JPH044560A - Alkaline storage battery ni electrode and its manufacture - Google Patents

Abstract

PURPOSE:To provide a high packing and capacity density and a high rate of active substance utilization by specifying the particle size range and distribution of a powder of nickel hydroxide. CONSTITUTION:A Ni electrode concerned is composed of an active substance layer 2, electrode basis 3, and electrode terminal 4. Powder of nickel hydroxide is used, whose particle sizes are below 50mum and the portion with particle sizes 10-30mum shares 50% or more. That is, a Ni electrode is composed of the active substance layer 2 and electrode basis 34, and the active substance layer 2 is obtained by spreading a hydrogen paste consisting of binder, additive, electroconductive agent, nickel oxide as active substance over the electrode basis 3. Favorable composition of the active substance layer 2 is 72-92wt.% nickel hydroxide, 5-15wt.% electroconductive agent, 2-8wt.% Co additive, and 1-15wt.% binder. This provides a high packing and capacity density and a high rate of active substance utilization.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is applicable to nickel electrodes of batteries using alkaline electrolytes, such as nickel-cadmium batteries, nickel-zinc batteries, and nickel-hydrogen batteries.

BACKGROUND OF THE INVENTION Nickel-cadmium batteries are currently the most commonly produced storage batteries that use alkaline electrolytes. The demand for this battery is increasing greatly due to the portability and cordless use of various electrical products, and its importance among commercially available batteries is increasing.

A nickel-cadmium electrode 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 electrodes 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 characteristics such as low internal resistance and rapid charging and discharging. However, there is a limit to uniformly and densely filling the active material into the micropores with a diameter of about 10 μm formed by the sintered body, and it is necessary to obtain a larger amount of discharged electricity from a battery of the same shape, that is, to increase the capacity density. cannot adequately meet the demands of

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. Looking at the application of this method to practical batteries, paste-type cadmium electrodes are quite popular in general-purpose 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 sintered electrodes. . As techniques for paste-type nickel electrodes, methods using foamed nickel as a base, methods using sintered metal fibers as a base, etc. have been proposed and announced. Furthermore, there are many inventions regarding the composition of the active material layer filled into these electrode substrates, and the effects of additives have also been clarified. For example, in U.S. Pat. No. 4,251,603, nickel hydroxide 87
wt%, nickel powder 10wt%, cobalt powder 3wt
A nickel electrode is produced by filling a foamed nickel base with a paste consisting of a 0.3 wt % carboxymethylcellulose aqueous solution. Also, JP-A-62
-283561 publication, nickel hydroxide 38wt%
A nickel electrode was fabricated by forming an active material layer consisting of 52 wt % nickel powder, 5 wt % cobalt powder, and 5 wt % sulfonic EPDM on a nickel wire mesh.

Problems to be Solved by the Invention The present invention relates to a paste-type nickel electrode for an alkaline storage battery that uses an alkaline electrolyte such as potassium hydroxide, lithium hydroxide, or sodium hydroxide. It is related to particle size.

Looking at the paste-type nickel electrodes that have been proposed in the past, the focus of the invention was mainly on the composition of the electrode base and the paste applied or filled therein, or on additives to improve the utilization rate of the active material. Ta. Therefore, it seems that sufficient attention was not paid to the particle size distribution of the nickel hydroxide powder, which is the active material. for example,
25-15 in U.S. Pat. No. 4,251,603.
Nickel hydroxide with a particle size of 0 μm was prepared in Japanese Patent Application Laid-Open No. 62-283.
In Publication No. 561, nickel hydroxide powder with a diameter of 40 to 150 μm was selected, and the packing capacity density of the resulting nickel electrode was at a level of 500 mAh/cur.

In view of the results of the prior art described above, an object of the present invention is to clarify the particle size range and distribution of nickel hydroxide powder that can simultaneously satisfy increased capacity density and improved active material utilization. That is, the preferable particle size range of nickel hydroxide is 50 μm or less, and in particular, the highest discharge capacity density was obtained when 10 to 30 μm accounted for 50 wt% or more of the total particle size.

The nickel electrode is composed of an active material layer and an electrode base. The active material layer is formed by spreading a hydrogen paste consisting of nickel hydroxide as an active material, a conductive agent, an additive, and a binder on an electrode base. The conductive agent may be any material such as nickel or carbon that is stable against alkaline electrolytes. Powder or fibrous materials can be used, but fibrous materials are preferred for forming a conductive network in the active material layer. The additive is a component added to improve the utilization rate of the active material or charging characteristics, and cobalt, cadmium, zinc, etc. are known to be effective.

As the binder, any material can be used as long as it is alkali resistant and has a high powder binding power, such as polystyrene, ED
These include those that are insoluble in water, such as M rubber, polytetrafluoroethylene, and polyvinyl chloride, and those that are soluble in water, such as polypyryl alcohol, carboxydimethylcellulose, and methylcellulose.

According to the inventors' study results, the preferred composition of the active material layer to obtain a high-capacity nickel electrode is 72 to 92 wt% of nickel hydroxide, 5 to 15 wt% of a conductive agent, 2 to 8 wt% of a cobalt additive, and a binder. The adhesive content is 1 to 5 wt%.

The electrode substrate is preferably made of metal from the viewpoint of strength and conductivity, and from the viewpoint of alkali resistance and cost, it is necessary that at least its surface be coated with nickel or an alloy mainly composed of nickel. . The shape of the base is more like a wire mesh than a three-dimensional mesh such as foamed metal or metal felt.
Flat substrates such as expanded metal and perforated plates are more desirable for increasing the filling capacity density. Also,
In order to obtain higher discharge capacity, it is desirable to have conductive protrusions formed on the surface of these flat substrates.

Wet kneading is suitable for kneading and applying the active material layer components of the nickel electrode, and by creating a water-based paste, it is possible to create a paste with high density and high fluidity. When the water content in the paste is 20 wt% or less, fluidity that allows application to electrodes can be obtained.

Function: In order to obtain a nickel electrode with high capacity density, it is sufficient to improve the filling capacity density and the active material utilization rate, and to increase the discharge capacity density, which is the product of both. The reason why there is an optimum particle size range of the nickel electrode active material when such improvements are attempted is as follows. First, as the particle size increases, the surface area of the active material decreases, making it impossible to secure a surface area effective for electrode reactions, resulting in a decrease in active material utilization. Experiments have revealed that a high discharge capacity density can be obtained by using nickel hydroxide with a particle size of 50 μm or less.

When the particle size is 10 μm or less, there is a tendency that the amount of conductive agent necessary to ensure electrical connection between particles is insufficient, resistance increases, and active material utilization rate decreases. This tendency is particularly noticeable when the particle size is 5 μm or less.

A broader particle size distribution is preferable in terms of packing capacity density, but this has to be balanced with the above-mentioned restrictions on active material utilization. Further, with respect to the active material paste, it is preferable that the amount of nickel hydroxide, which is the active material, is larger, but this also has restrictions on the active material utilization rate, so it is a trade-off between the two.

The smaller the amount of water in the aqueous active material paste applied to the substrate, the fewer voids there will be after drying (the higher the filling capacity density will be).

However, if it is too small, the fluidity of the paste will be poor and
It will not be possible to apply it evenly.

The optimal condition is when a liquid film is uniformly formed on the particle surface and there is no free water between the particles.

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

FIG. 1 is a plan view and a sectional view of a nickel electrode 1 for an alkaline storage battery, which is the object of the present invention. In the figure, 2 is an active material layer, 3 is an electrode base, and 4 is an electrode terminal. The main point of the present invention is that the particle size of the active material layer 2 (in particular, the active material nickel hydroxide) has been specified.The present invention will be described in more detail below with reference to Examples.

Example 1 Nickel electrodes were produced using dimethyl hydroxide having the following three types of particle size distributions.

A, 250-150 μm B, 150-50 μm C 650 μm or less The composition of the nickel electrode is 80 tvt% of nickel hydroxide, and 10 wt% of nickel powder (average particle size 4 μm) as a conductive agent.
, 5 wt % metal cobalt powder as an additive, and 5 wt % polytetrafluoroethylene fine powder as a binder. The electrode was manufactured as follows.

The predetermined amount of the mixed powder of nickel hydroxide, nickel fiber, and metal cobalt powder is kneaded with 19 wt% water in a kneader, and when it is sufficiently compacted, a dispersion of polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., Polyflon dispersion D-1) was added in the above prescribed amount. The resulting paste was applied to both sides of a 60-mesh nickel wire mesh (wire diameter 100 μm) using a calendar roll, air-dried, and dried in a dryer for 80 minutes.
It was dried at 0°C for 15 hours. Thereafter, it was pressurized and cut into a nickel electrode.

The filling capacity density was determined from the dimensions and weight of the obtained nickel electrode. In addition, in order to determine the discharge capacity density, a charge/discharge test was conducted using a cadmium electrode of sufficient capacity as a counter electrode. A nonwoven fabric (thickness: 0.23 mm) of polyamide resin was used as the separator. The electrolyte contains 30 wt% potassium hydroxide and 1.6
An aqueous solution containing wt% lithium hydroxide-hydrate was used. Charging current is 0.1 CmA, discharging current is 0.2 C
mA, charging time 15 hours, discharge end voltage 1. O.V.
And so. Since a tendency for the discharge capacity to increase was observed during the charge/discharge cycle, the value at which the discharge capacity became stable was defined as the respective discharge capacity. Table 1 shows the performance of the obtained nickel electrode.

From Table 1, it can be seen that in the order of A, B, and C, the smaller the particle size of the nickel hydroxide powder, the higher the filling capacity density and the discharge capacity density.

Example 2 Nickel electrodes were produced using nickel hydroxide powders having the following three types of particle size distributions.

D. All are 50μm or less, and 10μm or less is 50wt
% E, all below 50 μm, 10 μm to 30 μm is 5
0 wt% F, all of them are 50 μm or less, and 30 μm to 50 μm are
The composition of the 50 wt% active material layer is 85 wt% nickel hydroxide, 5 wt% conductive agent, 5 wt% cobalt powder, and 5 wt% polytetrafluoroethylene. The conductive agent is nickel-plated carbon fiber (wire diameter 7 μm), and the electrode base is nickel expanded metal (5Ni7410 manufactured by Taiyo Zenki Co., Ltd.).
was used. The amount of water added at the start of kneading is 23% of the powder weight.
It was wt%. The electrode manufacturing method and evaluation method are as shown in Example 1.
I did the same thing. The results obtained are shown in Table 2.

From Table 2 Table 2, nickel hydroxide of E, that is, 10 to 30 μm
It can be seen that powders mainly having a particle size in this range have high filling capacity density and discharge capacity density, and powders containing particle sizes in this range are suitable.

Example 3 Nickel electrodes were produced using nickel hydroxide having the following three types of particle size distributions.

G, all of them are 50 μm or less, and 10 μm to 30 μm are 2
0wt% H9 is all 50μm or less, 10μm to 30μm is 4
0wt% ■, all of them are 50 μm or less, and 10 μm to 30 μm are
50wt% J, all 50μm or less, 10μm to 30μm 6
0 wt%, all of them are 50 μm or less, and 10 μm to 30 μm are
The composition of the 80 wt% active material layer is 84 wt% of nickel hydroxide, 10 wt% of nickel fiber (wire diameter 4 μm) as a conductive agent, 3 wt% of cobalt powder as an additive, and 3 wt% of polytetrafluoroethylene. The electrode substrate used was a 60-mesh nickel wire mesh sprayed with nickel at a surface density of 12 Zcd. The active material paste was kneaded in the same manner as in Example 1 to produce a nickel electrode. In addition, when the paste was separated at the end of kneading and the water content was determined, the water content was 18~
It was 17 wt%. Filling capacity density A and discharge capacity density B of the nickel electrode were measured in the same manner as in Example 1.
The results are shown in FIG. According to Figure 2, 10~30μ
When m powder is 50 wt% or more, 600 mAh/
CNF or higher discharge capacity density was obtained, indicating that these particle size distributions are the most preferable. In addition, fluidity that allows paste application is obtained with a small moisture content of 20 wt% or less, and the filling capacity density of the resulting nickel electrode is 600 mAh/cn? ~71
It had a high value of 0 mAb/c&.

Effects of the Invention According to the present invention, by selecting the particle size distribution of the nickel hydroxide powder, a nickel electrode with a high filling capacity density and a high active material utilization rate can be obtained. Furthermore, a conductive agent,
By optimizing the electrode substrate, the composition of the active material layer, etc., a high discharge capacity density of 600 mAh/car or more has become possible. These are technologies that enable high capacity density alkaline storage batteries, and their industrial impact is staggering.

[Brief explanation of drawings]

Figure 1 shows a paste-type nickel electrode for alkaline storage batteries, which is the object of the present invention; (a) is a plan view, (b) is a cross-sectional view,
FIG. 2 is a characteristic diagram showing changes in the filling capacity density and discharge capacity density of the paste-type nickel electrode for alkaline storage batteries obtained according to the present invention, depending on the particle size composition of the nickel hydroxide powder. ■...Nickel electrode, 2...Active material layer, 3...Electrode base, A...Filling capacity density, B...Discharge capacity density knee, Agent Patent attorney Kunihiko Wakabayashi 1st Figure (a) (b) Powder ratio of particle size 10 to 30c @ (wtχ) A ゛ Filling capacity density B Hole capacitance

Claims (1)

[Scope of Claims] 1. Nickel for alkaline storage batteries, characterized in that it is formed using nickel hydroxide powder having a particle size of 50 μm or less and in which the portion with a particle size of 10 to 30 μm accounts for 50% or more. very. 2. At least an alkali-resistant conductive agent such as nickel or carbon, an alkali-resistant binder, and a nickel hydroxide powder with a particle size of 50 μm or less and in which the particle size of 10 to 30 μm accounts for 50% or more. A nickel electrode for an alkaline storage battery, characterized in that an active material layer containing the active material is formed on an electrode base. 3. The nickel electrode for an alkaline storage battery according to claim 2, wherein the conductive agent has a fibrous shape. 4. The nickel electrode for an alkaline storage battery according to claim 2 or 3, wherein the electrode substrate has conductive protrusions formed on a hand plate-like conductive porous body such as a wire mesh, an expanded metal, or a perforated plate. 5. A method for producing a nickel electrode for an alkaline storage battery selected from one of claims 1 to 4, wherein the active material paste having a water content of 20 wt% or less is coated on an electrode base.