JPS6322013B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the manufacturing method of electrode plates for lead-acid batteries, and in particular aims to improve the life characteristics of charge-discharge cycles including deep discharge.

There are many possible causes of capacity deterioration in lead-acid batteries. Among these, the most commonly thought of is the miniaturization and softening of the active material due to charge/discharge cycles. However, if deep discharge is repeated,
Capacity deterioration may occur before the long-term cycle in which this softening and shedding occurs. This is caused by the adhesion between the active material and the lattice. This phenomenon is more noticeable in lead-calcium alloy grids, which have been widely used in response to the recent demand for maintenance-free grids.

The present invention suppresses capacity deterioration in relatively early cycles in a pattern including this deep discharge.

That is, in general, an unformed plate is electrolyzed in dilute sulfuric acid to be chemically formed into an electrode plate having an active material capable of an electromotive reaction, but the present invention provides, prior to this chemical formation step,
It is characterized by including the step of anodizing the unformed plate in water that does not substantially contain electrolyte other than the dissolved matter eluted from the electrode plate.

Lead oxide, lead, and lead sulfate are present in the electrode plates. Lead and lead oxide turn into lead hydroxide at least in water, and have extremely low solubility of about 12 mg/kg at room temperature, and lead sulfate has a very small solubility of about 43 mg/kg/kg. It also has negligible solubility. In other words, water in which no electrolyte is dissolved other than these unavoidable dissolved substances is used as a medium for the electrochemical reaction. In the case of a very small amount of solution as described above, the impedance of ion conduction becomes extremely high, unlike when an electrolyte is added. Therefore, even when polarized, almost no current flows, and even if a voltage of 100V is applied, the current that flows hardly exceeds several milliamperes (around dm ² ). In such a situation, even if polarization is applied to form the electrode plate, the active material will not be formed, and even if it is done, it will take a very long time. In other words, the present invention means that polarization treatment is performed not from the viewpoint of conventional chemical conversion but from the viewpoint of modifying the electrode plate.

The deterioration of the battery targeted here is mainly on the positive electrode side, and when deep discharge is repeated in highly concentrated sulfuric acid, the impedance between the current collector (lead alloy) of this positive electrode plate and the active material increases. to degrade. This phenomenon is
The parts of the alloy surface that do not come into contact with the active material and are exposed in the space of the porous layer are oxidized and reduced, sometimes peeling off, and eventually reach the part of the alloy surface that is in contact with the active material, increasing impedance. It seems that it will.

On the other hand, when the electrode plate is anodically polarized in advance under conditions virtually equivalent to water according to the present invention, this deterioration is significantly suppressed. The reason for this is not yet fully understood, but the surface layer of the current collector that is oxidized in a mostly water state has a different crystal structure than the layer that is oxidized under electrolyte-rich conditions, especially in solutions containing sulfuric acid. Of course, it is expected that the situation will be the same. This oxidized layer seems to have the property of being less likely to peel or crack when oxidized in sulfuric acid. Therefore, it seems to have the effect of suppressing the rapid growth of a passive portion in the vicinity of the layer where the active material and the current collector are in contact.

The advantage of the present invention is that it provides the effect of protecting the exposed surface of the current collector as described above, but at this time, water does not enter the contact area of the active material, so there is a gap between the current collector and the active material. There is no danger of inhibiting conduction, and since the unformed board is extremely close to passivity and almost no current flows during electrolysis, there is no ability to chemically transform the unformed board. Therefore, regarding changes in the active material during subsequent chemical formation in dilute sulfuric acid,
There is little risk of any major impact.

Although the water used here is generally allowed to contain impurities to the extent used in conventional battery manufacturing, it is preferable to use ion-exchanged water or the like.

Whether it is processed in an electrolytic bath or incorporated into a battery as a pre-treatment for forming a battery into a battery, if the unformed board is immersed in water, it will be extremely difficult to leave it for some time. Trace amounts of compounds dissolve,
Helps move charges.

The surface area of the positive electrode current collector per cell is several tens of Ah.
For a battery of (5 to 10) x 10 ⁵ mm ² , assuming that the current collector is pure lead, and calculating from the atomic radius of lead of 1.75 Å, the number of atoms on the surface is (5 to 10) x 10 ¹⁸ , The number of atomic equivalents is approximately (1-2) x 10 ^-5 , and 0.5-1 mAh is sufficient to oxidize this one atomic layer. In reality, the proportion exposed within the void is much smaller than this. Therefore, the time for this anodic polarization treatment is assumed to be 5
If mA flows, more than one atomic layer will be oxidized in about 5 to 10 minutes or less. In reality, oxides in water are dense and have high resistance, and when oxidation begins, the current drops rapidly. A decrease in current means that there are fewer elements to be oxidized, so this decrease in current can be used as an indicator for management purposes. As mentioned above, the internal impedance of this type of electrolytic anodic polarization process is extremely high. Therefore, in order to speed up the time, several volts or more, if necessary, about 100 volts may be applied to the opposite electrode. The fact that there is almost no increase in current at this time may be due to the semiconductor nature of the surface oxide layer.

Hereinafter, the features and effects of the present invention will be described with reference to Examples.

A paste-type lead-acid battery electrode plate, in which a paste was applied to a lead-calcium-tin expanded grid using a conventional method, was housed in a battery case via a separator, and a battery with a nominal capacity of about 50 Ah was prototyped. Water is added to this until the electrode plate is submerged in water, and the positive electrode plate is anodically polarized. At this time, if it is desired to form a thick oxide film on the current collector, alternating current can be superimposed or polarity reversal can be repeated. In any case, it is best to end the process in an anodic polarized state, which should be selected in consideration of the characteristics and the required man-hours.

In this example, for positive polarization, the applied voltage with the opposite electrode is
25V/cell was used. The current initially flowed approximately 5 mA and gradually decreased. After the voltage decreased to about 100 μA, the water inside was released. There is no problem in drying this if necessary. Next, dilute sulfuric acid was added to adjust the specific gravity to 1.95 to 2.20, and formation charging was carried out for 40 to 50 hours at a current of 10 hours or less as in normal formation.

Battery A obtained as described above and battery B which was chemically formed directly from an unformed plate in dilute sulfuric acid without applying the present invention were subjected to slow discharge in which discharge was performed at a rate of 5 hours to a final voltage of 1.5V, and battery B which was chemically formed directly from an unformed plate in dilute sulfuric acid without applying the present invention. We investigated how the capacity was maintained when the battery was repeatedly charged with an amount of electricity equivalent to 120% of the nominal capacity. The results are shown in FIG.

As is clear from this figure, in A of the present invention, initial deterioration is more likely to occur in B.
It can be seen that this has been significantly improved. Moreover, the discharge characteristics are not particularly affected, at least initially.

Next, Figure 2 shows the capacity retention rate at the 20th cycle when polarization was performed by varying the applied voltage and electrolysis time. Of course, it is not inconvenient to take more time than this. Note that all batteries to which the present invention was not applied deteriorated between 10 and 20 cycles, so they are not shown in the figure. These results can be roughly classified into the range of applied voltage R of 2V or less, applied voltage Q of 2 to 5V, and applied voltage P of 5V or more, with some variation.

These trends indicate that even a small amount of treatment has an anodic polarization effect in water. Furthermore, when the applied voltage is low, it seems more effective to lengthen the time to some extent. Furthermore, it is shown that when the applied voltage is several volts or more, it is not affected by time very much and is not easily affected by the applied voltage. These phenomena include that the initial current for electrolysis rises rapidly at a voltage of several V or more, that the initial current does not increase much even if the applied voltage is changed further, that the current decreases as oxidation progresses, and that the current decreases at low applied voltages. This seems to be in good agreement with the fact that it takes time to oxidize the small, exposed monoatomic layer of the alloy.

As described above, the treatment of the present invention particularly suppresses deterioration caused by deep discharge, and is effective in increasing the reliability of lead-acid batteries.

[Brief explanation of the drawing]

FIG. 1 is a graph showing changes in discharge time during charging and discharging of a battery according to the present invention and a battery of a comparative example, and FIG. 2 is a graph showing the relationship between the applied voltage and electrolysis time in the anodic polarization step and the capacity retention rate.

Claims (1)

[Claims] 1. Includes the step of anodizing the unformed board in water that does not substantially contain an electrolyte other than the dissolved compound contained in the unformed board, and then the step of chemically converting the unformed board in dilute sulfuric acid. A method for producing electrode plates for lead-acid batteries characterized by: