JPS60253159A - Negative plate for lead storage battery - Google Patents

Abstract

PURPOSE:To obtain a negative plate which stably maintains the performance for a long period of time without increase of self-discharge by utilizing a copper grating where a covering layer of lead or lead alloy is formed on the copper of which surface is formed by the amalgam. CONSTITUTION:Since when amalgam layer is formed on the surface of copper, a hydrogen over voltage in diluted sulfuric acid becomes excessively higher than that of copper and becomes equal or more than that of lead, generation of hydrogen gas increases even if the lead plated layer is separated or there is defective area in the copper grating and thereby self-discharge is not enhanced. As a method for obtaining amalgam on the surface of copper, for example, the copper from which surface the oxide film is removed is immersed directly into silver or an electrical power is supplied to the cathode made of copper within the solution including silver ion.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improvements in negative electrode plates for improving the performance of lead-acid batteries, and particularly relates to improvements in negative electrode plates using copper for the negative electrode grid.

Lead or a lead alloy is used for the positive and negative electrode grids of lead-acid batteries, whether they are paste type or clad type. This is because the electrochemical or chemical properties of the lead alloy, such as corrosion and acid resistance in dilute acid, are suitable for lead-acid batteries, and the mechanical strength is almost sufficient, and furthermore, it is easy and inexpensive to manufacture. This is because it has many excellent characteristics. On the other hand, the disadvantage of lead alloy grid is that the density is about 111
/-, which is quite high, and the electrical resistance is approximately 20 μΩ・cm.
It has a high value of about 12 to 13 times that of copper. Therefore, when it comes to lead-acid batteries for dolls, especially tall lead-acid batteries, the resistance of the electrode plates increases significantly.
The further away from the terminal of the electrode plate, the less likely it is to participate in the charging/discharging reaction, and the charging/discharging reaction becomes less likely. 12 had the disadvantage that performance deteriorated to a poor degree. In order to prevent this, it is necessary to use a large amount of lead alloy in the grid to reduce the voltage drop, but on the other hand, the lead-acid battery mold is extremely heavy, and the volume increases, resulting in energy efficiency (Wh /9, Wh, l) is extremely poor and is of poor practical use.

As mentioned above, copper as a lattice material has a significantly lower electrical resistance than lead, and also has a low density of about 8.9 s/CIl+, so when comparing the same weight of ants, the electrical resistance is about 1/16 that of lead.
Furthermore, when compared with the same resistance, the weight is reduced to about 1/16. Copper is also a fairly stable metal in dilute sulfuric acid, and unless it is electrochemically oxidized by anodic polarization from the immersion potential or oxidized by dissolved oxygen, it will rarely leach into the electrolyte. Therefore, it cannot be used as a positive electrode grid, but it may be fully applicable as a negative electrode grid. For this reason, attempts have been made to use copper in the negative electrode grid instead of the lead alloy, but this has not yet been put to practical use because of the problem of increased self-discharge. This is because the hydrogen overvoltage in f6@acid is significantly lower than that in lead or lead alloy, so the amount of hydrogen gas generated from the negative electrode plate increases and the accompanying discharge reaction of the active material progresses.

The present invention eliminates the above-mentioned drawbacks when copper is used for the negative electrode grid of lead-acid batteries.The gist of the present invention is to form an alloy layer on the copper surface using a metal such as mercury, which has a hydrogen overvoltage equal to or higher than that of lead. , and to form a coating layer made of lead or a lead alloy on its surface.

The hydrogen overvoltage of copper is lower than that of lead, so in order to prevent self-discharge caused by this, the conventional method is to electrodeposit lead or a lead alloy on the copper surface to prevent the copper surface from coming into direct contact with the electrolyte. There is. When the electrodeposited layer of lead or lead alloy thus formed is microscopically observed, there are many pinholes and cracks, and the layer is not non-porous. Therefore, even if such an electrodeposited layer is formed, the electrolyte will penetrate through the pores and come into contact with the copper surface, so lead plating alone is not sufficient, and it is necessary to increase the hydrogen overvoltage of the copper mine body. . As is well known, mercury is a metal with a very high hydrogen overvoltage and is liquid at room temperature. Also, when mercury is made into an alloy (amalgam) with other metals, for example, to obtain an amalgam with copper, is it possible to directly put the copper with the surface oxide layer removed and place it in mercury? If you crush the
An amalgam layer of copper and mercury can be formed on its surface. This amalgam layer with copper has a high hydrogen overvoltage in dilute acid, and becomes a spear with lead and j'i1. The figure shows lead, pure copper, and pure copper surface amalgamated samples at 1.28 (20℃).
A potential scanning diagram in dilute sulfuric acid is shown. In addition, the potential scanning range is -0.70 when polarized with reference to the mercurous sulfate electrode.
V and up to the hydrogen gas generation potential during cathodic polarization. Further, the potential scanning speed was 20 mV/sec, and the surface area of the sample was 1-. As is clear from the figure, hydrogen gas generation with pure copper becomes slightly more active when the temperature exceeds about -1.0V, whereas hydrogen gas generation on board a ship starts from about -1.4V, compared to pure copper. It can be seen that the hydrogen gas generation potential is actually as low as about 0.4V.

Since the copper surface is amalgamated and the hydrogen gas generated becomes mossy when the voltage exceeds about -1.5V, it can be seen that it has a hydrogen overvoltage equal to or higher than that of lead.

When an amalgam layer is formed on the copper surface in this way, the hydrogen overvoltage in dilute sulfuric acid becomes significantly higher than that of copper, and is equal to or higher than that of lead.
Even if the lead plating layer peels off or has defects, the generation of hydrogen gas will not increase and self-discharge will not become large.

'J J3, as a method of amalgamating the copper surface,
In addition to the method described above, it is also possible to use a method in which -C current is applied using copper as a cathode in a solution containing mercury ions.

As detailed above, the negative electrode plate for lead-acid batteries according to the present invention is
It is characterized by the use of a copper lattice with an amalgamated surface and a coating layer of lead or lead alloy formed on the copper, thereby stabilizing the performance of the negative electrode plate over a long period of time without increasing self-discharge. It has the excellent advantage of being able to be maintained.

[Brief explanation of drawings]

The figure shows the potential-current curves obtained when the potential generated by hydrogen gas on each scale metal was investigated using the potential scanning method.

Claims (1)

[Claims] A negative electrode plate for a paste-type lead-acid battery using a copper grid, characterized in that a coating layer made of lead or a lead alloy is formed on the surface of amalgamated copper.