JP2001167766A - Positive electrode material for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode material for a lithium secondary battery, which comprises spinel lithium-manganese oxides, has an excellent high temperature cycle characteristic, and does not cause reduction in initial capacity. SOLUTION: The positive electrode material for a lithium secondary battery comprises, as active substances, spinel lithium-manganese oxides and lithium- copper oxides. The BET specific surface area ratio of spinel lithium-manganese oxides to lithium-copper oxides is in the range of 0.5 to 5.0.

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 The use of a carbon material capable of occluding and releasing lithium ions as a negative electrode active material in place of lithium metal has greatly improved safety, and lithium secondary batteries have 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,
Research is being actively conducted. 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, there is a problem that the charge / discharge cycle life in a high temperature environment is short. Various measures have been taken to solve the above-mentioned problems, but in the conventional method, improvement has been achieved at the expense of other characteristics. In particular, improvement is often attempted at the expense of initial capacity. Even if the high-temperature cycle characteristics are improved, if the initial capacity is reduced, the usage time per operation becomes short, so that frequent charging must be performed, which is not practical.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a positive electrode material for a lithium secondary battery containing a spinel-type lithium manganese oxide, which has excellent high-temperature cycle characteristics and lowers initial capacity. The object of the present invention is to provide a positive electrode material for a lithium secondary battery without any problem.

[0004]

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 improve the high-temperature cycle characteristics, at least A. 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. Therefore,
Lithium copper oxide was selected as a compound that plays a role in supplementing the irreversible capacity component of the negative electrode. And as a reason for further lowering the initial capacity,

[0005] It was considered that the cause was that the specific surface area balance between lithium manganese oxide and lithium copper oxide was not appropriate. If the specific surface area balance is not appropriate, it is presumed that poor contact and uneven mixing of the two may be caused, resulting in adverse effects such as increased resistance. Based on the above speculation, it is necessary to find an appropriate range of the specific surface area balance between lithium manganese oxide and lithium copper oxide in order to improve the cycle characteristics at high temperatures and not to decrease the initial capacity. Thought. That is, the gist of the present invention includes a spinel-type lithium manganese oxide and a lithium copper oxide as active materials, and the ratio of the BET specific surface area of the spinel-type lithium manganese oxide and the lithium copper oxide is:

[0006]

[Formula 2] 0.5 ≦ Spinel type lithium manganese oxide /
Lithium copper oxide ≦ 5.0

[0007] The positive electrode material for a lithium secondary battery is characterized in that In a preferred embodiment of the present invention, a spinel type lithium manganese oxide BET
The above-mentioned positive electrode material for a lithium secondary battery having a specific surface area of 0.3 to 1.5 m ² / g; the above-mentioned lithium, wherein a part of the Mn site of the spinel-type lithium manganese oxide is substituted with another element. Positive electrode material for secondary battery; Other element replacing Mn site of spinel type lithium manganese oxide is A
1, Ti, V, Cr, Fe, Co, Ni, Cu, Zn,
The above-mentioned positive electrode material for a lithium secondary battery selected from the group consisting of Mg, Ga, and Zr; for the above-mentioned lithium secondary battery, wherein the lithium copper oxide has a BET specific surface area of 0.3 to ^2.5 m ² / g. Positive electrode material: Li ₂ Cu is Li ₂ Cu
The positive electrode material for a lithium secondary battery, which is O ₂ ; the positive electrode material for a lithium secondary battery, wherein the content of lithium manganese oxide and lithium copper oxide is 5: 1 to 20: 1 by weight ratio Is mentioned.

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, another embodiment of the present invention includes a positive electrode for a lithium secondary battery as described above, a lithium secondary battery having a negative electrode and an electrolyte. The above-described lithium secondary battery in which the substance is a carbon material is exemplified.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below using a preferred embodiment. 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. The spinel-type lithium manganese oxide used in the present invention has a low crystal defect such as a low oxygen deficiency product or a low cation deficiency product, a device in which a part of the Mn site is substituted by another element, or a cubic system. Is preferred. The reversibility of lithium insertion / release can be improved by reducing crystal defects, replacing a part of the Mn site with another element, or using a cubic system.

In this case, 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, a part of the Mn site may be replaced by Li in some cases due to the charge, and a part of the Mn site may be replaced by Li together with the other elements.
The spinel-type lithium man 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 replaced by sulfur or a halogen element. Furthermore, there may be some non-stoichiometric oxygen content. 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, and most preferably at 0.6 m ² / g or more, preferably 1.5 m ² / g or less, more preferably 1.2 m ² /
g, most 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. 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 spinel-type lithium manganese oxide can be produced by various conventionally known methods.
It can be produced by mixing starting materials containing lithium and manganese, followed by firing and cooling in the presence of oxygen. Further, the spinel-type lithium manganese oxide in which a part of the Mn site is substituted with another element is produced by mixing the starting material containing another element with the starting material containing lithium and manganese in the above-mentioned production method. can do. Note that, in the above production method, a lithium manganese oxide in which Mn sites are not substituted was produced without using a starting material containing a substitution element, and the lithium manganese oxide was dissolved in an aqueous solution of a starting material containing a substitution metal element. After reacting in a salt or steam, the Mn site may be replaced with a replacement element by performing heat treatment again in order to diffuse the replacement element into the lithium-manganese composite oxide particles as necessary.

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. Manganese compounds used as starting materials include manganese oxides such as Mn ₂ O ₃ and MnO ₂ , MnCO ₃ , Mn (NO ₃ ) ₂ , MnSO ₄ ,
Manganese salts such as manganese acetate, manganese dicarboxylate, manganese citrate, manganese fatty acids, oxyhydroxides,
Hydroxide, halide and the like. As Mn ₂ O ₃ , a material prepared by heat-treating a compound such as MnCO ₃ or MnO ₂ may be used. Preferably Mn ₂ O ₃ , MnO
₂ , MnCO ₃ , manganese dicarboxylate, and oxyhydroxide.

Examples of the compound of the substitution element include oxides, hydroxides, oxyhydroxides, nitrates, sulfates, carbonates, dicarboxylates, fatty acid salts and ammonium salts.
Preferred are oxides, 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. As a method of firing and cooling the spinel-type lithium manganese oxide, for example, 600 to 90 after calcination
Perform baking in an oxygen atmosphere at a temperature of about 0 ° C.
A method of gradually cooling to about 00 ° C. or less at a rate of 10 ° C./min or less, or after calcination, 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.
The firing and cooling conditions are described in JP-A-9-306490.
JP, JP-A-9-306493, JP-A-9-2
No. 59880 and the like.

Lithium copper oxide used in the present invention
The substance is a composite oxide containing lithium and copper as main components.
And preferably Li_TwoCuO_TwoIt is. Li_TwoCuO_TwoIs oblique
It is a compound having a tetragonal structure (space group Immm). This
Lithium copper oxide, lithium or copper is part of other elements
Or has a small amount of oxygen deficiency or non-stoichiometric
May be. Also, some of the oxygen sites
And may be substituted with an element. In the present invention,
Lithium copper oxide having a BET specific surface area of preferably
0.3m^Two/ G or more, more preferably 0.5 m^Two/ G or less
Above, most preferably 0.6m ^Two/ G or more, preferred
2.5m^Two/ G or less, more preferably 2.0 m^Two/ G
Below, most preferably 1.0 m^Two/ G or less. Ratio table
If the area is too small, the cause of characteristic deterioration due to increased resistance
If the specific surface area is too large, storage stability may decrease.
There is a case.

The average particle size of the lithium copper oxide used in the present invention is usually 0.1 to 80 μm, preferably 0.5 to 50 μm.
μm, more preferably 1 to 20 μm. If the average particle size is too small, the storage stability may decrease. If the average particle size is too large, the output characteristics may decrease due to an increase in resistance or a problem may occur at the time of producing a coated electrode. Lithium copper oxide can be produced by conventionally known various methods. For example, in the case of an oxide represented by the general formula Li ₂ CuO ₂ , after mixing lithium, a starting material containing copper, and then air It can be manufactured by firing and cooling below. As the lithium compound used as a starting material, the same lithium compound as in the method for producing a lithium manganese oxide described above can be used. As a copper compound used as a starting material, Cu
Copper oxides such as ₂ O and CuO, CuCO ₃ , Cu (NO ₃ ) ₂
, CuSO ₄ , copper acetate, copper dicarboxylate, copper citrate,
Examples thereof include copper salts such as fatty acid copper, copper hydroxide, and copper halide, and preferably include Cu ₂ O, CuO, CuCO ₃ , copper dicarboxylate, copper citrate, and copper hydroxide. General formula L
As a method of firing lithium copper oxide represented by i ₂ CuO ₂ , for example, a method of firing by heating in the air at a temperature in the range of 500 to 1000 ° C. can be mentioned. Note that the firing atmosphere is preferably a atmosphere in which carbon dioxide gas has been removed. The form of the composite of lithium manganese oxide and lithium copper oxide is not particularly limited, and may be a physical mixture, and a film of one particle may be formed on the surface of one particle.

The spinel type lithium manganese oxide and lithium copper oxide used in the present invention have a BET specific surface area ratio of 0.5 ≦ spinel type lithium manganese oxide / lithium copper oxide ≦ 5.0. There is a feature. The ratio is more preferably 0.7 ≦ spinel lithium manganese oxide / lithium copper oxide ≦ 3.0, most preferably 0.9 ≦ spinel lithium manganese oxide / lithium copper oxide ≦ 1.5. . If this ratio deviates from the specified range, it becomes difficult to obtain desired performance.
The weight ratio of the spinel type lithium manganese oxide to lithium copper oxide is lithium manganese oxide: lithium copper oxide = normally 5: 1 to 20: 1, preferably 6: 1.
10 to 10. When the weight ratio of the lithium copper 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 positive electrode comprises 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. And by drying. 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, it is possible to provide a lithium secondary battery having excellent rate characteristics and high-temperature cycle characteristics by using the positive electrode containing the spinel-type lithium manganese oxide and lithium copper oxide as described above. it can. Therefore, in the present invention, a positive electrode containing the above-described spinel-type lithium manganese oxide and lithium copper oxide and various negative electrodes, and a negative electrode used in combination with the positive electrode of the present invention in which a lithium secondary battery is manufactured by combining an electrolyte. Examples of the active material include carbon materials, 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 (O
H) ₂ (M = Mg, P, B, Si, Ge, Sb or M
n, where 0 ≦ x <3), LiSiO ₂ , SiO ₂ or L
One type or a combination of two or more types selected from iSnO _{2 and the} like are exemplified, but not limited to these.

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, 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 negative electrode active material and a binder (binder) slurried with a solvent, applied and dried, can be used. Examples of the binder (binder) for the active materials of the negative electrode and the positive electrode include polyvinylidene fluoride, polytetrafluoroethylene, EPDM (ethylene-propylene-diene terpolymer), SBR (styrene-butadiene rubber), and NBR ( Acrylonitrile-butadiene rubber), fluororubber and the like, but are 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 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 invention, for example, known organic electrolytes, polymer solid electrolytes, gel electrolytes, inorganic solid electrolytes, and the like can be used, and among them, organic electrolytes are 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.

Particularly, as a solute dissolved in this solvent,
Any known, but not limited, use
Yes, LiClO_Four, LiAsF₆, LiPF₆, LiB
F_Four, LiB (C₆H_Five)_Four , LiCl, LiBr, CH_Three
SO_ThreeLi, CF_ThreeSO_ThreeLi and the like.
At least one kind can be used. High
Even when using a solid polymer electrolyte,
Can be used, especially for lithium ions.
It is preferable to use a polymer with high ion conductivity.
For example, polyethylene oxide, polypropylene
Oxides, polyethyleneimines, etc. are preferably used.
In addition to the above-mentioned solute for this polymer,
It can be used as a gel electrolyte by adding a solvent.
is there. When using an inorganic solid electrolyte,
Known crystalline and amorphous solid electrolytes can be used
You. As the crystalline solid electrolyte, for example, LiI, Li
_ThreeN, Li_{1 + x}M_xTi_2-x(PO_Four)_Three(M = Al, Sc,
Y, La), Li_{0.5- 3x}RE_{0.5 + x}TiO_Three(RE = L
a, Pr, Nd, Sm) and the like;
For example, 4.9 LiI-34.1Li_TwoO-61
B_TwoO_Five, 33.3Li_TwoO-66.7SiO_Two Such as oxide glass
And 0.45LiI-0.37Li_TwoS-0.26B_TwoS_Three, 0.30LiI
−0.42Li_TwoS-0.28SiS_TwoSulfide glass etc.
Can be Use at least one of these
Can be The following examples illustrate the method of the present invention.
As will be described more specifically, the present invention is not restricted by these.
It is not limited.

[0025]

The present invention will be described in more detail with reference to the following examples. 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
Is used, and a lithium copper oxide represented by the general formula Li ₂ CuO ₂ is added to the lithium manganese oxide so that the weight ratio of spinel lithium manganese oxide: lithium copper oxide is 6: 1. The mixture was used as a positive electrode active material. The spinel type lithium manganese oxide used here had a BET specific surface area of 0.94 m ² / g, and the lithium copper oxide had a BET specific surface area of 0.67 m ² / g.

Example 2 The same spinel type lithium manganese oxide as described in Example 1 and lithium copper oxide having a BET specific surface area of 0.32 m ² / g (general formula Li ₂ CuO ₂ ) were weighed. Ratio of spinel-type lithium manganese oxide: lithium copper oxide =
A mixture having a ratio of 6: 1 was used as a positive electrode active material.

Example 3 The same spinel-type lithium manganese oxide as described in Example 1 and a lithium copper oxide having a BET specific surface area of 1.00 m ² / g (general formula Li ₂ CuO ₂ ) were weighed. Ratio of spinel-type lithium manganese oxide: lithium copper oxide =
A mixture having a ratio of 6: 1 was used as a positive electrode active material.

Example 4 The same spinel-type lithium manganese oxide and lithium copper oxide as described in Example 1 were used in a weight ratio of spinel-type lithium manganese oxide: lithium copper oxide = 9: 1. Was used as a positive electrode active material.

Example 5 The same spinel-type lithium manganese oxide as described in Example 1 and the same lithium copper oxide as described in Example 3 were mixed in a weight ratio of spinel-type lithium manganese oxide: What mixed so that lithium copper oxide = 9: 1 was used as a positive electrode active material.

Comparative Example 1 The same spinel-type lithium manganese oxide as described in Example 1 and a lithium copper oxide having a BET specific surface area of 0.12 m ² / g (general formula Li ₂ CuO ₂ ) were weighed. Ratio of spinel-type lithium manganese oxide: lithium copper oxide =
A mixture having a ratio of 6: 1 was used as a positive electrode active material.

Comparative Example 2 The same spinel-type lithium manganese oxide as described in Example 1 and a lithium copper oxide having a BET specific surface area of 2.6 m ² / g (general formula Li ₂ CuO ₂ ) were weighed. Ratio of spinel-type lithium manganese oxide: lithium copper oxide =
A mixture having a ratio of 6: 1 was used as a positive electrode active material.

COMPARATIVE EXAMPLE 3 The same spinel-type lithium manganese oxide as described in Example 1 and the same lithium copper oxide as described in Comparative Example 2 were mixed in a weight ratio of spinel-type lithium manganese oxide: What mixed so that lithium copper oxide = 9: 1 was used as a positive electrode active material.

Comparative Example 4 The same lithium manganese oxide as 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 and Confirmation of Capacity Positive electrode active material 75% by weight, acetylene black 20% by weight, and 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. The positive electrode punched into 9 mmφ was used as a test electrode, a battery cell was assembled using Li metal as a counter electrode, and a constant current charge of 0.5 mA / cm ² , that is, a reaction of releasing lithium ions from the positive electrode was performed at an upper limit of 4.35 V. Qs (C) is the initial charge capacity per unit weight of the positive electrode active material when a constant current discharge of 0.5 mA / cm ² , that is, a test for inserting lithium ions into the positive electrode was performed at a lower limit of 3.2 V.
mAh / g, and the initial discharge capacity is 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. Assembly of Battery Cell Using a coin-shaped cell having the configuration shown in FIG. 3, 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 is almost equal to 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 current value of one hour rate 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 (100) 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 ratio P, that is, P [% ] = {Qh (100) / Qh (1)} × 100, and this value was used to compare the high-temperature characteristics of the batteries. The ratio of the specific surface area of lithium manganese oxide (A) and lithium copper oxide (B) in the examples and comparative examples of the present invention (A) / (B), mixing weight ratio (A) / (B) and these Table 1 shows the initial discharge capacity and the 100-cycle capacity retention rate in a 50 ° C. cycle test obtained from the battery used as the positive electrode active material, and FIGS. 1 and 2 show the cycle-discharge capacity correlation diagrams.

[0038]

[Table 1]

It can be seen that the examples according to the present invention have excellent high-temperature cycle characteristics and little decrease in the initial capacity.

[0040]

According to the present invention, there is provided a cathode material for a lithium secondary battery containing a spinel-type lithium manganese oxide, which is excellent in high-temperature cycle characteristics and does not lower the initial capacity. can do.

[Brief description of the drawings]

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

FIG. 2 is a cycle-discharge capacity correlation diagram.

FIG. 3 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

Claims (10)

[Claims] 1. A spinel type lithium manganese oxide and a lithium copper oxide as active materials, wherein the ratio of the BET specific surface area of the spinel type lithium manganese oxide to the lithium copper oxide is 0.5 ≤ spinel type lithium manganese oxide /
A positive electrode material for a lithium secondary battery, wherein lithium copper oxide is in the range of 5.0 or less. 2. B of spinel type lithium manganese oxide
ET specific surface area, the positive electrode material for lithium secondary battery according to claim 1, wherein it is 0.3 to 1.5 m ² / g. 3. M of spinel type lithium manganese oxide
3. The positive electrode material for a lithium secondary battery according to claim 1, wherein a part of the n-site is substituted with another element. 4. M of spinel type lithium manganese oxide
Other elements replacing the n-site are Al, Ti, V, Cr,
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 Fe, Co, Ni, Cu, Zn, Mg, Ga, and Zr. 5. The lithium copper oxide has a BET specific surface area of:
5. The positive electrode material for a lithium secondary battery according to claim 1, wherein the positive electrode material is 0.3 to ^2.5 m ² / g. 6. The positive electrode material for a lithium secondary battery according to claim 1, wherein the lithium copper oxide is Li ₂ CuO ₂ . 7. The lithium secondary battery according to claim 1, wherein the content of lithium manganese oxide and lithium copper oxide is 5: 1 to 20: 1 by weight. Cathode material for battery. 8. A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to claim 1. 9. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 8, a negative electrode and an electrolyte. 10. The lithium secondary battery according to claim 9, wherein the active material of the negative electrode is a carbon material.