JPH05283068A - Metal hydride storage battery - Google Patents

Abstract

PURPOSE:To improve the consumption speed of oxygen gas, and improve the cycle lifetime of a metal hydride storage battery. CONSTITUTION:In a battery having a hydrogen storage alloy negative electrode 2, which is mainly composed of hydrogen storage alloy, and a separator 3 impregnated with the electrolyte and a positive electrode 1, at the time of manufacture of the negative electrode 2, a layer made of graphite interlaminar compound, which can store and discharge hydrogen, or a layer made of the mixture of metal powder and graphite interlaminar compound is provided on the surface of an active material layer of the negative electrode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal hydride storage battery using, as a negative electrode material, a hydrogen storage alloy capable of storing and releasing hydrogen.

[0002]

2. Description of the Related Art Conventionally used storage batteries include nickel-cadmium storage batteries and lead storage batteries. However, in recent years, nickel-hydrogen alkaline storage batteries equipped with a hydrogen storage electrode using a hydrogen storage alloy as a negative electrode material have attracted attention because they may be lighter in weight, have higher capacity, and have higher energy density than these batteries. There is.

Here, as a method for producing a hydrogen storage alloy electrode, as disclosed in JP-A-61-66366, a binder such as polytetrafluoroethylene or polyethylene oxide and a hydrogen storage alloy powder are kneaded. A method of applying the paste to a core body such as punching metal or expanded metal and drying it is generally used.
Further, the hydrogen storage electrode thus produced and the spirally wound nickel positive electrode used in the nickel-cadmium storage battery with a separator interposed between the spirally wound one should be housed in a battery outer can. Thus, a nickel-hydrogen alkaline storage battery is manufactured.

In the battery thus manufactured, oxygen gas is generated from the positive electrode in the battery during overcharge. Then, the generated oxygen gas is consumed by the hydrogen storage alloy of the negative electrode as in the reaction formula shown below. 1/2 O ₂ + H ₂ O + 2e ^- OH ^- MH + 1/4 O ₂ M + 1/2 H ₂ O However, if the above oxygen gas consumption reaction does not occur promptly, the battery internal pressure will rise. There is a problem of doing.

Therefore, in order to accelerate the above reaction and improve the oxygen gas consumption capacity, Japanese Patent Laid-Open No. 63-1959 has been proposed.
In JP-A-60, it is proposed to form a carbon powder layer on the surface of the hydrogen storage alloy electrode of the negative electrode to improve the conductivity of the negative electrode surface. With such a configuration, the oxygen gas consumption capacity is improved for the following reasons. That is, normally
At the time of charging, the hydrogen storage alloy near the surface of the negative electrode is hard to be charged because it is charged from near the conductive support.
However, if a conductive layer such as carbon powder is formed on the surface of the negative electrode as in the above structure, the hydrogen storage alloy near the surface of the negative electrode is also easily charged. Therefore, it becomes possible to allow hydrogen to be present on the negative electrode surface from an early stage of charging, so that the oxygen gas consuming reaction quickly occurs between the oxygen gas and the hydrogen stored in the hydrogen storage alloy on the negative electrode surface. It depends on the reason to proceed.

[0006]

However, in the above-mentioned conventional method, since the carbon powder layer exists on the outermost surface of the negative electrode, the carbon powder interferes with the contact between oxygen gas and hydrogen. Further, there is a problem that sufficient oxygen gas consumption capacity cannot be obtained only by improving the conductivity of the negative electrode surface. Further, when the carbon powder layer is formed, the filling amount of the hydrogen storage alloy is reduced by that amount, which causes a new problem of lowering the capacity density of the negative electrode.

The present invention solves the above problems, and an object of the present invention is to provide a metal hydride storage battery capable of improving the oxygen gas consumption rate and the cycle life.

[0008]

In order to achieve the above object, in a metal hydride storage battery having a negative electrode containing a hydrogen storage alloy as a main component, a separator impregnated with an electrolytic solution, and a positive electrode, the negative electrode surface In addition, a layer made of a graphite intercalation compound capable of occluding and releasing hydrogen or a layer made of a mixture of the graphite intercalation compound and metal powder is formed.

Further, the amount of the graphite intercalation compound or the mixture of the graphite intercalation compound and the metal powder is 0.0001 g or more and 0.01 g or less per 1 cm ² . Further, the graphite intercalation compound is a compound obtained by doping graphite with at least one metal consisting of potassium, sodium or lithium.

[0010]

When a graphite intercalation compound capable of occluding and releasing hydrogen is formed on the surface of the negative electrode as in the above structure, not only the hydrogen occluding alloy near the surface occludes hydrogen during charging, but Will also absorb hydrogen. Therefore, the graphite intercalation compound does not hinder the contact between oxygen gas and hydrogen, and oxygen gas is promptly supplied with hydrogen on the surface of the negative electrode and reduced to water.

Further, the presence of a metal powder such as nickel having a catalytic property and a conductivity for the reduction reaction of oxygen gas to water near the graphite intercalation compound allows the reduction reaction to water to proceed more quickly. .. Such improvement of the oxygen gas consumption rate improves safety during overcharge, prevents leakage due to valve operation and deterioration due to oxidation of the hydrogen storage alloy, and improves cycle life.

In addition, since the graphite intercalation compound can store hydrogen during charging, it is possible to suppress a decrease in the storage amount of hydrogen due to the formation of the layer. In addition, if a graphite intercalation compound in which potassium or the like is doped in graphite is arranged on the negative electrode surface, the conductivity of the negative electrode surface is improved and the negative electrode surface is easily charged, so that the consumption of oxygen gas should be further improved. You can

[0013]

【Example】

[Embodiment 1] FIG. 1 is a cross-sectional view of a cylindrical sealed nickel-hydrogen battery according to an example of the present invention. A positive electrode 1 made of sintered nickel, a negative electrode 2 having a hydrogen storage alloy powder, and positive and negative electrodes 1 are provided. The electrode group 4 including the separator 3 inserted between the two is wound in a spiral shape. The electrode group 4 is arranged in an outer can 6 that also serves as a negative electrode terminal, and the outer can 6 and the negative electrode 2 are connected by a negative electrode conductive tab 5. A sealing body 8 is attached to the upper opening of the outer can 6 through a packing 7, and a coil spring 9 is provided inside the sealing body 8. This coil spring 9 is configured to be pressed in the direction of arrow A when the internal pressure of the battery inside the battery rises abnormally, and the gas inside is released into the atmosphere. Further, the sealing body 8 and the positive electrode 1 are connected by a positive electrode conductive tab 10.

Here, the cylindrical closed type nickel-water having the above structure is used.
A unit cell was produced as follows. First of all, water
Commercially available misch metal (M
m, a mixture of rare earth elements), nickel, cobalt and al.
The element ratio of minium and manganese is 1.0: 3.2: 1.
Weigh these to 0: 0.2: 0.6 and
Mix, melt and cast in a high frequency induction furnace. By this
MmNi_3.2CoAl _0.2Mn_0.6The composition of
You get money. The alloy mass was then mechanically crushed
A hydrogen storage alloy powder having an average particle size of 50 μm was produced.

Further, 1 wt% of polyethylene oxide with respect to the alloy powder and water as a dispersion medium are added to the alloy powder to prepare a slurry, which is applied to the surface of a conductive support made of punching metal. The base electrode was obtained by performing drying and pressurization. Next, polyvinyl alcohol as a binder and water as a dispersion medium are added to a graphite intercalation compound in which potassium is doped in natural graphite to obtain a slurry, and the slurry is applied to both surfaces of the base electrode and dried. And it rolled and the hydrogen storage electrode was obtained.

The amount of the graphite intercalation compound applied per cm ^{2 of the} base electrode was 0.001 g. Using a sintered nickel electrode as the positive electrode 1 and the hydrogen storage electrode prepared as described above as the negative electrode 2, these positive and negative electrodes 1
Wrap between the two via a separator 3 made of a non-woven fabric,
A spiral electrode group 4 was obtained. Then, this electrode group 4 was inserted into the outer can 6, and after pouring 30% by weight potassium hydroxide aqueous solution as an electrolytic solution, it was sealed and the nominal capacity was 1000 mA.
A sealed nickel-metal hydride battery of h was manufactured.

The battery thus manufactured is hereinafter referred to as (a) battery. [Example 2] To a mixture of nickel powder and a graphite intercalation compound in which potassium was doped in natural graphite, polyvinyl alcohol as a binder and water as a dispersion medium were added to obtain a slurry. A battery was produced in the same manner as in Example 1 except that the same base electrode as that produced in Example 1 was coated on both sides.

The nickel powder was mixed in an amount of 20 wt% with respect to the graphite intercalation compound, and the coating amount of the mixture of the nickel powder and the graphite intercalation compound per cm ² of the base electrode was 0.
It was 001 g. The battery thus produced is
(B) This is called a battery. Comparative Example 1 A battery was produced in the same manner as in Example 1 except that the base electrode produced in Example 1 was used as a completed electrode, that is, the graphite intercalation compound layer was not formed on the base electrode.

The battery thus produced is referred to below as (x ₁ )
It is called a battery. [Comparative Example 2] The above-mentioned Example except that polyvinyl alcohol as a binder and water as a dispersion medium were added to acetylene black to obtain a slurry, and this slurry was applied to the same base electrode as in Example 1 above. A battery was prepared in the same manner as in 1.

The acetylene black base electrode 1c
The amount applied per m ² was 0.001 g. The battery thus produced is hereinafter referred to as a (x ₂ ) battery. [Comparative Example 3] A battery was produced in the same manner as in Comparative Example 2 except that nickel powder was used instead of acetylene black.

The battery thus produced is referred to below as (x ₃ )
It is called a battery. [Experiment 1] (a) and (b) batteries of the present invention and (x
The pressure inside the battery during charging was measured using the batteries ₁ ) to (x ₃ ) and the results are shown in Table 1. The internal pressure of the battery is activated by repeating low-rate charging / discharging, and then a hole is provided at the bottom of the battery case, and a pressure sensor for measuring the internal pressure of the battery is attached to this hole. The internal pressure of the battery was measured.

As the measurement conditions, the battery was charged with a current of 1000 mA, and after the battery voltage reached the peak value,
Charging was stopped when the voltage dropped by 10 mV from this peak value, and the battery internal pressure was measured during this period.

[0023]

[Table 1]

As is clear from Table 1, (a) of the present invention
The battery and the battery (b) are (x) of the comparative example. ₁) Battery ~ (x₃)
Compared to the battery, the rise in internal pressure of the battery is suppressed.
Is recognized. That is, regarding the battery of the present invention (a),
Dope potassium into natural graphite on the surface of hydrogen storage alloy
Since a layer of graphite intercalation compound is formed,
At the same time, it is occluded in the graphite intercalation compound of the surface layer.
Hydrogen and oxygen gas from the positive electrode are directly on the outermost surface of the negative electrode
By contacting with
It is considered that the consumption rate of elementary gas is accelerated.

Further, in the battery of the present invention (b), in addition to the above effects, nickel powder having catalytic property and conductivity for reduction reaction of oxygen gas to water is added, so that the surface of the negative electrode can be more quickly. It is considered that the reduction reaction of oxygen gas to water proceeds. On the other hand, (x ₁ ) of the comparative example
It is considered that the increase of the battery internal pressure of the battery to the (x ₃ ) battery is due to the following reasons.

In the battery (x ₁ ) of the comparative example, the negative electrode surface has low conductivity, and hydrogen is less likely to be occluded in the vicinity of the negative electrode surface during charging, so that the oxygen gas consumption capacity is lowered and the battery internal pressure is increased. it is conceivable that. In addition, (x ₂ ) of the comparative example
Regarding the battery, the conductivity of the negative electrode surface is improved and the hydrogen storage alloy near the surface absorbs hydrogen from the beginning of charging, but the acetylene black on the outermost surface cannot absorb hydrogen. Therefore, it is considered that this acetylene black hindered the contact between oxygen and hydrogen and was not effective for the oxygen gas consumption reaction.

Further, regarding the (x ₃ ) battery of the comparative example,
By coating nickel powder on the surface of the negative electrode, the catalytic property of the oxygen gas consumption reaction is improved, but since the conductivity is insufficient, the hydrogen storage alloy near the surface cannot store hydrogen sufficiently from the beginning of charging. .. Further, it is considered that, like acetylene black, it cannot occlude hydrogen, which hinders the contact between hydrogen and oxygen gas, resulting in no effect on the oxygen gas consumption reaction. (A) cell Experiment 2] In the present invention, since the measurement of (b) of Comparative Example battery _{(x 1) ~ (x 3} ) cycle life by using a battery, the results are shown in Table 2.

The cycle conditions at the time of measurement are 5 for each battery.
The battery is charged at a current of 00 mA for 2.5 hours, then discharged at a current of 500 mA, and terminated when the battery voltage reaches 1.0 V. The cycle life was defined as the number of cycles at which the discharge capacity of the battery reached 50% of the initial capacity.

[0029]

[Table 2]

As is clear from Table 2, (a) of the present invention
The battery and the battery (b) are (x) of the comparative example. ₁) Battery ~ (x₃)
It is noted that the cycle life is longer than that of the battery.
This is (x₁) Battery ~ (x₃) In batteries
Increases the battery internal pressure during the charge / discharge cycle.
Then, the safety valve is activated and the gas in the battery is released. This
When the gas is released, part of the electrolyte is also released to the outside of the battery.
As a result, as the cycle progresses, the electrolyte in the battery
The quantity is running short. On the other hand, the battery (a) of the present invention,
(B) Since the battery internal pressure is suppressed from increasing in the battery,
This is because the amount of electrolytic solution can be maintained sufficiently. [Experiment 3] Base on the battery (a) of Example 1
When the amount of graphite intercalation compound applied to the electrode was changed
Mushroom, internal pressure of battery and change of cycle number were investigated
Therefore, the results are shown in Table 3.

The experimental conditions were the same as those in Experiments 1 and 2 above.

[0032]

[Table 3]

As shown in Table 3 above, as the amount of coating increases, the reaction of water generation on the surface of the negative electrode easily occurs, which is effective in reducing the internal pressure of the battery. However, when the applied amount is 0.015 g, the cycle life is significantly reduced. This is because as the coating amount increases, the amount of the electrolytic solution absorbed by the negative electrode also increases, and the liquid retaining property of the electrolytic solution of the separator decreases.
It is considered that this is because the internal resistance increases as the cycle progresses, causing a decrease in cycle life.

From the above results, the amount of graphite intercalation compound applied is preferably 0.0001 g to 0.01 g. [Experiment 4] With respect to the battery (b) of Example 2, changes in the internal pressure of the battery and the number of cycles when the amount of the mixture of the graphite intercalation compound and the nickel powder applied to the base electrode was changed were examined. Table 4 shows the results.

The experimental conditions were the same as those in Experiments 1 and 2 above.

[0036]

[Table 4]

As the coating amount increases, the reaction for producing water on the surface of the negative electrode easily occurs, which is effective in reducing the internal pressure of the battery. However, when the coating amount was 0.015 g, the above experiment was conducted. For the same reason as in No. 3, it is considered that the cycle life is shortened. From the above results, the coating amount of the mixture of the graphite intercalation compound and the nickel powder was 0.0001.
g to 0.01 g is desirable. [Experiment 5] Regarding the battery (b) of Example 2, the battery internal pressure when the addition amount of the nickel powder to the graphite intercalation compound of the mixture of the graphite intercalation compound and the nickel powder applied to the base electrode was changed, and The change in cycle life was investigated, and the results are shown in Table 5.

The experimental conditions were the same as those in Experiments 1 and 2 above.

[0039]

[Table 5]

As the amount of nickel powder added increases, the catalytic property of the reduction reaction of oxygen gas in the negative electrode to water improves, and the reduction reaction to water on the surface of the negative electrode rapidly proceeds, reducing the internal pressure of the battery. Therefore, it is considered that the cycle life is improved. However, it is considered that when the addition amount is 50 wt%, the addition amount of the nickel powder is high, so that the hydrogen overvoltage of the hydrogen storage alloy electrode is lowered, hydrogen gas is generated during charging, and the battery internal pressure is increased.

From the above results, the amount of nickel added was 5 w.
t% to 40 wt% is desirable. [Other Matters] In the above-mentioned examples, a graphite intercalation compound in which natural graphite is doped with potassium is used, but in addition to potassium, the same effect can be obtained by doping sodium, lithium, or the like. Be done.

Further, in the above embodiment, nickel powder was used as the metal powder when the mixture of the graphite intercalation compound and the metal powder was prepared. However, metal powder such as cobalt or copper was used instead of nickel powder. Also has the same effect.

[0043]

As described above, in the present invention, the graphite intercalation compound layer formed on the negative electrode using the hydrogen storage alloy as the main component improves the conductivity of the surface of the negative electrode, and further the graphite intercalation compound itself. Occludes and releases hydrogen, so that the oxygen gas consumption reaction is smoothly performed.

Further, instead of the graphite intercalation compound layer, by forming a layer of a mixture of metal powder and graphite intercalation compound on the negative electrode, oxygen gas consumption can be carried out more smoothly.
As described above, the oxygen gas consumption reaction rate is improved, and the increase in the battery internal pressure is suppressed, so that the cycle life of the battery is significantly improved.

[0045]

[Simple Drawing Description]

[0046]

FIG. 1 is a cross-sectional view of a sealed nickel-hydrogen battery according to an example of the present invention.

[0047]

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tsukasa Ito 2-18 Keihan Hondori, Moriguchi Sanyo Electric Co., Ltd. (72) Inventor Yoshikazu Ishikura 2-18 Keihan Hondori, Moriguchi Sanyo Electric Co., Ltd. Within

Claims (3)

[Claims] 1. A metal hydride storage battery having a negative electrode containing a hydrogen storage alloy as a main component, a separator impregnated with an electrolytic solution, and a positive electrode, wherein a graphite layer capable of storing and releasing hydrogen on the surface of the negative electrode. A metal hydride storage battery, wherein a layer made of a compound or a layer made of a mixture of the graphite intercalation compound and metal powder is formed. 2. The amount of the graphite intercalation compound or the mixture of the graphite intercalation compound and the metal powder is 0.0 per cm ^2.
The metal hydride storage battery according to claim 1, wherein the amount is 001 g or more and 0.01 g or less. 3. The metal hydride storage battery according to claim 1, wherein the graphite intercalation compound is a compound in which graphite is doped with at least one metal consisting of potassium, sodium or lithium.