JP2014110184A - Nickel hydrogen battery and capacitance recovery method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to effectively and efficiently recover a nickel hydrogen battery whose capacitance is reduced by accumulation of hydrogen to a negative electrode.SOLUTION: The capacitance recovery method of a nickel hydrogen battery includes: executing a first step for providing a third electrode 4 capable of selectively energizing one of a positive electrode 2 and a negative electrode 3, and energizing between the third electrode 4 and the positive electrode 2, in order to charge the positive electrode 2; and then, preparing for ordinary charging by executing a second step for discharging between the positive electrode 2 and negative electrode 3 and performing a recovery treatment of the nickel hydrogen battery.

Description

  The present invention relates to a nickel metal hydride battery that can be repeatedly charged and discharged and a capacity recovery method thereof.

The nickel metal hydride battery is a battery using a hydrogen storage alloy for the negative electrode and nickel hydroxide for the positive electrode. Nickel-metal hydride batteries are known to have a reduced discharge voltage and reduced capacity due to long-term use, and the cause of deterioration is irreversible, such as elution of an active material hydrogen storage alloy into the electrolyte, There is a reversible one such as a deviation in capacity balance between the positive electrode and the negative electrode.
The deviation in capacity balance between the positive electrode and the negative electrode is caused by the fact that oxygen generated from the positive electrode during charging does not recombine with hydrogen in the negative electrode and is consumed in the oxidation of the separator and the negative electrode active material. As a result, the positive electrode is prevented from being charged. Usually, the nickel-metal hydride battery has a positive electrode-regulated cell configuration in which the negative electrode capacity is larger than the positive electrode capacity, so that hydrogen accumulated excessively on the negative electrode cannot be removed by normal charge and discharge.

  Patent Document 1 proposes a method of charging and discharging a plurality of negative electrodes individually connected to the positive electrode as means for releasing hydrogen accumulated in the negative electrode. Normally, the positive electrode capacity is greater than the negative electrode capacity, but the negative electrode is connected to the positive electrode individually to create a negative electrode cell structure, and charging and discharging it completely removes hydrogen from the negative electrode. It becomes possible to remove.

JP-A-7-78636

  However, the recovery method proposed in Patent Document 1 can be applied only to a cell having a structure in which a plurality of negative electrodes can be electrically separated one by one, and when the number of negative electrodes increases, the time required for the recovery process There is a problem that increases.

  The present invention has been made to solve the above-described problems, and aims to recover a nickel-metal hydride battery having a reduced discharge capacity. Further, the present invention can also recover a nickel-metal hydride battery comprising a single negative electrode. To provide a nickel-metal hydride battery and a nickel-metal hydride battery capacity recovery method capable of effectively performing the treatment and shortening the time required for the treatment by performing a recovery process in which charging and discharging are each performed at least once. Objective.

  That is, the nickel-metal hydride battery of the present invention is characterized by having a positive electrode and a negative electrode, and a third electrode for capacity recovery capable of selectively energizing one of the positive electrode and the negative electrode.

Furthermore, the capacity recovery method of the nickel metal hydride battery of the second aspect of the present invention is the capacity recovery method of a nickel metal hydride battery comprising a positive electrode and a negative electrode.
Excluding the negative electrode, conducting a first step of charging only the positive electrode by energizing only the positive electrode, followed by a second step of discharging between the positive electrode and the negative electrode It is characterized by.

  According to a third aspect of the present invention, there is provided a method for recovering the capacity of a nickel-metal hydride battery, wherein a third electrode capable of selectively energizing one of the positive electrode and the negative electrode is provided, and energization is performed between the third electrode and the positive electrode. And performing the first step of charging the positive electrode, and then performing the second step of discharging between the positive electrode and the negative electrode.

  According to a fourth aspect of the present invention, there is provided the method for recovering the capacity of a nickel metal hydride battery according to the second or third aspect of the invention, wherein in the first step, the charge capacity to the positive electrode exceeds 50% of the total capacity of the battery. Features.

  According to a fifth aspect of the present invention, there is provided a method for recovering the capacity of a nickel-metal hydride battery, wherein, in any one of the second to fourth aspects of the invention, after the second step, a current is applied between the positive electrode and the negative electrode. A charging step is performed.

  This invention is particularly suitable for discharging the hydrogen accumulated in the negative electrode in order to recover a nickel metal hydride battery that has deteriorated due to the float holding, and after charging only the positive electrode, the surplus hydrogen in the negative electrode is discharged to hold the float. The potential balance between the positive electrode and the negative electrode can be restored to the original, and the charging rate of the positive electrode can be increased.

  When charging the positive electrode in the first step, a third electrode other than the positive electrode and the negative electrode can be used. The third electrode may be always provided in the cell of the nickel metal hydride battery, or may be installed in the cell or the like when performing the process. In short, it is only necessary to charge the positive electrode without charging the negative electrode without charging the negative electrode. If the third electrode can act as a counter electrode for charging the positive electrode, there is no particular limitation on the size thereof. The material may be any material that has conductivity and maintains activity in a strong alkaline electrolyte.

  The capacity when charging the positive electrode in the first step is desirably 50% or more of the total capacity of the positive electrode, and more desirably 80% or less. If the amount of charge to the positive electrode is too small, the negative electrode cannot be fully discharged when it is subsequently connected to the negative electrode, and a sufficient recovery effect cannot be obtained. On the other hand, if the charge capacity to the positive electrode is in the range of more than 80% and 100%, the charge loss increases. This is because the higher the charging rate of the positive electrode, the more easily the charging current is consumed by other reactions such as the generation of oxygen in the positive electrode, resulting in poor efficiency. Therefore, the range of 50% to 80% is appropriate as the amount of charge to the positive electrode in the first step.

  In the second step, discharge corresponding to the amount of charge in the first step can be performed, and thereby hydrogen remaining in the negative electrode can be reliably reduced. Since a normal nickel metal hydride battery has a large negative electrode capacity and a positive electrode regulation configuration, a series of processes including the first step and the second step may be repeated. However, when the series of charge / discharge is completed, if the positive electrode remains undischarged, the capacity balance between the positive electrode and the negative electrode shifts. Therefore, in the above charge / discharge, the positive electrode side is completely discharged, and the positive electrode capacity is 10%. The following is desirable.

  After the recovery process, normal charging can be performed to prepare for use as a nickel metal hydride battery. The recovery process can be performed periodically to recover the nickel metal hydride battery, or the recovery process may be performed in accordance with a change in the charge capacity.

  As described above, according to the present invention, the hydrogen accumulated in the negative electrode can be released, the balance between the positive electrode and the negative electrode can be restored, and the capacity of the nickel-metal hydride battery can be recovered. Moreover, there is an effect that the time required for the recovery process can be made relatively short.

It is a figure which shows the electrode structure of the nickel metal hydride battery of one Embodiment of this invention. It is a figure which shows the electrode structure in the conventional nickel metal hydride battery, and the hydrogen residual state in a negative electrode.

Below, the nickel metal hydride battery 1 of one Embodiment of this invention is demonstrated.
The nickel metal hydride battery 1 has the electrode configuration shown in FIG. That is, it has a positive electrode 2 and a negative electrode 3 that are used during normal discharge, and further has a third electrode 4. The third electrode 4 may be always provided in the cell, or may be arranged in the cell in preparation for the recovery process. Each electrode has a positive electrode terminal 2a, a negative electrode terminal 3a, and a third electrode terminal 4a.

The cell structure of the nickel metal hydride battery 1 is not particularly limited, and can be applied to various cell structures. In particular, it is suitable for a battery in which the negative electrode is connected to one current collector and cannot be electrically decomposed, or a battery having a space in which the third electrode can be mounted.
Also, the materials of the positive electrode and the negative electrode constituting the electrode are not particularly limited as the present invention, and known materials can be used. The third electrode is not limited to a specific material as long as it has conductivity and is active in the electrolytic solution. As the nickel metal hydride battery 1, a battery that is float-maintained is suitable.

FIG. 2 shows an electrode structure in a conventional nickel metal hydride battery 10, which includes a positive electrode 2 and a negative electrode 3, and each electrode is provided with a positive electrode terminal 2 a and a negative electrode terminal 3 a.
In the nickel metal hydride battery 10, hydrogen accumulates in the negative electrode 3 due to repeated charge and discharge, and residual hydrogen 30 remains in the negative electrode 3 even after the positive electrode is completely discharged. For this reason, the negative electrode 3 can be charged in accordance with the remaining hydrogen storage capacity 31. If this charge amount is smaller than the positive electrode chargeable amount, the negative electrode is regulated and sufficient charge capacity cannot be obtained. .

In the present embodiment, after the third electrode 4 is arranged in the nickel hydrogen battery 1 in which hydrogen is stored in this way, the positive electrode terminal 2a of the positive electrode 2 and the third electrode terminal 4a of the third electrode are provided. A first step of connecting to the external power source 5 and charging the positive electrode 2 is performed. When the nickel metal hydride battery 1 is in the float holding state, the charging of the positive electrode 2 and the negative electrode 3 is interrupted, and the first and subsequent steps are performed.
The charging in the first step is desirably performed until it exceeds 50% of the total capacity of the battery, and it is desirable to complete the charging at a stage not exceeding 80%.

  The positive electrode is sufficiently charged by the first step. Next, the positive electrode terminal 2a and the third electrode terminal 4a are disconnected, the positive electrode terminal 2a and the negative electrode terminal 3a are connected via the load 6, and a second step of discharging is performed. This discharge consumes residual hydrogen 30 in an amount commensurate with the charge capacity of the positive electrode and reduces it to residual hydrogen 32. As a result, the hydrogen storable amount 33 is sufficient to charge the positive electrode, and charging can be performed with positive electrode regulation.

  After that, an external power source can be connected between the positive electrode terminal 2a and the negative electrode terminal 3a to perform charging according to positive electrode regulation, and the capacity of the nickel metal hydride battery 1 is effectively recovered.

An embodiment of the present invention will be described below.
In a nickel metal hydride battery, the capacity of the negative electrode and the positive electrode was incorporated in the electrochemical cell so that the capacity was about 3: 1, and the capacity of the positive electrode was the capacity of the cell. Further, a short circuit was prevented between the positive electrode and the negative electrode through a separator having a thickness of about 0.2 mm.

  The cell was floated at 40 ° C. and a voltage of 1.4 V for 40 weeks after activation. During this time, discharge was performed at 0.2 C every two weeks, and the change in capacity was traced. The capacity monotonously decreased while the float was held, and the capacity was about 2000 mAh in the initial stage of the float, but about 1300 mAh in the discharge at 40 weeks. Decreased to. When the negative electrode potential after the discharge was confirmed, about 60% of the total capacity of hydrogen remained in the negative electrode even at the end of the discharge.

  20 mm × 20 mm × 0.8 mm thick porous nickel was inserted into this cell, connected to the positive electrode, and the positive electrode was charged with a current of 50 mA for 30 hours. Thereafter, the positive electrode and the negative electrode were connected and discharged at a current of 366 mAh. The discharge for 2 hours could be performed, and thereby the residual hydrogen of the negative electrode could be made zero.

Thereafter, when the capacity was confirmed by performing float holding at 40 ° C. for 2 weeks, the discharge capacity before the recovery process was restored to 1415 mAh, which was 1279 mAh.
As a comparative example, a change in capacity in a cell where no recovery process is performed is shown. The cell of the comparative example was also maintained at 40 ° C. for about 40 weeks, and the discharge capacity decreased from about 2000 mAh to 1435 mAh during this period. The capacity decreased from 1305 mAh to 1230 mAh when the float process was continued for 2 weeks without performing the recovery process.

  In this example, the capacity drop due to the 40 ° C. × 40 week float retention has not been fully recovered, but this is caused by deterioration factors other than potential balance (accumulation due to oxidation of the positive and negative electrode binders) by a high temperature deterioration acceleration test. This is due to a decrease in adherence and large elution of the negative electrode alloy component. The discharge capacity can be maintained by carrying out the recovery process of the present invention at an appropriate period at room temperature.

DESCRIPTION OF SYMBOLS 1 Nickel metal hydride battery 2 Positive electrode 2a Positive electrode terminal 3 Negative electrode 3a Negative electrode terminal 4 3rd electrode 4a 3rd electrode terminal 30 Residual hydrogen 31 Hydrogen storage capacity 32 Residual hydrogen 33 Hydrogen storage capacity

Claims (5)

  A nickel-metal hydride battery comprising: a positive electrode and a negative electrode; and a third electrode for capacity recovery capable of selectively energizing one of the positive electrode and the negative electrode. In a method for recovering the capacity of a nickel metal hydride battery comprising a positive electrode and a negative electrode,
Excluding the negative electrode, conducting a first step of charging only the positive electrode by energizing only the positive electrode, followed by a second step of discharging between the positive electrode and the negative electrode A method for recovering the capacity of a nickel-metal hydride battery.   A third electrode capable of selectively energizing one of the positive electrode and the negative electrode is provided, and the first step of charging the positive electrode by energizing between the third electrode and the positive electrode is performed. Then, a capacity recovery method for a nickel-metal hydride battery, comprising performing a second step of discharging between the positive electrode and the negative electrode.   The method for recovering the capacity of a nickel-metal hydride battery according to claim 2 or 3, wherein the charge capacity of the positive electrode in the first step exceeds 50% of the total capacity of the battery.   5. The method for recovering the capacity of a nickel-metal hydride battery according to claim 2, wherein after the second step, a normal charging step is performed by energizing the positive electrode and the negative electrode.

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