JP5322392B2 - Hydrogen storage alloy electrode, method for producing the same, and alkaline storage battery - Google Patents

Description

  The present invention relates to a hydrogen storage alloy electrode using a hydrogen storage alloy as a negative electrode active material, a method for producing the hydrogen storage alloy electrode, and an alkaline storage battery using the hydrogen storage alloy electrode.

In recent years, nickel-hydrogen storage batteries using a hydrogen storage alloy as a negative electrode active material have attracted attention as alkaline storage batteries because of high output and excellent environmental safety. Conventionally, a hydrogen storage alloy used for the negative electrode of this type of nickel-hydrogen storage battery is one in which a part of a LaNi ₅ type rare earth hydrogen storage alloy is replaced with an element such as aluminum (Al) or manganese (Mn). It was done. In recent years, as shown in Patent Document 1 (Japanese Patent Laid-Open No. 11-162459), a hydrogen storage alloy containing rare earth elements, nickel (Ni), magnesium (Mg), and aluminum (Al) as main constituent elements. Came to be proposed.

This hydrogen storage alloy mainly composed of rare earth elements, nickel (Ni), magnesium (Mg), and aluminum (Al) has a capacity per volume and a mass per mass as compared with conventional LaNi ₅ type rare earth hydrogen storage alloys. All of the capacities are high capacity. In addition, since it has a feature that it is activated quickly and is excellent in low-temperature discharge characteristics, it has come to be expected in applications of high output. In addition, as other techniques for increasing the output, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2000-82491) and Patent Document 3 (Japanese Patent Laid-Open No. 2000-030699) have been proposed.

Here, in the high output technique proposed in Patent Document 2, it is proposed to increase the electrode area. This is because if the inner area of the positive electrode and the negative electrode is increased, the current density of the current flowing between the two electrodes is made uniform. For this reason, even if this type of battery is operated at a high discharge rate, the electrode plate resistance in the electrode group can be prevented from increasing. Thereby, since the operating voltage does not decrease, it is based on the idea that a large discharge current can be taken out.
Further, in the technique for increasing the output proposed in Patent Document 3, it has been proposed to add nickel flakes or nickel short fibers to the hydrogen storage alloy electrode. This is based on the idea that by providing conductivity in the hydrogen storage alloy electrode, the contact resistance in the hydrogen storage alloy electrode is reduced and the resistance in the hydrogen storage alloy electrode is reduced.

By the way, a general hydrogen storage alloy has an AB ₂ type structure or an AB ₅ type structure. Among them, a hydrogen storage alloy composed of rare earth elements, nickel, and magnesium has an AB ₂ type structure unit and an AB ₅ type structure unit. It is known that various combinations of crystal structures are taken. For example, in Patent Document 4 (Japanese Patent Laid-Open No. 2002-164045), an AB ₂ type structure and an AB ₅ type structure have a hexagonal crystal structure (2H) in which two layers are stacked in a cycle. It is reported that the Ce ₂ Ni ₇ type structure hydrogen storage alloy improves the cycle life characteristics of hydrogen storage / release.
Japanese Patent Laid-Open No. 11-162459 JP 2000-82491 A JP 2000-30699 A JP 2002-164045 A

However, the hydrogen storage alloy mainly composed of rare earth elements, nickel (Ni), magnesium (Mg), and aluminum (Al) proposed in Patent Document 1 is composed of various crystal phases. For this reason, compared with the conventional LaNi ₅ type rare earth hydrogen storage alloy, the surface area is increased due to the presence of the boundary phase, and an effect of reducing the reaction resistance on the surface of the hydrogen storage alloy can be expected. Insufficient to use. As a solution, it is conceivable to increase the amount of nickel in the hydrogen storage alloy to increase the reaction active point. However, if the amount of nickel is increased to a certain value or more, the structure of the hydrogen storage alloy only changes. However, a new problem that a segregation phase appears was brought about.

Further, as proposed in Patent Document 2, the electrode area of a hydrogen storage alloy electrode made of a hydrogen storage alloy having rare earth elements, nickel (Ni), magnesium (Mg), and aluminum (Al) as main constituent elements is conventionally set. It has been found that when the area is increased beyond the range, the superiority in the output characteristics is not recognized. In general, the winding body (spiral electrode group) is highly bound as the electrode area increases and becomes thinner. With this high binding, a portion that cannot hold a sufficient electrolyte in the separator is formed, and a non-uniform portion of the electrolyte is generated in the hydrogen storage alloy electrode. In particular, hydrogen storage alloys containing rare earth elements, nickel (Ni), magnesium (Mg), and aluminum (Al) as main constituent elements are more easily oxidized than conventional LaNi ₅ type rare earth hydrogen storage alloys, and the consumption of electrolyte Large amount. For this reason, it is considered that the non-uniform distribution of the electrolytic solution is remarkably generated in the hydrogen storage alloy electrode, and the reaction resistance reduction effect due to the increase in the electrode area is offset.

Further, when the effect of adding nickel flakes or short nickel fibers in Patent Document 3 was examined, it was found that a clear output improvement effect at a low temperature was not recognized. This is because the reaction resistance on the surface of the hydrogen storage alloy becomes extremely high during low-temperature discharge, so even if the contact resistance in the hydrogen storage alloy electrode is somewhat reduced, the electrode resistance reduction effect on the hydrogen storage alloy electrode is not recognized. It is done. From the above, when the area of the hydrogen storage alloy electrode is expanded beyond a certain area, a hydrogen storage alloy containing rare earth elements, nickel (Ni), magnesium (Mg), and aluminum (Al) as main constituent elements is obtained. It became clear that it was necessary to raise the output characteristics at low temperatures in the hydrogen storage alloy electrode used.
Moreover, the hydrogen storage alloy having the structure proposed in Patent Document 4 has insufficient discharge characteristics (especially assist output at low temperature), and has satisfactory performance as a high output application far exceeding the conventional range. I don't have it.

  Therefore, the present invention has been made to solve the above problems, and it is possible to improve the output characteristics at a low temperature even if the electrode area is far beyond the conventional range. An object of the present invention is to provide a hydrogen storage alloy electrode and a production method thereof and an alkaline storage battery including such a hydrogen storage alloy electrode.

In the hydrogen storage alloy electrode of the present invention, the ratio Y / X (cm ² / Ah) of the surface area Y (cm ² ) to the electrode capacity X (Ah) of the hydrogen storage alloy electrode is 70 cm ² / Ah or more (Y / X ≧ 70 cm). ² / Ah), and the hydrogen storage alloy serving as the negative electrode active material contains at least a rare earth element, nickel, magnesium, and aluminum. The mother crystal phase of the hydrogen storage alloy is a Ce ₂ Ni ₇ crystal phase, Ce ₅ Co _19. It consists of a crystal phase and a crystal phase containing at least two of Pr ₅ Co ₁₉ crystal phases, and is added so that the amount of nickel flakes or nickel short fibers added is 0.5 mass% or more with respect to the mass of the hydrogen storage alloy. It is characterized by being.

Here, when nickel flakes or nickel short fibers are added to the hydrogen storage alloy electrode, these act as a conductive agent and have an effect of reducing the contact resistance between the hydrogen storage alloys in the hydrogen storage alloy electrode. However, the ratio Y / X (cm ² / Ah) of the surface area Y (cm ² ) to the electrode capacity X (Ah) of the hydrogen storage alloy electrode is 70 cm ² / Ah or more (Y / X ≧ 70 cm ² / Ah). In the hydrogen storage alloy electrode having an area far exceeding the range, the hydrogen storage alloy containing rare earth elements, nickel, magnesium and aluminum as the main constituent elements, nickel flakes or nickel short fibers relative to the mass of the hydrogen storage alloy If 0.5 mass% or more is added, the activity of the hydrogen storage alloy surface is improved in addition to the effect of reducing the contact resistance. In other words, an increase in reaction resistance at a low temperature can be suppressed by a catalytic action, and high output in a low temperature region that cannot be achieved only by a contact resistance reduction effect can be achieved.

In this case, the host crystal phase of the hydrogen storage alloy is Ce ₂ Ni ₇ crystal phase, Ce ₅ Co ₁₉ crystal phase, Pr ₅ Co ₁₉ ing a crystalline phase which contains at least two or more from the crystal phase. The apparent density of the added nickel flakes or nickel short fibers is preferably 0.8 g / cm ³ or more and 1.5 g / cm ³ or less, the long diameter is 10 μm or more, and the short diameter is 5 μm or less. The reason is that when nickel flakes or short nickel fibers having an apparent density of less than 0.8 g / cm ³ and a long diameter and short diameter of 5 μm to 10 μm are used, a decrease in discharge characteristics (output characteristics) was observed. . This is because nickel flakes or short nickel fibers having an apparent density of less than 0.8 g / cm ³ are not supported or contacted on the surface of the hydrogen storage alloy and do not perform catalytic action. It is presumed that flakes or nickel short fibers became contact resistance, resulting in deterioration of discharge characteristics.

  In producing such a hydrogen storage alloy electrode, at the time of slurry preparation, a hydrogen storage alloy powder mixing step by mixing the hydrogen storage alloy powder into a solution in which nickel flakes or nickel short fibers are mixed in a water-soluble binder, A water-insoluble binder mixing step of mixing a water-insoluble binder into the solution mixed with the hydrogen storage alloy powder, and a viscosity adjusting step of adjusting the viscosity of the solution in which the water-insoluble binder is mixed. It is desirable to prepare.

  This is because when nickel flakes or nickel short fibers are added to the step of mixing a water-insoluble binder or the step of adjusting the viscosity, the nickel flakes or nickel short fibers are fine powders, resulting in uneven diffusion and the surface of the alloy. Separation occurs. Therefore, in the present invention, the hydrogen storage alloy powder is mixed with a solution obtained by mixing nickel flakes or nickel short fibers with a water-soluble binder. Thereby, it becomes possible to uniformly support nickel flakes or nickel short fibers on the surface of the hydrogen storage alloy powder, and the effects of the present invention can be sufficiently exhibited.

  As described above, in the present invention, in the hydrogen storage alloy electrode having an electrode area exceeding the conventional range, the structure of the hydrogen storage alloy is defined, and by adding a certain amount of nickel flakes or nickel short fibers, It becomes possible to have high output characteristics far exceeding the range.

  Next, an embodiment of the present invention will be described in detail with reference to FIGS. 1 to 2 below. However, the present invention is not limited to this, and may be appropriately modified and implemented without departing from the scope of the present invention. be able to. In addition, FIG. 1 is sectional drawing which shows typically the alkaline storage battery of this invention. FIG. 2 is a graph showing the relationship between the amount of nickel (Ni) added (% by mass) and the assist output DCR (mΩ) at −10 ° C.

1. After mixing hydrogen storage alloy Ln (rare earth element including Y), Mg, Ni, Co, Al or Ln (rare earth element including Y), Mg, Ni, and Al at a predetermined molar ratio, these mixtures are mixed. After putting it into a high frequency induction furnace in an argon gas atmosphere and dissolving it, it was cooled to produce a hydrogen storage alloy ingot. About these hydrogen storage alloys, after measuring melting | fusing point using DSC (differential scanning calorimeter), it heat-processed for 12 hours at the temperature 30 degreeC lower than melting | fusing point of these hydrogen storage alloys. Thereafter, each hydrogen storage alloy was mechanically pulverized in an inert atmosphere to obtain hydrogen storage alloy powders a, b, and c having an average particle size of 25 μm. In this case, a compositional formula represented by Ln _0.9 Mg _0.1 Ni _3.2 Co _0.1 Al _0.2 is a hydrogen storage alloy a, a composition represented by Ln _0.9 Mg _0.1 Ni _3.5 Al _0.2 is a hydrogen storage alloy b, and Ln _0.9 The material represented by Mg _0.1 Ni _3.7 Al _0.1 was designated as hydrogen storage alloy c.

Subsequently, the crystal structures of these hydrogen storage alloy powders a, b, and c were identified by powder X-ray diffraction as follows. That is, using an X-ray diffraction measurement apparatus using a Cu-Kα tube as an X-ray source, the scan speed is 1 ° / min, the tube voltage is 40 kV, the tube current is 300 mA, the scan step is 1 °, and the measurement angle is 20 to 50Θ. X-ray diffraction measurement was performed at / degree. The crystal structure of each hydrogen storage alloy powder a, b was identified from the obtained XRD profile using a JCPDS card chart. The results are shown in the following Table 1. In Table 1, a compositional formula represented by Ln _0.9 Mg _0.1 Ni _3.7 Al _0.1 is a hydrogen storage alloy c, and is represented by MmNi _4.3 Co _0.6 Al _0.3 Mn _0.2. The result of the hydrogen storage alloy d is also shown.

As is clear from the results in Table 1 above, the hydrogen storage alloy a whose composition formula is Ln _0.9 Mg _0.1 Ni _3.2 Co _0.1 Al _0.2 is composed of a Ce ₂ Ni ₇ type crystal phase and a Ce ₅ Co ₁₉ type crystal phase. The hydrogen storage alloy b represented by Ln _0.9 Mg _0.1 Ni _3.5 Al _0.2 is composed of a Ce ₂ Ni ₇ type crystal phase, a Ce ₅ Co ₁₉ type crystal phase, and a Pr ₅ Co ₁₉ type crystal phase, and Ln _0.9 Mg It can be seen that the hydrogen storage alloy c represented by _0.1 Ni _3.7 Al _0.1 is composed of a Ce ₅ Co ₁₉ type crystal phase and a Pr ₅ Co ₁₉ type crystal phase. On the other hand, it can be seen that the hydrogen storage alloy d represented by Ln _0.9 Mg _0.1 Ni _3.7 Al _0.1 is composed of only a LaNi ₅ type crystal phase.
That is, the hydrogen storage alloy alloys a, b, and c made of rare earth element, nickel, and magnesium are at least one crystal from the Ce ₂ Ni ₇ type crystal phase, the Ce ₅ Co ₁₉ type crystal phase, and the Pr ₅ Co ₁₉ type crystal phase. It can be seen that it is composed of phases.

2. Hydrogen storage alloy electrode Water-soluble binder in which CMC (carboxymethylcellulose) is dissolved in water (or pure water) has an apparent density of 0.8 g / cm ³ or more and 1.5 g / cm ³ or less and a major axis of 10 μm. As described above, after adding a predetermined amount of nickel flakes or nickel short fibers having a minor axis of 5 μm or less, the above-described hydrogen storage alloy powder was mixed and kneaded. Subsequently, SBR (styrene butadiene latex) as a water-insoluble binder and water (or pure water) are added and mixed to adjust the viscosity so that the slurry density becomes 3.0 g / cm ^3, and then the hydrogen storage alloy. A slurry was prepared. In this case, CMC (carboxymethylcellulose) is adjusted to 0.1 mass% with respect to the mass of the hydrogen storage alloy powder, and SBR (styrene butadiene latex) is adjusted to 1.0 mass% with respect to the mass of the hydrogen storage alloy powder. did. Here, the apparent density of the nickel flakes or the nickel short fibers is a value that becomes the maximum and minimum when measured ten times by the method of JIS Z 2504. The major axis and minor axis of nickel flakes or nickel short fibers are values measured by SEM observation.

Thereafter, a negative electrode core made of a Ni-plated mild steel porous substrate (punching metal) is prepared, and a hydrogen storage alloy slurry is applied to the negative electrode core so that the filling density is 5.0 g / cm ^3. After wearing and drying, it was rolled to a predetermined thickness. Then, it cut | disconnected so that it might become a predetermined dimension, and produced the hydrogen storage alloy electrode 11 (a1-a6, b1, b2, c1, c2, d1, d2), respectively.

Here, a hydrogen storage alloy electrode using a hydrogen storage alloy a with no addition of nickel flakes or short nickel fibers, an electrode capacity X (Ah) of 10.8 Ah, and an electrode surface area Y (cm ² ) of 760 cm ² a1. Also, using hydrogen storage alloy a, the addition amount of nickel flakes or short nickel fibers is 0.5 mass%, the electrode capacity X (Ah) is 10.8 Ah, and the electrode surface area Y (cm ² ) is 760 cm ² Was used as a hydrogen storage alloy electrode a2. Also, using hydrogen storage alloy a, the amount of nickel flakes or nickel short fibers added is 1.0 mass%, the electrode capacity X (Ah) is 10.8 Ah, and the electrode surface area Y (cm ² ) is 760 cm ² Was used as a hydrogen storage alloy electrode a3. Also, using hydrogen storage alloy a, the amount of nickel flakes or short nickel fibers added is 2.0 mass%, the electrode capacity X (Ah) is 10.8 Ah, and the electrode surface area Y (cm ² ) is 760 cm ² Was used as a hydrogen storage alloy electrode a4.

Further, a hydrogen storage alloy electrode a5 using a hydrogen storage alloy a, having no nickel flakes or short nickel fibers, an electrode capacity X (Ah) of 5.8 Ah, and an electrode surface area Y (cm ² ) of 230 cm ^2. And hydrogen storage alloy a, the addition amount of nickel flakes or short nickel fibers is 0.5 mass%, the electrode capacity X (Ah) is 5.8 Ah, and the electrode surface area Y (cm ² ) is 230 cm ² Was a hydrogen storage alloy electrode a6.

Also, a hydrogen storage alloy electrode b1 using a hydrogen storage alloy b, having no nickel flakes or short nickel fibers, an electrode capacity X (Ah) of 10.8 Ah, and an electrode surface area Y (cm ² ) of 760 cm ^2. The hydrogen storage alloy b is used, the amount of nickel flakes or short nickel fibers added is 0.5 mass%, the electrode capacity X (Ah) is 10.8 Ah, and the electrode surface area Y (cm ² ) is 760 cm ² Was used as a hydrogen storage alloy electrode b2.

Further, a hydrogen storage alloy electrode c1 using a hydrogen storage alloy c, having no nickel flakes or nickel short fibers added, an electrode capacity X (Ah) of 10.8 Ah, and an electrode surface area Y (cm ² ) of 760 cm ^2. A hydrogen storage alloy c, an addition amount of nickel flakes or short nickel fibers of 0.5 mass%, an electrode capacity X (Ah) of 10.8 Ah, and an electrode surface area Y (cm ² ) of 760 cm ² Was used as a hydrogen storage alloy electrode c2.

Further, a hydrogen storage alloy electrode d1 using a hydrogen storage alloy d, having no nickel flakes or short nickel fibers, an electrode capacity X (Ah) of 10.8 Ah, and an electrode surface area Y (cm ² ) of 760 cm ^2. A hydrogen storage alloy d, nickel flakes or short nickel fibers added in an amount of 0.5 mass%, an electrode capacity X (Ah) of 10.8 Ah, and an electrode surface area Y (cm ² ) of 760 cm ² Was used as a hydrogen storage alloy electrode d2.
The contents of these hydrogen storage alloy electrodes a1 to a6, b1, b2, c1, c2, d1, and d2 are shown in Table 2 below.

3. Nickel electrode A porous nickel sintered substrate having a porosity of about 85% is immersed in a mixed aqueous solution of nickel nitrate and cobalt nitrate having a specific gravity of 1.75, and nickel salt and cobalt are placed in the pores of the porous nickel sintered substrate. Salt was retained. Thereafter, the porous nickel sintered substrate was immersed in a 25% by mass sodium hydroxide (NaOH) aqueous solution to convert the nickel salt and the cobalt salt into nickel hydroxide and cobalt hydroxide, respectively.

Next, after sufficiently washing with water to remove the alkaline solution, drying was performed, and the active material mainly composed of nickel hydroxide was filled into the pores of the porous nickel sintered substrate. Such an active material filling operation is repeated a predetermined number of times (for example, 6 times) so that the filling density of the active material mainly composed of nickel hydroxide in the pores of the porous sintered substrate becomes 2.5 g / cm ^3. Filled. Then, after making it dry at room temperature, it cut | disconnected to the predetermined dimension and the nickel electrode 12 was produced.

4). Nickel-hydrogen storage battery Thereafter, the hydrogen storage alloy electrode 11 and the nickel electrode 12 produced as described above are used, and a separator 13 made of a polypropylene nonwoven fabric is interposed between them to be spirally wound. The electrode group was produced. The core exposed portion 11c of the hydrogen storage alloy electrode 11 is exposed at the lower part of the spiral electrode group thus produced, and the core exposed part 12c of the nickel electrode 12 is exposed at the upper portion thereof. ing. Next, the negative electrode current collector 14 is welded to the core exposed portion 11c exposed at the lower end surface of the obtained spiral electrode group, and the core exposed portion 12c of the nickel electrode 12 exposed at the upper end surface of the spiral electrode group. A positive electrode current collector 15 was welded onto the electrode body to obtain an electrode body.

  Next, after the obtained electrode body was accommodated in a bottomed cylindrical outer can in which nickel was plated on iron (the outer surface of the bottom surface becomes a negative external terminal) 17, the negative electrode current collector 14 was attached to the outer can 17. Welded to the inner bottom. On the other hand, the current collecting lead portion 15a extending from the positive electrode current collector 15 serves as a positive electrode terminal and is welded to the bottom portion of the sealing body 18 having the insulating gasket 19 attached to the outer peripheral portion. The sealing body 18 is provided with a positive electrode cap 18a, and a pressure valve (not shown) composed of a valve body 18b and a spring 18c, which are deformed when a predetermined pressure is reached, is disposed in the positive electrode cap 18a.

  Next, after forming an annular groove portion 17 a on the upper outer peripheral portion of the outer can 17, an electrolytic solution was injected, and the outer peripheral portion of the sealing body 18 was mounted on the annular groove portion 17 a formed on the upper portion of the outer can 17. An insulating gasket 19 is placed. Thereafter, the nickel-hydrogen storage battery 10 (A1 to A6, B1, B2, C1, C2, D1, D2) is manufactured by caulking the opening edge 17b of the outer can 17. In this case, an alkaline electrolyte composed of a 30% by mass potassium hydroxide (KOH) aqueous solution was poured into the outer can 17 so as to be 2.5 g (2.5 g / Ah) per battery capacity (Ah).

  Here, a battery using the hydrogen storage alloy electrode a1 is referred to as a battery A1, a battery using the hydrogen storage alloy electrode a2 is referred to as a battery A2, a battery using the hydrogen storage alloy electrode a3 is referred to as a battery A3, and a hydrogen storage alloy electrode a4. A battery using A was used as battery A4, a battery using hydrogen storage alloy electrode a5 was used as battery A5, and a battery using hydrogen storage alloy electrode a6 was used as battery A6. The battery using the hydrogen storage alloy electrode b1 is referred to as a battery B1, and the battery using the hydrogen storage alloy electrode b2 is referred to as a battery B2. The battery using the hydrogen storage alloy electrode c1 was designated as battery C1, and the battery using the hydrogen storage alloy electrode c2 was designated as battery C2. Further, a battery using the hydrogen storage alloy electrode d1 was designated as a battery D1, and a battery using the hydrogen storage alloy electrode d2 was designated as a battery D2.

5. Measurement of output characteristics The output characteristics were then measured as follows. In this case, using the battery 10 (A1 to A6, B1, B2, C1, C2, D1, D2) manufactured as described above, first, the SOC is charged at a charging current of 1 It in a temperature atmosphere of 25 ° C. The battery was charged to 120% of (State Of Charge: depth of charge) and rested for 1 hour. Next, after standing (aging) for 24 hours in a temperature atmosphere at 70 ° C., the battery was discharged in a temperature atmosphere of 45 ° C. with a discharge current of 1 It until the battery voltage became 0.3V. Then, the battery A1 to A6, B1, B2, C1, C2, D1, and D2 were activated by repeating such a cycle of charging → pause → ripening → discharging for two cycles.

  Here, since the contribution of the hydrogen storage alloy in the battery to the discharge performance increases as the temperature decreases, the discharge characteristics (output characteristics) were evaluated at a low temperature as follows. That is, (1) after charging to 50% of SOC (State Of Charge) in a temperature atmosphere of 25 ° C. with a charging current of 1 It, and (2) resting for 1 hour. Next, (3) after charging for 20 seconds at an arbitrary charging rate in a temperature atmosphere of −10 ° C., (4) resting for 30 minutes. Subsequently, (5) discharge was performed at an arbitrary discharge rate for 10 seconds in a temperature atmosphere of −10 ° C. (6) Then, it was made to rest for 30 minutes in the temperature atmosphere of 25 degreeC.

  In this case, at the charge rate of (3), the charge current is increased in the order of 0.8 It → 1.7 It → 2.5 It → 3.3 It → 4.2 It, and at the discharge rate of (5), 1 The above processes (3) to (6) were repeated such that the discharge current was increased in the order of .7 It → 3.3 It → 5.0 It → 6.7 It → 8.3 It. And the battery voltage of each battery A1-A6, B1, B2, C1, C2, D1, D2 when 10 seconds passed at each discharge rate (charge rate) was measured. Then, each discharge rate (charge rate) is plotted on the horizontal axis (x-axis), and the obtained voltage (V) is plotted on the vertical axis (y-axis) to obtain the VI characteristic, and the obtained V− When the I characteristic was linearly regressed by the method of least squares and the slope was determined as the assist output DCR (mΩ) at −10 ° C., the results shown in Table 3 below were obtained.

In the calculated assist output DCR (mΩ) at −10 ° C., a decrease in the assist output DCR (mΩ) indicates an improvement in discharge characteristics (output characteristics), and an increase in the assist output DCR (mΩ) indicates discharge characteristics ( The output characteristics will be degraded.

As is apparent from the results in Table 3, the ratio (Y / X) of the surface area Y (cm ² ) to the electrode capacity X (Ah) of the hydrogen storage alloy electrode is 40 (cm ² / Ah). Even when the battery A5 provided with the hydrogen storage alloy electrode a5 and the battery A6 provided with the hydrogen storage alloy electrode a6 were compared, there was little difference in the assist output DCR (mΩ) at −10 ° C. Or it turns out that the reduction effect of assist output DCR (m (ohm)) at -10 degreeC by addition of a nickel short fiber is not recognized.

On the other hand, in the batteries A1 to A4 including the hydrogen storage alloy electrodes a1 to a4 using the hydrogen storage alloy a and having Y / X of 70 (cm ² / Ah), nickel flakes or nickel shorts are used. The fiber added (batteries A2 to A4 equipped with hydrogen storage alloy electrodes a2 to a4) has reduced assist output DCR (mΩ) at −10 ° C., that is, discharge characteristics at low temperature (output characteristics) ) Is improved.
From this, the ratio (Y / X) of the surface area Y (cm ² ) to the electrode capacity X (Ah) of the hydrogen storage alloy electrode is 70 (cm ² / Ah) or more, that is, an area far exceeding the conventional range. It can be said that it is desirable to use a hydrogen storage alloy electrode having

Even when comparing the battery D1 provided with the hydrogen storage alloy electrode d1 using the hydrogen storage alloy d composed only of the LaNi ₅ type crystal phase with the battery D2 provided with the hydrogen storage alloy electrode d2, whichever It can be seen that there is little difference in the assist output DCR (mΩ) at −10 ° C., and the effect of reducing the assist output DCR (mΩ) at −10 ° C. due to the addition of nickel flakes or short nickel fibers is not recognized.

In contrast, a battery A1 including a hydrogen storage alloy electrode a1 using a hydrogen storage alloy a composed of a Ce ₂ Ni ₇ type crystal phase and a Ce ₅ Co ₁₉ type crystal phase, and a hydrogen storage alloy electrode a2 When comparing batteries A2 to A4 with a4, the addition of nickel flakes or nickel short fibers reduces the assist output DCR (mΩ) at −10 ° C., that is, discharge characteristics at low temperatures ( It can be seen that the output characteristics are improved.

A battery B1 including a hydrogen storage alloy electrode b1 using a hydrogen storage alloy b composed of a Ce ₂ Ni ₇ type crystal phase, a Ce ₅ Co ₁₉ type crystal phase, and a Pr ₅ Co ₁₉ type crystal phase; When compared with the battery B2 having the hydrogen storage alloy electrode b2, the assist output DCR (mΩ) at −10 ° C. decreases when nickel flakes or nickel short fibers are added, that is, discharge at a low temperature. It can be seen that the characteristics (output characteristics) are improved.

Furthermore, the battery C1 provided with the hydrogen storage alloy electrode c1 using the hydrogen storage alloy c composed of the Ce ₅ Co ₁₉ type crystal phase and the Pr ₅ Co ₁₉ type crystal phase, and the hydrogen storage alloy electrode c2 were provided. When compared with the battery C2, the addition of nickel flakes or short nickel fibers reduces the assist output DCR (mΩ) at −10 ° C., that is, improves the discharge characteristics (output characteristics) at low temperatures. I understand that.

This has an area far exceeding the conventional range in which the ratio (Y / X) of the surface area Y (cm ² ) to the electrode capacity X (Ah) of the hydrogen storage alloy electrode is 70 (cm ² / Ah) or more. By using a hydrogen storage alloy electrode with a rare earth element, nickel, magnesium or aluminum as a main constituent element, the activity of the alloy surface is improved, that is, the reaction resistance is increased at a low temperature by a catalytic action. It is thought that it was possible to achieve a higher output in the low temperature region because of the suppression.
Therefore, the mother crystal phase of the rare earth element-nickel-magnesium-based hydrogen storage alloy is composed of at least two crystal phases, and is a Ce ₂ Ni ₇ type crystal phase, Ce ₅ Co ₁₉ type crystal phase, Pr ₅ It can be said that it is desirable to consist of at least one phase of a Co ₁₉ type crystal phase.

Here, in the batteries A1 to A4 provided with hydrogen storage alloy electrodes (a1 to a4) using the hydrogen storage alloy a and having Y / X of 70 (cm ² / Ah), nickel (Ni ) On the horizontal axis (x-axis) and assist output DCR (mΩ) at −10 ° C. on the vertical axis (y-axis), the graph is as shown in FIG. Results were obtained.

  As is apparent from the results of Table 3 and FIG. 2, the assist output DCR (mΩ) at −10 ° C. decreases as the addition amount (mass%) of nickel flakes or nickel short fibers increases. That is, it can be seen that the discharge characteristics (output characteristics) at low temperatures are improved. In this case, as is apparent from the results of FIG. 2, when the addition amount (mass%) of nickel flakes or short nickel fibers is 0.5 mass% or more, the effect of reducing the assist output DCR (mΩ) is saturated. In addition, it can be said that the nickel flakes or the nickel short fibers are desirably 0.5% by mass or more based on the mass of the hydrogen storage alloy.

6). Next, the apparent density of nickel fibers made of nickel flakes or short nickel fibers added to the hydrogen storage alloy slurry was examined. Therefore, in the same manner as described above, the water-soluble binder in which CMC (carboxymethylcellulose) is dissolved in water (or pure water) has an apparent density of 0.5 g / cm ³ or more and 0.7 g / cm ³ or less. After adding 2.0 mass% of nickel flakes or nickel short fibers having a major axis and a minor axis of 5 to 10 μm to the mass of the hydrogen storage alloy, the hydrogen storage alloy powder a was added and mixed and kneaded. Subsequently, SBR (styrene butadiene latex) as a water-insoluble binder and water (or pure water) are added and mixed to adjust the viscosity so that the slurry density becomes 3.0 g / cm ^3, and then the hydrogen storage alloy. A slurry was prepared.

Using the obtained hydrogen storage alloy slurry, a hydrogen storage alloy electrode a7 was prepared in the same manner as described above, and using this hydrogen storage alloy electrode a7, a nickel-hydrogen storage battery A7 was prepared in the same manner as described above. Subsequently, when the obtained nickel-hydrogen storage battery A7 was used as the assist output DCR (mΩ) at −10 ° C. in the same manner as described above, the results shown in Table 4 below were obtained. Table 4 below also shows the results of the above-described nickel-hydrogen storage battery A4.

As is clear from the results in Table 4 above, when nickel flakes or short nickel fibers having an apparent nickel density of 0.5 g / cm ³ or more and 0.7 g / cm ³ or less are used as in battery A7. It can be seen that the assist output DCR (mΩ) at −10 ° C. is significantly increased as compared with the battery A4, and the discharge characteristics (output characteristics) are greatly deteriorated. This is because when the apparent density of nickel is 0.5 g / cm ³ or more and 0.7 g / cm ³ or less, nickel flakes or nickel short fibers are not supported or contacted on the surface of the hydrogen storage alloy. In addition to not having a catalytic action, it is surmised that nickel flakes or short nickel fibers have contact resistance, resulting in a decrease in discharge characteristics (output characteristics).
From this, it can be said that it is desirable to use nickel flakes or nickel short fibers whose apparent density is 0.8 g / cm ³ or more and 1.5 g / cm ³ or less.

  In the above-described embodiment, an example in which the present invention is applied to a cylindrical nickel-hydrogen storage battery has been described. However, the present invention is not limited to a cylindrical nickel-hydrogen storage battery, and nickel-cadmium having various shapes and structures. Applicable to storage batteries.

It is sectional drawing which shows the alkaline storage battery of this invention typically. It is a graph which shows the relationship between the addition amount (mass%) of nickel (Ni) and assist output DCR (mΩ) at −10 ° C.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Hydrogen storage alloy electrode, 11c ... Core body exposed part, 12 ... Nickel electrode, 12c ... Core body exposed part, 13 ... Separator, 14 ... Negative electrode collector, 15 ... Positive electrode collector, 15a ... Current collector lead, DESCRIPTION OF SYMBOLS 17 ... Exterior can, 17a ... Annular groove part, 17b ... Opening edge, 18 ... Sealing body, 18a ... Positive electrode cap, 18b ... Valve plate, 18c ... Spring, 19 ... Insulation gasket

Claims (4)

A hydrogen storage alloy electrode using a hydrogen storage alloy as a negative electrode active material,
The ratio Y / X (cm ² / Ah) of the surface area Y (cm ² ) to the electrode capacity X (Ah) of the hydrogen storage alloy electrode is 70 cm ² / Ah or more (Y / X ≧ 70 cm ² / Ah),
The hydrogen storage alloy includes at least a rare earth element, nickel, magnesium, and aluminum, and a mother crystal phase of the hydrogen storage alloy is at least ₂ from a Ce ₂ Ni ₇ crystal phase, a Ce ₅ Co ₁₉ crystal phase, and a Pr ₅ Co ₁₉ crystal phase. Consisting of a crystalline phase containing at least two,
A hydrogen storage alloy electrode, characterized in that the addition amount of nickel flakes or nickel short fibers is 0.5 mass% or more with respect to the mass of the hydrogen storage alloy. The nickel flakes or nickel short fibers have an apparent density of 0.8 g / cm. ^Three And 1.5 g / cm ^Three The hydrogen storage alloy electrode according to claim 1, wherein: A method for producing a hydrogen storage alloy electrode according to any one of claims 1 to 2,
  At the time of slurry preparation, a hydrogen storage alloy powder mixing step by mixing a hydrogen storage alloy powder in a solution in which nickel flakes or nickel short fibers are mixed in a water-soluble binder,
  A water-insoluble binder mixing step of mixing a water-insoluble binder into the solution in which the hydrogen storage alloy powder is mixed;
  And a viscosity adjusting step for adjusting the viscosity of the solution mixed with the water-insoluble binder. A method for producing a hydrogen storage alloy electrode, comprising: An alkaline storage battery comprising: the hydrogen storage alloy electrode according to claim 1, a positive electrode, a separator, and an alkaline electrolyte in an outer can.

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