JP4767515B2 - Pocket hydrogen storage alloy electrode and nickel / hydrogen storage battery - Google Patents

Description

  The present invention relates to a pocket type hydrogen storage alloy electrode and a nickel / hydrogen storage battery.

In recent years, environmental issues have been greatly taken up, and management standards for nickel-cadmium storage batteries and lead storage batteries containing toxic substances have been raised, and regulations on use have progressed. Already, for small sealed storage batteries, replacement with lithium ion storage batteries or nickel / hydrogen storage batteries is rapidly progressing.
In particular, as a hydrogen storage alloy electrode used as a negative electrode for a conventional nickel / hydrogen storage battery, there is a paste type in which a negative electrode active material paste is applied to a porous substrate such as foamed nickel for a long time. In this case, the hydrogen storage alloy powder was dropped and oxidized, making it impossible to produce a storage battery that maintained satisfactory performance over a long period of time.
In order to solve this problem, an invention described in JP-A-4-280066 has been proposed. That is, the invention described in the publication provides a pocket type hydrogen storage electrode capable of maintaining a high capacity for a long time without using a conventionally added binder in order to prevent the hydrogen storage alloy powder from falling off. Therefore, an electrode body filled in a pocket-type or tube-type porous metal container with high alkali resistance together with hydrogen storage alloy powder alone or with conductive material powder is manufactured, and a plurality of peripheral parts thereof are connected and integrated with a current collector. There has been proposed a pocket type hydrogen storage electrode in which a lead wire is connected to the current collector.
Similarly, the invention described in Japanese Patent Application Laid-Open No. 2002-203544 also eliminates the disadvantage that the amount of hydrogen storage alloy or powder is reduced by the amount of addition of the binder. A pocket-type hydrogen storage electrode with improved life is proposed. That is, the invention relates to nickel obtained by filling hydrogen collector alloy powder between current collectors made of porous metal nickel strips folded in a U-shape, and then applying external pressure to the current collector to press-fit the current collector. / A cathode for a hydrogen storage alloy secondary battery is proposed.
On the other hand, in Japanese Examined Patent Publication No. 42-21236, as a cathode for an alkaline storage battery, a cadmium powder or a mixed powder of cadmium and iron powder is compressed and formed into a green compact (briquette) in a porous metal pocket. An invention relating to a pocket type cathode plate formed by filling and sealing is disclosed.
JP-A-4-280066 JP 2002-203544 A Japanese Patent Publication No.42-21236

However, as in the invention of Patent Document 1, a pocket-type hydrogen storage electrode in which a hydrogen storage alloy alone or a mixture with a conductive material is filled in a porous metal pocket container in a powder state has a capacity density. Is relatively small, resulting in a decrease in energy density and not being able to obtain a high-capacity battery, and during assembly into the battery, air is present between the particles of the filled powder and between the powder and the pocket. Intrusion or oxygen gas generated during use of the battery intrudes to form an oxide film on the particle surface, resulting in a decrease in electrical conductivity and an increase in electrical resistance. It will fall out of the pocket hole, so the battery will not be able to maintain high capacity for a long time, the polarization during discharge will be very large, resulting in inconveniences such as reduced energy density, reduced cycle life, reduced trickle life .
Such inconvenience is that, as in Patent Document 2, a hydrogen storage electrode in which powder sealed in a pocket is pressurized from the outside of the pocket and the pocket is pressure-bonded to the surface of the powder. Intrusion of oxygen gas can be prevented, but the above disadvantages can hardly be solved.
Further, in the pocket type cathode plate of Patent Document 3, since the powder was press-molded into a pocket, the packing density is increased, poor contact between the blanking Ricketts and the pocket, the electrical resistance increases, the conduction performance Resulting in lowering, increasing polarization during discharge, and deforming the pocket in the battery during assembly to the battery, weak mechanical strength, unable to maintain high capacity for a long time , Resulting in inconveniences such as cycle life reduction.
The present invention eliminates the above problems, increases the mechanical strength, reduces the polarization, improves the charge / discharge performance, maintains the high density energy, and improves the cycle life, trickle life, etc. An object of the present invention is to easily and reliably provide a pocket-type hydrogen storage alloy electrode that provides a storage battery.

According to the present invention, as described in claim 1, a briquette formed by compression molding a mixed powder of hydrogen storage alloy powder and nickel powder is placed in a porous metal pocket formed by folding a single perforated tape into a U-shape. A pocket type in which briquette loading pockets formed by loading and caulking and binding side edges that overlap each other are pressed from the outside with a flat plate press at a pressure of 500 MPa or more, and the pockets are pressure-bonded to the briquettes. It exists in the hydrogen storage alloy electrode.
Furthermore, the present invention relates to a nickel / hydrogen storage battery as described in claim 2, wherein the pocket type hydrogen storage alloy electrode of claim 1 is used as the negative electrode.

According to claim 1, the pocket type hydrogen storage alloy electrode is a porous metal pocket in which a briquette formed by compression molding a mixed powder of hydrogen storage alloy powder and nickel powder is folded into a U-shaped perforated tape. was loaded into a briquette loading pocket formed by caulking binding the side edges of polymerizing with each other, pressed at a pressure of 500MPa by the flat plate pressed from the outside, since the pocket was allowed crimped to the briquette, the said pocket A pocket-type hydrogen storage alloy electrode having high mechanical strength that can be crimped to the entire surface of the briquette and is not deformed by an external force can be obtained easily and reliably, and used as a negative electrode of a nickel / hydrogen storage battery as described in claim 2 Occasionally, the pocket-type hydrogen storage alloy electrode is subject to air oxidation during or after the battery is being installed. That with that oxidation is prevented by the oxygen gas, from falling out of the pocket hole of the hydrogen storage alloy powder and nickel powder disappears completely or almost, the electric resistance can be significantly reduced, the problems of the conventional pocket type hydrogen storage electrode In addition, the polarization at the time of discharge is remarkably reduced, excellent in high rate discharge, maintaining a high capacity for a long time, improving cycle life, trickle life, etc. Bring hydrogen storage battery.

Next, an embodiment of the present invention will be described in detail.
As the hydrogen storage alloy, an AB ₅ type alloy (A is a rare earth element, B is an element in which nickel and a part of nickel are substituted with a plurality of kinds of metals) can be used, and Ti—Cr type, Zr— AB ₂ type Laves hydrogen storage alloy such as Mn type can be used. As the conductive material, for example, nickel, carbon black and the like can be preferably used.

A production example of a pocket type hydrogen storage alloy electrode used as a negative electrode in the nickel / hydrogen storage battery of the present invention will be described below.
As AB ₅ type hydrogen-absorbing alloy, for example, MmNi _3.10 Mn _0.59 Al _0.21 (however, Mm is the mischmetal) nickel powder as hydrogen-absorbing alloy powder and a conductive material having the composition of, preferably, for example, INCO Co. # 255 A large amount of nickel powder was prepared, 90 parts by weight of the hydrogen storage alloy powder and 10 parts by weight of nickel powder were measured, and mixed with a mixer, for example, using a V blender to prepare a mixed powder. Next, the mixed powder is put into a briquette molding machine and subjected to pressure molding to produce a square briquette having a desired size. Next, the briquette is loaded into an alkali-resistant, highly conductive, thin porous metal pocket having a large number of small holes by perforation bent in a U-shape or U-shape, and a briquette loading pocket is produced. The pocket type hydrogen storage alloy electrode of the present invention is manufactured by pressurizing from the outside with a pressing force of 500 MPa or more with a flat plate press, and pressing both sides of the briquette on both side porous plate surfaces of the facing pockets. .

Thus, the pocket type hydrogen storage alloy electrode of the present invention is configured such that one of them has an area corresponding to the area of a predetermined negative electrode of a nickel / hydrogen storage battery, or a plurality of them are bonded together. Thus, it may be configured to have a predetermined negative electrode area or may be arbitrary.
The production method of these hydrogen storage alloy electrodes will be described. A briquette having a predetermined area corresponding to a required area of the negative electrode is produced from the mixed powder, and the briquette has an area suitable for loading the briquette. A pocket-type hydrogen storage alloy electrode can be manufactured with one briquette loading pocket by pressurizing a briquette loading pocket formed by loading into a porous metal pocket from the outside with a flat plate press at a pressure of 500 MPa or more.

In addition, while preparing a large number of rectangular briquettes in which the area of the predetermined negative electrode is equally divided in the vertical direction from the mixed powder, the U-shaped having the same length as the lateral (width) dimension of the negative electrode A large number of porous metal pockets are prepared, each briquette is loaded into each porous metal pocket, and the closing end portions of both side plates of the pocket projecting upward from the briquettes loaded on both sides thereof are folded inward. A plurality of briquette loading pockets are formed by sealing the opening surface of the U-shaped pocket to form a plurality of briquette loading pockets, and a number of briquette loading pockets corresponding to the vertical division of the negative electrode area The contact portions are bonded to each other by welding or the like, and then the briquette loading pocket coupling is pressed by a flat plate press at 500 MPa or more. It is possible to produce a pocket-type hydrogen storage alloy electrode in number of briquettes loading pocket.
As another manufacturing method, pressurization of 500 MPa or more by the flat plate press may be performed for each briquette loading pocket before connecting each briquette loading pocket.

  In addition, as a long U-shaped porous metal pocket, a long U-shaped porous metal pocket having a length several times the width of the negative electrode is produced, and a large number of the above-mentioned briquettes are loaded into this. After sealing, it may be cut to a predetermined size.

Furthermore, the briquette may be formed in a square shape or a regular square shape, and the porous metal pocket corresponding to the square shape may have a regular square surface and have a closing end portion.
Thus, the briquette loading pockets manufactured by these may be connected to each other in the vertical direction and / or the horizontal direction to produce a pocket type hydrogen storage alloy electrode having a required area.
Furthermore, the briquette loading pocket may be produced as follows. That is, a large number of U-shaped porous metal pockets formed in advance in half of the height of the briquette to be loaded were prepared, and briquettes were loaded into the U-shaped porous metal pocket. After that, the U-shaped porous metal pocket faced downward from the usual method is covered, the lower edges of both sides are brought into contact with the upper edges of both sides of the U-shaped porous metal pocket, and the abutting portions are welded. The briquette loading pocket may be produced by binding by caulking.

  In the pocket type hydrogen storage alloy electrode of the present invention manufactured by such various manufacturing methods, it is common to attach an electric lead tab to the corner portion of the upper edge by welding. In addition, it is generally preferable that a metal sheath for connecting the lead wire is fitted and pressed to both side edges to further increase the mechanical strength and improve the conductivity.

Next, production examples of various embodiments of the pocket type hydrogen storage alloy electrode suitable for use as the negative electrode of the nickel / hydrogen storage battery of the present invention will be described in detail.
Production Example 1
A hydrogen storage alloy powder having a composition of MmNi _3.10 Co _1.10 Mn _0.59 Al _0.21 and # 255 nickel powder manufactured by INCO were prepared. 10 mass parts of nickel powder was measured with respect to 90 mass parts of hydrogen storage alloy powder, and it mixed with V blender, and prepared mixed powder. This mixed powder was put into a briquette molding machine and pressed to produce a large number of negative electrode briquettes. Next, a briquette was loaded in a long porous metal pocket processed into a U-shape with an iron-nickel-plated 0.1 mm thick perforated tape with a molding machine without any gap, and then the upper surface opening of the long porous metal pocket was opened. After covering the surface with a long perforated tape, caulking and sealing the side edges that overlap each other to form a long briquette loading pocket that completely surrounds the four circumferences, the briquette After contacting the upper and lower surfaces in the length direction with each other by the number corresponding to the height of a predetermined electrode plate for manufacturing the loading pocket, the contact portions are pressure-bonded by an embossing roller, or After being bonded by welding, the briquette loading pocket connected body integrally connected to each other is cut at intervals equal to the width dimension of the negative electrode plate to be manufactured, and the cut surface is sealed with a U-shaped metal sheath. , Pressurized with 500MPa a flat press, fitted with a plate ears, thus, to produce a pocket-type hydrogen-absorbing alloy electrode of the present invention having a desired area. This electrode is referred to as negative electrode 1.

Production Example 2
Manufacture similar to Manufacture Example 1 except that the mixed powder used in Manufacture Example 1 is impregnated with a 5% PTFE treatment solution and then dried at 80 ° C. in an atmosphere of nitrogen gas before being pressed with a briquetting machine. A pocket type hydrogen storage alloy electrode is manufactured by the method, and this electrode is referred to as a negative electrode 2.

Production Example 3
Instead of the AB ₅ type hydrogen storage alloy powder of Production Example 1, a Laves alloy type hydrogen storage alloy powder having a composition of Zr _0.9 Ti _0.1 Ni _1.1 Co _0.1 Mn _0.6 V _0.2 was used, except that this was mixed with nickel powder. A hydrogen storage alloy electrode was produced by the same production method as in Production Example 1. Next, this was subjected to the following chemical conversion treatment to produce a pocket type hydrogen storage alloy electrode of the present invention.
That is, the chemical conversion treatment used a conventional pocket type nickel-cadmium battery manufacturing facility. The pocket type hydrogen storage alloy electrode manufactured above and the counter electrode of the stainless steel plate are stacked through a chemical separator, and are put into an electrolytic solution of a potassium hydroxide aqueous solution having a specific gravity of 1.30 (20 ° C.). The cycle of charging at current density for 4 hours and discharging for 2 hours was repeated 10 times. Then, it washed with water and dried at 80 degreeC in nitrogen gas, and manufactured the pocket type hydrogen storage alloy electrode which was formed. This electrode is referred to as the negative electrode 3.

Production Example 4
The same production method as in Production Example 1, except that the mixed powder used in Production Example 3 was impregnated with a 5% PTFE treatment solution and then dried at 80 ° C. in a nitrogen gas atmosphere before being pressed with a briquetting machine. A hydrogen storage alloy electrode was manufactured. Subsequently, this was subjected to the same chemical conversion treatment as in Production Example 3 to produce the hydrogen storage alloy electrode of the present invention. This electrode is referred to as a negative electrode 4.

For comparison, a sintered cadmium electrode was produced as follows.
That is, a slurry was prepared from nickel powder # 255 manufactured by INCO and an aqueous methylcellulose solution, applied to an iron-nickel punching sheet, dried, and fired in a decomposition gas to prepare a sintered substrate. Subsequently, nitric acid was added to an aqueous solution of cadmium nitrate to adjust the pH to prepare an impregnating solution on the sintered substrate, and the sintered substrate was impregnated and soaked with an aqueous sodium hydroxide solution, and filled with cadmium hydroxide. Finally, it was washed with water and dried to produce a sintered cadmium electrode. This electrode is referred to as the negative electrode 5.

Furthermore, a pocket type cadmium electrode was manufactured for comparison as follows.
Cadmium oxide powder and graphite powder were prepared. 5 parts by mass of graphite powder was measured with respect to 95 parts by mass of cadmium oxide powder, and mixed with a V blender. A pocket-type cadmium electrode was produced by the same treatment process as in Production Example 1, except that the mixed powder was not subjected to a process of pressing at 500 MPa by a flat plate press in the final process in the production method of Production Example 1. This electrode is referred to as the negative electrode 6.

Further, for comparison, a paste-type hydrogen storage alloy electrode was manufactured as follows.
That is, a hydrogen storage alloy powder and a carbon black powder having a composition of MmNi _3.10 Co _1.10 Mn _0.59 Al _0.21 were prepared. With respect to 99 parts by mass of the hydrogen storage alloy, 1 part by mass of carbon black was measured and mixed with a V blender. The mixed powder, 1% carboxymethylcellulose aqueous solution, and SBR dispersion were charged into a mixer and stirred to obtain a negative electrode paste. Next, the negative electrode paste was applied to an iron-nickel plating punching sheet, dried, and pressed with a roll press. Then, after baking in nitrogen gas, it cut and manufactured the paste type hydrogen storage alloy electrode which has the same area as manufacture example 1. This electrode is referred to as the negative electrode 7.

Next, the single electrode capacity of each negative electrode was confirmed as follows.
That is, a nickel tab was spot-welded to the negative electrodes 1 to 7 (10 mm × 30 mm × thickness arbitrary) manufactured as described above to produce electrodes. A flooded electrochemical cell was constructed using a nickel plate as the counter electrode, a mercury / mercury oxide electrode as the reference electrode, and a 1.30 / 20 ° C. potassium hydroxide aqueous solution as the electrolyte. After performing the initial charge for 25 hours with a current corresponding to 0.05 CA, the reference electrode was discharged to −0.75 V with a current corresponding to 0.2 CA. Next, charging was performed for 6 hours with a current equivalent to 0.2 CA, and discharging was performed to -0.75 V with respect to the reference electrode with a current equivalent to 0.2 CA for 3 cycles. From these, the capacity density of each storage alloy or cadmium active material was calculated. The results are shown in Table 1 below.

As is apparent from Table 1, the negative electrodes 1 to 4 which are pocket-type hydrogen storage alloy electrodes according to the present invention have a significantly larger capacity than the conventional sintered and pocket-type cadmium electrodes 5 and 6. Turned out to be. In particular, the negative electrodes 3 and 4 made of Laves alloy had a very large capacity. In addition, in the observation after the test was completed, a large capacity was obtained for the negative electrode 7 of the paste type AB ₅ hydrogen storage alloy, but the test condition was a flooded state without compression, so that the hydrogen storage was performed in the third cycle. The alloy layer was peeled off from the porous substrate and was just before dropping off. From this state, it was found that the paste type cannot be used in a bent type battery. In the negative electrodes 1 and 3 not subjected to PTFE treatment, the mixed particles were slightly removed, but no pocket deformation was observed. In the negative electrodes 2 and 4 treated with PTFE, neither the active material was removed nor the pockets were deformed. This was because PTFE was fiberized by pressurization and the particles of the mixed powder were tightly entangled and bound. Conceivable.

Next, the pressure applied by the flat plate press in the production of the pocket type hydrogen storage alloy electrode was changed from 0 to 1000 MPa, negative electrodes having different pressures were produced, the following tests were performed, and the potential change due to each pressure force The effect on (mV) was determined.
That is, each of the pocket type hydrogen storage alloy electrodes with different pressures was flooded using a nickel plate as a counter electrode, a mercury / mercury oxide electrode as a reference electrode, and a 1.30 / 20 ° C. potassium hydroxide aqueous solution as an electrolyte. A formula electrochemical cell was constructed. After performing the initial charge for 25 hours with a current corresponding to 0.05 CA, the reference electrode was discharged to −0.75 V with a current corresponding to 0.2 CA. Next, charging was performed for 6 hours with a current corresponding to 0.2 CA, and discharging was performed to −0.75 V with respect to the reference electrode with a current corresponding to 0.2 CA for 3 cycles. The polarization was obtained from the potential change of the. The results are shown in FIG.

As is clear from FIG. 1, the electric pressure between the particles of the mixed powder of briquette and between the briquette and the porous metal pocket is large and the potential change is large from the pressure of 0 to 500 MPa by the flat plate press. The potential change reached an equilibrium of 20 mV or less. From this result, if the pocket is pressure-bonded to the briquette with a pressure of 500 MPa or more, the polarization at the time of discharge becomes extremely small, and a pocket-type hydrogen storage alloy electrode with improved discharge characteristics is obtained. / It has been found that a hydrogen storage battery can be obtained.
Incidentally, the potential change was measured in the same manner as described above using the pocket type hydrogen storage alloy electrode manufactured in accordance with the example of the above-mentioned Patent Document 1. However, the potential change was 235 mV, and the polarization at the time of discharge was very high. Turned out to be great. This is because the mixed powder is only filled and encapsulated in a porous metal container, and an insulating binder is interposed between the particles of the mixed powder before filling and encapsulating, so that sufficient current collection is obtained. It is estimated that it was not.

  The negative electrodes 1 to 7 thus manufactured are stacked via a desired positive electrode and a separator to form an electrode plate group, which is incorporated into a nickel / hydrogen storage battery, and an alkaline electrolyte is injected, for example, into a bent type storage battery. To manufacture. As the separator, a polyolefin or hydrophilic polyolefin-based cloth or nonwoven fabric, a microporous separator made of PVC, or the like is preferably used.

There are desired types of positive electrodes to be combined with the negative electrodes 1 to 7, and some of the positive electrodes will be described below.
Production Example 1
Prepare nickel hydroxide powder and cobalt monoxide powder in which 3% zinc and 1% cobalt are dissolved, measure 95 parts by mass of nickel hydroxide powder and 5 parts by mass of cobalt monoxide powder, and mix with a V blender. Mixed powder was prepared. This mixed powder was put into a briquette molding machine and pressed to produce a large number of positive electrode briquettes. Next, a briquette was loaded in a long porous metal pocket processed into a U-shape with an iron-nickel-plated 0.1 mm thick perforated tape with a molding machine without any gap, and then the upper surface opening of the long porous metal pocket was opened. Cover the surface with a long perforated tape and caulk and bind the overlapping side edges to form a long briquette loading pocket completely enclosing the briquette, and then manufacture the briquette loading pocket After the side edges in the length direction are brought into contact with each other by the number corresponding to the height of the predetermined electrode plate, the contact portions are pressure-bonded by an embossing roller, or bonded by welding. After that, the briquette loading pocket array integrally connected to each other is cut at intervals equal to the width of the electrode plate, and the cut surface is sealed with a U-shaped metal sheath, and thus the pocket having the required area is obtained. It was produced a large number of expression nickel electrode plate. This electrode is referred to as a positive electrode 1.

Production Example 2
Prior to pressing the mixed powder with a briquette molding machine, the mixed powder was impregnated with PTFE 5% treatment liquid, dried in air at 80 ° C., and then put into a briquette molding machine and pressed. Many pocket type nickel electrodes were manufactured in the same manner. This electrode is referred to as a positive electrode 2.

Production Example 3
A large number of pocket type nickel electrodes were produced in the same manner as in Production Example 1 except that graphite was used instead of cobalt monoxide used as the conductive agent in Production Example 1. This electrode is referred to as a positive electrode 3.

Production Example 4
A slurry was prepared from INCO nickel powder # 255 and an aqueous methylcellulose solution, applied to an iron-nickel punching sheet, dried, and fired in a cracked gas to prepare a sintered substrate. Nitric acid is added to a mixed aqueous solution of nickel nitrate, cobalt nitrate, and zinc nitrate to adjust the pH to prepare an impregnating solution. The impregnated solution is repeatedly impregnated into the sintered substrate and soaked with an aqueous sodium hydroxide solution, and the sintered substrate is hydroxylated. Filled with nickel. Finally, an aqueous cobalt nitrate solution was impregnated, soaked, washed with water and dried to produce a sintered nickel electrode. Cobalt in the filled nickel hydroxide was 1% and zinc was 5%. This electrode is referred to as a positive electrode 4.

Production Example 5
A sintered nickel electrode was produced in the same manner as in Production Example 4 except that only the zinc nitrate used in Production Example 4 was used without using zinc nitrate. This electrode is referred to as a positive electrode 5.

  Next, in order to confirm the single electrode capacity of each of the positive electrodes 1 to 5, nickel tabs were spot welded to the respective single electrodes (10 mm × 30 mm × thickness is arbitrary) to prepare electrodes. A flooded electrochemical cell was constructed using a nickel plate as the counter electrode, a mercury / mercury oxide electrode as the reference electrode, and a 1.30 / 20 ° C. potassium hydroxide aqueous solution as the electrolyte. After carrying out preliminary charging for 2 hours at a current corresponding to 0.1 CA, the initial charging was performed for 7.5 hours at a current of 0.2 CA. Next, 3 cycles of discharge up to 0 V with respect to the reference electrode with a current equivalent to 0.2 CA and 6 hours of charging with a current equivalent to 0.2 CA were carried out. The utilization rate of nickel hydroxide was calculated. The results are shown in Table 2.

  As is apparent from Table 2, the pocket-type positive electrodes 1 and 2 showed high utilization rates similar to those of the sintered positive electrodes 4 and 5. When graphite was used as the conductive material, the utilization factor decreased as in the positive electrode 3. Use of a material other than graphite as the conductive material is preferred.

Next, the relationship between the presence or absence of briquette molding and the polarization was examined as follows.
As a pocket-type hydrogen storage alloy electrode, a negative electrode 8 formed by applying 500 MPa of pressure to the negative electrode 1 and the mixed powder used for the negative electrode 1 filled in a pocket without briquetting and sealed, Furthermore, a negative electrode 9 as a pocket-type cadmium electrode (not pressurized at 500 MPa) and a mixed powder used for the negative electrode 9 filled in a pocket and sealed with a pocket are subjected to a pressure of 500 MPa. A negative electrode 10 is prepared. Further, as a pocket-type iron electrode, an iron powder briquette-molded one is loaded into a pocket and sealed, and the negative electrode 11 is pressed with 500 MPa and filled with iron powder without briquetting. A negative electrode 12 is prepared by applying a pressure of 500 MPa to the sealed one, and these negative electrodes 1, 8, 9, 10, 11, and 12 are installed as electrodes, respectively. Nickel plate, mercury reference electrode / mercury oxide electrode, electrolyte with 1.30 / 20 ° C. of potassium hydroxide solution and the electro-chemical cell of flat Secluded expression. After performing the initial charge for 25 hours with a current corresponding to 0.05 CA, the reference electrode was discharged to −0.75 V with a current corresponding to 0.2 CA. Next, charging was performed for 6 hours with a current corresponding to 0.2 CA, and discharging was performed to −0.75 V with respect to the reference electrode with a current corresponding to 0.2 CA for 3 cycles. The polarization was obtained from the potential change of the. The results are shown in Table 3 below.

  As is clear from Table 3, there was no significant difference in polarization between the pocket type cadmium electrode and the pocket type iron electrode, with or without briquetting, but the pocket type hydrogen storage alloy electrode had a very large difference. Was recognized. This is because, in the case of a cadmium electrode and an iron electrode, since the charge / discharge reaction is a dissolution / deposition reaction, the metal ions dissolved during discharge are deposited as metal during the charge, whereas the interparticle conductivity is improved. In the case of a hydrogen storage alloy electrode, the charge / discharge reaction is not a dissolution / precipitation reaction, but a solid-phase reaction, and the surface is covered with an oxide film that cannot be reduced in an aqueous system. This is presumably because the conductivity cannot be improved. Therefore, in the pocket type hydrogen storage alloy electrode, it is particularly preferable to briquette the powder to enhance interparticle conductivity in order to improve polarization.

  Next, from the results of the unipolar tests of the negative electrodes 1 to 7 and the positive electrodes 1 to 5, an electrode was selected and a bent cell having a rated capacity of 50 Ah was produced by a conventional method. In this case, since the capacity density of the electrodes to be written is different, the negative electrode / positive electrode capacity ratio is fixed to 1.3, and the adjustment is made according to the electrode thickness without changing the area and the number of the electrodes. Produced. The configuration of each cell is shown in Table 4 below.

  For each of these test cells, after injecting the electrolyte solution, reconditioning was performed for 2 cycles at 0.1 CA, and the energy density of each cell was calculated. The results are shown in Table 5.

  As is apparent from Table 5, the test cell 2 in which the negative electrode 4 and the positive electrode 2 that are Laves-based hydrogen storage alloy electrodes were combined showed a very high energy density.

Next, a cycle life test and a high-temperature trickle life test were performed on various cells in order to evaluate the practicality as a bent battery.
The cycle life test was conducted at 0.2 CA for capacity confirmation after 50 cycles of discharging at 0.25 CA for 2.5 hours and charging at 0.25 CA for 3.5 hours at an ambient temperature of 25 ± 5 ° C. After measuring the discharge capacity up to a final voltage of 1.0 V, charging was performed at 0.2 CA for 8 hours, and this cycle was repeated.
In the high temperature trickle life test, the capacity is measured by discharging to a final low voltage of 1.0 V at 1.0 CA by leaving it charged for 7 days in a continuous low current charge word of 0.02 CA x 28 days at an ambient temperature of 45 ° C. The check cycle was repeated.
The results of the cycle life test are shown in FIG. 2, and the results of the high temperature trickle life test are shown in FIG.

  As is apparent from FIG. 2, the results of the cycle life test showed that the batteries using the pocket type hydrogen storage alloy electrodes of the batteries 1 to 4 and the battery 7 according to the present invention showed good results. In addition, even when compared with the nickel / cadmium batteries 5 and 6, the same results were obtained.

As is apparent from FIG. 3, the result of the above-mentioned high-temperature trickle life test is that there is no battery that shows a rapid capacity decrease in 20 cycles, and a bent nickel / hydrogen storage battery using the negative electrodes 2, 3, and 4 according to the present invention Were found to be suitable for practical use equivalent to bent-type nickel / cadmium batteries 5 and 6 using the negative electrode 5.
The cells 1 to 4 using the pocket type positive electrodes 2, 3 and 4 to which cobalt monoxide is added have a 1CA discharge capacity as compared with the cells 3 and 5 using the pocket type positive electrode 3 to which graphite powder is added. Because of its large size, the ratio of capacity to rated capacity at the beginning of the cycle remained high.
Furthermore, the cell 7 in which a microporous polyolefin film was provided on a part of a hydrophilic nonwoven polyolefin nonwoven fabric as a separator showed a better capacity retention rate. It is presumed that this is because the oxidation of the hydrogen storage alloy could be suppressed because the oxygen gas diffusion generated from the positive electrode during charging was more strongly suppressed.

As described above, according to the present invention, it is possible to provide a relatively inexpensive and high-performance bent battery, and to provide a battery that replaces a bent nickel / cadmium battery containing cadmium which is a conventional harmful substance. The value is very great.

The graph which shows the relationship between a press pressure and the voltage change at the time of electricity supply. The graph which shows the cycle life test result of various storage batteries. The graph which shows the high temperature trickle life test result of various storage batteries.

Claims (2)

A briquette made by compression-molding a mixed powder of hydrogen storage alloy powder and nickel powder is loaded into a perforated metal pocket with a perforated tape folded in a U-shape, and the side edges that overlap each other are caulked and bonded. A pocket-type hydrogen storage alloy electrode, characterized in that the briquette loading pocket formed by pressurizing the pocket from the outside with a flat plate press at a pressure of 500 MPa or more and crimping the pocket to the briquette.   A nickel / hydrogen storage battery comprising the pocket-type hydrogen storage alloy electrode according to claim 1 as a negative electrode.

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