JP3182790B2 - Hydrogen storage alloy electrode and method for producing the same - 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 using a hydrogen storage alloy which electrochemically stores and releases hydrogen and can be used as an electrode of a nickel-metal hydride storage battery, and a method for producing the same.

[0002]

2. Description of the Related Art Among various portable power supplies, lead storage batteries and alkaline storage batteries typified by nickel cadmium storage batteries are widely used as storage batteries. 2. Description of the Related Art In recent years, as electronic devices have become smaller and have higher performance, expectations for further increasing the energy density of batteries have increased. In recent years, an alkaline storage battery such as a nickel-hydrogen storage battery using a hydrogen storage alloy that reversibly stores and releases hydrogen has attracted attention.

[0003] The hydrogen storage alloy electrode used in the battery can be constructed in the same manner as cadmium or zinc, and can be used to form a battery. The actual discharge capacity density can be made larger than that of cadmium.
It has the feature that no dendrite is generated at the zinc electrode, and is regarded as promising as a high energy density, long life and non-polluting negative electrode for alkaline storage batteries.

Conventionally, the method of manufacturing the hydrogen storage alloy electrode includes a sintering method obtained by sintering the hydrogen storage alloy and a method using a punching metal, an expanded metal, a foamed metal, a metal fiber, or the like as a conductive core material. It can be broadly classified into a non-sintering type such as a paste type in which the occlusion alloy is applied in a paste form or filled, and a pressure type in which a pressure is formed by pressing. Among them, the sintering method is complicated and expensive, and the hydrogen storage alloy is easily deteriorated in the sintering process, and it is difficult to obtain sufficient performance. For this reason, non-sintering-type manufacturing methods, such as a paste coating type and a pressure type, which can be easily manufactured at a low cost, are becoming mainstream.

[0005] When a hydrogen storage alloy electrode is manufactured by the non-sintering type manufacturing method, conventionally, a porous material having three-dimensional conductivity such as foamed nickel or fibrous nickel is used as a core material (substrate). The one prepared by filling the core material with a hydrogen storage alloy was excellent as an electrode. The reason is that the current is collected by the porous core material having three-dimensional conductivity, the rapid charge / discharge characteristics are excellent due to its excellent current collection, and the electrode skeleton is mechanically strong. Therefore, the charge / discharge cycle life characteristics are good.

However, when an electrode is formed using the porous core material (substrate) having three-dimensional conductivity, the volume ratio of the conductive core material in the electrode plate is large. There are problems such as a decrease in density and an expensive three-dimensional conductive porous core material (substrate), and the solution has been demanded.

On the other hand, a method of obtaining a hydrogen storage alloy electrode by a paste coating method using a low-priced metal plate product such as punching metal or expanded metal as a conductive core material has been known. In this case, the electrode performance is caused by current collection and mechanical strength, such as a decrease in rapid charge / discharge characteristics due to low current collection of the electrode and dropout of an electrode active material during a charge / discharge cycle due to insufficient mechanical strength. Problems remain in the charge-discharge cycle life characteristics.

As a method of improving the performance of the paste-coated hydrogen storage alloy electrode, a binder or a conductive material for strongly binding the hydrogen storage alloy particles, which are active material holding materials, to each other to maintain the electrode function. It is important to improve the electrode strength as a result.

For example, the binder is required to have strong binding strength with a small amount of addition, to be chemically stable, and not to inhibit the battery reaction. As a conventional binder for a hydrogen storage alloy electrode, polyvinyl alcohol, carboxymethyl cellulose, polyethylene, thermoplastic elastomer, fluororesin, and the like have been known. In the case of a small amount of binder, the hydrogen storage electrode causes alloy refining, which is a unique phenomenon of hydrogen storage alloy, due to repeated charge and discharge.
In some cases, electrode strength was reduced and electrode performance was reduced.
Conversely, when a large amount of the binder is used, the stability in long-term use is improved, but the original battery reaction, such as rapid charge / discharge characteristics, gas absorption capacity in the battery, and charge / discharge capacity (utilization rate) )
Was causing a decline.

[0010]

In such a conventional configuration, a relatively inexpensive metal plate such as punched metal or expanded metal is used as a conductive core material, and a hydrogen storage alloy electrode is formed by a paste coating method. Had been created. In this case, as the electrode performance, there was a problem in the charge / discharge cycle life characteristics due to the current collecting properties and mechanical strength, such as a decrease in the rapid charge / discharge characteristics due to the low current collecting properties of the electrodes and the falling off of the active material.

When an electrode is formed using a porous core material (substrate) having three-dimensional conductivity, the volume ratio of the conductive core material in the electrode plate is large, so that the volume energy density of the electrode is low. There have been problems such as a decrease in the number and a cost of the three-dimensional conductive porous core material (substrate).

As a method for improving the performance of the paste-coated hydrogen-absorbing alloy electrode, there is a method of binding hydrogen-absorbing alloy particles, which are active material holding materials, to each other and selecting a binder or a conductive material for maintaining the electrode function. Or the resulting electrode strength is important.

In the case of the hydrogen storage electrode, when the amount of the binder is small, the refining of the alloy, which is a peculiar phenomenon of the hydrogen storage alloy, occurs due to repetition of charge and discharge, and the electrode performance deteriorates when the electrode strength is low. was there. Conversely, if a large amount of binder is used, the stability of long-term use is improved, but the original battery reaction, such as rapid charge / discharge characteristics, gas absorption capacity in the battery, and charge / discharge capacity (utilization rate) However, there was a problem that was reduced.

When a relatively inexpensive punching metal or expanded metal is used for the conductive core material and the hydrogen storage alloy electrode is manufactured by a paste coating method, the electrode performance, that is, the rapid charge / discharge characteristics decrease and the charge / discharge cycle are reduced. There was a problem that the life characteristics became insufficient.

The present invention solves such a problem, and selects a binder capable of obtaining excellent battery performance stably over a long period of time, withstands a long-term charge / discharge cycle, and enables rapid charge / discharge. It is an object of the present invention to provide a hydrogen absorbing alloy electrode and a method for manufacturing the same.

[0016]

To solve this problem, the present invention provides a hydrogen storage alloy powder pulverized to a predetermined particle size, a conductive short fiber material connecting the hydrogen storage alloy,
Mainly polymer binder , average particle size is 10μm
Is applied to a conductive porous body and integrally formed with a composition to which a hydrophilic granular powder having an upper limit of is added .

[0017]

[0018]

[0019]

[0020]

A short fiber made of a metal or a carbon material is added to the hydrogen storage alloy electrode of the present invention. The short fiber material improves the mechanical strength of the electrode by connecting the powder particles of the hydrogen storage alloy in a network. Further, since the short fibers have conductivity, the electron conductivity of the electrode can be improved.

The addition of a granular powder having an average particle diameter of 10 μm having hydrophilicity as an upper limit is effective in improving the active material utilization rate of the electrode and extending the life. As the granular powder, a metal oxide and a metal hydroxide are effective, but a metal powder such as nickel or copper is more preferable because it improves the electron conductivity of the electrode.

Examples of the polymer binder added to the electrode include fluoroplastics and polyvinyl alcohol, fluoroplastics and thermoplastic elastomers such as styrene-butadiene copolymer and styrene-isoprene copolymer, and fluorocarbon resins and carboxymethyl cellulose (CMC). ), A fluororesin and another polymer binder are used in combination. As a result, the gas absorption capacity at the time of rapid charging is promoted by the addition of a fluororesin such as an ethylene tetrafluoride resin or an ethylene tetrafluoride-propylene hexafluoride copolymer resin. Because paste application is difficult,
By using another polymer binder together, the binding property to the collector electrode is improved.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A hydrogen storage alloy electrode according to one embodiment of the present invention and a method for manufacturing the same will be described below with reference to the drawings.

[0024] After mechanical grinding the _{ZrMn 0.6 Cr 0. 1 V 0.2 Ni} 1.2 is one of the AB ₂ type Laves phase alloys as the hydrogen-absorbing alloy, the alloy powder carboxymethylcellulose - scan (CMC) aqueous solution and A water-soluble dispersion of a fluororesin was added and kneaded to form a paste. At this time, the addition amounts of carboxymethyl cellulose (CMC) and the fluororesin were 0.1 wt.
%, 0.5 wt%. Then, as short fibers, conductive carbon fibers adjusted to a diameter of 0.1 mm or less and a length of 1 to 3 mm are mixed with the paste so as to be 0.5 wt% with respect to the hydrogen storage alloy. This paste was kneaded. This paste composition is referred to as paste A.

Next, paste A has an average particle size of about 1 μm.
Was added so as to be 2 wt% with respect to the hydrogen storage alloy. A paste composition obtained by similarly kneading the mixture is referred to as paste B.

Next, as a comparative example, a paste composition paste C prepared by the same method without adding carbon fibers or granular nickel powder to pastes A and B was used.

The paste viscosities were adjusted so that the water content of these pastes A, B, and C was approximately 14%. Iron having a hole diameter of 0.15 mm, an opening ratio of 50%, and a thickness of 0.1 mm was added to nickel. It was applied to plated punched metal. This coating was performed by passing through a slit with the paste adhered to the punching metal. Paste A, B, C
, And then dried to remove water and pressurized by a roller press. The electrode thickness after pressing was adjusted to be 0.48 mm.

The paste-coated hydrogen-absorbing alloy electrodes A, B and C thus obtained were cut into a width of 33 mm and a length of 210 mm, and the lead plate was attached to a punched metal by spot welding.

First, these hydrogen storage alloy electrodes A, B, C
A description will be given of the results of a veneer test in an open type, which is rich in electrolyte.

As an electrolytic solution, an aqueous solution of potassium hydroxide having a specific gravity of 1.30 was used, and a change in discharge capacity during a charge / discharge cycle was determined using a sintered nickel electrode having an excess capacity as a positive electrode and a hydrogen storage alloy electrode as a negative electrode. Examined. The charging and discharging were performed at 20 ° C., the charging was performed at 0.1 A per 1 g of the alloy for 5.5 hours, and the discharging was performed at 0.05 A per 1 g of the alloy at a battery voltage of up to 0.8 V.

FIG. 1 shows the results. The vertical axis in FIG. 1 shows the discharge capacity per 1 g of the alloy. As is clear from the figure, regarding the performance of the hydrogen storage alloy electrodes A, B, and C, the discharge capacity in the initial cycle is larger in the order of the electrodes B>A> C. The discharge capacity of the electrode C decreases as the charge / discharge cycle progresses, but the electrodes A and B maintain the discharge capacity stably.

Among the above results, it is considered that the difference in the discharge capacity at the beginning of the charge / discharge cycle was attributed to the addition of the carbon fiber and the addition of the granular nickel powder. Also,
Regarding the stability of the discharge capacity during the charge-discharge cycle test, it is considered that the alloy of the electrode C was dropped from the electrode and the mechanical strength of the electrode was insufficient. But,
It is considered that the addition of the carbon fiber contributed to the improvement of the electrode strength, since the alloys did not fall off at the electrodes A and B.

Next, these hydrogen storage alloy electrodes A, B,
A sealed battery was constructed using C, and the battery performance was evaluated.

As a counter electrode, a known foamed nickel electrode,
In addition, polypropylene non-woven separator treated with hydrophilic treatment
A sealed nickel-metal hydride storage battery was formed by winding three layers of a negative electrode, a separator, and a positive electrode in a battery case in a spiral manner. Then, specific gravity 1.2 in the battery case
An electrolytic solution in which 25 g / l of lithium hydroxide was dissolved was poured into the aqueous caustic potassium solution of No. 5, and sealed. This sealed battery is su
The battery was of the bC type and had a battery capacity of 2.8 Ah.

The sealed batteries A, B, and C using the hydrogen storage alloy electrodes A, B, and C are charged and discharged for 5 cycles under relatively mild conditions. It was confirmed that the battery had a standard discharge capacity of 8 to 2.9 Ah. Thereafter, a rapid charge / discharge cycle test in which charging was performed at 20 ° C. at 2.8 A (1 C) for 1.5 hours and discharging was similarly performed at 2.8 A (1 C) until the battery voltage reached 0.9 V was performed.

In the rapid charge / discharge cycle test, batteries A and B showed superior performance as compared with sealed battery C. 1
FIG. 2 shows the measurement results of the rapid discharge at the 00th cycle (20 ° C., 1 C), and FIG. 3 shows the relationship between the charge / discharge cycle and the discharge capacity of the battery. As shown in FIG.
When the discharge starts, the voltage gradually decreases. Batteries A and B exhibited flat voltages and large discharge capacities. on the other hand,
Regarding the cycle life characteristics, as seen in FIG.
Although the discharge capacity of battery C sharply decreased from around 250 cycles, batteries A and B maintained a very stable discharge capacity and had a long life in charge and discharge up to 500 cycles. Was.

The charge at 20 ° C. measured separately at 2.8 A (1 C) for 1.5 hours and the discharge at 2.8 A (1 C) were measured separately.
In the rapid charge / discharge cycle test in which the battery voltage was increased to 0.9 V in C), the gas pressure in the battery during charging was measured. As a result, the maximum internal pressure was highest in battery C, and this internal pressure was significantly reduced in batteries A and B. Have been.

The hydrogen storage alloy of the present invention has a great effect particularly when the main alloy phase is an AB ₂ type Laves phase alloy mainly composed of zirconium or nickel. For example, MmNi _3.8 Co _0.5 Mn _0.4 Al _0.3
An alloy having an AB ₅ type CaCu ₅ type structure, such as an alloy, was also effective.

In this embodiment, the case where a punching metal is used as the current collector to which the paste is applied has been described. However, an expanded metal or the like is also effective as a current collector. Although the example using carbon fiber as the short fiber has been described, a metal fiber material such as nickel or copper is also effective. Further, as the polymer binder, fluororesin and polyvinyl alcohol, fluororesin and thermoplastic elastomer, fluororesin and carboxymethylcellulose (CM
Any of C) is particularly desirable. An example in which nickel powder was used as the granular powder having an average particle diameter of 10 μm or less having hydrophilicity was described. In addition, metal powders such as copper, and metals such as nickel oxide, nickel hydroxide, copper oxide, and copper hydroxide were also used. Oxides and metal hydroxides are similarly effective.

[0040]

As is apparent from the above description of the embodiment, according to the present invention, the conductive occluded fibers are added to connect the hydrogen storage alloy particles in a mesh-like manner, thereby improving the mechanical strength of the electrode. Let it. By using a fluororesin and a polymer material together as a binder for the electrodes, the gas absorption capacity at the time of quick charging is improved. As a result, by using the hydrogen storage alloy electrode of the present invention, a secondary battery having excellent rapid charge / discharge characteristics and charge / discharge cycle life characteristics can be configured.

[Brief description of the drawings]

FIG. 1 is a diagram showing a single plate test result of a hydrogen storage alloy electrode according to one embodiment of the present invention.

FIG. 2 is a diagram showing rapid discharge characteristics at the 100th cycle in the sealed battery.

FIG. 3 is a diagram showing charge-discharge cycle life characteristics of the sealed battery.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Shozo Fujiwara 1006 Kadoma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Tsutomu Iwaki 1006 Kadoma Kadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) References JP-A-63-110552 (JP, A) JP-A-1-267960 (JP, A) JP-A-2-135665 (JP, A) JP-A-63-284758 (JP, A) JP-A-3-102767 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/24 H01M 4/26 H01M 4/38 H01M 4/62

Claims (4)

(57) [Claims] 1. A hydrogen storage alloy powder pulverized to a predetermined particle size, a conductive short fiber material connecting said hydrogen storage alloy,
Mainly polymer binder , average particle size is 10μm
A hydrogen-absorbing alloy electrode formed by applying a composition to which a hydrophilic particulate powder having an upper limit of 加 え is added to a conductive porous body and integrally forming the composition . 2. The hydrogen storage alloy electrode according to claim 1, wherein the conductive short fiber material is a metal fiber or a carbon fiber. 3. The hydrogen storage alloy according to claim 1, wherein the average particle size of the hydrogen storage alloy is 40 μm as an upper limit, and the main alloy phase is an AB ₂ type Laves phase alloy mainly composed of zirconium or nickel. electrode. 4. The hydrogen storage alloy electrode according to claim 1, wherein the hydrophilic granular powder having an average particle size of not more than 10 μm is a metal powder, a metal oxide or a metal hydroxide.