JP3183414B2 - Hydrogen storage alloy electrode and alkaline secondary battery using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hydrogen storage alloy electrode and an alkaline secondary battery using the same.

[0002]

2. Description of the Related Art Nickel-hydrogen batteries and manganese dioxide
As a negative electrode of an alkaline secondary battery such as a hydrogen battery, a hydrogen storage alloy electrode using a hydrogen storage alloy as an active material is used. There is a property that the hydrogen storage alloy is pulverized.

As a result, the electrical contact between the hydrogen storage alloys becomes insufficient, the resistance increases, the discharge capacity decreases, and the cycle characteristics deteriorate.

[0004] Therefore, it has been proposed to improve conductivity and mechanical strength by applying nickel plating or nickel alloy plating to the surface of the hydrogen storage alloy (for example, Japanese Patent Application Laid-Open No. 63-22370).

In producing a hydrogen storage alloy electrode, the hydrogen storage alloy powder is mixed with polytetrafluoroethylene powder to spatially fix the hydrogen storage alloy,
It has also been considered to prevent a decrease in electrical contact due to pulverization of the hydrogen storage alloy.

[0006] However, although the former plating is effective in preventing the decrease in conductivity, it cannot be said that the mechanical strength is sufficiently improved, and when the latter is fixed with polytetrafluoroethylene, the hydrogen storage alloy is not used. Since the polytetrafluoroethylene enters the gaps, the conductivity decreases. Moreover, even if both are combined, sufficient conductivity cannot be obtained.

[0007]

SUMMARY OF THE INVENTION As described above, according to the present invention, the conventional method for improving a hydrogen storage alloy electrode cannot sufficiently improve both the conductivity and the mechanical strength of the hydrogen storage alloy electrode. To improve both the electrical conductivity and mechanical strength of the hydrogen storage alloy electrode, thereby improving the battery's discharge characteristics and cycle characteristics, and suppressing the internal pressure rise of the battery. I do.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a hydrogen storage alloy electrode using a metal-plated hydrogen storage alloy in which a resin having water repellency such as polytetrafluoroethylene is dispersed on the particle surface. Alternatively, the above object has been achieved by applying metal plating in which the above water-repellent resin is dispersed on the surface of the hydrogen storage alloy electrode.

That is, when metal particles in which a water-repellent resin such as polytetrafluoroethylene is dispersed are applied to the surfaces of the particles of the hydrogen storage alloy, the particles shown in FIG. 1 are obtained.

[0010] In these particles, the surface of the particles of the hydrogen storage alloy 1 is coated with a metal plating 2, and a resin 3 having water repellency is dispersed in the metal plating 2 to form a matrix of the metal plating 2. Metal improves conductivity,
By bonding the water-repellent resin 3 exposed on the surface of the metal plating 2 to the water-repellent resin exposed on the surfaces of other particles, the mechanical strength of the hydrogen storage alloy electrode is improved.

When the surface of the hydrogen storage alloy electrode is subjected to metal plating in which a resin having water repellency such as polytetrafluoroethylene is dispersed, the conductivity of the hydrogen storage alloy electrode is increased by the metal constituting the metal plating matrix. And the mechanical strength of the hydrogen storage alloy electrode is improved by the water-repellent resin dispersed in the metal plating.

In the present invention, as the water-repellent resin dispersed in the metal plating, in addition to the above-mentioned polytetrafluoroethylene, for example, polychlorotrifluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, Polyvinylidene fluoride, tetrafluoroethylene / ethylene copolymer, chlorotrifluoroethylene / ethylene copolymer, tetrafluoroethylene / perfluoroalkylvinyl ether copolymer, fluorine-based resin such as polyvinyl fluoride, further, polyethylene, Resins having relatively higher water repellency than metals, such as polyolefin resins such as polypropylene, polyvinyl chloride, and polystyrene, can be used. In particular, fluororesins have high water repellency and are preferably used in the present invention.

The metal used for metal plating includes, for example, copper, nickel, manganese, cobalt, iron, molybdenum, etc. These metals are used alone or as an alloy of two or more at the time of plating. You. These exemplified metals have high electric conductivity and are particularly suitable for improving the conductivity of the hydrogen storage alloy electrode.

Further, according to the hydrogen storage alloy electrode of the present invention, the water repellent treatment of the hydrogen storage alloy electrode required in an alkaline secondary battery such as a nickel-hydrogen battery or a manganese dioxide-hydrogen battery is unnecessary. Can be.

[0015] That is, a nickel-hydrogen battery using a hydrogen storage alloy as a negative electrode and a nickel electrode using nickel oxide as an active material as a positive electrode, or a carbon dioxide using a manganese dioxide electrode using manganese dioxide as an active material as a positive electrode. Manganese-
In an alkaline secondary battery such as a hydrogen battery, an oxygen gas is generated at the positive electrode during overcharge and reaches the negative electrode during overcharge as shown in the following reaction equation due to an electrochemical reaction in charging and discharging. _{^{OH - → 1 / 2H 2 O}} + 1 / 4O 2 + e -

At this time, at the negative electrode, a reaction O ₂ + 4MH → 4M + 2H ₂ O represented by the following formula (M in the formula represents a hydrogen storage alloy) occurs, so that oxygen generated at the positive electrode is originally consumed by the negative electrode. However, if the surface of the negative electrode is hydrophilic, the surface of the negative electrode is closely covered with the electrolytic solution, so that oxygen cannot reach the surface of the hydrogen storage alloy electrode of the negative electrode, and as a result, is not consumed. Oxygen that has been raised increases the internal pressure of the battery or moves the electrolyte to the top of the battery, causing the electrolyte to leak out of the battery.

Therefore, the surface of the hydrogen-absorbing alloy electrode is subjected to a water-repellent treatment with a vinyl-based polymer or polytetrafluoroethylene to change the surface of the hydrophilic hydrogen-absorbing alloy electrode to hydrophobic, so that oxygen is absorbed by the negative-electrode hydrogen-absorbing alloy. Although it is possible to reach the surface of the electrode, according to the hydrogen storage alloy electrode of the present invention, water repellency is imparted by a resin having water repellency such as polytetrafluoroethylene dispersed in metal plating. This eliminates the need for the above-described water-repellent treatment.

The metal plating may be performed by ordinary electroless plating, and the resin having water repellency is preferably dispersed in the metal plating by about 2 to 30% by volume.

The thickness of the metal plating is not particularly limited with respect to the thickness and the like, but is usually about 2 to 20% by weight based on the weight of the hydrogen storage alloy.

A hydrogen-absorbing alloy electrode in which a metal having a water-repellent resin such as polytetrafluoroethylene dispersed on the surface or the particle surface of the hydrogen-absorbing alloy as described above is applied to a nickel-hydrogen battery or a carbon dioxide It is used as a negative electrode for alkaline secondary batteries such as manganese-hydrogen batteries.

[0021]

Next, the present invention will be described more specifically with reference to examples.

Example 1 As a hydrogen storage alloy, MmNi _3.85 Co _0.65 Mn _0.3 Al
_0.2 was used, and hydrogen was absorbed and desorbed once to make the powder fine, thereby obtaining a fine powder of 100 μm or less. In MmNi _3.85 Co _0.65 Mn _0.3 Al _0.2 showing the composition of the hydrogen storage alloy, Mm is a misch metal and the composition is La
₂₃ Ce ₄₆ Pr ₁₉ Nd ₁₁ Sm ₁ .

As a plating solution, nickel chloride 30 g /
l, sodium hypophosphite 24 g / l, sodium acetate 16 g / l and polytetrafluoroethylene 5 g / l
Was prepared.

This plating solution was heated to 90 ° C., and the above-mentioned hydrogen-absorbing alloy was put into the plating solution, and stirring was continued for 20 minutes. gave. The plating weight was 5% by weight based on the weight of the hydrogen storage alloy.

The plated hydrogen storage alloy was pressed together with a nickel net as a current collector, and heat-treated at 300 ° C. in an Ar—H ₂ mixed gas atmosphere to produce a hydrogen storage alloy electrode.

Using this hydrogen storage alloy electrode as a negative electrode,
A known sintered nickel electrode using nickel oxide as an active material is used as a positive electrode, and a 30% by weight aqueous solution of potassium hydroxide (17 g / l of lithium hydroxide is dissolved) is used as an electrolytic solution. AA nickel-metal hydride batteries were manufactured.

Comparative Example 1 A hydrogen storage alloy electrode was prepared in the same manner as in Example 1 except that polytetrafluoroethylene was not included in the plating solution used in Example 1, and an AA nickel-hydrogen battery was manufactured. Manufactured.

The battery of Example 1 and the battery of Comparative Example 1 were charged at a charging condition of 0.1 C and 130%, and discharged under a discharging condition of 0.2.
C was charged and discharged, and the cycle characteristics were examined. The result is shown in FIG. Note that the discharge capacity (%) on the vertical axis in FIG. 2 is shown as a ratio when the initial capacity is 100%.

As shown in FIG. 2, the battery of Example 1 had a longer cycle life than the battery of Comparative Example 1, and the effect of nickel plating in which polytetrafluoroethylene was dispersed was clarified.

Further, the battery of Example 1 and Comparative Example 1
The internal pressure of the battery after saturation (after 100% charge) when the battery was charged while changing the charging current was measured. The result is shown in FIG.

As shown in FIG. 3, the battery of Example 1 had a lower internal pressure than the battery of Comparative Example 1. This is the first embodiment
This is considered to be due to the fact that the water repellency of polytetrafluoroethylene during nickel plating improved the ability of the negative electrode hydrogen storage alloy electrode to consume oxygen gas in the battery.

Example 2 V ₃₃ Ti ₁₇ Zr ₁₇ Ni ₃₃ was used as a hydrogen storage alloy, and hydrogen absorption and desorption was carried out once to make the powder fine, and 100 μm
The following fine powder was obtained.

As a plating solution, nickel chloride 10 g /
l, cobalt sulfate 34 g / l, sodium hypophosphite 2
A cobalt-nickel alloy plating solution containing 4 g / l, sodium acetate 16 g / l, and polytetrafluoroethylene 5 g / l was prepared.

The plating solution was heated to 90 ° C., and the above-mentioned hydrogen-absorbing alloy was put into the plating solution. Stirring was continued for 35 minutes to obtain cobalt-nickel in which polytetrafluoroethylene was dispersed on the surface of the particles of the hydrogen-absorbing alloy. The alloy was applied.

A hydrogen-absorbing alloy electrode was prepared in the same manner as in Example 1 except that the above-mentioned plated hydrogen-absorbing alloy was used, and an AA nickel-hydrogen battery was manufactured.

Comparative Example 2 A hydrogen storage alloy having a composition of V ₃₃ Ti ₁₇ Zr ₁₇ Ni ₃₃ was used in the same manner as in Example 2, and this hydrogen storage alloy and 2% by weight of polytetrafluoroethylene with respect to the hydrogen storage alloy were used. This mixture was pressed into a sheet together with a nickel net as a current collector. Thereafter, a hydrogen storage alloy electrode was prepared in the same manner as in Example 2, and an AA nickel-hydrogen battery was manufactured.

The discharge capacity of the battery of Example 2 and the battery of Comparative Example 2 when discharged at a discharge current of 3 A was measured. FIG. 4 shows the results.

As shown in FIG. 4, the battery of Example 2 had a larger discharge capacity than the battery of Comparative Example 2. This is considered to be because the battery of Example 2 had higher conductivity between the hydrogen storage alloy particles than the battery of Comparative Example 2.

[0039]

As described above, according to the present invention,
The conductivity and mechanical strength of the hydrogen storage alloy electrode can be improved.

As a result, the discharge characteristics and cycle characteristics of an alkaline secondary battery such as a nickel-hydrogen battery could be improved, and the internal pressure of the battery could be suppressed from rising.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically illustrating a hydrogen storage alloy in which metal plating in which a resin having water repellency is dispersed is applied to the particle surface in the present invention.

FIG. 2 is a view showing cycle characteristics of a battery of Example 1 and a battery of Comparative Example 1.

FIG. 3 is a diagram showing the relationship between the charging current of the battery of Example 1 and the battery of Comparative Example 1 and the internal pressure of the battery.

FIG. 4 is a view showing the discharge characteristics of the battery of Example 2 and the battery of Comparative Example 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hydrogen storage alloy 2 Metal plating 3 Water-repellent resin

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 10/24-10/34 H01M 4/36-4/62

Claims (5)

(57) [Claims] 1. A hydrogen storage alloy electrode using a hydrogen storage alloy as an active material, wherein the hydrogen storage alloy electrode is formed by dispersing a resin having water repellency on its surface or on a particle surface of the hydrogen storage alloy. A hydrogen-absorbing alloy electrode characterized by being subjected to the following. 2. The hydrogen storage alloy electrode according to claim 1, wherein the resin having water repellency is polytetrafluoroethylene. 3. The hydrogen storage alloy electrode according to claim 1, wherein the metal for metal plating is at least one selected from the group consisting of copper, nickel, cobalt, manganese, iron and molybdenum. 4. An alkaline secondary battery using the hydrogen storage alloy electrode according to claim 1 as a negative electrode. 5. The alkaline secondary battery according to claim 4, wherein the alkaline secondary battery is a nickel-metal hydride battery.