JPH1097865A - Alkali storage battery and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control reduction in discharge capacity when left for a long time or under the condition of high temperature by forming a positive electrode from a collector carrying a positive electrode material comprising a nickel hydroxide, an oxycobalt hydroxide and a tricobalt tetraoxide. SOLUTION: A positive electrode 2, a separator 3 and a negative electrode 4 are laminated to be spirally wound in a container 1 of bottomed cylindrical shape, thus accommodating a manufactured electrode group 5. The negative electrode 4 is arranged along the outermost periphery of the electrode group 5 making electrical contact with the container 1. An alkaline electrolytic solution is contained in the container 1. In this case, an alkali storage battery is provided with the positive electrode 2 containing a nickel hydroxide Ni(OH)2 , an oxycobalt hydroxide CoOOH and a tricobalt tetraoxide Co3 O4 . Consequently, high active material utilization factor can be ensured to improve capacity recovery factor after being left for a long time or under the condition of high temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline storage battery having a non-sintered nickel positive electrode and a method of manufacturing the same, and more particularly to an alkaline storage battery having an improved non-sintered nickel positive electrode and a method of manufacturing the same.

[0002]

2. Description of the Related Art The positive electrode of an alkaline storage battery is roughly classified into a sintered type and a paste type. From the viewpoint of increasing the capacity, a current collector is filled or coated with a paste containing nickel hydroxide particles as an active material. The paste type to be applied is often used. In this paste-type positive electrode, it is essential that a sufficient electrical connection between the particulate active material and the current collector be taken to improve the utilization factor. Addition of compounds has been performed.

Specifically, cobalt hydroxide is formed on the surface of nickel hydroxide particles, and such particles are subjected to a heat treatment in the presence of an alkali to convert the high-order cobalt oxide having high conductivity into nickel hydroxide particles. Forming on the surface has been performed.

However, in an alkaline storage battery provided with such a paste-type positive electrode to which a conductive auxiliary agent is added, there is a demand for an improvement in the capacity recovery rate when left for a long time or in a high-temperature environment.

[0005] Electrochem. Soc, 1
36 (1989), p. 1590, discloses that high-order cobalt oxide formed as a conductive network in a paste-type nickel electrode is stably present during normal charge and discharge by Oshitani et al. On the other hand, DENKI KAGAKU
63, No. 1 (1995), p. 952, that when an alkaline storage battery provided with a paste-type nickel positive electrode is left for a long period of time or at a high temperature, the battery voltage decreases and the capacity recovery rate upon recharging decreases. Have been described.

Japanese Patent Application Laid-Open No. Hei 5-314983 discloses that when a calcium compound is added to a positive electrode and the initial charge is performed in an atmosphere at 40 to 70 ° C., the calcium compound dissolves quickly, so that the initial performance is stable. It is disclosed that an alkaline storage battery can be obtained. On the other hand, Japanese Patent Laid-Open No. 5-2
Japanese Patent No. 75082 discloses a nickel positive electrode and a negative electrode containing an AB ₂ -based hydrogen storage alloy, wherein the initial charge is performed in an atmosphere at 50 to 70 ° C. to lower the charge efficiency of the positive electrode and reduce the initial performance of the negative electrode. The manufacture of an enhanced nickel-metal hydride battery is described. However, it has been difficult to sufficiently increase the capacity recovery rate when left for a long time or in a high-temperature environment by these initial charges.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to improve the utilization rate of an active material by improving a paste-type nickel positive electrode, and to suppress the decrease in discharge capacity due to leaving for a long period or in a high-temperature environment. An object of the present invention is to provide a storage battery and a method for manufacturing the storage battery.

[0008]

An alkaline storage battery according to the present invention includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte.
The positive electrode is characterized in that a positive electrode material containing nickel hydroxide, cobalt oxyhydroxide and cobalt trioxide is formed from a material supported on a current collector.

The method of manufacturing an alkaline storage battery according to the present invention is characterized in that a separator including a separator is interposed between a positive electrode and a negative electrode formed by filling or coating a current collector with a paste containing nickel hydroxide and a conductive additive. Electrode group,
A step of storing an alkaline electrolyte containing lithium hydroxide of 0.5 M or more in a container, and 40 ° C. to 100 ° C. so that the conductive additive in the positive electrode is converted into cobalt oxyhydroxide and cobalt tetroxide. And performing a first charge within the range.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery (for example, a cylindrical alkaline secondary battery) of the present invention will be described with reference to FIG. An electrode group 5 produced by stacking the positive electrode 2, the separator 3, and the negative electrode 4 and winding them in a spiral shape is accommodated in the bottomed cylindrical container 1. 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 supplied in the container 1
Housed within. A circular first 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 is 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 provided on the sealing plate 7 with the hole 6.
It is attached to cover. 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 circular holding plate 12 made of an insulating material having a hole in the center is provided on the positive electrode terminal 10 with a protrusion of the positive electrode terminal 10.
Are arranged to protrude from the holes. 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 positive electrode 2, the negative electrode 4, the separator 3
And the electrolyte will be described. 1) Positive Electrode 2 This positive electrode 2 has a positive electrode material containing nickel hydroxide {Ni (OH) ₂ } particles, cobalt oxyhydroxide (CoOOH) and cobalt trioxide (Co ₃ O ₄ ) supported on a current collector. Formed from

As the nickel hydroxide particles, for example, single nickel hydroxide particles or nickel hydroxide particles in which zinc and / or cobalt are coprecipitated with metallic nickel can be used. The latter positive electrode containing nickel hydroxide particles can further improve the charging efficiency in a high temperature state.

From the viewpoint of improving the charge / discharge efficiency of the alkaline storage battery, the peak half-value width of the (101) plane of the nickel hydroxide particles determined by the X-ray powder diffraction method is 0.8 ° / 2θ.
(Cu-Kα) or more is preferable. A more preferable nickel hydroxide powder is powder X-ray diffraction method (10
1) The half width of the surface peak is 0.9 to 1.0 ° / 2θ.
(Cu-Kα).

Examples of the current collector include those having a sponge-like, fibrous, or felt-like porous structure made of a metal such as nickel or stainless steel, a nickel-plated resin, or the like.

Preferably, a binder is added to the positive electrode material in order to improve the adhesion to the current collector. Examples of the binder include polytetrafluoroethylene, carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, and polyvinyl alcohol.

2) Negative Electrode 4 The negative electrode 4 is prepared by kneading a negative electrode active material, a conductive material, a binder and water to prepare a paste, filling the paste into a conductive substrate, drying the paste, and then forming the paste. It is manufactured by

Examples of the negative electrode active material include cadmium compounds such as metal cadmium and cadmium hydroxide, and hydrogen. Examples of the host matrix of hydrogen include a hydrogen storage alloy.

Above all, the hydrogen storage alloy is preferable because the capacity of the secondary battery can be improved as compared with the case where the cadmium compound is used. The hydrogen storage alloy is not particularly limited, and may be any 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 , Mm
Ni ₅ (Mm is a misch metal), LmNi ₅ (Lm is at least one selected from rare earth elements including La),
A part of Ni of these alloys is Al, Mn, Co, Ti, C
Examples thereof include a multi-element-based material substituted with an element such as u, Zn, Zr, Cr, and B, or a TiNi-based or TiFe-based material. In particular, the general formula LmNi _w Co _x Mn
_y Al _z (the total value of atomic ratios w, x, y, and z is 5.00 ≦
(W + x + y + z ≦ 5.50) The hydrogen storage alloy having the composition represented by the formula (1) is suitable because it can suppress the pulverization accompanying the progress of the charge / discharge cycle and improve the charge / discharge cycle life.

Examples of the conductive material include carbon black and graphite. Examples of the binder include polyacrylates such as sodium polyacrylate and potassium polyacrylate, fluorine-based resins such as polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CMC).

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; a felt-like porous metal;
Examples include a three-dimensional substrate such as a sponge-like porous metal body.

3) Separator 3 Examples of the separator 3 include a nonwoven fabric made of a polyamide fiber and a nonwoven fabric made of a polyolefin fiber such as polyethylene or polypropylene provided with a hydrophilic functional group.

4) Alkaline Electrolyte As the alkaline electrolyte, for example, an aqueous solution of sodium hydroxide (NaOH), lithium hydroxide (LiOH)
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixed solution, KOH and LiOH mixed solution, K
A mixed solution of OH, LiOH, and NaOH can be used.

In FIG. 1 described above, a separator is interposed between the positive electrode and the negative electrode, and the electrode group produced by spirally winding the separator is housed in the container.
For example, a laminate made by alternately stacking a positive electrode and a negative electrode with a separator interposed therebetween may be housed in a bottomed rectangular cylindrical container.

Such an alkaline storage battery can be manufactured, for example, by the following method. (1) Preparation of Positive Electrode A positive electrode formed by filling or applying a paste containing nickel hydroxide and a conductive additive to a current collector is prepared by the following method (a) or (b).

(A) A paste containing nickel hydroxide particles, cobalt-based particles as a conductive aid, a binder and water is prepared, and the paste is filled in a current collector, and dried.
After pressure molding, the resultant is cut into a desired size to produce a positive electrode having a structure in which a positive electrode material containing nickel hydroxide particles, cobalt compound particles, and a binder is supported on a current collector.

As the cobalt compound forming the cobalt-based particles, for example, dicobalt trioxide (Co ₂ O)
₃ ), cobalt metal (Co), cobalt monoxide (Co)
O), cobalt hydroxide {Co (OH) ₂ } and the like.

The amount of the cobalt particles added is such that the cobalt compound constituting the cobalt particles is C
It is set to convert to oOOH and Co ₃ O ₄ . (B) A paste containing a composite nickel hydroxide particle having a cobalt-based layer formed thereon as a conductive additive on its surface, a binder and water is prepared, and the paste is filled in a current collector. After pressing, the resultant is cut into a desired size to produce a positive electrode having a structure in which a positive electrode material containing composite nickel hydroxide particles and a binder is supported on a current collector.

Examples of the cobalt compound forming the cobalt-based layer include cobalt metal (Co), cobalt monoxide (CoO), and cobalt hydroxide @ Co (OH).
₂ }, dicobalt trioxide (Co ₂ O ₃ ) and the like. In particular, cobalt hydroxide is preferred.

The amount of the cobalt-based layer deposited is such that the cobalt compound constituting the cobalt-based layer upon initial charge is CoO
It is set to convert to OH and Co ₃ O ₄ . (2) Assembly of Battery An electrode group is produced by interposing the separator between the positive electrode and the negative electrode produced by the method described above. The electrode group and the alkaline electrolyte are housed in a container and sealed to assemble an alkaline storage battery.

As the alkaline electrolyte, 0.5M
(Mol / l) or more containing LiOH is used. L
When the concentration of iOH is less than 0.5M, it becomes difficult to convert the conductive additive in the positive electrode material into CoOOH and Co ₃ O ₄ by initial charging. On the other hand, the upper limit of LiOH is preferably set to 1.5M. If the concentration of LiOH exceeds 1.5M, the conductivity of the electrolytic solution may decrease, and the cycle life may decrease. Furthermore, since LiOH has a relatively low solubility, dissolution exceeding 1.5 M is difficult, and there is a possibility that LiOH may precipitate in a low temperature range. A more preferred concentration (M) of LiOH is 0.5 to 1.2.

In order to further improve both the high-temperature charging efficiency and the cycle life of the alkaline storage battery, 2.0 to 6.0 M KOH, 2.0 to 5 M 0.0M NaOH and 0.5-
It is preferable to use an electrolytic solution having a composition of 1.5 M LiOH.

(3) Initial Charge An initial charge is performed at a temperature in the range of 40 to 100 ° C. so that the conductive assistant in the positive electrode material is converted into CoOOH and Co ₃ O ₄ .

When the initial charging temperature is out of the above range, it becomes difficult to convert the conductive auxiliary into CoOOH and Co ₃ O ₄ . A more preferred initial charging temperature is in the range of 70C to 90C.

The charging current (charging voltage) and the charging time are as follows.
It is set to convert to OOH and Co ₃ O ₄ . According to the alkaline storage battery of the present invention as described above,
Nickel hydroxide {Ni (OH) ₂ }, cobalt oxyhydroxide (CoOOH), and cobalt trioxide (Co ₃ O)
₄ ) By providing a positive electrode formed from a positive electrode material supported on a current collector containing the positive electrode material, a high active material (nickel hydroxide) utilization rate is ensured, and after long-term storage and in a high-temperature environment, The capacity recovery rate after standing can be improved.

That is, when the alkaline storage battery is left for a long period of time or at a high temperature, the battery voltage decreases and the capacity recovery rate at the time of recharging decreases. This is presumed to be due to the fact that CoOOH having the following formula is reduced and loses conductivity, and the active material utilization rate is reduced. Co ₃ O ₄ has a lower solubility in an alkaline electrolyte than CoOOH and is stable.
By allowing Co ₃ O ₄ to be present in the positive electrode containing OOH, the reduction reaction of CoOOH during standing can be suppressed, and a decrease in the active material utilization can be suppressed. For this reason, the capacity recovery rate after standing can be improved.
The effect of suppressing the reduction of CoOOH by Co ₃ O ₄ is as follows.
Ni (OH) ₂ and Co are coated in such a form that the surface of the i (OH) ₂ particles is covered with a layer in which Co ₃ O ₄ and CoOOH coexist (eutectic).
It is most effectively expressed when OOH and Co ₃ O ₄ are present in the positive electrode.

The method for manufacturing an alkaline storage battery according to the present invention is characterized in that nickel hydroxide {Ni (OH) ₂ } and a conductive additive (for example, a cobalt compound having a valence of 2 or less such as Co, CoO, and Co (OH) ₂ ). Containing a separator between the positive electrode and the negative electrode formed by filling or coating a current collector with a paste containing, and an alkaline electrolyte containing lithium hydroxide of 0.5 M or more. And the conductive assistant in the positive electrode is cobalt oxyhydroxide (CoOOH) and cobalt tetroxide (Co ₃ O).
_{And 4} ) performing an initial charge in the range of 40 ° C. to 100 ° C. so as to convert into ₄ ). According to such a method,
It is possible to provide an alkaline storage battery having a significantly improved capacity recovery rate after being left for a long period of time and after being left at a high temperature while ensuring a high utilization rate. The divalent or lower valent cobalt compound is oxidized to CoOOH through the reaction shown in Chemical Formula 1 by the initial charge.

[0037]

Embedded image At this time, it is presumed that Co ₃ O ₄ is produced simultaneously or later by the reaction shown in Chemical Formula 2 below.

[0038]

Embedded image

When the divalent or less cobalt compound in the positive electrode is converted into CoOOH and Co ₃ O ₄ by such initial charging, the effect of Co ₃ O ₄ to suppress the reduction reaction of CoOOH can be effectively exhibited. This is because Ni (O
It is presumed that this is because a layer in which CoOOH and Co ₃ O ₄ coexist (eutectic) is formed on the H) ₂ particle surface.
In addition, when the alkaline storage battery is left for a long time or at a high temperature, if a cobalt compound having a valence of 2 or less is present in the positive electrode, the cobalt compound becomes a nucleus to form CoOO.
The reduction reaction of H may be accelerated. For this reason, it is preferable that the divalent or lower valent cobalt compound has at least a higher valence than divalent. According to the initial charge, a cobalt compound having a valency of 2 or less is converted into Co ₃ O
_{Since the} compound can be oxidized to ₄ , and the amount of the divalent or lower valent cobalt compound can be reduced, it is possible to suppress the reduction reaction of CoOOH caused by the cobalt compound serving as a nucleus. Therefore, according to the manufacturing method according to the present invention,
Since the reduction reaction of CoOOH during standing for a long period of time and at a high temperature can be significantly suppressed, it is possible to provide an alkaline storage battery whose capacity recovery rate after standing is dramatically increased.

[0040]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Example) <Preparation of positive electrode> 0.25 parts by weight of carboxymethylcellulose and 0.25 parts by weight of sodium polyacrylate were added to a mixed powder composed of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder as a conductive aid. And 3.0 parts by weight of polytetrafluoroethylene, and 30 parts by weight of water were further added to the mixture and kneaded to prepare a paste. This paste has a thickness of 1.
A 1 mm, 95% porosity nickel-plated fiber substrate was filled, dried, roll-pressed and roll-formed, so that the positive electrode material containing nickel hydroxide particles and cobalt monoxide particles was supported on the current collector. A positive electrode having a structure was prepared. <Preparation of Negative Electrode> LaNi _4.0 Co _0.4 Mn _0.3 Al _0.3
3 parts by weight of polytetrafluoroethylene powder, 1 part by weight of carbon powder, and 1 part by weight of carboxymethyl cellulose as a binder
A paste was prepared by adding parts by weight and mixing with 50 parts by weight of water. This paste was applied to a nickel net, dried, and then press molded to produce a hydrogen storage alloy negative electrode.

Next, a separator made of a nonwoven fabric made of polypropylene was interposed between the positive electrode and the negative electrode, and spirally wound to form an electrode group. These electrode groups and 1.
AA size (theoretical capacity: 1200 mAh) having the structure shown in FIG. 1 described above in which an alkaline electrolyte composed of 0 M LiOH and 7.0 M KOH is housed in a cylindrical container having a bottom.
Was assembled. <First charge> The obtained storage battery was charged at 0.1C for 15 hours in an atmosphere of 90 ° C for 150 hours, and then charged.
Discharge was performed at 0.2 C to 1 V. (Comparative Example) An alkaline electrolyte composed of 8.0 M KOH was used, and a temperature of 15
Except for the first charge of 150% charge over time,
A cylindrical nickel-metal hydride storage battery was manufactured in the same manner as in the example.

With respect to the storage batteries of the example and the comparative example, 0.
After charging at a current of 1 CmA for 16 hours, the battery was discharged at a current of 1.0 CmA until the terminal voltage became 1.0 V, and an initial capacity was calculated from the discharge duration, and an active material utilization rate ｛(initial capacity / theoretical capacity) ) × 100 °, and the results are shown in FIG. Furthermore, after storing these storage batteries in a discharged state at 65 ° C. for one month, charging them at a current of 0.1 CmA for 16 hours,
Charging and discharging were repeated three times at a current of 1.0 CmA until the terminal voltage reached 1.0 V, and the discharge capacity was measured to determine the recovery capacity. A recovery rate {(recovery capacity / initial capacity) × 100} was determined from the obtained recovery capacity, and the result is shown in FIG.

As is clear from FIGS. 2 and 3, the storage battery of the embodiment has a high initial active material utilization rate of 99% and a higher recovery rate after high-temperature storage than the storage battery of the comparative example. Recognize.

In order to confirm the cobalt compounds present in the positive electrodes of the batteries of Examples and Comparative Examples, the following experiments were performed. <Assembly of Test Cell> (Test Cell 1) A test cell similar to the example was assembled except that cobalt monoxide powder was used instead of nickel hydroxide powder. The obtained cell was initially charged under the same conditions as in the example. (Test Cell 2) A test cell similar to the comparative example was assembled except that cobalt monoxide powder was used instead of nickel hydroxide powder. The obtained cell was initially charged under the same conditions as in the comparative example. <X-ray powder diffraction measurement> Test cells 1 and 2 after first charge
Was disassembled, and X-ray powder diffraction measurement was performed for each positive electrode. The results are shown in FIG.

As is apparent from FIG.
The line powder diffraction pattern has a CoOOH peak (indicated by 〇) and a Co ₃ O ₄ peak (indicated by), which indicates that CoOOH and C were present in the positive electrode of the storage battery of the example.
It was confirmed that o ₃ O ₄ was present. On the other hand, in the X-ray powder diffraction pattern of the test cell 2, a peak of CoOOH (indicated by Δ) and a peak of Co (OH) ₂ (indicated by ×) are present. Co ₃
It was confirmed that there was no O ₄ and CoOOH and Co (OH) ₂ were present.

Therefore, based on the initial active material utilization rate in FIG. 2, the recovery rate after high-temperature storage in FIG. 3, and the X-ray powder diffraction pattern of the positive electrode in FIG. The storage battery of the example provided with a positive electrode comprising a positive electrode material supported on a current collector containing a positive electrode containing no cobalt tetroxide while maintaining a high initial active material utilization rate It can be seen that the capacity recovery rate after high-temperature storage can be improved as compared with the storage battery of the example.

The initial activation method (initial charge) of the above-described embodiment is based on the formation of a conductive matrix of cobalt and the formation of Ni (O).
H) The _two active materials are charged at the same time, and if the main focus is on the formation of the cobalt conductive matrix, CoO
The same effect can be obtained by charging at the same rate and in the same atmosphere so that the amount becomes 100% with respect to the added amount, and then performing charging under arbitrary conditions.

[0048]

As described above in detail, according to the present invention, while maintaining the active material utilization rate at the initial stage of the charge / discharge cycle at a high value, a decrease in the capacity when left for a long time or when left at a high temperature is suppressed. And a method for manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an alkaline storage battery (for example, a cylindrical alkaline storage battery) according to the present invention.

FIG. 2 is a characteristic diagram showing an initial active material utilization rate in a storage battery of an example of the present invention and a storage battery of a comparative example.

FIG. 3 is a characteristic diagram showing a capacity recovery rate after storage at a high temperature in a storage battery of an example of the present invention and a storage battery of a comparative example.

FIG. 4 is a characteristic diagram showing an X-ray powder diffraction pattern of a positive electrode in test cells 1 and 2.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... container, 2 ... positive electrode, 3 ... separator, 4 ... negative electrode, 7 ...
Sealing plate.

Continuation of front page (72) Inventor Takeshi Komiyama 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation

Claims (2)

[Claims] 1. A positive electrode, comprising a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte, wherein the positive electrode comprises nickel hydroxide, cobalt oxyhydroxide and cobalt tetroxide. An alkaline storage battery characterized in that a positive electrode material containing: is supported on a current collector. 2. An electrode group formed by interposing a separator between a positive electrode and a negative electrode formed by filling or applying a paste containing nickel hydroxide and a conductive auxiliary to a current collector; A step of storing the alkaline electrolyte containing lithium hydroxide in a container, and in a range of 40 ° C to 100 ° C so that the conductive auxiliary agent in the positive electrode is converted into cobalt oxyhydroxide and cobalt tetroxide. Performing a first charge.