JP5217826B2 - 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. As a substitute for the primary battery, the battery is widely used, and the demand for the battery is expanding dramatically.

  By the way, this type of nickel metal hydride storage battery includes a nickel electrode containing a positive electrode active material mainly composed of nickel hydroxide, a negative electrode mainly composed of a hydrogen storage alloy, a separator, and an alkaline electrolyte. Is. Among these battery constituent materials, the hydrogen storage alloy, which is the main material of the negative electrode, has a great influence on the performance of nickel-metal hydride storage batteries such as discharge capacity and cycle characteristics. Various hydrogen storage alloys have been studied in the past. Has been.

As the hydrogen storage alloy, a rare earth-Mg-Ni alloy such as a LaCaMgNi ₉ alloy having a PuNi ₃ type crystal structure (Patent Document 1) is known, and by using the alloy as a negative electrode of a nickel metal hydride storage battery, It has been reported that a discharge capacity exceeding that of an AB ₅ type rare earth-Ni alloy having a CaCu ₅ type crystal structure can be obtained.

JP-A-11-217643

  However, in a nickel-metal hydride storage battery using a conventional rare earth-Mg-Ni alloy as the negative electrode active material, the initial discharge capacity shows a relatively good value, but the discharge capacity gradually increases by repeating charging and discharging. There was a problem that it deteriorated, that is, a problem that cycle life characteristics were poor.

  In addition, in order to improve the cycle life characteristics of a nickel metal hydride storage battery using a rare earth-Mg—Ni-based alloy as an active material for a negative electrode, the following Patent Document 2 contains an additive powder made of metallic zinc or a zinc compound in the negative electrode A method is also disclosed.

JP 2006-236915 A

  However, even with the method described in Patent Document 2, it has been difficult to sufficiently improve the cycle life.

  SUMMARY OF THE INVENTION The present invention provides a nickel-metal hydride storage battery using a rare earth-Mg-Ni-based alloy as an active material for a negative electrode, and having improved cycle life characteristics. For the purpose.

In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, different crystal structures such as a crystal phase having a Pr ₅ Co ₁₉ type crystal structure and a crystal phase having a Ce ₂ Ni ₇ type crystal structure have been obtained. By using a rare earth-Mg-Ni-based hydrogen storage alloy formed by laminating a plurality of crystalline phases as a negative electrode and forming a nickel-metal hydride storage battery using an alkaline electrolyte containing zinc ions and sodium ions, The present inventors have found that a nickel metal hydride storage battery having improved life characteristics can be provided, and have completed the present invention.

That is, the present invention relates to a negative electrode comprising a rare earth-Mg—Ni-based hydrogen storage alloy in which two or more crystal phases having different crystal structures are laminated in the c-axis direction of the crystal structure, and zinc ions . And an alkaline electrolyte containing 0.1 mol / liter or more and 1.0 mol / liter or less and sodium ion of 3.0 mol / liter or more and 6.0 mol / liter or less .

  Furthermore, the present invention provides the nickel-metal hydride storage battery, wherein the alkaline electrolyte has a potassium ion concentration and a lithium ion concentration of less than 2.0 mol / liter, respectively.

According to the nickel metal hydride storage battery of the present invention, by using a hydrogen storage alloy in which two or more crystal phases having different crystal structures are stacked in the c-axis direction of the crystal structure as a negative electrode, charging and discharging can be performed. The distortion of the crystal phase caused by the storage and release of hydrogen at the time is relaxed, and the deterioration of the electrode is suppressed. In addition, by using an alkaline electrolyte containing zinc ions and sodium ions, oxidative deterioration of the hydrogen storage alloy by the alkaline electrolyte is prevented.
As described above, according to the present invention, both the deterioration of the electrode due to the distortion of the alloy due to charging and discharging and the oxidative deterioration of the electrode due to the alkaline electrolyte are prevented. The hydrogen storage battery has extremely excellent cycle life characteristics.
Furthermore, the degree of the effect of preventing the oxidative deterioration of the hydrogen storage alloy obtained by including sodium ions in the alkaline electrolyte is remarkably superior to that when other alloys are used. . Furthermore, this effect becomes even more excellent when zinc ions are included together with sodium ions, and the level of improvement exceeds the effect obtained when zinc ions are added alone. Moreover, the synergistic effect is a phenomenon observed only in the case of the hydrogen storage alloy having a configuration in which a plurality of crystal phases are stacked in the c-axis direction. Under these circumstances, the cycle life performance obtained by the present invention is remarkably excellent and far exceeds the level that can be expected from the prior art.

  A nickel-metal hydride storage battery according to the present invention includes a negative electrode including a rare earth-Mg-Ni-based hydrogen storage alloy in which a plurality of crystal phases having different crystal structures are laminated, and an alkaline electrolyte including zinc ions and sodium ions. It is equipped with.

As described above, the hydrogen storage alloy included in the negative electrode is a rare earth-Mg—Ni-based hydrogen storage alloy in which two or more crystal phases having different crystal structures are laminated in the c-axis direction of the crystal structure. It is.
Examples of the crystal phase include a crystal phase composed of a rhombohedral La ₅ MgNi ₂₄ type crystal structure (hereinafter also simply referred to as a La ₅ MgNi ₂₄ phase), and a crystal phase composed of a hexagonal Pr ₅ Co ₁₉ type crystal structure (hereinafter simply referred to as a simple phase). Pr ₅ Co ₁₉ phase), crystal phase composed of rhombohedral Ce ₅ Co ₁₉ type crystal structure (hereinafter also simply referred to as Ce ₅ Co ₁₉ phase), crystal phase composed of hexagonal Ce ₂ Ni ₇ type crystal structure (Hereinafter also simply referred to as Ce ₂ Ni ₇ phase), crystal phase composed of rhombohedral Gd ₂ Co ₇ type crystal structure (hereinafter also simply referred to as Gd ₂ Co ₇ phase), hexagonal CaCu ₅ type crystal structure Crystal phase (hereinafter also simply referred to as CaCu ₅ phase), crystal phase consisting of cubic AuBe ₅ type crystal structure (hereinafter also simply referred to as AuBe ₅ phase) crystal phase consisting of rhombohedral PuNi ₃ type crystal structure (hereinafter simply referred to as simply “AuBe ₅ phase”) PuNi _3-phase also called), and the like ani Rukoto can.
Among these, a hydrogen storage alloy formed by laminating two or more selected from the group consisting of La ₅ MgNi ₂₄ phase, Pr ₅ Co ₁₉ phase, Ce ₅ Co ₁₉ phase, and Ce ₂ Ni ₇ phase is preferably used. . The hydrogen storage alloy formed by laminating these crystal phases has excellent characteristics that the difference in expansion and contraction between the crystal phases is small, so that distortion is not easily generated, and deterioration is not easily caused by repeated storage and release of hydrogen. Have.

Here, the La ₅ MgNi ₂₄ type crystal structure is a crystal structure in which _four AB ₅ units are inserted between A ₂ B ₄ units, and the Pr ₅ Co ₁₉ type crystal structure is A ₂ B It is a crystal structure in which 3 units of AB ₅ units are inserted between ₄ units, and Ce ₅ Co ₁₉ type crystal structure is that 3 units of AB ₅ units are inserted between A ₂ B ₄ units. It is a crystal structure, and the Ce ₂ Ni ₇ type crystal structure is a crystal structure in which _two AB ₅ units are inserted between A ₂ B ₄ units. What is the Gd ₂ Co ₇ type crystal structure? , ₂ units of AB ₅ units are inserted between A ₂ B ₄ units, and the AuBe ₅ type crystal structure is a crystal structure composed of only A ₂ B ₄ units.

The A ₂ B ₄ unit is a structural unit having a hexagonal MgZn ₂ type crystal structure (C14 structure) or a hexagonal MgCu ₂ type crystal structure (C15 structure), and the AB ₅ unit is a hexagonal CaCu ₅ unit. It is a structural unit with a type crystal structure.
A represents any element selected from the group consisting of rare earth elements and Mg, and B represents any element selected from the group consisting of transition metal elements and Al.

  The order of lamination of the crystal phases is not particularly limited, and a combination of specific crystal phases may be such that the crystal phases are laminated with periodicity, and each crystal phase is randomly and periodically laminated. It may be.

The content of each crystal phase is not particularly limited, but the content of the crystal phase having the La ₅ MgNi ₂₄ type crystal structure is 0 to 50% by mass, and the Pr ₅ Co ₁₉ type crystal structure. The content of the crystal phase having _{3 to} 80% by mass, the content of the crystal phase having the Ce ₅ Co ₁₉ type crystal structure is 15 to 80% by mass, and the content of the crystal phase having the Ce ₂ Ni ₇ type crystal structure The rate is preferably 0 to 65% by mass.

  The crystal phase having each crystal structure can be identified by, for example, performing X-ray diffraction measurement on the pulverized alloy powder and analyzing the obtained X-ray diffraction pattern by the Rietveld method. .

A schematic diagram of an embodiment of the hydrogen storage alloy is shown in FIG. As shown in FIG. 1, the hydrogen-absorbing alloy as one embodiment, a CaCu ₅ phase, two and Pr ₅ Co ₁₉ phase adjacent the CaCu ₅ phase, two adjacent to the Pr ₅ Co ₁₉ phase The Ce ₂ Ni ₇ phase is laminated in the c-axis direction of the crystal structure.

It can be confirmed by observing the lattice image of the alloy using TEM that two or more crystal phases having different crystal structures are laminated in the c-axis direction of the crystal structure. An example of a lattice image of the first hydrogen storage alloy according to the present invention is shown in FIGS.
According to these figures, AB ₅ hydrogen storage alloy, a crystalline phase sequence AB ₅ unit is inserted 3 units worth between A ₂ B ₄ units are repeated, between A ₂ B ₄ units It is shown that the crystal phase in which the arrangement in which four units are inserted is repeated is laminated in the c-axis direction. The former crystal phase is a crystal phase composed of a Ce ₅ Co ₁₉ type crystal structure, and the latter is a crystal phase composed of a LaMgNi ₂₄ type crystal structure. Thus, by observing the lattice image by TEM, it is possible to confirm that the two or more crystal phases having different crystal structures are laminated in the c-axis direction, which is a constituent element of the present invention. it can.

As described above, the hydrogen storage alloy constituting the negative electrode in the present invention is formed by stacking two or more crystal phases having different crystal structures in the c-axis direction of the crystal structure. The distortion of the crystal phase at the time of occlusion is relaxed by the other adjacent crystal phase. Therefore, the negative electrode comprising the hydrogen storage alloy has an effect that the alloy is less likely to be pulverized even if hydrogen storage and release are repeated by charging and discharging, and deterioration is unlikely to proceed.
Further, since the hydrogen storage alloy is a rare earth-Mg-Ni based hydrogen storage alloy, there is an effect that the discharge capacity is large.

The rare earth-Mg—Ni-based hydrogen storage alloy according to the present invention contains a rare earth element, magnesium and nickel, and the ratio of the content of the B side element to the content of the A side element (B / A ratio. In the formula, the value represented by “c / (a + b)” is 3 or more and less than 5, among which the composition is represented by the general formula R1 _a R2 _b R3 _c (where R1 is a rare earth element including Y). One or more elements selected from the group consisting of R2 is one or more elements selected from the group consisting of Mg, Ca, Sr and Ba, R3 is Ni, Co, Mn, Al, One or more elements selected from the group consisting of Cr, Fe, Cu, Zn, Si, Sn, V, Nb, Ta, Ti, Zr and Hf, 10 ≦ a ≦ 30, 1 ≦ b ≦ 10, 65 ≦ c ≦ 90, satisfying a + b + c = 100) What is represented by these can be used conveniently.
In particular, from the viewpoint of setting the CaCu ₅ phase content to 15% by mass or less, R2 is mainly composed of Mg, R3 is mainly composed of Ni, and components other than Ni and Co are 5 atomic% or less. Furthermore, it is preferable that 3.0 ≦ c / (a + b) ≦ 4.0.

Further, the content of the cobalt (Co) element is preferably 2.0 atomic% or less, more preferably 1.0 atomic% or less, and in particular, substantially free of Co element (that is, More preferably, the content is 0.1 atomic% or less.
Co element was conventionally added to enhance the corrosion resistance of the hydrogen storage alloy with respect to the alkaline electrolyte, but in the nickel metal hydride storage battery according to the present invention, the predetermined hydrogen storage alloy and the alkaline electrolyte were provided. Thus, even when the content of the Co element is small, the corrosion resistance of the hydrogen storage alloy with respect to the alkaline electrolyte can be improved.
In addition, by limiting the content of the Co element to the above range, there is an effect that the recoverability when the charge / discharge of the nickel-metal hydride storage battery is repeated or left for a long time is remarkably improved.

The hydrogen storage alloy which comprises a negative electrode can be obtained with the following manufacturing methods.
That is, the method for producing a hydrogen storage alloy as one embodiment includes a melting step of melting an alloy raw material blended to have a predetermined composition ratio, a cooling step of cooling and solidifying the molten alloy raw material, And an annealing step of annealing the alloy in a temperature range of 860 to 1000 ° C. under an inert gas atmosphere in a pressurized state.

More specifically, first, a predetermined amount of raw material ingot (alloy raw material) is weighed based on the chemical composition of the target hydrogen storage alloy.
In the melting step, the alloy raw material is put in a crucible and heated to 1200 to 1600 ° C., for example, in an inert gas atmosphere or in a vacuum to melt the alloy raw material.

  In the cooling step, the molten alloy material is cooled and solidified. The cooling in this step is preferably rapid cooling. The rapid cooling has the effect of miniaturizing and homogenizing the alloy composition. In particular, such an effect is easily obtained when the cooling rate is 1000 K / second or more.

  The alloy raw material melted in the cooling step can be rapidly cooled by a melt spinning method or a gas atomizing method, such as a melt spinning method with a cooling rate of 100,000 K / second or more, a gas atomizing method with a cooling rate of about 10,000 K / second, or the like. It can be used suitably.

In the annealing step, heating is performed at 860 to 1000 ° C. using, for example, an electric furnace in a pressurized state under an inert gas atmosphere. As a pressurizing condition, 0.2 to 1.0 MPa (gauge pressure) is preferable. Moreover, it is preferable that the processing time in this annealing process shall be 3 to 50 hours.
The distortion of the crystal lattice is removed by such an annealing process, and the hydrogen storage alloy that has undergone the annealing process finally becomes a hydrogen storage alloy in which two or more crystal phases having different crystal structures are laminated.

The negative electrode constituting the nickel-metal hydride storage battery of the present invention includes the hydrogen storage alloy obtained as described above as a hydrogen storage medium. When the hydrogen storage alloy is used for an electrode as a hydrogen storage medium, the hydrogen storage alloy is preferably used after being pulverized.
The hydrogen storage alloy may be pulverized at the time of electrode fabrication either before or after annealing, but since the surface area is increased by pulverization, it is desirable to pulverize after annealing from the viewpoint of preventing surface oxidation of the alloy. The pulverization is preferably performed in an inert atmosphere to prevent oxidation of the alloy surface.
For the pulverization, for example, mechanical pulverization or hydrogenation pulverization is used.

Next, the alkaline electrolyte that constitutes the nickel-metal hydride storage battery according to the present invention will be described.
As the alkaline electrolyte, one containing zinc ions and sodium ions is used. Both zinc ion and sodium ion in alkaline electrolyte act to suppress alloy degradation by preventing elution of constituent elements of the alloy, and to suppress alloy degradation by suppressing oxygen generation at the positive electrode. And have. Although the detailed mechanism is not clear about the former effect | action, it is thought that the function which prevents the elution of the structural element which a protective film has exists increases by the said ion existing. Here, the protective coating is a compound in which a metal hydroxide-containing compound adheres to the alloy surface in a layered manner, and has an action of preventing elution of constituent elements. On the other hand, the latter action is due to the action of zinc ions and sodium ions to increase the oxygen generation overvoltage of the positive electrode. Due to this action, the generation of oxygen during charging is suppressed, and as a result, deterioration due to the corrosion of the hydrogen storage alloy by oxygen is suppressed.

The zinc ion may be added directly to the electrolytic solution by dissolving metallic zinc or zinc compound in the electrolytic solution, and zinc zinc or zinc compound or the like may be added to any member constituting the nickel-metal hydride storage battery. It may be added and dissolved in an alkaline electrolyte.
The concentration of zinc ions in the alkaline electrolyte is preferably 0.05 mol / liter to 1.0 mol / liter, more preferably 0.1 mol / liter to 0.8 mol / liter, It is particularly preferable that the amount be 4 mol / liter or more and 0.6 mol / liter or less.

On the other hand, the sodium ion concentration in the alkaline electrolyte is preferably 3.0 mol / liter or more, more preferably 4.0 mol / liter or more, and preferably 7.0 mol / liter or less.
In particular, when the sodium ion concentration in the alkaline electrolyte is 4.0 mol / liter or more and 7.0 mol / liter or less, a synergistic effect between the zinc ion and the sodium ion is easily exhibited, and cycle life characteristics are obtained. The improvement is extremely remarkable.

  Moreover, it is preferable to use what has a potassium ion density | concentration and a lithium ion density | concentration of 2.0 mol / liter or less as this alkaline electrolyte, respectively, and it is preferable to use what is 0-1.0 mol / liter. More preferred. When the potassium ion concentration and the lithium ion concentration are in the above ranges, there is an effect that the corrosion of the hydrogen storage alloy is further suppressed.

In the alkaline electrolyte, the total ion concentration of the sodium ion, the potassium ion, and the lithium ion is preferably 8.0 mol / liter or less, and is 5.0 to 7.0 mol / liter. Is more preferable.
Furthermore, a sodium ion single system may be used from a viewpoint of suppressing alloy corrosion.

  By using the alkaline electrolyte having the above configuration, it is possible to prevent adverse effects such as oxidation of the alkaline electrolyte on the rare earth-Mg-Ni-based hydrogen storage alloy. There is an effect that the deterioration of the hydrogen storage alloy in the immersed state is suppressed and the cycle life characteristics are improved.

  In addition, various additives can be added to the electrolytic solution in order to improve the corrosion resistance to the alloy, improve the overvoltage at the positive electrode, improve the corrosion resistance of the negative electrode, and improve self-discharge. As the additive, oxides such as yttrium, ytterbium, erbium, and calcium, hydroxides, and the like can be used singly or in combination.

On the other hand, the positive electrode of the nickel metal hydride storage battery is not particularly limited, but generally a nickel hydroxide composite oxide mainly composed of nickel hydroxide and mixed with zinc hydroxide or cobalt hydroxide. A positive electrode including a positive electrode active material can be preferably used, and a positive electrode including the nickel hydroxide composite oxide uniformly dispersed by a coprecipitation method can be more preferably used.
As additives other than the nickel hydroxide composite oxide, cobalt hydroxide, cobalt oxide and the like as a conductive modifier can be used, and the nickel hydroxide composite oxide is coated with cobalt hydroxide. A part of these nickel hydroxide composite oxides oxidized using oxygen or oxygen-containing gas, or a chemical such as K ₂ S ₂ O ₈ or hypochlorous acid can be used.
In addition, as the additive, as a substance for improving the oxygen overvoltage, a rare earth element compound such as Y or Yb or a Ca compound can 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 and the negative electrode may contain a conductive agent, a binder, a thickener, and the like as other components in addition to the main components as described above.
The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect battery performance. Usually, natural graphite (such as scale-like graphite, scale-like graphite, earth-like graphite), artificial graphite, carbon black, acetylene black, A conductive material such as ketjen black, carbon whisker, carbon fiber, vapor-grown carbon, metal (nickel, gold, etc.) powder, metal fiber, or the like can be included as one or a mixture of two or more.
As a method of mixing them, a method that can be as uniform as possible is preferable. For example, a powder mixer such as a V-type mixer, an S-type mixer, a grinder, a ball mill, a planetary ball mill, or the like may be dry or wet. The method used in the above can be adopted.
As the binder, usually, thermoplastic resins such as polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorine rubber A polymer having rubber elasticity such as can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 0.1 to 3% by mass with respect to the total amount of the positive electrode or the negative electrode.
As said thickener, polysaccharides, such as carboxymethylcellulose, methylcellulose, xanthan gum, etc. can be normally used as 1 type, or 2 or more types of mixtures. The addition amount of the thickener is preferably 0.1 to 0.3% by mass with respect to the total amount of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode are prepared by mixing the active material, the conductive agent, and the binder in an organic solvent such as water, alcohol, and toluene, and then applying the obtained mixed liquid onto a current collector and drying it. Produced suitably. As the application method, for example, a method of applying an arbitrary thickness and an arbitrary shape using means such as roller coating such as an applicator roll, screen coating, blade coating, spin coating, and per coating is preferable. It is not limited to.

As the current collector, an electron conductor that does not adversely affect the exchange of electrons with the active material in the battery that is configured can be used without particular limitation. As the current collector, for example, from the viewpoint of reduction resistance and oxidation resistance, nickel or nickel-plated steel plate can be suitably used as a material, and as a shape, a foam, a molded body of a fiber group, A three-dimensional base material subjected to uneven processing or a two-dimensional base material such as a punching plate can be suitably used. Moreover, there is no limitation in particular also about the thickness of this electrical power collector, The thing of 5-700 micrometers is used suitably.
Among these current collectors, for the positive electrode, it is necessary to use a material having a porous structure, which is made of nickel having excellent corrosion resistance and oxidation resistance to alkali, and having a structure excellent in current collection. preferable. In addition, as a negative electrode, it is preferable to use a punching plate obtained by applying nickel plating for improving reduction resistance to an iron foil which is inexpensive and excellent in conductivity.
The punching diameter is preferably 2.0 mm or less, and the opening ratio is preferably 40% or more. This makes it possible to improve the adhesion between the negative electrode active material and the current collector even with a small amount of binder.

As a separator of a nickel metal hydride storage battery, it is preferable that a porous film or a nonwoven fabric exhibiting excellent rate characteristics be used alone or in combination of two or more. Examples of the material constituting the separator include polyolefin resins such as polyethylene and polypropylene, and nylon.
The basis weight of the separator is preferably 40 g / m ² to 100 g / m ² . If it is less than 40 g / m ² , the short circuit and the self-discharge performance may be deteriorated, and if it exceeds 100 g / m ² , the proportion of the separator per unit volume increases, so that the battery capacity tends to decrease. The air permeability of the separator is preferably 1 cm / sec to 50 cm / sec. If it is less than 1 cm / sec, the internal pressure of the battery may increase, and if it exceeds 50 cm / sec, the short circuit and the self-discharge performance may be deteriorated. The average fiber diameter of the separator is preferably 1 μm to 20 μm. When the thickness is less than 1 μm, the strength of the separator decreases, and the defect rate in the battery assembly process may increase. When the thickness exceeds 20 μm, the short circuit and the self-discharge performance may decrease.
The separator is preferably subjected to a hydrophilic treatment. For example, the surface of polyolefin resin fibers such as polypropylene may be subjected to sulfonation treatment, corona treatment, fluorine gas treatment, plasma treatment, or a mixture of those already subjected to these treatments. In particular, separators that have been sulfonated have a high ability to adsorb impurities such as NO ₃ ⁻ , NO ₂ ⁻ , and NH ₃ ⁻ that cause the shuttle phenomenon and elements eluted from the negative electrode. ,preferable.

  The sealed nickel-metal hydride storage battery as one embodiment of the present invention is preferably produced by injecting the electrolyte solution before or after laminating the positive electrode, the separator, and the negative electrode, and sealing with an exterior material. Is done. 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 the separator is wound, the electrolyte is injected into the power generation element before or after winding. preferable. As an injection method, it is possible to inject at normal pressure, but a vacuum impregnation method, a pressure impregnation method, and a centrifugal impregnation method can also be used. Examples of the material of the outer package of the sealed nickel-metal hydride storage battery include nickel-plated iron, stainless steel, polyolefin resin, and the like.

  The configuration of the sealed nickel-metal hydride storage battery is not particularly limited, and batteries including a positive electrode, a negative electrode, and a single-layer or multi-layer separator, such as a coin battery, a button battery, a square battery, a flat battery, Alternatively, a cylindrical battery having a roll-shaped positive electrode, a negative electrode, and a separator can be given.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

(Preparation of positive electrode)
An ammonium complex and an aqueous sodium hydroxide solution were added to an aqueous solution in which nickel sulfate, zinc sulfate and cobalt sulfate were dissolved at a predetermined ratio to form an ammine complex. While vigorously stirring the reaction system, caustic soda is further added dropwise, the pH of the reaction system is controlled to 10 to 13, and spherical high-density nickel hydroxide particles serving as a core layer base material are converted into nickel hydroxide: zinc hydroxide: cobalt hydroxide. = 93: 5: 2 The weight ratio was synthesized.
The high-density nickel hydroxide particles were put into an alkaline aqueous solution adjusted to pH 10 to 13 with caustic soda, and an aqueous solution containing cobalt sulfate and ammonia at predetermined concentrations was added dropwise while stirring the solution. During this time, an aqueous caustic soda solution was appropriately added dropwise to maintain the pH of the reaction bath in the range of 10-13. The pH was maintained in the range of 10 to 13 for about 1 hour, and a surface layer made of a mixed hydroxide containing Co was formed on the surface of the nickel hydroxide particles. The ratio of the surface layer of the mixed hydroxide was 4% by mass with respect to hydroxide core layer base material particles (hereinafter simply referred to as core layer).
Further, the nickel hydroxide particles having a surface layer made of the mixed hydroxide are mixed with a 30% by mass (10 mol / liter) aqueous sodium hydroxide solution, heated in air at 110 ° C., and then washed with water. Filtration and drying were performed. To the obtained active material particles, 0.2% by mass of a carboxymethyl cellulose (CMC) aqueous solution, 0.3% by mass of polytetrafluoroethylene (PTFE), and 2% by mass of Yb ₂ O ₃ are added to obtain the active material particles. : CMC solute: PTFE: Yb ₂ O ₃ = 97.5: 0.2: 0.3: 2.0% by mass (solid content ratio) paste was filled in a nickel porous body of 350 g / m. . Then, after drying at 80 degreeC, it pressed to predetermined thickness and it was set as the 2000 mAh nickel positive electrode plate.

(Preparation of negative electrode)
A predetermined amount of a raw material ingot (alloy raw material) shown in Table 1 was weighed and placed in a crucible, and heated to 1200 ° C. to 1600 ° C. using a high-frequency melting furnace in a reduced pressure argon gas atmosphere to melt the material. . After melting, a melt spinning method was applied and quenched at a cooling rate of 1000 K / second or more to solidify the alloy.
Next, the obtained alloy ingot was heated in an electric furnace at 930 ° C. for 5 hours in an argon gas atmosphere pressurized to 0.2 MPa (gauge pressure, the same applies hereinafter).
Each obtained hydrogen storage alloy was pulverized to an average particle size D50 = 50 μm, and the powder was subjected to X under the conditions of 40 kV, 100 mA (Cu tube) using an X-ray diffractometer (manufactured by BrukerAXS, product number M06XCE). A line diffraction test was performed. Furthermore, analysis by the Rietveld method (analysis software: Rietan 2000) was performed, and the generation ratio of the crystal phase was calculated. The results are shown in Table 1.
Next, the alloy powder, a styrene-butadiene copolymer (SBR) aqueous solution, and a methyl cellulose (MC) aqueous solution were mixed at a solid content mass ratio of 99.0: 0.8: 0.2 to form a paste, and a blade Using a coater, it was applied to a punched steel plate in which iron was nickel-plated, dried at 80 ° C., and then pressed to a predetermined thickness to obtain a negative electrode. The amount of active material (alloy amount) contained in the negative electrode was 8.5 g.

(Production of evaluation battery)
The negative electrode, a 100 μm-thick polypropylene non-woven separator subjected to a sulfonation treatment, and the positive electrode are combined and wound into a roll, and 1.97 cc of an alkaline electrolyte having the composition shown in Table 1 is injected and opened. An AA-type sealed nickel-metal hydride storage battery (capacity 2000 mAh) having a valve with a valve pressure of 3.0 MPa was produced.
(Battery conversion treatment)

  This battery was charged with 0.1 ItA (200 mA) for 12 hours, and then the operation of discharging to 0.2 V with 1 ItA was repeated twice at 20 ° C., then stored at 40 ° C. for 48 hours, and formed (activated). .

(Measurement of cycle life characteristics)
The charging under the conditions of 0.5 It (A) and -dV = 5 mV, the pause for 30 minutes and the discharge until the end voltage becomes 1 V at 1 It (A) (20 ° C.) are repeated, and the discharge capacity is the initial capacity. The cycle number when 50% was reached was defined as the cycle life. The results are shown in Table 2.

(Measurement of self-discharge characteristics)
Charging / discharging was repeated 3 cycles in a constant temperature bath of 20 ° C. under a charging condition of 160% at 0.1 ItA and a discharging condition of 1 V at 0.2 ItA. Furthermore, after 160% charge at 0.1 ItA, it was stored in a 45 ° C. constant temperature bath for 2 weeks. Then, after storing for 3 hours in a constant temperature bath at 20 ° C., the battery was discharged at 0.2 ItA under the condition that the final voltage was 1 V, and the remaining capacity was measured. And the capacity | capacitance maintenance factor was computed based on the following formula.
Capacity maintenance rate (%) = remaining capacity / final discharge capacity before storage × 100
The results are shown in Table 2.

(Specific surface area measurement after 100 cycles)
The specific surface area of the hydrogen storage alloy powder was measured using a flow method BET single-point specific surface area measuring device (manufactured by Quantachrome, Monosorb). As the hydrogen storage alloy powder, the negative electrode taken out from the sealed nickel-metal hydride storage battery was washed with water and dried, and then removed from the punched steel sheet. The results are shown in Table 2.

From the above results, first, focusing on Comparative Example 1 and Comparative Example 2 which are rare earth-Mg-Ni-based alloys and c-axis stacked hydrogen storage alloys, the influence of Na ions in the electrolyte on the cycle life Was evaluated. As a result, as is apparent from the graph shown in FIG. 4, the cycle life of Comparative Example 1 containing no Na ions in the electrolyte is 310, whereas the cycle life of Comparative Example 2 containing Na ions is 360, indicating that 50 cycles have been improved.
On the other hand, in the case of a hydrogen storage alloy that is a rare earth-Mg—Ni alloy and is a c-axis laminated type but is not a c-axis laminated type, Na ions are contained in the electrolyte as is apparent from FIG. In contrast, the cycle life of Comparative Example 6 is 280, whereas the cycle life of Comparative Example 5 containing Na ions is 300, indicating that only 20 cycles of improvement have been achieved. Similarly, as is clear from FIG. 6, the cycle life of the comparative example 10 containing no Na ions and the containing comparative example 11 is the same for the AB ₅ type hydrogen storage alloy. It turns out that there is almost no improvement.
From the above, the degree of the effect of preventing the oxidative deterioration obtained by including sodium ions in the alkaline electrolyte is determined by using other alloys in the present invention having the c-axis stacked hydrogen storage alloy. It is clear that it is significantly superior to that of the case. Such a significant improvement is thought to be due to the enhancement of the function of the protective film of sodium ions. The reason is presumed that a new mechanism that has not been recognized so far worked when the alloy has a special structure of the c-axis laminated type. As this mechanism, for example, the compatibility between the protective film and the alloy surface is improved by including sodium ions.

Next, paying attention to Example 5 and Comparative Examples 1 to 3, which are rare earth-Mg-Ni alloys and c-axis stacked hydrogen storage alloys, the cycle life of Zn ions and Na ions in the electrolyte solution The effect on properties was evaluated. As a result, as is apparent from the graph shown in FIG. 4, the cycle life of Comparative Example 1 in which neither the Zn ion nor the Na ion is included in the electrolytic solution is 310, whereas the Zn ion in the electrolytic solution is The cycle life of Example 5 containing both Na ions is 435, and it can be seen that an improvement of 125 cycles is achieved.
On the other hand, the cycle life of Comparative Example 2 containing Na ions in the electrolytic solution is 360, and the cycle life of Comparative Example 3 containing Zn ions in the electrolytic solution is 370, compared with Comparative Example 1, , 50 cycles and 60 cycles have been improved.
Thus, the effect (+125) in the case of adding both Zn ions and Na ions greatly exceeds the sum (+110) of the effects (+60, +50) in the case of adding these individually, and the rare earth-Mg It is recognized that a synergistic effect of Zn ions and Na ions is exerted in the Ni-based c-axis stacked hydrogen storage alloy.
This synergistic effect is considered to be the result of a specific improvement in the action of the protective coating on the alloy surface. Such a specific improvement is thought to be because the action of increasing the function of the protective coating of both ions is remarkably enhanced by the combination of zinc ions and sodium ions. In other words, it is considered that the presence of zinc ions in addition to sodium ions makes the above-described new mechanism extremely effective and provides a specific improvement. Although it is presumed, it is highly possible that the compatibility between the protective coating and the alloy surface is specifically improved by including both ions.

Next, focusing on Comparative Examples 5, 6, 7, and 8, which are rare earth-Mg—Ni-based and non-c-axis stacked hydrogen storage alloys, the same evaluation was performed. As a result, as apparent from the graph shown in FIG. 5, the cycle life of Comparative Example 6 in which neither the Zn ion nor the Na ion is included in the electrolytic solution is 280, whereas the Zn ion in the electrolytic solution is The cycle life of Comparative Example 7 containing both Na ions is 365, and it can be seen that 85 cycles have been improved.
However, the cycle life of Comparative Example 5 containing Na ions in the electrolytic solution is 300, and the cycle life of Comparative Example 8 containing Zn ions in the electrolytic solution is 340. Cycle, 60 cycles are improved.
Then, the effect (+85) when both Zn ions and Na ions are added is similar to the sum (+80) of the effects (+60, +20) when these ions are added individually, and is not a c-axis stacked type. In the rare earth-Mg-Ni-based hydrogen storage alloy, it is recognized that the synergistic effect of Zn ions and Na ions is not exhibited.

Furthermore, focusing on Comparative Examples 9 to 12, which are AB ₅ type hydrogen storage alloys, the same evaluation was performed. As a result, as is apparent from the graph shown in FIG. 6, the cycle life of Comparative Example 10 in which neither the Zn ion nor the Na ion is included in the electrolytic solution is 300, and the Zn ion and the Na ion are added to the electrolytic solution. It can be seen that the cycle life of Comparative Example 9 including both is 335, and an improvement of 35 cycles is achieved.
However, the cycle life of Comparative Example 11 containing Na ions in the electrolytic solution is 300 (± 0 cycle), and the cycle life of Comparative Example 12 containing Zn ions in the electrolytic solution is 330 (+30 cycles). The effect of adding both Na ions (+35) is similar to the sum of the effects of adding these individually (+30). In the AB ₅ type hydrogen storage alloy, Zn ions and Na ions are added. It is recognized that the synergistic effect is not exhibited.

Subsequently, the influence of the Na concentration in the electrolytic solution on the cycle life characteristics was evaluated. As is clear from the graph shown in FIG. 7, when a rare earth-Mg—Ni-based and c-axis stacked hydrogen storage alloy is used and Zn is contained in the electrolytic solution, Na in the electrolytic solution is used. It can be seen that the cycle life characteristics are significantly improved as the concentration increases.
More specifically, the effect of improving the cycle life characteristics becomes remarkable when the Na concentration is in the range of 3.0 mol / liter or more, and in particular, the effect of improving the cycle life characteristics is more excellent at 4.0 mol / liter or more. It is recognized that

The schematic diagram which showed one Embodiment of the hydrogen storage alloy. The TEM image which showed an example of the hydrogen storage alloy. The figure which expanded and showed a part of FIG. The graph which showed the influence which Zn ion and Na ion in electrolyte solution have on a cycle life characteristic in rare earth-Mg-Ni type alloy (c axis lamination type). The graph which showed the influence which Zn ion and Na ion in electrolyte solution have on cycle life characteristics in a rare earth-Mg-Ni-based alloy (single layer). In AB ₅ type alloy, graph and Zn ions and Na ions in the electrolyte, showed the effect on the cycle life characteristics. The graph which showed the influence which Na ion concentration in electrolyte solution has on cycle life characteristics in rare earth-Mg-Ni type alloy (c axis lamination type).

Claims (2)

A negative electrode comprising a rare earth-Mg-Ni-based hydrogen storage alloy in which two or more crystal phases having different crystal structures are laminated in the c-axis direction of the crystal structure; and zinc ions at 0.1 mol / liter or more A nickel-metal hydride storage battery comprising : 1.0 mol / liter or less and an alkaline electrolyte containing sodium ions of 3.0 mol / liter or more and 6.0 mol / liter or less . The nickel-metal hydride storage battery according to claim 1 , wherein the alkaline electrolyte has a potassium ion concentration and a lithium ion concentration of less than 2.0 mol / liter, respectively.

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