JPH05121073A - Nickel-metal hydride storage battery - Google Patents

Abstract

PURPOSE:To provide a storage battery having a long charge/discharge cyclic lifetime and a low self-discharging speed by allowing a positive electrode to contain nickel hydroxide as a main active material and also Mn compound, and forming the body of a negative electrode from a hydrogen storage alloy. CONSTITUTION:A Ni-metal hydride storage battery has a specific self- discharging mechanism, and a minute quantity of hydrogen generated by a negative electrode is oxidated by a positive electrode. According to this constitution the Mn compounds added to the positive electrode pass through the process of dissolution and eduction into the electrolytic solution and move gradually to the surfaces of the positive electrode active substance and/or its electricity collecting body, and the positive electrode active substance lowers the oxidation reaction speed of the hydrogen at the surface of the collecting body. This lowers in turn the self-discharging speed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nickel-metal hydride storage battery in which the main active material of the positive electrode is nickel hydroxide and the main component of the negative electrode is a hydrogen storage alloy.

[0002]

2. Description of the Related Art A hydrogen storage electrode used for a negative electrode of a nickel-metal hydride storage battery has a hydrogen storage alloy. This hydrogen storage alloy has intermetallic compounds such as LaNi ₅ and ZiNi _2, and by substituting some of the constituent elements of these alloys with other elements, or by changing the stoichiometric number, Change the hydrogen storage capacity of these alloys,
It is used for electrodes by changing the equilibrium hydrogen pressure of these metal hydrides and improving the corrosion resistance of alloys in alkaline electrolytes.

In this hydrogen storage electrode, the powder of the above hydrogen storage alloy is held on a conductive support such as punching metal or foamed nickel, and an alkali resistant polymer such as polyvinyl alcohol, fluororesin or acrylic-styrene resin is used. There are those that are bonded by, and those that are sintered hydrogen storage alloy.

For the positive electrode combined with this negative electrode, a nickel hydroxide electrode of the same sintering type or foam metal type as that of an alkaline battery such as a nickel-cadmium battery is used.

An aqueous solution mainly containing potassium hydroxide or sodium hydroxide is used as the electrolytic solution.

[0006]

[Problems to be Solved by the Invention]
The metal hydride storage battery has a drawback that it has a higher self-discharge rate than the nickel-cadmium battery. This remarkably large self-discharge is caused by a self-discharge reaction in which, when a hydrogen storage alloy is used for the negative electrode, the hydrogen stored in the alloy is released and reaches the positive electrode, and the charge product of the positive electrode is reduced and discharged. It is presumed to be a thing.

[0007] This self-discharging is caused by the content ratio of manganese in the alloy, especially in the case of a hydrogen storage alloy in which the constituent element of LaNi ₅ , which is an intermetallic compound having a CaCu _{5 type} crystal structure, is replaced with another element. It was known that the higher the value, the more effectively it was suppressed.

However, not only CaCu _{5 type} but also ZrNi ₂ and
Even with hydrogen storage alloys such as TiNi, the higher the manganese content in the hydrogen storage alloy, the higher the deterioration rate of the hydrogen storage alloy with the progress of the charge / discharge cycle, and the shorter the charge / discharge cycle life of the battery. There is.

Therefore, the content of manganese in the hydrogen storage alloy of the negative electrode is low and the charge / discharge cycle life is long, and
A nickel-metal hydride storage battery with a low self-discharge rate has been desired.

[0010]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention uses nickel hydroxide as the main active material of the positive electrode and a hydrogen storage alloy as the main component of the negative electrode, and the positive electrode contains a manganese compound. Provided is a nickel-metal hydride storage battery containing the same.

[0011]

According to the present invention, by adopting the above configuration, the self-discharge of the nickel-metal hydride storage battery is suppressed even when the content of manganese in the hydrogen storage alloy of the negative electrode of the metal hydride storage battery is small. .. Therefore, it is possible to obtain a nickel-metal hydride storage battery in which the life of the hydrogen storage alloy of the negative electrode is suppressed from being shortened as the charging / discharging cycle proceeds and the self-discharge rate is low.

Although it is not clear why the self-discharge rate of the battery is reduced by adopting the configuration of the present invention, the reason is that the following hypothesis may explain the mechanism. unknown.

That is, as a self-discharging mechanism peculiar to the nickel-metal hydride storage battery, there is one in which a small amount of hydrogen generated from the negative electrode is oxidized at the positive electrode as described above. Then, when the means of the present invention is adopted, the manganese compound added to the positive electrode is gradually moved to the surface of the positive electrode active material or the current collector thereof via the dissolution and precipitation process in the electrolytic solution, and the positive electrode active material or It seems that the self-discharge rate decreases as a result of decreasing the hydrogen oxidation reaction rate on the surface of the current collector.

[0014]

EXAMPLES The present invention will be described by way of preferred examples. [Rechargeable Battery A] (Examples of the Present Invention) A sealed nickel-metal hydride rechargeable battery having a negative electrode mainly composed of a hydrogen storage alloy and an alkaline electrolyte and a rectangular outer shape was manufactured as follows.

As the negative electrode plate, five paste type plates each having a size of 15 mm × 55 mm × 0.4 mm were used. This electrode was manufactured as follows.

The hydrogen storage alloy has a composition of LmNi in atomic ratio.
The constituent elements were melted in a metallic state in a high-frequency induction furnace in a vacuum so as to be _3.8 Co _0.7 Al _0.5 , cast, and then pulverized. Here, Lm is a lanthanum rich misch metal which is a mixture of rare earth metals containing about 90% by weight of La. This alloy powder was dispersed in an aqueous solution of polyvinyl alcohol that functions as a thickener and a binder to form a paste. Then, this paste was applied to both sides of a nickel-plated iron punching metal, dried, pressed, and cut to manufacture a hydrogen storage electrode.

The weight of the hydrogen storage alloy contained in the five negative plates of this battery was about 5.3 g.

For the positive electrode, a known sintered nickel hydroxide electrode is immersed in an aqueous solution of manganese sulfate having a concentration of 0.1 M, and then neutralized with an alkaline aqueous solution to form the pores of the nickel hydroxide electrode. 4 sheets of manganese hydroxide were added, and then washed with water repeatedly to remove sulfate ions and dried, and 4 sheets were used.

The total weight of nickel hydroxide contained in the four nickel hydroxide electrodes of the positive electrode (the size of one sheet is 14 mm × 54 mm × 0.75 mm) is 3.9 g per cell. Therefore, assuming that nickel hydroxide follows a one-electron reaction, the theoretical capacity of the positive electrode of one battery is about 1.1 Ah.
To this electrode was added 0.04 grams of cobalt hydroxide per gram of nickel hydroxide.

In the test battery, the negative electrode and the positive electrode are alternately laminated via a separator obtained by sulfonating polystyrene, which is a non-woven fabric made of fibers of a mixture of polypropylene and polystyrene, and imparting hydrophilicity thereto. The group was stored in a rectangular closed metal battery case.

The electrolytic solution contained in the conventional battery A was 20 g / l.
6M KOH aqueous solution in which was dissolved LiOH was used. [Battery (B)] (Example of the present invention) Instead of the sintered nickel hydroxide electrode of the positive electrode in the battery (A), the following non-sintered nickel hydroxide electrode was used, and other configurations were as follows: Same as the storage battery (A),
The nickel-metal hydride storage battery (B) of the present invention was manufactured.

The non-sintered nickel hydroxide electrode has 100 parts by weight of an active material powder mainly composed of nickel hydroxide, 2 parts by weight of manganese hydroxide (chemical formula: Mn (OH) ₂ ) powder, and an active material utilization rate. A paste-like mixture was prepared by mixing 5 parts by weight of cobalt hydroxide powder, which is an additive for increasing the viscosity, with the produced water, and the paste-like mixture was filled in a nickel foam, dried, pressed and cut. I made it. The amount of nickel hydroxide in the positive electrode was the same as in the storage battery (A). [Storage Battery (C)] (Examples of the Present Invention) In the present invention, a powder of manganese sulfate was used instead of the powder of manganese hydroxide of the positive electrode in the storage battery (B), and other configurations were the same as those of the storage battery (B). A nickel-metal hydride storage battery (C) was manufactured. [Storage Battery (D)] (Example of the Present Invention) Manganese dioxide powder was used in place of the manganese hydroxide powder of the positive electrode in the storage battery (B), and the other configurations were the same as those of the storage battery (B). An inventive nickel-metal hydride storage battery (D) was made. [Rechargeable Battery (E)] (Conventional Example) A storage type nickel hydroxide electrode of the positive electrode in the storage battery (A) is the same as that of the storage battery (A) except that it is not filled with manganese hydroxide. A prismatic sealed nickel-metal hydride storage battery (E) was manufactured. [Battery (F)] (conventional example) Instead of using a hydrogen storage alloy having a composition of LmNi _3.8 Co _0.7 Al _0.5 by atomic ratio as the negative electrode hydrogen storage alloy in the storage battery (E), LmNi _3.8 Co _0.7 Al _0.2 Mn by atomic ratio is used. _A conventional prismatic sealed nickel-metal hydride storage battery (F) was manufactured by using _0.3 of the other components and making the other configurations the same as the storage battery (E). [Rechargeable Battery (G)] (Conventional Example) The non-sintered nickel hydroxide electrode of the positive electrode in the rechargeable battery (B) is the same as the rechargeable battery (B) except that manganese hydroxide is not added. A prismatic sealed nickel-metal hydride storage battery (G) was manufactured. [Battery (H)] (conventional example) Instead of using a hydrogen storage alloy having a composition of LmNi _3.8 Co _0.7 Al _0.5 by atomic ratio as a negative electrode in the storage battery (G), LmNi _3.8 Co _0.7 Al _0.2 Mn by atomic ratio is used. _A conventional prismatic sealed nickel-metal hydride storage battery (H) was manufactured by using _0.3 of the other components and making the other configurations the same as the storage battery (G).

These batteries were subjected to chemical charge and discharge under the condition that they were charged at a current of 10 hours rate for 15 hours and discharged at a current of 5 hours rate until the terminal voltage became 1 V, based on the theoretical capacity of the positive electrode. .. Next, at the current rate of 10 hours,
The discharge capacity before standing was measured under the condition that the battery was charged for an hour and discharged with a current at a rate of 5 hours until the terminal voltage became 1V. Then, charge it for 15 hours with a current of 10 hours rate, and
The discharge capacity after standing was measured under the condition that the battery was left for one day and then discharged at a current of 5 hours until the terminal voltage became 1V. Charge and discharge and leave after charging are all 25
Performed at ambient temperature of ° C.

In this test, the capacity retention rate after standing was defined as the discharge capacity after standing with respect to the discharge capacity before standing, and the value of the capacity retention rate of each battery obtained in the above test was examined.

These batteries were charged for 1.2 hours at a current of 1 hour rate, and the terminal voltage was 1.0 at a current of 1 hour rate.
A charge / discharge cycle test was performed under the condition that the battery was discharged to V. Then, the number of charge / discharge cycles until the discharge capacity of the battery decreased to 70% of the initial discharge capacity of the charge / discharge cycle was examined. This charge / discharge cycle test was also performed at an ambient temperature of 25 ° C.

The results of these tests are shown in Table 1.

[0027]

[Table 1] The following can be seen from Table 1.

That is, the batteries (A), (B), (C), and (D) in which the nickel hydroxide electrode of the positive electrode contains a manganese compound and the hydrogen storage alloy of the negative electrode does not contain manganese, Batteries (F) and (H) in which the nickel hydroxide electrode does not contain a manganese compound and the negative electrode hydrogen storage alloy contains manganese are the batteries (F) and (H) in which the positive electrode does not contain a manganese compound and the negative electrode hydrogen storage alloy contains manganese. Compared with the batteries (E) and (G) which do not contain, the capacity retention rate when the battery in the charged state is left is large. Therefore, if the nickel hydroxide electrode of the positive electrode contains a manganese compound,
Or, if manganese is contained in the hydrogen storage alloy of the negative electrode,
The self-discharge rate of the nickel-metal hydride storage battery is reduced.

On the other hand, batteries (A), (B), (C), (D), in which the hydrogen storage alloy of the negative electrode does not contain manganese.
(E) and (G) are charging / discharging until the discharge capacity is reduced to 70% of the initial discharge capacity as compared with the batteries (F) and (H) in which the negative electrode hydrogen storage alloy contains manganese. The number of cycles is large.

From the above experiments, the main active material of the positive electrode was nickel hydroxide, and the main component of the negative electrode was a hydrogen storage alloy,
The nickel of the present invention, wherein the positive electrode contains a manganese compound.
It is clear that the metal hydride storage battery has the advantages of a low self-discharge rate and a long charge / discharge cycle life.

In the above examples, the case where the manganese compound contains a hydroxide, an oxide and a sulfate has been described, but in addition to this, chalcogenides, metal compounds and various salts are also included. The same action and effect can be obtained even when it contains.

In the above embodiments, the case where a rare earth alloy having a specific composition is used as the hydrogen storage alloy for the negative electrode has been described. However, not only these alloys but also La alloy
Even when the constituent metal of the hydrogen storage alloy such as Ni ₅ , ZrNi ₂ , TiNi, and Ti ₂ Ni is replaced with another element, the same operation and effect as those of the above embodiment can be obtained.

In the above embodiment, the case where foamed nickel is used as the active material support of the non-sintered nickel hydroxide electrode has been described, but in addition to this, a sintered body of metal nickel fibers and nickel plating are used. The same effect can be obtained when a perforated plate of an alkali-resistant metal such as iron or the like, a nickel net, an expanded metal of nickel, or the like is used as the support.

Further, in the above embodiment, the case where cobalt hydroxide is added to the non-sintered nickel hydroxide electrode has been described. However, in addition to the above, the case where metal cobalt or cobalt oxide is added is also described above. The same effect as that of the embodiment can be obtained.

Further, in the above-mentioned embodiment, the prismatic closed type battery has been described, but the same operational effect as that of the above-mentioned embodiment can be obtained also in the case of the cylindrical type or the open type battery.

[0036]

As described above, the nickel-metal hydride storage battery of the present invention has the effects of a long charge / discharge cycle life and a low self-discharge rate.

Claims (1)

[Claims] 1. The main active material of the positive electrode is nickel hydroxide,
A nickel-metal hydride storage battery, wherein the negative electrode mainly comprises a hydrogen storage alloy, and the positive electrode contains a manganese compound.