JPH044574A - Secondary battery - Google Patents

Abstract

PURPOSE:To enhance the absorption ability for oxygen gas generated by a pos. electrode, maintain the inner pressure of a cell can at a low level at the time of quick charging, and provide the cell with a long life without causing change in the active substance filling efficiency of pos. electrode and neg. electrode by furnishing a gas absorbent at the pos. and neg. electrodes and in the center of electrode group wherein a separator is wound spirally. CONSTITUTION:Gas absorbent 1 is provided at a pos. and a neg. electrode and in the winding axis space of an electrode group 2 wherein a separator is wound spirally. Oxygen gas generated from the pos. electrode is absorbed by using gas absorbent 1 consisting of a material, which is unsoluble in electrolyte and has an electrochemical activity in the degree equal to or similar to the neg. electrode, or by adding a catalyst which enables chemical reaction of oxygen gas. In the battery, as described, the central part of the wound electrode group 2 is filled with the gas absorbent 1. This makes it possible to enhance the absorption ability for oxygen gas generated from the pos. electrode, maintain the inner pressure of the cell can at a low level at the time of quick charging, and provide the cell with a long life, that can be achieved without varying the active substance filling efficiency of the pos. and neg. electrodes occupied in the battery.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to oxygen gas generated from a positive electrode during charging,
In particular, it relates to the structure of a gas absorber that absorbs oxygen.

BACKGROUND OF THE INVENTION Demand for batteries to power portable and cordless devices is increasing. Generally, secondary batteries are the mainstream for devices that have moving parts and consume relatively large amounts of power. Among secondary batteries, alkaline storage batteries that use an alkaline aqueous solution as an electrolyte, such as nickel-cadmium batteries, are lighter than conventional lead-acid batteries because they are lighter, have higher energy density, and can withstand overcharging and discharging. As a result, the demand for small, sealed types is increasing significantly.

Nickel-cadmium batteries are designed to consume the gas generated within the battery during charging.

The capacity of the negative electrode (cadmium electrode) is made larger than the capacity of the positive electrode (Keckel electrode), and the positive electrode completes charging before the negative electrode, and the oxygen gas generated from the positive electrode is chemically By consuming it, the balance between pressure drop and capacity as well as electrolyte concentration is maintained within the battery.

2Cd+O! +HzO→2Cd (OH) z
(1) The conventional negative electrode is a sintered type, (1)
In the reaction shown in the formula, cadmium impregnated and precipitated on the surface of the Ni sintered body greatly contributes to the high specific surface area.

However, recently, high-capacity nickel-cadmium batteries are desired, and in order to achieve high capacity density, the sintered type requires a large volume of Ni sintered body, which is the base, Densification was becoming difficult. For this reason, a paste-type cadmium electrode has been developed in which cadmium is made into a paste and applied to a substrate. Since this paste-type cadmium electrode has a higher density than the sintered type, its porosity decreases and its oxygen gas absorption capacity also tends to decrease, so various studies were conducted to improve its absorption capacity. has been done. In the conventional technology, a conductive layer made of carbon powder is provided on the surface of a paste-type cadmium electrode plate to increase gas absorption capacity (Japanese Patent Application Laid-Open No. 60-63875), and a method is proposed in which a catalyst species for gas consumption is installed inside the battery. A method has been proposed in which a device is incorporated [Electrochemistry ■, 747 (1976)].

Problems to be Solved by the Invention The above-mentioned conventional techniques are considered to work effectively in absorbing oxygen gas generated from the positive electrode. However, when providing a carbon powder layer on the surface of a cadmium electrode, it is necessary to make the cadmium active material layer thin.

Furthermore, when carbon powder is mixed into the cadmium active material layer, it is thought that the filling amount of the active material decreases, thereby reducing the filling capacity density of the active material.

Furthermore, it is thought that providing the catalyst electrode on the outer periphery of the electrode reduces the volume ratio occupied by the positive electrode and the negative electrode within the battery, and the filling capacity of the positive electrode and negative electrode decreases. Therefore, in either case, increasing the filling capacity is considered to be disadvantageous.

The purpose of the present invention is to improve the absorption capacity of oxygen gas generated from the positive electrode without changing the active material filling efficiency of the positive electrode and negative electrode, so that a high capacity battery capable of night and stray light discharge can be obtained. .

Means for Solving the Problems In order to solve the above-mentioned problems, in the present invention, a gas absorber is installed in the winding core space of an electrode group in which a positive electrode, a negative electrode, and a separator are spirally wound. As the gas absorber,
Oxygen gas generated from the positive electrode is absorbed by a method using a material that is insoluble in the electrolyte and has the same or similar electrochemical activity as the negative electrode, or by adding a catalyst that enables a chemical reaction of oxygen gas. be able to.

Further, since the oxygen gas absorber is provided in the space of the wound electrode, the efficiency of the active material filling capacity of the positive electrode and the negative electrode is improved without reducing the filling efficiency of the positive electrode and the negative electrode that occupy the inside of the battery.

In the oxygen gas absorber mentioned above, cadmium, zinc, iron, and alloys containing these as main components are used as materials that have the same electrochemical activity as the negative electrode. Materials that can be used include platinum, palladium, rhodium, silver, and alloys containing these as main components. However, the substance is not limited to the above-mentioned substances, and as long as the oxygen gas absorber is supported on a material that is insoluble in the electrolytic solution and has an ability to absorb oxygen gas, it does not matter whether it is conductive or non-conductive.

In the method using the above-mentioned catalyst, the gas absorber forms a gas electrode, and the gas absorber forms a gas electrode and is coated, impregnated, or
Methods such as vapor deposition can be applied.

In addition, since it is a gas electrode, it is possible to make it water repellent by using a water repellent binder such as polytetrafluoroethylene (RTFE) to increase gas absorption ability.
An effective method is to support the catalyst on a conductive or high specific surface area carrier.

In addition, the shape of the oxygen gas absorber that fills the space in the center of the wound electrode may be cylindrical, cylindrical, hexagonal column, etc.
The shape is not limited as long as it fills the space and absorbs oxygen gas.

Furthermore, it is also possible to use the gas absorber as the axis of the wound electrode, resulting in a compact structure.

The gas absorber obtained in this way must have an electrical connection with the negative electrode, regardless of whether the gas absorption reaction uses a metal oxidation reaction or a catalytic reaction. . In other words, in the former case, the reaction that reduces the generated metal oxide to metal is an electrochemical reaction;
In the latter case, this is because the reaction of oxygen gas itself is an electrochemical reaction.

According to the present invention, by filling the center of the wound electrode group with a gas absorber in the battery, it is possible to improve only the oxygen gas absorption capacity without changing the volume of the positive electrode and negative electrode occupying the battery. Therefore, the capacity of the cadmium electrode can be increased. Furthermore, since the gas absorber is present in addition to the cadmium electrode, the gas absorption area increases, so the active material capacity of the cadmium electrode does not decrease. Furthermore, since the gas absorption area is increased, the gas absorption capacity is increased, which reduces the pressure inside the battery can during rapid charging.

The reactions that consume oxygen gas inside the battery in this way are represented by the following reactions (1) and (2).

2Cd+Oz+H! '0→Cd (OH) z
...(1) Oz+ 2HzO+ 4e →40H-
- (2) (1) is a case where the absorber has electrochemical activity to the same extent as the negative electrode, and although the case of cadmium is shown here as an example, other metals are also possible, and similar metals can be used. This is an oxidation reaction of oxygen. (2) is a case in which the absorber has a catalyst added thereto, and the reaction is an electrochemical reduction reaction of oxygen.

Having a built-in highly active oxygen gas absorber contributes to the longevity and safety of sealed batteries. That is, since the pressure inside the battery can is kept low, loss of electrolyte components due to opening of the safety valve is suppressed, and as a result, an increase in resistance due to depletion of the electrolyte can be prevented. Further, it is possible to prevent a short circuit of the assembled battery due to leakage of the electrolyte to the outside of the battery case or adhesion to devices, human bodies, etc.

Examples Example 1 A sealed cylindrical battery according to the present invention was produced, and its battery performance was measured. The test cadmium electrode was composed of the following materials. Cadmium oxide 80-t%, Ni powder 1 as conductive agent
0eet% powder and PTFE dispersion (Daikin Industries, Polyflon Dispersion D-1)
It was added to a Raikai machine and kneaded so that the amount of FE was 10-t%. It was attached to a 60-meter nickel wire mesh and dried to obtain a cadmium electrode for measurement.

The test nickel electrode used 80% nickel hydroxide as the active material.
t%, 10-t% of metal nickel powder as a conductive agent, 5wt% of metal cobalt powder as an activator for the active material, water, and 5wt% of PTFE dispersion as PTFE.
% in a Laikai machine and kneaded. It was attached to 60 meshes of nickel wire gauze and dried to obtain a nickel electrode for measurement.

A schematic cross-sectional view of the produced cylindrical battery is shown in FIG. The gas absorber 1 was filled in the center of the battery.

A cylindrical gas absorber made of the same material as the cadmium electrode under test was used. The terminal of the gas absorber was electrically connected to the cadmium electrode at the bottom of the can. The diameter of the gas absorber was 3φ. For comparison, a conventional battery was fabricated. The configuration of the battery was the same except for the gas absorber obtained in the present invention. A wound electrode 2 was formed by interposing the positive electrode and negative electrode with a separator interposed therebetween, and a gas absorber was filled in the center of the wound electrode 2, and the wound electrode 2 was housed in a battery case 3. And 300
g/j! An electrolyte of potassium hydroxide and 15 g/l lithium hydroxide was injected into the cell and subjected to charge/discharge cycles at 25°C. The battery internal pressure at that time was measured at a charging rate IC and a charging time of 1.5 hours. The results obtained are shown in FIG. In the figure, the battery 4 according to the present invention has an internal pressure of 2 kg/a during overcharging.
m", but the internal pressure does not rise any further and the gas absorption ability is excellent. On the other hand, in the battery 5 of the prior art, the battery internal pressure rose to 6 kg/am" during overcharging.

Further, the charging rate was changed stepwise from 0.20 to 30, and the internal pressure of the battery at that time was measured. The results are shown in FIG. In the battery 6 according to the present invention, the battery internal pressure remained constant even when the charging rate changed. On the other hand, the battery 7 of the prior art is
The internal pressure of the battery has increased significantly. Furthermore, as the charging rate increased, the pressure rapidly increased, causing electrolyte leakage. Therefore, it has been revealed that the battery according to the present invention has better oxygen gas absorption ability than the prior art, and does not cause leakage.

Example 2 An oxygen gas absorber using silver as a catalyst component was filled. Ag
Using N0:l as a starting material, it was reduced in a methanol solution to obtain Ag black. A gas absorber 8 in which Ag black was supported on a cylindrical nickel sintered body at an amount of 5 wt % as Ag was filled in the center of the battery. A schematic cross-sectional view of a sealed cylindrical battery is shown in FIG. The other nickel electrodes and cadmium electrodes were fabricated under the same conditions as in Example 1 to form a battery, and the battery was continuously charged at a charging rate of IC, and the internal pressure of the battery at that time was measured. A prior art battery was also measured for comparison. The results are shown in FIG. Conventional electrode 9
It has become clear that the battery 10 of the present invention has significantly superior oxygen gas absorption ability. Further, the oxygen gas absorber of this example was formed into a sheet having the same volume and thickness of 0.311III+, and was wound around the outer periphery of the same wound electrode, and the gas absorber was electrically connected to the cadmium electrode. A sealed cylindrical AA battery was produced by filling a can with the battery connected to the battery. The capacity of this battery was 720mAh. In contrast, the capacity of the AA battery according to the above example was 830 mAh. From this, it has become clear that the technology of the present invention greatly contributes to increasing capacity.

Example 3 A cylindrical gas absorber made of an alloy of 50-t% metal cadmium and 50-t% zinc was used as the winding shaft core, and the other nickel electrodes and cadmium electrodes were manufactured under the same conditions as in Example 1. The obtained electrode was wound around a gas absorber via a separator to form a wound electrode, and a battery was manufactured. The charging rate was 1.5 hours for IC1 charging, and the internal pressure of the battery was measured. For comparison, a conventional battery was also measured. The results are shown in FIG. The internal pressure of the battery 11 of the present invention is about 2 kg/cm2, whereas
In the conventional battery 12, the internal pressure increased to 6 kg/cm2. Therefore, it has become clear that the battery according to the present invention has better oxygen gas absorption ability than the conventional battery.

Effects of the Invention According to the present invention, since the gas absorber is provided in the center, which is the space of the wound electrode, the proportion occupied by the wound electrode in the battery does not change, so that the filling capacity of the active material for both the positive electrode and the negative electrode is reduced. will not deteriorate.

In addition, since it absorbs oxygen gas generated from the positive electrode in the same way as the active material of the cadmium electrode, the ability to absorb oxygen gas within the battery is improved. Therefore, since the pressure within the battery can does not increase, rapid charging is possible and the charging time can be shortened. Additionally, safety is improved because the gas pressure does not increase.

Furthermore, since there is no electrolyte leakage, the balance between the electrode and electrolyte is maintained, which is effective in extending the life of the battery.

[Brief explanation of the drawing]

1 and 4 are schematic cross-sectional views of a cylindrical battery, and FIGS. 2, 3, 5, and 6 are characteristic diagrams comparing the internal pressure of a battery can between the present invention and a conventional product. 1: gas absorber, 2: electrode group, 3: battery case, 4: product of the present invention, 6: product of the present invention, 8: gas absorber, IO2 product of the present invention, 11: product of the present invention. Figure 1 Figure 2 Charging time (Chikuin)) Figure 3 Figure 4 Figure 5 Electric claw cheese Figure 7 Number of cycles Battery can internal pressure (kg/c7712) Battery can internal pressure (kg/cm2)

Claims (1)

[Claims] 1. A secondary battery characterized in that a gas absorber is provided at the center of an electrode group consisting of a positive electrode, a negative electrode, and a separator. 2. The secondary battery according to claim 1, wherein the gas absorber is a negative electrode and is electrically connected. 3. The secondary battery according to claim 1, wherein the gas absorber operates by a mechanism utilizing a reaction between metal and oxygen. 4. The secondary battery according to claim 1, wherein the gas absorber supports a catalyst and absorbs gas through an electrochemical reaction. 5. The secondary battery according to claim 1, wherein a wound electrode formed by winding a separator, a positive electrode, and a negative electrode around the gas absorber is used.