JPH02155167A - Alkaline secondary battery - Google Patents

Abstract

PURPOSE:To enhance quick charge-discharge performance by using nickel powder having a particle size of 1-5mum prepared by thermal decomposition of tetracarbonyl nickel as a conductive material. CONSTITUTION:Nickel powder having a particle size of 1-5mum prepared by thermal decomposition of tetracarbonyl nickel is used as a conductive material of a positive electrode 2. The nickel powder obtained has small particle size and a large number of projections on the surface. Therefore, its specific surface area is very large. In the positive electrode 2 prepared with a powder molding press, particles are entangled through projections and the conductive material particles form a matrix to increase conductive effect. The internal resistance of a battery is decreased and quick charge-discharge performance is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an alkaline secondary battery using nickel oxide as a positive electrode active material.

[Invention (already required)]

The present invention provides an alkaline secondary battery in which the positive electrode is a compressed powder body containing a positive electrode active material mainly composed of nickel oxide and a conductive additive, in which the conductive additive is obtained by thermal decomposition of tetracarbonyl nickel. Particle size 1~5μ
By using nickel powder of m, the rapid charging and discharging characteristics are improved.

[Conventional technology]

In general, the positive electrode of an alkaline secondary battery is composed of a nickel oxide powder that directly participates in electrochemical redox reactions, a conductive agent such as nickel powder, and a binder such as Teflon (polytetrafluoroethylene). has been done. On the other hand, in recent years, negative electrodes have been proposed that use negative electrode active materials mainly consisting of hydrogen storage alloys that reversibly absorb and release hydrogen during battery reactions. BACKGROUND ART Secondary batteries are attracting attention as secondary batteries (hereinafter referred to as nickel-metal hydride batteries) that are non-polluting and can be expected to have high energy density.

[Problem to be solved by the invention]

However, the above-mentioned nickel-metal hydride batteries generally have a drawback of poor rapid charging and discharging characteristics.

The reasons for this are: (1) Nickel-metal hydride batteries are generally manufactured as button-type batteries, so they have a small counter electrode area, but there is a limit to the allowable current density, which results in long charging and discharging times; (2) The internal resistance of the battery increases due to the low conductivity of nickel oxide, which is the positive electrode active material. Of these (1)
The reason for (2) is related to the structure of the battery itself, so it is difficult to solve it simply.For reason (2), it is necessary to add a large amount of highly conductive material to the positive electrode active material as a conductive additive. Countermeasures have been taken, such as wrapping the positive electrode in a metal net, but this is not necessarily preferable because it significantly reduces the capacity of the battery.

Furthermore, the rapid charging and discharging properties of the sintered body as a positive electrode.

It also differs depending on whether a paste or a compressed powder body is used. Each of these three methods has its advantages and disadvantages, and among these, the use of a sintered body generally has the best rapid charging and discharging characteristics. However, in order to construct the positive electrode as a sintered body, a complex manufacturing process is required, which involves repeating the steps of impregnating nickel powder into the core material of the electrode plate with nickel salt, alkali treatment, washing with water, and drying. process, which increases manufacturing costs. From the viewpoint of manufacturing cost, it is most advantageous to use a compacted powder compact, but the rapid charging and discharging characteristics are not necessarily satisfactory.

Therefore, it is an object of the present invention to provide an alkaline secondary battery that solves the above-mentioned problems and can achieve excellent rapid charging and discharging characteristics even when a compression molded body is used for the positive electrode. .

[Failure to solve the problem]

As a result of repeated studies to achieve the above object, the present inventors used nickel powder with a particle size of 1 to 5 μm obtained by thermal decomposition of tetracarbonyl nickel as a conductive agent, and used it as a positive electrode active agent. The present invention was completed based on the discovery that good rapid charge/discharge characteristics can be achieved when the positive electrode is composed of a compacted powder compacted with the substance nickel oxide and a binder added as necessary. This is what I came to do.

That is, the alkaline secondary Ti pond according to the present invention has a positive electrode active material mainly composed of nickel oxide and a conductive material. Alkaline secondary "71" with a powder compression molded body containing an LT adjuvant as a positive electrode
The conductive auxiliary agent is a nickel powder having a particle size of 1 to 51 tm obtained by thermal decomposition of tetracarbonyl nickel.

One of the features of the present invention is that nickel powder obtained by thermal decomposition of tetracarbonyl nickel is used as a conductive aid. The nickel powder obtained by this method has an extremely small particle size compared to conventional nickel powder used for similar purposes, and has a unique surface texture, making it extremely useful as a conductive aid even when used in small amounts. If the zero particle size, which exhibits excellent performance in the battery, is larger than the above-mentioned range, the conductivity assisting effect tends to decrease, and a large amount must be used in order to lower the internal resistance of the battery. However, increasing the content of substances other than the positive electrode in this way leads to a decrease in battery capacity, which is undesirable.On the other hand, nickel powder with a particle size smaller than the above range is not suitable for industrial use. difficult to obtain.

Nickel oxide is used as the positive electrode active material. The nickel oxide normally used in alkaline batteries is a hydrate (nickel hydroxide). The particle size of this nickel oxide is set to 3 to 100 μm, but from the viewpoint of bringing the positive electrode active material into sufficient contact with the alkaline electrolyte to improve initial charge/discharge characteristics, it is more preferably selected to be 3 to 30 μm.

Furthermore, some kind of binder may be added to form a positive electrode, and it is preferable to use Teflon or the like as such binder.

Here, the mixing ratio of each material constituting the positive electrode is approximately 20 to 60 of nickel powder! fIfft%, nickel oxide is 35 to 75% by weight. Furthermore, if a binder is used, it should be about 5% by weight.

In the present invention, a powder compression molded body obtained by compression molding a mixed powder of these positive electrode active materials, a conductive auxiliary agent, and, if necessary, a binder added thereto, is used as a positive electrode.

One negative electrode is composed of a hydrogen storage alloy as a negative electrode active material. Here, examples of the hydrogen storage alloy include FeTi alloy and LaNi.

Conventionally known materials such as Mg-based alloys, Mg-based alloys, and Ni-based alloys can be used. A polymer absorbent, conductive carbon, etc. may be added to the hydrogen storage alloy.

In addition, any commonly used separators and alkaline electrolytes constituting the alkaline secondary battery of the present invention can be used.

[Effect]

In the present invention, a particle size of 1 to 5 μm obtained by thermal decomposition of tetracarbonyl nickel is used as a conductive auxiliary agent constituting the positive electrode.
m of nickel powder is used.

The nickel powder obtained in this way has a small particle size,
Moreover, since the particles have many protrusions on their surfaces, the specific surface area is extremely large. Inside the positive electrode created by powder compression molding, the particles are entangled with each other through the protrusions. It is thought that the spatial arrangement creates a matrix-like conductive effect, reduces the internal resistance of the battery, and makes it possible to improve the scattered and continuous light discharge characteristics.

(Example) Hereinafter, a preferred example in which the present invention is applied to a button-type nickel-metal hydride battery will be described with reference to the drawings.

Example As shown in FIG. 1, the button-type nickel-metal hydride battery according to this example consists of a positive electrode can (1) equipped with a positive electrode (2) and a negative electrode can (6) equipped with a negative electrode (5), which are separated by a separator. (3)
The openings of the positive electrode can (1) and negative electrode can (6) are sealed with a gasket (4), and the positive electrode can (1) is caulked.

The above-mentioned nickel-metal hydride battery was created as follows.

First, nickel powder with a particle size of 1 to 5 μm obtained by thermal decomposition of nickel hydroxide with a particle size of 3 to 30 μm as a positive electrode active material, and tetracarbonyl nickel as a conductive additive,
and Teflon powder as a binder were mixed according to the compounding ratio (wt%) A~ shown in Table 1 below, and this mixed powder was compression molded using a press machine at a pressure of 5 tons/cm''. A pellet with a diameter of 7.2 mm and a height of 1.2 mm was prepared, and this was used as a positive electrode.

Next, a 33% potassium hydroxide aqueous solution saturated with lithium hydroxide is dropped as an alkaline electrolyte into the positive electrode can, the positive electrode is inserted into the positive electrode can, and a microporous polypropylene film is further inserted into the positive electrode can. A separator and a gas get were placed.

On the other hand, 95% by weight of LaN15. +A
l o, s, 5ffli% Teflon powder as a binder was mixed and compression molded with a press machine to a diameter of 4.
．． A pellet with a size of 8 mm and a height of 1.2 mm was prepared, and this was used as a negative electrode.

The negative electrode thus prepared was placed on top of the separator, and the alkaline electrolyte was added dropwise again.

After Q, the negative electrode can was put on and the periphery of the positive electrode can was caulked and sealed to produce a button-type nickel-metal hydride battery.

Comparative Example For comparison with the above-mentioned examples, button-type nickel-metal hydride batteries were similarly prepared using nickel powders with particle sizes of 5 to 30 μm and 30 to looIIm as conductive aids.

(Hereinafter F margin) For each button-type nickel-metal hydride battery obtained in the Examples and Comparative Examples described above in Table 1, the change in internal resistance depending on the content of nickel powder in the positive electrode is shown in Figure 2. In the figure shown in Figure 0, the vertical axis represents the internal resistance (Ω), the horizontal axis represents the content of nickel powder (weight%), and the plot marked with . The marked plot is for 5 to 30 μm, and the Δ plot is for 30 to 1100 μm.
From this figure, which represents the case of 1I, when the nickel powder of the present invention with a particle size of 1 to 5 μm is used as a conductive aid, compared to the case where other nickel powders with a large particle size are used. It is clear that even with a small content, it is possible to significantly reduce the internal resistance.

Next, among the above-mentioned button-type nickel-metal hydride batteries, the rapid charging and discharging characteristics of the batteries prepared according to the blending ratio B were measured. That is, each button-type nickel metal hydride battery was charged with a charging current of 8 mA for 3 hours, and then a load of 120 Ω was connected to perform constant resistance discharge with a voltage of IV throughout. FIG. 3 shows the results of measuring the discharge characteristics after repeating such a continuous light discharge cycle 10 times. The vertical axis represents the voltage (■), the horizontal axis represents the discharge time (minutes), and the curve l is the curve ■ when the particle size of the nickel powder is 1 to 58 m.
represents the case of 5 to 30 μm, and the curve ■ represents the case of 30 to 10011 m.From this figure, when the nickel powder of the present invention with a particle size of 1 to 5 μm is used as a conductive additive, other particle sizes It is clear that the discharge time required to reach the final voltage 1 is longer than in the case of using nickel powder with a large nickel powder, and that the discharge characteristics are stable over a long period of time.

(Effects of the Invention) As is clear from the above explanation, if the present invention is applied, the internal resistance of the battery can be effectively reduced due to its excellent conductivity even when the content of the conductive aid in the positive electrode is small. , it becomes possible to improve the rapid charging and discharging characteristics.
The above positive electrode can be easily produced by powder compression molding. Therefore, an alkaline secondary battery with high energy density and excellent environmental protection can be provided with high productivity and economic efficiency.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing a configuration example of a button-type nickel-metal hydride 11 pond to which the present invention is applied. FIG. 2 is a characteristic diagram showing changes in internal resistance depending on the content of nickel powder in the positive electrodes of button-type nickel-metal hydride batteries according to examples and comparative examples of the present invention. FIG. 3 is a characteristic diagram showing the discharge characteristics of button-type nickel-metal hydride batteries according to Examples and Comparative Examples of the present invention after undergoing rapid charge/discharge cycles. Positive electrode can Positive electrode separate gasket Negative electrode

Claims (1)

[Scope of Claims] An alkaline secondary battery whose positive electrode is a compressed powder body containing a positive electrode active material mainly composed of nickel oxide and a conductive additive, the conductive additive being a thermally active material of tetracarbonyl nickel. An alkaline secondary battery characterized in that it is a nickel powder with a particle size of 1 to 5 μm obtained by decomposition.