JP3010724B2 - Hydrogen storage alloy electrode for batteries - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage alloy electrode for a nickel-hydrogen storage battery or the like.

2. Description of the Related Art Lead storage batteries and alkaline storage batteries are widely used as various power sources. Among these, alkaline storage batteries can be expected to have high reliability, and small batteries can be reduced in size and weight, and small batteries have been used for various portable devices and large batteries for industrial use.

In this alkaline storage battery, an air electrode, a silver oxide electrode, and the like are partially mentioned as a positive electrode, but in most cases, a nickel electrode. The characteristics have been improved from the pocket type to the sintering type, and the sealing has been made possible and the use has expanded.

On the other hand, in addition to cadmium, zinc, iron, hydrogen and the like are targeted as the negative electrode. Recently, attention has been paid to a nickel-hydrogen storage battery using a metal hydride, that is, a hydrogen storage alloy electrode, in order to achieve a higher energy density. In this case MmNi ₅ system alloy as a hydrogen absorbing alloy (Mm: in misch metal La, Ce, mixture of rare earth elements such as Nd) is large, then the subject, such as the development ZrMnCrNi alloy having AB ₂ type Laves phase structure Has become.

As a method for improving the manufacturing method, there is known a technique of forming a porous metal layer by plating the particle surface with nickel or copper in order to improve the hydrogen storage alloy powder, particularly the oxidation resistance and the utilization and moldability. . Further, in order to improve the characteristics, a process has been proposed in which a heat treatment is performed in a vacuum after the production of the alloy, or a process of immersing the alloy in an alkaline solution.

Further, when applied to a closed type, addition of a fluorine resin or a catalyst has been attempted in order to improve absorptivity of oxygen gas from the positive electrode during charging and hydrogen gas which may be generated during overcharging.

Problems to be Solved by the Invention There are two methods for producing a hydrogen storage alloy electrode: a method of sintering an alloy powder and a method of filling or coating a porous support such as foamed, fibrous, or punched metal. Of these, the paste method is the simplest one. Hydrogen storage alloys are relatively excellent in terms of electron conductivity, like cadmium electrodes and zinc electrodes, so that the possibility of non-sintered electrodes is great.

That is, the paste is formed into a paste together with a binder, and the paste is filled or coated on a porous conductive plate having a three-dimensional or two-dimensional structure. In this case, an MmNiMnAlCo-based alloy, which is one of the LaNi ₅ -based alloys as a hydrogen storage alloy, exhibits excellent discharge capacity, but has room for improvement in gas absorption characteristics.

On the other hand, ZrMnCr as an alloy having the AB ₂ type Laves phase structure
Ni, ZrMnVCrNi, ZrMnVAlNi, ZrMnMoCrNi, ZrMn
All of the AlNi-based alloys ultimately show even better discharge capacity and may be good in terms of gas absorption characteristics, but the initial characteristics of the cycle are many problems, and improvement of the initial activation characteristics has been a problem. Therefore, it is necessary to improve the discharge characteristics at the beginning of the charge / discharge cycle, the utilization factor, and the high-rate discharge characteristics. The sealed type can be used because it can absorb a gas under a load like the nickel-cadmium type, but further improvement in quick chargeability is desired.

Means to solve the problem CaCu based on LaNi ₅ and MmNi ₅ as hydrogen storage alloy
_{Based on} alloy with ₅ type structure and ZrMn ₂ , ZrV ₂ etc.
It is characterized by being composed of a mixture of alloys having an AB type ₂ Laves phase structure.

Further, the electrode is formed by a sintered body of a mixture of alloys.

In the present invention, the temperature indicating the equilibrium pressure is almost the same, and instead of mixing based on the temperature characteristics, an alloy having a CaCu _5- type structure and an AB ₂ having excellent capacity and gas absorption characteristics in a steady state are used. It is characterized by being mixed with an alloy having a Laves phase structure to form an excellent negative electrode, thereby overcoming the problem of the initial characteristics of the charge-discharge cycle, and at the same time, further improving the utilization factor and the high-rate discharge characteristics. And improvement of quick charge characteristics and the like.

Moreover, by heat-treating and sintering these mixtures to form electrodes, it is possible to more effectively improve the discharge characteristics, utilization factor and high-rate discharge characteristics at the beginning of the charge / discharge cycle.

EXAMPLES Attempts have been made to mix two or more different alloys. Many of the objects of the invention are to utilize alloys having different hydrogen equilibrium pressure-temperature characteristics by utilizing alloy-specific hydrogen equilibrium pressure-temperature characteristics so that the alloys can be used in a wide temperature range by mixing alloys having different temperatures.

The temperature at which such an equilibrium pressure is shown is almost the same, and rather than mixing based on temperature characteristics, MmNi, which has excellent capacity as a negative electrode of a sealed type battery, especially excellent initial capacity
Alloys with a CaCu _5- type structure such as MnAlCo or MmNiAlCo alloys, and ZrMnCrNi, ZrMnVCrNi, ZrMnVAlNi, and ZrMnMoCrNi with excellent steady-state capacity and gas absorption characteristics
And an alloy having an AB ₂ type Laves phase structure selected from the group consisting of ZrMnAlNi and the like.

 Examples will be described more specifically below.

(Example 1) MmNi _3.7 Mn having a CaCu ₅ type structure as a hydrogen storage alloy
_0.4 Al _0.3 Co _0.6 and ZrMn _0.4 , one of the AB ₂ type Laves phase alloys
After each V _0.2 Cr _0.1 Ni _1.3 alloy was pulverized and passed through a 300 mesh, they were mixed at a weight ratio of 1: 1 and polyethylene fine powder was added so that this resin became 3 parts with respect to the hydrogen storage alloy powder. Make a paste with 2.5% by weight PVA solution.
Then paste the paste 0.17mm thick, 1.8mm hole diameter, 5 aperture
A 3% iron-plated nickel-plated punched metal plate was applied and smoothed through a 0.6 mm slit. Thereafter, it was dried at 120 ° C. for 1 hour. The obtained electrode was passed through an embossed roller press kept at 135 ° C to a thickness of 0,0.
Adjusted to 5mm. Finally, 5% fluororesin dispersion was added and dried. This paste-type hydrogen storage alloy electrode was cut, and a lead plate was attached by spot welding.
This electrode is designated as A.

For comparison, MmNi _3.7 Mn _0.4 Al _0.3 Co _0.6 and ZrMn _0.4
V _0.2 Cr _0.1 Ni _1.3 alone and electrodes obtained in the same manner were added as B and C, respectively. First, to examine the characteristics of each negative electrode, a sintered nickel electrode was used as a counter electrode having a sufficiently large capacity so as to satisfy the negative electrode rule, and 25 g / l lithium hydroxide in an aqueous caustic potassium solution having a specific gravity of 1.25 as an electrolyte solution. It was used after dissolving. Open type with rich electrolyte.

140% constant current charge of negative electrode capacity at 5 hour rate-0.9V at 0.5A
As a result, the discharge capacity density of A became substantially constant after 273 mAh / g for one cycle and 291 mAh / g for two cycles. However, in B, 257 mAh / g per cycle, 2
266mAh / g cycle, 275mAh / g almost constant after 3 cycles
Met. In C, 52mAh / g for one cycle, 165mAh / g for two cycles, 251mAh / g for three cycles, and 362mAh for four cycles
/ g was almost constant after 5 cycles and was 267 mAh / g. From these results, it can be seen that in A, the cycle initial characteristics are improved and the utilization is high.

Next, different comparative examples will be described. A sealed nickel-hydrogen storage battery with a regulated positive electrode capacity was constructed as before. As a counter electrode, a known foamed nickel electrode and a hydrophilically treated polypropylene nonwoven fabric separator were used. As an electrolytic solution, 25 g / l lithium hydroxide was dissolved in an aqueous caustic potassium solution having a specific gravity of 1.25 and used. The battery was a C2 type. The capacity of the negative electrode with respect to the positive electrode was set to 150%. A battery using this electrode A is referred to as A '
And

The battery using the comparative electrode B was designated as B 'and the battery using the electrode C was designated as C'. First, the initial discharge voltage and the capacity were compared.
A constant current discharge of up to 0.9V at a constant current charge of -150A at a constant current of -2.0A at a rate of 5 hours. A 'average voltage is 1.24V.
The discharge capacity is almost constant after two cycles and is 2.75 to 2.
It was 80 Ah. However, in the case of B ', the average voltage was 1.22 V, and three cycles were required until the discharge characteristics were improved and became almost constant. In C ', the average voltage was 1.21 V, and four cycles were required until the discharge characteristics improved and became almost constant.

The quick charging characteristics were compared using 10 cells for each battery. Charge the battery at 1.2C with the ambient temperature set to 0 ° C
The pressure inside the battery at the time of% charging was examined. As a result, 1.9
~ 2.7 kg / cm ² while B 'was 3.5-4.5 kg / cm
² , and C 'was 2.5 to 3.2 kg / cm ² , and A' was excellent in gas absorption.

(Example 2) An example in which a sintered electrode is formed instead of the paste type of the previous example will be described.

Similarly as a hydrogen storage alloy, MmNi _3.7 Mn _0.4 Al _0.3 Co _0.6
ZrMn _0.4 V _0.2 Cr _0.1 Ni _1.3 Each alloy is pulverized and passed through 300 mesh, then mixed at a weight ratio of 1: 1 and these alloy powders are pressed and pressed around nickel mesh core material. I made it. Thereafter, the compact was sintered at 950 ° C. for 30 minutes in a vacuum heat treatment furnace, cut, and a lead plate was attached by spot welding to form an electrode. This is a sintered type A electrode.

For comparison, MmNi _3.7 Mn _0.4 Al _0.3 Co _0.6 and ZrMn _0.4
V _0.2 Cr _0.1 Ni _1.3 electrodes obtained independently in the same manner were added as sintering formula B and sintering formula C, respectively.

In order to investigate the characteristics of these sintered electrodes as negative electrodes, we conducted a charge-discharge test in an open type with abundant electrolytes, using a sintered nickel electrode as a counter electrode with a sufficiently large capacity as before. . 25 in aqueous caustic potassium solution with specific gravity of 1.25 as electrolyte
g / l lithium hydroxide was dissolved and used.

140% constant current charge of negative electrode capacity at 5 hour rate-0.9V at 0.5A
As a result, the discharge capacity density of A became substantially constant after 345 mAh / g for one cycle and 352 mAh / g for two cycles. However, in B, 239 mAh / g per cycle, 2
242 mAh / g for cycle 245 mAh / g, almost constant after 3 cycles
Met. Further, in C, 207 mAh / g for one cycle, 245 mAh / g for two cycles, 263 mAh / g for three cycles, and 265 mAh / g, which was almost constant after four cycles. From these results, it was found that in A, the cycle initial characteristics were improved and the utilization was high. Further, it has been clarified that the use of such a sintered electrode can improve the initial discharge characteristics as compared with the above-mentioned paste type. Presumably, the surface state of the alloy changed during the sintering process, and it can be expected that the electron conductivity was further improved.

A test for forming a sealed battery using this sintered electrode and a test for the internal pressure of the battery were performed in the same manner as in Example 1 above. As a result, alloys with a CaCu ₅ type structure and A
The case of a mixture of alloys with a B ₂ type Laves phase structure, similarly excellent cell performance as in Example 1 were obtained.

The conditions for producing this sintered electrode are delicately related to the particle size of the alloy and the like, but the treatment is preferably carried out in a vacuum or in an inert gas atmosphere at a temperature of about 800 ° C. or higher.

It is also effective to add a sintering aid such as 5 to 15 wt% Ni powder in addition to the hydrogen storage alloy powder. If there are additives
Sinters even at 700 ° C.

An alloy having a CaCu ₅ type structure according to the present invention, and an AB ₂ type La
The mixing ratio with the alloy having the ves phase structure varies considerably depending on the substantial alloy composition, but is preferably in the range of 5 to 95% by weight in order to effectively bring out the effects of the invention.

Further, the hydrogen storage alloy used in the present invention will be briefly described. LaNi _5, CaCu ₅ based on MmNi ₅
A wide range of material compositions have been known for hydrogen storage alloys having a die structure through many research and development, and in particular, Mm-Ni-Mn-Al
-CoCu or CaCu composed of Mm-Ni-Al-Co alloy
A hydrogen storage alloy having a _5- type structure is preferred. AB ₂ type
Many alloys have been proposed as alloys having a Laves phase structure. In particular, the A site is Zr and the B site is Ni and Mn, Cn.
r, Al, V, C15 type composed of Mo, etc., or C14 type Laves alloy is preferable, as a specific multi-component alloy is Zr-Mn-Cr
-Ni, Zr-Mn-V-Cr-Ni, Zr-Mn-V-Al-Ni
Alloys selected from the group consisting of Zr-Mn-Mo-Cr-Ni and Zr-Mn-Al-Ni.

In effect the present invention, it is possible to overcome the problem of initial characteristics of the charge-discharge cycle of the alloy, especially with promising AB ₂ type Laves phase structure traditional higher capacity as an alloy system possible. At the same time, the utilization rate, the high-rate discharge characteristics, the rapid charge characteristics, and the like are further improved.

──────────────────────────────────────────────────の Continued on the front page (72) Inventor Yoichiro Tsuji 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Tsutomu Iwaki 1006 Kazama Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-1-173573 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24-4/26 H01M 4/38 JOIS

Claims (5)

(57) [Claims] 1. An alloy having a CaCu ₅ type structure based on LaNi ₅ or MmNi ₅ and an AB ₂ type La based on ZrMn ₂ , ZrV ₂ or the like.
A hydrogen storage alloy electrode for a battery, comprising a mixture of alloys having a ves phase structure. 2. The hydrogen storage alloy electrode for a battery according to claim 1, wherein the electrode is formed of a sintered body of a mixture of an alloy having a CaCu ₅ type structure and an alloy having an AB ₂ type Laves phase structure. 3. An alloy having a CaCu ₅ type structure based on LaNi ₅ or MmNi ₅ is preferably an Mm—Ni—Mn—Al—Co system or Mm
The hydrogen storage alloy electrode for a battery according to claim 1, wherein the electrode is a Ni—Al—Co alloy. 4. An alloy having an AB ₂ type Laves phase structure is preferably Zr.
-Mn-Cr-Ni, Zr-Mn-V-Cr-Ni, Zr-Mn-V-
3. The hydrogen storage alloy electrode for a battery according to claim 1, wherein the electrode is an alloy selected from the group consisting of Al-Ni, Zr-Mn-Mo-Cr-Ni, and Zr-Mn-Al-Ni. 5. The mixing ratio of an alloy having a CaCu ₅ type structure of a hydrogen storage alloy and an alloy having an AB ₂ type Laves phase structure is 5 to 5.
3. The hydrogen-absorbing alloy electrode for a battery according to claim 1, which is in a range of 95% by weight.