JP2001160395A - Material for positive electrode of lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a material for positive electrode of lithium secondary batteries of improved cycle properties at high temperatures and of large capacity, by making the spinel-type lithium manganese oxide to, function as positive electrode active substance, with a stability. SOLUTION: This material for a positive electrode contains spinel-type lithium manganese oxide, a compound (A), and a compound (B) as active substances. In a lithium secondary battery having its positive electrode comprised of the positive electrode material, the compound (A) emits lithium ions during the primary stage of charging to the upper limit of potential for the antipole lithium reference, corresponding to the maximum voltage range of the battery, substantially not occluding lithium ions during the primary stage of discharging, and the compound (B) has a larger charge and discharge capacity per unit weight than the spinel-type lithium manganese oxide of the working voltage range of positive electrode, corresponding to the maximum voltage range of charge and discharge of the battery.

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. 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.

[0005] In a lithium secondary battery, a surface film is formed on the surface of the negative electrode during initial charging, and a lithium ion trap occurs in a negative electrode active material structure capable of inserting and extracting lithium ions. Furthermore, when lithium manganese oxide is used as the positive electrode active material, the irreversible consumption reaction of lithium ions is promoted at high temperatures. Lithium ions consumed in film formation, traps, and irreversible reactions at high temperatures cannot return to the positive electrode. As a result, the balance between the positive electrode and the negative electrode in the battery is lost, and the positive electrode active material itself is destabilized. It is considered that such irreversible consumption of lithium ions is a cause of high-temperature cycle deterioration particularly when lithium manganese oxide is used as a positive electrode active material.

As means for compensating for lithium ions irreversibly consumed by the negative electrode, Japanese Patent Application Laid-Open No. Hei 5-290846 discloses a composition formula Li1 + x MnY B2-Y having a two-stage discharge curve.
There is a proposal to use a material represented by O4 (X is a positive number, 1.6 ≦ Y ≦ 1.9) as a positive electrode active material, and to allocate the low-potential discharge capacity not taken out to the initial charge capacity. However, even if there is an increase in the irreversible capacity by this means,
There is a disadvantage that the cycle characteristics are rather deteriorated.
In Japanese Patent Application Laid-Open No. 10-208730, a positive electrode mixture layer containing a lithium-containing metal oxide as a positive electrode active material has a lithium ion release potential lower than the lithium ion release potential of the lithium-containing metal oxide. At least an amount corresponding to lithium ions consumed by reacting with the negative electrode during the initial charge (the amount of lithium ions not involved in the charge / discharge cycle after the initial charge, ie, the irreversible capacity of the negative electrode) is added. There are suggestions. By this means, excellent discharge capacity can be obtained by taking into account the irreversible capacity of the negative electrode at the first charge, but it does not necessarily lead to improvement in high-temperature cycle characteristics when lithium manganese oxide is used as the positive electrode active material. . Furthermore,
WO 97/48140 proposes using a combination of lithium manganese oxide and lithium copper oxide. However, a sufficient capacity could not be secured only by combining lithium copper oxide, and it was not practical.

[0007]

Accordingly, an object of the present invention is to provide a cathode material for a lithium secondary battery containing a spinel-type lithium manganese oxide, which does not require reversible insertion and extraction of lithium. And a compound that functions to compensate for the irreversible capacity of the negative electrode during initial charging and to compensate for lithium loss due to side reactions that occur during high-temperature cycling. To provide a high capacity positive electrode material for lithium secondary batteries that has a high capacity by allowing the spinel-type lithium manganese oxide to function stably as a positive electrode active material, and has excellent high-temperature cycle characteristics. That is.

[0008]

The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result of the above-mentioned prior art, the reason that the high-temperature cycle characteristics have not been achieved to a practical level is that a plurality of high-temperature cycle characteristics have not been achieved at high temperatures. We thought that it might be because the deterioration factors acted in conjunction. When lithium manganese oxide is used as a positive electrode active material, a side reaction at a high temperature is regarded as a problem, and is observed in a form such as a manganese elution phenomenon.

Based on the above presumption, in order to reduce or suppress the deterioration effect and to improve the high-temperature cycle characteristics, at least I. It was considered that it was an essential condition to include in the positive electrode a compound that plays a role of complementing the irreversible capacity of the negative electrode.

In order to further increase the capacity, II. A combination of a positive electrode operating voltage range corresponding to the voltage range of repeated charging and discharging and having a higher charging and discharging capacity than lithium manganese oxide is combined. I thought that it was an indispensable condition to improve it by combining the two points with the addition.

That is, the gist of the present invention is a positive electrode material containing a spinel-type lithium manganese oxide, a compound (A) and a compound (B) as an active material, wherein the compound (A) is a positive electrode comprising the positive electrode material. In the lithium secondary battery having, the lithium ion is discharged at the time of initial charge up to the upper limit potential based on the counter electrode lithium corresponding to the maximum voltage range of charge and discharge of the battery, and the lithium ion is substantially discharged at the time of initial discharge up to the lower limit potential. In the lithium secondary battery having the positive electrode, the compound (B) is used in the range of the potential of the positive electrode based on the counter electrode lithium corresponding to the maximum voltage range of charge and discharge of the battery. A positive electrode material for a lithium secondary battery characterized by having a larger charge / discharge capacity per unit weight than a lithium manganese oxide.

In a preferred embodiment of the present invention, a part of the Mn site of the spinel type lithium manganese oxide is
The positive electrode material for a lithium secondary battery described above, which is substituted with another element; the other element that substitutes for a Mn site is Al, Ti,
V, Cr, Fe, Co, Ni, Cu, Zn, Mg, G
a, the positive electrode material for a lithium secondary battery selected from the group consisting of a and Zr; the positive electrode material for a lithium secondary battery, wherein the crystal system of the spinel-type lithium manganese oxide is cubic; Wherein the specific surface area is 0.3 to 1.5 m ² / g; the above lithium secondary battery wherein the compounds (A) and (B) are lithium transition metal composite oxides Positive electrode material for
The compound (A) is a cathode material for a lithium secondary battery, wherein the compound (A) is Li ₂ CuO ₂ ; the compound (A) is a cathode material for a lithium secondary battery, wherein the compound (A) is LiFeO ₂ ; Positive electrode material for a lithium secondary battery as described above, which is a lithium nickel oxide having nickel;
The above positive electrode material for a lithium secondary battery, in which a part of the site is replaced by another element;
Al, Ti, V, Cr, Fe, Co, Mn, Cu, Z
The above positive electrode material for a lithium secondary battery selected from the group consisting of n, Mg, Ga, and Zr; the content of the spinel-type lithium manganese oxide and the compound (B) is 1: 1 to 2 by weight ratio.
0: 1, spinel type lithium manganese oxide and compound
The positive electrode material for a lithium secondary battery, wherein the content of the compound (A) and the content of the compound (A) are 1: 1 to 20: 1 by weight; lithium manganese oxide having a spinel structure; Examples of the positive electrode material for a lithium secondary battery include Li ₂ CuO ₂ and lithium nickel oxide having a layered structure as an active material. Another embodiment of the present invention is a positive electrode including the above-described positive electrode material for a lithium secondary battery.

Further, another embodiment of the present invention includes a lithium secondary battery comprising the above-mentioned positive electrode for a lithium secondary battery, a negative electrode and an electrolyte. The above-mentioned lithium secondary battery in which the active material is a carbon material.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described using a preferred embodiment, but unless departing from the gist of the present invention.
It goes without saying that the present invention is not limited to the following. The spinel-type lithium manganese oxide used in the present invention is a composite oxide containing lithium and manganese as main components. The lithium manganese oxide having a spinel structure 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 material in which a part of the Mn site is substituted by another element, a cubic crystal. A 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. By combining this with the compound (A) and the compound (B), the capacity and the high-temperature cycle characteristics can be further improved.

The other elements to be replaced at this time (hereinafter, referred to as replacement elements) are usually Al, Ti, V, Cr, F
e, Co, Ni, Cu, Zn, Mg, Ga, Zr, etc., preferably Al, Cr, Fe, Co, Ni, M
g and Ga, more preferably Al. The Mn site may be substituted with two or more other elements. In addition,
Due to the relationship with the preparation, a part of the Mn site may be replaced by Li, and a part of the Mn site may be replaced 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 2.5 of Mn.
Mol% or more, preferably 5 mol% or more of Mn, usually 30 mol% or less of Mn, preferably 20 mol% of Mn.
It is as follows. 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 average particle diameter of the spinel-type lithium manganese oxide used in the present invention is usually 0.1 to 30 μm.
m, preferably 0.2 to 10 μm, more preferably 0.1 μm.
It is 3-5 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 used in the present invention has a 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 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 measurement of the specific surface area follows the BET method.

The compound (A) used in the present invention is
A positive electrode containing a spinel-type lithium manganese oxide, a compound (A) and a compound (B) as an active material has a charge / discharge curve that contributes to the initial charge capacity but hardly contributes to the initial discharge capacity. I just need. That is,
In a lithium secondary battery having a positive electrode containing a spinel-type lithium manganese oxide, a compound (A) and a compound (B) as an active material, up to an upper limit potential on a counter electrode lithium basis corresponding to a maximum voltage range of charge and discharge of the battery. Is a compound which releases lithium ions at the time of initial charge and does not substantially occlude lithium ions at the time of initial discharge up to the lower limit potential based on the counter electrode lithium corresponding to the maximum voltage range of charge and discharge of the battery. Note that the initial charge up to the upper limit potential on the basis of the counter electrode lithium corresponding to the maximum voltage range of charge and discharge of the battery refers to the counter electrode lithium reference corresponding to the maximum voltage range of charge and discharge of the battery from the natural potential of the battery. Means the initial charge up to the upper limit potential, and the initial discharge to the lower limit potential, the battery completed the initial charge, the lower limit potential based on the counter electrode lithium corresponding to the maximum voltage range of charge and discharge of the battery. Means initial discharge. The amount of lithium ions in the initial charge of the compound (A) is, for example, 10 to 500 mAh / g.
Is the amount corresponding to

The phrase "does not substantially occlude lithium ions" means that only 10% or less of the lithium ions released at the time of initial charging is occluded. Means what happens in. Further, as the properties of the compound (A), it is preferable that the charge capacity per unit weight (the amount of released lithium) is larger than that of the spinel-type lithium manganese oxide. In addition, without releasing lithium at the initial charge,
It is preferable to have a reservoir-like property of releasing lithium little by little after the cycle.

The maximum voltage range in the present invention refers to a range from the highest voltage to the lowest voltage when the battery is used,
The maximum voltage range of the charge and discharge of the battery differs depending on the type of the positive electrode and the negative electrode used. For example, when lithium manganese oxide is used for the positive electrode and graphite is used for the negative electrode, the maximum voltage range is usually 4.1 to 4.0. It is around 3V, and the lower limit is around 2.7-3.2V. Assuming that the potential of the positive electrode at the counter electrode Li is V (C) and the potential of the negative electrode is V (A), the battery voltage V (B) is V (B) = V
Since (C) -V (A) is used, it is considered that V (A) of the negative graphite is usually used at about 0.1 V at the battery charging end and at about 0.5 V at the discharging end in a battery. And V (C) has an upper limit of about 4.2 to 4.4 V and a lower limit of about 3.2 to 3.7 V. The compound (A) releases lithium ions at the time of initial charge up to the upper limit potential on the basis of the counter electrode lithium corresponding to the maximum voltage range of charge and discharge of the battery, and does not substantially occlude lithium ions at the time of initial discharge up to the lower limit potential. This is because the initial discharge capacity when discharging to the lower limit potential is 10% or less of the initial charging capacity when charging to the upper limit potential at the counter electrode Li using the compound (A) as the positive electrode. is there.

As described above, the compound (A) used for the positive electrode of the present invention releases lithium ions during initial charging,
For example, it has a property that the polarization rapidly increases at the same time as the start of discharge, and the lithium ion is occluded or structurally collapsed below the lower limit voltage to lose the occlusion ability.

As the compound (A) having such properties,
Is preferably a compound containing lithium and another metal
And other metals include Cu, Fe, Cr, T
i, Mo, V, Mn, etc., and more preferably C
Transition metals such as u, Fe, Ti, Mo, V, and Mn.
Specific compounds (A) include Li_TwoCuO_Two , LiFe
O _Two , Li_FiveFeO_Four, LiMoO_Three, LiVTiO_Four, L
iMnTiO_FourLithium transition metal composite oxides such as
And particularly preferably Li_TwoCuO_TwoIt is.

The compound (B) used in the present invention is
In the positive electrode including the spinel-type lithium manganese oxide, the compound (A) and the compound (B) as an active material, in the positive electrode use potential range on the basis of the counter electrode lithium corresponding to the maximum voltage range, compared with the spinel-type lithium manganese oxide. What is necessary is just to have a large charge / discharge capacity. The charge / discharge capacity of the compound (B) is preferably greater than 1.0 times and not more than 5.0 times the charge / discharge capacity of the spinel-type lithium manganese oxide.

The compound (B) having such characteristics is preferably a compound containing lithium and another metal, and the other metal may be Ni, Co, Mn, I
r, etc., more preferably a transition metal such as Ni or Co, and particularly preferably Ni. Specific compounds
(B) includes LiNiO ₂ , LiCoO ₂ , LiMnO
₂ , Li ₂ IrO _{3 and the} like, more preferably Li
NiO ₂ and LiCoO ₂ , particularly preferably LiNiO ₂ .

When the compounds (A) and (B) are lithium transition metal composite oxides, a part of the transition metal may be replaced by another element, and the oxygen content may be non-stoichiometric. May be something. From the viewpoint of stabilizing the crystal structure of the oxide, it is preferable that part of the transition metal is substituted with another element. The other elements to be replaced at this time (hereinafter, referred to as replacement elements) are usually Al, Ti, V, Cr,
Fe, Co, Mn, Ni, Cu, Zn, Mg, Ga, Z
r, etc., preferably Al, Cr, Fe, Co,
Ni, Mg, Ga, more preferably Al. In addition,
The transition metal may be substituted with two or more other elements.

The substitution ratio by the substitution element is usually at least 5 mol% of the transition metal, preferably at least 10 mol% of the transition metal, usually at most 60 mol% of the transition metal, preferably at most 40 mol% of the transition metal. . If the substitution ratio is too small, the cycle characteristics of the resin itself may deteriorate, and if it is too large, the capacity may decrease. Compound (A)
The average particle size and specific surface area of the compound (B) and the average particle size and specific surface area of the active material usually used for the positive electrode are not problematic as long as they do not greatly deviate from the average particle size and specific surface area, but the contact efficiency with lithium manganese oxide is improved. From the viewpoint, 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 spinel-type lithium manganese oxide.

The form of the composite of the spinel-type lithium manganese oxide with the compound (A) and the compound (B) is not particularly limited, and may be a physical mixture. A coating may be formed. Spinel-type lithium manganese oxide can be produced by various conventionally known methods.For example, lithium, manganese, and a starting material containing a substitution element are mixed and then calcined and cooled in the presence of oxygen. can do.

In the above-mentioned production method, a spinel-type 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. After reacting in the aqueous solution of the raw material, molten salt or steam, the Mn site is replaced by the replacement element by performing heat treatment again to diffuse the replacement element into the spinel-type lithium manganese composite oxide particles as necessary. May be.

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 starting material
The manganese compound used as the manganese compound is Mn_TwoO_Three, Mn
O_TwoSuch as manganese oxide, MnCO_Three, Mn (NO_Three)
_Two , MnSO_Four, Manganese acetate, manganese dicarboxylate
Manganese such as manganese, manganese citrate and fatty acid manganese
Salts, oxyhydroxides, halides and the like. M
n_TwoO_ThreeAs MnCO_ThreeAnd MnO_TwoCompounds such as
May be used. Preferably Mn_Two
O _Three, MnO_Two, MnCO_Two, Manganese dicarboxylate,
Xylhydroxide.

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

As an example of the compound (A), the above-mentioned lithium copper oxide (general formula: Li ₂ CuO ₂ ) can be produced by various conventionally known methods.
After mixing the starting materials containing the substitution element, the mixture can be manufactured by heating and baking in air. Note that, in the above-described production method, a lithium copper oxide in which a Cu site is not substituted was produced without using a starting material containing a substitution element, and the lithium copper oxide was dissolved in an aqueous solution of a starting material containing a substitution metal element by melting. After reacting in a salt or steam, if necessary, heat treatment is performed again to diffuse the substitution element into the lithium-copper composite oxide particles.
The u site may be replaced by a replacement element.

As the lithium compound and the compound of the substitution element used as the starting materials, those similar to the above-mentioned method for producing the spinel-type lithium manganese oxide can be used. Examples of the copper compound used as a starting material include copper oxides such as Cu ₂ O and CuO, CuCO ₃ , C
u (NO ₃ ) ₂ , CuSO ₄ , copper acetate, copper dicarboxylate,
Examples thereof include copper salts such as copper citrate and fatty acid copper, and copper hydroxide, and preferably include Cu ₂ O, CuO, CuCO ₃ , copper dicarboxylate, copper citrate, and copper hydroxide.

As a method for mixing these starting materials, the same method as that for producing the spinel-type lithium manganese oxide can be used. Examples of the method of firing the lithium copper oxide represented by the general formula Li ₂ CuO ₂ include,
A method of heating and baking in a temperature range of up to 1000 ° C. can be mentioned. Note that the firing atmosphere is preferably a atmosphere in which carbon dioxide gas has been removed.

As an example of the compound (B), the above-mentioned layered lithium nickel oxide (general formula LiNiO ₂ ) can be produced by various conventionally known methods. For example, it contains lithium, nickel and a substitution element. After mixing the starting materials, they can be manufactured by heating and firing in an oxygen atmosphere. Note that, in the above production method, a lithium nickel oxide in which Ni sites were not substituted was produced without using a starting material containing a substitution element, and the lithium nickel oxide was dissolved in an aqueous solution of a starting material containing a substitution metal element. After the reaction in the salt or steam, the Ni site may be replaced by the replacement element by performing heat treatment again in order to diffuse the replacement element into the lithium nickel composite oxide particles as necessary.

As the lithium compound and the compound of the substitution element used as the starting materials, those similar to the above-mentioned method for producing the spinel-type lithium manganese oxide can be used. Nickel compounds used as starting materials include copper oxides such as NiO, NiCO ₃ , Ni
(NO ₃ ) ₂ , NiSO ₄ , nickel acetate, nickel dicarboxylate, nickel citrate, nickel salts such as fatty acid nickel, nickel hydroxide, halides and the like;
Preferred are NiO, NiCO ₃ , nickel dicarboxylate, nickel citrate and nickel hydroxide.

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. As a method for firing the layered lithium nickel oxide, for example, 600 to 1000 ° C. in an oxygen atmosphere
And baking in the above temperature range.
As disclosed in Japanese Patent Application Laid-Open No. 9-320598, air having been subjected to carbon dioxide gas removal treatment can be suitably used as the firing atmosphere.

The weight ratio of the spinel-type lithium manganese oxide to the compound (B) in the positive electrode is, as weight ratio, spinel-type lithium manganese oxide: compound (B) = normally 1: 1 to 2
0: 1, preferably 2: 1 to 15: 1, more preferably 4: 1 to 10: 1, most preferably 3: 1 to 6: 1. When the weight ratio of the compound (B) is out of the specified range, the safety may be lowered. On the other hand, when the weight ratio is low, the effect of improving the capacity may not be obtained. Next, the weight ratio of the combined weight of the spinel-type lithium manganese oxide and the compound (B) to the amount of the compound (A) is (weight ratio of the spinel-type lithium manganese oxide +
Compound (B)): Compound (A) = Normally 1: 1 to 20: 1, preferably 2: 1 to 15: 1, more preferably 3: 1 to 1
0: 1, most preferably from 6: 1 to 8: 1. Compound
When the weight ratio of (A) 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 a spinel-type lithium manganese oxide, a compound (A), a compound (B), a binder (binder) described later, and a conductive agent. And dried. 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 the positive electrode containing the spinel-type lithium manganese oxide as described above is used,
In particular, it is possible to provide a lithium secondary battery in which the positive electrode is stabilized under a high-temperature environment, and which has excellent cycle characteristics and storage characteristics under a high temperature. Therefore, in the present invention, a lithium secondary battery is manufactured by combining the positive electrode containing the above-described spinel-type 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 is a carbon material, 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. Particularly preferred is a carbon material.

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, a negative electrode active material and a binder (binder) slurried with a solvent, applied and dried, 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 preferred 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.

As the ionic conductor 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. Is preferred. The organic electrolyte is composed of an organic solvent and a solute. The organic solvent is not particularly limited, for example, carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, ethers,
Amines, esters, amides, phosphate compounds and the like can be used. When these representatives are listed, 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-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, dimethylformamide, dimethylsulfoxide, phosphoric acid A single solvent such as trimethyl and 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, CO ₂ , N ₂ O, CO, S
A gas such as O ₂ or an additive such as polysulfide S _x ²⁻ that forms a good film that enables efficient charge and discharge of lithium ions on the surface of the negative electrode may be added to the organic solvent at an arbitrary ratio.

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 method of the present invention will be described in more detail by way of examples, but the present invention is not limited thereto.

[0052]

EXAMPLES Example 1 Li _1.04 Mn as a spinel type lithium manganese oxide
_1.85 Al _0.11 O ₄ , part of Mn site is Li and Al
Lithium manganese oxide substituted with a lithium copper oxide having the composition Li ₂ CuO ₂ (compound (A))
And lithium nickel oxide (compound (B)) having the composition LiNi _1.8 Co _0.15 Al _0.05 O ₂ so that the weight ratio of lithium manganese oxide: lithium copper oxide: lithium nickel oxide = 6: 1: 2. The mixture was used as a positive electrode active material. The specific surface area of the lithium manganese oxide used here was 0.9 m ² / g.

When the capacity of this positive electrode using Li ₂ CuO ₂ (compound (A)) alone as the positive electrode active material was confirmed with a counter electrode Li metal in a battery evaluation method described later, the natural potential (2.
The initial charge capacity from 8 V) to the upper limit potential (4.35 V) was 366 mAh / g, and the initial discharge capacity from the lower limit potential (3.2 V) was 25 mAh / g. (At the time of initial charging, lithium ions are released, and at the time of initial discharging, lithium ions are not substantially occluded.) Furthermore, a spinel-type lithium manganese oxide having a composition of Li _1.04 Mn _1.85 Al _0.11 O ₄ alone was used as a positive electrode active material. When the capacity of the positive electrode was confirmed with a counter electrode Li metal in a battery evaluation method described later, the initial charge capacity was 114 mAh / g, the initial discharge capacity was 112 mAh / g, and the composition LiNi _1.8 Co _0.15
The capacity of the positive electrode using lithium nickel oxide alone as a positive electrode active material, which was Al _0.05 O ₂ (compound (B)), was confirmed by a counter electrode Li metal in a battery evaluation method described later. The initial charge capacity was 215 mAh / g, and the initial discharge capacity was Was 180 mAh / g. (Compound (B) has a larger charge / discharge capacity per unit weight than spinel-type lithium manganese oxide used as a positive electrode active material.)

Example 2 The same spinel-type lithium manganese oxide, lithium copper oxide (compound (A)) and lithium nickel oxide (compound (B)) as described in Example 1 were mixed in a weight ratio of lithium. A mixture of manganese oxide: lithium copper oxide: lithium nickel oxide = 6: 1: 1 was used as the positive electrode active material.

Comparative Example 1 The same spinel-type lithium manganese oxide as described in Example 1 was used as a positive electrode active material. (Composition Li ₂ C
Lithium copper oxide (compound (A)) of uO ₂ and composition Li
A lithium nickel oxide (compound (B)) of Ni _1.8 Co _0.15 Al _0.05 O ₂ was not mixed. )

COMPARATIVE EXAMPLE 2 The same spinel-type lithium mantle as described in Example 1.
Gun oxide and composition Li _TwoCuO_TwoBecome lithium copper oxide
(Compound (A)) in weight ratio of lithium manganese oxide:
Lithium copper oxide = 6: 1
It was used as a positive electrode active material. (Composition LiNi_1.8 Co_0.15
Al_0.05O_Two Lithium nickel oxide (compound
(B)) was not mixed. )

Comparative Example 3 The same spinel-type lithium manganese oxide as described in Example 1 and a lithium nickel oxide (compound (B)) having the composition LiNi _1.8 Co _0.15 Al _0.05 O ₂ were mixed in a weight ratio of lithium manganese. Oxide: lithium nickel oxide =
A mixture of 3: 1 was used as a positive electrode active material. (The lithium copper oxide (compound (A)) having the composition Li ₂ CuO ₂ was not mixed.)

Test Examples (Evaluation of Batteries) 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 A mixture of the positive electrode active material weighed at 75% by weight, acetylene black at 20% by weight, and polytetrafluoroethylene powder at 5% by weight was sufficiently mixed in a mortar to form a thin sheet having a diameter of 9 mm. Punch with 12mmφ punch. At this time, the total weight is adjusted to be about 8 mg and 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 into 9 mmφ is used. When assembling a battery cell with a negative electrode using a carbon material as an active material as a counter electrode, 12 mmφ is used.
The positive electrode punched was used. The positive electrode punched into 9 mmφ is a test electrode, and a battery cell is assembled with Li metal as a counter electrode,
A constant current charge of 0.5 mA / cm ² , that is, a reaction for releasing lithium ions from the positive electrode is performed at an upper limit of 4.35 V, and then a constant current discharge of 0.5 mA / cm ² , that is, a test for inserting lithium ions into the positive electrode, is performed at the lower limit. The initial charge capacity per unit weight of the positive electrode active material at 3.2 V was Qs (C) mAh / g,
Let the initial discharge capacity be Qs (D) mAh / g.

2. Preparation of Negative Electrode and Confirmation of Capacity As a negative electrode active material, graphite powder having an average particle size of about 8 to 10 μm (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 / cm2.
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 The battery performance was evaluated using the coin-shaped cell having the structure shown in FIG. 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)
A mixed solvent of volume ratio 3: 7 of C) was added to the inside of the battery to be sufficiently impregnated, and 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 batteries obtained in this manner, the 1-hour rate current value of the battery, that is, 1 C is calculated as 1 C [mA] = Qs (D) × amount of positive electrode active material [g]. And the following tests were performed. First, at room temperature, constant current 0.2C charge / discharge 2 cycles and constant current 1C
One charge / discharge cycle is performed, and then a constant current of 0.degree.
1C charge / discharge 1 cycle, then constant current 1C charge / discharge 100
A cycle test was performed. The upper limit of charging was 4.2 V and the lower limit voltage was 3.0 V. At this time, with respect to the discharge capacity Qh (1) in the first cycle of the 100-cycle charge / discharge test section at 50 ° C.
The ratio of the discharge capacity Qh (100) at the 100th cycle is defined as the high-temperature cycle capacity retention ratio P, that is, P [%] = {Qh (100) / Qh (1)} × 100, and the high-temperature characteristics of the battery are compared with this value. did. Table 1 shows the initial discharge capacity and 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.

[0062]

[Table 1] It can be seen that in the examples according to the present invention, the characteristics are significantly improved.

[0063]

According to the present invention, it is possible to provide a cathode material for a lithium secondary battery having a high capacity in which a spinel-type lithium manganese oxide functions stably as a cathode active material, has excellent high-temperature cycle characteristics, and has a high capacity. .

[Brief description of the drawings]

FIG. 1 Cycle-discharge capacity correlation diagram

FIG. 2 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) 5H003 AA02 AA04 BB05 BC01 BC06 BD00 BD05 5H014 AA01 EE07 EE10 HH00 HH06 5H029 AJ03 AJ05 AK03 AL06 AM03 AM04 AM05 AM07 BJ03 BJ16 DJ17 HJ02 HJ07 HJ13 HJ19

Claims (16)

[Claims] 1. A positive electrode material comprising a spinel-type lithium manganese oxide, a compound (A) and a compound (B) as an active material, wherein the compound (A) has a lithium secondary having a positive electrode made of the positive electrode material. In a battery, lithium ions are released at the time of initial charge up to the upper limit potential on the basis of the counter electrode lithium corresponding to the maximum voltage range of charge and discharge of the battery, and substantially do not occlude lithium ions at the time of initial discharge up to the lower limit potential. In the compound (B), in a lithium secondary battery having the positive electrode, in the working potential range of the positive electrode based on the counter electrode lithium corresponding to the maximum voltage range of charge and discharge of the battery,
A positive electrode material for a lithium secondary battery, which has a larger charge / discharge capacity per unit weight than the spinel-type lithium manganese oxide. 2. M of spinel-type lithium manganese oxide
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. 3. 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 claim 2, wherein the positive electrode material is selected from the group consisting of g, Ga, and Zr. 4. 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. 5. The positive electrode material for a lithium secondary battery according to claim 1, wherein the specific surface area of the spinel type lithium manganese oxide is 0.3 to 1.5 m ² / g. . 6. The positive electrode material for a lithium secondary battery according to claim 1, wherein the compounds (A) and (B) are lithium transition metal composite oxides. 7. The positive electrode material for a lithium secondary battery according to claim 1, wherein the compound (A) is Li ₂ CuO ₂ . 8. The positive electrode material for a lithium secondary battery according to claim 1, wherein the compound (A) is LiFeO ₂ . 9. The compound (B) is a lithium nickel oxide having a layered structure.
The positive electrode material for a lithium secondary battery according to any one of the above. 10. The positive electrode material for a lithium secondary battery according to claim 9, wherein a part of Ni sites of the lithium nickel oxide is substituted with another element. 11. The other element substituting a Ni site is A
1, Ti, V, Cr, Fe, Co, Mn, Cu, Zn,
The positive electrode material for a lithium secondary battery according to claim 10, wherein the positive electrode material is selected from the group consisting of Mg, Ga, and Zr. 12. The content of the spinel-type lithium manganese oxide and the compound (B) is 1: 1 to 20: 1 by weight,
The combined content of the spinel-type lithium manganese oxide and the compound (B) and the content of the compound (A) are 1: 1 by weight.
The cathode material for a lithium secondary battery according to any one of claims 1 to 11, wherein the ratio is 20 to 20: 1. 13. A positive electrode material for a lithium secondary battery, comprising as active materials lithium manganese oxide having a spinel structure, Li ₂ CuO ₂ and lithium nickel oxide having a layered structure. 14. A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to claim 1. 15. A lithium secondary battery comprising the positive electrode for a lithium secondary battery according to claim 14, a negative electrode and an electrolyte. 16. The lithium secondary battery according to claim 15, wherein the active material of the negative electrode is a carbon material.