JP4930674B2 - Sealed alkaline storage battery and its assembled battery - Google Patents

Description

  The present invention relates to a positive electrode in which a metal porous substrate is filled with an active material mainly composed of nickel hydroxide, a sealed alkaline storage battery using the positive electrode, and an assembled battery composed of a plurality of the positive electrodes, and more particularly to improvement in productivity. And over-discharge durability.

  In recent years, there has been a rapid increase in the number of electric devices that are required to be small and light, such as mobile electronic devices such as mobile computers and digital cameras. As a power source for these devices, a sealed alkaline storage battery using a positive electrode (= hereinafter referred to as a non-sintered nickel electrode plate) formed by filling a metal porous body with an active material mainly composed of nickel hydroxide, Energy per unit volume and unit mass is higher than nickel cadmium storage batteries and lead storage batteries using sintered nickel electrode plates. Of these, nickel-metal hydride storage batteries using an electrode made of a hydrogen storage alloy for the negative electrode are widely used as a power source that is particularly clean for the environment and as a power source for the electric equipment, such as hybrid electric vehicles (HEV) and conventional nickel cadmium. Applications have also begun in fields that require high output characteristics and long life characteristics, such as power tools such as power tools and toys that use batteries.

Non-sintered nickel electrode plates are formed by filling or coating an alkali-resistant metal porous body with an active material mainly composed of nickel hydroxide and a conductive agent precursor composed mainly of cobalt and a binder. It is manufactured by cutting to a predetermined dimension. The filling or coating of the active material is performed by making the powder into a paste with an aqueous solution in which a thickener is dissolved and immersing the metal porous body in the paste, or applying the paste to the metal porous body. .
Here, the “active material mainly composed of nickel hydroxide” (hereinafter sometimes abbreviated as “active material”) refers to hydroxides and oxides mainly composed of nickel and containing cobalt and zinc.

Compared with the sintered nickel electrode plate, the nickel electrode plate manufactured by this method has the advantages that it can be filled with a large amount of active material and that the process is simplified and the productivity is high. However, in such an electrode, the positive electrode powder mainly composed of active material particles is likely to drop off from the end face of the electrode plate, and the end of the metal porous body is easily exposed from the cut surface. When winding through the separator, there has been a problem that the dropped positive electrode powder or the metal piercing portion breaks through the separator and causes a short circuit, resulting in a defect.
The positive electrode powder is a mixture of a conductive agent precursor mainly composed of cobalt mixed with an active material mainly composed of nickel hydroxide, an additive such as a rare earth hydroxide or oxide, and a binder. Refers to that.

  In addition, even after the battery is assembled, the positive electrode plate repeatedly expands and contracts with charge and discharge, so that the positive electrode powder is likely to fall off. In such an electrode, when the positive electrode generates a decomposition gas of the electrolytic solution due to overcharge or overdischarge of the battery, the positive electrode powder mainly composed of active material particles is pushed out from the end face of the electrode plate and easily falls off. It was. In particular, it is difficult to prevent the positive electrode powder from falling off at the upper and lower edges of the positive electrode plate, so that there is a problem that a micro short-circuit progresses during use of the battery, and the battery cannot be used suddenly. It was.

Furthermore, in a non-sintered nickel electrode plate, a cobalt compound that generates divalent ions in an alkali is added to nickel hydroxide powder as an active material, or the surface of the nickel hydroxide powder is coated in advance. In addition, an electrical connection between a porous metal body having a large pore diameter and an active material as compared with the case of a sintered nickel electrode plate and an electrical connection between particles of active material powders are achieved. The cobalt compound is once dissolved in the alkaline electrolyte and reprecipitated on the surface of the electrode plate as Co (OH) ₂ . Furthermore, when this is electrochemically oxidized into a highly conductive cobalt oxide having a valence of 2 or more during the charging operation after battery assembly, a conductive network is formed between the nickel hydroxide active material particles that are originally poor in conductivity. Thus, a paste type nickel electrode capable of obtaining a sufficient discharge capacity is obtained. (For example, see Patent Document 1 and Patent Document 2)
JP 61-138458 JP 4-4698

  However, the non-sintered nickel electrode plate in which the conductive network is formed of the cobalt compound as described above does not have sufficient overdischarge performance. In normal battery use, once oxidized highly conductive cobalt oxide exists stably, for example, when it is momentarily discharged to a low voltage in a power tool application etc., 2 This is because a cobalt compound having a valence higher than that is reduced, and divalent cobalt as a reduction product is dissolved in an alkaline solution. The eluted Co ions diffuse into the separator or are taken into the internal pores of the active material, destroying the conductive network on the active material surface, making it impossible to maintain the electrical connection between the active material particles. It has been found that it causes a battery short circuit. In particular, when batteries are assembled and used as a power source for equipment, depending on the degree of variation in battery performance, a specific battery may be heavily loaded and reversed, causing overdischarge of the battery. There was a problem that the life of the assembled battery was reduced.

FIG. 1 shows a schematic structure of a cylindrical alkaline storage battery. In a battery requiring high output characteristics such as a hybrid electric vehicle (HEV), a power tool, a toy, etc., a pole group in which a long positive electrode plate and a negative electrode plate are spirally wound via a separator, It is comprised from the bottomed cylindrical exterior can which accommodates this, and the cover part which has a gas discharge valve which seals the opening part of this exterior can.
In order to collect the positive electrode and the negative electrode, one end in the longitudinal direction of each electrode plate is provided with an unfilled portion that is not filled with an active material or an additive, and these unfilled portions do not face each other. The pole group is wound around. A circular positive electrode current collector and a negative electrode current collector are welded to these unfilled portions protruding at both ends of the pole group, respectively, and then the positive electrode current collector and the lower surface of the lid portion are connected by current collecting leads. Each electrode plate is electrically connected, and current is collected from the entire circumference of the wound electrode group to ensure battery output. (Especially, this method of current collection is called the indirect current collection method, distinguishing it from a battery that collects current by removing the active material only in the longitudinal direction of the positive electrode plate and lead welding.)

In an indirect current collecting type battery that requires high output, an unfilled portion and a filled portion of an active material and an additive are formed in the longitudinal direction of a non-sintered nickel electrode plate, and these thicknesses are different from each other. For this reason, when the electrode group is wound, a pressure difference between the opposing negative electrode plate is generated, and the positive electrode powder mainly composed of the active material is dropped from the electrode plate in the boundary region between the unfilled part and the filled part. In order to solve the problem that the fracture end of the porous metal skeleton is easily exposed from the cut end surface of the electrode plate, a resin is applied to the boundary region between the unfilled portion and the filled portion of the non-sintered nickel electrode plate. Many proposals have been made. For example, a method of selectively surface coating with a hot-melt resin on a boundary region between an unfilled portion and a filled portion of a non-sintered nickel electrode plate is disclosed. (For example, see Patent Document 3 and Patent Document 4)
JP 2000-323136 A JP 2002-367607 A

  According to Patent Document 3 and Patent Document 4, in the battery assembly process, the positive electrode powder is detached from the boundary between the unfilled portion and the filled portion of the electrode plate, and the protruding portion of the metal porous body is exposed from the electrode plate. This can be suppressed to some extent. However, when a non-sintered nickel electrode plate with a thickness is wound up in a spiral shape, the electrode plate is wound up in a roughly circular shape, so that the active material is removed from the cracked portion. It is inevitable that the positive electrode powder as a main component falls off, and this method is insufficient to suppress the removal. Furthermore, on the negative electrode current collector side facing the lower end of the electrode plate on the side opposite to the current collector side of the positive electrode, an unfilled part and a filled part are formed in the same manner as the positive electrode. A pressure difference with the electrode plate is generated. Therefore, when the storage battery is charged / discharged, the positive electrode expands and contracts in volume, or gas generation from the positive electrode causes the positive electrode powder to fall off from the lower end of the positive electrode. For this reason, even the methods described in Patent Document 3 and Patent Document 4 do not lead to significant improvement.

Further, in order to improve the durability of the cobalt conductive network of the positive electrode, the surface of the active material particles mainly composed of nickel hydroxide is coated with a bivalent or higher cobalt compound, and the residual bivalent cobalt oxide compound is formed. A method of limiting is disclosed.
That is, at least a layer of cobalt hydroxide or cobalt oxyhydroxide on the surface of a powder composed of a hydroxide and oxide containing nickel and cobalt and zinc (defined as an active material mainly containing nickel hydroxide). (Hereinafter, referred to as “cobalt-coated nickel hydroxide active material”, sometimes abbreviated as “cobalt-coated active material”) (for example, Patent Document 5, Patent Document 6, and Patent Document 7). reference).
JP-A-8-148146 JP 2001-52695 A JP 2000-268820 A

  Conventionally, divalent cobalt has been converted to highly conductive cobalt oxide with higher conductivity by means of electrochemical oxidation (charging), which depends on slight differences in battery formation conditions. There is a problem that the electrical connection inside the positive electrode is insufficient, and a conductive network corresponding to the amount of the divalent cobalt compound which is dissolved and dispersed in the electrolytic solution is not formed. In the above method, the oxidation reaction of cobalt hydroxide is completed by using the means of chemical oxidation in the powder state in advance instead of the electrochemical oxidation (charging) after battery assembly. It is possible to form a divalent or higher valent cobalt compound that is not affected by various conditions such as conditions and charging current / time. However, since the conductive network generated by this method does not go through the process of dissolution and precipitation of divalent cobalt as in the prior art, it is only due to the contact between the particles, and the electrical connection between the particles is insufficient. For this reason, the non-sintered nickel electrode plate using the active material powder by these methods has a problem that the high-rate discharge performance is insufficient, and the battery is deep even if the above means are provided. In the event of overdischarge, cobalt reduction still occurs, so that sufficient overdischarge characteristics were not achieved.

  The present invention has been made in order to solve the above-mentioned problems, and it is possible to improve the short-circuit resistance and over-discharge durability of a sealed alkaline storage battery using a non-sintered nickel electrode plate, and a plurality thereof. For the purpose of improving the cycle life of the assembled battery, it is an object to provide a high-performance sealed alkaline storage battery and a plurality of the assembled batteries with high yield.

  In order to achieve the above-mentioned problems, the present inventors have conducted intensive studies, and as a result, have obtained a powder obtained by forming at least a cobalt hydroxide or cobalt oxyhydroxide layer on the surface of a powder mainly composed of nickel hydroxide. As a material, in a non-sintered nickel electrode plate filled with a porous material, impregnating a specific area of the lower edge of the electrode plate with a specific penetration resin can realize an alkaline storage battery with excellent short-circuit resistance. In addition, when filling the cobalt-coated active material powder, surprisingly, excellent short-circuit resistance is achieved by adding a specific amount of a specific rare earth hydroxide or oxide to the cobalt-coated active material powder. Alkaline power storage with excellent characteristics while maintaining the expansion and contraction of charge / discharge, overdischarge, and dropping due to gas generation caused by overcharge and suppressing the decrease in cobalt conductivity due to overdischarge Found that to obtain, it has completed the present invention. In addition, by making the battery created using these methods into an assembled battery, the durability of overcharge and overdischarge caused by the battery capacity variation unique to the assembled battery and the variation in charging and discharging characteristics can be improved. An assembled battery having extremely excellent cycle life performance can be obtained. In addition, for batteries that require high-rate discharge, specific batteries are not selectively damaged even when discharged to a low voltage instantaneously, and maintain high-rate discharge performance in assembled batteries. Thus, the present inventors have found that it is possible to realize an assembled battery having an extremely excellent overdischarge durability characteristic. The present invention employs the following means in order to solve the above problems.

(1) In the battery case, a layer of cobalt hydroxide or cobalt oxyhydroxide is formed on the surface of a powder composed of a metal porous substrate, nickel, mainly cobalt and zinc-containing hydroxide and oxide. A positive electrode plate filled with a mixture of rare earth hydroxide or oxide, a negative electrode plate, a cylindrical electrode group constituted by winding a separator, a positive electrode current collector, a negative electrode current collector, and an electrolyte solution, In a sealed alkaline storage battery comprising a lead that electrically connects a positive electrode plate and a positive electrode current collector to a lid electrically insulated from the battery case via an insulator, the positive electrode plate has upper and lower ends thereof Among them, at least the lower end portion is impregnated with a resin having a penetration of 0.15 mm or more and 2.6 mm or less at 25 ° C., which is impregnated from the lower end surface of the positive electrode plate filling portion by 0.2 mm or more. It is a storage battery. (Claim 1)
(2) The positive electrode plate is impregnated at least at the lower end with a resin having a penetration of 0.15 mm or more and 2.6 mm or less at 25 ° C. from the lower end surface of the positive electrode plate filling portion to 0.2 mm to 1.0 mm. (1) The sealed alkaline storage battery according to the above (1). (Claim 2)
(3) The sealed alkaline storage battery according to (1) or (2), wherein the resin is a saturated hydrocarbon. (Claim 3)
(4) The sealed alkaline storage battery according to any one of (1) to (3), wherein the rare earth contains at least ytterbium. (Claim 4)
(5) The rare earth hydroxide or oxide has at least a layer of cobalt hydroxide or cobalt oxyhydroxide formed on the surface of powder composed of hydroxide and oxide mainly containing nickel and cobalt and zinc. The sealed alkaline storage battery according to any one of (1) to (4), wherein 1 to 3 parts by weight in terms of oxide amount is added when the powder is 100 parts by weight. (Claim 5)
(6) The cobalt hydroxide or cobalt oxyhydroxide formed on the surface of the powder consisting of hydroxide and oxide containing cobalt and zinc mainly containing nickel contains cobalt and zinc mainly containing nickel. When 100 parts by weight of the powder in which at least a layer of cobalt hydroxide or cobalt oxyhydroxide is formed on the surface of the powder composed of hydroxide and oxide is 100 parts by weight, 4 to 8 parts by weight in terms of metallic cobalt is contained. The sealed alkaline storage battery according to any one of (1) to (5) above. (Claim 6)
(7) The negative electrode according to any one of (1) to (6), wherein the negative electrode is made of a hydrogen storage alloy powder composed mainly of a rare earth element that absorbs and desorbs hydrogen and a transition metal element containing nickel. It is a sealed alkaline storage battery. (Claim 7)
(8) An assembled battery comprising a plurality of the sealed alkaline storage batteries according to any one of (1) to (7), and a plurality of the batteries. (Claim 8)

In the present invention, the lower end surface (end surface opposite to the positive electrode current collector) of the positive electrode plate filling portion is used as an index indicating the degree of resin impregnation to the lower end portion (end portion opposite to the positive electrode current collector) of the positive electrode plate. The widths of “0.2 mm or more” and “0.2 mm to 1.0 mm” described in claims 1 and 2 are the thickness of the positive electrode plate parallel to the height and the thickness. On the other hand, in the cross section cut perpendicularly, it means the average width from the lower end surface of the positive electrode plate filling portion observed with a magnifying glass (the same applies to the following examples). The degree of resin impregnation can be defined by the amount of resin, such as the weight or volume of the resin. However, in the weight definition, the above-mentioned coating range is not unambiguous for various resins having different specific gravities, and In the volume definition, when the porosity of the positive electrode plate is different, the height when impregnated with a resin of the same volume is different and the covering range by the resin may not be unambiguous.
Further, the “penetration” of the resin in the present invention is an index representing the hardness of the material (resin), and the value of the penetration at 25 ° C. evaluated by the method prescribed in ASTM D1321 in the unit of mm. It is shown.

According to the first and second aspects of the present invention, a sealed alkaline storage battery having excellent overdischarge resistance can be provided with high yield.
According to claim 3 of the present invention, a sealed alkaline storage battery with high productivity can be provided.
According to the fourth and sixth aspects of the present invention, particularly excellent effects are exhibited regarding the overdischarge resistance of the cobalt conductive network.
According to claim 5 of the present invention, the effect of addition of rare earth hydroxide or oxide can be remarkably exhibited.
According to claim 7 of the present invention, sealed nickel-metal hydride having excellent environmental load characteristics in combination with the effect of providing overdischarge durability while maintaining short-circuit resistance according to claims 1 to 7. A storage battery can be provided.
According to claim 8 of the present invention, it is possible to provide an assembled battery having overdischarge durability while maintaining short circuit resistance.

As a result of intensive studies, the present inventors have confirmed that the positive electrode occupies a large part of the yield at the time of manufacturing the alkaline storage battery, the short circuit problem of the battery after repeating the cycle, and the performance deterioration at the time of battery overdischarge.
Therefore, in order to improve the yield at the time of battery assembly, strengthen the conductive network made of cobalt of the positive electrode in overdischarge and reduce the short-circuit occurrence rate after the cycle elapsed, we examined the configuration of the non-sintered nickel electrode plate, It has been found that by making the configuration specific, it is possible to obtain surprising yield improvement, overdischarge resistance, and short circuit occurrence rate reduction performance after a cycle.

  That is, cobalt hydroxide and rare earth hydroxide are formed on the active material in which a layer of cobalt hydroxide or cobalt oxyhydroxide is formed on the surface of a powder composed of hydroxide and oxide mainly containing nickel and cobalt and zinc. Alternatively, the high-rate discharge performance of the battery is obtained by impregnating the lower edge portion of the positive electrode plate mixed with oxide and impregnating 0.2 mm or more with a resin having a penetration of 0.15 mm or more and 2.6 mm or less at 25 ° C. Reinforcement of the cobalt conductive network is achieved without reducing the. This is because the cobalt coating layer is formed on the active material surface in advance to complete the oxidation conversion of cobalt from divalent to trivalent, and by adding cobalt hydroxide, cobalt bivalent dissolution and precipitation reaction Thus, the active material particles can be connected. Furthermore, by impregnating a specific area at the lower end of the positive electrode with a resin at a specific depth, the occurrence of short-circuit failure during battery assembly is greatly reduced, and the short-circuit occurrence rate of the battery is also greatly reduced during the cycle. I was able to. In particular, it was confirmed that when the resin impregnation was 0.2 mm or more with a resin having a penetration of 0.15 mm or more and 2.6 mm or less at 25 ° C., an extremely excellent yield improvement was obtained, which was preferable. By impregnating the electrode with resin in a specific range, the occurrence of burrs in the porous metal used as a substrate generated by rubbing the positive electrode and the guide when the positive electrode is wound is suppressed, and the nickel electrode plate is spirally formed. When the electrode plate is wound while being wound so as to be roughly circular when wound, the positive electrode powder mainly composed of the active material from the cracked portion is removed, and a new metal porosity is generated in the cracked portion. Since the breakthrough of the separator due to body piercing can be effectively suppressed, the battery assembly yield is also improved.

  The reason is not necessarily clear, but when a specific rare earth hydroxide or oxide is mixed and added to the positive electrode active material, the decrease in capacity, which is thought to be due to reduction of the conductive network due to cobalt and loss of conductivity, is suppressed. It has been found that the overdischarge resistance is improved. In the alkaline aqueous solution, the rare earth compound exists in the electrode plate as a hydroxide via an ionic form. The eluted rare earth ions present in the alkaline aqueous solution form a film that protects the cobalt network, and the divalent cobalt that is reduced during battery overdischarge dissolves as ions and suppresses the separation from the active material surface. It is thought to have. As a result of investigation, among heavy rare earth elements such as Dy, Ho, Er, Yb, and Lu, oxide or hydroxide of ytterbium has excellent dispersibility, or has excellent cobalt elution prevention performance. As a result, it was found that the overdischarge resistance was improved.

  However, in an active material powder in which a layer of cobalt hydroxide or cobalt oxyhydroxide is not formed in advance on the surface of a powder composed of hydroxide and oxide mainly containing nickel hydroxide and cobalt and zinc, If a cobalt compound that generates divalent ions at the same time and a rare earth hydroxide or oxide are mixed and added, the rare earth ions suppress the dissolution and precipitation of divalent cobalt in an alkaline aqueous solution. There is a risk of making the network vulnerable. For this reason, by previously forming a layer of cobalt hydroxide on the surface of the powder consisting of hydroxide and oxide mainly composed of nickel hydroxide, and more desirably, by setting the surface cobalt layer as nickel oxyhydroxide, It has been found that a strong conductive network can be formed.

When batteries with high output characteristics, such as HEVs, power tools and toys, are discharged to a low voltage instantaneously, the positive electrode conductive network is destroyed as described above, and the capacity of the positive electrode can be sufficiently discharged. Disappear. Such a positive electrode is overcharged with its capacity remaining in the next charging process, and is accompanied by an oxygen gas generation reaction, and further promotes active material shedding from the electrode plate. In addition, gamma-type nickel oxyhydroxide having a low density is formed as a by-product under overcharge conditions, electrode plate thickness expansion occurs, and the detachment of the positive electrode powder mainly composed of the active material is further promoted.
In the electrode plate from which the positive electrode powder mainly composed of the active material has fallen, the possibility of a short circuit inside the battery is increased, and the rated capacity similar to the initial value is charged even though the electrode plate capacity is reduced. As a result, it becomes a condition of overcharge, and the battery performance deterioration is promoted.
As a result of intensive studies, the present inventors have found that when the resin impregnation is 0.2 mm or more with a resin having a penetration of 0.15 mm or more and 2.6 mm or less at 25 ° C., extremely excellent overdischarge durability is obtained. . Although this is not necessarily clear, it is considered that the impregnated resin strongly binds the positive electrode powders or the positive electrode powder and the positive electrode substrate with the resin in the positive electrode plate, thereby suppressing the falling off of the positive electrode powder.
If the resin has a melting point exceeding 120 ° C., the active material may be damaged when melted and impregnated. If the melting point is less than 75 ° C., the battery is charged. Since the resin may melt again inside the battery due to heat generated during discharge, the impregnating resin preferably has a melting point of 75 ° C. or higher and lower than 120 ° C.
In applications where the battery is repeatedly discharged to a low voltage instantaneously, such as in high power applications, it is extremely excellent by strengthening the cobalt conductive network as in the present invention and at the same time suppressing positive electrode powder dropout. Effect.

Furthermore, in a battery with a high output application used as an assembled battery, the battery is instantaneously discharged to a low voltage, or is generated due to a capacity difference caused by a difference in charge rate due to a difference in capacity between batteries or a variation in battery temperature. Overdischarge is likely to occur. In this case, the capacity reduction due to the destruction of the cobalt network has been a major factor in the capacity reduction of the battery.
Also, in high-rate discharge batteries, the active material is pushed out of the porous metal body, which is the substrate, by a large amount of high-speed gas generated by overdischarge at a high rate, and the positive electrode powder mainly composed of the active material falls off. Likely to happen. Furthermore, in the case of an assembled battery, since the capacity of a battery whose capacity has been reduced by overdischarge is small, the capacity is further reduced, which has been a major factor in reducing the performance of the assembled battery.
By assembling a battery in which active material dropping is suppressed at the same time as strengthening the cobalt conductive network as in the present invention, a specific battery is selectively damaged even when it is momentarily discharged to a low voltage. Performance can be maintained without receiving.

  When forming a surface layer made of cobalt hydroxide or cobalt oxyhydroxide on the surface of powder consisting of hydroxide and oxide containing cobalt and zinc mainly containing nickel, it contains cobalt and zinc mainly containing nickel. When the powder in which at least a layer of cobalt hydroxide or cobalt oxyhydroxide is formed on the surface of the powder composed of hydroxide and oxide is 100 parts by weight, the amount is 4 to 8 parts by weight in terms of metallic cobalt. Such coating is preferable because a strong conductive network can be obtained while maintaining a sufficient battery capacity.

  Further, the amount of rare earth hydroxide or oxide added to the cobalt-coated active material powder is such that cobalt hydroxide or oxywater is added to the surface of the powder composed of nickel and cobalt-zinc-containing hydroxide and oxide. It is preferable to use 1 to 3 parts by weight in terms of oxide amount with respect to 100 parts by weight of the powder on which the surface layer made of cobalt oxide is formed because a strong conductive network can be obtained while maintaining the battery capacity. The addition of these rare earth compounds also has the effect of increasing the oxygen overvoltage of the nickel electrode, thus improving the charging efficiency of the battery. If the content is less than 1 part by weight, the overdischarge-resistant effect cannot be obtained. If the content exceeds 3 parts by weight, the function of forming the conductive network may be hindered, which may reduce the output characteristics.

The negative electrode is not particularly limited as long as it is a material usually used for alkaline storage batteries.
As the negative electrode, a hydrogen storage alloy capable of storing hydrogen generated from the positive electrode particularly during overdischarge is preferable. The hydrogen storage alloy may be any alloy that can store hydrogen, and can be suitably used if it is an AB ₂ or AB ₅ alloy.
In addition, when a hydrogen storage alloy containing a rare earth element such as La, Ce, Pr, or Nd and a transition metal element containing Ni as a main component is used, a battery having a particularly low environmental load can be obtained.
For AB ₅ form of the hydrogen storage alloy, MmNi ₅ (Mm represents a misch metal, La, Ce, mixture of rare earth elements Pr, etc.) Co a part of Ni of, Mn, Al, alloys obtained by substituting Cu, etc. Is preferable because it has excellent cycle life characteristics and high discharge capacity.
If a catalyst is applied to the hydrogen storage alloy in advance, the gas generated from the positive electrode that permeates the separator can be absorbed, and the generation rate of the gas in the direction of the end face can be slowed, or the life performance including overdischarge can be improved. preferable.
Among them, an alloy was immersed AB ₅ type alloy at a high temperature of an alkaline aqueous solution is preferred because it has extremely excellent hydrogen gas absorption.

When using a hydrogen storage alloy, it is preferable to add a rare earth in order to improve the corrosion resistance of the hydrogen storage alloy to the electrolyte.
Among them, Yb and Er hydroxides are preferable because they have extremely excellent anticorrosion properties.
As a method of addition, when these rare earths are added as oxides, they react with the alkali used as the electrolyte and chemically change into hydroxides, so that they are dispersed in extremely fine particles, so it is also preferable to add them as oxides. is there.
The anti-corrosion effect is preferably as the added amount is large, but in order to absorb hydrogen gas during overdischarge from the positive electrode, the hydrogen absorption voltage and the hydrogen storage amount are reduced in order to lower the hydrogen overvoltage of the hydrogen storage alloy, so Addition of 3% or more as an oxide to the storage alloy is not preferable.
Although yttrium and erbium oxides and hydroxides have been described as anti-corrosion additives, they may be previously contained as a metal in the hydrogen storage alloy.

  In order to obtain the hydrogen storage alloy powder in a predetermined shape, a pulverizer or a classifier is used, but the classification method is not particularly limited.

  As described above, the negative electrode active material that is the main constituent of the negative electrode has been described in detail. In addition to the main constituent, the hydrogen storage electrode includes a conductive agent, a binder, a thickener, a filler, and the like. It may be contained as a constituent component.

  The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance. Usually, natural graphite (such as scaly graphite, scaly graphite, earthy graphite), artificial graphite, carbon black, acetylene black, A conductive material such as ketjen black, carbon whisker, carbon fiber, vapor-grown carbon, metal (copper, nickel, gold, etc.) powder, metal fiber or the like can be included as one type or a mixture thereof.

  Among these, as the conductive agent, Ketjen black is desirable from the viewpoints of electron conductivity and coatability. The addition amount of the conductive agent is preferably 0.1% by weight to 2% by weight with respect to the total weight of the positive electrode or the negative electrode because it has conductivity and does not significantly reduce the capacity of the negative electrode. In particular, ketjen black is preferably used after being pulverized into ultrafine particles of 0.1 to 0.5 μm because the required carbon amount can be reduced.

  The binder is usually a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), ethylene-propylene-diene terpolymer (EPDM), sulfonated (EPDM), styrene. Polymers having rubber elasticity such as butadiene rubber (SBR) and fluorine rubber can be used as one kind or a mixture of two or more kinds. The addition amount of the binder is preferably 0.1 to 3% by weight with respect to the total weight of the positive electrode or the negative electrode.

  As said thickener, polysaccharides, such as carboxymethylcellulose (CMC) and methylcellulose (MC), etc. can be normally used as 1 type, or 2 or more types of mixtures. The addition amount of the thickener is preferably 0.1 to 3% by weight with respect to the total weight of the positive electrode or the negative electrode.

  As the filler, any material that does not adversely affect the battery performance may be used. Usually, olefinic polymers such as polypropylene and polyethylene, carbon and the like are used. The addition amount of the filler is preferably 5% by weight or less with respect to the total weight of the positive electrode or the negative electrode.

  The positive electrode and the negative electrode were prepared by mixing the active material, the conductive agent and the binder in an organic solvent such as water, alcohol and toluene, and then applying the obtained mixture onto a current collector described in detail below. It is preferably produced by drying. About the application method, for example, it is desirable to apply to any thickness and any shape using means such as roller coating such as applicator roll, screen coating, doctor blade method, spin coating, bar coater, etc. Is not to be done.

  As the positive electrode current collector, there is no particular choice as long as it is an electronic conductor that does not adversely affect the constructed battery. For example, nickel, a nickel-plated foam, a fiber group formed body, or a three-dimensional base material with uneven processing is preferably used. Although there is no particular limitation on the thickness, a thickness of 5 to 700 μm is used. Among these current collectors, the positive electrode used is a foam with a porous body structure that is excellent in corrosion resistance and oxidation resistance against alkali and has a structure with excellent current collection and powder retention. It is preferable to do.

Any negative electrode current collector may be used as long as it is an electronic conductor that does not adversely affect the battery. For example, nickel or a nickel-plated steel plate can be suitably used, and a two-dimensional device such as a punched steel plate can be used in addition to a foam, a formed group of fibers, and a three-dimensional device subjected to uneven processing.
Although there is no particular limitation on the thickness, a thickness of 5 to 700 μm is used. Among these current collectors, as the positive electrode, it is possible to use a material having a porous structure with Ni having excellent corrosion resistance and oxidation resistance against alkali and having a structure excellent in current collection. preferable.
As the current collector of the hydrogen storage electrode, it is preferable to use a punching body obtained by applying nickel plating for improving reduction resistance to an iron foil that is inexpensive and excellent in electrical conductivity.
Furthermore, it is preferable that the punching diameter of the steel sheet is 1.7 mm or less and the opening ratio is 40% or more, so that the adhesion between the negative electrode active material and the current collector is excellent even with a small amount of binder.

  In addition to calcined carbon and conductive polymer, use nickel treated surface treated with Ni powder, carbon, platinum, etc. for the purpose of improving adhesion, conductivity and oxidation resistance. Can do. The surface of these materials can be oxidized.

  A method of providing an unfilled portion of the positive electrode powder mainly composed of an active material for current collection in the longitudinal direction of the positive electrode plate having the above-described configuration is not particularly limited, but as an example, uniform After the metal porous body is filled with powder, it is cut into a predetermined thickness and size, and the powder at one end in the longitudinal direction of the electrode plate is removed by ultrasonic vibration.

  As the separator for a sealed alkaline storage battery, it is preferable to use a porous film or a nonwoven fabric exhibiting excellent rate characteristics alone or in combination. Examples of the material constituting the separator include polyolefin resins typified by PE and PP, and polyamide resin (nylon).

  The porosity of the sealed alkaline storage battery separator is preferably 80% by volume or less from the viewpoint of strength and gas permeability. Further, the porosity is preferably 20% by volume or more from the viewpoint of charge / discharge characteristics.

Moreover, it is preferable that the separator for sealed alkaline storage batteries is subjected to a hydrophilic treatment.
For example, a polyolefin resin such as polyethylene may be used in which the surface is subjected to sulfonation treatment, corona treatment, PVA treatment, or a mixture of those already subjected to these treatments.

  As the electrolytic solution, those generally proposed for use in alkaline batteries and the like can be used. Water can be used as a solvent, and examples of the solute include, but are not limited to, K, Na, Li alone or a mixture of two or more thereof.

  As the concentration of the electrolyte salt in the electrolytic solution, an aqueous solution containing potassium hydroxide 5 to 7 mol / l and lithium hydroxide 0.1 to 0.8 mol / l is preferable in order to reliably obtain a battery having high battery characteristics.

  The sealed alkaline storage battery according to the present invention is suitably produced by injecting an electrolyte before or after laminating the separator, the positive electrode, and the negative electrode, and finally sealing with an exterior material. . Further, in a sealed alkaline storage battery in which a power generation element in which a positive electrode and a negative electrode are stacked via a separator is wound, the electrolyte is preferably injected into the power generation element before and after the winding. As the injection method, it is possible to inject at normal pressure, but a vacuum impregnation method, a pressure impregnation method, and a centrifugal impregnation method can also be used.

  Examples of the material of the outer package of the sealed alkaline storage battery include nickel-plated iron, stainless steel, polyolefin resin, and the like.

  In the following, the present invention will be described in more detail based on examples, but the present invention is not limited by the following description, the test method and the positive electrode material of the battery, the negative electrode material, the positive electrode, the negative electrode, the electrolyte, The separator and battery shape are arbitrary.

(Synthesis of nickel hydroxide particles)
An ammonium complex and an aqueous sodium hydroxide solution were added to an aqueous solution in which nickel sulfate, zinc sulfate, and cobalt sulfate were dissolved at a predetermined ratio to form an ammine complex. While vigorously stirring the reaction system, sodium hydroxide is further added dropwise, and the pH of the reaction system is controlled to 10 to 13 to form spherical high-density nickel hydroxide particles serving as a core layer base material. Nickel hydroxide: zinc hydroxide: cobalt hydroxide Active material particles mainly composed of nickel hydroxide (hereinafter referred to as “nickel hydroxide particles”) were synthesized so as to have a weight ratio of 93: 5: 2.

(Formation of surface layer on nickel hydroxide particle surface)
The high-density nickel hydroxide particles were put into an alkaline aqueous solution controlled to pH 10-13 with caustic soda. While stirring the solution, an aqueous solution containing cobalt sulfate and ammonia at predetermined concentrations was added dropwise. During this time, an aqueous caustic soda solution was appropriately added dropwise to maintain the pH of the reaction bath in the range of 10-13. Cobalt-coated nickel hydroxide active material powder (hereinafter referred to as “cobalt-coated positive electrode”) in which the pH is maintained in the range of 10 to 13 for about 1 hour, and a surface layer made of a mixed hydroxide containing Co is formed on the surface of nickel hydroxide particles. It may be abbreviated as “active material powder”. The ratio of the surface layer of the mixed hydroxide was 6 parts by weight in terms of the amount of Co metal with respect to 100 parts by weight of the nickel hydroxide particles having the surface layer made of the mixed hydroxide containing Co.

(Oxidation treatment of surface layer)
50 g of nickel hydroxide particles having a surface layer made of the mixed hydroxide was put into a 30 wt% (10N) aqueous caustic soda solution at a temperature of 110 ° C. and sufficiently stirred. Subsequently, excess K ₂ S ₂ O ₈ was added to the equivalent of the cobalt hydroxide contained in the surface layer, and it was confirmed that oxygen gas was generated from the particle surface. The active material particles were filtered, washed with water and dried.

(Preparation of positive electrode plate)
₂ parts by weight of ytterbium oxide (Yb ₂ O ₃ ) and 0.2 parts by weight of carboxymethyl cellulose (CMC) were added to and mixed with 100 parts by weight of the cobalt-coated positive electrode active material powder. Purified water was added to the mixture obtained by the mixing and kneaded to form a paste, and the paste was filled into a 450 g / m ² nickel porous body (Nihon Celmet # 8 manufactured by Sumitomo Electric Industries, Ltd.). Then, after drying at 80 ° C., it was pressed to a predetermined thickness, the surface was coated with Teflon (registered trademark), and a nickel positive electrode plate with a capacity of 3000 mAh having a width of 34 mm (inside, uncoated part 1 mm) and a length of 260 mm was obtained.

(Resin impregnation of the end of the positive electrode plate)
An ethylene homopolymer having a penetration of 0.65 mm (Polywax ^TM 500 manufactured by Baker Petrolite) was melted at 110 ° C. The end portion of the positive electrode plate opposite to the uncoated portion was impregnated with the molten resin and solidified at room temperature, and then the surplus resin on the surface and the lower end surface was scraped off. At this time, the width of the resin that had penetrated into the positive electrode plate was 0.5 mm from the lower end surface of the positive electrode plate filling portion.

(Preparation of negative electrode plate)
(First step)
AB ₅ type rare earth type MmNi _3.6 Co _0.6 Al _0.3 Mn _0.35 composition with a particle size of 35 μm was pressed in a sealed container at 45 ° C. with hydrogen gas at 0.4 MPa, the alloy was taken out, and the hydrogen storage capacity Ten hydrogen storage alloys were obtained.
(Second step)
Next, the surface of the alloy and fine cracks inside the alloy were treated with an alkaline aqueous solution. That is, the hydrogen storage alloy powder after the hydrogen storage treatment was immersed in a 1.48 NaOH aqueous solution with a specific gravity of 20 ° C., and the treatment was performed at 100 ° C. for 2 hours.
(Third step)
Thereafter, the mixture was filtered under pressure and washed with water at a pH of 10 or less. Then, diluted acid was added to dissolve rare earth impurities, followed by pressure filtration, and hydrogen desorption with 80 ° C. hot water.
(4th process)
Thereafter, pressure filtration and water washing were performed, 4% hydrogen peroxide was added in the same amount as the alloy weight with stirring, and hydrogen was desorbed to obtain a hydrogen storage alloy for electrodes.
The obtained alloy, styrene-butadiene copolymer aqueous solution and hydroxypropyl methylcellulose (HPMC) aqueous solution were mixed at a solid content weight ratio of 99.05: 0.65: 0.30, dispersed in water to form a paste, Using a blade coater, it is applied to a punched steel sheet with nickel plated on iron, dried at 80 ° C., pressed to a predetermined thickness, and has a capacity of 34 mm in width (with an uncoated part of 1 mm) and a length of 260 mm. A 5100 mAh hydrogen storage alloy negative electrode plate was obtained.

(Production of evaluation battery)
The hydrogen-absorbing alloy negative electrode plate, a 120 μm-thick polypropylene non-woven separator subjected to sulfonation treatment, and the nickel electrode plate are combined and wound into a roll, and 0.8 N water is added to a 6.8 N potassium hydroxide aqueous solution. 4.8 g of alkaline electrolyte in which lithium oxide was dissolved was injected to produce a subC-type sealed nickel-metal hydride storage battery having a valve with a valve opening pressure of 2.4 MPa.

(Chemical formation)
This battery was stored at 40 ° C. for 12 hours, charged with 0.02 ItA at 600 mAh, charged at 0.1 ItA for 12 hours, discharged at 0.2 ItA to 1 V, charged at 0.1 ItA for 12 hours, The operation of discharging to 0.2 V at 0.2 ItA was repeated 4 times.

(Productivity evaluation at the time of winding body production)
In the production of the evaluation battery, 1000 pieces of wound bodies were produced by winding the positive electrode plate and the negative electrode plate on a roll, and the number of defective electrode groups generated in the process was investigated. The defective electrode group is a group of poles in which the height and outer diameter of the wound body deviate from the standard value due to winding slip, and the positive electrode powder mainly composed of the active material is significantly dropped during winding. This refers to the pole group that was short-circuited during winding.

(High rate discharge characteristics evaluation)
The formed battery was charged at 0.1 ItA for 16 hours and left in an atmosphere at 20 ° C. for 4 hours, and then discharged at a discharge rate of 10 ItA and a discharge cut voltage of 0.8 V. The capacity obtained by the discharge was discharged at 10 ItA. The discharge capacity was evaluated by the ratio (%) to the active material capacity (100%) in the production of the positive electrode plate. The discharge voltage at the middle of the discharge capacity was defined as the discharge intermediate voltage. In order to apply to applications that require high output such as HEVs and electric tools, it is desirable to obtain a capacity of 85% or more in the discharge.

(Overdischarge cycle life characteristics)
The formed battery was subjected to a charge / discharge cycle test at an ambient temperature of 20 ° C. The battery was charged at 1 ItA until −ΔV changed to 10 mV, discharged at a discharge rate of 3 ItA until the battery voltage reached −0.4 V, and then constant voltage discharge was performed at −0.4 V for 10 seconds. The charge / discharge cycle was repeated with this charge / discharge as one cycle, and the overdischarge cycle life of the battery was defined as the number of cycles in which the discharge capacity was cut off 70% of the discharge capacity in the first cycle of the charge / discharge cycle test. Note that the discharge capacity for determining the life does not include the capacity at the time of constant voltage discharge.
In an alkaline storage battery using nickel hydroxide as a positive electrode active material, the battery tends to deteriorate when a deep discharge is performed such that hydrogen gas is generated from the positive electrode. The overdischarge cycle test is a test assuming deep discharge due to voltage variation of single cells constituting an assembled battery in an application in which a plurality of batteries such as HEVs and electric tools are connected in series. In the cycle test, the cycle life is desirably 400 cycles or more, and more desirably 500 cycles or more.

Example 1 was the same as Example 1 except that the resin impregnated at the end of the positive electrode plate was replaced with Polywax ^™ 725 manufactured by Baker Petrolite. This example is referred to as Example 2. The penetration of the resin at this time was 0.15 mm.

Example 1 was the same as Example 1 except that the resin impregnated at the end of the positive electrode plate was replaced with Polywax ^™ 655 manufactured by Baker Petrolite. This example is referred to as Example 3. The penetration of the resin at this time was 0.2 mm.

Example 1 was the same as Example 1 except that the resin impregnated at the edge of the positive electrode plate was replaced with Polywax ^™ 400 manufactured by Baker Petrolite. This example is referred to as Example 4. The penetration of the resin at this time was 1.5 mm.

  Example 1 was the same as Example 1 except that the resin impregnated at the end of the positive electrode plate was replaced with BE SQUARE 175Wax manufactured by Baker Petrolite. This example is referred to as Example 5. The penetration of the resin at this time was 1.8 mm.

  Example 1 was the same as Example 1 except that the resin impregnated at the end of the positive electrode plate was replaced with Victory Wax manufactured by Baker Petrolite. This example is referred to as Example 6. The penetration of the resin at this time was 2.6 mm.

(Comparative Example 1)
Example 1 was the same as Example 1 except that the resin impregnated at the end of the positive electrode plate was replaced with Polywax ^TM 2000 manufactured by Baker Petrolite and melt impregnated at 130 ° C. This example is referred to as Comparative Example 1. The penetration of the resin at this time was 0.05 mm.

(Comparative Example 2)
Example 1 was the same as Example 1 except that the resin impregnated at the end of the positive electrode plate was replaced with Polywax ^TM 850 manufactured by Baker Petrolite. This example is referred to as Comparative Example 2. The penetration of the resin at this time was 0.1 mm.

(Comparative Example 3)
Example 1 was the same as Example 1 except that the resin impregnated at the end of the positive electrode plate was replaced with BE SQUARE 165Wax manufactured by Baker Petrolite. This example is referred to as Comparative Example 3. The penetration of the resin at this time was 3.0 mm.

  Table 1 shows the number of defects generated when 1000 wound bodies of Examples 1 to 6 and Comparative Examples 1 to 3 were produced.

According to the results shown in Table 1, if the penetration of the resin impregnated in the end portion of the positive electrode plate is 0.15 mm to 2.6 mm, the number of defects generated in the production of the wound body is very small, and the productivity is low. It can be said that it is good. On the other hand, when the penetration of the resin impregnated at the end of the positive electrode plate is smaller than 0.15 mm as in Comparative Examples 1 and 2, the positive electrode plate is cracked or broken from the portion impregnated with the resin when the pole group is wound. A large number of squeezes occurred, which resulted in an increase in the outer diameter of the wound body or a winding slip. In addition, short circuit defects occurred due to cracks and breakage of the positive electrode plate. Also, when the penetration of the resin exceeds 2.6 mm as in Comparative Example 3, the positive electrode powder containing the active material of the positive electrode together with the resin adheres to the separator because the resin is very soft and rich in viscosity. As a result, winding of the wound body often occurred. Further, the positive electrode powder peeled off from the positive electrode substrate together with the resin adhered to the positive electrode plate guide of the winding machine, and a defect that could not be wound occurred.
Therefore, the resin impregnated in the end portion of the positive electrode plate preferably has moderate flexibility and active material holding power, and the resin has a penetration of 0.15 mm to 2.6 mm.

  In Example 1, it was the same as Example 1 except that the width from the lower end surface of the resin impregnated in the end portion of the positive electrode plate was 0.2 mm. This example is referred to as Example 7.

  In Example 1, it was the same as Example 1 except that the width from the lower end surface of the resin impregnated at the end of the positive electrode plate was 1.0 mm. This example is referred to as Example 8.

(Comparative Example 4)
Example 1 was the same as Example 1 except that the step of impregnating the positive electrode plate with the resin was not performed. This example is referred to as Comparative Example 4.

(Comparative Example 5)
In Example 1, it was the same as Example 1 except that the width from the lower end surface of the resin impregnated in the end portion of the positive electrode plate was 0.1 mm. This example is referred to as Comparative Example 5.

(Reference Example 1)
In Example 1, it was the same as that of Example 1 except that the width from the lower end surface of the resin impregnated in the end portion of the positive electrode plate was 1.5 mm. This example is referred to Reference Example 1.

  Table 2 shows the 20 ° C. 10 ItA discharge characteristics, the discharge intermediate voltage, and the overdischarge cycle life for the batteries of Examples 1, 7, 8, Comparative Examples 4, 5, and Reference Example 1.

According to the results shown in Table 2, when the width of the resin impregnated in the end portion of the positive electrode plate is 0.2 mm or more from the lower end surface, an excellent durability with an overdischarge cycle life of 500 cycles or more was obtained. On the other hand, when the resin was not impregnated as in Comparative Examples 4 and 5, the overdischarge cycle life was 300 cycles or less when the width of the impregnated resin was 0.1 mm from the lower end surface. Although this is not necessarily clear, it is considered that the positive electrode active material is dropped by the hydrogen gas generated during the reversal of the positive electrode plate and the capacity is lowered as a factor of capacity deterioration accompanying the overdischarge cycle. The positive electrode powder is likely to fall off particularly from the end of the positive electrode plate, so that the active material is firmly held on the positive electrode substrate by covering the end with a resin having a specific width or more, and dropping is suppressed. It is considered that the overdischarge cycle life is improved. However, as shown in Reference Example 1, when the resin to be impregnated had a width of 1.5 mm, the overdischarge cycle life was excellent, but the 20 ° C. 10 ItA discharge characteristics and the discharge intermediate voltage were lowered. Although the positive electrode active material is firmly held by impregnating the resin, it is considered that the resin is poor in conductivity and impedes the discharge reaction if the impregnation width is too wide.
Therefore, the width of the resin to be impregnated is preferably 0.2 mm to 1.0 mm from the lower end surface of the positive electrode plate filling portion.

(About types of resin)
In addition, an unsaturated hydrocarbon such as polystyrene as the resin material was dissolved in an organic solvent, and then impregnated into the end portion of the positive electrode plate, and a battery was manufactured in the same manner as in Example 1, and the same overdischarge cycle life evaluation was performed as described above. However, even when any unsaturated hydrocarbon was used, the overdischarge cycle life was reduced. Although details are not clear, unsaturated hydrocarbon compounds generally have low oxidation resistance and are less effective in suppressing the falling off of the positive electrode powder due to oxidative decomposition during charging. This is thought to be because the balance was lost.

  In the resin impregnation processing of the end portion of the positive electrode plate in Example 1, the same as in Example 1 except that the positive electrode powder packed layer at the current collector side end portion of the positive electrode plate and the opposite end portion were impregnated with resin. It was. At this time, the impregnation width of the resin was 0.2 mm from the current collector side end face (upper end face) and 0.3 mm from the end face (lower end face) opposite to the current collector. This example is referred to as Example 9.

(Reference Example 2)
The resin impregnation process at the end of the positive electrode plate of Example 1 was the same as that of Example 1 except that the positive electrode powder packed layer at the current collector side end of the positive electrode plate was impregnated with resin. At this time, the impregnation width of the resin was 0.5 mm from the upper end surface of the positive electrode filling layer on the current collector side end surface. This example is referred to Reference Example 2.

  Table 3 shows the overdischarge cycle life of the batteries of Examples 1 and 9 and Reference Example 2 with different resin impregnation locations.

  According to the results shown in Table 3, at least the opposite end of the positive electrode current collector was impregnated with resin, but an excellent overdischarge cycle life was obtained, but only the current collector side edge was impregnated with resin. In the battery of Reference Example 2, the overdischarge cycle life decreased. However, since the overdischarge durability was superior compared to Comparative Example 4 in which the resin was not impregnated, the positive electrode powder dropout during overdischarge was suppressed even if the resin was impregnated in either the upper end or the lower end. It turns out that the effect to do is acquired. However, from the above results, in order to suppress the positive electrode powder dropout more effectively, it is preferable to impregnate at least the lower end on the opposite side of the current collector among the both ends of the positive electrode plate.

In preparation of the positive electrode plate of Example 1, in place of ytterbium oxide (Yb ₂ O _3), except for adding the mixed rare earth oxide purity of Yb ₂ O ₃ is 90 percent (Mm ₂ O ₃₎ carried Same as Example 1. This example is referred to as Example 10.

(Reference Example 3)
The production of the positive electrode plate of Example 1 was the same as Example 1 except that yttrium oxide (Y ₂ O ₃ ) was added instead of ytterbium oxide (Yb ₂ O ₃ ). This example is referred to Reference Example 3.

  Table 4 shows the overdischarge cycle life of the batteries of Examples 1 and 10 and Reference Example 3.

According to the results shown in Table 4, the rare earth oxide is ytterbium oxide to be added (Yb ₂ O ₃₎ single rare earth compound or ytterbium oxide (Yb ₂ O ₃₎ mixed rare earth compounds mainly (Mm ₂ O ₃₎ Is preferable because an excellent overdischarge cycle life exceeding 500 cycles can be obtained. However, when the rare earth compound to be added is Y ₂ O ₃ , the cycle life has been reduced. As one factor of the capacity reduction in the overdischarge cycle, the conductive network destruction of the positive electrode active material can be considered. During deep discharge with inversion, cobalt oxyhydroxide reduction reaction occurs, and some cobalt is eluted in the electrolyte, but if Yb ₂ O ₃ is added, the dissolution rate of Co is significantly reduced, so cobalt conductivity The destruction of the sex network is less likely to occur. On the other hand, when the rare earth additive is yttrium oxide (Y ₂ O ₃ ), a large amount of reduced cobalt is eluted, and cobalt is eluted off the electrolyte, resulting in a large decrease in conductivity and rapid capacity deterioration. It is thought that it became. For the above reasons, the rare earth compound to be added is preferably Yb ₂ O ₃ or a high purity mixed rare earth compound thereof.

The production of the positive electrode plate of Example 1 was the same as Example 1 except that 1 part by weight of ytterbium oxide (Yb ₂ O ₃ ) was added to 100 parts by weight of the cobalt-coated positive electrode active material powder. This example is referred to as Example 11.

The production of the positive electrode plate of Example 1 was the same as Example 1 except that 3 parts by weight of ytterbium oxide (Yb ₂ O ₃ ) was added to 100 parts by weight of the cobalt-coated positive electrode active material powder. This example is referred to as Example 12.

(Comparative Example 6)
Preparation of the positive electrode plate of Example 1 was the same as Example 1 except that ytterbium oxide (Yb ₂ O ₃ ) was not added to the cobalt-coated positive electrode active material powder. This example is referred to as Comparative Example 6.

(Reference Example 4)
Preparation of the positive electrode plate of Example 1 was the same as Example 1 except that 0.5 part by weight of ytterbium oxide (Yb ₂ O ₃ ) was added to 100 parts by weight of the cobalt-coated positive electrode active material powder. This example is referred to Reference Example 4.

(Reference Example 5)
Example 1 was the same as Example 1 except that 4 parts by weight of ytterbium oxide (Yb ₂ O ₃ ) was added to 100 parts by weight of the cobalt-coated positive electrode active material powder. This example is referred to Reference Example 5.

  Table 5 shows the 20 ° C. 10 ItA discharge characteristics and the overdischarge cycle life for the batteries of Examples 1, 11, 12, Comparative Example 6, and Reference Examples 4, 5.

According to the results shown in Table 5, an excellent overdischarge cycle can be obtained if the amount of ytterbium oxide added is 1 part by weight or more, but when the amount added is less than 1 part by weight, the overdischarge cycle life is reduced. have done. Moreover, when the addition amount was 4 parts by weight, the overdischarge cycle life was excellent, but the 20 ° C. and 10 ItA discharge characteristics were deteriorated.
The decrease in overdischarge cycle life when the addition amount is small is considered to be due to the destruction of the conductive network of the positive electrode active material during overdischarge as described above, and the addition amount of Yb ₂ O ₃ is less than 1 part by weight. If the amount is too small, the effect is not fully exhibited. On the other hand, when the added amount is more than 3 parts by weight, the added Yb ₂ O ₃ covers the reaction surface of the positive electrode active material or enters the active material particles to inhibit the electrochemical reaction of the positive electrode active material. Or, the high-rate discharge characteristics are degraded. Therefore, the amount of Yb ₂ O ₃ added to the cobalt-coated positive electrode active material is preferably 1 to 3 parts by weight.

  In the step of forming a surface layer composed of a mixed hydroxide containing Co on the surface of nickel hydroxide particles described in Example 1, the amount was 4 parts by weight in terms of the amount of Co metal. Same as 1. This example is referred to as Example 13.

  In the step of forming a surface layer composed of a mixed hydroxide containing Co on the surface of nickel hydroxide particles described in Example 1, the amount was 8 parts by weight in terms of the amount of Co metal. Same as 1. This example is referred to as Example 14.

(Reference Example 6)
In the step of forming the surface layer composed of the mixed hydroxide containing Co on the nickel hydroxide particle surface described in Example 1, the amount was 2 parts by weight in terms of the amount of Co metal. Same as 1. This example is referred to as Reference Example 6.

(Reference Example 7)
In the step of forming a surface layer composed of a mixed hydroxide containing Co on the surface of nickel hydroxide particles described in Example 1, the amount was 3 parts by weight in terms of the amount of Co metal. Same as 1. This example is referred to as Reference Example 7.

(Reference Example 8)
In the step of forming a surface layer composed of a mixed hydroxide containing Co on the surface of nickel hydroxide particles described in Example 1, the amount was 10 parts by weight in terms of the amount of Co metal. Same as 1. This example is referred to as Reference Example 8.

  Table 6 shows the overdischarge cycle life for the batteries of Examples 1, 13, 14 and Reference Examples 6-8.

  According to the results shown in Table 6, an excellent overdischarge cycle life was obtained, but when the amount was 3 parts by weight or less, the overdischarge cycle life was lowered. This is probably because when the amount of Co covering the nickel hydroxide is small, the reduction resistance during the overdischarge cycle is lowered, and the conductivity is lowered earlier due to the reduction of the higher order hydroxide of the coated Co. On the other hand, the overdischarge cycle life also decreased when the amount of Co covering nickel hydroxide exceeded 8 parts by weight. If the amount of Co hydroxide to be coated is too large, the volume of the positive electrode plate for making a battery of the same capacity will increase, resulting in a decrease in the remaining space and a higher proportion of the electrolyte occupying the remaining space. Absorption of oxygen gas generated from the positive electrode is delayed, the internal pressure is increased, the deterioration of the hydrogen storage alloy electrode is accelerated, the safety valve is easily activated, and the life is shortened. Furthermore, since the hydrogen gas generated from the positive electrode is blocked by the electrolyte solution that occupies the polar group space and becomes difficult to escape from the positive electrode plate pores, the time for which the positive electrode is exposed to the hydrogen gas becomes long, so that the coated Co is easily reduced. This is thought to be because it has become. As mentioned above, it is preferable that the amount of Co which coat | covers nickel hydroxide is 4 weight part-8 weight part in conversion of a metal amount. In Example 1, the cobalt hydroxide to be coated was pre-oxidized, but the same effect was obtained using a cobalt hydroxide-coated nickel hydroxide active material that was not subjected to this treatment.

In addition, it is necessary to coat at least nickel hydroxide with cobalt hydroxide or cobalt oxyhydroxide. However, even if cobalt hydroxide or cobalt oxyhydroxide is added to the cobalt-coated nickel hydroxide active material, The service life is improved. In the production of the positive electrode plate of Example 1, a battery was produced and evaluated in the same manner as in Example 1 except that 1 part by weight of cobalt hydroxide was mixed and added to 100 parts by weight of the cobalt-coated nickel hydroxide active material. The overdischarge cycle life was 570 cycles. Similarly, when the mixed addition amount of the cobalt hydroxide is 2 parts by weight and the battery is evaluated for production, the overdischarge cycle life becomes 590 cycles, both of which further improve the overdischarge cycle life, and the cobalt hydroxide is mixed and added. This is also preferable because the overdischarge durability is improved.
The same effect was obtained even when cobalt oxyhydroxide was similarly mixed and added instead of the cobalt hydroxide.

  In the following examples and comparative examples, sealed alkaline storage batteries were evaluated as assembled batteries to confirm the effects.

  A battery was produced in the same manner as in Example 1 except that the capacity of the positive electrode plate described in Example 1 was 2900 mAh. The battery and the battery of Example 1 were connected in series using a nickel plate having a width of 10 mm, a length of 30 mm, and a thickness of 0.2 mm. This assembled battery is referred to as Example 15. As described above, the assembled battery is composed of a combination of single cells having different capacities of 100 mAh.

(Comparative Example 7)
A battery was fabricated in the same manner as in Example 1 except that the capacity of the positive electrode plate described in Example 1 was 2900 mAh and the lower end portion was not impregnated with resin. The battery and the battery of Comparative Example 4 were connected in series using a nickel plate having a width of 10 mm, a length of 30 mm, and a thickness of 0.2 mm. This assembled battery is referred to as Comparative Example 7. The assembled battery is constituted by a combination of single cells having different 100 mAh capacities as in the previous period, and the positive electrode plate constituting each battery is not subjected to resin impregnation.

(Assembly battery cycle life evaluation)
The assembled batteries of Example 15 and Comparative Example 7 were subjected to a charge / discharge cycle test at an ambient temperature of 20 ° C. The battery was charged at 1 ItA until -ΔV changed to 20 mV, and discharged at a discharge rate of 3 ItA until the assembled battery voltage reached 0 V. The charge / discharge cycle was repeated with this charge / discharge as one cycle, and the overdischarge cycle life of the battery was defined as the number of cycles in which the discharge capacity was cut off 70% of the discharge capacity in the first cycle of the charge / discharge cycle test.

  Table 7 shows the cycle life of the assembled batteries of Example 15 and Comparative Example 7.

According to the results shown in Table 7, the assembled battery of Example 15 had an excellent cycle life exceeding 600 cycles, whereas the assembled battery of Comparative Example 7 had a reduced cycle life. In the cycle life test, a battery having a small capacity is more overdischarged due to a capacity difference between the batteries constituting the assembled battery when discharging to 0V. In the assembled battery of Example 16 in which the lower end portion of the positive electrode plate was impregnated with resin, it was considered that an excellent cycle life was obtained because the positive electrode powder was less likely to drop off during this overdischarge and the capacity reduction was suppressed. It is done.
As described above, in the evaluation test of the assembled battery, the same result as that obtained when the single battery was evaluated was obtained.
It is confirmed that by impregnating the end of the positive electrode plate with resin, durability against over-discharge due to capacity variation of the cells constituting the assembled battery is improved, and an assembled battery having an excellent cycle life can be obtained. It was done.

Claims (8)

  In the battery case, at least a layer of cobalt hydroxide or cobalt oxyhydroxide is formed on the surface of a powder composed of a hydroxide and an oxide mainly composed of a metal porous body, nickel as a main component and cobalt and zinc, and rare earth water. An insulator comprising a positive electrode plate filled with an oxide or an oxide, a negative electrode plate, a cylindrical electrode group formed by winding a separator, a positive electrode current collector, a negative electrode current collector, and an electrolytic solution. In a sealed alkaline storage battery having a lead electrically connected to a positive electrode plate and a positive electrode current collector on a lid electrically insulated from the battery case via the positive electrode plate, of the upper and lower ends thereof A sealed alkaline storage battery characterized in that at least a lower end portion is impregnated with a resin having a penetration of 0.15 mm or more and 2.6 mm or less at 25 ° C. from a lower end surface of a positive electrode plate filling portion by 0.2 mm or more.   The positive electrode plate has at least a lower end portion impregnated with a resin having a penetration of 0.15 mm or more and 2.6 mm or less at 25 ° C. from a lower end surface of the positive electrode plate filling portion of 0.2 mm to 1.0 mm. The sealed alkaline storage battery according to claim 1.   The sealed alkaline storage battery according to claim 1, wherein the resin is a saturated hydrocarbon.   The sealed alkaline storage battery according to any one of claims 1 to 3, wherein the rare earth contains at least ytterbium.   The rare earth hydroxide or oxide is a powder in which at least a layer of cobalt hydroxide or cobalt oxyhydroxide is formed on the surface of a powder composed of hydroxide and oxide mainly containing nickel and containing cobalt and zinc. The sealed alkaline storage battery according to any one of claims 1 to 4, wherein when the amount is in parts by weight, 1 to 3 parts by weight is added in terms of oxide amount.   The cobalt hydroxide or cobalt oxyhydroxide formed on the surface of the powder consisting of hydroxide and oxide containing cobalt and zinc mainly containing nickel is the hydroxide containing cobalt and zinc mainly containing nickel. And 4 parts by weight to 8 parts by weight in terms of the amount of metallic cobalt when 100 parts by weight of the powder in which at least a layer of cobalt hydroxide or cobalt oxyhydroxide is formed on the surface of the powder made of oxide. The sealed alkaline storage battery according to any one of claims 1 to 5.   7. The sealed alkaline storage battery according to claim 1, wherein the negative electrode comprises a hydrogen storage alloy powder composed mainly of a rare earth element that absorbs and desorbs hydrogen and a transition metal element containing nickel. . A battery pack comprising a plurality of sealed alkaline storage batteries according to claim 1, wherein the battery pack is composed of a plurality.