JPH0794187A - New negative active material alloy for alkaline storage battery and new negative active material alloy electrode - Google Patents

Abstract

PURPOSE:To provide a new negative active material alloy for an alkaline storage battery and a new negative active material electrode, which is an active material alloy completely different from conventional cadmium, and has high energy density, high discharge capacity, high quick charging capability, and long cycle life. CONSTITUTION:Alloy powder containing 20-50atom.% of a transition metal which is in a transition element series and has unfilled or half-filled (d) orbit and has internal paired (d) electrons, and having a particle size of 100mum or less is used as a new negative active material alloy for an alkaline storage battery. The alloy powder is mixed with 4-10wt.% polytetrafluoroethylene powder based on the weight of the alloy powder, and the mixture is press-molded to form a new negative active material alloy electrode. Boron, silicon, aluminum oxide, or silica may be contained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a negative electrode active material alloy for alkaline storage batteries and an electrode using the same.

[0002]

2. Description of the Related Art Alkaline storage batteries have an average battery voltage of 1.2V.
Therefore, it is required that the energy density, the discharge capacity (output density), the rapid charging / discharging property, and the cycle characteristics during charging / discharging are excellent. Currently, practically used alkaline storage batteries use nickel oxyhydroxide (NiOOH) as a positive electrode active material, cadmium (Cd) as a negative electrode active material, and an aqueous potassium hydroxide solution as an electrolytic solution. However, since this nickel-cadmium storage battery (Nicad storage battery) uses Cd as the negative electrode active material, it is regarded as a problem in terms of environmental compatibility, and moreover, it has recently been developed as an alternative storage battery for the alkali metal. The discharge capacity is smaller than that of hydride storage batteries.
On the other hand, this metal hydride storage battery is inferior to the former NiCd storage battery in rapid charge / discharge performance.

[0003]

SUMMARY OF THE INVENTION The present invention solves the problems of the conventional alkaline storage battery described above, and is an active material alloy of a type completely different from conventional Cd, and has a high energy density, a high discharge capacity, Provided are a novel negative electrode active material alloy for alkaline storage batteries and a new negative electrode active material alloy electrode, which have excellent rapid charge / discharge characteristics and cycle characteristics during charge / discharge.

[0004]

The present invention is directed to a transition metal having an internal pair of d electrons in the transition element series, the transition metal having an unfilled or semifilled d orbital in the transition element series in an atomic ratio of 20 to 20.
It is an alloy containing 50% and is a new negative electrode active material alloy for alkaline storage batteries, which is a powder with a particle size of 100 μm or less. Another aspect of the present invention is that a transition metal having an internal pair of d electrons in the transition element series contains 20 to 50% by atomic% of a transition metal in which the d orbital is unfilled or semi-filled, and the particles are Alloy powder with a diameter of 100 μm or less, and 4 to 10 wt% of polytetrafluoroethylene (PTF) based on the alloy powder.
E) A new negative electrode active material alloy electrode for alkaline storage batteries, which is mixed with powder and pressure-molded.

Cobalt (Co), iron (Fe), and the like are preferable as the transition metal having an internal pair of d electrons in the above transition element series, and as a transition metal in which the d-rail is unfilled or semi-filled in the transition element series. Is preferably molybdenum (Mo), tambusten (W), or the like. Furthermore, the above alloy is 5 atomic%
The following boron (B) or 10 atomic% or less silicon (S
i) or aluminum oxide (Al ₂
It is preferable to contain 20% by weight of O ₃ ) or silicon dioxide (SiO ₂ ).

[0006]

In the transition element series, the alloy of the metal on the left half side where the d orbital is unfilled or semi-filled and the metal on the right half side having internal pair d electrons shows catalytic activity during charge transfer in the hydrogen electrode reaction. There is a synergistic effect in increasing its exchange current density. Recently, the inventors of the present invention have particularly proposed Co-Mo (W) -based and Fe-Mo (W) -based alloy powders, which are considered as highly active catalysts for hydrogen generation reaction, into nickel-hydrogen using an alkaline electrolyte. When mixed and added to a Zr (Ti) -based Laves phase alloy powder as a negative electrode material of a compound storage battery and the charge and discharge characteristics of the storage battery were examined, a Co-Mo (W) system and Fe-M from now on.
It has been found that the o (W) -based alloy powder itself has a high discharge capacity, and further has a faster charge / discharge performance than the negative electrode of the nickel-hydride storage battery. Therefore, in the present invention, the alloy itself of the metal on the left-half side and the metal on the right-half side of this transition element series was examined for effectiveness as a negative electrode active material of an alkaline storage battery, and as a result, a Cd negative electrode active material of a conventional NiCd storage battery was obtained. It is an alloy composition having a charge / discharge characteristic superior to that of the substance.

In the above composition of the negative electrode active material alloy, d
The amount of transition metal whose orbital is unfilled or semi-filled is 20 ~
The reason for limiting to 50 atomic% is less than 20 atomic% and 50 atomic%
This is because the discharge capacity is reduced and the cycle characteristics are deteriorated when the value exceeds. In addition, a binder PTF for producing a negative electrode
The reason for limiting the mixing ratio of E to 4 to 10% by weight and the reason for limiting the particle size of the alloy powder to 100 μm or less are PTFE.
This is because if less than 4% by weight, the binding property is poor, and if more than 10% by weight and the alloy particle size exceeds 100 μm, the discharge capacity decreases and the cycle characteristics deteriorate.

As the third additive element, B and Si are each 5
The reason for limiting the content to the range of atomic% B, 10 atomic% Si or less and the reason for limiting the content of SiO ₂ or Al ₂ O ₃ to the alloy powder to 20% by weight or less exceeds the ratio of alloy addition or mixed addition. This is because the discharge capacity and cycle characteristics are reduced. The effect of mixing and adding SiO ₂ and Al ₂ O ₃ powder is to improve the permeability of the electrolyte solution between the alloy particles.

As a typical example, an alloy of Co or Fe and Mo or W was used, and the negative electrode after charge and discharge cycles was subjected to X-ray diffraction and surface analysis by EDX-SEM.
In the o-Mo (W) -based alloy, Co (OH) ₂ crystals are
In the —Mo (W) -based alloy, Fe (OH) ₂ crystals are generated, and after charging, Co (OH) ₂ and Fe (OH) ₂
In addition to, the metals Co and Fe were observed. Therefore high pH
Value electrolyte solution, so Co-Mo (W) and Fe-
It was found that Co and Fe in the Mo (W) -based alloy were eluted, and their charging / discharging mechanism was the same as that of the alkaline storage battery as in the conventional NiCd storage battery. Therefore, the total charge / discharge reaction of the negative electrode is Co + 2OH ⁻ ⇔ Co (OH) ₂ + 2e
^{− And} Fe + 2OH ⁻ ⇔ Fe (OH) ₂ + 2e ⁻ . The remaining Mo and W are generated Co (O
It was considered that they were dispersed in the H) ₂ and Fe (OH) ₂ layers and in the lower part of the layer, and acted as a catalytic activity of the charge / discharge reaction.

[0010]

Example A Co-Mo alloy having a predetermined composition was produced by arc melting in an argon atmosphere. This button-shaped sample alloy was annealed at a temperature of 850 ° C for 10 h in a vacuum and then diamond
Cutting powder was made with a wheel tool. For the charge / discharge test of the storage battery, an open type electrolytic cell was used, and an electrode obtained by press ^- molding Co—Mo alloy powder having a predetermined composition and a binder PTFE at 200 kgfcm ⁻² was used as a negative electrode, and a positive electrode was sintered NiOOH / Ni. (OH)
_It was performed at a temperature of 30 ° C. using 6 electrodes of 6 MKOH as an electrolyte. The procedure of the charge / discharge test is as follows. Charging was performed up to 450 mAhg ^-1 at a predetermined constant current, resting for 10 minutes, discharging to a final voltage of 1.0 V at a predetermined constant current, and resting for 10 minutes.

An example of a charge / discharge test using the novel negative electrode active material alloy for alkaline storage batteries according to the present invention will be described below. FIG. 1 shows the effects of the number of cycles and the charge flow density on the discharge capacity of a battery using a negative electrode in which 4 wt% PTFE was mixed and bound to Co-25 atomic% Mo alloy powder having a particle size of 53 μm or less. Here, the discharge current density is 32 mAg ^-1 . FIG. 2 shows the influence of the number of cycles and the discharge current density on the discharge capacity of the battery using the same alloy negative electrode. Here, the charging current density is 64 mAg ^-1 .

Except in the case of high discharge current density (FIG. 2),
In each case, the discharge capacity was very large in the first 1 to 3 cycles, and then decreased with the number of cycles, and after about 10 cycles, the charging current density was about 240 mAhg ^-1 up to 128 mAg ^-1 . (Figure 1). Until the discharge current density of influence about 128MAg ^-1 As can be seen from Figure 2, the discharge capacity even after about 10 cycles is as high as about 240~ 260mAhg ^-1, has excellent rapid charge and discharge performance. Here, the discharge capacity was calculated per unit mass of the Co-25 atomic% Mo alloy, but as described above, the charge / discharge reaction resulted in Co + 2OH ⁻ ⇔ Co (OH) ₂ + 2e ⁻ , so the unit of Co is When converted to the discharge capacity per mass, the discharge capacity is about 1.54 times larger. Therefore 240mA
The discharge capacity of hg ^-1 is 370 mAhg ^-1 , which is about twice that of the conventional Cd negative electrode active material of NiCd storage battery, which is about 180 mAhg ^-1 .

FIG. 3 shows the relationship between the discharge capacity and the cycle number of an alloy electrode obtained by adding a predetermined amount of B and Si as a third additive element to a Co-25 atomic% Mo alloy. FIG. 4 shows the results of the effect of adding SiO ₂ and Al ₂ O ₃ particles to the Co-25 atomic% Mo alloy powder and the effect of adding an inorganic compound which is considered to have some influence on the charge / discharge reaction. Here, the charge and discharge current densities are both 32 mAg ^-1 .

As can be seen from FIG. 3, even if alloys of B and Si are added in the range of 10 atomic% or less, there is no great difference in discharge capacity, but the alloy of 3 atomic% B is relatively excellent. Further, as can be seen from FIG. 4, the alloy electrode to which SiO ₂ and Al ₂ O ₃ are mixed and added by 10 wt% has relatively excellent charge and discharge characteristics. On the contrary, the mixed addition of Co ₃ O ₄ and Co (OH) ₂ seems to adversely affect the charge and discharge characteristics. In addition, although the said Example described Co-Mo alloy, this invention is not limited to this.

[0015]

As described above, the novel negative electrode active material alloy for alkaline storage batteries of the present invention is excellent in energy density, discharge capacity (output density), rapid charge / discharge characteristics and cycle characteristics at the time of charge / discharge. -It is a revolutionary alternative to the Cd negative electrode active material of cadmium (nicad) batteries.

[Brief description of drawings]

FIG. 1 shows a battery using the electrode of the present invention as a negative electrode,
It is a graph which shows the influence of the number of cycles and charging current density which affect discharge capacity.

FIG. 2 shows a battery using the electrode of the present invention as a negative electrode,
It is a graph which shows the influence of the number of cycles and discharge current density which affect discharge capacity.

FIG. 3 is a graph showing a relationship between a discharge capacity and a cycle number of an electrode obtained by adding a predetermined amount of B or Si as a third additive element to a Co—Mo alloy.

FIG. 4 is a graph showing the relationship between the discharge capacity and the cycle number of an electrode obtained by adding SiO ₂ , Al ₂ O ₃ or other inorganic compound particles to a Co—Mo alloy.

Claims (10)

[Claims] 1. An alloy containing 20 to 50% by atomic% of a transition metal having a d-orbital unfilled or semi-filled in a transition metal having an internal pair of d electrons.
A new negative electrode active material alloy for alkaline storage batteries, which is a powder with a particle size of 100 μm or less. 2. The transition metal having an internal pair of d electrons is
The novel negative electrode active material alloy for alkaline storage batteries according to claim 1, which is cobalt or iron. 3. The novel negative electrode active material alloy for an alkaline storage battery according to claim 1 or 2, wherein the transition metal having unfilled or semi-filled d-orbitals is molybdenum or tungsten. 4. The alkaline storage battery according to claim 1, wherein the alloy having the above composition further contains 5% or less of boron in atomic% or 10% or less of silicon. New negative electrode active material alloy. 5. The alloy powder having the above composition further has a particle size of 100 μm.
The novel negative electrode for an alkaline storage battery according to claim 1, 2 or 3, which is a mixed powder containing 20% by weight or less of a powder of aluminum oxide (Al ₂ O ₃ ) or silicon dioxide (SiO ₂ ) of m or less. Active material alloy. 6. A transition metal having an internal pair of d electrons in the transition element series, containing 20 to 50% by atomic% of a transition metal in which the d orbital is unfilled or semi-filled, and the particle diameter is
Alloy powder of 100 μm or less and 4 to 4 to the alloy powder
10% by weight of polytetrafluoroethylene (PTF
E) A new negative electrode active material alloy electrode for an alkaline storage battery, which is mixed with a powder and molded. 7. The transition metal having an internal pair of d electrons is
The novel negative electrode active material alloy electrode for an alkaline storage battery according to claim 6, which is cobalt or iron. 8. The novel negative electrode active material alloy electrode for an alkaline storage battery according to claim 6 or 7, wherein the transition metal whose d-orbital is unfilled or semi-filled is molybdenum or tungsten. 9. The novel alkaline storage battery according to claim 6, 7 or 8, wherein the alloy powder having the above composition further contains 5% or less of boron or 10% or less of silicon in atomic%. Negative electrode active material alloy electrode. 10. The alloy powder having the above composition further has a particle size of 100.
A novel alloy for alkaline storage battery according to claim 6, 7 or 8, which is a mixed alloy powder containing 20% by weight or less of aluminum oxide (Al ₂ O ₃ ) or silicon dioxide (SiO ₂ ) powder having a size of less than or equal to μm. Negative electrode active material alloy electrode.