JP3201247B2 - Sealed alkaline storage battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sealed alkaline storage battery using a hydrogen storage alloy for electrochemically storing and releasing hydrogen as a negative electrode.

[0002]

2. Description of the Related Art As a high-capacity alkaline storage battery replacing a nickel-cadmium storage battery, a nickel-hydrogen storage battery using a hydrogen storage alloy for a negative electrode has attracted attention. As the hydrogen storage alloy, a quinary hydrogen storage alloy of Mm (misch metal), which is a rare earth-based mixture, and Ni, Al, Mn, and Co is often used.

[0003] This Mm-Ni-Mn-Al-Co alloy can form a negative electrode with a relatively inexpensive material as compared with the La-based alloy, has a long cycle life, and has a small internal pressure rise due to gas generated during overcharge. Since a nickel-metal hydride storage battery can be obtained, it is widely used as an electrode material.

[0004] Currently used Mm-Ni-Mn-A
The l-Co alloy suppresses the pulverization of the alloy and prolongs the cycle life. Generally, however, a large amount of Co (at an atomic ratio of 0.6 to 1.0) is used to suppress the pulverization. It is known to need.

[0005]

Therefore, in order to reduce the cost of the alloy, if the amount of Co, which is materially expensive, is reduced, the life of the battery is shortened due to the pulverization of the alloy, and the battery performance deteriorates. As a factor, there is a point to be improved as a hydrogen storage alloy for a negative electrode of a sealed alkaline storage battery.

There is a proposal for improving the cycle life of a battery by reducing the amount of Co and increasing the amount of Ni (Japanese Patent Laid-Open No. 7-99055), but the effect can be confirmed at present. Not.

[0007] The present invention solves the above-mentioned problems, and Mm
By changing the composition of the -Ni-Mn-Al-Co-based alloy and adding a small amount of one element to it, despite the small amount of Co, the deterioration of the negative electrode due to the pulverization of the alloy is suppressed, A sealed nickel-metal hydride that has a long cycle life and is advantageous in terms of cost.It also increases the hydrogen absorption speed more than conventional alloys, thereby increasing the charge efficiency of the negative electrode and reducing internal pressure rise due to gas generated during overcharge. It is intended to provide a storage battery.

[0008]

The hydrogen storage alloy constituting the negative electrode of the battery of the present invention has a general formula of MmNi _a Mn _b Al _c C
o _d M _e (where Mm is a mixture of rare earth elements, M is Fe, C
at least one element selected from the group consisting of r and Cu, 3.8 ≦ a ≦ 4.1, 0.05 <d <0.5,
0.05 <e <0.3, 5.1 ≦ a + b + c + d + e ≦
5.4), the magnetization per unit weight when a magnetic field of 10 KOe is applied at a temperature of 20 ° C. is 0.27 to 9.5 e.
mu / g. Preferably, the average particle diameter of the powder is 15 μm to 100 μm, and the ratio of alloy particles having a particle size of 10 μm or less is 35% or less of the total by volume. Thereby, even if the Co content in the alloy is small, a nickel-metal hydride storage battery having a long life characteristic can be provided.

[0009] The present inventors have made various investigations, in order to suppress the pulverization of yet alloys by reducing the Co content in the hydrogen storage alloy, a non-stoichiometric composition of the AB ₅ type alloy composition (B site Rich) is effective. And, as a result of the test on the open type battery, the alloy of non-stoichiometric composition was able to suppress the pulverization and obtain a long-life battery, but when the sealed nickel-metal hydride storage battery was created, the internal pressure of the battery was high, The operation of the safety valve due to the increase in the internal pressure caused a decrease in the amount of the electrolyte, which caused a decrease in the cycle life characteristics of the battery.

[0010]

DETAILED DESCRIPTION OF THE INVENTION According to a first aspect of the present invention have the general formula _{MmNi a Mn b Al c Co d} M e ( where Mm is a mixture of rare earth elements, M is Fe, Cr, from among Cu At least one selected element, 3.8 ≦ a ≦ 4.
1, 0.05 <d <0.5, 0.05 <e <0.3,
By 5.1 ≦ a + b + c + d + e ≦ 5.4), even if the amount of Co in the alloy is reduced, pulverization of the alloy can be suppressed, and the life can be extended. The metal whose alloy structure has been broken from the hydrogen storage alloy appears as a ferromagnetic material because of the Ni,
These are Co, Fe, and Cr, and when the alloy structure is destroyed, these metals mainly appear on the alloy surface. These four elements improve the corrosion resistance of the hydrogen storage alloy in the form of metal or oxide. Ni, Co, and Cu are the charge / discharge potentials of the negative electrode. Since they exist in a metal state in an alkali, they also function as a hydrogen catalyst, so that the speed of absorbing hydrogen is improved, and the charging efficiency of the negative electrode is increased. A sealed alkaline storage battery with a small increase in internal pressure due to gas generated during charging can be obtained.
When a magnetic field of 10 KOe was applied at a temperature of 20 ° C., the magnetization per unit weight of the hydrogen storage alloy was 0.27.
If it is less than emu / g, the rate of hydrogen storage reaction of the alloy will decrease, causing an increase in battery internal pressure. 9.5 emu /
If the amount is more than g, the alloy structure is excessively destroyed and the capacity of the alloy is reduced. As a result, the capacity of the negative electrode is also reduced, which causes an increase in the internal pressure of the battery. Therefore, as a hydrogen storage alloy, 10K
The magnetization when applying a magnetic field of Oe is 0.27 to 9.5 emu.
/ G is preferable.

According to a second aspect of the present invention, the alloy has an average particle size of 15 μm to 100 μm,
m is controlled to 35% or less of the total by volume, and the amount of alloy particles of 10 μm or less that hardly participates in the hydrogen storage / release reaction is limited, and hydrogen suitable for reactivity and pulverization resistance is preferred. It is the average particle diameter of the storage alloy. Incidentally, the average particle is 15 μm or less, and 10 μm
If the ratio of the following alloy particles is 35% or more by volume integration, the amount of fine particles is too large, the alloy capacity is reduced, and the packing density of the negative electrode is also reduced. On the other hand, when the average particle diameter is 100 μm or more, the specific surface area of the alloy decreases and the reaction rate decreases.

Hereinafter, embodiments of the present invention will be described. (Embodiment) A method for producing a hydrogen storage alloy negative electrode according to the present invention will be described. Weigh and mix each metal sample of the above composition,
The molten metal obtained by heating and melting using a high-frequency melting furnace by induction heating was poured into a water-cooled mold to obtain a hydrogen storage alloy.
After coarsely pulverizing this hydrogen storage alloy, it was further controlled by a wet ball mill so as to fall within the above-mentioned range of the particle diameter of the hydrogen storage alloy to obtain a fine powder.

As a method for preparing the alloy powder, any method having the above-described particle size distribution may be used, and other means such as a gas atomizing method may be used.

However, from the viewpoint of price and properties of the alloy, if the alloy composition falls within the range described in claim 1,
Any composition may be used. More preferably, the amount of Co is preferably 0.2 to 0.4 atoms with respect to Mm. The total amount of Ni, Al, Co, and M is such that M is Fe, Cr,
In any case of Cu, the atomic ratio is more preferably 5.2 to 5.3 with respect to 1 of Mm.

Next, when a magnetic field of 10 KOe is applied to the alloy at 20 ° C., the magnetization per alloy weight is 0.27 to 9.5 em.
A method of controlling the ratio to u / g will be described. This method includes a method of immersing the pulverized hydrogen storage alloy powder in an aqueous alkaline solution, a method of treating the immersion solution at a high temperature, and a method of stirring. After that, the alloy is washed with pure water, suction filtered and dried.

In this adjustment process, the specific gravity of the processing solution is 1.
When the treatment temperature is maintained at 25 to 1.5 and the liquid is stirred while the treatment temperature is maintained at 60 to 100 ° C., the amount of magnetization can be controlled to a substantially desired range. As another method, treatment with an acidic solution such as hydrofluoric acid or hydrochloric acid is also effective. Further, better properties can be obtained by adding a nickel salt during the above treatment.

For the measurement of magnetization, a magnetization per magnet weight was measured using a vibrating sample magnetometer. A laser diffraction particle size distribution meter was used for the measurement of the alloy particle diameter.

Next, the hydrogen storage alloy powder after the treatment is
A paste was prepared by adding a binder, a conductive agent, and the like, and the paste was applied to a support made of punched metal and fixed. Other methods of preparing the hydrogen storage alloy electrode include a sintering method of sintering the alloy powder and a method of filling the porous support such as a foam or a fiber with the alloy powder. Also, carboxymethylcellulose (CM
C), styrene-butadiene copolymer, polyethylene (PE), polytetrafluoroethylene (PTFE) and the like are used. The addition amount of the binder is preferably 0.5 to 1.0% by weight based on the hydrogen storage alloy powder as a whole.
Examples of the conductive agent include carbon black and the like.
2 to 1.0% by weight is preferred.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail by taking a nickel-metal hydride storage battery as an example.

(Preparation of Open Battery) Carboxymethylcellulose was added to 100 g of the alloy powder having the above composition in an amount of 0.1 g.
A paste was prepared by adding 15% by weight, 0.3% by weight of carbon black, and 0.7% by weight of a styrene-butadiene copolymer, and further adding pure water as a dispersant. This paste was applied to a punching metal, dried and pressed to a desired thickness. These negative electrodes were cut into predetermined dimensions to obtain negative electrodes having a capacity of 2750 mAh. At this time, the weight of the alloy active material was about 9.5 g.
A publicly known foamed metal nickel positive electrode of 700 mAh is overlapped with a separator interposed therebetween, and at the time of charging, an acrylic plate is used to hold the active material from both the left and right sides so that the active material does not fall off. An open-type alkaline storage battery was constructed by immersion in an aqueous solution.

(Preparation of Sealed Battery) A negative electrode was prepared in the same manner as the negative electrode of the open battery. This negative electrode and capacity 1700
A known foam metal nickel positive electrode of mAh was formed in a spiral shape through a separator, and inserted into the case. Then
After injecting 2.35 ml of a KOH aqueous solution having a specific gravity of 1.3,
The sealed alkaline storage battery having a size of 4/5 A was sealed.

In the following embodiment, the above-mentioned open-type battery,
Both sealed batteries were made. Example 1 Mixture of rare earth elements (composition ratio: La 60)
%, Ce 28%, Nd 9%, Pr 0.3%, and other rare earth elements 2.7%), Ni, Mn, A
l, Co, Cu in alloy composition MmNi _4.0 Mn _0.4 Al
_After weighing and mixing each metal sample so as to obtain _0.3 Co _0.4 Cu _0.1 , the mixture was put in a crucible, fixed in a high-frequency melting furnace, and evacuated to 10 ^-4 to 10 ^-5 Torr,
After heating and melting in an Ar gas atmosphere, the alloy was poured into a water-cooled copper mold to obtain an alloy.

After coarsely pulverizing the above alloy, it is pulverized and classified by a wet ball mill so that the ratio of alloy particles having an average particle diameter of 35 μm and 10 μm or less becomes 10% of the whole by volume integration, and then the specific gravity is 1.3. It was immersed in an aqueous KOH solution at a temperature of 80 ° C. and stirred. Thereafter, it was washed with water, dehydrated and dried. A negative electrode was prepared from this alloy powder, and an open-type alkaline storage battery and a sealed-type alkaline storage battery were prepared. This is A.

Example 2 An alloy having the same composition as in Example 1 was coarsely pulverized and then subjected to wet ball milling to obtain an average particle diameter of 35 μm and 10 μm.
After pulverizing and classifying so that the ratio of alloy particles having a particle size of m or less becomes 10% of the total by volume, dehydration and drying were performed. A negative electrode was prepared from this alloy powder, and an open-type alkaline storage battery and a sealed-type alkaline storage battery were prepared. This is B.

Example 3 An alloy having the same composition as in Example 1 was roughly pulverized, and then subjected to wet ball milling to obtain an average particle diameter of 120 μm.
After pulverizing and classifying so that the ratio of the alloy particles having a size of μm or less becomes 5% of the whole by volume integration, the alloy particles were immersed in a KOH aqueous solution having a specific gravity of 1.3 and a liquid temperature of 80 ° C., followed by stirring. Thereafter, it was washed with water, dehydrated and dried. A negative electrode was prepared from this alloy powder, and an open-type alkaline storage battery and a sealed-type alkaline storage battery were prepared.
This is C.

Example 4 An alloy having the same composition as in Example 1 was coarsely pulverized and then subjected to wet ball milling to obtain an average particle diameter of 120 μm.
After pulverizing and classifying so that the ratio of the alloy particles having a particle size of μm or less becomes 5% of the whole by volume integration, the powder was dehydrated and dried. A negative electrode was prepared from this alloy powder, and an open-type alkaline storage battery and a sealed-type alkaline storage battery were prepared. This is D.

Example 5 An alloy having the same composition as in Example 1 was coarsely pulverized and then subjected to wet ball milling to obtain an average particle diameter of 12 μm and 10 μm.
After crushing and classifying so that the ratio of alloy particles having a particle size of m or less becomes 45% of the whole by volume integration, specific gravity is 1.3 and liquid temperature is 100 ° C.
Was immersed in an aqueous KOH solution and stirred. Thereafter, it was washed with water, dehydrated and dried. A negative electrode was prepared from this alloy powder, and an open-type alkaline storage battery and a sealed-type alkaline storage battery were prepared. This is E.

Example 6 An alloy having the same composition as in Example 1 was coarsely pulverized and then subjected to wet ball milling to obtain an average particle diameter of 16 μm and 10 μm.
After crushing and classifying so that the ratio of alloy particles having a particle size of m or less becomes 30% of the total by volume, specific gravity is 1.3 and liquid temperature is 100 ° C.
Was immersed in an aqueous KOH solution and stirred. Thereafter, a negative electrode was prepared from the alloy powder treated in the same manner as in Example 1, and an open-type alkaline storage battery and a sealed-type alkaline storage battery were prepared.
This is F.

Example 7 An alloy having the same composition as in Example 1 was coarsely pulverized and then subjected to wet ball milling to obtain an average particle diameter of 12 μm and 10 μm.
After crushing and classifying so that the ratio of alloy particles having a particle size of m or less becomes 45% of the whole by volume integration, specific gravity is 1.3 and liquid temperature is 100 ° C.
Was immersed in an aqueous KOH solution and stirred. Thereafter, a negative electrode was prepared from the alloy powder treated in the same manner as in Example 1, and an open-type alkaline storage battery and a sealed-type alkaline storage battery were prepared.
This is G.

Example 8 Mixture of rare earth elements (composition ratio: La 60%, Ce 28%, Nd 9%, Pr
0.3% and other rare earth elements 2.7%),
Ni, Mn, Al, Co, Cu are alloyed with MmNi
_4.1 Each metal sample was weighed and mixed so as to be _4.1 Mn _0.5 Al _0.3 Co _0.1 Cu _0.2 , the mixture was placed in a crucible, fixed in a high-frequency melting furnace, and evacuated to 10 ^-4 to 10 ^-5 Torr. Then, after heating and melting in an Ar gas atmosphere, the alloy was poured into a water-cooled copper mold to obtain an alloy.

The above alloy was treated in the same manner as in Example 1 to form a negative electrode, and an open-type alkaline storage battery and a sealed-type alkaline storage battery were prepared. This is H.

Example 9 A mixture of rare earth elements (composition ratio: La 60%, Ce 28%, Nd 9%, Pr
0.3% and other rare earth elements 2.7%),
Ni, Mn, Al, Co, Cu are alloyed with MmNi
_3.7 Mn _0.4 Al _0.3 Co _0.4 Cu _0.1 Each metal sample was weighed and mixed, and the mixture was put in a crucible, fixed in a high frequency melting furnace, and evacuated to 10 ^-4 to 10 ^-5 Torr. Then, after heating and melting in an Ar gas atmosphere, the alloy was poured into a water-cooled copper mold to obtain an alloy.

The alloy was treated in the same manner as in Example 1 to form a negative electrode, and an open alkaline storage battery and a sealed alkaline storage battery were prepared. This is I.

A total of 18 batteries of nine types A to I were prepared. (Measurement of cycle life) For these batteries, both the open-type alkaline storage battery and the closed-type alkaline storage battery
The battery was charged at 0 ° C. at a current value of 1 CmA for 72 minutes, and a current value of 1 Cm
A cycle life measurement of discharging to 1.0 V at A was performed.
Table 1 shows the number of cycles when the discharge capacity was reduced to 80% of the initial discharge capacity.

(Measurement of Battery Internal Pressure) Of the batteries in Table 1, the internal pressure of the sealed alkaline storage battery was measured at a current value of 1 CmA for 72 minutes in an atmosphere of 20 ° C.

[0036]

[Table 1]

From the results shown in Table 1, when the composition of the alloy was a + b + c + d + e <5.0, as in I, the life was significantly deteriorated in both the open and closed battery structures.
Although the cause is not clearly understood, observation of the negative electrode after the charge / discharge cycle with an electron microscope and other means revealed that the alloy was significantly pulverized and that corrosion was progressing. It was found that it was caused by deterioration. The composition is a + b + c + d as in Examples A to H.
If + e> 5.1, the result of the open alkaline storage battery is:
From the analysis result of the negative electrode plate after the life evaluation, it was found that the cycle life characteristics were satisfied, and that the pulverization of the alloy was suppressed. However, according to the results of the sealed alkaline storage battery, if the amount of magnetization per unit weight of the alloy is 0.27 or less when a magnetic field of 10 KOe is applied (Examples B and D), the reaction rate of the alloy is low, and The internal pressure of the battery rises due to the delay of gas absorption of the negative electrode during charging, and the safety valve operates due to the internal pressure rise associated with the charge / discharge cycle, and the electrolyte leaks out together with the gas to reduce the amount of the electrolyte. Caused a shortened life. On the other hand, if the magnetization amount is 9.5 or more (Examples F and G), the alloy structure is excessively destroyed, the alloy capacity involved in hydrogen absorption and desorption decreases, the anode capacity also decreases, and the internal pressure of the battery increases. Caused. Therefore, the magnetization per unit weight of the alloy when a magnetic field of 10 KOe was applied at 20 ° C. was preferably 0.27 to 9.5 emu / g. When the average particle diameter of the alloy is 15 μm or less (Examples E and G), the average particle diameter of 10 μm is considered not to be involved in hydrogen storage and release.
The proportions of the following alloys increased relatively. Therefore, the capacity of the alloy or the capacity of the negative electrode decreased, and the cycle life was shortened due to an increase in the internal pressure. In addition, the average particle diameter is 100μ
If it is not less than m (Examples C and D), the specific surface area of the alloy is reduced and the number of reactive active sites on the alloy surface is reduced, so that the reaction rate is slowed and the internal pressure is increased.

From these results, the average particle size of the alloy is generally 15 to 100 μm, and the ratio of alloy particles having a particle size of 10 μm or less is preferably 35% or less of the total volume.

The above results show that the element Cu in the alloy is replaced with Fe,
Alternatively, similar results were obtained even when the substitution was made with Cr. Further, C
Even if at least two elements of u, Fe and Cr are added at the same time, the total amount of addition is 0.05 to Mm of one atom.
The same effect was obtained when the number of atoms was 0.3 atoms.

[0040]

As described above, Mm-Ni-Mn-Al-C
By controlling the composition of the oM-based alloy, and further controlling the magnetization amount and the alloy particle diameter of the alloy powder, it is possible to suppress the deterioration of the negative electrode due to the pulverization of the alloy despite the small amount of Co. As a result, the cycle life of the battery is long and the cost is also advantageous, and the hydrogen absorption speed is higher than that of the conventional alloy, so that the charging efficiency of the negative electrode is increased and the internal pressure rise due to the gas generated during overcharge is tight. A nickel-metal hydride storage battery is obtained.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Koji Yuasa 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-6-290777 (JP, A) JP-A-4-137361 (JP, A) JP-A-4-292860 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) H01M 4/38 C22C 19/00-19/07

Claims (2)

(57) [Claims] 1. A mixture of the general formula _{MmNi a Mn b Al c Co d} M e ( where Shikichu Mm is a rare earth element, M is Fe, Cr, C
at least one element selected from u
3.8 ≦ a ≦ 4.1, 0.05 <d <0.5, 0.05
<E <0.3, 5.1 ≦ a + b + c + d + e ≦ 5.4)
An alkaline storage battery using a hydrogen storage alloy powder represented by the following formula for a negative electrode, wherein the hydrogen storage alloy powder is 10 KOe at 20 ° C.
The magnetization per unit weight is 0.27-
9.5 emu / g, a sealed alkaline storage battery. 2. The hydrogen storage alloy powder having an average particle size of 15
2. The sealed alkaline storage battery according to claim 1, wherein the proportion of the alloy particles having a size of μm to 100 μm and 10 μm or less is 35% or less of the whole by volume integration.