the final product was evaluated by inductively coupled high-frequency plasma spectroscopy (ICP) and atomic absorption analysis. The elemental analysis results are shown in Table 1.

Lattice constants (a = 2.8738 (3) A, c = 14.2940 (11) A) calculated from the peaks of the iron and cobalt-containing Li ₂ MnO ₃ obtained in this example are larger than the values described in the above document. According to chemical analysis (Table 1 below), Fe and Co are included in the amount of 50 mol% (n value) and 20 mol% (m value), respectively, and Li / (Mn + Fe Since the x value calculated from the (+ Co) value is 0.14, in this example, iron- and cobalt-containing Li ₂ MnO ₃ (that is, Li _1.14 (Fe _0.5 Mn _0.3 Co _0.2 ) _0.86 O ₂ ) is obtained. It is clear that

Comparative 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 = 5: 5) 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, and 100 ml of ethanol was added. This lithium hydroxide solution was placed in a titanium beaker and allowed to stand in a thermostatic oven, and the thermostatic oven was kept at −10 ° C. The metal salt aqueous solution was gradually added dropwise to the lithium hydroxide solution to form an Fe-Mn precipitate. It was confirmed that the reaction solution was completely alkaline (pH 11 or more), and the reaction solution containing the coprecipitate was stirred for 2 days at room temperature with air to oxidize the precipitate.

The obtained precipitate was washed with distilled water and filtered, and 25 g of this precipitate was placed in a polytetrafluoroethylene beaker together with 50 g of lithium hydroxide monohydrate, 50 g of potassium chlorate and 600 ml of distilled water, and stirred well. 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, and the generated precipitate is washed with distilled water to remove excess lithium hydroxide and the like. Salts were removed, filtered and dried to obtain a powdery product (iron-containing Li ₂ MnO ₃ ).

Next, in order to improve the crystallinity of the obtained product, 25 g of the product powder and a lithium hydroxide aqueous solution in which 10.49 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water were mixed, and the temperature was 100 ° C. The powder obtained after drying and pulverization was calcined at 650 ° C. for 20 hours in the air.

The calcined product is then washed with distilled water, filtered and dried to remove excess lithium salt, and the powdered product of Comparative Example 1 containing iron-containing Li ₂ MnO ₃ (ie, Li _{1+ x} (Fe _0.5 Mn _0.5 ) _1-x O ₂ ) was obtained.

で指数付けすることができた。 From the X-ray diffraction analysis of this final product, all peaks are shown as “M. Tabuchi, A. Nakashima, H. Shigemura, K. Ado, H. Kobayashi, H. Sakaebe, H. Kageyama, T. Nakamura, M. Layered rock salt-type iron-containing Li ₂ MnO ₃ (Li _1.26 Fe _0.22 Mn _0.52 O described in Kohzaki, A. Hirono and R. Kanno, Journal of the Electrochemical Society, 149, A509-524, (2002). ₂ ) Unit cell

I was able to index.

The composition of the final product was evaluated by inductively coupled high-frequency plasma spectroscopy (ICP) and atomic absorption analysis. The elemental analysis results are shown in Table 1.

The lattice constant (a = 2.8803 (2) A, c = 14.2741 (10) A) calculated from each peak of iron-containing Li ₂ MnO ₃ obtained in this comparative example is larger than the value described in the above document. Chemical analysis (
According to Table 1 below, Fe is contained in an amount of 50 mol% as charged, and the x value is 0.26. Therefore, in this comparative example, iron-containing Li ₂ MnO ₃ (ie, Li _1.26 (Fe _0.5 Mn _0.5 It was confirmed that _0.74 O ₂ ) was obtained.

Comparative Example 2
The process until obtaining the iron-containing Li ₂ MnO ₃ which is a powdery product by hydrothermal treatment after performing a co-precipitate from the Fe-Mn mixed aqueous solution and washing with water, filtering and drying is the same as in Comparative Example 1.

Next, in order to improve the crystallinity of the obtained product, 25 g of the product powder and a lithium hydroxide aqueous solution in which 10.49 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water were mixed, and the temperature was 100 ° C. The powder obtained after drying and pulverization was calcined at 700 ° C. for 20 hours in the air.

The calcined product is then washed with distilled water, filtered and dried to remove excess lithium salt, and the powdered product of Comparative Example 2 containing iron-containing Li ₂ MnO ₃ (ie, Li _{1+ x} (Fe _0.5 Mn _0.5 ) _1-x O ₂ ) was obtained.

で指数付けすることができた。 From the X-ray diffraction analysis of this final product, all peaks are shown as “M. Tabuchi, A. Nakashima, H. Shigemura, K. Ado, H. Kobayashi, H. Sakaebe, H. Kageyama, T. Nakamura, M. Layered rock salt-type iron-containing Li ₂ MnO ₃ (Li _1.26 Fe _0.22 Mn _0.52 O described in Kohzaki, A. Hirono and R. Kanno, Journal of the Electrochemical Society, 149, A509-524, (2002). ₂ ) Unit cell

I was able to index.

The composition of the final product was evaluated by inductively coupled high-frequency plasma spectroscopy (ICP) and atomic absorption analysis. The elemental analysis results are shown in Table 1.

The lattice constant (a = 2.8835 (3) A, c = 14.2985 (11) A) calculated from each peak of iron and cobalt-containing Li ₂ MnO ₃ obtained in this comparative example is more than the value described in the above document. According to the chemical analysis (Table 1), Fe is contained in an amount of 50 mol% as charged, and the x value is 0.28. Therefore, in this comparative example, iron-containing Li ₂ MnO ₃ (ie, It was confirmed that Li _1.28 (Fe _0.5 Mn _0.5 ) _0.72 O ₂ ) was obtained.

Comparative Example 3
Add 30.30 g of iron (III) nitrate nonahydrate and 50.93 g of cobalt (II) nitrate hexahydrate (total amount 0.25 mol, Fe: Co molar ratio = 3: 7) to 500 ml of distilled water and dissolve completely. It was. An aqueous sodium hydroxide solution (a solution in which 50 g of sodium hydroxide was dissolved in 500 ml of distilled water) was prepared in another beaker. This sodium hydroxide solution was gradually added dropwise to the aqueous metal salt solution to form an Fe—Co precipitate. After confirming that the reaction solution was completely alkaline (pH 11 or higher), air was blown into the reaction solution containing the coprecipitate with stirring at room temperature for 2 days to ripen the precipitate.

The obtained precipitate was washed with distilled water and filtered, and then an aqueous lithium hydroxide solution (12.59 g of lithium hydroxide monohydrate) prepared so that the charged Li / (Fe + Co) molar ratio was 1.2. And dissolved in 100 ml of distilled water), dried at 100 ° C., pulverized, and the obtained powder was calcined at 800 ° C. for 20 hours in the atmosphere.

The calcined product is then washed with distilled water, filtered and dried to remove the excess lithium salt, and the iron-containing LiCoO ₂ (ie, Li _{1 + x} ( Fe _0.3 Co _0.7 ) _1-x O ₂ ) was obtained.

で指数付けすることができた。 From the X-ray diffraction analysis of this final product, all peaks are shown as "R. Alkantara, JC Jumas, P. Lavela, J. Olivier-Fourcade, C. Plez-Vicente and JLTirado, Journal of Power Sources, 81-82, 547. -553, (1999). "Unit cell of layered rock salt type iron-containing LiCoO ₂ (ie LiFe _0.3 Co _0.7 O ₂ )

I was able to index.

The composition of the final product was evaluated by inductively coupled high-frequency plasma spectroscopy (ICP) and atomic absorption analysis. The elemental analysis results are shown in Table 1.

The lattice constant (a = 2.84509 (10) A, c = 14.2196 (4) A) calculated from each peak of the iron-containing LiCoO ₂ obtained in this comparative example is close to the value described in the above document, chemical analysis According to (Table 1 below), Fe is contained in an amount of 30 mol% as charged, and the x value is 0.024. Therefore, in this comparative example, iron-containing LiCoO ₂ (ie, Li _1.024 (Fe _0.3 Co _0.7 )) It was confirmed that _0.976 O ₂ ) was obtained.

Each sample obtained in Examples 1 and 2 was used as the positive and negative electrode material for charge / discharge test, and metallic lithium was used as the negative electrode material. As the electrolytic solution, a 1M solution in which LiPF ₆ as a supporting salt was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate was used. The charge / discharge characteristics as a coin-type lithium battery were examined at the start of charging at a test temperature of 30 ° C. (potential range: 3.0-4.3 V, current density: 42 mA / g). The charge / discharge characteristics of the lithium battery are shown in FIG. In FIG. 4, the upward curve corresponds to the charging curve, and the downward curve corresponds to the discharge curve. Q _1c and Q _10c shows the charge capacity of each initial and 10 th cycle, shows the initial discharge capacity at Q _1D3.5 and Q _1D3.0 respectively 3.5V and 3.0V or more, Q _10D3.5 and Q _{10D3 .0} is 3.5V each
And the discharge capacity at the 10th cycle at 3.0 V or higher. As shown in FIG. 4, the sample obtained in the example can be charged / discharged from the initial charge. The initial discharge capacity (Q _1d3.0 ) is 90mAh / g
Thus, a large capacity is shown at a high current density of 42 mA / g.

Table 2 shows the evaluation of charge / discharge characteristics of the lithium battery. According to Table 2, compared with the samples obtained in Comparative Examples 1 to 3, at the same current density, the present invention sample has an initial discharge capacity (Q _1d3.0 and Q _1d3.5 ) and a discharge capacity after 10 cycles ( Since Q _10d3.5 ) exhibits a large capacity, it is clear that it is useful as a lithium ferrite positive electrode material for lithium ion secondary batteries.

High temperature charge / discharge test A coin-type lithium secondary battery having the same structure as that used in the charge / discharge characteristic evaluation was used except that the material obtained in Example 1 was used as a positive electrode material and the negative electrode material was changed to graphite. Produced. Charge and discharge characteristics up to 10 cycles at the start of charging at a charge density of 2.5-4.3V (however, the maximum charge capacity is limited to 150mAh / g) and current density of 42mA / g. Evaluation was performed.

For comparison, a charge / discharge test was performed at 60 ° C. using a coin-type lithium secondary battery manufactured in the same manner as described above except that lithium manganese spinel (Li _1.1 Mn _1.9 O ₄ ) was used as the positive electrode material. . The Li _1.1 Mn _1.9 O ₄ used here was prepared by dry-mixing Mn ₂ O ₃ and LiOH at a molar ratio of 0.95: 1.1 and firing in the atmosphere at 900 ° C. for 20 hours.

FIG. 5 is a graph showing the charge / discharge characteristics at 60 ° C., the curve rising to the right is the charge curve, and the curve falling to the right is the discharge curve. In FIG. 5, “1c” is a curve indicating the initial charge capacity, “10c” is a curve indicating the charge capacity after 10 cycles, and “1d” is a curve indicating the initial discharge capacity. "10d" is a curve showing the discharge capacity after 10 cycles.

From the obtained charge / discharge characteristics (FIG. 5), the battery using the material of Example 1 had a low initial discharge capacity of 101 mAh / g, but the discharge capacity after 10 cycles was 147 mAh / g. Compared to batteries using manganese spinel (1st cycle discharge capacity 74 mAh / g, 10th cycle discharge capacity 41 mAh / g). In addition, the battery using the material of Example 1 has an average discharge voltage after 10 cycles of 3.26 V, which indicates that a high potential is maintained.

The above test evaluates the charge / discharge characteristics at high temperature using graphite, which is a negative electrode material that has been put into practical use. The above results are close to practical use in which the material of Example 1 uses graphite as the negative electrode. This shows that charging and discharging can be performed stably even in the battery configuration. From this result, it is clear that the composite oxide of the present invention has an advantage particularly in the high-temperature cycle test as compared with lithium manganese spinel which is an existing positive electrode.

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 X-ray diffraction patterns of iron and cobalt-containing Li ₂ MnO ₃ obtained in Examples 1 and 2. An electron micrograph of the resulting iron and cobalt containing Li ₂ MnO ₃ in Example 1 is an electronic image-processed drawings. Graph showing the initial and tenth cycle charge / discharge characteristics of two types of coin-type lithium batteries using the iron and cobalt-containing Li ₂ MnO ₃ obtained in Examples 1 and 2 as the cathode material and Li metal as the anode material, respectively. It is. It is a graph which shows the charging / discharging characteristic in 60 degreeC about the coin-type lithium secondary battery (graphite negative electrode) using the coin-type lithium secondary battery (graphite negative electrode) produced in Example 1 and lithium manganese spinel as a positive electrode material.

Claims (5)

Composition formula Li _{1 + x} (Mn _1-mn Fe _n Co _m ) _1-x O ₂ (However, 0 <x <1/3, 0.01 ≦ m ≦ 0.50, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n < A lithium ferrite complex oxide represented by 1) and having a layered rock salt structure. A mixed aqueous solution containing a manganese compound, an iron compound and a cobalt compound is made alkaline to form a precipitate, and the obtained precipitation product is hydrothermally treated under alkaline conditions together with an oxidizing agent and a water-soluble lithium compound. 1. A method for producing a lithium ferrite composite oxide described in 1. 3. The method for producing a lithium ferrite composite oxide according to claim 1, wherein after the hydrothermal treatment is performed by the method of claim 2, the obtained product is fired together with a lithium compound. Composition formula Li _{1 + x} (Mn _1-mn Fe _n Co _m ) _1-x O ₂ (However, 0 <x <1/3, 0.01 ≦ m ≦ 0.50, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n < A positive electrode material for a lithium ion secondary battery represented by 1) and comprising a lithium ferrite composite oxide having a layered rock salt structure. Composition formula Li _{1 + x} (Mn _1-mn Fe _n Co _m ) _1-x O ₂ (However, 0 <x <1/3, 0.01 ≦ m ≦ 0.50, 0.05 ≦ n ≦ 0.75, 0.06 ≦ m + n < A lithium ion secondary battery comprising as a constituent element a positive electrode material comprising a lithium ferrite composite oxide represented by 1) having a layered rock salt structure.

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