JPS5948945B2 - Alloy for lead-acid battery grid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a plate grid alloy that reduces self-discharge and improves overdischarge cycle life of lead-acid batteries.

The main lead alloys conventionally used for lead-acid battery electrode grids are Pb-Sb alloys (mainly Pb-Sb-A fed).
and a Pb-Ca based alloy.

Pb-Sb alloys have good mechanical properties and are relatively good in workability and stress corrosion. Therefore, this Pb-Sb alloy is most commonly used, but since the hydrogen overvoltage of Sb is small, self-discharge is large, and water in the electrolyte is easy to electrolyze during charging, so the liquid volume decreases quickly. The drawback was poor charging efficiency. Pb-Ca alloys were developed to improve these drawbacks, but this alloy has low self-discharge and good charging efficiency, but when deep discharge is performed, that is, when the end-of-discharge voltage is extremely low. The cycle life of the battery becomes extremely short, and furthermore, it becomes difficult to charge the battery after being left in a discharged state, making it difficult to obtain the desired capacity. Therefore, for practical use, the end-of-discharge voltage must be controlled during discharge, so although the price of the battery itself is not much different from batteries using Pb-Sb alloys, a charger and a device to control the end-of-discharge voltage are required. Batteries using Pb-Ca alloys had the disadvantage that they were much more expensive as a power source, including battery costs. The most important conditions necessary for a lead-acid battery electrode grid are that it has electrical conductivity and is excellent in stress corrosion.

In other words, when an active material raw material is applied and held on a lattice, the active material raw material expands and contracts in volume due to charging and discharging, so it is necessary to withstand this mechanical shock, and it is also necessary that the lattice is not destroyed by corrosion. In addition, if the mechanical strength is low, the workability is also low.A good mechanical strength is first of all weight, so several alloys have been proposed in the past, but none have been put into practical use. was only based on the two types of alloys mentioned above.

As a result of various studies on lead alloys to improve mechanical strength, it was discovered that Pb-Sn-Cd based alloys are superior, and the present invention develops this alloy to reduce self-discharge and improve overdischarge cycle life. This alloy is provided as an alloy for grids.

The alloy of the present invention contains 5n0.3-3.0% by weight, Cd0.
1-1.0% by weight, and A10.01-0.1% by weight
, Zn0.05-0.5% by weight, Ce0.005-0.
1% by weight of one type of lead is made of two or more types, the balance being lead.

Examples of the present invention will be described in detail below.

Pure Pb was heated to about 550°C in an Ar gas atmosphere, melted, and alloyed by adding Sn and aluminum in the proportions shown in Table 1, and molded at about 180°C with a width of 20 mm, a length of 100 mm, and a thickness of 2 mm. After casting into a plate shape, the sample was cooled in the atmosphere.

Transverse rupture strength, which is one of the mechanical properties, was measured for these samples. The reason for measuring the transverse rupture strength is that it is thought that the lattice in an actual electrode plate is not only subjected to tensile stress due to expansion of the active material, but also to bending stress. An example is shown in Table 1. Table 1 also shows the results of a bending test using another sample to evaluate the ease of bending the sample. The reason for conducting the bending test was because some samples were bent and some were broken during transverse rupture strength measurement. The bending test method is to fix sample 1 to jig 2 as shown in the figure,
The end portion of the sample was bent at right angles to the left and right, and the measurement was performed by the number of times the sample was cut. In addition, sample 1 was fixed to jig 2, bent at right angles, turned 180 degrees, and then bent 90 degrees in the opposite direction.
The number of bending operations was defined as one bending operation.

Practically speaking, the transverse rupture strength should be 500 kg/CTn2 or more, and from Table 1, the transverse rupture strength is SnO. 3wt% or more, Cd
O. It can be seen that the case of 1wt% or more is large.

In addition, the number of breaks decreases as the amount of u added increases, and
It can be seen that even if the amount of n increases, it has almost no effect. The transverse rupture strength has a tendency opposite to this tendency of the number of breaks, and in order to increase the transverse rupture strength, α must be increased, and as the amount of Cd increases, the number of breaks decreases, which means it becomes brittle. I understand. Next, to improve the brittleness of this alloy, Pb
-As a result of adding several metals as the fourth element to the Sn-Cd alloy, Al. Zn. It has been found that Ce may have an effect. This will be explained below.
The base alloys were selected from those shown in Table 1, with a focus on those with a low number of breaks and high mechanical strength. That is, Sn3. Owt%-Cd3. Owt
%-Pb,. Sna. 3wt%-Cdl. Owt%1P
b, Sn3. Owt%-Cdl. Owt%-Pb were selected and AIO. OO5, 0.0L0.05, 0.
1, 0.3 wt%, ZnO. OLO. O3, 0.05,
0.1, 0.3, 0.5, 1.0 wt%, CeO. OO
3, 0.005, 0.0L0.03, 0.05, 0.1
, 0.3 wt% was added, and the transverse rupture strength and the number of bending cuts were measured, and an example of the results is shown in Table 2. As is clear from Table 2, Al is effective in bending and cutting at 0.01 Wt% or more, and Zn is 0.05 Wt% or more.
It was found that 0.005 wt% or more of Ce is effective. It was also found that 0.3 wt% or more of Al was not alloyed but separated, and the number of bending and cutting in the conventional material was about 16. Next, we will examine the performance of these alloys when applied to actual batteries, and only representative examples will be shown below.

In the case of alloy composition, Pb-Sn-α alloy has SnO. lW
t%-CdO. lwt%-Pb. Sn3. Owt%-C
d3. Owt%-Pb,. sn3. OWt%-CdO.
lwt%-Pb. Sn3. Owt%-Cdl. Owt%
-Pb. SnO. 3wt%-Cdl. OWt%-Pb,
．． sn5. OWt%-Cd5. Regarding Owt%-Pb, in the case of a quaternary alloy, the base alloy is Sn3. Owt%
-Cdl. A battery using Owt%-Pb alloy is shown. These compositions were melted in an Ar gas atmosphere and
A 25 x 36 mm lattice with a normal structure was cast in a mold kept at about 180°C, and active material raw materials were applied to this lattice using a normal method, dried, and chemically formed to form an electrode plate. .

Next, regarding these electrode plates, there are 4 anode plates and 5 cathode plates.
A battery was constructed using H2SO4 with a specific gravity of 1.28 as an electrolytic solution. Charge these batteries at 240mA for 15 hours and
The initial capacity was confirmed by discharging at 80 mA. As a result, the initial capacity was found to be approximately constant, approximately 2.4 Ah, regardless of the alloy composition. Some of these batteries are intended for self-discharge, and the capacity is checked by leaving them in a charged state in an atmosphere at 40°C for 1 month and 3 months, then fully charging them, checking the capacity again, and checking the capacity before and after discharge. The capacity i in the fully charged state of
The ratio of the capacity after being left to the average value was determined and evaluated as the capacity retention rate. Table 3 shows the value obtained by subtracting the capacity retention rate from 100%, that is, the self-discharge rate.

Next, use another battery and charge it at 240mA for 16 hours at 5Ω/
A cycle life test was conducted with 8 hours of cell discharge as one cycle.

In this recital test, it was confirmed that the battery voltage after discharging at 5Ω/cell for 8 hours was approximately 0.3V, indicating a very deep discharge (overdischarge). The lifespan was evaluated at a cycle that reached 1/2 of the initial discharge duration. For reference, Pb-Sb5. O-AsO. 3 alloy, and the performance of the battery using Pb-CaO. Table 3 also shows the results of similar tests conducted on the performance of batteries using the L alloy.
In Table 3, Cd3. Owt% or more of an alloy, and a battery using Sn5. As for the battery using the OWt% alloy, when the battery was disassembled after the end of its life, it was found that the life was short-circuited.

In addition, in a quaternary alloy system, when Al exceeds 0.3 wt%, it does not alloy and the transverse rupture strength weakens, causing lattice destruction and reaching the end of its life.
% or more, especially 1.0 Wt% or more, corrosion was so severe that most of the lattice was corroded and the service life was reached. Regarding G, performance is 0.005w
If it is t% or more, there is almost no difference, but since the price of Ce is high, it is considered appropriate to add up to 0.1 wt% from the relationship between the amount added and the effect. Summarizing the above results and looking at the optimal addition range for each element, we get the following.

SnO. 3 to 3.0 wt%, CdO. l~1.0wt%
AlO. Ol~0.1wt%, ZnO. O5~0.5w
t%, CeO. OO5~0.1wt% This alloy also contains S
Charging efficiency is high because it does not use metals with low hydrogen overvoltage, and this means that when used in automobiles, water electrolysis is less likely to occur even during constant voltage charging, resulting in less water loss. It can be seen that there are advantages such as convenient handling.

As described above, according to the present invention, it is possible to obtain a lead-acid battery with less self-discharge and improved deep discharge cycle life.

[Brief explanation of drawings]

The figure is an explanatory diagram for measuring the bending brittleness of a lead alloy specimen.

Claims (1)

[Claims] 1 Sn0.3-3.0% by weight, Cd0.1-1.0% by weight, and Al0.01-0.1% by weight, Zn0.0
5-0.5 wt%, Ce0.005-0.1 wt% 1
An alloy for lead-acid battery electrode grids consisting of one or more species, the balance being lead.