JP2008084649A - Hydrogen storage alloy for alkaline storage battery, alkaline storage battery and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrogen storage alloy for an alkaline storage battery capable of having a high output characteristic well over a conventional range; an alkaline storage battery having a negative electrode containing the hydrogen storage alloy as a negative electrode active material; and its manufacturing method. <P>SOLUTION: This hydrogen storage alloy for an alkaline storage battery has a mixed phase comprising at least a Ce<SB>2</SB>Ni<SB>7</SB>type structure and a Ce<SB>5</SB>Co<SB>19</SB>type structure. The Ce<SB>5</SB>Co<SB>19</SB>type structure has a trigonal crystalline structure 3R where AB<SB>2</SB>type structures and AB<SB>5</SB>type structures are stacked on one another by using three layers as a cycle, and a discharge characteristic can be improved by a selective catalyst action of a Ni-rich part of the Ce<SB>5</SB>Co<SB>19</SB>type structure. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an alkaline storage battery including a hydrogen storage alloy negative electrode suitable for applications requiring a large current discharge, such as a hybrid vehicle (HEV: Hybrid Electric Vehicle) and an electric vehicle (PEV: Pure Electric Vehicle), and a manufacturing method thereof.

In recent years, alkaline storage batteries, particularly nickel-hydrogen storage batteries, have come to be used as power sources for devices that require high output, such as hybrid vehicles (HEV) and electric vehicles (PEV). Generally, a hydrogen storage alloy used for the negative electrode of a nickel-hydrogen storage battery is obtained by substituting a part of an AB ₅ type rare earth hydrogen storage alloy such as LaNi ₅ with an element such as Al or Mn. Since these AB ₅ type rare earth hydrogen storage alloys contain Al, Mn, etc. having a low melting point, it is known that segregation phases such as Al-rich phases and Mn-rich phases are likely to be generated at the grain boundaries and surfaces. It has been.

  And when the produced segregation phase repeats charging and discharging cycles, a large internal stress is generated due to expansion and contraction of the crystal lattice of the hydrogen storage alloy. Due to this large internal stress, the hydrogen storage alloy was pulverized or the hydrogen storage alloy was corroded due to elution of Al, Mn, etc., and there was a problem in corrosion resistance. Therefore, various methods for heat-treating such a hydrogen storage alloy to form a single phase without causing a segregation phase will be studied in, for example, Patent Document 1 (Japanese Patent Laid-Open No. 62-31947). Became.

  However, the method proposed in Patent Document 1 has the following drawbacks. That is, when the hydrogen storage alloy is converted into a single phase by heat treatment, there is no segregation interface, so that there is a problem that the contact area with the alkaline electrolyte is reduced and the initial activation performance is lowered. For this reason, there arises a problem that satisfactory charge / discharge characteristics and cycle life characteristics cannot be obtained for applications of hybrid vehicles (HEV) and electric vehicles (PEV) that require high output far exceeding the conventional range. It was.

Usually, a general hydrogen storage alloy has the AB ₅ type structure or the AB ₂ type structure as described above, but takes various crystal structures by combining the AB ₂ type structure unit and the AB ₅ type structure unit. It is known. Among these, a hydrogen storage alloy having a Ce ₂ Ni ₇ type structure in which an AB ₂ type structure and an AB ₅ type structure overlap each other with a period of two layers is disclosed in, for example, Patent Document 2 (Japanese Patent Laid-Open No. 2002-164045). It came to be considered. This Ce ₂ Ni ₇ type hydrogen storage alloy has a hexagonal crystal structure (2H) and can improve the cycle life characteristics of hydrogen storage / release.
Japanese Patent Laid-Open No. 62-31947 JP 2002-164045 A

However, the Ce ₂ Ni ₇ type hydrogen storage alloy proposed in Patent Document 2 and the like described above has insufficient discharge characteristics (assist output) and is satisfactory for high output applications far exceeding the conventional range. There was a problem of not having performance.
Accordingly, the present invention has been made to solve the above-described problems, and obtained a hydrogen storage alloy for an alkaline storage battery capable of having high output characteristics far exceeding the conventional range. An object of the present invention is to provide an alkaline storage battery having a negative electrode using an alloy as a negative electrode active material and having improved discharge characteristics, and a method for producing the same.

In order to achieve the above object, the hydrogen storage alloy for alkaline storage battery used as the negative electrode active material of the alkaline storage battery of the present invention has a mixed phase consisting of at least a Ce ₂ Ni ₇ type structure and a Ce ₅ Co ₁₉ type structure. And Here, the hydrogen storage alloy of Ce ₅ Co ₁₉ type structure has a trigonal crystal structure (3R) in which an AB ₂ type structure and an AB ₅ type structure are stacked with a period of three layers, and Ce ₂ Ni Compared with the _7- type structure, the a-axis and c-axis of the unit cell are short, the crystal lattice volume is small, and a Ni-rich structure can be achieved.

For this reason, a hydrogen storage alloy having a mixed phase composed of a Ce ₂ Ni ₇ type structure and a Ce ₅ Co ₁₉ type structure greatly improves discharge performance by the selective catalytic action of the Ni-rich portion in the Ce ₅ Co ₁₉ type structure. It becomes possible. Thus, an alkaline storage battery having improved discharge characteristics (assist output) can be obtained by using a hydrogen storage alloy having a mixed phase composed of a Ce ₂ Ni ₇ type structure and a Ce ₅ Co ₁₉ type structure for the negative electrode of the alkaline storage battery. It becomes possible.

In this case, the component ratio of the Ce ₂ Ni ₇ type structure and X (%), if the composition ratio of Ce ₅ Co ₁₉ type structure was _{Y (%), Ce 5 Co} 19 type structure ratio of the structure Y (%) The composition ratio X / Y of the composition ratio X (%) of the Ce ₂ Ni ₇ type structure with respect to is preferably 15 or less. This is because it became clear that the discharge output is improved when X / Y is 15 or less (X / Y ≦ 15). Further, in the hydrogen storage alloy produced with the above composition, when the constituent ratio of the LaNi ₅ type structure is Z (%), Z is preferably 15% or less (Z ≦ 15%). This is because, when the composition ratio of the LaNi ₅ type structure is more than 15%, elution oxidation of Al or the like occurs from the segregation phase of the LaNi ₅ type structure, and the corrosion of the hydrogen storage alloy increases and the corrosion resistance decreases. Because.

In producing the hydrogen storage alloy, the general formula is (R _1- αNdα) _1- βMgβNiε _- γ _- δAlγMδ (where R is an element selected from rare earth elements other than Nd and Group 4 elements, M is Ni, Al A hydrogen-absorbing alloy expressed as a group selected from Group 5 to Group 13 elements) except for a melting point temperature Tm (° C.) of the hydrogen-absorbing alloy that is 30 to 60 ° C. lower than Ta (Tm−60 ≦ Ta ≦ Tm It is desirable to have a heat treatment step for heat treatment at −30) ° C.
This is because when the hydrogen storage alloy is heat-treated at a temperature lower than the melting point temperature Tm-60 ° C., a segregation phase due to non-uniform dispersion of Al or Mg is generated, and the homogenization of the structure is hindered, resulting in a decrease in corrosion resistance. Because it becomes. On the other hand, when heat treatment is performed at a temperature higher than the melting point temperature Tm-30 ° C., Mg has a low boiling point, so Mg fume is generated, which causes a problem in safety during alloy production.
For this reason, it is desirable to perform heat treatment at a temperature Ta (Tm-60 ≦ Ta ≦ Tm-30) ° C. that is 30 to 60 ° C. lower than the melting point temperature Tm of the hydrogen storage alloy.

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 -10 ° C. assist output (A) and the composition ratio X / Y between the Ce ₂ Ni ₇ type structure ratio X (%) and the Ce ₅ Co ₁₉ type structure ratio Y (%). .

1. Hydrogen storage alloy Ni, Nd, Al, Mg, Co, Mn, La, Ce, Pr and the like are mixed at a predetermined molar ratio as shown in Table 1 below, and then the mixture is mixed with an argon gas atmosphere. The high-frequency induction furnace was charged and dissolved, and then cooled to produce a hydrogen storage alloy ingot. Next, heat treatment was performed for a predetermined time (in this case, 12 hours) at a temperature (Ta = Tm-30 ° C.) 30 ° C. lower than the melting point (Tm) of the obtained hydrogen storage alloy. Thereafter, these hydrogen storage alloy ingots were roughly pulverized and then mechanically pulverized in an inert gas atmosphere until the average particle size became 25 μm to prepare hydrogen storage alloy powders a to m.

In this case, a compositional formula represented by La _0.8 Ce _0.1 Pr _0.05 Nd _0.05 Ni _4.0 Al _0.3 Co _0.6 Mn _0.1 is a hydrogen storage alloy a, and (La _0.2 Pr _0.4 Nd _0.4 ) _0.8 Mg _0.2 Ni _3.1 Al _0.2 What was represented was designated as hydrogen storage alloy b. Further, a material represented by Nd _0.9 Mg _0.1 Ni _3.2 Al _0.2 Co _0.1 is a hydrogen storage alloy c, a material represented by Nd _0.9 Mg _0.1 Ni _3.3 Al _0.2 is a hydrogen storage alloy d, and Nd _0.9 Mg _0.1 Ni _3.4 What is represented by Al _0.2 is hydrogen storage alloy e, what is represented by Nd _0.9 Mg _0.1 Ni _3.5 Al _0.2 is hydrogen storage alloy f, and what is represented by Nd _0.9 Mg _0.1 Ni _3.6 Al _0.2 The alloy represented by Nd _0.9 Mg _0.1 Ni _3.7 Al _0.2 was designated as hydrogen storage alloy h. Further, a material represented by (La _0.2 Pr _0.3 Nd _0.5 ) _0.9 Mg _0.1 Ni _3.4 Al _0.2 is a hydrogen storage alloy i, and a material represented by (La _0.2 Pr _0.3 Nd _0.5 ) _0.8 Mg _0.2 Ni _3.3 Al _0.3 A hydrogen storage alloy j, which is represented by (La _0.3 Nd _0.7 ) _0.9 Mg _0.1 Ni _3.6 Al _0.1 is a hydrogen storage alloy k, and is represented by (La _0.3 Nd _0.7 ) _0.9 Mg _0.1 Ni _3.3 Al _0.4 The hydrogen storage alloy 1 was used, and the one expressed by (La _0.3 Nd _0.7 ) _0.7 Mg _0.3 Ni _3.6 Al _0.1 was used as the hydrogen storage alloy m.

  Next, the crystal structure was identified by a powder X-ray diffraction method using an X-ray diffraction measurement apparatus using a Cu-Kα tube as an X-ray source. In this case, X-ray diffraction measurement was performed at a scan speed of 1 ° / min, a tube voltage of 40 kV, a tube current of 300 mA, a scan step of 1 °, and a measurement angle (2θ) of 20 to 50 °. From the obtained XRD profile, the crystal structure of each of the hydrogen storage alloys a to m was identified using a JCPDS card chart. Here, the composition ratio of the crystal structure was calculated by applying the peak intensity value and the strongest intensity value of 42 to 44 ° to the XRD profile.

The composition ratio of each Ce ₂ Ni ₇ type structure of each hydrogen storage alloy a to m is X (%), the composition ratio of the Ce ₅ Co ₁₉ type structure is Y (%), and the composition ratio of the LaNi ₅ type structure And Z (%), and the composition ratio of the Ce ₂ Ni ₇ type structure to the Ce ₅ Co ₁₉ type structure is (X / Y), the results shown in Table 1 below were obtained. In Table 1 below, each hydrogen storage alloy a~m general formula _{(R 1- αNdα) 1- βMgβNiε -} γ - δAlγMδ ( wherein, R is selected from rare earth elements and group IV elements excluding Nd The values of α, β, γ, δ, and ε in the case where the element, M is an element selected from Group 5 to Group 13 elements excluding Ni and Al) are also shown. As will be described later, ε is the B component when (R ₁ -αNdα) ₁ -βMgβNiε _- γ _- δAlγMδ is represented by A component (R, Nd, Mg) and B component (Ni, Al, M). This represents the total amount, and since the A component is 1, it represents the AB ratio.

2. Hydrogen storage alloy negative electrode Thereafter, 0.5 parts by mass of SBR (styrene butadiene latex) as a water-insoluble binder with respect to 100 parts by mass of each obtained hydrogen storage alloy powder (am), and water (or Pure water) was added and kneaded to prepare a hydrogen storage alloy slurry. Next, a negative electrode core made of nickel-plated punching metal was prepared, and a hydrogen storage alloy slurry was applied to the negative electrode core, dried, and then filled at a predetermined thickness of 5.0 g / cm. Rolled to ³ Then, it cut | disconnected so that it might become a predetermined dimension (in this case, a negative electrode surface area (short-axis length x long-axis length x2) is 800 cm < ² >), and produced the hydrogen storage alloy negative electrode 11 (a1-m1), respectively. .

  Here, what used the hydrogen storage alloy a was made into the hydrogen storage alloy negative electrode a1, and what used the hydrogen storage alloy b was made into the hydrogen storage alloy negative electrode b1. Also, a hydrogen storage alloy negative electrode c1 using the hydrogen storage alloy c, a hydrogen storage alloy negative electrode d1 using the hydrogen storage alloy d, and a hydrogen storage alloy negative electrode e1 using the hydrogen storage alloy e, A hydrogen storage alloy negative electrode f1 was prepared using the hydrogen storage alloy f, a hydrogen storage alloy negative electrode g1 using the hydrogen storage alloy g, and a hydrogen storage alloy negative electrode h1 using the hydrogen storage alloy h. Further, a hydrogen storage alloy negative electrode i1 using the hydrogen storage alloy i, a hydrogen storage alloy negative electrode j1 using the hydrogen storage alloy j, a hydrogen storage alloy negative electrode k1 using the hydrogen storage alloy k, The hydrogen storage alloy negative electrode 11 was used as the hydrogen storage alloy negative electrode 11, and the hydrogen storage alloy negative electrode m 1 was used as the hydrogen storage alloy m.

3. Nickel-hydrogen storage battery Next, an example of producing a nickel-hydrogen storage battery using these hydrogen storage alloy negative electrodes 11 (a1 to m1) will be described below. First, 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 positive electrode 12 was produced.

  Thereafter, the hydrogen storage alloy negative electrode 11 and the nickel positive electrode 12 produced as described above are used, and a separator 13 made of a polypropylene non-woven fabric is interposed between them to form a spiral electrode group. Produced. The core exposed portion 11c of the hydrogen storage alloy negative electrode plate 11 is exposed at the lower part of the spiral electrode group thus produced, and the core exposed part 12c of the nickel positive electrode plate 12 is exposed at the upper part. Exposed.

  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 positive electrode 12 exposed at the upper end surface of the spiral electrode group. A positive electrode current collector 15 was welded to the top. Thereafter, a cylindrical positive electrode lead 16 was welded to the upper portion of the positive electrode current collector 15. In this case, the cylindrical positive electrode lead 16 is formed with an opening 16a communicating with the opening 15b at a position corresponding to the central opening 15b for inserting the welding electrode of the positive electrode current collector 15.

  Next, after being accommodated in a bottomed cylindrical outer can made of nickel-plated iron (the outer surface of the bottom surface becomes a negative electrode external terminal) 17, a welding electrode (not shown) is inserted through the opening 16a and the central opening 15b, and hydrogen The negative electrode current collector 14 welded to the storage alloy negative electrode 11 was welded to the inner bottom surface of the outer can 17. Next, an anti-vibration ring 19b was inserted into the upper inner peripheral side of the outer can 17 and grooving was performed on the upper outer peripheral side of the outer can 17 to form an annular groove 17a at the upper end of the anti-vibration ring 19b. Thereafter, an alkaline electrolyte composed of a 30% by mass potassium hydroxide (KOH) aqueous solution was injected into the outer can 17. The amount of alkaline electrolyte injected was 2.5 g (2.5 g / Ah) per battery capacity (Ah).

  Further, the sealing plate 18 a is disposed above the opening of the outer can 17 so that the bottom surface of the sealing plate 18 a contacts the cylindrical portion of the positive electrode lead 16. Here, a positive electrode cap (positive electrode external terminal) 18b is provided on the upper portion of the sealing plate 18a, and a valve body including a valve plate 18c and a spring 18d is provided in the positive electrode cap 18b. A gas vent hole is formed in the center, and a sealing body 18 is formed by the sealing plate 18a and the positive electrode cap 18b. Next, one welding electrode (not shown) is arranged on the upper surface of the positive electrode cap (positive electrode external terminal) 18b, and the other welding electrode (not shown) is arranged on the lower surface of the bottom surface (negative electrode external terminal) of the outer can 17. Arranged.

  Thereafter, while applying a predetermined pressure between the pair of welding electrodes, a predetermined voltage was applied between the welding electrodes in the discharge direction of the battery, and an energization process was performed to flow a predetermined pulse current. By this energization process, the contact portion between the bottom surface of the sealing plate 18a and the peripheral side edge of the positive electrode lead 16 is welded. As described above, by applying a voltage between the welding electrodes while applying a predetermined pressure between the pair of welding electrodes and applying an energization process, the height of the cylindrical positive electrode lead 16 varies. Even if it exists, it becomes possible to form a contact point between the circumferential edge of the cylindrical positive electrode lead 16 and the bottom surface of the sealing plate 18a. Thereby, the welding part excellent in welding strength can be formed now.

  Next, an insulating gasket 19a is fitted on the periphery of the sealing plate 18a of the sealing body 18, and a pressure is applied to the sealing body 18 using a press, so that the lower end of the insulating gasket 19a is provided on the upper outer periphery of the outer can 17. The sealing body 18 is pushed into the outer can 17 until it reaches the position of the annular groove 17a. Then, nickel-hydrogen storage batteries (A to M) were assembled by caulking the opening edge 17b of the outer can 17 inward to seal the battery. The cylindrical positive electrode lead 16 is crushed by the applied pressure at the time of sealing, and the cross-sectional shape becomes an elliptical shape in which a circular shape is crushed.

  Here, a battery using the hydrogen storage alloy negative electrode a1 was designated as battery A, and a battery using the hydrogen storage alloy negative electrode b1 was designated as battery B. A battery using the hydrogen storage alloy negative electrode c1 is referred to as a battery C, a battery using the hydrogen storage alloy negative electrode d1 is referred to as a battery D, a battery using the hydrogen storage alloy negative electrode e1 is referred to as a battery E, and the hydrogen storage alloy negative electrode f1 is used. A battery F was used, a battery G was used using the hydrogen storage alloy negative electrode g1, and a battery H was used using the hydrogen storage alloy negative electrode h1. Further, a battery using the hydrogen storage alloy negative electrode i1 is referred to as a battery I, a battery using the hydrogen storage alloy negative electrode j1 is referred to as a battery J, a battery using the hydrogen storage alloy negative electrode k1 is referred to as a battery K, and the hydrogen storage alloy negative electrode l1 is used. The battery L was used, and the battery M using the hydrogen storage alloy negative electrode m1 was used.

4). Battery Test (1) Output Characteristic Evaluation First, using the batteries A to M manufactured as described above, first, SOC (State Of Charge) at a charging temperature of 1 It in a temperature atmosphere of 25 ° C. The battery was charged to 120% and rested for 1 hour. Next, after being left in a temperature atmosphere of 70 ° C. for 24 hours, a cycle of discharging the battery voltage to 0.3 V with a discharge current of 1 It in a temperature atmosphere of 45 ° C. was repeated two times. Cells A to M were activated.

  After the activation was completed, the battery was charged to 50% of SOC (State Of Charge) with a charging current of 1 It in a temperature atmosphere of 25 ° C., and then rested for 1 hour. Next, the battery was charged for 20 seconds at an arbitrary charging rate in a temperature atmosphere of −10 ° C., and then rested for 30 minutes. Thereafter, the battery was discharged at an arbitrary discharge rate for 10 seconds in a temperature atmosphere of −10 ° C., and then rested in a temperature atmosphere of 25 ° C. for 30 minutes. In such a temperature atmosphere of −10 ° C., charging for 20 seconds at an arbitrary charging rate, pause for 30 minutes, discharging for 10 seconds at an arbitrary discharge rate, and pause for 30 minutes at a temperature atmosphere of 25 ° C. It was.

  In this case, an arbitrary charging rate increases charging current in the order of 0.8 It → 1.7 It → 2.5 It → 3.3 It → 4.2 It, and an arbitrary discharging rate is 1.7 It → 3.3 It. → 5.0 It → 6.7 It → 8.3 It increased the discharge current in the order, and measured the battery voltage (V) of each battery A to M at the time of 10 seconds at each discharge rate for each current. Then, a discharge VI plot approximate curve was obtained. Here, when the current when the battery voltage on the obtained VI plot approximate curve is 0.9 V is obtained as a discharge output (−10 ° C. assist output) as a discharge characteristic index, the results shown in Table 2 below are obtained. It became.

(2) Corrosion resistance evaluation General formula (R1 _- αNdα) _1- βMgβNiε _- γ _- δAlγMδ (where R is an element selected from rare earth elements other than Nd and Group 4 elements, M is Group 5 excluding Ni and Al) The hydrogen storage alloy represented by an element selected from Group 13 elements is composed of an A component (R, Nd, Mg) and a B component (Ni, Al, M). In general, the oxygen concentration is used as a corrosion resistance index. This represents the oxidation amount of the component A. When comparing alloys having different AB ratios (ε), the oxygen concentration is the corrosion resistance index because the formula weights are different. Not suitable as. Therefore, the oxidation ratio of the component A is used as an alloy deactivation rate and is used as an index of corrosion resistance. After evaluating the output characteristics, each battery is disassembled, and a hydrogen storage alloy is collected from each battery. Then, the binder was removed with pure water using an ultrasonic cleaner, and after drying, the oxygen concentration was measured. Next, when the alloy deactivation rate, which is the oxidation ratio of the A component, was calculated from the oxygen concentration and the atomic ratio of the A component, the results shown in Table 2 below were obtained.

As is clear from the results in Table 2 above, the battery A provided with the hydrogen storage alloy a having the main phase of LaNi ₅ in the negative electrode a1 has a large assist power of −10 ° C., but the deactivation rate of the hydrogen storage alloy is large. I understand that. On the other hand, it can be seen that the battery B provided with the hydrogen storage alloy b having the Ce ₂ Ni ₇ structure as the main phase in the negative electrode b1 has a small deactivation rate of the hydrogen storage alloy, but has a small −10 ° C. assist output. That is, it can be seen that the discharge characteristics and the corrosion resistance have a trade-off relationship.
On the other hand, the battery C provided with the hydrogen storage alloy c having a mixed phase composed of a Ce ₂ Ni ₇ type structure and a Ce ₅ Co ₁₉ type structure in the negative electrode c1 has a balance between discharge output and corrosion resistance, and discharge characteristics. It turns out that is excellent. This is considered to be due to the reaction resistance reduction effect due to the Ni-rich portion of the Ce ₅ Co ₁₉ type structure. Therefore, even if the mixed layer composed of the Ce ₂ Ni ₇ type structure and the Ce ₅ Co ₁₉ type structure is laminated irregularly. Good.

Here, using the batteries C to H, −10 ° C. assist for the composition ratio X / Y of the composition ratio X (%) of the Ce ₂ Ni ₇ type structure and the composition ratio Y (%) of the Ce ₅ Co ₁₉ structure. When the relationship with the output (A) was obtained, a result as shown in FIG. 2 was obtained. As is clear from the results of FIG. 2, the composition ratio X / Y between the composition ratio X (%) of the Ce ₂ Ni ₇ type structure and the composition ratio Y (%) of the Ce ₅ Co ₁₉ structure is 15 or less (X / If Y ≦ 15), it can be seen that the −10 ° C. assist output (A), that is, the discharge output is improved.

In addition, considering the results in Tables 1 and 2 above, (R _1- αNdα) _1- βMgβNiε _- γ _- δAlγMδ (where R is an element selected from rare earth elements other than Nd and Group 4 elements, M is In a hydrogen storage alloy expressed as “Group 5 to Group 13 elements excluding Ni, Al, and Co”, the A component is (R ₁₋ αNdα) _1- βMgβ, and the B component is Niε _- γ _- δAlγMδ. The molar ratio (α) is 0.5 or more and 1.0 or less (0.5 ≦ α ≦ 1.0), and the molar ratio (β) of Mg is 0.1 or more and 0.2 or less (0.1 ≦ β ≦ 0.2), the molar ratio (γ) of Al is 0.1 or more and 0.3 or less (0.1 ≦ γ ≦ 0.3), and the molar ratio (ε) of the entire B component, that is, B It can be seen that the / A ratio is preferably 3.5 or more and 3.9 or less (3.5 ≦ ε ≦ 3.9).

5. Examination of the heat treatment temperature of the hydrogen storage alloy Next, the heat treatment temperature of the hydrogen storage alloy was examined as follows. Therefore, an ingot of a hydrogen storage alloy having a composition represented by Nd _0.9 Mg _0.1 Ni _3.6 Al _0.2 was produced by the arc melting method in the same manner as described above. A hydrogen storage alloy ingot having this composition is heat-treated at a temperature (Tm-60 ° C) lower than the melting point (Tm = 1123 ° C) for a predetermined time (in this case, 12 hours), then coarsely pulverized, and an inert gas atmosphere In this, mechanically pulverized until the average particle size became 25 μm to prepare hydrogen storage alloy powder n. Similarly, a hydrogen storage alloy ingot having this composition is heat-treated at a temperature (Tm-90 ° C.) 90 ° C. lower than the melting point (Tm = 1123 ° C.) for a predetermined time (in this case, 12 hours), then coarsely pulverized, A hydrogen storage alloy powder o was prepared by mechanically pulverizing in an active gas atmosphere until the average particle size became 25 μm.

The crystal structures of these hydrogen storage alloys n and o are identified in the same manner as described above, the composition ratio X (%) of each Ce ₂ Ni ₇ type structure of each hydrogen storage alloy n and o, and the Ce ₅ Co ₁₉ type structure. Table 3 below shows the composition ratio Y (%), the composition ratio Z (%) of the LaNi ₅ structure, and the composition ratio (X / Y) of the Ce ₂ Ni ₇ structure to the Ce ₅ Co ₁₉ structure. The results shown were obtained. Table 3 also shows the results of the above-described hydrogen storage alloy g (heat treated at a temperature 30 ° C. lower than the melting point (Tm) (Tm-30 ° C.)).

As is apparent from the results in Table 3 above, the heat treatment temperature is 30 ° C. lower than the melting point (Tm = 1123 ° C.) (Tm−30 ° C.) and 60 ° C. lower than the melting point (Tm = 1123 ° C.) (Tm−60). It can be seen that the composition ratio of LaNi _{5 in} the crystal structure increases as the temperature decreases to 90 ° C. (Tm−90 ° C.) lower than the melting point (Tm = 1123 ° C.).

Next, using these hydrogen storage alloys n, o, the hydrogen storage alloy negative electrodes n1, o1 were prepared in the same manner as described above, and the nickel-hydrogen storage batteries N, O were prepared and activated in the same manner as described above. When a charge / discharge test similar to that described above was performed to obtain a discharge output (−10 ° C. assist output) as a discharge characteristic index, the results shown in Table 4 below were obtained. Also, the batteries N and O after the output characteristic evaluation test were disassembled, and the hydrogen storage alloy was sampled from each of the batteries N and O, and the oxygen concentration was measured. When the alloy deactivation rate, which is the oxidation ratio, was calculated, the results shown in Table 4 below were obtained. Table 4 also shows the results of the above-described battery G (battery using the hydrogen storage alloy g as a negative electrode).

As is apparent from the results of Table 4 above, it can be seen that the discharge characteristics (−10 ° C. assist output) and the corrosion resistance decrease as the heat treatment temperature decreases and the composition ratio of LaNi _{5 in} the crystal structure increases. Therefore, when the structure of the LaNi ₅ type structural phase was observed with EPMA, it became clear that the segregated phase was generally an Al-rich phase. That is, it is considered that the decrease in the discharge characteristics and the corrosion resistance is affected by the accelerated corrosion of the hydrogen storage alloy due to the elution of Al. From this, it can be seen that the composition ratio Z (%) of LaNi _{5 in} the crystal structure is desirably 15% or less.

  On the other hand, when the heat treatment temperature (Ta) is higher than the temperature (Tm-30 ° C.) 30 ° C. lower than the melting point (Tm) (Ta> Tm-30), Mg fume having a low boiling point is generated, Problems such as a decrease in productivity and compositional stability at the time of producing the hydrogen storage alloy occur. From the above, the heat treatment temperature (Ta) of the hydrogen storage alloy is set to a temperature 30 to 60 ° C. lower than the melting point temperature (Tm) of the hydrogen storage alloy ((Tm-60) ≦ Ta ≦ (Tm-30)). It is understood that is desirable.

It is sectional drawing which shows the alkaline storage battery of this invention typically. A graph showing the relationship between the Ce ₂ composition ratio X (%) of Ni ₇ type structure and Ce ₅ composition ratio Y (%) of Co ₁₉ type structure and -10 ° C. assist output to the configuration ratio X / Y of (A) is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Hydrogen storage alloy negative electrode, 11c ... Core body exposed part, 12 ... Nickel positive electrode, 12c ... Core body exposed part, 13 ... Separator, 14 ... Negative electrode collector, 15 ... Positive electrode collector, 16 ... Lead for positive electrode, DESCRIPTION OF SYMBOLS 17 ... Exterior can, 17a ... Annular groove, 17b ... Opening edge, 18 ... Sealing body, 18a ... Sealing plate, 18b ... Positive electrode cap, 18c ... Valve plate, 18d ... Spring, 19a ... Insulating gasket, 19b ... Anti-vibration ring

Claims (5)

A hydrogen storage alloy for alkaline storage batteries used as a negative electrode active material for alkaline storage batteries,
The hydrogen storage alloy for an alkaline storage battery, wherein the hydrogen storage alloy has a mixed phase composed of at least a Ce ₂ Ni ₇ type structure and a Ce ₅ Co ₁₉ type structure. The composition ratio Y (%) of the Ce ₅ Co ₁₉ structure when the composition ratio of the Ce ₂ Ni ₇ structure is X (%) and the composition ratio of the Ce ₅ Co ₁₉ structure is Y (%). _{2. The} hydrogen storage alloy for an alkaline storage battery according to claim 1, wherein the composition ratio X / Y of the composition ratio X (%) of the Ce ₂ Ni ₇ type structure with respect to is 15 or less. The hydrogen storage alloy further comprises a LaNi ₅ type structure, if the component ratio of the LaNi ₅ type structure was the Z (%), Z is characterized by 15% or less (Z ≦ 15%) The hydrogen storage alloy for alkaline storage batteries according to claim 1 or 2.   An outer can comprising a hydrogen storage alloy negative electrode using the hydrogen storage alloy for alkaline storage batteries according to any one of claims 1 to 3 as a negative electrode active material, a positive electrode, a separator separating these two electrodes, and an alkaline electrolyte. An alkaline storage battery characterized in that it is provided inside. A method for producing an alkaline storage battery comprising a hydrogen storage alloy negative electrode using a hydrogen storage alloy as a negative electrode active material, a positive electrode, a separator separating these two electrodes, and an alkaline electrolyte in an outer can,
The general formula is (R _1- αNdα) _1- βMgβNiε _- γ _- δAlγMδ (where R is an element selected from rare earth elements other than Nd and group 4 elements, and M is a group 5 to group 13 elements excluding Ni and Al) A heat treatment in which a hydrogen storage alloy represented by (selected element) is heat-treated at a temperature Ta ((Tm-60) ≦ Ta ≦ (Tm-30)) ° C. 30 to 60 ° C. lower than the melting point temperature Tm of the hydrogen storage alloy A method for producing an alkaline storage battery comprising a step.

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