JP2558624B2 - Nickel-hydrogen alkaline storage battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a nickel-hydrogen storage battery in which a hydrogen storage electrode made of an alloy or a hydride that reversibly stores and releases hydrogen is used as a negative electrode and a nickel oxide electrode is used as a positive electrode. In particular, it relates to the improvement of the negative electrode.

2. Description of the Related Art In an alkaline storage battery having a negative electrode of a hydrogen storage electrode using an alloy that reversibly stores and releases hydrogen (hereinafter referred to as a hydrogen storage alloy) or a hydride, the negative electrode is configured by the charge / discharge cycle of the battery. The hydrogen storage alloy or hydride is subdivided and falls off from the electrode support, or expands or cracks, resulting in deterioration of 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 the hydrogen storage alloy powder with copper (Cu) (Japanese Patent Laid-Open No. 50-111546). That is, by applying electroless plating of copper to the surface of the hydrogen-absorbing alloy powder, a negative electrode for a storage battery has been proposed which protects the alloy itself and increases the mechanical strength and electrical conductivity of the alloy itself. An alkaline storage battery is considered in which the hydrogen storage electrode is used as a negative electrode and is combined 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 improved in both the non-sintered and sintered electrodes, and the battery performance is improved. It can be improved. However, on the other hand, the metal that coats the surface of the alloy is selected to be a substance that does not react with hydrogen, so the hydrogen storage / release characteristics, that is, the energy storage capacity that is electrochemically regulated by hydrogen storage / release Is irrelevant. Therefore, if the amount of this metal portion is large, the capacity or output per unit weight is reduced by that amount. For example, when the capacity density of a hydrogen storage alloy is 0.25Ah / g (about 1Ah / cc), if the surface of the alloy particles is coated with copper by electroless polishing, a large amount of 20-40wt% of the total alloy content Since copper is used, the previous capacity density is reduced to 60-80%,
It becomes difficult to construct a storage battery with high energy density.

Originally, in alkaline storage batteries, the volume occupied by the positive electrode and the negative electrode in a given volume is fixed, so an increase in the volume occupied by the negative electrode leads to a decrease in the capacity occupied by the positive electrode, and the discharge capacity of the positive electrode law decreases. have.

Means for Solving the Problems The present invention is a nickel oxide positive electrode and reversibly occludes hydrogen.
Electrochemical characteristics that include a negative electrode made of a releasing alloy or hydride and an alkaline electrolyte, and can occlude and release hydrogen partially covered with a conductive metal such as copper, nickel, or an alloy thereof on the surface. The above-mentioned problems have been solved by containing a hydrogen storage alloy or hydride particles holding the above in the negative electrode or providing it on the surface of the negative electrode to form a nickel-hydrogen alkaline storage battery.

Further, the present invention, in the negative electrode, the surface of the surface of the negative electrode and the negative electrode of the paste type electrode containing a hydrogen storage alloy or hydride particles whose surface is partially coated with copper, nickel or their alloys and a binder. Is a hydrogen storage alloy or hydride particles partially coated with copper, nickel or an alloy thereof, either alone or with a binder, 850-100
It is a nickel-hydrogen alkaline storage battery using a sintered electrode sintered at a temperature of 0 ° C. as a negative electrode.

Hydrogen absorbing alloy powder and conductive metal such as copper,
By mixing hydrogen storage alloy powder coated with nickel or their alloys with a binder, pressurizing and drying through an electrode support to form an electrode, the hydrogen storage alloy monomer coated with a conductive metal Can significantly reduce the amount used, so that the capacity density per unit weight and volume is improved and the discharge characteristics (high discharge voltage and discharge capacity utilization rate) are excellent. A high-volume alkaline storage battery that cannot be obtained is created. Alternatively, by heat-treating (sintering) the mixture of the two 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 the electrode substrate made of the hydrogen storage alloy or hydride powder, the same mechanical This leads to an improvement in dynamic strength and an improvement in discharge capacity per unit weight and volume.
Also, it has excellent discharge characteristics (high rate discharge characteristics). This is because the conductive substance 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 is also discharged. Since it is related to the capacity, the capacity per weight and volume is increased. On the other hand, if the electrode surface is made of a hydrogen storage alloy powder coated with copper, nickel or an alloy thereof, the particles of the copper, nickel or alloy are in contact with each other on the coated surface, so that the electrode itself In addition to a decrease in resistance and an increase in mechanical strength, an increase in capacity per unit weight and volume can be expected.

EXAMPLES The present invention will be described with reference to Examples.

Example 1 Each sample of commercially available Mm (Misch metal, La: 60, Ce: 25, Nd: 7, Pr, and others 8), Ni (purity 99% or more), Co (purity 99% or more) was made into a fixed composition. Weigh in proportion and put in a water-cooled copper crucible,
The addition was carried out in an arc melting furnace to produce an MmNi ₃ Co ₂ alloy. Grind this alloy finely to less than 30 μm with a crusher,
The electrode alloy sample was designated as a.

Next, a part of the sample a 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 of this electroless plating are as follows.

At first glance, this alloy forms a uniform metal coating film on the surface of the alloy particles, but still has many holes and cracks. Due to the holes and cracks, a partial coating film is formed. It is considered that hydrogen is absorbed and released through these holes and cracks. This alloy sample coated with copper was designated as b.

Next, 80 wt% of a powder and 20 wt% of b powder were added and kneaded well with a binder such as polyvinyl alcohol, and applied on both sides of the electrode support (perforated plate: also known as punching metal). Pressurization. Dry. A lead is attached as a negative electrode, and a known nickel oxide positive electrode and a separator are used to form an electrode plate group,
The alkaline electrolyte is put into an alkaline storage battery, and this storage battery is designated as A. The structure of this storage battery is shown in FIG. An occlusion 1 made of a hydrogen occlusion electrode containing a metal-coated alloy or hydride, a positive electrode 2 made of nickel oxide, and a separator 3 located between both electrodes are immersed in an electrolytic solution 4. 5
Is a battery case, 6 is a lid, 7 is a liquid injection port, and 8 and 9 are negative and positive lead terminals.

FIG. 2 schematically shows an electrode structure made of a hydrogen storage alloy. FIG. 2A shows the electrode shown in the first embodiment. The ∘ mark indicates a, and the ● mark indicates b.

FIG. 2B shows the electrode shown in the second embodiment shown below.
FIG. 2C shows an electrode taken up as a conventional example.

The negative electrode in Example 1 had a size of 40 mm × 50 mm and a thickness of 1.2.
mm. In order to compare the negative electrode capacities, the positive electrode capacities were made larger than the negative electrode capacities, and the capacity was regulated by the negative electrode rule. Both charging and discharging current was 500mA. The charging time was about 1.3 times the discharging time. The final voltage was 1.0V.

As a conventional alkaline storage battery, the electrode structure of FIG. 2C is adopted in the battery configuration of FIG. 1, and the size of the negative electrode is 40 mm ×
The negative electrode had a volume of 50 mm and a thickness of 1.2 mm and had exactly the same volume as the former. A binder such as polyvinyl alcohol is added to the B powder, and the mixture is well kneaded and applied on both sides of the electrode support (perforated plate), dried under pressure, and a lead is attached to form a negative electrode. The electrode plate group with the separator,
An alkaline storage battery soaked in an alkaline electrolyte was constructed.
This storage battery is designated as B.

Figures 3 and 4 show a comparison of the discharge capacities of the batteries A and B. Figure 3 shows the performance at 500mA discharge (corresponding to 0.2C: 5 hour rate discharge). The battery of A holds the terminal voltage of 1.0 V or more for 5 hours, while the battery of B holds only 3.5 hours. The capacity of battery B is about 30% lower than that of battery A. This is the capacity per unit volume (Ah / c
c) is small, which means that there are few effective alloys.

Figure 4 shows the performance at 2500mA discharge (corresponding to 1C: 1 hour rate discharge). The capacity of the B battery is about 30% lower than that of the A battery. Moreover, it can be seen that high rate discharge characteristics such as 1C discharge are also excellent. Also, there is almost no difference in discharge voltage between the A and B batteries. 100 charge / discharge cycle life
The cycle has passed, but there is almost no change. Therefore, in addition to the conventional characteristics, the capacity of the battery of the present invention can be significantly improved in the battery system showing a constant volume.

Example 2 After filling the alloy powder (a) produced in Example 1 into an electrode support (foamed metal), hydrogenated alloy powder having both sides coated with copper (previously A hydrogenated sample powder (b ') with repeated occlusion and desorption was pressure-filled to form a layer b'. The weight ratio is approximately
10 wt% b'powder was used. Then, after pressurizing and drying, hot pressing was performed at high temperature in vacuum, or sintering treatment was performed at a temperature of 950 ° C. for 5 hours in vacuum. The powder particles on the surface were strongly sintered, and an electrode having high mechanical strength was formed. This electrode is designated as C. A capacity test was conducted on the assumption that the configuration of the storage battery and the charging / discharging conditions were all the same as in Example 1.

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

From the result of discharge capacity test of this storage battery, C battery is 2.4A
While the capacity of h was shown, the D battery showed a capacity of only about 1.7 Ah. Since this has a small capacity per unit volume, the battery capacity is low. As described above, the same tendency as in Example 1 is obtained for the sintered electrode. In addition, in the high rate discharge voltage and charge / discharge cycle life, almost no significant difference was observed between the C and D batteries.

Here, an open-type storage battery was made and the capacity of the negative electrode was compared, but the same effect can be expected when it is used as the negative electrode of the sealed storage battery. That is, since the active material is packed in a constant volume, the smaller the capacity per unit volume (Ah / cc), the more the negative electrode material is added to secure the predetermined capacity. The positive electrode material occupies a smaller portion by the increased amount, so the battery capacity must be reduced. Now, using the negative electrode prepared in Example 1,
When a sealed alkaline storage battery of a size is made and a capacity test is performed, the storage battery of the present invention has a capacity of 2.0 Ah, whereas the conventional storage battery has a capacity of 1.5 Ah. charging·
The discharge current was all 0.2 C.

Further, by forming the b layer on the surface of the electrode, it also has a role of preventing the negative electrode alloy from being oxidized by oxygen generated from the nickel positive electrode during overcharge, and the storage battery having the electrode having strong oxidation resistance. Will also be provided. In this respect, we can expect further longevity.

Although copper is described as the conductive metal in the examples, the same can be said for nickel. As described above, any metal or alloy capable of electroless plating and having conductivity can be used.

Although using MmNi ₃ Co ₂ as a hydrogen storage alloy, other rare earth - is the same nickel-based. Also, a titanium-nickel system such as Ti ₂ Ni may be used. The same effect is obtained whether a hydrogen storage alloy or a hydride is used as the initial starting material. In the case of electroless plating, hydrogenating the alloy makes the surface more active and makes plating easier. Therefore,
It is preferred to electrolessly plate the hydrogenated alloy.

The hydrogen storage alloy covering the metal has basically the same effect regardless of whether it is an alloy or a hydride, but if the amount is 10 wt% or less, the effect is small, and if it is 40 wt% or more, the capacity decreases. Becomes 10% or more, and the cost per capacity becomes high, making it impractical. Therefore, considering durability and cost, 10 to 40 wt% is the optimum range.

Although the sintering temperature mentioned in the examples was set to 950 ° C, 850 ° C to 10 ° C.
00 ° C is the best. At 850 ° C or lower, the strength during sintering is weak and no great effect is obtained, because the melting point of copper is 1083 ° C.
Above 1000 ° C, 850 ° C to 1000 ° C is optimal because it over-sinters to reduce the surface area and significantly reduce the capacity. In addition, as another sintering method, hot pressing can be performed simultaneously with pressing and sintering. The surface area and porosity are slightly smaller, but the mechanical strength is stronger.

EFFECTS OF THE INVENTION As described above, according to the present invention, in addition to having mechanical strength, long durability and long cycle life, and excellent high rate discharge characteristics, the capacity density of the negative electrode is high and discharge capacity is high. A large nickel-hydrogen alkaline storage battery is obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a nickel-hydrogen alkaline storage battery using an electrode of the present invention, FIGS. 2A, B and C are diagrams schematically showing an electrode configuration, and FIGS. 3 and 4 are It is the figure which showed the comparison of the discharge characteristic of the battery of this invention and the conventional type battery. 1 ... Negative electrode, 2 ... Positive electrode, 3 ... Separator.

Claims (5)

(57) [Claims] 1. A nickel oxide positive electrode, a negative electrode made of an alloy or hydride that reversibly absorbs and desorbs hydrogen, and an alkaline electrolyte, the surface of which is partially covered with a conductive metal to occlude hydrogen. A nickel-hydrogen alkaline storage battery comprising a hydrogen storage alloy or hydride particles to be released in the negative electrode or provided on the surface of the negative electrode. 2. A hydrogen storage alloy or a metal coated with hydride particles, which retains electrochemical characteristics capable of storing and releasing hydrogen, is made of copper, nickel or an alloy thereof. A nickel-hydrogen alkaline storage battery according to claim 1. 3. A negative electrode comprising a paste type electrode containing a hydrogen storage alloy or hydride particles whose surface is partially covered with copper, nickel or an alloy thereof and a binder. The nickel-hydrogen alkaline storage battery according to item 1. 4. A hydrogen storage alloy or hydride particle whose surface is partially coated with copper, nickel or an alloy thereof is placed on the negative electrode surface alone or together with a binder at 850 to 1000 ° C.
The nickel-hydrogen alkaline storage battery according to claim 1, wherein the negative electrode is a sintered electrode sintered at the temperature. 5. The total amount of hydrogen storage alloy or hydride particles whose surface is partially coated with copper or nickel or an alloy thereof is 10 to 40% by weight of the whole negative electrode. The nickel-hydrogen alkaline storage battery according to item 1.