JPH04349348A - Metal oxide-hydrogen storage battery - Google Patents

Abstract

PURPOSE:To make a capacity high, extend a charge-discharge cycle life, make quick charging and discharging possible, and improve the durability of a battery by setting a separator having high corrosion resistance on the positive plate side and a separator having high liquid retaining property on the negative plate side. CONSTITUTION:Separators of at least two kinds of different materials or of the same kind is used double between a positive pole 2 and a negative pole 4 and a highly corrosion resistant separator 1 made of, for example, polyolefine (polypropylene) is placed on the positive pole 2 side. A separator 3 having good liquid retaining property and made of, for example, polyamide (nylon) is placed on the negative pole 4 side. Consequently, in a battery whose capacity is limited by the positive pole, oxygen gas generated from the pole 2 at the time of overcharging is brought into contact with mainly the separator 1 facing to the pole 2 and less frequently brought into contact with the separator 3 having relatively low corrosion resistance, so that the durability of the separator can be maintained. Also, since the separator 3 touches the pole 4, a battery can have quick charging and discharging properties and the battery life can be extended and the capacity becomes relatively high.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal oxide-hydrogen storage battery using a hydrogen storage electrode made of a hydrogen storage alloy or hydride that electrochemically absorbs and releases hydrogen as a negative electrode.

0002

[Prior Art] A hydrogen storage electrode using a hydrogen storage alloy or its hydride that reversibly absorbs and releases hydrogen is used as a negative electrode.
In nickel oxide-hydrogen storage batteries that use metal oxide, especially nickel oxide, as the positive electrode, a separator is usually used between the negative electrode and the positive electrode to prevent short circuits between the electrodes. In order for this separator to be suitable for various battery applications, it must first have low electrical resistance, electrolyte resistance, and oxidation resistance.
It is required to have high mechanical strength, and also to be impervious to harmful substances and have a high ability to retain electrolyte. From an economic point of view, it is desired that batteries be easy to assemble and inexpensive. It is very difficult to satisfy all of these properties; for example, materials that are resistant to electrolyte, have low electrical resistance, and are inexpensive are quite limited. From this perspective, potential separators include nonwoven and woven fabrics made of polyamide resin (hereinafter referred to as nylon) and polyolefin resin (hereinafter referred to as polypropylene), polyvinyl chloride, polyester, acrylic resin, and phenolic resin. Porous polymer membranes and microporous polyethylene (
Possible options include low/high density) films, semi-permeable membranes made of polyvinyl alcohol or cellophane, etc., but the separators currently used in alkaline secondary batteries include non-woven fabrics, woven fabrics made of nylon or polypropylene, The main material is microporous polyethylene film.

Metal oxide-hydrogen storage batteries are basically similar in structure to nickel-cadmium storage batteries that are in practical use, and similar separators are used. However, since the negative electrode constituent materials are different from conventional ones, there are many technical issues.

[0004] Among these, polypropylene separators have excellent oxidation resistance, but are inferior in liquid retention and hydrophilicity, and although they can be expected to have a long life, the liquid injection speed is slow and the number of man-hours increases. This leads to increased costs. Particularly in a battery system where the amount of electrolyte is limited, the amount of electrolyte retained in the separator may decrease due to expansion of the electrodes, which may lead to deterioration of battery characteristics. On the other hand, nylon separators are excellent in liquid retention and hydrophilicity, but are inferior to polypropylene separators in oxidation resistance. Therefore, it is possible to reduce the number of work steps, which leads to a reduction in weight, but the cycle life is shortened. Furthermore, the mechanical strength (durability) is not sufficient for applications that require long life and service life. This becomes more noticeable especially when the number of overcharged regions increases. Therefore, the properties of the separator are improved depending on the purpose, or by special treatment.

First, a nickel-hydrogen storage battery was proposed in which the separator made of nonwoven or woven fabric made of polyolefin resin (polypropylene) was subjected to hydrophilic treatment such as plasma treatment and sulfonation treatment to increase affinity and liquid retention to some extent. (Japanese Unexamined Patent Publication No. 115657/1983). On the other hand, there are also nickel-hydrogen storage batteries in which sulfone groups or alkali salt groups are added to some of the nonwoven or woven fabric separators made of polyolefin resin (polypropylene) to improve affinity and increase liquid retention. It has been proposed (Japanese Unexamined Patent Publication No. 1-57568). Furthermore, in order to improve high-rate charge/discharge characteristics, attempts have been made to arrange nylon nonwoven fabric and polypropylene nonwoven fabric individually on both sides of the positive electrode, and to adjust the amount of electrolyte by utilizing the difference in the amount of liquid retained between the two separators. It has been proposed (Japanese Unexamined Patent Publication No. 63-241880). This proposal uses a separator to adjust the amount of electrolyte retained between the positive electrode and the separator, and in applications that require long life, such as stationary storage batteries, separators with weak mechanical strength (durability) can be directly connected to the positive electrode. There are some parts that are intervening, so it is not a solution to extending the life of the battery. In addition, a proposal was made to wrap the hydrogen storage electrode in a polypropylene microporous film and place it opposite the positive electrode to limit the movement of oxygen generated at the positive electrode to the negative electrode during overcharging, thereby extending its life (Japanese Unexamined Patent Publication No. 62 -108468). However, the separator has relatively high resistance and lacks liquid retention and hydrophilicity, making it difficult to adjust the electrolyte using the separator alone.

[0006]

[Problem to be Solved by the Invention] In a nickel oxide-hydrogen storage battery that uses a hydrogen storage electrode made of a hydrogen storage alloy or its hydride as the negative electrode and a metal oxide, such as nickel oxide, as the positive electrode, there is usually a gap between the negative and positive electrodes. To prevent short circuits between electrodes, separators mainly made of organic polymer resin are used.

This nickel oxide-hydrogen storage battery has a structure basically similar to the nickel oxide-cadmium storage battery currently in practical use, and is made of nonwoven fabric made of polyamide resin (nylon) or polyolefin resin (polypropylene). Depending on the woven fabric and the purpose, separators such as microporous polyethylene films and semipermeable membranes such as cellophane are mainly used. However, because the negative electrode composition material is different from conventional alkaline storage batteries, such as nickel oxide/cadmium storage batteries, nickel oxide/iron storage batteries, and nickel oxide/zinc storage batteries, cycle life, rapid charging/discharging, etc.
There are many technical issues such as self-discharge characteristics.

Among these, polypropylene separators have excellent oxidation resistance, but are inferior in liquid retention and affinity, and although they can be expected to have a long life, they do not have sufficient rapid charging/discharging characteristics, and The penetration rate of the electrolyte into the
The increase in liquid injection time results in an increase in man-hours, leading to an increase in costs. Particularly in battery systems where the amount of electrolyte is limited, the amount of electrolyte held in the separator decreases due to expansion of the electrodes, which may lead to deterioration of battery characteristics. Another problem is that self-discharge at high temperatures is greater than that of currently used nickel oxide/cadmium storage batteries.

On the other hand, nylon separators have excellent liquid retention and hydrophilic properties, but are inferior to polypropylene separators in oxidation resistance, resulting in a short charge/discharge cycle life and a long service life. It cannot be said to be sufficient for the required purpose. In particular, when the number of overcharged regions increases, the degree of deterioration becomes even more remarkable. Similar to the aforementioned polypropylene separator, this separator also has the problem of large self-discharge. In these polypropylene and nylon separators, metal generated by dissolution and precipitation from the negative electrode during charging and discharging is deposited in the separator pores, causing a slight short circuit and a decrease in capacity.

[0010] To prevent this phenomenon, polyethylene,
Microporous polypropylene films are used to suppress the formation of metal dendrites from the negative electrode, but this increases the internal resistance of the battery and does not extend the battery's lifespan. In particular, it is often used in nickel oxide/zinc storage batteries, etc., but the charging/discharging cycle is currently 300 cycles or less, which is relatively short. In addition to the relatively high resistance of the separator, it also lacks liquid retention and hydrophilicity, making it difficult to adjust the electrolyte.

On the other hand, in order to improve the high rate charge/discharge characteristics, an attempt was made to arrange nylon and polypropylene nonwoven fabrics on both sides of the positive electrode, and to adjust the amount of electrolyte using the difference in the amount of liquid retained between the two separators. There are storage batteries that do this. In applications that require long life and durability, such as stationary storage batteries, there are parts of the separator (made of nylon) with low mechanical strength (durability) that are in direct contact with the positive electrode, which reduces self-discharge and reduces self-discharge. No fundamental solutions have been found to extend battery life or improve high-rate discharge performance.

The present invention solves these drawbacks by combining two or more separators made of different materials or two or more of the same material, by making the separator on the positive electrode side hydrophilic, and by reducing the fiber diameter of the separator on the negative electrode side. , By controlling the pore diameter, it has a high capacity and a long charge/discharge cycle life.
The purpose of the present invention is to obtain a metal oxide-hydrogen storage battery that is capable of rapid charging and discharging, has little self-discharge, and has excellent durability.

[0013]

[Means for Solving the Problem] In order to solve this problem, the present invention provides a metal oxide positive electrode and a method for electrochemically absorbing and absorbing hydrogen.
A negative electrode made of a hydrogen storage alloy or its hydride to be released, and an alkaline electrolyte, a separator made of two or more different materials between the positive electrode and the negative electrode, and a separator with excellent corrosion resistance on the positive electrode side, A separator with excellent liquid retention is placed on each negative electrode side.

[0014] The present invention also provides that two or more separators made of at least polypropylene and nylon nonwoven fabrics or woven fabrics are interposed between the positive electrode and the negative electrode, and of these, a nonwoven fabric made of polypropylene that has been subjected to a hydrophilic treatment is provided. Alternatively, a separator made of woven fabric is placed on the positive electrode side.

Furthermore, the present invention surrounds the negative electrode with a bag-shaped separator made of two or more different materials, with a polypropylene separator with excellent corrosion resistance on the positive electrode side and a nylon separator with excellent liquid retention on the negative electrode side. The lower part of the negative electrode is either open or surrounded by a separator.

There is also a device in which a plurality of separators made of the same material or a composite separator with cellophane provided in the center are arranged between both electrodes.

[0017]

[Function] With this structure, the metal oxide hydrogen storage battery of the present invention uses a double separator of two or more different or the same kind of materials between the positive electrode and the negative electrode, and uses a separator with excellent corrosion resistance, such as polyolefin. (polypropylene) is placed on the positive electrode side, and a separator with excellent liquid retention properties, such as polyamide (nylon), is placed on the negative electrode side, so in batteries with positive electrode capacity restrictions, oxygen gas is generated from the positive electrode during overcharging. mainly contacts the polypropylene separator facing the positive electrode, which has excellent corrosion resistance, and less often contacts the nylon separator, which has relatively low corrosion resistance, so that the durability of the separator is maintained.

Moreover, since the negative electrode is always in contact with the nylon separator, which has excellent liquid retention and hydrophilicity, the electrolyte is retained inside the separator, suppressing the increase in internal resistance of the battery, and normally Because it maintains low internal resistance, it has excellent rapid charging and discharging characteristics, and has the effect of extending battery life.

Furthermore, since two or more separators of the same type or different types are interposed between the positive electrode and the negative electrode, minute short circuits caused by metal dendrites occurring at the negative electrode can be suppressed to a certain extent.

In a battery with positive electrode capacity regulation, when overcharged as mentioned above, the following (chemical formula 1), (chemical formula 2), (chemical formula 3) occur.
) reaction decomposes the electrolyte and releases oxygen (O2) from the positive electrode.
is generated, which causes the hydrogen (H+) of the hydride to be generated at the negative electrode.
Reacts with to produce water (H2O).

[0021]

[Chemical formula 1]

[0022]

[Case 2]

[0023]

[Chemical formula 3]

[0024] If this reaction proceeds stoichiometrically, most of the oxygen generated during overcharging will be absorbed at the negative electrode, thereby suppressing the pressure rise within the battery. At this time, oxygen passes through the polypropylene separator, and when it passes through the nylon separator, it reacts with hydrogen in the hydride on or near the negative electrode surface to which this separator is in close contact, so the polypropylene separator is exposed to the oxidizing agent atmosphere. Since the nylon separator maintains a state close to a reducing atmosphere and also retains an electrolytic solution, it is less susceptible to the effects of oxygen, thus improving the durability of the separator.

When a relatively high pressure can be maintained, such as in a sealed cylindrical battery, the reactions of (Chemical Formula 1), (Chemical Formula 2), and (Chemical Formula 3) described above proceed smoothly, but the electrolyte is relatively large, This reaction does not necessarily occur in all long-life battery systems that require a long service life. A part of it becomes a gas and is released to the outside, and the electrolyte decreases by the amount that is released as a gas. Therefore, if the electrolyte is replenished at regular intervals, the cycle life will be further extended. In this way, even if the amount of electrolyte decreases, the electrolyte in the separator on the positive electrode side will decrease first, so the electrolyte in the separator on the negative electrode side, which has a strong ability to retain electrolyte, will not decrease much, and the effect of oxygen will be reduced. This will prevent deterioration of the negative electrode, which is susceptible to deterioration, that is, deterioration of the hydrogen storage alloy as much as possible.

Regarding this durability, multiple separators made of different materials will work effectively, but using multiple separators of the same material will prevent minute short circuits between the positive and negative electrodes, resulting in a longer life. .

[0027] If a semi-permeable membrane or a microporous film is laminated to the separator described above, or if these are placed between the separators, short circuits between the electrodes due to the metal dendrites of the negative electrode can be prevented to some extent compared to a separator that is not laminated. , it becomes possible to manufacture batteries with long charge/discharge cycles. A similar effect can be seen even when placed between separators made of the same material. On the other hand, by reducing the diameter of the fibers that are the constituent elements of the separator, reducing the pore size, and making the separator even more dense, we can prevent short circuits between the electrodes due to metal dendrites that occur on the negative electrode side, and absorb hydrogen, which forms the negative electrode. It has the effect of suppressing corrosion (oxidation) of alloys.

[0028] Furthermore, if a nonwoven or woven fabric made of polypropylene in the separator is subjected to hydrophilic treatment such as plasma treatment or sulfonation treatment, self-discharge, especially at high temperatures, is improved compared to an untreated separator. Ru. When a separator that is difficult to absorb electrolyte and has low liquid retention properties is treated to make it hydrophilic, the separator itself becomes hydrophilic and the holding power of the electrolyte increases, and the hydrogen ions generated from the negative electrode form oxyhydroxide (NiOO) at the positive electrode.
H) to form nickel hydroxide (Ni(OH)2) is reduced. That is, it is thought that the hydrophilic groups of the hydrophilized separator are doped with hydroxyl ions (OH-) or hydrogen ions (H+), and the reaction with H+ is apparently suppressed.

Using these separators, the negative and positive electrodes are alternately separated from the sides so that the top and bottom of the electrodes are open, and the separators made of different or similar materials are laminated through the separators. However, the usual configuration is to create group electrodes. In this configuration, active material powder falls off from the positive electrode and hydrogen storage alloy powder falls off from the negative electrode during charging and discharging. There is a risk that this fallen powder may cause a slight short circuit between the electrodes, so a separator is made into a bag-shaped bag to surround one of the electrodes, especially the negative electrode, or both the positive and negative electrodes, and a polypropylene separator with excellent corrosion resistance is placed on the positive electrode side. In addition, it is recommended to place a nylon separator with excellent liquid retention on the negative electrode side. This has the effect of preventing short circuits within the battery case due to falling of the active material from the positive electrode and the hydrogen-absorbing alloy powder from the negative electrode, thereby extending the life of the charge/discharge cycle characteristics.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A metal oxide-hydrogen storage battery according to an embodiment of the present invention will be described in detail below with reference to the drawings.

Example 1 The metal constituting the hydrogen storage alloy is a commercially available product (purity 99.9%).
A hydrogen storage alloy with an AB5 type structure was manufactured using the high-frequency induction heating melting method.

As an example of the alloy composition of the AB5 type structure, Mm is described in the reference of patent application number 2-189018.
An alloy consisting of Ni3.8Mn0.4Al0.3Co0.5 was produced (where Mm indicates a mixture of rare earth metals). This alloy is mechanically crushed to a particle size (diameter) of 50 μm using a crusher.
The powder was finely pulverized to a particle size of less than m to obtain a hydrogen storage alloy powder for a negative electrode. A water-repellent fluororesin such as polytetrafluoroethylene resin (PTFE) is added as a binder made of an alkali-resistant organic synthetic resin to this hydrogen storage alloy powder together with a solvent to form a paste. It was applied to the surface of an expanded metal (opening plate) and then pressure-molded to form a negative electrode. Alternatively, as another example, a binder consisting of a solution of polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) as a hydrophilic resin is added to the hydrogen storage alloy powder to form a paste, and a foamed electrode support is formed. The material was filled under pressure into a porous nickel body to form a negative electrode. A commonly used sintered electrode was used as the positive electrode.

A double separator made of different materials is used between both electrodes, and a separator 1 made of polyolefin, such as polypropylene, which has excellent corrosion resistance is placed on the positive electrode 2 side, and a separator 1 made of polyamide, which has excellent liquid retention properties, such as polypropylene, is placed on the positive electrode 2 side. A nylon separator 3 was placed on the negative electrode 4 side to form an electrode group constituting a single cell. The structure of this electrode group is shown in FIG. 1, and the structure of a nickel oxide-hydrogen storage battery using this electrode group is shown in FIG. In FIG. 2, a double separator 5 (1 and 3) is interposed between the positive electrode 2 and the negative electrode 4, which are placed in a battery case 6. The lid 7 of this battery container 6 has a liquid filling plug (also used as a safety valve) 8 and a lead plate 9 connected to the positive and negative electrodes.
, 10 are provided, and the electrode group is immersed in an electrolytic solution 11. The amount of electrolyte was set to about the height of the separator. Select the positive and negative electrodes so that the capacity ratio is 1:2,
A 20 Ah battery was constructed by stacking a plurality of electrodes. This battery is called A.

Example 2 The separator 5 used between the positive electrode and the negative electrode consists of various separators made of polypropylene 1 and nylon 3, and at least one of the separators is coated with a semi-permeable membrane, a microporous film 12, a polyethylene film, Everything is the same as in Example 1 except for the case where lamination (integration) with cellophane or the like or separators placed between separators (see FIG. 3) are used. This battery is called B.

Example 3 The separator 5 used between the positive electrode and the negative electrode is a separator made of polypropylene 1 and nylon 3 nonwoven or woven fabric, and the fiber diameter and pore diameter of the nylon 3 separator disposed on the negative electrode side All of the structures are the same as in Example 1 except for the separator structure in which the separator structure is smaller than that of one separator made of polypropylene.
is the same as This time, the fiber diameter of the separator placed on the negative electrode side is about 3 to 10 μm, and the apparent pore diameter of the fiber space is about 10 to 50 μm. Compared with the fiber diameter and pore size of the separator placed on the positive electrode side, ~3 times smaller. This battery is called C.

Example 4 A double separator made of different materials was used between both electrodes,
A separator 1 made of polyolefin, such as polypropylene, which has excellent corrosion resistance is placed on the positive electrode 2 side, and a separator 3 made of polyamide, such as nylon, which has excellent liquid retention properties is placed on the negative electrode 4 side to constitute a cell. In the electrode group, the polyolefin (
Everything is the same as in Example 1 except that the separator (made of polypropylene) is subjected to hydrophilic treatment, such as plasma treatment or sulfonation treatment. This battery is designated as D.

Example 5 In Example 4, a separator structure was adopted in which the fiber diameter and pore diameter of the three nylon separators disposed on the negative electrode side were smaller than the one polypropylene separator, and the fiber diameter of the nylon separator was about 3 to 10 μm. The apparent pore diameter of the fiber space is about 10 to 50 μm, which is about 2 to 3 times smaller than the pore diameter of the polypropylene separator. This battery is called E.

Example 6 A double separator made of different materials was used between both electrodes,
A separator 1 made of polyolefin, such as polypropylene, which has excellent corrosion resistance is placed on the positive electrode 2 side, and a separator 3 made of polyamide, such as nylon, which has excellent liquid retention properties is placed so as to be in contact with the negative electrode 4 side.
The negative electrode was arranged in a bag shape as shown in FIG. 4 with the polypropylene separator 1 and nylon separator 3. Therefore, the negative electrode is surrounded by the bag-like separator 13 composed of separators 1 and 3. Everything is the same as in Example 1 except for using this bag-shaped separator. This battery is designated as F.

Example 7 The separator 13 used between the positive electrode and the negative electrode consists of various bag-shaped separators made of polypropylene 1 and nylon 3, and at least one of the separators is coated with a semipermeable membrane or a microporous film, such as a polyethylene film, Everything is the same as in Example 6 except for the case where a separator laminated with cellophane or the like is used. This battery is called G.

Example 8 The separator 13 used between the positive electrode and the negative electrode consists of various bag-shaped separators made of polypropylene 1 and nylon 3, and the fiber diameter and pore diameter of the nylon 3 separator placed on the negative electrode side are the same as the polypropylene 1 separator. Everything is the same as in Example 6 except for the separator structure which is smaller than the separator. This battery is designated as H.

Example 9 Everything was the same as in Example 6 except that the polypropylene separator disposed on the positive electrode side was subjected to hydrophilic treatment, such as plasma treatment or sulfonation treatment. This battery is designated as I.

Example 10 A double separator made of different materials was used between both electrodes, and a polypropylene separator with excellent corrosion resistance was placed on the positive electrode side, and a nylon separator with excellent liquid retention was placed on the negative electrode side. Everything was the same as in Example 6 except that a water-repellent synthetic resin was interposed between at least one of the various separators and the electrodes. Here, fine powder of fluororesin was interposed between the negative electrode and the nylon separator. This battery is called J.

Example 11 A double separator made of different materials was used between both electrodes,
A separator 14 made of polyolefin with excellent corrosion resistance, such as polypropylene, is arranged to surround the positive electrode 2 in a bag shape, while a separator made of polyamide with excellent liquid retention property,
For example, the negative electrode 4 is surrounded by a nylon separator 15 in a bag-like manner. The electrode group is shown in FIG. A battery as shown in FIG. 2 was constructed using this electrode group. This battery is called K.

Example 12 A double separator made of different materials was used between both electrodes,
The negative electrode 4 is surrounded in a bag shape with a separator 16 made of polyamide, such as nylon, which has excellent liquid retention properties, and the negative electrode and the positive electrode are alternately laminated with separators 17 made of polyolefin, such as polypropylene, which has excellent corrosion resistance. , a polypropylene separator is in contact with the positive electrode,
Furthermore, the lower end portion 18 of this separator is immersed in the electrolyte in the battery container 6. The structure of the electrode group is shown in FIG. 6, and the state in which it is arranged in the battery case is shown in FIG. The electrolytic solution other than electrolytic solution 19 was contained within the separator and the electrode, and the amount of electrolytic solution was regulated so as not to use excess electrolytic solution, so that it was difficult for the electrolytic solution to be released from inside the battery. This battery is called L.

Example 13 The separator 5 used between the positive electrode and the negative electrode is a polypropylene separator 1, which is composed of two or more sheets and arranged between the two electrodes (see FIG. 8). All other details are the same as in Example 1. Let this battery be M.

Example 14 The separator 5 used between the positive electrode and the negative electrode is a polypropylene separator 1 composed of two or more sheets, and a semipermeable membrane (for example, cellophane) or a microporous film ( For example, polyethylene film) 12
(see Figure 9). All other details are the same as in Example 1. This battery is called N.

Example 15 Everything was the same as Examples 13 and 14 except that two or more polypropylene separators placed between the positive electrode and the negative electrode were subjected to hydrophilic treatment. Let these batteries be O and P.

Comparative Example The positive and negative electrodes were produced in the same manner as in Example 1, and these two electrodes were used for comparison in a battery consisting of one nylon separator and one polypropylene separator each. . This battery for comparison is Q
,R.

[0049] As a test condition, first, the charging capacity was 20Ah.
The battery was charged at 20A for 1.25 hours and discharged at 20A to a final voltage of 1.0V. The test temperature was room temperature for all tests. When the electrolyte amount decreased and the capacity decreased, fluid replacement was performed and a cycle life test was subsequently performed. The electrolyte concentration is specific gravity 1.
A 3KOH solution was used.

The experimental results are shown in (Table 1).

[0051]

[Table 1]

Regarding the batteries A to P of the present invention, the initial capacity is 19 to 20 Ah, and the capacity after 2,000 cycles changes to 18.15 to 19.1 Ah, and the degree of deterioration is very small. This phenomenon is considered to be due to a decrease in the performance of the nickel positive electrode.

On the other hand, conventional batteries Q and R have an initial capacity of 20 Ah, but the capacity after 2,000 cycles has decreased to 14 to 16 Ah. This is not caused by a decrease in the capacity of the positive electrode, but rather the metal contained in the hydrogen storage alloy that makes up the negative electrode dissolves and precipitates during charge/discharge cycles, and fine metal particles accumulate in the separator. It is thought that a slight short circuit phenomenon occurred in the battery, leading to a decrease in charging efficiency, that is, insufficient charging, resulting in a decrease in capacity. After the experiment, when the separator inside the battery was replaced, the discharge capacity was regenerated to almost the initial capacity, indicating that the separator was the cause.

Among the batteries of the present invention, a separator laminated with a microporous film, such as cellophane, is better than simply using a separator made of a different material, although the capacity is slightly lower due to the film resistance, but the life is longer. can be expected. A microporous polyethylene membrane or cellophane may be provided between the electrode and the separator or between each separator. Similarly, a battery using a separator with a small fiber diameter and a small pore diameter on the negative electrode side also suffers less capacity loss and is less susceptible to the effects of metal dissolving from the negative electrode. Although these batteries have a longer lifespan, they also have the problem of increased membrane resistance, so it is desirable to reduce the thickness of the separator, and accordingly, the capacity can be increased. Compared to using this film alone, the properties are improved by using a composite separator.

On the other hand, using a bag-shaped separator
Capacity reduction due to falling of the hydrogen-absorbing alloy powder and minute short circuits caused by powder particles are also suppressed, so a longer life can be expected. In addition, since the battery K has bag-shaped separators made of different materials for both the positive and negative electrodes, the capacity decrease is relatively small, and a longer life can be expected.

In the battery of the present invention having an initial capacity of 20 Ah, rapid charging and discharging is possible because the amount of electrolyte is retained in the separator, but in conventional batteries, the amount of electrolyte in the separator decreases, When the number of cycles exceeds 500 due to metal deposition, etc., a difference appears in the rapid charging/discharging characteristics, and the rapid charging/discharging characteristics also deteriorate.

Furthermore, although batteries D and I using hydrophilized separators do not significantly improve capacity, they have a high discharge capacity retention rate after being left unused. That is, self-discharge is also smaller than conventional batteries. The same can be said of batteries B and G that are laminated with microporous films.

Batteries F, G, and H using bag-shaped separators
・Since I, J, and K do not have hydrogen-absorbing alloy powder falling off, batteries A, B, C, D, and E using laminated separators
It is considered to have a longer lifespan. In particular, regarding the battery L that combines both types of separators, if the amount of electrolyte is limited and the electrolyte is retained within the separator and electrodes, the capacity will be slightly lower, but the electrolyte will be reserved at the bottom of the battery. The lower end of the separator is immersed in this, and when the electrolyte in the separator decreases due to capillary action, the reserved electrolyte is sucked up, so the capacity decrease is small even after 2,000 cycles. In particular, it works to suppress the rise in battery internal pressure during charging. This battery required only a small number of fluid replacements, about once every 500 cycles. However, since other batteries use a relatively large amount of electrolyte, water in the electrolyte decomposes during overcharging and is discharged as a gas, resulting in a decrease in electrolyte. Therefore, fluids were replenished as necessary. Fluid replacement was performed approximately once every 300 cycles. Since Battery J has a fluororesin interposed between the electrode and the separator, gas absorption occurs at the negative electrode during overcharging.
Replenishment of electrolyte solution is also small, and only needs to be replenished once every 500 cycles, and is considered to have a certain degree of gas absorption effect.

On the other hand, in conventional batteries M/N, only a commercially available separator is interposed between the positive electrode and the negative electrode, so the amount of electrolyte held in the separator decreases with cycle life, and the capacity decreases. It is thought that this is making the decline even greater. In addition to the slight short circuit caused by the metal particles coming out of the hydrogen storage alloy, no significant recovery was seen even after replenishing the electrolyte. Capacity recovery cannot be seen unless the separator is replaced, but with the battery of the present invention, 2.
A lifespan of 000 cycles has been confirmed. The reason for this improvement is that the use of double separators and the placement of a polypropylene separator with excellent durability (oxidation resistance) on the positive electrode side prevent oxygen gas from being released during overcharging. It is thought that it is not easily affected.

On the other hand, since a nylon separator with excellent liquid retention properties is disposed on the negative electrode side, the electrolyte in the separator is relatively unlikely to run out, and the decrease in capacity is considered to be small. In this way, it has become possible to extend the life of the battery by duplicating separators made of different materials and using them for the positive and negative electrodes. In the battery of the present invention, the lack of electrolyte in the separator due to expansion of the electrodes during charging and discharging is improved by using double separators. Additionally, by using double separators of the same material, it is possible to prevent minute short circuits during charge/discharge cycles, which helps extend life. As seen in batteries M, N, O, and P, the rate of capacity decline is slightly higher than that of separators made of different materials, but there is no problem from a practical standpoint.

However, depending on the thickness of the separator, the high rate charge/discharge characteristics deteriorate as the resistance increases, but this can be improved by adjusting the thickness. Although it may not be possible to expect a cycle life as long as batteries A to L, they have a lifespan of over 2,000 cycles.

When using a plurality of separators made of the same material, polyolefin (polypropylene), polyamide (nylon), etc. were used, but the thickness was 0.8 to 0.25.
mm is optimal. If the thickness is less than 0.8 mm, even if a plurality of sheets are used, repeated charge/discharge cycles will cause a slight short circuit, resulting in a decrease in capacity. On the other hand, if the thickness is greater than 0.25 mm, there are problems such as high internal resistance of the battery and an increase in the size of the battery. Similarly, the thickness of cellophane and microporous film is 0.0
A range of 1 to 0.1 mm is preferable.

In this embodiment, separators made of nylon and polypropylene were used, but two or more separators made of other polyamides or polyolefins may be used. Further, other methods for improving wettability as a hydrophilic treatment may be used. In addition to the AB5-based multi-element alloy, the hydrogen storage alloy may also be an AB2-based, AB-based multi-element alloy, or a mixture thereof.

[0064] We have taken up an example in which the negative electrode is surrounded by a nylon separator in a bag shape, and the negative electrode and the positive electrode are alternately laminated with polypropylene separators. may be alternately laminated with nylon separators to form an electrode group, but in order to relatively limit the amount of electrolyte and reduce fluid replacement maintenance, it is preferable to have a small amount of electrolyte on the negative electrode side. It can be said that it is more effective to immerse a polypropylene separator in the reserved electrolyte. In this example, a sintered electrode was used as the positive electrode, but a foamed electrode, a porous metal fiber electrode, or a painted non-sintered electrode may also be used.

By combining a polyamide separator with good liquid retention and a polyolefin separator with good durability, a long-life battery can be obtained that has both electrolyte retention and durability at the same time. This separator is applicable not only to open-type stationary batteries but also to sealed-type batteries for portable devices. Further, using two or more separators made of the same material is also effective from the viewpoint of preventing minute short circuits and retaining a large amount of electrolyte, and can provide a battery with a somewhat long life. The thickness and number of sheets cannot be increased due to energy density, and there is an optimum point.

[0066]

[Effects of the Invention] As is clear from the above description of the embodiments, the metal oxide hydrogen storage battery of the present invention has a long charge/discharge cycle life, exhibits a relatively high capacity, and is capable of rapid charging and discharging. The present invention provides a metal oxide-hydrogen storage battery with excellent durability.

[Brief explanation of drawings]

[Fig. 1] A diagram showing an electrode configuration group used in the battery of the present invention.

[Fig. 2] A diagram showing the configuration of the metal oxide-hydrogen storage battery of the present invention.

[Figure 3] Diagram showing the configuration of a multilayer separator interposed between a positive electrode and a negative electrode

[Figure 4] Diagram showing an electrode group in which the negative electrode is surrounded by a bag-shaped multilayer separator.

[Fig. 5] A diagram showing an electrode group in which the negative electrode and the positive electrode are each surrounded by bag-like separators made of different materials.

[Fig. 6] A diagram showing an electrode group in which a negative electrode is surrounded by a bag-like separator and the negative electrode and positive electrode are alternately stacked.

[Fig. 7] A diagram showing a state in which the electrode group of Fig. 6 is built-in and the lower end of the separator on the positive electrode side is immersed in an electrolytic solution.

[Fig. 8] A diagram showing an electrode configuration group used in the battery of the present invention.

[Figure 9] Diagram showing the configuration of a multilayer separator interposed between a positive electrode and a negative electrode

[Explanation of symbols]

1 Separator (made of polyolefin) 2 Positive electrode 3 Separator (made of polyamide) 4 Negative electrode 5 Double separator 6 Battery case 7 Lid 8 Liquid injection tap 9 Lead plate 10 Lead plate

Claims (18)

[Claims] 1. A metal oxide positive electrode, a negative electrode made of a hydrogen storage alloy or its hydride that electrochemically absorbs and releases hydrogen, and an alkaline electrolyte, and between the positive electrode and the negative electrode there are two types of negative electrodes. A metal oxide-hydrogen storage battery in which separators made of different materials as described above are arranged, with the separator having excellent corrosion resistance placed on the positive electrode side and the separator having excellent liquid retention property placed on the negative electrode side. Claim 2: Two separators are used between the positive electrode and the negative electrode.
2. The metal oxide-hydrogen storage battery according to claim 1, wherein the metal oxide-hydrogen storage battery is made of at least one different material, and at least a polyolefin separator is disposed on the positive electrode side and a polyamide separator is disposed on the negative electrode side. Claim 3: A claim in which the separator used between the positive electrode and the negative electrode is made of two or more different materials, and both or one of the nonwoven fabric or woven fabric constituting the separator is laminated with a microporous film or cellophane. 1. The metal oxide-hydrogen storage battery according to 1. 4. The oxidation method according to claim 1, wherein in the separator of two or more types of separators made of at least polyolefin and polyamide non-woven fabric or woven fabric, the member having the smallest fiber diameter and the smallest pore diameter is disposed on the negative electrode side. Metal-hydrogen storage battery. 5. A metal oxide positive electrode, a negative electrode made of a hydrogen storage alloy or a hydride thereof that electrochemically absorbs and releases hydrogen, and an alkaline electrolyte, the at least one of which is interposed between the positive electrode and the negative electrode. A metal oxide-hydrogen storage battery in which a nonwoven or woven fabric made of polypropylene that has been subjected to a hydrophilic treatment is placed on the positive electrode side in a separator made of two or more different materials such as nonwoven fabric or woven fabric made of polypropylene and nylon. Claim 6: A separator made of two or more different materials made of at least polypropylene and nylon non-woven fabric or woven fabric, wherein a nylon separator with the smallest fiber diameter and smallest pore diameter is arranged on the negative electrode side. Item 5. The metal oxide-hydrogen storage battery according to item 5. 7. A bag comprising a metal oxide positive electrode, a negative electrode made of a hydrogen storage alloy or its hydride that electrochemically absorbs and releases hydrogen, and an alkaline electrolyte, the negative electrode being made of two or more different materials. The bag-shaped separator is a metal oxide hydrogen storage battery in which a polypropylene separator with excellent corrosion resistance is placed on the positive electrode side, and a nylon separator with excellent liquid retention is placed on the negative electrode side. 8. The negative electrode is surrounded by a bag-like composite separator made of two or more different materials, and the bag-like separator made of a plurality of sheets is made of at least a nonwoven fabric or a woven fabric made of polypropylene, nylon, and the like. 8. A metal oxide-hydrogen storage battery according to claim 7, wherein one side is laminated with a microporous film or cellophane. Claim 9: A separator made of two or more different materials at least made of polypropylene and nylon,
8. The metal oxide hydrogen storage battery according to claim 7, wherein a separator made of a nonwoven or woven fabric made of polypropylene that has been subjected to a hydrophilic treatment is disposed on the positive electrode side. Claim 10: In a separator made of two or more different materials consisting of at least polypropylene and nylon non-woven fabric or woven fabric, the nylon separator having the smallest fiber diameter and the smallest pore diameter is arranged on the negative electrode side. The metal oxide-hydrogen storage battery according to claim 7. 11. The negative electrode is surrounded by a bag-shaped separator made of two or more different materials, and the negative electrode is provided between at least a polypropylene separator with excellent corrosion resistance and the positive electrode, and between a nylon separator with excellent liquid retention and the negative electrode. 8. The metal oxide-hydrogen storage battery according to claim 7, wherein a binder such as a water-repellent synthetic resin is interposed between the metal oxide and hydrogen storage battery. 12. A metal oxide positive electrode, a negative electrode made of a hydrogen storage alloy or its hydride that electrochemically absorbs and releases hydrogen, and an alkaline electrolyte, and the positive electrode is made of a polypropylene bag with excellent corrosion resistance. A metal oxide-hydrogen storage battery in which the negative electrode is surrounded by a separator and the negative electrode is surrounded by a bag-like separator made of nylon with excellent liquid retention properties. 13. A metal oxide positive electrode, a negative electrode made of a hydrogen storage alloy or its hydride that electrochemically absorbs and releases hydrogen, and an alkaline electrolyte, and a polypropylene separator with excellent corrosion resistance is provided on the positive electrode side. The lower end of the separator is immersed in an electrolytic solution stored in a battery case, and the negative electrode is surrounded by a nylon separator with excellent liquid retention properties. 14. A metal oxide positive electrode, a negative electrode made of a hydrogen storage alloy or its hydride that electrochemically absorbs and releases hydrogen, and an alkaline electrolyte, and a plurality of electrodes are provided between the positive electrode and the negative electrode. A metal oxide-hydrogen storage battery with separators made of the same material. [Claim 15] A plurality of separators made of the same material are made of polyolefin, polyamide, cellophane, or a microporous film made of polyolefin, or a combination of two or more sheets of polyolefin or polyamide and cellophane or a microporous film, and a positive electrode and a negative electrode. The metal oxide-hydrogen storage battery according to claim 14, wherein the metal oxide-hydrogen storage battery is arranged between. Claim 16: Claim 1, wherein the plurality of separators made of the same material are made of polyolefin or polyamide, and a microporous film or cellophane is interposed between the plurality of separators.
5. The metal oxide-hydrogen storage battery according to 5. 17. In a plurality of polyolefin separators made of the same material, the separator is a nonwoven fabric or woven fabric made of polypropylene that has been subjected to a hydrophilic treatment, and is disposed between a positive electrode and a negative electrode. A metal oxide-hydrogen storage battery according to claim 1. Claim 18: The thickness of a plurality of separators made of the same material is 0.
．． The metal oxide according to claim 14, which has a thickness of 8 to 0.25 mm.
Hydrogen storage battery.