JP4997609B2 - Method for producing lithium manganese composite oxide - Google Patents

Description

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

  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.

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 battery safety during charging, and lithium manganese oxide has trivalent manganese that elutes into the electrolyte during high-temperature (about 60 ° C) charge and discharge. However, there is a problem that the battery performance is significantly deteriorated. For this reason, alternatives to these materials have not made much progress.

On the other hand, there is a substance called Li ₂ MnO ₃ consisting only of tetravalent manganese ions that does not contain trivalent manganese, which causes elution, among lithium manganese oxides, and this material has been considered impossible to charge and discharge. However, recent studies have found that charging and discharging is possible by charging to 4.8 V (see Non-Patent Document 1 below). However, further improvements are necessary with respect to charge / discharge characteristics.

In addition, lithium ferrite (LiFeO ₂ ) containing iron, which is more abundant in resources than manganese and nickel, is less toxic, and contains less expensive iron, is being investigated as a potential electrode material. However, lithium ferrite obtained by a normal manufacturing method, that is, a method in which an iron source and a lithium source are mixed and fired at a high temperature hardly charges or discharges and 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 inventors of the present invention have already described a layered rock-salt type solid solution (Li _{1 + x} (Fe _y Mn) composed of lithium manganese oxide (Li ₂ MnO ₃ ) and lithium ferrite, which are inexpensive and resource-rich after iron. _1-y ) _1-x O ₂ , (0 <x <1/3, 0 <y <1), hereinafter referred to as “iron-containing Li ₂ MnO ₃ ”) is used for lithium cobalt oxidation in charge / discharge tests at room temperature It has been found that it has an average discharge voltage close to 4V, which is comparable to that of ordinary products (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. (See Patent Document 5 below).

As described above, various reports have been made on lithium manganese based composite oxide positive electrode materials and lithium ferrite based positive electrode materials that can replace lithium cobalt based positive electrode materials. Optimization of the chemical composition and manufacturing conditions of the material is desired.
C. Gan, H. Zhan, X. Hu, and Y. Zhou, Electrochemistry Communication, 7, 1318-1322, (2005) Japanese Patent Laid-Open No. 10-120421 JP-A-8-295518 JP 2002-68748 A Japanese Patent Laid-Open No. 2002-121026 JP 2005-154256 A

  The present invention has been made in view of the current state of the prior art described above, and its main purpose is to further improve the lithium manganese composite oxide expected as a positive electrode material that can replace the lithium cobalt base positive electrode material. Another object of the present invention is to provide a novel production method capable of forming a complex oxide having charge / discharge performance.

  The present inventor has intensively studied to achieve the above-described object. As a result, a lithium manganese-based composite oxide represented by a specific general formula employs a production method including a precipitation formation step, a hydrothermal treatment step, and a firing step, and uses a raw material containing permanganate as a manganese raw material. In this case, compared to the case where other water-soluble manganese compounds are used as raw materials, the charge / discharge performance is greatly improved, and a lithium manganese composite oxide having excellent performance as a positive electrode material of a lithium ion battery is obtained. As a result, the present invention has been completed.

That is, the present invention provides the following method for producing a lithium manganese composite oxide and uses of the lithium manganese composite oxide obtained by the production method.
1. Composition formula (1): Li _{1 + x} (Mn _1−y−z Fe _y Ti _z ) _1−x O ₂ (where 0 <x <1/3, 0 ≦ y ≦ 0.75, 0 ≦ z ≦ 0.75) , 0 ≦ y + z <1), and a method for producing a lithium-manganese composite oxide containing a crystal phase of a layered rock salt structure,
It is obtained by forming a precipitate by making a raw material solution obtained by dissolving a manganese compound, an iron compound and a titanium compound in a solvent composed of water or a water-alcohol mixture at the same ratio as the element ratio in the composition formula (1) to be alkaline. And hydrothermally treating the precipitate with an oxidizing agent and a water-soluble lithium compound under alkaline conditions, and then firing the hydrothermally treated product in the presence of the lithium compound. A method for producing a lithium-manganese composite oxide, comprising a salt containing 20 mol% or more of the total amount of the manganese compound.
2. Lithium-manganese composite oxide has a composition formula (2): Li _{1 + x} (Mn _1-a Fe _a ) _1-x O ₂ (where 0 <x <1/3, 0.05 ≦ a ≦ 0.75) Item 2. The method according to Item 1, which is represented by:
3. Item 2. The method according to Item 1, wherein the ratio of permanganate in the manganese compound used as a raw material is 50 mol% or more.
4). Item 2. The method according to Item 1, wherein the manganese compound used as a raw material is potassium permanganate.
5. 5. Lithium ion secondary battery positive electrode material comprising a lithium manganese composite oxide obtained by the method of item 1 above. The lithium ion secondary battery which uses the lithium ion secondary battery positive electrode material which consists of lithium manganese type complex oxide obtained by the method of said claim | item 1 as a component.

  In the method for producing a lithium manganese composite oxide according to the present invention, the precipitate is made alkaline with a raw material solution obtained by dissolving a manganese compound and, if necessary, an iron compound and a titanium compound in a solvent comprising water or a water-alcohol mixture. And subjecting the resulting precipitate to hydromanganese treatment under alkaline conditions with an oxidizing agent and a water-soluble lithium compound, and then firing the hydrothermally treated product in the presence of the lithium compound. It is necessary to produce a system complex oxide.

The lithium manganese composite oxide, which is an object of the production method of the present invention, is a compound represented by Li ₂ MnO ₃ containing tetravalent Mn ions as a main constituent element, or a part of the Mn element of Li ₂ MnO _3. Since it is a compound substituted with iron ions and / or titanium ions, control of the valence of Mn ions is extremely important. When the valence of Mn ions deviates greatly from 4+ to 3.5+ or 3+, impurities such as LiMn ₂ O ₄ and LiMnO ₂ which are other lithium manganese oxides are likely to be generated. According to the production method including the hydrothermal method employed in the present invention, it is easy to control the valence of Mn ions, and the target lithium manganese composite oxide can be obtained in high yield.

  Hereafter, each process of the manufacturing method of the lithium manganese complex oxide of this invention is demonstrated concretely.

In the present invention, first, a raw material solution containing a manganese compound and, if necessary, an iron compound and a titanium compound is prepared. About these raw material compounds, the presence or absence of the use of an iron compound and a titanium compound and the usage ratio of each raw material compound may be determined according to the composition of the target lithium manganese composite oxide.

  In the present invention, it is particularly important that the manganese compound used as the raw material contains permanganate.

  Conventionally, it is not known that permanganate can be used as a raw material in a method for producing a lithium manganese composite oxide. According to the present invention, when a manufacturing method including a precipitation forming step, a hydrothermal treatment step and a firing step is employed, and a manganese raw material containing permanganate is used as a raw material used for the precipitation formation, An unexpected result was found that the charge / discharge characteristics of the obtained lithium manganese composite oxide were greatly improved as compared with the case of using a manganese compound as a raw material. Specifically, in addition to having excellent charge / discharge performance in a high temperature use environment of about 60 ° C., lithium manganese based composite oxidation that exhibits excellent discharge performance even when discharged under a large current density at low temperature You can get things.

The reason why a lithium manganese composite oxide having such excellent performance is obtained when using permanganate as a raw material is not clear, but as is clear from the results of Examples described later, permanganate By using salt as a raw material, the finally formed lithium manganese composite oxide is micronized, and this is presumed to be a cause of becoming a positive electrode material having excellent charge / discharge performance. It is also considered that there is an effect of suppressing the generation of spinel manganese ferrite MnFe ₂ O ₄ containing divalent manganese ions that may be generated during coprecipitation.

  In the present invention, the permanganate must be contained in an amount of 20 mol% or more, preferably 50 mol% or more, more preferably 70 mol% or more, based on the total amount of the manganese compound used as a raw material. . In particular, it is most preferable to use only permanganate as the manganese compound. As the permanganate, potassium permanganate or the like can be used.

  Examples of manganese compounds other than permanganate include water-soluble manganese compounds such as chlorides, nitrates, sulfates, oxalates, acetates, and hydroxides. These water-soluble manganese compounds may be either anhydrides or hydrates, and can be used alone or in combination of two or more.

  The iron compound used as a raw material is not particularly limited, and may be any water-soluble compound. Specific examples of such water-soluble iron compounds include water-soluble salts such as chlorides, nitrates, sulfates, oxalates and acetates, hydroxides and the like. These water-soluble iron compounds may be either anhydrides or hydrates. Further, even a water-insoluble compound such as a metal or an oxide can be used as an aqueous solution by being dissolved using an acid such as hydrochloric acid. An iron compound may be used independently and may use 2 or more types together.

  There is no particular limitation on the titanium compound as long as it is usually a water-soluble compound. Specific examples of such water-soluble titanium compounds include water-soluble salts such as chlorides, nitrates, sulfates, oxalates, and acetates, hydroxides, and the like. These water-soluble titanium compounds may be either anhydrides or hydrates. Further, even a water-insoluble compound such as a metal or an oxide can be used as an aqueous solution by being dissolved using an acid such as sulfuric acid. A titanium compound may be used independently and may use 2 or more types together.

  What is necessary is just to make it the mixing ratio of a manganese compound, an iron compound, and a titanium compound become the element ratio similar to each element ratio in the target lithium manganese type complex oxide. That is, the iron ion amount (y value: Fe / (Mn + Fe + Ti)) is 75 mol% or less of the total amount of manganese ion, iron ion and titanium ion (0 ≦ Fe / (Mn + Fe + Ti)) ≦ 0.75), preferably about 60 mol% or less (0 ≦ Fe / (Mn + Fe + Ti) ≦ 0.6). When the amount of Fe ions is excessive, not only is the dilution of Fe ions insufficient, but the number of Fe ions in the Li layer not involved in charge / discharge increases, which is not preferable in terms of battery characteristics.

  The amount of titanium ions (z value: Fe / (Mn + Fe + Ti)) is 75 mol% or less of the total amount of manganese ions, iron ions and titanium ions (0 ≦ Ti / (Mn + Fe + Ti) ≦ 0.75 ), Preferably 60 mol% or less (0 ≦ Ti / (Mn + Fe + Ti) ≦ 0.6). As will be described later, in the lithium manganese based composite oxide obtained by the method of the present invention, Ti ions are basically present in the layered rock salt structure in the form of replacing Mn ions and Li ions in the same manner as Fe ions. It seems to have done. Ti ions exist in a tetravalent state, which is thought to contribute to the suppression of Li deficiency and changes in powder characteristics. However, when using a large amount of Ti that is not involved in charge / discharge, charge / discharge is performed. This is not preferable because the capacity is reduced.

  The total amount of Fe ions and Ti ions may be in the range of about 0 ≦ y + z <1 in the composition formula.

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

  As a solvent for the raw material 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 raw material solution, the raw material solution may be made alkaline. Conditions for forming a good precipitate vary depending on the type and concentration of each compound contained in the raw material solution, and thus cannot be defined unconditionally. However, the pH is preferably about 8 or more, and preferably about 11 or more. More preferred.

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

  Examples of the alkali used for making the raw material 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 in the same manner as the above raw material solution.

  During precipitation, the temperature of the raw material solution is set to about -50 ° C to + 15 ° C, preferably about -40 ° C to + 10 ° C. Is suppressed and a homogeneous coprecipitate is easily formed.

  After making the raw material 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.

Hydrothermal treatment step The precipitate 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 an aqueous solution containing a precipitate, an oxidizing agent, and a 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 obtained in the above step 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 use amount of the water-soluble lithium compound is preferably about Li / (Mn + Fe + Ti) = 1 to 10 as a molar ratio of lithium element to the total number of moles of Mn, Fe and Ti, and about 3 to 7 More preferably.

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

  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. be able to.

  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. The pH value may be increased by adding hydroxide, ammonia or the like.

  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, for example, at a temperature of 80 ° C. or higher (usually about 100 ° C.) to obtain a lithium manganese composite oxide.

Firing process Lithium manganese complex oxide obtained by calcining the lithium manganese complex oxide obtained by the above-mentioned method together with lithium compound to control the Li content and powder characteristics and to have the basic rock salt type as the basic structure You can get things.

  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 usage-amount of a lithium compound should just be about 0.01-2 mol with respect to 1 mol of lithium manganese complex oxide obtained by the hydrothermal method.

  Usually, in order to improve the reactivity, it is preferable to add a lithium compound to the lithium manganese based composite oxide obtained by the hydrothermal method, 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.

  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 0.1 to 100 hours including the time to reach the firing temperature, and more preferably about 0.5 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 may be performed and, for example, heat drying may be performed at a temperature of 80 ° C. or higher, preferably about 100 ° C.

  Furthermore, if necessary, the heat-dried product is pulverized, a lithium compound is added, calcined, washed, and dried, and a series of operations are repeated. 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.

Lithium Manganese Composite Oxide Lithium Manganese Composite Oxide obtained by the above-described method has a composition formula (1): Li _{1 + x} (Mn _1-yz Fe _y Ti _z ) _1-x O ₂ (where 0 <x <1/3, 0 ≦ y ≦ 0.75, 0 ≦ z ≦ 0.75, 0 ≦ y + z <1).

Among the composite oxides represented by the composition formula (1), for example, the composition formula (2): Li _{1 + x} (Mn _1-a Fe _a ) _1-x O ₂ (where 0 <x < 1/3, 0.05 ≦ a ≦ 0.75) is a known compound, and the main component is a solid solution of layered rock salt structure composed of lithium manganese oxide (Li ₂ MnO ₃ ) and lithium ferrite In a charge / discharge test at room temperature, it has an average discharge voltage close to 4 V, comparable to that of lithium cobalt oxide.

Further, among the complex oxides represented by the composition formula (1), the composition formula (3): Li _{1 + x} (Mn _1-b Ti _b ) _1-x O ₂ (where 0 <x < 1/3, 0.01 ≦ b ≦ 0.75) is a novel compound not described in any literature. It is important that this complex oxide contains the specific amount of Ti ions described above. When a lithium-manganese composite oxide containing no Ti ions is baked at a high temperature when producing the composite oxide, Li tends to volatilize and become a Li-deficient composition. Li contained in the sample is a component that contributes to charge / discharge, and Li deficiency may deteriorate charge / discharge characteristics. According to the composite oxide of the composition formula (3), Li deficiency is remarkably suppressed due to the presence of Ti, and the Li component involved in charge / discharge is increased, which is further compared with the lithium-manganese composite oxide. It seems that the charge / discharge characteristics are improved. Moreover, the tendency that the primary particle diameter decreases by solid solution of Ti ions is recognized, and the specific surface area is increased. Therefore, it seems that charge / discharge characteristics are improved by pulverization. Furthermore, the generation of LiMnO _2, a peculiar manganese-based impurity, can be suppressed even during short-time firing by solid solution of Ti ions, which is thought to contribute to the improvement of charge / discharge characteristics.

Composition formula (1) obtained by the production method of the present invention: Li _{1 + x} (Mn _1-yz Fe _y Ti _z ) _1-x O ₂ (where 0 <x <1/3, 0 ≦ y ≦ 0.75) , 0 ≦ z ≦ 0.75, 0 ≦ y + z <1), a lithium manganese based composite oxide has a crystal structure based on a rock salt structure, and is a known substance such as LiCoO ₂ as shown in FIG. It contains a layered rock-salt structure similar to. 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 obtained by the method 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. The crystal phase of the layered rock salt structure in the lithium-manganese composite oxide obtained by the method of the present invention is that Li ions, Fe ions, Ti ions and Mn ions are present in the Co layer of LiCoO ₂ , and Li It is characterized in that Fe ions and Ti ions are partially substituted in the layer. This corresponds to a structure in which the ordered arrangement of both ions in the Mn-Li layer is indistinguishable in Li ₂ MnO ₃ (monoclinic crystal), one of the lithium manganese oxides shown in Fig. 2. To do.

  The lithium manganese composite oxide obtained by the production method of the present invention includes the crystal phase of the cubic rock salt type structure shown in FIG. 3 in addition to the crystal phase of the layered rock salt type structure described above. This crystal structure corresponds to a completely disordered structure in which the cation cannot be distinguished in FIGS. In this case, the ratio of the crystal phase of the layered rock-salt structure to the crystal phase of the cubic rock-salt structure is usually a layered rock-salt structure crystal phase: cubic rock-salt structure crystal phase (weight ratio) = 10: 90 to 90: The range is about 10.

  The composite oxide obtained by the method of the present invention has a lithium hydroxide, lithium carbonate, manganese compound, iron compound, titanium compound (with their hydration) in a range that does not significantly affect the charge / discharge characteristics (up to about 10 mol%). An impurity phase such as a product).

  When the lithium manganese composite oxide obtained by the production method of the present invention is used as a positive electrode material in a lithium ion secondary battery, the lithium manganese composite oxide is 60 ° C. compared with the lithium manganese composite oxide obtained by the conventional production method. The discharge capacity is high and the cycle characteristics are good in a high temperature use environment. Furthermore, excellent discharge performance can be exhibited even during discharge under a large current density at a low temperature.

A lithium ion secondary battery using the lithium manganese composite oxide obtained by the method of the present invention can be produced by a known method. That is, as the positive electrode material, other than using the lithium manganese composite oxide obtained by the method of the present invention, as the negative electrode material, a known metal lithium, a carbon-based material (activated carbon, graphite) or the like is used as an electrolyte. , Using a solution in which a lithium salt such as lithium perchlorate or LiPF ₆ is dissolved in a known solvent such as ethylene carbonate or dimethyl carbonate, and using other known battery components, What is necessary is just to assemble an ion secondary battery.

  According to the method for producing a lithium manganese composite oxide of the present invention, it has excellent charge / discharge performance in a high temperature use environment as compared with the lithium manganese composite oxide obtained by the conventional production method, and at a low temperature. Thus, it is possible to obtain a lithium-manganese composite oxide that exhibits excellent discharge performance even during discharge at a large current density.

  Therefore, according to the present invention, as will be apparent from the examples described later, the average discharge voltage can be maintained at 3 V or more by using inexpensive raw materials and elements, and is equivalent to or equal to the lithium cobalt oxide positive electrode material. A lithium manganese composite oxide useful as a positive electrode material having the above discharge capacity (200 mAh / g or more) and weight energy density (700 mWh / g or more) can be obtained.

  Unlike the conventional positive electrode material, the lithium manganese composite oxide obtained by the present invention has such a large capacity, and the discharge curve gradually decreases toward the end-of-discharge voltage (2.0 V or 1.5 V). This is because it has a shape that increases, and by reducing the discharge end voltage to about 2.0 V or about 1.5 V, it is possible to easily realize a large capacity.

  In addition, the lithium manganese composite oxide obtained by the method of the present invention has a large discharge capacity even at a low temperature of 30 ° C. or lower, and therefore can exhibit excellent performance even in a low temperature environment. Therefore, it is extremely useful as a positive electrode material for large-sized lithium ion secondary batteries for in-vehicle use.

  In particular, since the composite oxide obtained by the method of the present invention is composed of fine powder, it can exhibit excellent charge / discharge characteristics.

  The lithium manganese composite oxide obtained by the production method of the present invention has the above-described excellent performance, and is extremely useful as a positive electrode material for a lithium ion secondary battery having a high capacity and a low cost.

It is drawing which shows typically the crystal phase of a layered rock salt type | mold structure among the crystal phases which comprise the lithium manganese type complex oxide obtained by the manufacturing method of this invention. 1 is a drawing schematically showing a crystal phase of a monoclinic Li ₂ MnO ₃ structure. It is drawing which shows typically the crystal phase of a cubic rock salt type | mold structure among the crystal phases which comprise the lithium manganese type complex oxide obtained by this invention method. 1 is a drawing showing X-ray diffraction patterns of samples obtained in Example 1 and Comparative Example 1. It is the drawing which electronically image-processed the electron micrograph of the complex oxide obtained in Example 1, and the electron micrograph of the complex oxide obtained in Comparative Example 1. 3 is a graph showing initial charge / discharge characteristics measured in charge / discharge test 1; 4 is a graph showing the dependency of the discharge capacity measured in the charge / discharge test 1 on the number of charge / discharge cycles. 5 is a graph showing initial discharge characteristics measured in charge / discharge test 2. 4 is a graph showing initial discharge characteristics up to 2.0 V at each current density of 1 / 3C, 1C, 2C, 3C, 5C, and 10C measured in charge / discharge test 2; 2 is a drawing showing X-ray diffraction patterns of samples obtained in Example 2, Example 3 and Comparative Example 2. FIG. 4 is an electronic image processing of the electron micrograph of the composite oxide obtained in Example 2 and Example 3 and the electron micrograph of the composite oxide obtained in Comparative Example 2. 5 is a graph showing initial charge / discharge characteristics measured in charge / discharge test 3. FIG. 6 is a graph showing the dependency of the discharge capacity measured in the charge / discharge test 3 on the number of charge / discharge cycles. 2 is a drawing showing X-ray diffraction patterns of samples obtained in Example 4 and Comparative Example 3. 4 is an electronic image processing of an electron micrograph of the composite oxide obtained in Example 4 and an electron micrograph of the composite oxide obtained in Comparative Example 3. 5 is a graph showing initial charge / discharge characteristics measured in charge / discharge test 4. 4 is a graph showing the dependency of the discharge capacity measured in the charge / discharge test 4 on the number of charge / discharge cycles. 5 is a graph showing initial charge / discharge characteristics measured in charge / discharge test 5. 5 is a graph showing the dependency of the discharge capacity measured in the charge / discharge test 5 on the number of charge / discharge cycles. 6 is a drawing showing X-ray diffraction patterns of samples obtained in Example 5 and Comparative Example 4. 4 is an electronic image processing of an electron micrograph of the composite oxide obtained in Example 5 and an electron micrograph of the composite oxide obtained in Comparative Example 4. 5 is a graph showing initial charge / discharge characteristics measured in a charge / discharge test 6; 7 is a graph showing the dependency of the discharge capacity measured in the charge / discharge test 6 on the number of charge / discharge cycles.

  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 these examples.

Example 1
Iron (III) nitrate nonahydrate 50.50 g and potassium permanganate 19.75 g (total amount 0.25 mol, Fe: Mn molar ratio = 1: 1) were 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 lithium hydroxide aqueous solution was put into a titanium beaker, 150 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. 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 1 day to age the precipitate.

  The resulting precipitate was washed with distilled water and filtered, and the precipitated product was placed in a polytetrafluoroethylene beaker together with 50 g of lithium hydroxide monohydrate, 50 g of potassium chlorate, 309 g of potassium hydroxide and 600 ml of distilled water. 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 5 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 and filtered to obtain a powdery product (lithium manganese composite oxide).

  The powder obtained by filtration was mixed with lithium hydroxide aqueous solution in which 5.25 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water, stirred, dried overnight at 100 ° C, and pulverized to produce powder did.

Next, the obtained powder was heated to 850 ° C. in the air over 1 hour, fired at that temperature for 1 minute, cooled to room temperature in the furnace, and the fired product was removed in order to remove excess lithium salt. The product was washed with distilled water, filtered, and dried to obtain the target lithium-iron-manganese composite oxide (iron-containing Li ₂ MnO ₃ ) as a powder product.

The X-ray diffraction pattern of this final product is shown in FIG. From the Rietveld analysis results (the program uses RIETAN-2000), all the peaks except the peak derived from lithium carbonate indicated by ○ in the figure are unit cells of layered rock salt type iron-containing Li ₂ MnO ₃

Unit phase cell of the crystal phase (first phase: a = 2.8871 (18) Å, c = 14.259 (6) Å) and α-LiFeO ₂

(Second phase: a = 4.1028 (3Å, first phase and second phase abundance ratio 30:69). Index of lattice constant of the obtained layered rock-salt type crystal phase has already been reported. It was close to the value of the lithium-iron-manganese composite oxide (lattice constant a = 2.882Å, c = 14.287Å) (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.)
According to chemical analysis (Table 1 below), Fe contained 50 mol% (y value) close to the charged amount, and x value calculated from Li / (Fe + Mn) value was 0.21. In Example 1, it was confirmed that iron-containing Li ₂ MnO ₃ (Li _1.21 (Fe _0.50 Mn _0.50 ) _0.79 O ₂ ) was obtained.

FIG. 5 is an electronic image processed image of an electron micrograph of the iron-containing Li ₂ MnO ₃ obtained as a final product in Example 1. FIG. 5 clearly shows that, according to Example 1, iron-containing Li ₂ MnO ₃ aggregated to about 1 to 50 μm with a primary particle size of 100 nm or less is formed. The specific surface area is 24.2 m ² / g, which is larger than the value 21.8 m ² / g of Comparative Example 1 described later, and it is clear that a finer lithium manganese composite oxide was obtained.

Comparative Example 1
By adding 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 distilled water as raw materials Except for using the obtained Fe-Mn mixed aqueous solution, precipitate formation and hydrothermal treatment were performed in the same manner as in Example 1, and further, lithium hydroxide was added and fired in the same manner as in Example 1. The fired product was washed with distilled water, filtered, and dried to obtain iron-containing Li ₂ MnO ₃ as a powder product.

  The X-ray diffraction pattern of this final product is shown in FIG. All diffraction peaks are unit cells derived from the layered rock salt structure

Unit phase cell of cubic crystal salt type α-LiFeO ₂ with a crystalline phase (the first phase: a = 2.8854 (3) Å, c = 14.2964 (14) Å)

(Second phase: a = 4.1035 (7) Å, abundance ratio of the first phase and the second phase 77:23). From the above results, it was confirmed that a lithium-iron-manganese composite oxide containing a layered rock salt type crystal phase was produced. The lattice constant value of the obtained layered rock salt type crystal phase was close to the value of the already reported lithium-iron-manganese complex oxide (lattice constant a = 2.882Å, c = 14.287Å) (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.)
As a result of chemical analysis (Table 1 below), Fe contained 50 mol% (y value) as charged, and the x value calculated from the Li / (Mn + Fe) value was 0.20. The average composition of the sample obtained in 1 is (Li _1.20 (Fe _0.50 Mn _0.50 ) _0.80 O ₂ ). Thus, it can be seen that also in Comparative Example 1, iron-containing Li ₂ MnO ₃ having almost the same chemical composition as Example 1 could be produced.

FIG. 5 shows a drawing in which an electron micrograph of the iron-containing Li ₂ MnO ₃ obtained as the final product in Comparative Example 1 is electronically image-processed. From FIG. 5, it can be confirmed that in Comparative Example 1 as well as Example 1, iron-containing Li ₂ MnO ₃ aggregated to about 1 to 50 μm with a primary particle size of 100 nm or less was formed. It can be seen that the primary particle diameter is slightly larger than that of Example 1. The specific surface area of the oxide obtained in Comparative Example 1 is 21.8 m ² / g, which is smaller than the value 24.2 m ² / g of the oxide obtained in Example 1 described above, and more coarse powder. It is apparent that a lithium-iron-manganese composite oxide was obtained.

  From the above results, it is apparent that in Comparative Example 1, grain growth occurred despite the production under the same production conditions as in Example 1 except that the manganese source was manganese (II) chloride. From this result, it was confirmed that the effect of pulverization was obtained by using potassium permanganate as a raw material in Example 1.

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

Charge / discharge test 1
1M solution in which each composite oxide obtained in Example 1 and Comparative Example 1 was used as a positive electrode material, Li metal was used as a negative electrode material, and LiPF ₆ as a supporting salt was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate. A coin-type lithium battery was prepared using the electrolyte as an electrolyte. The charge / discharge characteristics of this lithium battery were examined at the start of charging at 60 ° C. (potential range 2.0-4.5 V, current density 42.5 mA / g).

FIG. 6 is a graph showing initial charge / discharge characteristics of lithium batteries using the positive electrode materials of Example 1 and Comparative Example 1. In FIG. 6, the upward curve corresponds to the charge curve, and the downward curve corresponds to the discharge curve. Figures 6 and Table 2, the batteries using the iron-containing Li ₂ MnO ₃ positive electrode material of Example 1 was prepared potassium permanganate as manganese starting material, iron was prepared manganese (II) chloride as manganese starting material containing Li ₂ It is clear that the initial charge / discharge capacity is large (238 mAh / g) and the charge / discharge efficiency is excellent (75%) as compared with the battery using the MnO ₃ positive electrode material.

FIG. 7 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 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-containing Li ₂ MnO ₃ composite oxide of the present invention prepared using potassium permanganate as a manganese raw material exhibits excellent charge / discharge characteristics in a charge / discharge test at a high temperature of 60 ° C. It has been confirmed that the lithium manganese-based positive electrode material for ion secondary batteries has excellent performance.

Charge / discharge test 2
1M solution in which each composite oxide obtained in Example 1 and Comparative Example 1 was used as a positive electrode material, Li metal was used as a negative electrode material, and LiPF ₆ as a supporting salt was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate. A coin-type lithium battery was prepared using as an electrolyte. The charge / discharge characteristics of this lithium battery were examined at the start of charging at 30 ° C. (potential range 2.0-4.8 V, current density 42.5 mA / g). The temperature at the time of discharge was changed to 0 ° C. and −20 ° C. in addition to 30 ° C. When discharging at -20 ° C., the current density was lowered to 8.5 mA / g and the characteristics were evaluated. In addition, charge-discharge-charge at 30 ° C. was performed at the same current density before the discharge test at each temperature.

  The discharge capacity measurement at 30 ° C. and 0 ° C. was performed at a current density of 42.5 mA / g, and the previous charging was performed at 30 ° C. with an upper limit voltage of 4.8 V and a current density of 42.5 mA / g. Further, the -20 ° C discharge capacity measurement was performed at a current density of 8.5 mA / g, and the previous charge was performed at 30 ° C with an upper limit voltage of 4.8 V and a current density of 8.5 mA / g.

  FIG. 8 shows three different temperatures after charging up to 30 ° C. and 4.8 V for lithium batteries using the positive electrode materials of Example 1 (solid line in the figure) and Comparative Example 1 (dashed line in the figure). It is a graph which shows the discharge characteristic in (degreeC, 0 degreeC, and -20 degreeC). Table 3 below shows the charge / discharge data values obtained in this test.

From FIG. 8 and Table 3, the battery using the iron-containing Li ₂ MnO ₃ positive electrode material of Example 1 has a large discharge capacity at any temperature as compared with the battery using the positive electrode material of Comparative Example 1, and in particular, It is clear that the ratio of both increases as the temperature decreases.

From the above results, the iron-containing Li ₂ MnO ₃ composite oxide obtained using potassium permanganate as the manganese raw material was not only at the time of the charge / discharge test as high as 60 ° C., but also at 30 ° C., 0 ° C., and −20 ° C. Also shows excellent discharge characteristics, and was confirmed to have excellent performance as a positive electrode material made of a lithium-iron-manganese composite oxide for a lithium ion secondary battery.

Further, each composite oxide obtained in Example 1 and Comparative Example 1 was used as a positive electrode material, Li metal was used as a negative electrode material, and 1M in which LiPF ₆ as a supporting salt was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate. A coin-type lithium battery was produced using the solution as an electrolyte. The charge / discharge characteristics of this lithium battery were examined at the start of charging in a potential range of 2.0 to 4.8 V at 30 ° C. Furthermore, the current density during discharge is 127.5mA / g as 1C, 42.5mA / g (1 / 3C), 127.5mA / g (1C), 255mA / g (2C), 382.5mA / g (3C), 637.5 Charging / discharging characteristics were evaluated by changing to mA / g (5C) and 1275 mA / g (10C). During charging, the current density was fixed to 1 / 3C (42.5 mA / g), and the characteristics were evaluated. In addition, charge-discharge-charge at 30 ° C. was performed at the same current density before the current density discharge test.

  FIG. 9 shows the six different current densities after charging up to 30 ° C. and 4.8 V for lithium batteries using each positive electrode material of Example 1 (solid line in the figure) and Comparative Example 1 (dashed line in the figure). It is a graph which shows the discharge characteristic to 2.0V in. Table 4 below shows the discharge capacity values obtained in this test.

From FIG. 9 and Table 4, the battery using the iron-containing Li ₂ MnO ₃ cathode material of Example 1 prepared using KMnO ₄ as a raw material was the iron-containing Li of Comparative Example 1 prepared using MnCl ₂ · 4H ₂ O as a raw material. It is clear that the discharge capacity is large at any current density compared to the battery using the ₂ MnO ₃ positive electrode material. The average discharge voltage at high current density of 3C or higher was also high.

Example 2
Precipitation preparation, precipitation ripening, hydrothermal treatment, water washing in the same manner as in Example 1 except that 39.51 g of potassium permanganate (total amount: 0.25 mol) was used as the starting material and the hydrothermal reaction time was 48 hours. Processing, filtration, and drying were performed to obtain a powdery product (lithium manganese composite oxide).

The X-ray diffraction pattern of this final product is shown in FIG. From the results of Rietveld analysis (program uses RIETAN-2000), all peaks are unit cells of layered rock salt type Li ₂ MnO ₃

I was able to index. The lattice constant values of the obtained crystal phase are a = 4.9242 (9) Å, b = 8.5346 (14) Å, c = 9.6173 (9) Å, β = 99.803 (19) °, which has already been reported It was close to the value of monoclinic Li ₂ MnO ₃ (lattice constant a = 4.921 (6) Å, b = 8.526 (3) Å, c = 9.606 (5) Å, β = 99.47 (5) °) (A. Riou, A. Lecerf, Y. Gerault and Y. Cudennec, Materials Research Bulletin, 27, p.269-275, 1992.).

According to chemical analysis (Table 5 below), the x value calculated from the Li / Mn value is 0.29. Therefore, in Example 2, the composition (Li _1.29 Mn) close to Li ₂ MnO ₃ (Li _1.33 Mn _0.67 O ₂ ). It was confirmed that _0.71 O ₂ ) was obtained.

FIG. 11 is a drawing in which an electron micrograph (100,000 times) of Li ₂ MnO ₃ obtained as a final product in Example 2 is electronically image-processed. From FIG. 11, it is clear that, according to Example 2, iron-containing Li ₂ MnO ₃ aggregated with a primary particle size of 100 nm or less was formed. The specific surface area was 44.0m ² / g, greater than the value 2.5 m ² / g of Comparative Example 2 described later, it is clear more the lithium manganese-based composite oxide fine powder was obtained.

Example 3
In the same manner as in Example 2, precipitation preparation, precipitation ripening, hydrothermal treatment, and water washing treatment were performed to obtain a powdery product (lithium manganese composite oxide).

  The powder obtained by filtration was mixed with lithium hydroxide aqueous solution in which 5.25 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water, stirred, dried overnight at 100 ° C, and pulverized to produce powder did.

  Next, the obtained powder is heated to 650 ° C. in the air over 1 hour, baked at that temperature for 20 hours, cooled to room temperature in the furnace, and the calcined product is removed in order to remove excess lithium salt. It was washed with distilled water, filtered, and dried to obtain the target lithium manganese composite oxide as a powder product.

The X-ray diffraction pattern of this final product is shown in FIG. From the results of Rietveld analysis (program uses RIETAN-2000), all peaks are unit cells of layered rock salt type Li ₂ MnO ₃

I was able to index. The lattice constant values of the obtained crystal phase are a = 4.9249 (9) Å, b = 8.5374 (14) Å, c = 9.6169 (10) Å, β = 99.787 (18) °, which has already been reported. It was close to the value of monoclinic Li ₂ MnO ₃ (lattice constant a = 4.921 (6) Å, b = 8.526 (3) Å, c = 9.606 (5) Å, β = 99.47 (5) °) (A. Riou, A. Lecerf, Y. Gerault and Y. Cudennec, Materials Research Bulletin, 27, p.269-275, 1992.).

Since the x value calculated from the Li / Mn value is 0.31 by chemical analysis (Table 5 below), in Example 3, the composition close to Li ₂ MnO ₃ (Li _1.33 Mn _0.67 O ₂ ) (Li _1.31 Mn It was confirmed that _0.69 O ₂ ) was obtained.

FIG. 11 is a drawing obtained by electronic image processing of an electron micrograph (100,000 times) of Li ₂ MnO ₃ obtained as a final product in Example 3. From FIG. 11, it is clear that, according to Example 3, iron-containing Li ₂ MnO ₃ aggregated with a primary particle size of 100 nm or less was formed. The specific surface area is 26.4 m ² / g, which is larger than the value of Comparative Example 2 described later, 2.5 m ² / g, and it is clear that a finer lithium manganese composite oxide was obtained.

Comparative Example 2
Precipitation preparation, precipitation ripening, hydrothermal treatment, Li salt, as in Example 3, except that 49.48 g of manganese (II) chloride tetrahydrate (total amount 0.25 mol) is used instead of potassium permanganate as the starting material. Addition, firing, and water washing treatment were performed to obtain a powdery product (lithium manganese composite oxide).

The X-ray diffraction pattern of this final product is shown in FIG. From the results of Rietveld analysis (program uses RIETAN-2000), all peaks are unit cells of layered rock salt type Li ₂ MnO ₃

I was able to index. The lattice constant values of the obtained crystal phase are a = 4.9266 (2) Å, b = 8.5270 (4) Å, c = 9.6084 (4) Å, β = 99.600 (3) °, which has already been reported. It was close to the value of monoclinic Li ₂ MnO ₃ (lattice constant a = 4.921 (6) Å, b = 8.526 (3) Å, c = 9.606 (5) Å, β = 99.47 (5) °) (A. Riou, A. Lecerf, Y. Gerault and Y. Cudennec, Materials Research Bulletin, 27, p.269-275, 1992.).

Since the x value calculated from the Li / Mn value is 0.32 by chemical analysis (Table 5 below), in Example 3, the composition (Li _1.32 Mn) close to Li ₂ MnO ₃ (Li _1.33 Mn _0.67 O ₂ ). It was confirmed that _0.68 O ₂ ) was obtained.

FIG. 11 is a drawing obtained by electronic image processing of an electron micrograph (10,000 magnifications) of Li ₂ MnO ₃ obtained as a final product in Comparative Example 2. From FIG. 11, it is clear from Comparative Example 2 that most of the fine particles are also formed with Li ₂ MnO ₃ having a primary particle diameter of 1 mm or more. The specific surface area was 2.5 m ² / g, which was smaller than the values 44.0 and 26.4 m ² / g of Examples 2 and 3, confirming that a coarser lithium manganese composite oxide was obtained.

  The elemental analysis results in Examples 2 and 3 and Comparative Example 2 are shown in Table 1 below.

Charge / discharge test 3
Each composite oxide obtained in Examples 2 and 3 and Comparative Example 2 was used as a positive electrode material, Li metal was used as a negative electrode material, and LiPF ₆ as a supporting salt was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate. A coin-type lithium battery was prepared using the 1M solution as an electrolyte. The charge / discharge characteristics of this lithium battery were examined at the start of charging at 30 ° C. (potential range 2.0-4.8 V, current density 42.5 mA / g).

  FIG. 12 is a graph showing initial charge / discharge characteristics of lithium batteries using the positive electrode materials of Examples 2 and 3 and Comparative Example 2. In FIG. 12, the upward curve corresponds to the charge curve, and the downward curve corresponds to the discharge curve. The charge / discharge data is shown in Table 6 below.

From FIG. 12 and Table 6, the batteries using the Li ₂ MnO ₃ positive electrode material of Examples 2 and 3 prepared using potassium permanganate as the manganese raw material were those of Comparative Example 3 prepared using manganese (II) chloride as the manganese raw material. Compared with the battery using the Li ₂ MnO ₃ positive electrode material, the average voltage is almost the same, and it is clear that the initial charge / discharge capacity and the initial discharge energy density are large.

FIG. 13 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 Li ₂ MnO ₃ positive electrode material of Examples 2 and 3 has a higher capacity over the number of cycles than the battery using the positive electrode of Comparative Example 3.

From the above results, the Li ₂ MnO ₃ composite oxide obtained by preparing potassium permanganate as a manganese raw material exhibits excellent charge / discharge characteristics in a charge / discharge test at 30 ° C., and is a lithium ion secondary battery. As a lithium manganese composite oxide positive electrode material for use, it was confirmed that it had excellent performance.

Example 4
As starting materials, 40.40 g of iron (III) nitrate nonahydrate, 40.00 g of 30% titanium sulfate (IV) aqueous solution, and 15.80 g of potassium permanganate (total amount 0.25 mol, Fe: Mn: Ti molar ratio = 2: 2: Except for using 1), precipitation preparation, precipitation ripening, hydrothermal treatment, and water washing treatment were performed in the same manner as in Example 2 to obtain a powdery product (lithium manganese composite oxide).

  The powder obtained by filtration was mixed with lithium hydroxide aqueous solution in which 5.25 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water, stirred, dried overnight at 100 ° C, and pulverized to produce powder did.

  Next, the obtained powder was heated to 750 ° C. in the air over 1 hour, fired at that temperature for 1 minute, cooled to room temperature in the furnace, and the fired product was removed in order to remove excess lithium salt. The product was washed with distilled water, filtered, and dried to obtain the target lithium manganese composite oxide as a powder product.

The X-ray diffraction pattern of this final product is shown in FIG. From the results of Rietveld analysis (program uses RIETAN-2000), all peaks are unit cells of layered rock salt type iron-containing Li ₂ MnO ₃

Unit Phase Cell of Crystal Phase with Crystalline (First Phase: a = 2.929 (5) Å, c = 14.253 (14) Å) and Cubic Rock Salt Type α-LiFeO ₂

 (Second phase: a = 4.1053 (2) Å, the abundance ratio of the first phase and the second phase 21:79). The obtained lattice constant of the layered rock-salt-type crystal phase was close to the previously reported value of the lithium-iron-manganese complex oxide (lattice constant a = 2.882 Å, c = 14.287 Å) (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.).

According to chemical analysis (Table 7 below), the x value calculated from the Li / (Mn + Fe + Ti) value is 0.18, the y value calculated from the Fe / (Mn + Fe + Ti) value is 0.40, Ti / ( Since the z value calculated from the (Mn + Fe + Ti) value is 0.19, in Example 4, the charge composition (Li _{1 + x} (Fe _0.4 Mn _0.4 Ti _0.2 ) _1-x O ₂ , 0 <x < It was confirmed that a composite oxide having a composition close to 1/3) (Li _1.18 (Fe _0.40 Mn _0.41 Ti _0.19 ) _0.82 O ₂ ) was obtained.

FIG. 15 is an image obtained by electronic image processing of an electron micrograph (100,000 times) of the iron- and titanium-containing Li ₂ MnO ₃ obtained as the final product in Example 4. From FIG. 15, it is apparent from Example 4 that iron and titanium-containing Li ₂ MnO ₃ having a primary particle diameter of 100 nm or less is formed. The specific surface area was 30.2 m ² / g, which was larger than the value 27.4 m ² / g of Comparative Example 3 described later, and because KMnO ₄ was used as the Mn source, a finer lithium manganese composite oxide was obtained. Is clear.

Comparative Example 3
Example 4 was used except that 19.79 g of manganese chloride tetrahydrate (total amount: 0.25 mol, Fe: Mn: Ti molar ratio = 2: 2: 1) was used instead of potassium permanganate as a starting material. Precipitation preparation, precipitation ripening, hydrothermal treatment, LiOH addition, baking, washing treatment, filtration, and drying treatment were performed to obtain the target powdery product (lithium manganese composite oxide) as a powdery product .

The X-ray diffraction pattern of this final product is shown in FIG. From the results of Rietveld analysis (program uses RIETAN-2000), all peaks are unit cells of layered rock salt type iron-containing Li ₂ MnO ₃

Unit cell of crystal phase (α = 1.8861 (16) Å, c = 14.280 (6) Å) and cubic rock salt type α-LiFeO ₂

 (Second phase: a = 4.1086 (3) Å, the abundance ratio of the first phase and the second phase 26:74). The obtained lattice constant of the layered rock-salt-type crystal phase was close to the previously reported value of the lithium-iron-manganese complex oxide (lattice constant a = 2.882 Å, c = 14.287 Å) (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.).

According to chemical analysis (Table 7 below), the x value calculated from the Li / (Mn + Fe + Ti) value is 0.18, the y value calculated from the Fe / (Mn + Fe + Ti) value is 0.40, Ti / ( Since the z value calculated from the Mn + Fe + Ti) value is 0.19, in Comparative Example 3, the charge composition (Li _{1 + x} (Fe _0.4 Mn _0.4 Ti _0.2 ) _1-x O ₂ , 0 <x < It was confirmed that a composite oxide having a composition close to 1/3) (Li _1.18 (Fe _0.40 Mn _0.41 Ti _0.19 ) _0.82 O ₂ ) was obtained.

FIG. 15 is an image obtained by electronic image processing of an electron micrograph (100,000 times) of the iron- and titanium-containing Li ₂ MnO ₃ obtained as the final product in Comparative Example 3. From FIG. 15, even in Comparative Example 3, it can be confirmed that aggregated iron and titanium-containing Li ₂ MnO ₃ with a primary particle size of 100 nm or less is formed, but the specific surface area is 27.4 m ² / g, The value of Example 4 was smaller than 30.2 m ² / g. Therefore, in Comparative Example 3, since MnCl ₂ was used as the Mn source, it is clear that a coarser lithium manganese composite oxide was obtained.

  The elemental analysis results in Example 4 and Comparative Example 3 are shown in Table 7 below.

Charge / discharge test 4
1M solution in which each composite oxide obtained in Example 4 and Comparative Example 3 was used as a positive electrode material, Li metal was used as a negative electrode material, and LiPF ₆ as a supporting salt was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate. A coin-type lithium battery was prepared using the electrolyte as an electrolyte. The charge / discharge characteristics of this lithium battery were examined at the start of charging at 60 ° C. (potential range 2.0-4.5 V, current density 42.5 mA / g).

  FIG. 16 is a graph showing initial charge / discharge characteristics of lithium batteries using the positive electrode materials of Example 4 and Comparative Example 3. In FIG. 16, the upward curve corresponds to the charge curve, and the downward curve corresponds to the discharge curve. Table 8 shows the initial charge / discharge data.

From FIG. 16 and Table 8, the battery using the iron and titanium-containing Li ₂ MnO ₃ positive electrode material of Example 4 prepared using potassium permanganate as the manganese raw material was a comparative example prepared using manganese (II) chloride as the manganese raw material. It is clear that the initial discharge capacity and energy density are large and the charge / discharge efficiency is excellent as compared with the battery using ₃ iron and titanium-containing Li ₂ MnO ₃ positive electrode materials.

FIG. 17 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 titanium-containing Li ₂ MnO ₃ positive electrode material of Example 4 has a high capacity over all the cycle numbers.

Charge / discharge test 5
1M solution in which each composite oxide obtained in Example 4 and Comparative Example 3 was used as a positive electrode material, Li metal was used as a negative electrode material, and LiPF ₆ as a supporting salt was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate. A coin-type lithium battery was prepared using the electrolyte as an electrolyte. The charge / discharge characteristics of this lithium battery were examined at the start of charging at 30 ° C. (potential range 2.0-4.8 V, current density 42.5 mA / g).

  FIG. 18 is a graph showing initial charge / discharge characteristics of lithium batteries using the positive electrode materials of Example 4 and Comparative Example 3. In FIG. 18, a curve that rises to the right corresponds to a charge curve, and a curve that falls to the right corresponds to a discharge curve. Table 9 shows the initial charge / discharge data.

From FIG. 18 and Table 9, the battery using the iron and titanium-containing Li ₂ MnO ₃ positive electrode material of Example 4 prepared using potassium permanganate as the manganese raw material was a comparative example prepared using manganese (II) chloride as the manganese raw material. It is clear that the initial discharge capacity and energy density are large and the charge / discharge efficiency is excellent as compared with the battery using ₃ iron and titanium-containing Li ₂ MnO ₃ positive electrode materials.

FIG. 19 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 titanium-containing Li ₂ MnO ₃ positive electrode material of Example 4 has a high capacity over all the cycle numbers.

From the above results, the iron- and titanium-containing Li ₂ MnO ₃ composite oxide prepared using potassium permanganate as a manganese raw material has excellent charge / discharge tests at 30 ° C. as well as high-temperature charge / discharge tests at 60 ° C. It shows discharge characteristics, and was confirmed to have excellent performance as a lithium manganese-based positive electrode material for lithium ion secondary batteries.

Example 5
As in Example 2, except that 60.00 g of 30% titanium sulfate (IV) aqueous solution and 27.66 g of potassium permanganate (total amount 0.25 mol, Mn: Ti molar ratio = 7: 3) were used as starting materials. Precipitation preparation, precipitation ripening, hydrothermal treatment, and water washing treatment were performed to obtain a powdery product (lithium manganese composite oxide).

  The powder obtained by filtration was mixed with lithium hydroxide aqueous solution in which 5.25 g of lithium hydroxide monohydrate was dissolved in 100 ml of distilled water, stirred, dried overnight at 100 ° C, and pulverized to produce powder did.

  Next, the obtained powder was heated to 550 ° C. in the air for 1 hour, fired at that temperature for 1 minute, cooled to room temperature in the furnace, and the fired product was removed in order to remove excess lithium salt. The product was washed with distilled water, filtered, and dried to obtain the target lithium manganese composite oxide as a powder product.

The X-ray diffraction pattern of this final product is shown in FIG. From the results of Rietveld analysis (program uses RIETAN-2000), all peaks are unit cells of layered rock salt type iron-containing Li ₂ MnO ₃

Unit cell of α-LiFeO ₂ with crystal phase (first phase: a = 2.8583 (8) Å, c = 14.239 (3) Å)

 (Second phase: a = 4.0791 (5) Å, the abundance ratio of the first phase and the second phase 43:57). The obtained lattice constant of the layered rock-salt-type crystal phase was close to the previously reported value of the lithium-iron-manganese complex oxide (lattice constant a = 2.882 Å, c = 14.287 Å) (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.).

According to chemical analysis (Table 10 below), the x value calculated from the Li / (Mn + Ti) value is 0.28, and the z value calculated from the Ti / (Mn + Ti) value is 0.29. The composition (Li _1.28 (Mn _0.71 Ti _0.29 ) _0.72 O ₂ ) close to the charged composition (Li _{1 + x} (Mn _0.7 Ti _0.3 ) _1-x O ₂ , 0 <x <1/3) was obtained. Was confirmed.

FIG. 21 is an image obtained by electronically processing an electron micrograph (100,000 times) of a titanium-containing Li ₂ MnO ₃ obtained as a final product in Example 5. From FIG. 21, it is clear that, according to Example 5, titanium-containing Li ₂ MnO ₃ aggregated with a primary particle size of 100 nm or less was formed. The specific surface area was 32.5 m ² / g, is equivalent to the value 34.3m ² / g of Comparative Example 3 to be described later, it was confirmed that the lithium-manganese-based composite oxide fine powder was obtained. The titanium-containing Li ₂ MnO ₃ obtained in Example 5 contains a cubic rock salt type phase, whereas the titanium-containing Li ₂ MnO ₃ obtained in Comparative Example 4 described later has a cubic rock salt type phase. This point is also considered to contribute to the improvement of charge / discharge characteristics.

Comparative Example 4
Precipitation was prepared in the same manner as in Example 5 except that 34.63 g of manganese chloride tetrahydrate ((total amount: 0.25 mol, Mn: Ti molar ratio = 7: 3)) was used instead of potassium permanganate as a starting material. Then, precipitation ripening, hydrothermal treatment, LiOH addition, firing, water washing treatment, filtration, and drying treatment were performed to obtain the target powdery product (lithium manganese composite oxide) as a powdery product.

The X-ray diffraction pattern of this final product is shown in FIG. From the results of Rietveld analysis (program uses RIETAN-2000), all peaks are unit cells of layered rock salt type iron-containing Li ₂ MnO ₃

It was possible to index only in a crystal phase having a first phase (a = 2.8634 (3) Å, c = 14.2525 (13) Å). The obtained lattice constant of the layered rock-salt-type crystal phase was close to the previously reported value of the lithium-iron-manganese complex oxide (lattice constant a = 2.882 Å, c = 14.287 Å) (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.).

According to chemical analysis (Table 10 below), the x value calculated from the Li / (Mn + Ti) value is 0.28, and the z value calculated from the Ti / (Mn + Ti) value is 0.29. The composition (Li _1.28 (Mn _0.71 Ti _0.29 ) _0.72 O ₂ ) close to the charged composition (Li _{1 + x} (Mn _0.7 Ti _0.3 ) _1-x O ₂ , 0 <x <1/3) was obtained. Was confirmed.

FIG. 21 is a drawing obtained by electronic image processing of an electron micrograph (100,000 times) of the titanium-containing Li ₂ MnO ₃ obtained as the final product in Comparative Example 4. From FIG. 21, it is clear that Comparative Example 4 forms titanium-containing Li ₂ MnO ₃ aggregated with a primary particle size of 100 nm or less. The specific surface area was 34.3m ² / g, it was confirmed that the value 32.5 m ² / g and an equivalent of lithium manganese-based composite oxide fine powder of Example 5 above were obtained.

  The elemental analysis results in Example 5 and Comparative Example 4 are shown in Table 1 below.

Charge / discharge test 6
1M solution in which each composite oxide obtained in Example 5 and Comparative Example 4 was used as a positive electrode material, Li metal was used as a negative electrode material, and LiPF ₆ as a supporting salt was dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate. A coin-type lithium battery was prepared using the electrolyte as an electrolyte. The charge / discharge characteristics of this lithium battery were examined at the start of charging at 30 ° C. (potential range 2.0-4.8 V, current density 42.5 mA / g).

  FIG. 22 is a graph showing initial charge / discharge characteristics of lithium batteries using the positive electrode materials of Example 5 and Comparative Example 4. In FIG. 22, a curve that rises to the right corresponds to the charge curve, and a curve that falls to the right corresponds to the discharge curve. Table 11 shows the initial charge / discharge data.

From FIG. 22 and Table 11, the battery using the titanium-containing Li ₂ MnO ₃ positive electrode material of Example 5 prepared using potassium permanganate as the manganese raw material was the same as that of Comparative Example 4 prepared using manganese (II) chloride as the manganese raw material. Compared to a battery using a titanium-containing Li ₂ MnO ₃ positive electrode material, it is clear that the initial discharge capacity and energy density are large and the charge and discharge efficiency is excellent.

FIG. 23 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 titanium-containing Li ₂ MnO ₃ positive electrode material of Example 4 has a high capacity over all the cycle numbers.

As described above, the titanium-containing Li ₂ MnO ₃ composite oxide prepared using potassium permanganate as the manganese raw material exhibits excellent charge / discharge characteristics in the charge / discharge test at 30 ° C., and is used for lithium ion secondary batteries. It was confirmed that the lithium manganese-based positive electrode material has excellent performance.

  From the results of the above examples and comparative examples, the lithium manganese composite oxide obtained by the production method of the present invention not only exhibits excellent charge / discharge characteristics in the temperature range of 60 ° C, but also at 30 ° C. It was found that it exhibited excellent charge / discharge characteristics, and it was confirmed that it had excellent performance as a positive electrode material for lithium ion secondary batteries.

Claims (4)

Composition formula (1): Li _{1 + x} (Mn _1-yz Fe _y Ti _z ) _1-x O ₂ (where 0 <x <1/3, 0 ≦ y ≦ 0.75, 0 ≦ z ≦ 0.75,
A method for producing a lithium manganese based composite oxide represented by 0 ≦ y + z <1) and including a crystal phase of a layered rock salt structure,
It is obtained by forming a precipitate by making a raw material solution obtained by dissolving a manganese compound, an iron compound and a titanium compound in a solvent composed of water or a water-alcohol mixture at the same ratio as the element ratio in the composition formula (1) to be alkaline. And hydrothermally treating the precipitate with an oxidizing agent and a water-soluble lithium compound under alkaline conditions, and then firing the hydrothermally treated product in the presence of the lithium compound. A method for producing a lithium-manganese composite oxide, comprising a salt containing 20 mol% or more of the total amount of the manganese compound. Lithium-manganese composite oxide has the composition formula (2): Li _{1 + x} (Mn _1−a Fe _a ) _1−x O ₂ (where 0 <x <1/3, 0.05 ≦ a ≦ 0.75) The method of claim 1, which is represented. The method according to claim 1, wherein the ratio of permanganate in the manganese compound used as a raw material is 50 mol% or more. The method according to claim 1, wherein the manganese compound used as a raw material is potassium permanganate.

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