JP2003115295A - Method of manufacturing electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode capable of quickly dispersing a positive active material into positive mix paste, quickly reaching object viscosity, and quickly manufacturing the electrode. SOLUTION: This method of manufacturing the electrode has a preliminary kneading process preparing preliminary paste by mixing a part of the positive active material, a conductive material, and a solvent; a main kneading process mixing the remaining positive active material with the preliminary paste; and a positive mix preparing process preparing the positive mix paste in which the positive active material and the conductive material are dispersed into the solvent. By adding first a part of the positive active material and kneading, since friction between conductive materials is reduced by the presence of the positive active material having larger particle size than that of the conductive material, the positive active material and the conductive material is quickly dispersed in the solvent, and viscosity is apparently reduced. By adding the positive active material having larger particle size, the shredding of the conductive material is apparently advanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing electrodes of lithium secondary batteries, nickel hydrogen secondary batteries and the like.

[0002]

2. Description of the Related Art With the miniaturization of personal computers, video cameras, mobile phones and the like, in the fields of information related equipment and communication equipment, secondary batteries have been used as a power source for these equipment. Among secondary batteries, lithium secondary batteries and nickel-hydrogen secondary batteries have been put into practical use and widely spread because of their high energy density. On the other hand, also in the field of automobiles, the development of electric vehicles has been rushed due to environmental problems and resource problems, and secondary batteries such as lithium secondary batteries are also being considered as a power source for this electric vehicle. .

For the electrodes of lithium secondary batteries and nickel-hydrogen secondary batteries, which are the secondary batteries that have recently received attention, the active material is mixed with a solvent in a solvent and the positive electrode mixture paste is applied to the surface of the current collector. It is manufactured by making it penetrate into the current collector.

As a conventional technique, in Japanese Patent Laid-Open No. 7-119919, a first step is to first mix an active material with a part of a solvent to form a putty having a high viscosity, and a remaining step is added to form a slurry. A method of manufacturing a paste type nickel electrode having two steps is disclosed. By this method, it is possible to achieve a high degree of homogeneity of dispersion of the active material and the like in the electrode mixture paste.

Further, in Japanese Unexamined Patent Publication No. 10-149819, there is disclosed a paste-type nickel electrode including a step of filling a low-viscosity electrode mixture paste in a current collector and a step of filling a high-viscosity electrode mixture paste. A manufacturing method is disclosed.
By this method, the active material density of the manufactured electrode can be increased.

[0006]

By the way, cost reduction is an essential issue in putting these secondary batteries into practical use. It is possible to contribute to cost reduction by rapidly performing the production of the electrode mixture paste, which is applied on the current collector. Since the electrode mixture paste is to be attached to the current collector, its viscosity has a proper range.

Among the conventional electrode mixture pastes used for the electrodes, the positive electrode mixture paste containing the conductive material as an essential component in addition to the active material cannot be uniformly dispersed when the components are mixed and kneaded. However, there is a problem that the initial viscosity becomes so high that uniform dispersion and reaching of an appropriate viscosity cannot be achieved quickly, which has been a cause of delaying the manufacturing time of the electrode.

Therefore, in the present invention, it is possible to rapidly reduce the viscosity of the positive electrode mixture paste, reach the target viscosity promptly, and manufacture the electrode promptly. It is a problem to be solved to provide a manufacturing method.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted diligent research for the purpose of solving the above problems. Focusing on the poor disintegration property, investigations were conducted to improve dispersibility and disintegration property. As a result, it becomes possible to rapidly disperse the conductive material and the positive electrode active material in the solvent by first mixing and kneading the constituent elements other than the positive electrode active material, and then adding the positive electrode active material, and the desired viscosity Found that you can get to quickly. Furthermore, it was discovered that the viscosity can be further lowered rapidly by adding the positive electrode active material in two or more portions.

The present invention has been made on the basis of the above findings. A preliminary kneading step of mixing a part of the positive electrode active material, a conductive material and a solvent to form a preliminary paste, and a balance of the positive electrode active material And a main kneading step of adding and mixing into the preliminary paste, and a positive electrode mixture preparing step of preparing a positive electrode mixture paste in which the positive electrode active material and the conductive material are dispersed in the solvent. It is a manufacturing method of an electrode.

That is, by adding a part of the positive electrode active material first and kneading, the friction between the conductive materials and the like is reduced in the presence of the positive electrode active material having a particle size larger than that of the conductive material, so that the solvent is rapidly added. It is considered that the dispersion was possible and the viscosity was lowered. It is also considered that the addition of the positive electrode active material having a larger particle size contributed to the progress of crushing. After that, when the rest of the positive electrode active material is added, the conductive material is already well dispersed and crushed, so that the positive electrode active material can be dispersed in the solvent early.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The method for producing an electrode according to the present invention is a method of adhering or permeating a positive electrode mixture paste on the surface or inside of a current collector, and thereafter removing a solvent in the positive electrode mixture paste. There is a feature in the positive electrode mixture preparation step of manufacturing the positive electrode mixture paste. The electrode that can be manufactured by the method for manufacturing an electrode of the present invention is a positive electrode such as a lithium secondary battery, a nickel-hydrogen secondary battery, a nickel-cadmium secondary battery, or a lead storage battery. In this embodiment, a case where the present invention is applied to a positive electrode of a lithium secondary battery as a typical electrode among them will be described. This is basically the same when manufacturing electrodes of other batteries.

The method of manufacturing an electrode for manufacturing the positive electrode of the lithium secondary battery according to the present embodiment comprises a positive electrode active material capable of absorbing and desorbing lithium ions, a conductive material, and other necessary components (eg, a binder). Mix and add a suitable solvent to make a positive electrode mixture paste (positive electrode mixture preparation step), coat it on the surface of a current collector made of metal foil such as aluminum, dry it, and then press it to make the positive electrode active material density. Formed by increasing.

As the positive electrode active material, a known positive electrode active material such as a lithium transition metal composite oxide can be used. The lithium-transition metal composite oxide is a preferable material for the positive electrode active material because it has low electric resistance, excellent lithium ion diffusion performance, high charge-discharge efficiency, and good charge-discharge cycle characteristics. For example, lithium cobalt oxide,
Lithium nickel oxide, lithium manganese oxide,
A material in which a transition metal such as Li, Al, and Cr is added or replaced is used. When these lithium-metal composite oxides are used as the positive electrode active material, they can be used not only individually but also as a mixture of two or more kinds.

The conductive material is for ensuring the electric conductivity of the positive electrode, and it is preferable to use one kind or a mixture of two or more kinds of carbon substance powders such as carbon black, acetylene black and graphite. it can. The particle size of the conductive material is very small compared to the positive electrode active material, and the gap between the positive electrode active materials can be efficiently filled to reduce the density of the positive electrode active material in the electrode mixture, Positive electrode active material −
The conductivity between the current collectors is secured.

The binder plays a role of binding the particles of the positive electrode active material and the particles of the conductive material, and is made of a fluororesin such as polytetrafluoroethylene, polyvinylidene fluoride and fluororubber, or a thermoplastic resin such as polypropylene and polyethylene. Can be used.

An organic solvent such as N-methyl-2-pyrrolidone or water can be used as a solvent for dispersing the positive electrode active material, the conductive material and the binder.

The positive electrode mixture preparing step includes a preliminary kneading step and a main kneading step, and is a step of preparing a positive electrode mixture paste in which a positive electrode active material and the like are highly dispersed in a solvent and whose viscosity is controlled.

The preliminary kneading step is a step of mixing a part of the positive electrode active material, the conductive material and the solvent to prepare a preliminary paste.
The order of adding a part of the positive electrode active material, the conductive material and the solvent is not particularly limited. The amount of a part of the positive electrode active material added in the preliminary kneading step is preferably 50% by mass or less, and more preferably 1 to 15% by mass based on the total mass.
This is because the positive electrode active material exerts an effect of sharply decreasing the viscosity even if it is added in a small amount, but if it is added in an excessively large amount in the pre-kneading step, the positive electrode active material itself causes an increase in viscosity. In the preliminary kneading step, it is not necessary to add a part of the positive electrode active material all at once, and a part of the positive electrode active material may be added in several times.

The main kneading step is a step of mixing the preliminary paste prepared in the preliminary kneading step with the rest of the positive electrode active material. This kneading step is performed until the positive electrode mixture paste has a desired viscosity. When the binder is added to the positive electrode mixture paste, it may be added during the positive electrode mixture preparation step, and may be added in either the preliminary kneading step or the main kneading step.

Thereafter, the prepared positive electrode mixture paste is applied and dried on the surface of the current collector. The method of applying the positive electrode mixture paste on the current collector is not particularly limited, and a usual method can be applied. For example, it can be carried out by applying the positive electrode mixture paste thinly on the surface of the current collector with a bar coater, a die coater or the like, and then passing the current collector through the dryer.

The current collector whose surface is coated with the positive electrode mixture paste is, if necessary, increased in density of the positive electrode active material by pressing or the like, and then combined with a negative electrode, a separator or the like manufactured by a conventional method to obtain a lithium secondary battery. Can be

[0023]

EXAMPLES The electrode manufacturing method of the present invention will be described in more detail.

Example 1 40 parts by mass of lithium nickel oxide as a positive electrode active material, 5 parts by mass of carbon black as a conductive material, and 5 parts by mass of PVDF as a binder were used as a solvent in N-methyl. 2-Pyrrolidone (50 parts by mass) was mixed to prepare a positive electrode mixture paste (positive electrode mixture preparation step).

First, the whole of the conductive material and the binder and a part of the positive electrode active material (1% by mass of the whole positive electrode active material) were added to the solvent. This mixture was dispersed in a circulation homogenizer to prepare a preliminary paste (preliminary kneading step). In this pre-kneading step, as shown in FIG. 1, the viscosity of the pre-paste became 100 mPa · s after 20 minutes from the start of dispersion. Therefore, the rest of the positive electrode active material was added to the pre-paste and dispersed in the homogenizer. Was continued (main kneading step). As shown in FIG. 1, the viscosity of the positive electrode mixture paste after 60 minutes from the start of the preliminary kneading step (40 minutes after the start of the main kneading step) was 3000 mP suitable for coating on the current collector.
It was less than a · s. In addition, in FIG. 1, a portion indicated by a broken line showing a change in viscosity shows an expected change in viscosity although there is no actually measured value. This also applies to Comparative Example 2.

Here, the viscosity is measured by using an E-type viscometer,
It was measured under the conditions of 0.5 rpm, 1.9 sec ^-1 , and 30 ° C.
This measurement condition is the same for the following viscosity measurement.

(Comparative Example 1) As in Example 1, 40 parts by mass of lithium nickel oxide as a positive electrode active material, 5 parts by mass of carbon black as a conductive material, and PV as a binder.
5 parts by mass of DF and 50 parts by mass of N-methyl-2-pyrrolidone as a solvent were mixed to prepare a positive electrode mixture paste. At this time, all components were mixed at once. When the viscosity was examined, as shown in FIG. 1, 60 minutes after the start of mixing and kneading, 7,000 mPa · s, and 60 minutes after 120 minutes.
It became 00 mPa · s.

Comparative Example 2 As in Example 1, 40 parts by mass of lithium nickel oxide as a positive electrode active material, 5 parts by mass of carbon black as a conductive material, and PV as a binder were used.
5 parts by mass of DF and 50 parts by mass of N-methyl-2-pyrrolidone as a solvent were mixed to prepare a positive electrode mixture paste. At this time, first, the constituent elements other than the positive electrode active material were mixed at once. As shown in FIG. 1, the initial viscosity is Comparative Example 1
Although higher than the above, the viscosity was 8000 mPa · s when examined 60 minutes after the kneading was started. This value was almost the same as the value of Comparative Example 1 in which all the constituents were mixed at the same time. After that, as a result of adding all the positive electrode active materials and continuing the mixing, as shown in FIG.
It became lower than the viscosity at the same time, and after 30 minutes,
It became 00 mPa · s.

(Discussion) As described above, in Comparative Example 1 in which all the constituents are mixed from the beginning, the decrease in viscosity is slow, whereas in Example 1 in which the positive electrode active material is divided and added, the positive electrode is added. It has been found that the viscosity of the mixture paste can be reduced significantly rapidly. In Comparative Example 2 in which the positive electrode active material was added after mixing the constituents other than the positive electrode active material, the viscosity could be reduced more quickly than in Comparative Example 1, but it was not sufficient compared with Example 1. It was

(Example 2) Similar to Example 1, 40 parts by mass of lithium nickel oxide as a positive electrode active material, 5 parts by mass of carbon black as a conductive material, and PV as a binder.
5 parts by mass of DF and 50 parts by mass of N-methyl-2-pyrrolidone as a solvent were mixed to prepare a positive electrode mixture paste. At this time, the change in viscosity when the proportion of the positive electrode active material added (% by mass relative to the whole positive electrode active material) was changed was examined. The viscosity was measured 20 minutes after the mixing was started.

The results are shown in FIG. It was found that when a very small amount (about 5 to 10% by mass) of the positive electrode active material was added, the viscosity had a minimum value, and then the viscosity increased linearly.
The preferable addition amount of the positive electrode active material whose viscosity decreases is
From FIG. 2, it became clear that 50 mass% or less is certainly preferable. Among them, 1 to 1 as a part of the positive electrode active material
It can be seen that it is more preferable to add 5% by mass in the pre-kneading step. Further, the more preferable addition amount of the positive electrode active material is 5 to 15.

[0032]

As described above, in the electrode manufacturing method of the present invention, a part of the positive electrode active material is added in the preliminary kneading step of the positive electrode mixture preparing step, and the rest of the positive electrode active material is added in the main kneading step. As a result, the viscosity of the positive electrode mixture paste can be rapidly reduced, the target viscosity can be reached quickly, and the electrode can be produced quickly.

[Brief description of drawings]

FIG. 1 is a graph showing the mixing time dependency of the electrode mixture paste viscosity in Example 1 and Comparative Examples 1 and 2.

FIG. 2 is a graph showing the dependency of the viscosity of the electrode mixture paste in Example 2 on the amount of the positive electrode active material added.

Claims (3)

[Claims] 1. A preliminary kneading step of mixing a part of the positive electrode active material, a conductive material and a solvent to form a preliminary paste, and a main kneading step of adding the rest of the positive electrode active material into the preliminary paste and mixing them. A method for manufacturing an electrode, further comprising a positive electrode mixture material preparation step of preparing a positive electrode mixture material paste in which the positive electrode active material and the conductive material are dispersed in the solvent. 2. The method for producing an electrode according to claim 1, wherein a part of the positive electrode active material mixed in the preliminary kneading step is 50% by mass or less based on the total mass of the positive electrode active material. 3. A part of the positive electrode active material mixed in the preliminary kneading step is 1 to 1 with respect to the total mass of the positive electrode active material.
It is 5 mass%, The manufacturing method of the electrode of Claim 2.