JP2001167764A - Positive electrode material for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an initial capacity, a high temperature cycle characteristic and a rate characteristic at a good balance, in a positive electrode for a lithium secondary battery containing spinel lithium-manganese oxides as an active material. SOLUTION: The positive electrode material for a lithium secondary battery contains, as an active material, spinel lithium-manganese oxides and lithium- copper oxides in which a portion of Li sites is substituted with other elements.

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 high voltage and high energy density, and also has the advantage of a large reserve and low cost compared to cobalt and nickel. However, a lithium secondary battery using a lithium manganese oxide as an active material has a problem that the high-temperature cycle characteristics are inferior. Conventionally, various studies for improving cycle characteristics under a high-temperature environment have been made and reported. For example, J. Electrochem.soc., Vol. 145, No. 8 (1998) 2728-2732
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 part of Mn is replaced by Co or part of oxygen is replaced by 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 a sufficient effect has not been obtained in combination with a substantial negative electrode material such as a carbon material. In fact, it is not enough to improve the initial capacity, rate characteristics and high-temperature cycle characteristics in a well-balanced manner.

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. For example, the surface of a positive electrode active material is treated, 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. Further, when trying to improve the high-temperature cycle characteristics by the above-described conventional technology, there is a concern that other battery characteristics, such as initial capacity and rate characteristics, may be reduced.

[0004]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a positive electrode for a lithium secondary battery containing a spinel-type lithium manganese oxide as an active material with a good balance between initial capacity, high-temperature cycle characteristics and rate characteristics. It is to improve.

[0005]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result of the above-mentioned prior art, high-temperature cycle characteristics have not been achieved to a practical level. We thought that it might be due to a deterioration factor acting. In a practical lithium secondary battery, the formation of a surface film on the negative electrode surface and lithium ion trapping in the negative electrode active material structure occur during the initial charge.
Lithium ions consumed by the film formation and the trap cannot return to the positive electrode. as a result,
The Li site in the positive electrode active material structure always has a vacant portion, and it is possible that the crystal structure is destabilized.

Based on the above presumption, in order to alleviate and suppress the deterioration effect and to improve the high-temperature cycle characteristics, at least A.I. It was considered that the indispensable condition is that a compound that plays a role of complementing the irreversible capacity of the negative electrode is included in the positive electrode. To further improve the performance balance without causing a trade-off in performance balance in consideration of other battery characteristics such as initial capacity and rate characteristics, B. It was also considered necessary to modify the compound that performs the function described in A.

That is, the gist of the present invention is to provide a positive electrode material for a lithium secondary battery, which comprises, as an active material, a spinel-type lithium manganese oxide and a lithium copper oxide in which a part of a Li site is substituted by another element. Exists. As a preferred embodiment of the present invention, the above-mentioned positive electrode material for a lithium secondary battery, in which the other element that partially replaces the Li site is selected from the group of alkali metal elements other than Li;

[0008]

[Formula 2] Li _2-x M _x CuO ₂ (0 <x ≦ 1.0)

The above positive electrode material for a lithium secondary battery, which is a compound represented by (M represents another element); wherein the Mn site of a spinel type lithium manganese oxide is partially substituted with another element. The positive electrode material for a lithium secondary battery of the above; the positive electrode material for a lithium secondary battery described above, wherein the crystal system of the spinel-type lithium manganese oxide is cubic;
The above positive electrode material for a lithium secondary battery having a capacity of 1.5 m ² / g; other elements that substitute for Mn sites are Al, Ti, V,
Cr, Fe, Co, Ni, Cu, Zn, Mg, Ga, Z
The above-mentioned positive electrode material for a lithium secondary battery selected from the group consisting of r; the content of the spinel-type lithium manganese oxide and the lithium copper oxide in which a part of the Li site is partially replaced by another element is 1: 1: The above-described positive electrode material for a lithium secondary battery having a ratio of 1 to 20: 1 is exemplified.

Another embodiment of the present invention is a positive electrode for a lithium secondary battery including the above-described positive electrode material for a lithium secondary battery. Further, as another embodiment of the present invention, the positive electrode for a lithium secondary battery described above, and a lithium secondary battery having a negative electrode and an electrolyte, preferably the lithium secondary battery in which the active material of the negative electrode is a carbon material Batteries.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described more specifically. The spinel-type lithium manganese oxide used in the present invention is a composite oxide containing lithium and manganese as main components. The spinel-type lithium manganese oxide is represented by the general formula LiMn ₂ O ₄ , but may have a small amount of oxygen deficiency or non-stoichiometric property.

[0012] The spinel-type lithium manganese oxide used in the present invention includes those having few crystal defects such as a low oxygen deficiency product and a low cation deficiency product, those in which a part of Mn site is substituted by another element, and those in cubic crystal. A system is preferred. Reversibility of lithium occlusion / release can be improved by reducing crystal defects, substituting a part of the Mn site with another element, or using a cubic system.

At this time, the other element which substitutes a part of Mn (hereinafter referred to as a substitution element) is 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 Al.
The Mn site may be substituted with two or more other elements. In addition, in relation to 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 spinel-type lithium manganese oxide in the present invention also includes these.

The substitution ratio by the substitution element is usually at least 2.5 mol% of Mn, preferably at least 5 mol% of Mn, usually at most 30 mol% of Mn, preferably at least 20 mol% of Mn.
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 replaced by sulfur or a halogen element. Furthermore, there may be some non-stoichiometric oxygen content.

The spinel-type lithium manganese oxide can be produced by various conventionally known methods. For example, after mixing a starting material containing lithium, manganese, and a substitution element, the mixture is calcined and cooled in the presence of oxygen. Can be manufactured by Note that, in the above production method, a spinel-type lithium manganese oxide in which Mn sites were not substituted was produced without using a starting material containing a substitution element, and the lithium manganese oxide was used as a starting material containing a substitution metal element. After reacting in aqueous solution, molten salt or steam,
If necessary, in order to diffuse the substitution element into the lithium-manganese composite oxide particles, the Mn site may be substituted with the substitution element by performing heat treatment again.

Lithium compounds used as starting materials include Li ₂ CO ₃ , LiNO ₃ , LiOH, LiO
H.H ₂ O, LiCl, LiI, CH ₃ COOLi, Li
Examples include ₂ O, Li acetate, Li dicarboxylate, Li citrate, Li fatty acid, alkyl lithium, halides, and the like, and preferably Li ₂ CO ₃ , LiOH · H ₂ O, and Li dicarboxylate.

The manganese compound used as a starting material includes manganese oxides such as Mn ₂ O ₃ and MnO ₂ ;
manganese salts such as nCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ , manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty acid, oxyhydroxide, hydroxide,
Halides and the like. MnC as Mn ₂ O ₃
A material prepared by heat-treating a compound such as O ₃ or MnO ₂ may be used. Preferably Mn ₂ O ₃ , MnO ₂ , MnC
O ₃ , manganese dicarboxylate and oxyhydroxide are exemplified.

Examples of the compound of the substitution element include oxides, hydroxides, nitrates, sulfates, carbonates, dicarboxylates, fatty acid salts, ammonium salts, citrates, oxyacid salts, and the like. Substances, hydroxides, carbonates and 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.

The method of firing and cooling the spinel-type lithium manganese oxide is, for example, 600 to 900 after calcination.
Baked in an oxygen atmosphere at a temperature of about
A method of gradually cooling at a rate of 10 ° C./min or less to about 0 ° C. or less, or a calcination, followed by main firing at a temperature of about 600 to 900 ° C. in an air or oxygen atmosphere, and then at a temperature of about 400 ° C. in an oxygen atmosphere. An annealing method may be used. Conditions for firing and cooling are described in JP-A-9-306490, JP-A-9-306493, and JP-A-9-25.
No. 9880 and the like.

The spinel-type 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, preferably 1.5 m ² / g or less, more preferably 1.0 m ² / g or less. If the specific surface area is too small, the rate characteristics and capacity will be reduced. If the specific surface area is too large, undesired reactions with the electrolyte and the like will be caused, and the cycle characteristics will be reduced.

The average particle diameter of the spinel-type lithium manganese oxide used in the present invention is usually 0.1 to 30 μm, preferably 0.2 to 10 μm, more preferably 0.3 to 5 μm.
m. 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 power. The lithium copper oxide used in the present invention is characterized in that lithium is partially substituted with another element.

In this case, the other element to be substituted (hereinafter, referred to as a substitution element) usually includes an alkali metal element other than lithium, preferably Na, K, and more preferably Na. Note that the lithium site may be substituted with two or more kinds of other elements. The lithium copper oxide,
Specifically, the following general formula

[0023]

[Formula 3] Li _2-x M _x CuO ₂ (0 <x ≦ 1.0)

(M represents another element). The lithium copper oxide represented by the above general formula is a compound having an orthorhombic structure. The lithium copper oxide may have a nonstoichiometric oxygen content. The substitution ratio by the substitution element is preferably 1.0 mol% or more of Li, more preferably 2.5 mol% or more of Li, and preferably 2 mol% or more of Li.
It is at most 5 mol%, more preferably at most 15 mol% of Li. If the replacement ratio is too small or too large, it is difficult to obtain a balanced improvement effect when a battery is used. The average particle size and the specific surface area of the lithium copper oxide are not problematic as long as they do not greatly deviate from the average particle size and the specific surface area of the active material usually used for the positive electrode. From the viewpoint of improving the surface roughness, it is preferable that the average particle size is smaller than the average particle size of the spinel-type lithium manganese oxide, and that the specific surface area is larger than the specific surface area of the spinel-type lithium manganese oxide.

The lithium copper oxide in which a part of the Li site is substituted by another element in the present invention can be produced by various methods known in the art, for example, starting materials containing lithium, copper, and a substitution element. After mixing the raw materials, it can be manufactured by heating and firing in the atmosphere. In particular,
A method of heating and firing at a temperature in the range of 500 to 1000 ° C. in the air can be used. Note that the firing atmosphere is preferably a atmosphere in which carbon dioxide gas has been removed. In order to obtain a more uniform substitution composition, it is preferable to perform firing for a longer time than in the case of no substitution.

In the above production method, a lithium copper oxide in which the Li site is not substituted is produced without using a starting material containing a substitution element, and the lithium copper oxide is
After reacting in the aqueous solution of the starting material containing the substitution metal element, the molten salt or the vapor, and then diffusing the substitution element into the lithium copper oxide particles as necessary, the Li site is subjected to a heat treatment again to reduce the Li site. It may be substituted with a substitution element. As the lithium compound and the compound of the substitution element used as the starting materials, the same compounds as those in the method for producing a lithium manganese oxide described above can be used.

The copper compounds used as starting materials include copper oxides such as Cu ₂ O and CuO, CuCO ₃ , Cu
(NO ₃ ) ₂ , CuSO ₄ , copper acetate, copper dicarboxylate, copper citrate, copper salts such as fatty acid copper, copper hydroxide, copper halide and the like, preferably Cu ₂ O, CuO, CuC
O ₃ , copper dicarboxylate, copper citrate and copper hydroxide are exemplified. As a method for mixing these starting materials, a method similar to the method for producing the spinel-type lithium manganese oxide can be used.

The content of the spinel-type lithium manganese oxide and the lithium copper oxide in which a part of the Li site is replaced by another element in the positive electrode is expressed in terms of the weight ratio of the spinel-type lithium manganese oxide: Lithium copper oxide substituted with an element = usually 1: 1 to 20: 1, preferably 2: 1 to 15: 1, more preferably 3: 1 to 10: 1,
Most preferably, it is 6: 1 to 8: 1. When the weight ratio of the lithium copper oxide in which a part of the Li site is substituted by another element is out of the specified range, the discharge capacity is reduced, and when the weight ratio is reduced, the effect of improving the rate characteristics and the cycle characteristics may be difficult to obtain. There is.

A spinel-type lithium manganese oxide;
There is no particular limitation on the form of the composite with the lithium copper oxide in which part of the i-site has been replaced by another element, and physical mixing can also be performed, 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 spinel-type lithium manganese oxide, lithium copper oxide, a binder (binder) described later, and a conductive agent, which is slurried with a solvent by a method described later and applied to the positive electrode current collector. Then, a dried product can be used.

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, by using a positive electrode containing the above-described lithium manganese oxide, a lithium secondary battery having excellent initial capacity, rate characteristics, and cycle characteristics at high temperatures can be provided.

Therefore, in the present invention, a lithium secondary battery is manufactured by combining the above-described positive electrode containing lithium manganese oxide and lithium copper oxide with various negative electrodes and electrolytes. The active material of the negative electrode used in combination with the positive electrode of the present invention includes a carbon material, SnO, SnO ₂ , Sn
_1-x M _x O (M = Hg, P, B, Si, Ge or Sb,
Where 0 ≦ x <1), Sn ₃ O ₂ (OH) ₂ , Sn _3-x M _{x
O 2 (OH) 2 (M} = Mg, P, B, Si, Ge, Sb or Mn, but 0 ≦ x <3), 1 kind or two kinds selected from among ₂ such LiSiO _2, SiO ₂ or LiSnO The combinations described above are exemplified, but not limited to these.

The carbon material is not particularly limited. Graphite, coal-based coke, petroleum-based coke, carbide-based pitch-based carbide, petroleum-based pitch-based carbide, or carbide obtained by oxidizing these pitches, needle coke, pitch-coke, Examples thereof include carbides such as phenolic resins and crystalline cellulose, and carbon materials partially graphitized thereof, furnace black, acetylene black, pitch-based carbon fibers, and the like. Mixtures of two or more of these are also preferably used.

As the negative electrode, a material obtained by slurrying the active material of the negative electrode and a binder (binder) with a solvent and applying 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.

As 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 preferred 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 large, the fluidity is too low and the pores of the separator may not be closed when heated.

As the electrolyte in the lithium secondary battery of the present invention, for example, known organic electrolytes, polymer solid electrolytes, gel electrolytes, inorganic solid electrolytes and the like can be used. Among them, organic electrolytes are preferable. . The organic electrolyte is
Consists of organic solvents and solutes. The organic solvent is not particularly limited, but, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers, amines, esters, amides And phosphoric ester compounds. To list these representatives, 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, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethylsulfoxide, trimethyl phosphate, A single solvent such as triethyl phosphate or a mixture of two or more solvents can be used. 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 of the present invention will be described more specifically.
Nothing is more restrictive.

[0040]

EXAMPLE 1 As a spinel-type lithium manganese oxide, Li _1.04 M
Part of the Mn site consisting of n _1.85 Al _0.11 O ₄ is Li and Al
And a Na-substituted lithium copper oxide having a composition of Li _1.95 Na _0.05 CuO ₂ , and a spinel-type lithium manganese oxide: Na-substituted lithium copper oxide = 6 by weight ratio. : 1 was used as the positive electrode active material. In addition,
BET specific surface area of the spinel-type lithium manganese oxide and Na substituted lithium copper oxide used herein were respectively 0.9m ² /g,0.2m ² / g.

Example 2 The same spinel-type lithium manganese oxide as described in Example 1 and the Na-substituted lithium copper oxide having the composition Li _1.9 Na _0.1 CuO ₂ were prepared by weight ratio of the spinel-type lithium manganese oxide: A mixture in which Na-substituted lithium copper oxide = 6: 1 was used as the positive electrode active material. The BET specific surface area of the Na-substituted lithium copper oxide used here was 0.2 m ² / g.

Comparative Example 1 The same spinel-type lithium manganese oxide as described in Example 1 and an unsubstituted lithium copper oxide having the composition Li ₂ CuO ₂ were prepared by weight ratio of lithium manganese oxide: lithium copper oxide. = 6: 1 was used as the positive electrode active material. In addition, the BET specific surface area of the unsubstituted lithium copper oxide used here was 0.3 m ² / g.

Comparative Example 2 The same spinel-type lithium manganese oxide as described in Example 1 was used as a positive electrode active material. (Lithium copper oxide was not mixed.) Test Example (Evaluation of Battery) The batteries of Examples and Comparative Examples of the present invention were evaluated by the following methods. 1. Preparation of positive electrode, confirmation of capacity and rate evaluation Positive electrode active material 75% by weight, acetylene black 20% by weight, polytetrafluoroethylene powder 5% by weight were weighed and thoroughly mixed in a mortar to form a thin sheet. Punch with 9mmφ, 12mmφ punches. At this time, the total weight is adjusted so as to be about 8 mg and about 18 mg, respectively.
This was pressed against an Al expanded metal to form a positive electrode. Here, when assembling a battery cell with Li metal as a counter electrode, a positive electrode punched to 9 mmφ is used, and when assembling a battery cell with a negative electrode using a carbon material as an active material, 12
A positive electrode punched into mmφ was used.

A battery cell was assembled using the positive electrode punched out to 9 mmφ as a test electrode, a 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.

Further, a constant current charge / discharge for rate evaluation is performed in the above-mentioned voltage range. As conditions, constant current charging was constant at 0.5 mA / cm ² , and constant current discharging was 0.5 mA / cm ² .
The operation is performed in the order of 5, 1, ^{3, 5} , 7, 9, and 11 mA / cm ² . 2. Preparation of negative electrode and confirmation of capacity As an active material for negative electrode, graphite powder (d
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. Assembly of Battery Cell Using the coin-shaped cell having the configuration shown in FIG. 1, 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) and diethyl carbonate (DEC) in which 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) was dissolved.
Using a mixed solvent having a volumetric ratio of 3: 7, the mixture was added to the inside of the battery and sufficiently impregnated. Then, a 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 was set so that the amount of the positive electrode active material [g] / the amount of the negative electrode active material [g] = (Qf / 1.2) / Qs (C). .

4. Test Method In order to compare the high temperature characteristics of the battery obtained in this manner, the 1 hour rate current value of the battery, that is, 1 C is calculated as follows: 1 C [mA] = Qs (D) × amount of positive electrode active material [g] And the following tests were performed. First, a constant current of 0.1 at room temperature.
Two cycles of 2C charge / discharge and one cycle of constant current 1C charge / discharge were performed, and then a test was performed at a high temperature of 50 ° C. at a constant current of 0.2C charge / discharge, followed by a constant current 1C charge / discharge of 100 cycles. The upper limit of charging was 4.2 V and the lower limit voltage was 3.0 V. At this time, the ratio of the 100th cycle discharge capacity Qh (80) to the 1st cycle discharge capacity Qh (1) of the 1C charge / discharge 100 cycle test portion at 50 ° C. is defined as a high-temperature cycle capacity retention rate P, that is, P [% ] = {Qh (80) / Qh (1)} × 100, and the high-temperature characteristics of the batteries were compared using this value. Table 1 shows the initial discharge capacity and the 80-cycle capacity retention rate in the 50 # C cycle test obtained in Examples and Comparative Examples of the present invention, and the current density and discharge current capacity retention rate in the 25 # C rate test (Li counter electrode). Is shown in Table 2.

[0048]

[Table 1]

[0049]

[Table 2]

It can be seen that in the examples according to the present invention, the performance balance of the initial capacity, high-temperature cycle, and rate characteristics is excellent.

[0051]

According to the present invention, in the positive electrode for a lithium secondary battery containing lithium manganese oxide and lithium copper oxide, the performance balance of the initial capacity, high-temperature cycle and rate characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a coin-type battery used in a test of a method for producing 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

 ────────────────────────────────────────────────── ─── Continued on the front page F-term (reference)

Claims (11)

[Claims] 1. A positive electrode material for a lithium secondary battery, comprising, as an active material, a spinel-type lithium manganese oxide and a lithium copper oxide in which a part of a Li site is substituted by another element. 2. The other element substituting a part of the Li site is:
The positive electrode material for a lithium secondary battery according to claim 1, wherein the positive electrode material is selected from a group of alkali metal elements other than Li. 3. The lithium copper oxide is a compound represented by the following general formula: Li _2-x M _x CuO ₂ (0 <x ≦ 1.0) (M represents another element). The positive electrode material for a lithium secondary battery according to claim 1 or 2, wherein: 4. M of spinel type lithium manganese oxide
The positive electrode material for a lithium secondary battery according to any one of claims 1 to 3, wherein a part of the n site is substituted with another element. 5. The positive electrode material for a lithium secondary battery according to claim 1, wherein the crystal system of the spinel-type lithium manganese oxide is cubic. 6. B of spinel type lithium manganese oxide
ET specific surface area, the positive electrode material for a lithium secondary battery according to any one of claims 1 to 5, characterized in that a 0.3 to 1.5 m ² / g. 7. The other element substituting the Mn site is Al,
Ti, V, Cr, Fe, Co, Ni, Cu, Zn, M
The positive electrode material for a lithium secondary battery according to any one of claims 1 to 6, wherein the positive electrode material is selected from the group consisting of g, Ga, and Zr. 8. A spinel-type lithium manganese oxide and L
The lithium according to any one of claims 1 to 7, wherein the content of the lithium copper oxide in which a part of the i-site is substituted by another element is 1: 1 to 20: 1 by weight ratio. Positive electrode material for secondary batteries. 9. A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to claim 1. 10. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 9, a negative electrode and an electrolyte. 11. The lithium secondary battery according to claim 10, wherein the active material of the negative electrode is a carbon material.