JP2000030702A - Nickel-hydrogen secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve low-temperature discharge characteristics, by forming a layer containing one or more kinds of rare-earth elements among Y, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, on at least part of surfaces of a hydrogen storage alloy included in a negative electrode. SOLUTION: Rare-earth elements, especially preferably, one or more kinds of Y, Er, and Yb, are included, as single substances or compounds such as oxides, in a hydrogen storage alloy at a weight ratio of 0.1 to 1.0 in terms of the elements to 100 of the alloy. A secondary battery equipped with a negative electrode including such an alloy is improved in low-temperature discharge characteristics and also in a charge/discharge cycle life. As the hydrogen storage alloy, it is preferable to use a rare-earth/nickel hydrogen storage alloy including one or more kinds of rare-earth elements among La, Pr, Ce, and Nd, and also to substitute Mn for part of Ni so that Mn becomes 0.6 to 2.6 wt.% of the alloy, whereby the improvement effect is further enhanced. The rate of oxides in a nickel layer formed on surfaces of the alloy in an alkaline electrolytic solution is decreased by a rare-earth element-containing layer, whereby lowering of activity is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-hydrogen secondary battery having an improved negative electrode containing a hydrogen storage alloy.

[0002]

2. Description of the Related Art A sealed nickel-metal hydride secondary battery is composed of a paste-type positive electrode containing nickel hydroxide as an active material and a paste-type negative electrode containing a hydrogen-absorbing alloy with an electrode group together with an alkaline electrolyte. It is housed in a container and has a closed structure. Such sealed nickel-metal hydride secondary batteries have been widely put into practical use as operating power supplies for various electronic devices such as portable telephones and portable imaging devices.
Accordingly, there is a demand for improving discharge characteristics at low temperatures.

[0003] Japanese Patent Application Laid-Open No. 2-256161 discloses that at least a part of the surface of a hydrogen storage alloy powder is L-coated.
It has been proposed to provide an oxide or hydroxide of a, Ce or Nd.

[0004]

However, this L
It is difficult to improve low-temperature discharge characteristics by using a hydrogen storage alloy in which an oxide or hydroxide of a, Ce or Nd is disposed.

An object of the present invention is to provide a nickel-hydrogen secondary battery having improved low-temperature discharge characteristics.

[0006]

The nickel-metal hydride secondary battery according to the present invention comprises Y, Sm, Eu, Gd, Tb, Dy,
A layer containing one or more rare earth elements selected from Ho, Er, Tm, Yb and Lu is provided with a negative electrode containing a hydrogen storage alloy powder formed on at least a part of the surface. .

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A nickel-metal hydride secondary battery (cylindrical nickel-metal hydride secondary battery) according to the present invention will be described below with reference to FIG.

An electrode group 5 produced by stacking a positive electrode 2, a separator 3, and a negative electrode 4 and spirally winding them is accommodated in a cylindrical container 1 having a bottom. 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 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
Is arranged between the periphery of the container and the inner surface of the upper opening of the container 1,
The sealing plate 7 is airtightly fixed to the container 1 via the gasket 8 by caulking to reduce the diameter of the upper opening inward. 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 mounted on the sealing plate 7 so as to cover the hole 6. Rubber safety valve 1
1 is arranged 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 so that the projection of the positive electrode terminal 10 is provided on the holding plate 1.
2 so as 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 negative electrode 4, the positive electrode 2, the separator 3
And the electrolyte will be described.

1) Negative Electrode 4 The negative electrode includes a hydrogen storage alloy powder having a layer containing a rare earth element formed on at least a part of its surface. The rare earth elements are Y, Sm, Eu, Gd, Tb, Dy,
It is composed of at least one selected from Ho, Er, Tm, Yb and Lu.

The hydrogen storage alloy is preferably a rare earth-nickel hydrogen storage alloy. The rare earth component includes:
It is preferable to use at least one or more elements selected from La, Pr, Ce and Nd. In the rare earth-nickel-based hydrogen storage alloy, a part of Ni is Co,
It may be replaced with at least one element selected from Mn, Al, Fe, Ti, Zr, Zn, Cr and B. In particular, it is preferable to include Mn as a substitution element.

In the rare earth-nickel-based hydrogen storage alloy in which a part of Ni is substituted by at least Mn, the content of Mn is preferably 0.6% by weight or more and 2.6% by weight or less. This is due to the following reasons. If the content exceeds 2.6% by weight, the amount of Mn eluted from the hydrogen storage alloy into the alkaline electrolyte increases, so that the activity of the hydrogen storage alloy decreases and the discharge capacity at low temperatures may decrease. There is. On the other hand, the content is set to 0.
When the content is less than 6% by weight, the amount of Mn eluted can be reduced, but the reactivity of the hydrogen storage alloy is reduced due to the lack of the Mn component, and the discharge capacity may be reduced even at a low temperature. Further, when Co is contained in the hydrogen storage alloy, the elution amount of Co may increase. When the amount of Co eluted increases, not only does the low-temperature discharge characteristic deteriorate, but also Co precipitates on the separator and forms a conductive path between the positive electrode and the negative electrode, which may cause an internal short circuit. A more preferable range of the Mn content is 1.1% by weight to 1.5% by weight.

[0013] By incorporating Co into the rare earth-nickel-based hydrogen storage alloy having a Mn content of 0.6 to 2.6% by weight, it is possible to suppress the progress of pulverization accompanying the charge-discharge cycle of the alloy. it can. Preferably, the Co content of the alloy is in the range of 5% by weight to 15% by weight. This is due to the following reasons. If the content is less than 5% by weight, it may be difficult to sufficiently obtain the effect of suppressing the progress of pulverization. On the other hand, if the content exceeds 15% by weight, the capacity of the alloy may be reduced. Further, cobalt is expensive, so that the production cost is high. A more preferred range of the Co content is
It is 10% to 12% by weight.

[0014] The rare earth - Examples of the nickel-based hydrogen-absorbing alloy, in particular the general formula _{LmNi w Co x Al y Mn z} ( However, Lm is a rare earth element, the atomic ratio w, x, y, z are 3.30 ≦ w ≦ respectively 4.50, 0.50 ≦ x ≦ 1.10.
0.20 ≦ y ≦ 0.50, 0.05 ≦ z ≦ 0.20,
And the total value is 4.90 ≦ w + x + y + z ≦ 5.50
Is preferably used. More preferable values of the atomic ratio w, x, y, z are 3.80 ≦ w ≦ 4.20, 0.70 ≦ x ≦ 0.90, respectively.
0.30 ≦ y ≦ 0.40, 0.08 ≦ z ≦ 0.13,
And the total value is 5.00 ≦ w + x + y + z ≦ 5.20
It is.

The layer containing a rare earth element formed on at least a part of the surface of the hydrogen storage alloy powder can be formed, for example, of at least one selected from a single element of a rare earth element and a compound of a rare earth element. Examples of the rare earth element compound include a rare earth oxide.

As the rare earth element, at least one selected from the above-mentioned types can be used. Among them, at least one selected from Y, Er and Yb from the viewpoint of further improving the discharge capacity at low temperatures. preferable. In particular, it is more preferable to use Er or Yb or both as the rare earth element.

It is preferable that the formation amount of the layer containing the rare earth element is 0.1 to 1.0% by weight in terms of the rare earth element based on 100% by weight of the hydrogen storage alloy powder in which the layer is not formed.
This is due to the following reasons. If the amount is less than 0.1% by weight, low-temperature discharge characteristics may be reduced. On the other hand, if the formation amount exceeds 1.0% by weight, the life characteristics of the secondary battery may be deteriorated. A more preferable range of the formation amount is 0.2 to 0.7% by weight.

The negative electrode 4 is prepared, for example, by adding a conductive material to the hydrogen-absorbing alloy powder and kneading it with a binder and water to prepare a paste, filling the paste into a conductive substrate,
It is manufactured by molding after drying.

Examples of the binder include carboxymethylcellulose, methylcellulose, fluorocarbon resins such as sodium polyacrylate and polytetrafluoroethylene, and polyvinyl alcohol.

As the conductive material, for example, carbon black or the like can be used.

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

2) Positive Electrode 2 The positive electrode 2 has a structure in which a positive electrode material containing nickel hydroxide particles as an active material, a conductive material and a binder is supported on a conductive substrate.

As the nickel hydroxide particles, for example, single nickel hydroxide particles or nickel hydroxide particles in which a metal such as zinc, cobalt, bismuth or copper is eutectic can be used. In particular, the latter positive electrode containing nickel hydroxide particles can further improve the charging efficiency in a high-temperature state.

The nickel hydroxide particles have a peak half width at (101) plane of 0.8 面 / 2θ by X-ray powder diffraction.
(Cu-Kα) or more is preferable. More preferable peak half width of nickel hydroxide particles is 0.9 to 1.0.
゜ / 2θ (Cu-Kα).

Examples of the conductive material include metal cobalt, cobalt oxide, cobalt hydroxide and the like.

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

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

The positive electrode 2 is prepared, for example, by adding a conductive material to nickel hydroxide particles as an active material, kneading it with a binder and water to prepare a paste, filling the paste into a conductive substrate, and drying the paste. Thereafter, it is manufactured by molding.

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

4) Alkaline Electrolyte As the alkaline electrolyte, for example, a mixed solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH),
A mixture of potassium hydroxide (KOH) and LiOH, KOH
And a mixed solution of LiOH and NaOH.

The nickel-metal hydride secondary battery according to the present invention described above comprises Y, Sm, Eu, Gd, Tb, Dy, Ho,
A negative electrode including a hydrogen storage alloy powder having a layer containing at least one rare earth element selected from Er, Tm, Yb and Lu is formed on at least a part of the surface. Such a secondary battery can improve low-temperature discharge characteristics and charge / discharge cycle life.

That is, in a nickel-metal hydride secondary battery using, for example, a rare earth-nickel-based hydrogen storage alloy as the hydrogen storage alloy of the negative electrode, after assembling, the elements constituting the hydrogen storage alloy elute into the alkaline electrolyte, and A nickel layer is formed on the surface of the storage alloy, and the reactivity of the hydrogen storage alloy is improved. This nickel layer enhances the reactivity of the rare earth-nickel-based hydrogen storage alloy, but is easily oxidized. When the nickel layer is oxidized, the activity of the hydrogen storage alloy decreases, so that the discharge capacity at low temperatures decreases.
As in the present invention, at least a part of the surface of the rare earth-nickel-based hydrogen storage alloy is Y, Sm, Eu, Gd, Tb, D
By forming a layer containing at least one rare earth element selected from the group consisting of y, Ho, Er, Tm, Yb and Lu, the proportion of the nickel oxide layer on the alloy surface can be reduced. A decrease in activity can be suppressed. As a result, a decrease in the discharge capacity of the nickel-metal hydride secondary battery at a low temperature can be suppressed. In addition, the secondary battery can improve the charge / discharge cycle life.

In the nickel-metal hydride secondary battery according to the present invention, the composition of the hydrogen storage alloy is such that the Mn content is 0.6 to 2.0.
By using a rare earth-nickel system of 6% by weight, low-temperature discharge characteristics and cycle life can be further improved.

That is, although Mn is an important element in improving the performance of a nickel-metal hydride secondary battery provided with a negative electrode containing a rare earth-nickel-based hydrogen storage alloy, it is contained in a large amount in the hydrogen storage alloy. If it is present, elution into the alkaline electrolyte is likely to occur, and the reactivity of the hydrogen storage alloy is impaired. By setting the Mn content of the hydrogen storage alloy in the above range, elution of Mn into the alkaline electrolyte can be suppressed, and the reactivity of the hydrogen storage alloy can be improved. As a result, the low-temperature discharge characteristics and cycle life of the nickel-metal hydride secondary battery can be further improved.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Negative Electrode> An oxide of Er (chemical formula Er)
A hydrogen storage alloy powder having a layer made of ₂ O ₃ ) was prepared. The hydrogen storage alloy powder has a composition of LmNi _3.8
Consists of _{Co 0. 8 Mn 0.1 Al 0.3 (} Lm is a misch metal Lantern Tomica), the particle size is 25~75μm
Met. The Mn content of the hydrogen storage alloy powder was 1.3.
By weight, the Co content was 11.2% by weight. The formation amount of the Er oxide layer is 0.5% in terms of rare earth element with respect to 100% by weight of the hydrogen storage alloy powder in which the layer is not formed.
% By weight.

To 100 parts by weight of the hydrogen storage alloy powder, 0.5 parts by weight of sodium polyacrylate, 0.12 parts by weight of carboxymethyl cellulose (CMC), and a dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60 parts by weight) %) In terms of solid content and 1.0 part by weight of carbon black as a conductive material, and mixed with 30 parts by weight of water to prepare a paste. These pastes were applied to a punched metal as a conductive substrate, dried, and pressed to produce a negative electrode.

<Preparation of Positive Electrode> A mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 part of carboxymethyl cellulose (CMC).
A paste was prepared by adding 0.5 parts by weight of a polytetrafluoroethylene dispersion (specific gravity 1.5, solid content 60% by weight) in terms of solid content and mixing with 45 parts by weight of pure water. . Subsequently, the paste was filled in a foamed nickel substrate, dried, and then rolled by roller pressing to produce a positive electrode.

Next, a separator made of a nonwoven fabric made of polyamide fiber was interposed between the negative electrode and the positive electrode, and spirally wound to form an electrode group. After such an electrode group is housed in a bottomed cylindrical container, an electrolyte composed of 7N potassium hydroxide and 1N lithium hydroxide is housed, and the structure shown in FIG. Then, an AAA-size sealed cylindrical nickel-metal hydride secondary battery having a theoretical capacity of 700 mAh was assembled.

Example 2 The composition of the hydrogen storage alloy powder was LmNi _3.6 Co _0.8 Mn _0.3 Al _0.3 (Mn content was 3.9% by weight and Co content was 11.2% by weight). Except for this, a sealed cylindrical nickel-metal hydride secondary battery having the same configuration as that of Example 1 was assembled.

Comparative Example 1 A hydrogen storage alloy powder was prepared in the same manner as in Example 1 except that no Er oxide layer was formed on the surface. A sealed cylindrical nickel-metal hydride secondary battery having the same configuration as that of Example 1 described above except that the hydrogen storage alloy powder was used was assembled.

Comparative Example 2 A hydrogen storage alloy powder having a layer of Nd ₂ O ₃ formed on a part of the surface was prepared. The composition and particle size of the hydrogen storage alloy powder and the formation amount of the Nd ₂ O ₃ layer were the same as in Example 1. A sealed cylindrical nickel-metal hydride secondary battery having the same configuration as that of Example 1 described above except that the hydrogen storage alloy powder was used was assembled.

The obtained secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were charged 150% with a current of 1 C,
The charge / discharge cycle of discharging the battery to a voltage of 1.0 V was performed at 25 ° C. for 20 cycles, and the discharge capacity at the 20th cycle was measured. In addition, the battery is charged 150% with a current of 1 C,
The atmosphere was set to 20 ° C., and when the battery temperature became −20 ° C., discharging was performed with a current of 1 C to a voltage of 1.0 V throughout, and the discharge capacity was measured. The ratio of the discharge capacity at −20 ° C. to the discharge capacity at 25 ° C. was calculated and defined as the low-temperature discharge capacity (%). The results are shown in Table 1 below.

The secondary batteries of Examples 1 and 2 and Comparative Examples 1 and 2 were charged 150% with a current of 1 C,
The charge / discharge cycle of discharging the battery to a voltage of 1.0 V throughout the current was repeated at 25 ° C. In such charge and discharge, the number of charge and discharge cycles when the discharge capacity became 80% or less of the initial value was determined. The results are shown in Table 1 below.

[0045]

[Table 1]

As is evident from Table 1, the secondary batteries of Examples 1 and 2 provided with the negative electrode containing the hydrogen-absorbing alloy powder having at least a portion of the surface containing a layer containing Er,
It can be seen that, compared to the secondary batteries of Comparative Examples 1 and 2, the decrease in discharge capacity at low temperatures is small and the cycle life is long.

(Examples 3 to 6) Except that the formation amount of the Er oxide layer was as shown in Table 2 below in terms of the amount of a rare earth element with respect to 100% by weight of the hydrogen storage alloy powder in which the layer was not formed.
A sealed cylindrical nickel-metal hydride secondary battery having the same configuration as that of Example 1 was assembled.

With respect to the obtained secondary batteries of Examples 3 to 6, the discharge capacity ratio at −20 ° C. to the discharge capacity at 25 ° C. and the cycle life were measured in the same manner as described above. It is described together. Table 2 shows Example 1
And the results of Comparative Example 1 are also shown.

[0049]

[Table 2]

As is clear from Table 2, the amount of the Er oxide layer formed was 100% by weight of the hydrogen-absorbing alloy powder without the layer.
The secondary batteries of Examples 1, 4, and 5 in which the amount was 0.1 to 0.9% by weight in terms of rare earth element with respect to
The discharge capacity at a low temperature is higher than that of the secondary battery of Example 3 in which the amount is less than 0.9% by weight, and the cycle life is longer than that of the secondary battery of Example 6 in which the formation amount exceeds 0.9% by weight. I understand.

Example 7 A hydrogen storage alloy powder having a layer of Yb ₂ O ₃ formed on a part of its surface was prepared. The composition and particle size of the hydrogen storage alloy powder and the amount of the Yb ₂ O ₃ layer formed were the same as in Example 1. A sealed cylindrical nickel-metal hydride secondary battery having the same configuration as that of Example 1 described above except that the hydrogen storage alloy powder was used was assembled.

(Example 8) A hydrogen storage alloy powder having a layer of Y ₂ O ₃ formed on a part of its surface was prepared. In addition,
The composition, particle size, and formation amount of the Y ₂ O ₃ layer of the hydrogen storage alloy powder were the same as in Example 1. A sealed cylindrical nickel-metal hydride secondary battery having the same configuration as that of Example 1 described above except that the hydrogen storage alloy powder was used was assembled.

Example 9 A hydrogen storage alloy powder having a layer of Dy ₂ O ₃ formed on a part of its surface was prepared. The composition and particle size of the hydrogen storage alloy powder and the amount of the Dy ₂ O ₃ layer were the same as in Example 1. A sealed cylindrical nickel-metal hydride secondary battery having the same configuration as that of Example 1 described above except that the hydrogen storage alloy powder was used was assembled.

Example 10 A hydrogen storage alloy powder having a layer of Gd ₂ O ₃ formed on a part of its surface was prepared. The composition and particle size of the hydrogen storage alloy powder and the formation amount of the Gd ₂ O ₃ layer were the same as in Example 1. A sealed cylindrical nickel-metal hydride secondary battery having the same configuration as that of Example 1 described above except that the hydrogen storage alloy powder was used was assembled.

With respect to the obtained secondary batteries of Examples 7 to 10, the ratio of the discharge capacity at −20 ° C. to the discharge capacity at 25 ° C. and the cycle life were measured in the same manner as described above. Shown in Table 3 also shows the results of Example 1 described above.

[0056]

[Table 3]

As is clear from Table 3, Y, Gd,
The secondary batteries of Examples 1, 7 to 10 each including the negative electrode containing the hydrogen storage alloy powder in which the layer containing Dy, Er, or Yb was formed on a part of the surface showed a decrease in the discharge capacity at low temperatures. It can be seen that the cycle life can be improved as well as being suppressed.

In the above-described embodiment, the separator is interposed between the positive electrode and the negative electrode, spirally wound and housed in a cylindrical container having a bottom. It is not limited to a simple structure. For example, the present invention is similarly applicable to a square nickel-metal hydride secondary battery in which a separator is interposed between a positive electrode and a negative electrode, and a laminate of a plurality of the separators is housed in a bottomed rectangular cylindrical container.

[0059]

As described above, according to the present invention, it is possible to provide a nickel-metal hydride secondary battery capable of maintaining a high capacity even at a low temperature and having a long charge-discharge cycle life.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a nickel-hydrogen secondary battery according to 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.

Claims (3)

[Claims] 1. Y, Sm, Eu, Gd, Tb, Dy, H
a layer containing at least one rare earth element selected from the group consisting of o, Er, Tm, Yb, and Lu; and a negative electrode containing a hydrogen storage alloy powder formed on at least a part of the surface thereof. Next battery. 2. The nickel-hydrogen secondary battery according to claim 1, wherein the hydrogen storage alloy powder is a rare earth-nickel-based hydrogen storage alloy powder. 3. The nickel-metal hydride secondary battery according to claim 2, wherein the rare earth-nickel-based hydrogen storage alloy powder has a Mn content of 0.6 to 2.6% by weight.