JP2002117830A - Positive electrode material for lithium secondary battery, positive electrode for lithium secondary battery and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a high temperature property in case lithium transition metal complex oxide is used as an active material. SOLUTION: This contains the lithium transition metal complex oxide and an organic semiconductor (A). The organic semiconductor (A) contains 0.1 to 5 mole% of an aromatic compound having a condensed ring or at least 4 benzene rings, and of at least one kind among isoviolanthrone, violanthrene, coterylene, 3,4,9,10-perylene tetracarboxylic acid diimide and metallic phthalocyanine.

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 and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art As a positive electrode active material for providing a practically usable lithium secondary battery, a lithium transition metal composite oxide is promising. Among these compounds, when cobalt, nickel, and manganese are used as transition metals, and lithium cobalt composite oxide, lithium nickel composite oxide, and lithium manganese composite oxide are used as the positive electrode active material, high performance battery characteristics can be obtained. it can. For this reason, research and development for practical use of these compounds have been actively conducted, but various problems need to be overcome even if these materials are used, in order to reach the practical use level.

[0003] One of the problems to be solved is characteristic deterioration in a high-temperature environment. Deterioration of the characteristics of a lithium secondary battery under a high temperature environment not only causes the lithium transition metal composite oxide used as a positive electrode active material to be in an active state, but also causes deterioration of the electrolyte itself, decomposition of an electrolytic solution, and negative electrode surface. It is thought to be caused by various factors, such as destruction of the film formed on the substrate.

[0004] In particular, lithium manganese composite oxides such as LiMn ₂ O ₄ have a larger reserve of manganese as a raw material than lithium cobalt composite oxide or lithium nickel composite oxide compared to cobalt or nickel. Although it has many advantages such as low cost and high safety in overcharging, the demand for improving high-temperature characteristics is particularly high because the battery performance (cycle characteristics) in the high-temperature environment is inferior.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such prior art, and an object thereof is to provide a lithium secondary battery having improved high-temperature characteristics including high-temperature cycle characteristics. It is in.

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve such problems, and as a result, the presence of an organic semiconductor (an organic substance exhibiting semiconductor characteristics based on electronic conduction) has been studied at high temperatures. Have been found to improve the characteristics of the present invention, leading to the present invention. That is, the gist of the present invention resides in the following (1) to (18). (1) Lithium transition metal composite oxide and organic semiconductor (A)
And a positive electrode material for a lithium secondary battery. (2) The specific resistance of the organic semiconductor (A) is 10 ⁻² to 10 ¹⁶
The positive electrode material for a lithium secondary battery according to (1), wherein the positive electrode material has a Ω · cm. (3) The positive electrode material for a lithium secondary battery according to (1) or (2), wherein the organic semiconductor (A) comprises an aromatic compound. (4) The positive electrode material for a lithium secondary battery according to any one of (1) to (3), wherein the organic semiconductor (A) is an aromatic compound having a condensed ring. (5) The positive electrode material for a lithium secondary battery according to any one of (1) to (4), wherein the organic semiconductor (A) is an aromatic compound having four or more benzene rings in a molecule. (6) The organic semiconductor (A) is an aromatic polycyclic compound in which four or more benzene rings are condensed (1).
The positive electrode material for a lithium secondary battery according to any one of (1) to (5). (7) The organic semiconductor (A) is at least one selected from the group consisting of isobiolanthrone, biolanthrene, cortellylene, 3,4,9,10-perylenetetracarboxylic diimide and metal phthalocyanine. The positive electrode material for a lithium secondary battery according to any one of (1) to (6). (8) The positive electrode material for a lithium secondary battery according to (7), wherein the metal phthalocyanine is at least one of copper phthalocyanine, magnesium phthalocyanine, and dilithium phthalocyanine. (9) Lithium transition metal composite oxide and organic semiconductor (A)
(1) to (8), wherein the material is a physical mixture of: (10) The positive electrode material for a lithium secondary battery according to any one of (1) to (9), wherein the ratio of the organic semiconductor (A) to the lithium transition metal composite oxide is 0.1 to 5 mol%. . (11) The lithium transition metal composite oxide is a lithium manganese composite oxide, (1) to (1).
0) The positive electrode material for a lithium secondary battery according to any one of the above. (12) The positive electrode material for a lithium secondary battery according to (11), wherein the lithium transition metal composite oxide is a lithium manganese composite oxide in which a part of a manganese site is substituted with another element. (13) Another element that partially replaces the manganese site is A
1, Ti, V, Cr, Fe, Co, Li, Ni, Cu,
The positive electrode material for a lithium secondary battery according to (12), wherein the positive electrode material is at least one element selected from the group consisting of Zn, Mg, Ga, and Zr. (14) A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to any one of (1) to (13) and a binder. (15) The positive electrode for a lithium secondary battery according to (14), wherein the lithium transition metal composite oxide and the organic semiconductor (A) are dispersed in the positive electrode. (16) A lithium secondary battery comprising at least the positive electrode, a negative electrode and an electrolyte for a lithium secondary battery according to (14) or (15). (17) The lithium secondary battery according to (16), wherein the active material of the negative electrode is a carbon material. (18) A lithium secondary battery using a lithium transition metal composite oxide as a positive electrode active material, further comprising an organic semiconductor (A).

The details of the reason why the organic semiconductor (A) exerts the improvement effect are unknown, but the organic semiconductor (A) having an appropriate electron conductivity acts on the surface of the positive electrode active material, and the electron conductivity is reduced. It is thought that the progress of the degradation reaction mainly occurring at the positive electrode active material-electrolyte interface under high-temperature environment was effectively suppressed while maintaining the high temperature environment. It is believed that it is acting as a stabilizer. In addition, the low-temperature characteristics are improved by having appropriate electron conductivity.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The organic semiconductor (A) used in the present invention is not particularly limited, and various properties such as powder and liquid can be used.
In mixing with the positive electrode active material, there is an advantage that handling is particularly easy and the production cost is low.

The specific resistance of the organic semiconductor used in the present invention is generally 10 ⁻⁴ Ω · cm or more, preferably 10 ⁻² Ω · cm.
Or more, more preferably 10 ² Ω · cm or more, particularly preferably 10 ⁵ Ω · cm or more, and usually 10 ²⁰ Ω · c
m, preferably 10 ¹⁸ Ω · cm or less, more preferably 10 ¹⁶ Ω · cm or less. If the specific resistivity is too low or too high, it may be difficult to obtain a desired improvement effect.

The structure of the organic semiconductor (A) used in the present invention is preferably an aromatic compound. By using an aromatic compound, appropriate electron conductivity can be ensured. More preferred are aromatic compounds having a condensed ring or aromatic compounds having four or more benzene rings in the molecule, and most preferred are aromatic polycyclic compounds in which four or more benzene rings are condensed. . On the other hand, the upper limit of the number of benzene rings in the aromatic compound is usually 30 and preferably 20.
And particularly preferred is 15. By condensing a large number of benzene rings or using a substance having a huge cyclic structure, the effect of the present invention is remarkably exhibited.

Further, it is also preferable that the structure has a heterocyclic ring having nitrogen or sulfur as a hetero atom. It is also preferable to bond a substituent (functional group) having an electron withdrawing group to a carbon atom constituting the ring. Organic semiconductor (A)
For example, Cs-pyrene, Cs-1,3,6,
8-tetranitropyrene, Cs-1,3,6,8-tetrachloropyrene, Cs-1,3,6,8-tetrabromopyrene, anthracene-1,3,5-trinitrobenzene (TNB) complex, biolanthrene -Br ₂ complex, biolanthrene-I ₂ complex, tetrathiafulvalene (TT
F) complexes, 7,7,8,8-tetracyanoquinodimethane (TCNQ) complexes, metal phthalocyanines such as copper phthalocyanine, coaterylene, 3,4,9,10-perylenetetracarboxylic diimide, chrysene, pentacene, coronene , Pyranthrene, pyranthrone, biolanthrene,
Biolantron, isobiolantron, ovalene, or the like can be used.

Among the above organic semiconductors, isoviolanthrone, biolanthrene, corterylene, 3,4,9,10
-Condensed polycyclic aromatic compounds such as perylene tetracarboxylic acid diimide and metal phthalocyanine are preferable, and when metal phthalocyanine is used, copper phthalocyanine, magnesium phthalocyanine, and dilithium phthalocyanine are particularly preferably used, and isoviolanthrone. 3,
Most preferred are 4,9,10-perylenetetracarboxylic diimide, copper phthalocyanine and magnesium phthalocyanine.

The above compounds may be used alone or in combination of two or more, or may be used in combination with other additives which are expected to have a synergistic effect. The reactivity of the compound can be adjusted by selecting a substituent. In the above-mentioned compounds, tautomers, if any, are included. The amount of the organic semiconductor (A) used is usually 0.0001 mol% or more, preferably 0.001 mol%, based on the lithium transition metal composite oxide.
Or more, more preferably 0.1 mol% or more, and usually 20 mol% or less, preferably 10 mol% or less,
More preferably, it is at most 5 mol%. When the amount used increases, the discharge capacity and the high-temperature cycle characteristics may decrease. On the contrary, when the amount decreases, the effect of improving the high-temperature cycle may be difficult to obtain.

In the present invention, the lithium transition metal composite oxide is used as an active material. In the present invention, the active material is a main material that causes an electromotive reaction of the battery, and means a material that can occlude and release Li ions. That is, the lithium transition metal composite oxide may be any material that can reversibly occlude and release Li as an active material.

As the transition metal used in the lithium transition metal composite oxide, manganese, nickel, cobalt,
Examples include iron, chromium, vanadium, titanium, and copper. Preferably, they are manganese, nickel and cobalt, particularly preferably manganese and nickel, most preferably manganese. Of course, a plurality of these can be used.

When these transition metals form a lithium transition metal composite oxide, a lithium manganese composite oxide,
Examples thereof include a lithium nickel composite oxide, a lithium cobalt composite oxide, a lithium iron composite oxide, a lithium chromium composite oxide, a lithium vanadium composite oxide, a lithium titanium composite oxide, and a lithium copper composite oxide. As a specific composition formula, for example, a general formula LiMn ₂ O ₄ , LiMnO
_{2, LiNiO 2, LiCoO 2,} LiFeO 2, LiCr
O ₂ , Li _{1 + x} V ₃ O ₈ , LiV ₂ O ₄ , LiTi ₂ O ₄ , Li
And the like compounds as represented by ₂ CuO _2, LiCuO _2. Among these lithium transition metal composite oxides, a lithium manganese composite oxide is preferable in that the effect of the present invention is remarkable, and particularly, a general formula LiMn ₂ O ₄
It is preferable to use a lithium manganese composite oxide having a spinel structure represented by

The above composition may have a small amount of oxygen deficiency and nonstoichiometry. Further, a part of the oxygen site may be replaced by sulfur or a halogen element. In the lithium transition metal composite oxide according to the present invention, a part of the site occupied by the transition metal may be replaced with an element other than the transition metal. As a result, the stability of the crystal structure can be improved, and by combining this with the compound, the high-temperature characteristics can be synergistically improved. This effect is particularly remarkable when a lithium manganese composite oxide is used.

At this time, the other element that replaces a part of the transition metal site (hereinafter, referred to as a substitution element) includes A
1, Ti, V, Cr, Mn, Fe, Co, Li, Ni,
Cu, Zn, Mg, Ga, Zr, etc., and preferably, Al, Cr, Fe, Co, Li, Ni, Mg, Ga,
More preferably, it is Al. The transition metal site is 2
It may be replaced by more than one kind of other element.

When a part of the manganese site of the lithium-manganese composite oxide is replaced with another element, the other element is
1, Ti, V, Cr, Fe, Co, Li, Ni, Cu,
It is preferably at least one element selected from the group consisting of Zn, Mg, Ga and Zr, and Al is particularly preferred. The substitution ratio by the substitution element is usually 2.5 mol% or more of the base transition metal element, preferably 5 mol% or more of the base transition metal element, and usually 30 mol% or less of the base transition metal element. , Preferably 20 mol% or less of the base transition metal element. 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.

The specific surface area of the lithium transition metal composite oxide used in the present invention is usually at least 0.01 m ² / g, preferably at least 0.3 m ² / g, more preferably at least 0.5 m ² / g, In addition, it is usually 10 m ² / g or less, preferably 5.
0 m ² / g or less, more preferably 3.0 m ² / g or less, particularly preferably 2.0 m ² / g or less. If the specific surface area is too small, the rate characteristics and the capacity will be reduced. If the specific surface area is too large, an undesirable reaction with the electrolytic solution or the like will be caused, and the cycle characteristics may be reduced. The measurement of the specific surface area follows the BET method.

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

In the present invention, when a lithium secondary battery is formed using the lithium transition metal composite oxide as an active material, the organic semiconductor (A) is further contained in the battery. That is, the organic semiconductor (A) is considered to act as a stabilizer for the electrolyte itself and the surface of the negative electrode, as well as to effectively suppress the degradation reaction at the interface between the positive electrode active material and the electrolyte. Although it may be present anywhere, it is preferable that it is contained in the positive electrode in order to sufficiently exhibit the effects of the present invention.

When the organic semiconductor (A) is present in the positive electrode, a positive electrode material containing the lithium transition metal composite oxide and the organic semiconductor (A) can be used. As a method for allowing the organic semiconductor (A) to be present in the positive electrode material containing the lithium transition metal composite oxide, a method using physical mixing,
The active material particles may be treated in the presence of the organic semiconductor (A) to form a coating of the organic semiconductor (A). In addition, as a method of treating the surface of the active material particles, coating by heat treatment or the like may be mentioned. However, depending on the treatment temperature at the time of coating, the organic semiconductor (A) may be lost or deteriorated, and the desired effect may be lost. There is a risk that it will. Therefore, when using this method, it is necessary to carefully select the coating treatment temperature. Therefore, among these methods,
It is preferred to use physical mixing. Physical mixing is not only a simple method without the above-mentioned temperature management, but also can exert the effects of the present invention sufficiently without fear of deterioration of the organic semiconductor (A). Physical mixing in the present invention means simply mixing a plurality of substances,
This means mixing without heat treatment at such a high temperature that the mixture is chemically changed. It is preferable to disperse the compound in a positive electrode material by stirring a plurality of substances.
Physical mixing may be dry mixing or wet mixing. For physical mixing, a mortar, a ball mill, a jet mill, a Loedige mixer, or the like can be used.

A lithium secondary battery is formed by a positive electrode, a negative electrode, an electrolyte layer and the like. The positive electrode according to the present invention contains a positive electrode material containing the lithium transition metal composite oxide and the organic semiconductor (A), and a binder. Also, usually
The positive electrode is obtained by forming a positive electrode layer containing the positive electrode material and a binder on a current collector. In the present invention, the lithium transition metal composite oxide in the positive electrode layer and the organic semiconductor (A)
Is preferably dispersed and present. By being dispersed, the effects of the present invention can be sufficiently exerted.

For example, the positive electrode layer is formed by kneading a lithium transition metal composite oxide, an organic semiconductor (A), a binder, and a conductive agent as necessary, and pressing the mixture on a positive electrode current collector. The slurry can be prepared by applying a slurry of the component with a solvent to a positive electrode current collector and drying. As described above, the lithium transition metal composite oxide and the organic semiconductor (A) may be physically mixed in advance before kneading or slurry preparation.

The positive electrode layer may further contain an active material capable of inserting and extracting lithium ions other than the lithium transition metal composite oxide, such as LiFePO ₄ . The ratio of the active material in the positive electrode layer is usually 10% by weight or more,
It is preferably at least 30% by weight, more preferably at least 50% by weight, usually at most 99.9% by weight, preferably at most 9% by weight.
9% by weight or less. If the amount is too large, the mechanical strength of the electrode tends to be inferior. If the amount is too small, the battery performance such as capacity tends to be inferior.

As the binder used for the positive electrode, for example, polyvinylidene fluoride, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, EPDM
(Ethylene-propylene-diene terpolymer), SB
R (styrene-butadiene rubber), NBR (acrylonitrile-butadiene rubber), fluorine rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose and the like. The proportion of the binder in the positive electrode layer is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 5% by weight or more, usually 80% by weight or less, preferably 60% by weight or less, more preferably It is at most 40% by weight, most preferably at most 10% by weight. If the proportion of the binder is too low, the active material cannot be sufficiently retained, the mechanical strength of the positive electrode becomes insufficient, and the battery performance such as cycle characteristics may be deteriorated. Sometimes.

The positive electrode layer usually contains a conductive agent to increase conductivity. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; carbon materials such as carbon black such as acetylene black; and amorphous carbon such as needle coke. The proportion of the conductive agent in the positive electrode is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably 1% by weight or more, and usually 50% by weight or less, preferably 30% by weight or less, It is preferably at most 15% by weight. If the proportion of the conductive agent is too low, the conductivity may be insufficient, while if it is too high, the battery capacity may be reduced.

The slurry solvent is not particularly limited as long as it dissolves or disperses the binder, but usually an organic solvent is used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyl triamine, NN
-Dimethylaminopropylamine, ethylene oxide,
Tetrahydrofuran and the like can be mentioned. In addition, the active material can be slurried with a latex such as SBR by adding a dispersant, a thickener and the like to water.

The thickness of the positive electrode layer is usually 1 to 1000 μm,
Preferably it is about 10 to 200 μm. If it is too thick, the conductivity tends to decrease, and if it is too thin, the capacity tends to decrease. As a material of the current collector used for the positive electrode, aluminum, stainless steel, nickel-plated steel, or the like is used, and aluminum is preferable. The thickness of the current collector is usually 1 to 1000 μm, preferably 5 to 500 μm
It is about. If the thickness is too large, the capacity of the lithium secondary battery as a whole decreases, and if it is too small, the mechanical strength may be insufficient.

The positive electrode layer obtained by coating and drying is preferably compacted by a roller press or the like in order to increase the packing density of the active material. As the active material of the negative electrode used for the negative electrode of the secondary battery of the present invention, a lithium alloy such as lithium or a lithium aluminum alloy may be used, but a carbon material capable of absorbing and releasing lithium with higher safety is used. preferable.

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 fibers, and the like.

Further, as the negative electrode active material, SnO, SnO
_Two, Sn_1-xM_xO (M = Hg, P, B, Si, Ge or
Is Sb, where 0 ≦ x <1), Sn_ThreeO_Two(OH)_Two , S
n_{3- x}M_xO_Two(OH)_Two(M = Mg, P, B, Si, G
e, Sb or Mn, provided that 0 ≦ x <3), LiSi
O_Two, SiO_TwoOr LiSnO_TwoEtc.
You. It should be noted that a mixture of two or more selected from these
It may be used as a pole active material.

The negative electrode is usually formed by forming a negative electrode layer on a current collector as in the case of the positive electrode. At this time, the same binder as that used for the positive electrode can be used as the binder, the conductive agent and the like used as needed, and the slurry solvent. As the current collector of the negative electrode, copper, nickel, stainless steel, nickel-plated steel, or the like is used, and copper is preferably used.

When a separator is used between the positive electrode and the negative electrode, a microporous polymer film is usually used, and the material is usually nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, What consists of polyolefin polymers, such as polyvinylidene fluoride, polypropylene, polyethylene, and polybutene, is used. The chemical and electrochemical stability of the separator is an important factor. In this respect, a polyolefin-based polymer is preferable, and it is preferable that the battery is made of polyethylene from the viewpoint of the self-closing temperature, which is one of the purposes of the battery separator.

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

As the electrolyte constituting the electrolyte layer in the lithium secondary battery of the present invention, for example, known organic electrolytes, solid polymer electrolytes, gel electrolytes, inorganic solid electrolytes and the like can be used. Organic electrolytes are 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-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, benzonitrile, butyronitrile, Valeronitrile, 1,2-
A single solvent such as dichloroethane, dimethylformamide, dimethylsulfoxide, trimethyl phosphate, triethyl phosphate, or a mixture of two or more solvents can be used.

The above organic solvent preferably contains a high dielectric constant solvent for dissociating the electrolyte. Here, the solvent having a high dielectric constant has a relative dielectric constant of 20 at 25 ° C.
The above compounds are meant. It is preferable that ethylene carbonate, propylene carbonate, and a compound in which a hydrogen atom thereof is replaced with another element such as halogen, an alkyl group, or the like in the high dielectric constant solvent be contained in the electrolytic solution. The proportion of the high dielectric constant compound in the electrolyte is preferably 20
% By weight, more preferably 30% by weight or more, most preferably 40% by weight or more. If the content of the compound is small, desired battery characteristics may not be obtained in some cases.

As a solute to be 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, LiN (SO_TwoCF_Three)_Two,
LiN (SO_TwoC_TwoF_Five)_Two, LiC (SO_TwoCF_Three)_Three, L
iN (SO_ThreeCF_Three)_TwoAnd the like. This
Two or more of these may be used. Also, CO_Two , N_Two
O, CO, SO_Two Such as gas and polysulfide S_x ^2-What
Enables efficient charge and discharge of lithium ions on the negative electrode surface
Additive that produces a good film
It may be added to a single or mixed solvent.

When a solid polymer electrolyte is used, a known polymer can be used as the polymer. In particular, it is preferable to use a polymer having high ion conductivity with respect to lithium ions. For example, polyethylene oxide, polypropylene oxide, polyethylene imine, and the like are preferably used. It is also possible to add the above-mentioned solvent to the polymer together with the above-mentioned solute and use it as a gel electrolyte.

When using an inorganic solid electrolyte,
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, 4.9LiI-3
4.1Li_TwoO-61B_TwoO_Five, 33.3Li_TwoO-66.
7SiO_TwoOxide glass such as 0.45LiI-0.3
7Li_TwoS-0.26B_TwoS_Three, 0.30LiI-0.4
2Li_TwoS-0.28SiS _TwoSulfide glass etc.
Can be Use at least one of these
Can be

[0042]

EXAMPLES The method of the present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the scope of the present invention. Example 1 Li _1.04 Mn _1.85 A as lithium transition metal composite oxide
l _0.11 O ₄ , a lithium manganese composite oxide having a cubic spinel structure in which a part of Mn sites is substituted by Li and Al, and copper phthalocyanine is added thereto in an amount of 1 mol% based on the lithium manganese composite oxide. And mixed with a mortar at room temperature to obtain a positive electrode material. The BET specific surface area of the lithium manganese composite oxide used here was 0.9 m ² / g, and the median diameter determined by laser diffraction particle size distribution measurement after ultrasonic dispersion for 5 minutes was 7.4 μm.

Example 2 A positive electrode material was obtained in the same manner as in Example 1, except that copper phthalocyanine was changed to magnesium phthalocyanine. Example 3 A positive electrode material was obtained in the same manner as in Example 1, except that copper phthalocyanine was changed to isobiolanthrone.

Example 4 In Example 1, copper phthalocyanine was added to 3,4,9,1
A positive electrode material was obtained in the same manner as in Example 1, except that 0-perylenetetracarboxylic acid diimide was used. Comparative Example 1 A positive electrode material was obtained in the same manner as in Example 1, except that the same lithium manganese composite oxide as in Example 1 was used as a positive electrode material, that is, copper phthalocyanine was not used.

Test Example (Evaluation of Battery) The batteries of Examples of the present invention and Comparative Examples were evaluated by the following methods. 1. Preparation of positive electrode and confirmation of capacity A mixture of 75% by weight of the positive electrode material, 20% by weight of acetylene black, and 5% by weight of polytetrafluoroethylene powder was thoroughly mixed in a mortar to form a thin sheet having a diameter of 9 mm. And a punch of 12 mmφ. At this time, the total weight was adjusted to be about 8 mmg and about 18 mg, respectively. This was pressed against an Al expanded metal to form a positive electrode.

Next, the capacity of the positive electrode was confirmed. That is, 9m
A battery cell was assembled with the positive electrode punched to mφ as a test electrode and Li metal as a counter electrode. 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
A constant current discharge of mA / cm ² , that is, a test for absorbing lithium ions in the positive electrode was performed at a lower limit of 3.2 V. The initial charge capacity per unit weight of the positive electrode active material at this time is Qs (C)
(MAh / g) and the initial discharge capacity is Qs (D) (mAh
/ G).

2. Preparation of Negative Electrode and Confirmation of Capacity A graphite powder (d002 = 3.35 °) having an average particle size of about 8 to 10 μm as a negative electrode active material and polyvinylidene fluoride as a binder were mixed in a weight ratio of 92.5: The mixture was weighed at a ratio of 7.5 and mixed in an N-methylpyrrolidone solution to prepare a negative electrode mixture slurry. 20 μm of this slurry
A negative electrode was applied to one side of a copper foil having a thickness, dried and evaporated to remove the solvent, punched out to a diameter of 12 mm, and pressed at 0.5 ton / cm ² .

A negative electrode active material was obtained by assembling a battery cell using the negative electrode as a test electrode and Li metal as a counter electrode, and performing a test at a lower limit of 0 V to occlude Li ions in the negative electrode at a constant current of 0.2 mA / cm ^2. The initial storage capacity per unit weight is Qf
(MAh / g). 3. Battery cell assembly Using a coin-shaped cell, battery performance was evaluated. That is,
Place the positive electrode punched to 12 mmφ on the positive electrode can,
A 25 μm porous polyethylene film was placed thereon as a separator, pressed with a polypropylene gasket, the above-mentioned negative electrode was placed, and a spacer for thickness adjustment was placed. Ethylene carbonate (EC) and lithium carbonate (DE) in which lithium fluorophosphate (LiPF ₆ ) is dissolved
A mixed solvent having a volume fraction of 3: 7 with C) was added to the inside of the battery to be sufficiently impregnated, and then the battery was sealed by mounting a negative electrode can.

At this time, the balance between the weight of the positive electrode active material and the weight of the negative electrode active material is almost the same.

[0050]

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

[0051]

## EQU2 ## 1 C [mA] = Qs (D) × amount of positive electrode active material [g]
/ [H] and the following test was conducted. First, a constant current of 0.1 at room temperature.
2C charge / discharge 2 cycles and constant current 1C charge / discharge 1 cycle are performed, and then constant current 0.2C charge / discharge 1 at a high temperature of 50 ° C.
Cycle and then 100 cycles of constant current 1C charge / discharge test. Note that the upper limit of charge is 4.2V and the lower limit voltage is 3.0.
V. FIG. 1 shows a change in the discharge capacity at the time of 100 cycles of constant current 1C charge / discharge measurement.

At this time, the ratio of the discharge capacity Qh (100) at the 100th cycle to the discharge capacity Qh (1) at the 100th cycle in the 1C charge / discharge 100 cycle test at 50 ° C. is defined as the high-temperature cycle capacity retention ratio P, ie,

[0053]

P [%] = {Qh (100) / Qh (1)} ×
The high-temperature characteristics of the batteries were compared using this value. The initial discharge capacity and the high-temperature cycle capacity retention ratio P in a 1C charge / discharge 100 cycle test at 50 ° C. in Examples and Comparative Examples.
Is shown in Table 1.

[0054]

[Table 1]

A comparison between the example and the comparative example (see FIG. 1 and Table 1) shows that the addition of the organic semiconductor (A) improves the cycle characteristics at high temperatures.

[0056]

According to the present invention, it is possible to provide a positive electrode material which is excellent in capacity and cycle characteristics, and which can be used in batteries having excellent safety and productivity. In particular, the cycle characteristics at high temperatures can be improved.

[Brief description of the drawings]

FIG. 1 is a cycle-discharge capacity correlation diagram of coin cells of Examples 1 to 4 and Comparative Example 1 of the present invention.

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Claims (18)

[Claims] 1. A positive electrode material for a lithium secondary battery, comprising a lithium transition metal composite oxide and an organic semiconductor (A). 2. The organic semiconductor (A) has a specific resistance of 10 ⁻² or more.
The positive electrode material for a lithium secondary battery according to claim 1, wherein the positive electrode material has a resistivity of 10 ¹⁶ Ω · cm. 3. The positive electrode material for a lithium secondary battery according to claim 1, wherein the organic semiconductor (A) comprises an aromatic compound. 4. The positive electrode material for a lithium secondary battery according to claim 1, wherein the organic semiconductor (A) is an aromatic compound having a condensed ring. 5. The positive electrode material for a lithium secondary battery according to claim 1, wherein the organic semiconductor (A) is an aromatic compound having four or more benzene rings in a molecule. 6. The positive electrode for a lithium secondary battery according to claim 1, wherein the organic semiconductor (A) is an aromatic polycyclic compound in which four or more benzene rings are condensed. material. 7. The organic semiconductor (A) is isobiolanthrone, biolanthrene, cortellylene, 3,4,9,10
The positive electrode material for a lithium secondary battery according to any one of claims 1 to 6, wherein the positive electrode material is at least one selected from the group consisting of -perylenetetracarboxylic diimide and metal phthalocyanine. 8. The positive electrode material for a lithium secondary battery according to claim 7, wherein the metal phthalocyanine is at least one of copper phthalocyanine, magnesium phthalocyanine, and dilithium phthalocyanine. 9. The method according to claim 1, wherein the lithium transition metal composite oxide and the organic semiconductor (A) are physically mixed.
9. The positive electrode material for a lithium secondary battery according to any one of items 1 to 8. 10. A lithium transition metal composite oxide,
The positive electrode material for a lithium secondary battery according to any one of claims 1 to 9, wherein a ratio of the organic semiconductor (A) is 0.1 to 5 mol%. 11. The positive electrode material for a lithium secondary battery according to claim 1, wherein the lithium transition metal composite oxide is a lithium manganese composite oxide. 12. The positive electrode material for a lithium secondary battery according to claim 11, wherein the lithium transition metal composite oxide is a lithium manganese composite oxide in which a part of a manganese site is substituted by another element. . 13. Another element that partially substitutes for a manganese site is Al, Ti, V, Cr, Fe, Co, Li, Ni,
The positive electrode material for a lithium secondary battery according to claim 12, wherein the positive electrode material is at least one element selected from the group consisting of Cu, Zn, Mg, Ga, and Zr. 14. A positive electrode for a lithium secondary battery, comprising the positive electrode material for a lithium secondary battery according to claim 1 and a binder. 15. The positive electrode for a lithium secondary battery according to claim 14, wherein the lithium transition metal composite oxide and the organic semiconductor (A) are dispersed in the positive electrode. 16. A lithium secondary battery comprising at least the positive electrode for a lithium secondary battery according to claim 14 or 15, a negative electrode and an electrolyte. 17. The lithium secondary battery according to claim 16, wherein the active material of the negative electrode is a carbon material. 18. A lithium secondary battery using a lithium transition metal composite oxide as a positive electrode active material, further comprising an organic semiconductor (A).