JPS6220244A - Nickel-hydrogen alkaline storage battery - Google Patents

Abstract

PURPOSE:To prevent tearing off of a hydrogen occlusion alloy and improve the cycle life, by containing in, or placing over the surface of, the negative electrode a hydrogen occlusion alloy or hydride, covered with a conductive metal. CONSTITUTION:The negative electrode 1 is formed pressing a mixture of a powder of hydrogen occlusion alloy with an electrochemical property to occlude and discharge hydrogen and a powder of hydrogen occlusion alloy covered with copper, nickel or the like onto an electrode base, or placing a hydrogen occlusion alloy or the like covered with copper or the like over the surface of an electrode base which is placed with only a hydrogen occlusion alloy or the like. The nickel-hydrogen alkaline storage battery is formed combining the said negative electrode 1, a positive electrode 2 made of nickel oxide, a separator 3, and an alkaline electrolyte 4. Therefore, as well as increasing the discharge capacity per unit weight or unit volume of the electrode, the mechanical strength of the electrode is improved, and the charge and discharge life can be made longer.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a nickel-hydrogen storage battery in which the negative electrode is a hydrogen storage electrode made of an alloy or hydride that reversibly stores and releases hydrogen, and the positive electrode is a nickel oxide electrode. Something,
In particular, it relates to improvements in negative electrodes.

Conventional technology In alkaline storage batteries whose negative electrode is a hydrogen storage electrode that uses alloys that store and release hydrogen reversibly (hereinafter referred to as hydrogen storage alloys) or hydrides, the negative electrode is formed by the charging and discharging cycles of the battery. The hydrogen storage alloy or hydride becomes fragmented (I7), falls off from the electrode support, expands, or cracks, resulting in a decrease in battery performance. This phenomenon is particularly noticeable in open-type alkaline storage batteries. Therefore, an attempt has been proposed to solve the above problems by coating the surface of hydrogen-absorbing alloy powder with copper (Cu).
JP-A-50-111546). In other words, a negative electrode for storage batteries has been proposed in which electroless copper plating is applied to the surface of hydrogen-absorbing alloy powder to protect the alloy itself and increase the mechanical strength and electrical conductivity of the alloy itself. An alkaline storage battery is being considered by using this hydrogen storage electrode as a negative electrode and combining it with a known nickel positive electrode via a separator.

Problems to be Solved by the Invention When the alloy whose surface is coated with copper is used for the negative electrode, the mechanical strength and conductivity of the electrode itself are good for both unsintered and sintered electrodes, and the battery performance is improved. It is conceivable to do this in the opposite direction. However, on the other hand, the metal that coats the surface of the alloy is selected to be a material that does not react with hydrogen, so the hydrogen storage and release characteristics, that is, the energy that is regulated by electrochemical hydrogen storage and release. It is independent of storage capacity. Therefore, if the metal portion increases, the capacity or output per unit weight will decrease by that amount. For example, the capacity density of hydrogen storage alloy is 0.25)h/j9
1 Ah/cc), when copper is coated on the surface of alloy particles by electroless plating, a large amount of copper is used, about 20 to 40 wt% of the total alloy amount, so the capacity density is It decreases by 60 to 80% at the age of 60 to 80%, making it difficult to construct a storage battery with high ray density and energy density.

Originally, in an alkaline storage battery, the volume occupied by the positive electrode and negative electrode in a given volume is fixed, so an increase in the volume occupied by the negative electrode causes a decrease in the capacity occupied by the positive electrode, and the discharge capacity according to the positive electrode rule decreases. There is a problem.

5 Means for Solving the Vane Problem The present invention comprises a nickel oxide positive electrode, a negative electrode made of an alloy or hydride that reversibly absorbs and releases hydrogen, and an alkaline electrolyte, the surface of which is coated with a conductive metal such as Hydrogen partially coated with copper 9 nickel 9 or their alloys,
The above nine problems were solved by incorporating a hydrogen storage alloy or hydride particles that have electrochemical properties that allow occlusion and desorption into the negative electrode or by providing them on the surface of the negative electrode to form a nickel-hydrogen alkaline storage battery. It is something.

Furthermore, the present invention provides a negative electrode of a base type electrode containing, in the negative electrode, a hydrogen storage alloy whose surface is partially coated with copper, nickel, or an alloy thereof or hydride particles and a binder; hydrogen storage alloy or hydride particles partially coated with copper, nickel or their alloys, alone or together with a binder, 850~
This is a nickel-hydrogen alkaline storage battery using a sintered electrode sintered at a temperature of 1000°C as the negative electrode.

Step 6: Hydrogen storage alloy powder and hydrogen storage alloy powder coated with a conductive metal such as copper, nickel, or an alloy thereof are mixed together with a binder and dried under pressure through an electrode support to form an electrode. By doing so, the amount used can be significantly reduced compared to using a single hydrogen storage alloy coated with a conductive metal, improving the capacity density per unit weight and volume, and improving the discharge characteristics (discharge voltage and discharge capacity). Because it has an excellent utilization rate (high utilization rate), it is possible to create an alkaline storage battery with a high volume that cannot be obtained with conventional storage batteries. By subjecting the mixture of the two to high-temperature heat treatment (sintering) via the electrode support, the mechanical strength of the electrode itself is improved, and the life of the charge/discharge cycle can be extended.

On the other hand, by forming a hydrogen storage alloy or hydride powder coated with a conductive metal such as copper, nickel, or an alloy thereof only on the surface of an electrode base made of the hydrogen storage alloy or hydride powder.

Similarly, it leads to improvement in mechanical strength and discharge capacity per unit weight and volume. Excellent discharge characteristics (high rate discharge characteristics)
It is also excellent. This is due to the fact that conductive material particles such as copper, nickel, or their alloys are in efficient contact with the hydrogen storage alloy powder inside the electrode, and the alloy itself coated with copper, nickel, or their alloys also discharges. Since it is related to capacity, the capacity is increased by 9 weight/volume.

On the other hand, if the electrode surface is made of hydrogen storage alloy powder coated with copper, nickel or an alloy thereof, the copper 9
Since the particles are in contact and bonded to each other on the nickel or alloy coated surface, it is expected that the resistance of the electrode itself will be reduced, 9 and the mechanical strength will be increased, as well as an increase in capacity per unit weight and volume.

Example 08: 25. Nd near, Pr, other s), N
i (purity 99 or higher), Go (purity 99 or higher)
Each sample was weighed to a certain composition ratio, placed in a water-cooled copper crucible, heated in an arc melting furnace,
, produced an alloy. This alloy is 3071771 in a crusher.
Thereafter, it was finely pulverized using a sieve, and the electrode alloy sample was designated as a.

Finally, a part of sample B of this electrode alloy was taken, and a copper coating film was partially formed on the surface of this alloy by electroless plating. The conditions for electroless plating are as follows.

At first glance, this alloy appears to form a homogeneous metal coating on the surface of the alloy particles, but there are many holes and cracks in the surface. Due to the presence of these nine cracks, a partial coating film is formed. This hole.

Go to 9-7 It is thought that hydrogen is absorbed and released through the cracks. This copper-coated alloy sample was designated as b.

Next, add 80 wt% of powder a and 2 wt% of powder b,
Mix well with a binder such as polyvinyl alcohol, apply to both sides of the electrode support (perforated plate, also known as bunching metal), pressurize, and dry.

The lead is attached as a negative electrode, a known nickel oxide positive electrode and a separator are used to constitute an electrode plate group, and an alkaline electrolyte is added to form an alkaline storage battery, and this storage battery is designated as A.

The configuration of this storage battery is shown in FIG. A negative electrode 1 consisting of a hydrogen storage electrode containing an alloy or hydride coated with a metal, a positive electrode 2 made of nickel oxide, and a separator 3 located between the two electrodes are immersed in an electrolytic solution 4. 5 is the battery case, 6 is the lid,
The reference numeral is the liquid injection port, and 8 and 9 are the negative and positive electrode lead terminals.

FIG. 2 schematically shows an electrode structure made of a hydrogen storage alloy. FIG. 2A shows the electrode shown in Example 1. The ○ mark indicates a, and the * mark indicates b.

FIG. 2B shows an electrode shown in Example 2, which will be described below. FIG. 2C shows an electrode taken as a conventional example.

The size of the negative electrode in Example 1 is 40IMX50wtb
, 1.2 words thick. In order to compare the negative electrode capacities, the positive electrode capacity was made larger than the negative electrode capacity, and the capacity was regulated using the negative electrode rule. Both charging and discharging currents were 500 mA. The charging time was approximately 1.3 times the discharging time. The final voltage is 1. ○V.

A conventional alkaline storage battery uses the battery configuration shown in Figure 1 and the electrode structure shown in Figure 2 C, and the negative electrode size is 40mm x 50mm and has a thickness of 1.2mm, which is exactly the same as the former. It was used as a volumetric negative electrode. Add a binder such as polyvinyl alcohol to powder B, mix well, apply to both sides of the electrode support (perforated plate), dry under pressure, attach a lead as a negative electrode, and use a known nickel oxide positive electrode. A group of electrode plates was formed by separating the electrodes and the electrodes, and immersing them in an alkaline electrolyte to form an alkaline storage battery. This storage battery is called B.

FIGS. 3 and 4 show a comparison of the discharge capacities of batteries A and B. Figure 3 shows a 500mA discharge (equivalent to 0.2G = 5
This is the performance at 5 hour rate discharge. Battery A is 1. ○V or later”
While the voltage at the second terminal is maintained for 5 hours, battery B is maintained for only 3.5 hours. The capacity of battery B is about 30 times lower than that of battery A. This means that the capacity per unit volume (Ah/cc) is small and the amount of alloy is effectively reduced accordingly.

FIG. 4 shows the performance at 2500 mA discharge (equivalent to 1 C: 1 hour rate discharge). Battery B is about 30 times smaller than battery A.
The lifting capacity is decreasing. Furthermore, it can be seen that the high rate discharge characteristics such as 1G discharge are also excellent. In addition, there is almost no significant difference between batteries A and B in terms of discharge voltage. The charge/discharge cycle life has also passed 100 cycles, but it remains almost unchanged. Therefore, in addition to the conventional characteristics, the battery of the present invention was able to significantly improve the capacity in a battery system exhibiting a constant volume.

Example 2 After filling the electrode support (foamed metal) with the alloy powder (a) produced in Example 1 and performing A, hydrogenated alloy powder (previously, The sample powder (layer b), which had been hydrogenated by repeatedly absorbing and desorbing hydrogen, was exposed to light under pressure to form layer b'. Note that b' powder was used in a weight ratio of approximately 10 wt%. Then, after pressurizing and drying, hot pressing was performed at high temperature in a vacuum, or sintering treatment was performed at a temperature of 960° C. in a shaking vacuum for 5 hours.

The powder particles on the surface were strongly sintered, creating an electrode with strong mechanical strength. This electrode is designated as C. Configuration and charging of storage batteries
A capacity test was conducted under all the same discharge conditions as in Example 1.

As a conventional electrode, an electrode D is obtained by filling only B powder into a foamed metal, pressurizing it, and then sintering it in a vacuum for 5 hours. The test conditions are exactly the same as in Examples, and the volume of the electrode is exactly the same as in C.

Based on the results of the discharge capacity test of this storage battery, the C battery has a 2.4
Whereas the capacity of D battery was 1.7A.
The capacity was only about 1 h. This has a small capacity per unit volume, resulting in a low battery capacity. In this way, the same tendency as in Example 1 exists for the sintered electrode as well. In fact, there was almost no significant difference between the C and N batteries in terms of high rate discharge voltage and charge/discharge cycle life.

Here, an open storage battery was created and the capacity of the negative electrode was compared, but similar effects can be expected when used as the negative electrode of a sealed storage battery. That is, since the active material is packed into a fixed volume, the smaller the capacity per unit volume (Ah/cc), the more negative electrode material must be added in order to secure a predetermined capacity. As the amount of positive electrode material increases, the portion occupied by the positive electrode material decreases, so the battery capacity inevitably decreases. Now, a AA size sealed alkaline storage battery was made using the negative electrode made in Example 1, and a capacity test was conducted. While conventional storage batteries have a capacity of OAh, they only have a capacity of 1.5Ah. All charging and discharging currents were conducted at a current equivalent to 0.20.

By forming a B layer on the surface of the electrode, it also has the role of preventing the negative electrode alloy from being oxidized by the oxygen generated from the nickel positive electrode during overcharging, improving oxidation resistance. It will also provide storage batteries with strong electrodes. Regarding this point.

Further longevity can be expected.

Although copper is mentioned as a conductive metal in the examples,
The same can be said about nickel.

In this way, any metal or alloy that can be plated electrolessly and is electrically conductive can be plated.

MmNi5CO2 is used as a hydrogen storage alloy,
The same applies to other rare earth-nickel systems. Also, Ti2
A titanium-nickel type material such as Ni may also be used. The same effect can be achieved whether a hydrogen storage alloy or a hydride is used as the initial starting material. In the case of electroless plating, hydrogenation makes the surface more active and easier to plate than alloy.

Therefore, it is preferable to electrolessly plate the hydrogenated alloy.

The hydrogen storage alloy that coats the metal has basically the same effect whether it is an alloy or a hydride157, but the effect is small when the amount d] is less than 10 wt%, and when it is more than 40 wt%. In this case, the capacity decrease becomes a factor of 10 or more, and the cost per capacity increases, making it impractical.

Therefore, considering durability and cost, 10 to 40
wt% is the optimum range.

The sintering temperature given in the example was 950''C.

The optimum temperature is 860°C to 1000"C. Below 850°C, the strength during sintering is weak and the effect is not great. Since the melting point of copper is 1083°C, above 1000°C, it will oversinter and reduce the surface area. In order to reduce the size and significantly reduce the capacity, 8
50'C to 100C is optimal. In addition, as another sintering method, pressing and sintering can be performed simultaneously by hot pressing. Although the surface area and porosity are slightly smaller, the mechanical strength is stronger.

Effects of the Invention As described above, the present invention has mechanical strength, long cycle life due to durability, and excellent high rate discharge characteristics, as well as high capacity density of the negative electrode and low discharge capacity. A large nickel-hydrogen alkaline storage battery is obtained.

[Brief explanation of the drawing]

FIG. 1 shows the structure of a nickel-hydrogen alkaline storage battery using the electrode of the present invention, and FIGS. 2A and 2B. C is a diagram schematically showing the electrode configuration, and FIGS. 3 and 4 are diagrams showing a comparison of the discharge characteristics of the battery of the present invention and a conventional battery. 1...Negative electrode, 2...Positive electrode, 3...
Sehaleta. Name of agent: Patent attorney Toshio Nakao and one other person (Takuyo Yaichi-N)

Claims (5)

[Claims] (1) Equipped with a nickel oxide positive electrode, a negative electrode made of an alloy or hydride that reversibly stores and releases hydrogen, and an alkaline electrolyte, the surface of which is partially coated with a conductive metal to store and release hydrogen. A nickel-hydrogen alkaline storage battery characterized in that hydrogen storage alloy or hydride particles are contained in the negative electrode or provided on the surface of the negative electrode. (2) The hydrogen storage alloy or the metal coated on the hydride particles having electrochemical properties capable of absorbing and desorbing hydrogen is made of copper, nickel, or an alloy thereof. The nickel-hydrogen alkaline storage battery according to item 1. (3) Claim 1, characterized in that the negative electrode is a hydrogen storage alloy whose surface is partially coated with copper, nickel, or an alloy thereof, or a paste-type electrode containing hydride particles and a binder. The nickel-hydrogen alkaline storage battery described in . (4) Sintering in which hydrogen storage alloy or hydride particles whose surface is partially coated with copper, nickel or their alloys are placed on the negative electrode surface alone or together with a binder and sintered at a temperature of 850 to 1000°C. The nickel-hydrogen alkaline storage battery according to claim 1, characterized in that the type electrode is a negative electrode. (5) Claim 1, characterized in that the total amount of the hydrogen storage alloy or hydride particles whose surface is partially coated with copper, nickel, or an alloy thereof is 10 to 40% by weight of the entire negative electrode. The nickel-hydrogen alkaline storage battery described in .