JP2000327339A - Li-Co-BASED COMPOUND OXIDE AND ITS PRODUCTION - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an Li-Co-based compound oxide useful as a positive pole active material for a nonaqueous electrolyte battery such as a lithium secondary battery and capable of improving charge and discharge cycle characteristics of the battery and to provide a method for producing the Li-Co-based compound oxide. SOLUTION: This particulate Li-Co-based compound oxide has the sum value A (μm) of respective lattice spacings in (104), (105), (009), (107), (108) and (113) indices of planes, the specific surface area B (m2/g) and the average particle diameter C (μm) satisfying the following formula: formula: 0.025<=[(A-11)/(B.C)]<=0.04. The method for producing the Li-Co-based compound oxide comprises carrying out water washing treatment of a particulate material of the Li-Co-based compound oxide, regulating the amount of water-soluble lithium compound-based impurities to <=0.05 wt.% and then heat-treating the resultant compound oxide at 400-700 deg.C for 0.5-50 h. The Li-Co-based compound oxide is suitable for producing a long-lived lithium secondary battery for various kinds of electrical equipment, especially for portable articles, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a Li-Co-based composite oxide and a method for producing the same, and more particularly to a Li-Co-based composite oxide useful as a positive electrode active material for a non-aqueous electrolyte secondary battery such as a lithium secondary battery. The present invention relates to an oxide and a method for producing the oxide.

[0002]

2. Description of the Related Art Li-Mn-based composite oxides, Li-Ni-based composite oxides, and Li-Co-based composite oxides have been proposed as positive electrode active materials for lithium secondary batteries. It has been put to practical use. Li-M among them
n-based composite oxides and Li-Ni-based composite oxides include Mn and N
i has abundant resources and can be manufactured at low cost.
The i-Mn-based composite oxide generally has a problem that it is difficult to manufacture a high-capacity secondary battery, while the Li-Ni-based composite oxide is chemically unstable and has a problem in terms of safety of the secondary battery. There's a problem. On the other hand, Li-Co-based composite oxide is Li-N
Compared to i-type composite oxides, they are chemically stable and easy to handle, and can produce a high-capacity secondary battery.

Recently, demands for further improving the battery characteristics of a secondary battery using a Li—Co-based composite oxide having such advantages have been increasing, and proposals and reports for that purpose have been made. For example, Japanese Patent Publication No. Hei 7-118318 discloses that in producing LiCoO ₂ , the use ratio of a lithium compound and a cobalt compound as raw materials is blended so as to make lithium rich, mixed, heated, and contained in a reaction product. It discloses that the unreacted lithium compound and by-produced lithium carbonate contained therein are removed by washing with water, and that the discharge capacity of the secondary battery is thereby improved. Japanese Patent Application Laid-Open No. 5-182667 discloses a method of coexisting lithium carbonate with LiCoO ₂ and a specific method thereof in order to prevent an explosion accident due to an abnormal battery reaction during operation of the battery. Have been.

[0004] Recent research conducted by the present inventors has shown that a Li-Co-based composite oxide formed of granules having a specific crystal structure and a specific specific surface area and a specific particle size is used as a positive electrode. It has been found that when used as an active material, the charge / discharge cycle characteristics of a lithium secondary battery can be improved.

[0005]

SUMMARY OF THE INVENTION The present invention has been developed and completed based on the above-mentioned new findings, and is useful as a positive electrode active material for non-aqueous electrolyte secondary batteries such as lithium secondary batteries. It is an object of the present invention to provide a Li-Co-based composite oxide capable of improving the charge / discharge cycle characteristics of the battery and a method for producing the same.

[0006]

The above object is achieved by the following L
The problem can be solved by an i-Co-based composite oxide and a method for producing the same. Surface indices (104), (105), (009), (1
07), (108), and (113), the total value A (μm) of the lattice spacings and the specific surface area B (m ²⁾
/ G) and an average particle size C (μm) are granular materials satisfying the following formula (1). 0.025 ≦ [(A-11) / (B · C)] ≦ 0.04 (1) The granular material has a specific surface area B of 0.1 to 0.3 m ² / g and an average particle diameter C of The above-described Li-Co-based composite oxide having a thickness of 10 to 25 µm. The above-mentioned or the above-described Li-Co-based composite oxide, wherein the amount of the water-soluble lithium compound-based impurity is 0.05% by weight or less when the amount of the impurity is converted into the amount of Li ₂ CO ₃ . The above for the positive electrode active material of the non-aqueous electrolyte secondary battery ~
The Li-Co-based composite oxide according to any one of the above. The particles of the Li—Co-based composite oxide are washed with water and the amount of the water-soluble lithium compound-based impurities is reduced by Li ₂ C
So as to be 0.05% by weight or less in terms of O ₃ amount,
Then 400 to 700 in air or in an inert atmosphere
The method for producing a Li—Co-based composite oxide according to any one of the above, wherein the heat treatment is performed at a high temperature of 0.5 ° C. for 0.5 to 50 hours. The above-described method for producing a Li-Co-based composite oxide, wherein the granular material having an average particle size C of 10 to 25 µm is washed with water and then heat-treated.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The Li—Co-based composite oxide of the present invention has a chemical structure in which LiCoO ₂ or a part of Co thereof is substituted with one or more kinds of other elements. May be represented by the general formula (2). Li _A Co _1-x Me _x O ₂ (2) In the general formula (2), A is 0.05 to 1.5, preferably 0.1 to 1.1, and X is 0.01 to 0. 5, preferably 0.02 to 0.2. As the element Me, a group 3-10 element of the new periodic table, for example, Zr,
V, Cr, Mo, Mn, Fe, Ni, etc., or 13 to
Group 15 element, for example, B, Al, Ge, Pb, Sn, Sb
And so on. In the case of a Li—Co-based composite oxide in which Co is substituted with two or more of these elements, the total amount of the two or more elements may be within the range of X described above.

The Li—Co-based composite oxide of the present invention has plane indices (104), (105), (009), (107),
The total value A (μm) and specific surface area B (m ² ) of the respective lattice plane intervals (d values) in (108) and (113)
/ G) and an average particle size C (μm) satisfying the formula (1). [(A-1
1) / (B · C)] is less than 0.025 or 0.1.
In the case where a particulate material larger than 04 was used as the positive electrode active material, no favorable improvement was observed in the charge / discharge cycle characteristics of the lithium secondary battery, and the present invention satisfied the following expression (3). Li-Co formed of fine particles
Based composite oxides are particularly preferred. 0.032 ≦ [(A-11) / (B · C)] ≦ 0.038 (3)

As long as the formula (1) is satisfied, the Li-
The Co-based composite oxide is not particularly limited in terms of the total value of the d values, the specific surface area, and the average particle size from the viewpoint of the charge / discharge cycle characteristics of the lithium secondary battery. However, when the sum of the d values is too small, the compressive strain in the crystal is large, while when it is too large, the tensile strain in the crystal is large, and in any case, the battery is charged. This is not preferred because it tends to lower the discharge cycle characteristics. Therefore, the total value is about 11.10 to 11.15,
In particular, about 11.11 to 11.14 is preferable. In addition, a Li-Co-based composite oxide having an excessively small average particle size is rich in reactivity and generally easily causes an abnormal battery reaction, while a Li-Co-based composite oxide having an excessively large average particle diameter has a large electric resistance. This leads to a reduction in the energy density per unit volume of the lithium secondary battery, and the average particle size is 10 to 25 μm.
Degree, particularly preferably about 15 to 20 μm. Li-Co
The preferred range of the specific surface area of the system composite oxide is 0.1 to 0.3 from the viewpoint of the charge and discharge cycle characteristics of the lithium secondary battery.
m ² / g approximately, in particular 0.15~0.25m ² / g approximately.

In the present invention, the total value of the d values, the specific surface area, and the average particle size of the granular material of the Li—Co-based composite oxide can be measured by the following methods. [Measurement of total value of d value] The divergence slit was 0.5 deg. , Scattering slit 0.5
deg. , Light receiving slit 0.15 mm, step width 0.
006 deg. The surface indices (104), (105),
(009), (107), (108), and (11)
The respective d values of 3) are measured, and the total value (μm) of the d values is calculated. [Method for Measuring Specific Surface Area] Among the adsorption methods described in pages 178 to 184 of “Material Chemistry of Powder” [Yasuo Arai, First Edition, 9th Edition, published by Baifukan (Tokyo), 1995] Gas phase adsorption method (single point method) using nitrogen as an adsorbent. [Measurement method of average particle diameter] The granular material of the Li-Co-based composite oxide is charged into an organic liquid such as water or ethanol, and 3
A dispersion obtained by performing a dispersion treatment for about 2 minutes while applying ultrasonic waves of about 5 to 40 kHz is used, and the amount of particulate matter in that case is determined by the laser transmittance of the dispersion (the output light amount with respect to the incident light amount). Ratio) is 70-95%, and then the dispersion is passed through a Microtrac particle size analyzer to scatter laser light to determine the particle size (D ₁ , D ₁ ) of each granular material.
_2, D ₃ ··), and the presence the number of each particle each diameter (N _1, N
₍₂ , N ₃ ...) Is measured (the particle diameter (D) of each granular material is automatically measured by a Microtrac particle size analyzer for each granular material having various shapes). .).
The average particle diameter (μm) is calculated by the following equation (4) from the number (N) of individual particles present in the visual field and each particle diameter (D). Average particle size (μm) = (ΣND ³ / ΣN) ^1/3 (4)

Next, the Li-Co-based composite oxide of the present invention
The method for producing the granular material will be described. In general, Li-
Co-based composite oxide particles are lithium as a starting material.
And cobalt oxides, hydroxides, halides, nitric acid
Lithiation using salts, oxalates, carbonates, etc.
A mixture of a compound and a cobalt compound, or a compound of the formula (2)
Li- in which a part of Co is replaced by another element as shown by
When producing a Co-based composite oxide, place in the above mixture.
A mixture containing a small amount of a compound of the
Let the mixture react, for example, in air at around 1000 ° C
Li for 1 to 50 hours
-The lump of the Co-based composite oxide is pulverized and separated if necessary.
And the total value of d values satisfying the expression (1), the specific surface area, and
And selectively obtain granules having an average particle size.
Wear. Especially, for the reasons described below,
The amount of the soluble lithium compound-based impurity is calculated by the following formula (5).
Li _TwoCO_Three0.05% by weight or less
Are preferred. In addition, water-soluble
The amount of the impurity compound is calculated according to the formula (5)._TwoCO
_ThreeIt means the conversion amount. The Li-C of the present invention
The granular material of the o-based composite oxide is obtained by pulverizing the mass
Particles of a Li-Co-based composite oxide such as
A water washing process described below for granules having an average particle size of 10 μm to 25 μm
After drying if necessary,
400 to 70 in an inert gas atmosphere such as nitrogen or argon
0.5 to 50 hours at 0 ° C, especially about 1 to 20 hours, preferably
Or 500-700 ° C for 0.5-50 hours, especially 1-20
It can be manufactured by heat treatment for about an hour.
Wear. Note that carbon dioxide gas exists in the atmosphere in which the heat treatment is performed.
And lithium carbonate are generated, leading to an increase in the content of impurities.
Therefore, the partial pressure of carbon dioxide in the atmosphere is 10 mmHg or less.
Is preferred.

In general, the mixing ratio of the lithium compound and the cobalt compound is determined because the lithium compound has a higher fugitive property due to vaporization than the cobalt compound.
Usually, it is made to be lithium rich. As a result, the Li—Co-based composite oxide obtained by heating and firing often contains lithium compound-based impurities such as lithium oxide, lithium hydroxide, and lithium carbonate.

In the present invention, the amount of such lithium compound-based impurities, particularly, water-soluble lithium compound-based impurities such as lithium hydroxide and lithium carbonate, is reduced to 0.05% by weight or less in the granular material by a water washing treatment. To remove
More preferably, when the washed product from which the water-soluble impurities have been removed is subjected to a heat treatment under the above conditions, the production yield of the granular material satisfying the formula (1) or (3) is improved, and the lithium secondary battery is further improved. The effect of improving the charge / discharge cycle characteristics of the semiconductor device also increases. Further, when the current collector is made of aluminum, there is a problem that the water-soluble lithium compound-based impurities corrode the current collector and deteriorate the charge / discharge cycle characteristics of the secondary battery. Is also preferable from this aspect. This water washing treatment can be carried out by a conventional method using distilled water or ion-exchanged water as washing water, and applying mechanical stirring or ultrasonic waves at the time of the treatment as necessary. The amount of lithium compound-based impurities (amount in terms of Li ₂ CO ₃ ) D remaining in the water-washed granules can be determined by the following method and calculation formula (5). [Quantitative determination method of water-soluble lithium compound impurity D] Li-
Approximately 10 g of Co-based composite oxide granules were added to 100 ml of pure water.
Suspended in water, stirred for 10 minutes, filtered off, and the filtrate was titrated with 0.1N hydrochloric acid, and the Li ion concentration L (mol / L) was calculated from the amount of the hydrochloric acid added dropwise. The compound-based impurity D (% by weight) is calculated by the following equation (5). D = L × (molecular weight of Li ₂ CO ₃ : 73.89) /2=36.95 L (5)

According to the study of the present inventor, the granular material of the Li—Co-based composite oxide is subjected to the above-mentioned washing or heat treatment.
In particular, although the average particle diameter does not substantially or substantially change by the water washing treatment and the heat treatment, the total value of the d value and the specific surface area change, and as a result, the formulas (1) and (3) are satisfied. It becomes easier to obtain granules.

The Li—Co-based composite oxide of the present invention can be used as a positive electrode active material of a non-aqueous electrolyte battery such as a lithium secondary battery. For example, other materials and members known for lithium secondary batteries are used. It can be used for the manufacture of a lithium secondary battery. The main materials or members are exemplified below.

Examples of the binder for the Li-Co-based composite oxide include polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, and ethylene-propylene-diene-based polymers. Examples of the conductive agent include fibrous graphite. Natural and artificial graphites such as flaky graphite and spheroidal graphite, and conductive carbon black. The amount of the binder used is about 1 to 10 parts by weight, especially about 2 to 5 parts by weight, per 100 parts by weight of the Li-Co-based composite oxide. It is about 3 to 15 parts by weight, especially about 4 to 10 parts by weight per part by weight. As the positive electrode current collector, a conductive metal such as aluminum, an aluminum alloy, or titanium having a thickness of 10 to 1
About 00 μm, especially about 15 to 50 μm foil or perforated foil, about 25 to 300 μm thickness, especially about 30 to 150 μm
A certain degree of expanded metal is preferred.

Preferred examples of the negative electrode active material include:
Various natural graphites and artificial graphites, for example, graphites such as fibrous graphite, flaky graphite, spheroidal graphite, and the binders thereof include polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, ethylene-propylene-diene. And the like. The amount of the negative electrode active material used is 80 to 96 per 100 parts by weight of the total amount of the negative electrode active material and the binder.
It is about parts by weight. As the negative electrode current collector, a conductive metal such as copper, nickel, silver, and SUS, having a thickness of 5 to 100 μm.
m, especially about 8 to 50 μm foil or perforated foil, thickness 2
Expanded metal having a thickness of about 0 to 300 μm, particularly about 25 to 100 μm is preferable.

Examples of the electrolyte include a solution in which salts are dissolved in an organic solvent. The salts include LiCl
_{O 4, LiBF 4, LiPF 6} , LiAsF 6, LiA
IlCl ₄ , Li (CF ₃ SO ₂ ) ₂ N, etc.
One or a mixture of two or more thereof is used.

As the organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate,
Diethyl carbonate, ethyl methyl carbonate, dimethyl sulfoxide, sulfolane, γ-butyrolactone, 1,2-dimethoxyethane, N, N-dimethylformamide, tetrahydrofuran, 1,3-dioxolan, 2-methyltetrahydrofuran, diethyl ether, and the like, One or a mixture of two or more thereof is used. The concentration of the above salts in the electrolyte is suitably about 0.1 to 3 mol / l.

[0020]

EXAMPLES The present invention will be described in more detail with reference to the following examples, and comparative examples will also be described to show the remarkable effects of the present invention.

Examples 1 to 3 and Comparative Examples 1 to 5 Co ₃ O ₄ 100 was prepared using Co ₃ O ₄ and Li ₂ CO _3.
42 parts by weight of Li ₂ CO ₃ are mixed per part by weight, and the homogeneous mixture is baked at about 980 ° C. for about 10 hours, and the massive LiCoO ₂ obtained by the calcination is pulverized and classified, and ultrasonically cleaned using ion-exchanged water. And then heat-treated in air, as shown in Table 1.
The LiCoO ₂ granules of Examples 1 to 3 and Comparative Examples 1 to 5 shown in Table 1 were obtained. The LiCoO ₂ granules of Comparative Examples 1 and ₂ were not subjected to the above-mentioned washing treatment and heat treatment.

With respect to each LiCoO ₂ particulate matter of Examples and Comparative Examples, the residual amount of water-soluble lithium compound impurities after ultrasonic cleaning, heat treatment conditions (temperature and time),
Sum A d-values of LiCoO ₂ granules after the heat treatment, the specific surface area B, the average particle diameter C, and [(A-11) / (B
C)] are shown in Table 1. In addition, each characteristic of each LiCoO ₂ granular material of Comparative Examples 1 and 2 not subjected to water washing and heat treatment shows a value in a state in which the treatment is not performed.

[0023]

[Table 1]

Each Li of Examples 1-3 and Comparative Examples 1-5
A slurry is prepared by mixing 90 parts by weight of CoO ₂ granules, 7 parts by weight of polyvinylidene fluoride as a binder, 3 parts by weight of acetylene black as a conductive agent, and 70 parts by weight of N-methyl-2-pyrrolidone. And This slurry is applied on both sides of a 20 μm-thick aluminum foil as a current collector, dried, and then rolled to obtain a positive electrode body having a positive electrode active material composition layer of 20 mg / cm ² per one side of the aluminum foil. Produced. On the other hand, flaky graphite 90
Parts by weight, 10 parts by weight of polyvinylidene fluoride, and N-
A slurry was prepared by mixing 200 parts by weight of methyl 2-pyrrolidone. This slurry was used as a current collector to a thickness of 14 μm.
Was coated on both sides of the copper foil, dried, and then rolled to prepare a negative electrode body having a negative electrode active material composition layer of 10.4 mg / cm ² per one side of the copper foil. Next, the positive electrode body and the negative electrode body were wound through a porous polyethylene separator to produce a cylindrical can type lithium secondary battery (discharge capacity: 1300 mAh) having a height of 65 mm and an outer diameter of 18 mm. As an electrolytic solution, 1 mole of LiPF per liter of a mixed solvent of ethylene carbonate, propylene carbonate, and diethyl carbonate (mixing volume ratio is 3: 2: 5)
_A solution obtained by dissolving ₆ was used, and this was impregnated between the positive electrode body and the negative electrode body.

Next, each lithium secondary battery was tested for charge / discharge cycle characteristics according to the following charge / discharge cycle test method, and the discharge capacity retention ratio (%) at the 100th cycle was measured. The results are shown in Table 1. Indicated. [Charge / Discharge Cycle Test Method] Under a constant current of 2.6 mA and a constant voltage of 4.2 V per 1 cm ² of area of the positive electrode body.
Charge for 5 hours, pause for 1 hour after charging, area of positive electrode body 1cm
The four steps of discharging until the terminal voltage reaches 3 V under a constant current of 1.3 mA per ^{2 and} resting for 1 hour after discharging as one cycle are repeated 100 times at room temperature (20 ° C.), and each cycle is repeated. The discharge capacity (mAH) is calculated from the discharge current value and the discharge time at. The ratio of the discharge capacity in each cycle to the initial discharge capacity is defined as a discharge capacity maintenance ratio (%).

From Table 1, each LiCoO ₂ particulate material of Comparative Examples 1 to 5 in which the value of [(A-11) / (BC)] is out of the range of the above formula (1) was used as a positive electrode active material. The lithium secondary battery has a discharge capacity retention ratio of 85% or less at the 100th cycle, whereas [(A-11) / (B
C)] LiCo of Examples 1 to 3 in which the value of
It can be seen that the lithium secondary battery using the O ₂ particles as the positive electrode active material has a high discharge capacity retention ratio of 90% or more even at the 100th cycle, and thus has excellent charge / discharge cycle characteristics.

[0027]

The Li-Co-based composite oxide of the present invention is useful as a positive electrode active material, and is particularly excellent in charge / discharge cycle characteristics, and is suitable for various electric appliances, especially for portable articles. It is suitable for manufacturing a long-life lithium secondary battery.

 ──────────────────────────────────────────────────続 き Continued on front page F-term (reference) 4G048 AA04 AB05 AC06 AD04 AE05 5H003 AA04 BA01 BB05 BC01 BC06 BD00 BD01 BD02 BD03 BD04 BD05 5H014 AA01 BB01 EE10 HH00 HH01 HH06 HH08 5H029 AJ05 AK03 AL06 AM03 DJ04 AM05 HJ00 HJ01 HJ02 HJ05 HJ07 HJ13 HJ14

Claims (6)

[Claims] 1. Surface indices (104), (105), (00)
9), (107), (108), and (113), the total value A (μm), specific surface area B (m ² / g), and average particle size C (μm) of the respective lattice spacings are expressed by the following equations. A Li-Co-based composite oxide, which is a satisfactory granular material. 0.025 ≦ [(A-11) / (B · C)] ≦ 0.04 2. The granular material has a specific surface area B of 0.1 to 0.3.
m is ² / g, average particle size C is Li-Co-based composite oxide according to claim 1, wherein the 10 to 25 [mu] m. 3. The granular material has a water-soluble lithium compound-based impurity content of 0.05% in terms of Li ₂ CO ₃ amount.
The Li-Co-based composite oxide according to claim 1, which is less than or equal to% by weight. 4. The Li-Co-based composite oxide according to claim 1, which is used for a positive electrode active material of a non-aqueous electrolyte secondary battery. 5. A method of subjecting a particulate Li—Co-based composite oxide to washing with water so that the amount of a water-soluble lithium compound-based impurity is 0.05% by weight or less in terms of Li ₂ CO _3. And then in air or in an inert atmosphere
The method for producing a Li—Co-based composite oxide according to claim 1, wherein the heat treatment is performed at a high temperature of 0 to 700 ° C. for 0.5 to 50 hours. 6. The Li-C according to claim 5, wherein the granular material having an average particle size C of 10 to 25 μm is washed with water and then heat-treated.
A method for producing an o-based composite oxide.