JP5769028B2 - Nickel metal hydride storage battery - Google Patents

Description

  The present invention relates to a nickel metal hydride storage battery.

  Nickel metal hydride storage batteries have high energy density, so they are used as power sources for small electronic devices such as digital cameras and notebook computers, and because the operating voltage is equivalent to and compatible with primary batteries such as alkaline manganese batteries. It is widely used as an alternative to the primary battery, and its demand is constantly expanding.

Such a nickel-metal hydride storage battery uses a hydrogen storage alloy as a negative electrode active material. As the hydrogen storage alloy, an AB ₅ type rare earth-Ni alloy having a CaCu ₅ type crystal structure has been put into practical use. ing.

On the other hand, as a new hydrogen storage alloy, for example, an AB ₃ type rare earth-Mg—Ni based alloy having a PuNi ₃ type crystal structure (Patent Document 1) has been developed, and by using these alloys as an electrode material, an AB ₅ type is developed. It has been reported that a discharge capacity exceeding that of the alloy can be obtained.

JP-A-11-217643

Although AB type ₅ alloy is excellent in cycle characteristics, it has a problem in long-term storage performance. This is because Co contained in the alloy for suppressing pulverization elutes during storage and precipitates on the surface of the separator or the positive electrode, causing a slight short circuit.

  On the other hand, rare earth-Mg-Ni-based hydrogen storage alloys do not necessarily require an elution element such as Co because they are excellent in pulverization resistance, and the battery has excellent self-discharge performance by designing a low equilibrium hydrogen pressure. Can be configured. However, in that case, the amount of La and Mg increases, so that the alloy is easily corroded, and a hydrogen-induced amorphous phase is partially formed, resulting in a large capacity deterioration. In order to prevent corrosion, it is necessary to reduce the reaction area of the alloy particles, and it is effective to set the initial particle size large. In addition, there is a method for preventing corrosion by forming a Ni-rich layer on the surface by performing an alkali treatment.

  In view of the above, the present invention is intended to provide a nickel-metal hydride storage battery that is excellent in recovery performance after long-term storage.

As a result of intensive studies, the inventor has used, as a negative electrode active material, a mixture of two kinds of rare earth-Mg—Ni hydrogen storage alloys and AB ₅ type alloys having different crystal structures in a predetermined ratio. It has been found that the recovery performance after long-term storage of the nickel-metal hydride storage battery is improved, and the present invention has been completed based on this finding.

  That is, the nickel-metal hydride storage battery according to the present invention is a nickel-metal hydride storage battery including a negative electrode containing a rare earth-Mg-Ni-based hydrogen storage alloy (A) and a rare-earth-Ni-based hydrogen storage alloy (B), Inclusion of the rare earth-Mg-Ni hydrogen storage alloy (A) relative to the total content of the rare earth-Mg-Ni hydrogen storage alloy (A) and the rare earth-Ni hydrogen storage alloy (B) in the negative electrode The amount ratio is 30 to 70% by mass.

  In the nickel metal hydride storage battery according to the present invention, the rare earth-Mg—Ni-based hydrogen storage alloy (A) has an average particle size (D50) that is equal to or greater than the average particle size (D50) of the rare-earth-Ni-based hydrogen storage alloy (B). It is preferable that Since the rare earth-Ni-based hydrogen storage alloy (B) is harder than the rare earth-Mg-Ni-based hydrogen storage alloy (A), a current collecting base material made of a perforated steel plate plated with Ni during electrode pressing ( Hereinafter, there is a risk of damage to an NPPS (Nickel Plated Punched Steel) current collector base material). Thereby, the Ni plating is damaged, and Fe is eluted from the NPPS current collecting base material. The eluted Fe moves into the positive electrode and causes a decrease in charging efficiency of the positive electrode. Since the elution of Fe is accelerated in the end-of-discharge state as compared with the charged state, the charging efficiency after recovery is greatly reduced particularly when left at the end of discharge. From the above, it is preferable that the rare earth-Ni-based hydrogen storage alloy (B) has an average particle size (D50) or less of the rare earth-Mg-Ni-based hydrogen storage alloy (A).

  The rare earth-Mg—Ni-based hydrogen storage alloy (A) has an equilibrium hydrogen pressure at 80 ° C. (a release pressure at a hydrogen storage amount H / M = 0.4) of 0.05 MPa or less. It is preferable that the equilibrium hydrogen pressure at 80 ° C. of the Ni-based hydrogen storage alloy (B) (discharge pressure at a hydrogen storage amount H / M = 0.4) is 0.1 MPa or more.

  Since this invention consists of the structure mentioned above, the recovery performance of the nickel-metal hydride storage battery after a long-term storage can be improved.

  Below, embodiment of the nickel metal hydride storage battery which concerns on this invention is described.

  The nickel metal hydride storage battery according to the present invention includes, for example, a negative electrode containing a hydrogen storage alloy as a negative electrode active material, a positive electrode (nickel electrode) containing a positive electrode active material mainly composed of nickel hydroxide, a separator, and alkaline electrolysis. And a liquid.

In the present invention, the negative electrode includes a rare earth-Mg-Ni hydrogen storage alloy (A) (hereinafter referred to as a hydrogen storage alloy (A)) and a rare earth-Ni hydrogen storage alloy (B) which is an AB type ₅ alloy. (Hereinafter referred to as a hydrogen storage alloy (B)) as a negative electrode active material. Here, the hydrogen storage alloy (A) is more specifically a hydrogen storage alloy having a crystal structure in which a plurality of AB ₅ units and A ₂ B ₄ units are laminated in the C-axis direction. PuNi ₃ , Ce ₂ Examples thereof include hydrogen storage alloys having a crystal structure such as Ni ₇ , Gd ₂ Co ₇ , Pr ₅ Co ₁₉ , and Ce ₅ Co ₁₉ .

The hydrogen storage alloy (A) is substantially represented by the general formula R1 _a R2 _b R3 _c (wherein R1 is at least one element selected from the group consisting of rare earth elements including Y, and R2 represents Mg. It may be essential and may further contain at least one element selected from the group consisting of Ca, Sr and Ba, R3 must be Ni, and Co, Mn, Al, Cr, Fe, Cu, Zn , Si, Sn, V, Nb, Ta, Ti, Zr, and Hf may be included, and a, b, and c are a + b + c = 100 (atomic%) Then, 10 ≦ a ≦ 30, 1 ≦ b ≦ 10, 65 ≦ c ≦ 90, and 3.0 ≦ c / (a + b) ≦ 4.0. It is preferably made of an alloy. Here, an alloy having substantially the composition represented by the general formula _R1 a _R2 b R3 _c, of its constituent elements, more than 80%, preferably 90% or more, more preferably more than 95%, R1, R2 and R3 occupy, but R1, R2 and R3 may occupy all (100%) of the constituent elements of the alloy, or other than these elements, unless the characteristics of the alloy are impaired. In the above, other elements may be contained.

  The hydrogen storage alloy (A) preferably has an equilibrium hydrogen pressure at 80 ° C. (hydrogen storage amount H / M = release pressure at 0.4) of 0.05 MPa or less. When the equilibrium hydrogen pressure is 0.05 MPa or less, the release of hydrogen is sufficiently suppressed, so that a nickel-metal hydride storage battery having excellent storage performance at the end of charging (remaining capacity at the end of charging) can be obtained.

The hydrogen storage alloy (B) is substantially the general formula R1 _d R4 _e (wherein R1 is at least one element selected from the group consisting of rare earth elements including Y, and R4 is Ni, Co, Mn and Al are essential, and at least one element selected from the group consisting of Cr, Fe, Cu, Zn, Si, Sn, V, Nb, Ta, Ti, Zr, Hf and Mg is included. D and e are values satisfying 15 ≦ d ≦ 18, 82 ≦ e ≦ 85, and 4.7 ≦ e / d ≦ 5.5, where d + e = 100 (atomic%). It is preferable that it consists of an alloy which has a composition represented by these. Here, the alloy having a composition substantially represented by the general formula R1 _d R4 _e is 80% or more, preferably 90% or more, more preferably 95% or more, among the constituent elements, R1 and R4 being Although R1 and R4 may occupy all (100%) of the constituent elements of the alloy, or other elements other than these elements, as long as the properties of the alloy are not impaired. It may be included.

  The hydrogen storage alloy (B) may have an equilibrium hydrogen pressure at 80 ° C. (hydrogen storage amount H / M = release pressure at 0.4) of 0.1 MPa or more. Even if the equilibrium hydrogen pressure of the hydrogen storage alloy (B) is high, as described above, by using an alloy having a low equilibrium hydrogen pressure as the hydrogen storage alloy (A), the storage performance at the end of charging of the nickel hydrogen storage battery Can be maintained at a sufficiently high level. In addition, by using an alloy having a low equilibrium hydrogen pressure as the hydrogen storage alloy (A) in this way, the hydrogen storage alloy (B) is superior in other performance without much consideration of storage performance at the end of charging. Since a thing can be used, the selection range of the said hydrogen storage alloy (B) spreads.

  In the present invention, the content ratio of the hydrogen storage alloy (A) and the hydrogen storage alloy (B) in the negative electrode is the content of the hydrogen storage alloy (A) and the hydrogen storage alloy (B) in the negative electrode. The ratio of the content of the hydrogen storage alloy (A) to the total is adjusted to be 30 to 70% by mass. When the content ratio of the hydrogen storage alloy (A) is within this range, a nickel metal hydride storage battery having excellent recovery performance after long-term storage can be obtained. In view of cost, the content ratio of the hydrogen storage alloy (A) is more preferably 50% by mass or less.

  The method for producing the hydrogen storage alloy (A) and the hydrogen storage alloy (B) is not particularly limited, and examples thereof include a melt spinning method, an arc melting method, a casting method, a gas atomizing method, and the like. By using these, the hydrogen storage alloy (A) and the hydrogen storage alloy (B) can be produced.

  The hydrogen storage alloy (A) and the hydrogen storage alloy (B) are preferably blended in the negative electrode in a powdered state. At this time, the average particle diameter (D50) of the hydrogen storage alloy (A) is equal to or greater than the average particle diameter (D50) of the hydrogen storage alloy (B) (average particle diameter (D50) of the hydrogen storage alloy (B) ≦ The average particle diameter (D50) of the hydrogen storage alloy (A) is preferable, the average particle diameter (D50) of the hydrogen storage alloy (B) ≦ 45 μm ≦ the average particle diameter of the hydrogen storage alloy (A) ( D50) is more preferable. From the viewpoint of durability of the negative electrode, it is preferable that the alloy has a larger particle size (smaller specific surface area). However, when the present inventors have studied, the average particle size of the hydrogen storage alloy (A) (D50) ) Is equal to or larger than the average particle diameter (D50) of the hydrogen storage alloy (B), it has been found that sufficient durability is imparted to the negative electrode.

  The negative electrode may contain a conductive agent, a binder (including a thickener), and the like in addition to the hydrogen storage alloy (A) and the hydrogen storage alloy (B).

  Examples of the conductive agent include natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker, carbon fiber, vapor-grown carbon, etc. Examples thereof include metal-based conductive agents; metal-based conductive agents composed of powders or fibers of metals such as nickel, cobalt, copper, etc .; These electrically conductive agents may be used independently and 2 or more types may be used together. Moreover, you may contain rare earth oxides, such as an yttrium oxide, as a corrosion inhibitor.

  The blending amount of the conductive agent is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 10 parts by mass with respect to a total of 100 parts by mass of the hydrogen storage alloy (A) and the hydrogen storage alloy (B). 2 to 5 parts by mass. When the blending amount of the conductive agent is less than 0.1 parts by mass, it is difficult to obtain sufficient conductivity. On the other hand, when the blending amount of the conductive agent exceeds 10 parts by mass, the effect of improving the discharge capacity is not good. May be sufficient.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyolefin resins such as polyethylene and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), and fluorine rubber. , Polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, xanthan gum and the like. These binders may be used independently and 2 or more types may be used together.

  The amount of the binder is preferably 0.1 to 0.5 parts by mass, more preferably 100 parts by mass in total of the hydrogen storage alloy (A) and the hydrogen storage alloy (B). Is 0.1 to 0.3 parts by mass. When the blending amount of the binder is less than 0.1 parts by mass, sufficient thickening is difficult to be obtained. On the other hand, when the blending amount of the binder exceeds 0.5 parts by mass, the performance of the electrode is improved. May fall.

  Examples of the positive electrode include an electrode in which a nickel hydroxide composite oxide obtained by mixing zinc hydroxide or cobalt hydroxide with nickel hydroxide as a main component is blended as a positive electrode active material. As the nickel hydroxide composite oxide, those uniformly dispersed by a coprecipitation method are preferably used.

The positive electrode preferably contains an additive for improving electrode performance in addition to the nickel hydroxide composite oxide. Examples of the additive include conductive modifiers such as cobalt hydroxide and cobalt oxide, and the nickel hydroxide composite oxide coated with cobalt hydroxide, and the nickel hydroxide composite oxide. Part of the product may be oxidized with oxygen or oxygen-containing gas, K ₂ S ₂ O ₈ , hypochlorous acid, or the like.

  As said additive, the compound containing rare earth elements, such as Y and Yb, and the substance which improves oxygen overvoltages, such as Ca compound, can also be used. Since some of rare earth elements such as Y and Yb are dissolved and disposed on the negative electrode surface, an effect of suppressing corrosion of the negative electrode active material can be expected.

  The positive electrode may further contain the above-described conductive agent, binder and the like, similarly to the negative electrode.

  Such a positive electrode and a negative electrode were obtained by kneading these with water or an organic solvent such as alcohol or toluene after adding the above-mentioned conductive agent, binder, or the like to each active material as necessary. The paste can be produced by applying it to a conductive support and drying it, followed by rolling.

  Examples of the conductive support include a steel plate and a plated steel plate obtained by plating a steel plate with a metal material such as nickel. Examples of the shape of the conductive support include a foam, a molded product of a fiber group, a three-dimensional base material subjected to unevenness processing, and a two-dimensional base material such as a punching plate. Of these conductive supports, for the positive electrode, a foam made of nickel having excellent corrosion resistance and oxidation resistance with respect to alkali and having a porous structure having a current collecting property is preferable. On the other hand, for a negative electrode, a punching plate obtained by applying nickel plating to an iron foil that is inexpensive and excellent in conductivity is preferable.

  The thickness of the conductive support is preferably 30 to 100 μm, more preferably 40 to 70 μm. When the thickness of the conductive support is less than 30 μm, the productivity may be reduced. On the other hand, when the thickness of the conductive support exceeds 100 μm, the discharge capacity may be insufficient. .

  When the conductive support is porous, the inner diameter is preferably 0.8 to 2 μm, more preferably 1 to 1.5 μm. If the inner diameter is less than 0.8 μm, the productivity may be lowered. On the other hand, if the inner diameter exceeds 2 μm, the holding performance of the hydrogen storage alloy may be insufficient.

  Examples of a method for applying each electrode paste to the conductive support include roller coating using an applicator roll and the like, screen coating, blade coating, spin coating, and per coating.

  Examples of the separator include a porous film and a nonwoven fabric made of a polyolefin resin such as polyethylene or polypropylene, acrylic, polyamide, or the like.

The basis weight of the separator is preferably 40 to 100 g / m ² . If the basis weight is less than 40 g / m ² , a short circuit or a decrease in self-discharge performance may occur. On the other hand, if the basis weight exceeds 100 g / m ² , the proportion of the separator per unit volume increases. Tend to go down. The separator preferably has an air permeability of 1 to 50 cm / sec. If the air permeability is less than 1 cm / sec, the internal pressure of the battery may be too high. On the other hand, if the air permeability exceeds 50 cm / sec, a short circuit or a decrease in self-discharge performance may occur. Furthermore, the average fiber diameter of the separator is preferably 1 to 20 μm. If the average fiber diameter is less than 1 μm, the strength of the separator may decrease, and the defect rate in the battery assembly process may increase. On the other hand, if the average fiber diameter exceeds 20 μm, the average fiber diameter may cause a short circuit or a decrease in self-discharge performance. Sometimes.

The separator is preferably subjected to a hydrophilic treatment on the fiber surface. Examples of the hydrophilization treatment include sulfonation treatment, corona treatment, fluorine gas treatment, and plasma treatment. Among them, the separator whose fiber surface has been sulfonated has a high ability to adsorb impurities such as NO ₃ ⁻ , NO ₂ ⁻ , NH ₃ ^{− and the} like, which cause a shuttle phenomenon, and an elution element from the negative electrode. The suppression effect is high and preferable.

  Examples of the alkaline electrolyte include alkaline aqueous solutions containing potassium hydroxide, sodium hydroxide, lithium hydroxide and the like. The said alkaline electrolyte may be used independently and 2 or more types may be used together.

  The concentration of the alkaline electrolyte is preferably a total ion concentration of 9.0 mol / L or less, more preferably 5.0 to 8.0 mol / L.

  Various additives may be added to the alkaline electrolyte in order to improve oxygen overvoltage at the positive electrode, improve corrosion resistance of the negative electrode, and improve self-discharge. Examples of such additives include oxides and hydroxides such as yttrium, ytterbium, erbium, calcium, and zinc. These additives may be used independently and 2 or more types may be used together.

  When the nickel-metal hydride storage battery according to the present invention is an open-type nickel-metal hydride storage battery, for example, the battery is sandwiched between a negative electrode and a positive electrode via a separator, and the electrodes are fixed so that a predetermined pressure is applied to these electrodes. It can be produced by injecting an alkaline electrolyte and assembling an open cell.

  On the other hand, when the nickel-metal hydride storage battery according to the present invention is a sealed nickel-metal hydride storage battery, the battery is injected with an alkaline electrolyte before or after the positive electrode, the separator, and the negative electrode are stacked, and sealed with an exterior material. Can be manufactured. Further, in a sealed nickel-metal hydride storage battery in which a power generation element in which a positive electrode and a negative electrode are stacked via a separator is wound, an alkaline electrolyte is injected into the power generation element before or after the power generation element is wound. Is preferred. The method of injecting the alkaline electrolyte is not particularly limited, and may be injected at normal pressure. For example, a vacuum impregnation method, a pressure impregnation method, a centrifugal impregnation method, or the like may be used. Moreover, as an exterior material of a sealed nickel-metal hydride storage battery, for example, a material made of iron, stainless steel, polyolefin resin, or the like plated with a metal material such as iron or nickel can be cited.

  The embodiment of the sealed nickel-metal hydride storage battery is not particularly limited. For example, a battery including a positive electrode such as a coin battery, a button battery, a square battery, and a flat battery, a negative electrode, and a single-layer or multi-layer separator, a roll And a cylindrical battery including a positive electrode, a negative electrode and a separator.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

A nickel-metal hydride storage battery was produced by the method described below.
<Production of hydrogen storage alloy>
The chemical composition is La _0.80 Ce _0.10 Pr _0.01 Nd _0.04 Y _0.05 Ni _3.80 Co _0.80 Mn _0.30 Al _0.25 and La _0.64 Pr _0.20 Mg _{0 .16} Ni _3.50 Al _0.15 Each of the raw material ingots was weighed into a crucible and placed in a crucible, and heated to 1500 ° C. using a high-frequency melting furnace in a reduced pressure argon gas atmosphere to dissolve the materials. . After melting, it was quenched by applying a melt spinning method to solidify the alloy.

Note that an alloy having a chemical composition of La _0.80 Ce _0.10 Pr _0.01 Nd _0.04 Y _0.05 Ni _3.80 Co _0.80 Mn _0.30 Al _0.25 is the hydrogen storage alloy ( B), an alloy having a chemical composition of La _0.64 Pr _0.20 Mg _0.16 Ni _3.50 Al _0.15 corresponds to the hydrogen storage alloy (A).

  Next, the obtained alloy was heat-treated at 1000 ° C. and 950 ° C. for 5 hours under a pressurized argon gas atmosphere, and then the obtained hydrogen storage alloy was pulverized to obtain an average particle size (D50). Were hydrogen storage alloy powders of 42 μm and 50 μm, respectively. The average particle diameter (D50) was measured using an MT3000 apparatus manufactured by Microtrack.

<Measurement of hydrogen equilibrium pressure>
Using the hydrogen storage alloy powder after pulverization, the equilibrium hydrogen pressure at 80 ° C. (discharge pressure at hydrogen storage amount H / M = 0.4) is used as a Siebelz PCT apparatus using a PCT characteristic measurement apparatus manufactured by Suzuki Shokan Co., Ltd. It was measured. The equilibrium hydrogen pressure is La _0.80 Ce _0.10 Pr _0.01 Nd _0.04 Y _0.05 Ni _3.80 Co _0.80 Mn _0.30 Al _0.25 alloy and La _0.64 Pr _{0 .20} Mg _0.16 Ni _3.50 Al _0.15 alloy with 0.14 MPa and 0.02 MPa, respectively.

<Preparation of sealed nickel-metal hydride storage battery negative electrode>
La _0.80 Ce _0.10 Pr _0.01 Nd _0.04 Y _0.05 Ni _3.80 Co _0.80 Mn _0.30 Al _0.25 alloy and La _0.64 obtained as described above. Pr _0.20 Mg _0.16 Ni _3.50 Al _0.15 alloy powders are mixed at mass ratios of 10: 0, 8: 2, 6: 4, 4: 6, 2: 8, and 0:10, respectively. Then, after being immersed in an 8M aqueous potassium hydroxide solution at 110 ° C. for 2 hours, washing with water was repeated until the pH reached 10. An aqueous solution in which a thickener (methylcellulose) is dissolved is added to 100 parts by mass of the powder after drying, and further 1 part by mass of a binder (styrene butadiene rubber) is added to form a paste, which is a perforated steel sheet having a thickness of 35 μm ( It was applied to both surfaces having an aperture ratio of 50% and dried, and then pressed to a thickness of 0.31 mm to obtain a negative electrode plate.

<Preparation of sealed nickel-metal hydride storage battery positive electrode>
Further, as the positive electrode active material, a nickel hydroxide surface containing 3% by mass of zinc and 0.6% by mass of cobalt in a solid solution state and coated with 6% by mass of cobalt hydroxide is used as an 18M sodium hydroxide solution. The product obtained by air oxidation treatment at 110 ° C. for 1 hour using was used. An aqueous solution in which a thickener (carboxymethylcellulose) is dissolved, an active material, and further 2% by mass of ytterbium oxide are mixed to prepare a paste, filled in a nickel foam substrate, dried, and then given a predetermined thickness. A positive electrode plate was formed by pressing to a thickness (0.77 mm).

<Production of sealed nickel-metal hydride storage battery>
The positive electrode and the negative electrode were wound on a spiral through a separator at a ratio such that the negative electrode capacity was 1.35 with respect to the positive electrode capacity 1 to form an electrode group, which was housed in a cylindrical metal case. Next, 1.95 mL of an electrolyte composed of 7M potassium hydroxide and 0.8M lithium hydroxide was injected and sealed with a metal lid provided with a safety valve to produce a 2400 mAh AA size nickel metal hydride storage battery. did. In addition, the capacity | capacitance of the positive electrode and the negative electrode was confirmed with the open battery using the reference electrode, respectively.

<Confirmation of negative electrode capacity>
As the positive electrode plate, a sintered nickel hydroxide electrode having a capacity three times the negative electrode capacity was used. A negative electrode was sandwiched between positive electrodes through a separator, these electrodes were fixed so that a pressure of 1 kgf was applied to these electrodes, and a 7M potassium hydroxide aqueous solution was injected to assemble an open cell. Then, at 20 ° C., charging for 15 hours at 0.1 ItA, resting for 1 hour, and repeating a charging / discharging cycle of discharging to −0.6 V against the Hg / HgO reference electrode at 0.2 ItA until the maximum capacity is reached. The number of cycles and the negative electrode capacity were determined.

<Confirmation of positive electrode capacity>
A hydrogen storage alloy electrode having a capacity three times the positive electrode capacity was used for the negative electrode plate. The positive electrode was sandwiched between the negative electrode through the separator, these electrodes were fixed so that a pressure of 1 kgf was applied to the electrodes, and a 7M potassium hydroxide aqueous solution was injected to assemble an open cell. And at 20 ° C., charging for 15 hours at 0.1 ItA, resting for 1 hour, charging / discharging cycle for discharging to 0 V with respect to the Hg / HgO reference electrode at 0.2 ItA, and the number of cycles until reaching the maximum capacity And the positive electrode capacity was determined.

<Initialization of sealed nickel-metal hydride storage battery>
All batteries were initialized by the following procedure. Charging was performed at 20 ° C. and 0.1 ItA for 15 hours, and then a cycle of discharging at 20 ° C. and 0.2 ItA until the final voltage reached 1 V was repeated three times. Thereafter, it was left at 40 ° C. for 2 days to form a chemical.

<End-of-life storage test for sealed nickel-metal hydride batteries>
First, charging was carried out at 20 ° C. and 0.1 ItA for 15 hours, then rested for 1 hour, and discharged at 20 ° C. and 0.2 ItA until the final voltage reached 1 V to obtain the initial capacity. Thereafter, charging was performed at 20 ° C. and 0.1 ItA for 15 hours, and then stored at 45 ° C. or 60 ° C. for 14 days. After leaving at 20 ° C. for 3 hours, the battery was discharged at 20 ° C. and 0.2 ItA until the final voltage reached 1 V, and the remaining capacity was determined. Further, after charging for 15 hours at 20 ° C. and 0.1 ItA, the cycle was rested for 1 hour and then discharged at 20 ° C. and 0.2 ItA until the final voltage reached 1 V, and the recovery capacity was determined by repeating three cycles. . Furthermore, the remaining capacity retention rate (%) and the recovery capacity retention rate (%) were determined according to the following formulas.

Remaining capacity maintenance ratio (%) = remaining capacity / initial capacity × 100
Recovery capacity retention rate (%) = Recovery capacity / initial capacity × 100

The obtained results are shown in Table 1 below. In Table 1, “hydrogen storage alloy (A)” means La _0.64 Pr _0.20 Mg _0.16 Ni _3.50 Al _0.15 alloy.

As shown in Table 1, as the ratio of La _0.64 Pr _0.20 Mg _0.16 Ni _3.50 Al _0.15 alloy increased, the remaining capacity retention ratio increased, but the recovery capacity retention ratio was somewhat Declined.

<End-of-discharge storage test for sealed nickel-metal hydride batteries>
First, charging was carried out at 20 ° C. and 0.1 ItA for 15 hours, then rested for 1 hour, and discharged at 20 ° C. and 0.2 ItA until the final voltage reached 1 V to obtain the initial capacity. Thereafter, it was stored at 45 ° C. for 112 days. After leaving at 20 ° C for 3 hours, charging was performed at 20 ° C and 0.1 ItA for 15 hours, then resting for 1 hour, and discharging at 20 ° C and 0.2 ItA until the final voltage became 1 V. 3 cycles Repeatedly, the recovery capacity was determined. The recovery capacity retention rate (%) was determined from the recovery capacity obtained in the same manner as described above. The obtained results are shown in Table 2 below. In Table 2, “hydrogen storage alloy (A)” means La _0.64 Pr _0.20 Mg _0.16 Ni _3.50 Al _0.15 alloy.

As shown in Table 2, when the ratio of La _0.64 Pr _0.20 Mg _0.16 Ni _3.50 Al _0.15 alloy is 100% by mass, the recovery capacity retention rate at the third cycle is 96.1%. Met. The decrease in the recovery capacity with the number of cycles is considered to be due to the negative electrode (deterioration of negative electrode capacity). When the ratio of La _0.64 Pr _0.20 Mg _0.16 Ni _3.50 Al _0.15 alloy was 20% by mass, the recovery capacity retention rate was 96%. This is a large proportion of the AB ₅ type alloy La _0.80 Ce _0.10 Pr _0.01 Nd _0.04 Y _0.05 Ni _3.80 Co _0.80 Mn _0.30 Al _0.25 alloy. For this reason, it is presumed that self-discharge due to a minute short circuit occurred. And when the ratio of La _0.64 Pr _0.20 Mg _0.16 Ni _3.50 Al _0.15 alloy is 40% by mass and 60% by mass, a high recovery capacity retention rate is obtained, and excellent long-term Storage performance was expressed.

Claims (3)

A nickel-metal hydride storage battery comprising a negative electrode containing a rare earth-Mg-Ni hydrogen storage alloy (A) and a rare earth-Ni hydrogen storage alloy (B),
Of the rare earth-Mg-Ni hydrogen storage alloy (A) with respect to the total content of the rare earth-Mg-Ni hydrogen storage alloy (A) and the rare earth-Ni system hydrogen storage alloy (B) in the negative electrode. the ratio of the content, Ri 30-70% by mass,
The rare earth-Mg—Ni-based hydrogen storage alloy (A) has an equilibrium hydrogen pressure at 80 ° C. (a release pressure at a hydrogen storage amount H / M = 0.4) of 0.05 MPa or less,
A nickel-metal hydride storage battery in which the rare earth-Ni-based hydrogen storage alloy (B) has an equilibrium hydrogen pressure at 80 ° C. (a release pressure at a hydrogen storage amount H / M = 0.4) of 0.1 MPa or more.   2. The nickel hydride according to claim 1, wherein an average particle diameter (D50) of the rare earth-Mg—Ni-based hydrogen storage alloy (A) is equal to or greater than an average particle diameter (D50) of the rare-earth-Ni-based hydrogen storage alloy (B). Storage battery. The nickel-metal hydride storage battery according to claim 1 or 2, wherein the rare earth-Mg-Ni hydrogen storage alloy (A) and the rare earth-Ni hydrogen storage alloy (B) contain aluminum.