JP3258728B2 - Hydrogen storage alloy electrode for metal / hydride secondary batteries - Google Patents

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 for a metal / hydride secondary battery, and more particularly to a hydrogen storage alloy electrode intended to improve rapid charge characteristics and high rate discharge characteristics. New and useful improvements to

[0002]

2. Description of the Related Art In recent years,
A metal / hydride secondary battery that uses a metal compound such as nickel hydroxide for the positive electrode and a new material, a hydrogen storage alloy, for the negative electrode has a lower energy density per unit weight and unit volume than other types of batteries. Because of its high capacity and high capacity, it is being spotlighted as a next-generation alkaline storage battery that replaces nickel-cadmium secondary batteries.

Conventionally, a hydrogen storage alloy electrode used as a negative electrode of this type of alkaline storage battery has been manufactured by binding and integrating a hydrogen storage alloy powder with a binder.

[0004] However, the hydrogen storage alloy powder, particularly a hydrogen storage alloy powder containing a rare earth metal as an alloy component, is liable to be oxidized on its surface in each step such as a step of pulverizing the block of hydrogen storage alloy, a step of manufacturing an electrode, and a step of assembling a battery. Therefore, the contact resistance between the hydrogen storage alloy powder in the hydrogen storage alloy electrode is considerably large. Incidentally, the contact resistance due to the surface oxidation increases as the particle size of the hydrogen storage alloy powder decreases.

[0005] When such a hydrogen storage alloy electrode having a large contact resistance between the hydrogen storage alloy powders, that is, using a low conductivity hydrogen storage alloy electrode as the negative electrode, the rapid charge characteristics and the high rate discharge characteristics are reduced.

For this reason, conventionally, in order to suppress the contact resistance, powder mixing of a hydrogen storage alloy powder with a metal powder having a high electron conductivity as a conductive agent is performed as required.

However, in the hydrogen storage alloy electrode obtained by this method, the metal powder is merely in powder contact with the hydrogen storage alloy powder. Therefore, the above-described surface oxidation cannot be effectively suppressed, and the contact resistance between the hydrogen storage alloy powders does not become so small.

As described above, in the conventional metal / hydride secondary battery, a hydrogen storage alloy electrode having a large contact resistance between the hydrogen storage alloy powders is used for the negative electrode. There was a problem that the characteristics and the high-rate discharge characteristics were not good.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in a conventional metal / hydride secondary battery, and it is an object of the present invention to provide a metal having excellent quick charge characteristics and high rate discharge characteristics. The object of the present invention is to provide a hydrogen storage alloy electrode having a small contact resistance between hydrogen storage alloy powders, which makes it possible to obtain a hydride secondary battery.

[0010]

In order to achieve the above object, a hydrogen storage alloy electrode according to the present invention (hereinafter referred to as "electrode of the present invention") is a molten liquid (hydrogen storage alloy) of a mixture of hydrogen storage alloy components. A hydrogen storage alloy lump obtained by incorporating metal fibers into a molten metal (alloy) and then solidifying the powder is powdered and integrated with a binder.

The metal fibers include Ru (ruthenium), Co (cobalt), Rh (rhodium), Ni (nickel), Pd (palladium), Ag (silver), Cu
A metal fiber made of (copper), Au (gold), Tl (thallium), Pb (lead) or Bi (bismuth) is exemplified as a preferable one. Any metal fiber that can be reduced can be used without particular limitation. In addition, these metal fibers may be used alone or in combination of two or more as necessary.

The hydrogen-absorbing alloy powder containing metal fibers in the present invention can be obtained, for example, by a method comprising the following steps (1) to (3), but is not limited thereto. (1) Metal fibers are added to and mixed with the melt of the hydrogen storage alloy component. (2) Solidification is performed at a predetermined cooling rate to form a foil-shaped hydrogen storage alloy lump containing metal fibers. (3) The hydrogen storage alloy block is pulverized to an appropriate size to obtain a hydrogen storage alloy powder.

The cooling rate during solidification is 1 × 10 ⁴ °
C / sec or more is preferable. By solidifying at such a rapid cooling rate, it is possible to obtain an alloy crystal in which the orientation of crystal grains (crystallites) is close to the irregular state at the time of melting, that is, an alloy crystal having a large number of grain boundaries. This is because a hydrogen storage alloy electrode that can exhibit high-rate discharge characteristics can be obtained. The method of rapid solidification is not particularly limited, and for example, a conventionally known roll method (single roll method, twin roll method, etc.) can be suitably used.

In order to improve the rapid charge characteristic and the high rate discharge characteristic, the metal fiber is contained in the hydrogen storage alloy powder at a ratio of 0.5 part by weight or more based on 100 parts by weight of the hydrogen storage alloy. Is preferred.

Examples of the hydrogen storage alloy in the present invention include LaNi ₅ , LaNi ₃ Co ₂ , and MmNi ₅ and MmNi _{3 in} which a part of La is partially substituted by another metal.
Co ₂ (Mm: mixture of misch metal and rare earth metal)
Rare earth hydrogen storage alloys such as Ti ₂ Ni, TiNi ₂ ,
Ti-Ni-based hydrogen storage alloys such as those obtained by partially replacing Ni with Co, Mn, Al, etc .; Ti-Mn-based hydrogen storage alloys; Ti-Fe-based hydrogen storage alloys; Mg-Ni-based hydrogen storage alloys A Ti-Zr-based hydrogen storage alloy; a Zr-Mn-based hydrogen storage alloy, but is not particularly limited.

[0016] As described above, the present invention provides a method for solidifying metal fibers to provide a hydrogen storage alloy electrode capable of obtaining a metal / hydride secondary battery having excellent rapid charge characteristics and high rate discharge characteristics. By adding the metal fiber to the hydrogen storage alloy powder by adding it to the molten alloy, which is a stage before alloying the metal alloy, the maximum is that the contact resistance between the hydrogen storage alloy powder is greatly reduced. It has the characteristics of Therefore, as for the kind of the binder used when preparing an electrode by binding and integrating these materials, various kinds of materials conventionally used or proposed for hydrogen storage alloy electrodes, for example, poly (poly), have been proposed. Tetrafluoroethylene (PTF
E), polyvinylidene fluoride (PVDF) and the like can be used without limitation.

[0017]

The hydrogen storage alloy powder used for the electrode of the present invention is:
Since the metal fibers are contained, the contact resistance between the hydrogen storage alloy powders is greatly reduced by the metal fibers exposed on the surface of the hydrogen storage alloy powder. Since the metal fibers are more easily exposed to the surface of the hydrogen storage alloy powder than the metal powder, the effect of reducing the contact resistance is particularly large.

In a metal / hydride secondary battery, oxygen gas generated at the positive electrode during overcharge is removed by reacting with hydrogen stored in the hydrogen storage alloy powder of the negative electrode. Since the hydrogen storage alloy powder to be produced contains metal fibers having a high reducing property, the hydrogen storage alloy powder has a higher oxygen gas reducing ability than that of the conventional hydrogen storage alloy electrode.

[0019]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples, and may be carried out by appropriately changing the scope of the present invention. Is possible.

(Example 1) Mm, Ni, Co, Al and Mn (all simple metals having a purity of 99.9% or more which are commercially available)
Are mixed in a molar ratio of 1: 3.1: 0.9: 0.2: 0.5, and are mixed in a high-frequency melting furnace in an inert gas (argon) atmosphere.
After melted by high-frequency induction heating, 10 parts by weight of Ni fiber is added to and mixed with 100 parts by weight of the melt, and then melt-drag method (a type of single roll method, which is horizontal to the roll cooling surface). This is a method of continuously obtaining a band-shaped hydrogen storage alloy while bringing the molten alloy into contact with the molten metal through a nozzle and pulling it upward by rotating the roll.)
After quenching at a cooling rate of ⁴ ° C / sec, the average particle size is 70 μm.
Pulverized to a degree, a composition formula MmNi containing Ni fibers
A hydrogen storage alloy powder represented by _3.1 Co _0.9 Al _0.2 Mn _0.5 was produced.

Next, 0.05 parts by weight of polytetrafluoroethylene (PTFE) as a binder was mixed with 1 part by weight of the Ni fiber-containing hydrogen storage alloy powder and rolled to obtain an alloy paste.

A predetermined amount of this alloy paste is applied to both surfaces of a negative electrode current collector made of nickel punching metal,
The electrode E1 of this invention was produced by drying.

(Example 2) An electrode E2 of the present invention was produced in the same manner as in Example 1 except that 5 parts by weight of Ni fiber was used instead of 10 parts by weight in the preparation of the hydrogen storage alloy powder.

(Example 3) An electrode E3 of the present invention was produced in the same manner as in Example 1 except that in the preparation of the hydrogen storage alloy powder, 3 parts by weight of Ni fiber was used instead of 10 parts by weight.

Example 4 An electrode E4 of the present invention was produced in the same manner as in Example 1, except that 1 part by weight of Ni fiber was used instead of 10 parts by weight in the preparation of the hydrogen storage alloy powder.

Example 5 An electrode E5 according to the present invention was prepared in the same manner as in Example 1 except that 0.5 parts by weight of Ni fiber was used instead of 10 parts by weight in the preparation of the hydrogen storage alloy powder.
Was prepared.

Example 6 An electrode E6 of the present invention was produced in the same manner as in Example 1 except that 10 parts by weight of Cu fiber was used instead of 10 parts by weight of Ni fiber in the preparation of the hydrogen storage alloy powder. .

(Example 7) An electrode E7 of the present invention was produced in the same manner as in Example 1 except that 5 parts by weight of Cu fiber was used instead of 10 parts by weight of Ni fiber in the preparation of the hydrogen storage alloy powder. .

Example 8 An electrode E8 of the present invention was produced in the same manner as in Example 1 except that 3 parts by weight of Cu fiber was used instead of 10 parts by weight of Ni fiber in the preparation of the hydrogen storage alloy powder. .

Example 9 An electrode E9 of the present invention was produced in the same manner as in Example 1 except that 1 part by weight of Cu fiber was used instead of 10 parts by weight of Ni fiber in the preparation of the hydrogen storage alloy powder. .

Example 10 In the preparation of a hydrogen storage alloy powder, Cu fiber was replaced with 0.5 part of Cu fiber instead of 10 parts by weight of Ni fiber.
An electrode E10 of the present invention was made in the same manner as in Example 1 except that the parts by weight were used.

Comparative Example 1 A comparative electrode CE1 was produced in the same manner as in Example 1 except that a hydrogen storage alloy powder represented by a composition formula of MmNi _3.1 Co _0.9 Al _0.2 Mn _0.5 containing no metal fiber was used. did.

Comparative Example 2 The same procedure as in Example 1 was carried out except that the Cu fiber was not added to the molten metal of the hydrogen storage alloy, and 100 parts by weight of the hydrogen storage alloy powder containing no Cu fiber and 10 parts by weight of the Cu fiber were mixed. Similarly, a comparative electrode CE2 was produced.

(High Rate Discharge Characteristics Test) Using the electrodes E1 to E10 of the present invention produced in Examples 1 to 10 or the comparative electrodes CE1 and CE2 produced in Comparative Examples 1 and 2 as negative electrodes, an AA nickel Hydride rechargeable batteries (in order, “Batteries BA1 to BA
10 and comparative batteries BC1, BC2 ". ) Assembled. In addition, a sintered nickel electrode was used as the positive electrode, a nylon nonwoven fabric was used as the separator, and 3
A 0% strength aqueous potassium hydroxide solution was used.

FIG. 1 shows the battery BA1 (BA2 to BA
10. The comparative batteries BC1 and BC2 are also batteries of the same shape. The battery BA1 shown in the figure has a positive electrode 1, a negative electrode (hydrogen storage alloy electrode) 2, a separator 3 separating these electrodes, a positive electrode lead 4, a negative electrode lead 5, a positive electrode external terminal 6, an alkaline electrolyte. Is injected into the negative electrode can 7 and the like.

The positive electrode 1 and the negative electrode 2 are housed in a negative electrode can 7 in a state of being spirally wound through a separator 3, and the positive electrode 1 is connected to a positive external terminal 6 through a positive electrode lead 4.
In addition, the negative electrode 2 is connected to a negative electrode can 7 via a negative electrode lead 5, so that chemical energy generated inside the battery BA1 can be taken out as electric energy.

A coil spring 9 is provided between the positive electrode external terminal 6 and the sealing member 8 so that when the internal pressure of the battery rises abnormally, it is compressed and gas in the battery can be released to the atmosphere. It has become.

The high-rate discharge characteristics of the batteries BA1 to BA10 and the comparative batteries BC1 and BC2 configured as described above were examined. The results are shown in FIG.

FIG. 2 shows batteries BA1 to BA4, BA6 to B
A9 and the high-rate discharge characteristics of the comparative batteries BC1 and BC2, the vertical axis represents the battery voltage (V), and the horizontal axis represents the discharge capacity ratio (%).
FIG.

The discharge capacity ratio was as follows: at room temperature (25 ° C.), the battery was charged to 1.3 V at 0.2 C and then charged at 1.0 at 0.2 C.
At room temperature with respect to the discharge capacity when discharged to V
This is a value expressed as a percentage of the discharge capacity when the battery is charged to 1.3 V at 2 C and then discharged to 1.0 V at 4.0 C.

FIG. 2 shows that the discharge capacity ratios of the comparative batteries BC1 and BC2 are as small as about 50%, whereas the discharge capacity ratios of the batteries BA1 to BA4 and BA6 to BA9 are as large as 70% or more. Electrodes E1-E4 and E6-
Batteries BA1-BA4 and BA6-BA9 using E9
Is compared to the comparative battery BC1 using the comparative electrode CE1,
It can be seen that the high rate discharge characteristics are much better.

In FIG. 3, the vertical axis represents the batteries BA1 to BA1.
A graph showing the relationship between the discharge capacity ratio and the mixing ratio of the metal fibers by taking the discharge capacity ratio (%) of the battery cell 0 and the comparative battery BC1, and the mixing ratio (%) of the metal fibers to the hydrogen storage alloy on the horizontal axis. It is.

FIG. 3 shows that the discharge capacity ratio was 70 when the mixing ratio of the metal fibers to the hydrogen storage alloy was 1 part by weight or more.
% Or more, in order to obtain a nickel-hydride secondary battery having particularly excellent high-rate discharge characteristics, 1% by weight or more of metal fiber is added to the hydrogen storage alloy powder with respect to 100 parts by weight of the hydrogen storage alloy. It turns out that it is preferable to contain.

[0044]

The electrode of the present invention has a low contact resistance between the hydrogen storage alloy powders and a high conductivity, so that it is possible to obtain a metal / hydride secondary battery having excellent quick charge characteristics and high rate discharge characteristics. The present invention has an excellent specific effect.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a nickel hydride secondary battery manufactured in an example.

FIG. 2 is a graph showing high-rate discharge characteristics.

FIG. 3 is a graph showing a relationship between a discharge capacity ratio (high-rate discharge characteristics) and a mixing ratio of metal fibers to a hydrogen storage alloy.

[Explanation of symbols]

 BA1 Battery (metal / hydride secondary battery) 1 Positive electrode (sintered nickel electrode) 2 Negative electrode (hydrogen storage alloy electrode) 3 Separator

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-110553 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24 H01M 4/26 H01M 4 / 38

Claims (2)

(57) [Claims] 1. A metal / hydride composite obtained by incorporating a metal fiber into a melt of a mixture of hydrogen storage alloy components and then solidifying the mixture to obtain a hydrogen storage alloy block, which is then powdered and integrated with a binder. Hydrogen storage alloy electrode for secondary batteries. 2. The method according to claim 1, wherein the metal fibers are Ru, Co, Rh, N
2. The hydrogen storage alloy electrode for a metal / hydride secondary battery according to claim 1, comprising at least one metal selected from the group consisting of i, Pd, Ag, Cu, Au, Tl, Pb and Bi.