JPH10134806A - Hydrogen storage alloy electrode and nickel-hydrogen storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the life characteristic particularly under a high temperature atmosphere by containing a metal fluoride such as CaF2 or the like in an electrode. SOLUTION: The surface of a hydrogen storage alloy is corroded when it makes contact with an alkali aqueous solution which is an electrolyte and covered with an oxide or hydroxide of alloy constituting element such as rare earth metal. Under a high temperature atmosphere, particularly, this corroding speed is extremely increased. When a metal fluoride is added, the dissolving speed of the constituting element of the hydrogen storage alloy into alkali and the generating speed of the oxide/hydroxide can be suppressed. As the metal fluoride used herein, at least one selected from the group consisting of CaF2 , YF3 , AlF3 , MnF2 , CuF2 FeF3 , LaF3 , CoF2 and NiF2 is preferably used. Its content ratio is preferably 0.1 part by weight or more and 10 parts by weight or less to 100 parts by weight of the hydrogen storage alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy electrode and a nickel-hydrogen storage battery using the electrode as a negative electrode.

[0002]

2. Description of the Related Art In recent years, a nickel-hydrogen storage battery using a hydrogen storage alloy powder for reversibly storing and releasing hydrogen for a negative electrode has attracted attention as a secondary battery having a high energy density and a long cycle life. In recent years, portable devices using secondary batteries have been improved in performance and diversification,
It is expected that the production of nickel-metal hydride storage batteries, which have better energy density and cycle life than conventional secondary batteries such as nickel-cadmium storage batteries, will further increase. In order to manufacture a nickel-hydrogen storage battery having a long cycle life, various proposals have been made as technologies for extending the life of the hydrogen storage alloy of the negative electrode. For example, a method of controlling the composition and structure of a hydrogen storage alloy, a method of surface treating a hydrogen storage alloy powder, a method of adding an additive to a negative electrode or an electrolytic solution to suppress corrosion of the alloy, and a method of rapidly cooling as a casting method of a hydrogen storage alloy. And the like.

[0003] hydrogen storage alloy, mainly the like and AB ₅ type made of a rare earth element / nickel (Ni), zirconium (Zr) / manganese (Mn) and the like AB ₂ type. The power source current such portable equipment, mainly AB ₅ type hydrogen storage alloy is used.
AB ₅ type hydrogen storage alloy has been
it is possible by o-doped suppressing pulverization of alloys, are known to improve the cycle life of the nickel-hydrogen storage batteries, hydrogen-absorbing alloy containing Co as a AB ₅ type long-life nickel-metal hydride battery (Japanese Patent Publication No. 5-86029, Japanese Unexamined Patent Publication No. Sho 61)
-91863). In addition, there is an example in which a long life is achieved by using a hydrogen storage alloy having a metal structure of two or more phases (for example, Japanese Patent Application Laid-Open No. 7-286225). A technique for extending the life by imparting corrosion resistance to the alloy by plating the hydrogen storage alloy powder in the negative electrode with Cu or the like and encapsulating the alloy (Japanese Patent Application Laid-Open No. 61-168866).
Japanese Patent Application Laid-Open No. 6-21576) and a technique for suppressing the oxidation of the negative electrode by incorporating yttrium in the negative electrode.
No. 5) has also been proposed. A technique has been proposed in which the surface of a hydrogen storage alloy powder is fluorinated to deactivate substances having surface poisoning (Japanese Patent Laid-Open No. 5-213601).
In addition, it has been proposed to produce a long-life hydrogen storage alloy by employing a super quenching method such as a gas atomizing method or a roll quenching method as a casting method of the hydrogen storage alloy (Japanese Patent Laid-Open No. 6-205). No. 163042).

[0004] As described above, efforts have been made to extend the life of nickel-metal hydride storage batteries, but batteries having a longer life are eagerly awaited in the market. In particular, when an electric vehicle application equipped with a nickel-metal hydride storage battery is developed in addition to a conventional portable device application, a long-life battery capable of repeating a charge / discharge cycle for about 10 years is required. Therefore, the life of the conventional nickel-metal hydride storage battery is insufficient. Furthermore, recently, a long-life battery that can withstand use in a high-temperature atmosphere is desired. However, the Co-containing technology, the quenching method, and the metal structure control technology described above suppress the pulverization of the hydrogen storage alloy. It is a technology mainly intended for this purpose, and cannot be said to be a technology particularly suitable for alloy corrosion at high temperatures.

Further, a hydrogen storage alloy having a long life alloy composition is not always excellent in other battery characteristics. For example, an alloy containing a large amount of Co has a good cycle life characteristic, but has a problem that the high-rate discharge characteristic is inferior to an alloy containing no Co. In addition, microencapsulation of the hydrogen storage alloy powder is a method that lowers the capacity density of the negative electrode plate, increases the cost, and is not suitable for mass production. The fluorination treatment of the hydrogen-absorbing alloy powder requires a complicated manufacturing process and costs for waste liquid treatment. Further, a technique using a super quenching method such as gas atomization has been considerably developed at an experimental level, but mass production is very difficult at present.

[0006]

SUMMARY OF THE INVENTION In view of the above, the present invention has a longer life than conventional nickel-metal hydride storage batteries, and has an excellent life characteristic especially when used in a high-temperature atmosphere. It is an object of the present invention to provide a hydrogen storage alloy electrode that provides a nickel-metal hydride storage battery that can be manufactured at low cost without the need.

[0007]

Means for Solving the Problems To solve this problem, the present invention includes a metal fluoride in a hydrogen storage alloy electrode. Here, as the metal fluoride, C
aF ₂ , YF ₃ , AlF ₃ , MnF ₂ , CuF ₂ , FeF ₃ ,
Desirably, it is at least one selected from the group consisting of LaF ₃ , CoF ₂ , and NiF ₂ .

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One of the main causes of deterioration of the cycle life of a nickel-metal hydride storage battery is corrosion oxidation of a hydrogen storage alloy. The surface of a hydrogen storage alloy of a nickel-metal hydride storage battery is corroded when it comes into contact with an alkaline aqueous solution as an electrolytic solution, and is covered with oxides or hydroxides of alloy constituent elements such as rare earth elements. In particular, under a high-temperature atmosphere, the corrosion rate becomes extremely high. When a metal fluoride is added to the hydrogen storage alloy electrode, the dissolution rate of the constituent elements of the hydrogen storage alloy in alkali and the generation rate of oxides / hydroxides can be suppressed. This improves the life characteristics of the nickel-metal hydride storage battery. In particular, the effect is remarkable under a high temperature atmosphere.
The metal fluorides used here are preferably those listed above, and their content is preferably from 0.1 to 10 parts by weight per 100 parts by weight of the hydrogen storage alloy.

[0009]

EXAMPLES Hereinafter, the hydrogen storage alloy electrode and the nickel-hydrogen storage battery of the present invention will be described in detail with reference to examples. Example 1 A sealed nickel-metal hydride battery whose capacity was regulated by the positive electrode was manufactured as follows. After each powder of nickel hydroxide, metallic cobalt, cobalt hydroxide, and zinc oxide was mixed well at a weight ratio of 100: 7: 5: 2.5, water was added to 20 g of the mixed powder to form a paste. . This paste was filled in a foamed nickel foam of 81 mm long × 60 mm wide and 3.1 g in weight, dried, and then compressed to a thickness of 1.74 mm to obtain a positive electrode plate. A nickel plate as a lead was spot-welded to a corner of the positive electrode plate. The metal cobalt in the mixture contributes to securing a discharge reserve, and the cobalt hydroxide contributes to improvement in charging efficiency. The theoretical capacity of one positive electrode plate is 5.05 Ah. Five positive electrodes were used for a test battery.

On the other hand, the negative electrode was manufactured as follows. That is, Mm (an alloy composed of La, Ce, Nd, and Pr), Ni, Mn, Al, and Co are mixed at a predetermined ratio, and the composition is MmNi _3.9 Mn _0.4 A in a high frequency melting furnace.
An ingot of l _0.3 Co _0.75 hydrogen storage alloy was produced. This alloy was heat-treated at 1000 ° C. for 10 hours in an Ar atmosphere. This ingot is pulverized to an average particle size of 30 μm.
Was obtained. CMC was added to 19.4 g of this alloy powder.
(Carboxymethylcellulose), SBR (styrene butadiene copolymer), the additives shown in Table 1, and water were mixed at a weight ratio of 100: 0.5: 1: 1: 20 and kneaded to form a paste. . 81 mm long x 60 mm wide, weight 2.
This paste was applied to 1 g of punching metal, dried, and then roll-pressed to a thickness of 1.20 mm to obtain a negative electrode plate. A nickel plate as a lead was spot-welded to a corner of the negative electrode plate. The theoretical capacity of one negative electrode plate is 5.63 Ah. Six negative electrodes were used for a test battery.

As shown in FIG. 1, a negative electrode 2 and a positive electrode 3 were alternately laminated via a separator 1 made of a sulfonated polypropylene non-woven fabric and arranged so that the negative electrode was located outside. The negative electrode lead was spot-welded to the nickel negative electrode terminal 4, and the positive electrode lead was spot-welded to the nickel positive electrode terminal (not shown). These electrode plates were made of acrylonitrile styrene resin having a thickness of 5 mm and a length of 108 mm and a width of 6 mm.
It was housed in a case 5 of 9 mm × 18 mm width. After injecting 54 cc of an electrolytic solution composed of an alkaline aqueous solution mainly composed of potassium hydroxide and having a specific gravity of 1.3, a sealing plate 7 made of acrylonitrile styrene resin was adhered to the opening of the case 5 with an epoxy resin and sealed. A safety valve 6 operating at 3 atm is attached to the sealing plate 7. Also, the negative electrode terminal 4
Are pressed and fixed to the sealing plate 7 via an O-ring 8 by tightening with a nut 9. The positive electrode terminal is similarly air-tightly and liquid-tightly attached to the sealing plate. Thus, a sealed battery was produced.

Comparative Example A battery was manufactured in the same manner as in Example except that a paste of a negative electrode to which no additive was added was used.

The batteries of the above Examples and Comparative Examples were subjected to a charge / discharge test in an atmosphere at 20 ° C. and 45 ° C. to examine the cycle life. In the charge / discharge test, charge / discharge in which the battery was charged at a 3-hour rate (8.43 A) for 1 hour and then discharged until the terminal voltage became 1 V at a 3-hour rate was repeated. The discharge capacity was measured every 50 cycles, and the number of cycles until the discharge capacity was reduced to 90% of the initial capacity (fifth cycle) was defined as the life. The discharge capacity was determined from the discharge time until the inter-terminal voltage became 1 V at a 5-hour rate (5.06 A) after charging at room temperature for 12 hours at a 10-hour rate (2.53 A). Table 1 summarizes the cycle life characteristics at 20 ° C. and 45 ° C. of the nickel-metal hydride storage batteries of Examples using various negative electrode additives and Comparative Examples not using the negative electrode additives.

[0014]

[Table 1]

As can be seen from Table 1, the cycle life of the battery of the embodiment in which the metal fluoride was added to the negative electrode was remarkably improved as compared with the comparative example. In particular, since the effect is remarkable at a life of 45 ° C., it is considered that the corrosion of the hydrogen storage alloy, which easily progresses at a high temperature, is suppressed by the metal fluoride as an additive. No. Since the cycle life of 1 and 5 is particularly long, CaF ₂ and YF ₃ are excellent as additives. Note that metal fluorides other than those shown in Table 1, such as N
Similar effects were obtained for batteries in which dF ₃ , CeF ₃ , SrF ₂ , CrF ₃ , and MgF ₂ were added to the negative electrode.

Example 2 A nickel-metal hydride storage battery was fabricated in the same manner as in Example 1 except that the addition ratio of the negative electrode additive was changed, and the cycle life at 45 ° C. was examined. The result is shown in FIG. As is clear from FIG. 2, although there is a slight difference depending on the negative electrode additive, the effect of improving the cycle life starts to appear when the addition ratio of the negative electrode additive is about 0.1 part by weight with respect to 100 parts by weight of the hydrogen storage alloy. . The effect of improving cycle life tends to increase as the amount of addition increases,
If the amount exceeds 10 parts by weight with respect to 100 parts by weight of the hydrogen storage alloy, there is no difference. Further, when the additive is added to the negative electrode in a larger amount, the ratio of the additive to the hydrogen storage alloy is too large, and the negative electrode capacity density decreases. Therefore, the addition ratio is preferably 10 parts by weight or less for 100 parts by weight of the hydrogen storage alloy in practical use. Here, as typical examples, YF ₃ , Ca
F _2, AlF ₃ have been described, but when the other metal fluoride used in Example 1 is contained in the negative electrode, the relationship between the added amount and the life is the same.

[0017]

As described above, according to the present invention, it is possible to suppress the corrosion of the hydrogen storage alloy of the negative electrode, and as a result, it is possible to provide a nickel-metal hydride storage battery having a long life especially in use in a high-temperature atmosphere.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a schematic configuration of a sealed nickel-metal hydride battery according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the addition ratio of a negative electrode additive and the cycle life of a battery at 45 ° C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Separator 2 Negative electrode 3 Positive electrode 4 Negative terminal 5 Case 6 Safety valve 7 Sealing plate 8 O-ring 9 Nut

 ──────────────────────────────────────────────────の Continued on the front page (72) Inventor Shinichi Yuasa 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A hydrogen storage alloy electrode comprising a metal fluoride. 2. The method according to claim 1, wherein the metal fluoride is CaF ₂ , YF ₃ or AlF.
_{3, MnF 2, CuF 2,} FeF 3, LaF 3, CoF 2, and the hydrogen storage alloy electrode according to claim 1, wherein from the group consisting of NiF ₂ is at least one selected. 3. The hydrogen storage alloy electrode according to claim 1, wherein the content of the metal fluoride is 0.1 to 10 parts by weight based on 100 parts by weight of the hydrogen storage alloy. 4. An electrolyte comprising a positive electrode containing nickel oxide or nickel hydroxide, a negative electrode containing a hydrogen storage alloy, a separator inserted between the positive electrode and the negative electrode, and an aqueous alkaline solution, A nickel-metal hydride storage battery, wherein the negative electrode contains a metal fluoride.