JPH09139230A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary battery, having improved electric charging efficiency in a high-temperature condition, and sufficient actual capacity (electric discharge capacity). SOLUTION: This alkaline secondary battery is equipped with a positive electrode 2 including nickel hydroxide powder, a negative electrode 4, a separator 3 interposed between the positive electrode 2 and the negative electrode 4, and an alkaline electrolyte. In this case, a nickel hydroxide has the peak half value width of a (101) surface, by an X-ray powder diffraction method, of 0.8 deg./2θ (Cu-Kα) or more; and the alkaline electrolyte has a composition of a potassium hydroxide of 2.0-6.0N, a sodium hydroxide of 2.0-5.0N, and a lithium hydroxide of 0.5-1.5N.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an alkaline secondary battery, and more particularly to an alkaline secondary battery having an improved alkaline electrolyte.

[0002]

2. Description of the Related Art In an alkaline secondary battery, an electrode group made by interposing a separator made of synthetic resin fiber between a nickel positive electrode and a negative electrode is housed in a container together with an alkaline electrolyte made of potassium hydroxide, for example. Have a structure. The nickel positive electrode is prepared by kneading nickel hydroxide powder, a conductive agent such as a cobalt compound such as cobalt oxide or metallic cobalt, a binder, and water to prepare a paste, and the paste is then three-dimensionally formed, for example. It is manufactured by filling an alkali-resistant metal porous body such as a sponge-like metal porous body or a metal fiber mat.

However, when the secondary battery having the above-described structure is charged at a high temperature, it participates in the charging reaction of the nickel hydroxide powder of the positive electrode shown in the following formula (1) and the oxygen gas generating reaction shown in the following formula (2). The potential difference becomes smaller. As a result, the charging voltage at the time of charging is eaten by the oxygen gas generating reaction of the above formula (2), so that there is a problem that the charging efficiency of the positive electrode is reduced.

Ni (OH) ₂ + OH ⁻ → NiOOH + H ₂ O + e ⁻ (1) 4OH ⁻ → 2H ₂ O + O ₂ ↑ + 4e ⁻ (2) From the above, a few% of cadmium or zinc is added to the nickel hydroxide powder. It has been practiced to contain it or add lithium hydroxide to the alkaline electrolyte. However, it is difficult to sufficiently improve the charging efficiency of the positive electrode in the high temperature state by these methods.

[0005]

SUMMARY OF THE INVENTION The present invention maintains a capacity retention rate (cycle life) during a practical cycle,
It is intended to provide an alkaline secondary battery having improved charging efficiency in a high temperature state and having a sufficient actual capacity (discharge capacity).

[0006]

According to the present invention, there is provided a positive electrode containing nickel hydroxide powder, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. The above-mentioned nickel hydroxide has a peak full width at half maximum of the (101) plane of 0.8 ° / 2θ (Cu
-Kα) or more, and the alkaline electrolyte is 2.
There is provided an alkaline secondary battery having a composition of 0 to 6.0 N potassium hydroxide, 2.0 to 5.0 N sodium hydroxide, and 0.5 to 1.5 N lithium hydroxide. It

Further, according to the present invention, it is provided with a positive electrode containing nickel hydroxide powder, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte,
The nickel hydroxide may be obtained by the X-ray powder diffraction method (10
1) Peak full width at half maximum of 0.8 ° / 2θ (Cu-Kα)
Above, and the said alkaline electrolyte is 2.0-6.
It is characterized by comprising 0 N potassium hydroxide, 2.0 to 5.0 N sodium hydroxide and 0.5 to 1.5 N lithium hydroxide, and having a composition containing sodium hydroxide as a main component. An alkaline secondary battery is provided.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The alkaline secondary battery of the present invention will be described below with reference to FIG. An electrode group 5 made by stacking a positive electrode 2, a separator 3, and a negative electrode 4 and winding them in a spiral shape is housed in a 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 contained in the container 1. Hole 6 in the center
The first sealing plate 7 having a circular shape is disposed at the upper opening of the container 1. 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 7 is connected to the container 1 through the gasket 8 by caulking to reduce the diameter of the upper opening inward. And airtightly fixed. 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.
The safety valve 11 made of rubber includes the sealing plate 7 and the positive electrode terminal 1.
It is arranged so as to close the hole 6 in a space surrounded by 0. A circular holding plate 12 made of an insulating material having a hole in the center is arranged on the positive electrode terminal 10 such that a projection of the positive electrode terminal 10 projects from the hole of the holding plate 12. 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 is a nickel hydroxide powder having a peak half width of (101) plane of 0.8 ° / 2θ (Cu-Kα) or more measured by X-ray powder diffractometry, a conductive agent, a binder, and It is prepared by preparing a paste containing water, filling the paste into an alkali-resistant metal porous body, drying and press-molding the paste, and then cutting it into a desired size.

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

The half width of the peak of the (101) plane of the nickel hydroxide powder measured by the powder X-ray diffraction method is defined as follows.
This is for the following reasons. The half width is 0.8
When the angle is less than ° / 2θ (Cu-Kα), the charge / discharge efficiency of the alkaline secondary battery including the positive electrode containing the nickel hydroxide powder decreases in relation to the alkaline electrolyte described later.
This decrease in charging / discharging efficiency occurs not only in the high temperature region but also in the low temperature region. The more preferable half-value width of the peak of the (101) plane of the nickel hydroxide powder by the powder X-ray diffraction method is
It is 0.9-1.0 degree / 2 (theta) (Cu-K (alpha)).

Examples of the conductive agent include cobalt compounds such as cobalt monoxide, dicobalt trioxide, and cobalt hydroxide. Examples of the binder include polytetrafluoroethylene, carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, and polyvinyl alcohol.

Examples of the alkali-resistant metal porous body include those having a sponge-like, fiber-like, or felt-like porous structure made of a metal such as nickel or stainless steel or a resin plated with nickel. it can.

2) Negative Electrode 4 This 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 conductive substrate with the paste, drying the paste, and then molding the paste. Manufactured by.

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

Above all, the hydrogen storage alloy is preferable because it can improve the capacity of the secondary battery 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 polyacrylic acid salts such as sodium polyacrylate and potassium polyacrylate, fluororesins such as polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CMC).

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

3) Separator 3 Examples of the separator 3 include a polyamide fiber non-woven fabric and a polyolefin fiber non-woven fabric such as polyethylene or polypropylene to which a hydrophilic functional group is added.

4) Alkaline Electrolyte This alkaline electrolyte contains 2.0 to 6.0 N potassium hydroxide (KOH), 2.0 to 5.0 N sodium hydroxide (NaOH) and 0.5 to 1.N. It has a composition of 5N lithium hydroxide (LiOH).

In the alkaline electrolyte solution comprising KOH, NaOH and LiOH, NaO in the electrolyte solution
The higher the normality (N) of H and LiOH, particularly the higher the normality of LiOH, the higher the oxygen generation potential of the above-mentioned formula (2) and the higher temperature charging efficiency can be improved. On the other hand, K in the electrolyte
The higher the normality (N) of OH, the more improved the capacity retention rate of the alkaline secondary battery containing the electrolyte solution during cycling.
The reasons for limiting the normality of KOH, NaOH and LiOH will be described below.

[KOH] This KOH is used to enhance the conductivity of the electrolytic solution. When KOH is less than 2.0 N, the electroconductivity of the electrolytic solution is lowered, and the capacity retention rate of the secondary battery including the electrolytic solution during the cycle is lowered. On the other hand, K
When OH exceeds 6.0 N, the amount of the added components NaOH and LiOH to KOH dissolved in the electrolytic solution decreases, that is, the normality of these alkaline components relatively decreases and the high temperature charging efficiency decreases. . The more preferable normality (N) of KOH is 2.5 to 5.5.

[NaOH] This NaOH has a function of increasing the oxygen generation voltage shown in the equation (2) during high temperature charging. If NaOH is less than 2.0 N, improvement in high temperature charging efficiency cannot be achieved. On the other hand, when the NaOH content exceeds 5.0 N, the normality of KOH in the electrolytic solution is relatively lowered, and the conductivity of the electrolytic solution is lowered. More preferable Na
The normality (N) of OH is 3.0 to 5.0.

[LiOH] This LiOH has the oxygen generation voltage shown in the above-mentioned equation (2) at the time of high temperature charging as NaO.
Has the effect of further increasing than H. When LiOH is less than 0.5 N, it becomes difficult to improve the high temperature charging efficiency. on the other hand,
When LiOH exceeds 1.5 N, the definition of KOH in the electrolytic solution is relatively lowered, and the conductivity of the electrolytic solution is lowered. further,
Since LiOH has a relatively low solubility, it is difficult to dissolve it over 1.5 N, and LiOH may be precipitated in a low temperature range. More preferable LiOH normality (N) is 0.5 to
1.2.

The total normality of KOH, NaOH and LiOH is preferably 7.5 to 9.5N. If the total normality is less than 7.5 N, the charge / discharge efficiency may decrease. On the other hand, the total regulation is 9.
If it exceeds 5N, the cycle characteristics may deteriorate.

In addition, since the charging efficiency and the self-discharging characteristic are particularly important in a battery used in a high temperature environment, it is preferable to use one of the alkaline electrolytes mainly containing NaOH. Where NaOH
An electrolytic solution having a composition containing as a main component means an electrolytic solution having the highest normality of NaOH among NaOH, KOH, and LiOH.

As the electrolyte, the total normality of NaOH, KOH and LiOH is in the range of 7.5 to 9.5 N, and the normality of NaOH is in the range of 4.0 to 5.0 N. Those having a composition in which the degree is in the range of 0.5 to 1.2 N are preferred.

Particularly in a battery used in a high temperature environment, if the normality of NaOH of the electrolyte is less than 4.0 N, the charging efficiency and the self-discharge characteristics may not be improved more effectively. . On the other hand, when the normality of NaOH exceeds 5.0 N, the conductivity of the electrolytic solution decreases.

Particularly in a battery used in a high temperature environment, if the normality of LiOH of the electrolyte is less than 0.5 N, the charging efficiency and the self-discharge characteristics may not be improved. On the other hand, when the normality of LiOH exceeds 1.2 N, the conductivity of the electrolytic solution is remarkably lowered, and the capacity retention rate during the cycle may be lowered. More preferred Li
The normality (N) of OH is 0.7 to 1.1.

According to the alkaline secondary battery of the present invention described above, the hydroxylation having a peak half width of (101) plane of 0.8 ° / 2θ (Cu-Kα) or more by X-ray powder diffraction method An alkaline electrolyte having a composition consisting of a positive electrode containing nickel powder, 2.0 to 6.0 N potassium hydroxide, 2.0 to 5.0 N sodium hydroxide, and 0.5 to 1.5 N lithium hydroxide. By including, it is possible to improve high temperature charging efficiency while maintaining a practical capacity retention rate during a cycle.

That is, according to the X-ray powder diffraction method (10
1) A positive electrode containing nickel hydroxide powder having a specific peak half width of a plane, and KOH, NaOH and LiOH
It is possible to increase the oxygen overvoltage of the positive electrode at the time of charging in a high temperature state by including the alkaline electrolyte in which the normality of the alkaline components is specified.
As a result, the charging reaction of the nickel hydroxide powder represented by the above formula (1) can be preferentially advanced in a high temperature state, so that the production amount of NiOOH is increased and the charging efficiency of the positive electrode is improved. You can Therefore, it is possible to provide an alkaline secondary battery having a high capacity retention rate during a practical cycle and a high actual capacity (discharge capacity).

Among the above-mentioned electrolytic solutions, the electrolytic solution containing NaOH as a main component more effectively improves both the charging efficiency and the self-discharge characteristics of the alkaline secondary battery used in a high temperature environment. be able to.

That is, by using NaOH as a main component, it is possible to further increase the oxygen overvoltage of the positive electrode during charging in a high temperature state, so that the charging efficiency of the positive electrode can be significantly improved. Also, (1) N
Due to the fact that the electrolyte has a low electrical conductivity because aOH is the main component, and (2) the relationship between the electrolyte and the cobalt form present in the positive electrode in the secondary battery including the positive electrode. It is presumed that self-discharge of the secondary battery is suppressed. In addition, when the normality of lithium hydroxide in the electrolytic solution is increased, the conductivity of the electrolytic solution is further lowered, so that further improvement of the self-discharge characteristics can be expected.

Therefore, 2.0 to 6.0 N potassium hydroxide, 2.0 to 5.0 N sodium hydroxide and 0.5
An alkaline secondary battery made of lithium hydroxide of up to 1.5 N and provided with an alkaline electrolyte containing sodium hydroxide as a main component can be used in a high temperature environment while ensuring a practical cycle capacity retention rate. It is possible to more effectively improve the charging efficiency as well as the self-discharge characteristic.

[0035]

Embodiments of the present invention will be described below in detail with reference to the drawings. Example 1 First, from 90 parts by weight of nickel hydroxide powder having a peak half width of (101) plane of 0.95 ° / 2θ (Cu-Kα) by X-ray powder diffraction method and 10 parts by weight of cobalt monoxide powder. Carboxymethylcellulose 0.
3% by weight and 2.0% by weight of polytetrafluoroethylene are added, and 35% by weight of water is further added to this mixture,
A paste was prepared by kneading. This paste was filled in a nickel-plated fiber substrate having a porosity of 95% as an alkali-resistant metal porous body, dried, and then roll-pressed to form a positive electrode.

In addition, LaNi _4.0 Co _0.4 Mn _0.3 Al
_To 95 parts by weight of hydrogen storage alloy powder having a composition of _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 are added and mixed with 50 parts by weight of water. To prepare a paste. 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 polypropylene non-woven fabric was interposed between the positive electrode and the negative electrode and wound in a spiral shape to prepare an electrode group. 4 / 3A having the structure shown in FIG. 1 in which these electrode groups and an alkaline electrolyte having the composition shown in Tables 1 to 5 below are housed in a cylindrical container having a bottom.
Twenty-two types of cylindrical nickel-hydrogen secondary batteries of size (theoretical capacity; 2800 mAh) were assembled.

[0038]

[Table 1]

[0039]

[Table 2]

[0040]

[Table 3]

[0041]

[Table 4]

[0042]

[Table 5]

For each of the obtained secondary batteries, first, 25 ° C.
1C, -ΔV control (10 mV cutoff voltage) charge, 25 ° C, 1C, 1 cut discharge, room temperature (25
℃) Confirm the reference capacity in charging, and then at 60 ℃, 1C, -ΔV control (cutoff voltage of 10 mV) charge, 25 ℃, 1C, 1 cut discharge, 60
Confirm the capacity at ℃, the above room temperature (25 ℃)
The charging efficiency (%) was measured by calculating the ratio with the reference capacity. The result is shown in FIG. Note that FIG.
The electrolyte has a total normality of 8.5N, KOH
The concentrations are NaOH concentration and LiO at arbitrary points in FIG.
It is shown as a value obtained by subtracting the sum of H concentrations from 8.5N.

Further, for each of the obtained secondary batteries, 25
400 at 1 ° C, -ΔV charge, 1C, 1V cut discharge
The cycle was charged and discharged, and the capacity retention rate (%) with respect to the initial capacity at this number of cycles was determined. The result is shown in FIG. The total normality of the electrolytic solution in FIG. 3 is 8.5.
N, and the KOH concentration is Na at any point in FIG.
It is shown as a value obtained by subtracting the sum of the OH concentration and the LiOH concentration from 8.5N.

As is clear from FIG. 2, KOH, NaO
Among secondary batteries provided with an alkaline electrolyte in which the total normality of alkali components is constant (8.5 N in this case) in the H and LiOH system, the alkaline electrolyte having a high normality of LiOH and NaOH is used. It can be seen that the higher the secondary battery, the higher the high temperature charging efficiency.

Further, as apparent from FIG. 3, KOH, N
Of the secondary batteries equipped with an alkaline electrolyte in which the total normality of alkali components is constant (8.5 N in this case) in the system of aOH and LiOH, LiOH and NaOH
It can be seen that the secondary battery having an alkaline electrolyte having a smaller normality, ie, a higher KOH normality, has a higher capacity retention rate during cycling.

Therefore, from the relationship between the high temperature charging efficiency of FIG. 2 and the capacity retention rate during the cycle of FIG.
In the H and LiOH system, the total normality of the alkaline component is constant at 8.5 N, for example, and LiOH is 0.5 to 1.
5N, NaOH is 2.0 to 5.0N (preferably 3 to
5.0N), the secondary battery provided with an alkaline electrolyte having a KOH of the total normality minus LiOH and NaOH has a high temperature charging efficiency while maintaining a practical cycle capacity retention rate. You can see that it will be improved.

(Reference Example) Nickel hydroxide powder as an active material of the positive electrode is one having a peak half-value width of 0.7 ° / 2θ (Cu-Kα) of (101) plane by X-ray powder diffractometry. LiOH 1.0N, N as alkaline electrolyte
A cylindrical nickel-hydrogen secondary battery of 4/3 A size (theoretical capacity: 2800 mAh) having the structure shown in FIG. 1 and having the structure shown in FIG. 1 was used, except that the composition of aOH 3.0 N and KOH 4.5 N was used. Assembled

With respect to the obtained secondary battery, the high temperature charging efficiency and the capacity retention ratio during cycling were examined under the same conditions as in Example 1. As a result, the charging efficiency was 53% and the capacity retention rate during the cycle was 60%. Therefore, although the composition of the electrolytic solution is the same as that of the present invention, the secondary battery of the reference example includes the positive electrode containing the active material having the peak half width of the (101) plane of 0.7 ° / 2θ by the X-ray powder diffraction method. Has the same half-width of 0.
It can be seen that both the charge / discharge efficiency and the capacity retention ratio during cycling are inferior to the secondary battery of the present invention provided with a positive electrode containing nickel hydroxide powder of 8 ° / 2θ (Cu-Kα) or more.

(Example 2) No. 1 shown in Table 4 above. 1
The self-discharge characteristics in a high temperature environment were measured for alkaline secondary batteries including 2 to 15 alkaline electrolytes.

<Assembly of Secondary Battery of Comparative Example> 4 / having the structure shown in FIG. 1 in the same manner as in Example 1 except that an alkaline electrolyte having a composition of LiOH 1.0N and KOH 7.0N was used. 3A size (theoretical capacity: 2800
A cylindrical nickel-hydrogen secondary battery of mAh) was assembled.

<Measurement of self-discharge rate under high temperature environment>
No. For the secondary batteries of 12 to 15 and the comparative example, 25
C, 1C, -ΔV control (10 mV cut-off voltage) charge, 25 ° C, 1C, 1V cut discharge, and normal temperature (2
(5 ° C) Confirmation of the reference capacity in charging, then at 25 ° C, 1C, -ΔV control (10 mV cutoff voltage) charging, after storing at 45 ° C for 2 weeks, 25 ° C, 1C, 1C
V-cut discharge was performed to confirm the storage capacity after storage in a high temperature environment. The self-discharge rate (%) was calculated by dividing the difference between the reference capacity at room temperature (25 ° C.) and the obtained holding capacity by the reference capacity, and the results are shown in Table 6 below.

[0053]

[Table 6]

As is clear from Table 6, No. 12 to 1
It can be seen that the secondary battery of No. 5 has a lower self-discharge rate than the comparative example. Among them, No. 1 provided with an alkaline electrolyte having a composition mainly composed of NaOH. 13 to 15 secondary batteries are KO
No. 1 provided with an electrolytic solution containing H as a main component. It can be seen that self-discharge when stored in a high temperature environment can be suppressed as compared with the secondary battery of No. 12.

Therefore, from the relationship between the self-discharge rate in Table 6, the high temperature charging efficiency in FIG. 2 and the capacity retention rate during the cycle in FIG.
In the system of KOH, NaOH and LiOH, the total normality of alkali components is constant at 8.5 N,
0.5-1.5N, NaOH 2.0-5.0N, K
Of the alkaline electrolytes in which OH is the normality obtained by subtracting LiOH and NaOH from the total normality, an alkaline secondary battery provided with an alkaline electrolyte whose main component is NaOH has a practical cycle capacity retention rate. It can be seen that the charging efficiency and the self-discharge characteristics when used in a high temperature environment can be improved more effectively while maintaining the above.

[0056]

As described in detail above, according to the present invention, an alkaline secondary battery having a high actual capacity (discharge capacity) which can improve the high temperature charging efficiency while maintaining the capacity retention rate during a practical cycle. Can be provided.

[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 characteristic diagram showing the relationship between the composition of the alkaline electrolyte and the charging efficiency in the example of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the composition of the alkaline electrolyte and the capacity retention rate during cycling in the example of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... container, 2 ... positive electrode, 3 ... separator, 4 ... negative electrode, 7 ...
Sealing plate, 8 ... insulating gasket.

Claims (2)

[Claims] 1. A positive electrode containing nickel hydroxide powder, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte, wherein the nickel hydroxide is an X-ray powder. Diffraction method (10
1) Peak full width at half maximum of 0.8 ° / 2θ (Cu-Kα)
Above, and the said alkaline electrolyte is 2.0-6.
An alkaline secondary battery having a composition of 0 N potassium hydroxide, 2.0 to 5.0 N sodium hydroxide, and 0.5 to 1.5 N lithium hydroxide. 2. The alkaline secondary battery according to claim 1, wherein the alkaline electrolyte contains sodium hydroxide as a main component.