JP2002093417A - Li-co base composite oxide, and positive plate and lithium ion secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery having excellent discharge load characteristic, a cycle characteristic, high coating intensity, and a high capacity, and Li-Co based composite oxide and a positive electrode plate used for the battery. SOLUTION: This lithium ion secondary battery and the positive plate use the Li-Co based composite oxide, in which the particle size mainly consists of a group of small particle size of 1 to 6 μm and a group of a large particle size of 15 to 22 μm, and a weight ratio of the small particle size group to the large particle size group is 0.25 to 0.60.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Li-Co (lithium-cobalt) composite oxide, a positive electrode plate having this oxide, and a lithium ion secondary battery including the positive electrode plate.

[0002]

2. Description of the Related Art Generally, a lithium ion secondary battery has a structure in which a separator impregnated with an electrolyte is sandwiched between a positive electrode plate and a negative electrode plate. The positive electrode plate and the negative electrode plate are coated with a positive electrode active material composition or a negative electrode active material composition obtained by mixing a conductive material or a binder with the positive electrode active material or the negative electrode active material on a current collector such as a metal foil, and then dried and rolled. To form a positive electrode active material layer or a negative electrode active material layer. As the positive electrode active material, a Li-Co-based composite oxide is most often used in practice because it is chemically stable, easy to handle, and can produce a high-capacity secondary battery. Graphitized carbon is generally used as the negative electrode active material.

[0003] The Li-Co-based composite oxide is usually used in a granular form, and the performance of the obtained lithium ion secondary battery is influenced by the average particle size. For example, when a finely powdered Li—Co-based composite oxide having an average particle diameter of 5 μm or less is used, a lithium ion secondary battery having excellent discharge load characteristics and a high capacity can be obtained. Further, for example, when a Li—Co-based composite oxide having an average particle size of 15 μm or more is used, the coating density when the positive electrode active material composition is coated on the current collector can be increased, and an abnormal battery reaction occurs. A highly safe lithium ion secondary battery can be obtained.

[0004]

However, in a lithium ion secondary battery using an Li—Co-based composite oxide having an average particle size of 5 μm or less, the density of the positive electrode active material is small, so that the positive electrode active material layer is not formed. As a result, the coating density when the positive electrode active material composition is applied onto the current collector is reduced, so that the volume capacity is reduced, and the discharge load characteristics are reduced due to an increase in the rolling reduction. Further, when the Li-Co-based composite oxide is in the form of fine powder, the crystallinity is deteriorated due to the repetition of charge / discharge cycles, so that there is a problem that the cycle characteristics are inferior.

Further, Li-Co having an average particle diameter of 15 μm or more is used.
In a lithium ion secondary battery using a system composite oxide, there has been a problem that the discharge load characteristics decrease due to an increase in resistance.

The present invention provides a lithium ion secondary battery having excellent discharge load characteristics and cycle characteristics, a high coating density and a high capacity, and a Li-Co-based composite oxide and a positive electrode plate used therein. It is intended to do so.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. The present invention is as follows. (1) A group of small particles having a particle size of 1 μm to 6 μm and a particle size of 15
Li-C mainly composed of a large particle size group of μm to 22 μm
An o-based composite oxide, wherein the weight ratio of the small particle size group to the large particle size group is 0.25 to 0.60.
i-Co-based composite oxide. (2) The Li-Co-based composite oxide according to the above (1),
A positive electrode plate for a lithium ion secondary battery having a positive electrode active material. (3) A lithium ion secondary battery including the positive electrode plate according to (2).

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The Li—Co-based composite oxide of the present invention has a particle size of 1 μm to 6 μm (hereinafter also referred to as a small particle group (A)). A Li—Co-based composite oxide having a particle size of 15 μm to 22 μm (hereinafter, referred to as “Li-Co based composite oxide
Also referred to as large particle size group (B). ).

The Li—Co-based composite oxide of the present invention has a small particle size group (A) and a large particle size group (B) each having the above particle size.
But a Li-Co-based composite oxide having a particle size other than the small particle size group (A) and the large particle size group (B) (hereinafter also referred to as other particle size group (C)). You may go out. Other particle size groups (C) include those having a particle size of less than 1 μm, those having a particle size of more than 6 μm and less than 15 μm, and those having a particle size of more than 22 μm. When the Li—Co-based composite oxide of the present invention contains 6% by weight or more having a particle size of less than 1 μm, there is a problem that crystallinity is reduced due to repetition of charge / discharge cycles.
When the content of more than 15 μm is more than 8% by weight, the coating density may be reduced, and
If the content exceeds 2 μm is contained in an amount of 5% by weight or more, there is a problem that the discharge load characteristics are deteriorated due to an increase in resistance. Therefore, in the Li—Co-based composite oxide of the present invention, it is desirable to reduce the content of the other particle size groups (C) as much as possible. The content of the other particle size group (C) is preferably 10% by weight or less, more preferably 5% by weight or less.

The particle size of the small particle size group (A), large particle size group (B) and other particle size group (C) can be measured by the following method. The Li-Co-based composite oxide to be measured is introduced into an organic solvent such as water or ethanol, and 35
A dispersion process is performed for about 2 minutes by applying ultrasonic waves of about kHz to 40 kHz. The amount of the Li-Co-based composite oxide to be measured is such that the laser transmittance (the ratio of the output light amount to the incident light amount) of the dispersion liquid after the dispersion treatment is 70% to 95%. Run this dispersion on a Microtrac particle size analyzer,
The particle diameter of each Li-Co-based composite oxide is measured by scattering of laser light.

In the Microtrac particle size analyzer, the particle size distribution of a spherical particle group having the theoretical intensity closest to the observed scattering intensity distribution is calculated. That is, assuming that the Li—Co-based composite oxide is a sphere having a cross-sectional circle having the same area as the projected image obtained by the irradiation of the laser beam, the diameter of this cross-sectional circle (equivalent sphere diameter) is measured as the particle diameter. Is done.

Further, the Li—Co-based composite oxide of the present invention comprises:
The weight ratio of the small particle size group (A) to the large particle size group (B) is 0.
It is 25-0.60, preferably 0.30-0.50. If the weight ratio is less than 0.25, there are problems such as a decrease in discharge load characteristics and a decrease in capacity. On the other hand, when the weight ratio exceeds 0.60, there are disadvantages such as a decrease in coating density and a decrease in cycle characteristics.

As the Li-Co-based composite oxide of the present invention, those represented by LiCoO ₂ and Li _A Co _1-x Me _X O ₂ can be mentioned. In the latter, A is 0.05-1.
5, preferably 0.1 to 1.1. X is 0.
It is preferably from 0.01 to 0.5, particularly preferably from 0.02 to 0.2. As the element Me, Zr, V, Cr, Mo, Mn,
Group 3-10 elements of the periodic table such as Fe and Ni, B and A
Group 13 to 15 elements such as l, Ge, Pb, Sn, and Sb. In the present invention, in the small particle size group (A) and the large particle size group (B), the Li—Co-based composite oxide may be the same or different from each other. Both the small particle size group (A) and the large particle size group (B)
It is preferably realized with CoO ₂ .

Next, a preferred method for producing the Li—Co-based composite oxide of the present invention will be described below. In the present invention, the method for producing the Li—Co-based composite oxide is not limited to the following method.

As a preferred example of the above production method, a lithium compound as a starting material and a cobalt compound are mixed so that the atomic ratio of cobalt to lithium is 1: 1 to 0.8: 1, and the mixture is used. At a temperature of 700 ° C. to 1200 ° C.
In an air atmosphere at a temperature of 3 ° C., the reaction is carried out by heating for 3 hours to 50 hours, etc., and the product obtained by the reaction is further pulverized into granules, and those having a particle size within the above-mentioned range are sorted from among them. Method.

Another preferable example of the above-mentioned manufacturing method is as follows.
A method of further heat-treating the granules obtained by the above-described pulverization.
To 750 ° C., particularly about 450 ° C. to 700 ° C., for 0.5 to 50 hours, particularly about 1 to 20 hours.

The heat treatment of the pulverized granular material can be performed in any atmosphere, for example, in an air atmosphere or an inert gas atmosphere such as nitrogen or argon. . However, if carbon dioxide gas is present in the atmosphere, lithium carbonate may be generated and the content of impurities may increase. Therefore, it is preferable to perform the process in an atmosphere where the partial pressure of the carbon dioxide gas is about 10 mmHg or less.

Examples of the lithium compound used as the starting material include lithium oxide, lithium hydroxide, lithium halide, lithium nitrate, lithium oxalate, lithium carbonate and the like, and mixtures thereof. Examples of the cobalt compound as a starting material include cobalt oxide, cobalt hydroxide, cobalt halide, cobalt nitrate, cobalt oxalate, cobalt carbonate, and the like, and a mixture thereof. Note that Li-Co represented by Li _A Co _{1 -x} Me _X O ₂
If a composite oxide is to be produced, a required amount of a compound of a substitution element may be added to a mixture of a lithium compound and a cobalt compound.

The Li-Co-based composite oxide according to the present invention is a Li-Co-based composite oxide comprising a combination of a small particle size group (A), a large particle size group (B) and another particle size group (C). Has an average particle size of preferably 6 μm to 14 μm, more preferably 8 μm to 1 μm.
It is realized to be 2 μm. The average particle size (μm)
When measuring the particle size (D1, D2, D3...) Of each granular material as described above using the above-mentioned Microtrac particle size analyzer, the number of particles (N1, N2, N3)・
..) can be measured and calculated from the particle size (D) of the obtained individual particles and the number of existing particles (N) for each particle size by using the following equation (1). Average particle size (μm) = (ΣND ³ / ΣN) ^1/3 (1)

In the present invention, the average particle diameter in the above range is realized by blending the small particle diameter group (A) and the large particle diameter group (B) at a specific weight ratio. Thereby, Li of the present invention
The -Co-based composite oxide can realize a high capacity lithium ion secondary battery having excellent discharge load characteristics by containing the small particle size group (A). At the same time, by having the large particle size group (B), a lithium ion secondary battery having a high coating density, thereby increasing the volume capacity and having excellent cycle characteristics can be realized. As described above, in the present invention, it is possible to obtain a high-quality lithium ion secondary battery that draws out advantages of the small particle size group (A) and the large particle size group (B). Further, unlike the case where the average particle size is set to more than 5 μm and less than 15 μm using a single particle size group, the small particle size group (A) is filled between the large particle size group (B). , The density is improved compared to the above case,
Therefore, the coating density when the positive electrode active material composition having the Li—Co-based composite oxide is coated on the current collector can be further improved.

The positive electrode plate for a lithium ion secondary battery of the present invention has the above-described Li-Co-based composite oxide as a positive electrode active material. The positive electrode plate has a positive electrode active material layer obtained by forming a positive electrode active material composition containing the Li-Co-based composite oxide, the granular conductive material, and the binder of the present invention in a layer on a current collector. In addition, the positive electrode active material layer referred to in the present specification refers to a layer obtained by applying the positive electrode active material composition on a current collector and forming the same into a layer, and does not include the positive electrode active material composition before the formation.

As the conductive material used in the present invention, those widely and generally used in the art can be suitably used, and are not particularly limited. For example, artificial or natural graphites, or Ketjen black , Acetylene black, oil furnace black,
Examples include carbon materials such as carbon blacks such as extra conductive furnace black.
The term “granular” as used in the present invention includes, but is not particularly limited to, a scale, a sphere, a pseudo sphere, a lump, and a whisker.

In the present invention, two or more conductive materials having particle sizes different from each other may be used. However, in order to obtain a lithium ion secondary battery having stable characteristics, one kind of conductive material must be used. It is preferably used. Such a conductive material preferably has a particle size of 0.5 μm to 6 μm, and more preferably 1 μm to 3 μm. When one kind of conductive material is used as described above, the particle size is 0.5 μm.
If it is less than m, there is a problem that the volume capacity is reduced due to a decrease in the coating density, so that it is not preferable. If it exceeds 6 μm, the dispersibility is reduced and the discharge load characteristics are reduced. It is not preferable because of such defects.

The particle size of the conductive material in the present invention refers to the diameter of a cross-sectional circle (equivalent sphere diameter) assuming that the particles constituting the conductive material are spherical, and can be measured using an electron microscope. Specifically, an electron microscope photograph is first taken with the magnification set so that 20 or more particles enter the visual field. Next, the area of the image of each particle in the photograph is calculated, and the diameter of a circle having the same area is calculated from the calculated area. The particles constituting the conductive material are assumed to be spheres having a cross section circle of this diameter, and this diameter is the particle size of the conductive material.

The amount of the conductive material used is preferably 4 to 7 parts by weight, more preferably 5 to 6 parts by weight, based on 100 parts by weight of the Li—Co-based composite oxide, as in the prior art. I just need.

As described above, in the positive electrode plate for a lithium ion secondary battery of the present invention, it is preferable to use a conductive material having one kind of particle size range. As described above, since the small particle size group (A) and the large particle size group (B) having different particle size ranges are blended, even if two or more kinds of conductive materials having different particle size ranges are used. There is also an advantage that the dispersibility of the Li-Co-based composite oxide and the conductive material in the positive electrode active material layer is improved as compared with the case where a Li-Co-based composite oxide having one kind of particle size is used. Therefore, it is possible to obtain a lithium ion secondary battery having less variation in quality and more stable characteristics.

As the binder for forming the positive electrode active material layer, the same binder as in the prior art, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, ethylene-propylene-diene-based polymer and the like are preferably used. . The binder comprises a positive electrode active material 100
It is preferably added in an amount of 3 to 5 parts by weight, more preferably 3.5 to 4.5 parts by weight, based on parts by weight.

In the present invention, as a current collector used for the positive electrode plate, for example, a foil or an expanded metal formed of aluminum, an aluminum alloy, titanium, or the like can be used.

Hereinafter, a preferred example of a method for forming a positive electrode active material layer in the present invention will be described. The method for forming a positive electrode active material layer in the present invention basically includes a kneading step, a coating step, a drying step, and a rolling step.

In the kneading step, the above-mentioned cathode active material composition is kneaded in a conventionally known N-methylpyrrolidone by using a conventionally known kneading apparatus such as a planetary dispersing kneading apparatus (manufactured by Asada Iron Works), and uniformly mixed. Into a slurry. The conditions in the kneading step are as follows. First, the positive electrode active material and the entire amount of the conductive material are charged, and then a solution of polyvinylidene fluoride (PVdF) in N-methylpyrrolidone is added so that the whole exhibits a certain degree of viscosity.

In the subsequent coating step, the slurry obtained as described above is coated on a current collector. The application of the slurry is performed by using a conventionally known device such as a comma roll type or a die coat type coating machine as generally performed in the art.

In the drying step, the slurry applied on the current collector is removed by using a conventionally known appliance such as a hot air drying oven.
Dry in a temperature range of 100 ° C. to 200 ° C. for 5 minutes to 20 minutes.

Subsequently, in a rolling step, the slurry dried on the current collector is rolled into a layer by using a device such as a rolling press to form a positive electrode active material layer. In the present invention, the rolling temperature is preferably 15 ° C to 35 ° C,
The rolling is carried out under rolling conditions which are generally 30% to 40% and are common in the art. The thickness of the positive electrode active material layer formed by rolling is not particularly limited, but is preferably about 60 μm to 140 μm.

The lithium secondary battery of the present invention further comprises a negative electrode plate, an electrolytic solution, and the like in addition to the positive electrode plate described above.
These are not particularly limited, and are preferably realized by conventionally known materials. Hereinafter, preferable examples of the negative electrode plate and the electrolytic solution used in the present invention will be described.

In the present invention, the negative electrode plate is formed by providing a negative electrode active material layer obtained by mixing a binder or the like with a negative electrode active material on a current collector. As the negative electrode active material, graphitized carbon is used in the same manner as a conventionally known negative electrode active material. Such a graphitized carbon preferably has a specific surface area of 2.0
m ² / g or less, more preferably 0.5m ² /g~1.5m
² / g, the interplanar distance (d002) of the crystal lattice is preferably 0.3380 nm or less, more preferably 0.3355 n.
m to 0.3370 nm, crystallite size in the c-axis direction (Lc)
Is preferably 30 nm or more, more preferably 40 nm or more.
Graphitized carbon of 70 nm is particularly preferably used. Examples of the graphitized carbon satisfying the above numerical range include mesophase-based graphitized carbon.

If the specific surface area is larger than 2.0 m ² / g, the decomposition reaction of propylene carbonate, which is an electrolytic solution component, occurs at the time of charging, and the battery capacity may be undesirably reduced. Further, the distance between planes of the crystal lattice (d002)
Exceeds 0.3380 nm, or the crystallite dimension (Lc) in the c-axis direction is less than 30 nm, the potential of the negative electrode plate may increase, and the average discharge potential of the battery may decrease.

The inter-plane distance (d002) of the crystal lattice and the crystallite size (Lc) in the c-axis direction can be measured by the Japan Society for the Promotion of Science. This will be specifically described below.

First, high-purity X-ray standard silicon is ground in an agate mortar to a size of 325 mesh standard sieve or less to prepare a standard substance, and this standard substance and the graphitized carbon of the sample to be measured are mixed in an agate mortar ( An X-ray sample is prepared using 100% by weight of graphitized carbon and 10% by weight of a standard substance. This X
For example, an X-ray diffraction apparatus RINT2000
(Rigaku Corporation, X-ray source: CuKα ray) A sample plate is uniformly filled. Next, the applied voltage to the X-ray tube was 40 kV,
The applied current was set to 50 mA, and the scanning range was 2θ = 2.
The 002 peak of carbon and the 111 peak of a standard substance are measured at 3.5 to 29.5 degrees and a scan speed of 0.25 degrees / min. Subsequently, from the obtained peak position and its half-value width, using the graphitization degree calculation software attached to the X-ray diffractometer, the interplanar distance (d) of the crystal lattice is used.
002) and the crystallite size (Lc) in the c-axis direction are calculated.

In the present invention, the measurement of the specific surface area of graphitized carbon is carried out by the method described in “Material chemistry of powder” [Yasuo Arai, First Edition, 9th printing,
Baifukan (Tokyo), 1995], pages 178 to 1
Among the adsorption methods described on page 84, a gas-phase adsorption method using nitrogen as an adsorbent (one-point method) can be used. The measurement of the specific surface area using such a gas-phase adsorption method using nitrogen as an adsorbent can be suitably performed using, for example, a specific surface area meter Monosorb (manufactured by Quantachrome).

In the present invention, the graphitized carbon is used in the form of particles similar to the usual graphite-based negative electrode active material. The shape of the particles constituting the graphitized carbon is not particularly limited, and may be flake-like, fibrous, spherical, pseudo-spherical, massive, or whisker-like.

In the lithium ion secondary battery of the present invention, the binder used together with the negative electrode active material includes:
As before, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, ethylene-propylene-
A diene polymer or the like can be used. Further, as the current collector used for the negative electrode plate, the same current collector as in the related art can be used, and examples thereof include a foil and an expanded metal formed of copper, nickel, silver, stainless steel, and the like.

The solvent of the electrolyte in the present invention includes at least one selected from diethyl carbonate (DEC) and ethyl methyl carbonate (EMC), and further includes ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate. (DM
C) is used. The mixing ratio of each component constituting the mixture is preferably 25% by volume to 50% by volume in at least one kind selected from diethyl carbonate and ethyl methyl carbonate,
More preferably, it is 30% by volume to 35% by volume. In ethylene carbonate, the mixing ratio is preferably from 4% by volume to 20% by volume, and more preferably from 6% by volume to 18% by volume. In propylene carbonate, the mixing ratio is preferably 3% by volume to 17% by volume, and preferably 5% by volume.
More preferably, it is from 15% by volume to 15% by volume. In dimethyl carbonate, the mixing ratio is preferably more than 40% by volume and 60% by volume or less,
More preferably, it is 55% by volume. When both diethyl carbonate and ethyl methyl carbonate are mixed with the electrolytic solution in the present invention, the total amount thereof satisfies the above mixing ratio.

In at least one selected from diethyl carbonate and ethyl methyl carbonate,
When the mixing ratio is less than 25% by volume, the freezing point of the electrolytic solution increases, and particularly at a low temperature of −20 ° C. or lower, the internal resistance of the battery increases, and the charge / discharge cycle characteristics and low-temperature characteristics may decrease. There is not preferred. On the other hand, if the mixing ratio is more than 50% by volume, the viscosity of the electrolytic solution increases, the internal resistance of the battery increases, and the charge / discharge cycle characteristics may decrease.

In the case of ethylene carbonate, if the mixing ratio is less than 4% by volume, it is difficult to form a stable film on the surface of the negative electrode plate, and the cycle characteristics may be deteriorated. On the other hand, when the mixing ratio exceeds 20% by volume, the viscosity of the electrolytic solution increases, the internal resistance of the battery increases, and the charge / discharge cycle characteristics may decrease.

In the case of propylene carbonate, if the mixing ratio is less than 3% by volume, the effect of suppressing the increase in impedance due to the charge / discharge cycle becomes small, and the cycle characteristics may be undesirably reduced. If the mixing ratio exceeds 17% by volume, the viscosity of the electrolytic solution increases, the internal resistance of the battery increases, and the charge / discharge cycle characteristics may deteriorate.

In the case of dimethyl carbonate, if the mixing ratio is 40% by volume or less, the viscosity of the electrolytic solution increases, the internal resistance of the battery increases, and the charge / discharge cycle characteristics are undesirably reduced. If the mixing ratio is more than 60% by volume, the freezing point of the electrolytic solution increases, and especially −20.
Under low temperature below ℃, increase the internal resistance of the battery,
The cycle characteristics and the low-temperature characteristics may deteriorate, which is not preferable.

In the lithium ion secondary battery according to the present invention, the electrolyte is LiCl
_{O 4, LiBF 4, LiPF 6} , LiAsF 6, LiAlC
One or two or more of lithium salts such as l ₄ and Li (CF ₃ SO ₂ ) ₂ N may be dissolved. The lithium salt concentration of the electrolytic solution is preferably 0.1 mol / L to 2 mol / L, more preferably 0.5 mol / L to
It is prepared to be 1.8 mol / L. If the concentration of the lithium salt is less than 0.1 mol / L, ionic conductivity as an electrolyte cannot be sufficiently obtained, and the function as a battery is undesirably impaired. On the other hand, if the concentration of the lithium salt exceeds 2 mol / L, the viscosity of the electrolytic solution increases, and the low-temperature characteristics and high-rate characteristics decrease, which is not preferable.

The method for producing the negative electrode plate is not particularly limited, and it can be suitably produced by a method generally used in the art. In addition, by assembling the positive electrode plate, the negative electrode plate, and the electrolyte using a widely used separator, battery can, and the like as generally performed in the art, the lithium ion secondary battery of the present invention is provided. A battery can be suitably manufactured.

[0049]

EXAMPLES The present invention will be specifically described below with reference to examples. Actually, a lithium ion secondary battery of the present invention was produced and evaluated. Example 1 [Preparation of Positive Electrode Plate] The small particle size group A1 (particle size: 3 μm) and the large particle size group B1 (particle size: 17 μm) were compared with the large particle size group B1 by a weight ratio of 0 to 0. The Li—Co-based composite oxide of the present invention (LiCoO
₂ ) 90 parts by weight and MCMB (particle size: 6μ) to be a conductive material
m) A positive electrode active material composition obtained by uniformly dispersing 6 parts by weight and 4 parts by weight of polyvinylidene fluoride (PVdF) as a binder in N-methylpyrrolidone was mixed with a planetary disperser kneader (manufactured by Asada Iron Works). ) To obtain a slurry. The average particle size of the entire Li—Co-based composite oxide was 13 μm. The particle size, average particle size, and particle size of the conductive material of the above-described Li-Co-based composite oxide are measured using a microtrack particle size analyzer SALD-3000J (manufactured by Shimadzu Corporation)
It measured using. The specific surface area of the above-mentioned Li—Co-based composite oxide and the conductive material was measured using a specific surface area meter Monosorb (manufactured by Quantachrome). The slurry is applied on both sides of an aluminum foil (thickness: 20 μm) serving as a current collector, dried, and then rolled at room temperature at a rolling reduction of 35% to form a positive electrode active material layer. A positive electrode plate having 18 mg / cm ² of a Li—Co-based composite oxide per one side was prepared.

[Preparation of negative electrode plate] Graphitized carbon (fibrous graphite, specific surface area: 1.0 m ² / g,
95 parts by weight of a plane distance between crystal lattices: 0.3360 nm, crystallite size in the c-axis direction: 50 nm), 5 parts by weight of polyvinylidene fluoride (PVdF) as a binder, and 50 parts by weight of N-methylpyrrolidone To make a slurry,
This slurry was applied to both surfaces of a copper foil (thickness: 14 μm) serving as a current collector, and dried. The specific surface area of the negative electrode active material was measured using a specific surface area monosorb (manufactured by Quantachrome) in the same manner as described above. The distance between the planes of the crystal lattice of the negative electrode active material and the crystallite size in the c-axis direction are determined by using an X-ray diffractometer R
INT2000 (Rigaku Corporation, X-ray source: CuKα ray)
Was measured under the conditions described above. Next, the copper foil was subjected to a rolling treatment under rolling conditions of a rolling temperature of 120 ° C. and a rolling ratio of 22% to obtain a negative electrode plate.

[Preparation of electrolyte solution] Diethyl carbonate 4
LiPF ₆ in a mixed solvent of volume%, 29% by volume of ethyl methyl carbonate, 11% by volume of ethylene carbonate, 9% by volume of propylene carbonate, and 47% by volume of dimethyl carbonate at a concentration of 1.0 mol / L.
(To the prepared electrolyte solution) to prepare an electrolyte solution.

[Assembly of Lithium-ion Secondary Battery] The positive electrode plate and the negative electrode plate prepared above were
It was wound through a polypropylene composite separator and housed in a cylindrical battery can (outer diameter 18 mm, height 650 mm). Further, the electrolyte solution obtained above was impregnated in a separator to obtain a lithium ion secondary battery.

Example 2 The small particle size group A1 and the large particle size group B1 were replaced with the large particle size group B1.
A lithium ion secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of the small particle size group A1 to the mixture was 0.45. The average particle size of the entire Li—Co-based composite oxide was 10 μm.

Example 3 The small particle size group A1 and the large particle size group B1 were replaced with the large particle size group B1.
A lithium ion secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of the small particle size group A1 to the mixture was 0.55. The average particle size of the entire Li—Co-based composite oxide was 7 μm.

Example 4 Small particle size group A2 (particle size: 5 μm) and large particle size group B1
And the weight ratio of the small particle size group A2 to the large particle size tool B1 is 0.1.
A lithium ion secondary battery was fabricated in the same manner as in Example 1, except that the mixture was adjusted to 30. The average particle size of the entire Li—Co-based composite oxide was 14 μm.

Example 5 The above-mentioned small particle size group A2 and large particle size group B1
A lithium ion secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of the small particle size group A2 to the mixture was 0.60. The average particle size of the entire Li—Co-based composite oxide was 8 μm.

Example 6 The small particle size group A1 and the large particle size group B2 (particle size: 21 μm)
m) was mixed in the same manner as in Example 1 except that the weight ratio of the small particle group A1 to the large particle group B2 was 0.40. Li-Co
The average particle size of the entire system composite oxide was 12 μm.

Example 7 The small particle size group A1 and the large particle size group B2 were replaced with the large particle size group B2.
A lithium ion secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of the small particle size group A1 to the mixture was 0.55. The average particle size of the entire Li—Co-based composite oxide was 9 μm.

Comparative Example 1 The above-described small particle size group A1 and large particle size group B1
A lithium ion secondary battery was manufactured in the same manner as in Example 1, except that the weight ratio of the small particle size group A1 to the mixture was 0.20. The average particle size of the entire Li—Co-based composite oxide was 16 μm.

Comparative Example 2 The small particle size group A1 and the large particle size group B1 were replaced with the large particle size group B1.
A lithium ion secondary battery was fabricated in the same manner as in Example 1, except that the weight ratio of the small particle size group A1 to the mixture was 0.70. The average particle size of the entire Li—Co-based composite oxide was 5 μm.

Comparative Example 3 A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the above-mentioned small particle size group A1 was used alone.

Comparative Example 4 A lithium ion secondary battery was fabricated in the same manner as in Example 1 except that the above-mentioned small particle size group A2 was used alone.

Comparative Example 5 A lithium ion secondary battery was produced in the same manner as in Example 1, except that the above-mentioned large particle size group B1 was used alone.

Comparative Example 6 A lithium ion secondary battery was produced in the same manner as in Example 1, except that the large particle size group B2 was used alone.

Comparative Example 7 A lithium ion secondary battery was manufactured in the same manner as in Example 1 except that the other particle size group C1 (particle size: 10 μm) was used alone.

Comparative Example 8 A lithium ion secondary battery was produced in the same manner as in Example 1, except that another particle size group C2 (particle size: 24 μm) was used alone.

For the lithium ion secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 8 fabricated as described above, a cycle characteristic test and a discharge load characteristic test were performed in the following procedure.

[Cycle Characteristics Test] For each of the lithium ion secondary batteries obtained above, 1 CA (1600 m
A) charging for 2.5 hours with the upper limit of the voltage at 4.2 V at the constant current of A), pause for 1 hour after charging, and discharging until the voltage reaches 3.0 V at the constant current of 1 CA; The four steps of 1-hour pause after discharge as one cycle were repeated 100 times at room temperature (20 ° C.), and the discharge capacity (mA · H) at the 100th cycle was divided by the initial discharge capacity to obtain a capacity retention ratio. (%) Was calculated.

[Discharge Load Characteristic Test] Each of the lithium ion secondary batteries obtained above was charged at 1 CA for 2.5 hours until the charging voltage became 4.2 V, paused for 1 hour, and then turned to 3. 0.2 CA (3200 m
Discharge was performed in A). After a one-hour pause, the battery is charged for 2.5 hours at 1 CA until the charging voltage becomes 4.2 V, and then paused for one hour. Then, 2 CA (3200 m
Discharge was performed in A). The ratio (%) of the discharge capacity (mA · H) in the discharge at 2 CA to the discharge capacity (mA · H) in the discharge at 0.2 CA was calculated. Example 1
7 in Table 1 and Comparative Examples 1 to 8 in Table 2.
The results of each of the above tests are shown below.

[0070]

[Table 1]

[0071]

[Table 2]

[0072]

As is apparent from the above description, according to the present invention, a lithium ion secondary battery having excellent discharge load characteristics and cycle characteristics, a high coating density, and a high capacity, and its use. Li-Co-based composite oxide,
A positive electrode plate can be provided. The lithium ion secondary battery obtained by the present invention can be suitably used for portable devices such as mobile phones and notebook computers.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4G048 AA04 AC06 AD04 5H029 AJ03 AJ12 AK03 AL07 AM03 AM04 AM05 AM07 DJ16 HJ01 HJ05 5H050 AA08 AA15 BA17 CA08 CB08 EA10 EA23 FA17 HA01 HA02 HA05

Claims (3)

[Claims] 1. A Li—Co-based composite oxide mainly composed of a group of small particles having a particle size of 1 μm to 6 μm and a group of large particles having a particle size of 15 μm to 22 μm. A Li-Co-based composite oxide, wherein the weight ratio of the particle size groups is from 0.25 to 0.60. 2. A positive electrode plate for a lithium ion secondary battery, comprising the Li—Co-based composite oxide according to claim 1 as a positive electrode active material. 3. A lithium ion secondary battery comprising the positive electrode plate according to claim 2.