JPS6048870B2 - Manufacturing method for lead-acid battery electrode substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Conventionally, electrode plate substrates for lead-acid batteries have been made of binary or ternary lead alloys containing lead as a main ingredient and a small amount of one or more of antimony, tin, arsenic, and calcium. Generally, this material is melted and cast into a lattice shape, but elongation decreases over time after casting.

For example, if this lattice substrate is filled with an active material and used as an electrode plate, and when it is incorporated into a battery, over time, the elongation of the material of the four circumferential ribs and the vertical and horizontal small bones that make up the lattice substrate decreases. . For example, if a piece is left at room temperature for one day after casting, it will elongate by several percent, but if it is left for 10 days, the elongation will drop to less than 1%. Therefore, the elongation of the grid substrate of the electrode plate incorporated in the battery usually shows a very small value of 1% or less12-1.
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The elongation rate (%) of the string is x100 in Table 1.The measurement is as follows: For example, the height of the electrode plate substrate before charging and discharging is measured with a caliper, and the grid is measured by repeating charging and discharging. After the bone was fractured, the height dimension 10 at the same location was measured, and the elongation (%) of the substrate was determined from the above formula.

When a battery is constructed of electrode plates in which a lattice substrate exhibiting such a small elongation is used, the life of the battery is shortened for the following reasons. That is, during use of the battery, stress due to volumetric expansion due to charging and discharging of the active material filled in the lattice substrate acts on the lattice bones. Stress accompanying the growth of an oxide layer generated on the surface of the lattice bones by repeated one-way charging and discharging acts on the lattice bones.

In reality, the combination of these two stresses acts on the lattice bones, but as mentioned above, the elongation of the lattice bones is extremely small, so this combined stress causes them to mechanically break.
In addition, the grain boundaries and eutectic portions of the lattice bones undergo so-called stress corrosion and are further fractured. Thus, premature rupture of the lattice bones results in shedding of the active material, and if rupture occurs in the outer framework bones,
The electrode plates can cause short circuits, which can damage the battery and shorten its lifespan.

The present invention provides a lead-acid battery electrode substrate that significantly improves the problem of active material falling off due to fracture of lattice bones due to stress corrosion etc., since the elongation rate of lead metal is as small as about 1 to 2%. The material is made of a lead alloy that does not contain calcium, and is cast onto a lattice substrate for 5 to 7 seconds at room temperature.
It is characterized by being subjected to heat softening treatment after being left for a day. The heat softening treatment is a treatment in which the temperature of the substrate is raised by heating, and the temperature is maintained for a predetermined time at a temperature above which the hardness of the metal suddenly decreases, that is, the metal becomes soft. Thus, it was confirmed that the substrate of the present invention, once subjected to heat softening treatment, maintains a mechanical elongation of 4% or more throughout the normal use period of the battery, and provides an electrode in which the above-mentioned conventional disadvantages are significantly reduced.

The heat softening treatment can be arbitrary, such as radiation heating, current heating, high frequency heating, etc., and it is sufficient to soften the lead alloy to be treated at a temperature below its melting point. In particular, once it is in a semi-softened state, 4% as the final substrate is used. By using the softening treatment condition of heating 50 to 7 powder at preferably 130°C or higher, it is possible to obtain a substrate with a high elongation economically, and it is possible to obtain a substrate with a high elongation while being used as an electrode. Both can have an elongation of 3%.

As will become clear in the examples below, when the softening treatment J is performed immediately after casting the substrate, a substrate that maintains an elongation rate of 4% or more cannot be obtained.

It has been found that in order to increase the elongation of a calcium-free lead alloy cast grid substrate to 4% or more, the heat softening treatment must be carried out after the substrate is left at room temperature for 5 to 7 days after casting. Example 1. Using a Pb-4.0%Sb alloy containing trace amounts of As and Sn, a grid substrate for an automobile battery electrode was cast by a conventional method, and after being left at room temperature for 5 days after casting, the elongation was 0.5 to 1.0%. A softening process is performed on the substrate with an indentation heating at 170°C.
A substrate of the present invention having an elongation of 5% was obtained.

This substrate was used as an electrode plate filled with an active material, and a battery was assembled using this and a life test was performed for up to 300 cycles.The number of fractures in the outer frame bone and the active material falling rate were measured for the anode plate. . The results per sheet are shown in Table 1 below. For comparison, a conventional substrate having an elongation of 0.5 to 1.0% without softening treatment was similarly filled with an active material and used as an electrode, and a battery assembled using this was similarly tested and measured. the result. are also listed in the same table. Furthermore, for comparison, the elongation rate of the lattice substrate after the casting was immediately subjected to a softening treatment by minute heating at 170 DEG C. was 2.5 to 3.5%.

After assembling a battery using this and carrying out a life test for up to 300 cycles, the number of fractures of the outer frame ribs measured per anode plate was 21, and the falling off rate was 11.5%. The elongation rate of the substrate after 180 days was 1.5~
It dropped to 2%. On the other hand, the group treated with this method maintained the initial growth rate of 4 to 5% even after 180 days. Example 2. A grid substrate was cast using a Pb-2.5%Sb alloy by a conventional method, and the elongation after being left at room temperature for 7 days was 1 to 1.5.
% was subjected to a softening treatment by heating at 150° C. for 60 minutes to obtain a substrate of the present invention having an elongation of 5 to 6%.

This substrate was filled with an active material to form an electrode plate, a battery was assembled using this, and the same test as in Example 1 was conducted. The measurement results are shown in Table 2 below. A battery was made using a conventional unsoftened substrate with an elongation of 1 to 1.5%, and a comparative test was conducted.
The results shown in the table were obtained. For comparison, the lattice substrate after casting was immediately subjected to a softening treatment by heating at 150 DEG C. for 6 minutes, and the elongation rate was 3.5 to 4.5%.

After assembling a battery using this and conducting the same test as in Example 1, the number of fractures of the outer frame measured per anode plate was 1.2, and the dropout rate was 10.5%. . The elongation rate of the substrate after 180 days was 2.5% to 3%%.
It declined to . On the other hand, the substrate treated with this method maintained its initial growth rate of 5 to 6% even after 180 days. As described above, according to the present invention, a grid substrate made of a lead alloy that does not contain calcium is cast and then left at room temperature for 5 to 7 days and then subjected to heat softening treatment. A substrate that maintains an elongation rate of 4% or more, which cannot be obtained with this kind of lead alloy substrate that is treated immediately after casting, can be obtained, and can be used as a battery electrode plate, and the rupture of the lattice bones and falling out of the active material can be significantly reduced. It has the effect of allowing

Claims (1)

[Claims] 1. A method for producing a lead-acid battery electrode substrate, which comprises casting a lattice substrate made of a lead alloy that does not contain calcium, leaving it at room temperature for 5 to 7 days, and then subjecting it to a heat softening treatment.