JPS588557B2 - Positive electrode grid for lead-acid batteries - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a grid for the positive electrode of a lead-acid battery, and aims to prevent the active material from softening and falling off, which is one of the causes of the lifespan of the positive electrode, by improving the grid alloy. do.

In the past, the life of the positive electrode of a lead-acid battery was mostly due to corrosion of the lattice or softening or falling off of the active material.

For many years, lead-based alloys have been used in the grids of lead-acid batteries.

This is because the electrochemical properties and cost of lead make it suitable as a grid material.

Since lead itself has low mechanical strength, it is usually used in the form of an alloy.

For example, a Pb-Sb alloy containing 3 to 5% by weight (hereinafter simply expressed as %) of antimony Sb is one of the most commonly used alloys because it has good castability and high physical strength. .

However, when this alloy is used, Sb in the lattice is eluted and electrodeposited on the negative electrode during charging of the battery, lowering the hydrogen overvoltage of the negative electrode, increasing hydrogen gas generation from the negative electrode during charging, and self-discharge. This resulted in drawbacks such as a decrease in water content in the electrolyte, making maintenance difficult.

Other Pb-C with calcium Ca added instead of Sb
A-alloys are mainly used in small sealed batteries.

This alloy has the characteristic of low self-discharge and low moisture loss during charging, but has the disadvantage that depending on the usage conditions for charging and discharging, an insulating coating layer is formed between the lattice and the active material, making charging impossible. have.

To improve these drawbacks, Pb-Ca-tin (Sn) alloy, Pb-strontium (Sr)-aluminum (Al)-Sn alloy, or Pb-Sr-Al-
Silver (Ag) alloys and the like have been proposed.

By adjusting the content of additive elements, these can have high mechanical strength, have little effect on the negative electrode, and can be made from Pb-C.
It has excellent characteristics as a positive electrode lattice, such as not being unable to be charged unlike a-alloy.

However, it has little effect on softening and falling off of the positive electrode active material as the charge/discharge cycle progresses.

Softening and falling off of the positive electrode active material occurs when the active material becomes finer as the charge/discharge cycle progresses and the adhesion between the active materials deteriorates, especially when the active material expands and contracts during charging and discharging. It happens because of something.

Then, the active material becomes finer near the interface between the lattice and the active material, and the voltage drops with unreacted Pb02 remaining in the electrode plate, resulting in a decrease in capacity.

In the present invention, cerium Ce is added to Pb-Sr-At-Ag.
The above-mentioned disadvantages are solved by using an alloy with added .

The reason why the life of the electrode is extended by using the positive electrode grid of the present invention is considered as follows.

FIG. 1 shows a model of the interface between the positive electrode lattice and the active material, where 1 is the lattice, 2 is the active material coated on this, and 3 is the layer in which the lattice is oxidized.

4 is a lead oxide layer formed by Ce added to the lattice being eluted into the active material.

Lead dioxide, which is the positive electrode active material, becomes lead sulfate during discharge and returns to its original state when charged.

When the adhesion between the active material particles deteriorates due to such repeated charging and discharging, sulfate ions easily reach the lattice interface, and the discharge reaction proceeds faster at the lattice interface than at the electrode plate surface.

As a result, the active material particles on the lattice surface become finer, and the capacity decreases due to falling off and the like.

On the other hand, the lead oxide of layer 4 formed as described above does not participate in charge/discharge reactions, unlike the active lead dioxide formed by charging, which has a slightly lower oxygen content than the stoichiometric ratio. It is inert PbO2 and has electronic conductivity.

Therefore, it is considered that the discharge reaction can proceed from the surface of the electrode plate to the inside, and that it is possible to suppress the miniaturization of the active material due to the reaction at the lattice interface.

As already proposed, the composition of the base alloy Pb-Sr-Al-Ag used in the present invention is Sr0.07~
0.3%, Al0.05-0.1%, Ag0.05-0
．． 3% is appropriate.

If the Sr content is less than 0.07%, sufficient mechanical strength cannot be obtained, and if the Sr content is more than 0.5%, the strength will further increase, but corrosion will increase, making it unsuitable for practical use.

In terms of cost, it is preferably 0.3% or less, and about 0.1%.
Close quarters are best.

If the amount of Al is less than 0.05%, the mechanical strength will be low even if the amount of Sr is appropriate, and if the amount added is large, Al will be likely to segregate.

A value near 0.1% is most appropriate.

Ag is effective in improving the corrosion resistance of the alloy.

However, if a large amount is added, Ag will be eluted and deposited on the negative electrode when the battery is charged, and the potential of the negative electrode will move in the positive direction. Therefore, when the battery is charged at a constant voltage, oxygen gas will be easily generated from the positive electrode, and the electrolyte will be Inconveniences such as rapid decrease occur.

Moreover, if it is 0.05% or less, the effect of improving corrosion resistance becomes small.

In addition, when a battery is left in an over-discharged state like a Pb-Ca alloy, an insulating coating layer is formed on the surface of the positive electrode grid, making it impossible to charge the battery.

From the point of view of cost, about 0.1% is preferable, and this amount also provides sufficient corrosion resistance.

The appropriate amount of Ce added to the above base alloy is 0.02 to 0.2%, and if the amount is more than this, corrosion will increase.

The present invention will be explained below with reference to Examples.

First, SrO. 1%, Al0.1%, Ag0.1 to balance P
The alloy consisting of B was melted in a crucible in an argon stream, and Ce was added in various proportions to make a quinary alloy.
A lattice consisting of a middle rib 5 and an outer rib 6 as shown in Figure 3 was cast.

This grid is filled with paste by a conventional method and chemically converted to form a positive electrode plate.

On the other hand, a negative electrode plate was similarly prepared using a Pb-0.1%Ca alloy lattice.

A battery with a discharge capacity of 3 Ah at a 10 hour rate was constructed using the above two positive electrode plates and three negative electrode plates, and at 20°C.
A charge/discharge cycle of charging at 5V/cell for 8 hours and discharging to 1.8V at 3Ω/cell was repeated.

Note that the maximum charging current was 1A. Figure 4 shows the change in capacity retention rate with charging and discharging.

Curve a in the figure shows Pb-0.1%Sr-0.1% in the positive electrode grid.
The characteristics of a battery using Al-0.1%Ag alloy are shown, b
, c, d, e, f, g each contain 0.01 Ce in the alloy.
%, 0.02%, 0.1%, 0.2%, 0.3%, 0.
The characteristics of a battery using an alloy containing 5% are shown.

Next, a battery with the same configuration as above was discharged at 50Ω/cell for 7 days to reach an overdischarged state, then stored at 40°C for 15 days, and then charged at room temperature for 24 hours at a constant voltage of 2.5V. The initial capacity recovery rates were compared.

As a result, a battery using a Pb-0.1%Ca alloy for the positive electrode grid had a Pb-0.1% Ca alloy of 4% Pb-0.1%. 1%Sr-0.1%Al-0
．． 98% using 1%Ag alloy, Pb-0.1%
The percentage using the Sr-0.1%Al-0.1%Ag-0.1%Ce alloy was 92%.

The following table shows the results of measuring the transverse rupture strength of each alloy.

As is clear from FIG. 3, the Pb Sr-AL of the present invention
-Batteries using Ag-Ce alloy for the positive electrode grid have a capacity retention rate of 60-73% even after 400 cycles, but Pb
In the case of -Sr-Al-Ag alloy, the capacity retention rate deteriorates to 50% after about 240 cycles.

When this battery was disassembled, softening of the positive electrode active material was observed.

In addition, in the test for overdischarge, Pb-Sr-Al-Ag
Although it tends to be slightly inferior to alloys, it was confirmed that it does not deteriorate significantly like Pb-Ca alloys.

Further, the transverse rupture strength is not much different from that of the Pb-Sr-Al-Ag alloy, and has a value that can be used practically.

If the Ce content exceeds 0.2%, the corrosion of the lattice will be large and the service life will be shortened, and if the Ce content is less than 0.02%, the Pb
-S The superiority over the r-Al-Ag alloy is lost.

In addition, in the above example, the base alloy was Pb-0.1%S.
r-0.1%Al-0.1%Ag alloy was used, but Sr
0.07-0.3%, Al0.05-0.1%, Ag
Almost the same results as above were obtained in the range of 0.05 to 0.3%.

As described above, according to the present invention, Pb-Sr-Al-A
The charge/discharge cycle life can be greatly improved without impairing the characteristics of the g-alloy.

[Brief explanation of the drawing]

FIG. 1 is a model diagram of the vicinity of the interface between the positive electrode lattice and the active material in an example of the present invention, FIG. 2 is a front view showing the main parts of the lattice, and FIG. 3 is a sectional view taken along the line FIG. 4 shows changes in capacity retention rate during charging and discharging of batteries using various alloys in the positive electrode grid.

Claims (1)

[Claims] 1 0.07-0.3% by weight Sr, 0.05-0
．． 1% by weight Al, 0.05-0.3% by weight Ag, 0
．． A positive electrode grid for a lead-acid battery characterized by being made of an alloy consisting of 02 to 0.2% by weight of Ce and the balance Pb.