JPH0417263A - Positive electrode for alkaline storage battery - Google Patents

Abstract

PURPOSE:To obtain a nickel electrode, which can discharge quickly and has a high capacity density, with simple method by forming a conductive fiber layer on the surface of a paste type nickel electrode with high density. CONSTITUTION:A layer 3 made of conductive fiber is provided on the surface of a positive electrode which consists of the active material 1 made of nickel compound and the conductive material and the binding agent. Namely, the conductive fiber layer 3 is formed on the surface of the paste type nickel electrode to form a two-dimensional conductive net work on the surface of the electrode, and electrical connection with an electrode substrate 2 near the surface of the electrode becomes well. Capacity of a battery at the time of high- rate-discharge is thereby improved efficiently, and a nickel electrode, which can discharge quickly and has a high capacity density, can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to storage batteries, and particularly to alkaline storage batteries using alkaline electrolytes such as nickel-cadmium batteries, nickel-iron batteries, nickel-zinc batteries, and nickel-hydrogen batteries.
Regarding batteries.

BACKGROUND OF THE INVENTION Nickel-cadmium batteries are currently the most commonly produced alkaline storage batteries that use alkaline electrolytes. The importance of this battery among commercially available batteries is increasing as the demand for this battery increases as various electrical products become portable and cordless.

A nickel-cadmium battery is composed of a nickel electrode, a cadmium electrode, and a separator interposed between the two. Conventionally, so-called sintered electrodes have been used for both nickel and cadmium electrodes.

A sintered electrode is an electrode obtained by impregnating and precipitating an active material into a porous nickel sintered body formed on a nickel-plated perforated steel plate. This electrode has excellent properties such as low internal resistance and rapid charging and discharging. However, the diameter of the sintered body formed is lOμm.
There is a limit to the ability to uniformly and densely fill the active material into the micropores of the same size, and it is not possible to fully meet the demand for higher capacity density, which is the desire to obtain more discharged electricity from batteries of the same shape. . Therefore, there is a need for an electrode in which the proportion of the active material is larger, and in response to this demand, paste-type electrodes have been proposed. This method is a method in which the active material powder is directly filled into the current collector, and since no nickel sintered body is used, more active material can be filled. This method has been applied as a practical technology to the cadmium electrodes of cylindrical nickel-cadmium batteries. A commonly used method for manufacturing paste-type cadmium electrodes is to apply a slurry of cadmium oxide, which is the active material, onto a nickel-plated perforated steel plate, which is used as the core material of the sintered electrode substrate. There is.

On the other hand, in the paste-type nickel electrode technology, simply filling the base with an active material together with a conductive agent and a binder does not provide sufficient conductivity, and proposals have been made to improve the conductivity. For example, JP-A-5678072, JP-A-56
JP-A-84876 and the like proposes applying nickel plating to the surface of the prepared paste-type nickel electrode.

Problems to be Solved by the Invention As the production volume and applications of nickel-cadmium batteries increase, higher performance is desired for each application. The main ones are high capacity density,
Rapid charging and rapid discharging.

An object of the present invention is to provide an alkaline storage battery that can simultaneously achieve high capacity density and rapid discharge. In order to increase the capacity density, it is necessary to increase the capacity density of both nickel electrodes and cadmium electrodes, but at present, increasing the capacity density of cadmium electrodes is ahead of the others, and increasing the capacity density of nickel electrodes is strongly desired. It is rare.

In addition, since nickel electrode capacity dominates battery capacity for rapid discharge, it is also necessary to improve the nickel electrode. Looking at conventional technologies related to these purposes, conventional sintered nickel electrodes have excellent rapid discharge characteristics, but
Capacity density of 400 to 450 mAh/C♂ is the practical limit, and it is not possible to expect a significant increase in capacity beyond that with this structure. In addition, the capacity density of conventional paste-type nickel electrodes that use foamed metal, metal fiber sintered bodies, etc. as electrode bases and fill them with active material slurry is 500 to 550 m2.
Ah/d value, and it is possible to produce a battery with a higher capacity than the above-mentioned sintered type. However, its rapid discharge characteristics tended to be lower than those of the sintered type. Furthermore, in order to increase the capacity density of the negative layer, it is possible to make the electrode substrate into a flat plate shape and apply a high-density paste of active material to both sides, but the rapid discharge characteristics are not as good as those of the conventional method. They tended to be at the same level as technology or even lower. As a method for improving this, it is being considered to apply nickel plating to the surface of the produced nickel electrode to improve conductivity. (Unexamined Japanese Patent Publication No. 56-780
(No. 72, Japanese Unexamined Patent Publication No. 56-84876) However,
This method requires a step of plating the two-layer electrode after applying and molding the active material, making the process complicated. As a result, the characteristic of paste-type nickel electrodes, which is a simple process, is lost, and there are other problems such as chemical reactions and adsorption caused by contact between the components of the plating solution and the components of the active material layer, resulting in inactivation of the active material. There is a point. It is desired to develop a simpler and more effective method.

Means for Solving the Problems The present invention is characterized by forming a conductive fiber layer on the surface of a high-density paste-type nickel electrode in order to solve the above-mentioned problems of the prior art. We have achieved a nickel electrode that has a high capacity density and is capable of rapid discharge.

The conductive fiber layer is located on one or both sides of the nickel electrode surface, and has a composition different from that of the active material layer. If the conductive fiber layer is too thick, the capacitance density of the electrode itself will be reduced. However, if it is too thin, the effect of the conductive fiber layer will be insufficient. Practically speaking, the preferred thickness is 100 μm = 10 μm, although it depends on the material of the conductive fiber. Further, the conductive fiber layer does not only extend in a plane on the electrode surface, but also has a structure in which a portion thereof reaches in the thickness direction, that is, into the active material layer.

The material forming the conductive fiber layer must be stable under the conditions of use, that is, it must have alkali resistance and be stable in the operating potential range of the nickel electrode.

Examples of such materials include nickel, alloys containing these as main components, and carbon. Further, the conductive fiber itself does not necessarily need to be entirely composed of conductive material. For example, it is possible to use a material in which the surface of fibers made of a dielectric material such as synthetic resin or ceramics is coated with a conductive material, or a material in which dielectric fibers and conductive fibers are mixed. The conductive fiber layer can be either an aggregate of short fibers or continuous long fibers. It is also possible that the fibers form a continuous body such as non-woven fabric or woven fabric. Further, the conductive fiber layer may contain a binder for binding the conductive fibers in addition to the conductive fibers. As the binder, it is possible to use either water-soluble binders such as carboxymethyl cellulose, polyvinyl alcohol, sodium polyacrylate, and methylcellulose, or water-insoluble binders such as polyvinyl chloride, polytetrafluoroethylene, polyethylene, and polystyrene. be.

The conductive fiber layer can be formed by forming the fiber alone or together with a binder into a sheet in advance and stacking it on the active material layer, or by forming the fiber alone or with the binder together with the active material layer. Any method of forming by spreading on a layer is possible. The process of forming a conductive fiber layer on the active material layer can be performed either when the active material paste has been applied to the electrode base and the paste has not yet dried, or after it has dried. The former is preferable in consideration of adhesion. When forming the conductive fiber layer, or after that, use a roller press, if necessary.
It is desirable to apply pressure treatment such as a hydraulic press.

Effect The effect of the present invention is related to the change in electrical resistance due to charging and discharging of the nickel electrode active material. In other words, the charging and discharging reaction of a nickel electrode is generally expressed as: The charging reaction product is a conductor with a conductivity of 10-'S/cm, while the discharging reaction product is a conductor with a conductivity of 10-'S/cm.
- It is an insulator that exhibits a conductivity of S/0m. Therefore, the resistance of the nickel electrode active material layer increases as the discharge reaction progresses. Sintered nickel with a sufficiently formed conductive network At the pole, the effect of this change is small, and the capacity drop during rapid charging and discharging is also small.

However, this change has a large effect on paste-type nickel electrodes where the volume occupancy of the active material is increasing, and in order to improve the conductivity of the active material layer, nickel powder and plastic fibers with nickel plating on the surface are used. A conductive agent is mixed. However, the conductive network formed by the conductive agent has insufficient continuity compared to that formed by the nickel sintered plate of the sintered nickel electrode, and the rapid discharge characteristics also deteriorate. When the conductive fiber layer of the present invention is formed on the surface of such a paste-type nickel electrode, a two-dimensional conductive network is formed on the surface of the electrode. Even before the formation of the conductive fiber layer, there must be a point where conductivity with the electrode base is ensured by the added conductive agent on at least a part of the surface of the active material layer, and this point is The surface comes into contact with a two-dimensionally extending conductive fiber layer, resulting in good electrical connection with the electrode base near the electrode surface. It is thought that due to such a mechanism, the formation of the conductive fiber layer on the electrode surface reduced the substantial resistance, resulting in improved rapid discharge characteristics.

Example The present invention will be explained in more detail based on the drawings.

FIG. 1 is a cross-sectional view of a paste-type nickel electrode for a nickel-cadmium battery, which is the object of the present invention. In the figure, 1 is an active material layer, and 2 is an electrode base, which also serves as a current collector. 3 is a conductive fiber layer. Figure 1 a, b
Of these, b is a paste-type nickel electrode according to the prior art in which no conductive fiber layer is provided. a is a nickel electrode according to the present invention provided with a conductive fiber layer. FIG. 2 is an enlarged view of the surface portion of the nickel electrode (FIG. 1a) according to the present invention. As is clear from the figure, depending on the distribution of the conductive agent 5 in the nickel electrode, there are parts with relatively good conductivity and parts with poor conductivity. By forming the conductive fiber layer 3 thereon, two-dimensional conductivity is ensured, and the distance between the portions with insufficient conductivity and the portions with good conductivity is reduced, and the resistance is reduced.

Example 1 A method for manufacturing a paste-type nickel electrode used to carry out the present invention will be described. A 60 mesh unit wire mesh with a wire diameter of 100 μm was used as the electrode base. An active material paste was applied thereon. The active material paste has an average particle size of 10μ as an active material.
m nickel hydroxide 80wt%, as a conductive agent, wire diameter 4
μm nickel fiber 10wt%, particle size 5 as additive
It was obtained by adding water to a mixed powder consisting of 5 wt % of μm metal cobalt powder, thoroughly kneading it, and then adding 5 wt % of polytetrafluoroethylene fine powder as a binder. Immediately after applying the active material paste, nickel fiber nonwoven fabrics (wire diameter: 4 μm, basis weight: 10 cm, 1 ctl) were placed on both sides of the nickel electrode, and pressure bonded using a roller press. Thereafter, it was air-dried for 15 hours and further dried at 80°C for 3 hours.

In this way, a nickel electrode with a conductive fiber layer formed on the surface was obtained. For comparison, an untreated nickel electrode without a conductive fiber layer was similarly produced. The packing capacity density of the obtained nickel electrode was 655 mAh/a+r with the conductive fiber layer, and 663 mAh/a+r without the conductive fiber layer.
It was Ah/cnf. The discharge rate characteristics of these nickel electrodes were measured. A paste-type cadmium electrode having a sufficient capacity was used as the counter electrode, and a nickel-cadmium battery was assembled with a separator made of polyamide resin nonwoven fabric interposed therebetween. As the electrolyte, an aqueous solution containing 1.6 wt% lithium hydroxide hydrate and 30 wt% potassium hydroxide was used.
Charge and discharge was performed at room temperature. The obtained results are shown in A of FIG. Similar measurements were also made on untreated nickel electrodes.

The results are shown in D of FIG. As shown in the figure, the discharge rate characteristics were improved by the present invention, and the utilization rate was improved by 20% or more with 3 CmA discharge.

Example 2 A conductive fiber layer was formed using nickel-plated and nickel-coated carbon fibers.

The carbon fibers are PAN-based carbon fibers and have a wire diameter of 7 μm. A 0.25 μm thick nickel layer was formed thereon. This fiber was cut into short fibers of 6 mm and uniformly dispersed on both sides of a nickel electrode coated in the same manner as in Example 1 to form a conductive fiber layer. The density of the conductive fiber layer was 2 mg/crl per side. Thereafter, the electrode was treated under the same conditions as in Example 1 to obtain a nickel electrode. The packing capacity density of the obtained nickel electrode was 644 m
It was Ah/cnf.

The discharge rate characteristics were measured using this nickel electrode in combination with a cadmium electrode. The measurement method and conditions were all the same as in Example 1. The results are shown in Figure 3B.

The figure shows that the discharge rate characteristics of the nickel electrode of this example are also significantly improved compared to the comparative example.

Example 3 A conductive fiber layer was formed using a carbon fiber nonwoven fabric. The carbon fiber used is a PAN-based material (manufactured by Toshiku II) (Trading Card Mat). The density of the conductive fiber layer is 2mg per side.
/cnr. All electrode preparation methods are the same as in Example I. The filling capacity density of the obtained nickel electrode was 631
It was mAh/cnr. The discharge rate characteristics of this nickel electrode were measured in the same manner as in Example 1. The results are shown in Figure 3C. As can be seen from the figure, the discharge rate characteristics of the nickel electrode of this example are also significantly improved compared to the untreated comparative example, and the active material utilization rate reaches 80% at 3 CmA discharge.

As shown in the above embodiments, the technology of the present invention improves the discharge rate by forming a conductive fiber layer on the surface of a paste-type nickel electrode with a high packing density of 600 mAh/crt or more. The characteristics have been greatly improved, making it possible to create an excellent paste-type nickel electrode with high capacity density and rapid discharge.

Furthermore, since the present invention is a technology related to nickel electrodes for alkaline storage batteries that use an alkaline electrolyte, it is applicable not only to nickel-cadmium batteries but also to nickel-zinc batteries, nickel-hydrogen batteries, nickel-iron batteries, etc. .

Effects of the Invention According to the present invention, the electrical connection between the electrode surface portion and the electrode base is improved by forming a conductive fiber layer on the surface of a paste-type nickel electrode, which is simpler than the conventional method. As a result, the active material utilization rate is over 80% at a discharge rate of 3 CmA, which is extremely effective in improving battery capacity during high-rate discharge, and enables high capacity density and rapid discharge. A nickel electrode was obtained. Furthermore, since the conductive fiber layer exists only on the surface of the active material layer, it has little effect on the active material packing density.

[Brief explanation of drawings]

Fig. 1a is a cross-sectional view of a nickel electrode with a conductive fiber layer formed on its surface, which is an embodiment of the present invention, Fig. 1 is a cross-sectional view of a paste-type nickel electrode which is a known example, and Fig. 2 is a cross-sectional view of a paste-type nickel electrode according to the present invention. FIG. 3 is an enlarged cross-sectional view of the surface portion of a nickel electrode with a conductive fiber layer formed on the surface, which is an example of the present invention. FIG. It is a characteristic curve diagram. ■... Active material layer, 2... Electrode base, 3... Conductive fiber layer, 4... Active material, 5... Conductive agent, A... Electrode of Example 1, B... ... Electrode of Example 2, C ... Electrode of Example 3 Patent attorney Kunihiko Wakabayashi Figure 1 Figure 2, 3 Discharge rate (C□A) A, B, C: Electrode of the present invention

Claims (1)

[Claims] 1. An active material made of a nickel compound such as nickel hydroxide or nickel oxyhydroxide, a positive electrode made of a conductive material, a binder, etc., and an active material made of cadmium, iron, zinc, hydrogen, etc. negative electrode, lithium hydroxide, sodium hydroxide,
1. A positive electrode plate for an alkaline storage battery using an alkaline electrolyte containing potassium hydroxide or the like as an electrolyte, the positive electrode plate having a layer made of conductive fibers on the surface of the positive electrode. 2. The positive electrode plate for an alkaline storage battery according to claim 1, wherein the conductive fiber layer forms a layer made of nickel, carbon, or a fibrous material coated with these on the electrode.