JPH0785866A - Hydrogen storage alloy electrode and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide a hydrogen storage alloy electrode of high activity, high capacity and a long life by applying Ni plating having Co powder or hydrogen storage alloy powder,dispersed, to a surface of the hydrogen storage alloy electrode, or further soaking this electrode in a high temperature alkali. CONSTITUTION:As an example, a hydrogen storage alloy expressed by ZrMn 0.6 V 0.2 Cr 0.2 Ni 1.15, being one of C15 type Laves phase alloys, is subjected to Ni plating by means of an Ni plating bath wherein powder of ZrMn 0.8 V 0.1 Ni 1.1 is dispersed, and a well-known nickel oxide electrode is used as a positive electrode, to constitute a battery. Then, an electrode excellent in initial activation and capable of quick charging/discharging can be provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode using a hydrogen storage alloy and its manufacturing method. More specifically, the present invention relates to a hydrogen storage alloy electrode useful for an alkaline storage battery such as a nickel-hydrogen storage battery and a method for producing the same.

[0002]

2. Description of the Related Art Recently, in order to achieve a higher energy density of an alkaline storage battery, a nickel-hydrogen storage battery using a hydrogen storage alloy electrode instead of a cadmium electrode has been attracting attention, and many proposals have been made for its manufacturing method. ing. The hydrogen storage alloy electrode can be manufactured by sintering alloy powder, or by foaming, fibrous, punching metal or other three-dimensional or two-dimensional method.
There is a paste type in which a three-dimensional porous support is filled or coated with alloy powder. Of these, the paste method is the easiest to manufacture. Since hydrogen storage alloys are relatively excellent in electron conductivity, as is the case with cadmium and zinc, there is great potential for non-sintered paste electrodes.

In order to improve the characteristics of this paste-type hydrogen storage alloy electrode, for example, a technique of plating the surface of hydrogen storage alloy powder particles with nickel or copper to form a porous metal layer is particularly advantageous in terms of oxidation resistance, It is known to improve the utilization rate and moldability (Japanese Patent Laid-Open No. 02-201870).

[0004]

The battery using the conventional hydrogen storage alloy does not have sufficient charge / discharge characteristics, utilization rate and high rate charge / discharge characteristics at the beginning of the charge / discharge cycle. In particular, the discharge capacity per weight of the alloy in the actual electrode is about 80% of the capacity of the alloy.
That is, when a hydrogen storage alloy is used as an electrode, it is used in an actual battery such as a paste-type electrode as compared with the discharge capacity of an ideal electrode prepared by mixing a large amount of Ni powder with the alloy powder. The discharge capacity of the electrode is reduced to about 80%. The improvement of the utilization rate is an important issue for increasing the capacity of the electrode. The characteristics are not sufficient even by the method of plating the particle surface of the alloy powder described above,
In addition, plating all the alloy particles causes a decrease in energy density per weight of the electrode. The present invention, in order to solve the problems of the prior art, to improve the utilization rate of the alloy,
It is an object of the present invention to provide a high capacity, highly active hydrogen storage alloy electrode and a method for producing the same.

[0005]

In order to achieve the above object, the hydrogen storage alloy electrode of the present invention is an electrode formed of a hydrogen storage alloy that electrochemically stores and releases hydrogen, and the electrode surface Is plated with Ni containing Co powder or Ni containing hydrogen absorbing alloy powder. Here, in the plating containing the hydrogen-absorbing alloy powder, the hydrogen-absorbing alloy powder has a larger content of elements that are easily eluted in the alkaline solution than the hydrogen-absorbing alloy in the electrode, and further, the hydrogen equilibrium pressure is low. Is preferred. In this structure, the main component of the hydrogen storage alloy is represented by the general formula ABα (α = 1.5 to 2.5), and the alloy phase is substantially intermetallic compound Lavas.
Phase and its crystal structure is hexagonal C14 type and / or
Alternatively, it is preferably cubic C15 type.

The ratio of metal powder in the plating is 10 to 10.
30% by weight, the plating amount on the electrode formed of the hydrogen storage alloy powder is 1 to 1 with respect to the weight of the hydrogen storage alloy.
About 0% by weight is preferable. Next, a method for producing a hydrogen storage alloy electrode of the present invention is a method for producing an electrode formed of a hydrogen storage alloy powder that electrochemically stores and releases hydrogen, wherein the Co The method is characterized by including a step of electrolytic plating using a nickel plating solution in which a powder or a hydrogen storage alloy powder is dispersed, and a step of immersing this electrode in an alkaline aqueous solution at a high temperature, particularly 80 ° C. or higher.

[0007]

According to the structure of the present invention, the surface of the electrode is plated with Ni containing Co powder or hydrogen storage alloy powder, or further, the plated electrode is immersed in a high temperature alkaline solution. As a result, the utilization factor of the alloy can be improved and a high capacity, highly active hydrogen storage alloy electrode can be obtained. That is, the capacity of the electrode can be increased, the rapid charge / discharge characteristics, and the life can be improved.

Regarding the action of Co powder during plating,
o Particles enter the grain boundaries of the plating and the surface of the plating becomes rougher than when no powder is added, increasing the surface area,
It is considered that overvoltage is being reduced. Therefore, it is more effective than the method of simultaneously plating in an alloy state from a plating bath containing Ni and Co salts. Furthermore, by immersing this electrode in hot alkali,
It is considered that Co is partially eluted to increase the surface area. On the other hand, when the hydrogen storage alloy powder is included in the plating, the catalytic effect is added together with the similar surface area increasing effect. Not just applying this to the surface,
By holding it during plating, the catalytic effect can be effectively exhibited. Particularly, by plating a hydrogen storage alloy having a low hydrogen equilibrium pressure, that is, having a high gas absorption capacity, it is possible to efficiently perform gas absorption during rapid charging. In addition, Mn, V, and Co, which are easily dissolved in alkali
By plating a hydrogen storage alloy having a high content of, for example, the activation effect when immersed in high temperature alkali can be further enhanced, and an electrode with high activity can be obtained.

If the size of the particles dispersed during plating is too large, the connection of Ni as a matrix is weakened, and the particles themselves easily fall off. Therefore, it is necessary to be at least smaller than the hydrogen storage alloy powder in the electrode, and preferably about 10 μm or less. The effects as described above are obtained not only for the AB ₂ type Larvus phase alloys such as those shown in the examples below, but also for MmNi _3.7 Mn _0.3.
It can be obtained for other hydrogen storage alloy electrodes such as AB ₅ type having a CaCu ₅ structure such as Al _0.3 Co _0.7 . Also,
The hydrogen storage alloy dispersed during plating is also effective if a hydrogen storage alloy having a different structure is combined, such as an AB ₂ type alloy electrode containing an AB ₅ type alloy in the plating.

[0010]

EXAMPLES The present invention will be specifically described below with reference to examples. [Example 1] As a hydrogen storage alloy, the main alloy phase was C1.
ZrMn _0.6 V as an example of an alloy that is a 5 type Larvus phase
_{A 0.2} Ni _1.3 alloy is used. This was mechanically crushed to 38 μm or less, a 3% by weight aqueous solution of polyvinyl alcohol was added to form a paste, and the paste was then porosity 95%.
%, 0.8 mm thick foamed nickel plate is filled and pressed. This electrode is immersed in a known Watt's bath, 10 g / L of Co powder having a particle size of 5 μm or less is further added, and plating is performed while stirring. The electrode thus obtained is called electrode A. Further, this electrode was immersed in a potassium hydroxide aqueous solution at 100 ° C. for 1 hour, and was designated as an electrode B. As a comparative example, an electrode not plated is electrode C, and an electrode plated only with Ni is electrode D. The amount of plating is 5% by weight with respect to the weight of the electrode.

These electrodes are used as negative electrodes, nickel hydroxide electrodes having an excess electric capacity are arranged on the counter electrodes, and an aqueous solution of potassium hydroxide having a specific gravity of 1.30 is used as an electrolytic solution. Charging and discharging were performed in an open system in which the capacity was regulated by the storage alloy negative electrode. Charging is 100 mA / g of hydrogen storage alloy for 5.5 hours, and discharging is 50 / g of alloy.
The terminal voltage was set to 0.8 V at mA. This result is shown in Figure 1.
Shown in. The electrode C has a low discharge capacity at the beginning of the charge / discharge cycle, requires 4 cycles or more to reach the saturated discharge capacity, and has a saturation capacity of 0.335 Ah / g. Also,
Electrode D is activated faster and has a saturation capacity of 0.350A.
It is increasing to h / g. Electrodes A and B are activated faster than electrode D and have a saturation capacity of 0.36 Ah / g
It has increased to above. Therefore, it can be seen that the electrode according to the present invention has an excellent initial activity and an improved utilization rate of the alloy.

Next, the results of constructing a sealed battery using this electrode will be described. The electrodes A, B, C and D are each 3.9 cm in width, 9.5 cm in length and 0.35 in thickness.
The thickness is adjusted to mm, combined with the positive electrode and the separator, and formed into a spiral shape and housed in an AA size battery case. The positive electrode is
Known foamed nickel electrode, width 3.9 cm, length 7.
It is 8 cm. The separator is a polypropylene non-woven fabric having hydrophilicity. An electrolyte solution in which 30 g / L of lithium hydroxide is dissolved in an aqueous potassium hydroxide solution having a specific gravity of 1.30 is poured and then sealed to obtain a sealed battery. This battery has a nominal capacity of 1.2 Ah according to the positive electrode capacity regulation. Batteries using the electrodes A, B, C, and D are batteries a, b, and
Let c and d.

The results of evaluating 10 by making 10 of each of these batteries and charging / discharging cycle test will be explained. At 20 ° C, the capacity is 150 at a constant current for 5 hours.
%, And the charging / discharging in which a constant current was similarly discharged to 1.0 V at a rate of 5 hours was repeated, and the discharge capacities of the batteries a, b, and d were about 1.2 Ah from the first cycle. In other words, it is considered that the battery is regulated by the positive electrode. However, the discharge capacity of the battery c was 0.8 Ah in one cycle, and
From the second cycle, the discharge capacity was about 1.2 Ah. It is considered that this is because the activation of the negative electrode was accelerated by the plating treatment. These batteries were repeatedly charged and discharged repeatedly and sufficiently activated, and then charged at 20 ° C. for 5 hours at a rate of 150% and at 20 ° C. or 0 ° C. for 1 hour at a final voltage of 1.0 V. The rate discharge characteristics were investigated. Table 1 shows the intermediate voltage at the time of discharge and the discharge capacity ratio to the discharge capacity at 20 ° C. for 5 hours.

[0014]

[Table 1]

As can be seen from Table 1, batteries a and b show excellent characteristics at high rate discharge. In particular, the discharge voltage is high,
It is considered that the discharge overvoltage was reduced by the plating.

[Example 2] As a hydrogen storage alloy, Z was used as an example of an alloy whose main alloy phase is a C15 type Larvus phase.
An rMn _0.6 Cr _0.2 V _0.2 Ni _1.15 alloy is used. First,
The electrode production will be described. This alloy is mechanically 38μ
Mill to m or less and add 3% by weight of polyethylene powder.
This mixture is made into a paste with alcohol, and this paste is filled into a foamed nickel plate having a porosity of 95% and a thickness of 0.8 mm and pressed to obtain an electrode. ZrMn _0.8 V _0.1 Ni _1.1 alloy is used as the hydrogen storage alloy dispersed in the plating bath. This alloy has a lower hydrogen equilibrium pressure than the alloy used for the electrode and has a large Mn content, so that it is easily eluted in an alkaline solution. This is pulverized to obtain a powder having a particle size of 10 μm or less. This powder is placed in a known Watt bath at a rate of 5 g / L, and the above electrodes are plated with stirring. The electrode thus obtained is referred to as an electrode E. Further, an electrode F is obtained by immersing the electrode E in a potassium hydroxide solution at 100 ° C. for 1 hour. As a comparative example, an electrode not plated is an electrode G,
An electrode plated with Ni is referred to as an electrode H. The amount of plating is 5% by weight with respect to the weight of the hydrogen storage alloy of the electrode.

These electrodes are used as negative electrodes, nickel hydroxide electrodes having an excessive electric capacity are arranged on the counter electrodes, and an aqueous solution of potassium hydroxide having a specific gravity of 1.30 is used as an electrolytic solution. Charging and discharging were performed in an open system in which the capacity was regulated by the storage alloy negative electrode. Charging is 100 mA / g of hydrogen storage alloy for 5.5 hours, and discharging is 50 / g of alloy.
The terminal voltage was set to 0.8 V at mA. This result is shown in Figure 2.
Shown in. The electrode G has a low discharge capacity at the beginning of the charge / discharge cycle, requires 7 cycles or more to reach the saturated discharge capacity, and has a saturated capacity of 0.322 Ah / g. Also,
Electrode H is activated faster and has a saturation capacity of 0.339A.
It is increasing to h / g. Electrodes E and F are activated faster than electrode H and have a saturation capacity of 0.350 Ah / g.
It is increasing to the extent. In particular, the electrode F immersed in the alkaline solution is activated very quickly.

Next, the result of constructing a sealed battery using these electrodes will be described. The electrodes E, F, G,
Each H has a width of 3.9 cm, a length of 9.5 cm, and a thickness of 0.
It is adjusted to 35 mm, combined with a positive electrode and a separator to form a spiral shape, and is housed in an AA size battery case. The positive electrode is a known foaming nickel electrode, and has a width of 3.9 cm and a length of 7.8 cm. The separator is a polypropylene non-woven fabric having hydrophilicity. An electrolyte solution obtained by dissolving 30 g / L of lithium hydroxide in a potassium hydroxide aqueous solution having a specific gravity of 1.30 is poured and then sealed to obtain a sealed battery. This battery has a nominal capacity of 1.2 Ah according to the positive electrode capacity regulation. Batteries using the electrodes E, F, G, and H are batteries e, f, and
g and h.

The results of making 10 of each of these batteries and evaluating them by a charge / discharge cycle test will be described. 150% of capacity at a constant current of 5 hours at 20 ° C
When charging and discharging were repeated for 5 hours at a constant current of 1.0 V, the discharge capacities of the batteries e and f were about 1.2 Ah from the first cycle. In other words, it is considered that the battery is regulated by the positive electrode. However, the discharge capacities of the batteries g and h did not reach 1.2 Ah in one cycle, and the discharge capacities increased as the number of cycles increased, so that the battery g required 5 cycles and the battery h required 3 cycles before the positive regulation. And After sufficiently repeating the charge / discharge cycle, charge at 20 ° C. for 5 hours at a rate of 150%, and
The high rate discharge characteristics were examined under the condition of discharging at a final voltage of 1.0 V at a rate of 1 hour at 0 ° C or 0 ° C. Table 2 shows the intermediate voltage at the time of discharge and the discharge capacity ratio to the discharge capacity at 20 ° C., 5 hour rate discharge.

[0020]

[Table 2]

As can be seen from Table 2, the batteries e and f show excellent characteristics at high rate discharge. In particular, the discharge voltage is high,
It is considered that the discharge overvoltage was reduced by the plating. Next, the rapid charge characteristics were examined. The battery was charged at 20 ° C. at an hourly rate to 200% of the battery capacity, and the battery internal pressure at that time was measured. As a result, the internal pressure of the battery g exceeded 20 atm and the liquid leaked, and the battery h rose to 10 atm, but the batteries e and f were suppressed to 3.4 atm and 2.7 atm, respectively. Furthermore, the cycle life was examined. The change of the discharge capacity was examined by charging and discharging at a constant current of up to 1.0 V at a half hour rate of 120% and at a half hour rate of discharge. The result is shown in FIG. The batteries e and f according to the present invention have an initial discharge capacity of 9 even after 500 cycles.
It can be seen that the capacity is maintained at 0% or more and the cycle characteristics are excellent.

[0022]

As described above, according to the present invention, it has become possible to improve the initial activity and utilization rate of the alloy, which has been a problem in the past, and to improve the charge / discharge efficiency. An electrode can be provided.

[Brief description of drawings]

FIG. 1 is a diagram comparing discharge characteristics in an open system of hydrogen storage alloy electrodes of an example of the present invention and a conventional example.

FIG. 2 is a diagram comparing discharge characteristics in an open system of hydrogen storage alloy electrodes of an example of the present invention and a conventional example.

FIG. 3 is a diagram comparing the cycle characteristics of sealed batteries using hydrogen storage alloy electrodes of an example of the present invention and a conventional example.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Naoko Maekawa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. An N containing Co powder on the surface of an electrode made of a hydrogen storage alloy powder capable of electrochemically storing and releasing hydrogen.
A hydrogen storage alloy electrode, wherein i is plated. 2. A hydrogen storage alloy electrode, characterized in that Ni containing hydrogen storage alloy powder is plated on the surface of the electrode made of hydrogen storage alloy powder which stores and releases hydrogen electrochemically. 3. A step of electrolytic plating in a nickel plating solution in which Co powder or hydrogen storage alloy powder is dispersed on the surface of an electrode made of hydrogen storage alloy powder that electrochemically stores and releases hydrogen, and then this step A method for producing a hydrogen storage alloy electrode, comprising a step of immersing the electrode in a high temperature alkaline aqueous solution.