JP2001243954A - Positive electrode material for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve high temperature characteristics of a lithium secondary battery using lithium manganese oxide of a spinel structure as a main active material. SOLUTION: The lithium secondary battery comprises a positive electrode material containing (A) a lithium manganese oxide having a spinel structure, and (B) a lanthanide transition metal complex oxide which is formed by a part of lanthanide element substituted by lithium and has a defective perovskite type structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode material for a lithium secondary battery, and more particularly to a positive electrode containing the positive electrode material and a lithium secondary battery having the positive electrode.

[0002]

2. Description of the Related Art In place of lithium metal as a negative electrode active material, the use of a carbon material capable of occluding and releasing lithium ions has greatly improved safety, and the lithium secondary battery has entered the practical stage. . On the other hand, as a positive electrode active material of a lithium secondary battery, LiMn ₂ O ₄ , which is a composite oxide of manganese and lithium and has a spinel structure, has been proposed and has been actively studied. It has the advantages of high voltage and high energy density, more reserves than Cobalt and Nickel, low cost, and high safety in overcharging. The charge / discharge cycle life at room temperature, which has been a problem, has been improved to a practical stage level. However, manganese-based lithium secondary batteries have a problem that they are inferior in high-temperature stability, and thus have not reached a practical level for demands used in high-temperature environments.

Conventionally, various studies have been made with the aim of improving the cycle characteristics under a high temperature environment, and reports have been made. For example, J. Electrochem.soc., Vol. 145, No. 8 (1998) 2726-2732
In this article, a part of Mn is replaced with other elements such as Ga and Cr, Electrochemical Society Proceedings Volume 97
-18.494 shows that those in which a part of Mn is replaced with Co or a part of oxygen is replaced with F to improve the stability of the crystal structure have an effect of improving the high-temperature cycle characteristics. However, these are the results when metallic lithium is used as the negative electrode, and in fact, a sufficient effect has not been obtained in combination with a practical negative electrode material such as a carbon material.

[0004] Further, it has been pointed out that manganese-based lithium secondary batteries are liable to elute manganese in a high-temperature environment as a problem of high-temperature cycle deterioration. Investigations, such as adding a substance having an effect of suppressing Mn elution, are also being made. However, the cycle characteristics in a high-temperature environment have not yet reached a practical level with these conventional techniques.

In a lithium secondary battery using lithium manganese oxide having a spinel structure (general formula LiMn ₂ O ₄ ) as a positive electrode active material, lithium cobalt oxide (general formula LiCoO ₂ ) and lithium nickel oxide (LiN
Since the charge / discharge capacity is lower than in the case of using iO ₂ ), deep charge / discharge is repeated in an attempt to extract the capacity as much as possible. In particular, lithium manganese oxide, from which most of the lithium at the charging end has been released, tends to cause an undesirable reaction with the lithium ion conductivity or the electrolytic solution, so that it may be transformed into a structure that cannot function as an active material,
It is thought to cause manganese elution.
In particular, it is considered that the degradation reaction is accelerated in a high temperature environment. In order to suppress such deterioration factors, it was considered necessary to simultaneously impart ionic conductivity to the active material and reduce the catalytic activity.

Conventionally, a hand for assisting lithium ion conductivity
As the step, in JP-A-7-235291,
A solid lithium ion conductor in the pole, specifically Li_x
Co_{1 -y}Ni_yO_Two(Where 0 <x <1, 0 ≦ y ≦ 1)
There is a proposal to make it. However, this means alone
I can't overcome the problem drastically, especially L
i_xCo_1-yNi_yO_TwoIf you use
The problem of safety during charging remains.

[0007]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a lithium secondary battery using a lithium manganese oxide having a spinel structure as a main active material, the lithium secondary battery having improved high-temperature characteristics. An object is to provide a positive electrode material for a secondary battery, a positive electrode for a lithium secondary battery, and a lithium secondary battery.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a compound having a high lithium ion conductivity without a risk of impairing the safety during overcharge has a defect perovskite. The inventor has found that the incorporation of a lanthanoid transition metal composite oxide having a structure improves high-temperature characteristics, particularly high-temperature cycle characteristics, and has completed the present invention. Lithium-substituted lanthanide transition metal composite oxides with defective perovskite structure have high lithium ion conductivity and safety issues during overcharge such as lithium cobalt oxide and lithium nickel oxide. It is guessed that the absence of the above and the fact that it also has the properties as a dielectric may be involved in the reason for solving the above problem.

That is, the gist of the present invention is to provide (A) a lithium manganese oxide having a spinel structure, and (B) a lanthanide-transition metal composite oxide having a defective perovskite structure in which a part of the lanthanoid element is substituted by lithium. And a positive electrode material for a lithium secondary battery. As a preferable gist of the present invention, a lanthanoid transition metal composite oxide has the following general formula:

[0010]

_{Embedded image} Ln _{2 / 3-x} Li _3x □ _{1 / 3-2x} MO ₃ (In the above formula, 0 <3x <0.5, Ln is La, Ce, Pr, N
d, Pm, Sm, Eu, Gd, Tb, Dy, Ho, E
represents one or more lanthanoid elements selected from r, Tm, Yb, and Lu; M represents one or more transition metal elements selected from Ti, Nb, and Ta; and □ represents a defect site. The above positive electrode material for a lithium secondary battery represented by); the above positive electrode material for a lithium secondary battery in which a part of the Mn site of the lithium manganese oxide is substituted with another element; the Mn site of the lithium manganese oxide Are replaced by Al, Ti, V, Cr, Fe, Co, Ni, C
the above-mentioned positive electrode material for a lithium secondary battery selected from the group consisting of u, Zn, Mg, Ga and Zr; the above-mentioned lithium secondary battery having a lithium manganese oxide having a BET specific surface area of 0.3 to 1.5 m ² / g. Positive electrode material for a secondary battery; the above lithium secondary wherein the content of (A) lithium manganese oxide and (B) defective perovskite-type lithium-substituted lanthanoid transition metal composite oxide is 2: 1 to 100: 1 by weight. Positive electrode materials for batteries.

Another aspect of the present invention is a positive electrode including the above-described positive electrode material for a lithium secondary battery. In still another embodiment, the above-described positive electrode for a lithium secondary battery, a negative electrode, and an electrolyte And a preferable gist thereof is the above-described lithium secondary battery in which the active material of the negative electrode is a carbon material.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The lithium manganese oxide having a spinel structure used in the present invention is LiMn ₂
Although represented by O _4, it may have a small amount of oxygen deficiency and nonstoichiometry. The lithium manganese oxide used in the present invention is preferably one in which a part of the Mn site is substituted by another element. Since a part of the Mn site is substituted with another element, the stability of the crystal structure can be improved. By combining this with a lithium-substituted lanthanoid transition metal composite oxide of a defective perovskite type, higher temperatures can be achieved. Cycle characteristics can be improved.

At this time, the other elements that substitute for the Mn site (hereinafter, referred to as substitution elements) are usually Al, Ti,
V, Cr, Fe, Co, Ni, Cu, Zn, Mg, G
a, Zr and the like, preferably Al, Cr, Fe,
Co, Ni, Mg, Ga, and more preferably A
l. The Mn site may be substituted with two or more other elements.

[0014] Due to the relationship with the preparation, a part of the Mn site may be substituted by Li, and a part of the Mn site may be substituted by Li together with the other elements. The lithium manganese oxide in the present invention also includes these. The substitution ratio by the substitution element is usually Mn
2.5 mol% or more of Mn, preferably 5 mol% or more of Mn, usually 30 mol% or less of Mn, preferably 2 mol% of Mn.
0 mol% or less. 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, a part of the oxygen site may be substituted with sulfur or a halogen element. Furthermore, there may be some non-stoichiometric oxygen content. The lithium manganese oxide can be produced by various conventionally known methods. For example, after mixing the starting materials containing lithium and manganese,
It can be produced by firing and cooling in the presence of oxygen. Further, the lithium manganese oxide in which the Mn site is substituted by another element can be produced by, for example, mixing a starting material containing lithium, manganese, and the substituted element, followed by firing and cooling in the presence of oxygen.

In the above production method, a lithium manganese oxide in which Mn sites are not substituted is produced without using a starting material containing a substitution element, and the lithium manganese oxide is replaced with a starting material containing a substitution metal element. Aqueous solution,
After the reaction in the molten salt or steam, the Mn site may be replaced with 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, preferably Li_TwoCO_Three, LiOH ・ H
_TwoO, and dicarboxylic acid Li. As a starting material
The manganese compound used is Mn_TwoO_Three, MnO
_TwoSuch as manganese oxide, MnCO_Three, Mn (NO_Three)_Two ,
MnSO_Four, Manganese acetate, manganese dicarboxylate,
Manganese salts such as manganese enate and fatty acid manganese, oki
And hydroxides and halides. Mn_TwoO_ThreeWhen
And MnCO_ThreeAnd MnO_TwoHeat-treated compounds such as
You may use what was manufactured. Preferably Mn_TwoO _Three, Mn
O_Two, MnCO_Three, Manganese dicarboxylate, oxyhydroxide
Things.

Examples of the compound of the substitution element include oxides, hydroxides, nitrates, carbonates, dicarboxylates, fatty acid salts, ammonium salts, ketone salts, and oxyhydroxides. Oxides, carbonates, dicarboxylates. 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.

As a preferable method of sintering and cooling lithium manganese oxide for stabilizing the crystal structure, for example, after calcination, main calcination is performed at about 600 to 900 ° C. in an oxygen atmosphere, and then 500 ° C. 10 ° C /
min or less, or after calcining,
A method of performing baking at a temperature of about 00 ° C. in an air or oxygen atmosphere and then annealing at a temperature of about 400 ° C. in an oxygen atmosphere can be used. Conditions for firing and cooling are described in JP-A-9-306490 and JP-A-9-306.
No. 493, JP-A-9-259880 and the like.

The lithium manganese oxide used in the present invention has a BET specific surface area of preferably 0.3 m ² / g or more, more preferably 0.5 m ² / g or more, and preferably 1.5 m ² / g. Or less, more preferably 1.0 m ² / g
It is as follows. If the specific BET surface area is too small, the rate characteristics and capacity will be reduced. If it is too large, undesired reactions with the electrolyte and the like will be caused, and the cycle characteristics will be reduced. The lanthanoid transition metal composite oxide in the present invention has a defective perovskite structure, and it is essential that a part of the lanthanoid element is replaced with lithium. The lanthanoid transition metal composite oxide is preferably represented by the following general formula.

[0021]

_{Embedded image} Ln _{2 / 3-x} Li _3x □ _{1 / 3-2x} MO ₃ (where 0 <3x <0.5, Ln is La, Ce, Pr, N
d, Pm, Sm, Eu, Gd, Tb, Dy, Ho, E
represents one or more lanthanoid elements selected from r, Tm, Yb, and Lu; M represents one or more transition metal elements selected from Ti, Nb, and Ta; and □ represents a defect site. ) Ln in the above formula is preferably La,
Ce, Pr, Nd, more preferably La, Nd.
Further, M in the above formula is preferably Ti, Nb,
More preferably, it is Ti. In the above formula, the range of 3x is preferably 0.25 ≦ 3x ≦ 0.4.

In the lanthanoid transition metal composite oxide used in the present invention, part of the transition metal element may be replaced by another element, the oxygen content may be non-stoichiometric, It may be replaced by more than one kind of other element. Further, a part of the oxygen site may be substituted with sulfur or a halogen element. Further, the lanthanoid transition metal composite oxide need not necessarily be a single phase.

The average particle diameter and the specific surface area of the lanthanoid transition metal composite oxide do not matter as long as they do not largely deviate from the average particle diameter and the specific surface area of the active material usually used for the positive electrode. In order to improve the efficiency, the average particle size is preferably smaller than the average particle size of the lithium manganese oxide, and the specific surface area is preferably larger than the specific surface area of the lithium manganese oxide.

The lanthanoid transition metal composite oxide can be produced by various conventionally known methods. For example,
It can be produced by mixing starting materials containing lithium, a lanthanoid element Ln, and a transition metal element M, followed by firing and cooling in the presence of oxygen. The lanthanoid transition metal composite oxide in which the transition metal site (B site in the perovskite structure) is substituted with another element is, for example, lithium, a lanthanoid element Ln, a transition metal element M,
It can be produced by mixing the starting materials containing the substitution element, followed by firing and cooling in the presence of oxygen.

In the above-mentioned production method, a lanthanoid transition metal composite oxide in which a transition metal site is not substituted is produced without using a starting material containing a substitution element, and the lanthanoid transition metal composite oxide is replaced with a substitution metal element. After reacting in the aqueous solution, molten salt or steam of the starting material contained, the transition metal site is replaced by performing heat treatment again in order to diffuse the substitution element into the lanthanoid transition metal composite oxide particles as necessary. It may be replaced by an element.

As the lithium compound used as a starting material, Li ₂ CO ₃ , LiNO ₃ , LiOH, LiO
H.H ₂ O, LiCl, LiI, CH ₃ COOLi, Li
₂ O, Li dicarboxylic acid, Li fatty acid, alkyl lithium and the like, preferably Li ₂ CO ₃ , LiOH · H
₂ O and Li dicarboxylate. The lanthanoid compounds used as starting materials include Ln ₂ O ₃ and Ln ₂ O ₃ .
oxides such as nO ₂ , Ln ₂ (CO ₃ ) ₃ and its hydrates, L
n (NO ₃ ) ₃ and its hydrate, Ln ₂ (SO ₄ ) ₃ and its hydrate, Ln (CH ₃ COO) ₃ and its hydrate, dicarboxylic acid Ln and its hydrate, fatty acid Ln, etc. Salts, hydroxides, halides, sulfides, oxysulfides and the like. As the oxide, an oxide obtained by heat-treating a compound such as a carbonate or a sulfide may be used. Preferred are oxides, carbonates, and dicarboxylates such as oxalic acid Ln.

The transition metal compounds used as starting materials include oxides such as MO, M ₂ O ₃ , MO ₂ , M ₂ O ₅ ,
Examples include nitrates and hydrates thereof, sulfates and hydrates thereof, acetates, dicarboxylates and hydrates thereof, transition metal salts such as fatty acid salts, hydroxides, halides and sulfides. As the oxide, an oxide obtained by heat-treating a compound such as a carbonate or a sulfide may be used. Preferably, dicarboxylates such as oxides and oxalates are used.

Examples of the compound of the substitution element include oxides, hydroxides, nitrates, carbonates, dicarboxylates, fatty acid salts, ammonium salts, ketone salts, and oxyhydroxides. Oxides, carbonates, dicarboxylates. 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.

As a method of calcining the lanthanoid transition metal composite oxide, for example, after calcining in the air at a temperature of about 500 to 1000 ° C., perform calcination in the air at a temperature of about 1000 to 1200 ° C. The method of cooling to room temperature can be mentioned. For firing conditions, refer to Solid
State Ionics 86-88 (1996)
257-260 or Solid State Commu
nations, Vol. 86, No. 10, p
p. 689-693, 1993. Etc. are described in detail.

The amount ratio of lithium manganese oxide and lithium-substituted lanthanoid transition metal composite oxide in the positive electrode is as follows:
By weight ratio, lithium manganese oxide: lanthanoid transition metal composite oxide = usually 2: 1 to 100: 1, preferably 3: 1 to 50: 1, more preferably 5: 1 to 20: 1,
Most preferably, it is 8: 1 to 10: 1. When the weight ratio of the lanthanoid transition metal composite oxide exceeds the specified range and increases, the discharge capacity decreases, and when the weight ratio decreases, the effect of improving the cycle characteristics may be difficult to obtain.

The form of the composite of the lithium manganese oxide and the lithium-substituted lanthanoid transition metal composite oxide is not particularly limited, and may be a physical mixture, and a film of one particle is formed on the surface of one particle. You may let it. The positive electrode includes a positive electrode current collector and a positive electrode layer containing a positive electrode active material. The positive electrode layer is composed of a lithium manganese oxide, a lanthanoid transition metal composite oxide, a binder (binder) described below, and a conductive agent. Can be manufactured.

Incidentally, an active material capable of occluding and releasing lithium ions, such as a layered lithium manganese oxide, a lithium iron oxide, and LiFePO ₄ , may be further combined. Examples of the conductive agent for the positive electrode include, but are not limited to, graphite fine particles, carbon black such as acetylene black, and amorphous carbon fine particles such as needle coke. In addition, aluminum, stainless steel, nickel-plated steel, or the like is used for the positive electrode current collector.

In the present invention, when a positive electrode containing the above-described lithium manganese oxide is used, the positive electrode is stabilized in an electrolytic solution, particularly under a high temperature environment, and the cycle characteristics and storage characteristics at a high temperature are excellent. A secondary battery can be provided. Therefore, in the present invention, a lithium secondary battery is manufactured by combining the above positive electrode containing lithium manganese oxide, various negative electrodes, a separator, and an electrolytic solution containing a lithium salt.

The active material of the negative electrode used in combination with the positive electrode found in the present invention includes carbon materials, SnO, S
nO ₂ , Sn _1-x M _x O (M = Hg, P, B, Si, Ge
Or Sb, provided that 0 ≦ x <1), Sn ₃ O ₂ (OH)
₂ , Sn _3-x M _x O ₂ (OH) ₂ (M = Mg, P, B, S
i, Ge, Sb or Mn, where 0 ≦ x <3), LiS
1 selected from iO ₂ , SiO _2, LiSnO _2, etc.
Examples include, but are not limited to, species or combinations of two or more.

The carbon material is not particularly limited. Graphite, coal-based coke, petroleum-based coke, coal-based pitch carbide, petroleum-based pitch carbide, or carbide obtained by oxidizing these pitches, needle coke, pitch coke And carbon materials such as phenolic resin and crystalline cellulose, and carbon materials partially graphitized thereof, furnace black, acetylene black, pitch-based carbon fiber, and the like. A mixture of two or more of these can also be used preferably.

As the negative electrode, one obtained by applying a slurry of the active material of the negative electrode and a binder (binder) with a solvent and then drying the slurry can be used. Negative and positive electrode active material binders
Examples of the (binder) include polyvinylidene fluoride, polytetrafluoroethylene, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), and fluororubber. But not limited thereto.

As a solvent for forming a slurry, an organic solvent that dissolves or disperses a binder is usually used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, N-N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, and the like can be mentioned, but are not limited thereto. . In some cases, the active material is slurried with latex such as SBR by adding a dispersant, a thickener, and the like to water.

For the current collector of the negative electrode, copper, nickel, stainless steel, nickel-plated steel or the like is used. When a separator is used, a microporous polymer film is used, and a material made of a polyolefin polymer such as nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polypropylene, polyethylene, and polybutene is used. Can be 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 high-temperature shape retention, 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 large, the fluidity is too low and the pores of the separator may not be closed when heated. Further, as the ion conductor in the lithium secondary battery of the present invention, for example, a known organic electrolyte, a polymer solid electrolyte, a gel electrolyte, an inorganic solid electrolyte, and the like can be used.
Among them, an organic electrolyte is preferable. The organic electrolyte is composed of an organic solvent and a solute.

The organic solvent is not particularly restricted but includes, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines and esters. ,
Amides, phosphate compounds and the like can be used. When these representatives are listed, dimethyl carbonate, diethyl carbonate, 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,
-Methyl-1,3-dioxolane, diethyl ether,
A single solvent or a mixture of two or more solvents such as sulfolane, methylsulfolane, acetonitrile, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethylsulfoxide, trimethyl phosphate, triethyl phosphate, etc. it can. When a plurality of these compounds are used, the battery performance can be improved by adding a small amount of these compounds to the electrolyte as an additive. Further, an additive such as CO ₂ , N ₂ O, CO, SO _2, or a polysulfide S _x ²⁻ which can form an excellent film capable of efficiently charging and discharging lithium ions on the surface of the negative electrode is added at an arbitrary ratio. It may be added to an organic solvent.

The solute to be dissolved in this solvent is not particularly limited, but any of the conventionally known ones can be used, and LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiB
F ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl, LiBr, CH ₃
SO ₃ Li, CF ₃ SO ₃ Li and the like can be mentioned, and at least one or more of these can be used. In the case of using a polymer solid electrolyte, a known polymer can be used as the polymer, and it is particularly preferable to use a polymer having high ionic conductivity with respect to lithium ions.For example, polyethylene oxide, polypropylene oxide, Polyethyleneimine or the like is 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,
Use of known crystalline and amorphous solid electrolytes for inorganic substances
Can be. Examples of the crystalline solid electrolyte include Li
I, Li_ThreeN, Li_{1 + x}M_xTi_2-x(PO_Four)_Three(M = A
l, Sc, Y, La), Li_{0.5- 3x}RE_{0.5 + x}TiO
_Three(RE = La, Pr, Nd, Sm) and the like.
As a crystalline solid electrolyte, for example, 4.9 LiI-34.1 L
i_TwoO-61B_TwoO_Five, 33.3Li_TwoO-66.7SiO_Two Etc. acid
Oxide glass and 0.45LiI-0.37Li_TwoS-0.26B_TwoS_Three,
0.30LiI-0.42Li_TwoS-0.28SiS_TwoEtc. sulfide gala
And the like. At least one or more of these
Can be used. Hereinafter, the present invention will be described by way of examples.
The method will be described more specifically.

[0043]

EXAMPLES Example 1 (A) Li _1.04 Mn _1.85 as lithium manganese oxide
Al _0.11 O ₄ , a lithium manganese oxide having a cubic spinel structure in which a part of the Mn site is substituted by Li and Al, is used, and (B) has a defective perovskite structure, Lanthanum titanium composite oxide (Li _0.44 La _0.52 □ _0.04 T
iO ₃ ) by weight ratio of (A) lithium manganese oxide:
(B) The lanthanum-titanium composite oxide was mixed at a ratio of 9: 1 to obtain a positive electrode material (a lithium manganese oxide was an active material in the positive electrode material). The specific surface area of the lithium manganese oxide used here was 0.9 m ² / g. Using the obtained cathode material, a cathode was manufactured as described below.
Further, a lithium secondary battery was manufactured using the obtained positive electrode as described later.

Comparative Example 1 The same lithium manganese oxide as described in Example 1 was used as a positive electrode material (a lanthanoid transition metal composite oxide composite oxide was not mixed) to produce a positive electrode as described later. did. Further, a lithium secondary battery was manufactured using the obtained positive electrode as described later. Test Examples (Battery Evaluation) The batteries of Examples and Comparative Examples of the present invention were evaluated by the following methods. 1. Preparation of positive electrode and confirmation of capacity Positive electrode material weighed at 75% by weight, acetylene black at 20% by weight, and polytetrafluoroethylene powder at 5% by weight were thoroughly mixed in a mortar, made into a thin sheet, and punched into a 12 mmφ punch. Punched out. At this time, the total weight is 1
Adjusted to 8 mg. This was pressed against an Al expanded metal to form a positive electrode. A battery cell was assembled using this positive electrode as a test electrode, and Li metal as a counter electrode, and 0.5 mA / c
m ² constant current charging, that is, a reaction for releasing lithium ions from the positive electrode was performed at an upper limit of 4.35 V, and then 0.5 mA
The initial charge capacity per unit weight of the positive electrode active material when the constant current discharge of / cm ² , that is, the test for inserting lithium ions into the positive electrode at a lower limit of 3.2 V, was Qs (C) mAh / g, and the initial discharge capacity was Qs (D) mAh / g.

2. Preparation of Negative Electrode and Confirmation of Capacity As a negative electrode active material, graphite powder (d) having an average particle size of about 8 to 10 μm was used.
002 = 3.35 °) and polyvinylidene fluoride (hereinafter abbreviated as PVdF) as a binder in a weight ratio of 92.0%.
The mixture was weighed at a ratio of 5: 7.5 and mixed in an N-methylpyrrolidone (hereinafter abbreviated as NMP) solution to prepare a negative electrode mixture slurry. This slurry was applied to one side of a copper foil having a thickness of 20 μm, dried, and the solvent was evaporated.
And pressed at 0.5 ton / cm ² to obtain a negative electrode. A battery cell was assembled using the negative electrode as a test electrode and Li metal as a counter electrode, and L was applied to the negative electrode at a constant current of 0.2 mA / cm ^2.
The initial storage capacity per unit weight of the negative electrode active material when the test for storing i ions was performed at the lower limit of 0 V was defined as Qf mAh / g.

3. Assembling of Battery Cell Using the coin-shaped cell having the structure shown in FIG. 2, battery performance was evaluated. That is, the positive electrode 2 is placed on the positive electrode can 1, a 25 μm porous polyethylene film is placed thereon as the separator 3, pressed with a polypropylene gasket 4, the negative electrode 5 is placed, and the spacer 6 for thickness adjustment is placed. After that, as a non-aqueous electrolyte solution, ethylene carbonate (EC) in which 1 mol / l of lithium hexafluorophosphate (LiPF ₆ ) was dissolved and diethyl carbonate (DE)
After using a mixed solvent of volume ratio 3: 7 of C), which was added to the inside of the battery and sufficiently permeated, the negative electrode can was placed and the battery was sealed. At this time, the balance between the weight of the positive electrode active material and the weight of the negative electrode active material is almost the same.

[0047]

## EQU1 ## Positive electrode active material amount [g] / negative electrode active material amount [g] =
(Qf / 1.2) / Qs (C) was set. 4. Test method In order to compare the high temperature characteristics of the battery obtained in this way, the 1 hour rate current value of the battery, that is, 1C, was measured.

[0048]

## EQU2 ## The following test was performed by setting 1 C [mA] = Qs (D) × amount of positive electrode active material [g]. First, a constant current of 0.1 at room temperature.
2C charge / discharge 2 cycles and constant current 1C charge / discharge 1 cycle are performed, and then constant current 0.2C charge / discharge 1
Cycle and then 100 cycles of constant current 1C charge / discharge test. Note that the upper limit of charge is 4.2V and the lower limit voltage is 3.
0 V was applied. At this time, the 1st cycle discharge capacity Qh (1) of the 1C charge / discharge 100 cycle test section at 50 ° C.
The ratio of the discharge capacity Qh (100) at the 00th cycle is defined as the high-temperature cycle capacity maintenance rate P,

[0049]

P [%] = {Qh (100) / Qh (1)} × 100, and the high-temperature characteristics of the batteries were compared using this value. Table 1 shows the 100-cycle capacity retention rate in the 50 ° C. cycle test obtained in Examples and Comparative Examples of the present invention, and FIG. 1 shows a cycle-discharge capacity correlation diagram.

[0050]

[Table 1]

It can be seen that the examples according to the present invention have improved high-temperature cycle characteristics.

[0052]

According to the present invention, in a positive electrode for a lithium secondary battery using a spinel-type lithium manganese oxide as a main positive electrode active material, the lithium manganese oxide functions stably as a positive electrode active material to improve high-temperature cycle characteristics. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a cycle-discharge capacity retention rate correlation diagram.

FIG. 2 is a longitudinal sectional view of a coin-type battery used in a test of a method of manufacturing an active material for a non-aqueous electrolyte secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Positive electrode 3 Separator 4 Gasket 5 Negative electrode (counter electrode) 6 Spacer 7 Negative electrode can

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 4G048 AA04 AA05 AB01 AB05 AC06 AD04 AD08 AE05 5H029 AJ02 AK03 AL02 AL03 AL06 AM00 AM03 AM04 AM05 AM07 AM12 AM16 BJ03 5H050 AA05 BA17 BA18 CA07 CA09 CB02 CB03 CB07 HA01 HA07

Claims (9)

[Claims] (1) a lithium manganese oxide having a spinel structure; and (B) a lanthanoid transition metal composite oxide having a defective perovskite structure in which a part of a lanthanoid element is substituted by lithium. Characteristic cathode material for lithium secondary batteries. 2. A lanthanoid transition metal composite oxide represented by the following general formula: Ln _{2 / 3-x} Li _3x □ _{1 / 3-2x} MO ₃ (where 0 <3x <0.5, Ln is La, Ce, Pr, N
d, Pm, Sm, Eu, Gd, Tb, Dy, Ho, E
represents one or more lanthanoid elements selected from r, Tm, Yb, and Lu; M represents one or more transition metal elements selected from Ti, Nb, and Ta; and □ represents a defect site. The positive electrode material for a lithium secondary battery according to claim 1, wherein: 3. The positive electrode material for a lithium secondary battery according to claim 1, wherein a part of the Mn site of the lithium manganese oxide is substituted with another element. 4. The other element substituting the Mn site of the lithium manganese oxide is Al, Ti, V, Cr, Fe, C
The positive electrode material for a lithium secondary battery according to any one of claims 1 to 3, wherein the positive electrode material is selected from the group consisting of o, Ni, Cu, Zn, Mg, Ga, and Zr. 5. The positive electrode material for a lithium secondary battery according to claim 1, wherein the lithium manganese oxide has a BET specific surface area of 0.3 to 1.5 m ² / g. (A) lithium manganese oxide and (B)
The content of the defective perovskite-type lithium-substituted lanthanoid transition metal composite oxide is from 2: 1 to 100: 1 by weight.
The positive electrode material for a lithium secondary battery according to claim 1, wherein: 7. A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to claim 1. 8. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 7, a negative electrode and an electrolyte. 9. The lithium secondary battery according to claim 8, wherein the active material of the negative electrode is a carbon material.