JP2001126731A - Positive electrode material for lithium secondary cell, positive electrode for lithium secondary cell, and the lithium secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for a lithium secondary cell and lithium secondary cell having superior cell performance at high temperature. SOLUTION: A positive electrode material for a lithium secondary cell comprises (1) a lithium-manganese complex oxide, having a spinel crystal structure and substituting a position of Mn sites by another element, and (2) a compound substituting a portion Mn sites of a tetragonal system lithium-manganese complex oxide represented by Li2Mn2O4 by another element other than Li element and/or a lithium-manganese oxide having a laminated structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode material for a lithium secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery.

[0002]

2. Description of the Related Art In recent years, as portable electronic devices have become smaller and lighter, a secondary battery having a high output and a high energy density has been demanded as a power source thereof. In particular, lithium secondary batteries are being actively developed to satisfy the above requirements. As a positive electrode active material of a lithium secondary battery, LiCo
Lithium composite oxides such as O ₂ , LiNiO ₂ , and LiMn ₂ O ₄ have been proposed and are being actively studied. Among them, complex oxides containing lithium and manganese as main components (hereinafter sometimes referred to as “lithium-manganese complex oxide”) have a large reserve of Mn compared to Co or Ni and are inexpensive. Attracts attention from.

Various studies have been made to improve active materials using lithium manganese composite oxides. JP-A-8-
Patent No. 7883 discloses a lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel crystal structure and a LiMn, in order to suppress a decrease in capacity by supplementing Li irreversibly incorporated into the negative electrode active material at the time of initial charge. It describes that a mixture of a lithium manganese composite oxide (LiMnO ₂ ) having a layered structure having a larger capacity per unit weight than ₂ O ₄ is used as a positive electrode active material.

Japanese Patent Application Laid-Open No. Hei 9-306475 discloses a lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel crystal structure in order to suppress a decrease in capacity by compensating for Li which is irreversibly taken in during initial charging. And Li ₂ Mn
Tetragonal lithium manganese composite oxide represented by ₂ O ₄ (hereinafter referred to as tetragonal lithium manganese composite oxide)
Are described.

Japanese Patent Application Laid-Open No. H10-149828 discloses a lithium manganese composite oxide (Li ₁₊ ) having a spinel crystal structure in order to solve the problem of trapping lithium ions in a negative electrode at the time of initial charging and to reduce cycle deterioration. _x Mn
_A positive electrode active material comprising a tetragonal lithium manganese composite oxide represented by _2- xO ₄ , 0 <x <0.2) and Li ₂ Mn ₂ O ₄ is described.

However, none of the above methods is still satisfactory, and there is a problem that the capacity is significantly reduced under high temperature conditions. When a lithium manganese composite oxide having a spinel structure is used as a positive electrode active material,
Since there is a problem that the capacity is greatly reduced due to charge / discharge cycles and storage under high temperature conditions, there is a problem particularly in applications used in a high temperature environment. Even when a lithium manganese composite oxide having a layered structure is used as a positive electrode active material,
When the active material is repeatedly charged and discharged, the transition to the spinel structure proceeds, so that the same problem occurs.

[0007] The causes of performance degradation at high temperatures are considered to be instability of the crystal structure due to charge and discharge, elution of Mn from the lithium manganese composite oxide, and the like. In addition, Li ₂
Conventionally, a tetragonal lithium manganese composite oxide represented by Mn ₂ O ₄ is produced by a method of producing a spinel lithium manganese composite oxide by refluxing in a LiI-containing acetonitrile solution, or a spinel lithium manganese composite oxide. A method in which a battery is prepared by using an oxide as a positive electrode and a Li metal as a negative electrode and electrochemically discharged, a spinel-type lithium manganese composite oxide is refluxed in a hexane solution containing n-butyllithium to obtain Li ₂ Mn ₂ O Only methods for obtaining ₄ , etc. are known, and these methods are industrially disadvantageous production methods.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to suppress the above-mentioned deterioration in performance at high temperatures (capacity reduction due to charge / discharge cycles and storage under high-temperature conditions), and to improve battery characteristics at high temperatures. It is another object of the present invention to provide a material for a lithium secondary battery and a lithium secondary battery.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, the present inventors have found that (1) a lithium manganese composite having a spinel crystal structure and a part of the Mn site substituted by another element. An oxide and (2) a compound in which a part of the Mn site of a tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ is substituted with another element other than Li and / or
Alternatively, it has been found that by combining a lithium manganese composite oxide having a layered structure, battery performance at high temperatures can be significantly improved, and the present invention has been completed. Further, they have found that a compound in which a part of the Mn site of a tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ is substituted with another element other than Li can be produced by an industrially advantageous method, (1) a lithium manganese composite oxide having a spinel crystal structure and a part of Mn sites substituted by another element; and (2) a tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ It has also been found that a combination with a compound in which a part of the Mn site is substituted by an element other than Li is industrially advantageous, and the present invention has been completed.

That is, the first gist of the present invention is (1) spine
Crystal structure, and part of the Mn site is replaced with another element.
Lithium manganese composite oxide and (2) Li_TwoMn_Two
O_Four Of tetragonal lithium manganese composite oxide represented by
Compound in which part of the Mn site has been replaced with another element other than Li
And / or lithium manganese composite having a layered structure
For lithium secondary batteries characterized by containing a composite oxide
Exists in the positive electrode material.

A second gist of the present invention is as follows: (1) a lithium manganese composite oxide having a spinel crystal structure and a part of Mn sites substituted by another element; and (2) lithium manganese having a layered structure. A positive electrode material for a lithium secondary battery, comprising a composite oxide. Third of the present invention
The gist of (1) is a lithium manganese composite oxide having a spinel crystal structure and a part of Mn site is substituted by another element, and (2) tetragonal lithium represented by Li ₂ Mn ₂ O ₄ The positive electrode material for a lithium secondary battery is characterized in that the manganese composite oxide contains a compound in which a part of the Mn site is substituted by an element other than Li.

A fourth gist of the present invention is that the other element that substitutes for the Mn site of a lithium manganese composite oxide having a spinel crystal structure is Al, Ti, V, Cr, Fe, Li,
The positive electrode for a lithium secondary battery according to any one of the first to third aspects, wherein the positive electrode is one or more other elements selected from the group consisting of Co, Ni, Cu, Zn, Mg, Ga, and Zr. It depends on the material.

A fifth gist of the present invention is that the other element that substitutes for the Mn site of the lithium manganese composite oxide having a spinel crystal structure is Al, Cr, Fe, Li, Co, N
The positive electrode material for a lithium secondary battery according to any one of the first to third aspects, wherein the positive electrode material is one or more other elements selected from the group consisting of i, Mg, and Ga. The sixth gist of the present invention is that the other element that substitutes the Mn site of the lithium manganese composite oxide having a spinel crystal structure is Al, L
The positive electrode material for a lithium secondary battery according to any one of the first to third aspects, wherein the positive electrode material is one or more other elements selected from the group consisting of i and Mg.

According to a seventh aspect of the present invention, there is provided the lithium manganese composite oxide having a spinel crystal structure, wherein a weighted average valence of another element substituting the Mn site is less than 3.5. 1 to 6. The positive electrode material for a lithium secondary battery according to any one of 1 to 6. According to an eighth aspect of the present invention, in the lithium-manganese composite oxide having a spinel crystal structure, the substitution ratio of the Mn site by another element is 1 to 30 mol% or less of Mn.
7. The positive electrode material for a lithium secondary battery according to any one of the items 7 to 7.

According to a ninth aspect of the present invention, there is provided a lithium manganese composite oxide having a layered structure, wherein a part of the Mn site is substituted with another element.
The positive electrode material for a lithium secondary battery according to any one of the above aspects. The tenth gist of the present invention is that a part of the Mn site of the lithium manganese composite oxide having a layered structure has Al, Ti, V, Cr, Fe, Li, Co, Ni,
The gist of any of the first, second, and fourth to eight above, wherein the gallium is substituted with one or more other elements selected from the group consisting of Cu, Zn, Mg, Ga, Zr, Nb, Mo, and Pb. Wherein the positive electrode material for a lithium secondary battery is described.

An eleventh aspect of the present invention is that a part of the Mn site of a lithium manganese composite oxide having a layered structure is:
The positive electrode material for a lithium secondary battery according to any one of the first, second, fourth, and tenth aspects, wherein the positive electrode material is substituted by another element having a weighted average valence of less than 3.5. . A twelfth aspect of the present invention is that the other element that substitutes a part of the Mn site of the tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ is composed of Al, Ti, V, Cr, F
e, Li, Co, Ni, Cu, Zn, Mg, Ga, Z
The positive electrode material for a lithium secondary battery according to any one of the above items 1, 3 to 11, wherein the positive electrode material is one or more other elements selected from the group consisting of r, Nb, Mo, and Pb.

A thirteenth aspect of the present invention resides in Li ₂ Mn ₂ O ₄
Of the tetragonal lithium manganese composite oxide represented by
The positive electrode material for a lithium secondary battery according to any one of the first to third aspects, wherein the weighted average valence of another element that substitutes a site is less than 3.5. A fourteenth aspect of the present invention is represented by (1) a lithium manganese composite oxide having a spinel crystal structure and a part of an Mn site substituted with another element, and (2) Li ₂ Mn ₂ O _4. The weight ratio of the tetragonal lithium manganese composite oxide to the compound in which a part of the Mn site is substituted by an element other than Li and / or the lithium manganese composite oxide having a layered structure is 10:90 by weight. To 98: 2, wherein the positive electrode material for a lithium secondary battery according to any one of the first to thirteenth aspects is provided.

A fifteenth aspect of the present invention is as follows: (1) a lithium manganese composite oxide having a spinel crystal structure in which a part of an Mn site is substituted by another element; and (2) Li ₂ Mn ₂ O
M of tetragonal lithium manganese composite oxide represented by ₄
The weight ratio of the compound in which a part of the n-site is substituted by an element other than Li and / or the lithium manganese composite oxide having a layered structure is 50:50 to 95: 5 by weight. The positive electrode material for a lithium secondary battery according to any one of the first to fourteenth aspects described above.

A sixteenth aspect of the present invention is the above-mentioned first to fifteenth aspects.
The positive electrode for a lithium secondary battery contains, as an active material, the positive electrode material for a lithium secondary battery described in any one of the above aspects. A seventeenth aspect of the present invention is directed to a lithium secondary battery positive electrode including the lithium secondary battery positive electrode material according to any one of the first to fifteenth aspects as an active material, and including a carbon material as an active material. A lithium secondary battery comprising a negative electrode and an electrolyte layer.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.
You. The lithium manganese composite oxide in the present invention,
A composite oxide mainly composed of lithium and manganese
You. Lithium manganese composite acid with spinel crystal structure
Is LiMn_TwoO_FourRepresented by the formula and having a layered structure
Mumanganese composite oxide is LiMnO_TwoRepresented by the tetragonal system
Lithium manganese composite oxide is Li_TwoMn_TwoO_Four Represented by
But may have a small amount of oxygen deficiency and non-stoichiometric
No. In the present invention, the lithium manganese composite oxide
(Lithium-manganese composite oxidation with spinel crystal structure
, Lithium manganese composite oxide having layered structure, L
i_TwoMn_TwoO_FourThe tetragonal lithium manganese composite represented by
Part of the Mn site of the oxide is replaced by elements other than Li
Is used as an active material. The book
In the invention, an active material is a source of an electromotive reaction of the battery.
The main substances that can store and release Li ions
means.

In the present invention, a lithium manganese composite oxide having a spinel crystal structure (hereinafter sometimes referred to as “spinel type lithium manganese composite oxide”) requires that a part of the Mn site is replaced by another element. And The other element that substitutes for the Mn site (hereinafter, referred to as a substitution element) is not particularly limited, but Al, Ti, V,
Cr, Fe, Li, Co, Ni, Cu, Zn, Mg, G
a, Zr and the like, preferably Al, C
r, Fe, Co, Li, Ni, Mg and Ga, and particularly preferably Al, Li and Mg. The Mn site may be substituted with two or more kinds of other elements, and when substituted with Li, it is preferable that the Mn site is further substituted with another element other than Li. The substituted element preferably has an average valence calculated by a weighted average considering the composition (hereinafter, referred to as a weighted average valence) of less than 3.5 for the spinel-type lithium manganese composite oxide. If the average valence is too large, the crystal structure is greatly deteriorated due to charge and discharge, and there is a problem that Mn elution at a high temperature tends to proceed. The average valence is determined by the following equation.

[0022]

(1) (Σ_i(X_i× n_i)) / Σ_in_i  X_i: Valence of substitution element i, n_i: Molar fraction of substitution element i Li in the present invention_TwoMn_TwoO_FourThe tetragonal crystal represented by
-Based lithium manganese composite oxide has a part of Mn site L
Indispensable to be replaced by other elements other than i
Lithium manganese composite oxide with a structure has Mn sites
May be partially replaced by another element. Li_TwoMn_TwoO
_FourOf the tetragonal lithium manganese composite oxide represented by
Conversion of part of the n site to another element other than Li
The compound must be manufactured by an industrially advantageous method described below.
, Unsubstituted tetragonal lithium manganese composite oxide
More advantageous than The weighted average valence of the substitution element is 3.5
It is preferably less than. Weighted average valence is too large
Transition to spinel type due to charge and discharge, and
Outing is easy to progress. There is no particular limitation on the substitution element,
Al, Ti, V, Cr, Fe, Li, Co, Ni, C
gold such as u, Zn, Mg, Ga, Zr, Nb, Mo, Pb
And Al, Cr, Fe, L
i, Co, Ni, Mg, Ga, and particularly preferably A
1, Cr, Fe, Li, Co, and Ni. Note that Mn
The site may be substituted by two or more other elements,
Lithium manganese composite oxide having a helical structure is Li
If substituted, it is further substituted with an element other than Li.
Are preferred, and the tetragonal lithium manganese complex
In the case of a composite oxide, Li is replaced with an element other than Li.
Are preferred.

[0023] Further, the lithium manganese composite oxide having a spinel crystal structure is represented by another element that partially replaces the Mn site of the lithium manganese composite oxide, and the lithium manganese composite oxide having a layered structure or Li ₂ Mn ₂ O _4. It may be the same or different from the other element that partially replaces the Mn site of the tetragonal lithium manganese composite oxide. The substitution ratio of the lithium manganese composite oxide having a spinel crystal structure by the substitution element is usually 30 mol% or less of Mn, preferably 20 mol% or less, and usually 1 mol% or more, preferably 3 mol% or more. is there. If the substitution ratio is too small, the effect of improving the high-temperature cycle may not be sufficient, and if it is too large, the capacity of the battery may decrease.

In the case of a lithium manganese composite oxide having a layered structure, the substitution ratio of the substitution element is usually 7% of Mn.
0 mol% or less, preferably 60 mol% or less, more preferably 30 mol% or less. If the replacement ratio is too large, the capacity of the battery may decrease.
In the case of a tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ ,
Is at most 30 mol%, preferably at most 20 mol%, usually at least 1 mol%, preferably at least 3 mol%. If the substitution ratio is too small, the effect of improving the high-temperature cycle may not be sufficient, and if it is too large, the capacity of the battery may decrease.

Further, lithium manganese composite oxide having a spinel crystal structure, lithium manganese composite oxide having a layered structure, and tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ are part of oxygen sites. May be substituted with sulfur or a halogen element. Furthermore, there may be some non-stoichiometric oxygen content. (1) a lithium manganese composite oxide having a spinel crystal structure and a part of Mn sites substituted with another element;
(2) A compound in which a part of the Mn site of a tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ is substituted with an element other than Li and / or a lithium manganese composite oxide having a layered structure There is no particular limitation on the form of the composite with the particles, and they may be physically mixed, and a film of one particle may be formed on the surface of one particle.

The positive electrode material for a lithium secondary battery of the present invention is used as an active material of a positive electrode. (1) A lithium manganese composite oxide having a spinel crystal structure and a part of Mn site substituted by another element And (2) a compound in which a part of the Mn site of the tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ is substituted with an element other than Li and / or a lithium manganese composite having a layered structure The mixing ratio with the oxide is 10:90 to 98: 2, preferably 20:80 to 97: 3, more preferably 30: 7 by weight.
0 to 95: 5, most preferably 50:50 to 95: 5. In the present invention, the total amount of (1) and (2) is the main component, but other components may be contained.

The spinel-type lithium manganese composite oxide in which a part of the Mn site is substituted by another element can be produced by various conventionally known methods.
It can be produced by mixing starting materials containing manganese and a substitution element, followed by firing and cooling in the presence of oxygen. In the above production method, a lithium manganese composite oxide in which Mn sites are not substituted without using a starting material containing a substitution element is produced, and the lithium manganese composite oxide is converted into an aqueous solution of a starting material containing a substitution metal element, a molten salt. Alternatively, after reacting in steam, the Mn site may be replaced by the replacement element by performing heat treatment again in order to diffuse the replacement element into the lithium-manganese composite oxide particles as necessary.

Lithium compound used as starting material
As Li_TwoCO_Three, LiNO_Three , LiOH, LiO
H ・ H_TwoO, LiCl, LiI, CH_ThreeCOOLi, Li
_TwoO, Li dicarboxylic acid, Li fatty acid, Alkyl lithium
And the like. Manganese used as a starting material
As the compound, Mn_TwoO_Three, MnO_TwoManganese oxidation
Material, MnCO_Three, Mn (NO_Three)_Two, Dicarboxylic acid manga
Manganese salts such as manganese, fatty acid manganese, oxyhydroxide, etc.
Is mentioned. Mn_TwoO_ThreeAs MnCO_ThreeAnd MnO_TwoWhat
Any of the compounds prepared by heat treatment may be used.

Examples of the compound of the substitution element include oxides, hydroxides, nitrates, carbonates, dicarboxylates, fatty acid salts and ammonium salts. These starting materials are usually mixed by a method such as wet mixing, dry mixing, ball mill pulverization, and coprecipitation. A pulverizing step may be added before, during and after mixing.

The method of firing and cooling the spinel-type lithium manganese composite oxide is, for example, 600 to 9 after calcination.
A method of performing baking in an oxygen atmosphere at a temperature of about 00 ° C. and then gradually cooling it to a temperature of about 500 ° C. or less at a rate of 10 ° C./min or less, or a temperature of about 600 to 900 ° C. after air or oxygen atmosphere And then annealing at a temperature of about 400 ° C. in an oxygen atmosphere. The firing and cooling conditions are described in US Pat.
The conditions described in column 3L54 of No. 9 to L21 of column 4 (however, the portion of “600 to 850 ° C.” in column 3L62 is “600 to 900 ° C.” in the present invention) may be used.

The spinel-type lithium manganese used in the present invention
The specific surface area of the composite oxide is usually 0.01 m^Two/ G or less
Above, preferably 0.3m^Two/ G or more, more preferably
0.5m^Two / G or more and usually 10 m^Two/ G or less,
Preferably 1.5m^Two/ G or less, more preferably 1.0
m^Two/ G or less. If the specific surface area is too small,
If it is too large, it may cause a decrease in capacity and capacity.
It causes undesired reactions and degrades cycle characteristics.
Sometimes The measurement of the specific surface area follows the BET method.

The average particle diameter of the lithium transition metal oxide used in the present invention is usually 0.1 μm or more, preferably 0.2 μm or more.
m or more, more preferably 0.3 μm or more, most preferably 0.5 μm or more, usually 300 μm or less, preferably 100 μm or less, more preferably 50 μm or less, and most preferably 20 μm or less. If the average particle size is too small, the cycle deterioration of the battery may increase, or a problem may occur in safety. If the average particle size is too large, the internal resistance of the battery may increase, making it difficult to output.

The lithium manganese composite oxide having a layered structure belonging to a hexagonal system, an orthorhombic system, or a monoclinic system can be produced by various conventionally known methods. Hexagonal lithium manganese composite oxide is, for example, γ-MnOOH
And an aqueous solution of LiOH by a hydrothermal method. As a reaction condition, there is a report that the reaction is performed at 300 ° C. and 150 ° C. for 5 days. (Japanese Unexamined Patent Publication No. 10-3921) An orthorhombic lithium manganese composite oxide is, for example, γ-MnO
After crushing and mixing OH, LiOH and H ₂ O, 1000 bar
By pressing into 1-inch pellets, wrapping with Nifoil, and baking at 300-450 ° C. under Ar flow. (J. Electrochem. Soc. 149, 3396 (19
93)) It is known that a monoclinic lithium manganese composite oxide can be synthesized, for example, by synthesis of NaMnO ₂ and ion exchange thereof (Nature 381,499).
(1996)). NaMnO ₂ can be obtained by a solid phase reaction of Na ₂ CO ₃ and Mn ₂ O ₃ (700-730 ° C. 18-72 hr under
Ar flow) and ion exchange can be performed by refluxing in a solution of LiBr in n-hexanol.

Lithium manganese composite oxides belonging to hexagonal system, orthorhombic system, and monoclinic system, having a layered structure, and having a part of Mn sites substituted by other elements, can be prepared by various known methods. For example, after mixing starting materials containing lithium, manganese, and other elements (substituting elements), they can be manufactured by calcining and cooling in an inert gas atmosphere. It can also be manufactured. It can also be produced by firing and cooling in the flow of a reducing gas and in the presence of a reducing agent. It can also be produced by heating an organic solvent containing a spinel-type lithium manganese composite oxide and an alkyl lithium.

Further, it belongs to hexagonal system, orthorhombic system and monoclinic system.
It has a layered structure, and part of the Mn site is replaced with another element.
Lithium manganese composite oxide is part of the Mn site
Oxides and lithium compounds substituted by other elements
And a method of manufacturing by firing. original
Manga in which part of the Mn site was replaced with another element
The oxide is preferably a compound in which the valence of Mn is trivalent.
Manganese oxide, for example, Mn_Two O_ThreeAnd Th
e American Menalogist V
ol. 50 (1965) pp. 1296_Two
O_ThreeCan be mentioned. Note that these compounds
Dry water may be added, but if the amount is too large,
A smaller amount is desirable because the yield is reduced.

As other elements (substituting elements), Al, Ti,
V, Cr, Fe, Co, Ni, Cu, Zn, Mg, G
a, at least one metal element selected from Zr, Nb, Mo and Pd, preferably Al,
V, Cr, Fe, Co, Ni, Mg, Cu, Zn. These other element compounds are not particularly limited, and various oxides, hydroxides, inorganic acid salts, carbonates, organic acid salts, and ammonium salts can be appropriately used.

There is no particular limitation on the method for producing a manganese oxide in which a part of the Mn site is substituted by the other element, but it is desirable that the other element is uniformly distributed in the oxide. Such a manganese oxide in which other elements are uniformly distributed can be produced, for example, by performing the following steps (1) to (4). These steps may be performed separately from each other, or may be partially performed in an overlapping manner. (A) a step of dissolving or suspending at least one compound containing Mn and at least one other element compound in water, an organic solvent or a mixture thereof (b) the solution or suspension formed in step (a) (C) separating the coprecipitated compound, drying and calcining in the presence of oxygen; and (c) separating the coprecipitated compound by increasing the OH 2 ^- concentration of the suspension. One kind of compound and at least one other elemental compound are not particularly limited, but inorganic salts such as nitrates and sulfates, organic acid salts such as acetates and oxalates, carbonates, ammonium salts,
Oxides and the like. These compounds may be used as they are, or may be used in the form of a sol. The ratio of the number of moles of the other element to the sum of the number of moles of Mn and the number of moles of the other element (substituting element) is 0.005 or more and 0.5 or less, preferably 0.01 or more and 0.4 or less. The concentration of the sum of Mn and other elements (substitution elements) in the solution or suspension is
0.01 to 10 mol / l, preferably 0.02 to 5 m
ol / l. In this step, it is desirable to stir the solution or suspension. There is no particular limitation on the liquid temperature, and the temperature may be changed on the way.

In the step (b), there is no particular limitation on the method for increasing the OH ^- concentration of the solution or suspension produced in the step (a). There is a method of adding. Examples of the alkali metal hydroxide include sodium hydroxide and lithium hydroxide. An oxidizing agent such as hydrogen peroxide or oxygen may be added before, during, or after increasing the OH ^- concentration. Although the liquid temperature is not particularly limited, an appropriate temperature can be selected when adding the oxidizing agent, and heating may be performed in order to control the particle properties of the coprecipitated compound generated by precipitation. The heating temperature is appropriately selected usually in the range of 100 ° C. or lower, preferably 90 ° C. or lower, and usually in the range of 30 ° C. or higher. In this step, it is desirable to stir the solution or suspension.

In the step (c), various conventionally known methods can be used for separating the coprecipitated compound formed in the step (b). For example, centrifugal filtration, vacuum filtration, centrifugal separation, decantation and the like can be used. No. In any case, it is desirable to wash the cake after separation after separation, and it is desirable to control the pH of the washing solution so that the cake is not eluted. The drying and baking of the cake may be performed independently, but the drying may be performed continuously as a part of the baking operation, or only the baking may be performed. Examples of the method for drying the coprecipitated compound include a method in which the coprecipitated compound is heated at 30 to 200 ° C. for 2 to 24 hours under air. The firing temperature is 200 to 1200 ° C, preferably 350 to 1100.
C., more preferably 450-1000.degree. Outside the above range, it is difficult to adjust the Mn valence to trivalent.

The firing time is preferably from 1 hour to 50 hours. Below the above range, the effect of firing is not sufficiently exhibited, and above the above range, it is difficult to recognize a difference in the effect of firing. The firing atmosphere is desirably under an oxygen-containing gas, for example, under air. A gas containing oxygen may be passed.
Drying and baking may be performed in a continuous manner or in a batch manner.

As another method for producing a manganese oxide in which a part of the Mn site is replaced by another element, a method of dry-mixing and pulverizing a Mn compound and a compound of the other element, followed by firing in the presence of oxygen is also used. good. The firing can be performed under the same conditions as in the above step (c). In the method for producing a lithium-manganese composite oxide according to the present invention, the manganese oxide or a hydrate thereof in which a part of the Mn site obtained by the above-mentioned production method is substituted with another element is mixed with a lithium compound to obtain an unreacted manganese oxide. By firing under an active gas, a lithium manganese composite oxide having a layered structure can be produced.

As the lithium compound, Li ₂ CO ₃ , L
Inorganic acid salts such as iNO ₃ , hydroxides such as LiOH, LiOH · H ₂ O, halides such as LiCl and LiI, Li
Oxides such as ₂ O, CH ₃ COOLi, dicarboxylic acid Li,
Organic acid salts such as fatty acid Li, and alkyl lithium such as butyl lithium are exemplified. As a method for mixing the manganese oxide and the lithium compound, a conventional mixing method is used, and examples thereof include wet mixing and spray drying, dry mixing, and ball mill pulverization.

The mixture of the manganese oxide and the lithium compound is calcined under an inert gas. Examples of the inert gas at this time include nitrogen, argon, and helium. The firing temperature is from 350 ° C to 1200 ° C, preferably from 500 ° C to 1000 ° C. Below the above-mentioned range, Li does not diffuse sufficiently, and above the above-mentioned range, there is a possibility that Li volatilizes, and neither is preferable. The firing time is from 1 hour to 72 hours, preferably from 2 hours to 50 hours.
Within hours. Below the above range, the effect of firing cannot be sufficiently obtained, and it is difficult to recognize a difference in effect even if firing is performed for a long time beyond this range.

In a solid-phase reaction by firing a lithium compound and a manganese compound, lithium manganese composite oxides having various crystal structures such as a spinel type can be formed. It is an oxide. By using a manganese oxide in which part of the Mn site is replaced with another element as a manganese compound,
By a simple operation method of mixing and firing each component compound of lithium and manganese, and by appropriately selecting the firing conditions, a lithium-manganese composite oxide having a layered crystal structure can be appropriately selectively manufactured. it can. For example, the oxygen concentration under firing is 10,000 ppm
Hereinafter, the layered lithium manganese composite oxide can be manufactured by preferably reducing the content to 1000 ppm or less, or performing the calcination in air under a reducing atmosphere.

The particle size of the primary particles of the lithium manganese composite oxide having a layered structure obtained by the above method is 0.01 μm or more and 50 μm or less, preferably 0.02 μm or more and 30 μm or less. When the particle size is smaller than the above range, when used as a positive electrode active material of a lithium secondary battery, a side reaction with an electrolytic solution may be induced, and when the particle size exceeds the above range, diffusion of Li between the active material and the electrolytic solution may occur. This is not preferred because it can be hindered and cause problems in use at high current densities. There is no particular limitation on the shape of the primary particles. The particle size of the secondary particles is
The thickness is from 0.1 μm to 100 μm, preferably from 0.2 μm to 60 μm. When the particle size is smaller than the above range, it is difficult to handle, and when the particle size is larger than the above range, it becomes difficult to prepare a coated electrode, which is not preferable. There is no particular limitation on the shape of the secondary particles. Specific surface area is 0.05 m ² / g or more and 100
m ² / g or less, preferably 0.1 m ² / g or more 50 m ² /
g or less. Below the above range, L between the active material and the electrolytic solution
The diffusion of i is inhibited, and if it is larger than the above range, a side reaction with the electrolyte may be induced.

The tetragonal lithium manganese composite oxide in which a part of the Mn site is substituted by an element other than Li is Mn.
It can be produced by a method of mixing and sintering a compound, a lithium compound, and another metal element compound. As another production method, a manganese oxide in which a part of the Mn site is substituted with another element, or manganese oxyhydroxide in which a part of the Mn site and / or the H site is substituted with another element, and a lithium compound Can be also adopted.

The compounds of the other elements are not particularly limited, and various oxides, hydroxides, inorganic acid salts, carbonates, organic acid salts, and ammonium salts can be used as appropriate. When this other element compound is mixed and sintered with a Mn compound and a lithium compound, a carbonate, an oxide, a hydroxide, or the like is preferable, and a manganese oxide in which a part of the Mn site is substituted with another element, or When used as manganese oxyhydroxide in which a part of the Mn site and / or H site is substituted with another element, nitrates, sulfates, and the like suitable for preparing these oxides and manganese oxyhydroxide can be used. Salts soluble in solvents such as inorganic acid salts and organic acid salts such as oxalates are preferred.

As the lithium compound, Li ₂ CO ₃ , L
Inorganic acid salts such as iNO ₃ , hydroxides such as LiOH, LiOH · H ₂ O, halides such as LiCl and LiI, Li
Oxides such as ₂ O, CH ₃ COOLi, dicarboxylic acid Li,
Organic acid salts such as fatty acid Li, and alkyl lithium such as butyl lithium are exemplified. Manganese oxide and manganese oxyhydroxide can also be used as the Mn compound. As the manganese oxide, a compound in which the valence of Mn is trivalent is preferable. For example, Mn ₂ O ₃ or The Amer
ican Menalogist Vol. 50
(1965) can be mentioned γ-Mn ₂ O ₃ described on pages 1296. Although a small amount of water may be added to these compounds, it is preferable that the amount of the added compound is small because a large amount of the compound decreases the yield after firing. Mn as manganese oxide
A manganese oxide in which a part of a site is substituted with the above-described other element can also be used. As the manganese oxyhydroxide, those in which the Mn site and / or the H site are substituted with the above-mentioned other elements can also be used. As the manganese oxide or manganese oxyhydroxide substituted with these other elements, those substituted with a plurality of other elements can be used. Manganese oxides and the like substituted by a plurality of other elements may not be able to simultaneously substitute a plurality of other elements by coprecipitation or the like when manufacturing them. And a manganese oxide substituted with a lithium compound together with a compound containing another kind of other element.

There is no particular limitation on the method for producing a manganese oxide in which a part of the Mn site is substituted by another element, but it is desirable that the other element is uniformly distributed in the oxide. Such a manganese oxide in which other elements are uniformly distributed can be produced, for example, by performing the following steps (1) to (3). These steps may be performed separately from each other, or may be partially performed in an overlapping manner. (1) A step of dissolving or suspending at least one compound containing Mn and at least one other element compound in water, an organic solvent or a mixture thereof. (2) A solution or suspension formed in the step (1). OH of Nigoeki ^- step of generating a coprecipitated compound by increasing the concentration, containing Mn in (3) separating the coprecipitated compound, dried, process steps (1) to calcination in the presence of oxygen The at least one compound and the at least one other element compound are not particularly limited, but each includes an inorganic acid salt such as a nitrate and a sulfate, an organic acid salt such as an acetate and an oxalate, a carbonate, an ammonium salt, and an oxide. Is mentioned. These compounds may be used as they are, or may be used in the form of a sol.
The ratio of the number of moles of the other element to the sum of the number of moles of Mn and the number of moles of the other element is 0.005 to 0.5, preferably 0.01 to 0.4. The concentration of the sum of Mn and other elements in the solution or suspension is 0.01 to 1
0 mol / l, preferably 0.02 to 5 mol / l. In this step, it is desirable to stir the solution or suspension. There is no particular limitation on the liquid temperature, and the temperature may be changed on the way.

In the step (2), there is no particular limitation on the method for increasing the OH ^- concentration of the solution or suspension produced in the step (1). Is added.
As hydroxides of alkali metals, sodium hydroxide,
Lithium hydroxide and the like. An oxidizing agent such as hydrogen peroxide or oxygen may be added before, during, or after increasing the OH ^- concentration. The temperature of the solution is not particularly limited, but an appropriate temperature can be selected when the oxidizing agent is added, and the solution may be heated to control the particle properties of the coprecipitated compound formed by precipitation. The heating temperature is appropriately selected usually in the range of 100 ° C. or lower, preferably 90 ° C. or lower, and usually in the range of 30 ° C. or higher. In this step, it is desirable to stir the solution or suspension.

In the above step (3), any of various conventionally known methods can be used for separating the coprecipitated compound formed in the step (2), for example, centrifugal filtration, vacuum filtration, centrifugal separation, decantation, etc. Is mentioned. After the separation, the obtained cake is desirably washed, and the pH of the washing solution is desirably controlled so that the cake is not eluted. The drying and baking of the cake may be performed independently, but may be performed continuously, in which case the drying may be performed as part of the baking operation. Examples of the method for drying the coprecipitated compound include a method in which the coprecipitated compound is heated at 30 to 200 ° C. for 2 to 24 hours under air.

The sintering temperature is 200 to 1200 ° C., preferably 350 to 1100 ° C., and more preferably 450 to 100 ° C.
0 ° C. Outside the above range, it is difficult to adjust the Mn valence to trivalent. The firing time is preferably from 1 hour to 50 hours. Below this range, the sintering effect is not sufficiently exhibited. On the other hand, even if sintering is performed over this range, it is difficult to recognize a significant difference in the effect. The firing atmosphere is desirably under an oxygen-containing gas, for example, under air. A gas containing oxygen may be passed. Drying and baking may be performed in a continuous manner or in a batch manner.

As another method for producing a manganese oxide in which a part of the Mn site is substituted by another element, a manganese compound and a compound of another element are dry-mixed and crushed, and then calcined in the presence of oxygen. good. The firing can be performed under the same conditions as in the step (3). When producing a tetragonal lithium manganese composite oxide in which the Mn site is replaced by another element, a conventional mixing method is used as a method of mixing the Mn compound, the lithium compound, and the other element compound, for example, Examples include wet mixing and spray drying, dry mixing, and ball mill pulverization.

As a sintering method, firing in an inert gas atmosphere may be mentioned. Examples of the inert gas include nitrogen, argon, and helium. The firing temperature is 350 ° C to 1200 ° C, preferably 500 ° C to 1000 ° C
It is as follows. Below the above-mentioned range, Li does not diffuse sufficiently, and above the above-mentioned range, there is a possibility that Li volatilizes, and neither is preferable. Firing time is from 1 hour to 72 hours,
Preferably, it is 2 hours or more and 50 hours or less. Below the above range, the effect of firing cannot be sufficiently obtained, and it is difficult to recognize a difference in effect even if firing is performed for a long time beyond this range.

In a solid-phase reaction by firing a lithium compound and a manganese compound, lithium manganese composite oxides having various crystal structures such as a spinel type can be formed, but it is considered difficult to form a tetragonal lithium manganese composite oxide. I was However, by replacing a part of the Mn site with another element, a tetragonal lithium manganese composite oxide can be obtained by an easy operation method of mixing and firing the above component compounds.

The tetragonal lithium manganese composite oxide in which a part of the Mn site is substituted by another element can be selectively and appropriately produced by appropriately selecting the calcination conditions. For example, if the oxygen concentration under firing is 10,000 pp
m or less, preferably 1000 ppm or less, or by sintering in air under a reducing atmosphere.

The primary particles of the tetragonal lithium manganese composite oxide have a particle size of 0.01 μm or more and 50 μm or less, preferably 0.02 μm or more and 30 μm or less. If the particle size is too small, it may induce a side reaction with the electrolyte when used as a positive electrode active material of a lithium secondary battery, and if it is too large, diffusion of Li between the active material and the electrolyte is hindered, and It is not preferable because a problem may occur in use at a current density. There is no particular limitation on the shape of the primary particles. The particle size of the secondary particles is 0.1 μm or more and 100 μm or less, preferably 0.2 μm or more and 60 μm or less. If the particle size is too small, it is difficult to handle, and if it is too large, it becomes difficult to prepare a coated electrode, which is not preferable. There is no particular limitation on the shape of the secondary particles.
The specific surface area is 0.05 m ² / g or more 100 m ² / g or less, preferably 0.1 m ² / g or more 50 m ² / g. If it is less than the above range, diffusion of Li between the active material and the electrolytic solution is inhibited, and if it is larger than the above range, a side reaction with the electrolytic solution may be induced.

The positive electrode material for a lithium secondary battery of the present invention comprises:
Used as the active material of the positive electrode of lithium secondary batteries,
Such a positive electrode usually contains the active material, the binder, and the conductive agent. As the binder, for example, polyvinylidene fluoride, polytetrafluoroethylene, E
PDM (Ethylene-propylene-diene terpolymer)
, SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine rubber and the like. Examples of the conductive agent include fine particles of graphite, carbon black such as acetylene black, and fine particles of amorphous carbon such as needle coke. The contents of the active material, the binder, and the conductive agent in the positive electrode are usually 20 to 90% by weight, 10 to 50% by weight, and 1 to 2, respectively.
It is about 0% by weight. The positive electrode can be obtained by applying and drying a slurry containing the above materials.

The positive electrode is used as a lithium secondary battery in combination with the negative electrode and the electrolyte layer. As the active material used for the negative electrode, any of the materials usually used for this type of lithium secondary battery can be used. For example, a carbon-based material favorably used as a negative electrode agent of a lithium ion battery can be used. Also, lithium metal, Al,
MoO ₂ , WO ₂ , TiS ₂ , which can be reversibly doped and undoped with lithium at a relatively low potential of 2 V or less with respect to lithium alloys such as Si, Sn, Pb, In, Bi, Sb, and Ag, and Li metal, Transition metal oxides or sulfides such as TiO _2, as well as amorphous tin composite oxides and lithium nitrides can be used. As the carbon-based material, natural graphite, artificial graphite, and even coal-based and petroleum-based cokes / pitches, resin compositions such as phenolic resins, and carbonized various celluloses at high temperatures can be used. . Further, a composite of two or more of these carbon-based materials or a composite of two or more of the above-described non-carbon-based materials and carbon-based materials can also be used. The use of the above-mentioned negative electrode active material is not particularly limited, but natural graphite, artificial graphite, and even a single or composite amorphous carbon material using pitch coke as a raw material are generally used. Have been.

The negative electrode usually contains the above active material and a binder. As the binder, the same material as that for the positive electrode can be used. Also, the same method as that for the positive electrode can be used for the production. The electrolyte layer is usually composed of an ion conductor made of an electrolyte and a separator.

In the case of using a separator, a microporous polymer film is usually used. Is used. The chemical and electrochemical stability of the separator is an important factor. In this respect, a polyolefin-based polymer is preferable, and it is preferable that the battery is made of polyethylene from the viewpoint of the self-closing temperature, which is one of the purposes of the battery separator.

In the case of a polyethylene separator, ultrahigh molecular weight polyethylene is preferable from the viewpoint of maintaining high-temperature shape, and the lower limit of the molecular weight is preferably 500,000, more preferably 1,000,000, and most preferably 1.5 million. On the other hand, the upper limit of the molecular weight is preferably 5,000,000, more preferably 4,000,000, and most preferably 3,000,000. If the molecular weight is too small, the blocking property becomes too high and there is a problem in use at a high temperature. If the molecular weight is too large, the fluidity is too low and the pores of the separator may not be blocked when heated.

As the ion conductor in the lithium secondary battery of the present invention, for example, known organic electrolytes, solid polymer electrolytes, gel electrolytes, inorganic solid electrolytes and the like can be used. Is preferred. The organic electrolyte is composed of an organic solvent and a solute. The organic solvent is not particularly limited, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers,
Amines, esters, amides, phosphate compounds and the like can be used. When these representatives are listed, propylene carbonate, ethylene carbonate, vinylene carbonate, tetrahydrofuran,
2-methyltetrahydrofuran, 1,4-dioxane,
4-methyl-2-pentanone, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone,
1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethylsulfoxide, A single solvent such as trimethyl phosphate and triethyl phosphate or a mixture of two or more solvents can be used.

As a solute to be dissolved in this solvent,
Although not limited to, any conventionally known
LiClO_Four, LiAsF₆, LiPF₆, Li
BF_Four , LiB (C₆H_Five)_Four, LiCl, LiBr, CH
_ThreeSO_ThreeLi, CF_ThreeSO_ThreeLithium salts such as Li
Use at least one of these
Can be.

When a polymer solid electrolyte is used, any known polymer may be used. In particular, it is preferable to use a polymer having high ionic conductivity with respect to lithium ions. Polypropylene oxide, polyethyleneimine and the like are preferably used, and the polymer can be used as a gel electrolyte by adding the above solvent together with the above solute.

When an inorganic solid electrolyte is used, a known crystalline or amorphous solid electrolyte can be used for the inorganic substance. Examples of the crystalline solid electrolyte include Li
I, Li ₃ N, Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ (where M = at least one selected from the group consisting of Al, Sc, Y and La), Li _0.5-3x RE _{0.5 + x} TiO ₃
(However, RE = at least one selected from the group consisting of La, Pr, Nd and Sm). Examples of the amorphous solid electrolyte include 4.9LiI-34.1Li ₂ O-6.
_{1B 2 O 5, 33.3Li 2 O} -66.7SiO oxide glass or 0.45LiI-0.37Li ₂ such as _{2 S-0.26B 2 S 3,} 0.30LiI
-0.42Li ₂ S-0.28SiS ₂ sulfide glass etc. and the like. At least one or more of these can be used.

[0067]

EXAMPLES The method of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. [High-temperature cycle characteristics test] High-temperature cycle characteristics were as follows: charge / discharge current density 1 mA / cm ² , voltage range from 4.2 V to 3.0
It was evaluated by a charge / discharge cycle test in which constant current charge / discharge was performed between V. The capacity retention rate was calculated by the following equation.

Capacity maintenance rate (%) = [(capacity at 100 cycles)
/ (Maximum capacity in 1-100 cycles)] &times; 100 Example 1 (1) Spinel crystal structure in which Mn site is substituted by Al
Lithium manganese composite oxide (LiMn)_1.85A
l_0.12Li_0.03O_Four) Production of lithium hydroxide monohydrate (LiOH-H_TwoO), trioxide
Dimanganese (Mn_TwoO_Three ), Boehmite (AlOOH)
With the respective molar ratios of Li, Mn, and Al (Li: Mn: A
l) is 1.03: 1.85: 0.12.
Weighed, mixed well and fired at 880 ° C. for 24 hours. So
Powder XRD results were compared with JCPDS card 35-0782
As a result, lithium manganese composite with spinel crystal structure
It was confirmed to be an oxide.

(2) Li _1.05 Mn lithium-manganese composite oxide having a layered structure in which Mn sites are substituted by Cr
Production of _0.9 Cr _0.1 O ₂ 34.4 g of manganese (II) nitrate hexahydrate and 5.3 g of chromium (III) nitrate nonahydrate were dissolved in 350 g of water, and air was blown into the mixture at room temperature while stirring. After an aqueous solution containing 11.8 g of lithium hydroxide and 2.45 g of hydrogen peroxide was dropped into the solution, the solution was kept at 80 ° C. for 3 hours, and then cooled. The liquid containing the generated precipitate was centrifugally filtered and washed, and the obtained cake was dried at 60 ° C. in air for 3 hours, and calcined at 800 ° C. in air for 24 hours. 1.18 g of the powder thus obtained and 0.66 g of lithium hydroxide monohydrate were weighed (Li: Mn: Cr = 1.05: 0.
9: 0.1), mix well, and add 1
It was baked for 0 hours. XRD for the powder obtained after firing
The result of the measurement is described in J. Electrochem. Soc.
Vol. 145 (1998) L45, it was confirmed that it was a layered lithium manganese composite oxide belonging to a monoclinic system.

(3) Preparation of Positive Electrode Material and Positive Electrode As the positive electrode active material, the lithium manganese composite oxide having a spinel crystal structure produced in the above (1) and the above (2)
A lithium manganese composite oxide having a layered structure manufactured by the above method was mixed at a weight ratio of 3: 1, acetylene black was used as a conductive agent, and polytetrafluoroethylene resin was used as a binder. The active material: the conductive agent: the binder was mixed at a ratio of 75: 20: 5 to prepare a positive electrode material. Next, the positive electrode mixture was formed into a sheet to obtain a positive electrode.

(4) Manufacture of negative electrode Graphite and polyvinylidene fluoride (PVd) as a binder
F) was used at a ratio of 90:10 by weight, and was pasted with N-methylpyrrolidone as a solvent.
μm copper foil on one side, dry and evaporate the solvent,
A negative electrode was prepared by performing a press treatment at a pressure of 0.5 t / cm ² , and the obtained coated negative electrode was punched into a diameter of 12 mmφ.

(5) Preparation of Battery A battery was prepared using the above positive electrode and negative electrode. That is, a porous polypropylene film was placed as a separator on the positive electrode, and the negative electrode (a lithium foil having a diameter of 12 mm and a thickness of 0.5 mm) was pressed onto a sealing can fitted with a polypropylene gasket. 1 mol / l Li as non-aqueous electrolyte
A mixed solution of ethylene carbonate and diethyl carbonate in which PF ₆ is dissolved (50 vol%: 50 vol)
%) Was added on the separator and the negative electrode.
Then, seal the battery and recharge the lithium secondary battery (button type)
And

Example 2 (1) Lithium manganese composite oxide (LiMnO ₂ ) having a layered structure in which the Mn site is not substituted by another element
Production of lithium hydroxide monohydrate (LiOH · H ₂ O) and manganese oxyhydroxide (MnOOH) in such amounts that the molar ratio of Li and Mn (Li: Mn) becomes 1.05: 2.00. And baked at 900 ° C. for 10 hours under nitrogen flow. The powder XRD is transferred to a JCPDS card 35-0749.
As a result, it was found that the oxide was a layered lithium manganese composite oxide belonging to orthorhombic.

(2) Preparation of Battery A lithium manganese composite oxide (L) having a layered structure in which the Mn site obtained in (2) of Example 1 was replaced with Cr was obtained.
i _1.05 Mn _0.9 Cr _0.1 O ₂ ) in the same manner as in Example 1 except that the obtained lithium manganese composite oxide having a layered structure in which the Mn sites obtained above were not substituted with other elements was used instead of the battery. It was created.

Comparative Example 1 (1) Spinel in which Mn site is not substituted by another element
Production of lithium manganese composite oxide having crystal structure Lithium hydroxide monohydrate (LiOH.H_TwoO), trioxide
Dimanganese (Mn_TwoO_Three ) Is the molar ratio of each of Li and Mn.
(Li: Mn) in such an amount as to be 1.04: 1.96.
It was weighed, mixed well, and fired at 800 ° C. for 24 hours. Profit
Of XRD of powder obtained and JCPDS card 35-078
2 and the spinel-type lithium manganese composite oxidation
It turned out that the thing was obtained.

(2) Production of Battery Instead of lithium manganese composite oxide (LiMn _1.85 Al _0.12 Li _0.03 O ₄ ) having a spinel crystal structure in which the Mn site obtained in (1) of Example 1 was substituted by Al, instead of Al The lithium-manganese composite oxide having a spinel crystal structure in which the Mn site obtained above is not substituted with another element is used, and the Mn site obtained in (2) of Example 1 is replaced with Cr. Instead of the lithium manganese composite oxide having a structure (Li _1.05 Mn _0.9 Cr _0.1 O ₂ ),
The lithium manganese composite oxide (LiM) having a layered structure in which the Mn site obtained above is not substituted with another element
A battery was prepared in the same manner as in Example 1 except that nO ₂ ) was used.

Comparative Example 2 Only a lithium manganese composite oxide (LiMn _1.85 Al _0.12 Li _0.03 O ₄ ) having a spinel crystal structure in which the Mn site obtained in Example 1 (1) was substituted by Al was used as a positive electrode active material. (Mn obtained in (2) of Example 1)
A battery was prepared in the same manner as in Example 1 except that a lithium manganese composite oxide having a layered structure in which sites were replaced with Cr (Li _1.05 Mn _0.9 Cr _0.1 O ₂ ) was not mixed.

Comparative Example 3 Example 1 was repeated except that only the lithium manganese composite oxide having a spinel crystal structure in which the Mn site obtained in (1) of Comparative Example 1 was not substituted with another element was used as the positive electrode active material. A battery was prepared in the same manner as described above.

[0079]

[Table 1]

In Table 1, “with spinel substitution” means “lithium-manganese composite oxide having a spinel crystal structure and a part of Mn site substituted with another element”, and “without spinel substitution” means “without spinel substitution”. Mn site represents a lithium manganese composite oxide having a spinel crystal structure not substituted with another element ", and" with layered substitution "means" lithium manganese composite oxide having a layered structure in which Mn site is substituted with another element ". "No layered substitution" means "lithium manganese composite oxide having a layered structure in which Mn sites are not substituted with other elements", and "-" means that the compound is not blended.

Comparative Example 1 is a combination known in JP-A-8-7883 and the like, but Examples 1 and 2 have a remarkable effect as compared with Comparative Example 1. This is due to a synergistic effect of a combination of a lithium manganese composite oxide having a spinel crystal structure in which a part of the Mn site is substituted with another element and a lithium manganese composite oxide having a layered structure. Actually, the difference in the effect of only the presence or absence of the substitution of the Mn site by another element in the lithium manganese composite oxide having the spinel crystal structure is the same as the difference in the cycle retention ratio between Comparative Examples 2 and 3. Comparative Example 2 and Comparative Example 1 have a marked difference in the cycle maintenance ratio.

Example 3 (1) Tetragonal lithium manganese composite oxide (Li _{2 .05} Mn _1.76 Ni _0.20 O ₄ ) in which Mn sites are substituted by Ni
7.92 g of manganese oxyhydroxide, 0.93 g of nickel (II) hydroxide, 4.41 of lithium hydroxide monohydrate
g [Li: Mn: Ni = 1.05: 0.9: 0.
1], mixed and crushed, and then heated at 900 ° C under nitrogen stream for 10 minutes.
The firing was performed for a time. When the result of the XRD measurement of the obtained powder after calcination was compared with the result described in JCPDS card 38-0299, it was confirmed that the powder was a substituted tetragonal lithium manganese composite oxide.

(2) Production of Battery The lithium manganese composite oxide (L) having a layered structure in which the Mn site obtained in (2) of Example 1 was substituted with Cr was obtained.
i _1.05 Mn _0.9 Cr _0.1 O ₂ ) Instead of using the obtained tetragonal lithium manganese composite oxide (Li _{2 .05} Mn _1.76 Ni _0.20 O ₄ ) in which the Mn sites obtained above were substituted with Ni, A battery was prepared in the same manner as in Example 1.

Example 4 (1) Tetragonal lithium manganese composite oxide (Li _{2 .05} Mn _1.76 Co _0.20 O ₄ ) in which Mn site is substituted by Co
Production of 34.4 g of manganese (II) nitrate hexahydrate and 3.9 g of cobalt (II) nitrate hexahydrate were dissolved in 350 g of water, and air was blown into the solution at room temperature while stirring. An aqueous solution containing 11.1 g was added dropwise. The resulting mixture was subjected to centrifugal filtration and washing, and the obtained cake was dried at 60 ° C for 3 hours under air, and then dried at 800 ° C under air for 24 hours.
The firing was performed for a time. 1.19 Powder obtained in this way
g and 0.66 g of lithium hydroxide monohydrate were weighed (Li:
Mn: Co = 1.05: 0.9: 0.1), mixed well, and fired at 900 ° C. for 10 hours under a nitrogen stream. The result of XRD measurement of the powder obtained after firing was determined by JCPD.
When compared with the result described in S card 38-0299,
It was confirmed that it was a substituted tetragonal lithium manganese composite oxide.

(2) Production of Battery A lithium manganese composite oxide (L) having a layered structure in which the Mn site obtained in (2) of Example 1 was replaced with Cr was obtained.
i _1.05 Mn _0.9 Cr _0.1 O ₂ ) Instead of using the obtained tetragonal lithium manganese composite oxide (Li _{2 .05} Mn _1.76 Co _0.20 O ₄ ) in which the Mn sites obtained above were substituted with Co, instead of using _i.sub.1.05 Mn _0.9 Cr _0.1 O ₂ ). A battery was prepared in the same manner as in Example 1.

[0086]

[Table 2]

[0087]

According to the present invention, performance degradation at high temperatures (capacity reduction due to charge / discharge cycles and storage under high temperature conditions)
And a material for a lithium secondary battery having excellent battery characteristics at high temperatures and a lithium secondary battery can be provided.

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5H029 AJ02 AK03 AL06 AL12 AM03 AM04 AM05 AM07 DJ16 DJ17 HJ01 HJ02 HJ13 5H050 AA05 BA17 CA09 CB07 CB12 EA10 EA24 EA28 FA17 FA18 FA19 HA01 HA02 HA13

Claims (17)

[Claims] 1. A tetragonal system represented by (1) a lithium manganese composite oxide having a spinel crystal structure and a part of Mn sites substituted with another element, and (2) Li ₂ Mn ₂ O ₄ A positive electrode material for a lithium secondary battery, comprising: a compound in which a part of the Mn site of the lithium manganese composite oxide is substituted with an element other than Li and / or a lithium manganese composite oxide having a layered structure. 2. A lithium manganese composite oxide having a spinel crystal structure and a part of Mn sites substituted with another element, and (2) a lithium manganese composite oxide having a layered structure. A positive electrode material for a lithium secondary battery, comprising: 3. A tetragonal system represented by (1) a lithium manganese composite oxide having a spinel crystal structure and a part of Mn sites substituted with another element, and (2) Li ₂ Mn ₂ O _4. A positive electrode material for a lithium secondary battery, comprising a compound in which part of the Mn site of a lithium manganese composite oxide is substituted with another element other than Li. 4. Another element that substitutes for a Mn site in a lithium manganese composite oxide having a spinel crystal structure is A
1, Ti, V, Cr, Fe, Li, Co, Ni, Cu,
The positive electrode material for a lithium secondary battery according to any one of claims 1 to 3, wherein the positive electrode material is one or more other elements selected from the group consisting of Zn, Mg, Ga, and Zr. 5. Another element that substitutes for an Mn site in a lithium manganese composite oxide having a spinel crystal structure is A
The positive electrode for a lithium secondary battery according to any one of claims 1 to 3, wherein the positive electrode is one or more other elements selected from the group consisting of 1, Cr, Fe, Li, Co, Ni, Mg, and Ga. material. 6. Another element that substitutes for a Mn site in a lithium manganese composite oxide having a spinel crystal structure is A
The positive electrode material for a lithium secondary battery according to any one of claims 1 to 3, wherein the positive electrode material is one or more other elements selected from the group consisting of l, Li, and Mg. 7. The lithium-manganese composite oxide having a spinel crystal structure, wherein a weighted average valence of another element that substitutes for an Mn site is less than 3.5.
7. The positive electrode material for a lithium secondary battery according to any one of claims 6 to 6. 8. The lithium manganese composite oxide having a spinel crystal structure, wherein the substitution ratio of the Mn site by another element is 1 to 30 mol% or less of Mn. The positive electrode material for a lithium secondary battery according to the above. 9. The lithium secondary battery according to claim 1, wherein a part of the Mn site of the lithium manganese composite oxide having a layered structure is partially substituted with another element. Positive electrode material for secondary batteries. 10. The lithium manganese composite oxide having a layered structure, wherein part of the Mn site is Al, Ti, V, C
r, Fe, Li, Co, Ni, Cu, Zn, Mg, G
1 selected from the group consisting of a, Zr, Nb, Mo, and Pb
The positive electrode material for a lithium secondary battery according to claim 1, wherein the positive electrode material is substituted with the other element. 11. A part of a Mn site of a lithium manganese composite oxide having a layered structure has a weighted average valence of 3.
The positive electrode material for a lithium secondary battery according to any one of claims 1, 2, 4 to 10, wherein the positive electrode material is substituted by another element that is less than 5. 12. The other element substituting a part of the Mn site of the tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ is Al, Ti, V, Cr, Fe, Li, C
o, Ni, Cu, Zn, Mg, Ga, Zr, Nb, M
12. The positive electrode material for a lithium secondary battery according to claim 1, wherein the positive electrode material is one or more other elements selected from the group consisting of o and Pb. 13. The tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ , wherein the weight-average valence of another element substituting the Mn site is less than 3.5. Item 13. The positive electrode material for a lithium secondary battery according to any one of Items 1, 3 to 12. 14. (1) Mn having a spinel crystal structure,
A lithium manganese composite oxide in which a part of the site is substituted by another element, and (2) a part of the Mn site of the tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ is Li
14. The compound according to claim 1, wherein the weight ratio of the compound substituted with another element and / or the lithium manganese composite oxide having a layered structure is 10:90 to 98: 2. The positive electrode material for a lithium secondary battery according to any one of the above. 15. (1) Mn having a spinel crystal structure;
A lithium manganese composite oxide in which a part of the site is substituted by another element, and (2) a part of the Mn site of the tetragonal lithium manganese composite oxide represented by Li ₂ Mn ₂ O ₄ is Li
15. The compound according to claim 1, wherein the weight ratio of the compound and / or the lithium manganese composite oxide having a layered structure substituted with other elements is 50:50 to 95: 5. The positive electrode material for a lithium secondary battery according to any one of the above. 16. A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to claim 1 as an active material. 17. A positive electrode for a lithium secondary battery containing the positive electrode material for a lithium secondary battery according to claim 1 as an active material, a negative electrode containing a carbon material as an active material, and an electrolyte layer. A rechargeable lithium battery.