JP4540045B2 - Hydrogen storage alloy, hydrogen storage electrode and nickel metal hydride storage battery - Google Patents

Description

The present invention relates to a hydrogen storage alloy having a rare earth element and nickel (Ni) as main components and having a crystal structure of CaCu _{5 type} as a main crystal structure, and a nickel metal hydride storage battery including a hydrogen storage electrode to which the hydrogen storage alloy is applied. Is.

  Nickel metal hydride storage battery, a type of alkaline storage battery, has a higher energy density than nickel cadmium storage battery, which is one type of alkaline storage battery, and does not contain harmful cadmium. It is widely used as a power source for portable small electronic devices such as telephones, small electric tools, and small personal computers, and the demand is rapidly increasing with the spread of these small electronic devices. In addition, the use as a power source for small electronic devices has been expanded, and further improvement in discharge capacity has been demanded.

As a hydrogen storage alloy electrode used in a conventional nickel metal hydride storage battery, a hydrogen storage alloy having a CaCu _{5 type} crystal structure mainly composed of a transition metal element such as a rare earth element and nickel is widely used. Although the hydrogen storage alloy electrode using the hydrogen storage alloy is excellent in cycle performance, the discharge capacity is low, and there is a problem that it is difficult to further improve the discharge capacity according to the above demand.

In recent years, AB _{3 type} and AB _{3.5 type} hydrogen storage alloys have been proposed in place of the AB _{5 type} which has been widely used as a high capacity hydrogen storage alloy. (For example, Patent Document 1)

JP, 11-323469, A The hydrogen storage alloy electrode which applied the hydrogen storage alloy of patent documents 1 is inferior in durability, although a discharge capacity is large compared with the above-mentioned conventional hydrogen storage alloy electrode, and this hydrogen storage alloy However, the hydrogen storage alloy electrode using the material had a disadvantage that the cycle performance was inferior.

Further, in the AB ₅ form of hydrogen-absorbing alloy powder, the composition of the hydrogen storage alloy La of 24 to 33 wt%, a high capacity by a composition containing Mg or Ca 0.1 to 1.0 wt% A hydrogen storage alloy having a long life in which pulverization is suppressed even after repeated charge and discharge has been proposed. (For example, see Patent Document 2)
However, if the ratio (atomic ratio) B / A between element B and element A, which is described as being particularly preferable in Patent Document 2, is 5 to 6, the hydrogen storage amount of the hydrogen storage alloy is small. There is a drawback that the effect is insufficient in improving the discharge capacity.

  The present invention has been made in view of the disadvantages of the conventional hydrogen storage alloy and nickel-metal hydride storage battery, and applies a hydrogen storage alloy having a large discharge capacity without reducing the cycle performance of the hydrogen storage alloy electrode. Therefore, a nickel-metal hydride storage battery with improved discharge capacity is provided.

This invention solves the said subject by setting a hydrogen storage alloy and a nickel metal hydride storage battery as the following structures.
Nickel-metal hydride storage battery according to the present invention, the symbol A is a rare earth element, the symbol B is M g, at least one element symbol C is selected Co, Mn, Al, Fe and Cu, Formula AwBxNiyCz W + x = 1, 0.04 ≦ x ≦ 0.09, 3.5 ≦ y ≦ 4.3, 4.0 ≦ y + z ≦ 4.7, 0 < z, 4.75 ≦ (x + y + z) / w ≦ It is a nickel hydride storage battery provided with the hydrogen storage electrode using the hydrogen storage alloy represented by 5.35.
The hydrogen storage electrode of the nickel metal hydride storage battery according to the present invention includes a hydrogen storage alloy powder and cerium (Ce), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb). It is preferable that at least one kind of hydroxide and oxide of rare earth elements selected from lutetium (Ru) and yttrium (Y) are supported on a conductive substrate.

According to the onset bright, large discharge capacity as compared to conventional nickel-metal hydride storage battery, and can cycle performance obtain conventional nickel-metal hydride storage battery equal to or greater than the nickel-metal hydride storage battery.

The hydrogen storage alloy according to the present invention, the symbol A is a rare earth element, the symbol B is M g, at least one element symbol C is selected Co, Mn, Al, Fe and Cu, the formula A _{In w} B _x Ni _y C _z , w + x = 1, 0.04 ≦ x ≦ 0.09, 3.5 ≦ y ≦ 4.3, 4.0 ≦ y + z ≦ 4.7, 0 < z, 4.75 It is a hydrogen storage alloy represented by ≦ (x + y + z) /w≦5.35.

Method for producing a hydrogen-absorbing alloy is not particularly limited, casting, gas atomization, melt spinning method can be applied either in arc melting method, among Mg, Ca of elements constituting the hydrogen storage alloy were dissolved Sometimes, it tends to dissipate by evaporation, and an alloy having a predetermined composition may not be obtained. A casting method, a gas atomizing method, and a melt spinning method are preferable methods for suppressing dissipation due to evaporation of Mg and Ca.

The hydrogen storage alloy according to the present invention mainly has a CaCu _{5 type} crystal structure. Here, primarily that described with CaCu ₅ form of crystals, it was observed to include an investigation CaCu ₅ type crystal in mixed partially PuNi ₃ shapes and Ce ₂ Ni ₇ crystalline form with a powder X-ray diffraction This is because the.

The hydrogen storage alloy according to the present invention has an Mg content ratio (atomic ratio) x of 0.04 to 0.09 in the composition display. When Mg or Ca is present in a system containing a rare earth element, the number of hydrogen storage / release sites of the hydrogen storage alloy increases and the discharge capacity of the hydrogen storage alloy increases. Further, the presence of Mg and Ca has an action of stabilizing the crystal by relaxing the expansion and contraction of the crystal lattice of the hydrogen storage alloy when the hydrogen storage alloy absorbs and releases hydrogen. When the ratio x is less than 0.04, the effect of adding Mg and Ca is not exhibited, and it is difficult to obtain a high capacity. Further, Mg and Ca are easily eluted in an alkaline electrolyte per se, and if Mg and Ca are present in the hydrogen storage alloy, the hydrogen storage alloy is easily corroded (elution). For these reasons, when x exceeds 0.17, a high capacity can be obtained, but the alloy has low durability and poor cycle performance. In addition, if said x is 0.04-0.09, since favorable cycling performance is obtained, it is preferable.

  In the hydrogen storage alloy according to the present invention, the content ratio (atomic ratio) y of Ni in the composition display is 3.5 to 4.3, and preferably 3.7 to 4.1. If the ratio y is less than 3.5, the corrosion resistance of the hydrogen storage alloy to the alkaline electrolyte is low, and it is easy to miniaturize when repeated charge and discharge, and the hydrogen storage capacity decreases with the miniaturization. Inferior. On the other hand, if y exceeds 4.3, the hydrogen storage amount of the hydrogen storage alloy is small and the discharge capacity may be lowered. In addition, it is preferable if the ratio y is 3.7 to 4.1 because good cycle performance can be obtained.

In the hydrogen storage alloy according to the present invention, the content ratio (atomic ratio) z of one or more elements selected from Co, Mn, Al, Fe and Cu satisfies 0 < z, and the content ratio of Ni ( Atomic ratio) The sum y + z of y and z is preferably 4.0 to 4.7, and y + z is preferably 4.45 to 4.7. Among one or more elements selected from Co, Mn, Al, Fe, and Cu, Co suppresses the reduction in capacity due to the miniaturization of the hydrogen storage alloy when the hydrogen storage alloy repeatedly stores and releases hydrogen. There is an effect to. The presence of an appropriate amount of Mn has the effect of reducing the hydrogen equilibrium pressure of the hydrogen storage alloy and improving the hydrogen storage capacity. Al has the effect of improving the chemical stability of the hydrogen storage alloy and increasing the durability. Moreover, cost reduction can be achieved by adding Fe and Cu.
When the ratio y + z is less than 4.0, the corrosion resistance of the hydrogen storage alloy to the alkaline electrolyte is low, so that the durability is inferior and the capacity is low. When y + z exceeds 4.7, the hydrogen storage amount of the hydrogen storage alloy is small and the discharge capacity is reduced. In addition, if this ratio y + z is 4.45 to 4.7, since favorable cycling performance is obtained, it is preferable.

  In the hydrogen storage alloy according to the present invention, the ratio (x + y + z) / w of the sum x + y + z of x, y, and z (x + y + z) / w in the composition display is 4.75 to 5.35, and 4.85 to 5.15. preferable. If the ratio is less than 4.75, the corrosion resistance of the hydrogen storage alloy to the alkaline electrolyte is low, so the durability is poor. On the other hand, when the ratio exceeds 5.35, the hydrogen storage amount of the hydrogen storage alloy is small and the discharge capacity is low. In addition, if this ratio (x + y + z) / w is 4.85-5.15, since favorable cycling performance is obtained, it is preferable.

  The hydrogen storage electrode according to the present invention includes at least one rare earth selected from Ce, Dy, Ho, Er, Tm, Yb, Ru and Y in addition to the powder of the high capacity hydrogen storage alloy according to claim 1. By containing at least one elemental hydroxide and oxide, excellent cycle performance can be achieved by increasing the corrosion resistance of the hydrogen storage alloy while maintaining a high capacity. The ratio of the rare earth element oxide or hydroxide to the hydrogen storage alloy powder is not particularly limited, but is preferably 0.5 to 3% by weight, more preferably 0.5 to 1.5% by weight. If the ratio is less than 0.5% by weight, the effect of adding these compounds is difficult to obtain, and if it exceeds 3% by weight, the conductivity of the hydrogen storage electrode may be reduced and current collection may be hindered.

The details of the present invention will be described below with reference to examples, but the present invention can be applied to all nickel-metal hydride storage batteries including the hydrogen storage alloy having the above-described configuration and a hydrogen storage electrode using the same, and the following implementations It is not limited to the embodiment shown in the example.
(Preparation of hydrogen storage alloy powder)
(Examples 1-9 , Reference Examples 1-12 )
Each metal element was weighed in the atomic ratios shown in Examples 1 to 9 and Reference Examples 1 to 12 in Table 1, dissolved using a high-frequency dissolution method, and then cooled in a water-cooled mold. The obtained alloy (ingot) was heated at 900 ° C. for 3 hours in an argon atmosphere and allowed to cool in the furnace. The obtained ingot was mechanically pulverized under an argon atmosphere to produce a hydrogen storage alloy powder having an average particle size (D50) of 50 μm. The respective hydrogen storage alloy powders are referred to as Examples 1 to 9 and Reference Examples 1 to 12 . In Table 1, Mm represents Misch metal, which is a mixture of rare earth elements composed of La65%, Ce25%, Pr2%, and Nd8% in atomic ratio.
(Comparative Examples 1-4)
Each metal element was weighed at the atomic ratio shown in Comparative Example 1 to Comparative Example 4 in Table 1, and hydrogen storage alloy powders were prepared in the same manner as in Examples 1 to 9 and Reference Examples 1 to 12 below. . The obtained hydrogen storage alloy powders are referred to as Comparative Examples 1 to 4, respectively.

(Investigation by powder X-ray diffraction)
The powder X-ray diffraction measurement of the hydrogen storage alloy powder which concerns on Examples 1-9, Reference Examples 1-12 , and Comparative Examples 1-4 was performed using the copper tube.

(Examples 1-9 , Reference Examples 1-12 )
(Preparation of hydrogen storage electrode for unipolar test 1)
After adding 10 parts by weight of Inco Corporation nickel powder (INCO # 210) to 100 parts by weight of the hydrogen storage alloy powders according to Examples 1 to 9 and Reference Examples 1 to 12 , 0. An aqueous solution dissolved at a concentration of 5% and an aqueous dispersion of styrene butadiene rubber (SBR) as a binder were added and kneaded as a solid content to the hydrogen storage alloy powder to obtain a paste. The paste was applied to both surfaces of a substrate made of a perforated steel plate (nickel plated) having a thickness of 35 μm, an aperture ratio of 60%, and an aperture diameter of 1 mm, and pressed to a predetermined thickness (0.3 mm) after drying. . The hydrogen storage electrodes are referred to as Examples 1 to 9 and Reference Examples 1 to 12 , respectively.
(Comparative Examples 1-4)
Using the hydrogen storage alloy powders according to Comparative Examples 1 to 4, hydrogen storage electrodes were prepared in the same procedure as in Examples 1 to 9 and Reference Examples 1 to 12 . Let this hydrogen storage electrode be Comparative Examples 1-4.

(Hydrogen storage electrode single electrode test)
The hydrogen storage electrodes according to Examples 1 to 9, Reference Examples 1 to 12 , and Comparative Examples 1 to 4 were cut to 30 × 30 mm, and lead pieces were joined to the end portions to form hydrogen storage electrodes for a single electrode test. . An open cell was assembled with one hydrogen storage electrode in the middle and two nickel electrodes on each side. It should be noted that the capacity of the nickel electrode was excessively large relative to the capacity of the hydrogen storage electrode (the capacity of the nickel electrode / the capacity of the hydrogen storage electrode = 3.5). An aqueous solution containing 6.8 M / l KOH and 0.8 M / l LiOH was used as the electrolytic solution. The cell was charged and discharged at an ambient temperature of 20 ° C. After charging 150% of the capacity of the hydrogen storage electrode at 0.1 ItA (40 mA), the battery was discharged at 0.2 ItA (80 mA). The discharge was stopped when the potential of the hydrogen storage electrode relative to the reference electrode (Hg / HgO electrode) became −0.6V. The charge / discharge cycle is repeated, the cycle is repeated, the discharge capacity at the 10th cycle is defined as the discharge capacity of the hydrogen storage electrode, and the discharge capacity (mAh) is divided by the filling amount (g) of the hydrogen storage alloy. (MAh / g) was used as an index for evaluating the discharge capacity.

(Measurement of mass saturation magnetization of hydrogen storage alloy powder)
The hydrogen storage alloy powder was recovered from the negative electrode plate taken out after dismantling the open cell (discharged) after the end of the discharge test, and the mass saturation magnetization of each powder was measured. After precisely weighing 0.3 g of hydrogen storage alloy powder and filling the sample holder, it is obtained by applying a 5 k Oersted magnetic field using a vibrating sample magnetometer (model BHV-30) manufactured by Riken Denshi Co., Ltd. The obtained value was defined as the mass saturation magnetization of the hydrogen storage alloy powder.

(Measurement of specific surface area of hydrogen storage alloy powder)
The hydrogen storage alloy powder was recovered from the negative electrode plate taken out by dismantling the open cell (discharged) after the discharge test was completed, 1.0 g of the hydrogen storage alloy powder was precisely weighed, and the value measured by the BET method was The specific surface area of the hydrogen storage alloy powder was used.

FIG. 1 shows a powder X-ray diffraction diagram of the hydrogen storage alloy powder according to Example 3, Reference Example 4 and Comparative Example 2, and FIG. 2 shows a powder X-ray diffraction diagram of the hydrogen storage alloy powder according to Comparative Example 1.
Table 1 shows the compositions of hydrogen storage alloy powders according to Examples 1 to 9, Reference Examples 1 to 12 , and Comparative Examples 1 to 4, hydrogen storage electrode monopolar test results, mass saturation magnetization measurement results, and specific surface area measurement results. Show.

1A is a powder X-ray diffraction diagram of the hydrogen storage alloy powder according to Reference Example 4 , FIG. 1B is Example 3 and FIG. 1C is a powder X-ray diffraction pattern of the hydrogen storage alloy powder according to Comparative Example 2. is there. While Comparative Example 2 does not contain Mg, the hydrogen storage alloy powders of Example 3 and Reference Example 4 both contain Mg, and Example 3 and Reference Example 4 have different Mg content ratios. However, as shown in FIG. 1, both Example 3 and Reference Example 4 have a CaCu _{5 type} crystal structure as in Comparative Example 2. Although details are omitted , other examples and other reference examples shown in Table 1 also had a crystal structure mainly composed of CaCu _{5 type} .
On the other hand, in the case of Comparative Example 1 in which the Mg content ratio was increased, it was found from the powder X-ray diffraction diagram shown in FIG. 2 that the crystal structure was different from that of the CaCu ₅ form.

Comparative Example 2 is an MmNiCoMnAl-based hydrogen storage alloy powder having a composition that does not contain Mg or Ca, and has been widely used in the past. In contrast, Example 1-9, the hydrogen storage alloy powder as in Reference Example 1 to 12, a hydrogen-absorbing alloy powder having a new composition comprises Mg or Ca, the content ratio (atomic ratio x) is a hydrogen storage alloy powder having 0.04 to 0.17.
As shown in Table 1, the hydrogen storage alloys according to Examples 1 to 9 and Reference Examples 1 to 12 have a discharge capacity (mAh / g) per unit weight of 1.13 to 1.25 times that of Comparative Example 2. . Compared with Comparative Example 2, the discharge capacity of the Example is larger than the presence of Mg and Ca in the hydrogen storage alloy and the content ratio (y + z) of Ni, Co and Al is 4.70 or less. This is because the hydrogen storage capacity of the hydrogen storage alloy was increased by keeping it lower than 5.00 in Example 2. Incidentally, in the case of Comparative Example 1 in which the Mg content ratio is further increased and the value of (y + z) is as low as 3.50 as compared with the Examples, the discharge capacity is as high as 380 mAh / g. Comparative Example 3 with a large (y + z) has a lower discharge capacity than Comparative Example 2. FIG. 3 shows the relationship between the capacity of the hydrogen storage alloy and (y + z). As shown in FIG. 3, it can be seen that the smaller the (y + z), the larger the capacity of the hydrogen storage alloy. Further, Comparative Example 4 in which the ratio of Mg + Ni + Co + Al and La {(x + y + z) / w} is as small as 4.51 is also because the hydrogen storage capacity of the hydrogen storage alloy is small or the discharge capacity is small. became.
According to the test results shown in Table 1, the x was 0.04 to 0.17, y was 3.5 to 4.3, (y + z) was 4.0 to 4.7, and (x + y + z) / w was 4.75 to 5.35. It turns out that Examples 1-9 and Reference Examples 1-12 have a large discharge capacity compared with Comparative Examples 2-4. Although not described in detail, when the Ni content ratio y exceeds 4.3, the discharge capacity is low.

In both the examples and comparative examples, the mass saturation magnetization of the hydrogen storage alloy powder before the hydrogen storage electrode single electrode test was less than 0.1 Am ² / kg, and the specific surface area was less than 0.3 m ² / g. During the hydrogen storage electrode unipolar test, the surface of the hydrogen storage alloy powder is corroded by the electrolyte, and when Ni and Co are isolated, the mass saturation magnetization of the hydrogen storage alloy powder increases. Further, when the surface is etched, the specific surface area of the hydrogen storage alloy powder increases. From this, it can be considered that the smaller the mass saturation magnetization and the specific surface area of the hydrogen storage alloy powder after the test suggests that the corrosion resistance of the hydrogen storage alloy powder to the electrolytic solution is higher. After the test, the mass saturation magnetization of the hydrogen storage alloy powder according to the example is 4.2 Am ² / kg or less and the specific surface area is 1.1 m ² / g or less, whereas Ni or Ni + Co + Mn In the case of Comparative Example 3 where the ratio (y + z) is small (3.80 or less) and Comparative Example 3 where the content ratio of rare earth elements is small {(x + y + z) / w is large as 5.55} Magnetization is as high as 5.7 Am ² / kg and specific surface area is as high as 1.2 m ² / g or more.The corrosion resistance of the hydrogen storage alloys of these comparative examples is (y + z) is 4.0 or more, (x + y + This suggests that z) / w is inferior to that of 5.35 or less.
In addition, as shown in FIG. 1, since the mass saturation magnetization and specific surface area of the hydrogen storage alloys according to Examples 1 to 9, Reference Examples 1 to 12 and Comparative Example 2 are smaller than those of Comparative Example 1, CaCu ₅ It is considered that the hydrogen storage alloy having the crystal structure of the shape has better corrosion resistance than the hydrogen storage alloy having a crystal structure different from the CaCu _{5 type} .
From the results shown in FIG. 1 and Table 1, in order to obtain a hydrogen storage alloy powder having a high capacity and excellent corrosion resistance, x is 0.04 to 0.17, and (y + z) is 4.0 to 4.7. It can be seen that a hydrogen storage alloy having (x + y + z) / w of 4.75 to 5.35 and mainly having a CaCu _{5 type} crystal structure is good.
Although not described in detail, when the Ni content ratio y is less than 3.5, there is a drawback that the corrosion resistance of the hydrogen storage alloy to the electrolyte is poor.

(Evaluation using nickel metal hydride storage battery)
(Examples 1-9 , Reference Examples 1-12 )
(Preparation of positive electrode plate)
A concentration of 0 is added to 80 parts by weight of a nickel electrode active material powder in which a coating layer made of 4% by weight of cobalt oxyhydroxide is formed on the surface of a nickel hydroxide powder containing 3% by weight of zinc and 1% by weight of cobalt in a solid solution state. 20 parts by weight of a 7 wt% carboxymethylcellulose (CMC) aqueous solution was added and kneaded to obtain a paste. The paste was filled in a foam nickel substrate having a surface density of 450 g / m 2 and a thickness of 1.3 mm, dried, and pressed to a predetermined thickness (0.75 mm). The nickel electrode plate was cut into a predetermined size to obtain a positive electrode plate (nickel electrode) having a capacity calculated from the filling amount of the active material of 2450 mAh.

(Preparation of negative electrode plate)
A hydrogen storage electrode produced in the same manner as the electrode plate for the monopolar test of the hydrogen storage electrode except that 1 part by weight of Inco Corporation nickel powder (INCO # 210) was added to and mixed with 100 parts by weight of the hydrogen storage alloy powder. Examples 1 to 10 and Reference Examples 1 to 20 ) were cut into predetermined dimensions to form negative electrode plates (hydrogen storage electrodes). The filling amount of the hydrogen storage alloy powder in the negative electrode plate was a constant amount (8.93 g).
(Production of cylindrical nickel-metal hydride storage battery)
The positive electrode plate and a separator made of a polypropylene nonwoven fabric subjected to a hydrophilic treatment and a negative electrode plate were laminated, and the laminate was wound so that the positive electrode plate was on the inside to form a wound electrode plate group. Insert the electrode plate group into a metal battery case, connect the positive electrode plate and the positive electrode terminal (cap), connect the negative electrode plate and the negative electrode terminal (battery can) respectively, and add 7.8M / l KOH and 0.8M / l LiOH After injecting 2.55 g of the electrolyte solution comprising the aqueous solution, the open end of the battery case can be hermetically sealed by a predetermined method to produce an AA size, cylindrical sealed nickel-metal hydride storage battery. The thus produced cylindrical nickel-metal hydride storage batteries are referred to as Examples 1 to 10 and Reference Examples 1 to 20 .

(Comparative Examples 1-4)
Using a hydrogen storage electrode (Comparative Examples 1 to 5) produced in the same manner as the electrode plate for a single electrode test of the hydrogen storage electrode , the same procedure as in Examples 1 to 10 and Reference Examples 1 to 20 was used. A size and cylindrical sealed nickel-metal hydride storage battery was produced. The produced nickel metal hydride storage batteries are referred to as Comparative Examples 1-5.

(Measurement of chemical conversion and discharge capacity)
The sealed nickel-metal hydride storage batteries according to Examples 1 to 10, Reference Examples 1 to 20, and Comparative Examples 1 to 5 were formed at an ambient temperature of 20 ° C. After first charging at 0.1 ItA (245 mA) for 10 hours, the battery was discharged at 0.2 ItA with a discharge cut voltage of 1.0 V. In the second to tenth cycles, the battery was charged with 0.1 ItA (230 mA) for 15 hours, and then discharged with a discharge cut voltage of 1.0 V at 0.2 ItA. The discharge capacity obtained by the tenth discharge was used as the discharge capacity of the battery.

(Charge / discharge cycle test)
The sealed nickel-metal hydride electricity storage according to Examples 1 to 10, Reference Examples 1 to 20 , and Comparative Examples 1 to 5 was subjected to a charge / discharge cycle test at an ambient temperature of 20 ° C. The battery was charged until a voltage drop of 5 mV was observed at a charge rate of 0.5 ItA (dV = -5 mV), paused for 30 minutes, and then discharged with a discharge cut voltage of 1.0 V at a discharge rate of 0.3 ItA. The charging / discharging was set as one cycle, charging / discharging was repeated, and the cycle life was defined as the time when the discharge capacity was reduced to 60% of the discharge capacity at the first cycle.

Table 2 shows the NP ratio of the sealed nickel-metal hydride storage batteries of Examples 1 to 9, Reference Examples 1 to 12 , and Comparative Examples 1 to 4 (N / P, N represents the capacity of the negative electrode, and P represents the capacity of the positive electrode) The charge / discharge cycle test results are shown. N is a value obtained as a product of the capacity (mAh / g) obtained in the monopolar test and the active material filling amount (8.93 g) of the negative electrode, and P is the capacity of the positive electrode plate (2450 mAh). ).

When the discharge capacity of the negative electrode plate is increased, the NP ratio (N / P) can be increased. When the NP ratio is large, a large charge reserve can be secured in the negative electrode plate, and charge / discharge cycle performance can be improved. When the results shown in Table 1 (mass saturation magnetization of hydrogen storage alloy powder, specific surface area) are compared, the corrosion resistance of the hydrogen storage alloy powders according to Examples 1 to 9 and Reference Examples 1 to 12 is Comparative Example 2. It cannot be said that it is expensive compared to. Nevertheless, as shown in Table 2, the nickel hydride storage batteries according to Examples 1 to 9 and Reference Examples 1 to 12 were able to achieve better cycle performance than Comparative Example 2. Such a result was obtained because the NP ratio (N / P) of Examples 1 to 9 and Reference Examples 1 to 12 was larger than that of Comparative Example 2, and the NP ratio (N / P) was high. The reason is that the capacity per unit weight (mAh / g) of the hydrogen storage alloy powder could be increased as compared with Comparative Example 2. And the high capacity | capacitance of such hydrogen storage alloy powder itself was able to be achieved by making the composition of a hydrogen storage alloy into the novel composition shown in Examples 1-9 of Table 1 and Reference Examples 1-12. .

As shown in Table 2, the nickel-metal hydride storage batteries according to Examples 1 to 9 and Reference Examples 1 to 12 are superior in cycle performance to Comparative Examples 1 and 3 and 4. 4 shows the mass saturation magnetization and cycle life of the hydrogen storage alloy powder after the test shown in Table 2 above, and FIG. 5 shows the relationship between the specific surface area and the cycle life. FIG. 4 shows that the cycle life is better when the mass saturation magnetization is smaller, and FIG. 5 shows that the cycle life is better when the specific surface area is smaller. From this, in the case of the nickel-metal hydride storage battery according to the example, it is considered that the cycle life was improved because the corrosion resistance of the hydrogen storage alloy was improved as compared with Comparative Examples 1, 3 and 4 .

FIG. 6 is a graph showing the relationship between the cycle life of a nickel metal hydride storage battery and (y + z) of the hydrogen storage alloy powder applied thereto. According to FIG. 6, it can be seen that (y + z) is in the range of 4.0 to 4.7, and the cycle life is better when it is closer to 4.7.
According to the results shown in Table 2, if x is 0.04 to 0.09, y is 3.7 to 4.1, (y + z) is 4.45 to 4.7, and (x + y + z) / w is 4.85 to 5.15. It can be seen that this is preferable because particularly excellent cycle performance can be obtained.

(Example 10, Reference Examples 13 to 20 )
(Preparation of hydrogen storage electrode and hydrogen storage electrode unipolar test)
Y ₂ O ₃ powder, CeO ₂ powder, Dy ₂ O ₃ powder, Ho ₂ O ₃ powder, Er ₂ O ₃ powder, Tm ₂ O ₃ powder, Yb with respect to 100 parts by weight of the hydrogen storage alloy powder of Reference Example 4 1 part by weight of ₂ O ₃ powder and Lu ₂ O ₃ powder were mixed and added. Otherwise, a hydrogen storage electrode was produced in the same procedure as in Reference Example 4 (hydrogen storage electrode single electrode test). The produced electrodes are referred to as Reference Examples 13 to 20.
(Comparative Example 5)
1 part by weight of Yb ₂ O ₃ powder was mixed and added to 100 parts by weight of the hydrogen storage alloy powder according to Comparative Example 1. Otherwise, a hydrogen storage electrode was produced in the same procedure as in Comparative Example 1 (hydrogen storage electrode single electrode test). The produced electrode is referred to as Comparative Example 5.
In the same manner as in Examples 1 to 9 and Reference Examples 1 to 12 , a unipolar test of the hydrogen storage electrode according to Example 10, Reference Examples 13 to 20 and Comparative Example 5 was performed.

Table 3 shows the hydrogen storage electrode monopolar test results according to Example 3, Example 10, Reference Example 4, Reference Examples 13 to 20, and Comparative Examples 1 and 5.
Example 3 and Example 10, Reference Example 4 and Reference Examples 13 to 20 , Comparative Example 1 and Comparative Example 5 have the same compositions of applied hydrogen storage alloys. Examples 3 and 10, a comparison of Example 4 and Example 13 to 20, Example 10 Example 3, Reference Example 13 to 20 have substantially the same volume as in Reference Example 4, the hydrogen storage The mass saturation magnetization of the alloy powder is small. This means that the corrosion resistance of the hydrogen storage alloy can be improved without reducing the discharge capacity by adding the rare earth element compounds shown in Table 2 to the hydrogen storage electrode in Example 10 and Reference Examples 13 to 20. It suggests. On the other hand, in the case of Comparative Example 5 in which the content ratio of Mg in the hydrogen storage alloy is high, the addition of a rare earth element compound is not effective in improving the corrosion resistance. As a result, the specific surface area was not significantly different.

(Evaluation using nickel metal hydride storage battery)
In Reference Examples 13 to 20 of the hydrogen storage electrode single electrode test, 1 part by weight of Inco Corporation nickel powder (INCO # 210) was added to 100 parts by weight of the hydrogen storage alloy powder. In addition, the filling amount of the hydrogen storage alloy powder was 8.85 g, and nickel hydrogen was applied by applying a negative electrode plate (hydrogen storage electrode plate) prepared in the same manner as in Reference Examples 13 to 20 of the hydrogen storage electrode single electrode test. A storage battery was produced. The produced nickel metal hydride storage batteries are referred to as Reference Examples 13-20 .
(Example 10 )
One part by weight of Inco nickel powder (INCO # 210) was mixed and added to 100 parts by weight of the hydrogen storage alloy powder of Example 10 of the hydrogen storage electrode single electrode test. In addition, the filling amount of the hydrogen storage alloy powder was 8.85 g, and other than that, the negative electrode plate (hydrogen storage electrode plate) produced by the same procedure as in Example 10 of the hydrogen storage electrode single electrode test was applied to form a nickel metal hydride storage battery. Produced. The produced nickel metal hydride storage battery is referred to as Example 10 .
(Comparative Example 5)
One part by weight of Inco nickel powder (INCO # 210) was mixed and added to 100 parts by weight of the hydrogen storage alloy powder of Comparative Example 5 of the hydrogen storage electrode single electrode test. In addition, the filling amount of the hydrogen storage alloy powder was 8.85 g, and a nickel hydride storage battery was applied by applying a negative electrode plate (hydrogen storage electrode plate) manufactured in the same manner as in Comparative Example 5 of the hydrogen storage electrode single electrode test. Produced. The produced nickel metal hydride storage battery is referred to as Comparative Example 5.
Table 4 shows the NP ratio (N / P) and charge / discharge cycle test results of the nickel-metal hydride storage batteries according to Example 3, Example 10, Reference Example 4, Reference Examples 13 to 20 , and Comparative Examples 1 and 5.

As shown in Table 4, Example 10 has a higher cycle life than that of Example 3 , and Reference Examples 13 to 20 have a higher cycle life than that of Reference Example 4 . In Example 10 and Reference Examples 13 to 20 , the corrosion resistance of the hydrogen storage alloy powder could be improved by adding a rare earth compound to the hydrogen storage electrode, so that compared to Example 3 and Reference Example 4 , respectively. It is considered that the cycle life of the battery has been improved.
Although the cycle characteristics of Comparative Example 5 are improved as compared with Comparative Example 1, they are inferior to those of Examples. The hydrogen storage alloy powder having a high Mg content and a crystal structure different from the CaCu _{5 type} shown in Comparative Example 1 has a high capacity but is poor in corrosion resistance to an electrolytic solution. However, the disadvantage of poor cycle characteristics cannot be resolved. On the other hand, the hydrogen storage electrode and nickel metal hydride storage battery to which the hydrogen storage alloy according to the present invention is applied are compared with the hydrogen storage alloy electrode and nickel metal hydride storage battery to which a hydrogen storage alloy not containing Mg, which has been widely used conventionally, is applied. A hydrogen storage alloy electrode and nickel-metal hydride storage battery with high capacity and excellent cycle characteristics, and the addition of the rare earth element oxide or hydroxide further improves the cycle characteristics. Electrode, nickel metal hydride storage battery.

  The present invention provides a nickel-metal hydride storage battery having a hydrogen storage electrode using a hydrogen storage alloy powder as an active material, and having a cycle performance equivalent to or higher than that of a conventional battery and having a high capacity. It has high industrial value.

FIG. 4 is a powder X-ray diffraction diagram of a hydrogen storage alloy powder having a CaCu _{5 type} crystal structure according to the present invention and a comparative example. Comparative Example relates, is a powder X-ray diffraction pattern of a hydrogen storage alloy powder having a crystal structure different from the CaCu ₅ form. 4 is a graph showing the relationship between the discharge capacity of a hydrogen storage alloy and (y + z). It is a graph which shows the relationship between the cycle life of a nickel hydride storage battery, and the mass saturation magnetization of a hydrogen storage alloy. It is a graph which shows the relationship between the cycle life of a nickel metal hydride storage battery and the specific surface area of a hydrogen storage alloy. 3 is a graph showing the relationship between the cycle life of a nickel metal hydride storage battery and (y + z) of a hydrogen storage alloy.

Claims (1)

Symbol A is at least one element selected from among rare earth elements including yttrium (Y), the symbol B is M g, one that symbol C is Co, Mn, Al, selected from Fe and Cu In the chemical formula A _w B _x Ni _y C _z , w + x = 1, 0.04 ≦ x ≦ 0.09, 3.5 ≦ y ≦ 4.3, 4.0 ≦ y + z ≦ 4.7 , 0 < z, 4.75 ≦ (x + y + z) /w≦5.35, a nickel-metal hydride storage battery provided with a hydrogen storage electrode using a powder of a hydrogen storage alloy represented by