JP3308229B2 - Li-Co based composite oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a Li-Co-based composite oxide, 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.

[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 when a Li-Co-based composite oxide having a specific specific surface area and a specific particle size is used as a positive electrode active material, the charge / discharge cycle characteristics of a lithium secondary battery are reduced. It has been found that it 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 of a lithium secondary battery. An object is to provide a Li—Co-based composite oxide that can improve characteristics.

[0006]

The above object is achieved by the following L
The problem can be solved by using an i-Co-based composite oxide. flat
A Hitoshitsubu diameter 10Myuemu～25myuemu, and wherein the product of the specific surface area (m ² / g) and average particle diameter ([mu] m) is a particulate material satisfying the following formula (1), lithium secondary
Li-Co-based composite oxide for a positive electrode active material of a battery . 7 ≦ [20 / (specific surface area × average particle size)] ≦ 9 (1) The Li-Co-based composite oxide particles are heated to 400 to 750 ° C.
Obtained by heat treatment at a high temperature of 0.5 to 50 hours.
The product of the specific surface area (m ² / g) and the average particle size (μm) is
The lithium secondary battery is a granular material satisfying (1).
Li-Co based composite oxide for extreme active material. 7 ≦ [20 / (specific surface area × average particle size)] ≦ 9 (1)

[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. Expression (2) may be used. _{Li A Co 1-X Me x} O 2 (2) In the formula (2), A is about 0.05 to 1.5, and preferably about 0.1 to 1.1, X is from 0.01 to 0 .5
Degree, particularly preferably about 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 a group 13-15 element such as B, Al, Ge, P
b, Sn, Sb, and the like. 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.

[0008] The Li-Co-based composite oxide of the present invention is formed of a granular material whose product of the specific surface area and the average particle size satisfies the formula (1). When a particulate material having a value of [20 / (specific surface area × average particle size)] of less than 7 or more than 9 is used as a positive electrode active material, a favorable improvement is seen in the charge / discharge cycle characteristics of the lithium secondary battery. However, in the present invention, L formed of a granular material satisfying the following formula (3)
An i-Co-based composite oxide is particularly preferred. 7 ≦ [20 / (specific surface area × average particle size)] ≦ 8.5 (3)

As long as the Li—Co-based composite oxide of the present invention satisfies the above formula (1) or (3), each of the specific surface area and the average particle size is considered from the viewpoint of the charge / discharge cycle characteristics of the lithium secondary battery. There is no particular limitation on the size. However, since the average particle diameter of the Li-Co-based composite oxide is too small, it is generally rich in reactivity and generally easily causes an abnormal battery reaction.
Average particle size is 10μm from the viewpoint of safety of lithium secondary battery
The above are preferred. Further, the Li-Co-based composite oxide having an excessively large particle diameter has a large electric resistance, which leads to a reduction in the energy density per unit volume of the lithium secondary battery. Therefore, the average particle diameter is preferably 25 µm or less. On the other hand, the preferable range of the specific surface area of the Li—Co-based composite oxide is about 0.1 to 0.3 m ² / g, particularly 0.15 to 0.25 from the viewpoint of the charge and discharge cycle characteristics of the lithium secondary battery.
It is about m ² / g.

The Li—Co-based composite oxide of the present invention is obtained by mixing a lithium compound and a cobalt compound as starting materials with an atomic ratio of cobalt to lithium of 1: 1 or another atomic ratio;
Particularly, the mixture is mixed so that lithium is slightly larger than that of cobalt, and the mixture is reacted by a well-known method. For example, the mixture is heated and fired at about 1000 ° C. in the air for 1 to 50 hours, and thus produced. The lump of the Li-Co-based composite oxide thus obtained is pulverized, and then a material having a specific surface area and an average particle size satisfying the formula (1) or (3) is classified and collected. Alternatively, granules of Li-Co-based composite oxide such as those obtained by pulverizing the above-mentioned masses, especially granules having an average particle diameter of 10 μm to 25 μm
It can also be produced by heat treatment at a high temperature of about 0 to 750 ° C, especially about 450 to 700 ° C for about 0.5 to 50 hours, especially about 1 to 20 hours. This heat treatment may be performed in the air or in an inert gas atmosphere such as nitrogen or argon.However, if carbon dioxide gas is present in the atmosphere in which the heat treatment is performed, lithium carbonate is generated and leads to an increase in the content of impurities. , The partial pressure of carbon dioxide in the atmosphere is 10 mm
It is preferable to be about Hg or less.

Examples of the above-mentioned lithium compound and cobalt compound as starting materials include lithium and cobalt oxides, hydroxides, halides, nitrates, oxalates, carbonates and the like. As shown in equation (2), ie, C
In the case of producing a Li-Co-based composite oxide in which a part of o is substituted with another element, it is preferable to add a necessary amount of the compound of the substituted element to the above mixture and heat and calcinate the mixture. In general, Li-Co-based composite oxides generally include lithium oxide, lithium hydroxide, lithium carbonate, cobalt oxide,
Cobalt carbonate or other impurities (eg, iron, copper,
Metal compound such as nickel) in many cases, but in the Li-Co-based composite oxide of the present invention, the total amount of lithium compound impurities is 0.5% by weight or less, and the total amount of cobalt compound impurities is 1%. If the total amount of other impurities is 0.06% by weight or less, the content of such impurities can be allowed.

According to the study of the present inventor, the average particle diameter of Li-Co based composite oxide particles generally does not change so much or substantially by heat treatment, but the specific surface area tends to decrease. Although the reason is not yet clear, there is an effect of improving the charge / discharge cycle characteristics of the lithium secondary battery.
Thus, in the present invention, a Li-Co-based composite oxide whose specific surface area has been reduced by the above-mentioned heat treatment, particularly the degree of reduction of the specific surface area is 10% or more, is particularly preferable. Note that the degree of decrease in the specific surface area is represented by a ratio (%) of the difference between the specific surface area before the heat treatment and the specific surface area after the heat treatment to the specific surface area after the heat treatment.

In the present invention, 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, respectively. [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 in a state where an ultrasonic wave of about 5 to 40 kHz is applied is used, and the amount of particulate matter in this 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 number of particles present for each particle size (N ₁ ,
(N ₂ , N ₃ ...) Is measured (the particle diameter (D) of each particle) is automatically measured by a Microtrac particle size analyzer for each particle 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)

The Li—Co-based composite oxide of the present invention can be used as a positive electrode active material for a non-aqueous electrolyte secondary battery such as a lithium secondary battery. It can be used for the manufacture of a lithium secondary battery by using it together with a member. The main other 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 electrolytic solution include those 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.

[0019]

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 1-4, Comparative Examples 1-5_ThreeO_FourAnd Li_TwoCO_ThreeAnd Co_ThreeO_Four100
Li per part by weight_TwoCO _ThreeAnd 42 parts by weight of
The mixture is fired at about 980 ° C. for about 10 hours, and obtained by firing.
Lumpy LiCoO_TwoCrushed and classified, and then heat in air
After processing, each of Examples 1-4 and Comparative Examples 1-5 shown in Table 1
LiCoO_TwoGranules were obtained. Each Li of Comparative Examples 1 to 3
CoO_TwoGranular materials have not been subjected to the above heat treatment.
No.

Table 1 shows each LiCo of Examples and Comparative Examples.
Heat treatment conditions (temperature and time) for O ₂ granules,
The average particle size B, the specific surface area A, the degree of decrease in specific surface area (ΔA) due to the heat treatment, and the value of [20 / (AB)] of the LiCoO ₂ particles after the heat treatment are shown. The average particle size B and the specific surface area A of the LiCoO ₂ granules of Comparative Examples 1 to 3 not subjected to the heat treatment indicate the values of the granules not subjected to the heat treatment.

[0022]

[Table 1]

Each Li of Examples 1-4 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 subjected to a rolling treatment. Thus, a positive electrode body having a positive electrode active material composition layer of 20 mg / cm ² per one side of the aluminum foil Was prepared. Separately, 90 parts by weight of flake graphite, 10 parts by weight of polyvinylidene fluoride, and 200 parts by weight of N-methyl-2-pyrrolidone were mixed to form a slurry. This slurry is used as a current collector with a thickness of 1
The coating was applied to both sides of a 4 μm 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 surface 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 the electrolytic solution, a solution prepared by dissolving 1 mol of LiPF ₆ per liter of a mixed solvent of ethylene carbonate, propylene carbonate, and diethyl carbonate (mixing volume ratio is 3: 2: 5) was used. Between the body and the anode body.

Next, the charge / discharge cycle characteristics of each lithium secondary battery were measured according to the following charge / discharge cycle test method, and the discharge capacity retention ratio (%) at the 100th cycle was measured.
Are shown in Table 1. [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, it can be seen that each of LiCoO _{2 of} Comparative Examples 1 to 5 in which the value of [20 / AB] is out of the range of the above formula (1)
Lithium secondary batteries using granular materials as the positive electrode active material,
While the discharge capacity retention rate at the 100th cycle was 85% or less, each of the LiCoO ₂ granules of Examples 1 to 4 in which the value of [20 / AB] was within the range of the formula (1) was used as the positive electrode active material. The lithium secondary battery used as the material has a high discharge capacity retention ratio of 90% or more even at the 100th cycle,
Thus, it can be seen that the battery has excellent charge / discharge cycle characteristics.

[0026]

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 the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C01G 51/00 H01M 4/02 H01M 4/58 H01M 10/40 CA (STN)

Claims (2)

(57) [Claims] (1) an average particle size is 10 μm to 25 μm;
And wherein the product of the specific surface area (m ² / g) and average particle diameter ([mu] m) is a particulate material satisfying the following formula, lithium
Li-Co-based composite oxide for a positive electrode active material of a lithium secondary battery . 7 ≦ [20 / (specific surface area × average particle size)] ≦ 9 2. The method according to claim 1 , wherein the granular material of the Li—Co-based composite oxide is
Obtained by heat treatment at a high temperature of 0 to 750 ° C for 0.5 to 50 hours
The specific surface area (m ² / g) and average particle size (μm)
Is a granular material whose product satisfies the following formula.
Li-Co based composite oxide for positive electrode active material of pond. 7 ≦ [20 / (specific surface area × average particle size)] ≦ 9