JPH04109556A - Closed-type secondary battery - Google Patents

Abstract

PURPOSE:To obtain a simple, effective and practical manufacturing method by causing materials to be contained in a positive electrode to be oxidized at potential at which all of the materials are oxidized more easily than a positive electrode active material, i.e., the one which is lower than the charging reaction potential of the positive electrode. CONSTITUTION:In a secondary battery comprising a negative electrode, a positive electrode and a separator, all of which are composed mainly of a hydrogen storage alloy, and an electrolyte distributed over all of them, the positive electrode contains components which are oxidized at potential lower than the charging reaction potential of time positive electrode. The components contained in the positive electrode generate hydrogen during their oxidation process. The oxidation reaction product of the components contained in the positive electrode works in favor of the reaction of positive electrode active material. The components contained in the positive electrode are desirably such metals as lithium, magnesium, aluminium, manganese, iron, cobalt, zinc, cadmium and the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a secondary battery, and particularly to a sealed secondary battery having a negative electrode mainly composed of a hydrogen storage alloy, such as a nickel-metal hydride battery.

2. Description of the Related Art With the rapid spread of various small cordless devices, the demand for batteries as power sources is also increasing. There are two types of small batteries used: primary batteries and secondary batteries, but they generally have moving parts.
As a power source for heavy-load and frequently used applications, secondary batteries are preferably used mainly for economical reasons.

As demand for these secondary batteries increases, demands for higher capacity, rapid charging and discharging, etc. are increasing from the viewpoint of ease of use.

Among these, there is a deep-rooted consumer demand for higher capacity devices that can extend the usage time of devices with a single charge, and the development of technology in this regard has continued unremittingly.

In addition to increasing the capacity of existing batteries, new types of batteries have been actively developed. Among them, nickel-metal hydride batteries, which have a negative electrode mainly composed of hydrogen-absorbing alloys, have almost the same battery voltage and discharge characteristics as nickel-cadmium batteries, and are compatible with nickel-cadmium batteries, but have a battery capacity of 3.
It has been attracting attention as a battery that can be expected to increase by 0 to 50%. This battery can be sealed like a nickel-cadmium battery. The sealing method is based on the so-called Neumann sealing principle, in which the amount of electrolyte is regulated and the ratio of the chargeable capacity of the positive electrode to the negative electrode is shifted toward the negative electrode, so that the positive electrode reaches overcharging first. oxygen gas generated from the positive electrode,
is recovered through the oxidation reaction of the negative electrode metal to construct a closed system. This method makes it possible to prepare for overcharging. In order to prevent overdischarge, it is necessary to provide the negative electrode with a discharge reserve capacity called a discharge reserve in advance.

This makes it possible to prevent shortening of life due to over-discharge or deterioration of the negative electrode, making it possible to create a durable, high-capacity battery with a long life.

Problems to be Solved by the Invention An object of the present invention is to provide a simple and effective practical manufacturing method for a sealed secondary battery such as a nickel-metal hydride battery having a negative electrode mainly composed of a hydrogen storage alloy. .

In conventional sealed nickel-cadmium batteries, methods such as chemical conversion treatment of the negative electrode or filling with metal cadmium have been used to provide a discharge reserve to the negative electrode (cadmium electrode). However, in nickel-metal hydride batteries,
Since the negative electrode active material is gaseous hydrogen or hydrogen atoms in metal, it becomes difficult to handle it. That is, in order to fill the hydrogen storage alloy with hydrogen after forming or before forming the negative electrode, (1) M + 1 /2H2→ goods (solid-gas reaction) (2) M + H20+ e → MH Shikan - (solid-liquid reaction) Reaction) M: There are two methods such as hydrogen storage alloy. Method (1) is a method in which a hydrogen storage alloy is stored in an atmosphere with a hydrogen partial pressure higher than the hydrogen storage equilibrium pressure. Method (2) is a method of electrochemically incorporating hydrogen into a hydrogen storage alloy, which is the charging reaction of the negative electrode of a nickel-metal hydride battery, and corresponds to the chemical conversion treatment of the cadmium electrode.

No matter which method the negative electrode is obtained, after each pretreatment, in the battery assembly process, it is placed in an atmosphere different from that of the pretreatment, so the hydrogen charged by the pretreatment dissipates from the negative electrode, causing the battery to assemble. There was a tendency for the effectiveness of the treatment to be significantly reduced. In order to solve this problem, improvements such as creating a hydrogen atmosphere in the battery assembly process have been considered. However, in this case, the battery assembly equipment becomes complicated, resulting in lower workability and efficiency.Also, since the process is conducted in a hydrogen atmosphere, the risk of leakage increases, and additional equipment is required to install equipment to prevent it. Problems such as increased complexity arise.

Means for Solving the Problems The present invention is characterized in that, in order to solve the above-mentioned problems of the prior art, a new component is built into the positive electrode for a sealed secondary battery, so that it can be used after the sealed battery is sealed. Alternatively, the purpose is to provide a discharge reserve to the negative electrode made of a hydrogen storage alloy at the time of initial charging.

As a result, the process of assembling the battery in a hydrogen atmosphere, which was a problem in the prior art, becomes unnecessary.

Methods for providing a discharge reserve to the negative electrode within the can after sealing include (1) incorporating something that reacts with the electrolyte in the can to generate hydrogen, and (2) incorporating something that oxidizes during charging. is necessary. It is necessary that all substances to be incorporated be oxidized more easily than the positive electrode active material, that is, oxidized at a potential lower than the charging reaction potential of the positive electrode.

Further, it is desired that the oxidation reaction products of these built-in substances do not become inhibitors of the electrode reaction, and preferably that they have a positive effect on the electrode reaction. Materials for which method (1) can be applied include metals such as lithium and aluminum. Substances that can be used in method (2) include magnesium;
Metals include manganese, iron, cobalt, zinc, and cadmium.

As a result of studies, it has become clear that cobalt is particularly preferable among the above-mentioned built-in substances when the sealed battery to which the present invention is applied is a nickel-metal hydride battery. A particularly desirable addition amount was 5 to 20 G1 t%. 5wt%
This is because the amount of discharge reserve obtained below is too small and the effect is unclear, and when it exceeds 20 wt%, the relative electrode capacity decreases greatly.

The built-in substance can be added to the positive electrode by mixing it uniformly with the active material during electrode molding, or by molding it separately from the positive electrode and electrically connecting it to the positive electrode. If it has a useful effect on the reaction, it is preferable to mix it uniformly with the active material.

Function The function of the present invention is to provide a discharge reserve to a negative electrode made of a hydrogen storage alloy in a sealed can. The mechanism is different between case (]) and case (2) above. That is, in (1), hydrogen is generated by the reaction between the additive and the electrolytic solution, and the hydrogen reacts with the hydrogen storage alloy according to the above formula (1) to provide a negative electrode discharge reserve. In (2), the additive is electrochemically oxidized prior to the positive electrode active material during charging. During this time, the reaction of formula (2) above proceeds at the negative electrode, and normal charging progresses. Therefore, there is a discrepancy in the amount of charge on the positive and negative electrodes, and the amount on the negative electrode is larger. This difference becomes the discharge reserve of the negative electrode.

Moreover, the effect of cobalt is particularly remarkable because, in addition to providing the above-mentioned discharge reserve to the negative electrode, cobalt hydroxide, an oxidation product, forms a solid solution with nickel hydroxide, an active material, and distorts the crystal lattice. It is thought that the discharge reaction rate is improved, or that cobalt oxyhydroxide, which is a higher order oxide, is precipitated on the surface of the active material particles and its electronic conductivity contributes to reducing the resistance inside the active material layer. In addition, zinc, cadmium, and other substances that contribute to improving the high-temperature characteristics of batteries were also clearly ignored.

EXAMPLE The present invention will be explained in more detail by way of an example in which the present invention is applied to a sealed nickel-metal hydride battery.

Example 1 The nickel electrode used to carry out the present invention had a porosity of 9
This is a paste type electrode that uses 5% foamed nickel as the electrode base. A sufficient amount of water was added to 84-t% nickel hydroxide as an active material, 15 wt% metal cobalt powder, and 1 tst% polyvinyl alcohol as a binder to form a slurry, and the slurry was filled into a adhesive electrode substrate. After drying, a nickel electrode of a predetermined thickness was obtained using a roller press. The filling capacity density of nickel electrode active material is 5
It was 70mAh/cm3.

The metal hydride electrode contains LaN1a as a hydrogen storage alloy,
6Mno-2Alo, z powder was used. It was manufactured using the same substrate and binder as the nickel electrode described above, and by the same manufacturing method.

A single-cell sealed nickel-metal hydride battery was fabricated using these electrodes. The resulting electrode has a thickness of 0.17
It was wound up with a polypropylene resin nonwoven fabric separator of 1.0 mm in diameter interposed therebetween, and inserted into a battery can. 31wt% in electrolyte
A small amount of lithium hydroxide was added to an aqueous solution containing potassium hydroxide. For comparison, a single-beam sealed nickel-metal hydride was used, which was the same as the above example except that the active material of the nickel electrode, nickel hydroxide, was 96 wt% and the metal cobalt powder was 3 wt%. A battery was created. The filling capacity of both batteries is 10510
It was set to 5O. These batteries were charged and discharged at room temperature. In the first cycle, charge to 150% of the capacity at 0°ICmA,
It was discharged at 0.2 CmA to a final voltage of 1.0 V. The second cycle charges 150% of the capacity at 0.3CmA,
0.2Cn+71 is the final voltage of 1. It was discharged to Ov.

Thereafter, the battery was overdischarged at 0.2 CmA, and the residual capacity of the negative electrode was determined from the voltage transition. As a result, a negative electrode residual capacity of 380 mAh in this example and 70 mAh in the comparative example was confirmed.

Next, a battery prepared in the same manner as above and charged/discharged for the 1st cycle was charged to 150% of the capacity at 0.3 CmA, and
．． At 2CmA, the final voltage is 1. A cycle test evaluation was conducted in which discharge was repeated until OV. The results are shown in the drawing. A according to the invention exhibits a cycle life superior to Comparative Example C according to the prior art.

Example 2 The composition of the nickel electrode is hydroxide nickel 844 as the active material
A single-cell sealed nickel-metal hydride battery was produced in the same manner as in Example 1, except that 10iyt% of metal cobalt powder and 54% of metal zinc powder were added.

In the same manner as in Example 1, the negative electrode residual capacity after two cycles of discharge was determined. As a result, a remaining capacity of 310 mAh was obtained.

Next, a cycle test evaluation was performed in the same manner as in Example 1. The results are shown in B of the drawing. With B according to the present invention, a cycle life superior to that of Comparative Example C, which is the prior art, was obtained.

Effects of the Invention As is clear from the results of the above examples, according to the present invention, in a sealed secondary battery such as a nickel-metal hydride battery, after the battery is sealed, a hydrogen storage alloy made of a hydrogen storage alloy is placed in a sealed can. It was possible to effectively provide discharge reserve to the negative electrode. As a result, we were able to produce high-performance, long-life batteries as shown in the drawings, without going through the process of assembling batteries in a hydrogen atmosphere, which requires complicated equipment, low work efficiency, and is highly dangerous. were able to provide.

Furthermore, the present invention relates to technology related to nickel-metal hydride batteries, but not only nickel-zinc batteries, nickel-iron batteries, silver oxide-metal hydride batteries, manganese dioxide-metal hydride batteries, and sealed lead-acid batteries. This technology can also be applied to other sealed secondary batteries such as

[Brief explanation of drawings]

The drawings are diagrams showing cycle test results of a nickel-metal hydride battery according to the present invention and a nickel-metal hydride battery according to the prior art.

Claims (1)

[Scope of Claims] 1. A secondary battery composed of a negative electrode, a positive electrode, a separator, and an electrolyte distributed in each of these parts, the main component of which is a hydrogen storage alloy, wherein the positive electrode has a charge reaction potential higher than its charging reaction potential. A sealed secondary battery that is formed by containing a component that is oxidized at a low potential. 2. The sealed secondary battery according to claim 1, wherein the component contained in the positive electrode generates hydrogen during its oxidation process. 3. The sealed secondary battery according to claim 1, wherein the oxidation reaction product of the components contained in the positive electrode has an advantageous effect on the reaction of the positive electrode active material. 4. The sealed type battery according to any one of claims 1 to 3, wherein the component contained in the positive electrode is a metal such as lithium, magnesium, aluminum, manganese, iron, cobalt, zinc, or cadmium. Next battery.