JP2623409B2 - Hydrogen storage electrode and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen storage electrode used as a negative electrode of a sealed alkaline storage battery and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a hydrogen storage electrode mainly composed of a hydrogen storage alloy capable of storing and releasing hydrogen has been known as a negative electrode of an alkaline sealed storage battery utilizing hydrogen as a negative electrode active material. The hydrogen storage electrode is manufactured mainly by mixing a hydrogen storage alloy powder with a PTFE powder or a PE powder as a binder and heating and melting the mixture, or by forming an unfired PTFE powder into fibers to form a network of the binder. It has been practiced to bind the alloy powder to prevent the alloy powder from falling off. In this case, a conductive material such as Ni powder is mixed to increase the conductivity of the electrode, or a thickening material such as CMC is mixed to form a slurry, which is applied to a porous conductive substrate, dried, and roll-formed. Then, generally, the electrode molded body is heat-treated in a vacuum to produce a hydrogen storage electrode.

[0003]

However, the hydrogen storage electrodes manufactured by the above-mentioned various conventional manufacturing methods are used as negative electrodes of storage batteries. It cannot be prevented that the powder is pulverized and drops from the electrode. As a result, the battery capacity is reduced, and the mechanical strength and the conductivity of the electrode are significantly reduced due to the effect of pulverization, making it difficult to maintain the electrode plate capacity for a long period of time.

[0004]

SUMMARY OF THE INVENTION The present invention is to provide a hydrogen storage electrode which solves the above-mentioned disadvantages of the conventional hydrogen storage electrode, improves the charge / discharge cycle life, and improves the capacity retention ratio. The volume fraction after the heat treatment was set to 42 to 84 vol. %, Binder 3 to 13 vol. %, Conductive material 3 to 15 vol. %, Residual pores 10 to 30 vol.
% To become, the binder material is a polyvinylidene fluoride, an average particle diameter of the conductor material is less der Rukoto 1.3μm
Features .

[0005]

The structure of the hydrogen storage electrode of the present invention is the same as that of the body after heat treatment.
The integration rate was set to 42 to 84 vol. %, Binder 3 to 13 vol. % And conductive material 3 to 15 vo
l. % And residual pores of 10 to 30 vol. The percent range, and as the binder material, using a polyvinylidene fluoride, an average particle diameter of the conductor material by Rukoto to and 1.3μm or less, to reveal the below, dropping of hydrogen absorbing alloy powder Thus, an electrode can be obtained in which the charge and discharge cycle life and the capacity retention ratio are large and the internal pressure of the battery can be kept low. In the production of the hydrogen storage electrode of the present invention, polyvinylidene fluoride is used as the binder, and the binder particles are melted or melted at about 160 to about 200 ° C. in a vacuum or an inert gas atmosphere. As a close state, they are bound to each other to form a network. With this network, countless alloy particles whose surfaces are coated with conductive fine particles are firmly bound and held so that they can adapt to the expansion and contraction of the volume. The binding network can maintain the initial state for a long time even in the alkaline electrolyte, so that the alloy particles can be prevented from falling off, and the charge / discharge cycle life is long,
This is effective for improving the capacity maintenance rate.

[0006]

EXAMPLES Examples of the hydrogen storage electrode of the present invention and a method for producing the same will be described below. The hydrogen storage alloy used for manufacturing the hydrogen storage electrode of the present invention may be an MmNi-based alloy or any other known alloy composition. When the compounding amount of the alloy is 42 vol. %, The predetermined capacity cannot be obtained, and 84 vol. %, The amount of the binder, the conductive material, etc. is relatively reduced, and the retention of the alloy particles becomes insufficient.
The conductivity also decreases, and a predetermined electrode cannot be obtained. In particular, polyvinylidene fluoride (PVdF) used as a binder is
A resistance alkali resistance, also about the heating temperature is about 160 Thus 20
This is advantageous in comparison with polytetrafluoroethylene (PTFE), which requires a low heating temperature of 0 ° C. and a very high melting temperature of about 350 ° C. and requires a special processing furnace. Such binding of the binder powder particles is advantageous in that the alloy particles are firmly bound to each other and a binding network having a followability corresponding to expansion and contraction of the alloy volume is generated. . If the heating temperature is lower than about 160 ° C., the binder particles do not bind to each other and the alloy particles cannot be sufficiently held. About 200 ° C
If it is higher, the surface of the alloy is likely to be inactivated, which is not preferable. As the conductive material, a material having good electric conductivity such as carbonyl nickel powder is preferable. If the average particle size is larger than 1.3 μm, it is difficult to penetrate between the alloy particles, and the It is difficult to coat well and the utilization rate of the electrode decreases. The thickener is necessary when preparing a slurry-like mixture, and any known material such as CMC, MC, and PVA can be used as the material. Thus, the desired hydrogen storage alloy powder, PV
A slurry having a predetermined viscosity is prepared by mixing a thickener such as dF powder and CMC with an appropriate amount of water or an organic solvent, and this is applied to both sides of a conductive porous substrate such as a nickel porous sheet to an appropriate thickness. After drying and rolling to produce an electrode compact, it is placed in a heating furnace, and is heated in a vacuum or in an inert gas atmosphere such as nitrogen for about 160 to about 200 hours.
C. for a required time, leaving 10-30 v of residual pores.
ol. % Of the hydrogen storage electrode of the present invention. Residual pores 10 vol. %, The gas absorption of the electrode becomes poor, and the vol. %, The active material tends to fall off, and a high capacity cannot be obtained.

Further, embodiments of the present invention will be described in detail. MmNi
_An alloy powder obtained by mechanically pulverizing a hydrogen storage alloy composed of _3.5 Co _1.0 Al _0.5 , polyvinylidene fluoride (PVdF) powder as a binder, and carbonyl nickel having an average particle diameter of 1.3 μm as a conductive material The powder and the powder are blended in the ratio shown in Table 1 below, a predetermined amount of a 1% aqueous solution of CMC is added as a thickener, and the resulting mixture is stirred and uniformly mixed, and the respective slurries are applied to both sides of a nickel porous sheet. After drying, rolling and forming a hydrogen-absorbing electrode plate, the formed plate was placed in a heating furnace and heat-treated under a vacuum atmosphere at a temperature in the range of about 160 to about 200 ° C., for example, at 170 ° C. for 2 hours. Thus, each of the hydrogen storage electrodes A to Q was manufactured. Also, for comparison,
Electrode R was manufactured by the same manufacturing method as described above, except that polyethylene (PE) powder was blended in place of the PVdF powder as the binder. Further, the above-mentioned PVd is used as a binder.
F powder instead of polytetrafluoroethylene (PTF
E) A powder is blended, without adding CMC as a thickening agent, a mixture containing fiberized mixed PTFE is pressure-bonded to both sides of the nickel porous sheet to form electrodes, and the heat treatment is not performed. The electrode S was manufactured. Further, an electrode T was manufactured by the same manufacturing method as described above, except that carbonyl nickel having an average particle size of 2.8 μm was blended in place of the carbonyl nickel powder having an average particle size of 1.3 μm as the conductive material. The remaining pores of each of the electrodes A to T were as shown in Table 1.

[0008]

[Table 1]

Each of the above-mentioned electrodes A to T is used as a negative electrode, a nickel electrode plate is used as a positive electrode, and a 0.18 mm-thick nylon separator is interposed between them to form a wound electrode plate group. Into a nickel-plated iron can in the usual manner, cover it tightly, inject a predetermined alkaline electrolyte,
The container was sealed to produce a cylindrical sealed storage battery. The positive electrode plate was prepared by mixing nickel hydroxide powder and carbonyl nickel powder, further adding a 1.2% CMC aqueous solution to form a paste, filling the foamed nickel substrate, drying and rolling. It is. Thus, the electrodes A to T
The corresponding storage batteries manufactured using the as a negative electrode are hereinafter referred to as AT batteries.

These A to T batteries were subjected to a charge / discharge cycle test, an internal pressure test, and a rate-specific discharge test as described below. A to T batteries have a rated AA-Type of 1100 mA.
h .

1) Charge / discharge cycle test: In the charge / discharge cycle test, the battery was charged at 1100 mA for 75 minutes,
Discharging was performed at 1100 mA with an end voltage of 1 V. The temperature was room temperature. The result is shown in FIG. As is evident from FIG. 1, the AK batteries have the following characteristics as the charge / discharge cycle progresses.
The decrease in the capacity was extremely small.
In the T battery, the capacity decrease increased. The cause of this is clearly shown in Table 1, and the amount of the binder is too small as in the case of the negative electrode L of the L battery, or the amount of the binder is low as in the negative electrode R of the R battery and the negative electrode S of the S battery. Even if the compounding amount of the material is sufficient, PV
In the case of heat-melted PE or unheated fibrous PTFE instead of dF, the alloy powder easily falls off the electrode due to the pulverization of the hydrogen storage alloy, and the mechanical strength and conductivity of the electrode decrease. On the contrary, when the amount of the binder is too large, as in the case of the negative electrode M of the M battery, the polarization characteristics of the negative electrode are deteriorated, and the utilization factor is considered to decrease. When the amount of the conductive material is too small, as in L, the conductivity is poor and the service life is reduced. Conversely, when the amount of the conductive material is too large, as in the negative electrode O of the O battery, the effect is further improved in proportion to this. When the residual pores are remarkably low, such as the negative electrode P of a P battery, the gas absorption is inferior and good charge / discharge characteristics cannot be maintained. Is considered
Conversely, if the residual pores are too high, as in the negative electrode Q of the Q battery, the alloy tends to fall off and the utilization tends to decrease rapidly. It is considered that if the particle size of the particles is too large, the conductivity is adversely affected and the utilization rate tends to decrease. In contrast, A ~
The hydrogen storage alloys such as the negative electrodes A to K of the K battery, the binder, the composition ratio of the conductive material and the ratio of the residual pores, and PVdF was used as the binder, and the average particle size of the conductive material was 1.3 μm. Ah
When heat-treated, the network formed by the binding of the molten particles of the binder restrains the alloy from falling off due to pulverization and increases the mechanical strength of the electrode. Adhering to the surface of the alloy particles like plating to provide good utilization by good conductivity,
The ratio of the remaining pores leads to good gas absorption, good penetration and diffusion of the electrolytic solution into the electrode, and good absorption and desorption of hydrogen. As a result, as shown in FIG. Even with the progress of the cycle, the capacity decrease is extremely small, and it is considered that the capacity is maintained almost as high as the initial capacity. 2) Internal pressure test: In the internal pressure test, charging was performed at 1100 mA for 4.5 hours, and discharging was performed at 220 mA with a final voltage of 1 V. The temperature was 20 ° C. Table 2 shows the results.

[0012]

[Table 2]

As is apparent from Table 2, the internal pressures of the AK cells were all extremely low. On the other hand, LT batteries are
Even when overcharging with such a large current, the internal pressure was remarkably high. The difference between the internal pressures of these batteries depends on the amount of each component of the electrode shown in Table 1, the difference in the binder, the difference in the conductive material, the presence or absence of heat treatment, etc. Occlusion /
It is considered that the properties such as discharge performance, charge / discharge performance, conductivity by the conductive material, binding property, and gas absorbability are produced. 3) Discharge test by rate: Discharge test by rate is 7.5 mA at 220 mA.
220mA (0.2C), 1650mA with time and end voltage as 1V
(1.5 C) and 3300 mA (3.0 C). The temperature was 20 ° C. The results are shown in Table 3.

[0014]

[Table 3]

As is apparent from Table 3, A to K batteries are L
It can be seen that, even when the discharge current is increased, the rate of decrease in the discharge characteristics is small and good discharge characteristics are maintained, as compared with the T cells.

As described above, the AK batteries were good in all of the above-mentioned charge / discharge cycle test, internal pressure test, and rate-specific discharge test. Then, when the structure of the electrodes A to K was further variously studied, the structure was as follows.
l.%, PVdF binder 3 ~ 13vol.%, conductive material 3 ~ 15
vol.%, residual pores 10-30vol.%, conductive material average particle size 1.3
μm or less, and about 1
As long as the hydrogen storage electrode is obtained by heat-treating the electrode formed body at 60 to about 200 ° C. in a vacuum or an inert atmosphere, each of the above excellent cycle life, discharge characteristics, and internal pressure reduction characteristics can be obtained. I confirmed that

[0017]

As described above, according to the present invention, the volume fraction of the hydrogen-absorbing electrode after the heat treatment is reduced to the hydrogen-absorbing alloy 42-84.
vol. %, PVdF binder 3 to 13 vol. %, A conductive material having an average particle size of 1.3 μm or less, 3 to 15 vol. %, Residual pores 10 to 30 vol. When the electrode molded body is heat-treated in a vacuum or an inert gas atmosphere at about 160 to about 200 ° C. in the production thereof, the production is relatively easy and inexpensive, and the charge-discharge cycle life, discharge A negative electrode for an alkaline sealed storage battery having excellent characteristics and a small decrease in battery capacity is provided.

[Brief description of the drawings]

FIG. 1 is a graph showing charge / discharge cycle characteristics of a hydrogen storage electrode of the present invention together with a comparative example.

[Table 1]

[Table 2]

[Table 3]

Claims (2)

(57) [Claims] (1) The volume fraction after heat treatment is as follows:
2-84 vol. %, Binder 3 to 13 vol. %, Conductive material 3 to 15 vol. %, Residual pores 10 to 30 vol. %
Become pressurized, et al., The binder material is a polyvinylidene fluoride,
The average particle diameter of the conductor material is characterized by the following Der Rukoto 1.3μm
Hydrogen absorbing electrode to be. 2. The method for producing a hydrogen storage electrode according to claim 1, wherein an electrode molded body is produced by using polyvinylidene fluoride as a binder, and the molded electrode is formed in a vacuum or in an inert gas atmosphere for about 160 to about 200 hours. A method for producing a hydrogen storage electrode, comprising heat-treating in the range of ° C.