JP5425433B2 - Hydrogen storage alloy and alkaline storage battery using hydrogen storage alloy as negative electrode active material - Google Patents

Description

  The present invention relates to a hydrogen storage alloy used as a negative electrode active material of an alkaline storage battery suitable for applications requiring a large current discharge, such as a hybrid vehicle (HEV) and an electric vehicle (PEV), and the hydrogen storage The present invention relates to an alkaline storage battery using an alloy as a negative electrode active material.

In recent years, alkaline storage batteries, particularly nickel-hydrogen storage batteries, have been used as power sources for devices that require output such as hybrid vehicles (HEV) and electric vehicles (PEV). Generally, a hydrogen storage alloy used as a negative electrode active material of a nickel-hydrogen storage battery is a part of the B component (Ni) of an AB ₅ type rare earth hydrogen storage alloy such as LaNi ₅ which is aluminum (Al) or manganese (Mn). Those substituted with an element such as are used. In addition to the AB ₅ type rare earth hydrogen storage alloy, an AB ₂ type structure is also known. It is also known to take various crystal structures by combining an AB ₂ type structure and an AB ₅ type structure.

Among these, various hydrogen storage alloys having an A ₂ B 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 are disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-164045. It came to be considered. This hydrogen storage alloy having an A ₂ B ₇ type structure has a hexagonal crystal structure (2H), and can improve the cycle life characteristics of hydrogen storage / release. However, the hydrogen storage alloy of the A ₂ B ₇ type structure has a problem that the discharge characteristics (assist output) are insufficient and the performance is not satisfactory for output applications far exceeding the conventional range. .

Here, as a crystal structure that can be a metastable structure, an A ₅ B ₁₉ type structure and the like are known in addition to the A ₂ B ₇ type structure. In this case, in the A ₅ B ₁₉ type structure, the AB ₂ type structure and the AB ₅ type structure are stacked with a period of three layers, and the nickel (Ni) ratio per unit crystal lattice is higher than that of the A ₂ B ₇ type structure. Since the number of active sites can be increased, the number of active sites that promote the adsorption and dissociation of hydrogen molecules into hydrogen atoms can be increased.
JP 2002-164045 A

However, in the hydrogen storage alloy of A ₅ B ₁₉ type structure, nickel (Ni) is compared with other elements of B component (aluminum (Al), cobalt (Co), manganese (Mn), zinc (Zn), etc.)). It is known that the atomic radius is small. Here, in the A ₅ B ₁₉ type structure, when the ratio of nickel (Ni) is increased, there arises a problem that gaps between metal atoms constituting the unit cell are reduced. When the gap between the metal atoms is reduced, hydrogen atoms are less likely to enter the metal lattice, so that an unstable metal hydride is formed, and the hydrogen equilibrium pressure is increased.

  For this reason, when a nickel-hydrogen storage battery using a hydrogen storage alloy with such a small gap between metal atoms as a negative electrode active material is used for a large current charge / discharge application, the pulverization of the hydrogen storage alloy is accelerated. Durability will be reduced. Moreover, when the hydrogen equilibrium pressure increases, hydrogen reduction reaction proceeds at the nickel positive electrode, self-discharge is promoted, and battery performance deteriorates. As a result, this type of alkaline storage battery can be used for output performance (extremely high output characteristics), durability performance (extremely high durability) and self-discharge performance (extremely high self-discharge) such as hybrid vehicles (HEV) and electric vehicles (PEV). There is a problem in using it as a power source for applications that require a small number of applications.

  Therefore, the present invention has been made to solve the above-described problems, and has an output characteristic far exceeding the conventional range by specifying the alloy structure of the hydrogen storage alloy, particularly the A component element. It is an object of the present invention to provide a hydrogen storage alloy that can be used and an alkaline storage battery that uses this hydrogen storage alloy as a negative electrode active material.

In order to achieve the above object, the hydrogen storage alloy of the present invention is composed of a rare earth element represented by Ln and an A component composed of magnesium and a B component composed of an element containing at least nickel and aluminum. The alloy main phase has an A ₅ B ₁₉ type structure, and the general formula is Ln _lx Mg _x Ni _yab Al _a M _b (wherein M is at least one element selected from Co, Mn, and Zn, 0.1 ≦ x ≦ 0.2, 3.6 ≦ y ≦ 3.9, 0.1 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.1), and the rare earth element Ln is lanthanum (La) And samarium (Sm) , and the hydrogen storage pressure (Pa) when the hydrogen storage amount H / M (atomic ratio) at 40 ° C. is 0.5 is 0.03 to 0.17 MPa. It is characterized by that.

Here, in the hydrogen storage alloy, rare earth elements (Ln) constituting the A component contribute to the storage and release of hydrogen. In this case, when the number of elements of the rare earth element (Ln) increases, the interaction parameter in the liquid phase between the constituent elements during alloy casting increases, and a second phase such as segregation is likely to be generated. And in the alkaline storage battery which uses as a negative electrode active material the hydrogen storage alloy in which the 2nd phases, such as segregation, were produced, pulverization of a hydrogen storage alloy comes to be accelerated with repeating a charging / discharging cycle. However, when regulating the number of elements of the rare earth element (Ln) to two yuan element of La and Sm atomic radius is larger among the rare earth elements (Ln), so that the mutual parameter is decreased in the liquid phase between the constituent elements during alloy cast become. Thereby, it becomes easy to suppress generation | occurrence | production of 2nd layers, such as segregation, and it becomes possible to suppress pulverization of the hydrogen storage alloy accompanying a charging / discharging cycle.

And, it was found that such a suppression effect appears remarkably in the A ₅ B ₁₉ type structure which is a metastable structure. Therefore, the alloy main phase has an A ₅ B ₁₉ type structure, and the general formula is expressed as Ln _lx Mg _x Ni. _{When expressed as yab} Al _a M _b (wherein M is at least one element selected from Co, Mn, and Zn), 0.1 ≦ x ≦ 0.2, 0.1 ≦ a ≦ 0.2 , 0 ≦ b ≦ 0.1, 3.6 ≦ y ≦ 3.9 must be satisfied. This is because 0.1 ≦ x ≦ 0.2, 0.1 ≦ a ≦ 0.2, and 0 ≦ b ≦ to make the A ₅ B ₁₉ type structure which is such a metastable structure an alloy main phase. Even if the condition of 0.1 is satisfied, it is not recognized in the conventional stoichiometric ratio region where the B component stoichiometric ratio y is about 3.5, but the stoichiometric ratio region of 3.6 or more and 3.9 or less ( This is because it is possible only in the region of 3.6 ≦ y ≦ 3.9.

  In this case, by including La having a large atomic radius among the rare earth elements (Ln), the stored hydrogen equilibrium pressure (Pa) when the hydrogen storage amount H / M (atomic ratio) at 40 ° C. is 0.5 is obtained. It becomes possible to set it as 0.03-0.17 Mpa, and it becomes possible to improve self-discharge performance. This is because when the equilibrium pressure is greater than 0.17 MPa, the hydrogen concentration on the surface of the hydrogen storage alloy increases, and this contributes to the reduction reaction of the positive electrode. In applications, the reduction in capacity due to self-discharge is significant. On the other hand, if the stored hydrogen equilibrium pressure (Pa) is less than 0.03 MPa, the output voltage is lowered due to a decrease in the operating voltage.

From these facts, in order to exhibit output characteristics and achieve both durability and self-discharge performance, the alloy main phase has an A ₅ B ₁₉ type structure, and the general formula is Ln _lx Mg _x Ni _yab Al _a M _b (In the formula, M is at least one element selected from Co, Mn, and Zn, and 0.1 ≦ x ≦ 0.2, 3.6 ≦ y ≦ 3.9, and 0.1 ≦ a ≦ 0. .2, 0 ≦ b ≦ 0.1), the rare earth element Ln is composed of two elements of La and Sm , and the hydrogen storage amount H / M (atomic ratio) at 40 ° C. is 0.5. It is necessary to use a hydrogen storage alloy having a storage hydrogen equilibrium pressure (Pa) of 0.03 to 0.17 MPa.

In addition, it is desirable that the nickel molar ratio ((yab) / (y + 1)) of the hydrogen storage alloy represented by the general formula is 74% or more. In addition, the general formula Ln _lx Mg _x Ni _yab Al _a M
_It is desirable that the element M as a nickel-substitution element of the hydrogen storage alloy represented by _b does not contain cobalt (Co) and manganese (Mn) . Also, since the hydrogen storage alloy of the above composition having a durability, the powder consisting of a hydrogen storage alloy is capable of volume cumulative frequency 50% particle size (D50) is to 20μm or less, even higher output Characteristics can be obtained.

  In the present invention, since the alloy structure of the hydrogen storage alloy and the A component element are specified, a hydrogen storage alloy having output characteristics (assist output) far exceeding the conventional range is obtained, and this hydrogen storage alloy By using as a negative electrode active material, it is possible to obtain an alkaline storage battery that exhibits output characteristics and has both durability and self-discharge performance.

  Next, embodiments of the present invention will be described in detail below. However, the present invention is not limited to these embodiments, and can be appropriately modified and implemented without departing from the scope of the present invention. In addition, FIG. 1 is sectional drawing which shows typically the alkaline storage battery of this invention.

1. Hydrogen storage alloys Lanthanum (La), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Samarium (Sm), Magnesium (Mg), Nickel (Ni), Aluminum (Al), Cobalt (Co), Manganese ( After mixing metal elements such as Mn) and zinc (Zn) at a predetermined molar ratio as shown in Table 1 below, these mixtures are put into a high frequency induction furnace in an argon gas atmosphere to be dissolved. Thereafter, the molten metal is rapidly cooled so as to form an alloy ingot having a thickness of 0.5 mm or less, and thin plate-like hydrogen storage alloys a to k are produced.

In this case, the compositional formula represented by La _0.8 Ce _0.1 Pr _0.05 Nd _0.05 Ni _4.2 Al _0.3 (Co, Mn) _0.7 is referred to as a hydrogen storage alloy a, and Nd _0.9 Mg _0.1 Ni _3.2 Al _0.2 Co _0.1 One is represented by hydrogen storage alloy b, and one represented by La _0.3 Nd _0.5 Mg _0.2 Ni _3.5 Al _0.2 is represented by hydrogen storage alloy c. Further, a material represented by Nd _0.9 Mg _0.1 Ni _3.7 Al _0.1 is a hydrogen storage alloy d, a material represented by La _0.2 Pr _0.2 Nd _0.5 Mg _0.1 Ni _3.7 Al _0.1 is a hydrogen storage alloy e, and La _0.2 Nd _0.7 A material represented by Mg _0.1 Ni _3.6 Al _0.1 Zn _0.1 is designated as hydrogen storage alloy f. Also, La _0.2 Nd _0.7 Mg _0.1 Ni _3.7 Al _0.1 represents hydrogen storage alloy g, La _0.4 Nd _0.5 Mg _0.1 Ni _3.7 Al _0.1 represents hydrogen storage alloy h, and La _0.5 Sm _0.4 A material represented by Mg _0.1 Ni _3.7 Al _0.1 is referred to as a hydrogen storage alloy i. Further, La _0.4 Sm _0.5 Mg _0.1 Ni _3.7 Al _0.1 is represented by hydrogen storage alloy j, La _0.8 Mg _0.2 Ni _3.8 Al _0.1 is represented by hydrogen storage alloy k, and La _0.6 Sm _0.2 Mg _0.2. A material represented by Ni _3.5 Al _0.1 is referred to as a hydrogen storage alloy l. When the above results are summarized in a table, the results shown in Table 1 below are obtained.

In Table 1 below, each of the hydrogen storage alloys a to l is represented by the general formula Ln _lx Mg _x Ni _yab Al _a M _b (M is an element composed of at least one of Co, Mn, and Zn). The values of x (stoichiometric ratio of Mg), a (stoichiometric ratio of Al), b (stoichiometric ratio of M) and y (stoichiometric ratio of B component (Ni + Al + M)) are also shown. The value of the nickel molar ratio ((y−a−b) / (y + 1)) is also shown.

  Subsequently, the melting points (Tm) of the obtained hydrogen storage alloys a to 1 were measured using DSC (differential scanning calorimeter). Thereafter, heat treatment was performed for a predetermined time (in this case, 10 hours) at a temperature (Ta = Tm−30 ° C.) lower by 30 ° C. than the melting points (Tm) of these hydrogen storage alloys a to k. And when the hydrogen storage equilibrium pressure Pa (MPa) of each hydrogen storage alloy ak after heat processing was calculated | required, it became the result shown in Table 2. In this case, under an atmosphere of 40 ° C., the dissociation pressure when the hydrogen storage amount (H / M) is 0.5 is defined as the storage hydrogen equilibrium pressure Pa (MPa), and JIS H7201 (1991) “Pressure of the hydrogen storage alloy— It measured based on the measuring method of a composition isotherm (PCT curve).

  Thereafter, these hydrogen storage alloys a to l are coarsely pulverized and then mechanically pulverized in an inert gas atmosphere to obtain a hydrogen storage having a particle size (D50) of 20 μm at a volume cumulative frequency of 50%. Alloy powders a to l were prepared. Next, the crystal structures of the hydrogen storage alloy powders a to l were identified by a powder X-ray diffraction method using an X-ray diffraction measuring 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 k was identified using a JCPDS card chart.

Here, in the composition ratio of each crystal structure, the A ₅ B ₁₉ type structure is a Ce ₅ Co ₁₉ type structure, a Pr ₅ Co ₁₉ type structure and an Sm ₅ Co ₁₉ type structure, and the A ₂ B ₇ type structure is Nd ₂ Ni. ₇ type structure and Ce ₂ Ni ₇ type structure, AB ₅ type structure is LaNi ₅ type structure, the intensity value of the diffraction angle of each structure according to JCPDS and the strongest intensity value of 42-44 °, each intensity ratio, When the composition ratio of each structure was calculated by applying to the obtained XRD profile, the results shown in Table 2 below were obtained.

From the results shown in Tables 1 and 2, the following has become clear. That is, the alloy a does not satisfy the conditions of 0.1 ≦ x ≦ 0.2, 0.1 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.1, and the B component (Ni + Al + M) is stoichiometric. When the ratio y is increased to 5.2, an AB ₅ type structure is obtained. Moreover, even if the conditions of 0.1 ≦ x ≦ 0.2, 0.1 ≦ a ≦ 0.2, and 0 ≦ b ≦ 0.1 are satisfied as in the case of the alloy b, the stoichiometry of the B component (Ni + Al + M) When the ratio y is as small as 3.5, the A ₂ B ₇ type structure becomes the alloy main phase.

On the other hand, as in alloys c to l, the conditions of 0.1 ≦ x ≦ 0.2, 0.1 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.1 are satisfied, and the B component (Ni + Al + M) When the stoichiometric ratio y is 3.6 or more and 3.9 or less, the A ₅ B ₁₉ type structure is an alloy main phase (in this case, the composition ratio of the A ₅ B ₁₉ type structure in the alloy 1 is 46%. It can be said that the nickel main ratio ((yab) / (y + 1)) is 74% or more and the Ni ratio can be increased. Further, even when the stoichiometric ratio y of the B component (Ni + Al + M) is 3.6 or more and 3.9 or less, the AB ₅ type structure is segregated when the rare earth element (Ln) is a three element like the alloy e. You can see that

2. Hydrogen Storage Alloy Electrode Next, using the above-described hydrogen storage alloys a to l, hydrogen storage alloy electrodes 11 (a1 to l1) are respectively produced as follows. In this case, first, 0.5% by mass of nickel flakes having an apparent density of 1.5 g / cm ³ was added to a water-soluble binder in which CMC (carboxymethylcellulose) was dissolved in water (or pure water), and hydrogen was added thereto. The occlusion alloy powders (a to k) are 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 3.1 g / cm ^3, and then the hydrogen storage alloy. Each slurry is prepared. In this case, CMC (carboxymethylcellulose) is 0.1% by mass with respect to 100 parts by mass of the hydrogen storage alloy powder, and SBR (styrene butadiene latex) is 1.0% by mass with respect to 100 parts by mass of the hydrogen storage alloy powder. Adjust to.

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 respectively added to the negative electrode core so that the filling density is 5.0 g / cm ^3. After coating and drying, rolling to a predetermined thickness. Then, it cut | disconnects so that it may become a predetermined dimension (in this case, a negative electrode surface area (short-axis length x long-axis length x2) may be 800 cm < ² >), and each hydrogen storage alloy electrode 11 (a1-l1) is produced. .

  Here, the one using the hydrogen storage alloy a is referred to as a hydrogen storage alloy electrode a1, and the one using the hydrogen storage alloy b is referred to as a hydrogen storage alloy electrode b1. Also, the hydrogen storage alloy electrode c1 is a hydrogen storage alloy electrode c1, the hydrogen storage alloy d is a hydrogen storage alloy electrode d1, and the hydrogen storage alloy e is a hydrogen storage alloy electrode e1. The one using the hydrogen storage alloy f is referred to as a hydrogen storage alloy electrode f1, the one using the hydrogen storage alloy g is referred to as a hydrogen storage alloy electrode g1, and the one using the hydrogen storage alloy h is referred to as a hydrogen storage alloy electrode h1. Further, the hydrogen storage alloy electrode i1 is a hydrogen storage alloy electrode i1, the hydrogen storage alloy j is a hydrogen storage alloy electrode j1, and the hydrogen storage alloy k is a hydrogen storage alloy electrode k1. A material using the hydrogen storage alloy l is defined as a hydrogen storage alloy electrode l1.

3. Nickel electrode On the other hand, 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 a nickel salt is placed in the pores of the porous nickel sintered substrate. And retain cobalt salts. Thereafter, the porous nickel sintered substrate is 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 is performed, and the active material mainly composed of nickel hydroxide is filled in 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. To fill. Then, after drying at room temperature, the nickel electrode 12 is produced by cutting into predetermined dimensions.

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 non-woven fabric is interposed between them, and the spiral is wound. The electrode group is 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 is welded to the electrode body to form 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. Weld 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. Then, the nickel-hydrogen storage battery 10 (AL) is produced 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 is 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 A, a battery using the hydrogen storage alloy electrode b1 is referred to as a battery B, a battery using the hydrogen storage alloy electrode c1 is referred to as a battery C, and the hydrogen storage alloy electrode d1. Is a battery D, a battery E is a battery using the hydrogen storage alloy electrode e1, a battery F is a battery using the hydrogen storage alloy electrode f1, and a battery G is a battery using the hydrogen storage alloy electrode g1. A battery using the hydrogen storage alloy electrode h1 is referred to as a battery H, a battery using the hydrogen storage alloy electrode i1 is referred to as a battery I, a battery using the hydrogen storage alloy electrode j1 is referred to as a battery J, and the hydrogen storage alloy electrode k1 is used. The battery K is referred to as the battery K, and the battery L using the hydrogen storage alloy electrode 11 is referred to as the battery L.

5. Battery Test (1) Output Characteristic Evaluation First, using the batteries A to L manufactured as described above, an SOC (State Of Charge) of 120 at a charging current of 1 It in a temperature atmosphere of 25 ° C. % Charge and rest for 1 hour. Next, the battery A was allowed to stand for 24 hours in a temperature atmosphere at 70 ° C., and then a cycle of discharging the battery voltage to 0.3 V with a discharge current of 1 It in a temperature atmosphere at 45 ° C. was repeated two times. Activate ~ L.

  After the activation, the battery is charged to 50% of SOC (State Of Charge) with a charging current of 1 It in a temperature atmosphere of 25 ° C. and then rests for 1 hour. Next, the battery is charged for 20 seconds at an arbitrary charging rate in a temperature atmosphere of −10 ° C., and then rested for 30 minutes. Then, after discharging at an arbitrary discharge rate for 10 seconds in a temperature atmosphere of −10 ° C., it is paused for 30 minutes in a temperature atmosphere of 25 ° C. 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 in a temperature atmosphere of 25 ° C. are repeated.

  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 was increased in order of the discharge current, the battery voltage (V) of each of the batteries A to L at the time of 10 seconds at each discharge rate was measured for each current, respectively. Thus, a discharge VI plot approximate curve was obtained.

  Here, 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, and the battery B using the hydrogen storage alloy b is obtained. When the −10 ° C. assist output was set as the reference (100) and the relative ratio thereof was determined as the −10 ° C. assist output ratio (vs. battery B), the results shown in Table 3 below were obtained.

(2) Measurement of atomization amount of hydrogen storage alloy powder (change in particle size before and after activation) Next, as an index of corrosion resistance of hydrogen storage alloy, the amount of atomization of hydrogen storage alloy powder (particle size before and after activation (volume cumulative frequency) Was 50% of the particle size (D50)). Here, the amount of pulverization is represented by the difference between the particle size immediately after pulverization and the particle size after activation, and is an indicator of the pulverization behavior of the hydrogen storage alloy during charge and discharge during activation. In this case, when the pulverization amount of the battery B using the hydrogen storage alloy b is taken as the reference (100) and the relative ratio thereof is obtained as the pulverization amount ratio (vs. the battery B), the result shown in Table 3 below It became.

Next, based on the obtained -10 ° C assist output and the pulverization amount of the hydrogen storage alloy powder, as the output / durability index, the ratio of the -10 ° C assist output to the pulverization amount (output / durability index = -10) The temperature was obtained as shown in Table 3 below.

  From the results in Table 3 above, the following became clear. That is, the batteries C to L using the hydrogen storage alloys c to l are, in other words, 0.1 ≦ x ≦ 0.2, 0.1 ≦ a ≦, than the battery B using the hydrogen storage alloy b. The larger the stoichiometric ratio y of the B component (Ni + Al + M) that satisfies the conditions of 0.2 and 0 ≦ b ≦ 0.1, the greater the −10 ° C. assist output (low temperature output), and the assist output tends to improve. In addition, it can be seen that the ratio of the −10 ° C. assist output to the amount of pulverization tends to be improved.

  However, even if the conditions of 0.1 ≦ x ≦ 0.2, 0.1 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.1 are satisfied and the stoichiometric ratio y of the B component (Ni + Al + M) is large, When a hydrogen storage alloy d containing only neodymium (Nd) instead of lanthanum (La) is used as in the battery D, the hydrogen equilibrium pressure (Pa) is large, the pulverization amount is large, and the pulverization is performed. It can be seen that the ratio of the −10 ° C. assist output to the amount also decreases. This is because if the rare earth element (Ln) is neodymium (Nd), which has a smaller atomic radius than lanthanum (La), the gap between the metal atoms constituting the unit cell becomes small, making it difficult for hydrogen atoms to enter the metal lattice. It is considered that an unstable metal hydride is formed and the hydrogen equilibrium pressure is increased. And, when the hydrogen storage alloy with a small gap between metal atoms is used as a negative electrode active material for large current charge / discharge applications, it is considered that the pulverization of the hydrogen storage alloy is accelerated and the durability is lowered. .

  Further, even if the conditions of 0.1 ≦ x ≦ 0.2, 0.1 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.1 are satisfied and the stoichiometric ratio y of the B component (Ni + Al + M) is large, When the rare earth element (Ln) is composed of three elements of lanthanum (La), praseodymium (Pr), and neodymium (Nd) as in the battery E, the amount of pulverization is large and the ratio of the −10 ° C. assist output to the amount of pulverization is It turns out that it falls further. This is because when the number of elements of the rare earth element (Ln) constituting the component A increases, the interaction parameter in the liquid phase between the constituent elements at the time of casting the alloy increases, and a second phase such as segregation is likely to be generated. And when 2nd phases, such as segregation, were produced, pulverization was accelerated and it was thought that the amount of pulverization became large.

A comprehensive consideration of the results in Tables 1 to 3 is as follows. That is, the alloy main phase of a hydrogen storage alloy composed of an A component composed of a rare earth element represented by Ln and magnesium and a B component composed of an element containing at least nickel and aluminum has an A ₅ B ₁₉ type structure. When the general formula is _expressed as Ln _lx Mg _x Ni _yab Al _a M _b (wherein M is at least one element selected from Co, Mn, Zn), 0.1 ≦ x ≦ 0.2, 0.1 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.1, 3.6 ≦ y ≦ 3.9, and the rare earth element (Ln) contains at least two elements including lanthanum (La) When a hydrogen storage alloy made of is used, the nickel molar ratio ((y−a−b) / (y + 1)) becomes 74% or more, the Ni ratio increases, and the hydrogen storage amount at 40 ° C. H / M (atom Ratio) is 0.5 to 0.17. The hydrogen storage equilibrium pressure (Pa) is 0.03 to 0.17. Pa next, -10 ° C. assist output (low temperature output) is large, and also improves the ratio of -10 ° C. assist output for micronized amount.

In the above-described embodiment, an example in which samarium (Sm) or neodymium (Nd) is used as the rare earth element (Ln) other than lanthanum (La) has been described. However, praseodymium other than samarium (Sm) and neodymium (Nd) is described. Lanthanoids such as (Pr) and cesium (Ce) may be used. In general formula _{Ln lx Mg x Ni yab Al a} M b element M consisting of nickel substitution elements of the hydrogen storage alloy represented by the free of cobalt (Co) and manganese (Mn) is preferable. This is because self-discharge performance (very low self-discharge) is required for applications that are left in a high temperature environment such as for hybrid vehicles and electric vehicles, and the negative electrode contains cobalt (Co) and manganese (Mn). This is because these elements are eluted when left for a long time and re-deposited on the separator, resulting in a decrease in self-discharge performance.

It is sectional drawing which shows the alkaline storage battery of this invention typically.

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, 16 ... Positive electrode lead, DESCRIPTION OF SYMBOLS 17 ... Exterior can, 17a ... Circular groove part, 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 comprising an A component composed of a rare earth element represented by Ln and magnesium, and a B component composed of an element containing at least nickel and aluminum,
The alloy main phase of the hydrogen storage alloy has an A ₅ B ₁₉ type structure,
General formula _{Ln 1-x Mg x Ni y} -a-b Al a M b ( where, M is at least one element selected from among Co, Mn, and Zn, 0.1 ≦ x ≦ 0. 2, 3.6 ≦ y ≦ 3.9, 0.1 ≦ a ≦ 0.2, 0 ≦ b ≦ 0.1),
The rare earth element (Ln) is composed of two elements of lanthanum (La) and samarium (Sm) , and the hydrogen storage equilibrium pressure (Pa) when the hydrogen storage amount H / M (atomic ratio) at 40 ° C. is 0.5. ) Is 0.03 to 0.17 MPa. Said general formula _{Ln 1-x Mg x Ni y} -a-b Al a M b nickel molar ratio of hydrogen-absorbing alloy represented by ((y-a-b) / (y + 1)) is 74% or more The hydrogen storage alloy according to claim 1. Wherein the general formula _{Ln 1-x Mg x Ni y} -a-b Al a M b element M consisting of nickel substitution elements of the hydrogen storage alloy represented by the free cobalt (Co) and manganese (Mn) The hydrogen storage alloy according to claim 1 or 2. The hydrogen storage alloy according to any one of claims 1 to 3 , wherein the hydrogen storage alloy powder has a volume cumulative frequency of 50% and a particle size (D50) of 20 µm or less. A hydrogen storage alloy electrode comprising the hydrogen storage alloy according to any one of claims 1 to 4 as a negative electrode active material, a positive electrode, a separator that separates both electrodes, and an alkaline electrolyte are provided in an outer can. An alkaline storage battery characterized by that.

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