JP2003045414A - Electrode and lithium secondary battery using the same - Google Patents

Abstract

(57) [Abstract] [Object] An electrode formed on a current collector surface as an electrode active material-containing layer of a layered lithium-based composite oxide, which is suitably used as a positive electrode of a lithium secondary battery. Provided are an electrode which does not decrease and has excellent rate characteristics, and a lithium secondary battery using the electrode as a positive electrode. The present invention is an electrode comprising an electrode active material-containing layer formed on a current collector surface, wherein the electrode active material-containing layer contains the following components (A), (B), and (C) An electrode having a density of 2.0 to 2.7 g / cm ³ , and a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte including the electrode. (A) a layered lithium-based composite oxide comprising lithium atoms (Li) and at least two selected from transition metal atoms consisting of nickel (Ni), manganese (Mn), and cobalt (Co) ( B) Conductive agent (C) Binder

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electrode having an electrode active material-containing layer of a layered lithium-based composite oxide formed on the surface of a current collector, and a lithium secondary battery using the electrode.

[0002]

2. Description of the Related Art Conventionally, lithium secondary batteries are excellent in high energy density and high output density and can be made compact and lightweight, so that they are used as a power source for portable devices such as laptop computers, mobile phones and handy video cameras. In addition to showing rapid growth, it is also attracting attention as a power source for electric vehicles and the like.

The positive electrode of the lithium secondary battery includes a current collector and a positive electrode active material formed on the surface of the current collector.
A positive electrode active material-containing layer containing a conductive agent and a binder, and as the positive electrode active material, a composite oxide of lithium and a transition metal such as cobalt, nickel or manganese has high performance battery characteristics. Since it can be obtained, it has been put to practical use.

Furthermore, for the purpose of stabilizing the composite oxide, increasing the capacity of the battery or improving the battery characteristics at high temperature, etc., considering the economical efficiency, etc., a part of these transition metal atoms is considered. Research on various complex oxides substituted with other metal atoms is also underway. Among them, LiNi _1-a Mn _a O ₂
Layered lithium nickel manganese composite oxides represented by (0 <a <1) have attracted attention, and for example, Solid State Ionics
311-318 (1992), J. Mater. Chem. 1149-1155 (1996),
J. Power Sources 629-633 (1997), J. Power Sources 4
6-53 (1998) et al. Reported a single-phase synthesis example of a layered composite oxide with 0 ≦ a ≦ 0.5, and the 41st Battery Symposium 2D20
(2000) reported a single-phase synthesis example in which a = 0.5, that is, Ni / Mn = 1.

On the other hand, the density of the positive electrode active material-containing layer is usually 3.0 g / cm ³ since a high energy density is required.
As described above, according to the study by the present inventors, Ni, M including the above layered lithium-based composite oxide is included.
In the layered lithium-based composite oxide containing at least two kinds selected from the group of transition metal atoms consisting of n and Co, the density conventionally used decreases the discharge capacity under a large current and deteriorates the rate characteristics. It turned out to be an inherent problem. The discharge capacity under a large current is particularly required at the time of starting in a high power tool, an electric vehicle or the like, which has recently received a great deal of attention, and the decrease thereof is a serious problem.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems in the layered lithium-based composite oxide as the prior art. Therefore, the present invention provides a layered lithium on the surface of the current collector. An electrode that is formed as an electrode active material-containing layer of a system-based complex oxide and is suitably used as a positive electrode of a lithium secondary battery, which does not reduce the initial discharge capacity and has excellent rate characteristics, and a positive electrode for the electrode. The purpose of the present invention is to provide a lithium secondary battery used as.

[0007]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that the density of the electrode active material-containing layer of the layered lithium-based composite oxide is higher than the density generally used conventionally. The present invention has been found to be able to achieve the above-mentioned object by making the specific range to be much smaller, and accordingly, the present invention provides an electrode having an electrode active material-containing layer formed on the surface of a current collector. Then, the electrode active material-containing layer contains the following component (A), component (B), and component (C), and its density is 2.0 to 2.7 g / c.
m ³ , an electrode, and a positive electrode, a negative electrode composed of the electrode,
And a lithium secondary battery composed of an electrolyte. (A) A layered lithium-based composite oxide containing a lithium atom (Li) and at least two kinds selected from a transition metal atom group consisting of nickel (Ni), manganese (Mn), and cobalt (Co) ( B) Conductive agent (C) Binder

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The layered lithium-based composite oxide of the component (A) constituting the electrode active material-containing layer in the electrode of the present invention includes lithium atom (Li) and nickel (N).
A complex oxide containing i), at least two kinds selected from the group of transition metal atoms consisting of manganese (Mn), and cobalt (Co) and represented by the following general formula (I) is preferable.

[0009]

Embedded image Li _v Ni _w Mn _x Co _y Q _z O ₂ (I)

[In the formula (I), v is 0.8 ≦ v ≦ 1.2
And w, x, y, and z are at least two of w, x, and y are greater than 0, and 0 ≦ z ≦ 0.3,
And 0.8 is a number satisfying the relationship of 0.8 ≦ w + x + y + z ≦ 1.2, and Q is Be, B, Mg, Al, Ca, Sc,
Any one selected from the atomic group consisting of Ti, V, Cr, Fe, Cu, Zn, and Ga is shown. ]

In the above formula (I), v is 0.9≤v
≦ 1.1 is preferable, and 0.95 ≦ v ≦ 1.05
Is more preferable. Also, w + x + y + z is 0.
It is preferable that 9 ≦ w + x + y + z ≦ 1.1, and 0.
More preferably, 95 ≦ w + x + y + z ≦ 1.05. When v exceeds the above range and w + x + y + z is less than the above range, the crystal structure of the layered composite oxide becomes unstable, and the battery capacity tends to decrease when used in a battery. On the other hand, v is less than the above range. And w + x + y + z
However, if the above range is exceeded, the amount of lithium that can be involved in charging / discharging of the battery decreases, and the battery capacity tends to decrease.

Further, w, x, y are 0 <w ≦ 0.7, 0 <
It is preferable that x ≦ 0.7 and 0 <y ≦ 0.7, and
It is preferable that 0.65 ≦ w + x ≦ 1.0, and 0.7
More preferably, 5 ≦ w + x ≦ 1.0. If w + x is less than the above range, the battery capacity tends to decrease when used in a battery, while if it exceeds the above range, it is disadvantageous in terms of economy. Furthermore, 0.7 ≦ w / x ≦ 9 is preferable, 0.8 ≦ w / x ≦ 1.2 is more preferable, and 0.9 ≦ w / x ≦ 1.1 is preferable. More preferably, 0.95 ≦ w / x ≦ 1.05 is particularly preferable. If w / x is less than the above range, it tends to be difficult to obtain a layered composite oxide in a single phase, while if it exceeds the above range, it is disadvantageous in terms of economy.

Further, z is preferably 0≤z≤0.25, and more preferably 0≤z≤0.2. When z exceeds the above range, the battery capacity tends to decrease when used in a battery. Incidentally, as Q, Mg, A
1, Ca, Cr and Fe are preferable, and Al is particularly preferable.

In the present invention, the layered lithium-based composite oxide of the component (A) has an average primary particle diameter measured by SEM observation of usually 0.01 μm or more, preferably 0.
02 μm or more, more preferably 0.1 μm or more,
It is usually 30 μm or less, preferably 5 μm or less, and more preferably 25 μm or less. The average secondary particle diameter measured by a laser diffraction / scattering type particle size distribution analyzer is usually 1 μm or more, preferably 4 μm or more, and usually 50 μm or less, preferably 40 μm or less. Further, the specific surface area by the BET method is usually 0.1 m ² /
g or more, preferably 0.5 m ² / g or more, more preferably 2.0 m ² / g or more, usually 10.0 m ² / g or less, preferably 8.0 m ² / g or less, more preferably 7. It is 0 m ² / g or less.

The layered lithium-based composite oxide of the component (A) in the present invention is, for example, a lithium source compound and at least two kinds selected from the group consisting of a nickel source compound, a manganese source compound, and a cobalt source compound. Further, if necessary, a magnesium source compound, an aluminum source compound, a calcium source compound, a chromium source compound, and an iron source compound, and the like, after pulverizing and mixing using a dry pulverizer, a dry method of firing, or, These compounds are added to a medium such as water and pulverized and mixed by using a wet pulverizer such as a medium agitation pulverizer, or after pulverizing these compounds by a dry pulverizer, water and the like A slurry prepared by a method such as mixing in a medium is dried by spray drying or the like, and can be manufactured as a powder by a wet method of firing, In the invention, preferably by the latter wet method.

Here, in the above-mentioned preferred wet method, as the solid content concentration of the entire compound in the slurry, the powder particle diameter formed by subsequent drying such as spray drying is ensured within an optimum range. In the above, it is usually 10% by weight or more, preferably 12.5% by weight or more, and in order to secure a uniform slurry, it is usually 50% by weight or less, preferably 35% by weight or less.

The average particle size of each compound in the slurry is usually a value measured by a laser diffraction / scattering type particle size distribution measuring device in order to secure reactivity in subsequent firing and high bulk density. 2 μm or less, preferably 1 μm or less, more preferably 0.5 μm or less,
From the viewpoint of economy, the thickness is usually 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more.

The viscosity of the slurry is a value measured by a BM type viscometer, and is usually 50 mPa · sec in order to secure the powder particle diameter formed by the subsequent drying such as spray drying in an optimum range. Or more, preferably 100 mPa
-Seconds or more, more preferably 200 mPa-seconds or more,
Moreover, in order to ensure the handling of the slurry, it is usually 3000 m.
Pa · sec or less, preferably 2000 mPa · sec or less, and more preferably 1600 mPa · sec or less.

Further, here, a lithium source compound, a nickel source compound, a manganese source compound, and a cobalt source compound,
Also, as the magnesium source compound, the aluminum source compound, the calcium source compound, the chromium source compound, the iron source compound and the like, each oxide of lithium, nickel, manganese, cobalt, magnesium, aluminium, calcium, chromium and iron, Hydroxide, carbonate, nitrate,
Examples thereof include sulfates, oxalates, carboxylates, alkylates, and halides, and among these, dispersion or solubility in a medium in slurry formation, reactivity to complex oxides, and NO during firing. It is selected in consideration of non-occurrence of _x , SO _{x and the} like.

Specific examples of the lithium source compound include Li ₂ O, LiOH, LiOH.H ₂ O,
Li ₂ CO ₃ , LiNO ₃ , LiOCOCH ₃ , Li ₃
(OCOC) ₃ H ₄₀ H, LiCH ₃ , LiC ₂ H ₅ ,
LiCl, LiI, etc. are mentioned, of which LiOH.H ₂
O, Li ₂ CO ₃ , LiNO ₃ , and LiCH ₃ CO ₂ are preferable, and LiOH.H ₂ O is particularly preferable.

Specific examples of the nickel source compound include
Is, for example, NiO, Ni (OH) ₂, NiOOH, N
iCO₃・ 2Ni (OH)₂・ 4H₂O, Ni (N
O₃)₂・ 6H₂O, NiSO_Four, NiSO_Four・ 6H₂
O, Ni (OCO)₂・ 2H₂O, Ni (OCOCH
₃)₂, NiCl₂Etc., among them, NiO, Ni
(OH)₂, NiOOH, NiCO₃・ 2Ni (OH)
₂・ 4H₂O, NiC₂O _Four・ 2H₂O is preferred, N
iO, Ni (OH)₂, NiOOH are particularly preferred.

Specific examples of the manganese source include
For example, MnO₂, Mn₂O₃, Mn ₃O_Four, MnOO
H, MnCO₃, Mn (NO₃)₂, MnSO_Four, Mn
(OCOCH₃)₂, Mn (OCOCH₃)₃, Mn₃
[(OCOC)₃H_Four0H]₂, MnCl₂, MnCi
₃And the like, among which MnO₂, Mn₂O₃, Mn₃
O_Four, MnOOH is preferred, and MnO₂, Mn₂O₃,
Mn₃O_FourIs particularly preferable.

Specific examples of the cobalt source compound include CoO, Co ₂ O ₃ , Co ₃ O ₄ and Co.
_{(OH) 2, Co (NO} 3) 2 · 6H 2 O, Co (SO
_{4) 2 · 7H 2 0,} Co (OCOCH 3) 2 · 4H
₂ O, CoCl _2, etc., among which CoO, Co ₂
O ₃ , Co ₃ O ₄ , and Co (OH) ₂ are preferable, and Co
(OH) ₂ is particularly preferred.

Specific examples of the magnesium source compound include MgO, Mg (OH) ₂ and Mg (NO).
_{3) 2 · 6H 2 O,} MgSO 4, Mg (OCO) 2 · 2
_{H 2 O, Mg (OCOCH 3} ) 2 · 4H 2 O, MgCl
_{2, and the} like, of which, MgO and Mg (OH) ₂ are preferable, and Mg (OH) ₂ is particularly preferable.

Specific examples of the aluminum source compound include Al ₂ O ₃ , Al (OH) ₃ and AlO.
_{OH, Al (NO 3) 3} · 9H 2 O, Ai 2 (SO 4)
₃ , AlCl _{3 and the} like, among which Al ₂ O ₃ , Al
(OH) ₃ and AlOOH are preferable, and AlOOH is particularly preferable.

Specific examples of the calcium source compound include CaO, Ca (OH) ₂ , CaCO ₃ ,
_{Ca (NO 3) 2 · 4H} 2 O, CaSO 4 · 2H 2 O,
Ca (OCO) ₂ · H ₂ O, Ca (OCOCH ₃ ) ₂ ·
H ₂ O, CaCl _{2 and the} like can be mentioned. Among them, CaO, Ca
(OH) ₂ and CaCO ₃ are preferable, and Ca (OH) ₂ is particularly preferable.

As the chromium source compound,
Is, for example, CrO, CrO₂, Cr ₂O₃, Cr (O
H)₂, Cr₂O₃・ NH₂O, CrSO_Four・ 7H
₂O, Cr ₂(SO_Four)₃, Cr (OCOCH₃)₂・
2H₂O, Cr (OCOCH₃)₃, CrCl₂, Cr
Cl₃Etc. Among them, among them, CrO, CrO₂, Cr₂
O₃, Cr (OH)₂, Cr₂O₃・ NH₂O is preferred
CrO, CrO₂, Cr ₂O₃Is particularly preferable.

Specific examples of the iron source compound include
For example, Fe₂O₃, Fe₃O_Four, FeOOH, Fe (N
O₃)₃・ 9H₂O, FeSO_Four・ 7H₂O, Fe
₂(SO _Four)₃・ NH₂O, Fe (OCO)₂・ 2H₂
O, FeCl₂, FeCl₃Etc., among which, Fe
₂O₃, Fe₃O_Four, FeOOH is preferable, and Fe₂O
₃, FeOOH are particularly preferred.

In the wet method, which is preferable,
Spray drying for drying the crushed and mixed slurry is a known drying method in which the slurry is sprayed and dispersed in a heated gas stream and rapidly dried while being conveyed by the gas stream to obtain a powder. In the present invention, the method of injecting the slurry by the pressurized gas from the tip of the nozzle is preferable, and the nozzle is not particularly limited, but, for example, as described in Japanese Patent No. 2977080. A nozzle having a triple pipe structure that injects a pressurized gas from the center and the outer periphery and injects a slurry in a ring shape from the inner periphery is preferable, and as the pressurized gas, air, nitrogen or the like is used. The gas linear velocity is usually 100 m /
Second or more, preferably 200 m / sec or more, more preferably 300 m / sec or more, and usually 1000 m / sec or less. Also, the heated gas flow is usually 50 ° C or higher,
It is preferable to use heated air, nitrogen, etc., which has a temperature of preferably 70 ° C. or higher and usually 120 ° C. or lower, preferably 100 ° C. or lower, as a gas flow down-flowed from the upper part to the lower part. It is preferable that the slurry is sprayed in a direction orthogonal to the gas flow with the spraying direction being horizontal.

By this spray drying, a spherical powder as a pulverized mixture of the above-mentioned compounds is obtained. The average particle diameter of the powder can be controlled by the above-mentioned spraying method, nozzle shape, pressurized gas injection rate, slurry supply rate, heated gas flow temperature, etc., but with a laser diffraction / scattering particle size distribution measuring device. The measured value is preferably 50μ
m or less, more preferably 30 μm or less, usually 4 μm
Or more, preferably 5 μm or more.

The powder obtained by the spray drying is, for example, in an apparatus such as a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln or the like, in an oxygen-containing gas such as air or in an oxygen gas atmosphere, or nitrogen, argon. In an inert gas atmosphere such as
Preferably, it is heat-treated and baked in an oxygen-containing gas or oxygen gas atmosphere.

The firing temperature at that time is usually 700 ° C. or higher, preferably 750 ° C. or higher, more preferably 800 ° C. or higher in order to ensure reactivity, and a layered composite oxide having no defects is formed. Above, usually below 1050 ° C,
The temperature is preferably 1000 ° C. or lower, more preferably 950 ° C. or lower, and the heating time at that time is 0.5 to 5
It is preferable that the heating time is about 0 hours, and after the heat treatment, the material is gradually cooled at a rate of 5 ° C./minute or less.

As the conductive agent of the component (B) which constitutes the electrode active material-containing layer in the electrode of the present invention, a conventionally known one is used, and specifically, for example, graphite such as natural graphite or artificial graphite, Examples thereof include carbon black such as acetylene black and Ketjen black, and carbonaceous fine particles such as amorphous carbon such as needle coke.

Further, as the binder of the component (C) which constitutes the electrode active material-containing layer in the electrode of the present invention, conventionally known binders are used, and specifically, for example, polyvinylidene fluoride. , Polytetrafluoroethylene,
Examples thereof include resins such as polymethylmethacrylate and polyethylene, styrene-butadiene rubber, acrylonitrile-butadiene rubber, rubber such as ethylene-propylene rubber and fluorine rubber, and polymeric substances such as polyvinyl acetate and cellulose.

The above (A) in the electrode active material-containing layer
The respective content ratios of the layered lithium-based composite oxide of the component, the conductive agent of the component (B), and the binder of the component (C) are
The component (A) is usually 10% by weight or more, preferably 30% by weight in order to secure battery characteristics such as battery capacity.
The above is more preferably 50% by weight or more, particularly preferably 60% by weight or more, and usually 99% by weight or less, preferably 97% by weight in order to secure the mechanical strength of the electrode.
Hereafter, it is more preferably 95% by weight or less. The component (B) is usually 0.01% by weight or more, preferably 0.1% by weight in order to secure battery characteristics such as conductivity.
As described above, more preferably 1% by weight or more, and usually 50% by weight or less, preferably 30% by weight or less, more preferably 20% by weight or less in order to secure battery characteristics such as battery capacity. Further, the component (C) is usually 0.1% by weight or more, preferably 1% by weight or more, more preferably 3% by weight or more, particularly preferably 5% in order to secure the mechanical strength of the electrode. In order to secure battery characteristics such as battery capacity and conductivity, the content is usually 80% by weight or less, preferably 60% by weight or less, more preferably 30% by weight or less,
It is particularly preferably 20% by weight or less. In the present invention, the positive electrode active material-containing composition may further contain, as the positive electrode active material, an active material capable of inserting and extracting lithium ions such as LiFePO ₄ .

The electrode of the present invention is prepared by a conventionally known method.
No coating liquid in which the layered lithium-based composite oxide of the component (A) as an electrode active material, the conductive agent of the component (B), and the binder of the component (C) are dispersed in a solvent. The coating solution is applied to the surface of the current collector, dried, and then preferably subjected to consolidation treatment by a uniaxial press or a roll press to form an electrode active material-containing layer. It is preferably used as a positive electrode.

Examples of the solvent used here include ether solvents such as ethylene oxide and tetrahydrofuran, ketone solvents such as methyl ethyl ketone and cyclohexanone, ester solvents such as methyl acetate and methyl acrylate, diethyltriamine, N, N. -Amine-based solvents such as dimethylaminopropylamine, aprotic polar solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, and the like.

The current collector is usually made of aluminum, stainless steel, nickel-plated steel or the like and has a thickness of 1 to 1.
A foil having a thickness of 000 μm, preferably 5 to 500 μm, and more preferably 5 to 100 μm can be used, and an aluminum foil is preferable as a current collector for the positive electrode. The thickness of the electrode active material-containing layer in the positive electrode is usually 1 to 1000 μm, preferably 5 to 200 μm.

The electrode active material-containing layer in the electrode of the present invention contains the layered lithium-based composite oxide of the component (A), the conductive agent of the component (B), and the binder of the component (C). Te becomes, as essential that the density of 2.0~2.7g / cm ^3, it is preferable density of 2.2~2.7g / cm ^3, 2.3~2.7g / cm More preferably, it is ³ . If the density is less than the above range, the discharge capacity at low current density will decrease, while if it exceeds the above range, the discharge capacity at high current density will decrease.

The density of the electrode active material-containing layer can be controlled by the type and shape of the components (A) to (C), the content ratio, and the forming conditions on the surface of the current collector.
For example, as described above, when the electrode active material-containing layer is formed by applying the coating liquid on the surface of the current collector, drying, and then performing the consolidation treatment, the conditions of the electrode active material-containing layer and the consolidation, particularly It can be easily controlled by the pressing pressure at the time of consolidation, and the higher the pressing pressure, the higher the density tends to be.
As the layer thickness increases, the density tends to decrease even with the same pressing pressure. Since the relationship between the pressing pressure and the density is not necessarily linear, it is preferable to previously grasp the relationship between the pressing pressure and the density in the constituent components of the layer and determine the pressing pressure for obtaining the desired density.

In the present invention, the electrode obtained as described above serves as a positive electrode, and a negative electrode and an electrolyte constitute a lithium secondary battery.

Here, the negative electrode is formed by a conventionally known method.
The negative electrode active material is used as a coating liquid in which a binder is dispersed in a solvent, and the coating liquid is applied to the surface of the current collector and dried,
Preferably, a negative electrode is formed by forming a negative electrode active material-containing layer on the surface of the current collector by performing a consolidation treatment by a uniaxial press, a roll press or the like.

Here, as the negative electrode active material used,
For example, lithium, lithium aluminum alloy, graphite,
Coal and petroleum coke carbides, coal and petroleum
Ji carbide, needle coke, pitch coke, feather
Carbides such as knoll resin and crystalline cellulose, furnace
Carbon black such as rack and acetylene black, and
, SnO, SnO₂, Sn_1-xM_xO (M is Hg,
P, B, Si, Ge, or Sb, and x is 0 ≦ x <1
Is. ), Sn₃O₂(OH)₂, Sn_3-xM _xO₂
(OH)₂(M is Mg, P, B, Si, Ge, Sb, or
Is Mn and x is 0 ≦ x <3. ), LiSiO
₂, SiO₂, LiSnO₂Etc., and also binding
The same agents and solvents as those used for forming the positive electrode are listed.
You can The current collectors are copper, nickel, stainless steel.
Foils such as stainless steel, nickel-plated steel, etc.
Copper foil is preferable as the electric body.

As the electrolyte, a conventionally known organic electrolyte solution, for example, an electrolyte dissolved in an organic solvent, or
Polymer solid electrolytes, gel electrolytes, inorganic solid electrolytes and the like are used, among which organic electrolytes are preferred.

Examples of the electrolyte used for the organic electrolytic solution include LiCl, LiBr, LiClO ₄ , Li
AsF ₆ , LiPF ₆ , LiBF ₄ , LiB (C
₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , L
iN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C
₂ F ₅ ) ₂ , LiN (SO ₃ CF ₃ ) ₂ , LiC (SO
₂ CF ₃ ) _{3 and the} like.

The organic solvent used is, for example, diethyl ether, 1,2-dimethoxyethane,
1,2-diethoxyethane, tetrahydrofuran, 2-
Methyl tetrahydrofuran, 1,4-dioxane, 1,
Ethers such as 3-dioxolane and 4-methyl-1,3-dioxolane, ketones such as 4-methyl-2-pentanone, esters such as methyl formate, methyl acetate and methyl propionate, dimethyl carbonate,
Carbonates such as diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate, lactones such as γ-butyrolactone and γ-valerolactone, halogenated hydrocarbons such as 1,2-dichloroethane and sulfolane. , Sulfolane compounds such as methylsulfolane, nitriles such as acetonitrile, propionitrile, butyronitrile, valeronitrile and benzonitrile, amines such as diethylamine, ethylenediamine and triethanolamine, phosphorus such as trimethyl phosphate and triethyl phosphate. Examples thereof include aprotic polar solvents such as acid esters, N, N-dimethylformamide, N-methylpyrrolidone and dimethylsulfoxide.

Among the organic solvents mentioned above,
A high-dielectric-constant solvent having a relative dielectric constant of 20 or more at 25 ° C., such as ethylene carbonate, propylene carbonate, and a compound in which a hydrogen atom thereof is substituted with a halogen atom, an alkyl group, or the like, is preferable, and it occupies in the organic solvent. The proportion of the high dielectric constant solvent is preferably 20% by weight or more, more preferably 30% by weight or more,
It is particularly preferable that the amount is 40% by weight or more.

In the lithium secondary battery, if necessary, a separator may be interposed between the positive electrode and the negative electrode. The separator may be a polyolefin such as polyethylene or polypropylene, polyvinylidene fluoride, or poly (vinylidene fluoride). Tetrafluoroethylene, polyester,
Microporous films of polymers such as polyamide, polysulfone, polyacrylonitrile, cellulose and cellulose acetate, and non-woven fabric filters such as polymer fibers and glass fibers thereof are used.

Among them, in the present invention, a polyethylene microporous film is preferable, and the polyethylene has a molecular weight of preferably 500,000 or more, and more preferably 1,000,000 or more in order to secure shape retention at high temperature. Particularly preferably, it is 1.5 million or more, and in order to secure the microporous occluding property at high temperature, preferably 5 million or less, more preferably 4 million or less, particularly preferably 3 million or less, ultra high molecular weight polyethylene is preferable. .

[0050]

EXAMPLES The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

<(A) Production Example of Layered Lithium Composite Oxide> Lithium hydroxide monohydrate [LiOH.H ₂ O] as a lithium source compound, nickel hydroxide [Ni (OH) as a nickel source compound. ₂ ], manganese trioxide [Mn ₂ O ₃ ] as a manganese source compound, and cobalt hydroxide [Co (OH) ₂ ] as a cobalt source compound,
The molar ratio of each atom in the finally obtained layered lithium nickel manganese cobalt composite oxide is lithium atom [Li]: nickel atom [Ni]: manganese atom [M
n]: cobalt atom [Co] = 1.00: 0.45:
An amount of 0.45: 0.10 was added to pure water to prepare a slurry having a solid content concentration of 12.5% by weight, and this slurry was circulated medium agitation type wet pulverizer (manufactured by Shinmaru Enterprises Co., Ltd.). "Dyno-mill KD-20B type") and mixed until about 6 hours until the average particle size of each compound in the slurry reaches 0.3 μm as a value measured by a laser diffraction / scattering particle size distribution analyzer. Wet milled.

Then, the obtained slurry was down-flowed with a spray dryer ("Four fluid nozzle type spray dryer" manufactured by Fujisaki Electric Co., Ltd.) at a flow rate of 1.2 m ³ / min and heated to 90 ° C. Jetted from the nozzle with 1.3 m ³ / min of pressurized air in a direction orthogonal to the flow,
After drying by spray drying, the obtained powder particles are calcined in air at 900 ° C. for 10 hours to give a molar ratio of lithium atom [Li]: nickel atom [Ni]: manganese atom [Mn]: Cobalt atom [Co] = 1.0
A layered lithium nickel manganese cobalt-based composite oxide powder of 0: 0.45: 0.45: 0.10 was produced.

The obtained layered lithium nickel manganese cobalt-based composite oxide powder was a particle having a substantially spherical shape, and when powder X-ray diffraction was measured, it was a rhombohedral layered lithium nickel-manganese-cobalt composite oxide. It was confirmed. Further, the specific surface area measured by the BET method using a fully automatic powder specific surface area measuring device (“AMS8000 type” manufactured by Okura Riken) was 3.4 m ² / g.

Examples 1-2, Comparative Examples 1-2 Layered lithium nickel manganese cobalt composite oxide powders obtained in the above production examples, acetylene black as a conductive agent ("Denka Black" manufactured by Denki Kagaku Kogyo KK), as well as,
Polyvinylidene fluoride powder as a binder is
An amount of 0% by weight: 5% by weight: 5% by weight was added to N-methylpyrrolidone and mixed to form a coating solution. The coating solution was applied to one side of an aluminum foil (thickness 20 μm) and dried. After that, it was punched out into a circle having a diameter of 12 mm, and the density as an electrode active material-containing layer was 1.76 g / cm ³ , by performing a consolidation treatment by changing the pressure with a press.
2.23 g / cm ³ , 2.34 g / cm ³ , and 2.7
Four kinds of positive electrodes of 2 g / cm ³ were prepared.

Subsequently, a diameter of 16 mm was placed on the positive electrode can.
An aluminum expanded metal was placed thereon, and 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) was dissolved as an electrolyte in a mixed solvent of ethylene carbonate and diethyl carbonate (volume ratio 3: 7). The positive electrode in which the electrolytic solution was sufficiently impregnated under reduced pressure was placed with the electrode active material-containing layer on the upper side, and a microporous polyethylene film (thickness 25 μm) as a separator was placed on the positive electrode. After pressing with a gasket made of metal, a negative electrode having a diameter of 16 mm and a thickness of 0.5 mm of metallic lithium was placed thereon, and a spacer for adjusting the thickness was further placed thereon. Then, a negative electrode can was placed on the container and the container was sealed to prepare a coin cell.

0.5 m for the obtained coin type cell
With a constant current of A / cm ² , a charge upper limit voltage of 4.3 V, a discharge lower limit voltage of 3.0 V, a charge / discharge 2 cycle test was conducted, and then the 3rd to 8th cycles were conducted at 0.5 mA /
constant current charging ^{cm 2, 1mA / cm 2,} 3mA / c
^{m 2, 5mA / cm 2,} 7mA / cm 2, 9mA / cm
² and a discharge of 11 mA / cm ² were tested. At this time, the discharge capacity (mAh / g) at 0.5 mA / cm ² in the first cycle, and 11 mA / c in the eighth cycle
The discharge capacity (mAh / g) at m ² was measured, and the results are shown in Table 1.
It was shown to.

[0057]

[Table 1]

[0058]

According to the present invention, a layered lithium-based composite oxide is formed on the surface of a current collector as an electrode active material-containing layer,
An electrode that is preferably used as a positive electrode of a lithium secondary battery, does not have a reduction in initial discharge capacity, is excellent in rate characteristics, and an object thereof is to provide a lithium secondary battery using the electrode as a positive electrode. To do.

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 4G048 AA04 AA05 AC06 AD06                 5H029 AJ02 AJ03 AK03 AL02 AL03                       AL06 AL07 AL08 AL12 AM00                       AM02 AM03 AM04 AM05 AM07                       AM12 AM16 DJ08 DJ17 EJ04                       EJ12 EJ14 HJ01 HJ02 HJ08                 5H050 AA02 AA08 BA16 BA17 CA08                       CA09 CB02 CB03 CB07 CB08                       CB09 CB12 DA10 DA11 EA10                       EA24 HA01 HA02 HA08

Claims (5)

[Claims] 1. An electrode comprising an electrode active material-containing layer formed on the surface of a current collector, wherein the electrode active material-containing layer comprises the following components (A), (B) and (C): And an electrode having a density of 2.0 to 2.7 g / cm ³ . (A) A layered lithium-based composite oxide containing lithium (Li) atoms and at least two kinds selected from a transition metal atom group consisting of nickel (Ni), manganese (Mn), and cobalt (Co) ( B) Conductive agent (C) Binder 2. The electrode according to claim 1, wherein the layered lithium-based composite oxide of the component (A) is a composite oxide represented by the following general formula (I). Embedded image Li _v Ni _w Mn _x Co _y Q _z O ₂ (I) [In the formula (I), v is a number of 0.8 ≦ v ≦ 1.2,
w, x, y, and z are such that at least two of w, x, and y are greater than 0, and 0 ≦ z ≦ 0.3 and 0.8.
Is a number that satisfies the relationship of ≦ w + x + y + z ≦ 1.2, and Q
Is Be, B, Mg, Al, Ca, Sc, Ti, V, C
Any one selected from the atomic group consisting of r, Fe, Cu, Zn, and Ga is shown. ] 3. The w and x in the general formula (I) are 0.
The electrode according to claim 2, which is larger and satisfies the relationship of 0.7 ≦ w / x ≦ 9.0. 4. The total amount of component (A) is 10 to 10.
99% by weight, 0.01 to 50% by weight of component (B),
The electrode according to claim 1, wherein the content of the component (C) is 0.1 to 80% by weight. 5. A lithium secondary battery comprising a positive electrode comprising the electrode according to any one of claims 1 to 4, a negative electrode, and an electrolyte.