JP2001052696A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the utilization factor of a positive electrode of an alkaline secondary battery, enlarge the capacity of the battery, and maintain high capacity by recovering the capacity through recharging in the case the self-discharge progresses resulting from storage for a long period of time, in particular at a high temperature. SOLUTION: This alkaline secondary battery is equipped with a positive electrode 2 of such a structure that an electricity collector is filled with a paste containing nickel hydroxide particles as active material, a negative electrode 4, a separator 3 interposed between the positive 2 and negative electrodes 4, and an alkaline electrolytic solution. Each particle of nickel hydroxide is covered uniformly with a cobalt-based film consisting of a trivalent cobalt compound region having electric conductivity and a cobalt type region having an oxidation number lower than that of the first named, and part of the trivalent cobalt compound region has such a form as reaching the surfaces of the nickel hydroxide particles from the film surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery provided with a paste-type positive electrode containing nickel hydroxide as an active material.

[0002]

2. Description of the Related Art An alkaline secondary battery has a structure in which an electrode group and an alkaline electrolyte prepared by interposing a separator between a positive electrode and a negative electrode are housed in a container. Conventionally, a sintered positive electrode has been used as the positive electrode. The sintered positive electrode is obtained by sintering nickel particles on a two-dimensional substrate such as perforated steel or a nickel mesh, impregnating an aqueous solution of nickel salt into pores of about ten microns of the obtained porous plate, and then performing an alkali treatment. It is produced by changing the impregnated nickel salt to nickel hydroxide.

However, the above-mentioned sintered positive electrode requires complicated active material impregnation operations such as a nickel salt impregnation step and an alkali treatment step in its production. In addition, in order to impregnate a predetermined amount of the active material, the above operation is usually performed in 4 to 10
It needs to be repeated about once. As a result, there is a problem that the manufacturing cost increases. Further, if the porosity of the nickel particle sintered body obtained by the sintering is more than 80%, it becomes difficult to maintain the mechanical strength, so that it is impossible to increase the filling amount of the active material. was there.

[0004] For this reason, a paste is prepared by adding and mixing a conductive material, a binder and water to nickel hydroxide particles as an active material, and this paste is used as a sponge-like porous metal or metal fiber mat. It has been studied to manufacture a positive electrode by filling a conductive core having such a three-dimensional structure. The positive electrode manufactured by such a method is called a non-sintered positive electrode (or a paste positive electrode) with respect to the sintered positive electrode. The paste-type positive electrode has an advantage that the porosity and average pore diameter of the porous metal body are larger than that of the sintered-type positive electrode, so that the active material can be easily filled and the amount of the active material can be increased.

[0005] As the conductive material used for the paste-type positive electrode, for example, a cobalt compound such as cobalt hydroxide and cobalt monoxide, and metallic cobalt have been known. In the secondary battery, these conductive materials once dissolve into the electrolytic solution during aging performed after assembly and precipitate on the surface of the nickel hydroxide particles. Next, at the first charge, it is electrochemically oxidized and converted into cobalt oxyhydroxide having high conductivity. Since the cobalt oxyhydroxide improves the conduction between the nickel hydroxide particles and the conduction between the nickel hydroxide particles and the conductive core, the utilization rate of the positive electrode is improved.

However, it is difficult to uniformly mix particles or powders in the paste preparation step, and it is difficult to uniformly disperse the conductive material in the positive electrode. Therefore, in the secondary battery manufactured by the above-described method, the distribution of cobalt oxyhydroxide in the positive electrode is biased, so that the positive electrode does not always have a sufficient utilization rate.

Further, in a secondary battery provided with a positive electrode containing this cobalt oxyhydroxide, it is difficult to recover the capacity by recharging when self-discharge progresses due to long-term storage and the capacity decreases. There was a problem that it is. This problem was remarkable when the secondary battery was stored at a high temperature.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to increase the capacity of a positive electrode by increasing its utilization rate, and to recharge the battery when self-discharge has progressed due to long-term storage, especially at high temperatures. It is an object of the present invention to provide an alkaline secondary battery capable of recovering capacity and maintaining high capacity.

[0009]

According to the present invention, there is provided an alkaline secondary battery having a structure in which a current collector is filled with a paste containing nickel hydroxide particles as an active material, a negative electrode, the positive electrode and the negative electrode. Wherein the nickel hydroxide particles are a trivalent cobalt compound region having conductivity and a cobalt species having a lower oxidation number than the separator. Region is uniformly coated with a cobalt-based film comprising
A part of the valence cobalt compound region has a form reaching the surface of the nickel hydroxide particles from the film surface.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the method for manufacturing an alkaline secondary battery according to the present invention, a uniform layer composed of cobalt species is formed on the surface of nickel hydroxide particles, and the paste containing the composite nickel hydroxide particles is used as a current collector. The current value is gradually increased in an alkaline secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. By performing the initial charge for performing the constant current charging, the composite nickel hydroxide particles are subjected to hydroxylation whose surface is coated with a cobalt-based film comprising a conductive trivalent cobalt compound region and a cobalt species region having a lower oxidation number. At least a part of the trivalent cobalt compound region of the cobalt-based film reaches the surface of the nickel hydroxide particles from the surface of the cobalt-based film while being converted into nickel particles. It is characterized in that the state.

The uniform layer composed of cobalt species of the composite nickel hydroxide particles is, for example, cobalt hydroxide (Co).
(OH) ₂ ), cobalt monoxide (CoO), metallic cobalt or the like. Among them, composite nickel hydroxide particles having a cobalt seed layer composed of one or both of cobalt monoxide and cobalt hydroxide are preferable.

The composite nickel hydroxide particles can be produced, for example, by the following methods (1) and (2).

(1) Precipitating cobalt hydroxide on the surface of the nickel hydroxide particles to form a uniform layer of the cobalt species containing the cobalt hydroxide, thereby producing composite nickel hydroxide particles.

(2) The nickel hydroxide particles are used as the base particles and the cobalt species are used as the child particles. The nickel hydroxide particles are dispersed and adhered to the surface of the mother particles by a mechanical impact force or are bonded by a mechanochemical method. A uniform layer composed of cobalt species is formed on the surface to produce composite nickel hydroxide particles.

[0015] Of the methods (1) and (2),
The method (1) is preferred.

The method (1) will be described.

The nickel hydroxide particles have an average particle size of 5
It is preferable that the tap density is 1.8 g / cm ³ or more. The nickel hydroxide particles have a specific surface area of 8 to 25 m ^2. / G.

The nickel hydroxide particles preferably have a spherical shape or a shape similar thereto.

The cobalt species is trace amounts of CoO ₂ , Co ₃
It is allowed to contain cobalt oxide such as O ₄ .

The positive electrode containing the composite nickel hydroxide particles can be produced, for example, by the following methods (A) and (B).

(A) A paste is prepared by adding a binder and water to the composite nickel hydroxide particles and kneading them. The positive electrode is prepared by filling the paste into a current collector, drying the paste, and then molding the paste.

Examples of the binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene and the like.

Examples of the current collector include a mesh-like, sponge-like, fiber-like, or felt-like porous metal body made of nickel, stainless steel, or nickel-plated metal.

In this positive electrode, the cobalt seed layer is
It is preferable that the nickel hydroxide particles are attached to the composite nickel hydroxide particles in an amount of 3% by weight to 20% by weight in terms of metal cobalt. This is due to the following reasons. If the cobalt seed layer is less than 3% by weight in terms of metallic cobalt, the initial utilization rate of the positive electrode may decrease, and it is difficult to recover the capacity by recharging after storage for a long time or at a high temperature. There is a risk of becoming. On the other hand, the cobalt seed layer has a metal cobalt equivalent of 20.
If the content is more than 10% by weight, the proportion of the cobalt species in the positive electrode may become too large and the amount of nickel hydroxide particles may decrease. More preferably, the cobalt seed layer is attached to the nickel hydroxide particles in an amount of 5% by weight to 10% by weight in terms of metal cobalt with respect to the composite nickel hydroxide particles.

(B) A paste is prepared by adding a binder, a cobalt seed powder and water to the composite nickel hydroxide particles and kneading them. The positive electrode is prepared by filling the paste into a current collector, drying the paste, and then molding the paste.

Examples of the cobalt seed powder include water
Cobalt oxide powder, cobalt monoxide powder, metallic cobalt
Powders and the like can be mentioned. Among them, cobalt monoxide
Powder or cobalt hydroxide powder, or
Cobalt seed powders comprising both are preferred. The above
The cobalt seed powder is an inert tricobalt tetroxide (Co _Three 
O_Four ) Is allowed.

Examples of the binder include those similar to those used in the method (A).

Examples of the current collector include those similar to those used in the method (A).

In this positive electrode, the cobalt seed layer is attached to the nickel hydroxide particles in an amount of 1% by weight or more in terms of metallic cobalt with respect to the composite nickel hydroxide particles, and the total amount of cobalt species in the positive electrode is reduced to the composite water. It is preferable that the content be 3 wt% to 20 wt% in terms of metal cobalt with respect to the nickel oxide particles. This is due to the following reasons. If the cobalt seed layer is less than 1% by weight in terms of metallic cobalt, it may be difficult to form the cobalt seed layer uniformly over the entire surface of the nickel hydroxide particles. In other words, there is a possibility that the surface of the nickel hydroxide particles themselves is exposed and becomes non-uniform. When the total amount of the cobalt species is less than 3% by weight in terms of metallic cobalt,
The initial utilization rate of the positive electrode may decrease, and it may be difficult to recover the capacity by recharging for a long time or after storage at a high temperature. On the other hand, if the total amount of the cobalt species exceeds 20% by weight in terms of metallic cobalt, the proportion of the cobalt species in the positive electrode becomes too large, and the amount of nickel hydroxide particles may decrease. In the positive electrode, the cobalt seed layer is attached to the nickel hydroxide particles by 3% by weight or more in terms of metal cobalt with respect to the composite nickel hydroxide particles, and the total amount of cobalt species in the positive electrode is reduced by the composite nickel hydroxide. More preferably, the content is 5% by weight to 10% by weight in terms of metal cobalt with respect to the particles.

Of the above-mentioned positive electrode preparation methods, the method (A) can dramatically improve the capacity recovery rate after storage for a long period of time or at a high temperature. On the other hand, in the method (B), the total amount of the cobalt species in the positive electrode can be adjusted according to the type of the alkaline secondary battery by changing the addition amount of the cobalt seed powder. Thus, the mass productivity of the alkaline secondary battery can be improved as compared with the case where the cobalt species is provided only from the composite nickel hydroxide particles.

The first charge will be described.

The above-mentioned initial charge is performed by performing a constant current charge for increasing the current value stepwise. This stepwise constant current charging may be performed in two stages, or may be performed in two or more stages.

The constant current charging is performed at 0.02 CmA to 0.
It is preferable to increase the current value stepwise within the range of 5 CmA. This is due to the following reasons. When the current value is less than 0.02 CmA, an electrochemical reaction is likely to occur unevenly on the electrode surface, and the electrode characteristics may be degraded. In addition, there is a possibility that the time required for applying a desired amount of charged electricity is increased, and the problem in production is increased. On the other hand, if the current value exceeds 0.5 CmA, the charge polarization resistance increases, and not only the oxidation reaction of cobalt species but also the oxidation reaction of nickel hydroxide occurs simultaneously. Correlation with the amount of species oxidation may be reduced.

An example of an alkaline secondary battery (for example, a cylindrical alkaline secondary battery) manufactured by the method of the present invention will be described with reference to FIG.

As shown in FIG. 1, an electrode group formed by laminating a paste-type positive electrode 2, a separator 3, and a paste-type negative electrode 4 in a cylindrical container 1 having a bottom and spirally winding the same. 5 are stored. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. A circular sealing plate 7 having a hole 6 in the center is arranged at the upper opening of the container 1. The ring-shaped insulating gasket 8 is disposed between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the sealing plate is formed on the container 1 by caulking to reduce the diameter of the upper opening inward. 7
Are hermetically fixed via the gasket 8. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6. A rubber safety valve 11 is disposed so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. A holding plate 12 made of an insulating material and having a hole in the center is disposed on the positive electrode terminal 10 such that a projection of the positive electrode terminal 10 projects from the hole.
The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

Next, the paste-type positive electrode 2, the paste-type negative electrode 4, the separator 3, and the electrolyte will be described.

The paste type positive electrode 2 has a conductivity of 3
A nickel-based particle having a surface coated with a cobalt-based film comprising a cobalt compound region having a valence of less than and a cobalt species region having a lower oxidation number, and at least a part of the trivalent cobalt compound region having a surface area of at least It has a form reaching the surface of the nickel hydroxide particles.

Examples of the conductive trivalent cobalt compound include cobalt oxyhydroxide (CoOO).
H).

As the cobalt species having an oxidation number lower than trivalent, cobalt hydroxide (Co (OH) ₂ ) can be exemplified. However, the cobalt species may include small amounts of cobalt monoxide (CoO) and metallic cobalt.

The trivalent cobalt compound in the cobalt-based film is preferably present at a ratio of 20% to 80% in terms of the number of cobalt atoms. This is due to the following reasons. If the existence ratio is less than 20%, the initial capacity of the secondary battery may decrease. On the other hand, if the abundance exceeds 80%, the amount of the cobalt compound having an oxidation number lower than trivalent is small,
Alternatively, it may be difficult to recover the capacity of the secondary battery by recharging after storage at a high temperature.

The trivalent cobalt compound region having conductivity is allowed to contain a small amount of inert tricobalt tetroxide.

The above-mentioned cobalt species region having an oxidation number lower than trivalent allows a trace amount of inactive tricobalt tetroxide to be contained.

The negative electrode 4 has a structure in which a paste containing an active material, a binder and water is filled in a conductive substrate.

As the active material, for example, a substance which directly participates in the charge / discharge reaction such as a cadmium compound or a substance which absorbs / releases a substance directly involved in the charge / discharge reaction such as a hydrogen storage alloy may be used. it can. Among them, a secondary battery provided with a negative electrode containing a hydrogen storage alloy as the active material can discharge at a larger current than a secondary battery provided with a negative electrode containing a cadmium compound powder, and may cause environmental pollution. Is small, so that it is preferable.

The hydrogen storage alloy is not particularly limited as long as it can store hydrogen electrochemically generated in an electrolytic solution and can easily release the stored hydrogen during discharge. . For example, LaNi ₅ , MmN
i ₅ (Mm; misch metal), LmNi ₅ (Lm; lanthanum-enriched misch metal), or Ni
A part of Al, Mn, Co, Ti, Cu, Zn, Zr,
Examples thereof include a multi-element type substituted by elements such as Cr and B, or a TiNi type, TiFe type, ZrNi type, or MgNi type. Among them, the general formula LmNi
_x Mn _y A _z (However, A is Al, shows at least one metal selected from Co, the atomic ratio x, y, z is the total value of 4.8 ≦ x + y + z ≦ 5.4) hydrogen represented by It is desirable to use an occlusion alloy.

Examples of the binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene and the like.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, a perforated rigid plate, and a nickel net, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal substrate. Can be mentioned.

In the case where a hydrogen storage alloy is used as the active material in the negative electrode, it is allowed to contain a conductive powder such as carbon black or graphite.

Examples of the separator 3 include a nonwoven fabric made of a polyamide-based synthetic resin fiber (eg, nylon 6,6 fiber), and a nonwoven fabric made of a polyolefin-based synthetic resin fiber which has been subjected to a hydrophilic treatment. it can. Examples of the polyolefin include polyethylene and polypropylene. Also,
Examples of the hydrophilic treatment include a plasma treatment, a sulfonation treatment, and a method of graft copolymerizing a vinyl monomer having a hydrophilic group. In particular, the non-woven fabric made of the polyolefin-based synthetic resin fiber that has been subjected to the hydrophilic treatment has a high electrolytic solution holding performance, and has excellent oxidation resistance. It is preferable because it is suppressed.

Examples of the alkaline electrolyte include an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of lithium hydroxide (LiOH), an aqueous solution of potassium hydroxide (KOH), a mixed solution of NaOH and LiOH, and a mixture of KOH and LiOH.
, A mixture of KOH, LiOH and NaOH, and the like.

According to the method for producing an alkaline secondary battery of the present invention, a uniform layer made of cobalt species is formed on the surface of nickel hydroxide particles, and the obtained paste containing composite nickel hydroxide particles is used as a current collector. A positive electrode, a negative electrode, a separator, and an alkaline secondary battery including an alkaline electrolyte are prepared by filling the composite water, and the initial charge is performed by performing constant current charging to gradually increase the current value. The nickel oxide particles are converted into nickel hydroxide particles whose surface is coated with a cobalt-based film composed of a conductive trivalent cobalt compound region and a cobalt species region having a lower oxidation number. At least a part of the cobalt compound region is formed so as to reach the surface of the nickel hydroxide particles from the surface of the cobalt-based film.

By charging a paste-type positive electrode containing a cobalt species having an oxidation number lower than trivalent and an alkaline electrolyte, the cobalt species is oxidized to a trivalent cobalt compound in the positive electrode. Reaction and the nickel hydroxide are converted to nickel oxyhydroxide (NiOO)
The reaction oxidized to H) occurs simultaneously. Further, the oxidation-reduction potential at which the oxidation reaction of the cobalt species occurs is closer to the base than the oxidation-reduction potential at which the oxidation reaction of nickel hydroxide occurs. As a result, for example, when the constant current charging is performed on the secondary battery, the potential of the positive electrode increases as the set current value increases, so that the oxidation reaction of the nickel hydroxide is preferentially performed as the constant current charging increases. Occurs. In the case of performing the initial charge of charging with a constant current over the entire positive electrode total capacity (the sum of the capacity of the cobalt species and the capacity of the nickel hydroxide) as in the conventional method, the oxidation reaction of the cobalt species becomes dominant. Set to such a current value. In order not to change this current value during the initial charge, if all of the cobalt species in the positive electrode are oxidized to cobalt oxyhydroxide, which is a conductive trivalent cobalt compound, and the potential of the positive electrode is not sufficiently increased, The oxidation reaction of the nickel hydroxide does not become dominant. In other words, when the initial charge of charging at a constant current over the entire capacity of the positive electrode is performed, the only cobalt species present in the positive electrode is cobalt oxyhydroxide.

As described above, a secondary battery provided with a positive electrode containing only cobalt oxyhydroxide as a cobalt species is stored for a long period of time, or is stored at a high temperature and self-discharge proceeds to increase the capacity. There is a problem that the capacity cannot be recovered by recharging when the battery charge decreases. It is considered that when self-discharge proceeds in such a secondary battery, cobalt oxyhydroxide in the positive electrode is reduced and changes to a cobalt compound having no conductivity again, so that the utilization rate of the positive electrode decreases. Can be Therefore, the reason that the capacity of the conventional secondary battery stored under the above-described conditions cannot be improved by recharging is that the utilization rate of the positive electrode lowered by the storage cannot be recovered by recharging. it is conceivable that.

According to the production method of the present invention, it is possible to shift to the oxidation reaction of nickel hydroxide before all the cobalt species having an oxidation number lower than trivalent are oxidized to the trivalent cobalt compound. That is, when the constant current charging with the current value reduced first is performed, the potential of the positive electrode is low, so that the oxidation reaction of the cobalt species can occur preferentially. Next, when the current value is increased, the value of the polarization resistance is increased, so that the potential of the positive electrode is changed from the potential at which the oxidation reaction of the cobalt species occurs preferentially while the cobalt species remains, so that the oxidation reaction of the nickel hydroxide is performed. The potential can be shifted to a preferentially generated potential. Therefore, as the first charge,
First, constant current charging is performed at a small current value such that the oxidation reaction of the cobalt species becomes dominant, and then constant current charging is performed at a large current value that provides a sufficient charge polarization to mainly cause the oxidation reaction of nickel hydroxide. By charging, the amount of oxidation of the cobalt species can be controlled.

That is, when an alkaline secondary battery is manufactured by the method of the present invention, in the secondary battery, after assembling, a cobalt species having an oxidation number lower than trivalent in the positive electrode is dissolved in the alkaline electrolyte and a blue complex is formed. Ion (HCo
O ₂ ^-) is changed to. The elution reaction to the electrolyte when the cobalt species is cobalt monoxide is shown in the following formula (1).

CoO + OH ⁻ → HCoO ₂ ⁻ (1) When the secondary battery is first subjected to constant current charging with a reduced current value, the blue complex ion becomes nickel hydroxide according to the reaction formula shown in the following formula (2). The nickel hydroxide particles are precipitated as cobalt hydroxide on the surface of the particles, and the surface of the nickel hydroxide particles is coated with a film composed of cobalt species having a lower oxidation number than trivalent and containing cobalt hydroxide as a main component.

HCoO ₂ ⁻ + H ₂ O → Co (OH) ₂ + OH ⁻ (2) After the cobalt seed film is formed, the surface of the cobalt seed film is contacted with hydroxide ions (OH ⁻ ), and then electricity is applied. Cobalt oxyhydroxide (Co
OOH) into a conductive trivalent cobalt compound. The oxidation reaction when the cobalt species is cobalt hydroxide is shown in the following formula (3).

Co (OH) ₂ + OH ⁻ → CoOOH + H ₂ O + e ⁻ (3) This oxidation reaction proceeds from the surface of the film toward the inside. When at least a part of the generated trivalent cobalt compound region reaches the surface of the nickel hydroxide particles, the set current value of the constant current charging is increased, and the potential of the positive electrode is preferentially oxidized by the oxidation reaction of the nickel hydroxide. To the potential generated at As a result, the surface of the nickel hydroxide particles can be covered with a cobalt-based film formed from the trivalent cobalt compound region and the cobalt species region having a lower oxidation number, and the trivalent cobalt compound region At least a part of the film may reach the surface of the nickel hydroxide particles from the film surface.

It is important to make the distribution of the cobalt seed region uniform in the cobalt-based film. For example,
When a paste is prepared by kneading a powder of cobalt species having an oxidation number lower than trivalent with a mixer, nickel hydroxide particles and a binder by a mixer, and filling the paste into a current collector, a positive electrode is prepared. In the distribution of the cobalt species. When the initial charge is applied to the alkaline secondary battery having such a positive electrode, a cobalt seed film having a variation in thickness due to the uneven distribution of the cobalt seed powder is easily formed, and the variation in the thickness is increased. In some cases, a thinner portion of a cobalt-based film obtained by oxidizing this film tends to have less unoxidized region. Depending on the amount of oxidation of the cobalt seed film, the unoxidized region may not remain at the thin portion. When such a secondary battery is stored under severe conditions such as high temperature and the conductivity of the trivalent cobalt compound region in the film is significantly impaired, the thickness of the cobalt-based film is reduced. Since there is no cobalt species to be newly oxidized in the thin portion, the conductivity cannot be restored by recharging. As a result, in the cobalt-based film formed after the recharging, there is a portion that cannot function as a conductive path, so that there is a possibility that the conduction varies, and a high utilization rate is obtained depending on the variation. There is a risk of disappearing.

According to the production method of the present invention, a uniform layer composed of cobalt species is formed on the surface of the nickel hydroxide particles,
After preparing a paste using the composite nickel hydroxide particles, a positive electrode is prepared by filling the paste into a current collector, so that a uniform layer made of the cobalt species is desired on the surface of the nickel hydroxide particles. The cobalt species can be uniformly dispersed in the positive electrode because they are adhered or joined with a sufficient strength. By performing the initial charge on a secondary battery having such a positive electrode,
Converting the composite nickel hydroxide particles into nickel hydroxide particles whose surface is coated with a uniform thickness cobalt-based film comprising a conductive trivalent cobalt compound region and a cobalt species region having a lower oxidation number. And at least a part of the trivalent cobalt compound region of the cobalt-based film can be formed to reach the surface of the nickel hydroxide particles from the surface of the cobalt-based film. The regions can be evenly dispersed.

Since the cobalt-based film can function as an excellent conductive path, the conduction between the nickel hydroxide particles and the conduction between the nickel hydroxide particles and the current collector can be improved. As a result, the initial utilization rate of the conventional positive electrode can be improved, so that the initial capacity of a secondary battery including the positive electrode can be improved.

When the secondary battery is stored for a long period of time or stored at a high temperature and self-discharge proceeds to reduce the capacity, the trivalent cobalt compound in the cobalt-based film is reduced. Although the conductivity of the region is impaired and the utilization rate of the positive electrode is reduced, when recharging is performed, the cobalt seed region in this film is oxidized to form a new conductive trivalent cobalt compound region. Can be. Since the cobalt seed region is uniformly distributed in the cobalt-based film, the conductivity of the entire cobalt-based film can be improved by the oxidation due to the recharging. as a result,
The capacity of the secondary battery can be improved by recovering the utilization rate of the positive electrode, and the secondary battery can maintain a high capacity even after being stored under the above-described conditions.

In addition, according to the production method of the present invention, the amount of cobalt species added can be reduced as compared with the case where cobalt species is added to the positive electrode by the mixing method. The capacity can be improved.

Further, by making the trivalent cobalt compound region in the cobalt-based film 20% to 80% in terms of the number of cobalt atoms by the initial charge, it is necessary to improve the initial positive electrode utilization rate. It is possible to simultaneously secure the amount of a trivalent cobalt compound having high conductivity and the amount of a cobalt species having an oxidation number lower than trivalent necessary to make the cobalt-based film function as a conductive path again after long-term storage. . Therefore, it is possible to manufacture an alkaline secondary battery in which both the initial capacity and the capacity recovery rate after long-term storage or storage at high temperature are dramatically improved.

The nickel hydroxide particles having a uniform layer of cobalt species formed on the surface described above can be produced by a mechanochemical method or a precipitation method. The above-mentioned precipitation method pays attention to the fact that nickel hydroxide is usually obtained by dissolving nickel metal in an acid such as a sulfuric acid solution and neutralizing and precipitating this with a base such as a sodium hydroxide solution. That's how it came out. Therefore, according to the precipitation method, composite nickel hydroxide particles can be obtained by a simple process of precipitating cobalt hydroxide on the surface of nickel hydroxide particles. The composite nickel hydroxide particles can be produced relatively easily and in high yield as compared with the mechanochemical method for forming a layer.

[0066]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Examples 1-4 Commercially available lanthanum-enriched misch metals Lm and N
i, Co, Mn, Al, Lm
A hydrogen storage alloy having a composition of Ni _4.0 Co _0.4 Mn _0.3 Al _0.3 was produced. Mechanically pulverizing the hydrogen storage alloy,
This was passed through a 200 mesh sieve. To 100 parts by weight of the obtained alloy powder, 0.5 parts by weight of sodium polyacrylate and carboxymethyl cellulose (CM
C) 0.125 parts by weight, 1.5 parts by weight of polytetrafluoroethylene dispersion (specific gravity 1.5, solids content 60 wt%) in terms of solids and 1 part by weight of carbon powder as a conductive material and 50 parts by weight of water A paste was prepared by mixing with This paste was applied to a punched metal as a conductive substrate, dried, and then molded under pressure to produce a paste negative electrode.

Further, composite nickel hydroxide particles were prepared by a precipitation method. First, nickel hydroxide particles having an average particle diameter of 10 μm are washed with water and dried, then transferred to a solution in which only a certain concentration of cobalt ions is present, and stirred for a certain time, so that the cobalt ions are sufficiently introduced into the pores of the nickel hydroxide particles. Soaked. Subsequently, this solution was added dropwise to a sodium hydroxide aqueous solution in which convection was caused to form a uniform layer made of cobalt hydroxide on the surface of the nickel hydroxide particles, thereby producing composite nickel hydroxide particles. The amount of cobalt hydroxide formed on the surface of the composite nickel hydroxide particles was 4% by weight in terms of metallic cobalt with respect to the total composite nickel hydroxide particles produced by the concentration regulation of the solution containing only the cobalt ions. And The amount of cobalt hydroxide (in terms of metallic cobalt) formed on the surface of the composite nickel hydroxide particles is determined by dissolving the particles in hydrochloric acid and quantifying by known atomic absorption spectrometry. It was calculated by subtracting the amount of precipitated cobalt.

[0069] Based on 100 parts by weight of the obtained composite nickel hydroxide powder, 0.25 parts by weight of carboxymethyl cellulose, 0.25 parts by weight of sodium polyacrylate, 3 parts by weight of polytetrafluoroethylene, and 30 parts by weight of water as a binder. A paste was prepared by adding and kneading parts. Subsequently, the paste was filled in a nickel-plated fiber substrate as a conductive substrate, dried, and molded to produce a paste-type positive electrode.

Next, a non-woven fabric made of a polypropylene fiber and a polyethylene fiber, which has been subjected to a hydrophilic treatment, is used as a separator, the separator is interposed between the negative electrode and the positive electrode, and spirally wound. To form an electrode group. Such an electrode group and 7N KOH and 1
An electrolytic solution composed of N LiOH was housed in a cylindrical container having a bottom, and a cylindrical alkaline secondary battery having the structure shown in FIG. 1 described above and having an AA size and a nominal capacity of 1100 mAh was assembled.

After the obtained secondary battery was initially charged under the conditions shown in Table 1 below, the terminal voltage was 1.0 CmA and the terminal voltage was 1.0 V
Discharged until.

Comparative Examples 1 and 2 A mixed powder comprising 90 parts by weight of nickel hydroxide powder as an active material and 10 parts by weight of cobalt hydroxide powder as a conductive material was mixed with carboxymethyl cellulose 0.2 as a binder.
5 parts by weight, 0.25 parts by weight of sodium polyacrylate,
A paste was prepared by adding 3 parts by weight of polytetrafluoroethylene, adding 30 parts by weight of water thereto, and kneading. Subsequently, the paste was filled in a nickel-plated fiber substrate as a conductive substrate, dried, and molded to produce a paste-type positive electrode.

The same separator as in Examples 1 to 4 was interposed between the positive electrode and the negative electrode as in Examples 1 to 4, and spirally wound to form an electrode group. Such an electrode group and an electrolytic solution having the same composition as those of Examples 1 to 4 were housed in a cylindrical container having a bottom, and had the structure shown in FIG. 1 described above, and had a size of AA and a nominal capacity of 1100 mAh. An alkaline secondary battery was assembled.

After the obtained secondary battery was initially charged under the conditions shown in Table 1 below, the terminal voltage was 1.0 CmA and the terminal voltage was 1.0 V
Discharged until.

Reference Example 1 A cylindrical alkaline secondary battery assembled in the same manner as in Examples 1 to 4 was subjected to initial charging under the conditions shown in Table 1 below, and then was applied at 1.0 CmA and a terminal voltage of 1.0 V Discharged until.

Reference Examples 2 to 5 After the cylindrical alkaline rechargeable batteries assembled in the same manner as in Comparative Examples 1 and 2 were initially charged under the conditions shown in Table 1 below, the terminal voltage was 1.0 CmA and the terminal voltage was 1 The battery was discharged until the voltage became 0.0V.

Examples 1 to 4 with initial charging, Comparative Example 1
, And the secondary batteries of Reference Examples 1 to 5 were measured for initial capacity. After charging each secondary battery at 0.1 CmA for 16 hours, it was discharged at 1.0 CmA until the terminal voltage became 1.0 V, and the initial capacity was calculated from the discharge duration time. The results are shown in Table 1 below.

The secondary batteries of Examples 1 to 4, Comparative Examples 1 and 2 and Reference Examples 1 to 5 showed that the charge electricity consumed for the oxidation of cobalt was determined from the change in the charge voltage curve of the batteries at the time of the first charge. The amount was determined, and the proportion of the trivalent cobalt compound in the cobalt species present in the positive electrode was determined in terms of the number of cobalt atoms. The results are shown in Table 1 below.

The secondary batteries of Examples 1 to 4, Comparative Examples 1 and 2 and Reference Examples 1 to 5 in which the initial capacity was confirmed were 65%
After storage at 28 ° C. for 28 days, the charge / discharge cycle was repeated five times under the same charge / discharge conditions as the initial capacity measurement, and the recovery capacity at the fifth cycle was measured. The recovery rate was determined by dividing the recovery capacity at the fifth cycle by the initial capacity, and is also shown in Table 1 below together with the recovery capacity at the fifth cycle.

[0080]

[Table 1]

As is clear from Table 1, the secondary batteries of Examples 1 to 4 have a high initial capacity and a high temperature in which the ratio of the trivalent cobalt compound in the cobalt species present in the positive electrode is 18 to 78%. It can be seen that both the high capacity recovery rate after storage is satisfied at the same time. In particular, it can be seen that the secondary batteries of Examples 1 to 4 can significantly improve the capacity recovery rate after high-temperature storage as compared with the secondary batteries of Comparative Examples 1 and 2 and Reference Examples 1 to 5. With respect to the secondary batteries of Examples 1 to 4, the nickel hydroxide powder of the positive electrode was observed by SEM (scanning electron microscope), EDS (energy dispersive X-ray analysis), and XPS (X-ray photoelectron spectroscopy). As shown in FIG. 2, the nickel hydroxide powder 20 of the positive electrode has a conductive trivalent cobalt compound region 21 (mainly composed of cobalt oxyhydroxide) and a cobalt seed region 22 whose oxidation number is lower than trivalent.
(Mainly composed of cobalt hydroxide) is coated with a cobalt-based film 23 having a uniform thickness, and a part of the trivalent cobalt compound region 21 is formed from the surface of the film 23 to the surface of the nickel hydroxide powder. , And it was confirmed that the cobalt seed region 22 was uniformly present. The cobalt compound region 21 includes:
A trace amount of tricobalt tetroxide was contained.

On the other hand, in the secondary batteries of Comparative Examples 1 and 2 and Reference Example 1, the cobalt species present in the positive electrode was only a trivalent cobalt compound, and although the initial capacity was high, the capacity recovery rate after high-temperature storage was low. It turns out that it is extremely low. In the secondary batteries of Reference Examples 2 to 5, the proportion of the trivalent cobalt compound in the cobalt species present in the positive electrode was 23 to 83%,
It can be seen that the initial capacity is as high as the secondary batteries of Examples 1 to 4, but the capacity recovery rate is slightly lower than the secondary batteries of Examples 1 to 4. This is because the dispersion of the cobalt hydroxide powder by simple mixing causes a bias in the distribution of the cobalt species region in the cobalt-based film covering the surface of the nickel hydroxide particles, and the degree of conductivity recovery differs depending on the position of the positive electrode. It is.

In the above embodiment, the electrode group produced by spirally winding the separator 4 between the negative electrode 4 and the non-sintered positive electrode 2 was housed in the bottomed cylindrical container 1. Although an example in which the present invention is applied to a cylindrical alkaline secondary battery having a structure is described, a separator is interposed between a plurality of negative electrodes and a plurality of positive electrodes to form a laminate, and the laminate is placed in a bottomed rectangular cylindrical container. The present invention can also be applied to a prismatic alkaline secondary battery having a structure accommodated in a battery.

[0084]

As described above in detail, according to the alkaline secondary battery of the present invention, a high capacity can be realized in the initial capacity, and self-discharge can be achieved by storage for a long time, particularly at high temperature. When this occurs, the capacity can be recovered by charging and discharging, and a remarkable effect such as maintaining a high capacity even after such storage can be achieved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an alkaline secondary battery according to the present invention.

FIG. 2 is a schematic diagram showing nickel hydroxide powder of a positive electrode in the alkaline secondary batteries of Examples 1 to 4 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate, 8 ... Insulating gasket, 13 ... Outer tube.

Continuing from the front page (72) Inventor Kenichi Kanno 3-4-1-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation (72) Inventor Hidekazu Ohata 3-4-1-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Stock In company

Claims (2)

[Claims] A positive electrode having a structure in which a current collector contains paste containing nickel hydroxide particles as an active material; a negative electrode; a separator interposed between the positive electrode and the negative electrode; Wherein the nickel hydroxide particles are uniformly coated with a cobalt-based film comprising a conductive trivalent cobalt compound region and a cobalt species region having a lower oxidation number. And a part of the trivalent cobalt compound region has a form reaching the surface of the nickel hydroxide particles from the surface of the film. 2. The alkaline secondary battery according to claim 1, wherein the trivalent cobalt compound in the cobalt-based film is present in a ratio of 20% to 80% in terms of the number of cobalt atoms.