JPH0773900A - Maintenance method for stationary type nickel-hydrogen storage battery - Google Patents

Abstract

PURPOSE:To mitigate a drop of a capacity after maintenance and lengthen an interval of maintenance by setting an operating pressure of a valve for use in maintenance lower than an operating pressure of a safety valve during an electric charging/discharging cycle for the purpose of overcharging. CONSTITUTION:An operating pressure for use in maintenance is set lower than an operating pressure of a conventional valve, i.e., an operating pressure (3atm or higher) of a safety valve, more preferably set to 1.5-2.5atm, followed by overcharging (releasing overcharging). Although a battery capacity of the positive electrode, which is reduced after maintenance by the electric overcharging, is recovered from M2 to M1, an extra capacity S is generated in the negative electrode at the time of electric charging after maintenance. Consequently, electric charging is principally dependent on the positive electrode until hydrogen is completely stored in the extra capacity S. As a result, it is possible to mitigate a drop of the capacity after maintenance and lengthen an interval of maintenance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a maintenance method for recovering the capacity of a stationary nickel-hydrogen storage battery whose battery capacity has decreased due to repeated charge / discharge cycles.

[0002]

2. Description of the Related Art Oxygen gas is generated from the positive electrode at the end of charging of a stationary nickel-hydrogen storage battery used as a power source for various measuring instruments such as gas meters. If the generated oxygen gas is completely consumed by the reaction with the hydrogen of the negative electrode, the internal pressure of the battery (internal pressure) does not rise and the capacity balance between the positive and negative electrodes is not disturbed.

However, since a part of the oxygen gas generated during charging is consumed for the oxidation of the easily oxidizable member such as the separator, hydrogen remains in the negative electrode. As a result, hydrogen is gradually accumulated in the negative electrode during repeated charge / discharge cycles, and eventually the charge becomes dominant in the negative electrode, resulting in a decrease in battery capacity. Therefore, it is necessary to perform regular maintenance in order to recover the battery capacity when it has decreased to some extent.

Conventionally, for this maintenance, hydrogen accumulated in the hydrogen storage alloy is transferred to a hydrogen gas from a safety valve with an operating pressure of 3 atm or more provided on the upper surface of the battery case in order to prevent the internal pressure of the battery from rising during charge / discharge cycles. As a result, overcharging (open overcharging) is performed while discharging the battery.

FIG. 5 is an explanatory view of this conventional method. FIG. 5 (A) is a capacity diagram of both positive and negative electrodes before maintenance, and FIG.
(B) is a capacity diagram of the positive and negative electrodes after maintenance. Since hydrogen accumulates in the negative electrode due to repeated charge / discharge cycles, as shown in FIG.
The battery capacity, which was 1, decreases to M2 before maintenance.

The maintenance is an operation for releasing hydrogen accumulated in the negative electrode to the outside of the battery system to recover the lowered battery capacity M2 to M1, but not only hydrogen gas but also oxygen gas is overcharged. If a large amount is released outside the battery system,
This leads to a shortage of electrolyte and shortens the cycle life. Therefore, it is necessary to overcharge the battery so that a large amount of oxygen gas is not released to the outside of the battery system. Therefore, in the conventional method, in reality, it is necessary to terminate the overcharge before the oxygen gas is intensely generated from the positive electrode. It is for this reason that the charge depths of the positive and negative electrodes after the maintenance shown in FIG. Note that hatched portions a and b in FIGS. 5A and 5B are portions where hydrogen is accumulated.

However, the above-mentioned conventional method has a problem that the battery capacity is reduced in a short cycle during the charge / discharge cycle after maintenance and that the cycle life is short. Therefore, there has been a demand for the development of a better maintenance method.

The present invention has been made in order to meet such a demand, and an object thereof is to provide an operating pressure of a valve used for releasing hydrogen gas generated in the battery system during maintenance to the outside of the battery system. It is to provide a new and useful maintenance method that does not have the above-mentioned problems.

[0009]

The method for maintaining a stationary nickel-metal hydride storage battery according to the present invention (hereinafter, referred to as the "method of the present invention") according to the present invention for achieving the above-mentioned object is an operating pressure lower than 3 atm. This is a method of overcharging while releasing the hydrogen gas generated in the battery system from the valve that opens in step 1 to outside the battery system.

The above-mentioned valve may be provided separately from the safety valve for preventing an abnormal rise in the internal pressure of the battery during the charge / discharge cycle, and the operating pressure of the safety valve during the charge / discharge cycle (3 atm or more). May be adjusted to be lower than 3 atm for maintenance.

The preferred operating pressure of the valve in the method of the present invention is 1.5 to 2.5 atmospheres. If a valve with a too low operating pressure is used, oxygen gas is released to the outside of the battery system in addition to the hydrogen gas to be released, resulting in a shortage of the electrolytic solution, resulting in a shortened cycle life. On the other hand, when a valve having an excessively high operating pressure is used, the equilibrium hydrogen pressure inside the battery becomes high, so that a large amount of hydrogen is likely to be absorbed in the negative electrode during overcharge during maintenance. As a result, the accumulated hydrogen is insufficiently extracted from the negative electrode, the rate of capacity recovery is reduced, and the cycle life is shortened.

[0012]

In the method of the present invention, the operating pressure of the valve used for maintenance is set to the operating pressure of the safety valve (3
Since it is overcharged at a pressure lower than the atmospheric pressure), the amount of hydrogen stored during overcharge is smaller than that in the conventional method in which the safety valve is used as it is during charge / discharge cycles. As a result, a large amount of hydrogen accumulated in the negative electrode is released to the outside of the battery system as hydrogen gas, and the decrease in the battery capacity in the charge / discharge cycle after maintenance becomes gradual. The principle of the method of the present invention will be described below.

Since maintenance is an operation of releasing hydrogen accumulated in the negative electrode as hydrogen gas to the outside of the battery system, a condition under which the amount of hydrogen stored in the negative electrode during overcharge is reduced, that is, the equilibrium hydrogen pressure inside the battery is lowered. It should be preferable to overcharge.

The method of the present invention was developed on the basis of such findings. That is, according to the method of the present invention, the operating pressure of the valve used for maintenance is set lower than the operating pressure of the valve of the conventional method, that is, the operating pressure of the safety valve (3 atm or more) to perform overcharge (open overcharge). The amount of hydrogen (accumulated hydrogen) remaining in the negative electrode after discharge after maintenance is made smaller than that in the conventional method.

FIG. 1 is an explanatory view of the method of the present invention.
(A) is a capacity diagram of both positive and negative electrodes before maintenance, Fig. 1
(B) is a capacity diagram of the positive and negative electrodes after maintenance. As shown in FIG. 1B, the point that the lowered battery capacity M2 is restored to M1 after maintenance is almost the same as in the case of the conventional method, but in the method of the present invention, the extra capacity S at the time of charging after maintenance is Is generated in the negative electrode, the charging depth of the negative electrode can be made shallower than in the conventional method.

Therefore, until the hydrogen is completely accumulated in the extra capacity S, the charging is performed under the control of the positive electrode, and the capacity hardly decreases during that time. After the hydrogen is completely accumulated in the extra capacity S, the charging is controlled at the same time, and then the charging is controlled by the negative electrode, so that the capacity is reduced, but there is a period in which the capacity is hardly reduced. As a result, the capacity decrease after maintenance becomes gentle, and the maintenance interval can be lengthened.

Further, in the conventional method, the accumulated hydrogen can be released only to such an extent that the charge depths of the positive and negative electrodes are at the same height in each maintenance.
As the maintenance is repeated, a large amount of hydrogen that cannot be released even by the maintenance gradually accumulates. Therefore, the conventional method has a problem that the cycle life of the storage battery is short.

On the other hand, in the method of the present invention, the operating pressure of the valve is set so as not to be excessively low, and only hydrogen gas is released with almost no release of oxygen gas. Maintenance can be performed without causing a reduction in cycle life.

FIG. 2 shows, on the vertical axis, the state of changes in the battery capacity with the progress of the charging / discharging cycle after each maintenance by the method of the present invention and the conventional method.
And the number of cycles (times) on the horizontal axis. L in the figure is the time when maintenance is performed.

As shown in FIG. 2, the charge / discharge cycle after the maintenance by the method of the present invention (shown by the solid line).
In the above, since the charging is performed under the control of the positive electrode until hydrogen is accumulated in the extra capacity S described above and becomes full, the battery capacity hardly decreases. On the other hand, in the charge / discharge cycle (indicated by the broken line) after performing the maintenance by the conventional method, since there is no extra capacity S in the negative electrode after the maintenance, the subsequent charging is promptly performed from the simultaneous control immediately after the maintenance. Transition to negative electrode control. Therefore, the battery capacity decreases rapidly.

[0021]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the examples described below, and various modifications may be made without departing from the scope of the invention. Is possible.

[Battery Internal Pressure and Battery Capacity Before and After Maintenance] Square-shaped cells A1 to A8 whose appearance is shown in FIG. 3, and
Single cell A, except that it does not have a maintenance valve
A unit cell B (not shown) having the same structure as 1 to A8 was produced (rated capacity: 100 Ah). Illustrated cells A1 to A8
The positive electrode terminal 32 and the negative electrode terminal 3 on the upper surface of the battery case 31.
3, a safety valve 34 and a maintenance valve 35 are provided. The operating pressure of each safety valve 34 is 3 atm,
The operating pressure of each valve for maintenance of the unit cells A1 to A8 is as shown in Table 1.

[0023]

[Table 1]

A charging / discharging cycle test was carried out on each of these unit cells, in which one cycle includes a process of charging at 1C for 1 hour and then discharging at 1C to a discharge end voltage of 1V.
After the cycle, maintenance was performed by overcharging with a charge capacity of 150 Ah. Note that the maintenance valve 35 was not operated during the charge / discharge cycle. Among these maintenances, the maintenance of the cells A1 to A8 corresponds to the method of the present invention, and the maintenance of the cell B which substitutes the safety valve 34 as a valve for maintenance corresponds to the conventional method. Table 1 shows the battery capacity and internal pressure before and after maintenance. The internal pressure before and after maintenance was 0.
It is the internal pressure after charging at 1 C until the internal pressure reaches 3 atm and left for 1 hour. Further, the battery capacity (Ah) before and after the maintenance is the battery capacity when the battery is charged at 0.1 C to a charge end pressure of 3 atm and then discharged at 0.1 C to a discharge end voltage of 1 V.

As shown in Table 1, the unit cells A1 to A8 maintained by the method of the present invention have a lower internal pressure after the maintenance and the capacity recovery compared to the unit cells B maintained by the conventional method. Is large.

The internal pressure is low because the amount of hydrogen accumulated is small and the amount of hydrogen gas generated at the end of charging after maintenance is small. The reason for the large capacity recovery rate is as follows. That is, the depths of charge of the positive and negative electrodes are uniform after the maintenance by the conventional method. Therefore, at the end of charging, oxygen gas is generated from the positive electrode and hydrogen gas is generated from the negative electrode. As a result, the time required for the internal pressure to reach 3 atmospheres is shortened, and full charge cannot be achieved. On the other hand, in the method of the present invention, oxygen gas is similarly generated from the positive electrode at the end of charging, but since there is an extra capacity S, the amount of hydrogen gas generated from the negative electrode is small. as a result,
It takes a long time to reach the operating pressure of the safety valve 34, which is 3 atm, and more charging is performed.

[Cycle Life] With respect to the unit cells A1 to A8 and the unit cell B, a cycle test was conducted under the same conditions as above,
The cycle life was examined by repeating the maintenance of overcharging with a charge capacity of 150 Ah every 300 cycles. For comparison, the cell B was also examined for cycle life when no maintenance was performed.

The cycle life is 0.50 every 50 cycles.
After charging up to 3 atm at the end-of-charge pressure at 1 C, discharge to 0.1 V at the end-of-discharge voltage, measure the battery capacity, and evaluate the total number of cycles until the battery capacity drops to 50% of the initial capacity. did. The results are shown in Table 2.

[0029]

[Table 2]

As shown in Table 2, the unit cells A1 to A8 maintained by the method of the present invention generally have a longer cycle life than the unit cell B maintained by the conventional method.

This is because the accumulated hydrogen was released relatively favorably in each maintenance, and the accumulation rate of hydrogen, which could not be released even by the maintenance, became slow.

The short cycle life of the cells A1 and A2 having a low operating pressure of the valve 35 is due to the lack of electrolyte due to the release of oxygen gas, and the operating pressure of the valve 35 is the maintenance of the cell B. The short cycle life of the unit cell A8 close to the operating pressure of the valve (safety valve) 34 is due to the same reason as the short cycle life of the unit cell B described above. From the results shown in Table 2, the operating pressure of the valve 35 is 1.5
It can be seen that it is preferable to set the pressure to 2.5 atm.

In the above embodiment, the method of providing the maintenance valve separately from the safety valve for preventing the abnormal rise of the internal pressure of the battery during the charge / discharge cycle has been described as an example. The same excellent effect can be obtained when a low-adjusted one is used.

In the embodiments, the case where the method of the present invention is applied to the capacity recovery method of a single battery has been described as an example, but the method of the present invention is an assembled battery in which a plurality of pairs of positive and negative electrodes are connected in series. The capacity recovery method can also be applied in the same manner. FIG. 4 shows an example of this assembled battery. In the illustrated assembled battery G, a positive electrode terminal 42, a negative electrode terminal 43, a safety valve 44, and a maintenance valve 45 are provided on the upper surface of a battery case 41. Inside the battery case 41, a plurality of pairs of positive electrodes and negative electrodes (not shown) connected in series are housed.

[0035]

According to the method of the present invention, the decrease in capacity after maintenance is gentle and the maintenance interval can be lengthened. Further, by setting the operating pressure of the valve used for maintenance to a level at which oxygen gas is hardly released, it is possible to perform maintenance without shortening the cycle life due to insufficient electrolyte.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a method of the present invention, (A) is a capacity diagram of positive and negative electrodes before maintenance, and (B) is a capacity diagram of positive and negative electrodes after maintenance.

FIG. 2 is a graph showing how the battery capacity changes during a charge / discharge cycle after performing each maintenance according to the method of the present invention and the conventional method.

FIG. 3 is a perspective view of a unit cell manufactured in an example.

FIG. 4 is a perspective view of an assembled battery.

5A and 5B are explanatory views of a conventional method, in which FIG. 5A is a capacity diagram of positive and negative electrodes before maintenance, and FIG. 5B is a capacity diagram of positive and negative electrodes after maintenance.

Claims (4)

[Claims] 1. Maintenance of a stationary nickel-hydrogen storage battery, characterized in that hydrogen gas generated in a battery system is released from a valve that opens at an operating pressure lower than 3 atmospheres to overcharge while releasing the hydrogen gas to the outside of the battery system. Method. 2. The maintenance method for a stationary nickel-hydrogen storage battery according to claim 1, wherein the valve is provided separately from a safety valve for preventing an abnormal rise in battery internal pressure during charge / discharge cycles. 3. The valve has an operating pressure of 3 during a charge / discharge cycle.
The method for maintenance of a stationary nickel-hydrogen storage battery according to claim 1, wherein the operating pressure of the safety valve at atmospheric pressure or higher is adjusted to be lower than 3 atmospheric pressure. 4. The method for maintaining a stationary nickel-hydrogen storage battery according to claim 1, wherein the operating pressure of the valve is 1.5 to 2.5 atmospheric pressure.