JPH02112158A - Metal-hydrogen alkaline storage battery - Google Patents

Abstract

PURPOSE:To enhance charge-discharge cycle performance and to increase high rate discharge performance after repeating charge-discharge cycles by increasing the amount of a binder in a hydrogen storage alloy layer on the surface of an electrode than its current collector side. CONSTITUTION:When an electrode is manufactured, the concentration of a binder in negative paste is decreased on the current collector side and that is increased on the electrode surface side so that the binder has concentration gradient in a hydrogen storage alloy layer. Movement of hydrogen storage alloy fine particles formed from current collector side to electrode surface side is retarded, and increase in binder concentration in the vicinity of a current collector can be retarded. Electric conductivity in the electrode is kept high, and high rate discharge performance after repeating charge discharge cycles is improved. Since the binder concentration on the surface of the electrode is high, coming off of hydrogen storage alloy powder existing on the electrode surface is retarded, and charge-discharge cycle performance is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a metal-hydrogen alkaline storage battery having a negative electrode equipped with a hydrogen storage alloy capable of storing and releasing hydrogen.

Storage batteries that have been commonly used include alkaline storage batteries such as nickel-cadmium storage batteries, and lead storage batteries. In recent years, metal-hydrogen alkaline storage batteries, which have a negative electrode equipped with a hydrogen-absorbing electrode made of a hydrogen-absorbing alloy, have attracted attention because they are lighter, have higher capacity, and can have higher energy density than these batteries.

Examples of hydrogen storage alloys used in the negative electrode of this type of battery include the Special Publication No. 5! ]-49671, La Nis and its improved three-element system La Ni Co, La Ni
aCu and L a N i4. , F e5.2 and other alloys are known, and a mixture of these hydrogen storage alloy powders and conductive material powder is fixed to an electrode support using an electrolyte-resistant particulate binder to form a hydrogen storage electrode. A negative electrode is manufactured by the method (Japanese Patent Publication No. 57-30273). Specifically, a hydrogen storage alloy powder and a binder are uniformly mixed and pressed onto a current collector.

In addition to the above-mentioned alloys, various rare earth hydrogen storage alloys have been developed that use Mm (Misoshmetal) instead of IL aO, and as positive electrodes, sintered Nisokel electrodes used in nickel-cadmium storage batteries, etc. is used.

However, in the conventional metal-hydrogen alkaline storage battery, the concentration of the binder in the hydrogen-absorbing alloy layer is uniform; The above-mentioned atomized hydrogen storage alloy powder moves from the inside of the electrode (current collector side) toward the electrode surface.As a result, the hydrogen storage alloy powder falls off from the negative electrode and the charge/discharge characteristics deteriorate.In addition, hydrogen storage As the amount of binder on the current collector side of the hydrogen storage alloy layer increases due to the movement of the alloy powder, the electrical resistance of the negative electrode increases and the high rate discharge characteristics after charging/discharging/recycling deteriorate. Was.

The present invention has been made in consideration of the above-mentioned problems, and is a metal-hydrogen alkaline storage battery that can improve charge-discharge cycle characteristics and improve high-rate discharge characteristics after a charge-discharge cycle. The offer is targeted at 1.

In order to achieve the purpose of this invention, a negative electrode with a current collector surface 6 formed with a binder, a dihydrogen storage alloy layer, and a metal In a metal-hydrogen alkaline storage battery comprising a positive electrode made of an oxide and an alkaline electrolyte, the binder in the hydrogen storage alloy layer is
It is characterized in that it is contained more on the electrode surface side than on the current collector side.

After repeatedly charging and discharging a metal-hydrogen alkaline storage battery using a conventional negative electrode, the battery was disassembled and the negative electrode was analyzed and observed. It was found that the bonding with the negative electrode plate was becoming weaker. Therefore, when this negative electrode was examined in detail in the thickness direction of the hydrogen storage alloy layer, it was found that the pulverized hydrogen storage alloy powder was mainly distributed on the electrode surface, while the inside of the electrode (current collector side) It was observed that the hydrogen storage alloy powder was small and the binder mixed during electrode paste production was extremely large. Furthermore, by comparing the particle size and X-ray diffraction of the hydrogen storage alloy inside the electrode and the hydrogen storage alloy on the surface of the electrode, it was confirmed that the hydrogen storage alloy inside the electrode is slow to atomize and has little change in composition. , which shows that the charge/discharge reaction is not progressing very much. On the other hand, it was confirmed that on the surface of the electrode, the utilization rate due to the charge/discharge reaction is high, the hydrogen storage alloy is pulverized, and the composition change is also large, indicating that the charge/discharge reaction is progressing. . This is thought to be because the hydrogen storage alloy, which was pulverized by the charge/discharge reaction, moved to the highly electrochemically reactive electrode surface and reacted with it.

By the way, as in the present invention, when manufacturing the electrode, the concentration of the binder in the negative electrode paste on the current collector side is lowered, and the concentration of the binder on the electrode surface side is increased, thereby creating a gradient in the concentration of the binder in the hydrogen storage alloy layer. By holding the hydrogen storage alloy powder, it is possible to suppress the movement of the finely divided hydrogen storage alloy powder from the current collector side to the electrode surface side, and to suppress the binder concentration from increasing near the current collector. Therefore, the electrical conductivity of the electrode is maintained, and the high rate discharge characteristics after the charge/discharge cycle are improved. Furthermore, since the flow rate of the binder on the electrode surface side is high, the hydrogen storage alloy powder present on the electrode surface side is suppressed from falling off, and the charge/discharge cycle characteristics can be improved. In addition, if the binder concentration on the electrode surface side increases, the wettability between the hydrogen storage alloy particles and the electrolytic solution decreases. Therefore, since the contact surface between the alloy particles and oxygen gas increases, the consumption efficiency of oxygen gas increases, and thereby the oxygen gas absorption efficiency can be improved.

-LlfL Example- The first embodiment of the present invention is based on FIGS. 1 and 2.
This will be explained below.

〔Example〕

95 parts by weight of pulverized and atomized 1,aNiS as a hydrogen storage alloy, and PTFE (
After adding 5 parts by weight of Tispersion (fluorocarbon resin), these were mixed uniformly to form the PTFE into fibers. Next, water is added to the above mixture to create a paste, and then the above paste is pressure-bonded to both sides of a nickel-plated punched metal current collector, and the paste is dried. Next, the electrode is immersed in the PTFE dispersion and immediately pulled out to dry. This results in
A negative electrode having a concentration gradient such that the concentration of the binder on the current collector side is low and the concentration of the binder on the electrode surface side is high is produced. Thereafter, the negative electrode and a known sintered nickel positive electrode are wound together with an alkali-resistant separator to produce a spiral electrode body. Thereafter, after inserting the spiral electrode body into the battery outer can, an alkaline electrolyte was injected, and the battery outer can was further sealed 11 to produce a metal-hydrogen alkaline storage battery with a nominal capacity of 1200 mAh.

The battery thus produced is hereinafter referred to as the (A) battery.

[Comparative example]

A battery was produced in the same manner as in Example 2, except that the negative electrode was produced without immersing the electrode in the PTFE dispersion.

The battery thus produced is hereinafter referred to as the (X) battery.

[Experiment 1] A cycle test was conducted on the battery (A) of the present invention and the battery (X) of the comparative example, and the results are shown in FIG. still,
The charging and discharging conditions were: 16 hours of charging at 120mA, 240m
The test was carried out under the condition that the battery was discharged at A until the battery voltage reached 1.0 .

As is clear from FIG. 1, the battery capacity of the battery (X) of the comparative example decreases to 70% after approximately 100 cycles, whereas the battery capacity of the battery (A) of the present invention does not decrease after 200 cycles. It is observed that the battery capacity does not decrease to 70%. As a result, the battery (A) of the present invention is different from the battery (A) of the comparative example.
X) It can be seen that the cycle characteristics have been dramatically improved compared to batteries.

By the way, (A) battery during the charge/discharge cycle described above and (
When the X) battery was disassembled, it was observed that atomized hydrogen storage alloy powder had fallen from the negative electrode in the battery (X) of the comparative example, but almost none was observed in the battery (A) of the present invention. .

In addition, when the (A) battery and the (X) battery were observed in the thickness direction of the hydrogen storage alloy layer of the negative electrode, it was found that the (A) battery had approximately
The presence of hydrogen-absorbing alloy powder was observed in the (X) battery, but it was observed that the hydrogen-absorbing alloy layer on the current collector side was whitish. As a result, in the (X) battery, the hydrogen storage alloy layer on the current collector side has a high PTFE concentration,
It can be seen that the amount of hydrogen storage alloy powder is decreasing.

Here, as mentioned above, in the battery (A) of the present invention, the hydrogen storage alloy powder is uniformly present in the negative electrode because the binder is contained more on the electrode surface side than on the current collector side at the time of negative electrode production. This is thought to be due to the fact that the ability to fix the hydrogen storage alloy on the electrode surface, which has a good response of 14°, is improved and the movement of the hydrogen storage alloy is suppressed.

[Experiment■]

After charging the battery (A) of the present invention and the battery (X) of the comparative example 5 times and 50 times, the high rate discharge characteristics were investigated when discharging at 2.4A. The results are shown in Figure 2. Shown below.

As is clear from FIG. 2, after 5 cycles, the (A) battery and the (X) battery are in the middle of the road. However, after 50 cycles, the (A) battery has a higher operating voltage than the (X) battery;
It is recognized that excellent high rate discharge characteristics are exhibited even after the charge/discharge cycle has passed.

Fourth Practical Example A second example of the present invention will be described below with reference to FIG.

〔Example〕

After pressing the paste onto both sides of the punched metal aggregate and drying the paste, 10 parts by weight of PTFE dispersion as a binder was added to 90 parts by weight of L a Ni5 fine powder. P T Fr
E Except for press-bonding the highly concentrated paste, the above 1st
A battery was produced in the same manner as in the example.

The battery thus produced is hereinafter referred to as the (B) battery.

[Comparative example]

As a comparative example, the battery (X) was used.

〔experiment〕

50% of the battery (B) of the present invention and the battery (X) of the comparative example.
The high rate discharge characteristics after cycling were investigated and the results are shown in FIG. The experimental conditions were the same as in Experiment 1 of the first example.

As is clear from Figure 3, it is recognized that the (B) battery of the present invention has a higher operating voltage than the comparative example (X) battery, and exhibits excellent high rate discharge characteristics even after the charge/discharge cycle has elapsed. .

By the way, when I disassembled and observed the battery (B) above, I found that
As with the battery (A), it was found that the hydrogen storage alloy powder was uniformly dispersed in the hydrogen storage alloy layer and that the electrical conductivity was also good.

A third embodiment of the present invention will be described below with reference to FIG. 4.

〔Example〕

After preparing a paste in the same manner as in the first embodiment, the paste is pressed onto one side of a current collector made of a nickel lath mesh to prepare an electrode plate. Next, a negative electrode was produced by foaming PTFE dispersion on the current collector side surface of this electrode plate using compressed air. A battery was produced in the same manner as in the first embodiment except that the negative electrode was produced in this manner.

The battery thus produced is hereinafter referred to as the (C) battery.

[Comparative Example 1] A battery was produced in the same manner as in the above example except that a PTFE dispersion was foamed and applied to the electrode surface.

The battery thus produced is hereinafter referred to as a (Y) battery.

[Comparative example ■]

As Comparative Example (2), the battery (X) was used.

〔experiment〕

The high rate discharge characteristics of the battery (B) of the present invention and the battery (X) and battery (Y) of the comparative example were examined after 50 cycles, and the results are shown in FIG. The experimental conditions were the same as in Experiment 11 of the first example.

As is clear from FIG. 4, the (C) battery of the present invention has a higher operating pressure than the comparative examples (X) battery and (Y) battery, and exhibits excellent high rate discharge characteristics even after the charge/discharge cycle. It is recognized that

By the way, when we disassembled and observed the (C) battery and (Y) battery, we found that there was less hydrogen storage alloy powder near the current collector in the hydrogen storage alloy layer of the (Y) battery. (C) In the battery, it is observed that the hydrogen storage alloy is uniformly dispersed. Also, compared to (Y) battery, (C
) It was also observed that the electrical conductivity of the battery was improved.

From the first to third embodiments above, if the binder concentration in the hydrogen storage alloy layer of the negative electrode is made higher on the electrode surface side than on the current collector side, the charge/discharge cycle characteristics and the high rate discharge characteristics after the charge/discharge cycle have passed. However, in order to find out whether similar effects can be achieved with other battery systems (such as Soquel cadmium batteries, nickel-zinc batteries, and nickel-iron batteries), we will use a similar method to A battery was created. However, no significant effect was observed in any of the battery systems. Therefore, it can be seen that the present invention is particularly noticeable in metal-hydrogen alkaline storage batteries, and is unique to metal-hydrogen alkaline storage batteries. This is due to the fact that in the other battery systems mentioned above, the active material does not become atomized even after repeated charging and discharging. Furthermore, when we observed the negative electrodes of other battery systems after the charge/discharge cycle had elapsed, we found that the active material was uniformly distributed in the negative electrode, and the concentration of the binder on the current collector side was lower than that seen in metal-hydrogen alkaline storage batteries. This is clear from the fact that no phenomenon of increasing the value was observed.

In addition, in the above-mentioned first to third embodiments, L is used as the hydrogen storage alloy.
Although aNi5 was used and PTFE was used as the binder, the present invention is not limited thereto, and it goes without saying that any other hydrogen storage alloy and binder may have the same effect as described above.

Light radiation As explained above, according to the present invention, it is possible to suppress the movement of the atomized hydrogen storage alloy powder from the current collector side to the electrode surface side, so that it can be prevented from binding near the current collector. It is possible to suppress the concentration of the agent from increasing. Therefore, the electrical conductivity of the electrode is maintained, and the high rate discharge characteristics after a charge/discharge cycle are improved by 4°. Furthermore, since the binder concentration on the electrode surface side is high, the hydrogen storage alloy powder present on the electrode surface side is suppressed from falling off, and the charge-discharge cycle characteristics can be improved. In addition, since the contact surface between the hydrogen storage alloy particles and oxygen gas increases, the consumption efficiency of oxygen gas increases, and thereby,
Oxygen gas absorption efficiency can be improved.

These results have the effect of dramatically improving the performance of metal-hydrogen alkaline crystal batteries.

[Brief explanation of the drawing]

The first is a graph showing the cycle characteristics of the (A> battery of the present invention and the (X) battery of the comparative example), and the second is a graph showing the cycle characteristics of the (A) battery and the (X) battery after 5 cycles. A graph showing the subsequent high rate discharge characteristics, FIG. 3 is (B) of the present invention.
Figure 4 is a graph showing the high rate discharge characteristics after 50 cycles of the battery and the comparative example (X) battery, and the comparison example (X) battery and the comparative example battery (Y). ＋jru5
It is a graph showing high rate discharge characteristics after 0 cycles. 41 Vision 1-(G)〉

Claims (1)

[Claims] (1) In a metal-hydrogen alkaline storage battery comprising a negative electrode in which a hydrogen storage alloy layer is formed on the surface of a current collector with a binder, a positive electrode made of a metal oxide, and an alkaline electrolyte, the hydrogen storage alloy layer A metal material characterized in that the binder contained therein is contained in a larger amount on the electrode surface side than on the current collector side.
Hydrogen alkaline storage battery.