JP2013100197A - Lithium manganese-based compound oxide and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new material which can keep an average discharge voltage of about 3 V in a long-term charge-discharge cycle, has a discharge capacity equal to or higher than that of a lithium cobalt oxide-based positive electrode material, can be obtained using inexpensive materials with little resource restriction, and can exhibit more excellent charge-discharge characteristics as compared with known low-cost positive electrode materials.SOLUTION: The new material is a lithium manganese-based compound oxide represented by composition formula: Li(MgMMn)O(wherein M is at least one element selected from the group consisting of Fe and Ti, the ranges of x, y and z are: 0≤x≤1/3, 0.08≤y≤0.35, and 0≤z≤0.6). The compound oxide includes a crystal phase having a monoclinic layered halite type structure.

Description

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

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

Currently, in lithium ion secondary batteries, a lithium cobalt oxide (LiCoO ₂ ) material is mainly used as a positive electrode material, and a carbon material such as graphite is used as a negative electrode material. In this positive electrode material, Li is desorbed while cobalt in the lithium cobalt oxide is oxidized from trivalent to tetravalent by charging, and Li is supplied to the negative electrode. During discharge, Li is desorbed from the carbon material of the negative electrode, and the tetravalent When this cobalt is reduced to trivalent, Li is inserted into the positive electrode side, so that it operates as a battery.

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

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

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

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

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

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

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).

In addition, the present inventors have shown that lithium manganese oxides (titanium-containing Li ₂ MnO ₃ and iron and titanium-containing Li ₂ MnO ₃ ) containing titanium, which are resource-rich and inexpensive, together with iron exhibit high capacity. In particular, it has been found that a specific chemical composition and transition metal ion distribution are excellent in discharge characteristics under high current density at room temperature and discharge characteristics at low temperature (see Patent Document 6-8 below).
As described above, various reports have been made on lithium manganese-based positive electrode materials that can replace lithium cobalt-based positive electrode materials. However, in order to further improve the charge / discharge characteristics, the optimum chemical composition and manufacturing conditions of the positive electrode materials are required. Is desired. On the other hand, the lithium-containing composite oxide containing magnesium, in Patent Document 9, the general formula Li _p N _x M _y O _z lithium-containing composite oxide represented by F _a are described, Co as the element N , At least one element selected from the group consisting of Mn and Ni is shown, and as a specific example of the element M, an alkaline earth metal element such as Mg is shown. However, in the lithium-containing composite oxide represented by the above general formula, as the first step, the lithium source, the N element source, and the M element source containing at least Al are mixed and fired, and then the second step. As described above, the lithium-containing composite oxide powder obtained in the first step and the M element salt aqueous solution containing at least Zr and / or Ti are mixed and baked. It merely shows that an alkaline earth metal element such as Mg may be present in the lithium-containing composite oxide obtained by a specific method. Moreover, y indicating the ratio of M element is 0 <y ≦ 0.05, and the presence of a very small amount of M element is only allowed.

  The lithium-containing composite oxide powder described in Patent Document 10 below also permits the presence of alkaline earth metals such as Mg, but this oxide has a specific structure containing zirconium in the surface layer. It is only described that a small amount of magnesium may be contained in the lithium-containing composite oxide having such a specific structure.

Japanese Patent Laid-Open No. 10-120421 JP-A-8-295518 JP 2002-068748 A Japanese Patent Laid-Open No. 2002-121026 JP 2005-154256 A JP 2008-063211 A JP 2009-179501 A JP 2009-274940 A Japanese Patent Publication No. 2007-52712 Special republication 2007-102407

  The present invention has been made in view of the current state of the prior art described above, and its main object is to maintain an average discharge voltage of about 3 V in a long-term charge / discharge cycle, and a lithium cobalt oxide-based positive electrode material. Is a material having a discharge capacity equivalent to or higher than that, can be obtained by using raw materials with less resource restrictions and cheaper, and more excellent than known low-cost positive electrode materials. 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 to achieve the above-described object. As a result, a lithium-iron-manganese-based oxide solid solution or lithium-titanium-manganese-based oxide solid solution having a specific composition obtained using a relatively inexpensive raw material is used as a basic structure. By dissolving magnesium in a specific range greater than the magnesium content in the composite oxide, it does not contain magnesium, or has excellent charge / discharge characteristics compared to oxides with low magnesium content, especially It has been found that the charge / discharge capacity after repeated charge / discharge increases. As a result, it was found that by using the oxide as a positive electrode material for a lithium ion secondary battery, a battery excellent in charge / discharge cycle characteristics can be produced using inexpensive raw materials and metal elements. It came to complete.

That is, the present invention provides the following lithium manganese composite oxide, a production method thereof, a lithium ion secondary battery positive electrode material and a lithium ion secondary battery comprising the lithium manganese composite oxide.
Item 1. Compositional _{formula: Li 1 + x (Mg y} M z Mn 1-yz) during the _1-x O ₂ (wherein, M is at least one element selected from the group consisting of Fe and Ti, x, y and z The range is 0 ≦ x ≦ 1/3, 0.08 ≦ y ≦ 0.35, and 0 ≦ z ≦ 0.6), and a lithium manganese composite oxide including a crystal phase having a monoclinic layered rock salt structure.
Item 2. 2. The lithium manganese based composite oxidation according to item 1, comprising a single phase of a monoclinic layered rock salt structure or a mixed phase of a crystal phase of a monoclinic layered rock salt structure and a crystal phase of a cubic rock salt structure. object.
Item 3. A magnesium compound, a manganese compound, and, if necessary, an aqueous solution containing at least one compound selected from the group consisting of a titanium compound and an iron compound is made alkaline to form a precipitate. Item 3. The method for producing a lithium manganese composite oxide according to Item 1 or 2, which is fired in the presence.
Item 4. Item 4. The method according to Item 3, which comprises a step of oxidizing and aging the precipitate by blowing air into an aqueous solution containing the formed precipitate after forming the precipitate.
Item 5. Item 5. The method according to Item 3 or 4, comprising a step of hydrothermally treating the precipitate with an oxidizing agent and a water-soluble lithium compound under alkaline conditions before firing the formed precipitate.
Item 6. Item 6. The method according to any one of Items 3 to 5, wherein the precipitate is baked in the presence of an organic substance in an inert atmosphere.
Item 7. Item 6. The method according to any one of Items 3 to 5, wherein the precipitation is performed by a two-stage baking method in which the precipitate is baked in the presence of a lithium compound and then baked in the presence of an organic substance in an inert atmosphere.
Item 8. Item 3. A positive electrode material for a lithium ion secondary battery comprising the lithium manganese composite oxide according to Item 1 or 2.
Item 9. A lithium ion secondary battery comprising as a constituent element a positive electrode material for a lithium ion secondary battery comprising the lithium manganese composite oxide according to Item 1 or 2.

Hereinafter, the lithium manganese composite oxide and the method for producing the same of the present invention will be specifically described.
(1) a lithium-manganese-based composite oxide of the lithium manganese-based composite oxide present invention, the composition _{formula: Li 1 + x (Mg y} M z Mn 1-yz) during the _1-x O ₂ (wherein, M is Fe and A compound represented by at least one element selected from the group consisting of Ti, and the ranges of x, y, and z are 0 ≦ x ≦ 1/3, 0.08 ≦ y ≦ 0.35, and 0 ≦ z ≦ 0.6) It is based on a rock salt structure, which is a general crystal structure of oxides, and is a space group similar to the well-known substance Li ₂ MnO ₃

Including a monoclinic layered rock-salt crystal phase.

  The lithium manganese based composite oxide of the present invention only needs to contain the crystal phase of the above monoclinic layered rock salt structure, and other rock salt structures (for example, cubic rock salt structures) having different cation distributions. A mixed phase including a crystal phase may be used.

For example, it may be a single phase of the monoclinic layered rock salt structure described above, or it is similar to α-LiFeO ₂ which is a known substance in addition to the crystal phase of such a monoclinic layered rock salt structure. Space group

It may be a mixed phase including a crystal phase of a cubic rock salt structure having It is considered that both the monoclinic layered rock salt structure crystal phase composite oxide and the cubic rock salt structure crystal phase composite oxide exhibit excellent charge / discharge performance.

In this case, the ratio of the crystal phase of the layered rock salt type structure to the crystal phase of the cubic rock salt type structure is usually as follows. The range is about zero. 1 and 2 schematically show the crystal structure of the monoclinic layered rock salt structure (Li ₂ MnO ₃ ), which is the lithium manganese oxide of the present invention, and the cation arrangement in the Mn-Li layer. FIG. 3 is a drawing schematically showing a crystal phase (α-LiFeO ₂ ) having a cubic rock salt structure.

  In FIG. 1, it has a structure in which a Li layer consisting only of Li ions and a Mn-Li layer containing both Mn and Li ions are alternately stacked via an oxide ion layer formed by an oxide ion array. In FIG. 2, the Mn ions in the Mn-Li layer show a hexagonal network-like regular arrangement, and the Li ions occupy a hexagonal center position composed of six Mn ions. Other cations Fe, Ti, and Mg ions can enter both the Li layer and the Mn-Li layer, and can enter either the Mn position or the Li position in the Mn-Li layer.

  On the other hand, in FIG. 3, Mn, Ti, and Mg ions occupy the lattice positions containing Li and Fe.

  The lithium manganese composite oxide of the present invention is based on a single phase of the crystal phase of the layered rock salt type structure or a mixed phase with the crystal phase of the cubic rock salt type structure, and a predetermined amount of Mg which is a divalent element. It is a solid solution. A complex oxide in which a predetermined amount of Mg is dissolved in a lithium-manganese complex oxide having such a specific rock salt structure is an excellent charge / discharge when used as a positive electrode material for a lithium ion secondary battery. In particular, even when the cycle characteristics are improved and charge / discharge is repeated, a high discharge capacity can be maintained. Furthermore, depending on the composition of the lithium manganese composite oxide, the initial charge / discharge characteristics are also good.

  The amount of Mg ions to be dissolved (y value: Mg / (Mg + M + Mn); M is at least one of Fe and Ti) is a lithium manganese oxide positive electrode driven in a wide voltage range (2.0-4.8V). In order to fully exhibit the effect of Mg, it should be about 8 mol% to 35 mol% (0.08 ≦ Mg / (Mg + M + Mn) ≦ 0.35) of the total amount of metal ions other than Li ions, and 9.5 mol% It is preferable to be about ~ 32 mol% (0.095 ≦ Mg / (Mg + M + Mn) ≦ 0.32), and about 10 mol% to 30 mol% (0.10 ≦ Mg / (Mg + M + Mn) ≦ 0.30). More preferably. If the amount of Mg is too small, the effect of adding Mg cannot be sufficiently exhibited. On the other hand, if the amount of Mg is too large, the amount of excess Li contained in the structure represented by x in the above composition formula decreases. This is not preferable because it leads to a decrease in charge / discharge capacity.

  Furthermore, in the lithium manganese composite oxide of the present invention, at least one element selected from the group consisting of Fe and Ti represented by M in the above general formula can be dissolved as necessary. These elements are all components that have a favorable effect on the charge / discharge characteristics. For example, when Fe is present, the initial charge voltage can be reduced, and when Ti is present, lithium manganese-based When producing the composite oxide, Li deficiency during low-temperature firing can be suppressed.

The amount of at least one element selected from the group consisting of Fe and Ti (z value: M / (Mg + M + Mn)) is about 60 mol% or less of the total amount of metal ions other than Li ions (0 ≦ M / ( Mg + M + Mn) ≦ 0.60), preferably about 40 mol% or less (0 ≦ M / (Mg + M + Mn) ≦ 0.40). Fe and Ti are components considered to be dissolved in the composite oxide of the present invention as LiFeO ₂ and Li ₂ TiO ₃ components, respectively, and both components are difficult to electrochemically desorb and insert Li. When these components are contained in a large amount, the charge / discharge capacity is significantly reduced, which is not preferable.

In the lithium manganese based composite oxide of the present invention, as long as the layered and cubic crystal structure can be maintained, Li _{1 + x} (Mg _y M _z Mn _1-yz ) _1-x O ₂ x is a transition A value between 0 and 1/3 can be taken depending on the average valence of the metal ion. Preferably the range of x is 0.05-0.30.

  Further, the composite oxide of the present invention has a lithium hydroxide, lithium carbonate, titanium compound, iron compound, manganese compound, magnesium compound (with their water content) in a range that does not significantly affect the charge / discharge characteristics (up to about 10 mol%). An impurity phase such as a hydrate and a composite compound may also be included.

Method for Producing Lithium Manganese Composite Oxide There is no particular limitation on the method for producing the composite oxide of the present invention. For example, it is one of wet chemical production methods that allow uniform mixing of Mg, M, and Mn ions. An Mg-M-Mn coprecipitate is prepared using a coprecipitation method, via a hydrothermal reaction as necessary, and then the coprecipitate or hydrothermal reaction product is dissolved in Li salt and optionally in water. According to the method of mixing with an organic material and baking, a composite oxide having excellent charge / discharge performance can be easily formed. The method of the following term is demonstrated concretely.

(I) Formation of precipitates The step of preparing a Mg-M-Mn coprecipitate using the coprecipitation method includes Mg, Mn, and, if necessary, a metal compound as a raw material for the element M in water, water / alcohol. This is a step of forming a Mg-M-Mn coprecipitate by subjecting a precipitate obtained by making a mixed solution dissolved in a mixture or the like alkaline to a wet oxidation treatment.

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

  What is necessary is just to make it the mixing ratio of each said metal compound in this mixed aqueous solution become an element ratio similar to each element ratio in the target complex oxide.

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

  As a solvent for the mixed aqueous solution, water may be used alone, or a water-alcohol mixed solvent containing a water-soluble alcohol such as methanol or ethanol may be used. By using a water-alcohol mixed solvent, a precipitate can be formed at a temperature lower than 0 ° C. The amount of alcohol used may be appropriately determined according to the target precipitation temperature, but it is usually appropriate to use about 50 parts by weight or less with respect to 100 parts by weight of water.

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

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

  During precipitation, the temperature of the mixed aqueous solution is about -50 ° C to + 15 ° C, preferably about -40 ° C to + 10 ° C, so that it differs from the target composition accompanying the generation of heat of neutralization during the reaction. Generation of impurities such as spinel oxide is suppressed, and a fine and homogeneous precipitate is easily formed.

  After the mixed aqueous solution is made alkaline, air is further introduced into the reaction solution at about 0 to 150 ° C. (preferably about 10 to 100 ° C.) for several hours to about 7 days (preferably about 0.5 to 4 days). It is preferable to oxidize and age the precipitate while blowing.

The obtained Mg-M-Mn coprecipitate 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.
(Ii) Hydrothermal treatment Next, the coprecipitate obtained by the above-described method is subjected to a hydrothermal treatment under alkaline conditions together with a water-soluble lithium compound and an oxidizing agent as necessary. Hydrothermal treatment can be performed by heating the aqueous solution containing the coprecipitate, the water-soluble lithium compound, and the oxidizing agent under alkaline conditions. Heating is usually performed in a sealed container. In the aqueous solution used for the hydrothermal reaction, the content of the constituent metal coprecipitate 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 / (M + Mn) = 1 to 10, preferably about 3 to 7, as the molar ratio of lithium element to the total number of moles of constituent metals in the precipitation product. 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.
Further, by performing hydrothermal treatment in the presence of an oxidizing agent, by-production of orthorhombic LiMnO ₂ , which is an undesirable impurity phase in terms of charge / discharge characteristics, can be suppressed. In particular, a lithium manganese composite oxide having a relatively high manganese element ratio, for example, in the composition formula Li _{1 + x} (Mg _y M _z Mn _1-yz ) _1-x O ₂ , the Mn ratio (1- When an oxide having a value of y−z) of about 0.5 or more is obtained, orthorhombic LiMnO ₂ is easily formed as a by-product, which is effective in that this can be suppressed.

  The oxidizing agent can be used without particular limitation as long as it decomposes during hydrothermal reaction and generates oxygen. Specific examples include potassium chlorate, lithium chlorate, lithium perchlorate, sodium chlorate, hydrogen peroxide. Water etc. can be mentioned. An oxidizing agent can be used individually by 1 type or in mixture of 2 or more types. 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 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 hydroxide such as potassium hydroxide or sodium hydroxide. In addition, ammonia may be added to increase the pH value.

  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 washing, for example, water, a water-alcohol mixed solution, alcohol, acetone, or the like can be used. Next, the product is filtered and dried at a temperature of 80 ° C. or higher (usually about 100 ° C.) to obtain a constituent metal material for firing described later.

(Iii) Firing treatment Next, the coprecipitate or hydrothermal reaction product obtained before hydrothermal treatment is fired together with a lithium compound to control the Li content, the metal blending ratio, and the powder characteristics. An Mg-containing lithium manganese composite oxide can be obtained. 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 1500 ° C, and more preferably about 300 to 1200 ° 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.

  The lithium compound used in the firing step can be used without particular limitation as long as it is a compound containing lithium element. Specific examples include lithium salts such as lithium carbonate, lithium chloride, lithium nitrate, and lithium acetate, lithium hydroxide, and water thereof. A Japanese thing etc. can be mentioned. These lithium compounds can be used singly or in combination of two or more. What is necessary is just to make the usage-amount of a lithium compound into about 0.01-3 times mole amount with respect to the preparation molar amount of the metal component in the raw material for precipitation formation.

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

  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.

  In the present invention, in order to reduce the average valence of the transition metal that constitutes, it is particularly preferable to fire in a reducing atmosphere, which facilitates control of the Li content, Mn valence, and powder characteristics, The intended lithium manganese composite oxide can be obtained easily.

  The method for firing in a reducing atmosphere is not particularly limited. For example, the reducing property can be reduced by firing in the presence of an organic substance in an inert atmosphere such as an inert gas stream such as nitrogen or argon gas. Firing in an atmosphere is possible.

  There are no particular limitations on the organic material, and any carbon-containing compound that can be decomposed into a reducing atmosphere at the firing temperature described below can be used. In particular, when a water-soluble organic substance is used, it is advantageous because it can be dispersed and mixed with the lithium manganese composite oxide powder in an aqueous solution (specific examples of such an organic substance include sucrose, glucose, starch, polyethylene glycol, etc. Can be mentioned.

  The amount of the organic substance used is preferably about 0.001 to 5 times mol, more preferably about 0.01 to 1 times mol in terms of the molar ratio of carbon to the charged molar amount of the metal component in the raw material for precipitation formation. preferable. In the case of using as an aqueous solution, the concentration of the organic substance may be appropriately determined so as to be in the above range of use amount.

  The method for firing in the presence of an organic substance is not particularly limited, and the above-described lithium compound and organic substance are added to the firing raw material and mixed, and then heated at a temperature of 80 ° C or higher, preferably about 100 ° C. After drying, it may be pulverized and fired. The firing temperature is preferably about 150 to 1000 ° C, more preferably about 200 to 800 ° C.

  The atmosphere during firing may be an inert gas atmosphere such as in nitrogen gas so that a strong reducing atmosphere is obtained by the decomposition of the organic matter. 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.

  By firing by the above-described method, it is possible to easily control the Li content, the constituent metal average valence, the powder characteristics, and the like of the target lithium manganese composite oxide. For example, the lithium content in the lithium manganese composite oxide can be adjusted by appropriately setting the amount of the lithium compound added during firing. Moreover, the particle size of the lithium manganese composite oxide can be increased by increasing the firing temperature. Furthermore, it is possible to further reduce the average valence of the constituent metal elements by increasing the amount of the organic substance added and further increasing the firing temperature.

  The firing process described above may be a two-stage firing process in which a lithium compound is added to a lithium manganese-based composite oxide and fired, and then an organic substance is added and fired. When performing a two-step firing process, it is possible to more easily control the Li content, the constituent metal average valence, the powder characteristics, and the like.

  In this case, with respect to the first stage baking treatment performed by adding the lithium compound to the lithium manganese composite oxide, the amount of the lithium compound used may be the same as the above baking treatment. As for the conditions for the first stage baking treatment, any atmosphere such as air, oxidizing atmosphere, inert atmosphere, reducing atmosphere, etc. can be selected as the firing atmosphere. 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 the first-stage baking treatment is performed by the above-described method, the second-stage baking treatment in which an organic substance is added and fired may be performed. The conditions for the second stage baking treatment may be the same as those in the case where the baking treatment is performed by simultaneously adding the lithium compound and the organic substance.

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

  Further, if necessary, the heat-dried product is pulverized, a lithium compound and an organic material are added, baked, washed, and dried to repeatedly perform a series of operations, whereby the lithium manganese composite oxide is excellent. The characteristics (stable charge / discharge characteristics, high capacity, etc. in the operating voltage range as a positive electrode material for a lithium ion secondary battery) can be further improved.

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

According to the present invention, it is possible to obtain a novel composite oxide useful as a positive electrode material that can maintain an average discharge voltage of 3 V or more by using inexpensive raw materials and metal elements and is excellent in charge / discharge cycle characteristics.

  Unlike the conventional positive electrode material, the lithium manganese composite oxide of the present invention has such a characteristic that the discharge curve gradually decreases toward the end-of-discharge voltage (2.0 V). By lowering the discharge end voltage to about 2.0V, it is possible to easily achieve high capacity, and it is extremely useful as a positive electrode material for large-sized lithium ion secondary batteries not only for small consumers but also for vehicles. Useful.

  In particular, the composite oxide of the present invention does not contain Mg or has a charge / discharge capacity after repeated charge / discharge compared to a composite oxide having the same composition except that the Mg content is low. It has the characteristic of being high. For this reason, good characteristics can be maintained for a longer period of time.

  The lithium manganese composite oxide according to 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.

Drawing showing the crystal structure of the monoclinic layered rock-salt structure (Li ₂ MnO ₃ ) in the crystalline phase composing the lithium manganese composite oxide of the present invention (crystal structure drawing software VESTA Drawing using). Drawing showing the Li and Mn ion arrangement in the Mn-Li layer in the crystal structure of Li ₂ MnO ₃ among the crystal phases constituting the lithium manganese composite oxide of the present invention (using the crystal structure drawing software VESTA drawing). Of the crystal phases composing the lithium manganese composite oxide of the present invention, a drawing schematically showing the crystal structure of the crystal phase α-LiFeO ₂ having a cubic rock salt structure (drawn using the crystal structure drawing software VESTA) . The X-ray diffraction pattern of the sample obtained in Example 1 and Comparative Example 1. Charge and discharge curves of the lithium secondary battery using the samples obtained in Example 1 and Comparative Example 1 as the positive electrode for the first time and after 10 cycles (upward-right curves indicate charge curves, and downward-right curves indicate discharge curves). The X-ray diffraction pattern of the sample obtained in Example 2 and Comparative Example 2. Charge and discharge curves of a lithium secondary battery using the samples obtained in Example 2 and Comparative Example 2 as a positive electrode for the first time and after 50 cycles (upward-right curves indicate charge curves, and downward-right curves indicate discharge curves). The X-ray diffraction pattern of the sample obtained in Example 3 and Comparative Example 3. Charge and discharge curves of a lithium secondary battery using the samples obtained in Example 3 and Comparative Example 3 as a positive electrode for the first time and after 50 cycles (upward-right curves indicate charge curves, and downward-right curves indicate discharge curves). The X-ray diffraction pattern of the sample obtained in Example 4 and Comparative Example 4. Charge and discharge curves of the lithium secondary battery using the samples obtained in Example 4 and Comparative Example 4 as positive electrodes for the first time and after 50 cycles (upward-right curves are charge curves, and downward-right curves are discharge curves). FIG. 3 is an X-ray diffraction pattern of samples obtained in Example 5 and Comparative Example 2. Charge and discharge curves of the lithium secondary battery using the samples obtained in Example 5 and Comparative Example 2 as a positive electrode for the first time and after 50 cycles (upward-right curves are charge curves, and downward-right curves are discharge curves).

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

Example 1
Add 12.82 g of magnesium (II) nitrate hexahydrate and 39.58 g of manganese (II) chloride tetrahydrate (total amount 0.25 mol, Mg: Mn molar ratio = 2: 8) to 500 ml of distilled water and completely Dissolved to form an aqueous metal salt solution. In another beaker, an aqueous lithium hydroxide solution (a solution of 60 g of anhydrous lithium hydroxide dissolved in 1000 ml of distilled water) was prepared, and the aqueous metal salt solution was added to the titanium beaker while stirring the aqueous solution. Over 3 hours, it was gradually added dropwise at room temperature (about 20 ° C.) to form an Mg-Mn precipitate. After confirming that the reaction solution was completely alkaline (pH 11 or more), the reaction solution containing a coprecipitate was blown with air at room temperature for 1 day with stirring to ripen the precipitate.

  The obtained precipitate was filtered off, and hydroxide obtained by dissolving 15.74 g of lithium hydroxide monohydrate corresponding to 1.5 times the molar amount with respect to the charged molar amount of the metal component in the raw material for precipitation formation was dissolved in 200 ml of distilled water. The lithium aqueous solution and the precipitate separated by filtration were mixed, stirred, dried overnight at 100 ° C., and pulverized to prepare a powder.

  The obtained powder was heated to 650 ° C. in the air over 1 hour, held at that temperature for 20 hours, and then cooled in the furnace. Next, after pulverizing the obtained powder, sucrose (2.14 g) corresponding to a molar amount of carbon 0.3 times the charged molar amount of the metal component in the raw material for precipitation was dissolved in 100 ml of distilled water. After being dispersed in an aqueous sugar solution, it was dried and ground at 100 ° C.

  In order to remove excess lithium salt, etc., after heating the obtained powder to 300 ° C in nitrogen for 3 hours, firing at that temperature in nitrogen for 1 hour, cooling to near room temperature in the furnace The fired product was washed with distilled water, filtered and dried to finally obtain a powdery product.

  The product is washed with distilled water to remove excess salts such as lithium hydroxide, filtered and dried at 100 ° C to produce the target magnesium-containing lithium manganese composite oxide powder I got a thing.

Comparative Example 1
Except for using as the metal salt aqueous solution an aqueous solution of 49.48 g (total amount 0.25 mol) of manganese (II) chloride tetrahydrate not containing magnesium nitrate as a raw material for forming a precipitate, The intended powdered product of lithium manganese composite oxide was obtained.

Evaluation by X-ray diffraction FIG. 4 shows X-ray diffraction (XRD) diagrams of the powder products obtained in Example 1 and Comparative Example 1. Rietveld analysis was performed on these XRD patterns using the analysis program RIETAN-2000 (F. Izumi and T. Ikeda, Mater. Sci. Forum, vol. 321-324 p.198-203 (2000).) The crystallographic parameters shown in Table 1 were calculated.

From the X-ray diffraction peaks of the samples obtained in Example 1 and Comparative Example 1 shown in FIG. 4, both samples of Li ₂ MnO ₃ unit cells having a monoclinic layered rock salt structure previously reported ( Space group

a = 4.937 (1) ,, 8.532 (1) Å, c = 5.030 (2) Å, β = 109.46 (3) °, P. Strobel and B. Lambert-Andron, Journal of Solid State Chemistry, 75, 90- 98 (1988).) Can be indexed, and the Li ₂ MnO ₃ crystal phase single phase having a monoclinic layered rock salt structure can be fitted without any problem.

  From the above results, it was confirmed that the powdered products obtained in Example 1 and Comparative Example 1 were only the target monoclinic layered rock salt type crystal phase.

Evaluation by chemical analysis
ICP emission analysis was used to determine the chemical composition and transition metal valence of the powdered products obtained in Example 1 and Comparative Example 1. The results are shown in Table 2.

  From the results of elemental analysis shown in Table 2, the powdery composition of Example 1 obtained by the above method has both x and y values in the chemical composition formula within the composition range of the oxide of the present invention. I understand.

Evaluation of charge / discharge characteristics A lithium secondary battery was prepared using each sample obtained in Example 1 and Comparative Example 1 as a positive electrode active material, and a charge / discharge test was performed under the following battery configuration and charge / discharge test conditions. It was. The results are shown in Table 3 below and FIG.
<Battery configuration and charge / discharge test conditions>
Positive electrode: Active material 5 mg + AB 5 mg + PTFE 0.5 mg mixed and crimped on Al mesh Negative electrode: Lithium metal electrolyte: LiPF ₆ dissolved in EC + DMC solvent Test temperature: 30 ° C
Current density (per active material): 40 mA / g,
Potential range: 2.0-4.8 V
(Charge-only constant current up to 4.8V-constant-voltage charge (method of maintaining 4.8V until 10 mA / g)
AB: Acetylene black, PTFE: Polytetrafluoroethylene, EC: Ethylene carbonate, DMC: Dimethyl carbonate

図5および表３に示す結果より、実施例１で得られた試料は、比較例１で得られた試料と比較すると、初期充電容量がかなり低いにもかかわらず、初期放電容量は同等に近いものであった。その結果、実施例１で得られた試料は、初期充放電効率が86%であり、比較例1で得られた試料（初期充放電効率74 %）と比較して、初期充放電効率が大幅に改善されていた。

From the results shown in FIG. 5 and Table 3, the initial discharge capacity of the sample obtained in Example 1 is close to that of the sample obtained in Comparative Example 1, although the initial charge capacity is considerably low. It was a thing. As a result, the sample obtained in Example 1 had an initial charge / discharge efficiency of 86%, and the initial charge / discharge efficiency was significantly higher than that of the sample obtained in Comparative Example 1 (initial charge / discharge efficiency 74%). It was improved.

  Although the sample obtained in Example 1 containing Mg had a low initial discharge energy density and an average initial discharge voltage, the initial charge / discharge efficiency was high, and a discharge capacity after 10 cycles was obtained in Comparative Example 1. Since it is larger than the sample, it is clear that the charge / discharge cycle characteristics are superior to the sample obtained in Comparative Example 1 containing no Mg.

Example 2
Magnesium (II) nitrate hexahydrate 6.41 g, 30% titanium (IV) sulfate solution 60.00 g and manganese (II) chloride tetrahydrate 29.69 g (total amount 0.25 mol, Mg: Ti: Mn molar ratio = 1: 3 : 6) was added to 500 ml of distilled water and completely dissolved to prepare an aqueous metal salt solution. A water-ethanol solution of lithium hydroxide (a solution in which 50 g of lithium hydroxide monohydrate was dissolved in 500 ml of distilled water and 150 ml of ethanol) was prepared in another beaker. This lithium hydroxide solution was put into a titanium beaker, fixed in a thermostatic chamber cooled to −10 ° C., and stirred. The metal salt aqueous solution was added dropwise to the stirred lithium hydroxide solution over 2 to 3 hours, and an Mg-Ti-Mn precipitate was formed. After confirming that the reaction solution was completely alkaline (pH 11 or higher), air was blown into the reaction solution containing the coprecipitate under stirring at room temperature for 2 days to ripen the precipitate.

  The obtained precipitate was filtered off, and hydroxide obtained by dissolving 15.74 g of lithium hydroxide monohydrate corresponding to 1.5 times the molar amount with respect to the charged molar amount of the metal component in the raw material for precipitation formation was dissolved in 200 ml of distilled water. The lithium aqueous solution and the precipitate separated by filtration were mixed, stirred, dried overnight at 100 ° C., and pulverized to prepare a powder.

  The obtained powder was heated to 850 ° C. in the air over 1 hour, held at that temperature in the air for 1 hour, and then cooled in the furnace. The product is washed with distilled water to remove excess salts such as lithium hydroxide, filtered and dried at 100 ° C. to obtain the target magnesium- and titanium-containing lithium manganese composite oxide powder. A product was obtained.

Comparative Example 2
As a raw material for forming a precipitate, an aqueous solution containing 80.00 g of 30% titanium (IV) sulfate solution and 29.69 g of manganese (II) chloride tetrahydrate (total amount: 0.25 mol, Ti: Mn molar ratio = 4: 6) is used. Except for the above, the same operation as in Example 2 was performed to obtain a powder product of a titanium-containing lithium manganese composite oxide.

Evaluation by X-ray diffraction Fig. 6 shows X-ray diffraction (XRD) diagrams of the powder products obtained in Example 2 and Comparative Example 2. Rietveld analysis was performed on these XRD patterns using the analysis program RIETAN-2000 (F. Izumi and T. Ikeda, Mater. Sci. Forum, vol. 321-324 p.198-203 (2000).) The crystallographic parameters shown in Table 4 were calculated.

From the X-ray diffraction peak of the sample obtained in Example 2 shown in FIG. 6, a unit cell (space group of Li ₂ MnO ₃ having a monoclinic layered rock-salt structure previously reported)

a = 4.937 (1) ,, 8.532 (1) Å, c = 5.030 (2) Å, β = 109.46 (3) °, P. Strobel and B. Lambert-Andron, Journal of Solid State Chemistry, 75, 90- 98 (1988).) Can be indexed, and the Li ₂ MnO ₃ crystal phase single phase having a monoclinic layered rock salt structure can be fitted without any problem. On the other hand, in the sample of Comparative Example 2, in addition to the layered rock salt type Li ₂ MnO ₃ phase, there is a peak derived from the impurity indicated by the arrow in the figure, which is not seen in the sample of Example 2, so that the cubic spinel type Li ₄ Ti ₅ O ₁₂ unit cell with structure (space group

a = 8.352 (4) Tsuji, K. Kataoka, Y. Takahashi, N. Kijima, J. Akimoto, K. Ohshima, Journal of Physics and Chemistry of Solids (2008) 69, p1454-p1456.) It was necessary to fit using. The abundance ratio of the layered rock salt type crystal phase and the cubic spinel phase was 98: 2.

  From the above results, the powdered products obtained in Example 2 and Comparative Example 2 both contain a monoclinic layered rock salt type crystal phase, but the sample of Comparative Example 2 that does not contain Mg has a spinel phase. Therefore, it was confirmed that the introduction of Mg has the effect of suppressing the formation of the spinel phase, which is an impurity phase.

Evaluation by chemical analysis
ICP emission analysis was used to determine the chemical composition and transition metal valence of the powdered products obtained in Example 2 and Comparative Example 2. The results are shown in Table 5.

  From the results of elemental analysis shown in Table 5, the powdery composition of Example 2 obtained by the above method has an x value, y value, and z value in the chemical composition formula, all within the composition range of the oxide of the present invention. It can be seen that it is.

Evaluation of charge / discharge characteristics A lithium secondary battery was prepared using each sample obtained in Example 2 and Comparative Example 2 as a positive electrode active material, and charged under the same battery configuration and charge / discharge test conditions as in Example 1. A discharge test was conducted. The results are shown in Table 6 below and FIG.

  From the results shown in FIG. 7 and Table 6, the sample obtained in Example 2 had a higher initial charge / discharge capacity than the sample obtained in Comparative Example 2. The initial charge / discharge efficiency of the sample obtained in Example 2 is 64%, which is inferior to that of the sample obtained in Comparative Example 2 (initial charge / discharge efficiency 75%). Since the voltage and the discharge capacity after 50 cycles were larger than the sample obtained in Comparative Example 2, the sample obtained in Example 2 containing Mg was the sample obtained in Comparative Example 2 not containing Mg. It is clear that the charge / discharge initial characteristics and cycle characteristics are excellent as compared with the above.

Example 3
A metal salt aqueous solution for forming a precipitate was prepared in the same manner as in Example 2. Precipitation preparation, aging, lithium hydroxide addition, and baking in the air at 850 ° C. were performed in the same manner, and then cooled in the furnace. Next, the obtained powder was pulverized, and sucrose (2.14 g) corresponding to a molar amount of carbon 0.3 times the charged molar amount of the metal component in the precipitate-forming raw material was dissolved in 100 ml of distilled water. It was dispersed in an aqueous sugar solution, dried and ground at 100 ° C.

  The obtained powder was heated to 600 ° C. in nitrogen over 3 hours, then calcined in nitrogen at that temperature for 1 hour, and cooled to near room temperature in a furnace. The product is washed with distilled water to remove excess salts such as lithium hydroxide, filtered and dried at 100 ° C. to obtain the target magnesium- and titanium-containing lithium manganese composite oxide powder. A product was obtained.

Comparative Example 3
Except for using the same metal salt aqueous solution as in Comparative Example 2, the same operation as in Example 3 was performed to obtain a powder product of a titanium-containing lithium manganese composite oxide.

Evaluation by X-ray diffraction FIG. 8 shows X-ray diffraction (XRD) diagrams of the powder products obtained in Example 3 and Comparative Example 3. Rietveld analysis was performed on these XRD patterns using the analysis program RIETAN-2000 (F. Izumi and T. Ikeda, Mater. Sci. Forum, vol. 321-324 p.198-203 (2000).) The crystallographic parameters shown in Table 7 were calculated.

From the X-ray diffraction peaks of the samples obtained in Example 3 and Comparative Example 3 shown in FIG. 8, a unit cell (space group of Li ₂ MnO ₃ having a monoclinic layered rock-salt structure previously reported)

a = 4.937 (1) ,, 8.532 (1) Å, c = 5.030 (2) Å, β = 109.46 (3) °, P. Strobel and B. Lambert-Andron, Journal of Solid State Chemistry, 75, 90- 98 (1988).) And unit cells of Li ₂ TiO ₃ having a cubic rock salt structure (space group)

a = 4.1405 (3) Å, M. Tabuchi, A. Nakashima, H. Shigemura, K. Ado, H. Kobayashi, H. Sakaebe, K. Tatsumi, H. Kageyama, T. Nakamura and R. Kanno, Journal of Materials Chemistry, 13, 1747-1757 (2003).) And indexing was possible, and it was found that fitting was possible with a structural model in which both crystal phases coexist. The ratio of monoclinic phase and cubic phase in the two-phase structure model was 25:75 for the sample of Example 3 from Table 7 and 18:82 for the sample of Comparative Example 3.

  From the above results, it can be confirmed that the powdered products obtained in Example 3 and Comparative Example 3 both contain the monoclinic layered rock salt crystal phase and the cubic rock salt crystal phase, which are target substances. It was.

Evaluation by chemical analysis
ICP emission analysis was used to determine the chemical composition and transition metal valence of the powdered products obtained in Example 3 and Comparative Example 3. The results are shown in Table 8.

  From the results of elemental analysis shown in Table 8, the powdery composition of Example 3 obtained by the above method has an x value, y value, and z value in the chemical composition formula, all within the composition range of the oxide of the present invention. It can be seen that it is.

Evaluation of charge / discharge characteristics A lithium secondary battery was prepared using each sample obtained in Example 3 and Comparative Example 3 as a positive electrode active material, and charged under the same battery configuration and charge / discharge test conditions as in Example 1. A discharge test was conducted. The results are shown in Table 9 and FIG.

  From the results shown in FIG. 9 and Table 9, the sample obtained in Example 3 has a higher initial charge / discharge capacity, initial charge / discharge efficiency, and initial discharge energy than the sample obtained in Comparative Example 3. It can be seen that the density, average initial discharge voltage, and discharge capacity after 50 cycles are excellent. That is, it is clear that the sample obtained in Example 3 containing Mg is superior in charge and discharge initial characteristics and cycle characteristics as compared with the sample obtained in Comparative Example 3 not containing Mg. .

Example 4
Magnesium (II) nitrate hexahydrate 6.41 g, iron (III) nitrate nonahydrate 30.30 g and manganese (II) chloride tetrahydrate 29.69 g (total amount 0.25 mol, Mg: Fe: Mn molar ratio = 1: 3: 6) was added to 500 ml of distilled water and completely dissolved. A water-ethanol solution of lithium hydroxide (a solution in which 50 g of lithium hydroxide monohydrate was dissolved in 500 ml of distilled water and 200 ml of ethanol) was prepared in another beaker. This lithium hydroxide solution was placed in a titanium beaker and stirred in a thermostatic chamber cooled to −10 ° C. The metal salt aqueous solution was gradually added dropwise to the stirred and cooled lithium hydroxide solution over 2 to 3 hours to form a Mg-Fe-Mn precipitate. After confirming that the reaction solution was completely alkaline (pH 11 or more), the reaction solution containing a coprecipitate was blown with air at room temperature for 1 day with stirring to ripen the precipitate.

  The resulting precipitate was filtered off and filtered in a polytetrafluoroethylene beaker with 310 g of potassium hydroxide, 50 g of lithium hydroxide monohydrate and 50 g of potassium chlorate in 200 ml of distilled water and stirred. The precipitate was added and well dispersed. This polytetrafluoroethylene beaker was placed in a hydrothermal reactor and hydrothermally treated at 220 ° C. for 48 hours. After the hydrothermal treatment, the beaker was taken out from the hydrothermal reactor that had been cooled to room temperature, and the solid was washed several times with 2000 ml of distilled water to remove potassium hydroxide and filtered to obtain a powdered product. .

  Mix the aqueous solution of lithium hydroxide in which 5.25 g of lithium hydroxide monohydrate equivalent to 0.5 times the molar amount of the metal component in the raw material for precipitation formation was dissolved in 100 ml of distilled water, and the filtered precipitate. After stirring, the powder was dried overnight at 100 ° C. and pulverized to produce a powder.

  The obtained powder was heated to 750 ° C. in the air over 1 hour, held at that temperature in the air for 5 hours, and then cooled in the furnace. The product is washed with distilled water to remove excess salt such as lithium hydroxide, filtered and dried at 100 ° C to obtain the target magnesium- and iron-containing lithium manganese composite oxide powder The product was obtained.

Comparative Example 4
An aqueous solution containing 40.40 g of iron (III) nitrate nonahydrate and 29.69 g of manganese (II) chloride tetrahydrate (total amount 0.25 mol, Fe: Mn molar ratio = 4: 6) as raw materials for the formation of the precipitate. Except for use as an aqueous metal salt solution, the same operation as in Example 4 was carried out to obtain the target iron-containing lithium manganese composite oxide powder product.

Evaluation by X-ray diffraction Fig. 10 shows X-ray diffraction (XRD) diagrams of the powder products obtained in Example 4 and Comparative Example 4. Rietveld analysis was performed on these XRD patterns using the analysis program RIETAN-2000 (F. Izumi and T. Ikeda, Mater. Sci. Forum, vol. 321-324 p.198-203 (2000).) The crystallographic parameters shown in Table 10 were calculated.

From the X-ray diffraction peaks of the samples obtained in Example 4 and Comparative Example 4 shown in FIG. 10, a unit cell (space group of Li ₂ MnO ₃ having a monoclinic layered rock salt structure previously reported)

a = 4.937 (1) ,, 8.532 (1) Å, c = 5.030 (2) Å, β = 109.46 (3) °, P. Strobel and B. Lambert-Andron, Journal of Solid State Chemistry, 75, 90- 98 (1988).) Can be indexed, and the Li ₂ MnO ₃ crystal phase single phase having a monoclinic layered rock salt structure can be fitted without any problem.

  From the above results, it can be confirmed that the powdered products obtained in Example 4 and Comparative Example 4 both contain the monoclinic layered rock-salt crystal phase that is the target substance regardless of the presence or absence of Mg. It was.

Evaluation by chemical analysis
Using ICP emission analysis, the chemical composition and transition metal valence of the powdered products obtained in Example 4 and Comparative Example 4 were determined. The results are shown in Table 11.

  From the results of elemental analysis shown in Table 11, the powdered composition of Example 4 obtained by the above method has an x value, y value, and z value in the chemical composition formula, all within the composition range of the oxide of the present invention. It can be seen that it is.

Evaluation of charge / discharge characteristics A lithium secondary battery was prepared using each sample obtained in Example 4 and Comparative Example 4 as a positive electrode active material, and charged under the same battery configuration and charge / discharge test conditions as in Example 1. A discharge test was conducted. The results are shown in Table 12 below and FIG.

  From the results shown in FIG. 11 and Table 12, the sample obtained in Example 4 has substantially the same initial charge / discharge capacity, initial charge / discharge efficiency, and initial discharge energy density as the sample obtained in Comparative Example 4. However, since the average initial discharge voltage is high and the discharge capacity after 50 cycles is large, the sample obtained in Example 4 containing Mg is compared with the sample obtained in Comparative Example 4 not containing Mg. It is clear that the charge / discharge cycle characteristics are excellent.

Example 5
As raw materials for the formation of precipitates, magnesium nitrate (II) hexahydrate 19.23 g, 30% titanium sulfate (IV) solution 20.00 g and manganese chloride (II) tetrahydrate 29.69 g (total amount 0.25 mol, Mg: Ti : Mn molar ratio = 3: 1: 6) The powder product of the target magnesium- and titanium-containing lithium manganese composite oxide was obtained in exactly the same manner as in Example 2 and Comparative Example 2, except that an aqueous solution containing Obtained.

Evaluation by X-ray diffraction Fig. 12 shows X-ray diffraction (XRD) diagrams of the powder products obtained in Example 5 and Comparative Example 2. Rietveld analysis was performed on these XRD patterns using the analysis program RIETAN-2000 (F. Izumi and T. Ikeda, Mater. Sci. Forum, vol. 321-324 p.198-203 (2000).) The crystallographic parameters shown in Table 13 were calculated.

From the X-ray diffraction peak of the sample obtained in Example 5 shown in FIG. 12, a unit cell (space group of Li ₂ MnO ₃ having a monoclinic layered rock-salt structure previously reported)

a = 4.937 (1) ,, 8.532 (1) Å, c = 5.030 (2) Å, β = 109.46 (3) °, P. Strobel and B. Lambert-Andron, Journal of Solid State Chemistry, 75, 90- 98 (1988).) Can be indexed, and the Li ₂ MnO ₃ crystal phase single phase having a monoclinic layered rock salt structure can be fitted without any problem. On the other hand, in the sample of Comparative Example 2, in addition to the layered rock salt type Li ₂ MnO ₃ phase, a peak derived from an impurity indicated by an arrow in the figure, which is not seen in the sample of Example 5, exists, so that the cubic spinel type Li ₄ Ti ₅ O ₁₂ unit cell with structure (space group

a = 8.352 (4) Tsuji, K. Kataoka, Y. Takahashi, N. Kijima, J. Akimoto, K. Ohshima, Journal of Physics and Chemistry of Solids (2008) 69, p1454-p1456.) It was necessary to fit using. The abundance ratio of the layered rock salt type crystal phase and the cubic spinel phase was 98: 2.

  From the above results, the powdered products obtained in Example 5 and Comparative Example 2 both contain a monoclinic layered rock salt type crystal phase, but the sample of Comparative Example 2 not containing Mg has a spinel phase. It is apparent that the introduction of Mg has the effect of suppressing the formation of the spinel phase, which is an impurity phase.

Evaluation by chemical analysis
ICP emission analysis was used to determine the chemical composition and transition metal valence of the powdered products obtained in Example 5 and Comparative Example 2. The results are shown in Table 14.

  From the results of elemental analysis shown in Table 14, the powdery composition of Example 5 obtained by the above method has an x value, y value, and z value in the chemical composition formula, all within the composition range of the oxide of the present invention. It can be seen that it is.

Evaluation of charge / discharge characteristics A lithium secondary battery was prepared using each sample obtained in Example 5 and Comparative Example 2 as a positive electrode active material, and charged under the same battery configuration and charge / discharge test conditions as in Example 1. A discharge test was conducted. The results are shown in Table 15 below and FIG.

  From the results shown in FIG. 13 and Table 15, the sample obtained in Example 5 has a higher initial charge / discharge capacity, initial charge / discharge efficiency, and initial discharge energy density than the sample obtained in Comparative Example 2. It was. The sample obtained in Example 5 contains Mg because the average initial discharge voltage is inferior to that of Comparative Example 2 but the discharge capacity after 50 cycles is larger than that of the sample obtained in Comparative Example 2. It is clear that the sample obtained in Example 5 is superior in charge / discharge initial characteristics and cycle characteristics as compared with the sample obtained in Comparative Example 2 containing no Mg.

Claims (9)

Compositional _{formula: Li 1 + x (Mg y} M z Mn 1-yz) during the _1-x O ₂ (wherein, M is at least one element selected from the group consisting of Fe and Ti, x, y and z The range is 0 ≦ x ≦ 1/3, 0.08 ≦ y ≦ 0.35, and 0 ≦ z ≦ 0.6), and a lithium manganese composite oxide including a crystal phase having a monoclinic layered rock salt structure. 2. The lithium manganese based composite oxidation according to claim 1, comprising a single phase of a monoclinic layered rock salt structure crystal phase, or a mixed phase of a crystal phase of a monoclinic layered rock salt structure and a crystal phase of a cubic rock salt structure. object. A magnesium compound, a manganese compound, and, if necessary, an aqueous solution containing at least one compound selected from the group consisting of a titanium compound and an iron compound is made alkaline to form a precipitate. The method for producing a lithium manganese composite oxide according to claim 1, wherein the firing is performed in the presence. The method according to claim 3, further comprising the step of performing oxidation and aging treatment of the precipitate by blowing air into an aqueous solution containing the formed precipitate after forming the precipitate. The method according to claim 3 or 4, comprising a step of hydrothermally treating the precipitate together with an oxidizing agent and a water-soluble lithium compound under alkaline conditions before firing the formed precipitate. The method according to any one of claims 3 to 5, wherein the calcination of the precipitate is performed in the presence of an organic substance in an inert atmosphere. The method according to any one of claims 3 to 5, wherein the precipitate is fired by a two-stage firing method in which the precipitate is fired in the presence of a lithium compound and then fired in the presence of an organic substance in an inert atmosphere. The positive electrode material for lithium ion secondary batteries which consists of a lithium manganese type complex oxide of Claim 1 or 2. The lithium ion secondary battery which uses the positive electrode material for lithium ion secondary batteries which consists of a lithium manganese type complex oxide of Claim 1 or 2 as a component.

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