JPH1140139A - Positive electrode for battery and nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery which is superior surely in high rate discharge performance and to make full use of conductive agent in a depolarizing mix for cell for positive active material effectively, even when active material with variation in particle diameters is used. SOLUTION: In a positive electrode for a battery consisting of active material of lithium transition metal compound oxide, a depolarizing mix for cell composed of a conductive agent and a binder, and a two dimensional collector, the conductive agent contains carbon material in a carbon black base, the carbon material in a carbon black base has as physical property such that an absorption amount of di-n-butyl phthalate is not more than 2.5 ml per 1 g, and has a specific resistance of 10 Ω cm when the depolarizing mix for cell is pressurized by 150 kgf/cm<2> under dry condition. It acts effectively, especially when a composition of the lithium transition metal compound oxide is indicated by Lix Mn2- YAy O4 (0.1<=x<=1.1, 0<=y<=0.3, and A is made of not less than 1 kind of metal selected from transition metal excluding Mn).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode for a battery and a non-aqueous electrolyte secondary battery, and more particularly to improvement of a high-rate discharge characteristic (load characteristic) of the battery.

[0002]

2. Description of the Related Art Conventionally, in the field of rechargeable secondary batteries, lead-acid batteries, nickel-cadmium batteries, nickel-
Aqueous solution batteries such as hydrogen batteries were the mainstream. However, in recent years, with the rapid spread of mobile phones and notebook personal computers, smaller and higher-capacity batteries have been required. In response to such demands, lithium secondary batteries using a lithium transition metal composite oxide such as lithium cobalt oxide for the positive electrode and a carbon material capable of inserting and removing lithium ions for the negative electrode have been developed. A lithium secondary battery using a carbon material that allows lithium ions to be inserted and desorbed from the negative electrode has a lower energy density than the same battery using metallic lithium as the negative electrode, but is safer than conventional aqueous batteries. Has the advantage of high energy density and is rapidly expanding its market.

A positive electrode for a lithium secondary battery is generally manufactured as follows. A slurry obtained by kneading and dispersing an active material powder composed of a lithium transition metal composite oxide and a conductive agent in an organic solvent together with a binder solution is applied to an aluminum foil that is a two-dimensional current collector, The dried product is pressed and fixed. Since the positive electrode has low conductivity of the active material itself, if the electrode is formed only with the active material and the binder, there is a problem that the ohmic loss of the electrode is large and a desired discharge capacity cannot be obtained. Therefore, for example, Japanese Patent Application Laid-Open
In JP-83607, the average particle size is 1 to 1 as a conductive agent.
It has been proposed that the carbon powder having a thickness of 10 μm is contained in an amount of 2 to 10 parts by weight based on 100 parts by weight of the positive electrode active material, thereby improving the current collecting property and improving the charge / discharge cycle characteristics and the high rate discharge characteristics of the battery. ing.

[0004]

However, the above-mentioned positive electrode active materials have various average particle sizes and particle size distributions depending on the composition and the production method. In particular, when the positive electrode active material is a manganese-based composite oxide, the particle size distribution of the positive electrode active material greatly depends on the particle size distribution of electrolytic manganese, which is a typical starting material. Therefore, many positive electrode active materials composed of a manganese-based composite oxide have a wide particle size distribution from about 0.1 μm to 100 μm. If the particle size distribution of the active material varies, the conductive agent powder tends to be localized when the active material and the conductive agent powder are mixed. In the localized state, it is difficult to say that the conductive agent is effectively utilized, and a desired battery performance may not be obtained in some cases. Therefore, Japanese Patent Application Laid-Open No. 8-83
Even if the technology of JP-A-607 is adopted, the conductive agent does not always work effectively. The problem to be solved by the present invention is to provide a positive electrode for a battery in which even when active material particles having a variation in particle diameter are used, they are surely excellent in high-rate discharge performance and can effectively utilize a conductive agent. is there.

[0005]

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention relates to an active material comprising a lithium transition metal composite oxide, a mixture comprising a conductive agent and a binder, and a two-dimensional current collector. In the battery positive electrode, the conductive agent includes a carbon black-based carbon material.
It has physical properties such that the absorption amount of dibutyl phthalate per g is 2.5 ml or less, and the mixture is dried at 150 kgf / cm
It is characterized in that the specific resistance of the mixture when pressurized in ² is 10 Ω · cm or less. As the conductive agent, other conductive carbon materials such as graphite and metal powders such as Al can be used in addition to carbon black-based carbon materials. As the carbon black in the present invention, so-called acetylene black, furnace black, thermal black and the like can be suitably used. The reason why it is preferable to use a carbon black-based carbon material having a dibutyl phthalate (hereinafter abbreviated as DBP) absorption amount of 2.5 ml or less per 1 g will be described below. Since the carbon black-based carbon material has a relatively large specific surface area, the electrical contact between the active material powders is made good, and the electrolyte absorbing property is greatly improved.
There is an advantage of improving the contact between the electrolyte and the positive electrode. On the other hand, in the step of preparing an active material mixture containing a carbon black-based carbon material, when mixing the slurry of the mixture, the carbon black absorbs a large amount of liquid, the slurry becomes unstable, and the carbon blacks further aggregate. I do. The aggregation causes localization of the conductive agent in the active material mixture. Therefore, carbon black as a conductive agent for a battery electrode needs to have physical properties that do not absorb liquid more than necessary. That is, the physical properties are such that the DBP absorption amount per gram of carbon black is 2.5 ml or less. The DBP absorption of carbon black was measured using a known dibutyl phthalate absorbometer under the same conditions for all measurements.

The present inventor has found that the positive electrode for a battery having the above specific resistance has excellent high-rate discharge performance as a result of earnest studies. This is effective even when the particle diameters of the active material particles vary, and can solve the above-mentioned problem. In the measurement of the specific resistance, a positive electrode in a dry state punched to φ14 was placed at 150 kgf / cm with a SUS cylindrical rod from above and below the thickness direction.
Pressurize with ² , and measure the resistance value at that time in milliohm meter (4328MILIOHMMETER manufactured by Yokogawa Hewlett-Packard Company)
Is calculated at room temperature under the condition that an alternating current of 100 V at the maximum and a frequency of 1 kHz is applied by the following equation (1). Thus, the specific resistance of the mixture can be measured using the battery positive electrode in which the mixture containing the active material is applied to one or both surfaces of the two-dimensional current collector.

Specific resistance = (resistance value × pressing electrode area) / (mixture thickness) (1) The mixture thickness in equation (1) is a value obtained by subtracting the thickness of the two-dimensional current collector from the electrode thickness. . When actually measuring the specific resistance, the resistance value for the thickness of the two-dimensional current collector is added, but since that value is negligibly small compared to that of the mixture, There is no problem in measurement. Also, when measuring the specific resistance of the active material mixture once in contact with the electrolytic solution, since the mixture is kept in a dry state, no movement of ions in the electrolytic solution occurs, so that there is no problem in the measurement.

The total content of the conductive material in the active material mixture of the positive electrode for a battery according to the present invention is determined by using a lithium transition metal composite oxide 10
It is desirable to use 1 to 10 parts by weight for 0 part by weight. When the content is less than 1 part by weight, the effective current collecting property is impaired. Further, when the content is more than 10 parts by weight, the volume capacity density of the electrode is reduced, and it is inevitable that the energy density is reduced at the stage of designing the battery.

In any positive electrode active material comprising a lithium transition metal composite oxide, the effect of improving electrode characteristics according to the present invention can be seen, but Li _x Mn _2-y A _y O ₄ (0.1 ≦ x
≦ 1.1, 0 ≦ y ≦ 0.3, A: made of any one of transition metals such as Co, Al, and Fe), the effect is particularly remarkable.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail using a positive electrode for a lithium secondary battery and a lithium secondary battery as examples. The method for producing a positive electrode according to the present invention is described below.
Lithium manganate (LiMn ₂ O ₄ ) having a particle size distribution of about 0.1 μm to 100 μm, which is an active material, is used as a conductive agent. : 5 to 8 μm) 8 parts by weight and DBP
2 parts by weight of carbon black (acetylene black) having an absorption amount of 2.5 ml / g and 10 parts by weight of polyvinylidene fluoride as a binder were added, and N was added as a dispersing solvent.
An active material mixture slurry to which -methylpyrrolidone was added and kneaded was applied to both sides of an aluminum foil as a two-dimensional current collector having a thickness of 20 µm, and then dried, pressed, and cut to obtain a positive electrode having a thickness of 200 µm. The specific resistance of this positive electrode is 5
Ω · cm.

(Production Method of Negative Electrode) Polyvinylidene fluoride as a binder is added to graphite powder in graphite 100
10 parts by weight with respect to parts by weight, N-methylpyrrolidone as a dispersion solvent was added thereto, and the kneaded slurry was applied to both sides of a 10 μm-thick rolled copper foil as a two-dimensional current collector, and then dried, pressed, 130μm thickness by cutting
A negative electrode was obtained.

The positive electrode and the negative electrode produced by the above method are
After being wound through a 25 μm-thick polyethylene separator, the wound group is inserted into a cylindrical battery container, the upper lid is swaged, and after sealing, a predetermined amount of electrolytic solution is injected from the injection port and sealed to form a cylindrical lithium battery. A secondary battery was obtained. As the electrolytic solution, a solution obtained by dissolving lithium hexafluorophosphate (LiPF ₆ ) at 1 mol / liter in a mixed solution of ethylene carbonate and dimethyl carbonate was used. The battery capacity of the design value of this battery is 1300 mAh.

The method for producing the positive electrode and the battery according to the present invention is not particularly limited, and a binder, a negative electrode active material, and an electrolyte commonly used for a positive electrode mixture can be used. Examples of the binder other than those used in this example include Teflon, polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber,
A simple substance such as polysulfide rubber, nitrocellulose, cyanoethylcellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloropyrene fluoride, or a mixture thereof can be suitably used. However, matching of these with the electrolytic solution is important. The binders listed above can be suitably used even when the electrolyte is a non-aqueous electrolyte (organic electrolyte) as in this example. The positive electrode active material made of a lithium transition metal composite oxide other than the one used in this example is a material into which lithium can be inserted and desorbed, and a material into which a sufficient amount of lithium has been inserted in advance is preferable. For example, there are a lithium-cobalt composite oxide, a lithium-nickel composite oxide, a lithium-vanadium composite oxide, and the like. Further, in these and the lithium-manganese composite oxide used in this example, part of manganese was replaced with other transition metals (Co, Al,
Fe or the like. There is no particular limitation on the negative electrode active material. In addition to those used in this example, for example, lithium metal, lithium alloy, various graphite materials, carbonaceous materials such as coke, and conductive polymers such as polyacetylene can be suitably used. Among them, various graphite materials which are capable of inserting and removing lithium, carbonaceous materials such as coke, conductive polymers such as polyacetylene, and the like are particularly preferable, similarly to the positive electrode active material. As the electrolytic solution, an electrolytic solution obtained by dissolving a general lithium salt as an electrolyte in an organic solvent is used. However, the lithium salt or organic solvent used is not particularly limited. Examples of electrolytes other than those used in this example include LiClO ₄ , L
iAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO
₃ Li, CF ₃ SO ₃ Li, etc., and mixtures thereof are used. Further, as the organic solvent, propylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran,
A single solvent such as 3-dioxolan, 4-methyl-1,3-dioxolan, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitonyl and the like, or a mixed solvent of two or more thereof can be used.

In this embodiment, the present invention has been described by taking the positive electrode for a lithium secondary battery and the lithium secondary battery as examples, but the battery system is not particularly limited.

[0015]

EXAMPLES In addition to the lithium secondary battery (Example 1) described in the above-described embodiment of the present invention, Examples 1 and 2 were the same as those of Example 1 except that the type of conductive agent and the amount of conductive agent for the positive electrode were as shown in Table 1. Lithium secondary batteries (Examples 2 to 7, Comparative Examples 1 to 4) manufactured under the same conditions were manufactured. Table 1 also shows the specific resistance of each positive electrode and the designed battery capacity.

The above batteries were compared with respect to discharge capacity and high-rate discharge performance. In the discharge capacity test, the battery was charged at a constant current at an 8-hour rate (1/8 C) for 8 hours, and then discharged at an 8-hour rate (1/8 C) to a final voltage of 3.2 V. Table 1 shows the battery capacity of each battery under these conditions. The battery capacity was shown as a ratio (%) when the discharge capacity of the battery of Example 2 was set to 100%. The high-rate discharge performance is as follows: after the charge / discharge efficiency is stabilized after the initial capacity test, the battery is charged at a constant current for 8 hours at an 8-hour rate, the discharge is performed at an 8-hour rate (1 / 8C), and the final voltage = 3.2 V.
Discharge capacity at the time of 1 hour, charge at 1 hour rate (1C) for 1 hour, discharge at 2 hour rate (2C), end voltage = 3.2V
, And the ratio is shown in Table 1. The high-rate discharge was represented by a 2C discharge capacity ratio (%) to a 1 / 8C discharge.

[0017]

[Table 1]

As is clear from Table 1, the specific resistance of the electrode is 10 Ω · cm or less, and the DBP absorption is 2.5 ml / cm 2.
g or less, the lithium secondary batteries of Examples 1 to 10 have stable battery capacity and high rate discharge (2C / (1 / 8C)).
Ratio) of 75% or more. On the other hand, Comparative Examples 1 to 4 having a specific resistance higher than 10 Ω · cm
Indicates that both the discharge capacity and the high-rate discharge performance are very low. From these results, it can be seen that the batteries of Examples of the present invention can provide batteries having better discharge capacity and higher rate discharge performance than conventional batteries. Further, when the DBP absorption amount of carbon black as the positive electrode conductive agent was Comparative Example 4, it was 2.5 ml / g.
, The specific resistance of the electrode exceeds 10 Ω · cm. This is the carbon black DBP
If the amount of absorption is more than 2.5 ml / g, the slurry properties deteriorate, causing troubles in the coating process, and as a result, the conductive agent is localized in the positive electrode active material mixture. It is considered that the conductive agent was not effectively used (from the data of the discharge capacity and the high-rate discharge characteristics). Therefore, the DBP absorption amount needs to be 2.5 ml / g or less.

On the other hand, when the amount of the positive electrode conductive agent is less than 1 part by weight, there is a tendency that the high-rate discharge characteristics slightly decrease. On the other hand, when the amount of the conductive agent is more than 10 parts by weight, the amount of the active material charged is reduced more than the improvement of the discharge capacity of the positive electrode, so that the battery capacity at the design stage is significantly reduced. From this,
The total amount of the conductive agent is preferably 1 part by weight or more and 10 parts by weight or less. In this example, lithium manganate was used as the positive electrode, graphite was used as the negative electrode, and lithium hexafluorophosphate dissolved at 1 mol / l in a mixed solution of ethylene carbonate and dimethyl carbonate was used as the electrolyte. However, the present invention is not limited to the above-described material constitution, and the same effect has been confirmed in batteries having other material constitutions as long as the specific resistance of the positive electrode is 10 Ω · cm or less.

[0020]

As described above, according to the present invention, the positive electrode conductive agent contains a carbon black-based carbon material, and the carbon black-based carbon material has a physical property of absorbing 2.5 ml or less of dibutyl phthalate per 1 g. And the specific resistance of the positive electrode active material mixture when pressurized to 150 kgf / cm ² is 10Ω ·
cm or less, it is possible to always provide an optimal state of the conductive agent even in various positive electrode active materials having different particle size distributions. As a result, a battery having excellent discharge capacity and high rate discharge characteristics can be obtained. .

Claims (4)

[Claims] 1. A battery positive electrode comprising a two-dimensional current collector and an active material comprising a lithium-transition metal composite oxide, a mixture comprising a conductive agent and a binder, wherein the conductive agent comprises a carbon black-based carbon material. The carbon black-based carbon material has physical properties such that the absorption amount of dibutyl phthalate per 1 g is 2.5 ml or less, and the specific resistance of the mixture when the mixture is pressurized at 150 kgf / cm ² in a dry state. A positive electrode for a battery, which has a resistance of 10 Ω · cm or less. 2. The positive electrode for a battery according to claim 1, wherein the total content of the conductive agent is 1 to 10 parts by weight based on 100 parts by weight of the active material. 3. The composition of an active material comprising a lithium transition metal composite oxide is Li _x Mn _2-y A _y O ₄ (0.1 ≦ x ≦ 1.1,
The positive electrode for a battery according to claim 1, wherein 0 ≦ y ≦ 0.3, and A is at least one selected from transition metals other than Mn. 4. A non-aqueous electrolyte secondary battery using the battery positive electrode according to claim 1.