JP5415043B2 - Negative electrode for alkaline storage battery and alkaline storage battery - Google Patents

Description

  The present invention relates to an alkaline storage battery including a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline electrolyte, and an alkaline storage battery negative electrode used for the negative electrode of the alkaline storage battery, and in particular, Mg-Ni-rare earth hydrogen. When the negative electrode for an alkaline storage battery using a storage alloy is improved and the alkaline storage battery using the negative electrode for an alkaline storage battery is repeatedly charged and discharged, the hydrogen storage alloy is oxidized by the alkaline electrolyte or the inside of the battery This is characterized in that an increase in resistance is prevented and an alkaline storage battery excellent in charge / discharge cycle characteristics is obtained.

  Conventionally, nickel-cadmium storage batteries have been widely used as alkaline storage batteries, but in recent years they have a higher capacity than nickel-cadmium storage batteries and are superior in environmental safety because they do not use cadmium. Therefore, nickel-hydrogen storage batteries using a hydrogen storage alloy for the negative electrode have come to attract attention.

  In recent years, alkaline storage batteries made of such nickel / hydrogen storage batteries have come to be used in various portable devices and hybrid electric vehicles, and it is expected that the capacity of these alkaline storage batteries will be further increased. .

Here, in such an alkaline storage battery, as a hydrogen storage alloy used for the negative electrode, a rare earth-nickel hydrogen storage alloy having a CaCu ₅ type lattice crystal as a main phase or a Laves type AB ₂ lattice crystal is generally used. In general, a hydrogen storage alloy having a main phase of is used.

  However, each of the above hydrogen storage alloys does not necessarily have sufficient hydrogen storage capacity, and it has been difficult to further increase the capacity of the alkaline storage battery.

Therefore, in recent years, in order to improve the hydrogen storage capacity in the rare earth-nickel hydrogen storage alloy, as shown in Patent Document 1 and the like, the rare earth-nickel hydrogen storage alloy contains Mg or the like. Thus, it has been proposed to use a Mg—Ni-rare earth-based hydrogen storage alloy having a crystal structure such as Ce ₂ Ni ₇ type or CeNi ₃ type other than CaCu ₅ type.

  Here, the hydrogen storage alloy as described above is generally prone to cracking, and a new surface with high reactivity contributes to the discharge reaction. Therefore, discharge characteristics at low temperatures and discharge capacity at high rate discharge are relatively good. On the other hand, there is a problem that the corrosion resistance of the hydrogen storage alloy is deteriorated and the cycle life of the alkaline storage battery is greatly reduced.

  For this reason, conventionally, as disclosed in Patent Document 2, the composition of the Mg—Ni-rare earth-based hydrogen storage alloy as described above is improved to improve the oxidation resistance of the hydrogen storage alloy. What has been proposed.

  However, even when the composition of the Mg—Ni—rare earth-based hydrogen storage alloy is improved to improve the oxidation resistance of the hydrogen storage alloy, the hydrogen storage alloy powder is still alkaline. It was not possible to sufficiently prevent oxidation by the electrolytic solution or increase in the internal resistance of the battery, and the cycle life of the alkaline storage battery could not be sufficiently improved.

  Conventionally, as shown in Patent Document 2, a fluorine resin such as polytetrafluoroethylene is mixed with the negative electrode of the alkaline storage battery using the Mg—Ni-rare earth-based hydrogen storage alloy as described above. Improves the cycle life of alkaline storage batteries by suppressing the above-mentioned hydrogen storage alloy powder in the negative electrode from being atomized or oxidized when the alkaline electrolyte is prevented from penetrating into the negative electrode and charging and discharging are repeated. Some have been proposed.

However, even in an alkaline storage battery in which a fluororesin such as polytetrafluoroethylene is mixed in the negative electrode as described above to prevent the alkaline electrolyte from penetrating into the negative electrode, the hydrogen storage alloy powder is still in the alkaline state. It is difficult to sufficiently oxidize the electrolyte or raise the internal resistance of the battery, and it is difficult to sufficiently improve the cycle life of the alkaline storage battery.
JP 2002-69554 A JP 2004-221557 A JP 2005-190863 A

  An object of the present invention is to solve the above-mentioned problems in an alkaline storage battery using a hydrogen storage alloy as a negative electrode, and in particular, a fluorine resin is contained in a Mg—Ni-rare earth-based hydrogen storage alloy. In the alkaline storage battery using the negative electrode for alkaline storage battery, the above hydrogen storage alloy is sufficiently prevented from being oxidized by the alkaline electrolyte or the internal resistance of the battery is increased, and the cycle life of the alkaline storage battery is sufficiently increased. The problem is to improve.

In the negative electrode for an alkaline storage battery according to the present invention, in order to solve the above-described problems, the general formula Ln _1-x Mg _x Ni _yab Al _a M _b (where Ln is a rare earth element including Y, Zr and Ti). And at least one element selected from the group consisting of V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B. (It is one element and satisfies the conditions of 0.05 ≦ x ≦ 0.30, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 2.8 ≦ y ≦ 3.9.) And a tetrafluoroethylene-perfluorovinyl ether copolymer.

In addition, when the tetrafluoroethylene-perfluorovinyl ether copolymer is contained in the alkaline storage battery negative electrode, the tetrafluoroethylene-perfluorovinyl ether copolymer is provided on the surface of the negative electrode by coating or the like . Applying a perfluorovinyl ether copolymer - A alkaline electrolyte penetrates into the negative electrode in for this alkaline storage battery, in order to the hydrogen absorbing alloy is appropriately prevented from being oxidized by the alkaline electrolyte, tetrafluoroethylene Ru is provided on the surface of the negative electrode by such.

  Further, the negative electrode for an alkaline storage battery described above contains a styrene / butadiene copolymer as a binder in addition to the hydrogen storage alloy and the tetrafluoroethylene-perfluorovinyl ether copolymer. It is preferable to fix the tetrafluoroethylene-perfluorovinyl ether copolymer to the negative electrode for an alkaline storage battery by the copolymer.

  When the styrene / butadiene copolymer as a binder is contained in this way, the tetrafluoroethylene-perfluorovinyl ether copolymer is fixed to the negative electrode due to the adhesiveness of the styrene / butadiene copolymer. When the charging / discharging is repeated, even if the alkaline electrolyte moves in the battery, the effect of adding the tetrafluoroethylene-perfluorovinyl ether copolymer can be stably obtained.

  And in the alkaline storage battery in this invention, the above negative electrodes for alkaline storage batteries were used for the negative electrode.

As in the present invention, the general formula Ln _1-x Mg _x Ni _yab Al _a M _b (where Ln is at least one element selected from rare earth elements including Y, Zr and Ti, and M is It is at least one element selected from V, Nb, Ta, Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B, and 0.05 ≦ x ≦ 0 .30, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 2.8 ≦ y ≦ 3.9.)) For an alkaline storage battery negative electrode using a hydrogen storage alloy , tetrafluoroethylene - contain a perfluoro vinyl ether copolymer, tetrafluoroethylene - when Ru perfluoro vinyl ether copolymer is present on the surface of the anode, the tetrafluoroethylene - sufficient negative by perfluorovinyl ether copolymer Na Water repellency is imparted.

  As a result, in the alkaline storage battery using the negative electrode for alkaline storage battery as described above, the alkaline electrolyte is appropriately prevented from penetrating into the negative electrode, and the hydrogen storage alloy is oxidized by the alkaline electrolyte, It is sufficiently prevented that the alkaline electrolyte in the separator is reduced and the internal resistance of the battery is increased, and the cycle life of the alkaline storage battery is sufficiently improved.

  Here, the above-mentioned tetrafluoroethylene-perfluorovinyl ether copolymer (hereinafter abbreviated as PFA) and other fluororesins such as polytetrafluoroethylene (hereinafter abbreviated as PTFE) and tetrafluoroethylene-hexafluoro. When compared with a propylene copolymer (hereinafter abbreviated as FEP), these fluororesins themselves have substantially the same water repellency, but when an alkaline storage battery is produced using a negative electrode containing these fluororesins. , The water repellency of the negative electrode containing PFA is higher than the water repellency of the negative electrode containing PTFE and FEP, and the penetration of the alkaline electrolyte into the negative electrode is appropriately suppressed, and PTFE and FEP are contained. Compared to the case of using a negative electrode, the above hydrogen storage alloy is oxidized by an alkaline electrolyte or separated. The internal resistance of the battery alkaline electrolyte is decreased or increased is sufficiently prevented in the middle, so that the cycle life of the alkaline storage battery is sufficiently improved.

  Here, the water repellency as described above is generally determined by the physical surface state in addition to the water repellency characteristic of the material. If the material has the same water repellency, there are many fine irregularities. However, the water repellency is increased.

  Since the above PFA is more resistant to mechanical deformation than PTFE and FEP, when a force such as bending or rubbing is applied when a negative electrode or an alkaline storage battery is added by adding these fluororesins, the above PFA is used. The particles are less likely to be crushed than the PTFE particles and the FEP particles, and are in a state in which the unevenness is maintained. Thus, it is considered that the negative electrode containing PFA has higher water repellency than the negative electrode containing PTFE or FEP.

  In addition, as described above, PFA is resistant to mechanical deformation and is not easily crushed when a force such as bending or rubbing is applied to the negative electrode. However, the force as described above is concentrated on the bonding portion between the PFA and the hydrogen storage alloy. Easily peel off. Here, when the styrene / butadiene copolymer as a binder is contained as described above, the PFA can be firmly fixed to the negative electrode due to the rubber property and adhesiveness of the styrene / butadiene copolymer. .

  Hereinafter, the negative electrode for an alkaline storage battery according to an embodiment of the present invention and the alkaline storage battery using the negative electrode for an alkaline storage battery will be described, a comparative example will be given, and the alkaline storage battery using the negative electrode for an alkaline storage battery according to an embodiment of the present invention. , It is clarified that the hydrogen storage alloy is appropriately prevented from being oxidized by the alkaline electrolyte and the cycle life is improved. In addition, the negative electrode for alkaline storage batteries and alkaline storage battery in this invention are not limited to what was shown to the following Example, In the range which does not change the summary, it can implement suitably.

Example 1
In Example 1, when producing an alkaline storage battery, a negative electrode and a positive electrode produced as described below were used.

[Production of negative electrode]
In producing the negative electrode, Nd, Sm, Mg, Ni and Al are mixed so as to have a predetermined alloy composition, and this is melted in a high-frequency induction melting furnace in an argon gas atmosphere. After cooling, an ingot of hydrogen storage alloy was obtained.

Next, the hydrogen storage alloy ingot was heat treated in an inert atmosphere to be homogenized, and then the hydrogen storage alloy ingot was mechanically pulverized in an inert atmosphere and classified to obtain a mass integral of 50 %, A hydrogen storage alloy powder having an average particle size of 65 μm was obtained. Here, as a result of analyzing the composition of the hydrogen storage alloy thus obtained by high-frequency plasma spectroscopy (ICP), the composition was Nd _0.36 Sm _0.54 Mg _0.10 Ni _3.33 Al _0.17 .

  Then, 1 part by mass of styrene / butadiene copolymer rubber (SBR) as a binder, 0.2 part by mass of sodium polyacrylate, and 0. 2 parts by mass, 1 part by mass of ketjen black and 50 parts by mass of water were added, and these were kneaded in an environment of 25 ° C. to prepare a paste.

Next, the paste is uniformly applied to both surfaces of a conductive core made of punching metal, dried and pressed, and then a dispersion of tetrafluoroethylene-perfluorovinyl ether copolymer (PFA) is applied to the surface. Was applied so that the amount of PFA applied to the solid content was 0.4 mg / cm ² , dried, and cut into a predetermined size to produce a negative electrode.

  Then, 5 μl of pure water droplets were dropped on the surface of the negative electrode thus prepared, and the contact angle of the droplets in contact with the negative electrode surface was measured from the horizontal direction with a microscope. As a result, the contact angle was 151 degrees. It was. Note that the greater the contact angle, the higher the water repellency of the negative electrode surface.

[Production of positive electrode]
In preparing the positive electrode, nickel hydroxide powder containing 2.5% by mass of zinc and 1.0% by mass of cobalt was charged into a cobalt sulfate aqueous solution, and 1 mol of sodium hydroxide aqueous solution was added while stirring the powder. Was gradually added dropwise to cause the reaction to pH 11, and then the precipitate was filtered, washed with water, and dried under vacuum to obtain nickel hydroxide having a surface coated with 5% by weight of cobalt hydroxide. .

  Next, the nickel hydroxide thus coated with cobalt hydroxide was impregnated with a 25% by mass sodium hydroxide aqueous solution so as to have a mass ratio of 1:10. Then, this was washed with water and dried at 65 ° C. to obtain a positive electrode active material in which the nickel hydroxide surface was coated with sodium-containing higher cobalt oxide. In addition, the valence of cobalt in said cobalt oxide was a value exceeding 2 valences.

  Next, 95 parts by mass of this positive electrode active material, 3 parts by mass of zinc oxide, and 2 parts by mass of cobalt hydroxide were added to 50 parts by mass of a 0.2% by mass hydroxypropylcellulose aqueous solution. These were mixed to prepare a slurry.

Then, this slurry is filled in a nickel foam having a basis weight of about 600 g / m ² , a porosity of 95% and a thickness of about 2 mm, dried and rolled, and then cut to a predetermined size and non-baked. A positive electrode made of a sintered nickel electrode was produced. In addition, the density of the positive electrode active material in this positive electrode was about 2.9 g / cm ³ -void.

  And as a separator, the nonwoven fabric made from a polypropylene which carried out the fluorination process by the fluorination gas and the sulfurous acid gas and introduce | transduced the sulfone group is used, and KOH, NaOH, and LiOH are 15: 2: as an alkaline electrolyte. Using an alkaline electrolyte containing a mass ratio of 1 and having a specific gravity of 1.30, an alkaline storage battery having a cylindrical shape as shown in FIG. 1 and an AA size with a design capacity of 1500 mAh was produced.

  Here, in producing the alkaline storage battery, as shown in FIG. 1, the separator 3 is interposed between the positive electrode 1 and the negative electrode 2, and these are wound in a spiral shape in the battery can 4. The positive electrode 1 is connected to the positive electrode lid 6 via the positive electrode lead 5, and the negative electrode 2 is connected to the battery can 4 via the negative electrode lead 7. After injecting 2 g of liquid, the battery can 4 and the positive electrode lid 6 were sealed with an insulating packing 8 between them, and the battery can 4 and the positive electrode lid 6 were electrically separated by the insulating packing 8. Further, a closing plate 11 urged by a coil spring 10 is provided between the positive electrode cover 6 and the positive electrode external terminal 9 so as to close the gas discharge port 6a provided in the positive electrode cover 6, and the battery When the internal pressure of the battery rises abnormally, the coil spring 10 is compressed so that the gas inside the battery is released into the atmosphere.

(Comparative Example 1)
In Comparative Example 1, in the production of the negative electrode in Example 1 above, the dispersion of the PFA was not applied to the surface of the negative electrode, and the rest was the same as in Example 1 above. The alkaline storage battery of Example 1 was produced.

  In addition, 5 μl of pure water droplets were dropped on the surface of the negative electrode, and the contact angle of the droplets in contact with the negative electrode surface was measured with a microscope from the horizontal direction. As a result, the contact angle was 87 degrees.

(Comparative Example 2)
In Comparative Example 2, in the production of the negative electrode in Example 1 described above, instead of the above-mentioned PFA dispersion, polytetrafluoroethylene (PTFE) dispersion was used, and the solid PTFE coating amount was 0.4 mg. An alkaline storage battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the negative electrode was produced by coating the surface of the negative electrode so as to be / cm ² .

  In addition, 5 μl of pure water droplets were dropped on the surface of the negative electrode, and the contact angle of the droplets in contact with the negative electrode surface was measured with a microscope from the horizontal direction. As a result, the contact angle was 144 degrees.

(Comparative Example 3)
In Comparative Example 3, in the production of the negative electrode in Example 1 described above, instead of the above-mentioned PFA dispersion, a dispersion of tetrafluoroethylene-hexafluoropropylene copolymer (FEP) was used. The negative electrode was produced by applying the negative electrode surface so that the coating amount was 0.4 mg / cm ² , and an alkaline storage battery of Comparative Example 3 was produced in the same manner as in Example 1 above. .

  In addition, 5 μl of pure water droplets were dropped on the surface of the negative electrode, and the contact angle of the droplets in contact with the negative electrode surface was measured with a microscope from the horizontal direction. As a result, the contact angle was 141 degrees.

  Each of the alkaline storage batteries of Example 1 and Comparative Examples 1 to 3 manufactured as described above was charged at a current of 150 mA for 16 hours, and then discharged at a current of 1500 mA until the battery voltage reached 1.0 V. This was regarded as one cycle, and 3 cycles of charge / discharge were performed to activate each alkaline storage battery.

  Next, each of the alkaline storage batteries of Example 1 and Comparative Examples 1 to 3 activated in this way was charged until the battery voltage reached the maximum value at a current of 1500 mA, respectively, until the battery voltage decreased by 10 mV, and left for 30 minutes. After that, the battery is discharged at a current of 1500 mA until the battery voltage reaches 1.0 V and left for 30 minutes, and this is repeated as one cycle, and the number of cycles until the discharge capacity of each alkaline storage battery reaches 1000 mAh is determined. The number of cycles in the alkaline storage battery of Comparative Example 1 was determined as the cycle life 100, the cycle life ratio in each alkaline storage battery was determined, and the results are shown in Table 1 below.

  Moreover, after charging / discharging each alkaline storage battery of Example 1 and Comparative Examples 1-3 activated as mentioned above for 200 cycles similarly to the above case, each alkaline storage battery was disassembled, and these After washing with water to remove the alkaline electrolyte and drying, the hydrogen storage alloy powder in the negative electrode of each alkaline storage battery was taken out, and each oxygen extraction device (manufactured by LECO) was used to extract each of the hydrogen storage alloy powders in an inert gas by a melt extraction method. The oxygen concentration (mass%) in the hydrogen storage alloy powder was measured, and the oxygen concentration ratio of the hydrogen storage alloy powder in each alkaline storage battery was determined with the oxygen concentration of the hydrogen storage alloy powder in Comparative Example 1 being 100. It is shown in Table 1.

As a result, each of Example 1 and Comparative Examples 2 and 3 in which the negative electrode using the hydrogen storage alloy represented by the above general formula was used with the negative electrode coated with fluororesin PFA, PTFE, or FEP on the surface. Compared to the alkaline storage battery of Comparative Example 1 in which no fluororesin is added, the alkaline storage battery has a greatly increased contact angle value on the surface of the negative electrode, and the water repellency at the negative electrode is greatly improved. Compared with Comparative Examples 2 and 3 using PTFE or FEP, the value of the contact angle on the surface of the negative electrode is larger in Example 1 using PFA and the water repellency in the negative electrode is further improved. Was.

Moreover, each alkaline storage battery of Example 1 and Comparative Examples 2 and 3 using a negative electrode having a fluororesin PFA, PTFE, or FEP coated on its surface is the alkaline storage battery of Comparative Example 1 to which no fluororesin is added. In comparison with the above, the cycle life in the case of repeated charge / discharge is greatly improved, and the oxygen concentration in the negative electrode after the 200 cycles of charge / discharge is also greatly reduced. Oxidation of the storage alloy was suppressed.

Also, PFA and fluorine resins, PTFE and, when compared with the alkaline storage batteries of Example 1 and Comparative Examples 2 and 3 were used a negative electrode was coated with FEP to the surface, PFA is is applied to the surface water repellent The alkaline storage battery of Example 1 using the highest negative electrode was obtained by repeatedly charging and discharging the alkaline storage battery of Comparative Examples 2 and 3 using the negative electrode coated with PTFE or FEP on the surface . The cycle life was further improved.

It is a schematic sectional drawing of the alkaline storage battery produced in Example 1 and Comparative Examples 1-3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery can 5 Positive electrode lead 6 Positive electrode cover 6a Gas discharge port 7 Negative electrode lead 8 Insulation packing 9 Positive electrode external terminal 10 Coil spring 11 Closure board

Claims (3)

General formula Ln _1-x Mg _x Ni _yab Al _a M _b (where Ln is at least one element selected from rare earth elements including Y, Zr and Ti, and M is V, Nb, Ta, It is at least one element selected from Cr, Mo, Mn, Fe, Co, Ga, Zn, Sn, In, Cu, Si, P, and B, and 0.05 ≦ x ≦ 0.30, 0.05 ≦ a ≦ 0.30, 0 ≦ b ≦ 0.50, 2.8 ≦ y ≦ 3.9.) And a tetrafluoroethylene-perfluorovinyl ether copolymer. unrealized, the tetrafluoroethylene - perfluoro vinyl ether copolymer, a negative electrode for an alkaline storage battery, characterized in that present on the surface of the negative electrode. 2. The negative electrode for an alkaline storage battery according to claim 1, further comprising a styrene / butadiene copolymer as a binder in addition to the hydrogen storage alloy and the tetrafluoroethylene-perfluorovinyl ether copolymer. Negative electrode for alkaline storage battery. An alkaline storage battery comprising a positive electrode, a negative electrode using a hydrogen storage alloy, and an alkaline electrolyte, wherein the negative electrode for an alkaline storage battery according to claim 1 or 2 is used for the negative electrode. An alkaline storage battery.

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